Messages

6591

General Mach Discussion / Re: Mach3 always hesitates in arcs and circles

« on: September 22, 2017, 10:57:39 AM »

Hi,
I've done the same sort of thing on my mill.

The stepper/ planetary gearbox/ ballscrew resolution is 1um. The manufacturer of the planetary gearbox claims less than 2 arc min backlash equivalent
to 0.7um lash.

When I did the same measurement that Roger describes I got 4um lost motion? As it turns out I'm using some cheap aluminium shaft couplers with a spiral
slot cut into them. They wind and unwind a bit like a spring and there is my lost motion. I have retained those things because they are a bit weak, I've had
the occasional crash and the coupler twists itself up and shears rather than some other component breaking. While I didn't intend it they serve as a mechanical
fuse.

With the gearboxes and mechanical advantage of the screws the stall thrust of my axes is over 1500 N or 150kg thrust, enuf to crush things like hands and so
on. This machine is tiny, machining volume of 200mmx200mmx200mm, and yet its till got the grunt to injure badly. Was quite a surprise when I realised that.
As I've said before 'some surprises are surprisingly more surprising than others'.

Craig

6592

Mach4 General Discussion / Re: Homing sequence triggering by limit switch possible?

« on: September 22, 2017, 10:35:28 AM »

Hi,
I'm happy enuf with your explanation re industrial version of the software, If you had the gold you wouldn't be buying Mach4 for this job anyway.

I just noticed something that is worth thinking about maybe trying:

LUA Syntax:
rc = mc.mcMotorSetHomePos(
      number mInst,
      number motorId,
      number count)

Note the syntax that the position set occurs at a number 'count' in encoder counts from the switch. The C++ syntax for the same statement is that count is
integer. I'm thinking that because you've set count to zero then the switch will still be active whereas if you try backing off a wee bit....who knows?

Craig

6593

General Mach Discussion / Re: Interference with axis motors

« on: September 22, 2017, 10:06:01 AM »

Hi,
kool, mystery solved. Maverick you may want to do a bit of research and find a manual for your controller, just what its capable of and how you
set it up are going to be critical to you getting the best from your machine.

Craig

6594

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 09:56:47 AM »

Hi,
crazy thing about Aussies, you have to hit them with a stick to make them realise when something is good! You've paid for and got Mach4 but stick with
Mach3.

I'll send you an email...I've got some bottom land to sell you...bottom of what you ask....don't worry I'm Kiwi...would I put you crook? LOL

Craig

6595

General Mach Discussion / Re: Servos progressing well, but question about index

« on: September 22, 2017, 09:48:39 AM »

Hi,
you don't need it, as you say the loop is closed by the drive. You may have noted that there is an alarm that triggers if the servo deviates by
some small programmable amount, say 20 encoder counts. If you have a 10000 count per rev encoder that means your servo will alarm if it
lags by 3/4 of a degree from where its supposed to be....that's right 3/4 degree from where it supposed to be at say 1000 rpm! This thing is so
damn accurate it was intended as an axis servo not just a mere spindle motor.

The actual and programmed speed should be within a few parts per million.....you are wasting time and money if you try improve on that.
No doubt if I read the manual closely there will be an encoder output. This could be used by Mach to measure the rpm and display it if
you want to be totally anal retentive about it.

There is talk of the ESS having an API but given it has yet to get backlash compensation and THC support and I've been waiting for months I wouldn't
hold my breath....anoxia is a bad way to go! I don't intend this as a complaint about Warp9 either, I use an ESS and luv it, I just don't need a lot of
bull********* stuff.

I don't know whether you have done any control systems programming but PID programs are not for the faint hearted...you have to worry about loop
parameters, integrator wind up, how to generate a low numerical noise speed signal, usually done by a high gain integrator loop, and if you have to ask
you do not want to try it!

If you've already got full speed range control with step/direction signalling then using analogue voltage for speed control is going backwards...you already have
position control, and not just any position control but the full blown modern sense of position control...that is a final position accuracy of (programmable)
four encoder counts say, 8.6 min of arc, just a bit over a tenth of a degree!

The bottom line is you stumped up with I'm guessing $1000 for a servo and drive, ie you paid good and what you've got is good, in fact very good! If your
going to worry about stuff you might try worrying about who's going to win the next Melbourne Cup!

Craig

6596

General Mach Discussion / Re: Interference with axis motors

« on: September 22, 2017, 06:40:24 AM »

Hi Roger,
I read a book by Sean Lemming, a real Windows guru and interrupts, in something like 15 levels of priority, are normal in Windows for all manner
of inter thread communication. The problem is that you can't stop Windows from using interrupts, it would crash immediately yet you need to run pretty high
priority interrupts to drive your timer for Mach.

How Art got it to work is a marvel still. I'm bloody glad he put his talent into that rather than hacking nuclear missiles, I mean hacking missiles would be easy for him!

Craig

6597

General Mach Discussion / Re: Z Depth ??'s

« on: September 22, 2017, 06:32:12 AM »

Hi,
what direction have you got your Z axis set for.

I follow the usual standard where Z=0 is the top of the material z=-1 is 1mm below the surface and Z=-10 is a humungous 10mm cut and it had better be soft
or something is going to break and Z=20 is 20mm above the material and out of harms way.

Craig

6598

General Mach Discussion / Re: Interference with axis motors

« on: September 22, 2017, 06:20:29 AM »

Hi Roger,
that's what intrigues me about Mavericks system, he posted a listing for his board, a parallel port BOB but hes plugging into a Windows 10
machine. I'm convinced that the PCI card he has installed is rather more than a PCI to DB25 card but I'd luv to find out!

Craig

6599

General Mach Discussion / Re: Interference with axis motors

« on: September 22, 2017, 06:15:45 AM »

Hi Roger,
sure Windows 10 can run a parallel port to drive a printer, that's easy, what Windows 10 doesn't allow is the code necessary to produce accurate pulse
streams required by a control system. The DB25 socket is just a convenient way to simultaneously signal a bunch of devices, generating all those signals
in the first place is the trick.

Craig

6600

FAQs / Re: How can I control ac servo motors using mach3? help!!

« on: September 22, 2017, 06:08:03 AM »

Hi,
Mach is a program that interprets Gcode and plans a trajectory. The trajectory is a sequence of numbers that describe a position and velocity over time,
called PVT for short.

A motion controller has a table of all the PVT data and its job is to calculate the pulses necessary to make the motors follow the PVT data.

In the early days this task was done right on the PC by its own CPU. X86 CPUs are not especially good at generating pulse streams, they don't have
sophisticated hardware timers like industrial controllers and FPGAs. Also the CPU has to make these really accurately timed pulses AND run Windows,
Mach and all of the other stuff. Machs Pulse Engine or Port Driver almost had to shoulder Windows out of the way to do it. It was a very clever piece of
code and is still used by lots of people and called the 'parallel port'. It does use the old style printer port that's true but the real smart stuff is the code that
generates the pulse streams. The parallel port is an example of a motion controller, ie 'a device that can generate accurate pulse streams'.

The original parallel port is not without its problems, its fairly slow, its timing is subject to some jitter, it can stop altogether if some other software is running
that competes with it and it can ONLY be run on 32bit operating systems. For this reason a number of companies have made external motion controllers
which use an FPGA or DSP ICs to generate pulse streams. They tend to be faster and more accurate. They are now pretty well known and work really well
on 32 and 64 bit systems but of course you have to buy one, the cheapest are about $100 and the dearest can be up to $2000. Plenty of good ones for
around $200.

The combination of Mach and a motion controller, whether the controller is part of the PC or a separate board hooked up by USB or Ethernet, produce
step and direction pulses to the motor drivers. The motors can be steppers or if you can afford them AC servos, as far as Mach goes it doesn't care which.

Craig