JPS59225409A - Positioning control system of dc motor - Google Patents

Abstract

PURPOSE:To attain accurate speed control by applying phase locking control to a rotation speed control of a motor and also digitizing the control system. CONSTITUTION:A control circuit section 1 comprising a microprocessor or the like measures a rectangular wave position signals A, B from a waveform shaping circuit 2 and outputs a speed command pulse signal S in a prescribed period based on this position information. A phase comparator 10 compares the phase between both the signals S and A or B and outputs a signal DP corresponding to the phase difference. A logical circuit 11 outputs an error signal DER based on the phase difference signal DP, the duty cycle of the driving output is changed by this signal DER and the rotating speed of the motor 6 is controlled via PWM circuit 8' and drive circuit 9. When the motor reaches a stop position, the position detecting mode is obtained, split position signals E, F are applied to the logical circuit 11, the distance from the stop position is discriminated and the restoring force to the stop position is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a positioning control system for a DC motor. .

<Prior Art> The configuration of a conventionally well-known positioning control system is shown in FIG. The system operates in a mode to obtain high speed (velocity detection mode) and a mode to obtain high positioning accuracy (position detection mode).

Speed commands to the system are generated from a control circuit section l consisting of a microprocessor or the like. This command measures the rectangular wave position signals A and B of the waveform shaping circuit 2 (signals obtained by digitizing the approximate sine wave position signals A' and B' from the encoder 3), and based on the motor position information obtained from this measurement. will be updated accordingly.

Based on this position information, the control circuit unit 1 calculates the system speed with respect to the amount of operation, and outputs a speed instruction signal D of a predetermined bit.
Output as COM. The speed instruction signal DCOM is D/
The signal is converted into an analog signal by the A converter 4 and applied to one input terminal of the error amplifier 5.

When the motor 6 is stopped and the control circuitry 1 requests movement to a new position, the system initially operates in open loop because there is no feedback e-back signal from the encoder 3.

The feedback signal is F/'V (frequency/voltage)
In the converter 7, the frequencies of the approximate sinusoidal position signals A' and B' are converted into analog voltage values and provided as a speed signal AV corresponding to the motor speed. Now this feed ψ
Since there is no back signal, PWM (pulse width modulation) circuit 8
The drive circuit 9 supplies the motor 6 with a maximum current determined by the system.

When the motor 6 reaches the maximum speed, the speed signal Av is transmitted to the control circuit! It works to cut off the signal from the engine and reduce the acceleration torque. As a result, the motor 6 is controlled in a closed loop, but continues to rotate at maximum speed.

When the target position approaches, the control circuit section 1 lowers the speed command value. As a result, the drive circuit 9 causes current to flow in the opposite direction, and the motor 6 is braked.

This braking is applied progressively until the motor 6 reaches its lowest speed. Finally, the control circuit 1 switches to the position detection mode using the approximate sine wave position signal A' or B', and drives the motor 6 to the final target position.

In this position detection mode, the zero crossing point of the approximate sine wave position signal A' or B' is utilized, and the approximate sine wave position signal A
' or B' to the error amplifier 5 to form a high gain feedback loop with respect to the position of the motor 6, which operates to hold the motor 6 electrically in a constant position.

FIG. 2 shows a time chart of changes in speed and motor current in the above.

In this way, the rotational speed of the motor 6 in the speed detection mode is determined by the speed signal Av (analog signal) generated from the approximate sine wave position signals A' and B' and the control circuit section I to D/D.
This is carried out using a frequency control method in which control is performed by comparing the A-converted and supplied speed instruction signal ACOM (analog signal). Then, when the motor 6 is rotated and approaches the final target stop position and enters the position detection mode, accurate positioning is performed by analog control using the approximate sine wave position signal A' or B'.

Note that the PWM circuit 8 generates a pulse width modulation signal whose duty is changed according to the error signal AER (analog signal). This is provided for the purpose of reducing the power loss in the drive circuit 9, which increases when the drive circuit 9 operates linearly.

As mentioned above, the conventionally well-known positioning control system is so-called analog control. - Because it is analog control, it is difficult to integrate it into LSI. - There are many external parts and the system configuration is complicated. - It is difficult to reduce power loss in the drive circuit. However, it has drawbacks such as the need for special consideration, making it difficult to reduce costs.

Furthermore, in conventional systems, the rotational speed of the motor is controlled by a frequency control method. That is, in the F/V converter 7, the rotation frequency of the motor is detected from two approximate sinusoidal position signals A' and B' having a phase difference of 90° from each other.
The rotational speed of the motor 6 is determined by generating a speed signal AV converted into a voltage value and comparing this speed signal AV with a speed specified value (analogized speed instruction signal A COM ) instructed from the control circuit section l. I try to control it.

However, as is generally known, in the frequency control method, a steady deviation (deviation in speed) always occurs between the specified speed value and the motor rotation speed, and the steady deviation differs depending on the magnitude of the load. Therefore, the rotational speed of the motor also fluctuates as the load fluctuates, which has the disadvantage that it is not suitable for accurate speed control.

<Object of the invention> The present invention provides phase synchronization control (P
(LL control), the control system is digitized, the speed of the motor is controlled accurately, and a positioning control system that does not vary depending on the load is provided.

PLL control controls the rotational speed of a motor by comparing the phase of a position signal generated by rotation of the motor with a pulse signal for speed instruction. Since PLL control is a method of directly controlling the phase, there is no difference in the motor rotational speed on the steady side with respect to the speed instruction value, and accurate speed control is performed.

<Example> An example of the present invention will be described in detail below with reference to FIG. In this embodiment, the position detection mode is also digitally controlled.

A control circuit unit 1 consisting of a microprocessor or the like measures the rectangular wave position signals A and B from the waveform shaping circuit 2, and based on the motor position information obtained by this measurement, a control circuit unit 1 performs a predetermined cycle (
A speed instruction pulse signal S is output with a frequency). The phase comparator 10 compares the phases of the speed instruction pulse signal S and the rectangular wave position signal A or B, and outputs a phase signal Dp (digital code signal) corresponding to the phase difference. The logic circuit 11 outputs an error signal DER based on the phase difference signal Dp, and the duty cycle of the drive output is changed according to the magnitude of the error signal DEH, thereby controlling the rotational speed of the motor 6. Here, the PWM circuit 8' is configured as a digital circuit for interfacing with the drive circuit 9, and there is no need to take special consideration to reduce power loss in the drive circuit 9.
It can also be used as the M circuit 8'.

When the final target stop position is approached in this way, the mode is switched to the position detection mode. In this position detection mode,
Two divided position signals E, F with a phase difference made from approximate sinusoidal position signals A', B' are used. These divided position signals E, F are approximate sinusoidal position signals A', B'. is generated by passing it through the divided position signal generator 12.

The two divided position signals E and F are digital signals created by detecting multiple voltage levels of a position signal with an approximate sinusoidal waveform, and in the position detection mode, they have a phase difference from each other so that the direction of rotation of the motor can be determined. There is.

FIG. 4 shows the correspondence between approximate sine wave position signals A', B', rectangular wave position signals A, B, and divided position signals E, F.

The divided position signals E and F are approximate sinusoidal position signals A'.

B' (here, A' where the target stopping position P is determined)
can be created by detecting the voltage level of FIG. 5 shows an example of the circuit, in which the approximate sinusoidal position signal A' is amplified by an amplifier 13 and inputted to a voltage comparator +4.14°...6 different reference voltages ■7. ■6. ..., ■0 and -
Vl, -V2. ..., the voltage level of 0, that is, the approximate sine wave position signal A' in this case, which is compared with -V7, is detected in 16 steps and an exclusive or game is performed) 15.15.・・・
Exclusive OR logic of every other comparison output is performed at .times., and division position signals E1 and F are generated by OR gates 16E and 16F. In the approximate sinusoidal position signal A' in Fig. 4,
The corresponding reference voltages 7 to -V7 are shown, and in this example, divided position signals E and F of four pulses with a phase difference can be generated in a half cycle of the approximate sinusoidal position signal A'.

In the position detection mode, such divided position signals E,
F is supplied to the arithmetic circuit 11, and the distance from the target stop position P can be determined by counting the number of pulses of the divided position signals E and F, including forward and reverse pulses, and checking the states of E and F. Therefore, it becomes possible to control the return force to the stop position depending on the distance from the target stop position.

FIG. 6 is a circuit diagram showing the main parts extracted to explain the operation in the position detection mode, and FIG. 7 is a diagram illustrating the divided position signals E and F in comparison with the contents of this circuit.

The up/down counter 17 receives divided position signals E, -F.
is input to determine the rotational direction of the motor 6, and the number of pulses is counted up or down.

That is, up/down is controlled by the phase difference relationship between the division position signals E and 'F, and the number of pulses is counted by detecting the fall of the division position signal F. The output is 2 bits, al and a2.

The division position detection circuit 18 receives the 2-bit output a1. of the up/down counter I7. a2 and division position signal E.

The position within this mode area is detected by looking at the state of F. When the contents al and a2 of the up/down counter 17 are 0.1 and the division position signals E and F are 0 and 0, there are still al and a2.
The output of the divided position detection circuit]8 controls the PWM circuit 8' so that the motor drive current becomes 0 when E and F are 1.0 and E and F are 0.1, or in a range that includes both of these. Then, the motor 6 can be stopped at a predetermined position with high precision. In this embodiment, as shown in FIG. 7, the return force to the stop position can be controlled in a maximum of eight steps in the forward and reverse directions.

In the case of the analog control described as a conventional example, the pulling force that tries to pull back changes linearly as it moves away from the target stop position (using the feedback of the approximate sine wave position signal A' or B'). Easy delivery. In the case of digital control, if square wave position signals A or B are used, the force that attempts to return to the target stop position changes discontinuously in the forward and reverse directions before and after the stop position, which tends to cause vibrations and cause the stop to stop. Poor stability in position.

To improve this point, it is necessary to control the return force to the stop position so that it changes as linearly as possible depending on the distance from the target stop position, and for this, a high-resolution encoder is required. However, there are limits in terms of cost and mechanical accuracy.

In this example, a high-resolution rectangular wave position signal is created from an approximate sine wave position signal through circuit processing, thereby realizing a digital control system with good stability at the stopping point.

Also a split position signal generator! 2, the reference voltages v7 to -V7 for slicing the approximate sinusoidal position signal A' are:
The correspondence may be made as shown in the relational diagram of FIG. This: - Avoids slicing near the unstable peak value of the approximate sinusoidal position signal A'. Prevents counting errors due to waveform deformation.

・The voltage detection level near the target stop position P is made finer.
More accurate positioning control to the final position is possible. - - Within the position detection mode area, there is enough time to count the divided position signals E and F, making it easy to initialize the up/down counter 17. In the example shown in FIG. 4, the position detection mode area is set and initialized in synchronization with the rectangular wave position signal B, etc.

It has the following advantages and is very useful.

In the embodiment shown in FIG. 3, the divided position signal E or G may be used instead of the phase control using the rectangular wave position signal A or B. The divided position signal F is an approximate sine wave position signal A
', resulting in a partially discontinuous pulse waveform as shown in FIG. Therefore, in order to control the phase of the rectangular wave position signal B, the divided position signal G generated from the approximate sine wave position signal B' is used. The division position signal G is also shown in FIG.

FIG. 9 shows another embodiment, in which PLL control is performed using the rectangular wave position signal A or B when the rotation speed is high, and using the divided position signal E or G when the rotation speed is low.

That is, according to this embodiment, digital control can be performed by I)LL control in both the speed detection mode and the position detection mode, and there is an advantage that the digital circuit can be further simplified.

<Effects of the Invention> As described above, the present invention uses digital phase synchronization control to control the rotational speed of a motor, and the control system can be digitalized and integrated into an LSI, reducing the cost of the control system. Therefore, it is possible to provide a positioning control system for a DC motor that can control the motor speed accurately and that does not fluctuate due to load.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram showing a conventional example, Fig. 2 is a time chart showing the relationship between speed and motor current, Fig. 8 is a system configuration diagram showing an embodiment of the present invention, and Fig. 4 is a system configuration diagram showing an example of the present invention. 8 is a diagram showing the relationship between the signals of each part, FIG. 5 is a block diagram showing the details of the main part of FIG. 3, FIG. 6 is a block diagram showing the details of other main parts, and FIG. FIG. 8 is a diagram showing the relationship between signals of each part in another embodiment, and FIG. 9 is a system showing still another embodiment of the present invention. FIG. ■... Control circuit section, 2... Waveform shaping circuit, 3...
Encoder, 6...Motor, 8'...PWM circuit,
10... Phase comparator, 11... Logic circuit, I2...
・Divided position signal generator.

Claims (1)

[Claims] 1. It has a speed detection mode that includes high-speed rotation control and a position detection mode that provides high positioning accuracy,
A positioning control system for a DC motor, characterized in that, in the speed detection mode, a rotational speed control mechanism of the motor is configured by digitally processed phase synchronization control.