|SERCOS interface Improves Veneer Cutter
*Reprinted courtesy of Industrial Indexing Systems.
Servo controls allow a veneer-slicing machine to cut sheets as thin as 0.005 in. with a +/-0.001-in. tolerance. The five-axis SERCOS interface servo control system that makes this possible is supplied by Industrial Indexing Systems (IIS), Victor, New York.
The slicer, developed by Capital Machine Co., Indianapolis, IN, consists of a flitch table to which a half log (called a flitch) fastens, and a carriage with an attached blade. The carriage incrementally feeds the blade toward the wood when the flitch table is in the up position. The flitch table and half log then move downward, cutting a thin slice of wood from the log which gets carried away on a conveyor mounted above the carriage. The blade retracts at the bottom of the flitch table stroke and increments at the top of the stroke to get ready for the next cycle. At a typical speed of 90 strokes/min, the machine can cut between 20,000 and 30,000 pieces of veneer in a single 8-hr shift.
One factor that makes it difficult to cut a thin sheet with any consistency is the varying size, shape, and density of the logs. They can be up to 18 ft long and weigh as much as 10,000 lb. The machine’s most critical motion is that of the carriage which feeds the blade into the wood. A 15-hp servomotor moves the large weight of the knife carriage. A pressure-bar adjustment compresses the wood as it passes the blade. This makes for a smooth sheet of veneer by eliminating much of the wood’s natural inconsistencies. Two 1.3-hp servomotors adjust the gap between the blade and the pressure bar.
A pair of hydraulic cylinders with embedded magnetostrictive feedback transducers, one at each end of the blade, controls the lead angle of blade attack on the flitch. The hydraulic cylinders, controlled by hydraulic servo valves, can change the blade angle to compensate for blade wear and dulling. Dulling changes the effective angle of attack on the wood, potentially creating rough cuts. The operator adjusts the blade angle via the servo controller in a matter of seconds. The same task once took 1 to 2 min when done manually and was usually done at least a dozen times every 8-hr shift.
Blades are normally changed once per shift, more frequently if they hit embedded objects like fence wire, nails, or bullets. This is typically a 15 to 40-min process.
The machine control system uses the Industrial Indexing Systems Inc. EMERALD controller with the SERCOS interface to control the three electric servos and both hydraulic servos for precise coordinated positioning. The ability to quickly and accurately adjust carriage, pressure bar and lead angle contributes to precisely cut fine-face wood veneer.
Servo controls also let operators adjust sheet thickness with the push of a button. Adjustments in manually controlled machines were made via ratchet feed gears and took about 20 min.