Mechanism and Machine Theory最新文献

Flexure-jointed grippers provide compliant grasping capability, have low-cost and flexible manufacturing, and are insusceptible to joint friction and wear. However, their grasp stiffness can be limited by flexure compliance such that loss-of-grasp is prone to occur for high object loads. This paper examines the application of inverted-flexure joints in a cable-driven gripper that can avoid flexure buckling and greatly enhance grasp stiffness and stability. To analyze behavior, an energy-based kinetostatic model is developed for a benchmark grasping problem and validated by hardware experiments. A multi-objective design optimization study is conducted, considering key metrics of peak flexure stress, grasp stiffness, and cable actuation force. Results show that the inverted-flexure design has significantly higher grasp stiffness (63% higher in a targeted design optimization) and requires lower actuation forces (¿20% lower in all optimization cases), compared with equivalent direct-flexure designs. An application study is conducted to validate the predicted operating performance under gravity loading of the grasped object. The results demonstrate that stable and high stiffness grasping can be achieved, even under overload conditions that lead to loss-of-grasp for conventional direct-flexure designs.

Series elastic actuators with increasing nonlinear stiffness(NlSEA) have promising applications in human-machine interactions for the existence of a nonlinear elastic mechanism that supplies inherent safety and can implement high torque resolution under low load and quick dynamic response under high load. In this study, a novel design method for a nonlinear elastic mechanism that can be applied in NlSEA is proposed. By combining the S-shaped cantilever beam and specialized cam surface, this study proposed an analytical approach to design a nonlinear elastic mechanism satisfying a given stiffening torque-deformation relationship. The geometric parameters constraints were discussed to support parameter determination. Two kinds of cases of nonlinear elastic mechanisms with increasing and constant stiffness characteristics were conducted to verify the effectiveness and generalizability of the proposed design method by simulations. Moreover, a nonlinear elastic mechanism with an increasing stiffness characteristic was designed and a prototype was fabricated. A torque-deformation verification experiment, regulation response experiments, and sinusoidal tracking experiments were conducted to verify the accuracy, response performance, and tracking performance of the prototype. The designed nonlinear elastic mechanism has a large torque-to-mass ratio in a compact and lightweight structure.

Soft robots are high-dimensional nonlinear systems coupled with both geometric and material nonlinearity. Control of such a system is complex and time-consuming. In this study, a real-time trajectory tracking control framework is established based on the reduced order extended position-based dynamics. In contrast to the common nonlinear model order reduction methods that require to collect a large number of data to create the motion subspace, this article's motion subspace is constructed based on the model configuration and material properties. The linear modes of the model and the related modal derivatives provide the reduced order matrix, which streamlines and increases the efficiency of model construction. Then, coupled with the instantaneous optimal control, a real-time reduced order model-based control framework of soft robots can be constructed. Experiments on trajectory tracking of a soft manipulator are conducted to verify the accuracy and efficiency of the proposed controller. The average error of all experiments is within 1 cm; and the single-step calculation time of the controller is about 0.057 s, which is less than the sampling period 0.1 s.

Road irregularities affect vehicle comfort by causing vertical and longitudinal acceleration oscillations. While the current ride comfort enhancement solutions are based on the compensation of the vertical acceleration of the sprung mass, the compensation of the longitudinal dynamics excited by road irregularities has been successfully explored only for in-wheel powertrains. The scope of this study is to demonstrate that also on-board electric powertrains with torsional dynamics of the half-shafts have the potential for effective compensation, thanks to the road profile preview. This paper presents a proof-of-concept nonlinear model predictive controller (NMPC) with road preview, which is assessed with a validated simulation model of an all-wheel drive electric vehicle. Three powertrain layouts are considered, with four in-wheel, four on-board, and two on-board electric machines. The control function is evaluated along multiple manoeuvres, through comfort-related key performance indicators (KPIs) that, for the four on-board layout along a road step test at 40 km/h, highlight >80% improvements. Finally, the real-time implementability of the algorithms is demonstrated, and preliminary experiments are conducted on an electric quadricycle prototype, with more than halved oscillations of the relevant variables.

In this paper, the impact of parameter variations on the deployable motion characteristics, mobility, input singularity, and deploying/folding performance of plane-symmetric Bricard mechanisms is studied. Firstly, two classes of revolute pair axes used to construct deployable polygon mechanisms (DGMs) are reviewed, and their value ranges are further refined. Secondly, all possible axes arrangement schemes for plane-symmetric 6R DGMs are presented for the first time. Then, an improved schematic synthesis method is proposed, which can be used to design all plane-symmetric 6R DGMs that belong to the plane-symmetric Bricard mechanisms. Thirdly, the improved design method is applied to create a series of single-degree-of-freedom plane-symmetric 6R DGMs. Then, feasible domain searches are performed, and some of them are prototyped. Subsequently, the input singularity of plane-symmetric 6R DGMs is analyzed. Finally, two deploying/folding performance indices are proposed to evaluate the performance of plane-symmetric 6R DGMs with different fully deployed and fully folded states based on actual application scenarios. This work expands the variety and quantity of DGMs, which will also advance the development of robotics, mechanical metamaterials, and kirigami mechanisms.

Compliant deployable mechanisms (CDMs), as a novel and promising type of mechanisms, have been gradually used in medical industry, aerospace and other engineering fields that require high space utilization and compactness. Therefore, it is necessary to develop a general and efficient methodology to design and analyze CDMs. This paper proposes a general framework for designing and analyzing CDMs. The proposed framework has been verified by finite element method (FEM) first. Then, for practical validation, we design two types of compliant deployable mechanisms for different application scenarios within this framework, and experimental testing has been conducted to prove the feasibility of the proposed framework. Compared to the existing methods for designing CDMs, this framework demonstrates a more general scheme where different engineering scenarios can be taken into account to meet the design requirements, presenting several desired advantages over the existing methods, such as higher accuracy and less computational expense.

The objective of this paper is to propose a novel approximate solution for determining the reactions of joints in mechanical systems, which involves the influence of Coulomb friction. It is widely acknowledged that if Coulomb friction is used in determining an exact solution to the equilibrium equations for a mechanism, then it will involve nonlinear systems of equations. With the abundance of computer tools now available, tasks of this kind, especially numerical computations, are not particularly challenging. However, new analytically tractable approximate methods are still valuable as a straightforward way of solving the problem. Several studies have been carried out in this field to find a simple solution. In this paper, a new approach based on friction circle concept and Babylonian algorithm is developed for various mechanisms, which is exceptionally well-suited for calculating and streamlining the solution process for mechanical systems by eliminating the necessity for iterative steps at each stage of the force analysis.

Small jumping robots widely adopt complex catapult mechanisms. This paper presents a novel jumping strategy using dead point instead of traditional catapult mechanisms, achieving efficient energy storage and release without increasing mechanical complexity. Single degree-of-freedom (DOF) planar six-bar linkages are widely used in bionic mechanism design due to their simple control and strong design flexibility. However, their complex configuration and numerous parameters make it challenging to carry out multi-objective and multi-constraint designs. In this paper, a design method of single DOF six-bar linkages based on dead-point constraints is proposed to design a frog-inspired leg mechanism. By enumerating the basic configuration atlas and using a stepwise closed-loop method, initial value screening is completed to improve the efficiency of objective function optimization. The dead-point constraints are simplified with graphical geometric properties. The resulting mechanism satisfies multiple objectives and constraints, including shape, motion posture and trajectory, demonstrating the feasibility of the method. Simulations and experiments confirmed the excellent jumping performance of the 147.1-g prototype, with a jump height of 8.55 times leg length and an energy-storing capacity of 35.39 J/kg.

Tensegrity robots have increasingly attracted attention in recent years. Traditionally, these robots rely on rigid struts and cables to maintain equilibrium configurations. However, the inflexibility inherent in these rigid struts curtails the robot’s capacity for deformation, thereby amplifying structural intricacy and imposing limitations on potential applications, particularly in the realm of pipe inspection. Drawing inspiration from the V-expander tensegrity structure, this paper presents a design, analysis, and validation of a flexible struts tensegrity robot. The integration of flexible struts enables the robot to exhibit a compact structure, passive compliance, and excellent adaptability. Through the actuation of three active cables, the robot exhibits inchworm-like motion capabilities for pipes ranging from 50 mm to 110 mm in diameters. A kinetostatics modeling approach is presented to predict the shapes of flexible struts and control the motion behaviors of the robot. To validate the capabilities of the proposed robot and assess the effectiveness of the kinetostatics model, a prototype was constructed and subjected to a series of experiments. The results demonstrate that the prototype exhibits remarkable shape changeability, mobility, and adaptability, while precisely controlling the contact force.

To enhance the bearing capacity and minimize the loaded transmission error for unparallel beveloid gears, a continuous optimization method of micro geometry is proposed. Considering that the conjugate characteristic of tooth surfaces is destroyed by misalignments and modification, an unload contact analysis model is first developed. This includes a contact tooth sequence determination model and an unloaded transmission error calculation model for multi-tooth contact. To determine contact due to deformation, a potential contact point matching model of non-contact tooth surfaces is introduced. Further, a numerical loaded contact analysis model based on the influence coefficient method for unparallel beveloid gear is developed. For multi-tooth contact of modified tooth surfaces, the transmission error compatibility condition is introduced. Based on the loaded contact model, a continuous optimization model for the comprehensive performance of contact pressures and loaded transmission error within a meshing cycle is established. To improve optimization efficiency, a calculation strategy for continuous optimization is developed. The feasibility of the proposed method is validated using a numerical example.