Study Of Control Method For Underactuated Deformable Trusses Mechanism

Under-actuated mechanism has more degrees of freedom than its independentcontrol inputs. Some joints are passive joints or free joints because there are noactuating devices, motors for instance, in them. Different with full-actuatedmechanisms, under-actuated mechanisms have less actuating devices so that theyhave more advantages, such as slighter weight, lower cost, more compact structure,etc. Besides, the control method of an under-actuated mechanism is more complexthan that of a full-actuated mechanism, so it becomes a beneficial issue to study thecontrol method of under-actuated mechanisms. The studied object of this paper isunder-actuated deformable trusses mechanism. The dynamic model of thisunder-actuated deformable trusses mechanism is established. Based on this model,some common principles of under-actuated mechanisms have been analyzed, andthen control methods are proposed and simulated. The main content is as follows:First and foremost, the physical structure of under-actuated deformable trussesmechanism is presented. Based on this structure, the dynamic model of thisunder-actuated deformable trusses mechanism is established by using Lagrangemechanics method along with plural vector method. The impact of gravity isconsidered so that it is also suitable if the mechanism is put inverted vertically.Moreover, some common principles, or called properties, of under-actuatedmechanisms are analyzed by transforming the dynamic model into the form ofaffine nonlinear system. The properties include equilibrium points, non-integrityand stabilizability, which are important for the design of control methods.Besides, with the foundation of dynamic model and some properties, themotion interval of under-actuated deformable trusses mechanism is divided into twoparts. And the control goal is considered as being stabilized in the verticalequilibrium point. To achieve this goal, feedback linearization method is considered.We first make the nonlinear model linearized in the equilibrium point, and designcontrol methods by using linear system theory. The method of pole placement andLQR are utilized in this paper and control rules are proposed.Last but not least, based on the control rules and the original nonlineardynamic model, simulation is conducted in MATLAB environment by buildingsimulink models. The result shows that the feedback control rule can realize thegoal of stabilization in the vertical equilibrium point and the system hasanti-interference ability, which means that this method is correct and effective.