Question

Keldog · Jun 19, 2006

I got a request at the sawmill i maintain. They have a bull edger that when a log is detected it brings the blades into 4" but they would like it to bring them to 3.5".

It moves a value into a Bit telling the piston how far to move the blades in.

1 = 3"
2 = 4"
4 = 5"
8 = 6"

Inorder to move it to 3.5, should i make a value of say 3 and divide it by 2 to get 1.5 Would that work?? Or is there a way to make a value of 3.5.

I know this probably sounds vague and i apologize it's hard to explain.

Jimmie_Ohio · Jun 19, 2006

The current situation looks like a choice of 4 options. The 3.5" option is a new choice so that requires a whole new set of rules.

I'm sure we would need to see your code to see what they previously did with the four past options. Then, there would most likely need to be some addditional code required to accommodate the fifth (3.5") choice.

Keldog · Jun 19, 2006

Yeah that's what i figured.

504bloke · Jun 19, 2006

I agree with Jimmy

Keldog · Jun 19, 2006

I kinda missed a part of the explanation. They only want the blades to move into 3.5" when it sees a 4" chamfer coming in. So it's not putting in a new setting, they won't be able to manually set it to 3.5" like they can set the rest they just want it to automatticly set to 3.5 when it senses a 4" log. Sorry about that

Jimmie_Ohio · Jun 19, 2006

Then do the following:

1) Change any reference to 4" in the program or HMI to refer to 3.5".

2) Alter the PLC program to do whatever it takes to make the 3.5" operation function properly instead of the settings for 4". This may include positional commands to a drive or what have you.

This should be all you need to do...

bernie_carlton · Jun 19, 2006

The #2 part of Jimmie_Ohio's post is the critical part. HOW are the blades being positioned? What is the reference? The answers to that are the operative part of the question. They will determine how much has to be changed in the physical process and how much in the PLC program. The program may be as simple as, 'Go to first limit switch, go to second limit switch etc.' It may be a complex series of commands to a servo positioner.

Keldog · Jun 19, 2006

there is a servo that controlles the blades i think

bernie_carlton · Jun 19, 2006

Your "I think" speaks volumes. You will have to get very familiar on the PLC control of the servo. Hopefully this isn't one of the "make it this way as it wil NEVER EVER EVER change" specifications. At best the programmer will have made a distance change easy with detailed comments. (Any bets?) At worst you have a great opportunity to learn the intimate insides of this system.

tomalbright · Jun 19, 2006

It's "Silly question" time. (I play that one a lot...)

How is your end device operated? Do the bits set a discrete position, or analog equivalent?

What happens if you set bits 1 and 2 simultaneously?

Silly, silly....

...but sometimes you get serious answers. At least you will understand the process more.

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