Messages

801

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 22, 2022, 07:13:22 PM »

Hi,
I would still use microstepping, say 1/5, 1/8, 1/10, or 1/16, to get advantage of the smoothness of motion, but when you consider your machines
'actual' resolution, calculate it as if you are using 1/2 steps, while the 'theoretical' resolution would be 1/5 or 1/8 or whatever provided there was zero load
on the stepper.

In short what you have done by implementing 1/10 th stepping is good, you get the smoothness that you want but the actual resolution will be 10um,
not 2um as you previously calculated. Still 10um is pretty damn good for any machine!

Craig

802

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 22, 2022, 06:01:10 PM »

Hi Steve,

If you are micro stepping you do not get the full torque if you only displace the shaft a small fraction of a full step. This is why the full enhanced resolution is not available in the real world. If your load required very low torque, then you could get closer to the ideal target location. Microstepping can offer significant advantages in some light duty instruments such as telescopes, but does not gain you much resolution for a router or milling machine.

Very nicely and concisely  worded.

Craig

803

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 22, 2022, 05:59:18 PM »

Hi,
one of the few advantages of closed loop steppers is increased resolution.

As I posted earlier open loop steppers can reliably step in 1/2 steps, ie 0.9⁰ per pulse, but even with microstepping cannot reliably achieve any higher resolution.
With a closed loop stepper however the feedback to the drive will allow the drive to alter the A and B currents UNTIL the rotor shifts to it desired position as measured by the feedback
encoder. Thus the drive could be commanded to shift the rotor by 1/10th of a step, ie 0.18⁰ and the drive will alter the A & B currents until 0.18⁰ has been achieved.

Craig

804

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 22, 2022, 05:48:29 PM »

Hi,

increase the pulse number 10 times, the resolution of motion with 300 pulse and 3000 pulse for 1 turn can not be same i think

Does not work, it would be nice but anything beyond 1/2 stepping, that is 400 pulses/rev does NOT result in increased resolution.

Let say that you have set 10 microsteps per full step, ie 2000 pulse per rev, and the current location of the rotor is at fullstep position 0.
The current in the A winding is max, say 1A, and the current in the B winding is 0A. If the driver gets a pulse it will alter the currents to:
A will reduce by 1/10th, ie 0.9A and the B winding will increase to 0.1A. The rotor would like to assume a postion 1/10th of one fullstep (1.8⁰)
or 0.18⁰, but the torque available to make that move is the difference between the holding torque at position 0 verses the torque at position 0.1
and that is ONLY 1/10th of the RATED holding torque. It is highly probable that the load will exceed the available torque and the rotor WILL NOT move as you had hoped.

If the drive gets a second pulse, now the A current will be 0.8A and the B current will be 0.2A. The torque from position 0 to position 0.2 is 2/10ths of the holding torque, again
probably not enough to overcome the load.

If the drive gets yet another pulse then A=0.7A and B=0.3A and the torque from 0 to 0.3 is 3/10ths which may or may not be enough to cause the rotor to move.

So you can see because of the very much reduced torque between each partial steps  the rotor will probably not move, until some indefinite number of steps
have accumulated until the is sufficient torque to overcome the load and then the rotor will move a number of microsteps and once. This is not ideal. You'd want
the rotor to move exactly 1/10th a full step at each pulse, but you may get three, four or five pulses where the rotor does not move, then all of a sudden it will, and
catch up.

If you were using 1/2 stepping most drives apply A=1A and B=1A for a torque from position 0 to position 0.5, ie 1/2 a step of 1.41 times the holding
torque and surely the rotor will move.

For this reason 1/2 stepping, ie 400 pulse per rev is the highest reliable resolution you can get from a two phase stepper.

Craig

805

General Mach Discussion / Re: Looking for help with a spindle motor.

« on: February 22, 2022, 02:34:42 PM »

Hi,
Mach3's parallel port has by default a kernel frequency of 25kHz. With a well behaved PC you might be able to increase that to 45kHz or maybe 65kHz, or with an extremely
well sorted PC 100kHz.

The kernel frequency is the maximum pulse rate the parallel port can produce. In the case of a default installation that is 25kHz. Lets also guess that your servo requires 10,000
pulses to turn one revolution. At a max pulse rate of 25kHz then the servo could rotate only 2.5 revolutions per second or 150 rpm. As you can see the kernel frequency limits what the servo can do.

What is the encoder resolution of your servo? Is it programmable, ie have 'electronic gearing'. If so you need to set it to about 500 pulse per revolution. The at 25kHz pulse input:
25,000 / 50 =50, so the servo could do 50 revolutions per second or 3000rpm.

According to the manual the lowest resolution you can get with the servo is 1600 pulse/rev. With a pulse rate of 25kHz:
25000 /1600 =15.625 revs/sec or 937 rpm. With a default parallel port installation this is as fast as you could expect  for a Step/Direction driven servo.

You either have to increase the kernel frequency to 65kHz or more, possible but commonly fraught with difficulties, PCs just don't like it OR get an external motion controller like a UC100 (max frequency 100kHz)\
or an ESS (max frequency 4MHz).

Craig

806

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 21, 2022, 05:13:48 PM »

Hi,

So the correct approach in microstepping should be adjusting it to a lowest value which is enough for the required movement precision, 2 micron is what i adjusted it for today,

Close, but not quite. Increasing microstepping does not increase resolution, its nice to think it would but in practice 1/2 stepping is the highest practical and reliable resolution. You might
get an increase at 1/4 stepping but it will not be consistent. This derives from the fact the the differential torque between microsteps diminishes rapidly with increasing microstepping, and
consequently there is insufficient torque to step one micro step, but there is enough to step 1/2 step, and sometimes enuogh to step 1/4 step, but not enough to step 1/8 step.

The true value of microstepping is increased smoothness of motion. Microstepping was first proposed and implemented by astronomers whom were wishing to acieve a smoother motion from
the steppers in their telescope mounts. Microstepping, to some reasonable value, will reduce or eliminate mid-band resonance, which plagues steppers. Microstepping beyond that value it pointless,
you gain little extra 'smoothness', no extra resolution and an increased signal rate. In practice microstepping of 1/8, 1/10, and 1/16 are the maximum practical microstep regimes.

Craig

807

Mach4 General Discussion / Re: Mach4/Uc100 problem with jogging

« on: February 21, 2022, 03:06:53 PM »

Hi,
I am not familiar with the UC100, however all motion controller plugins should be in the Mach4Hobby/Plugins folder.
There you should see the plugin, it will be of type '.M4PW', but also there should be a signature file  of the same name but of type '.sig'.
Are both of those files present?

Craig

808

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 20, 2022, 08:05:53 PM »

Hi,

u mean instead of g28 it should code g92?

No, I just mean that these are two codes that can produce unexpected excursions of the machine, and often not recognised if you are reading code trying to determine a fault.

Craig

809

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 20, 2022, 05:41:40 PM »

Hi,

yes u are right about ess and mach4 but as it seems this looks like mach4 related to me because its the one which shifts the zero point by 400mm,

I've been using Mach4 for seven years, and other users for as long and longer. If there were such a fault in Mach4 do you not think that it would have been detected by now?

One possibility is an extraneous g28 in the Gcode. I have seen some post processors that include g28's which will result in large unexpected excursions by the machine.
It possibility is an extraneous g92.

Craig.

810

Mach4 General Discussion / Re: dangerous malfunction of a machine driven by Mach4

« on: February 20, 2022, 04:51:45 PM »

Hi,

i remember adjusting it as the highest it can get so maybe mach4 and ess can not catch the required pulse number when fro increased.

Mach produces numeric data so is in no way limited by FeedRate or otherwise. The ESS has a max output frequency of 4MHz so it too is very unlikely to be pulse rate
limited. Your BoB however may be pulse rate limited and almost certainly the steppers drivers will have some  max input pulse rate.

Mai I suggest that you reduce the microstepping such that the pulse rate at max axis speed is 100kHz or less.

Craig