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Author Topic: AC servomotor calibration problem  (Read 2758 times)

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Re: AC servomotor calibration problem
« Reply #20 on: September 03, 2017, 09:10:06 AM »
Hi,
nice of you to say but you haven't met me...easy to be nice over the internet...but you may want to shoot me in real life.

Craig
haha yeah that´s right. It´s just nice to have people who offers their own time to help other. Hope i some day can repay, by helping other who needs my knowledge.
Re: AC servomotor calibration problem
« Reply #21 on: September 03, 2017, 09:30:45 AM »
Hi,
nice of you to say but you haven't met me...easy to be nice over the internet...but you may want to shoot me in real life.

Craig
I can´t find anything about the input terminals construction. Do you know if they are galvanic isolated either with buffer or optocoupler, so i can go direct to the driver without any bob
Re: AC servomotor calibration problem
« Reply #22 on: September 03, 2017, 12:01:08 PM »
Hi,
if you require your spindle to do indexing operations then you need to use position control per section 6 in the manual. 'Position
with Following Error' is the right dynamics mode (sounds and vibes) and on the screen on page 6.3 the right choice is about 4000 pulse
per rev.

If you just want to get your spindle going and make some chips then you use section 7 Drive Control with Analogue Interface. On the screen on
page 7.2 you can set the voltage, offset and speed that you wish. Note that at no time do you need to set the 'pulse per rev' that's required
for position control not speed control.

Just as an aside this servo doesn't have an encoder at all, it has a resolver, a very VERY groovy technique from
analogue days, makes me come over all misty eyed! The pulse per rev setting is actually a programmatic setting for the 'Resolver to Digital' converter
in the drive. Thats how Bosch managed to achieve what is to all intents and purposes a programmable resolution encoder...CLEVER!

Anyway back to analogue speed control....with the settings made per 7.1 and 7.2 all that is now required is to enable the drive and apply a voltage.
To enable the drive (fig 10.56 page 10.54) apply +24VDC to pin 1 X4 with 0V pin 4 X4 and have your BoB or even a short bit of wire apply 24V to pin 3 X4.
Lets for the moment imagine that you selected 10V as max command value and 2000 rpm as max commanded speed. For the moment assume 0V offset.
If you apply 5V between pins 1 and 2 connector X3 per page 7.3 then the servo will run at half speed, ie 1000 rpm. Apply 1V and it will run at 1/10 full speed ie 200 rpm.
The voltage applied could come from PWM from Mach via a low pass filter on your Bob or even easier from a potentiometer hooked to your drive.
Some PWM don't actually quite get to 0V, some hang up about one diode drop above earth at 0.7V. If your PWM is like this use the offset of 700mV
to counteract it. A potentiometer should get to 0V so the offset can be 0mV.

Given how simple having a potentiometer is you should probably have a go just to prove to yourself that you can. On page 7.4 is a circuit diagram of the analogue
input. Note that it says a max of 15V input, DON'T exceed it or will blow it up. Ideally you would get a 10 or 12V regulated DC supply or if you want spindle to go
backwards a -12V, 0V, +12V supply. Why  would you want to go backwards though? You'll need a potentiometer, anywhere between 1 kOhm to 10 kOhm  will be
fine, 10 kOhm is a bit like an arsehole...everyones got one! Hook one of the outside pot terminals to +10V, the other outside terminal to 0V AND pin 1 X3. The centre
pot terminal to pin 2 X3 and the servo should run. If it seems to be going backwards swap the connections between pins 1&2.

Craig
So now it is setup and tested. It works perfect, but then another issue turned up. The jog feature does not work in analog speed mode. This means that when i stop the spindle with enable still active the motor brakes with torque and if i disengage enable switch, then the 24v motorbrake is active,,,darn.
Yet one more issue. When set to spin manually with only a potmeter, the motor stops so hard when start is disabled, that the chuck unscrews and falls off.

It is also very sensitive about the tuning of the offset. i have found my zeropoint at -0.15mv any diffeerence in either way makes the spindle turn either cw or ccw. Quite funny that i can get CCw at full speed just by setting this offset at -10v.
This was a little update and as usual with a few questions as well... Have a greeeat sunday everyone

Re: AC servomotor calibration problem
« Reply #23 on: September 03, 2017, 02:21:06 PM »
Hi,
when you disable the servo it stops at its max acceleration. You can set that....although why you would set it less than its capable of...you have
paid for all that luvly grunt and now you don't want it?

The offset must be perfect if you expect it to stop. In your lathe you will use the disable pin under Machs control to stop.

I think you can program the brake so that it doesn't come on when the drive is disabled. When disabled you should be able to jog, when enabled
it is in primary control mode and it ignores jog which is its secondary control mode as per previous post.

Craig
My wife left with my best friend...
     and I miss him!
Re: AC servomotor calibration problem
« Reply #24 on: September 03, 2017, 02:51:54 PM »
Hi,
when you disable the servo it stops at its max acceleration. You can set that....although why you would set it less than its capable of...you have
paid for all that luvly grunt and now you don't want it?

The offset must be perfect if you expect it to stop. In your lathe you will use the disable pin under Machs control to stop.

I think you can program the brake so that it doesn't come on when the drive is disabled. When disabled you should be able to jog, when enabled
it is in primary control mode and it ignores jog which is its secondary control mode as per previous post.

Craig

somewere in the manual it says that jog is only available in step and position mode. so i think i have to use the software to go back to syepmode before jog is an option again. I haven't seen any program option in the software were i can do anything to either brake or toeque. Torque can only be worked with if i choose analog torgue instead of analog speed.
If you do not have a solution i guess i have to overcome this with a switch on the power cord to the brake and then put it in stopmode so the torque is 0.
Re: AC servomotor calibration problem
« Reply #25 on: September 03, 2017, 02:54:11 PM »
Hi,
look at 'Torque Limits' on page 10.7. You can set the max torque by setting or you can use an analogue setting per fig 10.8.

The analogue setting could be under Mach PWM control which would allow you to have variable torque limits depending on current requirements.

Craig
My wife left with my best friend...
     and I miss him!
Re: AC servomotor calibration problem
« Reply #26 on: September 03, 2017, 03:01:13 PM »
Hi,
when you get your ESS and get it set up in step/dir mode per your original plan then all of this becomes meaning less. You will not have to disable
the drive to get it to stop...just have Mach stop iussing step pulses and the brake will never come on. Likewise you will be able to jog from Machs
screen, you won't have to go anywhere near the drive.

The point of setting it up in analogue it simply that you could experiment and learn something about your drive and servo. Have you learnt some
new stuff?. I bet you have and if so the hobby is succeeding.

Craig
My wife left with my best friend...
     and I miss him!
Re: AC servomotor calibration problem
« Reply #27 on: September 03, 2017, 03:21:09 PM »
 :) yeah i am sitting here with a big smile, yup i am learning and you are right it gets meaning less, but i got caught up in this and just want it to be perfect in case the noise issue in stepmode continues. Yes hobby it is and great when it becomes a succes.

you asked why i didn´t want all that grunt. The anser is my jaw chuck is screwed on the spindle and there is no lock so if the spindle stops in an instant the jaw chuck continues and result is a chuck running over the floor.

I read this manual like 15 times but much is just going right thru without any understanding until you point me in the right direction and explains were, what and how. Then things starts to be understood.

Thanks Craig and now i think i have to let you rest before you give up on me haha. I will play a little tomorrow with what you just told me and then wait for the board. I´ll be back with info on how everything went.
Re: AC servomotor calibration problem
« Reply #28 on: September 03, 2017, 04:43:50 PM »
Hi,
kool, I thought you might have a smile.

While it may be a bit agressive at start up and slow down you really want all that torque at other times. When cutting
the cutting forces slow the spindle sown and you want the torque of the servo to bring it up to speed again.
The last thing you want to do is imasculate it stop the chuck from coming off.

Remeber under step/dir control the speed up and slow down will be controlled by Mach that you set in Motor Tuning
and when at constant speed the drive and servo can utilise max torque to do it, perfect.

My servo doesn't have a brake. My understanding is that the brake is normally on so that if the power is suddenly
removed or the drive goes into emergency shutdown then the brake comes on. You need to power the brake coil in
order to release it and spin the spindle. A simple test is remove the input power to the drive, does the brake activate?
If it does then you will have to permanently power the brake coil in order to avoid the brake from interfering.
Look in the brake section for the circuit diagram, I'm at work and don't have the manual here.

Craig
My wife left with my best friend...
     and I miss him!