JPH01114703A - Image formation type displacement gauge - Google Patents

Abstract

PURPOSE:To simultaneously measure the displacement in the in-plane direction of an object to be measured and the displacement in the out-of-plane direction by splitting a beam from a light source into two beams and radiating them to the object to be measured, and scanning one beam thereof in the in-plane direction of the object to be measured. CONSTITUTION:The object to be measured 13 is a DAT use tape, and a beam from a light source 1 becomes a circularly polarized light through a collimator lens 2 and a lambda/4 plate 3, made incident on a polarized light beam splitter 4 and split into two beams. Subsequently, one beam thereof radiates the tape surface of the object to be measured 13 through a beam splitter 7 and an objective lens 8, and its reflected light forms an image on a photodetector 11 through a condensing lens 9 and a cylindrical lens 10, and detects the displacement quantity in the out-of-plane direction. Next, the other beam radiates a tape edge part of the object to be measured 13 by the lens 8, and its reflected light forms an image on a photodetector 12. In this case, a signal of the detector 12 is fedback to a fine adjustment mechanism 14 and moves a movable mirror 6, and allows the beam to follow up the displacement of the tape edge part, therefore, the displacement in the in-plane direction can also be measured simultaneously.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an imaging type displacement meter, and in particular, to a displacement meter that can measure several points simultaneously by dividing a beam from a laser diode LD into two or more. Regarding the meter. .

[Conventional technology]

Among optical displacement meters using a laser diode LD, an example in which the beam is divided into two beams and each beam is used to perform two-point measurement is the Japanese Patent Publication No. 61-524.
No. 03, [i'Applied Optics ff Vol. 123 No. 15 (1984) Surface roughness measurement using R2 beam optical system J (A applied optics V
ol, 23 No. 15 (1984) Surfa
ce profile measurement wi
th a dual-bean+ opticals
system) + Proceedings of the 1986 Society for Precision Engineering Spring Conference, pp. 785-786, ``Development of vibration-isolated surface roughness measurement technology using an optical interference microscope'', etc.

The example of the above-mentioned patent publication is equipped with a two-beam type movable optical reading head and a fixed scale having a position detection marker as an optical position detection device.

The marker is read by the head, converted into a digital signal, and positioning is detected using this signal. Here, the pitch interval of markers on a fixed scale is determined, detection is performed using two spots, and highly accurate positioning is possible through arithmetic processing.

In addition, in the example of the foreign literature mentioned above, the beam is similarly divided into two beams, and the amount of displacement in the out-of-plane direction of the two points is detected,
The surface to be measured is scanned and the surface roughness is measured. Here, the direction outside one plane is the direction perpendicular to the surface to be measured, that is,
Beam direction.

Furthermore, the paper by the Japan Society for Precision Engineering is an example of a total of 4I measurements performed at 3 points, where one point is used as a reference point on the measurement surface, and by calculation processing of this reference and the measured values of the remaining 2 points, disturbances are reduced. It constitutes an unaffected surface roughness meter.

In this way, conventionally, the format was 2-point measurement or 3-point measurement, but the information obtained by each beam was determined by setting the marker pitch to "1".

It was a signal expressed in rOJ and a displacement signal in the out-of-plane direction. [Problem that the invention seeks to solve] In the above conventional technology, the pitch of the marker is "1".

This is a method of expressing it as "0" and measuring two points, or a method of measuring the amount of out-of-plane displacement at two or three points, which is just a two-dimensional measurement method of the out-of-plane displacement amount component and time.

Strictly speaking, the movement of an object exhibiting minute displacement behavior includes in-plane behavior components as well as out-of-plane behavior components. The in-plane component is a component in the direction of the surface to be measured, and a component in the direction perpendicular to the beam. In conventional methods, this in-plane direction component is not measured, only the amount of one out-of-plane displacement is measured, and the overall behavior is discussed. Therefore, there is a drawback that the measurement system is affected by in-plane direction components due to vibration of the measurement system, air flow, and the like.

The purpose of the present invention is to simultaneously measure the amount of displacement in both in-plane and out-of-plane directions in such minute behavior measurements, and to
An object of the present invention is to provide an imaging type displacement meter that can more accurately grasp the behavioral state of an object by three-dimensionally measuring time.

[Means for solving problems]

In order to achieve the above object, the present invention provides an imaging displacement meter that divides a beam from a light source into at least two beams, irradiates the object to be measured, and measures displacement at at least two points. An imaging type displacement device that is equipped with a mechanism that scans at least one of the plurality of beams in the in-plane direction of the object to be measured, and simultaneously measures the displacement in the out-of-plane direction and the displacement in the in-plane direction of the object to be measured. This paper proposes a meter.

The beam scanning mechanism may be a mechanism that scans at least one of the plurality of divided beams with a fixed beam as a reference.

Further, the beam scanning mechanism may include a servo circuit that always maintains a constant relative position of the scanning beam with respect to the object to be measured.

Specifically, the servo circuit controls the scanning beam to be held on the edge of the object to be measured.

[Effect]

The function of each beam used in the present invention will be explained.

The principle of in-plane displacement measurement according to the present invention is shown in FIGS. 2 and 3. Beam splitter 7 directs the beam to the object to be measured 1
The beam is bent to the third side, focused by the objective lens 8, and irradiated onto the edge portion of the object to be measured 13.

The reflected light is guided to a photodetector 12 by a condensing lens 10. The photodetector 12 detects the light amount distribution state and measures the displacement of the object to be measured 13 in the in-plane direction.

What is the amount of movement e of the object to be measured from the optical axis in the in-plane direction?

From Fig. 2 and Fig. 3, it becomes f. where a is the gain constant (conversion coefficient), X is the amount of image movement on the photodetector side, f is the focal length of the objective lens 8, 2 is the distance from the objective lens 8 to the object to be measured, and ro is the beam This is the effective radius.

Further, the degree of leakage of out-of-plane behavior into in-plane measurement δ is expressed by δ. From equation (2), to minimize the degree of leakage δ,
It can be seen that it is sufficient to use ezO, that is, the movement 'iAe in the in-plane direction from the optical axis, approximately 0, and that it is effective to measure Z center f, that is, in a slightly defocused state.

Furthermore, looking at the relationship between the image entering the photodetector and the amount of light received by the detector, the total amount of light is proportional to the in-plane behavior of the object to be measured, and the output is almost linear at the center of the optical axis. Measure using a detection method.

The problem here is the amount of displacement in the in-plane direction. That is, if this amount of displacement is larger than the beam waist, there is a possibility that the edge of the object to be measured may be missed.

Therefore, in the present invention, the detection beam of the in-plane displacement measurement method using edges is of a scanning type. FIG. 4 shows the configuration of a beam scanning feedback circuit for measuring in-plane displacement.

Normally, the beam is irradiated so that the edge of the object to be measured is at the center of the beam waist, as shown in C. At this time, the image formation state on the photodetector becomes C. If the object to be measured is displaced in the in-plane direction from this state, the beam shifts from the edge center as shown in b or d, and on the photodetector side, bl
, detected as d-engine. When it is completely off the edge as shown in a and e, even if further displacement occurs in the in-plane direction, the detected light amount distribution does not change from the state of al or el, and the displacement becomes undetectable. To solve this,
It is necessary to make the beam follow the displacement of the edge of the object to be measured.

First, a detection beam is irradiated onto the edge portion of the object to be measured 13, and the amount of displacement in the in-plane direction of the edge portion is detected by the photodetector 12 as a light amount distribution state by the reflected light, and the signal processing circuit 1
8, the phase compensation circuit 15 in the servo circuit 17 and the drive circuit 16 feed back to the fine movement mechanism 14 (for example, a piezoelectric type piezo element) to drive the movable mirror 6.

The beam is transmitted by this movable mirror 6 to a polarizing beam splitter 4. Via the beam splitter 7, the movement of the edge portion of the object to be measured in the in-plane direction can be followed. According to this method,
The beam always follows the edge of the object to be measured, making it possible to measure displacement in the in-plane direction.

On the other hand, for out-of-plane displacement measurement, a conventional astigmatism method is used. The principle of the astigmatism method is shown in FIG. A beam from an LD (not shown) is made into a parallel beam by a collimator lens system, bent by a beam splitter 7, and irradiated onto an object to be measured 13 by an objective lens 8.

At this time, due to the displacement in the out-of-plane direction that occurs in the object to be measured 13, (A) when focusing (when the focus of the objective lens 8 is on the surface to be measured), (B) when the lens is too close, (C) ) There are three possible cases when the lens is too far away. In case (A), since the focus of the objective lens 8 is on the surface to be measured, the reflected light becomes a parallel beam, and the condenser lens 9. The beam image on the light receiving surface that has passed through the cylindrical lens 10 becomes circular. In the case of (B), the beam becomes a diverging beam from the objective lens 8 and the condensing lens 9. Cylindrical lens 10
The image of the beam on the light receiving surface that has passed through it.

It becomes a vertically long ellipse. Similarly, in case (C), the beam becomes a focused beam and forms a vertically elongated ellipse on the light receiving surface.

Using this optical system, the sixth
Perform signal processing as shown in the figure. A four-split light receiving element is used as the photodetector 11, the amount of light on each of the four light receiving surfaces is detected, and the amount of out-of-plane displacement is determined by the calculation process A+B+C+D A+B+C+D A+B+C+D.

〔Example〕

Next, the present invention will be explained in detail with reference to FIG. 1 and FIGS. 7 to 16.

FIG. 1 is a diagram showing the configuration of an optical system for measuring displacement behavior of a displacement meter that measures the behavior of a DAT tape as an object to be measured 13. FIG. The DAT tape 13 is wrapped around the cylinder surface, and when the cylinder rotates at high speed, the head on the cylinder surface causes minute displacement behavior. In this embodiment, an LD is used as the light source 1, the emitted beam is converted into parallel light by a collimator lens 2, and this linearly polarized beam is passed through a λ/4 plate 3 and incident on a polarizing beam splitter 4 as circularly polarized light. The polarizing beam splitter 4 splits the incident beam into two beams having different polarization directions. One beam passes through the polarizing beam splitter 4 orthogonally, is focused by the objective lens 8 via the beam splitter 7, and is directly irradiated onto the tape surface of the object to be measured 13. This detection beam is for detecting displacement in the out-of-plane direction, and its reflected light is imaged on the photodetector 11 (quadrant light receiving element) via the condensing lens 9 and the cylindrical lens 1o, and the above-mentioned It is used to measure the amount of displacement in the out-of-plane direction using the astigmatism method.

The other divided beam is irradiated onto the tape edge portion of the object to be measured 13 by the objective lens 8 in order to detect the amount of displacement in the in-plane direction, and the reflected light is sent to the photodetector 12 via the condensing lens 10. An image is formed on the object, and the amount of light changes depending on the in-plane displacement of the object to be measured, and is used to measure the amount of in-plane displacement.

At this time, as explained in the previous section, if the detection beam deviates from the edge, measurement becomes impossible, so as shown in FIG. Feedback is sent to the fine movement mechanism 14 (piezoelectric piezo element) through the phase compensation circuit 15 and drive circuit 16 inside, moves the movable mirror 6, and directs the displacement detection beam in the inner direction to the tape edge portion of the object to be measured 13. make it follow.

In this way, if one beam has a scanning function and is made to follow the displacement in the in-plane direction, the displacement in the out-of-plane direction and the displacement in the in-plane direction can be measured simultaneously.

Another embodiment of the invention is shown in FIG. In this embodiment, as in the embodiment shown in FIG. 1, the beam is split into two beams by a polarizing beam splitter 4, one beam is used for out-of-plane displacement measurement,
The other is for in-plane displacement measurement and is equipped with a fine movement mechanism that scans the beam in parallel. Some specific examples of this fine movement mechanism 19 are shown in FIG.

In (A), two wedge-shaped optical elements 23 with the same θ are used, of which 23A is fixed and 23B is several leaf springs 24.
It is supported by a coil spring.

This is driven in the optical axis direction by a drive mechanism 25 to scan the incident beam in parallel.

(B) shows a structure in which a beam of light is scanned in parallel by two movable mirrors. The mirror 6 includes a drive mechanism 25 and is controlled by signals sent from a control circuit 27 via each drive circuit 26 .

(C) is an example in which a hole is made at the center of the paraboloid x128 and the beam is made to enter through this hole. A swingable mirror 6 is provided at the focal point of the parabolic mirror 28, and the swinging of the mirror 6 scans the incident beam in parallel.

In (D), two mirrors 6 are installed in parallel, the base itself is slightly swung around the center, and the incident beam is scanned in parallel.

(E) consists of a fiber connector 20, an optical fiber 21, and a fiber connector 22. In this case, the incident beam is captured by the fiber connector 20, and the beam is irradiated from the fiber connector 22 via the optical fiber 21.

The fiber connector 20 is fixed, and the fiber connector 25
is driven perpendicular to the optical axis to scan the beam in parallel.

By using these fine movement mechanisms, it is possible to obtain a displacement meter that can simultaneously measure displacements in out-of-plane and in-plane directions by scanning a beam.

FIG. 9 shows an embodiment of a surface profile measuring device using the beam scanning method described above. The present embodiment is basically the same optical system as that shown in FIG. 1, but the measurement operation will be explained below in 6, in which displacement in the out-of-plane direction is detected at both points.

In FIGS. 10(A) and 10(B), a is a fixed spot.

b is a scanning spot, and its positional relationship is shown. That is, the feature of this embodiment is that point b can be scanned in the horizontal direction when viewed from point a. Specifically, it measures the grooved part of the workpiece during lathe cutting (Figure 11), the state of wear on the disk surface due to pressure when pressing the R/W head of the magnetic disk device, the cutting condition of the optical disk guide groove (group), etc. be. At this time, the signals at points a and b contain disturbance components such as one rotation and vibration, and as shown in FIG. 10, they become very noisy. However, that a,
Since the signals at point b are close to each other, they are almost synchronized even in the presence of wind disturbances. Therefore, when the b signal is subtracted from the a signal, a clean signal from which the disturbance component has been removed is obtained, as shown by b - a in (C). As a result, accurate surface shape measurement with less noise becomes possible.

The configuration of the signal processing system at this time is shown in FIG. First, a scanning beam drive signal (for example, a sine wave) is generated by a reference signal generation circuit. This signal is passed through a sawtooth wave generation circuit to drive the actuator. Since the upper and lower edge portions of this sawtooth wave are rounded, only the straight line portion in the middle is used. For example, the slice level is determined in advance so that the portion with good linearity is entered into the actual signal processing system. The signal from the chopping circuit is used as a trigger synchronization signal, and normal signal processing is performed only when the previous ba signal is obtained, that is, when the B signal chopping circuit is high. FIG. 13 shows the signals at this time. When the processing results obtained in this way are displayed in chronological order, FIG. 10(D) is obtained.

Next, a method for solving problems with this scanning method will be explained.

Now, the rotation speed of an optical disc with a diameter of 130 m is 60 rps.
(=3600 rpm), and the installation point of point a is 50 no from the center of the disk. On the other hand, the movable range of point b is set to 50
．． 1 to 50.3 m (7) 0.2 mrJ1. 14th
As shown in the figure, when the beam is scanned in a direction perpendicular to the rotational direction of the disk, the beam scanning direction will not be a straight line unless the scanning speed is infinite as shown in (A);
), resulting in a pattern similar to an arc.

Therefore, first, when calculating the moving speed of the disk at point a, V a =2πfr=27cX60X0.05=IR,
115 (m/s). Next, let's find out about point b.

When r1=50.1mm, V, =18.887(+
m/s) r, = 50.3 mm, V, = 1
8.962 (m/s). For example, as shown in FIG. 15, if the angle between the direction perpendicular to the disk rotation direction and the scanning beam direction is θ, then this angle θ is 10
'To make it below, j a n-1(Va/Vb) <10@However, vb
is the scanning beam velocity. The scanning beam velocity vb is 10
You can see that it is best to move it at a speed of 7.115 m/5 (7).

Also, in this cycle, the measurement interval is set to Δ2.

Considering the time (positional shift) for the beam to go and return under the condition of 2XΔXXtanθ>Δ2, Δz=o, 0704■.

The beam scanning repetition frequency fc at this time is Va/Δ
For example, if Δz=0°0704m+m is made to correspond to 1■, then it is sufficient to install fc=18°85 KHz, so this embodiment can be implemented.

Another embodiment of the present invention in which one beam from the LD is divided into four beams, two of which are scanning beams, is described in the first embodiment.
It is shown in Figure 6. □In this embodiment, two Wollaston prisms 29 are used for beam splitting. In this case the divided 2
The two scanning beams are used, for example, to divide the in-plane direction displacement component into two-dimensional components along the x-Y axes and detect them.
Therefore, the in-plane displacement component can be measured more precisely.

〔Effect of the invention〕

According to the present invention, the emitted beam from the LD is divided into two or more beams by a polarizing beam splitter, and since a mechanism is provided for scanning at least one beam, it is possible to measure out-of-plane behavior as well as in-plane behavior. Also, measure two or more points at the same time, and use one point as a reference for the measurement surface.
It is possible to remove disturbance components (effects of vibration, air flow, etc.) at this time from the displacement information of a certain specific surface.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical system for measuring displacement behavior in an embodiment of an imaging type displacement meter according to the present invention, and FIGS. 2 and 3 are diagrams showing the principle of in-plane direction displacement measurement according to the present invention. , FIG. 4 is a diagram showing the configuration of a beam scanning type feedback circuit for measuring displacement in the in-plane direction, and FIGS. 5 and 6 are diagrams showing the principle and signal processing method of the astigmatism method for measuring displacement in the out-of-plane direction. , FIG. 7 is a diagram showing a specific example of the scanning mechanism of the optical system for measuring displacement behavior according to another embodiment of the present invention, FIG. 8 is a diagram showing a specific example of the scanning mechanism of the beam for measuring in-plane displacement, and FIG. FIG. 9 is a diagram showing the configuration of an optical system for surface shape measurement according to still another embodiment of the present invention, FIG. 10 is a diagram showing a surface shape signal processing method in the embodiment of FIG. 9, and FIG. A diagram showing the relationship between a workpiece and a groove cutting tool. Figure 12 is a diagram showing the signal processing system for surface shape measurement.
3 is a diagram showing the actuator drive signal, FIG. 14 is a diagram showing the relationship between the disc rotation direction and the beam scanning direction on the optical disc surface, FIG. 15 is a diagram showing the moving direction of the scanning beam on the disc surface, and FIG. The figure shows the configuration of an optical system when a beam is divided into four parts. DESCRIPTION OF SYMBOLS 1... Laser diode LD, 2... Collimator lens, 3... λ/4 plate, 4... Polarizing beam splitter, 5... Fixed mirror, 6... Movable mirror, 7...
・Beam splitter, 8... Objective lens, 9... Cylindrical lens, 10... Condensing lens, 11...
・Photodetector (4D), 12...Photodetector (ID or 2D), 13...Object to be measured, 14...Fine movement mechanism, 1
5... Phase compensation circuit, 16... Drive circuit, 17...
・Servo circuit, 18... Signal processing circuit, 19... Fine movement mechanism, 20.22... Fiber connector, 21...
・Optical fiber, 23... Wedge-shaped optical element, 24...
- Leaf spring, 25... Drive mechanism, 26... Drive circuit,
27... Control circuit, 28... Parabolic mirror, 29...
Wollaston prism. Agent Patent Attorney Tatsuno Unuma 1 Figure 6-----Duomi 2- Figure 3 +3--M1 knob';l'j't 4 M +a+ (b) (c) (d) re>Figure 5 (A) (B
(C) Figure 6 +8--1-→No. 23 buried well Figure 7 Figure 8 ) (D) % bite - (E) 20.22------F2 pressure 3?2 ri2+------
Figure 9 Figure 10 (A) (C) a b b-6 11
Figure 13 Figure 12 Figure 14 Figure 15

Claims (4)

[Claims] (1) In an imaging displacement meter that divides a beam from a light source into at least two beams and irradiates the object to be measured to measure displacement at at least two points, at least one of the plurality of divided beams An imaging type displacement meter comprising a mechanism for scanning the object to be measured in an in-plane direction, and simultaneously measuring an out-of-plane displacement and an in-plane displacement of the object to be measured. (2) Imaging according to claim 1, wherein the beam scanning mechanism is a mechanism that scans the at least one beam among the plurality of divided beams with a fixed beam as a reference. Mold displacement meter. (3) In claim 1 or 2, the beam scanning mechanism includes a servo circuit that always maintains a constant relative position of the scanning beam with respect to the object to be measured. Image type displacement meter. (4) The imaging type displacement meter according to claim 3, wherein the servo circuit is a servo circuit that holds the scanning beam on an edge of the object to be measured.