JP2014090607A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller capable of detecting and controlling rotational speeds of a motor with a simple small configuration.SOLUTION: The motor controller includes: a control motor A with a piezoelectric element 20; a charge amplifier 30 that converts an output signal of the piezoelectric element 20 into a voltage; processing means 40 that analyzes a frequency of a signal output from the charge amplifier 30 and transmits a control signal according to the analysis result; and a motor driver 50 that supplies electric power corresponding to the control signal of the processing means 40 to the motor 10.

Description

  The present invention relates to a motor control device that detects and controls the rotational speed of a small motor.

  In recent years, OCT (optical coherence tomography) technology using light coherence has attracted attention as a method of image diagnosis. Near-infrared light having a wavelength of about 1300 nm is often used as a light source, but near-infrared light is non-invasive to living bodies and has a shorter wavelength than ultrasonic waves, so it has excellent spatial resolution, approximately 10 to 20 μm. Since it can be identified, it is expected to play an active role especially in the medical field. A typical structure of an OCT endoscope is, for example, as shown in Patent Document 1.

  In the OCT endoscope shown in Patent Document 1, the light incident on the lens unit (39) is image-processed while the lens unit (39) is rotated by the rotational force of a small motor (44). . For this reason, it is necessary to control the rotation speed of the lens unit (39) with high accuracy so as not to disturb the image. In the OCT endoscope of Patent Document 1, the rotation shaft (146) that rotates synchronously with the motor (44). Is detected by an encoder (46), and the motor (44) is controlled so that the rotation speed becomes a designated speed.

  However, in the above-described prior art, an exposed rotating portion such as the rotating shaft (146) is required for detecting the number of rotations by the encoder (46), and the installation location of the encoder (46) is likely to be restricted. In addition, since the encoder (46) includes an LED, a light receiving element, a disk, and the like, the configuration is complicated and easily increased in size.

JP 2004-223269 A

  The present invention has been made in view of the above-described conventional circumstances. The problem is to provide a motor control device that has a simple and small structure and enables speed control of a small motor.

  One means for solving the above problem includes a motor, a piezoelectric element fixed to a non-rotatable portion of the motor, and a processing means for obtaining a rotational speed based on a result of frequency analysis of an output signal of the piezoelectric element. It is characterized by that.

  Since the present invention is configured as described above, it is possible to control the speed of a small motor with a simple and small structure.

It is a block diagram which shows an example of the motor control apparatus which concerns on this invention. It is a perspective view which shows the motor control apparatus. It is a figure which shows the amplitude waveform calculated based on the output signal of a piezoelectric element. It is the table | surface and graph which show the relationship between instruction | command rotation speed and detection rotation speed. It is sectional drawing which shows the other example of the motor for control.

The first feature of the present embodiment includes a motor, a piezoelectric element fixed to a non-rotatable portion of the motor, and processing means for obtaining a rotation speed based on a result of frequency analysis of an output signal of the piezoelectric element. did.
Here, the non-rotatable portion may be a portion that does not rotate relative to a rotating portion (for example, a rotor, an output shaft, etc.) in the motor. As a specific example, it is provided around the stator or the stator. Case, bearing member, and the like.
According to the above configuration, since the piezoelectric element only needs to be fixed to a non-rotatable portion of the motor, there are few restrictions on the installation position of the piezoelectric element as compared with the prior art in which the rotating portion is detected. In addition, the sensing portion can have a simple and small structure mainly including a piezoelectric element.

  A second feature is a mode in which high-accuracy speed control is performed, and the processing means performs feedback control so that the rotation speed approaches a command rotation speed input in advance.

  The third feature is as a specific mode for calculating the rotational speed with high accuracy, the processing means detects the output signal of the piezoelectric element for each frequency, and obtains the frequency at which the level of the output signal is maximized, This frequency is converted into a rotation speed.

  The fourth feature is that the maximum diameter of the motor is 3 mm or less as a more specific embodiment.

  The fifth feature is an inner rotor type motor in which the motor has a stator and a rotor that rotates within the stator, and the piezoelectric element is the stator. Is fixed to the outer periphery of the thin film.

  According to a sixth aspect, as a specific aspect with higher productivity, the piezoelectric element is formed in a flexible film shape and is wound around the outer periphery of the stator.

  According to a seventh feature, as another specific aspect with higher productivity, the piezoelectric element is made of a synthetic resin material having piezoelectricity, and is integrally formed in a cylindrical shape on the outer periphery of the stator.

Further, although included in the present embodiment, the invention having a preferable feature independent of the above features includes a motor having a stator and a rotor that rotates within the stator, and is fixed to the outer periphery of the stator. And a thin film piezoelectric element. A control motor is configured.
According to this control motor, the vibration, speed and acceleration of the motor can be measured with a thin film piezoelectric element, and the rotational speed of the motor can be obtained by frequency analysis of the output signal of the piezoelectric element. The motor can be controlled in accordance with the rotational speed.

  Next, a preferred specific example of the present embodiment including the above features will be described in detail with reference to the drawings.

  As shown in FIG. 1, the motor control apparatus 1 includes a control motor A including a piezoelectric element 20, a charge amplifier 30 that converts an output signal of the piezoelectric element 20 into a voltage, and a signal output from the charge amplifier 30 as a frequency. The processing means 40 which analyzes and emits a control signal according to the analysis result, and the motor driver 50 which supplies the electric power according to the control signal of the processing means 40 to the motor 10 are provided.

  The control motor A includes a motor 10 and a thin film piezoelectric element 20 fixed to the outer periphery of the motor 10.

The motor 10 includes a cylindrical stator 11, a rotor 14 (see FIG. 5) rotatably supported via a bearing member or the like so as to rotate within the stator 11, and the center of the rotor 14. This is an inner rotor type motor comprising an output shaft 12 fixed to the unit so as to be integrally rotatable (see FIGS. 1 and 2). More specifically, this is an inner rotor magnet type brushless DC motor in which an electromagnetic coil is disposed on the inner peripheral portion of the stator 11 and the rotor 14 is made of a permanent magnet.
The maximum diameter of the motor 10 (the outer diameter of the stator 11 according to the illustrated example) is 3 mm or less.

The stator 11 has electromagnetic coils arranged in a predetermined pattern in a cylindrical casing. An electrode (not shown) for supplying power is fixed to the electromagnetic coil, and an electric wire 13 is connected to the electrode. The electric wire 13 is exposed to the outside of the stator 11 (see FIG. 2) and is electrically connected to an output terminal of a motor driver 50 described later.
The piezoelectric element 20 is fixed in contact with the outer peripheral surface of the stator 11.

The piezoelectric element 20 is a piezoelectric acceleration sensor that generates an electric charge when it receives an inertial force due to the rotational vibration of the motor 10.
More specifically, the piezoelectric element 20 is a rectangular piezoelectric film having flexibility, specifically, a so-called piezoelectric film made of polyvinylidene fluoride (PolyVinylidene DiFluoride, PVDF). An electric wire 21 (see FIG. 2) for signal output is connected.

And according to the illustrated preferred example, the piezoelectric element 20 is continuous over substantially the entire length of the stator 11 in the axial direction, and is also continuous over substantially the entire circumference of the stator 11 in the circumferential direction. It is wound around the outer peripheral surface and fixed via an adhesive or the like.
According to this configuration, the contact area between the piezoelectric element 20 and the motor 10 can be made relatively large, and the sensing accuracy by the piezoelectric element 20 can be improved.

  As shown in FIG. 1, the charge amplifier 30 is an electronic circuit that converts electric charges generated by the piezoelectric element 20 into a voltage and outputs the voltage.

  The processing means 40 detects the voltage signal output from the charge amplifier 30 according to the output signal of the piezoelectric element 20 for each frequency (frequency analysis), obtains the frequency at which the signal level is maximum, and sets this frequency as the rotational speed. It is an electronic circuit that converts and outputs a control signal to the processing means 40 so that the rotational speed approaches a command rotational speed (target value) input in advance. The processing means 40 can be configured by appropriately combining, for example, an FFT analyzer and a microprocessor.

FIG. 3 shows an input signal from the charge amplifier 30 which is discretely sampled by an FFT analyzer and the sampling result is displayed on the display.
The processing means 40 automatically selects the frequency (the peak waveform frequency indicated by the arrow in FIG. 3) at which the signal level is maximum for the signal waveform input from the charge amplifier 30. Then, the rotational frequency (RPM) per minute is calculated by multiplying the selected frequency by 60.
Then, the processing means 40 compares the rotational speed calculated as described above (hereinafter referred to as a detected rotational speed) with a command rotational speed (target value) input in advance, and reduces the difference. A feedback signal is output to the motor driver 50.

In addition, in order to improve the accuracy of automatic selection of the peak waveform, processing such as filtering the signal waveform to emphasize the peak waveform or selecting a peak waveform from a preset selection range is added. May be.
In the example shown in FIG. 3, the input signal of the charge amplifier 30 is expressed by a value converted into a vibration amplitude value. However, as another example, the input signal may be expressed as a value of speed or acceleration. Is possible.

  The motor driver 50 is an electronic circuit that controls the rotational speed of the motor 10 by changing the power supplied to the motor 10 in accordance with the feedback signal input from the processing means 40.

Next, experimental results obtained by measuring the relationship between the command rotational speed (target value) and the detected rotational speed using the control motor A having the above configuration will be described.
The experimental apparatus of this experiment has substantially the same configuration as the motor control apparatus 1 configured as described above. However, the feedback control is not performed, and a control command corresponding to the input command rotational speed is applied to the motor driver 50, so that the motor driver 50 The motor 10 is rotated by the electric power output from the charging amplifier 30 and the rotation speed at that time is detected by the charge amplifier 30 and the processing means 40.

In the table and graph of FIG. 4, the command rotational speed (Output Speed) is a rotational speed (target value) input in advance to the processing means 40 and stored in a storage device (not shown). In the table and graph, the detected rotation speed (Motor Rotating Speed) is a rotation speed calculated by the processing means 40 based on the output signal of the piezoelectric element 20.
As shown in the table and graph of FIG. 4, the relationship between the command rotational speed and the detected rotational speed is R2 (determination coefficient) = 0.9999≈1, indicating that there is a high correlation.

Therefore, if the motor 10 is feedback-controlled using the motor control device 1 of the present embodiment, highly accurate speed control is possible.
Further, according to this motor control device 1, since the piezoelectric element 20 is wound around the outer periphery of the motor 10, the motor control device 1 is compared with the conventional technology in which the amount of rotation of the rotary shaft is detected using an encoder. In particular, even when applied to a small motor having an outer diameter of 3 mm or less, the piezoelectric element 20 can be easily mounted, so that the productivity is excellent.

  Next, a control motor B (see FIG. 5) which is another embodiment will be described. The control motor B is obtained by changing a part of the control motor A. Therefore, the changed part will be mainly described in detail, and overlapping description of the same part will be omitted.

The control motor B has a configuration in which the piezoelectric element 20 is replaced with a piezoelectric element 20 ′ with respect to the control motor A configured as described above.
The piezoelectric element 20 ′ is made of a synthetic resin material having piezoelectricity (polyvinylidene fluoride (PVDF) as a preferable example) continuously on the outer peripheral surface of the motor 10 including the stator 11 and the rotor 14 over the entire circumference. It is formed by integrally molding into a cylindrical shape and providing an electrode (not shown) for signal output on this synthetic resin material.
The control motor B constitutes a motor control device (not shown) that is substantially the same as the motor control device 1 by being replaced with the control motor A of the motor control device 1.

According to the motor control device (not shown) using the control motor B, since the motor 10 and the piezoelectric element 20 ′ are integrally formed, the transmission efficiency of vibration from the motor 10 to the piezoelectric element 20 ′ is increased. As a result, the rotational speed sensing accuracy is improved.
Further, since the piezoelectric element 20 ′ has a structure that is difficult to peel off from the motor 10, it is easy to handle and excellent in productivity and durability.

  The control motor A (or B), the charge amplifier 30, the processing means 40, and the motor driver 50 may be configured by electrically wiring separate devices, or part or all of them. It is good also as an aspect which comprised these.

  Further, according to the above-described embodiment, the outer diameter of the motor 10 is set to 3 mm or less as a preferable example particularly for application to an OCT endoscope. However, as another example, the outer diameter of the motor 10 is set to be less than 3 mm. It is also possible to enlarge it.

  Further, according to the above embodiment, the piezoelectric element 20 (or 20 ′) is provided on the outer periphery of the motor 10 as a specific example with particularly high productivity, but as another example, the piezoelectric element 20 (or 20 ′) is provided. It is also possible to provide in non-rotatable parts (for example, bearing members before and behind the motor 10) other than the outer periphery of the motor 10. Further, it is possible to configure an outer rotor type motor, and to provide the piezoelectric element 20 (or 20 ′) on the fixed shaft on the center side of the motor.

  Moreover, according to the said embodiment, although the piezoelectric element 20 (or 20 ') is comprised by the polyvinylidene fluoride (PVDF), it is also possible to comprise from another piezoelectric material.

  Further, according to the above-described embodiment, the piezoelectric element 20 (or 20 ′) is provided over the entire axial length and the entire circumference of the motor 10 as an aspect with particularly high sensing performance. As another example, the piezoelectric element 20 ( Alternatively, a mode in which 20 ′) is provided in a part in the circumferential direction, a mode in which a part in the axial direction of the motor 10 is provided, or the like is also possible.

Further, according to the above embodiment, the motor 10 is an inner rotor magnet type brushless DC motor in order to constitute a small control motor with particularly good speed controllability.
This motor may be a rotary motor having a non-rotatable portion.
As another example, a permanent magnet is disposed on the inner periphery of the stator 11 and a permanent magnet field commutator motor using an electromagnet as a rotor, or a stepping motor, servo motor, AC motor, etc. It is also possible.

DESCRIPTION OF SYMBOLS 1: Motor control apparatus 10: Motor 11: Stator 14: Rotor 20, 20 ': Piezoelectric element 30: Charge amplifier 40: Processing means 50: Motor driver A, B: Motor for control

Claims (7)

  A motor control device comprising: a motor; a piezoelectric element fixed to a non-rotatable portion of the motor; and processing means for obtaining a rotational speed based on a result of frequency analysis of an output signal of the piezoelectric element.   The motor control device according to claim 1, wherein the processing unit performs feedback control so that the rotation speed approaches a command rotation speed input in advance.   The said processing means detects the output signal of the said piezoelectric element for every frequency, calculates | requires the frequency from which the level of the said output signal becomes the maximum, and converts this frequency into a rotational speed, The Claim 1 or 2 characterized by the above-mentioned. Motor control device.   The motor control device according to claim 1, wherein a maximum diameter of the motor is 3 mm or less.   The motor is an inner rotor type motor having a stator and a rotor that rotates in the stator, and the piezoelectric element is fixed to the outer periphery of the stator in a thin film shape. The motor control device according to any one of 1 to 4.   The motor control device according to claim 5, wherein the piezoelectric element is formed in a flexible film shape and is wound around an outer periphery of the stator.   6. The motor control device according to claim 5, wherein the piezoelectric element is made of a synthetic resin material having piezoelectricity, and is integrally formed in a cylindrical shape on an outer periphery of the stator.