Stiffness Control With Shape Memory Polymer in Underactuated Robotic Origamis

Abstract

Abstract-Under-actuated systems offer compact designs with easy actuation and control but at the cost of limited stable configurations and reduced dexterity compared to the directly driven and fully actuated systems. Here, we propose a compact origami-based design to control the stable configurations and the overall stiffness of an under-actuated robotic finger by modulating the material stiffness of the joint. The design of the robotic finger is based on the robotic origami design principle in which multiple functional layers are integrated to make a nominally 2D robot with a desired functionality. To control the stiffness of the structure, we controlled the elastic modulus of a shape memory polymer (SMP) via embedded customized stretchable heater. We monitor the configuration of the finger using the feedback from the customized curvature sensors embedded in each joint. We studied the stable configurations and the contact forces of a finger with 3 joints at different stiffness settings. A scaled down version of the design was used in a gripper with two fingers and different grasp modes were demonstrated through activating different set of joints.

Soft Robotic Grippers

“…The stiffness change enables two grasping modes: a stiff mode to exert large forces, and a soft mode to gently handle the object, a sponge in this case. Moreover, the same group showed another gripper with similar tendon‐origami configuration, which exhibited independent stiffness control of every SMP joint for achieving various finger shapes, or multiple grasping modes thanks to different origami patterns enabling bending about multiple axes (Figure b) …”

Principles and methods for stiffness modulation in soft robot design and development

“…As a result, the finger would bend at low stiffness joints when pressurized air flows in the air chamber. Except for soft pneumatic fingers, SMP has also been applied in tendon-driven under-actuated robotic origamis for stiffness control [15].…”

“…What's more, we will also present a possible alternative for stiffness modulation in soft robotic design and development. Gripper [13], robotic origami [15], legged robot [22] and load bearing functional part [16,23] Viscosity-based methods Electric/magnetic field Viscosity change ERF, MRF, electroactive gel…”

Stiffness Control of Deformable Robots Using Finite Element Modeling

“…Della Santina et al [16] present an impedance controller for a soft continuum robot using a Piecewise Constant Curvature assumption to link the soft robot to an equivalent rigid robot representation. In the soft robot community, numerous works have focused on obtaining actuators with variable stiffness using, for example, particle jamming [17], shape memory polymers [18], magnetorheology [19], and antagonistic soft actuation [20]. These approaches allow local modification and control of stiffness, but do not necessarily take into account the compliance of the whole structure of the robot or consider the apparent end-effector stiffness.…”