JP2012233755A - Optical encoder and absolute position detecting method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the assembling ease of a main scale without losing the intrinsic absolute position detecting function.SOLUTION: An optical encoder has a main scale 12 comprising consecutively arrayed light transmitters or light reflectors, a light receiver having a plurality of light receiving elements arranged to be shiftable relative to the main scale and associated with the pitch of the light transmitters or the light reflectors, and a light emitter that irradiates the light receiver with light via the main scale, wherein the main scale has optically discontinuous parts in the relative shifting direction, a plurality of the discontinuous parts S41 to S44 are symmetrically arranged on each of the two sides of the central position of the main scale, and the discontinuous parts on each side have discontinuity patterns of different types.

Description

  The present invention relates to an optical encoder and an absolute position detection method that are used for displacement measurement and enable absolute position detection.

  The optical encoder basically includes a main scale on which an optical grating is formed, a light source that irradiates light to the main scale, a light receiving element array that transmits or reflects the optical grating of the main scale, and receives the returning light. It is set as the structure provided with.

  This optical encoder is said to be an incremental type, and the amount of movement can be detected by increasing or decreasing the pulse with respect to the movement of the scale. A problem of the incremental type is that the absolute position is unknown, so that a sensor for detecting the absolute position is required separately.

  Therefore, as means for solving this problem, Patent Document 1 proposes a method of obtaining an absolute reference position by providing a missing portion in the main scale and reading a change in the amplitude of the output signal.

  FIG. 4 is a perspective view of a transmissive optical encoder. A light receiving unit 13 in which a main scale 12 and a photodiode array 14 are arranged is sequentially positioned below the light source 11. The main scale 12 is movable in the direction of the arrow with respect to the other optical members.

  FIG. 5 is a plan view of the main scale 12, and rectangular slits S1, S2,... Are arranged on the main scale 12 at equal intervals. However, only the slit S10 is a missing portion of the light-opaque region and is a singular point for detecting the origin.

  FIG. 6 is a perspective view of a reflective optical encoder, which includes a main scale 16 that can move in the direction of the arrow relative to the light receiving portion 13, and the main scale 16 has a reflective portion and a non-reflective portion at fine intervals. And provide a light and dark distribution on the light receiving unit 13. Further, the above-described singular point for origin detection is provided on the main scale 16 by a non-reflecting portion.

  FIG. 7 shows the arrangement of the photodiode array 14. The photodiodes P 1, P 2, P 3, and P 4 are arranged regularly and repeatedly as light receiving elements so as to have a relationship of 0 °, 90 °, 180 °, and 270 °. The light beam emitted from the light source 11 is applied to the main scale 12, and the light beam transmitted through the slit S of the main scale 12 is applied to the photodiode array 14 on the light receiving unit 13. The light intensity distribution at that time is shown by the waveform 15 in FIG.

  FIG. 8 shows the configuration of the processing circuit. A current commensurate with the amount of received light obtained from the photodiodes P1 to P4 of the photodiode array 14 is converted into a voltage in the current voltage circuit 21, and the converted signal is differentially input to the differential amplifier 22, and the encoder signals A and B are can get. The sum signal C of the photodiodes P1 to P4 is output from the summation circuit 23.

  FIG. 9 shows four output signals of the current / voltage circuit 21. A section 31 by a light beam transmitted through the slit S of the main scale 12 shows the relationship of output phase differences of the photodiodes P1, P2, P3, and P4. In section 32, the output when the missing slit S10 overlaps the photodiode array 14 is shown. Since the amount of light from the missing slit S10 that should originally exist as the slit S does not reach the photodiodes P1 to P4, the amplitude that should have the output of transmitted light for three slits is the slit 1 Decreases by one and becomes a regular 2/3 output.

  The upper stage of FIG. 10 is a waveform diagram in which the signals of the photodiodes P1 to P4 are all superimposed, the middle stage shows the outputs A and B of the differential amplifier 22 at that time, and the lower stage is the sum that is the output of the summing circuit 23. It shows how the signal C changes. As shown here, under the influence of the missing slit S10, the output signal of the sum signal C of the amount of received light is reduced to about 2/3 over three periods as a waveform period. The length of these three periods coincides with the length of the number of periods of the photodiode array 14. At the same time, the amplitudes of the output signals A and B of the differential amplifier 22 also decrease. As a result, the output change point of the sum signal C and the amplitude change points of the differential amplifier outputs A and B can be used as the origin signal.

  FIG. 11 is a plan view of the main scale 12 different from FIG. 5, and the missing slit S is not provided at one place, but two slits S <b> 13 are provided apart from the slit S <b> 10. FIG. 12 shows the state of the output signal at this time, and the width of the region where the amplitude and output decrease is longer than that of the missing slit S10 shown in FIG.

  Further, FIG. 13 is provided with two missing slits S10 and S11 continuous to the main scale 12. FIG. 14 shows the state of the output signal at this time, and the output of the sum signal C drops to about ３ over two periods.

  As can be seen from FIGS. 5 to 14, different output signals can be obtained depending on the arrangement pattern of the missing slits S.

JP 2005-291980 A

  The main scale used for the optical encoder basically needs to be longer than the moving distance of the object whose displacement is to be measured. The position of the origin (absolute position) detection slit at the full length of the main scale depends on the device using the optical encoder and the origin detection sequence, and is not necessarily the center position of the main scale. .

  Here, consider a case where the missing slit S51 is provided at the end of the main scale 12 as shown in FIG. When such a main scale 12 is present, it is necessary to incorporate the main scale 12 in a predetermined direction when incorporating the main scale 12 into the apparatus, which is a factor that hinders the workability of the assembly operator. Can be one. However, if the same missing slits S52 and S53 are provided at both ends of the main scale 12 in order to improve assemblability as shown in FIG. 16 and the directionality is lost, which of the two missing slits S52 and S53 is missing. I don't know if the slit was detected. For this reason, the original function of origin detection is lost.

(Object of invention)
An object of the present invention is to provide an optical encoder and an absolute position detection method for an optical encoder that can improve assemblability of a main scale without losing the original absolute position detection function.

  To achieve the above object, an optical encoder according to the present invention includes a main scale in which a light transmitting portion or a light reflecting portion is continuously arranged, a relative movement with respect to the main scale, and the light transmitting portion or the light reflecting portion. A light-receiving unit having a plurality of light-receiving elements arranged in relation to the pitch of the unit, and a light-emitting unit that irradiates light to the light-receiving unit through the main scale, the main scale being the relative An optical encoder having optically discontinuous portions in a moving direction, wherein the discontinuous portions are arranged on both sides symmetrically with respect to a central position of the main scale, and the discontinuous portions on one side are arranged. Are characterized by having different types of discontinuity patterns.

  According to the present invention, the assemblability of the main scale can be improved without losing the original absolute position detection function.

It is a top view which shows the main scale in the Example of this invention. It is a flowchart which shows an absolute position detection process. It is a flowchart which shows a missing pattern detection process. It is a perspective view which shows the conventional transmission type optical encoder. It is a top view of the main scale which provided one conventional missing slit. It is a perspective view which shows the conventional reflection type optical encoder. It is a figure which shows the arrangement | sequence and light intensity distribution of the conventional photodiode array. It is a figure which shows the structure of the conventional processing circuit. It is a figure which shows the output waveform of photodiode P1-P4. FIG. 6 is a diagram illustrating outputs of a differential amplifier and a summing circuit in the case of FIG. 5. It is a top view of the main scale which provided two missing slits at intervals. It is a figure which shows the output of the differential amplifier and summing circuit in the case of FIG. It is a top view of the main scale which provided two missing slits continuously. It is a figure which shows the output of the differential amplifier and summing circuit in the case of FIG. It is a top view of the main scale which provided only one missing slit on one side. It is a top view of the main scale which provided the missing slit on both sides one by one.

  The mode for carrying out the present invention is as described in the following examples. The examples do not limit the present invention, and not all combinations of features described in the examples are essential to the present invention.

  As shown in FIGS. 4 and 6, the optical encoder of the present invention has a main scale in which light transmission parts or light reflection parts are continuously arranged. In addition, the light receiving unit includes a plurality of light receiving elements that are movable relative to the main scale and are arranged in association with the pitch of the light transmitting unit or the light reflecting unit. Moreover, it has the light emission part which irradiates light to a light-receiving part via a main scale.

  FIG. 1 is a plan view of a main scale 12 in an embodiment of the present invention. The main scale 12 is provided with four missing slit patterns S41 to S44 that constitute optical discontinuous portions in the relative movement direction. The missing slit patterns S41 and S44, and S42 and S43 are arranged on both sides in a plurality of sides on each side at symmetrical positions with respect to the central position of the main scale 12, and are shown as an example of two on one side. Then, the slits are made in a missing state by the same pattern, and are formed as discontinuous portions. Here, the missing slit patterns S41 and S44 are patterns in which two slits are missing (hereinafter referred to as A pattern), and the missing slit patterns S42 and S43 are patterns in which one slit is missing (hereinafter referred to as B pattern). ). The A pattern and the B pattern constitute different types of discontinuity patterns. Thus, by arranging a plurality of missing slit patterns symmetrically at the center position, the directivity of the main scale 12 is eliminated, and the assemblability can be improved.

  The lower part of FIG. 1 shows the output of the sum signal C in the main scale 12. As described with reference to FIGS. 5, 10, 13, and 14, the voltage drop level and the drop time of the sum signal C differ depending on the corresponding main scale missing slit pattern. Therefore, it is possible to identify whether the missing slit pattern is the A pattern or the B pattern by the output of the sum signal C.

  Next, an absolute position detection method for the main scale 12 of FIG. 1 will be described with reference to the flowchart of FIG. Therefore, for the sake of explanation, the absolute positions of the missing slit patterns S41, S42, S43, and S44 in FIG. 1 are denoted by L2, L1, R1, and R2.

  First, initialization processing is performed in step S101. In step S101 of the initialization process, the light source 11 (light emitting unit) is turned on, the internal processing flag is cleared, and the like. Next, in step S102, the current position of the optical encoder at the time of activation is set as a temporary absolute position (temporary origin). Subsequently, the actuator is operated to detect the absolute position (S103), and the first missing slit pattern is searched (S106). Here, the driving direction is a predetermined direction, for example, the right direction in FIG.

  When the first (first) missing slit pattern is detected (S107), the type of the first missing slit pattern (A pattern or B pattern) is stored (S108), and the temporary absolute of the missing slit pattern is stored. The position is also stored (S109). At this time, if the drive range end is reached before the missing slit pattern is found (S104), the search is performed in the reverse direction or error processing is performed (S105).

  Here, the detection method of a missing slit pattern will be described with reference to the flowchart of FIG. 3 and the output signal waveform of FIG. First, the value x of the sum signal C of the outputs of the photodiode arrays P1 to P4 is acquired (S201). Then, it is determined whether or not the value x of the sum signal C is within a predetermined level (LV1 <x <LV2) (S202). If the value not within the predetermined output level falls within the predetermined level (S203), the missing start position Pos1 is stored as the temporary absolute position of the optical encoder when the predetermined level is entered. (S204), a missing measurement flag is set (S205). Setting this missing measurement flag indicates that the output of the sum signal C is currently within a predetermined level.

  When the signal once within the predetermined level goes out of the predetermined level (S206), the missing end position Pos2 is also stored as a temporary absolute position when the signal deviates from the predetermined level, and the missing measurement flag is cleared. (S207, S208). The missing width of the missing slit pattern can be obtained from the missing start position Pos1 and the missing end position Pos2 (S209), thereby determining whether or not it is a predetermined missing width (S210). It is assumed that the type of the missing slit pattern is determined from the output level and missing width of the sum signal C passing through the missing slit pattern, thereby detecting the missing slit pattern (S211). At the same time, the midpoint is calculated as the temporary absolute position of the missing slit pattern from the missing start position Pos1 and missing end position Pos2 (S212).

  The absolute position detection method will be described again using the flowchart of FIG. Following the search for the first missing slit pattern, the second (second) missing slit pattern is then searched. Subsequently, the actuator is operated (S110), and the second missing slit pattern is detected (S111). At this time, even if a search is performed within a predetermined distance from the first missing slit pattern, if the second missing slit pattern is not found (S113), the first missing slit pattern is classified according to the type of the first missing slit pattern. It is possible to determine which missing slit pattern of S41 to S44 the missing slit pattern is (S114). The predetermined distance here is substantially equal to the distance between the missing slit patterns S41 and S42.

  If the type of the first missing slit pattern is A pattern, the second missing slit pattern is not found even if it moves a predetermined distance. It can be seen that this is S42 (S116), whereby the provisional absolute position of the first missing slit pattern becomes equal to the absolute position L1. Similarly, when the type of the first missing slit pattern is pattern B, it is found that the first missing slit pattern is S44 (S118), and as a result, the absolute position R2 is obtained (S119).

  On the other hand, when the second missing slit pattern is found by the search, the absolute positions R1 and L2 can be obtained from the types of the first and second missing slit patterns.

  Thus, the missing slit patterns S41 to S44 can be identified by the driving direction and the detection order of the two types of missing slit patterns, and the absolute position can be obtained thereby.

12 Main scale S41, S42, S43, S44 Missing slit pattern L1, L2, R1, R2 Absolute position

Claims (3)

A main scale in which light transmission parts or light reflection parts are continuously arranged;
A light-receiving unit having a plurality of light-receiving elements that are relatively movable with respect to the main scale and are arranged in relation to the pitch of the light-transmitting part or the light-reflecting part;
A light emitting unit that irradiates light to the light receiving unit through the main scale,
In the optical encoder, the main scale has an optically discontinuous portion in the relative movement direction,
The discontinuous portions are arranged on both sides symmetrically with respect to the center position of the main scale, and are arranged on both sides.
The optical encoder characterized in that the plurality of discontinuous portions on one side have different types of discontinuous patterns.   The optical encoder according to claim 1, wherein the discontinuous portion is formed by removing at least one portion of the light transmission portion or the light reflection portion. An absolute position detection method for an optical encoder for detecting the absolute position of the optical encoder according to claim 1 or 2,
Driving the main scale in a predetermined direction;
Detecting a discontinuity pattern and a temporary absolute position of the first discontinuous portion, and storing the detected discontinuity pattern and the temporary absolute position of the discontinuous portion;
Detecting a discontinuity pattern of the second discontinuity;
Whether the discontinuity pattern of the second discontinuous portion is detected within a predetermined distance from the temporary absolute position of the first discontinuous portion, and the type of discontinuity pattern of the first discontinuous portion And a step of detecting an absolute position of the discontinuous portion.

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