JPH04213701A - Control circuit - Google Patents

Abstract

PURPOSE:To offer the control circuit which can suppress enough the influence caused by a disturbance, while securing the stability of a disturbance feedback loop. CONSTITUTION:In the control circuit for controlling a control object 2 so as to follow a prescribed target value, this control circuit constitutes a characteristic feature of having a disturbance observer 15 for estimating a controlled variable of said control object 2, based on said target value, and deriving a disturbance component worked on said control object 2 from this estimated controlled variable and an actual controlled variable of said control object 2, and an integration circuit 7 which is placed in a disturbance feedback loop to said control object 2, and integrates the disturbance component derived by said disturbance observer 15.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to a control circuit having a disturbance observer, particularly to a step-and-repeat type exposure apparatus used in the semiconductor manufacturing field, a stage position servo control system in a so-called stepper, and an optical disk device. The present invention is applied to a servo control system that requires highly accurate control, such as a position servo control system for a pickup, and relates to a control circuit for ensuring against disturbances applied to the servo control system.

0002

[Prior Art] The present applicant previously proposed a system as shown in FIG.
A control circuit that estimates a disturbance using a disturbance observer and feeds back the estimated disturbance to suppress the disturbance was proposed in an application filed by the applicant dated December 3, 1990 (name: Control circuit). There is. FIG. 8 shows that by inputting the target value r, a controlled object [G(s)] such as a stage in a stepper or a pickup in an optical disk device is controlled.
]2 shows a device that servo-controls the position of point 2. In this figure, 1 and 1' are compensators such as PID compensators [Gc(s)], and z is the actual controlled object [G(s)]. ], the position of the controlled object z is subjected to feedback control by the compensator 1, and is moved so that the controlled amount y becomes equal to the target value r.

3 is the identified value (model) of the actual controlled object z
The identification value 3 is determined in advance by measuring the control amount for the input value in a state where no disturbance d is input to the controlled object z. This identified value [G(s)*]3 is subjected to feedback control by a compensator 1', and a controlled variable estimated value y* is generated at its output. 4 is the actual controlled object z
This filter circuit 4 inputs the difference between the actual controlled variable y + △y affected by the disturbance d and the estimated controlled variable y* from the identified value 3. It has the opposite characteristics of the transfer function.

5 is the disturbance feedback loop gain [H
], and its output is returned between the compensator 1 and the controlled object 2. Further, in FIG. 8, the part surrounded by the dotted line is the disturbance observer 15.

In this example, if there is no disturbance feedback loop, the characteristic from the disturbance d to the control amount Δy (Δy is the variation due to the disturbance d) is expressed by equation (1).

[0006]

[Outside]

In this example, if a closed-loop system model is constructed from the identified value [G(s)*]3 of the compensator 1 and the controlled object 2, and the estimated control amount y* is calculated, this estimated output y* and the control The difference from the actual control amount y+Δy from the object 2 is only the variation Δy due to disturbance. Also, from equation (1), the relationship between the disturbance d and Δy is expressed as equation (2).

[0007]

[Outside]

If the right side of equation (2) is the filter circuit 4, the estimated value d* of the disturbance can be obtained at its output. If a feedback gain [H]5 is applied to the estimated value d* of the disturbance and feedback is performed, the transfer function from the disturbance d to the control amount △y becomes

[0008]

[Outside]

becomes. Therefore, according to this example, by increasing the gain H, the influence Δy due to disturbance can be suppressed.

[0009]

[Problems to be Solved by the Invention] In this example, a proportional gain H is applied to the estimated disturbance d* for feedback, but when actually applied,
There is a problem in that it is necessary to ensure sufficient stability of the disturbance feedback loop, and as a result, the gain H cannot be set too large.

An object of the present invention is to provide a control circuit that can sufficiently suppress the effects of disturbance while ensuring the stability of the disturbance feedback loop.

[0011]

[Means and operations for solving the problems] In order to achieve such an object, the present invention provides a control circuit that controls a controlled object so as to follow a predetermined target value. a disturbance observer that estimates a controlled variable of the controlled object and calculates a disturbance component acting on the controlled object from the estimated controlled variable and the actual controlled variable of the controlled object; placed,
The present invention is characterized in that it includes an integrating circuit that integrates the disturbance component obtained by the disturbance observer.

According to the present invention, the integration circuit provided in the disturbance feedback loop makes it possible to effectively remove low-frequency disturbances that are a problem in actual control systems.

[0013]

[Example] Figure 1 shows an example of the present invention.
An example is shown in which the present invention is applied to a position servo control device that controls the position of a controlled object [G(s)] 2, such as a stage in a stepper or a pickup in an optical disk device, in accordance with an input target value r.

In FIG. 1, 6 is a low-pass filter [F(s)], and 7 is an integrator circuit [H(s)]. They are arranged in the order of circuit 7. The target value r is set to each of the compensators 1 and 1' as {r-(y+△y)} or {r-y*} as in the example of FIG. 8 described above.
is entered as . The disturbance observer 15 may be configured in the form of software in a computer (not shown), but is not limited to this. The other configurations are the same as those in FIG. 8 described above, so the description will not be repeated here.

FIG. 2 shows an example of the controlled object 2. In this figure, positioning control of a linear motor supported by a spring,
For example, a focus servo system for an optical pickup is illustrated. In FIG. 2, 8 is a current amplifier that performs amplification according to the command voltage V, 9 is a voice coil motor, and 10 is a movable member including a moving coil of the voice coil motor 9.
I support optical pickup. 11 is a parallel plate spring that supports the movable member movably in the y direction; 12 is a permanent magnet of the voice coil motor 9; and 13 is a base that supports the voice coil motor 9 and the parallel plate spring 11. f is base 1
3 shows the external force (disturbance d) acting on

FIG. 3 shows an example of a transfer function from the command voltage V of the controlled object [G(s)] 2 to the position y. This is a general spring-mass system and has second-order lag characteristics. In such a system, the compensator [Gc(s)]1,1'
As such, integral compensation and phase lead compensation are generally adopted,
The system is stabilized.

Next, returning to FIG. 1, the low pass filter 6
Explain how it works.

In the filter 4 in the disturbance observer 15,
As is clear from equation (2) above, the calculation of [1/G(s)] is required. That is, since the inverse characteristic of the transfer function shown in FIG. 3 is calculated, the filter circuit 4 has a double differential characteristic on the high frequency side. These differentiating circuits tend to pick up high-frequency noise, which can lead to system instability. Therefore, a low pass filter 6 is installed in the disturbance feedback loop.
It is necessary to configure a feedback loop by adding a In this embodiment, a second-order low-pass filter is used at 1 KHz to provide flat characteristics in the high range.

Using the closed-loop system model, that is, the compensator 1' of the disturbance observer 15 and the identified value 3, the estimated control amount y*
Calculate this and the actual control output y+△y from controlled object 2
FIG. 4 shows the transfer function d*/d between the estimated disturbance value d* and the disturbance d after this difference Δy passes through the filter 4 and the low-pass filter 6. The reason why the gain decreases from around 1KHz and the phase lags is due to the low pass filter 6.
This is because it employs

FIG. 4 shows the open loop transfer characteristic of the disturbance feedback, and when stability is determined, the gain margin (margin to O (dB) of the gain characteristic when the phase is -180°) is 10 (dB). ). This means that if the gain is increased by 10 (dB) or more, the feedback loop will oscillate. Therefore, when performing feedback with a proportional gain H as in the example in Fig. 8, the maximum limit is H = 3 [approximately 10 dB] (taking into account that a gain margin of 10 dB or more is actually required, H = 1
degree). In the example of FIG. 8 as well, from equation (3) above, it is possible to suppress the influence of the disturbance d to about 1/4 compared to the case where there is no disturbance feedback loop. This is insufficient as a disturbance suppression characteristic for accurate positioning.

Therefore, in this embodiment, instead of the gain H,
The following integration circuit 7 is adopted. An example of the integrating circuit 7 is shown in the following equation (4) using a complex parameter S.

[0022]

[Outside]

The frequency characteristics of this integrating circuit 7 are shown in FIG. here,
A circuit with a gain of approximately 40 dB at frequencies below 10 Hz was adopted. As mentioned above, the disturbance that actually becomes a problem is often of low frequency; for example, a disturbance such as floor vibration that becomes a problem in a stepper stage position servo system has a period of several Hz.

The integrating circuit 7 is for improving the characteristics in the low frequency range, as described above. There is no adverse effect on the gain margin g. Therefore, while keeping the system stable, it is possible to suppress the influence of disturbances that actually cause problems.

In FIG. 6, when there is no disturbance feedback loop (curve A) and when H=1 in the example of FIG.
) and the disturbance characteristics Δy/d when the equation H(s)=(4) is adopted in this embodiment (curve C) are shown, respectively. Compared to the case of feedback with H=1, this embodiment employing the integrating circuit 7 can sufficiently suppress disturbances in the low frequency range. Further, FIG. 7 shows the control amount when a 10 Hz torque disturbance f is applied to the base 13 of FIG. 2. In the control system of this example,
There is no effect of disturbance at all (according to calculations, it is about 1/1
00), the effect can be confirmed.

[0025]

[Other Embodiments] (1) When the order of the compensator Gc(s) and the controlled object G(s) is low, the filter circuit 4 can be configured with an analog filter, but when the order is high, the filter circuit 4 can be configured with a DSP ( It is more advantageous in terms of accuracy and cost to configure it using a digital arithmetic unit (digital arithmetic unit) or the like.

(2) In addition to this embodiment, as an integrator,

[0027]

[Outside]

Such a configuration is also possible. In this way, H(s) can be freely set within a range that does not impair stability.

[0028]

As explained above, the present invention provides a control circuit that feeds back the disturbance estimated by an observer and suppresses the influence of the disturbance, by providing an integrating circuit in the disturbance feedback loop. This makes it possible to sufficiently suppress low-frequency disturbances.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control circuit embodying the present invention.

FIG. 2 is a schematic diagram of a positioning mechanism using a voice coil motor.

FIG. 3 is a diagram showing a transfer characteristic (y/v) from v to y in FIG. 2;

FIG. 4 is a diagram showing a transfer characteristic (d/d) from the disturbance d in FIG. 1 to the estimated value d of the disturbance.

FIG. 5 is a diagram showing the transfer characteristics of the integrating circuit employed in the present invention.

FIG. 6 is a diagram showing the disturbance characteristics (Δy/d) of the case without disturbance compensation, the example of FIG. 8, and the present example.

FIG. 7 is a diagram showing fluctuations in the control amount when a disturbance f is added.

FIG. 8 is a diagram showing a control circuit previously proposed by the applicant.

[Explanation of symbols]

1 Compensator 2 Controlled object 3 Identified value (model) of controlled object 4 Filter with inverse transfer characteristics from disturbance to controlled amount 5 Feedback gain H 6 Low-pass filter circuit 7 Integrating circuit 8 Motor amplifier 9 Voice coil linear Motor 10 Member including moving coil 11 Parallel plate spring 12 Permanent magnet 13 Base

Claims (1)

[Claims] 1. In a control circuit that controls a controlled object so as to follow a predetermined target value, a controlled variable of the controlled object is estimated based on the target value, and the estimated controlled variable and the controlled variable of the controlled object are It has a disturbance observer that calculates a disturbance component acting on the controlled object from an actual control amount, and an integration circuit that is placed in a disturbance feedback loop to the controlled object and integrates the disturbance component calculated by the disturbance observer. A control circuit characterized by: