Flowchart to ladder follow-up and good free e-book

Lloyd had caused me to remember a Trilogi PLC that I had bought many years ago for some project that got shelved and had forgotten I had.
So, with all the wonderful advice in my last thread, I found the PLC and started reading.
I found a nice, free beginner's book in ladder. http://www.tri-plc.com/reqplcbook.htm
I've passed my first stumbling block and I can "see" it in my head once I understood some misconception I had. PLCs are WAY cool! I imagine all kinds of possibilities. The only PLC machine we have now was farmed out to a "guy" that one of the mechanics knew from a previous job. This guy did a great job and the machine works just fine but I haven't even looked at the program yet.
Thanks for all the ideas and support guys!
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"Tom Gardner" wrote in message

They sure beat the heck out of wiring and re-wiring a bunch of relays! Sometimes I get something running quick and dirty, then clean it up and refine later. I have found hind sight is generally better than fore sight so after the machine has been running a while I see if there are ways to make it better.
Flow charts are more like a series of steps while the PLC is more like everything is running in parallel. Once you get your flow chart steps mapped out to PLC conditions you can make things work like your flow chart. Starting out I had some problems with things executing when I didn't want them to, like performing a calculation, one shots or edge detection type instructions (depends what they are called on your PLC) solve that problem, they can be used to cause something to happen once per cycle.
Example if step3 then increment some number.
this will cause the "some number" to increment every scan while the program is on step 3. To solve this you would do something like: If step3 and one-shot then increment some number.
The one-shot will be true only one scan cycle when "step3" becomes true causing "some number" to increment one time per "step3".
When I was doing PLC programming for customers I had to use the PLC they wanted. I learned to program using mostly a few instructions that were common to most PLC's, it kept me and the customers technicians from having to learn their PLC's unique advanced instructions.
RogerN
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On 5/6/2012 7:43 AM, RogerN wrote:

I understand just enough to start to "see" it in my head. This project is perfect for learning, it's just replacing 8 mechanical relays and 8 switches. No counters, timers or math to do. I plan to build a trainer and explore more uses and get all my staff interested.
The most complex machine I want to control is for making twisted knot brushes. I envision a machine that will be programmed for the many, many variables that are a total BITCH on the mechanical adjustment/relay systems I use now. I have four of these machines that are hydraulic powered, A new machine will be servos and will make any size, any twist, any other variation all with a change of programs and a change of quick change of fixtures.
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"Tom Gardner" wrote in message
<snip>

Like electric servos with ball screws/linear actuators? At the place I used to work we had a bender that was programmable. It used a hydraulic cylinder with LDT position feedback and either a proportional valve or servo valve. I designed a servo hydraulic press for a GM line that used an Allen Bradley 1771-QB linear positioning module, MTS TempoSonic linear displacement transducer, and Atchley servo valves. This was high $ stuff but it can be done for less money. The press for the GM line pressed control arm bushings in the control arms and measured the position of the parts while being pressed, the idea was to get more consistent front end alignment.
For the Allen Bradley card, once everything else was set up, you just had to set a position and tell it to move, the card controlled the valve and read the position to move the hydraulic cylinder to the set point. You should be able to set up something to control position with an analog output and scale the output to inches, mm's, or whatever units you want. It's do-able with electric servo motors or hydraulics, whatever works best for your application.
For your application where you change setups, you can use different sets of data and select the one you want to run. For example if you have 100 variables to define a "recipe" for a certain brush type, then just select the "recipe" for the type of brush you want to run. If everything is servo adjustable your changeovers can become simplified.
RogerN
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On 5/6/2012 5:41 PM, RogerN wrote:

I have the basic machine designed, all electric except for one air cylinder. One servo twists, another pulls the twister back and a stepper indexes the disk. The disk holder has two stations so the operator is loading and unloading one station while the other station is being twisted. The whole machine will be about 3 cubic feet. My current machines are 4'x4'x8'. Ain't technology wonderful?
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I ran across the software in the link below. For Allen Bradley's MicroLogix 1000 and 1100 there is free software, free linx lite for online programming, free emulation software. So anyone can write a program, get it working in the emulator, get an ebay deal on a MicroLogix, load program and go.
http://www.ab.com/linked/programmablecontrol/plc/micrologix/downloads.html
RogerN
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