Piston Ringer Assembly: Rewriting the Code
| By: Shahrokh Yousefi, Controls Engineer at Patti Engineering
One of Patti Engineering’s customers in the heavy equipment manufacturing industry came to us with a project to upgrade the controls program for a piston ringer assembly. The fully-automated subsystem contains a 6-axis robot and 6 rotary tables which install 3 piston rings on each piston set. The assembly process was as follows:
- Pallet arrives at the robot pick-up station.
- The piston set is pushed off the pallet and picked up by the robot.
- The data is transferred to the Ringer PLC and the appropriate ring is selected.
- The robot moves the piston set to the correct rotary table and the ringing process begins.
- Concurrently with #4, the unloaded pallet leaves the pick-up station and moves towards the drop-off station.
- When the piston set assembly is complete, the robot moves it to the pallet waiting at the drop-off station.
- The piston set is pushed onto the pallet.
- The robot is ready to pick up the next piston set from the pick-up position.
The customer requested some improvements on the automation system. The decision was made to address the following known issues:
- Absence of proper recovery if the assembly cycle was unintentionally interrupted.
- All six rotary tables were not coded for the same ringing assembly process.
- The ring tower data on the rotary tables was not tracked properly.
- The recipe data was not transferred directly from the upper layer production control system, rather it was transferred indirectly from another PLC.
The existing control system code was not easy to trace or debug, so it was more efficient to rewrite the entire logic in order to address the known issues and to optimize the process and machine motions. The recipe transactions were handled by the upper layer production system PLC rather than transferring them indirectly through the adjunct PLC.
After implementing the project, the cycle time for a single piston pallet was 55 seconds, down from 70 seconds, when the robot runs at 100% speed. The customer was very happy with the implementation of the new controls program for the piston ringer assembly. The operations team reported that the system is running faster and with fewer problems than before the upgrade. The new recovery feature makes it easier and faster for the operator to get the machine back online after a mechanical jam. The new controls program was written with the ladder logic sequence approach, which makes troubleshooting and debugging quick and painless.