A study on a soft microgripper using MEMS-based divided electrode type flexible electro-rheological valves

• A novel soft microgripper using electro-rheological fluid valve was proposed.
• MEMS fabrication process using two-stage electroforming was developed.
• A divided electrode type electro-rheological valve was successfully fabricated.
• Static characteristics of the valve were experimentally clarified.
• The microfinger was fabricated and experimentally characterized.

This paper presents a novel soft microgripper whose finger consists of a hydraulic rubber actuator and an ER valve to manipulate tools and objects on an in-pipe working micromachine flexibly. The microgripper can also manipulate fragile objects such as biological cells safely. The electro-rheological fluid (ERF) flow into the hydraulic rubber actuator is controlled by the ER valve through its apparent viscosity increase due to the applied electric field. The ER valve in this study is a proposed divided electrode type flexible ER microvalve (DE-FERV) which has axially divided parallel plate electrode pairs in a flexible tube and has high bending flexibility and high axial rigidity. The hydraulic rubber actuator has plural walls inside to restrict the radial expansion and axially extends by the inner pressure increase. The microfinger is composed of a hydraulic rubber actuator and a DE-FERV on the side and bends by the extension of the hydraulic rubber actuator. To miniaturize the soft microgripper, MEMS fabrication process was developed and applied. A 2.8 mm long DE-FERV was designed and successfully fabricated with the electrode total length of 2.8 mm, width of 1 mm, and gap height of 0.1 mm. The pressure change ratio up to 6.3 was shown experimentally. A 3 mm long hydraulic rubber actuator was fabricated by molding process and attached to the DE-FERV. Based on air pressure tests, it was estimated that the microgripper will be able to grasp 0.4 mm wide objects with a grasping force 2.4 mN.