Sawmill Head Positioning

[cdisher 0]

I’m not sure where to post my question, since I’ll be using AB products, Ill post it here. Last year I wrote a program to control a sawmill and associated conveyors. To position the saw, it is raised and a step block is positioned and the saw lowered onto the correct step on the block. They are changing the method they use the saw and want to be able to position the saw anywhere between 0 inches to 24 inches above the log conveyor. What type on device should I be looking at to determine the position? The present PLC is a Micrologix 1500. Is this processor capable of controlling the position of the saw? My experience is in punch presses and I’m not familiar with this type of control. Your suggestions would be appreciated. Charlie

[Guest Guest_Peter Nachtwey]

Normally the position feed back is done by a Temposonic or Balluff rod in a hydraulic or pneumatic cylinder. If servo motors are used the one nomally uses a quadrature encoder. The MicroLogix may be able to control the motion is it is slow and doesn't need to be that accurate. If this position needs to change from board to board and is used to cut dimensioned lumber then I would recommend you get a motion controller with the correct feedback interface.

[Gerry 13]

Slightly off-topic - I worked in a sawmill some decades ago. The highest paid guy there was the head sawyer and what he did was signal setworks movements to a guy riding the log carriage (I said decades ago, right?). This guy could make or break the mill, based on his decisions on how to cut the logs. The point is, the value of the head-rig setworks control to the sawmill is considerable. You should not feel compelled to offer the cheapest solution that you can think of. Efficient and productive operation of the head-rig is the life-blood of any saw mill. One log is probably worth more than the ML1500!

[Guest Gerry, is right about value]

Now the logs are scanned using lasers and line scan cameras. A computer optimizes the cuts to provide the most value. This infomation is relayed to the PLC that does the sequencing. At the proper time the PLC tells a hydraulic motion controller to move to the proper position. These positions are specified to .001" inches at the highest speed possible to increase production. Now the most valuable man should be the person that maintains this equipment in optimum working condition. Common hydraulic controllers used in saw mills. 1771QB fits in the PLC/5 rack 1746QS fits in a SLC5/04-SLC5/05 rack. Simple, straight forward. Great diagnostics. RMC100 communicates to just about any PLC using Etherent, Profibus DP, Modbus Plus, serial or digital I/O. May not need a PLC for simple applications. Great diagnostics. 1756HYD02 Coming soon to ControLogix. Actually some are beta testing this now. Works like a M02AE. All of these use the Temposonic or Balluff rods for position feedback. Find info on these at: Allen Bradey Delta Computer Systems, Inc. Balluff Temposonic There are many experts out there that can install these with ease.

[cdisher 0]

Many thanks to each one who replied! I have found control packages on the net that are designed to control the saw head. I will research them and make a proposal to the owner if I feel it is worth the effort. The entire sawmill was (designed?) by the owner and his brother and neither has much metal fabricating experience. The hydraulics are the pits, leak city. Too many corners were cut during manufacture and it may never be right. Again, Thanks for your help.