Calculate Counterbalance using Air cyclinder

[lookieuk]

Hi peeps

Am after a little help with a project been asked to do, please see images below
Showing a linear rail system on load cells.

My question is trying to figure out the loading if I use two air cylinders on the load cells to act as a counterbalance when the linear carriage is fully out, / what kind of air cylinder could use? what would be the force?
Is there some simple cals i can do to work this out?

Thanks very much

 

[drawoh]

Is counterbalancing a good use for air cylinders? I presume the air cylinders are providing air to something. What happens if someone decides the air cylinders are not needed any more and they don't realize they are counterbalances?

--
JHG

 

[rb1957]

1) are the air cylinders permanent or only temporary (like when you test, with the load cells?) ?

2) why do you think you need to counterbalance the load ? does it overload the LH supports and the counter-balance is a "quick fix" ?

3) how heavy are these air cylinders ? You could side-step the above concern by inerting the cylinders, filling with concrete (or water), painting a different colour (so they don't look like air cylinders), sticking a label on them ("this is not an air cylinder, it is ballast. leave in place").

another day in paradise, or is paradise one day closer ?

 

[jlnsol]

Why not two simple fixed blocks to avoid the lineair rail system to jump up from the load cells at the proposed air cylinder locations? Or do you still want to use the cells as measurement instruments?

 

[jlnsol]

Besides my comment above I suggest that you look into the specs of the cells and also how they are connected to the construction. Many loadcells can handle pull as well as push forces. So it might be possible that you can skip the idea of adding air cylinders completely.

 

[lookieuk]

Hi all

thanks for your comments regarding this, was thinking could use the air cylinders as a counter balance to push down on the load cells at the RH side, will make a bracket with rubber feet to stop any damage

The air cylinders will be a permanent fix to stop any damage to the load cell when the carriage is fully out

yes will need to use all load cells for measurements instruments, so by using a air cylinder i can control it on and off to push down and stop the load cell from getting damage

am thinking of air cylinder as this is in a clean environment, and a dust environment so must be a no explosive method

maybe can make some bracket with a set coil spring to stop the load cells from over extending?

 

[rb1957]

I imagine you're using the load cells to verify the weight of the load.

then how about verifying the load (reading the load cells with the load between the posts (in it's starting position).
Then deploy a catch over the RH loadcell (to react up load).

If you use the load cells to measure the load dropped (when the load is travelled to the left), you can still do this using the LH load cells (and a different scale).

another day in paradise, or is paradise one day closer ?

 

[lookieuk]

yeah that right am using the load cells to measure the load in the start position and once i have reach the weight required
move the carriage to unload position

when you say deploy a catch over what do you mean, guess that where am coming with the air cylinder to push down on the load cell
to stop them over stretching with the weight at the unload position

 

[zeusfaber]

I'm assuming that by "Air cylinder" you mean some sort of pneumatic actuator, rather than the dead weight of a storage cylinder and, like jlnsol, I'm assuming that your aim is to prevent the load cells from being put into tension when the carriage is run out.

Do the rails actually have to be attached to the load cells, or would it be sufficient for them just to rest on top of the cells? Have you considered fitting a hard stop above the rail (which will react your counterbalance loads exactly as they present themselves with no need for fine pressure control) and then let the end of the rail float in a small clearance between the load cell below and the stop above? You would need to add structure to restrain sideways movement of the rails - but adding structure (if only to attach the other end of your actuators to something) always was going to be part of your plan.

A.

 

[lookieuk]

Yes and Yes Zeusfaber

yeah the rails do need to be attached to the load cells as it tells me the measurement of the load and the rail are resting on top of the load cell as shown in the image above

Yeah have thought about making a hard stop and with some adjustment as well so you can set it up easier, may go with that idea as its low cost

with is project really need to find out what happening with the machine and the fault, just was told a brief description of looking into this method to fix it but not sure its the right way to go

 

[zeusfaber]

Just to pick away at this a little: "Resting on" and "Attached to" are slightly different things and in this case, it looks like you need one more than you need the other.

I wonder how much lateral loading the cells see in the current design? Are they OK with that?

If you can't make it work with a fixed stop, a simpler solution in control terms would be to use your pneumatic actuators to withdraw latches from above the rails (or to rotate away a cam that bears down on the top of the rails) for the period you need to make your measurements. That way, the pressure needed in the actuators is independent of the weight in the carriage, you can interlock the carriage drive so it only works once the latches have sprung back home and you aren't going to get nearly as embarrassed if the air supply fails when the carriage is run fully out (an idea pretty similar to what rb1957 proposed).

A.

 

[rb1957]

can you answer zeus's query "I'm assuming that by "Air cylinder" you mean some sort of pneumatic actuator, rather than the dead weight of a storage cylinder" as I've assumed the dead weight option.

I understand you want to avoid tension on the RH load cell, or having the rail lift off the load cell. As zeus posts "resting on" is different to "attached to".

My "catch" idea is a mechanical link that you'd put on the rail which would allow compression of the load cell but would react tension loads. So in the RH position you should be able to read the weight on all load cells. In the LH position (only the LH load cells would be active (the RH ones would be "locked out") but you can still determine the load (from the solution of the beam reactions, the LH reaction is directly proportional to the load).

another day in paradise, or is paradise one day closer ?