DE1183701B - Photoelectric device for measuring the position or length of an object - Google Patents

Description

Photoelectric device for measuring the position or length sizes for an object It is a device for measuring width, thickness or length known, in which two photoelectric transducers are provided, their sensitivity axes wander in opposite directions across the measurement object with a narrow field of vision. In the known device is a device for measuring hot rolled material, which itself lights up and by means of a lead sulfide cell over a rotating polygon mirror is scanned periodically. But it can also be objects that are not self-luminous act in which a photocell picks up reflected light, and instead of one Polygon mirror, for example, a lens wheel can be provided. Each of the transducers delivers a pulse when its sensitivity axis is over the edge of the target deletes. The radiation falling on the radiation receiver then changes erratic, and this jump appears as an impulse after electrical differentiation, which by means of suitable pulse shapers can still be given a certain, well-defined shape is brought.

Each of these impulses ignites an AC powered thyratron, whose anode voltage is synchronous with the deflection of the sensitivity axis.

Such a thyratron then acts as a controlled rectifier and supplies a direct current measured value dependent on the position of the measuring lens edge.

When the pulse appears when the positive half-wave of the If the supply voltage has set in at the thyratron, then the thyratron practically burns during this entire half-wave, before it occurs again when the negative half-wave begins clears. If, on the other hand, the ignition pulse does not appear until the end of the positive half-wave the grid of the thyratron is given, then the thyratron ignites only briefly and immediately extinguishes as soon as the applied anode voltage reverses its sign. The direct current through the thyratron or the voltage drop across one of them So resistance changes continuously from a maximum value down to zero, depending according to the phase position of the ignition pulses to the supply voltage of the thyratron and thus the position of the edge of the rolled material. Once the thyratron has ignited, others have Impulses on its grid no longer have any influence. Due to the opposite movement of the Sensitivity axes are achieved that with one transducer the pulse becomes effective when passing through one edge of the measuring object first, and at the other transducer receives the pulse generated when passing the other edge of the DUT occurs.

In the known arrangement, the length display by additive Superposition of the two measured position values. This sum depends, as we can see lets linear from the length (or width or thickness) of the object to be measured. pre-condition What is in this case is that the measured direct current values obtained are linear with the position change the edges of the target. In the known arrangement, this is only an approximation the case, and it has been shown in practice that this leads to difficulties obtained when there are either greater fluctuations in the width or position of the object to be measured or places high demands on the measurement accuracy.

An arrangement for measuring the width of sheet metal strips is known (U.S. Patent 2548 590) which avoids these difficulties. There are also two transducers - provided here in the form of two television cameras, through which two fields of view are scanned periodically, in which the two The edges of the sheet metal strip lie. As soon as the probe beam or the sensitivity axis runs over the edge of the sheet metal strip, there is an impulse that depends on its phase position ignites one of two AC powered thyratrons which is fed to a forward or a return winding of a servomotor. This servomotor controls the entire head of the transducer (television camera) Moved across the sheet metal strip to be measured, until the edge of the sheet metal strip lies in the middle of the field of vision. The shift of the two television cameras is measured and gives a measure of the width of the sheet metal strip to be measured. here serves the television camera and the downstream arrangement does not as a measured value transmitter in the true sense of the word, but only as a zero indicator. The distance between the two is simply measured automatically on the edges of the Sheet metal tape adjusting television cameras.

This arrangement requires a frame on which the cameras can be slid are led. The accuracy of the measurement depends on how accurate the television cameras are can be aligned to the edges of the sheet metal strip and how exactly then the Distance between the television cameras is measured. This either requires a lot of effort, z. B. a very stable guide for the television cameras, or gives only a limited one Measurement accuracy. Another disadvantage is that there is a side shift of the entire measurement object without a change in width but the entire adjustment mechanism in Function must occur because every camera is on the edge of the object to be measured (sheet metal strip) must be aligned. As a result, the known arrangement has a considerable inertia, so that with oscillating or fluttering movements of the object to be measured, as z. B. in rolling stock occur very often, a measurement is practically impossible.

Based on such a photoelectric device for measuring the position or length values for an object with a defined scanning area periodically sweeping scanning element, in which when detecting the object an ignition pulse to a controlled rectifier, for example a thyratron, is output which, from a synchronized with the sampling, periodically fed by voltage going to zero, a direct current signal determined by the measured variable supplies, in such a way that the relative phase position of the ignition pulse and supply voltage of the controlled rectifier changes according to the measurand to be determined, The invention consists in the fact that in the case of stationary scanning means Phase position can be changed by means of electrical phase-shifting means.

So there is no shifting and tracking of the entire probe head, as in the known arrangement, but an electrical phase shift. It turns out that a strict and linear measurement is obtained in this way too, as will be explained in more detail below.

The invention is not based on a length measurement of the described Kind of restricted. The invention can also be used for a simple position measurement or Use position control. The invention can be applied in such a way that by the phase shift through an adjustment - similar to the known arrangement the displacement of the probes - is effected. However, due to the phase shift a setpoint can also be set, as will be described in more detail below will.

It is known per se, one through the phase position of two measurement signals measured variable determined to one another by actuating a phase shifter which changes the phase position to represent. Known arrangements of this type are rangefinders for long distances where the finite speed of propagation of light is used for distance measurement. For this purpose the light is amplitude modulated, and from the phase difference between the forward and backward light will be on the distance closed. By means of adjustable mirrors or the like, the optical path length of a Beam changed and the phase difference adjusted to zero, the The travel of the mirror can be read off as a measured length value. But it is there rectifier not controlled by the ignition and that of the rectifier according to the invention Measuring principle occurring problems.

In many cases, the scans will include the scan area sweep at a sufficiently constant speed. But it is useful if as a scanning device, a photoelectric receiver with rotating, from one Synchronous motor driven optical members and a concave mirror in the way cooperates that a linear relationship between the position of the scanning elements consists in the measuring plane and the angle of rotation of the optical members.

The expression "length" is intended in the preceding and in the following Description all types of dimensions, i.e. thickness, width, diameter, etc., are recorded will. "Position" is the distance from a fixed reference point.

The invention is based on the drawings of exemplary embodiments explained.

Some exemplary embodiments of the invention are shown in the figures and described below: Fig. 1 shows an embodiment of an inventive Device for length measurement, e.g. B. a device for measuring the width of Rolling stock; 2 illustrates the mode of operation of the arrangement; Fig.3 shows a Modification of the arrangement according to FIG. 1; F i g. 4 shows another embodiment of a Length measuring device; F i g. 5 shows a modification of the arrangement according to FIG. 4; 6 shows a device for measuring the cutting length of rolled stock; Fig. 7 shows an "optical stop" with adjustable end position; F i g. 8 shows schematically the structure of the probe head in the arrangement according to FIG. 4, and FIG. 9 shows the associated top view; Fig. 10 shows a probe head in which the opposite Scanning of the field of view by means of a single synchronous motor driven rotating polygon mirror takes place; Fig. 11 shows a "linear" Probe head.

In Fig. 1, two probes of the same design are designated by Kt and K2, which each have a field of view or periodically and in opposite directions with a narrow angle of view scans, as indicated in Fig. 1 by the arrows. An example of one Probe head is shown in FIG. This is a "linear" Probe head. From a photocell 10 or some other suitable radiation receiver becomes a field of view via a rotating polygon mirror 11 and a concave mirror 12 periodically scanned in a measuring plane ME. The mirror 12 is, as shown in Fig. 11 can be seen, shaped so that a linear relationship between the position the sensitivity axis in the measuring plane and the angular position of the mirror 11 consists.

The two probe heads Kt and K2 scan one over the edges 13, 14 object to be measured 15, z. B. a sheet metal strip in the rolling mill. The photocell 10 of each probe head delivers when the edge 13 or 14 a jump signal 16, 16 ', which is generated by a differentiating alternating current amplifier V, or V2 is converted into a pulse 17, 17 '. The speed of the Mirror 11 and the number of its sides is chosen so that the pulses 17 and 17 'appear with a frequency of 100 Hertz.

The pulses 17 and 17 ', the position of which depends on the position of the edges 13 and 14, are placed on the grids of thyratrons 18, 19. The thyratrone 18 and 19 are each driven by a pulsating rectified alternating voltage 20 fed. The voltage 20 is rectified by a line frequency AC voltage obtained by means of two Graetz rectifiers 21, 22. The AC voltage is from the secondary windings 23, 24 of a transformer 25 removed. There are two separate ones Secondary windings are provided around the circles of the two thyratrons galvanically in front of each other and to enable a transfer of the DC measured values obtained. The primary winding 26 is fed from the network via a phase shifter 27.

The circuit of the thyratrone goes from the positive pole of the rectifier 21 or 22, via the thyratron 18 or 19, each have a cathode resistor 28 or

29 and the line 31 or 32 to the minus pole of the rectifier. the The cathode of the thyratron 18 is connected to the negative end of the cathode resistor 29 connected by thyratron 19. The negative end of resistor 28 is grounded. Between this and the cathode of the thyratron 19 is a DC voltage, which is the sum corresponds to the currents flowing in the two thyratron circles.

This voltage is at a zero amplifier 33 of a constant reference voltage connected in the opposite direction, which is derived from the mains voltage by means of a rectifier 34 is produced. The zero amplifier 33 controls a motor M, and this rotates the Phase shifter 27 until the DC voltage dropping across resistors 28 and 29 is equal to the reference voltage. With the motor M one is calibrated in units of length Display device 35 connected.

The mode of operation of the arrangement can be seen with reference to FIGS. 2, a to h, illustrated. In these figures, the one on thyratrons 18 and 19 is shown as Supply voltage applied rectified alternating voltage 20 shown as well given on the grid of the thyratrone when sweeping over the measuring objectanten Pulses 17 (Fig. 2, a, c, e, g) and 17 '(Fig. 2, b, d, f, h). The thyratrone 18, 19 ignite when the impulses 17 or 17 'appear and then burn until the voltage 20 goes through zero. Then the anode voltage drops, and so does the Tyratron clears. The current flowing through the thyratrone and resistors 28 and 29, respectively is given by the hatched area, and accordingly The voltage drop across resistors 28 and 29 is also large.

It is to be assumed from a "target state" in which the Pulses 17 and 17 'each appear at the maximum of the supply voltage 20 (Fig. 2, a and b). Then each Tyratron burns for half the period, and so be it appropriate assume that in this state the falling across resistors 28 and 29 The voltage just corresponds to the voltage on the rectifier 34. The zero amplifier 33 receives no voltage. The motor M and the phase shifter 27 remain at rest.

In Fig. 2, c and d, the case is shown that the band 15 shifts to the left without changing its width. Then the pulse comes 17 a Time x earlier, the pulse 17 'comes the same time difference x later. One sees easily that the area A B CD by which the current of the thyratron 18 has increased is exactly as large as the area BCEF (Fig. 2, d) by which the current flows through the thyratron 19 becomes smaller. For the sake of clarity, the areas ABCD and the pulse 17 in FIG. 2, d, again shown in dashed lines. The total voltage so remains at the resistors 28 and 29 with a pure lateral displacement constant without change in width. The zero amplifier 33 and the phase shifter 27 remain unaffected by the shift.

The situation is different if the width of the sheet metal strip is different changes. In Fig. 2, e and f, the case is shown that the left edge 13 of the Tape 15 in the shifted position according to FIG. 2, c, remains, but the right edge 14 by widening the band 15 compared to the one shown in FIG. 2, d Location moves to the right. Then comes the pulse 17 'in FIG. 2, f, around the time y earlier than in Fig. 2, i.e. Pulse 17 'of Figure 2, d, is in Figure 2. 2, f, the For the sake of clarity, again shown in dashed lines. This has the consequence that the current through the thyratron 19 increases by the amount shown in FIG. 2, f, double hatched area GHJK. The resistance at the resistors increases accordingly 28 and 29 dropping voltage, which is then no longer equal to that at the rectifier 34 lying tension is. The zero amplifier 33 responds and the motor M rotates the phase shifter 27. This changes the phase position of the supply voltage 20 compared to the unchanged pulses 17 and 17 '. In Fig. 2, g and h is shown for the sake of simplicity that the pulses 17 and 17 'compared to the fixed supply voltage are shifted, which amounts to the same thing and is also technically feasible, as will be explained further below will be.

If the phase of the supply voltage or the pulses shifted by y / 2 has been, then the relationships result which are shown in Fig. 2, g and h are. Compared to Fig. 2, e and f, the current through the thyratron 18 is around the area L NO P has become smaller. The current through the thyratron 19 is around the area GHQ U got smaller. Both currents are smaller because the ignition pulses for both thyratrons come later. It can now be seen that the area LNOP in FIG. 2, g, is equal to the area QUKJ in Figure 2, h. The area to the left of LN (Fig. 2, g) was yes (see Fig. 2, e and f) equal to the area to the right of JK (Fig. 2, h). The areas HG U Q, around which the current through the thyratron 19 has decreased during the phase shift and the area LNOP by which the current through the thyratron 18 was reduced, thus complement each other to the area GHJK, around which the total signal as a result of the broadening of the sheet metal strip 15 got bigger. After the phase reversal by y / 2, the widening y is compensated and that at the resistors 28 and 29 dropping voltage equal to the voltage of the rectifier 34. The motor M and the phase shifter 27 come to rest. The position of the phase shifter 27 is displayed by means of a display device 35 and depends absolutely linearly with the change in width of the band 15 together. The sinusoidal shape of the supply voltage has no effect whatsoever on the display Influence. An adjustment movement is only required when the width of the belt changes, so that flutter movements of the goods, such as those especially when rolling wire and the like. can occur, have no influence on the measurement.

Fig.3 shows a slightly different circuit of the thyratrone. Here are two thyratrons 36, 37 are provided, which are in phase opposition from a transformer 38 are fed with center tap 39. The primary winding 41 of the transformer 38 is at the output of a phase shifter 42. The thyratrons 36 and 37 have one common cathode resistor 43, at which a DC voltage according to the Sum of the two currents flowing through the thyratrone 36 and 37 is tapped. The test object is scanned in opposite directions by means of two probe heads K and K2 as in the example of FIGS. 1 and 2, and these supply ignition pulses via amplifiers V1 and V2 44 and 44 '(similar to 17 and 17') on the grids of the thyratrons 36 and 37. The pulse frequency can be 100 Hertz, as in the previous example. This is done alternately one pulse of each head K1 and K2 is suppressed, namely when at the anode of the corresponding thyratron the negative half-wave is applied.

The voltage drop across resistor 43 is again like that Embodiment according to FIG. 1, at a zero amplifier 45 of a constant reference voltage in the opposite direction, which is supplied by a rectifier 46. The rectifier 46 is connected to the same network as the phase shifter 42, so that network voltage fluctuations remain without influence on the measurement. The null amplifier 45 controls a motor M, and this adjusts the phase shifter 42 and at the same time a display device 47 until the voltage across resistor 43 is equal to that across rectifier 46 Reference voltage is.

With these two arrangements according to FIG. 1 to 3 becomes the phase position the supply voltage of the thyratrone changed compared to the fixed position of the pulses. However, the phase position of the pulses can also be shifted when the length changes and leave that of the supply voltage unchanged. Such an example is shown in FIG. 4, 8 and 9.

The probe head has two mirror rotors that are offset from one another 48 and 49 are provided, which are each driven by a synchronous motor 51 and 52 will. Two photocells 53 and 54 probe the measurement object 55 (here as a rolled profile the height a shown) on the mirror rotors 48 and 49 periodically. It is the beam path of the cell 53 is still guided via an additional mirror 56, so that one scan from top to bottom and the other from bottom to top he follows. Instead of this, of course, the motors 51 and 53 can also rotate in opposite directions.

In FIG. 4, the two heads K1 and 2 are with the motors 51 and 52 shown schematically. Cells 53 and 54 provide through amplifiers V1 and Vt Pulses on the grid from two thyratrons fed in antiphase. The thyratron circuit corresponds to that of FIG. 3, and it is therefore for the same switching elements the same reference numerals have been used as there. In contrast to Fig.3 lies Here, however, the primary winding 41 of the transformer 38 directly on the network while The drive motors 51 and 52 of the probes Kt and K2 via the phase shifter 42 be fed. The phase of the thyratron supply voltage actually remains here stand, while the position of the ignition pulses 44, 44 'relative to this by corresponding Drive of the mirror rotors 48, 49 changed via the phase shifter 42 relative to this will.

Here one strictly obtains the relationships shown in Fig. 2, g and h are.

Instead of two mirror rotors 48 and 49 as in FIG. 8 and 9 can be used also provide a common rotor for both scanning beams, which of one single synchronous motor is driven. Such an arrangement facilitates the accurate Phase setting and adjustment via the motor phase.

Such an arrangement is shown in FIG.

In this arrangement, two photocells 57 are scanned and 58 via a single polygon mirror 59. The beam path of one cell 57 is passed through two plane mirrors 61 and 62, that of the second cell through one single plane mirror 63.

In this way, one cell is sampled Measurement object 64 from bottom to top, through the other a scan from top to below.

In the arrangements described so far, a comparison is carried out automatic re-rotation of the phase shifter. Its travel is a measure of the length to be measured.

In the embodiment according to FIG. 5 is through the phase shifter 42 a setpoint is set by hand, which is displayed on a display device 47 will. The deviation from this target value is measured by means of an instrument 65 central zero point directly indicated at which the voltage drop across the cathode resistor 43 of the constant voltage of the rectifier 46 is connected in the opposite direction. The rest The structure corresponds to that of FIG. 3, and here, too, the same parts are used Reference numerals provided as there.

Such an arrangement is of great importance for the profile or Strip width control in the rolling mill. A setpoint is set there, and the AS deviations that are relatively small compared to the setpoint are displayed directly. The fact is used that the deviation of the resistor 43 falling Voltage from the voltage of the rectifier 46 is a measure of the length deviation from the setpoint. You always work with the same phase angle Thyratrone 36, 37 and in the same measuring range of the instrument 65, while the setpoint at the phase shifter 42 despite the sinusoidal shape of the supply voltage over a large measuring range can adjust linearly.

This would be with the other possibility, namely the Change in the reference voltage at rectifier 46, not the case. Then one would have a non-linear setpoint adjustment, and the Emp delicacy of the instrument 65 becomes smaller, the smaller the smaller it is, in an entirely undesirable manner the setpoint is because with a small setpoint the phase angle is in the 0 ° or 1800 range takes place and phase shifts of the ignition pulses there only little influence on the have current flowing through the thyratrone.

The arrangement according to FIG. 6 is a device for cutting length measurement in the rolling mill. Actually, it's not a length measurement in the sense of the previous examples, but a position measurement. The position of the leading edge 66 of rolling stock 67 in relation to a pair of scissors is optisoh 68 measured. The rolling stock runs up on a roller table69 and through the scissors 68 a piece is cut off, the length of which is due to the arrangement according to the invention measured and displayed.

For this purpose, the measuring range by means of a probe head K, the z. B. can be constructed in the manner of FIG. Ii, scanned periodically. This delivers as in the examples already described, via an amplifier V ignition pulses 71 on the grid of a thyratron 72. The thyratron 72 is powered by a phase shifter 73 and a Graetz rectifier 74 with a rectified AC voltage 75 fed. The voltage drop across the cathode resistor 76 of the thyratron 72 is connected in opposition to a constant reference voltage at a null amplifier 77, which is supplied by a rectifier 78. The null amplifier 77 controls a servomotor M, which adjusts the phase shifter 73 until the voltage difference disappears at the null amplifier.

A display device is coupled to the phase shifter, which indicates the cutting length. As can be easily seen, the display is complete linear, even if the supply voltage is sinusoidal. Since the leading edge of the Thyratrons also always takes place in the same angular range, remains the absolute Accuracy of the display, which is mainly due to the responsiveness of the zero amplifier is determined, constant over a large measuring range.

Fig. 7 shows a similar arrangement. But not only that Cutting length is measured, but it is a function of the measured value obtained the roller table is controlled so that the rolling stock is in a preset position in which so the end face 81 of the rolling stock a pre-settable distance behind the scissors 83 lies, comes to rest.

A probe head K in the manner of FIG. 11 outputs via an amplifier V Pulses 84 on the grid of a thyratron 85. The thyratron 85 is controlled by a phase shifter 86, which is connected to the network, via a transformer 87 and a Graetz rectifier 88 fed with a rectified AC voltage. The phase shifter 86 is adjustable by hand and connected to a display device 88 on which the End position of the rolling stock, d. H. the cutting length can be read off. In a circle 89 becomes the voltage dropped across the cathode resistor 91 from a rectifier 92 supplied constant reference voltage is connected in the opposite direction.

The pulses 84 are also applied to the grid of a second thyratron 93 given. The thyratron 93 is powered by a second secondary winding 94 of the transformer 87 for the purpose of galvanic isolation via a Graetz rectifier 95 also with rectified alternating current. At the cathode resistor 96 of the thyratron 93 then likewise a voltage 97 corresponding to the position of the edge 81 drops. This is differentiated by means of a differentiator 98, and one obtains one speed proportional measured value, which in a circle 99 that of the thyratron 85 and the rectifier 92 derived differential measured value is connected in the opposite direction. A control unit 100 is acted upon by the sum or difference signal obtained in this way, which controls the roller table motors in a manner not shown.

With the arrangement described, the phase shifter can conveniently and precisely the end position of the rolling stock and thus the cutting length can be set. The described speed feedback ensures that the rolling stock enters this end position without overshooting and oscillation. In the final state is that connected speed measurement value zero, and the phase angle of the thyratron 85 takes place so that the voltage across resistor 91 is equal to the reference voltage of the rectifier 92 is.

The foregoing description shows that the invention is broad Has application area, and the application examples shown are by no means exhaustive. Instead of a thyratron, i.e. a gas-filled, smoother-controlled one Electron tube, could also use another, equivalent-acting switching element find, for example, a semiconductor switching element. The term controlled rectifier in the description and claims it is to be understood that such equivalents with includes.

Claims (12)

Claims: 1. Photoelectric device for measuring the position or of length values for an object with a defined scanning area periodically sweeping scanning element, in which an ignition pulse when the object is detected is delivered to a controlled rectifier, for example a thyratron, which, from one synchronized with the sampling, periodically going through zero Voltage, supplies a direct current signal determined by the measured variable, in such a way, that the relative phase position of the ignition pulse and supply voltage of the controlled rectifier changes according to the measured variable to be determined, thereby marked e i c h n e t that with stationary scanning means the phase position by means of electrical phase-shifting means is changeable. 2. Photoelectric position or length measuring device according to claim 1, characterized in that the controlled rectifier of a rectified AC voltage is fed. 3. Apparatus according to claim 1 or 2, characterized in that as a scanning device, a photoelectric receiver with rotating, from one Synchronous motor driven optical members and a concave mirror in the way cooperates that a linear relationship between the position of the scanning elements consists in the measuring plane and the angle of rotation of the optical members. 4. Photoelectric position or length measuring device according to claim 3, characterized in that the synchronous motor is fed via a phase shifter will. 5. Photoelectric position or length measuring device according to one of the Claims 1 to 3, characterized in that the supply voltage of the controlled Rectifier is fed via a phase shifter. 6. Apparatus according to claim 4, characterized in that the scanning area scanned in a known manner by two scanning devices in opposite directions is driven by a common synchronous motor or by two of the same Voltage fed synchronous motors are driven, and that each scanning device a controlled rectifier is assigned and that of the controlled rectifiers supplied direct current signals are additively superimposed. 7. Apparatus according to claim 5, characterized in that the scanning area periodically in a manner known per se by two scanning devices in opposite directions is scanned and that each scanning device is assigned a controlled rectifier and that the direct current signals supplied by the controlled rectifiers are additively superimposed and that the phase position of the supply voltages of the both rectifiers can be changed in the same way. 8. Apparatus according to claim 6 or 7, characterized in that the phase shifter is adjustable in such a way that the sum of the direct current signals assumes a predetermined value and that the adjustment of the phase shifter provides a measure of the length to be measured. 9. Apparatus according to claim 8, characterized in that the sum the direct current signals of a reference voltage at a zero amplifier are switched opposite is and that the independent servo drive controlled by the zero amplifier Adjusting the phase shifter is effected. 10. Apparatus according to claim 6 or 7, characterized in that the phase shifter can be set manually for setting a predetermined setpoint and that the sum of the direct current signals at one is the deviation from the nominal value measuring instrument indicating a constant reference voltage is connected in the opposite direction. 11. Apparatus according to claim 4 or 5, characterized in that the direct current signal supplied by the controlled rectifier of a constant Reference voltage is connected opposite a zero amplifier and that one of the zero amplifier controlled servo drive causes the automatic adjustment of the phase shifter, the adjustment of which provides a measure for the position size to be measured. 12. Photoelectric position measuring device according to claim 4 or 5 for a good transported on a conveyor device, characterized in that the phase shifter can be adjusted manually for setting a setpoint and that the measured direct current value supplied by the controlled rectifier is controlled by control means for the conveyor is fed in such a way that the material in the phase shifter adjustable position comes to rest. Publications considered: German Auslegeschriften No. 1 005 741, 1 025 636, 1 026 542, 1 056 842, 1 063 394, 1 092 541; Swiss U.S. Patent No. 301,849; U.S. Patent No. 2,548,590.