JPH01165911A - Photoelectric type position detector - Google Patents

Abstract

PURPOSE:To increase an operation distance and a focusing detection range, to make the title apparatus compact and to measure the position of the surface of an object to be inspected without moving the whole of the apparatus, by forming a light source image between two fixed lens groups of a receiving/transmitting optical system and changing the distance between the lens groups to measure change quantity. CONSTITUTION:The beam from a semiconductor laser 1 is projected on the surface 9 of an object to be inspected by a receiving/transmitting optical system and a part of the reflected beam from said surface 9 is allowed to be incident on a two-split beam detection element 10 for detecting a beam position and the position of the surface 9 of the object is detected from the output of said element 10. This optical system is constituted of two fixed lens groups 3, 6 and the image of the laser 1 is formed between said lens groups and a right-angled prism 5 is driven in a direction separating the prism 5 from a beam reflecting means 4 in parallel as an optical distance altering means by a prism driver 7. Then, the displacement quantity X of an optical distance is detected from the displacement quantity Y of the prism 5, when the variation quantity of the position of the reflected image coincides with the distance altering quantity between the lens groups 3, 6 by a position detection means 8. The moving direction thereof is discriminated on the basis of the difference between output signals of the beam detection elements A, B.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a photoelectric method that measures the position and displacement of an object surface by focusing light using an objective lens and detecting deviation from the focal point. The present invention relates to a position detection device.

[Prior Art] Generally, the astigmatism method, critical angle method, and knife edge method are known as methods for detecting minute changes in the distance between the objective lens and the object surface to be measured by detecting the focal position. There is.

Hereinafter, a photoelectric position detection device using a knife edge method will be explained as an example. The principle of the knife edge method is
This method takes advantage of the fact that when a focusing error occurs when light that is partially blocked by a knife edge is projected from the objective lens onto the surface of the object being tested, the shape of the image of the projected light generated through the objective lens becomes asymmetrical. It's a method. FIG. 2 specifically shows the principle of the knife edge method. The knife edge that blocks part of the light beam is used as a mirror 14, and the light beam from the semiconductor laser 1 placed at the image point of the objective lens 6 is directed to the objective lens 6. It also serves as a guide. The light beam of the semiconductor laser 1 forms an image on the object point of the objective lens 6, and the light beam reflected from the object surface 9 to be measured at this position is focused on the two-split light receiving element 1 arranged at the image point of the objective lens 6.
0 (each indicated by AlB) is imaged in the central dead zone. In this case, the output signals of the two light receiving elements A and B become equal in the state shown in FIG. 3(b). When the object surface 9 to be measured moves in the direction of the measurement optical axis and a focusing error (+ΔF, -ΔF) occurs, the image point moves back and forth, and the shape of the image on the two-split light receiving element changes to the third one. The state will be as shown in Figures (a) and (c). Therefore, the in-focus state can be determined by calculating the difference (A-B) between the output signals of the two light receiving elements.

The knife-edge method or the other methods mentioned above are also characterized by relatively high sensitivity, but the linear range of focusing error and output is very narrow, at most a few microns.

Therefore, it is suitable for use in measuring the roughness of precision machined parts without contact and without worrying about scratches. However, in general measurements, this is insufficient, and the in-focus position is detected by changing the position of the objective lens or the entire device based on the output signal. If the objective lens is very small,
It is suitable to detect the focus position by moving the objective lens, but depending on the device, it may be necessary to increase the working distance (W, D, In addition, it becomes difficult to move accurately. In this case, it is more appropriate to move the entire device. Mechanically, the latter is more suitable if you want to measure the amount of movement rather than just focusing.

[Problem that the invention seeks to solve]

Therefore, with the configuration of the conventional device as it is, its range of use is limited to devices such as those that perform roughness measurement using minute focusing errors and the linear range of the output signal, or devices with very small objective lenses.

The present invention was made in view of these conventional problems, and it has a large working distance and focus detection range, is compact, and can measure the position of the object surface without moving the entire device. The purpose is to obtain a photoelectric position detection device.

[Means for solving problems]

In order to solve the above problems, the present invention has two light emitting and receiving optical systems.
It is composed of two fixed lens groups 3.6 to form a light source image (So) therebetween, and has an optical path length that changes the optical distance between the two fixed lens groups. It is characterized in that it is provided with variable means 5.8 and measuring means 11.12.13 for measuring the amount of change in optical distance.

[For production]

In the present invention, when the optical distance between the two fixed lens groups constituting the light emitting/receiving optical system is changed, the distance between the light source side lens group 3 and the light source 1 remains unchanged. The distance to the lens group 6 on the front side changes. The lens group 6 forms the light source image (So) on the test object surface 9, but if the distance changes at this time, the lens group 6 and the light source image (S'' on the test object surface) ) also changes.

Therefore, if the beam splitting means for guiding the light beam to the light receiving element 10, which is provided conjugately with the light source 1, is provided closer to the light source than the means for changing the distance between the two lens groups constituting the light emitting/receiving optical system, the lens group 6 and Even if the distance to the test object changes, the light 6JX1,
A conjugate relationship between the light source image (So) on the object surface and the light receiving element 10 can be satisfied.

If a two-split light-receiving element is used as the light-receiving element, whether or not the conjugate relationship has been established can be determined by calculating the signal difference (A-B) between the lens group 6 and the light source image (S''
) has a certain relationship with the distance change between the two lens groups, so if this distance change is measured by a measuring means, it can be determined from the amount of change. Further, the displacement measurement range of the object surface to be tested is determined by the amount of change in the optical distance between the lens groups. Therefore, the measurement range can be much larger than that of conventional devices that utilize the linear range of signals.

〔Example〕

FIGS. 1(a) and 1(b) are diagrams showing a first embodiment of the present invention. In FIG. 1, half of the light beam emitted from the semiconductor laser 1 is incident on the light emitting/receiving optical system 3.4.5.6 by the light beam splitting means 2, as shown by diagonal lines in the figure. The light beam from the fixed lens group 3 on the light source 1 side of the light emitting/receiving optical system 3.4.5.6 is turned by 90 degrees by one surface of the light beam reflecting means 4, which has total reflection mirrors on both sides forming a right angle to a right angle prism. and enters the right angle prism 5. The light beam that has entered the right-angle prism 5 is turned by 180 degrees by the right-angle prism 5 and enters the other surface of the light beam reflecting means 4 again. The right angle prism 5 is guided in the direction of arrow P by a linear guide (not shown), and is linearly moved by a prism driving means 7. At this time, in the reference state shown in FIG. 1(a), the configuration is such that the light source image (S'') by the lens group 3 is formed on the midpoint M of the right-angle prism 5.The light beam exiting the right-angle prism 5 is The light source image ( S”
) to form. The light beam reflected by the object surface 9 to be inspected passes through an optical path opposite to that of the projected light beam, and forms an image on the midpoint M of the rectangular prism 5, that is, at a position coinciding with the light source image (S'). The image is formed on the two-split light-receiving element 10 by the lens group 3 and the light beam splitting means 2 which reflects the light beam asymmetric with respect to the optical axis shown outside the shaded area. That is, the two-split light receiving element 10 is arranged conjugately with the semiconductor laser 1.

The image on the test object 9 formed by the lens group 6 described above is a light source image (
The position and size of the two-split light-receiving element are determined so that when the two-split light-receiving element coincides with S'), the image of the reflected light from the object surface 9 to be inspected is formed in the central zone of the two-split light-receiving element.

Next, considering the case where the object surface 9 to be tested approaches the lens group 6 by the amount of displacement (X), the right angle prism 5 is
At the same position, the light source image and the image of the reflected light from the test object surface 9 do not match, and the image of the test object surface 9 due to the reflected light approaches the lens group 3 . Therefore, the image of the reflected light by the light emitting/receiving optical system is formed farther than the position of the two-split light-receiving element 10, and the two
The image on the divided light-receiving element 10 is as shown in FIG. 3(C).

On the other hand, if the object surface 9 to be inspected is in a direction away from the lens group 6, the state shown in FIG. 3(a) will occur. Therefore, in order to match the image of the reflected light formed by the lens group 6 with the light source image (S'), it is necessary to increase the optical distance between the lens groups 3 and 6 of the light transmitting and receiving optical system. In this embodiment, as a distance changing means for this purpose, the prism driving means 7 moves the right angle boob 7=rhythm 5 in a direction parallel to and away from the light beam reflecting means 4. When the amount of change in the position of the reflected image matches the amount of change in the distance between the lens groups, Figure 1 (b
), the difference between the output signals of the two light-receiving elements A and B is A-B.
becomes zero, and if the amount of displacement of the prism 5 at this time is Y, then the amount of displacement X of the optical distance can be determined from this amount. Therefore, a position detecting means 8 for reading the displacement amount Y of the prism 5 is provided. Therefore, the moving direction of the prism can be determined by the value of the difference A-B between the output signals of the two light-receiving elements A, , B, and the displacement 1x of the object surface 9 to be examined is the displacement 1x of the right-angle prism 5 when the difference A-B is zero. It can be found from the amount of displacement. The right-angle prism 5 may be operated by applying a servo to reduce the signal to zero based on the difference A-B to drive a motor or the like constituting the prism drive means 7, but the right-angle prism 5 may be vibrated at a certain period to reduce the difference. It is also possible to synchronize and read the displacement amount of the length measuring means when A-B becomes zero.

An example of the latter will be explained with reference to FIG.

FIG. 5 is a signal processing block diagram when the rectangular prism 5 is vibrated at a certain period using a voice coil or the like, and the amount of vibration is measured by a known non-contact measurement means using eddy current. This is the time chart 1. The displacement of the right angle prism 5 is measured by a displacement measuring means 8 (substantially the same as the prism position detecting means 8 described above) such as an eddy current sensor. Each light receiving element A of the two-split light receiving element 10,
The output signal B is outputted by a differential amplifier 101 into a differential output A-IB. The output of the comparator 102 changes at the moment the differential output A-B crosses the zero point, and this change causes the one-shot circuit 103 to output a sample pulse. The sample and hold circuit 105a samples and holds the displacement signal of the right angle prism using this sample pulse. This voltage is a value corresponding to the object distance. However, since this value does not have a linear relationship with the displacement of the object to be inspected, the output of the nonlinear correction circuit 106 is used as the measured value.

Note that the sample and hold circuit 105b, which inputs the sample pulse of the one-shot circuit 103, samples and holds the addition signal (by the addition amplifier 104) of each of the light receiving elements A and B of the two-split light receiving element 10, and converts this hold value into A/ The measured value may be obtained by D conversion and digital calculation.

Furthermore, the slope of the zero-crossing portion of the output signal of the differential amplifier 101 varies depending on the reflectance of the surface of the object to be inspected. When the reflectance is low, the slope becomes gentle, resulting in large variations in measured values, which adversely affects measurements. To avoid this, the sum signal of the two-split light receiving elements A and B (summing amplifier 1
04 output) is sampled and held by the sample pulse of the one-shot circuit 103 (sample hold circuit 1
05b), and the light source intensity control circuit 107 may adjust the output light intensity of the light source 1 so that this value becomes constant.

FIG. 6(a) shows the output of the displacement measuring means 8, which is zero when the prism 5 is at the reference position shown in FIG. 1(a), positive when the optical distance of the lens group 3.6 is increased, and optical It is negative if it decreases the target distance.

FIG. 6(b) shows the output of the differential amplifier 101, which is positive when the output of light-receiving element A is larger than the output of light-receiving element B, negative in the opposite case, and zero at the in-focus position where both coincide. becomes. Figure 6(d) shows one-shot circuit 1
03, a pulse is generated when the output of the differential amplifier 101 becomes zero. Therefore, if the sample and hold circuit 105a reads the signal shown in FIG. 6(a) when the pulse shown in FIG. 6(d) occurs, the position of the prism 5 can be known.

Note that FIG. 6(C) is an example of the output signal of the summing amplifier 104.

The example shown in FIG. 5 is preferable because a large amount of displacement can be obtained, but if a piezo element is used as the driving means and position detecting means of the rectangular prism 5, driving and measurement (the driving voltage corresponds to the displacement) can be performed using one element. You can do it with

In addition, the non-contact measurement method using eddy current described above can enlarge the measurement area to a certain extent, has good sensitivity and response speed, and uses a part of the metal fitting that holds the rectangular prism 5 as the eddy current measurement part. If you use , you can get a small one.

In addition, in order to minimize the error caused by the movement of the right-angle prism 5, if the right-angle prism 5 is moved in the direction of arrow P in FIG. It should be placed vertically. In other words,
The right-angle prism 5 is a two-piece mirror, so even if it is tilted, the component of inclination in the plane of the paper shown in Figure 1 will not occur, and axis misalignment can be made extremely small by paying careful attention to the machining accuracy of the linear guide. be. Since the direction perpendicular to the paper is not the measurement direction,
Most of the errors that occur can be canceled out.

Next, a second embodiment of the present invention will be described with reference to FIG.

Components with the same symbols as in FIG. 1 are members with the same functions. In FIG. 4, a half mirror 15 is provided between the light beam reflecting means 4 and the lens group 6, and a part of the projected light beam indicated by diagonal lines in the figure is divided, and the lens group 11 is used to detect the two-dimensional optical position detection element 13.
image on top. The optical position detection element 13 is a right angle prism 5
It is arranged so that it becomes conjugate with the semiconductor laser 1 by the lens group 3.11 when it is at the reference position.

When the right-angle prism 5 moves back and forth from the reference position, the image of the semiconductor laser formed by the lens group 11 also moves back and forth on the optical position detection element. At this time, if a slit-shaped aperture is provided outside the optical axis near the lens group 11, the fluctuation in the image position can be converted into a movement of the slit image on the optical position detection element 13. That is, by detecting the movement of this slit image on the optical position detection element 13, the displacement of the right angle prism 5 can be measured. This method is effective because the distortion of the right angle prism 5 does not cause a measurement error in the displacement of the prism 5.

According to the above-described embodiments of the present invention, the measurement range is determined by the amount of movement of the rectangular prism, so it is possible to obtain a much wider measurement range than in the conventional method that uses the linear portion of the signal. Furthermore, since the objective lens is fixed, it is possible to increase W and D, that is, to increase the size of the objective lens.Furthermore, if the light source image (S") is formed near the center of the right-angle prism 5, the prism The light beam becomes narrowest near the prism 5. Therefore, the shape of the prism 5 can be made extremely small, and the load on the driving means can be greatly reduced.

There is no need to move the entire device as described above (W.

D is large and compact, and it is possible to take a certain measurement range.

There are various surface shapes of the object to be measured, but in the case of an optical method, the angle of the projected light beam is small;
Moreover, if the spot shape does not change, it is less affected by the surface shape. In the case of the embodiment of the present invention, the projection angle is determined by the triangulation principle or the Shine Probe condition (Sc
It is much smaller than the conventional non-contact displacement meter using Heimpf Jug' 5 Condition), and
In the measurement state, the surface of the object to be measured, the light source, and the detection element are always conjugate, so they are not easily affected by the surface shape of the object to be measured.

Therefore, it is effective if applied to non-contact probes of three-dimensional measuring machines where the surface shape of the object to be inspected cannot be limited and requires precision.

In addition, in order to change the optical distance between the two fixed lens groups 3.6, in addition to the above-mentioned stripping that moves the prism 5, it is also possible to use a means such as an electro-optical element whose refractive index changes depending on an electric signal. can be used.

In addition to the above-mentioned knife edge method, the method of changing the distance between the lens groups constituting the light emitting/receiving optical system and measuring the displacement of the object to be measured from the amount of change, which is the basic idea of the present invention, can be used as well. It is similarly applicable to the astigmatism method, the critical angle method, etc., which are based on the principle of detecting the focal position.

(Effects of the Invention) As described above, according to the present invention, the photoelectric type has a large working distance and focus detection range, is compact, and can measure the position of the object surface without moving the entire device. A position detection device can be obtained.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams showing the optical system of the first embodiment of the present invention, FIG. 11F(a) is a diagram showing the state of the optical system at the reference position, and FIG. 1(b) 2 is a diagram showing the state of the optical system when the object surface to be tested is displaced, FIG. 2 is a diagram showing the optical system of one conventional embodiment, and FIGS. FIG. 3(a) is a diagram showing the state of the reflected image on the two-split element corresponding to the displacement of the test object surface, and FIG. FIG. 3(c) shows the case where the object surface to be tested is at the reference position, and FIG. 4 shows the case where the object surface to be tested is in front of the reference position. 5 is an electrical block diagram used together with FIG. 1, and FIG. 6 is a timing chart for explaining the operation of FIG. 5. (Explanation of symbols of main parts) 1... Semiconductor laser, 2... Luminous flux splitting member, 3...
...Fixed lens group, 5...Right angle prism, 6...
・Fixed lens group, 7... Prism drive device. Applicant Nippon Kogaku Kogyo Co., Ltd.

Claims (1)

[Scope of Claims] Light from a light source is projected as a light spot onto the surface of the object to be tested by a light projection/reception optical system, and a part of the light reflected from the surface of the object to be tested is used for light position detection by the light projection/reception optical system. In a photoelectric position detection device that detects the position of the object surface to be detected from the output of the light receiving element by inputting the light onto a light receiving element, the light emitting and receiving optical system is constituted by two fixed lens groups, and the light emitting and receiving optical system is composed of two fixed lens groups. an optical path length variable means for forming an image of the light source between the two fixed lens groups and changing an optical distance between the two fixed lens groups; and an amount of change in the optical distance. a measuring means for measuring;
A photoelectric position detection device characterized by being provided with.