Showing papers in "Journal of Mechanisms and Robotics in 2019"

Lower-Limb Prostheses and Exoskeletons With Energy Regeneration: Mechatronic Design and Optimization Review

Abstract: Lower-limb biomechatronic devices (i.e., prostheses and exoskeletons) depend upon onboard batteries to power wearable sensors, actuators, and microprocessors, therein inherently limiting their operating durations. Regenerative braking, also termed electrical energy regeneration, represents a promising solution to the aforementioned shortcomings. Regenerative braking converts the otherwise dissipated mechanical energy during locomotion into electrical energy for recharging the onboard batteries, while simultaneously providing negative mechanical work for controlled system deceleration. This paper reviewed the electromechanical design and optimization of lower-limb biomechatronic devices with electrical energy regeneration. The technical review starts by examining human walking biomechanics (i.e., mechanical work, power, and torque about the hip, knee, and ankle joints) and proposes general design principles for regenerative braking prostheses and exoskeletons. Analogous to electric and hybrid electric vehicle powertrains, there are numerous mechatronic design components that could be optimized to maximize electrical energy regeneration, including the mechanical power transmission, electromagnetic machine, electrical drive, device mass and moment of inertia, and energy storage devices. Design optimization of these system components is individually discussed while referencing the latest advancements in robotics and automotive engineering. The technical review demonstrated that existing systems (1) are limited to level-ground walking applications and (2) have maximum energy regeneration efficiencies between 30% and 37%. Accordingly, potential future directions for research and innovation include (1) regenerative braking during dynamic movements like sitting down and slope and staircase descent and (2) utilizing high-torque-density electromagnetic machines and low-impedance mechanical power transmissions to maximize energy regeneration efficiencies.

A screw theory based semi-analytical approach for elastodynamics of the tricept robot

Abstract: Taking the well-known Tricept robot as an example, this paper presents a semi-analytical approach for elastodynamic modeling of five or six degrees of freedom (DOF) hybrid robots composed of a 3-DOF parallel mechanism plus a 2- or 3-DOF wrist. Drawing heavily on screw theory combined with structural dynamics, the kinetic and elastic potential energies of the parallel mechanism and of the wrist are formulated using the dual properties of twist/wrench systems and a static condensation technique. This results in a 9-DOF dynamic model that enables the lower-order dynamic behavior over the entire workspace to be estimated in a very efficient and accurate manner. The lower-order natural frequencies and mode shapes estimated by the proposed approach are shown to have very good agreement with those obtained by a full-order finite element (FE) model. It thus provides a very time-effective tool for optimal design within a virtual prototyping framework for hybrid robot-based machine tools.

An Ankle Exoskeleton Using a Lightweight Motor to Create High Power Assistance for Push-Off

Abstract: Active exoskeletons have capacity to provide biologically equivalent levels of joint mechanical power, but high mass of actuation units may lead to uncoordinated walking and extra metabolic consumption. Active exoskeletons normally supply assistance directly during push-off and have a power burst during push-off. Thus, the requirements on power of motors are high, which is the main reason for the high mass. However, in a muscle-tendon system, the strategy of injecting energy slowly and releasing quickly is utilized to obtain a higher peak power than that of muscle alone. Application of this strategy of peak power amplification in exoskeleton actuation might lead to reductions of input power and device mass. This paper presents an ankle exoskeleton which can accumulate the energy injected by a motor during the swing phase and mostly the stance phase and then release it quickly during push-off. An energy storage and release system was developed using a four-bar linkage clutch. In addition, evaluation experiments on the exoskeleton were carried out. Results show that the exoskeleton could provide a high power assistance with a low power motor and reduced the requirement on motor power by 4.73 times. Besides, when walking with the exoskeleton, the ankle peak power was reduced by 25.8% compared to the normal condition. The strategy which imitates the working pattern of the muscle-tendon system leads to a lightweight and effective exoskeleton actuation, and it also supplies ideas for the designs of lightweight actuators that work discontinuously in other conditions.

Wrench Analysis of Cable-Suspended Parallel Robots Actuated by Quadrotor Unmanned Aerial Vehicles

Abstract: Aerial cable towed systems (ACTSs) can be created by joining unmanned aerial vehicles (UAVs) to a payload to extend the capabilities of the system beyond those of an individual UAV. This paper describes a systematic method for evaluating the available wrench set and the robustness of equilibrium of ACTSs by adapting wrench analysis techniques used in traditional cable-driven parallel robots to account for the constraints of quadrotor actuation and dynamics. Case studies and experimental results are provided to demonstrate the analysis of different classes of ACTSs, as a means of evaluating the design and operating configurations.

Kinematics of continuum robots with constant curvature bending and extension capabilities

Abstract: Continuum robots are becoming increasingly popular due to the capabilities they offer, especially when operating in cluttered environments, where their dexterity, maneuverability, and compliance represent a significant advantage. The subset of continuum robots that also belong to the soft robots category has seen rapid development in recent years, showing great promise. However, despite the significant attention received by these devices, various aspects of their kinematics remain unresolved, limiting their adoption and obscuring their potential. In this paper, the kinematics of continuum robots with the ability to bend and extend are studied, and analytical, closed-form solutions to both the direct and inverse kinematics are presented. The results obtained expose the redundancies of these devices, which are subsequently explored. The solution to the inverse kinematics derived here is shown to provide an analytical, closed-form expression describing the curve associated with these redundancies, which is also presented and analyzed. A condition on the reachable end-effector poses for robots with six actuation degrees-of-freedom (DOFs) is then distilled. The kinematics of robot layouts with over six actuation DOFs are subsequently considered. Finally, simulated results of the inverse kinematics are provided, verifying the study.

SpinyHand: Contact Load Sharing for a Human-Scale Climbing Robot

Abstract: We present a hand specialized for climbing unstructured rocky surfaces. Articulated fingers achieve grasps commonly used by human climbers. The gripping surfaces are equipped with dense arrays of spines that engage with asperities on hard rough materials. A load-sharing transmission system divides the shear contact force among spine tiles on each phalanx to prevent premature spine slippage or grasp failure. Taking advantage of the hand’s kinematic and load-sharing properties, the wrench space of achievable forces and moments can be computed rapidly. Bench-top tests show agreement with the model, with average wrench space errors of 10–15%, despite the stochastic nature of spine/surface interaction. The model provides design guidelines and control strategy insights for the SpinyHand and can inform future work.

Elephant’s Trunk Robot: An Extremely Versatile Under-Actuated Continuum Robot Driven by a Single Motor

Abstract: Continuous-bodied “trunk and tentacle” robots have increased self-adaptability and obstacle avoidance capabilities, compared with traditional, discrete-jointed, robots with large rigid links. In particular, continuous-bodied robots have obvious advantages in grasping objects across a wide range of external dimensions. Not only can they grasp objects using end effectors like traditional robots, but their bodies can also be regarded as a gripping device, and large objects with respect to the robot’s scale can be captured by the entire structure of the robots themselves. Existing trunk-like robots have distributed multidrive actuation and are often manufactured using soft materials, which leads to a complex actuator system that also limits their potential applications in dangerous and extreme environments. This paper introduces a new type of elephant’s trunk robot with very few driving constraints. The robot consists of a series of novel underactuated linkage units. With a single-motor drive, the robot can achieve stable grasping of objects of different shapes and sizes. The proposed robot simplifies the requirements of the sensing and control systems during the operation process and has the advantage of accomplishing the capture task without determining the exact shape and position of the target object. It is especially suitable for operations such as non-cooperative target capture in extremely dangerous environments, including those in outer space. Based on theoretical analysis and model design, a trunk robot prototype was developed, and a comprehensive experimental study of the bending/extension and grasping operation functions was conducted to verify the validity of the proposed robot design.

A Novel Variable Stiffness Compliant Robotic Gripper Based on Layer Jamming

Abstract: In this paper, we present a novel compliant robotic gripper with three variable stiffness fingers. While the shape morphing of the grippers is cable-driven, the stiffness variation is enabled by layer jamming. The inherent flexibility makes compliant grippers suitable for tasks such as grasping soft and irregular objects. However, their relatively low load capacity due to low structural stiffness limits their applications. Variable stiffness robotic grippers have the potential to address this challenge as their stiffness can be tuned on demand based on the needs of tasks. Layer jamming is an emerging method for variable stiffness due to its advantages of light weight, simple and quick actuation. In our design, the compliant backbone of the fingers is made of 3d printed PLA material. Four thin film materials are attached to each side of the skeleton. The working process of the robotic gripper follows two basic steps. First, the compliant skeleton is bent to a desired shape by actuating a tension cable via a servo motor. Second, upon application of a negative pressure by a vacuum pump, the finger is stiffened up owing to the increasing of the friction between contact surfaces of layers preventing their relative movement. Since the structural stiffness of the fingers is increased, their load capacity will be increased proportionally. When the air pressure is sufficiently large, the morphed shape can even be locked (no slipping). Test for stiffness of individual finger and load capacity of the robotic gripper are conducted to validate capability of the design. The results showed a 69-fold increase in stiffness of individual finger and a 30-fold increase in gripper’s load capacity.

Layer-Jamming Suction Grippers With Variable Stiffness

Abstract: The soft grippers driven by pneumatics have an advantage of effectively lifting soft materials and heavier objects with clean air. They provide multiplanar compliant stability when compared with standard claw-like grippers because of the larger contact area. Such grippers can work on objects with a greater surface area than the gripper itself. However, until now, to enhance the gripping on heavier objects, multiple suction cups are used, which involve tubing and a vacuum pump for each individual cup, which ultimately makes the setup bulky and immovable. Furthermore, using a bigger suction gripper requires bigger tubing and higher negative pressure. To tackle this limitation, we are introducing layer-jamming suction grippers with kirigami pattern for stiffness tuning. The kirigami-patterned base and sheets make a channel from the air tubing to each hole that acts as multiple suction cups. The sheets incorporated within the suction cups, working as layer-jamming, control the stiffness of the prototype. Results highlight that the gripper has the capability of lifting 200 times its own weight with a planar surface and has a strength and durability to withstand a maximum force of 87 N. One important characteristic of the gripper is its adaptability to the curved surfaces, which has an enhanced grasp and is able to lift 154 times its own weight. The ease of fabrication, low cost, and higher lifting capabilities open up a wide area of opportunities to see the advancements in technologies with the suction grippers.

A Survey on the Computation of Quaternions From Rotation Matrices

Abstract: The parameterization of rotations is a central topic in many theoretical and applied fields such as rigid body mechanics, multibody dynamics, robotics, spacecraft attitude dynamics, navigation, 3D image processing, computer graphics, etc. Nowadays, the main alternative to the use of rotation matrices, to represent rotations in $\R^3$, is the use of Euler parameters arranged in quaternion form. Whereas the passage from a set of Euler parameters to the corresponding rotation matrix is unique and straightforward, the passage from a rotation matrix to its corresponding Euler parameters has been revealed to be somewhat tricky if numerical aspects are considered. Since the map from quaternions to $3{\times}3$ rotation matrices is a 2-to-1 covering map, this map cannot be smoothly inverted. As a consequence, it is erroneously assumed that all inversions should necessarily contain singularities that arise in the form of quotients where the divisor can be arbitrarily small. This misconception is herein clarified. This paper reviews the most representative methods available in the literature, including a comparative analysis of their computational costs and error performances. The presented analysis leads to the conclusion that Cayley's factorization, a little-known method used to compute the double quaternion representation of rotations in four dimensions from $4{\times}4$ rotation matrices, is the most robust method when particularized to three dimensions.

An Analytical and Modular Software Workbench for Solving Kinematics and Dynamics of Series-Parallel Hybrid Robots

Abstract: Parallel mechanisms are increasingly being used as modular subsystem units in various robots and man-machine interfaces for their superior stiffness, payload-to-weight ratio, and dynamic properties. This leads to series-parallel hybrid robotic systems that are challenging to model and control due to the presence of various closed loops. Most model-based kinematic and dynamic modeling tools resolve loop closure constraints numerically and hence suffer from inefficiency and accuracy issues. Additionally, they do not exploit the modularity in robot design. In this paper, we present a modular and analytical approach toward kinematic and dynamic modeling of series-parallel hybrid robots. This approach has been implemented in a software framework called hybrid robot dynamics (hyrodyn) and its application is demonstrated with the help of a series-parallel hybrid humanoid robot recently developed at DFKI-RIC.

A General Purpose Robotic Hand Exoskeleton With Series Elastic Actuation.

Abstract: This paper describes the design and control of a novel hand exoskeleton. A subcategory of upper extremity exoskeletons, hand exoskeletons have promising applications in healthcare services, industrial workplaces, virtual reality, and military. Although much progress has been made in this field, most of the existing systems are position controlled and face several design challenges, including achieving minimal size and weight, difficulty enforcing natural grasping motions, exerting sufficient grip strength, ensuring the safety of the users hand, and maintaining overall user friendliness. To address these issues, this paper proposes a novel, slim, lightweight linkage mechanism design for a hand exoskeleton with a force control paradigm enabled via a compact series elastic actuator. A detailed design overview of the proposed mechanism is provided, along with kinematic and static analyses. To validate the overall proposed hand exoskeleton system, a fully integrated prototype is developed and tested in a series of experimental trials.

Active Disturbance Rejection Control for Handling Slip in Tracked Vehicle Locomotion

Abstract: This paper describes the use of an active disturbance rejection controller (ADRC) to estimate and compensate for the effect of slip in an online manner to improve the path tracking performance of autonomous ground vehicles (AGVs). AGVs with skid-steer locomotion mode are extensively used for robotic applications in the fields of agriculture, transportation, construction, warehouse maintenance, and mining. Majority of these applications such as performing reconnaissance and rescue operations in rough terrain or autonomous package delivery in urban scenarios, require the system to follow a path predetermined by a high-level planner or based on a predefined task. In the absence of effective slip estimation and compensation, the AGVs, especially tracked vehicles, can fail to follow the path as given out by the high-level planner. The proposed ADRC architecture uses a generic mathematical model that can account for the scaling and shift in the states of the system due to the effects of slip through augmented parameters. An extended Kalman filter (EKF) observer is used to estimate the varying slip parameters online. The estimated parameters are then used to compensate for the effects of slip at each iteration by modifying the control actions given by a low-level path tracking controller. The proposed approach is validated through experiments over flat and uneven terrain conditions including asphalt, vinyl flooring, artificial turf, grass, and gravel using a tracked skid-steer mobile robot. A detailed discussion on the results and directions for future research is also presented.

Design and Experimental Investigation of a New 2R1T Overconstrained Parallel Kinematic Machine With Actuation Redundancy

Abstract: Two rotations and one translation (2R1T) parallel kinematic machines (PKMs) are suitable for the machining of complex curved surfaces, which requires high speed and precision. To further improve rigidity, precision, and avoid singularity, actuation redundancy, and overconstrained PKMs with fixed actuators and limited-degrees of freedom (DOF) limbs are preferred. However, there are few 2R1T PKMs with these features. This paper introduces a new 2R1T overconstrained PKM with actuation redundancy, which is called Tex4. The Tex4 PKM consists of four limited-DOF limbs; that is, two PUR limbs and two 2PRU limbs (where P denotes an actuated prismatic joint, U denotes a universal joint, and R denotes a revolute joint). The kinematic model of the proposed 2PUR-2PRU machine is presented along with the results of mobility, inverse kinematics, and velocity analysis. By considering the motion/force transmissibility, the dimensional parameters of the Tex4 PKM were optimized to obtain an improved satisfactory transmission workspace without singular configurations. Finally, a prototype based on the optimized parameters was fabricated, and its feasibility and accuracy were validated by motion and position error experiments. The Tex4 PKM has the advantages of high rigidity, simple kinematic model, and zero singularity in the workspace, which suggests that it has potential for use in the high-speed machining of curved surfaces.

Origami Kaleidocycle-Inspired Symmetric Multistable Compliant Mechanisms

Abstract: Compliant kaleidocycles can be widely used in a variety of applications, including deployable structures, origami structures, and metamorphic robots, due to their unique features of continuous rotatability and multistability. Inspired by origami kaleidocycles, a type of symmetric multistable compliant mechanism with an arbitrary number of units is presented and analyzed in this paper. First, the basic dimension constraints are developed based on mobility analysis using screw theory. Second, the kinematic relationships of the actual rotation angle are obtained. Third, a method to determine the number of stabilities and the position of stable states, including the solution for the parameterized boundaries of stable regions, is developed. Finally, experimental platforms are established, and the validity of the proposed multistable mechanisms is verified.

An Improved Design of Gravity Compensators Based on the Inverted Slider-Crank Mechanism

Abstract: The static balancing of mechanical systems is an important issue because it allows one to significantly decrease the size of actuators for equivalent displacements of the end effector. Indeed, the actuators do not have to produce the required input energy to counterbalance the variation of the potential energy of the robot. However, the literature review shows that in many cases the gravity balancing of mechanical systems is carried out by neglecting the masses of auxiliary links associated with the principal mechanism. For many balancing schemes, it is a source of errors.This paper deals with an improved solution for gravity compensators based on the inverted slider-crank mechanism considering the masses of the coupler and the spring. To achieve this, the torques are determined due to auxiliary links. Subsequently, they are introduced into the balancing equation for minimization of the residual unbalance. Hence, a more accurate balancing of gravity compensators based on the inverted slider-crank mechanism can be achieved. The efficiency of the suggested approach is illustrated by numerical simulations.

Trajectory-Planning and Normalized-Variable Control for Parallel Pick-and-Place Robots

Abstract: Trajectory planning and an efficient control scheme play a crucial role in improving the performance of pick-and-place robots. This paper introduces a novel method of trajectory planning with cycle time and path constraints. Assuming that a smooth trajectory is given, to be followed within a prescribed cycle time, the newly proposed method of trajectory planning removes the torque peaks of the actuators by a suitable scheduling of the velocity of the moving plate. Since pick-and-place robots are usually expected to meet the end poses in a certain time span, while disregarding the intermediate poses, the velocity can be tuned properly around the critical points of the trajectory by means of a time-scaling function. Moreover, the authors report the formulation of a linear quadratic regulator (LQR) controller with normalized variables to be used in conjunction with our trajectory-tracking control scheme for an in-house-developed Schönflies-motion generator. This parallel robot offers a functionally symmetric, single-loop architecture, with an isostatic kinematic chain, and virtually unlimited rotatability of its gripper. A comparison between two actuation systems developed by the authors is conducted via simulation results.

Design, Modeling and Experimentation of a Bio-Inspired Miniature Climbing Robot with Bilayer Dry Adhesives

Abstract: This paper presents the design, modeling, and analysis of the force behavior acting on a wheel-legs (whegs) type robot which utilizes bilayer dry adhesives for wall-climbing. The motion of the robot is modeled as a slider-crank mechanism to obtain the dynamic parameters of the robot during movement. The required forces and moment to maintain equilibrium as the robot is in motion is then extensively analyzed and discussed. Following the analysis, fundamental measures to attain an operative climbing robot, such as adhesive requirement and torque specification, are then identified. The outcomes of the analysis are verified through experiments and working prototypes that are in good agreement with the design guidelines.

Biologically Inspired Design and Development of a Variable Stiffness Powered Ankle-foot Prosthesis

Abstract: Recent advancements in powered lower limb prostheses have appeased several difficulties faced by lower limb amputees by using a Series-Elastic Actuator (SEA) to provide powered sagittal plane flexion. Unfortunately, these devices are currently unable to provide both powered sagittal plane flexion and 2-DOF at the ankle, removing the ankle’s capacity to invert/evert, thus severely limiting terrain adaption capabilities and user comfort. The developed 2-DOF ankle system in this paper allows both powered flexion in the sagittal plane and passive rotation in the frontal plane; a SEA emulates the biomechanics of the gastrocnemius and Achilles tendon for flexion, while a novel universal-joint system provides the 2-DOF. Several studies were undertaken to thoroughly characterize the capabilities of the device. Under both level and sloped-ground conditions, ankle torque and kinematic data was obtained by using force-plates and a motion capture system. The device was found to be fully capable of providing powered sagittal plane motion and torque very close to that of a biological ankle, while simultaneously being able to adapt to sloped terrain by undergoing frontal plane motion, thus providing 2-DOF at the ankle. These findings demonstrate that the device presented in this paper poses radical improvements to powered PAFD design.

Design of Cylindrical and Axisymmetric Origami Structures Based on Generalized Miura-Ori Cell

Abstract: Origami has shown its potential in designing a three-dimensional folded structure from a flat sheet of material. In this paper, we present geometric design methods to construct cylindrical and axisymmetric origami structures that can fit between two given surfaces. Due to the symmetry of the structures, a strip of folds based on the generalized Miura-ori cells is first constructed and then replicated longitudinally/circumferentially to form the cylindrical/axisymmetric origami structures. In both designs, algorithms are presented to ensure that all vertexes are either on or strictly within the region between the target surfaces. The conditions of flat-foldability and developability are fulfilled at the inner vertexes and the designs are rigid-foldable with a single degree-of-freedom. The methods for cylindrical and axisymmetric designs are similar in implementation and of potential in designing origami structures for engineering purposes, such as foldcores, foldable shelters, and metamaterials.

Design of Planar Large-Deflection Compliant Mechanisms With Decoupled Multi-Input-Output Using Topology Optimization

Abstract: This paper presents a method for topology optimization of large-deflection compliant mechanisms with multiple inputs and outputs by considering the coupling issue. First, the objectives of the design problem are posed by modeling the output loads using several springs to enable control of the input–output behavior. Second, a scheme is proposed to obtain a completely decoupled mechanism. Both input coupling and output coupling are considered. Third, with the implementation of an energy interpolation scheme to stabilize the numerical simulations, the geometrical nonlinearity is considered to appropriately capture the large displacements of compliant mechanisms. Finally, several numerical examples are presented to demonstrate the validity of the proposed method. Comparison studies with the obtained results without considering the coupling issues are also presented.

A relationship between sweep angle of flapping pectoral fins and thrust generation

Abstract: Propulsive capability of manta rays' flapping pectoral fins has inspired many to incorporate these fins as propulsive mechanisms for autonomous underwater vehicles. In particular, geometrical factors such as sweep angle have been postulated as being influential to these fins' propulsive capability, specifically their thrust generation. Although effects of sweep angle on static/flapping wings of aircrafts/drones have been widely studied, little has been done for underwater conditions. Furthermore, the findings from air studies may not be relatable to the underwater studies on pectoral fins because of the different Reynolds number (compared to the flapping wings) and force generation mechanism (compared to the static wings). This paper aims to establish a relationship between the sweep angle and thrust generation. An experiment was conducted to measure the thrust generated by 40 fins in a water channel under freestream and still water conditions for chord Reynolds number between 2.2 × 104 and 8.2 × 104. The fins were of five different sweep angles (0 deg, 10 deg, 20 deg, 30 deg, and 40 deg) that were incorporated into eight base designs of different flexibility characteristics. The results showed that the sweep angle (within the range considered) may have no significant influence on these fins' thrust generation, implying no significant effects on thrust under uniform flow condition and on the maximum possible thrust under still water. Overall, it can be concluded that sweep angle may not be a determinant of thrust generation for flapping pectoral fins. This knowledge can ease the decision-making process of design of robots propeled by these fins.

Vertex-Splitting on a Diamond Origami Pattern

Abstract: A diamond origami pattern is a well-known origami pattern consisting of identical six-crease vertices. As each vertex can be modeled as a spherical 6R linkage with three degrees of freedom (DOF), the tessellated pattern with multiple vertices is a multi-DOF system, which makes it difficult to fully control the motion in the desired symmetric manner. Here, two splitting schemes on the diamond vertex are proposed to generate three types of unit patterns to reduce the DOF. This vertex-splitting technique is applied to the multivertex diamond origami pattern to produce several one-DOF basic assemblies, which form a number of one-DOF origami patterns. Two of the one-DOF origami patterns are discussed: one of which is a flat-foldable origami pattern mixed with four- and six-crease vertices and the other is a nonflat-foldable one mixed with four-, five-, and six-crease vertices. In the one-DOF patterns, the symmetrically kinematic property of the original diamond origami pattern is well kept. Such property would significantly facilitate engineering applications comparing to the multi-DOF origami patterns. It also paves a new road to construct one-DOF origami patterns.

A Hybrid Tracked-Wheeled Multi-Directional Mobile Robot

Abstract: This paper presents the novel design and integration of a mobile robot with multi-directional mobility capabilities enabled via a hybrid combination of tracks and wheels. Tracked and wheeled locomotion modes are independent from one another, and are cascaded along two orthogonal axes to provide multi-directional mobility. An actuated mechanism toggles between these two modes for optimal mobility under different surface-traction conditions, and further adds an additional translational axis of mobility. That is, the robot can move in the longitudinal direction via the tracks on rugged terrain for high traction, in the lateral direction via the wheels on smooth terrain for high-speed locomotion, and along the vertical axis via the translational joint. Additionally, the robot is capable of yaw axis mobility using differential drives in both tracked and wheeled modes of operation. The paper presents design and analysis of the proposed robot along with a dynamic stabilization algorithm to prevent the robot from tipping over while carrying an external payload on inclined surfaces. Experimental results using an integrated prototype demonstrate multi-directional capabilities of the mobile platform and the dynamic stability algorithm to stabilize the robot while carrying various external payloads on inclined surfaces measuring up to 2.5 kg and 10 deg, respectively.

Dynamic Trajectory Planning for Failure Recovery in Cable-Suspended Camera Systems

Abstract: The use of cable-driven parallel robots (CDPR) in real-world applications makes safety a major concern for these devices and a relevant research topic. Cable-suspended camera systems are among the earliest and most common applications of CDPRs. In this paper, we propose a novel after-failure approach for cable-suspended camera systems. This strategy, which is applied after a cable breaks, seeks to drive the end effector, i.e., the camera, toward a safe pose, following an oscillatory trajectory that guarantees positive and bounded tensions in the remaining cables. The safe landing location is optimized to minimize the trajectory time while avoiding collisions with the physical boundaries of the workspace. Results of numerical simulations indicate the feasibility of the proposed approach.

Passive Discrete Variable Stiffness Joint (pDVSJ-II): Modeling, Design, Characterization, and Testing Toward Passive Haptic Interface

Abstract: In this paper, the modeling, design, and characterization of the passive discrete variable stiffness joint (pDVSJ-II) are presented. The pDVSJ-II is an extended proof of concept of a passive revolute joint with discretely controlled variable stiffness. The key motivation behind this design is the need for instantaneous switching between stiffness levels when applied for remote exploration applications where stiffness mapping is required, in addition for the need of low-energy consumption. The novelty of this work lies in the topology used to alter the stiffness of the variable stiffness joint. Altering the stiffness is achieved by selecting the effective length of an elastic cord with hook's springs. This is realized through the novel design of the cord grounding unit (CGU), which is responsible for creating a new grounding point, thus changing the effective length and the involved springs. The main features of CGU are the fast response and the low-energy consumption. Two different levels of stiffness (low, high) can be discretely selected besides the zero stiffness. The proposed physical-based model matched the experimental results of the pDVSJ-II in terms of discrete stiffness variation curves, and the stiffness dependency on the behavior of the springs. Two psychophysiological tests were conducted to validate the capabilities to simulate different levels of stiffness on human user and the results showed high relative accuracy. Furthermore, a qualitative experiment in a teleoperation scenario is presented as a case study to demonstrate the effectiveness of the proposed haptic interface.

Three Novel Symmetric Waldron-Bricard Metamorphic and Reconfigurable Mechanisms and Their Isomerization

Abstract: This paper explores a class of metamorphic and reconfigurable linkages belonging to both Waldron's double-Bennett hybrid linkage and Bricard linkages, which include three novel symmetric Waldron–Bricard metamorphic and reconfigurable mechanisms, and further presents their three extended isomeric metamorphic linkages. The three novel Waldron–Bricard metamorphic and reconfigurable linkages are distinguished by line-symmetric, plane-symmetric, and line-plane-symmetric characteristics. The novel line-symmetric Waldron–Bricard metamorphic linkage with one Waldron motion branch and two general and three special line-symmetric Bricard motion branches is obtained by integrating two identical general Bennett loops. The novel plane-symmetric Waldron–Bricard reconfigurable linkage with two plane-symmetric motion branches is obtained by coalescing two equilateral Bennett loops. The novel line-plane-symmetric Waldron–Bricard metamorphic linkage with six motion branches is obtained by blending two identical equilateral Bennett loops, including the plane-symmetric Waldron motion branch, the line-plane-symmetric Bricard motion branch, the spherical 4R motion branch, and three special line-symmetric Bricard motion branches. With the isomerization that changes a mechanism structure but keeps all links and joints, each of the three novel Waldron–Bricard linkages results in an extended isomeric metamorphic linkage. This further evolves into the study of the three isomeric mechanisms. The study of these three novel metamorphic and reconfigurable mechanisms and their isomerization are carried out to demonstrate the characteristics of bifurcation and to reveal motion-branch transformation. Furthermore, by exploring the intersection of given motion branches and using the method of isomerization, more metamorphic and reconfigurable linkages can be discovered to usefully deal with transitions among possible submotions.

Design of Translational and Rotational Bistable Actuators Based on Dielectric Elastomer

Abstract: Dielectric elastomer (DE), as a group of electro-active polymers, has been widely used in soft robotics due to its inherent flexibility and large induced deformation. As sustained high voltage is needed to maintain the deformation of DE, it may result in electric breakdown for a long-period actuation. Inspired by the bistable mechanism which has two stable equilibrium positions and can stay at one of them without energy consumption, two bistable dielectric elastomer actuators (DEAs) including a translational actuator and a rotational actuator are proposed. Both the bistable actuators consist of a double conical DEA and a buckling beam and can switch between two stable positions with voltage. In this paper, the analytical models of the bulking beam and the conical DEA are presented first, and then the design method is demonstrated in terms of force equilibrium and moment equilibrium principle. The experiments of the translational bistable DEA and the rotational bistable DEA are conducted, which show that the design method of the bistable DEA is effective.

Kinetostatic Modeling and Optimization of a Novel Horizontal-Displacement Compliant Mechanism

Abstract: This paper presents kinetostatic modeling of a compliant mechanism for translational motion. This mechanism arranges all compliant members in an inverted way, which enables the robustness against beam buckling due to the heavy payload. To enable quick design and analysis of the mechanism, a nonlinear analytical model is then derived based on the chained beam constraint model, which is validated by nonlinear finite element simulation. Geometric parameter optimization is further carried out for desired motion characteristics. Finally, a prototype is fabricated and tested to verify the analytical model.

Design and Analysis of a High-Payload Manipulator Based on a Cable-Driven Serial-Parallel Mechanism

Abstract: In this paper, a lightweight high-payload cable-driven serial-parallel manipulator is proposed. The manipulator comprises one 3-degree-of-freedom (3-DOF) shoulder joint and one single-DOF elbow joint. Using a special tension-amplifying principle, which is an ingenious two-stage deceleration method, the proposed manipulator has a higher load/mass ratio than those of conventional manipulators. In this paper, the special tension-amplifying principle is discussed in detail. The shoulder and elbow joints of the proposed manipulator are driven by cables. The design of this cable-driven mechanism and the mobility of the joints are analyzed, and the structural parameters of the joints are optimized to improve the payload capacity. The size of the manipulator is close to that of a human arm because the actuators of the cable-driven mechanism can be rear-mounted. Because the elbow joint is located at the end of the shoulder joint and the driven cables of the elbow joint are coupled with the rotation of the shoulder joint, the manipulator is designed with decoupled cable routing. The overall configuration and cable routing of the manipulator are presented, and then, kinematics, joint stiffness, strength, and workspace of the manipulator are analyzed. Finally, we report on the fabrication of a physical prototype and testing of its joint stiffness, payload capacity, workspace, speed, and repeatability to verify the feasibility of our proposed manipulator.