Equipping an Automated Wheelchair with an Infrared Encoder Wheel Odometer

Smart wheelchairs are designed to be operated by people who are unable to use traditional control systems. Instead, they are equipped with a combination of automated functionality and steering mechanisms specialized to meet an individual's needs. One feature common to the automated capabilities of smart wheelchairs is the tracking system. The wheelchair's microcontroller needs to know how far the chair has travelled, its speed, and the rotational direction of its wheels in order to successfully navigate through an environment. The purpose of this research was to develop an odometer to track the motion of a motorized wheelchair. Due to federal regulations that prohibit changing the structure or internal mechanics of a medical device, the odometer had to be designed as a separate, removable part. The final design for the odometer consisted of two infrared sensors that measure edge transitions of a segmented encoder wheel. The sensor output was then run through two comparator op amps and a high pass filter to produce a clean, crisp square wave signal output. A microcontroller was programmed to compare the sensor signal with its internal clock, sense edge transitions, and thereby extrapolate the speed, travelled distance, and rotational direction of the wheelchair.