Redundant manipulator POLYCRANK without joint limits-preliminary design study

Abstract

Some new results concerned with design and dynamics analysis of the redundant POLYCRANK manipulator with eight DOFs are presented. The main links of an arm in the form of light skew hollow cranks are connected one to the other by cross-roller bearings. In the new concept of the POLYCRANK manipulator all drive units are mounted coaxially in the base. The three first DOFs with vertical axes and the three next DOFs with parallel horizontal axes are driven by electric direct drive units while the last two DOFs are driven by electric motors with gears. The first link is driven directly, the second and third are driven remotely by special skew parallelograms. The other DOFs are driven remotely in a similar way by using skew parallelograms and bevel gears mounted on the third link. The kinematics scheme of this redundant manipulator is very simple and it has some specific properties. Inside of its vertex workspace the POLYCRANK manipulator can realize various high-speed cyclic gross motions. However, a big problem is strong reaction forces occurring in the joints. This may be the case in emergency situations too, e.g. when the power supply breaks down. A method of solving these problems has been presented. The possibility of easy manipulation of large bodies using two redundant POLYCRANK manipulators is stressed. Finally, a method of virtual design, which was used for the development of the conception of the manipulator, has been presented.