JPH0442788A - Driving circuit of ultrasonic motor - Google Patents

Abstract

PURPOSE:To realize the sine wave driving with little loss and current ripple by a method wherein a power is supplied to the primary side of a transformer through an inductance element and an inductance element whose inductance value cancels the equivalent parallel capacitance of the piezoelectric device of an ultrasonic motor is connected in parallel to the piezoelectric device. CONSTITUTION:The inductance value Lc of a choking coil (Lc) which is connected to the center tap of the primary side of a step-up transformer 3 is selected to be sufficiently larger than the inductance value L1 to realize a constant current operation on the primary side. That is, if Lc>>L1 is satisfied, the AC component IAC of a current Ic supplied from a power supply Vc becomes infinitely close to zero and only the DC component IDC is supplied, so that a flyback converting operation is realized in a driving circuit 2. The parallel capacitance Ca of the equivalent circuit of an ultrasonic motor 1 is cancelled by parallel resonance with the inductance Lt of an inductance element (Lt) and the transient response (voltage resonance) of an LCR series resonance circuit is realized in the equivalent circuit and a current is supplied by an electromagnetic energy stored in the step-up transformer 3 in accordance with the voltage resonance, so that a sine wave driving voltage Vd can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic motor drive circuit that achieves low loss drive and low current ripple.

[Summary of the Invention] The present invention provides an ultrasonic motor drive circuit that performs switching on the primary side of a transformer. By using the series resonance system of the sonic motor to perform voltage resonance type switching drive using sine waves and enabling seven-way cross switching, it is possible to realize sine wave drive with less loss, power supply current, and pull. This is what I did.

[Prior Art] Conventionally, ultrasonic motors have been put into practical use that generate rotational motion by applying a drive signal near the resonance frequency to a piezoelectric element such as a ceramic or glass vibrator to generate ultrasonic vibrations. There is.

An ultrasonic motor includes a stator section that has a piezoelectric element and excites traveling wave vibrations, and a rotor (slider) section that converts the vibrations of the stator section into rotational motion. The stator section is made up of a piezoelectric element bonded to a ring-shaped elastic body such as metal, and a drive voltage is applied to this piezoelectric element from a drive circuit to cause it to resonate and create a traveling wave of flexural vibration on the end face of the stator section. to occur. This traveling wave causes elliptical motion at the top of the stator section. On the other hand, the rotor part has a friction material fixed thereto and is brought into pressure contact with the top of the stator part. Therefore, the rotor section is rotated by the elliptical movement of the stator section via the friction material.

A conventional drive circuit for driving such an ultrasonic motor is shown in FIG. 101 is an ultrasonic motor shown as an equivalent circuit, and 102 is a drive circuit for the ultrasonic motor 101.

The equivalent circuit of the ultrasonic motor 101 includes an inductance L, a capacitance C, and a resistance R connected in series, and a capacitance Ca in parallel with them. In the drive circuit 102, Lt is a variable inductance element for forming a parallel resonant circuit with parallel capacitance Ca, 103 is a step-up transformer whose secondary side is connected to the ultrasonic motor 101 (more specifically, a piezoelectric element), sw, , sw , is a transistor or MOSFET
It is a switching element such as, and performs switching on the primary side of the step-up transformer IO3 in a separately excited type by an oscillation circuit not shown. The primary side of the step-up transformer 103 has a center tap, and the power supply voltage Vc is directly connected to the center tap, and both ends of the primary side of the step-up transformer 103 have switching elements SW, SW, whose one end is connected to the signal ground.
, are connected to each of them.

FIG. 6 is an operational waveform diagram of a conventional example having the above configuration. Fifth
In the conventional example shown in the figure, HI3 is the resonant frequency of the ultrasonic motor, and the drive frequency is set around it due to problems such as vibration and noise.

In the conventional driving method of such an ultrasonic motor, 50%
Switching elements sw,,s with a smaller duty ratio
Pseudo-sine wave driving was performed by alternately turning on w and optimizing the duty ratio to match the resonance (time constant) of the ultrasonic motor 101. In the above, the step-up transformer 03 performs step-up according to the turns ratio by forward conversion during the on-period of the drive cycle TDRV, and performs fly noise during the off-period.

The motor drive voltage Vd is made into a pseudo sine wave by the Kucon heart in accordance with the resonance of the ultrasonic motor.

Incidentally, as an example of these drive circuits, Japanese Patent Application Laid-Open No. 63-1
It is disclosed in No. 78777 and Japanese Patent Application Laid-open No. 107681/1984.

[Problems to be Solved by the Invention] However, in the conventional ultrasonic motor drive circuit described above, the voltage is boosted at the switching part by forward conversion, so the drive voltage Vd only becomes a trapezoidal wave close to a sine wave. The traveling waves generated in the stator of an ultrasonic motor also do not form a clean sine wave. Such a trapezoidal wave includes harmonic components in addition to the fundamental sine wave, and these harmonic components result in loss. On the other hand, step-up transformer 1
On the primary side of 03, a pulse-like current 1c with a large ripple flows through the portion where forward conversion switching is performed, which increases the loss of the switching element and further increases the power supply noise.

The present invention was devised to solve the above problems, and an object of the present invention is to provide an ultrasonic motor drive circuit that realizes sine wave drive with less loss and current ripple.

[Means for Solving the Problems] The configuration of the ultrasonic motor drive circuit of the present invention for achieving the above object is such that switching is performed on the primary side of the transformer, and drive voltage is applied to the ultrasonic motor on the secondary side of the transformer. In a drive circuit for an ultrasonic motor that applies power, power is supplied to the primary side of the transformer through an inductance element, and an inductance element that cancels the equivalent parallel capacitance of the piezoelectric element of the ultrasonic motor is connected in parallel to the piezoelectric element. It is characterized by connecting.

[Function] The present invention provides constant current operation by supplying power to the primary side of a switching transformer through an inductance element without fixing the voltage, and reduces the parallel capacity of an ultrasonic motor serving as a load on the secondary side. The load is made into a series resonant system by canceling the current, and the current is made to flow according to the voltage resonance phenomenon of the series resonant system. By making the motor drive voltage a sine wave, harmonic components are eliminated and losses are reduced. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

This embodiment differs from the conventional example shown in FIG. 5 in the way the negative power supply Vc is connected. The other configurations are the same. That is, this embodiment consists of an ultrasonic motor 1 and its drive circuit 2 shown as an equivalent circuit, and the equivalent circuit of the ultrasonic motor 1 includes an interface L, a capacitance tc, and a resistance R connected in series. It has a capacity of 1ca parallel to them. In addition, in the drive circuit 2, Lt is a parallel capacitance Ca
3 is a step-up transformer whose secondary side is connected to the ultrasonic motor 1 (more specifically, a piezoelectric element); Transistor or MOSFE
This is a switching element such as a T (field effect transistor). These switching elements sw, , sw2 perform switching on the primary side of the step-up transformer 3 in a separately excited type by an oscillation circuit (not shown). The primary side of the step-up transformer 3 has a center tap, and in this embodiment, a power supply voltage Vc is connected to the center tap through a choke coil Lc. One end of each switching element SW, SW2 is connected to the signal ground, and the other end of each switching element SW, SW2 is connected to the primary side terminal of the step-up transformer 3, forming a push-pull switching circuit. It is formed.

The operation and effect of the embodiment configured as above will be described.

FIG. 2 is an operational waveform diagram in the above embodiment. The value of the inductance of the choke coil Lc connected to the center tap on the primary side of the step-up transformer 3 can be made sufficiently larger than the inductance on the primary side of the transformer 3. This allows constant current operation on the negative side. That is, if L c >>L, then the power supply Vc
Since the alternating current component IAC of the current 1c supplied by the converter becomes extremely close to zero, and only the direct current component IDC flows, the drive circuit 1 performs a flyback conversion operation. Therefore, −
Control of the switching elements sw, , sw on the next side does not require optimizing the duty ratio as in the forward convert operation, and the duty ratio can be simply set to 50%. The switching element SW and the switching element SW are controlled in an inverse relationship to each other. That is,
When one is on, the other is controlled off.

In the above operation, in the equivalent circuit of the ultrasonic motor that serves as the load, a parallel capacitor 1c is connected by the interface element Lt.
A is canceled by the parallel resonance, and the transient response (voltage resonance) of the LCR series resonant circuit occurs.The electromagnetic energy key stored in the step-up transformer 3 causes current to flow in response to the voltage resonance, and the drive voltage d becomes a sine wave. becomes. Furthermore, transformer 3
Since the drive voltage Vd on the secondary side is a sine wave, the voltages vl+vff on both terminals on the primary side are half-wave voltages with a 180° phase difference, and the switching elements 5WSW and 5WSW are both voltage-wise low-cross switching. becomes.

In the above, in this embodiment, the supply current 1c of the power supply ~'C
Since the alternating current component IAC, that is, the current ripple, becomes smaller, the loss of the switching elements sw, , sw2 becomes smaller, the power supply noise decreases, and the drive voltage V
Since it is a sine wave and has no harmonic components, it can be driven efficiently without loss. Therefore, the parallel capacitance Ji Ca of the equivalent circuit is canceled by the interface element Lt, and the resonant frequency 1/2πJL determined by the LC of the ultrasonic motor is obtained.
As long as it is driven near , ideal driving can be achieved.

From the above explanation, it can be seen that this embodiment is a battery-excited flexible flypack voltage resonance switching drive, but by inserting a choke coil Lc and supplying power, it can be operated as a flyback converter. A major feature is that the constant that determines resonance is determined by the mechanical resonance of the ultrasonic motor.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

This embodiment shows a configuration example in which a traveling wave type ultrasonic motor is driven in two phases. In the configuration of this embodiment,
11 is the A phase of the ultrasonic motor.

It is a piezoelectric element driven by two phases: B phase, 12 is a drive circuit for A phase, 13 is a drive circuit for B phase, 14 is an oscillation circuit that determines the drive frequency, 15 is a human phase, and 15 is a piezoelectric element that determines the phase relationship of phase B. The phase shift circuit 16 and 17 is an inverter that inverts the input signal. The drive circuits 12 and 13 for each phase are constructed in the same manner using members and elements having the same reference numerals as those described in the embodiment of FIG. Here, the A-phase drive circuit 12
The switching element SW2 is turned on/off by a 50% duty timing signal output from the oscillator 14, and the switching element SW2 is turned on/off by a timing signal a obtained by inverting the timing signal A by an inverter 16.

Furthermore, the switching element SW of the B-phase drive circuit 13 receives a timing signal d which is the output of the phase shift circuit 15.
The switching element SW receives a timing signal C obtained by inverting the timing signal d by an inverter 17.
is turned on/off. The phase shift circuit 15 inputs the output of the oscillation circuit 14, that is, the timing signal d, shifts the phase by 900 degrees, and outputs the timing signal d.

FIG. 4 is an operational waveform diagram showing the timing relationship of the above embodiment. As a result of the human-phase drive circuit 12 being switched by timing signals a and b having a duty of 50% and having an inverse relationship with each other, the A-phase drive voltage vdA becomes a sine wave as shown in the embodiment of FIG. In addition, the B-phase drive circuit 13
is similarly switched by timing signals c and d with a duty of 50%, and as a result, the B-phase driving voltage V d e also becomes a sine wave, but the timing signals c and d are only 90' from the Z timing signals a and b. Since the phase is shifted, it has a cosine wave relationship with respect to the A-phase drive voltage dA. Such a driving voltage VdA.

For example, the ring-shaped piezoelectric element 11 of the ultrasonic motor
When applied to the two sets of electrodes and set to a driving frequency that causes seven wavelengths to ride on the ring, vibrations of traveling waves traveling in one direction are excited, and rotational motion of the rotor section is obtained. As described above, in this embodiment as well, an ideal ultrasonic motor can be driven with less loss and less current ripple by sine wave driving without harmonic components.

In the embodiment, a separately excited drive circuit has been described, but the present invention can also be applied to a self-excited drive circuit. Furthermore, it is applicable to various types of ultrasonic motors such as single-phase drive in addition to two-phase drive. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

[Effects of the Invention] As is clear from the above explanation, according to the ultrasonic motor drive circuit of the present invention, (1) Despite switching drive, sine wave drive without harmonic components is performed. This makes it possible to generate clean traveling waves with little loss.

(2) Voltage zero-cross switching becomes possible, and switching loss can be reduced.

(3) There is less ripple in the power supply current, which reduces power supply noise.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is an operation waveform diagram of the above embodiment, Fig. 3 is a circuit configuration diagram showing another embodiment of the invention, and Fig. 4 is the above FIG. 5 is a circuit diagram of the conventional example, and FIG. 6 is an operational waveform diagram of the conventional example. 1... Ultrasonic motor, 2... Drive circuit, 3... Step-up transformer, 11... Piezoelectric element, 12.13... Drive circuit,
14...Oscillation circuit, 15...Phase shift circuit L1
6.17... Inverter, LC... Choke coil, sw, , sw,... Switching element, Lt...
variable inductance.

Claims (1)

[Claims] (1) In an ultrasonic motor drive circuit that performs switching on the primary side of a transformer and applies a driving voltage to the ultrasonic motor on its secondary side, power is supplied to the primary side of the transformer via an inductance element, A drive circuit for an ultrasonic motor, characterized in that an inductance element for canceling the equivalent parallel capacitance of the piezoelectric element of the ultrasonic motor is connected in parallel to the piezoelectric element.