JPH0261706A - Servo control method - Google Patents

Abstract

PURPOSE:To prevent hunting by increasing an incompletely integrated term of a speed feedback loop at the time of detecting that the deviation is equal to or smaller than a prescribed reference value and setting this integral term to 0 thereafter to keep the integral value. CONSTITUTION:A system block to realize the control in a digital servo system is the machine system of a control object, and the move command inputted to this block is inputted to an adding circuit 2 together with a backlash correction signal and a pitch error correction signal, and a deviation Ep from a fed- back position signal is operated. An operation block 3 operates a speed command Vcmd in accordance with this deviation, and a deviation Er from a feedback speed signal Vf is operated through an adding circuit 4. A speed control part 5 has a speed control block 5a and an incompletely integrated term switching part 5b. This switching part 5b switches an incomplete integral term K3 of said block 5a to a prescribed value according as the deviation Ep is equal to or larger than the reference value or not.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a servo control method for controlling a servo motor by digital control, and particularly to a servo control method that can prevent hunting at a stop position.

<Prior art> In a normal digital servo system, 1 as a position command
When a pulse is input, the output of the integrator increases linearly, and when the torque corresponding to the integrator output exceeds the static friction force of the mechanical system, the mechanical system starts moving. In such servo control, by switching the incomplete integral term of the speed feedback loop, the driving force can be increased in a short time, and the positional deviation at the time of stopping can be reduced to zero, and overshoot can be reduced. That is, when the positional deviation is greater than or equal to a predetermined value (for example, 1), by setting the incomplete integral term to a small value, the increase rate of the output torque command is set as a linear function, and the position command is given. This shortens the time it takes for the mechanical system to actually start moving, or allows it to move in one pulse. In addition, when the position error is less than a predetermined value, by setting the incomplete integral term to a large value, the torque command is attenuated exponentially, eliminating overshoot during positioning of the mechanical system and improving positioning accuracy. Improving.

<Problems to be Solved by the Invention> As mentioned above, in conventional servo control, the torque command is exponentially attenuated by increasing the incomplete integral term when the position deviation becomes smaller than the reference value. In the end, the overshoot was prevented by setting it to zero.

However, in the conventional system, since the motor does not generate torque while stopped, when disturbance torque such as a spring element or torsion element is applied to the mechanical system, the motor is moved, resulting in a negative positional deviation.

As a result, the torque command from the integrator increases and the position is returned to such a position that the positional deviation becomes zero. Then, since the torque command from the integrator becomes zero, the positional deviation is again affected by the disturbance. Therefore, by repeating this process, there is a problem in that a phenomenon called hunting occurs, which causes vibration even when the engine is stopped.

From the above, it is an object of the present invention to provide a servo control method that can maintain a high level of response accuracy to one pulse feed, prevent overshoot, and prevent hunting at a stop position.

〈Means for solving problems〉 FIG. 1 is a block diagram showing one embodiment of the present invention.

1 is a mechanical system, 2 is an adder circuit, 3 is an arithmetic block, and 5 is a speed control section.

<Operation> The adder circuit 2 calculates the deviation Ep between the position signal from the mechanical system 1 and the movement command, and when the deviation Eρ becomes equal to or less than a predetermined reference value, the speed control block 5 detects an error in the speed feedback loop. Set the complete integral term k to a large value (for example, 3=1
), when the integral value calculated based on the incomplete integral term becomes smaller than the set value, the incomplete integral term is set to zero to hold the integral value, and thereby the speed feedback The torque command T cmd output to the loop is held constant. Note that the torque command '['c@d is maintained at a constant value that is less than or equal to the frictional force that the mechanical system 1 has.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a system block diagram that realizes control using a digital servo system. Reference numeral 1 denotes a mechanical system to be controlled, in which an input/output relationship is defined by a transfer function including a coefficient represented by motor inertia JII+. The movement command input to this servo system is input to the addition circuit 2 together with backlash correction and pitch error correction signals, and here the deviation Ep from the position signal fed back from the linear scale, induct sin, or pulse coder is input.
is calculated. The calculation block 3 including the position gain 1 (P) calculates the speed command Vca+d from the deviation EP, and the speed command Vcmd is input to the addition circuit 4, where the deviation Er from the speed signal Vf fed back from the pulse coder is calculated. be done.

5 is a speed control section, which has a speed control block 5a and an incomplete integral term switching section 5b. Speed side k.

It has an integrator, a proportional calculation section that calculates 2.Er, and an addition section that synthesizes 2.Er and 2.Er and outputs a torque command Tcmd. The incomplete integral term switching unit 5b operates depending on whether the position deviation EP is greater than or equal to a reference value (for example, 1), or depending on whether the integral value in the speed control block 5a is smaller than a predetermined set value. Then, the incomplete integral term of the speed control block 5a is switched to a predetermined value. In other words, when the target position is approached and the deviation Ep becomes less than a predetermined reference value, the incomplete integral term of the speed feedback loop is significantly shifted (
(from zero to 1), and the incomplete integral term k.

The integrator output i (=to1・Er・e
When xρ (-, t)) becomes smaller than the set value, set 3 to zero for the incomplete integral term and make the integral value at that time,
- Hold Er, thereby keeping the torque command TCIIld output to the speed feedback loop constant. Note that the torque command Tend is maintained at a constant value that is less than or equal to the frictional force that the mechanical system 1 has.

Torque command T output from this speed control block 5
cmd determines the command current to the servo motor that immediately moves the mechanical system 1 via the current control block 6. A feature of the present invention is that the speed control block 5 controls the incomplete integral term of the speed feedback loop using the deviation EP and the integral value.

Overshoot in the mechanical system 1 due to stick-slip etc. is prevented, and hunting during stoppage is also prevented.

Next, the control of the incomplete integral term in the speed control block 5a will be explained with reference to the analog servo system and its signal waveform shown in FIG.

In FIG. 2(a), 4 is an analog addition circuit that outputs a speed deviation Er, which is the difference between the speed command Vand and the speed signal Vf, and 5a is a speed control block, which connects the amplifier 12 to the amplifier 12. Two resistors 1 connected in parallel
It has a capacitor 15 connected in parallel to a 3.14 series circuit and a resistor 14. The resistance value R1 of the resistor 13 is the first
The proportional gain of the speed control block 5a shown in the figure corresponds to 2, the resistance value R2 of the resistor 14 corresponds to the incomplete integral term of 3, and the capacitance C of the capacitor 15 connected in parallel with the resistor 14 corresponds to 2.
8 corresponds to the integral gain k of the speed control block 5a.

First, the control of the incomplete integral term by the deviation Ep will be explained. In Fig. 2(b), a one-pulse movement command is input at the time, and the positional deviation Ep becomes the reference value (=1).
When this happens, the resistance value R is made infinite (the incomplete integral term is made zero).

As a result, the torque command 'rc+*d increases along the straight line a proportional to time, becomes equal to or higher than the torque Ts according to the static friction characteristics of the mechanical system 1, and a movement corresponding to one pulse is performed at time t2. When the positional deviation Ep becomes less than the reference value (becomes zero) due to this movement, the resistor R2 is set to a predetermined value and the incomplete integral gain is set to a large value (=1).

In other words, if the resistance R2 is made small before the movement of the mechanical system 1 starts (if the incomplete integral term is made large),
), the 1-lux gradually increases along the curve shown by the dotted line a', so even if there is a one-pulse movement command, it cannot overcome the static friction torque and there appears to be backlash, and the positioning angle is 9 degrees. to degrade. On the other hand, if the resistance R2 remains infinite even after the mechanical system 1 starts moving (time t2) (the incomplete integral term is set to zero), one point will appear in the mechanical system after the movement starts (time t2). As shown by the chain line, excessive overshoot occurs.

However, as mentioned above, the point in time when the deviation Eρ between the position signal from the mechanical system 1 and the movement command exceeds a predetermined reference value is detected;
If we control □ to the incomplete integral term included in the integral gain of the velocity feedback loop.

A torque command curve like the solid line C shown in FIG. 2(b) is obtained, and excess torque does not cause overshoe 1-.

Next, control of the incomplete integral term based on the integral value of the speed control block 5a will be explained. In Figure 2 (C),
When a one-pulse movement command is input at time t1, the torque command Tcmd rises along a straight line a proportional to time,
Actual positional movement is performed at time t2 when a predetermined value Ts corresponding to the static friction characteristics of the mechanical system 1 is exceeded. When a movement equivalent to a pulse is detected at time t2, the incomplete integral term corresponding to the resistance R2 is greatly increased, and the torque command Tc1ld is
decays exponentially. When the torque command Tcmd attenuates and reaches a constant value Tc set below the frictional force Ts of the mechanical system 1 (time t), the incomplete integral term is reset to zero, and the integral value at that time ( Torque command) kl・Er
is held constant. By controlling as described above, it is possible to stop without overshooting, and hunting can be prevented during stopping by applying a constant torque that does not exceed the frictional force during stopping.

FIG. 3 is a flowchart of the process of the present invention, and the case where there is a position command for one pulse will be explained step by step. Speed command V calculated based on deviation EP in calculation block 3
cmd and the speed signal Vf obtained from the speed feedback loop, in the adder circuit 4, E r = Vc
md - Vf to calculate the speed signal deviation Er (steps 101 to 103).

Next, in step 104, the incomplete integral term switching unit 5b checks whether the positional deviation Ep is less than a predetermined reference value (=1).
), if it is less than the reference value, it is further checked whether the integrator output i (=, ·Er·exp(k3t)) of the speed control block 5a is less than the set value Ts (step 1o5
).

It is determined in step 104 that the positional deviation EP is a predetermined reference value (
±1) or more, for example, if there is one pulse input and it is before movement, in other words, time t-t → t in Figure 2 (Q)
2, the incomplete integral term should be set small (to zero) at step 108), and the integrator output i (=1·Er−t) increases linearly in accordance with the sequentially added deviation Er. A torque command Tend (= i + k2·Er) is calculated (step 107) and is output to the speed feedback loop.

On the other hand, if the positional deviation Ep is less than the predetermined reference value (Ep=O) and the integrator output i is more than the set value Tc, in other words, during the time t2 → and in FIG. 2(c), For the incomplete integral term, increase by 1, e.g. k.

= 1 (step 106), and the incomplete integral term is set to 3.
The integrator output i (=1Er−ex
p(L t )), the torque command Tcmd (=i
Step 107).

This is output to the velocity feedback loop.

In addition, if the integrator output i becomes smaller than the set value as determined in step 105, in other words, the time shown in FIG.
), the torque command Tc1IId is determined by the constant integrator output.
Step 107).

This is output to the velocity feedback loop.

<Effects of the Invention> According to the present invention, the deviation between the position signal from the mechanical system and the movement command is calculated, and when the deviation becomes equal to or less than a predetermined reference value, the incomplete integral term of the speed feedback loop is calculated. Largely, when the integral value calculated based on the incomplete integral term becomes smaller than a set value, the incomplete integral term is set to zero to hold the integral value, and this is output to the speed feedback loop. Since the structure is configured to hold the torque command given, the response accuracy to one pulse feed can be maintained at a high level and overshoot can be prevented.

Hunting at the stop position can be prevented after the positional deviation is reduced to zero.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
Fig. 2(a) is a circuit configuration diagram corresponding to the analog servo system of the same embodiment, and Fig. 2(b) is a control explanatory diagram for an incomplete integral term due to the deviation Ep. FIG. 2(c) shows the incomplete integral term k due to the integral value. Control explanatory diagram. FIG. 3 is a flowchart of the process of the present invention. 1. Mechanical system. 2.Addition circuit, 3.Calculation block, 5.Speed control section.

Claims (2)

[Claims] (1) In a servo control method that has a loop of position feedback and speed feedback with the mechanical system, the deviation between the position signal from the mechanical system and the movement command is calculated, and the deviation is below a predetermined reference value. The incomplete integral term of the speed feedback loop is increased at the point in time, and when the integral value calculated based on the incomplete integral term becomes smaller than the set value, the incomplete integral term is set to zero and the integral value is increased. A servo control method comprising: holding a torque command, thereby holding a torque command output to the speed feedback loop. (2) The torque command is maintained at a constant value that is less than or equal to the frictional force of the mechanical system.
Servo control method described in section.