差速器三維建模設計（說明書+三維圖）

差速器三維建模設計（說明書+三維圖）,差速器,三維,建模,設計,說明書 差速器三維建模 3.1 軟件簡介 Pro/E是美國PTC（Parametric Technology Corporation,參數(shù)技術公司）于1989年開發(fā)的一種先進的工業(yè)造型及工程設計自動化（MDA）軟件，在支持產(chǎn)品并行開發(fā)環(huán)境方面有獨到之處。Pro/E軟件通過一系列相關的模塊把多個設計部門聯(lián)系起來，使各個相關部門同時致力于單一產(chǎn)品的開發(fā)之中，具有工業(yè)設計和機械設計多項功能。 一、Pro/E的主要特點： 1、實體造型 Pro/E具有三維實體建模技術，在三維環(huán)境中將模型真實地呈現(xiàn)在設計者面前，建立的模型具有體積與表面積數(shù)據(jù)，因此，可以輕易地計算出產(chǎn)品的質量特性，如重量、慣性矩、重心等。 2、單一數(shù)據(jù)庫及其相關性 Pro/E中建立的所有工程資料全部來自一個數(shù)據(jù)庫。Pro/E具備所有應用的相關性。也就是說，Pro/E的所有模塊都是相關的，在產(chǎn)品開發(fā)過程中某一處的修改能擴展到整個設計中，同時更新所有的工程文件，包括裝配體、二維工程圖及加工數(shù)據(jù)。 3、參數(shù)化設計 Pro/E借助其獨特的單一數(shù)據(jù)庫設計，將每個尺寸視為可變的參數(shù)，設計者只要修改這些尺寸參數(shù)，相關的實體模型就會依照尺寸的變化重新生成，同時，設計者還可以利用邏輯關系式或數(shù)學運算方式建立尺寸與尺寸之間的聯(lián)系，達到設計的一致性。 4、特征造型 使用工程人員熟知的一些特征如：圓角、倒角、孔、殼等作為產(chǎn)品幾何模型的構成要素，通過給定這些特征的合理參數(shù)（包括幾何參數(shù)以及非幾何屬性），即可建立三維模型。 二、Pro/E的主要功能 草繪、生成零件圖、生成裝配圖、生成工程圖、運動仿真、加工仿真等。 3.2差速器建模 3.2.1建立錐齒輪式差速器的零件模型 差速器建模過程中相關零件模型的建立。 1．圓錐齒輪 錐齒輪的建模較為復雜。參數(shù)化設計錐齒輪的過程中應用了大量的參數(shù)與關系式。 錐齒輪建模分析（如圖3-1所示）： （1）輸入關系式、繪制創(chuàng)建錐齒輪所需的基本曲線 （2）創(chuàng)建漸開線 （3）創(chuàng)建齒根圓錐 （4）創(chuàng)建第一個輪齒 （5）陣列輪齒 圖3-1錐齒輪建模分析 2.錐齒輪建模過程 （1）輸入基本參數(shù)和關系式 a.打開Pro/E使用軟件，點擊文件中“設置工作目錄”，設置文件的保存地點； b.單擊，在新建對話框中選擇“零件”，輸入文件名點擊確定，進入繪圖界面。如圖3-2所示； 圖3-2新建窗口 c.在主菜單上單擊 “工具”→ “參數(shù)”，系統(tǒng)彈出“參數(shù)”對話框，如圖3-3所示； 圖3-3參數(shù)對話框 在“參數(shù)”對話框內(nèi)單擊按鈕，可以看到“參數(shù)”對話框增加了一行，依次輸入新參數(shù)的名稱、值、和說明等。 d．在主菜單上依次單擊 “工具”→ “關系”，系統(tǒng)彈出“關系”對話框，在“關系”對話框內(nèi)輸入齒輪的基本關系式； 圖3-4關系式對話框 (2)創(chuàng)建基本曲線 圖3-5基本曲線 （3）建立錐齒輪基體 圖3-6建立基體 圖3-7建立陣列 3．行星齒輪軸的建模過程 （1）開Pro/E使用軟件，同齒輪建模步驟，首先設置文件工作目錄。 （2）單擊新建按鈕，新建零件，進入繪圖窗口。 （3）點擊草繪標志，選取參照面，進入草繪界面，如圖3-8所示。 圖3-8草繪對話框 （4）繪制一個圓，輸入所需直徑，單擊完成按鈕，完成草繪；單擊拉伸按鈕，選擇所繪制的圓，輸入要拉伸的軸長，點擊完成，就完成了行星齒輪軸的建模，如圖3-9所示。 圖3-9行星齒輪軸 4．車輪的建模 （1）初始步驟與行星齒輪軸的建模一樣，先進入草繪界面繪制所需的圓進行拉伸，得到一個較窄的圓柱體，再將兩邊倒圓角，形成車輪的大致模樣(圖 3-10) 圖3-10車輪大致形狀 （2）再次使用草繪按鈕，草繪如圖3-11所示的形狀，單擊完成退出草繪界面。 圖3-11草繪 （3）使用拉伸按鈕，選擇上面所繪制的圖形，輸入適合的深度，點擊去除材料按鈕，將其去除，就可得到最后形狀的車輪（圖3-12）。若想改變齒輪的外觀，可點擊按鈕更改外觀。 圖3-12完成的車輪 3.2.3 錐齒輪式差速器的組件（裝配） 1．首先新建一個組件窗口（圖3-11），進入裝配界面； 圖3-11新建裝配窗口 2. 裝配兩錐齒輪。 選定以right和front為基本面，基軸原點為參考點，首先導入主動錐齒輪，具有一個旋轉自由度，所以選定銷釘連接，設置為對齊和配對，參照基準平面，然后進行定位。再導入從動錐齒輪與主動錐齒輪對齊配合，同樣具有一個旋轉自由度，進行平移調整合適的位置使其與主動輪配合如圖3-12所示。 圖3-12主、從動齒輪裝配 3．裝配差速器錐齒輪。 仍然選定上面的參照作為主參照導入半軸齒輪，與從動輪是軸對齊，調整兩個半軸齒輪至合適的位置；因為行星齒輪室和從動錐齒輪一起旋轉，則從錐齒輪選定兩個參照，創(chuàng)建參照平面，兩個差速器行星齒輪，添加齒輪斷面和參照平面距離的裝配關系，導入行星齒輪軸，添加差速器行星齒輪的軸和差速器行星齒輪軸孔為插入的裝配關系，使其定位，如圖3-13所示。 圖3-13差速器錐齒輪的裝配 4．行星齒輪軸固定端的裝配。 導入兩個固定端，添加其與行星齒輪軸為插入的裝配關系，并使其與從動錐齒輪齒面裝配關系為配對，設置配對角度90°，最后裝配如圖3-14所示。 圖3-14固定端的裝配 5．車輪的裝配。 車輪和半軸齒輪是一起旋轉的，所以添加車輪上連接的軸與半軸齒輪周孔為插入的裝配關系，是剛性連接，軸端面與半軸齒輪端面為配對關系，然后采用軸對齊便可進行裝配，裝配后如圖3-15所示.，然后裝配另一半齒車輪，也是和半軸齒輪是剛性連接，最后總裝配圖如3-16所示。 圖3-15車輪裝配 圖3-16裝配完成的差速器 第四章 基于ADAMS軟件的差速器運動仿真 4.1 虛擬樣機仿真軟件ADAMS的介紹 ADAMS,即機械系統(tǒng)動力學自動分析(Automatic Dynamic Analysis of Mechanical Systems)，該軟件是美國MDI公司(Mechanical Dynamics Inc。)開發(fā)的虛擬樣機分析軟件。目前,ADAMS己經(jīng)被全世界各行各業(yè)的數(shù)百家主要制造商采用。根據(jù)1999年機械系統(tǒng)動態(tài)仿真分析軟件國際市場份額的統(tǒng)計資料,ADAMS軟件銷售總額近八千萬美元,占據(jù)了51%的份額。 ADAMS軟件使用交互式圖形環(huán)境和零件庫,約束庫,力庫,創(chuàng)建完全參數(shù)化的機械系統(tǒng)幾何模型,其求解器采用多剛體系統(tǒng)動力學理論中的拉格郎日方程方法,建立系統(tǒng)動力學方程。對虛擬機械系統(tǒng)進行靜力學,運動學和動力學分析,輸出位移,速度,加速度和反作用力曲線。ADAMS軟件的仿真可用于預測機械系統(tǒng)的性能,運動范圍,碰撞檢測,峰值載荷以及計算有限元的輸入載荷等。 ADAMS一方面是虛擬樣機分析的應用軟件,用戶可以運用該軟件非常方便地對虛擬機械系統(tǒng)進行靜力學,運動學和動力學分析.另一方面,又是虛擬樣機分析開發(fā)工具,其開放性的程序結構和多種接口,可以成為特殊行業(yè)用戶進行特殊類型虛擬樣機分析的二次開發(fā)工具平臺。 ADAMS軟件由基本模塊,擴展模塊,接口模塊,專業(yè)領域模塊及工具箱5類模塊組成。用戶不僅可以采用通用模塊對一般的機械系統(tǒng)進行仿真,而且可以采用專用模塊針對特定工業(yè)應用領域的問題進行快速有效的建模與仿真分析。 4.2 運用ADAMS軟件對差速器進行運動學仿真 4.2.1導入等效仿真模型和設置基本參數(shù) 由于ADAMS軟件的建模模塊功能有限，一般先在常用三維建模軟件（PROE）建立等效的仿真模型，然后通過中間格式的文件（*.x_t）導入ADAMAS軟件，這樣可以大大提高ADAMAS建模效率。 1.導入差速器的等效模型 啟動ADAMS/VIEW程序，彈出一個打開方式對話框，如圖4-1，選擇Import a file，找到保存文件所在的目錄文件夾，點擊確定。系統(tǒng)彈出文件導入對話框，在File Type處空白區(qū)域左擊鼠標，選擇Parasolid類型；在File To Read右處空白區(qū)域右擊鼠標，選擇路徑Browse，選擇文件chasuqi.x_t；在Model Name處空白區(qū)域新建文件名dc，選擇OK，文件就被成功導入了，如圖4-2。 圖4-1 文件導入對話框 圖4-2 差速器等效三維模型 （1） 設置基本環(huán)境 由于導入ADAMAS的模型上各參數(shù)都是默認的，為了后面的仿真工作的順利進行，一般都要根據(jù)實際情況重新設置基本參數(shù)。 1)檢查默認單位系統(tǒng) 在Settings 菜單選擇 Units 命令，顯示單位設置對話框，當前的設置應該為MMKS系統(tǒng)（MM, KG, N, SEC, DEG, H）。 2)設置工作柵格 在Settings 菜單選擇 Working Grid 命令，彈出對話框如圖4-3，設置：Size X=400， Size Y=400，Spacing X=10, Spacing Y=10， Showing Working Grid=on;選擇ok按鈕，設置完成。 3)設置圖標 在Settings 菜單選擇Icon命令，這時系統(tǒng)彈出如圖4-4所示對話框；在New Size欄輸入10；選擇OK按鈕。 圖4-3 柵格設置對話框 圖4-4 圖標設置對話框 圖4-5 重力設置對話框 4）檢查重力 設置在Settings 菜單選擇Gravity命令，顯示對話框如圖4-5，將當前的重力設置應該為X=0, Y=-9806.65, Z=0, Gravity=ON;選擇OK按鈕。 5）設置剛體屬性 首先鼠標右擊模型中的左車輪剛體，顯示如圖4-6；然后鼠標左擊 modify，顯示對話框如圖4-7；在Category欄選擇Mass Properties，在Define Mass By 欄選擇Geometry and Material Type,在 Material Type欄右擊選擇Material→Guesses→steel；點擊OK按鈕，左輪的材料屬性的修改完成。按照同樣的方法完成差速器剩余其余構件右輪、兩個行星輪齒、左半軸的錐齒、右半軸的錐齒、行星輪架、大錐齒、傳動錐齒的材料屬性修改。 圖4-6 剛體屬性選擇對話框 圖4-7 剛體屬性修改對話框 4.2.2添加約束 （1）添加剛體間的約束 在主工具箱中右擊，然后選擇，顯示對話框如圖4-8，在幾何模型對話框中選擇，選擇左半軸錐齒和左輪，完成左半軸錐齒與左輪固定在一起。采用相同的方法分別將右半軸錐齒和右輪、行星輪連桿和大錐齒固定一起。 圖4-8 幾何模型對話框 （2）添加旋轉副和齒輪副 1）添加旋轉副 在主工具箱中右擊，然后選擇，顯示對話框如圖4-9，在幾何模型對話框中左擊，在對話框下面的Construction 欄選擇 2 Bodies-1 Location 和 Pick Geometry Feature，然后依次選擇傳動軸錐齒、地面，錐齒中心的位置，控制好沿著傳動軸的方向，點擊確定，完成的轉動副如圖4-10。 采用相同的方法，將左半軸錐齒、右半軸錐齒、兩個行星輪、行星輪架加上旋轉副，完成轉動副后的模型如圖4-11。 圖4-9 約束對話框 圖4-10 傳動錐齒旋轉副 圖4-11 差速器的六個旋轉副 2）添加齒輪副 點擊幾何模型對話框中的，創(chuàng)建Marker坐標，在Marker欄選擇Add to Ground，在Orientation欄選擇Global XZ，選擇行星輪和左半軸錐齒嚙合的地方，點擊OK按鈕，完成Marker坐標的創(chuàng)建，如圖4-12高亮處；點擊約束對話框中的，出現(xiàn)對話框，如圖4-13，在Joint Name欄選擇在前面建好的行星輪旋轉副和左半軸旋轉副，在Common Velocity Marker欄選擇剛剛建好的Marker坐標，點擊OK按鈕，完成齒輪副的創(chuàng)建，如圖4-14。 圖4-12 齒輪副嚙合點 圖4-13 齒輪副對話框 圖4-14 行星輪與左半軸錐齒的齒輪副 如上述方法，可將剩余的行星輪與半軸錐齒、傳動錐齒與大錐齒的齒輪副添加完成，完成后的齒輪副如下圖4-15 圖4-15 差速器的五個齒輪副 4.2.3施加驅動 鼠標左擊主工具箱中的，在主工具箱下面的Speed 欄輸入 -10* time，然后選擇傳動錐齒輪的旋轉副，加好后的驅動如下圖4-16： 圖4-16 傳動錐齒的驅動 采用相同的方法在左半軸錐齒和右半軸錐齒的旋轉副上分別添加一個驅動，并使其轉速為1*time。 4.2.4建立差速器的仿真腳本 在Simulate菜單中，選擇Simulation Script→new命令，彈出對話框如圖4-17。然后在Script 欄新建腳本名line，在Script Type 欄選擇Adamas/Solver Commands， 在命令框內(nèi)創(chuàng)建如下圖的腳本，點擊OK按鈕，完成直線行駛的控制腳本。 圖4-17 直線行駛控制腳本對話框 采用相同的方法，建立左轉彎和右轉彎行駛時的控制腳本，如圖4-18、 圖4-19。 圖4-18 左轉彎控制腳本 圖4-19右轉彎控制腳本 4.3差速器的運動學仿真后處理 4.3.1差速器的運動學仿真 在Simulate菜單中，選擇Scripted Controls命令，彈出對話框如圖4-20。在Simulation Script Name欄點擊右鍵依次選擇Simulation_Script→Guesses→line，接著單擊腳本仿真對話框中的按鈕，可以看到差速器的運轉情況。 圖4-20 腳本仿真對話框 4.3.2差速器的運動學仿真的運動分析 在主菜單下依次Review→Postprocessing（F8）或者直接單擊主工具箱里的按鈕，彈出ADAMS/PostProcessor窗口，如圖4-21，在該窗口下可對機械手進行運動學跟動力學的分析。 在后處理窗口上方單擊按鈕，新建一個后處理圖，在File菜單下的類型選擇Plotting，然后再在后處理窗口下方的Measure欄選擇左半軸錐齒、右半軸錐齒、行星輪架的加速度，單擊右側的Add Curves按鈕，即可生成三條角速度隨時間變化的曲線，如圖4-22 圖4-21 差速器后處理窗口 圖4-22 直線行駛時左、右半軸和行星輪架的角速度隨時間變化的曲線 為了使曲線圖表達更完善明確，可修改曲線的一些說明。單擊Page_2下的title按鈕，將其曲線名稱修改為zhixianyundong；單擊Curve_1按鈕，修改其名稱為xingxinglunjia，單擊Curve_2按鈕，修改其名稱為zuolun，單擊Curve_3按鈕，修改其名稱為youlun，修改后的曲線圖如圖4-23。 圖4-23 修改后直線行駛時左、右半軸和行星輪架的角速度隨時間變化的曲線 采用相同的方法，依次可以完成差速器在左轉彎和右轉彎時的運動仿真，并且生成左轉彎[圖4-24(a)]和右轉彎[圖4-24(b)]時左、右半軸和行星輪架的角速度隨時間變化的曲線。 (a)左轉彎 （b）右轉彎 圖4-24轉彎時左、右半軸和行星輪架的角速度隨時間變化的曲線 4.3.3差速器的仿真結果的分析 通過Adamas仿真軟件對所設計的差速器進行了運動學的仿真，可以很清晰的看到差速器順暢的運行過程，驗證了該方案的可行性。同時通過虛擬樣機技術，也虛擬仿真出了左右半軸錐齒和行星輪架的運動角速度，從上面的輪齒隨時間變化的曲線可以得出一個結論：（左半軸轉速）+（右半軸轉速）=2（行星輪架轉速）。當汽車直行時，左、右車輪與行星輪架三者的轉速相等處于平衡狀態(tài)，而在汽車轉彎時三者平衡狀態(tài)被破壞，導致內(nèi)側輪轉速減小，外側輪轉速增加。這也剛好吻合了差速器設計的基本要，通過仿真技術可以大大提高設計的可靠性，為結構設計提供了良好的基礎。 131Closed-loop Sensor System for Automated Manufacturing Machines A.A. Shaik1, G. Bright2 and W. L. Xu31Council for Scientific and Industrial Research, Material Science and Manufacturing, South Africa, ashaikcsir.co.za2University of Kwa- Zulu Natal, School of Mechanical Engineering, South Africa, brightgukzn.ac.za3Massey University, Institute of Technology and Engineering, New Zealand, w.l.xumasey.ac.nzAbstract. Many automated multi- axis machines operate under open loop control. The exact position in space of the end effecter or tool head is not sensed directly. The software controlling the robots or automated manufacturing machines make a calculated estimate of where the tool- head should be. This is often achieved by monitoring sensors on axes that track linear translation and rotations of shafts or gears. For low precision applications this system is appropriate. However, positional errors often occur. This method may not be suitable for high precision robots and automated machine tools. There exists a need for a sensor system that is capable of acquiring the exact spatial coordinates of the tool point or end effector directly. The aim of this research project was to design a low cost sensor system that would precisely locate the tool points spatial coordinates directly by closed loop control. This aided in the reduction of errors encountered in open loop control. The system was capable of seamless integration with existing techniques for motion control. The sensor system was able to locate the tool head in 2D space. With simple additions and modifications it rendered itself applicable to 3Dspace location of the tool head. It was modular, sufficiently robust and error immune such that it would work in almost any environment.Keywords: Automation, Manufacturing, Closed Loop Control 1. Introduction The need for a sensor system that provides direct feedback of the end effectors spatial coordinates is essential for precise assembly and machining. The objective of this research project was to design a parallel robot that would have an integrated sensor system. The sensor system should be low cost and be capable of locating the tool points spatial coordinates directly or aid in reducing the errors encountered in the open loop control. The system should be capable of seamless integration with existing techniques for motion control and should be able to locate the tool head in 2D space. With simple modifications it should render itself applicable to location in 3D space. It should be modular, sufficiently robust and error immune to work in almost any environment. There are numerous technologies available for the purpose of locating objects in space. These are the Global Positioning System (GPS with 10 m accuracy, a Differential GPS solution by 1 reduces the errors to less than 5 cm); proximity location through Bluetooth, WiFi and Cellular networks (position is deduced by knowing the cell with which a device is communicating) and triangulation systems (using lasers, ultrasound, etc.). In addition there are imaging methods used to determine position. 2 Discusses a low cost solution employing a camera and LCD (Liquid Crystal Display) screen to locate an objects coordinates in 2D with high accuracy. VSLAM (Visual Simultaneous Location and Mapping) systems used in mobile robotics use cameras to build a map of its surroundings for navigation purposes. There are also image processing techniques that can determine movement from consecutive frames provided by a camera. These images also provide information regarding the surroundings and are completely passive. The accuracy and resolution however depend on how far from the object the camera is and the resolution of the camera itself. All these technologies are suitable for locating large objects in a relatively large space, for instance locating people in buildings 3. In industry, however, robotic arms used for assembly, welding or spray- painting move in a confined space and the position of the end effector must be determined with millimeter to sub- millimeter resolution. For manufacturing purposes the resolution of computer numerically controlled (CNC) machines range from micrometers to nanometers. For such purposes Laser interferometer technologies are sometimes used. These position sensing systems have excellent resolution as well as accuracy and are used in manufacturing environments for IC (Integrated Circuit) design, prototyping and manufacturing. An optical heterodyne interferometer designed at NASAs Jet Propulsion Laboratory can measure linear displacements with an error of 20 pm (Pico- meters, 10- 12m). Grid encoders offer another solution; grids made by OPTRA have a coverage range up to 380 mm 380 mm. Their accuracy and repeatability lie in the same range as Laser Interferometers (i.e. micro- to nanometer resolution). Both Grid encoders and Laser Interferometers are expensive technologies, usually costing hundreds of thousands to millions of dollars. Furthermore, they can not measure absolute position directly; they both use fringe patterns (due to light wave interference) to measure relative displacement. The integration of these displacement measurements coupled with the knowledge of the end- effectors initial position yields the current position. 308 A.A. Shaik, G. Bright and W. L. Xu 2. Proposed Sensor Feedback System The problem of locating the end effector of a robot in real world space is first reduced to finding its position in a 2D plane with regard to a point reference. The general problem of location in 3D space is solved by attaching two 2D planes at right angles. With such an arrangement 2 axes coincide and if the reference point of each plane coincides, the result is a 3 axis sensor system for position location. This paper attempts to document a solution of finding the end effector in a 2D plane. After consideration of the available physical quantities (ultrasound, infrared light, radio waves, etc.) used when locating objects, it was decided that a laser would be most suitable for the reasons that follow. A laser light sensor can be conditioned to provide a digital output. Comparatively analogue sensors require digitization for use in digital systems. Analogue signals are compromised by atmospheric effects, temperature, humidity and unshielded noise from surrounding machinery. Triangulation utilizing radio, ultrasound or infrared waves is not suitable as multiple reflections from surrounding surfaces cause interference and provide unreliable results. They also require modulation and demodulation to distinguish the signals generated from any that can be created by the environment. The proposed sensor concept utilizes a direct approach, with a laser attached to the end effector and a sensor grid (a grid of laser sensors equally spaced in rows and columns) mounted directly above it. This is a natural choice as the coherent nature of laser light makes finding the end effector in 2D space easy if the laser beam remains perpendicular to the sensor plane at all times. The end effectors location is the same as the sensor which is stimulated (in a 2D plane, depth has no meaning). This perpendicular constraint can be enforced by the use of tilt sensors that can tell the orientation of an object, corrections can then be made to keep the end effector perpendicular. Also the inherent nature of the robot can be sufficient to force this condition. The Flex-Picker is one such example as its arms force the end-effector to remain parallel to its base at all times. It must be stressed that this sensor system requires only bit (1 or 0) information for each sensor. Each sensor is either stimulated or not stimulated. This makes data processing and transfer far simpler and makes control easier. The resolution is limited to the spacing between sensors. If the spot light is smaller than the spacing between sensors, these will represent a dead zone where beam tracking will be lost completely. The laser light detectors are phototransistors with a Darlington configuration. Current fabrication techniques can accommodate millions of transistors on a sliver of silicon. These fabrication methods can be used to construct a detector screen with an exceptional and practical resolution. Resolution affects data output, a greater resolution implies more data per unit area (more sensors). A hybrid type system would involve a sensor grid with a comparatively lower resolution. Each sensor provides a checkpoint. Knowing the exact spatial distance between these detectors provides the controller a means to limit the errors incurred. Instead of accumulating errors from one extremity to the next, errors only exist between successive detectors Figure 1.1. Block Diagram of intended sensor system. 3. Mechatronic Design The mechatronic design consists of 3 parts the mechanical, electronic and software components. As stated in 4, the term mechatronics is used for the integration of microprocessor control systems, electrical systems and mechanical systems. The mechanical structure was designed to test the electronic hardware and software control, the purpose of which is to validate the proposition. The mechanical design was also undertaken to explore parallel mechanisms. The design is documented to deliver a simple prototype. The specification on resolution was relaxed as it was stated that fabrication techniques can produce a screen with a realistic resolution. More emphasis was placed on creating a cheap system that could reduce errors. Mechanical Structure: The mechanical structure is based on a Flex- Picker pick and place parallel kinematics industrial robot. It is a scaled adaptation. The design consists of 4 articulated arms; 4 servo motors; a plate end effector with attached laser; ball- cup joints and a mounting frame. The entire mechanical structure is 600mm in length, 400mm wide and 500mm high. Figures 1.2 and 1.3 illustrate the parts and the assembly. Figure 1.2. Significant mechanical parts that position the laser: (a) Ball from bearing, (b) Cup from modified bearing socket, (c) Servo motor with upper arm attached and mounting bracket, (d) Lower arm component, (e) Laser and laser mounting It must be noted that the lower arm components are held together via 2 springs (not shown), one just below the elbow and the other just above the wrist for each Closed- loop Sensor System for Automated Manufacturing Machines 309 forearm. The ball cup joints give a large degree of freedom. These were made from ball in socket bearings. The upper arms swing from side to side whereas the lower arms can move up, down, left and right and can even rotate about the elbow by sequencing pairs of its basic motion (induced by rotating pairs of servos). The laser can move about a section of space, which is roughly a hemisphere below the sensitivity area (the square cut- out on the servo mounting frame, Figure 1.3 (a). The guidelines for parallel mechanism design were followed as provided in 5. Figure 1.3. Assembly of all components resulting in the final structure: (a) All servos mounted with upper arm and lower arm attached to laser, (b) Lower arm attachment to laser end effector, (c) Articulated arm elbow joint, (d) Complete Assembly Electronic Hardware: The system designed is a hybrid type as mentioned in section 1.2. The resolution is low due to the 5 mm diameter of the LED type package of the laser sensor. Also the PCB tracks routing sensors to buffers and data converters occupy significant space, which could not be avoided. To improve resolution a smaller package should be used, preferably surface mount, however these could not be sourced at the time this screen was made. Each sensor grid consists of 64 BP103 phototransistors arranged on an 8x8 grid. The resolution (distance between the centres of 2 successive sensors) is 18 mm on both the rows and columns. This phototransistor has a daylight filter to prevent wrongful stimulation by ambient light. It is sensitive to light wavelengths in the range 600900 nm. A 650 nm key- ring laser is being used as a sensor stimulant. This is a cheap and effective solution. Although the output power of this laser is less than 1 mW, it is sufficient to turn the phototransistor on. The sensed signal has to be buffered/amplified to ensure that the voltage level output from the LPT133 is within the proper digital range (0 0.8 V for a logic 0 and 3.5 5 V for a logic 1), according to 6 for proper electronic design. For this purpose each sensor on a column is passed to a transistor driver within a ULN2803, which consists of 8 transistor drivers. Eight driver chips are used, one for each column. The outputs from each ULN2803 are fed to a parallel to serial data converter, the 74LS166 to serialize the data for transfer to a PC. The 8 output serial lines from the data converters are fed to an ATMEL ATmega8515 microcontroller. There are eight bytes of data and each bit represents one sensors current state. The controller is used to transfer the 8 bytes of data to the PC via its USART transceiver and the PCs RS232 serial port. It also controls the 74LS166 data converters and the servo motors. The microcontroller enables the data converters and clocks the data out of each of them. Software: The software has two parts to it, i.e. the microcontroller code and the user interface. Microcontroller Code: There are 4 parts to the microcontroller code, i.e. receiving and interpreting commands from the PC; sensor data acquisition; data transfer and servo rotation.Receiving and Interpreting Commands There are commands for activation, sensor data acquisition, data transfer and servo rotation. These tell the controller when to run the corresponding routines. Sensor Data Acquisition - This routine enables/disables; clears and clocks the data out the parallel to serial converters. See 7 for a complete description of how this is achieved. Data Transfer - Once the Sensor Data Acquisition routine completes, the 8 bytes of data await transfer. The serial port of the PC works with the ASCII character set. Each data byte representing a number in the range 0- 255 must be sent out the microcontrollers serial port via 3 ASCII characters (one character for each of the hundreds, tens and units digits) representing numbers (0-9 which in ASCII is 0 x30- 0 x39 in hexadecimal notation). In total there are 32 character bytes (4 character bytes per data byte, including byte completion character) transferred from controller to PC. Using a Baud Rate of 9 600 (bits per second) and including a parity check bit (9 bits per byte) this takes 0.03 s to complete. Servo Rotation - As there are 4 servo motors, 4 pulse-width modulated signals have to be generated. Incoming commands indicate a particular servo and the length of its pulse- width. The pulse- width value will be received in 3 bytes. In total there are 16 character bytes transferred from PC to controller (4 bytes per servo) to position the laser as required. The time taken to do this is 0.015 s (9 600 Baud). Timers within the controller will ensure that the PWM signals comply with the desired range of 1- 2 ms. User Interface- The user interface provides a visual display of the data received, 64 colored circles represent the 64 phototransistors. The display routine searches through each data byte (columns) for low bits (rows) and changes the color of the corresponding circle (blue when not stimulated, red when stimulated). The interface also allows the user 2 options for control; either via a mouse or a selection grid. With the mouse the user can manually control the laser and move it anywhere within its mechanical constraints. When the selection grid is active the laser will position itself, first finding a reference point and then move along rows and columns. It will pass over all sensors which have been selected by the user.310 A.A. Shaik, G. Bright and W. L. Xu Control Design Overview: The sensor grid provides direct feedback of the position of the laser/tool head at discrete points in space. The purpose of the grid is to reset accumulated errors in the positioning control system. The coordinates of the sensors are stored in the controlling software. When errors are accumulated and need to be reset the end effector is moved to sensor that is closest to the end effector. Once it is positioned and the sensor is not stimulated it knows that there are errors in its positioning and it then spirals out to locate the sensor and reset the error. 4. Performance/Operation The novelty of this sensor system lies with the fact that it can determine the position of the end effector directly, provided that the constraints mentioned are strictly adhered to. It does not determine position from calculation as in laser triangulation systems and it does not integrate displacements as in laser interferometers. The novelty of the mechanical design is with respect to the 4 arms that attach to the end effector. The arrangement and configuration has the advantage of easier control, a simplified kinematics model and added stiffness. Sensor Grid: The sensor grid operates as intended after having integrated all the functions described on the microcontroller. The project is still in the testing phase and is currently being integrated into the system. Much work is still needed to ensure the screen works properly with all data conversion and transfer routines. The second version of the screen is currently being designed to improve resolution and system repeatability. Mechanical Structure: The most important aspect of the mechanical structure is the articulated arms. A simulation model was created to simulate and animate its movement, to ensure that it complies with the requirements of the design. The results are shown in Figure 1.4. A motion generator is attached to each servo head and is set to follow a harmonic function. The end effectors motion spanned the entire range of the sensitivity area. Most importantly the laser mounting remained parallel to the sensor grid PCB (sensor plane) throughout its motion, this ensures that the laser beam is always perpendicular to a detector. The singularities for this mechanism occur when the arms are completely extended or folded, when the upper and lower legs are co- linear. This situation was avoided in the simulation and can be avoided in reality. 5. Conclusion The objective of creating a parallel robot with an integrated sensor system has been met. The mechanical system works with the control system designed. The only issue with the mechanical aspect is that the ball joints. They do not provide sufficient positioning accuracy and repeatability. The use of high performance ball joints or compliant joints in a future version of the robot will eliminate this problem. The sensor system is of low cost and provides direct feedback. Resolution is currently the only problem, but as mentioned fabrication techniques can resolve this issue. This system is modular and facilitates inclusion in existing systems. 3D location is possible with two of these sensor grids placed at right angles to each other. The sensor grid is also robust and is not affected by ambient light. A fair comparison with best practices of industry can only be made with a sensor system that has roughly the same resolution and accuracy. This project sought to test the theory that such a system could be created, and if it would be useful. As such it has accomplished its purpose, but a fabricated screen could provide proper quantitative performance measures. Figure 1.4. Simulation of laser tool head movement: a and b Bottom views, c and d Side views, e and f Top views References 1 Willgoss, R., V. Rosenfeld and J. Billingsley 2003, High Precision GPS Guidance of Mobile Robots. 2 Ziegert, J. 2005, Active Vision/Display Sensors for Precision Positioning. University of Florida, USA. 3 Dempsey, M, 2003, Indoor Positioning Systems in Healthcare, a Basic Overview of Technologies. Radianse, Inc. 4 Bolton, W. 2