JP2003097911A - Displacement measuring device and displacement measuring method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement measuring device employing a confocal optical system which has no movable member and can detect the position of focused focal point at a slower speed in order to improve the measurement accuracy, and provide a displacement measuring method using the displacement measuring device. SOLUTION: The displacement measuring device has a laser light source 12 emitting laser light, a beam splitter 13 transmitting or reflecting the laser light, a collimating lens 14, an object lens 15 and a detector 18 detecting the reflected light. In the displacement measuring device and the displacement measuring method using it, a liquid crystal lens 101 is disposed between the collimating lens 14 and the object lens 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement measuring device adopting a confocal optical system. More specifically, the present invention relates to a measuring device that measures the position of a measurement surface by detecting the distance between the objective lens that projects light onto the measurement surface and the measurement surface.

[0002]

2. Description of the Related Art As a displacement measuring device adopting a confocal optical system, there is a displacement measuring device described in, for example, JP-A-7-113617. FIG. 5 shows a displacement measuring device described in Japanese Patent Laid-Open No. 7-113617.

In the displacement measuring device described in this publication, a confocal optical system is adopted, so that the laser light is emitted from the object 16 to be measured.
Is irradiated at a point, and the reflected light is also focused on the detector (photodiode 18) through the pinhole 17a. With this confocal optical system, high resolution is realized, and unnecessary scattered light can be largely removed, so that an image with high contrast can be obtained. As a feature of this confocal optical system, the brightness and the resolution are peaked at the focal position. That is, the maximum brightness and the in-focus position match.

In FIG. 5, a laser power control circuit 11
The emitted light of the laser power diode 12 driven by
It passes through the beam splitter 13, the collimator lens 14, and the objective lens 15, and is projected on the DUT 16.
The reflected light from the DUT 16 passes through the objective lens 15 and the collimator lens 14, is reflected by the beam splitter 13, and enters the photodiode 18 through the pinhole 17a of the optical diaphragm 17.

The objective lens 1 is attached to one end of the tuning fork 21.
The peripheral edge of 5 is attached. The objective lens 15 having a solenoid 24 for vibrating the tuning fork 21 on the side of the other end of the tuning fork 21 is made to vibrate with a predetermined amplitude by the vibration of the tuning fork 21. .

That is, the control current from the tuning fork amplitude control circuit 25 is supplied to the solenoid 24, and the output signal of the amplifier 23 is applied to the tuning fork amplitude control circuit 25 to apply the tuning fork 21.
Is controlled so that the amplitude of is constant.
The tuning fork 21 has, for example, 800 Hz and an amplitude of ± 0.3 m.
It is designed to vibrate at m.

Here, the amplitude of the objective lens 15 is
It is detected by the sensor 22. The detection amplitude signal detected by the sensor 22 that detects the amplitude of the tuning fork 21 is input to the amplifier 23, and the output signal Y thereof is input to the calculation unit 20.

When the objective lens 15 vibrates, the distance between the objective lens 15 and the object 16 to be measured changes, and when the light projected and projected on the object 16 to be measured is focused, the light receiving output of the photodiode 18 instantaneously. It will be maximum. The signal photoelectrically converted by the photodiode 18 is input to the amplifier 19, and its output signal X is input to the arithmetic unit 20. In this displacement measuring device, the displacement is measured from the signal when the focused point occurs and the signal of the sensor 22 at that time.

[0009]

However, in the above displacement measuring apparatus, since the objective lens 15 is attached to the tuning fork 21 and vibrated to change the distance from the object 16 to be measured, the objective lens 15 and the object to be measured are changed. It is not possible to detect the in-focus position by reducing the displacement speed of the object 16. That is, in order to vibrate the tuning fork 21 with a constant amplitude, it is necessary to vibrate at the natural frequency, and therefore the displacement speed cannot be reduced. If the in-focus position is detected at a lower speed, the measurement accuracy will be further improved.

Further, since the position of the objective lens 15 is changed by the tuning fork 21 and the position of the tuning fork 21 is detected by the sensor 22 to measure the displacement indirectly, an error occurs and there is a problem in high accuracy. . Furthermore, the objective lens 15 and the tuning fork 2
Since the structure including the solenoid 1, the solenoid 24, and the sensor 22 is complicated and the device becomes large in size, and there are many moving parts, reliability is a problem.

An object of the present invention is to provide a small displacement measuring device employing a confocal optical system which does not have a movable part and which can detect the in-focus position at a lower speed in order to improve the measurement accuracy. It is to provide a measuring method.

[0012]

In order to achieve the above object, a displacement measuring device and a displacement measuring method using the displacement measuring device according to the present invention employ the following means.

The displacement measuring device according to the present invention comprises a laser emission source for emitting a laser beam, a beam splitter for transmitting and reflecting the laser beam, a collimating lens, an objective lens, and a detector for detecting the reflected light. A displacement measuring apparatus having the above, characterized in that a liquid crystal lens is provided between the collimator lens and the objective lens.

The displacement measuring method of the present invention comprises a laser emission source for emitting a laser beam, a beam splitter for transmitting and reflecting the laser beam, a collimating lens, an objective lens, and a detector for detecting the reflected light. A displacement measuring method using a displacement measuring apparatus in which a liquid crystal lens is provided between the collimator lens and the objective lens, wherein a focal length is obtained by applying a first voltage to the liquid crystal lens. By a predetermined amount at a first speed, the focal length at which the light receiving output of the detector is maximized is set as a first focal length, and then a second voltage is applied to the liquid crystal lens, First
Near the focal length, the liquid crystal lens changes the focal length at a second speed lower than the first speed, and the focal length at which the amount of light received by the detector becomes maximum is the second focal length. The feature is that the displacement is measured by

[Operation] The displacement measuring device according to the present invention is
A liquid crystal lens is arranged between the objective lens and the collimating lens. The liquid crystal lens used here is one that changes the focal length by changing the refractive index distribution on a plane perpendicular to the optical axis by applying a voltage. By using this liquid crystal lens, a displacement measuring device is used. The focal length of can be changed.

The liquid crystal lens used here has a variable focal length resolution that is higher than the desired measurement accuracy. By using this, the desired displacement measurement can be performed without contact.

When the distance between the object to be measured and the objective lens and the focal length of the displacement measuring device match, the amount of received light detected by the detector of the displacement measuring device becomes maximum, and the focal length at that time is the objective lens and the object to be measured. It becomes the distance of things. Since the focal length at the time of applying the voltage is known, the distance of the object to be measured can be known by the applied voltage.

Further, the displacement measuring device according to the present invention is
Since the distance is measured by changing the voltage applied to the liquid crystal lens, the objective lens can be measured without moving with respect to the object to be measured. Therefore, the object to be measured and the displacement measuring device can be measured without a risk of collision, and the reliability is improved because there is no movable part.

Further, the size of the liquid crystal lens is 10 in length and width.
Since the millimeter and the thickness are several millimeters or less, and it can be easily inserted into the space between the collimator lens and the objective lens, the entire measuring device can be downsized.

The displacement measuring method according to the present invention is a measuring method using a measuring device in which a liquid crystal lens is arranged between an objective lens and a collimator lens and a voltage is applied to the liquid crystal lens for measurement. This measuring method is a measuring method in order to improve the measuring accuracy and to suppress the increase of the measuring time. Measure the approximate distance of the object to be measured at high speed, and measure it at low speed with high accuracy.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An optimum embodiment of the present invention will be described below with reference to the drawings. First, the configuration of a displacement measuring device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a drawing schematically showing a configuration of a displacement measuring device used in displacement measurement of the present invention.

As shown in FIG. 1, the emitted light of a laser diode 12 which is a laser emission source controlled by a laser power control circuit 11 passes through a beam splitter 13, a collimator lens 14, a liquid crystal lens 101 and an objective lens 15. Then, the object 16 to be measured is projected. The reflected light from the DUT 16 passes through the objective lens 15, the liquid crystal lens 101, and the collimator lens 14, is reflected by the beam splitter 13, and passes through the pinhole 17a provided in the optical diaphragm 17 to detect the reflected light. The light is incident on the photodiode 18, which is a detector.

As is clear from FIG. 1, since this displacement measuring apparatus employs a confocal optical system, laser light is applied to the object 16 to be measured at a point, and reflected light is also detected through the pinhole 17a. The light is focused on the (photodiode 18).
The confocal optical system achieves high resolution and can significantly eliminate unnecessary scattered light, resulting in a high-contrast image. Then, as a feature of the confocal optical system, the brightness and the resolving power have peaks at the focal position. That is, the maximum brightness and the in-focus position match. And the pinhole 17a
Has a diameter suitable for forming a confocal optical system.

The signal photoelectrically converted by the photodiode 18 is input to the amplifier 19, and its output signal is input to the control unit 103. Since this displacement measuring device employs a confocal optical system, strong light is incident on the photodiode 18 only when a focal point is generated.

Here, the liquid crystal lens will be described. The liquid crystal lens is a lens having a variable focal length that utilizes the characteristics of liquid crystal whose refractive index changes by changing the applied voltage. An example of the liquid crystal lens will be described with reference to FIG. 2. In the liquid crystal lens 31, a spherical concave lens 32 formed of a transparent substrate and a flat glass plate 33 also formed of a transparent substrate are opposed to each other, and transparent electrode layers 35 and 36 are provided on the opposing surfaces, respectively. Is provided, and the liquid crystal 37 is enclosed in a space formed when these are bonded together with an adhesive via the spacer 34.

Alignment treatment is applied to the sides of the two transparent electrode layers 35 and 36 which are in contact with the liquid crystal 37 so that the liquid crystal molecules are aligned in a specific direction, and in FIG.
When a voltage is applied to the liquid crystal lens 31, the liquid crystal lens 31
The molecules of the liquid crystal 37 inside rotate so as to align the major axis direction of the molecules with the direction of the electric field. As a result, the refractive index can be changed.

In FIG. 1, the liquid crystal lens 101 changes the focal length according to a command signal from the control unit 103. That is, the control unit 103 applies the applied voltage corresponding to the focal length instructed via the liquid crystal lens control circuit 102 to the liquid crystal lens 101. Then, when the distance between the objective lens 15 and the DUT 16 and the focal length instructed by the control unit 103 coincide with each other, the focal point is achieved, and strong light enters the photodiode 18 and is input to the amplifier 19.

In the displacement measuring device according to the present invention, the liquid crystal lens 10 is provided between the objective lens 15 and the collimator lens 14.
1 is arranged. Then, the liquid crystal 3 of the liquid crystal lens 101
By applying a voltage to 7, the refractive index of the liquid crystal 37 can be changed to change the focal length of the displacement measuring device.

As a result, when the distance between the object to be measured 16 and the objective lens 15 and the focal length of the displacement measuring device coincide, the amount of light received detected by the detector of the displacement measuring device becomes maximum,
The focal length at that time is the objective lens 15 and the object 16 to be measured.
It becomes the distance. Since the focal length when this voltage is applied is known, the distance of the DUT 16 can be known from the applied voltage.

Since the displacement measuring apparatus according to the present invention measures the distance by changing the voltage applied to the liquid crystal lens 101, the objective lens 15 can be measured without moving with respect to the DUT 16. Therefore, it is possible to perform the measurement without the risk of the object to be measured 16 and the displacement measuring device colliding with each other.

Next, the operation of the displacement measuring device of the present invention thus constructed will be described. Laser power control circuit 11
When a drive current is supplied to the laser diode 12 from the laser diode 12, the laser diode 12 emits laser light. The emitted light passes through the beam splitter 13, the collimator lens 14, the liquid crystal lens 101, and the objective lens 15, and the DUT 16 is measured.
Is projected to. The reflected light reflected by the DUT 16 is the objective lens 15, the liquid crystal lens 101, and the collimator lens 14.
It is reflected by the beam splitter 13 through the optical diaphragm 17
Only the light projected to the side and transmitted through the pinhole 17a is incident on the photodiode 18.

Since the configuration of the displacement measuring device according to the present invention employs the confocal optical system, the maximum brightness and the in-focus position match. That is, most of the light passes through the pinhole 17a in the focused state, but the amount of light passing through the pinhole 17a decreases drastically in the unfocused state.

Laser light is applied to the object 16 to be measured at a point, and the reflected light is also focused on the photodiode 18, which is a detector, at a point through the pinhole 17a. Therefore, unnecessary scattered light can be largely removed.

In the displacement measuring device used in the present invention, the focal length can be changed by the liquid crystal lens 101. Then, when the distance between the DUT 16 and the objective lens 15 and the focal length match, that is, when the focal point of the light projected on the DUT 16 occurs on the DUT 16, the photodiode 18
The light-receiving output of is instantly maximized, a signal corresponding to this light-receiving output is input to the amplifier 19, and an output signal is output from the amplifier 19 and input to the control unit.

Next, the displacement measuring method according to the present invention will be described. FIG. 3 is a diagram for explaining this measuring method. For example, a method of using this displacement measuring method when a displacement measuring device having a measuring range of ± 0.3 mm is used will be described.

The displacement measuring device having a measuring range of ± 0.3 mm uses the liquid crystal lens 101 to adjust the focal length from the reference position by ±.
It can be changed in the range of 0.3 mm. In FIG. 3, a position 201 indicates a position of −0.3 mm, and a position 20
2 indicates a position of +0.3 mm.

First, from -0.3 mm (position 201 in FIG. 3) to +0.3 mm (202 in FIG. 3) of the entire measurement range,
An applied voltage that changes the focal length is applied to the liquid crystal lens 101. The application time of the applied voltage at this time is, for example, 0.1
In seconds, the voltage application rate at this time is the first application rate.

Then, the focal length at which the light receiving output of the photodiode 18 instantly becomes maximum is obtained. The focal length is P1. At this time, the focal length P1 includes an error due to the response speed of the liquid crystal or the like. Therefore, in order to perform the measurement with higher accuracy, next, for example, (P1
From -0.03) mm to (P1 + 0.03) mm is changed at a second voltage application speed which is, for example, 10 times slower than the first speed, and the focal length at which the light receiving output of the photodiode 18 instantly becomes maximum is obtained. The focal length is P2.

Further, next, for example, (P2-
The focal length at which the light-receiving output of the photodiode 18 instantly becomes maximum is obtained by changing from 0.003) mm to (P2 + 0.003) mm at the third voltage application speed which is 10 times slower than the second speed, and P3 is obtained. Then, let P3 be the measured value. Furthermore, if necessary, the vicinity of P3 may be repeatedly measured.

According to this displacement measuring method, the speed at which the focus position is detected can be lowered and the detection can be performed with high accuracy. Furthermore, the entire measuring range (± 0.3m
m) When the voltage application speed is reduced over the entire length, the measurement time increases, but this measurement method can suppress the increase in measurement time and improve the measurement accuracy.

Next, an embodiment of the displacement measuring device of the present invention will be described with reference to FIG. FIG. 4 is a conceptual diagram of the displacement measuring device of the present invention.

As shown in FIG. 4, the emitted light of the laser diode 12 controlled by the laser power control circuit 11 passes through the beam splitter 13, the collimator lens 14, the liquid crystal lens 110, the liquid crystal lens 101, and the objective lens 15. And is projected onto the DUT 16. The reflected light from the DUT 16 passes through the objective lens 15, the liquid crystal lens 110, the liquid crystal lens 101, and the collimator lens 14 and is reflected by the beam splitter 13, and the pinhole 17
The light is incident on the photodiode 18 through a. In FIG. 4, reference numeral 17 is an optical stop, and the pinhole 17 a is provided in the optical stop 17.

As is clear from FIG. 4, since this displacement measuring device employs a confocal optical system, laser light is applied to the object 16 to be measured at a point, and reflected light is also detected through the pinhole 17a. The light is focused on the (photodiode 18).
The confocal optical system achieves high resolution and can significantly eliminate unnecessary scattered light, resulting in a high-contrast image. Then, as a feature of the confocal optical system, the brightness and the resolving power have peaks at the focal position. That is, the maximum brightness and the in-focus position match. And the pinhole 17a
Has a diameter suitable for forming a confocal optical system.

The signal photoelectrically converted by the photodiode 18 is input to the amplifier 19, and its output signal is input to the control unit 103. Since this displacement measuring device employs a confocal optical system, strong light is incident on the photodiode 18 only when a focal point is generated.

The liquid crystal lenses 101 and 110 change the focal length according to a command signal from the control unit 103. That is, the control unit outputs a signal indicating the focal length via the liquid crystal lens control circuit 102. That is, when the distance between the objective lens 15 and the DUT 16 and the focal length instructed by the control unit coincide with each other, the light is focused and intense light is incident on the photodiode 18.

Next, the operation of the displacement measuring device configured as described above and used in the displacement measuring method of the present invention will be described.

When a drive current is supplied from the laser power control circuit 11 to the laser diode 12, the laser diode 12 emits laser light. This emitted light is reflected by the beam splitter 13, the collimator lens 14, the liquid crystal lens 101,
It is projected onto the DUT 16 through the 110 and the objective lens 15.

The reflected light reflected by the DUT 16 passes through the objective lens 15, the liquid crystal lenses 101 and 110, and the collimator lens 14 and is reflected by the beam splitter 13 to be projected to the optical diaphragm 17 side and transmitted through the pinhole 17a. Only the generated light is incident on the photodiode 18.

Since the displacement measuring apparatus according to the present invention employs the confocal optical system, the maximum brightness and the in-focus position match. That is, most of the light passes through the pinhole 17a when in focus, but the amount of light passing through the pinhole 17a decreases drastically when out of focus.

Laser light is applied to the object 16 to be measured at a point, and the reflected light is also focused on the photodiode 18, which is a detector, at a point through the pinhole 17a. Therefore, unnecessary scattered light can be largely removed.

In the displacement measuring device used in the present invention, the focal length can be changed by the liquid crystal lenses 101 and 110. When the distance between the DUT 16 and the objective lens and the focal length match, that is, when the focus of the light projected on the DUT 16 occurs on the DUT 16, the light receiving output of the photodiode 18 instantly becomes maximum. A signal corresponding to the received light output is input to the amplifier 19, and an output signal is output from the amplifier 19 and input to the control unit.

In this embodiment, a liquid crystal lens having a maximum liquid crystal layer thickness of 100 μm and a maximum liquid crystal layer thickness of 10 μm is used. The lens 101 has a maximum liquid crystal layer thickness of 100 μm and a radius of curvature of 31.3 mm. Here, the refractive index of the glass substrate is 1.52. The refractive index of the liquid crystal changes in the range of 1.5 to 17 depending on the applied voltage.

The liquid crystal lens 110 has a liquid crystal layer thickness of 10 μm.
And the radius of curvature is 312 mm. In this displacement measuring device, the measurement range of the liquid crystal lens 101 is ±
It is 200 μm. Further, since the measurement range by the liquid crystal lens 110 is ± 20 μm, and the response speed of the liquid crystal is proportional to the square of the thickness of the liquid crystal layer, the liquid crystal lens 110 having the maximum liquid crystal thickness of 10 μm is about 100 times larger than the liquid crystal having the maximum liquid crystal thickness of 100 μm. Response speed becomes faster.

In the displacement measuring apparatus shown in FIG. 4, the liquid crystal lens 101 (the thickness of the liquid crystal layer is 100 μm) ensures the entire measurement range (± 200 μm), and the liquid crystal lens 110
By (the thickness of the liquid crystal layer is 10 μm), an arbitrary measurement range (± 20 μm) within the entire measurement range can be measured at higher speed and with high accuracy.

Next, a measuring method by the displacement measuring device according to the present invention will be described with reference to FIG. The measuring range of this displacement measuring device is ± 200 μm by the liquid crystal lens 101. That is, the liquid crystal lens 101 can change the focal length within a range of ± 200 μm from the reference position. Position 201 is -2 in FIG.
It is assumed that the position of 00 μm is shown and the position 202 shows the position of +200 μm.

First, the focus is changed from -200 .mu.m (position 201 in FIG. 3) to +200 .mu.m (position 202 in FIG. 3) of the entire measurement range by the liquid crystal lens 101, and the light receiving output of the photodiode 18 instantly becomes the maximum focus. Find the distance. The focal length is P1.

Here, for example, when the height of the object to be measured is exchanged, if the measurement range is ± 20 μm, the applied voltage of the liquid crystal lens 101 (measurement range ± 200 μm) is at the position P1. Hold it, liquid crystal lens 1
The measurement is performed by changing the applied voltage of 10 (measuring range ± 20 μm).

[0058]

As is apparent from the above description, the displacement measuring device according to the present invention using the confocal optical system and the liquid crystal lens has the liquid crystal lens between the objective lens and the collimating lens. Then, by applying a voltage to the liquid crystal of the liquid crystal lens, the refractive index of the liquid crystal can be changed to change the focal length of the displacement measuring device.

When the distance between the object to be measured and the objective lens and the focal length of the displacement measuring device match, the amount of light received detected by the detector of the displacement measuring device becomes maximum, and the focal length at that time is It is the distance to the object to be measured. At this time,
Since the focal length when the applied voltage is known, the distance of the object to be measured can be known from the applied voltage.

Further, since the displacement measuring device used in the displacement measuring method according to the present invention measures the distance by changing the voltage applied to the liquid crystal lens, the objective lens is measured without moving relative to the object to be measured. it can. Therefore, it is possible to perform measurement without concern that the object to be measured and the displacement measuring device may collide with each other.

Further, in the displacement measuring method using the measuring device using the confocal optical system and the liquid crystal lens, since the speed at which the focal position is detected and the measuring range can be changed, highly accurate displacement measurement can be performed. it can.

Further, in the displacement measuring device using the confocal optical system and the liquid crystal lens according to the present invention, since the two liquid crystal lenses having different measurement ranges are provided, the measurement can be performed with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a displacement measuring device and a displacement measuring method using the same according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a displacement measuring device and a liquid crystal lens used in a displacement measuring method using the same according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a displacement measuring device and a displacement measuring method using the same according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining a displacement measuring device and a displacement measuring method using the same according to an embodiment of the present invention.

FIG. 5 is a view for explaining a displacement measuring device according to a conventional technique.

[Explanation of symbols]

11 Laser power control circuit 12 Laser diode 13 Beam splitter 14 Collimating lens 15 Objective lens 16 DUT 17 Optical diaphragm 17a pinhole 18 photodiodes 19 amplifier 101 liquid crystal lens 102 Liquid crystal lens control circuit 103 control unit 110 LCD lens

Claims (3)

[Claims] 1. A displacement measuring device having a laser emission source for emitting a laser beam, a beam splitter for transmitting and reflecting the laser beam, a collimating lens, an objective lens, and a detector for detecting the reflected light. And a liquid crystal lens provided between the collimator lens and the objective lens. 2. The displacement measuring apparatus according to claim 1, wherein the liquid crystal lens is composed of a plurality of lenses. 3. A displacement measuring method using the displacement measuring device according to claim 1, wherein a first voltage is applied to the liquid crystal lens to change a focal length to a first focal length.
The focal length at which the received light output of the detector is maximized is changed to a first focal length by varying a predetermined amount at a speed of, and then a second voltage is applied to the liquid crystal lens to set the first focal length. A second speed lower than the first speed in the vicinity of the distance
The displacement measuring method is characterized in that the displacement is measured by varying the focal length with the liquid crystal lens at a speed of, and setting the focal length at which the amount of light received by the detector is maximum as the second focal length.