Kinematic Accuracy Reliability Research Articles

Kinematic accuracy reliability evaluation method of space deployable mechanism based on dynamic model

Space deployable mechanisms are widely used in aerospace missions. The uncertainties in the geometric or physical parameters seriously affect the kinematic accuracy of the mechanism during the deployment process. In this paper, a kinematic accuracy reliability evaluation method of the space deployable mechanism based on dynamic model and adaptive hybrid surrogate models is presented. Firstly, the dynamic model of the space deployable mechanism is established based on the Lagrange method, and the motion error function considering the factors such as the mass, dimension and load is established. In order to improve the efficiency, an adaptive hybrid surrogate model reliability evaluation method based on improved weight measurement method is further proposed. The weight measurement method considers the global errors and local errors of the models. Finally, the Monte Carlo method is used to verify the accuracy of the hybrid surrogate model method. The relative error of the failure probability calculated by the proposed method is within 2.5 %, indicating that the proposed method has high calculation accuracy and efficiency.

Reliability Estimation of Retraction Mechanism Kinematic Accuracy under Small Sample

Due to intricate operating conditions, including structural clearances and assembly deviations, the acquisition of test data of landing gear retraction mechanism is limited, posing challenges for reliability analysis. To solve the problem, a Bayesian-based reliability analysis method by fusing prior and test data is proposed, focusing on the mechanism kinematic accuracy under small-sample conditions. Firstly, a dynamic simulation model is established to collect prior data, and retraction tests are conducted to obtain test data. Then, based on Bayesian theory, the motion accuracy parameter estimation model integrating prior and test samples is established. To obtain accurate hyper parameters, the prior samples are expanded using neural network. Finally, taking the retraction mechanism as the research object, the kinematic accuracy reliability is quantified, and the impact of uncertainty factors is analyzed in depth. The results show that the proposed method is superior to the classical interval estimation method in stability and effectively mitigates the impact of uncertainty factors.

Reliability modeling for dependent competing failure processes based on planar mechanism

Considering the influence of external random shock on the kinematic accuracy of mechanism, a new reliability model of dependent competing failure processes (DCFP) is proposed in this paper. The kinematic accuracy of the mechanism is limited by the original errors such as the dimension error and joint clearance error, and it is also affected by aging and wear-out during service life, thus eventually leading to functional failure. Meanwhile, according to the magnitude of the external random shock, the random shock has different effects on the degradation process of the mechanism. In this study, a DCFP model with accuracy degradation process and multi-type mixed shock is considered. The time-dependent kinematic accuracy reliability model of the planar mechanism is established based on the Gamma degradation theory, effective length model, mechanism kinematic error theory and the fourth moment technique. Moreover, the magnitude of random shock is divided into different regions when the extreme shock, cumulative shock, and δ-shock on mechanism reliability are considered. Finally, a numerical example of the pantograph mechanism is conducted to demonstrate the feasibility and effectiveness of the proposed model. The results show that the kinematic accuracy reliability of the pantograph mechanism reduces with the increasing of wearing capacity and external shocks. According to sensitivity analysis, an effective way to improve the reliability of the planar mechanism is to optimize its strength of the mechanism. The proposed method can be used to evaluate the reliability of planar mechanisms with dependent competing failure modes.

Parameter Optimization of Large-Size High-Speed Cam-Linkage Mechanism for Kinematic Performance

The cam-linkage mechanism is a typical transmission mechanism in mechanical science and is widely used in various automated production equipment. However, conventional modeling methods mainly focus on the design and dimensional synthesis of the cam-linkage mechanism in the slow-speed scenario. The influence of component dimensions is not taken into consideration. As a result, the model accuracy dramatically falls when analyzing large-size cam-linkage mechanisms, especially in high-speed environments. The kinematic aspects of cam design have been investigated, but there are few studies discussing the motion characteristic and accuracy analysis models of the large-size cam-linkage mechanism under high-speed scenarios. To handle such issues, this paper proposes a parameter optimization methodology for the design analysis of the large-size high-speed cam-linkage mechanism considering kinematic performance. Firstly, the mathematical model of the cam five-bar mechanism is presented. The cam curve and motion parameters are solved forward with linkage length and output speed. Then, a particle swarm-based multi-objective optimization method is developed to find the optimal structure parameters and output speed curve to minimize cam pressure angle and roller acceleration and maximize linkage mechanism drive angle. A Monte Carlo-based framework is put forward for the reliability and sensitivity analysis of kinematic accuracy. Finally, a transverse device of a sanitary product production line is provided to demonstrate the applicability of the proposed method. With the parameter optimization, the productivity of the transverse device is doubled, from 600 pieces per minute (PPM) to 1200 PPM.

Dimensional Optimization for Minimally Invasive Surgery Robot Based on Double Space and Kinematic Accuracy Reliability Index

Abstract To improve the kinematic performance of the remote center mechanism for surgical robot, a double space index and kinematic accuracy reliability index are proposed to optimize the dimensional sizes of mechanism. First, the influence of the angular error on the position error and the operability of the remote center in the workspace are analyzed. The position error space and operability space index are weighted to establish the double space index. Second, a kinematic accuracy reliability index is established based on the influence of joint clearance on output position accuracy. Finally, the dimensional sizes of remote center adjustment mechanism and double parallelogram mechanism are optimized based on proposed optimization indices. Multipopulation genetic algorithm is used to obtain the optimal size parameters under the corresponding index. The optimized double space index is 56.7%, which is 56.5% higher than before optimization. The optimized kinematic accuracy reliability is 0.91, which is 22.9% higher than before optimization. The kinematic performance of remote center mechanism has been significantly improved after optimization.

A computational framework of kinematic accuracy reliability analysis for industrial robots

A new computational method to evaluate comprehensively the positional accuracy reliability for single coordinate, single point, multipoint and trajectory accuracy of industrial robots is proposed using the sparse grid numerical integration method and the saddlepoint approximation method. A kinematic error model of end-effector is constructed in three coordinate directions using the sparse grid numerical integration method considering uncertain parameters. The first-four order moments and the covariance matrix for three coordinates of the end-effector are calculated by extended Gauss–Hermite integration nodes and corresponding weights. The eigen-decomposition is conducted to transform the interdependent coordinates into independent standard normal variables. An equivalent extreme value distribution of response is applied to assess the reliability of kinematic accuracy. The probability density function and probability of failure for extreme value distribution are then derived through the saddlepoint approximation method. Four examples are given to demonstrate the effectiveness of the proposed method.

A New Study on the Relative Kinematic Accuracy Reliability of a Novel Exoskeleton with Series-Parallel Topology

An excellent exoskeleton worn by the operator might be able to move with a high degree of accuracy and repeatability. Based on the previous kinematic accuracy reliability model, this article proposes two new definitions of the relative kinematic accuracy reliability to investigate the motion accuracy ability of a novel exoskeleton with series-parallel topology thoroughly. According to the new definitions, the calculating results show that x-, y-, and z-directions of the exoskeleton end-effector have different motion accuracy abilities, the motion accuracy ability of x is the best of all, and the motion accuracy ability of y is better than that of z. To study error sources, we illustrated the geometric tolerances and driving errors, which cause the uncertainties of the exoskeleton end-effector. The effects of geometric tolerances and driving errors on kinematic accuracy reliability and relative kinematic accuracy reliability, which are the sensitivity analyses, were numerically simulated and elucidated. The results reveal that the error sensitivity in the x-direction is the lowest and the error sensitivity in the y-direction is lower than that in the z-direction. Besides this, the effects of driving errors on the motion ability of all directions of the exoskeleton end-effector are larger than those of geometric tolerances. This approach for modeling and calculating kinematic accuracy reliability, relative kinematic accuracy reliability, and their sensitivity analysis provides a novel and unique reference standard for exoskeleton and other mechanism design.

A method to determine kinematic accuracy reliability of gear mechanisms with truncated random variables

Gears are widely used as transmission components in various types of precision machinery, such as machine tools, vehicles and robots. The performance of these mechanical systems is directly related to the kinematic accuracy of the gear mechanism. This paper presents a novel method to evaluate the reliability of the kinematic accuracy of gear mechanisms with truncated random variables. The influence of errors originating from factors such as the gear eccentricity, profile deviation and assembly error on the transmission error are systematically analyzed and discussed. The statistical moments of the transmission error were obtained combined with the international standards for gear accuracy, tolerances, deviations and fits. A fit of the probability density function and cumulative distribution function of the transmission error was obtained using the saddlepoint approximation technique. A model was established to enable reliability analysis for gear mechanisms. Finally, a discussion of the practical applications along with a detailed analysis to evaluate the efficiency of the proposed method is presented.

Analysis of the Kinematic Accuracy Reliability of a 3-DOF Parallel Robot Manipulator

Kinematic accuracy reliability is an important performance index in the evaluation of mechanism quality. By using a 3-DOF 3-PUU parallel robot manipulator as the research object, the position and orientation error model was derived by mapping the relation between the input and output of the mechanism. Three error sensitivity indexes that evaluate the kinematic accuracy of the parallel robot manipulator were obtained by adapting the singular value decomposition of the error translation matrix. Considering the influence of controllable and uncontrollable factors on the kinematic accuracy, the mathematical model of reliability based on random probability was employed. The measurement and calculation method for the evaluation of the mechanism's kinematic reliability level was also provided. By analysing the mechanism's errors and reliability, the law of surface error sensitivity for the location and structure parameters was obtained. The kinematic reliability of the parallel robot manipulator was statistically computed on the basis of the Monte Carlo simulation method. The reliability analysis of kinematic accuracy provides a theoretical basis for design optimization and error compensation.

Kinematic accuracy reliability research of a novel exoskeleton with series-parallel topology

A novel type of lower extremity exoskeleton with series-parallel topology was described. Position analysis of a simplified leg was conducted to provide a basis of the kinematic accuracy reliability. Considering both assembly-machining errors and driving errors, the fuzzy reliability of kinematic accuracy was obtained based on the fuzzy probability theory. With a set of optimized length parameters and joint ranges of motion given, the fuzzy reliability of space distribution and the average fuzzy reliability were respectively calculated and shown in figures. These analyses of kinematic accuracy reliability provide a unique method to judge, analyze, and design exoskeleton mechanisms.

Design and research of a novel type of mechanical presses driven by three servo motors in parallel

A novel type of mechanical presses design driven by three servo motors in parallel is proposed to develop high stamping capacity based on the theory of generalized function sets, and then is improved to enhance its practicability in engineering practice. The inverse and forward kinematics analyses are conducted later. Based on the fuzzy probability theory, the computing method of fuzzy reliability of kinematic accuracy of slider is then obtained. Finally, with a set of optimized length parameters of the presses given, the fuzzy reliability is calculated, on the basis of which a typical deep-drawing process is simulated.

Reliability Analysis of Kinematic Accuracy of a Three Degree-of-Freedom Parallel Manipulator

The reliability of kinematic trajectory of manipulators describes the ability that manipulators keep kinematic accurate. It is an important parameter to evaluate the performance of manipulators. The kinematic accuracy of manipulators can be improved when piezoelectricity material are used as a transducer to suppress the vibration of flexible manipulators. First, a 3 degree-of-freedom parallel manipulator system and its dynamic equations are introduced. The theory and experiment of a vibration suppression system are then presented. The calculation method of both error and reliability of kinematic trajectory of manipulator is further implemented. Finally, the reliability of kinematic accuracy are calculated and analyzed for the 3 degree-of-freedom parallel manipulator with or without vibration suppressing control. The results show that the reliability of kinematic accuracy is improved using vibration suppressing control.

Modeling for Time-Variant Reliability of Mechanism

A novel time-variant reliability model is developed after studying the traditional dynamic performance of mechanism. The expression of reliability is given based on stochastic process. A two-dimensional description of the error generating process is established by studying mechanism output kinematic accuracy. The reliability of mechanism output kinematic accuracy can be obtained according to this description. The model proposed can be used to calculate the reliability of mechanism directly, if the distribution of mechanism output kinematic accuracy is known.