Collocation Accuracy of Visuo-Haptic System: Metrics and Calibration

Human resolution of collocation error between haptic and stereoscopic displays influences the design of visuo-haptic rendering algorithms, yet it is not well characterized. In the present study, we propose quantified metrics to measure the visuo-haptic collocation error and a prototype based on half-silvered mirror is established to validate the metrics. After defining collocation error in terms of the spatial correspondence between a tool and a surface, a mathematical model is derived that relates collocation error to the visual and haptic rendering modules within the computational pipeline. A calibration method consisting of Perspective Calibration (PC) and Model Calibration (MC) is then proposed to compensate for manufacturing and assembly tolerances. Based on measurement values by a precise measurement apparatus, i.e., the FARO Arm, parameters for the PC and MC were determined. System performance is evaluated by measuring the collocation error between a real handle and its visual avatar. The average collocation error was 1.8 mm within the XwYwOw plane, and the error never exceeded 7 mm within an 80 mm × 80 mm × 80 mm workspace.