JPS5914380A - Position control system for servo motor - Google Patents

Abstract

PURPOSE:To stop a servo motor at the stopping position in a short time irrespective of load conditions by measuring a motor shaft speed immediately before reaching the stopping position, applying reversely energizing torque in response to the motor shaft speed, thereby improving damping characteristics. CONSTITUTION:A paper feed data DATA is loaded at the timing of a paper start pulse signal P.F of a position counter 11, and counting is performed up or down by feedback pulse FWDPLS, PVSPLS from an encoder of a servo motor. When reaching the stopping position, a signal Y0 of a decoder 12 resets a flip- flop 24 through a monostable multivibrator 21, and the value of a counter 16 is loaded to a counter 28. When the counter 28 counts up a reference clock and counts the prescribed value, it sets the flip-flop 24 through a NAND gate 23. A signal A obtained through an inverter 25 from the output of the flip-flop 24 is combined with a position controller to become the input of a servo amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a position control method for a digitally controlled servo motor.

FIG. 1 shows an example of a digital control system for a servo motor used in a paper feeding device of a conventional line printer. The paper feed amount is controlled by using feedback pulses from the encoder 2 that are output every time the servo motor 1 rotates by a predetermined angle. The speed control circuit 3 is used for acceleration control and constant speed control of paper feeding. The speed control circuit 6 generates an acceleration pulse to accelerate the paper to a predetermined paper feed speed and a speed correction pulse to maintain the predetermined speed, and controls the paper to be fed at a constant speed. This speed method is P T,
Since this is a general technology called TJ or PWM, a detailed explanation will be omitted here.

A deceleration control circuit 4 is applied to the deceleration control. The deceleration control circuit 4 decelerates the servo motor speed by generating deceleration pulses with fixed time intervals in order to stop at the line feed position. The position control circuit 5 has the function of stopping the paper at a predetermined line feed position and holding the C servo motor shaft at a predetermined stop position against disturbances during printing. The specific control operation is an operation for converging the count value of a position counter consisting of an up/down counter (not shown) to zero, which is controlled by forward rotation pulses and reverse rotation pulses obtained from the two-phase outputs of the encoder 2 and υ. be.

The control amount for position control is determined by a weighted pulse width based on the count value of the position counter and an appropriate sampling period.

The position control is controlled by the position counter, and when the motor does not stop at a predetermined position, the above-mentioned control amount of current is intermittently supplied for position correction until the position counter converges to zero. No current flows when it is stopped at a given position. FIG. 3 shows the relationship between the output of the position counter in the position control circuit 5 and the torque applied to one shaft of the servo motor by the above current.

FIG. 2 shows the relationship between the drive signals generated by the control circuits 3 to 5 and the actual shaft displacement of the servo motor 1. In the servo amplifier 6 consisting of four transistors, transistors 7 and 8 are driven in response to acceleration pulse speed control pulses and position control pulses when the position counter is positive, and supply current to the servo motor 1 in the forward rotation direction. However, the deceleration pulse and the position control pulse when the position counter is negative drive the transistors 9 and 10 to supply current in the reverse rotation direction.

When the paper is accelerated, decelerated, and stopped at a predetermined position, if there is an overshoot as shown in Figure 2, the position counter will be -N, and the output of the position counter will go along the solid arrow in Figure 3. A current is supplied in the opposite direction so that the current becomes zero, and a negative torque is applied to one axis of the servo motor. Then, when undershoot occurs, a current is supplied in the forward rotational direction along the broken line arrow in FIG. 3 so that the position counter becomes zero, and positive torque is applied. Position control is performed in this manner, and the paper is stopped at a predetermined position.

The disadvantage of the position control of the prior art described above is that the position control circuit 5 does not have the function of compensating the speed of the axis of the servo motor 1 when it approaches the stop position, so if the 7 riction of the control system is inappropriate, it is difficult to The problem is that it does not settle and it takes time for it to settle. Specifically, if the circuit conditions are determined so that it will settle quickly when using light paper such as 1-copy paper, it will take longer to settle when using heavy paper such as 6-copy paper with a large amount of overshoot and undershoot. That's true.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to settle a servo motor to a target position within a short time.

In a position control system for a digitally controlled servo motor, the present invention measures the speed of the motor shaft just before reaching the stop position, applies a reverse biasing torque according to the motor shaft speed, and adjusts the damping characteristics. This has been improved so that the servo motor can be stopped at the stop position in a much shorter time regardless of the load conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to an embodiment in which the present invention is applied to a paper feeding device of a line printer. The speed control, deceleration control, and position control methods are omitted because they are the same as those in the prior art, and the position control method according to the present invention, which is used in combination with the position control method in the prior art, will be omitted.

FIG. 4 is a block diagram showing an embodiment of a configuration embodying the position control method of the present invention, and FIG. 5 is a time chart for explaining the operation of FIG. 4.

Signals FWD・PLS and :RVS PLS are feedback pulses 1.1 and 1.RVS generated from the encoder when the servo motor 1 rotates forward and reverse, respectively. Signal DATA is data that instructs the paper feed amount, signals P and F are pulses generated at the start of paper feed, and No. 16 POei Tion has a logical value of 1 when the count value of position counter 11, which will be described later, is 4 or less.
This is the signal. In addition, the signal 20th i'l'on is,
It is assumed that the logic f straight turns to 1 when the count value is 4 or less,
This is a value determined from the deceleration control circuit 4, and may be any other numerical value.

The position number 1 counter 11 is loaded with paper feed data DATA at the timing of the signals P and F, and
When LS, R'V8, and PLS occur, they count down and count up, respectively.

The contents of the lower four digits of the position counter 11 are subcoded by the decoder 12, and the decoder 12 outputs the corresponding position signals Y, Q, , Yl, Y2, .
..., outputs Yl4 and Yl5. YO.

For Yl, f2,..., Yl4, Yl5, the output of the position counter 11 is 0.1.2..., 14 (=2), respectively.
, 15 (-1). below,
In the output of the position counter 11, 14.15 etc. are -2, -
It is written as 1. The sign of the output of the position counter 11 is positive when the servo motor shaft is located nine points before the stop position (the count value of the position counter 11 is zero), and negative when it is over the stop position.

Now, when the count value of the position counter 11 becomes 2 or -2, that is, when Y2 or Y14 becomes a logical value 0, this signal is applied to the clear terminal of the counter 16 via the invert OR gate 13. , the counter 16 is cleared. Next, the count value of the position counter 11 is 1 or -1
, signal Y1 or Y15 is applied to AND gate 15 via invert or game) 14. As a result, the counter 16 counts the reference clock 1 supplied to the trigger input terminal via the AND gate 15, and its contents are transferred to the counter 28 via the OR gates 17 to 20.
It is not added to the data input end of the .

Next, when the servo motor 1 reaches the stop position, the signal YO
is applied to the load terminal of the counter 28 while resetting the flip-flop 24 via the monomulti 21,
The count value of counter 16 is loaded into counter 28. The output pulse of monomulti 21 is short enough to load counter 28. The counter 28 counts up the reference clock 2, and when the predetermined value is counted, that is, when the count reaches 15,
Set the Noritsubu frog 24 through the Nant gate 23. The output of the F/J block flop 24 becomes a signal A via an inverter 25. The pulse width d of the signal A depends on the speed of the shaft of the servo motor 1 when approaching the stop position, that is, the pulse width of the signal Y1 or Y15. is short.

- Also, if the speed of the axis of the servo motor 1 when approaching the stop position is too slow, the pulse width of the signals Y1 and Y15 is too long and the count ii& of the counter 16 becomes 15 or more, and the flip-flop is transferred via the Nant gate 27. In order for the flip-flop 22 to be set and the data 15 to be input to the counter 28 through the OR gates 17-20, the flip-flop 24 is reset and at the same time is set ν1, so that the signal A is not outputted.

The signal A is combined with the position control circuit 5 shown in FIG. 1, and is logically summed with, for example, a forward signal and a reverse signal depending on the direction of rotation, and the output thereof is applied to the servo amplifier 6.

FIG. 6 shows the relationship between the output of the position counter 11 and the torque acting on the shaft of the servo motor 1 when the position control method of the prior art and the position control method of the present invention are combined. When the shaft of the servo motor 1 is located before the stop position, the torque is applied to the servo motor in the direction of the solid arrow in FIG. 6 in accordance with the position control method of the prior art in order to converge the output of the position counter 11 to zero. However, when the output of the position counter 11 becomes zero, according to the position control method of the present invention, a current in the reverse rotation direction is supplied to the servo motor 1 based on the signal A, and the servo motor 1 is reversely biased. Provides torque, that is, deceleration torque. If the speed approaches the target stop position quickly, a large amount of deceleration torque is applied, and if the speed approaches the target stop position slowly, a small amount of deceleration torque is applied. Furthermore, when the delay is sufficiently slow, the signal A is not generated by the flip-flop 22, so that the position control of the axis of the servo motor 1 follows only the position control method of the prior art.

Conversely, when the servo motor shaft is located behind the stop position, the position control method of the prior art is followed until the stop position in the direction of the dashed arrow in FIG. 6, and when the output of the position counter 11 becomes zero, the present invention According to the position control method described above, a deceleration torque is applied to the shaft of the servo motor 1 based on the signal AK. The periods of the reference clock 1 and the clock 2 are determined by the inertia, flixirane, etc. of the control system.

In the above embodiment, the speed of the servo motor 1 is measured when the count value of the position counter 11 is 1 or -1, and when the count value becomes 0, the reverse biasing torque is applied. 11 count value is any N or -N
Measure the speed of servo motor 1 when the count value is )
A similar effect can be obtained by trapping the reverse biasing torque to work when it becomes I-1 or -N-1.

According to the present invention, when the servo motor is position-controlled, it is possible to perform position control that compensates for the speed of the motor shaft when it reaches the reference stop position, making it resistant to load fluctuations in the control system and shortening the settling time. can.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the conventional technology, Fig. 2 is a characteristic diagram showing the relationship between the drive signal and the displacement of the servo motor shaft according to the conventional technology, and Fig. 6 is a characteristic diagram showing the relationship between the position counter output and the displacement of the motor shaft according to the conventional technology. FIG. 4 is a block diagram showing an embodiment of the configuration embodying the position control method of the present invention. FIG. 5 is a time chart for explaining the operation of FIG. FIG. 6 is a characteristic diagram showing the relationship between the position counter output and the torque applied to the motor shaft when the position control method of the prior art and the position control method according to the present invention are combined. In the figure, 1 is a servo motor, 2 is an encoder, 6 is a speed control circuit, 4 is a deceleration control circuit, 5 is a position control circuit,
6 is a servo amplifier, 7 to 10 are transistors, 11 is a position counter, 12 is a decoder, 13.14 is an invert or gate, 15 is an AND gate, 16 is a counter, 1
7-2o is or gate, 21 is monomulti, 22.24
1J Tsubu flop, 23.27 is Nante Gate, 2
5.26 is an inverter, and 28 is a counter. Name of Patent Applicant Hitachi Koki Co., Ltd. No. 1 [¥] Off Figure 3 Figure 4 // Avxj P, F- Off Roy Kichi Seshi A Figure 437

Claims (1)

[Claims] A speed control circuit, a deceleration control circuit, and a position control port for digitally controlling a servo motor, and a servo amplifier for driving the servo motor. A position control method for a servo motor, characterized in that the speed of the servo motor immediately before reaching a stop position is measured, and a reverse biasing torque corresponding to the speed is applied to the servo motor.