Eight-bar Mechanism Research Articles

Design and rigid-flexible dynamic analysis of a morphing wing eight-bar mechanism

Design and rigid-flexible dynamic analysis of a morphing wing eight-bar mechanism

Biofusion design and parameter optimization for a novel passive assisted knee exoskeleton robot based on eight-bar mechanism

Abstract In an effort to alleviate the issue of knee joint fatigue and injury during lower limb ambulation, a novel passive assisted exoskeleton robot with human–machine interaction is investigated to assist the movement of the human knee joint. The design of the exoskeleton configuration takes into consideration the physiological structure and gait function of the knee joint, ensuring that it satisfies the requirements for motion, force, and gait function of the knee joint. To explore the interaction between the wearer and the exoskeleton, a human–machine kinematic model after wearing exoskeleton is established, which is instrumental in analyzing the integration motion of the wearer and exoskeleton. In addition, the dynamic and static models of the knee joint after wearing the exoskeleton are established, utilizing the Newton–Euler method and force polygon method, respectively, to evaluate the effectiveness of the exoskeleton. Moreover, the size parameters and spring stiffness of the exoskeleton are optimized, using both human body kinematic model and mechanic model. Furthermore, the effectiveness of the exoskeleton in proving assistance is evaluated through human body simulation, using OpenSim. The results indicate that the exoskeleton significantly reduces the knee joint torque by 48.42%.

Design method of a single degree-of-freedom planar linkage bionic mechanism based on continuous position constraints

Single degree-of-freedom (DOF) planar linkage mechanism has been widely used in bio-inspired robots because of its simple control. However, designing a single DOF mechanism to meet the complex motion law of creatures is difficult, and the multiple variables of six- or eight-bar mechanism further increase the design difficulty. A design method of single DOF planar linkage bionic mechanism is proposed in this paper. Through the continuous constraints on the position of all reference points with constraint descent method, the requirements of the bionic mechanism in shape, motion trajectory, and posture are met. As for the mechanism by which reference point coordinates cannot be expressed as the analytical solution of the driving angle, a single DOF mechanism is equivalent to a double DOF mechanism containing additional optimization variables, which further improves the design efficiency. For example, the design process of six- and eight-bar bionic mechanisms is given, confirming the feasibility of the method. Then, the effects of the constraint conditions on the design process are analyzed in detail. This study provides a reference for the design of bio-inspired robots.

Optimum design and analysis of a novel planar eight-bar linkage mechanism

Planar mechanisms are essential for many applications. The metal forming process is a vital application for industrial sectors such as automotive and space. Manufacturing precision and generating dwell motion are also important issues. These properties cannot be realized on conventional mechanical presses. Therefore, a novel single degree of freedom (1DOF) eight-bar planar mechanism was developed in this study. The main advantages of the new mechanism are slider balance and dwell motion without a servo motor. Thanks to these advantages, manufacturing difficulty and cost can be reduced. In this study, the new mechanism was modeled kinematically and verified. An optimization methodology was also presented for determining the mechanism dimensions. In order to achieve the desired dwell motion, dimensions of the mechanism for three cases (stroke capacities with 60 mm, 600 mm (crank length ≤ 300 mm), and 600 mm (crank length ≤ 250 mm)) were optimized by using the Genetic Algorithm (GA). The optimized dimensions were also compared kinematically, and the comparison results were shown. The best-optimized dimensions were determined based on the position, velocity, and acceleration simulations of the new mechanism.

Integrated design of a lower limb rehabilitation mechanism using differential evolution

In the last years, one degree of freedom mechanisms has been incorporated into rehabilitation machines. Their designs usually involve kinematic synthesis leaving aside their complex dynamic nature. An integrated methodology to design a one degree of freedom eight-bar mechanism for lower limb rehabilitation is presented in this paper. The methodology simultaneously considers kinematic synthesis, structure shape design, and dynamic performance. A non-linear constrained dynamic optimization problem is proposed where the design objective relates the accuracy in the prescribed movement and the energy consumption reduction. This problem is solved by using different differential evolution variants for finding the most suitable synergistic solution. The results show that the obtained design can follow the path with 52.13% less energy consumption compared to a design that does not consider such integration. This also results in less control effort, and hence the velocity regulation accuracy is improved. The three-dimensional printed prototype illustrates the obtained solution.

Kinematic comparison of single degree-of-freedom robotic gait trainers

Single degree-of-freedom mechanized gait trainers employing linkage mechanisms can imitate the gait trajectory of the human user at a potentially lower cost than current commercial solutions. Our goal was to evaluate recently introduced four-, six- and eight-bar designs from the standpoint of kinematics, that is, the ability to follow a natural gait pattern. Based on a gait database of 113 healthy individuals, we synthesized mechanisms allowing two link length adjustments and compared trajectory and path accuracy of the ankle position across mechanisms. We used cross-validation to obtain data-independent accuracy measures. We used gait trajectories from a large human database and predicted additional trajectories to represent the effects of varying heights and speeds. We found that trajectory error was significantly lower in the eight-bar mechanism (3.76 ± 0.18 cm, mean ± SD) than the four- (6.84 ± 0.37 cm) and six-bar (7.15 ± 0.48 cm) configurations (p < 0.0001). However, we did not observe differences in time-independent path error between configurations or in mechanical advantage (p > 0.05). We conclude that the optimized eight-bar configuration is best when the mechanism is tied to a constant velocity actuator, whereas the optimized four-bar mechanism performs as well if the actuator is well-controlled.

Experimental investigation for the solubilities of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) in polyol ester, polyvinylether, and polyalkylene glycol base oils

• Dimensional synthesis compared four-, six- and eight-bar mechanism gait trainers. • Eight-bar configuration had greater kinematic accuracy with constant input velocity. • Kinematic accuracy was similar for all mechanisms with well-controlled input. Knowledge of the solubility of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) in lubricant oil is an indispensable factor for designing refrigeration system and choosing suitable lubricant oil. In this work, the solubilities of R1234yf in polyol ester (POE) base oil, polyvinylether (PVE) base oil, and polyalkylene glycol (PAG) base oil were measured in the temperatures range from 273 K to 353 K based on the isochoric method. The experimental solubility data were correlated using the Peng-Robinson (PR) equation of state and Wilson activity coefficient model. The absolute average relative deviations of the experimental data and calculated values for the R1234yf + POE base oil system, R1234yf + PVE base oil system, and the R1234yf + PAG base oil system are 2.47%, 1.66%, and 1.29%, respectively.

Pareto optimal synthesis of eight-bar mechanism using meta-heuristic multi-objective search approaches: application to bipedal gait generation

The structural complexity of the bipedal locomotion may be reduced by using mechanisms with fewer actuators, which ideally do not degrade the performance and functionality of the robot. However, when the mechanism design considers conflicting design objectives, the search for design solutions with specific trade-offs becomes hard. This work studies different multi-objective search approaches the dominance-based, the decomposition-based and the metric-driven in the dimensional synthesis of the eight-bar mechanism for the bipedal locomotion application in the sagittal plane stated as a mixed discrete-continuous nonlinear multi-objective optimisation problem. This work also proposes a dominance-based multi-objective differential evolution algorithm called Multi-Objective Specialist Population-based Differential Evolution (MOSPDE), which endows specialised subpopulations to exploit different regions of the Pareto front to favour the search for design trade-offs with a suitable generation of the gait and force transmission during the stance phase. The comparative study includes algorithms reported in the specialised literature based on dominance (MOPSO, MODE variants and NSGA-II), decomposition (MOEA/D-DE) and metric-driven (SMS-EMOA). The statistical analysis reveals that using the Pareto dominance search approach based on differential evolution and the inclusion of exhaustive exploitation can promote the reconfigurability of the bipedal locomotion mechanism with better trade-offs that satisfy the conflicting design objectives.

Design method of one-DOF bio-inspired mechanism based on layered constraint conditions

Bio-inspired mechanism not only needs to be able to reproduce the movement laws of creature, but also has its shape. In order to simplify the design process and improve the design efficiency of one-degree-of-freedom (DOF) bio-inspired mechanism (especially six-bar or eight-bar mechanism), a design method based on layered constraint conditions is proposed in this paper. On the basis of the one-DOF kinematic chain, the frame is selected and the links are added in turn. At the same time, the constraint conditions are given in layers in the form of inequalities. When a closed loop is formed, the kinematic model needs to be established, and the positions of the target points or the attitudes of the target links can be represented by the driving angles or given angles. Thus, the feasible configurations and the ranges of the link lengths can be obtained. By cycling the above process, the target points can approach the reference points quickly and the design efficiency of the mechanism can be improved. The effect of the different basic kinematic chain, closed-loop forms and constraint conditions on configurations and design efficiency is analyzed in detail. It provides a reference for the design of other one-DOF mechanisms with multiple constraint conditions.

Integration Design Method of Configuration and Dimension for One DOF Eight-bar Bio-inspired Mechanism

Integration Design Method of Configuration and Dimension for One DOF Eight-bar Bio-inspired Mechanism

Synergistic Design of the Bipedal Lower-Limb through Multiobjective Differential Evolution Algorithm

The complexity in the design of bipedal robots has motivated the use of simple mechanisms to accomplish the desired locomotion task with a minimum control effort. Nevertheless, a diverse set of conflictive design criteria must be met to develop the bipedal gait. In this paper, the synergy in the eight-bar mechanism design criteria to satisfy the bipedal lower-limb behavior is promoted by proposing a Pareto-based Nonlinear Mixed Discrete-Continuous Constrained Multiobjective Optimization Problem and by improving the search in the optimizer through the inclusion of the Multiselection Strategy into the multiobjective differential evolution algorithm, where the conflictive design objectives are the continuous path generation based on an approximation error to track twenty precision points of the bipedal gait and also the force transmission exerted when the foot reaches the ground. The manufacture of a prototype with a specific design trade-off experimentally validates the obtained synergistic design with the proposed design approach. In addition, the empirical analysis in simulation through a statistical validation indicates that the Multiselection Strategy explores and exploits the design solutions promoting the diversity, convergence, and capacity features of the obtained Pareto front with respect to other four multiobjective optimizers and consequently improves the reconfigurability in the design such that more alternatives result to the designer decision making.

Design and Experimental Evaluation of a Single-Actuator Continuous Hopping Robot Using the Geared Symmetric Multi-Bar Mechanism

This paper proposes the design and performance evaluation of a miniaturized continuous hopping robot RHop for unstructured terrain. The hopping mechanism of RHop is realized by an optimized geared symmetric closed-chain multi-bar mechanism that is transformed from the eight-bar mechanism, and the actuator of RHop is realized by a servo motor and the clockwork spring, thereby enabling RHop to realize continuous hopping while its motor rotates continuously only in one direction. Comparative simulations and experiments are conducted for RHop. The results show that RHop can realize better continuous hopping performance, as well as the improvement of energy conversion efficiency from 70.98% to 76.29% when the clockwork spring is applied in the actuator. In addition, comparisons with some state-of-the-art hopping robots are conducted, and the normalized results show that RHop has a better energy storage speed.

Nonanthropomorphic exoskeleton with legs based on eight-bar linkages

This article presents the principles upon which a new nonanthropomorphic biped exoskeleton was designed, whose legs are based on an eight-bar mechanism. The main function of the exoskeleton is to assist people who have difficulty walking. Every leg is based on the planar Peaucellier–Lipkin mechanism, which is a one degree of freedom linkage. To be used as a robotic leg, the Peaucellier–Lipkin mechanism was modified by including two more degrees of freedom, as well as by the addition of a mechanical system based on toothed pulleys and timing belts that provides balance and stability to the user. The use of the Peaucellier–Lipkin mechanism, its transformation from one to three degrees of freedom, and the incorporation of the stability system are the main innovations and contributions of this novel nonanthropomorphic exoskeleton. Its mobility and performance are also presented herein, through forward and inverse kinematics, together with its application in carrying out the translation movement of the robotic foot along paths with the imposition of motion laws based on polynomial functions of time.

Redundant singularities versus constraint singularities in parallel mechanisms

The paper discusses the redundant singularities versus constraint singularities in relation to the main structural parameters of parallel mechanisms. The formulae of mobility, connectivity, overconstraint and redundancy of parallel mechanisms, recently proposed by the second author of this paper, are used to characterise these singularities and the transition phase between them. By using these formulae, the main properties of three types of singularity are identified. A new combined constraint-redundant singularity is defined and characterised, in connection with constraint and redundant singularities. A reconfigurable eight-bar single-loop mechanism is used to illustrate the three types of singularities. This mechanism has an interesting property to continually transit from one type of singularity to another by remaining always in a singular configuration. The properties of the redundant and constraint-redundant singularities are defined in this paper in relation to the four main structural parameters of a mechanism.

A spatial single loop kinematotropic mechanism used for biped/wheeled switchable robots

In this paper, we propose a novel biped walking robot on the basis of a spatial eight-bar mechanism. The kinematotropic characteristic of the mechanism is investigated and the geometric constrains deriving the kinematotropy are specified. The mechanism possesses two motion branches with different degrees of freedom. A detailed kinematic analysis is presented for both motion branches. A biped/wheeled switchable robot is further designed. In the motion branch I, the mechanism is used as a biped walking mechanism. In the motion branch II, it is utilized as a wheeled robot and completes the switch process between two modes. At last, we demonstrate the gait motion of the robot in the biped mode and the switch process.

Two-Objective Optimization of Drawing Mechanism Based on Genetic Algorithm

Multi-bar linkage mechanism is one of the most important directions to the development of mechanical presses. But there are a large number of bars, so how to choose each bar size to ensure the best kinematical characteristic and to achieve longer drawing depth as soon as possible is a key to the design. This paper established kinematics mode of the eight-bar drawing mechanism by bar-group method, and deduced kinetics expressions of all bars, then developed application simulated system by Visual Basic, characterizing Windows universal interface. In addition, proposed two-objective optimization functions-drawing depth and drawing speed, and optimized the mechanism by genetic algorithm. The optimization results shows that its motion performance has been improved in a great degree.

Parametric Optimization of an Eight-bar Mechanism of a Wheel Loader Based on Simulation

Parametric Optimization of an Eight-bar Mechanism of a Wheel Loader Based on Simulation

Single degree-of-freedom exoskeleton mechanism design for finger rehabilitation.

This paper presents the kinematic design of a single degree-of-freedom exoskeleton mechanism: a planar eight-bar mechanism for finger curling. The mechanism is part of a finger-thumb robotic device for hand therapy that will allow users to practice key pinch grip and finger-thumb opposition, allowing discrete control inputs for playing notes on a musical gaming interface. This approach uses the mechanism to generate the desired grasping trajectory rather than actuating the joints of the fingers and thumb independently. In addition, the mechanism is confined to the back of the hand, so as to allow sensory input into the palm of the hand, minimal size and apparent inertia, and the possibility of placing multiple mechanisms side-by-side to allow control of individual fingers.

Kinematic Design of a Radius-Variable Gripper with 1-D.O.F. Used in High-Voltage Hot-Line Cleaning Robot

This paper presents the design of a novel radius-variable-gripper (RVG) for use as end-effector of high-voltage hot-line cleaning robot (HVCR). A eight-bar linkage mechanism is proposed to obtain the aim of 1-dof acutuation. According to the shape of insulators, the dimension design and kinematic analysis of RVG have been carried out. The optimization is performed to locate the joint points of arm segments, on which the brushes are mounted, approximately on the position circles in the whole opening-and-closing process of RVG. The prototype has been given finally, and it is showed that RVG is feasible to this special application.

A generalized exact gradient method for mechanism synthesis

Currently no single method, analytical or numerical, exists that is well suited for the dimensional synthesis of general mechanisms. One of the main reasons that even the state-of-the-art optimization methods are not utilized for developing a generalized mechanism synthesis methodology is due to the difficulties in obtaining the partial derivatives necessary for optimization. This paper presents the development of a new exact gradient method that offers an efficient, reliable, and accurate solution procedure for the optimal synthesis of generic mechanisms. The application of this exact gradient method is illustrated with the aid of practical six-bar and eight-bar mechanism examples.