Log 9/2

A project log for ThIRd Eye: Ground Level Detection for Wheelchairs

Using three IR distance sensors, this mounted system can detect drop-offs and obstacles at ground level and alert the wheelchair user.

Adam PorterAdam Porter 09/03/2017 at 05:590 Comments

Currently, the ThIRd Eye system works as follows: Analog readings from three IR distance sensors (mounted to the front of a power wheelchair in a pyramidal fashion, one per wheel castor and one leading in front) are routed to an Arduino Uno microcontroller. The Arduino issues an audible beep by a piezoelectric buzzer if either of the three sensors measures a distance ~10cm greater than or less than the initial distance of the sensor to the floor. The sensor mounting system is fully 3D-printable, but I recommend that printed screws and nuts are not used. The castor mounts utilize threaded round clips to mitigate the possibility of vibration shaking the sensors around. I have written Arduino code for an LCD display to provide realtime distance measurements by each sensor, which includes conversion of analog sensor data to centimeters. 

Current Problems:

     I'm noticing that the IR sensors have major accuracy problems. Readings can vary up to ~35% between the sensors when pointed at the same object. This is a pretty bad problem given that the integrity of the device depends on very small changes in terrain as measured by the three sensors mounted to the wheelchair. Changes to the current Arduino code can mediate this, as taking mean values between clusters of sensor readings can eliminate extreme values and therefore also various false positives.

   The mounting system also requires an arm to hold the middle IR sensor to the wheelchair, which I haven't yet designed. This is due to the fact that an arm clamped to the wheelchair under the seat would obviously be an obstruction to a patient's legs and feet. The center IR sensor mount must therefore be able to reach beyond the chair's footplate, so attaching the mount to the footplate is currently an option.