Growing environmental and commercial pressures have meant that vegetable and salad producers are moving away from the use of herbicides. Whilst inter-row cultivation provides a relatively efficient method of removing weeds between crop rows, it often needs to be supported by hand labour.
Tillett and Hauge Ltd, in conjunction with Garford Farm Machinery, have developed a solution in the form of a hydraulically driven, ‘vision guided’ hoe system. Each tractor driven implement consists of precision guided hoes which automatically recognise the variable position and size of each plant.
Hydraulic fluid power is a readily available and flexible power source, allowing the system to directly use the tractor hydraulics or a separate PTO driven power pack.
Crop foliage is filmed and processed by a computer which determines high concentrations of green pixels. Based on the resulting data, a steering system accurately aligns the hoe with the average crop row centreline. The area between the rows can then be cleared by fixed blades. Weeds growing in the centre are removed by a crescent shaped blade that rotates between plants. As the exact position of individual crops along the row is determined, the control system alters the rotational speed of the blade and compensates for variations in plant pitch. This ensures that crop damage is kept to a minimum.
Each rotating blade drive includes a Rexroth type 4WRA 6 valve, a hydraulic motor and a high resolution optical position encoder. The high power density and flexibility of the hydraulic drive ensures that the hoe system performs effectively in all soil conditions. This is due to the inherent ability to rapidly increase the drive torque which maintains the instantaneous angular position. The cresent shaped blade rotates at up to 180 rpm and each row can be hoed at a rate of two plants per second.
Dr Nick Tillett from Tillett and Hauge Ltd, said: “The excellent dynamic performance of the Rexroth 4WRA 6 valve allows the angular position of the hoe to be controlled within plus or minus five degrees at a rotation speed of up to 180 rpm.”
The Rexroth drive is proportional and directional, in cetop three format without onboard electronics. Tillett and Hauges’ optimised control software combined with the standard valve dynamic performance, eliminated the need for a higher performance valve with spool position feedback.