SWX 2004 limit mates bug

There seems to be a bug in distance limit mates when an assembly with
limit mates is inserted into another assembly as a flexible
subassembly. For instance, imagine a hydraulic cylinder with limit
mates to control the stroke of the cylinder rod. If the cylinder is
placed into another assembly as a flexible subassembly, the limit mate
shows as being overconstrained. My VAR doesn't care. If anyone else
does care, and you can confirm this behavior, could you submit this
for your VAR for an SPR #?

Thanks,
Eric

 

I have an upper assembly open right now with several
cylinders/mechanisms that were inserted with limit mates and flexible
and I have no problems. I am able to move them all within their limits
in the upper assembly.

Dave H

 

Actually, you don't even need flexible assemblies to show this bug
(feature?).

Say you have cylinder in which retracted length is 10" and extended is
20".
You add a limit mate to limit the stroke.
All is well.
Now, you decide to constrain the length of the cylinder with a distance
mate of, say, 15"....BAM!!! mate errors! Even though the limit mate and
'fixed' mate can both be mutually solved, they over constrain each
other.

This is not the behavior I (or apparently you) were hoping for with
limit mates. IMO, an error should occur ONLY when another mate pushes a
limit mate outside its limits (say we set our 'fixed' mate to 9" in the
above example).

Flexible assemblies are really nothing more than SWX solving the
subassembly mates concurrently along with the parent assembly's mates,
just as if the subassembly parts were actually in the parent assembly.
Thus, I am betting that by placing your cylinder in an assembly as a
flexible assembly, you are constraining its length similar to how I
added a mate in my above example and getting the same mate errors.

Quote

EndQuote
Perhaps it is time for a different VAR?

 

Same here.

Richard

 

I would expect an error if I am understanding you correctly. You are asking
it to provide motion within the range while at the same time requiring it to
be at a fixed distance. How does this system know which one to honor? In
what situation would you want both mates?

An analogous situation would be if you fixed it at 15" from one end and 5"
from the other. Although the mates don't conflict with each other, they are
redundant and the system is over constrained.

JJ

 

I disagree. The fixed distance mate is telling it that it is fixed at a
particular dimension and the limit mate says it can move. They are
conflicting with each other and should result in an error if one or the
other is not supressed.

Dave H

 

What I do is creat a configuration for the mode that I need.
Limit mate when the cylinder is in context of its assembly, fully extended
and fully retracted for drawing purposes and free floating for when I want
to pull the pistion clear out of the barrel!

 

Exactly the same thing I do.

Dave H

 

This is it exactly!

I guess I can understand the VAR tech's confusion given some of the responses here.

Have you submitted it for a fix?

Regards,
Eric

 

I see your point, but I respectfully disagree. Perhaps is is just a
difference in perception on the function of the limit mate.
You see the limit mate as a mate that requires motion in a specified
range.
I see the limit mate as not requiring motion, but rather to limit how
that component can be constrained in an assembly.

Getting back to the cylinder example, I think limit mates should allow
one to apply the limit mate, documenting the cylinder's limits. Then,
other constraints (weather they are in the cylinder assy, or up a level
when used as a flexible subassembly) should be allowed to fully define
the cylinder length. Thus, when the length constraining mate constrains
the cylinder WITHIN the limits of the limit mate, all is well. BUT,
when something pushes the cylinder beyond the constrains of the limit
mate, errors and warnings should pop up.

To me, it is all about design intent. SWX does allow redundant mates
(usually) to help capture design intent. To mate a bolt in a hole, you
only need a concentric mate and a POINT on a surface. Yet, using two
flat surfaces helps capture design intent (the bolt head is flat on the
surface) AND it is allowed by SWX. A rather drastic example, I admit,
but does illustrate my point.

Arlin
(remove '351' from email to reply)

 

I believe SolidWorks intended it to be a motion type mate as described in
the help file. Note the word "move".

Limit mates allow components to move within a range of values for distance
and angle mates. You specify a starting distance or angle as well as a
maximum and minimum value.

Dave H

 

Yeah, they see it too (I sent them an assembly), I suppose they just
see it the same as most of the other responses here. The behavior is
probably what SWX intended but it doesn't make any sense for my
application. Arlin's responses hit it dead on as to how this thing
should function.

Eric