Compensation for dead band of force measurement based on the coefficient of restitution in a hybrid simulator

In order to develop space robotic technologies, the feasibility and reliability of the systems have to be verified by repetitive operation tests. A hybrid simulator (also referred to as a Hardware-in-the-loop simulator) is one of the effective ways to examine orbital operations on the ground. The simulator embeds a hardware experiment in a numerical simulation loop. However, it is known that the hybrid simulator has a serious problem that energy increase arises in contact with a hardware experiment in the loop. In general, the energy increase in the hybrid simulator occurs due to the dead time in the system. However, this paper presents that dead band in force/torque measuring also causes the energy increase. The dead band in the force/torque measuring is necessary to avoid unexpected motion of the hybrid simulator due to the noise data in the force/torque sensor. This paper proposes two compensation methods for the energy increase problem due to the dead band. The first method is to insert a virtual damper to absorb the increased energy during the contact. The second method is to extrapolate force/torque data that is lost through the dead band processing right after the contact. The experimental verification with uniaxial contact in hybrid simulator is carried out to validate the proposed compensation methods.