JP2005106549A - Profile measuring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a desired contact load without waiting for the attenuation of vibration of a probe vibrating at a mechanical resonance frequency. <P>SOLUTION: A processor 119 lowers a probe toward a surface to be measured without waiting for attenuation of vibration of a probe vibrating at mechanical resonance frequency, decelerates the lowering of the probe on the basis of the output of a comparator 108 for comparing a signal converted from frequency included in the output signal of a D/A converter 106 corresponding to the displacement of the probe, to a voltage, with a specific voltage 109. The processor also initiates fine control of contact pressure of the probe based on the output of a comparator 110 for comparing the signal converted from the frequency to the voltage with a specific voltage 111, terminates the lowering of the probe based on a comparator 117 comparing a signal having extracted a direct current component included in the output signal of the D/A converter 106 and a specific voltage 118 and initiates the measurement. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a shape measuring device that measures the shape of a surface to be measured in an optical element, a mold or the like using a contact probe.

  Conventionally, in order to measure the shape of a surface to be measured in an optical element, a mold or the like, a shape measuring apparatus using a contact probe has been developed.

  FIG. 5A is a longitudinal sectional view showing an example of a contact probe used in the shape measuring apparatus.

  In the figure, a true sphere 1 that comes into contact with the object to be measured is attached to the tip of the stylus 2. A displacement meter 3 is disposed at a position facing the upper end of the stylus 2 as a detection unit for detecting the displacement of the stylus 2.

  The stylus 2 is supported in a non-contact state in the housing 4 by a static pressure air bearing 5 supplied from an air supply hole 6. Here, the stylus 2 is restrained in the lateral direction and can be displaced in the vertical direction without sliding resistance. At the upper end of the stylus 2, there is a spring 7 that supports the stylus 2 and is fixed to the housing 4.

  Next, the basic operation of the shape measuring apparatus using the contact probe will be described.

  When the true sphere 1 is not in contact with the surface to be measured, the weight of the stylus 2 and the true sphere 1 and the spring force of the spring 7 are balanced. This is the initial position.

  From this state, the shape of the surface to be measured (not shown) is measured. First, the true sphere 1 at the tip of the stylus 2 is brought into contact with the surface to be measured. As a result, the stylus 2 moves to a position where the spring force by the spring 7 and the reaction force from the surface to be measured are balanced. Therefore, the displacement meter 3 obtains a displacement when the stylus 2 moves from the initial position to the position. By controlling the vertical position of the contact probe so that the amount of displacement is constant, the contact load of the stylus 2 can be controlled to a constant amount. Thus, the shape of the surface to be measured can be measured by scanning the surface to be measured while keeping the contact load of the stylus 2 constant.

  In the contact probe of the principle as described above, the stylus 2 is likely to vibrate at the mechanical resonance frequency. In particular, in a contact probe before the start of measurement, the true sphere 1 is not in contact with the surface to be measured and is very likely to resonate. On the other hand, in order to accurately measure the shape of the surface to be measured, the contact load of the stylus 2 needs to be a desired contact load. In order to obtain a desired contact load, it is necessary to accurately grasp the initial position of the stylus 2. However, there is a problem that the initial position of the stylus 2 cannot be detected when the stylus 2 is vibrating at the mechanical resonance frequency.

  Various shape measuring devices that solve the problem of such a contact probe have been proposed. For example, Patent Document 1 discloses one of such shape measuring devices.

  This shape measuring apparatus also detects the displacement of the stylus 2 located at the initial position by the displacement meter 3 in the structure of FIG. However, as shown in FIG. 5B, this shape measuring apparatus has arithmetic processing means 8 that performs arithmetic processing on this detection signal.

  FIG. 5C is a graph illustrating the sampling period of the output signal of the displacement meter 3. Here, the displacement dz of the stylus 2 is sampled at a predetermined sampling time ts. 6A and 6B show an example in which an averaging process is used as an arithmetic process for the output signal of the displacement meter 3 as shown in FIG. 5C. That is, FIG. 6A shows a process in which the amplitude of vibration of the displacement dz attenuates with time. FIG. 6B shows a result obtained by sampling such a displacement dz at a predetermined sampling time ts and performing a moving average process a predetermined number of times m. The initial value of the stylus 2 after a predetermined time (about 4 seconds) is shown in FIG. The position.

  7A and 7B show an example in which a low-pass filter is used as a calculation process for the output signal of the displacement meter 3 as shown in FIG. 5C. That is, analog processing or digital processing is used as a low-pass filter for the displacement dz whose amplitude attenuates with time as shown in FIG. The data after filtering in that case is shown in FIG. Here, the initial position of the stylus 2 is a predetermined time (about 3 seconds).

FIG. 8 shows an example in which the unbiased variance σ ² is obtained as a calculation process for the displacement dz shown in FIG. When the vibration of the stylus 2 goes in the convergence direction, the unbiased variance σ ² decreases. The initial position is when the unbiased variance σ ² becomes smaller than a predetermined value.
JP 2003-97940 A

  In any of the conventional techniques shown in FIGS. 6A to 8, the vibration of the stylus 2 that vibrates at the mechanical resonance frequency is detected by the displacement meter 3 and is calculated by the arithmetic processing means 8. . By doing so, it is determined that the vibration has attenuated and converged, and the position of the stylus 2 at this time is regarded as the initial position. Therefore, in order to obtain a desired contact load of the stylus 2, it is necessary to wait until the vibration of the stylus 2 is attenuated and converges and the initial position of the stylus 2 can be grasped.

  The present invention has been made in view of the above points, and can obtain a desired stylus contact load without waiting for the vibration of the stylus vibrating at the mechanical resonance frequency to attenuate. An object is to provide a shape measuring apparatus.

In order to achieve the above object, a shape measuring apparatus according to the present invention comprises:
In a shape measuring device comprising a stylus and a detection unit for detecting the displacement of the stylus,
An electrical conversion circuit for converting an output signal of the detection unit into an electrical signal;
A frequency / voltage conversion circuit that converts a frequency contained in the output signal of the electrical conversion circuit into a voltage;
A first comparator for comparing the output signal of the frequency / voltage conversion circuit with a first predetermined voltage;
A second comparator for comparing the output signal of the frequency / voltage conversion circuit with a second predetermined voltage;
A DC extraction circuit for extracting a DC component contained in the output signal of the electrical conversion circuit;
A third comparator for comparing the output signal of the DC extraction circuit with a third predetermined voltage;
A processing unit for determining an output of the first to third comparators;
Comprising
The processor is
The stylus is lowered toward the surface to be measured (without waiting for the vibration of the stylus vibrating at the mechanical resonance frequency to attenuate),
Based on the output of the first comparator, the descending of the stylus is decelerated,
Based on the output of the second comparator, fine adjustment of the contact pressure (i.e., the vertical position) of the stylus is started,
Based on the output of the third comparator, the descent of the stylus is stopped and measurement is started.
It is characterized by that.

  ADVANTAGE OF THE INVENTION According to this invention, the shape measuring apparatus which can obtain a desired contact load can be provided, without waiting for the vibration of the stylus vibrating at the mechanical resonance frequency to attenuate.

  Therefore, the waiting time until the actual measurement is started becomes unnecessary, and the total time until the measurement is completed can be shortened.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 3 is a conceptual diagram showing a contact probe used in the shape measuring apparatus according to this embodiment and a processing circuit for processing an output signal of a displacement meter of the probe. Since the structure of the contact probe is the same as that described in the background art, its description is omitted.

  In FIG. 3, a displacement meter 3 is a detection unit that detects the displacement of the stylus 2 in the contact probe. The voltage conversion circuit is a circuit that converts the output signal of the displacement meter 3.

  The output terminal of the displacement meter 3 is connected to the input terminal of the voltage conversion circuit 10. The output terminal of the voltage conversion circuit 10 is connected to the F / V converter 11. Here, the F / V converter 11 converts the frequency included in the output signal (b) of the voltage conversion circuit 10 into a voltage. The output terminal of the F / V converter 11 is connected to one input terminal of a comparator 12 as a first comparator and one input terminal of a comparator 13 as a second comparator. . Here, a first predetermined voltage (c) is applied to the other input terminal of the comparator 12. Therefore, the comparator 12 compares the output signal (d) of the F / V converter 11 with the first predetermined voltage (c). A second predetermined voltage (f) is applied to the other input terminal of the comparator 13. Therefore, the comparator 13 compares the output signal (d) of the F / V converter 11 with the second predetermined voltage (f).

  On the other hand, the output terminal of the voltage conversion circuit 10 is further connected to a DC extraction circuit 14. The DC extraction circuit 14 extracts a DC component contained in the output signal (b) of the voltage conversion circuit 10. Here, the DC extraction circuit 14 includes a DC component removing unit 15 and a subtracter 16. Among these, the DC component removing unit 15 removes the DC component of the output signal (b) of the voltage conversion circuit 10. The subtractor 16 outputs a difference between the output signal (h) of the DC component removal unit 15 and the output signal (b) of the voltage conversion circuit 10. The output terminal of the DC extraction circuit 14, that is, the output terminal of the subtractor 16 is connected to one input terminal of a comparator 17 as a third comparator. Here, a third predetermined voltage (j) is applied to the other input terminal of the comparator 17. Therefore, the comparator 17 compares the output signal of the DC extraction circuit 14, that is, the output signal (i) of the subtractor 16 with the third predetermined voltage (j).

  FIG. 4 is a timing chart showing the state of each output signal of the processing circuit shown in FIG. Here, a process until a contact probe is brought into contact with a surface to be measured and a desired contact load is obtained is shown. 3 are the same as the symbols (b), (c),... In FIG. Moreover, in FIG. 4, as a process until obtaining a desired contact load, there are the following (A) to (C). That is, a process (a) in which a contact type probe that is not in contact with the surface to be measured is lowered at a constant speed by a drive unit (not shown) until the true sphere 1 of the stylus 2 contacts the surface to be measured. The contact load is controlled to be constant from the time (t1) from when the true sphere 1 contacts the surface to be measured until the desired contact load is reached (b) and from the time (t2) when the desired contact load is reached. This is the process (c) of shifting to servo operation.

  First, prior to the measurement, the contact probe is slowly moved by a driving unit (not shown) to bring the true sphere 1 into contact with the surface to be measured from the non-contact state. Subsequently, a load is applied to the true sphere 1, and the relationship of the stylus pressure corresponding to the displacement of the contact probe is obtained in advance.

  Thereafter, the drive probe (not shown) returns the contact probe to a state where it is not in contact with the surface to be measured (non-contact state). At this time, the stylus vibrates at the mechanical resonance frequency.

  In this embodiment, the contact-type probe is lowered at a constant speed without waiting for the vibration of the stylus to attenuate.

  At this time, the displacement of the output signal of the displacement meter 3 of the contact probe is converted into a voltage by the voltage conversion circuit 10. In the process (a) of descending at a constant speed, the probe stylus 2 vibrates at the mechanical resonance frequency because the force of the spring 7 is very small. Assuming that the output signal of the voltage conversion circuit 10 in the initial position (no vibration) is 0V, the waveform of the signal (b) in the state of oscillating at the mechanical resonance frequency oscillates around 0V.

  When the measured surface and the true sphere 1 come into contact (t1), the true sphere 1 elastically collides with the measured surface, so that the stylus 2 receives an external force. Therefore, a harmonic component signal is superimposed on the output signal (b) of the voltage conversion circuit 10.

  The frequency component included in the output signal (b) of the voltage conversion circuit 10 is converted into a voltage by the F / V converter 11. As the output signal (d) of the F / V converter 11, a voltage corresponding to the mechanical resonance frequency of the stylus 2 is output in the process (A). When the true sphere 1 comes into contact with the measurement surface (t1), a high frequency component is generated in the output signal (b). This harmonic component appears as a large voltage change in the output signal (d) of the F / V converter 11 (voltage change at t1). Therefore, the voltage of the output signal (d) is compared with a predetermined voltage (first predetermined voltage (c)) using the comparator 12, and the output voltage of the F / V converter 11 is compared with the predetermined voltage. By detecting that it has become larger than (c), it is possible to instantaneously detect when the true sphere 1 contacts the surface to be measured.

  Thus, after the constant velocity descent starts, the output signal (e) of the comparator 12 is monitored, and it is detected by the output signal (e) of the comparator 12 that the true sphere 1 is in contact with the surface to be measured. If so, the drive speed of the contact probe is reduced.

The maximum speed at which the contact probe is lowered at a constant speed is greater than the distance that the contact probe moves from the time when the true sphere 1 contacts the surface to be measured to the time when the descent speed is reduced and stopped. The speed must be such that 1/2 of the distance (stroke) that the needle 2 can move in the housing 4 becomes longer. For example, if the descending speed of the contact probe changes from the initial speed V ₀ to the speed V,
V <2-V ₀ ² = 2aS
Where a: acceleration of the probe
S: The relationship of the probe moving distance is established. When the stroke of the stylus 2 is x, when the contact probe stops (when V = 0), the movement amount of the stylus 2 is ½ or less of the stroke.
−V ₀ ² ≦ 2 × a × (x / 2) (Formula 1)
Need to be satisfied. Therefore, the contact type probe needs to decelerate at an acceleration of a ≧ (−V ₀ ² ) / x.

  In a period during which the acceleration is decelerated, that is, in the process (A), since the true sphere 1 is in contact with the surface to be measured, the mechanical resonance frequency changes. Furthermore, since it is in contact with the surface to be measured, the vibration of the stylus 2 is rapidly attenuated. Therefore, the output signal (b) of the voltage conversion circuit 10 is similarly attenuated. At this time, the output voltage (d) of the F / V converter 11 also changes so as to gradually decrease as shown in the process (A). Then, when the resonance frequency becomes small and out of the operation range, the output is stopped (c). Therefore, the output voltage (d) of the F / V converter 11 is compared with a predetermined voltage (second predetermined voltage (f)) using the comparator 13, and the output voltage of the F / V converter 11 is By detecting that the voltage has become equal to or lower than the predetermined voltage, it can be confirmed that the stylus 2 is stable.

  Thus, after starting the deceleration, the output signal (g) of the comparator 13 is monitored, and it is waited that the stylus 2 can be confirmed to be stable by the output signal (g) of the comparator 13. .

  On the other hand, in the DC extraction circuit 14 that extracts only the DC component contained in the output signal (b) of the voltage conversion circuit 10, the DC component of the output signal (b) of the voltage conversion circuit 10 is converted by the DC component removal unit 15. Removed. The subtracter 16 obtains the difference between the output signal (h) of the DC component removal unit 15 and the output signal (b) of the voltage conversion circuit 10. The output signal of the subtracter 16 becomes the output signal (i) of the DC extraction circuit 14. Thus, the output signal (i) is a signal of only a direct current component included in the signal (b) obtained by converting the displacement of the stylus 2 by the voltage conversion circuit 10.

  In the process (A), since the stylus 2 is displaced in the direction approaching the displacement meter 3, the output signal (i) of the DC extraction circuit 14 changes. Therefore, the comparator 17 compares the output signal (i) of the DC extraction circuit 14 with a predetermined voltage (third predetermined voltage (j)). Here, the predetermined voltage (j) corresponds to the output voltage of the voltage conversion circuit 10 that provides a desired contact load. As described above, this predetermined voltage (j) is obtained by changing the distance between the stylus 2 and the surface to be measured in advance from the non-contact state to the slow contact state prior to the main measurement operation. The value obtained by measuring the relationship between the contact load and the output voltage of the voltage conversion circuit 10 is used.

  Thus, the output signal (k) of the comparator 17 is monitored, and when the voltage (i) which is the output signal of the subtractor 16 matches the predetermined voltage (j), a desired contact load is obtained. Then, the descent of the contact type probe is stopped.

  Then, in the subsequent process (c), a servo operation is performed to drive the contact probe in the vertical direction so that the contact load is constant.

  Next, the shape measuring apparatus according to the present embodiment will be described with reference to FIG. The shape measuring apparatus according to the present embodiment includes a contact probe as shown in FIG. 3 and a processing circuit that processes an output signal of a displacement meter of the probe.

  In FIG. 1, the configuration of the contact probe 104 is basically the same as that of the contact probe of FIG. 3, so only the changed part will be described. In the contact probe 104, a linear scale 100 is attached to the stylus instead of the displacement meter 3 of FIG. 3, and an encoder head 101 that reads the displacement of the linear scale 100 is provided in the probe 104. Further, instead of the voltage conversion circuit 10 of FIG. 3, a counter circuit 105 for digitizing the output signal of the encoder head 101 and a D / A converter 106 for converting this output into a voltage are provided. The F / V conversion circuit 107 that processes the output signal of the D / A converter 106, the comparator 108, and the comparator 110 are the same as the F / V converter 11 and the comparators 12 and 13 shown in FIG. The comparator 108 receives a predetermined voltage 109 corresponding to the first predetermined voltage (c), and the comparator 110 receives a predetermined voltage 111 corresponding to the second predetermined voltage (f). Has been.

  In addition, a predetermined unit and a subtracter 16 are provided in order to extract a DC component included in the output signal of the D / A converter 106. The predetermined unit corresponds to the DC component removing unit in FIG. 3 and includes a capacitor 113, a resistor 114, and buffers 112 and 115. The subtraction circuit 116 obtains the output signal of this unit and the difference signal of the D / A converter 106, and corresponds to the subtracter 16 in FIG. Both are configured using OP amplifiers. Further, a comparator 117 is equivalent to the comparator 17 of FIG. The comparator 117 receives the output signal of the subtraction circuit 116 and a predetermined voltage 118 corresponding to the third predetermined voltage (j).

  Then, the output signals (e), (g), (k) of the three comparators 108, 110, 117 and the output signal (i) of the subtraction circuit 116 are supplied to the processing unit 119. ing. As this processing unit 119, a dedicated processing device may be incorporated, or a personal computer or the like may be used.

  On the other hand, the contact probe 104 is fixed to a Z-axis stage 103 that moves in the vertical direction. The linear scale 102 of the Z-axis stage 103 is provided to manage the movement amount of the Z-axis stage 103.

  Further, the surface to be measured can be freely moved using an XY stage (not shown). The XY stage has a linear encoder (not shown), and positioning control is performed using the output of the linear encoder.

  The X and Y coordinates of the XY stage moving on the surface to be measured and the Z coordinate of the Z axis stage 103 are measured by an X axis laser length measuring device, a Y axis laser length measuring device, and a Z axis laser length measuring device (not shown). The The data of each length measuring device is simultaneously captured by the processing unit 119 and stored as shape data.

  The operation of the shape measuring apparatus having such a configuration will be described with reference to the flowchart of FIG.

  First, the contact probe 104 is slowly brought into a contact state from a non-contact state, and a load is applied to the contact probe 104. Then, a relationship (correlation between the contact load and the voltage value) with the voltage value of the D / A converter 106 corresponding to the displacement of the stylus (relative displacement between the linear scale 100 and the encoder head 101) is obtained in advance. deep.

  Thereafter, before the measurement of the shape of the surface to be measured is started, the contact probe 104 is returned to the position above the surface to be measured so as to be positioned in a non-contact state.

  Then, the processing unit 119 controls a driving unit (not shown) to lower the contact probe 104 that is in a non-contact state with the surface to be measured at a constant speed (step S1). At this time, the lowering of the contact probe 104 is performed without waiting for the vibration of the stylus vibrating at the mechanical resonance frequency to attenuate.

  The contact of the true sphere at the tip of the contact probe 104 with the surface to be measured is detected by comparing the output signal of the F / V conversion circuit 107 with a predetermined voltage 109. That is, the determination can be made using the output signal (e) of the comparator 108. Here, the output signal (e) of the comparator 108 corresponds to the signal waveform (e) of FIG. That is, the processing unit 119 determines that the tip (true sphere) of the contact probe 104 has contacted the surface to be measured when the output signal (e) becomes active (step S2). In response to such contact detection, the processing unit 119 controls a driving unit (not shown) to decelerate the descending speed of the contact probe 104 (step S3).

  After starting the deceleration of the descending speed in this way, the processing unit 119 waits for confirmation that the stylus of the contact probe 104 is stable (step S4). Whether or not the stylus of the contact probe 104 is stable can be determined by comparing the output signal of the F / V conversion circuit 107 with a predetermined voltage 111. That is, the determination is made using the output signal (g) of the comparator 110. Here, the output signal (g) of the comparator 110 corresponds to the signal waveform (g) of FIG.

  On the other hand, in the unit that removes the DC component, first, the capacitor 113 is used to cut the DC component included in the output signal of the D / A converter 106 to make only the AC component. The resistor 114 is for discharging the capacitor 113. A time constant of about 2 to 3 Hz is sufficient. The difference signal between the AC signal and the output signal of the D / A converter 106 is input to the subtraction circuit 116, and only the DC component is extracted.

  The output signal (i) of the subtraction circuit 116 is the displacement of the stylus (relative displacement of the linear scale 100 and the encoder head 101). An output signal (k) is obtained from the output signal (i) and a predetermined voltage 118 using a comparator 117. The desired contact load is when this output signal (k) becomes active.

  Thus, when the processing unit 119 confirms that a desired contact load is obtained from the output signal (k) of the comparator 117 (step S5), the processing unit 119 stops the lowering of the contact probe 104 (step S6). .

  Thus, after stopping the descent of the contact probe 104, the processing unit 119 enters an actual measurement operation (step S7). That is, first, the value of the D / A converter 106 is stored in a storage unit (not shown), and a servo operation for controlling the vertical position of the Z-axis stage 103 is started so that this value becomes constant. If the servo operation of the Z-axis stage is started, next, the surface to be measured is moved in the XY directions. When the surface to be measured is moved in the XY direction, the output of the encoder head 101 of the contact probe (the output of the D / A converter 106) changes due to the change in the height of the surface to be measured (Z direction). At this time, servo operation is performed so that this value becomes constant. As a result, the contact probe 104 can be made to follow the surface to be measured while keeping the contact load constant. Then, the X coordinate and Y coordinate of the surface to be measured are measured with the X axis laser length measuring device and the Y axis laser length measuring device, and the Z coordinate of the contact probe 104 at this time is measured with the Z axis laser length measuring device. To measure the shape of the surface to be measured.

  Thus, in the shape measuring apparatus of this embodiment, a desired contact load can be obtained without waiting for the vibration of the stylus vibrating at the mechanical resonance frequency to attenuate. Therefore, the waiting time until the actual measurement is started becomes unnecessary, and the total time until the measurement is completed can be shortened.

  Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications and applications are naturally possible within the scope of the gist of the present invention.

  Note that noise may be superimposed on the output signals of the displacement meter 3 and the encoder head 101 due to external vibration or noise from a driving unit (motor) (not shown) that drives the contact probe.

  For example, it is assumed that a high frequency component is superimposed on the output signal (d) of the F / V converter 11 or the F / V conversion circuit 107. In this case, as shown in FIG. 2B, the descending speed of the contact type probe is decelerated in accordance with the contact detection by the output signal (e) of the comparator 12 or the comparator 108 (step S2). Then, it is confirmed whether the DC component signal, which is the output signal (i) of the subtractor 16 or the subtractor circuit 116, is displaced (step S11). If the stylus is in a non-contact state, the output signal (i) does not change. Therefore, in this case, the process returns to step S1 and the above-described uniform speed lowering is performed again. In step S11, if the change in the output signal (i) of the subtractor 16 or the subtractor circuit 116 can be confirmed, it can be determined that the contact state has occurred. In that case, the process proceeds to step S4, and the above-described process is performed. Perform the action.

  By adding such processing, a processing circuit that is strong against disturbance such as noise can be obtained, and malfunction can be prevented.

It is a figure which shows the structure of the shape measuring apparatus which concerns on embodiment of this invention. (A) is a figure which shows the flowchart for demonstrating operation | movement of the shape measuring apparatus which concerns on embodiment, (B) is a figure which shows the flowchart for demonstrating operation | movement of a modification. It is a conceptual diagram which shows the contact type probe used for the shape measuring apparatus which concerns on embodiment, and the processing circuit which processes the output signal of the displacement meter of this probe. It is a timing chart figure which shows the state of each output signal of the processing circuit shown in FIG. 3 in the process until a contact type probe is made to contact a to-be-measured surface and a desired contact load is obtained. (A) is a longitudinal sectional view showing an example of a contact type probe used in a conventional shape measuring apparatus, and (B) is a view showing an arithmetic processing means for performing arithmetic processing on a detection signal of a displacement meter of the contact type probe. FIG. 6C is a graph illustrating a sampling period of the output signal of the displacement meter. (A) is a diagram showing a process in which the amplitude of the vibration of the displacement is attenuated with time, and (B) is a result of sampling such a displacement at a predetermined sampling time and performing a moving average process a predetermined number of times. FIG. (A) is a figure which shows the process in which the amplitude of the vibration of a displacement attenuate | damps with time, (B) is a figure which shows the data after filtering at the time of using a low-pass filter with respect to such a displacement. . It is a figure which shows the result of having calculated | required unbiased dispersion | distribution (sigma) 2 as arithmetic processing with respect to the displacement shown to FIG. 6 (A).

Explanation of symbols

    DESCRIPTION OF SYMBOLS 1 ... True sphere, 2 ... Stylus, 3 ... Displacement meter, 4 ... Housing, 5 ... Static pressure air bearing, 6 ... Air supply hole, 7 ... Spring, 8 ... Arithmetic processing means, 10 ... Voltage conversion circuit, 11 ... F / V converter, 12, 13, 17, 108, 110, 117 ... comparator, 14 ... DC extraction circuit, 15 ... DC component removal unit, 16 ... subtractor, 100, 102 ... linear scale, 101 ... encoder head, DESCRIPTION OF SYMBOLS 103 ... Z-axis stage, 104 ... Contact type probe, 105 ... Counter circuit, 106 ... D / A converter, 107 ... F / V conversion circuit, 109, 111, 118 ... Predetermined voltage, 112, 115 ... Buffer, 113 ... Capacitor, 114, resistor, 116, subtracting circuit, 119, processing unit.

Claims (2)

In a shape measuring device comprising a stylus and a detection unit for detecting the displacement of the stylus,
An electrical conversion circuit for converting an output signal of the detection unit into an electrical signal;
A frequency / voltage conversion circuit that converts a frequency contained in the output signal of the electrical conversion circuit into a voltage;
A first comparator for comparing the output signal of the frequency / voltage conversion circuit with a first predetermined voltage;
A second comparator for comparing the output signal of the frequency / voltage conversion circuit with a second predetermined voltage;
A DC extraction circuit for extracting a DC component contained in the output signal of the electrical conversion circuit;
A third comparator for comparing the output signal of the DC extraction circuit with a third predetermined voltage;
A processing unit for determining an output of the first to third comparators;
Comprising
The processor is
The stylus is lowered toward the surface to be measured,
Based on the output of the first comparator, the descending of the stylus is decelerated,
Based on the output of the second comparator, start fine adjustment of the contact pressure of the stylus,
Based on the output of the third comparator, the descent of the stylus is stopped and measurement is started.
A shape measuring apparatus characterized by that.   The processing unit, after decelerating the descending of the stylus, confirms the contact of the stylus with the measurement surface based on the output signal of the DC extraction circuit. The shape measuring apparatus according to claim 1, wherein the descent at a constant speed is resumed.

Images