Cincinnati made it way to easy to adjust the gains from the control using the handy "Increase/Decrease" button. Unfortunately, this changes some numbers that were factory calculated, which affect the analog output to your drive.
Basically, we send the drive +/-10vdc to tell it how fast to go. Both the control manufacturers and the drive manufacturers want their products to be universal. We might put a drive on our machine that only accepts +/-5VDC as a command. By Increasing or Decreasing the gain, we are changing a value on the 950 called "motor rpm/volt". Basically, how fast does our motor turn for 1 volt of command we give it.
We can actually view this number by going to MDI, Select, Servo Set, Gain Set.
Example: We have an axis that has a 200ipm max feedrate. The gear ratio calculates out to be 8 turns of the motor to give us an inch of travel. So at 200 inches per minute, our motor should be turning 1600rpm. A good number to start with in the Motor RPM/Volt table would be 160, so 10v would give us 1600rpm.
We want this scaled to use as much of the analog as possible. It's completely possible to make the drive and control be scaled so 2 volts is rapid. This is bad because when we want to run at 10% or rapid, or 20ipm we are sending out .2 volts as a command. 2ipm would be .02 volts. Now, any ripple on the analog command is treated as a lot of rpm on the motor.
Overdriving the analog is also possible. We only have +/-10vdc to work with, but the 950 will put out as much as 12volts. If the drive is scaled wrong, and it needs 14 volts for rapid, we will run out of command voltage before we get there!
First: Lets briefly talk about excess errors/servo fails. When we go to the servo page from MDI, Select, Servo, we see Gain and following area. Jogging the machine, we want the gain to be 1.00 and the following error displayed will actually be the feedrate of the machine when you multiply it by 1000. When you are moving the machine at 75ipm, we should see .075 in the following error column. If the gain is off, the following error will be wrong. If we are going 100ipm, and the gain is .5 you are now actually moving 150ipm.
The excess error limit is usually set to 10% over the max feedrate of the machine. We are going to use .220 for this example. Any time your following error gets over .220, the control will alarm out. If we try to move at 200ipm with our .5 gain setting, we are going to hit the excess error limit because the axis is moving faster than what it is supposed to.
Lets get to work!
Ok, most of the time we are out there with no helper person, and we need to jog the machine while we are in the back panel. Lets write a quick loop to simulate a helper.
:Q1G91G1X24F100
G4F1
X-24
G4F1
G11L-1
I chose 100ipm because with my .5 gain, I won't be able to get to rapid, plus it's easier to calculate, 100ipm should be around 5volts at the drive.
Make sure your program will not smash anything (I don't have the article ready yet for that yet!) or run into a travel limit, press cycle start and head to the back cabinet. Stick your meter on the analog input of the drive. We want to see around 4.5 volts here. I like to scale my drives just a little bit less than the 10vdc so we have a little bit of room for error.
Get your drive manual out and figure out which pot we need to adjust. Sometimes its called "scaling", "tach", "velocity"... Carefully turn the pot. You should see the meter change instantly. By adjusting the pot, the motor is slowing down, the control sees this and puts out more analog. During the course of adjustment, we may actually hit the excess error limit. If so, pick a different feedrate, or go press the increase/decrease gain button for a little bit so the axis doesn't alarm out.
Don't try to adjust your servos at any less than 10% of rapid. The gain/following error display sometimes goes crazy at low feedrates.
If we can get the adjustment done without alarming, now go to the Servo Set page and adjust the Increase/Decrease button until you get your desired gain of 1. Go ahead and try running rapid and double check your analog voltage.
Balance:
For this adjustment, we do not want the axis moving.
I always manually set the balance number in the Gain Set table to zero. Pull up our trusty servo page. You probably will need a real helper here. Have your wingman watch the control while you consult the manual and adjust your "drift", "balance", "offset", ... pot until the following error display reads as close to zero as possible. I do not like using the Balance button on the screen. Sometimes it throws big nasty numbers into the Gain Set table.