Configuration-based optimization for six degree-of-freedom haptic rendering for fine manipulation

Six-degree-of-freedom (6-DOF) haptic rendering for fine manipulation in narrow space is a challenging topic because of frequent constraint changes caused by small tool movement and the requirement to preserve the feel of fine-features of objects. In this paper, we introduce a configuration-based constrained optimization method for solving this rendering problem. The six-dimensional configuration (position and orientation) of the graphic tool is defined as the solution variable of the optimization problem. Contact constraints are obtained based on identifying principal contacts between the graphic avatar of the haptic tool, called the graphic tool, and the virtual task environment. In order to maintain stability during contact switch, a hybrid method combining collision detection, local search and parallel optimization is introduced. Based on parallel optimization and selection of local solution, we can maintain the local solution of the optimization model. Our method has been validated in experiments of moving a convex tool to probe a narrow cavity with or without bulges. Force rendering is stable even when the free space is very small and involves fine features of objects. Non-penetration between the tool and the object forming the cavity are maintained under frequent contact switches. Update rate of the simulation loop including the optimization and constraint identification is maintained at about 1kHz.