Rectangular patterned features along curve are unequally spaced

[bswenson]

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)

[m.carroll.kti]

Hi, I'm pretty sure it's not the start point. I have attached a screencast to better illustrate my problem. The Rectangular Pattern feature maps the distance between points as Arc Length and not Minimum Distance between points. I believe Message 11 illustrates exactly what I'm trying to do but I can't figure out how @JDMather did that. In my screencast it shows how the parts come apart as they travel along the curve (seen as the center holes don't match up anymore)

[JDMather]

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@m.carroll.kti wrote:

 I have attached a screencast to better illustrate my problem. 

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No Screencast, no Inventor file(s)?

[m.carroll.kti]

Sorry about missing the attachment. Here it is

[johnsonshiue]

Hi! It will be much easier if you attach the Inventor files (iam and ipt in zip). Forum experts can take a look and find out why the chain does not behave.

Many thanks!

[m.carroll.kti]

Here are the Files

[johnsonshiue]

Hi! Many thanks for sharing the files! I tried driving the constraint and the chain seemed to work correctly. Could you elaborate on what I need to do to see the issue?

Thanks again!

[m.carroll.kti]

The issue is demonstrated in the video I posted in message 23. I will attach it again. The rectangle pattern maps to arc length and not minimum distance which makes the points closer together along the arc of the drive chain. I would like to know how to make the pattern map to the minimum distance so that the links don't break apart when they travel on the arc.

[johnsonshiue]

Hi! Many thanks for sharing the video! I should have reviewed it. I think I know where the problem is. I don't think there is an easy solution here. The challenge here is the workpoint pattern. The path-based pattern spacing is literally based on the distance along the path, not the distance between two instances. In your case, in linear segment, the distance is 4". However, at the arc segment, the 4" is the arc length, not the chord length. As a result, it will be slightly off.

I was trying to recreate Sketch6 using polygons. The problem is that the distance cannot be constrained as such and also keep adaptive working.

There could be other ways to do it. But, I am not able to find a good solution at the moment.

Many thanks!

[trevorauman]

@johnsonshiue that can be a problem, but what is going on here has to do with patterning along a path. Inventor uses the arc length to calculate where the next occurrence is, but when you are using chain links the chordal length needs to be used, not the arc length. Inventor really should have a drop down in the tool to allow the pattern length based on "path length" OR "point to point length", could also be called "chordal length". This would be extremely useful. The chain tool in Inventor works this way, but the chain tool doesn't always have all of the link types that are needed and adding them is just not easy or in many cases feasible due organization restrictions and the content center.

The above solution works great for a known number of links, but if you are creating an iLogic tool that resizes the equipment the number of links changes and the solution is no longer valid. Seems since the feature already exists on the chain tool it would be easy enough to program in the pattern tool OR make it easier to add a custom chain link that doesn't impact the content center and doesn't do all of the fancy power calculations.

[Manuelcamposcosta]

You should make a post in the ideas forum, I would vote!

That would be very useful 

[kacper.suchomski]

Hi @bswenson 

Look on this video:

https://www.youtube.com/watch?v=G4ZsCWFlvNc

The idea is to prepare translation constraints on the surface instead of the edge pattern.

There is a bit of work here, but it gives the intended effect.

Instead of a full loop, prepare the surface based on the parameters @JDMather showed you.

Good luck