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For liquid transfer system in three-dimensional space, the use of multijoint robot arm provides much flexibility. To realize quick point-to-point motion with minimal sloshing in such system, we propose an integrated framework of trajectory planning and sloshing suppression. The robot motion is decomposed into translational motion of the robot wrist and rotational motion of the robot hand to ensure the upright orientation of the liquid container. The trajectory planning for the translational motion is based on cubic spline optimization with free via points that produces smooth trajectory in joint space while it still allows obstacle avoidance in task space. Input shaping technique is applied in the task space to suppress the motion induced sloshing, which is modeled as spherical pendulum with moving support. It has been found through simulations and experiments that the proposed approach is effective in generating quick motion with low amount of sloshing.

Vibration-free motion in minimal time is desired for industrial robotic applications. Hence, these criteria have to be considered during trajectory planning for a robot arm, wherein polynomial splines are often used for interpolating the trajectory through several via points. Among polynomial splines, the cubic spline is the lowest-degree spline that can provide jerk limitation, a feature that is important for reducing vibration during motion. However, using jerk limitation alone does not eliminate vibration completely and sometimes restricts the performance of industrial robots. This paper proposes an implementation of cubic spline optimization with free via points for reducing motion time, combined with input shaping for suppressing vibration. Experiments are conducted on a semiconductor wafer transfer robot arm to demonstrate the effectiveness of the proposed approach.

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