Resonant frequency tracking system and method for use in a radio frequency (RF) power supply

• US 6,316,756 B1
• Filed: 01/31/2000
• Issued: 11/13/2001
• Est. Priority Date: 07/10/1998
• Status: Expired due to Term

• Current Assignee: Ambrell Corporation (inTEST Corporation)
• Original Assignee: Ameritherm, Inc. (inTEST Corporation)
• Inventors: Thompson, Leslie L., Lincoln, Daniel J., Schwenck, Gary A.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US09/495,159
• Time in Patent Office: 652 Days
• Field of Search: 219/663, 219/665, 219/666, 219/667, 219/661, 219/670, 219/650, 219/779, 363/74, 363/95, 363/97, 323/284, 323/285
• US Class Current: 219/666
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: H05B 6/04 Sources of current
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power

Abstract

A radio frequency (RF) power system for providing RF power to a load. The RF power system comprises a tank circuit; a direct current (DC) voltage source that provides a DC voltage within a first predetermined range; an amplifier, coupled to said DC voltage source, to provide an alternating voltage to said tank circuit; a frequency controller, coupled to said amplifier, to control a frequency of said alternating voltage provided by said amplifier; and a power sensor being coupled to said tank circuit for providing a signal to said frequency controller, wherein said frequency controller controls said frequency of said alternating voltage based on said signal provided from said power sensor.

Claims

1. A radio frequency (RF) power system for heating a workpiece, comprising:

a circuit;

a direct current (DC) voltage source that provides a DC voltage within a first predetermined range;

an amplifier, coupled to said DC voltage source, to provide an alternating voltage to said circuit;

a frequency controller, coupled to said amplifier, to control a frequency of said alternating voltage provided by said amplifier; and

a power sensor being coupled to said circuit for providing a signal to said frequency controller, wherein said frequency controller controls said frequency of said alternating voltage based on said signal provided from said power sensor, and wherein said power sensor senses both forward and reflected power, and said signal represents a ratio of said reflected power to said forward power, wherein

said frequency controller comprises a resonant frequency tracking means for tracking a resonant frequency of said circuit while the workpiece is being heated, thereby enabling said frequency controller to control said frequency of said alternating voltage so that said frequency of said alternating voltage tracks said resonant frequency of said circuit while the workpiece is being heated, wherein said resonant frequency tracking means uses said signal that represents a ratio of said reflected power to said forward power to track said resonant frequency of said circuit.

2. A method for inductively heating a workpiece, comprising the steps of:

applying an alternating voltage to a circuit having a resonant frequency that changes while the workpiece is being heated, the alternating voltage having a frequency and having a first voltage level;

determining an estimate of the resonant frequency of the circuit;

setting said frequency of said alternating voltage provided to said circuit to said determined estimate of said resonant frequency;

increasing said voltage level of the alternating voltage from said first voltage level to a second voltage level after determining said estimate of said resonant frequency of said circuit; and

tracking said resonant frequency of said circuit until a heat off indication is generated.

3. The method of claim 2, wherein the step of tracking said resonant frequency of said circuit until a heat off indication is generated comprises the steps of:

(a) determining a ratio of power applied to said circuit to power reflected from said circuit;

(b) modifying said frequency of said alternating voltage applied to said circuit;

(c) determining a ratio of power applied to said circuit to power reflected from said circuit;

(d) comparing the magnitude of said ratio determined in step (a) to the magnitude of said ratio determined in step (b);

(e) modifying said frequency of said alternating voltage applied to said circuit based at least in part on a result of said comparison of the magnitude of said ratio determined in step (a) to the magnitude of said ratio determined in step (b); and

(f) repeating steps (a) through (e) until said heat off indication is generated.

4. A radio frequency (RF) power system for heating a workpiece, comprising:

a tank circuit;

a direct current (DC) voltage source that provides a DC voltage within a first predetermined range;

an amplifier, coupled to said DC voltage source, to provide an alternating voltage to said tank circuit;

a frequency controller, coupled to said amplifier, to control a frequency of said alternating voltage provided by said amplifier; and

a power sensor being coupled to said tank circuit for providing a signal to said frequency controller, wherein said frequency controller controls said frequency of said alternating voltage based on said signal provided from said power sensor, and wherein said power sensor senses both forward and reflected power, and said signal represents a ratio of said forward power to said reflected power, wherein

said frequency controller comprises a resonant frequency tracking means for tracking a resonant frequency of said tank circuit while the workpiece is being heated, thereby enabling said frequency controller to control said frequency of said alternating voltage so that said frequency of said alternating voltage tracks said resonant frequency of said tank circuit while the workpiece is being heated, wherein said resonant frequency tracking means uses said signal that represents a ratio of said forward power to said reflected power to track said resonant frequency of said tank circuit.