Limit switch

[kwame]

HI folks
i i need a linear actuator with a stroke length of 4''(inches) .Unfortuantely,there is no reseller of linear actuators in my country.The only ones on the local market are fitted to giant free to air satellite dishes with a stroke length of 15''(inches) which is too much and importing a single actuator from the west is very expensive.
Is there a way i can restrict the stroke to 4''? I thinking of trying a limit switch but i am this wont work since the actuator already has a limit inside.Folks i need some guidance from you.Will a limit switch work ?If yes which type of limit switch and how is the wiring of the limit switch going to look like?

Kwame

 

[crutschow]

One way is to simply wire the normally-closed contacts of the limit switch is series with the motor. Just place the limit switch actuator such that it opens when the desired stroke position is reached.

 

[kwame]

I want the linear actuator to move back and forth.

 

[crutschow]

I want the linear actuator to move back and forth.

So what causes the actuator to reveres directions now? Don't you just reverse the voltage polarity to the motor?

 

[RCinFLA]

The satellite dish acme screw drives have hall effect pulse indicators near the motor shaft. You keep track of the position and count the pulses for movement accuracy. They are very accurate but you need to keep memory of last position.

 

[kwame]

TCinFLA this is above my head!How do i 'count the pulses' manually,visually,with a counter? It appears not all linear actuators use the acme screw.Most actuators use something known as 'permanent magnet'.

 

[crutschow]

Ignore the counting of pulses for the moment. You don't necessarily need to do that if you use a limit switch.

"Permanent magnet" is just a type of DC motor which still drives an acme screw.

The motor is likely reversed just by reversing the DC polarity to the motor. Thus you power it in one direction until it reaches the limit switch. Then reverse the polarity to reverses direction until it stops from the other limit switch.

 

[aljamri]

In our Motorized valve, we are using two limit switches for OPEN and CLOSE, and two torque switches to break the circuit when limit switch dose not take action.

 

[KeepItSimpleStupid]

Actuators may have mechanical pulses, hall effect pulses or potentiometer feedback. It's likely to find only one mechanism in use.

Adjustible limits seem to be foreign, but fixed limits at the extreme ends of travel do appear to exist.

 

[SABorn]

Try searching locally for an actuator for opening gates as these are similar to the ones you are looking at, and often have adjustable limit switches so as to set the gate opening arc needed.

They are also avaliable on Ebay if that is an option for you.

Pete.