JP2009210389A - Absolute optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absolute optical encoder capable of shortening an action time on detecting a starting point, capable of improving the operational efficiency of an apparatus to which the encoder is attached, having a short action time for returning to the starting point, capable of high speed action and having a high resolution. <P>SOLUTION: The absolute optical encoder is configured by including a scale 1 having a measuring track in which a coding pattern for measurement is formed with a same pitch and a starting point detecting track 3, and a photo pickup part for obtaining a signal corresponding to the code from the scale 1, and prepares absolute data from 2 different signals having different phase obtained from this photo pickup part, wherein the starting point detecting track 3 in the scale 1 has a plurality of starting point marks 4a, 4b, 4c and starting point position confirmation marks 5a, 5b, 5c formed between the starting point marks 4a, 4b, 4c. The distances between the starting point marks 4a, 4b, 4c and the starting point position confirmation mark 5a, 5b, 5c are different in any of the position. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical absolute encoder that measures the relative movement amount or displacement amount between two objects or a rotating body, and more particularly, to an optical absolute encoder having an origin position detection function.

  In a machine tool or the like, it is extremely important to accurately measure the relative movement amount of a tool with respect to a workpiece, and various measuring apparatuses for this purpose have been commercialized. One of them is an absolute type optical encoder, and an optical scale using moire fringes obtained by superimposing two optical gratings is known.

  FIG. 14 is a perspective view showing an outline of such an optical scale. In this figure, one surface of an elongated main scale 101 is engraved with a grid of the same pitch formed by vapor-deposited chromium or the like, and an index scale is formed on one surface of a U-shaped holder 104 that holds the main scale 101. 103 is fixed. The surface of the index scale 103 facing the main scale is engraved with a grid having the same pitch formed by vapor deposited chrome similarly to the main scale 101, and on the back side of the index scale 103 is a photoelectric conversion element. 113 is provided.

  Further, a light source 105 is fixed to the surface of the U-shaped holder 104 on the opposite side of the main scale 101 as shown in FIG. 15, and the main scale 101 and the index scale 103 are movable relative to each other. Yes. As described above, the grid of the index scale 103 is opposed to the grid of the main scale 101 with a small interval as shown in FIG.

  A cross-sectional view of the principle structure of this optical scale is shown in FIG. The light emitted from the light source 105 passes through the glass main scale 101, passes through the moire fringes formed by the grid engraved on the main scale and the index scale 103, and further passes through the glass index scale 103. After being transmitted, the light is received by the photoelectric conversion element 113. The photoelectric conversion element 113 outputs an A-phase signal and a B-phase signal having a phase difference of 90 ° from each other, and the moving direction and the moving distance can be measured from these two signals. The photoelectric conversion element 113 is provided with three photoelectric conversion elements, two of which output the A phase signal and the B phase signal, and the remaining one outputs a reference level signal. Output. The reason is that the light received by the photoelectric conversion element changes in a sine wave shape, but the signal at the reference level (zero level) is not clear. Therefore, the average signal level of the received light is output from the third photoelectric conversion element as a reference level signal.

  Next, FIG. 16 shows a block diagram of a processing circuit for signals output from the optical scale shown in FIG. In this figure, the light emitted from the light emitting diode 120 as the light source passes through the main scale and index scale gratings as described above, and is received by the photodiode 121 as the photoelectric conversion element 113. The A-phase signal and B-phase signal received by the photodiode 121 are amplified by the photoelectric conversion amplifier 122 and applied to the interpolation circuit 123. The interpolation circuit 123 generates an interpolation pulse that finely divides the lattice interval P, and the interpolation pulse is added or subtracted by the position data backup counter 124 according to the moving direction to obtain position data. It is supplied to a processing circuit (not shown).

  The output pulse of the interpolation circuit 123 is supplied to a control device using position data such as a numerical control (NC) device as data indicating position data by the number of pulses. This data is normally composed of an A-phase pulse signal and a B-phase pulse signal, and is data indicating a moving direction and a moving amount. When the interval P between the grids provided on the main scale and the index scale is 40 microns, the interpolation circuit 123 interpolates 40 pulses in one cycle of the A phase signal or the B phase signal. Then, the resolution can be a scale of 1 micron.

  The optical scale constructed in this way is mounted on an NC machine tool and measures the relative movement between the workpiece and the tool, but is generally programmed as the movement from the origin when performing numerical control. Therefore, this relative movement amount needs to be measured as a movement amount from the origin. Therefore, the origin position is usually provided in the main scale in advance, and when the index scale passes through this origin position, the origin is detected, and this origin detection signal is supplied to the NC device to reset the NC device, thereby setting the origin position. I was trying to set up the NC unit. Therefore, the setting of the origin has to be performed each time the NC apparatus is powered on.

  However, since the work of setting the origin every time the power is turned on is complicated, an optical absolute scale that always backs up the position of the scale has been proposed. The optical absolute scale is supplied with a backup power as shown in FIG. 16, and the scale position data is backed up by the backup power even when the NC apparatus is turned off. In addition, since the tool or the work table may be moved even if the NC power is turned off, the optical scale must always measure its position data. Therefore, as shown in FIG. 16, the backup power supply supplies power to the entire optical absolute scale.

  According to the backup system shown in FIG. 16, even if the relative position of the machine tool and the work table moves, the optical scale can always back up the position accurately, but the entire optical scale is backed up. Therefore, power consumption increases. However, since a battery is normally used as the backup power source, the backup time is limited.

  On the other hand, various methods for suppressing current consumption by blinking a light emitting diode as a light source have been proposed in the following literature and rotary encoders, but high speed is required for linear scales that require high speed and high resolution. Reading errors increased during movement, making it difficult to apply to high-speed and high-resolution ones.

  For this reason, for example, as disclosed in Japanese Patent No. 2688883 (Japanese Patent Laid-Open No. 7-174585), an interpolation circuit with large power consumption suppresses current consumption without backing up, and the grid interval is set by the interpolation circuit when power is turned on. A linear encoder that is obtained by calculating a position between P has been proposed.

  A block diagram of an optical absolute scale disclosed in this document is shown in FIG. In the optical absolute scale shown in FIG. 17, the light emitted from the light emitting diode 131 serving as the light source passes through the lattice of the pitch P engraved on the main scale and the index scale, and is then reflected by the photodiode 132 serving as the photoelectric conversion element. Received light. The A-phase signal and B-phase signal received by the photodiode 132 are amplified by the photoelectric conversion amplifier 133 and applied to the comparator 134 as binary data. The binary data is added or subtracted according to the moving direction every time the pitch P is moved by the position data backup counter 135, and is converted into position data in units of the pitch P.

  Further, the A-phase signal and the B-phase signal from the photoelectric conversion amplifier 133 are supplied to the absolute interpolation circuit 136, and the absolute interpolation circuit 136 counts the interpolation pulses that finely divide the lattice pitch P. Interpolated data obtained by dividing the pitch P is output to a processing device (not shown). Further, based on the signal applied from the absolute interpolation circuit 136, the phase division circuit 137 generates an output pulse signal indicating the interpolation data obtained by dividing the pitch P by the number of pulses, and a numerical control (NC) device. To supply. This output pulse signal is usually composed of an A-phase pulse and a B-phase pulse signal, and is data indicating the moving direction and moving amount.

  When the interval P between the grids provided on the main scale and the index scale is 40 microns, 40 pulses are counted in one cycle of the A phase signal or B phase signal input to the absolute interpolation circuit 136. By doing so, an optical scale with a resolution of 1 micron can be obtained. At the time of backup, power is supplied from the backup power source to the position data backup counter 135, the comparator 134, the photoelectric conversion amplifier 133, and the light emitting diode 131, but power is not supplied to the absolute interpolation circuit 136 and the phase division circuit 137. Thus, the power consumption is reduced.

The signals inputted to the comparator 134 and the position data backup counter 135 are not interpolated signals, that is, the position data backup counter 5 only counts every 40 microns when the grating pitch P is 40 microns. Therefore, power consumption is further reduced. That is, at the time of backup, only the position data with the grid interval P as a unit is detected and held in the position data backup counter 135, and when the power is turned on, the interpolation data obtained by dividing the grid pitch P is absolute interpolation circuit 136. The current position is calculated by processing the count data of the position data backup counter 135 and the interpolation data obtained by dividing the pitch P from the absolute interpolation circuit 136 by the processing device. The current position data is set to the NC unit. For this reason, it is possible to perform backup with low power consumption without reducing the resolution. The absolute interpolation circuit 136 includes a phase modulation circuit 141, a low-pass filter 142, a comparator 143, a carrier wave generation circuit 144, a frequency divider 145, a counter 147, a clock generator 148, and the like. The operation and operation are omitted here.
Japanese Patent No. 2689883 Japanese Patent No. 3239295 JP 62-132104 A

  However, even with such a backup type encoder, when the initial setting is performed, or when the power is turned off under a predetermined condition or the machine recovers from an abnormal state, the origin position is confirmed once and the internal position information is calibrated or reset. There is a need to. However, since the origin mark normally has only one point on the encoder scale, if the origin mark is stopped at a position far from the origin, the distance to move to the origin detection is long, and as a result, much time is required. In particular, in the case of a linear scale having a long linear distance, the time required for the origin detection operation is long, which has a considerable influence on the operating rate of the apparatus. Various attempts have been made to speed up the origin detection operation of the encoder. However, if the speed is increased too much, the origin mark may be overlooked and a detection error may occur. On the other hand, if the mark is enlarged to such an extent that there is no oversight (detection error), there is a problem that the positioning accuracy is remarkably lowered.

An object of the present invention is to provide an optical absolute encoder capable of shortening the operation time at the time of detecting the origin and improving the operation efficiency of the attached device.
In particular, the object is to provide an optical absolute encoder with a high resolution that can be operated at a high speed with a short home return operation time on a linear scale.

  In the present invention, a plurality of origin marks are provided on a scale on which a code pattern for measurement is formed, and a part of the origin marks is made to have a different pitch so that a specific length corresponds to a specific position. Thus, the absolute position can be specified.

That is, the above object is achieved by the following configuration of the present invention.
(1) a scale 1 having a measurement track in which measurement code patterns are formed at the same pitch and an origin detection track 3;
An optical pickup unit for obtaining a signal corresponding to a code from the scale 1;
Create absolute data with two signals with different phases obtained from this optical pickup unit,
The origin detection track 3 of the scale 1 includes a plurality of origin marks 4a, 4b, 4c formed at the same pitch, and origin position confirmation marks 5a, 5b, 5c formed between the origin marks 4a, 4b, 4c. 5c,
An optical absolute encoder in which the distance between the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c is different at any position.
(2) When the pitch between the origin marks 4a, 4b, 4c is 2d (d: any real number),
The distance between the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c is
d + rn (r: any real number, n: positive integer)
The optical absolute encoder according to (1), wherein any one of r1, r2,... Rn is assigned to each position on the scale.
(3) Calculate counting data corresponding to the distance from the reference position from the distance between the origin position confirmation marks 5a, 5b, 5c and the origin marks 4a, 4b, 4c;
Find the difference data with the counting data indicating the current position,
The optical absolute encoder according to (1) or (2), wherein the count data indicating the current position is corrected based on the difference data.
(4) Any of the above (1) to (3), which is a linear scale that photoelectrically converts the moire fringe pattern obtained from the scale 1 and counts the phase difference 2 signals of the A phase and B phase obtained therefrom. Optical absolute encoder.
(5) having a counter for sequentially counting the phase difference 2 signal of the A phase and the B phase;
The counter value is latched at the time of detecting the origin mark and the origin position confirmation mark, respectively, and a count value corresponding to the distance between the origin mark and the origin position confirmation mark is calculated from the latch data,
Further, a correction value for the reference position is calculated from the counted value,
The optical absolute encoder according to (4), wherein the value of the counter is corrected with the obtained correction value to obtain current position data.
(6) A current / voltage conversion amplifier for current / voltage converting the signal from the optical pickup unit, a comparator for outputting the voltage converted signal as a binary output, and a position for sequentially counting A and B phase signals from the comparator. A data backup counter, a backup drive circuit for emitting light emitting diodes during backup operation, and
An interpolation unit for creating interpolation data from the phase-difference two signals of the A phase and the B phase;
The interpolation data obtained from the interpolation unit is interpolated into a position data backup counter, and has at least a calculation unit that creates position data,
The optical absolute encoder according to the above (4) or (5), which backs up other than the interpolating unit and the calculating unit.
(7) The optical absolute encoder according to any one of (1) to (3), which is a rotary encoder.

  ADVANTAGE OF THE INVENTION According to this invention, the optical absolute encoder which can shorten the operation time at the time of origin detection, and can improve the operation efficiency of the apparatus to attach can be provided. In particular, it is possible to provide an optical absolute encoder that has a short origin return operation time on a linear scale, a high-speed operation, and a high resolution. Further, it can be suitably applied to a backup type encoder.

  The optical absolute encoder of the present invention has a scale having a code pattern for measurement, and an optical pickup unit that obtains a signal corresponding to the code from the scale, and two phases obtained from the optical pickup unit are different in phase. An absolute encoder that obtains absolute data by signals, and has a plurality of origin marks formed at regular intervals on the same track of the scale, and the origin position confirmation corresponding to each position between the origin marks Each origin position confirmation mark has an origin function in which the pitch from the origin mark is different.

  Thus, by having a plurality of origin marks, the movement distance required for origin detection is reduced and the origin detection time can be shortened. Also, since each origin position confirmation mark has a different pitch from the origin mark, each origin mark and origin position confirmation mark can be identified, and absolute values can be specified from these identified origin marks and origin position confirmation marks. The position can be derived.

  Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a part of the scale of the optical encoder of the present invention. In FIG. 1, a measurement code pattern 2 is formed at the same pitch P on the scale body 1 to form a measurement code track. The interval P of the code pattern 2 for measurement is arbitrarily determined depending on the resolution required for the encoder, the measurement accuracy, and the like. This is read by an optical system to be described later, and a phase difference 2 signal composed of A phase and B phase having different phases is obtained. Arise. In this example, the code pattern has a lattice shape in which light transmitting portions and non-light transmitting portions are formed at regular intervals. Such a code pattern is formed by evaporating a metal such as chromium. Note that the lattice pattern in the illustrated example is drawn more coarsely than the actual one for ease of understanding, but in practice, for example, over the entire measurement area of the scale with a pitch of about several tens of microns. Is formed.

  An origin detection track 3 is formed adjacent to the measurement code track. Origin marks 4a, 4b, 4c and origin position confirmation marks 5a, 5b, 5c are formed on the origin detection track 3. The origin marks 4a, 4b, 4c are formed over the entire measurement area of the scale at equal intervals 2d. The interval between the origin marks 4a, 4b, and 4c may be set within a distance that can be moved within the time allowed for the origin detection operation. However, if the distance is too close, pattern formation becomes complicated, or an origin position described later. There arises a problem that the pitch of the confirmation mark is restricted. Actually, it is preferable to have a size of about several tens of millimeters. The origin detection track 3 can also be formed in the same manner as the measurement code track, and both can be formed simultaneously.

  Between the two origin marks 4a, 4b, 4c, origin position confirmation marks 5a, 5b, 5c are formed. The origin position confirmation marks 5a, 5b, and 5c have different distances d + r from one of the origin marks 4a, 4b, and 4c, and are not identical. That is, r of d + r is a positive real number, and is sufficiently small with respect to d to the extent that the existence of different r is acceptable. Moreover, it is necessary to have a size larger than the minimum resolution of the encoder so that the length can be detected. Further, in order to facilitate the later-described calculation and pattern formation, it is desirable that all r are integer multiples of the minimum number. For example, in the illustrated example, if r1 is the minimum value, r2 is preferably an integer multiple such as twice r1, and r1, r2,.

  As described above, since the distance between the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c is different at any position, the origin position confirmation having a specific distance from the origin marks 4a, 4b, 4c. Only one mark 5a, 5b, 5c exists, and the absolute positions of the origin position confirmation marks 5a, 5b, 5c and the origin marks 4a, 4b, 4c adjacent thereto can be detected. That is, the absolute position can be easily detected by measuring the distance between the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c by the measurement operation using the measurement code track. As a result, the same function as the origin detection can be provided. In addition, since the origin detection track and the origin marks 4a, 4b, and 4c have conventionally existed, the above functions can be provided with a slight modification to the conventional encoder, which is advantageous in terms of cost and economical. is there.

  Next, a procedure for performing an operation similar to the origin detection operation using the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c will be described. FIG. 2 is a waveform diagram showing the state of the origin signal obtained from the origin marks 4a, 4b, 4c and origin position confirmation marks 5a, 5b, 5c of the scale of FIG. FIG. 3 is a timing chart showing the operation when detecting the origin. For convenience, the first origin mark 4a, 4b, 4c at the left end of FIG. 1 in FIG. 1 is set as the calculation zero position, and the distance d + r1 to the adjacent origin position confirmation marks 5a, 5b, 5c is 10.02 mm, and the next. The distance d + r2 between the origin marks 4a, 4b and 4c and the adjacent origin position confirmation marks 5a, 5b and 5c is 10.04 mm. That is, d = 10, r1 = 0.02, r2 = 0.04, and the distance 2d between the two origin marks 4a, 4b, 4c is 20. The resolution of the encoder is 10 μm, and when the distance 2d between the origin marks 4a, 4b, 4c is moved, 2000 count signals are output.

  In FIG. 3, the A-phase and B-phase signals obtained from the measurement code track are two phase difference signals having a phase difference of 90 °, and the measurement operation of the encoder is performed by counting these signals. Here, COUNT A is a counter that counts the measurement code pattern 2 in the measurement code track, confirms the level of the A phase at the edge of the B phase, and counts up / counts down by its H / L. Is done. In addition, when the B phase is at the L level, the initial value is set to be an even number. COUNT C stores a numerical value output as the corrected final count data. The origin signal is output in synchronization with the A phase and B phase signals, and is output when both the A phase and the B phase are at the H level. In the following, for the sake of convenience, the operation of passing through the first origin marks 4a, 4b, 4c serving as reference positions and detecting the next origin marks 4a, 4b, 4c and origin position confirmation marks 5a, 5b, 5c will be described.

When the origin marks 4a, 4b and 4c are detected and the origin signal is output (3), the data of COUNT A is latched COUNTA L1 at the rising edge. At this time, since the count value of COUNT A is 100 (4), 100 is latched in the latch COUNTA L1 (5). At this time, the level of the B phase is confirmed from the value of the latch COUNTA L1, and the value of OFFSET A1 is determined. Here, the value of OFFSET A1 takes −1 or 0 as follows.
Phase B level: L (COUNT A is an even number) OFFSET A1: 0
Phase B level: H (COUNT A is an odd number) OFFSET A1: -1
In this example, since COUNT A is an even number, it becomes OFFSET A1: 0 (6).

  Next, when the distance d + r1 = 10.04 mm is moved to the adjacent origin position confirmation marks 5a, 5b, 5c, the next origin signal is output (3). Again, the COUNT A data is latched COUNTA L2 at the rising edge of the origin signal, as described above. At this time, the count value of COUNT A moves 10.04 mm to 1104 (4), so 1104 is latched in the second latch COUNTA L2 (7). Further, when the level of the B phase is confirmed from the value of the second latch COUNTA L2, and the value of OFFSET A2 is determined. Again, because COUNT A is an even number, it becomes OFFSET A1: 0 (8). Thereby, the distance between the origin marks 4a, 4b, 4c and the origin position confirmation marks 5a, 5b, 5c is measured, and the B phase level at that time is also confirmed. There is no problem even if the operation so far is performed once, but it may be performed a plurality of times in order to eliminate the influence of reading error and the like.

Next, offset data for counting data correction is calculated by the following calculation.
OFFSET B = (Distance-ref) / 2 × 2000-COUNTA L1
here
Distance = Distance to origin position confirmation marks 5a, 5b, 5c d + r2
Distance = (COUNTA L2 + OFFSET A2)
-(COUNTA L1 + OFFSET A1) = 1004 (9)
ref = the distance d + r1 to the origin position confirmation marks 5a, 5b, 5c at the reference position
2000 = a count value corresponding to the distance 2d between the two origin marks 4a, 4b, 4c OFFSET B = (1004-1002) / 2 × 2000-100
OFFSET B = 1900
(10).

Since the offset data for correction is obtained by the above operation, this is added to the position data CUNT C to correct the position data.
CUNTC = CUNT A + OFFSET B
CUNT C = 1105 + 1900 = 3005
Thus, a numerical value indicating the distance from the reference position is set in the position data CUNT C. In the subsequent counting operation, numerical data counted from the zero point, that is, the reference position can be obtained.

  Next, an optical absolute scale which is a preferred embodiment of the present invention will be described in more detail with reference to the drawings. FIG. 4 is a side view of such an optical scale, and FIG. 5 is a plan view. The optical scale of this embodiment includes a main scale 101 provided with a lattice so that a light transmitting portion and a non-light transmitting portion are arranged at a predetermined pitch on one surface of a transparent glass scale 100, and one surface of a transparent glass scale 102. And an index scale 103 provided with a lattice so that the light transmitting portions and the non-light transmitting portions are arranged at a predetermined pitch. Further, as shown in FIG. 4, the index scale 103 is opposed to the main scale 101 with a minute interval, and the index scale 103 is inclined at a minute angle with respect to the lattice of the main scale 101 as shown in FIG. Is arranged.

  The grids provided on the main scale 101 and the index scale 103 are formed by engraving lines having the same pitch formed by vacuum-depositing and etching chromium on the glass scales 100 and 102. When arranged in this manner, moire fringes shown in FIG. 6 are generated. The interval between the moire fringes is W, and a dark portion or a bright portion is generated for each interval W. The dark part or the bright part moves from the top to the bottom or from the bottom to the top according to the direction in which the index scale 103 moves relatively to the left and right relative to the main scale 101. In this case, if the grid pitch of the main scale 101 and the index scale 103 is P, and the mutual inclination angle is θ [rad], the moire fringe spacing W is expressed as W = P / θ, and the moire fringe spacing W Is an interval obtained by optically expanding the lattice interval P to 1 / θ times. For this reason, when the grating moves P, the moiré fringes move W, and the amount of movement of the grating can be accurately measured by reading the enlarged change in W.

  Therefore, the photoelectric conversion element 110 that optically detects the change in moire fringes is provided on the index scale, and the light source is provided on the opposite side of the main scale, while moving the index scale 103 relative to the main scale 101. When the change of the current flowing through the photoelectric conversion element 110 is read, it is as shown in FIG. That is, when the index scale 103 is in the state of A with respect to the main scale 101, the amount of light irradiated to the photoelectric conversion element 110 is the largest, and the current flowing through the photoelectric conversion element 110 becomes the maximum value I1. Next, when the light is relatively moved to the B state, the amount of light applied to the photoelectric conversion element 110 is slightly reduced, and the current is I2. Further, when the light is moved to the C state, the photoelectric conversion element 110 has The least amount of light is irradiated and the current is the smallest I3. When the light is further moved to the D state, the amount of light applied to the photoelectric conversion element 110 is slightly increased, and the current becomes I2, and when the state moves to the E state, the position where the light amount is the highest again becomes the current. Becomes the maximum value I1. As described above, the current flowing through the photoelectric conversion element 110 changes in a sine wave shape, and the main scale 101 and the index scale 103 are relatively moved by the lattice interval P when the change passes for one cycle.

  In FIG. 7, only one photoelectric conversion element 110 is provided. However, as shown in FIG. 8, when two photoelectric conversion elements 111 and 112 are provided with a 90 ° shift from one cycle (interval W). The current flowing in the B-phase photoelectric conversion element 112 with respect to the current flowing in the A-phase photoelectric conversion element 111 is a current shifted by 90 ° as shown in FIG. That is, if the current flowing through the A-phase photoelectric conversion element 111 is a sine wave, the current flowing through the B-phase photoelectric conversion element 112 is a cosine wave. In this case, depending on the relative movement direction of the main scale 101 and the index scale 103, the phase of the current flowing in the B phase photoelectric conversion element 112 with respect to the current flowing in the A phase photoelectric conversion element 111 is advanced by 90 ° or 90 °. Since the phase is delayed, if two photoelectric conversion elements arranged 90 ° apart are provided, the relative movement direction can be detected by detecting the phase between them.

  Next, a signal processing method of such an optical scale will be described. FIG. 10 is a block diagram showing a signal processing circuit of an optical scale. In FIG. 10, a light emitting element as a light source, for example, a light emitting diode 11 is given a light emitting current by an LED drive circuit during operation. Light from the light-emitting element passes through a grid with a pitch P engraved on the main scale and the index scale, and is received by the photodiode 12 which is a photoelectric conversion element. The A-phase signal and B-phase signal received by the photodiode 12 are voltage-converted by the current / voltage conversion amplifier 13, further amplified by the amplifier 14, and sent to the comparator 15 as binary data. This binary data is added or subtracted according to the moving direction every time the pitch P moves by the position data backup counter 16, and is converted into position data in units of the pitch P.

  An origin signal is also output from the current-voltage conversion amplifier 13 when the origin is detected. Since the origin signal is a single output unlike the A phase and B phase signals having the reference signal or the reverse phase component, the origin dedicated amplifier 41 adjusts and amplifies the DC component and adjusts the level to the comparator 42. It is sent to binary data. Then, like the above, it is supplied to the position data backup counter 16 and used for the latch processing as described above.

  The A phase signal and the B phase signal from the amplifier 13 are supplied to the absolute interpolation unit 30. The absolute interpolation unit 30 counts the interpolation pulses that finely divide the lattice pitch P, and outputs the interpolation data obtained by dividing the pitch P to the interpolation division unit 22 of the arithmetic unit 20.

  When the interval P between the grids provided on the main scale and the index scale is 20 microns, 20 pulses are counted in one cycle of the A-phase signal or B-phase signal input to the absolute interpolation unit 30. By doing so, an optical scale with a resolution of 1 micron can be obtained.

  The absolute interpolation unit 30 includes a phase modulation circuit 31 that gives the carrier a phase shift according to the level of the input A-phase signal and B-phase signal, and a phase-shifted step-like shape of the phase modulation circuit 31. It has a low-pass filter (LPF) 32 that smoothes the output signal and a comparator 33 that binarizes the output signal of the low-pass filter 32, and has a function of dividing the scale pitch P in order to improve the resolution. Is.

  The phase modulator 31 can have a configuration described in, for example, Japanese Patent Laid-Open No. 62-132104. As shown in FIG. 11, the detailed configuration is as follows. The input A-phase signal is supplied to the resistor network RT via the operational amplifier OP1 operating as a buffer, and is inverted by the operational amplifier OP2 and supplied to the resistor network RT. . The B-phase signal is supplied to the resistance network RT through the operational amplifier OP3 that operates as a buffer, and is inverted by the operational amplifier OP4 and supplied to the resistance network RT.

  That is, the A phase signal, the inverted A phase signal, the B phase signal, and the inverted B phase signal are mixed and added by the resistor network RT, and a mixed signal divided into eight of the same voltage with the opposite phase is created. These are supplied to the input terminals (0) to (7), respectively. The selection signals A, B, and C shown in FIG. 12C are input to the input terminals C1, C2, and C3 of the multiplexer AM, and the input signals (0) to (0) to ( 7) are sequentially selected, and the step-like output signal S shown in FIG. 12A is output from the output terminal to. The frequency of the signal S output from the multiplexer AM is the same as the cycle of the selection signal C as shown in FIG. 12. As a result, the phase of the selection signal C as a carrier wave is changed to an A phase signal (B phase signal). The output signal S balanced-modulated by the level of) is output from the multiplexer AM. That is, a carrier wave whose phase is shifted according to the level of the A phase signal (B phase signal) is output.

  The balance-modulated carrier wave is applied to the low-pass filter (LPF) 32 to form a smooth sine wave as shown in FIG. 12B, and the comparator 33 forms an edge at the zero level. Converted to a value signal. FIG. 13 shows the relationship between the phase of the binary signal output from the comparator 33 and the levels of the A-phase signal and B-phase signal input to the absolute interpolation unit 30. The signals changing in a sine wave form shown on the left side of this figure are the A phase signal and the B phase signal, and the pulse waveform shown on the right side is a binary signal of the carrier wave from the comparator 33 that has undergone the phase shift, The position of the broken line is the position of the zero phase of the carrier wave supplied to the phase modulation circuit 31.

  As shown in FIG. 6A, when the A-phase signal is at the maximum positive level and the B-phase signal is at the zero level, a binary signal shifted by 90 ° is obtained. When the phase signal is the maximum positive level in the figure B, it is a binary signal shifted by 180 °, and when the A phase signal is the maximum negative level and the B phase signal is the zero level in FIG. In the case of the same figure in which the A phase signal is zero level and the B phase signal is the negative maximum level, it is shifted by 360 ° and the original phase is not shifted. The binary signal is returned to the state.

  In this way, interpolation data obtained by dividing the lattice pitch P can be obtained. For example, interpolation data obtained by dividing the lattice pitch P can be obtained by counting the clock from the zero phase position of the carrier wave until the (c) selection signal c shown in FIG. 12 rises. Therefore, if counting is started by the edge of the carrier wave and counting is stopped by the rising edge of the binary output of the comparator 33, the interpolation data obtained by dividing the lattice pitch P can be detected.

  The count data of the position data backup counter 16 is supplied to the count memory calculation unit 21 of the calculation device 20 to calculate the current position data at the time of detecting the origin as described above, to perform correction work, Is stored and saved. Further, the interpolation data supplied from the interpolation unit 30 is supplied to the interpolation division unit 22 of the calculation device 20, and further supplied to the position data creation unit 23 together with the data of the count memory calculation unit. In the position data creating unit 23, the interpolated data is interpolated into the data of the count memory calculating unit to obtain high resolution position data. The position data generation unit 23 can also use position data in a format used by a machine such as an NC apparatus, a machining apparatus, or the like. Further, the data output unit 24 converts the signal into a signal corresponding to a communication form such as serial data, and sends the position data to a device that requires it. Such an arithmetic unit 20 can be normally constituted by a microprocessor or the like, and all of the above processes can be performed by software. Further, some of the functions may be performed by a gate array, a digital IC, or the like.

  Further, in this apparatus, when backup such as power interruption is required, the backup power source 17 supplies power to the current / voltage conversion amplifier 13, the amplifier 14, the comparator 15, the position data backup counter 16 and the backup drive circuit 18 that emits light from the light emitting diode 11. Is supplied. Thereby, position data can be measured and stored even in a power-off state. Therefore, in the normal operation, the current position data can be used as it is without performing the origin detection operation when the power is turned on. Here, as described in, for example, Japanese Patent No. 3239295, the backup drive circuit 18 applies an optimum voltage corresponding to the variation in the forward voltage of the light emitting diode and is driven by constant current driving. By using a circuit that suppresses power, it is possible to further reduce power consumption.

  In this encoder, power consumption is reduced by not supplying power to the absolute interpolating unit 30, the origin dedicated amplifier 41, and the arithmetic unit 20. Further, the switches SW1 and SW2 are opened so that the circuit which is not turned on is cut off from the backed up circuit. The comparator 14 and the position data backup counter 16 can further reduce power consumption by using a CMOS element or the like. These elements constituting the device of the present invention can be constituted by a combination of logic elements such as a gate array and digital elements except for the arithmetic unit 20.

  Further, the signals input to the comparator 15 and the position data backup counter 16 are not interpolated signals, that is, the position data backup counter 16 only counts every 20 microns when the grating pitch P is 20 microns. Therefore, power consumption is further reduced. That is, in this embodiment, at the time of backup, only the position data having the grid interval P as a unit is detected and held in the position data backup counter 16, and the interpolation data obtained by dividing the grid pitch P at the time of power-on is obtained. It is only necessary that the absolute interpolation unit 30 and the calculation unit 20 form the interpolation and calculation. For this reason, it is possible to perform backup with low power consumption without reducing the resolution.

  In the above example, a linear scale has been described as an application example of the optical absolute encoder of the present invention. However, the present invention is not limited to this, and can be suitably used for, for example, a rotary encoder. However, in the case of a linear encoder, since the moving distance to the origin is large, it is particularly effective when applied to a linear encoder.

  The present invention can be applied to an optical encoder that measures the amount of movement and displacement of an object, the amount of rotation of a rotating body, and the like, and can be suitably applied to a linear encoder that moves over a long linear distance. In addition, even in the case of a backup type encoder, it is possible to shorten the movement distance of the operation that conventionally required the origin detection, such as when initial setting or recovery from the above state, and to greatly reduce the detection time. Useful.

It is a top view which shows one form of the scale of an optical encoder. It is a wave form diagram which shows the mode of an origin signal. It is a timing chart which shows the operation | movement of the counting process of this invention. It is a side view of the optical scale which is an Example of this invention. It is a top view of an optical scale which is an example of the present invention. It is the figure which showed the moire fringe produced by the grating | lattice of a scale. It is a graph which shows the change of the electric current which flows into a photoelectric conversion element. It is the figure which showed the arrangement position of the photoelectric conversion element with respect to a moire fringe. FIG. 9 is an output waveform diagram of the photoelectric conversion element arranged at the position shown in FIG. 8. It is a block diagram which shows the signal processing circuit of the optical scale of an Example. It is the circuit diagram which showed the structural example of the phase modulator. It is the figure which showed the waveform of each part of a phase modulator. It is the figure which showed the relationship between the phase of the binary signal output from a comparator, and the level of the A phase signal and B phase signal which are input into an absolute interpolation part. It is an external appearance perspective view which shows the conventional optical scale. It is a cross-sectional view showing the principle structure of the optical scale. It is a block diagram which shows the signal processing circuit of the encoder of FIG. It is a block diagram of an optical absolute scale having a conventional backup power supply.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scale main body 2 Code pattern 3 Origin detection track 4a, 4b, 4c Origin mark 5a, 5b, 5c and origin position confirmation mark 11 Light emitting diode 12 Photo diode 13 Current / voltage conversion amplifier 14 Amplifier 15 Comparator 16 Position data backup counter 17 Backup power supply 18 Backup drive circuit 19 LED drive circuit 20 Calculation unit 21 Count memory calculation unit 22 Interpolation division unit 23 Position data creation unit 24 Data output unit 30 Interpolation unit 31 Modulation circuit 32 Low-pass filter 33 Comparator 41 Amplifier 42 Comparator

Claims (7)

A scale (1) having a measurement track and an origin detection track (3) in which measurement code patterns are formed at the same pitch;
An optical pickup unit that obtains a signal corresponding to the sign from the scale (1),
Create absolute data with two signals with different phases obtained from this optical pickup unit,
The origin detection track (3) of the scale (1) is formed between a plurality of origin marks (4a, 4b, 4c) formed at the same pitch and the origin marks (4a, 4b, 4c). With origin position confirmation marks (5a, 5b, 5c),
An optical absolute encoder in which the distance between the origin mark (4a, 4b, 4c) and the origin position confirmation mark (5a, 5b, 5c) is different at any position. When the pitch between the origin marks (4a, 4b, 4c) is 2d (d: any real number)
The distance between the origin mark (4a, 4b, 4c) and the origin position confirmation mark (5a, 5b, 5c) is
d + rn (r: any real number, n: positive integer)
The optical absolute encoder according to claim 1, wherein any one of r1, r2,... Rn is assigned to each position on the scale. Count data corresponding to the distance from the reference position is calculated from the distance between the origin position confirmation mark (5a, 5b, 5c) and the origin mark (4a, 4b, 4c);
Find the difference data with the counting data indicating the current position,
3. The optical absolute encoder according to claim 1, wherein count data indicating a current position is corrected based on the difference data.   The optical absolute according to any one of claims 1 to 3, wherein the optical scale is a linear scale that photoelectrically converts a moire fringe pattern obtained from the scale (1) and counts two phase difference signals of A phase and B phase obtained therefrom. Encoder. A counter that sequentially counts the phase difference 2 signals of the A phase and the B phase;
The counter value is latched at the time of detecting the origin mark and the origin position confirmation mark, respectively, and a count value corresponding to the distance between the origin mark and the origin position confirmation mark is calculated from the latch data,
Further, a correction value for the reference position is calculated from the counted value,
5. The optical absolute encoder according to claim 4, wherein the value of the counter is corrected with the obtained correction value to obtain current position data. A current / voltage conversion amplifier for current / voltage converting the signal from the optical pickup unit, a comparator for outputting the voltage-converted signal as a binary output, and a position data backup counter for sequentially counting A and B phase signals from the comparator And a backup drive circuit that causes the light emitting diode to emit light during backup operation,
An interpolation unit for creating interpolation data from the phase-difference two signals of the A phase and the B phase;
The interpolation data obtained from the interpolation unit is interpolated into a position data backup counter, and has at least a calculation unit that creates position data,
The optical absolute encoder according to claim 4 or 5, wherein the optical part other than the interpolating part and the arithmetic part is backed up.   4. The optical absolute encoder according to claim 1, wherein the optical absolute encoder is a rotary encoder.

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