topic Re: equal constraints? in Inventor Forum

equal constraints?

Anonymous — Fri, 02 Mar 2018 16:35:39 GMT

Hi All,

I have an assembly that contains a purchased parallel gripper consisting of the gripper body and the two jaws. I have constrained the jaws to the body so that they only travel the distances that they should.

Is it possible to link the constraints together in such a way that if I drag one jaw partially closed, the other matches its travel? If so, how do I do this?

When I insert this gripper assembly into another assembly and set it to adaptive, I want to be able to close the jaws on the part, not necessarily the end of travel.

Thanks.

Re: equal constraints?

mcgyvr — Fri, 02 Mar 2018 16:41:10 GMT

What you want is certainly possible..

It would really help to have at the very least an image of your assembly and even better if you can post the iam/ipt files so what they can see the current constraints you have applied and maybe suggest others to achieve the movement you want..

You may just need to add a mate constraint of the tip/line of the jaws so that those lines stay lined up..

Re: equal constraints?

TheCADWhisperer — Fri, 02 Mar 2018 16:46:05 GMT

Adaptive? or Flexible?

Re: equal constraints?

Anonymous — Fri, 02 Mar 2018 16:54:21 GMT

I currently have 2 flush constraints (1 for each jaw) with min and max travel set. To clarify, the jaws are synchronous. Where can I upload the file?

I typically use adaptive.

Re: equal constraints?

mcgyvr — Fri, 02 Mar 2018 16:58:29 GMT

@Anonymous wrote:

I currently have 2 flush constraints (1 for each jaw) with min and max travel set. To clarify, the jaws are synchronous. Where can I upload the file?

I typically use adaptive.

Zip up the iam and any ipt files and use the "Attachments" section below where you type your post body to choose the zip file..

And flexible is what allows subassemblies to move (up to their allowed degrees of freedom) when used in another assembly.

Adaptive is a different beast..

If you created a gripper as an assembly and then want to included that assembly into another assembly and have the gripper have the same movements it could in the gripper subassembly then "flexible" is the solution not adaptive..

Re: equal constraints?

Anonymous — Fri, 02 Mar 2018 17:25:24 GMT

You guys are correct. Looking at the icon in the tree, I guess I do use flexible, although either one is working in this instance.

I was able to get the desired outcome by placing a mid-plane between the two opposite sides of the body and grounding it along with the body. Then used a single symmetry constraint between the outside edges of the jaws and the plane.

I usually don't use that constraint, your comments flipped on the light switch. It's been an off day. 🙂

Thank you.

Re: equal constraints?

mcgyvr — Fri, 02 Mar 2018 17:29:35 GMT

@Anonymous wrote:

You guys are correct. Looking at the icon in the tree, I guess I do use flexible, although either one is working in this instance.

I was able to get the desired outcome by placing a mid-plane between the two opposite sides of the body and grounding it along with the body. Then used a single symmetry constraint between the outside edges of the jaws and the plane.

I usually don't use that constraint, your comments flipped on the light switch. It's been an off day. 🙂

Thank you.

That is one way..

Probably not what I would have done as it required additional plane to be created..

But if it works for you.. good.. 🙂

Re: equal constraints?

Anonymous — Fri, 02 Mar 2018 17:44:56 GMT

mcgyvr wrote
That is one way..
Probably not what I would have done as it required additional plane to be created..
But if it works for you.. good.. 🙂

For the sake of learning, I've attached the assembly.

When downloaded, everything comes in with a fix constraint. I removed it on the jaws and dowels, then constrain them as needed.

If there is an easier way or even just different, I am open to it.

Re: equal constraints?

mcgyvr — Fri, 02 Mar 2018 17:53:22 GMT

@Anonymous wrote:

For the sake of learning, I've attached the assembly.

When downloaded, everything comes in with a fix constraint. I removed it on the jaws and dowels, then constrain them as needed.

If there is an easier way or even just different, I am open to it.

Now that I can see what you are working with what you have done is a good solution..

Re: equal constraints?

MechMachineMan — Fri, 02 Mar 2018 18:24:46 GMT

@mcgyvr wrote:

@Anonymous wrote:

For the sake of learning, I've attached the assembly.

When downloaded, everything comes in with a fix constraint. I removed it on the jaws and dowels, then constrain them as needed.

If there is an easier way or even just different, I am open to it.

Now that I can see what you are working with what you have done is a good solution..

Aside from the fact the origin plane of the assembly would have worked just fine as well. But there could be perks to creating/naming/designating a new workplane for the task.

Re: equal constraints?

johnsonshiue — Fri, 02 Mar 2018 19:52:17 GMT

Hi! I think you want to use Flexible instead. Flexible subassembly allows you to subassembly occurrences have different positioning. Adaptive allows the geometry of one particular component to be influenced assembly constraints. You can only make one occurrence of a given component adaptive. Other occurrences cannot be adaptive. Flexible does not allow geometry to be changed but you can make as many occurrence flexible as you want.

Many thanks!

Re: equal constraints?

SBix26 — Sat, 03 Mar 2018 02:14:03 GMT

Here's a different solution (note: one additional part file, all other parts the same). Unfortunately, I don't have 2017, so this is in 2018 format.

This technique comes from before the Symmetry constraint existed. The Linkage part is simply a sketch line 75mm long, with its center constrained to the origin of the part. A workpoint is added to each end of the sketch line.

The linkage is placed in the gripper assembly and its rotational axis is constrained to the Z-axis of the gripper, then the two workpoints constrained to faces of the gripper fingers. Voilá, the fingers always remain symmetric around the center of the gripper. The same technique can be used for 3-jaw grippers. Of course you would turn off the visibility of the linkage part in normal use.

2-jaw Linkage3-jaw Linkage

Sam B

Inventor Professional 2018.2.3
Windows 7 SP1

Re: equal constraints?

Anonymous — Mon, 05 Mar 2018 16:09:29 GMT

@SBix26 wrote:
Here's a different solution (note: one additional part file, all other parts the same). Unfortunately, I don't have 2017, so this is in 2018 format.

This technique comes from before the Symmetry constraint existed. The Linkage part is simply a sketch line 75mm long, with its center constrained to the origin of the part. A workpoint is added to each end of the sketch line.

The linkage is placed in the gripper assembly and its rotational axis is constrained to the Z-axis of the gripper, then the two workpoints constrained to faces of the gripper fingers. Voilá, the fingers always remain symmetric around the center of the gripper. The same technique can be used for 3-jaw grippers. Of course you would turn off the visibility of the linkage part in normal use.

2-jaw Linkage3-jaw Linkage

Sam B

Inventor Professional 2018.2.3
Windows 7 SP1

Sam, That is some out of the box thinking there. I like it! Definitely will come in handy with 3 jaw grippers.