Assembly in Action: Control System Integrator Implements Electrohydraulic Controls
Horizon Technology Group (Wyandotte, MI) recently incorporated electrohydraulic controls into the control system for a bushing press. This saved Horizon hundreds of thousands of dollars in production costs for its customer. It also streamlined the pump manufacturing process to eliminate unneeded fixtures and setup costs.
Horizon’s previous system used standard on and off solenoid valves to control the press cylinder. Limit switches attached to the fixture provided gross information to the controlling programmable logic controller (PLC) to tell it where the cylinder was. The motion was fine-tuned using timing loops run on the PLC without providing precise distance information. The cylinder encountered a hard stop at the maximum distance that the bushing could be inserted. The PLC set the press force to be initially low and then increased it as the bushing was inserted farther into the case. The reaction force was transferred to another cylinder via a sliding plate, where a load cell measured force. Because of static friction and hysteresis, it was difficult to maintain precise control. A data acquisition system recorded the press force and alarmed the operator if the distance was not met or if the required force to accomplish the task was below or above acceptable limits. The window of acceptable force was set to be relatively large to avoid false alarms.