JP2001066155A - Image formation type encoder using lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply realize high resolution by executing electric division of a detection signal. SOLUTION: Slits 5 having a fixed width are formed at a fixed pitch on an scale plate 4 of this encoder, and each slit 5 is extended in the direction perpendicular to the moving direction of the scale plate 4. A slit transmitted light image (striped pattern of light and shade) obtained through the scale plate 4 is projected on four photodiode light-receiving face 11a-14a through a lens 6. The image forming position of the projected image can be set so as not to be positioned on the light-receiving face 11a-14a by adjusting distances (a), (b). As a result, a Lissajous's waveform of the projected image on the light- receiving face 11a-14a is brought close to a true circle, and detection signals A, B become a sine-wave shape. Therefore, the resolution of the encoder 1 can be heightened simply by executing electric division of the detection signals like these.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging encoder using a lens, and more particularly, to an imaging encoder using a lens capable of easily obtaining high resolution.

[0002]

2. Description of the Related Art FIG. 1 shows an example of the configuration of an imaging type encoder using a general lens. Referring to FIG. 1, in the imaging encoder 1, light from the light emitting diode 2 is applied as scattered light via the diffusion plate 3 to the scale plate 4 attached to a moving body (not shown). The scale plate 4 is formed with light transmitting slits 5 having a constant width and extending at a constant pitch in a direction orthogonal to the moving direction. Accordingly, a stripe-shaped slit transmitted light image is obtained via the scale plate 4, and the slit transmitted light image is transmitted through the cylindrical lens 6 to the light receiving surfaces of the first to fourth photodiodes (PD) 11 to 14. 11a to 1
4a.

The light receiving surfaces 11a to 14a of the first to fourth photodiodes are arranged at a constant pitch in the scale plate moving direction, and each light receiving surface extends in a direction perpendicular to the scale plate moving direction. The width of the light receiving surface. The photodiode output is supplied to the signal processing circuit 7, and the first and third photodiodes 11 and 13
An A-phase signal is generated based on the difference in the amount of received light, and a B-phase signal is generated based on the difference in the amount of received light between the second and fourth photodiodes 12 and 14. Based on these signals,
Movement information such as the moving speed, moving position, and moving direction of the moving body to which the scale plate is attached can be obtained.

Here, as shown in FIG. 2, the light receiving surfaces 11a to 14a of the first to fourth photodiodes are
They are arranged at a pitch Pd (= 2Bd) that is twice the width Bd. In this case, the pitch P is four times the light receiving surface pitch Pd.
In general, the slit transmitted light image is formed on the light receiving surface by i.

In this way, the light quantity distribution of the slit transmitted light image shows a rectangular wave value as shown in FIG. 3, and the Lissajous waveform at the image forming position (on the light receiving surface) is shown in FIG.
As shown in FIG.

[0006]

Here, in order to increase the resolution of the encoder having this configuration by electric division, A
The phase and B phase signals need to change sinusoidally, and if these signals change sinusoidally, the Lissajous waveform approaches a perfect circle. As described above, a sharp imaging optical system which is generally considered to be good is not suitable for increasing the resolution of an encoder.

On the other hand, in the imaging encoder, as described above, the slit transmitted light image obtained through the scale plate is enlarged and projected on the light receiving surface via the lens. When the light receiving surface pitch is large, it is necessary to increase the magnification of the imaging optical system, and for that purpose, it is necessary to increase the distance from the scale plate to the light receiving surface. As a result, the size of the encoder is increased, and the amount of light received on each light receiving surface is reduced, so that the output level of the encode signal is reduced.

[0008] In view of the above, an object of the present invention is to provide:
An object of the present invention is to propose an imaging type encoder using a lens capable of easily realizing high resolution. Another object of the present invention is to propose an imaging type encoder capable of realizing miniaturization and improvement of an output level.

[0009]

In order to solve the above-mentioned problems, the present invention provides a method in which a stripe-shaped slit transmitted light image obtained through a scale plate is arranged at a predetermined pitch through a cylindrical lens. First to fourth
Projecting on the light receiving surface of the photodetector, and generating an A-phase signal based on the difference in the amount of light received on the light receiving surfaces of the first and third photodetectors;
The following configuration is employed in an imaging encoder using a lens that generates a B-phase signal based on the difference between the amounts of light received on the light receiving surfaces of the second and fourth photodetectors.

First, in the first invention of the present application, the projection image obtained through the cylindrical lens is formed so as to form an image at a position different from the first to fourth photodetector light receiving surfaces. A distance between a scale plate and the cylindrical lens, and a distance between the cylindrical lens and the first lens.
The distance between the light receiving surfaces of the fourth to fourth photodetectors is set.

That is, as shown in FIG. 1, by adjusting the distance a between the scale plate 4 and the lens 6 and the distance b between the lens 6 and the photodiode light receiving surfaces 11a to 14a, the image formation position by the lens 6 is adjusted. Can be shifted, for example, rearward from the photodiode light receiving surface, so that the slit light image projected on the photodiode light receiving surface can be defocused. As a result, the harmonic components in the change in the amount of light accompanying the movement of the slit plate obtained on the light receiving surface of the photodiode are reduced, and the waveforms of the A-phase and B-phase signals have a shape close to a sine wave. It can be close to a perfect circle.

In a case where a Lissajous waveform close to a perfect circle is obtained, for example, if distances at which a theoretically sharp image is obtained are a and b, distance b is held as it is and distance a
Is increased or decreased by about several tens percent. An example of a Lissajous waveform obtained in this case is shown in FIG.

Next, according to a second aspect of the present invention, there is provided an imaging type encoder using a lens, wherein
The pitch of the projected image formed on the photodetector light-receiving surface is 4 / n of the pitch of the first to fourth photodetector light-receiving surfaces.
(N is an odd number of 3 or more).

For example, in the case shown in FIG. 6, the imaging pitch Pi of the projected image is set to four times (4 · ・) the theoretical value of the light receiving surface pitch.
This is a case where Pd is reduced to about 1/3. When the positional relationship of each part is defined so as to satisfy such a condition, the enlargement ratio of the projected image is small, so that the encoder can be downsized accordingly. Further, since the amount of received light increases, the output signal level of the photodiode increases, the amplification factor of those output signals can be reduced, and the S / N ratio of the obtained encoded signal can be improved.

[0015] Next, in the third invention of the present application, the scale plate is formed with a light transmission slit having a predetermined width and extending at a predetermined pitch in a direction different from the moving direction of the scale plate. Each of the first to fourth photodetector light receiving surfaces has a fixed width that is different from the moving direction of the scale plate and extends in a different direction with respect to the light transmitting slit. It is characterized by being a surface.

Here, the relationship between the slit shape in the scale plate and the shapes of the first to fourth light detector light receiving surfaces may be as follows.

First, the slit has a constant width inclined at a predetermined angle with respect to a direction perpendicular to the scale plate moving direction, and the light receiving surface has a constant width extending in a direction perpendicular to the scale plate moving direction. This is the case. Second, on the contrary, the slit has a constant width extending in a direction perpendicular to the scale plate moving direction, and the light receiving surface side is inclined at a predetermined angle with respect to the direction perpendicular to the scale plate moving direction. This is the case.

For example, as shown in FIG. 7A, when the slit 5A formed in the scale plate 4 is inclined by a predetermined angle with respect to a direction orthogonal to the scale plate moving direction (arrow A). Since the light quantity distribution of the slit transmitted light image obtained through the scale plate changes to a trapezoidal shape as shown in FIG. 7B, the light quantity change obtained on the light receiving surface with the scale plate movement is , A shape close to a sine wave.
Therefore, as shown in FIG. 8B, the shape is closer to a perfect circle as compared with a square Lissajous waveform as shown in FIG. 8A obtained in the case of a light quantity change as shown in FIG. A Lissajous waveform is obtained.

In order to obtain a similar effect, the following configuration is adopted in the fourth invention of the present application. That is, in the scale plate, slits for transmitting light extending in a direction different from the moving direction of the scale plate are formed at a predetermined pitch, and the light receiving surfaces of the first to fourth photodetectors are formed. Each is a light receiving surface of a fixed width extending in a direction different from the moving direction of the scale plate, and further, a boundary portion of the slit for light transmission in the moving direction of the scale plate is such that the transmitted light amount continuously increases or It is characterized by a decrease.

For example, as shown in FIG. 9A, a slit portion 5 of one pitch portion formed on the scale plate 4 is provided.
B is a light transmitting portion 51, a light shielding portion 52, a transition portion 53 in which the light transmittance gradually decreases along the slit plate moving direction from the light transmitting portion 51 to the light shielding portion 52, and a light shielding portion. A transition portion 54 where the light transmittance gradually increases from 52 toward the light transmitting portion 51 along the slit plate moving direction.
It has.

Even when the slit plate 4 is configured in this manner, as shown in FIG. 9B, the light quantity distribution of the transmitted light image of the scale plate has a trapezoidal shape.

Further, in order to obtain the same effect, the fifth invention of the present application is characterized by having the following configuration.
That is, in the scale plate, slits for transmitting light extending in a direction different from the moving direction of the scale plate are formed at a predetermined pitch, and the light receiving surfaces of the first to fourth photodetectors are formed. Each is a light receiving surface of a constant width extending in a direction different from the moving direction of the scale plate, and further, a boundary line of the slit for light transmission in the moving direction of the scale plate is along the moving direction of the scale plate. It is characterized by a broken line or a curve so that the amount of transmitted light continuously increases or decreases.

For example, FIG. 10A shows the scale plate 4
In this example, slits of a constant width are formed inclining with respect to a direction perpendicular to the direction of movement of the scale plate, and the boundaries of the slits are defined by broken lines. Even if the slit 5C having such a shape is adopted, as shown in FIG.
The light quantity distribution of the slit transmitted light image obtained through the scale plate has a shape close to a sine wave, and therefore, the Lissajous waveform can be made closer to a perfect circle. (Other Embodiments) In the above description, the light emitting diode is used as the light source. However, it goes without saying that other light sources may be used. Further, the number of light sources may be plural.

The lens is not limited to a single lens, but a plurality of lenses may be used, or a compound lens may be used.

Further, the number of photodetectors can be four or more. If the number of photodetectors is increased, the level of the detection signal can be increased accordingly.

[0026]

As described above, in the imaging type encoder using the lens according to the present invention, the slits are set so that the change in the amount of light received on the light receiving surface of the photodetector due to the movement of the slit plate approaches a sine wave. The shape of the slit of the plate, the shape of the light receiving surface of the photodetector, or the image forming position of the projected image obtained via the lens is adjusted. Therefore, according to the present invention, a sine wave detection signal can be obtained instead of the conventional rectangular wave detection signal, and the encoder resolution can be easily increased by electric division.

Further, according to the present invention, the light receiving surface of the photodetector does not have to be located at the image forming position of the projected image obtained through the lens, so that the optical path length of the encoder optical system can be shortened. Accordingly, the encoder can be downsized. Further, since the magnification of the slit transmitted light image on the light receiving surface in the image forming optical system can be reduced, the detection signal level can be easily improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a general configuration example of an imaging type encoder using a lens.

FIG. 2 is an explanatory diagram showing a relationship between a pitch of a light receiving surface of a general photodetector and a light and dark pitch of a projected image obtained through a lens.

FIG. 3 shows a slit shape formed on a general scale plate,
FIG. 4 is an explanatory diagram showing a light amount distribution obtained by the scale plate.

FIG. 4 is a graph showing a Lissajous waveform at an image forming position in the encoder of FIG. 1;

FIG. 5 is a graph showing a Lissajous waveform at a position shifted from an image forming position in the encoder of FIG. 1;

FIG. 6 is an explanatory diagram showing a case where a pitch of a light receiving surface of a photodetector and a light and dark pitch of a projected image obtained through a lens are 4/3 times a pitch of a light receiving surface of the photodetector.

FIG. 7 is an explanatory view showing an example in which a slit formed in a scale plate is inclined with respect to a moving direction of the slit plate;
FIG. 4 is an explanatory diagram showing a light amount distribution obtained through the slit plate.

FIG. 8 is a graph showing a Lissajous waveform when a slit light image (bright and dark stripes) obtained via a scale plate extends in a direction orthogonal to a slit plate moving direction, and
It is a graph which shows the Lissajous waveform obtained when a slit light image inclines with respect to the direction orthogonal to a slit board movement direction.

9A and 9B are an explanatory diagram showing a case where a portion where a light transmission amount gradually increases and a portion which gradually decreases are formed on a scale plate, and an explanatory diagram showing a light amount distribution of transmitted light obtained by the scale plate.

10A and 10B are an explanatory diagram showing an example in which a slit having a polygonal boundary line is formed in a scale plate, and an explanatory diagram showing a light amount distribution of transmitted light obtained by the scale plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Encoder 2 Light emitting diode 3 Diffusion plate 4 Scale plate 5, 5A, 5B, 5C Slit 6 Cylindrical lens 7 Signal processing circuit 11 to 14 Photodiode (PD) 11a to 14a Light receiving surface

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Sawamura 1856-1, Oazamaki, Hodaka-cho, Minamiazumi-gun, Nagano F-term in Harmonic Drive Systems Co., Ltd. Hotaka Plant 2F103 BA37 CA01 CA02 DA01 EA02 EB06 EB12 EB15 EB16 EB23 EB33 EC01 FA12

Claims (5)

[Claims] 1. A slit-shaped transmitted light image of a predetermined pitch obtained through a scale plate is projected through a cylindrical lens onto first to fourth photodetector light-receiving surfaces arranged at a predetermined pitch, and An A-phase signal is generated based on the difference between the amounts of light received on the first and third photodetector light-receiving surfaces, and a B-phase signal is generated based on the difference between the amounts of light received on the second and fourth photodetector light-receiving surfaces. In the imaging type encoder using the generated lens, a projection image obtained through the cylindrical lens is:
The distance between the scale plate and the cylindrical lens, and the distance between the cylindrical plate and the first to fourth light detectors so that an image is formed at a different position from the first to fourth light detector light receiving surfaces. An imaging encoder, wherein a distance between the light receiving surfaces of the devices is adjusted. 2. A method of projecting a striped slit transmitted light image having a predetermined pitch obtained through a scale plate, through a cylindrical lens, onto first to fourth photodetector light receiving surfaces arranged at a predetermined pitch, and An A-phase signal is generated based on the difference between the amounts of light received on the first and third photodetector light-receiving surfaces, and a B-phase signal is generated based on the difference between the amounts of light received on the second and fourth photodetector light-receiving surfaces. In the imaging type encoder using the generated lens, the pitch of the projected images formed on the first to fourth photodetector light receiving surfaces is equal to the pitch of the first to fourth photodetector light receiving surfaces. An imaging encoder characterized by being 4 / n times (n is an odd number of 3 or more). 3. A stripe-shaped slit transmitted light image of a predetermined pitch obtained through a scale plate is projected through a cylindrical lens onto first to fourth photodetector light receiving surfaces arranged at a predetermined pitch, and An A-phase signal is generated based on the difference between the amounts of light received on the first and third photodetector light-receiving surfaces, and a B-phase signal is generated based on the difference between the amounts of light received on the second and fourth photodetector light-receiving surfaces. In the imaging type encoder using the generated lens, the scale plate is formed with a predetermined width of light transmission slit extending at a predetermined pitch extending in a direction different from the movement direction of the scale plate, and Each of the first to fourth photodetector light-receiving surfaces is a light-receiving surface having a fixed width extending in a direction different from the moving direction of the scale plate and also in a different direction with respect to the slit for transmitting light. That there is Imaging system encoder to butterflies. 4. A stripe-shaped slit transmitted light image having a predetermined pitch obtained through a scale plate is projected through a cylindrical lens onto first to fourth photodetector light-receiving surfaces arranged at a predetermined pitch, and An A-phase signal is generated based on the difference between the amounts of light received on the first and third photodetector light-receiving surfaces, and a B-phase signal is generated based on the difference between the amounts of light received on the second and fourth photodetector light-receiving surfaces. In the imaging type encoder using a lens to be generated, the scale plate is formed with a light transmission slit extending at a predetermined pitch extending in a direction different from a direction in which the scale plate moves, and Each of the photodetector light-receiving surfaces of No. 4 is a light-receiving surface of a constant width extending in a direction different from the moving direction of the scale plate, and a boundary portion of the slit for transmitting light in the scale plate moving direction is transmitted light. Imaging system encoder but which is characterized in that continuously increase or decrease. 5. A stripe-shaped slit transmitted light image of a predetermined pitch obtained through a scale plate is projected through a cylindrical lens onto first to fourth photodetector light receiving surfaces arranged at a predetermined pitch, and An A-phase signal is generated based on the difference between the amounts of light received on the first and third photodetector light-receiving surfaces, and a B-phase signal is generated based on the difference between the amounts of light received on the second and fourth photodetector light-receiving surfaces. In the imaging type encoder using a lens to be generated, the scale plate is formed with a light transmission slit extending at a predetermined pitch extending in a direction different from a direction in which the scale plate moves, and Each of the photodetector light-receiving surfaces of No. 4 is a light-receiving surface of a constant width extending in a direction different from the direction of movement of the scale plate, and a boundary of the light transmission slit in the scale plate movement direction is the scale. Imaging system encoder, wherein the quantity of transmitted light along Le plate movement direction so as to increase or decrease continuously, is defined by a polygonal line or a curve.