Skip to main content
M
meccanico1-Visitor
1-Visitor
October 6, 2018
Solved

Creo parametric 5: some tips on mechanism/gear

  • October 6, 2018
  • 2 replies
  • 13872 views

Hello,
I'm starting to use the mechanisms with Creo and would like to play a kinematics with a bevel gear (or conical pair ,  I do not know the translation of "coppia conica" in italian),   similar to the one in the video I've linked (they're only 3mb). 

The assembly is very simple, it is composed of:

A)a fixed body (the vertical shaft to which the first gear is fixed , they do not rotate and does not move)

B) the moving bodies: the horizontal shaft (motor), which being free to turn both on its axis and on the vertical one, will turn the box into  which it is inserted (with tho radial spherical bearings ).

I should also understand how to set the ratio so that 90 degrees of rotation on the vertical axis correspond to 90 degrees of rotation of the horizontal shaft axis, in practice 1: 1.

Reading the guide I understand that to use the mechanisms in Creo Parametric  you must use the constraints defined by the user instead of the automatic contraints , my problem is to understand where to put them.

 

For example, I would have left like this:
1) the vertical shaft placed as default / fixed
2) Its ring is  fixed on the shaft with automatic constraint , without any degree of freedom.
3) horizontal shaft with pin constraint , to allow rotation on its axis,  inside the box
4) pin contrant also for the box, free to rotate around the vertical axis (or should I to constraint it   to the horizontal shaft by matching the axes of the box holes with the orizontal shaft axis, plus the corresponding horizontal planes?)
Then I would go into applications> mechanism and define a bevel gear (translate conical pair gear) . However, here it allows me to select only axes that can rotate, so that of the horizontal shaft and that of the box (if constrained with pin)
Basically, how do I tell Creo that one of the two gears is fixed ( that at the base of the box) while the other turning around moves on a circle of radius r = radius conical gear?

p.s.I just have to set the movement just to do a kinematic, not dynamic, analysis

(view in My Videos)

Best answer by gfraulini

I've seen your assembly. It's correct. If you want 1:1 transmission ratio you can do this (see pic attached).
In addition you have 0 redundancies and 0 dof (zero because the one dof of mechanism is taken by the motor).

Bye

2 replies

G
gfraulini17-Peridot
17-Peridot
October 6, 2018

Hi,
the video you posted is awaiting approval yet, so I can't understand exactly all you've written.
Could you attach the assembly?


In the meantime I want to give you some tips on mechanism.
Here one have two kind on constranits: the "standard" and the "mechanism" ones.
The firsts are what program suggest you when you add new components to the assembly (mate, alling, tangent, fix, defoult, etc...); the seconds you have to switch to pin, planar, slot, bearing, etc...
Linking compononents with the standard ones mean to create a body, a set of components rigidly linked.
The second ones serve to link different bodies together.
Each body has 6 dof (degree of freedom) in the space; you have to impose mechanism constraints in order to remove dofs.
Eg: a simple bshaft rotating around its axis.
A shaft is 1 body with 1 component and 6 dofs where you have to give it only 1 dof: the rotation on its axis. So you have to remove 5 dofs; a simple pin constrain is what you're going to need.

Bye

    M
    meccanico1-VisitorAuthor
    1-Visitor
    October 6, 2018

    Hello Gfraulini, thanks for your reply and for the clarity of your  explanation ,I knew more or less what you told me but it was a useful confirmation because the movement is a topic that during the PTC course in which I participated, we have not talked about this topic.

     

    I am attaching the file with the assembly. I have gotten this result by chance, after numerous attempts and  before reading your answer. the movement give an idea of what I would like to get but it is not correct because it is not 1: 1, and even the  constraints I do not think are applied in the right way,The same for the gear
    I attach the files to better clarify the moving parts and how this  assembly is composed.

    bye

     

     

    G
    gfraulini17-Peridot
    17-Peridot
    October 10, 2018

    I'm honest, I've never used gear connections outside the generic-user defined one.
    And this because I'm, almost always, interested on studying the system kinematic/dynamic and not the support forces.
    So, if I define a gear, I'm interested only on setting the ratio. I've never use bevel gear, and aspecially bevel gear with pitch and diameter ratio definition; but now I see that in this manner you can't specify the pitch circle diameter of the second gear...Maybe it's a bug? But I have the same behaviour both on Creo 3 and 5...

    S
    SweetPeasHub17-Peridot
    17-Peridot
    October 6, 2018
    i have not looked at your model but i have done the “stationary” gear thing before. i am not in my office so not able to look it up at the moment. my memory is that you should make a subassembly where the shaft rotates on a pin joint and define a gear connection. then assemble the subassembly to your “ground body” assembly with the moving shaft fixed in position. Basically this is how you make a gearbox rotate rather than the output shaft rotate. There are other ways to do this of course.

    in short. make a gearbox subassembly with rotating output shaft. then rather than assembling the gearbox housing to ground assemble the output shaft to ground.
    Terms & ConditionsCookie settingsAccessibility statement