Control and Stability Analysis of Practical Load-Sense Systems

摘要

complete hydraulic load sense system such as that found in an excavator is a naturally complex model. Components such as the engine, hydraulic pump, valves, uncertain load dynamics as well as uncertain operator behavior can instigate instability in various ways in a complex load-sense system. Many researchers has confronted this situation in different ways. Most of these papers ignored some practical aspects such as effect of load-sense control spool area etc. For a typical load sense system if the engine speed is assumed to be constant, the operator input to the valve is the only external input or effect into the system that drives the stability of the whole system. The variation in the load could be considered as external disturbance. Even though it is possible to formulate a control algorithm with one input for the whole system, the analytical solution would be very difficult to obtain because of the complexity of the involved nonlinear dynamics. Therefore to simplify the scenario, we considered two control elements: a) operator input and b) effective opening area of the load sense spool. In this paper, we have considered a typical load sense system with PC, LS spool, servo and bias piston as well as swash plate kit. For simplicity the valve (which is operated by operator somewhat directly) is replaced with a variable area orifice controlled by operator input. We also consider a single acting hydraulic actuator with variable load to demonstrate the effectiveness of the control law through simulation. The paper will start with Chapter 1 –Introduction, where the motivation and objective of the authors are presented. This chapter will also contain a relevant literature review in context of the content of the paper. The Chapter 2 will describe the differential equations involved in a typical load-sense system. The chapter will also define the states and a state space model of the system. Chapter 3 will discuss the control objectives which is partial back-stepping control. We will discuss how a partial back-stepping could be applied to derive the proposed control algorithm. In Chapter 4, a simulation is conducted to show the usefulness of the control law discussed in Chapter 3 and finally, some concluding remarks.