JP4437340B2 - Photoelectric encoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric encoder, and more particularly to a photoelectric encoder that facilitates assembly and adjustment.
[0002]
[Prior art]
In a photoelectric encoder configured by assembling a main scale and a detection head that moves relative to the main scale, various posture adjustments during assembly are important to achieve high performance. Specifically, the gap between the main scale and the detection head, the rotation around the measurement axis (X axis) set in the main scale (rolling direction), and the axis (Y axis) orthogonal to the measurement axis in the main scale plane It is necessary to adjust the posture such as rotation around the pitch (pitching direction), rotation around the Z axis perpendicular to the X and Y axes (moire direction) that causes moire interference between the main scale and the index scale (for example, actual No. 7-5361).
[0003]
In particular, when an optical grating having a fine pitch formed by a holography technique or the like is used as the main scale or the index scale, the output signal amplitude is greatly reduced if there is a posture change in the moire direction. Therefore, the tolerance for posture fluctuation in the moire direction is as small as, for example, about 0.6 ° (± 0.3 °), and extremely precise mechanical adjustment is required.
[0004]
[Problems to be solved by the invention]
Conventionally, various techniques for mechanically adjusting the posture fluctuation of the photoelectric encoder in the moire direction and the like have been used, but the mechanical adjustment has a limit.
The present invention has been made in view of the above circumstances, and has as its object to provide a photoelectric encoder that increases the tolerance for posture fluctuation in the moire direction and thus facilitates mechanical adjustment.
[0005]
[Means for Solving the Problems]
The present invention includes a main scale in which a first optical grating is formed along a measurement axis, and an index scale in which a second optical grating that is opposed to the main scale and moves relative to the measurement axis is formed. In the photoelectric encoder including the detection head, one of the first optical grating and the second optical grating is elongated in a scale width direction orthogonal to the measurement axis, and is a rectangle having a constant width in the measurement axis direction. The other of the first optical grating and the second optical grating has a substantially rhomboid shape whose width in the measurement axis direction decreases from the central part in the scale width direction toward the peripheral part. It is characterized by comprising a grid.
[0006]
Specifically, in the present invention, for example, when the detection head includes an index scale and a light receiving element that receives the transmitted light, the index scale includes a non-transmissive portion that constitutes the second optical grating on a transparent substrate. The transmissive portions are formed in an array, and either one of the non-transmissive portions and the transmissive portions is patterned in a substantially rhombus shape.
Alternatively, in the present invention, for example, when the detection head has a light receiving element array that also serves as an index scale, either one of the light receiving elements constituting the lattice of the light receiving element array and the space between them is patterned in a substantially diamond shape. The
Corresponding to the configuration of these detection heads, the main scale is configured as, for example, a transmissive scale in which a transmissive part and a non-transmissive part of a rectangular pattern constituting the first optical grating are arranged on a transparent substrate.
[0007]
According to the present invention, moiré interference does not occur when the substantially rhombic lattice and the rectangular lattice overlap each other between the main scale and the index scale with respect to the posture variation in the moire direction. Accordingly, the tolerance for posture fluctuation in the moire direction is increased. The offset component of the output signal is increased by using a diamond-shaped lattice on one side of a combination of normal rectangular lattices, but if the peak value of the output signal is stable, the offset component can be easily removed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]
FIG. 1 shows a configuration of a photoelectric encoder according to the first embodiment. This encoder is composed of a main scale 1 and a detection head 2 which is disposed opposite to the main scale 1 and moves relatively along a measurement axis x set in the main scale 1. In the case of this embodiment, the main scale 1 is a transmissive scale in which an optical grating is formed by arranging non-transmissive portions 11 and transmissive portions 12 at a predetermined pitch on a transparent substrate 10.
[0009]
The detection head 2 includes an index scale 3 that is disposed opposite to the main scale 1 and receives light transmitted through the main scale 1, and light receiving elements 4 a and 4 b that receive light transmitted through the index scale 3. The index scale 3 is a transmissive scale in which an optical grating is formed by arranging non-transmissive portions 31 and transmissive portions 32 at a predetermined pitch on a transparent substrate 30. Specifically, at least two grating portions for obtaining A and B phase outputs having a 90 ° phase difference from each other are arranged on the index scale 3, and the light receiving elements 4a and 4b correspond to these grating portions. Is provided.
[0010]
A light source 5 is disposed on the detection head 2 so as to face the light receiving unit with the main scale 1 interposed therebetween. The light source 5 includes, for example, an LED 5a and a concave mirror 5b that collimates the output light. Collimated light from the concave mirror 5b is irradiated to the main scale 1.
[0011]
FIG. 2 shows the optical lattice patterns of the main scale 1 and the index scale 3 in correspondence with each other. The opaque portion 11 constituting the optical grating on the main scale 1 is elongated in the scale width direction orthogonal to the measurement axis x0 set on the main scale 1 and is patterned into a rectangle having a constant width in the measurement axis x0 direction. . On the other hand, the opaque portion 31 constituting the optical grating on the index scale 3 is patterned into a flat rhombus whose width in the measurement axis direction decreases from the central portion in the scale width direction toward the peripheral portion.
[0012]
According to this embodiment, since the opaque portion 31 of the index scale 3 is formed in a rhombus pattern so as to be thin at the periphery, the measurement axis x0 on the main scale 1 is set in a plane parallel to the main scale 1. On the other hand, even if the axis x1 of the index scale 3 is slightly rotated, that is, even if there is a posture change in the moire direction, moire does not occur. This is specifically shown in FIG.
[0013]
FIG. 3 shows a state where the opaque portion 11 of the main scale 1 and the opaque portion 31 of the index scale 3 overlap. In the ideal state (solid line), the axes x0 and x1 coincide with each other. Even if the two axes x0 and x1 are rotated by θ from this ideal state, as long as the opaque portion 31 of the index scale 3 is within the range of the opaque portion 11 of the main scale 1 as shown by the broken line, the main scale There is no difference in the optical coupling between 1 and the index scale 3, and no moire occurs.
[0014]
Specific numerical examples will be given. It is assumed that the pattern dimension of the opaque portion 11 of the main scale 1 is length L = 1 mm and width D = 10 μm. It is assumed that the opaque portion 31 of the index scale 3 is a rhombus inscribed in the opaque portion 11 of the main scale 1. At this time, as shown in FIG. 3, the allowable rotation angle θ at which moire does not occur is θ = tan ⁻¹ (2d / L) = 1.1 °.
In the case of a combination of a main scale having a normal rectangular pattern and an index scale, the tolerance for posture fluctuation in the moire direction is assumed to be about 0.6 ° as described above, and according to this embodiment, this tolerance is 0. It will spread to 6 ° + 1.1 °. Therefore, the mechanical posture adjustment at the time of assembly becomes easy.
[0015]
[Embodiment 2]
FIG. 4 shows the pattern of the optical grating of the main scale 1 and the index scale 3 according to another embodiment corresponding to FIG. In the previous embodiment, out of the opaque portion 31 and the transparent portion 32 of the index scale 3, the opaque portion 31 has a rhombus pattern, whereas in this embodiment, the transparent portion 32 has a diamond pattern. Yes.
Even in this way, the optical coupling between the main scale 1 and the index scale 3 does not change until a certain range of rotation between the axes x0 and x1. Accordingly, as in the previous embodiment, the tolerance for moiré variation is widened.
[0016]
[Embodiment 3]
FIG. 5 shows a configuration of a photoelectric encoder according to still another embodiment. Portions corresponding to those in FIG. 1 are denoted by the same reference numerals as those in FIG. In this embodiment, the light receiving section is constituted by a light receiving element array 6 that also serves as an index scale. The light receiving elements 61 of the light receiving element array 6 are arranged at a pitch of 3λ / 4 with respect to the scale pitch λ of the main scale 1, for example, so that outputs of A, BB, B, and AB phases can be obtained. Yes.
[0017]
FIG. 6 shows a pattern of the light receiving element 61 of the light receiving element array 6. As shown in the figure, the light receiving element 61 has a rhombus pattern similar to the non-transmissive portion 31 in the first embodiment or the transmissive portion 32 in the second embodiment.
Also in this embodiment, the tolerance for the moire fluctuation is increased on the same principle as the previous embodiment. As is clear from the relationship between the first and second embodiments, the same effect can be obtained by making the pattern of the space 62 between the light receiving elements 61 a rhombus.
[0018]
[Embodiment 4]
In the first to third embodiments described above, the linear encoder in which the measurement axis x is a straight line has been described. However, if the measurement axis x of the main scale 1 draws a circle, the first to third embodiments are not changed. The same applies to the encoder. For example, in the fourth embodiment in which the first embodiment is applied to a rotary encoder, the configuration of the optical gratings of the main scale 1 and the index scale 3 is shown in FIG. 7 corresponding to FIG. As shown in the figure, in the index scale 3, an optical grating having a rhombus pattern may be arranged along the axis x1 having the same radius of curvature as that of the measurement axis x0 of the disk-shaped main scale 1.
[0019]
[Embodiment 5]
In the present invention, one of the opposing optical gratings is formed as a flat rhombus pattern so that a certain posture variation can be allowed. Therefore, the detection head can be commonly used for the linear encoding and the rotary encoder by utilizing this characteristic. It can be configured as a part. FIG. 8 shows the main scale 1 and the index scale 3 in such a rotary encoder of the fifth embodiment, corresponding to FIG.
[0020]
The measurement axis x0 on the main scale 1 draws a circle as shown, whereas on the index scale 3, the axis x1 of the optical grating array is a straight line as in the first embodiment. The optical grating on the main scale 1 is inclined little by little in the range covered by the index scale 3 with reference to x1 of the index scale 3, but if the inclination angle θ is equal to or smaller than the allowable range angle described in FIG. There is no hindrance to the measurement. Therefore, the detection head having the index scale 3 of this embodiment can be applied to both a rotary encoder and a linear encoder.
The detection heads shown in the second and third embodiments can be similarly applied to a certain range of rotary encoders.
[0021]
In the present invention, the rhombus need not be a rhombus in a strict sense, but may be a “substantially rhombus”, in other words, a substantially rhombus. For example, as shown in FIG. 9, it may be a flat octagonal pattern with the four vertices of the rhombus slightly shaved, or a pattern that draws a smooth arc as shown in FIG. Shall be included.
In the embodiments described so far, the grid on the main scale 1 side is a rectangular pattern, and the rhombus pattern is used on the light receiving side (that is, the intec scale or the light receiving element array). A rectangular lattice may be used as usual, and a transmission part or non-transmission part on the main scale side may be a substantially rhombus.
Furthermore, although the case where a transmission type main scale is used has been described in the embodiment, the present invention can be similarly applied to a photoelectric encoder using a reflection type main scale.
[0022]
【The invention's effect】
As described above, according to the present invention, by using a combination of a lattice of a rectangular pattern and a substantially rhombus pattern, a photoelectric encoder that increases the tolerance for posture variation in the moire direction and facilitates mechanical adjustment. Can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a photoelectric encoder according to an embodiment of the present invention.
FIG. 2 is a diagram showing an optical lattice pattern of a main scale and an index scale of the same embodiment.
FIG. 3 is a diagram showing a state of coupling of the main scale and the index scale of the embodiment.
FIG. 4 is a diagram showing optical grating patterns of a main scale and an index scale according to another embodiment.
FIG. 5 is a diagram illustrating a configuration of a photoelectric encoder according to another embodiment.
FIG. 6 is a view showing a layout of a light receiving element array according to the same embodiment;
FIG. 7 is a diagram showing an optical grating pattern of a main scale and an index scale according to another embodiment.
FIG. 8 is a diagram showing optical grating patterns of a main scale and an index scale according to another embodiment.
FIG. 9 shows another example of a substantially rhombus pattern.
FIG. 10 shows another example of a substantially rhombus pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Main scale, 10 ... Transparent substrate, 11 ... Impervious part, 12 ... Transmitting part, 2 ... Detection head, 3 ... Index scale, 30 ... Transparent substrate, 31 ... Impervious part, 32 ... Transmitting part, 4a, 4b ... light receiving element, 5 ... light source, 6 ... light receiving element array.

Claims (5)

A detection head including a main scale on which a first optical grating is formed along the measurement axis, and an index scale on which a second optical grating that is disposed opposite to the main scale and moves relative to the measurement axis is formed; In the photoelectric encoder with
One of the first optical grating and the second optical grating is configured by arranging rectangular gratings that are elongated in the scale width direction orthogonal to the measurement axis and have a constant width in the measurement axis direction,
The other of said first optical grating and the second optical grating, the width of the scale width direction of the measuring axis direction at the center portion of the measuring axis direction of the front grille Kinori shaped width substantially the same and, wherein the length of the scale width direction of the scale width direction of the rectangular grid at substantially the same as the length at the center portion of the measuring axis direction, the scale width direction of the center measuring axis direction of the width toward the periphery from Is arranged by arranging approximately rhombic lattices,
And, when the allowable rotation angle between the main scale and the index scale is theta, edges are oblique with respect to the scale width direction of the grating of the substantially rhombic to the scale width direction each inclined by an angle theta, in a state where the center of the grid of the substantially rhombic and the center of the rectangular grid is matched, when the lattice of the substantially rhombic rotates by the allowable rotation angle theta, the substantially rhombic The photoelectric encoder is in the range of the rectangular lattice.   The detection head includes the index scale and a light receiving element that receives the transmitted light, and the index scale includes a transparent substrate on which a non-transmissive portion and a transmissive portion constituting a second optical grating are arranged, and 2. The photoelectric encoder according to claim 1, wherein either one of the non-transmission portion and the transmission portion is patterned in the substantially diamond shape.   The detection head has a light receiving element array also serving as the index scale, and any one of the light receiving elements of the light receiving element array and a space therebetween is patterned in the substantially rhombus. 1. A photoelectric encoder according to 1.   4. The transmissive scale according to claim 2, wherein the main scale is a transmissive scale in which a transmissive portion and a non-transmissive portion of a rectangular pattern constituting the first optical grating are arranged on a transparent substrate. Photoelectric encoder.   5. The detection head according to claim 1, wherein the detection head is configured as a general-purpose component applicable to both a linear encoder in which the measurement axis draws a straight line and a rotary encoder in which the measurement axis draws a circle. A photoelectric encoder according to claim 1.

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