Showing papers in "Journal of Mechanisms and Robotics in 2018"

Modeling Large Deflections of Initially Curved Beams in Compliant Mechanisms Using Chained Beam-Constraint-Model

Abstract: Understanding and analyzing large and nonlinear deflections are the major challenges of designing compliant mechanisms. Initially, curved beams can offer potential advantages to designers of compliant mechanisms and provide useful alternatives to initially straight beams. However, the literature on analysis and design using such beams is rather limited. This paper presents a general and accurate method for modeling large planar deflections of initially curved beams of uniform cross section, which can be easily adapted to curved beams of various shapes. This method discretizes a curved beam into a few elements and models each element as a circular-arc beam using the beam constraint model (BCM), which is termed as the chained BCM (CBCM). Two different discretization schemes are provided for the method, among which the equal discretization is suitable for circular-arc beams and the unequal discretization is for curved beams of other shapes. Compliant mechanisms utilizing initially curved beams of circular-arc, cosine and parabola shapes are modeled to demonstrate the effectiveness of CBCM for initially curved beams of various shapes. The method is also accurate enough to capture the relevant nonlinear load-deflection characteristics.

Kinematic Analysis and Design of a Novel Shoulder Exoskeleton Using a Double Parallelogram Linkage

Abstract: The design of an innovative spherical mechanism with three degrees-of-freedom (DOFs) for a shoulder joint exoskeleton is presented in this paper. The spherical mechanism is designed with a double parallelogram linkage (DPL), which connects two revolute joints to implement the motion as a spherical joint, while maintaining the remote center (RC) of rotation. The design has several new features compared to the current state-of-the-art: (1) a relative large range of motion (RoM) free of singularity, (2) high overall stiffness, (3) lightweight, and (4) compact, which make it suitable for assistive exoskeletons. In this paper, the kinematics and singularities are analyzed for the spherical mechanism and DPL. Dimensional analysis is carried out to find the design with maximum RoM. The new shoulder joint is finally designed, constructed, and integrated in a four degree-of-freedom wearable upper-body exoskeleton. A finite element analysis (FEA) study is used to assess the structural stiffness of the proposed design in comparison to the conventional 3R mechanism.

Single-Motor Controlled Tendon-Driven Peristaltic Soft Origami Robot

Abstract: Origami-based paper folding is being used in robotics community to provide stiffness and flexibility simultaneously while designing smart structures. In this paper, we propose a novel design inspired by origami pattern service robot, which transforms its shape in the axial direction and introduce peristaltic motion therein. Here, servo motor is being used for translational actuation and springs maneuver self-deployable structure when necessary. Self-deployable springs are compressed by the application of axial force as the string gets wound around the servo motor programed to rotate with a particular speed for specified time duration. Specially coated photopolymer resin structures have been used to provide external rigidity to the springs so to avoid buckling while operation. In future, this friction coated origami service robot is envisioned to be used in an unstructured environment as the scope of applications increases at the nexus of surgical robotic navigation, houses to disaster areas.

Learning-based Variable Compliance Control for Robotic Assembly

Abstract: The assembly task is of major difficulty for manufacturing automation. Wherein the peg-in-hole problem represents a group of manipulation tasks that feature continuous motion control in both unconstrained and constrained environments, so that it requires extremely careful consideration to perform with robots. In this work, we adapt the ideas underlying the success of human to manipulation tasks, variable compliance and learning, for robotic assembly. Based on sensing the interaction between the peg and the hole, the proposed controller can switch the operation strategy between passive compliance and active regulation in continuous spaces, which outperforms the fixed compliance controllers. Experimental results show that the robot is able to learn a proper stiffness strategy along with the trajectory policy through trial and error. Further, this variable compliance policy proves robust to different initial states and it is able to generalize to more complex situation.

Dexterous Workspace Optimization for a New Hybrid Parallel Robot Manipulator

Abstract: In this paper, a new hybrid parallel robot (HPR) manipulator is introduced. First three kinematic limbs of six-legged general Stewart platform (6DOF GSP) manipulator are disconnected. Afterward, each passive universal joint of remaining three-legged parallel manipulator (three-UPS) is mounted at the center of each second passive revolute joint of RPR planar parallel manipulator (3DOF PPM) where underlined letters present active joints. Active actuators of PPM mounted between base platform of GSP and ground perform translations along x and y-axes, and rotation about z-axis. Remaining three limbs of GSP mechanism provide translation z-axis, and rotation about x- and y-axes only. Thus HPR can perform motion with full dimensions (translation and rotation about x-, y-, and z-axes). Optimizations are performed by using particle swarm optimization algorithm. Optimization results demonstrated that HPR provides better dexterity and singularity-free workspace characteristics than GSP.

A pseudo-static model for dynamic analysis of distributed compliant mechanisms

Abstract: This paper presents a pseudo-static modeling methodology for dynamic analysis of distributed compliant mechanisms to provide accurate and efficient solutions. First, a dynamic stiffness matrix of the flexible beam is deduced, which has the same definition and a similar form as the traditional static compliance/stiffness matrix but is frequency dependent. Second, the pseudo-static modeling procedure for the dynamic analysis is implemented in a statics-similar way based on D'alembert's principle. Then, all the kinematic, static and dynamic performances of compliant mechanisms can be analyzed based on the pseudo-static model. The superiority of the proposed method is that when it is used for the dynamic modeling of compliant mechanisms, the traditional dynamic modeling procedures, such as calculation of the elastic and kinetic energies as well as using Lagrange's equation, are avoided and the dynamic modeling is converted to a statics-similar problem. Comparison of the proposed method with an elastic-beam-based model in previous literature and finite element analysis for an exemplary XY precision positioning stage reveals its high accuracy and easy operation.

Design and Kinematic Analysis of a 3RRlS Metamorphic Parallel Mechanism for Large-Scale Reconfigurable Space Multifingered Hand

Abstract: Capturing noncooperative targets in space has great prospects for aerospace application. In this work, the knuckle unit of a large-scale reconfigurable space multifingered hand (LSRSMFH) for multitask requirements is studied. A plurality of knuckle units is connected in series to form a finger of the LSRSMFH. First, the lockable spherical (lS) joint, a new metamorphic joint that can function as a Hooke (lS1) or spherical (lS2) joint and is driven by shape memory alloy (SMA) material, is proposed. Based on the lS joint, this paper presents a new metamorphic parallel mechanism (MPM) (i.e., 3RRlS MPM), which has four configurations, namely, 3RRlS1, 3RRlS2, 2RRlS1-RRlS2, and 2RRlS2-RRlS1 configuration. The degree-of-freedom (DOF), overconstraint, and parasitic motion of the 3RRlS MPM are analyzed using screw theory, of which the DOF can be changed from 1 to 3. The 3RRlS1 configuration has a virtual constraint, and the 3RRlS2 configuration has parasitic motions. The results indicate that the mechanism motion screws can qualitatively represent the mechanism parasitic motions, and it is verified by deriving the kinematic equation of the 3RRlS MPM based on its spatial geometric conditions, the workspace of the 3RRlS MPM is further solved. The kinematic analysis indicates that the 3RRlS MPM can realize the folding, capturing, and reconfiguring conditions of the LSRSMFH.

Novel Design of Legged Mobile Lander with Decoupled Landing and Walking Functions and Singularity Property

Abstract: During extraterrestrial planetary exploration programs, autonomous robots are deployed using a separate immovable lander and rover. This mode has some limitations. In this paper, a concept of a novel legged robot with decoupled functions was introduced that has inbuilt features of a lander and rover. Currently, studies have focused mainly on performance analysis of the lander without a walking function. However, a systematic type synthesis of the legged mobile lander has not been studied. In this paper, a new approach to the type synthesis used for the robot was proposed based on the Lie group theory. The overall concept and design procedure were proposed and described. The motion requirements of the robot and its legs were extracted and described intuitively. The layouts of the subgroups or submanifolds of the limbs were determined. A family of particular joints with one rotation and one translation was proposed for the first time. The structures of the limbs were synthesized. Numerous structures of the legs were produced and listed corresponding to the desired displacement manifolds. Numerous novel structures of the legs for legged mobile lander were evaluated and listed. Then, four qualitative criteria were introduced. Based on the proposed criteria, a particular case of legs' configuration with a rhombus joint was selected as the best one among them. A typical structure of the legged mobile lander was obtained by assembling the structures of the proposed legs with a rhombus joint. Finally, the typical robot was used as an example to verify the capabilities of the novel robot using a software simulation (adams).

Development of an Insect-Inspired Hexapod Robot Actuated by Soft Actuators

Abstract: Insects are one of the most diverse group of animals on the planet and are almost ubiquitous. Their walking locomotion has inspired engineers and provided effective solutions for designing transport methods for legged robots. In this paper, we introduce a hexapod walking robot that mimics the design and walking motions of insects. The robot is characterized by small size, light weight, simple structure, and considerably fast walking speed. Three pairs of its legs are driven by three five-degrees-of-freedom (5DOF) soft actuators based on dielectric elastomer (DE) actuators which can provide up to five movements (including three translations and two rotations) within a compact structure. The robot imitates the crawling motion of an insect using the alternating tripod gait. The experiments show that the robot can achieve an average walking speed of 5.2 cm/s (approximately 21 body-lengths per minute) at 7 Hz of actuation frequency on flat rigid surfaces. Furthermore, the robot also demonstrates the omnidirectional capabilities of walking sideways and rotating its body direction, which enhance the potential of applying the proposed robot in practical uses.

Rigid Foldability of Generalized Triangle Twist Origami Pattern and Its Derived 6R Linkages

Abstract: Rigid origami is a restrictive form of origami that permits continuous motion between folded and unfolded states along the predetermined creases without stretching or bending of the facets. It has great potential in engineering applications, such as foldable structures that consist of rigid materials. The rigid foldability is an important characteristic of an origami pattern, which is determined by both the geometrical parameters and the mountain-valley crease (M-V) assignments. In this paper, we present a systematic method to analyze the rigid foldability and motion of the generalized triangle twist origami pattern using the kinematic equivalence between the rigid origami and the spherical linkages. All schemes of M-V assignment are derived based on the flat-foldable conditions among which rigidly foldable ones are identified. Moreover, a new type of overconstrained 6R linkage and a variation of doubly collapsible octahedral Bricard are developed by applying kirigami technique to the rigidly foldable pattern without changing its degree-of-freedom. The proposed method opens up a new way to generate spatial overconstrained linkages from the network of spherical linkages. It can be readily extended to other types of origami patterns.

Design, Modelling and Integration of a Flexible Universal Spatial Robotic Tail

Abstract: This paper presents the novel design of a bioinspired robot capable of generating spatial loading relative to its base. By looking to nature at how animals utilize their tails, a bioinspired structure is developed that utilizes a redundant serial chain of rigid links to mimic the continuous deformation of a biological tail. Individual links are connected by universal joints to enable a spatial robot workspace capable of generating spatial loading comprised of pitch, yaw and roll direction contributions. Two sets of three cables are used to create two actuated segments along the robot. A dynamic model of the robot is derived using prescribed cable displacement trajectories as inputs to determine the resulting joint angle trajectories and cable tensions. Sensors are integrated on-board the robot to calculate joint angles and joint velocities in real-time for use in feedback control. The loading capabilities of the robot are analyzed, and an experimental prototype is integrated and demonstrated.

Kinematics, Workspace and Singularity Analysis of a Parallel Robot with Five Operation Modes

Abstract: Most multi-mode parallel robots can change operation modes by passing through constraint singularities. This paper deals with a comprehensive kinematic study of a 3-DOF multi-mode 3-PRPiR parallel robot developed at Heriot-watt University. This robot is able to reach several operation modes without crossing any constraint singu-larity by using lockable Pi and R joints. Here a Pi joint may act as a 1-DOF planar parallelogram if its lockable P (prismatic) joint is locked or a 2-DOF RR serial chain if its lockable P joint is released. The operation modes of the robot include a 3T operation mode and four 2T1R operation modes with two different directions of the rotation axis of the moving platform. The inverse kinematics and forward kinematics of the robot in each operation mode are dealt with in detail. The joint space and workspace analysis of the robot allow us to know the regions of the workspace that the robot can reach in each operation mode. It is shown that the robot is able to change assembly mode in one operation mode by passing through another operation mode. 1 Introduction Reconfigurable Parallel Manipulators (PMs), such as multi-mode PMs [1–12], have received much attention from a number of researchers in the past decade [13]. The main characteristics of multi-mode PMs include [7–9]: a) fewer actuators are needed for the moving platform to realize several specified motion patterns; and b) less time is needed in reconfiguring the PM since there is no need to disassemble the PM in the process of reconfiguration. A number of interesting multi-mode PMs have been proposed, such as multi-mode PMs with a 3-DOF (degrees-of-freedom) translational mode and a 3-DOF planar mode or a 4-DOF 3T1R mode [7, 8], PMs with two 3T1R (also Schonflies motion) operation mode which has three translational DOF and one rotational DOF operation modes [4], PMs with two 2T1R operation modes [5, 6], and 2-DOF 3-4R PMs with both spherical translation mode and sphere-on-sphere rolling mode [9]. References [14, 15] show 4-DOF 3T1R PMs that have an extra 2-DOF or 3-DOF motion mode in addition to the required 4-DOF 3T1R motion mode. It is noted the metamorphic PMs based on reconfigurable U (universal) or S (spherical) joints [16,17] and the multi-mode PMs with lockable joints [18,19] are in fact kinematically redundant PMs in nature and do not belong to multi-mode PMs that this paper focuses on. In addition, several methods have been proposed [14, 15, 19–25] to the reconfiguration analysis of multi-mode PMs for identifying all the operation modes and the transition configurations of a PM.

Two-Digit Robotic Exoskeleton Glove Mechanism: Design and Integration

Abstract: This paper presents the design and integration of a two-digit robotic exoskeleton glove mechanism. The proposed glove is designed to assist the user with grasping motions, such as the pincer grasp, while maintaining a natural coupling relationship among the finger and thumb joints, resembling that of a normal human hand. The design employs single degree-of-freedom (DOF) linkage mechanisms to achieve active flexion and extension of the index finger and thumb. This greatly reduces the overall weight and size of the system making it ideal for prolonged usage. The paper describes the design, mathematical modeling of the proposed system, detailed electromechanical design, and software architecture of the integrated prototype. The prototype is capable of recording information about the index finger and thumb movements, interaction forces exerted by the finger/thumb on the exoskeleton, and can provide feedback through vibration. In addition, the glove can serve as a standalone device for rehabilitation purposes, such as assisting in achieving tip or pulp pinch. The paper concludes with an experimental validation of the proposed design by comparing the motion produced using the exoskeleton glove on a wooden mannequin with that of a natural human hand. [DOI: 10.1115/1.4038775]

Branch Reconfiguration of Bricard Linkages Based on Toroids Intersections: Line-Symmetric Case

Abstract: This paper for the first time investigates a family of line-symmetric Bricard mechanisms by means of two generated toroids and reveals their intersection that leads to a set of special Bricard mechanisms with various branches of reconfiguration. The discovery is made in the concentric toroid-toroid intersection. By manipulating the construction parameters of the toroids any possible bifurcation point is explored. This leads to the common bi-tangent planes that present singularities in the intersection set. The study reveals the presence of Villarceau and secondary circles in the toroids intersection. Therefore, a way to reconfigure the Bricard linkage to two different types of Bennett mechanism is uncovered. Further a linkage with two Bricard and two Bennett motion branches is explored. In addition, the paper reveals the Altmann linkage as a member of the family of special line-symmetric Bricard linkages studied in this paper.

A Model for Multi-Input Mechanical Advantage in Origami-Based Mechanisms

Abstract: Mechanical advantage is traditionally defined for single-input and single-output rigid-body mechanisms. A generalized approach for identifying single-output mechanical advantage for a multiple-input compliant mechanism, such as many origami-based mechanisms, would prove useful in predicting complex mechanism behavior. While origami-based mechanisms are capable of offering unique solutions to engineering problems, the design process of such mechanisms is complicated by the interaction of motion and forces. This paper presents a model of the mechanical advantage for multi-input compliant mechanisms and explores how modifying the parameters of a model affects their behavior. The model is used to predict the force-deflection behavior of an origami-based mechanism (Oriceps) and is verified with experimental data from magnetic actuation of the mechanism.

Design and Experimental Validation of a Large-Displacement Constant-Force Mechanism

Abstract: This paper presents the design and experimental validation of a passive large-displacement constant-force mechanism (CFM). Unlike previous studies, without using extra stiffness-compensation components and active control devices, the presented CFMs can utilize the interaction between the components of a cam and sliders to directly achieve the constant-force characteristic over the entire flexibly designed large displacement once the cam is advisably designed with the consideration of friction effect by using the profile curve identification method (PCIM). Corresponding to the different requirements of conventional and extreme engineering environments, two versions of the mechanism, the basic and ultra-large-displacement CFM models are proposed, respectively. The basic version is designed directly based on the PCIM, whereas the ultra-large-displacement CFM is proposed using the relay-mode action of the multistage sliders. According to the theoretical design method, we design and fabricate two corresponding CFM prototypes. Validation experiments are then conducted, and the results show that both of the prototypes can satisfy the design requirements and possess large-displacement constant-force characteristics owing to the consistency of experimental and design data. Therefore, the proposed design theory for the cam-based large-displacement CFMs is validated and the designed CFMs will have extensive applications in relevant fields for force regulation and overload protection.

Differential Noncircular Pulleys for Cable Robots and Static Balancing

Abstract: In this paper, we introduce a mechanism consisting of a pair of noncircular pulleys with a constant-length cable. While a single noncircular pulley is generally limited to continuously winding or unwinding, the differential cable routing proposed here allows to generate non-monotonic motions at the output of the arrangement, i.e. the location of the idler pulley redirecting the cable. The equations relating its motion to rotation angles of the noncircular pulleys and to the cable length are presented in the first part of this paper. Next, we introduce a graphical method allowing us to obtain the required pulley profiles for a given output function. Our approach is finally demonstrated with two application examples: the guiding of a cable-suspended robot along a complex trajectory using a single actuator, and the static balancing of a pendulum with a 360 degree rotational range of motion.

Mechanical Computing Systems Using Only Links and Rotary Joints

Abstract: A new paradigm for mechanical computing is demonstrated that requires only two basic parts, links and rotary joints. These basic parts are combined into two main higher level structures, locks and balances, and suffice to create all necessary combinatorial and sequential logic required for a Turing-complete computational system. While working systems have yet to be implemented using this new paradigm, the mechanical simplicity of the systems described may lend themselves better to, e.g., microfabrication, than previous mechanical computing designs. Additionally, simulations indicate that if molecular-scale implementations could be realized, they would be far more energy-efficient than conventional electronic computers.

Branch Reconfiguration of Bricard Linkages Based on Toroids Intersections: Plane-Symmetric Case

Abstract: This paper for the first time reveals a set of special plane-symmetric Bricard linkages with various branches of reconfiguration by means of intersection of two generating toroids, and presents a complete theory of the branch reconfiguration of the Bricard plane-symmetric linkages. An analysis of the intersection of these two toroids reveals the presence of coincident conical singularities, which lead to design of the plane-symmetric linkages that evolve to spherical 4R linkages. By examining the tangents to the curves of intersection at the conical singularities, it is found that the linkage can be reconfigured between the two possible branches of spherical 4R motion without disassembling it and without requiring the usual special configuration connecting the branches. The study of tangent intersections between concentric singular toroids also reveals the presence of isolated points in the intersection, which suggests that some linkages satisfying the Bricard plane-symmetry conditions are actually structures with zero finite degrees-of-freedom (DOF) but with higher instantaneous mobility. This paper is the second part of a paper published in parallel by the authors in which the method is applied to the line-symmetric case.

Geometry of Transformable Metamaterials Inspired by Modular Origami

Abstract: Modular origami is a type of origami where multiple pieces of paper are folded into modules, and these modules are then interlocked with each other forming an assembly. Some of them turn out to be capable of large scale shape transformation, making them ideal to create metamaterials with tuned mechanical properties. In this paper, we examine 2D modular origami assemblies using mathematical tiling and patterns and carry out mechanism analysis, which leads to the development of various patterns consisting of interconnected quadrilateral modules. Due to the existence of 4R linkages within the patterns, they become transformable, and can be compactly packaged. Moreover, by the introduction of paired modules, we are able to adjust the expansion ratio of the pattern. Moreover, we demonstrate that transformable patterns with higher mobility exist for other polygonal modules. Our findings provide more design flexibility to achieve truly programmable metamaterials.

Design and Modeling of a Compliant Link for Inherently Safe Corobots

Abstract: In this paper, we propose a variable width compliant link that is designed for optimal trade-off of safety and control performance for inherently safe corobots. Intentionally introducing compliance to mechanical design increases safety of corobots. Traditional approaches mostly focus on the joint compliance, while few of them study the link compliance. 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 two-dimensional beams with a variable width. Given a safety threshold, i.e., HIC constraint, the width distribution along the link is optimized to give a uniform distribution of HIC, which guarantees inherent safety for human operators. This solution is validated by a human–robot impact simulation program built in MATLAB. A static model of the variable width link is derived and verified by finite element simulations. Not only stress in the link is reduced, this new design has a better control and dynamic performance quantified by a larger natural frequency and a larger bandwidth compared with designs made of uniform beams and compliant joints (CJs). The proposed variable width link takes full advantage of the link rigidity while keeps inherent safety during a human–robot impact. This paper demonstrates that the compliant link solution could be a promising alternative approach for addressing safety concerns of human–robot interactions. [DOI: 10.1115/1.4038530]