JP2008164558A - Surface shape measuring device - Google Patents

Abstract

Provided is a surface shape measuring apparatus capable of quickly and accurately detecting contact abnormality of a stylus generated during measurement of a surface shape of a test object.
A surface shape measuring apparatus (1) for measuring a surface shape of a test object (13) by horizontally scanning the stylus (2) in contact with the test object (13) within a predetermined time. The contact state between the stylus 2 and the test object 13 is determined on the basis of the calculation unit for obtaining the frequency corresponding to the variation of the displacement amount of the stylus 2 and the relative time variation of the frequency. And a determination unit.
[Selection] Figure 1

Description

  The present invention relates to a surface shape measuring apparatus such as an optical related element.

  Conventionally, as a device for evaluating the surface shape of optical-related elements such as lenses and molds, surface shape measurement that employs a contact scanning measurement method in which the stylus follows the surface of the test object such as optical-related elements An apparatus is used (for example, refer to Patent Document 1). Hereinafter, the measurement principle of the present apparatus will be described with reference to FIG.

  A stylus shaft 102 having a stylus 101 at its tip is held by a hydrostatic bearing 103 in a state in which it can slide smoothly. The sliding distance of the stylus shaft 102 can be measured by a displacement meter 104, and the hydrostatic bearing 103 and the displacement meter 104 are placed on a flat plate member 105 and configured as a stylus unit.

  When the rear part of the angle adjusting member 106 is raised in the positive Y-axis direction, the entire stylus unit is inclined with respect to the horizontal direction. At this time, since the stylus shaft 102 is slidably held by the hydrostatic bearing 103, a force to advance in the tilt direction (Z-axis negative direction) acts by its own gravity. As a result, the stylus 101 slides toward the test object 107 located in front and contacts the surface thereof.

When the test object 107 is scanned in the X-axis direction by the drive mechanism 108 in a state where the stylus 101 is in contact with the test object 107, the stylus 101 follows the shape of the test object 107, Accordingly, the stylus shaft 102 is displaced. The shape of the test object 107 is obtained by acquiring the position coordinates of the stylus shaft 102 to be displaced by the displacement meter 104 and the position coordinates of the scanned test object 107 by the displacement meter 109 in time series. In this apparatus, in order to generate a force (hereinafter referred to as a measuring force) for bringing the stylus 101 into contact with the surface of the test object 107, a stylus shaft is used regardless of the elastic force of a spring or the pressure of air. A self-weight tilt method using the gravity of 102 is adopted. According to this apparatus, it is possible to obtain a very small measuring force, for example, 5 mgf, and the measuring force can be easily adjusted by the angle adjusting member 106.
JP 2005-502876 gazette

  However, in this device, the gap between the stylus shaft 102 and the hydrostatic bearing 103 is very narrow, about several μm, and the measurement force depends only on gravity. When foreign matter enters the gap or condensation occurs in the gap, the stylus shaft 102 does not slide smoothly in the hydrostatic bearing 103 and accurately follows the surface of the test object 107. It may disappear. Furthermore, the sliding may stop depending on the degree of contamination and the state of contamination.

  When such a state occurs during measurement, the obtained measurement data does not reflect the shape of the test object and becomes meaningless. In addition, even if the occurrence of such a state is noticed during the measurement, it takes extra time because re-measurement is required.

  The present invention has been made in view of the above circumstances, contact abnormality of the stylus generated during the measurement of the surface shape of the test object (state that is not in contact with the test object despite being measured) It is an object of the present invention to provide a surface shape measuring apparatus capable of detecting a swift and accurate detection.

  The surface shape measuring device of the present invention is a surface shape measuring device for measuring the surface shape of the test object by relatively horizontally scanning the stylus in contact with the test object, for a predetermined time. And a determination unit for determining a contact state between the stylus and the test object based on a relative time change amount of the frequency. It is characterized by providing.

  According to the surface shape measuring apparatus of the present invention, it is possible to determine the contact state between the stylus and the test object during the measurement of the surface shape of the test object. The occurrence of an abnormal condition such as not following can be detected quickly.

  The computing unit may obtain the frequency using Fourier transform or wavelet transform. In this case, the fluctuation of the displacement amount of the stylus during measurement can be appropriately converted into a frequency.

  The determination unit may determine the contact state by observing a time transition of the frequency obtained by the calculation unit and detecting presence / absence of a discontinuous point of the relative time change amount of the frequency. . In this case, a change in frequency can be detected with high accuracy.

  The determination unit observes the frequency obtained by the calculation unit, and based on a predetermined table that associates the value of the frequency and the relative positional relationship between the stylus and the test object, The contact state may be determined. In this case, the state of the stylus can be accurately determined from the table.

  ADVANTAGE OF THE INVENTION According to this invention, the contact abnormality of the stylus which generate | occur | produces during the surface shape measurement of a test object can be detected rapidly and accurately.

  A first embodiment of the present invention will be described with reference to FIGS. Unless otherwise specified, “front” and “rear” refer to the negative and positive directions of the Z-axis, respectively. The surface shape measuring apparatus 1 according to the present embodiment includes a stylus 2, a Y-axis drive mechanism 3, an X-axis drive mechanism 4, and a computer 5.

The stylus 2 is slidably disposed in the hydrostatic bearing 6 while passing through the hydrostatic bearing 6, and the hydrostatic bearing 6 is fixed on the base plate 8 with the stylus 2 facing forward. The
The Y-axis drive mechanism 3 is a known mechanism such as a motor and is fixed on the base 11. A tilt angle adjusting mechanism 9 for adjusting the tilt angle of the hydrostatic bearing 6 is provided at the upper rear of the Y-axis drive mechanism 3, and the hydrostatic bearing 6 is tilted at the tilt angle adjusting mechanism 9 in front of the tilt angle adjusting mechanism 9. A support column 10 is provided as a fulcrum when tilting. The tilt angle adjusting mechanism 9 is configured by an actuator that can be expanded and contracted in the Y-axis direction, for example, but instead is configured by using a screw and an angle adjusting member as described in Patent Document 1 described above. Other mechanisms may be used. A displacement meter 12 that detects the position of the stylus 2 in the Y-axis direction is provided behind the Y-axis drive mechanism 3.
A base flat plate 8 is placed on the tilt angle adjusting mechanism 9 and the column 10. Therefore, the hydrostatic bearing 6 and the stylus 2 are configured to be movable in the Y-axis direction (vertical direction in FIG. 1) by the Y-axis drive mechanism 3.

  The X-axis drive mechanism 4 is composed of, for example, a motor or a piezoelectric actuator, and is provided on the base 11 and in front of the Y-axis drive mechanism 3. On the X-axis drive mechanism 4, a holding member 14 that supports and fixes a test object 13 such as a lens, a mold, or an optical element is provided. The test object 13 supported and fixed to the holding member 14 is configured to be movable in the X-axis direction (direction perpendicular to the paper surface in FIG. 1) by the X-axis drive mechanism 4. A displacement meter 15 for detecting the displacement of the test object 13 in the X-axis direction is provided in front of the X-axis drive mechanism 4.

  FIG. 2 is a block diagram showing the configuration of the computer 5. The computer includes a control unit 16, a calculation unit 17, and a determination unit 18. The control unit 16 is connected to the Y-axis drive mechanism 3 and the X-axis drive mechanism 4 and controls the operation of the entire surface shape measuring apparatus 1. The calculation unit 17 and the determination unit 18 measure the shape of the test object 13 and determine the state of the stylus 2 described later. Each displacement meter 7, 12 and 15 is connected to the control unit 16, and each detected value is input to the control unit 16.

The operation of the surface shape measuring apparatus 1 having the above configuration will be described below.
First, the test object 13 is supported and fixed to the holding member 14 such that the surface on which the shape measurement is performed faces the stylus 2. Next, when the inclination angle adjusting mechanism 9 is operated to move the rear portion of the base flat plate 8 upward, the base flat plate 8 is inclined with the support column 10 as a fulcrum. The stylus 2 held by the hydrostatic bearing 6 slides smoothly in the hydrostatic bearing 6 due to its own gravity, and its tip moves forward and contacts the surface of the test object 13. Stop.

  In this state, the control unit 16 drives the X-axis drive mechanism 4 and the Y-axis drive mechanism 3 to move the test object 13 and the stylus element 2 relatively, so that the surface of the test object 13 is touched. Scan by child 2. The detection values of the displacement meters 7, 12, and 15 are input to the control unit 16, analyzed and reconstructed by the calculation unit 17, and the surface shape of the test object 13 is measured. At this time, by analyzing the detection value of the displacement meter 7 in parallel, the contact state between the test object 13 and the stylus 2 and the presence / absence of abnormality of the stylus 2 are determined.

  The determination of the contact state and the like will be described with reference to FIGS. FIG. 3 is a flowchart for determining the contact state and the like performed in the computer 5.

First, in step S1, the control unit 16 determines whether the measurement is completed. If the determination result is “YES”, the series of processing is terminated, and if the determination result is “NO”, the process proceeds to step S2.
In step S2, the control unit 16 acquires the output value Z of the displacement meter 7 at a predetermined sampling frequency and accumulates it as point cloud data. The sampling frequency is set to 1 MHz, for example, but is not limited to this and may be another frequency.

  Next, in step S3, as shown in FIG. 4, the arithmetic unit 17 performs a Fourier transform on the point cloud data accumulated in, for example, 0.1 second in step S2.

In step S4, the arithmetic unit 17 is transmitted to the determining unit 18 obtains a first-order peak frequency f _t from the power spectrum obtained after conversion, in the surface shape measurement of the test object 13, to continue monitoring the f _t.

In step S5, the determination unit 18 determines whether or not the difference between the acquired value of the frequency _{ft and} the value of the frequency _ft−1 acquired at the immediately preceding timing is an amount within a predetermined range. If the determination result is "YES", the process returns to step S1, the monitoring of f _t is continued. If the result is "NO", the variation of the frequency f _t is above the predetermined range, determines that the change in the frequency f _t is discontinuous. At this time, since there may be some change in the contact state between the stylus 2 and the test object 13 or the stylus 2 itself, the determination unit 18 transmits the determination result to the control unit 16. To do.

  In step S6, the control unit 16 performs a process of notifying the occurrence of abnormality or prompting the confirmation of the state of the stylus 2 on a display (not shown) or outputting as a sound from a speaker (not shown). The operator is notified, and the series of processing ends.

According to the surface shape measuring apparatus 1 of the present embodiment, since continually monitored for change in the value of the frequency f _t being measured, Ya if Hariko 2 catalyst during the measurement is separated from the surface of the test object 13 When the stylus 2 itself is damaged, it is possible to automatically detect that some change has occurred in the stylus 2. Therefore, it is possible to quickly and flexibly cope with these problems, for example, by suspending measurement and performing remeasurement.

Next, a second embodiment of the present invention will be described with reference to FIGS. The difference between the present embodiment and the first embodiment described above is that the contact state between the test object 13 and the stylus 2 and the determination of the presence or absence of abnormality of the stylus 2 are referred to a preset table. It is a point to do.
The surface shape measuring apparatus of this embodiment includes a computer 25 shown in FIG. The computer 25 includes a determination unit 28 instead of the determination unit 18. Components other than the computer 25 are the same as those in the first embodiment.

  Hereinafter, the operation of the surface shape measuring apparatus of the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart for determining the contact state between the test object 13 and the stylus 2 and the presence or absence of abnormality of the stylus 2 in the present embodiment.

First, in step S <b> 1 to step S <b> 4, the value of the frequency f _t is calculated by the same procedure as in the first embodiment and transmitted to the determination unit 18.

In step S15, in order to identify the state corresponding to f _t obtained in step S4, with reference to Table 1, the determination unit 28 is prepared in advance, it determines the state of the touch Hariko 2.

Table 1 shows the frequency f _t band at a certain time t, the contact state between the stylus 2 and the test object 13 or the state of the stylus 2 itself, and the return value d _t corresponding to this state. And are stored. For example, when f _t is less than a predetermined value f ₁ , a return value d ₁ indicating that the stylus 2 and the test object 13 are in contact (contact) is returned to the determination unit 28. Similarly, when it is determined that the stylus 2 is not in contact with anything (non-contact), the return value d ₂ is returned to the determination unit 28, and the tip of the stylus 2 is damaged or foreign matter is attached. When it is determined that the state is abnormal (abnormal), the return value d ₃ is returned to the determination unit 28.

In step S16, whether any d ₂ and d ₃ is returned as a return value determining unit 28 determines. If the determination result is "NO", the process returns to step S1, the monitoring of f _t is continued. When the determination result is “YES”, since there is a possibility that some change has occurred in the contact state between the stylus 2 and the test object 13 or the stylus 2 itself, the determination unit 28 displays the determination result. It transmits to the control part 16.

  In step S17, the control unit 16 displays on the display (not shown) or informs a speaker (not shown) as a sound to notify the occurrence of an abnormality or prompt the confirmation of the state of the stylus 2 according to the return value. This process is performed to notify the operator of the apparatus, and a series of processes is completed.

According to the surface shape measuring apparatus of the present embodiment, by referring to Table 1, in order to specifically identify in accordance with the state of the touch Hariko 2 to the value of the frequency f _t, any change in the measured touch Hariko In addition to what happened in step 2, it is possible to automatically detect a specific state. Therefore, the operator can deal with the trouble of the stylus 2 more quickly and appropriately.

  Furthermore, if the entire device is configured and controlled to automatically perform treatments according to each detected state, it is possible to provide a surface shape measuring device that not only detects abnormalities but also automatically handles troubles. It is.

Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in each of the embodiments described above, the Fourier transform is performed on the output value Z of the displacement meter 7, but instead of this, the determination process may be performed after performing other transformations such as wavelet transformation. Good. In the second embodiment described above, the "contact" state of Hariko 2 tactile, "non-contact" are classified into three "abnormal", but not limited to, the bandwidth of the frequency f _t It is also possible to automatically perform more detailed state detection by causing the determination unit 28 to refer to a table storing states and parameters defined more finely by the user.

  The present invention can be used for a surface shape measuring apparatus such as an optical related element.

It is a left view of the surface shape measuring apparatus of 1st Embodiment of this invention. It is a block diagram which shows the structure of the computer in the same embodiment. It is a flowchart of stylus state judgment in the embodiment. It is a figure which shows the output spectrum of the displacement meter of the embodiment, and the power spectrum after a Fourier transform. It is a block diagram which shows the structure of the computer in the surface shape measuring apparatus of 2nd Embodiment of this invention. It is a flowchart of stylus state judgment in the embodiment. It is a figure which shows the structure of the conventional surface shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface shape measuring apparatus, 2 ... Stylus, 13 ... Test object, 17 ... Calculation part, 18, 28 ... Determination part

Claims (4)

A surface shape measuring apparatus for measuring the surface shape of the test object by bringing the stylus into contact with the test object and relatively horizontally scanning the test object,
A calculation unit for obtaining a frequency corresponding to a variation in the displacement of the stylus within a predetermined time;
A determination unit that determines a contact state between the stylus and the test object based on a relative time change amount of the frequency;
A surface shape measuring apparatus comprising:   The surface shape measuring apparatus according to claim 1, wherein the calculation unit obtains the frequency using Fourier transform or wavelet transform.   The determination unit determines the contact state by observing the time transition of the frequency obtained by the calculation unit and detecting the presence or absence of a discontinuous point of the relative time change amount of the frequency. The surface shape measuring apparatus according to claim 1 or 2.   The determination unit observes the frequency obtained by the calculation unit, and based on a predetermined table that associates the value of the frequency and the relative positional relationship between the stylus and the test object, The surface shape measuring apparatus according to claim 1, wherein a contact state is discriminated.

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