Electrohvdraulic System For Large-scale Power Spinning Machines

Large-scale power spinning machines (LPSMs), whose workpieces are widely used in the areas of national strategy development, such as large launch vehicles, intercontinental missiles, space satellites, wide-bodied planes, marine development equipment and new-type nuclear power stations etc., are indispensable basic equipment in manufacturing industry. The machine tool of LPSMs is spinning roller, which locally pushes a rotating blank progressively, introducing a change in its shape according to the profile of the mandrel and a reduction in its thickness. Due to the strong spinning forces for high-tensile workpieces, the motion of spinning rollers is mainly driven and controlled by an electrohydraulic system in most LPSMs. During power spinning process, the electrohydraulic system which moves spinning rollers works with the following features:1) the spinning counter-forces acting on it are high-strength, and are nonlinear with respect to feed speed; 2) the electrohydraulic system is highly nonlinear with parametric uncertainty; 3) the hydraulic actuators have to achieve centimillimetre-level (0.01mm) positioning accuracy and high-precision contouring motion control; 4) for some LPSMs with multi-roller and split-type structure, motion coordinating of spinning rollers is required, in order to improve the stress situation of the machine body and the quality of workpieces. In summary, research in depth on a high performance electrohydraulic control system for LPSMs is of academic value, practical significance and necessity.In this dissertation, taking into account the particular characteristics associated with the dynamics of the electrohydraulic system in LPSMs, especially focusing on the one with three-roller and split-type structure, relevant control technologies are studied systematically and comprehensively by means of theoretical control development, experimental research and simulation analysis. A systemic set of control technologies are proposed for the electrohydraulic system of LPSMs, including adaptive robust control (ARC) with flow force compensation for a high-response dual proportional solenoid valve (HDPSV), state observer and hydraulic passivity based ARC (SPARC)for the electrohydraulic linear axis of LPSMs, SPARC and orthogonal global task coordinate (GTC) based contouring motion control (GTC-SPARCC) for the biaxial electrohydraulic system of LPSMs, and GTC-SPARCC based coordination control technology for LPSMs with multi-roller and split-type structure. The effectiveness and performance of these technologies presented above are tested and verified through experiment or simulation. Partial research findings are already applied in practice or tested on a prototype.The outline of this thesis is as follows,Chapter 1 details the research background of the electrohydraulic control system for LPSMs, and concludes the difficulties faced in controlling the electrohydraulic system of LPSMs. The progresses of researches on the key technologies involved are reviewed. The contributions and significance of the dissertation research are summarized.Chapter 2 develops an ARC controller with flow force compensation for a HDPSV, which has the potential of gaining faster response and stronger disturbance rejection. The current-force gain of proportional solenoids is modeled by a modified tanhO function to capture its nonlinear characteristics. An incremental differential allocation strategy is raised to coordinate the action of the two proportional solenoids. The model of flow force is built with parametric uncertainty and reconstructed to address its non-differentiability. To deal with the parametric uncertainties and uncertain nonlinearities appearing in the dynamic model of the HDPSV, discontinuous projection based ARC is extended to synthesize the HDPSV controller. Both the simulation and experimental results show that with the proposed controller, the flow forces are well compensated, while the HDPSV achieves disturbance rejection, high precision, fast transient response and broad bandwidth.Chapter 3 presents SPARC for the electrohydraulic linear axis of LPSMs. The nonlinear dynamic models of the horizontal electrohydraulic linear axis and the vertical one are built. The models of spinning forces are of general form, which can be replaced by specific mathematical functions in actual applications. The large gravity load acting on the vertical axis is countered by a hydraulic balance system to improve the symmetry of control performance. The balanced deviation is treated as damping friction in the model. The balance pressure is regulated via a relief valve and a pressure reducing valve. The controller of the electrohydraulic linear axis is designed by combining hydraulic passivity theory and ARC by means of a desired pressure allocation strategy and backstepping design. A time-optimal state observer is introduced in the controller to supplement parameter adaptation. The passivity theory helps to improve the feedforward compensation for pressure dynamics. The experimental and simulation results verify that the proposed SPARC achieves well model compensation ability, strong disturbance rejection and precise control performance.Chapter 4 designs GTC-SPARCC for the biaxial electrohydraulic system of LPSMs. Combined with SPARC, orthogonal global task coordinate based contouring motion control theory is extended to synthesize GTC-SPARCC for the biaxial electrohydraulic system of LPSMs, which has 3-order dynamics. GTC-SPARCC inherits the advantages of SPARC and GTC based contouring motion control theory. Thus it not only achieves the excellent ability of coordinating contouring control and tracking control, but also gains the superiority of SPARC. Finally, the effectiveness of GTC-SPARCC is validated by both experiment and simulation.Chapter 5 gives a coordination control strategy for LPSMs with multi-roller and split-type structure. The motion rules for spinning rollers are summarized according to processing technic in actual spinning. Based on GTC-SPARCC and considering the motion rules, a feasible and effective coordination control strategy is proposed. The working planes for every spinning roller are projected around the central axis of workpieces onto a single plane, where the spinning rollers are sequenced in the light of their distance away from the desired point. According to their sequence and contour error, every roller is assigned its tracing target. When the spinning rollers move following the strategy, global stability is guaranteed. Taking a LPSM with three-roller and split-type structure as the controlled plant, the performance of the proposed coordination control strategy is confirmed by simulation.Chapter 6 summarizes main research work that has been done, also concludes major innovations of the research and further-prospect.