OPTICAL ROTARY ENCODER

Abstract: An optical rotary encoder produces the rotational angle of a shaft (13) which is rotatably supported by a base member, i.e., by a flange (11) in the form of an electric digital quantity. A light-receiving system (18) having at least one photo-electric converter element is secured at a predeter­ mined position of the flange (11). A fixed shielding plate (19) having a predetermined projecting pattern is secured to the flange so as to be opposed to the light-receiving surface of the light-receiving system. A rotary shielding plate (15) having a predetermined projecting pattern is secured to the shaft so as to be opposed to the fixed shielding plate. A light source support member (20) is provided on the flange to turn about the axis of the shaft. A light source having light projecting elements (22, 23; 123, 223) is mounted on the light source support member so as to be opposed to the rotary shielding plate. The light source support member is adjusted for its position and is secured onto the flange by a securing element (25).

Description: The present invention relates to an optical rotary encoder, and more particularly, to an optical rotary encoder for converting a rotational angle of a shaft rotatably supported in a base member such as a flange into an output of an electrical digital quantity. Generally, in low resolution type optical rotary encoders with an output of about several hundred pulses (for example, 200) per one revolution, wide use is made of a structure in which a light source such as a light-emitting diode (LED), a laser-beam projector or the like is attached to and positioned mechanically at a predetermined location with respect to a light-receiving system including a light-detecting element, i.e., a photoelectric conversion element such as a photodiode, a photoconductor or the like. In the case of such an attaching structure, since an attaching position for the light source is unequivocally fixed, attachment thereof is easy and can be automated. However, since the position of the light source cannot be adjusted, the reliability of the encoders decreases upon variations in the orientation of the light source, the dimensional precision of component parts, etc. Therefore, such an attaching structure is not suitable for high resolution rotary encoders. In a high resolution optical rotary encoder with an output of several thousand pulses (for example, 2000) or more, wide use is made of a method of adjusting the three-dimensional position of the light source by hand, to obtain the optimal output waveform of an photoelectric conversion system, then fixing the light source to a fixed support by an adhesive. However, in the case of using such a method, the direction of the adjustment of the position of the light source is not defined, so adjustment is not made by set amounts, which factor results in a certain time must be taken for the adjustment. Further, since such a non-set manual adjustment is required, it is difficult to assemble the encoders automatically. DE-A-2919890, EP-A-0020991 and GB-A-1444851 disclose various adjustment means in optical encoders, but all use imprecise pin and slot type arrangements. EP-A-0003153 discloses an optical rotary encoder for converting a rotational angle of a shaft rotatably supported in a base member into a digital electrical output signal and comprising: a light receiving system fixed in a certain position to the base member; a stationary encoding plate fixed to the base member so as to face a light-receiving surface of the light-receiving system; a rotary encoding plate fixed to the shaft so as to face the stationary encoding plate; a light-source support member mounted on the base member via complementary cylindrical surfaces which are coaxial with the shaft; light source means attached to the light-source support member so as to face the rotary encoding plate; and fixing means for holding the light-source support member to the base member; and, according to the invention, such an encoder is characterised in that the light-source support member comprises at least part of a ring portion with an inner cylindrical surface which closely surrounds an outer cylindrical surface around the periphery of the base member whereby the light-source support member is rotatable relatively to the base member for adjusting alignment between the light-source means and the light-receiving system; in that the fixing means is arranged to lock the light-source support member against rotation relatively to the base member after the adjustment; and in that the light-source means is supported on an arm portion of the light-source support member extending radially inwardly from the ring portion. In the above-mentioned encoder, the alignment of the light source in relation to the light-receiving system can be easily performed by adjusting the position of the light-source support member in the direction of rotation thereof. That is, in the first place, the rotary encoding plate is matched in position with the stationary encoding plate, and then the light-source support member is matched in place with the base member in the direction of rotation thereof. The light-source support member is then fixed to the base member by means of the fixing means at the position where the waveform of the output from the light-receiving system is optimal. In this way, since the light-source support member supporting the light source can only rotate about the axis of the shaft, the adjustment of the position of the light source can be performed easily by set amounts, thus enabling automation of the assembly of the encoder and adjustment work for the light source. Consequently, it is possible easily to manufacture high resolution type optical rotary encoders. In a preferred embodiment of the present invention, the light-receiving system includes at least a pair of light-detecting elements, i.e., photoelectric conversion elements, arranged and spaced from each other by a certain distance in the circumferential direction of the shaft, and the light source includes at least a pair of light-emitting elements opposite to the light-detecting elements, respectively. In this case, the light-emitting elements may be spaced from each other by a certain distance in the circumferential direction of the shaft and fixed to a single light-source support member. The light-emitting elements, however, may be fixed to a pair of inner and outer light-source support members, respectively, so that the positions of the light-emitting elements can be adjusted individually. This modification makes possible not only individual adjustments of the photoelectric conversion outputs of the different phases, corresponding to the light-emitting elements, but also adjustment of the positional relationship among the phases. In the accompanying drawings: Figure 1 is a longitudinal sectional view of an optical rotary encoder illustrating a first embodiment according to the present invention; Fig. 2 is a front view of a light-source support member in the encoder shown in Fig. 1; Fig. 3 is a longitudinal sectional view of an optical rotary encoder illustrating a second embodiment according to the present invention; Fig. 4 is a front view of a light-source support member in the encoder shown in Fig. 3; and Fig. 5 is a partial sectional side view of an optical rotary encoder illustrating a third embodiment according to the present invention. Figures 1 and 2 show a first embodiment according to the present invention. Referring to these Figures, an optical rotary encoder comprises a disk-shaped base member, i.e., a flange 11. The flange has at its center a cylindrical bearing bore 12. A shaft 13 passing through the flange 11 is rotatably supported by a bearing 14 arranged in the bearing bore 12 of the flange. When the rotary encoder is applied, for example, to a servo motor (not shown), the flange 11 is attached to the housing of the servo motor and the shaft 13 is connected to the output shaft of the servo motor. The shaft 13 has fixed thereto a rotary encoding plate 15 which is formed with a predetermined light-transmitting pattern (not shown) by means of a mask evaporation or the like. A mount 16 having an endface opposite to the rotary encoding plate 15 and a concavity 17 provided in the endface is positioned at a predetermined location in the endface of the flange 11 and fixed thereto by means of a screw, an adhesive or the like. In the bottom portion of the concavity 17 of the mount 16, a light-receiving system 18 having a photoelectric conversion element, i.e., a light-detecting element (not shown) such as a photodiode, a photoconductor or the like is positioned at a predetermined location and fixed to the mount 16 by means of a screw, an adhesive or the like. A stationary encoding plate 19 is positioned at a predetermined location on the endface of the mount 16 and fixed thereto by means of an adhesive or the like. The stationary encoding plate 19 is formed with a predetermined light-transmitting pattern (not shown) by means of a mask evaporation or the like. The rotary encoder comprises an annular light-source support member 20 which has an inner cylindrical fitting face 21. The light-source support member 20 is provided with an arm portion 20a extending inward in the radial direction thereof. The arm portion 20a is formed with fitting holes 22. Two pairs of light-emitting diodes 23 which act as a light source are inserted into the fitting holes 22, respectively, and fixed to the arm portion by means of an adhesive or the like. The flange 11 has an outer cylindrical fitting face 24 which is coaxial with the bearing bore 12 and fittable to the fitting face 21 of the light-source support member 20. Therefore, the light-source support member 20 is positioned in the radial direction with respect to the shaft 13 upon the fitting engagement of the fitting faces 21 and 24, but is movable in the circumferential direction along the fitting face 24 of the flange 11. The rotary encoder comprises a fixing means 25 for fixing the light-source support member 20 to the flange 11. In this embodiment, the fixing means 25 includes tightening bolts 26. The light-source support member 20 is formed with elongate holes 27 extending in the circumferential direction of the shaft 13. The tightening bolt 26 passes through the corresponding elongate hole 27 of the light-source support member 20 and is screwed into a threaded hole (not shown) formed in the flange 11. The bolt 26 supports a printed circuit board 28 on which electric circuits connected to the light-emitting diodes 23 and the light-receiving system 18 are provided. A spacer 29 is inserted between the printed circuit board 28 and the light-source support member 20. As the fixing means, an adhesive also may be used. In the above-described optical rotary encoder, when performing the adjustment of the position of the light-emitting diode 23 in relation to the light-receiving system 18, the light-transmitting patterns of the rotary encoding plate 15 and the stationary encoding plate 19 are matched in position, and then the shaft 13 is fixed to the flange 11. Next, while monitoring the photoelectric output waveform from the light-receiving system 18, the light-source support member 20 is moved in the circumferential direction of the shaft 13. The light-source support member 29 is then fixed to the flange 11 by means of the bolts 26 at the position of the optimal photoelectric output. The fitting face 24 of the flange 11 and the fitting face 21 of the light-source supporting member 20 are formed by a cylindrical forming process, so the forming precision can be easily ensured. Further, the positional adjustment of the light-emitting diodes 23 can be performed only by moving the light-source support member 20 in the circumferential direction of the shaft 13, so adjustment can be easily performed by set amounts. Therefore, the assembly work for the rotary encoder and the positional adjustment work for the light-emitting diodes 23 can be easily automated. Figures 3 and 4 show a second embodiment of the present invention. In these Figures, constitutional elements the same as in the above-mentioned embodiment bear the same reference numerals. Referring to these Figures, the optical rotary encoder comprises an inner light-source support member 120 and outer light-source support member 220. The light-source support members 120 and 220 have arm portions 120a and 220a, respectively, extending inward in the radial direction. The arm portions 120a and 220a are provided with fitting holes 122 and 222. A pair of light-emitting elements 123 and 223 as a light source are fitted into and fixed to the fitting holes 122 and 222. Although not shown, the light-receiving system is provided with a pair of photoelectric conversion elements opposed to the pair of light-emitting diodes 123 and 223, respectively. The light-source support members 120 and 220 have inner fitting faces 121 and 221. The flange 11 is provided with a fitting face 124 arranged coaxially with the bearing bore (not shown) and fittable to the fitting face 121 of the inner light-source support member 120. The inner light-source support member 120 is provided at the outside thereof with a fitting face 224 arranged coaxially with the inner fitting face 121 and fittable to the fitting face 221 of the outer light-source support member 220. In this embodiment, it is possible to perform the positional adjustment of the inner light-source support member 120 and outer light-source support member 220 independently, so the adjustment of the photoelectric output having two phases from the light-receiving system can be performed independently, and the adjustment of the phase relationship (for example, 90 degrees) of the two phases can be performed precisely. Therefore, according to this embodiment, it is possible to easily ensure the high phase-accuracy in the two phases particularly required in the high resolution optical rotary encoder. Figure 5 shows a third embodiment of the present invention. The optical rotary encoder according to this embodiment is the same as that of the above-mentioned second embodiment except that the fitting face 224 fittable to the inner fitting face 221 of the outer light-source support member 220 is provided on the flange 11. Since it is possible to use the bearing bore of the flange 11 as a reference surface in order to form the fitting face 224, it is possible to prevent any decrease of accuracy upon the accumulation of the dimensional tolerances, in comparison to the second embodiment. It is sufficient that the light-source support member be rotatable about the axis of the shaft, so it can be formed as a part of the ring to obtain a lightweight. Further, the light source may include a light-emitting element such as an optical fiber lens. CAPABILITY OF EXPLOITATION IN INDUSTRY The present invention can be effectively applied particularly to high resolution optical rotary encoders.

Claims: An optical rotary encoder for converting a rotational angle of a shaft (13) rotatably supported in a base member (11) into a digital electrical output signal and comprising: a light receiving system (18) fixed in a certain position to the base member (11); a stationary encoding plate (19) fixed to the base member so as to face a light-receiving surface of the light-receiving system (18); a rotary encoding plate (15) fixed to the shaft (13) so as to face the stationary encoding plate (19); a light-source support member (20,120) mounted on the base member via complementary cylindrical surfaces (21,24) which are coaxial with the shaft; light source means (23,123,223) attached to the light-source support member so as to face the rotary encoding plate; and fixing means (25) for holding the light-source support member to the base member; characterised in that the light-source support member (20,120) comprises at least part of a ring portion with an inner cylindrical surface (21,121) which closely surrounds an outer cylindrical surface (24) around the periphery of the base member whereby the light-source support member is rotatable relatively to the base member for adjusting alignment between the light-source means (23,123,223) and the light-receiving system (18); in that the fixing means (25) is arranged to lock the light-source support member against rotation relatively to the base member after the adjustment; and in that the light-source means (23,123,223) is supported on an arm portion (20a,120a,220a) of the light-source support member (20,120) extending radially inwardly from the ring portion. A rotary encoder according to claim 1, wherein the light-receiving system includes at least a pair of light-detecting elements stationarily supported on the base member (11) spaced in the circumferential direction of the shaft (13) and the light-source means includes at least a pair of light-emitting elements (23,123,223) facing respective ones of the light-detecting elements. A rotary encoder according to claim 2, wherein the pair of light-emitting elements (123,223) are also spaced from each other in the axial direction of the shaft. A rotary encoder according to claim 1, wherein there is also a second light-source support member (220) also provided with a ring portion and a radially inwardly extending arm portion (220a) supporting a second light-source means (223) facing the light receiving system; the ring of the second light-source support member having an inner cylindrical surface (221) which closely surrounds an outer cylindrical surface (224) of the first light-source support member (12), whereby the second light-source support member is independently rotatably adjustable relatively to the base member. A rotary encoder according to claim 4, wherein the first and second light-source means (123,223) are spaced from each other in circumferential and axial directions of the shaft. A rotary encoder according to any one of the preceding claims, wherein the light-source means (23,123,223) comprise at least one light-emitting diode element, and wherein the light-receiving system comprises at least one photo-diode.

Inventors: UCHIDA, HIROYUKI
Applicants: FANUC LTD.
Application year: 1985
Main classification: G01D5
IPC codes: G01D5