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Intermittent motion

gfraulini
17-Peridot

Intermittent motion

Hi all,

in those mechanisms that transform rotational motion into an intermittent motion, like globoidal cams or geneva wheels, It would be convenient to insert a special type of "mechanism link", like that there already been, like gears or cams.

In this manner you can link two motion axis (rotational) and move those with only one motor.

In my mind it would be like a gear where as input you get the rotation angle of the motion axis (like a shaft), and the output is a periodic rotation that is function of the input, like a cycloid.


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11 REPLIES 11

You can do this now. Just have a pin constraint on the output shaft and gear that to the other input shaft. You also have rack and pinion gears if you need to change rotational motion to axial motion. There are some restrictions, of course, but it has proven very useful.

Sorry but...I don't see the manner you can have an intermittent motion now if not using two different servomotors.

This example only uses one servo motor. The rest is fully linked with assembly constraints.

User defined gears will take any pin constrained part and create a motion axis.

You can tie that axis to another pin-constrained axis by creating a spur gear with user defined radio.

Do you have a specific example in mind that you can show an image of?

Index Drives

intermittore globoidale 3D globoidal Indexing drive index table positioning table - YouTube

In your example, the "slow axis" is always in motion: for large part of the revolution period it goes very slow.

Examples are a great thing! Makes discussion more direct.

You are right, these are technically cam drives. However, Creo cams are not quite powerful enough to recognize these types of surfaces.

My assumption was that you already had the motion linked in constraints.

I, like you, prefer to use servo motors rather than try to make constraints or make other mechanism feature work.

If I have an unusual motion profile, I will try to capture it in the 3D trace curve and convert that to a points file which can become a servo motor profile.

If your surface are planer or cylindrical, you should be able to do this with a cam. The globoidal cam will not be recognized but the trace curve will follow the feature created to generate the slot. This is typically derived from the motion desired.

I tried a mechanism of a Z-cam, a particular globoidal cam, making the 3D curve of the center of one of its six followers' rollers and constraining that point on that curve with a slot.
It worked. But I found that this kind of constrain is much sensible and you might occur that, especially in big assemblies, the regeneration doesn't bring back the parts to the point where you has set the regeneration in the constrain tab; or, if you does more than one turn, for example 460° (and the regeneration point is at 0°) it turns back of only 460-360=100°.

For PTC making a feature like a "intermittent gear" based on the revolution period of a rotational axis of motion, might be very easy.
The actual gear feature of mechanism works that the transfer function of the mote from the first to the second axis, is a straight line, continuous on the 360° of revolution, with a slope that is function of the transmission ratio. It would be sufficient insert the possibility change the equation of the "straight line" into a different kind of curve (piecewise curve with cicloide or 5° polynomial) where the variable it would be the angle that could vary from 0° to 360°.
Something similar for translation motions.

The one tip that has saved me a lot of trouble is the snapshots.

They are a bear to keep up to date but they do bring things back to where they expect themselves to be.

Slot followers are great except that they cannot leave the track. It is one way screw a nut onto a bolt, for instance.

Even this seemingly simple mechanism was a lot of work...

Maybe someone of PTC's developers will listen this request and will answer us...

[holding breath... ... holding........ ................ ......]

The real answer is collision based mechanism kinematic solutions that only require initial kinematic displacements to operate. This is the basis for simulation using the Physics Bullet engine. No bullets required.

Anyone of PTC can tell us if a feature like this will be developed in a future release? (Creo 4.0?..)

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