JPH04184512A - Servo motor control system - Google Patents

Abstract

PURPOSE:To improve the servo rigidity while working and to reduce the overshoot of a servo motor when it is stopped by making the integration of a speed loop integrator incomplete only at the time of stopping the servo motor. CONSTITUTION:A numerical controller (NC) 20 writes moving commands in a shared RAM 21 at every IPT period (distribution period) and the processor CPU of a digital servo circuit 22 read the movement commands from the RAM 21 and performs a position and speed loop processes at time intervals produced by dividing the IPT period. When a servo motor is normally operated, a speed loop integrator (for integration process) performs perfect integration. When the motor is stopped, on the other hand, the integrator is switched to incomplete integration from the distribution period one period prior tothe distribution period in which the moving command becomes '0' so that the integrated value can become smaller when the moving command becomes '0'. Therefore, when the servo motor is stopped, the servo rigidity can be obtained and, at the same time, the overshoot of the motor can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control system for a servo motor that drives a feed axis of a machine tool or an arm of a robot.

Prior Art FIG. 4 is a block diagram of a position/speed control system that controls a servo motor.

In FIG. 4, 10 is a block that decomposes the movement command Me distributed at each predetermined distribution period from a control device such as a numerical control device that controls a machine tool or robot into movement commands Pc for each position/velocity loop processing period; 11 is an integrator (error register) block in position loop processing;
The position deviation εp is obtained by integrating the value obtained by subtracting the position feedback amount Pf for each position/velocity loop processing cycle from the movement command Pc output from the block 10 for each velocity loop processing cycle. Reference numeral 12 denotes a position gain block, which multiplies the position deviation εp by a position gain Kp to obtain a speed command Vc. 13 is an integrator block for speed loop processing, which receives the speed feedback amount Vf from the speed command VC.
The speed deviation εV obtained by subtracting is integrated. 14 is a block of integral constant in the velocity loop, 15 is a proportional constant block of the velocity loop, which calculates the value obtained by multiplying the output Sv of the integrator 13 by the integral constant kl and the value obtained by multiplying the proportional constant by 2 from the value obtained by multiplying the output Sv of the integrator 13 by 2. The torque command Tc is determined by subtracting the torque command Tc. 16 is a block representing the transfer function of the mechanical part of the servo motor, Kt represents the torque constant, and Jm represents the inertia.

The movement command Mc issued for each distribution layer period is decomposed into movement commands Pc for each position/velocity loop processing cycle, and the value obtained by subtracting the movement amount Pf of the servo motor for each position/velocity cycle from the movement command Pc is integrated. The actual speed Vf of the servo motor is subtracted from the speed command Vc from the position loop process obtained by multiplying the position deviation εp by the position gain Kp to obtain the speed deviation εV. Then, this speed deviation εV is integrated by the integrator 13, and the actual speed Vf of the servo motor is calculated from the value obtained by multiplying the integral value SV by 1 by the integral constant.
The torque command (current command) Tc is obtained by subtracting the value obtained by multiplying the proportionality constant by 2. The servo motor is then driven via an inverter or the like.

The above-mentioned servo motor control methods are conventionally well known, including methods in which the servo motor is controlled by a servo circuit composed of analog circuits, and digital servo control performed by software using a pulse processor.

When the servo circuit shown in FIG. 4 is implemented by software using a processor, the processing of the integrator 13 of the velocity loop is performed as follows.

The output of the speed loop integrator in the speed loop processing period n is 5v(n), and the speed command in the same period n is vc(n).
, the velocity feedback amount in the same period n is Vf(n)
Then, the velocity loop integrator 13 calculates the following first equation to obtain the output 5v(n).

Sv (n) = Sv (n = 1) + (Vc (n) - Vf (n)) ... (1) The calculation shown in the first equation above is a process of complete integration, and the following second equation In some cases, we perform incomplete integration as shown.

Sv (n) = 3 ・Sv (n-1) ten (Vc (
n) -Vf (n) )...(2) Note that k3 is a constant and O<k3<1.

When the servo circuit is configured with an analog circuit, there is a leakage current from the capacitor of the integrator of the speed loop, so in the case of the analog servo circuit, incomplete integration shown in the second equation above is performed.

Problems to be Solved by the Invention When the integrator of the speed loop performs the complete integration shown in equation 1, the speed command Vc and the speed feedback amount Vf completely match in the steady state, so the position during stop The deviation εp becomes "0". Further, the positional deviation εp at a constant speed is constant regardless of friction or disturbance torque, and the servo rigidity (disturbance suppression characteristic) is high.

However, the movement command Pc and speed command Vc become "0",
Even if the input to the integrator of the speed loop becomes "0", a certain value will be held in the integrator, so this value is output as the torque command Tc, and the magnitude of this torque command Tc is If the static friction level is higher than the static friction level of the mechanical system driven by the servo motor, it will not be possible to stop as instructed, resulting in overshoot.

FIG. 5 is an explanatory diagram illustrating that overshoot occurs when perfect integration is used in the integrator of the velocity loop.

To make the explanation easier to understand, it is assumed that "1" is output as the movement command Pc, as shown in FIG. 5(a). At first, the servo motor did not rotate due to mechanical friction, etc., and the fifth
As shown in FIGS. (b) and (d), the position feedback signal Pf and velocity feedback signal Vf are not generated. Therefore, as shown in FIG. 5(C), the position loop integrator 1
1 holds the positional deviation εp (=1). This position deviation εp becomes the speed command Vc, and the integrator 13 of the speed loop
, and the output Sv of the integrator 13 increases sequentially as shown in FIG. 5(e). Then, the output Sv of this integrator
The torque command Tc generated from
), the static friction of the mechanical system is determined by the torque command Tc
When Pf is exceeded, the sobo motor rotates and the position feedback Pf.

The speed feedback Vf is output, and the position deviation εp is
0". Therefore, the output Sv of the integrator will hold the integral value at that time. On the other hand, the torque command Tc becomes a value that is decreased by multiplying the speed feedback amount Vf by the proportionality constant by 2 (see FIG. 5(f)). However, when this decreased torque command Tc is larger than the dynamic friction of the mechanical system, the servo motor continues to rotate, the movement position overshoots the command position, and a speed feedback signal Vf is output (see Fig. 5). b).

(see (d)). As a result, the positional deviation εp becomes a negative value,
Due to the speed command Vc generated by this positional deviation, the output of the integrator of the speed loop changes to a negative value, and a torque command Tc in the opposite direction is output. When this negative torque command exceeds the static friction torque of the mechanical system, the servo motor rotates in the opposite direction, the rotational position of the servo motor becomes the command position, and the position deviation εp also becomes "0".

If the integrator of the velocity loop is implemented with complete integration in this way, an overshoot will occur when stopping. On the other hand, if incomplete integration as shown in the second equation is performed using the integrator of the speed loop, the problem of overshoot will be reduced because the value of the output Sv of the integrator will become smaller, but the problem of overshoot will be reduced. Since the speed feedback signal Vf and the speed feedback signal Vf are not equal to each other, a positional deviation occurs during stopping.

Then, problems arise such as position deviation fluctuating due to disturbance torque received by the servo motor while moving at a constant speed.
Servo rigidity deteriorates.

Therefore, an object of the present invention is to provide servo rigidity, and
An object of the present invention is to provide a control method for a servo motor that reduces overshoot when stopped.

Means for Solving the Problems The present invention provides a control system for a servo motor in which position/velocity loop processing is performed by a processor, in which a movement command in a distribution cycle set one or more ahead of the current distribution cycle is "0". '', by switching the integral processing in the velocity loop processing from complete integral to incomplete integral, the integral of the velocity loop integrator becomes incomplete integral only when stopped, and the servo rigidity is increased during operation. Make the integrator output small so that the position does not overshoot only when stopping.

Operation During normal operation, the velocity loop integrator (integration process) performs complete integration, so the servo rigidity is maintained at a high level. On the other hand, when stopping, the above-mentioned integrator (integration processing) is switched to incomplete integration from a distribution cycle one or more before the distribution cycle at which the movement command becomes "0", and the movement command becomes "O".
When the value of the integral becomes small,
Prevents overshoot.

Embodiment FIG. 3 is a block diagram of a digital servo control device implementing an embodiment of the present invention. Since the configuration is the same as that of a conventional digital servo control device, it is shown schematically.

In FIG. 3, 20 is a numerical control device (hereinafter referred to as NC), 21 is a shared RAM, and 22 is a processor (CPU).
, digital servo circuit having ROM, RAM, etc., 23
24 is a servo motor, and 25 is a pulse coder that generates pulses as the servo motor 24 rotates.

The NC 20 writes a movement command to the shared RΔM 12 every IPT period (distribution period), and the CPU of the digital servo circuit 21
reads this movement command from the shared RAM 12 and sends it to the IT
Position/velocity loop processing is performed in a cycle in which the P cycle is divided into N parts. The movement command Pc(n) in the position/velocity loop processing is determined so that the movement command output from the NC 20 is evenly distributed during each ITP cycle, and the movement command Pc(n) and the position from the pulse coder 25 are calculated. Position loop processing is performed based on the difference between the current position of the servo motor 24 obtained by the feedback pulse Pf, and the speed command V is
c is obtained, and then a speed loop process is performed using the speed command Vc and the actual speed Vf of the servo motor 24 obtained from the feedback pulse from the pulse coder 25, and the torque command (
Find current command) Tc. Then, current loop processing is performed, a PWM command is created, and the servo motor 24 is driven via the servo amplifier 23.

FIGS. 1 and 2 are flowcharts of the movement command reading process for each ITP cycle, and the position loop process and speed loop process for each position/velocity loop process cycle, which are executed by the CPU of the digital water supply circuit 22 in this embodiment. It is.

Figure 1 is a flowchart of the processing performed every ITP period. First, the CPU of the digital servo circuit performs NC processing every ITP period.
20 is read via the shared RAM 21 (step SL).

Then, it is determined whether this movement command is "0" (step S2), and if it is "0", it is determined whether the movement command stored in the register before the IITP cycle is rOJ or not (step S3), rOJ If so, the movement command Mc read in step S1 is stored in register R (Mc) (step S6). That is, the register R (Mc) stores the movement command Mc one cycle before the current cycle.

When the movement command Mc read in step S1 is not rOJ, the flag F is set to "0" and the counter CNT
is set to "0" in steps S7 and S8), and the process moves to step S6. As a result, when there is a one-cycle light movement command Mc than an ITP period movement command that performs position/velocity loop processing as described later, the flag F and the counter CN are
T is set to rOJ, and flag F and counter CNT are always set to rOJ at the start of movement.

In addition, the movement command Mc read in step S1 is "0".
, and when the value of register R (Mc) is not rOJ (
When stopping the movement), the flag F is set to "1", the counter CNT is set to an arbitrary value A (steps S4 and S5), and the process moves to step S6.

On the other hand, in the position/velocity loop cycle, the process shown in the flowchart in Fig. 2 is executed every cycle, and first, register R (M
e) Each position / position based on the movement command MC stored in
Obtain the movement command for each speed loop processing cycle in the same way as before (
Step 5100), based on the movement command, position loop processing is executed in the same manner as in the past to obtain a velocity command Vc (step 5101). That is, since position/velocity loop processing is performed based on the movement command stored in the register R (Mc), the movement command M for each ITP cycle shown in FIG.
To read e (step SL), move command Me is 117
This means that P cycles are read ahead.

Next, in step 510, it is determined whether the flag F is "1" or not.
2), the flag F is the movement command Mc of the next ITP cycle.
Since it is set to "0" when is not "0", the flag F is set to "0" at the time of starting movement or when movement has already started, and in this case, the speed loop processing Complete integration is performed. That is, the first integral value Sv is determined by adding a value (velocity deviation) obtained by subtracting the velocity feedback amount Vf from the velocity command Vc determined in step 5101 to the integral value Sv stored in the register.
Complete integration of the equation is executed (step 5108), and the torque command Tc is obtained by multiplying the integral value Vs by the integral constant kl and subtracting the value obtained by multiplying the speed feedback amount Vf by the proportional constant kl by 2.
is calculated (step 8106), the torque command Tc is transferred to the current loop process (step 5107), and the position/velocity loop process is ended.

Further, when the flag F is "1" in step 5102, that is, the ITP in the position/velocity loop processing is
The movement command Me for the ITP period of one period of light is “0” from the period.
When the movement command of the relevant ITP cycle is not "0" (1 17P cycle before stopping movement), the flag F is set to "1" and the counter CNT is set to A (see steps 82 to S5). Since the flag F is "1", the process moves from step 5102 to step 5103, and if the counter CNT is not "0" (it is not "0" at the beginning),
Subtract “1” from counter CNT (step 5104)
, performs the incomplete integration shown in the second equation (step 5105).
, the torque command Tc is obtained from the obtained integral value Sv and delivered to the current loop (steps 5106 and 5107).

Thereafter, as long as the flag F for each position/velocity loop processing cycle is "1", the processing of steps 8100 to 5107 is executed until the counter CNT becomes "0", and the integral processing of the velocity loop processing is performed using incomplete integration. It will be executed.

As a result, the movement command Mc of the ITP period becomes "0"1
Since incomplete integration processing is executed from each position/velocity loop process of the previous ITP cycle to the velocity loop process, each velocity loop process of the position/velocity loop process cycle obtained by dividing the ITP cycle into N. The integral value Sv of the integral processing at
gradually becomes smaller, and when the movement command Pc in the position/velocity loop process becomes "0", the integral value Sv
is a small value, and overshoot is less likely to occur when stopping.

When the counter CNT reaches rOJ, the process moves to step 5108, returns to complete integration, and if there is a next movement command, that movement command Me is executed.
Flag F in the previous ITP cycle.

The counter CNT will be set to "0" (see steps S7 and 88).

In addition, in the above embodiment, the movement command M in the ITP cycle
Before the IITP cycle when e reaches rOJ, the velocity loop integration process is changed to incomplete integration process, but in addition,
It is also possible to switch to incomplete integration before 2 ITP cycles or 31 TP cycles.

Effects of the Invention The present invention makes the integral process of the velocity loop process an incomplete integral immediately before the servo motor stops its rotation, and makes the integral process of the velocity loop process a complete integral during normal driving of the servo motor. As a result, servo rigidity is maintained and overshoot is less likely to occur when stopping.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of the processing executed by the processor of the digital servo circuit for each distribution period (ITP period) in an embodiment of the present invention, and FIG. 2 is the position/velocity process executed by the processor of the digital servo circuit in the embodiment. A flowchart of the loop processing, Fig. 3 is a block diagram of the digital servo control device implementing the same embodiment, Fig. 4 is a block diagram of the servo motor position/speed control system, and Fig. 5 is a complete diagram of the integrator of the velocity loop. FIG. 3 is an explanatory diagram illustrating that overshoot occurs when integration is used. 20... Numerical control device, 21... Shared RAM 122
...Digital servo circuit, 23...Servo amplifier,
24... Servo motor, 25 River pulse coder.

Claims (1)

[Claims] In a servo motor control system in which a processor executes position/velocity loop processing in response to a movement command issued every distribution cycle, if the movement command in a distribution cycle set one or more ahead of the current distribution cycle is "0", '', a servo motor control method is characterized in that, in order to prevent overshoot, integration processing in velocity loop processing is switched from complete integration to incomplete integration.