A Multi-mode Electronic Load Sensing Control Scheme with Power Limitation and Pressure Cut-off for Mobile Machinery

In mobile machinery,hydro-mechanical pumps are increasingly replaced by electronically controlled pumps to improve the automation level,but diversified control functions(e.g.,power limitation and pressure cut-off)are integrated into the electronic controller only from the pump level,leading to the potential instability of the overall system.To solve this problem,a multi-mode electrohydraulic load sensing(MELS)control scheme is proposed especially considering the switching stability from the system level,which includes four working modes of flow control,load sensing,power limitation,and pressure control.Depending on the actual working requirements,the switching rules for the different modes and the switching direction(i.e.,the modes can be switched bilaterally or unilaterally)are defined.The priority of different modes is also defined,from high to low:pressure control,power limitation,load sensing,and flow control.When multiple switching rules are satisfied at the same time,the system switches to the control mode with the highest priority.In addition,the switching stability between flow control and pressure control modes is analyzed,and the controller parameters that guarantee the switching stability are obtained.A comparative study is carried out based on a test rig with a 2-ton hydraulic excavator.The results show that the MELS controller can achieve the control functions of proper flow supplement,power limitation,and pressure cut-off,which has good stability performance when switching between different control modes.This research proposes the MELS control method that realizes the stability of multi-mode switching of the hydraulic system of mobile machinery under different working conditions.

Compliance motion control of the hydraulic dual-arm manipulator with adaptive mass estimation of unknown object

Given the limited operating ability of a single robotic arm,dual-arm collaborative operations have become increasingly prominent.Compared with the electrically driven dual-arm manipulator,due to the unknown heavy load,difficulty in measuring contact forces,and control complexity during the closed-chain object transportation task,the hydraulic dual-arm manipulator(HDM)faces more difficulty in accurately tracking the desired motion trajectory,which may cause object deformation or even breakage.To overcome this problem,a compliance motion control method is proposed in this paper for the HDM.The mass parameter of the unknown object is obtained by using an adaptive method based on velocity error.Due to the difficulty in obtaining the actual internal force of the object,the pressure signal from the pressure sensor of the hydraulic system is used to estimate the contact force at the end-effector(EE)of two hydraulic manipulators(HMs).Further,the estimated contact force is used to calculate the actual internal force on the object.Then,a compliance motion controller is designed for HDM closed-chain collaboration.The position and internal force errors of the object are reduced by the feedback of the position,velocity,and internal force errors of the object to achieve the effect of the compliance motion of the HDM,i.e.,to reduce the motion error and internal force of the object.The required velocity and force at the EE of the two HMs,including the position and internal force errors of the object,are inputted into separate position controllers.In addition,the position controllers of the two individual HMs are designed to enable precise motion control by using the virtual decomposition control method.Finally,comparative experiments are carried out on a hydraulic dual-arm test bench.The proposed method is validated by the experimental results,which demonstrate improved object position accuracy and reduced internal force.

大跨度桥梁桥下净空对加劲梁气动特性的影响

为研究桥下不同净高对大跨度桥梁加劲梁气动特性的影响,以大带东桥主桥加劲梁为例,采用雷诺时均Navier-Stokes(RANS)方程和SST k-ω湍流模型,数值模拟了自然风场内不同桥下净高加劲梁断面绕流场,获得了加劲梁气动参数,并与文献报道的风洞试验结果进行了对比,分析了加劲梁气动参数随净高变化的流动机理。研究表明,桥下净高对加劲梁表面压力分布、升力和阻力,以及漩涡脱落St数均有一定程度影响。桥下净高减小,升力和阻力系数均增大;相比桥下净高5B,桥下净高仅为0.4B时升力和阻力系数分别增大87.8%和13.3%;漩涡脱落St数也随桥下净高的减小而稍增大。加劲梁表面压力监测表明,桥下净高小时,风嘴前缘下斜腹板峰值压力增大,且加劲梁上下表面迎风侧棱角的负压峰值同时减小,但上表面迎风侧棱角减小更显著。研究认为,当大跨度桥梁桥下净高明显偏小时,桥下水面对加劲梁产生明显的气动力干扰效应,从桥梁抗风的角度,需考虑桥下净高明显偏小可能导致的加劲梁风荷载增大。