Low-Cost Force Sensors For Small Size Humanoid Robot

We present a new design of foot pressure sensors in the context of small low-cost robots. We design the robot in the context of RoboCup kid-size humanoid league (i.e. the robot size must be lower than 90 cm). A new challenge is to walk on artificial grass of 3 cm height, which essentially means a soft irregular floor. In this context, one cannot use full 6-axis force sensors for cost and mechanical integration reasons. Classically, FSR sensors are used to handle foot pressure with unclear efficiency. Instead of that, we propose to use low cost strain gauge originally designed for scales. The strain gauge is made of resistors network glued on a aluminium beam. In our design, the aluminium beams are themselves full parts of the mechanical structure of the foot. Therefore, we measure directly the deformation of the foot and thus the force applied on it in a robust way. We use this system in order to measure the position of the centre of pressure under the foot, in order to balance motor primitives of the robot: perturbation rejection, locomotion, shoot. First experiments are promising and we plan to set up a rigorous comparison with the ZMP.