JP4103018B2 - Servomotor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a permanent magnet type synchronous servo motor, and more particularly to a small servo motor incorporating a magnetic encoder.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there are servo motors in which an encoder unit is separately attached to the shaft end of the servo motor, and the overall configuration is as shown in the block diagram of FIG. That is, the signal processing circuit 3 performs a signal of the encoder 2 for detecting the rotational position and speed attached to the motor 1 and feeds back the output to the control circuit 4 to control the motor 1. The control circuit 4 includes a speed calculation circuit 41, a position amplifier 42, a speed amplifier 43, a current amplifier 44, a power circuit 45, and a current sensor 46, respectively.
As a method of the encoder 2, there are mainly a magnetic type and an optical type. As an example of a magnetic type, there is one in which a code plate is a permanent magnet magnetized with multiple poles, and a magnetic sensor for detecting a leakage flux of the permanent magnet is provided in the vicinity thereof. A magnetic sensor for detecting magnetism is provided in each pattern row by increasing the number of pattern rows of permanent magnets magnetized in accordance with the detection accuracy.
On the other hand, an optical example has a structure as shown in FIG. In this configuration, a separate encoder 2 is connected in series to the shaft end of the motor 1. Light from the LED 231 is irradiated onto a rotary slit plate 233 having a slit as a code plate, received by a PD (photodiode) 232, and photoelectrically converted to detect a rotational position and a rotational speed.
As another example of the optical type, an optical fiber and a rotating slit plate are used without using an LED or PD, and the light guided from the optical fiber is irradiated to the slit portion, and the reflected light is received by the optical fiber. Some have detected the rotational position and rotational speed by photoelectrically changing the amount of reflected light depending on the presence or absence (Journal of Precision Engineering vol.63, No.8, p1075, 1997). In this configuration, the light amount detection unit and the photoelectric conversion unit are arranged outside because they are large.
[0003]
[Problems to be solved by the invention]
However, since the conventional servo motor is separate from the magnetic or optical encoder, there is a limit to downsizing. In order to increase accuracy in the magnetic type, a plurality of magnet pattern rows that are code plates are required, which increases the axial length. Even in the optical system, the size of the slit of the rotary slit plate and the size of the LED and PD can be reduced to a few millimeters, which cannot be further reduced. If the accuracy is to be increased, the number of slits in the code plate and the corresponding optical fiber must be increased, and the size cannot be reduced. In addition, both the magnetic and optical encoders have a large number of parts, and there is a problem that the manufacturing cost is high. Further, since the volume of the encoder section is as large as or larger than that of the motor section, there is a problem that the torque per unit volume, that is, the torque density is also small.
Accordingly, an object of the present invention is to provide an ultra-compact servo motor having a simple structure, low cost, high performance and high torque density.
[0004]
[Means for Solving the Problems]
In order to solve the above problems, the present invention relates to a motor comprising a stator having an armature core and an armature coil, a rotor having a permanent magnet provided on the inner diameter side of the stator via a gap, and a rotational position of the rotor. In the servo motor comprising the encoder for detecting, the permanent magnet of the rotor is a magnet having linear anisotropy having two magnetic poles magnetized in a direction perpendicular to the rotation axis, and the encoder is The magnetic sensor for detecting the magnetic field is used.
Further, four magnetic sensors may be arranged at intervals of 90 degrees in the circumferential direction so as to take a signal differential between the magnetic sensors facing each other at 180 degrees.
Further, the magnetic sensor may be arranged at either the axial end or the center of the rotor.
The magnetic sensor may be a Hall element or a magnetoresistive effect element.
The permanent magnet may be any of ferrite, Sm—Co, and Nd—Fe—B.
With the above configuration, it is possible to obtain an ultra-compact servo motor with a simple structure and high performance and high torque density.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a servomotor showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG. In the figure, 11 is a stator, 12 is a frame, 15 is a rotor, and 2 is a magnetic encoder. The servo motor of the present invention has a two-pole, two-phase, four-slot structure, connects the stator 11 and the encoder 2, fixes the frame 12 to both end faces, and the rotor 15 is held by bearings 18 of the frame 12. ing. The stator 11 includes a salient pole portion 13 having an armature core made of a magnetic material, and an armature coil 14 wound around the salient pole portion 13. The rotor 15 includes a permanent magnet 17 fixed around the rotating shaft 16. The permanent magnet 17 is a linearly anisotropic magnet made of Nd—Fe—B, and is longer than the axial length of the salient pole portion 13 of the stator 11. And it is magnetized to two poles of N pole and S pole in a direction perpendicular to the axis. The encoder 2 includes a circular sensor holder 21 having a permanent magnet 17 as a magnetism and a magnetic sensor 22 provided on the inside thereof. The sensor holder 21 is made of a plastic plate insulating material. The magnetic sensor 22 includes four Hall elements 221 to 224 and is fixed inside the sensor holder 21 at an interval of 90 degrees. The material of the frame 12 is not particularly limited, but when the motor dimensions are particularly small, the use of a magnetic material has no waveform distortion and noise is cut off, so that the accuracy is further improved.
Next, the operation will be described.
When a voltage is applied to the armature coil 13 from a power source (not shown), the rotor 15 rotates. The leakage magnetic flux of the permanent magnet 17 acts on the Hall elements 221 to 224. FIG. 3 shows the magnetic flux distribution of the leakage magnetic flux generated from the permanent magnet 17. Since the permanent magnet 17 is magnetized perpendicularly to the rotation axis, the leakage flux is continuously distributed in the circumferential direction. Signals from the Hall elements 221 to 224 are processed by a signal processing circuit shown in FIG. The signal processing circuit 3 takes the signals V _a1 and V _a2 of the Hall elements 221 and 223 opposite to each other by 180 degrees by the differential amplifier 31 and the signals V _b1 and V _b2 of the 222 and 224 by the differential amplifier 32, respectively. Signal processing is performed as A-phase and B-phase signals V _a and V _b . Two sinusoidal waveforms of sin θ and cos θ that are 90 degrees out of phase with each other are obtained by the differential amplifiers 31 and 32. FIG. 5 shows two sine wave waveforms for the A phase and the B phase. Next, when the A-phase and B-phase output signals are input to the angle calculation circuit 323, θ = arctan (Vb / Va) is calculated, and the angle of the absolute position can be detected. FIG. 6 shows the detection angle and detection error of this embodiment with respect to the rotation angle θ of a high-precision reference encoder (resolution: 1 million pulses / rotation). From this figure, it can be seen that the rotation angle θ can be detected with an accuracy of 0.1%. That is, since the rotation angle can be known from the output value, the position of the rotor 15 can be controlled by feeding back the deviation from the set value. A drive current is supplied to the A phase and the B phase according to the position of the rotor 15, and a rotational force is applied to the motor 1 by the generated rotating magnetic field and the magnetic force of the rotor 15. Even if the rotor 15 rotates eccentrically, the A phase and the B phase take a differential of the A ₁ phase and the A ₂ phase and the B ₁ phase and the B ₂ phase, which are 180 degrees out of phase with each other. Offset.
As a result of measuring the detection output of the encoder, an absolute position signal with high detection accuracy obtained by dividing 32,000 revolutions was obtained despite the small and simple structure. On the other hand, as a result of measuring the driving torque, the torque density (torque / volume) was improved to a little over 200% compared to the conventional servo motor with the encoder as a separate body.
FIG. 7 is a sectional view of a servo motor showing another embodiment of the present invention.
In this embodiment, the attachment position of the magnetic sensor 22 is installed in the central portion of the rotor 15 in the axial direction. Two stators 11 having the same shape are produced and aligned in series, and a sensor holder 21 to which a magnetic sensor 22 is fixed is coupled therebetween. Four magnetoresistive elements were used as the magnetic sensor 22, and Sm—Co based material was used as the permanent magnet 17. Other configurations are the same as those of the above-described embodiment.
The detection output of the encoder and the drive torque were good results as in the previous embodiment. In the present embodiment, since the encoder 2 is arranged at the center of the motor 1, the magnetic field generated by the permanent magnet 17 is uniform and stable, and as a result, the detection accuracy is further improved.
In this embodiment, the structure of the motor is 2 poles, 2 phases, 4 slots. However, the present invention is not limited to this, and the number of poles is 3 phases, and the number of coils and slots is 3, 6, It may be increased to 8. Further, the armature core may be a ring-shaped structure having no salient pole structure.
Further, although Nd—Fe—B and Sm—Co based linear anisotropic magnets are used for the permanent magnets 17, ferrite magnets may be used if the motor dimensions are relatively large. Alternatively, a dispersion composite magnet in which a Sm—Co-based or Nd—Fe—B-based material is bonded with a polymer material may be used.
[0006]
【The invention's effect】
As described above, according to the present invention, a linearly anisotropic magnet is used as the permanent magnet of the rotor, which is magnetized into two poles in a direction perpendicular to the rotation axis, and a part of the leakage flux of the permanent magnet is reduced. Since the position is detected and detected, there is an effect of obtaining a small servo motor having a simple structure, low cost, high performance and high torque density.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a servo motor of the present invention.
FIG. 2 is a cross-sectional view taken along line AA ′ of FIG.
FIG. 3 is a magnetic flux distribution diagram showing a magnetic flux distribution of a permanent magnet used in the servomotor of the present invention.
FIG. 4 is a block diagram showing a signal processing circuit used in an embodiment of the present invention.
FIG. 5 is a waveform diagram of A phase and B phase of the magnetic encoder used in the present invention.
FIG. 6 is a waveform diagram showing the magnetic flux density with respect to the rotation angle of the magnetic encoder used in the present invention.
FIG. 7 is a sectional view of a servomotor showing another embodiment of the present invention.
FIG. 8 is a cross-sectional view showing a conventional servo motor.
FIG. 9 is a control block diagram showing the overall configuration of the servo motor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Motor 11 Stator 12 Frame 13 Armature core 14 Armature coil 15 Rotor 16 Rotating shaft 17 Permanent magnet 18 Bearing 2 Encoder 21 Sensor holder 22 Magnetic sensors 221 to 224 Hall element 23 Optical sensor 231 LED
232 PD (photodiode)
233 Rotating slit plate 3 Signal processing circuits 31 and 32 Differential amplifier 33 Angle calculation circuit 4 Control circuit 41 Speed calculation circuit 42 Position amplifier 43 Speed amplifier 44 Current amplifier 45 Power circuit 46 Current sensor

Claims (3)

In a servomotor comprising a stator having an armature core and an armature coil, a rotor having a permanent magnet provided on the inner diameter side of the stator via a gap, a magnetic encoder for detecting the rotational position of the rotor, and a frame ,
A cylindrical permanent magnet having linear anisotropy is magnetized into two poles in a direction perpendicular to the rotation axis, a part of the cylindrical permanent magnet is used as a permanent magnet of the rotor, and a part of the cylindrical permanent magnet is used. A servo motor characterized in that is used as a magnetic generator of the magnetic encoder . Claim 1, the magnetic encoder, the calling said the magnet body and the magnetic sensor and a magnetic sensor from the installation the circular sensor holder, characterized in that a said sensor holder between the said stator frame Servo motor described . Claim constituting said stator together stator the same shape in two series, the magnetic sensor a circular sensor holder installed, characterized in that arranged between the two same shape stator 1 Servo motor described .

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