JP2000205835A - Shape measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect abnormality such as collision of a probe within a sampling time needed for positioning control when a probe is provided and moved in one direction, e.g. reciprocated vertically to measure a shape. SOLUTION: The instrument is equipped with a current limiter 7 which calculates the stationary current value of a motor 3 to the force that a spring 2 generates from the spring constant (k) of the spring 2 and the motor thrust constant and position signal X of the motor 3, regards the value obtained by adding a specific value to the current value as the upper-limit or lower-limit of the current of the motor 3, and compares a manipulated variable ic with the upper-limit or lower-limit. When the manipulated variable varies above the upper-limit or below the lower-limit, abnormality occurrence can be detected and the calculation of the upper-limit or lower-limit and the comparison with the manipulated variable ic are low-grade operations, so they can be completed within the sampling time needed for positioning control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning control device for a linear actuator, and more particularly to a shape measuring device provided with a probe on a linear actuator.

[0002]

2. Description of the Related Art A three-dimensional measuring apparatus having a probe and measuring the shape of a surface by reciprocating the probe in one direction, for example, up and down, includes a shape measuring device described in Japanese Patent No. There is a positioning control device disclosed in Japanese Patent Publication No. 308283. FIG. 8 shows a shape measuring device described in Japanese Patent No. 2638157. A linear motor 52 supported by a spring 51 reciprocates in one direction. A Z moving unit 53 is attached to the linear motor 52, and the Z moving unit 53 is
Driven in the axial direction. Light rays are emitted from the Z moving unit 53 to the measurement surface 57 to be measured. The light beam is collected by the objective lens 56 of the probe. The position of the Z moving unit 53 is detected by the position detector 54 and transmitted to the servo circuit 55. The servo circuit 55 transmits a predetermined control signal to the linear motor 52 based on the position of the Z moving unit 53 detected by the position detector 54.

In the positioning control device described in Japanese Patent Application Laid-Open No. 9-308283, a carriage to be subjected to positioning control is driven by a motor. This positioning control device has a disturbance observer for estimating the state quantity of the motor. The abnormality of the positioning control device is detected based on the value of the disturbance estimated by the disturbance observer.

[0004]

In the shape measuring device described in Japanese Patent No. 2638157, the Z moving portion 53 in the Z-axis direction collides with the measuring surface 57, or is overloaded.
An abnormality of the linear motor 52 cannot be detected. Therefore, the objective lens 56 of the probe may be damaged.

In the positioning control device described in Japanese Patent Application Laid-Open No. 9-308283, if the nominal model used for designing the disturbance observer is a spring-supported model, the above abnormality can be detected. However, in order for the disturbance observer to function, a high-dimensional operation is required, and the load on the operation unit that performs the controller operation increases. Therefore, there is a possibility that the calculation cannot be performed in time for the sampling time required for the positioning control.

Accordingly, the present invention provides a shape measuring apparatus having a probe, which reciprocates the probe in one direction, for example, up and down, to measure the shape of the surface. It is an object to detect in time within the sampling time.

[0007]

SUMMARY OF THE INVENTION The present invention provides a linear actuator supported by a spring and driven by a motor, a position detector for detecting a displacement of the linear actuator and outputting it as a position signal, a target position of the linear actuator, The present invention relates to a shape measuring device including a positioning controller that compares position signals and outputs an operation amount, and a motor driver that outputs a motor drive current according to the operation amount and drives a linear actuator.

[0008] The shape measuring device includes a current limiter.
The current limiter calculates (a) a constant current value of the motor with respect to the force generated in the spring from the spring constant of the spring, the motor thrust constant and the position signal, and (b) adds a predetermined value to the current value. The upper limit or lower limit of the current of the motor is used as the upper limit or lower limit. (C) The upper limit or lower limit is compared with the operation amount or the current of the motor.

The upper limit or lower limit is compared with the operation amount or the motor current. If the operation amount exceeds the upper limit or falls below the lower limit, it can be detected that an abnormality has occurred. Moreover, the calculation of the upper limit or the lower limit and the comparison with the manipulated variables are not high-dimensional calculations but low-dimensional calculations,
It is possible to make it within the sampling time required for the positioning control.

Further, in the present invention, the current limiter may set the upper limit value or the lower limit value of the motor current to a different value according to the driving direction of the motor. The overload setting of the actuator according to the driving direction can be set separately.

Further, in the present invention, the current limiter includes a low-pass filter to which an operation amount or a motor current is input, and a comparator for comparing an upper limit value or a lower limit value of the motor current with an output of the low-pass filter. Is also good.

The low-pass filter can prevent a malfunction due to the operation amount or noise of the motor current. Further, by changing the cutoff frequency of the low-pass filter, the response performance of the abnormality detection can be adjusted.

Further, according to the present invention, the current limiter may include a determiner for determining whether or not the output of the low-pass filter has been larger than the upper limit value of the motor current for a predetermined time.

It is possible to prevent a malfunction caused by an operation amount, a motor current, and a noise component that instantaneously increase due to a transient response.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a shape measuring apparatus according to a first embodiment of the present invention. The carriage 1 having a mass M is suspended by a spring 2. However, since the spring 2 actually has a portion showing elasticity and viscosity, the spring 2 is represented by an elastic portion 2a and a viscous portion 2b. The carriage 1 is driven vertically by a voice coil motor 3. Therefore, the carriage 1 functions as a linear actuator. The position signal X, which is the amount of displacement of the carriage 1 from the origin, is detected by a linear encoder 4 attached to the carriage 1. The position of the carriage 1 is determined using the position signal X output from the linear encoder 4.

On the carriage 1 is mounted a focus probe 11 for detecting the distance to the object 12 in a non-contact manner. By performing tracking control using the output signal of the focusing probe 11, the surface shape of the test object is measured. Note that a contact probe may be mounted instead of the focus probe 11.

Here, assuming that the motor thrust constant is Kf, the motor current is I, the motor thrust is F, the spring constant of the elastic portion 2a is k, and the damping coefficient of the viscous portion 2b is C, the carriage 1 suspended by the spring The model is represented by equations (1) and (2).

[0018]

(Equation 1)

Therefore, the transfer function from the motor current I to the position signal X is expressed by the following equation (3).

[0020]

(Equation 2)

The position signal X detected by the linear encoder 4 and the target position Xref
And a current command value ic (operating amount) corresponding to the deviation is output. The current command value ic is input to the current limiter 7 and compared with the motor current limit value ilim. Current command value i
When c is equal to or smaller than the motor current limit value ilim, it is input to the motor driver 6 as ic '. Motor driver 6
Drives the carriage 1 in the vertical direction by flowing a motor current I proportional to the current command value ic to the voice coil motor 3. The current command value ic is the motor current limit value ilim
Is exceeded, an actuator error is detected and ic '
To stop the operation of the linear actuator.

The current limiter 7 calculates the motor current limit value ilim according to equation (4).

[0023]

(Equation 3)

In the equation (4), the motor current limit value ilim is constantly calculated from the spring constant k, the motor thrust constant Kf, and the position signal X, and is used as the motor current limit value in the current limiter 7. In addition, iadd is a predetermined value set in consideration of an external force applied to the linear actuator other than the spring force, a transient response characteristic of the motor, a parameter variation, and the like.

FIG. 2 shows the operation of the abnormality detection. As the position signal X changes, the motor current limit value ilim changes in proportion. The current command value ic also changes as the spring force increases. The current limiter 7 has a current command value ic.
Is larger than the motor current limit value ilim. If it does, then something has gone wrong.
Then, ic 'is operated to stop the linear actuator.

According to the first embodiment of the present invention, the external force other than the spring force applied to the actuator supported by the spring is limited so as not to be a predetermined value, and abnormalities such as overload and collision of the actuator are prevented. A shape measuring device provided with a mechanism for detecting can be provided. Moreover, the motor current limit value ilim
And the comparison with the current command value ic are not high-dimensional calculations but low-dimensional calculations, so that the calculation can be completed within the sampling time required for positioning control.

The shape measuring apparatus according to the second embodiment of the present invention differs from the first embodiment in the method of obtaining the motor current limit value ilim. That is, the current limiter 7
, A motor current limit value ilim (n) calculated in advance and set as a table in a stepwise manner is selected by the position signal X. If the current command value ic exceeds the motor current limit value ilim (n), the linear actuator Is detected, and ic 'is operated to stop the linear actuator. In order to select ilim (n) based on the position signal X, for example, the following table is created.

[0028]

(Equation 4)

FIG. 3 shows the operation of the abnormality detection. As the position signal X changes, the current command value ic changes continuously and the motor current limit value ilim (n) changes stepwise. The current command value ic is the motor current limit value ilim (n)
If it exceeds, the abnormality of the linear actuator is detected.

According to the second embodiment of the present invention, since the motor current limit value ilim (n) can be selected without being calculated, the calculation load can be reduced.

The shape measuring apparatus according to the third embodiment of the present invention differs from the first embodiment in the method of obtaining the motor current limit value ilim. The carriage 1 has a position signal X
Is moving the part where it becomes negative. In the current limiter 7, when the carriage 1 is driven in the positive direction or an external force is acting in the negative direction, the value calculated by equation (5) is set as the upper limit of the current command value ic. Current command value i
If c becomes larger than ilim +, it means that the carriage 1 has an abnormality.

[0032]

(Equation 5)

The carriage 1 is driven in the negative direction,
Alternatively, when an external force acts in the positive direction, the value calculated by the equation (6) is set as the lower limit of the current command value ic. If the current command value ic becomes smaller than ilim-, the carriage 1
Has an abnormality.

[0034]

(Equation 6)

In the equation (5), the motor current limit value ilim + is constantly calculated from the spring constant k, the motor thrust constant Kf, and the position signal X, and is used as the motor current limit value in the current limiter 7. Further, iadd + is a predetermined value set in consideration of an external force applied to the actuator other than the spring force, a transient response characteristic of the motor, a parameter variation, and the like. Similarly,
In the equation (6), the motor current limit value ilim- is always calculated. Predetermined value iadd used in equations (5) and (6)
By changing + and ilim-, the motor current limit value can be changed depending on the driving direction of the actuator or the direction of the external force.

FIG. 4 illustrates the operation of the abnormality detection. As the position signal X changes, the upper limit value of the motor current ilim
+ And the lower limit value ilim- change. When the carriage 1 is driven in the positive direction or an external force is applied in the negative direction, if the current command value ic becomes larger than ilim +, it means that the carriage 1 has an abnormality. When the carriage 1 is driven in the negative direction or when an external force is applied in the positive direction, the current command value ic becomes ilim.
If it becomes smaller, it means that the carriage 1 has failed.

According to the third embodiment of the present invention, the threshold level of abnormality detection can be changed depending on the direction of the applied external force. Can be set to

For example, if the threshold level in the case of driving in the negative direction is made small, the force applied to the probe mounted on the carriage 1 such as the focus type probe 11 at the time of collision can be made small, and the probe can be prevented from being damaged. Can be.

In the shape measuring apparatus according to the fourth embodiment of the present invention, the configuration of the current limiter 7 according to the first embodiment is specified. FIG. 5 shows the configuration of the current limiter 7. The current command value ic output from the positioning controller 5 or the detected motor current is input to the current limiter 7. In the current limiter 7, a noise component and a pulse component are removed from the current command value ic through a low-pass filter 8. The current command value ic and the position signal X that have passed through the low-pass filter 8 are input to the comparator 9. The comparator 9 compares the current command value ic with a motor current limit value calculated or selected from the position signal X to detect whether or not the linear actuator is abnormal. When the abnormality of the linear actuator is detected, the abnormality is notified, and at the same time, the linear actuator is stopped by the switching device 10.

According to the fourth embodiment of the present invention, it is possible to prevent malfunction due to noise of the operation amount or the motor current. Further, by changing the cut-off frequency of the low-pass filter, the input / output response performance of the low-pass filter can be changed, so that the response time of abnormality detection can be adjusted.

In the shape measuring apparatus according to the fifth embodiment of the present invention, the method of detecting the abnormality of the linear actuator is different from that of the first embodiment. The current command value ic output from the positioning controller 5 is input to the limiter 7 and compared with the motor current limit value ilim. Time t when current command value ic exceeds motor current limit value ilim
When c exceeds a predetermined time tlim, the controller detects an abnormality of the actuator and stops the actuator. That is, an abnormality is detected as shown in equation (7).

[0042]

(Equation 7)

FIG. 6 shows the operation of the abnormality detection. When the current command value ic exceeds the motor current limit value ilim, the abnormality is not detected unless it exceeds a predetermined time tlim. If it exceeds, an abnormality is detected.

According to the fifth embodiment of the present invention, it is possible to prevent a malfunction due to an operation amount, a motor current, and a noise component that instantaneously increase due to a transient response.

The shape measuring apparatus according to the sixth embodiment of the present invention differs from the first embodiment in the method of obtaining the motor current limit value ilim and the method of detecting an abnormality of the linear actuator. The carriage 1 is moving in a position where the position signal X becomes negative. In the current limiter 7,
When the carriage 1 is driven in the positive direction or an external force is acting in the negative direction, ilim + is changed to the current command value i.
c is the upper limit. Here, as shown in Expression (8), the time tc + when the current command value ic becomes larger than ilim +
Exceeds a predetermined time tlim +, an abnormality of the linear actuator is detected.

[0046]

(Equation 8)

The carriage 1 is driven in the negative direction.
Alternatively, when an external force acts in the positive direction, the value calculated by the equation (6) is set as the lower limit of the current command value ic. Here, as shown in Expression (9), the current command value ic is ilim
-The time tc that has become smaller is a predetermined time tlim-
If it exceeds, the abnormality of the linear actuator is detected.

[0048]

(Equation 9)

By setting the predetermined times tlim + and tlim- to different values, the abnormality detection threshold level can be changed depending on the driving direction of the actuator or the direction of the external force.

FIG. 7 shows the operation of the abnormality detection. When the carriage 1 is driven in the positive direction or when an external force is applied in the negative direction, if the time tc + at which the current command value ic becomes larger than ilim + exceeds a predetermined time tlim +, the linear actuator malfunctions. Is detected.
When the actuator is driven in the negative direction or an external force is applied in the positive direction, if the time tc- when the current command value ic becomes smaller than ilim- exceeds a predetermined time tlim-, an abnormality of the linear actuator is determined. Detect.

According to the sixth embodiment of the present invention, the overload time of the linear actuator according to the driving direction of the linear actuator can be set separately.

[0052]

According to the present invention, the upper limit or lower limit of the motor current is compared with the operation amount or the motor current. If the operation amount exceeds the upper limit or falls below the lower limit, an abnormality occurs. Can be detected. In addition, the calculation of the upper limit value or the lower limit value and the comparison with the operation amount and the like are not high-dimensional calculations but low-dimensional calculations, so that the calculations can be made within the sampling time required for positioning control.

According to the present invention, the overload setting of the actuator according to the driving direction can be set separately.

Further, according to the present invention, since the current limiter includes the low-pass filter, it is possible to prevent the malfunction due to the operation amount or the noise of the motor current. Further, by changing the cutoff frequency of the low-pass filter, the response performance of the abnormality detection can be adjusted.

According to the present invention, the current limiter is
By determining whether the output of the low-pass filter has increased for a predetermined time with respect to the upper limit value of the motor current,
It is possible to prevent a malfunction due to an operation amount, a motor current, and a noise component that instantaneously increase due to a transient response.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a shape measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an operation of detecting an abnormality of the shape measuring apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an operation of detecting an abnormality of a shape measuring apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an operation of detecting an abnormality of a shape measuring apparatus according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a current limiter 7;

FIG. 6 is a diagram showing an operation of detecting an abnormality of a shape measuring apparatus according to a fifth embodiment of the present invention.

FIG. 7 is a diagram showing an operation of detecting an abnormality of a shape measuring apparatus according to a sixth embodiment of the present invention.

FIG. 8 is a configuration diagram of a conventional shape measuring apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carriage 2 Spring 2a Elastic part 2b Viscous part 3 Voice coil motor 4 Linear encoder 5 Positioning controller 6 Motor driver 7 Current limiter 8 Low-pass filter 9 Comparator 10 Switching device 11 Focusing probe 12 Test object 51 Spring 52 Linear motor 53Z Moving part 54 Position detector 55 Servo circuit 56 Objective lens 57 Measurement surface

Claims (4)

[Claims] A linear actuator supported by a spring and driven by a motor; a position detector for detecting a displacement of the linear actuator and outputting it as a position signal; comparing a target position of the linear actuator with a position signal to operate; A shape controller having a positioning controller that outputs an amount, and a motor driver that outputs a motor drive current in accordance with the operation amount and drives the linear actuator, wherein a spring constant of the spring, a motor thrust constant of the motor, and From the position signal, a steady-state current value of the motor with respect to the force generated in the spring is calculated, and a value obtained by adding a predetermined value to the current value is set as an upper limit value or a lower limit value of the motor current, and the upper limit value is set. Alternatively, a current limiter for comparing the lower limit value with the operation amount or the motor current is provided. A shape measuring device comprising: 2. The shape measuring apparatus according to claim 1, wherein the current limiter sets the upper limit value or the lower limit value of the current of the motor to a different value according to a driving direction of the motor. 3. The low-pass filter to which the operation amount or the motor current is input, and a comparator that compares the upper limit value or the lower limit value of the motor current with the output of the low-pass filter. The shape measuring apparatus according to claim 1, further comprising: 4. The current limiter further comprises: a determiner for determining whether or not the output of the low-pass filter has been larger than the upper limit of the current of the motor for a predetermined time. The shape measuring apparatus according to any one of claims 1 to 3.