Controlling four Linak actuators.......

[kitarusapien]

The units are Linak medical bed actuators, run on 12 or 28V, usually run by a hand-controller and usually without installed potentiometers. What I would like to do is operate four of these units with some sort of controller/power board and a standard PC control-stick so that they mimic the control-sticks' inputs as accurately as they can operate under normal operating conditions to basically computer-mix the actuators(stick back, all actuators extend, stick forward, all retract, any position in between, all actuators assume their proper position to reflect the stick's position.) If if this can be done, please let me know.

Thanks so much!!!!

 

[itsmoked]

TWO INCHES?![flush]

What are you using this for?

 

[kitarusapien]

controlling panel movement.

 

[itsmoked]

Okay.

37.5 Watts

Times 3 = 112.5 Watts

Pretty small potatoes. Use three 100W switchers. Or three 50W unregulated supplies.

 

[Skogsgurra]

One also needs to take the rather low efficiency of the worm gears into account. That may mean that you need three or four times the mechanical power to supply the motor.

On the other hand, it is not plausible that the actuators will be delivering full power all of the time. It is not even probable that they have to deliver full power at any time.

What forces do you need to move the panels? The 750 N is the spec of the actuator, but what force is excerted on the panel? And what does the duty cycle look like? Do you move tem once in a while or do you move them back and forth continuously?

All these considerations go into the design of a system like this.



Gunnar Englund

http://www.gke.org

 

[itsmoked]

Yes skogs, but it will all be parcelled out a little bit at a time.

This will be a complete design by forum taking 3.5 years and 3,000 posts.

It's a s l o w work in progress.

Scotty beam me out.

 

[kitarusapien]

FLOL!!! Sorry for the sea of questions from me; I really like your "Scotty" remark! Skogs, the system will have the actuators moving back and forth constantly, but after an initial engagement of full throw and relatively static positioning(approx 450 N), the units will move back and forth only incrementally, and have very little load on them(approx 75 N)for the duration of their duty cycle. The maximum time of duty will be less than 3 hours per unit. THANKS AGAIN ALL!!!

 

[Skogsgurra]

Is that a business idea Smoked? Doing design in teams on the Eng-Tips. Sounds like some fun - but I think that the poor customer (Kitarusapien in this case) may want a somewhat faster design cycle.

Your 3.5 years and 3000 posts estimate seems to be quite well underpinned. It is not very unlike some design cycles I have lived through even without computers and internet.Postings were then paper letters, meetings and phone calls.

Gunnar Englund

http://www.gke.org

 

[itsmoked]

Hi skogs.

Naw! I was just expressing my frustration at having important required details dribbled out a little at a time in some misplaced desire for secrecy. As if everything hasn't been done or tried. Everyone thinks they have the next Ipod brewing. (me included)

The OP can't have it both ways. If he wants tight secrecy he shouldn't be here. OR.... He should at least have his specific requirements very clearly defined. Otherwise if he doesn't have the specific requirements or know how to derive them we need a lot more information on what he wants to do so we can cogitate the specific requirements needed in a timely reasonable manner. I mean, is he trying to keep a ball bearing balanced on the platform, or point something, or heat water by sloshing it? Who knows?!? This would completely change possible control strategies.

At this point I feel we are providing free engineering services for a secret product for the OP to develop and sell.

I would rather provide tips.

 

[Skogsgurra]

Big grin!

Gunnar Englund

http://www.gke.org

 

[Barry1961]

You have probably already looked at this....

Hospital bed actuator motors have an extremely low duty cycle, not much better than a starter motor on a car. I see that the motors are not going to be fully loaded but if they are going to be starting and stopping at full voltage/speed you may have a problem.

It has been a long time since I looked at those actuators but I think the motor would burn in less than a minute of operation. These motors have to start hard to overcome the static friction of the worm.

Barry1961

 

[kitarusapien]

ITSMOKED, I can appreciate your frustration at my dribbling out info, but it's not because I have a great idea, it's because what I'm trying to do is not S.O.P., so when I tell people what it's really for, I get a very MUTED response, if any response at all! So, PLEASE, forgive me for dribbling, but truth be told, you folks have gotten me farther with your info not knowing what it's for, than 100 posts on other boards, telling folks exactly what I'm doing!!!! BTW, it's not illegal, immoral, illegitimate, somebody else's idea, or a better mouse trap....FLOL!!!! Now, about that duty cycle question, I don't see that as an issue due to the really low loadings after initial actuation at half-travels back and forth for possibly thirty seconds at the most, BUT I'm not the expert here, so please....elaborate. THANKS!

 

[Barry1961]

You would probably have to test a unit to see if the motor will burn. These actuators are made for a very definite purpose so you may not get good data from Linak. When the engineers designed these they did it to the absolute minimum requirements. That is part of why they are so cheap.

Acme screws often have a very high static coefficient of friction. It is often very hard to move a short distance with a motor/controller that can not produce full torque at a very low rpm. Many DC motor/controllers just reduce the voltage to the stator for low speed with also gives the motor very low torque. If you give the motor enough voltage to “break” the acme screw free it will often over run the target.

So depending on your setup you may end up with an imposed mechanical resolution of a few revolutions of the motor. You can try giving the motor short full voltage pulses but that opens up a new set of problems. It does not sound like you have the budget for even a pseudo servo control.

Barry1961