JPS586963B2 - Servo method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo system that performs highly accurate positioning of a mechanism supported by a spring.

In the production of increasingly miniaturized semiconductor integrated circuits, 0.1 μm is required for mask alignment between photo mask and pattern.
Accuracy on the order of m is required.

For such high-precision positioning, the support and guide mechanisms are a major problem.For example, with conventional guide mechanisms that use bearings, offset of the servo system due to nonlinear elements such as friction and backlash is a problem. becomes.

For this reason, it is conceivable to construct a support and guide mechanism using an essentially linear spring, but when positioning a mechanism supported by a spring using a normal servo control system, the spring Offset occurs due to deflection force, which is a major obstacle to high-precision positioning.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to eliminate offset caused by the deflection force of a spring in a positioning control system for a mechanism supported by a spring.

The above object is to configure a positioning mechanism with a mechanism supported by a spring and an actuator that applies force to the mechanism, and to transmit a signal to the positioning mechanism that continuously reduces the positioning error according to a predetermined time constant. A system created from the error and applied to the actuator, and a system provided in parallel with the system to sample the positioning error caused by the deflection force of the spring at regular intervals sufficiently longer than the time constant, convert it into a digital signal, and sequentially convert it into a digital signal. This is achieved by providing a system that integrates the integrated value, converts the integrated value into an analog signal, and applies it to the actuator.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual diagram of a positioning mechanism consisting of a support mechanism using a spring and an actuator that exerts a force on the support mechanism.

A controlled object 1 to be positioned is supported on a base 4 by springs 2 and 3, and an actuator 5 applies a force to this controlled object 1 in the direction shown by the arrow.

FIG. 2 is a block diagram of a uniaxial positioning control system for the positioning mechanism of FIG. 1.

In Fig. 2, xt is the target position, x is the position of the controlled object, e is the positioning error, AX is the gain of the position signal amplifier, and C
ONT is the servo control circuit, KM is the force constant of the actuator 5 (for example, a motor), AP is the gain of the amplifier for driving the actuator 5, SP is the support mechanism, F is the force applied to the support mechanism, CPS is the compensation circuit, K is the deflection force of the spring.

3 control circuits CO that amplify the error signal e between the target position xt and the actual position x and give it to the control circuit CONT to obtain a control signal;
The NT is a conventional servo control circuit designed to give the control system the desired response.

A force F is applied to the support mechanism SP by amplifying the control signal with a power amplifier and driving a motor or the like.

As shown in Fig. 1, the support mechanism SP is supported by springs 2 and 3, and if the springs 2 and 3 are to be positioned at a position deviated from the balanced position, a deflection force will be applied to the springs 2 and 3. occurs.

That is, since the return force K of the springs 2 and 3 acts, the motor stops at a position where the force F of the motor 5 and the force K of the springs 2 and 3 are balanced.

Therefore, in this case, the error signal e does not become 0.

Therefore, in the present invention, the positioning error caused by the deflection force K of the spring is removed by adding a compensation circuit CPS shown within the dotted line in FIG. 2 to the general positioning control system.

FIG. 3 is a block diagram of the compensation circuit in FIG. 2.

In Figure 3, SPL is a sampler, ACT is an operating circuit, and A/
D is an analog-to-digital converter, D/A is a digital-to-analog converter, ACM is an integration circuit, and AC is the gain of the entire compensation circuit.

The sampler SPL starts sampling T seconds after the target value is set by the operating circuit ACT, and thereafter the error signal is sampled at a constant period of T seconds and converted into a digital signal by the A/D converter.

This is further integrated in sequence by the integration circuit ACM, and D/
It is converted into an analog quantity by the A converter.

Such a procedure is the same as integral compensation.

As in the case of integral compensation, it is difficult to perform addition (integration) at regular intervals in an analog manner, so it is first converted into a digital quantity, integrated, and then converted back into an analog quantity.

The overall gain of the compensation circuit CPS is controlled by the control circuit C by AC.
It is matched to the ONT's DC gain.

To simplify the explanation, the response of the control system excluding the compensation circuit CPS will be represented by one time constant τ.

Further, the sampling period T of the compensation circuit CPS takes a sufficiently large value with respect to the time constant τ.

FIG. 4a is a response curve diagram when stepwise target value setting is performed in the servo system of FIG. 3, and FIG. 4b is a response curve diagram for a general control system excluding a compensation circuit.

After the target position xt is set, the compensation circuit C is activated after T seconds.
PS operates, and thereafter the error signal e is integrated at regular intervals T, and the integrated value is added to the input of the actuator, thereby sequentially canceling out the spring force K of the support mechanism SP.

The positioning error at the i-th sample is e(iT)
Then, the following formula holds true.

Here, k is the spring constant of the spring system, xt is the target setting value (distance from the equilibrium position), and AF=AX・AC
・AF・KM.

Therefore, in FIG. 4a, the compensation circuit CPS does not operate yet in the period from 0 to T, the support mechanism SP approaches the target position xt with a certain time constant τ, and T
) position is reached.

The positioning error e(T) at this time is as follows from equation (i) above.

If the compensation circuit CPS is not provided, as shown in FIG. ) error e1 remains the same value even after time elapses and does not become 0.

On the other hand, in FIG. 4a, the error signal e(T) shown in equation (ii) above is sampled and integrated after T seconds, and e(T) is sampled and integrated.
The deflection force K of the spring is canceled by a force F proportional to T).

After 2T seconds, the position approaches x(2T), where the error signal e2 between xt and x(2T) is sampled and integrated, and the spring force K is applied again with a force F proportional to the integrated value. erase.

Furthermore, after 3T seconds, by repeating the sampling, the compensation circuit CPS completely corrects the positioning error e due to the spring deflection force K, and moves the support mechanism SP to the target position x.
reach t.

In addition, the control system including this compensation circuit CPS forms a feedback loop, and the compensation circuit CPS responds to parameter fluctuations in the control system (for example, various gain fluctuations, heat constants such as actuator force constants, spring constants, etc.). The control circuit CONT accurately corrects disturbances with relatively long time constants such as physical fluctuations), and the control circuit CONT corrects disturbances with short time constants such as external vibrations.

In the embodiment, compensation for uniaxial positioning control has been described, but the same explanation can be applied to angle and other controls.

As described above, according to the present invention, it is possible to accurately correct the offset in a servo mechanism using a spring, thereby enabling highly accurate positioning of, for example, about 0.1 μm.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of a positioning mechanism using the servo system of the present invention, Fig. 2 is a block diagram of a uniaxial positioning control system showing an embodiment of the present invention, and Fig. 3 is a block diagram of the compensation circuit in Fig. 2. , FIGS. 4a and 4b are response curve diagrams when the compensation circuit according to the present invention is added, and response curve diagrams when the compensation circuit is excluded. 1: Controlled object, 2, 3: Spring, 4: Base, 5: Actuator, xt: Target position, x: Actual position of controlled object, e: Positioning error, AX: Amplification gain for position signal, CONT: Servo control circuit, KM: force constant of actuator, AP: amplification gain of signal that drives the actuator, SP: support mechanism, F: force of actuator, K: spring force, CPS: compensation circuit, ACT: actuation circuit, ACM :
Integration circuit, AC: gain of the entire compensation circuit, SPL: sampler, A/D: analog-to-digital converter, D/A: digital-to-analog converter.

Claims (1)

[Claims] 1 A positioning mechanism is constituted by a mechanism supported by a spring and an actuator that applies force to the mechanism, and a signal is generated from the positioning error to the positioning mechanism to continuously reduce the positioning error according to a predetermined time constant. a system that applies the force to the actuator; and a system that is installed in parallel with the system and samples the positioning error caused by the deflection force of the spring at fixed time intervals sufficiently longer than the time constant, converts it into a digital signal, and successively integrates the signal. A servo system comprising a system for converting a value into an analog signal and applying it to the actuator.