Abstract
Disclosed is a reflective encoder which is capable of measuring movement amount and detecting movement direction by using one emergent light beam, and achieving high reliability and miniaturization through a simple structure. In the reflective encoder, a light beam emitted by a laser oscillator is caused to be incident on a reflective diffraction grating disposed on a side of a scale, and diffracted light beams reflected by the reflective diffraction grating are received by light receiving elements. An interference optical system is provided between the light receiving elements and the reflective diffraction grating. An optical system is thus constructed to measure movement amount and detect movement direction by using only one emergent light beam.
Claims
1. A reflective encoder, comprising: light receiving elements, and a diffraction grating disposed opposite to the light receiving elements and moving horizontally with respect to surfaces of the light receiving elements with movement or rotation of a scale, wherein the light emitted from a laser oscillator and shining towards the diffraction grating can fall on the light receiving elements after being reflected by the diffraction grating, wherein an interference optical system are provided between the light receiving elements and the diffraction grating.
2. The reflective encoder according to claim 1, wherein the interference optical system comprises a component including a plurality of diffraction gratings.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a reflective encoder according to the embodiment of the present disclosure;
[0017] FIG. 2 shows light paths of the reflective encoder shown in FIG. 1;
[0018] FIG. 3 shows basic light paths of the reflective encoder shown in FIG. 1;
[0019] FIG. 4 shows light paths related to monitor signal of the reflective encoder shown in FIG. 1;
[0020] FIG. 5 shows light paths related to Z signal of the reflective encoder shown in FIG. 1; and
[0021] FIG. 6 is a side view of the reflective encoder for illustrating the rationale of the reflective encoder.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0022] Preferable embodiments of the present disclosure are described in the following with reference to FIGS. 1 to 6, in which same elements are indicated with a same reference sign.
[0023] FIG. 1 shows a perspective view of a reflective encoder according to the embodiment of the present disclosure. FIGS. 2 to 5 show all light paths of the reflective encoder and each light path of the reflective encoder respectively. FIG. 6 is a side view of the reflective encoder for illustrating the rationale of the reflective encoder. Circuits of all elements, and specific structures of the scale 9 acting as a rotor, supporting elements of the encoder, and an overall view of the reflective diffraction grating 4 disposed on the scale, are not shown in the Figures.
[0024] As shown in FIGS. 1 to 3, the reflective encoder provided in the present embodiment is configured as follows. A semi-conductor laser 1 and four light receiving elements 7a, 7b, 7c, 7d are provided on a sub-mount 8. A reflective diffraction grating 4 and a reflector 6a are provided on a disc-like scale 9 which acts as a rotor. The receiving elements and the scale 9 are provided therebetween with an interference optical system 10 which comprises an optical lens 2, transmissive diffraction gratings 3a, 3b, 3c, phase shifter 5, and reflectors 6b, 6c. The reflective diffraction grating 4 forms a circle, and only a small part of the circle is shown in the Figures.
[0025] As shown in FIGS. 2, 3, and 6, the present embodiment is configured as follows. Light emitted from the semi-conductor laser 1 is turned into a parallel light beam by the optical lens 2, so that a central once-diffracted light beam of three once-diffracted light beams passing through the transmissive diffraction grating 3a is incident on the reflective diffraction grating 4 and the reflector 6a on the scale 9. As shown in FIG. 2, part of the left once-diffracted light beam passing through the transmissive diffraction grating 3a is reflected by the reflector 6b to become incident on the light receiving element 7c, thereby serving as a monitor signal. The rest of the non-reflected once-diffracted light beam is reflected by the reflector 6c to become incident on the transmissive diffraction grating 3a. As shown in FIG. 6, the right once-diffracted light beam is reflected by the reflector 6d to, like the left light beam, become incident on the transmissive diffraction grating 3a.
[0026] FIGS. 2, 3, and 6 show light paths of light from the reflective diffraction grating 4 on the scale 9 towards the light receiving elements. In the present embodiment, of two twice-diffracted light beams reflected by the reflective diffraction grating 4, one twice-diffracted light beam, after a 90-degree shift in phase caused by the phase shifter 5, passes through the transmissive diffraction grating 3b, becomes again incident on the transmissive diffraction grating 3a, and then becomes incident on the light receiving element 7a after being interfered by the once-diffracted light beam reflected by the reflector 6c; the other twice-diffracted light beam passes through the transmissive diffraction grating 3c, becomes again incident on the transmissive diffraction grating 3a, and then becomes incident on the light receiving element 7b after being interfered by the once-diffracted light beam reflected by the reflector 6d. In this way, a rotation amount and a rotation direction of the scale 9 can be obtained based on output of the light receiving elements 7a and 7b.
[0027] With such a structure, the reflective encoder of the present embodiment can measure both the rotation amount and rotation direction by using one emergent light beam, thus achieving relatively high reliability through a simple structure and realizing miniaturization. That is, in the present embodiment, there is only one light beam incident on the scale 9. Consequently, the reflective diffraction grating 4 disposed on the scale 9 is formed only in one channel, and hence there will be no such an issue as aforementioned that an upper value of the resolution of the encoder will be determined by the relatively narrow pitch of the inner channel. The displacement amount of the scale 9 can thus be measured.
[0028] In addition, as shown in FIGS. 2, 4, and 5, in the present embodiment, the scale 9 and the interference optical system 10 are provided thereon with the reflector 6a and the reflector 6b, respectively, which reflect only a part of the incident light beam. Specifically, the once-diffracted light beam reflected by the reflector 6b is incident on the light receiving element 7c, and the once-diffracted light beam reflected by the reflector 6a is incident on the light receiving element 7d. In this case, signal from the reflector 6b is sent to the light receiving element 7c by the action of the semi-conductor laser 1, and signal from the reflector 6a is sent to the light receiving element 7d each time when the scale 9 completes a full-circle rotation, namely a cycle. Therefore, in the present embodiment, the action information can be confirmed by the monitor signal obtained from the light receiving element 7c and the number of rotation cycles detected by Z signal obtained from the light receiving element 7d can be counted, while measurement of the displacement can be guaranteed.
[0029] In the present embodiment, all optical elements are provided on substrates 11, and the interference optical system is constructed, with the support of the substrates 11, on a spacer 12 serving as a side wall. When it comes to the configuration of these optical elements, because, theoretically, self-aligning of the optical system can be done by merely adjusting the positions of the elements two-dimensionally, it is easy to construct the optical system. Moreover, in the present embodiment, the semi-conductor laser 1 as a light emitting element and the light receiving elements 7a, 7b, 7c, and 7d are all configured on a same layer. It is hence unnecessary to provide three-dimension wiring in the present embodiment, which enables it possible to form the optical system and the circuitry with simple structures.
[0030] Furthermore, as shown in FIG. 6, in the present embodiment, after the light emitted by the semi-conductor laser 1 serving as a light emitting element is turned into a parallel light beam by the optical lens 2, it shines vertically on the reflective diffraction grating 4. Therefore, in the encoder provided by the present disclosure, no limitation is imposed on the distance between the detecting elements (i.e., the light receiving elements 7a, 7b, 7c, 7d) and the diffraction grating (i.e., the reflective diffraction grating 4) on the moving portion, which allows more freedom to design the encoder on the condition that the diffracted light can be incident on the light receiving elements 7a, 7b, 7c, 7d and that the reflective encoder can function normally.
[0031] To conclude, the reflective encoder provided by the present disclosure is capable of measuring the movement amount and detecting the movement direction of the scale by using one light beam, and achieving high reliability and miniaturization through a simple structure.
LIST OF REFERENCE SIGNS
[0032] 1 semi-conductor laser [0033] 2 optical lens [0034] 3a. 3b, 3c transmissive diffraction grating [0035] 4 reflective diffraction grating [0036] 5 phase shifter [0037] 6a, 6b, 6c. 6d reflector [0038] 7a, 7b. 7c, 7d light receiving element [0039] 8 sub-mount [0040] 9 scale [0041] 10 interference optical system [0042] 11 substrate [0043] 12 spacer
