Servo motor with FX3U

[python01 1]

Is it possible to control servo motor with FX3U PLC? I think I would not be able to connect servo controller to this plc so the connection would have to be done directly from PLC to amp and software would have to control the whole setup but I have never done it before so some insight would be greatly appreciated. Any schematics/program sample of how it would be done will be greatly appreciated.

[kaare_t 155]

In the FX3U you have program instructions to control the servo amplifier with pulses (transistor output models). Haven't done it myself, but as long as your amplifier supports pulse inputs you should be good to go!

[python01 1]

So I guess no positioning of any type would be possible, just on/of and direction of movement? I guess position could be calculated based on pulses send but is there any way to read encoder?

[Crossbow 295]

What exactly are you trying to accomplish? There is a motion control module for the FX3U which allows for the connection of the Mitsubishi MR-J3-B servo families. There is also pulse/direction output capabilities if you are using someone else's servo or stepper controller. You can read the pulses from an encoder using a high speed counter input. But you always need to communicate to the servo amplifier or stepper controller, you never directly connect a servo motor without an amplifier.

[JRoss 84]

The FX motion instruction set includes DRVI and DRVA which allow you to send a specific number of pulses at a specific frequency. That's what you would use to control a stepper or servo using pulse train. There is a special data register associated with those commands that keeps track of how many pulses have been sent so that you know where you should be. You can double-check this by using a high-speed counter to track the actual motion. Most drives that I've dealt have a pulse train output that mirrors the actual motion. It's often used to daisy chain to another servo for simple synchronization, but you can feed it back to the PLC just as easily. Keep in mind that you will have to home the servo on startup or power cycle. If you want more control or true synchronization for multiple axes, you will need to use some sort of motion controller, like the module that Crossbow refers to.

[python01 1]

Thanks guys for all the great info, I will look into that.