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Messages - joeaverage

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6761
General Mach Discussion / Re: AC servomotor calibration problem
« on: September 03, 2017, 07:14:28 AM »
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

6762
General Mach Discussion / Re: Probing for XYZ in Mach on a mill help
« on: September 03, 2017, 02:31:57 AM »
Hi Rich,
looks like cheap n' cheerful wins out over fancy....that's exactly what I needed to know. I'm not going to buy it...I promise....it just the
'Buy Now' button, I think calls to me when I'm sleeping.

On Friday I succumbed to a 'Buy Now' and spent $366.00 + GST on an Arbitrary Function Generator, I've been looking around for a while but
still this particular 'Buy Now' button seemed more seductive than most!

Craig

6763
Hi,
I don't know anything about HiCon I'm sorry but when you downloaded the plugin there should have been two files
M4HICON.m4pw
but also
M4HICON.sig

The last file is some sort of digital signature that is supplied to Vital Systems by Artsoft as an approved developer and the plugin wont work without it.
Have a look in Mach4Hobby/Plugins and see if both files are there.

Craig

6764
General Mach Discussion / Re: circles have a flat spot
« on: September 02, 2017, 08:53:25 PM »
Hi,
and for all you ever wanted to know, or even dreamed of about rack and pinion...
http://atlantadrives.com/systems.htm

I bought off Ebay an Atlanta Drive right angle servo reducer with the idea of making a fourth axis. Despite having the specs in front of me when I bought
it the physical reality of its size surprised me....'its big for the size of it!' and 'some surprises are surprisingly more surprising than other surprises!'. I haven't
yet got around to making my fourth axis yet, but I will one day. Its a beautifully built unit with only 2 arc backlash.

Craig

6765
General Mach Discussion / Re: circles have a flat spot
« on: September 02, 2017, 08:31:31 PM »
Hi Frank,
you might be interested, I found this outfit and was impressed with prices:
http://www.automation-overstock.com/products.asp?cat=190

Craig

6766
General Mach Discussion / Re: circles have a flat spot
« on: September 02, 2017, 06:38:41 PM »
Hi Frank,
yep, sure does. Its called rack and pinion and is very common in large plasma tables.

What you need to do is measure its backlash. I would suggest you use a dial gauge and see if you can measure any free movement by pushing the
gantry fore and aft. Ideally there would be no backlash but there will be. Some setups have the servo and pinion floating under spring pressure to
increase the engagement between the pinion and its rack. Its a good idea until the pinion gets worn then the peak of the teeth bottom in the groove
of the rack and will not allow any further engagement. This problem requires a good eye for mechanical detail to detect.

There are other methods for achieving low lash, variations on a split pinion, where two pinions along side each other engaged in the same rack but
with one pinion displaced, radially usually under spring pressure, by a fraction of a degree to effectively 'increase the width of the tooth to fill the gap'.
Clever, expensive and prone to wear.

No matter what if any backlash reducing system may be used its critical that you measure it. If its greater than 0.5mm you will have noticeable faults.

Craig

6767
General Mach Discussion / Re: Unusual stepper issue on lathe
« on: September 02, 2017, 06:19:45 PM »
Hi David,
from the way your talking you are of the opinion that this problem while sub-threshold has been there a while?

I have had the occasional noise issue as well and have found the practice of 'defining a load' on any given signal line reduces my problems no end.
By 'defining a load' I mean have the TTL output buffer be required to either source or sink a modest current in either state. Any noise current
impulse would then have to be larger than the standing current before the noise could attempt to change the logic state of the signal.

Take for example your disable input to your Gecko drive. Without looking at the specs its quite probable that the input impedance of the pin is 10kOhm
or more. If your BoB  is logic low and is dragging the input pin low it will have to sink 5V/10k=0.5mA or less. Thus if a noise impulse happens along with an induced
current of more than 0.5mA the pin will change state and cause problems. If the input pin were a lower impedance or deliberately paralleled with a resistor
to make it so, then the BoB would have to sink more current and the pin would be less sensitive to noise. Most Bobs will source or sink 15-20mA, some will
do considerably better than that. While I don't advocate loading a BOB output to the max I try to see to it that it is  loaded to about 5mA, ie an impedance
of about 1kOhm. If a 1kOhm resistor was fitted to your Gecko drive input to 5V then your BoB would have to sink a little over 5mA to pull it low.
Likewise it would take a negative going noise current impulse of at least 5mA to cause the pin to go low when in fact the Bob is inactive ie the signal is
meant to be logic high.

I have fairly recently used a servo and drive for a spindle motor and looking at the Allen Bradley documentation the step/dir inputs to the drive are about
10kOhm. I don't know what your drive is but guess it would be similar. You can see that the step/dir inputs to my drive are reasonably sensitive to induced
noise. I have elected to use a shielded twisted pair cable (one pair each for step and direction) rather than 'load' the servo input with a resistor.  I was concerned
that I may reduce the communication speed by excessive load and so tried to increase noise immunity by shielding.

It may be that other signal lines in your machine could benefit the idea of being suitably loaded.

Craig

6768
General Mach Discussion / Re: Probing for XYZ in Mach on a mill help
« on: September 02, 2017, 05:28:18 PM »
Hi,
in industrial practice you would use a multi axis touch probe, the good ones are very accurate but VERY expensive.

This one:
https://www.homanndesigns.com/index.php?main_page=product_info&cPath=58_42&products_id=347&zenid=jebt2ol2047oqe9qf24e8ggs06
is more in my price range.

I doubt its as good as a Reinshaw but it sure does look the part. Has anyone used one like this and if so what do you think about it?

Craig

6769
General Mach Discussion / Re: circles have a flat spot
« on: September 02, 2017, 05:20:05 PM »
Hi,
what sort of mechanism moves the axes? Are they rack and pinion gears or ballscrews or leadscrew and nuts? How are the steppers hooked
up to each axis?

I go with tweakie, there is some lost motion in one or more axes. Can you measure any backlash in the Y axis? This is a common and pretty much
unavoidable problem with rack and pinion driven axes.

Craig

6770
General Mach Discussion / Re: AC servomotor calibration problem
« on: September 01, 2017, 10:32:38 PM »
Hi,
apologies those page references should be 6.1 and 6.2.

Note also in figure 6.4 Stepping Motor Interface on page 6. 4 that the max switching frequency is 175kHz.

I'd be tempted to say you could push that a wee bit, 200kHz you would probably get away with. My Allen Bradley drive allows step/dir signals to 500kHz.

Craig

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