Ideas for tension and compression test stand

[jqm]

Hello,
I currently work for a company that manufactures weigh scale devices.  A majority of the devices are either patient weight scales ( the kind you stand on at the doctors ) or a tension load cell (displays patient weight when on a lifter).  Typically the devices can weigh up to 1000lbs full scale.
My job usually consists of performing engineering test / evaluation of these devices.  A majority of the testing involves me slinging massive amounts of weight all day…  I usually have to do repeatability testing, linearity runs (ascending / descending), etc.    Currently this technique is purely physical… I am looking for ideas to make it a LabView controlled technique that is relatively CHEAP.

Desired:
1) Relatively accurate (at 1000 lbs) accurate AND REPEATABLE to 0.05 lbs
2) Once at a particular load it must remain stable to 0.00 lbs ( sometimes air compression devices oscillate)
3) Can be configured for tension loads or compression loads  (can be manual to configure)
4) Automation – Would like to run either tension testing OR compression testing but to be able to just walk away and have the system automagically perform the repeatability/linearity runs, etc.

Ideas so  far:
A) A lever arm whose fulcrum point changes based on a linear motor and a known load.
B  Some kind of linear motor that can be securely mounted vertically:  would have to have various types of attachments to configure tension / compression testing.

I haven’t even begun to research linear motors… I don’t even know if they are appropriate or not for the application.

Any brainstorming ideas would be greatly appreciated

 

Thank you for your time

[AnalogKid2DigitalMan]

Personally, I would not try to reinvent the wheel. First to enter my mind is compressive/tensile testing with off-the-shelf equipment from Instron or similar manufacturer. They have highly capable automation/data collection software too. Not cheap as you wanted, but precise, repeatable, traceable, and pretty much out of the box solution, less custom fixturing. Realize you request 0.005% repeatability at 1000lbs full scale, keep in mind the time, cost, and labor you may incur trying to design, build, test, and certify an in-house built solution.

If not, maybe you can get some ideas by looking at how such equipment works.

Voice-coil mass drivers may be a means to apply forces.

May the force be with you

[unclebump]

Take a look at these linear servo actuators. They can be operated in force mode or distance mode.

http://www.exlar.com/

[johnsold]

For cheap repeatability and stability nothing beats a physical mass. Look at an old mechanical balance, one that lifts weights on/off the balance arm. Perhaps you could adapt the concept to the scale you need using motors or solenoids to add/subtract weights.

Lynn