If you have any clients who drive power wheelchairs, it is important to have a basic understanding of programming. Programming affects the performance and drivability of a power wheelchair and can potentially be the difference between a client being able to drive safely or not.
Therapists are often tasked with evaluating a client's ability to operate a power wheelchair, especially when the client transitions into a long-term care facility with a chair previously used in the community. It's important to recognize that the wheelchair's programming may not be optimized for the new environment. Without understanding how programming adjustments can improve usability, therapists might mistakenly determine that a client cannot operate the chair safely. In some cases, fine-tuning the programming could enable the client to meet the requirements of a driving assessment, allowing them to continue using the power wheelchair and maintain their independence.
So, what are the basics of programming? Where should we start? For now, let's think about the common adjustments that can be made to the programming of a power wheelchair. We are going to keep this simple and assume that we are looking only at programming a proportional joystick – where the amount of deflection of the joystick gimbal corresponds to a given rate of movement, in the same way that the gas pedal in a car works.
Common programming adjustments
Although power wheelchairs come from the factory with pre-set programming, it is important that the chair is programmed specifically for the client and for the environment(s) in which the client will use the wheelchair. Common adjustments for programming power wheelchairs often include setting the minimum & maximum speeds, accelerations, and decelerations available in forward motion, in reverse, and in turns.
Acceleration and deceleration
Acceleration is how quickly the power chair reaches the programmed maximum speed, while deceleration is the rate at which the power chair will come to a stop after the joystick gimbal is released. Forward acceleration, for example, can be set to provide a slow start useful for inexperienced clients or those with slower reaction times. Likewise, depending upon the programming, forward deceleration can be a slow, coasting stop (that might not be quick enough to avoid sudden obstacles) or it can be programmed for a more sudden stop. Client postural control and balance are two factors that will influence optimal programming in acceleration and deceleration for a given client.
Speed values
The speed values are expressed as a percentage of the maximum available speed. For example, the minimum speed going in a forward direction may be set at 20% and the maximum speed may be set at 70% of the maximum available speed for that power base. The picture below illustrates the programming parameters that can be made for forward speed, with the numbers showing a percentage of the maximum.
Drive profiles
In the picture above, the letters across the top (Pr1, Pr2, Pr4, Pr5) represent five different drive profiles. If the client is driving the wheelchair in different environments, the client may need to have the programming optimized for each environment. For example, the parameters may be lower for an indoor environment and higher for an outdoor environment. If the client regularly fatigues during the day or participates in different activities, specific programming can be made in different drive profiles to accommodate the different needs. Bear in mind that the picture above is just one snapshot of programming for the forward direction. Programming must also be done for turns and for reverse, setting maximum acceleration, deceleration, and speed for each.
Torque
Other common parameters of programming that can be adjusted include torque and power. Torque is a function of power. Torque in power chairs is needed at low speeds to enable the power chair to climb curbs, perform maneuvers from a stopped position like turning, and climb a steeper ramp (for example, into a van). Without sufficient torque, the client may be unable to climb a curb cut-out without having a "running start."
Power
Power refers to the maximum amount of power that can be drawn from the battery. The amount of power influences the speed and torque that are available. The higher the power limit, the more power that is drawn from the battery. The maximum power is needed in certain conditions, such as when the power chair is stuck in a ditch and requires the use of maximum power to overcome the situation. Typically, when a client is a new power wheelchair rider, temporary programming to decrease power can assist the client's learning and success. Temporarily decreasing the power while a client is in the initial learning phase can decrease the damage that is done to walls, doorways, and furniture!
Tremor dampening
Another adjustment to the drive parameter is tremor dampening. This decreases the joystick sensitivity. This reduces the responsiveness of the wheelchair to the small, unintended movements made on the input device, lessening the effects of the tremor so that the wheelchair responds to the intended, directed movements made on the joystick gimbal.
Deadband
Deadband is the neutral zone around the center of the gimbal through which the joystick must pass before the motors are engaged. The size of the deadband can be programmed to suit the needs of the individual. For example, a client who uses a goal post joystick to operate a power chair may unintentionally deflect the gimbal away from the center due to the weight of the hand on the goal post and gravity pulling the goal post to either side. Increasing the size of the deadband increases the size of the neutral zone and means that the client must move the joystick through the neutral zone before the wheelchair will start to move. Note: deadband as a programming function is not available on all electronics.
Active throw
Active throw can be useful for clients with reduced range and strength. Active throw is used to decrease the distance that a client must deflect the joystick gimbal to achieve the maximum programmed speed. For example, if active throw is set to 50%, the client only needs to move the gimbal forward half as much distance, compared to factory presets, to achieve maximum speed. This may be a workable solution for a client who has muscle weakness and has difficulty maintaining full deflection of the joystick.
Active orientation
The last programming change we'll discuss is active orientation. This allows for a change in the axis or direction of the joystick orientation. This might be helpful if you want to midline mount with the joystick mounted sideways. The joystick can also be programmed such that pulling back rather than the typical pushing forward on the gimbal results in forward movement of the wheelchair.
To learn more about power wheelchair programming, check out these resources:
Originally written by Sheilagh Sherman, OT, with edits and updates by Erica Walling and Amy Bjornson