JP2007271337A - Surface property measuring device and surface property measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface property measuring device and a surface property measuring method, capable of performing measurement with a set fixed measurement force with respect to variations in the ambient temperature, and improving the accuracy, handleability, and reliability, as a result. <P>SOLUTION: The surface property measuring device includes a sensor 1 having a stylus, an excitation element 4, and a detection element 5; a drive actuator 11 for causing it to move relative to an object to be measured; an oscillator 34 for oscillating and outputting an excitation signal of a set frequency; a first variable amplifier 35 for correcting an amplitude of the excitation signal from the oscillator according to a set gain and providing it to the excitation element of the sensor; and a control means 31. The control means includes a frequency correction means for detecting the detection signal from the detection element and correcting the set frequency of the oscillator to a frequency with the maximum amplitude of the detection signal, and an excitation gain adjustment means for adjusting the set gain of the first variable amplifier 35, according to the difference between a new set frequency that has been newly set by the frequency correction means and old set frequency. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface texture measuring device. For example, the present invention relates to a surface property measuring apparatus and a surface property measuring method for measuring surface properties such as the shape and surface roughness of an object to be measured with a vibration 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. 7, 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. 8, 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. 9 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. 10 between the attenuation rate 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. 10, 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.

FIG. 11 is an example of a shape measurement system using the force sensor 1. This shape measuring 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 peak hold circuit 22. A calculator 23 for calculating a deviation between the output (force sensor signal) and the target measurement force, a force control compensator 24 having the output from the calculator 23 as an input, and an output from the force control compensator 24 A drive amplifier 25 that drives the drive actuator 11 based on the signal and a counter 26 that counts a signal from the detector 12 and outputs the measurement position information of the force sensor 1 as a position measurement value.
In this shape measuring system, if a circuit for latching the current position is incorporated when the attenuation rate reaches a desired value, it can be used as an ultra-high accuracy contact sensor with a constant measuring force.

However, the shape measuring system using the force sensor 1 having the structure described above has the following problems.
<Fluctuation in measuring force due to changes in ambient temperature>
FIG. 12 shows the relationship between the temperature change and the detection signal (output voltage) at the time of non-contact. From FIG. 12, it can be seen that the detection signal changes despite the non-contact state.
When the attenuation rate k for setting the measurement force to 135 [μN] at the ambient temperature Td0 ° C. is obtained, the attenuation rate at the measurement force of 135 [μN] is 90% (k = 0.9) from FIG. It is. The voltage at that time is shown in FIG.
Vd0 [V] × 0.9 = 0.9 Vd0 [V]
It is.
Here, when the ambient temperature rises by ΔT [%] and changes to Td1 ° C., the detection signal at the time of non-contact becomes Vd1 [V] from FIG. 12, and measurement is performed with a measuring force of 135 [μN] in this state. When the contact of the stylus 3 is controlled so that the detection signal becomes 0.9 Vd0 [V],
Attenuation factor k = 0.9Vd0 / Vd1
It becomes. Since Vd0 <Vd1, the attenuation factor k is smaller than 0.9.
When the measurement force is obtained from the relationship of FIG. 10 using this attenuation factor k (an attenuation factor k smaller than 0.9), the measurement force is greater than 135 [μN], and the measurement force 135 [ [μN] cannot be measured.

<Fluctuation of resonance frequency due to changes in ambient temperature>
The main cause of fluctuations in measurement force due to changes in ambient temperature is that the resonance signal frequency of the stylus changes due to the change in ambient temperature, causing a deviation from the excitation signal frequency, resulting in a decrease in the voltage of the detection signal. it is conceivable that. Regarding this phenomenon, the resonance frequency of an object has the following relationship with temperature, and it is physically inevitable that the resonance frequency changes due to the change in ambient temperature.

First, the resonance frequency f of the object is obtained from the sound velocity ν and the resonance wavelength λ by the following equation.
Resonant frequency f = sonic velocity ν / resonant wavelength λ
The speed of sound in this equation is obtained from the following equation from the Young's modulus E and density ρ of the object.
Sound velocity ν = √ Young's modulus E / density ρ
The density ρ in this equation is the mass per volume of the object, and the volume of the object changes due to thermal expansion and contraction due to temperature change.
From this, it can be seen that a change in resonance frequency is unavoidable as a physical phenomenon when the temperature changes and the volume changes.

In order to solve the temperature change of the detection signal and the temperature change of the resonance frequency described above,
(I) A force sensor is made of a material whose output voltage does not easily change with temperature change.
(Ii) Making the shape and structure of the force sensor insensitive to temperature changes.
It is conceivable.
However, since the relationship between the material and shape of the force sensor, the vibration element and the detection element, and the adhesive used to fix them influences in a complicated manner, it has been difficult to solve the problem. In addition, fluctuations in characteristics of electrical circuits with respect to temperature changes were considered to be non-negligible factors.

Therefore, there has been proposed an application for correcting the frequency of the excitation signal with respect to the change in the resonance frequency of the stylus due to the change in the ambient temperature described above.
The minute inner diameter measuring method described in Patent Document 1 has a configuration in which the resonance frequency of the stylus is measured again during measurement interruption, and the frequency to be excited is finely adjusted so that the resonance amplitude is maximized.
In the surface shape measuring device described in Patent Document 2, the stylus and the temperature in the vicinity of the stylus are measured, and a frequency corresponding to the natural frequency of the stylus changed according to the measured temperature is given as an excitation signal. It is.

JP 2003-4433 A JP 2004-61322 A

  In Patent Document 1 and Patent Document 2 described above, an excitation signal can be given at a frequency corresponding to the natural frequency of the stylus that has changed in accordance with a change in ambient temperature, but if the frequency of the excitation signal is changed in advance, There is a deviation from the frequency set under the predetermined temperature condition. As a result, a difference occurs in the vibration energy of the stylus, and there remains a problem that a difference occurs with the set measurement force. That is, it becomes difficult to perform measurement with a set constant measurement force.

  An object of the present invention is to provide a surface texture measuring device and a surface capable of performing measurement with a set measuring force even with respect to a change in ambient temperature, and as a result, improving accuracy, improving usability, and improving reliability. The object is to provide a property measuring method.

  The surface texture measuring apparatus of the present invention includes a sensor having a stylus having a contact portion at the tip, a vibration element that vibrates the stylus, a detection element that detects a vibration state of the stylus and outputs it as a detection signal. Relative movement means for relatively moving the measurement object, and position detection means for outputting the measurement position of the measurement object by the sensor as measurement position information, the contact portion of the stylus contacting the surface of the measurement object, A surface texture measuring device for measuring the surface texture of an object to be measured from measurement position information of the position detecting means when a detection signal from a detection element substantially matches a set value, and oscillates an excitation signal of a set frequency. An oscillating means for outputting, an oscillating signal amplitude correcting means for correcting the amplitude of the oscillating signal from the oscillating means in accordance with a set gain, A frequency correction means for detecting a detection signal from the detection element and correcting the set frequency of the oscillation means to a frequency at which the amplitude of the detection signal is maximized; and a new set frequency newly set by the frequency correction means And an excitation gain adjusting means for adjusting a set gain of the excitation signal amplitude correcting means in accordance with a difference from the old set frequency.

According to the present invention, when the contact portion of the stylus is brought into contact with the surface of the object to be measured and the detection signal from the detection element coincides with the set value, the measurement position information of the position detection means is taken in, and the measurement object is obtained from this measurement position information The surface properties of the object are measured.
For example, if the relative distance between the sensor and the object to be measured is controlled by controlling the relative movement means so that the detection signal from the detection element matches the set value, the shape of the surface of the object to be measured can be measured with a constant measuring force. And roughness can be measured. In addition, if the contact portion of the stylus is brought into contact with an arbitrary point of the object to be measured and the measurement position information of the position detection means when the detection signal from the detection element matches the set value is obtained, the coordinate value of the contact point is obtained. be able to. Then, the shape of the object to be measured can be measured based on the coordinate values of the plurality of contact points.

By the way, when the ambient temperature changes, the resonance frequency changes depending on the temperature characteristics of the member material constituting the sensor. Then, since the vibration amplitude of the detection signal from the detection element decreases, the detection sensitivity fluctuates and stable measurement cannot be performed.
In the present invention, since the frequency correction means is provided, for example, before the start of measurement, the detection signal from the detection element is detected, the frequency at which the amplitude of the detection signal is maximized is obtained, and this is set as the set frequency of the oscillation means. Therefore, the detection sensitivity can be kept high.
As a result, the vibration element is vibrated at the newly set frequency, but if the frequency deviates from the set frequency set under the specified temperature, a difference occurs in the vibration energy of the stylus and the setting is made. There will be a difference with the measuring force.
In the present invention, since the excitation gain adjustment means is provided, the setting gain of the excitation signal amplitude correction means is adjusted according to the difference between the new setting frequency newly set by the frequency correction means and the old setting frequency. Thus, these differences can be corrected. That is, the influence due to the difference in frequency can be eliminated by correcting the amplitude of the excitation signal.
As a result, the detection sensitivity can be kept constant, so that high accuracy can be achieved. In addition, the temperature range of the operating environment can be greatly expanded, contributing to improved usability and the ability to perform constant measurements with low measuring force, thus preventing damage to the measurement object and improving reliability. .

  Another surface texture measuring device of the present invention includes a sensor having a stylus having a contact portion at a tip, a vibration element that vibrates the stylus, and a detection element that detects a vibration state of the stylus and outputs it as a detection signal. And a relative movement means for relatively moving the object to be measured and a position detection means for outputting the measurement position of the object to be measured by the sensor as measurement position information, and the contact portion of the stylus is brought into contact with the surface of the object to be measured. A surface texture measuring device for measuring the surface texture of the object to be measured from the measurement position information of the position detection means when the detection signal from the detection element substantially matches a set value, wherein an excitation signal of a set frequency is Oscillating means that oscillates and applies to the excitation element of the sensor; and a detection signal from the detection element is detected, and the oscillation means has a frequency that maximizes the amplitude of the detection signal. Frequency correction means for correcting a constant frequency, detection signal amplitude correction means for correcting and outputting the amplitude of the detection signal from the detection element according to a set gain, and the amplitude of the detection signal from the detection means set in advance And a detection gain adjusting means for correcting a set gain of the detection signal amplitude correcting means so that the amplitude of the detection signal becomes a reference amplitude based on a ratio to the reference amplitude.

In the surface texture measuring apparatus, the detection gain adjusting unit takes in a detection signal from the detection unit, and multiplies a set gain of the detection signal amplitude correction unit by a ratio between the amplitude of the detection signal and the reference amplitude. Thus, it is preferable to set this as a set gain after correction by the detection signal amplitude correcting means.
According to the present invention, since the detection gain adjusting means is provided, the detection signal amplitude is set so that the amplitude of the detection signal becomes the reference amplitude based on the ratio of the amplitude of the detection signal from the detection means to the reference amplitude. The set gain of the correction means can be corrected. As a result, for example, even if the amplitude of the excitation signal is corrected by the gain adjustment of the excitation signal amplitude correcting means described above, the amplitude of the detection signal can be adjusted to a constant reference amplitude, and an electric circuit or the like can be adjusted by changing the ambient temperature. Even if the characteristics fluctuate, it is possible to correct more accurately including fluctuations in characteristics due to temperature changes of the electric circuit or the like.

In the surface texture measuring apparatus according to the present invention, the frequency correction unit sequentially sets a plurality of primary extraction frequencies obtained by extracting a predetermined range before and after a reference frequency at regular intervals as set frequencies in the oscillation unit, and the detection signal After obtaining the primary peak frequency having the largest amplitude, a plurality of secondary extraction frequencies obtained by extracting the primary extraction frequency range before and after the primary peak frequency at intervals smaller than the constant interval step are obtained. By sequentially setting the oscillation means as a set frequency, a secondary peak frequency having the largest amplitude of the detection signal is obtained, and the secondary peak frequency or the secondary peak frequency is used as a center from the secondary extraction frequency. It is preferable to set the third and subsequent peak frequencies obtained at fine intervals as the set frequency of the oscillation means.
According to this invention, first, a first peak frequency is obtained by sequentially setting a plurality of primary extraction frequencies obtained by extracting a predetermined range before and after the reference frequency at regular intervals, and subsequently, the first peak is obtained. A secondary peak frequency is obtained by sequentially setting a plurality of secondary extraction frequencies extracted in narrow intervals before and after a narrow range based on the frequency, and this secondary peak frequency or similarly. Since the obtained peak frequency after the third order is set as the set frequency of the oscillation means, the resonance frequency can be searched efficiently and accurately.

A surface texture measuring method of the present invention includes a stylus having a contact portion at a tip, a vibration element that vibrates the stylus upon receiving a vibration signal, and a detection element that detects a vibration state of the stylus and outputs it as a detection signal. And a relative movement means for relatively moving the sensor and the object to be measured, and a position detection means for outputting the measurement position of the object to be measured by the sensor as measurement position information, and the contact portion of the stylus is the object to be measured. The measurement position information of the position detecting means when the attenuation of the detection signal from the detection element is lowered to a preset attenuation rate is brought into contact with the surface, and the surface property of the object to be measured is measured from the measurement position information. A surface texture measuring method, wherein a detection signal from the detection element is detected, and the frequency of the excitation signal is supplemented to a frequency at which the amplitude of the detection signal is maximized. A frequency correction step, and when the frequency of the excitation signal is corrected by the frequency correction step, the attenuation rate of the detection signal is set so that the measurement force that the stylus receives by contact with the object to be measured is substantially constant. And an attenuation rate correcting step for correcting.
According to this invention, even if the ambient temperature changes, the detection signal from the detection element is detected, and the frequency of the excitation signal is corrected to the frequency at which the amplitude of the detection signal is maximized. Can be maintained.
In addition, even if the frequency of the excitation signal is corrected, the attenuation rate of the detection signal is corrected so that the measurement force becomes substantially constant, so that measurement can always be performed with a constant measurement force.

<Description of overall configuration (FIG. 1)>
FIG. 1 is a block diagram showing an embodiment of a surface shape measuring apparatus according to the present invention. In the description of the figure, the same components as those in FIG. 11 are denoted by the same reference numerals, and the description thereof is omitted or simplified.
The surface shape measuring apparatus of the present embodiment includes a probe 10 and a controller 30 that controls the probe 10.
As in FIG. 11, the probe 10 includes a force sensor 1, a drive actuator 11 as a relative movement means for moving the force sensor 1 relative to the object W (advancement / retraction), and the drive actuator 11. It comprises a detector (consisting of a scale and a detection head) 12 as position detecting means for detecting a displacement amount of the force sensor 1 (that is, measurement position information of the object measured by the force sensor 1).

  The controller 30 includes a control means (Digital Signal Processor) 31, a storage means 32 having a ROM (Read Only Memory) / RAM (Random Access Memory), an interface (I / F) 33, and an oscillator (Direct Digital Synthesizer) 34, a first variable amplifier (Amp1) 35 as an excitation signal amplitude correction means, a second variable amplifier (Amp2) 36 as a detection signal amplitude correction means, a peak hold circuit 37, and an AD converter ( An analog digital converter (38), a DA converter (digital analog converter) 39, a contact detection circuit 40, an actuator drive circuit 41, and a counter 42 are included.

  The control means (DSP) 31 has a function as a microprocessor, and serves to control the entire system together with the storage means 32 having a ROM and a RAM. Further, the control means (DSP) 31 detects a detection signal from the detection element 5, and a frequency correction means for correcting the set frequency of the oscillator 34 to a frequency at which the amplitude of the detection signal is maximized. Excitation gain adjusting means for adjusting the setting gain of the first variable amplifier 35 in accordance with the difference between the new setting frequency and the old setting frequency, and the amplitude of the detection signal from the detection element 5 and a preset reference amplitude Based on the ratio, the detection gain adjustment means for correcting the set gain of the second variable amplifier 35 is configured so that the amplitude of the detection signal becomes the reference amplitude.

The interface (I / F) 33 has a communication function with a host such as a PC.
The oscillator (DDS) 34 oscillates an excitation signal having a set frequency and supplies it to the first variable amplifier 35, and the oscillation frequency is set by the control means (DSP) 31.
The first variable amplifier 35 adjusts the oscillation amplitude of the oscillator (DDS) 34 to the excitation amplitude that matches the target measurement force, and supplies it to the excitation element 4, and the control means (DSP) 31 via the DA converter 39. To set the gain.
The second variable amplifier 36 converts the signal of the detecting element 5 that changes depending on the amplitude of the excitation signal into a signal having a constant amplitude that does not depend on the amplitude of the excitation signal. The second variable amplifier 36 controls the control means (DSP) 31 via the DA converter 39. To set the gain.
The peak hold circuit 37 converts the detection signal (AC signal) from the second variable amplifier 36 into a DC signal and supplies it to the AD converter 38.

The AD converter 38 converts the DC signal supplied from the peak hold circuit 37 into a digital signal and supplies it to the control means (DSP) 31.
The DA converter 39 outputs a coarse drive signal to the actuator drive circuit 41 and sets the gain of the first variable amplifier 35 and the second variable amplifier 36 based on a command from the control means (DSP) 31. . Further, a contact (touch) level in the contact detection circuit 40 is set.
The contact detection circuit 40 generates a latch signal (touch signal) for latching the counter 42 from the detection signal (DC signal) from the peak hold circuit 37 and the contact level set by the DA converter 39 and supplies the latch signal (touch signal) to the counter 42.
The actuator drive circuit 41 drives the drive actuator 11 by the coarse motion part drive signal from the DA converter 39.
The counter 42 counts the amount of displacement of the force sensor 1 in order to count the signal from the detector 12 and calculate the tip measurement position of the force sensor 1 and the probe drive control feedback.

<Measurement preparation>
In the above-described surface texture measuring device, in order to realize a constant measuring force, the relationship between the resonance frequency, attenuation factor, and measuring force of the stylus 3 under a reference temperature condition is measured in advance. Based on this information, the oscillation frequency of the oscillator (DDS) 34 and the gains of the first variable amplifier 35 and the second variable amplifier 36 corresponding to the desired measurement force are obtained.
These setting states are stored as setting data in the storage means 32 of the control means (DSP) 31, and the oscillation frequency of the oscillator (DDS) 34, the first variable amplifier 35, The gain of the second variable amplifier 36 is set. However, if the ambient temperature during measurement is different from the reference temperature,
(A) Resonance frequency changes (b) Since the relationship between the attenuation factor and the measuring force changes, the oscillator (DDS) 34, the first variable amplifier 35, and the second variable amplifier 36 are subjected to the following method before the measurement is started. Correct the setting status of.

<(1) Resonance frequency correction>
The excitation frequency is varied within a certain range centering on a preset reference frequency, the detection signal amplitude at that time is observed, and the resonance frequency is corrected to the frequency at which the detection signal amplitude is maximized.
2 and 3 are flowcharts showing an example of a program for searching for a resonance frequency with a minimum resolution of 1 [Hz] in a range from −1000 [Hz] to +1000 [Hz] around a reference frequency.
On the condition that i = 0 in step 1 (abbreviated as ST1) and i <21 in ST2, “reference frequency−1000 Hz + (i × 100 Hz)” is set in the oscillator (DDS) 34 and excited (ST3 ), DATA [i] = Amplification from detection element (including averaging process) (ST4), “i = i + 1” (ST5) is repeated. On the condition that i <21 is not satisfied in ST2 (i = 21), the maximum is searched from DATA [0] to DATA [20], and the frequency at that time is set as the peak frequency 1 as the primary peak frequency (ST6). ). In other words, in ST1 to ST6, the peak frequency 1 is searched in increments of 100 Hz from −1000 Hz to +1000 Hz around the reference frequency.

  Subsequently, on ST11, i = 0 and on condition that i <21 in ST12, “peak frequency 1-100 Hz + (i × 10 Hz)” is set in the oscillator (DDS) 34, and excitation (ST13), DATA [i] = Ensuring amplitude from detection element (including averaging process) (ST14), “i = i + 1” (ST15) is repeated. On the condition that i <21 is not satisfied in ST12 (i = 21), the maximum of DATA [0] to DATA [20] is searched, and the frequency at that time is set as the peak frequency 2 as the primary peak frequency (ST26). ). That is, in ST11 to ST16, the peak frequency 2 is searched in steps of −100 Hz to +100 Hz from the peak frequency 1 in increments of 10 Hz.

  Finally, on the condition that i = 0 in ST21 and i <21 in ST22, “peak frequency 2−10 Hz + (i × 1 Hz)” is set in the oscillator (DDS) 34, and excitation (ST23), DATA [i] = Amplification from detection element (including averaging process) (ST24) and “i = i + 1” (ST25) are repeated. On the condition that i <21 is not satisfied in ST22 (i = 21), the maximum of DATA [0] to DATA [20] is searched and the frequency at that time is set as the post-search frequency (ST26). In other words, in ST21 to ST26, the post-search frequency is searched from -10 Hz to +10 Hz in steps of 1 Hz with the peak frequency 2 as the center. By setting this as the setting frequency of the oscillator (DDS) 34, the resonance frequency can be corrected.

<(2) Excitation signal amplitude correction (first variable amplifier gain correction)>
In this system, in order to realize a constant measurement force, the relationship between the resonance frequency and attenuation rate of the stylus 3 under the reference temperature condition and the measurement force is measured in advance, and the desired measurement force is obtained based on the information. Excitation is performed at the corresponding resonance frequency. However, when the resonance frequency is searched for by the above-described method and the frequency deviates from the preset frequency, a difference occurs in the vibration energy of the stylus 3 and a difference occurs from the set measurement force. .
Therefore, a difference between the resonance frequency searched by the above-described method and a resonance frequency (resonance frequency under a reference temperature condition) obtained in advance is obtained, and the gain of the first variable amplifier 35 is determined according to the ratio of this difference. Adjust to adjust.

Specifically, this is performed as follows.
When the same excitation signal voltage is applied when the frequency is shifted, the characteristics of the force sensor 1 change as shown in FIG. In FIG.
f: characteristics of the force sensor when resonating at the reference frequency f,
+ Δf: characteristics of the force sensor when the frequency is shifted by + Δf with respect to the reference frequency f,
-Δf: The characteristic of the force sensor when the frequency is shifted by -Δf with respect to the reference frequency f.
In advance, the excitation signal voltage is changed from V1 to V10 at predetermined pitch intervals, and the graph shown in FIG. 4 is acquired. That is, a graph is obtained for each of the excitation signal voltages V1 to V10.
Further, when acquiring the characteristics of ± Δf, the temperature is acquired for a temperature outside the range of the probe's accuracy guarantee environment temperature, for example, 20 ± 10 ° C. (10 ° C., 20 ° C., 30 ° C.).
Here, for example, under the condition where the attenuation rate k (amplitude ratio of the sensor signal) is 85%, the measuring force at −Δf (100 μN in FIG. 4), the measuring force at f (150 μN in FIG. 4). ), A measuring force at + Δf (200 μN in the case of FIG. 4) is obtained. From these three data, the relationship between the measuring force and the frequency (for example, the slope of three approximate straight lines) is obtained for each excitation signal voltage. From this, the relationship between the excitation signal voltage, the change measurement force per unit frequency, and the standard measurement force (measurement force when the amplitude ratio is 85%) is obtained. That is, the following Table 1 is obtained.

Consider a case where the ambient temperature changes, for example, the frequency changes from f to f ′ as shown in FIG. As an example, it is assumed that the excitation signal voltage is V2 and ff ′ = − 400 Hz.
If the excitation signal voltage remains at V2, the measuring force becomes 150 μN to 130 μN.
Here, the following Table 2 is obtained from the second column of Table 1.

It can be seen that if the measurement force is set to 150 μN, the excitation signal voltage may be set between V2 and V3. The excitation signal voltages V2 to V3 can be obtained by approximation by linear interpolation or interpolation by multipoint approximation.
In this way, the influence due to the difference in frequency can be eliminated by correcting the amplitude of the excitation signal. Therefore, it is possible to correct measurement force fluctuations due to frequency fluctuations.

<(3) Detection Signal Amplitude Correction (Gain Correction of Second Variable Amplifier)>
In order to perform correction more accurately including fluctuations in characteristics due to temperature changes in the electric circuit, the gain of the second variable amplifier 36 is adjusted and corrected. The excitation frequency set by the oscillator (DDS) 34 is set to the frequency corrected by the resonance frequency search program, and the gain of the first variable amplifier 35 that determines the excitation signal amplitude is also set to the set value after correction.
The gain of the second variable amplifier 36 is configured as a circuit that can change the detection signal level in proportion. The gain of the second variable amplifier 36 is corrected by multiplying the current gain of the second variable amplifier 36 by a ratio between the current detection signal amplitude of the second variable amplifier 36 and a preset reference amplitude of the detection signal. As a result, the amplitude of the detection signal can be adjusted to a constant reference amplitude even when the ambient temperature changes, so that more accurate correction can be performed, including fluctuations in characteristics due to temperature changes in the electric circuit.
Further, the following process is performed to improve the correction accuracy.
(A) A sampling value is averaged for the purpose of removing random noise components.
(B) The correction process is repeated a plurality of times.

FIG. 6 is a flowchart illustrating an example of the detection signal amplitude correction program.
First, a standard set value is set for the gain of the second variable amplifier 36 (ST31), DATA OLD = amplitude from the detection element is secured (including averaging processing) (ST32), “i = 0” (ST33), and ST34. I <repetition count, the corrected gain of the second variable amplifier 36 = (the ratio of DATA OLD to the reference amplitude) × the current gain of the second variable amplifier 36 ”(ST35), DATA OLD = After securing (including averaging processing) (ST36) the amplitude from the detection element, the processing of “i = i + 1” (ST38) is repeated on the condition that DATA OLD = reference amplitude is not satisfied in ST37. The detection signal amplitude correction processing is terminated on condition that i <repetition count is not satisfied in ST34 and that DATA OLD = reference amplitude in ST37.

<(4) Resonance Frequency Correction and Signal Amplitude Correction Timing>
In the present invention, the main factor of the temperature change in question is the change in the ambient temperature of the environment in which the force sensor 1 is used. Since the change in the ambient temperature has a long time constant for change compared to the measurement time performed using the force sensor 1, it is possible to perform a more accurate measurement by performing the measurement before the start of the correction that is proposed this time. Is possible.
In addition, this correction method can be corrected at any time when the force sensor 1 is not in contact with the object to be measured, so when using a part program with a long measurement time, use a moving section that is not in contact with the object to be measured. It can also be corrected.

<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, (1) resonance frequency correction, (2) excitation signal amplitude correction (gain correction of the first variable amplifier), and (3) detection signal amplitude correction (gain correction of the second variable amplifier) are increased. (1) After correcting the resonance frequency, (2) Excitation signal amplitude correction (first variable amplifier gain correction) or (3) Detection signal amplitude correction (second variable amplifier gain correction) Good. Of course, it is more preferable to execute (2) and (3) after (1).

In the above embodiment, (2) in the excitation signal amplitude correction,
a) Prepare a table showing the relationship between the excitation signal voltage, the change measuring force per unit frequency, and the standard measuring force in advance.
b) calculating a change measuring force in each excitation signal voltage from the detected frequency change;
c) Adjust the change measurement force from the standard measurement force at each excitation signal voltage,
d) obtaining an excitation signal voltage capable of realizing the target measuring force;
Although the measurement force variation due to frequency variation was corrected in the procedure, (3) the detection signal amplitude correction can be performed in the same manner.

That means
a) A table representing the relationship between the detection signal amplitude ratio, the change measuring force per unit frequency, and the standard measuring force is prepared in advance.
b) Calculate the change measuring force at each amplitude ratio from the detected frequency change,
c) Adjust the change measurement force from the standard measurement force at each amplitude ratio,
d) Find the amplitude ratio that can achieve the target measuring force,
Even in the procedure, it is possible to perform correction more accurately including fluctuations in characteristics due to temperature changes in the electric circuit.

In addition, the method for keeping the measuring force constant with respect to the frequency correction is not limited to the method described in the above embodiment, and the following method may be used.
First, a detection signal from the detection element 4 is detected, and the frequency of the excitation signal is corrected to a frequency at which the amplitude of the detection signal is maximized (frequency correction step), whereby the frequency of the excitation signal is corrected. The attenuation rate of the detection signal may be corrected (attenuation rate correction step) so that the measurement force (measurement force that the stylus receives by contact with the object to be measured) becomes substantially constant. That is, as shown in FIG. 5, when the frequency changes, the measurement force changes at the same attenuation rate. Therefore, the attenuation rate is corrected so that the measurement force becomes the same.
In this way, even if the ambient temperature changes, the detection signal from the detection element is detected, and the frequency of the excitation signal is corrected to the frequency at which the amplitude of the detection signal is maximized. In addition, even if the frequency of the excitation signal is corrected, the attenuation rate of the amplitude of the detection signal is corrected so that the measurement force becomes substantially constant. It can be carried out.

In the above-described embodiment, the base 2 and the stylus 3 of the sensor 1 are integrally configured. 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.
In the above embodiment, the stylus 3 is vibrated in the axial direction. However, 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.

  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.

The block diagram which shows one Embodiment of the surface shape measuring apparatus which concerns on this invention. The flowchart which shows the procedure (ST1-16) of the resonance frequency search process of embodiment same as the above. The flowchart which shows the procedure (ST21-26) of the resonance frequency search process of embodiment same as the above. The figure which shows the characteristic of a force sensor when applying the same excitation signal voltage when frequency shifts in embodiment same as the above. The figure which shows the characteristic of a force sensor when ambient temperature changes in FIG. 4 and a reference frequency changes. The flowchart which shows the procedure of the detection signal amplitude correction | amendment of embodiment same as the above. 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. The figure which shows the relationship between the ambient temperature in which a force sensor is used, and a detection signal.

Explanation of symbols

1 ... Excitation force sensor,
DESCRIPTION OF SYMBOLS 3 ... Stylus 4 ... Excitation element 5 ... Detection element 10 ... Probe 30 ... Controller 31 ... Control means (frequency correction means, excitation gain adjustment means, detection gain adjustment means)
34. Oscillator (oscillation means)
35. First variable amplifier (vibration signal amplitude correcting means)
36. Second variable amplifier (detection signal amplitude correcting means)
Pi ... Excitation signal Qo ... Detection signal W ... Measurement object.

Claims (5)

A stylus having a contact portion at the tip, a vibration element for vibrating the stylus, a sensor having a detection element for detecting the vibration state of the stylus and outputting it as a detection signal, and relative movement for relatively moving the sensor and the object to be measured And a position detection means for outputting the measurement position of the measurement object by the sensor as measurement position information, the contact portion of the stylus is brought into contact with the surface of the measurement object, and a detection signal from the detection element is a set value. A surface texture measuring device for measuring the surface texture of the object to be measured from the measurement position information of the position detecting means when substantially matching
An oscillation means for oscillating and outputting an excitation signal of a set frequency;
An excitation signal amplitude correction unit that corrects the amplitude of the excitation signal from the oscillation unit according to a set gain and applies the correction signal to the excitation element of the sensor;
A frequency correction means for detecting a detection signal from the detection element and correcting the set frequency of the oscillation means to a frequency at which the amplitude of the detection signal is maximized;
And an excitation gain adjusting means for adjusting a set gain of the excitation signal amplitude correcting means according to a difference between a new set frequency newly set by the frequency correcting means and an old set frequency. Surface texture measuring device. A stylus having a contact portion at the tip, a vibration element that vibrates the stylus, a sensor having a detection element that detects a vibration state of the stylus and outputs it as a detection signal, and a relative movement that relatively moves the sensor and the object to be measured And a position detection means for outputting the measurement position of the measurement object by the sensor as measurement position information, the contact portion of the stylus is brought into contact with the surface of the measurement object, and a detection signal from the detection element is a set value. A surface texture measuring device for measuring the surface texture of the object to be measured from the measurement position information of the position detecting means when substantially matching
An oscillating means for oscillating a vibration signal of a set frequency and applying it to the vibration element of the sensor;
A frequency correction means for detecting a detection signal from the detection element and correcting the set frequency of the oscillation means to a frequency at which the amplitude of the detection signal is maximized;
Detection signal amplitude correction means for correcting and outputting the amplitude of the detection signal from the detection element according to a set gain;
Based on the ratio between the amplitude of the detection signal from the detection means and a preset reference amplitude, the detection gain adjustment for correcting the set gain of the detection signal amplitude correction means so that the amplitude of the detection signal becomes the reference amplitude And a surface texture measuring device. In the surface texture measuring device according to claim 2,
The detection gain adjustment means takes in the detection signal from the detection means, multiplies the ratio of the amplitude of the detection signal and the reference amplitude by the set gain of the detection signal amplitude correction means, and uses this to detect the detection signal. A surface texture measuring apparatus characterized by having a set gain after correction by an amplitude correcting means. In the surface texture measuring device according to any one of claims 1 to 3,
The frequency correction means sequentially sets a plurality of primary extraction frequencies obtained by extracting a predetermined range before and after the reference frequency at regular intervals as set frequencies in the oscillation means, and a primary peak having the largest amplitude of the detection signal. After obtaining the frequency, a plurality of secondary extraction frequencies obtained by extracting the primary extraction frequency range before and after the primary peak frequency at intervals smaller than the predetermined interval are sequentially set as set frequencies in the oscillation means. Then, the secondary peak frequency having the largest amplitude of the detection signal is obtained, and the secondary peak frequency or the third order obtained with a finer interval than the secondary extraction frequency with the secondary peak frequency as the center. The subsequent surface frequency measuring apparatus is characterized in that a subsequent peak frequency is set as a set frequency of the oscillating means. A sensor having a stylus having a contact portion at the tip, a vibration element that vibrates the stylus upon receiving a vibration signal, a detection element that detects a vibration state of the stylus and outputs it as a detection signal, and the sensor and the object to be measured A relative movement means for relatively moving, and a position detection means for outputting the measurement position of the measurement object by the sensor as measurement position information, the contact portion of the stylus is brought into contact with the surface of the measurement object, and from the detection element A surface property measuring method for capturing the measurement position information of the position detecting means when the attenuation of the detection signal of the sensor signal decreases to a preset attenuation rate, and measuring the surface property of the object to be measured from the measurement position information,
A frequency correction step of detecting a detection signal from the detection element and correcting the frequency of the excitation signal to a frequency at which the amplitude of the detection signal is maximized;
Attenuation rate correction step of correcting the attenuation rate of the detection signal so that the measurement force that the stylus receives by contact with the object to be measured becomes substantially constant when the frequency of the excitation signal is corrected by the frequency correction step. A surface texture measuring method comprising:

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