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Controlling a Linear Actuator with a PLC

01/31/2018 12:33 PM

Hey Guys, I want to control a 24V DC actuator with an OMRON PLC, but I am struggling with position control. The actuator can be controlled with a potentiometer but i need to control it via the PLC which will communicate with an RFID (Radio-frequency identification) system to adjust the height of the linear actuator to a specific distance. Any ideas? Any help would be greatly appreciated

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#1

Re: Controlling a Linear Actuator with a PLC

01/31/2018 12:58 PM

The idea requires a datasheet of the linear actuator.

While you provide it, you can get an analog output module for the PLC because you will need it.

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#2

Re: Controlling a Linear Actuator with a PLC

01/31/2018 4:00 PM

I haven't had to do fine position control with a linear actuator you require (which is fairly fine based on your application you previously mentioned). Simple solutions like limit switches or time based logic control won't really work.

Ideally the linear actuator supplier should have an actuator add on or special actuator series with a built in sensor and output signal which you can monitor for fine position sensing which is what you really need.

Have you checked the actuator supplier website for something like this?

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#3

Re: Controlling a Linear Actuator with a PLC

01/31/2018 6:48 PM

This looks like a continuation of the earlier thread.

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#4

Re: Controlling a Linear Actuator with a PLC

02/01/2018 4:23 AM

Use a compare function to set a unique flag when the RFID chip being read is matched to a list preset in the PLC. Use the flag to 'goto' a look-up register that contains a "run time". When a new chip is read the actuator resets to a known position, i.e. limit switch, and then drives for the required "run time" to the target position. More sophisticated RFID chips can hold the run time information but the standard cheap chips only hold their own identity data.

Trying to go directly from one target position to to the next target position without homing to a "known fixed point" requires either live position feedback from the actuator (expensive) or the assumption that you will not get tolerance build-up (unreliable). Sell (convince the users) the extra few seconds it takes to home and then drive to the target gives a positive feedback that the system has operated. i.e you have to do it so why not promote it as an enhancing feature. If two target positions are only a couple of mm it is easy to miss that the system has reset to the correct height.

When a new user enters the system switch to a "key operated" teach mode. Use normally disabled (unless you want to keep the buttons active for casual users) up/down buttons to drive to the new target height which adds to or subtracts from to a new run time. When the user is happy with the position turning off the teach key records both the new RFID tag and the accumulated run time into the database.

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