JP3609596B2 - Ultrasonic motor drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor drive circuit for driving an ultrasonic motor.
[0002]
[Prior art]
Conventionally, an ultrasonic motor using ultrasonic vibration as a driving force is known. In a traveling wave type ultrasonic motor, which is a type of ultrasonic motor, a stator is formed by attaching a piezoelectric body to an annular elastic body, and a rotor attached to a drive shaft is in pressure contact with the stator. Has been.
[0003]
The drive circuit of the ultrasonic motor supplies two-phase drive signals (sin wave and cos wave) having a phase difference of 90 ° at a predetermined frequency to the piezoelectric body. Due to the mechanical vibration of the piezoelectric body generated by the two-phase drive signal, ultrasonic vibration (traveling wave) in which the antinodes and nodes of the vibration move in an annular shape along the elastic body is excited in the elastic body. By this traveling wave, the rotor and the drive shaft that are in pressure contact with the elastic body are rotated.
[0004]
As shown in FIG. 7, the ultrasonic motor is driven at the start of driving by first supplying a drive signal having a frequency sufficiently higher than the audible sound generation band and then driving the drive signal frequency slightly higher than the audible sound generation band. The frequency is gradually lowered to within the frequency band, and driving is performed while maintaining the frequency within the driving frequency band.
[0005]
The drive circuit for driving the ultrasonic motor is composed of a microcomputer, an oscillation circuit, a switching control circuit, a drive signal generation circuit, a band-pass filter, and the like, and an AC voltage corresponding to the oscillation frequency output from the oscillation circuit is a drive signal. The ultrasonic motor is driven by being generated by a generation circuit and supplying the AC voltage to the piezoelectric body of the ultrasonic motor.
[0006]
In addition, a rotation sensor is attached to the ultrasonic motor, and a predetermined device can be driven to a predetermined position by counting rotation pulse signals output from the rotation sensor with the microcomputer.
[0007]
The ultrasonic motor may be used for, for example, a so-called tilt mechanism or a telescopic mechanism of an automobile steering device. In such a case, the ultrasonic motor operates by being supplied with electric power from a vehicle battery power source (for example, 12V). FIG. 3 shows an outline of a main part of the automobile steering device.
[0008]
The steering device 90 includes a steering gear box (not shown) for turning a wheel (not shown), and one end of a steering shaft 94 is connected to the steering gear box.
[0009]
The other end of the steering shaft 94 is connected to the steering wheel 92. Further, a part of the steering shaft 94 is covered with a steering column 96, and in the steering column 96, the tilt mechanism (not shown) for moving the steering wheel 92 in the vertical direction, the steering wheel 92 The telescopic mechanism (not shown) for moving the vehicle in the axial direction of the steering shaft 94 is mounted.
[0010]
The tilt mechanism and the telescopic mechanism may obtain the driving force of the ultrasonic motor and move the steering wheel 92 in the vertical direction or the axial direction of the steering shaft 94 by an operator's operation. it can.
[0011]
Further, the position of the steering wheel 92 can be stored, and when the key is removed, the steering wheel 92 can be moved to the initial position, and when the key is inserted, the steering wheel 92 can be moved to the stored position. . In such a case, when the steering wheel 92 is driven to the stored position, the rotation pulse signal output from the rotation sensor attached to the ultrasonic motor is counted and stored by the microcomputer. It is possible to drive to the stored position by calculating the distance to the position.
[0012]
However, when the voltage of the battery power supply for the vehicle becomes unstable due to the influence of the engine on / off, etc., the voltage supplied to the rotation sensor also becomes unstable, so that the rotation pulse signal is disturbed and accurate. There is a problem in that the rotation pulse signal cannot be counted, and the steering wheel 92 cannot be moved to the accurately stored position.
[0013]
[Problems to be solved by the invention]
In consideration of the above facts, the present invention provides an ultrasonic motor drive circuit capable of accurately moving a predetermined device driven by an ultrasonic motor to a predetermined position even when the voltage supplied to the ultrasonic motor is reduced. Is the purpose.
[0014]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an ultrasonic motor that obtains a driving force by a voltage supplied from a battery power supply for a vehicle, and a rotation pulse output from a rotation sensor provided in the ultrasonic motor. In an ultrasonic motor drive circuit that drives a predetermined device to the predetermined position by driving the ultrasonic motor until the counted value reaches a count value corresponding to the predetermined position, the engine is turned on / off. In the case where the voltage becomes unstable due to the influence, when the voltage supplied from the battery power supply for the vehicle is equal to or higher than a first predetermined threshold value, the ultrasonic motor is driven, and the rotational pulse signal counts, the voltage supplied from the battery power source for the vehicle, if it becomes less than the second predetermined threshold, wherein It stops the driving of the ultrasonic motor, and controls so as to stop the counting of the rotation pulse signal.
[0015]
According to the first aspect of the present invention, the voltage supplied from the vehicle battery power supply is monitored, and when the voltage is equal to or higher than the first predetermined threshold, the ultrasonic motor is driven. The rotation pulse signal is counted. When the voltage falls below the second predetermined threshold, the driving of the ultrasonic motor is stopped and the count of the rotation pulse signal is stopped. When the voltage returns to the first predetermined threshold value or higher, the ultrasonic motor is started again and the rotation pulse signal is started. The counted value corresponds to the predetermined position. By driving the ultrasonic motor until the value is reached, the predetermined device is moved to a predetermined position. For this reason, even if the voltage supplied from the battery power supply for vehicles becomes unstable, the predetermined device can be accurately moved to the predetermined position.
[0016]
The invention according to claim 2 of the present invention is characterized in that the first predetermined threshold is higher than the second predetermined threshold.
[0017]
According to the second aspect of the present invention, the predetermined device can be moved to the predetermined position more accurately by setting the first predetermined threshold value higher than the second predetermined threshold value.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0019]
FIG. 2 shows a traveling wave type ultrasonic motor 10. The ultrasonic motor 10 includes an annular elastic body 12 made of a copper alloy or the like, and a piezoelectric body 14 is attached to the elastic body 12 to form a stator 28.
[0020]
The piezoelectric body 14 is made of a piezoelectric material that converts an electrical signal into a mechanical signal, and is configured by being divided and arranged in an annular shape by a large number of electrodes. On the other hand, the rotor 18 attached to the drive shaft 16 is formed by adhering an annular slider 22 to a rotor ring 20 made of aluminum alloy or the like, and the slider 22 is in pressure contact with the elastic body 12 by a spring 24. Has been. As the slider 22, for example, an engineering plastic or the like is used in order to obtain a stable frictional force and coefficient of friction, whereby the rotor 18 can be driven with high efficiency.
[0021]
A piezoelectric element 26 (see FIG. 1) is attached to the elastic body 12. As shown in FIG. 1, one end of the piezoelectric element 26 is grounded, and the other end is connected to the input end of the band-pass filter 40 of the drive circuit 30.
[0022]
The piezoelectric element 26 detects the vibration of the elastic body 12 and outputs an AC signal (vibration feedback signal) having an amplitude and a period corresponding to the vibration. The output end of the band pass filter 40 is connected to one signal input end of the microcomputer 32. The band pass filter 40 detects the vibration feedback signal output from the piezoelectric element 26 and outputs it to the microcomputer 32.
[0023]
A rotation sensor 46 is attached to the ultrasonic motor 10. The output end of the rotation sensor 46 is connected to the other signal input end of the microcomputer 32, and the output end of the battery power supply 31 is connected to the input end of the rotation sensor 46.
[0024]
The rotation sensor 46 includes a magnet (not shown) and a Hall element (not shown). The rotation sensor 46 detects a change in the magnetic flux on the magnet surface by the Hall element. When the rotor 18 rotates, the rotation speed of the rotor 18 is transferred to the microcomputer 32. A pulse signal with a period corresponding to is output.
[0025]
The power input terminal of the microcomputer 32 is connected to the branched output terminal of the battery power supply 31 and monitors the voltage level output from the battery power supply 31. The oscillation circuit 34 is connected to one output terminal of the microcomputer 32, and the other output terminal is connected to one input terminal of the switching control circuit 36. The output terminal of the oscillation circuit 34 is connected to the other input terminal of the switching control circuit 36. The oscillation circuit 34 oscillates at an oscillation frequency corresponding to the drive frequency signal from the microcomputer 32.
[0026]
One output terminal of the switching control circuit 36 is connected to one input terminal of the A-phase amplifier circuit 42 of the drive signal generating circuit 48, and the other output terminal is connected to the B-phase amplifier circuit 44 of the drive signal generating circuit 48. Connected to one input end. The switching control circuit 36 outputs a drive pulse to the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 while switching the drive pulse in accordance with the oscillation frequency oscillated from the oscillation circuit 34.
[0027]
The other input terminal of the A-phase amplifier circuit 42 and the other input terminal of the B-phase amplifier circuit 44 are connected to the output terminal of the voltage generation circuit 38. The voltage generation circuit 38 boosts the DC voltage supplied from the battery power supply 31 to a predetermined AC voltage, further rectifies and smoothes the voltage to a predetermined DC voltage, and boosts the DC voltage to a predetermined DC voltage. To supply power.
[0028]
The circuit configuration of the voltage generation circuit 38 is as shown in FIG.
The voltage generation circuit 38 includes a transformer 120, and is connected to one end of a capacitor 116 and a battery power source 31 (represented by Vcc in the figure) via a power line 118 at the midpoint of the primary side coil 120 </ b> A of the transformer 120. The other end of the capacitor 116 is grounded.
[0029]
One end of the primary side coil 120A of the transformer 120 is connected to the drain of the MOSFET 110 as a switching element. The gate of the MOSFET 110 is connected to one output terminal of the duty control circuit 114, and the source of the MOSFET 110 is grounded.
[0030]
The other end of the primary coil 120A of the transformer 120 is connected to the drain of the MOSFET 112 as a switching element. The gate of the MOSFET 112 is connected to the other output terminal of the duty control circuit 114, and the source of the MOSFET 112 is grounded.
[0031]
One end of the secondary coil 120B of the transformer 120 is connected to the anode of a diode 122 as a rectifying element, and the other end is connected to the anode of a diode 124 as a rectifying element. Further, the middle point of the secondary coil 120B of the transformer 120 is grounded.
[0032]
The cathodes of the diodes 122 and 124 are connected to one end of a coil 126 as an inductance element. The other end of the coil 126 is connected to one end of a capacitor 128, and the other end of the capacitor 128 is grounded. Further, the other end of the coil 126 is connected to one input terminal of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44, and a DC voltage is supplied from the voltage generation circuit 38 to the input terminal.
[0033]
The A-phase amplifier circuit 42 is connected to the piezoelectric body 14A of the ultrasonic motor 10 and supplies a sine wave signal (sin wave) to the piezoelectric body 14A. The B-phase amplifier circuit 44 is connected to the piezoelectric body 14B of the ultrasonic motor 10, and supplies the piezoelectric body 14B with a sine wave signal (cos wave) that is 90 ° out of phase with the sine wave signal supplied by the A-phase amplifier circuit 42. To do. The other ends of the piezoelectric bodies 14A and 14B are grounded. The piezoelectric bodies 14A and 14B constitute the piezoelectric body 14 of the ultrasonic motor 10.
[0034]
The circuit configurations of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44 are as shown in FIG. The A-phase amplifier circuit 42 includes a transformer 100, and one end of the power supply line 84 that is branched is connected to the midpoint of the primary coil 100A of the transformer 100. The other end of the power supply line 84 is It is connected to the output terminal of the voltage generation circuit 38 described above.
[0035]
One end of the primary coil 100 </ b> A of the transformer 100 is connected to the drain of the MOSFET 90 as a switching element, and the other end is connected to the drain of the MOSFET 92. The sources of the MOSFETs 90 and 92 are grounded. Further, both ends of the secondary coil 100B of the transformer 100 are connected to the piezoelectric body 14A.
[0036]
The B phase amplifier circuit 44 includes a transformer 102, and the other end of the branch of the power supply line 84 is connected to the midpoint of the primary side coil 102 </ b> A of the transformer 102.
[0037]
One end of the primary side coil 102 </ b> A of the transformer 102 is connected to the drain of the MOSFET 94 as a switching element, and the other end is connected to the drain of the MOSFET 96. The sources of the MOSFETs 94 and 96 are grounded. Further, both ends of the secondary coil 102B of the transformer 102 are connected to the piezoelectric body 14B.
[0038]
The gates of the MOSFETs 90, 92, 94, 96 are connected to the switching control circuit 36, and each of the MOSFETs 90, 92, 94, 96 is supplied with the switching signals A ₁ , A ₂ , B ₁ , It is turned on and off in accordance with B _2.
[0039]
Next, the effect | action in embodiment of this invention is demonstrated in detail, referring drawings.
[0040]
When a predetermined device is driven to a predetermined position by the ultrasonic motor 10, first, a drive frequency signal is output from the microcomputer 32 to the oscillation circuit 34. The oscillation circuit 34 starts oscillating at a drive frequency specified by the microcomputer 32.
[0041]
In the voltage generation circuit 38, a voltage is supplied from the battery power supply 31 (indicated by Vcc in the figure) to the primary coil 120A of the transformer 120, and a switching signal is input from the duty control circuit 114 to the gates of the MOSFETs 110 and 112 at a predetermined timing. Thus, the current to the primary side coil 120A of the transformer 120 is turned on / off. Then, an AC voltage is induced in the secondary side coil 120B of the transformer 120, this AC voltage is full-wave rectified by the diodes 122 and 124, smoothed by the coil 126 and the capacitor 128, and the DC voltage is converted into the A-phase amplifier circuit 42, B This is supplied to the phase amplifier circuit 44.
[0042]
The switching control circuit 36 outputs switching signals A ₁ , A ₂ , B ₁ , B ₂ for turning on and off the MOSFETs 90, 92, 94, 96 of the A-phase amplifier circuit 42 and the B-phase amplifier circuit 44.
[0043]
As shown in FIG. 6, this switching signal turns on / off any one of the MOSFETs 90, 92, 94, 96 at a predetermined duty ratio, and turns off the other MOSFETs and drives the MOSFETs that are turned on / off. The signal is switched in the order of the MOSFETs 90, 94, 92, and 96 every quarter of the period of the frequency fs of the driving signal at the start. As a result, AC drive signals are induced in the secondary side coils 100B and 102B of the transformers 100 and 102, respectively, with the frequency fs at the start of driving and 90 ° different in phase.
[0044]
By supplying this drive signal to the piezoelectric bodies 14A and 14B, a traveling wave is excited in the elastic body 12 of the ultrasonic motor 10, and the drive shaft 16 and the rotor 18 are rotated. Further, the vibration of the elastic body 12 is converted into an electric signal by the piezoelectric element 26, and is input to the microcomputer 32 through a band pass filter 40 as a vibration feedback signal. Further, a rotation pulse signal corresponding to the rotation speed of the rotor 18 is input to the microcomputer 32 from the rotation sensor 46 attached to the ultrasonic motor 10.
[0045]
In the microcomputer 32, while monitoring the vibration feedback signal, the MOSFETs 90 and 92 are turned on and off so that the frequency of the drive signal gradually approaches and matches the optimum drive frequency of the ultrasonic motor 10 and further follows the optimum drive frequency. , 94, 96 are changed to control the frequency of the drive signal.
[0046]
Further, the microcomputer 32 counts the rotation pulse signal while monitoring whether or not the voltage level output from the battery power source 31 is equal to or lower than a second predetermined threshold value (for example, 8 V). The ultrasonic motor 10 is driven until the counted value reaches the count value corresponding to the predetermined position. When the voltage level becomes equal to or lower than the second predetermined threshold value, the driving of the ultrasonic motor 10 is stopped and the count of the rotation pulse signal is also stopped.
[0047]
When the voltage level becomes equal to or higher than a first predetermined threshold value (10 V as an example), the driving of the ultrasonic motor 10 is started again and the rotation pulse signal is started to be counted. The ultrasonic motor 10 is driven until the signal reaches a predetermined count value, and the predetermined device is moved to a predetermined position.
[0048]
The above voltage monitoring control will be described with reference to the flowchart shown in FIG.
First, in step 50, the stop flag is turned off and the process proceeds to step 52, where the voltage level of the voltage output from the battery power supply 31 is captured. Next, in step 54, it is compared whether or not the voltage level has become 8V or less. If the determination is affirmative, the process proceeds to step 56. If the determination is negative, the process proceeds to step 62.
[0049]
In step 56, the driving of the ultrasonic motor 10 is stopped, and in step 58, counting of the rotation pulse signal is stopped. In step 60, the stop flag is turned on, and the process returns to step 52.
[0050]
In step 62, it is determined whether or not the stop flag is on. If the determination is affirmative, the process proceeds to step 64. If the determination is negative, the process returns to step 52. In step 64, it is compared whether or not the voltage level is 10 V or higher. If the determination is affirmative, the process proceeds to step 66. If the determination is negative, the process returns to step 52.
[0051]
In step 66, the drive stop of the ultrasonic motor 10 is released, and in step 68, the stop of the count of the rotation pulse signal is released. In step 70, the stop flag is turned off and the process returns to step 52.
[0052]
The ultrasonic motor 10 is driven under the control as described above, and the predetermined device is moved to a predetermined position.
[0053]
As described above, when the voltage output from the battery power supply 31 is equal to or lower than the second predetermined threshold value, the driving of the ultrasonic motor 10 is stopped and the count of the rotation pulse signal is stopped. Even if the voltage output from 31 becomes unstable and the rotation pulse signal is disturbed, the predetermined device can be accurately moved to the predetermined position. In addition, since the first predetermined threshold is set higher than the second predetermined threshold, the predetermined device can be moved to the predetermined position more accurately.
[0054]
In the present embodiment, the first predetermined threshold is set higher than the second predetermined threshold. However, the present invention is not limited to this. For example, the first predetermined threshold may be set to the same value and can be set freely. .
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic motor and an ultrasonic motor driving circuit.
FIG. 2 is a partial cross-sectional perspective view showing a schematic configuration of an ultrasonic motor.
FIG. 3 is a schematic configuration diagram showing a main part of the steering device.
FIG. 4 is a circuit diagram showing a voltage generation circuit in an ultrasonic motor drive circuit.
FIG. 5 is a circuit diagram showing an example of a drive signal generation circuit.
FIG. 6 is a diagram showing a switching signal output from a switching control circuit and a drive signal induced by a transformer.
FIG. 7 is a diagram showing a change in impedance of the ultrasonic motor, a resonance frequency, an audible sound generation band, a driving frequency band, and the like accompanying a change in the driving frequency of the ultrasonic motor.
FIG. 8 is a flowchart showing the operation of a program for performing voltage monitoring control in the microcomputer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Ultrasonic motor 30 Drive circuit 31 Battery power supply 32 Microcomputer 34 Oscillation circuit 36 Switching control circuit 38 Voltage generation circuit 40 Band pass filter 42 A phase amplification circuit 44 B phase amplification circuit 46 Rotation sensor

Claims (2)

An ultrasonic motor that obtains a driving force by a voltage supplied from a battery power supply for a vehicle, and counts a rotation pulse signal output from a rotation sensor provided in the ultrasonic motor, and the counted value is placed at a predetermined position. In the driving circuit of the ultrasonic motor that drives the predetermined device to the predetermined position by driving the ultrasonic motor until the corresponding count value is reached, when the voltage becomes unstable due to the influence of the engine on / off,
When the voltage supplied from the vehicle battery power source is equal to or higher than a first predetermined threshold value, the ultrasonic motor is driven and the rotation pulse signal is counted, and the vehicle battery When the voltage supplied from the power source becomes equal to or lower than a second predetermined threshold value, the driving of the ultrasonic motor is stopped and the count of the rotation pulse signal is stopped. An ultrasonic motor drive circuit. 2. The ultrasonic motor drive circuit according to claim 1, wherein the first predetermined threshold value is higher than the second predetermined threshold value.

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