JP2008292233A - Surface property measurement device and surface property measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface property measurement device capable of correcting measured values based on it by simply finding the change of the length of a stylus changed by an ambient temperature in a short time. <P>SOLUTION: The surface property measurement device includes: a sensor 1 having a stylus, an excitation element 4 and a detection element 5; an actuator 11 for drive for relatively moving it to an object to be measured; a detector 12 for outputting a measurement position of the object to be measured by the sensor as measurement position information; an oscillator 34 given to the excitation element by oscillating the excitation signal of a set frequency; and a control means 31. The control means includes: a frequency correction means for correcting the set frequency of the oscillator in a frequency in which the amplitude of a detection signal from the detection element is maximum; a stylus length information acquisition means for acquiring length information of the stylus regarding the set frequency corrected by the frequency correction means as a resonance frequency; and a measurement position information correction means for correcting the measurement position information regarding the stylus length information acquired by the stylus length information acquisition means as a correction value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface texture measuring device and a surface texture measuring method. 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 that detects the surface of the object to be measured based on a minute displacement when 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.
Therefore, 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 determined using a driving actuator or the like so that the attenuation rate k (Ax / Ao) is always constant. If controlled, the shape and roughness of the workpiece W can be measured with a constant measuring force.

By the way, the shape measuring system using the force sensor 1 having the structure described above has the following problems.
Recently, the force sensor 1 has been reduced in size and increased in accuracy for the measurement of micro parts. However, when the temperature changes in the measurement environment, the stylus 3 thermally expands or contracts. The length change of the stylus 3 due to the contraction cannot be ignored in terms of measurement accuracy. For example, when considering the linear expansion coefficient of an iron-based stylus, the length change of the stylus is on the order of 10 to the minus fifth power. If the length of the stylus is 100 mm, it becomes 1 μm.
As a method for solving this, a method is known in which a stylus is brought into contact with a master ball or the like fixed on spatial coordinates, the master ball is measured, and the tip coordinate of the stylus is corrected from the measured value at this time. (For example, refer to Patent Document 1).

JP 2005-181293 A

  However, in the method of measuring the master ball by bringing the stylus into contact with the master ball and correcting the tip coordinate of the stylus from the measured value, it is necessary to prepare the master ball separately, and the measurement takes time and effort. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide a surface texture measuring device that can easily and quickly obtain stylus length information that changes with temperature, and that can realize high-accuracy measurement by correcting measurement values based on this information. The object is to provide a surface texture 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. Oscillating means to be applied to the exciting element, and a detection signal from the detecting element is detected, and the set frequency of the oscillating means is set to a frequency at which the amplitude of the detection signal is maximized. Resonance frequency correction means for correction, stylus length information acquisition means for acquiring the stylus length information using the set frequency corrected by the resonance frequency correction means as a resonance frequency, and the stylus length information acquisition means And measuring position information correcting means for correcting the measuring position information of the position detecting means using the stylus length information as a correction value.

According to this configuration, 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 stylus thermally expands or contracts, and the stylus length changes. Then, the position of the contact portion where the stylus contacts the object to be measured changes, resulting in a measurement error.
In the present invention, since the frequency correction means is provided, for example, the detection signal from the detection element is detected immediately before the start of measurement, 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. Set as. If the frequency at which the amplitude of the detection signal is maximum, that is, the resonance frequency is obtained, stylus length information can be obtained from the resonance frequency.
That is, in the present invention, since the resonance frequency is obtained from the detection signal and the stylus length information is obtained based on the resonance frequency, the stylus length change that varies depending on the ambient temperature is compared with the conventional method of measuring the master ball. It can be obtained simply and in a short time. In addition, since the measurement position information of the position detector can be corrected using the stylus length information as a correction value, measurement errors based on the stylus length change due to temperature changes can be reduced.

  In particular, the present invention detects a component that vibrates the stylus and a vibration state of the stylus and outputs it as a detection signal in a measurement principle in which the stylus is vibrated and the contact point of the object to be measured is obtained from the change of the vibration state. Since the resonance frequency of the stylus can be detected by using the components, that is, the oscillation means, the excitation element, the detection element, etc., there is no need to separately provide a device for detecting the resonance frequency, and a device configuration used for measurement is provided. Can be used as is. Therefore, there exists an advantage which can be comprised economically.

  In the surface texture measuring device of the present invention, the surface texture measuring device has frequency information detecting means for obtaining resonance frequency information of the stylus based on a detection signal from the detecting element, and the stylus length information acquiring means is provided by the frequency information detecting means. The length information of the stylus may be obtained from the frequency information of this or the phase difference information between the frequency information and the excitation signal frequency information.

ただし、ｆ：スタイラスの共振周波数
λ：モードの次数、
Ｅ：スタイラスのヤング率
ｒ：スタイラスの半径
ｗ：スタイラスの重さ
Ｌ_０：基準温度でのスタイラスの長さ In the surface texture measuring apparatus of the present invention, it is preferable that the stylus length information acquisition unit acquires the stylus length L information from the following equation.

Where f: resonance frequency of the stylus
λ: mode order,
E: Stylus Young's modulus
r: radius of the stylus
w: Weight of stylus
L ₀ : length of the stylus at the reference temperature

  According to this configuration, since the stylus length information can be obtained from the above calculation formula, if the stylus parameters (λ, E, r, w) are obtained in advance, the stylus can be easily and quickly obtained. Is obtained.

The surface texture measuring method of the present invention includes 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 the sensor and the target. 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 property measurement method for measuring the surface property of an object to be measured from measurement position information of the position detection means when a detection signal from a detection element substantially matches a set value, and oscillates an excitation signal of a set frequency. A vibration signal applying step to be applied to the vibration element, and a detection signal from the detection element is detected, and the oscillation means is set at a frequency at which the amplitude of the detection signal is maximized. A resonance frequency correction step for correcting the frequency, a stylus length information acquisition step for acquiring the stylus length information using the set frequency corrected in the resonance frequency correction step as a resonance frequency, and the stylus length information acquisition step. And a measurement position information correction step of correcting the measurement position information of the position detection means using the obtained stylus length information as a correction value.
According to this invention, the same effect as the surface texture measuring device can be expected.

In the surface texture measurement method of the present invention, it is preferable that the resonance frequency correction step and the stylus length information acquisition step are executed immediately before the start of measurement or immediately after the start of measurement.
According to this configuration, since the resonance frequency correction step and the stylus length information acquisition step are executed immediately before the start of measurement or immediately after the start of measurement, the stylus length information is obtained in an environment closest to the temperature at the time of measurement. And errors due to temperature changes can be further reduced.

<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 FIG. 1, the same components as those in FIG. 7 described above 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 shown in FIG. 2, 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 workpiece W (advancement / retraction), and the drive actuator. 11 includes 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 by 11 (that is, measurement position information of an object to be measured by the force sensor 1). The force sensor 1 has the same structure as that shown in FIG.

  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, peak hold circuit 37, AD converter (Analog Digital Converter) 38, DA converter (Digital Analog Converter) 39, contact detection circuit 40, actuator drive circuit 41, and counter 42. It is configured.

  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 corrects the set frequency of the oscillator 34 to a frequency at which the amplitude of the detection signal becomes maximum, and this resonance frequency correction means. The stylus length information acquisition means for acquiring the length information of the stylus 3 based on the new set frequency corrected by the stylus length information acquisition means as the position detection means using the stylus length information acquired by the stylus length information acquisition means as a correction value. A measurement position information correcting unit for correcting the measurement position information of the detector 12 is configured.

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 excitation element 4, and the oscillation frequency is set by the control means (DSP) 31.
The peak hold circuit 37 converts the detection signal (AC signal) from the detection element 5 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 drive signal to the actuator drive circuit 41 and sets the contact (touch) level in the contact detection circuit 40 based on a command from the control means (DSP) 31.

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 applies the latch signal (touch signal) to the counter 42. .
The actuator drive circuit 41 drives the drive actuator 11 with a 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 work>
In the measurement, processing is performed according to the flowchart shown in FIG.
First, if the environmental temperature at the time of measurement is different from the reference temperature, the length of the stylus 3 changes and causes a measurement error. Therefore, prior to the measurement, the resonance frequency correction step (ST1) and stylus length information acquisition are performed. Step (ST2) is performed. That is, after correcting the frequency (resonance frequency) set in the oscillator 34 in the resonance frequency correction step, the length of the stylus 3 is obtained from the corrected resonance frequency in the stylus length information acquisition step.
Thereafter, in the measurement step (ST3), after measuring the object to be measured, the measurement position information obtained in the measurement step is corrected using the stylus length information as a correction value (measurement position information correction step). . For example, the stylus length information is corrected with respect to the coordinate value in the same axial direction as the stylus length direction in the measurement position information obtained in the measurement process.

Here, the relationship between the length of the stylus and the resonance frequency will be described.
First, L: length of the stylus (distance from the fulcrum to the contact portion)
L ₀ : length of the stylus at the reference temperature (here 20 ° C.)
(In Fig. 5, about 3mm)
ΔT: temperature change r: radius of the stylus (about 10 μm in FIG. 5)
λ: Order of mode E: Young's modulus of stylus ρ: Density of stylus f: Resonance frequency of stylus w: Weight of stylus α: Linear expansion coefficient of stylus β: Volume expansion coefficient of stylus 1) to (10) are obtained.

Expression (5) is an expression obtained by substituting Expression (4) into Expression (3).
Expression (6) is an expression obtained by substituting Expressions (5) and (2) into Expression (1).
Equation (7) is an equation representing the constant K in Equation (6),
Expression (8) is an expression obtained by rewriting Expression (2).
Equation (9) is an equation obtained by substituting Equation (8) into Equation (6).
Expression (10) is an expression representing the relationship between the stylus length L and the resonance frequency f.
Therefore, in Equation (10), constants K and L ₀ (the stylus length at the reference temperature) are known, and thus the stylus length L can be obtained by obtaining the resonance frequency f of the stylus.

In order to obtain the resonance frequency f of the stylus, for example, the processing of the flowchart shown in FIG. 4 is performed.
In ST 11, the frequency of the vibration signal is changed by a preset frequency, this changed frequency is set in the oscillator (DDS) 34, and the stylus 3 is vibrated via the vibration element 4.
In ST12, the detection signal from the detection element 5 is captured and the amplitude of the detection signal is detected.
In ST13, it is determined whether the amplitude of the detected detection signal is the maximum among the amplitudes detected so far. If not, the process proceeds to ST15. If it is the maximum, the process proceeds to ST14.
In ST14, the corrected frequency of the excitation signal is stored.
In ST15, it is determined whether or not the process is finished. If not, the processes of ST11 to ST14 are repeated. If completed, proceed to ST16.
In ST16, the stored frequency (resonance frequency) is set in the oscillator (DDS) 34, and the stylus 3 is vibrated via the vibration element 4.

  Therefore, the resonance frequency of the stylus 3 whose length has changed can be obtained from the frequency stored in ST14. Then, the length L of the stylus 3 can be obtained by substituting the obtained resonance frequency into the equation (10).

<Effect of embodiment>
(1) In order to obtain the resonance frequency from the detection signal and obtain the length information of the stylus 3 based on the resonance frequency, the length change of the stylus 3 that changes depending on the ambient temperature, compared to the conventional method of measuring the master ball, It can be obtained easily and in a short time. Further, since the measurement position information of the position detection means can be corrected using the length information of the stylus 3 as a correction value, measurement errors based on the stylus length change due to temperature change can be reduced.

(2) Further, in the measurement principle for obtaining the contact point of the object to be measured from the change of the vibration state of the stylus 3, the component that vibrates the stylus 3 and the vibration state of the stylus 3 are detected and used as a detection signal. Since it is possible to detect the resonance frequency of the stylus 3 using the output components, that is, the oscillator 34, the vibration element 4, the detection element 5, and the like, it is not necessary to separately provide a device for detecting the resonance frequency, and it is used for measurement. Can be used as it is. Therefore, there exists an advantage which can be comprised economically.

(3) Since the length of the stylus 3 is obtained from the equation (10), if the parameters (λ, E, r, w) of the stylus 3 are obtained in advance, it is easy and quick. The length information of the stylus 3 is obtained.
(4) Further, since the resonance frequency correction step and the stylus length information acquisition step are executed immediately before the start of measurement, the length information of the stylus 3 is obtained in an environment closest to the temperature at the time of measurement. And errors due to temperature changes can be further reduced.

<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-described embodiment, the processing of the flowchart shown in FIG. 4 (peak scan method) is performed every time when the resonance frequency f of the stylus 3 is obtained, but first, the oscillator is processed by the processing of the flowchart shown in FIG. After the resonance frequency of the stylus 3 is set in the (DDS) 34, the resonance frequency of the stylus 3 may be obtained by the method shown in FIG.

In FIG. 5, a synchronous detection circuit 35 is added as a frequency information detection means for synchronously detecting a detection signal from the detection element 5 to extract frequency information and supplying this frequency information to the control means (DSP) 31.
According to this configuration, when the detection signal from the detection element 5 is synchronously detected in the synchronous detection circuit 35 and the frequency information is supplied to the control means (DSP) 31, the control means (DSP) 31 The length information of the stylus 3 can be obtained by substituting the information into the equation (10).

In FIG. 6, in addition to the synchronous detection circuit 35, the phase of the frequency information from the synchronous detection circuit 35 and the excitation signal frequency information from the oscillator 34 are compared, and this phase difference information (frequency change information) is controlled by control means ( DSP) 31 is provided with a phase comparator 36.
According to this configuration, when the phase difference information (frequency change information) is given to the control means (DSP) 31 by the synchronous detection circuit 35 and the phase comparator 36, the control means (DSP) 31 Change information) can be obtained as a change in the length of the stylus 3.

  In the above-described embodiment, the length L of the stylus 3 is obtained using the equation (10). However, the relationship between the resonance frequency and the length L of the stylus 3 is experimentally obtained, and this is associated with the table. The length L corresponding to the obtained resonance frequency may be read from the table, and the length L of the stylus 3 may be acquired.

  In the above-described embodiment, the resonance frequency changing step and the stylus length information acquiring step are performed before the measurement is started. Since it is possible, it may be performed immediately after the end of the measurement process, or may be performed using a moving section that is not in contact with the object to be measured.

In the above-described embodiment, 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.
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 figure which shows the probe of embodiment same as the above. The flowchart which shows the measurement procedure of embodiment same as the above. The flowchart which shows the procedure of the resonance frequency acquisition process of embodiment same as the above. The block diagram which shows the modification of the surface texture measuring apparatus which concerns on this invention. The block diagram which shows the other modification of the surface texture measuring apparatus which concerns on this invention. 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.

Explanation of symbols

1 ... Excitation force sensor,
3 ... stylus,
4 ... Excitation element,
5 ... detecting element,
10 ... probe,
30 ... Controller,
31 ... Control means (resonance frequency correction means, stylus length information acquisition means,
Measurement value information correction means),
34. Oscillator (oscillation means),
35 ... Synchronous detection circuit (frequency information detection means),
Pi: Excitation signal,
Qo: Detection signal,
W: Object to be measured.

Claims (5)

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 an excitation signal having a set frequency and applying the oscillation signal to the excitation element;
Resonance 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;
Stylus length information acquisition means for acquiring the stylus length information using the set frequency corrected by the resonance frequency correction means as a resonance frequency;
A surface texture measuring device, comprising: measurement position information correcting means for correcting measurement position information of the position detecting means using the stylus length information acquired by the stylus length information acquiring means as a correction value. In the surface texture measuring apparatus according to claim 1,
Having frequency information detection means for obtaining resonance frequency information of the stylus based on a detection signal from the detection element;
The stylus length information acquisition means obtains the stylus length information from the frequency information from the frequency information detection means or phase difference information between the frequency information and the vibration signal frequency information. apparatus. In the surface texture measuring apparatus according to claim 1,
The stylus length information acquisition means acquires the stylus length L information from the following equation.

Where f: resonance frequency of the stylus
λ: Mode order
E: Stylus Young's modulus
r: radius of the stylus
w: Weight of stylus
L ₀ : length of the stylus at the reference temperature 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. Is a surface property measurement method for measuring the surface property of the object to be measured from the measurement position information of the position detection means when substantially matching,
An excitation signal applying step of oscillating an excitation signal of a set frequency and giving the excitation signal to the excitation element;
A resonance frequency correction step of 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;
A stylus length information acquisition step of acquiring the stylus length information using the set frequency corrected by the resonance frequency correction step as a resonance frequency;
A surface property measurement method comprising: a measurement position information correction step of correcting measurement position information of the position detection means using the stylus length information acquired in the stylus length information acquisition step as a correction value. In the surface texture measuring method according to claim 4,
The method for measuring surface properties, wherein the frequency correction step and the stylus length information acquisition step are executed immediately before the start of measurement or immediately after the start of measurement.

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