Messages

2661

Mach4 General Discussion / Re: probe error : no contact with probe

« on: April 13, 2019, 10:32:44 AM »

Hi,
now I am confused, at the start of the thread you said you are using a parallel port and now you are talking ESS.

What motion controller are you using?
Have you tried the manual procedure I have suggested?

Craig

2662

Mach4 General Discussion / Re: probe error : no contact with probe

« on: April 13, 2019, 07:58:39 AM »

Hi,
did it work when you MDI'd a g31?

Craig

2663

Mach4 General Discussion / Re: Connecting a VFD to Mach4 through Modbus (RS485)

« on: April 13, 2019, 01:30:43 AM »

Hi,
I cant find any specification from any manufacturer about the rotational inertia of the rotor of a 2.2kW asynchronous
spindle.

Rotational inertia is a specified parameter in servos and so I will use the servo data for a 2kW AC servo from Delta.
Its specified rotational inertia is:

0.00149 kg.m²  (more correctly called 'the first moment of inertia', usually given the symbol 'I')

Lets assume that if you had a direct coupled tool holder and smallish endmill that the rotational inertia would be approx:

0.002 kg.m².

The kinetic energy of the rotor/toolholder/ tool combination  at 3000 rpm is:
E(joules)=0.5 x I (kg.m²). w² (rad/sec) (note w is  the rotational speed in radians/second)
E=0.5 x 0.002 x (2 xPI x3000/60)²
E=98.7 joules

If the spindle were required to decelerate very quickly this kinetic energy would be fed back into the drive. In absence
of any braking resistance that energy would be added to the DC link capacitors. The voltage rise that would cause is:

E(Joules)= 0.5 X C (Farads, the capacitance of the link capacitors) x V_rise²

Rearranging and evaluating:

V_rise= (2 X 98.7/ 10000uF )^1/2
V_rise=140.5V
Note for the purposes of this calculation I have assumed 10,000uF DC link capacitors, as is common in single phase
servo drives and VFDs.

Thus your DC links capacitors (on a 230V single phase driver) are normally charged to 320VDC, and because of the sudden
deceleration of the rotating component cause a voltage rise of 140.5V to a total of 460VDC. Note that the vast majority of
DC link capacitors, all aluminum electrolytic types, are rated to 450V. Thus your DC link capacitors are on the verge of blowing
up. This is exactly why braking resistors are required, to dissipate the kinetic energy WITHOUT the DC link capacitors
going over voltage.

My servo drive has a  braking resistor threshold of 340VDC and a safety threshold of 380VDC. Thus if the voltage increased to
340VDC the braking resistor MOSFET is switched on and the braking resistor is now directly across the DC link. If the
voltage further increases, ie the braking resistor does not 'hold the voltage  down' to 380VDC the servo drive faults
'over voltage' and switches off allowing the servo to coast to a stop.

If the deceleration is a matter of safety, ie the operator of the machine hit the Estop, we want the spindle to slow as quickly
as possible. If however you program a 'crash' stop the servo drive and braking resistor combination may not handle it and
shut down, allowing the servo to coast. This would be very bad design. In trying to decelerate we have caused the drive
to fault and therefore achieve a much lower deceleration than might have been possible had we allowed for the limited ability
of the driver/ resistor to absorb the energy.

Craig

2664

Mach4 General Discussion / Re: probe error : no contact with probe

« on: April 12, 2019, 09:55:00 PM »

Hi,
OP has previously established (reply #2) that the probe LED operates as expected ie the BoB is correctly signaling
Mach.

Craig

2665

Mach4 General Discussion / Re: probe error : no contact with probe

« on: April 12, 2019, 09:03:42 PM »

Hi,
before you commit to the expense of a controller.....

A g31 move is a special example of an ordinary g1 move. For example:
g31 z-5 f100
means 'move from the current z location to z=-5mm at a rate of 100 mm/min. It moves as if it were a g1 move.
Where it differs is that if the motion device detects a probe event while the move is in progress the machine stops,
aborts (clears) the remainder of the motion buffer and reports its X,Y,Z coordinates to Mach.

Firstly note that the Z axis coordinate is in 'work coordinates' not 'machine coordinates'. Lets say for example that the
current work coordinate is -10mm. When Mach encounters the g31 command above it will move upwards form its current
z=-10mm to z=-5mm and it wont encounter a probe event while doing so.

The point being that if the work coordinate system is out of kilter with the work surface (or touch off surface) unexpected
results can occur. Given that you don't have home switches it would be easy to have the work coordinates out of kiliter
along the lines I have suggested or some other combination that produces unexpected and failing results.

May I suggest homing your machine as normal. Jog to the touch off plate and lower until your probe is just or nearly
touching the plate. Then zero the work coordinates using the DRO buttons. Jog the machine upwards a mm or two.
Now try an MDI of:
g31 z-10 f100 (metric)
g31 z-.5 f4    (inch....bloody queer Yankees)
and see what happens.

Craig

2666

Mach4 General Discussion / Re: Is a short blocking delay in PLC script acceptable?

« on: April 12, 2019, 08:08:18 PM »

Hi,
yes it is a boon if you manage to break Mach4 as I did. The PLC script is a bit of a trap, its easy to end up with infinite
loops and therefore you cannot access the screen editor to repair it.

Before Daz told me about the command line switch I had to reload Mach4 from scratch. I was, and still am, unfamiliar with
profile.xml

I've only had to use the command line switch a couple of times so I just ran through the process to be sure I had it straight.

1) Close Mach4, using WindowsTaskManager if necessary to ensure all elements of Mach4 are closed
2) Open a Command window
3) Change directories to C:\Mach4Hobby (or wherever you have put the root Mach4 directory)
4) type Mach4GUI.exe/e <enter>
5) Select your profile <enter>

Mach4 will now open your profile but in screen edit mode, thus you can remove faulty code.

Craig

2667

Mach4 General Discussion / Re: probe error : no contact with probe

« on: April 12, 2019, 05:31:41 PM »

Hi,
Mach4 was always intended to be paired with an external controller. Having said that I am surprised that you can't get
the Darwin parallel port to probe correctly. I may miss on some of the realtime functions like THC but it does do probing.

Craig

2668

Mach4 General Discussion / Re: Is a short blocking delay in PLC script acceptable?

« on: April 12, 2019, 03:19:31 PM »

Hi,
its not that big a problem if you know that trick.

The first time I did it I was creating some code in the PLC script and used a wxMessageBox() as a diagnostic.
As you know each time a message box comes up you have to dismiss it. Then within milliseconds the PLC script
runs again.....another message box, ie a infinite loop of message boxes which can't be halted to allow you to get
to the screen editor a remove the offending code.

Daz-the-Gaz told me about the command line switch. I had to use it a couple of times.

Craig

2669

General Mach Discussion / Re: My Y axis doesn't retract far enough off the limit to continue to my next axis.

« on: April 12, 2019, 01:37:51 PM »

Hi,
the ESS (if genuine) is a very much better board. What was it that you had trouble with?

Craig

2670

FAQs / Re: Getting Started With Mach 3

« on: April 12, 2019, 01:04:32 AM »

Hi,

suggest you get CNC Programming Handbook by Peter Smid

Its a very dry read but very thorough, over 500 pages. It is THE REFERENCE.

Craig