Multiple zone induction coil power control apparatus and method

• US 4,506,131 A
• Filed: 08/29/1983
• Issued: 03/19/1985
• Est. Priority Date: 08/29/1983
• Status: Expired due to Term

• Current Assignee: Inductotherm Corp
• Original Assignee: Inductotherm Industries, Inc. (Inductotherm Group)
• Inventors: Mortimer, John H., Rowan, Henry M., Turner, Robert C., Boehm, Paul C.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US06/527,148
• Time in Patent Office: 568 Days
• Field of Search: 219/10.77, 219/10.71, 219/10.75, 219/10.41, 219/10.43, 219/485, 219/490, 219/497, 219/503, 323/329, 323/331
• US Class Current: 219/662
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power
• CPC Class Codes: H05B 6/104 metal pieces being elongated like wires or bands

Abstract

A plurality of zones of an induction heating coil are individually controlled by varying the current through one or more zones of the coil to obtain a desired temperature profile in a workpiece. The current flow through a zone of the coil is determined by the conduction state of an associated saturable reactor, which is controlled in accordance with a preselected value or a variable value generated, for example, by a computer.

Claims

1. Induction heating apparatus for providing a desired temperature profile in a workpiece to be heated, comprising:

(a) an induction heating coil having a plurality of zones,

(b) a high-frequency induction power supply for delivering power to the coil,

(c) control means for individually controlling the power delivered to each zone of the coil, the control means comprising;

(i) means for measuring the power in each zone,

(ii) means for comparing the power in each zone to a predetermined reference and generating a first control signal based on the comparison for each respective zone,

(iii) means operatively associated with each zone and responsive to the first control signal associated with the respective zone for diverting electric current around the respective zone to thereby control the power delivered to the respective zone,

(iv) means for determining total power delivered by the power supply,

(v) means for adding the power in each zone to determine a total power in all zones, and

(vi) means for comparing the total power in all zones to the total power delivered by the power supply and generating a second control signal based on the comparison for controlling the total power delivered by the power supply.

2. Apparatus according to claim 1, wherein the high-frequency induction power supply is directly responsive to the second control signal.

3. Apparatus as in claim 2, wherein the power supply includes at least two switch means connected in series between a positive voltage source and a negative voltage source, each switch means being controlled by the second control signal.

4. Apparatus as in claim 3, wherein the switch means are silicon controlled rectifiers.

5. Apparatus according to claim 1, wherein the means for measuring the power in each zone includes means for sensing the potential across the portion of the coil in the respective zone and means for sensing the current through the portion of the coil in the respective zone.

6. Apparatus according to claim 5, wherein the means for sensing the potential is a potential transformer.

7. Apparatus according to claim 5, wherein the means for sensing the current is a current transformer.

8. Apparatus as in claim 1, wherein the means operatively associated with each zone and responsive to the first control signal associated with the respective zone for diverting electric current around the respective zone is a saturable reactor connected in parallel with the portion of the coil in the respective zone.

9. Apparatus as in claim 1, wherein the means for determining total power delivered by the power supply includes means for sensing total current delivered by the power supply.

10. Apparatus as in claim 9, wherein the means for sensing total current is a current transformer.

11. Induction heating apparatus for providing a desired temperature profile in a workpiece to be heated, comprising:

(a) an induction heating coil having a plurality of zones,

(b) a high frequency induction power supply for delivering power to the coil,

(c) control means for individually controlling the power delivered to each zone of the coil, the control means comprising;

(i) means for sensing the voltage and current in each zone,

(ii) means for computing the power in each zone from the sensed voltage and sensed current in the respective zone,

(iii) means for comparing the power in each zone to a predetermined reference and generating a first control signal based on the comparison for each respective zone,

(iv) shunt means connected in parallel with the coil section in each zone and responsive to the first control signal associated with the respective zone for shunting electric current around the respective zone to thereby control the power delivered to the respective zone,

(v) means for sensing total current delivered by the power supply,

(vi) means for calculating from the sensed total current the total power delivered by the power supply,

(vii) means for adding the power in each zone to determine a total power in all zones, and

(viii) means for comparing the total power in all zones to the total power delivered by the power supply and generating a second control signal based on the comparison to limit the output of the power supply to a predetermined maximum.

12. Apparatus as in claim 11, wherein the shunt means is a saturable reactor, the control winding of which is controlled by the first control signal associated with the respective zone and the load winding of which is connected in parallel with the coil section in the respective zone.

13. Induction heating apparatus for providing a desired temperature profile in a workpiece to be heated, comprising:

(a) an induction heating coil having a plurality of zones,

(b) a high-frequency induction power supply for delivering power to the coil, the power supply having at least two switch means connected in series between a positive voltage source and a negative voltage source, the output of the power supply being controllable in response to the conduction state of the switch means,

(c) control means for individually controlling the power delivered to each zone of the coil, the control means comprising;

(i) means for sensing the voltage and current in each zone,

(ii) means for computing the power in each zone from the sensed voltage and sensed current in the respective zone,

(iii) means for comparing the power in each zone to a predetermined reference and generating a first control signal based on the comparison for each respective zone,

(iv) a saturable reactor operatively associated with each zone and having its load winding connected in parallel with the coil section in the respective zone for shunting electric current around the respective zone to thereby control the power delivered to the respective zone, the control winding of the saturable reactor being controlled by the first control signal associated with the respective zone,

(v) means for sensing total current delivered by the power supply,

(vi) means for calculating from the sensed total current the total power delivered by the power supply,

(vii) means for adding the power in each zone to determine a total power in all zones, and

(viii) means for comparing the total power in all zones to the total power delivered by the power supply and generating a second control signal based on the comparison to control the conduction state of the switch means in the power supply.

14. Method for individually controlling the power delivered to each of a plurality of zones of an induction heating coil so as to provide a desired temperature profile in a workpiece heated by the coil, comprising the steps of:

(a) delivering high frequency power to the coil,

(b) measuring the power in each zone of the coil,

(c) comparing the power in each zone to a predetermined reference and generating a first control signal based on the comparison for each respective zone,

(d) diverting electric current around each zone in response to the first control signal associated with the respective zone to thereby control the power delivered to the respective zone,

(e) determining the total power delivered to the coil,

(f) adding the power in each zone to determine the total power in all zones, and

(g) comparing the total power in all zones to the total power delivered to the coil and generating a second control signal based on the comparison for controlling the total power delivered to the coil.

15. Method for individually controlling the power delivered to each of a plurality of zones of an induction heating coil so as to provide a desired temperature profile in a workpiece heated by the coil, comprising the steps of:

(a) delivering variable magnitude high frequency power to the coil,

(b) sensing the voltage and current in each zone of the coil,

(c) computing the power in each zone from the sensed voltage and sensed current in the respective zone,

(d) comparing the power in each zone to a predetermined reference and generating a first control signal based on the comparison for each respective zone,

(e) shunting current around each zone in a path connected electrically in parallel with the coil section in the respective zone in response to the first control signal associated with the respective zone to thereby control the power delivered to the respective zone,

(f) sensing total current delivered by the power supply,

(g) calculating from the sensed total current to the total power delivered by the power supply,

(h) adding the power in each zone to determine a total power in all zones, and

(i) comparing the total power in all zones to the total power delivered by the power supply and generating a second control signal based on the comparison to limit the high frequency power delivered to the coil to a predetermined maximum.