﻿In indexing mode, you tell the drive what you want it to do by filling in some tables with what
position to go to at some speed and accelerations and how long to dwell at that location. Then fill
in the next one and the next one, etc., to build your motion profile. You can loop backward
or forward to any of the 64 possible indexes and each index can be repeated up to 65,000 times.
The L7C servo system handles multiple types of indexing moves.
In this video, we’ll cover the absolute and relative moves, in Part 2 we'll cover blended and
registration moves and in Part 3 we'll cover rotary moves which have their own unique way of doing things.
Of course, the best way to see how all of his works is with live examples, so let’s do it.
I’m going to assume you have seen the quick start videos and you're already familiar with the
DriveCM software – which you can download for free at AutomationDirect.com. So I’m
going to breeze through a lot of the setup steps. Check out those videos if you need a refresher.
I’ll go to Setup, Return to Factory setting so you know exactly where I am starting from. Yes
we really want to do that. Give it a second for this dialog to go away and it’s done. You can
either power cycle the drive or just hit this guy to reset the drive processor. Yes we want to do
that. Wait for it to reconnect and we are ready to go. That ensures that the drive is in a known clean
state before proceeding. Don’t forget to do that. Setup wizard - we want to be online with the drive
and yes we want to read the drive's current configuration. Auto encoder. We want indexing
mode. We’re doing the linear mode in this video – we’ll use the rotary mode in Part 3.
You can specify which of the 64 indexes the drive should start at when you kick off indexing.
We’ll be controlling the starting index with digital inputs, so we need to turn this off.
Rotation is fine. Let’s change the gearing so that 100,000 pulses
gives us one rotation. The encoder on the motor I am using has 2 to the 17th pulses per revolution
and we’ll electronically gear that to 100,000 user units per revolution just to make the math
easy in our demo. The linear slide we’ll be using travels 5 millimeters for each rotation
so now 100,000 pulses will give us 5mm of travel.
All of this is fine. Using digital inputs, we need to be
able to enable the servo, select a couple indexes, and start and stop the indexing. I have signals
wired to Input 2 for home and Inputs 7 and 8 for over travel limits for other demos, so I’ll assign
those just to remind us they are there. We won’t be using them in this demo but we do need to flip
the sense so they don’t interfere with us. For the outputs, let’s keep an eye on the
origin and the position signals – we’ll use those in Part 2. I’ll clear out the rest.
I’ll select Homing Mode 35 as the default in case we need to quickly clear the position
register to zero. That doesn’t actually move the motor, it just clears the position register.
Write all of that to the drive. Give it a second and it’s done. And again,
we always reset the drive's controller after making changes to ensure all loose ends got cleaned up.
Wait for it to reconnect and we are good to go. I put this ruler here and added this black paper
triangle, so we can see how far the slide travels. I’ll go to jog to move the carriage somewhere near
the center of the slide. And I’ll move the ruler so it aligns with 100 millimeters.
Let’s go to homing which we set up to Mode 35. All that does is clear the position register
to zero making this the new origin. Great, we’re all set up so now we can
finally do some indexing examples. Click on this guy to go to the indexing setup.
Let’s do an absolute move to go to the 100,000 pulse mark
which should be 1 rotation which should make the carriage move 5mm.
I’ll put the velocity and accelerations at relatively slow values, so we can see what’s
happening here in the video. We don’t care about registration right now, and we’ll only do this once,
and let’s dwell at that position for 500 milliseconds.
Remember that you have to hit the enter key to get rid of the red which tells you it has
been entered into the drive’s volatile memory. Hit this button down here if you want it to be
permanently written to the drive so when you power cycle the drive it's still there.
We don’t care about the next index because we are going to stop after this move.
All of this get’s written immediately to the drive, so we are ready to go.
We’ll control the drive from the digital input panel. This allows us to override
any digital inputs that may be wired to the drive and create new ones that aren’t like
this start and stop signal we are using here – they aren’t actually wired to the drive.
Let’s enable the servo’s output, and if we watch the slide as I toggle the start
signal, yep, it moved the expected 5mm. Perfect. If I toggle the start again, hmm, nothing.
Why? We told it to move 100,000 pulses, right? No. We told it to go to Position 100,000.
If we bring up the jog panel, we see that we are at 100,000. So now when we toggle start,
we are telling it to go to the 100,000 position again. But we are already at the 100,000 position
so it does nothing. That’s an absolute move – it goes to the position you tell it to.
If we switch that to a relative move – it now says move an additional
100,000 pulses relative to where you are. If we watch the slide each time we toggle
the start signal, the motor moves another 5mm relative to where we were.
To get back to zero we could do relative -400,000 pulses. Instead, let’s just do an absolute move
directly to zero. Toggle start and we are back to where we started from.
Let’s do a relative move, 100,000 pulses – or 5mm – but this time repeat that 3 times.
And let’s dwell for 2 seconds and then make the next index, Index 1. We’ll have Index 1 return to
Absolute Position 0 at a speed of 1 million pulses per second. And I’ll speed up the accelerations
too. So we should move rapidly back to zero. I’ll toggle start and we see the three 5mm moves
execute, then a 2-second dwell, and then the Index 1 move rapidly back to zero.
Notice that the dwell only affected the time between Index 0 and 1.
It didn’t affect the time between the three iterations of Index 0. Those executed one right
after the other. Just something to be aware of. Do you have to go to the next index? Nope. You
can jump to any index you want. And you can start at any index you want.
For example, in the setup wizard we only setup two of the 6 possible index select bits. You can
see from this table in the user manual that when none of the 6 bits are enabled the drive starts
at Index 0. When the first bit is enabled it starts at Index 1. When the second one is
enabled it starts at Index 2 and when both of those are enabled it starts at Index 3. When
they are all enabled, it starts at Index 63. So it’s selecting indexes based on a binary pattern.
Since we are only using two of the index select bits, we can only select indexes zero
through three before the pattern repeats. But any one of those four starting indexes
could jump to any of the other indexes which can jump to any other index
and so on. So even though our two selector bits only allows us to have 4 starting points, that
doesn’t limit the number of total moves at all. You still have all 64 indexes available to you.
And remember – if you run out of digital inputs, all 6 of the index select bits can be controlled
via Modbus. Don’t forget you have that option. One side note - if you scroll through the indexes
all the way up to Index 64 and then back again, your screen will be blank.
Why? Well, you just asked the drive to transfer a lot of information and it takes a while to
catch up. When I timed it, it took around 45 seconds. I don’t have that kind of patience,
so I just toggle the drive offline and then back on again to quickly refresh the display.
It’s important to know that the starting index we specified using the digital inputs
is only read when the start signal toggles. So, you can change these to get ready for your
next sequence while the move is in progress. It won’t impact the current move at all.
Of course, if you need to stop the move just toggle the stop signal.
The absolute and relative moves are really powerful all by themselves.
But the L7C drive doesn’t stop there. It also provides a blended move and the ability to
move relative to a registration mark and it has moves specifically designed for rotary motion.
Join us in Part 2 and Part 3 where we’ll see how all of that works.
Meanwhile, click here to learn more about the L7C Servo System.
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