The Design and Analysis of a Compliant Constant-Force Mechanism

Compliant constant-force mechanisms (CFM) are a type of compliant mechanism which produce a reaction force at the output port that does not change for a large range of input motion. This paper describes a new compliant CFM, introduces its design and configuration-improvement process. A finite element analysis (FEA) model of the compliant CFM was created to evaluate its constant force behavior. The FEA result shows that when the displacement is Δ = 4 mm, the compliant CFM maintains a nearly constant force in the operational displacement range of 1.31 mm to 4 mm with an error of 5.05%. The operational range accounts for 67% of the total motion. This compliant CFM can be used to regulate the contact force of a robot end-effector or as an electrical connector.

Towards Computer Aided Design and Analysis of Spatial Flexure Mechanisms

Flexure mechanisms are the central part of numerous precision instruments and devices that are used in a wide range of science and engineering applications and currently, design of flexure mechanisms often heavily relies on designers’ previous hands-on experience. Therefore, a design tool that will speed up the design process is needed and this paper will introduce a systematic approach for building the necessary equations that are based on screw theory and linear elastic theory to analyze flexure mechanisms. A digital library of commonly used flexure elements must be available for a design tool and therefore, we first present the compliance matrices of commonly used flexure components. Motion twists and force wrenches of the screw theory can be related with these compliance matrices. Then, we introduce an algorithm that constructs the required linear system equations from individual compliance equations. This algorithm is applicable to flexure mechanisms with serial, parallel or hybrid chains. Finally, the algorithm is tested with a flexure mechanisms and it is shown that this approach can be the core of a future design tool.

Integrated Design of Compliant Mechanisms and Embedded Rotary Actuators and Bending Actuators for Motion Generation

This paper presents an integrated design approach, a new topology optimization technique, to simultaneously synthesizing the optimal structural topologies of compliant mechanisms (CMs) and actuator placement — bending actuators and rotary actuators — for motion generation. The approach has the following salient features: (1) the use of bending actuators and rotary actuators as the actuation of CMs, (2) the simultaneous optimization of the CM and the location and orientation of the actuator that is embedded in the CM, (3) the guiding of a flexible link from an initial configuration to a series of desired configurations (including precision positions, orientations, and shapes), and (4) a new connectivity checking scheme to check whether the regions of interest in a design candidate are well connected. A program was employed for the geometrically nonlinear finite element analysis of large-displacement CMs driven by either bending actuators or rotary actuators. Two design examples were presented to demonstrate the proposed approach. The design results were 3D printed, and they all achieved desired shape changes when actuated.

Design of a Virtual Reality Haptic Robotic Central Venous Catheterization Training Simulator

Central venous catheterization (CVC) is a medical procedure where a surgeon attempts to place a catheter in the jugular, subclavian, or femoral vein. While useful, this procedure places patients at risk of a wide variety of adverse effects. Traditionally, training is performed on CVC mannequins, but these mannequins cannot vary patient anatomy. This work describes the development of a mobile training platform utilizing a haptic robotic arm and electromagnetic tracker to simulate a CVC needle insertion. A haptic robotic arm with custom syringe attachment used force feedback to provide the feeling of a needle insertion. A virtual ultrasound environment was created and made navigable by a mock ultrasound probe containing a magnetic tracking device. The effectiveness of the system as a training tool was tested on 12 medical students without CVC experience. An average increase in successful first insertion of 4.2% per practice scenario was seen in students who trained exclusively on the robotic training device. The robotic training device was able to successfully vary the difficulty of the virtual patient scenarios which in turn affected the success rates of the medical students. These results show that this system has the potential to successfully train medical residents for future CVC insertions.

Synthesis Design and Analysis of a Hybrid Controller for Robotic Arms

In this paper, a hybrid controller for robotic arms is proposed and designed by combining a proportional-integral-derivative controller (PID) and a model reference adaptive controller (MRAC) in order to further improve the accuracy and joint convergence speed performance. The convergence performance of the PID controller, the model reference adaptive controller and the PID+MRAC hybrid controller for 1-DOF and 2-DOF manipulators are compared. The comparison results show that the convergence speed and its performance for the MRAC and the PID+MRAC controllers are better than that of the PID controller, and the convergence performance for the hybrid control is better than that of the MRAC control.

Dynamic Characteristics Analysis of Cable-Rib Tension Deployable Antenna

Balancing stiffness and weight is of substantial importance for antenna structure design. Conventional fold-rib antennas need sufficient weight to meet stiffness requirements. To address this issue, this paper proposes a new type of cable-rib tension deployable antenna that consists of six radial rib deployment mechanisms, numerous tensioned cables, and a mesh reflective surface. The primary innovation of this study is the application of numerous tensioned cables instead of metal materials to enhance the stiffness of the entire antenna while ensuring relatively less weight. Dynamic characteristics were analyzed to optimize the weight and stiffness of the antenna with the finite element model by subspace method. The first six orders of natural frequencies and corresponding vibration modes of the antenna structure are obtained. In addition, the effects of structural parameters on natural frequency are studied, and a method to improve the rigidity of the deployable antenna structure is proposed.

Soft Spherical Tensegrity Robot Design Using Rod-Centered Actuation and Control

This paper presents the design, analysis and testing of a fully actuated modular spherical tensegrity robot for co-robotic and space exploration applications. Robots built from tensegrity structures (composed of pure tensile and compression elements) have many potential benefits including high robustness through redundancy, many degrees of freedom in movement and flexible design. However to fully take advantage of these properties a significant fraction of the tensile elements should be active, leading to a potential increase in complexity, messy cable and power routing systems and increased design difficulty. Here we describe an elegant solution to a fully actuated tensegrity robot: The TT-3 (version 3) tensegrity robot, developed at UC Berkeley, in collaboration with NASA Ames, is a lightweight, low cost, modular, and rapidly prototyped spherical tensegrity robot. This robot is based on a ball-shaped six-bar tensegrity structure and features a unique modular rod-centered distributed actuation and control architecture. This paper presents the novel mechanism design, architecture and simulations of TT-3, the first untethered, fully actuated cable-driven six-bar tensegrity spherical robot ever built and tested for mobility. Furthermore, this paper discusses the controls and preliminary testing performed to observe the system’s behavior and performance.

Development of Autonomous Robotic Cataract Surgery Device

The current rate of incidence of cataracts is increasing faster than treatment capacity, and an autonomous robotic system is proposed to mitigate this by carrying out cataract surgeries. The robot is composed of a three actuator RPS parallel mechanism in series with an actuated rail mounted roller that moves around the eye, and is designed to perform a simplified version of the extracapsular cataract surgery procedure autonomously. The majority of the design work has been completed, and it is projected that the system will have a tool accuracy of 0.167 mm, 0.141 mm, and 0.290 mm in the x, y, and z directions, respectively. Such accuracies are within the acceptable errors of 1.77mm in the x and y directions of the horizontal plane, as well as 1.139 mm in the vertical z direction. Tracking of the tool when moving at 2 mm/s should give increments of 0.08 mm per frame, ensuring constant visual feedback. Future work will involve completing construction and testing of the device, as well as adding the capability to perform a more comprehensive surgical procedure if time allows.

Design of Mechanism and Preliminary Field Validation of Low-Cost Transfemoral Rotator for Use in the Developing World

Transfemoral (above-knee) amputees face a unique and challenging set of restrictions to movement and function. Most notably, they are unable to medially rotate their lower-leg and subsequently cross their legs. The best and most common solution to this issue today is a transfemoral rotator, which allows medial rotation of the leg distal to the knee through a lockable turntable mechanism. However, currently available transfemoral rotators can cost thousands of dollars, and few equivalent technologies exist in the developing world. This paper, supported by the results of field studies and user testing, establishes a framework for the design of a low-cost and easily manufacturable transfemoral rotator for use in the developing world. Two prototypes are presented, each with a unique internal locking mechanism and form. A preliminary field study was conducted on six transfemoral amputees in India and qualitative user and prosthetist feedback was collected. Both prototypes successfully allowed all subjects to complete tasks such as crossing legs, putting on pants, and tying shoes while maintaining functionality of walking and standing. Future iterations of the mechanism will be guided by a combination of the most positively received features of the prototypes and general feedback suggestions from the users.

Parameter Characterization for Elastic Energy Absorption of an Embedded Corrugated Wave Padding Concept

The parameters of an innovative padding concept were investigated using Finite Element Analyses (FEA) and physical testing. The concept relies on a compliant corrugation embedded in an elastic foam to provide stiffness for force distribution and elastic deformation for energy absorption. The shape of the corrugation cross section was explored as well as the wavelength and amplitude by employing a full factorial design of experiments. FEA results were used to choose designs for prototyping and physical testing. The results of the physical tests were consistent with the FEA predictions although the FEA tended to underestimate the peak pressure compared to the physical tests. A performance metric is proposed to compare different padding configurations. The concept shows promise for sports padding applications. It may allow for designs which are smaller, more lightweight, and move better with an athlete than current technologies yet still provide the necessary protective functions.