Messages

1971

General Mach Discussion / Re: Servio motor Delta adas b2 Software and electronic gear ratio

« on: October 29, 2019, 02:36:03 PM »

Hi,

I will study it a bit later however why only 5000cpr are required (seems low) ?

If the effective cpr is 5000 and the distance traveled is 5mm ( the pitch of the screw) in one revolution:

resolution=5/5000
              =0.001 mm
              =1um

As I posted earlier 1um resolution is entirely adequate. I could have much more resolution but why?

Does delta encoder have any some special encoding (X4?).

Yes, in fact the B2 series encoder has 40,000 lines which (x4) means 160,000cpr. The numerator and denominator
of the electronic gear ratio are based on 160,000. No need to confuse yourself with lines vs counts per rev.

You can program the drive to output a simulated encoder of anywhere from 4 lines to 40,000 lines should you require an
encoder output stream, that does not affect the basic encoder built into the servo nor the numerator/denominator
of the gear ratio.

Lets imagine that you wanted the max resolution that the servo can achieve, in this case 160,000 cpr or
8.1 arc sec (31nm if direct coupled to a 5mm pitch screw) then at 3000 rpm the required step rate would be:

step rate=160,000 x 3000
             =480 MHz
That is well in excess of the step rate of the ESS and you could never signal a servo drive down a cable at that
frequency anyway.

Note that the B2 series  Delta servos can be signaled at 4Mhz in its highspeed differential mode. But still the question
is why bother? I have used my existing mini-mill for years with a 1um resolution and never had need for finer resolution
so why do I require more with this new mill......I don't. That decision has made the design of the signaling that much simpler.

I am not familiar with Argon but Yaskawa is of course justifiably famous.......and about twice to three times the price and quite
frankly, they are not anything like two to three times as good.

There is only one instance that I would consider Yaskawa an that is if I required Ethercat, Yaskawa has a market leading position
in Ethercat capable servos. Mach4 at this time is natively step/direction. There is a current development by Kingstar/Interval Zero
that has made Mach4 Ethercat capable but it is not yet mainstream. I have, at this time, no need to step up to Ethercat so
why bother with (expensive) Yaskawa servos?

Craig

1972

General Mach Discussion / Re: Servio motor Delta adas b2 Software and electronic gear ratio

« on: October 29, 2019, 08:57:13 AM »

Hi,

my math:
32mm ball screw diameter / 1um of CNC machine accuracy = 32,000 ppr,
encoder resolution = 32,000 * 4 = 128,000 cpr (below delta encoder spec)

No, not quite.....the diameter of the screw is 32mm, the pitch is 5mm per rev. Thus for a resolution of 1um
I require an effective pulse rate of 5000 cpr, the numerator/denominator could be:

160,000=5000 x N/D
so N/D =32

Thus the choice of N and D is very wide, for instance if D=1 then N=32 OR
D=10 then N=320 OR
D=25 then N=800 and so on.

At 3000 rpm (50 rev per sec) the pulse rate is:
pulse rate=50 x 5000
              =250kHz.

As you point out the ESS has a max rate of 4Mhz, so at 250kHz its cruising. 250kHz is a little faster than the max recommended
single ended (open collector) signaling rate but very comfortably within the 'low speed' differential signaling spec of the servo
drive of 500kHz.

I have some experience with an Allen Bradley servo which I wanted to signal at 466.66kHz. Its servo drive has a recommended
max differential signal rate of 500kHz and a single ended rate of 200kHz. I can assure you that while 466.66kHz is possible
its much easier to signal at a lower rate. Thus I reduced the angular resolution to 2000 cpr (from the encoder max of 8000cpr)
and got the signaling rate down to 116.66kHz which can be done comfortably with a single ended transistor.
Note that this servo is used as a direct drive spindle which gives a resolution of 10.8 arc min ( with 2000 cpr) from a max
resolution of 2.7 arc min (with 8000 cpr). I practice even 10.8 arc min is much greater than I require. Reducing the resolution
has made the whole thing easier to do and still exceed my actual requirements.

My existing mini-mill has a linear resolution of 1um and is very adequate. Thus I am quite happy to aim for 1um resolution
in this new build. I could, given the capacity of the servo encoder, have a resolution of 0.03125um ( 31nm!!!) but at the
expense of complexity of the signaling side of the design. I struggle to even measure 1um......let alone 30nm so why
bother?

The rated speed of the 750W B2 series servos is 3000 rpm. Direct coupled to a 5mm pitch ballscrew results in a max axis
speed of 15m/min which is a marked increase from my existing mill of 1.2m/min. I have experimented with pushing the
max speed parameter out to 5000rpm, the servos max speed (cf rated of 3000rpm) and they still work a treat.
Thus I could have rapids (G0's) of 25m/min in field weakened mode  and full rated thrust for machining moves (G1's) of
15m/min while still maintaining 1um resolution and a max signaling rate of 416.66kHz, well within the 'low speed'
differential spec of the drives. As far as I'm concerned that is speed AND resolution beyond what I ever anticipated
I could achieve with a hobby machine. If I want to use the full acceleration potential of my existing mini-mill (I can
tune it to 1g accel easily enough) I have to tie the machine to the wall or the machine tries to dance all over the floor.
The practical limit for the machine is about 0.05 g without undue machine motion and still provides excellent tool path
following (at modest axis speeds).

These 750W servos offer at least a 50 fold improvement in potential over the existing stepper/reduction drives I currently
use. Thus with the X axis bed/ballscrew/rails/vice/workpiece weighing over 200kg if I tune the axis to 1g acceleration
(of which the servos are more than capable of) then I'm going to have to bolt this machine to a concrete floor just to stop
it lurching around threatening to crush any-one or any-thing in its path!

The speed, torque and resolution of these servos continues to exceed my expectations. 15 m/min G1's sounds fine on paper
but when you see the axis machining at 15m/min you realize just how much power and even how much potential damage
can be done.....its scary!! Fun scary.....but still scary.

Craig

1973

Mach4 General Discussion / Re: Probe not matching with edge finder when measuring Y

« on: October 28, 2019, 06:13:34 PM »

Hi,

I do wonder how/if backlash amount using compensation affect this?

Backlash comp is a realtime process and is handled by the motion controller not Mach4. If indeed backlash comp is screwing it up
you need to take it up with the manufacturer of the motion controller.

Craig

1974

General Mach Discussion / Re: Mach3-The machine stop in execut program

« on: October 28, 2019, 03:22:11 PM »

Hi,
Mach3 lathe Demo line limit is 50 lines, mill limit is 500 lines.

Craig

1975

General Mach Discussion / Re: Mach3-The machine stop in execut program

« on: October 28, 2019, 01:08:25 PM »

Hi,
is Mach3 licensed?. In absence of a valid license file it will run in Demo mode for 500 lines of Gcode trhen stop.

Craig

1976

Mach4 General Discussion / Re: Newbie with Mach 4 Lathe - again - Mach 4 and dial ind do not agree

« on: October 23, 2019, 07:16:28 PM »

Hi Dale,
give us some numbers and we'll calculate the steps per unit and see how close you are.

Craig

1977

General Mach Discussion / Re: Limiter switch not being detected

« on: October 22, 2019, 07:13:45 PM »

Hi,
there are lots of posts about those boards, they go by different names, Bitsensor, RnR and others depending on who is selling
them. They all have one thing in common.....no manufacturer support.

There are a number of well known, liked, even loved AND most importantly SUPPORTED motion control boards
by US and European manufacturers.

Is the time you are wasting on this board, in view of the work backlog, worth the difference between cheap Chinese and the real deal?

Craig

1978

Mach4 General Discussion / Re: Gcode

« on: October 21, 2019, 11:13:13 PM »

Hi,
that is the difference between absolute movement and incremental movement, the two different modes are called into effect by either g90 or g91.

Usually your X-Y moves on a plasma table are absolute, so the torch will move to x₁y₁, x₂y₂, x₃y₃
etc in sucession. The Gcode for that would look like this:
g90 ; Absolute mode
g1 x₁ y₁
g1 x₂ y₂
g1 x₃ y₃

If you want to move the Z axis incrementally between moves it would look like this:
g90 ; Absolute mode
g1 x₁ y₁
g91 ;Incremental mode
g1 z 0.05
g90 ;Absolute mode
g1 x₂ y₂
g1 x₃ y₃

Note that what you cant do is have one axis move incrementally while the others move absolutely, Mach is in one mode or the other. You need to switch
between modes.

As a consequence it can be problematic to use both modes within a Gcode program, it so easy to lose track of which mode you are in and call
a move g1 x5 y5, expecting the machine to go to x=5, y=5 but in fact its in incremental mode and it goes 5 to the right and 5 backwards, not what
you intended at all!

Use with caution.

Craig

1979

Mach4 General Discussion / Re: Keyboard Jogging Not Working

« on: October 20, 2019, 08:12:11 PM »

Hi,
have you enabled the keyboard plugin?
Have you enabled keyboard jogging?

Craig

1980

Mach4 General Discussion / Re: How do you know what probe "Overshoot amount" should be?

« on: October 20, 2019, 08:10:35 PM »

Hi,

Oh, to throw another wrench in this. My Z axis has a brake on it that is controlled by the servo drive.

I would not expect the brake to come on UNLESS the servo is disabled. Even then, its common for the brake to take 10ms or so to come
on and so unless you have long  deceleration times programmed into your machine then it will have decelerated and stopped
BEFORE the brake has come on.

If you probe sufficently slowly relative to the machine acceleration overrun should be vanishingly small. That overun has been included
in the calculation is for those circumstances where it is significant or for nit-picking perfectionists who demand to chase every last micrometer.

Craig