Variable frequency ultrasonic generator with constant power output

• US 5,276,376 A
• Filed: 06/09/1992
• Issued: 01/04/1994
• Est. Priority Date: 06/09/1992
• Status: Expired due to Term

• Current Assignee: BJG Nelson Holdings, Inc.
• Original Assignee: Ultrasonic Power Corporation
• Inventors: Puskas, Peter J.
• Primary Examiner(s): Budd, Mark O.
• Application Number:
  US07/895,624
• Time in Patent Office: 574 Days
• Field of Search: 310/316, 310/317, 310/319, 310/323, 318/116, 55/15, 366/108, 366/114, 366/116, 366/117, 366/127
• US Class Current: 310/317
• CPC Class Codes: B06B 1/0246 with a feedback signal
• CPC Class Codes: B06B 2201/71 Cleaning in a tank
• CPC Class Codes: H03L 5/02 of power

Abstract

A generator for driving an ultrasonic transducer for use in ultrasonic cleaning. The generator is based on a voltage controlled oscillator which drives an output circuit which includes the ultrasonic transducer. The output circuit has a resonant frequency, and a resonance follower produces a control voltage which tunes the voltage controlled oscillator to the resonant frequency. Operating in conjunction with the automatic tuning elements is a constant power control which allows the user to set a desired power level, and monitors the actual output power by means of an output wattmeter circuit, to cause the actual output power to match the level selected by the user. The constant output power circuit is effective even during resonance tracking of the system, or during frequency modulation of the ultrasonic output energy.

Claims

1. A generator for driving an ultrasonic transducer comprising, in combination:

an output circuit including the ultrasonic transducer and a coupled load, the output circuit having a resonant frequency which is affected by the magnitude of the load presented to the ultrasonic transducer,

a voltage controlled oscillator for driving the output circuit, the voltage controlled oscillator having a frequency variable within a predetermined limited range,

a resonance follower having an input connected to the output circuit and being coupled to the voltage controlled oscillator for tuning the voltage controlled oscillator to the resonant frequency of the output circuit, the resonance follower including means for sweeping the voltage controlled oscillator through at least a part of the operating frequency range thereof until the resonance follower determines that the output circuit is oscillating at about the resonance frequency of the load,

a power control circuit including a user settable power level control for setting a power demand signal, a wattmeter connected in the output circuit for producing a signal relating to the actual power delivered by the output circuit, and means for modulating the DC power supplied to the output circuit to cause the actual power to be at a level established by the demanded power, the output power setting means being effective across at least a part of the range of the voltage controlled oscillator for matching the delivered power to the demanded power over the range of frequencies at which the load can resonate.

2. The combination as set forth in claim 1 further including modulating means for establishing a frequency modulating signal and applying said frequency modulating signal to the voltage controlled oscillator, thereby to modulate the frequency of the output circuit about the resonant frequency.

3. The combination as set forth in claim 2 further including user adjustable means for establishing the characteristics of the frequency modulating signal including the modulating frequency and the modulating depth.

4. The combination as set forth in claim 1 further including duty cycle control means for alternating the output stage between an on condition in which ultrasonic power is generated at the level established by the power setting control, and an off condition in which the output stage delivers substantially no power to the load.

5. The combination as set forth in claim 2 further including duty cycle control means for alternating the output stage between an on condition in which ultrasonic power is generated at the level established by the power setting control, and an off condition in which the output stage delivers substantially no power to the load.

6. The combination as set forth in claim 2 further including duty cycle control means for cooperating with the modulating means for alternating the frequency of the output circuit between an on condition in which frequency modulation is applied to the resonant frequency and an off condition in which no frequency modulation is applied.

7. The combination as set forth in claim 2 wherein the resonance follower is provided with a time constant which prevents the resonance follower from tuning the voltage controlled oscillator to cancel modulation introduced by the modulating means.

8. The combination as set forth in claim 1 wherein the power control circuit includes a thyristor connected to modulate the voltage level of the DC power supplied to the output circuit, and means responsive to the power demand signal and the actual power signal for modulating the phase of the triac thereby to match the actual power level to the demanded level.

9. The combination as set forth in claim 8 in which the wattmeter include an analog multiplier having a voltage input and a current input, the respective inputs being transformer coupled in the output circuit for providing isolated signals related to the voltage and current levels in the output circuit.

10. A generator for driving an ultrasonic transducer comprising, in combination:

an output stage connected to the transducer and forming an output circuit therewith,

a controlled oscillator coupled to the output stage for establishing the operating frequency thereof,

a variable DC supply connected to the output stage for supplying power thereto,

first control means coupled to the controlled oscillator for automatically seeking the resonant frequency of the output circuit,

second control means coupled to the variable DC supply for adjusting the output power to a desired level, the second control means including a power setting control for setting the desired power level, a wattmeter connected to the output circuit for measuring the actual output power, and means responsive to the power setting control and the wattmeter for adjusting the variable DC supply to match the actual power to the desired power,

frequency modulation means coupled to the controlled oscillator for modulating the operating frequency about the resonant frequency,

the respective control means being sufficiently independent to allow the user to independently adjust power level and frequency modulation at the automatically tuned resonant frequency.

11. A generator for driving an ultrasonic transducer comprising, in combination:

an output circuit including an output stage for driving a load including the ultrasonic transducer, a wattmeter connected in the output circuit for determining the actual output power delivered to the load,

a voltage controlled oscillator having an output frequency variable over a predetermined limited range and connected to the output stage for establishing the output frequency at which the load is driven,

means for establishing a control voltage for the voltage controlled oscillator and comprising;

a resonance follower having an input coupled to the driver circuit for sensing conditions in the load and adapted to produce an output signal which tunes the voltage controlled oscillator to the resonant frequency of the load,

frequency modulation means having a user settable control for establishing a modulating frequency, and being coupled to the control circuit for causing the voltage controlled oscillator to produce an output frequency which is modulated about the automatically tuned resonant frequency, and

a second control loop including a user adjustable power setting and means responsive to the power setting and the wattmeter for modulating the level of the voltage supply for the output stage to cause the power delivered to the load to be at the user adjusted level as the frequency of the ultrasonic load is modulated about the automatically tuned resonance frequency.

12. The combination as set forth in claim 11 further including a duty cycle control for switching the characteristics of the output signal driving the ultrasonic transducer.

13. The combination as set forth in claim 12 in which the duty cycle control is coupled to the amplitude modulated power circuit for switching the output stage on and off at a rate selected by the duty cycle control.

14. The combination as set forth in claim 12 in which the duty cycle control includes means coupled to the frequency modulation means for switching the frequency modulation on and off at a rate determined by the duty cycle control.

15. The combination as set forth in claim 11 wherein the resonance follower is coupled to the wattmeter for detecting the load current or voltage in the load as a measure of the operating characteristics of the output circuit.

16. The combination as set forth in claim 11 in which the second control loop includes a thyristor connected to modulate the voltage supply for the output stage, and an error amplifier connected to compare a signal relating to the user adjustable power setting and a signal relating to the power delivered to the load, and having an output for phase modulating the thyristor to produce an output voltage level which establishes the actual power level at the demanded level.

17. The combination as set forth in claim 11 in which the voltage controlled oscillator has an operating frequency range, and the resonance follower includes means for sweeping the output frequency of the voltage controlled oscillator from one end of the range toward the other until the resonant frequency is attained.

18. A generator for driving an ultrasonic transducer coupled to a cleaning tank, the tank being adapted to hold a volume of cleaning liquid for ultrasonic cleaning of parts immersed in the liquid, the generator comprising, in combination:

an output circuit including the ultrasonic transducer and a coupled load, the output circuit having a resonant frequency which is affected by the magnitude of the load presented to the ultrasonic transducer,

a voltage controlled oscillator for driving the output circuit, the voltage controlled oscillator having a frequency variable within a predetermined range,

a resonance follower coupled to the voltage controlled oscillator for tuning the voltage controlled oscillator to the resonant frequency of the output circuit,

a power control circuit including a user settable power level control for setting a power demand signal, means for determining the actual power delivered to the output circuit, and means for matching the actual power to the demanded power,

and means for operating the generator in a degas mode, such means including means for frequency modulating the output frequency of the voltage controlled oscillator at a rate and to a depth capable of eliminating bubbles from the liquid in the ultrasonic cleaning tank.

19. A method for driving an ultrasonic transducer coupled to a load including a cleaning tank, the tank being adapted to hold a volume of cleaning liquid for ultrasonic cleaning of parts immersed in the liquid, the method being adapted to de-gas the liquid in the tank by eliminating bubbles from said liquid, the method comprising the steps of:

driving the transducer at a frequency determined by a controlled oscillator,

tuning the controlled oscillator to a resonant frequency of the transducer and coupled load,

controlling the power delivered to the transducer to a level determined by a power setting control so as to operate the transducer at the set power level, and

frequency modulating the output frequency of the oscillator about the automatically tuned frequency at a rate and to a depth capable of eliminating bubbles from the liquid in the ultrasonic cleaning tank, thereby to de-gas the liquid.