JPH0697163B2 - Displacement converter - Google Patents

Description

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

More specifically, the position of the lens is moved so that the measurement target surface is irradiated with light through the lens and the focus is always on the measurement target surface, and the displacement of the measurement target surface is calculated from the movement amount of the lens at this time. It relates to a displacement transducer adapted to measure a quantity.

[Conventional technology]

Conventionally, as an example of an optical displacement transducer, a device as shown in FIG. 9 has been put into practical use. The displacement converter shown in the figure irradiates a parallel light beam emitted from a light source 1 onto a measurement target surface 3 via a lens 2, and the luminous flux of the lens 2 is always focused on the measurement target surface 3. The position is moved, and the displacement amount of the measurement target surface 3 is measured from the movement amount of the lens 2 at this time. Here, the cylindrical lens 4 and the four-division sensor 5 are used to detect whether or not the measurement target surface 3 is in focus, and the reflected light from the measurement target surface 3 is arranged behind the lens 2. The mirror 6 guides the light to the cylindrical lens 4, and the four-division sensor 5 detects the shape change of the light spot obtained by the cylindrical lens 4.

That is, the shape of the light spot projected on the four-division sensor 5 is as shown in FIG. 10, and when the focus is on the measurement target surface 3 (hereinafter, this is referred to as a focused state). Since the light beam incident on the cylindrical lens 4 is a parallel light beam, the shape of the light spot on the four-division sensor 5 is circular as shown by the solid line a in the figure. Further, when the light beam is not in focus, the light beam incident on the cylindrical lens 4 is not a parallel light beam, so that the light spot has a coasting circular shape in which the tilt direction differs depending on the focus shift, as indicated by broken lines b and c. Therefore, the outputs S1 to S4 in the four-division sensor 5 are, for example, (S1 + S3) −
By performing the arithmetic processing as (S2 + S4), the shape of the light spot can be detected and the position of the focal point can be known. The output of the four-division sensor 5 is used as a feedback signal of an automatic focusing mechanism that moves the lens 2 and always focuses on the measurement target surface 3.

[Problems to be solved by the invention]

However, in the displacement converter using the cylindrical lens 4 and the four-division sensor 5 as described above,
If the surface 3 to be measured is tilted, the position of the light spot projected on the four-division sensor 5 deviates from the center, as shown in FIG. Outputs S1 to S4 are not balanced and accurate autofocus operation cannot be performed. Therefore, the inclination of the surface 3 to be measured must be suppressed within ± 1 °.

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

Another object of the present invention is to realize a displacement converter capable of simultaneously measuring the amount of displacement of the surface to be measured and its inclination.

[Means for solving problems]

Displacement transducer of the present invention, while irradiating light to the measurement target surface through the lens, the position of the lens is moved so as to always focus on the measurement target surface, from the amount of movement of the lens at this time In a displacement converter configured to measure the amount of displacement of the measurement target surface, a position where light incident from a point light source is irradiated onto the measurement target surface through a lens and the incident position of light can be detected The sensor is equivalently placed at the same position as the point light source or at a certain distance from it, and the output of the former position sensor is used as a feedback signal for the automatic focusing mechanism that moves the position of the lens and point light source. In addition, the inclination of the measurement target surface is measured by utilizing the difference between the outputs of the two position sensors.

[Work]

As described above, when the point light source is used as the light source and the first position sensor is equivalently arranged at the same position as the point light source, in the focused state, the reflected light from the measurement target surface is the first light source. Since a real image is formed at the position of the position sensor (point light source), and the incident position of the reflected light at this time on the first position sensor is always constant, measurement is performed from the output state of the first position sensor. It is possible to detect whether or not the target surface is in focus, and by using the output of the first position sensor as a feedback signal of the automatic focusing mechanism, the displacement amount of the measuring target surface is automatically measured. be able to. Further, since the position where the reflected light from the surface to be measured forms a real image is constant (the position of the point light source) regardless of the path of the light flux, even if the surface to be measured is inclined, the reflected light is reflected on the lens. The amount of displacement can be accurately measured as long as it is incident. Further, as described above, since the second position sensor is arranged at a constant interval with respect to the first position sensor used for measuring the displacement amount, the output of the second position sensor is measured. It corresponds to the inclination of the target surface,
By detecting the difference between the outputs of these position sensors, the inclination of the measurement target surface can be measured at the same time.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the displacement converter of the present invention. In the figure, the same parts as those in FIG. 9 are designated by the same reference numerals. Reference numeral 7 is a point light source arranged on the axis of the lens 2, and 8 is equivalently a point light source 7 via the half mirror 6.
The first position sensor 9 is arranged at the same position as, and the second position sensor 9 is arranged at a certain distance from the first position sensor 8 via the half mirror 10. The light flux emitted from the point light source 7 is reflected by the lens 2
Has a constant angle with respect to the axis of, and is irradiated onto the measurement target surface 3 via the lens 2. The light reflected by the surface 3 to be measured is reflected by the lens 2 and the half mirror.
It is incident on the first and second position sensors 8 and 9 via 6 and 10. Further, the lens 2, the half mirrors 6 and 10, the point light source 7 and the position sensors 8 and 9 are integrally supported, and are moved by an automatic focusing mechanism (not shown) so that the distance to the measurement target surface 3 can be arbitrarily set. Is adjusted to.

FIG. 2 is a configuration diagram showing an example of the position sensors 8 and 9 for detecting the incident position of the reflected light incident through the lens 2. In the figure, the first position sensor 8 is illustrated. As shown in the figure, the position sensor 8 has a uniform p-type resistance layer on one or both sides of the high resistance silicon 81 (i layer).
82 is provided, a PN junction having a photoelectric effect is formed in the surface layer, and a pair of electrodes A and B for extracting a signal is further provided at both ends of the layer. In the position sensor 8 having such a configuration, if the distance between the electrodes A and B is L, the resistance is RL, the distance from the electrode A to the incident position of light is x, and the resistance of that portion is Rx, The photo-generated electric charge generated at the incident position of light becomes a photocurrent Io proportional to the incident energy of light and is divided according to the resistance values Rx and (RL−Rx), and the currents IA and IB are divided into electrodes A, Taken from B. Therefore, this current IA, IB becomes IA = Io (RL−Rx) / RL = Io (L−x) / L IB = Io.Rx / RL = Io · x / L, and the ratio IA of each current IA, IB Since / IB is IA / IB = (L−x) / x, the light incident position can be known by obtaining the values of the currents IA and IB, regardless of the magnitude of incident energy.

FIG. 3 shows a two-dimensional structure of the position sensor 8 having the above-described operation principle. As shown in the figure, the ratio of the current drawn from each electrode Ax, Ay, Bx, By is
The position information in the X-axis direction and the Y-axis direction at the incident position of light is included, and the two-dimensional incident position can be known by calculating these.

Now, returning to FIG. 1, when the measurement target surface 3 is in focus (in focus), the distance between the point light source 7 and the lens 2 is l1, and the distance between the lens 2 and the measurement target surface 3 is If the distance is l2 and the focal length of the lens 2 is f, the relational expression of 1 / l1 + 1 / l2 = 1 / f is established, and the reflected light from the measurement target surface 3 passes through the lens 2 and then the point light source 7 It will come back to form a real image at the position. At this time, since the first position sensor 8 is equivalently arranged at the position of the point light source 7,
The reflected light is incident on the position sensor 8, and the incident position is detected by the position sensor 8.

Hereinafter, the description will be made focusing on the incident state of the reflected light on the first position sensor 8.

Now, assuming that the measurement target surface 3 is displaced to the position 3'in the figure, the measurement target surface 3 is out of the focus position of the illuminating light flux, so the path of the reflected light moves as shown by the broken line. Along with this, the incident position of the reflected light on the position sensor 8 also moves. Further, at this time, the image forming position of the reflected light is also deviated from the position sensor 8, so that a spot having a certain extent of spread enters the position sensor 8.

FIG. 4 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 in-focus state is P0, the spot diameter at this time is the smallest, and as the measurement target surface 3 shifts from the focal position, the incident position also becomes the P1, P2 direction or P3, P4 direction. The spot diameter gradually increases. For example, if the incident position moves in the P1 direction when the measurement target surface 3 is closer to the focus position, then when the measurement target surface 3 is further from the focus position,
On the contrary, the incident position moves in the P3 direction.

In this way, if the position sensor 8 is equivalently placed at the same position as the point light source 7, the incident position of the reflected light on the position sensor 8 changes according to the position of the measurement target surface 3, so the position sensor 8 The in-focus state can be known from the output of the lens 2, and if this output is used as a feedback signal to configure an automatic focusing mechanism, the lens 2 can always focus the light beam emitted from the point light source 7 on the measurement target surface 3. Etc. can be moved, and the displacement amount of the measurement target surface 3 can be automatically measured from the movement amount at this time.

Here, consider the case where the surface 3 to be measured is tilted. In this case, the path of the light reflected from the measurement target surface 3 is different from that in the case of FIG. 1, but due to the nature of the lens 2, if the focus position is on the measurement target surface 3, the reflected light Since the position where the image is formed does not change, the incident position of the reflected light on the position sensor 8 does not change, and the focus state can be accurately detected from the output of the position sensor 8 as in the case described above. When the measurement target surface 3 is inclined, the incident position of the reflected light on the position sensor 8 changes as shown in FIG. 5, for example, and moves with the displacement of the measurement target surface 3. As is apparent from the figure, since the incident position P0 when the measurement target surface 3 is at the focus position is equal to the position shown in FIG. 4, the output of the position sensor 8 at this time is also the same value. The displacement amount can be measured without being affected by the inclination of 3.

Next, the operation of measuring the inclination of the measurement target surface 3 using the output of the second position sensor 9 will be described.

As shown in FIG. 1, the second position sensor 9 is arranged so as to have an equivalent constant interval with respect to the first position sensor 8. Therefore, in a state where the automatic focusing mechanism is activated and the measurement target surface 3 is in focus, the reflected light returning through the lens 2 is in an image forming state with respect to the first position sensor 8. Then, the light beam that enters the fixed position (P0) and deviates from the image forming state enters the second position sensor 9.

FIG. 6 shows such first and second position sensors.
The incident states of the reflected light in 8 and 9 are illustrated along with the optical axes. As shown in the figure, in the in-focus state, the light passing through the fixed position (P0) of the first position sensor 8 enters the second position sensor 9, and the fixed position (P0) changes. Therefore, if the path of the reflected light changes according to the inclination of the measurement target surface 3, only the incident position on the second position sensor 9 changes.

FIG. 7 shows the incident position of the reflected light on the second position sensor 9. For example, when the measurement target surface 3 is tilted about the X axis, the incident position moves in the direction of the arrow x. Then, when the surface 3 to be measured is tilted around the Y axis, it moves in the direction of the arrow y.

In this way, the incident position of the reflected light on the second position sensor 9 changes according to the inclination of the measurement target surface 3, so that the output of the second position sensor 9 determines the measurement target surface 3
It is possible to measure the slope of. In the displacement transducer of the present invention, the difference between the outputs of the first and second position sensors 8 and 9 is obtained, and the inclination of the measurement target surface 3 is measured by comparing this with the data measured in advance. is doing. As described above, since the output (incident position) of the first position sensor 8 is always constant, it is possible to obtain the inclination of the measurement target surface 3 only from the output of the second position sensor 9.

Further, as described above, the path of the reflected light can be detected from the difference between the outputs of the first and second position sensors 8 and 9. Therefore, if this information is used, the reflected light can be reflected by the lens 2 when measuring. It is possible to know which part of the lens is passing through and it is possible to correct the measurement error due to the aberration of the lens 2. In general, in the lens 2, the influence of the received aberration is different depending on the position where the reflected light passes. Therefore, if the path of the reflected light is known in advance, the measurement result can be corrected accordingly, and more accurate measurement can be performed. Can be done.

FIG. 8 is a block diagram showing an example of an automatic focusing mechanism used in the displacement converter of the present invention. In the figure, reference numeral 8 is a first position sensor, which generates an output signal S (X, Y) corresponding to the incident position of the reflected light, as described above. Reference numeral 11 denotes a servo amplifier, which is a drive signal Sd for moving the lens 2 or the like according to the difference ΔS between the target value SET and the feedback signal S (X, Y).
To occur. Reference numeral 12 is a power amplifier, and 13 is a motor for moving the lens 2 and the like.

In the automatic focusing mechanism configured as described above, the target value SET is the output S of the position sensor 8 in the focused state.
Since the servo amplifier 11 drives the motor 13 so that the deviation ΔS becomes zero, the lens 2 and the like keep the focal point of the luminous flux always on the measurement target surface 3. Be moved to. Therefore, since the drive amount of the motor 13 is proportional to the displacement amount of the measurement target surface 3, the displacement amount of the measurement target surface 3 is measured by detecting the drive amount or the movement amount of the lens 2 or the like. be able to.

Further, as described above, when the measurement target surface 3 has an inclination, the incident angle of the reflected light on the position sensor 8 changes, and therefore the output of the position sensor 8 with respect to the displacement of the measurement target surface 3 The change rate (gain) of can be changed according to the inclination of the measurement target surface 3. Therefore, based on the inclination of the measurement target surface 3 measured as described above, the gain of the position sensor 8 corresponding thereto is estimated, and the servo gain of the servo amplifier 11 is changed according to the data given in advance. Then, the controllability of the automatic focusing mechanism can be improved.

In the above description, the point light source 7 is arranged on the axis of the lens 2, and the position sensor 8 is equivalently arranged at the same position as the point light source 7 using the half mirror 6. The positional relationship between the point light source 7 and the position sensor 8 is not limited to this. Further, the means for changing the paths of the light emitted from the point light source 7 and the reflected light from the measurement target surface 3 is not limited to the half mirrors 6 and 10, and may be, for example, a prism or a polarization beam splitter. It may be. Furthermore, the lens 2 that irradiates the measurement target surface 3 with a light beam and forms an image of the reflected light from the measurement target surface 3 on the position sensor 8 is not limited to a single lens, but an independent partial lens may be used. It may be a combination. In particular, since the position where the light emitted from the point light source 7 is incident on the lens 2 does not change at all times, the lens portion around it is often unnecessary.

Also, in the above description, two position sensors
Although the case where the inclination of the measurement target surface 3 is measured using 8 and 9 is illustrated, the lens 2 is moved by a certain amount and the incident state equivalent to that of the second position sensor 9 is provided on the first position sensor 8. Is generated, the inclination of the measurement target surface 3 can be measured by only one position sensor 8. That is, when the lens 2 and the like are displaced from the focused state by a certain amount and the output change in the position sensor 8 at this time is measured, the change amount and the changing direction of the incident position of the reflected light at this time are Since it corresponds to the route, the inclination of the measurement target surface 3 can be known by comparing with the data measured in advance.

〔The invention's effect〕

As described above, in the displacement converter of the present invention, while irradiating the measurement target surface with light through the lens, the position of the lens is moved so that the measurement target surface is always in focus,
In the displacement converter configured to measure the displacement amount of the measurement target surface from the movement amount of the lens at this time, the light beam emitted from the point light source is irradiated onto the measurement target surface through the lens, and the light is incident. A position sensor capable of detecting the position is equivalently arranged at the same position as the point light source or at a position with a certain distance from the position, and the output of the former position sensor moves the positions of the lens and the point light source. In addition to being used as a feedback signal of the automatic focusing mechanism, the difference between the outputs of the two position sensors is used to measure the tilt of the measurement target surface. Will connect the solid line at the position of the position sensor (point light source), and the incident position of the reflected light on the position sensor will always be constant. It is possible to detect from the output state of the position sensor whether or not the measurement target surface is in focus, and the displacement amount can be accurately measured even when the measurement target surface has a relatively large inclination. In addition, the displacement transducer capable of simultaneously measuring the inclination of the measurement target surface can be realized with a simple configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a displacement converter of the present invention,
2 and 3 are configuration diagrams showing an example of the position sensor used in the displacement converter of the present invention, and FIGS. 4 and 5 show the incident position of reflected light and the state of the spot on the position sensor. Explanatory diagrams, FIGS. 6 and 7 are explanatory diagrams showing incident states of reflected light on the first and second position sensors 8 and 9, and FIG. 8 is an automatic focusing mechanism used in the displacement converter of the present invention. 9 is a configuration diagram showing an example of
FIG. 10 is a configuration diagram showing an example of a conventional displacement converter, and FIGS. 10 and 11 are explanatory diagrams showing spot shapes of incident light in a four-division sensor used in the displacement converter shown in FIG. 1 ... Light source, 2 ... Lens, 3 ... Measurement surface, 4 ...
Cylindrical lens, 5 ... 4-division sensor, 6, 10 ...
Half mirror, 7 …… Point light source, 8,9 …… Position sensor, 11 …… Servo amplifier, 12 …… Power amplifier, 13 ……
Motor, SW ... Switch.

Claims (1)

[Claims] 1. A surface to be measured is irradiated with light through a lens, and the position of the lens is moved so that the surface of the object to be measured is always in focus. In a displacement converter configured to measure the amount of displacement, it is equivalent to a point light source that is arranged on the axis of the lens, emits a light beam having a certain angle with respect to the axis of the lens, and moves with the lens. A first position sensor arranged at the same position as the point light source and moving together with the lens, and a second position sensor arranged at a position equivalent to the first position sensor at a constant distance. And an automatic focusing mechanism that receives the output of the first position sensor and moves the position of the lens so that the output has a constant value. The addition to measuring the amount of displacement of the object surface, displacement transducer formed by the difference between the outputs of the first and second position sensor to measure the inclination of the object surface.