Messages

2381

Mach4 General Discussion / Re: Mach4 5 Axis RTCP

« on: June 24, 2019, 03:44:57 AM »

Hi,
this post should probably be on the main Mach4 Discussion board, more people will see it and respond.

how does Mach4 handle 5 axis tool specifically RTCP? (I see there is a plugin for Mach3

Not quite sure what you mean? Mach4 can have up to six axes moving in coordinated fashion, all that is required to do so
is Gcode to call all axes in use.

Displaying a tool path is a different matter. For instance a trunnion style 4th axis with an upward facing rotary axis would
produce a different looking tool path than a continuously rotating fourth axis sitting atop a rotating stage. Both are known
configurations of five axes yet have different toolpath displays.

To my knowledge Mach4 does not handle 4 and 5 axis  toolpath displays well. The best simulation you are likely to get for
the Gcode you have generated comes from the CAM simulator itself.

Craig

2382

Mach4 General Discussion / Re: Breakout board will not enable, Mach4, ESS and C11G Breakout board.

« on: June 23, 2019, 10:05:39 PM »

Hi,
I use an ESS and have no problem.

From what you have described Mach is not communicating with the ESS/breakout board combination.
In the first instance we should try to establish whether Mach can communicate with the ESS.

Do you have the ESS plugin enabled and set as the active motion controller in Mach's control plugin?. Note that if you need to change either of these
settings you will have to shut down and restart Mach for the changes to be 'cemented' in.

Craig

2383

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

« on: June 23, 2019, 09:40:15 PM »

Hi,
the general trend in CNC is for each servo/servo drive to be ever smarter.

In the early days of CNC servo drives were just amplifiers, they required a precision analogue input from the motion controller.
The controller would monitor the encoder/resolver and make adjustments to its analogue output to effect feedback control. So all the
smarts were in the controller and the servodrive was dumb.

A more recently the controller offers step/direction commands to the servo drive. The encoder is hooked NOT to the controller
but to the servodrive. The servo drive has the smarts built in to close the loop. Mach4 is natively a step/direction controller
and this is the sort of servo/ servodrive I would recommend.

The latest and greatest servodrives actually have a partial motion controller built in and they do their own motion control for its own axis.
Ethercat is an example of this. Mach still plans the trajectories and communicates to each servodrive but each servodrive does it own motion
control. This is an example of 'distributed motion control'. Mach is not 'yet' quite ready for Ethercat, but it will be. Whether you and I will be ready
any time soon is another question!

As to your current question if you use a modern servo and drive (prefered) or alternately a closed loop stepper (less advantageous but useful) you
can achieve what you want.

If your axis is coupled to a ballscrew then the rotational position MUST be directly linked to the linear position. Thus the encoder of the servodrive (or closed loop
stepper dive) performs identically to a linear scale attached to the axis and can signal a fault if the commanded position deviates from the actual position.
Given that this is monitored by the drive (realtime) then there is no issue with delays/buffering with Mach.

As an example I have a secondhand Allen Bradley servo I bought for a spindle motor. It is not new by any stretch of the imagination but is stil really really good.
It has an 8000 count per rev encoder. It has two (among many)  parameters that I can program. One called 'following error window' I can program from as low as 4 encoder counts
up to 8000 counts. The default (where I tend to leave it) is 20 counts. If the output shaft of the servo gets more that 20 counts (0.9 deg) away from where it should be
it faults. The other is called the 'zero window. Its default is 4 counts. It means that when the servo shaft is within 4 counts (0.18 deg) of its commanded position
it ceases to try to close the loop any further.

If you had such a servo hooked to your axis would that suffice? It relies on the smarts in the servodrive which as I started with is the current trend in CNC.
Using a linear encoder and a smart controller is more the way things used to be done.

Craig

2384

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

« on: June 23, 2019, 07:58:58 PM »

Hi,

Would the ESS board (on its own firmware) be able to detect a "following error"?

No. The ESS is not a feedback controller.

As I have previously explained, due to comm delays/buffering, neither is Mach4 capable of direct feedback control.

The principle function of the MPG read inputs of the ESS is to hook up handwheel. The ESS reports to Mach that the handwheel
has been operated and Mach can then issue move instructions to the ESS and thereby move the machine. There is a small
time delay, inconsequental for manual handwheel operations but inadequate for closed loop feedback.

Craig

2385

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

« on: June 23, 2019, 02:57:03 PM »

Hi,

Is Mach4 capable of detecting a "following error" and performing an emergency stop? Consider a step loss situation detected by the encoder reading.

The ESS can read the linear encoder and can transmit the result to Mach4 but with a communication delay of several or maybe tens
of milliseconds. Mach would then compare the actual position result with its 'assumed' position. Remember that Mach believes
that machine is at position A, because it has sent moves to that effect, but those moves have been buffered so the machine
may not have made those moves yet and still be some way short of position A. The concept of where Mach 'thinks' the machine
and where it actually is, is indeterminate because of the comm delay is one direction and the variance of the length of
the buffer in the other.

The problem is that Mach4, or rather the Windows PC it runs on is not a real time system. The communication delays and
the motion buffer prevent you from having a real time feedback loop.

Controllers like the Hicon can be activated (at a cost) or the CSMIO/A can be feedback controllers because all of the feedback
processing is done on board in real tume without the comm delays of reporting bac to Mach.

If you use a modern servo and servo drive it will have a 'following error' function built in. Thus if the accumulated commanded
position from Mach differs by more than so many encoder counts (programmable) it would raise a fault.

Craig

2386

Mach4 General Discussion / Re: Lathe Electronic Leadscrew / Gearbox

« on: June 22, 2019, 07:49:34 PM »

Hi,
a series of Ytube videos using a microcontroller:

https://www.youtube.com/watch?v=7QaQrqn4yeI

Craig

2387

Building or Buying a Wood routing table.. Beginnners guide.. / Re: Newbies

« on: June 22, 2019, 03:41:07 PM »

Hi,
all CAD programs have similarities. Drawing is a matter of composing geometry and then extruding, sweeping etc
to create 3D bodies.

If you wish to use CAD/CAM you'll just have to stick with it until you get the hang of it.

Craig

2388

General Mach Discussion / Re: Spindle drive specification

« on: June 21, 2019, 07:36:43 PM »

Hi,
I'd had little to do with AC servos until I bought one second hand (1.8 kW Allen Bradley) for use as a spindle
motor for my mini-mill. It has been a revelation. I have from University days been familiar with the great torque characteristics
of DC servos, but its the hugely increased range of control options that put DC servos into the shade.

Servos, either AC or DC, have superb torque density, that is they produce more torque for a given size motor than
an induction motor. They can be exceeded, but only at low speeds by large steppers. In addition they have superb
overload characteristics, they continue to work in overload until the onset of overheat whereas induction motors once they hit
their stall torque, seldom more than 50% rated, stall completely. Likewise hit the torque limit of a stepper, reducing at increasing
speed, and it stalls.

Yet another advantage of AC servos, not often used in servo drives, but extensively used in brushless spindle motors is 'field
weakening'. Its where you can enter a mode that induces the rotating magnetic field by the stator has its normal quadrature
(torque producing) component but also an anti-parallel component which in effect redues or 'weakens' the permanent magnetic
field of the rotor and thereby reduces the back EMF allowing for higher speed operation with the same power supply.

You may have  noted that high end production CNC machines will list traverse speeds say of 50m/min but max cutting speeds
of 30m/min. This is the classic means of utilizing field weakening. In the field weakened condition the servo can spin faster
albeit at reduced torque but sufficient to get great traverse speeds. When the servo reverts to its normal non-field weakened
condition it regains its full torque to produce its maximum cutting speed. Great flexibility  can be achieved with field oriented
control that is just not possible with DC servos.

Craig

2389

General Mach Discussion / Re: Spindle drive specification

« on: June 21, 2019, 07:04:39 PM »

Hi,
since this thread was started (2011) AC servos have become MUCH more common, including a good supply of second hand
units on EBay. Trying to preserve old DC motors is becoming an expensive proposition despite otherwise good performance.
AC servos offer at least as good torque characteristics and a VASTLY improved range of control modes, including indexing,
torque, velocity and position modes.

Induction motors and a VFD are pretty good, especially on a budget but a servo (AC or DC) will have torque to zero speed
for which an induction motor will overheat rapidly.

Craig

2390

Mach4 General Discussion / Re: Lathe Electronic Leadscrew / Gearbox

« on: June 21, 2019, 06:45:26 PM »

Hi,
another thought or possibility has occurred to me.

There is  a thread on the Mach3 board wherein Hood tells us that a CSMIO controller can directly interpret an MPG (encoder)
input direct to step/direction outputs.

https://www.machsupport.com/forum/index.php?topic=41252.msg270653#msg270653

I presume that if the CSMIO has that realtime ability in Mach3 it would also work in Mach4.

In this circumstance the CSMIO plugin would take Mach4 parameters, things like jog steps and motor tuning, and program
the CSMIO as firmware and thereafter the CSMIO works autonomously. A CSMIO costs about 600 Euro.

Craig