A Design of Bump Sensor Mechanism for Robotic Fish

Aims: This work aims at finding out the effectiveness of a commercial micro-switch as the base component for building bump sensor for a design of a robotic fish.
Methodology: A pair of micro switch (the type commonly used in computer mouse and similar devices) were assembled between the robot fish tip (actually a cone with the Mackerel fish profile) and the body, such that when the robot collides with a hard object, the switches will be depressed thus sending signal to its controller. The void between the switches were filled with collapsed polyurethane foam. The switches contact are continuously poled and the side that closes first is the side the robot is steered away from. False signals due to mechanical contact bounce was suppressed via software switch debounce algorithm. Test was focused on the debounce algorithm and the load to activate the switches. Furthermore, a modified IFD (compressive tests) on 1cm3 foam sample was perfomed.
Results: A spectrum analyzer sampling of the undebouncce switches signal indicates the natural frequency of the vibration to be approximately 8.5kHz. Thus the controller will be sampling the switches contact at about 941.18 per second when operating at the design 8MIP (million instruction per second). The activation load test indicates that the minimum load to activate the left switch (3.42N) is less than that of the right (5.50N). The modified IFD test indicates that the force to compress the collapsed polyurethane foam by 50% is between 0.32N to 0.41N. A field test on the robot shows the robot respond well to the switch input as designed.
Conclusion: The bump sensor as used in this research performed as expected despite the problems associated with mechanical switches. The limiting factor to this design as implemented is the minimum speed to activate the switches. The hydrodynamic drag force (0.00128N) is much less than the 5.86N force required to activate the sensor at the calculated minimum speed of 0.096 m/s. The force required to activate the switches is high due to the water proof coating used for them. The idea of the minimum speed to activate the bump switch is to ensure a fail safe operation when deployed. This design can be used for dark cave and also for cloudy water and where so much debris exists. It can also be used to augment other navigational techniques.