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Author Topic: Servos vs Hybrid Steppers with CS labs controller  (Read 3165 times)

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Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #20 on: October 07, 2017, 04:07:51 AM »
Hi Craig
Buying new servos is not an option. Looking for more feedback on using existing DC servos. With Cs Labs controller.

Cheers
Mick
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #21 on: October 07, 2017, 04:49:32 AM »
Hi Mick,
yeah, servos even cheap ones are still expensive and if you try to buy to match your budget then you are entirely likely to end up with under
specified servos and all that doe-ray-me would be wasted. Go on....your amongst friends....you can admit that the missus will discombobulate you!

What condition are your existing servos in? I'm wondering if you could not build a simple analogue circuit and hook it to your drivers to see how
the servos responded. You certainly don't want to be investing in controllers if your existing servos and/or their drives are faulty.

My training and job is electronics. In the situation where I was trying to evaluate your machine for overhaul/repair or modification I would grab
my function generator and set it to sinusoidal wave of about 5V peak to peak at 1/4 Hz and put that directly into the analogue input of the drives.
Provided you didn't crank the frequency up to much and therefore try to accelerate beyond the servos max then it should move backwards and
forwards smoothly. A sawtooth wave could also be used; the reversal of a sawtooth wave represents a spike in acceleration. The need to keep the
amplitude down and the frequency of reversal low would be paramount otherwise the acceleration spikes would be such that the servo has no real
chance to stay in sync with the input and it would fault out 'following error'

You may have noticed on Ebay Direct Digital Synthesis function generators of modest but adequate performance can be had for less than $20, God
bless or Chinese friends. If you don't have a signal generator or know someone you could borrow one then one of these cheap units would do the
trick.

Craig
My wife left with my best friend...
     and I miss him!
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #22 on: October 07, 2017, 05:59:49 AM »
Hi Craig

Lol yes the wife would have a fit or insist on spending the same on lotions and haircuts.

I don't think there are any issues with the servo's as they were working fine last year up until a point when I changed the membrane on the operator panel keyboard. Since then the keyboard or part of it stopped working not allowing me to do anything with the machine.     

Do like the idea of what you are saying though but you will have to go slow. Ill have a look at the Norwin wiring manual to see if I follow you.

Cheers
Mick   
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #23 on: October 07, 2017, 06:17:34 AM »
Hi Mick,
Quote
Lol yes the wife would have a fit or insist on spending the same on lotions and haircuts.
don't want too much of that going on, the UK balance of trade may never recover!

Even a simple potentiometer with a 9V battery would be enuf to cause the servo to move.
Twiddle the pot backwards and forwards and the axis should follow. With just one 9V battery I would expect the axis to be restricted to one half
its travel, the right half say, and if you reversed the battery then it would work in its left half. You will have to coax it, if you attempt to cause the
axis to move from point A near one end of it travel to point B at the other end instantaneously as in changing the battery polarity it will fail as a
following error. None the less you should be able to get the axes to move. It will probably require an enable signal.

Given that you are of the opinion that the servos are OK then maybe fooling around with bits of wire and batteries doesn't appeal.

Craig
My wife left with my best friend...
     and I miss him!
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #24 on: October 07, 2017, 06:47:35 AM »
Hi Craig

Happy to knock a circuit up. Have loads of electronic stuff about. I can make a circuit that has 0 to 10v adjustable. The frequency part was confusing me in your previous post.

Would I connect this to pins 4 and 5 and the Norwin Drive?

Cheers
Mick 
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #25 on: October 07, 2017, 07:04:31 AM »
Hi Craig

Sorry meant pins 10 and 11?

Cheers
Mick
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #26 on: October 07, 2017, 09:19:52 AM »
Hi,
yes. Looks like all of it needs to be hooked up. the -15V,0,+15V supply outputs can be used to synthesise the command input. An +15V enable signal
must be applied to term #8.

0V is applied to pin #10 and a voltage between +10V and -10V applied to pin #11. This voltage could the output of a pot spanning -15V and +15V
or a slowly varying signal from a signal genertor. The speed of the servo should follow the input voltage.

The servo/drive combination has no ability in itself to detect or fault out under following error. It does have an armature over current fault, Thus if the
command input is stepped in a sufficiently aggressive manner the servo will attempt to follow but fail to do so as the armature goes over-current and
faults out.

If you had an oscilloscope you could monitor the encoder output to ensure that it is available for the position control loop.

Craig
My wife left with my best friend...
     and I miss him!
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #27 on: October 07, 2017, 09:26:39 AM »
Hi,
what sort of encoder is fitted?. It will have a bearing on the controller.

Craig
My wife left with my best friend...
     and I miss him!
Re: Servos vs Hybrid Steppers with CS labs controller
« Reply #28 on: October 07, 2017, 01:05:42 PM »
Hi Craig

Thanks for the info. Will give it a go tomorrow. The encoders are ACCU CODER 755.
5VDC.

Cheers