Theoretical and Experimental Study of Factors Affecting the Suction Force of a Bernoulli Gripper

Abstract

A Bernoulli noncontact gripper can generate suction force to achieve noncontact handling by use of axisymmetric radial airflow. An experimental and theoretical study of the factors that affect the suction force and its variation is conducted. First, a theoretical model of the pressure distribution is developed, taking into consideration the inertial effect of airflow deceleration, viscous effect, total pressure of the central air-supply hole, and gap height between the gripper and the workpiece. Based on the model, the suction force is calculated. Then, the pressure distribution and suction force are measured experimentally. The theoretical calculation and experimental results reveal that the inertial effect causes a negative pressure distribution and resulting suction force, while the viscous effect and the total pressure of the central air supply give rise to positive distributions and a resulting repulsive force. Because the repulsive force is inversely proportional to the gap height to a higher power (the third power) than the suction force, the repulsive force is absolutely dominant when the gap height is very small and is gradually prevailed over by the suction force as the gap height is increased. As a result, the curve of the resultant force and gap height (the F-h curve) has a part with a positive slope (referred to as the stable levitation region), where the levitation of the workpiece is stable. It also has another part with a negative slope (referred to as the unstable levitation region), where the levitation of the workpiece is unstable. Finally, the effect of the separation phenomenon that occurs behind the entrance to the gap is investigated, and it is found that it can retard the decline of the suction force in the unstable levitation region, which results in an expansion of the levitation region.