Research on optimal measurement area of flexible coordinate measuring machines

When we measure a workpiece in the optimal measurement area of the flexible coordinate measuring machines (FCMMs), the measuring precision can be improved. The flexible CMM’s measuring space is given. Then its spatial error distribution model is build by using support vector machine theory. Finally, the two solutions of the optimal measurement area are discussed and solved through experiments. The high precision measurement results can be realized by using a low-precision measuring machine without any increase in hardware manufacturing cost. This is of great theoretical value and practical significance for the flexible CMM’s further development.     

高精度三维螺纹测量机接触式扫描测头 动态特性研究

扫描测头是高精度三维螺纹综合测量机的核心部件,其动态特性严重影响了整机的精度。为了提高测量机的精度,对高精度螺纹三维尺寸测量线性扫描测头的动态特性进行了研究。首先分析了三维螺纹综合测量机用扫描测头的测量原理,然后建立了动态特性模型并提出了影响动态测量结果的因素,最后通过实验验证了这种测头结构的动态特性和测量处理方式的有效性。实验结果验证了影响因素的正确性,优化影响最大的采样间距因素可以过滤80%的无效数据点,从而使该段拟合平均残差平方和误差减小了91.0%,线性误差减小了67.4%,进而提高了三维螺纹测量机的测量精度。     

新型关节臂坐标测量机的设计

关节臂坐标测量机是一种新型非正交系坐标测量设备,相比传统的三坐标测量机,具有体积小、重量轻、灵活、轻便等特点,现已在机械制造、电子、汽车和航空航天等领域得到应用,具有巨大的应用前景.在前期工作的基础上设计出一种六自由度关节臂坐标测量机,该关节臂坐标测量机关节零件采用航空铝合金材料、连杆采用碳纤维材料,因而具有强度高、重量轻的特点,内置式平衡机构可减轻操作者劳动强度,精密的关节角度传感器保证了测量机的高精度.基于Open CASCADE和VC++6.0平台开发了关节臂坐标测量机的测量软件和标定软件,并进行了整机的联机调试,验证了系统的可靠性.     

Development of a parametric model and virtual machine to estimate task specific measurement uncertainty for a five-axis multi-sensor coordinate measuring machine

Any combination of contact and non contact sensors on a single coordinate measuring machine makes it a multi-sensor or hybrid coordinate measuring machine. The ability to change the probing device without re-establishing the part coordinate system is a significant advantage and consequently the reason for their wide acceptance and usage. In addition to the existing three linear stages in a conventional or hybrid coordinate measuring machine, the number of axes can be augmented with two rotary stages in order to make them more versatile. This not only complicates the metrology loop but also adds more parametric errors to existing list of known 21 errors for a three stage conventional measuring machine. Also different probing sensors in the system have different metrology loops. Literature survey reveals that there is no previous or current work on estimation of task specific uncertainty for machines of this class with a wide potential for measuring complex parts quickly and with great ease. The current work focuses on developing a virtual measuring machine of this class which incorporates a parametric model of a five-axis multi-sensor coordinate measuring machine, techniques to estimate the parametric errors in the model and error correction strategies for the same. The virtual machine is used to mimic real time measurements in order to come up with estimates for task specific measurement uncertainty.     

数控研磨机研磨去除量的在线监控系统试验研究

将光栅测量系统和数控技术用于高速研磨机上,从而给研磨机增加监控功能,这是新型高速研磨机的发展方向。光栅测量系统具有数字化、精度高和安装方便等优点,故选用光栅测量系统测量压头的位移,并利用计算机实现相应的控制。介绍了光栅测量系统的组成、工作原理及主要技术参数,并对数控研磨机监控装置的组成和监控原理进行了分析,对高速研磨机的设计优化具有参考价值。     

Novel CMM-based implementation of the multi-step method for the separation of machine and probe errors

Coordinate measuring machines (CMMs) are subject to periodic verification to ensure measurement capability. However, users also need to rapidly diagnose the source of accuracy degradation to guide corrective actions. This paper presents a novel CMM-based implementation of the multi-step method for the separation of machine and reference sphere errors on one side and triggering probe and probe tip errors on the other. The procedure uses multiple redundancy probing of the machine's own reference sphere and result in a mathematical system similar to that of the multi-step method. The procedure's effectiveness is demonstrated for a variety of stylus lengths and shows its ability to detect changes in lobing errors. A metrological validation is conducted by measuring the errors of the probe and errors of the machine using independent methods.     

Elimination of Settling Error Due to Clamping Forces in On-Machine Measurement

When using OMM (on machine measurement), accuracy in the measurement of finished, machined parts is important; these parts are commonly measured by CMMs (coordinate measuring machines). This paper reports on new OMM hardware (and its operating software) developed to enhance accuracy in measurement. In assessing the value of the system, measurement accuracy was evaluated by comparing results of both CMM and OMM. Factors that can affect accuracy (sensor installation error, repeatability of the CNC machine tool, and settling error in the set-up of the workpiece) were then analysed quantitatively. The results show that the major source of error in OMM accuracy is settling error due to clamping forces, specifically in the workpiece clamping system (for example, a pallet). Therefore, the greatest improvement in measurement accuracy can be achieved by estimating and compensating for settling error beforehand.     

Evaluating a task-specific measurement uncertainty for gear measuring instruments via Monte Carlo simulation

Evaluating the measurement uncertainty for gears with analytical or experimental methods is usually very time- and cost-consuming. In this paper we therefore present a Monte Carlo based method for evaluating the measurement uncertainty of gear measurements on gear measuring instruments, the VCMM-Gear, which is based on the method of the VCMM for coordinate measuring machines. Necessary extensions of the mathematical model of the measurement process in order to consider the significant uncertainty influences from rotary tables, workpiece clamping and scanning are described. Additionally the statistical reliability of the evaluated measurement uncertainty and the consideration of systematic error contributions to the measurement uncertainty are discussed. Finally the results of some first verification measurements are presented, giving a reliable impression of the capability and suitability of the VCMM-Gear.     

使用普通车床加工英制和公制螺旋类零件

为了满足越来越多的单件小批生产中英制和公制螺旋类零件的加工需求,详细阐述了如何利用普通车床和简便的加工方法解决此类问题,例如,这类零件的加工设备的选择、大导程螺距的测量和不完整螺距的计算方法,以及按螺纹的齿型车削各种螺纹、按螺纹不同牙形角和牙型加工螺纹、多线螺旋类零件的分线方法等。     

High‐Speed Scanning of Critical Structures in Aviation Using Coordinate Measurement Machine and the Laser Ultrasonic

Aviation is one of the know‐how spheres containing a great deal of responsible sub‐assemblies, in this case landing gear. The necessity for reducing production cycle times while achieving better quality compels metrologists to look for new and improved ways to perform inspection of critical structures. This article describes the ability to determine the shape deviation and location of defects in landing gear using coordinate measuring machines and laser ultrasonic with high‐speed scanning. A nondestructive test is the basis for monitoring microcrack and corrosion propagation in the context of a damage‐tolerant design approach. This article presents an overview of the basics and of the various metrological aspects of coordinate measurement and a nondestructive testing method in terms of high‐speed scanning. The new test method (laser ultrasonic) promises to produce the necessary increase in inspection quality, but this is limited by the wide range of materials, geometries, and structure aeronautic parts used. A technique combining laser ultrasonic and F‐SAFT (Fourier‐Synthetic Aperture Focusing Technique) processing has been proposed for the detection of small defects buried in landing gear. The experimental results of landing gear inspection are also presented. SCANNING 34: 387‐394, 2012. © 2012 Wiley Periodicals, Inc.     

激光制导测量机器人运动系统设计

激光跟踪测量系统是目前最新型的便携式空间大尺寸坐标测量系统,但在测量大型被测对象时,人工布点及测量过程繁杂,测量效率低,并造成被测对象几何形状变形,严重影响其测量精度。为解决以上问题,提出了新型的“光束运动—光靶跟踪”激光跟踪测量方法,建立了新型激光跟踪测量方法论,并在此理论基础上,研制开发了一种能够在水平和垂直被测对象表面上运动小型轮臂复合式激光制导测量机器人。该机器人机构融合轮式机构、爬行臂式结构和真空吸附式机构优点,并且具有重量轻、体积小、运动灵活和反应快速等特点,可以根据不同的被测对象表面特征变换测量模式,利用轮式结构实现机器人在水平被测表面上高速远距离运动,利用爬行臂式和真空吸附式机构实现机器人在倾斜光滑表面上灵活地爬行和转向。对其运动特性进行了详细的分析。最后利用激光跟踪仪和三坐标测量机对研制激光制导测量机器人进行了性能测试,试验结果证明了该机器人能跟踪激光束自动高效地完成被测对象实体测量。     

Precision tracking control of a horizontal arm coordinate measuring machine in the presence of dynamic flexibilities

One of the major sources that affect measurement accuracy and limit the use of high motion speeds in coordinate measuring machines (CMM) is the position error. In fact, static and dynamic probe errors are more direct factors in measuring machine accuracy, but are not the subject of this research. However the accuracy of acquisition of component position errors using a CMM in motion is also of importance, hence the dynamics of a CMM need to be considered. Therefore, this research aims to model the dynamics of a horizontal arm CMM by considering drive flexibility at joints and evaluates the characteristics of the system for fine motion control purposes. Design of a precision tracking controller (PTC) to perform superior tracking for enhancing the measurement accuracy and the probing speed in providing less inspection time at high motion speeds is carried out. A dynamic model for the CMM is developed including drive flexibilities represented with lumped springs at the joints. Due to the non-collocated nature of the control scheme in the flexible CMM dynamics, a non-minimum phase system is observed in the proposed CMM model. Using the derived CMM model with joint flexibilities, tracking motion control simulations are conducted at different probing speeds for the cases where a PI controller and a feedback PTC are employed. A comparison of the PI controller with the feedback PTC is also performed. Results demonstrate that the effects of joint flexibilities on the contour error and probing speeds are significant and the PI controller is not capable of providing good accuracy during challenging tasks such as corner tracking. However, the simulation results indicated that by using the proposed feedback precision tracking controller, contour errors in corner tracking that are caused by joint flexibilities can be reduced effectively .     

简易式形位误差测量仪的研制

形位公差是机械零件主要的技术要求之一,然而通常采用V型块附加百分表的方式进行测量,测量过程麻烦,且受人的影响较大,故精度不高。文中在综合分析形位公差项目的基础上,对测量方式进行组合,并研制了简易式形位误差测量仪,可与计算机连接自动显示并判断是否符合形位公差标准。     

Machining strategy development and parameter selection in 5-axis milling based on process simulations

Fused deposition modeling (FDM) is one of the most popular additive manufacturing technologies for fabricating prototypes with complex geometry and different materials. However, current commercial FDM machines have the limitations in process reliability and product quality. In order to overcome these limitations and increase the levels of machine intelligence and automation, machine conditions need to be monitored more closely as in closed-loop control systems. In this study, a new method for in situ monitoring of FDM machine conditions is proposed, where acoustic emission (AE) technique is applied. The proposed method allows for the identification of both normal and abnormal states of the machine conditions. The time-domain features of AE hits are used as the indicators. Support vector machines with the radial basis function kernel are applied for state identification. Experimental results show that this new method can potentially serve as a non-intrusive diagnostic and prognostic tool for FDM machine maintenance and process control.     

Development of a fast mechanical probe for coordinate measuring machines

To decrease inspection times of workpieces, not only do coordinate measuring machines (CMMs) need to operate faster, but also the mechanical probing process requires attention in this field. This paper shows that impact forces attributable to probing are much higher than generally accepted measurement forces, which can result in workpiece damage. Furthermore, it is shown that probe tip bouncing can slow down the probing process and requires mechanical damping to reduce it. Based upon these findings, a fast mechanical probe system has been developed, equipped with an optical measurement system able to measure six degrees of freedom at high speed. The probe system is suitable for high-speed, single-point measurements as well as scanning purposes. The measurement uncertainty of the prototype is approximately 1 μm for probing speeds up to 70 mm/s.     

Evaluation of the uncertainty of an optical machine with a vision system for contact-less three-dimensional measurement

Optical machines with a vision system containing a video camera are designed to perform contact-less three-dimensional measurements. They are becoming more widely used in the industrial sector because of the many possibilities for automation they permit and because of the speed and economies in measurement tasks that can consequently be obtained. Within dimensional control these machines introduce significant characteristics of flexibility, savings and reliability. Therefore the purpose is to identify the principal metrological characteristics of such machines and so characterise the metrological traceability of the measurements obtained from them. The aim is to qualify each part of the optical machine as well as on the whole. Previously, no metrological traceability of this equipment has been provided in primary metrology, either at national (SIT—Sistema di Taratura in Italia—Calibration System in Italy) or at international level (EA–European co-operation for Accreditation). For this reason we develop a mathematical model that permits the evaluation of the measurement uncertainties in the use of such a device. The purpose is to obtain the certification of the measurement results furnished by the optical machine in as broad a context as possible. The experimental results of the tests are introduced for validating the proposed method. This paper provides the basis of the expression of the uncertainty of a measurement result obtained using the optical measurement machines and it shows the necessary requirements for the numerical evaluation of such uncertainty.     

锁紧装置在数控轧辊磨床测量的应用

数控轧辊磨床主要用于冶金系统中轧制板材的各型轧辊等的磨削,在磨削过程中需要使用测量臂对工件进行测量,得出误差值,为补偿加工提供依据,满足工件的高精度要求。原设计在使用过程中出现了液压驱动无法将测量臂可靠精确定位的问题,经过分析,采用锁紧装置将测量臂锁死,解决了测量精度的误差问题,保证了测量可靠性。     

Circular test for three-coordinate measuring machines and machine tools

Today, two principles are used in testing the accuracy of three-coordinate measuring machines and machine tools: measurement of the machine components, and measurement (or production) of master-pieces. Both methods are in themselves insufficient to fulfil the users' demands but combining the two should lead to better results. In the circular test a standard disc is used. The disc is measured in different positions in the working area of the machine. The calculated mean square fit diameters, standard deviations and Fourier analysis result in an analysis of the error sources and of the geometric error components     

Reliability aspects of tribology

There is an increasing need for improved methods of determining the reliability and predicting the lifetime of machines and production systems more accurately. The paper deals with the role of tribology in the large and complex scope of reliability engineering and the different tribology-related methods to improve reliability, such as reliability design, component lifetime, condition monitoring and diagnostics. To be of value for reliability estimations, the tribological data should be expressed in terms of endurance life and probability of failure. Tribological effects are today expressed on different geometrical scales, all the way from nanotribology even up to teratribology. However, the required task of scaling-up of our knowledge from nano- and microtribology level will perhaps need other, more non-linear approaches than the strict reductionism to which we are accustomed.     

Software compensation of rapid prototyping machines

This paper addresses accuracy improvement of rapid prototyping (RP) machines by parametric error modeling and software error compensation. This approach is inspired by the techniques developed over the years for the parametric evaluation of coordinate measuring machines (CMM) and machine tool systems. The confounded effects of all errors in a RP machine are mapped into a “virtual” parametric machine error model. A generic artifact is built on the RP machine and measured by a master CMM. Measurement results are then used to develop a machine error function and error compensation is applied to the files which drive the build tool. The method is applied to three test parts and the results show a significant improvement in dimensional accuracy of built parts.