Design and Fabrication of a Soft Robotic Hand With Embedded Actuators and Sensors

Abstract

This paper details the design and fabrication process of a fully integrated soft humanoid robotic hand with five finger that integrate an embedded shape memory alloy (SMA) actuator and a piezoelectric transducer (PZT) flexure sensor. Several challenges including precise control of the SMA actuator, improving power efficiency, and reducing actuation current and response time have been addressed. First, a Ni-Ti SMA strip is pretrained to a circular shape. Second, it is wrapped with a Ni-Cr resistance wire that is coated with thermally conductive and electrically isolating material. This design significantly reduces actuation current, improves circuit efficiency, and hence reduces response time and increases power efficiency. Third, an antagonistic SMA strip is used to improve the shape recovery rate. Fourth, the SMA actuator, the recovery SMA strip, and a flexure sensor are inserted into a 3D printed mold which is filled with silicon rubber materials. The flexure sensor feeds back the finger shape for precise control. Fifth, a demolding process yields a fully integrated multifunctional soft robotic finger. We also fabricated a hand assembled with five fingers and a palm. We measured its performance and specifications with experiments. We demonstrated its capability of grasping various kinds of regular or irregular objects. The soft robotic hand is very robust and has a large compliance, which makes it ideal for use in an unstructured environment. It is inherently safe to human operators as it can withstand large impacts and unintended contacts without causing any injury to human operators or damage to the environment.

Modeling and Validation of a Novel Bending Actuator for Soft Robotics Applications

“…Therefore, it requires a large current to be actuated, which leads to a low energy efficiency. 12 To overcome the high current consumption and low efficiency in directly heating of the SMA strips, Ni-Cr resistance wires are wrapped around the SMA strip to indirectly heat the SMA. The resistivity of Ni-Cr material is about 15 times that of Ni-Ti SMA material.…”

“…The detailed fabrication process can be referred from. 12 A relatively wide SMA strip, which is trained in the flexion direction, is placed in the middle of the finger for grasping (flexion SMA). To increase releasing rate and avoid twisting, two pieces of narrow SMA strips, which are programmed in the antagonistic direction of the flexion SMA, are placed on both sides for releasing the targets (extension SMA).…”

“…Mirzaeifar et al 20 developed the bending model of a superelastic SMA beam, but the unloading portion lacks accuracy. Since sensory feedback control of the SMA beam has been studied in our previous research, 12 we did not attempt to derive a precise transient model by referring their modeling approaches. Instead, an efficient static model is derived to guide users to select appropriate parameters of the actuator, given a specific performance requirement.…”

“…11 These drawbacks are partially attributed to directly heating of SMA and can be overcome, to some degree, if indirectly heating approaches are used. 12 The modeling of the actuators of the soft robot is another challenge because of the large deformation of flexible members and complex motion. The kinematics models used in 13,14 assumed that the curvature along the actuator is constant.…”

Data-Driven Bending Angle Prediction of Soft Pneumatic Actuators with Embedded Flex Sensors

“…Readings from the embedded flex sensors were clustered so that a trained algorithm can identify grasped objects based on the combined readings from all soft fingers. Another recent attempt for embedding simple flex sensors within soft gripper fingers was presented by (She et al, 2015), were the feedback was used to control the shape of the soft fingers actuated using shape memory alloys. The main advantage of this approach compared to using conductive silicone rubber or conductive EGaIn channels, is the fact that it relies on simple and inexpensive commercially available sensors that can be easily wired and embedded within the strain limiting layer of SPAs.…”