An innovative flexible head for the harvesting of cardoon (Cynara cardunculus L.) in stony lands

Abstract

Cardoon (Cynara cardunculus L.) is a promising crop for utilizing marginal lands. In these terrains, the lack of adequate tillage or soil levelling and the excessive presence of stones requires a high cutting height during harvesting, with remarkable biomass loss occurring. CREA-ING designed a new flexible bar driven by a system for sensing and signalling the presence of obstacles during the forward of motion of a combine harvester. A test-track was prepared to monitor the activation sequence of three sensor systems placed on the cutter bar as follows: four piston transducers measuring the flexion of the blade and counter-blade, two opposite wire transducers computing the movements of the blade-holder hinged on the left and right side of the frame, and one wire transducer placed between the head and the combine for measuring the lifting of the head operated by the hydraulic system. The combine was driven at an average speed of 0.7 km h−1 on a row of progressively higher obstacles (from 10 to 40 cm) placed in lateral, intermediate and central positions. The tests were carried out in the left half of the cutter bar. The output sent by the different sensors varied as a function of their position and the position of the obstacle, thus highlighting that the presence of an obstacle was correctly perceived by the sensor system. The signals originated from the left and right transducers had opposite trends. At the narrow “bell-shape” showed by the graph of the left transducer corresponded to a “reversed” bell generated by the right transducer, thus representing graphically the flexibility of the bar. The four piston transducers detected the necessary flexion, then lift and return the cutter bar to the starting point in response to each obstacle. The head lifting varied from 1.25 s to 2.51 s, but a threshold value could be observed as follows: below 25 cm the lifting occurred between 1.0 s and 1.5 s, while for higher obstacles the head lifting required 2.0–2.5 s. Such movement was the result of the signals sent by the sensors to the control unit before the head lifting began. The difference between the input sent by the transducers and the head lifting ranged from 1.22 s to 2.54 s in relation to the position of the obstacle. The tests showed that the head elements activated efficiently during the overcoming of an obstacle. However, if increasing speeds are needed, the reduction of ΔAct or Dsig will require a modification of the electrohydraulic components.