For a uni project i need to design a linear wear testing machine with a pin rubbing on a plate but there must be a constant force of 500N being
applied to the top of the pin.
Can linear actuators being controlled this precisely to hold a constant force?
It onl has to be designed and not made, so as long as its doable then ill use that.
Or any other suggestions of how to apply a constant force?
Just put 500N of weight (f.e. 2 sierra diffs) on the pin ?
quote:
Originally posted by Breaker
Just put 500N of weight (f.e. 2 sierra diffs) on the pin ?
Hydraulics?
Just need some kind of simple pump controled by a pressure switch and you're done. depends how accutrate/toleranced it needs to be.
Pneumatic cylinder. Pressure is easily regulated and monitored.
But why not a 50kg weight.
I guess I don't understand the problem well enough.
Matt
wel i guess a 50kg weight would be the simplest option, one we did think about and might still use, just wondering if its possible to do it with either electronic/pneumatic or hydralics actuators
if you don't want to add the 51kg to the top of the pin, assuming it would be reciprocating, 2 identical hydraulic cylinders one rigidly fixed
and loaded with 51kg, then a flexi to the other cylinder on the rig.
minimal reciprocating mass and constant force application.
tom
quote:
Originally posted by Miks15
just wondering if its possible to do it with either electronic/pneumatic or hydralics actuators
Is the pin reciprocating, or is the wear plate turning / reciprocating?
Add the weight to the pin using a series of CF springs. This will be the most compact method and can be used with either the wear plate or the pin
moving.
the plate will be reciprocating, with the pin placed on top
The answer to whether you could do it with pneumatics,hydralics or electrics is almost certainly yes but the best solution starts with the
specification.You say you need 500N but is that 500+/- 1 or 50. Lecturers generally set very open ending questions but when you approach these kinds
of problems you need to clarify the spec to understand the requirements and therefore what you can get away with. A weight my be adequete but if the
plate moves quickly the additional accel decel may well push it out of range.
I'd have a think (brainstorm if a group) on what you could use and also go back on the spec and question it and then you can start working your
list.
good luck
Pete
well like you said the spec is very open ended, just saying a force of 500n needs to be placed on top.
We dont need to design anyof the electrical compnents so we can just say computer controlled to maintain a 500n force on top.
it wouldn't be much more effort to include some more detail and show you actually understand the problem. that's where the marks are
are you in first year? if so, i suppose you can go for easy street....if not though, get it in there and get yourself some marks. better first year
grades help you get better placements if you're on a sandwich degree too
tom
Remember the KIS principle ---- don't get involved in electronics or hydraulic or pneumatic regulators simply use a weight. If don't want sit the weight directly on top of the pin apply it remotely by levers or hydraulics - as used in a Budenberg Dead Weight Tester used for calibrating pressure gauges.
I think were just going to go for a weight on an arm, to reduce the actual weight we have to have in there, cheers guys
Just some things to think about:
Is the reciprocating plate flat and even thickness - If the height of the top surface varies a lot (e.g. curved) and you move it quickly, you will
have inertia of the weights to consider.
Is the plate strong - how is it supported - a 50kg point load would produce a fair flex even in a fairly strong plate, obviously depending on length
and shape of the sample.
You may be able to devise something with two arms pivoted at the end,with one each side of the plate, a wide wheel on the lower one and the wear pin
on the other arm. Pull the arms together with a pneumatic/hydraulic actuator (allowing for leverage), and top up the pressure to keep the force the
same as the pin wears out (or if the plate is not even thickness).
Have you ever been to Ikea? They have various wear testing machines on display that may give you some ideas (or they did 5 years ago when I was there
last).
Just some things to think about,
Regards
Hugh
Depends on what they want is the real answer, suggesting a fixed mass on top of the pin is fine but might not get many marks if it's at the end
of a hydraulic control system module 
Remember the critical evaluation of your solution is the thing that gets the marks (things like inertia of a 50kg weight will need to be worked out if
you're presenting that as a solution).
It's not hard to do with hydraulics if I remember stuff I did 20 years ago. I think you need a load sensor between the pin and the cylinder and
some kind of simple control algorithm. Would probably be best to have a Kalman filter in there if you're happy to talk about them.
The advantage of a computer controlled system is it's a lot more compact at the test head end and you can change the force applied on the fly if
it's necessary.
Most complex solution is never the best.
Simplest solution is most often the best.
quote:
Originally posted by iank
Remember the critical evaluation of your solution is the thing that gets the marks (things like inertia of a 50kg weight will need to be worked out if you're presenting that as a solution).
quote:
Originally posted by MikeRJ
quote:
Originally posted by iank
Remember the critical evaluation of your solution is the thing that gets the marks (things like inertia of a 50kg weight will need to be worked out if you're presenting that as a solution).
Sounded to me like the pin was stationary and the plate was being moved underneath it?
quote:
Originally posted by iank
While the big weight may be the best solution I have a doubt that it's what a degree level course prof has in mind as the solution, unless it's a trick question to weed out the people who over design of course.
quote:
Originally posted by indykid
quote:
Originally posted by iank
While the big weight may be the best solution I have a doubt that it's what a degree level course prof has in mind as the solution, unless it's a trick question to weed out the people who over design of course.
the marks are most probably in choosing the best solution, whatever that may be, then justifying it and discussing the limitations.
a pure simple solution is something many of the lads on my course would be totally unable to conceive.
just because its uni, it doesn't mean it needs to be complicated. it may seem like common sense, but we have it. some people need a shove
tom
quote:
Originally posted by iank
Remember the critical evaluation of your solution is the thing that gets the marks.