伺服控制技术

作者:xingyang                         时间：2010-12-02

轴承及轴承相关技术文章（轴承型号查询网提供） 关键字：轴承,机床 Kinematic Analysis and Modeling of 6-PSSVirtual-Axis Machine ToolDING Hong-sheng(School of Mechanical Engineering and Automation, Beijing Institute of Technology, Beijing　100081)ZHANG Tong-zhuang(School of Mechanical Engineering and Automation, Beijing Institute of Technology, Beijing　100081)YANG Wei-qiang(School of Mechanical Engineering and Automation, Beijing Institute of Technology, Beijing　100081)Abstract：A new form of 6-PSS virtual-axis machine tool was established, and its kinematic modeling was proposed. To avoid the constructional interference between the ‘legs’ and to keep 6 freedoms during the processing, a method was adopted that requires the moving platform not to rotate around its own axis, and the lost freedom to give place to the rotation of tools. And on the basis of the modeling, forward and inverse velocities were analyzed. The data-changing curves of the actuators' displacements and velocities were confirmed by a simulation software. A reasonable kinematic model can make the description of the manufacture process simple and intuitiveKey words：spatial mechanisms; virtual-axis machine tool; kinematic analysis▲[img]http://www.c-cnc.com/news/file/2008-4/2008428153949.gif[/img]图1　6-PSS型机构简图1　6-PSS虚拟轴机床运动分析　　Stewart并联机构的研究随着该机构向机器人、新型数控机床等领域的拓展而日趋深入［1，2］。6-PSS构型是在6-SPS型Stewart并联机构的基础上，通过机构变异而构思出的并联机构形态［3］。与6-SPS型相比，6-PSS型机构因驱动装置全部固定在基座上，大大减轻了可动构件的质量，从而可显著减小惯性，有利于改善装置的动特性；其动连杆直径显著变小，容易避免杆间的结构干涉(SPS型的驱动装置是装在连杆上的，容易产生结构干涉)。　　图1为6-PSS构型虚拟轴机床简图(机架支撑未全部画出)，图中机床机座为台体，动杆为定长，上端以球铰副与导轨上的滑块相连，下端以球铰副与动平台相连，导轨的倾斜度可调。2　运动学建模　　建立si(xe,ye,ze,φx,φy,φz)显式表达式，其中：xe,ye,ze为动平台上刀具刀尖坐标。设刀具垂直于动平台，则φx,φy,φz分别表示刀具矢量与各坐标轴夹角。如图2所示的坐标系中，台体下表面中心为绝对坐标系原点O，动平台中心为参考坐标系原点O′，动杆长度L和刀具长度L′为定长，动平台中心绝对坐标为O′(xp,yp,zp)，设pi为动平台上某点，其绝对坐标为(xi,yi,zi)，pi相对坐标为(xpi,ypi,zpi)，si坐标为(spi,spi,spi)(i=1,…,6)，则：pi点坐标(xi,yi,zi)可经过矩阵变换求得：[img]http://www.c-cnc.com/news/file/2008-4/200842815400.gif[/img]图2　运动学模型　　(1) [img]http://www.c-cnc.com/news/file/2008-4/2008428154017.gif[/img]　　因动平台具有6个自由度，绕轴y′转动自由度可由安装在动平台上刀具的转动代替［4］，所以求坐标变换矩阵T时可限定动平台不绕其自身主轴y′转动。设其先绕z′轴转α(-π/2，π/2)角，再绕x′轴转β(-π/2,π/2)角，这样处理大大降低了动杆之间干涉的可能性，故有

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