The moment a legged robot touches the ground, the tip of its toe can experience a significant impact force. It is preferable to keep the landing impact force small because it causes imbalance and damage to the frame, motors, gears, and other components of the robot legs. In this paper, we propose a control method to mitigate the landing impact force by preliminary motion based on the proximity information of the tiptoe before landing. A proximity sensor is mounted on the tiptoe to detect the ground before landing, and feedback control is applied according to the sensor output to reduce the impact force. In landing experiments using a one-legged robot equipped with a proximity sensor on a tiptoe, we evaluated the effects of changing the sensor offset distance and the feedback gains on impact force mitigation. The results show that the landing impact force was mitigated by reducing the relative velocity of the tiptoe and the ground using the proposed proximity feedback control.
Magneto-Plasma Sail (MPS) is a sail space propulsion system to accelerate the spacecraft in the solar wind direction by capturing the solar wind energy. MPS's significant feature is it's a utilization of magnetic field inflation process, in which a small magnetosphere by on-board coils is inflated by low-speed plasma released from the spacecraft. In this study, a parametric survey is conducted using the axis-symmetric two-dimensional magnetohydrodynamic (MHD) simulation to investigate the relation between the thrust characteristics and the injected plasma parameters (the mass flow rate and the thermal beta value at the injection point). As a result, the thrust gain, which is defined as the ratio of the MPS spacecraft thrust force to the Magnetic Sail thrust force, and the specific impulse have the maximum value against the thermal beta value, and in addition, increases with lower mass flow rate. It is indicated that the maximum value of the thrust gain is 3.77 when the thermal beta value is 25 and the mass flow rate is 100 in the non-dimensional parameter (when a magnetic moment of the spacecraft is assumed 6.28x10 7 Wb m, the thrust force is 60 N and the mass flow rate is 3.6 mg/s).
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