Gap flow with circumferential velocity in annular skirt of vortex gripper

Abstract

The vortex gripper is a noncontact gripper that uses vortex flow that enables it to grip objects without coming into physical contact with them, thus avoiding such damage to the workpiece as mechanical scratches, local stress concentrations, frictional static electricity, and surface stains. This study involves theoretically and experimentally investigating the flow characteristics of the gap flow with a rotational velocity component between the workpiece and the annular skirt of the vortex gripper. Based on this, we discuss the effect of an important structural parameter of the gripper, i.e., the width of the annular skirt, on its performance. We first propose a theoretical model of the pressure gradient of the gap flow in the radial direction, where the pressure gradient is determined by the viscous term dominated by radial velocity, and the inertial terms are dominated by the radial and circumferential velocities. According to this theoretical model, we then analyze the distributions of radial velocity and circumferential velocity in the radial direction when the gap between the workpiece and the gripper varies, and the influence of the viscous term and the inertial terms on the pressure gradient. Further, we clarify the significance of the inertial term dominated by circumferential velocity on the pressure distribution. The validity of the theoretical model was verified by comparing its output with the results of experiments. Finally, by analyzing the force characteristic curves and pressure distributions of the grippers with annular skirts of four widths, we concluded that an increase in the width of the annular skirt can increase the influence of the inertial term dominated by circumferential velocity, and can thus change the region of stable suspension of the gripper and increase its suction capacity.