JP2003345402A - Position control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a calculation load of a control system and improve its responsiveness by realizing a simplified disturbance observer in a position control device which is suitable for a drive control of a stage or the like which is driven to the direction of at least one axis. <P>SOLUTION: The position control device comprises: a position detector which detects a position of a member to be driven to the direction of at least one axis and outputs a value of the position detection; a driving device which drives the member to be driven based on the value of the position command; a PID controller which creates a target drive value of the driving device from a difference between the value of the position detection and the value of the position command; and a disturbance observer which calculates an estimated load disturbance value based on an estimated command value gained by filtering the target drive value in a frequency band where a disturbance needs to be restrained and an estimated load input value gained from the value of position detection. The device compensates for the target drive value to nullify the disturbance value based on the estimated load disturbance value calculated. The disturbance observer is composed by a forward controller only. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position control device, and more particularly to a position control device suitable for drive control of a stage or the like driven in at least one axis direction.

[0002]

2. Description of the Related Art As an example of a position control device of a device for moving and positioning a mechanism constituted by a motor and a load, such as an XY stage device, there is a device provided with a disturbance compensator. FIG. 11 shows an example of a position control device provided with a disturbance observer 6 as a disturbance compensator.

The position control device shown in FIG. 1 is based on a PID control system, and is roughly composed of a position controller 1 composed of a PID controller and a disturbance observer 6. The position controller 1 performs proportional (P), integral (I), and derivative (D) processing on the deviation (xc−x) so that the position command value xc matches the position detection value x, and The current target value ic to the driver 2 is calculated.

The disturbance observer 6 includes a low-pass filter 7
The subtractor 22 calculates a difference between the torque command value τc to the motor driver 2 filtered by the filter and the estimated load input torque estimated from the position detection value x by the input torque estimation filter 8, and the motor obtains the difference from the obtained difference. In the torque constant inverse model 9, a current value corresponding to the estimated load disturbance torque is calculated.

Then, the current value corresponding to the estimated load disturbance torque is subtracted from the current target value ic by the subtractor 21 to correct the current target value ic so as to cancel the disturbance torque. Calculate the value ir. Although the current command value ic is given to the motor driver 2, the low-pass filter 7 obtains a torque command value τc by multiplying the current command value ic by a constant Kt.

[0006]

SUMMARY OF THE INVENTION As described above, the control unit 1
The configuration in which the disturbance observer 6 is provided in addition to the position controller 1 in the position controller 8 is very effective in a target value tracking characteristic, a speed stability characteristic, and the like, as compared with a control system including only normal PID control.

However, as described above, in the conventional position control device, the motor driver 2 filtered by the low-pass filter 7 in the disturbance observer 6 is used.
Is calculated from the torque command value τc to the estimated load input torque estimated from the position detection value x by the input torque estimation filter 8 in the motor torque constant inverse model 9. Due to the configuration, the process of calculating the estimated load disturbance torque of the disturbance observer 6 is complicated, and there is a problem that the response is reduced.

Specifically, the control unit 18 is, for example, a PMAC
(Programmable Multi-Axis Controller) or the like, and the disturbance observer 6 uses the extended servo calculation of the PLCC0 provided in the controller. However, in the configuration in which the extended servo calculation of the PLCC0 is used for estimating the disturbance torque of the disturbance observer 6, the calculation load becomes a problem, and it becomes difficult to increase the control cycle.

The present invention has been made in view of the above points, and provides a position control device which realizes a simple disturbance observer to reduce a calculation load on a control system and improve responsiveness. With the goal.

[0010]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by taking the following means.

According to a first aspect of the present invention, there is provided a position detector which detects a position of a driven member driven in at least one axis direction and outputs a position detection value, and drives the driven member based on a position command value. A driving device, a PID controller that generates a target driving value of the driving device based on a difference between the position detection value and the position command value, and a command estimation value obtained by filtering the target driving value in a frequency band in which disturbance is to be suppressed. And a disturbance observer that calculates an estimated load disturbance value based on the estimated load input value estimated from the position detection value, and the target drive is configured to cancel the disturbance value based on the calculated estimated load disturbance value. In a position control device for correcting a value, the disturbance observer is constituted by only a forward controller.

According to a second aspect of the present invention, in the position control device of the first aspect, the disturbance observer removes a low-frequency disturbance serving as a disturbance element and a stability filter for guaranteeing stability. And a low-frequency disturbance prevention filter.

According to the first and second aspects of the present invention, since the disturbance observer includes only the forward controller, the configuration of the control system can be simplified and the processing speed can be increased.

According to a third aspect of the present invention, in the position control device of the first or second aspect, a notch filter is used as the disturbance observer.

According to the present invention, since the notch filter is used as the disturbance observer, it is not necessary to perform the extended servo arithmetic processing for the disturbance estimation processing, and the processing can be sped up.

According to a fourth aspect of the present invention, in the position control device according to any one of the first to third aspects, the driving device is a linear motor.

According to a fifth aspect of the present invention, in the position control device according to any one of the first to fourth aspects, the driven member is a stage driven in at least one axial direction. It is a feature.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

First, a stage apparatus to which the present invention is applied will be described for one axis with reference to FIG. Various types of stage devices are conceivable. Usually, an X-Y stage is formed by stacking an X-axis stage and a Y-axis stage so as to be orthogonal to each other.

However, here, for convenience of explanation, 1
The axes are illustrated and described. However, the present invention is not limited to a single axis, but can be applied to a multi-axis stage apparatus having two or more axes.

The stage device has a motor 3 (a linear motor in the example shown in FIG. 1) serving as a driving device and a slide guide 4a serving as a guide system mounted on a base, and a movable stage 4 serving as a load is mounted on the slide guide 4a. It is configured to be assembled. In some cases, instead of a linear motor that directly achieves a linear motion, a drive system that uses a rotary motor and a ball screw to convert the rotational motion into a linear motion is employed. The guide system is roughly classified into a contact ball / roller bearing system and an air static pressure bearing (air slider) system, which are generally used. In a high-precision product, an air static pressure bearing is advantageous.

When a disturbance observer is considered, the mechanical rigidity of each part needs to be high, and a stage device of a direct drive configuration using a linear motor using a hydrostatic bearing system can be expected to exert its effect most.

On the other hand, the position of the movable stage 4 is detected by a linear encoder (position detector) 5. In this type of linear motor 3, the movable part has a detector,
The relative position is calculated by fixing the linear scale to the guide portion (fixed portion) and counting the number of pulses corresponding to the moving distance. Of course, the same function can be realized with a laser interferometer other than the linear encoder, for example.

As the control unit 10, a high-speed processor such as a DSP (digital signal processor) is used. The control unit 10 is realized by a general-purpose servo control board having a PID controller and an analog output port for providing a calculation result to the motor driver 2 and an input port for receiving a detection signal from the linear encoder 21.

Here, for convenience of explanation, a block diagram of the disturbance observer 6 is shown in FIG. 2 for the types of control system described above with reference to FIG. Since the present invention aims at simplifying the disturbance observer 6, the illustration of the position controller 1 is omitted in FIG. The transfer functions of the low-pass filter 7 and the input torque estimation filter 8 are as described in the corresponding blocks.

In addition, among the codes written in the blocks shown in FIG. 2, a book indicated by reference numeral 9 is a motor torque constant inverse model, and a book indicated by reference numeral 11 includes a motor and a load. The transfer function of the mechanism is entered,
The book indicated by reference numeral 12 contains the torque constant of the motor. Further, in the figure, M is an inertia term between the motor 3 and the load,
ζ indicates a filter attenuation coefficient, ω indicates a filter cutoff frequency, and s indicates a Laplace operator.

The low-pass filter 7 includes a motor driver 2
Is filtered in the disturbance suppression frequency band to calculate an estimated torque command value eτc. The input torque estimation filter 8 is an inverse model of the transfer function Kt from the input torque to the position of the mechanism including the motor 3 and the load (1/1).
Kt) and the input torque (τc +
τd) is obtained (eτc + eτd). This input torque estimation filter 8 also has the same filter characteristics as the low-pass filter 7, and calculates the input torque estimation value (eτc + eτd) only in the disturbance suppression frequency band.

Further, in the motor torque constant inverse model 9, the torque command estimated value eτc and the input torque estimated value (eτc
+ Eτd) is subtracted by the subtractor 22 to calculate a disturbance torque estimated value eτd which is the difference between the two. The calculated disturbance torque eτd is added to the motor torque constant inverse model (1
/ Kt) to calculate a current correction value eid. Subtractor 1
In step 5, the current correction value eid is subtracted from the current target value ic to obtain a current command value ir to the motor driver 2.

As described above, the disturbance estimation used in the conventional disturbance observer uses the inverse model of the controlled object (motor torque constant inverse model 9) to calculate the disturbance between the control input and the control output. Then, the correction is performed at the stage of generating the value of the control input. However,
In this disturbance estimation method, a motor torque constant inverse model (1
/ Kt) cannot be expressed as an appropriate controller, so that an equivalent and appropriate controller is usually realized by using a filter sufficiently considered for the inverse model 9 of the motor torque constant.

However, the expression of the block diagram of the disturbance observer 6 shown in FIG. 2 is a complicated expression as compared with the structure of a controller derived by classical control theory or modern control theory. Therefore, it is considered to develop and arrange the controller shown in FIG.

Specifically, the forward controller and the inverse model controller are completely separated, and the forward controller is arranged. FIG. 3 shows a configuration in which the input torque estimation filter 8 and the motor torque constant inverse model 9 which are the inverse model controllers shown in FIG. FIG. 4 shows the low-pass filter 7 as a forward controller in the configuration shown in FIG. And finally, the controller shown in FIG. 2 is developed as shown in FIG. From the figure, it can be seen that the transfer functions of the forward controller and the inverse model controller are controllers configured by “integrator + first-order lag” having the same structure.

Next, the estimation of disturbance and the consistency with the control purpose of the controller developed as shown in FIG. 5 will be examined. First, the reduction in sensitivity to disturbance is realized by an integral characteristic generated by a controller for disturbance estimation.

Here, it is assumed that a PID controller is provided in a loop outside the disturbance observer 6, and the main mixed disturbance is a torque disturbance. At this time, since the second-order integrator is configured before the disturbance is mixed, it is understood that the disturbance input can be asymptotically removed up to the step-like disturbance according to the principle of the internal model.

That is, it can be predicted that the transfer function indicated by the block indicated by reference numeral 14 in FIG. 5 mainly functions as a low-frequency disturbance prevention filter. The transfer function indicated by the block indicated by reference numeral 14 can be expected to mainly function as a stability filter.

On the other hand, the inverse model controller 15 indicated by reference numeral 14 is a feedback of acceleration from its structure. The present invention is characterized in that the inverse model controller 15 which is the feedback of the acceleration which does not function for preventing the low-frequency disturbance is removed.

By removing the inverse model controller 15, the configuration of the disturbance observer can be simplified. As a specific means for removing the inverse model controller 15, the inverse model controller 15 and the subtractor 21 shown in FIG.
Is cut at a position where the connection is made, and a cutting portion 16 is provided. Therefore, the inverse model controller 15 can be removed relatively easily.

Next, a description will be given of the result of a simulation for seeing how the influence of disturbance is suppressed in the position controller having the simplified disturbance observer shown in FIG. Specifically, a stage device driven by one axis as shown in FIG. 1 was assumed, and a simulation was performed on the stage device.

In the following simulation, it is assumed that the PMAC is used as the control unit 10. Further, the disturbance estimation process, which is the process of the disturbance observer, is performed without using the extended servo operation of the PLCC0 of the PMAC, and a "Notch filter" provided as a standard controller of the PMAC is used as a forward controller for disturbance estimation. It is going to be used as.

The notch filter of the PMAC is a second-order discrete transfer function, and its variables can be freely determined. Therefore, a simple disturbance estimation can be realized by substituting the discrete variables of the disturbance estimation controller into the variables of the notch filter.

Subsequently, in the simplified disturbance observer obtained in FIG. 5, variables for disturbance estimation are determined.
FIG. 6 shows a simplified disturbance observer and a control system including the motor driver 2, the motor 3, the control unit 10 (PMAC), and the like expressed by an equivalent model. In the equivalent model shown in the figure, each element (parameter) of the control system
Were set as shown in FIG.

Here, even in the case of the simple disturbance observer, the method of determining each element (parameter) is the same as the method of determining a conventional disturbance observer which has been conventionally performed. It shall be described below.

In the case of a simple disturbance observer

[0043]

(Equation 1) For a normal disturbance observer

[0044]

(Equation 2) FIG. 8 shows the result of the simulation. FIG.
FIG. 8A shows the result of only the PID control, and FIG.
FIG. 8B shows the result of control in which a PID controller and a conventional disturbance observer are combined, and FIG.
9 shows a result of control in which a D controller and a simple disturbance observer according to the present invention are combined. In each figure,
The horizontal axis represents time, and the vertical axis represents displacement due to disturbance.

As shown in FIG. 8A, the influence of the disturbance cannot be eliminated only by the PID controller, so that the vibration due to the disturbance occurs. On the other hand, FIG.
It can be seen that in the control in which the PID controller shown in (1) and the conventional disturbance observer are combined, the influence of the disturbance is suppressed.

In the control in which the PID controller according to the present embodiment is combined with the simple disturbance observer according to the present invention, as shown in FIG. 8C, the PID shown in FIG.
As with the control in which the controller and the conventional disturbance observer are combined, the influence of the disturbance is suppressed. That is, even if the inverse model controller 15, which is the feedback of acceleration that does not function for low-frequency disturbance prevention, is removed from the conventional disturbance observer, and the disturbance observer is simplified, the influence of disturbance can be reliably suppressed. Proven.

FIG. 9 shows a follow-up deviation when the position controller 1 having the structure shown in FIG. 1 is used and the control system provided with the simplified disturbance observer according to the present embodiment is used.
The following is a comparison between the following deviation when using a control system including only the I controller and the following deviation when using a conventional control system provided with a disturbance observer. As shown in the figure, the configuration provided with the simplified disturbance observer according to the present embodiment (in the figure, shown as a simple disturbance rejection controller) has a tracking error (mainly a movable stage 4) that appears as a whole. It can be seen that the influence of the disturbance moving observer is reduced to about the same level as that provided with the disturbance observer.

From the above experiments, it has been proved that even with a simple disturbance observer in which the inverse model controller is omitted, the low-frequency disturbance can be gradually removed and the same effect as that of the conventional disturbance observer can be obtained. Was. Further, in the present embodiment, PMAC is used as the control unit 10, and the disturbance estimation processing is performed not by the extended servo mechanism of the PLCC0 of the PMAC.
Since the "Notch filter" provided as a standard controller of PMAC is used, it is possible to increase the control frequency, and it is possible to perform disturbance suppression control with higher accuracy and quick response. It becomes possible.

Next, a method of determining an adjustable variable by partial model matching in the control system to which the simplified disturbance observer according to the present embodiment shown in FIG. 6 is applied will be described. Normally, a filter introduced to make disturbance estimation an appropriate controller often employs a secondary system in general in order to improve its estimation characteristics and to facilitate adjustment. However, as long as the disturbance suppression characteristics in the low frequency range are actually compensated for, the variable may be any value that compensates for the stability.
Here, the controller shown in FIG. 10 is adopted so that the degree of freedom can be particularly ensured for the forward controller. When the control system shown in FIG. 10 is developed, the following equation is obtained.

[0050]

(Equation 3) The characteristic polynomial is given by the following equation.

[0051]

(Equation 4) At this time, in the other characteristic polynomial, there is no complete degree of freedom of the variable of the third or fourth order, and perfect matching cannot be performed.
Therefore, the partial model matching is considered here. When the partial model matching is employed, usually, the variables are determined so as to match the following equation in order from the low-order term. Therefore, when the response frequency ω is increased, the system often becomes oscillatory.

R (s) = (s + ω)ⁿ Therefore, the PID system which is an adjustable variable together with the response frequency ω
Assuming that the integral element Ki of the controller is 0, perfect matching is performed.
Now. Characteristic polynomial assuming integral element Ki is 0
Is as follows:

[0053]

(Equation 5) When perfect matching (s + ω) ⁿ is performed on this system,
Each adjustable variable is obtained from a fourth-order simultaneous equation. Then, according to the obtained simultaneous equations, the adjustable variables K ₀ ,
The response frequency ω can be freely selected based on K ₁ , K ₂ , and l ₁ . Further, in the discrete model of the disturbance rejection controller at that time, it is given by the following equation.

[0054]

(Equation 6) Correct the proportional gain K _[rho at k _n at that time, and finally to determine the parameters. As described above, if the control system is designed with the response frequency ω set, the control performance can be determined by comparing with the response frequency ω of the equivalent secondary system. Further, since the differential gain _Kd is a completely free parameter, it is possible to change the speed loop characteristic while maintaining the position loop characteristic.

Although the present invention has been described above by applying the present invention to a precision stage mechanism, it goes without saying that the present invention can be widely applied to a speed control system and a position control system of a device for moving and positioning an object. .

[0056]

As described above, according to the present invention, since the disturbance observer is constituted only by the forward controller, the structure of the control system can be simplified and the processing can be speeded up. Further, by using the notch filter as the disturbance observer, it is not necessary to perform the extended servo calculation process in the disturbance estimation process, and it is possible to speed up the process.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a stage mechanism to which a position control device according to an embodiment of the present invention is applied with respect to one axis.

FIG. 2 is a block diagram illustrating a control system of a position control device to which a conventional disturbance observer is applied.

FIG. 3 is a block diagram showing a state where the control system shown in FIG. 2 is developed.

FIG. 4 is a block diagram showing a state in which the control system shown in FIG. 3 is further developed.

FIG. 5 is a block diagram showing a state where the control system shown in FIG. 4 is further developed.

6 is a diagram expressing a control unit of the stage mechanism shown in FIG. 1 by an equivalent model.

FIG. 7 is a diagram showing conditions of the equivalent model shown in FIG. 6;

8A and 8B are diagrams showing simulation results when the control unit is driven under the conditions shown in FIG. 6; FIG. 8A shows neither a conventional disturbance observer nor a simple disturbance observer according to the present invention; (B) shows the result of simulation of the control unit provided with the conventional disturbance observer, and (B) shows the result of simulation of the control unit.
(C) shows the result of a simulation of the control unit provided with the simple disturbance observer according to the present invention.

FIG. 9 shows the following deviation of the control unit provided with the simple disturbance observer according to the present invention, the following deviation of the control unit not provided with any of the conventional disturbance observer and the simple disturbance observer according to the present invention, and the conventional disturbance. It is a figure which compares and shows the following deviation of the control part provided with the observer.

FIG. 10 is a diagram for explaining a method of determining an adjustable variable by a partial model matching for a controller.

FIG. 11 is a block diagram illustrating a control system of a position control device to which a disturbance observer is applied, which is an example of the related art.

[Explanation of symbols]

1 Position controller 2 Motor driver 3 Motor 4 Load 5 Position detector 6 disturbance observer 7 Low-pass filter 8 Input torque estimation filter 9 Motor torque constant inverse model 10 control unit 13 Stability filter 14 Low frequency disturbance prevention filter 15 Inverse model controller 16 Cutting part

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 5H004 GA02 HA07 HB07 JB03 JB04                       JB22 KB02 KB04 KB06 MA12                       MA15                 5H303 BB02 BB07 BB12 CC04 DD04                       EE03 FF09 HH01 KK02 KK03                       KK04 KK11

Claims (5)

[Claims] A position detector that detects a position of a driven member that is driven in at least one axis direction and outputs a position detection value; a driving device that drives the driven member based on a position command value; A PID controller for generating a target driving value of the driving device based on a difference between a position detection value and the position command value; a command estimation value obtained by filtering the target driving value in a frequency band in which disturbance is to be suppressed; A disturbance observer for calculating an estimated load disturbance value based on the estimated load input value estimated from the position, and a position for correcting the target drive value so as to cancel the disturbance value based on the calculated estimated load disturbance value. In the control device, the disturbance observer is constituted by only a forward controller. 2. The position control device according to claim 1, wherein the disturbance observer includes a stability filter for guaranteeing stability, and a low-frequency disturbance prevention filter for removing low-frequency disturbance serving as a disturbance element. A position control device comprising: 3. The position control device according to claim 1, wherein a notch filter is used as the disturbance observer. 4. The position control device according to claim 1, wherein the drive device is a linear motor. 5. The position control device according to claim 1, wherein the driven member is a stage that is driven in at least one axial direction.