Powered Mobility

Overview

• Introduction

• Types of powered mobility

• Outcomes

• Components of a powered wheelchair

• Future designs

The use of powered mobility?

• Means of independent mobility for people who may not be able to self propel a manual wheelchair.

• Not limited to those who cannot manually self propel a manual wheelchair.

• Not limited to those who cannot walk (social, cognitive, and functional benefits)

Why use it? • Mobility is essential for self-care, work, school, play or

leisure

• Intentional movement and active exploration is critical in the development of a child’s knowledge concerning his body, his movement and his environment(Lewis B.J.)

• Strong evidence that social integration leads to reduced mortality risks, and to a better state of mental health... social isolation and non-supportive social interactions can result in lower immune function(Seeman, 1999)

Types of powered mobility

• Scooters

• Add-on Power devices

• Power wheelchairs

Mobility Scooters

Similar to powered wheelchairs but have handlebars to steer

The seat usually swivels to facilitate easy access

Tend to be used for individuals who have systemic or whole-body disabling conditions such as coronary or lung issues or some forms of arthritis.

Add-on Power devicesAdd-on Power devices provide motorised power to the standard manual wheelchair

Some are designed either to: • assist the attendant push the wheelchair• assist the user to self-propel the wheelchair

manually• or to convert the manual chair into a

powered wheelchair controlled by a joystick.

A key feature is that they can be easily attached to

and removed from the manual wheelchair

Motor and battery built into the hub of the wheel

Powered wheelchair

• Rear wheel, Mid wheel and Front wheel drive versions

• Indoor and outdoor

• Typically controlled by a joystick but there are various other inputs

• Tilt-in-space and reclining systems are available

Positive outcomes

• Increased functional ability• Greater social inclusion• Access to education and employment• Reduced dependence on carers• Reduced fatigue• Better performance & efficiency

Challenges...?

• Access adaptations such as wheelchair spaces on public transport and wheelchair lifts are frequently designed around a typical manual wheelchairs

• Because of the weight and size they typically cannot be self propelled by the user

• Require daily charging• Generally non-foldable and requiring tie-downs

in a van for transportation• Expensive

History

• 1950s - Everest & Jennings (USA) developed the first powered wheelchair

• 1980s - wheelchairs now were microprocessor-controlled and provided customization of controls to meet the need

• 1980-90s - the revolution in powered wheelchair design with various new controls, styles, range in distance, suspension, maneuverability, and seating options

Major System Components

An input device is used by the user to specify velocity and directional when driving or to navigate within a menu displayed on the controller

Various types– Proportional (joystick). – Non-proportional (switch inputs, sip and

puff). • Scan-control can be used to reduce the number

of switches required

Switch

Finger joystick

Sip and puff

Mini joystick

Standard joystick

Switch array

Proportional Non-Proportional

Switch scanner

• Microprocessor-based• The controller translates signal from the input

device to a velocity and direction command for the power controller

• If provides feedback to the user via the display• Monitors performance of wheelchair• Contains the custom adjustable control

parameters of the chair

What controller parameters (or adjustments) do you think may be adjusted for a user?

Most common adjustments

• Max speed

• Acceleration

• Deceleration

• Turning speed

• Turning acceleration

• Turning deceleration

• The battery provides the energy for the power wheelchair to drive

• They are connected to the Power controller

• 24V (commonly 2 x 12V)

• Lead-Acid / Deep Cycle Gel Cell

Battery Protection

• To protect the batteries and the system cables from external short circuits a thermal circuit is installed

• If the battery Voltage falls below 21V damage to the battery may occur. The controller alerts the user of low voltage condition. Typically controller reduces the performance of the power chair.

?

Why are the use of “gel-cell” batteries an important safety issue?

“gel-cell” batteries are sealed and so no acid will leak in the event that the chair falls over

• The Power Controller sends the power to the motors and to the other modules

• It controls the electrical energy delivered to the motors.

• The motors control the power wheelchair speed and direction

• 24V AC or DC • resistance of different motor types

varies typically between 20 and 350 mΩ

• Current rating 60 – 120 A• Fail-safe electro-magnetic parkbrakes

attached to the motors prevent the power chair moving when it is not actively driven or when the power is turned off.

?

How is a wheelchair with two motors steered?

Motors rotate wheels at different speeds

The turning angle is relative to the difference

Modern power chairs now have the options to control a PC, mobile phone or aspects of the environment

Could this be the future?

electric drive motor with gyroscopic sensors to help the driver to move

Summary

• Mobility is essential for quality of life

• Powered mobility provides a means of independence

• There are various types of powered mobility devices to suit a user needs

• Enables the user to have control of their environment

Bibliography1. Albert M. Cook, Susan M. Hussey 2002 Assistive technologies: principles

and practice

2. Learner J, Beverly J, 2008, Learning Disabilities and Related Mild Disabilities

3. Chan J, Davey C, Bath Institute of Medical Engineer, Buyers Guide Add on power devices for manual wheelchairs Aug 2008

4. D.A. Hobson,September 1999, viewed 10th May 2010 http://www.wheelchairnet.org/

5. DX System Manual, Dynamic Controls, http://www.dynamiccontrols.com/index.cfm/1,81,html

6. Wikipedia, Mobility scooter, viewed 10th May 2010<http://en.wikipedia.org/wiki/Mobility_scooter>