Olivier Company

Clément Robert, Alain Vissiere, Olivier Company et al.

Thermal expansion is a significant source of positioning error in high-precision hexapod robots (Gough-Stewart platforms). Any variation in the temperature of the hexapod's parts induces expansion, which alters their kinematic model and reduces the robot's accuracy and repeatability. These variations may arise from internal heat sources (such as motors, encoders, and electronics) or from environmental changes. In this study, a method is proposed to anticipate and therefore correct the thermal drift of one of the hexapod precision electro-mechanical actuators. This method is based on determining a model that links the expansion state of the actuator at any given moment to the temperature of some well-chosen points on its surface. This model was initially developed theoretically. Its coefficients were then adjusted experimentally on a specific test-bench, based on a rigorous measurement campaign of actuator expansion using a high-precision interferometric measurement system. Experimental validation demonstrates a reduction of thermally induced expansion by more than 80%. This paves the way for thermal drift correction across the entire robot or similar robotics parts.

Vinayak Jagannathrao Kalas, Alain Vissiere, Olivier Company et al.

Calibration is crucial for hexapods with high-accuracy positioning capability. Many of these calibration procedures require measurement of hexapod's platform pose (position and orientation) at constant temperature. Consequently, thermal deflection of the hexapod's platform during pose measurements impacts the accuracy of calibrated parameters. This paper presents a method to eliminate the impact of thermal deflection of hexapods on their pose measurement. In this method, a reference pose is measured before each measurement of any particular pose. The measurements of reference pose are used to estimate thermal deflection of hexapod's legs. This is in turn used to estimate and correct the resulting pose error at the particular pose to be measured. The advantage of using the proposed method is demonstrated experimentally by means of pose measurements of a high-precision hexapod using a CMM.