Eliminating non-smooth nonlinearities with compliant manipulator design

Compliant mechanism design enables the development of revolute joint-based manipulators without the backlash and Coulomb friction that impede precision position and especially force control. Conventional approaches to compliant mechanism design entail several limitations, however, such as severely limited ranges of motion, poor kinematic behavior, and significant deformation under multiaxis loading. The authors have developed an approach to compliant mechanism design that enables a considerably larger range of motion and significantly better multiaxis revolute joint characteristics than conventional approaches. The approach is based upon the development of a revolute joint that enables the implementation of high bandwidth spatially-loaded revolute joint-based manipulators with well-behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise impede precision control. The approach has been incorporated into the design of a small-scale three degree-of-freedom manipulator with an approximately spherical workspace two centimeters in diameter. Though applied to a small-scale manipulator, the design approach is also suited to conventional scale devices. Data from the small-scale manipulator indicates that positioning resolution is limited by digital quantization and sensor noise, and not by more fundamental physical limitations, such as backlash or Coulomb friction.