Magnetostriction oscillator driving circuit and method

Details Magnetostriction oscillator driving circuit and method Magnetostriction oscillator driving circuit and method

1999-10-08

2001-02-13

Ramirez, Nestor (Department: 2834)

Electricity: motive power systems

Magnetostrictive motor

C114S119000, C114S126000

Reexamination Certificate

active

06188186

ABSTRACT:

BACKGROUND OF THE INVENTION
SUMMARY OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetostriction oscillator which is used for generating a high output ultrasonic wave, more particularly, to a circuit and a method for driving a magnetostriction oscillator by using a pulse width modulation.
2. Prior Art
Generally, a method which removes or prevents scales in heat exchange equipment is performed by washing a pipe by means of a strong acid, or by using an ultrasonic wave generated by means of a magnetostriction oscillator.
An impulse voltage of a high voltage is alternately supplied to each of a pair of magnetostriction oscillators. This removes scales or prevents a generation thereof by an ultrasonic vibration by emitting an ultrasonic wave generated by each magnetostriction oscillator to an inner wall of a pipe in the heat exchanger equipment.
U.S. Pat. No. 3,633,424 issued to Lawrence W. Lynnworth et al. on Jan. 11, 1972 discloses a magnetostriction ultrasonic transducer in which the number of unwanted pulses due to internal reflections is minimized.
FIG. 1
is a circuitry diagram for showing a conventional magnetostriction oscillator driver.
The conventional magnetostriction oscillator driver includes first and second diodes D
1
and D
2
, first and second capacitors C
1
and C
2
, and first and second silicon controlled rectifiers SCR
1
and SCR
2
. When an alternating current voltage AC is applied to first and second diodes D
1
and D
2
, the first and second diodes D
1
and D
2
perform half-wave rectification of the AC for half cycle by forward and reverse directions. The first and second silicon controlled rectifiers SCR
1
and SCR
2
alternately perform switching operations so that a predetermined distributed voltage is supplied to first and second magnetostriction oscillators M
1
and M
2
. A resistor R
3
, a zener diode D
3
, and a diode D
5
are connected to a gate of the first silicon controlled rectifier SCR
1
in series. The resistor R
3
, zener diode D
3
, and diode D
5
serve to switch the first silicon controlled rectifier SCR
1
. A resistor R
4
, a zener diode D
4
, and a diode D
6
are connected to a gate of the second silicon controlled rectifier SCR
2
in series. The resistor R
3
, zener diode D
3
, and diode D
5
serve to switch the second silicon controlled rectifier SCR
2
.
A resistor R
5
and a capacitor C
4
are connected to an anode of the diode D
5
and generate a switching signal according to a time constant thereof. A resistor R
6
and a capacitor C
5
are connected to an anode of the diode D
6
and generate a switching signal according to a time constant thereof. A capacitor C
3
is connected between the first and second silicon controlled rectifiers SCR
1
and SCR
2
and serves to form the predetermined distributed voltage. Resistors R
1
and R
2
are connected to the capacitors C
1
and C
2
in parallel, respectively.
An operation of the conventional magnetostriction oscillator driver will now be described.
When an alternating current voltage AC is applied to the first diode D
1
through a fuse F for half cycle by a forward direction, the first diode D
1
performs half-wave rectification of the AC and outputs a half-wave rectified voltage. The half-wave rectified voltage from the first diode D
1
is smoothed by a capacitor C
1
and a resistor R
1
, and the smoothed voltage is supplied to a resistor R
5
and a capacitor C
4
through a first magnetostriction oscillator M
1
to thereby charge the capacitor C
4
.
When a predetermined time according to a time constant formed by the resistor R
5
and capacitor C
4
elapses, the capacitor C
4
discharges the charged voltage through a path formed between the capacitor C
4
and a diode D
5
. When the discharge voltage is higher than a predetermined voltage, the zener diode D
3
triggers a gate of the first silicon controlled rectifiers SCR
1
through a resistor R
3
. Accordingly, the smoothed voltage from the capacitor C
1
defines a closed circuit through a capacitor C
3
by the switching of the first silicon controlled rectifiers SCR
1
. At this time, since the capacitor C
1
and C
3
are connected in parallel to each other, excessive current flows through the first magnetostriction oscillator M
1
by the parallel capacitances of the capacitors C
1
and C
3
. Accordingly, an impulse of a high voltage is generated in the first magnetostriction oscillator Ml so that the first magnetostriction oscillator Ml oscillates an ultrasonic signal.
On the other hand, when the alternating current voltage AC is applied to the second diode D
2
through a fuse F for half cycle by a reverse direction, the second diode D
2
performs half-wave rectification of the AC and outputs a half-wave rectified voltage. The half-wave rectified voltage from the second diode D
2
is smoothed by a capacitor C
2
and a resistor R
2
, and the smoothed voltage is supplied to a resistor R
6
and a capacitor C
5
through the charged capacitor C
3
to thereby charge the capacitor C
5
.
When a predetermined time according to a time constant formed by the resistor R
5
and capacitor C
4
elapses, the capacitor C
5
discharges the charged voltage through a path formed between the capacitor C
5
and a diode D
6
. When the discharge voltage is higher than a predetermined voltage, the zener diode D
4
triggers a gate of the second silicon controlled rectifiers SCR
2
through a resistor R
4
. Accordingly, the voltage charged in capacitors C
2
and C
3
is discharged into the second magnetostriction oscillator M
2
. The discharged voltage, that is, an impulse of a high voltage operates the second magnetostriction oscillator M
2
.
As described previously, when a high voltage is alternately applied to first and second magnetostriction oscillators M
1
and M
2
according to half cycles by forward and reverse directions of the AC power, first and second magnetostriction oscillators M
1
and M
2
vibrate to generate an ultrasonic signal of a predetermined frequency. Such an ultrasonic signal is used for removing scales or preventing generation thereof.
In the conventional magnetostriction oscillator driver, a high voltage of 1000 volts is used. This means that output efficiency of an ultrasonic wave is lower than input power so that power for operating a system is wasted. An increase of noise due to non-resonant vibrations of magnetostriction oscillator and peripheral circuits thereof according to an impulse of high voltage causes fatigue fracture so that the system cannot be used for a long time. In order to operate the system, two magnetostriction oscillators should be alternately used. Thus, when something is wrong with either one of the two, the system cannot operate.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention, for the purpose of solving the above mentioned problems, to provide a magnetostriction oscillator driving circuit and method capable of generating an ultrasonic wave of a high output by low voltage driving and low consumption power by using a pulse width modulating method.
In order to attain the object, according to the present invention, there is provided a magnetostriction oscillator driving circuit, said circuit comprising:
a controller for outputting first and second variable digital signals in order to control a duty cycle of a magnetostriction oscillator;
a pulse width modulating circuit for generating a variable pulse width modulating signal based on the first and second variable digital signals from the controller; and
a driver for driving the magnetostriction oscillator according to the variable pulse width modulating signal from the pulse width modulating circuit.
Preferably, the pulse width modulating circuit include first and second digital/analog converters for converting the first and second variable digital signals from the controller into first and second variable analog direct current voltages, respectively; a triangle waveform generator for generating a triangle waveform signal according to a level of the first variable analog direct current voltage from the

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