JPS63103681A - Speed controller for servo-motor - Google Patents

Abstract

PURPOSE:To avoid speed ununiformity at the time of constant-speed control in a low speed area, by setting a correction processing means for generating the output of speed signal corrected within one pulse component of pulse signal according to speed change. CONSTITUTION:From a speed control section 3, the output of torque command according to a deviation between speed command Vcmd and speed signal v is generated. The input of the output of an adder 4 every sample cycle T2, to a current control section 5 is provided, and driving current to a servo-motor 1 is set. The rotating speed of the servo-motor 1 is detected by a pulse coder 6, and every sample cycle T2, the output of feedback pulse Pv is directed to a pulse correction circuit 7. From the pulse correction circuit 7, the output of the speed signal v corrected within one pulse component according to speed change is generated. The speed signal v is fed to an adder 2 as negative input, and is fed to the negative input of an adder 4 via a constant element B.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a servo motor speed control device that controls the speed of a servo motor using a microprocessor.

(Prior art) In the so-called soft servo method, in which a microcomputer controls a servo motor used to drive the control axis of an NC machine tool, the feedback signal used to control the speed of the servo motor is shared with the position signal. may be formed from incremental pulses, such as a pulse encoder. In other words, the speed signal is fed back as a digital signal, and it is compared with the speed command of the servo motor.
The servo motor is torque-controlled by outputting a predetermined torque command to the current control section.

In such speed control calculations, when the servo motor rotates at high speed and the pulse signal returned within a unit calculation period is large, if the number of rotations per pulse, that is, the weight for speed is small, it corresponds to the accuracy of this pulse cog. Relatively accurate speed control is possible. However, when the rotation speed decreases, the weight of the torque command per pulse from the pulse cog changes, and even if the precision of the pulse cog is good, that is, even if the number of pulses generated in one revolution of the servo motor is large, the relative The weight of a torque command for one pulse increases, and generally speaking, the lower the speed, the more difficult it becomes to form an accurate torque command.

(Problem to be Solved by the Invention) By the way, the above sampling period is determined by the unique phase of the control device, whereas the pulse cog that feeds back the speed signal often has a phase shift. Even when pulse signals of the same frequency are fed back, a count error of one pulse usually occurs when the speed control section counts the pulses. When attempting to accurately perform speed control at low speeds, vibrations occur in the robot arm or the like to be controlled by the servo motor, since the torque command for one pulse has a large weight. Also, for the same reason, acceleration and deceleration at low speeds causes uneven rotation of the servo motor, and these problems cannot be fundamentally solved by simply increasing the precision of the pulse coder or shortening the calculation cycle. There wasn't.

The present invention has been made in view of the above points, and an object of the present invention is to provide a servo motor speed control device that eliminates excessive rotational vibration at low speeds and enables stable speed control of the servo motor even in the low speed range. It is an object.

(Means for Solving Problems) The servo motor speed control device of the present invention compares the speed command of the servo motor with the speed signal fed back from the servo motor, and performs torque control using a current control section. In the speed control device, a pulse cog returns a pulse signal proportional to the speed of the servo motor, and a determining means determines an increase or decrease in the actual speed from the pulse signal fed back from the pulse cog and counted at a predetermined period.
This invention provides a speed control device for a servo motor, comprising a correction processing means for outputting a speed signal corrected within the range of one pulse of the pulse signal according to the determined speed change. Further, the correction processing means is characterized in that the correction processing means subtracts 1/2 pulse when the servo motor accelerates, and adds 1/2 pulse when decelerating the servo motor.

(Function) In the servo motor speed control device of the present invention, it is possible to obtain a speed signal equivalent to γ pulses (0 x γ x 1) that is corrected for the pulse signal from the pulse cog according to speed changes. This eliminates speed irregularities during constant speed control in the low speed range and enables stable servo control with little vibration.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a speed control block diagram of a servo motor showing an embodiment of the present invention.
The m-structure is realized by an arithmetic processing system configured with a microcomputer.

Speed control of the servo motor 1 is executed according to a speed command Vcd given from predetermined software that controls this system. Reference numeral 2 denotes an adder that compares the speed command Vcmd with the fed back speed signal, and outputs a speed deviation to the speed control section 3. In this speed control section 3, the speed deviation is converted into torque using an integral element (kx/(1-Z-1)) which performs arithmetic amplification for predetermined speed control, and a torque command corresponding to the speed is sent to the adder 4. is outputting.

The current control unit 5 samples the calculation output of the adder 4 at a sampling period T.
The torque command U is received as a torque command U through the sampler No. 2, and based on this, the drive current to the servo motor I is set, and the servo motor 1 is controlled to the commanded rotational speed with a predetermined torque. Further, the rotation speed of the servo motor 1 is detected by a pulse cog 6 which outputs a pulse signal proportional to the rotation speed.

It is output to the pulse correction circuit 7 as a feedback pulse Pv. In this pulse correction circuit 7, the feedback pulse Pv is counted at a period defined by a sampler having the same period T2 as the torque command U, is stored in a speed register, etc., and is corrected according to an increase or decrease in the speed signal. It outputs a speed signal V. This speed signal V is directly supplied to the adder 2 as a negative input, and is also supplied to the input capacitor of the adder 4 via a constant element 8 (k2).

FIG. 2 is for explaining pulse processing in the pulse correction circuit 7 in the block diagram of FIG. 1, and shows a case where the rotation of the servo motor 1 is controlled to be constant in a low speed region.

For example, if the pulse coater 6 has a capacity of 8000 pulses per revolution of the servo motor 1 and the sampling period T2 is 2 seconds, then the weight for the number of revolutions per pulse (RP layer), that is, the speed, is 3. .75rpm
Therefore, the speed command Vc to the servo motor l is 1lr.
The feedback pulse Pv when the signal is p is 3 or 2 pulses per sampling period. Conventionally, it has been impossible to precisely execute speed control at low speeds due to the one-pulse count error that occurs when counting pulses in the speed control section 3, but in this embodiment, Pulse correction circuit 7
As the corrected speed signal V, from 3 pulses to 2
An increment value γ (0 to 1) is added to the pulse train decreasing to a pulse in a manner described below, and the pulse train is supplied to the speed control unit 3. Therefore, even in the low speed range where the weight for the torque command for 7 l pulses is large, the control target by the servo motor,
For example, vibrations in robot arms are reduced.

FIG. 3 is a flowchart showing the procedure of one pulse processing in the pulse correction circuit 7 described above.

In the pulse correction circuit 7, which sets the count value of the i-th feedback pulse output from the pulse coater 6 as Pv(i), first, the count value for at least two cycles is stored (step a), and Pv(i ) and P v (i
-1), it is determined whether the actual speed of the servo motor l increases or decreases (step b). This includes a count error of one pulse that occurs. Therefore, based on the above discrimination result, Pv (i
) < P v (i-1) In other words, if it is determined that the vehicle is decelerating, an increment value γ (0 to 1) set within the range of one pulse of the pulse signal is added to the count value P v (i). (Step c), Pv(i)>Pv(i-1) In other words, if it is determined that acceleration is occurring, a similarly set decrement value γ is subtracted from the count value Pv(i) (Step d)
.

Pv(i) = Pv(i-1), that is, during constant speed rotation, the count value Pv(i) is output as it is as a speed signal V without being corrected (step e).
When there is a change in the rotational speed, Pv(i) is replaced with Pv(i-1) in order to determine the speed in the next cycle (steps f, g). This causes a count of 7 minutes for 1 pulse. Errors are ignored. Then, speed control quickly follows the feedback pulse, and the sample values of 3, 3, 2, 3, etc., as shown in FIG. The speed signal V corrected to * is output, and the speed control section 3 calculates the torque command U=k.

The quasi Σ(Vend −v) k2V is executed (step h).

FIG. 4(a) shows a speed signal when the speed is decelerated by one pulse every two periods of the sampling period T2,
FIG. 4B shows a speed signal when the speed is accelerated by one pulse every two sampling periods T2.

During deceleration, the feedback pulses supplied as 5.4.4.3.3.2 are 5.4+γ, 4.3+γ, 3
．． It is corrected to a speed signal V of 2+γ, and when accelerating, it is 2.3
-γ, 3.4-γ, 4.5-γ speed signals are corrected,
Stability during acceleration and deceleration at low speeds is improved.

Note that in the high-speed region, the weight of the torque command for one pulse is relatively small, and the effect of such correction can be ignored. Generally, when considering the correction effect for both acceleration and deceleration, both the increment value and the decrement value are set to γ = 1/2, and the pulse correction circuit 7 uses 1/2 when accelerating.
Although it is preferable to subtract the pulse amount and add 1/2 pulse amount during deceleration for correction, it is not necessary to make the two values equal.

Although one embodiment of the present invention has been described above, various different embodiments can be easily constructed without departing from the spirit of the present invention. The present invention is not limited to the embodiments.

(Effects of the Invention) According to the present invention, it is possible to obtain a speed signal that is corrected for the pulse signal from the pulse coater by the amount equivalent to γ pulse (0 × γ × 1) according to the speed change. It is possible to provide a speed control device for a servo motor that eliminates excessive vibration during rotation and enables stable speed control of the servo motor even in a low speed range.

[Brief explanation of the drawing]

Fig. 1 is a speed control block diagram of a servo motor showing an embodiment of the present invention, Fig. 2 is a timing diagram explaining pulse correction processing in the same embodiment, and Fig. 3 is a procedure for l-pulse processing. Flowchart showing FIG. 4(a),(b)
) is a diagram showing a mode of correction of a speed signal for each sampling period during acceleration and deceleration. 1... Servo motor, 3... Speed control section, 6...
Pulse coater, 7...Pulse correction circuit. Patent Applicant Fanuc Co., Ltd. Representative Patent Attorney Minoru Tsuji Figure 1 Figure 2-'U° E 2+3 Figure 3 Figure 4

Claims (2)

[Claims] (1) In a servo motor speed control device that compares the speed command of the servo motor with a speed signal fed back from the servo motor and performs torque control using a current control section, a pulse signal proportional to the speed of the servo motor is fed back. a determination means for determining an increase or decrease in the actual speed from a pulse signal fed back from the pulse coater and counted at a predetermined period; What is claimed is: 1. A speed control device for a servo motor, comprising: a correction processing means for outputting a speed signal obtained by the servo motor. (2) The correction processing means subtracts 1/2 pulse when accelerating the servo motor, and adds 1/2 pulse when decelerating. A speed control device for a servo motor according to item (1).