Effect of Heat-Induced Adjustable Stiffness at the Contact Interface on the Gripping Force of a Bipolar Electrostatic Chuck

This research endeavor aims to investigate the effect of heat-induced adjustable stiffness at the contact interface on the gripping force of a bipolar electrostatic chuck (ESC).<br/><br/>The bipolar ESC serves as a gripping mechanism specifically designed for delicate objects such as thin films and plates, functioning through the utilization of two electrodes that generate an electric field upon the application of a potential difference. This electric field induces charges or dipoles on the surface of the object, facilitating its attraction to the chuck via Coulomb forces. Given the device's dependence on this distinctive gripping mechanism, the condition and material properties of the contact surface play a pivotal role in determining the gripping force. Previous investigations have predominantly focused on enhancing the structural aspects of the device, encompassing surface smoothening techniques and the incorporation of rotational freedom for the end-effector. Nonetheless, owing to its inherently rigid structure, the ESC encounters difficulty in establishing a substantial real contact area, consequently constraining the gripping force within the boundaries defined by the applied voltage and the ESC's dimensions.<br/><br/>To address this inherent limitation, the present study proposes a novel concept revolving around the manipulation of the contact surface's stiffness. Specifically, two variations of bipolar ESCs were fabricated, differing in the materials employed for the contact surface (ABS, Nylon). By supplying current to the electrodes, the generation of heat was facilitated, thereby enabling to exert control over the stiffness of the covering material through temperature adjustments. To determine the gripping force exerted by the two ESC variants, a glass slide was employed as the target object, and the magnitudes of forces acting the object and the proposed ESC were meticulously recorded under the multiple conditions. The influence of the adjustable stiffness was subsequently observed by analyzing the variations in the device's gripping force. Additionally, experiments were conducted wherein voltage was not applied, serving to quantitatively evaluate the adhesive forces at play, particularly those arising from van der Waals interactions. The results unveiled a noteworthy increase in the gripping force upon the reduction of the contact surface's stiffness, with the ABS-type exhibiting a gripping force enhancement of 1.682 times, while the Nylon-type witnessed a 1.833-fold increase. Furthermore, it was discerned that the gripping force surpassed the combined magnitudes of the electrostatic and adhesive forces, thereby underscoring the existence of a complex interplay between these two dominant forces. In an attempt to gain further insights into the underlying mechanisms, the ESC/glass system was modeled as a two-body problem, subsequently subjecting the influence of low stiffness to comprehensive analysis from the vantage points of contact and fracture mechanics.<br/><br/>The findings of this study represent a significant stride towards the development of bipolar electrostatic chucks endowed with tunable stiffness, thereby facilitating the reliable and repeatable manipulation of delicate objects. By surmounting the constraints imposed by conventional ESCs, this research endeavor holds the potential to engender a more effective gripping capability, spanning across a broader spectrum of objects. This acquired knowledge would contribute to the future progress of robotics in the field of film or plate handling.