JP2540113B2 - Encoder - Google Patents

Description

TECHNICAL FIELD The present invention relates to an encoder for measuring displacement of an object to be measured, such as a rotational state or a moving state, and particularly to an encoder for generating a bit signal provided on the object to be measured. A light beam is made incident on a code plate provided with a plurality of tracks made of binary coded code, and electrical data is obtained from the light beam reflected or transmitted from the code plate, and the absolute displacement of the measured object is obtained from this. The present invention relates to an absolute encoder suitable for obtaining a state.

(Prior Art) Conventionally, a photoelectric encoder is often used as a measuring device for detecting rotation, movement, position, etc. of an object to be measured and rotation amount, rotation speed, etc. of a rotating mechanism.

FIG. 5 is a schematic diagram showing an example of a so-called absolute type encoder for measuring the absolute amount of the displacement state of a conventional measured object.

In the figure, reference numeral 51 denotes a rotating disk that rotates about a rotating shaft 50, and a binarized data element is generated on the rotating disk 51 according to an arbitrary (quantized) angular position. A plurality of tracks 56 are provided concentrically. Each track 56 is provided with a plurality of slits 52 which are optically binarized data, for example, a transmissive region and a non-transmissive region.

Reference numeral 53 denotes a fixed slit row, which has a plurality of openings for selectively passing a light beam from a slit provided on each track 56. 54 is a light projecting means having a plurality of light projecting elements,
Reference numeral 55 denotes a light receiving means having a plurality of light receiving elements, both means sandwiching the rotating disk 51 and the fixed slit row 53 so that each light projecting element and each light receiving element respectively correspond to each opening of the fixed slit row 53. Are arranged as follows.

In the structure shown in the figure, the light flux emitted from each light projecting element of the light projecting means 54 enters the light receiving means 55 through the slit 52 and the fixed slit 53. At this time, the absolute rotational position of the rotary disc 51 is obtained from the combination of the output signals of the respective light receiving elements. In order to reduce the size of the device as a whole in such a configuration, it is necessary to increase the information density of each track, and increase the parallel density of the light projecting element and the light receiving element together, for example, to achieve high-density integration of each element.

Further, in order to achieve high resolution, it is necessary to detect a fine area with high accuracy.For this reason, a fixed slit plate having a narrow slit width is used to limit the irradiation area and to generate a parallel light flux with a sufficient light quantity. Need to irradiate.

However, miniaturization and high resolution of the entire device conflict with each other, and it was difficult to satisfy the companions.

For example, if a condenser lens having a long focal length is used, a good parallel light flux can be obtained, but the illuminance of the irradiated area is reduced by the longer focal length. Further, if a large-capacity light source or a large-sized light receiving element is used, a sufficient amount of light and a signal can be obtained, but the light projecting means and the light receiving means tend to become larger.

(Problems to be Solved by the Invention) According to the present invention, when a code plate including a plurality of tracks provided with bit signal generating patterns is provided on an object to be inspected and a light beam is incident on the code plate through an illumination system. By specifying the shape of the light flux and improving the irradiation density, it is possible to reduce the size of the entire apparatus and to detect the absolute amount of displacement such as rotation or movement of the detected object with high resolution. The purpose is to provide an encoder.

(Means for Solving Problems) A code plate having a plurality of tracks for generating bit signals connected to an object to be measured is provided with a linear light beam having a shape longer in the track arrangement direction than in the moving direction of the code plates. In the encoder that receives the optical signal from the code plate and detects the displacement state of the object to be measured, and a collimator lens that emits a light beam from a light source as parallel light, and a cylindrical lens in order from the collimator lens side. The lens, the reflecting element, and the spherical lens are integrally formed and positioned, and the parallel light flux from the collimator lens is a focused light flux in the moving direction of the code plate and is wider than the entire track width in the array direction of the tracks. And a beam shaping optical system for making parallel light incident on the code plate.

(Embodiment) FIG. 1 is a schematic view of an embodiment when the present invention is applied to an absolute type rotary encoder. In the figure, reference numeral 1 is a light source, which is a semiconductor laser in the present invention. A collimator lens 2 emits a divergent light beam from the semiconductor laser as a parallel light beam. A beam shaping optical system 3 shapes the parallel light flux from the collimator lens 2 into a light flux having a predetermined shape, for example, a linear light flux, and emits the light. Reference numeral 4 is a reflecting mirror, and 7 is a code section for obtaining an absolute signal, which is composed of a plurality of tracks 7 _{1 to} 7 ₈ each composed of a binary code consisting of a transmission section and a light shielding section. 8
Is a light receiving means in which a plurality of light receiving elements are arranged in one direction, and 9 is a rotating shaft which is an object to be measured provided with the code part 7.

2 and 3 are a plan view and a side view of the main part of FIG. 1, respectively. In the present embodiment, the beam shaping optical system 3 integrally forms a cylindrical lens 31, a reflecting reflection prism 32, and a spherical lens 33 from the incident side of the light flux with the same material.
Alternatively, they are laminated together. It should be noted that they may be made of different materials, and in this case, the light quantity loss may be reduced by joining after processing the antireflection film or the like.

Then, as shown in FIG. 2, the light beam incident on the plane orthogonal to the generatrix direction of the cylindrical lens 31 is once converged by the cylindrical lens 31 and then reflected as a divergent light beam on each surface of the prism 32, and then on the spherical lens. A collimated light beam of a predetermined size is made incident on the track surface of the code plate 7 by 33.

On the other hand, as shown in FIG. 3, the light beam incident on the surface of the cylindrical lens 31 in the generatrix direction passes through the cylindrical lens 31 in a substantially parallel light beam state, is reflected by each surface of the prism 32, and then the spherical lens 33. Thus, the spherical lens 33 converges on the track surface of the code plate 7 arranged at the substantially focal position. Incidentally, the arrangement positions of the cylindrical lens 31 and the spherical lens 33 may be reversed.

As described above, the light beam incident on the optical member 7
As shown in the drawing, a light beam L having a long shape in the arrangement direction of each track of the code plate 7 is made incident as a light beam having, for example, a slit shape or an elliptical shape.

 Next, a specific operation of this embodiment will be described.

A light beam emitted from the semiconductor laser 1 is made into a parallel light beam having a circular diameter of about 2 mm by a collimator lens 2 having an effective diameter of about 2 mm, and then enters a beam shaping optical system 3. The beam shaping optical system 3 causes the emitted light flux to enter and enter the surface of the code plate 7,
It has a long elliptical shape of about 8 mm x 0.1 mm with the long axis in the track arrangement direction. Code plate 7 has 8 tracks
The total track width is about 4 mm. That is, the width of one track is about 0.5 mm. As described above, in this embodiment, the parallel light flux from the collimator lens 2 is expanded by the beam shaping optical system 3 on the surface of the code plate 7 in the direction of arrangement of the tracks 7 _{1 to} 7 ₈ which is larger than the total track width 4 mm × 0.1 mm. mm
The incident light is a parallel elliptical light beam of a certain degree. The central 4 mm of the oblong-shaped light beam that enters the code plate 7
By selectively using the light flux L of about × 0.1 mm,
As a result, the detection accuracy is improved by using a region (a region where the light intensity distribution is uniform) in which the variation in the light amount is small in the used light beam region.

Then, the transmitted light flux from the code plate 7 is received by the light receiving means 8 composed of eight light receiving elements arranged at the same pitch 0.5 mm as the track pitch, and the output signal from the light receiving means 8 is used to Is obtained to obtain the rotation state of the code plate 7.

In the present embodiment, the dimension of the light flux incident on the code plate 7 in the moving direction of the track is determined by the pitch dimension between the transmitting portion and the light shielding portion of the track for generating the minimum bit signal, that is, the bit width in the moving direction. The length may be small, and the bit signal from the track can be detected. This avoids detection of the information from adjacent bits,
An accurate absolute signal can be formed.

In this embodiment, instead of using the light flux passing through the code plate 7, the reflected light flux from the code plate 7 may be used.
In this case, the reflecting mirror 4 may be a semitransparent mirror and the light receiving means 8 may be arranged above the semitransparent mirror 4.

Although the present embodiment shows the case where the present invention is applied to the absolute type rotary encoder, the present invention can be applied to the absolute type linear encoder as it is.

Further, since the utilization efficiency of the light flux is good, the present applicant can also directly apply it to a rotary encoder having an absolute function using diffraction and interference of laser light, such as Japanese Patent Application No. 62-69937. You can

(Effect of the Invention) According to the present invention, the parallel light flux from the collimator lens can be made to enter the code plate in a high density and uniformly as a light flux state of a predetermined shape by using the optical member having the above-described configuration. Therefore, it is possible to achieve a small absolute encoder that has high resolution and does not use a fixed slit or the like. In addition, the parallel light flux from the collimator lens is focused on the code plate in the moving direction of the code plate,
With respect to the track arrangement direction, it is possible to selectively use the luminous flux of a region (a part where the intensity distribution is substantially uniform) in which there is little variation in the amount of light by making parallel light incident that is wider than the entire track width. According to this, the detection accuracy can be further improved.

Further, since a sufficient amount of light can be secured, the track interval and the arrangement pitch of the respective light receiving elements can be made fine, and the size can be further reduced. Further, since the fixing slit is not required, the assembling can be facilitated and the safety against vibration etc. can be improved.

Further, by adjusting the optical member in which the respective elements are integrally joined, it is possible to easily change the line width of the light beam incident on the code plate and read the code on the track with a fine pitch with high accuracy. Further, since the respective elements constituting the beam shaping optical system are integrally formed, the positioning can be easily performed, and the provision of the reflecting means makes it possible to realize a compact encoder.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment when the present invention is applied to an absolute type rotary encoder, FIG. 2, and FIG.
FIG. 4 is a plan view and a side view of the main part of FIG. 1, and FIG.
Explanatory drawing which shows the state with the light beam which injected into a part of figure, 5th
The figure is an explanatory view of a conventional absolute type encoder. In the figure, 1 is a semiconductor laser, 2 is a collimator lens, 3
Beam shaping optics, the fourth reflecting mirror, 7 code plate, the light receiving unit 8, the rotation axis of the rotating object, 7 _{1-7 8} tracks 9, 31
Is a cylindrical lens, 32 is a prism, and 33 is a spherical lens.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tetsuji Nishimura Inventor Tetsuji Nishimura, 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Canon Inc. Tamagawa Plant (72) Inventor Satoshi Ishii 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa In-house (56) References JP 61-66926 (JP, A) JP 54-25756 (JP, A) JP 59-3306 (JP, A)

Claims (3)

(57) [Claims] 1. A linear luminous flux having a shape longer than the moving direction of the code plate is incident on a code plate having a plurality of tracks for generating a bit signal connected to an object to be measured. In an encoder that obtains an optical signal from the code plate and detects the displacement state of the measured object, a collimator lens that emits a light beam from a light source as parallel light,
A cylindrical lens in order from the collimator lens side,
A reflecting element and a spherical lens are integrally formed and positioned, and a parallel light beam from the collimator lens is a focused light beam in the moving direction of the code plate, and a parallel light beam that is wider than the entire track width in the arrangement direction of the tracks. And a beam shaping optical system for making the beam incident on the code plate. 2. The encoder according to claim 1, wherein a shape of a light beam incident on the code plate by the beam shaping optical system is an elliptical shape. 3. A linear light flux obtained by the beam shaping optical system, wherein only a portion having a substantially uniform intensity distribution is selectively used to illuminate the plurality of tracks. The encoder according to claim 1.