Electronic Thesis and Dissertation Repository

Thesis Format



Master of Engineering Science


Mechanical and Materials Engineering


Knopf, George K.


Pneumatically-driven soft robotic grippers can elastically deform to grasp delicate, curved organic objects with minimal surface damage. However, common actuators have complex geometries and are fabricated with ultra-soft hyperelastic elastomers not originally intended for scientific applications. The complexity of the actuator geometry and extreme nonlinearity of their material’s stress-strain behaviour make it difficult to predict the actuator’s deformation prior to experimentation. In this work, a compact soft pneumatic gripper made with polydimethylsiloxane (PDMS) is developed for grasping delicate organic objects, analyzed through computational modelling and experimentally validated. COMSOL Multiphysics is used to simulate the impact of geometrical parameters on the actuator’s behaviour, allowing for the refinement of the proposed geometry prior to fabrication. Optimal parameters are selected for fabrication, with experimental tests matching simulations within ± 1 mm. Gripper performance is evaluated for three actuator wall thicknesses in terms of contact area with target, contact force, and maximum payload before slippage. The comparative assessment between simulations and experiments demonstrate that the proposed soft actuators can be used in robotic grippers tailored for grasping delicate objects without damaging their surface. Furthermore, analysis of the actuators provides additional insight on how to design simple but effective soft systems.

Summary for Lay Audience

Air-powered soft robotic grippers are made of rubber-like materials that can stretch and inflate to collect delicate objects like fruits and vegetables. However, the soft “finger” components of the robotic gripper commonly have complex geometries, and the rubber materials used in their fabrication were not meant for scientific applications. The combination of these complex geometries and the extreme unpredictability of non-standard soft materials make it difficult to calculate the “finger’s” movement before performing experiments. In this work, a compact and soft air-powered gripper is developed and fabricated using a silicone material commonly used in the scientific community, polydimethylsiloxane (PDMS). The gripper is designed for grasping delicate produce. The inflation and behaviour of the soft gripper components are first analyzed using computer simulations based on geometrical dimensions and air pressure. Data acquired from these simulations is used to improve the proposed soft component geometry before building it, reducing the number of trial-and-error tests needed to previously develop soft robotic “fingers”. After fabricating soft “finger” components, experiments are performed to compare the simulated data with experimental results. This comparison shows a match between simulations and experiments within ± 1 mm. The “fingers” are then assembled into three different grippers and tested to assess each gripper’s effectiveness at grasping objects of different shapes and weights. The comparison between computer simulations and real experiments demonstrate that the proposed soft “fingers” can be used in grippers designed for picking up delicate objects without damaging them. Furthermore, analysis of the soft components provides additional insight on how to design simple but effective soft robots.