I have been contracted by a new customer to develope a control system utilizing a X Y table to locate sonic welds on their products. I am quite experienced with PLCs, but have not done this type of work before(since school. and we all know how much you learn there). I am planning on using a Direct Logix 205, 250-1 cpu, and anolog input and output modules. I would just like some help, and examples on the way this would be written. Thank you all for your help!

 

I would use a motion controller because the motion algorithms are done. You can go to X and Y positions using Move Absolute commands where you just specify the X and Y locations, the speeds and accelerations. This is easy if you know where to move.

A DL250 may be cheaper up front but you will waste more much more time re-inventing the wheel and the PLC solution will cost much more in the long run.

You haven't said how you intend to detect the welds or what you intend to do once you know where they are. So more help can't be provided.

I do have an example program for an XY system that assumes the object/weld is moving along on a conveyor. The program assume there is a scanner that detects a object/weld and puts the object/weld information in a queue. The conveyor encoder position and the position across the width of the conveyor is saved in the queue. The XY part of the program gets the next defect or point out of the queue and does a calculation that predicts where the XY can synchronize with the moving object/weld. The XY must move at the conveyor speed and do what ever it needs to do and then hurry back to the chase the next point in the queue.

 

What kind of motors? Servo? Stepper? Low end PLC's do not usually do motion control very well. Assuming you just need point to point positioning, you might consider the SureServo drives and motors with a Modbus connection to the PLC. The drives will control the position loop and the PLC will send the position command data through Modbus at the appropriate time.

Bill Sturm
Abbeytronics LLC