Machine vision for soil roughness measurement and control of tillage machines during seedbed preparation

•A soil roughness measurement system based on stereo cameras was developed.•A correlation between surface roughness, aggregate size distribution and tillage intensity was found.•Based on roughness measurements the tillage intensity of a power harrow was controlled in real-time.•The effects of implements for tillage on aggregate size distribution and soil roughness were investigated. To address inhomogeneous soil properties during seedbed preparation, a system for site-specific tillage is proposed. The aim of this study was to develop a system to control the rotational speed of the power harrow based on visual detection of the soil roughness with a stereo camera. The basis for the control is the causal relationship between the measurement of soil roughness with stereo cameras, tillage intensity and the aggregate size distribution through dry sieving of the top seedbed. The stereo camera based roughness measurement system developed during this study, focused on robustness and real-time capabilities. Environmental influences on the measurement system were investigated and countermeasures were implemented. The measurement system outputs a roughness index which was the input for a control algorithm. The system was integrated into an ISOBUS Class III application which controls the PTO speed of a tractor in order to prepare a homogeneous soil roughness. During tests several seedbeds with different roughness were prepared with a power harrow following different primary tillage operations. The results of the study have been the basis for the development of a control-approach. The correlations between the aggregate size measured with sieve analysis and soil roughness measured by the stereo vision system was estimated to evaluate the system. Additionally, the comparison between soil roughness and tillage intensity showed high correlation. During validation of the controller, the homogenizing effect on the soil roughness could be shown.