Homegrown Setworks

[ronwood]

Shannon,

On my previous post I mentioned about the chain on the head. What I found was that if the chain is not tension properly the setworks would not be as repeatable. This was based on observing the pointer each time I stopped in increments of say 1 inch. Even thought it was not a lot it the accumulated effect could be a issue.  The chain may be a problem.

Ron

[rs1626]

Sounds interesting my mill is homebuilt has .2 pitch leadscrews to move up and down instead of a chain do you think this would be a problem?   let me know when you get a price ironed out   and i think i can help you with alum. wheels

[Chico]

Does your set up have a linear positioner so the head knows where it's at at any time or do you just use as a setworks using preset heights

[shaworth]

60 amp at 12V sounds correct.

There are also table saw digital gages that can measure position up to multiple feet.  The gage is mounted on a aluminum bar and the detector can slide up and down the bar.

They use a positional coded tape so the reader know distant and position.  There is a problem with vibration that makes reading position difficult.

This is why I asked!  My gut instinct was way off on this one.

[shaworth]

Shannon,

On my previous post I mentioned about the chain on the head. What I found was that if the chain is not tension properly the setworks would not be as repeatable. This was based on observing the pointer each time I stopped in increments of say 1 inch. Even thought it was not a lot it the accumulated effect could be a issue.  The chain may be a problem.

Ron

When I'm at my brother's place (where the sawmill is) I'll take a good long look at the chain tension arrangement.  I hate to admit it but this something that I've pretty much ignored up to this time.  Thanks for the tip!

[sgschwend]

I like these guys, on this page there are multiple encoder options:

http://www.sparkfun.com/commerce/advanced_search_result.php?keywords=encoder&x=0&y=0&search_section=products

[shaworth]

Does your set up have a linear positioner so the head knows where it's at at any time or do you just use as a setworks using preset heights

Currently I am tracking the position relative to the last cut, with an accuracy of 1/32".  Nothing is pre-determined as far as the set points are concerned.  You use the joystick and buttons to specify the distance you want to move the sawhead, and then move it.  The distance can anything between 1/4" to the available amount of travel.

Now, I would REALLY like to know the absolute position off of the deck.  And I'm looking at techniques to always have that as a precise measurement.  Obviously that would be the best.

However for now the position is relative to the current blade position. 

[shaworth]

Sounds interesting my mill is homebuilt has .2 pitch leadscrews to move up and down instead of a chain do you think this would be a problem?   let me know when you get a price ironed out   and i think i can help you with alum. wheels

The chains vs the leadscrews is not going to matter.  However I need to see how the drive-chain for the saw-head works to determine how and if I can measure the position of the sawhead. 

Another reason why I'm keeping my eye out for a linear sensor that can be adapted.  A direct measurement of distance will always be better than an inferred measure of distance.

[shaworth]

I like these guys, on this page there are multiple encoder options:

http://www.sparkfun.com/commerce/advanced_search_result.php?keywords=encoder&x=0&y=0&search_section=products

SparkFun rocks, I actually have an order of stuff arriving from them the day after tomorrow.  Their enclosed encoding wheel is interesting, however I'm concerned about long-term durability.  If the hall effect sensor doesn't pan out I will be giving that little package a lot more attention.

[sgschwend]

For a linear digital length reader I used these guys (digi-fence).  Be sure and go with the digital encoded version, you will need to call them to get access to that model.  The table saw version measures just fine but it does not have a position value.  That means if the sawmill's vibration causes a miss read the encoded version will still provide the correct answer, the table saw version will have an error.

http://www.digi-kit.com/digiscale.htm


I used mine for about a year, and decided that my manual sight scale was certainly accurate, so this digital scale was redundant, and it was another thing to take care off.  It was very handy for the jobs that you wanted to drop the saw an exactly amount.

[sgschwend]

Actually I was thinking about the wheel encoder.  The kit would provide the wheel and the board.  Attach the wheel to the sprocket and a sheet metal bracket to hold the board side.  Or let the wheel rub on the beam and assume there is no slip.

[Magicman]

However you do it, remember sawdust.  It can/will get into any open space and has a way of covering everything.  Be sure that a layer of sawdust will not affect any measuring device.

[shaworth]

However you do it, remember sawdust.  It can/will get into any open space and has a way of covering everything.  Be sure that a layer of sawdust will not affect any measuring device.

Very good point, sawdust is exactly why I decided to start with the magnetic encoding wheel.

[pineywoods]

BTW Shannon a belated big welcome to the forestry forum. I completely agree with your take on the advantages of using a dedicated micro processor instead of adapting a laptop. You see, I have this old lunchbucket that has a monochrome plasma display, and my mill already has all the relays and drivers in the form of the remote control. A hall effect pickup on the head drive pulley to trigger the data in pin on the serial port..Now lets see, 8 output pins on the parallel port, 1 for head up, and another for head down. Two more for head forward and backward, another to activate the clutch to start the band moving......Might be simpler to program it in machine code, but I've done bit of that. You can probably see where all this is headed, and NAW I'll probably never do it.  ;D  Seriously, thanks for posting the links, I already checked them out. It's been decades since I did any of this sort of tinkering and I'm impressed. I think I may be purchasing a butterfly....

[shaworth]

BTW Shannon a belated big welcome to the forestry forum. I completely agree with your take on the advantages of using a dedicated micro processor instead of adapting a laptop. You see, I have this old lunchbucket that has a monochrome plasma display, and my mill already has all the relays and drivers in the form of the remote control. A hall effect pickup on the head drive pulley to trigger the data in pin on the serial port..Now lets see, 8 output pins on the parallel port, 1 for head up, and another for head down. Two more for head forward and backward, another to activate the clutch to start the band moving......Might be simpler to program it in machine code, but I've done bit of that. You can probably see where all this is headed, and NAW I'll probably never do it.  ;D  Seriously, thanks for posting the links, I already checked them out. It's been decades since I did any of this sort of tinkering and I'm impressed. I think I may be purchasing a butterfly....

Thanks for the welcome.  Before you make up your mind about the butterfly, you might seriously consider this:  http://www.sparkfun.com/commerce/product_info.php?products_id=766, it obviously has the low-power relays in hand, sadly only 4.  Since it has a RS232 port you can use your laptop as a display / input.  To program it you will need a programmer, I'm using this one: http://www.sparkfun.com/commerce/product_info.php?products_id=13  I've got one and it is a blast to interface with (the screw terminals means no soldering) and is a seriously powerful platform.  It uses the same family of CPU as the butterfly, so everything I've said earlier about the tool chain applies to this board as well.

Happy hacking,

Shannon

[Chico]

Have you considered using a potentiometer in tandem with your electronics to tell the micro processor where it's at in space I don't know if it'd help I use a cam system currently as a setworks but I'm working on a simple electronic system that everyone can afford Be sure and get your work patented and copyrighted I lost a mint  on one because I was naive enough to believe you could trust folks jmo

[shaworth]

Have you considered using a potentiometer in tandem with your electronics to tell the micro processor where it's at in space I don't know if it'd help I use a cam system currently as a setworks but I'm working on a simple electronic system that everyone can afford Be sure and get your work patented and copyrighted I lost a mint  on one because I was naive enough to believe you could trust folks jmo

I'm afraid a pot isn't suitable for my micro-controller, otherwise it would be an ideal solution.  Thanks for the advice.

Shannon

[rs1626]

would scales like these guys sell work? they take them and turn them into dro
http://www.hobbymetrix.com

[shaworth]

would scales like these guys sell work? they take them and turn them into dro
http://www.hobbymetrix.com

Nice catch!  These are very interesting, especially since they have a data port.  Although I have concerns about long term durability and their ability to survive the elements.  I see more research in my immediate future.

Thanks for the lead

[shaworth]

I'm curious, has anyone used an industrial servo to drive their saw-head?

Thanks,

Shannon

[sgschwend]

I don't think so, there are two driven methods that I know of:  DC motor and hydraulic motor.

Did you look at the wheel encoder kit?  The wheel could be mounted to a rotating part, the encoder could be held with a the bracket.

[shaworth]

I don't think so, there are two driven methods that I know of:  DC motor and hydraulic motor.

Did you look at the wheel encoder kit?  The wheel could be mounted to a rotating part, the encoder could be held with a the bracket.

I did look at the wheel encoder kit very early in the process with pretty much the same thoughts concerning how to mount it.  The wheels didn't make the short list when I decided to eliminate all non-sealed optical sensors all together.  All it would take is one insect or chunk of sawdust to interferer with the operation of an non-sealed optical sensor.

The hall effect sensor that I am using is proving to be very reliable and is immune to things like saw dust.  I currently have six magnets on the pulley wheel, which give me about 1/70th of an inch resolution.  If I bump the number of sensors up to 12, 18 or even 24 I can achieve very precise measurements.  In theory as high as 1/280th of an inch resolution. 

I ordered a logic analyzer and frequency generator which should arrive today.  With the frequency generator I will be able to test the limits of the software.  By the end of the week I will know exactly how many sensor events a second that I can service before the system becomes overwhelmed.  I suspect the answer will be in the tens of thousands - well beyond the requirements of this system.

With that answer in hand I can then fashion an encoder wheel with a greater number of magnets and bump the precision of the system up considerably.

As it stands I can position the saw-head relative to the current position with significant precision (1/70th") with hall effect sensors.

However, even if I am able to detect the position of the saw head to within say 1/140th of an inch I will not be able to implement a desired feature.   My brother (my customer) wants to be able to specify the position of the saw head relative to the current cut or the deck of the saw bed.  To that end I am searching for a low cost linear distance sensor that does not use optics, or is completely sealed.  The other important requirement is that it should have a accuracy of 1/32 of an inch or better at a distance of 5 feet or more. 

I've examined ultrasound, encoding strips and a number of other technologies.  The current gold standard is a sealed optical encoder wheel attached to a chain.  Although there are quite a few issues that arise with such a system as well.  For instance the distance to the deck is still inferred and the position will need to be recalibrate each time the key is switched to the "off" position.

Mostly I am looking ahead to version 2.0.  The current version is working well and is going to allow my brother to achieve uniform results without having to "jog" the saw head up and down manually.

The not-so-small issue of my anniversary this weekend was brought to my attention.  So rather than travel to my brother's place and mount the newest version on my brother's saw I'm going to spend some quality time with the wife.  I'm REALLY glad that she mentioned the anniversary before I mentioned my plans to visit with my brother for the entire weekend.  Dodged that bullet.

Shannon


Version 2.0 wish-list:  The ability to precisely know how far off of the deck the saw head is.  That combined with the ability to set cut points relative to the saw deck. 

[Magicman]

I'm REALLY glad that she mentioned the anniversary before I mentioned my plans to visit with my brother for the entire weekend.  Dodged that bullet.

Sometimes, being lucky is better than being good.... ....

[mburrow]

I have been reading this with some interest as I have worked with a few of the atmel mcu's mainly the old 90s2313 and the tiny2313 also the atmega128.

the simplest way to get both the movement and position is by using a multiple turn pot as it will give 2 readings from 1 unit. although this may not work with your present setup it CAN be done

[shaworth]

I have been reading this with some interest as I have worked with a few of the atmel mcu's mainly the old 90s2313 and the tiny2313 also the atmega128.

the simplest way to get both the movement and position is by using a multiple turn pot as it will give 2 readings from 1 unit. although this may not work with your present setup it CAN be done

I over simplified things quite a bit when discussing the pot.  It can be done, however I don't relish keeping track of revolutions and the other housekeeping involved in implementing a pot.  I should have said I'm too lazy to do it with a pot.   

Now... a multiple turn pot - this is news to me.  Looks like more research in my future.  And honestly if this works like I imagine it works....  it might be a winner.  Ahh, the pitfalls of being a software guy.

The tiny2313 is the first AVR that I touched, and it got me seriously hooked on these little gems.

Thanks for the tip!

Shannon