topic Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits in Inventor Forum

Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

SEC_MECH — Fri, 04 Sep 2020 00:49:38 GMT

I was following the demo by @Neil_Cross on YouTube for angular constraint limits but ran into issues when I want to have asymmetric angular limits beyond 180 degrees. I can't share my project but have attached a demo hinge to show what I mean.

Say I want my blue beam to be in-line with my red beam and travel the long arc up to the 210 degree angle.

(A second scenario is where I want the blue beam to be +30 to -120 degrees from aligned with the beam).

1) Inventor won't let me enter a Maximum limit of 210 degrees

2) If I enter a smaller Maximum e.g. 120 degrees (with Min=0) then the constraint is applied symmetrically so that the blue beam can move PLUS and MINUS 120 degrees from zero.

Is this bad implementation or am I just using it wrongly? How would I limit the angular constraint for large angles (above 180 degrees) and for asymmetric limits?

NOTE: Inventor allows vectors to be entered (i.e. negative angles) but always treats them as positive.

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

swalton — Fri, 04 Sep 2020 13:05:15 GMT

I'd use the directed angle option and define a reference axis. That will help Inventor understand what to do with angles larger than 180 deg and negative values.

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

johnsonshiue — Sat, 05 Sep 2020 18:27:42 GMT

Hi! Steve is right. Undirected angle is only meaningful between 0 and 180. Any value beyond the range is not valid. I suggest you use Explicit Reference option so you can specify the full range (+-360). But, you need to select a rotational direction, which helps avoid flipping.

Many thanks!

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

SEC_MECH — Sun, 06 Sep 2020 22:05:51 GMT

It is not possible to use limits with Directed Angle. When Directed Angle is selected the Limits fields become greyed out and unavailable.

Undirected Angle - Limits available

Directed Angle - Limits not available

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

swalton — Mon, 07 Sep 2020 20:34:53 GMT

Sorry, I used the wrong name for the angle option.

I meant the Explicit Angle Reference option (right-most button). That option allows you to define a reference vector that uses the right-hand-rule to define the + and - directions for the angle value.

See: https://help.autodesk.com/view/INVNTOR/2020/ENU/?guid=GUID-AD4679FD-EE9B-47C0-9E32-04B990BDD29E

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

SEC_MECH — Mon, 07 Sep 2020 22:22:27 GMT

This has to be a bug or a very poor implementation.

Even by using the Explicit Reference Vector I could not restrain the movements as required.

Min::Max::Expectation::Result

FAIL - 0::70::The blue beam to be limited from 0 - 70 degrees :: Beam limited to +/- 70 degrees (i.e. 140 degrees travel)

FAIL - 0.5::70:: Limit travel 0.5 - 70 degrees :: Beam limited to +/- 70 degrees (i.e. 140 degrees travel)

FAIL - 1::70:: Limit travel 1 - 70 degrees :: Beam limited to +/- 70 degrees (i.e. 140 degrees travel)

PASS - 5::70:: Limit travel 5 - 70 degrees :: Beam limited to 5 - 70 degrees from parallel

PASS - 5::170:: Limit travel 5 - 170 degrees :: Beam limited to 5 - 170 degrees from parallel

FAIL 5::180:: Limit travel 5 - 180 degrees :: Beam can travel the long arc between 5 degrees and -5 degrees from parallel (i.e. 350 degrees travel)

I cannot see a simple way to achieve the limits that I need to apply.

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

imajar — Mon, 07 Sep 2020 22:46:20 GMT

See attached. Is that what you need it to do?

I generally have had a good experience using explicit reference vector, although selecting a good vector (that is orthogonal to the angle) is essential to get it to work right.

Re: Assembly Angular Constraint Limits - Large Angles and Asymmetric Limits

SEC_MECH — Wed, 09 Sep 2020 00:55:52 GMT

@imajar You're da man! Thank you so much for your solution. It works brilliantly with large angles and asymmetric limits. I just wish that AutoDesk would have made it more intuitive. Thank you for taking the time to post the solution.