JP2007248287A - Control gain adjustment method of measurement control circuit, and measurement control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control gain adjustment method and a measurement control circuit, capable of acquiring a proper control gain, even if measurement object is changed and contributing improvement in operability, measurement accuracy, and measurement speed. <P>SOLUTION: The measurement control circuit includes a probe 10 having a force sensor 1, a detector 12, and a driving actuator 11; a force control loop RF in which a force detection signal from the force sensor is made as a force feedback signal; a position control loop RP, in which a measurement position information from the detector is made as a position feedback signal; and a switch 30 validating either one of the control loops. The measurement position information from the detector is subject to high-pass filter processing so as to be made into an observation value. In a state where the force control loop is validated, the force sensor is brought into contact with a measurement object, and an observation value is then observed, while gradually increasing a control gain of the force control loop. The gain is in such a state that the observation value has a prescribed margin to a vibration limit value before the state where the observation value is vibratory is acquired, and is set as the control gain of the force control loop. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control gain adjustment method for a measurement control circuit and a measurement control circuit. For example, the present invention can be applied to a measurement control circuit of a surface property measuring apparatus that measures surface properties such as the shape and surface roughness of an object to be measured using an excitation type sensor.

Surface texture measuring devices that measure the surface properties such as the shape and surface roughness of the object to be measured by scanning the surface of the object to be measured, such as roughness measuring machine, contour measuring machine, roundness measuring machine, and three-dimensional measuring machine It has been known.
In such a measuring machine, an excitation type force sensor is used as a sensor for detecting the surface of the object to be measured based on a minute displacement in which the contact portion contacts the surface of the object to be measured.

<Excitation type force sensor>
As shown in FIG. 5, the vibration-type force sensor 1 includes a metal base 2, a stylus 3 formed integrally with the base 2, and a vibration that vibrates (vibrates in the axial direction) the stylus 3. It is composed of an element 4 and a detection element 5 that detects the vibration state of the stylus 3 and outputs it as a detection signal. A stylus 6 as a contact portion composed of a diamond tip, a ruby or the like is bonded and fixed to the tip of the stylus 3. The vibration element 4 and the detection element 5 are composed of a single piezoelectric element, and are bonded and fixed to the front and back of the base 2 one by one.

Now, as shown in FIG. 6, when an excitation signal Pi (voltage signal) having a specific frequency and amplitude is given to the vibration element 4 of the force sensor 1, the detection element 5 has a specific frequency and amplitude. Detection signal Qo (voltage signal) is obtained.
FIG. 7 shows the amplitude change of the detection signal Qo accompanying the contact with the workpiece W. When the excitation signal Pi having a constant amplitude at the resonance frequency of the stylus 3 is applied to the excitation element 4 when the stylus 3 is not in contact with the workpiece W, the stylus 3 resonates and the detection element 5 has an amplitude. Ao detection signal Qo is obtained. When the stylus 3 comes into contact with the workpiece W, the amplitude of the detection signal Qo is attenuated from Ao to Ax.

There is a relationship shown in FIG. 8 between the attenuation factor k (Ax / Ao) and the measuring force.
Here, the case where the detection signal Qo when the stylus 3 (force sensor 1) contacts the workpiece W is attenuated to 90% of the non-contact state (a state where the attenuation factor k = 0.9) is taken as an example. Take. From the relationship of FIG. 8, it can be seen that the measuring force in this contact state is 135 [μN].
Accordingly, when the force sensor 1 is brought into contact with the workpiece W, the distance between the force sensor 1 and the workpiece W is controlled using a driving actuator or the like so that the attenuation rate k is always constant. The shape and roughness of the workpiece W can be measured with a constant force.

<Contact type scanning probe system using force sensor>
FIG. 9 shows an example of a contact-type scanning probe system using a force sensor. This system includes a probe 10 and a controller 20 that controls the probe 10.
The probe 10 includes a force sensor 1, a drive actuator 11 that moves the force sensor 1 back and forth with respect to the object W to be measured, and a displacement amount of the force sensor 1 by the drive actuator 11 (that is, a measurement target by the force sensor 1. It consists of a detector (comprising a scale and a detection head) 12 for detecting an object measurement position information).

  The controller 20 includes an oscillator 21 that applies an excitation signal to the force sensor 1 to vibrate the force sensor 1, a peak hold circuit 22 that converts a detection signal from the force sensor 1 into a DC signal, and a signal from the detector 12. And a counter 26 for outputting the measured position information of the force sensor 1 as a position measurement value, a calculator 23 for calculating a deviation between an output (force feedback signal) from the peak hold circuit 22 and a target measurement force, and this calculation A force control compensator 24 having an output from the generator 23 as an input, a time differentiating circuit 31 for differentiating the position signal from the counter 26 into a speed signal, an output from the time differentiating circuit 31 and a switch 30. The calculator 32 for obtaining a deviation from the output from the force control compensator 24 captured in this way, and the drive actuator 11 is driven based on the output from the calculator 32. Drive amplifier 25, calculator 33 that calculates the deviation between the measured value (position information) of the counter 26 and the target position, and the position from which the output from the calculator 33 is input and the output is given to the calculator 32 through the switch 30 And a control compensator 34.

When performing constant force scanning measurement with this system, it is performed as shown in FIG.
(A) Approach the object to be measured by positioning control.
(B) When the probe contacts the object to be measured, the control is switched to constant force scanning control.
(C) Drive the probe or the object to be measured, and scan the surface of the object to be measured in a constant force scanning control state.
(D) During scanning, the position of the probe or the position of the object to be measured is read as the shape measurement position.
(E) When the constant force scanning measurement is completed, the control is switched to the positioning control and retracted to the retracted position.

In the case of the system as shown in FIG. 9, in order to perform measurement stably and quickly, it is desired to use the control loop as high as possible while the control loop is stable. However, the force control gain in the case of performing the constant force scanning measurement described with reference to FIG. 9 differs in the amount for controlling the position of the force sensor depending on the hardness of the surface of the object to be measured. It was necessary to use. That is, as shown in FIG. 11, it is necessary to switch the force control gain of the force control compensator 24 to an appropriate gain for each object to be measured depending on the hardness of the surface of the object W to be measured.
Therefore, an automatic adjustment technique for obtaining an appropriate control gain for each object to be measured and a target measurement force has been required.

<Relationship between surface hardness and force sensor sensitivity>
In the contact-type measurement, both the surface of the object to be measured and the probe (force sensor) are elastically deformed by the measuring force with the object to be measured. The force sensor detects the reaction force of this elastic deformation as a measuring force.
FIG. 12 shows the relationship between the position of the probe and the amount of deformation at the time of contact. From FIG. 12, the relationship among the position Z of the probe, the deformation amount Z1 of the force sensor 1, and the deformation amount Z2 of the surface of the workpiece W is expressed by the following equation.
Z = Z1 + Z2 (1)

Further, since the relationship between the deformation amount and the measuring force can be expressed by the deformation amount, the surface of the object to be measured, and the spring constant of the force sensor 1, the following equation is obtained.
F1 = K1 × Z1 (2−1)
F2 = K2 × Z2 (2-2)
F1 = F2 (2-3)
F1: Acting force due to deformation of the force sensor 1 (measuring force)
F2: Reaction force due to deformation of the surface of the object to be measured
K1: equivalent spring constant of force sensor 1
K2: Equivalent spring constant of the surface of the object to be measured

From the relationship of the above formulas (1) (2-1) to (2-3), the relationship between the probe position Z and the measuring force F is
Z = Z1 + Z2 = (F1 / K1) + (F2 / K2) = F (1 / K1 + 1 / K2)
……… (3)
It becomes. When arranged, it becomes as shown in FIG.
From FIG. 13, except when the equivalent spring constant of the force sensor is sufficiently smaller than the equivalent spring constant of the surface of the object to be measured (K1 << K2), the relationship between the probe position and the measuring force is the equivalent spring constant of the surface of the object to be measured. It changes according to (the hardness of the surface of the object to be measured). That is, since the sensitivity of the force sensor changes according to the hardness of the surface of the object to be measured, it can be seen that the force control gain needs to be adjusted to an appropriate value according to the object to be measured.
In addition, from this relationship, if the equivalent spring constant of the force sensor is made sufficiently small, the problem of dependence of the control gain on the object to be measured will be improved, but the amount of deformation (measurement error) of the force sensor will increase, so that the accuracy will be high. This method cannot be adopted in a force sensor of a probe that performs dimension measurement.

<Conventional method>
As a method for determining the control gain that has been considered so far, there has been a method of observing how the force feedback signal of the force control loop changes with respect to the change of the control gain.
FIG. 14 shows a conceptual diagram of the conventional method. When the force sensor 1 is in contact with the workpiece W with a constant force, the control gain of the force control loop is gradually increased until the force control loop oscillates. An appropriate point is obtained by observing the state of the force feedback signal in the meantime.

  As another method for determining the control gain, there is a method disclosed in Patent Document 1. This is the content to specify the feedback gain by frequency analysis of the output from the acceleration sensor that detects the acceleration due to the vibration by the excitation device and the position sensor that detects the position of the excitation device in the mold oscillation device of the continuous casting machine It is. Here, the acceleration feedback gain is designated based on the amplitude of the signal for each frequency, or the proportional gain is designated.

Japanese Patent No. 2932235

In the case of the method shown in FIG. 14, when the probe mounting side and the object to be measured vibrate due to high-frequency disturbance vibration or the like that the force control loop cannot respond to, the force feedback signal is disturbed, and this disturbance is caused by adjustment of the control loop. It was difficult to identify whether it was due to a disturbance or not.
For example, as shown in FIG. 15, when the workpiece W vibrates due to high-frequency disturbance vibration or the like, the force feedback signal is also disturbed. As a result, is this disturbance caused by adjustment of the force control loop or due to disturbance? It was difficult to isolate. For this reason, automatic adjustment of the force control gain by this method can be realized only in a system in which no disturbance exists, and is difficult in practice.

  In the method described in Patent Document 1, it is determined that the speed feedback gain is appropriate, high, or low according to the amplitude for each frequency, and based on the determination result, the acceleration feedback gain is determined based on a predetermined adjustment amount or calculation. Since the adjustment is performed with the calculated adjustment amount, it takes time to adjust until the optimum gain is obtained.

  An object of the present invention is to provide a measurement control circuit capable of obtaining an appropriate control gain without being affected by disturbance even when the object to be measured changes, and contributing to improvement in usability, measurement accuracy, and measurement speed. A control gain adjustment method and a measurement control circuit are provided.

  The control gain adjustment method of the measurement control circuit according to the present invention is a force sensor that detects a measurement force generated upon contact with a measurement object and outputs it as a force detection signal, and detects and measures a measurement position of the measurement object by the force sensor. A probe having position detecting means for outputting as position information, and a relative moving means for relatively moving the force sensor and the object to be measured, and comparing the force detection signal from the force sensor with a force setting value as a force feedback signal A force control loop for driving the relative movement means so that the force feedback signal coincides with the force setting value, and the measured position information from the position detecting means is compared with the position setting value as a position feedback signal, and the position feedback signal A position control loop for driving the relative movement means so that the value matches a position set value, and the force control loop and the position control loop. A control gain adjustment method for adjusting a control gain of the force control loop in a measurement control circuit including a control loop switching unit that enables one of the force detection signal, the force detection signal from the force sensor, and the position detection Filtering any of the measurement position information from the means to extract an observation value representing the vibrational movement of the relative movement means, in a state where the force control loop is enabled by the control loop switching means, After the force sensor is brought into contact with the object to be measured, the observed value is observed while gradually increasing the control gain of the force control loop, and the state before the relative moving means becomes oscillating from the change in the observed value In addition, a gain in a state having a predetermined margin with respect to the vibration limit value is obtained and used as a control gain of the force control loop.

According to the present invention, when adjusting the control gain of the force control loop, either the force detection signal from the force sensor or the measured position information from the position detection unit is filtered to perform the vibrational movement of the relative movement unit. While the force control loop is enabled by the control loop switching means and the force sensor is in contact with the object to be measured, the control gain of the force control loop is gradually increased. Observe observations.
For example, when high-pass filter processing is performed on the measurement position information from the position detection means to obtain observation values, no disturbance vibrations appear in the observation values for high-frequency disturbance vibrations in which the force control loop cannot respond.
For low-frequency disturbance vibrations to which the force control loop can respond, constant force control is executed by the force control loop. Then, since the force sensor and the object to be measured are relatively moved by the relative moving means, an amplitude component of low-frequency disturbance vibration appears in the measurement position information of the position detecting means. However, since the measurement position information of the force sensor and the object to be measured that are relatively moved by the constant force control is removed by the high-pass filter process, it does not appear in the observed value.
When the control gain is gradually increased, the force control loop oscillates at the high resonance frequency of the mechanical system and reaches the control limit. That is, when the relative movement means vibrates, such a high-frequency vibration component appears in the observed value without being removed by the high-pass filter process. Therefore, from this change in the observed value, a gain in a state before the relative moving means becomes oscillating and having a predetermined margin with respect to the vibration limit value is obtained, and this is obtained as a control gain of the force control loop. can do.
In this way, even if the object to be measured changes, an appropriate control gain can be obtained without being affected by disturbances, which can contribute to improved usability, measurement accuracy, and measurement speed.

In the control gain adjusting method of the measurement control circuit according to the present invention, it is preferable that the measurement position information from the position detection means is subjected to high-pass filter processing to obtain an observed value.
At this time, it is preferable that the cut-off frequency of the high-pass filter process is substantially matched with the cut-off frequency of the force control loop.
According to the present invention, disturbance vibration below the cutoff frequency of the force control loop is blocked by the high-pass filter and does not appear in the observed value, so that only abnormal vibration of the probe can be extracted. Therefore, even if the object to be measured changes, an appropriate control gain can be obtained.

In the control gain adjustment method of the measurement control circuit of the present invention, the observed values are sampled a plurality of times, a standard deviation of the sampled observed values is calculated, and the standard deviation exceeds a preset threshold. It is preferable to multiply the control gain by a margin coefficient to obtain the optimum control gain.
According to the present invention, even when disturbance vibration exceeding the cutoff frequency of the force control loop is included, the observation values are sampled a plurality of times, and the standard deviation of these sampled observation values is calculated. The influence of disturbance can be reduced, and abnormal vibration of the force control loop can be detected based on whether or not the standard deviation exceeds a preset threshold value.

  The measurement control circuit according to the present invention detects a measurement force generated upon contact with the object to be measured and outputs it as a force detection signal, detects a measurement position of the object to be measured by the force sensor, and outputs the measurement position information. A force detection signal, a probe having position detection means, and a relative movement means for relatively moving the force sensor and the object to be measured; a force detection signal from the force sensor as a force feedback signal and a force setting value; The force control loop for driving the relative movement means so that the value coincides with the force set value, and the measured position information from the position detecting means is compared with the position set value as a position feedback signal, and the position feedback signal becomes the position set value. The position control loop for driving the relative movement means so as to coincide, and either the force control loop or the position control loop are enabled. Control loop switching means, and a filter for extracting an observation value representing the vibrational movement of the relative moving means by applying a filter process to any of the force detection signal from the force sensor and the measured position information from the position detecting means When the force control loop is enabled by the circuit and the control loop switching means, and the force sensor is in contact with the object to be measured, the observed value when the control gain of the force control loop is gradually increased is observed. Then, from the change of the observed value, a gain in a state before the relative movement means becomes oscillating and having a predetermined margin with respect to the vibration limit value is obtained, and this is controlled by the control of the force control loop. Control gain automatic adjustment means for gain is provided.

In the measurement control circuit of the present invention, the filter circuit is configured by a high-pass filter circuit that performs high-pass filter processing on the measurement position information from the position detection unit to obtain an observation value, and the cutoff frequency of the high-pass filter circuit is set as the force It is preferable to substantially match the cutoff frequency of the control loop.
Even in such a measurement control circuit, the same effect as the control gain adjustment method of the measurement control circuit described above can be expected.

<Description of overall configuration (FIG. 1)>
FIG. 1 is a block diagram showing an embodiment in which a measurement control circuit according to the present invention is applied to a surface shape measuring apparatus. In the description of the figure, the same components as those in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted or simplified.
Although the basic configuration of the surface shape measuring apparatus of this embodiment is the same as that of the system of FIG. 9, a high-pass filter circuit 40 that allows only the high-frequency component of the position feedback signal from the counter 26 to pass through the system of FIG. And a control gain automatic adjustment circuit 41 that automatically sets the control gain of the force control compensator 24 to the optimum control gain based on the position feedback signal that has passed through the high-pass filter circuit 40 is added. In other words, in the present invention, by using the position feedback signal of the position control loop, it is insensitive to high-frequency disturbances that the force control loop cannot respond to, and against oscillation due to the high gain of the force control loop. Is configured so that the situation can be grasped.

The force sensor 1 includes a peak hold circuit 22, a calculator 23, a force control compensator 24, a calculator 32, a speed compensator 28, a drive amplifier 25, and a drive actuator 11. A force control loop RF for driving the driving actuator 11 as a relative movement means is configured so that the force measurement signal is compared with the target measurement force (force setting value) as a feedback signal and the force feedback signal matches the target measurement force.
The measurement position from the detector 12 as position detection means, including the detector 12, counter 26, calculator 33, position control compensator 34, calculator 32, speed compensator 28, drive amplifier 25 and drive actuator 11. A position control loop RP is configured to compare the information as a position feedback signal with a position set value (target position) and drive the driving actuator 11 as a relative movement means so that the position feedback signal matches the target position.
The switch 30 constitutes a control loop switching unit that enables either the force control loop RF or the position control loop RP.

The high-pass filter circuit 40 performs high-pass filter processing on the position feedback signal from the counter 26 and extracts an observed value representing the vibrational movement of the driving actuator 11. The cutoff frequency of the high-pass filter circuit 40 is controlled by force control. It is configured to substantially match the cutoff frequency of the loop RF.
In the control gain automatic adjustment circuit 41, the switch 30 is switched to the force control loop RF side, that is, the force control loop RF is enabled and the force sensor 1 is in contact with the object to be measured. The observed value when the control gain is gradually increased is observed, and from the change in the observed value, the drive actuator 11 is in a state before it becomes oscillating and has a predetermined margin with respect to the vibration limit value. A function for obtaining a gain and setting it as a control gain of the force control compensator 24 of the force control loop is provided.

<(1) Method for separating disturbance that can be responded by force control loop>
Consider a case in which low-frequency disturbance vibration capable of responding to the force control loop RF enters the probe mounting side or the object to be measured. 2 and 3 are conceptual diagrams of this method.
Since force constant control is performed to cancel the force disturbance due to disturbance vibration, the driving actuator 11 moves the position of the force sensor 1. As a result, the amplitude component of low-frequency disturbance vibration appears in the measured value. Expressed as a formula:
P _m = P _err + P _{v_res} (4)
Where P _m : measured value
_Perr : Vibration due to high gain of the force control loop
P _{v_res} : A disturbance vibration component that can be responded to by the force control loop.

In this embodiment, the measurement value obtained by passing the high-pass filter circuit 40 is used as the observation value in the automatic adjustment function. Since the cutoff frequency of the high-pass filter circuit 40 is substantially matched with the cutoff frequency of the force control loop, the position information of the probe moved by the response of the constant force control is removed by the high-pass filter circuit 40 and appears in the observed value. No (see Figure 2).
Therefore, only the vibration component due to the high gain of the force control loop remains in the disturbance of the observed value. Expressed as a formula:
P = P _HPF · P _m = P ′ _err (5)
However, P _HPF : High-pass filter characteristics
_P'err : Vibration due to high gain of the force control loop (only high frequency components)
It becomes.
In many mechanical systems, when the control gain is increased, the mechanical system oscillates at a resonance frequency in a high frequency range, and reaches the control limit. In equation (5), the mechanical high-frequency vibration component of the probe (vibration of the driving actuator 11) appears in the observed value without being removed by the high-pass filter circuit 40 (see FIG. 3). From the change in value, a gain in a state before the driving actuator 11 becomes oscillating and having a predetermined margin with respect to the vibration limit value is obtained, and this gain is obtained by the force control compensator 24 of the force control loop. It can be set as a control gain.

<(2) Method for separating a disturbance in which the force control loop cannot respond>
In (1) described above, a case was considered in which low-frequency disturbance vibration capable of responding to the force control loop entered the probe mounting side or the workpiece W.
With respect to high-frequency disturbance vibrations in which the force control loop cannot respond, disturbance vibrations hardly appear in the observed values due to the characteristics of the frequency response region itself of the force control loop. However, for high-frequency disturbances that the force control loop cannot respond to, the damping force is small only with the high-frequency damping characteristics of the force control loop, and there are cases where it is necessary to consider the influence of high-frequency disturbance components included in the automatic gain adjustment results. Conceivable.

Here, in the control gain automatic adjustment circuit 41, the observed value P obtained through the high-pass filter circuit 40 is averaged n times to eliminate the influence of high-frequency disturbance vibration.
The disturbance of the measured value due to the disturbance vibration is equivalent to the addition of a high-frequency disturbance component to Equation (4). Expressed as a formula:
P _m = P _err + P _{v_res} + P _{v_nores} (6)
Where P _m : measured value
_Perr : Vibration due to high gain of the force control loop
P _{v_res} : Disturbance vibration component to which the force control loop can respond
P _{v_nores} : The force control loop is a disturbance vibration component that cannot respond.

As in the case of the equation (5), the observation value after passing through the high-pass filter circuit 40 is represented by the equation:
P = P _HPF · P _m = P ′ _err + P ′ _{v — nores} (7)
Where P is the observed value
P _HPF : High-pass filter characteristics
_P'err : Vibration due to high gain of the force control loop (only high frequency components)
_{P'v_nores} : Disturbance vibration component (only high frequency component) that force control loop cannot respond to
It becomes.

In general, the vibration P ′ _err due to the high gain of the force control loop shows a steady response, whereas the high-frequency disturbance component P ′ _err often behaves transiently, that is, randomly. . Therefore, averaging for the purpose of removing random noise is effective.
When the observation value P in the equation (7) is averaged n times, and P _n ,

It becomes. here,

Is a random noise component, so after n times of averaging

It is thought that it approaches. If n is large enough,

Therefore, equation (8) becomes

Which means that it is approximately equal to the average value of _P'err .
As described above, it is possible to remove only the influence of high-frequency disturbance vibration and observe only the vibration caused by the high gain of the force control loop.

<(3) Example of automatic adjustment algorithm>
FIG. 4 shows a flowchart of automatic adjustment. In order to perform automatic adjustment of the control gain, it is only necessary to build a method that can gradually increase the control gain and determine from the observed values the state in which the force control loop becomes unstable and oscillates.

In the example shown in FIG. 4, the following method is adopted.
(A) In order to determine the magnitude of oscillation (vibration), the standard deviation of the observed value is calculated.
(B) In order to determine how much the control gain is increased, a threshold value of the standard deviation of the observed value is provided. Since this threshold value causes variations in measurement data, it is determined in advance based on the measurement accuracy of this probe and experimental values.
(C) Multiply the gain exceeding the threshold by the stability margin coefficient.

The flowchart of FIG. 4 will be described in detail.
Sampling observation is performed by approaching the object to be measured with the initial value of the force control gain (ST1), sampling the observed value that has passed through the high-pass filter circuit 40 at a specified time and a specified time period (ST3) on condition that the approach is completed (ST2). A standard deviation of values is calculated (variation is calculated) (ST4).
The standard deviation is compared with a predetermined threshold value. When the standard deviation is less than the threshold value, the process of increasing the control gain (ST6) is performed, and then the process of returning to ST3 is repeated.
When the standard deviation is equal to or greater than the threshold value, a stability margin is taken, and the control gain is multiplied by a margin coefficient to obtain an optimum control gain (ST7), and the process is terminated.

<Description of modification>
The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.
In the above embodiment, the position feedback signal is branched from the detector 12 (counter 26), the high-pass filter circuit 40 is connected to the branch side, and high-pass filter processing is performed on the position feedback signal from the detector 12 (counter 26). However, the present invention is not limited to this, and a force feedback signal from the force sensor 1 may be used.
In this case, the force feedback signal from the force sensor 1 is branched, a low-pass filter circuit is connected to the branch side, and a low-pass filter process is applied to the force feedback signal to detect the vibrational movement of the driving actuator 11. As for the value, the same effect as the above embodiment can be expected.

In the embodiment described above, the structure of the force sensor 1 is configured such that the base 2 and the stylus 3 of the force sensor 1 are integrally formed. That is, the base 2 and the stylus 3 may be configured separately and the stylus 3 may be bonded and fixed to the base 2. Although the stylus 3 is vibrated in the axial direction, the present invention is not limited to this, and the stylus 3 may be vibrated in a direction intersecting the axis of the stylus 3.
In the above embodiment, the vibration-type force sensor 1 is used. However, the present invention is not limited to this, and any other sensor can be used as long as it can detect a measurement force generated upon contact with an object to be measured and output it as a force detection signal. There may be.

  In the above embodiment, the detector 12 is composed of a scale and a detection head, but other detectors may be used as long as the displacement of the force sensor 1 can be detected. Moreover, it is not limited to detecting the displacement of the force sensor 1, but when the object to be measured is configured to be movable with respect to the force sensor, the displacement of the object to be measured may be detected.

  The present invention can be applied to a surface roughness measuring machine, a shape measuring machine, a contour measuring machine, a roundness measuring machine, a three-dimensional measuring machine, and the like that measure the surface roughness of an object to be measured. In particular, it is suitable for measuring fine shapes.

1 is a block diagram showing an embodiment of a measurement control circuit according to the present invention. The figure which shows the change of the measured value when the low frequency disturbance vibration which can respond to a force control loop enters in embodiment same as the above. The figure which shows the change of the measured value and observed value when the control gain of a force control loop is made into high gain in embodiment same as the above. 4 is a flowchart showing an automatic adjustment process of a force control gain in the embodiment. The disassembled perspective view which shows the structure of a force sensor. The figure which shows the vibration signal and detection signal which are given to a force sensor. The figure which shows the change of a detection signal when a force sensor contacts a to-be-measured object. The figure which shows the relationship between the attenuation factor of the detection signal of a force sensor, and measurement force. The block diagram which shows the shape measurement system using a force sensor. FIG. 10 is a diagram illustrating a constant force scanning control operation in the system of FIG. 9. The figure for demonstrating changing a force control gain with surface hardness in the system of FIG. FIG. 10 is a diagram showing the relationship among the probe position, the deformation amount of the force sensor, and the deformation amount of the surface of the object to be measured in the system of FIG. 9. The figure which shows the relationship of Formula (3) in the system of FIG. The figure which shows the method of determining the control gain of the conventional force control loop in the system of FIG. The figure for demonstrating a problem when disturbance vibration enters in the system of FIG.

Explanation of symbols

1 ... Excitation type force sensor (force sensor)
DESCRIPTION OF SYMBOLS 3 ... Stylus 4 ... Excitation element 5 ... Detection element 10 ... Probe 11 ... Actuator for drive (relative movement means)
12 ... Detector (position detection means)
30 ... Switch (control loop switching means)
40 ... High-pass filter circuit 41 ... Control gain automatic adjustment circuit (control gain automatic adjustment means)
RF: Force control loop RP: Position control loop.

Claims (6)

A force sensor that detects a measurement force generated when contacting the object to be measured and outputs it as a force detection signal, a position detection unit that detects a measurement position of the object to be measured by the force sensor and outputs it as measurement position information, and the force A probe having relative movement means for relatively moving the sensor and the object to be measured;
A force control loop that compares the force detection signal from the force sensor as a force feedback signal with a force setting value and drives the relative movement means so that the force feedback signal matches the force setting value;
A position control loop that compares the measured position information from the position detection means with a position set value as a position feedback signal and drives the relative movement means so that the position feedback signal matches the position set value;
In a measurement control circuit including a control loop switching unit that enables either the force control loop or the position control loop, a control gain adjustment method for adjusting a control gain of the force control loop,
Filtering any one of the force detection signal from the force sensor and the measurement position information from the position detection means to extract an observation value representing the vibrational movement of the relative movement means,
In the state where the force control loop is enabled by the control loop switching means, after the force sensor is brought into contact with the object to be measured, the observed value is observed while gradually increasing the control gain of the force control loop,
From the change in the observed value, a gain in a state before the relative movement means becomes oscillating and having a predetermined margin with respect to the vibration limit value is obtained, and this is determined as a control gain of the force control loop. A control gain adjustment method for a measurement control circuit. The control gain adjustment method of the measurement control circuit according to claim 1,
A control gain adjustment method for a measurement control circuit, wherein the measurement position information from the position detection means is subjected to high-pass filter processing to obtain an observed value. In the control gain adjustment method of the measurement control circuit according to claim 2,
A control gain adjustment method for a measurement control circuit, wherein a cutoff frequency of the high-pass filter processing is made to substantially coincide with a cutoff frequency of the force control loop. In the control gain adjustment method of the measurement control circuit according to any one of claims 1 to 3,
The observed value is sampled multiple times, the standard deviation of these sampled observed values is calculated, and on the condition that this standard deviation exceeds a preset threshold value, the control gain is multiplied by a margin coefficient to obtain the optimal control gain. A method for adjusting the control gain of the measurement control circuit. A force sensor that detects a measurement force generated when contacting the object to be measured and outputs it as a force detection signal, a position detection unit that detects a measurement position of the object to be measured by the force sensor and outputs it as measurement position information, and the force A probe having relative movement means for relatively moving the sensor and the object to be measured;
A force control loop that compares the force detection signal from the force sensor as a force feedback signal with a force setting value and drives the relative movement means so that the force feedback signal matches the force setting value;
A position control loop that compares the measured position information from the position detection means with a position set value as a position feedback signal and drives the relative movement means so that the position feedback signal matches the position set value;
Control loop switching means for activating any one of the force control loop and the position control loop;
A filter circuit that performs filtering on any of the force detection signal from the force sensor and the measurement position information from the position detection unit to extract an observation value representing the vibrational movement of the relative movement unit;
When the force control loop is enabled by the control loop switching means and the force sensor is in contact with the object to be measured, the observed value when the control gain of the force control loop is gradually increased is observed, Based on the change in the observed value, a gain in a state before the relative movement means becomes oscillating and has a predetermined margin with respect to the vibration limit value is obtained, and this is used as the control gain of the force control loop. A measurement control circuit comprising control gain automatic adjustment means. The measurement control circuit according to claim 5,
The filter circuit is constituted by a high-pass filter circuit that performs high-pass filter processing on the measured position information from the position detection means to obtain an observation value, and the cutoff frequency of the high-pass filter circuit substantially matches the cutoff frequency of the force control loop. A measurement control circuit characterized by the above.

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