Spring returning components in joints

[peteGCAB6]

Hi everyone,

I have a mechanism I am working on that has a few sliding components, and I am having a problem with the motion. I am using contact sets between the two components. 

The main component (grey with slot in screenshots) drives the rest of the motion. It consists of a flat plate that slides forward and backward in one axis only. I has a slot, which fits over a pin that protrudes from the second component. The second component (blue in screenshots) is sprung so that it always slides away from the first component (in the downward direction on screenshot). 

When the first component is slid up (towards top on screenshot), to start with, the second component stays still, as the slot in the first component moves around the pin. After about 6mm of motion, the end of the slot catches the pin and drags the second component with it, against the force of the spring. 

When the first component is allowed to slide back down again, the force of the spring should keep the pin on the second component into the bottom of the slot, and the two components should move as one. 

What is happening is when the first component is slid back, the second component is staying still, until it meets the top end of the slot, and is then being pushed back, which puts the whole mechanism out of phase. 

The spring Im talking about is not modelled, please note the two springs in the screenshot are part of another area of the mechanism, and not part of this problem. 

Is there a way to tell a component that it always springs towards a certain direction when allowed to by the rest of the motion links? 

[chrisplyler]

Yes. Use the Rest position setting within the Joint Limits....

[peteGCAB6]

Hi, thanks for that, its working but theres still a problem... The parts seem to jump around, and the pin jumps out of the slot, the motion is very jerky and unpredictable. Im assuming its just a bug, as nothing seems wrong in the setup, but its frustratingly jumping about all over the place.

Pete. 

[jeff_strater]

@peteGCAB6 - it would be easier if you could share the design here.  The first thing I would recommend is turning off contact sets totally.  My guess is that those are responsible for the jumping around - the performance of contact sets on anything but very simple models will be unacceptable.  Instead, do everything with Joint Limits and Rest position.  I realize that some mechanisms cannot be emulated with this toolset, but a lot of them can be.