The present invention relates to apparatus for establishing an electrical circuit between a plurality of contact points. More particularly, the present invention relates to devices for completing the electrical circuit between a plurality of contact points on a momentary basis. Still further, this invention is concerned with apparatus for completing an electrical circuit between a plurality of contact points for only so long as the switch is continuously actuated, the electrical contact being automatically opened when actuation is removed. Although various applications of the present invention will be readily apparent, the invention is especially useful in conjunction with surgical apparatus which requires sealing of the contact switch externally so that it can perform reliable long-term operations without being internally contaminated from seepage while tolerating relatively high temperature and/or chemical fluid environment exposures such as are associated with sterilization of surgical instruments.
A relatively large variety of momentary switch devices have developed in the past. For instance, U.S. Pat. No. 2,343,060 by Horning shows a resilient casing for a switching apparatus wherein raised buttons on the casing indicate the switch positions. By pressing on a selected one of these raised portions, an underlying rocker switch arrangement can be actuated through deflection of the external casing. Similarly, U.S. Pat. No. 3,732,384 by Fischel shows an elongated flexible plunger arrangement for deforming metal contacts into electrical connection.
More recently, there has been extensive activity towards the development of inexpensive switches for use in various keyboard operations such as the input keyboard for a calculator. Many such devices use a generally rigid key cap which is held in a guiding frame and overlies a spring-like metal dome. By pushing the cap downward through its guideway and against the upper perimeter of the metal dome, the dome is deformed temporarily downward against the contact points to establish the circuit therebetween. It has also been suggested that these keyboard caps can be molded as a single unit for application over a dome cage. For instance, U.S. Pat. No. 3,684,842 by Boulanger shows examples of both aforementioned key input arrangements. An arrangement for providing externally sealed switches of possible use in electro-surgical applications is shown in copending application Ser. No. 315,678, filed Dec. 15, 1972 entitled SWITCHING DEVICE FOR ELECTRO-SURGICAL INSTRUMENTS by J. W. Jarrard, now U.S. Pat. No. 3,911,241, which is assigned to the same assignee of the present application.
There has been a continuing need for a keyboard switch actuating cap arrangement which is adaptable for any keyboard configuration somewhat like the relatively rigid plastic cap apparatus but which is suitable for total sealing of the keyboard cap from the environment. Further, there is a need for such a keyboard actuator switch cap which does not require special molds for all potential key positions but which can employ a relatively standard cap arrangement. This need is particularly acute in conjunction with surgical apparatus which is exposed to various potential contaminants and which must be capable of enduring sterilization processing particularly using elevated temperatures in a chemical fluid environment. The use of momentary contacts for hand-held devices as electro-surgical switch controls hazards several problems which have not been satisfactorily resolved by the prior art devices. For instance, entry of blood which is a good electrical conductor into the switch housing not only can erroneously short the switch contacts but also can provide a path for the radio frequency or RF signals into the hand of the surgeon. In addition, the switch arrangement must be such as to prevent migration of contaminants or foreign matter from the switch into the sterile field or wound area.