JP2009294117A - Absolute encoder and method for detecting absolute position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absolute encoder utilizing an architecture of an incremental encoder. <P>SOLUTION: A wheel 100 includes a circular wheel body 102 and a plurality of grids 104. The grids 104 include a primary grid 104A which is a main grid arranged on a reference line, and secondary grid units 104B, 104C which are a plurality of sub-grids arranged on at least one adjustment line. The number of grids of the sub-grids 104B, 104C is smaller by one than the number of grids of the main grid 104A. For example, if the number of grids of the main grid 104A is 2,500, the number of grids of each sub-grid 104B, 104C is 2,499. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an absolute encoder (absolute position detector), and more particularly to an absolute encoder that utilizes the architecture of an incremental encoder (relative position detector).

  Conventional AC servo motors typically include an optical encoder to sense rotor angle information, which can be used to determine stator drive current. Therefore, the speed of the AC servo motor can be accurately controlled.

  FIG. 1 shows a schematic diagram of a prior art AC servomotor. The angular position of the rotor in the motor 10 is detected by the optical encoder 12 and processed by the signal processor 20 to obtain angle information. The angle information is processed by the speed estimator 14 to obtain the estimated motor rotation speed. The speed controller 30 receives the estimated motor rotation speed and speed commands for controlling the controller module 32 and the IGBT module 34 to generate a motor speed control signal. The motor speed control signal can be used to accurately control the rotation speed of the motor 10.

  In particular, in the servo motor, the position sensor attached to the motor shaft is the optical encoder 12. When the optical encoder 12 can be classified into an incremental type encoder and an absolute type encoder, the position accuracy of the servo motor depends on the resolution of the optical encoder.

  An incremental encoder can provide information about the previous position, and if the position is not reset, the absolute position of the encoder wheel cannot be known after a power failure. Thus, an incremental encoder cannot know that the absolute position of its encoder wheel after power is just restored after a power failure. On the other hand, the absolute encoder can always know the absolute position of the output shaft without being troubled by a power failure. The reset operation is not necessary after power-on due to a power failure, and the operation is simplified.

  FIG. 2 shows a schematic diagram of an optical encoder. The light from the light source 260 reaches the optical sensor 240 after passing through the rotating wheel 200 and the fixed mask 220. The signal received by the optical sensor 240 is changed by changing the position of the rotating wheel 200. Therefore, the position change of the rotating wheel 200 can be known by detecting the signal strength of the optical sensor 240.

FIG. 3 shows a schematic diagram of an absolute encoder wheel 300, which is a 6-bit encoder wheel. The absolute encoder wheel 300 includes a circular wheel body 302 and a plurality of gratings 304. The grating 304 includes a first grating 304A that occupies the innermost track and ½ circumferential surface, two second gratings 304B that occupy the second innermost track and ¼ circumferential surface, 3 gratings 304C, a fourth grating 304D, a fifth grating 304E, and 32 sixth gratings 304F that occupy the outermost orbit and each circumferential surface of 1/64. A signal that varies in intensity can be obtained along the radial direction, and a position resolution of 2 ⁶ = 64 can be obtained along the circumferential direction. However, if 1-bit resolution is to be enhanced in the absolute encoder wheel 300 shown in FIG. 3, more trajectories are required. If more resolution is required, the absolute encoder wheel 300 occupies more space. The absolute encoder wheel 300 shown in FIG. 3 has a limited resolution when its size is limited.

  FIG. 4A shows a schematic diagram of an encoder wheel 400 for an incremental optical encoder, the encoder including a circular wheel body 402 and a plurality of grids. The grating includes a main grating 404A, a first sub-grating 404B, and a second sub-grating 404C, where the first sub-grating 404B and the second sub-grating 404C are two opposite of the main grating 404A. Placed on the surface. FIG. 4B shows a mask 420 associated with encoder wheel 400, which includes four rows of grids 420A. FIG. 4C shows a light sensor device 440 associated with the encoder wheel 400, which is a main light sensor unit 442A, 444A, 442B, 444B (A + / B + / A− / B) corresponding to the main grid 404A. -Labeled). When the encoder wheel 400 rotates, the primary light sensor units 442A, 444A, 442B, 444B (labeled A + / B + / A− / B−) generate four sinusoid-like signals. A signal like four sinusoids has a phase of 0/90/180/270 degrees. In order to obtain the sine signal A without in-phase noise, the A + / A− signal with a phase difference of 180 degrees follows the difference calculation. In order to obtain the cosine signal B without in-phase noise, the B + / B− signal with a phase difference of 180 degrees follows the difference calculation. To determine forward or backward rotation, a sine signal A and a cosine signal B with a 90 degree phase difference can be used.

  The incremental optical encoder can obtain position information of an increment based on the sine signal A and the cosine signal B. In order to obtain absolute position information, origin light sensor units 446A, 446B (Z + / Z−) are further provided. However, after power-up from a power failure, the incremental origin mark on the encoder should be sensed by the origin sensor unit to obtain absolute position information. This process is not suitable for applications that are time consuming and do not require a return to the origin mark.

  The present invention seeks to provide an absolute encoder that takes advantage of an incremental encoder architecture, thereby enhancing its resolution.

  Therefore, the absolute encoder of the present invention includes an absolute encoder wheel. The absolute type encoder wheel includes a primary optical grating unit and two secondary optical grating units, and the two secondary optical grating units are arranged outside and inside the primary optical grating unit, and are 1 more than the primary optical grating unit. Includes fewer optical gratings. The encoder wheel rotates to find the zero point in the light detection signal of the secondary optical grating unit, and the corresponding light detection value of the primary optical grating unit is also determined. The absolute position of the encoder wheel can be calculated in relation to the corresponding light detection value. Absolute encoders can also be used as incremental encoders to provide more flexibility.

  For prior art absolute optical encoders, physical coding, such as binary code or gray code, is necessary to obtain absolute position information. Furthermore, the resolution of an absolute optical encoder also depends on the number of sensors. As the number of sensors increases, the size and cost of absolute optical encoders increases. In the present invention, the incremental encoder architecture is exploited to provide absolute position sensing functionality. An additional grating is provided in the incremental encoder to generate a modulated signal. A 360 degree sine signal (or cosine signal) can be generated by a modulation signal. Absolute position information can be obtained by interpolation of a sine signal (or cosine signal).

  FIG. 5A shows a schematic diagram of an encoder wheel 100 in an absolute optical encoder according to the present invention. The wheel 100 includes a circular wheel body 102 and a plurality of grids 104. The grating 104 includes a primary grating unit 104A composed of a plurality of main gratings arranged on a reference line and at least one secondary grating unit composed of a plurality of sub-grids arranged on at least one adjustment line (in this figure, two Secondary grating units 104B and 104C). The number of sub-lattices is one less than the number of main lattices. For example, when the number of lattices of the main lattice is 2500, the number of lattices of the sub lattice is 2499.

  FIG. 5B shows a schematic diagram of the mask 120, which includes four columns of gratings 120A corresponding to the photosensor devices. FIG. 5C shows a schematic diagram of the photosensor device 140, which is the main photosensor unit 142A, 144A, 142B, 144B (ie, A + / B +) corresponding to the location of the main grid of the primary grid unit 104A. Area marked with / A− / B−). Photosensor device 140 further includes adjusted photosensor units 146A, 146B (ie, areas marked with M + / M−) corresponding to the sub-gratings of secondary grating units 104B, 104C, respectively.

  In the present invention, the wheels and associated components in the incremental encoder are modified to provide absolute position information. Referring again to FIGS. 5A, 4A, and 4C, the portion on the wheel 100 corresponding to the Z + / Z− area of the wheel 400 comprises sub-grids each having one less jaggedness than the main lattice of the primary lattice unit 104A. . For ease of demonstration, the operation of the absolute encoder is as follows: 16 main grids in the primary grid unit 104A, 15 sub grids in the secondary grid unit 104B, and 15 sub grids in the secondary grid unit 104C. Illustrated by a lattice.

  FIG. 6 shows the signal detected by the optical sensor device 140. With one rotation of the wheel 100, the main light sensor units 142A, 142B (corresponding to the areas marked A + / A-) are differentiated into the 16th period (each period has a 360 degree phase). 1 sine curve (solid line) is generated. With one rotation of the wheel 100, the adjusting light sensor unit 146A or 146B (corresponding to the area marked with M + / M) is the second sine of 15 periods (each period has a 360 degree phase). Generate a curve (dashed line). A third sine curve (thick dashed line) for one period (360 degrees) can be obtained by sampling the first sine curve with a zero at the second sine curve, which will be detailed later. . When power is supplied again to the absolute encoder of the present invention after a power failure, the controller (not shown, which can be the speed estimator 14 of FIG. 1) moves the gap corresponding to one grid pitch of the sub-grid. To drive the wheel 100 (ie in this case 24 degrees with 15 sub-grids). The 2π zero A is found in the second sinusoid sensed by the adjusting light sensor unit 146A during the movement, and the first sinusoid is sampled at the 2π zero A. As can be seen from FIG. 6, the third sinusoid generated by sampling is a sinusoid (thick dashed line) of one period (360 degrees). The absolute position of the encoder is known from the value of the third sine curve indicated by the 2π zero point A.

  The absolute position of the encoder has a resolution of 24 degrees based on the example of 16 main grids and 15 sub-gratings. The resolution can be enhanced with more main grids 104A (eg, 2500).

  Similarly, the cosine curve generated by the main light sensor units 144A, 144B (corresponding to the areas marked B + / B−) is also the 2π zero point of the result sensed by the adjusting light sensor unit 146A (or 146B). Can be sampled. The absolute position of the encoder is known from the sampled result value. In the present invention, the absolute position of the encoder is obtained with the help of a grid with a resolution similar to the incremental encoder. Therefore, the absolute position resolution is enhanced. Furthermore, if the higher harmonic components in the original sine and cosine curves are sufficiently small, the resolution can be further enhanced by interpolation.

The advantages of the present invention can be summarized as follows.
1. Absolute position information is available with an incremental encoder-like architecture.
2. The position resolution can be enhanced by interpolation of the increased position signal.
3. Signals from the main light sensor unit and the conditioning light sensor unit are differentially amplified to remove common mode noise.

  Furthermore, the absolute encoder of the present invention is demonstrated in terms of an optical encoder. It should be noted that the scheme of the present invention can be applied to other types of encoders or angle resolvers based on electromagnetic or capacitive signals.

The features of the invention believed to be novel are set forth with particularity in the appended claims. However, the present invention itself may be best understood by reference to the detailed description of the invention, which is taken in conjunction with the accompanying drawings and describes exemplary embodiments of the invention.
1 shows a schematic diagram of a prior art AC servomotor. 1 shows a schematic diagram of an optical encoder. A schematic view of an absolute encoder wheel is shown. 1 shows a schematic diagram of an encoder wheel for an incremental optical encoder. 4B shows a mask associated with the encoder wheel of FIG. 4A. 4B illustrates an optical sensor device associated with the encoder wheel of FIG. 4A. 1 shows a schematic diagram of an encoder wheel in an absolute optical encoder according to the present invention. 1 shows a schematic view of a mask according to the invention. 1 shows a schematic diagram of an optical sensor device. Fig. 4 shows a signal detected by a light sensor device.

Claims (14)

The wheel body,
A primary lattice unit having a first number of main lattices, wherein the main lattice is disposed around a peripheral surface of the wheel body;
At least one secondary optical grating unit having a second number of sub-gratings, the sub-grating comprising: the secondary optical grating unit disposed around another circumferential surface of the wheel body;
The absolute number optical encoder wheel, wherein the second number is one less than the first number.   The absolute optical encoder wheel according to claim 1, wherein the absolute encoder wheel includes one secondary optical grating unit, and the secondary optical grating unit is disposed inside the primary grating unit.   2. The absolute optical encoder wheel according to claim 1, wherein the absolute encoder wheel includes one secondary optical grating unit, and the secondary optical grating unit is arranged outside the primary grating unit.   2. The absolute type encoder wheel according to claim 1, wherein the absolute type encoder wheel includes two secondary optical grating units, and the secondary optical grating units are disposed inside and outside the primary grating unit, respectively. Optical encoder wheel.   The absolute optical encoder wheel according to claim 1, wherein the first number is 2500 and the second number is 2499. An absolute optical encoder for determining the absolute position of the wheel body with respect to the light source,
A primary lattice unit having a first number of main lattices, wherein the main lattice is disposed around a peripheral surface of the wheel body;
At least one secondary optical grating unit having a second number of sub-gratings, the sub-grating being arranged around another circumferential surface of the wheel body, wherein the second number is the first number One less said secondary optical grating unit;
A plurality of main light sensor units that are arranged corresponding to the primary grating units and receive light from a light source that passes through the primary grating units;
At least one adjusting light sensor unit corresponding to at least one secondary optical grating unit and receiving light from a light source passing through the primary grating unit;
A controller electrically connected to the main light sensor unit and the adjustment light sensor unit, wherein the absolute position of the wheel body is obtained according to a sensed result of the main light sensor unit and the adjustment light sensor unit. An absolute optical encoder comprising the controller configured as described above.   7. The absolute optical encoder according to claim 6, wherein the absolute encoder includes one secondary optical grating unit, and the secondary optical grating unit is disposed inside the primary grating unit.   7. The absolute optical encoder according to claim 6, wherein the absolute encoder includes one secondary optical grating unit, and the secondary optical grating unit is disposed outside the primary grating unit.   7. The absolute optical encoder according to claim 6, wherein the absolute encoder includes two secondary optical grating units, and the secondary optical grating units are disposed inside and outside the primary grating unit, respectively. .   The absolute optical encoder according to claim 6, wherein the main light sensor unit includes four sensor units with a signal phase difference of 90 degrees.   The absolute optical encoder according to claim 6, wherein the adjustment optical sensor unit includes two optical sensor units with a signal phase difference of 180 degrees. A method for sensing the absolute position of an optical encoder wheel, comprising:
With a light source,
A primary lattice unit having a wheel body and a first number of main lattices, wherein the main lattice comprises a primary lattice unit disposed around a peripheral surface of the wheel body and a second number of sub-lattices. At least one secondary optical grating unit, wherein the sub-grating is arranged around another circumferential surface of the wheel body, and the second number is one less than the first number. It has an absolute encoder wheel including a lattice unit,
Driving the wheel body to rotate a distance corresponding to the grating pitch of the sub-grating, finding a zero point of the sensed result corresponding to the sub-grating,
Finding a sample value of a sensed result for the main grid relative to the zero point and finding an absolute position of the encoder wheel based on the sample value.   13. The method of claim 12, wherein all sample values at all zeros of the sensed result corresponding to the sub-grid are 360 degree sinusoids.   13. The method of claim 12, wherein all sample values of all zeros of the sensed result corresponding to the sub-grid are 360 degree cosine curves.

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