A new approach to automatic basecutter height control : SRDC final report BS81S
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The three and a half year project to develop a basecutter height controller utilising basecutter speed as the height sensor was completed in December 1995. Initial testing of basecutter speed variations with basecutter height setting on both underslung and leg basecutters confirmed that there was sufficient sensitivity for use of basecutter speed as a control mecahnism. These tests also indicated that an allowance should be made for harvester cutting speed effects on basecutter speed. A prototype controller was developed based on the cane loss monitor circuitry from Agridry Rimik and fitted to the BSES harvester at Bundaberg. The proportional electric\hydraulic control valve fitted to the harvester was utilised in conjunction with the controller for adjusting basecutter height.Initial testing of basecutter speed variations with basecutter height setting on both underslung and leg basecutters confirmed that there was sufficient sensitivity for use of basecutter speed as a control mechanism. These tests also indicated that an allowance should be made for harvester cutting speed effects on basecutter speed.A prototype controller was developed based on the cane loss monitor circuitry from Agridry Rimik and fitted to the BSES harvester at Bundaberg. The proportional electric/hydraulic control valve fitted to the harvester was utilised in conjunction with the controller for adjusting basecutter height.During the 1993 season testing of the prototype controller was carried out and a number of software changes were made to improve controller performance. Response time of the proportional valve was also reduced from 300 mS to 100mS by fitting a faster controller. The controller was also modified to allow logging of the different control functions including basecutter speed, control setting, harvester forward speed and controller function. Checking of changes in basecutter speed with basecutter height and harvester forward speed allowed refinement of the control software. Ramp tests were also carried out to determine speed of response to sudden changes in row height. It was found that the controller took some time to adjust for these changes - approximately6 8 metres for a sudden lowering of row height and approximately 4 for a sudden raising of row height. This means that the controller is not capable of adjusting for sudden changes in row height in the field such as washouts. This finding is likely to apply to all similar systems due to the need for averaging control signals and hysteresis in the control hydraulics.Following the 1993 season the controller was modified and fitted to commercial harvesters at Bundaberg, Mackay and Proserpine. These included a wheeled Cameco, a full track Austoft 7000 with an underslung basecutter and a full track Austoft 7700 with leg basecutter, respectively. Field testing of the controller was carried out in each district and this highlighted two problems: basecutter speed was affected by the extra lading on the harvester in lodged cane and by large changes in soil hardness within a field. This caused the controller to raise the basecitter and leave stubble in lodged sections of the cane row or at boundaries of soil types within a block. A sensitivity adjustment was tested late in 1994 to attempt to overcome the soil type effect.the project was extended into the 1995 season to allow full evaluation of the sensitivity control, and to test the value of adjusting the basecutter rpm set point for changes in engine rpm. It was felt that this may allow for the loading effect of lodged cane on basecutter rpm. During 1995 further testing was carried out at Bundaberg, Mackay and Proserpine. In mid season the Mackay controller was shifted to an Austoft 7700 harvester in Tully to obtain mill soil in cane readings with and without automatic basecutter height control.