DE2930559A1 - METHOD AND CIRCUIT FOR CONTROLLING THE SPEED OF A DC MOTOR - Google Patents

Description

The invention relates to a method for controlling the speed of a DC motor according to the preamble of claim 1 and a circuit arrangement for performing this method according to the preamble of claim 4.

Such systems for controlling motors are commonly used in particular in precision servo mechanisms. they provide the speed control of the motor in both directions of rotation safely. The direction of the controls is through signal sequences controls which are given by choppers. The cyclical ratio of these signal sequences is determined by the size of the operating signal that is sent to the motor. Among the different Ways to operate the bridge that is formed by the four branches mentioned, for example, the one cited at which the control elements of the first two branches are made conductive by a first signal emanating from a chopper, while the control elements of the second pair of branches are conductive in phase opposition to the conduction of the control elements in the first arm be made.

With this type of circuit, the two control elements in a first branch arm are simultaneously conductive or blocked. If those As a result, both elements become conductive, the current starts from the positive pole to the negative pole of the supply source one of the controls, the motor armature and the other control

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build up. If these two elements are not made conductive, the current can only continue to flow to the source with recovery of energy / whereby the voltage of the motor is necessarily higher than that of the supply source.

If the supply source does not have a sufficiently low resistance or Self-induction impedance, considerable overvoltages can occur at the motor connections. These lead to Interferences and are dangerous for the semiconductors that make up the control elements. This effect can also occur in the course of a Phase occur, which is called the "braking" phase and in which the current flowing through the motor armature this in a Seeks to rotate in the opposite direction to the actual direction of rotation of the motor.

The circuit arrangement described above also has the disadvantage that the motor is subjected to polarity reversals at the same time as the chopper frequency, which is undesirable.

Since, after all, all control elements of the bridge are constantly in chopper mode running, there are significant energy losses during the transitions from the locked and the conductive state.

The object of the present invention is to meet the various above mentioned To eliminate disadvantages.

As far as the method according to the invention is concerned, this task is

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solved by the invention described in the characterizing part of claim 1; advantageous developments of this method are in claims 2 and 3 specified.

As far as the circuit arrangement itself is concerned, the one according to the invention Solution described in the characterizing part of claim 4; advantageous embodiments of the invention are in claims 5-16 specified.

An exemplary embodiment of the invention is described below with reference to FIG Drawing explained in more detail; the single figure shows a circuit diagram of a supply device according to the invention.

In the drawing, the general reference numeral 1o denotes a supply device for a DC motor 12 having an armature control. This is connected in a bridge, which powers the motor so that it rotates in the first or second direction depending on the user's preference.

The current is fed from a supply source, which consists of a voltage source. This delivers via a Line 14 has a positive voltage. The bridge contains two branches 16,18 that connect to the ends of the motor 12 and the supply source are connected. This enables a current to flow in the motor in a first direction. A pnp transistor 2o is in the arm 16 switched, the "all-or-nothing" control of the current flow serves. In the same way, an npn transistor 22 is connected into arm 18, which acts as an "all-or-nothing" control element for the

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Current flow is used. The bridge also includes a second pair of arms 24,28, which with the ends of the motor 12 and with the Supply source are connected so that a current flow in the motor in a second direction, opposite to the first direction, is possible is. A pnp transistor is arranged in arm 24 and forms a "All-or-nothing" control element for current flow. Similarly, an npn transistor 3o is provided in the arm 18, its Sehaltfunktion that of the transistors 2o, 22,28 is identical. As previously mentioned, this type of bridge is known to those skilled in the art of controlling DC motors, particularly at Precision servo mechanisms, known. The description of the bridge concludes with the remark that each end of the motor 12 to the supply line 14 via the oppositely connected diodes 32,34, which are parallel to the emitter-collector paths of the

is. Transistors 2o, 28 are connected / As in more detail later explained, the task of these diodes is to transfer the energy supplied by the motor in the braking phase to the supply source to dissipate. Each end of the motor 12 is also connected in a corresponding manner to a resistor 36, which in turn has opposite directions connected diodes 38 and 4o is connected to ground. In addition, each of the emitters of the transistors is 22.3o over one Resistor 42 connected to ground. The diodes are 38.4o, as is known from servomechanisms, also "freewheeling" diodes called.

The bridge just described is generated as a function of the size of a control signal generated by a voltage generator 44

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is operated by an electronic device. The size of the signal which is emitted by the generator 44 can be determined opposite sides of a mean value (in the described embodiment O) develop, thereby the direction and the speed of motor rotation can be controlled as a function of this quantity. If the value of the signal which from the generator 44 is equal to the mean value, the motor 12 is not rotated. If, generally speaking, the Motor is operated in a first direction of rotation, which corresponds to the flow of current in the branches 16,18, so are through the electronic device made the transistors 2o, 3o conductive in a complementary manner, i.e. in phase opposition by following cyclical pulses; At the same time, the transistors 22, 28 are operated so that the transistor 22 is conductive and the transistor 28 Is blocked. If, on the other hand, the motor is operated in the second direction of rotation, which is opposite to the first direction, the transistors 28, 22 are made conductive in a complementary manner, that is to say in phase opposition, by following cyclic pulses the transistors 2o, 3o are correspondingly blocked or conductive. The electronic device includes a first generator that a first comparator 50 and a second comparator 52. These compare the signal emitted by the generator 44 with a periodic, sawtooth-shaped signal generated by a generator 54 is delivered. The comparator 5o outputs an operating signal which controls the conductivity of the transistor 2o, if the The signal output by the generator 54 is smaller than the signal output by the generator 44. On the other hand, the comparator 52 inputs Operating signal which controls the conduction of transistor 3o,

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when the sawtooth-shaped signal emitted by the generator 54 is greater than the signal output by the generator 44. The electronic device also contains a second generator, which comprises a third comparator and a fourth comparator 58. These compare the sawtooth signal generated by the generator 54 with a reference signal which is generated by an amplifier 6o with the gain -1. Whose entrance receives the operating signal which is developed at the output of the generator 44. The comparator 56 outputs a signal that the line of the The effect of transistor 28 is when the signal generated by generator 54 is less than the signal supplied by amplifier 6o. In appropriate The comparator 58 outputs a signal for actuation of the conduction of the transistor 22 when the output from the generator 54 is output Signal is greater than the signal generated by the amplifier 6o. It can be seen that the two generators only each could comprise a comparator whose output signal then the line of the transistor pairs, which are assigned to each generator, would steer in phase opposition. Nevertheless, for reasons that will become clear in the course of the following description, preferred when each comparator contains two comparators.

If the signal generated by the voltage generator 44 has a positive value which corresponds to the mean value by the motor 12 corresponding current that flows through the arms 16,18, then the transistors 2o, 3o by "chopping" (chopping) operated in phase opposition, while the transistors 28, 22 are blocked or conductive. If, on the other hand, the generator 44

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output signal has a negative value, which is a mean Current in the motor 12 corresponds to which flows in the arms 24,26, the transistors 28,22 are in phase opposition by "chopping" operated while the transistors 2o, 3o are blocked or conductive.

In short, the first generator device indicates 50, 52 the control elements 2o, 3o, which lie in the arms 16,26 (which are connected to the first end of the motor), at least an operating signal which the line of the elements 2o, 3o in in a complementary manner, i.e. in phase opposition. The second generator device indicates 56, 58 in a similar manner the control elements 28,22 which are connected in the branches 24,18 (which in turn are connected to the second end of the motor 12), at least one second operating signal which controls the conduction of the elements 28, 22 in a complementary manner. The two generator devices respond to the magnitude of the control signal emitted by generator 44. That way will normally the first operating signal is generated cyclically and the second operating signal is generated permanently or vice versa, depending on whether the size of the control signal stands for the operation of the motor in the first direction of rotation or in the second direction of rotation.

The circuit arrangement also contains a comparator 7o, which the voltage at the terminals of the resistor 36 (the is representative of the total current flowing through the "free wheeling" diodes) to a reference voltage based on its negative input is given. This creates an initial

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signal generated that locks the comparators 52,58 in a state in which the transistors 22 and 3o are not conductive. As the voltage at the terminals of the resistor 36 for the braking current is representative, a device is thus realized in which the intensity of braking is limited. Of course the braking current can also be measured in a way other than a resistor, e.g. an optoelectronic device.

The circuit arrangement also contains a comparator 8o. This compares the voltage at the terminals of the resistor 42 with a further reference voltage which is present at the inverter terminal 82 is delivered. As a result, an output signal is generated which blocks the comparators 5o, 56 in a state in which the transistors 2o, 28 are not conductive. As the voltage at the terminals of the resistor 42 for the drive intensity is representative, has the blocking of the transistors 2o, 28, which takes place when the drive intensity is greater than a certain one Value is, a current flow results that through the motor through the diode 38 and the transistor 22 or through the diode 4o and the transistor 3o flows. If the drive current falls below the threshold value at which the comparator 8o was triggered, the transistors 2o, 28 are no longer blocked by the comparator 8o.

Since the transistors 2o, 3o operated in phase opposition during operation as well as the transistors 22, 28, it is necessary to take precautionary measures in the event of a short circuit. This could e.g. be generated when transistor 3o becomes conductive,

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before transistor 2o has stopped conducting, or vice versa. For this purpose, the comparators 52,58 are connected so that they switch from the blocking to the conductive state with a low hysteresis compared to the moment in which the The sawtooth signal becomes larger than the reference signal. This means that the transition takes place at a moment when it is certain that either the Transistor 2o or transistor 28 is blocked. Similarly, the electronic device contains a suppressor, which prevents the transmission of the entire, pulsed operating signals that are output from the comparators 52,54 and off the comparison of the sawtooth-shaped signal with the signals emitted by the generator 44 and the inverter 6o result. More accurate: The suppression device blocks the transmission of a pulse from the transistors 22,3o shortly before the end of this pulse. For this purpose, the suppression device contains a device which detects the instant in which the value of the sawtooth-shaped Signal is equal to or near the peak value, i.e. just before a command to effect conduction to the transistor or transmitted to transistor 28. In this way, the amplifiers 52, 58 are acted upon in such a way that the transistors 22, 3o be blocked. The aforementioned detection device is formed by a comparator 9o, which the sawtooth-shaped signal compares with a reference signal and momentarily emits a signal which blocks the transistors 22,3o by means of the comparators 58,52, when the sawtooth signal has a value that is greater than the reference signal. This happens until the moment in which the sawtooth signal becomes klsinar as the control signal, which is supplied by generator 4 4,

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- 18 The supply facility described above works as follows:

First, assume that the engine is in a steady state is running, i.e. a constant value control signal (e.g., a positive control signal) is generated by the generator 44 such that the Engine speed is stabilized. Assuming that the value of the control signal is positive, it follows that the comparators 5o, 52 feed chopped operating signals to the transistors 2o, 3o, which make them conductive in phase opposition. Given the The polarity of the transistors 2o, 3o can be seen that the operating signals applied to their base connections are identical if these transistors are to be made conductive in phase opposition. Nevertheless, a bridge can be built where the Chopping signals are complementary in a strict sense.

On the other hand, it follows from the magnitude of the voltages which are applied to the input terminals of the comparators 56, 58 that the Transistor 28 is normally permanently blocked and that transistor 22, in contrast, is permanently conductive. The motor is thus operated at a speed which is a function of the cyclic ratio of the chopped signal which is on the transistors 2o, 3o is connected, i.e. which is a function of the size of the operating signal output by the generator 44.

The permanent state is divided into two alternating cyclical phases: when transistor 2o is made conductive, and the transistor 3o is blocked, the current flows from the line

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14 through transistor 2o, motor 12, transistor 22 and resistor 42 to ground. The current running through the motor increases at a rate that is essentially limited by the inductance of the motor. When the transistor 2o blocked and the transistor 3o is made conductive, is the self-induction effect, which results is greater than the back electromotive force of the motor; the current then continues to flow through the engine while it takes off. The current then flows through the freewheeling diode 38, the motor 12 and the transistor 22. It is to recognize that the npn transistor 3o cannot conduct any current from earth to the motor, although it is made conductive. The result is that all of the current flows through diode 38.

When the operating signal output by the generator 44 decreases is, but retains the same positive polarity, two operating modes can be generated: In the first operating mode, in which the size of the signal is only slightly modified, the modification of the cyclic ratio of the chopper signal is sufficient, which is applied to the transistors 2o, 3o does not act to reverse the direction of the current flowing through the motor. It a sequence of increases and decreases in drive current is then generated in a manner which is substantially identical with the operation in the steady state, however the mean value of the current decreases progressively until a new steady one State is reached. In the second operating mode, it is sufficient to modify the cyclic ratio, the direction of the Reverse current over the course of time periods when transistor 3o is rendered conductive. The braking current then flows through the

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Diode 4ο, the motor 12, the transistor 3o and the resistor 42. This operating phase then corresponds to a period of rheostatic braking. If during this braking period the one at the resistor applied braking current reaches a value that is higher than the specified one Threshold, does the comparator 7o block the switching on of the transistor 3o into the conductive state? the current then flows back to the source with energy recovery through diode 32.

When the polarity of the operating signal output by the generator 44 is changed (from the positive to the negative), the transistor 2o is permanently blocked and the transistor 3o is made permanently conductive. The transistors 2 8, 22, on the other hand, are made conductive in phase opposition.

As long as the voltage of the back electromotive force of the motor is of opposite sign than the mean value of the new one The operating voltage of the motor is determined by the cyclic ratio of the chopper signal applied to the base electrodes of the transistors 2, 8.22 is determined, the motor is traversed by a braking current, which in the diode 4o, the motor 12 and the transistor 3o flows. This braking phase lasts until the moment in which the voltage of the counter-electromotive force has its sign changes. Then the motor is rotated in the opposite direction by the energy coming from the source.

It is quite obvious that the function of the utility, which has just been described is completely symmetrical. In other words: the circuit arrangement works as well if

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the engine is in a steady state with a negative value of the operating signal and when this signal is in the direction of positive values is changed. In this case, the transistors 2 8,22 are made conductive by chopping at the beginning, while the transistors 2o, 3o are blocked or conductive.

The elements which the current flow in the described embodiment controlled are transistors; however, it will be apparent that other equivalent devices such as thyristors or triacs, are also suitable.

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Claims (9)

Claims 1.} Method for controlling the speed of a DC motor with an armature control that is connected to a bridge, which on the one hand includes a first pair of branches connected to each end of the DC motor and to the terminals a supply source are connected in such a way that they can be flowed by a current which controls the rotation of the motor controls in a first direction and, on the other hand, a second pair of branches connected to each end of the motor and with the connections of the supply source are connected so that they can be traversed by a current which the Controls rotation of the motor in a second direction of rotation, with an "all-or-nothing" control element in each branch of the two pairs is connected, characterized in that the control elements (2o, 3o), which in the two arms {16,26} the bridge are placed, which with one end of the motor (12) 90988R / 0900 ~ ² ~ are connected, made conductive cyclically in phase opposition are, and that at the same time the controls (28,22), which are connected in the two arms (24,18) of the bridge, which are connected to the other end of the motor (12), normally be made conductive or non-conductive. 2. The method according to claim 1, characterized in that the control elements (2o, 3o), which are made cyclically conductive, operated by periodic pulses, the cyclic ratio of which is representative of the operating voltage of the DC motor (12) is. 3. The method according to claim 1 or 2, characterized in that one (2o) of the cyclically made conductive control elements is made conductive after the other (3o) of these elements has become non-conductive. 4. Circuit arrangement for a DC motor with armature control, which is connected in a bridge which, on the one hand, comprises a first pair of branches connected to each end of the DC motor and are connected to the connections of a supply source so that a current flows through them which controls the direction of rotation of the motor in a first direction, as well as a second pair of branches on the other hand, which are connected to each end of the motor and to the terminals of the supply source so that they are from a Current can be traversed, which is the rotation of the motor 909886/0900
ORIGINAL INSPECTED controls in a second direction, one element for "all-or-nothing" control of the current flow is switched in each branch of the two pairs, characterized in that they a first generator device i'5o, 52) contains which at least a first operating signal to the corresponding control elements (2o, 3o) in the two arms (16,26) of the bridge, the connected to the first end of the motor (12), which provides the conduction of said elements in phase opposition controls, as well as a second generator device (56,58), which in the same way to the corresponding control elements (28,22) in the two branches (24,18) of the bridge that connect to the other End of the motor (12) are connected, emits at least one second operating signal, which the line of these elements in Controls phase opposition, the two generator devices responding to a control signal which is used for the operating voltage of the motor is representative, so that they correspond to the first operating signal in a cyclical manner and the second Operating signal in an essentially permanent manner or vice versa output, depending on whether the control signal is for a rotation of the motor in the first or in the second direction. 5. Circuit arrangement according to claim 4, characterized in that the first generator device has at least one comparator (5o) which compares a periodic, sawtooth-shaped signal with a certain polarity with the control signal, wherein the latter can assume a first or a second polarity, depending on whether the motor is in the first or the second direction of rotation. 9098 8 6/0900 device is driven, this comparator (5o) emits the first operating signal. 6. Circuit arrangement according to claim 5, characterized in that the second generator device has at least one comparator (56) which comprises the periodic, sawtooth-shaped signal with a reference signal, the magnitude of which is opposite to that of the control signal, this comparator (56) emits the second operating signal. 7. Circuit arrangement according to claim 5 or 6, characterized in that that the first generator device (5o, 52) contains a first comparator (5o) which outputs an operating signal that the line of a first (2o) control element, which is connected to the branch (16) which controls the first The end of the motor (12) connects to a first connection (14) of the supply source, as well as a second comparator (52), which emits an operating signal that controls the line of a second (3o) control element, which is connected to the arm (26) which connects the first end to the other connection of the supply source, the two comparators (5o, 52) Emit signals which, in phase opposition, cause the two control elements to conduct. 8. Circuit arrangement according to claim 7, characterized in that the second generator device (56,58) has a third Contains comparator (56) which outputs an operating signal that 9 0 9 8 8 a / 0 9 0 0 controls the line of a third (28) control element which is connected to the branch (24) which connects the second end of the motor (12) to the first connection (14) of the supply source, as well as a fourth comparator (58) which is a Outputs operating signal which controls the line of a fourth (22) control element, which is connected to the Z ¹ WaLg (18), which connects the second end of the motor (12) to the other terminal of the supply source, the third and fourth comparator Emit signals that cause the conduction of the third and fourth control element in a complementary manner. 9. Circuit arrangement according to claim 7, characterized in that it contains a suppression device, which on a of the first two comparators (5o, 52) acts, whereby the Operating signal emitted by one of the comparators is suppressed at the beginning and at the end of this operating signal. 10. Circuit arrangement according to claim 8, characterized in that that it contains a suppression device which acts on one of the two further comparators (56,58), whereby the operating signal output by said comparator. is suppressed at the beginning and at the end of this operating signal. 11. Circuit arrangement according to claim 9 or 1o _f, characterized in that said comparator (52) of the first generator 909086/0 3 00 device (5o, 52), which on the suppression device responds, is connected so that it generates a signal that makes the associated control element (3o) conductive when the sawtooth-shaped signal is greater than the control signal, the suppression device being a further device (9o) includes, which detects the transition of the saw-tooth-shaped signal in the vicinity of the maximum value and the transmission of the Operating signal prevented in the case of this detection, whereby the end of the operating signal is accelerated. 12. Circuit arrangement according to the combined claims 11 and 1o, characterized in that the comparator (58) of the second generator device (56, 58), which responds to the suppression device, is connected in such a way that it emits a signal generated, which makes the associated control element (22) conductive when the sawtooth-shaped signal is greater than the value of the signal, which is opposite to the value of the control signal, wherein the detection device (9o) the transmission of the operating signal prevented when the detection is present, whereby the end of the operating signal is accelerated. 13. Circuit arrangement according to the combined claims 9 and 1o, characterized in that the one connection (14) of the supply source connected in a manner known per se to the ends of the motor (12) via two freewheeling diodes (32,34) is, the parallel to the control elements (2o, 28), which the first (5o) of the first two comparators (5o, 52) and the one (56) of the two further comparators (56,58) are assigned, 909886/0900 - 7 - are connected, a device being provided which measures the current flowing through the freewheeling diodes, as well as a Device which acts on said one of the first two comparators (5o, 52), and the line of the associated Control element interrupts when the current is greater than a second specific value. 14. Circuit arrangement according to claim 13, characterized in that that the device causing the interruption in the same way on the named of the two further comparators (56, 58) acts and interrupts the line of the associated control element if the current is greater than the second determined Is worth. 15. Circuit arrangement according to claim 13, characterized in that that a device is included, which by the control elements (2o, 28), which are parallel to the freewheeling diodes (32,34) are connected, measuring the flowing current, as well as a device which is based on the second of the first two comparators (5o, 52) acts, whereby the line of the associated control element (3o) is interrupted when the current is greater than a third certain value is. 16. Circuit arrangement according to claim 15, characterized in that that the device causing the interruption of the line, acts in the same way on the other of the two further comparators (56, 58), whereby the line of the associated 9 0 9 8 8 6/0900 Control element (22) is interrupted when the current is greater than the third specific value. Description - 9 - 909886/0900