JPH0450720A - Optical length measuring instrument - Google Patents

Abstract

PURPOSE:To make the optical length measuring instrument easy to assembly and to eliminate the adverse influence of stray light by providing plural lenses which serve as both a collimation lens and a condenser lens, providing a common light source at the center position of the respective lenses, and providing plural photodetecting elements. CONSTITUTION:Lenses L which have the same focal length (f) are arranged above a main scale 2 and an index scale 3 so that their optical axes 4 are parallel to one another and the focuses are on the same plane perpendicular to the optical axes 4. Further, photodiodes PD detect light-dark patterns at four positions which are 90 deg. out of phase. The photodiodes PD at positions which are 180 deg. out of phase are connected to a 1st amplifier 8 to obtain the (a)-phase signal of only an AC signal and the photodiodes PD at the positions which are 90 deg. out of phase are connected to a 2nd amplifier 9 to obtain a (b)- phase signal which is 90 deg. out of phase. Then the leading or delay of the (a)- and (b)-phase signals is detect to discriminate the moving directions of both the scales 2 and 3 and the signals are counted to measure the movement distance.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention detects changes in brightness and darkness patterns that occur due to the relative movement of two gratings arranged facing each other, and detects the relative movement distance of each grating. This invention relates to an optical length measuring device that measures .

[Conventional technology]

For example, a length measuring device using an optical grating is known as a device for highly accurately reading the amount of movement of a processing table of a machine tool or the like.

FIG. 6 shows an example of this type of optical length measuring device.

This length measuring device has a main scale 100 and an index scale 101, each of which has a grating formed by scored lines having the same pitch, and which are disposed facing each other at a predetermined interval. A plurality of photodiodes 102 are provided above the index scale 101 with their light-receiving surfaces facing downward, and further above the photodiodes 102 are provided a collimation lens 103 and a light source 104.

Light from the light source 104 passes through the collimation lens 103 to become parallel light, and passes between the photodiodes 102 . The light then passes through the index scale 101 and is reflected by the marked lines of the main scale 100, passes through the index scale 101 again, and enters the photodiode 102.

Here, when the main scale 100 and the index scale 101 move relatively, the photodiode 102
The reflected light incident on the photodiode 102 has a bright and dark pattern, and the photodiode 102 generates an electric signal corresponding to the change in this pattern.

Note that for position measurement, a two-phase body symbol whose phase is shifted by 90° is required. Here, four photodiodes 1
02 is 90° phase difference 0°90° 180°, 270
By detecting each ° signal and differentially amplifying the signals that are shifted by 180 degrees from each other, the DC component in the detection signal corresponding to the background brightness is removed, and a stable two-phase signal with little DC offset is obtained. That's what you're getting.

Other conventional optical length measuring devices include one in which a half mirror 105 is placed between a collimation lens 103 and an index scale 101, and a photodiode 102 is placed on the side thereof, as shown in FIG. . In addition, as shown in FIG. 8, a collimation lens 103
There is also one in which the optical axis of the photodiode 102 is tilted so that the photodiode 102 is located away from the incident path. Furthermore, as shown in FIG. 9, there is also one in which the optical axis of the collimation lens 103 is tilted, and a condensing lens 106 with the optical axis tilted is used to collect light on a photodiode 107.

[Problem to be solved by the invention]

According to the apparatus shown in FIG. 1
02 had to be disposed in a hollow space between the collimation lens 103 and the index scale 101, and there was also the problem that the light beam was blocked by the photodiode 102.

According to the apparatus shown in FIG. 7, since a half mirror 105 is used, the amount of light goes to the station and returns to the station, and becomes even % of that amount, and the amount of light that enters the photodiode 102 decreases. Therefore, the size of the photodiode 102 had to be increased, resulting in a problem of slow response speed.

According to the apparatus shown in FIG. 8, there was a problem in that the parts had to be arranged diagonally at a predetermined angle, making assembly difficult.

According to the device shown in FIG. 9, a condenser lens 10 is provided on the light receiving side.
By using the light source 104 and the photodiode 10, stray light can be prevented from being received and the size of the photodiode 107 can be reduced to increase the response speed.
7 must correspond in a one-to-one relationship, and if two-phase signals are required, two or more of these combinations are required.

Therefore, there is a problem in that new countermeasures against temperature characteristics and changes over time of the plurality of detection systems are required.

The present invention has been made in view of the above-mentioned problems, and is easy to assemble and can be miniaturized. A plurality of light receiving elements can be arranged for one light source, and a light beam can be illuminated by receiving condensed light. It is an object of the present invention to provide an optical length measuring device in which the size of a light receiving element is reduced and the adverse effects of stray light are eliminated.

(Means for Solving the Problems) The optical length measuring device of the present invention detects a change in a brightness pattern that occurs due to the relative movement of two gratings disposed facing each other, and An optical length measuring device that measures moving distance includes a common light source, a plurality of lenses that guide light from the light source to the grating and condense reflected light from the grating, and a common light source for each of the lenses. A plurality of photodetecting elements are provided on the focal plane at positions symmetrical to the light source with respect to the optical axes of the lenses.

[For production]

Light emitted from a common light source enters each lens, becomes parallel rays, and is reflected by the grating. The reflected light is focused by each lens and is incident on each photodetector element on a focal plane located at each position symmetrical to the light source with respect to each optical axis of each lens.

(Example) An optical length measuring device 1 according to a first example of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, 2 and 3 are a main scale and an index scale that are relatively movable. A grating is formed on each of these scales 2 and 3, and a bright and dark pattern such as moiré fringes changes as the scales 2 and 3 move relative to each other.

Four lenses L are provided above both scales 2.3. These four lenses L have the same focal length f, their respective optical axes 4 are parallel to each other, and their focal points lie within the same plane perpendicular to the optical axis 4. That is, each lens L shares a focal plane 5, and is arranged in a pattern such that each optical axis 4 is located at each vertex of a square in a plane parallel to the focal plane, as shown in FIG. There is.

Note that these four lenses L are integrally molded and constitute one component of the device.

A substrate 6 is provided above the lens L in parallel with the focal plane 5, and on its lower surface is provided with one light source 7 and a photodiode P as a light detection element.

There are four D. The light source 7 and photodiode PD are located within the focal plane 5. And light source 7
is provided at the center of each lens L, and the four photodiodes PD are arranged at four positions symmetrical to the light source 7 with respect to each optical axis 4 of each lens L.

The four photodiodes PD described above are designed to detect the bright and dark patterns occurring on both scales 2 and 3 at four positions with a phase difference of 90°. Then, two photodiodes PD located at the 0° position and the 180° position, which differ in phase by 180°, are connected to the first amplifier 8, whereby the outputs of both photodiodes PD and PD are processed differentially. The direct current component is canceled out, and one signal (a-phase signal) consisting only of an alternating current signal is obtained. Furthermore, two photodiodes PD at 90° and 270° positions are connected to the second amplifier 9,
Similarly, a b-phase signal having a phase difference of 90° from the a-phase signal is obtained.

Therefore, by detecting the advance and delay of the a-phase signal and the b-phase signal, the moving direction of both scales 2.3 can be determined.
Further, by counting this two-phase signal, the distance traveled can be measured.

Next, the operation of the above configuration will be explained. As shown in FIG. 1, the distance between the optical axis 4 and the light source 7 in the focal plane 5 is h. Light from the common light source 7 passes through each lens L and becomes a parallel ray having an angle W with respect to each optical axis 4, and the relationship between them is expressed by the following equation.

h=-ftanW This light passes through the index scale 3 and is reflected by the main scale 2. The reflected light passes through each lens L again and becomes a parallel ray having an angle -W with each optical axis 4. Then, this light is transmitted to the light source 7 with respect to each optical axis 4 of each lens L.
The light is focused on each photoode PD located at a symmetrical position.

In this way, according to this embodiment, one light source 7 can be associated with four photodiodes PD.

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

This embodiment differs from the first embodiment in that it includes three lenses L and three photodiodes PDI~3, and in the circuit configuration for processing the output signal of each photodiode PDI~3. There is.

Each lens L has a common focal plane, and a common light source 10 is located approximately in the center of the focal plane, and the common light source 10 is provided for each optical axis 4 of each lens L. The points located symmetrically to the above are the same as in the first embodiment.

The two photodiodes PC1 and PD2 are configured to detect a bright and dark pattern in which a direct current component and an alternating current component are superimposed, from positions with a 90° phase difference. The other photodiode PD3 is for reference and is designed to detect DC components. And the photodiodes PDI, P
Each output of D2 is input to the inverting input terminal of operational amplifiers 11 and 12, respectively, and the reference photodiode P
The output of D3 is input to the inverting input terminal of each operational amplifier 11, 12 via resistors R1 and R2, respectively. As a result, if the outputs from the photodiodes PDI and PD2 and the output from the photodiode PD3 are appropriately amplified and processed, the respective operational amplifiers 11 and 12 will have a phase difference of 90'' from each other, excluding the DC component. For details of the signal processing circuit configuration and the like in this embodiment, please refer to Japanese Patent Publication No. 61-5081 filed by the present applicant.

Next, FIG. 4 shows a third embodiment of the present invention. Since this device is provided with an aperture 2o at the focal point, it is not particularly susceptible to adverse effects from external light. Other configurations and effects are the same as in the first embodiment.

Next, FIG. 5 shows a fourth embodiment of the present invention. This device has a single auxiliary lens 22 between a common light source 21 and a lens L, which allows the light source 21 to be provided at a position closer to the lens L than the focal plane 5 of the lens L. The degree of freedom in design increases. Other configurations and effects are the same as in the first embodiment.

[Effects of the Invention] According to the present invention, a plurality of lenses that serve as collimation lenses and condensing lenses are provided, a common light source is provided at the center position of each lens, and a focal plane that is symmetrical to the light source with respect to each optical axis of each lens is provided. A plurality of light receiving elements are provided at each position within the space. Therefore, according to the present invention, there are the following effects.

■A common light source and multiple light receiving elements can be assembled in the same focal plane, and if an auxiliary lens is used, the light source can be placed close to the lens. That is, there is a large degree of freedom in arranging parts, and an arrangement that is easy to assemble can be adopted. Furthermore, it is easy to assemble because there is no need to attach the parts while tilting them at a predetermined angle as in the conventional case.

(2) The device can be made more compact compared to conventional devices with component arrangements as shown in FIGS. S6 and 7.

■Since light is focused, the size of the light receiving element can be reduced. If it is small, the junction capacitance of the light receiving element will be small, so the response time can be shortened. In addition, it becomes difficult to receive stray light.

■Multiple light-receiving elements can be arranged for one light source, making it easy to respond to temperature characteristics and changes over time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a diagram showing the arrangement of lenses, etc. in the same embodiment, and FIG. 3 is a diagram showing the arrangement of lenses, etc. in the second embodiment. 4 is a sectional view showing the third embodiment, FIG. 5 is a sectional view showing the fourth embodiment, FIG. 6 is a perspective view showing the arrangement of parts in an example of a conventional optical length measuring device, and FIG. Fig. 7 shows another conventional example using a half mirror, Fig. 8 shows another conventional example in which the optical axis of the lens is tilted, and Fig. 9 shows another conventional example using a condensing lens. FIG. 1... Optical length measuring device, 4... Optical axis, 5...
・Focal plane, 7.10.21-...Light source, L...Lens, PD,
PDI~3...Photodiode as a photodetection element. Patent Applicant Futaba Electronics Co., Ltd. Agent/Patent Attorney Norihiro Nishimura No. 270” No. 6 No. 104

Claims (1)

[Claims] An optical length measuring device that detects changes in brightness and darkness patterns that occur due to the relative movement of two gratings disposed facing each other, and measures the relative movement distance of each grating, comprising: a light source; a plurality of lenses that guide light from the light source to the grating and condense reflected light from the grating; An optical length measuring device comprising a plurality of photodetecting elements provided at respective positions symmetrical to a light source.