topic Re: Rectangular patterned features along curve are unequally spaced in Inventor Forum

Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 15:25:06 GMT

The goal was to make a 'chain' of identical features between two parts within an assembly. Drew the curve between the two parts, placed a work point at the start and attempted using a rectangular pattern to create an evenly space the remaining points in the direction of the sketch. However, once this pattern encounters the curve in the sketch, the work points are no longer equally spaced throughout.

Along the initial straight, point pairs were spaced at 20mm (the set value). The deviation begins at the point pair where the transition from straight to curve is located in between with a spacing of 19.996mm. However, interestingly enough the point pairs contained entirely within the curve are evenly spaced at 19.578mm but this still differs from the 20mm set dimension. The second transition yields another value of 19.975mm before returning to 20mm spacing along the final straight.

Is there a way to have these points be evenly spaced to make a chain of features or is this an intentional behavior? I'll attach a mock up of the path by itself for anybody to see what I'm on about. (The missing constraint is intentional and doesn't effect the behavior of what I'm inquiring about)

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 15:50:26 GMT

Are you measuring Arc Length?

Re: Rectangular patterned features along curve are unequally spaced

aurel_e — Tue, 03 Mar 2020 16:04:11 GMT

There is nothing wrong in it. Inventor is considering the curve length, not the minimum distance.

Have a look to my attempt attached. Maybe is what you are looking for.

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 15:54:31 GMT

@JDMather wrote:
Are you measuring Arc Length?

Straight line length. Imagine center to center of chain links

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 15:55:35 GMT

@bswenson wrote:

@JDMather wrote:

Are you measuring Arc Length?

Straight line length. Imagine center to center of chain links

That is not what you have modeled.

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 15:55:53 GMT

So attached is a screenshot of my accumulated amount using the measuring tool and each of the distances between the points pairs.

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 15:59:34 GMT

I will Attach example in a bit - I have to leave my computer for about 30 minutes.

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 16:26:14 GMT

Yes, that is sort of what I am looking for. The only thing that troubles me is how that will behave once the curve changes shape which I wasn't sure was necessary up until now.

The 'origin point' of the chain would be the portion attached to a fixed feature within the assembly and the free end would be attached to a separate feature that can move forward and back thus changing the length of the straights. The points would need to maintain a 20mm straight line distance between them as the assembly moves so as to not break the chain segments that have a pitch of 20mm. That is what I'm attempting to achieve

Re: Rectangular patterned features along curve are unequally spaced

aurel_e — Tue, 03 Mar 2020 16:31:27 GMT

See screencast please

https://autode.sk/3amqzrM

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 18:00:48 GMT

Alright so it was how I imagined. This solves the points being equidistant but in doing so this does open up a new issue that I didn't think was necessary to include in the original post but perhaps it might've been. What's below is in message 8 but I'll place it here for less scrolling.

@aurel_e @JDMather The 'origin point' of the chain would be the portion attached to a fixed feature within the assembly and the free end would be attached to a separate feature that can move forward and back thus changing the length of the straights. The points would need to maintain a 20mm straight line distance between them as the assembly moves so as to not break the chain segments that have a pitch of 20mm. That is what I'm attempting to achieve. Constraining the components to a sketch seemed the only way to have a chain reliably follow a path without collapsing on itself. The chained feature is a cable carrier and thus doesn't use a cassette like a bicycle to set the path.

@aurel_eIn your model, the equal length lines are constrained to the original sketch geometry but because the original sketch geometry is in segments, there are situations within the above parameters that would cause the points to separate from the curve. (You can see this if d2 is kept as driven and the top end point is pulled in either direction.) So instead of chain links traveling around the curve which may have a link going from being along the straight to start and ending on the curve, they stay constrained to the straight. I'll attach am imagine at one of these points to show what I'm on about.

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 18:35:06 GMT

Constant length position motion.

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Tue, 03 Mar 2020 18:52:12 GMT

Yes! That is exactly it! Now I just need to figure out how to replicate it

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 19:10:26 GMT

I will post an example when I get a chance (I didn't save the file).

It only takes a few minutes to recreate it.

The circle in my video isn't needed - I just included it for visualization.

I created a static variable Chain_Length.

I created a variable Offset_Distance (and Animated Parameter this variable).

I created a variable named Remainder.

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Tue, 03 Mar 2020 21:12:20 GMT

Run this file in Inventor Studio.

Articulating Cable Tray

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Wed, 04 Mar 2020 13:44:41 GMT

Thank you for the response. I've not much experience within Inventor Studio so it took me a few minutes to get there but I managed to get the motion I was looking for.

The only issue I have is that I'm still running into the problem of the points not being equally spaced in terms of minimum distance. A method was provided earlier where the original curve was turned into construction geometry and equal length lines were constrained to the curve segments achieving the equal minimum distance using the rectangular pattern. The problem with this method was that the lines were constrained to segments of the path instead of the path as a whole which resulted in the line segments separating from the path instead of following it.

When I used the original model I provided and added the drive animations the points did follow the path but attaching a reference annotation to a pair of points near the transition from straight to curve revealed the point to point distance was changing near the transitional zones and on the curve was still different to the specified spacing. I cannot tell from your screencast in Message 11 if the points are equally spaced or not though they appear to be. If so, is there a way of constraining those line segments to ensure they'll follow the path and not deviate?

Thanks again for the help so far and I apologize for the multiple questions

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Wed, 04 Mar 2020 14:03:21 GMT

@bswenson wrote:

A method was provided earlier where the original curve was turned into construction geometry and equal length lines ….

I missed an important consideration in the design.

Sometimes I get hung up on one path and just need to step away from the problem for a moment to clear the thoughts.

You prompted me to see my mistake.

I will try to find time to work up another solution.

Re: Rectangular patterned features along curve are unequally spaced

JDMather — Wed, 04 Mar 2020 14:39:51 GMT

Do you have one of the links modeled.

I have the solution, but it is quite involved and if I am going to make a video - I would prefer to have something that looks real-world, rather than mere "sticks".

Re: Rectangular patterned features along curve are unequally spaced

bswenson — Wed, 04 Mar 2020 14:52:23 GMT

Attached is the chain link model being used.

Re: Rectangular patterned features along curve are unequally spaced

m.carroll.kti — Wed, 25 Aug 2021 13:30:48 GMT

Hello JD, has there been any progress on this video? I am working on this exact issue now and would love a little more guidance.

Re: Rectangular patterned features along curve are unequally spaced

johnsonshiue — Wed, 25 Aug 2021 19:32:58 GMT

Hi! Likely the start point for the path direction isn't coincident with the first pattern instance. Please edit the pattern and select a different start point right at the center of the first instance. Or, share the files here so forum experts can help take a look.

Many thanks!