26 eccentric mechanism kho tài liệu bách khoa

Pick the axis of the shaft, then select the axis of the center hole of the eccentric... Pick the front surface of eccentric part as sketching plane, and then pick assembly TOP datum plan

A component can be placed as a connection within mechanism assembly The

following six joint types are available:

Pin Joint

Cylinder Joint

Planar Joint

Slider Joint

Ball Joint

Bearing Joint

PREPARE THE PARTS FOR MECHANISM

Download the part files eccentric_mechanism.zip There are eleven parts that make up the mechanism:

5

6

link.prt

CREATE AN SUB-ASSEMBLY eccentric_asm.asm

Sub-assembly called eccentric_asm.asm will be consisted of six component parts – eccentric, shaft, clip-1, clip-2, washer-1, and washer-2

Create a new assembly called ECCENTRIC_ASM

Bring in eccentric.prt and constrain

it at default location by picking

Pick , then Open

eccentric.prt

The assembly is shown below

Next, place shaft.prt to the assembly Pick , then Open shaft.prt

Pick the axis of the shaft, then select the axis of the center hole of the eccentric

Pick the surfaces as shown below

The resulted assembly is shown below

Mate both surfaces

Open clip-1.prt and place it in the groove of the pin of eccentric part – see figure below

Place washer-1.prt right behind clip-1 – see figure below

The resulted assembly is shown below

Perform Global Interference check of the assembly Make sure there is no

interference in the assembly

Analysis -> Model Analysis

Choose Global Interference under

Type

Click There are NO interference parts in the assembly

Save the assembly

Click , and open bushing.prt Place the bushing at the most left hole in the base – see figure below

Place again the bushing into the hole located on the right of the base

Hint: Use Repeat option of the assembly

Edit -> Repeat etc

Click , and open post.prt Place the post at the most left hole in the base – see figure below

Perform the Global Interference check and make sure there are NO interference

Save the assembly

CREATE AN SUB-ASSEMBLY arm_asm.asm

Click ,

Enter the name of arm_asm

OK

Click Then open arm.prt and assemble it at default location by selecting

Open clip-1.prt and place it in the groove of the pin of arm part – see figure below

Place washer-1.prt right behind clip-1 – see figure below

The resulted assembly is shown below

Be sure to turn on the datum axis only

Click the Connect tab for Connections

For Axis alignment, align the axis of shaft A_2 with axis of the bushing A_2

Select Move tab, and choose Translate Pick eccentric_asm then move it

backward as shown in the figure below

Click on Place tab

For Translation, select the surface of eccentric, then select the front surface of the bushing as shown below

Click back on Axis alignment, and be sure that under Component Reference, the selection as indicated in the figure

If not, re-select both axes of the shaft and bushing

The orientation as shown in the figure on the left is incorrect The eccentric assembly must be flipped

Click

Here below is the correct orientation of the assembly

Click OK

Perform Global Interference check of the assembly

Analysis -> Model Analysis

Close the Model Analysis dialog box

To investigate the interference, the assembly model will be cut at location where the interference occurred The amount of interference will be measured, then fixed by changing the dimensions of the part that causes the interference

Click to turn on the datum planes display

Click Then select ->

Pick the front surface of eccentric part as sketching plane, and then pick assembly

TOP datum plane as Reference for Top Orientation – see figure below

Click on Sketch

Pick the needed references as shown in the figure

Pick front surface

of eccentric part

as sketching

plane

Pick this as reference

Also, pick this as another reference

Draw a rectangle as shown on the left figure The dimensions of the rectangle do not matter Most important the rectangle should cover the area of the model that will be removed

Click to continue

Choose thru all cut Then click

Turn off ALL datums display

Change the view to the RIGHT side view

Zoom in to the interference area of the parts

There are interference between clip-2, bushing, and washer-2 These interferences can be avoided by extending the left portion of the shaft – from the left face to the groove

We will measure the length distance needed to

be extended

Analysis -> Measure

Pick two edges indicated by red in the figure on the left

The resulted distance is 0.096

in

Click , and open shaft.prt

Double-click

.89 dimension Change the dimension to

1.84+0.096

in

Click the update tool Then pick to save the part

Go to eccentric_mechanism.asm and select Window -> Activate

Click Regenerate Model tool

The model has been updated

Perform the Model Analysis again to make sure there is no global interference

The resulted analysis shows no interference The cut has to be deleted

Click Then open sub-assembly arm_asm.asm

Select Connect tab to create a Pin connection

Align the axis A_2 of top hole of the arm_asm sub-assembly with the axis A_2 of post – see figure below

For Translation constraint,

OK

washer and arm

As Axis alignment constraint, select the axis A_4 of the right hole of the link, and then pick the axis A_4 of the pin at eccentric

For Translation constraint, select the back face of the link, and then pick the front large face of the eccentric

For Translation

constraint, select the back face of the link, and then pick the front face of the arm

Click OK to complete the pins creation

Open Clip-2 and assemble it into the groove of the post The assembly constraints are shown below

Open washer-2, and assemble it right behind clip-2 as shown in the following figure

Here below is the total assembly of the mechanism

Perform the Global Interference check, and there are no interfering parts

Select Pick the eccentric, and swing the mechanism

Click the Close button

Pin Connection

CREATING A VELOCITY SERVO MOTOR

From MECHANISM pull down menu, select

Servo Motors

Or click

Pick the New button

The Servo Motor Definition dialog box appears

For the Driven Entity, select Joint Axis, and pick the most right Pin connection

Connection_1.axis_1 – joint axis (created between eccentric_asm sub-assembly and base_asm

Select Profile tab

Pick this Pin Connection

Change the Specification to Velocity Uncheck the Current box under Initial Condition.

Be sure Constant is selected under

Magnitude Enter the following value for A

= 100 deg/sec

Uncheck Velocity box and select the

Position check box

Click the Graph button to see a graph of the servo motor function over 10 seconds

Click the OK button, then

File -> Exit to close the graph window Then click

OK button of Servo Motor Definition

Click the Close button on the Servo Motors dialog box

Specify the Zero Reference

Select Mechanism -> Jt Axis Settings The Joint Axis Settings dialog box appears

Pick the joint axis with the servo motor -

Connection_1.axis_1 Under the Zero Refs tab, check Specify References

Select ASM_TOP datum plane of

eccentric_mechanism as the Green Body Reference

Select ASM_RIGHT datum plane of

eccentric_asm subassembly as the

Orange Body Reference

On the Regen Value tab, select Specify

Regeneration Values, and enter 0 for

Regeneration Value Click Preview, then pick OK button

Run the Connection Analysis

Select Mechanism -> Connect

Click Run There is no need to lock any

of the bodies or connectors

Mechanism design uses the regeneration value previously entered to assemble the mechanism

Click Yes

CREATING AND RUNNING A KINEMATIC ANALYSIS

From MECHANISM menu, select

Click Motors tab, and make sure

ServoMotor1 is selected

Click the OK button

Pick the Run button

Pick the Close button in the Analyses

window

Select the Global Interference

option, then click the Play button

Note:

If there is any interference, it will

be highlighted in red

There is no interference in this mechanism

Use options on the Animate dialog box

to run the results of motion study Click to begin the animation Click to stop

When finish with capturing, click Close

on the Animate dialog box

The

AnalysisDefinitionq.pbk

file can be opened int the future by clicking on the Playbacks dialog box and selecting the playback file

Click in the

Playbacks dialog box.

From above, we notice that the velocity

at the end of 10 seconds is 18.229 deg/sec

Click Pick this joint

Exit from the GraphTool

Creating a Trace Curve

A trace curve graphically represents the motion of a point or vertex relative to a part

in your mechanism

Mechanism -> Trace Curve

Select base.prt as the Paper Part, then pick a point near the lower hole as the trace point

Note:

Paper Part—Select a body on your assembly or subassembly to serve as the

reference on which to trace the curve If you visualize a pen tracing on paper, you can think of this part as the paper The trace curve you generate will be a feature of the part you select as the paper part You can access trace curves and cam synthesis curves from the model tree

To trace the motion of a body relative to ground, select a body that is in ground for the paper part

The point must be on a different body from the one you selected for the paper part Mechanism Design uses the trajectory of this point to define the trace curve If you visualize a pen tracing on paper, this location is like the tip of the pen

Highlight AnalysisDefinition1 as the Result Set.

Click OK to close the dialog box The trace curve appears on your model

Close out the Mechanism option and save the assembly

Pick a point here as trace point