JP6466642B2 - Encoder - Google Patents

Description

  The present invention relates to an encoder having an origin position detection function.

  Currently, encoders are used as means for detecting position and speed. An example of an encoder is an incremental encoder. The detection position in the incremental encoder is accumulated by a counter or the like due to the relative displacement between the scale and the sensor, but the position is not known because the counter is reset immediately after the power is turned on. Therefore, when the power is turned on, the sensor and scale are relatively displaced to detect the origin position, and the counter is reset when the origin position is recognized by the origin signal. This is called origin detection. After the origin detection, position detection from the origin position becomes possible.

  In Patent Document 1, the same photodiode array as that in the displacement detection sensor is used as the origin detection sensor, and a plurality of origin signal generation patterns having the same pitch as the displacement detection signal generation pattern are used as the scale pattern. Then, by processing the output signals obtained from them by the origin signal processing unit, the origin area is determined and the origin signal is output.

JP 2013-36945 A

  However, in Patent Document 1, if the photodiode array of the origin detection sensor exists for two cycles or more of the output signal of the origin detection sensor, there is a possibility that the origin area may be erroneous depending on the processing. This is because an output signal in a region other than the origin region may partially satisfy a condition that the origin signal processing unit regards as the origin.

  In view of such a problem, an object of the present invention is to provide an encoder capable of suppressing erroneous detection of an origin signal.

An encoder as one aspect of the present invention includes a scale on which an origin detection pattern is formed, an origin detection unit that reads the origin detection pattern, and a processing unit that outputs an origin signal, and the origin detection unit has two sets of the detecting element group, the detecting element group, the first detector, a second detector, have a third detector and the fourth detector, the first detector And the second detection unit, the third detection unit and the fourth detection unit are arranged symmetrically with respect to the center of the detection element group, and in the detection element group, the first detection unit and the second detection unit The second detection unit is arranged outside, the third detection unit and the fourth detection unit are arranged inside, and the origin detection pattern is physically different from the origin periphery detected by the origin detection unit. The length in the detection direction of the characteristic characteristic is the length in the detection direction of the detection element group. The origin detection unit includes a first signal based on the first detection unit and the third detection unit, a second detection unit, and a second detection unit. 4 outputs a second signal based on the four detection units, and the processing unit processes the first signal and the first threshold value, the third signal obtained by processing the first signal, and the second signal. The fourth signal obtained by processing the second threshold value and the fifth signal obtained by processing, the origin detection pattern is adjacent between the two sets of detection element groups The second detection element arranged in the first detection unit arranged in one detection element group of the two detection element groups and the other detection element group in the two detection element groups detecting an origin by detecting the signal change of the first signal and the second signal obtained when parts and relative The output as an origin signal, by comparison with the first threshold or the second threshold value, characterized in that adjustable output position of the origin signal.

  ADVANTAGE OF THE INVENTION According to this invention, the encoder which can suppress the misdetection of an origin signal can be provided.

2 is a diagram illustrating a configuration of an encoder according to Embodiment 1. FIG. It is a figure showing the track of a scale. It is a figure showing an optical system. It is a figure showing the detection block of a displacement detection sensor. It is a figure showing the signal from a displacement detection sensor. It is a figure showing the signal which binarized the signal from a displacement detection sensor. It is a figure showing the phase signal calculated | required from the signal from a displacement detection sensor. It is a figure showing the detection block of an origin detection sensor. It is a figure showing the 1st signal and 2nd signal of Example 1, and the 1st threshold value and the 2nd threshold value. It is a figure showing the process part of an origin detection process part. It is a figure showing a 3rd signal and a 4th signal. It is a figure showing a 5th signal. It is a flowchart of an origin signal process. It is a figure showing the relationship between the origin pattern length of a 1st signal and a 2nd signal. It is a figure showing the relationship between an origin pattern length and a crosspoint voltage. FIG. 6 is a diagram illustrating a configuration of an encoder according to a second embodiment. It is explanatory drawing regarding operation | movement of a multiplier. It is a figure showing the relationship between an origin signal, an origin pulse, and a position fluctuation margin. It is a figure showing the 1st signal, the 2nd signal, and the 5th signal in case the 1st and 2nd threshold values are equal. It is a figure showing the 1st signal, the 2nd signal, and the 5th signal in case the 1st threshold is the low voltage side and the 2nd threshold is the high voltage side. It is a figure showing the 1st signal, the 2nd signal, and the 5th signal in case the 1st threshold is the high voltage side and the 2nd threshold is the low voltage side. 6 is a diagram illustrating a rotary scale of Example 3. FIG. It is a figure showing resolution and a spatial frequency response. It is a figure showing the 1st signal and 2nd signal of Example 3, and the 1st threshold value and the 2nd threshold value. FIG. 10 is a diagram illustrating a linear stage according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  In this embodiment, a linear encoder that detects the amount of movement in one axis direction will be described as an example. FIG. 1 is a diagram illustrating a configuration of an encoder according to the present embodiment. The encoder includes a scale 10, a displacement detection sensor (displacement detection unit) 20, an origin detection sensor (origin detection unit) 30, a displacement detection signal processing unit 40, and an origin signal processing unit 50. The encoder according to the present embodiment is a reflective optical incremental encoder that detects relative displacement between the scale 10 and the displacement detection sensor 20 and the origin detection sensor 30. The scale 10 is attached in the uniaxial movement direction of the measurement target, and the displacement of the measurement target is detected by attaching the displacement detection sensor 20 to the fixed member. When the positional relationship between the scale 10 and the origin detection sensor 30 is at the origin position, the origin signal is sent from the origin detection sensor 30 to the displacement detection signal processing unit 40 as a digital pulse.

  As shown in FIG. 2, the scale 10 includes two tracks 11 and 12. The track 11 is for displacement detection, and the track 12 is for origin detection. In each track, the black part represents the reflection part, and the white part represents the non-reflection part. The track 11 has a period of 200 μm, and the reflection part and the non-reflection part are arranged every 100 μm. The track 12 has a length of 400 μm in the detection direction in the center of the reflection portion 13.

  As shown in FIG. 3, the displacement detection sensor 20 and the origin detection sensor 30 are mounted on the same mounting board 22 together with the light source 21. The displacement detection sensor 20 receives the reflected light of the light irradiated on the track 11 from the light source 21, and the origin detection sensor 30 receives the reflected light of the light irradiated on the track 12. This configuration is a divergent beam configuration in which there is no parallel beam lens that bundles the beam in parallel between the light source and the scale. The divergent light beam configuration is a configuration in which light emitted from a light source travels in a uniform manner without being collimated or concentrated at one point. In this embodiment, an image of a pattern having a width of P on the scale 10 is enlarged to 2P on each sensor. In this embodiment, each sensor is mounted on the same mounting board 22, but each sensor may be mounted on another board. In the present embodiment, the same light source 21 is used for each sensor, but separate light sources may be used for each sensor. In this embodiment, the displacement detection and the origin detection are performed using an optical method, but may be performed using a magnetic method.

  The displacement detection sensor 20 has a detection block shown in FIG. In FIG. 4, the light receiving elements A to D output a voltage proportional to the amount of received light. The light receiving elements are arranged in the order of B, C, D, and A from the end, and this repeating unit is arranged for 8 periods in the light receiving unit 23. Each of the light receiving elements A to D has a length of 100 μm in the displacement detection direction, and the light receiving unit 23 has a length of 3200 μm.

  The voltage output from each of the light receiving elements A to D is differentiated with A and C as a set by the differential amplifier 1 with reference to the center voltage, and B and D as a set and the differential amplifier 2 as a set. The differential is taken with reference to. The output of the differential amplifier 1 is the displacement detection signal 1 and the output of the differential amplifier 2 is the displacement detection signal 2.

  Here, since the track 11 on the scale 10 has a pattern in which the brightness changes with a period of 200 μm, the reflected light is doubled on the light receiving part 23 and becomes an image with a change in brightness with a period of 400 μm. This is the period in which the light receiving elements A to D are arranged.

  From the above relationship and the positional relationship between the light receiving elements A and B and the light receiving elements C and D, the light receiving element C receives the 180 ° phase difference signal of the light receiving element A, and the light receiving element D receives the 180 ° phase difference signal of the light receiving element B. Output.

  From this relationship, the light receiving elements A to D can be counted as a set of light receiving element arrangement groups. A group represents a minimum constituent unit of a light receiving element for outputting displacement detection signals 1 and 2 in the displacement detection sensor 20. The displacement detection signals 1 and 2 have a phase difference of 90 °. When the scale 10 and the displacement detection sensor 20 are relatively displaced, the amount of light received by each of the light receiving elements A to D changes according to the displacement, and the displacement detection signals 1 and 2 are output as sinusoidal signals.

FIG. 5 shows a displacement detection signal 1 and a displacement detection signal 2 when the scale 10 moves relative to the displacement detection sensor 20 by 1000 μm. In FIG. 5, the horizontal axis represents displacement, and the vertical axis represents the voltage value. As described above, since the reflected light from the scale 10 is a sine wave having the period of each of the light receiving elements A to D on the light receiving element, the period of each displacement detection signal is also 200 μm which is the period of the track 11. . Further, since the displacement detection signal 1 and the displacement detection signal 2 have a phase difference of 90 °, the displacement detection signal 1 and the displacement detection signal 2 have a phase difference of 50 μm which is a 90 ° phase difference in a cycle of 200 μm. Since the power supply voltage of the displacement detection sensor 20 is 3.3 V and the differential amplifiers 1 and 2 are differential with respect to the power supply voltage with respect to the center voltage, the center voltage is ½ Vcc, 1.65 V. It has become. The displacement detection signals 1 and 2 swing to the low voltage side and the high voltage side with respect to the center voltage. The amplitude varies depending on the amount of light and the positional relationship between the sensor and the scale, but is set to 2.0 Vp-p in this embodiment.

  The displacement is detected by the displacement detection signal processing unit 40 based on the two-phase signals. The displacement detection signal processing unit 40 detects the displacement for each period by binarizing and counting the two-phase signals. A signal obtained by binarizing the displacement detection signals 1 and 2 is shown in FIG. In FIG. 6, a signal obtained by binarizing the displacement detection signal 1 is a digital signal 1, and a signal obtained by binarizing the displacement detection signal 2 is a digital signal 2. Both digital signal 1 and digital signal 2 have waveforms rising every 200 μm, which is the period of displacement detection signal 1 and displacement detection signal 2. The displacement detection signal processing unit 40 determines the displacement direction from the combination of rising edges of the digital signals 1 and 2 and increases or decreases the count for each period.

  Further, the displacement detection signal processing unit 40 takes the voltage value of the displacement detection signal as a digital value and performs an arctangent calculation based on the two-phase voltage value in order to detect the displacement within the cycle. FIG. 7 shows the phase values when 2π is 256 and the displacement detection signals 1 and 2 are calculated by arctangent calculation. In FIG. 7, the horizontal axis represents displacement, and the vertical axis represents the phase of a sine wave. The phase takes a value of 0 to 255 within a sine wave cycle, and this is repeated if there are multiple cycles. That is, when the phase advances to 255, the next phase becomes zero. In this embodiment, since the cycle is 200 μm, when the scale 10 moves relative to the displacement detection sensor 20 by 1000 μm, this repetition is repeated five times.

The displacement within one period is obtained by dividing the phase calculated by the arc tangent calculation by 256 which is 2π. This is combined with a counter value for each period obtained from the binarized digital signal 1 and digital signal 2, and the detected displacement is obtained by the following equation (1). Position is a detected displacement, cnt is a count value for each period of the displacement detection signals 1 and 2, and θ is a phase in a sine wave period obtained by performing an arctangent operation on the displacement detection signals 1 and 2.

  Next, origin detection according to the present embodiment will be described. The origin detection sensor 30 has a detection block shown in FIG. In FIG. 8A, the light receiving elements (detecting units) A, B, C, and D output a voltage proportional to the amount of received light. The light receiving elements are arranged in the order of B, C, D, A from the end, and this light receiving element array group (detecting element group) is arranged in the light receiving unit 31 for two cycles. Each of the light receiving elements A to D has a length of 400 μm in the detection direction, and the light receiving unit 31 has a length of 3200 μm. In the present embodiment, each light receiving element A to D is represented as one element in the origin detection sensor 30, but a plurality of light receiving elements are connected in the detection direction as shown in FIG. May be regarded as one light receiving element.

  The voltage output from each of the light receiving elements A to D is differentiated with A and C as a set by the differential amplifier 3 with reference to the center voltage, and B and D as a set and the differential amplifier 4 as a set. The differential is taken with reference to. The output of the differential amplifier 3 is a first signal, and the output of the differential amplifier 4 is a second signal.

If the detection direction of the light receiving portion 31 at the origin detection sensor 30 the length and x, from the sequence in FIG. 8 (A), the phase difference between the first signal and the second signal becomes x / 8 on the light receiving portion 31 , Which corresponds to x / 16 on the scale. This indicates that the phase difference between the generated first signal and the second signal is 400 μm on the light receiving unit 31, that is, 200 μm on the scale.

  As a reference signal for detecting the origin position from the first signal and the second signal, a first threshold value and a second threshold value are prepared for each. These are signals for determining whether or not each of the first signal and the second signal has a signal value on the origin.

  In this configuration, the first signal and the second signal, and the first threshold value and the second threshold value when the track 12 having the reflection part 13 having a width of 400 μm in the detection direction is read by the origin detection sensor 30 are shown. 9 shows. In FIG. 9, the horizontal axis represents displacement, and the vertical axis represents the voltage value. The power supply voltage of the origin detection sensor 30 is 3.3 V, similar to the displacement detection sensor 20. Further, since the differential amplifiers 3 and 4 are differential with respect to the power supply voltage with respect to the center voltage, the center voltage is 1.65 V which is 1/2 Vcc. The first signal and the second signal swing to the low voltage side and the high voltage side with respect to the center voltage. The amplitude varies depending on the amount of light and the positional relationship between the sensor and the scale, but in this embodiment, it swings from 0 to 3.3V.

  As shown in FIG. 8A, the origin detection sensor 30 has two sets of light receiving element array groups each composed of the light receiving elements A to D, so that the response output to the reflection unit 13 of the origin detection sensor 30 is provided. Is a signal for two cycles for both the first and second signals. In the detection direction, the light receiving elements A and B connected to the non-inverting inputs of the differential amplifiers 3 and 4 and the light receiving elements C and D connected to the inverting inputs of the differential amplifiers 3 and 4 are the center of the light receiving element array group. Are arranged symmetrically with respect to each other. In the light receiving element array group, the light receiving elements A and B are arranged outside, and the light receiving elements C and D are arranged inside. Therefore, the light receiving elements A and B for outputting the first signal and the second signal to a higher voltage side than the center voltage at the time of light reception are adjacent only at the center of the light receiving unit 31 and are discrete in other regions. Will be arranged. For this reason, the first signal and the second signal are output to the higher voltage side than the center voltage only at the center. In addition to the central portion, when the first signal is output to a higher voltage side than the central voltage, the second signal is output to a lower voltage side than the central voltage, and the first signal is higher than the central voltage. When the signal is output to the low voltage side, the second signal is output to the higher voltage side than the center voltage.

  The origin signal processing unit 50 has a processing part shown in FIG. Each of the comparators 51 and 52 compares the first signal with the first threshold value and outputs a third signal, and compares the second signal with the second threshold value and outputs a fourth signal. The comparator 51 outputs a high level signal when the voltage value of the first signal is higher than the first threshold, and outputs a low level signal otherwise. Similarly, the comparator 52 outputs a high level signal when the voltage value of the second signal is higher than the second threshold, and outputs a low level signal otherwise. FIG. 11 is a diagram illustrating the third signal and the fourth signal. Since each signal is output for two cycles, the output from each comparator is also a binary output for two cycles. The AND circuit 53 calculates the logical product of the third signal and the fourth signal and outputs a fifth signal. Since both the first signal and the second signal are at the high level only in the central portion of the light receiving unit 31, when the logical product is obtained by the AND circuit 53, as shown in FIG. A fifth signal, which is a signal, is generated. In this embodiment, when the fifth signal becomes high level, the displacement detection signal processing unit 40 determines that the measurement target is located at the origin position, and resets the count value for each period to zero. In the present embodiment, the origin signal processing unit 50 includes the comparator 51, the comparator 52, and the AND circuit 53. However, any signal may be used as long as the same signal as the fifth signal can be obtained.

  A specific example of the above processing will be described with reference to the flowchart of FIG. After starting the origin signal processing in step S200, first, it is evaluated whether or not the first signal has a voltage value higher than the first threshold value (step S201). If this evaluation is satisfied, the process proceeds to the next evaluation, and if not satisfied, the process ends (step S204). In step S202, it is evaluated whether or not the second signal has a voltage value higher than the second threshold value. When this evaluation is satisfied, an origin signal is output (step S203). In this embodiment, the first signal and the first threshold are evaluated first, and the second signal and the second threshold are evaluated later, but this order does not matter. Moreover, you may evaluate whether all are satisfy | filled after evaluating simultaneously.

As described above, the fifth signal is effective when both the first signal and the second signal have a value higher than the center voltage. Therefore, the first threshold value and the second threshold value may be set within the ranges shown in equations (2) and (3), respectively. Voffset1 and Voffset2 are the first signal and the center voltage of the second signal, respectively, and Vref1 and Vref2 are the first threshold and the second threshold, respectively. Vcross is higher than the center voltage and is a voltage at which the first signal and the second signal cross (hereinafter referred to as a cross-point voltage).

These expressions indicate that the values of the first threshold value and the second threshold value, which are reference signals, are determined only by the center voltage and the cross-point voltage, and are not affected by peripheral signals. However, the center voltage and the cross point voltage have fluctuation components such as light quantity fluctuation, origin pattern fluctuation, and amplitude fluctuation, respectively. Therefore, the expressions (2) and (3) can be rewritten as the following expressions (4) and (5). Vom is a center voltage variation factor, and vcm is a cross-point voltage variation factor.

In addition, in the configuration in which a differential is taken from the voltages from the light receiving elements at different positions, the cross point voltage has a different value depending on the length of the reflection unit 13 in the detection direction (hereinafter referred to as the origin pattern length). This is because the first and second signals, which are the output values of the differential amplifiers 3 and 4 in FIG. 8, are calculated by the following equations (6) and (7). V1 is the first signal, V2 is the second signal, and Voffset is the center voltage.

The values of VA, VB, VC, and VD change according to the change in the physical property to be detected. Since the present embodiment is an optical encoder, the physical characteristic to be detected is assumed to be the amount of reflected light. For example, when the amount of reflected light at a certain position is viewed in the first signal, if (the amount of reflected light applied to the light receiving element A)> (the amount of reflected light applied to the light receiving element C), the signal is higher than the center voltage value. Is output. If (the amount of reflected light applied to the light receiving element A) <(the amount of reflected light applied to the light receiving element C), the signal is output to a lower voltage side than the center voltage value. If (the amount of reflected light applied to the light receiving element A) = (the amount of reflected light applied to the light receiving element C), the signal becomes the center voltage. Since the length of the reflected light on the light receiving element in the detection direction varies depending on the length of the origin pattern in the detection direction (hereinafter referred to as the origin pattern length), the cross-point voltage also varies depending on the origin pattern length. Further, in this processing system that takes the logical product of the in-phase signals on the higher voltage side than the center voltage, the origin detection margin increases as the cross-point voltage increases. Therefore, it is necessary to set the origin pattern length to an optimal value in order to increase the origin detection margin.

  FIG. 14 is a diagram showing the relationship between the origin pattern length of the first signal and the second signal, and FIG. 15 is a diagram showing the relationship between the origin pattern length and the crosspoint voltage value. In FIG. 14, the horizontal axis represents displacement and the vertical axis represents voltage value. 14A to 14C show the first signal and the second signal when the origin pattern length is 200 μm, 600 μm, and 800 μm, respectively. In FIG. 15, the horizontal axis represents the origin pattern length and the vertical axis represents the voltage. In FIG. 15, the solid line plots the cross-point voltage, and the broken line plots the center voltage. From FIG. 15, the cross-point voltage gradually increases from the center voltage as the origin pattern length increases from 0 μm, and the reflected light from the origin pattern is applied to both the light receiving elements A and B adjacent in the center of the light receiving unit 31. It becomes the maximum when it becomes 400 μm which is the condition to be satisfied. Thereafter, it decreases again, and when it reaches 800 μm, which is a condition for irradiating all the light receiving elements in one light receiving element array group, it becomes the same value as the center voltage again.

  Therefore, the origin pattern length may be a value less than 800 μm, which is a condition that the cross point voltage takes a value higher than the center voltage, and this is the length in the detection direction of the reflected light formed by the reflecting portion 13 in the track 12. Is a value that is less than the length in the detection direction of one light receiving element array group. In this embodiment, the origin pattern length is set to 400 μm at which the cross-point voltage has the maximum value.

  With the above configuration, it is possible to perform good origin detection with a low possibility of erroneously recognizing a signal other than the origin as being on the origin.

  In this embodiment, the displacement detection sensor 20 and the origin detection sensor 30 exist on the same plane as the light source 21, and the reflection type configuration that detects the displacement and the origin position by receiving the reflected light from the scale 10 has been described. . However, the present invention can also be applied to a transmissive configuration in which each sensor exists on a different plane from the light source 21 and the scale 10 exists between the light source 21 and each sensor.

  Further, in this embodiment, a displacement detection sensor different from the origin detection sensor is used for displacement detection. However, the origin detection sensor has a configuration other than the number of arrangements of the light receiving element array groups. Since it is similar to the detection sensor, the origin detection sensor of the present invention may be used for displacement detection.

  In this embodiment, the origin detection process is performed by a circuit, but may be performed by software if a signal similar to the fifth signal can be obtained.

  In the present embodiment, a multiplier 60 is provided instead of the displacement detection signal processing unit 40 of the first embodiment. FIG. 16 is a diagram illustrating the configuration of the encoder of the present embodiment. FIG. 17 is an explanatory diagram regarding the operation of the multiplier. The origin detection processing method is the same as in the first embodiment.

  In FIG. 17, the multiplier 60 outputs a digital signal having a period obtained by dividing the displacement detection signals 1 and 2 by 50 as the multiplied pulses 1 and 2. At this time, the pulse length of each multiplied pulse is 4 μm. The origin pulse is synchronized with the edges of the multiplied pulses 1 and 2 and is output at the origin pulse output phase when the origin signal is input. The origin pulse output phase is a phase in which the displacement detection signals 1 and 2 take the same value on the lower voltage side than the center voltage.

  FIG. 18 is a diagram illustrating the relationship between the origin signal, the origin pulse, and the position variation margin. In FIG. 18, when the origin pulse output phase is in the center with respect to the origin signal, the position fluctuation margin width 1 and the position fluctuation margin width 2 are substantially the same value, which is equivalent to the position fluctuation in either direction. It means having. On the other hand, when the origin pulse output phase is unevenly distributed with respect to the origin signal, the tolerance of the position fluctuation of the position fluctuation margin width 1 is inferior to the position fluctuation margin width 2. This means that the displacement detection sensor 20 and the origin detection sensor 30 have a position variation margin that is biased in one direction.

  Hereinafter, a method for dealing with the problem of the phase shift between the phase of the output of the displacement detection sensor 20 and the origin signal output from the origin signal processing unit 50 will be described. The problem here is that the origin pulse output phase deviates from the origin signal due to the decrease in the position fluctuation margin due to the phase shift, and the origin pulse is not output at the desired position.

In the present embodiment, the output position of the origin position is adjusted with respect to the origin pulse output phase. The wave width of the fifth signal that is the origin signal is determined by the first threshold value and the second threshold value. For example, in order to obtain a signal having a wave width of 100 μm, the first threshold value and the second threshold value may be set to an intermediate value between the center voltage and the crosspoint voltage. This is because the phase difference between the first signal and the second signal is determined by the arrangement of the light receiving elements, and the value is always 200 μm at the center voltage, and decreases as the threshold value is increased. This is because it becomes 0 at the position where the second signal intersects. Since the first signal and the second signal have linearity from the center voltage to the cross point voltage, the relationship between the origin signal wave width and the threshold value can be expressed by the following equation (8). λ is the origin signal wave width, and X is the phase difference between the first signal and the second signal at the center voltage. For simplification, Vref1 = Vref2 = Vref and Voffset1 = Voffset2 = Voffset.

  In this configuration, when the position of the fifth signal that is the origin signal is adjusted, the first threshold value and the second threshold value that are the respective threshold values in the first signal and the second signal are individually changed in opposite directions. Let 19A to 19C show the first signal, the second signal, and the fifth signal when the values of the first threshold value and the second threshold value are changed from the state where the first threshold value and the second threshold value are equal to each other. Represents the signal. For example, when the origin position is moved to the right (from the state of FIG. 19A to the state of FIG. 19B), the first threshold value Vref1 is changed to the low voltage side, and the second threshold value Vref2 is changed to the high voltage side. Conversely, when the origin position is moved to the left (from the state of FIG. 19A to the state of FIG. 19C), the first threshold value Vref1 is changed to the high voltage side, and the second threshold value Vref2 is changed to the low voltage side. At this time, the absolute values of changes in the respective threshold values should be the same. This is because when the change value has an individual absolute value, the width is narrower or wider than the origin signal width when Vref1 = Vref2.

When the origin position when Vref1 = Vref2 = Vref is set as the initial position, the adjustment width ΔOrg of the origin position can be expressed by the following equation (9).

Further, considering the center voltage variation factor Vom and the cross-point voltage variation factor vcm, equation (9) can be rewritten as the following equation (10).

  With the above configuration, since the output position of the origin signal can be adjusted even when connected to the multiplier 60, the origin detection of the present invention is also applied to the system that outputs the origin pulse using the origin signal synchronized with the displacement detection signal. Processing can be applied. Note that the present embodiment can also be applied to systems having different signal detection methods and processing unit configurations as in the first embodiment.

  Similarly to the first embodiment, the encoder of the present embodiment also includes a scale 10, a displacement detection sensor 20, an origin detection sensor 30, a displacement detection signal processing unit 40, and an origin signal processing unit 50. However, unlike the first embodiment, the scale 10 has a single track configuration in which the displacement detection pattern and the origin detection pattern are combined. In this embodiment, a rotary type configuration that detects the rotation angle of the scale will be described.

  FIG. 20 is a diagram illustrating a rotary type single track scale according to the present embodiment. A pattern periodically arranged throughout is a displacement detection pattern, and a pattern expressed in a form connected to the displacement detection pattern in the upper part is an origin detection pattern. Both the displacement detection sensor 20 and the origin detection sensor 30 receive an optical signal in which the reflected light from the displacement detection pattern and the reflected light from the origin detection pattern arranged in the same track are combined. In this embodiment, unlike the first embodiment, it is essential that the resolutions of the displacement detection sensor 20 and the origin detection sensor 30 are different, that is, the arrangement of the light receiving element array groups is different. Here, the resolution represents a scale pitch at which the displacement detection sensor 20 and the origin detection sensor 30 exhibit the strongest response.

  Since the displacement detection sensor 20 and the origin detection sensor 30 have different arrangements of light receiving element arrangement groups, they have different spatial frequency responses. For example, the displacement detection sensor 20 responds most strongly to an optical signal having a pitch of 400 μm on the light receiving unit 23. Since the optical signals of other pitches are canceled out to show the same output values in A and C and B and D which are in a differential relationship in each light receiving element, the response becomes weak.

The spatial frequency response characteristics of the displacement detection sensor 20 and the origin detection sensor 30 are shown in FIG. In FIG. 21, the horizontal axis represents the spatial frequency and the vertical axis represents the response of each sensor output normalized. As shown in FIG. 21, the origin detection sensor 30 is an optical signal light is mixed from the displacement detection pattern with the origin detection pattern, it does not respond to optical signals from the pattern output displacement detection, for origin detection Respond to patterns only. On the contrary, the displacement detection sensor 20 does not respond to the optical signal from the origin detection pattern, but responds only to the optical signal from the displacement detection pattern.

  As a result, the optical signals mixed by the displacement detection pattern and the origin detection pattern arranged in the same track are separated by the displacement detection sensor 20 and the origin detection sensor 30 having different spatial response frequencies. The response in the optical signal is shown.

  Also in the present embodiment, as in the first embodiment, the first threshold value and the second threshold value are set in order to determine whether the first signal and the second signal have signal values on the origin. .

  FIG. 22 shows the first signal and the second signal of the origin detection sensor 30, and the first threshold value and the second threshold value. In FIG. 22, the horizontal axis represents displacement, and the vertical axis represents voltage value. The amplitude varies depending on the amount of light and the positional relationship between the sensor and the scale, but in this embodiment, it swings to about 0.5 to 3.0V. In this embodiment, the origin detection sensor 30 receives an optical signal in which the reflected light from the displacement detection pattern and the reflected light from the origin detection pattern are mixed. However, as shown in FIG. 22, the reflected light from the displacement detection pattern is almost ignored due to the spatial frequency response characteristic of the origin detection sensor 30, and the component of the reflected light from the origin detection pattern is particularly output. I understand.

  In a configuration in which each detection pattern is arranged on a separate track, when each sensor is displaced in a direction perpendicular to the detection direction with respect to the scale, each sensor exceeds the range of each detection pattern based on the track boundary. Each sensor cannot be read. On the other hand, in the configuration in which each detection pattern is arranged in the same track, since there is no track boundary, each sensor is in each detection pattern even if each sensor is displaced in a direction perpendicular to the detection direction with respect to the scale. Is not misread. For this reason, by arranging the origin detection pattern and the displacement detection pattern in the same track, the variation in the radial direction of each sensor becomes stronger than the configuration existing in another track. In a rotary scale, the direction perpendicular to the detection direction is the eccentric direction of the scale, which means that it is resistant to eccentric fluctuations.

  By using the signal from the origin detection sensor 30 obtained in this way, the origin signal can be obtained by performing the same processing as in the first embodiment. Note that the present embodiment can also be applied to systems having different signal detection methods and processing unit configurations as in the first embodiment.

  FIG. 23 shows the linear stage of this embodiment. The linear stage includes a scale 10, a motor 70, a ball screw 80, a stage 90, an encoder 100, and a controller 110. The encoder 100 includes the displacement detection sensor 20, the origin detection sensor 30, the displacement detection signal processing unit 40, and the origin signal processing unit 50 of the first embodiment. The encoder 100 is a reflective optical encoder as in the other embodiments.

  The ball screw 80 can convert the rotational motion of the motor 70 into a linear motion, and the stage 90 moves in the moving direction of FIG. 23 according to the amount of rotation of the motor 70 by the ball screw 80. The scale 10 is attached to the side surface of the stage 90 so as to detect the uniaxial movement direction, and the encoder 100 is attached so as to read the scale 10. The controller 110 detects the displacement of the stage 90 based on the signal from the encoder 100 and controls the position of the stage 90 by controlling the rotation amount of the motor 70.

  The displacement is detected by the displacement detection pattern of the displacement detection sensor 20 of the encoder 100 and the track 11 of the scale 10. The displacement detection sensor 20 outputs a two-phase sine wave signal according to the relative displacement with the scale 10, and the encoder 100 converts this into a position signal and transmits it to the controller 110.

  In this configuration, the controller 110 needs to know the displacement of the stage 90 from the reference position. This is to avoid a malfunction in which the controller 110 erroneously tries to keep the motor 70 rotating even though the stage 90 reaches the limit position in the uniaxial movement direction. A limit sensor may be used as long as the limit position in the uniaxial movement direction is known. However, in order to increase the number of components by providing a limit sensor in addition to the encoder 100, this is not used in this embodiment. The component here refers to a peripheral circuit component in the encoder 100 or limit sensor.

  In this embodiment, therefore, an origin detection pattern for the track 12 is prepared separately from the displacement detection pattern for the track 11 as a reference for the absolute position on the scale 10, and the origin detection sensor 30 of the encoder 100 detects the origin detection pattern. To do.

In this embodiment, when the power is turned on, in order to detect the origin, the origin is detected by moving the stage 90 and searching for the origin pattern. When the origin detection pattern reaches the origin detection sensor 30 of the encoder 100, the fifth signal is sent to the controller 110 as the origin signal through the origin signal processing unit 50. The controller 110 that recognizes that the stage 90 is located on the origin by receiving the origin signal resets the detection position at this time to 0. As a result, the displacement can be detected with the origin detection pattern in the region where the origin detection pattern exists, and the stage 90 can be accurately controlled.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

10 scale
3 0 Origin detection sensor (origin detection unit)
31 Light receiving unit 50 Origin signal processing unit (processing unit)

Claims (7)

A scale on which an origin detection pattern is formed;
An origin detection unit for reading the origin detection pattern;
A processing unit for outputting an origin signal,
The origin detection unit has two sets of detection element groups,
The detecting element group, the first detector, a second detector, the third detector and the fourth detector possess, first detector and the second detector, the third detector And the fourth detection unit are arranged symmetrically with respect to the center of the detection element group, and in the detection element group, the first detection unit and the second detection unit are outside, the third detection unit Part and the fourth detection part are arranged inside,
The origin detection pattern has a detection direction in which a detection direction length of a physical characteristic different from that of the origin periphery detected by the origin detection unit is shorter than the detection direction length of the detection element group. Has a length,
The origin detection unit outputs a first signal based on the first detection unit and the third detection unit, and a second signal based on the second detection unit and the fourth detection unit. ,
The processing unit includes a third signal obtained by processing the first signal and the first threshold value, and a fourth signal obtained by processing the second signal and the second threshold value. And a fifth signal obtained by processing the signal, one detection element group of the two sets of detection element groups , wherein the origin detection pattern is adjacent between the two sets of detection element groups. The first signal obtained when facing the second detection unit arranged in the other detection element group of the first detection unit and the two detection element groups of the two sets of detection element groups, and By detecting the origin by detecting the signal change of the second signal, it is output as the origin signal,
An encoder characterized in that the output position of the origin signal can be adjusted by comparing the first threshold value or the second threshold value.   The processing unit outputs the fifth signal as the origin signal by detecting the origin when the first signal and the second signal are output to a higher voltage side than the center voltage. The encoder according to claim 1. A displacement detection unit that outputs a displacement detection signal by reading a displacement detection pattern formed on the scale;
The displacement detection pattern and the origin detection pattern are formed in different tracks,
The encoder according to claim 1 or 2, wherein the origin detection unit and the displacement detection unit read the origin detection pattern and the displacement detection pattern, respectively. A displacement detection unit that outputs a displacement detection signal by reading a displacement detection pattern having a resolution different from the resolution of the origin detection pattern formed on the scale;
The displacement detection pattern and the origin detection pattern are formed in the same track,
The encoder according to claim 1, wherein the origin detection unit and the displacement detection unit read an optical signal in which the reflected light from the displacement detection pattern and the reflected light from the origin detection pattern are combined. .   The encoder according to claim 3 or 4, wherein the origin signal is asynchronous with the displacement detection signal and is used for origin detection.   The encoder according to claim 3 or 4, wherein the origin signal is used to output an origin pulse used for origin detection in synchronization with the displacement detection signal.   The apparatus which has an encoder of any one of Claim 1 to 6.