Electromechanical replacement for pneumatics
Electromechanical replacement for pneumatics
(OP)
I have an existing system consists of a 5.5" long arm which pivots on bearings at one end, and loads against a product at the other. The load of the pivoting arm is provided by a pneumatic dashpot (a low friction air cylinder, essentially).
We have applications which require this pivoting arm, but they do not have a compressed air source.
I am looking for an electronically driven alternative to a small (1/2" bore) air cylinder. Some general requirements.
1) Must be easily back-driven / low stiction. So anything with a lead-screw or substantial gear reduction (worms, multi-stage) is out.
2) The arm needs to see ~1Nm (8.85 lbf-in) torque.
3) The arm swing is 90deg. For reference, I'm looking at a 1-2" stroke for a linear solution. (Of course this depends on the force capabilities of the actuator).
4) Adjustable and linear force. Spring generally don't have enough adjustment range and their force increases with increasing displacement.
Thoughts so far:
Simple Brushed DC Motor (Mabuchi or similar), gear driven ~10:1 or so to the shaft. It's simple, inexpensive, and gives me the torque, adjustability, and easy back-drive I'm looking for.
I'm worried about the motor/brushes survival since they are not actually designed to be nearly stationary 24/7. The motor could be oversizde such that a lower current can be used. So long as the motor can dissipate the heat, will it survive? Or is this just terrible practice...?
Solenoid actuator:
They seem to be more designed for engaging/disengaging things. I have not been able to find any that actually function like a pneumatic cylinder.
Motor Driving a clutch:
Avoids the motor eating-itself-alive problem, but the cost of an adjustable clutch (hysteresis, whatever) can be prohibitive.
Any ideas? Thanks.
We have applications which require this pivoting arm, but they do not have a compressed air source.
I am looking for an electronically driven alternative to a small (1/2" bore) air cylinder. Some general requirements.
1) Must be easily back-driven / low stiction. So anything with a lead-screw or substantial gear reduction (worms, multi-stage) is out.
2) The arm needs to see ~1Nm (8.85 lbf-in) torque.
3) The arm swing is 90deg. For reference, I'm looking at a 1-2" stroke for a linear solution. (Of course this depends on the force capabilities of the actuator).
4) Adjustable and linear force. Spring generally don't have enough adjustment range and their force increases with increasing displacement.
Thoughts so far:
Simple Brushed DC Motor (Mabuchi or similar), gear driven ~10:1 or so to the shaft. It's simple, inexpensive, and gives me the torque, adjustability, and easy back-drive I'm looking for.
I'm worried about the motor/brushes survival since they are not actually designed to be nearly stationary 24/7. The motor could be oversizde such that a lower current can be used. So long as the motor can dissipate the heat, will it survive? Or is this just terrible practice...?
Solenoid actuator:
They seem to be more designed for engaging/disengaging things. I have not been able to find any that actually function like a pneumatic cylinder.
Motor Driving a clutch:
Avoids the motor eating-itself-alive problem, but the cost of an adjustable clutch (hysteresis, whatever) can be prohibitive.
Any ideas? Thanks.





RE: Electromechanical replacement for pneumatics
RE: Electromechanical replacement for pneumatics
Or that's what I'm told. It's entirely possible this is one of "those" sales/marketing things.
RE: Electromechanical replacement for pneumatics
Sounds like what you are looking for is a servomotor. I'm not sure that you will want servomotor prices, but it is perhaps a starting point for some creative Googling.
RE: Electromechanical replacement for pneumatics
RE: Electromechanical replacement for pneumatics
Best, or least worst, choice is a small air compressor and an air cylinder.
Mike Halloran
Pembroke Pines, FL, USA
RE: Electromechanical replacement for pneumatics
Out of shear morbid curiosity, what prevents a "solenoid air cylinder" from being made? I'm envisioning something a bit like a coil-gun, with a linear pot for position feedback to an inexpensive uC controlling the individual coils (I guess each coil needs its own mosfet h-bridge, which could get expensive). In effect, a linear brushless DC motor.
Off to the patent office...?
RE: Electromechanical replacement for pneumatics
http://www.ultramotion.com/products/
Or maybe an electric governor actuator, only thing might be hard to find 90 degree rotation direct from the actuator by adding a non-linkage may increase effective travel
http://www.governors-america.com/225_series.html
Or a governor linear actuator,
http://www.governors-america.com/alr_series.html
Not sure if these will work but there are other suppliers with similar devices and different ranges. voltages, and control inputs like Woodward, Heinzmann and Bosch.
Hope that helps, Mike L.
RE: Electromechanical replacement for pneumatics
There are literally hundreds of manufacturers of these things. I'm not sure they go small enough for what you need, but I haven't really looked in detail.
RE: Electromechanical replacement for pneumatics
Interesting idea, but it looks like they're mostly synchronous motors designed to run off 60hz. Not so sure that would work if the actuator is effectively stalled and repeatedly back-driven.
Looks like there isn't an obvious solution to this one that I've missed. I suspect I'll wind up (ahem) with a compromised solution involving a torsion spring with many coils.
Thanks everyone.
RE: Electromechanical replacement for pneumatics
Similar devices are used to actuate zone valves on hydronic heating systems - they often contain a Slo-Syn motor and a little gearbox with spring return; these devices sit in an energised stalled state for long periods of time.
RE: Electromechanical replacement for pneumatics
RE: Electromechanical replacement for pneumatics
http://ab.rockwellautomation.com/Motion-Control/Ac...
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RE: Electromechanical replacement for pneumatics
RE: Electromechanical replacement for pneumatics
sounds like $ 200 total? 1 pc or many?
i will guess ballpark prices of approaches:
- $500 servo motor + 500 servo drive
- $1000 torque motor + 500 servo drive
- $50 stepper +$100 stepper drive
- $150 cheap linear actuator with say 12vdc motor
- $500 linear motor + $300 driver (http://nipponpulse.com/products/overview/linear-sh...)
- $100? your cheap dc motor/gearbox
We sell/apply all but the last choice. I think our nippon linear motor sounds right but not sure of price you need. I also do not see why you think your cheap dc motor would not survive sitting in one spot pushing for long time - brushes wear out for 2 reasons: 1) friction of going around and around & 2) sparking - from going around and around at high current or voltage. Your app would do neither so therefore your little cheap motor should last nearly forever based on the data given so far.....
RE: Electromechanical replacement for pneumatics
Just concerned with overheating it. Although I guess that can be avoided with the right power supply method.
I am going to investigate the HVAC damper thing some more.