JPH0399220A - Encoder - Google Patents

Abstract

PURPOSE:To obtain high resolution when the moving state such as the moving amount or the moving direction of a body to be measured is detected by utilizing a light transmitting part, a light shielding part and a periodic scale by inputting the maximum or minimum amount of light into a photodetector every time the scale is relatively moved by a quarter of a pitch. CONSTITUTION:Luminous flux from a light source 1 is made to be the parallel luminous flux through a collimator lens 2 and inputted into a scale 3. The luminous flux is made to transmit through the light transmitting part and reflected from two reflecting surfaces 4a and 4b of a light reflecting means 4. The luminous flux is outputted into the reverse direction with respect to the incident direction and inputted again into the scale 3. Then, the luminous flux which has passed through the scale 3 is converged on the light receiving surface of a photodetector 6 by the use of a condenser lens 5. When the light transmitting part of the scale 3 at this time is shifted by a half of a pitch with respect to the ridge line, the entire luminous flux which is reflected from the reflecting surfaces 4a and 4b is shielded with the shielding part and is not outputted to the side of the photodetector 6. When the part is shifted by a quarter of a pitch furthermore, the luminous flux is incident on the photodetector 6.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an encoder, and in particular uses a scale that periodically provides light-transmitting parts and light-blocking parts to measure the movement state of an object to be measured, such as the amount of movement and direction of movement. This paper is about a rechargeable encoder that detects electricity.

(Prior Art) Photoelectric rotary encoders and linear encoders have conventionally been widely used as devices for detecting displacement states related to rotation, movement, etc. of an object to be measured.

FIGS. 8(A) and 8(B) are schematic plane and side views of essential parts of an optical system of a conventional linear encoder designed to detect the state of linear movement of an object to be measured.

In the figure, a light beam from a light source 51 such as an LED is turned into a substantially parallel light beam by a projection lens 52 and projected onto a main scale 53 . The main scale 53 is composed of a slit array in which light-transmitting portions and light-shielding portions of equal width are periodically provided on a transparent substrate such as glass or a thin metal plate by a method such as etching.

The light flux that has passed through the main scale 53 is incident on a subscale 54 having a pattern with the same period as the main scale 53, and the light flux that has passed through the subscale 54 is received by a light receiving means 55.

The main scale 53 is a detection head section 60 surrounded by a dashed line.
It is configured to be movable in the eight directions indicated by the arrows.

Here, the sub scale 54 has, for example, four scales 54-1 to 54-4 as shown in FIG. 9, and each of these scales consists of a slit row having the same period as the main scale 53.
It is arranged in the light beam projected from the light projection lens 52. Also, regarding the positional relationship of each scale 54-1 to 54-4, for example, if scale 54-1 is taken as a reference, scale 54-2 is shifted from scale 54-1 by 1/2 of the slit pitch; 3 is 1/4 of the slit pitch
, the scale 54-4 is shifted by 3/4 of the slit pitch.

The light receiving means 55 includes four photodetectors 55 as shown in FIG.
-1 to 55-4, each scale 54-1 to 54-4
They are arranged in correspondence with each other at the rear of the . Here, the scales 54-1 to 54-4 are arranged for the purpose of determining the direction of movement of the main scale 53 and removing the DC offset component.

FIG. 10 is an explanatory diagram of output signals obtained from the photodetectors 55-1 to 55-4 when the main scale 53 and the detection head section 60 relatively move by a predetermined amount in the linear encoder shown in FIG. be.

The output signal waveforms shown in the figure all change periodically with the slit pitch as a unit. (A) to (D) in the figure are output waveforms from the photodetectors 55-1 to 55-4 in order.

Now, if we take the output waveform of Fig. 10 (A) as a reference, we will obtain the output waveform shown in Fig. 10 (B) based on the positional relationship of the sub scales. (C). (D)
The output waveforms of are out of phase by 180 degrees, 90 degrees, and 270 degrees, respectively.

A conventional linear encoder uses these four output signals to calculate a DC offset from, for example, the differential output shown in FIG. 10 (A) and FIG. 10 (B), and the differential output shown in FIG. 10 (C) and FIG. The amount and direction of movement of the main scale 53 are detected by a well-known method from the phase relationship of each two differential outputs, excluding the variation.

(Problems to be Solved by the Invention) In the conventional linear encoder shown in Fig. 8, one way to improve the detection resolution of the moving state of the measured object is to reduce the periodic pattern pitch of the transparent part and the light-blocking part of the scale. There is a way to do it.

However, reducing the pattern pitch of the scale is difficult in terms of manufacturing, and becomes a factor in increasing costs.

In addition, the light-transmitting part and the light-blocking part of the scale act as a diffraction grating, and the light beam diffracted by the scale mixes into the signal light, becoming a noise component and reducing detection accuracy.

For example, the wavelength of the luminous flux from an LED as a light source is 0.9 μm.
When the pattern pitch of the scale is 10 μm, the diffraction angle θ of the first-order diffracted light is 5.2 degrees for θ since sin θ=0.9/10.

The diffracted light that spreads at this diffraction angle leaks from the subscale and becomes a bias component of the output signal, reducing the contrast of the output signal and causing a reduction in detection accuracy.

As described above, in conventional linear encoders, the pattern pitch cannot be made very small, making it very difficult to achieve high resolution.

The present invention is an encoder that can obtain an output signal based on a cycle of half the pattern pitch when using a scale with the same pattern pitch as the conventional one, and thereby achieves high resolution detection accuracy of the moving state of the object to be measured. The purpose is to provide.

Note that in the present invention, the encoder includes both a rotary encoder and a linear encoder.

(Means for Solving the Problems) The encoder of the present invention includes an irradiation means for irradiating a parallel light beam onto an optical scale along a predetermined optical path, and a irradiation means for irradiating a parallel light beam onto an optical scale, which is regularly reflected by the optical scale. Reflecting a reflected light flux or a transmitted light flux that has passed through the optical scale and traveling straight along the optical path, and inverting the reflected light flux or the transmitted light flux with respect to the direction in which the optical scale is displaced relative to the parallel light flux. and a means for charging and converting the light from the optical scale illuminated with the parallel light flux from the reflection means, and a means for charging and converting the light from the optical scale illuminated with the parallel light flux from the reflection means. It is characterized in that the displacement is measured based on the signal.

(Embodiment) FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a light source, which is composed of, for example, an LED or the like. Reference numeral 2 denotes a collimator lens which makes the light beam from the light source 1 enter the scale 3 as a substantially parallel light beam. The light source 1 and the collimator lens 2 constitute a light projecting means 101. The scale 3 is made up of a slit row in which light-transmitting parts and light-blocking parts of the same width are arranged periodically. Reference numeral 4 denotes a light reflecting means, which is composed of a right-angled prism with slopes 4a and 4b as reflecting surfaces (reflecting surfaces using vapor deposition of metal films or total reflection);
The light beam that has passed through the scale 3 is reflected and made to enter the scale 3 again. A condensing lens 5 condenses the light beam from the scale 3 and makes it incident on the photodetector 6.

The condensing lens 5 and the photodetector 6 constitute a light receiving means 102. Reference numeral 103 denotes a detection head, which is constructed by housing each of the above-mentioned elements except for the scale 3 in a housing. The scale 3 is movable relative to the detection head 103 in eight directions indicated by arrows in the figure.

In this embodiment, the light beam from the light source 1 is transferred to the collimator lens 2.
The light beam is made into a substantially parallel light beam and is made incident on the scale 3. Then, the light passes through the light-transmitting part of the scale 3, is reflected by the two reflecting surfaces 4a and 4b of the light reflection stage 4, and is emitted from a direction opposite to the direction of incidence, and is made to enter the scale 3 again. The light beam that has passed through the scale 3 is focused by a condensing lens 5 onto the light receiving surface of a photodetector 6.

Incidentally, at this time, the light beam from the scale 3 may be made to directly enter the light receiving surface of the photodetector 6 without using the condensing lens 5.

Figure 2 (^) ． (B) is an explanatory diagram showing only the scale 3 and the light reflecting means 4 in an enlarged manner, out of the explanation showing the positional relationship between the light beam reaching the photodetector 6 and the scale 3 in this embodiment.

In FIG. 2(A), the light beam 1a that has entered the scale 3 and passed through its transparent part is reflected by the two reflecting surfaces 4a of the light reflecting means 4.
, 4b and exit from symmetrical positions across the ridge lines of the reflecting surfaces 4a, 4b of the light reflecting means 4. At this time, as shown in the figure, the light shielding part of the scale 3 is 1/
If the positions are shifted by 2 pitches, these reflective surfaces 4a and 4b
The light beam reflected by
It does not shoot to the side.

On the other hand, the light-transmitting part and the light-blocking part of scale 3 in Fig. 2 (B) are
If the position is further shifted by 1/4 pitch from the position shown in Figure (A), that is, the position is symmetrical with respect to the ridgeline, as is clear from the figure, the light beam passing through the scale 3 will be reflected by the reflecting surfaces 4a and 4b.
After being reflected, the light passes through the transparent part of the scale 3 and enters the photodetector 6 again.

As can be seen from the above description, the maximum or minimum amount of light is incident on the photodetector each time the scale 3 moves relative to each other by 1/4 pitch.

FIG. 3 is an explanatory diagram showing the output signal waveform obtained from the photodetector 6 with respect to the relative movement of the scale 3 at this time.

As described above, this waveform is a repeating waveform with brightness and darkness every 1/4 bit, that is, a period of 1/2 bit. still,
If a perfectly parallel light beam emitted from a point light source is irradiated, the waveform will be triangular, but if a light source with a finite emission size such as an LED is used, a light beam with an angle of view will be emitted from the collimator lens. As shown in the figure, the waveform is somewhat distorted and has a periodic waveform similar to a sine wave.

To measure the relative movement amount of the scale 3 from this output signal waveform, a normal known processing method can be used, that is, a method of shaping the waveform to form a pulse waveform and then counting it with a pulse counter.

When determining the moving direction of the scale 3, it can be determined in the same manner as described above by arranging a sub-scale as described in the conventional example of FIG. 8 just in front of the condensing lens 5.

In addition, the following method may be used to determine the moving direction of the scale 3.

Figure 4 (A). (B) is an explanatory diagram of the vicinity of the light reflecting means 4 showing an example of this case. The same figure (A) is a top view, and the same figure (B) is a side view. In the figure, 7 is a parallel plane glass, which is arranged on the exit surface side of the light reflecting means 4.

The parallel flat glass 7 is arranged so that, for example, only the lower half of the light beam can pass through. Furthermore, the parallel flat glass 7 is tilted within the plane of FIG. It is set to shift in parallel by 1/8 of the pitch.

If the light beam that has passed through the parallel flat glass 7 and the light beam that has not passed through the parallel plate glass 7 and has gone straight are received by separate photodetectors, the two output signal waveforms from the photodetectors at this time will have a phase shift of 90 degrees from each other. Therefore, by using these two output signal waveforms, the moving direction of the scale 3 can be determined by a method similar to the conventional method.

FIG. 5 is an explanatory diagram showing another example in which the moving direction of the scale 3 is determined. 4-1 and 4-2 in the figure are light reflecting means similar to those explained in FIG.

In this embodiment, as shown in the figure, both are superimposed and bonded together with slight lateral deviations from each other.

The amount of deviation at this time is that the reflected light beams are 1/1/2 of each other, as described above.
It is set to be shifted by 8 pitches. Light reflecting means 4-1
．． 4-2 is placed in the same position as the light reflecting means 4 in FIG. If the light is received at , the direction of movement of the scale 3 can be determined in the same manner as before.

6 and 7 are schematic diagrams of main parts of optical systems according to second and third embodiments of the present invention. In the figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

In the second embodiment shown in FIG. 6, a light beam from a light source 1 is made into a substantially parallel light beam by a collimator lens 2, and after passing through a scale 3, it is made incident on one surface of a condenser lens 8. The light is then focused by a condenser lens 8, and reflected by a mirror 9 disposed on the focal plane of the condenser lens 8 in a direction opposite to the incident direction from a symmetrical position with respect to the optical axis. The light is made to re-enter the scale 3 as a substantially parallel light beam. Next, the light beam from the scale 3 is made incident on the surface of a photodetector 6 through a condensing lens 5. As a result, the same effect as the first embodiment shown in FIG. 1 is obtained.

In the third embodiment shown in FIG. 7, a light beam from a light source 1 is passed through a half mirror 10, turned into a substantially parallel beam by a collimator lens 2, and passed through a scale 3, and then condensed by a condensing lens 8. After being reflected by a mirror 9 placed on the focal plane of the optical lens 8, the original optical path is reversed and the beam is made to enter the scale 3 again. The light beam from the scale 3 is reflected by a half mirror 10 via a collimator lens 2, and then is made to enter a photodetector 6.

With this configuration, the same effects as the first embodiment shown in FIG. 1 can be obtained. In this embodiment, the number of members is reduced compared to the second embodiment shown in FIG. 6, and the overall device is made lighter and smaller.

Incidentally, in each of the above embodiments, the present invention is applied to a linear encoder, but the present invention can be similarly applied to a rotary encoder.

(Effects of the Invention) According to the present invention, by configuring each element as described above, even if the same pattern pitch scale as the conventional encoder is used, a resolution twice as high as that of the conventional encoder can be obtained, and highly accurate detection can be achieved. possible encoder can be achieved. In other words, it is possible to use a scale with a pattern pitch twice as coarse as that of conventional scales to obtain the same resolution, which simplifies the manufacture of the scale, and also allows for high-precision scales that prevent the negative effects of scale diffraction. It is possible to achieve an encoder that has features such as being able to perform detection, and also being able to perform basic detection using only one scale.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of the optical system of the first embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of the detection principle in the encoder of FIG. 1, and FIG. FIG. 5 is an explanatory diagram of an example of detecting the determination of the moving direction of the object to be measured in the present invention, and FIGS. 6 and 7 are illustrations of the second embodiment of the present invention. Schematic diagram of main parts of the third embodiment, 8th to 1st
FIG. 0 is an explanatory diagram of a conventional linear encoder and its detection principle. In the figure, 101 is a light projecting means, 102 is a light receiving means, 103 is a detection head, l is a source, 2 is a collimator lens, 3 is a scale, 4.4-1.4-2 is a light reflecting means, 5. 8 is a condenser lens, 6 is a photodetector, 7 is a parallel plane glass, 9 is a mirror, and 10 is a half mirror.

Claims (4)

[Claims] (1) An irradiation means for irradiating a parallel light beam onto an optical scale along a predetermined optical path, and a reflected light beam irradiated by the irradiation means and specularly reflected by the optical scale, or transmitted through the optical scale and transmitted to the optical scale. reflects the transmitted light beam that has traveled straight through the optical scale, and inverts the reflected light beam or the transmitted light beam with respect to the direction in which the optical scale is displaced relative to the parallel light beam, and directs the generated parallel light beam toward the optical scale again. An encoder comprising a reflecting means and a means for photoelectrically converting light from the optical scale illuminated with a parallel light beam from the reflecting means, and measuring the displacement based on a signal from the photoelectric converting means. (2) The encoder according to claim 1, wherein the scale is made up of light-transmitting parts and light-blocking parts arranged alternately along the direction, and the reflecting means reflects the transmitted light flux. (3) The encoder according to claim 1, wherein the scale includes reflective portions and non-reflective portions arranged along the direction, and the reflecting means reflects the reflected light beam. (4) The encoder according to claim 1, wherein the irradiation means causes the parallel light flux to be perpendicularly incident on the scale, and the reflection means allows the parallel light flux to be perpendicularly incident on the scale.