HK1123082B - Motor-drive metering pump - Google Patents

Description

Metering pump driven by motor

Technical Field

The invention relates to an electric motor driven metering pump with a rotationally driven electric motor and an oscillating piston, wherein the rotary motion of the electric motor is converted by a transmission into an oscillation of a connecting rod, so that a displacement device actuated thereby oscillates linearly with the continuous rotation of the electric motor, thus conveying the medium to be metered in a metering head which is arranged along the longitudinal axis of the connecting rod and cooperates alternately with an outlet and an inlet valve to produce a pressure stroke and a filling stroke.

Background

Motor-driven metering pumps of this type are known and can be fitted with accessories to meet various requirements. They work on a volume basis, wherein metering is performed by conveying a closed volume through displacement means. Thus, the metered volume per stroke corresponds to the difference in volume in accordance with the movement of the displacement means.

In general, such motor-driven metering pumps convert the continuous rotary motion of the drive motor into a linear oscillatory motion of the displacement device via a transmission. The rotational speed and torque of the motor is reduced in the transmission and matched to the speed and power required by the displacement device. The output shaft of the transmission drives a device for converting a rotational movement into a lateral, i.e. a deflection movement at right angles to the axis of rotation, for example by means of a spring/gear tooth or cam drive. The lateral offset may drive a connecting rod which is slidably guided in the bearing in the offset direction. This transmits the movement and power to the displacement device which, in the metering head arranged in the direction of the longitudinal axis of the connecting rod, cooperates alternately with the outlet valve and with the inlet valve, producing a pumping stroke (i.e. a pressure stroke) and a filling stroke, thus moving the medium to be metered.

The differences between the various embodiments are above all the type of electric motors, which are usually asynchronous, synchronous and stepper motors, which are mounted either externally or internally in existing pump housings. The various metering pump types also differ in the type of drive, which can be worm gears, spur gears or belt conveyors. The drive for the connecting rod can be passively guided or actively locked by the biasing means only when the biasing means is moved forward. In the pressure stroke, the connecting rod is driven by the biasing means, while in the subsequent filling situation it is driven by a return spring which places the connecting rod in the vicinity of the counter-biasing means. The return spring is compressed by a pressure stroke and is dimensioned to provide the force required for filling. The various types of pumps also differ in the power coupling from the connecting rod to the diaphragm as displacement means, either through a rigid connector or through a hydraulic intermediate circuit. Since the hydraulic fluid (typically oil) is incompressible, the hydraulic coupling operates like a rigid coupling. In addition to the systems described here with one metering head, pump arrangements with two or more metering heads which are driven by a common drive are also known. In one example, two opposite connecting rods may be arranged on one side of the cam along the same axis, driven in opposite directions, and each having its own displacement device. In another embodiment, it is also known to work with a plurality of metering heads with an elongated camshaft with several commonly driven cams, each cam driving a unit formed by a connecting rod arranged transversely to the cam axis and a metering head with displacement means placed in the direction of the connecting rod axis.

In the simplest case, all moving parts are mounted in ball bearings or slide bearings in one common pump housing, in other cases the individual functional groups are grouped in another housing or device and mounted as modules, some of which may be filled with oil. An example of this is a unit mounted outside the pump housing formed by the motor and reduction gears with a mounting flange and mounted output shaft.

In the simplest case, the drive motor is operated continuously for continuous measurement or for a specific period of time for measuring individual strokes. Other types control the drive motor by means of a frequency converter according to a predetermined time pattern, whereby the motor rotation speed and the metering power are more repeatable and independent of electrical parameters such as frequency or the actual level of the power supply.

The motor rotational speed is predetermined by the electronic frequency of the motor drive and determines the period of each stroke, along with the gear reduction and gear characteristics that are sinusoidal with the cam gear. When driven continuously, the period of each stroke is given by the effective motor rotation speed under load and gear reduction. When the opening/closing operation is performed, i.e. a single or a set of strokes, between which the motor itself is stopped, for example at the filling dead centre, the starting and decelerating times must be taken into account, the period of each stroke being thus extended. During continuous operation, the stroke frequency is given by the period of each stroke, which is determined by the motor switching cycle rate (repetition rate) at the time of on/off operation, which naturally cannot be faster than the time required to perform a stroke.

The stroke length can be adjusted by limiting the lateral offset. This can be done by adjusting the eccentric, for example by using a swinging cylinder based on two inclined planes, which can rotate in opposite directions. Another possibility is an adjustable buffer, which may be an unforced offset system. The damper is in the form of a mechanically adjustable spindle which, when adjusted, limits the reverse movement of the connecting rod during filling to an adjustable position before reaching the rear dead centre of the biasing means. The buffer provides a starting point for the stroke movement and an end position is a completion position of the offset movement. In one possible embodiment, a stroke adjustment pin is screwed into a thread in the pump housing and has an externally accessible calibration knob which constitutes the connecting rod damper during filling. With hydraulic systems, the stroke adjustment is performed by, for example, a slidable sleeve whose position can be adjusted by a calibration knob accessible to the operator, which is screwed into a thread in the pump housing. The sleeve covers a bypass orifice in the connecting rod which, after a certain distance of movement, opens a shunt in the oil circuit and increases the power coupling from the connecting tube to the diaphragm.

The movement of the displacement means is caused by a combination of gears and other mechanical elements. During the forward movement, the drive means work against the force of the return spring acting on the connecting rod through the displacement means. In the opposite movement, the displacement system is subjected to a force such that the connecting rod is pulled back by the drive, while by means of a side actuation, the return spring pushes the connecting rod back and thus generates the motive force for filling the metered medium. In this way, the movement of the connecting rod follows the characteristics of the offset device, for example, for a cam, the movement is sinusoidal, between two dead centers of the full stroke length of the cam stroke. When operating with a reduced stroke length, the movement behind the adjustment cam is still purely sinusoidal but its amplitude is reduced, whereas in the case of a rigid connection system with adjustable damper or a hydraulic system with bypass orifice, the initial movement and amplitude of the offset device can be maintained but can no longer be performed completely; furthermore, the movement of the connecting rod intersects at the start and end regions (stop phases) according to the adjusted stroke length and the coupling system. The forward movement of performing the pressure stroke is performed in accordance with the driving of the motor in a time period of less than one second (e.g., about 200 ms). The filling stroke is carried out in a time period similar to the pressure stroke, depending on the setting of the displacement device. This results in a high instantaneous velocity of the metering medium in both stroke phases, the maximum being half the travel path for an eccentric drive.

In the case of the embodiment consisting of several units consisting of connecting rods and metering heads, the connecting rods and the metering heads are driven by the same camshaft operating with several cams, so that those cams can be arranged on the shaft in a phase-shifted manner, so as to distribute the required peak power to the individual metering heads in one complete revolution of the camshaft and thus optimize the use of the available motor power.

A particular embodiment, known as a diaphragm metering pump, employs a partially flexible diaphragm as the displacement device. The diaphragm is not rigid but is elastically deformed by a specific amount in the flexible region when the pressure of the metering medium acts thereon. The amount of deformation occurring in the first part of the stroke movement which is not used for metering loses the effective stroke movement, as a result of which the metered amount decreases as the operating pressure rises. In normal use, this degradation characteristic is much more than the metering accuracy allows. Thus, motor-driven metering pumps are generally not adjustable to the required accuracy over a wide range of operating pressures; in addition, errors caused by calibration will be increasingly severe in subsequent further calculations. However, the calibration measurements that have to be carried out in use under practical operating conditions are a very difficult step, especially when aggressive chemicals are used.

The existing commonly used motor driven metering pumps are efficient and have good metering performance for many processes, but have insufficient hydraulic performance compared to the ideal. Examples which may be mentioned are the relatively strong dependence of the measured quantity on the operating pressure of the metering circuit, and the disadvantages of flow noise or pressure drop due to the high instantaneous flow velocity of the metering medium.

Disclosure of Invention

A particular object of the present invention is to overcome the known drawbacks related to the hydraulic characteristics of the metering process and to provide a variable, wide operating range for an electric motor driven metering pump without negatively affecting the manufacturing costs.

The invention therefore provides a metering pump with a rotary drive motor and an oscillating piston, in which the rotary motion of the drive motor is converted by a transmission into oscillation of a connecting rod, so that a displacement device actuated thereby oscillates linearly with continuous rotation of the drive motor, so that the medium to be metered is conveyed in a metering head which is arranged along the longitudinal axis of the connecting rod and cooperates alternately with outlet and inlet valves to produce a pressure stroke and a filling stroke, wherein a reference element is associated with the connecting rod, the position of which connecting rod is detected by a position sensor, wherein the position sensor provides an actual signal which is in fixed relation to the position of the reference element and thus of the displacement device and which signal also provides information about the motion performed by the displacement device, so that an electronic control system of the metering pump can react to the operating conditions of the metering circuit and the pump, the signals read from the position sensor concerning the position of the connecting rod are transmitted to the control circuit within the control accuracy of the control circuit and influence the rotational speed of the drive motor and thus the linear movement of the connecting rod and thus the displacement device so as to follow a predetermined nominal pattern.

In addition, the movement of the connecting rod and the connected displacement device should be matched to the reference details so that the metrology process itself is adjustable and the electronic control system can take into account any imperfections due to manufacturing and adverse characteristics of the module (e.g., the elastic diaphragm, if any). By using on-board electronics to avoid or detect defective operating conditions and to compensate for defects generated during manufacturing and/or maintenance, these measurements should ensure accurate metering of the intended metering medium during the metering process.

This problem is solved by means of a reference element associated with the connecting rod, the position of which is detected by a position sensor, wherein the position sensor provides an actual signal (x1) which is in fixed relation to the position of the reference element and thus to the position of the displacement device and which provides information about the movement of the displacement device, so that the electronic control system of the metering pump can react to the operating conditions of the metering circuit and the pump.

The position sensor acquires the movement of the connecting rod and the electronic control system evaluates it. Thus, starting from limited conditions, the control system responds by comparing the characteristic features and by influencing the motor drive to detect the movement, thereby metering in the best possible manner and eliminating inaccuracies due to the characteristics of the diaphragm.

If the position sensor operates on the principle of non-contact, it is possible to ensure non-abrasive operation of the sensor, which is advantageous and necessary in practice due to the large number of strokes that exist during the service cycle of the metering pump.

The flexibility of the space required for the precursor is increased if the position element associated with the connecting rod is located outside the metering head.

If the reference element can influence the beam path of the light source and if the position sensor fixed to the pump housing or to another stationary component, which cooperates therewith, is operated as a light-sensitive receptor, wear-free operation is ensured, which is important because of the large number of strokes present during the service cycle of the metering pump and the moving parts can be scanned without having to touch them. Another advantage of such an arrangement is that the structure of such a position sensor is insensitive to stray magnetic fields.

If the reference element is a shadow-generating body or a shadow-providing edge and the cooperating position sensor fixed in the pump housing or in another stationary part is composed of a series of photo-electric coupling devices (CCD), such a device has important optical properties which must be met by the position sensor. Firstly, the device works on the principle of optical function without wear and is insensitive to stray magnetic fields, and secondly, such a sensor is practically free of linear defects.

If the position sensor is disposed on its own sensor carrier that is secured to the pump housing or other stationary component, such a device can be pre-assembled into a module and tested to facilitate assembly. In addition to this, the electrical insulation between the sensor element and the metal part of the housing or the gear is simplified if the sensor carrier is formed as an uninsulated plastic part.

If the light source, shadow-generating body or shadow-generating edge and the receptor constitute a light box (lightbox) type device and the measured values are fed continuously or stepwise to the electronic control system, such a device provides position data to the electronic control system at a suitable rate.

If the photoreceptor of the position sensor consists of a plurality of linearly arranged receptors (pixels), preferably 128 pixels, such an apparatus can easily determine the position by determining the shadow edges between illuminated and non-illuminated cells, clearly with a resolution equal to the branches of the receptor cells.

If the light source is a Light Emitting Diode (LED) arranged opposite the light receiver of the position sensor so that the light beam directed to the receiver is not disturbed by the connecting rod, this has the advantage that an inexpensive LED has a near point light source which is important for high light resolution and has an almost unlimited lifetime. Arranging it opposite the position sensor, away from the connecting rod, results in a larger spacing between the light source and the receptacle, which makes the projection angle of the associated light beam relatively independent of the mounting position of the element.

If the start value of the position sensor is generated by the luminance values of several pixels inserted in the shadow transition, the resolution of the start signal of the position sensor is finer than it is determined by the mechanical step (pitch) of the CCD receptor unit.

The resistance to interference with the position sensor is improved if a filtering device is employed in processing the signals from the position sensor.

If the zero position error of the position sensor is eliminated by reference to a memory or the position sensor scale error is eliminated by including one or more reference positions, the sensitivity of the position sensor to changes in mechanical displacement during assembly and operation, for example during heating of the bearing or wear of the bearing, will be reduced.

If the illumination variation of the position sensor is leveled out by controlling or adjusting the light source with the luminance values taken from the pixels, the sensitivity of the position sensor to the module parameters will be reduced.

The effect of dust on the photoreceptor can be reduced if the brightness variations between the pixels of the photoreceptor are compensated for by incorporating a reference memory for the sensitivity of the individual pixels.

If the value set by the travel adjustment pin is determined by measurement during the metering process directly by the position sensor, an additional sensor for mechanically positioning the attached on-board element can be dispensed with.

The reliability of the metering can be improved if the electronic control system detects a blockage or an incomplete stroke in the displacement device by evaluating the signal of the position sensor. For prior art metering pumps without position sensors, sensors for detecting the metering movement are usually added, for example by passing a reference mark during each stroke and transmitting a detection signal to an electronic control system, whereby the stroke period is measured and deduced in order to perform the correct metering process. In contrast to such sensors, the use of a position sensor as already described has the advantage that the required information can be acquired at any point of the metering stroke, rather than only when the reference mark passes, so that such an additional sensor can be dispensed with.

If, for example, an asynchronous motor is used, the drive motor slips during operation, and if the electronic control system determines a nominal stroke frequency or a nominal stroke period for the displacement device from the nominal rotational speed of the drive motor and known gear characteristics, and also determines the actual stroke frequency or the actual stroke period of the displacement device by evaluating the position sensor, wherein the slip of the drive motor is obtained by comparing the actual stroke frequency with the nominal stroke frequency or comparing the actual stroke period with the nominal stroke period, in addition, if the nominal rotational speed of the drive motor changes so that finally the displacement device moves at the desired stroke frequency, this will improve the accuracy of the metering by eliminating errors in the stroke frequency due to the slip of the drive motor. The prior art metering pump systems without position sensors often use sensors which monitor the metering movement, for example by passing a reference mark during each stroke and transmitting a check pulse to an electronic control system, whereby the stroke period can be measured and corrected, such additional sensors being dispensed with when position sensors are used.

If, for example, with an asynchronous motor, the drive motor slips during operation, and if the electronic control system determines a nominal stroke frequency or a nominal stroke period for the displacement device from the nominal rotational speed of the drive motor and the known characteristics of the gear for the piston, and also determines an actual stroke frequency or an actual stroke period of the displacement device by evaluating the position sensor signal, wherein the slip of the drive motor is obtained by comparing the actual stroke frequency with the nominal stroke frequency or the actual stroke period with the nominal stroke period, and, in addition, if the electronic control system determines the force acting on the displacement device from the slip found in the drive motor and the known characteristics of the gear and reduces the working pressure of the metering medium, this information means that a monitoring function and a compensation function can be carried out, this will improve the reliability and accuracy of the metering. If the electronic control system determines the nominal speed for the displacement device at each moment of the metering process by means of the nominal rotational speed of the drive motor and the known gear characteristics, and also determines it by estimating the actual speed of the displacement device from the position signals, wherein it calculates the instantaneous slip of the drive motor by comparing the actual instantaneous speed with the nominal speed of the displacement device, and thereby also in relation to the known gear characteristics, correlating it with the instantaneous energy pattern in the displacement device, then at any point of the metering process the required information about the energy can be obtained, so that the required detection and compensation functions can be performed a different number of times, increasing the reliability and accuracy of the metering.

If the electronic control system reduces the operating pressure of the metering medium in accordance with the dynamic pattern observed in the displacement device, this will compensate for the destructive effect of the operating pressure in the metering process.

If the electronic control system detects from the observed operating pressure of the metering medium an operating condition outside a certain pressure range, or if it adjusts the metering according to a condition exceeding a predetermined maximum allowable pressure specified by the metering pump or by the operator, or according to a condition below a predetermined minimum pressure, then problematic operating conditions such as overpressure conditions or pressure loss due to pipe damage can be detected, while safe measurements such as adjusting the metering can be made, which will improve the reliability of the metering. This makes it possible to dispense with additional operating devices which are otherwise required, such as overpressure limiters, as long as the metering pump is the only booster system in the process. The possibility of controlling the operating pressure within a specific metering pump pressure range widens the possibility of pressure detection under conditions where the detection system of prior art metering pumps, in which the detection system is only operated when the metering pump is blocked, cannot be used.

This improves the accuracy of the metering if the displacement device is a partially elastic diaphragm and transmits to the electronic control system a possible metering error caused by the elastic deformation of the diaphragm and determined by the measured operating pressure of the metering medium and the known degree of dependence of the metering efficacy on the operating pressure, and if it influences the rotational speed of the drive motor and the stroke frequency so as to compensate for the expected metering error.

If the rotational speed of the drive motor is influenced by a signal (x) read by a position sensor for the position of the connecting rod via a control loop within a control accuracy range₁) And consequently the linear movement of the connecting rods and of the displacement device, thereby following a given nominal pattern, can be used on the displacement devicePossible influences are to achieve or improve good hydraulic performance in metering, for example in slow metering and/or metering accuracy in partial strokes.

Advantageously, the metering pump has a control device in addition to the position sensor, and it is influenced by the control device alternately by varying the rotational speed of the drive motor to the position of the displacement device (here x)₁Index), velocity (here v)₁Finger) or acceleration. The control of the velocity allows direct control of the flow rate of the dosing medium, which is necessary to avoid e.g. cavitation at slow start-up. On the other hand, the control of the position to bring the approach to a stop is controlled, in which the information on the velocity generated by the difference between the displacement signals becomes small and cannot be efficiently handled by the control means. Control of position can avoid this problem and can be advantageously used for e.g. electronic stroke limitation or slow metering. Controlling the acceleration facilitates a simple control of the adjustment, since the acceleration of the object to be moved constitutes a direct image of the motor power for fast processing.

If, in addition to the position sensor, the metering pump has a control device, and if it is in the filling phase and/or the compression phase, the v of the displacement device is reduced₁Pressure loss or cavitation due to flow resistance can be eliminated. When metering highly viscous media, such as lecithin, a large pressure drop occurs at narrow locations, such as at valves, when the flow rate is too high. Additional power from the drive must be used to overcome these pressure drops and v can be taken to the displacement means₁To keep it at a lower level. In addition, flow noise generated due to the reduced flow velocity can be effectively reduced. When metering a gas-containing medium, such as a chlorine-containing bleach, especially at very high flow rates during filling, cavitation often occurs as the pressure drops below the evaporation pressure of the metered medium, which leads to increased mechanical wear. V for controlling displacement device during filling phase and/or pressure phase₁Can haveThis phenomenon is advantageously avoided.

If, in addition to the position sensor, the metering pump has a control device and if the desired stroke length is transmitted to the control device and the movement of the displacement device is electronically limited by the control device to the stroke length to be carried out, wherein the control device, after carrying out the desired stroke length, stops the drive motor, switches it into reverse rotation and then carries out a filling stroke, and then stops the motor or carries out the next pressure stroke, a large number of mechanical adjusting elements can be dispensed with.

If the metering pump has, in addition to the position sensor, a control device and if the control device dispenses the forward movement of the displacement device during the pressure phase by driving the electric motor within a time period given by the cycle rate of the metering stroke, so that the metering medium is dispensed in as smooth a manner as possible, even if the very slow metering stroke lasts for several minutes, concentration variations in the metering medium can be substantially avoided.

Metering accuracy can be improved if the displacement means is a partially elastic diaphragm, and the electronic control system detects the opening of the outlet valve from the instantaneous power pattern and measures the area of rest due to elastic deformation of the diaphragm from this observation, and then influences the actual stroke path by intentionally stopping the stroke movement as a function of the diaphragm deformation, thereby significantly reducing the dependence of the metered amount on back pressure. This improvement is obtained by eliminating the error caused by the elastic deformation of the diaphragm, which is due to the operating pressure, so that the deformation does not contribute to the metering. By means of the reduction in the dependence of the metering mass on the operating pressure, subsequent calibrations, which are required when operating parameters such as the operating pressure change significantly, can be dispensed with. When estimating motor slip, it is advantageous to compensate for diaphragm deformation by observing the power pattern, since this is a good reflection of the actual power demand and no additional measurements need to be taken.

The metering accuracy can be improved if, in addition to the position sensor, the metering pump has a control device, the displacement device being a partially elastic diaphragm, and the actual stroke path being influenced by the deformation of the diaphragm, wherein, after opening the outlet valve and completing the desired stroke length, the control device stops the drive motor, switches it back into reverse, and then executes a filling stroke, stops the motor or performs the next pressure stroke, so as to eliminate the error caused by the deformation of the diaphragm (relative to the stroke path or the metered volume), which deformation does not contribute to the metering. The reduced dependence of the metered quantity on the operating pressure means that subsequent calibration, which is necessary when operating parameters such as the operating pressure change, can be dispensed with, while the linearity of the relationship between the set stroke length and the actually metered quantity of metering medium is improved. Determining the amount of diaphragm deformation by observing the power pattern is particularly advantageous when estimating the slip of the motor, since this is a good pattern of the actual power demand and no additional measurements are required.

If the displacement device is a partially elastic diaphragm and the metering pump has a control device in addition to the position sensor, and the actual stroke frequency is influenced by the determined diaphragm deformation, wherein the control device determines a correction for the error caused by the diaphragm deformation (relative to the stroke path or the metered quantity) by which the rotational speed of the drive motor is changed, so that the error caused by the diaphragm deformation is eliminated, the dependency of the metered quantity on the operating pressure decreases.

Drawings

We will now describe in detail one embodiment of the cam-driven motor-driven diaphragm metering pump of the present invention and its various uses. The attached drawings show:

FIG. 1: a cross-sectional view through a motor driven metering pump with a position sensor;

FIG. 2: an exploded view of the position sensor (enlarged view of section X in fig. 1);

FIG. 3: an element of a position control loop;

FIG. 4: elements of a speed control loop;

FIG. 5: a top view of the position sensor along the axial direction;

FIG. 6: a side view of a position sensor at right angles to the axis;

FIG. 7: a schematic of a shaded region of the position sensor;

FIG. 8: luminance values of pixels in actual shadows;

FIG. 9: a schematic of position sensor measurements according to a geometric arrangement;

FIG. 10: interpolation of position resolution (interpolation);

FIG. 11: a schematic diagram of a position resolution interpolation calculation basis;

FIG. 12: a graphical representation of metering performance as a function of mechanical stroke length and operating pressure.

Detailed Description

Figure 1 shows the structure (partially cut away) of an electric motor driven metering pump. As is generally known, an electric motor driven metering pump basically comprises three sets of elements, namely a drive motor 2 with gearing, a cam driver in a cam housing 1, and an electronics housing 28 in which electronic control means are housed and on-board electronic modules and blocks are mounted. A support plate 4 with a fixing hole is arranged below the electronic shell 28; a cam housing 1, which is positioned on and fixed to the electronics housing, carries a drive motor 2 with a transmission, which is fixed to the cam housing with, for example, screws.

The housing consisting of the cam housing 1 and the electronics housing 28 has the elements of the cam drive in its upper part, namely the cam housing 1. The elements of the cam driver are accommodated in a cam carrier 22 which ensures that the elements are accurately positioned and fixed in the cam housing 1. The three-phase asynchronous motor 2 is externally flange-mounted on the cam housing 1 together with a reduction gear 11, which is formed as a bevel gear and is fixed by screws. The output shaft of the electric motor is at right angles to the axis of the motor shaft and either forms the drive shaft for the cam drive directly or, as in the present embodiment, is fixed coaxially thereto by means of a coupling. The drive shaft of the cam drive, i.e. the camshaft 17, is rotatably mounted in a cam carrier 22 and carries the cams which are fixed to the carrier. The camshaft together with the cams passes through a suitably cut pusher arm 20. The camshaft 17 is rotated by the electric motor/gear unit via a shaft coupling for driving the electric motor 2 and drives the push arm 20 by means of the outer surface of the cam onto the inner surface of its cutout, i.e. the stop surface. The push arm 20 drives a connecting rod 19 fixed to the push rod, which connecting rod is injected. The unit consisting of the pusher arm 20 and the connecting rod 19 is longitudinally displaceable along the two guide bushes. The axis of the camshaft 17 and the longitudinal axes 18 of the push arm 20 and the connecting rod 19 lie in a horizontal plane and are at right angles to one another. One of the two guide bushes 26 for the connecting rod 19 is located in a bearing plate 24 which is fixed on the pressure head side to the cam carrier 22, and the other guide bush 27, which serves as a sleeve for the push arm 20 on the side turned towards the metering head, is located in the stroke adjusting pin 8. Coaxial to the longitudinal axis 18 of the connecting rod 19 is a manually actuable adjusting device 7 for adjusting a stroke adjusting pin 8 screwed into the thread of the cam carrier 22, so that the axial movement of the pusher arm 20 is limited during filling, and thus the stroke of the metering pump is limited.

In the lower part of the housing in the sealed chamber, the housing also contains an electronic housing 28, i.e. an electronic control system. The housing is sealed in order to prevent spray and to protect the cam drive and the electronic control unit from moisture and corrosion, since metering pumps are usually used for chemically aggressive media. The electronic control system consists of level control electronics 34 and electronics 6, the level control electronics 34 controlling the motor controller 29 and forming an integrated frequency converter, the electronics 6 being arranged in the housing cover 5 with the input and display elements required for operating the metering pump. The control element is protected by a cover 9. Below the cover 9 is a connector for a control line 10 or power supply.

On the side of the control line 10 or power connector, coaxial to the longitudinal axis 18 of the connecting rod, is a metering head 12 in which a diaphragm, for example made of plastic, acts as a displacement device, the diaphragm being fixed at its periphery. The metering head 12 also carries an inlet valve 14 and an outlet valve 15 for urging a metered medium filled into a metering chamber 16 between the diaphragm and the metering head 12 via the inlet valve 14 and into the metering tube via the outlet valve 15. The motor drives the metering pump to operate volumetrically, i.e. to fill a predetermined volume in each stroke and then to push it out through the outlet valve 15. The diaphragm 13 is moved in an oscillating motion by a cam driver which moves the connecting rod 19 back and forth along the longitudinal axis. On the side of the stroke adjusting pin 8, the unit consisting of the push arm 20 and the connecting rod 19 works with the aid of the adjusting device 7 as a manually adjustable device. At the other end, the portion of the connecting rod 19 facing the metering head 12 is fixed to the central core 30 of the diaphragm 13 and moves in an oscillating motion.

Between the push arm 20 and the collar 25 of the bearing sleeve 24 is a compression spring 23, for example a helical spring, which keeps the push arm 20 constantly against the cam. In the forward phase of the cam movement, i.e. the movement of the connecting rod towards the metering head, the pusher arm moves together with the connecting rod towards the compression spring, while the diaphragm 13 is pushed into the metering chamber 16, which means that an excessive pressure is built up in the metering chamber, while the outlet valve 15, e.g. a spring-loaded ball valve, opens, pushing the metered medium into the metering tube. In the opposite phase of the cam movement, i.e. the movement of the connecting rod away from the metering head, the push arm 20 is moved in the opposite direction with the movement of the cam towards the stroke-adjusting pin 8 under the action of the compression spring 23, which may be formed, for example, as a helical spring, which means that the connecting rod 19 moves the diaphragm 13, creating a negative pressure in the metering chamber 16, which opens the inlet valve 14, so that another batch of metered medium can be poured into the metering chamber. The diaphragm 13 pushes the metered media into the metering tube by an alternating oscillating motion of the cam. During the metering stroke, the cam drive produces a sinusoidal movement formed by the push arm 20, the connecting rod 19 and the diaphragm 13. If the stroke length is set to be reduced by means of the stroke adjustment pin 8, the movement in the filling phase can be braked beforehand by means of an adjustable buffer of the stroke adjustment pin 8 before the dead point is reached, whereby the sinusoidal paths of the movement intersect and the phase of the stroke movement is changed.

The position of the unit consisting of the pusher arm 20, the connecting rod 19 and the diaphragm 13 is detected by a position sensor 36, the signal from which is in a predetermined relationship with this position; the relationship may be, for example, a strictly proportional relationship. The signal of the position sensor 36 is thus constantly related to the position occupied by the movable unit part. This fixed point is formed by a reference element, which is abstracted here. Depending on the requirements of the position sensor, it may be formed as an off-the-shelf add-on element to be incorporated, but it may alone form a feature, such as an edge or a face, on one of the required elements, such as the push arm 20.

In this embodiment, the cam carrier 22 has a sensor carrier 31 (see also fig. 6) fixed thereto, which carries a longitudinally oriented photosensitive CCD unit 32 (electrical coupling device) on one side and a light source 33, for example a light emitting diode, on the other side.

The sensor carrier 31 fixed to the cam carrier and the element fixed to the sensor carrier form an optical box from which the light beam is partially blocked by the push arm. The reference element is formed in the region of the light box arrangement by a shadow-providing edge 35 of the push arm 20. When the connecting rod 19 swings, the shadow-providing edge 35 passes through the photosensitive unit 32 but does not contact it. As can be seen in particular in fig. 5, which shows a top view in the axial direction, the light source 33 must be arranged so that the light beam is not interrupted by the connecting rod 19 on its way from the light source to the photosensitive element; this means that, for example, the light source 33 and the photosensitive CCD unit 32 are arranged above or below the connecting rod 19. As can be seen in particular in fig. 7, the shadow-providing edge of the light source 33 casts a shadow onto the light-sensitive cells 32, which divides these cells into illuminated (h) and non-illuminated (d) cells. The transition situation shown in fig. 8 occurs because the orientation of the columns of photosensitive cells is parallel to the longitudinal axis 18, for example 128 pixels covering a distance of about 8mm are only partially illuminated or in shadow in the transition region. The height of the surface at right angles in fig. 8 represents the brightness of the pixel. One particular process, which will be described below with reference to fig. 10, takes advantage of this transition situation to accurately determine the location of the shadow-providing edge, and thus the location of the tie-bar or diaphragm. This measuring device, consisting of a shadow-providing edge on the side of the push arm and a light-sensitive CCD on a sensor carrier with opposite light sources, is used to measure the actual position or speed of the connecting rod in the swing and uses this information to achieve the function described.

The connecting rod, which sets the diaphragm movement to an oscillating movement, covers a distance in each stroke corresponding to the length of the mechanical stroke. In order to be able to carry out assembly changes, the longitudinal extent of the photosensitive CCD unit must be slightly larger, which can in principle be achieved with the aid of all other conceivable position sensors.

When using position sensor signals (as shown in fig. 3 and 4) to specifically control the diaphragm, or more generally displacement movement, the following mechanical and electronic components are required. The abbreviations used in these two figures have the following meanings:

x_s: a nominal value of the position of the displacement device;

x₁: an actual value of the position of the displacement device;

x_s1: an offset in the position of the displacement device;

v_s: a nominal value of the speed of the displacement device;

v₁: of displacement meansAn actual value of speed;

v_s1: a shift in the speed of the displacement device;

SG: a controller output;

KSG: a corrected controller output;

MA (U, f): the driving value (voltage or frequency) of the motor drive.

The moving part of the actuator whose movement is to be controlled is made up of a pusher arm 20 and a connecting rod 19 to which a diaphragm core 30 is fixed. The return spring 23 returns the pusher arm after a working stroke and thus performs filling. The outer ring of the diaphragm 13 is fixedly mounted in the metering head 12 and a metal diaphragm core 30 injected into the diaphragm moves the central surface of the diaphragm along the metering head as a displacement means. The inlet valve 14 is closed on the filling side and the outlet valve 15 on the pressure side of the metering head, and thus provides the possibility of connection to external piping. The reference element is connected to the connecting rod 19 or to a module connected thereto, for example at the end facing the metering head, in this case for example a push arm 20, the position of which is detected by a position sensor 36, which does not have to be in contact for operation. In the embodiment shown, the reference element is the shadow-providing edge 35 of the push arm 20, while the position sensor is a light box type device consisting of the light source 33 described above in combination with a series of light-sensitive cells 32 which optically determine the position of the shadow-providing edge 35 so as not to have to touch its shadow structure. Since the connecting rod 19 is the actual connector and power coupling connected to the diaphragm 13, and the push arm and connecting rod are fixed together in this example, the following description always refers to the movement of the connecting rod 19, although this movement is actually the movement of the shadow providing edge 35 of the push arm 20 as measured.

The position sensor 36 generates the actual signal x₁This signal is proportional to the position of the shadow providing edge 35. For the speed controller, in this embodiment, by a time differentiator 37 (dx)₁Dt) to the controller and thereby to the controllerGenerating the actual signal v₁This signal is proportional to the speed. Obviously, other methods may be applied to the control step, which may generate a signal proportional to the speed of the diaphragm. Depending on the control type and metering requirements, a position x may be generated_sOr velocity v_sNominal value of (d) versus time. The difference comparator 39 determines the difference x as a position difference_s1＝(x_s-x₁) Or the difference in velocity v_s1＝(v_s-v₁) And these results are given by PID control (proportional integral derivative control). The output value, i.e. the controller output value SG, corresponds to the value of the drive. In order to improve the stability of the controller, the controller output value SG is further processed with a position corrector 41. The position corrector takes into account the fact that the motor speed depends on the angle of rotation of the cam (offset from the connecting rod position), which is a function of the sinusoidal characteristic to convert the drive of the cam into a speed at the connecting rod. The position corrector 41 then converts the start signal for the PID controller 40 via the reverse characteristic of the cam drive into a corrected controller output value KSG which represents the required motor drive value relative to the input to the reduction gear 11 in order to obtain at the output from the cam drive a movement of the connecting rod 19 corresponding to the required controller output value SG. An amplifier 42 formed as a frequency converter maintains the power level and drives the motor at the required rotational speed at the accompanying pressure and frequency. Conversion of the corrected controller output value KSG into the actual rotational speed used by the frequency converter and, if required, the overall speed signal v, on the basis of the correction of the position₁The offset constant of the conversion is set by three scaling factors k1, k2, k 3. The factor k1 for the correction according to the position is selected according to the characteristics of the cam drive, and the two factors k2 for the amplifier and k3 for the speed signal deviation can be selected according to practical situations, such as operation with the most readily available use sizes, and the like.

Fig. 3 shows a control loop for a position regulator, and fig. 4 shows a control loop employing a speed controller. The control loop described here will predetermine position x_sOr velocity v_sThe time pattern of nominal values of (c) is clearly transmitted within the control and regulation range that it can.

The creation of a realistic picture of position, velocity or acceleration and the switching between these operating modes is described below, for example taking into account functional limitations such as control speed, achievable accuracy etc.

With such control, the motor-driven metering pump can be used to predetermine the desired speed of the diaphragm 13 (and more generally the displacement means) and thereby control the effective flow rate of the metered medium.

In this way, the diaphragm position can be directly controlled. This function allows the position to be reached at a selected phase and can be done at rest if desired.

By using a position indicator to control motion, as opposed to uncontrolled operation, changes in operating parameters can respond to changes that occur suddenly over time or due to environmental conditions or changes, i.e., statistical deviations in a product line, and their deleterious effects can be minimized. Examples which may be mentioned are the diaphragm stiffness or the viscosity of the metering medium. These two factors require a driving force that must be added to the force used to generate the operating pressure on the diaphragm surface. By determining their influence and adjusting the drive of the motor accordingly, these detrimental effects can be compensated for. For an unregulated metering pump with a predetermined motor speed, it is subject to these effects even if it is controlled to stabilize it. In addition, due to the sinusoidal nature of the cam drive, it is not possible to accurately predict the instantaneous speed of the displacement device without knowing the position of the connecting rod, i.e. the cam angle.

In addition, in contrast to the spontaneous metering process on an unregulated basis, the use of position indicators to control motion allows for reaction to internal and external influences, as will be described below, and for establishing operating conditions that may utilize or avoid certain hydraulic conditions or metering. One example is to avoid cavitation during filling, as will be described below.

The appliances of the motor-driven metering pump of the type described above, which has a position sensor and which reduces the operating conditions of the metering circuit by evaluating the position signal or influences the movement of the diaphragm by controlling and regulating the motor drive, will be described in detail below.

Detecting the position of the regulating control in the stroke length

The metering pumps of the prior art are usually operated such that the metering stroke performed is converted directly from the dispensed volume of the piston chamber (stroke length) into the total volume metered, which is expressed, for example, by a volumetric flow rate in l/h. For such a function, the strokes set by the operator must be known, since the volume metered per stroke is related to it. In the metering pumps of the prior art, the position of the stroke adjustment device must therefore be converted into an electrical signal by a separate sensor and read into the control system. An example of a practical embodiment is a linear potentiometer on the stroke adjustment device 7, which potentiometer detects the adjustment by means of a probe.

A metering pump that can detect the actual diaphragm path with an integral position sensor 36 during travel does not require an additional sensor. The stroke length can be calculated directly and used in the subsequent steps by means of the difference between the two position values at the end positions, which can be measured immediately after the mechanical buffer is reached, when the movement stops.

Detecting blocked or incomplete travel

Prior art metering pumps without position sensors typically employ a sensor that provides pulses to an electronic control system to monitor the metering motion during each stroke. One known device is for example a small permanent magnet fixed to the output shaft of the gear and thus axially outward on the camshaft 17, which permanent magnet is associated with a stationary hall sensor which generates a signal when the magnet is passed at a certain angle of the camshaft as the shaft rotates. The electronic control system measures the stroke cycle from this signal, which is the same as the speed of the camshaft, and from this it can be deduced that the metering process is proceeding correctly. If a blockage occurs during the execution of a metering stroke due to an excessive pressure situation (for example, a blockage in the metering tube which is unintentionally closed), the hall sensor signal is switched off, and after a monitoring period has elapsed, an alarm is given and further action is taken, for example, the metering pump is stopped. With such existing systems, the required information is only available after the monitoring period has elapsed.

The use of the position sensor 36 means that the speed of the connecting rod 19 in relation to the drive of the motor 2 can be set at any time during the metering stroke and that the occurrence of a blockage can be determined at substantially any time.

Slip compensation

If the motor 2 is a synchronous motor, the effective mechanical rotational speed at the motor output shaft, which for example carries the load, is usually slightly less than the value given by the frequency of the electronic control system. The difference between the two rotational speeds, known as slip, is dependent on the parameters of the motor and is generally proportional to the torque under load over a reasonable load range. Various methods may be employed to measure this slip, as will be explained below. It can be used to calculate a correction value, which can be incorporated in the motor speed by means of a frequency converter, for compensation, in the form of an increase in frequency.

The slip can be determined, for example, by comparing the measured stroke period with a period given by the electronic control means. This method is also used for prior art metering pumps by measuring the time difference of the two hall sensor pulses. In the case of a metering pump with a position sensor, a characteristic point, for example a half-way point, is determined in the path of travel, so that the period is measured, and for a continuous metering process the time to pass through the point is recorded, and the difference between these two times is the desired period.

In motor driven metering pumps with position sensors 36, a direct method of determining slip can be used, which is to observe the instantaneous speed of the connecting rod 19. From the motor rotational speed, derived from the electronic control, the desired connecting rod speed can be calculated using known gear and cam characteristics. Comparing the ideal speed with the measured speed yields the slip at any point in the cam cycle, which can be corrected by readjusting the frequency of the motor drive.

Determining pressure

If an asynchronous motor is used, the slip measured by one of the methods described above can be used to determine the force on the displacement device, so that the operating pressure of the metering medium can be reduced. It should be noted, however, that the cam converts the force acting on the connecting rod 19 in a sinusoidal manner, depending on the instantaneous angle reached by the motor 2 via the gear 11. At the two dead points, i.e. the turning points of the stroke movement, the motor is decoupled from the force of the connecting rod, i.e. no load, and between these two points the cam transmits the maximum load moment to the motor. Thus, for a given constant coupling rod force, the torque on the output shaft of the electric motor has the same form, so that the slip also varies almost sinusoidally. This change is therefore a reflection of the connecting rod force.

If, as mentioned above, the deviation of the stroke cycle from the ideal value is determined, this represents the slip transmitted by the sinusoidal pattern of the cam, which is also a measure for the average stroke force, i.e. the operating pressure. If slip is determined continuously by comparing the motor speed given by the electronic control system with the connecting rod speed, the force pattern at the connecting rod 19 can be calculated using the known cam characteristics and knowledge of the instantaneous angle of the cam determined by the connecting rod position. The force pattern on the connecting rod can also be used to derive the operating pressure.

This feature can be suitably applied to the offset mechanism if it is provided by other means than a cam.

Identification of pressure limits, pressure drops

If the operating pressure is determined according to the method described above, it can be monitored so that it is within certain limits, and a query to the monitoring system can generate an alarm as well as other actions, such as stopping the metering pump. The monitoring of the out-of-limit condition protects the pump or other components and in some cases the operational limit can be set and monitored to be 130% of the maximum pressure of the metering pump, but the monitored limit can also be within a particular metering pump operational limit if, for example, a sensing element must be protected and, in this case, can be set by the operator. It is also possible to monitor according to preset operating conditions, in which case an alarm can be given if, for example, the operating pressure set as a reference value rises or falls by a certain percentage point. If the operating pressure is monitored on the basis of a pressure of at least 1bar, it is possible, for example, to monitor a leak caused by damage to the line.

Pressure compensation

In the embodiment employed, the actual dosage of the motor-driven metering pump is influenced in different ways by the operating pressure. On the other hand, when the drive motor 2 is an asynchronous motor, it is affected by the amount of slip that rises as the operating pressure rises, the effect of this phenomenon being a drop in the rotational speed and a concomitant drop in the stroke frequency. On the other hand, the diaphragm used as the displacement device 13 undergoes elastic deformation under the influence of the operating pressure. At the beginning of the metering stroke, when the outlet valve 15 is closed, the internal pressure in the metering chamber 16 continues to rise, wherein as the pressure rises, the diaphragm core 30 is displaced into the metering chamber by the connecting rod 19, while the elastically deformed region of the diaphragm 13 gives a pressure which overcomes the movement of the diaphragm core 30. The diaphragm 13 deforms towards itself and virtually no volume change occurs at all, since the metering medium is virtually incompressible and at this point both valves are closed. At the end of this deformation phase, the chamber pressure corresponds to the external operating pressure. The path taken by the connecting rod 19 corresponds to the deformation of the diaphragm, reaching the rest zone where the metering starts and substantially not contributing to the metering. The deformation or rest area is typically in the range of 0.1mm to 0.5mm, depending on the size of the diaphragm, operating pressure, etc. At the pressure equilibrium point, the outlet valve 15 on the operating side is opened. The pressure acting on the diaphragm 13 is now virtually equal to the external operating pressure and remains almost constant for the remainder of the metering stroke, similar to the diaphragm deformation. The pressure balance point at which the outlet valve opens on the operating side marks the actual starting point for metering, so that the diaphragm deformation causes a loss of metering stroke, i.e. the effective stroke length is the mechanical length minus the amount of diaphragm deformation. Since diaphragm deformation itself is substantially proportional to operating pressure, the metering curve generally decreases as operating pressure increases. For shorter stroke lengths, the negative offset is more pronounced.

With prior art metering pumps, metering is not only pressure dependent, but is not strictly proportional to the mechanical stroke length under partial stroke conditions. In addition, the effective metering is only initiated at a point in the stroke after the initial quiescent zone where diaphragm deformation is greatest (while the outlet valve 15 is also open). If a steady-state behavior is produced in which a metering pattern is displayed as a function of the length of the mechanical stroke, a straight-line rising curve is generated which shows the curve with the rest region x_T1、x_T2、x_T3…x_TnThe corresponding actual dose after the minimum stroke length (see fig. 12). Since this minimum stroke length corresponds to the diaphragm deformation, it depends on the operating pressure p₁、p₂、p₃…p_n。

x_T1、x_T2、x_T3…x_TnThis switching in the steady-state characteristic means recalibration in real operating conditions, in which the current stroke length changes significantly, since the new metering performance cannot be determined with sufficient accuracy from the current and new stroke lengths by proportional calculation.

If the operating pressure is determined by using one of the methods described above, the described dependency relationship, which allows a quantitative determination of a class of devices in advance, can be used to determine and compensate for the effect of the operating pressure on the metering performance resulting from errors in advance. For this purpose, the determined operating pressure and the used stroke length as described above can also be measured with a position sensor, and the resulting pressure and length can be used to calculate a correction value, which is calculated from a known error relationship, which is added to the used stroke frequency. It should be noted that for practical and economic reasons only the system part of the influence can be eliminated. The pressure-dependent measurement performance error is mainly determined by the material properties and the measurements made on the components employed, both of which can be altered to some extent by adaptation or by product changes. Such variations are not included in the methods described herein that use a predetermined module parameter or series of measurements to correct for errors caused by diaphragm deformation; furthermore, in the present invention, the actual relationship must be redefined at regular intervals or on each trip.

If the above-mentioned effects caused by the deformation errors of the diaphragm, in which the operating pressure is determined by using one of the above-mentioned methods and the frequency of the stroke used is changed by means of a correction value, the calibration error in the partial stroke operating mode is also eliminated, so that the metering pump can be operated virtually over the entire useful range, for example from 20% to 100% of the stroke length, without recalibration being necessary, which is currently required in the metering pumps of the prior art, in which an adjustment of, for example, more than 10% of the stroke length is required in order to ensure a certain metering accuracy.

Avoiding flow losses in the case of highly viscous media

For the membrane 13, especially for high viscosity media (e.g. lecithin), adjusting the speed of the displacement device means that flow losses at valves and other seals can be limited. The high flow rate of such a medium has an adverse effect on the metering accuracy by the additional pressure drop caused by the flow resistance. Furthermore, this situation is advantageous due to the limited speed if the valve has more time to open and close. Both effects improve the metering accuracy in high viscosity media. To achieve this effect, the diaphragm speed is limited to a selectable maximum throughout the metering process. This maximum speed depends on the viscosity of the actual medium to be metered and is in the form of several predetermined values, for example selected by the operator or set directly. The position sensor described above, and the adjustment of the speed of the displacement device, may be used to ensure the desired diaphragm speed limit.

Cavitation protection

For gas-containing media, such as chlorine-containing bleaches, particularly during the filling stroke, but also during the metering stroke, excessively high flow rates can cause cavitation at narrow points due to a local reduction in the evaporation pressure, which is dependent on the chemical composition of the metering medium and its temperature, which leads to increased wear. By limiting the speed by adjusting the rotational speed or simply setting it at a value well below the critical speed flow rate, cavitation can be avoided during the pressure stroke as well as during filling, i.e. the return stroke of the membrane 13. Thus, setting the speed requirement of the control loop, or in the simplest case the motor rotation speed, it is possible to limit the corresponding diaphragm speed to e.g. 1mm/50 ms.

Cavitation is particularly likely to occur for the filling procedure because the static pressure is particularly low here and the safety margin for pressure drop below the evaporation pressure is therefore small. In order to improve the method, it is advisable to limit the diaphragm speed during filling to a speed less than that used during the pressure stroke. A reasonable value is 1mm/50ms in the pressure stroke or 1mm/100ms in the filling, although other values are obviously possible. For each process of the metering phase, it is important that the position sensor can determine the actual position of the diaphragm at any time so that the start of the filling phase can be reliably determined.

Electronic stroke length adjustment

The invention allows the omission of the mechanical means for adjusting the stroke length (adjustment means 7 as well as stroke adjustment pin 8). For this purpose, the control device is electronically informed of the required stroke length, for example by input from an operator. If the required stroke length is completed, the position reached by the diaphragm 13 is stopped by braking the motor 2, which is then reversed to perform the filling phase. The next stroke may be started by rotating the motor past the filling dead center in the opposite direction (pressure phase reversal, while filling phase runs in the normal direction), or in the same sequence as the previous stroke; in the first case, the motor braking and starting procedure between strokes can save time and energy. It should be noted that the constant change in direction means that the fan fixed to the motor shaft does not work effectively, so in this case the use of an externally driven fan is important and necessary for the cooling of the motor.

Slow metering to avoid concentration variations

For applications requiring good mixing with the medium flow to be treated, the metering medium is distributed into the treatment process as uniformly as possible. Certain applications also require that small quantities can be metered as uniformly as possible over a long period of time to produce an almost continuous metering. For these cases, it is known in the prior art to drive a metering pump with an electric motor, for example, and a self-locking gear. In such metering pumps, a complete stroke is completed at a reduced rotational speed, or the complete stroke is divided into several steps with intermediate stop periods in between, and at the end of the complete stroke, a complete (rapid) filling phase takes place, after which the metering process is continued in the already described manner.

By means of the motor-driven metering pump with adjustable movement, the available time determined by the cycle frequency of the metering stroke can be allocated, so that the remaining part after filling can be used to the maximum extent for the forward movement, in order to achieve a short stop phase. The speed to be adjusted is thus calculated from the covered path (set stroke length) and the available time. In contrast to prior art motor metering pumps, the use of the position sensor 36 and the adjustment means that the position of the connecting rod 19, which is always known, gives the instantaneous angle of the cam drive, which can be incorporated into the motor speed, thereby compensating for the offset device characteristic, which is sinusoidal when using a cam, while the metering stroke is an accurate linear movement with a correspondingly constant metered medium dispensing. This speed can be in a very wide range, for example from 1mm/min to 1mm/s, or outside this range.

The above-described use of a position setting device for a part in combination with a control device shows that the use of a position sensor on the connecting rod during, for example, the entire stroke and filling process, can indicate the actual position of the displacement device and the device it can monitor. Locating and monitoring means that by measuring the actual value, it is possible to practically comply with control parameters that depend on the circumstances that may lead to the described advantages.

Position sensor

As already explained, the reference element of the position indicator in the described embodiment is a shadow providing edge 35 on the push arm 20 for detecting the position, the shadow of which edge is projected onto a row of CCD (electrically coupled device) cells 32. The active sensor element used to detect the position, described in detail in this example, is on the push arm 20 towards the side of the metering head. The light source 33 is an LED and the light receiver is an electronic module with a CCD unit 32, which in this case is mounted on an intermediate part, i.e. the sensor carrier 31. Mounting the position sensor 36 on the sensor carrier 31 allows it to be handled as a separate module during production and to be subjected to e.g. individual pre-assembly and testing away from the final construction site. In addition, the described light box type device constitutes a sensor that does not touch and therefore does not wear.

It is not important for the basic function to locate the sensor in the area of the movement unit formed by the push arm 20 and the connecting rod 19, which can be determined by considerations such as space, order of assembly, etc. Furthermore, the fixedly mounted parts described here (light source 33, receptacle 32) and those moving with the connecting rod (shadow-providing edge 35) can be exchanged in function.

In this example, the CCD unit 32 is controlled by an evaluation unit comprising a microprocessor and generating the required control signals. In addition to a microprocessor, the evaluation unit may also be generated by a DSP (digital signal processor) or discrete technology.

Any element may be used as the light source 33 as long as it can generate a sufficiently narrow spot. This width, together with the geometry in fig. 7, determines the shadow region SV (see also fig. 8).

The light source 33 may also be composed of several elements or of one line light source, whereby the shadow SV can be generated to meet the requirements of the characteristics. One example is to produce very high brightness but without affecting the sharpness in the direction of motion.

The CCD unit 32 is a linear arrangement of M photoreceptors (referred to herein as pixels) arranged in a regular array at a pitch R of several μ M. For example, there are 128 pixels with a pitch of 64 μm over an overall length of about 8 mm.

The control signal generated by the evaluation unit sets the light emission time during which the pixels of the respective CCD unit 32 integrate the incident light in the amplifier in the CCD module and save it for subsequent processing. This integration step is performed not only over the illumination period, but also over the photosensitive surface of each pixel. After illumination, the luminance values of the pixels are read continuously as analog values from the CCD module by other control signals and acquired by the evaluation unit.

The illumination and the reading of the brightness values are alternated in the simplest case. Some commercial CCD line structures can also perform both steps simultaneously, where they store the integrated illumination measurement and immediately empty the integrator for the next measurement. Simultaneously outputting the measurement results at the illumination phase for subsequent processes may improve the measurement speed.

The graph in fig. 8 shows the integrated luminance values H of the actual shadows in the affected pixel areas in the example. In this example, the shaded region SV is from pixel #60 to # 63.

As a simple estimation process, a decision threshold H is set_v(shown by a dotted line in fig. 8) is set to, for example, half the maximum luminance, and the luminance value H in the seek shadow region first falls to the threshold value H_vThe following pixel, in this example, is pixel # 62.

In other embodiments, the brightness may be in the opposite direction, with increasing pixel numbers from unlit to lit CCD cells; depending on the arrangement of the elements of the light source 33, the CCD unit 32 and the shadow-providing body 35, and the internal structure of the CCD unit 32 employed. In such a case, the pixel whose brightness first exceeds the threshold value is sought.

Position values are generated after the three phases are illuminated, read and processed. These three phases determine the frequency at which the position value is obtained. The measurement resolution is the pixel pitch R of the CCD unit corrected by the geometric relationship a, which is given by the mounting distance between the respective elements.

For ratio a (see fig. 9):

A＝s’/s＝x₃/x₂

wherein:

s-shadow provides the actual movement of the edge

s' -shadow provides the projected motion of the edge on the CCD plane

x₂Providing a distance between an edge and a light source for optical shading

x₃Distance between CCD plane and light source

This process determines the position by calculating the pixels, and is therefore a digitisation process. The shifting and conversion of the linearity parameters such as module sensitivity has virtually no effect on the results compared to the simulation process. If the ratio a is determined for the actual value, the variation of the assembly also has only a minor effect. At x₃＝21mm、x₂In a practical embodiment of 20mm, a nominal value of the ratio a of 1.05 is obtained, that is to say the specific distance over which the shadow-providing edge 35 is moved can produce a 1.05-fold transformation in the shadow region SV in the plane of the CCD unit 32. Assuming an assembly variation x of + -0.3 mm₃I.e. possible variations in the distance of the CCD-unit 32 from the light source 33, and x at the upper end₃21.3mm and x₂The assembly tolerance range of 20mm, so the ratio a in this case is 1.065. The ratio change in this example was 1.065/1.05-1.014, or + 1.4%. This offset can be eliminated by a single calibration, for example, in production. This linearity is almost entirely determined by the accuracy of the pixel pitch in the chip geometry, and its offset is almost small.

While the above-described method for determining the position of the shadow providing edge 35 and thus the position of the diaphragm 13 has given exact and linear position values, interpolation may result in a more accurate position resolution. In this broadened embodiment, the estimate of pixel luminance H yields a position score, for example, between pixels 61 and 62A resolution (see fig. 10) which is finer than the pixel pitch R, in which the luminance values of the pixels are inserted in the region of the determination threshold. The purpose of this is to determine the luminance pattern and the decision threshold H_vThe position of the intersection is assigned to the intersection according to the value of the virtual position scale, the x value of which corresponds to the actual number of pixels among the pixels.

To this end, a decision threshold H is sought_vAnd the left and right two pixels of the threshold value, and determines the distance ah of the luminance values from the threshold value. As shown in fig. 10 or 11:

ΔH₁＝H₁-H_v

ΔH_r＝H_r-H_v

the distance Δ x, which is a multiple of the pixel width at the intersection, calculated from the central axis of each of two adjacent pixels (pixels #61 and #62 in this example) and the luminance distance Δ H of the pixel #61 (left adjacent pixel) to the left of the intersection are in the following relationship:

Δx₁/(Δx₁+Δx_r)＝ΔH₁/(ΔH₁+ΔH_r)

when (Δ x)₁+Δx_r) 1 (one pixel width):

Δx₁＝ΔH₁/(ΔH₁+ΔH_r)

with respect to pixel #62 to the right of the intersection to be found (right neighbor pixel), the following relationship exists:

Δx_r/(Δx₁+Δx_r)＝ΔH_r/(ΔH₁+ΔH_r)

when (Δ x)₁+Δx_r) 1 (one pixel width):

Δx_r＝ΔH_r/(ΔH₁+ΔH_r)

in this example, the value at the intersection is 61.7. If the luminance in the interpolated region is an ideal straight line, both calculations may yield the same result, and in principle one of the two calculations may be performed. However, both calculations are performed and the results averaged to minimize errors caused by the luminance profile or measurement inaccuracies that are not exactly straight lines in the transition region under consideration, which averaging is desirable.

In other embodiments, the conditions on either side of the intersection of the non-illuminated and illuminated CCD elements may be swapped; in this case, the left and right indicators may swap their functions as needed, with the interpolation formula also changing.

In addition, other embodiments may be adopted in which luminance values of two or more pixels are employed. The position can then be obtained by performing a number of calculations and averaging several results. In another useful approach, a different linear interpolation than that discussed herein may be employed, or an interpolation with data from pixels that are not immediately adjacent.

The shift and transformation of the linear parameters like module sensitivity only have an influence on the result in the interpolation region. The slope of the luminance pattern in the shadow transition region, which is obtained by the shadow providing the sharpness of the shadow with which the edge is cast on the CCD plane, is not important, since the interpolation is largely unaffected by it, only the linearity of the luminance pattern has a significant influence on the accuracy of the interpolation.

Regardless of the method described above, other procedures for improving sensor performance may be employed, which are based on the basic principles already described. These procedures are described below:

using filtering to improve interference immunity

The immunity of the sensor can be increased by the filter. The luminance values and the position determination itself of the pixels may be filtered. In the first case the program operates with a luminance value which is an average of a number of pixels or a number of pass events, while in the second case a number of initially determined position results are collected together, a position value is derived, which is then used for further processing.

Compensating for assembly variations

In a defined phase, for example in the stop phase before the actual metering of the stroke, the position value of the phase can be determined and stored in a reference memory. In the active motion phase, the position values associated with the previously determined reference values are processed. This procedure allows automatic compensation of the stop position assembly variations that occur during production and the offset that occurs during operation (e.g. thermal expansion), thus improving accuracy.

Compensating for scale errors

In another alternative, two or more known positions, referred to as reference positions, may be used to calibrate the position sensor. This may be done once in the production or testing procedure or repeatedly during the operation.

In the first case, the reference position is provided by an external device, for example a distance position or an external measuring device. From the measured position values at these reference positions and from knowledge of the actual positions of the reference positions, a correction value for calibrating the position sensor can be determined and stored for further processing.

In the second case where the scale determination is repeated, for example, a known position of the mechanical buffer or a reference signal from other available devices is necessary to determine the position. If the diaphragm is in such a known position during operation, the position value resulting from this positioning may generate a correction value for calibrating the position sensor, and the position value may be stored for further processing.

Compensation of light sensing parameters

In another embodiment, fully illuminated pixels are used as a representative value of the illumination intensity. To this end, for example, suitable groups of pixels may be employed to provide the average brightness. The illumination intensity can be used to control the illumination so that the available range can be optimally utilized, for example, the brightness or on-time of the light source can be controlled so that the illumination intensity of a fully illuminated pixel is slightly below the burn-out limit of the CCD module. For each measurement, the illumination intensity is corrected using the previously obtained ratio, thereby eliminating variations in the illumination parameters due to, for example, aging.

Compensation for dust and pixel offset

In another embodiment, the mechanical structure of the sensor may be configured such that the entire pixel range or a large part thereof may be illuminated in a defined phase, for example in a stop phase in which an actual metering stroke is performed. One possible example is to use, for example, the shadow-providing edge 35 facing the diaphragm for evaluation, whereby during the course of the stroke movement the shadow-providing edge sweeps over the sensor and obscures a part of the area of the CCD-cell which was illuminated in the previous rest position. In this phase, the brightness of all relevant pixels is determined separately and stored in the reference memory. The deviation of the measured value of an individual pixel from the ideal value can be compensated for, for example, in the form of a correction. In the active motion phase, the brightness of each pixel is first corrected, and then corrected in each measurement using the previously obtained reference value. With this procedure, it is possible to compensate for the sensitivity shift of each pixel caused by the manufacturing process and to some extent by dust, thereby improving the accuracy or operational reliability.

Naturally, it is also possible to arrange the CCD receptors in two or more rows, thereby improving safety against signal loss due to contamination with an increased number, or improving measurement accuracy by averaging. For particularly large run lengths, two or more CCD rows may be combined, thereby widening the measurement area of a single row beyond the functional limitations of the single row.

The motor driven metering pump detailed in the examples may vary in detail, and elements such as motors, gears, cams and other structural details may also vary. It is important, however, that the oscillating movement generated by the drive means is detectable by a position sensor, which position sensor provides an actual signal which is in a fixed relationship with the position of the reference element and thus also with the displacement means, so that with this value information about the movement of the displacement means can be obtained.

List of labels

1 cam case

2 electric motor (asynchronous motor)

3 case lug

4 support plate

5 casing cover

6 electronic device in housing cover

7 adjusting device

8 stroke adjusting pin

9 cover

10 control line

11 Gear (reduction gear)

12 measuring head

13 diaphragm

14 inlet valve

15 outlet valve

16 measuring cavity

17 camshaft

18 longitudinal axis

19 connecting rod

20 push arm

21 cam impact surface

22 cam carrier

23 compression spring (Return spring)

24 support plate

25 compression spring collar

26 bushing in bearing plate

27 bushing in stroke adjustment pin

28 electronic shell

29 Power setting for Motor drive

30 diaphragm core

31 sensor carrier

32 receiver, CCD unit

33 light source

34 drive electronics

35 as a reference element

36 position sensor

37 differentiator

38 nominal value setting

39 nominal value-actual value comparison

40 PID regulation

41 position correction

42 amplifier

SV shadow pattern

h bright area

d dark space

#58- #65 CCD cell (Pixel)

H pixel luminance

H_vComparing threshold (VS) brightness

H₁Luminance of a pixel left of the intersection point (left-hand side adjacent pixel) having luminance VS

ΔH₁Luminance difference between luminance values of left-hand side neighboring pixels and comparison threshold

H_rLuminance of pixel on the right of intersection point (right-hand adjacent pixel) with luminance VS

ΔH_rLuminance difference between luminance values of right-hand adjacent pixel and comparison threshold

Δx₁Left hand adjacent pixel location demarcation midline of intersection point with brightness VS

Δx_rRight hand adjacent pixel position demarcation midline of intersection point with brightness VS

x₁Distance between shadow-providing edge and CCD plane

x₂Distance between shadow-providing edge and light source

x₃Distance between CCD plane and light source

p₁Operating pressure p₁

p₂Operating pressure p₂

p₃ Operating pressure p₃

p₄Operating pressure p₄

x_T1Operating pressure p₁Lower quiescent zone

x_T2Operating pressure p₂Lower quiescent zone

x_T3Operating pressure p₃Lower quiescent zone

x_T4Operating pressure p₄Lower quiescent zone

s-shading provides the actual movement of the edge

The s' shadow provides the projected motion of the edge

D measurement Performance

Length of HL mechanical stroke

SG controller output

KSG corrected controller output values

MA (U, f) Motor drive (pressure, frequency)

Factor of k1 location-dependent location correction

Factor of k2 performance amplifier

Factor of k3 velocity signal offset

x_sNominal value of position of displacement means

Actual value of the position of the x-displacement means

x_s1Controlled shifting of the position of a displacement device

v_sNominal value of speed of displacement device

v₁Actual value of speed of displacement device

V_s1Controlled deflection of speed of displacement device

Claims (31)

1. Metering pump with rotary drive motor and oscillating piston, in which the rotary motion of the drive motor (2) is converted by a transmission into an oscillation of a connecting rod (19) so that a displacement device actuated thereby performs a linear oscillation with the continuous rotation of the drive motor (2), thus conveying the medium to be metered in a metering head (12) which is arranged along the longitudinal axis of the connecting rod (19) and cooperates alternately with outlet and inlet valves to produce a pressure stroke and a filling stroke, characterized in that a reference element (35) is associated with the connecting rod (19), the position of said connecting rod being sensed by a position sensorIs detected by a detector (36), wherein the position sensor provides an actual signal (x)₁) In fixed relation to the position of the reference element and thus of the displacement device, and which also provides information relating to the movement performed by the displacement device, so that the electronic control system of the metering pump can react to the operating conditions of the metering circuit and of the pump, reading from the position sensor (36) a signal (x) relating to the position of the connecting rod (19)₁) Is transmitted to the control circuit within the control accuracy of the control circuit and influences the rotational speed of the drive motor (2) and thus the linear movement of the connecting rod and the displacement device so as to follow a predetermined nominal pattern (38).

2. Dosing pump according to claim 1, characterized in that the position sensor (36) detects the position of the reference element (35) on the non-contact principle.

3. Metering pump according to claim 1, characterized in that the reference element (35) associated with the connecting rod (19) and the position sensor (36) is outside the metering head.

4. Dosing pump according to claim 1, characterized in that the reference element (35) influences the path from the light source (33) to a position sensor (36) cooperating therewith, which is fixed to the pump housing or another stationary component, operating in a photosensitive manner.

5. Metering pump according to claim 4, characterized in that the reference element (35) is a shadow-generating body or a shadow-providing edge, and the position sensor (36) fixed to the pump housing or another stationary component in cooperation with the reference element is constituted by a light receptor (32) in the form of a series of photo-electric coupling devices (CCD).

6. Dosing pump according to claim 1, characterized in that the position sensor (36) is arranged on its own sensor carrier (31) which is fixed to the pump housing or another stationary component.

7. Dosing pump according to claim 5, characterized in that the light source (33), the shadow-generating body or shadow-providing edge (35) and the light receiver (32) constitute a light box type device, the measured values being fed continuously or intermittently to an electronic control system.

8. Dosing pump according to claim 5, characterized in that the light receptor (32) of the position sensor (36) consists of a number of linearly arranged receptors (32).

9. Dosing pump according to claim 8, characterized in that the photoreceptor (32) of the position sensor (36) consists of 128 pixels.

10. Metering pump according to claim 4, characterized in that the light source (33) is a Light Emitting Diode (LED) which is arranged relative to the light receiver (32) of the position sensor (36) so that the light beam directed by the LED to the receiver is not interrupted by the connecting rod (19).

11. Dosing pump according to claim 9, characterized in that the start value of the position sensor (36) is generated by inserting the luminance values of a plurality of pixels into the shadow transition region.

12. Dosing pump according to claim 1, characterized in that filtering is adopted when processing the signal for the position sensor (36).

13. Dosing pump according to claim 1, characterized in that the zero error of the position sensor (36) is eliminated by reference to a memory.

14. Dosing pump according to claim 1, characterized in that the calibration error of the position sensor (36) is eliminated by using one or more reference positions.

15. Dosing pump according to claim 9, characterized in that the light source (33) is controlled or adjusted by using the pixel brightness values obtained to compensate for variations in the illumination of the position sensor (36).

16. Dosing pump according to claim 9, characterized in that the brightness variations between the pixels of the photoreceptor (32) are compensated for by using a reference memory for the sensitivity of each pixel.

17. Metering pump according to claim 1, characterized in that the value to be set by the stroke adjustment device (7) is determined directly by the position sensor (36) by measuring during the metering process.

18. Dosing pump according to claim 1, characterized in that the electronic control system recognizes that the blockage or stroke in the displacement device is not fully completed by evaluating the signal for the position sensor (36).

19. Metering pump according to claim 1, characterized in that the drive motor (2) is operated with slip, in which case an asynchronous motor is used, while the electronic control system defines a nominal stroke frequency or a nominal stroke period for the displacement device as a function of the nominal rotational speed of the drive motor and known characteristics of the transmission, and also determines the actual stroke frequency or the actual stroke period of the displacement device by evaluating the signal of the position sensor (36), wherein the slip of the drive motor can be calculated and the nominal rotational speed can be changed by comparing the actual stroke frequency of the displacement device with the nominal stroke frequency or comparing the actual stroke period with the nominal stroke period, so that the displacement device is finally moved at the desired stroke frequency.

20. Metering pump according to claim 1, characterized in that the drive motor (2) is operated with slip, in which case an asynchronous motor is used, at the same time, the electronic control system defines a nominal stroke frequency or nominal stroke period for the displacement device in dependence on the nominal rotational speed of the drive motor and known characteristics of the transmission, and also determines the actual stroke frequency or the actual stroke period of the displacement device by evaluating the signal of the position sensor (36), wherein by comparing the actual stroke frequency of the displacement device with a nominal stroke frequency, or comparing the actual stroke period with a nominal stroke period, a slip of the drive motor can be calculated, and the electronic control system may determine the force acting on the displacement device by the determined drive motor slip and known transmission characteristics to reduce the operating pressure of the metering medium.

21. Metering pump according to claim 1, characterized in that the drive motor (2) is operated with slip, when an asynchronous motor is used, while the electronic control system determines a nominal speed for the displacement device at each instant during metering, depending on the nominal rotational speed of the drive motor and on known transmission characteristics, and also determines the actual speed of the displacement device by evaluating the signal of the position sensor (36), wherein the instantaneous slip of the drive motor can be calculated by comparing the actual instantaneous speed of the displacement device with the nominal speed, and also in connection with the known transmission, the instantaneous force in the displacement device can be deduced.

22. The metering pump of claim 21 wherein the electronic control system uses the observed force pattern on the displacement means to reduce the operating pressure of the metering medium.

23. Metering pump according to claim 20 or 22, characterized in that the electronic control system recognizes an operation outside a specific pressure range from the determined operating pressure of the metering medium and regulates the metering when a maximum permissible pressure, indicated by the specification of the metering pump or set by the operator, is exceeded or when a predetermined minimum pressure is not reached.

24. Metering pump according to claim 20 or 22, characterized in that the displacement means is a partially elastic diaphragm (13), wherein the electronic control system determines the expected metering error from the determined operating pressure of the metering medium and the known relationship of the metering performance to the operating pressure, and influences the rotational speed of the drive motor (2) and thus the stroke frequency to counter the expected metering error.

25. Dosing pump according to claim 1, characterized in that the control device influences the position, speed or acceleration of the displacement device alternately by changing the rotational speed of the drive motor (2).

26. Dosing pump according to claim 1, characterized in that the control device can deliberately reduce the speed of the displacement device during the filling phase and/or during the pressure phase in order to counteract the pressure drop caused by the flow resistance.

27. Metering pump according to claim 1, characterized in that the desired stroke length is transmitted by the operator to a control device for electronically limiting the movement of the displacement device to the stroke length to be performed, wherein the control device stops the drive motor (2) after the desired stroke length has been completed, switches it to reverse, then performs a filling stroke, and then stops the motor or performs the next pressure stroke.

28. Metering pump according to claim 1, characterized in that the control device during the pressure phase dispenses the forward movement of the displacement device by driving the drive motor (2) for a period of time which is determined by the cycle rate of the metering stroke, so that the metered medium is dispensed as uniformly as possible even in the case of a slow metering stroke.

29. Dosing pump according to claim 21, characterized in that the displacement means are partly in the form of an elastic diaphragm (13), the electronic control system observing the opening of the outlet valve (15) from the instantaneous forces acting on the diaphragm (13) and measuring the rest area due to the elastic deformation of the diaphragm (13) with the aid of said observation.

30. Metering pump according to claim 29, characterized in that the actual stroke is not affected by the derived deformation of the diaphragm, wherein after the desired stroke length has been reached the control device stops driving the motor (2) by opening the outlet valve (15), switches the motor to reverse, then performs the filling stroke, then stops the motor or performs the next pressure stroke, thereby eliminating the error caused by the deformation of the diaphragm with respect to the stroke or the metered volume and substantially reducing the dependency of the metered amount on the back pressure.

31. Metering pump according to claim 29, characterized in that the actual centre frequency is not influenced by the derived diaphragm deformation, wherein the control device determines a correction for the error caused by the diaphragm deformation with respect to the stroke or the metered volume and, with the aid of said correction, varies the nominal rotational speed of the drive motor (2) so as to eliminate the error caused by the diaphragm deformation.