Friction compensation controller for load varying machine tool feed drive

The load applied to a machine tool feed drive changes during the machining process as material is removed. This load change alters the Coulomb friction of the feed drive. Because Coulomb friction accounts for a large part of the total friction the friction compensation control accuracy of the feed drives is limited if this nonlinear change in the applied load is not considered. This paper presents a new friction compensation method that estimates the machine tool load in real time and considers its effect on friction characteristics. A friction observer based on a Kalman filter with load estimation is proposed for friction compensation control considering the applied load change. A specially designed feed drive testbed that enables the applied load to be modified easily was constructed for experimental verification. Control performance and friction estimation accuracy are demonstrated experimentally using the testbed.     

Digital Twin-driven machining process for thin-walled part manufacturing

Thin-walled parts are widely used in the aerospace, shipbuilding, and automotive industry, but due to its unique structure and high accuracy requirements, which leads to an increase in scrapped parts, high cost in production, and a more extended period in the trial machining process. However, to adapt to fast production cycles and increase the efficiency of thin-walled parts machining, this paper presents a Digital Twin-driven thin-walled part manufacturing framework to allow the machine operator to manage the product changes, make the start-up phases faster and more accurate. The framework has three parts: preparation, machining, and measurement, driven by Digital Twin technologies in detail. By establishing and updating the workpiece Digital Twin under a different status, various manufacturing information and data can be integrated and available to machine operators and other Digital Twins. It can serve as a guideline for establishing the machine tool and workpiece Digital Twin and integrating them into the machining process. It provides the machine operator opportunities to interact with both the physical manufacturing process and its digital data in real-time. The digital representation of the physical process can support them to manage the trial machining from different aspects. In addition, a demonstrative case study is presented to explain the implementation of this framework in a real manufacturing environment.     

Autonomous Visual Measurement for Accurate Setting of Workpieces in Robotic Cells

This paper introduces a new method of adapting the virtual world of an offline programming model to an actual robotic cell by attaching a CCD camera to the robot. This method requires no specific camera attachment location or optical camera calibration. Furthermore, there is no operational requirement for setting robotic camera location. Robot motion is autonomously generated to identify the camera view line. The view line is adjusted to pass through the designated target point, utilizing visual feedback motion control. This method calibrates reference points between the virtual world of an offline model to an actual robotic cell.     

Modeling and analysis of workpiece stability based on the linear programming method

After being located on a machine bed, a workpiece will be subject to gravity and cutting forces during the machining operation. In order to keep the locating precision as well as the production safety, it is necessary to maintain the workpiece stability. In this paper, a linear programming method is proposed for stability analysis of the workpiece. Based on the linear approximation of the friction cone, a quantitative criterion is established to verify the workpiece stability in association with the rationality of the clamping sequence, magnitude of clamping forces and clamping placement. This criterion allows designers to plan reasonably the clamping sequence, magnitude of clamping forces as well as clamping placement. Compared with existing methods, the main advantage of this approach lies in that the sophisticated computing of contact forces between fixture elements and the workpiece is avoided. In this work, both friction and frictionless cases can be easily taken into account in stability analysis. Mathematical formulations of the method are given and some numerical tests are finally demonstrated to validate the proposed method.     

高熔点材料混粉电火花加工技术的研究

利用自行研制的混粉电火花加工装置,对高强度、高熔点的特殊材料的加工进行研究,通过优化工艺参数,成功地在直径为φ50 mm的圆面积上使加工表面粗糙度值达到Rα0.174μm.经过与常规电火花加工实验的对比,对两种方法加工工件的表面性能进行检测与分析,结果表明混粉电火花对此类材料的加工比常规电火花加工更具明显优势.     

圆柱内壁件下压装配机械手结构实现及弹簧参数优选

根据特定产品生产工艺要求,设计了一种用于圆柱内壁件作业的内撑式抓取与下压装配机械手。该机械手在手指系统与筒状手掌之间采用弹性连接。在高速作业过程中,这类弹性连接形成手指系统的残留振动。在对机械手结构设计思想与结构介绍的基础上,对机械手系统采用Adams运动仿真,分析了弹簧系统参数对手指系统的残留振动的影响,并对影响机械手振动特性的关键参数——连接弹簧的参数进行了优化选择。实际机械手的运行结果表明,该机械手结构与弹性参数的选择可以很好地满足特定对象的作业要求。     

高精度机器人打磨系统标定算法研究与实现

针对自主研发的机器人打磨系统打磨精度差等问题,通过误差源分析,分别在工具、工件标定算法及实现方面进行了研究。针对打磨使用刀具的特点,选择合适的工具标定算法,设计辅助标定工装,完成了打磨工具的位姿标定,提高了打磨工具的标定精度。同时根据打磨工件标定算法及工件的特点,设计标定块,利用辅助特征点三点标定方法及合理的测量方法,完成了工件的高精度匹配。通过离线编程生成打磨程序,从而实现了高质量、高精度的机器人打磨作业。     

一种新的卧式加工中心工作台常压系统的研究

介绍了一种卧式加工中心常压工作台结构,卧式加工中心是机床中自动化程度较高、工序较为集中的机床之一。应用传统的夹具在一定程度上限制了卧式加工中心优越性的发挥,采用工作台通油技术,为夹具提供动力,保证夹具动作的完成,从而增加了卧式加工中心的使用范围及自动化程度。实践证明:该技术设计合理、实用性强、可靠性高。     

Workpiece modelling for computer-aided process planning

Different concepts can be applied for representation of workpiece data for CAPP. Instead of waiting for future standards, a practical method is required, which can be used for actual workpieces or those that have been designed in the past by using already existing CAD systems. Therefore, for developing the CAPP system an approach has been chosen which consists of (1) a structure and geometry recognition of the workpiece and (2) an editor for technological data.This paper shows the main characteristics of a workpiece model which can be used for process planning. The results of an analysis of workpieces in industry give an overview of the topological relationships between geometrical elements which is an essential part of workpiece modelling for future design and planning systems. Also, a link between the workpiece model and the CAPP system is presented and briefly discussed.     

工件特征点三维坐标非视觉测量方法综述

对工件上特征点的三维坐标非视觉测量方法进行了综述,其中包括平台高度尺法、电子经纬仪法、坐标测量机法、雷达测量法、莫尔条纹测距法、跟踪式激光干涉仪测距方法等。对每种方法的特点及其测量精度进行了详细的分析,并介绍了目前的发展及应用现状。