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Mechanism Connection Parameters and Relations

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Mechanism Connection Parameters and Relations

I would also like to see if this is possible. 

I have an assembly where I have a wheel that needs to rotate to several different positions around its axis.  I tried using angle offset and using a parameter and relations to rotate the wheel to the set positions, but I can't get the angle past 180°.  I read some posts about using mechanism to control rotation beyond 180° but now I don't have a dimension I can use in my relation.  I tried looking in the connection parameters, but I don't see one that corresponds to its current position.

The following is my relations code:

POSITION:21=0
<current position>=0
IF WHEEL_POS=="SKIMV"
<current position>=90
POSITION:21=12.5
ELSE
IF WHEEL_POS=="SKIMH"
<current position>=180
POSITION:21=12.5
ELSE
IF WHEEL_POS=="ENGAGE"
<current position>=30
POSITION:21=0
ELSE
IF WHEEL_POS=="HOOK"
$<current position>=-15
POSITION:21=0
ELSE
IF WHEEL_POS=="GUIDE"
<current position>=70
POSITION:21=0
ELSE
IF WHEEL_POS=="START"
<current position>=0
POSITION:21=0
ENDIF
ENDIF
ENDIF
ENDIF

Each position has dimensions of parts set to specific values.  I can set all those values at once by entering the wheel position parameter value for that position.

Anyone know how I can do this (or if I can do this) with basic creo 3.0?

I added a secondary constraint set using Angle Offset.  I have a dimension, but it still has issues with positions past 180.

8 REPLIES 8

Re: Mechanism Connection Parameters and Relations

I was able to use values over 180° (my 90° was actually supposed to be 270° - the direction was flipped from my original angle offset attempt).

 

Using the pin connection to control the movement, then a secondary constraint set with an Angle Offset gave me all I needed to show the wheel in its different positions. Go WPI Engineers!!!

Re: Mechanism Connection Parameters and Relations

Forget it.  In order to get to the correct Guide (290°) and Engage (330°) positions, I have to first set my Skimv (270°) position, which has to first have Start (0°) set.  Hook and Skimh also need Start set first.

I guess the connection isn't helping.

Re: Mechanism Connection Parameters and Relations

I don't think you are setting up the mechanism connections correctly.  For a pin connection, you have to specify at least two reference pairs:

1) to specify the axis of rotation ("Axis alignment" in the connection definition)

 

2) to specify the placement along the axis of rotation axis of the rotating body with respect to the stationary body ("Translation" in the connection definition)

 

If you stop there, then the part is free to rotate without constraints.

However, you have the option of specifying the 3rd pair of references which will allow you to control the angle of rotation ("Rotation axis" in the connection definition).  There, you can "enable regeneration value", and then you will have a placement dimension that you can drive via relations...

 

One warning: if you set the value of this angle to a negative value, then the "sense", i.e., the positive direction of rotation will be reversed.  So best to stick to positive values only.  If you want a rotation of -5 degrees use the value of 355 degrees, or otherwise your part will start to move in the opposite direction upon subsequent regenerations...

 

 

Re: Mechanism Connection Parameters and Relations

I am able to sucessfully create the pin connection both unconstrained radially (using only the rotation axis and translation constraints) and also constrained (adding the rotation constraint). I can rotate the part freely to the max and min I set while in the assembly mode using CTRL-ALT & LMB but once I'm out and try to move them Creo tells me it is suppressing the connection because of incorrect constraints. I still didn't have a dimension I could use in my relations. And as I stated I set up the Angle Offset foe the sole purpose of obtaining said dimension only to have issues with the angle.
Having said that, I have never used the Regeneration Value setting, but now I will give that a go to see if that was the missing piece in my setup. Thank you.

Re: Mechanism Connection Parameters and Relations

The error message about suppressing the connection because of incorrect constraints is indicative of another constraint in the assembly that is locking up the movement.  These errors are relatively hard to fix because the message is rather unhelpful.  A common issue is that a component is constrained by references from more than one "parent".  For example, a seemingly benign instruction to "align" the center-plane of a pivot arm to the center-plane of the assembly may lock up its movement if its pivot axis is aligned to another component in the assembly.

 

I suggest using the "insert here" function immediately after the rotating component, and then trying to use the "drag components" operation to see if the pin connection works.   If it does, then move the "insert here" arrow down one component in the assembly's model tree and repeat the "drag components" operation.  Eventually you'll stumble on the one that is causing the lock up.

 

Though it kind of sounds like the problem is the additional angle-offset constraint you mentioned.  I think you should read up more on mechanism constraints.  I know PTC help isn't the greatest, though, so please ask if you get stumped.

Re: Mechanism Connection Parameters and Relations

I had the error message before I tried to use angle offset to obtain a dimension to control in my relation, so that isn't complicating the connection.  However, if I get time I will use the "insert" method to try to determine what is keeping the connection from working correctly (with the angel offset turned off temporarily as that would turn control over to the relation).

I tried enabling a regeneration value, but that did NOT give me the dimension I needed or add a parameter I could vary in my relation.

Looks like I am stuck with my Angle Offset constraint.  I am using it now to orient my wheel to check subsequent component positions, so having to reset the position to the initial before moving the next won't stop me for now.

Re: Mechanism Connection Parameters and Relations

Yes, well, to be frank, it sounds like you are working on a model of a house of cards...  I recommend you build a solid foundation before working out the assembly relations.  Good luck!

 

 

Re: Mechanism Connection Parameters and Relations

You're right about the house of cards... I inherited this model.  The relations came from a completed assembly I created a few months ago that someone copied, modified, then handed back to me to complete.  I had the relations working on the initial assembly; however, I did not use a mechanism connection.  I was able to use rigid contraints and it worked, because the limits were -15° (for simplicity's sake) to 90°.  Now the limits are -15° to 180°.

 

I'd throw it out and start over if I wasn't able to get some function out it, even if it requires some finagling.

 

Thanks for the insight.