Design and Fabrication of a Multi-purpose Four Arm Electrothermal Microgripper; A Novel Approach to Control Maximum Gripping Force Limit

The development of microgrippers requires accurate control of force and position for the grasping mechanisms in micromanipulation. This controllability ensures the safe transfer of sensitive micro-objects, such as living cells. The design of microgrippers is often limited by the dimensions and adaptability of the micro-objects being manipulated. Therefore, microgrippers should be customized for each micro-object. Additionally, complex sensor mechanisms are required to control the gripping force. This study introduces a novel design of a four-arm MEMS electrothermal microgripper intended for versatile micromanipulation purposes. The microgripper design procedure is compatible with a list of constraints, including biological and microfabrication constraints. The jaw form is designed to manipulate micro-objects with a wide range of dimensions (1 to 360μm). Furthermore, a novel approach is presented here to control the force threshold of gripping without a sensor during manipulation. The proposed solution involves using structure stiffening to control the force and prevent damage to micro-objects. GA and analytical models (transient behaviour of structure) are used to satisfy the long list of constraints. The device is fabricated through UV-LIGA, utilizing nickel and copper as the structural and sacrificial layer. The experimental and simulation results demonstrate that the microgripper can achieve a 60μm jaw displacement at a voltage of 0.329V. The gripping arms can provide a force of 15 to 450μN for the handling of micro-objects. The maximum gripper temperature of 98ºC makes it suitable for biological applications. The innovative form and systematic design of the microgripper enable its adaptability for various applications.