A pragmatic framework for detecting (identifying the on-off state of) the external force applied to a construction manipulator (front load) by using a hydraulic sensor is proposed. Such a load detecting system requires high accuracy and robustness considering the uncertainty in pressure-based force measurement. The proposed framework first identifies the dominant error force component, including self-weight and driving force, using theoretical and experimental estimation and binarizes the analog cylinder external force. It then evaluates detection conditions to address indeterminate conditions such as stroke-end, singular posture, and impulsive or oscillatory force and redefines three-valued outputs such as on, off, or not determinate (ND). It finally outputs the front load decision by combining all the cylinder decisions to improve robustness through priority analysis. Experiments were conducted using an instrumented hydraulic arm. Results indicate that the proposed framework detects on, off, and ND outputs of the front load more accurately, robustly, and stably in various detection conditions.
2012 The Society of Instrument and Control Engineers