JPH0654231B2 - Non-contact displacement meter - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a non-contact displacement meter, and particularly suitable for use in a non-contact roughness meter and an autofocus device for a microscope,
An illumination system that irradiates the measuring object with minute spot light and an imaging lens that forms an image of the minute spot light are included, and a change signal corresponding to the deviation from the in-focus point of the measuring object is output. The present invention relates to a non-contact displacement meter.

2. Description of the Related Art Conventionally, the roughness of a machined surface has been measured by a stylus method.
However, if the measurement object is a soft material, it may be scratched, so a non-contact type roughness meter has been developed. Many of the non-contact type displacement detectors for roughness gauges that have been developed so far apply the optical sensor used in the focus detection device such as a video disk, and the critical angle method and the astigmatism method. Etc. Among them, the displacement detector by the critical angle method is, for example, the actual Kaisho 6
Although disclosed in 1-6707, an illumination system that irradiates a measurement object with minute spot light, a collimator lens that converts reflected light from the measurement object into parallel rays, and a critical angle that transmits the parallel rays by total reflection. A prism and two light receiving elements are included, and when the object to be measured is deviated from the in-focus surface, the parallel rays exhibit a diverging or converging tendency and the reflectance changes suddenly, which causes displacement. It is for generating a signal. Further, the astigmatism method utilizes that the astigmatism characteristic becomes elliptic when the object to be measured deviates from the focusing surface.

[Problems to be Solved by the Invention]

However, each of the conventional non-contact type displacement detectors uses a complicated optical system and requires highly accurate optical parts. Therefore, there is a problem that adjustment is difficult and the cost is high, and a displacement detector using a simpler optical system has been required.

[Object of the Invention]

The present invention has been made to solve the above conventional problems, and provides a non-contact displacement meter capable of detecting displacement with a high SN ratio using a simple optical system and having a wide measurement range. The purpose is to

[Means for solving problems]

The present invention provides a non-contact displacement meter, an illumination system for irradiating an object to be measured with minute spot light, an imaging lens for forming two images of the minute spot light, and a center in the optical path of the optical axis. And a ring-shaped mask inserted so as to coincide with one another, and one of the images is arranged so that its center is aligned with the optical axis by deviating from the focusing image plane of one of the images, and one of the focal spots is defocused by the minute spot light. A first sensor having a circular or ring-shaped light-receiving portion for outputting a signal corresponding to the position of the center of gravity of the light amount distribution in the radial direction of the image whose image is limited by the ring-shaped mask, It is arranged so that the center of the other image is aligned with the optical axis with a deviation amount different from that of the first sensor from the focused image forming surface.
The other defocused image due to the minute spot light is a circular image in the light receiving portion for outputting a signal corresponding to the light amount barycentric position in the radial direction around the optical axis of the image limited by the ring-shaped mask. A ring-shaped second sensor is used, and a displacement signal corresponding to the displacement of the measuring object from the focusing surface is output based on the output difference between the first sensor and the second sensor. Thus, the above-mentioned object is achieved.

[Action]

According to the present invention, the defocused image due to the minute spot light irradiating the object to be measured is the position of the center of gravity of the light amount distribution in the radial direction around the optical axis of the image limited by the ring-shaped mask inserted in the imaging optical path. A signal corresponding to the above is detected by a sensor which is disposed while being displaced from the focusing image plane of the image of the minute spot light, and a displacement signal corresponding to the deviation of the measuring object from the focusing plane is output. I am trying to do it. Therefore, the displacement can be detected with a high SN ratio using an optical system simpler than the conventional one. Further, when the sensor is composed of two light receiving elements arranged in a concentric circle shape, and outputs of the two light receiving elements are differentially amplified to generate the displacement signal, The sensor can be easily configured. Further, the sensor is composed of a circular semiconductor position detector having a central electrode and a peripheral electrode, and the displacement signal is generated by dividing a difference signal of outputs from the two electrodes by their sum signal. In such a case, the sensor can be easily downsized. Further, two images of the minute spot light radiated to the object to be measured are formed, and the defocused images of each are the positions of the center of gravity of the light amount distribution in the radial direction of the image limited by the ring-shaped mask. A signal corresponding to is output by two sensors arranged with different displacements from each focusing image plane, and a displacement signal corresponding to the displacement of the measuring object from the focusing plane based on the output difference of each sensor. Is output, it becomes possible to easily identify the direction in which the defocused image is displaced due to the minute spot light, and the measurement range can be expanded.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. In the comparative example which is a premise of the present invention, as shown in FIG. 1, a minute spot light 20 is applied to the measuring object 10 by an illumination system including a laser diode 12, a collimator lens 14, a beam splitter 16, and an objective lens 18. An image of the minute spot light 20 is formed by an imaging lens composed of the objective lens 18 and the condenser lens 22. A ring-shaped mask 24 for improving the SN ratio is provided in front of the condenser lens 22, but this mask can be omitted. FIG. 1 shows a state in which the minute spot light 20 is focused on the measuring object 10, that is, a state in which the measuring object 10 is on the focusing surface. The surface on which the image of the minute spot light 20 is formed is defined as the collective image formation surface. The sensor 26 is changed from the combined image forming plane downward in the drawing.
Is provided, and signals a 1 and b 2 are output from the sensor 26, which are input to a differential amplifier 28 to generate a displacement signal d 2. As shown in detail in FIG. 2, the sensor 26 includes an inner light receiving element 30 and an outer light receiving element 32, which are divided into concentric circles.
And the common electrode 34 is connected to the back surface, for example. As the light receiving elements 30 and 32, for example, a photo diode or a photo transistor can be used. The operation of the comparative example will be described below with reference to FIGS. 3 and 4. When the measuring object 10 is displaced in the Z direction from the focusing surface and coincides with the displacement surface of P1 or P2, the focal point of the image of the minute spot light 20 is Q1 or Q2. At this time, in the sensor 26, the image of the defocused image of the minute spot light limited by the rinse mask 24 is shown in FIG. 4 (A) (when the displacement surface is P1 and the focal point is Q1) or FIG. (B) (when the displacement surface is P2 and the converging point is Q2). Therefore, the sensor 26 outputs a signal corresponding to the position of the center of gravity of the light amount distribution in the radial direction centered on the optical axis of this defocused image, which is output from the displacement Z of the measuring object 10 and the differential amplifier 28. The relationship of the displacement signal d 1 is as shown in FIG. 5, for example. Therefore, since the displacement signal d is zero, it can be detected that the displacement surface is the in-focus surface. According to this comparative example, the displacement can be detected with a very simple structure. In this comparative example, since the ring-shaped mask 24 is provided, the SN ratio is high, that is, if the mask is not provided at all, the image at the center cannot be completely removed. In this case, an output is also generated in the inner light receiving element 30 of the sensor 26, the background component becomes large, and the SN ratio decreases. Further, in the case of a disk-shaped mask that shields only the central portion as in Japanese Patent Laid-Open No. 61-120912, the image on the outside is not shielded. Therefore, especially in the case of FIG. It spreads not only to the element 30 but also to the outer light receiving element 32 and becomes a background component, resulting in a reduction in contrast and a reduction in the SN ratio. On the other hand, when the ring-shaped mask 24 is present, the background component is small and the SN ratio is high in any of FIGS. 4A and 4B. Next, with reference to FIG. 6, an embodiment of the present invention which is particularly suitable for use as a sensor portion of an autofocus device such as a microscope will be described in detail. Also in this embodiment, similarly to the comparative example, the first sensor 26 is disposed so as to be displaced from the focusing image plane. Further, as compared with the comparative example, the objective lens 18, the second beam splitter 40, and the second condensing lens 42 similar to those of the comparative example are provided.
And an optical system for forming an image of the minute spot light 20 at a different position. Further, the second sensor 44 is provided by displacing it from the focusing image plane in the opposite direction to the displacement direction of the first sensor 26 similar to the comparative example. Both the first sensor 26 and the second sensor 44 have the same structure as the sensor 26 of the comparative example, and the detection circuit 46 includes the output signals a 1, b 1 of the first sensor 26 and the second sensor 4
Differential amplifiers 46A and 46B for respectively differentially amplifying the output signals a 2 and b 2 of 4 and the differential amplifiers 46A and 46B
Of the differential amplifier 46C for generating the displacement signal (focus signal) e by inputting the outputs d 1 and d 2 thereof. Since the other points are the same as those of the comparative example, description thereof will be omitted. The operation of the embodiment will be described below. When only one sensor 26 is provided as in the comparative example, as shown in FIG. 7, the defocus image due to the minute spot light formed on the sensor 26 by the displacement Z of the measuring object 10 is It is impossible to distinguish between the case of the convergent light A and the case of the convergent light B. However, the displacement signal e, which is differential from the output of the second sensor 44, has different values, and these two cases are distinguished. Therefore, according to this example, the measurement range can be expanded as compared with the comparative example. In this embodiment, it is possible to obtain the effect of averaging by vibrating the condenser lens with a voice coil or the like. Next, another example of the sensor and the detection circuit will be described with reference to FIGS. 8 and 9. As shown in detail in FIG. 9, the sensor 50 has a central electrode 50 on the upper surface of a three-layer semiconductor including a P-type semiconductor layer 50A, an I-type layer (intrinsic semiconductor layer) 50B, and an N-type semiconductor layer 50C.
D and a peripheral electrode 50 formed in a circular shape centering on D
It is a semiconductor position detector having E and having a common electrode 50F formed on the lower surface. Each electrode is composed of, for example, a nickel thin layer. Further, as the semiconductor material, silicon Si, gallium-aluminum-phosphorus Ga AlP, etc. can be used. As shown in detail in FIG. 8, the detection circuit 52 includes current-voltage converters 52A and 52B for current-voltage converting the output signal i of the peripheral electrode 50E and the output signal j of the center electrode 50D, and the current-voltage converter 52A. , 52B output signals i ', j'difference signal k (= i'-j'), sum signal l (= i '+ j')
Difference calculator 52C and sum calculator 52D for respectively outputting
By dividing the difference signal k by the sum signal l
and a divider 52E for obtaining m (= k / l). This displacement signal m becomes a signal corresponding to the position of the center of gravity of the light amount distribution of the light incident on the sensor 50 in the radial direction, and thus can be used as the sensor of the present invention.

【The invention's effect】

As described above, according to the present invention, displacement can be detected with a high SN ratio using a simple optical system. It also contributes to diversification of technology in the field of non-contact displacement detection. Furthermore, since two sets of sensors are provided, there is an excellent effect that the measurement range can be expanded.

[Brief description of drawings]

FIG. 1 is a front view showing a configuration of a comparative example which is a premise of a non-contact displacement meter according to the present invention, FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1, and FIG. 4 is a front view of an optical system for explaining the operation of the comparative example, FIG. 4 is a plan view showing an image similarly formed on the sensor, and FIG. 5 is a diagram showing an example of displacement signals of the comparative example. FIG. 6 is a front view showing the configuration of an embodiment of the present invention, FIG. 7 is a diagram for explaining the operation of the embodiment,
FIG. 8 is a front view showing a modification of the sensor and the detection circuit used in the above embodiment, and FIG. 9 is a transverse sectional view taken along the line IX-IX in FIG. 10 ... Object to be measured, 12 ... Laser diode, 14 ... Collimator lens, 16, 40 ... Beam splitter, 18 ... Objective lens, 20 ... Micro spot light, 22, 42 ... Condensing lens, 24 ... Ring mask, 26, 44, 50 ... Sensor, 28, 46A, 46B, 46C ... Differential amplifier, d, e, m ... Displacement signal, 30 ... Inner light receiving element, 32 ... Outer Light receiving element, 46, 52 ... Detection circuit, 50D ... Central electrode, 50E ... Peripheral electrode, 52C ... Difference calculator, 52D ... Sum calculator, 52E ... Divider.

Claims (1)

[Claims] 1. An illumination system for irradiating an object to be measured with minute spot light, an image forming lens for forming two images of the minute spot light, and a center of the image forming optical path aligned with the optical axis. The inserted ring-shaped mask and one of the images are arranged so that their centers are aligned with the optical axis by deviating from the focused image-forming plane of the one image, and one of the defocused images by the minute spot light is the ring-shaped image. A first sensor whose light-receiving portion is circular or ring-shaped for outputting a signal corresponding to the position of the center of gravity of the light amount distribution in the radial direction around the optical axis of the image limited by the mask, and the other image of the other image. The defocus amount from the focused image plane is different from that of the first sensor, and the center is aligned with the optical axis. The other defocused image due to the minute spot light is limited by the ring-shaped mask. Signal corresponding to the position of the center of gravity of the light intensity of the captured image in the radial direction around the optical axis For outputting, the light receiving unit includes a circular or ring-shaped second sensor, based on the output difference between the first sensor and the second sensor,
A non-contact displacement meter, which outputs a displacement signal according to a displacement of an object to be measured from a focusing surface.