Drawbar Forces Research Articles

DEM simulation of stress transmission under agricultural traffic Part 3: Evaluation with field experiment

In a concurrent paper, we compared a continuum model and a discrete element method (DEM) model in simulating stress transmission in soil under a wheel. Here, those models are evaluated with measurements of vertical normal stress (σz) under the wheels of a tractor-slurry spreader setup. It was found that the variation in the measured σz could be explained by the heterogeneous stress distribution in our structured soil, similar to what is observed in the DEM simulation. Furthermore, comparison of the continuum and DEM model showed that the lack of horizontal forces and dynamic load transfer at the boundary condition in the continuum model lead to a systematic underestimation of the measured σz. Traction and drawbar forces have a significant impact on the stress state under a wheel. The continuum model and its boundary conditions should be modified to include these forces accurately.

DEM simulation of stress transmission under agricultural traffic Part 1: Comparison with continuum model and parametric study

The discrete element method (DEM) is an appealing technique to study the effect of wheel loads and traction on the soil. Unlike in continuum-based soil mechanics, the soil is modelled as an assembly of particles, which move and interact with each other and transmit stress through force chains. In this study, the simulation of stress transmission under wheeling with the continuum method and with DEM was compared. Both methods showed a good agreement in the simulation of the vertical normal stress. The horizontal stresses were strongly different due to traction and draw-bar forces. Stresses in the DEM simulation were transmitted via a heterogeneous network of force chains: there was a coexistence of a distinct load-bearing and a dissipative force network in the shallow layers. Furthermore, the effect of the DEM material parameters (normal and shear stiffness and cohesion, and friction angle), wheel radius and traffic speed on the transmission of stress was evaluated. The normal and shear stiffness mainly influenced the depth of the stress transmission, and the friction angle influenced the horizontal stress transmission. The wheel radius influenced the stress distribution in the topsoil, but did not have a significant effect in deeper layers. Contrary to findings in literature on soil compaction, the increased traffic velocity caused higher stresses. DEM allows to simulate the geomechanical process of soil compaction and can give more insight in the role of heterogeneous stress transmission.

Power delivery efficiency of a wheeled tractor at oblique drawbar force

The offset position of an implement creates an oblique drawbar force. This force occurs when the resistance direction of the implement is at a certain angle with respect to the longitudinal axis of the tractor (tractor traction direction). The focus of this study was to demonstrate the dependence of wheeled tractor power delivery efficiency on wheel slippage for central and oblique drawbar forces, both on plowed and unplowed stubble. For this purpose, the travel speed of tractor, wheel slippage, drawbar force and engine speed were measured. Mathematical models were formed using a nonlinear regression analysis, and after that, an algorithm for calculating the power delivery efficiency of wheeled tractors depending on the drawbar force and the angle of the drawbar force was developed. This method allowed us to determine the dependence of the power delivery efficiency on the wheel slippage for different angles of the drawbar force. The highest power delivery efficiency of a tractor is achieved at a central drawbar force (angle of the oblique drawbar force equals zero). Results showed the influence of oblique drawbar force on the power delivery efficiency of the wheeled tractor on soft and loose types of soil. Power delivery efficiency of the tractor on unplowed stubble decreased by 6.7% when the angle of the oblique drawbar force increased to 10 degrees, and by 15.0% when the angle of the oblique drawbar force increased to 20 degrees. On plowed stubble, power delivery efficiency decreased by 10.4% at a 10 degree angle of oblique drawbar force and by 21.9% at an angle of oblique drawbar force of 20 degrees. The importance of properly attaching the implement to the tractor was also confirmed.

Research Trends for Performance, Safety, and Comfort Evaluation of Agricultural Tractors: A Review

Department of Biosystems Machinery Engineering, Chungnam National University, Daejeon, Korea Machinery Technology Group, Advanced RD Revised: January 28th, 2014; Accepted: January 28th, 2014 Background: Significant technological development and changes happened in the tractor industries. Contrariwise, the test procedures of the major standard development organizations (SDO’s) remained unchanged or with a little modification over the years, demanding new tractor test standards or improvement of existing ones for tractor performance, safety, and comfort. Purpose: This study focuses on reviewing the research trends regarding performance, safety and comfort evaluation of agricultural tractors. Based on this review, few recommendations were proposed to revise or improve the current test standards. Review: Tractor power take-off power test using the DC electric dynamometer reduced human error in the testing process and increased the accuracy of the test results. GPS signals were used to determine acceleration and converted into torque. High capacity double extended octagonal ring dynamometer has been designed to measure drawbar forces. Numerical optimization methodology has been used to design three-point hitch. Numerous technologies, driving strategies, and transmission characteristics are being considered for reducing emissions of gaseous and particulate pollutants. Engine emission control technology standards need to be revised to meet the exhaust regulations for agricultural tractors. Finite Element Analysis (FEA) program has been used to design Roll-Over Protective Structures (ROPS). Program and methodology has been presented for testing tractor brake systems. Whole-body vibration emission levels have been found to be very dependent upon the nature of field operation performed, and the test track techniques required development/adaptation to improve their suitability during standardized assessment. Emphasizes should be given to improve visibility and thermal environment inside the cab for tractor operator. Tractors need to be evaluated under electromagnetic compatibility test conditions due to large growing of electronic devices. Research trends reviewed in this paper can be considered for possible revision or improvement of tractor performance, safety, and comfort test standards.

Identification of Toolholder-Spindle Joint Based on Receptance Coupling Substructure Analysis

Stiffness identification of toolholder-spindle joint is a basic work for machine tool dynamic research. In this paper, an identification method based on receptance coupling substructure analysis is described. Once the frequency response functions of the toolholder, the spindle and the toolholder-spindle assembly are obtained, the analytical stiffness could be calculated. The method is verified efficiency through dynamic response experiment. Identified stiffness results under different drawbar forces are also discussed.

Influence of eccentric drawbar force on power delivery efficiency of a wheeled tractor

Power delivery efficiency shows how much engine power is used for a tractor drawbar. Eccentric traction is a factor influencing the power delivery efficiency of a wheeled tractor. It occurs as a consequence of the offset position of a tractor implement, that is, when the traction line of the tractor and resistance line of the implement are parallel and do not coincide. This paper presents research on the power delivery efficiency of wheeled tractors and its dependence on wheel slippage of central and eccentric drawbar forces on unplowed and plowed stubble. For this purpose, mathematical models and one algorithm were developed. The best power delivery efficiency of the tractor on both unplowed and plowed stubble surfaces was obtained with central drawbar force. Power delivery efficiency of the tractor on unplowed stubble decreased by 5.72% if eccentricity increased up to 0.16 m and by 12.33% if eccentricity increased up to 0.32 m. Power delivery efficiency of the tractor on plowed stubble decreased by 8.88% if eccentricity increased up to 0.16 m and decreased by 19.05% if eccentricity increased up to 0.32 m.

Mechanical Design of Robotic In Vivo Wheeled Mobility

A new approach to laparoscopic surgery involves placing a robot completely within the patient. These in vivo robots are then able to provide visual feedback and task assistance that would otherwise require additional incisions. Wheeled in vivo robots can provide a mobile platform for cameras, graspers, and other sensory devices that assist in laparoscopy. Development of wheeled in vivo mobile robots was achieved through a design process that included modeling, finite element analysis (FEA), bench top testing, and animal tests. Laboratory testing using a wheel test platform identified a helical wheel design as the best candidate. Finite element simulations were then used to better understand how changing the helical wheel geometric parameters affected drawbar force. Several prototype mobile robots were then developed based on these results. The drawbar forces of these robots were measured in the laboratory to confirm the FEA results. Finally, these robots were successfully tested during animal surgeries.

Double extended octagonal ring (DEOR) drawbar dynamometer

A drawbar dynamometer is required to measure drawbar forces in field research on energy inputs for agricultural field equipment. In this study, a 2D double extended octagonal ring (DEOR) drawbar dynamometer with a draft capacity of 180 kN was developed. The two extended octagonal rings were oriented vertically on either side of the tractor drawbar which provided a better match of strain to expected drawbar draft and vertical load than could be achieved with a horizontal orientation in previous designs. Strain distributions in the extended octagonal rings were analyzed using a finite element method to locate optimal strain gage positions to minimize cross sensitivity between draft and vertical force measurements. The DEOR was fabricated from high strength ANSI 4130 steel. Vertical and draft calibrations of the DEOR dynamometer were done in a laboratory universal testing machine. Calibration results show that the DEOR dynamometer had a linearity of 0.99 and negligible cross sensitivity for both horizontal and vertical outputs. The DEOR dynamometer was tested in a field to measure the draft and vertical force of a sweep-type liquid manure injector. No mechanical problems were observed for the dynamometer in the field test and its draft outputs were comparable to those reported in the literature for manure injectors.

Modeling the HSK Toolholder-Spindle Interface

The HSK toolholder-spindle connection was developed to overcome shortcomings of the 7/24 steep-taper interface, especially at higher speeds. However, the HSK system was standardized quickly, without detailed evaluation based on operational experience. Several issues concerning the reliability, maintainability, and safety of the interface have been raised within the international engineering community. This study was undertaken to analytically investigate factors which influence the performance and limitations of the HSK toolholder system. Finite Element Models were created to analyze the effects of varying toolholder and spindle taper geometry, axial spindle taper length, drawbar/clamping load, spindle speed, applied bending load, and applied torsional load on HSK toolholders. Outputs considered include taper-to-taper contact pressures, taper-to-taper clearances, minimum drawbar forces, interface stiffnesses, and stresses in the toolholder. Static deflections at the end of the holder predicted by the models agreed well with measured values. The results showed that the interface stiffness and load-carrying capability are significantly affected by taper mismatch and dimensional variations, and that stresses in the toolholder near the drive slots can be quite high, leading to potential fatigue issues for smaller toolholders subjected to frequent clamping-unclamping cycles (e.g., in high volume applications). The results can be used to specify minimum toolholder material properties for critical applications, as well as drawbar design and spindle/toolholder gaging guidelines to increase system reliability and maintainability.

The Effect of Drawbar Force on Metal Removal Rate in Milling

The metal removal rate in milling is often limited by the tool-spindle dynamics. Higher stiffness and damping as seen at the tool tip allow higher metal removal rates. While increasing the drawbar force leads to greater static stiffness in the tool-spindle interface, dynamic measurements indicate that higher drawbar forces also diminish the damping. Whether higher drawbar force is beneficial for stable metal removal depends on whether the gain in stiffness is greater than the loss in damping. This paper presents test-stand measurements of stiffness and damping for tool holder-spindle interfaces at various drawbar forces, and similar measurements in spindles.

Mathematical modelling to simulate the transient dynamic longitudinal force in draw bars of a train-consist

This paper deals with the theory and development of a computer-oriented mathematical model to determine the transient response and coupling (draw-bar) forces of a train-consist subjected to different train handling conditions. The longitudinal motion is assumed to take place independently and the equations of motion for the system are set up in a matrix form. A transfer matrix method is adopted to determine the free vibration characteristics. The response of the system due to the transient forces is obtained by modal analysis with account taken altogether of five modes, including the rigid body mode. The displacement response and the draw-bar forces obtained for a typical train-consist are presented in tables and figures. The computer programs developed can be used to lay down train handling and make up procedures to avoid possible dangerous conditions of draw-bar failures. For a typical train-consist, trial runs to observe the draw-bar failures under certain severe conditions of driving were conducted. Dynamometer records were made next to the locomotive of a freight train for different conditions of train handling. For a specific train-consist the results obtained from the mathematical model are compared with the field data collected and a reasonably close agreement has been observed.

Draft Reduction by Vibratory Soil Cutting

With the increasing size of cultivating and excavating equipment, engineers have been faced with the problem of transmitting large drawbar forces, yet keeping the weight of tractors or machines to a minimum. This paper shows how draft forces can be reduced significantly by vibrating the soil-cutting blade. A fully instrumented laboratory testing facility was designed and constructed to test various types of vibrating blades. A carriage, which was pulled the length of the test bed along two parallel shafts by a hydraulic motor, supported a hydraulic servo-valve, actuator, and linkage which vibrated the blade. It was possible to conduct tests in three modes of vibration; horizontal, vertical, and at 45 degrees. Draft was recorded by a strain gauge force transducer attached to the carriage. Preliminary testing of a knife-edged, vertical blade for laying underground cable was undertaken. The blade, which was pulled at a depth of 9 in., was vibrated at frequencies up to 30 Hz and amplitudes (zero to peak) up to 1.0 in. It was found, for example, that a frequency and amplitude of 10 Hz and 0.5 in., respectively, yielded draft force reductions as high as 80%.