GB2025230A

GB2025230A - Control circuits for electrosurgical devices

Info

Publication number: GB2025230A
Application number: GB7826892A
Authority: GB
Original assignee: Dentsply International Inc
Current assignee: Dentsply Sirona Inc
Priority date: 1978-06-14
Filing date: 1978-06-14
Publication date: 1980-01-23
Also published as: GB2025230B; GB2023380A; GB2023380B

Abstract

A control circuit for a radio frequency electrosurgical device includes a manually operable switch (26) that is electrically isolated from the R.F. circuit supplying electrodes 22,23 of the device. The switch is connected in series with a photovoltaic cell (58) and relay means (44,46). The photovoltaic cell is illuminated by a lamp 66 so that closing of contacts 33 or 37 of the switch causes energisation of the relay means. The relay means is connected to actuate the electrosurgical device. The voltage at the switch is limited to the low voltage produced by the photovoltaic cell. <IMAGE>

Description

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GB 2 025 230 A 1

SPECIFICATION

Control circuit for an electrical device

5 This invention relates to a control circuit for an electrical device.

In many types of electrical devices, it is necessary to isolate a switch from circuits controlled by the switch, and an object of this invention is to provide a 10 control circuit in which a device controlled by the switch is electrically isolated from the switch.

In radiofrequency electrosurgical devices, it can be desirable to have a switch close to an active electrode as in a handpiece. However, if conventional 15 switch leads carrying substantial currents extend to the handpiece, there is a danger of leakage of current from the switch leads to a switch actuator to cause burns and other injuries. In a preferred form of this invention a switch is provided for an electrosurgical 20 device in which current in switch leads is limited to prevent such buning.

According to the invention there is provided a control circuit for a radiofrequency electrosurgical device including a radiofrequency generator, a 25 handpiece, an active electrode supported on the handpiece, and switching means mounted in the handpiece which comprises a photovoltaic cell and relay means connected in series with the switching means, means for illuminating the photovoltaic cell, 30 whereby closing of contacts of the switching means causes actuation of the relay means, and means connected to the relay means for causing the radiofrequency generator to power the active electrode, voltage at the switching means being limited by the 35 voltage produced by the photovoltaic cell.

The invention also provides a control circuit for an electrical device which comprises a photovoltaic cell, switching means, relay means, means for illuminating the photovoltaic cell, closing of contacts of the 40 switching means causing actuation of the relay means, and means connected to the relay means for actuating the electrical device, voltage at the switching means being limited by the voltage produced by the photovoltaic cell.

45 The invention further provides a combination optical radiation source and photovoltaic cell intended to illuminate a photovoltaic electrical generator source, which electrical generator source operates a relay to operate secondary circuits intended to pro-50 vide isolation to such secondary circuits to prevent undesirable leakage currents from the primary electrical power source.

The system of the invention inherently limits the current which circulates in switch leads. 55 The photovoltaic cell can be powered by a radiating source or lamp which, in turn, can be powered by an appropriate electrical power source, which can be a portion of the device controlled by the switch circuit. The power circuits of the device are fully iso-60 lated from the photovoltaic cell because there is no direct connection therebetween, and the power circuits are similarly isolated from the leads which extend to the switch. The current supplied by the photovoltaic cell is limited by the electrical charac-65 teristics of the photovoltaic cell and inherently cannot exceed a given output voltage at optical saturation, which can be sufficiently low that there is limited potential danger if the voltage at the switch contacts reaches an operator. When the device con-70 trolled by the switch is an electrosurgical device, and the switch is in a handpiece, an active lead of the electrosurgical device can be shielded and can be closely related to earth so that there can be no substantial leakage of radiofrequency current from 75 the active lead to the switch leads.

The accompanying drawing is a schematic view showing a switch circuit constructed in accordance with an embodiment of this invention, the switch circuit being shown in conjuction with a radiofre-80 quency electrosurgical device.

The drawing shows a circuit for a radiofrequency electrosurgical device which includes a radiofrequency generator 10 (not shown in detail). The radiofrequency generator 10 is coupled through a condenser 85 12 to a primary winding 13 of a coupling transformer 14. One side of a secondary winding 15 of the coupling transformer 14 is coupled to an active power lead 16 through a condenser 17. The active power lead 16 can be the inner or shielded conductor of a coaxial 90 cable 18. The outer conductor or shield of the coaxial cable 18 is connected to a return side of the secondary winding 15 and through a condenser 19 and a monitor device 21 to earth. The monitor device can be of the type shown in my co-pending U.S. Patent 95 application Serial No. 543,489 filed January 23,1975, and provides a low impedance path from the shield of the coaxial cable 18 to earth.

The active power lead 16 powers an active electrode 22. A passive electrode 23 is coupled to the 100 return side of the secondary winding 15 through a condenser 24.

Operation of the radiofrequency generator 10 is controlled by a switch assembly 26 mounted in a handpiece 27 which supports the active electrode 22. 105 The switch assembly 26 includes switch arms 28 and 29, which are carried on a shaft 31. The shaft 31 is pivotally mounted in appropriate bearings (not shown). When a push button 32 is depressed, the switch arm 29 engages a contact 33 to which a lead 110 34 is attached. When a push button 36 is depressed, the switch arm 28 engages a contact 37 to which a lead 38 is attached. A lead 39 is attached to the switch arms 28 and 29. The lead 39 is also attached to a tubular electrical shield 41. The leads 34 and 38 115 extend through the electrical shield 41.

The leads 34 and 38 are connected through radiofrequency inductances 47 and 48 to relay coils 44 and 46, respectively. The relay 44 includes contacts 44A and 44B, which are attached to leads 51 and 52, 120 respectively. The leads 51 and 52 can be part of the control circuitry of the radiofrequency generator 10 (not shown in detail), which leads 51 and 52, when connected together, permit the radiofrequency generator to deliver a selected radiofrequency elec-125 trosurgical current, such as a cutting current, to the transformer 14, the active power lead 16 and the active electrode 22. The relay 46 includes contacts 46A and 46B which are attached to leads 54 and 56, respectively. The leads 54 and 56 can be part of the 130 control circuitry of the radiofrequency generator 10,

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GB 2 025 230 A

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which leads 54 and 56, when connected together, permit the radiofrequency generator to deliver another selected radiofrequency electrosurgical current, such as a coagulating current, to the trans-5 former 14, the active power lead 16 and the active electrode 22.

Power for actuating the relay coils 44 and 46 is supplied by a photovoltaic cell 58. A lead 59 connects the photovoltaic cell 58 to the relay coils 44 and 10 46. A lead 61 connects the photovoltaic cell 58 to earth and to the shield 41. Capacitors 63 and 64 are connected between the lead 34 and the leads 38 and 61, respectively, and permit radiofrequency current which may reach the leads 34 and 38 to return to 15 earth without passing through the photovoltaic cell

58 and the relay coils 44 and 46. The radiofrequency inductances 47 and 48 prevent such radiofrequency current passing through the photovoltaic cell 58 and the sensitive relay coils 44 and 46.

20 The photovoltaic cell 58 can be illuminated by an appropriate lamp 66, which can be powered by leads

59 and 61. The leads 59 and 61 can be connected to an appropriate portion of the circuitry of the radiofrequency generator to provide the necessary voftage

25 to operate the lamp 66. The photovoltaic cell 58 can be designed to have an output of 0.6 volts D.C. and a current of 60 milliamperes. Such a cell can operate a sensitive relay such as a Potter-Brumfield relay MDP-2109. The lamp 66 can be a low voltage annun-30 ciator incandescent tungsten filament lamp such as a Sylvania 6RB or 12RB annunciator lamp. Such a lamp, when operated at 50% of full output rating, has a very long life and supplies sufficient radiant energy to optically the photovoltaic cell saturate. 35 The voltage atthe contacts of the switch operating push buttons 32 and 36 is limited by the characteristics of the photovoltaic cell 58 and cannot exceed the output voltage of the photovoltaic cell 58 at optical saturation, which can be sufficiently low that there is 40 no substantial danger of radiofrequency burns to the operator atthe push buttons. The switching leads 34 and 38 are isolated from the active power lead 16 by the shield 18 of the coaxial cable which surrounds the active power lead 16 and the shield 41 surround-45 ing the switching leads 34 and 38 to prevent leakage of radiofrequency current between the active power lead 16 and the switching leads 34 and 38.

Claims

1. Acontrol circuitfora radiofrequency elec-50 trosurgical device including a radiofrequency generator, a handpiece, an active electrode supported on the handpiece, and switching means mounted in the handpiece which comprises a photovoltaic cell and relay means connected in 55 series with the switching means, means for illuminating the photovoltaic cell, whereby closing of contacts of the switching means causes actuation of the relay means, and means connected to the relay means for causing the radiofrequency generator to 60 power the active electrode, voltage at the switching means being limited by the voltage produced by the photovoltaic cell.

2. A control circuit as claimed in Claim 1, wherein there is an active power lead powered by the radiof-

65 requency generator and connected to the handpiece to power the active electrode, switch lead means connecting the switching means with the relay means and the photovoltaic cell, and an electrical shield separating the active power lead from the switch lead means.

3. A control circuit as claimed in Claim 2, wherein the electrical shield surrounds the active power lead.

4. A control circuit as claimed in Claim 2 or 3, wherein the electrical shield surrounds the switch lead means.

5. A control circuit as clafmed in Claim 2, wherein the electricaf shield includes first shield means surrounding the active power lead and second shield means surrounding the switch, lead means.

6. A control circuit as claimed in any preceding claim, wherein there is a radiofrequency inductance means m series with the switching means, the relay means and the photovoltaic cell to protect the photovoltaic cell and the relay means from radiofrequency current.

7. A control circuit as claimed in any preceding claim, wherein there is a switch lead means connecting the switching means with the relay means and the photovoltaic cell and a capacitor means coupling the switch lead means to earth to direct radiofrequency current from the photovoltaic cell and the relay means.

8. A control circuit for an electrical device which comprises a photovoltaic cell, switching means,

relay means, means for illuminating the photovoltaic cell, closing of contacts of the switching means causing actuation of the relay means, and means connected to the relay means for actuating the electrical device, voltage atthe switching means being limited by the voltage produced by the photovoltaic cell.

9. A control circuit for an electrical device including a handpiece and switching means mounted in the handpiece which comprises a photovoltaic cell, relay means connected in series with the switching means, means for illuminating the photovoltaic cell, whereby closing of contacts of the switching means causes actuation of the relay means, and means connected to the relay means for causing actuation of the electrical device, voltage at the switching means being limited by the voltage produced by the photovoltaic cell.

10. Acontrol circuit for an electrical device substantially as herein described with reference to the accompanying drawing.

11. A combination optical radiation source and photovoltaic cell intended to illuminate a photovoltaic electrical generator source, which electrical generator source operates a relay to operate secondary circuits intended to provide isolation to such secondary circuits to prevent undesirable leakage currents from the primary electrical power source.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1979.

Published atthe Patent Office. 25 Southampton Buildings, London, WC2A1AY, from which copies may be obtained.

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