Parametric Drawing Using Constraints

Transcription

1 CHAPTER 10 Parametric Drawing Using Constraints PROJECT EXERCISE This project exercise provides point-by-point instructions for creating the objects shown in Figure P10 1. In this exercise, you will apply the skills acquired in Chapters 1 through 10. FIGURE P10 1 Completed project drawing The purpose of this project is to demonstrate how constraints can be used to simulate the interaction between a piston, a connecting rod, and a crankshaft in a reciprocating engine. When the drawing is completed, if either end of the connecting rod is moved, the other end stays on the path intended. The crankshaft end will always stay on the circle that describes the path of the journal. The piston end will always stay on the line that describes the path of the piston and the piston will stay connected to the rod. In this project, you will learn to do the following: Apply geometric constraints to objects. Apply dimensional constraints to objects. 10-1

2 10-2 SET UP THE DRAWING AND DRAW A BORDER Step 1: Step 2: Step 3: Start the AutoCAD program. To create a new drawing, invoke the NEW command from the Quick Access toolbar. AutoCAD displays the Select template dialog box. Select acad.dwt as the template file and choose Open. AutoCAD creates a new drawing. Invoke the LIMITS command, and set the limits to the lower left and upper right coordinates as shown in the Settings/Value table. Set the grid, snap, and ltscale values as shown also. Settings Value UNITS LIMITS Decimal Lower left corner: 4, 4 Upper right corner: 12,4 GRID 0.5 LTSCALE 0.01 LAYERS NAME COLOR LINETYPE Conrod Yellow Continuous Construction Red ACAD_ISO03W100 Journal Green Continuous Piston Magenta Continuous Step 4: Step 5: Step 6: Step 7: Step 8: Invoke the LAYER command from the Layers panel. AutoCAD displays the Layer Properties Manager dialog box. Create six layers, rename them as shown in the table, and assign the appropriate color and linetype. Set Construction as the current layer. Invoke the ZOOM ALL command to display the entire limits on screen. Invoke the CIRCLE command Center, Radius method from the Draw panel to draw the circle representing the path of the crankshaft journal, as shown in Figure P10 2. Specify center point for circle or 0,0 Specify radius of circle or 2.75 Invoke the LINE command from the Draw panel to draw a line from the center of the circle to the right of the circle. Specify first point: 0,0 Specify next point or #4,0 Specify next point or (ENTER) Repeat the LINE command to draw a horizontal line on the right side of the circle. Specify first point: 5,0 Specify next point or #8.5,0 Specify next point or (ENTER)

3 Chapter 10 Parametric Drawing Using Constraints 10-3 FIGURE P10 2 Construction Layer objects Step 9: Step 10: Step 11: Set Piston as the current layer. Draw the piston and piston pin hole as shown in Figure P10 3. Invoke the LINE command to draw four lines representing the piston. Specify first point: 5.5,-1.5 Specify next point or #5.5,1.5 Specify next point or #10.5,1.5 Specify next point or #10.5,-1.5 Specify next point or c Invoke the CIRCLE command Center, Radius method to draw the circle representing the piston end of the connecting rod. Specify center point for circle or 8.5,0 Specify radius of circle or 0.5 FIGURE P10 3 Added lines outlining the piston and circle for piston pin Step 12: Step 13: Set Journal as the current layer. Invoke the CIRCLE command Center, Radius method to draw the circle representing the crankshaft journal as shown in Figure P10 4.

4 10-4 Specify center point for circle or 0,2.75 Specify radius of circle or 0.5 FIGURE P10 4 Added circle for crankshaft journal Step 14: Step 15: Set Conrod as the current layer. Invoke the LINE command to draw the line representing the connecting rod as shown in Figure P10 5. Specify first point: 0,2.75 Specify next point or #8.5,0 Specify next point or (ENTER) FIGURE P10 5 Line representing connection rod The previous steps created the objects to be used in the exercise. The next steps will be to apply constraints to control the movement of the objects. The crankshaft end of the connecting rod will be restricted to the path that the journal travels. The piston and the piston end of the connecting rod will be restricted to the path that the piston pin travels.

5 Chapter 10 Parametric Drawing Using Constraints 10-5 Step 16: Invoke the Fix constraint from the Geometric panel (see Figure P10 6) located in the Parametric tab. FIGURE P10 6 Invoking the Fix Constraint from the Geometric panel AutoCAD prompts: Select point or (Select Circle C1 as shown in the left view of Figure P10 7) FIGURE P10 7 Applying the Fix Constraint to Circle C1 Step 17: The right view of Figure P10 7 shows with the constraint icon. An X is also displayed at the center of the circle to indicate the object being constrained. Invoke the Coincident constraint from the Parametric panel. AutoCAD prompts: Select first point or (Right-click and select Object from the shortcut menu) Select object: (Select Circle C1 as shown in Figure P10 8) Select point or (Select Line L1 close to the selected circle so that the endpoint shows the constraint point locater).

6 10-6 FIGURE P10 8 Applying the Coincident Constraint to Circle C1 and Line L1 AutoCAD constrains the endpoint of the line to the path of the circle. A Coincident constraint icon is displayed where the line touches the circle. NOTE If you select a circle in response to the first prompt to Select point, as in the application of the Fix constraint, AutoCAD uses the center of the circle as the constraint point. When you right-click and choose the Object option as the first selection, AutoCAD constrains the point on the second item to the path of the circle. Step 18: Invoke the Fix constraint from the Parametric panel. AutoCAD prompts: Select point or (Right-click and select Object from the shortcut menu) Select object : (Select Line L2 as shown in Figure P10 9) FIGURE P10 9 Applying Fix Constraint to Line L2 using the Object Option Step 19: Invoke the Colinear constraint from the Parametric panel. AutoCAD prompts: Select first object or (Select Line L2 as shown in Figure P10 10) Select second object: (Select Line L3 as shown in Figure P10 10)

7 Chapter 10 Parametric Drawing Using Constraints 10-7 FIGURE P10 10 Applying the Colinear Constraint to the two lines Step 20: Invoke the Radius Dimensional constraint from the Dimensional panel (see Figure P10 11) located in the Parametric tab. FIGURE P10 11 Invoking the Radius Dimensional Constraint from the Dimensional panel AutoCAD prompts: Select arc or circle: (Select Circle C1 as shown in the Figure 10 12) Specify dimension line location:(specify the dimension line location as shown in Figure 10 12) When the dimension text is highlighted, it can be edited. Editing is not necessary for this example, so click an area outside the dimension and AutoCAD uses the default dimension (Figure P10 12). FIGURE P10 12 Applying the Radius Dimensional Constraint to the circle

8 10-8 Step 21: To constrain the connecting rod to the construction line, invoke the Coincident constraint from the Geometric panel. AutoCAD prompts: Select first point or (select the right end of Line L1 as shown in Figure P10 13) Select second point or (select right end of Line L3 as shown in Figure so that the right endpoint shows the constraint point locator) FIGURE P10 13 Step 22: Applying the Coincident Constraint to the connecting rod and construction line AutoCAD constrains the connecting rod to the endpoint of the construction line. To constrain the connecting rod to the small circle representing the hole for the piston pin, invoke the Coincident constraint from the Geometric panel. AutoCAD prompts: Select first point or (select right end of Line L1 as shown in Figure P10 14) Select second point or (select Circle C2 representing the hole for the piston pin as shown in Figure P10 14) FIGURE P10 14 Step 23: Applying the Coincident Constraint to the connecting rod and piston pin To constrain the connecting rod to the small circle representing the crankshaft journal, invoke the Coincident constraint from the Geometric panel. AutoCAD prompts: Select first point or (select left end Line L1 as shown in Figure P10 15) Select second point or (select Circle C3 representing the crankshaft journal as shown in Figure P10 15)

9 Chapter 10 Parametric Drawing Using Constraints 10-9 FIGURE P10 15 Applying the Coincident Constraint to the connecting rod and crankshaft AutoCAD constrains the endpoint of the line to the center of the circle. To constrain one of the corners of the piston, invoke the Coincident constraint from the Geometric panel. AutoCAD prompts: Select first point or (select Line L4 toward the bottom outlining the piston as shown in Figure 10 16A) Select second point or (select Line L5 toward the left outlining the piston as shown in Figure P10 16B) FIGURE P10 16 Applying the Coincident Constraint to endpoints of two lines

10 10-10 Step 24: AutoCAD constrains the endpoint of the first selected line to the endpoint of the second selected line. Repeat the above step for the other three corners of the rectangle until the two lines at all four corners are constrained where they meet (Figure P10 17). FIGURE P10 17 Step 25: Applying the Coincident Constraint to all four corners of piston Apply the Horizontal constraint from one end of the piston to one end of the connecting rod. Invoke the Horizontal Dimensional constraint from the Dimensional panel (see Figure P10 18). FIGURE P10 18 Invoking the Horizontal Dimensional Constraint from the Dimensional panel AutoCAD prompts: Select first constraint point or (select Line L4 towards the bottom outlining the piston as shown in Figure P10 19A) Select second constraint point or (select the right end of Line L1 as shown in Figure P10 19B) Specify dimension line location: (specify a point to draw the dimension line as shown in Figure P Do not edit text)

11 Chapter 10 Parametric Drawing Using Constraints FIGURE P10 19 Applying the Horizontal Dimensional Constraint to the lower left corner of the rectangle and the end of the connecting rod FIGURE P10 20 Result of applying the Horizontal Dimensional Constraint Step 26: Invoke the Vertical constraint and select Line L4 (Figure P10 21A). Invoke the Vertical constraint again and select Line L6 (Figure P10 21B).

12 10-12 FIGURE P10 21 Applying the Vertical Constraint to the vertical lines of the piston Step 27: Invoke the Horizontal constraint and select Line L5. Invoke the Horizontal constraint again and select Line L7. Step 28: Invoke the Aligned Dimensional constraint from Dimensional panel. AutoCAD prompts: Select first constraint point or (select Object option from the shortcut menu) Select object:(select Line L1 as shown in Figure P10 22) Specify dimension line location: (specify a point to draw the dimension line and change the text to a value of as shown in Figure P10 22) You should note a change in the location of the piston when the dimension is changed, making the new dimension the value of the constraint. FIGURE P10 22 Applying the Aligned Dimensional Constraint to the connecting rod

13 Chapter 10 Parametric Drawing Using Constraints Step 29: The drawing is now complete and the next step will demonstrate the effects of the constraints that were applied. By moving the grip at the crankshaft end of the connecting rod, the piston moves in a horizontal direction, simulating the actions of a reciprocating engine s piston, rod, and crankshaft. Select the connecting rod so the grips will appear. Hold down the Pick button and move that end of the connecting rod away from its original position. Watch as the piston moves. Because the end of the connecting rod is constrained to the large circle, it cannot be moved off of the circle. FIGURE P10 23 Moving the grip on the connecting rod counterclockwise Step 30: After moving the grip on the crankshaft end of the connecting rod counterclockwise around the circle, the piston moves horizontally, maintaining the length specified for the connecting rod (Figure P10 23). A clockwise move will move the piston to the right (Figure P10 24). FIGURE P10 24 Piston moves to the right as a result of moving the grip clockwise

14 10-14 EXERCISE 10 1 The purpose of this exercise is to have four lines maintain their positions relative to each other when one of the corner points is moved, without using the PLINE command or making them into a Block. Draw a series of four lines (A, B, C, and D) to form a rectangle starting at 0,0, to0,4, to 7,0, to7,0, and close to 0,0 (Figure Ex10 1-1). FIGURE EX Rectangle created from four separate lines with constraints applied Apply the Coincident constraint to each of the four corners to tie the adjoining lines. Apply the Horizontal constraint to Lines B and D. Apply the Vertical constraint to Lines A and C. After the constraints have been applied, select Line C so that grips are displayed. Move the grip (Figure Ex10 1-2). FIGURE EX Moving the grip at the upper right corner When one corner is moved, all of the lines maintain their positions relative to each other.

15 Chapter 10 Parametric Drawing Using Constraints EXERCISE 10 2 The purpose of this exercise is to constrain the center of a circle to the center of an arc and then an endpoint of the arc to the endpoint of a line so that when the line is moved to widen the bracket, the arc follows the line and the circle stays centered. Set up the drawing with the Limits set at 3, 1.5 and 11,8. Set the Grid and Snap to 0.5 with the Snap set to ON. Draw the Angle Bracket using five lines (A, B, C, D and E), Arc A, and Circle C, as shown in Figure Ex FIGURE EX Angle bracket with five lines, an arc, and a circle Apply the Fix constraint to Line C at its upper end (3,6). Apply the Coincident constraint to Lines C and D where they meet (3,3). Apply the Coincident constraint to Line D and Arc A where they meet (7.5,3). Apply the Concentric constraint to Arc A and Circle C. Apply the Fix constraint to the lower endpoint of Arc A (7.5,0). Constraint icons are shown in Figure Ex FIGURE EX Angle bracket with constraint icons displayed Line D is selected so that the grips are displayed. Using the midpoint grip, move Line D upward 1.0 units (Figure Ex10 2-3).

16 10-16 FIGURE EX Moving the grip at the upper right corner After Line D is moved, Line C is shortened, Arc A is lengthened, and Circle C remains at the center of the horizontal arm of the bracket (Figure Ex10 2-4). FIGURE EX Result of moving Line D upward 1.0 unit

17 Chapter 10 Parametric Drawing Using Constraints EXERCISE 10 3 The purpose of this exercise is to have the same constraints as Exercise 10 2 and also have the circle maintain a diameter that is 1.0 unit less than the width of the lower bracket arm and diameter of the arc. Start with the drawing that Exercise 10 2 started with, as shown in Figure Ex10 3-1, with the constraints added (see Figure Ex10 2-2). FIGURE EX Angle bracket with five lines, an arc, and a circle with added constraints Apply the Vertical Dimensional constraint to Arc A, which is the same width as the lower arm of the bracket, as shown in Figure Ex FIGURE EX Angle bracket with Vertical Dimensional Constraint applied to Arc A Apply a Radius Dimensional constraint to Arc A and override the default with an equation that makes it 1/2 of d1. Apply a Diameter dimensional constraint to Circle C and override the default with an equation that makes it 1.0 less than d1 (Figure Ex10 3-3).

18 10-18 FIGURE EX respectively Applying Radius and Diameter Dimensional Constraints to Arc A and Circle C After changing the value of d1 to 4.00 (Figure Ex10 3-4A), Arc A is changed and Circle C is changed in accordance with the equations in their respective dimensional constraints (Figure Ex10 3-4B). The lower bracket arm is widened in accordance with the Coincident constraint at 7.5,3, which is moved to 7.5,4. FIGURE EX Result of changing the value of d1 to 4.00