Pro E mechanism: cam spherical axial follower

[barry84]

Hi,

I'm new to the forum and new to Pro/e mechanism. I have searched the forum and the internet for possible solutions to my problem unsuccessfully.

I am trying to define the connection between an axial cam and its spherical follower (the follower translates axially in relation to the cam axis of rotation). The follower is supposed to run in a groove on the cam disc, whose diameter is smaller than that of the ball (therefore there should be contact at two points between the ball and cam).

It seems that the cam connection of mechanism does not work in this case. I have tried using a bearing constraint but this does not seem to be the correct approach. I also tried using a slot constraint and managed to get the centre point of the follower to follow the curve of the cam surface profile. However I realised then that this is not the solution since I must define CONTACT between the surfaces of the cam and follower. Can anyone make a suggestion as to how I might approach the problem?

Thank you for any tips!

 

[barry84]

P.S. an image is attached showing what I am talking about.

 

[hydromech]

Use the trajectory curve of the cut in the cam.

Show it in the mechanism assembly and use it as the path for the ball.

If you don't have have the original curve, construct it from the geometry in the part.

 

[barry84]

Thank you for your reply hydromech.

This is actually what I do now - I use a slot constraint to constrain the centre point of the ball to the trajectory curve of the cam profile, as you suggest. This trajectory is set up so that the centre point of the ball is positioned exactly where it would be if the ball were rolling in the groove with contact at two points. However, there is no contact defined, and therefore the ball does not roll.

I have experimented by defining a 3d contact between the ball and a flat cam profile (no trajectory, no groove), and this works i.e. the ball rolls.

My aim is to calculate the torque required to rotate the cam, when the ball is subject to a force in the downward vertical direction. This amounts to calculating the horizontal component of the downward force applied to the ball, which is felt by the cam. I need to consider static and rolling friction.

I wonder if using the slot constraint without a contact definition is sufficient for this purpose? Is there any way of defining contact between the two surfaces in this case i.e. getting the ball to roll?

barry84.

 

[hydromech]

Try using the gear connection.

Set up a ratio so that the ball rotates as is moves along the curve.

 

[sukidawg]

hello,

I am having some trouble with a similar problem, but I'm pretty new to pro/e having just come over from NX... maybe someone can give me a pointer or two??

I have an axial cam with a plain cylindrical follower, and I would like to mate them up such that i can measure the axial to angular displacement relationship. I am sure this shouldn't be too difficult, but as I say am pretty much a novice user of the software so its proving a little tough...

I've attached a pic - the profile is created using a variable helix - I do have the defining graph etc, but have gone as far as cutting the path in half to maybe obtain a trajectory off the edge curve...

Any advice appreciated!

Thanks,


David.

 

[barry84]

Hello David,

Although I am also inexperienced with Mechanism, perhaps sharing my experiences so far might help.

I was not able to define a contact between the cam surface and my follower (I tried cam connection and 3d contact). It seems the cam connection only works for radial cams. It also seems that 3d contact only works on planar surfaces (I could be wrong here, and if so I would appreciate being enlightened).

Therefore I instead used a slot connection between the follower and the cam surface profile. This allowed me to calculate forces between the cam and follower. You could use this approach too if you do not find a better solution.

 

[sukidawg]

Hi Barry,

Thanks for the comment - I noticed you'd mentioned this above - but "slot connection" doesn't seem to be present in the vcersion I am using (wildfire 4). I searched the help and it mentioned this only as legacy functionality...

:/