Reducing the energy consumption of robots using the bidirectional clutched parallel elastic actuator

Parallel elastic actuators (PEAs) have shown the ability to reduce the energy consumption of robots. However, regular PEAs do not allow us to freely choose at which instant or configuration to store or release energy. This paper introduces the concept and design of the bidirectional clutched parallel elastic actuator (BIC-PEA), which reduces the energy consumption of robots by loading and unloading a parallel spring with controlled timing and direction. The concept of the BIC-PEA consists of a spring that is mounted between the two outgoing axes of a differential mechanism. Those axes can also be locked to the ground by two locking mechanisms. At any position, the BIC-PEA can store the kinetic energy of a joint in the spring such that the joint is decelerated to zero velocity. The spring energy can then be released, accelerating the joint in any desired direction. Such functionality is suitable for robots that perform rest-to-rest motions, such as pick-and-place robots or intermittently moving belts. The main body of our prototype weighs 202 g and fits in a cylinder with a length of 51 mm and a diameter of 45 mm. This excludes the size and weight of the nonoptimized clutches, which would approximately triple the total volume and weight. In the results, we also omit the energy consumption of the clutches. The BIC-PEA can store 0.77 J and has a peak torque of 1.5 N.m. Simulations show that the energy consumption of our one-degree-of-freedom setup can be reduced by 73%. In hardware experiments, we reached peak reductions of 65% and a reduction of 53% in a realistic task, which is larger than all other concepts with the same functionality.