Dynamic Analysis in
Pro/MECHANISM
With Pro/MECHANISM we can also do a Dynamic Motion analysis. Your Pro/ENGINEER assembly can now be used to do the following:
·
Verify the mechanism’s correct motion. You can
simulate the motion and check the position, velocity, and acceleration of the
mechanism’s components.
·
Check for interference between the mechanism’s
parts as it moves.
·
Find the correct configuration of parts for your
final assembly by using packaged components and Motion’s assembly analysis.
·
Determine the motion and reactions resulting from
given applied loads.
·
Determine the loads at bearings and joints.
As an
example we will analyze the compressor assembly from an earlier exercise as a
mechanism. The procedure is identical to the kinematic analysis done in an
earlier exercise. Let us assume all parts are made out of steel and the crank
is rotating at 1000 RPM.
1.
Define the material properties of the components.
Assume
all parts to be made of steel: Click on the ‘Define Mass
Properties’ tool icon on the right 
, or Edit -- Mass Properties. Select
a part, pull down Define Property by and select Density. Enter value 7.827e-9 tonne/mm3 (for
steel) – click Apply and repeat process for
all other parts, next click OK.
2.
Rotating the Crank:
In our
simulation we want to look at the piston-crank mechanism for a single
revolution. Since the crank rotates at 1000 rpm one revolution will take 60/1000
= 0.06 seconds. The position of the crank will change in the simulation
duration from 0 to 360o. The slope of the ramp
defining the crank position is then calculated to be:
360 / period = 360 / 0.06 = 6000 deg/sec
To modify
the existing driver rotating the crank:
Select in the Mechanism section of the ModelTree the Servo Motor called Crank. Right-click it and select Edit Definition. Next select the Profile tab and set Specification to Position and as Magnitude Ramp. Enter 6000 in the B field, leave the Constant A field at 0. The start position will be 12 o’clock. Click OK.
3.
Setup the Analysis:
Click
on the Define
Analysis-icon 
, or use Analysis -- Mechanism Analysis.
The model is now ready for a
motion analysis. Call it Crank.
Check that Type is set as Dynamic. Under Preferences tab set Graphical
Display
parameters to:
Select Length and
Frame Count
Duration: 0.06
Frame
Count: 101
4.Run the Analysis:
Select Run to start the analysis. The model display will start moving
as the analysis is running.
Once the model has
finished running, select Ok to exit "Analysis
Definition" dialogue box. The
motion analysis results are now available.
5.To look at the mechanism in
motion:
Select Replay previously run analyses tool 
, or Analysis – Playback to activate the "Playbacks" dialogue
box. We can view the mechanism in motion and can check for
interference between components also. Click on the appropriate checkbox for interference
checking.
6.
To produce a motion envelope a FRA-file needs to
be generated by clicking on the Create Fra File icon.
To
obtain graphs of velocity, acceleration, reaction forces and torques use:
You can view measure results and create new measures
by clicking 
, or use Analysis – Measures to access the Measure Results dialog box.
In the Measure Results window popping up create your measures by
clicking on the Create new measure icon 
and
select the desired variables to plot. Note reaction forces are selected under Connection Reaction.