An electro-hydraulic servo system is a feedback control system that operates based on the principle of error-driven control. In practical operation, factors such as the inertia of the load and system components, as well as the compressibility of the hydraulic fluid, mean that the output does not change instantaneously in response to a change in the input signal; instead, a transitional process occurs. During this process, the system output and the states of its various components change over time-a phenomenon known as a transient or dynamic process. If the system reaches a new equilibrium state after the dynamic process concludes, this state is referred to as the steady state or static state.
Generally, oscillations within a system diminish over time due to energy loss, allowing the system to quickly reach a steady state. However, if the inertia of the piston-load assembly is high, fluid compressibility is increased by entrapped air, the rigidity of hydraulic cylinders and lines is insufficient, or the system structure and component parameters are poorly selected, oscillations may persist or even intensify, rendering the system inoperable. A system exhibiting such behavior is considered unstable. Consequently, stability is the primary requirement for an electro-hydraulic servo system; an unstable system cannot function at all. Beyond stability, system performance is evaluated based on three key criteria: stability, speed, and accuracy. Stability and speed characterize the performance of the transient process-ideally, the system should be both fast and stable. High dynamic accuracy is indicated when the output deviates minimally from the desired value and the duration of this deviation is short. Additionally, the steady-state error must remain within permissible limits for the control system to be of practical value-this corresponds to the requirement for accuracy. Thus, a high-quality electro-hydraulic servo system must demonstrate stability, speed, and accuracy throughout the entire control process.
