The dynamics of towed seeding equipment
Date
2017-04-25
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Degree Level
Masters
Abstract
Seed depth consistency is a critical performance metric of agricultural seeding equipment. To improve productivity, equipment manufacturers have historically focused on increasing the equipment working width of hoe-opener style seeding drills (hoe drills). However, the physical limitations of hoe drill size do present a design challenge. Increasing seeding speed to improve equipment productivity continues to be a challenge for equipment designers. Most operating conditions restrict hoe-drill seeding speeds to approximately 2.2 m/s (5 mph); depth consistency generally degrades above this speed with current hoe drill technology.
This research focused on developing an understanding of why this performance degradation occurs as speed increases. The general industry hypothesis points vaguely to "excessive motion" of the components to which the soil-engaging tools connect (the row units). However, little research on the dynamics of towed agricultural implements was found in the open literature. An understanding of the mechanism(s) causing this "excessive motion" was sought during this research.
A 2-D simulation tool was developed in MATLAB to provide equipment designers with the capability to conduct performance trade-off and sensitivity studies early in the prototype stage of a project. The simulation tool was compartmentalized so that changes to equipment geometry, component-soil contact models, or hydraulic systems could be modified with little or no change to other parts of the program.
Operational data were also collected using a small plot drill based on a New Holland P2070 Precision Hoe Drill. Data were collected at multiple operating speed up to 4.4 m/s (10 mph) to characterize depth consistency issues present at higher speeds. Various geometric seed depth and hydraulic pressure settings were also tested. Kinematic parameters (acceleration, position), force, hydraulic pressure, and video of the instrumented row unit were recorded during steady-state the operation of the machine in typical seeding conditions.
Measured data aided in calibrating aspects of the simulation tool, and the tool enabled certain performance features in the measurement data to be explored further. Frequency domain acceleration power spectra revealed that row unit acceleration power was generally concentrated at two frequencies. The terrain profile of the test field contained furrows from the previous seeding operation; this resulted in acceleration power to be concentrated at a distinct speed-dependent frequency related to the furrow spacing. While somewhat expected, this indicated the general inability of the current design to attenuate terrain inputs. The small packer wheel provided little compliance between the row unit and soil, so improving the attenuation performance of the system could improve depth consistency performance in future designs.
The second major acceleration spectra feature was related to the arrangement of the hoe opener and trailing packer wheel; both rigidly connect to the row unit body. The row unit position changed when the packer wheel encountered a terrain bump or dip; this resulted in a change in the vertical position of the hoe opener located in front of the packer wheel. Immediate changes in the operating depth of the hoe opener tool resulted. Also, depth changes generally modified the terrain such that a new bump or dip was created in the soil surface preceding the packer wheel, thus creating a feedback path between the hoe opener and packer wheel.
Considering the simplifications of the 2-D model, agreement between simulated and measured data was encouraging. The frequencies of the above phenomena were in reasonable agreement throughout the speed range of interest. Power spectra amplitude differences were likely due to both input terrain differences between simulation and test terrains, and simplifications made in representing soil-tire and soil-tool contact. Future work to improve these sub-models, and to further explore the observed non-linear effect of hydraulic pressure changes would improve the predictive accuracy of the model presented.
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Keywords
simulation, dynamics, vibration, seed depth, seeding
Citation
Degree
Master of Science (M.Sc.)
Department
Mechanical Engineering
Program
Mechanical Engineering