Design Methodology of Hydraulically-driven Soft Robotic Gripper for a Large and Heavy Object

Abstract

This paper presents a design methodology of a hydraulically-driven soft robotic gripper for grasping a large and heavy object -- approximately 10 - 20 kg with 20 - 30 cm diameter. Most existing soft grippers are pneumatically actuated with several hundred kPa pressure, and cannot generate output force sufficient for such a large and heavy object. Instead of pneumatic actuation, hydraulic actuation has a potential to generate much larger power by several MPa pressure. In this study, we develop a hydraulically-driven soft gripper, in which its basic design parameters are determined based on a mathematical model that represents the relationship among the driving pressure, bending angle, object mass and grasping force. Moreover, we selected materials suitable for grasping a heavier object, based on the finite element analysis result of the detailed design. We report experimental results on a 20 kg object grasping and closed-loop control of the finger bending angle.

Figures (15)

• Figure 1: (a) Soft fingers are connected to the high-pressure side of the hydraulic pump while a reservoir is connected to the low-pressure side. The pump generates differential pressure, sending oil from the reservoir to the soft fingers. (b) Structure and bending mechanism of fiber-constrained soft finger. Fiber-constrained soft fingers utilize the expansion of soft materials under pressure and deform only in a certain direction by embedding inelastic materials. (c) Structure of reservoir. The reservoir consists of a circular sheet made of NBR, along with a ring-shaped metal part and base.
• Figure 2: Geometric Model of hydraulic soft gripper. (a) Soft finger. (b) Cross section of finger. (c) Reservoir made of rubber sheet. Reservoir consists of a circular sheet made of NBR, along with a ring-shaped metal part and base, as shown in Fig. \ref{['fig:simple_diagram']} (b).
• Figure 3: Maximum payload of soft gripper estimated for bending angles of 40$^\circ$, 50$^\circ$, 60$^\circ$, and 70$^\circ$.
• Figure 4: Four-finger hydraulic soft robot gripper. The gripper is composed of soft fingers, pressure sensors, a reservoir for storing oil, a hydraulic pump, and a motor for driving the pump.
• Figure 5: Fabricated soft finger. (a) Structure of soft finger, (b) Resistive flexible sensor, (c) Image of finger shell bending.