Product variation reduction is critical to improve process efficiency and product quality, especially for multistage machining process（MMP）. However, due to the variation accumulation and propagation, it becomes qui...Product variation reduction is critical to improve process efficiency and product quality, especially for multistage machining process（MMP）. However, due to the variation accumulation and propagation, it becomes quite difficult to predict and reduce product variation for MMP. While the method of statistical process control can be used to control product quality, it is used mainly to monitor the process change rather than to analyze the cause of product variation. In this paper, based on a differential description of the contact kinematics of locators and part surfaces, and the geometric constraints equation defined by the locating scheme, an improved analytical variation propagation model for MMP is presented. In which the influence of both locator position and machining error on part quality is considered while, in traditional model, it usually focuses on datum error and fixture error. Coordinate transformation theory is used to reflect the generation and transmission laws of error in the establishment of the model. The concept of deviation matrix is heavily applied to establish an explicit mapping between the geometric deviation of part and the process error sources. In each machining stage, the part deviation is formulized as three separated components corresponding to three different kinds of error sources, which can be further applied to fault identification and design optimization for complicated machining process. An example part for MMP is given out to validate the effectiveness of the methodology. The experiment results show that the model prediction and the actual measurement match well. This paper provides a method to predict part deviation under the influence of fixture error, datum error and machining error, and it enriches the way of quality prediction for MMP.展开更多
This paper investigates State Space Model Predictive Control (SSMPC) of an aerothermic process. It is a pilot scale heating and ventilation system equipped with a heater grid and a centrifugal blower, fully connected ...This paper investigates State Space Model Predictive Control (SSMPC) of an aerothermic process. It is a pilot scale heating and ventilation system equipped with a heater grid and a centrifugal blower, fully connected through a data acquisition system for real time control. The interaction between the process variables is shown to be challenging for single variable controllers, therefore multi-variable control is worth considering. A multi-variable state space model is obtained from on-line experimental data. The controller design is translated into a Quadratic Programming (QP) problem, in which a cost function subject to actuators linear inequality constraints is minimized. The outcome of the experimental results is that the main control objectives, such as set-point tracking and perturbations rejection under actuators constraints, are well achieved for both controlled variables simultaneously.展开更多
为了解决现有激光SLAM(simultaneous localization and mapping)方法忽略垂直方向漂移而导致的高度不准确和地图重影问题,提出了一种基于垂直约束的紧耦合激光惯性SLAM方法。该方法结合激光雷达传感器的安装高度以及点到激光雷达的距离...为了解决现有激光SLAM(simultaneous localization and mapping)方法忽略垂直方向漂移而导致的高度不准确和地图重影问题,提出了一种基于垂直约束的紧耦合激光惯性SLAM方法。该方法结合激光雷达传感器的安装高度以及点到激光雷达的距离提取精确的地面点,基于提取的地面点设计了一种考虑垂直方向残差的激光里程计,使用两步列文伯格-马夸尔特(Levenberg-Marquardt,L-M)方法来求解姿态变换,这些残差将有助于在垂直方向上收敛到最优解。使用简单有效的基于欧氏距离的回环检测方法避免地图重影问题。为验证算法的优越性,在KITTI数据集及真实场景下均进行了相关实验。在KITTI数据集上,与LeGO-LOAM、LIO-SAM和Point-LIO相比,轨迹均方根误差(root mean square error,RMSE)分别降低了47.62%、33.14%和73.79%。在实测校园环境中,与LeGO-LOAM、LIO-SAM和Point-LIO相比,RMSE分别降低了83.56%、13.55%和82.04%,从而验证了提出方法具有更高的定位精度。展开更多
在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建...在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建模,避免无人机区域重叠带来的干扰问题。其次,引入基站负载传输协议(Base Station Load Transfer Protocol,BSLTP),当接入基站的用户数量超过给定阈值时,超载用户由无人机提供服务。此外,分别分析了地面基站和无人机的覆盖性能,得到了系统整体覆盖概率,并研究了无人机高度、覆盖半径、激增用户密度对网络覆盖性能的影响。最后,通过仿真验证了理论结果的正确性,且所提部署方案能够有效提升网络覆盖性能。展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51205286,51275348)
文摘Product variation reduction is critical to improve process efficiency and product quality, especially for multistage machining process（MMP）. However, due to the variation accumulation and propagation, it becomes quite difficult to predict and reduce product variation for MMP. While the method of statistical process control can be used to control product quality, it is used mainly to monitor the process change rather than to analyze the cause of product variation. In this paper, based on a differential description of the contact kinematics of locators and part surfaces, and the geometric constraints equation defined by the locating scheme, an improved analytical variation propagation model for MMP is presented. In which the influence of both locator position and machining error on part quality is considered while, in traditional model, it usually focuses on datum error and fixture error. Coordinate transformation theory is used to reflect the generation and transmission laws of error in the establishment of the model. The concept of deviation matrix is heavily applied to establish an explicit mapping between the geometric deviation of part and the process error sources. In each machining stage, the part deviation is formulized as three separated components corresponding to three different kinds of error sources, which can be further applied to fault identification and design optimization for complicated machining process. An example part for MMP is given out to validate the effectiveness of the methodology. The experiment results show that the model prediction and the actual measurement match well. This paper provides a method to predict part deviation under the influence of fixture error, datum error and machining error, and it enriches the way of quality prediction for MMP.
文摘This paper investigates State Space Model Predictive Control (SSMPC) of an aerothermic process. It is a pilot scale heating and ventilation system equipped with a heater grid and a centrifugal blower, fully connected through a data acquisition system for real time control. The interaction between the process variables is shown to be challenging for single variable controllers, therefore multi-variable control is worth considering. A multi-variable state space model is obtained from on-line experimental data. The controller design is translated into a Quadratic Programming (QP) problem, in which a cost function subject to actuators linear inequality constraints is minimized. The outcome of the experimental results is that the main control objectives, such as set-point tracking and perturbations rejection under actuators constraints, are well achieved for both controlled variables simultaneously.
文摘为了解决现有激光SLAM(simultaneous localization and mapping)方法忽略垂直方向漂移而导致的高度不准确和地图重影问题,提出了一种基于垂直约束的紧耦合激光惯性SLAM方法。该方法结合激光雷达传感器的安装高度以及点到激光雷达的距离提取精确的地面点,基于提取的地面点设计了一种考虑垂直方向残差的激光里程计,使用两步列文伯格-马夸尔特(Levenberg-Marquardt,L-M)方法来求解姿态变换,这些残差将有助于在垂直方向上收敛到最优解。使用简单有效的基于欧氏距离的回环检测方法避免地图重影问题。为验证算法的优越性,在KITTI数据集及真实场景下均进行了相关实验。在KITTI数据集上,与LeGO-LOAM、LIO-SAM和Point-LIO相比,轨迹均方根误差(root mean square error,RMSE)分别降低了47.62%、33.14%和73.79%。在实测校园环境中,与LeGO-LOAM、LIO-SAM和Point-LIO相比,RMSE分别降低了83.56%、13.55%和82.04%,从而验证了提出方法具有更高的定位精度。
文摘在用户数量激增的应急通信场景下,为保证地面用户的通信质量,提出了基于距离约束的用户自适应接入方案。首先采用泊松点距离约束策略(Poisson Point under Distance Constraint,PPDC)对无人机(Unmanned Aerial Vehicle,UAV)的位置进行建模,避免无人机区域重叠带来的干扰问题。其次,引入基站负载传输协议(Base Station Load Transfer Protocol,BSLTP),当接入基站的用户数量超过给定阈值时,超载用户由无人机提供服务。此外,分别分析了地面基站和无人机的覆盖性能,得到了系统整体覆盖概率,并研究了无人机高度、覆盖半径、激增用户密度对网络覆盖性能的影响。最后,通过仿真验证了理论结果的正确性,且所提部署方案能够有效提升网络覆盖性能。
