Reusable and scalable fibrillar adhesive for soft grippers

• Main Author: Mohamed Haziq Mohamed Hafiz
• Other Authors: K Jimmy Hsia
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/158993
• Institution: Nanyang Technological University

Adhesive soft grippers are gaining more popularity in the robotics industry over the last decade. Compared to other technologies, adhesive soft grippers have the most potential to achieve a universal soft gripper suitable for many applications. However, current designs are still facing challenges in optimising the adhesion performance due to the choice of adhesive materials. The common adhesives chosen are non-reusable and have a fixed stiffness, resulting in poor scaling efficiencies and weak tolerance towards misalignments. Hence, this report proposes an adhesive soft gripper design that uses shape memory polymers (SMPs) to address these challenges. The proposed adhesive is shaped in the form of fibrils, taking inspiration from the natural adhesives present in animals such as geckos. SMPs are chosen as they can switch between the soft (rubbery) state and stiff (glassy) state through heat manipulation. When heated, the SMP temporarily deforms and adapts to the surface of an object it is in contact with, maximising contact area regardless of the contact surface. Upon cooling, it stiffens and forms strong bonds which improves the adhesion performance and tolerance towards tilting of the fibrils. When heat is reintroduced, the adhesive reverts to its original form, causing detachment. Thus, the shape memory effect offers improved adhesion strength and reusability to the design. Adhesion tests were conducted to study the benefits of using SMPs further. Test results boasts a peak average of 1.8 MPa of adhesion strength and very minimal drop in strength (<5 %) in the presence of misalignment while in the glassy state. Meanwhile, the adhesive averages 89 kPa in adhesion strength in the rubbery state, which eases the detachment process. Furthermore, the adhesive has a great adaptability to multiple surfaces. It achieved high levels of adhesion with surfaces that were smooth (glass bottle), rough (red brick) and non-adhesive (Teflon). SMPs were found to have great scaling efficiencies and switch ratios as the contact area was increased from 23.242 to 1091.842 mm2. The scaling efficiency was recorded to be in the power of -0.144 and -0.236 in the glassy and rubbery state respectively. This reflects the ability of SMPs to produce high levels of adhesion even when it is scaled up. Hence, demonstrations were conducted using an SMP in a fibrillar array with arbitrary shaped objects such as a spherical helmet and a slender bolt. The success of the demonstrations suggests that SMPs will have a positive impact in the study of soft grippers. The simplicity of using SMP in soft grippers can expand to everyday usage, beyond industrial applications. It has the potential to achieve a truly universal soft gripper and revolutionize the robotics industry.