Proportional control

The standard EPW joystick commonly prescribed in the clinic is a type of proportional control, so named because the device’s output (the wheelchair’s velocity) increases as the stick is progressively moved away from center. These devices also can be referred to as movement-sensing joysticks (MSJ) because the stick physically moves as a user exerts force on it. Other proportional input devices, such as trackballs, some head arrays, and touchpads, are also available. Similar controls used by unimpaired individuals are automobile accelerator pedals and video game joysticks. Efficient use of proportional controls generally requires a certain amount of intact proprioception, joint mobility, and dexterity.

Individuals who do not have the ability to operate proportional controls must use a combination of switches with or without scanning control. Although discussion of switch and scanning control is outside the scope of this article, the reader should be aware that many options are available besides the technology mentioned in this article, and switches can be added to some of the newer joysticks.

Profiles and features overview

Most joysticks have a variety of profiles that can each contain a plethora of different parameter settings. What follows is a detailed description of the most common parameters and features used to date. Some devices contain off-the-shelf profiles such as those for a new user, which can be used as a starting template. A clinician may want to have available a wide array of profiles set up to appropriately evaluate clients for power mobility. Each consumer may want more than one profile to accommodate for variations in his or her condition (eg, to accommodate for fatigue or during times of disease flares). The number of parameter combinations is almost limitless, so it is important to have a few standard templates established as a starting point for further customization. Decisions about the types of devices and settings to select for an individual depend on a person’s current level of function and the individual’s prognosis. Underuse of these features is probably one of the biggest obstacles to harnessing the potential of modern joystick technology.

Profiles and features overview

Most joysticks have a variety of profiles that can each contain a plethora of different parameter settings. What follows is a detailed description of the most common parameters and features used to date. Some devices contain off-the-shelf profiles such as those for a new user, which can be used as a starting template. A clinician may want to have available a wide array of profiles set up to appropriately evaluate clients for power mobility. Each consumer may want more than one profile to accommodate for variations in his or her condition (eg, to accommodate for fatigue or during times of disease flares). The number of parameter combinations is almost limitless, so it is important to have a few standard templates established as a starting point for further customization. Decisions about the types of devices and settings to select for an individual depend on a person’s current level of function and the individual’s prognosis. Underuse of these features is probably one of the biggest obstacles to harnessing the potential of modern joystick technology.

Controllers

The joystick is composed of the interface between the user and the device (ie, the stick) and a controller that acts as the intermediary between the human input on the stick and the output of the EPW. Controllers contain the electronics and software, modify the signals from the interface, and convert them to output that is passed along to the device being controlled. The controller can be integral (ie, the main controller is integrated into the chair and used by the client) or remotely placed, such as one used by an attendant. A nonexpandable controller regulates the speed and direction of the power wheelchair drive mechanism and can be used to control up to 2 power seating actuators that allow the user to change the orientation of the seat. Typically, nonexpandable controllers can accept only a proportional joystick as an input device. An expandable controller can accommodate many other proportional input devices besides a standard joystick, such as a touchpad or proportional head array, and nonproportional input devices, such as a sip and puff or head array switches. This type of controller also operates 3 or more power seating actuators, sometimes requiring an additional component to do so. An expandable controller may be used to operate such devices as a separate display for a different control interface, an alternative and augmentative communication device, a computer, or an attendant control.

Mounting and compatibility issues

Appropriate mounting of the input devices is critical to functional operation for any user and requires a thorough clinical assessment to determine the best access point for the device. Some joysticks have a built-in handrest for stability, and the shape of the stick often can be changed to accommodate the body part that is being used to operate it. Not all control interfaces can be used with all EPW bases. Intellectual property issues and incompatibility issues between components and brands limits a clinician’s ability to create a truly fully customizable device, which is another hurdle to advancements in this field. Software also must be updated frequently, which may require a secure digital (SD) card, a flash upgrade, or download via computer. Some systems, when taken “off the shelf” have factory settings, and a programmer or SD card may be needed to modify the device for a particular user. On the other hand, some systems are “plug and play,” which means that some of the modules can be recognized and programmed automatically.

Programming

Many different joystick parameters can be programmed or customized. Usually a separate programming device is used to program these features, but some parameters can be programmed through the display on the input device itself. In other cases, programming files can be transferred by mini-USB or memory stick. Some devices may allow memory back-up of a program for later use. This feature may be particularly important for clinicians who spend a great deal of time creating a custom program and want to use it for similar clients or tweak it later for the same clients. Occasionally, a new programming device may be needed if the control interface technology changes substantially. If an input device is not programmed appropriately, the device may be difficult to control, which could result in the client appearing to fail an initial assessment for power mobility, an unsafe driving condition, or fatigue during use.

Some programming devices also allow programming of parameters during use of the EPW so they can be tested in real time. Diagnostics may be available that can help the programmer troubleshoot errors. Parameters such as the wheelchair speed or angle of seat tilt sometimes can be monitored in real time.

Several different parameters can be programmed. Changing torque can provide more power at lower speeds. Sensitivity and acceleration also can be set, which controls how quickly the EPW responds to the user input. Some manufacturers refer to changing the sensitivity as “tremor damping”; however, this use of the term does not refer to filtering a specific frequency of movement. The dead zone (also sometimes called the deadband or neutral zone) is the distance through which the joystick can be moved but for which no EPW output is generated. Some models offer an alternate mode in which the EPW’s other features, such as a communication device, can be used but the chair is disabled from driving mode. Another difference among interfaces is the tracking technology, which is used to reduce the compensatory movements a user must make, such as for caster alignment after making a turn.