PCDC Encoder Calibration

Hello. My name is Darren Hawkinson. Today, I'm going to show you what causes the majority of x-axis accuracy issues on a PCDC.

We're going to be looking at the encoder assembly, and I'm going to show you how mechanically it will affect your accuracy. Now, let's go look at the tools that I'm going to use today.

All right. So now we're going to discuss the tools that were used during the calibration. First of all, the level. The reason I prefer a machinist level is it gives you a lot more of where you actually are being level. Next, tape measure.

Calibration should always be done with a calibrated tape. Always cut a foot or an inch in the front of it, so that you're not using the tab. The calibrated tape should only be used during calibration, or if you think the machine is off.

Most people will use this type of a tape measure. What happens is the tabs get bent. Tape measures do stretch. That is the importance of not using your calibrated tape every day, but only for accuracy checks or for calibration. Next, the dial indicator. Dial indicator is only going to show you if your encoder wheel is bent. Then we have our metric Allen wrenches, that we use a 6-millimeter, 5-millimeter, and a 13-millimeter to make our adjustments.

Always Loctite all bolts after you are done. Once you get the assembly level, take each bolt out one at a time, Loctite it, and put it in, and properly torque the bolts.

Always cut part of the tape measure you're using. I like to cut a foot.

This gives me an accurate measurement that I am at, my 1 inch that I programmed. My next mark was supposed to be at 15 feet, 1 inch. And we can see that we're almost 3/16 of an inch off. So now I'm going to do a physical inspection of the machine to see if I got what I have mechanically that might be causing this.

All right. So now that I've established my baseline that this beam is almost 3/16 of an inch off, now I'm going to do some visual inspections to see if I have anything mechanically that can contribute to this inaccuracy. So one of the first and easiest things that I like to check is the bearings for the tower. I'm looking for cracks.

And a crack is going to be very noticeable. I'll check the outsides, and I check the insides. What will happen is if you get cracked bearings, you're going to end up with losing clamping force, which will obviously affect your accuracy.

All right. My bearings are good. So now I'm going to go over to the encoder assembly.

All right. So my bearings are good. So now I'm going to check my encoder assembly itself. I'm going to be checking it for tightness I'm going to be checking the encoder wheel for levelness. I'm also going to be checking it for runout, for a warped disk.

So the first thing I'm going to do is just physically grab it. I'm looking for any slop and any play in it. Everything seems to be tight. My bearings seem to be tight.

My next step, take my level.

Set it on there.

Right now, I am leaning in toward the machine.

So right now, what I've done is I've seen to see how much I really need to come up as I put feeler gauges underneath here to get level my level. And I can see the gap underneath there of how far I have to move that assembly up to be level. And I'm going to find--

I'm just about the exact same amount in that direction that I have to come up.

So now I'm going to make my adjustments. To level the encoder wheel this way, I'm going to loosen the bolts down here that are in the bearings. And I'm going to just tilt this assembly until I'm level. Then I'm going to lock it back down and Loctite the bolts in tight.

The next step of the leveling is we've got to level it this way. This is achieved by using these bolts and these adjustment screws until we can get the assembly level from when it's all the way down and all the way up. Then we'll have a level encoder assembly. We'll put the dial indicator on here and spin it to make sure that the encoder wheel is not bent.

So if you do have a bad encoder wheel, that is where you're going to see it on this dial indicator you'll see the indicator move usually more than one rotation around.

All right. So now that I've found my encoder wheel is not bent, but my assembly is out of level. So now I need to level that assembly. And then I'm going to rerun my marks. All I'm going to do is move it over a little bit about a half an inch in a program to see what difference I made without making any scale factor changes to the machine.

So now that I've leveled up my assembly, I'm going to run the same program. I'm just going to move the hole over to the layout mark over about a half an inch to see what difference I've made. And if it's off, then I'll make a scale factor change, and the machine should be calibrated.

[MACHINE WHIRRING]

This is our new mark.

I'm making sure that it is at 1 inch. That is our reference position. And it is. So now we'll run down and we'll check what our mark is down here. So our mark should have been at 16, 1. It was programmed at 15, 1, it is now at 15 feet, 1 inch, and an eighth inch. So I'll need to make a scale factor adjustment of an eighth.

Now we know our machine is mechanically sound, and we know that it is an 1/8 inch off from where we programmed. So now we're going to make a scale factor change in the control to make up that difference. But the scale factor is based off of the encoder diameter and the encoder pulse counts.

This is not something that operators normally have to mess with. They just need to know where that scale factor is and how to get to it, and the formula for making a change to the scale factor.

The formula for scale factor is very simple. You take your old scale factor times your measured move divided by your commanded move. That gives you your new scale factor. So now what I'm going to do is I'm going to show you how to get into the control, where to go to make an adjustment to the scale factor.

All right. So first thing we're going to do is come up here and find our setup. We're going to put in our password, which is SUNRISE.

All capital letters.

Then we're going to go down to our machine data.

And then we have a button user views.

So when a user views under our x-axis, we have our first category right here. That's 34,100 in parentheses 0, which is our x reference. So if our x reference was off, then we'd make a slight change here to accommodate for that.

Next, we have our encoder.

This 31, 0, 10, with a 0, that is your entry encoder.

The one in parentheses is your exit encoder.

Right now, we're dealing with the entry which you have a scale factor of 0.20304.

So what I'm going to do is I'm going to take and take that scale factor, 0.04

times 181.125

equal, it gives me 36 divided by 181 equal 0.20318. So that's where I'll enter this in.

And after I push the yellow input key, then I'm going to do a reset of the control. Always e-stop it before you do the reset.

The keyboard will flash as it's doing its reset.

All right, the keyboard has stopped flashing.

The control has been reset. We can go back in, and now we're ready to run another test mark to make sure that we are actually calibrated. If our mark comes out at 181 inches, no more adjustments need to be made for our x-axis here.

[MACHINE WHIRRING]

Still at my 1 inch.

And now we're at our 15 feet, 1 inch, because we cut a foot off the front of the tape measure. So now our machine is calibrated.

So people always ask me how the encoder wheel gets bent. Well, it gets bent because when the machine is relaxed in an e-stop state like it is now, the encoder wheel is extended out. It is past your datum line.

So if an operator is running his conveyors and does not take the machine out of e-stop, he can run a beam into it, and hit this encoder wheel. Once you hit this beam and start it on a downward track, it's going to continue to follow that down, and you're going to end up bending your disk, and that's when you really have accuracy issues.

So now to recap what we've done, we now have a calibrated machine. And I want to leave you with a couple of things that will help you to ensure that you have good, accurate parts starting at the beginning of your day. It is as simple as taking your level, putting it on here, checking it. Am I level?

Turning it? Am I level? I'm good there. Then just taking the beam. The longest beam you can.

During any calibration, always do at least 30-foot move. The longer the better for x-axis calibration, whatever your long beam is, make your mark at 1 inch at the front and the longest you can do. And for an example, 35 feet, 1 inch.

Now I take my calibrated tape and check my 1 inch. Then I can go see if I am 35 feet mark to mark.

If I am, then I know this machine is calibrated and ready to run.

And also remember, always follow your state, local, and company lockout/tagout procedures before working on any Peddinghaus machine. Send an email to myservice@peddinghaus.com.