A Low-Cost, Compact, Sealed, Three-Axis Force/Torque Sensor for Walking Robots

Ensuring both feasibility and reliability when measuring forces and torques in legged robots is challenging. Different transducer technologies and structural designs can be used to develop force/torque sensors with multiple measurement axes, high accuracy, and durability. Among the said technologies, strain gauges are frequently used, due to their high accuracy and compatibility with various materials. However, strain gauges also cause design challenges, because of their requirement for typically large housing structures, heavy workload during installation, and susceptibility to error from thermal expansion and fluids. This typically results in a high production cost that is further multiplied with the number of measuring axes. As a consequence, the sensors become extremely expensive and unsuitable for legged robots and outdoor applications. We propose a new design for a three-axis force/torque sensor that is low-cost, compact, and hermetically sealed. It uses a single torsion full-bridge strain gauge in combination with on-board data processing. We demonstrate the advantages of the sensor design in terms of error reduction without using Wheatstone Bridges for all axes, and subsequently, the measuring accuracy in all angles. Furthermore, we demonstrate the three-axis force sensing capabilities of the sensor on a bio-inspired walking robot. Accordingly, our results demonstrate error reduction methods that (1) offer an alternative to conventional methods, and (2) have suitable accuracy for applications such as foot sensors in walking robots. We believe that the sensor's on-board data processing and mass production compatibility can make force/torque sensing more accessible, leading to novel robotic applications in the future.