A vacuum lifter uses the principle of vacuum adsorption, with a vacuum pump or centrifugal blower as the vacuum source to create vacuum at the suction cups, firmly gripping various workpieces. It then transports the workpieces to designated positions via a rotatable mechanical arm or hoist.
In a workshop, a copper foil vacuum lifter failed to rise automatically after placing the copper foil. This seemingly minor issue stumped several technicians. It was repaired by day and night shift mechanics, but the problem persisted. One technician replaced the solenoid valve with little effect; another broke the cap of the cylinder throttle valve while adjusting it, yet no improvement; a third kept tuning the vacuum switch parameters, still to no avail.
Cause Analysis
The copper foil can be picked up and released normally in manual mode, ruling out faults in the solenoid valve, cylinder, and throttle valve. Failure to rise in automatic mode indicates an unmet automatic operation condition.
During manual pick-up and release of copper foil, the output indicator of the vacuum switch switches normally, proving the vacuum switch parameters are correct and the vacuum system functions properly.
The proximity switch for cylinder lifting positioning senses normally, and the position is accurate.
The cylinder only rises after descending to the proper position and detecting that the vacuum has been released (i.e., the copper foil is unloaded). Inspection of the vacuum switch wiring revealed the root cause.
Upon inspecting the wiring, the issue became obvious: exposed copper strands on the vacuum switch wiring caused occasional short-circuiting between the black wire and the negative pole. This kept the signal activated, making the PLC detect that the vacuum release was incomplete, thus preventing upward movement.
After repairing the wiring, the equipment returned to normal operation.Lesson learned: When equipment works fine in manual mode but malfunctions in automatic mode, inspect sensors and their wiring to verify signal integrity.
