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Industry: Lumber
Project: Sawmill Setworks

Overview: The OEM customer required an absolute position control system that can position logs on a large carriage table by controlling on/off AC hydraulic valves that operate a hydraulic motor.  The position of the log determines the thickness of wood that will be sliced off of the log as it passes through a stationary saw blade from end to end.  The board thickness tolerance is 1/64th of an inch.  The control system must be simple for lumber industry workers to setup and operate. 
System Objectives
  • Provide absolute position system (no homing sequence)
  • Position log within plus or minus 1/64th of an inch
  • Make system easy to setup and operate for non-technical personnel
  • Provide at least 8 thickness presets that are easily selected during operation
  • Provide at least 6 predefined cut sequences that users can program
 Design Challenges
  • Maintain 1/64th inch tolerance using standard on/off AC valves
  • Make system easy to setup, operate, and maintain
  • Provide an inexpensive MMI that is intuitive to operators
System Solutions
  • Absolute linear transducer with 4-20 mA output used to monitor log position
  • Omron PLC with high resolution analog input card controls AC valves
  • Maple 4 line 20 character LCD MMI inputs and displays machine information
  • High and low speed logic employed to move log quickly until it gets close to desired position before slowing down and then stopping accurately
  • Logic in PLC program monitors positioning accuracy and compensates for changes in machine performance (ex: stiff when cold, looser as it warms up)
 Customer Benefits
  • Position system that is easy to setup, operate and maintain (all setup information entered in engineering units – kerf automatically factored in to cut positions)
  • Accurate board thickness produced by relatively inexpensive and simple positioning system without compromising move times
  • 6 customer predefined cut sequences available to minimize waste
  • OEM can program PLC from handheld device which downloads program stored in non-volatile memory chip (computer and software not required for PLC programming)

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