Design of a robotic manipulator using variable geometry trusses as joints

Parallel robotic manipulators are generally believed to be stiffer under load and more precise than conventional serial manipulators. This is because of their closed loop construction which allows forces to be shared through multiple paths to the ground. Unfortunately, most proposed parallel manipulator designs have severe workspace restrictions. The introduction of Variable Geometry Trusses (VGT’s) represents an opportunity to overcome this limitation.

The lack of stiffness in many serial manipulators is primarily due to compliance at the joints. The disadvantage of the series connected device include limitations in lilting capacity and vibration problems. Difficulties of this sort result from the cantilever structure of the device. These factors often limit the degrees of freedom that can be provided in the serial configuration. By replacing the revolute joints with the ‘VGT joints’, it may be possible to add considerable rigidity at the joints and hence design a highly dextrous manipulator.

The objective of this thesis is to study the feasibility of a design of manipulators using Variable Geometry Trusses. A modeling scheme capable of solving the inverse problem in closed form and finding the range of all possible solutions for a planar VGT has been presented. Another aspect that has been dealt with is in utilizing the extra degree of freedom that becomes available in the proposed manipulator. Enhancing the performance of the manipulator by optimizing relevant parameters has been carried out for a demonstrative case involving a planar truss.