The Jacobian condition number as a dexterity index in 6R machining robots

The use of robots for machining operations is growing because of their flexibility to perform a broad spectrum of tasks at a lower cost when compared with machine tools. In this paper the Jacobian condition number is used as a performance index intended to make a better use of revolute-jointed six-degree-of-freedom serial robots in five-axis machining. This index is of the kinetostatic type, low-frequency dynamic effects not being relevant to this study. Indeed, dynamic effects can be neglected because, during machining, the robot is not working at high speed, the spindle motion affecting only the structural, high-frequency modes of the system. The condition number is known to be a measure of Jacobian invertibility; it is used here as an index to improve joint-rate distribution. A low condition number is shown to translate into a smoother joint-rate time history.

► The optimum use of six-dof serial robots in five-axis machining is discussed.
► The condition number in addition to the five parameters of the task is used to define all joint rates.
► The condition number is used as an index to improve joint-rate distribution in this paper.
► A minimum condition number is shown to translate into a smoother joint-rate time history.
► This index is used to avoid robot-motor saturation.