JP2697939B2 - Rotary encoder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rotary encoder, and more particularly, to a rotary encoder that photoelectrically detects a signal corresponding to a rotation amount of a cylindrical rotating body.

<Prior Art> As a measuring instrument for measuring the rotation amount of a cylindrical rotating body, there is a rotary encoder proposed by the present applicant in Japanese Patent Application Laid-Open No. 63-81212.

This rotary encoder is an excellent measuring device that can measure the amount of rotation of a cylindrical rotating body with a simple configuration and relatively high resolution.

This effect is achieved by providing an imaging optical system inside the rotating body (hollow portion), and using this imaging optical system, the image of the grating in the first area on the side surface of the rotating body can be converted into the first area with respect to the rotation axis of the rotating body. This is achieved by projecting onto the grid of the second region on the side opposite to that of FIG.

<Summary of the Invention> The present invention relates to an improvement of the rotary encoder disclosed in the above publication, and an object of the present invention is to provide a rotary encoder that can be further downsized.

In order to achieve this object, a rotary encoder according to the present invention includes a light irradiation unit, a cylindrical rotator, and a photoelectric conversion unit, and the cylindrical rotator rotates around an axis parallel to a generating line of the cylinder. Then, on the side surface of the cylindrical rotating body, a lattice is formed by alternately arranging the light transmitting portions and the light shielding portions along the rotation direction of the rotating body, and the light from the light irradiation means is formed on the side surface of the rotating body. The first region is irradiated, and the light that has passed through the lattice of the first region is directed to a second region on the side surface of the rotating body opposite to the first region with respect to the rotation axis of the rotating body. Receiving the light passing through the grating of the first region and converting the light into an electric signal, wherein the light irradiation means and the rotator are configured to project the Fourier image of the grating of the first region onto the grating of the second region. doing.

In the present invention, since the Fourier image of the grating in the first region is projected onto the grating in the second region, it is not necessary to provide an imaging optical system inside (hollow portion) of the cylindrical rotator. Therefore, the diameter of the rotating body can be easily reduced, and an extremely small rotary encoder can be provided.

In a preferred embodiment of the present invention, when the pitch of the grating is P and the wavelength of light from the light irradiation means is λ, the diameter d of the cylindrical rotating body is Is set to satisfy. In addition, the light transmitting part and the light shielding part are
In the case where the rotors are arranged alternately and correctly on the entire side surface of the cylindrical rotator, the pitch P of the grating is given by: Becomes

<Embodiment> FIG. 1 is a perspective view showing an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor laser which emits a coherent light beam having a wavelength λ. Reference numeral 2 denotes a collimator lens system that converts a divergent light beam from the semiconductor laser 1 into a substantially parallel light beam,
The semiconductor laser 1 and the collimator lens system 2 constitute light irradiation means. Reference numeral 3 denotes a cylindrical rotating body, which rotates in a direction indicated by an arrow with a shaft 5 parallel to the generatrix of the cylinder as a rotation axis. The rotating body 3 is connected to a drive shaft such as a motor via a connector (not shown), and is used as an optical scale for detecting a rotation amount of the drive shaft. Also, the shaft 5 and the center axis of the drive shaft coincide, and the center axis of the rotating body and the shaft 5 also substantially coincide. The rotator 3 is made of an opaque member such as a metal, and a plurality of slits 30a are arranged at equal intervals on the side surface 30 of the rotator 3 along the rotation direction of the rotator 3 with the pitch P. Therefore, the light incident on the side surface 30 of the rotating body 3 passes through the slit 30a, and a portion between the slits 30a.
It is shaded by 30b. That is, 30a is a light-transmitting portion, 30b is a light-shielding portion, and these light-transmitting portions 30a and the light-shielding portion 30b are alternately and correctly regulated along the rotation direction to form a grating, thereby forming an optical scale. . 4 is a photoelectric conversion element,
Consists of a photodetector. And the photoelectric conversion element 4
Outputs an electric signal corresponding to the intensity of light incident on the light receiving surface 40.

The optical axis 12 of the light irradiation means (1, 2) is orthogonal to the axis 5,
The optical axis 12 is located between the first area 31 and the second area 31 on the side surface 30 of the rotating body 3.
Cross with both 32. The first region 31 and the second region 32
The light from the light irradiating means (1, 2) is set on the opposite sides of the rotator 3 with respect to the axis 5, and the light from the light irradiating means (1, 2) is 4 light receiving surface
Pointed at 40. The first region 31 and the second region 32 are set on the side surfaces opposite to each other with respect to the axis 5 and are arranged symmetrically in order to reduce a measurement error due to the eccentricity between the center axis of the rotating body 3 and the axis 5. It is.

Of the lattice of the first region 31 and the lattice of the second region 32 of the rotating body 3,
The distance d along the optical axis 12 (hereinafter referred to as the “diameter d of the rotating body”) is represented by Is set to meet. Thus, the rotating body 3
Is set, the image of the lattice of the first region 31 on the side surface 30 of the rotator 3 is directly projected onto the lattice of the second region 32 without providing an imaging optical system in the hollow portion of the rotator 3. it can.
The grid image projected here is called a Fourier image, and is generated by the self-imaging action of the grid accompanying the light diffraction phenomenon. Since the rotating body 3 of the present embodiment has a cylindrical shape, the Fourier image is slightly curved and the contrast is apt to be reduced. However, the light irradiation means (1,
If the rotator 3 is configured as 2), there is no practical problem.

Next, the principle of measuring the rotation angle of the rotating body 3 of the encoder shown in FIG. 1 will be described in detail with reference to FIGS.

The light beam from the semiconductor laser 1 is converted into a parallel light beam by the collimator lens system 2, and the first region 31 of the rotating body 3 is irradiated with the parallel light beam. This parallel light beam is transmitted to the first area 31.
Is diffracted by the grating of the first region 31 and is 0 order, ± 1
Then, diffracted light of the second order and ± 2 order is generated, and interference between two or three light beams of the 0th order light and the ± 1st order diffracted light causes an area.
The Fourier image of the 31 grid is projected onto the grid of the region 32 of the rotator 3. The light and dark pitches of this Fourier image are equal to the pitch P of the lattice in the area 31. Further, as described above, the Fourier image is curved, but the curvature occurs along the curved surface of the region 32 and does not significantly affect the measurement accuracy.
In order to reduce the curvature of such a Fourier image,
What is necessary is just to make the diameter d of the rotating body 3 small.

As shown in FIG. 3, if the rotating body 3 is rotating in the direction of arrow 100 (CCW direction), the Fourier image moves in the direction of arrow 110 (CW direction). At this time, the grid in the area 32 where the Fourier image is projected has moved in the direction of the arrow 100. Therefore, the relative angle change between the Fourier image and the grid of the region 32 when the rotating body 3 rotates by the angle θ is 2θ, and the rotation angle can be measured with twice the resolution of the grid pitch.

The grating in the region 32 is illuminated with the Fourier image of the grating in the region 31, and light passing through the grating in the region 32 enters the light receiving surface 40 of the photoelectric conversion element 4. The photoelectric conversion element 4 converts the received light into an electric signal, and the rotation angle of the rotating body 3 is measured based on the signal. In the rotary encoder of this embodiment,
As described above, when the rotating body 3 rotates the angle θ,
The Fourier image of the grid of 31 and the grid of the region 32 have an angle of 2
Therefore, if the total number of the slits 3 of the rotator 3 is n, 2n sine-wave pulses are output from the photoelectric conversion element 4 per rotation of the rotator 3. The measurement of the rotation angle is performed by sequentially counting the sine wave pulses. Further, the rotation speed of the rotating body 4 can be detected based on the sine wave pulse from the photoelectric conversion element 4.

FIGS. 4 (A) and 4 (B) are views showing a state where the encoder shown in FIG. 1 is unitized and attached to a rotary drive shaft 8 (such as a motor) which is an object to be measured. FIG. 4A is a perspective view, and FIG. 4B is a sectional view.

As shown in FIGS. 4A and 4B, the rotating body 3 having a function as an optical scale is directly attached to the rotary drive shaft 8. On the other hand, the semiconductor laser 1, the collimator lens system 2, and the photoelectric conversion element 4 are
It is attached to and fixed. Here, a rod-shaped refractive index type distributed lens is used as the collimator lens system 2 to facilitate the unitization and to make the whole compact.

In the embodiment shown in FIG. 1, the parallel light beam is applied to the region 31 on the side surface 30 of the rotating body 3, but the light beam applied to the region 31 is used to correct the curvature of the Fourier image of the lattice of the region 31. It may be non-parallel. In this case, the divergent light beam is applied to the region 31 or the convergent light beam is applied to the region 31 according to the direction in which the curvature is to be corrected.

The reason why the semiconductor laser is used as a light source in the embodiment of FIG. 1 is that it emits monochromatic light that is small and has good coherence. Other light sources can be used as long as they emit light that can be projected onto the grid of the region 32. On the other hand, when a small-sized photoelectric conversion element 4 is used and it is desired to prevent a decrease in measurement sensitivity, a condenser lens may be provided between the rotating body and the photoelectric conversion element.

Further, in the embodiment shown in FIG. 1, the rotating body is made of metal and a plurality of slits are provided. However, the rotating body may be made of a transparent material such as acrylic. When the rotator is made of a transparent material, a large number of light shielding portions may be arranged at equal intervals on the inner or outer side surface of the hollow or solid (cylindrical) rotator. As a form of the light-shielding portion, for example, a V-shaped groove as described in Japanese Patent Application Laid-Open No. 62-3616 by the present applicant can be cited. The groove is formed on the inner peripheral surface of the rotating body, and the light incident on the groove is totally reflected to block the light.

<Effects of the Invention> As described above, in the present invention, the light irradiation means and the rotator are configured to project the Fourier image of the lattice of the first region of the cylindrical rotator onto the lattice of the second region. Therefore, it is possible to measure the amount of rotation of the rotator with high resolution without using an imaging optical type inside (hollow portion) of the rotator. Therefore, it is possible to provide a small-sized rotary encoder having high resolution.

Further, in the present invention, the cylindrical rotating body with respect to the rotating shaft,
The measurement accuracy does not deteriorate even if the mounting surface oscillates or thrust displacement occurs.

In addition, since the cylindrical rotating body can be reduced in size, inertial force is reduced, and vibration of the rotating body during measurement is reduced. Therefore,
Measurement accuracy is stable.

Further, even if the cylindrical rotating body expands and contracts in the radial direction due to the influence of heat or the like, the positional relationship between the Fourier image of the grating in the first area and the light irradiating means of the grating in the second area in the optical axis direction is kept constant. Therefore, measurement accuracy does not deteriorate due to heat or the like.

In addition, since the imaging optical system is defective, positioning of each element such as the light irradiating means, the cylindrical rotator, and the photoelectric conversion means is easy, and the unit is easily formed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention. FIG. 2 and FIG. 3 are plan views for explaining the measurement principle of the encoder shown in FIG. FIGS. 4 (A) and 4 (B) are a perspective view and a sectional view showing a state where the encoder shown in FIG. 1 is unitized. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Collimator lens system 3 ... Cylindrical rotating body 4 ... Photoelectric conversion element 5 ... Rotation axis 31 ... 1st area | region (grating) 32 ... 2nd area | region (grating)

Claims (3)

(57) [Claims] A cylindrical rotator which rotates about an axis parallel to a generatrix of the cylinder, and is provided on a side surface of the cylindrical rotator; A lattice is formed by alternately arranging light-transmitting portions and light-shielding portions along the rotation direction of the rotating body, and irradiates light from the light irradiating means to a first region on a side surface of the rotating body; Of the light passing through the grating in the second area is received by the photoelectric conversion unit, and the light passing through the grating in the second area is directed to the second area on the side surface of the rotating body opposite to the first area with respect to the rotation axis of the rotating body. A rotary encoder for converting an electric signal into an electric signal, wherein the light irradiating unit and the rotating body are configured to project a Fourier image of a lattice of the first area onto a lattice of the second area. 2. When the pitch of the grating is P and the wavelength of light from the light irradiation means is λ, the diameter d of the rotating body is The rotary encoder according to claim 1, wherein the following conditions are satisfied. 3. When the total number of light transmitting portions of the grating is n, The rotary encoder according to claim (2), wherein the rotary encoder is satisfied.