Metal such as chrome, etc., or a dielectric substance such as silicon oxide, etc., are formed, as a film, on the scale used in a photoelectric type encoder such as a linear encoder and a rotary encoder, and patterns are formed thereon.
In particular, in the incremental encoder, an origin pattern is provided in addition to an INC pattern, and for example, the origin pattern is forcedly passed through immediately after the power is turned on, and correction of a detection position is carried out.
Here, as an encoder in which an INC pattern and origin pattern (reference mark) or the absolute position (ABS) code pattern (collectively called “ABS pattern”) are altogether disposed on the scale thereof, conventionally it has been proposed that, as shown in FIG. 1 corresponding to FIG. 2(a) of Japanese Published Unexamined Patent Application No. 2001-82984 (Patent Document 1), for example, an INC pattern 1.2 of graduation cycle TPM and a reference mark (origin pattern) 1.3 are juxtaposed in parallel on the supporting body 1.1 of a scale 1. In FIG. 1, “X” denotes the measurement direction.
Also, as shown in FIG. 2 corresponding to FIG. 1 of Japanese Translation of International Application (Kohyo) No. 2004-529344 (Patent Document 2), such a technology has been proposed, in which an INC pattern 10 shown in Stage A and having repeated patterns of reflection lines 12 and non-reflection lines 14 and an ABS pattern 16 shown in Stage B and having reflection lines 12 and non-reflection lines 14 are combined to make a scale 18, and as shown in Stages C and D, a part (22) of reflection lines 20 of the INC pattern 10 are fractured, and the fractured portion 22 is made into the ABS data. In FIG. 2, reference numeral 20 denotes a reflection line as it is in an original state, and 22 denotes a cut-off reflection line.
Further, in Patent Document 2, as shown in FIG. 3 corresponding to FIG. 8 thereof, a detector 50 of the INC pattern and a detector 26 of the ABS pattern are disposed in the axial direction of measurement apart from each other. In FIG. 3, reference symbols LS1 and LS2 denote light sources. Reference numeral 18 denotes a scale, 25 denotes an image-forming lens, 52 denotes an index grating, and 54 denotes a reading head.
On the other hand, although not being a technology pertaining to the encoder, such a technology has been proposed in Japanese Published Unexamined Patent Application No. S58-144804 (Patent Document 3) as shown in FIG. 4 corresponding to FIG. 1a thereof, which heights of the multi-layered bodies 11 and 21 formed on a layer-supporting body 31 in particular a minute map type recording supporting body having a multi-color minute structure are changed. In FIG. 4, reference numerals 41, 61, 71 and 91 denote metallic layers, reference numeral 51 denotes a non-absorbing interference layer of an inorganic material corresponding to the first color tone, and reference numeral 81 denotes a non-absorbing interference layer of an inorganic material corresponding to the second color tone.
However, in the technology according to Patent Document 1, it is necessary to widely set the width of the direction (the left and right direction in the drawing) orthogonal to the measurement direction X of the scale 1, wherein the scale and finally the encoder are large-sized.
In addition, if a part of the INC pattern is fractured as in FIG. 2 corresponding to FIG. 1 of Patent Document 2, the detection accuracy of INC displacement at a part free from any INC pattern is worsened.
Further, in the case of a configuration of FIG. 3 corresponding to FIG. 8 of Patent Document 2. Since there is a gap between the detector 50 and the detector 26, the interval between both of the detectors changes due to linear expansion of the members for holding both detectors when the temperature is subjected to fluctuation. Therefore, there is a problem that the detection value of the INC pattern is not in agreement with the detection value of the ABS pattern.
On the other hand, since Patent Document 3 has a multi-color minute structure with the pattern heights changed in a minute map, the technology does not pertain to the scale of a photoelectric encoder.
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