Abstract: The independent metering control system(IMCS) increases the system's intelligence level with electronic feedback and sophisticated control strategies. However, the higher safety risk prohibits the system from wide commercial application. Towards the machinery safety standard ISO 13849, the evaluation method of the safety performance for the IMCS is presented. To address the features including multi-control DOFS, multi-variable feedback, and multi-mode switching, a safety model covering the four operating quadrants is built by the fault-tree analysis and Boolean algebra. Then, the mapping from the fault-tree model to the predefined safety structure in ISO 13849 is established, such that the calculations of the system safety level PL and its PFH_d are derived. Considering the normal controller, fault detection, and fault-tolerant control, the transformation of the safety structure from Cat.1 with the single channel to Cat.3 with dual channels is captured. The evaluation demonstrates that the PL of the IMCS only reaches the b level, which can not meet the requirements of the d level for the earth-moving machinery. By introducing fault detection,PL only increases to the c level. PL value of d or even the highest e level can be obtained by the fault-tolerant control. Complying with machine functional safety, the investigation contributes an evaluation and guidance for the control and fault diagnosis/tolerance design in the intelligent electro-hydraulic system.

Key words: independent metering control, safety performance, ISO 13849, fault-tree analysis, fault diagnosis and tolerance