Latest Papers

ASME Journal of Mechanisms and Robotics

  • Synthesis and Analysis of Plane–Space Switching Mechanisms Based on a Plane-Symmetric Eight-Bar Linkage
    on February 5, 2024 at 12:00 am

    AbstractThis paper proposes a novel synthesis method for constructing plane–space switching mechanisms based on the symmetric plane of the regular prism. First, the structure equation and motion characteristic of plane-symmetric eight-bar linkage are presented. Then, the plane-symmetric seven-bar linkage and rhombic Bricard linkage are obtained by locking the joint of the eight-bar linkage. Four types of plane–space switching mechanisms are constructed based on the synthesis method and switching linkage units. These switching mechanisms can expand completely into planar configurations and fold completely into spatial configurations. Subsequently, the kinematics of the coupled branch chain is analyzed, through which the folded and contractive characteristics of the mechanism are revealed. Then, the concept of the distributed circle of joints is proposed, and the enveloping performance of the mechanism is approximately analyzed. This paper provides a new idea and synthesis method for designing new deployable mechanisms.

  • A Dimensionless Large Displacement Model for Flexure Hinges of Elliptical Geometry
    on February 5, 2024 at 12:00 am

    AbstractFlexure hinges are joints typically used in the design and manufacturing of compliant mechanisms, especially when small dimensions do not allow for conventional mechanical devices. In this paper, a closed-form solution is proposed for a nonlinear stiffness model used to describe the static displacements obtained on a flexure hinge of elementary geometry as a function of applied loads. A comparison with the most widely used linear model demonstrates the effectiveness of the proposed nonlinear approach, highlighting the advantages of its use in its scope of application. The obtained results are verified by finite element (FE) simulations, taken as a reference of the actual behavior assumed for the joints studied.

  • A Novel Elbow-Inspired Cable-Driven Tensegrity Joint: Bionic Design, Coupled Kinematics, and Load Performance
    on February 5, 2024 at 12:00 am

    AbstractTensegrity-based robot joint offers mechanical compliance under external impact and in man-robot interaction. So its practical bionic design has become a research hotspot. A variety of tensegrity-based flexible joints have been proposed and verified, but the research is not in-depth enough on control and motion modeling, transmission characteristics, and load performance analysis for robot joints with coupled driving cables and tensegrity structure. Based on the current situation, an elbow-inspired rotary joint is proposed following human anatomy. With the help of tensegrity node balance, the inherent relationships between the joint's rotation and translation and between the driving cables” tension and the joint's rotation are derived. The load performance of the joint is also explored, and the end load is calculated from the deviation between cables' tension of a no-load condition. A prototype and an antagonistic cable driver with tension sensors are designed and manufactured to verify the proposed model, and the experimental results are well in agreement with the theoretical prediction. In the future, the model and the method proposed will be applied to bionic joints with similar structures.

  • Complete Kinematics/Dynamics Modeling and Performance Analysis of a Novel SCARA Parallel Manipulator Based on Screw Theory
    on February 5, 2024 at 12:00 am

    AbstractIn this paper, a novel Selective Compliance Assembly Robot Arm (SCARA) high-speed parallel manipulator that can realize three-translation and one-rotation motion is proposed, and an accurate dynamic modeling methodology is investigated. The mechanism is composed of four limbs with a double parallelogram structure and a single moving platform. The high bearing capacity and high dynamic response of the novel mechanism make it a viable alternative choice for this kind of automation equipment. The degree-of-freedom (DOF) of the mechanism is analyzed by the screw theory. At the same time, the velocity mapping model of the mechanism is established by the twist screw and the actuated Jacobian matrix. Then, the acceleration mapping model of the mechanism, including the generalized kinematic pairs, is established by reduced acceleration state, the modified Lie screw, and the acceleration Hessian matrix. On this basis, the complete dynamic model with a compact form of the mechanism is deduced by the combination of screw theory and virtual work principle, and the correctness of the developed model is verified by multibody simulation software. Finally, considering the inertial characteristics of the mechanism, the dynamic performance distribution in the reachable workspace of the mechanism is analyzed by the Joint-Reflected Inertia (JRI) index and Coefficient of Variation of joint-space Inertia (CVI) index, and some areas are selected as the task workspace using the above index to guarantee good dynamic performance.

  • Novel and Robust Forward Kinematic Algorithm for Real-Time Control of General Six-Degree-of-Freedom Parallel Robot for Tele-Manipulation and Tele-Navigation
    on February 5, 2024 at 12:00 am

    AbstractThe forward kinematics (FK) of a 6-6 universal-prismatic-spherical (UPS) structure of a parallel robot is highly nonlinear, coupled, and has a one-to-many nature of mapping. There exists no close form solution to a forward kinematic problem (FKP), and real-time kinematic control is extremely difficult. This paper presents the implementation of time efficient and robust solution for FKP using a trajectory modifier algorithm along with a Newton Raphson (NR) method. One micrometer in translation and 0.001 deg in orientation accuracy with an average pose computation time of 2.3 ms are achieved. The novel algorithm is elaborated and the detailed performance parameters are tabulated. The paper presents trajectory following experiments to show robust, real-time FK solution and efficient kinematic control on both standalone and master–slave modes to be used for robot-assisted neurosurgery. The neuro-registration using the FK solutions in real time in a tele-manipulation mode is demonstrated.

A Curved Compliant Differential Mechanism With Neutral Stability

Abstract

Differential mechanisms are remarkable mechanical elements that are widely utilized in various systems; nevertheless, conventional differential mechanisms are heavy and difficult to use in applications with limited design space. This paper presents a curved differential mechanism that utilizes a lightweight, compliant structure. This mechanism acquires its differential characteristic by having a high rotational stiffness when the mechanism is symmetrically actuated on two sides, while having a low rotational stiffness when actuated only on one side. To make the mechanism neutrally stable, the intrinsic elastic strain energy required for deformation of the compliant differential is compensated for by the reintroduction of potential energy, which is provided by two preloaded springs. The rotational stiffness of the one-sided actuation of the compliant differential mechanism around the neutral position is hypothesized to be adjustable by changing the preload of the springs. The stiffness can be positive, zero, or negative, indicating that the mechanism can be neutral or bistable. This hypothesis is investigated using a simulated model in Ansys Parametric Design Language (APDL) using optimized parameters to achieve the desired stiffness for the mechanism. The simulated model is validated using an experimental setup for both the one-sided and symmetrical actuation stages. The experimental results showed a high correlation with the simulation results. The mechanism with optimized dimensions and preload demonstrated neutral stability over a 16deg range. Bistability was discovered for preloads greater than the optimized preload. At θ = 0, a linear relationship was discovered between the spring preload and the rotational stiffness of the mechanism. Furthermore, an output/input kinematic performance of 0.97 was found for the simulated results and 0.95 for the experimental results.

Read More

Journal of Mechanisms and Robotics Open Issues