Sensor activation for wheelchair driving in confined spaces with a tongue controlled oral interface

A tongue controlled oral interface for assistive devices has been designed with air-core inductive sensors in printed circuit board technology. The oral interface provided the functionality of a full character set keyboard in keyboard mode, as well as the functionality of a proportional mouse similar to that of a joystick, with control buttons, in wheelchair mode. A keypad of ten sensors and a mousepad of eight sensors were encapsulated with driving electronics in a mouthpiece. An activation unit made of soft ferromagnetic material has been attached to the tongue as the upper ball of a piercing. Gliding the activation unit at the surface of the one of the two pads ensured optimal activation of sensors. Sensor performance with respect to optimal activation has been analyzed while a healthy subject drove three times a powered wheelchair controlled by the oral interface along one linear track of 8.34 m and two triangular tracks of 7.2 m in both directions. The search time defined as the ratio between the time with no sensor activation and the total test time in percentage was of 18.3%, 25.8%, 10.9%, 4.55%, and of 7.2% from the total driving time on triangular tracks (both directions) and on the linear track respectively. Analysis of the search time associated with the sensor activation vector may improve the user and application dependent design of the pointing device.