Lead-Lag-Shaped Interactive Force Estimation by Equivalent Output Injection of Sliding-Mode

Estimation of interactive forces, which are mostly unavailable for a direct measurement on the interface between the system and its environment, is an essential task in various motion control applications. This paper proposes an interactive force estimation method, based on the well-known equivalent output injection of the second-order sliding mode. The equivalent output injection is used to obtain a dynamic quantity, which is first not appropriately shaped in the frequency domain, but appears as a matched external disturbance that encompasses interactive forces. Afterwards, a universal lead-lag shaper, which depends on the inherent dynamics of the motion control system coupled with environment, is used to extract an interactive force quantity. Once identified, the lead-lag shaper can be applied to the given system structure. An experimental case study with valve-controlled hydraulic cylinder and dynamic load is demonstrated. An accurate estimation of the interactive force, in comparison to the reference measurement, is shown.