Encoder

Abstract

To provide an encoder capable of cancelling influence of external noise to measure displacement with high accuracy.SOLUTION: An encoder 4 comprises a rotor 41, a stator 42, and calculation means 45. The stator 42 comprises an even number of detection means 43 for reading a scale 40 and outputting a signal. The calculation means 45 comprises a phase calculation unit 55 that calculates a phase based on the signal output by each of the detection means 43, and an averaging unit 56 that averages a phase calculated by the phase calculation unit 55 based on the signal output by each of the detection means 43. The even number of detection means 43 are arranged to be displaced from each of the adjacent detection means 43 along a measurement direction by an integer multiple of a period of the scale 40, and are configured so that a first signal S1 output by half of the even number of detection means 43 and a second signal S2 output by the remaining half of the detection means 43 have opposite polarities when input to the phase calculation unit 55.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an encoder. [Background technology]

[0002] Conventionally, there is known an encoder including a scale having graduations and a head that moves relatively along a measurement direction facing the scale. For example, an electromagnetic induction type rotary encoder disclosed in Patent Document 1 includes a stator provided with a transmission winding and a reception winding corresponding to the head, and a rotor provided with a magnetic flux coupler corresponding to the scale. In this electromagnetic induction type rotary encoder, a transmission current whose direction changes periodically flows through the transmission winding. The magnetic flux coupler generates an induced current based on a magnetic field generated by the transmission current flowing through the transmission winding. The reception winding detects a magnetic field generated by the induced current flowing through the magnetic flux coupler, and detects a signal according to the strength of the magnetic field.

[0003] In such encoders, noise can adversely affect detection performance. In Patent Document 2, the rotary encoder is placed near a motor or the like through which a large current flows. Since the motor wiring and the rotary encoder wiring are often passed through the same wiring tube, high-frequency noise generated when the motor is driven is induced in the power line of the rotary encoder. In position detection, if external noise is mixed into the power supply or high-frequency noise is mixed into the signal, the noise is superimposed on the detected signal, which may cause an error in position calculation. To address this problem, the rotary encoder of Patent Document 2 is equipped with noise suppression components that suppress the noise from being superimposed on the detected signal. However, when the driving output of the motor is large or the feedback frequency is high to increase the responsiveness of the driving output, the high-frequency noise from the driving current is also large, so the number of noise suppression components to be installed must be increased.

[0004] Moreover, high-frequency noise is induced in the analog circuit of the electrical equipment of the rotary encoder via the motor housing, the drive shaft, the rotary encoder housing, etc. The rotary encoder of Patent Document 3 attenuates the high-frequency noise induced in the analog circuit using a low-pass filter. However, in this case, the detected signal is also attenuated along with the noise, which may result in a deterioration in accuracy or an increase in flickering of the angle detection data.

[0005] As a method for suppressing noise from being superimposed on a detected signal without using noise suppression components and without attenuating the noise along with the detected signal, Patent Document 4 discloses a rotary encoder that arranges two detection sensors so that the signal outputs have a phase difference of 180° from each other, and cancels noise by averaging the position calculation results, which are the signals output from the two detection sensors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-322927 A [Patent Document 2] JP 2020-193887 A [Patent Document 3] JP 2020-134505 A [Patent Document 4] JP 2019-109093 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the rotary encoder of Patent Document 4, the physical distance between the two detection sensors must be (integer + 1 / 2) times the pitch of the scale, and it is difficult to obtain the effect of noise cancellation when the sensors are arranged at an interval that is an integer multiple of the pitch. Therefore, when using two detection sensors to cancel noise, the rotary encoder has a problem in that there are physical limitations and it may not be possible to cancel noise efficiently.

[0008] An object of the present invention is to provide an encoder capable of canceling the influence of external noise and measuring displacement with high accuracy. [Means for solving the problem]

[0009] The encoder of the present invention comprises a scale having graduations arranged at a predetermined period along a measurement direction, a head disposed opposite the scale and movable relative to the scale along the measurement direction, and a calculation means for calculating a relative displacement between the scale and the head. The head comprises an even number of detection means for reading the graduations and outputting a signal corresponding to the relative displacement between the scale and the head, the calculation means comprises a phase calculation unit for calculating a phase based on the signals output by each detection means, and an averaging unit for averaging the phases calculated by the phase calculation unit based on the signals output by each detection means, the even number of detection means being disposed at an integer multiple of the period of the scale from each of the adjacent detection means along the measurement direction, and configured such that a first signal output by half of the even number of detection means and a second signal output by the remaining half of the detection means have opposite polarities when input to the phase calculation unit.

[0010] According to the present invention, the first signal output by half of the even number of detection means and the second signal output by the remaining half of the detection means are configured to have opposite polarities when input to the phase calculation unit, and the calculated phases are averaged to cancel out the effects of external noise superimposed on the signal. Therefore, even in an environment where external noise is likely to occur, highly accurate displacement detection can be performed without the need for noise suppression components.

[0011] In this case, it is preferable that the encoder is an electromagnetic induction type encoder, the scale has a scale coil as a scale mark, and the head has a transmitting coil as a detection means for generating magnetic flux in the scale coil, and a receiving coil for receiving changes in magnetic flux from the scale coil.

[0012] With this configuration, even if the encoder is an electromagnetic induction type, it can cancel out the effects of external noise without having to be equipped with noise suppression components, so that highly accurate displacement detection can be performed without having to be equipped with noise suppression components, even in environments where external noise is likely to occur.

[0013] In the electromagnetic induction type encoder as described above, it is preferable that a transmission current flows in the opposite direction between the transmission coils in half of the plurality of detection means and the transmission coils in the remaining half.

[0014] With this configuration, the detection means can output signals such that the first signals output by half of the even number of detection means and the second signals output by the remaining half of the detection means have opposite polarity when input to the phase calculation unit, and the effects of external noise can be offset and cancelled out. Therefore, the encoder can perform highly accurate displacement detection without having to be equipped with noise suppression components, even in an environment where external noise is likely to occur.

[0015] In the present invention, it is preferable that half of the detection means and the remaining half are configured to output signals of the same polarity depending on the amount of relative displacement between the scale and the head, and that the polarity of the second signal is reversed to that of the first signal (i.e., the positive and negative signs of the signals are swapped) in the propagation path from the detection means to the input to the phase calculation section in the calculation means.

[0016] According to this configuration, the calculation means is configured so that the first signals output by half of the even number of detection means and the second signals output by the remaining half of the detection means have opposite polarities when input to the phase calculation unit, and the calculated phases are averaged to cancel out the effects of external noise superimposed on the signals. Therefore, even in an environment where external noise is likely to occur, highly accurate displacement detection can be performed without the need for noise suppression components. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a front view showing a digital micrometer according to a first embodiment. [Diagram 2] FIG. 2 is a schematic plan view showing the configuration of the rotor of the first embodiment. [Diagram 3] FIG. 2 is a schematic plan view showing the configuration of a stator according to the first embodiment. [Figure 4] FIG. 2 is a circuit block diagram showing a configuration of a calculation means according to the first embodiment. [Diagram 5] This figure shows the principle by which an error occurs in a calculation result due to external noise. Fig. 5(A) shows an example of a waveform of a two-phase signal at the input of a phase calculation unit 55. Fig. 5(B) shows a Lissajous waveform drawn from the two-phase signal shown in Fig. 5(A). [Figure 6]6 is a graph showing the principle of canceling out external noise. Fig. 6(A) shows an example of a waveform of a two-phase signal obtained from a first signal S1 detected by a first group of detection means. Fig. 6(B) shows an example of a waveform of a two-phase signal obtained from a second signal S2 detected by a second group of detection means. Figs. 6(C) and (D) show Lissajous waveforms drawn by the two-phase signals shown in Figs. 6(A) and (B), respectively. [Figure 7] FIG. 11 is a schematic plan view showing the configuration of a stator and a rotor according to a second embodiment. [Figure 8] FIG. 11 is a schematic diagram showing a calculation means of the second embodiment. [Figure 9] FIG. 11 is a schematic diagram showing a calculation means in a modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [First embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the following description, the same members are given the same reference numerals, and the description of members that have already been described will be omitted as appropriate.

[0019] 1 is a front view showing a digital micrometer 1 incorporating an encoder 4 according to an embodiment of the present invention. The encoder 4 is installed inside the digital micrometer 1 and detects the amount of change in movement of a probe 2.

[0020] 1, digital micrometer 1 includes a probe 2 and an encoder 4. Probe 2 has a structure in which a contact surface 22 is provided at one end of a cylindrical spindle 21. Contact surface 22 is a surface provided at the tip of spindle 21 for contacting the surface of a measurement target.

[0021] Digital micrometer 1 includes a thimble 31 and a ratchet knob 32 as mechanisms for moving contact point 2. Digital micrometer 1 moves spindle 21 toward and away from the measurement target by rotating thimble 31 or ratchet knob 32 around spindle 21 as an axis in the directions of the arrows in the figure.

[0022] The digital micrometer 1 further includes a clamp 11 for fixing the spindle 21, operation units 12a to 12c for receiving operations from a user and performing various setting operations on the digital micrometer 1, an anvil 13, and an arm unit .

[0023] The anvil 13 is a reference position in the digital micrometer 1, and is disposed opposite the contact surface 22 of the gauge head 2. The arm section 14 is formed in a substantially U-shape. The gauge head 2, a thimble 31, a ratchet knob 32, etc. are disposed on one end of the arm section 14. The anvil 13 is disposed on the other end of the arm section 14. The digital micrometer 1 measures the length from the contact surface 22 of the gauge head 2 to the anvil 13 on the object to be measured by sandwiching the object to be measured between the contact surface 22 of the gauge head 2 and the anvil 13.

[0024] The measurement results obtained by the digital micrometer 1, such as the measured value, are displayed on the display means 10. The display means 10 displays at least the measured value and is composed of a liquid crystal panel. The display means 10 mainly displays the measured value and the like on a seven-segment digital display.

[0025] 2 and 3 are schematic plan views showing the configuration of the encoder 4 of the present embodiment. The encoder 4 is an electromagnetic induction type rotary encoder, and includes a rotor 41, a stator 42, and a calculation means 45. The encoder 4 detects the amount of movement displacement of the probe 2 from a reference position (for example, the position where the contact surface 22 contacts the anvil 13).

[0026] 2, the rotor 41 has a scale coil 40 as a scale arranged in a measurement direction (circumferential direction) at a predetermined pattern period P. The rotor 41 faces the stator 42 and is rotatably provided around a rotation axis O.

[0027] The stator 42 corresponds to a head and is disposed opposite the rotor 41. As shown in Fig. 3, the stator 42 includes an even number of detection means 43 that detect the amount of displacement (i.e., the amount of rotational displacement) of the rotor 41 relative to the stator 42 and output a signal according to the amount of displacement. Each detection means 43 is disposed at a position shifted from an adjacent detection means 43 along the measurement direction by n times (n is a natural number equal to or greater than 1) the pattern period P of the scale coil 40. With this arrangement, each detection means 43 detects a common phase in the periodic pattern of the scale coil 40.

[0028] Each detection means 43 includes a transmitting coil 6 and a receiving coil 7. An AC transmitting current is applied to the transmitting coil 6 by a transmitting circuit 44. This transmitting current causes the transmitting coil 6 to generate an AC magnetic field. In the rotor 41, the scale coil 40 facing the transmitting coil 6 generates a magnetic flux so as to cancel out the AC magnetic field generated by the transmitting coil 6.

[0029] In this embodiment, a transmission current flows in the opposite direction between the transmitting coils 6 in half of the multiple detecting means 43 (hereinafter referred to as the first group) and the transmitting coils 6 in the remaining half (hereinafter referred to as the second group). That is, when a transmission current flows in the clockwise direction through the transmitting coils 6 in the first group, a transmission current flows in the counterclockwise direction through the transmitting coils 6 in the second group. In association with such a transmission current, the scale coils 40 of the rotor 41 that face the transmitting coils 6 in the first group and that face the transmitting coils 6 in the second group generate magnetic fluxes that are opposite in direction. Note that, since this embodiment is configured to have two detecting means 43, the first group and the second group each have one detecting means 43.

[0030] The receiving coil 7 receives the change in the magnetic flux generated by the scale coil 40 as a signal corresponding to the position (amount of displacement). The receiving coil 7 includes three sets of receiving coil wires 70 to receive a three-phase signal from the magnetic flux generated by excitation by the transmitting coil wire 60. That is, the receiving coil wires 70 include a first receiving coil wire 701 for receiving a signal SC1 with a phase of 0°, a second receiving coil wire 702 for receiving a signal SC2 with a phase of 120°, and a third receiving coil wire 703 for receiving a signal SC3 with a phase of 240°. In the following description, the signals SC1, SC2, and SC3 detected by the receiving coils 7 of the first group may be referred to as a first signal S1, and the signals SC1, SC2, and SC3 detected by the receiving coils 7 of the second group may be referred to as a second signal S2.

[0031] As described above, the scale coils 40 of the rotor 41 generate magnetic flux in opposite directions between the one facing the transmitting coils 6 of the first group and the one facing the transmitting coils 6 of the second group, so the first signal S1 detected by the receiving coils 7 of the first group and the second signal S2 detected by the receiving coils 7 of the second group have opposite polarities. The first signal S1 and the second signal S2 are input to the calculation means 45 and propagate within the calculation means 45 so that they have opposite polarities when input to the phase calculation unit 55.

[0032] 4 is a circuit block diagram showing the configuration of the calculation means 45 included in the encoder 4 of this embodiment. As shown in FIG. 4, the calculation means 45 includes a first amplifier 51, a three-phase to two-phase conversion circuit 52, a second amplifier 53, an A / D converter 54, a phase calculation unit 55, an averaging unit 56, and an output unit 57. Among these, the first amplifier 51, the three-phase to two-phase conversion circuit 52, the second amplifier 53, the A / D converter 54, and the phase calculation unit 55 are provided separately for each detection means 43. On the other hand, only one averaging unit 56 and one output unit 57 are provided in the calculation means 45. The calculation means 45 calculates the movement displacement amount of the probe 2 from the signal via the rotor 41 and the stator 42. The rotor 41 is provided so as to be movable relative to the stator 42 along the measurement direction.

[0033] The first amplifier 51 receives the signals S1 and S2 detected by the detection means 43, amplifies these signals, and outputs them. The first amplifier 51 is realized by using, for example, an operational amplifier. The three-phase to two-phase conversion circuit 52 converts the signals S1 and S2, which are three-phase signals through the first amplifier 51, into analog two-phase signals. The second amplifier 53 is an amplifier to which the signals converted into analog two-phase signals by the three-phase to two-phase conversion circuit 52 are input. The A / D converter 54 converts the analog two-phase signals through the second amplifier 53 into digital two-phase signals. The phase calculation unit 55 calculates the phase from the digital two-phase signals output by the A / D converter 54. As described above, the first amplifier 51, the three-phase to two-phase conversion circuit 52, the second amplifier 53, the A / D converter 54, and the phase calculation unit 55 are provided separately for each detection means 43 (i.e., separately for the signals S1 and S2), so that the phase calculated from the signal S1 and the phase calculated from the signal S2 are obtained.

[0034] The averaging unit 56 averages the phases calculated by each phase calculation unit 55, and further calculates the amount of displacement from the phase. The output unit 57 outputs the amount of displacement calculated by the averaging unit 56 to, for example, a display means 10 (see FIG. 1) such as a monitor, or a data storage device such as a personal computer.

[0035] FIG. 5 is a graph showing the principle of how an error occurs in the calculation result of the phase due to external noise. Specifically, FIG. 5(A) is a graph showing an example of the waveform of a two-phase signal at the input of the phase calculation unit 55 for a signal detected by the receiving coil 7. In FIG. 5(A), the vertical axis is the amplitude of the signal (digital signal value), and the horizontal axis is time. FIG. 5(B) shows a Lissajous waveform drawn by the two-phase signal shown in FIG. 5(A). The numbers 0 to 3 on the time axis of the graph in FIG. 5(A) correspond to the numbers 0 to 3 in the Lissajous waveform in FIG. 5(B). External noise N is superimposed on the signals DA1 and DB1 shown in FIG. 5(A) at time X. Although this does not apply to the micrometer 1 of this embodiment, in an implementation in which a motor that passes a large current is provided near the encoder 4, the motor wiring and the encoder wiring are often passed through the same wiring tube, and external noise N is easily superimposed on the signal detected by the receiving coil 7. This external noise N causes a sudden change in the waveform indicated as NR in the Lissajous waveform shown in FIG. 5(B), and causes an error NG in the phase calculated by the phase calculation unit 55.

[0036] In the encoder 4 of this embodiment, the phases calculated based on the signals detected by the detection means 43 are averaged to cancel errors caused by external noise N. Fig. 6 shows the principle by which errors caused by external noise N are canceled by averaging.

[0037] FIG. 6(A) shows an example of a waveform of a two-phase signal obtained from a first signal S1 detected by the detection means 43 of the first group. FIG. 6(B) shows an example of a waveform of a two-phase signal obtained from a second signal S2 detected by the detection means 43 of the second group. In FIG. 6(A) and (B), the vertical axis represents the amplitude of the two-phase signal, and the horizontal axis represents time. FIG. 6(C) and (D) show Lissajous waveforms drawn by the two-phase signals shown in FIG. 6(A) and (B), respectively. The numbers 0 to 3 on the time axis in FIG. 6(A) and (B) correspond to the numbers 0 to 3 in the Lissajous waveforms in FIG. 6(C) and (D). Lissajous waveform The signals S1 and S2 that are the source of the Lissajous waveforms in FIG. 6(C) and (D) have opposite polarities. Therefore, please note that the phases corresponding to the same time in the Lissajous waveforms in FIG. 6(C) and FIG. 6(D) are shifted by 180 degrees.

[0038] As shown in Figs. 6(A) and (B), an external noise N is superimposed on each two-phase signal at time X. When a Lissajous waveform is drawn based on the two-phase signals on which the noise N is superimposed, a fluctuation NR occurs in the Lissajous waveform due to the external noise N, as shown in Figs. 6(C) and (D), and an error NG occurs in the calculated phase. Since the external noise N superimposed on the two-phase signals at time X changes the amplitude to the positive as shown in Figs. 6(A) and (B), the Lissajous waveform fluctuates to the upper right due to the external noise N, as shown by NR in Figs. 6(C) and (D). The fluctuation of the Lissajous waveform due to the external noise N becomes an error NG that delays the phase in the Lissajous waveform based on the signal S1 (Fig. 6(C)). On the other hand, in the Lissajous waveform based on the signal S2 (Fig. 6(D)), it becomes an error NG that advances the phase. In this way, the phase calculated from signal S1 and the phase calculated from signal S2 have opposite effects on the phase, so the error NG can be cancelled out and removed by averaging the phase calculated from signal S1 and the phase calculated from signal S2. This allows the encoder 4 to remove the effects of external noise and calculate the amount of displacement with high accuracy.

[0039] According to the first embodiment, the following actions and effects can be achieved. (1) The first signal S1 output by half of the even number of detection means 43 and the second signal S2 output by the remaining half of the detection means 43 are configured to have opposite polarities when input to the phase calculation unit 55, and the calculated phases are averaged to cancel out the effects of external noise superimposed on the signals S1 and S2. Therefore, the encoder 4 can perform highly accurate displacement detection without having to be equipped with noise suppression components, even in an environment where external noise is likely to occur.

[0040] (2) By configuring the current flowing through the transmitting coil 6 in the detection means 43 of the first group and the current flowing through the transmitting coil 6 in the detection means 43 of the second group to be in the opposite direction, and simply averaging the phase calculated based on the signals detected by the multiple detection means 43, the effects of external noise can be canceled out without making any major changes to the configuration of the conventional encoder.

[0041] Second Embodiment A second embodiment of the present invention will now be described with reference to the drawings. In the following description, parts that have already been described will be given the same reference numerals and descriptions thereof will be omitted.

[0042] FIG. 7 is a schematic plan view showing the configuration of a stator and a rotor in an encoder 4A of this embodiment. In the first embodiment, the encoder 4 is an electromagnetic induction type rotary encoder, but in the second embodiment, the encoder 4A is an optical rotary encoder, which is different from the first embodiment. As shown in FIG. 7, the rotor 41A and the stator 42A in the encoder 4A have a configuration substantially similar to that of a conventional optical rotary encoder. That is, the rotor 41A forms a scale on whose surface a scale 40A is engraved in an annular shape with a predetermined period P. The stator 42A has an even number of detection means 43A. Each detection means 43A is disposed at a position shifted from the adjacent detection means 43A along the measurement direction by n times the period P of the scale 40A (n is a natural number equal to or greater than 1). With this arrangement, each detection means 43A detects a common phase in the periodic pattern of the scale 40A, and half of the detection means 43A and the other half (i.e. all of the detection means 43A) output signals of the same polarity depending on the relative displacement between the scale and the head.

[0043] Each detection means 43A includes a light source 6A that irradiates light onto the scale 40A, and a light receiving unit 7A that receives the light that has passed through the scale 40A and outputs a signal according to the position (amount of displacement). The signal output by the light receiving unit 7A is input to the calculation means 45A.

[0044] FIG. 8 is a schematic diagram showing the calculation means 45A of the second embodiment. As shown in FIG. 8, the calculation means 45A has a configuration substantially similar to that of the calculation means 45 of the first embodiment shown in FIG. 4. As shown in FIG. 8, in the calculation means 45A, the signals S1 from half of the even number of detection means 43A are input to the first amplifier 51 without any particular processing. On the other hand, the signals S2 from the remaining half of the even number of detection means 43A are input to the first amplifier 51 with the polarity of the signal reversed (positive and negative switched) as shown by K1 in FIG. 8. In this way, the signal S1 from the detection means 43A of the first group and the signal S2 from the detection means 43A of the second group propagate through the calculation means 45A so that they have opposite polarities when input to the phase calculation unit 55. As a result, as in the first embodiment, even if external noise is superimposed on the signal, the influence of the external noise can be removed by averaging the phase calculated by the phase calculation unit 55. Therefore, the encoder 4A can calculate the amount of displacement with high accuracy even in an environment where external noise is likely to occur.

[0045] FIG. 9 is a schematic diagram showing a calculation means 45B in a modified example of the second embodiment. This calculation means 45B can be replaced with the calculation means 45A of the second embodiment. In the calculation means 45A (see FIG. 8), as shown by K1 in FIG. 8, the polarity of the signal S2 from the detection means 43A of the second group is reversed from that of the signal from the first group at the input part of the first amplifier 51. However, the position where the polarity of the signal is reversed may be between the three-phase to two-phase conversion circuit 52 and the second amplifier 53, as shown by K2 in FIG. 9, instead of the input part of the first amplifier 51. In this case, the calculation means 45B converts the signal S2 from the detection means 43A of the second group into a two-phase signal in the three-phase to two-phase conversion circuit 52 while keeping the polarity the same as that of the signal S1 from the detection means 43A of the first group, and inputs the converted two-phase signal to the second amplifier 53 by switching the polarity. In this way, the signal S1 from the detection means 43A of the first group and the signal S2 from the detection means 43A of the second group propagate through the calculation means 45B so that they have opposite polarities when input to the phase calculation unit 55. As a result, even in this modification, even if external noise is superimposed on the signal, the influence of the external noise can be removed by averaging the phase calculated by the phase calculation unit 55. Therefore, the encoder 4A can calculate the displacement amount with high accuracy even in an environment where external noise is likely to occur. Note that the position where the polarity of the signal is reversed may be other than that shown in the second embodiment and its modification, as long as the polarity of the second signal is reversed to that of the first signal (i.e., the positive and negative of the signal are reversed) in the propagation path from the detection means to the input to the phase calculation unit in the calculation means.

[0046] In this embodiment as well, the same advantageous effect as that of (1) in the first embodiment can be achieved.

[0047] [Modifications of the embodiment] The present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of the present invention are included in the present invention. For example, in the above-described embodiments, the device in which the encoder 4, 4A is used is a digital micrometer 1, but it may be an indicator, a vernier caliper, or another measuring device such as an encoder, or any device other than a measuring device. In the above-described embodiments, the encoder 4, 4A is a rotary encoder, but it may be a linear encoder. In the second embodiment, the encoder 4A is an optical type, but any type such as an electromagnetic induction type, a magnetic type, or a capacitance type may be used.

[0048] In each of the above-mentioned embodiments, the receiving coil 7 and the light receiving unit 7A detect a three-phase signal, but the signal they output may be a two-phase signal or a four-phase signal instead of a three-phase signal. The calculation means 45, 5A in each of the above-mentioned embodiments includes a three-phase to two-phase conversion circuit 52, but when a four-phase signal is handled, a four-phase to two-phase conversion circuit may be provided, and when a two-phase signal is handled, the conversion circuit may not be provided.

[0049] In the above embodiments, the rotor corresponding to the scale moves relative to the stator corresponding to the fixed head, but the head may move relative to the fixed scale. That is, it is sufficient that one of the scale and the head is provided so as to be movable relative to the other in the measurement direction. In the case of a linear encoder or the like, a configuration in which the head moves relative to a fixed scale is common.

[0050] Furthermore, any combination of features of the above-described embodiments, in which a person of ordinary skill in the art has appropriately added or deleted components or modified the design, is also included within the scope of the present invention as long as it contains the gist of the present invention. [Industrial Applicability]

[0051] As described above, the present invention can be suitably applied to an encoder used in a noisy environment. [Explanation of symbols]

[0052] Measuring instrument (digital micrometer) 1 Probe 2 Encoder 4 Scale 40 Scale (Rotor) 41 Head (stator) 42 Calculation method 5,5A~5B Detection means 6, 6A, 7, 7A Phase calculation section 55 Averaging section 56

Claims

1. An encoder comprising: a scale having graduations arranged at a predetermined period along a measurement direction; a head disposed opposite to the scale and movable relative to the scale along the measurement direction; and a calculation means for calculating a relative displacement amount between the scale and the head, The head is an even number of detection means for reading the graduations and outputting a signal corresponding to the amount of relative displacement between the scale and the head; The calculation means is a phase calculation unit that calculates a phase based on signals output from each of the detection means; an averaging unit that averages the phases calculated by the phase calculation unit based on the signals output by the individual detection means, the even number of detection means are disposed so as to be shifted from each other adjacent detection means along the measurement direction by an integer multiple of the period of the scale, An encoder characterized in that a first signal output by half of the even number of detection means and a second signal output by the remaining half of the detection means are configured to have opposite polarities when input to the phase calculation unit.

2. the encoder is an electromagnetic induction type encoder, The scale is A scale coil is provided as the scale, The head includes the detection means: a transmission coil for generating a magnetic flux in the scale coil; 2. The encoder according to claim 1, further comprising a receiver coil for receiving the change in magnetic flux from the scale coil.

3. 3. The encoder according to claim 2, wherein a transmission current flows in an opposite direction between the transmission coils in half of the detection means and the transmission coils in the remaining half of the detection means.

4. half of the detection means and the remaining half output signals of the same polarity in response to the amount of relative displacement between the scale and the head; 3. The encoder according to claim 1, wherein the polarity of the second signal is made opposite to that of the first signal in a propagation path from the detection means to an input to the phase calculation section in the calculation means.

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