Adaptive Skew Force Free Model Based Synchronous Control and Tool Center Point Calibration for a Hybrid 6-DoF Gantry-Robot Machine

This article develops a high-stiffness, high-precision, hybrid tool center point (TCP) mode and a skew force free model-based (SFFMB) synchronous gantry-type design for a hybrid gantry-robot machine. For the new SFFMB synchronous gantry-type design, newly developed active/passive control models are presented to prevent gantry skew. The force ratio between the slave and master axes is generated, and experimental results show that the driving currents for the master/slave linear motor axes are lower when the SFFMB synchronous control function is enabled. This function makes the machine move smoothly even when deviations from squareness occur. These design approaches aim to improve the accuracy and performance at high speed to reduce the working cycle time for a machine with multiple degrees of freedom. This article makes three contributions to the literature. First, by considering the skew force issue, a new SFFMB synchronous gantry-type design is proposed to prevent gantry skew phenomenon. Second, to ensure exact omnidirectional linear movement, a novel hybrid TCP mode is proposed to decouple coordinate transformations into individual translation and rotation components. Third, based on the SFFMB synchronous control strategy and the hybrid TCP mode, we propose an effective calibration method to enhance the TCP accuracy. The new SFFMB synchronous gantry-type design and the accurate hybrid TCP mode are experimentally verified and demonstrated using a hybrid gantry-robot machine developed in our laboratory, which is based on our proposed synchronous control strategy.