Yu She

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

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.

A transformable wheel robot with a passive leg

In this paper, we present a novel wheeled robot that transforms from a circled configuration to a spoke-like legged configuration. Wheeled mobile robots are able to quickly and efficiently move on flat surfaces. However they may sink into a terrain with dynamic surface such as snow, sand, dirt, moss, and small gravel. The transformable wheel robot presented in this paper is able to overcome obstacles and navigate these dynamics surfaces, yet can still move quickly over flat ground. The wheel is comprised of five spokes or legs, four of which are actively driven by a motor via four slider-crank linkages. The last one is designed be passive in order to significantly decrease the actuation force of the transformer mechanism. Analysis shows that the maximum driving force required to actuate the passive leg design is 1/187.5 times that of the active leg design. Experiments demonstrate that the passive leg design allows the mobile robot to open the transformation mechanism with a maximum external loading of 1.809 times the original robot weight. The diameter of the legged configuration wheel is 1.576 times that of the circled configuration.

Dynamic modeling of a 2D compliant link for safety evaluation in human-robot interactions

In this article, we build dynamic models of 2D compliant links to evaluate injury level in a human-robot interaction. Safety is a premium concern for co-robotic systems. It has been studied that using compliant links in a robot can greatly reduce the injury level. Since most safety criteria are based on tolerance of acceleration of the operators head during the impact, an efficient and yet accurate dynamic model of compliant links is needed. In this paper, we compare three dynamic models for calculating acceleration and head injury criterion: the compliant Beam-Spring-Mass (BSM) model, the Mass-Spring-Mass (MSM) model and the Link-Spring-Mass (LSM) model. For the MSM model and LSM model, we obtain analytic expressions of acceleration. While numerical results are achieved for the compliant BSM model. To develop the compliant BSM model, we compared three different methods: the Pseudo-Rigid-Body (PRB) model, the Finite-Segment-Model (FSM), and the Assumed-Mode-Method (AMM). Finally, all these models are validated by human-robot impact simulation programs built in Matlab. The acceleration from these simulations can be used to quantitatively measure the injury level during an impact.

Shape Optimization of 2D Compliant Links for Design of Inherently Safe Robots

In this paper, we represent a preliminary work towards the design of compliant mechanisms for human safe co-robots. We developed a shape optimization framework for design of planar compliant links for inherently safe robotic manipulators. It is well known intentionally introducing compliance to mechanical design can increase safety of robots. However traditional approaches such as elastic joints or uniform compliant links, were either at the cost of significantly reduced performance or with increased extra complexity and cost. Here, we propose a novel method to design compliant robotic links with a safety constraint which is quantified by Head Injury Criterion (HIC). The robotic links are modeled as a 2D beam with a variable width. Given a safety threshold i.e. HIC constraint, the width of the beam is optimized to give a uniform distribution of HIC along the longitudinal direction of the link. Links with a uniform HIC distribution have a better control performance. Finally, this solution is validated by an huamn-robot impact simulation program built in Matlab.Copyright

On the impact force of human-robot interaction: Joint compliance vs. link compliance

In this paper, we study the effect of mechanical compliance on the impact force of human-robot interactions, more specifically the maximum impact force during a collision. Here we consider two methods of introducing compliance to industrial manipulators: joint compliance and link compliance. To compare their effect on the maximum impact force, we study two designs of a 2D robot link: a rigid link with torsion spring at the joint and a uniform compliant link. The dynamic impact model is based on the Hertz contact model. The results show that the compliant joint solution could produce a larger impact force than that of the compliant link solution if the arm mass is larger than that of the end mass, given the same lateral stiffness and all other inertial parameters (e.g. mass). Simulations and experiment have been done and verified this conclusion. The research demonstrates that the compliant link solution could be a promising approach for addressing safety concerns of human robot interactions.