Hello,
I have an application in which 2 robots operate (no touch) on an object moving on the conveyor. The robots are 7-axis ones and their bases move along the object. They must continue their work even when the conveyor is stopped or accelerating/decelerating.
My initial idea is to have A-B ControlLogix5555 system with DeviceNet scanner in the chassis. The robot manufacturer provides DeviceNet interface. The encoder is multi-turn, absolute, with DeviceNet interface, too. The idea is to read the conveyor position using the encoder, send it to the PLC, PLC sends the current position to the robots, so they increment their position accordingly.
I am afraid the overall system speed is going to be too slow and the robots are not going to be enable to "catch up" with the object. Let's see: The conveyor max. speed is approx. 30ft/min = 6in/sec. The PLC reads the encoder position, performs some basic math operations, sends it to the robots, they read it and reposition their bases. Let's assume, that the PLC's scan time is 20ms and all the read/calculate/write operations (including the scan time) will take up to
100ms. This means, the resolution achieved is 0.6in/sec. It is below my expectations. It is going to affect the quality of the work performed to a great extent.Another solution would be to use a dedicated small, very fast controller with DNet card, to handle the robots and the encoder only and to pass other data to and from main PLC via Ethernet/IP.
One more solution, suggested by the robot manufacturer, is to buy from them two encoder cards for the robots and an encoder with its signal splitter. Unfortunately, this solution presents a huge cost impact to the project.
General note: DeviceNet speed can be set to 500kbps. The distance is not an issue here.
Has anyone had experience with similar cases? Any ideas, examples, links, brand names, comments are welcome.
Thank you, Gregory Pal