JPS6283612A - Displacement transducer - Google Patents

Abstract

PURPOSE:To automatically measure the quantity of the displacement of the surface to be measured by using a point light source, arranging a photosensor with a dead zone in equivalently the same position as that of the point light source and utilizing the output of the photosensor as the feedback signal of an autofocus mechanism. CONSTITUTION:Since a photosensor 8 is provided with a dead zone, when the spot diameter of reflected light is decreased when in focus, most part of the reflected light falls on the dead zone and the output of the photosensor is minimized. Since the output of the photosensor 8 is thus changed in accordance with the position of the surface 3 to be measured when the photosensor 8 having the dead zone in part of a light receiving surface is positioned in equivalently the same position as that of a point light source 7, an in-focus condition can be known from the output of the photosensor 8. When an autofocus mechanism having the output of the photosensor 8 as a feedback signal is constituted, a lens 2 or the like can be displaced such that the light beam emitted from the point light source 7 is always focused on the surface 3 to be measured and the quantity of the displacement of the surface 3 can be automatically measured from the quantity of the displacement of the lens 2 or the like.

Description

[Detailed description of the invention] [Industrial application field] 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 hot spot is always on the surface to be measured, and the amount of movement of the lens at this time is used to determine the surface to be measured. This invention relates to a displacement transducer that measures the amount of displacement.

[Conventional technology]

Conventionally, as an example of an optical displacement converter, a device as shown in FIG. 7 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 phosphorescent lens 4 and a four-part sensor 5 are used to detect whether or not the focus is on the measurement target surface 3, and the reflected light from the measurement target surface 3 is placed behind the lens 2. The half mirror 6 guides the light to the cylindrical lens 4, and a four-division sensor 5 detects changes in the shape of the light spot obtained by the cylindrical lens 4.

That is, the shape of the light spot projected onto the four-part sensor 5 is as shown in FIG. 8, and when it is focused on the measurement target surface 3 (hereinafter referred to as the 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-split sensor 5 is a circular bar 1, as shown by the solid line a in the figure. In addition, when the focus is out of focus, the light beam that enters the cylindrical lens 4 is no longer parallel, so the light spot becomes an ellipse whose inclination direction changes depending on the focus shift, as shown by broken lines and C. . Therefore, the outputs 51 to S4 in the 4-split sensor 5 are, for example, (S1+
By performing arithmetic processing such as 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 this four-part sensor 5 (puni,
This signal 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.

[Problems to be Solved by the Invention] However, in the displacement transducer using the cylindrical lens 4 and the four-part sensor 5 as described above,
If there is an @ mark on the measurement target surface 3, the position of the light spot projected onto the 4-split sensor 5 will be shifted from the center, as shown in Fig. 9, so even in the focused state The outputs S1 to S4 of the sensor 5 are not balanced, making it impossible to perform accurate autofocusing. For this reason, the inclination of the surface 3 to be measured must be suppressed within ±1".

The present invention eliminates the drawbacks of the conventional device F as described above, and provides 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. The purpose is to achieve this goal.

[Means for solving problems]

The displacement transducer of the present invention irradiates the surface to be measured with light through the lens, and moves the position of the lens so that the surface is focused on the surface to be measured, and from the amount of movement of the lens at this time. In the displacement converter configured to measure the amount of displacement of the surface to be measured, a light beam emitted from a point light source is irradiated onto the surface to be measured through a 1/lens, and a dead zone is provided in a part of the light receiving surface. At the same time, an optical sensor that generates an output proportional to the amount of incident light is placed equivalently at the same position as the point light source, and the output of this optical sensor is reflected by an automatic focusing mechanism that moves the position of the lens and point light source. It is designed to be used as a 17 signal.

[For production]

In this way, if a point light source is used as a light source and an optical sensor with a dead zone is placed equivalently at the same position as the point light source, in the focused state, the reflected light from the surface to be measured will be transmitted to the optical sensor. A real image is formed at the second fixed position (dead zone position), and the output of the optical sensor becomes the minimum value, so it is detected from the output state of the optical sensor whether or not it is focused on the surface to be measured. By using the output of the optical sensor as a feedback signal of the automatic focusing mechanism, the amount of displacement of the surface to be measured can be automatically measured. In addition, the incident position of reflected and reflected light in the focused state is
Since it is constant regardless of the ff path of the light beam, even if the surface to be measured is tilted, the output of the optical sensor becomes minimum in the focused state, and the amount of displacement can be accurately measured.

[Embodiment 1] FIG. 1 is a configuration diagram showing an embodiment of a displacement transducer of the present invention. In the figure, IIi, the same components as in FIG. This is an optical sensor placed at the same position as 7. The light beam emitted from the focused beam 57 has a spread comparable to the diameter of the lens 2, and is irradiated onto the measurement surface 3 via the nozzle 2. Further, the light reflected by the measurement target surface 3 enters the optical sensor 8 via the lens 2 and the half mirror 6. Furthermore, lens 2. Half mirror 6
, the point light source 7 and the optical sensor 8 are supported by the body and are moved by an automatic focusing mechanism (not shown), and the distance to the measurement target surface 3 is arbitrarily determined. Here, the optical sensor 8 is, for example, a crosshair or a partial mask provided on the front surface of a light-receiving element such as a photodiode to form a dead zone in a part of the light-receiving surface, and the position of this dead zone is , is adjusted to the incident position of the reflected light in the focused state.

Now, in the displacement converter of the present invention configured as described above, when the focus is on the measurement target surface 3 (in-focus state), the distance between the point light source 7 and the lens 2 is Ql, and the distance between the point light source 7 and the lens 2 is Ql. 2 and the measurement target surface 3 as Q2. If the focal length of the lens 2 is f, then the relational expression 1/Qi +1/+12-1/f holds true, and after the reflected light from the poor measurement surface 3 passes through the lens 2, it is reflected at the position of the point light source 7. It will come back like a real image. At this time, since the optical sensor 8 is placed equivalently at the position N of the point light source 7, the reflected light enters the optical sensor 8, and the spot diameter projected onto the optical sensor 8 is minimized.

Furthermore, if the measurement target surface 3 is displaced and deviates from the focal position of the irradiated light beam, the imaging position of the reflected light will shift from above the optical sensor 8, so the optical sensor 8 has ff1
A spot with a certain degree of curvature is projected depending on the amount of displacement of the image plane 3.

FIG. 2 shows how the spot diameter of the reflected light incident on the optical sensor 8 changes depending on the displacement of the surface 3 to be measured. In the figure, if the spot diameter of the reflected light in the focused state is PO, then the spot diameter at the second time is also smaller, and as the measurement target surface 3 deviates from the focal position,
The spot diameter also varies from PO to Pi, P3 and P2. F'
It gradually increases to 4. Here, Figure 2 is
! ltI! This is an example of a case where the measurement target surface 3 has no inclination and the axis of the irradiated light beam is perpendicular to the surface. In such a case, even if the measurement target surface 3 is displaced 2, the optical axis of the reflected light does not change. Therefore, the incident position does not change, and only the spot diameter of the reflected light incident on the optical sensor 8 changes.

Therefore, if the measurement target surface 3 is displaced from a position closer to the focal position to a farther position, the spot diameter of the reflected light projected onto the optical sensor 8 will change from P2 to Pl as the measurement target surface 3 approaches the focal position. and P at the focal position.
On the raft, which has become O, the measured value 4 and 3 will increase from P3 to P4 as it moves away from the focal position.

At this time, since the optical sensor 8 is provided with a dead zone,
In the focused state, when the spot diameter of the reflected light becomes small, most of the reflected light falls on the dead zone, and the output of the optical sensor 8 becomes minimum. Furthermore, when the position of the measurement target surface 3 deviates from the focused state, the spot diameter of the reflected light increases and the light enters areas other than the dead zone, so the output of the optical sensor 8 changes depending on the spread of the spot. Increase accordingly. It becomes like this.

Therefore, the detection characteristic of the optical sensor 8 takes a minimum value in the focused state (Q2-QO), as shown in FIG.

In this way, the optical sensor 8 has a dead zone in a part of the light receiving surface.
If it is equivalently placed at the same position as the point light source 7, the output of the optical sensor 8 will change depending on the position of the measurement target surface 3, so the in-focus state can be known from the output of the optical sensor 8. If an automatic focusing mechanism is configured using this output as a feedback signal, the lens 2 etc. can be moved so that the light flux emitted from the point light source 7 is always focused on the measurement target surface 3, and the movement at this time It is possible to automatically measure the amount of change in the surface to be measured 3 from the beginning. As an example of the automatic focusing mechanism described above, a dither (11 watts is superimposed on a 1-noise, 2-stop, 1-movement circuit) is used. By using a servo system that can achieve the following two functions, it is possible to obtain measurement accuracy that exceeds the resolution capability of the optical sensor 8.

Next, consider a case where the measurement target surface 3 has an inclination.

In this case, the path of the light reflected from the measurement target surface 3 will be different from the one-convex case shown in FIG. 1, but due to the nature of the lens 2, if the focal position is on the measurement target surface 3, Since the position where the reflected light forms an image does not change, the incident position and spot diameter of the reflected light on the optical sensor 8 do not change either, and the in-focus state can be accurately detected from the output of the optical sensor 8, as in the case above. can do. Note that when the measurement target surface 3 is tilted, the optical axis of the reflected light changes depending on its displacement, so the spot diameter and the incident position of the reflected light projected onto the optical sensor 8 are, for example, as shown in FIG. As such, it changes with the displacement of the surface 3 to be measured. In the figure, if the incident position moves in the directions P1' and P2' 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 opposite direction. It moves in the direction of P3' and P4'. Here, the reason why the spot shape is elliptical is that a part of the reflected light is deviated from the lens 2 due to the inclination of the surface 3 to be measured.

FIG. 5 is a block diagram showing another embodiment of the displacement converter of the present invention, in which the light source and optical sensor are extracted. In the figure, the same parts as in FIG.
It is. The displacement transducer shown in the figure consists of two optical sensors 8.9
is placed in the aerobatics of the imaging position in the reflected light, and
The in-focus state is detected from the difference in the outputs of these optical sensors 8.9. That is, when the first optical sensor 8 is placed in front of the imaging position and the second optical sensor 9 is placed after the imaging position via the half mirror 10, the detection characteristics of both are as shown in FIG. Since there is a constant deviation with respect to the movement of the lens 2, etc., by finding the difference between these outputs and operating the automatic focusing mechanism so that this becomes zero, the displacement converter shown in FIG. A similar measurement operation can be performed.

In addition, in the above description, the case where the point light source 7 is arranged on the axis of the lens 2 and the optical sensor 8 is arranged equivalently at the same position as the point light source 7 using the half mirror 6 is illustrated. The directivity relationship between the focal light Ti 7 and the optical sensor 8 is not limited to this. Further, the means for changing the path 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 mirror 6, but may be, for example, a prism or a polarizing beam splitter. Good too. Furthermore, the light source is not limited to the point light source 7, and parallel light rays may also be used. In this case, a second lens is inserted after the half mirror 6, and the optical sensor 8 is placed at the focal point of this second lens. In this way, when parallel light beams are used, automatic focusing can be performed by simply moving only the lens 2, and the supporting and driving mechanism for the lens 2''g can be easily configured.

〔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 black point is always aligned with the surface to be measured.
In a displacement converter that measures the amount of displacement of the surface to be measured from the amount of movement of the lens at this time, the beam emitted from the point light source is irradiated onto the surface to be measured through the lens, and the light receiving surface is An optical sensor that has a dead zone in part and generates an output proportional to the amount of incident light is equivalently placed at the same position as the point light source, and the output of this optical sensor is transferred to the position of the lens, point light source, etc. Since it is used as a feedback signal for the automatic focusing mechanism that moves, in the focused state, the reflected light from the measurement target surface forms a real image at a certain position (dead zone position) on the optical sensor.
Since the output of the optical sensor becomes the minimum value, it is possible to detect whether or not the surface to be measured is in focus from the output state of the optical sensor. However, a displacement transducer that can accurately measure the amount of displacement can be realized with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the displacement transducer of the present invention,
FIGS. 2 and 4 are explanatory diagrams showing the spot diameter of the reflected light on the optical sensor and its incident position, FIG. 3 is a diagram showing the detection characteristics of the optical sensor in FIG. 1, and FIG. Block diagram showing another embodiment of the displacement transducer of the present invention, No. 6
The figure shows the detection characteristics of the optical sensor in Figure 5, and Figure 7 shows the detection characteristics of the optical sensor in Figure 5.
This figure is a block diagram showing an example of a conventional displacement converter, and FIGS. 8 and 9 are explanatory diagrams showing the spot shape of incident light on a four-split sensor used in the displacement converter shown in FIG. 7. 1...Light source, 2...Lens, 3...Measurement target surface,
4... Cylindrical lens, 5... 4-split sensor, 6, 10... Half mirror 17... Point light source, 8
゜9... Optical sensor. Figure 1 Section 2 Figure 4 Figure 31 2512! Figure 7 Figure 8 CQ Figure 9

Claims (1)

[Claims] Light is irradiated onto the surface to be measured through a lens, and the position of the lens is moved so that it is always focused on the surface to be measured, and the amount of displacement of the surface to be measured is measured from the amount of movement of the lens at this time. In the displacement converter, a point light source that moves together with the lens, an optical sensor that has a dead zone on a part of its light receiving surface and is equivalently placed at the same position as the point light source and moves together with the lens, and a light sensor that moves together with the lens, and A displacement converter comprising an automatic focusing mechanism that receives an output from a sensor and moves the position of the lens so that the output becomes a minimum value.