Previous studies suggest that bipedal robots that have prismatic compliance in the legs can achieve efficient walking. However, how this efficiency can be achieved still remains an open research problem. In this study, we developed a 2-degree-of-freedom planar bipedal robot comprising Neidhart springs and five-bar parallel mechanisms. The five-bar parallel mechanism allows the robot to achieve prismatic compliance. In addition, a lightweight torque limiter function is achieved by Neidhart springs with an original design. We implemented a simple controller and conducted walking experiments. Experimental results showed that the robot walked effectively using the regenerative energy stored in the prismatic springs.

Applying robots in narrow and cluttered disaster environments such as oil refineries requires a slim body and a wide range of motion. It is also necessary to have abilities to absorb unexpected contact with the environment and to walk on scattered debris. In this paper we propose new compact and high performance torque-controlled actuators for legged robots to satisfy the above mentioned requirements. For axial compactness, torque sensors are designed as ring-shaped thin cylinders surrounding motors or gears with strain gauges for sensing. To achieve broad bandwidth of torque control, we introduced an analog differentiator circuit into an analog digital converter (ADC) board in order to suppress noise in the differential control of joint torque. We also propose methods to reduce torque ripple caused by the deformation of the harmonic drive gear and electromagnetic interference (EMI) from a motor and a motor driver. Finally, experiments of a collision with objects and movement on scattered debris were executed with a fully torque-controlled legged robot built with the proposed actuators.