Kinematics, Workspace Optimization, and Performance Evaluation of a 3-Leg 6-DOF Robot in RRRS Configuration

Underactuated parallel manipulators that achieve 6 DOF via multiple controllable degrees of freedom per leg are often pursued and reported due to their large workspaces. This benefit comes at a cost to the manipulator’s performance, however. Such manipulators must then be evaluated in order to characterize their kinematics in terms of position and motion. This paper establishes a pair of inverse kinematic solutions for a previously proposed and prototyped 3-leg, 6-DOF parallel robot. These solutions are then used to define the robot’s workspace with experimental validation and to optimize the robot’s geometry for maximum workspace volume. The linear components of the Jacobian are then defined, allowing for analysis of the manipulability of the robot. The full Jacobian is also defined, and singularities are examined throughout the workspace of the robot.

Kinematics of the Morph Origami Pattern and its Hybrid States

A new degree-four vertex origami, called the Morph pattern, has been recently proposed by the authors (Pratapa, Liu, Paulino, Phy. Rev. Lett. 2019), which exhibits interesting properties such as extreme tunability of Poisson’s ratio from negative infinity to positive infinity, and an ability to transform into hybrid states through rigid origami kinematics. We look at the geometry of the Morph unit cell that can exist in two characteristic modes differing in the mountain/valley assignment of the degree-four vertex and then assemble the unit cells to form complex tessellations that are inter-transformable and exhibit contrasting properties. We present alternative and detailed descriptions to (i) understand how the Morph pattern can smoothly transform across all its configuration states, (ii) characterize the configuration space of the Morph pattern with distinguishing paths for different sets of hybrid states, and (iii) derive the condition for Poisson’s ratio switching and explain the mode-locking phenomenon in the Morph pattern when subjected to in-plane deformation as a result of the inter-play between local and global kinematics.

Hinges and Curved Lamina Emergent Torsional Joints in Cylindrical Developable Mechanisms

Cylindrical developable mechanisms are devices that conform to and emerge from a cylindrical surface. These mechanisms can be formed or cut from the cylinder wall itself. This paper presents a study on adapting traditional hinge options to achieve revolute motion in these mechanisms. A brief overview of options is given, including classical pin hinges, small-length flexural pivots, initially curved beams, and an adaptation of the membrane thickness-accommodation technique. Curved Lamina Emergent Torsional (LET) joints are then evaluated in detail, and a thin-walled modeling assumption is checked analytically and empirically. A small-scale cylindrical developable mechanism is then evaluated with Nitinol curved LET joints.

Design Framework for Multi-Section Shape Memory Alloy Axial Actuators Considering Material and Geometric Uncertainties

Shape memory alloys are metallic materials with the capability of performing as high energy density actuators driven by temperature control. This paper presents a design framework for shape memory alloy (SMA) axial actuators composed of multiple wire sections connected in series. The various wire sections forming the actuators can have distinct cross-sectional areas and lengths, which can be modulated to adjust the overall thermomechanical response of the actuator. The design framework aims to find the optimal cross-sectional areas and lengths of the wire sections forming the axial actuator such that its displacement vs. temperature actuation path approximates a target path. Constraints on the length-to-diameter aspect ratio and stress of the wire sections are incorporated. A reduced-order numerical model for the multi-section SMA actuators that allows for efficient design evaluations is derived and implemented. An approach to incorporate uncertainty in the geometry and material parameters of the actuators within the design framework is implemented to allow for the determination of robust actuator designs. A representative application example of the design framework is provided illustrating the benefits of using multiple wire sections in axial actuators to modulate their overall response and approximate a target displacement vs. temperature actuation path.

Neuroadaptive Controller for Physical Interaction With an Omni-Directional Mobile Nurse Assistant Robot

Robot-assisted healthcare could help alleviate the shortage of nursing staff in hospitals and is a potential solution to assist with safe patient handling and mobility. In an attempt to off-load some of the physically-demanding tasks and automate mundane duties of overburdened nurses, we have developed the Adaptive Robotic Nursing Assistant (ARNA), which is a custom-built omnidirectional mobile platform with a 6-DoF robotic manipulator and a force sensitive walking handlebar. In this paper, we present a robot-specific neuroadaptive controller (NAC) for ARNA’s mobile base that employs online learning to estimate the robot’s unknown dynamic model and nonlinearities. This control scheme relies on an inner-loop torque controller and features convergence with Lyapunov stability guarantees. The NAC forces the robot to emulate a mechanical system with prescribed admittance characteristics during patient walking exercises and bed moving tasks. The proposed admittance controller is implemented on a model of the robot in a Gazebo-ROS simulation environment, and its effectiveness is investigated in terms of online learning of robot dynamics as well as sensitivity to payload variations.

A Novel Compliant Bistable Mechanism Incorporating a Fixed-Guided Flexural Member

This paper presents the design of a novel compliant bistable mechanism. Bistable mechanisms are commonly used in switches and other devices that operate in two distinct modes. This mechanism is a single monolithic structure with simple geometry and does not require external components or post-manufacture assembly. As such, the design is ideally suited for additive manufacturing at large, or micro, scales. The design features a fixed-guided flexural member with surrounding geometry. When a load is applied to the mechanism in a stable configuration, the flexural member exhibits an inflection point that enables bifurcated behavior. As a result, the mechanism snaps between two stable positions in an on-off operation mode. This paper describes the mechanism geometry and its operation. Preliminary design modeling equations are formulated. A finite element simulation is presented that verifies the design equations. Lastly, a prototype is presented to confirm the operation and facilitate force and displacement measurements.

Design of an Ankle Rehab Robot With a Compliant Parallel Kinematic Mechanism

In this paper, we present the design of a novel ankle rehabilitation robot (ARR), called the Flex-ARR, that employs a compliant parallel kinematic mechanism (PKM) with decoupled degrees of freedom. The Flex-ARR is designed to collocate the biological center of rotation of the ankle with that of the robot’s center of rotation to allow natural ankle motion. While multiple ARR designs have been developed in research labs and some are commercially available, their clinical adoption has been limited because they do not emulate the natural motion of the ankle. The Flex-ARR leverages a unique PKM design that uses compliance to absorb minor misalignments between the center of rotation of the ankle and the robot, thereby allowing natural ankle motion. Also, because of its unique design, the PKM inherently accommodates variations in user foot sizes with minimal adjustments. The Flex-ARR is designed to provide multiple training modes that allow for both rehabilitation and assessment modalities. This paper provides a review of the literature to identify the key factors that have limited the clinical adoption of existing ARRs. Based on this, functional requirements and design specifications for an optimal ARR are defined. This is then used to develop a design strategy, followed by conceptual and detailed design.

Novel Design of a 3D Printed Anthropomorphic Soft Prosthetic Hand

Human hands play a key role in almost all activities of daily living (ADLs) because it is an incredibly versatile tool capable of complex motion. For individuals who have had a complete loss of the hand, the ability to perform ADLs is impaired. Effective prosthetics accurately simulate the movements of a human hand by providing a high number of degrees of freedom, an efficient control system, and an anthropomorphic appearance. In this paper, the design and construction process of a highly anthropomorphic soft robotic prosthetic hand is outlined. The design specifications of the hand are based on feedback from current and former prosthetic users. The hand endoskeleton was 3D printed using fused deposition modeling techniques and was enclosed in a silicone coating modeled, after a real human hand. The hand presents anthropomorphic design in its realistic bone shapes and in its external covering that is like skin in texture and mechanical properties. The hand utilizes the flexibility of silicone instead of antagonistic tendons which would otherwise add complexity and weight to the prosthetic design. The prototype also includes adduction/abduction of the fingers, which is a common omitted movement in other prosthetics. Testing showed that the hand is capable of effective power and precision grasping.

Design and Analysis of a Wire-Driven Multifunctional Robot for Single Incision Laparoscopic Surgery

Single Incision Laparoscopic Surgery (SILS) is a fast-growing method in the field of MIS (Minimally Invasive Surgery) that has the potential to represent the future of laparoscopic surgeries. The major benefits of SILS results from a single incision which makes surgeries essentially scar-less, and it can reduce wound infection substantially as well as recuperation time. Many new researches are now focusing on developing cutting edge technologies to support SILS; however, the practical applications of SILS are constrained by a number of intricacies such as space limitation, absence of dexterous multitasking tools, lack of sufficient actuation force and poor visualization. Deployment and retraction of surgical tools or robots are done manually in the absence of a multitasking tool manipulator which increases the surgery time, risk of injury and surgeon’s fatigue. Our research focuses on designing a novel operative hardware (multitasking manipulator) to facilitate the SILS technique with automatic tool changing capability. A wire driven mechanism has been implemented in the design to minimize the damage to the electronic hardware during sterilization since the electronic actuation and sensing components are located remotely from the end-effector which requires heat or chemical sterilization before surgery. And a wire-driven articulated robotic arm has also been designed to support the manipulator. The details of the robotic design and analysis are conducted in the paper. The feasibility of this robotic method has been demonstrated by experiments.

Bioinspired Origami: Case Studies Using a Keyword Search Algorithm

Numerous folding patterns, structures, and behaviors exist in nature that may provide design solutions to engineering problems. While applying biological solutions to engineering design is evidently valuable, the retrieval of useful design inspiration remains a primary challenge preventing the transfer of knowledge from biology to the engineering domain. In prior research, information retrieval techniques are employed to retrieve useful biological design solutions and a text-based search algorithm is developed to return passages where folding in nature is observed. The search algorithm, called FoldSearch, integrates tailored biological keywords and filtering methods to retrieve passages from an extensive biological corpus. The objective of this paper is two-fold — 1) to demonstrate the functionality of FoldSearch, and 2) to create abstract models of the retrieved biological systems from FoldSearch which can be used for the development of novel origami crease patterns and foldable structures. In this paper, the utility of FoldSearch is demonstrated through two case studies where the retrieved biological examples undergo a design abstraction process that leads to the development of bioinspired origami crease patterns and novel foldable structures. The abstraction process is presented as a systematic design methodology for bioinspired origami for the growing research field of origami engineering.