Pneumatic positioning systems (PPS) are widely used in fields were mechatronics applications exist. In order to improve the performance and robustness, either by designing new controllers or studying other characteristics of PPSs under different load conditions, a test bench with a load simulator is required. Hydraulic load simulators (HLS) are one of the most significant applications of hydraulic force control systems. The HLS aims to control the forces according to static and dynamic requirements. Typically, a force control system interacts with the external environment such that a good performance and robustness are not easily achieved. Different approaches are being discussed in the literature consisting on increasing the system compliance. System compliance can be controlled or modified in active or passive ways. Active compliance is obtained by force-based feedback control, allowing more flexibility to perform tasks where compliance is required. On the other hand, passive compliance is typically obtained by introducing mechanical elastic components between the actuator and the environment. In this paper, the influence of PPS compliance in the force controlled tuning of HLS is discussed. Because HLS is applying a controlled force against to a very compliant system like a pneumatic system, stable force responses could be expected. However, the dynamic interaction between the HLS with the PPS effected the force responses. This paper focuses in analyzing these effects, highlighting the design of PI and QFT controllers for force control based on these characteristics. Both of Systems are analyzed mathematically via simulation.

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