Re: Sometimes a PLC is the right solution
Posted: Sun Dec 30, 2018 12:04 am
Lance,
Thanks for your interest in using a PLC. First of all, a PLC is probably overkill for most users, not because it wouldn't add possibilities, but because the Acorn does a great job on its own. The ClearPath/DMM issue was what caused me to look for other possibilities. Normally, I just hack together something on an Arduino or Raspberry Pi, and then have some proto boards made. Even easier is to use a few transistors to invert signals, but even that requires having a circuit board made (or keeping the cabinet door closed so that nobody ever sees my rat's nest of wires).
One of my sons is an electrical engineer specializing in process control for oil refineries. His job takes him all over the United States. In that field, PLCs are used to facilitate implimentation of changes and improvements at reasonable cost. He just happened to send me some texts containing photos of PLCs that he uses. That was enough to have the proverbial lightbulb moment. A few minutes later, late in the day, just before AutomationDirect closed for their Christmas break, I ordered a CLICK PLC with a power supply and two 16-circuit I/O modules. I figured with their 30-day money back guarantee, that it was worth taking a chance. I'm sure that almost anyother PLC could do the job. The CLICK (ethernet model) with the extra I/O is overkill for this particular job.
As the screen shots show, it only takes 27 rungs to capture the data and then to act on it (less than 1 millisecond PLC scan time). I grab the state of the input signals, store them in memory and then combine a little logic to get the desired result. In this first test, I use the Acorn's NoFault output on Output 8 to signal when the Acorn is ready. Using that signal, I have the PLC issue Enable signals to the ClearPath motors to keep them energized (otherwise, I would have to use a brake or counterbalance to hold vertical position).
Normally, I use self-latching contactors for motor power supplies; however, it seems that both Teknic and DMM require that power to the servos be cycled if a fault occurs (to clear the fault), so the PLC controls sequencing of the power supplies. Because I have extra PLC I/O available, I'll probably use three-way switchs (Auto, OFF, ON) for the motor power supplies and because the PLC can easily perform latching signals, I won't have to hard-wire the latching circuitry.
Right now my test bench is a maze of wires. I tend to make things overly complex and then to simplify when each part of the control works as expected. Someday I'll post photos of a "finished" controller. One thing that I like to do is to separate all signals, i.e., the state of each servo's fault signal is captured and stored, then a signal is sent to the Acorn. The same applies to the E-Stop circuit. Each condition that should cause an emergency stop is sampled and stored and then a single signal is sent to the Acorn. With a PLC, I can sequence Power Supply power-up to keep surges to a minimum. I can also delay the DriveOK signal to the Acorn until all circuits have had time to stabilize. Currently, I use 5 of the 500 available timers in the CLICK to keep the start-up process orderly.
After watching Marty's videos, Gary's videos, Franco's videos and CNCKeith's videos (many of them many times), I'm still blown away with what the Acorn can do. Now that I know basically what IT can do, I needed an easy way to mix and match any component that I wanted to use to get the job done. In my case, I prefer the ClearPath servos, but I need signals that the DMM servos have. I needed a way to easily cycle power to any or all of the drives without over-cycling power supplies. I needed a way to keep the servos enabled. Add to that things that I would like to do and a PLC for my purposes became viable and almost a necessity.
p.s. It's good to know of that South Jordan is on your map too.
Thanks for your interest in using a PLC. First of all, a PLC is probably overkill for most users, not because it wouldn't add possibilities, but because the Acorn does a great job on its own. The ClearPath/DMM issue was what caused me to look for other possibilities. Normally, I just hack together something on an Arduino or Raspberry Pi, and then have some proto boards made. Even easier is to use a few transistors to invert signals, but even that requires having a circuit board made (or keeping the cabinet door closed so that nobody ever sees my rat's nest of wires).
One of my sons is an electrical engineer specializing in process control for oil refineries. His job takes him all over the United States. In that field, PLCs are used to facilitate implimentation of changes and improvements at reasonable cost. He just happened to send me some texts containing photos of PLCs that he uses. That was enough to have the proverbial lightbulb moment. A few minutes later, late in the day, just before AutomationDirect closed for their Christmas break, I ordered a CLICK PLC with a power supply and two 16-circuit I/O modules. I figured with their 30-day money back guarantee, that it was worth taking a chance. I'm sure that almost anyother PLC could do the job. The CLICK (ethernet model) with the extra I/O is overkill for this particular job.
As the screen shots show, it only takes 27 rungs to capture the data and then to act on it (less than 1 millisecond PLC scan time). I grab the state of the input signals, store them in memory and then combine a little logic to get the desired result. In this first test, I use the Acorn's NoFault output on Output 8 to signal when the Acorn is ready. Using that signal, I have the PLC issue Enable signals to the ClearPath motors to keep them energized (otherwise, I would have to use a brake or counterbalance to hold vertical position).
Normally, I use self-latching contactors for motor power supplies; however, it seems that both Teknic and DMM require that power to the servos be cycled if a fault occurs (to clear the fault), so the PLC controls sequencing of the power supplies. Because I have extra PLC I/O available, I'll probably use three-way switchs (Auto, OFF, ON) for the motor power supplies and because the PLC can easily perform latching signals, I won't have to hard-wire the latching circuitry.
Right now my test bench is a maze of wires. I tend to make things overly complex and then to simplify when each part of the control works as expected. Someday I'll post photos of a "finished" controller. One thing that I like to do is to separate all signals, i.e., the state of each servo's fault signal is captured and stored, then a signal is sent to the Acorn. The same applies to the E-Stop circuit. Each condition that should cause an emergency stop is sampled and stored and then a single signal is sent to the Acorn. With a PLC, I can sequence Power Supply power-up to keep surges to a minimum. I can also delay the DriveOK signal to the Acorn until all circuits have had time to stabilize. Currently, I use 5 of the 500 available timers in the CLICK to keep the start-up process orderly.
After watching Marty's videos, Gary's videos, Franco's videos and CNCKeith's videos (many of them many times), I'm still blown away with what the Acorn can do. Now that I know basically what IT can do, I needed an easy way to mix and match any component that I wanted to use to get the job done. In my case, I prefer the ClearPath servos, but I need signals that the DMM servos have. I needed a way to easily cycle power to any or all of the drives without over-cycling power supplies. I needed a way to keep the servos enabled. Add to that things that I would like to do and a PLC for my purposes became viable and almost a necessity.
p.s. It's good to know of that South Jordan is on your map too.