Rotation speed stabilizer for electric motors of types DPR, DPM and others. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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Quite often, in various devices of mechanics, automation, it is required to very accurately stabilize the rotation speed of a DC electric motor (EM). Most of the devices that can be found in the literature offer stabilization of the ED rotation speed by changing the current consumed by it during an increase in the load on the shaft. At the same time, a resistance is switched on in series with the ED. This is acceptable if the power of the ED is low. If the ED is more powerful and the current consumed by it is more than 1 A, then the losses on the resistor will be large. In addition, such a scheme stabilizes the speed in a narrow range of changes in the load on the shaft.

The DC EM speed stabilizer proposed by me does not have the above disadvantages and is capable of maintaining the speed on the EM shaft with very high accuracy. It allows you to connect ED with different supply voltage and power consumption. Such stabilization is ensured by feedback from the sensor located on the EM shaft, and also by the fact that with an increase in the load on the shaft, the circuit increases the voltage on the EM up to the maximum, and with an increase in the EM speed (for any reason), the voltage on it decreases. Thus, an oscillatory process occurs, as a result of which the optimal voltage is established on the EM at a certain load. The stabilizer was used with a Polish-made electric motor with a power of about 30 W (I don’t know its name), as well as with a DLM-30 type electric motor, and in both cases showed good results.

Schematic diagram of the speed stabilizer is shown in Fig.1. It is based on the KR1108PP1A microcircuit, switched on in the digital-to-analogue converter (DAC) mode.

(click to enlarge)

The signal from the speed sensor (Fig. 2) is fed through a stable pulse generator, made on the DD1.1 chip, to the DAC input.

At the output of the DAC (pin 13 DA1) a sawtooth voltage is obtained, the amplitude of which is the higher, the higher the frequency at the DA1 input. This voltage is reduced three times, smoothed by the chain R6, R7, C7 and fed to the direct input of the op-amp DA2. An exemplary voltage is supplied to the inverting input of the op-amp, taken from the divider on resistors R8, R9, R10 and the stabilizer DA5. The reference voltage is compared with the voltage from the DAC DA1. If the input voltage of the op-amp is less than the exemplary one, then a low level is set at the output of the latter, which is fed to the transistor VT1 through the diode VD1 (protecting the transistor VT1 from negative voltage). The transistor remains closed, and the current of the resistor R13 through the smoothing circuit R3, C8 opens the transistors VT2, VT3. The maximum voltage is applied to the ED, and it starts to rotate.

As the EM accelerates, the frequency of the signal from the sensor increases and, accordingly, the input voltage at the direct input of the op-amp. As soon as it equals the exemplary one, a high level will be set at the output of the op-amp and the transistor VT1 will open, and the transistors VT2, VT3 will start to close as the capacitor C8 is charging. The ED speed will decrease. As a result, a decreasing oscillatory process is obtained (with a duration of approximately 0,5 s, depending on the capacitance of the capacitor C8), after which the EM speed will be set at which the rotational speed makes it possible to obtain a voltage equal to the exemplary one at the direct input of the op-amp. At the output of the op-amp during operation, a certain duty cycle of the pulses is set, which varies depending on the rotation speed and the load on the EM shaft. These pulses are smoothed by capacitor C8. In principle, they can not be smoothed, but the operation of an ED with a changing voltage on it, and not a duty cycle, seemed to me more preferable.

The circuit is powered by an unstabilized voltage of ~20 V and a stabilized +30 V relative to the common wire. The voltage of +30 V can be changed over a very wide range, necessary for the type of EM used. If it should exceed the maximum allowable input voltage of the stabilizer DA3 and transistors VT1-VT3, then it is necessary to replace the transistors with others (with a more allowable collector-emitter voltage), and power DA3 from a separate unstabilized +20 V source.

The speed sensor is a disk made of opaque material (it is very convenient to make it from textolite), in which 30-60 holes are drilled in a circle (Fig. 3).

The disk is fixed on the ED shaft. The circuit shown in Fig. 2 converts the rotation of the disk into rectangular pulses. If a disk with 60 holes is used, then a frequency meter with a measurement time of 1 s can be connected to the sensor output. It will show the rotation speed in RPM.

The printed circuit board is shown in Figure 4. It contains all the elements from Fig. 1, except for the transistor VT3 and the potentiometer R9.

The unused pins of the DD1 microcircuit are connected to ground and a power source (not shown in the diagram). Transistor VT3 should be located on the radiator, the surface area of ​​which is chosen depending on the power of the ED. When using an ED of the DPM-30 type, I used an aluminum plate with dimensions of 50x100 mm, curved with the letter P. Fixed resistors and capacitors are planar size 1206 (except for R8, R10 type C3-23 or MLT-0,125 resistors). Electrolytic capacitors type K50-35. Trimmer resistor type SP-16v or another suitable size.

Resistor R9 is desirable to use type SP5-35a, although any other is possible. As a voltage stabilizer, I used the circuit described in the magazine "Radio" 2/1981, pp. 44-46. As a sensor (see Fig. 2), you can use any other circuit that outputs pulses with an amplitude of 12 ... 15 V at the output.

To tune the circuit, instead of resistors R8, R10, it is convenient to install two tuning resistors. First, they are set to minimum resistance. The slider of the resistor R9 is set to the lower (according to the scheme) position, and the resistance R5 is selected as the maximum. Having connected the ED, rotate the regulator R9, increasing the rotation speed. In this case, you need to control the voltage at pin 13 DA1 with a voltmeter. If the voltage on it reaches 10 V, and the speed of rotation of the ED is still insufficient, then the resistance R5 is reduced so that at the maximum speed of rotation of the shaft of the ED, the voltage at pin 13 DA1 is 10 ... 10,5 V. Then, using resistors R8 and R10 set respectively the maximum and minimum limits, regulated by the resistor R9. After that, the resistances R8, R10 are measured and replaced by constants. This completes the setup.

Details. Instead of the KR1108PP1A chip, you can use the KR1108PP1B. OU KR140UD6 can be replaced by any other, for example KR140UD7, KR544UD1. Voltage stabilizer KR142EN8E can be replaced with KR142EN8V; 79L15 - KR1168EN15, 78L05 - KR1170EN5, KR1157EN502.

The K561LA7 chip can be replaced with the K561LE5. In the sensor circuit (see Fig. 2), instead of the K561TL1 microcircuit, you can use K561LA7, K561LE5 (in this case, it is desirable to turn on three of their inverters in series).

Author: I.A. Korotkov

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