JPH0528762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical displacement transducer.

More specifically, light is irradiated onto the surface to be measured through a lens, and the position of the lens is moved so that the surface is always focused on the surface to be measured, and the displacement of the surface to be measured is calculated from the amount of movement of the lens at this time. The present invention relates to a displacement transducer adapted to measure a quantity.

[Conventional technology]

Conventionally, as an example of an optical displacement converter, a device as shown in FIG. 3 has been put into practical use. The displacement converter shown in the figure irradiates parallel light beams emitted from a light source 1 onto a surface to be measured 3 via a lens 2, and also irradiates a parallel light beam emitted from a light source 1 to a surface to be measured 3 through a lens 2. The position is moved, and the amount of displacement of the surface to be measured 3 is measured from the amount of movement of the lens 2 at this time. Here, a cylindrical lens 4 and a four-split sensor 5 are used to detect whether or not the focus is on the surface to be measured 3, and a half-split sensor placed behind the lens 2 uses a cylindrical lens 4 and a four-split sensor 5 to direct the reflected light from the surface to be measured 3. A mirror 6 guides the light to the cylindrical lens 4, and a four-part sensor 5 detects changes in the shape of the light spot obtained by the cylindrical lens 4.

That is, the light spot and shape projected onto the 4-split sensor 5 are as shown in FIG. Since the light beam incident on the cylindrical lens 4 is parallel, the shape of the light spot on the four-part sensor 5 is circular, as shown by the solid line a in the figure. Furthermore, when the focus is out of focus, the light beam incident on the cylindrical lens 4 is no longer parallel, so the light spot is formed as shown by broken lines b and c.
The image becomes a circular shape with a different direction of inclination depending on the shift of focus. Therefore, the output sent to the 4-split sensor 5
By processing S1 to S4 as, for example, [S1+S3]-[S2+S4], the shape of the light spot can be detected and the position of the focal point can be determined. Note that the output of each of the four-split sensors 5 is used as a feedback signal for an automatic focusing mechanism that moves the lens 2 to always focus on the surface 3 to be measured.

[Problem that the invention seeks to solve]

However, in the displacement transducer using the cylindrical lens 4 and the 4-split sensor 5 as described above, if the measurement target surface 3 is tilted, the light projected onto the 4-split sensor 5 as shown in FIG. Since the position of the spot is shifted from the center, even in the focused state, the output of the 4-split sensor 5
S1 to S4 become unbalanced, making it impossible to perform accurate autofocus operation. For this reason,
The inclination of the surface 3 to be measured must be kept within ±1°.

The present invention eliminates the drawbacks of the conventional position as described above, and realizes a displacement transducer with a simple configuration that can accurately measure the amount of displacement even when the surface to be measured has a relatively large inclination. It is intended to.

[Means for solving problems]

The displacement converter of the present invention irradiates light onto a surface to be measured through a lens, moves the position of the lens so that the surface is always focused on the surface to be measured, and uses the amount of movement of the lens at this time to determine the measurement target surface. In a displacement transducer designed to measure the amount of displacement of a target surface, two light beams consisting of parallel light beams each having an optical axis parallel to the lens axis are incident on the lens at an on-axis position and at other positions, and the lens A second lens is placed in the optical path of the reflected light that returns via the The output of the position sensor is used as a feedback signal for an automatic focusing mechanism that moves the position of the lens.

[Effect]

In this way, by arranging the second lens in the optical path of the reflected light and arranging the position sensor at the focal position of this second lens, in the focused state, the reflection from the surface to be measured is The light forms a real image at the position of the position sensor, and since the incident position of the reflected light on the position sensor is always constant, it is possible to determine whether the focus is on the surface to be measured based on the output state of the position sensor. By using the output of the position sensor as a feedback signal for the automatic focusing mechanism, it is possible to automatically measure the amount of displacement of the surface to be measured. In addition, the position where the reflected light from the surface to be measured forms a real image is constant regardless of the path of the light beam, so even if the surface to be measured is tilted, as long as the reflected light enters the lens, The amount of displacement can be measured accurately. Furthermore, the structure is configured so that measurement can be performed using two light beams with different incident positions on the lens, so by selectively using these light beams, , it is possible to widen the permissible range of inclination on the surface to be measured.

〔Example〕

FIG. 6 is a block diagram showing the specific principle of the displacement transducer of the present invention. Note that the displacement transducer shown in the figure has already been invented by the inventor of the present application. In the figure, the same parts as in FIG. 3 are designated by the same reference numerals. 7 is a second lens placed in the optical path of the reflected light returning via lens 2; 8 is a position sensor placed at the focal point of second lens 7; The light beam emitted from the light source 1 has an optical axis parallel to the axis of the lens 2, and is incident on a position other than the axis of the lens 2, and is irradiated onto the surface to be measured 3 via the lens 2. . Further, the light reflected by the measurement target surface 3 enters the position sensor 8 via the half mirror 6 and the second lens 7. moreover,
The lens 2 is moved by an automatic focusing mechanism (not shown), and the distance to the measurement target surface 3 is arbitrarily adjusted.

FIG. 7 is a configuration diagram showing an example of a position sensor 8 that detects the incident position of reflected light incident through the second lens 7. As shown in the figure, the position sensor 8 has a uniform p-type resistance layer 82 on one or both sides of a high-resistance silicon 81 (i-layer), and also has a PN junction with a photoelectric effect formed on the surface layer. , a pair of electrodes A and B for extracting signals are provided at both ends of the layer. In the position sensor 8 having such a configuration, the distance between the electrodes A and B is L, the resistance is RL,
If the distance from electrode A to the light incident position is x, and the resistance of that part is Rx, then the photogenerated charge generated at the light incident position becomes a photocurrent I ₀ that is proportional to the incident light energy, and the resistance value is It is divided according to Rx and (RL-Rx) and taken out from electrodes A and B at both ends as currents IA and IB. Therefore, the currents IA and IB are IA=I ₀ (RL-Rx)/RL=I ₀ (L-x)/L IB=I ₀・Rx/RL=I ₀・x/L, and each current The ratio IA/IB of IA and IB is IA/IB = (L-x)/x, so by finding the values of currents IA and IB, the incident position of the light can be determined regardless of the magnitude of the incident energy. be able to.

FIG. 8 shows a two-dimensional structure of a position sensor 8 having the operating principle as described above.
As shown in the figure, the ratio of the current taken out from each electrode Ax, Ay, Bx, By includes positional information in the X-axis direction and Y-axis direction at the light incident position, and is calculated by processing this information. , it is possible to know the two-dimensional incident position.

Now, returning to Fig. 6, when the focus is on the measurement target surface 3 (in-focus state), the reflected light returning via the lens 2 has an optical axis parallel to the axis of the lens 2. Since the reflected light becomes a parallel light ray, after passing through the second lens 7, it forms a real image at its focal position. At this time, since the position sensor 8 is placed at the focal point of the second lens 7, the reflected light is incident on the position sensor 8, and the position of incidence is detected by the position sensor 8. Ru.

Next, if the measurement object surface 3 is displaced to the position 3' in the figure, the measurement object surface 3 is removed from the focal point of the irradiated light beam, so the path of the reflected light moves as shown by the broken line, Along with this, since the reflected light is no longer a parallel light beam, the incident position of the reflected light on the position sensor 8 also moves.
Furthermore, at this time, since the imaging position of the reflected light is also shifted from the position sensor 8, a spot with a certain extent of spread comes to be incident on the position sensor 8.

FIG. 9 shows the relationship between the incident position of reflected light on the position sensor 8 and the size of the spot. In the figure, if the incident position of the reflected light in the focused state is P0, the spot diameter at this time is the smallest, and as the measurement target surface 3 deviates from the focal position, the incident position also changes in the P1, P2 direction or P3,
The spot diameter gradually increases as it moves toward P4. For example, if the incident position moves in the P1 direction when the measurement target surface 3 becomes closer than the focal position, then when the measurement target surface 3 becomes further away from the focal position, the incidence position moves in the P3 direction. .

In this way, when the position sensor 8 is placed at the focal position of the second lens 7, the incident position of the reflected light on the position sensor 8 changes depending on the position of the measurement target surface 3, so the position The focus state can be known from the output of the sensor 8, and if an automatic focusing mechanism is constructed using this output as a feedback signal,
The lens 2 can be moved so that the light beam emitted from the light source 1 is always focused on the surface to be measured 3, and the amount of displacement of the surface to be measured 3 can be automatically measured from the amount of movement at this time. I can do it.

Also, if we consider the case where the surface to be measured 3 is tilted, in this case the path of the light reflected from the surface to be measured 3 will be different from that shown in FIG. 6, but the lens 2 and 7, if the focal position is on the measurement target surface 3, the reflected light becomes a parallel light beam having an optical axis parallel to the axis of the lens 2, and the reflected light forms an image through the second lens 7. Since the position does not change, the incident position of the reflected light on the position sensor 8 also does not change, and the in-focus state can be accurately detected from the output of the position sensor 8, as in the above case. Note that when the measurement target surface 3 is tilted, the incident position of the reflected light on the position sensor 8 changes as shown in FIG. 10, for example.
It moves along with the displacement of the surface 3 to be measured. As is clear from the figure, since the incident position P0 when the measurement target surface 3 is at the focal position is equal to the position shown in FIG. 9, the output of the position sensor 8 at this time is also the same value, The amount of displacement can be measured without being affected by the inclination of the surface 3.

Here, in the displacement converter shown in FIG.
Measurement can be performed even when the slope of the surface 3 to be measured is large to some extent, but if the optical axis of the reflected light coincides with the axis of the lens 2 due to the degree of slope of the surface 3 to be measured, The position sensor 8 becomes insensitive to the displacement of the measurement target surface 3,
Automatic focus operation becomes impossible.

The present invention solves this problem,
FIGS. 1 and 2 are block diagrams showing one embodiment of the displacement transducer of the present invention. In the figure, 9, 10
are first and second light beams B1 and B2 each consisting of parallel rays having optical axes parallel to the axis of lens 2;
These light beams B1 and B2 are incident on the lens 2 on the axis and at other positions. The light sources 9 and 10 are driven by a command from an automatic focusing mechanism to be described later, and selectively emit two light beams B1 and B2 having different optical axes.

In the displacement transducer configured as above,
As shown in FIG. 1, if the surface to be measured 3 is not tilted, the reflected light B1' by the first light beam B1 passes through the same optical path (axis of the lens 2) as the incident light (B1) and reaches the position. enters the sensor 8, and the second luminous flux B
The light B2' reflected by the light B2' is incident on the position sensor 8 through a different optical path from that of the incident light (B2). As is clear from the figure, the position sensor 8 has sensitivity to the reflected light B2' as in the case of FIG. 6 described above, but it is sensitive to the reflected light B1'. Even if the target surface 3 is displaced, only the diameter of the spot changes and the position of incidence remains unchanged, so there is no sensitivity. Therefore, in such a case, if the measurement operation is performed using the second light beam B2 (indicated by hatching in the figure), normal measurement can be performed.

Furthermore, as shown in FIG.
When the optical axis of lens 2' coincides with the axis of lens 2,
The reflected light B1' from the first light beam B1 takes an optical path deviating from the axis of the lens 2 and enters the position sensor 8. Therefore, the position sensor 8 uses the reflected light B2' instead of the reflected light B2'.
1', and in such a case, it is sufficient to perform the measurement operation using the first beam B1 (indicated by hatching in the figure).

Therefore, in the displacement transducer of the present invention,
Of the two light beams B1 and B2 with different optical axes,
By selecting the light flux to which the position sensor 8 has greater sensitivity and performing the measurement operation, the position sensor 8 eliminates the state where it has no sensitivity,
The permissible range of inclination on the measurement target surface 3 can be widened. Note that detection of sensitivity in the position sensor 8 is performed using one function of an automatic focusing mechanism.

FIG. 11 is a configuration diagram showing an example of an automatic focusing mechanism used in the displacement converter of the present invention. In the figure, 8 is a position sensor, and as mentioned above, the output signal S(X,
Y) is generated. 11 is the servo amplifier and the target value
Depending on the difference ΔS between SET and feedback signal S (X, Y),
A drive signal Sd for moving the lens 2 is generated. 12 is the power amplifier, 13 is the lens 2
14 is a position sensor 8
This is a sensitivity measurement circuit that detects the sensitivity of the sensor and selects the luminous flux to be used. SW is servo amplifier 11
This is a switch that selectively supplies the output of the power amplifier 12 and the output of the sensitivity measurement circuit 14 to the power amplifier 12.

In the automatic focusing mechanism configured as described above, the target value SET is set equal to the output S (X, Y) of the position sensor 8 in the focused state, and the servo amplifier 11 has a deviation ΔS of zero. Since the motor 13 is driven, the lens 2 is moved so that the focal point of the irradiated light beam is always on the surface 3 to be measured. Therefore, this motor 13 and the amount of drive are proportional to the amount of displacement of the surface to be measured 3, so by detecting this amount of drive or the amount of movement of the lens 2, the amount of displacement of the surface to be measured 3 can be measured. can do. Note that the switch SW is normally connected to the servo amplifier 11 side.

The autofocus operation is performed as described above, but before this autofocus operation, the sensitivity of the position sensor 8 to the first and second light beams B1 and B2 is detected, and the light beam to be used is selected. . In this case, the switch SW is the sensitivity measurement circuit 14.
The output of the sensitivity measurement circuit 14 is supplied to the power amplifier 12. Thereafter, the sensitivity measurement circuit 14 turns on one of the light sources 9 and 10 (for example, 9), moves the lens 2 by a certain amount via the motor 13, and changes the amount of change in the output of the position sensor 8 at this time ( Sensitivity). Next, the sensitivity measurement circuit 14 turns on the other light source (10) of the light sources 9 and 10, and detects the sensitivity of the position sensor 8 in the same manner as described above. At this time, when the inclination of the measurement target surface 3 changes, the optical axes of the reflected lights B1' and B2' change, and the sensitivity of the position sensor 8 according to the respective luminous fluxes B1 and B2 also changes, so the sensitivity can be measured. The circuit 14 receives the first signal detected as described above.
Then, the sensitivities to the second light beams B1 and B2 are compared, and the drive of the light sources 9 and 10 is switched to the light beam side that can obtain greater sensitivity. Therefore, if the automatic focusing mechanism is operated after the selection operation of the light sources 9 and 10 is completed, the measurement operation can always be carried out in the best condition.

Here, as described above, when the surface to be measured 3 has an inclination, the sensitivity of the position sensor 8 also changes, so the sensitivity detected by the sensitivity measurement circuit 14 is based on the sensitivity as described above. If the gain of the servo amplifier 11 is adjusted in this way, the controllability of the automatic focusing mechanism can be improved.

Furthermore, by utilizing the sensitivity change in the position sensor 8 as described above, that is, the property of the change in the incident position of reflected light, it is also possible to conversely measure the inclination of the measurement target surface 3 from the sensitivity change of the position sensor 8. It is. That is, by displacing the lens 2 by a certain amount from the focused state, the position sensor 8 at this time
If we measure the output change at , the amount of change and the direction of change in the incident position of the reflected light at this time correspond to the inclination of the measurement target surface 3, so by comparing it with the data measured in advance, The inclination of the surface 3 to be measured can be known.

In the above description, the means for changing the path of the reflected lights B1' and B2' from the measurement target surface 3 is as follows:
The mirror 6 is not limited to the half mirror 6, and may be, for example, a prism or a polarizing beam splitter. Further, the light sources 9 and 10 are not limited to two light sources, and may be realized as one light source by a combination of a half mirror, a shielding plate, a chopper, or the like.

〔Effect of the invention〕

As explained above, in the displacement converter of the present invention, light is irradiated onto the surface to be measured through the lens, and the position of the lens is moved so that the surface to be measured is always in focus. In a displacement converter that measures the amount of displacement of the surface to be measured from the amount of movement of the lens, two light beams each consisting of a parallel light beam each having an optical axis parallel to the axis of the lens are transmitted to positions on and off the axis of the lens. A second lens is disposed in the optical path of the reflected light that is incident on the lens and returns via the lens, and a position sensor that can detect the incident position of the light is installed at the focal position of the second lens. Since the output of this position sensor is used as a feedback signal for the automatic focusing mechanism that moves the lens position, in the focused state, the reflected light from the surface to be measured is transmitted to the position sensor. A real image will be formed at the position of , and since the incident position of the reflected light on the position sensor at this time will always be constant, it can be determined from the output state of the position sensor whether or not it is focused on the surface to be measured. With a simple configuration, it is possible to realize a displacement transducer that can accurately measure the amount of displacement even when the surface to be measured has a relatively large inclination.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing one embodiment of the displacement transducer of the present invention, FIG. 3 is a block diagram showing an example of a conventional displacement converter, and FIGS.
Explanatory diagram showing the spot shape of incident light in the 4-split sensor used in the displacement transducer shown in the figure, No. 6
7 and 8 are block diagrams showing an example of a position sensor used in the displacement transducer of the present invention, and FIGS. 9 and 10 are block diagrams showing the measurement principle of the displacement transducer of the present invention. The figure is an explanatory diagram showing the incident position of reflected light and the state of the spot on the position sensor, and FIG. 11 is a configuration diagram showing an example of an automatic focusing mechanism used in the displacement converter of the present invention. 1, 9, 10... light source, 2... lens, 3...
Surface to be measured, 4... Cylindrical lens, 5...
...4-split sensor, 6...Half mirror, 7...Second lens, 8...Position sensor, 11...
Servo amplifier, 12... Power amplifier, 13...
Motor, 14...Sensitivity measurement circuit, SW...Switch.

Claims (1)

[Claims] 1. Irradiate the surface to be measured with light through a lens, move the position of the lens so that it is always focused on the surface to be measured, and measure the amount of displacement of the surface to be measured from the amount of movement of the lens at this time. In the displacement transducer, first parallel light beams each having an optical axis parallel to the axis of the lens;
and a light source that selectively emits a second light beam and makes these light beams incident on the lens at axial and other positions, and a second light source disposed in the optical path of the reflected light returning via the lens. a position sensor disposed at the focal position of the second lens; and an automatic focusing mechanism that receives the output of the position sensor and moves the position of the lens so that the output becomes a constant value. and a first light source emitted from the point light source.
Then, the lens is moved by a certain amount with respect to the second light beam, and the sensitivity of the position sensor at this time is detected, and the amount of displacement is measured using the light beam that can obtain greater sensitivity. A displacement transducer characterized by performing a motion.