JP2008014806A - Photoelectric encoder and displacement detecting device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance an averaging effect even in the case of a moving body comprising a code wheel. <P>SOLUTION: The moving body 14 has a plurality of slits 15A, 15B, etc., 15F having each approximate (1/2)P width arrayed in the circumferential direction at each prescribed array pitch P. A light receiving part 16 is arrayed in the linear direction, and among photodiodes 16A-16P constituting the light receiving part 16, each length of photodiodes 16E-16L positioned on a center part is 'L', and each length of photodiodes 16A-16D, 16M-16P positioned on the ends is 'L'' (<L). Hereby, the ratio of a domain irradiated with light used as a noise component is reduced, and the ratio of a domain not irradiated with light used as a signal component is also reduced, in the photodiodes 16A-16D, 16M-16P positioned on the ends, to thereby improve degradation of the S/N ratio of a generated electric signal and the averaging effect thereof. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric encoder and a displacement detection device that detects displacement information such as the position, moving speed, and moving direction of a moving body using the photoelectric encoder.

  As a device for detecting the position and movement of an object that moves along a specific path, transmission that moves a moving body having slits at regular intervals so as to block the optical path between the light emitting part and the light receiving part Type photoelectric encoder has been developed.

  Conventionally, the transmissive photoelectric encoder is used for precise measurement of linear displacement, angular displacement, and the like. This transmissive photoelectric encoder includes a light emitting unit, a moving body (linear scale or code wheel) in which a light shielding region and a light transmitting region are alternately formed, and a side opposite to the light emitting unit with respect to the moving body. And a light receiving portion arranged. The light receiving unit includes, for example, four light receiving elements (for example, photodiodes).

  Hereinafter, the operation of the transmissive photoelectric encoder will be briefly described. The light emitting unit irradiates light toward the light receiving unit. If it does so, the light from the said light emission part will pass the translucent area | region of the said mobile body, and while changing the intensity | strength of light to a sine wave form, four optical signals from which a phase mutually differs will be produced | generated. Each optical signal is received and photoelectrically converted by a light receiving element corresponding to each phase, and displacement information such as the position, moving speed, and moving direction of the moving body is detected using the generated electric signal. .

  Here, the four optical signals having different phases are an A + phase (0 degree) optical signal, a B + phase (90 degree) optical signal whose phase is shifted by 90 degrees from the A + phase, and an A + phase 180. That is, an A-phase (180 degrees) optical signal whose phase is shifted by a degree and a B-phase (270 degrees) optical signal whose phase is shifted by 270 degrees from the A + phase.

  The reason why the B + phase optical signal is used in addition to the A + phase optical signal is to determine the moving direction of the moving body based on whether the A + phase or the B + phase is detected first. In addition to the A + phase optical signal and the B + phase optical signal, the A− phase optical signal and the B− phase optical signal obtained by inverting these optical signals are used in (1) A + phase light. This is for removing the DC component contained in the signal and the B + phase optical signal, (2) ensuring the reliability of the optical signal, and (3) ensuring the high-speed tracking capability.

  If there are a number of light receiving elements corresponding to a plurality of optical signals having different phases, in principle, measurement is possible. Accordingly, when four optical signals having different phases are generated, for example, as disclosed in Japanese Patent Publication No. 3-76428 (Patent Document 1), there may be four light receiving elements.

  Further, as disclosed in, for example, Japanese Patent No. 3203643 (Patent Document 2), a light emitting unit, a moving body in which a reflective area and a non-reflective area are alternately formed, and the light emission to the moving body. A reflection type photoelectric encoder composed of a light receiving unit arranged on the same side as the unit has been developed. Since the signal forming principle of the reflective photoelectric encoder is the same as the signal forming principle of the transmissive photoelectric encoder, the description will be given below using the transmissive photoelectric encoder.

  By the way, due to the light intensity distribution of the light emitting unit and the dirt in the light transmitting region of the moving body, there may be a variation in the amount of light incident on the light receiving unit. In this case, if the light receiving unit is composed of four light receiving elements, each phase of the optical signal is detected by only one light receiving element, so that it is easily affected by the variation in the amount of incident light.

  Therefore, it is common to arrange a plurality of sets of the light receiving elements in an array along the moving direction of the moving body. By doing so, the place where the optical signal of each phase is detected is dispersed over a wide range, so that the influence of the variation in the incident light quantity can be reduced. Hereinafter, this is referred to as an “averaging effect”.

  FIG. 5 is a diagram showing a positional relationship between a signal forming photodiode and a slit (translucent region) of the moving body in a conventional photoelectric encoder when the moving body is a linear scale. The moving body 1 in this photoelectric encoder has a plurality of slits (translucent areas) 2A, 2B,..., 2F arranged in the width direction (movement direction) at a predetermined arrangement pitch P. Each of the slits 2A, 2B,..., 2F has a width of approximately (1/2) P.

  A light emitting unit (not shown) is disposed on one side of the moving body 1 (the front side of the sheet in FIG. 5). Further, the light receiving unit 3 is disposed on the other side of the moving body 1 (the side facing the paper surface in FIG. 5) so as to face the light emitting unit.

  As can be seen from FIG. 5, the light receiving unit 3 includes photodiodes 3 </ b> A to 3 </ b> P having a length L arranged in the same direction as the slit arrangement direction at an arrangement pitch (1/4) P. Each of the photodiodes 3A to 3P has a width of approximately (1/4) P.

  As described above, an averaging effect can be obtained by arranging four photodiodes as one set.

  Incidentally, increasing the averaging effect is important for improving measurement accuracy. However, the S / N ratio at the end of the light receiving element array is getting worse due to the recent downsizing of the moving body (code wheel) and the reduction of the optical axis radius.

  FIG. 6 is a diagram showing a positional relationship between a signal forming photodiode and a slit (translucent region) of the moving body in a conventional photoelectric encoder when the moving body is a code wheel. The moving body 4 in this photoelectric encoder has a circumferential direction centered on the rotation center of the moving body 4 at a predetermined arrangement pitch P in the locus 6 of the center of the optical axis of the light emitting unit (not shown). .., 5F arranged in the direction). The slits 5A, 5B,..., 5F have a width of approximately (1/2) P in the locus 6 at the center of the optical axis of the light emitting section.

  On the other hand, the photodiodes 7A to 7P constituting the light receiving unit 7 are arranged in a linear direction. The arrangement pitch of the photodiodes 7A to 7P is (1/4) P, the length is L, and the width is approximately (1/4) P.

  Thus, the arrangement direction of the photodiodes 7A to 7P is a linear direction, whereas the arrangement direction of the slits 5A to 5F is a circumferential direction. Therefore, the degree of mismatch between the phase of the light transmitted through the slits 5A to 5F and the phase of the photodiode increases as the photodiode is positioned at the end of the photodiode array.

  The phase mismatch degree will be described with reference to FIG. 7, taking the slit 5B in the state shown in FIG. 6 as an example. The light that has passed through the slit 5B must irradiate the photodiodes 7A and 7B, but actually irradiates the photodiodes 7A and 7B and the region 7C ′ of the photodiode 7C. In this case, the light received in the region 7C ′ becomes a noise component in an electric signal generated by photoelectric conversion by the photodiode 7C. Further, in the photodiodes 7A and 7B, since there are regions 7A ′ and 7B ′ that are not irradiated with light, the amount of received light is reduced, and the amplitude of an electric signal generated by photoelectric conversion by the photodiodes 7A and 7B is reduced. Will be reduced.

FIG. 8 shows a region 8 where light that becomes a noise component is irradiated in the photodiodes 7A to 7P shown in FIG. As can be seen from FIG. 8, the area of the shaded region 8 increases as the photodiode is located at the end of the photodiode array, and the S / N ratio of the electrical signal generated by photoelectric conversion deteriorates.
Japanese Patent Publication No. 3-76428 Japanese Patent No. 3203643

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photoelectric encoder capable of enhancing the averaging effect even with a moving body composed of a code wheel, and a displacement detection device using the photoelectric encoder.

In order to solve the above problems, the photoelectric encoder of the present invention is
A moving body in which light-transmitting regions and light-shielding regions are alternately formed in the moving direction;
A light emitting unit that emits light toward the moving body;
A light receiving unit that receives light emitted from the light emitting unit and transmitted through the light transmitting region of the moving body, and outputs a movement information signal representing movement information of the moving body;
The light receiving part is
A plurality of photodiodes arranged opposite to the light-transmitting region and the light-shielding region adjacent to the light-transmitting region and arranged in an array in the moving direction of the moving body;
The length in the direction orthogonal to the arrangement direction of the photodiodes arranged at the end of the array is the length in the direction orthogonal to the arrangement of the photodiodes arranged in the center of the array. It is characterized by being shorter than that.

  According to the above configuration, when the moving body is a code hole, at the end of the photodiode array where a large shift occurs between the arrangement direction of the light transmitting region and the light shielding region and the arrangement direction of the photodiode, The length of the photodiode is shortened by deleting the front end of the photodiode where the position of the light transmitting region and the light shielding region and the position of the photodiode are greatly shifted. Accordingly, in a certain target photodiode, the ratio of the region irradiated with light to be irradiated to other photodiodes is reduced, and the S / N ratio of the electric signal generated by the target photodiode is improved. In addition, the ratio of the region that is not irradiated with the light to be irradiated to the target photodiode is reduced, and the amount of light received by the target photodiode is improved. That is, the averaging effect can be enhanced as compared with the case of the conventional photoelectric encoder.

  Furthermore, when the moving body is a linear scale, the arrangement direction of the light-transmitting region and the light-shielding region and the arrangement direction of the photodiode are the same, so as in the case of a conventional photoelectric encoder, An averaging effect can be obtained.

  Here, the “substantially moving direction of the moving body” means “the moving direction of the moving body” when the moving body is a linear scale, and “when the moving body is a code hole”. The direction of the straight line in contact with the arc representing the moving direction of the moving body is meant.

The photoelectric encoder of the present invention is
A moving body in which reflection areas and non-reflection areas are alternately formed in the movement direction;
A light emitting unit that emits light toward the moving body;
A light receiving unit that receives light emitted from the light emitting unit and reflected by the reflection region of the moving body, and outputs a movement information signal representing movement information of the moving body;
The light receiving unit is
The moving body is arranged on the same side as the light emitting unit, facing the reflective area and the non-reflective area adjacent to the reflective area, and arranged in an array in the moving direction of the moving body. A plurality of photodiodes,
The length in the direction orthogonal to the arrangement direction of the photodiodes arranged at the end of the array is the length in the direction orthogonal to the arrangement of the photodiodes arranged in the center of the array. It is characterized by being shorter than that.

  According to the above configuration, when the moving body is a code hole, at the end of the photodiode array where a large shift occurs between the arrangement direction of the reflection region and the non-reflection region and the arrangement direction of the photodiode, The length of the photodiode is shortened by deleting the front end of the photodiode where the position of the reflective region and the non-reflective region and the position of the photodiode are greatly shifted. Accordingly, in a certain target photodiode, the ratio of the region irradiated with light to be irradiated to other photodiodes is reduced, and the S / N ratio of the electric signal generated by the target photodiode is improved. In addition, the ratio of the region that is not irradiated with the light to be irradiated to the target photodiode is reduced, and the amount of light received by the target photodiode is improved. That is, the averaging effect can be enhanced as compared with the case of the conventional photoelectric encoder.

  Furthermore, when the moving body is a linear scale, the arrangement direction of the reflective region and the non-reflective region and the arrangement direction of the photodiode are the same, so as in the case of a conventional photoelectric encoder, An averaging effect can be obtained.

  Here, the “substantially moving direction of the moving body” means “the moving direction of the moving body” when the moving body is a linear scale, and “when the moving body is a code hole”. The direction of the straight line in contact with the arc representing the moving direction of the moving body is meant.

In the photoelectric encoder of one embodiment,
The plurality of photodiodes having different lengths are arranged symmetrically with respect to the optical axis center of the light emitting unit.

  According to this embodiment, four optical signals having different phases, that is, an A + phase (0 degree) optical signal, a B + phase (90 degree) optical signal that is 90 degrees out of phase from the A + phase, and an A + phase It is possible to ensure the balance of the amplitude of the electric signal between the A-phase (180 degrees) optical signal whose phase is shifted by 180 degrees and the B-phase (270 degrees) whose phase is shifted by 270 degrees from the A + phase. it can.

Further, the displacement detection device of the present invention is
The photoelectric encoder is used to detect displacement information including a position, a moving speed, and a moving direction of the moving body.

  According to the above configuration, even when the moving body is a code hole, the S / N ratio of the electrical signal generated by the photodiode is improved, the amount of light received by the photodiode is improved, and the averaging effect is enhanced. The photoelectric encoder which can be used is used. Therefore, displacement information such as the position, moving speed, and moving direction of the moving body can be detected with higher accuracy, and displacement detection with excellent transmission characteristics and high reliability can be performed.

  As is clear from the above, the photoelectric encoder of the present invention is a transmission type photoelectric encoder and a reflection type photoelectric encoder, and when the moving body is a code hole, the light irradiation position at the end of the photodiode array. The length of the photodiode is shortened by deleting the front end of the photodiode where the position of the photodiode is greatly shifted. Therefore, compared with the conventional photoelectric encoder, the S / N ratio of the electric signal generated by the photodiode can be improved, the amount of light received by the photodiode can be improved, and the averaging effect can be enhanced.

  Further, since the displacement detection device of the present invention uses a photoelectric encoder that can improve the S / N ratio and enhance the averaging effect even when the moving body is a code hole, the position of the moving body Therefore, displacement information such as moving speed and moving direction can be detected more accurately. That is, a highly reliable displacement detection with excellent transfer characteristics can be performed.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

First Embodiment FIG. 1 is a diagram showing a positional relationship between a signal forming photodiode and a slit of a moving body (linear scale) in a photoelectric encoder when the moving body is a linear scale.

  In FIG. 1, as in the case of the conventional photoelectric encoder shown in FIG. 5, the moving body 11 has a plurality of substantially (1/2) P widths arranged in the width direction (movement direction) at a predetermined arrangement pitch P. Slits (translucent regions) 12A to 12F.

  On the other hand, the light receiving unit 13 is arranged to face the slits 12B to 12E, which are the light transmitting regions, and the light shielding regions adjacent to the slits 12B to 12E, and is arranged in the same direction as the arrangement direction of the slits. The photodiodes 13A to 13P are configured. Unlike the case of the conventional photoelectric encoder shown in FIG. 5, the length of the photodiodes 13 </ b> E to 13 </ b> L located at the center of the photodiodes 13 </ b> A to 13 </ b> P constituting the light receiving unit 13 is “L”. On the other hand, the lengths of the photodiodes 13A to 13D and 13M to 13P located at the end portions are set to “L ′ (<L)”. The arrangement pitch of the photodiodes 13A to 13P is (1/4) P, and the width is substantially (1/4) P.

  In the photoelectric encoder shown in FIG. 1, since the moving body 11 is a linear scale, an averaging effect can be obtained as in the case of the conventional photoelectric encoder shown in FIG.

Second Embodiment FIG. 2 is a diagram showing a positional relationship between a signal forming photodiode and a slit of a moving body (code wheel) in a photoelectric encoder when the moving body is a code wheel.

  In FIG. 2, as in the case of the conventional photoelectric encoder shown in FIG. 6, the moving body 14 is arranged in the circumferential direction (moving body) at a predetermined arrangement pitch P in the locus of the center of the optical axis of the light emitting section (not shown). 14 (moving direction of 14), a plurality of slits (translucent regions) 15A to 15F. Note that the width of each of the slits 15A to 15F is approximately (1/2) P in the locus of the center of the optical axis of the light emitting unit.

  On the other hand, the light receiving unit 16 is disposed to face the slits 15B to 15E, which are the light transmitting regions, and the light shielding regions adjacent to the light transmitting regions 15B to 15E, and is in contact with the locus of the optical axis center of the light emitting unit. The photodiodes 16A to 16P are arranged in a straight line direction. As in the case of the photoelectric encoder in the first embodiment shown in FIG. 1, among the photodiodes 16A to 16P constituting the light receiving unit 16, the lengths of the photodiodes 16E to 16L positioned at the center are set. On the other hand, the length of the photodiodes 16A to 16D and 16M to 16P located at the end portions is “L ′ (<L)”. The arrangement pitch of the photodiodes 16A to 16P is (1/4) P, and the width is substantially (1/4) P.

  Hereinafter, the degree of mismatch between the phase of the light transmitted through the slits 15A, 15B,..., 15F and the phase of each of the photodiodes 16A to 16P will be described by taking the slit 15B in the state shown in FIG. explain. The light that has passed through the slit 15B must irradiate the photodiodes 16A and 16B, but actually irradiates the photodiodes 16A and 16B and the region 16C ′ of the photodiode 16C. However, the value of “(area of region 16C ′) ÷ (area of photodiode 16C)” is “(area of region 7C ′) ÷ (area of photodiode 7C) in the case of the conventional photoelectric encoder shown in FIG. It is clear that it is smaller than the value of “)”. Therefore, it can be seen that the mixing ratio of the noise component in the electric signal generated by photoelectric conversion by the photodiode 16C is improved as compared with the conventional photoelectric encoder shown in FIG.

  In the photodiodes 16A and 16B, there are regions 16A ′ and 16B ′ that are not irradiated with light. However, the value of “(area of area 16A ′) ÷ (area of photodiode 16A)” is “(area of area 7A ′) / (area of photodiode 7A” in the case of the conventional photoelectric encoder shown in FIG. It is clear that it is smaller than the value of “)”. The same applies to the photodiode 16B. Therefore, it can be seen that the reduction rate of the amount of received light in the photodiodes 16A and 16B is improved as compared with the conventional photoelectric encoder shown in FIG.

  FIG. 4 shows a region 17 irradiated with light that becomes a noise component in the photodiodes 16A to 16P shown in FIG. As apparent from the hatched region 8 in the case of the conventional photoelectric encoder shown in FIG. 8, the area of the hatched region 17 is significantly reduced as the photodiode is located at the end of the photodiode array. It is possible to improve the deterioration of the S / N ratio of the electrical signal generated by the conversion and the averaging effect.

  Of the four optical signals having different phases, the A + phase (0 degree) optical signals are photodiodes 16A, 16E, 16I, and 16M, and the B + phase (90 degrees) optical signals are photodiodes 16B, 16F, and 16J. 16N, A-phase (180 degrees) optical signals are received by photodiodes 16C, 16G, 16K, and 16O, and B-phase (270 degrees) optical signals are received by photodiodes 16D, 16H, 16L, and 16P, respectively. Is done. Therefore, the lengths “L” and “L ′” of the photodiodes 16A to 16P are set in advance so that the total light receiving areas of the four photodiodes that receive the optical signals of the respective phases are the same. Thus, the balance of the amplitude of the electric signal between the phases can be ensured. This is the same when the moving body 11 in the first embodiment is a linear scale.

  The lengths “L” and “L ′” in the photodiodes 13A to 13P and 16A to 16P in the above case may be set so as to be symmetric with respect to the optical axis center of the light emitting unit. .

  As described above, according to the second embodiment, the S / N ratio and the averaging effect of the electrical signal generated by the light receiving unit 16 can be reduced even with the moving body 14 including the code wheel. This can be improved over the encoder. Therefore, if the displacement detecting device is configured using the photoelectric encoder in the second embodiment, displacement information such as the position, moving speed, and moving direction of the moving body can be detected with higher accuracy, and the transfer characteristics can be improved. Excellent and highly reliable displacement detection can be performed.

  In each of the above embodiments, the lengths of the photodiodes 13A to 13P and 16A to 16P constituting the light receiving portions 13 and 16 are set in two stages of “L” and “L ′”. However, the present invention is not limited to two stages, and may be set to three or more stages.

  In each of the above embodiments, four sets of four photodiodes arranged at an arrangement pitch (1/4) P are used. However, the number of sets is not limited to four, and the arrangement pitch is not limited to four. Is not limited to (1/4) P. In short, in the photodiodes in which a plurality of sets are arranged, the above-described effects can be achieved by appropriately shortening the photodiode length located at the end of the light receiving portions 13 and 16 from the photodiode length located at the central portion. Can do it.

  In each of the above embodiments, for the sake of clarity, a transmissive photoelectric encoder in which the moving bodies 11 and 14 exist between the light emitting unit and the light receiving units 13 and 16 is described. . However, the present invention is not limited to the transmissive photoelectric encoder described above, and may be applied to a reflective photoelectric encoder in which the light emitting unit and the light receiving unit are arranged on the same side with respect to the moving body. Needless to say.

It is a figure which shows the positional relationship of the photodiode and slit of a moving body (linear scale) in the photoelectric encoder of this invention. It is a figure which shows the positional relationship of the photodiode and slit of a moving body (code wheel) in the photoelectric encoder different from FIG. It is explanatory drawing of the mismatch degree of the phase of the light which permeate | transmitted the slit in FIG. 2, and the phase of a photodiode. It is a figure which shows the area | region where the light used as a noise component is irradiated in the photodiode shown in FIG. It is a figure which shows the positional relationship of the photodiode in the conventional photoelectric encoder whose moving body is a linear scale, and the slit of the said moving body. It is a figure which shows the positional relationship of the photodiode in the conventional photoelectric encoder whose moving body is a code wheel, and the slit of the said moving body. It is explanatory drawing of the mismatch degree of the phase of the light which permeate | transmitted the slit in FIG. 6, and the phase of a photodiode. It is a figure which shows the area | region where the light used as a noise component is irradiated in the photodiode shown in FIG.

Explanation of symbols

11, 14 ... moving body,
12A-12F, 15A-15F ... slit,
13, 16 ... light receiving part,
13A to 13P, 16A to 16P ... photodiode,
17: Area irradiated with light that becomes a noise component.

Claims (4)

A moving body in which light-transmitting regions and light-shielding regions are alternately formed in the moving direction;
A light emitting unit that emits light toward the moving body;
A light receiving unit that receives light emitted from the light emitting unit and transmitted through the light transmitting region of the moving body, and outputs a movement information signal representing movement information of the moving body;
The light receiving part is
A plurality of photodiodes arranged opposite to the light-transmitting region and the light-shielding region adjacent to the light-transmitting region and arranged in an array in the moving direction of the moving body;
The length in the direction orthogonal to the arrangement direction of the photodiodes arranged at the end of the array is the length in the direction orthogonal to the arrangement of the photodiodes arranged in the center of the array. A photoelectric encoder characterized by being shorter than that. A moving body in which reflection areas and non-reflection areas are alternately formed in the movement direction;
A light emitting unit that emits light toward the moving body;
A light receiving unit that receives light emitted from the light emitting unit and reflected by the reflection region of the moving body, and outputs a movement information signal representing movement information of the moving body;
The light receiving part is
The moving body is arranged on the same side as the light emitting unit, facing the reflective area and the non-reflective area adjacent to the reflective area, and arranged in an array in the moving direction of the moving body. A plurality of photodiodes,
The length in the direction orthogonal to the arrangement direction of the photodiodes arranged at the end of the array is the length in the direction orthogonal to the arrangement of the photodiodes arranged in the center of the array. A photoelectric encoder characterized by being shorter than that. The photoelectric encoder according to claim 1 or 2,
The plurality of photodiodes having different lengths are arranged symmetrically with respect to the optical axis center of the light emitting unit. A displacement detection apparatus that detects displacement information including a position, a moving speed, and a moving direction of the moving body using the photoelectric encoder according to any one of claims 1 to 3.

Images