Research and experimental analysis of precision degradation method based on the ball screw mechanism

As a key transmission component in computer numerical control(CNC) machine tools,the ball screw mechanism(BSM) is usually investigated under working load conditions. Its accuracy degradation process is relatively long,which is not conducive to the design and development of new products. In this paper,the normal wear depth of the BSM nut raceway is calculated under the variable speed operation condition using the fractal wear analysis method and the BSM’s accelerated degradation proportional wear model. Parameters of the acceleration degradation model of the double-nut preloaded ball screw pair are calculated based on the physical simulation results. The accelerated degradation test platform of the BSM is designed and manufactured to calculate the raceway wear model when the lubrication condition is broken under the variable-speed inertial load and the boundary lubrication condition under the uniform speed state. Three load forces and two samples are selected for the accelerated degradation test of the BSM. The measured friction torque of the BSM is employed as the evaluation index of the accuracy degradation test. In addition,the life cycle of the accuracy retention is accurately calculated by employing the parameters of the physical simulation model of the BSM. The calculations mentioned above can be used to estimate BSM’s accuracy performance degradation law under normal operating conditions. The application of the proposed model provides a new research method for researching the precision retention of the BSM.

Variation analysis ofprecision mechanical assembly consideringform errors and local deformation

A method to analyze the effect of form errors and local deformation on the assembly accu- racy and its stability in a non-rigid assembly system is proposed. The contact finite element method was used to obtain local deformation of mating surfaces, which was superposed onto form errors to obtain real mating surface data of assemblies. Then mating variation was obtained by establishing vir- tual contact planes. Finally, an experiment of the assembly of two cylindrical components was car- ried out to verify the validity of the proposed method. By comparing the calculation accuracies of 3D assembly with and without taking into account local deformation, the results showed that the effects of local deformation of mating surfaces on calculation accuracy of mating variation was not neglect- able compared with form errors.

Research progress on the mechanism of improving peanut yield by single-seed precision sowing

The contradiction between the supply and demand of edible vegetable oil in China is prominent,and the self-sufficiency rate is less than 35%.Peanut has a very outstanding status in ensuring the security of edible oil and food.The emphasis of increasing peanut yield should be the improvement of pod yield per unit area,because the total yield of peanut has not increased as required.This is attributed to mainly two factors-low increase in the crop productivity and the competition for land for grain and cotton crops.For traditional double-seed sowing pattern,it is difficult to further increase the peanut yield due to the serious contradiction between populations and individuals and the declining population quality under high-yield conditions.Single-seed precision sowing was proven to be a new way to increase the economic coefficient(economic yield/biological yield)with the basic stability of the total biomass,which could make plants distribute evenly,reduce the competition among individuals and attain the full production potential of single plant.In order to reveal the mechanism of increasing peanut yield by single-seed precision sowing,the effects on the ontogenetic development(plant character,physiological characteristic and nutrient utilization)and population structure(population uniformity and photosynthesis,source-sink relationship and yield composition)were systematically expounded.This study reports establishment of the high-yield cultivation technology system with the key technology of single-seed precision sowing and the supporting technology of fertilizing and management.We anticipate its wider application for the improvement of peanut yield.

A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy

High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.

Effects of Mechanical Sowing and Transplanting on Characteristics of Dry Matter Production in Middle-season Hybrid Rice

To clarify the effects of mechanical sowing and transplanting on dry mat- ter production of middle-season hybrid rice, a two-factor split plot design was used to study the effects of different sowing and transplanting methods and their interac- tion with the seedling number per hill or seeding time on dry matter accumulation, distribution and transformation of F You 498, a middle-season hybrid rice variety, under field conditions in 2012 and 2013. The results showed that there was a marked effect of the sowing and transplanting methods and their interaction with the seedling number per hill or seeding time on dry matter accumulation, distribution and transformation. The total population dry matter accumulation of the treatments with mechanical direct seeding （MDS） and machine-based transplanting （MT） was lower than that of the treatment with traditional manual transplanting （TMT）. How- ever, MDS had higher dry matter accumulation and accumulating rate in the joint- ing-earing stage,and maintained higher stem-sheath exportation, export rate and transformation than MT and TMT; MT had higher dry matter accumulation and ac- cumulating rate in the heading-maturity period than MDS and TMT. Moreover, the treatments with low seedling number per hill or early seeding enhanced the assimi- lation of dry matter after heading,the ratio of dry matter accumulation after earing to biomass yield and the contribution rate of dry matter accumulation after earing, and a reasonable early sowing was favorable to increase the harvest index of middle- season hybrid rice under mechanical sowing and transplanting conditions.

Precision loss of ball screw mechanism under sliding-rolling mixed motion behavior

The sliding-rolling mixed motion behavior degrades the ball screw’s precision at different levels.Based on the sliding-rolling mixed motion between ball and screw/nut raceway,the ball screw’s precision loss considering different given axial loading and rotational speed working conditions was investigated.Since creep and lubrication relate to sliding and rolling motion wear,the creep and lubrication characteristics are analyzed under different working conditions.Besides,the precision loss was calculated considering the sole influence of sliding behavior between ball and screw and compared with the results from other current models.Finally,research on precision loss owing to the sliding-rolling mixed motion behavior was realized under given working conditions,and suitable wear tests were carried out.The analytical results of precision loss are in good agreement with the experimental test conclusions,which is conducive to better predicting the law of precision loss in stable wear period.

Influence of velocity on the transmission precision of the ball screw mechanism

Ball screw mechanism(BSM)is an important force-motion transfer device which is used in high-precision machine tools such as the computer numerical control.Performance parameters such as contact angle,helix angle,and the pitch radius of the screw can greatly affect the transmission precision,and the transmission precision of the BSM are not yet well resolved.In this study,ball contact point motion model is derived to assess the influence of contact angle,helix angle,and the pitch radius of the screw on transmission precision under uniform motion of the BSM.For the purpose of verifying the kinematic characteristics of the contact points between the balls and raceways under a state of uniform motion,a kinematic model is developed and values are computed for a set of boundary conditions.Comparing the simulated data to measured data,the laws of motion for the ball contact points developed in this study are confirmed.Moreover,the effect of the screw velocity on contact angle,helix angle and the pitch radius of the screw directly affects the velocity of the nut.Under the accelerated and uniform motion state of the screw,larger angular velocity of the screw results in an increase in the displacement deviation of the nut,and these parameters of the nut are considered to improve the transmission precision of the BSM.The verification of the research results provides a new research method for the study of the precision retention of ball screw mechanism.

Clarification of abrasive jet precision finishing with wheel as restraint mechanisms and experimental verification

According to the critical size ratio for the characteristic particle size to film thickness between grinding wheel and work, the machining mechanisms in abrasive jet precision finishing with grinding wheel as restraint can be categorized into four states, namely, two-body lapping, three-body polishing, abrasive jet machining and fluid hydrodynamic shear stress machining. The critical transition condition of two-body lapping to three-body polishing was analyzed. The single abrasive material removal models of two-body lapping, three-body polishing, abrasive jet finishing and fluid hydrodynamic shear stress machining were proposed. Experiments were performed in the refited plane grinding machine for theoretical modes verification. It was found that experimental results agreed with academic modes and the modes validity was verified.

Mesoplasticity Approach to Studies of the Cutting Mechanism in Ultra-precision Machining

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.

Feedback Mechanism of Employment and Entrepreneurship of Poor College Students from the Perspective of Precision Poverty Alleviation

The employment problem of graduates has become a common problem faced by colleges and universities in the era of postpopularization of higher education. There are many factors that make it difficult for graduates to find jobs, such as the huge number of employees, the quality of graduates, the development of real economy, and the concept of graduates' choosing jobs, but the fundamental reason is the imbalance between supply and demand of talents. It is an important way for colleges and universities to promote full employment of graduates by establishing a feedback mechanism to track the employment of graduates, grasping the changes of poor talents and adjusting the process of talent training accordingly. And through entrepreneurship and employment to improve poverty, to achieve the goal of precise poverty alleviation.

Feedback Mechanism of Employment and Entrepreneurship of Poor College Students from the Perspective of Precision Poverty Alleviation

The employment problem of graduates has become a common problem faced by colleges and universities in the era of postpopularization of higher education. There are many factors that make it difficult for graduates to find jobs, such as the huge number of employees, the quality of graduates, the development of real economy, and the concept of graduates'choosing jobs, but the fundamental reason is the imbalance between supply and demand of talents. It is an important way for colleges and universities to promote full employment of graduates by establishing a feedback mechanism to track the employment of graduates, grasping the changes of poor talents and adjusting the process of talent training accordingly. And through entrepreneurship and employment to improve poverty, to achieve the goal of precise poverty alleviation.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

A Measuring Solution for Mechanical Characteristics of MO Disks

Mechanical characteristics of MO disk are vital for the designer of the drives and the manufacturers who provide the mass-product MO disks. So measuring mechanical characteristics is very significant. We compares the existing measuring methods and gives some novel measuring methods we adopted in details. The measuring system based upon these methods was introduced too. Some typical measuring results are also shown in this paper.

Research on Large Depth Diameter Ratio Ultra-precision Aspheric Grinding System

In this paper, the factors of affecting surface roughness and profiles accuracy of the machined larege depth diamter ratio aspheric surfaces in ultra-precision grinding process are analyzed theoretically. An ultra-precision aspheric grinding system is then designed and manufactured. Aerostatic form is adopted to build the spindle of the workpiece, transverse guideway, longitudinal guideway and the spindle of the grinder in this system. The following specification is achieved, such as the turning accuracy of the spindle of the workpiece is 0.05 μm, radial rigidity of the spindle is GE 220N/μm, axial rigidity is GE 160 N/μm, radial rigidity of the guideway is GE 200N/μm, the highest rotational speed of the grinder is 80 000 rev/min and its turning accuracy is 0.1 μm, the resolution of linear displacement of the transverse and longitudinal guideway is 4.9 nm. Adjusting range of this adjusting mechanism is 2 mm in the Y direction, the adjusting accuracy of the precise adjusting mechanism is 0.1 μm. Micro displacement measuring system of this ultra-precision aspheric grinding adopts two-backfeed strategy, and angle displacement back-feed is realized by photoelectric encoder, it’s resolution is 655 360 pulse/rev. after 4 frequency multiplication, it’s angle displacement resolution is achieved 2 621 440 pulse/rev. Straight-line displacement is monitored by single frequency laser interferometer (DLSTAX LTM-20B, made in Japan). This CNC system adopts inimitable bi-arc step length flex CN interpolation algorithm, it’s CN system resolution is 5 nm.So this aspheric grinding system ensures profile accuracy of the machined part. The resolution of this interferometer is 5 nm. Finally, lots of ultra-precision grinding experiments are carried out on this grinding system. Some optical aspheric parts, with profiles accuracy of 0.3 μm, surface roughness less than 0.01 μm, are obtained.

Modelling and Simulation of System Dynamics of Hybrid-Driven Precision Press

Different from conventional mechanical systems with single degree of freedom (DOF), the main idea of the system of hybrid-driven precision press is to combine the motion of a constant speed motor with a servomotor via a two-DOF mechanism to provide flexible output. In order to make the feasibility clear, this paper studies theoretically the dynamic characteristics of this hybrid-driven mechanical system.Firstly,the dynamics model of the whole electromechanical system is set up by combining dynamic equations of DC motors with those of two-DOF nine-bar mechanism deduced by the Lagrange′s formula. Secondly through the numerical solution with the fourth Runge-Kutta, computer simulation about the dynamics is done, which shows that the designed and optimized hybrid-driven precision press is feasible in theory. These provide theoretical basis for later experimental research.

RESEARCH ON INFLUENCE OF TEMPERATURE ON A PRECISION FORGING PROCESS OF BLADE WITH A TENON

The blade precision forging process is a forming process with high temperature and large plastic deformation. Interaction of deformation and heat conduction leads to large uneven distribution of temperature. The unevenness of temperature distribution has a great effect on mechanical properties and the microstracture of materials. So it is necessary to consider the influence of temperature on the precision forging process of blades. Taking a blade with a tenon into consideration, a 3D mechanical model in precision forging is built up. The distribution laws of temperature field and the influence of the temperature on the equivalem stress in the process are obtained by using 3-D coupled thermo-mechanical FEM code developed by the authors Theresuits obtained illustrate that the influence of the temperature field on the blade forging process is considerable. The achievements of predicting microstructure and mechanical properties for forged blades is significant.

An Electro-Mechanical Controller for Adjusting Piston Pump Stroke On-the-Go for Site-Specific Application of Crop Nutrients

Nutrient application systems are designed to apply a relatively uniform amount of a fertilizer to agricultural fields. However, considerable variation in soil texture and other characteristics often occurs within and across production fields, which could have a major impact on fertilizer management strategies. Therefore, uniform application of a fertilizer over the entire field can be both costly and environmentally unsound. Due to their rugged and fool-proof design, crankshaft type piston pumps are widely used in agriculture. The on-the-go outlet flow of these pumps can only be varied by changing the drive shaft speed for each pump stroke setting. But only a limited range of flow rates can be achieved by changing the drive shaft speed. There is a need for an electronic controller, which can adjust the pump stroke on-the-go, for real-time, variable-rate application of crop nutrients. The Clemson “Electro-me-chanical controller for adjusting pump stroke on-the-go” was designed to replace the current manual stroke adjustment system on positive displacement piston pumps. This affordable system can be retrofitted on most John Blue - piston pumps for real-time adjustment of the pump stroke and can be controlled using pre-described position sequences (map-based) or real-time sensor commands (such as optical, pressure, and flow sensors) combined with fertilizer calculation algorithms. In addition, it can adjust pump stroke manually, using an eclectic dial from the tractor’s cab.

基于EDEM仿真的机械式辣椒精量排种装置设计与试验

针对辣椒漂浮育苗中,人工点播存在的劳动强度大、播种效率低和劳动成本高等问题,在磁力回位型排种器的基础上,提出一种适配辣椒漂浮育苗的机械式辣椒精量排种装置,使用SOLIDWORKS等软件对关键结构进行设计和运动分析,并利用EDEM仿真软件对排种装置进行仿真。选取曲柄电机转速、种量和曲柄直径为影响因子,单粒率、重播率和漏播率为评价指标,进行基于Box-Behnken设计的响应曲面法试验,并对试验结果进行分析,采用权重结合隶属度计算综合得分对排种装置的参数组合进行评价,得到排种装置的最优的参数组合为:曲柄电机工作转速260 r·min^(-1),种量4 000粒,曲柄直径28 mm。样机试验播种单粒率、重播率和漏播率分别为91.46%、7.29%和1.25%,满足辣椒漂浮育苗生产技术要求。

汽车后大灯镜壳大型薄壁精密注塑模设计

根据汽车后大灯镜壳的结构特点,设计了一副大型薄壁精密注塑模具。模具采用定模成型内表面、动模成型外表面及动模侧向抽芯机构,有效地解决了成型塑件脱模困难问题;模具采用三级定位机构,显著提高了模具刚度和寿命;模具采用随形水路温度控制系统,成型周期降低了10%,成型塑件最大变形量下降了20%,成型塑件的尺寸精度达到了设计要求的MT3;模具采用推杆先复位机构,有效地消除了滑块和推杆汽相撞的风险,保证了侧向抽芯机构安全可靠。模具投产后运行平稳,成型塑件尺寸稳定。

基于成果导向理念的工程流体力学课程教学设计与实践

工程流体力学是能源与动力工程专业的学科基础课,对学生后续课程学习和专业技能提升具有重要的支撑作用。该课程理论强、学时短、公式推导多、学习难度大。为此,将OBE教育理念融入工程流体力学教学设计实践中,按照教学大纲的要求,完善课程目标和内容,以产出为导向,优化教学方法、手段及考核方式。通过教师专业素质提高,成果转化、思政融入,案例库构建,教学资源整合等措施,构建产学研融合、混合式教学的培养模式,设计过程性耦合结果性考核方式,全方位调动学生学习的积极主动性和自主学习创新能力,精准化达成课程培养目标。