Design of a Single Mechanical Joint for Multitype Angular Position Sensors Used in Gait Analysis

OBJECTIVES: Gait and motion analysis are important tools in assessment of athletic performance and clinical evaluation. Wearable sensor based solutions have advantages over video based systems by their prices and ease. Resistive, magnetic or optic Encoders, flexible resistors and accelerometers are common sensor types unsed in gait analysis systems used in rehabilitation. All these sensors have similar mounting and electronic instrumentation approach but all have separate mechanical joint design. The purpose of this study is to develop a single mechanical joint for multitype angular position sensors used in gait analysis. METHODS: Single turn analog encoder, flexible resistor and 3 axis accelerometer was used as angular position sensor. Constant voltage source (7805) was used for instrumentation of analog encoder and 3 axis accelerometer driver circuit. A voltage divider was used for flexible resistor driver circuit. Mechanical design was made to obtain small and light mechanical joint where all sensors can be mounted. RESULTS: Flexible sensor and encoder was mounded on the center of mechanical joint. Encoder is mounted outside and flexible sensor was mounted in side of the mechanical joint center. Accelerometer was mounted on lower (movable) arm of mechanical joint. Encoder has direct connection with upper and lower arms of mechanical joint. Root of flexible sensor is mounted on one side o the mechanical joint and driven by a mechanical dial on the other arm. Range of motion for analog encoder is 0-360 degree in a single plane, flexible is 0-180 degree for single plane and accelerometer is 0-360 degree for tree planes. CONCLUSION: Most difficult part of the design was to obtain highest range for flexible resistor. This sensor have 3 inclenght and changes its restinte related to its bending angle. It’s possible to obtain measurement by directly paste it on skin and it’s also easy to have measurement on mechanical joints in narrow angles. For a conventional mechanical joint the range can not be lower then 180 degrees. The length of resistor limits the range. This design problem was solved by adding a secondary mechanical shaft to joint center, winding the sensor over it a mechanical dial. This design can be used in training and research purpose where double check is needed. Future studies may focus on adding contless sensors and integrated circuit type angular sensors to mechanical joint.