0


Research Papers

J. Mechanisms Robotics. 2015;7(4):041001-041001-9. doi:10.1115/1.4029116.

In order to obtain a comprehensive list of possible mechanisms with various choices of both R and P pairs and mechanism inversion of planar mechanisms, a new structural synthesis method is developed by integrating Assur groups (AGs) as elements in the newly developed group-based adjacency matrix. This extended adjacency matrix is proposed with the diagonal elements representing three fundamental elements as the frame link, driving link, AG and augmented AG (AAG) if metamorphic mechanisms are to be synthesized. The off-diagonal elements provide information on group combination and connection forms of the above three fundamental elements and that on the associated kinematic pairs. Based on the extended adjacency matrix, all assembly modes for the given AGs can be established and isomorphism mechanisms can be identified at the same time. Considering all types of the AGs in the extended adjacency matrix, group permutation and combination are used and connection forms are generated including variation of the driving link and mechanism inversion. The structural synthesis is then extending to generating a comprehensive list of types of mechanisms and illustrated by the synthesis for class II 6-bar planar mechanisms with both R and P pairs, generating a list of 588 types of mechanisms that are derived for the first time. The paper further applies the approach to metamorphic mechanisms, and obtained five connection forms of the 7-bar 2DOF metamorphic mechanisms.

Topics: Linkages
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041002-041002-11. doi:10.1115/1.4029117.

In this paper, a rolling mechanism constructed by a spatial 8-bar linkage is proposed. The eight links are connected with eight revolute joints, forming a single closed-loop with two degrees of freedom (DOF). By kinematic analysis, the mechanism can be deformed into planar parallelogram or spherical 4-bar mechanism (SFM) configuration. Furthermore, this mechanism can be folded onto a plane at its singularity positions. The rolling capability is analyzed based on the zero-moment-point (ZMP) theory. In the first configuration, the mechanism can roll along a straight line. In the second configuration, it can roll along a polygonal region and change its rolling direction. By alternatively choosing one of the two configurations, the mechanism has the capability to roll along any direction on the ground. Finally, a prototype was manufactured and some experiments were carried out to verify the functions of the mechanism.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041003-041003-9. doi:10.1115/1.4029498.

Rolling contact has been used by robotic devices to drive between configurations. The degrees of freedom (DOFs) of rolling contact pairs can be one, two, or three, depending on the geometry of the objects. This paper aimed to derive three kinematic inputs required for the moving object to follow a trajectory described by its velocity profile when the moving object has three rotational DOFs and thus can rotate about any axis through the contact point with respect to the fixed object. We obtained three contact equations in the form of a system of three nonlinear algebraic equations by applying the curvature theory in differential geometry and simplified the three nonlinear algebraic equations to a univariate polynomial of degree six. Differing from the existing solution that requires solving a system of nonlinear ordinary differential equations, this polynomial is suitable for fast and accurate numerical root approximations. The contact equations further revealed the two essential parts of the spin velocity: The induced spin velocity governed by the geometry and the compensatory spin velocity provided externally to realize the desired spin velocity.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041004-041004-8. doi:10.1115/1.4029499.

A parallel kinematic machine (PKM) topology can only give its best performance when its geometrical parameters are optimized. In this paper, dimensional synthesis of a newly developed PKM is presented for the first time. An optimization method is developed with the objective to maximize both workspace volume and global dexterity of the PKM. Results show that the method can effectively identify design parameter changes under different weighted objectives. The PKM with optimized dimensions has a large workspace to footprint ratio and a large well-conditioned workspace, hence justifies its suitability for large volume machining.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041005-041005-12. doi:10.1115/1.4029401.

In this paper, we study five aspects of design for wheeled inverted pendulum (WIP) platforms with the aim of understanding the effect of design choices on the balancing performance. First, we demonstrate analytically and experimentally the effect of soft visco-elastic tires on a WIP showing that the use of soft tires enhances balancing performance. Next, we study the effect of pitch rate and wheel velocity filters on WIP performance and make suggestions for design of filters. We then describe a self-tuning limit cycle compensation algorithm and experimentally verify its operation. Subsequently, we present an analytical simulation to study the effects of torque and velocity control of WIP motors and describe the tradeoffs between the control methodologies in various application scenarios. Finally, to understand if motor gearing can be an efficient alternative to bigger and more expensive direct drive motors, we analyze the effect of motor gearing on WIP dynamics. Our aim is to describe electromechanical design tradeoffs appropriately, so a WIP can be designed and constructed with minimal iterative experimentation.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041006-041006-7. doi:10.1115/1.4029186.

We use the recently introduced factorization theory of motion polynomials over the dual quaternions and cubic interpolation on quadrics for the synthesis of closed kinematic loops with six revolute joints that visit four prescribed poses. The resulting 6R linkages are special in the sense that the relative motions of all links are rational. They exhibit certain elegant properties such as symmetry in the rotation angles and, at least in theory, full-cycle mobility. Our synthesis approach admits either no solution or two one-parametric families of solutions. We suggest strategies for picking good solutions from these families. They ensure a fair coupler motion and optimize other linkage characteristics such as total rotation angle or linkage size. A comprehensive synthesis example is provided.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041007-041007-8. doi:10.1115/1.4029808.

This paper presents a new kinematics model for linear-actuated symmetrical spherical parallel manipulators (LASSPMs) which are commonly used considering their symmetrical kinematics and dynamics properties. The model has significant advantages in solving the forward kinematic equations, and in analytically obtaining singularity loci and the singularity-free workspace. The Cayley formula, including the three Rodriguez–Hamilton parameters from a general rotation matrix, is provided and used in describing the rotation motion and geometric constraints of LASSPMs. Analytical solutions of the forward kinematic equations are obtained. Then singularity loci are derived, and represented in a new coordinate system with the three Rodriguez–Hamilton parameters assigned in three perpendicular directions. Limb-actuation singularity loci are illustrated and forward kinematics (FK) solution distribution in the singularity-free zones is discussed. Based on this analysis, unique forward kinematic solutions of LASSPMs can be determined. By using Cayley formula, analytical workspace boundaries are expressed, based on a given mechanism structure and input actuation limits. The singularity-free workspace is demonstrated in the proposed coordinate system. The work gives a systematic method in modeling kinematics, singularity and workspace analysis which provides new optimization design index and a simpler kinematics model for dynamics and control of LASSPMs.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041008-041008-8. doi:10.1115/1.4029437.

This paper describes the design and optimization of a novel five-finger haptic glove mechanism, which uses a worm-geared motor and an antagonistically routed cable mechanism at each finger as both active and passive force display actuators. Existing haptic gloves either restrict the natural motion and maximum output force of the hand or are bulky and heavy. In order to tackle these challenges, the five-finger haptic glove is designed to minimize the size and weight and maximize the workspace and force output range of the glove. The glove is a wireless and self-contained mechatronic system that mounts over the dorsum of a bare hand and provides haptic force feedback to each finger. This paper describes the mechatronic design of the glove and the method to optimize the link length with the purpose of enhancing workspace and the force transmission ratio. Simulation and experimental results are reported, showing the future potential of the proposed system in haptic applications and rehabilitation therapy.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041009-041009-9. doi:10.1115/1.4029438.

This article presents a new spatial mechanism with single degree of freedom (DOF) for three-dimensional path generation. The path can be defined by prescribing at most seven precision points. The moving platform of the mechanism is supported by a U-R (universal-revolute) leg and two S–S (spherical–spherical) legs. The driving unit is the first axis of the universal pair. The U-R leg is synthesized first with the problem of order defects being considered. Precision points then lead to prescribed poses of the moving platform. Two S–S legs are then synthesized to meet these poses. This spatial mechanism with a given input is analogous to a planar kinematic chain so that all possible configurations of the spatial mechanism can be constructed. A strategy consisting of three stages for evaluating branch defects is developed with the aid of the characteristic of double configurations and the technique of coding three constituent four-bar linkages. Two numerical examples are presented to illustrate the design, the evaluation of defects, and the performance of the mechanism.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041010-041010-10. doi:10.1115/1.4028623.

This paper presents a finite element method (FEM) for the kinematic solution of parallel manipulators (PMs), and this approach is applied to analyze the kinematics of a parallel hip joint manipulator (PHJM). The analysis and simulation results indicate that FEM can get accurate results of the kinematics of the PHJM, and the solution process shows that using FEM can solve nonlinear and linear kinematic problems in the same mathematical framework, which provides a theory base for establishing integrated model among different parameter models of the PHJM.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041011-041011-11. doi:10.1115/1.4029439.

This paper describes a new design that improves several aspects of the mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA). The proposed design avoids premature wear and attachment issues found in the cable transmission used in previous MACCEPA designs and allows the use of high-performance compact compression springs. The mechanical configuration of the actuator provides an adjustable stiffness with a nonlinear stiffening output torque. The output position of the actuator and its global stiffness are independent from each other. In this work, we provide a mathematical description of the actuation principle along with an experimental verification of its performance in a powered ankle–foot prosthesis. This work is part of the CYBERLEGs project funded by the European Commissions 7th Framework Programme.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041012-041012-8. doi:10.1115/1.4029402.

This paper shows that the equilibria of a wide class of multibody systems with quasi-rigid, frictional, or frictionless supports correspond to local minima of their potential energy; hence they are stable against small perturbations of external forces. This is a generalization of a theorem by Howard and Kumar on the stability of a single rigid body held by a gripper. It is also demonstrated that ambiguous equilibria (those, which coexist with the possibility of accelerating motion) may be stable. These results help finding safe grasps on nonrigid objects and assessing the stability of quasi-static robots moving over complex terrains.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041013-041013-9. doi:10.1115/1.4029188.

Performance evaluation is one of the most important issues in the analysis and design of parallel manipulators. The internal forces and torques in parallel manipulators contribute to manipulating the end-effectors and resisting the external loads. In this work, we propose a transmission index to evaluate the force and torque transmission quality of parallel manipulators. The index is normalized and used to analyze the exactly constrained parallel manipulators, based on the transmission matrix spanned by transmission wrench screws (TWSs). Furthermore, the index is applied to parallel manipulators with different degrees of freedom (DOF) in order to illustrate and validate the proposed approach and index. Finally, a typical parallel manipulator is selected to address the comparison analysis between different indices, which demonstrates that the proposed index, possessing respective merits, could be complementary to other existing indices.

Topics: Manipulators , Torque
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041014-041014-9. doi:10.1115/1.4029705.

Fluid filled fiber reinforced elastomeric enclosures (FREEs) have been a popular choice for actuators in prosthetics and soft robots owing to their high power density and cost effective manufacturing. While a narrow class of FREEs known as McKibben's actuators have been extensively studied, there is a wide unexplored class that could be potentially used as actuators and soft structural members. This paper analyzes the mobility of generalized FREEs based on simple geometric relationships that result from the inextensibility of fibers and fluidic actuation. The analysis conducted can be classified into instantaneous kinematics and global or large deformation kinematics. Instantaneous kinematics reveals that the most general deformation pattern of the FREE is a screw motion about the axis of its cylinder, whose pitch is a function of fiber orientations. Furthermore, a set of fiber angles, which do not deform under volumetric actuation were identified as the locked manifold (LM). Global kinematic analysis revealed that every FREE continued to deform until its fiber configuration approached the LM. These insights were corroborated with finite element analysis (FEA) and testing for a small sample of FREE actuators.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041015-041015-12. doi:10.1115/1.4029440.

In this paper, a novel parallel kinematic mechanism (PKM) with Schönflies motion has been proposed under the guidance of a graphical type synthesis method. This PKM is composed of four identical arms and a single platform and has high rotational capability. The single-platform structure used in the proposed PKM can reduce structural complexity, increase dynamic response. In addition, the composite parallelogram structure in each arm brings in better limb stiffness. Based on the proposed concept, optimal design is carried out to make the PKM realize its high rotational potential. In this process, an input transmission index (ITI) and an output transmission index (OTI) (the two indices can be used to numerically evaluate motion and force transmission performance of PKMs, respectively) are taken as the performance evaluation criteria. On this basis, some other indices are defined and the corresponding performance atlases are also plotted to investigate the potential workspace. Consequently, dimensional parameters of the discussed PKM are derived on the precondition that the rotational capability should reach at least ±90 deg, and the workspace has also been identified. Based on these foundations, a parallel robot X4 has been developed which can realize high-speed pick-and-place manipulation in industrial lines.

Topics: Robots , Design , Rotation
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041016-041016-9. doi:10.1115/1.4029556.

This paper deals with nonlinear analytical models of a class of compound multibeam parallelogram mechanisms (CMPMs) along with the static characteristic analysis. The CMPM is composed of multiple compound basic parallelogram mechanisms (CBPMs) in an embedded parallel arrangement. First, nonlinear analytical models for the CBPM are derived using the free-body diagram method through appropriate approximation strategies. The nonlinear analytical models of the CMPM are then derived based on the modeling results of the CBPM. Nonlinear finite element analysis (FEA) comparisons, experimental testing, and detailed stiffness analysis for the CBPM are finally carried out. It is shown that the analytical primary motion model agrees with both the FEA model and the testing result very well but the analytical parasitic motion model deviates from the FEA model over the large primary motion/force. It is also shown from the analytical characteristic analysis that the primary translational stiffness increases with the primary motion but the parasitic motion stiffness decreases with the primary motion, and the stiffness ratio of the parasitic motion stiffness to the primary translation stiffness also decreases with the primary motion. It is found that the larger the beam slenderness ratio is, the larger the stiffness or stiffness ratio is, and the more apparent the change of the stiffness or stiffness ratio is. The varied stiffness ratio indicates the mobility change of the CBPM.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041017-041017-9. doi:10.1115/1.4028935.

In this paper, the kinematics modeling of a notched continuum manipulator is presented, which includes the mechanics-based forward kinematics and the curve-fitting-based inverse kinematics. In order to establish the forward kinematics model by using Denavit–Hartenberg (D–H) procedure, the compliant continuum manipulator featuring the hyper-redundant degrees of freedom (DOF) is simplified into finite discrete joints. Based on that hypothesis, the mapping from the discrete joints to the distal position of the continuum manipulator is built up via the mechanics model. On the other hand, to reduce the effect of the hyper-redundancy for the continuum manipulator's inverse kinematic model, the “curve-fitting” approach is utilized to map the end position to the deformation angle of the continuum manipulator. By the proposed strategy, the inverse kinematics of the hyper-redundant continuum manipulator can be solved by using the traditional geometric method. Finally, the proposed methodologies are validated experimentally on a triangular notched continuum manipulator which illustrates the capability and the effectiveness of our proposed kinematics for continuum manipulators and also can be used as a generic method for such notched continuum manipulators.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041018-041018-8. doi:10.1115/1.4029118.

Parallel manipulators (PMs) with multiple operation modes are novel reconfigurable PMs, which use less number of actuators and can be reconfigured without disassembly. This paper deals with the type synthesis of 2-DOF (degrees-of-freedom) PMs with both spherical translation mode and sphere-on-sphere rolling mode. A spherical translation is the 2-DOF spatial translation under which the trajectory of any point on the moving link is a sphere. A sphere-on-sphere rolling refers to the rolling of a sphere without slipping and spinning on another sphere of the same diameter. At first, a 2-DOF 3-4R overconstrained PM is proposed based on an existing 5-DOF US equivalent PM. From this 2-DOF PM, we further obtain a 3-4R PM for sphere-on-sphere rolling and a 3-4R PM for spherical translation. By finding the common conditions for the 2-DOF 3-4R PM for spherical translation and 2-DOF 3-4R PM for sphere-on-sphere rolling, the types of 2-DOF 3-4R PMs with both spherical translation mode and sphere-on-sphere rolling mode are then obtained. The 2-DOF 3-4R PMs with both spherical translation mode and sphere-on-sphere rolling mode fall into two classes. In one class of PMs with both spherical translation mode and sphere-on-sphere rolling mode, the moving platform has four instantaneous DOF in a transition configuration. In another class of PMs with both spherical translation mode and sphere-on-sphere rolling mode, the moving platform has at most three instantaneous DOF in a transition configuration. This work enriches the types of PMs with multiple operation modes and overconstrained mechanisms.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041019-041019-11. doi:10.1115/1.4029891.

An orienting platform is a mechanism which allows rotation of a spatial object without translational motion of that object. In this work, we study a parallel platform with one passive nonholonomic spherical joint and two series of spherical, actuated prismatic and universal joints (the platform is also known in literature as an (nS)-2SPU wrist). To solve the control and motion planning problems, an analytic approach is used. The design of practical stabilization and tracking algorithm is based on transverse functions and a method for motion planning respecting mechanical singularities is derived from endogenous configuration space approach. It is shown that the system is controllable and locally equivalent to the chained form system. Then, the stabilization, tracking, and motion planning algorithms are proposed. Results are verified with computer simulations. A combination of the open-loop motion planning algorithm and the closed-loop tracking provide a tool for designing a motion planning algorithm respecting mechanical singularities and robust to input disturbances.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041020-041020-6. doi:10.1115/1.4029501.

We study 4-universal-prismatic-universal (UPU) parallel manipulators performing Schoenflies motion and show that they can have extra modes of operation with three degrees of freedom (3DOF), depending on the geometric parameters of the manipulators. We show that the transition between the different modes occurs along self-motion of the manipulator in the Schoenflies mode.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041021-041021-16. doi:10.1115/1.4030163.

In this paper, we discuss an incremental forward kinematics of wire-suspended mechanical systems. In order to deal with a mechanical system of this type, we have to take into account the characteristic property of a wire, in that it cannot take any compressive force. We give a general formulation and its solution of the incremental forward kinematics problem taking account of the slack condition of a wire. We also consider the influence of displacement of the mass center position of the suspended platform on the kinematic behavior of the system. An interval arithmetic approach is proposed to deal with the uncertainty in the kinematic parameters. One of the important points is that the number of possible solutions of the formulated incremental kinematics problem is often more than one. We introduce a kind of parallelism, referred to as the “many-worlds interpretation” taken from the quantum mechanics theory, to this problem and offer an approach to deal with plural possible kinematic states simultaneously. The developed approach is based on basic equations in general form and is applicable to various wire-suspended mechanical systems. The feasibility of the proposed incremental kinematics approach is demonstrated by example calculations of three-, six-, and eight-wire systems. On the basis of the example forward kinematics calculation results, we conclude the following. The influence of displacement of mass center position of the platform is not insignificant. The number of possible kinematic states becomes large in the case of the neighborhood of singular configuration. In spite of an incremental kinematics based on linearization, the required computational cost of the proposed parallelism approach is considerable; it is, however, demonstrated that the proposed approach is still fairly practical from the viewpoint of computation. The developed approach cannot deal with drastic change in kinematic configuration in a single incremental step, since it is based on linearization of the kinematic relation; however, the approach can distinguish such discontinuity.

Topics: Kinematics , Wire , Tension
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041022-041022-9. doi:10.1115/1.4029957.

This paper introduces a new concept of applying a parallel mechanism in automated fiber placement (AFP) for aerospace part manufacturing. By investigating the system requirements, a 4DOF parallel mechanism consisting of two revolute–prismatic–spherical joints (2RPS) and two universal–prismatic–spherical joints (2UPS) limbs with two rotational (2R) and two translational (2T) motions is proposed. Both inverse and forward kinematics models are obtained and solved analytically. Based on the overall Jacobian matrix in screw theory, singularity loci are presented and the singularity-free workspace is correspondingly illustrated. To maximize the singularity-free workspace, locations of the 2UPS limbs with the platform and base sizes are used in the optimization which gives a new design of a 4DOF parallel mechanism. A dimensionless Jacobian matrix is also defined and its condition number is used for optimizing the kinematics performance in the optimization process. A numerical example is presented with physical constraint considerations of a test bed design for AFP.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041023-041023-11. doi:10.1115/1.4030584.

A two-phase synthesis method is described, which is capable of solving quite challenging path generation problems. A combined discrete Fourier descriptor (FD) is proposed for shape optimization, and a geometric-based approach is used for the scale–rotation–translation synthesis. The combined discrete FD comprises three shape signatures, i.e., complex coordinates (CCs), centroid distance (CD), and triangular centroid area (TCA), which can capture greater similarity of shape. The genetic algorithm–differential evolution (GA–DE) optimization method is used to solve the optimization problem. The proposed two-phase synthesis method, based on the combined discrete FD, successfully solves the challenging path generation problems with a relatively small number of function evaluations. A more accurate path shape can be obtained using the combined FD than the one-phase synthesis method. The obtained coupler curves approximate the desired paths quite well.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041024-041024-12. doi:10.1115/1.4030653.

Recent research on exoskeletons and braces has examined the ways of improving flexibility, wearability or overall weight-reduction. Part of the challenge arises from the significant loading requirements, while the other part comes from the inflexibilities associated with traditional (rigid link-moving joint) system architectures. Compliant mechanisms offer a class of articulated multibody systems that allow creation of lightweight yet adjustable-stiffness solutions for exoskeletons and braces, which we study further. In particular, we will introduce the parallel coupled compliant plate (PCCP) mechanism and pennate elastic band (PEB) spring architecture as potential candidates for brace development. PCCP/PEB system provides adjustable passive flexibility and selective stiffness to the user with respect to posture of knee joint, without need for mediation by active devices and even active sensors. In addition to the passive mode of operation of the PCCP/PEB system, a semi-active design variant is also explored. In this semi-active design, structural stiffness reconfigurability is exploited to allow for changes of preload of the PEB spring to provide force and torque customization capability. The systematic study of both aspects (passive and semi-active) upon the performance of PCCP/PEB system is verified by a lightweight 3D printed physical brace prototype within a ground-truth (optical motion tracking and six degrees-of-freedom (6DOF) force transducer) measurement framework.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):041025-041025-18. doi:10.1115/1.4030775.

This paper describes a human-inspired method (HIM) and a fully integrated navigation strategy for a wheeled mobile robot in an outdoor farm setting. The proposed strategy is composed of four main actions: sensor data analysis, obstacle detection, obstacle avoidance, and goal seeking. Using these actions, the navigation approach is capable of autonomous row-detection, row-following, and path planning motion in outdoor settings. In order to drive the robot in off-road terrain, it must detect holes or ground depressions (negative obstacles) that are inherent parts of these environments, in real-time at a safe distance from the robot. Key originalities of the proposed approach are its capability to accurately detect both positive (over ground) and negative obstacles, and accurately identify the end of the rows of bushes (e.g., in a farm) and enter the next row. Experimental evaluations were carried out using a differential wheeled mobile robot in different settings. The robot, used for experiments, utilizes a tilting unit, which carries a laser range finder (LRF) to detect objects, and a real-time kinematics differential global positioning system (RTK-DGPS) unit for localization. Experiments demonstrate that the proposed technique is capable of successfully detecting and following rows (path following) as well as robust navigation of the robot for point-to-point motion control.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Mechanisms Robotics. 2015;7(4):044501-044501-6. doi:10.1115/1.4029187.

This paper proposes a simple and general approach for the identification of the dead center positions of single-degree-of-freedom (DOF) complex planar linkages. This approach is implemented through the first order equivalent four-bar linkages. The first order kinematic properties of a complex planar linkage can be represented by their instant centers. The condition for the occurrence of a dead center position of a single-DOF planar linkage can be designated as when the three passive instantaneous joints of any equivalent four-bar linkage become collinear. By this way, the condition for the complex linkage at the dead center positions can be easily obtained. The proposed method is a general concept and can be systematically applied to analyze the dead center positions for more complex single-DOF planar linkages regardless of the number of kinematic loops or the type of the kinematic pairs involved. The velocity method for the dead center analysis is also used to verify the results. The proposed method extends the application of equivalent linkage and is presented for the first time. It paves a novel and straightforward way to analyze the dead center positions for single-DOF complex planar linkages. Examples of some complex planar linkages are employed to illustrate this method in this paper.

Topics: Linkages
Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):044502-044502-4. doi:10.1115/1.4029809.

Tensegrity mechanisms using linear springs as tensioned elements constitute an interesting class of mechanisms. When considered as manipulators, their workspace remains however to be defined in a generic way. In this article, we introduce a workspace definition and at the same time a computation method, based on the estimation of the workspace boundaries. The method is implemented using a continuation method. As an example, the workspace assessment of a two degrees of freedom (DOF) planar tensegrity mechanism is presented.

Commentary by Dr. Valentin Fuster
J. Mechanisms Robotics. 2015;7(4):044503-044503-6. doi:10.1115/1.4030467.

There is an increasing need for XY compliant parallel micromanipulators (CPMs) providing good performance characteristics such as large motion range, well-constrained cross-axis coupling, and parasitic rotation. Decoupled topology design of the CPMs can easily realize these merits without increasing the difficulty of controlling. This paper proposes an improved 4-PP model on the basis of a classical 4-PP model and both of them are selected for manufacturing and testing to verify the effectiveness of the improvement. It has shown from experimental results that there is a large improvement on the performances of improved 4-PP compliant parallel manipulator (CPM): large range of motion up to 5 mm × 5 mm in the unidirection in the dimension of 311 mm × 311 mm × 24 mm, smaller compliance fluctuation (only 36.63% of that of the initial 4-PP model), smaller cross-axis coupling (only 28.10% of that of the initial 4-PP model generated by a single-axis 5 mm actuation), smaller in-plane parasitic yaw (only 57.14% of that of the initial 4-PP model generated by double-axis 5 mm actuation).

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In