Performance difference of Bowden Cable relocated and non-relocated master actuators in virtual environment applications

It is the goal of this paper to present performance differences between a Direct Drive master actuator (DD) and a Bowden Cable relocated master actuator (BCD) in a typical force-feedback tele-manipulation experiment with a virtual slave. The BCD actuator is a candidate actuator for implementation in a wearable exoskeleton, in order to reduce mass and inertia on each joint of the movable structure. The BCD performance matches the one of the DD in terms of torque and position tracking in a 4 channel control. The maximum rendered contact stiffness is suitable for implementation in the ESA human arm exoskeleton, with a maximum of about 36 Nm/rad. When, instead of the DD, a relocated BCD actuator is implemented in an exoskeletons movable structure, the mechanical output power-density can be increased by more than 5 fold up to 31 mNm/cm³, with comparable performance. The specific power is then increased by more than 6 fold, to 13 Nm/kg. The Bowden Cable transmission wrapping angle alters the free movement friction only marginally by about 50 mNm only. The tracking performances are hardly affected and the contact stiffness increases with increasing wrapping angle. Transmission wrapping angles of up to 270 Deg. are tested.