Customized Foot Switches

For Medical Applications

Ms. Dawn Etta, Application Engineer, STEUTE Schmersall

The use of high technology in the medical industry continues to precipitate improved equipment for the diagnosis and treatment of patients. In many of these applications, the use of foot switches to control equipment frees the operator's, technician's or physician's hands for other critical tasks while enhancing the functionality of the system.Ex Feat Foot Sw

Dental chair multi-function foot switch

Once used only as a simple on/off switch providing control of power or unidirectional motion, today's foot switches are required to provide multi-directional motion control, as well as address multiple other control functions. In addition, they must often meet a variety of unique performance requirements characteristic of medical applications, including tolerance to cleansing solutions, disinfectants and washdown; suitable use in an anesthesia environment; special color coding for ease of use; special shield geometry for functional and safety considerations; multiple-stage operation; and compliance with domestic and international standards and
directives.

Standard, off-the-shelf foot switches typically do not address such needs. The diversity of applications and the various levels of complexity dictate designs that address each of the unique requirements for operational functionality and ease-of-use. Two such custom-designed foot switches are described below. These examples illustrate to the system designer the ease with which he or she can go beyond the simple on/off foot switch to achieve optimum productivity, functionality, and ease-of-operation.

Foot Switch for Microsurgical Microscope

A multi-function foot switch control designed specifically for a microsurgical microscope was developed to meet the specifications of microscope system design engineers. It features six pushbutton actuators for on/off and other optional control func tions; two pivoted rocker-style actuators for the bi-directional motion control; and a joystick for X-Y displacement control.Ex Feat Foot Sw2

Surgical microscope control

The specific functions controlled included a number of on/off, focus, zoom, and other control features. As a multifunction control, this foot switch enabled the microscope designer to achieve their goals of overcoming the limitations of a fixed focus surgical microscope, as well as eliminate the need to move the entire microscope to adjust focus or field-of-view.

In addition to meeting the control requirements, the foot switch meets the stringent requirements of IEC 601; features an IPX8 (according to IEC 529) rating to tolerate submersion in cleansing solutions, disinfectants, or other liquids; and features color-coded control actuators for easier identification and operation. It also conforms to the standards and directives necessary to bear the CE-mark (according to the Medical Device Directive 93/42/EEC) and qualify for TUV's GM (approved medical device) certification.

Dental Chair Multi-Function Foot Switch Control

Designed expressly to meet the specifications for a state-of-the-art dentist chair, a multi-function foot switch control was designed to feature a multi-directional (4 degrees of motion) X-Y position control; an analog output actuator for controlling drill speed; four optional actuators for controlling ancillary functions such as water dispensing, air, lamp on/off, etc.

 The introduction of the Medical Device Directive (93/42/EEC) on January 1, 1995 precipitated requirements for new tests and procedures for certifying the quality and safety of medical equipment. No longer could the former GS mark, governed by the now defunct Medical Equipment Ordinance, be used to indicate conformity.

To fill this void, TUV RHEINLAND developed new standards for conformity. Equipment that meets these requirements are permitted to bear TUV's GM mark. The following conditions must be met before a device is awarded GM (approved medical device) certification:

  • A 'type-examination' must be presented that certifies the device meets the 'essential requirements' of the Medical Device Directive.
  • This is a third-party examination conducted by an approved, independent testing agency/notified body assuring that the device conforms to the rele- vant standards and directives listed in the product's Declaration of Conformity.
  • Additional requirements that must be fulfilled and verified are agreed upon by the manufacturer.
  • Contractual agreements regarding the maintenance of these additional re- quirements are concluded with the manufacturer.
  • Manufacturer agrees to enclose the GM certificate, in which these special features are described, with each device.
  • Manufacturer agrees to be subject to factory surveillance with annual inspection to verify continued conformance.

This customized foot switch control relieves the dentist and the dental technician from hand operation of these functions, enabling them to perform other tasks more efficiently. In addition to meeting the functional requirements, the foot switch also satisfies the requirements of IEC 601. Like the foot switch for the microsurgical microscope, this device also conforms to the standards and directives necessary to bear the CE-mark (according to the Medical Device Directive 93/42/EEC) and qualify for TUV's GM (approved medical device) certification.

Custom Configurations and Options

The above examples present only a small selection of the custom options available to satisfy the specific requirements of the application. Other custom foot switch options include combinations of the following:

  • Special actuator colors & markings.
  • Custom foot rests.
  • Custom pedal covers.
  • Special cables & connectors.
  • Custom shields.
  • Slow or snap-acting switch inserts.
  • Reed or miniature switch contacts.
  • Analog outputs for variable control functions.
  • Momentary or latching operation.
  • Multiple pedal configurations.
  • 2- and 3-stage operation.
  • Suitable for use in anesthesia (AP) environment.
  • Choice of environmental (IP) ratings to IPX8 (per IEC529).
  • Optional materials of construction.

These options can be combined to meet the safety, hygienic, and functional requirements specific to the equipment and its operating environment. In addition to satisfying the relevant Directives for CE-marking, custom foot switches can now be designed to satisfy UL, CSA and the recently enacted Medical Device Directive (93/42/EEC) without compromising functionality.

For more information, contact Schmersal, 5 West Cross Street, Hawthorne, NY 10532. 914-769-4169. Circle 500.

Originally published in the November  1998 issue of designfax.
Please Note: some pictures or diagrams are only available through the printed media.