A new approach for the geometrical calibration of parallel kinematics machines tools based on the machining of a dedicated part

A main limitation of parallel kinematics machine tools (PKM) in high-speed machining tasks is their low level of accuracy compared with serial kinematics machine tools, which is largely due to geometrical transformation errors. These errors can be reduced by identifying the geometrical parameters of the inverse kinematics model integrated in the controller by exteroceptive calibration. The aim of this paper is to propose a new external measurement method in order to perform the geometrical calibration of PKM, taking into account machining requirements. This method is implemented in three steps: machining of a dedicated part, measurement, and identification of the geometrical parameter values. In this paper, the method is described with a particular emphasis on the machined surface profiles of the dedicated part and on the numerical calibration approach. Measurement errors on the machined surface enable the identification of the PKM geometrical parameters. Thus, calibration is performed with respect to machined surface defects without taking into account the entire tool pose defect, as is the case in usual calibration methods. The study is illustrated using the Verne PKM, which is located at IRCCyN (Nantes, France).     

Qualification of parallel kinematics machines in high-speed milling on free form surfaces

Serial milling machines may one day find their limits in high-speed milling due to their limited dynamic characteristics. Indeed, the major drawback of a serial structure is that it consists of a pile of actuated joints; hence the mass on board for the axis underneath can be huge. This is mainly the reason why parallel structures are of interest in milling: in order to go faster.Such structures have been developed since 1980 for robotic tasks, while the first parallel kinematics machine tool appeared only 14 years later. Since then, very few papers have been published that deal with the potential of these structures in milling. The objective of this study is to show the potentialities of parallel structures in milling and especially in high-speed milling of free form surfaces, in comparison to serial structures. To do so, experiments have been realised on four serial kinematics machines (SKMs) and four parallel kinematics machines (PKMs). These experiments were of two kinds: either a real piece has been milled, or the output axis encoder data have been saved (this method of measurement has been previously developed in our team).So far, a comparison between the two structures (serial and parallel) has been possible, which permitted us to show that PKMs can provide interesting results in terms of time and precision. Hence, the goal of this study has been reached, as the PKMs potentialities in milling free form surfaces have been highlighted. With more experiments, a generalisation, by taking into account all the parameters (shape and material of the part, structure of the machine, etc.), will be attempted. In parallel, the development of our simulator for PKMs is necessary in order to be able to predict milling on these machines.     

Kinematic and dynamic synthesis of a parallel kinematic high speed drilling machine

Typically, the term “high speed drilling” is related to spindle capability of high cutting speeds. The suggested high speed drilling machine (HSDM) extends this term to include very fast and accurate point-to-point motions. The new HSDM is composed of a planar parallel mechanism with two linear motors as the inputs. The paper is focused on the kinematic and dynamic synthesis of this parallel kinematic machine (PKM). The kinematic synthesis introduces a new methodology of input motion planning for ideal drilling operation and accurate point-to-point positioning. The dynamic synthesis aims at reducing the input power of the PKM using a spring element.     

并联机器人机构的创新与应用研究进展

简要介绍并联机器人的研发历史和现状,重点介绍了实用化进程较高的Stewart平台、Delta并联机器人和Tricept并联机床的应用,同时介绍了我国在并联机床研制方面的情况.评述了近年来在少自由度并联机器人机构的机型创新与应用方面的研究进展.认为具有各自应用背景的新型并联机器人机构成为并联机器人研究的热点.提出了并联机器人机构研究需要解决的问题.     

Investigation of surface integrity in high speed end milling of a low alloyed steel

Understanding the effects of cutting speed, feed rate and cutting depth on surface integrity is very important for the control of workpiece quality. This paper presents a global experimental study of surface integrity in the case of high speed end milling. In the global term, we include measurements of residual stresses, surface roughness and cutting forces. Our observations and conclusions are mainly concentrated on the effect of depth of cut with a set of constant parameters, such as cutting speed, feed rate, and tool/material couple. This set of constants has been determined using the theory of stability lobes. All experiments have been performed with an electro-spindle equipped with magnetic bearings. The results lead to a good understanding of the influence of cutting conditions on surface integrity in high speed milling of a low alloyed steel. The discussion examines a specific point where the residual stress and residual stress gradient are lowest and also the origin of the residual stress value.     

高速铣削与模具制造

分析了传统电火花加工工艺在模具制造中存在的主要问题，介绍了高速铣削技术加工模具的优越性和局限性。指出高速铣削技术是现代模具制造的发展方向之一，且高速铣削在模具制造中有广阔的应用和发展前景。并论述了今后我国高速铣削技术应用实践中的发展思路。     

扩大并联机床工作空间方法的研究

在计算并联机床工作空间时,由于其约束条件较多,因此在一定程度上影响了它的加工能力,为了扩大它的工作空间,在机床的工作台上安装一个转台,这就涉及到从刀位文件中进行转台转角分解的问题。采用传统的分解方法,住往产生章动角超出机床工作空间的问题。因此,针对机床坐标系和工件坐标系的关系,采用一致坐标系转台转角分解和非一致坐标系转台转角分解方法来解决这个问题。非一致坐标系转台分解是在一致坐标系转台转角分解的基础上进行二次分解,在工件定位时设定初始角,使章动角回到机床的工作空间内,从而达到扩大并联机床工作空间的目的。     

名优茶并联采摘机器人逆向运动学分析

结合并联机构的特点及茶叶采摘技术,创新性地开展了名优茶并联采摘机器人的研究。建立了机器人逆向运动学模型,利用齐次坐标变换计算出机器人运动学逆解;并在给定运动激励下,在MATLAB中绘制出动平台驱动臂的转角曲线。运用Pro/E绘制机器人三维图并导入ADAMS,建立了机器人虚拟样机模型,通过仿真获得驱动臂的转角曲线。上述两种方法的比较结果验证了机器人逆向运动学问题计算的正确性,同时表明了ADAMS仿真结果具有较好的精确性,并在此基础上制作了机器人原理样机。     

A direct comparison of the machining performance of a variax 5 axis parallel kinetic machining centre with conventional 3 and 5 axis machine tools

The current trend within the Tool and Die manufacturing sector is to machine components directly from hardened material using high speed 5-axis machining. This has been driven by the increasing requirements for cost competitiveness and lead-time reduction. Significant research effort has been applied to the optimisation of the process with factors such as tooling and machining strategies being considerably improved. However, the underlying structures of the machine tools used have remained unchanged and still consist of a serial kinematic chain. One of the standard justifications for the development of machines designed around parallel kinematic chains is that they should exhibit inherently greater stiffness, have higher axis accelerations and be capable of generating significantly higher cutting forces than conventional serial machines. This suggests that they should be ideally suited to the direct manufacture of tools and dies from hardened material.The comparison of different machine tool types is a complex and difficult process, particularly when their structures are fundamentally different. This paper describes an approach used to compare the performance of three very different types of machines. The technique uses two parameters; surface finish and geometric accuracy to assess the relative performance of different machine tools when cutting hardened material. The method is used to compare a serial kinematic 5-axis machining centre, a serial kinematic 3-axis machining centre and a parallel kinematic 6-axis machining centre.The results of the comparison are presented in this paper and show that all the machine tools performed to an equal standard for materials with a hardness of 54HRc but for very hard materials, 62HRc, the parallel kinematic machine out performed the serial machine tools.     

High Speed Face Milling of a Aluminium Silicon Alloy Casting

High speed machining of aluminium silicon alloy castings has gained significant interest from automotive industry involved in the development of the new generation of lightweight vehicles. This paper investigates the influence of workpiece microstructure, namely the secondary dendritic arm spacing (SDAS), tool material and geometry on tool wear mechanisms, cutting forces and surface integrity when face milling at cutting speeds of 5,000 m min⁻¹. It was found that the SDAS is the parameter with the main influence on tool wear rate; higher SDAS values require polycrystalline diamond (PCD) tooling due to the lower wear rates when compared with carbide tools. Finite Element Analysis (FEA) was employed to study the influence of tool wear on temperature and shear stress distribution in the workpiece material.     

高速激光雕刻的加速度优化控制算法及应用

针对高速激光雕刻提出了一种新的加速度优化控制算法，该算法将控制参数简化为三个，从而方便对噪声、动态误差、可靠性和工作效率的控制，实现高速高精度的细腻雕刻。最后给出了采用该算法的激光雕刻样图和激光雕刻机结构图。该加速度优化控制算法同样适用于其它类型的数控机床。     

3-RPC机构的安全工作空间设计

影响并联机器人安全工作空间的因素很多,如:奇异位型、机构结构尺度、静态受力等。以3-RPC并联机器人为研究对象,基于机构位置分析,以雅克比条件数为基准,采用数值迭代法得到机构杆长极限尺度。通过运动仿真验证机构在极限杆长空间内杆件的干涉性和静态受力,从而保证机构工作空间的安全性。最后,采用极坐标搜索法计算了机构的安全工作空间。     

叶片高速铣多轴编程技术的研究

根据叶片几何模型特点和高速切削工艺特点,从螺旋铣切削轨迹、回转式进退刀轨迹、高速切削参数三个方面进行高质、高效的叶片多轴高速切削加工轨迹研究,设计出叶片螺旋铣高速切削多轴编程算法,提高了叶片加工质量和效率。     

钛合金高速铣削的切削力实验研究与建模

针对难加工材料Ti6Al4V(TC4)进行高速铣削的铣削力研究,通过多因素正交试验,分析切削参数对切削力的影响,得出对难加工材料宜采用高速小切削的方法加工。将铣削加工中的切削力分解为纵向铣削力、横向铣削力和轴向铣削力,根据铣削力和切削加工参数之间的关系,采用最小二乘法等概率统计方法和回归分析原理,建立了三向铣削力模型。对所建立的铣削力模型进行回归参数显著性检验,分析所构建模型的置信度和残差,结果表明所建立的铣削力模型能很好地符合原始实验数据,可靠性好,能用于铣削力的预测和控制,为高速铣削钛合金的参数优化提供可靠依据。     

高速铣削参数对工件表面质量的影响

切削参数对工件的表面质量有着重要的影响,本文通过单因素实验,研究高速铣削参数对已加工工件表面粗糙度、残余应力及残余应力分布的影响规律.实验表明,高速铣削能够获得较好的工件表面质量.     

MasterCAM X7高速铣削及其三维编程的实现

高速铣削编程在MasterCAM X7中的使用,使机械零件数控加工的编程方法、加工质量和效率都有很大程度的改进和提高。通过运用这种编程方法,有助于实现机械零件高效精确的加工,同时减少刀具及机床的磨损。在三维零件加工编程中的使用,则可以方便地实现以往多步骤设置编程才能够达到的加工效果;不同加工策略的灵活运用,使复杂曲面的加工编程和刀具路径的生成更加稳定、可靠,加工质量和效率显著提高。     

A hexapod-based machine tool with hybrid structure: Kinematic analysis and trajectory planning

This paper shows kinematic analysis and trajectory planning for a novel machine tool structure consisting of a six degree-of-freedom hexapod machine and a two-degree-of-freedom rotary table. Accordingly, to operate the proposed machine tool, eight coordinates should be defined. Since a conventional part programming can define at the most five axes, the three remaining coordinates should be defined by using appropriate trajectory planning. An analytical model is developed that defines the relationships among the parameters in the proposed structure. A rule-based model is also developed to select the redundant coordinates without going through any complex and time-consuming calculations.     

液压支架顶梁焊接机械臂的运动学分析与仿真

针对液压支架顶梁焊接过程中焊接工艺不完善、焊接难度大的现状,设计一种五自由度焊接机械臂,以保证顶梁的焊接效率和质量。基于改进D-H参数建模方法,对顶梁焊接机械臂进行正、逆运动学分析求解;采用蒙特卡罗法对液压支架顶梁焊接机械臂的有效工作空间进行分析;使用MATLAB中Robotics Toolbox工具箱对焊接机械臂进行建模和轨迹规划分析和仿真,得到各关节的角位移、角速度以及角加速度曲线;使用Adams得到机械臂的实时跟踪轨迹,经验证可知MATLAB的轨迹规划是正确的。分析仿真结果可得,设计的顶梁焊接机械臂轨迹平稳并连续,满足运动学要求,为后续顶梁焊接机械臂的动静力学分析和优化设计以及运动控制奠定了基础。