Engineering : Robotics


Dynamic Predictor Improves Machine Control

The researcher now has developed a new dynamic predictor that rapidly and accurately calculates the motion trajectory of a system that is only partially constrained by joint inputs. This dynamic predictor achieves stable and accurate results for stiff systems. To do this, the predictor applies conditions achieving such results at both a first and second joint position at the start and end of a motion time step.

More specifically, the relationship between joints is described as a differential equation to be solved by the predictor. The predictor parameterizes the motion of the unconstrained joints in such a way as to match the conditions the solution needs to satisfy at both the start and end of a motion time step. As this parameterization is expressed by polynomial coefficients, motions of the remaining joints are readily determined by the kinematic predictor.

Two-Axis, Non-Singular, Revolute Joint Robotic Wrist for Industrial and Research Applications

A UW-Madison researcher has developed a two-axis pointing device for robotic wrist applications that uses only revolute joints, needs actuators only at the base, maintains a constant distance from the pointer to the pointing center and is non-singular.  The wrist consists of the parallel combination of a revolute-spherical-revolute (R-S-R) linkage and a revolute-universal (R-U) linkage.  With only these revolute linkages, the wrist is never overconstrained.  Actuation is required only at the base of the R-joints for each linkage, which keeps the device from being overactuated.  Locking is eliminated by maintaining spherical motion while the distance between the pointer and pointing center are held constant, as opposed to linkages that require that distance to vary.  Non-singularity provides constant velocity motion through 180 degrees of deflection in any direction by orienting the R-U linkage transversely with respect to the R-S-R linkage.