METHOD AND APPARATUS FOR CONTROLLING FREQUENCY OF PIEZOELECTRIC TRANSDUCERS

• US 3,676,720 A
• Filed: 01/26/1971
• Issued: 07/11/1972
• Est. Priority Date: 01/26/1971
• Status: Expired due to Term

• Current Assignee: Charles C. Libby, Raymond C. Mcdaniel
• Original Assignee: Charles C. Libby, Raymond C. Mcdaniel
• Inventors: Libby, Charles C., McDaniel, Raymond C.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Reynolds, B. A.
• Application Number:
  US05/109,816
• Time in Patent Office: 532 Days
• Field of Search: 310/8.1,8,8.7,8.9,9.2,26 318/133,114,116,118 331/116
• US Class Current: 310/315
• CPC Class Codes: B06B 1/0261 taken from a transducer or electrode connected to the driving transducer
• CPC Class Codes: B06B 2201/55 Piezoelectric transducer

Abstract

The resonant frequency of a high Q piezoelectric transducer is selectively varied by adjusting the magnitude of the supply voltage for the said transducer. In one apparatus embodiment, the supply voltage to the transducer is automatically adjusted, so as to maintain the resonant frequency of the transducer nearly constant in the presence of external factors tending to shift the said frequency. The system is especially suited to transducers operating from a constant frequency supply system.

Claims

1. A system for maintaining a kilowatt power piezoelectric transducer at a nearly constant sonic resonant frequency in the presence of external factors tending to shift said frequency, comprising:

a. a high Q piezoelectric resonant structure transducer;

b. an alternating current power supply operable to provide an output voltage of a constant frequency and at a frequency slightly less than that of said resonant structure transducer;

c. means for applying said voltage to said transducer to drive said transducer; and

d. means to selectively adjust the level of said voltage applied to said transducer in accordance with shifts induced by said external factors, e. said last named means including a reactor connected in series with said power supply and said transducer, f. means selecting said voltage at the transducer to equal the supply voltage less the reactor voltage drop at a pre-selected load-current value, whereby to compensate for said shift and thereby maintain said transducer resonant frequency substantially constant.

2. A system in accordance with claim 1 wherein said power supply is a synchronous motor driven rotating type of supply.

3. A system in accorDance with claim 1 wherein said adjusting means includes power transfer detector means at said transducer for detecting shifts in said resonance frequency and generating an error signal for controlling said potential level.

4. A method for maintaining a substantially constant difference in frequency between a constant frequency power supply and the resonant frequency of a high Q piezoelectric transducer, whereby to maintain the capacity of said transducer to perform work in the presence of external factors tending to shift said resonant frequency and lower said work capacity, said method comprising:

choosing the said resonant frequency at said transducer to be slightly higher than the frequency of said power supply; and

inserting a reactor in series with said power supply and transducer, whereby shifts in said resonant frequency effect changes in the potential drop across said reactor such as to vary the potential at said transducer in a direction tending to restore said resonant frequency to its original value.