Electromechanical Linear Actuators

[draynor]

Hi everyone,

Could anyone give me a simple description of how, once a pilot has triggered a linear actuator on an aircraft, what is transmitted through the cable, through the 6-pin connector and finally to the DC motor? Is it just a case of the pilot making a circuit and current flowing to the motor to start it and once the pilot has turned the switch off, the current and hence motor ceases? I know this is a simple question on here but any help would be greatly appreciated.

I am currently designing an LVDT to go around the casing of a linear actuator to monitor the position and limit it's stroke so it doesn't overshoot. Therefore i need to build a circuit around the actuator and LVDT that will switch the motor off once a certain voltage has been reached. Any ideas on what the circuit should contain?

Many Thanks.

 

[buzzp]

There are options in actuator technology to do exactly what you want. They may have limit switches (older tech.) or they use PWM feedback or other type of signal (4-20mA). I would talk with your vendor and they can help you get what you want without reinventing the wheel. The 6 pin connector does not help much as they use the same number of conductors for all the available technologies to drive the actuator (PWM, mA signals, etc ) The data sheet should reveal which one you have.

 

[draynor]

Thanks for your response. The linear actuator i am currently designing the LVDT system around has two micro-switches to stop the overshoot of the ram. This actuator is based on the Hawk aircraft currently.

I am aiming to intergrate an LVDT into the loop to slow down and stop the ram on both extension and retraction by halting the motor, but am having difficulty in designing a circuit that would do this. Any suggestions would be of massive help.

 

[buzzp]

So your purpose is really to slow it down before slamming (hitting the micro switch)?

I suppose you are aware that actuators are available with feedback (LVDT) built in to indicate position (PWM or analog signal represents position). Can't you use one these to know where the actuator is? Is the actuator electrical or pneumatic operated?
The electrical units I am familiar with are either on or off (full voltage or no voltage). I assume there are other flavors that would allow more precise positioning with PWM or analog.
I have designed a system using pneumatic actuators with a proportional valve supplying the air. I assume the same type of system could be done with electrical actuators.
- are electrical actuators available that can be driven with PWM? If not advertised as such could still be done since PWM is really the same as a reduced voltage so actuator will move slower.

If it were me, I would get an actuator with the LVDT built in and work with that signal and change the supply (electric or air) to slow down and stop the actuator.

 

[draynor]

The problem is it's a fairly old linear electrical actuator with a stroke of approx. 50mm. The supply is typical aerospace 28V dc and controls the elevator trim of the aircraft. Currently the pilot activates the actuator via one switch, to extend or retract the actuator until he feels the aircraft is trimmed.

My project aim is to position an LVDT around the actuator casing that will slow down and stop the ram in both directions, hence being able to remove the costly microswitches. The LVDT will also provide a voltage that the Hawk's systems could eventually interpret and convert it into a signal that will give the pilot the actual position of the elevator when trimmed.

I see where you are coming from with the air valve idea, but as i need to demonstrate it i need to build the sensor around the casing.

 

[EdDanzer]

Have considered linear resistors? Penny Giles

http://www.pennyandgiles.com/products/products.asp?strAreaNo=402_10

make some that are inexpensive and fairly rugged. It might require 2, one to decelerate each end of the stroke. A PLC or motion control device would be required with the LVDT to read the position and control the signal. Galil

http://www.galilmc.com

makes stand alone motion control systems that are easy to program and set up.

 

[buzzp]

Ed has a good solution for an external sensor. You might want to look at ultrasonic or laser sensors as well for detecting "distance" and hence, location.
I would be consulting with manufacturers if you have not already for an OEM solution rather than a custom one. I guess this depends on the quantities too.
Good luck.