Jcor (Customer) asked a question.
Sensor setup to measure length, width and thickness of wood.
Looking for a sensor setup that would measure length, width and thickness of wood coming out a planer. Max= 8" thick x 14" wide x 32 ft long, min= 3/4" x 3 1/2" x 96". Max speed is 350 ft per min. accuracy is low, within .125.
Dusty enviroment with vibration. Wood exits onto a roller conveyor. There are some very exspensive solutions out there, just want something simple if possible. Thickness and width are not the main issue, that can be done with lasers.
Can you set up an encoder wheel to roll along the wood to measure the length? To get an accuracy of 0.125" you'll need to start/stop counting pulses withing 0.0017s - which is pretty fast, but not unreasonable. The hardest part will be mounting the encoder in a location that it starts rolling immediately when the wood gets to it. You'll have to figure out how to prevent slip which is really tricky when the encoder is ramping up to match the speed of the wood. You may have to measure the conveyor speed or something that keeps the encoder moving at the same speed as the wood. Then put a decent thru-beam sensor to pick up the leading/trailing edge of the wood to enable the counter. I'm partial to a CLICK Plus C2-01CPU with a C2-14D1 I/O. The high speed counter function with handle the start signal and count encoder pulses. If you have a 2" measuring wheel, a 500ppr encoder will be plenty accurate, but you'll need to work out the actual mechanics.
Anything making contact would probably get destroyed rather quickly as we run so many different sizes. Was trying to stay away from contact.
How about an encoder driven by the conveyor, and have a photoeye sensing presence of plank and only count pulses when photoeye is blocked? Of course, if the plank slips (not positively driven) on conveyor then length measurement will be inaccurate.
I was thinking a similar thing as well. Along the lines of knowing the conveyor speed (350ft/min) you could simply count the time the photo sensor was blocked then divide by the speed to calculate a rough length, since the measurement needs to only be within 1/8 it should be accurate enough especially if using a BRX PLC. You can set up the start of a timer on the photo eye using an interrupt to make it highly accurate, and if the PLC isnt doing anything but monitor the photo eye, run a timer, calculate math for length, and store in an array, then the PLC should have scan time under a quarter millisecond from what I remember.
I think the problem with any photo eye though is the dust that was mentioned. Might take serious maintenance of continually wiping it off every 15-30 minutes to ensure it doesnt false read. Im sure there already is a somewhat expensive dust collection system in place, but I would also bet it is still pretty dusty coming off the planar.
I build equipment for a portable cooler maker and their environment is dirty as well. They have me use the Keyence LR-TB2000 for that reason: specs HERE
It's not inexpensive but works well as the laser burns through dust easily. In a separate application where I had an issue with paper dust, I had the exhaust of a nearby pneumatic valve that operated for every piece that passed, blow that air onto the sensor to prevent dust buildup.
That's a tough one. Non-contact, in the direction of motion, while at speed, eliminates any standard solution. How is the wood pushed through the planer? Is there some type of pinch roller holding the wood that you could track? I'd be tempted to look at a current sensor to identify when the planar is cutting and measure the feed roller. I don't know if the current sensor would be fast enough. I'd need to see a diagram of the process for any better ideas.
The outfeed conveyor is on a VFD, the heavier the board the faster the conveyor runs.
The planer is also on a VFD as is the infeed.
This company has a solution, very expensive, Sick also has a sensor
Acuity Laser Triangulation Method One-Sheet Overview.pdf