US3440932A - Plunger travel speed governing devices to be employed when pressing on hydraulic presses - Google Patents

Description

April 29, 1969 E. J. GUTNIKOV ET AL 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Filed March 1, 1967 Sheet of 7 I'- 2 i a 7 Apnl 29, 1969 E. J. GUTNIKOV ET AL 3, 0,932

PLUNGER TRAVEL S PEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Filed March 1. 1967 Sheet 3 of 'r April 29, 1969 E. J. GUTNIKOV T L 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Sheet Filed March 1, 1967 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I /m P II|II IIII II I I |||I l|k W W m um H N II I g m E ARI \N r \Q L 1-1 1 E n I IN KIIIMI l I I I I I I I I I ll L a" a ma w 6 n N g TIL L April 29, 1969 E. J. GUTNIKOV T L 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Filed March 1, 1967 Sheet 4 April 29, 1969 E. J. GUTNIKOV ET L 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES 5,

Filed March 1, 1967 Sheet April 29, 1969 E. J. GUTNIKOV ET 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Filed March 1, 1967 Sheet 6 Of 7 April. 29, 1969 E. J. GUTNIKOV ET AL 3,440,932

PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HYDRAULIC PRESSES Sheet Filed March 1, 1967 E E & n .5

a; it E United States Patent 3,440,932 PLUNGER TRAVEL SPEED GOVERNING DEVICES TO BE EMPLOYED WHEN PRESSING ON HY- DRAULIC PRESSES Eduard Julievich Gutnikov, ul. Botanichespaya 23, kv. 19; Oleg Nikolaevich Melnikov, ul. Bazhova 125, kv. 117; German Borisovich Matjunin, ul. Studencheskaya 13, kv. 66; and Iosif Ilich Alferman, ul. Krasnykh Komaudirov 126, kv. 2, all of Sverdlovsk, U.S.S.R.

Filed Mar. 1, 1967, Ser. No. 619,730 Int. Cl. F15b 11/04 US. Cl. 91-435 19 Claims ABSTRACT OF THE DISCLOSURE A press plunger speed governing device for use on hydraulic presses which ensures high-quality pressing speed control within the speed range from 0.02 to 100 mm./sec. with the minimum duration of plunger travel when performing the control signal.

The essence of the proposed governor consists in that it is provided with a unit serving to shape a single pulse or a set of pulses and a signal to disconnect the control system, said unit shaping the command pulses whose duration is a function of the amount of mismatch, of the given value of the speed, and of the pressure drop in the governing throttle f(Av/ v, v Ap), and shaping the signal for disconnecting the governing system, which is a function of the speed f(v).

The function f(Av/v, v AP) is so selected as to en sure elimination of any mismatch appearing during one or two pulses.

After the command pulse has been fed into the control system the governing system opens for the time necessary to complete the transient processes. The duration of opening of the system is determined depending on the speed at which pressing is performed.

The first command pulse after the appearance of a mismatch is fed into the control system without any delay, and its duration ensures complete or almost complete adjustment of the mismatch. Consequently, lagging of the system is close to the minimum value possible.

The present invention relates to plunger travel speed governing devices to be employed when pressing on hydraulic presses.

Known in the art are plunger travel speed governing devices, employed when pressing on hydraulic presses, in which the actual speed of travel of the plunger is compared with the preset one, and the difference value thus obtained is fed to the control circuit of the actuating mechanism or servomotor of the governor valve which controls the travel speed of the hydraulic press plunger. (Cf. Uralski N. P. and Pavlov S. V., Automatic Speed Governor for Hydraulic Presses, in: Advanced Scientific, Technical and Industrial Experience (No. 3-63-739/ 9,1963, PP.18-25).

The disadvantage inherent to the plunger travel speed governing devices known heretofore and employed when pressing on hydraulic presses resides in the impossibility to provide a wide range of control of the pressing speed with sufficiently good characteristics of transient processes in the control system. Difficulties encountered when solving such a problem are due to the astatic character of the control system and also due to the fact that within the working range of speeds the press parameters, such as its time constant, governor valve gain coefiicient and others vary within wide limits and therefore require changes to be introduced in the block diagram of the governing device when passing from one subrange of speeds being controlled over to another one.

It is an object of the present invention to eliminate the above disadvantages.

It is an object of the present invention to provide a plunger travel speed governing device to be used when pressing on hydraulic presses which will ensure a wide range of pressing speed control with minimum time of the plunger travel when performing the control signal.

The specific and novel feature of the invention resides in that the plunger travel speed governing device used when pressing on hydraulic presses, in which the plunger travel speed measuring unit and the plunger travel speed setting unit are coupled to the comparison unit, connected with the actuating mechanism or servomotor of the speed governor valve, which controls the travel speed of the plunger, according to the invention, is provided with a unit serving to shape a single pulse or a set of pulses and a signal to disconnect the control system, said unit being arranged between the comparison unit and the actuating mechanism or servomotor of the speed governor valve.

For registering the pressure drop at the plunger governor valve, at least one pressure gage, eg a differential manometer, may be coupled to the unit which shapes a single pulse and a signal to disconnect the control system.

When the governing device is equipped with a range selector switch for switching over the pressing speed, it is expedient to install a unit between the comparison unit and the unit shaping a single pulse and a signal to disconnect the control system said unit installed between the two aforementioned units serving to convert the difference in speeds into the relative difference therebetween.

The unit converting the difference in speeds into the relative difference may be combined with the comparison unit.

The unit shaping a single pulse may be connected with the plunger travel speed measuring unit, or with the plunger travel speed setting unit.

It is expedient to provide the governing device with a block or unit adapted to select the maximum speed between the two, viz., between the measured speed and the preset one, said unit being connected with the unit shaping a single pulse.

The unit shaping a single pulse or a set of pulses and a signal to disconnect the control system may comprise a piecewise linear converter employing diodes and estabilshing a root dependence on the speed difference signal, said converter being connected with a flip-flop which operates when the converter signal exceeds the operating threshold value; a flip-flop reset circuit connected with the output of said flip-flop and ensuring an approximately linear increase of cutoff voltage with time; a one-shot multivibrator whose mark-to-space ratio varies in accordance with the preset speed, said one-shot multivibrator being connected with the flip-flop reset circuit; a voltage divider controlled by the pressure drop at the speed governor valve in such a manner that the rate of increase of the cutoff voltage depends on the preset speed and the pressure drop at the speed governor valve; :an auxiliary one-shot multivibrator connected with a range selector switch and with the flip-flop and being triggered by the latter, the connection between the flip-flop and the auxiliary one-shot multivibrator being so effected that when the auxiliary one-shot multivibrator operates the flip-flop is blocked and the control system becomes thereby disconnected.

For facilitating the adjustment of the governing device on the press and improving the quality of control, it is expedient to employ correcting sections and a correcting potentiometer geared with the plunger travel speed setting unit and electrically connected via separate plates of the range selector switch with the correcting sections employing resistors and diodes.

Given below is a description of exemplary embodiments of the present invention with due reference to the accompanying drawings, wherein:

FIGS. 1 to show block-diagrams of various possible embodiments of the plunger travel speed governing device according to the invention;

FIG. 6 shows a detailed block diagram of the same governing device according to the invention;

FIG. 7 shows a gearing diagram of the speed transmitter according to the invention; and

FIGS. 8, 9 and show an electric circuit diagram of the governing device according to the invention.

The plunger travel speed governing device to be used when pressing on hydraulic press 1 comprises plunger travel speed measuring unit 2 connected with comparison unit 3 to which plunger travel speed setting unit 4 is also coupled. The comparison unit 3 is coupled with unit 5 adapted to shape a single pulse and a signal to disconnect the control system which, for the sake of brevity, will be termed here and hereafter as pulse and interval shaping unit 5.

A pulse with duration t arising due to a mismatch between the preset and measured speeds is fed to actuating mechanism or servomotor 6 ensuring the required travel of speed governor valve 7 which restores the preset speed of pressing. Due to the inertia of the entire control system and, particularly, of the object being controlled, i.e., of the press 1, the command is performed with a considerable delay (ranging from fractions of a second up to a dozen of seconds and more). The duration of interval t following the produced pulse is so selected that the mismatch could be adjusted during the interval.

The pulse and interval shaping unit 5 produces pulses which ensure the travel of the speed governor valve to be proportional to the mismatch value and depending on its characteristic of the governor valve within the given range, i.e., on the speed of pressing.

If a conventional electric motor is used as the actuatlng mechanism or servomotor 6, for ensuring optimum conditions of travel of the governor valve 7 (as regards the minimum of time required for the purpose), said travel duty corresponding to the travel with constant acceleration and deceleration, the pulse duration 2 should be proportional to the square foot of the mismatch value (1f a single pulse is produced). The dependence of the pulse parameters on the speed is determined by the specific characteristic of the speed governor valve 7 and, therefore, cannot be preset in advance. Only the limits of this function are known. In particular, when using the absolute difference in the speeds for the mismatch signal, the linear characteristic of the governor valve requires no correction with respect to the speed, i.e., t =a /AV, where t is the time of the governor valve travel, constituted by the acceleration time t equal to the pulse duration, and deceleration time t t =t +t When operating with constant accelerations, I is proportional to t .i.e t =mt where m is a constant factor, m 1;

a is a constant factor,

AV is a deviation of the measured speed from the preset one.

When using a governor valve with an exponential characteristic, its time of travel may be expressed by the following relation:

where V is the speed of pressing. and a is a constant factor generally different from a.

If the relative difierence in speeds AV/ V is used as the mismatch signal, the linear characteristics of the governor valve results in the function of the form and the exponential characteristic of the governor valve, respectively, in the function The exponential characteristic of the speed governor valve is the best from the point of view of the fast response of the system, since in this case the range of duration of actuating pulses is minimized and determined only by the mismatch range.

The linear characteristic of the governor valve is the easiest for realization. Therefore, actual characteristics of governor valves lie between these two extreme characteristics and the pulse and interval shaping unit 5 makes it possible to obtain the required dependence for actually available governor valves.

Besides, to preclude overcontrol in cases of casual excessively great deviations of the speed, e.g., when switching over to another range, when switching on the governing device with the preset speed widely differing from the actual value, the pulse duration t should be limited by a certain critical value.

The adoption of said dependence of the pulse duration on the difference in speeds and the establishment of the required dependence on the speed make it possibile to effect optimum control at a constant pressure drop at the speed governor valve 7.

In fact, this pressure drop may vary within a sufficiently wide range, approximately, from 30 kg./sq. cm. to 200 kg./ sq. cm., and in some cases even reach zero.

If the characteristic of the governor valve 7 is exponential, the required duration of the adjustment performance command does not depend on the pressure drop. In the general case, however, this dependence does take place, and for the adjustment of the mismatch during one pulse the duration 1, of the latter should be selected in accordance with the pressure drop. To this end, fed to the pulse and interval shaping unit 5 are not only the values of the difference in speeds and of the plunger travel speed, but also the value of the pressure drop at the governor valve 7 from pressure drop transmitter 8, thus ensuring the required increase in the pulse duration t if the pres sure drop diminishes.

Under normal conditions of operation of the control system, the values of the measured speed and of the preset speed of the plunger travel are close, and therefore any of these two speeds may be taken for a correction parameter, as shown in FIG. 1, where the speed signal in fed to the shaping unit from the comparison unit.

Shown in FIG. 2 is a block, diagram of the control system, where the speed signal is fed to the pulse and interval shaping unit 5 directly from the speed measuring unit 2 and, hence, the actual speed of pressing is used as the correction parameter.

The use of the actual speed of pressing as the correction parameter improves transient processes in the system, reducing the time required for adjusting the mismatch between the speeds when passing over from great preset speeds to small ones, since in this case, while the operating speed of the press considerably exceeds the preset one, the performance command correspond to said great speeds ad ensure great travel distances to be covered by the speed governor valve 7. However, when the speed setting is changed over from small values to great ones, the performance commands remain reduced in time (corresponding to the actual speed), and the mismatch adjustment becomes prolonged.

Shown in FIG. 3 is a block diagram of the control system, where the speed signal is fed to the pulse and interval shaping unit 5 from the speed setting unit 4, i.e., where the preset speed of pressing is used as the correct tion parameter. A J l I I This version of the circuit provides optimum conditions for the transient process (minimum of time) when passing over from small speeds to great ones, since in this case performance commands correspond to the respective opening of the governor valve. However, the process of passing from great speeds over to small ones in this case is prolonged. The best solution providing a good adjustment of the mismatch in case of considerable deviations in both senses, can be attained by employing the circuit, presented in FIG. 4. In this diagram, fed to the pulse and interval shaping unit as the correction parameter is a signal, determined by the greatest of the two speeds, viz., the actual or the preset one. The comparison and selection of the speed is effected in speed selection unit 9, connected with the speed measuring unit 2 and the setting unit 4. To simplify the circuit diagram, in multirange governing devices the speed setting signal fed to the speed selection unit 9 may he stepped. Each fixed value of the preset speed may correspond to one certain range. In multirange governing devices the speed signal fed to the speed selection unit 9 may be functionally transformed, say, into the logarithm of the speed. In this case the signal fed to the speed selection unit 9 will be also in the form of the logarithm.

Presented in FIG. 5 is a block diagram of the control system, in which the signal of mismatch, before being fed to the pulse and interval shaping unit 5, is converted in conversion unit 10 into the relative difference. When the relative difference between the speeds is used as the mismatch signal, a constant value of the mismatch signal is ensured at the same percentage of speed deviation within all ranges, whereby both the schematic and structural embodiment of the governing device become simplified.

Besides, in order to preclude useless opening of the governor valve 7 when there is no pressure drop at it and to preclude waste of time for closing the governor valve 7 after the metal starts issuing from the press 1, the governing device of the invention is provided with output stage 11 combined with a unit inhibiting the opening of the speed governor valve 7 when the pressure drop at it is lower than a certain preset level. This inhibiting sign-a1 does not depend on the actual speed of the plunger travel.

Shown in FIG. 6 is a detailed block diagram of the governing device which controls the speed of travel of plunger 1' of the hydraulic press 1.

Geared with the transverse of the dydraulic press 1 is frequency speed transmitter 12. The output of the speed transmitter 12 is coupled to the input of preamplifier 13 and the output of said preamplifier 13 is coupled to the input of frequency-to-voltage converter 14. The frequency-to-voltage converter 14 and the speed setting unit 4 are coupled to the comparison unit 3, which, in turn, is connected with power amplifier 16 through modulator 15. The comparison unit 3 is made in combination with the unit 10 serving to convert the difference in speeds into the relative difference. The output of the power amplifier 16 is connected With demodulator 17 and phase demodulator 18. The demodulator 17 is connected with piecewise linear converter 19 which, in its turn, is connected with converter 20 determining the pulse duration t The second input of the converter 20 is connected with the output of functional converter 21, whose inputs are connected with correction unit 22, said correction unit being connected with the speed setting unit 4 and with pressure difference amplifier 23, the inputs thereof through amplifiers 24 and 25 being connected with pressure transmitters 26 and 27. The outputs of the converter 20 and phase demodulator 18 are coupled to the inputs of the output stage 11 combined with the inhibition unit, said output stage being connected with electric motor amplifier 28, said amplifier being connected with servomotor 29 of the governor valve 7. The output of the preamplifier 13 is also connected with the input of logarithmic frequency-tologarithm converter 30, which, in turn, is connected with speed registering device 31.

The proposed governing device operates as follows. During the travel of the plunger 1' of the press 1 in the course of pressing the pulses from the plunger travel speed transmitter 12 are fed to the preamplifier 13. The amplified and amplitude-limited signal, whose frequency is proportional to the speed of plunger travel, is fed to the frequency-to-voltage converter 14 which is essentially a two-channel analog frequency meter. Its output current i proportional to the frequency, i.e., to the actual speed of pressing (of the plunger travel) and current i proportional to the preset speed taken from the output of the speed setting unit 4 are fed to the comparison unit 3.

At the output of the comparison unit 3 the mismatch value is obtained as voltage AU.

The mismatch value is converted by the modulator 15 into alternating voltage which is amplified by the power amplifier 16 and then again, by means of the demodulator 17, is converted into constant voltage and fed to the piecewise linear converter 19, wherefrom the value proportional to the square root of the mismatch value, Le. /AV/ V is taken.

Voltage AU= /AV/ V is fed to the converter 20. Voltage U which is a function of the preset speed V and obtained in the correction unit 22 and with voltage U; determined by the pressure drop AP at the speed governor value, taken from the pressure difference am lifier 23 through converter 21, are also fed to the converter 20, where the required duration of the pulse 1 and the duration of the interval t are determined.

Thus, the duration of control pulses is a function of the mismatch value, of the preset speed and of the pressure drop at the governor valve.

As the pressure transmitters 26, 27 electric manometers are employed whose output signals are amplified by the amplifier 24 and 25.

The pulse of duration t equal to b /AV/ V, where b is a proportionality factor, which in the general case may be a function of speed V and pressure drop AP, is fed to the output stage 11 where it is converted into a back-toback sawtooth current pulse of duration t Also fed to the output stage 11 is a signal of the mismatch sign, taken from the phase demodulator 18.

From the output stage 11 to the control windings of the electric motor amplifier 28 a 'back-to-back sawtooth current pulse of controlled duration is fed, which, through the servomotor 29 actuates the speed governor valve 7 thereby adjusting the traveling speed V of the plunger 1' of the press 1 so as to make it correspond to the preset speed V For registering the speed of pressing over the entire range of speeds on the logarithmic scale, the governing device is provided with converter 30.

As the plunger travel speed transmitter 12 a positiontype impulser is employed, which is essentially an opticomechanical converter, in which the value, proportional to the speed is the number of pulses per unit of time, i.e., frequency.

The gearing diagram of the impulser is given in FIG. 7. The impulser comprises two aluminum disks 32 on which optical gratings 33 are fixed protruding beyond the edges of said aluminum disks. Each disk is set on its shaft 34 and is provided with driving pulley 35. Both pulleys 35 are connected by means of endless steel Wire rope 36 with the plunger 1 of the press and with tensioning device 37. Thus during the plunger travel the disks are imparted rotary motion to. At one side of the disks 32 source of light 38 is arranged, photodiode 39 being arranged at the other side of said disks. To stabilize the rotation of the disks, eddy current braking is employed. The braking moment is created by a system of direct current coils 40, the

aluminum disks 32. of the impulser rotating between the poles thereof.

The disks rotating, a luminous flux of variable intensity falls on the photodiode 39. The photodiode 39 produces signals, whose frequency is proportional to the plunger travel speed. i

The output signal of the photodiode 39 is amplified by the preamplifier 13 (FIG. 6).

Shown in FIG. 8 is an electric circuit diagram of the speed measuring unit 2, which is essentially a combination of the plunger travel speed transmitter (or impulser) 12, preamplifier 13, frequency-to-voltage converter 14, comparison unit 3 combined with the conversion unit 10, speed setting unit 4, correction unit 22 and frequency-tologarithm converter 30.

The frequency-to-voltage converter 14 is essentially a two-channel analog frequency meter with switchable filters operating for a common load.

The converter 14 comprises two shaping stages, blocks of charging capacitors, a rectifier bridge, a two-sectional RC-filter, an integrating amplifier and a cascode amplifier which serves as the load for the converter.

The entire range of speeds being measured (i.e. the range of frequencies) is subdivided into subranges by means of range selector switch 41 provided for the purpose (FIG. 6), this corresponding to the range of speeds from 0.05 to 100 mm./sec. For obtaining a faster response of the converter at preset frequencies of the transmitter or impulser corresponding to the working range of speeds, the frequency is doubled in the converter circuit, this being effected by measuring the frequency via two channels thereof operating for common load.

The circuit operates as follows.

The amplified and limited signal taken from the preamplifier 13 of the speed transmitter, the frequency of said signal being proportional to the speed of pressing, through coupling capacitor 42 is fed to the grid of the first shaping stage, assembled on the left half of tube 43.

By the signal from the plate of the left half of the tube 43 through coupling capacitor 44 a balanced flip-flop circuit is actuated, said flip-flop circuit being assembled on tube 45 and serving as the second shaping stage of the frequency-to-voltage converter.

From the plates of the tube 45 square pulses are fed to the two channels of the converter constituted by the blocks of charging capacitors 46 and 47 and rectifier bridge 48. Voltage pulses are obtained by fixing the level of opening of the tube 45 by means of cutoffs formed by diodes 49 and 50 coupled to a source of reference voltage of +100 v. The plates of the tubes are fed with stabilized voltage of 250 v. The output voltage of the measuring unit is filtered by the two-sectional RC-filter, whose first section is constituted by capacitors 51, 52, 53, 54, 55 and input impedance or resistance of tube 56 operating in a cascode duty. The voltage (current) filtered by the first section of the filter, proportional to the frequency, is impressed in the negative polarity to the cathode of the tube 56, said cathode being the input of the cascode circuit.

The filtering capacitors 51, 52 of the first ranges of the first section of the filter are connected to the load (to the input of the cascode circuit) through the integrating amplifier assembled on tube 57. The use of the integrating amplifier makes it possible actually to increase the capacity of the filtering capacitors by (1+K) times, where K is the amplification factor of the tube 57, equal, approximately, to 20. The second section of the filter, constituted by capacitors 58 and resistor 59, is inserted between the halves of the tube 56 in the plate circuit of the left half thereof. In the circuit of the plate of the left half of the tube 56 microammeter 60 is inserted serving as a speed indicator.

The speed setting unit comprises double potentiometer 61, 62, the proper setting potentiometer 61 being connected to the voltage divider, constituted by resistors 65, 64 and the potentiometer 62 being a correcting one.

In the plate of the right half of the tube 56 the current being measured is compared with the preset current. The value of the preset current is inversely proportional to the impedance of the circuit constituted by the resistor of the potentiometer 61 and a divider assembled on the resistors 63, 64. The same current setting circuit also serves as the resistance load of the comparison unit.

The output voltage from the load is equal to where C is the proportionality factor, R=U /i U being the voltage across the divider, constituted by the resistors 63, 64 under no load.

Hence,

AV AU -d where V zi and d is a constant factor.

Thus the combination in one block of the setting unit and the comparison unit made it possible to effect therein also the conversion of the difference in speeds into the relative difference.

When toggle switch 65 is closed, the plate of the right half of the tube 56 becomes grounded.

With the toggle switch 65 being in this position, the preset speed of pressing is determined by the reading of microammeter 66. In case the values of preset current and of the current being measured are equal, the potential of the right plate of the tube 56 is equal to zero. If the measured current i is different from the preset current i the mismatch, proportional to the relative difference between these two-values, taken from the plate of the right half of the tube 56 is fed to the modulator 15 (FIG. 6), said modulator 15 being an input element of the pulse and interval shaping unit 5.

For registering the speed of pressing in the course of operation, an additional speed measuring channel is provided in the measuring unit. Due to the great range of speeds being measured and to the necessity of taking measurements with a constant relative accuracy, said channel is made as a frequency-to-voltage converter, the voltage being proportional to the logarithm of the frequency, said converter comprising a shaper, converting the fed frequency signal into square pulses of constant amplitude, and a plurality of series-connected rectifier networks, each such network having its own load shunted by a capacitor, the voltage being summed thereat.

As the shaper of the square pulses of the converter, a limiting amplifier is used, assembled on tube 67 (FIG. 8), in whose plate and cathode circuit silicon stabilitrons 68, 69 are inserted. Square pulses, taken from said stabilitrons 68 and 69, through charging capacitors 70, 71, 72 and 73 are simultaneously fed to four rectifier networks 74, 75, 76 and 77, resistors 78, 79, 80 and 81 serving as their respective loads. Capacitors 82, 83, 84 and 85 function as filters of said rectifier networks. The joint voltage from the series-connected rectifier networks is fed to the grid of a cathode follower assembled on the right half of the tube 43. The initial current of the cathode follower is balanced from the negative source of voltage by resistor 85. The output current of the cathode follower, proportional to the logarithm of the frequency (speed) is registered by the registering device 31 which is inserted into the cathode circuit of the cathode follower through resistor 87.

The correction unit 22 which provides the obtaining of the integral correction dependence for matching the governing device operation with the actual characteristics of the governor valves is described hereinbelow in connection with FIG. 9.

Shown in FIG. 9 is the electric circuit diagram of separate blocks of the pulse and interval shaping unit: of the modulaotr 15 (FIG. 6), of the power amplifier 16, demodulator 17, phase demodulator 18, converters 19, 20, 21

and of half-wave phase demodulator 88 (FIG. 9) with a microammeter serving for visual following over the control process.

The function of the pulse and interval shaping unit consists in the determination of the duration t of the command, required to adjust the control system depending on the mismatch value, on the pressure drop at the governor valve and on the preset speed value, as well as to determine the duration t of the interval (i.e. of the system being disconnected) as a function of the preset speed V The mismatch value obtained in the form of voltage AU in the comparison unit, is fed to the modulator employing transistors 89, 90, where it is converted into alternating voltage whose amplitude is proportional to the mismatch value AV/ V and whose phase depends on the mismatch sign.

The voltage dividers assembled on resistors 91, 92, 93, 94 with diodes 95, 96 provide cutoffs which limit the mismatch value to be within 25 percent of the preset speed.

From the modulator, through coupling capacitor 97 the modulated mismatch signal is fed to the grid of the power amplifier assembled on tube 98. Transformer 99 serves as the load of the power amplifier.

The amplified signal is demodulated by the demodulator 17, then filtered and in the negative polarity is fed to the piecewise linear converter 19 (FIG. 6).

From winding 100' of the transformer 99 the signal is fed to the half-Wave phase demodulator 88 assembled on transformer 101 and diodes 102 and 103, microammeter 104, serving as the load for said demodulator 88, intended for visual observation of the mismatch value in the percent during the process of pressing.

Assembled on winding 105 of the transformer 99, on stabilitrons 106, 107 and tubes 108, 109 (FIG. is the phase demodulator intended to determine the mismatch sign. The load for the tubes 108, 109 of the demodulator are direct current electromagnetic relays 110 and 111.

Since in the control system as the servomotor 6 (FIG. 6) of the governor valve 7 a direct current motor is employed, controlled by the armature voltage and operating at a constant acceleration and deceleration duty, it is evident, that the distance, travelled by the governor slide valve is proportional to the squared acceleration time of the motor 29, i.e., Ah=e where Ah is the travel of the governor slide valve, and e is a constant factor.

In view of the above, the pulse duration should be determined as the square root of the mismatch value, i.e., Z1='\/AV/ V.

If the characteristic of the governor valve is exponential, then to one and the same value of travel Ah of the governor slide valve there corresponds the same relative increment of speed AV/ V. In this case factor b becomes constant and equal to a/m.

The piecewise linear converter 19 together with the converter provides the required dependence to be obtained.

On transistor 112 (FIG. 9) there is assembled a block serving to correct the shape of the curve of the piecewise linear converter 19 (FIG. 6) as a function of the preset speed, said unit increasing the slope of the converter characteristic in the initial portion.

It functions as follows.

With collector current flowing through the transistor 112 (FIG. 9) which is controlled by the current which is a function of the setting current i taken from the plate of a one-shot multivibrator assembled on tube 113, the voltage across the reference voltage divider of the converter, assembled on resistors 114, 115, 116, 117, changes and in such a manner that the voltage across the resistor 114 decreases and that across the resistor 117 increases, which results in an increased steepness of the approximated curve in its initial portion. The steepness of the final portion of the curve beyond the inflection points thereof is varied by means of resistor 118.

From the piecewise linear converter through resistor 10 119 the signal is fed to the grid of a cathode follower (the input of the converter 20, (FIG. 6) assembled on tube 120. From the output of the cathode follower the ilzglnal is fed to the grid of a flip-flop, assembled on tube l 1 The flip-flop is in the normal state when its left half is conducting and its right half is non-conducting. The mismatch signal of negative polarity resets the flip-flop and voltage appears at the cathode of the right half thereof, said voltage being impressed to the grid of a cathode follower assembled on tube 122. Inserted in the plate circuit of the tube 122 is relay 123 setting the pulse duration t The fiip-fiop is reset at the moment, when the voltage across its control grid becomes equal to zero.

Thus, when the mismatch signal value exceeds the dead zone value, the flip-flop assembled on the tube 121 operates and the relay 123 is energized determining the beginning of pulse t i.e., the beginning of control. Simultaneously, the relay 123 being energized, there appears a voltage across the cathode of the tube 122, said voltage blocking diode 124, whereby one of capacitors 125, 126, 127 starts to be charged via a circuit comprising diode 128, the plate of the left half of the tube 113, resistor 129, resistor 130 and divider 131, 132 in the plate circuit of the left half of tube 133. The increasing voltage from the capacitors 125, 126, 127 is applied to the grid of a cathode follower assembled on the right half of the tube 133, and from the cathode thereof, through resistor 134 it is fed to the grid of the tube 120 of the cathode follower, where it is compared with the mismatch value.

When the feedback voltage reaches the value equal to that of the mismatch, the flip-flop assembled on the tube 121 is cut off, the blocking voltage is removed from the d ode 124, and the capacitors 125, 126, 127 through the diode 124 and low-ohmic resistor 135 inserted in the cathode circuit of the tube 122 are quickly discharged, preparing the circuit for the next cycle.

When the flip-flop is cut off, the trailing edge of its pulse triggers a one-shot multivibrator assembled on tube 136, whose output voltage in the positive polarity is fed to the grid of the flip-flop and inhibits its repeated cutting in, thereby disconnecting the control system for the time t required for the completion of the transient process, determined by the delay of the press, the speed measurmg unit and by the free run of the servomotor of the speed governor valve. The duration of the pulse of the one-shot multivibrator is determined by the time constant of RC-circuit 137, 138. In the circuit described herein the duration of the pulse of the one-shot multivibrator and, hence, the duration of the interval between control pulses is adjusted dependmg on the speed of pressing, this being effected by connectmg capacitors 139, and 141 in parallel to the capac1tor 138.

To make the adjustment of the proposed governing device more convenient, the possibility of varying the proportionality factor between the mismatch value and the control pulse duration 1 is envisaged in the circuit.

By switching over the charging capacitors 125, 126, 127, time intervals are varied in steps multiple to two. A smooth adjustment within these steps is attained by varying the charging current of the capacitors 125, 126, 127 through varying the value of the resistor 130 of the charging network.

The rate of increase of feedback voltage determines the duration t of control pulses, since as soon as the feedback voltage becomes equal to the mismatch value, the flip-flop and relay 123 are cutoff, and the performance of the command for controlling the servomotor of the governor valve is finished. The rate of increase of the feedback voltage and, hence, the duration t of control pulses in the circuit described herein is a function of the preset current (preset speed of pressing) and also on the pressure drop at the speed governor valve, this being effected in the following manner.

Charging current to the capacitors 125, 126, 127 is fed through the series-connected charging resistors 129, 130, connected to the voltage divider constituted by the resistors 131, 132, inserted into the plate circuit of the left half of the tube 133. To the control grid of said valve voltage is fed from potentimeter 142, inserted into the cathode circuit of a pressure difference amplifier, assembled on tube 143 (FIG. The output voltage of the potentiometer 142 is determined by the value of the pressure drop at the governor valve. Depending on the value of the pressure drop, the current flowing through the left half of the tube 133 (FIG. 9) varies, and, hence, the voltage across the resistors 131, 132, wherefrom the charging current is taken. At a considerable value of the charging current the rate of increase of the feedback voltage is higher and, hence, the duration t of the control pulse is smaller, and vice versa, at a smaller value of the charging current the duration of control pulses is greater.

In this manner the duration of control pulses is cor rected in accordance with the pressure drop at the speed governor valve.

As stated above, the charging network of the capacitors 125, 126, 127 comprises the one-shot multivibrator assembled on the tube 113, which is triggered by negative pulses of a constant frequency, say, of 100 c.p.s.

To the left grid of the one-shot multivibrator assembled on the tube 113, through resistor 144 voltage is fed, said voltage being a function of the setting current i (of the preset speed of pressing) and taken from the speed correction unit 22 (FIGS. 6, 8). The voltage is taken from the moving arm of the potentiometer 62 geared with the speed setting potentiometer 61.

The speed correction unit is constituted by five correction sections (according to the number of ranges), mounted on plates 145, 146 of the range selector switch. Each correction section comprises fixed resistor 147, variable resistor 148 and diode 149. Two correcting sections of the last two ranges comprise no diodes.

The moving arm of the plate 146 of the selector switch is connected with one end of the correction potentiometer 62 which is geared with the setting potentiometer 61. The correction potentiometer 62 is electrically connected with the load of a cathode follower assembled on tube 150. The moving arm of the plate 145 of the range selector switch is connected with the input of said cathode follower. Coupled to the input of the cathode follower is a voltage divider composed by resistors 151, 152 and serving for setting the initial potential at the grid of the cathode follower. The input resistance of the voltage divider is equal to the resistance of the correction potentiometer 62.

The correction unit operates as follows.

When the selector switch is set in the first position as shown in FIG. 8, the voltage taken from the moving arm of the potentiometer 62 is determined by the initial voltage at the output of the cathode follower and by the position of the moving arm of the potentiometer 62 together with the value of the variable resistor 148 of the correction section of the first range. When the range selector switch is set to the second position, the correction section of the first range through the plate 145 of the selector switch is connected to the input of the cathode follower, and the correction section of the second range through the plate 146 of the selector switch is connected to the potentiometer 62. Consequently, the voltage, taken from the moving arm of the potentiometer in the second position of the range selector switch (the second range) is determined by the voltage taken from the output of the cathode follower, said voltage being equal to the maximum voltage of the first range, and by the position of the moving arm of the potentiometer together with the resistance value of the correction section of the second range. The output voltage of the cathode follower, equal to the maximum voltage of the first range in this case is determined by the additional voltage drop at the input resistance of the cathode follower from the correction section of the first range. In the subsequent position of the range selector switch, to the input of the cathode follower through the plate 145 of the selector switch the correction section of the second range is connected and also the correction section of the first range through the diode 149, the correction section of the third range being connected through the plate 146 of the selector switch to the potentiometer 62. In this case the voltage at the output of he cathode follower is determined by the volt- 'age drop at the input resistance of the cathode follower from the correction sections of the first and second ranges, said voltage being equal to the maximum voltage of the second range.

Thus in any position of the range selector switch the initial voltage at the output of the cathode follower is determined by the voltage drop at the input resistance of the cathode follower from the correction sections of all the preceding ranges, i.e., it is equal to the maximum voltage of the preceding range, and the output voltage of the device is determined as the sum of the output voltage of the cathode follower and of the voltage taken from the moving arm of the potentiometer, which is determined by the current of the correction section of the respective range.

The voltage taken from the correction unit, which is a function of the setting current, is fed through the resistor 144 to the left grid of the one-shot multivibrator assembled on the tube 113 (FIG. 9). This voltage changes the mark-to-space ratio of the one-shot multivibrator and, hence, the rate of charging of the capacitors 125, 126, 127. If the left half of the tube 113 is open for the most part of the period, then the most part of the charging current is shunted by the tube, and the balancing of the mismatch by the feedback voltage at the input of the cathode follower assembled on the tube 120 takes longer time and, hence, the duration of control pulses increases. Thus, by varying the mark-to-space ratio of pulses on the one-shot multivibrator depending on the setting current i the duration of control pulses is varied.

Thus in the pulse and interval shaping unit command pulses are obtained, whose duration t is a function of the mismatch value AV/ V, the value of the setting current i (the preset speed) and of the pressure drop AP at the speed governor valve.

Presented in FIG. 10 are: an electric circuit diagram of the output stage together with the inhibition unit which inhibits the command for opening the speed governor valve when the pressure drop thereat is insufiicient and which also converts square voltage pulses into back-toback sawtooth current pulses for controlling the electric motor amplifier 28 of the servomotor 6, the phase demodulator 18 of the pulse and interval shaping unit 5, the pressure transmitters 26, 27, and also the circuit adapted for an automatic cutting in of the governing device for pressing duty after molding.

The inhibition unit and the output stage 11 of the governing device are assembled on tube 153 which functions as an amplifier. When there is no mismatch, the tube 153 is blocked by the negative bias voltage fed to the grid of the tube from a source of negative voltage through normally closed contact 154 of the relay 123 (FIG. 9). A voltage divider constituted by resistors 155, 156 (FIG. 10), and diode 157 are intended for setting the Working point of the amplifier. From the source of positive voltage through normally open contact 158 of the relay 123 and resistor 159 voltage is fed to the grid of the valve 153 at the moment of the mismatch. In the anode circuit of the output stage 11 through normally open contacts 160, 161 of the relays and 111 are inserted the control windings of the electric motor amplifier.

On the tubes 108, 109 in the plate circuits of which the electromagnetic relays 110 and 111 are inserted the output part of the phase demodulator 18 is assembled (FIG. 6). a

The duty of the tubes 108, 109 (FIG. is so selected that in case the mismatch is absent the tubes are blocked by the constant negative voltage taken from the voltage divider constituted by resistors 162, 163 (FIG. 9) and normally closed contact 164 of relay 165 (FIG. 10). To the control grids of said tubes a signal is fed taken from the stabilitrons 106, 107 (FIG. 9), inserted into the winding 105 of the transformer 99. The screen grids of the tubes of the stage are fed with alternating voltage. The signal from the stabilitrons 106, 107 is fed to the grids of both tubes 108, 109 of the demodulator, but only that tube is enabled, in which the phase of the signal fed from the stabilitrons coincides with the phase of voltage feeding the screen grid.

The mismatch arising, the corresponding relay 110, 111 is cut in and with its normally open contact 160 or 161 (FIG. 10) closes the load circuit of the tube 153, cutting in the corresponding Winding of the electric motor amplifier. When the relay 123 is cut in, the blocking voltage is removed from the grid of the tube 153 (the contact 154 breaking) and to the grid through the contact 158 and 'resistor 159 linearly increasing voltage is applied. During the period of the relay 123 being cut in, fed into the load of the output stage, said load being the control winding of the electric motor amplifier, is linearly increasing current, the rate of increase thereof being constant and determined by the value of fed voltage, capacitor 166 and the resistor 159.

Assembled on the tube 167 are the amplifiers 24 and 25 of signals from the pressure transmitters 26, 27 in the hydraulic system and the cylinder, transformers 168 and 169 serving as respective loads thereof.

The voltage of the secondary windings of the transformers 168, 169 is rectified by rectifier bridges 170, 171, smoothed by capacitors 172, 173 and appears across loading resistors 174, 175.

From the loading resistors 174, 175 the voltage proportional to the difi'erence in pressures in the cylinder and the hydraulic system of the press, is fed to the grid and to the cathode of the pressure difference amplifier assembled on the left half of the tube 143, and from the output of said amplifier the voltage determined by the difference in pressures in the hydraulic system and the cylinder, through potentiometer 176 is fed to the grid of the right half of the tube 143, into the load circuit thereof an inhibition unit being inserted, said unit being essentially relay 177 serving to block the output of the governing device when the command is given for opening the governor valve, in those cases when the pressure drop at the governor valve happens to be less than the preset value. The relay 177 operates and with its normally closed contact disconnects the supply circuit of the screen grid of the tube 153. The command for closing the governor valve is not inhibited, since when the relay 11 operates (i.e. the governor valve is being closed) its normally open contact 179 shunts the open contact 178 of the relay 177. The operation of the relay 177 is set by means of the potentiometer 176.

Assembled on tube 180 is one more stage for amplifying the signal of the transmitter 27 of the pressure in the press cylinder. In the load circuit of the tube 180 relay 181 is inserted, said relay being intended for switching in the governing device for pressing duty after the molding.

The signal, proportional to the value of pressure in the cylinder, is taken from one half of the primary winding of the transformer 168 and through coupling capacitor 182 is sent to rectifier constituted by diodes 183. The rectified voltage is filtered and fed to the control grid of the tube 180. Fed to the same grid of the tube 180 through plate 184 of the selector switch is negative bias voltage from a voltage divider constituted by resistors 185, 186, 187, 188, 189. By means of stepwise variation of the bias various settings of the relay 181 are attained, i.e. the relay operates at various values of pressure in the cylinder and sends a command for the governing device to be cut in the pressing duty, disconnecting the circuit of the relay with its normally closed contact 190. This is necessary due to the fact that depending on the material and temperature of ingots being pressed the issuing of metal at the moment of the pressing being started takes place at different pressure values in the cylinder. For very soft alloys, e.g., of aluminum, the moment when the governing device should be cut in to operate in the process of pressing is determined not by the value of pressure in the cylinder, but by time.

When the moving arm of the plate 184 of the selector switch is in its final position, full negative voltage from the negative voltage source is fed to the control grid of the valve 180. From the moving arm of plate 191 of the selector'switch to the same grid voltage is fed from capacitor 192, which is charged from the source of pO tive voltage through charging resistors 193, 194, when contact is closed by the press control circuit (not shown in the drawing).

The time delay required for cutting in the pressure relay 181 when the moving arms of the plates 184, 191 of the selector switch are in their final positions, is determined by the time constant of the charging network of the capacitor 192 and is adjusted within 1-5 by means of the variable resistor 194.

The proposed governing device operates in the following manner when being used in the course of molding ingots.

By closing contacts 195' which operate simultaneously with contacts 195 the relay 165 is enabled and by normally open contact 196 is set for self-supply. Simultaneously by means of normally closed contact 197 the circuit of the screen grid of the tube 153 is disconnected and the output of the governing device is shunted by normally open contacts 198. Besides, when the relay 165 is enabled, the normally closed contact 164 disconnects the circuit of the bias voltage divider of the phase demodulator 18 (the valves 108, 109). The tubes are thus cut off by the full negative voltage of the source. Thus, in the process of molding no voltage is fed to the control windings of the electric motor amplifier. The molding is carried out by using a by-pass valve (not shown in the drawing). Normally closed contact 199 of the relay 165 is inserted into the electric circuit of the governing device which serves to actuate the slide valve of the by-pass valve (not shown in the drawing).

When the pressure in the cylinder of the press reaches the value preset by the plate 184 of the selector switch, or after the required time delay, the relay 181 is energized. The output stage is connected and the governing device is ready to operate in the pressing duty.

As is known, the speed of pressing, to preclude rejects, is limited by a certain upper critical value, depending on the brand of metal (or alloy) being pressed, on the shape of the die and on the coefiicient of elongation (if the speed of pressing is measured by the plunger travel speed, as is usually the case). In case of manual control, due to the impossibility of accurately maintaining of the speed at the upper level, the pressing is carried out at lower speeds, which reduces the efi'iciency of the press. The employment of proposed governing device makes it possible to increase the average value of the speed of pressing by approaching the upper critical value of the speed, this resulting in an increase of the equipment efliciency and in a practically complete elimination of rejects, arising when the permissible speed is casually surpassed.

The governing device disclosed hereinabove provides higher quality of control than the systems known heretofore. Its adjustment on the press is excessively simple and consists in the determination and setting of only two relations, viz., the duration of commands and functional dependence of the command duration on the speed of pressing and on the pressure drop at the speed governor valve.

Said adjustment does not require any special tests and may be carried out in the course of normal service of the press.

What is claimed is:

1. A governing device to control the travel speed of the plunger when pressing on hydraulic presses, comprising: a plunger travel speed measuring unit; a plunger travel speed setting unit; a comparison unit, said plunger travel speed measuring unit and said plunger travel speed setting unit being connected thereto; an actuating mechanism or servomotor of the speed governor valve of the press, said actuating mechanism or servomotor being connected with said comparison unit, said speed governor valve serving to control the travel speed of the plunger; a unit adapted to shape a set of pulses and a signal to disconnect the control system, disposed between said comparison unit and said actuating mechanism or servomotor of the speed governor valve.

2. A governing device to control the travel speed of the plunger when pressing on hydraulic presses, comprising: a plunger travel speed measuring unit; a plunger travel speed setting unit; a comparison unit, said plunger travel speed measuring unit and said plunger travel speed setting unit being connected thereto; an actuating mechanism or servomotor of the speed governor valve of the press, connected with said comparison unit, said speed governor valve serving to control the travel speed of the plunger; a unit adapted to shape a single pulse and a signal to disconnect the control system, disposed between said comparison unit and said actuating mechanism or servomotor of the speed governor valve.

3. A governing device as claimed in claim 2, wherein to said unit adapted to shape a single pulse and a signal to disconnect the control system at least one pressure gage, preferably a differential manometer, is connected for registering the pressure drop at the speed governor valve.

4. A governing device according to claim 2, wherein, when the governing device is equipped with a range selector-switch for switching over the pressing speed, a unit serving to convert the diiference in speeds into the relative dilference therebetween is arranged between said comparison unit and said unit adapted to shape a single pulse and a signal to disconnect the control system.

5. A governing device according to claim 3, wherein, when the governing device is equipped with a range selector switch for switching over the pressing speed, a unit serving to convert the difference in speeds into relative the difference therebetween is arranged between said comparison unit and said unitt adapted to shape a single pulse and a signal to disconnect the control system.

6. A governing device according to claim 5, wherein said unit serving to convert the difference in speeds into the relative difference is made in combination with said comparison unit.

7. A governing device according to claim 2, wherein said unit adapted to shape a single pulse and a signal to disconnect the control system is connected with said speed measuring unit.

8. A governing device according to claim 2, wherein said unit adapted to shape a single pulse is connected with said plunger travel speed setting unit.

9. A governing device according to claim 6, wherein said unit adapted to shape a single pulse is connected with said plunger travel speed setting unit.

10. A governing device according to claim 2, wherein a range selector switch is employed, connected with said plunger travel speed measuring unit and with said unit adapted to shape a single pulse and a signal to disconnect the control system.

11. A governing device according to claim 6, wherein a range selector switch is employed, connected with said plunger travel speed masuring unit and with said unit adapted to shape a single pulse and a signal to disconnect the control system.

12. A governing device according to claim 9, wherein a range selector switch is employed, connected with said plunger travel speed measuring unit and wtih said unit adapted to shape a single pulse and a signal to disconnect the control system.

13. A governing device according to claim 2, wherein to said unit adapted to shape a single pulse a unit serving to select the maximum speed between the two, i.e., between the actual and the preset one, is connected.

14. A governing device according to claim 3, wherein to said unit adapted to select the maximum speed between the two, i.e., between the actual and the preset one, is connected.

15. A governing device according to claim 6, wherein to said unit adapted to shape a single pulse a unit serving to select the maximum speed between the two, i.e, between the actual and the preset one, is connected.

16. A governing device according to claim 11, wherein to said unit adapted to shape a single pulse a unit serving to select the maximum speed between the two, i.e., between the actual speed and the preset one, is connected.

17. A governing device according to claim 12, wherein said unit adapted to shape a single pulse and a signal to disconnect the control system comprises a piecewise linear converter employing diodes, said converter establishing a root dependence on the signal of difference in speeds; a flip-flop connected with said piecewise linear converter and operating when the converter signal exceeds the threshold value; a flip-flop reset circuit providing an approximately linear increase of the reset voltage with time; a oneshot multivibrator, whose niark-to-space ratio varies in accordance with the preset speed, said one-shot multivibrator being connected with said flip-flop reset circuit; a voltage divider controlled by the pressure drop at the speed governor valve in such a manner that the rate of increase of the reset voltage depends on the preset speed and on the pressure drop at the speed governor valve; an auxiliary one-shot multivibrator connected with said range selector switch and said flip-flop, said auxiliary one-shot multivibrator being triggered by the aforementioned flip-flop and so connected therewith, that during the time of operation thereof said auxiliary one-shot multivibrator is blocked and the control system is thereby disconnected.

18. A governing device as defined in claim 17, wherein, to facilitate the adjustment and improve the quality of control, correction sections and a correction potentiometer are employed, said correction potentiometer being geared with said plunger travel speed setting unit and electrically connected, through separate plates of said range selector switch, with said correction sections assembled on resistors and diodes.

19. A governing device according to claim 18, wherein, to improve the quality of control, an inhibition unit is provided, said inhibition unit being connected with the actuating mechanism or servomotor of the speed governor valve, and inhibiting the opening of said speed governor valve when the pressure drop thereat is less than the preset one.

References Cited UNITED STATES PATENTS JOHN J. CAMBY, Primary Examiner.

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