Messages

1311

General Mach Discussion / Re: Please help

« on: December 19, 2020, 11:32:59 PM »

Hi,
Mach's parallel port will only run on 32 bit Windows 7 and earlier PC's. So yes, get another XP PC if you can find one.

Mach will run quite happily on a Windows 10 or any 64 bit OS but you MUST use an external motion controller.

There are plenty of them, one of the most popular is a UC100. It is USB connected to the PC and has a familiar DB25
plug output. You might say it is a USB to parallel converter but that is doing it an injustice, inside it has an FPGA and is way WAY
too smart to be called a converter, its a genuine external motion controller. They are about $120. Don't buy a cheap (Chinese
knock-off) one off EBay or Amazon, get the real deal or don't bother.

While USB works its prone to problems, Ethernet connected external controllers work better. Additionally the UC100 has one parallel
port equivalent output, ie 17inputs and outputs. If you go with an Ethernet connected controller like an Ethernet SmoothStepper it
has 51 IOs, a 57cnc has 57 IOs or a UC300 has 85 IOs. So you can have alot more IO if you wish.

I use and like an Ethernet SmoothStepper by Warp9TD at $180. It has a mach3 AND a Mach4 plugin so you can upgrade to Mach4 if you wish.
I have used Mach4 for six years now and its streets ahead of Mach3 in my opinion.

Craig

1312

General Mach Discussion / Re: mach 4 learning the machine drive ratios

« on: December 19, 2020, 04:08:07 PM »

Hi,
a braked servo has an electromagnetic brake that comes on when its depowered.

With a normal servo when its depowered the armature may turn with only modest amounts of torque to overcome
friction and bearing drag. With such a servo if and when the Z axis is depowered gravity will act on the axis and potentially
the ballscrew will turn and the axis will sag.  With a brake however, when the servo is depowered the brake comes on to prevent
unintentional movement.

The brake could also be used to lock an axis say. If you drive a servo to a given position the servo drive will use its available power
and control to hold its position. There will always be a small amount of deflection about the controlled position however. It may be
that an electromagnetic brake is better in that circumstance.

I am not planning to use the brake it that manner....but who knows...things may change. My intention is to use the braked servo
on the Z axis so that on intentional, or otherwise, de-power the Z axis does not sag into the work zone. The spindles (two)
I have and use on my existing mini-mill will be used on my newbuild mill and they are light enough that I do not expect the Z axis
to sag under their weight.

I do, at a future time, plan to build a third spindle based on a largish AC servo of 2.7kW at torques of 14Nm. That servo and associated spindle,
which I envisage will be ATC, would be heavy enough that Z axis sag would be an issue. I decided therefore to bite the bullet and buy
a suitably equipped servo for that future plan.

I paid  $460 (excl shipping) for a 750W un-braked servo kit (servo, drive and cables) and the braked one cost $600....so you pay a premium for them.

In the case of my 750W Delta servo, and I imagine other brands would be similar, the brake is 24V at 250mA. So I need an auxiliary
power supply of 24V for the purpose. The brake is switched on or off by a electronic switch within the drive and that switch is in turn controlled
by the motion controller. There are a number of programmable parameters that govern how and when the brake operates within the drive,
but the typical brake-on and brake-off delays are 20ms.

Craig

1313

General Mach Discussion / Re: Multiple MPG encoders MACH3

« on: December 19, 2020, 02:56:43 PM »

Hi,
I thought you would have to have four wires/inputs for an MPG....

A+,A- and B+,B- ..........they are after all, quadrature devices.

Craig

1314

General Mach Discussion / Re: Can't move zeroes to DRO for Machine Coordinates ( MACH3 )

« on: December 19, 2020, 02:50:52 PM »

Hi,
the only way to zero machine coordinates is to reference (home) your machine.

You can change and/or set work coordinates at will but not machine coordinates.

Note that if you do not have home switches installed and assigned a machine will 'HomeInPlace', that is when you
hit <RefAll> Mach will assume that its current axis (axes) position is in the Home position and zero (or set to the
axis offset if programmed) where it is. If however you have a home switch assigned the machine will drive that
axis until the home switch activates and then zero (or set to the axis offset if programmed) the machine coordinates
of that axis.

Craig

1315

Mach4 Plugins / Re: Mach4 plus Ethernet SmoothStepper with encoder or linear scale.

« on: December 18, 2020, 09:11:41 PM »

Hi,
yes, that is indeed possible with LinuxCNC because the Linux distro on which it runs has realtime extensions, and can therefore be a realtime controller.
The Windows OS precludes realtime operation and all Windows CNC solutions must be buffered (hence not be realtime). To get closed loop performance
with a Windows OS machine requires an external hardware controller, like a Hicon or CSMIO/A, to provide the realtime processing loop.

There is another exotic solution for deterministic realtime on a Windows PC....but is rather getting away from the point. If you are interested you will
find some great videos by IntervalZero  about it. It is by use of the this solution that Mach4 is able to run Ethercat, which is by definition a deterministic
realtime communication protocol. A very worthy and interesting development in Mach4 and available from Automation Solutions, a complete CNC system
without need of a motion controller or BoB.

Just as a side note Linux with RTE (RealTimeExtensions) on most PC hardware has a runtime jitter of about 4us, pretty respectable but it is not deterministic,
also called 'hard realtime'. By this I mean that while on average the jitter is 4us the system cannot guarantee it.There is an industrial standard which requires
absolute determinism and the system MUST be able to respond within a certain time frame. This standard is often applied to safety systems, medical equipment,
automotive and areospace systems. Linux with RTE does not (quite!) satisfy that standard.

Craig

1316

Mach4 Plugins / Re: Mach4 plus Ethernet SmoothStepper with encoder or linear scale.

« on: December 18, 2020, 07:10:57 PM »

Hi,

Identical? Ahhh, not quite. Closed loop motor position is being read prior to the drivetrain, (and most significantly before any slop that drivetrain contains, couplers, ball nut, thrust bearings, wear) unlike linear scale position which is being determined after the drivetrain

Quite correct, however you need a controller that can close the loop about a linear scale and that is not possible with an ESS. As has been pointed out Hicon
and CSMIO/A can do so....at greatly added cost and complexity.

There are two other alternatives:
1) Use a better quality preloaded ballscrew which reduces backlash to zero and lost motion to nearly zero....or
2) Use a load sensing servo drive, for example A2 series Delta servos.

To explain this last option somewhat better: all AC servos absolutely require a close coupled rotary encoder on the servo shaft so the 'Field Oriented Control'
algorithm can work. Any effective 'slop' in the rotary feedback will cause major and unsurmountable instability with the Field Oriented Control loop.

Thus, and for example, the Delta B2 series has a 160,000 cpr encoder built into the servo and that connects directly to the servo drive and it uses it to close
the Field Oriented Control loop and incidentally the load position via the angle-to-linear drivetrain. There is no opportunity to close the loop about a linear scale say.
The A2 series however can. It has a second encoder input and the position loop is closed on that encoder, which could be a linear scale.
The A2's built in encoder ( 1,280,000 cpr) is still required and used for the Field Oriented Control loop. You get the best of both worlds. The A2 series servos are about an
extra $50 by comparison to the B2 series.

This idea of a 'load sensing' encoder channel is not new nor is it restricted to Delta, almost all of the top end manufacturers offer the same or similar thing.
Neither is the secondary load sensing encoder limited to a linear scale. You could use an LDVT or even an interferometric sensor. Both of these devices are used to
'fine' control semiconductor processing equipment which has accuracy demands in the nanometer range.

For my new build mill I elected the first alternative, that is high quality preloaded ballscrews. They a re C5 ground, double nut screws by THK. I estimate that any
inaccuracy or lost motion will be smaller than my machine resolution. Such screws are not cheap, but then neither is the premium you pay for load sensing
servo drives and the linear encoders necessary to drive them.

Craig

1317

General Mach Discussion / Re: mach 4 learning the machine drive ratios

« on: December 18, 2020, 06:43:44 PM »

Hi,
my 750W Delta B2 series are 80mm across the flange and 19mm shaft with keyway and seal.

I think you are right to go with servos despite the initial cost. If you get good quality and capable units they will give
twenty years untroubled service and even hold resale value whereas underperforming units will not.


Craig

1318

General Mach Discussion / Re: mach 4 learning the machine drive ratios

« on: December 18, 2020, 04:16:48 AM »

Hi,
not sure what to make of the quill, I don't know how it works and the forces involved. The X and Y axes are a little more straight forward.

Lets assume that you wish to get close to the performance that I posted earlier, ie 10m/min rapids and 0.5g.

If the ballscrews have a pitch of 6mm, per your previous post, then to achieve 10m/min the ballscrews must rotate at
10,000/6 =1666 rpm.

There is your first hurdle, steppers lose torque badly with speed, and only very few of them can maintain any useful torque above 1000rpm.
You could use an increasing gear reduction but that would require even more torque from the steppers, I suspect its unlikely to happen.

Per my previously posted calculation you can get about 0.2g with 1Nm, so to get 0.5g will require 0.5/0.2= 2.5Nm. Note also that this makes no allowance
for friction nor ballscrew efficiency, so I would suggest that around 2.5Nm should be considered the minimum torque. Note that this torque is required
at top speed.

A very low inductance (1mH) stepper may retain 40-50% of its torque at 1000 rpm, which would suggest that the stepper needs at least 5-6Nm at low
speed. Steppers that have that sort of torque and low (sub 2mH) inductance are rear beasts. A more normal 34size stepper may well have adequate torque
at low speed but 34 size steppers have inductances of 4mH and more. Such a stepper is going to run out of 'puff' at 500-750rpm.

Side note: 1Nm= 130oz.in
                2.5Nm=325oz.in
                5Nm=650oz.in

All in all I think steppers may well provide enough torque at low speed but I suspect that they will fail to satisfy at speed. High speed operation
is always steppers Achilles Heel.
I think 34 size steppers of around 800oz.in and 4mh (or less is preferred) would work OK, but maybe fail to get to 10m/min, but more likely 5m/min.

The other alternative is servos. Servos come in a wide variety of specs, but the readily available brands likely to be affordable for hobbyists are:
200W 3000rpm =0.65Nm cont, 1.9Nm peak
400W 3000rpm = 1.27Nm cont, 3.81Nm peak
750W 3000rpm = 2.4Nm cont, 7.2Nm peak

If you used any of these three servos with a 2:1 reduction then you would get very close to your desired 10m/min rapids.

The 200W servo would, after the 2:1 reduction, have barely enough torque without dipping into overload all the time.

The 400W servo would after the 2:1 reduction would have plenty of torque, (1.27 x 2 =2.54Nm) without using overload.

The 750W servo has enough torque without reduction. Without reduction you could have rapids of 20m/min, alternately
with reduction you could still get near 10m/min but have a surfeit of torque for even higher accelerations.

So servos will certainly provide the best performance but they cost more than steppers, and steppers will do OK except
at high speed.

For my new build mill have bought three (one braked) 750W Delta B2 series servos. They cost (excluding the braked one) $460USD each, which
includes the drive and cables, plus shipping. I found that the 750w models were only $40 more than 400W ones, so I got the 750W's.

I notice that many US buyers favor Clearpath (US) over DMM (Canadian made in China) or Delta (Taiwanese made in China) but they are
more expensive, about $480USD for 350W. For various reasons, cost primary among them I went with Delta, almost twice the power for less money!

Ultimately your budget will determine what you do. I would recommend 750W servos if you can afford them.

Craig

1319

General Mach Discussion / Re: Machine Coords not zeroing...

« on: December 17, 2020, 09:03:54 PM »

Hi,

Not sure why any of that would prevent the Mach3 software from allowing me to manually zero the machine coords.

To my knowledge the only way to 'zero' the machine coordinates is to reference (home) the machine. You can manipulate the
work coordinates at will but the machine coordinates are set relative to the home switches.....period. There is no way to set them at will.

Craig

1320

General Mach Discussion / Re: mach 4 learning the machine drive ratios

« on: December 17, 2020, 01:44:17 PM »

Hi,
I'm a little confused by your terminology.

You say 'Z axis and spindle'....what exactly do you mean?. My interpretation is the the Z axis is the Knee casting/screw/dovetail ways
and the spindle is the Quill, which also goes up and down?

Usually the Knee screw is very stiff, after all it is supporting the X axis , Y axis, the saddle and the Knee casting.
The quill on the other hand is much lighter but also usually only has 4 inches or so of travel.

With deep reduction (belt or gears) you can have a small motor do a big axis but at reduced speed.

My suggestion is specify both the acceleration and max speed you want of each axis and then do the calculation to see what sort
of motor and reduction is required to achieve it. If you choose really high accelerations and speeds (for production say) then don't
be surprised that you will require large and expensive motors.

To follow a toolpath high acceleration capacity is very desirable. Consider a toolpath that changes 90 degrees, like a corner.
In order for the machine to follow it must slow down and stop in one direction and the accelerate off in the new direction. If the machine
is to do this change quickly acceleration/deceleration must be high. Production industrial machines can be a s high as 10g.
My new build mill will be 0.25 g at rated torque and 0.75g at peak torque.

Maximum speed is another question to be pondered. There are two aspects, the first is the rapid or traverse speed. When traversing there is no cutting
forces and so all of the available motor torque is used to accelerate and maintain a given maximum axis speed. In industrial machines its common
to see traverse speeds of 30m/min and production machines up to 100m/min. My own new build mill will be 15m/min and with field weakening
(a  technique for exceeding rated servo speed) 25m/min.

The other speed aspect is maximum machining speed. Now the available motor torque has to accelerate and maintain axis speed AND supply cutting thrust.
Its not uncommon to see industrial machines with speeds of 40m/min traverse and 20m/min cutting say.

I would suggest for a hobbyist machine you aim for accelerations in the order 0.2g to 1 g and speeds of 10m/min rapid and 5m/min cutting.
Note that your machine has the mass and rigidity to go faster.....but do you have the budget to do it??

Craig