JPS6013212A - Optical type encoder - Google Patents

Abstract

PURPOSE:To simplify assembling and adjustment and to improve resolution, by using a hologram, regenerating the real image of bright and dark lattice fringes on a scale, thereby eliminating the effect of the diffraction of light. CONSTITUTION:A hologram 10 regenerates a real image 12 corresponding to bright and dark lattice fringes 4, which are marked on a scale 3 based on light 9 from a light source 8 on the lattice fringes 4 of the scale 3. A light receiving element 7 receives the transmitted light and the reflected light of the lattice fringes 4. The scale 3 and the hologram 10 are relatively moved with respect to a body to be checked. The amount of one-dimensional displacement of the body to be checked is detected by the output of the element 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an encoder that optically detects the amount of one-dimensional displacement, such as rotational displacement or linear displacement, of an object to be detected.

Conventionally, there has been an encoder shown in FIG. 1 that detects the rotational displacement of an object to be detected. In the figure, (1) is a light source such as a light emitting diode or lamp, and (2) is a light source (1).
A lens (3) for making the light emitted from the
) is a pulse scale made of a rotatable disk, (4) is a light and dark lattice stripe carved at equal pitches along the circumferential direction of the pulse scale (3), and (5) is the rotation axis of a motor (not shown), that is, the detected object. Pulse scale directly connected to the object (3)
, (6) is a fixed index scale with the same bright and dark lattice stripes as the pulse scale (3), and (7) is a light receiving element placed on the opposite side from the light source (1).

Next, the operation of the encoder with the above configuration will be explained.

Light emitted from a light source (1) is converted into parallel light by a lens (2) and then enters a pulse disk (3). The transmitted light from the bright and dark checkered stripes (4) of the pulse scale (intermediate) enters the index scale (6) with a light intensity distribution of bright and black corresponding to the light and dark pattern of the bright and dark checkered stripes (4). The intensity of light transmitted through the index scale (6) is
When the bright part of the transmitted light of the pulse scale (3) overlaps with the bright part of the index scale (6), it becomes maximum, and when it overlaps with the dark part, it becomes minimum. The transmitted light of the index scale (6) spatially modulated as described above enters the light receiving element (7) and is converted into an electrical signal. Axis of rotation(
When the pulse scale (3) rotates due to the rotation in step 5), the brightness distribution of the transmitted light also rotates. As a result, a sinusoidal output signal as shown in FIG. 2 (al) is obtained from the light receiving element (7).

This output signal is shaped by a waveform shaping circuit (not shown) and then
The rotational displacement amount of the object to be detected can be detected by counting the number of pulses after the rectangular wave shown in FIG.

Generally, the output from an encoder is rarely used as a single output. On the index scale (6), 2
A group or three groups of lattice stripes are provided, and two-phase main signals or three-phase signals (two-phase main signals and a zero signal) having a 90° phase difference are output.

With this configuration, the rotation direction can be determined by detecting the phase relationship between the main signals. Furthermore, by counting the rising and falling portions after the pulse is formed as shown in FIG. 2 (as shown in C1), the detection resolution can be increased up to four times.

However, since conventional encoders are configured as described above, in order to increase the number of generated pulses, it is necessary to reduce the pitch of the light and dark lattice stripes of the pulse scale and the intelligence scale. Due to the influence of the diffraction phenomenon, it was necessary to reduce the scale spacing corresponding to the above-mentioned bi-notches. For example, when the pitch is 10 μm, the scale interval is 0.1
fi, and the placement accuracy is 10 μm.
It is necessary to keep the following in mind. This makes assembly and adjustment extremely difficult, and even after assembly, maintenance is troublesome in order to maintain accuracy.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by using a hologram that reproduces a real image of bright and dark lattice fringes on a pulse scale instead of the conventional index scale. The purpose of the present invention is to provide a high-resolution optical encoder that eliminates the need for optical encoders, suppresses the effects of light diffraction, and facilitates assembly and adjustment.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, (8) is a semiconductor laser (hereinafter referred to as LD)
, (9) is the laser beam emitted from LD (8), (1
0) is a hologram in which part of the bright and dark lattice fringes (4) is recorded as an object, (11) is the hologram reconstructed image plane that coincides with the pulse scale (3) plane, and (12) is the hologram (
This is a real image of the same checkered pattern as the bright and dark checkered pattern (4) reproduced by 10). The hologram recording and reproducing system is constructed so that a real image (12) is reproduced on a Norse scale (3).

Next, the operation of the optical encoder with the above configuration will be explained.

Laser (9) as diverging light emitted from LD (8)
) enters the hologram (10). The light diffracted by the hologram (10) creates a real image (12) of bright and dark lattice fringes (4) on the reproduction image plane (11), that is, on the pulse scale (3). This real image (12) is a light and dark checkered pattern (
4), so when the pulse scale (3) rotates, the intensity of the transmitted light is such that the bright part of the real image (12) is incident on the bright part of the bright and dark lattice stripes (4). It is modulated in such a way that it reaches its maximum when it hits that dark area, and it reaches its minimum when it enters that dark area. This modulated transmitted light is transmitted to the light receiving element (
7) and is converted into an electrical signal, yielding the same output signal as shown in FIG. 2(a). Thereafter, the amount of displacement of the object to be detected can be detected by performing signal processing similar to the conventional case.

Here, the recording and reproducing system of the hologram (10) will be explained. FIG. 4(a) shows a recording system, and FIG.

A reference light (14), for example, as a convergent light, which is incident on the surface of a dry plate (13) at a predetermined angle (θ), and an object light (15) transmitted through an index scale (6) having lattice stripes of a predetermined pitch prepared in advance. The dry plate (13) is exposed to n light. After exposure, the dry plate (13) is developed and a bologram (10
).

In this case, the index scale (6) and the dry plate (13)
The interval can be arbitrary. As shown in FIG. 4 (0)), the reproduction system for the hologram (10) reproduces the hologram (10) using a reference beam (9), e.g., as a diverging beam, having a wavefront conjugate with the reference beam (14), that is, a laser beam (9). ) to illuminate. As a result, the real image (12) is reproduced at the original position where the index scale (6) was placed.

In the above embodiment, the hologram was recorded using convergent light as the reference light, parallel light as the object illumination light, and reproduced using diverging light as the illumination light, but a real image of bright and dark lattice fringes is reproduced on the pulse scale. Of course, other recording and reproducing systems may be used if possible.

Further, in the above embodiment, an LD is used as the light source, but a light emitting diode, a lamp, etc., or a combination of these and an interference filter may also be used.

Further, in the above embodiment, a case has been described in which transmitted light of a pulse scale is detected by a light receiving element, but it may be configured to detect reflected light from a pulse scale.

Furthermore, in the above embodiment, the encoder detects the amount of rotational displacement of the object to be detected, but as shown in FIG.
6), it is also possible to detect a one-dimensional displacement amount by linking this with the object to be detected.

As described above, according to the present invention, a real image of light and dark lattice fringes is reproduced on a scale using a hologram. Therefore, it is possible to obtain a high-resolution optical encoder that is easy to assemble.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a conventional optical rotary encoder, Fig. 2 (al, (bl, TO)) is a waveform diagram of the output signal of the optical encoder, and Fig. 3 (al, (b) is a diagram showing the waveform of the output signal of the optical encoder. A perspective view showing an optical encoder according to one embodiment, FIG. )...Light source, (2)...Lens, (3)...
・Pulse scale, (4)...light and dark lattice stripes, (5)・
... Rotation axis, (6) ... Index scale, (7
)...Photodetector, (8)...Semiconductor laser, (9)
...Laser light, (10) ...Bologram, (11)
...Reproduced image surface, (12)...Real image. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa (2 idiots) Figure 2 Figure 3

Claims (1)

[Scope of Claims] (11) a light source, a scale on which bright and dark checkered stripes are carved, a hologram that reproduces a real image corresponding to the bright and dark checkered fringes on the bright and dark checkered fringes of the scale based on the light from the light source, and A light-receiving element that receives transmitted light or reflected light from the bright and dark lattice stripes is provided, the scale and the hologram are moved relative to the object to be detected, and the output of the light-receiving element causes one-dimensional displacement of the object to be detected. (2) The optical encoder according to claim 1, characterized in that a semiconductor laser is used as a light source.