Navigation Aids: Enhance Foot Control Usability

Introduction

The ever-increasing functional capabilities of emerging medical devices have precipitated new requirements for the multi-function foot controls used to operate the equipment. These foot controls typically consist of multiple actuators … one for each required control function.

For example, it is not uncommon to find foot controls for electrosurgical generators with 3 functions, foot controls for endoscopic surgical apparatus with 5 or 6 functions, cataract surgery systems requiring 6 to 9 control functions, and surgical microscopes requiring 10 or more functions.

This increasing foot control complexity has placed new challenges on the manufacturer to offer and produce foot controls that are easy to navigate and easy-to-use. Optimum usability requires creative ways to quickly locate the foot control unit and each of its functional actuators.

To address these challenges, visual and non-visual aids can (and are) being designed into the medical-grade foot controls to enhance their usability.

Visual navigation aids include:

  • Use of different actuator types.
  • Use of different actuator colors.
  • Use of graphics, text, and internationally-recognized icons.
  • Use of lighting.

Non-Visual navigation aids include:

  • Foot rests/landing pads.
  • Protection braces/carrying handles.
  • Console geometries that facilitate easier/intuitive actuator location.
  • Actuator geometry/location.

Each of these types of navigation aids are presented below, with selected application examples for clarity.

Visual Navigation Aids

Actuator Styles:

One visual tool for aiding in navigation is the use of different types of actuators for differentiating between various control functions. Medical device OEMs can choose between a wide selection of actuator types/styles including:

  • Pedals.
  • Rocker-style switches.
  • Push buttons.
  • Joy sticks.
  • Joy pads.
  • Custom-designed actuators.

The choice may be influenced by their basic control function (e.g. on/off vs. proportional control) and/or their frequency-of-use during a specific procedure. Appendix A provides a brief review of these options and a sampling of typical applications for each.

Figure1 and Figure 2 shows examples of the use of some of these type actuators in a selection of medical device applications.

Figure 1. Surgical Microscope Foot Control – Here the joystick enables the positioning of the microscope in the surgical field (X- and Y-axis). Two rocker switches provide control of “Zoom” and “Focus”. Pushbutton actuators at the four corners provide light “Dimming/Brightness” control for optimal contrast, a light “On/Off” switch, and a camera control for capturing a desired image.
Figure 2. Biopsy Sampling System Control / Foot Control – Here the easily-located pedal and pushbuttons provide easy management of the sample acquisition process.

Color, Graphics, Text and Icons

Another effective technique for enhancing user-friendliness is the use of color and graphics to identify the specific function performed by each actuator. For example, the use of blue and yellow pedals is standard for identifying the “cut” and “coagulation” functions on foot controls used with high-frequency electrosurgical generators (Figure 3.) Often functions are identified by text, graphics and/or easily-recognized icons. Effective use of graphics is illustrated in Figure 4. for a unit which positions an examination chair.

Lighting

Some applications require use of a foot control in a darkened/low-light environment. In such instances, foot controls can be equipped with LED’s that cast a “glow” around the unit to allow the user to easily locate it on the floor. Depending upon the design of the foot control console, the LEDs may be located such that they are not visible via a direct line-of-sight. Here they simply provide an “aura” … or soft glow that is quite visible when ambient light is low.

Figure 3. High-Frequency Electrosurgical / Generator Foot Control – Integral “landing pad” and extended height side walls serve as convenient reference surfaces for locating desired pedal.
Figure 4. Examination Chair Foot Control – Custom graphics foster ease-of-use and fast user acclimation to foot control.

Non-Visual Navigation Aids

Some users may prefer aids that enable them to locate or navigate without the need to look at the foot control … that is, without having to take their eyes from the surgical field, or a computer display. To accomplish this, a number of tactile techniques are available. These include:

Foot rests/Landing pads

This is simply an area provided on the foot control console where the user can rest their foot until the next control action is required. With this as a reference point, the operator (through familiarity with the unit) can move their foot to the desired control actuator without the need to take their eyes off the procedure. Typical examples of such foot rest/landing pads are shown in Figure 3 and Figure 5. Located at the center of the console, between the two actuator pedals, the user simply moves their foot left or right to initiate the desired control function.

Figure 5. Medical Image Retrieval System / Foot Control – Center foot rest serves as convenient reference point for locating desired pedal.

Physical Reference Surfaces

Another effective technique is the use of physical references surfaces designed into the unit. This can be seen in Figure 3. Here the height of the console’s outer left and right sidewalls enable the user to simply move their foot to the right or left to determine on which of the two pedals their foot is currently positioned. Thus, regardless of where the operator’s foot is at any given moment, it is easy to determine its’ location without looking down.

Figure 6. PHACO Emulsification Foot Control – This configuration of actuators provides an easy tactile pattern to locate and actuate each of the specific control functions tactilely after only a few user experiences.

Carrying Handles/Protection Braces

One example of this optional accessory is shown in Figure 2. Such “handles” not only serve as a foot rest and point of reference, but afford an easy means of carrying the foot control (thus eliminating the possible damage to the cable at the strain relief). In some laser-based device applications, they also serve as a recognized and acceptable protection guard against inadvertent operation as required by IEC 60601-2-22.

Depending upon the design of the handle, it can also serve as an easy means of moving the foot control during the procedure. This is accomplished simply by using one’s instep to lift the unit and reposition it (without having to reach down or touch the unit during the procedure).

Such handles can often be designed to be collapsible … e.g. to fold-down upon release of an integral mechanical latch. Doing so reduces the overall height of the unit for ease of storage on a cart’s docking station or in cabinet.

Console Geometry

Depending upon the application, and its’ control requirements, the basic foot control console (which serves as the host for the control actuators and provides the wiring compartment for accommodating the electric/electronic components), can be designed to assist with navigation. One example is the angled console shown in Figure 6. Designed for cataract surgery (PHACO emulsification procedures), this unit features a bidirectional pedal (X and Z axes) capable of analog or digital control, and four pushbuttons … located at the four corners of the console … toe left, toe right, heel left, and heel right. This pattern allows for easy selection of the appropriate control function from the rest position on the pedal, or from the touch point at the base of the unit.

Summary

As new medical devices continue to be developed, their capabilities may require use of multifunction-foot controls. If so, the medical device OEM has the luxury of:

  • Providing integral navigation aids, while satisfying their functional, ergonomic and aesthetic foot control needs with a wide selection of “off-the-shelf” consoles, actuators, handles, colors and graphics assembled into a “customized’ solution … and without the need for any non-recurring engineering development costs or tooling investments.
  • Or, if desired, optimizing the usability with a fully-custom design, that addresses the functional, ergonomic, and aesthetic needs with new actuators, or other custom accessories. One such example is shown in Figure 7 … a custom dental system foot control.

Since the foot control is often the primary user interface gating the customer’s experience, consideration and implementation of some navigation aids can optimize the medical device’s usability and enhance this experience.

Figure 7. Dental Chair-Handpiece / System Foot Control – Here custom slide-operated switches (left and right), a custom 4-function joy pad (center), a custom dual-action slide actuator (center-front), and a custom carrying handle/foot rest have been combined into a compact unit providing one (1) proportional and nine (9) on/off control functions. Arranged for easeof-navigation, each function is easy to locate and operate.

Appendix A

Style Actuator Type of Control Available Typical Application
Pedal Digital (“On/Off”) and/or Analog (Proportional … e.g. speed, power, vacuum, et al) Typically used where the controlled function is operated frequently and/or for relatively long “on” intervals during a procedure.
Rocker Switch Digital (“On/Off”) or Analog (Proportional … e.g. speed, power, vacuum, et al) This two-function actuator is typically used for bidirectional positioning control or the control of complementary functions (e.g. liquid dispensing-aspiration).
Pushbutton Digital (“On/Off”) Often used to control a function that is required/ used relatively infrequently (compared to other control functions) e.g. mode selection, direction control, power setting, light dimming, “preset” control, et al.
Joy Stick Digital (“On/Off”) Typically used for the bidirectional (+/-) control of two discrete axes (e.g. up/down, left/right, tilt up/tilt down, forward/reverse).
Joy Pad Digital (“On/Off”) Typically used for the bidirectional (+/-) control of two discrete axes (e.g. up/down, left/right, tilt up/tilt down, forward/reverse).