JPH0423017A - Servo controller - Google Patents

Abstract

PURPOSE:To surely eliminate the influence of the Coulomb's friction and to attain the highly accurate servo control by obtaining the estimated value of the frictional force of a machine by a frictional force estimating means and presetting always the maximum value of the estimated frictional force to a frictional force feedforward control means. CONSTITUTION:An angle theta and an angular velocity omega (=theta') are detected from a machine 13 and then inputted to a subtractor 11 and a single terminal of an adder/subtactor 14 and a frictional force estimating part 22 respectively. Then the estimated value of the Coulomb's frictional force (d) is obtained and a prescribed operation is carried out at the part 22. The estimated value of the frictional force, i.e., the computing result is outputted to a frictional force feedforward control part 21. Thus only the maximum value of the past is held at the part 21 and therefore only the force (d) is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a servo system in which deviation increases due to friction.

[Prior Art] As shown in FIG. 3, a conventional servo control device performs integral control to cancel the influence of friction, and obtains a force to overcome friction by integrating the deviation.

That is, as shown in FIG. 3, the target value θr is input to the subtracter 11 and the target value feedforward control section 12.

Then, the detected angle θ of the controlled machine 13 is subtracted from the target value θr input to the subtracter 11 to obtain a deviation signal, and the deviation signal is multiplied by the position control gain cp.

This multiplication result is input to the adder/subtractor 14, where it is added to the differential output θr of the feedforward control unit 12, and the angular velocity ω of the machine 13 is subtracted, resulting in a speed deviation signal, which is input to the PI control unit 15. This PI control section 15
The output signal is manually inputted to the adder 16 and added to the inertial force jθr' from the feedforward control section 12 to obtain the torque command T of the machine 13.

[Problems to be Solved by the Invention] As described above, the conventional servo control device performs integral control to cancel the influence of friction, but it takes a certain amount of time to integrate the deviation. For this reason, there has been a problem in that the deviation due to friction cannot be suppressed instantaneously, and there are situations in which the deviation becomes large.

The present invention has been made in view of the above points, and an object of the present invention is to provide a servo control device that can quickly eliminate the influence of friction.

[Means for Solving the Problems] The present invention provides a servo control device that performs position control on a controlled object, which calculates an estimated value of frictional force based on the input torque to the controlled object and the angular velocity of the controlled object, and maintains the maximum value. However, a compensation torque is calculated based on this estimated maximum frictional force value and the target angular velocity, and this compensation torque is added to the input torque to the controlled object.

[Operation] By estimating the frictional force of the controlled object and holding the maximum value as described above, and calculating the compensation torque based on this estimated maximum frictional force value and the target angular velocity, it is possible to eliminate the delay in the estimated frictional force value. However, the compensation torque can be calculated without being affected by this.

Therefore, even if the speed suddenly increases, it can be canceled out by instantaneously outputting a compensation torque and using feedforward control, making it possible to reliably eliminate the effects of friction and perform highly accurate servo control.

[Example code] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a servo control device according to the present invention. In the servo control device shown in FIG.
A friction force estimating section 22 is provided to estimate the friction force from the angular velocity ω, and the friction force estimating section 22 controls the friction force feed forward control section 21.

The target value feedforward control unit 12 differentiates the target value θr to obtain the speed signal θr', differentiates the command value θr twice to calculate the acceleration, and further multiplies the inertia J to obtain the inertial force control aJijθ'′ Find the above speed signal θr
′ is input to the 10 terminal of the adder/subtractor 14 and also to the friction feed forward control section 21 . Also,
The friction force feed forward control section 21 is given an estimated friction force value d from the friction force estimating section 22 . The friction force feed forward control unit 21 holds the maximum value of the estimated friction force value d from the friction force estimation unit 22, presets it to the N target value of the Coulomb friction model, and calculates a torque sufficient to cancel the friction force. In this case, the friction force feed forward control section 21 stores the friction force when the absolute value d1 of the estimated friction force value d sent from the friction force estimation section 22 becomes larger than the estimated value d held in the memory. Rewrite the content,
The maximum estimated frictional force value is always maintained.

Then, the result of calculating : on the above side 'aJH21 is TpR+c
is input to the adder 23 and added to the inertia force control amount jθr' from the target value feedforward control section 12.

The feedforward force added by this adder 23 is
It is input to the adder 16 and added to the output of the PI control unit 15, and is sent to the machine 13 and the friction force estimation unit 22 as a torque command T.
is input.

The frictional force estimation section 22 includes a first calculation section 24. Second calculation unit 25
and a subtractor 26 , the torque command T is input to the friction force estimation section 22 , and the angular velocity ω from the machine 13 is input to the adder 23 . The calculation result of the first calculation unit 24 is input to the + terminal of the subtracter 26, the calculation result of the second calculation unit 25 is input to one terminal of the subtractor 26, and the subtraction output of the subtractor 26 is the estimated frictional force value d. The frictional fluid is sent to the feed forward control section 21.

The rest of the configuration is the same as the circuit in Figure 3, so the third
The same reference numerals as in the drawings are used to omit detailed explanation.

Next, the operation of the above embodiment will be explained.

The angle θ and the angular velocity ω (−〇′) are detected by the machine 13 , the angle θ is input to the subtracter 11 , and the angular velocity ω is input to one terminal of the adder/subtractor 14 and the frictional force estimator 22 . The equation of motion of the machine 13 is as follows: Jθ'-T-Dθ'-dsign(θ' )...■
It can be calculated using the formula.

Therefore, the Coulomb friction force d is d sign (θ') - T - Dθ' - Jθ'...
It can be determined using the equation (2), but since it is necessary to determine the acceleration from the speed signal θ', it is determined by differentially returning θ'. When calculating the estimated value of the Coulomb friction force d by Laplace transform, where S is the Laplace operator and ToB is the first-order lag time constant.

The calculation of the above equation 0 is performed in the friction force estimating section 22,
The estimated frictional force value d, which is the calculation result, is output to the frictional force feedforward control section 21.

Normally, the smaller the first-order lag time constant ToB is, the wider the differentiable frequency band can be obtained, but if there is vibration or play in the machine, the first-order lag time constant T. The value of B must be increased. As a result, there is a delay in the calculated estimated value d, which makes it impossible to respond to instantaneous changes in friction.
The above-mentioned delay can be eliminated by storing the friction value in memory and controlling it by presetting it to the friction value of the Coulomb friction model.

That is, in the friction feedforward control section 21, T PRIC-d sign (θ'r)
-...■ However, T, R, and c are the outputs of the control section 21, and θ' r is the target speed.

In this case, the estimated frictional force value d sent from the frictional force estimating section 22 is not always substituted into equation (2), but is held when it reaches the largest value. In this way, by holding only the past maximum value in the control section 21, even if there is a delay in the estimated frictional force value d, the Coulomb friction is maintained without being affected, as shown in characteristic a in Fig. 2. Only the minutes can be taken out. FIG. 2 shows the relationship between the command value θr and the drive torque, where the symbol a indicates the characteristic of the present invention, and the symbol d indicates the characteristic of the conventional device.

Conventionally, since integral control is performed, a dead time to occurs due to integration until torque is generated to overcome friction. However, in the present invention, since the friction compensation torque is obtained by maintaining the maximum value of the estimated friction force, the influence of Coulomb friction can be removed without causing any delay.

On the other hand, the target value feedforward control section 12 performs feedforward control of speed and inertia force.

The position loop has proportional control, and the speed loop has PI sub-control.

Note that the compensator is not particularly limited, and PID, state feedback, etc. can be used independently of friction force control.

Therefore, by performing the above-described frictional force control, the moment when the sign of the speed changes (when the speed passes 0), a force opposing the friction can be generated in a feedforward manner immediately, without causing any delay.

[Effects of the Invention] As detailed above, according to the present invention, the estimated value of the friction force of the machine is obtained by the friction force estimating means, and the maximum value is always preset in the friction feed forward control means. Even when the speed suddenly increases, the Coulomb friction can be instantaneously output and canceled by feedforward control, making it possible to reliably eliminate the effects of Coulomb friction and perform highly accurate servo control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a circuit configuration of a servo control device according to an embodiment of the present invention, FIG. 2 is a diagram showing control characteristics of the present invention and a conventional servo control device, and FIG. 3 is a diagram showing a conventional servo control device. FIG. 2 is a block diagram showing the circuit configuration of the device. 11... Subtractor, ]2... Target value feedforward control unit, 13... Controlled machine, 15... PI control unit, 21... Friction feedforward control unit, 22
...Frictional force estimation section. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In a servo control device that performs position control on a controlled object, there is provided a means for calculating an estimated frictional force based on the input torque to the controlled object and the angular velocity of the controlled object; A servo control device comprising: means for calculating a compensation torque based on an estimated force value and a target angular velocity; and means for adding the compensation torque calculated by the means to an input torque to the controlled object.