We propose a bipedal walking and impact reduction algorithm for a bipedal robot with pneumatically driven knees. The proposed algorithm is meaningful in that unlike in the existing studies on fully pneumatically driven robots and their control, it can overcome the low control performance of pneumatic actuators while utilizing the high compliance of pneumatic actuators through the high control performance of other joints in robots that apply pneumatic actuators only to the knee joint. Our algorithm takes advantage of whole-body control to overcome the low control performance of pneumatic systems and utilizes pneumatic compliance by simultaneously controlling the force and stiffness of the pneumatic actuators. Since a pneumatic actuator outputs a force, a force and torque converter is added to the general whole-body control framework, and a torque limit is considered as a function of the joint angle. In addition, a mechanism for selecting the stiffness of the knee is added. In particular, a force control method based on maintaining the minimum stiffness is applied to reduce the impact force when the ground conditions suddenly change. The pneumatics and the robot system were accurately modeled in a simulation, and the proposed algorithm was applied in the simulation to realize bipedal walking and to confirm the impact reduction effect in the event of a sudden ground condition change.
integrator and an over-sampling comparator, generates a Abstract-A 300mW single-chip CMOS class-D audio power quantized digital signal. From this signal, a unit power is amplifier employing new control methods is proposed. A high delivered to the output load through the power transfer frequency modulator that is suitable for portable applications is circuit. adopted in this power amplifier. Zero voltage switching (ZVS) and adaptive power control (APC) are used to minimize the power loss. The new class-D amplifier chip is implemented A-Modulator using a standard 0.35gm CMOS process, and the test results are -. Modulator shown. ZVin Vout shown.~~~~~~~~~~~~~~~~~~± Power / X / f I * ĨT r a n s f e r I. INTRODUCTIONCict
This paper proposes an (EHA) system driven in three modes to improve the low reactivity of the existing EHA system. By using a small high-pressure accumulator, servo valve, and mode switching valve, the circuits can be changed so that they are suitable for each mode according to the driving conditions. Each of the three modes consists of the EHA mode, the hybrid mode, and the charging mode, and the EHA mode operates on the same principle as the existing EHA system. The hybrid mode is activated when high-speed position control is performed, and with the help of an add-on servo valve controller, the control volume of the hydraulic cylinder can be stiffened quickly while minimizing the use of high-pressure fluids. The charge mode serves to periodically charge the accumulator under motionless conditions in applications that allow piston holding. Simulations and experiments confirm that the responsiveness of the proposed system is much improved compared to that of the existing EHA system.INDEX TERMS Electrohydrostatic actuation, high-pressure accumulator, hybrid actuation, add-on control, cylinder holding.
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