A Versatile and Safe Mobility Assistant*

Kim, Min-Jung2001/6/12

Special Topics in RoboticsSpecial Topics in Robotics

Design and Control of Devices for Human-Movement Assistance

Article review

*A. Lankenau and T. Rofer, IEEE Robotics & Automation Magazine, March, 2001, pp. 29~37

Bremen Autonomous Wheelchair project

• Covers mainly – Spatial cognition– Safe system– Mobility assistant for the

handicapped

• Implements – Obstacle avoidance +

Driving and routing assistant in a shared-control system

Principle idea

• A shared-control system– The wheelchair changes the

dangerous target command into a safe one.

Safety Layer (1/4)

• Local Obstacle Map– A quadratic array of cells,

each of which encodes the presence of an obstacle at the corresponding position in the environment of the wheelchair

– The wheelchair’s current rotational deviation to the map is continuously updated

Safety Layer (2/4)

• Adaptive Sonar Firing Strategy– 27 ultrasonic sensors– Can only fire 2 of its 27 sensors simultane

ously. It involves the risk of overlooking relevant obstacles.

Firing strategy is needed

Safety Layer (3/4)• Adaptive Sonar Firing Strategy

– Determine the firing sequence from• The wheelchair’s current movement direction,

steering angle, and the data represented in the map

A static firing strategy The adaptive static firing strategy

Safety Layer (4/4)

• Stopping in time– The following things must be

considered• The wheelchair’s deceleration and its

reaction time• The travel distance to the closest

obstacle

Elementary skills (1/3)

• Smooth speed control– Early detection of obstacles can

make the wheelchair decelerate in a smooth manner

– The user can concentrate on steering

Elementary skills (2/3)

• Obstacle avoidance– The assistive system

infers the will of the user whether the user moves to right or left and reinforce the trend

Elementary skills (3/3)

• Turning around– Wheelchair

turning is difficult because of the kinematical restriction

– It resembles the problem of parking a car

– Automatic turning is needed

The mobility assistant

• The driving assistant– It combines above three elementary

skills for the users to concentrate on steering

• The route assistant– The large scale navigation is done by

it especially for the users who have amnesia*

*amnesia: Partial or total loss of memory, usually resulting from shock, psychological disturbance, brain injury, or illness

Conclusion

• The Bremen Autonomous Wheelchair is designed for the handicapped in a shared-control manner

• Implemented safety layer and elementary skills for the user’s safe and comfortable navigation