Loads on the Hydraulic Cylinders of a Trailed Stone Picker Determined from the Kinematics of Its Mechanisms: Hopper Lifting and Tipping, Drawbar Lifting and Working Unit Folding

A trailed stone picker lifts and tips a hopper holding several tonnes of stones, raises its front on the drawbar and folds its working units using hydraulic cylinders supplied by the tractor at 180–200 bar. Whether a cylinder works safely within the relief valve setting depends on the driven mechanism’s geometry, not only on cylinder size. Cylinder forces and pressures in the SCS-100 machine were determined from mechanism kinematics using the principle of virtual work and independently verified from static equilibrium (agreement within 10−9). The hopper lifting mechanism, reconstructed from the manufacturer’s drawings as a parallelogram linkage, reproduced the documented lifting height, height increase during tipping and discharge angle. At the rated payload of 6 t, the lifting and tipping cylinders require 147–159 bar, a margin of 1.13–1.23 relative to the 180 bar setting. The drawbar lifting cylinders are critical: with an empty hopper, they require 195–207 bar. The folding cylinders require at most 65 bar. Monte Carlo analysis, including joint friction, confirmed this ranking; abruptly stopping lowering can raise the pressure trapped by the counterbalance valves by about 100 bar. Drawbar lifting with an empty hopper is therefore predicted to govern hydraulic safety; this prediction requires confirmation by measurement.