Encoders

[Guest Ohmboy]

Hi to all, Been programming AB PLC's for a while, this is a SLC5/04 that I am going to have to drive a servo motor that has a encoder attached. What are the basics for sensing where the shaft that it's driving at, positon etc. We are moving a base at a pretty slow speed, not an issue. Homes when retracted by a limits switch. TIA

[Guest jlada]

Hi Ohmboy; I did this recently with an A-B 1762-28BXB (SLC 1500) and a couple of 1398-DDM servo drives. The 1500 generates pulse trains (including ramps) to the drives which take care of closing the loop with their own motor encoders. You could consider something similar if you can generate a pulse train from the 5/04 rack, but I wouldn't try closing the loop on a 5/04 without using a dedicated 1746-HSRV servo module or something similar... Jeff

[Keith Menges 0]

Hi Ohmboy- You might look into a 1746-HSCE2, which is a two channel quadrature encoder input card. The downfall to this card is it can only accept higher level signals (> 12VDC). The encoder on your servo may not be able to drive this. Either way you may not want to run this encoder into the counter module as the encoder is probably used for motor commutation by the drive. With any luck the drive will put out a buffered encoder signal you can use. You can do VERY low bandwidth position loop closure with limited accuracy in the plc. You will need to run the drive in velocity mode, generate your own velocity profile for the drive to follow and correct slowly and gently. This seems to contradict the use of a servo unless you needed to torque in a small package. Typically servos are used in high bandwidth applications and that calls for a high speed position controller, which the plc is not. I hope this helps. Keith