Encoder

Abstract

To provide a technique of increasing the power generation efficiency of an encoder.SOLUTION: An encoder includes: a power generation element; a magnetic sensor; a first magnet near the magnetic sensor, the first magnet rotating around the axis of rotation and being rotationally symmetric; and a second magnet near the power generation element, the second magnet rotating around the axis of rotation, being rotationally symmetric, and being continuous in the circumferential direction.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to an encoder.

Background Art

[0002] Patent Document 1 discloses a rotation detector that detects the amount of rotation of a rotation shaft of a motor. Patent Document 1 discloses that the rotation detector includes a power generation magnet that is rotatably attached to the rotation shaft and has four or more magnetic poles in the outer circumferential direction, at least one power generation element including a magnetosensing portion and an induction coil, a first magnetic sensor, and a second magnetic sensor. Further, Patent Document 1 discloses that the rotation detector further includes a magnetic flux control member that changes its position together with the power generation magnet by the rotation of the rotation shaft and generates an exciting voltage in at least one of the first magnetic sensor and the second magnetic sensor. Patent Document 1 discloses that the rotation detector drives the first magnetic sensor and the second magnetic sensor with the electric power generated by the power generation element when the power generation magnet rotates.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a battery-less encoder, a power generation element that generates power using the Barkhausen effect may be used. In the power generation element, it is required to improve the power generation efficiency.

[0005] The present disclosure provides a technique for increasing the power generation efficiency in an encoder.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, there is provided an encoder including a power generation element, a magnetic sensor, a rotationally symmetric first magnet that rotates about a rotation axis and is provided near the magnetic sensor, and a rotationally symmetric second magnet that rotates about the rotation axis, is provided near the power generation element, and is provided continuously in the circumferential direction.

Advantages of the Invention

[0007] According to the encoder of the present disclosure, the power generation efficiency can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

[0009] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that, regarding the descriptions in the specification and drawings according to each embodiment, for components having substantially the same or corresponding functional configurations, the same reference numerals may be given, and redundant descriptions may be omitted. In addition, for ease of understanding, the scales of each part in the drawings may be different from the actual ones.

[0010] ≪First Embodiment≫ The encoder according to the first embodiment will be described. The encoder according to the first embodiment includes a power generation element, a magnetic sensor, a rotationally symmetric first magnet that rotates about a rotation axis and is provided near the magnetic sensor, and a rotationally symmetric second magnet that rotates about the rotation axis, is provided near the power generation element, and is continuously provided in the circumferential direction.

[0011] <Servo Motor System> First, a servo motor system using the encoder according to the present embodiment will be described. FIG. 1 is a diagram for explaining a servo motor system 1 using an encoder 12 which is an example of the encoder according to the first embodiment.

[0012] The servo motor system 1 includes a servo motor 10 and a servo controller 20. The servo controller 20 acquires at least one of the position information and the rotation information of the rotation shaft 11a from the servo motor 10. The servo controller 20 controls the servo motor 10 using at least one of the acquired position information and rotation information.

[0013] The servo motor 10 includes a motor 11 and an encoder 12. The motor 11 is connected to the servo controller 20 via the wiring L1. The encoder 12 is connected to the servo controller 20 via the wiring L2.

[0014] The motor 11 rotates the rotating shaft 11a in the direction of the arrow AR based on a command from the servo controller 20. Specifically, the motor 11 rotates the rotating shaft 11a in the direction of the arrow AR based on the electric power supplied from the servo controller 20. The servo controller 20 controls the motor 11 by supplying the controlled electric power from the wiring L1. The motor 11 is, for example, an AC (Alternating Current) motor, a DC (Direct Current) motor, or the like.

[0015] The encoder 12 detects a change in the magnetic field and detects at least one of the position information and rotation information of an object such as the rotating shaft 11a of the motor 11. Further, the encoder 12 outputs at least one of the detected position information and rotation information to the servo controller 20 via the wiring L2. Note that the position information of the rotating shaft 11a is, for example, the angle in the rotation direction of the rotating shaft 11a. The rotation information of the rotating shaft 11a is, for example, the rotation speed of the rotating shaft 11a or the number of rotations indicating how many rotations the rotating shaft 11a has made since a predetermined time point.

[0016] <Servo motor 10> Next, the configuration of the servo motor 10 using the encoder 12, which is an example of the encoder according to the first embodiment, will be described. FIG. 2 is a diagram for explaining the configuration of the servo motor 10 using the encoder 12, which is an example of the encoder according to the first embodiment. Note that the line with an arrow indicates the flow of power or current supply.

[0017] [Motor 11] The motor 11 rotates the rotary shaft 11a. The motor 11 includes well-known elements such as a bearing that supports the rotary shaft 11a, a winding that constitutes a stator for rotating the rotary shaft 11a, an iron core, and a permanent magnet that constitutes a rotor, but the description thereof is omitted here. The motor 11 includes a disk 11d provided on the encoder 12 side of the rotary shaft 11a. As will be described later, a first magnet 12m1 provided symmetrically with respect to the rotary shaft 11a and a second magnet 12m2 provided side by side continuously in the circumferential direction of the rotary shaft 11a are attached onto the disk 11d. The first magnet 12m1 and the second magnet 12m2 rotate about the rotary shaft 11a.

[0018] The disk 11d is fixed to the rotary shaft 11a. The disk 11d rotates together with the rotary shaft 11a as it rotates in the direction of the arrow AR of the rotary shaft 11a. The first magnet 12m1 and the second magnet 12m2 are fixed to the surface of the disk 11d on the encoder 12 side.

[0019] Each of the first magnet 12m1 and the second magnet 12m2 is a permanent magnet formed of neodymium or the like. When each of the first magnet 12m1 and the second magnet 12m2 rotates together with the disk 11d, the magnetic field on the encoder 12 side changes.

[0020] The first magnet 12m1 is provided so as to have an N pole and an S pole in a direction parallel to the surface of the disk 11d. The first magnet 12m1 generates a magnetic field detected by each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2.

[0021] The second magnet 12m2 generates a magnetic field for generating electricity in the power generation element 12g. The second magnet 12m2 is provided continuously in the circumferential direction of the rotary shaft 11a. Details of the second magnet 12m2 will be described later.

[0022] [Encoder 12] The encoder 12 will be described. The encoder 12 detects at least one of the position information and the rotation information of the rotation shaft 11a by a magnetic field that changes due to the rotation of the first magnet 12m1 and the second magnet 12m2. The encoder 12 is an absolute encoder. The encoder 12 operates as at least a multi-turn encoder. That is, the encoder 12 counts how many rotations the rotation shaft 11a has made. Also, the encoder 12 generates the electric power necessary to operate the encoder 12 by a magnetic field that changes due to the rotation of the second magnet 12m2.

[0023] The encoder 12 includes a power generation element 12g, a rectifier circuit 12a, a stabilized power supply circuit 12b, and a polarity detection circuit 12d. The encoder 12 also includes drive circuits 12e1 and 12e2, first magnetic sensors 12h1 and 12h2, signal processing circuits 12f1 and 12f2, a control circuit 12p, and a storage unit 12r. Furthermore, the encoder 12 includes a first magnet 12m1 and a second magnet 12m2. Note that the rectifier circuit 12a and the stabilized power supply circuit 12b are collectively referred to as a power supply circuit 12n. Also, the polarity detection circuit 12d, the drive circuits 12e1 and 12e2, the signal processing circuits 12f1 and 12f2 are collectively referred to as a rotation detection circuit 12k.

[0024] The encoder 12 includes a power generation element 12g that generates electricity by a change in magnetic flux due to movement, and first magnetic sensors 12h1 and 12h2 that measure a magnetic field. Each of the power generation element 12g, the first magnetic sensor 12h1, and the second magnetic sensor 12h2 is provided on the motor 11 side of the encoder 12 so as to be easily affected by the magnetic field generated by the first magnet 12m1 and the second magnet 12m2.

[0025] [Power generation element 12g] The power generation element 12g is an element that converts magnetic energy into an electric pulse to generate electricity. The power generation element 12g is a power generation element that generates electricity by utilizing the Barkhausen effect. The power generation element 12g is, for example, a Wiegand wire which is an environmental power generator (EHG: Energy Harvest Generator).

[0026] The power generation element 12g includes a hard core and a soft layer wound around the hard core. The hard core is formed of a material with a large coercive force. The soft layer is formed of a material with a small coercive force. When the direction of the external magnetic field is reversed, a power generation pulse is generated in the power generation element 12g.

[0027] For example, the Wiegand wire generates an electric pulse near the zero point where the external magnetic field is reversed, regardless of the change rate of the external magnetic flux. Therefore, the Wiegand wire generates a constant power regardless of the rotation speed of the rotation axis 11a. The Wiegand wire generates a stable electric pulse (voltage pulse) even with a gentle magnetic flux change due to a low-speed rotation (movement). An electric pulse is generated in the Wiegand wire at the timing when the magnetic field is reversed.

[0028] In the power generation element 12g, by using an environmental power generator, the encoder 12 does not require a battery or an external power source. That is, the encoder 12 is a battery-less encoder. Since the Wiegand wire generates a constant power regardless of the rotation speed of the rotation axis 11a, and a stable power generation waveform can be obtained especially at low-speed rotation, it is suitable for use as the power generation element 12g of the encoder 12 which is a battery-less encoder.

[0029] Note that the power generation element 12g is not limited to the Wiegand wire, and any power generation element that generates electricity by utilizing the Barkhausen effect may be used.

[0030] The power generation element 12g generates electricity by the magnetic field of the second magnet 12m2.

[0031] [First Magnetic Sensor 12h1 and Second Magnetic Sensor 12h2] Each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 detects a magnetic field. More specifically, each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 detects the magnetic field generated by the first magnet 12m1 described later.

[0032] Each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 is, for example, a Hall element. The Hall element detects a magnetic field across a semiconductor element through which a drive current flows. In the encoder 12, each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 mainly detects the magnetic field generated by the first magnet 12m1. The Hall elements constituting each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 are constituted by semiconductor elements such as indium antimonide (InSb) and gallium arsenide (GaAs), for example. The Hall element outputs a voltage proportional to the drive current and the magnetic flux density across the drive current.

[0033] The first magnetic sensor 12h1 outputs a detection signal of the magnetic field to the signal processing circuit 12f1. The first magnetic sensor 12h1 is supplied with a constant current Idr from the drive circuit 12e1. Also, the second magnetic sensor 12h2 outputs a detection signal of the magnetic field to the signal processing circuit 12f2. The second magnetic sensor 12h2 is supplied with a constant current Idr from the drive circuit 12e2.

[0034] The first magnetic sensor 12h1 is supplied with the electric power generated by the power generation element 12g, rectified by the rectifier circuit 12a, and further converted into a constant current (constant current Idr) by the drive circuit 12e1. Also, the second magnetic sensor 12h2 is supplied with the electric power generated by the power generation element 12g, rectified by the rectifier circuit 12a, and further converted into a constant current (constant current Idr) by the drive circuit 12e2.

[0035] The second magnetic sensor 12h2 has a magnetic sensitivity direction with a 90-degree phase difference from that of the first magnetic sensor 12h1. The encoder 12 has magnetic sensitivity directions with a 90-degree phase difference from each other due to the first magnetic sensor 12h1 and the second magnetic sensor 12h2. In other words, the magnetic sensors (the first magnetic sensor 12h1 and the second magnetic sensor 12h2) in the encoder 12 have magnetic sensitivity directions with a 90-degree phase difference from each other.

[0036] Note that the encoder 12 includes two magnetic sensors, but the number of magnetic sensors is not limited to two. The encoder 12 may include three or more magnetic sensors. Also, the measurement of the magnetic field is not limited to the Hall element as long as it is an element (magnetic detection element) capable of detecting magnetism. For example, a magnetoresistive effect element or the like may be used as the magnetic sensor.

[0037] The circuit configuration of the encoder 12 will be described with reference to FIG. 3. FIG. 3 is a diagram for explaining the circuit configuration of the encoder 12 which is an example of the encoder according to the present embodiment.

[0038] [Rectifier circuit 12a] The rectifier circuit 12a rectifies the power generated by the power generation element 12g to generate a positive voltage. The rectifier circuit 12a includes a full-wave rectifier circuit 12a1 and a capacitor 12a2.

[0039] The full-wave rectifier circuit 12a1 rectifies the positive and negative pulses of the voltage Vgn generated by the power generation element 12g into positive pulses. The full-wave rectifier circuit 12a1 is a so-called diode bridge circuit. For example, when the power generation element 12g is a Weigand wire, the power generation element 12g generates positive and negative pulses. The full-wave rectifier circuit 12a1 converts the positive and negative pulses generated by the power generation element 12g into positive pulses.

[0040] The capacitor 12a2 stores the electric power generated by the power generation element 12g. Further, the capacitor 12a2 smoothes the positive pulse generated by the full-wave rectifier circuit 12a1. The capacitor 12a2 is provided between the output terminal of the full-wave rectifier circuit 12a1 and the common potential. By smoothing the positive pulse by the capacitor 12a2, a smoothed voltage Vrc is output from the rectifier circuit 12a.

[0041] [Stabilized power supply circuit 12b] The stabilized power supply circuit 12b outputs the voltage output from the rectifier circuit 12a as a substantially constant voltage. The stabilized power supply circuit 12b includes a regulator 12b1. The regulator 12b1 is, for example, an LDO (Low Dropout) regulator.

[0042] When a voltage of a predetermined magnitude is input to the stabilized power supply circuit 12b, a substantially constant voltage Vdd is output.

[0043] [Polarity detection circuit 12d] The polarity detection circuit 12d detects the polarity of the electric power generated by the power generation element 12g. FIG. 4 is a diagram for explaining the circuit configuration of the polarity detection circuit 12d in the encoder 12. The polarity detection circuit 12d includes a comparator 12d1, a filter circuit 12d2, and a diode 12d3. The diode 12d3 prevents current from flowing from the polarity detection circuit 12d to the power generation element 12g. The filter circuit 12d2 is a low-pass filter including a resistor 12d2a and a capacitor 12d2b.

[0044] Comparator 12d1 compares the voltage Vgns with a reference potential (reference potential Vref2) and outputs the comparison result to the control circuit 12p. Comparator 12d1 is a so-called comparator. Comparator 12d1 includes a differential amplifier 12d1a, a resistor 12d1b, a resistor 12d1c, and a resistor 12d1d. The differential amplifier 12d1a is supplied with power of voltage Vdd from the stabilization power supply circuit 12b. The differential amplifier 12d1a compares the voltage Vgns obtained by smoothing the output voltage Vgn of the power generation element 12g by the filter circuit 12d2 with the reference potential Vref2 generated by dividing the voltage Vdd with the resistor 12d1c and the resistor 12d1d. Then, the differential amplifier 12d1a outputs the comparison result to the control circuit 12p as a polarity signal Spl which is a voltage signal. Resistor 12d1b is a feedback resistor.

[0045] [Drive circuits 12e1 and 12e2] Drive circuits 12e1 and 12e2 are so-called constant current circuits that supply a constant current Idr to the first magnetic sensor 12h1 and the second magnetic sensor 12h2, respectively. Each of drive circuits 12e1 and 12e2 operates as a constant current source. Encoder 12 drives each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2, which are Hall elements, with the constant current Idr.

[0046] Drive circuit 12e1 supplies drive power to the first magnetic sensor 12h1 so that a constant current flows as a drive current through the first magnetic sensor 12h1 which is a Hall element. Also, drive circuit 12e2 supplies drive power to the second magnetic sensor 12h2 so that a constant current flows as a drive current through the second magnetic sensor 12h2 which is a Hall element.

[0047] FIG. 5 is a diagram for explaining the circuit configurations of the drive circuit and the magnetic sensor in the encoder 12 which is an example of the encoder according to the present embodiment. Since the drive circuit 12e1 and the drive circuit 12e2 have the same circuit configuration, in FIG. 5, each of the drive circuit 12e1 and the drive circuit 12e2 will be described as the drive circuit 12e. Further, in FIG. 5, each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 which are Hall elements is equivalently shown as the magnetic sensor 12h using a bridge circuit including resistors 12ha, 12hb, 12hc, and 12hd.

[0048] The drive circuit 12e includes a transistor 12ea, a current detection resistor 12eb, and a differential amplifier 12ec. The drive circuit 12e also includes a resistor 12ed, a Zener diode 12ee, and a capacitor 12ef.

[0049] The transistor 12ea is controlled so that a constant current flows through the magnetic sensor 12h. The output terminal of the differential amplifier 12ec is connected to the gate terminal of the transistor 12ea. The differential amplifier 12ec outputs a voltage based on the potential difference between the + terminal and the - terminal from the output terminal. The drive circuit 12e is controlled so that a voltage input to the + terminal and a constant current (constant current Idr) based on the resistance value of the current detection resistor 12eb flow between the drain and the source of the transistor 12ea.

[0050] The magnetic sensor 12h is driven by the constant current Idr and outputs a voltage Vh+ and a voltage Vh- that are proportional to the constant current Idr and the magnetic flux density crossing the magnetic sensor 12h.

[0051] Note that the drive circuit 12e is driven by the voltage Vdd supplied from the stabilization power supply circuit 12b.

[0052] [Signal processing circuits 12f1 and 12f2] The signal processing circuits 12f1 and 12f2 respectively process the detection signals from the first magnetic sensor 12h1 and the second magnetic sensor 12h2 to detect the direction of the magnetic field of the first magnet 12m1. Also, the signal processing circuits 12f1 and 12f2 output the magnetic field intensity of the first magnet 12m1 to the control circuit 12p based on the detection signals from the first magnetic sensor 12h1 and the second magnetic sensor 12h2 respectively. The signal processing circuits 12f1 and 12f2 will be described with reference to FIG. 3. Since the signal processing circuits 12f1 and 12f2 have the same circuit configuration, in FIG. 3, the signal processing circuit 12f1 will be used for the description.

[0053] The signal processing circuit 12f1 includes a differential amplifier 12fa, a comparator 12fb, and a quantizer 12fc.

[0054] (Differential amplifier 12fa) The differential amplifier 12fa amplifies the potential difference between the voltage Vh+ and the voltage Vh- output from the magnetic sensor 12h and outputs the amplified voltage Vd to the comparator 12fb. The differential amplifier 12fa is supplied with power of the voltage Vdd from the stabilization power supply circuit 12b.

[0055] (Comparator 12fb) The comparator 12fb compares the voltage Vd output from the differential amplifier 12fa with a reference potential (reference potential Vref) and outputs the comparison result to the control circuit 12p. The comparator 12fb is a so-called comparator. The comparator 12fb includes a differential amplifier 12fb1, resistors 12fb2, 12fb3, and 12fb4. The differential amplifier 12fb1 is supplied with power of the voltage Vdd from the stabilization power supply circuit 12b. The differential amplifier 12fb1 compares the voltage Vd of the output of the differential amplifier 12fa with the reference potential Vref generated by dividing the voltage Vdd with the resistors 12fb3 and 12fb4, and outputs the comparison result to the control circuit 12p as a magnetic pole signal Smg1 which is a voltage signal. The resistor 12fb2 is a feedback resistor.

[0056] (Quantizer 12fc) The quantizer 12fc quantizes the voltage Vd output from the differential amplifier 12fa and outputs the quantization result to the control circuit 12p. The quantizer 12fc is a so-called analog / digital converter (AD converter). The quantizer 12fc quantizes the voltage Vd output from the differential amplifier 12fa and outputs, for example, an 8-bit digital value as a magnetic field intensity signal Dmg1 to the control circuit 12p.

[0057] [Control Circuit 12p] Based on the inputs from the polarity detection circuit 12d, the signal processing circuit 12f1, and the signal processing circuit 12f2 respectively, the control circuit 12p calculates at least one of the position information and the rotation information such as the rotation position and the rotation speed of the rotation shaft 11a of the motor 11. Further, the control circuit 12p records at least one of the detected position information and the rotation information of the rotation shaft 11a of the motor 11 or transmits it to an external control system, for example, a servo controller 20.

[0058] The control circuit 12p is, for example, a microcomputer, an ASIC (application specific integrated circuit), etc. Also, the control circuit 12p may be, for example, an FPGA (Field-Programmable Gate Array), a PLD (Programmable Logic Device), etc.

[0059] The control circuit 12p is connected to a storage unit 12r provided externally. Note that the control circuit 12p may be provided internally with a non-volatile memory such as a ferroelectric memory instead of the external storage unit 12r.

[0060] The control circuit 12p includes at least a terminal PWR, a terminal SIG1, a terminal row SIG1d, a terminal SIG2, a terminal row SIG2d, and a terminal SIG3.

[0061] The terminal PWR of the control circuit 12p is a terminal to which a plus-side power supply is supplied. Electric power of voltage Vdd is supplied from the stabilized power supply circuit 12b to the terminal PWR. The control circuit 12p operates when electric power is supplied to the terminal PWR.

[0062] Each of the terminals SIG1, SIG2, and SIG3 of the control circuit 12p is a terminal to which a signal is input from the outside. The terminal rows SIG1d and SIG2d of the control circuit 12p are terminal rows to which a multi-bit signal is input from the outside.

[0063] The terminal SIG1 is connected to the signal processing circuit 12f1. From the terminal SIG1, a magnetic pole signal Smg1, which is a detection result detected by the signal processing circuit 12f1, is input. The magnetic pole signal Smg1 is a signal indicating the direction of the magnetic field detected by the first magnetic sensor 12h1. The terminal SIG2 is connected to the signal processing circuit 12f2. From the terminal SIG2, a magnetic pole signal Smg2, which is a detection result detected by the signal processing circuit 12f2, is input. The magnetic pole signal Smg2 is a signal indicating the direction of the magnetic field detected by the second magnetic sensor 12h2.

[0064] The terminal row SIG1d is connected to the signal processing circuit 12f1. From the terminal row SIG1d, a magnetic field intensity signal Dmg1, which is a detection result detected by the signal processing circuit 12f1, is input. The magnetic field intensity signal Dmg1 is a signal indicating the intensity of the magnetic field detected by the first magnetic sensor 12h1. The terminal row SIG2d is connected to the signal processing circuit 12f2. From the terminal row SIG2d, a magnetic field intensity signal Dmg2, which is a detection result detected by the signal processing circuit 12f2, is input. The magnetic field intensity signal Dmg2 is a signal indicating the intensity of the magnetic field detected by the second magnetic sensor 12h2.

[0065] The terminal SIG3 is connected to the polarity detection circuit 12d. From the terminal SIG3, a polarity signal Spl, which is a detection result detected by the polarity detection circuit 12d, is input. The polarity signal Spl is a signal indicating the power generation polarity of the power generation element 12g.

[0066] The encoder 12 counts the number of rotations of the rotating shaft 11a. The control circuit 12p counts the number of rotations of the rotating shaft 11a using the magnetic pole signal Smg1 and the polarity signal Spl. Further, the control circuit 12p uses the magnetic pole signal Smg1 and the polarity signal Spl to detect in which region of the regions obtained by dividing one rotation of the rotating shaft 11a into 90-degree intervals the rotating shaft 11a is located. Then, the control circuit 12p stores the result of counting the number of rotations of the rotating shaft 11a and the result of detecting in which region the rotating shaft is located in the storage unit 12r. Also, the control circuit 12p stores the last detected magnetic pole signal Smg1, magnetic pole signal Smg2, and polarity signal Spl in the storage unit 12r.

[0067] Further, the control circuit 12p obtains the rotation angle of the rotating shaft 11a using the magnetic field intensity signal Dmg1 and the magnetic field intensity signal Dmg2. For example, the control circuit 12p calculates the rotation angle of the rotating shaft 11a from the ratio of the magnetic field intensity signal Dmg1 to the magnetic field intensity signal Dmg2 using the arctangent function.

[0068] [Storage unit 12r] The storage unit 12r stores, for example, the rotation count and the like. The storage unit 12r is, for example, a ferroelectric memory. The control circuit 12p stores in the storage unit 12r at least the count value indicating the number of rotations of the rotating shaft 11a, the position of the rotating shaft, and the last detected magnetic pole signal Smg1, magnetic pole signal Smg2, and polarity signal Spl.

[0069] <Configuration of the encoder> The configuration of the encoder 12 will be described in detail. The magnet in the encoder 12 will be described.

[0070] The magnet included in the encoder 12 will be described. FIG. 6 is a plan view for explaining the configuration of the magnet in the encoder 12 which is an example of the encoder according to the first embodiment. FIG. 7 is a cross-sectional view for explaining the configuration of the magnet in the encoder 12 which is an example of the encoder according to the first embodiment. In FIG. 6, in order to indicate the polarity of the magnet, the direction of the magnetic flux is indicated by an arrow. The disk 11d is fixed to the rotation axis 11a and rotates in synchronization with the rotation of the rotation axis 11a. FIG. 6 is a diagram showing the arrangement of the magnets at a certain point in time. Note that the rotation axis 11a extends in a direction perpendicular to the plane of the paper in FIG. 6 (see FIG. 7). In FIG. 6, the counterclockwise angle θ is shown.

[0071] The encoder 12 includes a rotationally symmetric first magnet 12m1 provided on the disk 11d, and a rotationally symmetric second magnet 12m2 provided outside with respect to the rotation axis of the first magnet 12m1. The first magnet 12m1 is composed of two poles, an S pole and an N pole, and is a one-rotationally symmetric magnet. In the present embodiment, the second magnet 12m2 is composed of four poles and is a two-rotationally symmetric magnet. By making the first magnet 12m1 and the second magnet 12m2 rotationally symmetric in this way, there is an effect that the rotational torque (moment) is smaller than that of a rotationally asymmetric magnet, and the load on the motor 11 is reduced.

[0072] Also, the encoder 12 includes a magnetic body 15 between the first magnet 12m1 and the second magnet 12m2. By providing the magnetic body 15, the encoder 12 can suppress the magnetic forces of the first magnet 12m1 and the second magnet 12m2 from interfering with each other and weakening the magnetic field.

[0073] The encoder 12 includes, as the second magnet 12m2, unit magnets 12m2a, 12m2b, 12m2c, and 12m2d having a C-shaped form. The second magnet 12m2 is a magnet formed by combining the unit magnets 12m2a, 12m2b, 12m2c, and 12m2d having a C-shaped form in a ring shape. The second magnet 12m2 is integrally provided in the circumferential direction. By being integrally provided in the circumferential direction on the second magnet 12m2, the area efficiency and volume efficiency of generating the magnetic field by the second magnet 12m2 can be improved. By improving the area efficiency and volume efficiency of generating the magnetic field by the second magnet 12m2, the power generation efficiency in the power generation element 12g can be improved.

[0074] Note that the second magnet 12m2 includes four unit magnets, but the number of unit magnets is not limited to four. The second magnet may be a magnet formed by combining 2×n (n is an integer of 1 or more) unit magnets having a C-shaped form.

[0075] Each of the unit magnets 12m2a, 12m2b, 12m2c, and 12m2d has a magnetization direction in a direction perpendicular to the rotation axis direction (a direction parallel to the paper surface in FIG. 6).

[0076] By configuring the second magnet 12m2 by combining unit magnets having a C-shaped form, it can be easily assembled when assembling the magnet. For example, when assembling a magnet, the assembly work may be difficult due to the attraction or repulsion of the magnet. According to the encoder 12, by combining unit magnets having a C-shaped form and continuously providing them in the circumferential direction, the assembly can be facilitated. Further, according to the encoder 12, by combining unit magnets having a C-shaped form and continuously providing them in the circumferential direction, the area efficiency and volume efficiency of generating the magnetic field can be improved as compared with the case where the magnets are provided dispersedly in the circumferential direction. Further, the C-shaped unit magnets are widely distributed, inexpensive, and easily available.

[0077] The first magnet 12m1 is a rectangular magnet with two poles and a through-hole. In the disk 11d, a rectangular folder 11e having an inner shape approximately the same size as the outer shape of the first magnet 12m1 is integrally formed. The first magnet 12m1 is fitted inside this folder 11e and fixed with an adhesive. Further, the first magnet 12m1 has a through-hole 12m1h.

[0078] The first magnet 12m1 has a magnetization direction in the direction of zero magnetic field in the second magnet 12m2, that is, the direction between adjacent unit magnets. More specifically, it has a magnetization direction in the direction between the unit magnet 12m2a and the unit magnet 12m2d.

[0079] Since the first magnet 12m1 is a rectangular magnet, by simply fitting the first magnet 12m1 into the folder 11e formed in the disk 11d, the alignment of the magnetization direction of the first magnet 12m1 can be easily achieved. Note that the folder 11e does not need to surround the entire circumference of the first magnet 12m1. For example, any shape that can determine the magnetization direction of the first magnet 12m1, such as a shape that can position two corners of the rectangular magnet, is acceptable.

[0080] Also, in the above example, the second magnet is composed of unit magnets having a C-shaped configuration. However, the second magnet may be a ring magnet having 2×n poles (n is an integer of 1 or more). The ring magnet is easier to manufacture and assemble on the disk 11d compared to the case of combining C-shaped unit magnets.

[0081] Next, the signal waveforms in the encoder 12 will be described. FIGS. 8 and 9 are diagrams for explaining the signal waveforms in the encoder 12, which is an example of the encoder according to the first embodiment. FIG. 8 shows the waveforms when the first magnet 12m1 and the second magnet 12m2 rotate counterclockwise in FIG. 6. FIG. 9 shows the waveforms when the first magnet 12m1 and the second magnet 12m2 rotate clockwise in FIG. 6.

[0082] Assume that the first magnetic sensor 12h1 has a magnetic sensitivity direction in the horizontal direction in FIG. 6, and the second magnetic sensor 12h2 has a magnetic sensitivity direction in the vertical direction in FIG. 6.

[0083] In FIGS. 8 and 9, the horizontal axis represents the angle θ, and the vertical axis represents the signal intensity normalized so that the maximum value is 1. Line Lc represents the signal output from the first magnetic sensor 12h1, line Ls represents the signal output from the second magnetic sensor 12h2, line Lg1 represents the signal generated by the power generation element 12g when rotating counterclockwise, and line Lg2 represents the signal generated by the power generation element 12g when rotating clockwise.

[0084] As shown in FIGS. 8 and 9, due to the magnetic field of the first magnet 12m1, the first magnetic sensor 12h1 and the second magnetic sensor 12h2 output sine waves with a 90-degree phase shift. Also, the power generation element 12g generates power near angles that are multiples of 45 degrees. Note that the polarity of power generation is different depending on the direction of rotation. The power generation polarity when rotating counterclockwise is opposite to the power generation polarity when rotating clockwise. Also, since the power generation characteristics of the power generation element 12g have hysteresis, the angle at which the power generation element 12g generates power deviates from an angle that is a multiple of 45 degrees. Note that the direction of deviation when rotating counterclockwise is opposite to the direction of deviation when rotating clockwise.

[0085] As shown in FIGS. 8 and 9, since each of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 outputs and the power generation element 12g generates power, the encoder 12 can measure the direction of rotation and the rotation position with an angular resolution of 90 degrees.

[0086] The attachment of the magnet will be described. FIG. 10 is a cross-sectional view for explaining the configuration of an encoder 12 which is an example of an encoder according to the first embodiment. The first magnet 12m1 and the second magnet 12m2 are fixed by an adhesive and attached to the disk 11d. Then, the disk 11d is fixed by a bolt B1 to a bolt hole provided in the rotary shaft 11a. The encoder 12 includes a first magnet 12m1 which is a square magnet with a through hole. By fixing the bolt B1 through the through hole in the first magnet 12m1, when attaching the disk 11d to which the first magnet 12m1 and the second magnet 12m2 are assembled to the rotary shaft 11a, it can be easily assembled. Also, when replacing the disk 11d, it can be easily replaced by fixing the bolt B1 through the through hole in the first magnet 12m1.

[0087] In addition, according to the above embodiment, the first magnet 12m1 has a through hole 12m1h, but the through hole 12m1h may not be provided. That is, the first magnet 12m1 may be a square magnet without a through hole. In other words, the first magnet 12m1 may be a square magnet. In this case, when attaching the first magnet 12m1, a square magnet without a through hole is fixed to the bolt head of the bolt B1 with an adhesive.

[0088] Also, in the above embodiment, each of the unit magnets 12m2a, 12m2b, 12m2c, and 12m2d has a magnetization direction in a direction perpendicular to the rotary shaft direction (a direction parallel to the paper surface in FIG. 6), but the magnetization directions of the unit magnets 12m2a to 12m2d may be in the rotary shaft direction (a direction perpendicular to the paper surface in FIG. 6).

[0089] <<Second Embodiment>> The encoder according to the second embodiment will be described. The magnet in the encoder according to the second embodiment will be described. FIG. 11 is a plan view for explaining the configuration of the magnet in the encoder according to the second embodiment. In FIG. 11, in order to indicate the polarity of the magnet, the direction of magnetic flux is indicated by an arrow. Further, in FIG. 11, a magnetic field perpendicular to the plane of the paper is indicated by a black dot in a circle for a magnetic field facing forward and a cross in a circle for a magnetic field facing backward. Note that since the disk 11d rotates in synchronization with the rotation of the rotation axis, FIG. 11 is a diagram showing the arrangement of the magnets at a certain point in time. Note that the rotation axis extends in a direction perpendicular to the plane of the paper in FIG. 11. In FIG. 11, a counterclockwise angle θ is indicated.

[0090] The encoder according to the second embodiment includes a rotationally symmetric first magnet 112m1 provided on the disk 11d, and a rotationally symmetric second magnet 112m2 provided outside with respect to the rotation axis of the first magnet 112m1. Further, the encoder according to the second embodiment includes a magnetic body 15 between the first magnet 112m1 and the second magnet 112m2. By providing the magnetic body 15, the encoder according to the second embodiment can suppress the magnetic forces of the first magnet 112m1 and the second magnet 112m2 from interfering with each other and weakening the magnetic field.

[0091] The encoder according to the second embodiment includes, as the second magnet 112m2, unit magnets 112m2a, 112m2b, 112m2c, and 112m2d having a C-shaped configuration. The second magnet 112m2 is a magnet formed by combining the unit magnets 112m2a, 112m2b, 112m2c, and 112m2d having a C-shaped configuration.

[0092] In this embodiment, each of the unit magnets 112m2a, 112m2b, 112m2c, and 112m2d is assumed to have a magnetization direction in the rotation axis direction (the direction perpendicular to the plane of the paper in FIG. 6), but the magnetization direction may be a direction perpendicular to the rotation axis direction (the direction parallel to the plane of the paper in FIG. 6).

[0093] By configuring the second magnet 112m2 by combining unit magnets having a C-shaped form, it can be easily assembled when assembling the magnets.

[0094] The first magnet 112m1 is a two-pole ring magnet. The first magnet 112m1 has a through hole 112m1h. Note that the first magnet 112m1 may be a two-pole cylindrical magnet.

[0095] By forming the first magnet 112m1 in a ring shape or a cylindrical shape, the magnetic flux distribution becomes more uniform in the circumferential direction than in the case of a rectangular shape. As a result, it is possible to obtain the effect that distortion does not occur in the two-phase signals of the first magnetic sensor 12h1 and the second magnetic sensor 12h2 and the angular error can be reduced.

[0096] The first magnet 112m1 has a magnetization direction in the direction of zero magnetic field in the second magnet 112m2, that is, the direction between adjacent unit magnets, more specifically, the direction between the unit magnet 112m2a and the unit magnet 112m2d.

[0097] Also, in the above example, the second magnet is formed by combining unit magnets having a C-shaped form, but the second magnet may be a ring magnet having 2×n (n is an integer of 1 or more) poles. The ring magnet makes it easier to manufacture and assemble the magnet compared to the case of combining C-shaped unit magnets.

[0098] ≪Third Embodiment≫ The encoder according to the third embodiment will be described. The magnet in the encoder according to the third embodiment will be described. FIG. 12 is a plan view for explaining the configuration of the magnet in the encoder according to the third embodiment. In FIG. 12, in order to indicate the polarity of the magnet, the direction of the magnetic flux is indicated by an arrow. Note that since the disk 11d rotates in synchronization with the rotation of the rotation axis, FIG. 12 is a diagram showing the arrangement of the magnets at a certain point in time. The first magnetic sensor 12h1, the second magnetic sensor 12h2, and the power generation element 12g are mounted on a circuit board.

[0099] The encoder according to the third embodiment includes a rotationally symmetric second magnet 212m2 provided on the disk 11d, and a rotationally symmetric first magnet 212m1 provided outside the rotation axis of the second magnet 212m2. Note that a magnetic body 15 may be provided between the first magnet 212m1 and the second magnet 212m2.

[0100] The first magnet 212m1 is a two-pole ring magnet. The second magnet 212m2 is provided inside the first magnet 212m1.

[0101] The encoder according to the third embodiment includes, as the second magnet 212m2, unit magnets 212m2a, 212m2b, 212m2c, and 212m2d having a fan shape. The second magnet 212m2 is a magnet formed by combining the unit magnets 212m2a, 212m2b, 212m2c, and 212m2d having a fan shape.

[0102] In this embodiment, each of the unit magnets 212m2a, 212m2b, 212m2c, and 112m2d is assumed to have a magnetization direction in a direction perpendicular to the rotation axis direction (a direction parallel to the paper surface in FIG. 6), but the magnetization direction may be a direction perpendicular to the rotation axis direction (a direction parallel to the paper surface in FIG. 6).

[0103] By configuring the second magnet 212m2 by combining unit magnets having a fan shape, it can be easily assembled when assembling the magnet.

[0104] The first magnet 212m1 has a magnetization direction in the direction of zero magnetic field in the second magnet 212m2, that is, the direction between adjacent unit magnets, more specifically, the direction between the unit magnet 212m2a and the unit magnet 212m2d.

[0105] It should be considered that all the embodiments disclosed this time are illustrative and not restrictive in any way. The above embodiments may be omitted, replaced, or changed in various forms without departing from the scope and gist of the appended claims.

Description of Symbols

[0106] 1 Servo Motor System 10 Servo Motor 11 Motor 11a Rotation Axis 11d Disk 12 Encoder 12g Power Generation Element 12h1 First Magnetic Sensor 12h2 Second Magnetic Sensor 12m1, 112m1, 212m1 First Magnet 12m2, 112m2, 212m2 Second Magnet 12m2a, 12m2b, 12m2c, 12m2d, 112m2a, 112m2b, 112m2c, 112m2d, 212m2a, 212m2b, 212m2c, 212m2d Unit Magnet 20 Servo Controller

Claims

1. A power generation element, a magnetic sensor, a rotationally symmetric first magnet that rotates about a rotation axis and is provided near the magnetic sensor, a rotationally symmetric second magnet that rotates about the rotation axis, is provided near the power generation element, and is provided continuously in the circumferential direction, and an encoder.

2. The second magnet is a magnet formed by combining 2×n (n is an integer of 1 or more) C-shaped unit magnets, The encoder according to claim 1.

3. The second magnet is a ring magnet having 2×n (n is an integer of 1 or more) poles, The encoder according to claim 1.

4. The first magnet is a two-pole cylindrical magnet, The encoder according to claim 1.

5. The first magnet is a two-pole rectangular magnet, The encoder according to claim 1.

6. The first magnet is a two-pole ring magnet, The encoder according to claim 1.

7. The first magnet is a two-pole rectangular magnet with a through hole, The encoder according to claim 1.

8. The magnetic sensor has magnetic sensitivity directions with a 90-degree phase difference from each other, The encoder according to any one of claims 1 to 7.

9. A magnetic material is provided between the first magnet and the second magnet, The encoder according to any one of claims 1 to 7.

10. The first magnet has a magnetization direction in the direction where the magnetic field is zero in the second magnet, The encoder according to any one of claims 1 to 7.

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