DE2706230A1 - Speed control system for DC motor - involves motor acting briefly as generator to obtain actual speed signal for difference control signal generation - Google Patents

Abstract

The speed control system for a direct current motor, has its running time broken up into a sequence of alternate working and measuring intervals. During the measuring interval the motor acts as a generator whose output is used to generate a difference control signal for adjusting the speed. The ratio between the working and measuring intervals is fixed. The motor is in series with a switch controlled by a clock such that it alternates between working and measuring steps. The difference signal controls a pulse modulator for the motor power supply.

Description

Dfpl.-Phys.

Dr. Hermann von HoernPr Leopoldstrasse 20 6856 Oftersheim and Dipl.-Phys.

Berthold Sulger Gegenbaurstr. 5 6900 Heidelberg Procedure for regulation the speed of a direct current motor and device for carrying out the method The invention relates to a method for regulating the speed of a direct current motor with comparison and setting device and a device for carrying out the method.

To control DC motors, it is known to use the motor shaft a tachometer generator to generate a voltage that is directly proportional to the motor voltage To set the tachometer generator voltage. This generator voltage, which is the actual value of the control loop represents, is simultaneous with one for example of a changeable resistor tapped reference or guide voltage, which represents the target value, into a Differential amplifier given.

The control difference signal of the differential amplifier is used in an actuator given, which is e.g. a transistor output stage in series with the motor and the voltage source.

In principle, a tachometer generator is used for precise regulation possible, but such a tachometer generator is expensive and prone to failure. In case of overspeeding of the motor, the tachometer generator is usually damaged first.

Furthermore, it is known to use small DC motors by means of their To renew the current, which is roughly proportional to the speed. This method however, it is imprecise.

The invention is therefore based on the object of a method and a device for regulating the speed of a DC motor with comparison and to create adjusting device with which the speed of the engine over a wide Range can be regulated with great accuracy without the need for a tachometer generator Is used.

The solution to the problem is that according to the invention during the running of the engine the running time in a sequence of alternating work and measuring cycles are broken down and the motor is used as a generator during the measuring cycles becomes, whereby from the generator voltage during the measuring cycles and the lead voltage a control difference signal for influencing the actuating device is formed. Preferably can work at a fixed basic frequency - a fixed cycle ratio to the measuring cycle have, wherein the work cycle for energy supply by means of a pulse energy modulation is modulated. A pulse length or pulse height can be used as pulse energy modulation - or a pulse frequency modulation can be used.

The method according to the invention has advantages over the prior art the salient advantage that it works without a tachometer generator and at the same time a Control has the greatest accuracy over a wide range of engine speeds. Because in a highly advantageous manner, the running time in a sequence of working and measuring cycles is broken down, with the motor during the measuring cycle runs as a generator and its own tachometer device, as it were, during the measuring cycle works.

A device for carrying out the method according to the invention with a DC motor and a comparison device lying in series with an adjusting device is characterized in that the motor is in series with a switch which is controlled via a clock generator into a working cycle and a measuring cycle state of the measuring cycle from the generator voltage and the control voltage obtained in the comparison device controls a pulse energy modulator synchronized with the working cycle of the clock generator, which during the working cycle with a control difference signal Energy pulse the actuating device switches.

In a preferred embodiment of the invention, a differential amplifier is used as the comparison device and a transistor output stage is used as the control device and switch. whereby, according to the invention, the true difference signal is one uZL cY storing vein Delaying, synchronized with the measuring cycle of the clock generator, whose output signal is fed to a pulse length modulator synchronized with the working cycle of the clock generator, which emits a switching pulse during the working cycle to the output stage with a length proportional to the stored or delayed output signal.

In a further embodiment according to the invention, the storing or delaying circuit a voltage storing sample + hold circuit consisting of a field effect transistor, which is used by a pulse generator as Clock generator is controlled, a capacitor and a differential amplifier, its output signal with the pulse of the pulse generator initiating the work cycle is fed to the pulse length modulator.

The provision according to the invention combines in a highly advantageous manner Way the advantages of a latching or delaying circuit along with a pulse regulator modulator for the corresponding energy modulation of the work cycle. The use of a pulse length modulator has proven to be particularly advantageous, which emits an energy pulse of variable length with each work cycle, accordingly of the stored or delayed in the latching or delaying circuit Voltage value.

This highly advantageous combination of a storing or retarding Circuit with a pulse energy modulator, both of a clock generator, A pulse generator can be controlled, enables the most precise control of the Motor speed, with a pulse length generator for the energy shutdown of the work cycle has proven to be most beneficial.

Furthermore, in stimuli after the output stage and in front of the engine Slowing down the voltage rise and for measuring the decrease in the generator voltage Choke be arranged after the generator voltage on the motor side during the measuring cycle is tapped. The choke causes a slow voltage increase, why the control difference signal after the comparison device simply to a very small one Worth wKeln. There are therefore large jumps in voltage with short-term loads or idling of the engine is avoided.

Furthermore, a quick-stop circuit is arranged parallel to the motor. There is also a special circuit to improve the start-up behavior of the motor intended.

Further refinements of the invention emerge from the subclaims emerged.

The invention is illustrated in the following description with reference to FIG Drawing illustrated embodiment examples explained in more detail. Show: Figure 1 shows a basic circuit diagram to explain the method according to the invention, FIG. 2 a block diagram of a device for performing the method according to the invention, FIG. 3 shows a representation of the various appearing in the circuit according to FIG Pulses, Figure 4 different pulse sequences of the pulse length modulator with different Last, Figure 5 four time diagrams with respect to Figure 2 to illustrate the time Behavior of the individual function blocks of Figure 2 with changing load and figure 6 shows a detailed circuit diagram corresponding to the block diagram of FIG.

Figure 1 shows a basic circuit diagram for implementing the invention Method for regulating the speed of a direct current motor.

A DC motor 7 is in series with a switch 5, a Steligliel 3 and a battery 11 at the supply voltage U Indes B. The desk 5 can back and forth between two switching states in the direction indicated by the arrow be moved. A clock generator 6 is used to generate the measuring and the work cycle, wherein the switch 5 is placed in the position shown in the working cycle state is. The second switch contact leads to a voltage-storing or delaying one Circuit 4, the output signal of which via a line 10 into a differential amplifier 2 is given, which represents the comparison device of the control loop. Over a Line 9 is the differential amplifier in its second input a reference or lead voltage URef, which is tapped from a variable resistor 1 will. A second voltage source j2 supplies the reference voltage. The control difference signal on the line 8 of the differential amplifier 2 is given to the control device 3, to set this according to the size of the control difference signal. The clock generator 6 is further coupled to the circuit 4 for the task of the measuring unit to the same.

The way this circuit works is as follows: Of the Clock generator 6 generates a pulse train, each of which switches the switch 5 to its in the position shown in the drawing or in the opposite position. In the position shown, the consumer 7 works as a motor.

In the next following cycle, the measuring cycle, switch 5 is thrown, whereby the motor continues to run due to its inertial mass and now a generator bias voltage generated. This generator voltage is input into the circuit 4 and here it is wäryfer Duration of the measuring cycle saved or delayed.

The output signal of the circuit 4, which is identical to the actual value deegelkreises is, is at the end of the measuring cycle shortly before the start of the work cycle the differential amplifier 2 is supplied. Its control difference signal is now influencing the actuator 3 in a corresponding manner.

FIG. 2 shows a block diagram for implementing what has just been explained Principle.

The control circuit consists of a differential amplifier 13, the one of variable resistor 22 via a line 21 the reference or lead voltage is fed. At the same time, the second input of the differential amplifier 13 The generator voltage of the motor 20 is supplied via a line 23 during the measuring cycle, during which the motor 20 is running as a generator. The output signal of the differential amplifier 13, the control difference signal, is fed to a voltage-storing circuit 14, the output signal of which is given to a pulse length modulator circuit 15.

The circuits 14 and 15 are each operated by a pulse generator 16 controlled, which during the running time of the motor 20, a sequence of measuring and work cycles outputs which are fed to the circuit 14 and the circuit 15, respectively.

The output signal of the circuit 15 controls a transistor output stage 17, which also represents an electronic switch. The power amplifier 17 is supplied with the supply voltage U index B via a line 18. With the Reference numeral 19 in Figure 2 denotes an element which is used to slow down it serves to increase the voltage on motor 20 and on which the generator voltage is used during the measuring cycle is tapped.

The mode of operation of the block diagram is now based on FIGS. 2 and 3 2 explained in more detail: The pulse generator 16 generates a pulse train 24 of a fixed frequency. It is assumed that the first pulse is a pulse to initiate a measuring cycle is. This measuring clock pulse is given to the voltage-storing circuit 14, which thereby picks up and saves the pending control difference signal of the measuring cycle. The second pulse of the pulse train 24 of the pulse generator 16 is now a work cycle Pulse that feeds the output signal at the output of circuit 14 into the pulse length modulator 15 admits delta with a certain time delay. With the beginning of the work cycle 8 the storing circuit 14 is thus inactive. The third pulse of the pulse train 24 is in turn a measuring clock pulse, which in turn activates the circuit 14, whereby the in turn pending control difference signal of the differential amplifier 15 in the circuit 14 is initiated. AD output of the spetching circuit 14 is thus created a pulse train 25, the pulses of which are present during the measuring cycle.

With the initiation of the working cycle, a pulse is now generated in the pulse length modulator 15, the length of which tot is the level of the output signal of the latching circuit 14.

A pulse train thus arises at the output of the pulse length modulator 15 26, which controls the output stage 17, the output stage 17 during the individual pulse duration the pulse train 26 is conductive.

The motor 20 thus works during the measuring cycle and during activation of the circuit 14 as a tachometer generator, during the pulse duration of the output signal of the pulse length modulator 15 as a motor and is during the remaining time of the work cycle switched off (whereby the motor due to the high pulse frequency of the pulse train 24, e.g. 100 hz, and continues to run due to its inertial mass). At the exit of the engine a time sequence of its various states 27 is thus created.

FIG. 4 shows different lengths of the output pulses of the pulse length modulator 15, the pulse train 28 a low load, the pulse train 29 a medium Load and the pulse train 30 represents a high load. The output pulse of the pulse length modulator 15 can thus maximally during the entire duration of the work cycle to be available.

Due to the change in the clock ratio between the measuring cycle and the work cycle, however, any ratio can be set.

FIG. 5 shows the time dependency in a graphical representation of the pulse generator 16 and the circuits 14 and 15 as the load changes.

The pulse generator 16 in turn generates a pulse train 31, wherein alternately one pulse a measuring cycle pulse and the next pulse a work cycle pulse represent. Now the load should change according to curve 32, this change may fall into a work cycle. At the beginning of next measuring cycle the generator voltage of the motor 20 has changed accordingly, which is why the Output of the circuit 14 is shown according to the curve 33, another Assumes value. The pulse length modulator is now active during the next working cycle 15 has a length that is pulse-changed in accordance with the changed output signal 33 34 from, which now activates the output stage 17 correspondingly longer, thereby reducing the speed change to be reversed according to the load change.

FIG. 6 shows an overall circuit diagram of a device according to the invention. The circuit diagram is divided into blocks drawn with dashed lines, which represent the blocks correspond to FIG.

Block 35 is the comparison device (Figure 2, reference number 13), Block 37 represents the memory circuit (Figure 2, reference number 14), block 38 contains the pulse length modulator (FIG. 2, reference number 15), while block 40 represents the output stage (FIG. 2, reference azimuth 17).

With the reference number 39 is the pulse generator, with the reference number 41 the engine marked. Blocks 42 and 43 will be explained below.

The comparison device 35 consists of a differential or operational amplifier 44, at its inverting input via a voltage divider 46, 47 the generator voltage is placed over a line 9o. At the same time there is another at this entrance Voltage divider 48, 49 placed the reference voltage UreS, which is a variable Voltage divider So is tapped. The inverting input of the operational amplifier 44 is connected to ground via a resistor 45.

The output signal 51, the handle difference signal, is stored in the voltage Circuit 37 supplied. This is a sample + hold circuit and consists of an FeJ effect transistor 52, a resistor 53, a capacitor 55 and a Operational amplifier 54. The gate of the FET 52 is connected to the measurement clocks via a line 59 of the pulse generator 39 is controlled. The FET 52 is opened at each measuring cycle, whereby the Hegeldifrerenzsignal on line 51 is stored in capacitor 55 will. The output of the sample + hold circuit leads via a resistor 56 to Pulse length modulator 38, which preferably consists of a monolithic timer circuit 57 exists. At the same time, the pulses of the work cycles are transmitted via a line 58 of the pulse generator 39 is given to the 2 encoder circuit 57. With the beginning of the job it becomes the output of the ochaltkreises 37 in the timer circuit 57verurfatet which generates an output signal on line bo, the length of which depends from the input voltage of the timer circuit 57. About a resistor 61 control the output signals of the pulse length modulator 38 to the output stage 40.

This consists in principle of a power transistor 65, whose Base is controlled via a transistor 62. Resistor 61 is with the base 62 connected, the collector of which is connected to the voltage supply via resistors 63, 64 + U and its emitter is connected to ground. The base of the pnp transistor 65 is connected to the center tap of the two resistors 63, 64. The supply voltage + U is fed in via the imitter of transistor 65, at the collector of which a Throttle 66 is placed. The output of the throttle 67 leads on the one hand to the motor 41, on the other hand via line 90 back to the inverting input of the operational amplifier 47.

Furthermore, two switching blocks 42, 43 are shown in FIG. which on the one hand serve to improve the start-up behavior (block 42) of the motor, on the other hand, represent a quick-stop device (block 43) of the motor 41.

The circuit 42 consists essentially of a pp transistor 83, whose emitter is connected to ground and whose collector is connected via a line 81 the center tap of the voltage divider 48, 49 is connected, the center tap is blocked against ground by means of a capacitor 83. The base of the transistor 83 is controlled via the collector-emitter path of a further transistor 86, at the same time, the base of the transistor 83 is connected to the supply voltage via a resistor 88 U placed at the same time via a voltage divider 84, 85 and a Zener diode is led to one pole of a switch 77. The center tap of the voltage divider 84, 85 is connected on the anode side to the base of transistor 86 via a diode 87.

The quick stop circuit 43 consists essentially of two npn transistors 68, 70 in Darlington connection, with the common collectors connected to the line 67 are connected, the emitter of transistor 70 is grounded and the base of transistor 68 through a resistor 73 and a Zener diode 72 through the line 89 can be controlled by a Stari stop switch 77. Furthermore is the Collector of an npn transistor 76 connected to the base of transistor 62, wherein the base of transistor 76 is connected to line 89 through a resistor 74 while the emitter of transistor 76 is grounded.

When the switch 77 is pressed, the resistor 78 is connected to the line 79 incoming voltage U + pulled to ground. This means that there is no positive voltage more about the Zener diode 91, the resistor 85 to the diode 87, which is basic is connected to a PNP transistor 86, the emitter of which is connected to ground. As a result, U reaches the base 86 via the resistor 84 and the diode 87 86 becomes conductive. The collector 86, which is connected to the base of a PNP transistor 83 is connected, the emitter of which is also connected to ground, and its collector is connected to the center tap of the voltage divider 48'49, the pulls before U coming through a resistor 88 to base 83 to ground. The transistor en 83 is blocked. With the capacitor located at the center tap 48.49 82 specific time constants, URef is applied to the inverting input of the amplifier 44. This enables signal path 51, 60, 67 and the engine runs. Simultaneously the transistor 76, the base of which is connected to line 79 via resistor 74, became its Emitter is grounded and its collector is connected to the base of 62, blocked by pulling the line 79 to ground.

At the same time, the Darlington pair, consisting of the NPN Transistors 68 and 70 blocked. This removes the short circuit across motor 41. The transistors 68, 70 are connected to the line 67 with their collectors, with the emitter of 70 tied to ground. The base of 68 is via a zener diode 72 and a resistor 73 connected to the line 79.

When the switch 77 is opened, the line 79 becomes positive, which means i6 conductive and the Darlington stage 68.70 also becomes conductive. At the same time will thereby also blocking transistor 86, transistor 83 conducting, whereby the capacitor 82 is discharged over 83.

L e r s e i t e

Claims (9)

Patent claims learn to control the speed of a DC motor with comparing and adjusting device, characterized in that during the run the engine's running time in a sequence of alternating work and Measurement cycles are broken down and the motor is used as a generator during the measurement cycles, whereby from the generator voltage during the measuring cycles and the reference voltage Leverage difference signal for influencing the oteleinrichtung is formed. 2. The method according to claim 1, characterized in that at crJ, n penetrating basic frequency the working cycle to the measuring cycle have a fixed cycle ratio, the working cycle for energy supply being modulated by means of pulse energy modulation. 3. The method according to claim 2, characterized in that as Pulsenergiemodulatlon pulse length or pulse height or pulse height modulation is used. 4. Apparatus for performing the method according to the response 1 and 2 with a DC motor lying in series with an adjusting device and a comparison device, characterized in that the motor (7, 20) is in series with a switch (5, 17) which is controlled via a clock generator (6, 16) into a working cycle and a measuring cycle state, the control difference signal obtained during the measuring cycle from the generator voltage and the lead voltage in the comparison device being a pulse energy modulator (15) synchronized with the working cycle of the clock generator (6, 16) controls, which during the work cycle with a signal from the control difference j Energy pulse switches the actuating device (3, 17). 5. Apparatus according to claim 4 with a differential amplifier as a comparison device and a transistor output stage as an adjusting device and switch, characterized in that the control difference signal controls a storing or delaying circuit (14) synchronized with the measuring cycle of the clock generator (16), the output signal of which is a Pulse length modulator (15) synchronized with the working cycle of the clock generator is supplied, which emits a switching pulse s to the output stage (17) during the working cycle, the length of which depends on the level of the stored tder delayed output signal of the circuit (14). 6. Apparatus according to claim 5, characterized in that the circuit is a voltage-storing sample + hold circuit (14), consisting of one Fel.ieffekttransistor (52), from a pulse generator (S9) as a clock generator is controlled, a capacitor (55) and a differential amplifier (54) whose Output signal with the pulse of the pulse generator initiating the work cycle is fed to the pulse length modulator. 7. Apparatus according to claim 5 or 6, characterized in that in series after the output stage (40) and before the motor (41) to slow down the voltage application a throttle (66) is arranged, according to the motor side during the measuring cycle Generator voltage tapped. will. 8. Apparatus according to claim 7, characterized in that parallel a quick-stop circuit (43) is arranged for the motor, which consists of two transistor circuits (7C; 68,70), the transistor circuit when a start-stop switch (78) is actuated (76) blocks the input of the output stage (40) and the transistor circuit (68, 70) at the same time aen output of the output stage (40) short-circuits. 9. Device according to one of claims 5 is 8, characterized in that that to improve the motor start-up when switching on URef with the time constant an RC element (82, 48) reaches the inverting input of an amplifier (44).