Abstract
In this article, we introduce a new soft finger with a pneumatic-actuated movable joint that is optimized and characterized in terms of the degrees of freedom (DoF), workspace, and fingertip force. The finger consists of one soft link as the body and the bending pneumatic joint as the actuator. Due to the additional translation and rotation movement capabilities of the joint, carried out by two stepper motors, the finger can bend in any direction while having different lengths, thanks to a configurable bending point. This results in more dexterity for the finger when dealing with a target inside its 3D workspace by increasing the number of configurations it can use to reach the target and exert force. The finite element method (FEM) and the Nondominated Sorting Genetic Algorithm II (NSGA-II) algorithm are applied to optimize the joint geometry and so maximize the bending angle and minimize the joint dimensions. Furthermore, the variations of each design parameter and consequent effects on the optimization objectives are analyzed. The optimal geometrical parameters are used to fabricate a prototype with silicone rubber. Tests on the bending angle and tip force variability are conducted on the prototype to validate the numerical modeling. The experimental results show that the finger exerts force up to 650 mN with a response time of fewer than 3 s. The stiffness of the finger can be changed by applying pneumatic pressure in the hollow space inside the link. This consequently varies the amount of applied force at the tipping point of the finger up to two times.
Highlights
The 2D workspace comparison between the proposed finger and a traditional design shows that changing the position of bending increases the number of a) accessible points while the tipping point workspace of previous traditional Fluidic Elastomer Actuation (FEA) is assumed to be a constant arc [20]
Controlling the whole process including reading sensors, switches, and electric motors are performed by an Arduino Uno board which is connected to the computer via a USB wire
As for measuring the force applied by the fingertip, a force sensor is situated below the tipping point of the finger and directly transfers the force data to the computer (Figure 9c)
Summary
The optimization procedure is described for a finger with the approximate dimensions of the human finger (diameter=10 mm and length=150 mm).
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