查看更多>>摘要：This study presents the design and analysis of a one-degree-of-freedom (DOF) translational partly compliant mechanism (TPCM) with variable motion direction. The variable motion direction is achieved by using rigid-body internal DOFs to change the poses of flexure beams. The use of rigid-body internal DOFs overcomes the small deflection limit of compliant joints and enables continuous changes in the motion direction. First, a simplified model is developed through mobility analysis and shows that the motion direction of the proposed TPCM can be changed continuously in a spatial manner. Then, the compliance ratio is obtained by decomposing the compliance matrix. It shows that the compliance ratio drops quickly near the singularity and that the motion direction should be limited. Finite element analysis and experiments are conducted to evaluate the design.
查看更多>>摘要：This paper presents the theoretical study and experimental verification regarding an improved design for accomplishing the complete rotating balance of assembled type conjugate disk cams. In particular, a pair of assembled conjugate cams consisting of two arc-slotted disk cams and an axially outward counterweight bump integrally formed on each cam is conceptually designed for simultaneously satisfying the conditions of static and dynamic balance. In order to find the feasible solutions of the counterweight bumps, a theoretical approach is developed, and an optimization model is established for searching the optimal solution. Subsequently, two hardware prototypes of conjugate cam mechanisms with a pair of original or counterweighted conjugate cams were designed and constructed, and experiments were conducted for measuring and comparing their yielded shaking forces and vibrations. Experimental results showed that with the use of counterweighted conjugate cams, the yielded shaking forces could be lowered, some of the yielded vibrations could be restrained, and most importantly, the intensity of resonance phenomena could be decreased. Therefore, the presented improved design is feasible and effective for enhancing the dynamic performance of conjugate cam mechanisms.
查看更多>>摘要：Helix-based structures have been popularly used in flexible surgical tool designs due to their large bending range. However, the helix structures also have low compressional and torsional stiffness, which results in a limited payload. In this paper, we addressed these limitations by presenting a novel helix-based structure that mimicks the DNA double helix structure. This DNA-inspired helical continuum manipulator (DHCM) contains a helix structure and a constraint structure (a slender shaft or reinforced rings) that mimicks the base pairs of the DNA structure. Simulation results revealed that the stiffness of the helix structure is improved with the constraints. At the same bending stiffness, compared to the simple helix structure, the compressional and torsional stiffness of DHCM with the shaft constraint were improved by 12.3 times and 3.2 times, respectively. The kinematics of the DHCM were derived to predicate the deformation of the DHCM based on the piecewise constant curvature assumption. The model predicted deformation of the DHCM with a mean error of 4.16 mm (6.9%). The equivalent stiffness model of the DHCM was proposed and used to derive the statics of the DHCM. The mean error of distal end between statics predictions and experiment results was 1.01 mm (1.7%).
查看更多>>摘要：In this study, an approach using moving end-constrained spline (ECS) curves with variable widths is presented for the explicit topology optimization of compliant mechanisms. The proposed approach uses a series of spline curves to represent the topology of the compliant mechanism. Instead of using a fixed width, we let the width of such spline curves vary along the curve. The optimized design is obtained by optimizing the width of the spline curves and the position of the control points. To avoid infeasible solutions in the design process, the end points of several specific spline curves are constrained according to the design region. The validity of the proposed method is demonstrated using different types of splines, such as the Bézier curve and B-spline curve, for the design of a force inverter, a compliant gripper and a compliant orthogonal displacement amplification mechanism.
查看更多>>摘要：This paper presents the reconfigurable legged mobile lander (ReLML) with three operation modes of adjusting, landing, and roving, to provide strong survivability to the hostile extraterrestrial landforms. Its single leg is a complete reconfigurable mechanism system composed of the metamorphic execution mechanism and the metamorphic transmission mechanism based on the metamorphic variable-axis revolute joint. The metamorphic joint connects execution and transmission and is designed with good compatibility for mode switch and functional operation. Based on the reconfigurable mechanism system, the ReLML can adjust the touchdown poses of four legs and overall lander to adapt to the hostile extraterrestrial landform intelligently, then carry out the stable landing, finally implement the roving detection by legged roving locomotion. This study firstly aims at the multi-mode unified modeling for execution, transmission, and overall lander; next, the operation capability synergistic evaluation in aspects of motion, transmission, velocity, payload, stiffness; finally, two new conceives of autonomous soft-landing and propulsive-landing are proposed and compared to expand the detection range for hostile landforms. Results show these new detection patterns by reconfigurable principle can provide possible approaches to the hostile extraterrestrial landforms where the current human technology cannot visit securely.
查看更多>>摘要：The creative design of mechanisms has been widely believed as one of the most important branches in the theory of mechanisms. Beside, the structural synthesis of kinematic chains (KCs) of mechanisms has been well-known as a fundamental technique for establishing novel theories towards intelligent design of mechanisms. This has thus motivated an increasing number of researchers to devote their efforts to exploiting new methods and techniques for structural synthesis of mechanisms over the past half century. In this paper, we present a comprehensive review on the structural synthesis methods for various plane KCs and mechanisms, including contracted graphs of KCs, non-fractionated and fractionated simple joint KCs, inversions of KCs, KCs with prismatic pairs, multiple joint KCs, Baranov trusses and Assur groups, as well as the automatic sketching of KCs. Moreover, the idea of intelligent design based on the automatic synthesis of mechanisms is discussed. The presented review discusses the history of structural synthesis of mechanisms and the recent research progress, and concludes the research trends and future work in this area, offering theoretical guidance for people engaged in the structural synthesis and intelligent design of mechanisms.
查看更多>>摘要：In this paper, a novel cable-driven antagonistic joint of variable stiffness is presented. The joint features antagonistic, series-elastic actuation with novel variable stiffness mechanisms (VSMs). The VSM is able to achieve adjustable quadratic torque–deflection characteristics through an easy offline adjustment of its design parameters. This makes it possible for us to simultaneously and independently control both joint position and stiffness in different manners, which increases the adaptability of the system to application variability and change. In the paper, mechanics models are developed for both antagonistic joint and VSM, with which an optimization method is used to optimize the VSM to produce desired quadratic behaviors. The models and optimization method are first validated by simulations and then demonstrated experimentally with a prototype. The proposed joint is finally applied in a wearable exoskeleton.
查看更多>>摘要：This article proposes a two-degrees-of-freedom robot for wrist rehabilitation, referred to as MOCH. The MOCH mechanism comprises a remote center of motion (RCM) mechanism with a rotation center outside of the robot structure. When the patient holds the robot end-effector, coinciding the RCM of the robot with the rotation axis of the wrist allows pure rotational motion of the hand. As the rotation point lies out of the robot structure, there is less risk of interference between the patient and the robot. Furthermore, MOCH benefits a novel actuation that enables the actuators to be grounded, reducing the inertia and the size of the robot, and eliminating difficulties with feeding power to actuators on moving linkages. The optimal design of MOCH is provided considering the mechanical criteria and requirements of the wrist rehabilitation robot. Based on the proposed design, a prototype of the robot is developed with a mass of 1.3 kg using 3D printing. To validate the efficacy of MOCH in practice, a trajectory tracking control strategy is implemented for passive wrist rehabilitation.
查看更多>>摘要：Cable-driven parallel robots (CDPRs) are gaining increasing attention due to their low weight, low cost, and power consumption characteristics. However, cable-driven systems have limited rotational capabilities without additional actuator systems. In this paper, we propose a new type of spatial CDPR that provides an unlimited rotation axis without the need for an additional actuator system. This novel capability relies on the cable wrapping over end-effector, which was specifically designed for this purpose. Herein, the principle of the unlimited rotation is demonstrated. Then, the kinematics modelling and the static equilibrium of the spatial CDPRs are established, and the resulting workspace is analysed. The results of the experiment showed that this spatial CDPR exhibits an unlimited rotation axis without additional actuator systems, while the control of the robot remained identical to that of the traditional cable robot.
查看更多>>摘要：Reconfigurable parallel mechanisms have legs or end-effectors with additional degrees of freedom or with the ability to change their mobility. This allows them to reconfigure into a variety of conventional parallel mechanisms. One type of reconfigurable parallel mechanism can be obtained by replacing the end-effector with a closed-loop linkage. The parts of this linkage that are connected to the legs may be considered as the end-effectors, having their own mobility relative to the base and a coupled mobility with each other. Classical methods for mobility analysis cannot be directly applied to this type of mechanism. This article presents a general method to calculate and represent the coupled mobility of the multiple end-effectors using nullspace operations on a matrix of mobility. The nullspace approach provides an efficient way to calculate the mobility in a closed-loop chain while the matrix of mobility allows for calculating the multiple end-effectors mobility interaction. The general method can be performed analytically to obtain insights on the mechanism in any configuration, or algorithmically to obtain numerical values of the mobility in a particular configuration. Two illustrative examples showcasing the method are presented.
NSTL
Elsevier