Do-more H2 (Micro Modular PLC) Videos

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Before we can use the encoder we have to do

a few things. First, we have to wire the encoder to the

CTRIO2. For this example we will be using the CTRIO2 Channel 1A and 1B inputs and the

common is 1M. Now we have to configure the inputs on the

CTRIO2 module. To do that we go back to System Configuration, Module Configuration, and we

double click on our module. Click on Configure IO to setup all the individual IOs. This one is setup from before where we had

assigned channel 1’s output 0 and 1 to be a Step and Direction for our stepper motor. Now we want to add a single quad encoder to

the inputs. Well, I just say I want a quad counter. That takes up channels A and B because

we had two wires and I can even count those encoder pulses as one count per quadrature

cycle, 2 counts or even 4 counts per quadrature cycle. We’ll leave it at 1 right now to

keep things simple. And that’s all there is to configuring the CTRIO2 Module. We have

our outputs and our inputs, so we hit OK, OK and OK. So, we have wired the CTRIO for the encoder,

and configured the CTRIO IO. Now we just use it! To enable the encoder, you just go into the

configuration block and tell it which CTRIO2 Channel to use. We wired ours to Channel 1,

so we should probably use that one. Here is the key point. It is rare that your

Encoder PPR will match your stepper PPR. So right here you need to put the ratio of the

two: Divide the Motor PPR by the Encoder PPR – just like it shows in the parenthesis

here, and put that number here. In our example we have a 20,000 PPR motor divided b a 360

PPR encoder and so our ratio is going to be 55.56.

Because of that mis-match, the CTRIO can’t always get exactly the right number of pulses

it needs and it will try to bounce back and forth between the count on either side of

perfect. You can eliminate that jitter by specifying a dead band here. We’re not going

to fool with that in this demo, but just know you have it available. Also know that these don’t have to be constants.

You could put registers here and change both of these on the fly as the program is running.

Again, we don’t need to mess with that right now. So all we did was check our encoder channel

- which looks like I missed – Channel 1 – and setup our ratio of the motor PPR to

the encoder PPR. Now that the config block has told the CTRIO

how to handle the encoder we just use it. For this demo we’ll just use a Trapezoid

Function, and nothing changes. We use the same CTRIO module, we’re still going to

do a relative move. And we are going to specify a target position to be put in D0. So no changes

required there at all. This is important, now that we have enabled

the encoder in our config block – all positions you use with the CTAX commands need to be

in encoder PPRs. Using this Trapezoid Function, let’s move

the carriage 10 shaft rotations. Remember, in the previous video, that took 200,000 pulses.

Now that we have encoders enabled, we only need 3600 pulses. Notice that down here I added some more logic

for our convenience. If X7 is on, we are going to put 3600 into D0. If X7 is off, we are

going to put a -3600 in D0. That just gives me a convenient way to flip back and forth. I’m going to turn on X7, which will write

a +3600 to D0. And now when we set X0, we expect the carriage to move 10 shaft rotations.

And sure enough it does. And since this was a relative move I can do it again.

Turn X7 off, which writes a -3600 to D0, now when I engage X0, the carriage moves back.

But again, it moves back 3600 pulses, not 200,000 because we are using encoders. Note that while we used the Trapezoid function

in this example, these comments apply to all of the CTAX commands on the CTRIO2. We’ll, that’s all there is to using encoders

with the CTRIO2 and the Do-more processor. Do-more designer software makes it easy and

it just works the way you would expect it to. Be sure to check out the other videos

in this series for more on using motion. And as always, please send us any comments you

may have, we appreciate the feedback. Spend Less. Do-more. From AutomationDirect.