Accuracy of performance of farm machinery

Precision of the working height, or depth, of earth-moving equipment and other farm machinery can have a marked effect on the quality of the operation. The main factors affecting a machine's performance in maintaining the correct working height are its geometric parameters and the soil surface upon which it operates. The soil surface profile is defined by the “mean slope”, by the “root-mean-square” (RMS) of the deviations from the mean slope, and by the wavelengths calculated by Fourier analysis. The shortest wavelength with an amplitude above 1 cm was used in this study to find the effect of the soil surface waves on the accuracy of farm machinery operations. The machine's geometric parameters affecting its accuracy are its wheelbase and the lengthwise location of the working point (above or under ground) in relation to the wheels. A computer simulation analysis showed that the minimum deviations from the required height are found at the wheels of the machine. The deviations increased at the middle of the machine's span and rose steeply outside the span. The shorter the wheel-span of the machine relative to the wavelengths, the smaller the deviations will be. Smoothed surfaces have longer wavelengths and smaller deviations and as a result, higher accuracy of the working height, or depth, of the machines working on them.     

Improved operator comfort and off-road capability through pendulum arm technology

The Nordic forest industry requires just-in-time wood deliveries. Operations must continue regardless of season, weather and terrain. Soil compaction and deep ruts must be avoided while providing high performance and a reasonable working environment for operators.The Xt28 pendulum arm forwarder is a full-size concept forwarder with six hydrostatic propelled wheels on pendulum arms built on a three-piece frame connected with two articulation joints. The Xt28 concept machine was tested according to Skogforsk standard machine tests. Rut depth test focused on soil interaction where rut depth was measured related to number of passes. Machine dynamics were measured using standardized test track with focus on operator comfort.The project proved the potential of pendulum arm technology in off-road transportation. Automatic pendulum arm levelling, equalized ground pressure between wheels and improved operator comfort through reducing adverse vibrations and roll angles, simultaneously reducing dynamic forces transferred to the forest floor. Pendulum arm technology improves travel speed in adverse terrain, providing unparalleled side slope capability and enhanced productivity.     

An in-situ determination of virgin compression line parameters for predicting soil displacement resulting from agricultural tire passes

This paper demonstrates the determination of the virgin compression line parameters from initial soil density, contact pressure and resulting rut depth in uniform soil conditions for which a constant soil density change to a depth of 500 mm was obtained in soil bin experiments (whereby total soil depth was 750 mm). The density change was determined with a “non-invasive” technique determining soil displacement (strain) by placing talcum powder lines into the soil during preparation of the soil bin and measuring the change in their relative position. The soil compaction model COMPSOIL with these parameters predicted wheel rut depth to within ±5%, from which in turn an absolute soil density increase can be determined to within ±3%. The model was successfully validated against data for uniform initial densities of 1.2 g/cm³ and 1.6 g/cm³ and a simulated layered field condition. The estimation of the virgin compression line was validated in the field as well. The parameters of the virgin compression line were estimated using soil density change data for the corresponding average contact pressures of different tires with loads of 4.5–10.5 t.     

Geomechatronics – Interaction between ground and construction machinery and its application to construction robotics

“Geomechatronics” is a technical field in which “Geotechniques” is fused with “Mechatronics” that is the technical field to promote the automatic control of machines by using the electronics. In the field of “Geomechatronics”, a construction machine, which treats geotechnical materials such as soil and rock, automatically evaluates the properties and conditions of the ground and determines the optimum controlling method of itself for the ground with the base of the machine–ground interaction. Some researches for practical use in the field of geomechatronics are introduced, and then the progressing view of this research and technical filed is explained in this paper.     

“Variable mass braking system” un nouveau systeme de freinage de vehicule automobile

This paper proposes an alternative to the standard anti-lock braking system.We call it “variable mass braking system”.This new system of braking avoids the locking of the wheels mostly in the case of high speeds; that cannot do the first one.These two systems of braking, are not incompatible; and if they are coupled, they will be able to complete each other harmoniously; the first operating in the case of low speeds requiring no great braking forces for the immobilization of the vehicle without blockage of the wheels, the second operating rather in the case of the high speeds, that requires great braking forces for the instantaneous stop of the vehicle without blockage of the wheels.     

A novel rigid wheel for agricultural machinery applicable to paddy field with muddy soil

The working performance of agricultural machinery is largely determined by the walking performance of the wheel when driving in complex unstructured soil. However, the driving performance of existing wheels is not satisfactory for paddy field with muddy soil. The purpose of the current study is therefore to propose a novel rigid wheel for agricultural machinery which is applicable to paddy field with muddy soil. Firstly, a novel arc edge shaped wheel was designed based on the principles of mechanics on the ground. Then the driving performance of this arc edge shaped wheel was evaluated using FE modeling of interaction between rigid wheel and soil. Finally, the structure originally designed arc edge shaped wheel was improved according to FE modeling results, and this improved design was further evaluated by both FE simulation and prototype experiments. Both FE modeling and experimental results indicate that the improved arc edge shaped wheel proposed in this study has a good driving performance with regarding to wheel sinkage and soil reaction force. The proposed arc edge shaped wheel could be used as an effective component of rice harvester for paddy field with muddy soil.     

How to predict soil compaction from agricultural tires

A concept of how to predict soil compaction with regard to agricultural machinery, tires and soil is proposed. This approach should provide criteria for choosing vehicles and tires, as well as for the choice of soil testing equipment. It should be stressed that, till now, the concept has only been tested for a few kinds of soil. Therefore, its application to other soil types has to start with one of the proposed “soil calibration tests”.     

基于表面织构技术改善摩擦学性能的研究进展

利用表面织构技术改善材料表面摩擦学性能已被大量应用于许多工程领域. 然而,通过表面织构技术提高材料表面的减摩耐磨性能的确切机理仍不清楚,因此,研究人员进行了大量表面织构几何特征和工况条件的优化来研究表面织构技术的机理及应用范围. 本文作者回顾了近年来表面织构技术在控制摩擦方面的主要研究成果,从不同润滑条件下的减摩机制与理论模型展开讨论,重点从表面织构的几何特征和实际工况条件两个方面来评述改善材料表面摩擦学性能的最新进展,其中,几何特征包括表面织构的纹理形状、直径、深度、面密度和排列方式;实际工况条件取决于摩擦形式及操作条件,根据摩擦系数、磨损量、承载能力、阻力系数及升力系数等体现摩擦学性能的参数,对改善表面摩擦学性能的参数和条件进行分析和总结. 深入研究精确的理论模型和普适性的模拟方法并开发改善摩擦学性能的参数优化方法是未来的研究重点和方向.      

The optimum height of application of force and eccentricity of a wheeled vehicle running on a loose sandy soil

In earthmoving sites, multi-wheeled vehicles are used to excavate a sandy soil or to pull other construction machinery. In this paper, the mechanism of a 5.88 kN weight, two-axle, four-wheel vehicle running on a loose sandy soil is theoretically analysed. For given terrain-wheel system constants, the combination of the effective braking force of the front wheel during pure rolling state and the effective driving force of the rear wheel during driving action will clarify the relation between effective effort of the vehicle and slip ratio and the relation between amounts of sinkage the front and rear wheels and slip ratio, etc. The maximum effective tractive effort of the vehicle varies with the height of application force and the position of the center of gravity of the vehicle. The optimum height of application of force and the eccentricity of the center of gravity to obtain the largest value of the maximum effective tractive effort can be explained with an analytical simulation program. Results of this study showed that the optimum height of application force should be 30 cm and the optimum eccentricity of the center of gravity is 0.05 for a vehicle considered for this study.     

Total axle load effects on soil compaction

Theoretical and applied research has shown that the pressure at a point in the subsurface soil is a function of both the surface unit pressure and the extent of the area over which it is applied (total load). Thirty years ago, most of the soil compaction from vehicle traffic was in the plow layer and was removed by normal cultural practices. As equipment has increased in size and mass, machine designers have increased tire sizes to keep the soil surface unit pressure relatively constant. However, the increase in total axle loads is believed to have caused an increase in compaction at any given depth in the soil profile, resulting in significant compaction in the subsoil.Two tires of different sizes, a standard agricultural tire and a flotation tire were used to support equal loads. Soil pressures were measured at three depths in the soil profile directly beneath each of the tires. Two soils were used and each was prepared first in a uniform density profile, and then they were prepared with a simulated traffic pan (layer of higher density) at a depth of approximately 30 cm.Results showed that the presence of a traffic pan in the soil profile caused higher soil pressures above the pan and lower pressures below it than was the case for a uniform soil profile. The soil contact surface of the flotation tire was approximately 22% greater than the agricultural tire. The greater contact surface did reduce soil pressures at the soil surface, of course, but the total axle load was still the dominant factor in the 18–50 cm-depth range used in this study.     

用ADINA确定热电厂磨煤机打击轮磨损极限

利用ＡＤＩＮＡ程序计算磨损后打击轮的应力分布状态；根据强度理论，得到磨损极限，为打击轮维修提供了依据．实践证明，不超过磨损极限的打击轮修复以后可以满足使用精度要求，其使用期限与新的打击轮相同．磨损极限的确定为国家创造了经济效益     

Progress in tire rating based on soil compaction potential

The general trend in soil protection is to reduce the detrimental soil compaction by loaded wheels of power and transport equipment. This paper reports on the progress in research of soil compaction risk assessment by means of Compaction Capacity (CC) tire rating originally introduced as compaction number (CN) rating [Grečenko A. Tire load rating to reduce soil compaction. J Terramech 2003;40:97–115]. The CC rating evaluates soil dry density along a vertical column 20–50 cm below the ground surface. The unique feature of the CC approach is that it converts laboratory compaction measurements directly to soil compaction profiles under evaluated tires without touching the stresses in the ground. The laboratory soil compaction is done with round pressure plate and similarly the tire contact area is represented by a virtual plate loaded by the same mean contact pressure. This paper describes laboratory testing procedures with fundamentals of data conversion and gives examples of CC rating application.     

Soil compaction: State-of-the-art report

Three prior state-of-the-art reviews are used as a foundation for this one. Soil compaction research is divided into three areas: (1) Machines designed to compact the soil, or vehicles used intentionally to do so; (2) Incidental compaction of soil by machinery being used for other purposes; and (3) Management practices for controlling undersired soil compaction. Background research is discussed in each category, and the relevant papers for the Eight International Conference are summarized. It is concluded that the soil compaction problem is better understood and more effectively researched today than ever before. Continuation of the trend of the past half century toward larger and heavier agricultural machinery appears to be in jeopardy with the recognition of (1) total axle loads as the basic cause of subsoil compaction and (2) the nearly opposite soil conditions required for effective performance by wheels and crops.     

Changes in some mechanical properties of a loamy soil under the influence of mechanized forest exploitation in a beech forest of central Belgium

Modification of some soil mechanical properties (penetration resistance and consolidation pressure) induced by vehicle compaction during mechanized forest exploitation was studied in an acid and loamy leached forest soil of the loessic belt of central Belgium. In situ penetration tests and laboratory Bishop–Wesley cell tests were undertaken for the two main soil horizons of a beech high-forest, i.e. the eluvial E horizon (5–30 cm depth) and the underlying clay-enriched B_t horizon (30–60 cm depth). Both undisturbed and wheel-rutted soil areas were studied (E and B_t horizons vs. E_g and B_tg horizons).

Results show that: The experimental overconsolidation pressure of the eluvial reference horizon (E) is about 50 kPa higher than the value calculated from soil overburden pressure; this probably results from suction action during dry periods. The clay-enriched reference horizon (B_t) shows the same trends. In wheel-rutted areas, seven years after logging operations, the E_g horizon memorizes only 14.5% of the wheel induced stress due to forest machinery.

In the compacted B_tg horizon, the experimental overconsolidation pressure represents 96% of the exerted theoretical stresses due to harvesting actions. The good recording of the exerted stresses, after seven years, can be explained by: (1) The B_tg depth which keeps it from seasonal variations i.e. from desiccation–moistening or freeze–thaw cycling; (2) amorphous and free iron accumulation inducing a “glue” effect of the B_tg soil matrix, which could stabilize the soil structure and prevent recovery to initial conditions. These results provide clear evidence that on loessic materials, soil compaction due to logging operations leads to modifications in both physical (bulk density, total porosity) and mechanical (penetration resistance and consolidation pressure) soil properties.     

Prediction of tractive response for flexible wheels with application to planetary rovers

Planetary rovers are typically developed for high-risk missions. Locomotion requires traction to provide forward thrust on the ground. In soft soils, traction is limited by the mechanical properties of the soil, therefore lack of traction and wheel slippage cause difficulties during the operation of the rover. A possible solution to increase the traction force is to increase the size of the wheel-ground contact area. Flexible wheels provide this due to the deformation of the loaded wheel and hence this decreases the ground pressure on the soil surface. This study focuses on development of an analytical model which is an extension to the Bekker theory to predict the tractive performance for a metal flexible wheel by using the geometric model of the wheel in deformation. We demonstrate that the new analytical model closely matches experimental results. Hence this model can be used in the design of robust and optimal traction control algorithms for planetary rovers and for the design and the optimisation of flexible wheels.     

Parametric analysis of lugged wheel performance for a lunar microrover by means of DEM

The purpose of this study was to develop a numerical tool to simulate the performance of lugged wheels designed for a lunar microrover. The performance was analyzed using a Discrete Element Method (DEM) whose accuracy was validated for interactions between lugged wheels and soil. DEM analysis indicated that, on flat horizontal lunar surfaces, wheels with 18 10-mm-high lugs would provide less net traction than would wheels with 36 5-mm-high lugs.     

Effects of longitudinal grooves on the Couette–Poiseuille flow

The effects of longitudinal grooves on the flow resistance in a channel where the flow is driven by movement of one of the walls and modified by a streamwise pressure gradient have been studied. The reducedorder geometrymodel has been used to extract geometric features that are hydraulically relevant. Three distinct zones leading to the reduced resistance have been identified, depending on the flow pressure gradient and the groove wave number. Two of these zones correspond to grooves with long wavelengths and one to grooves with short wavelengths. Optimization has been used to determine shapes that provide the largest flow rate. In the case of the long-wavelength grooves, the optimal shapes depend on the constraints. These shapes are well approximated by a certain universal trapezoid for grooves that have the same height and depth. There exists an optimum depth which, combined with the corresponding shape, defines the optimal geometry in the case of the unequal-depth grooves; this shape is well approximated by a Gaussian function. No optimal shape exists for the short-wavelength grooves if the groove amplitude is sufficiently small; the shortest admissible wavelength dominates system performance under such conditions. The most effective groove wave number does exist for higher grooves, but the optimal shape cannot be determined due to numerical limitations.     

Characteristics of normal and tangential forces acting on a single lug during translational motion in sandy soil

Lugs (i.e., grousers) are routinely attached to the surfaces of wheels/tracks of mobile robots to enhance their ability to traverse loose sandy terrain. Much previous work has focused on how lug shape, e.g., height, affects performance; however, the goal of this study is to experimentally confirm the effects of lug motion on lug–soil forces. We measured normal and tangential forces acting on a single lug as functions of inclination angle, moving direction angle, sinkage length, horizontal displacement, and traveling speed. The experimental results were mathematically fitted by using least square method to facilitate quantitative analyses on effects of changes in these motion parameters. Moreover, we compared the measured tangential forces to values calculated from a conventional tangential force model to evaluate the effects of the lug-tip surface, which is generally ignored in existing terramechanics models. The conclusions from this study would be useful for estimating the traveling performance of locomotive mechanisms equipped with lugs, modeling interaction mechanics between lugged wheels and soil, etc.     

Soil-vehicle interaction

Progress in modelling, predicting and measuring soil-vehicle interaction performance is reviewed. Topics include soil properties, track systems, rigid and lugged wheels, pneumatic tyres and soil working systems. Methods range from the highly theoretical to the largely experimental. Substantial progress has been made in computer modelling methods for predicting the tractive performance of track systems and lugged wheels. A generally accepted method for describing the strength/deformation properties of surface soils has yet to evolve.     

包含几何误差的机械结合面法向刚度研究

对包含几何误差的机械结合面进行离散化,离散后的微表面的基准平面高度满足结合面几何误差分布.每个微表面内,微凸体的高度只受粗糙度的影响.基于接触理论建立了微表面的法向刚度模型,通过对微表面模型集成获得了结合面的法向刚度模型.通过对所建模型的数值仿真,揭示了结合面法向刚度与间隙的非线性关系,几何误差的幅值和波长对法向刚度的影响以及非线性刚度对结合面振动特性的影响.计算结果表明:法向刚度随着间隙的减少而迅速增加,几何误差会导致结合面宏观上的局部接触和应力集中;在相同干涉量下,法向刚度随着几何误差幅值的增加而增加,但与结合面的波长没有关系;非线性刚度会导致结合面固有频率的下降和振动位移的不对称.