第2章正投影法原理.pps

1、,Form of Projection 投影的形成 Types of Projection 投影法分类 Features of Orthographic Projection 正投影特性 Three-view of Component 物体的三视图 Exercises 练习题,Principles of Orthographic Projection 正 投 影 法 原 理,请点击相应标题显示其内容,Form of Projection 投影的形成,Projection method : When the line of projection passes through the object

2、 and the pre - established plane, there will be graphics produced on the plane. This method is called projection.,投影法： 投影法是投射线通过物体，向选定的平面投射， 并在该面上得到图形的方法。,请点击鼠标左键显示后面内容,Types of Projection 投影法分类,Projection method 投影法,Central projection method 中心投影法,( The central projection is mainly used for the pic

3、torial drawings of buildings. 一般多用于建筑图样 ),Parallel projection method 平行投影法,( It is used in most engineering drawings. 广泛用于机械、电子、化工等行业的图样),请点击鼠标左键显示后面内容,3. Homophyly: When planar features or lines are inclined to the 类似性 projection plane in general, the projection produces similar shapes of the origi

4、nal feature. The length of projected lines will be shorter than the real length. 当图形或直线倾斜于投影面时，图形的投影成类似形,线 段的投影长度比实长短。,2. Accumulation: When planar features or lines are orthogonal to the 积聚性 projection plane, the projection accumulates to a line or a point. 当图形或直线垂直于投影面时,其投影积聚成一直线或点。,1. Authenticit

5、y: When planar features or lines are in parallel with the 真实性 projection plane, the projection shows the real shape or true length of the features being projected. 当平面图形或直线平行于投影面时,其投影反映实形或实长。,Features of Orthographic Projection 正投影特性,请点击鼠标左键显示后面内容,1. Form of three-view drawings 三视图的形成,Three-View of

6、Component 物体的三视图,请点击鼠标左键显示后面内容,Single orthographic projection 单面正投影,How shall we do it? 如何解决？,A plan of an object is not always sufficient to describe it completely. 仅有物体的一个投影不能确定 它的空间形状。,Additional orthographic views can be drawn to sufficiently describe an object. It is necessary to use multiple v

7、iews in engineering drawings. 为了确定物体的空间形状, 需要增加投影面。故在工程图样中多采用多面视图。,These axes meet at a point which is called the origin. 三投影轴垂直相交于原点O.,Y-axisY轴,Three-View of Component 物体的三视图,请点击鼠标左键显示后面内容,1) Set up three-view projection system 建立三面投影体系 The three projection planes are orthogonal from each other. Ma

8、ke up of one projection system. 采用三个相互垂直的投影面,构成投影体系。,V-plane Vertical plane 正(垂直)平面,H-plane Horizontal plane 水平面,W-plane Wall(Auxiliary vertical) plane 侧(辅助垂直)平面,The intersection lines of the three projection planes are called the axes of projection. 三投影面的交线为投影轴,X-axisX轴,Z-axisZ轴,To draw three-view

9、drawings on a drawing sheet 将三投影面展成一个平面 The V-Plane is first fixed. V面不动 The H-Plane turns down 90. H面向下转90,Y轴记为YH , The W-Plane turns right 90. W面向右转90,Y轴记为YW 。,The drawing produced on the profile projection plane (W-Plane). 由左向右观察将物体向W面投影而得到的视图。,2) Draw three views 画三视图,Front view 主视图：,Top view俯视图

10、:,The drawing produced on the frontal plane (V-Plane). 由前向后观察将物体向V面投影而得到的视图；,The drawing produced on the horizontal projection plane (H-Plane) 由上向下观察将物体向H面投影而得到的视图；,Llft view左视图:,请点击鼠标左键显示后面内容,Three-View of Component 物体的三视图,2. View positions and rules for producing three-view drawings 三视图的位置关系和投影规律,

11、1) Positions 位置关系,2) Rules 投影规律,45,The height of the front view and the left-side view should be aligned and is equal. 主、侧视图高平齐；,The width of the top view and the left-side view should also be aligned and is equal. 俯、侧视图宽相等。,The length of the front view and the top view should be aligned and is equa

12、l. 主、俯视图长对正；,请点击鼠标左键显示后面内容,Three-View of Component 物体的三视图,Front view 主视图,Left-side view 侧视图,Length align 长对正,Height align 高平齐,Width equality 宽相等,Top view 俯视图,(图线有重合时的优先顺序为：粗实线、虚线、细点画线、双点画线、细实线),1) Define the scale, select the size of drawing sheet.确定图幅和比例；,2) Choose a direction for front view projec

13、tion. 确定主视图的观察方向；,(使其主要表面平行或垂直于投影面,能表达更多的结构形状),3)Draw the datum line, noticing that each view is in proper distance. 布置各视图的位置；,4) Project the object from three different directions and draw the corresponding views. 按照三等规律画其三视图；,5) Check and correct , erase all unnecessary lines. 校核有无错漏，擦去多余线条；,6) Dr

14、aw deeply according to the demand. 按标准图线加深视图。,(画出基准线、对称中心线、轴线）,(加深顺序为：圆形、圆弧、水平线、垂直线、斜线),(可见轮廓线画粗实线，不可见轮廓线画虚线),请点击鼠标左键显示后面内容,Three-View of Component 物体的三视图,3. Steps for producing three-view drawings. 画物体三视图步骤,请点击鼠标左键显示后面内容,Plan or topview,Front view,Left view,1.Draw three views according to pictorial

15、 drawing. 根据立体图画出主、俯、左三个视图。,由于投影面的大小与视图 无关。因此,在画三视图时, 不必画出投影面的边框。,Exercises 练习题,1. Find out the right three views for each pictorial drawing, and make out the right number in bracket. 找出与立体图相对应的三视图，并在括号内填写相应编号。,2. Draw three views according to pictorial drawing ( the front view is looked from S). 根据

16、立体图 (所给主视图观察方向S)，画出相应的三视图。,3. Draw three views according to pictorial drawing ( the front view is looked from S). 根据立体图(所给主视图观察方向S)，画出相应的三视图。,请点击相应题目显示其内容,本 小 节 结 束,谢谢您的认真学习！,退出,前一页,S （Sight or center of projection 投射中心）,Central projection： When the lines of projection meet at a point, it is called

17、central projection. 中心投影法: 投射线汇交于一点的投影法称为中心投影法。,请点击鼠标左键显示后面内容,Central projection method 中心投影法,Projection lines（投射线）,Object (物体),P Projection plane (投影面),Projection (投影),Lines of projection will be parallel (投射线平行),空间物体用大写字母表示。,投影用小写字母表示。,Parallel projection: When the lines of projection are parallel

18、 with each other, it is called parallel projection. 平行投影法 投射线互相平行的投影法称为平行投影法。,请点击鼠标左键显示后面内容,Parallel projection method 平行投影法,Object (物体),P Projection plane (投影面),Projection (投影),S,(一般作为辅助图样),Axonometric projection 轴测图,Parallel Projection method 平行投影法,(光线SP投影面),Oblique projection method 斜投影法,Orthogonal projection 正投影图,(作为正式的工程图样),Orthographic projection method 正投影法,(光线SP投影面),p,s,s,请点击鼠标左键显示后面内容,90,90,S,S,Orthogonal projection 正投影图,正投影图准确,真实,作 图简单,但立体感不强。,Axonometric projection 轴测图,轴测图立