Soft Fingers with Controllable Compliance to
Enable Realization of Low Cost Grippers
Grippers are needed to manipulate objects using robotic arms. In many applications, grippers need to meet the following 3 criteria:
• Grippers need to conform to shape of objects being manipulated to handle irregularly shaped objects.
• Grippers need to apply force on the object or resist the gravity force (e.g., need to be able to lift heavy objects).
• Grippers need to be low cost to enable new applications.
Traditional multi-finger grippers with built-in sensors are able to the meet the first two requirements. However, they tend to be expensive. Robotic grippers based on the jamming of granular material are able to meet the first and third
requirements. However, they cannot apply large compressive force on the object. Recently there has been significant interest in grippers with soft fingers [1–9]. We believe that grippers with soft fingers can meet all three requirements listed above. This paper reports redesign of a conventional soft finger by integrating a structural member that can be used to control its compliance. Our
focus is on a design that is easier to manufacture and low cost. We have built a three-fingered pneumatically actuated gripper that only requires simple pneumatic actuation. Our gripper is attached to a UR5 robot arm. The robot arm is able to lift heavy objects using the new gripper.
We are interested in developing a design that is pneumatically actuated to ensure that it is compatible with the existing soft finger designs. To design the structural member with controllable compliance, we decided to only pursue design concepts that can be actuated by air either with pressure or vacuum. The main idea behind our soft robotic fingers lies in embedded sealed chamber which is made up of a non-stretchable polymer sheet. The chamber is filled with floating compliant sheets. When air is pumped out to create vacuum inside the sealed chamber, floating sheets inside the sealed chamber adhere to each other, increasing the friction due to an increase in the contact area. When the structural member is set in low stiffness mode, floating sheets can easily slide with respect to each other due to the sheet separation created by positive air pressure. If air is vacuumed out of the chamber, the sheets are stacked together. This prevents sheets from sliding over each other. This leads to the structural member appearing stiff under bending loads. By controlling the vacuum inside the chamber, we can control the stiffness of the structural member and the finger. Figure 1 shows the design concept. The design has been realized by using in mold assembly process. Molds were printed using FDM process. Figure 2 shows the traditional soft finger. Figure 3(a) shows the soft finger and structural element with controllable stiffness. Soft finger is actuated using positive air pressure. Structural element is actuated using negative air pressure. Figure 3(b) shows the final assembly of the finger. Our design allows easy replacement of sheet media to control stiffness.
https://link.springer.com/chapter/10.1007/978-3-319-63537-8_48
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