Study on the disaster caused by the linkage failure of the residual coal pillar and rock stratum during multiple coal seam mining:mechanism of progressive and dynamic failure

Multi-seam mining often leads to the retention of a significant number of coal pillars for purposes such as protection,safety,or water isolation.However,stress concentration beneath these residual coal pillars can significantly impact their strength and stability when mining below them,potentially leading to hydraulic support failure,surface subsidence,and rock bursting.To address this issue,the linkage between the failure and instability of residual coal pillars and rock strata during multi-seam mining is examined in this study.Key controls include residual pillar spalling,safety factor(f.),local mine stiffness(LMS),and the post-peak stiffness(k)of the residual coal pillar.Limits separating the two forms of failure,progressive versus dynamic,are defined.Progressive failure results at lower stresses when the coal pillar transitions from indefinitely stable(f,>1.5)to failing(f,<1.5)when the coal pillar can no longer remain stable for an extended duration,whereas sud-den(unstable)failure results when the strength of the pillar is further degraded and fails.The transition in mode of failure is defined by the LMS/k ratio.Failure transitions from quiescent to dynamic as LMS/k.<1,which can cause chain pillar instability propagating throughout the mine.This study provides theoretical guidance to define this limit to instability of residual coal pillars for multi-seam mining in similar mines.

A Study on the Interest Linkage Mechanism of the Taxus Industry Chain in Pengshui Miao and Tujia Autonomous County

At the Taxus base of Pengshui Miao and Tujia Autonomous County,Chongqing,the comprehensive development and utilization of Taxus was carried out with seedling cultivation,understory economy,product processing,ecotourism and other aspects as the main line.The benefit linkage mechanism of the operation of the Taxus industrial chain was explored and analyzed,so as to extend and supplement the Taxus industrial chain.The two models of"company+farmer"and"company+village collective+farmer"are relatively close benefit linkage models,which indirectly promote the increase of farmers income and smoothly guarantee the operation of the industrial chain,thereby playing a positive role during the development of the Taxus industry.This study provides reliable countermeasures and suggestions for the sustained and healthy development of the Taxus industry in Pengshui County.

Macro-micro behaviors and failure mechanism of frozen weakly cemented mudstone

Understanding the mechanical properties and multiscale failure mechanism of frozen soft rock is an important prerequisite for the construction safety of tunnels,artificially frozen ground and other infrastructure in cold regions.In this study,the triaxial compression test are performed on mudstone in the weakly cemented soft rock strata in the mining area of western China,and the mechanical characteristics and failure mechanism of weakly cemented mudstone are systematically investigated under the combined action of freezing and loading.Furthermore,the quantitative relationship between the microstructural parameters and the macroscopic strength and deformation parameters is established based on fractal theory.Thus,the failure mechanism of frozen weakly cemented mudstone is revealed on both micro- and macro-scales.The results show that temperature and confining pressure significantly affects the elastic modulus and peak strength of weakly cemented mudstone.With decreasing temperature,the compressive strength increases,while the corresponding peak strain decreases gradually.On the deformation curve,the plastic deformation stage is shortened,and the brittle fracture feature at the post-peak stage is more prominent,and the elastic modulus correspondingly increases with decreasing temperature.Under low-temperature conditions,most of the weakly cemented mudstone undergoes microscopic shear failure along the main fracture surface.The micro-fracture morphology characteristics of weakly cemented mudstone under different temperatures are quantified via the fractal dimension,and an approximately exponential relationship can be obtained among the fractal dimension and the temperature,compressive strength and elastic modulus.

Driving Torque Reduction in Linkage Mechanisms Using Joint Compliance for Robot Head

The conventional linkage mechanisms with compliant joint have been widely studied and implemented for increasing the adaptability of the mechanism to external contacts. However, the analysis of how compliant joints in linkage mechanism can reduce the energy consumption isn＇t still studied deeply. In a mobile service robot head, the actions of blinking the eyes and moving the eyeballs are realized by the planar linkage mechanism respectively. Therefore, minimizing the driving torques through motion trajectories for the linkage mechanism, which will be beneficial to extend the working time for mobile service robots. The dynamic modeling of the linkage mechanism with springs-loaded compliant joint is established. An optimization procedure for obtaining the optimal parameters of springs is proposed for minimizing the max value of driving torques within a range of desired operating conditions. The Simulations prove that the linkage mechanism with compliant joints can effectively reduce the driving torques, and reduce the energy consumption consequently. The framework can also be applied in other similar applications to reduce the driving torque and save energy. Compared with previous efforts, this is the first attempt that the linkage mechanism with complaint joint is applied in the robot head for reducing the driving torque.

Modeling and Optimal Design of Planar Linkage Mechanism of Coupled Joint Clearances for Manufacturing

The uncertainty of the mechanism motion error is mostly caused by the manufacturing process,so the motion error cannot be effectively predicted at the design phase.The problems of manufacturing complexity and the relationship between design and manufacturing are analyzed,and the influence of dimensional tolerance and fit tolerance on the motion accuracy of the system is considered in the design process.Then based on the Monte Carlo simulation,an optimal design model of planar linkage mechanism is set up.A typical offset slider-crank mechanism is used as an illustrative example to carry out the optimal design.Compared with the result of typical robustness design,the similar variation characteristics of the mean value and the standard deviation can be found,so the proposed method is effective.The method is furthermore applied in the optimization of the schemes with different fit tolerances and the prediction of motion errors in the design phase is achieved.A set of quantitative evaluation system for mechanism optimal design is provided.Finally,a basic strategy is presented to balance the motion precision and manufacturing cost.

CONJUGATE CAM WITH FIVE-BAR LINKAGE MECHANISM FOR RAPIER DRIVE OF FLEXIBLE RAPIER LOOMS

A new type of rapier drive for flexible rapier loom through conjugate cams with five-bar linkage mechanism is raised and analyzed. Two designs suitable for the conversion of 1515-190.5 shuttle looms are given as examples. This mechanism can be applied to traditional shuttle looms as well as to new flexible rapier loom design.

Research and Application for the Regularity of Distribution about Curvature Radius and Curvature Center of the Linkage Point Track in a Link Mechanism

It is illustrated that there exists an inflection circle on the linkage rigid body by the principle of relative motion. Confirmed methods of the inflection circle, curvature radius and curvature center of the point track on the linkage rigid body are given in the case of the different contact type of move instantaneous center line and static instantaneous center line. The regularity of distribution of curvature radius and curvature center of the point track is researched. The identification methods called determination parameters and auxiliary vertical line of the diameter and direction of the inflection circle in the four bar mechanism are pointed out. A design method of the crane hoisting mechanism is discussed in the end of this paper.

Dynamic Modeling of Variable Stiffness and Damping for Spatial Linkage Weft Insertion Mechanism with Clearance

In order to further analyze the influence of clearance on the kinematic performance of spatial linkage weft insertion mechanism,it is necessary to study the dynamic characteristics of contact impact force model with the variable stiffness and damping coefficient.Firstly,the parameters in the output process of the system are solved by describing of the flexible joint clearance.Then,based on Lankarani-Nikravesh contact force model,the contact impact stiffness and damping coefficient is modified from fixed values to time-varying coefficients.The dynamic model of spatial linkage weft insertion mechanism with modified clearance is established by Lagrange method,and the dynamic characteristics of the system are calculated.The results show that the joint clearance can directly affect the output performance of the mechanism.With the increase of the clearance value,the curve fluctuations of acceleration,driving torque and collision force are obvious,and it will be further intensified with the increase of spindle speed,which greatly affects the stability of mechanism and fabric quality.Finally,the virtual prototype is established by the SolidWorks software and simulated by the ADAMS software.The simulation results are compared with the numerical results,which verifies the accuracy of the modeling method in this paper.

An Underactuated Linkage Finger Mechanism for Hand Prostheses

The underactuated fingers used in numerous robotic systems are evaluated by grasping force, configuration space, actuation method, precision of operation, compactness and weight. In consideration of all such factors a novel linkage based underactuated finger with a self-adaptive actuation mechanism is proposed to be used in prosthetics hands, where the finger can accomplish flexion and extension. Notably, the proposed mechanism can be characterized as a combination of parallel and series links. The mobility of the system has been analyzed according to the Chebychev-Grübler-Kutzbach criterion for a planar mechanism. With the intention of verifying the effectiveness of the mechanism, kinematics analysis has been carried out, by means of the geometric representation and Denavit-Hartenberg (D-H) parameter approach. The presented two-step analysis followed by a numerical study, eliminates the limitations of the D-H conversion method to analyze the robotics systems with both series and parallel links. In addition, the trajectories and configuration space of the proposed finger mechanism have been determined by the motion simulations. A prototype of the proposed finger mechanism has been fabricated using 3D printing and it has been experimentally tested to validate its functionality. The kinematic analysis, motion simulations, experimental investigations and finite element analysis have demonstrated the effectiveness of the proposed mechanism to gain the expected motions.

Research on the Linkage Mechanism between Essential Medicine List and Healthcare Insurance List

Objective: To put forward suggestions to improve the linkage mechanism between China’s essential medicine list and healthcare insurance medicine list. Methods: Comparative study of the organization setting, selection criteria, adjustment procedures, and reimbursement of essential medicine list and healthcare insurance medicine list, containing both the foreign experience and China’s status quo. Results: When two lists exist at the same time, they are often managed separately abroad, setting more selection criteria for the essential medicine, and giving the essential medicine a higher payment ratio. The two lists in China are managed and adjusted separately, but lack of connection. As a result, some essential medicines cannot be reimbursed. Conclusion: The two lists’ linkage mechanism needs to be improved. It is recommended to make it clear that essential medicines should be selected from the healthcare insurance medicine list, and enhance the consistency of medicine evaluation through mutually scientific evidence.

Dynamic Analysis of aSelected Spatial One-DOF Linkage Mechanism with Friction in Joints

The dynamic analysis of a one-DOF RSRRR spatial linkage mechanism, including four rotational joints R and one spherical joint S, is presented in the paper. It is assumed that friction occurs in the rotational joints, whereas a spherical joint can be treated as an ideal one. The mechanism in the form of a closed-loop kinematic chain was divided by cut joint technique into two open-loop kinematic chains in place of the spherical joint. Joint coordinates and homogeneous transformation matrices were used to describe the geometry of the system. Equations of the chains＇ motion were derived using formalism of Lagrange equations. Cut joint constraints and reaction forces, acting in the cutting place---i.e, in the spherical joint, have been introduced to complete the equations of motion. As a consequence, a set of differential-algebraic equations has been obtained. In order to solve these equations, a procedure based on differentiation twice of the formulated constraint equations with respect to time has been applied. In order to determine values of friction torques in the rotational joints in each integrating step of the equations of motion, joint forces and torques were calculated using the recursive Newton-Euler algorithm taken from robotics. For the requirements of the method, a model of a rotational joint has been developed. Some examples of results of the numerical calculations made have been presented in the conclusions of the paper.

ANALYSIS AND CALCULATION ON FRICTION AND WEAR RELIABILITY OF SOME PLANE′S FLAP MECHANISM

The mathematical model of the motion of some plane′s flap mechanism is set up by the method of establishing mathematical model of space mechanism. When the input parameter is given, the theoretical output parameter of the flap mechanism is achieved by the model. The wear and tear volume is introduced into the mathematical model, and if the input parameter is the same, the real output parameter of the flap mechanism worn can be obtained. On the basis of this, it is able to achieve the friction and the wear reliability of the flap mechanism.

基于串联式Triple-LET的LEMs滑块机构分析

设计了一种基于串联式的Triple-LET新型柔性铰链,给出了该铰链的三维结构,并对其进行了弯曲等效刚度的理论分析,推导了该结构形式铰链的弯曲等效刚度计算公式并给出了修正系数。基于修正的弯曲等效刚度理论计算公式,对设计实例进行了分析计算,同时建立了该设计实例的有限元仿真模型,通过理论计算结果和仿真分析结果的比较,验证了该铰链设计的可行性。将该新型铰链应用于LEMs柔顺滑块机构的设计中,建立了该机构的基于修正弯曲等效刚度的伪刚体模型,并加工了该串联式Triple-LET铰链的滑块机构铍青铜实物模型,理论计算和实测结果基本一致,验证了理论模型的正确性和机构设计的可行性,同时也表明该滑块机构在工作状态具有较大变形,能保持较好的稳定性。

ACCURACY ANALYSIS FOR PLANAR LINKAGE WITH MULTIPLE CLEAR-ANCES AT TURNING PAIRS

Clearance at turning pair has a strong impact on the kinetic accuracy of linkage, but there is short of a generic model to analyze it so far. Clearance error, input error, and manufacturing tolerance of links are taken into consideration as the random variables synthetically. The kinematics and dynamics accuracy analysis models for planar linkages with multiple clearances at joints are built up as well. At last a typical planar linkage is selected for nurnerical illustration. These models stated in matrix resolve the relativity of output parameter errors of mechanism and therefore are of vital significance for the reliability analysis and synthesis of mechanism with clearances.

Game Analysis and Countermeasures on Increasing Prices of Agricultural Products under Triple Supply Chain

From the perspective of supply chain of agricultural products,by establishing Stackelberg game model based on triple supply chain,this paper researches the price formation and profit distribution mechanism of agricultural products under circumstance of non-cooperation and cooperation.The results show the main factors responsible for the hiking of prices of agricultural products as follows:the cost of agricultural products climbs incessantly;the circulation cost hovers at high level;the factor inputs of agricultural products are short;inflation pressure is incessantly mounting;the profit distribution of supply chain is irrational.Finally,corresponding countermeasures are put forward.

Dynamic Analysis of Four-Bar Beating-up Mechanism with Joint Clearance

For the four-bar beating-up mechanism of air-jet loom,the plain bearing of linkage is the bearing with dynamic load,and is immersed in the lubricant-box.If the joint clearance is considered,the research on linkage movement could be very complicated.In this paper,the kinematic characteristics of four-bar beating-up mechanism with joint clearance were studied by analyzing the trace of journal center and the balance of radial,tangential forces,and bearing load.The region of principal vibration and its forming causes were discussed.And the results could interpret the measuring curves of four-bar beating-up mechanism completely.

Simulation and Analysis of Spatial Weft Insertion Mechanism Considering Flexibility and Clearance

A 3D model of the spatial four-bar weft insertion mechanism was built with unigraphics NX(UG) according to the actual requirement,and dynamics simulation was carried out by importing the model into ADAMS.Without considering the clearance,the motion characteristic curve of the sword belt was generated through ADAMS combined with MATLAB.In this paper the hinge between the rod and the sector gear was selected as an example with different values of clearance,outputting the motion characteristic curve of the sword belt.Finite element analysis(FEA)was conducted,the flexible body was generated by importing the forked frame into ANSYS,and flexible dynamics simulation was carried out by importing the flexible body into ADAMS to replace the rigid rod.A comprehensive comparison of the output characteristics of the sword belt was conducted in the consideration of the clearance or flexible.Analysis of the force on the left hinge of the rod was carried out with the ADAMS post processing module.With the same clearance,considering the flexibility,amplitude of fluctuation of the force on the hinge increased obviously.

THE EXTENDING OF JOUKOWSKY'S LEVER METHOD AND ITS APPLICATIONS IN LINKAGE PROBLEMS

Joukowsky’s Lever Method is the method used to find out the equilibrant and balancingmoment of various mechanisms.The advantage of this method is to save the complicated processof finding out the reactional forces in kinematic pairs.But,the method is only limited to thosemechanisms composed of rigid bar linkages and with negligible friction.In practical cases,hydropneumatic elements and spring constraints may be included in the mechanism;and alsowith the development of high load,high speed and high accuracy of mechanism,the friction maynot be neglected.So,the authors have tried to develop the Generalized Joukowsky’s LeverMethod,which can be used to find out the equilibrant and balancing moment of the mechanismwhen the hydropneumatic elements and spring constraints are included and the friction inkinematic pairs has to be considered.Three examples are here analyzed to show the applicationsof this method.

CALCULATION OF NATURAL FREQUENCIES FOR THE PLANAR SIX-BAR LINKAGE OF WATT TYPE

By using transfer matrix,the lower-order natural frequencies of the Watt type planar six-barlinkage are calculated in this paper.The experiment of the modal analysis is done with the SignalProcessor 7T17S,and the experiment results agree with the calculated ones.This method only re-quires calculation of lower-order transfer matrix and determinant values,so that, it can be done ona minicomputer such as IBM/PC.The method adopted in this paper is also suitable for vibrationanalysis of other types of linkages.

Active Vibration Control of Macroscopically Smart Mechanisms

This paper presents an investigation on the active vibration control of flexible linkage mechanisms featuring piezoceramic actuators and strain gauge sensors. The dynamic equation of the macroscopically smart mechanism is decoupled by means of the complex mode theory. The state-space expression of the controlled system is developed, which includes the system noise and the observation noise. Moreover, a discrete linear quadratic Gaussian （LQG） state feedback controller and a discrete Kalman filter are designed separately. Finally, the proposed method is applied to the on-line vibration control of a macroscopically smart mechanism. The experimental results reveal that the strain amplitude of the flexible link ig suppressed by 80% and the dynamic performance of mechanism has been ameliorated significantly.