This paper describes in two parts a new method and device for measuring motion accuracy of numerical control (NC) machine tools. In the first part, the measurement principle and the characteristics of the prototype device are proposed. The device consists of a double-bar linkage with two rotary encoders. The working range of the device is disc-shaped with a radius of almost the double the link length, except a small area around the centre of the disc and an outer area both around the change points of the linkage at the centre and the circumference of the disc. Because the method has high resolution for any measuring point within the working range, it can be applied to measure most items of motion accuracy of NC machine tools. The method is particularly suitable to measure the trajectory accuracy of circular motions. The device has a compact structure and its installation on a machine tool to be measured is simple and quick. The experimental results show that the prototype device has very good response to small displacement and good repeatability with high precision to the measurement of circular motion trajectories. The influence of measurement noise is hardly observed in the experimental results.

This paper presents a method that applies XML technology to structure the design process data of products. The design process data includes product data, process data and process management data. Applying XML technology can build a structural and platform-independent Design Data Model (DDM), and make it possible to reuse design data in the life cycle of a product. DDM is based on a Process-based CAD (PCAD) model and a software prototype based on PCAD has been developed using Java and XML technologies that are platform independent. A Document Object Model (DOM) technology is used to operate XML documents and an example is presented to demonstrate this method.

建立一种设计过程数据的获取和管理结构——设计过程数据模型。设计过程数据包括产品数据、过程数据和过程管理数据。建立设计过程数据模型的原则是便于数据展示、共享、复用和知识提取。采用XML技术管理的设计数据具有平台及语言的无关性和独立性，非常适合于表示数据、概念和上下文，并能很方便地被不同的使用者在不同的环境下重复使用，便于网络上的传输与共享，并可供整个产品生命周期重用。设计数据模型已在一个基于过程的计算机辅助设计软件原型系统中实现。

A precise evaluation of the form deviations of two-dimensional (2D) engineering contours is of essential importance in precision manufacturing. In this paper, we propose a practical approach towards evaluating form deviations of 2D contour profiles based on coordinate measurement data. Using this approach, a 2D contour is divided into straight and curved parts. Each straight part is directly presented by the original definition of the part; and each curved part is further represented by its optimal interpolation circular arc segments whose interpolation accuracy can be specified arbitrarily. The approximate contour curve consisting of the straight and circular arc segments has the fewest interpolation segments under the condition of satisfying the pre-specified interpolation accuracy. The form deviation of a measured point is defined as the distance from the point to its corresponding straight or circular segment. The geometrical form deviation of the contour profile is evaluated using the least square method. It has been demonstrated that the difference between the deviation definitions, relative to the original contour or to the approximate contour, is not larger than the pre-specified accuracy value for circular arc interpolation. Therefore, the evaluation precision of the form deviation can be sufficiently guaranteed. The approach is easy and convenient for engineering applications. The effectiveness and the efficiency of the approach are verified with a practical example of a planar cam contour in the paper.