Development and Validation of a Tractor Drawbar Force Measurement and Data Acquisition System (DAQ)

Abstract

ABSTRACT. Matching agricultural tractors to implements towed by the drawbar is one of the important aspects of machinery management for ensuring optimum performance and fuel cost savings. A field deployable tractor draft force measurement and data acquisition system was developed and evaluated as part of this research project. A drawbar instrumented to measure draft force in field operating conditions was developed and statically calibrated. The drawbar was calibrated by applying loads from 4.45 to 134 kN using a hydraulic cylinder connected to a 444.8 kN load cell. Testing was conducted with the drawbar installed on a tractor on a concrete track. The Nebraska Tractor Test Laboratory (NTTL) load car was used for applying draft loads to evaluate the instrumented drawbar. The track test consisted of seven loads corresponding to maximum power in seven gears. The draft forces as measured by the drawbar were compared to the draft measurements recorded by the load car. The error between draft force measurements of the instrumented drawbar and the load car measurements ranged from 0.21 kN (0.27%) to 0.99 kN (2.88%).There were no statistically significant differences between drawbar and load car measurements confirming that the drawbar force measurement and data acquisition (DAQ) system developed as part of this research can be used for field use. Keywords. Data acquisition, Draft load, Drawbar, LabVIEW, Strain gages, Tractor.he tractor drawbar is the most widely used method of towing an implement. An accurate robust method to measure the draft load developed by a towed implement had been a critical industry need for some time. Tractor tests were conducted as far back as 1908 in the Winnipeg Tractor Trials (Ellis, 1913). Some approaches for draft force measurement have included: attaching a strain gage load cell to the drawbar; or a hydraulic cylinder acting as a load cell (used by the Nebraska Tractor Test Laboratory (NTTL) for official drawbar draft measurements until being replaced by load cells in 2011); installing an instrumented drawbar pin (Zoerb et al., 1983); or instrumenting the drawbar itself (Grevis-James and Bloome, 1982). A primary benefit of these types of sensors was to minimize alterations to the tractor components while determining the amount of force generated by a towed implement. Fastening a load cell to the end of the drawbar was discounted, as such a system created a cantilevered load that affected the tractive efforts of the tractor (Zoerb et al., 1983). In addition, the load cell needed to be rigidly mounted to prevent excessive lateral movement during turning or stopping. The result was potential damage to the load cell and the tractor, as well as an unacceptable risk of personal injury to the operator. A design complication of using a load cell that would not pivot was that the load cell would prove less effective in measuring lateral loads as seen in contour or headland operations. Another method of integrating the load cell into the drawbar (proof-ring) was to permanently alter the drawbar w...

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