Tài liệu Oscillating Cam Mechanism doc

Click OK to accept the definition and return to the Measure Results dialog box... On the Measure Results dialog box, select Follower_Position in the Measures list and click Copy selected

ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN

Oscillating Cam Mechanism

Pro/ENGINEER Wildfire 2.0

Dr Herli Surjanhata

There are 5 parts, one subassembly, and one assembly need to be created:

• base.prt — the ground body, comprised of two parts

• cam.prt — a rounded, elongated solid with flat faces

• roller.prt — a wheel with flat faces with that serves as the second cam

• follower.prt — a holder for the roller

• pin.prt – a cylindrical pin for attaching roller to the follower

• follower.asm—a subassembly connecting roller.prt and follower.prt with a pin

PART: BASE.PRT

Create a part called base.prt as shown below Note that a datum point PNT0 should

be inserted a center of the hole of the top portion of base.prt The location of datum point is in the bottom surface of the top portion of base.prt

PART: ROLLER.PRT

Create a part named roller.prt

PART: FOLLOWER.PRT

Create a part called follower.prt

Insert a datum point PNT0 at the center of shaft as shown in the figure

CREATE A SUB-ASSEMBLY - follower.asm

Create an assembly called

follower.asm The assembly should have default datum planes –

ASM_FRONT, ASM_RIGHT, and ASM_TOP.

Bring in the part follower.prt, and click to assemble the

follower.prt at default location

Bring in pin.prt, and constrain the pin

Bring in the part roller.prt, and click on

Connect tab to create a pin

Conection_1 as shown below

• Align the axis of the roller with the axis of the pin as Axis alignment constraint

• Align the FRONT datum plane of the roller with the ASM_FRONT

datum plane of the follower assembly as Translation

constraint

Save the follower.asm assembly

CREATE AN ASSEMBLY – cam_follower.asm

Create a new assembly called

cam_follower.asm The assembly should have default datum planes – ASM_FRONT, ASM_RIGHT, and ASM_TOP.

Bring in the part base.prt, and and click to assemble the

base.prt at default location

Bring in the assembly follower.asm, and select Connect tab

to create a type Slider Conection_1 between

follower.asm and base.prt – see figure below

• Align the axis of the follower.prt of the follower.asm with the axis of the

hole of the top portion of base.prt as Axis alignment constraint

• Mate/Align the ASM_FRONT datum plane of the follower.asm with the

ASM_FRONT datum plane of the cam_follower.asm assembly as

Rotation constraint

Make sure to move the follower assembly so that its position as shown in the figure

below

Bring in the part cam.prt, and click on

a pin Conection_2 as shown below

• Align the axis of the shaft of the cam with the axis of the hole of the bottom portion of base.prt as Axis

alignment constraint

• Align offset the back surface of the

cam.prt with the front surface of the bottom portion of base.prt as

Translation constraint The offset distance is 17.5 mm

Rotate the cam to the position as shown in the figure below

CREATING A CAM-FOLLOWER CONNECTION, SPRING, AND DAMPER

CREATING A CAM-FOLLOWER CONNECTION

From Application pull down menu select,

Mechanism - Mechanism Design begins

Click (Drag) The Drag dialog box opens

Click (Point Drag) and pick the narrow end of cam.prt When an diamond appears on the model, move the cursor to rotate the cam Notice that the cam's motion does not affect the position of the follower

subassembly Click the middle mouse button to stop dragging, and click Close

to exit the Drag dialog box

Select Mechanism -> Cams or click The

Cam-Follower Connections dialog box opens

On the Cam1 tab, select the

Autoselect check box Mechanism Design completes the selection of a set

of surfaces after you select enough surfaces to define a cam

Use the arrow button in the Surfaces/Curves area to select the curved surface on cam.prt

Note: Use Right-Mouse-Button

pop-up menu Pick From List to pick the needed surfaces

Done Sel

Select the Cam2 tab

Select the Autoselect check box

Use the arrow button to select the curved surface on roller.prt

Note: Use Pick From List to pick the needed surfaces

Done Sel

Click OK to accept the definition, and

Close to exit the Cam-Follower Connections dialog box Mechanism Design adds a cam-follower icon to your mechanism

Select Mechanism -> Drag The Drag dialog box opens

CREATING A SPRING

There is a cylinder joint connecting follower.prt to the top portion of base.prt In the following sections you add a point-to-point spring and a point-to-point damper between the follower and the base

Click Mechanism -> Springs or click

(Define Springs) The Springs

dialog box opens

Click New The Spring Definition dialog box opens

Select Point-to-Point under Reference Type, and use the arrow button to select

PNT0 on base.prt and PNT0 on

follower.prt.

In the Properties area enter 100 for k, the spring stiffness constant, and 60 for

U, the unstretched spring length

Clear the Default check box and enter

20 in the Icon Diameter area

Click OK to accept the definition, and

Close to exit the Springs dialog box Mechanism Design adds a spring icon to

CREATING A DAMPER

Click Mechanism -> Dampers or click

(Define Dampers) The

Dampers dialog box opens

Click New The Damper Definition

dialog box opens

Select Point-to-Point under Reference Type, and use the arrow button to select

PNT0 on base.prt and PNT0 on

follower.prt.

Enter 100 for C, the damping coefficient, in the Properties area.Click OK to accept the definition, and

Close to exit the Dampers dialog box Mechanism Design adds a damper icon

to your mechanism

CREATING A SERVO MOTOR

On the Model Tree, under

CONNECTIONS -> JOINTS, expand JOINT_2 (CAM- FOLLOWER) by clicking the plus sign (see figure)

Highlight ROTATION AXIS, right-click, and select Servo Motor

The Servo Motor Definition

dialog box opens

On the Entities tab, for the Driven Entity, the joint axis you selected is listed

On the Profile tab, under Specification, select

Velocity

Accept the default Magnitude , which is

Constant Enter the value 72 for A Under Graph, select Position.

Click (Graph) to see a graph plotting position versus time for your servo motor

Close the graph and click OK

to accept your servo motor definition

CREATING AND RUNNING A DYNAMIC ANALYSIS

From Mechanism pull down menu, select Analyses or click

The Analyses dialog box opens

Under Name, enter Dynamic Oscillation Under Type, select

Dynamic

On the Preferences tab, accept the default values

On the Motors tab, be sure

ServoMotor1 is listed If it is not, click

Add all motors)

Click Run The model moves through the specified motion

To view the analysis results in later sessions of Mechanism Design, you must save them as a playback file

Click OK, then Close the Analyses

dialog box

CREATING AND GRAPHING MEASURES

Click Mechanism > Measures The

Measure Results dialog box opens Note that Dynamic Oscillations is listed under Result Set

Accept Measure vs Time as the Graph Type

Click (Create new measure) The

Measure Definition dialog box opens

Enter Follower_Position under Name, and select Position under Type

Use the arrow button to select PNT0 on

follower.prt Accept the WCS as the

Coordinate System

Select Y-component under

Component, and Each Time Step

under Evaluation Method A shaded arrow appears with its tip on the selected point showing the Y direction

Click OK to accept the definition and return to the Measure Results dialog box

On the Measure Results dialog box, select Follower_Position in the

Measures list and click (Copy selected measure) Select

copy_of_Follower_Position, and click

(Edit selected measure) The

Measure Definition dialog box opens

Change the Name entry to Follower Velocity, and select Velocity for the

PNT0 – Datum point of the

A shaded arrow showing Y-direction

On the Measure Results dialog box, select Follower Position in the

Measures list and click (Copy selected measure) Select copy of

Follower Position, and click (Edit selected measure) The Measure Definition dialog box opens

Change the Name entry to Follower Acceleration, and select Acceleration

for the Type Click OK to accept the definition

Click (Create new measure)

On the Measure Definition dialog box, enter Spring_Load under Name, and select Net Load under Type Use the

arrow button to select the spring on

your mechanism, and accept Each Time Step as the Evaluation Method

Click OK to accept the definition and return to the Measure Results dialog box

Click (Create new measure)

On the Measure Definition dialog box, enter Damper_Load under Name, and select Net Load under Type Use the

arrow button to select the damper on

your mechanism, and accept Each Time Step as the Evaluation Method

Click OK to accept the definition and return to the Measure Results dialog box

Click (Create new measure)

On the Measure Definition dialog box, enter Servo_Load under Name, and select Net Load under Type Use the

arrow button to select the servo motor

on your mechanism, and accept Each Time Step as the Evaluation Method

Click OK to accept the definition and return to the Measure Results dialog box

Note: Servo motor is located at pin joint between cam.prt and base.prt

On the Measure Results dialog box, select Follower Position, Follower Velocity, and Follower Acceleration

under Measures Select Dynamic Oscillation under Result Set

Click (Graph) to see a graph that compares the three measures

SAVING AND REVIEWING RESULTS

For the future sessions of Mechanism Design, the dynamic analysis results should

be saved as playback file that can be reviewed later

Replay results Click Mechanism -> Playback The Playbacks dialog box opens, with Dynamic Oscillations

listed under Result Set

Click (Play) The Animate dialog box opens

Click (Play)

Click to stop

To capture the animation in MPEG movie file:

Click button, then OK button

Click Close to close the Animate dialog box

On the Playbacks dialog box, click (Save result set)

Accept the default name, which is based on the analysis name, or change

it The default directory is the current working directory You can accept

it, or browse to find another directory to save the file

When you click OK, Mechanism Design saves the file with the

extension pbk You can retrieve this file in future sessions by clicking (Restore) on the

Playbacks or Measure Results dialog box

On the Display Arrows tab, select Spring Load, Damper Load, and Servo Load under

Measures Under Scale, select

Force and change the value to 150%

Accept the defaults on the Movie Schedule and Interference tabs

Click (Play) As the dynamic analysis runs, the size of the arrows changes to reflect the size

of the measures

Save the cam_follower mechanism