JPS63298113A - Structure of image forming optical system of optical range detector - Google Patents

Abstract

PURPOSE:To enhance an SN ratio in detection, by arranging a mirror, which has suitable rotary symmetrical surfaces on the side of an image in an image forming optical system, and condensing the image of a bright spot on a body, on which an annular image is formed when the mirror is not provided, at a position, which is close to the axis of the optical system. CONSTITUTION:A rotary symmetric (cylindrical or conical) mirror Ms is arranged in an image forming optical system. The radius of an annular image L is made small. Even if the radius of the annular image I is made small, the amount of movement of the image with respect to the change in a range on an image position detecting element P is not changed. Therefore, range detecting sensitivity is not decreased, but can be increased so that the amount of the detected light is approximately proportional to the inverse ratio of the radius. Thus an SN ratio can be enhanced. In another example, the light, which is associated with image formation, is bent in the direction of a rotary symmetrical axis As. The image is formed at a position close to the rotary symmetrical axis As.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to the configuration of an imaging optical system of an optical distance detection device that detects the distance in the projection direction of a light beam in a non-contact manner. The present invention relates to the configuration of an imaging optical system of an optical distance detecting device having highly accurate and highly stable distance detecting characteristics suitable for use as a probe for measuring instruments and the like.

(Prior art) A cylindrical mirror is placed between an imaging lens and an object, and a bright spot is generated on the object by projecting a light beam in the optical axis direction.
A type of optical distance that detects the radial image position of a bright spot generated by entering the imaging lens after being reflected by a cylindrical mirror, and detects distance information in the direction of light beam projection based on the principle of triangulation. A detection device has been devised. Furthermore, in order to keep the width of the imaging optical system narrow, a structure in which a rotationally symmetrical mirror is arranged on the image side of the imaging system has been devised. Furthermore, we devised a configuration of a distance detection device that uses a rotationally symmetrical mirror for image formation in the imaging optical system.

A conventional optical distance detection device is shown in FIGS. 4a to 5b. Figures 4a and 4b show the imaging lens L and the object ○.
5a and 5b show the configuration of an optical distance detector using a rotationally symmetrical imaging mirror ML.

In either configuration, the distance i in the light beam B projection direction (symmetry axis direction) is the brightness generated on the surface of the object 0 by projecting the light beam B by the image position detection element P arranged on the observation surface. It is obtained by detecting the image position (■) of point T. The image I of the bright spot obtained on the observation surface has an annular shape as shown in FIGS. 4b and 5b, respectively. Since the radius of the annular image I differs depending on the distance at which the bright spot is generated, a one-dimensional image position detecting element P is arranged in the moving direction (radial direction) of the image as shown in the figure. The device is configured to detect directional position.

(Problems to be Solved by the Invention) As can be seen from FIGS. 4b and 5b, only a small portion of the light involved in forming an annular image is projected onto the one-dimensional image position detection element P. Since much light is not effectively used for image position detection, the S/N of the detection signal is often
This results in a decrease in the ratio, which is disadvantageous in improving detection accuracy.

(Means for Solving the Problems) In order to solve the above problems, increase the amount of detected light, and improve the S/N ratio of position signal detection, the present invention uses a rotationally symmetric internal mirror that is located on the axis of symmetry. Taking advantage of the property that the image of a point light source converges on its axis of symmetry in the radial direction, it is equivalently formed close to the axis of symmetry of a rotationally symmetric internal mirror, and then converted into a one-dimensional image.゛It is characterized by detecting with a position detection element.

(Function) By arranging a mirror with a suitable rotationally symmetrical surface on the image side of the imaging optical system, the image of a bright spot on an object, which would otherwise be imaged in an annular shape, can be brought close to the optical axis of the optical system. By arranging the image position detection element on or near the optical axis, the light that was projected between the one-dimensional image position detection elements and was not used effectively in the conventional method can be effectively focused. This makes it possible to increase the S/N ratio of signal detection. Further, by a plane mirror placed outward surrounding the light, the image to be generated in the signal close to the optical axis is reflected, and an image is formed at a position symmetrical to the position close to the optical axis on the opposite side of the mirror. Therefore, when arranging multiple image position detection elements,
It becomes easier.

(Effects of the Invention) According to the present invention, in the conventional method, an annular image is obtained,
Even light that is projected between the image position detection elements and cannot be effectively detected can be effectively focused on the image position detection elements, so that the S/N ratio of the image position detection signal can be increased. In particular, when an imaging system using a rotationally symmetrical mirror is used, the equivalent imaging position can be completely aligned on the optical axis, so the effect is remarkable.

(Embodiment) In order to increase the amount of light involved in image position detection, it is effective to configure the image forming position to be close to the axis of symmetry and to make the radius of the annular image small. In an optical system using such a rotationally symmetrical mirror, light emitted from a point on the axis of symmetry always converges onto the axis of symmetry after being reflected by the rotationally symmetrical mirror. Therefore, if the imaging position of the bright spot is made to coincide with the axis of symmetry and the image position detection element is arranged on the axis of symmetry, all the light related to imaging should be able to be used for image position detection. Also, by making the image formation position as close to the axis of symmetry as possible and making the radius of the annular image small, the ratio of the amount of light incident on the image position detector can be increased, and the S/N of image position detection can be increased. This is advantageous in improving the ratio. The present invention utilizes the properties described above, and specifically can be realized as follows.

Figures 1a and 1b show an optical distance detector according to the present invention, which is configured by arranging a rotationally symmetric (cylindrical or conical) mirror MS in the imaging optical system so that the radius of the annular image becomes small. This is an example.

Even if the radius of the annular image (2) becomes smaller, the amount of movement of the image on the image position detection element P with respect to a change in distance does not change. Therefore, the amount of detected light can be increased almost in proportion to the inverse ratio of the radius without reducing the distance detection sensitivity, and the S/N ratio can be increased.

2a and 2b show an embodiment of an optical distance detector constructed by introducing a rotationally symmetrical prism (conical lens) Ls into an imaging optical system based on the present invention. Due to the rotationally symmetrical prism L, the light involved in imaging is directed along the rotationally symmetrical axis A.
, is bent in the force direction, and is configured to be imaged at a position close to the axis of rotational symmetry As. A suitable rotationally symmetrical prism L.

By arranging them appropriately, it becomes possible to align the imaging position with the axis of rotational symmetry. In that case, the radius of the annular image I becomes zero in the limit, and the distance can be determined by detecting the rotational symmetry axis A, the rotational symmetry axis A of the upper image II, and the position in the force direction. FIG. 2 shows an example of a configuration in which the imaging position is slightly off from the axis of rotational symmetry.

3a and 3b show an embodiment of an optical distance detector constructed by introducing a rotationally symmetrical prism L and a plane mirror M into an imaging optical system based on the present invention. If the mirror M is not arranged in this configuration, the image of the bright spot will be formed on the rotational symmetry axis A as IV. Since it is not necessarily easy to arrange the image position detection element P so that it coincides with the axis of rotational symmetry, plane mirrors M are arranged and the image is formed at a position that is in a mirror image relationship with the axis of symmetry with respect to these plane mirrors. This is an embodiment in which a one-dimensional image position detection element P is arranged at an image forming position corresponding to each mirror. This provides an effect equivalent to arranging the one-dimensional image position detection element P virtually on the axis of symmetry. In this configuration,
Four plane mirrors M are arranged, and each one images the light emitted from the bright spot in different directions corresponding to each one, so the one-dimensional image position is placed at the corresponding imaging position. There is also a possibility that the amount of light received by the detection element P can be detected separately and the difference between them can be used to obtain information regarding the inclination of the surface of the object.

In the configuration shown in Figure 3, even if the virtual imaging position of the bright spot does not coincide with the axis of symmetry, the actual imaging position can be moved to a position away from the axis of symmetry without changing the imaging conditions. One of the great advantages is that the degree of spatial freedom is increased in the arrangement of the one-dimensional image movement detection element and the optical system.

[Brief explanation of the drawing]

1a and 1b are a side optical view and an axial plan view of the image position detection element portion of a configuration example in which a rotationally symmetrical mirror is used to reduce the imaging radius of the image according to the present invention, and FIGS. 2a and 1b are 2b is a side optical view of a configuration example in which the imaging radius of an image is reduced by a rotationally symmetrical prism (cylindrical lens) according to the present invention, and an axial plan view of the image position detection element portion; FIGS. 3a and 3b; FIG. 1 is a side optical view showing an example of a configuration in which a plane mirror is further arranged based on the present invention so that an image that should originally be formed on the axis of symmetry is deviated from the axis of symmetry, and an axial direction of the image position detection element portion A plan view, FIG. 4(a), and FIG. 4(b) are a side optical view of a configuration example of an optical distance detector that combines a rotationally symmetrical mirror and an imaging lens, and an axial plane of an image position detection element portion, respectively. 5(a) and 5(b) are a side optical view and an axial plan view of an image position detecting element portion, respectively, of a configuration example of an optical distance detector using a rotationally symmetrical imaging mirror. (Explanation of symbols) L...Imaging lens, Mi...Rotationally symmetrical mirror, B...Light beam, T...
Bright spot, 0...Object, P...Image position detection element, ■...Image, A,...
...Axis of symmetry, ML...Rotationally symmetrical imaging mirror, M
S...Rotationally symmetrical mirror, L...Rotationally symmetrical prism (conical lens), M
...Flat mirror, ...Virtual image, Pv...Virtual image position detection element.

Claims (4)

[Claims] (1) A light beam is projected in the direction of the rotationally symmetrical axis of the optical system, and a bright spot generated on the surface of the object is projected and imaged onto an observation surface by a rotationally symmetrical imaging optical system, and a bright spot image is formed on this observation surface. In an optical distance detection device of the type that acquires distance information from a position to the surface of the object, on the image side of the rotationally symmetrical imaging optical system, a bright spot image on the observation surface is reduced in the direction of the rotationally symmetrical axis. 1. A configuration of an imaging optical system of an optical distance detection device, characterized in that a reduction optical system is provided. (2) The optical distance detection according to claim 1, wherein the reduction optical system is a rotationally symmetrical mirror that brings the bright spot image closer to or coincides with the rotationally symmetrical axis. Configuration of the imaging optical system of the device. (3) The optical distance detection according to claim 1, wherein the reduction optical system is a rotationally symmetrical prism that brings the bright spot image close to or coincides with the rotationally symmetrical axis. Configuration of the imaging optical system of the device. (4) The reduction optical system includes a rotationally symmetrical plane mirror or a rotationally symmetrical prism, and an outwardly directed image that reflects the reflected image of this mirror or the image after passing through the rotationally symmetrical prism onto an image position detection element that is arranged facing each other. The configuration of an imaging optical system of an optical distance detecting device according to claim 1, characterized in that the imaging optical system comprises a plane mirror.