Linear Actuator's Duty Cycle?
Linear Actuator's Duty Cycle?
(OP)
Hello all,
I'm looking at linear actuators and a bit confused about the duty cycle parameter.
Most of them has the duty cycle parameter in the datasheet and it ranges between 10-20% (under load), when few of the manufacturers state this parameter under partial load (Duty Cycle of 50% under 25% load) and some of them exclude this parameter all together, despite using the same general construction and mechanics.
Dose all electrical actuators have duty cycles?
It might be a stupid question but for example, I've disassembled an old veterinarian ventilator that delivers an alternating air flow by pushing a piston using a linear actuator, and that ventilator doesn't have any restrictions on the "ON" time or any specification for the “resting” time.
So basically it seems that the machine doesn't have a duty cycle.
I understand that this parameter is relative, but none of the actuators state the maximum "ON" time, just the 10% or 20% of duty cycle.
So by that logic it doesn't matter if I run an actuator for 10 minutes or 10 hours as long as I let it rest 90% or 80% of the time (depending on the product specifications).
So it doesn’t make any sense, if the duty cycle is there to protect the product from wear and tear, how this parameter can be applied for the same product if the wear is vastly different for 10 minutes or 10 hours of usage.
I'm looking at linear actuators and a bit confused about the duty cycle parameter.
Most of them has the duty cycle parameter in the datasheet and it ranges between 10-20% (under load), when few of the manufacturers state this parameter under partial load (Duty Cycle of 50% under 25% load) and some of them exclude this parameter all together, despite using the same general construction and mechanics.
Dose all electrical actuators have duty cycles?
It might be a stupid question but for example, I've disassembled an old veterinarian ventilator that delivers an alternating air flow by pushing a piston using a linear actuator, and that ventilator doesn't have any restrictions on the "ON" time or any specification for the “resting” time.
So basically it seems that the machine doesn't have a duty cycle.
I understand that this parameter is relative, but none of the actuators state the maximum "ON" time, just the 10% or 20% of duty cycle.
So by that logic it doesn't matter if I run an actuator for 10 minutes or 10 hours as long as I let it rest 90% or 80% of the time (depending on the product specifications).
So it doesn’t make any sense, if the duty cycle is there to protect the product from wear and tear, how this parameter can be applied for the same product if the wear is vastly different for 10 minutes or 10 hours of usage.





RE: Linear Actuator's Duty Cycle?
RE: Linear Actuator's Duty Cycle?
I don't think you quite understand what duty cycle means.
Let's say I have a machine with a 100 second cycle time. The linear actuator runs for a total of 10 seconds out of every 100 second cycle.
If I turn that machine on and let it run for one hour, the duty cycle of that machine is 100% for that hour. If I turn the machine on and let it run until the end of time, the duty cycle of the entire machine is still 100%.
In both cases, the duty cycle of the actuator relative to the whole system is 10%. How long the machine is left to run is immaterial.
The duty cycle limit is not put in place to prevent normal wear of the parts- the duty cycle is there to prevent things like overheating of motors which would cause premature failure. This is a small but subtle difference.
Using your ventilator as an example- I am absolutely sure that a ventilator designed for use in a hospital during surgery or for a patient on life support is designed for 100% duty cycle- meaning it can be turned on and left to run indefinitely.
The actuator that moves the piston is not running 100% of that time- it might be moving down 25% of the time, and then back up 25% of the time, for a total duty cycle of 50%.
The duty cycle of an entire system and the duty cycles of its individual components may be the same, but they are not the same by definition.
RE: Linear Actuator's Duty Cycle?
There are limits on the 'on' time that a unit can handle.
And all of this is thermally limited.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Linear Actuator's Duty Cycle?
Duty cycle typically prevents failure of mechanical components due to excessive heat. Most linear actuators use a worm drive of some kind. Many have plastic gears. These are the components that typically fail.
RE: Linear Actuator's Duty Cycle?
This is what confuses me, if the duty cycle of an hour and for eternity is still 10%, why is it relevant? even if it is there to prevent over
heating.
I'll try to rephrase my question, if I have two exact same actuators, with 10% duty cycle, and run them under the same conditions (force, speed, voltage etc.) but one of them runs for 1 minute (with 10 minutes off time) and the other one runs for 100 hours (with 1000 hours off time). Both of them have 10% of duty cycle but the second actuator is stressed way more the first one. What can I infer from this 10% duty cycle?
Because even if maintain the 10% on and 90% off time the chance for the second actuator to fail is way higher than for the first one.
Without a fixed time frame reference this 10% won't give me an indication of how to use the actuator without it failing, as the off time is irrelevant for determining if the actuator will fail.
How come the total duty cycle of the actuator is 50% if this parameter indicate the ratio between the ON time and OFF time, so while the piston is moving back and forth it can be considered as ON time and OFF time will be when it stopes to change direction.
RE: Linear Actuator's Duty Cycle?
RE: Linear Actuator's Duty Cycle?
A linear actuator extends or retracts and then comes to the end of the stroke. Then it STOPS.
The time it takes to travel the full stroke is the "quantum" of time you must bear in mind when evaluating duty cycle.
Let's assume it takes the actuator 5 seconds to fully stroke in or out. After a 5 second stroke, you should wait for 20 seconds before moving again to get a 20% duty cycle.
5 / (20+5) = 0.20
STF
RE: Linear Actuator's Duty Cycle?
TTFN (ta ta for now)
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RE: Linear Actuator's Duty Cycle?
RE: Linear Actuator's Duty Cycle?
It does make it sound like the actuator is under-designed, when I put it that way...
STF
RE: Linear Actuator's Duty Cycle?
As I can produce the same amount of haet when runing the actuator for 10 seconds and for 10 minutes.
There should be provided a graph of heating as a funtion of ON time and load applied, and for each set of those parameters a duty cycle can be deduced.
RE: Linear Actuator's Duty Cycle?
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Linear Actuator's Duty Cycle?
In my experience, linear actuators are always waaay over designed- because A) the manufacturer usually has a warranty of some kind and B) the buildup of heat (which the duty cycle limit is meant to control) depends heavily on circumstances out of their control, namely the airflow around the actuator body. So they test and determine duty cycle ratings based on worst or near-worst case scenarios, such as the actuator being inside a very small volume that is well insulated with no airflow and no exchange of the hot air, etc.
If you mean that you run the actuator continuously for 1 minute and then rest for 9 minutes, or 100 hours and then rest for 900 hours, in both cases the duty cycle of the actuator is 100%. Duty cycle at the component level, where you're working here, is based on the component, not the rest of the system.
If the operation of the machine is a square wave function, duty cycle is the width of the peak divided by the period.
IR has it right- these numbers are based on the actuator's real world cycle time.
Any decent manufacturer (a manufacturer, not a reseller who buys offshore actuators and labels them without any real engineering, which is very common) will have a very in-depth table of duty cycle for a given series of actuators.
This table will start at the top with a very short period of time for which the actuator is rated at 100% duty cycle, and then progress through lower percentages and longer periods, until some inflection point at or below which infinite periods of operation are allowed.
RE: Linear Actuator's Duty Cycle?
The only way to know for sure is to test on your own.
RE: Linear Actuator's Duty Cycle?
Constant electrical type loads make it easier to visualize...for example, I believe Miller welders (maybe others, too?) specify the duty cycle as a percentage of a 10 minute period, at a given amperage output.
RE: Linear Actuator's Duty Cycle?