基于非线性摩擦补偿的液压执行器运动控制：在柴油机可变气门系统中的应用。
Motion control of hydraulic actuators with nonlinear friction compensation: Applied to variable valve systems of diesel engine.
机构信息
College of Power and Energy Engineering, Harbin Engineering University, Harbin, Heilongjiang, 150001, China.
College of Power and Energy Engineering, Harbin Engineering University, Harbin, Heilongjiang, 150001, China.
出版信息
ISA Trans. 2023 Jun;137:561-573. doi: 10.1016/j.isatra.2023.01.037. Epub 2023 Jan 31.
Friction force plays an important role in motion control systems. Research shows that friction force is strongly nonlinear in most applications. And the nonlinear friction force has great influence on control performance, especially in motion control systems of hydraulic actuators. To improve control performance, many model-based controllers have been developed. In the past years, LuGre model has been widely used in most hydraulic actuators. However, for systems with one-way seals whose friction force is asymmetric between instroke and outstroke stage, LuGre model is no longer suitable. The paper developed a friction force test bench and studied the transient friction force of a hydraulic actuator which includes one-way seals. Experiment results show that friction force at instroke stage is bigger than that of outstroke stage for the variable valve actuator. Based on the experiment results, a bristle direction hypothesis is proposed. The bristle of the friction surface is thought to have an initial direction. For actuators with two-way seals or without seals, the bristle is thought to be perpendicular to the friction surface. And for actuators with one-way seals, the angle between bristles and friction surface is not 90° anymore. To apply the bristle direction hypothesis to controllers, a bristle direction coefficient is introduced to LuGre model to explain asymmetric friction behaviors. The simulation results have good agreements with experiment results. Based on the improved LuGre model, a backstepping controller is developed to compensate the nonlinear friction force. The friction force and system matched uncertainty are estimated by an extended state observer. Finally, some comparative experiments are implemented to verify the advantages of the improved LuGre model. The experiment results show that the improved LuGre model can help to reduce the engine valve lift tracking errors. At outstroke stage (engine valve close), the maximum absolute errors can be reduced by 40.6% to 65.0%, and the mean absolute errors can be reduced by 21.2% to 59.4%.
摩擦力在运动控制系统中起着重要作用。研究表明，在大多数应用中，摩擦力具有很强的非线性。非线性摩擦力对控制性能有很大影响，特别是在液压执行器的运动控制系统中。为了提高控制性能，已经开发了许多基于模型的控制器。在过去的几年中，LuGre 模型已广泛应用于大多数液压执行器。然而，对于具有单向密封的系统，其摩擦力在冲程内和冲程外阶段是不对称的，LuGre 模型不再适用。本文开发了一种摩擦力测试台，并研究了包含单向密封的液压执行器的瞬态摩擦力。实验结果表明，对于可变阀致动器，冲程内的摩擦力大于冲程外的摩擦力。基于实验结果，提出了刷毛方向假设。摩擦表面的刷毛被认为具有初始方向。对于具有双向密封或无密封的致动器，刷毛被认为垂直于摩擦表面。对于具有单向密封的致动器，刷毛与摩擦表面之间的角度不再是 90°。为了将刷毛方向假设应用于控制器，引入了刷毛方向系数来解释不对称摩擦力行为。仿真结果与实验结果吻合较好。基于改进的 LuGre 模型，开发了一种反推控制器来补偿非线性摩擦力。通过扩展状态观测器估计摩擦力和系统匹配不确定性。最后，进行了一些对比实验来验证改进的 LuGre 模型的优势。实验结果表明，改进的 LuGre 模型有助于减少发动机气门升程跟踪误差。在冲程外阶段（发动机气门关闭），最大绝对误差可降低 40.6%至 65.0%，平均绝对误差可降低 21.2%至 59.4%。
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