Sweep scan path planning for efficient freeform surface inspection on five-axis CMM

Compared with the traditional 3-axis coordinate measuring machine (CMM), a 5-axis CMM equipped with the capability of continues sweep scanning can provide much denser data points while taking much shorter time. This paper presents an automatic sweep scan path planning system that generates a continuous sweep scanning path for the inspection of an arbitrary free-form surface using a 5-axis CMM with three translational axes and a rotary head with two very light rotary axes. The system strives to significantly improve the scanning efficiency by utilizing the superb kinematic advantages of the two rotary axes, which have very low moment of inertia, to cover a larger area, while tremendously reducing the speed and acceleration demand on the three translational axes which have much larger inertia. The path is generated from a mesh model of the freeform surface and an iterative approach is used to ensure that the stylus contacts the surface at an acceptable angle during the entire scan. Physical scanning experiments are performed and the test results show significant improvement in scanning efficiency by the proposed sweep scan path planning method when compared with some existing continuous scanning path planning approaches such as the standard isoparametric or zigzag method.     

A robot motion position and posture control method for freeform surface laser treatment based on NURBS interpolation

Laser surface treatment, such as laser cladding, laser quenching and laser cleaning, for the freeform surface can dramatically enhance the properties of the working surface. During the laser surface treatment, the posture of the treatment tool to the surface influences the size and shape of the laser spot, which further influences the quality of the laser surface treatment. Thus, accurate posture and high synchronization between position and posture are crucial. Industrial robots have the irreplaceable advantages of high flexibility, large workspace and cost-effectiveness over the 5-axis machine tools, therefore, they have become more and more popular in freeform surface laser treatment. However, the research on industrial robot motion mainly concentrates on position control, while less attention has focused on posture control and synchronization of position and posture control. In this paper, a robot motion position and posture (P&P) control method based on the non-uniform rational B-spline (NURBS) interpolation is proposed to realize the high-order continuity and synchronization of P&P as well as the self-adaptive motion control. Firstly, simultaneously considering the position and posture, a novel path generation method based on 6-dimensional NURBS is proposed to provide smooth, continuous and collision-free P&P coordinates of the designed scanning path. Next, a self-adaptive path segmentation method is introduced to recognize the corners and divide the whole treatment path into safe and dangerous segments. Based on the kinematical characteristics of the industrial robot, the joint motion constraint is especially considered in addition to the chord error limit and the centripetal acceleration constraint, and the self-adaptive motion parameters are obtained to match with safe and dangerous segments to avoid mechanical shock and ensure the accessibility of joint servos. Moreover, a synchronized look-ahead method with a dynamically refreshed window is employed to obtain the optimal node speed between adjacent segments and relieve the heavy computational burden, after which a series of smooth, accurate and synchronized motion instructions for the freeform surface laser treatment is generated in real time. Finally, simulations and experiments of a NURBS scanning path for a turbine blade laser surface cladding are conducted. The results show the proposed method can realize the high-order continuity and synchronization of P&P as well as the self-adaptive motion control for the freeform surface laser treatment.     

Kinematics analysis of a hybrid manipulator for computer controlled ultra-precision freeform polishing

As one of the final processing steps of precision machining, polishing process is a very key decision for surface quality. This paper presents a novel hybrid manipulator for computer controlled ultra-precision (CCUP) freeform polishing. The hybrid manipulator is composed of a three degree-of-freedom (DOF) parallel module, a two DOF serial module and a turntable providing a redundant DOF. The parallel module gives the workpiece three translations without rotations. The serial module holds the polishing tool and gives it no translations on the polishing contact area due to its particular mechanical design. A detailed kinematics model is established for analyzing the kinematics of the parallel module and the serial module, respectively. For the parallel module, the inverse kinematics, the forward kinematics, the Jacobian matrix, the workspace and the dexterity distribution are analyzed systematically. Workspaces are also investigated for varying structural parameters. For the serial module, the inverse kinematics, the forward kinematics, the workspace and the precession motion analysis are carried out. An example of saddle surface finishing with this manipulator is given and the movement of actuators with respect to this shape is analyzed theoretically. These analysis results illustrate that the proposed hybrid manipulator is a very suitable machine structure for CCUP freeform polishing.     

Control of the quality of laser surface texturing

Since the conception of the first lasers in the 60’s, the knowledge and consequently the applications of laser have been widely increased. Laser surface texturing is a specific field among the various applications of the laser. This technique is employed in the aim of improving tribological performances for instance. This paper presents the laser surface texturing of a heterogeneous material. This material is lamellar cast iron. It has been chosen for its good friction properties. The textured surface is composed of grooves or dimples. The dimensions are micrometric. For the grooves, different cross sections have been engraved: semicircular, rectangular, trapezoidal and triangular. The dimples are cylindrical. All these laser textured surfaces are engraved with the laser manufacturing machine: DML 40 SI of Gildemeister (Germany). This machine is equipped with a galvanometric scanner, which allows tilted surfaces to be engraved. Various machining strategies and the following results are discussed in function of the different desired laser surface texturing results. In addition, to increase the aspect of the engraved surfaces, laser polishing is employed. Thanks to a defocalisation of the laser beam on the surface, the material is not ablated but melted. To be able to compare the different laser machining process, several techniques of control have been used: roughness profilometry, scanning electron microscopy and non contacting optical measurement. The rules of use of these methods must be defined bearing in mind their inherent limitations.     

多功能激光微织构加工软件系统设计与开发

针对激光微织构加工软件设计中存在的功能不齐全、人机交互性差、可视化程度低等问题,以激光微织构加工需求为背景,基于QT开发一套多功能激光微织构加工软件系统,设计四大功能模块,支持多种工艺加工。考虑到加工过程中存在的定位精度不高、表面形貌不易观测等问题,应用机床三维坐标变换技术等关键技术设计软件功能,实现了加工平台微米级精度运动,以及激光器与加工平台协同工作,改善了激光微织构形貌观测难度。利用激光微织构加工设备构建实验环境,对软件进行功能测试。结果表明:软件能够满足激光微织构加工的功能需求。软件功能设计完善、集成度高、人机交互感好,为激光微织构加工和激光表面形貌研究提供了技术支撑。     

Machine models and tool motions for simulating five-axis machining

This paper presents a method of determining the tool motion of a five-axis machine. The method is motivated by the imprint point method, where points on the machined surface are computed based on the tool position and tool motion. While simple linear motion can be used as a coarse approximation to this motion, this paper looks at more accurate models of tool motion based on machine kinematics that can be generalized and applied to any CNC machine with one tool head. A kinematic chain is created by decomposing the linear motion of a machine’s translational and rotational axes into parameterized affine transformations, and a hierarchical model of the machine combines the transformations to provide an accurate model of machine motion.     

Three-Dimensional Robotic Vision Using Ultrasonic Sensors

This article describes a three-dimensional artificial vision system for robotic applications using an ultrasonic sensor array. The array is placed on the robot grip so that it is possible to detect the presence of an object, to direct the robot tool towards it, and to locate the object position. It will provide visual information about the object's surface by means of superficial scanning and it permits the object shape reconstruction. The developed system uses an approximation of the ultrasonic radiation and reception beam shape for calculating the first contact points with the object's surface. On the other hand, the position of the array's sensors has been selected in order to provide the sensorial head with other useful capabilities, such as edge detection and edge tracking. Furthermore, the article shows the structure of the sensorial head for avoiding successive rebounds between the head and the object surface, and for eliminating the mechanical vibrations among sensors.     

Software-based tool path evaluation for environmental sustainability

Currently available life cycle assessment (LCA) tools provide only a rough estimation of the environmental impact of different manufacturing operations (e.g. energy consumption). To address this limitation, a web-based and application programming interface (API) based process analysis software tools were developed to estimate the energy consumption of a computer numerically controlled (CNC) machine tool operation and to evaluate its environmental impact as a first step towards sustainable manufacturing analysis. Acceleration/deceleration of machine tool axes and the direction of axes movement were considered to estimate the total energy demand and processing time of the machine tool operation. Several tool path generation schemes were tested to analyze the energy consumption and resulting green house gas emission of CNC machine tool operation. It showed that tool path generation schemes affect the amount of energy and the processing time required to machine the same part, and location of the machining resulted in different amount and characteristics of green house gas emission.     

基于LOM技术的大尺寸薄壁机械零件自动化加工方法研究

现有的大尺寸薄壁机械零件自动化加工方法均存在着加工效率低、加工质量低的弊端,为了解决上述问题,引入LOM技术对大尺寸薄壁机械零件自动化加工方法进行设计与研究。根据大尺寸薄壁机械零件加工的特点采用LOM技术对加工目标曲面进行求解,以此为基础,采用截面线法对加工目标曲面信息进行提取,根据得到的加工目标曲面信息建立三维稳态切削力模型,以三维稳态切削力模型为依据,采用UG软件对数控机床加工程序进行编写与执行,实现了大尺寸薄壁机械零件的自动化加工。通过仿真对比实验得到,与现有的大尺寸薄壁机械零件自动化加工方法相比,提出的大尺寸薄壁机械零件自动化加工方法极大地提升了加工效率与质量,充分说明提出的大尺寸薄壁机械零件自动化加工方法具备更良好的加工性能。     

Intelligent desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance control capability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots. Tools attached to the tip of the z-axis are ball-end abrasive tools. The control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feed-forward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Further, the position feed-forward loop leads the tool tip along cutter location data. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash that causes the position inaccuracy at the tip of an abrasive tool, through a simple position/force measurement. Through a similar measurement and a surface following control experiment along a lens mold, the basic position/force controllability with high resolutions is demonstrated. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Flexible fabrication of three-dimensional multi-layered microstructures using a scanning laser system

In this paper, we developed a scanning laser system, which allows rapid processing of freeform multi-layered microstructures. More importantly it enables rapid prototyping of three-dimensional (3D) microdevices at low cost. The capabilities of three-dimensional manufacturing, inclined patterning, and multi-layered manufacturing have been demonstrated. Specifically, both in-plane and out-of-plane processing is feasible using spot-by-spot controllable laser pulsing. The laser processing perpendicular to the specimen surface is realized by fine tuning the focus level and laser intensity. A large number of microfluidic components such as cantilever beams, embedded channels and other shapes requiring gaps between layers are demonstrated in a single layer. Compared to the existing manufacturing techniques, our direct laser writing method greatly simplifies fabrication processes, potentially reducing the design-to-fabrication cycle to a few hours.     

研磨实验曲面的NURBS模型建立和特性分析

CAD/CAM软件——Catia,MasterCAM等在曲面数学模型部分是不公开的[1,2],不适于研究工具新轨迹。利用9片3阶NURBS曲面拼接的方法建立了一个实验曲面,它具有9阶NURBS曲面的描述能力,但在计算量上等同于3阶模型。用Matlab编制了计算机程序,可用于研究研磨新理论。曲面数学模型对使用者是透明的,可以按控制顶点和权系数调整曲面形状,可分析曲面特征及对曲面做分片处理,为研磨工具轨迹的创新奠定了基础。     

Feature design on deformation of freeform surfaces using range control

This research is to develop a freeform surface design method which uses a feature-based design approach to process surface deformation. Using this method, called range control, a user modifies or changes the position of a characteristic control point of the control polyhedron for a Bspline surface, and regional surface deformation is then carried out through automatic displacements of a group of control points surrounding the characteristic point. The position changes of the group of control points are the interpolations of the maximum movement of the characteristic point related to a feature dimension and zero movements of some fixed points on the designated boundary. In this range control surface deformation method, three interpolating approaches are proposed to smooth out the changes between the characteristic vertex and fixed vertices. they are based on the linear interpolation under the consideration of index, distance and angle distributions. The ideas are implemented on a feature-based designing system for shoe lasts. Design examples are given to show that the range control method is simple, fast and practically applicable for shape deformation of freeform surfaces.     

Volumetric feature recognition for machining components with freeform surfaces

This paper describes a procedure for the extraction of features of a part containing a combination of 2.5D features and freeform surfaces. This work invokes a previous algorithm that was designed to recognize machining features from 2.5D parts destined to be machined on a 3-axis milling machine. The essence of that algorithm was a volume decomposition based on a recursive descent into the part, yielding a feature graph that captured both the geometry and the spatial relationships of the features. This work augments the previous algorithm with the ability to handle a limited class of components having freeform surfaces. Freeform features are defined similar to the 2.5D features as comprising a planar contour, but substituting a bottom freeform surface for the depth. Covering faces, defined as projection of the freeform surface on the faces of the bounding box of the surface, are used as equivalent planar faces for performing the recursive descent. Inter-feature open edges are used to signal the relationship between the freeform feature and other neighboring features. Examples of molds and components that were machined using the proposed algorithms are also presented.     

云环境下基于PLC模拟量优化的机床自动控制系统设计

为解决机床控制过程中存在抖振现象和控制误差过高等问题,在云环境下通过对PLC模拟量的优化,从硬件和软件两个方面优化设计机床自动控制系统;加设可编程逻辑控制器,改装传感器、电机与驱动器,调整系统电路的连接方式,完成机床自动控制硬件系统的优化;根据机床生产任务,规划执行刀具移动轨迹,设定机床加工强度与速度参数;在云环境下自动采集机床模拟量与位姿,根据当前机床运行参数与设定参数之间偏差,利用优化PLC的模拟量并生成机床控制指令,实现机床自动控制功能;通过系统测试得出结论：综合两种实验场景,与传统控制系统相比,优化设计系统在机床执行刀具位置、运行速度和执行应力三个方面的控制误差分别降低约13.8 mm、0.26 mm/s和3.4 N,同时机床抖振现象得到显著抑制。     

Recent development in CNC machining of freeform surfaces: A state-of-the-art review

Freeform surfaces, also called sculptured surfaces, have been widely used in various engineering applications. Freeform surfaces are primarily manufactured by CNC machining, especially 5-axis CNC machining. Various methodologies and computer tools have been developed in the past to improve efficiency and quality of freeform surface machining. This paper aims at providing a state-of-the-art review on recent research development in CNC machining of freeform surfaces. This review primarily focuses on three aspects in freeform surface machining: tool path generation, tool orientation identification, and tool geometry selection. For each aspect, first concepts, requirements and fundamental research methods are briefly introduced. The major research methodologies developed in the past decade in each aspect are presented with details. Problems and future research directions are also discussed.     

A tool path generation method for freeform surface machining by introducing the tensor property of machining strip width

Due to the complexity of geometry, the feed direction with maximal machining strip width usually varies among different regions over a freeform surface or a shell of surfaces. However, in most traditional tool path generation methods, the surface is treated as one machining region thus only local optimisation might be achieved. This paper presents a new region-based tool path generation method. To achieve the full effect of the optimal feed direction, a surface is divided into several sub-surface regions before tool path computation. Different from the scalar field representation of the machining strip width, a rank-two tensor field is derived to evaluate the machining strip width using ball end mill. The continuous tensor field is able to represent the machining strip widths in all feed directions at each cutter contact point, except at the boundaries between sub-regions. Critical points where the tensor field is discontinuous are defined and classified. By applying critical points in the freeform surface as the start for constructing inside boundaries, the surface could be accurately divided to such that each region contain continuous distribution of feed directions with maximal machining strip width. As a result, tool paths are generated in each sub-surface separately to achieve better machining efficiency. The proposed method was tested using two freeform surfaces and the comparison to several leading existing tool path generation methods is also provided.     

The research of an automatic object reconstruction method based on limit visible region of the laser-scanning vision system

This paper presents an automatic multi-view selection approach for 3D reconstruction by means of a laser scanning vision system. It is realized based on the visual region of the laser scanning vision system. The candidate next best view (NBV) position is obtained by computing the unknown space area according to the limit visual region of the vision system. The final NBV position, which can acquire the maximal visual area, is obtained by comparing the above candidate’s view positions. Experimental results show successful implantation of the proposed view planning method for digitization and reconstruction of freeform objects.     

数控龙门铣床数据采集系统综述

龙门铣床是机床族的重要机型,其应用广泛,尤其是数控龙门铣床在航空制造领域的地位举足轻重。数据采集系统是机床监控系统的前端子系统和关键组成部分,数据采集系统设计的成功与否,决定了机床监控系统的数据有效性。对应用于龙门铣床的数据采集系统进行研究,具较大的现实意义。在介绍数控龙门铣床的结构及功能的基础上,分析了数控龙门铣床的数据采集的核心需求,针对性地分析和总结了数据采集的手段和方法,并概述了数控龙门铣床数据采集系统的发展方向。为数控龙门铣床数据采集系统的设计提供了技术支撑。     

造船龙门起重机大车纠偏控制系统的设计与应用

造船龙门起重机随着造船业的迅速发展也跟着快速发展起来。在大车行走过程中,由于龙门起重机的刚腿和柔腿之间的跨距较大,因此要求刚腿和柔腿的位移要始终保持一致,如果偏差过大则会造成大车偏斜运行等严重后果。本文结合软硬件的设计,详细介绍了大车纠偏控制系统从位置检测到位置闭环控制是如何实现大车的实时纠偏。