Publication news

Soft soil track interaction modeling in single rigid body tracked vehicle models

P. Edwin, K. Shankar, K. Kannan

Volume 77, June 2018, Pages 1-14, ISSN 0022-4898
https://doi.org/10.1016/j.jterra.2018.01.001.

Abstract: Single rigid body models are often used for fast simulation of tracked vehicle dynamics on soft soils. Modeling of soil-track interaction forces is the key modeling aspect here. Accuracy of the soil-track interaction model depends on calculation of soil deformation in track contact patch and modeling of soil resistive response to this deformation. An algorithmic method to calculate soft soil deformation at points in track contact patch, during spatial motion simulation using single body models of tracked vehicles, is discussed here. Improved calculations of shear displacement distribution in the track contact patch compared to existing methods, and realistically modeling plastically deformable nature of soil in the sinkage direction in single body modeling of tracked vehicle, are the novel contributions of this paper. Results of spatial motion simulation from a single body model using the proposed method and from a higher degree of freedom multibody model are compared for motion over flat and uneven terrains. Single body modeling of tracked vehicle using the proposed method affords quicker results with sufficient accuracy when compared to those obtained from the multibody model.

Keywords: Soil track interaction; Tracked vehicle

Terrain classification using ToF sensors for the enhancement of agricultural machinery traversability

Francisco Yandun Narváez, Eduard Gregorio, Alexandre Escolà, Joan R. Rosell-Polo, Miguel Torres-Torriti, Fernando Auat Cheein

Volume 76, 2018, Pages 1-13, ISSN 0022-4898,
https://doi.org/10.1016/j.jterra.2017.10.005.

Abstract: Ground properties influence various aspects of mobile machinery navigation including localization, mobility status or task execution. Excessive slipping, skidding or trapping situations can compromise the vehicle itself or other elements in the workspace. Thus, detecting the soil surface characteristics is an important issue for performing different activities in an efficient, safe and satisfactory manner. In agricultural applications, this point is specially important since activities such as seeding, fertilizing, or ploughing are carried on within off-road landscapes which contain a diversity of terrains that modify the navigation behaviour of the vehicle. Thus, the machinery requires a cognitive capability to understand the surrounding terrain type or its characteristics in order to take the proper guidance or control actions. This work is focused on the soil surface classification by implementing a visual system capable to distinguish between five usual types of off-road terrains. Computer vision and machine learning techniques are applied to characterize the texture and color of images acquired with a Microsoft Kinect V2 sensor. In a first stage, development tests showed that only infra-red and RGB streams are useful to obtain satisfactory accuracy rates (above 90%). The second stage included field trials with the sensor mounted on a mobile robot driving through various agricultural landscapes. These scenarios did not present illumination restrictions nor ideal driving roads; hence, conditions can resemble real agricultural operations. In such circumstances, the proposed approach showed robustness and reliability, obtaining an average of 85.20% of successful classifications when tested along 17 trials within agricultural landscapes.

Keywords: Agricultural robotics; Terrain classification; Pattern recognition

Driving force distribution based on tyre energy for independent wheel-drive vehicle on rough ground

Ryosuke Eto, Kazuomi Sakata, Junya Yamakawa
Journal of Terramechanics, Volume 76, 2018, Pages 29-38, ISSN 0022-4898
https://doi.org/10.1016/j.jterra.2017.10.007.


Abstract: 
The driving force of a wheel is an important factor to determine the travelling performance of vehicles on rough grounds. An excessive driving force induces a large slip, whereas insufficient driving force prevents vehicles from overcoming obstacles. Hence, an optimum driving force distribution is necessary to improve the travelling performance of off-road vehicles on rough grounds. In this study, the driving force distribution method of four independent wheel-drive vehicles based on the energy-loss ratios of the wheels is proposed. The squared sum of the energy-loss ratios is minimized in the proposed method. To validate the proposed method, travelling tests were conducted using a model vehicle on a rough and rigid ground and a soft ground. Moreover, simulation tests were performed on a rough and rigid ground. The results obtained using the proposed method were compared with those of the distributions based on the tyre workload, even force, and wheel-velocity control. The experimental and simulation results confirm that the proposed method is the most efficient for vehicles moving on a rigid ground. The movement of the vehicle on the soft ground was the most stable when the proposed method was employed.
Keywords: Off-road vehicle; Driving force distribution; Slip; Rough ground; Driving efficiency

Experimental and DEM analyses on wheel-soil interaction, Journal of Terramechanics

Mingjing Jiang, Yongsheng Dai, Liang Cui, Banglu Xi
Volume 76, 2018, Pages 15-28, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.12.001.


Abstract: 

In this paper, the wheel-soil interaction for a future lunar exploration mission is investigated by physical model tests and numerical simulations. Firstly, a series of physical model tests was conducted using the TJ-1 lunar soil simulant with various driving conditions, wheel configurations and ground void ratios. Then the corresponding numerical simulations were performed in a terrestrial environment using the Distinct Element Method (DEM) with a new contact model for lunar soil, where the rolling resistance and van der Waals force were implemented. In addition, DEM simulations in an extraterrestrial (lunar) environment were performed. The results indicate that tractive efficiency does not depend on wheel rotational velocity, but decreases with increasing extra vertical load on the wheel and ground void ratio. Rover performance improves when wheels are equipped with lugs. The DEM simulations in terrestrial environment can qualitatively reproduce the soil deformation pattern as observed in the physical model tests. The variations of traction efficiency against the driving condition, wheel configuration and ground void ratio attained in the DEM simulations match the experimental observations qualitatively. Moreover, the wheel track is found to be less evident and the tractive efficiency is higher in the extraterrestrial environment compared to the performance on Earth.

Keywords: Wheel-soil interaction system; TJ-1 lunar soil simulant; Contact model; DEM simulation; Tractive efficiency
 

Dynamics modeling and robotic-assist, leader-follower control of tractor convoys

Joshua T. Cook, Laura E. Ray, James H. Lever
Journal of Terramechanics, Volume 75, 2018, Pages 57-72, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.05.002.

Abstract: 
This paper proposes a generalized dynamics model and a leader-follower control architecture for skid-steered tracked vehicles towing polar sleds. The model couples existing formulations in the literature for the powertrain components with the vehicle-terrain interaction to capture the salient features of terrain trafficability and predict the vehicles response. This coupling is essential for making realistic predictions of the vehicles traversing capabilities due to the power-load relationship at the engine output. The objective of the model is to capture adequate fidelity of the powertrain and off-road vehicle dynamics while minimizing the computational cost for model based design of leader-follower control algorithms. The leader-follower control architecture presented proposes maintaining a flexible formation by using a look-ahead technique along with a way point following strategy. Results simulate one leader-follower tractor pair where the leader is forced to take an abrupt turn and experiences large oscillations of its drawbar arm indicating potential payload instability. However, the follower tractor maintains the flexible formation but keeps its payload stable. This highlights the robustness of the proposed approach where the follower vehicle can reject errors in human leader driving.


Keywords: Multi-body dynamics; Tracked vehicle; Leader-follower control
 

ROPS designs to protect operators during agricultural tractor rollovers

Paul Ayers, Farzaneh Khorsandi, Xinyan Wang, Guilherme Araujo
Journal of Terramechanics, Volume 75, 2018, Pages 49-55, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.05.003.


Abstract: Although it is well known that properly used Rollover Protective Structures (ROPS) can virtually prevent agricultural tractor rollover fatalities, the U.S. still has hundreds of these fatalities per year. An estimated 1.6 million tractors are not equipped with ROPS. Many of these tractors do not have ROPS commercially available although they were originally designed to support a ROPS. Some tractors have foldable ROPS that are not used properly. Other ROPS, although meet appropriate performance standards, are not effective at eliminating continuous rolls. To meet this need, a Computer-based ROPS Design Program (CRDP) was developed to quickly generate ROPS designs based on agricultural tractor weights and dimensions. The ROPS designed with the CRDP for the Allis Chalmers 5040 tractor successfully passed the SAE J2194 static longitudinal, transverse, and vertical tests. A simple foldable ROPS lift assist was designed and tested to ease in the raising and lowering of ROPS; decreasing the raising torque from 90Nm to less than 50Nm, while also lowering the resisting torque to lower the ROPS. A model to determine the critical ROPS height CRH based on off-road vehicle dimensions and center of gravity (CG) height was developed and evaluated.


Keywords: ROPS; Tractor rollover; Foldable ROPS

Modeling the effect of liquid movement on the center of gravity calculation of agricultural vehicles


Farzaneh Khorsandi, Paul D. Ayers, Robert S. Freeland, Xinyan Wang
Journal of Terramechanics, Volume 75, 2018, Pages 37-48, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.09.005.

Abstract: Due to a high center of gravity (CG) location, agricultural vehicles are more vulnerable to overturns. The CG location can be calculated using the lifting axle method of ISO 16231-2:2015. But, as a vehicle is lifted, its liquid payloads are not entirely contained. The liquids will shift both in position and form, affecting the CG height calculation. A mathematical model was developed to predict the effect of liquid movement on the CG height calculation of a tilted vehicle. The model was validated using an agricultural utility tractor and a prototype. The developed model was applied to calculate the CG location considering the effect of the liquid shift. Results showed tilting produced a higher calculated center of gravity due to liquid movement, but by increasing the tilting angle, the calculated CG height decreased. The effect of the liquid shift on CG height measurement for the wagon with 16.0% liquid mass was 14.8% and for the tractor with 1.2% liquid mass was 0.41%. The model error was less than 1.3% for all tests. Considering the effect of the liquid shift in CG height calculation, the error in CG height calculation decreased from 11.9% to 2.6% for the wagon.


Keywords: Center of gravity; Stability; ISO 16231-2:2015; Liquid shift; Tractor; Overturn; Safety

Development of a dynamic simulation model of a towed seeding implement

Ian W.P. Paulson, Allan T. Dolovich, Scott D. Noble
Journal of Terramechanics, Volume 75, 2018, Pages 25-35, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.10.006.

Abstract: As the size of western Canadian farms increase and the productivity demands on seeding equipment rise, improvement in the depth consistency performance of seeding implements at higher seeding speeds is a future focus of equipment designers. The objective of this work was to develop a dynamic simulation tool for predicting the motion of a hoe-opener style seeding implement with independent row units. The model was developed using simple low-order models available in the literature to compute the forces generated at soil-tire and soil-tool interfaces. By maintaining low computational cost, early-stage parameter sensitivity and design trade-off studies can assess the risk of a given design change. The amplitude of the power spectral density (PSD) of simulated row unit motion was typically lower with sharper peaks than measured results up to 3.3 m/s; these differences were due to both input amplitude differences, and the sensitivity of the model itself. Frequency agreement of major measured and simulated PSD peaks was acceptable considering the model simplifications. Row unit motion was dominated by two phenomena – a strong periodic input in the terrain surface, and feedback between the hoe-opener and packer wheel of the row unit.


Keywords: Vehicle dynamics; Soil-tire interaction; Soil-tool interaction; Vibration; Seeding depth

The Hohenheim Tyre Model: A validated approach for the simulation of high volume tyres – Part II: Validation

Paul Witzel
Journal of Terramechanics, Volume 75, 2018, Pages 15-24, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.09.004.

Abstract: 
This publication series describes the development of the Hohenheim Tyre Model – an approach that considers the properties of high volume, agricultural tyres. The research project was conducted in accordance with the V-Model, which proposes a standardised development methodology for mechatronic systems. The previous publication described amongst others the model structure and parameterisation. This paper elucidates the validation, which is an essential part of the V-Model. Validation received special attention and is divided into three parts. First, three-dimensional tyre behaviour on level surfaces was investigated. Within the second step, single tyre behaviour is validated during obstacle passages. Similar obstacles were then used in the final step that shows up the correlation between measured and simulated whole vehicle behaviour. Throughout the validation avery high level of accuracy is achieved.


Keywords: Tyre model; Handling; Comfort analysis; Multi-body simulation