In this study, sensorless position control of hydraulic cylinders is investigated. Direct driven hydraulics units are utilized as a prime mover. Direct driven hydraulics is a valveless pump controlled hydraulic system that uses an electric motor to drive pumps for a single actuator. This brings energy saving and controllability advantages to traditional valve controlled hydraulics. Advantages and disadvantages of various types of position sensors, which are available on the market were investigated for hydraulic cylinder application. These sensors, while accurate, have been noted to be rather expensive and not suitable for harsh environment applications. Virtual sensors can provide an alternative to physical position sensors. Using only torque and speed data received from electric motor controller it is possible to simulate the position of a cylinder, provided that all relevant parameters are known. Simulation model of direct driven hydraulic system of a mining loader test platform was realized using Matlab/Simulink Simscape blocks. Results within the simulation show that the model can reach an accuracy within a few millimeters for a single cycle. A cumulative error for repeated cycles was observed, which recommends simple cylinder end or middle point proximity sensors to be used as reference points.
Keywords: Sensorless position control, Virtual sensors, Direct driven hydraulics, Electrohydraulic actuator