Method for estimating an external force acting on an electrohydrostatic actuator

A method for controlling an electrohydrostatic actuator, the actuator comprising a ram including a first chamber, a second chamber and a piston situated between the first chamber and the second chamber, a pump capable of injecting fluid into the chambers for controlling a movement of the piston, an electric motor driving the pump, by means of a control unit executing the following steps:

• generating a control signal to control the electric motor,
• estimating the external force acting on the electrohydrostatic actuator,
• determining a correction variable of the control signal depending on the estimated external force, and
• applying the correction variable to the control signal, so as to limit the fluid pressure difference between the chambers of the ram, the estimation of the external force comprising the steps of:
• estimating, by means of at least one state observer, a dynamic component and a static component of an equivalent fluid pressure difference between the first chamber and the second chamber from a rotation speed of the electric motor, a position of the piston and a supply current of the electric motor,
• estimating said external force by means of a post-processing module as a combination of the dynamic component and of the static component of the estimate fluid pressure difference.