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Mike Richards
Registered
Username: Richards
Post Number: 51
Registered: 05-2006
| | Posted on Thursday, November 09, 2006 - 11:34 am: | 
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Gerald,
If you connect a SPST switch to the FAULT and GND connections on J6, the outputs of the PMDX board will be OFF (high impedence) when the switch is closed (FAULT line connected to GND line). Closing the switch before changing cutters would keep the spindle from turning on unexpectedly (assuming that the PMDX board is controlling the spindle). To be truly safe, however, you would need a contactor that broke (disabled) all three of the 3-phase lines between the VFD and the spindle. Personally, I haven't studied VFD and spindle circuits enough to know what would happen if such a contactor were inserted into the circuit. At the least, the spindle would be turned off, but breaking the lines when the spindle was running could possibly fry the VFD.
You are certainly correct in stating that a VFD creates enough electrical noise to give false triggering to other devices. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 410
Registered: 11-2005
| | Posted on Thursday, November 09, 2006 - 12:01 pm: |
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Mike, another practical chap told me today: "The charge pump should be pretty foolproof. If you are getting enough noise to trigger it I think you have a pretty serious problem anyway. One thing you can try is to fit a 1K resistor between the charge pump pin on the parallel connector and +5V. This should increase the noise immunity. You shouldn't have too much trouble finding +5V on the PMDX board. Note that if the board is optically isolated you must make sure you use the 5V that is on the PC side of the optos."
And he is right, I obviously have the potential for other noise (false signal) events aside from just the charge pump safety issue, so I do have to filter the VFD more with some input filters/chokes/reactors.
For the safety side, looking at the Delta specs, the right thing is a switch/contactor on the VFD input. |
Mike Richards
Registered
Username: Richards
Post Number: 52
Registered: 05-2006
| | Posted on Thursday, November 09, 2006 - 08:47 pm: |
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Gerald,
I'm playing with my PMDX-122 a little to see if I can find a simple fix, but, right now, I can't see that simple solution.
Looking back at your earlier post, you basically stated that things work fine when the Mach software is running, but things don't work properly when either the PC is off or when the PC is on, but not running Mach software. To fix that, assuming active LOW input signals where 0V = ON and 5V = OFF, each of the INPUT lines into the PMDX board should be tied high, through a pull-up resistor (4.7K is what I normally use on a 5V system) to 5V on the PMDX board. It is important that the 5V is NOT being furnished by the PC or any other device that may be turned off when the PMDX is turned on. That simple solution would force the input lines to be OFF, which would assure that the output lines are also OFF.
The next problem to create a fail-safe ENABLE circuit. That circuit would have to receive a 0V signal from the PC to enable the board to operate (because the ENABLE input would normally be tied to 5V through the pull-up resistor mentioned above). Therefore, the work-around on the PMDX-122 board would be to solder pull-up resistors to the INPUT lines and then to add a 7404 type inverter to the FAULT line on J6. The input to the 7404 gate would be the ENABLE signal coming from the PC's parallel port. It would also be tied to 5V through a pull-up resistor, meaning that the output of the 7404 gate would be LOW, which would disable the PMDX's output lines. When the output signal went LOW on the parallel port line that was connected to the 7404's input gate, the FAULT signal would be 5V, and the PMDX's outputs would be enabled.
The drawback to this simple fix, is that one of the parallel port's output lines would have to be dedicated to control the ENABLE signal - and there are very few output lines available. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 417
Registered: 11-2005
| | Posted on Thursday, November 09, 2006 - 09:39 pm: |
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At this stage I don't plan to modify the board at all. If a board is to be recommended to other folk around the world then it should work without any mods. Right now I don't have enough experience of these boards to say which is the best one to use. It could well still be the PMDX122, which was recommended to me by other very reputable people.
The VFD induced problems will not apply to router users, so that's a large group of people who can sleep peacefully with the PMDX122
Those that are using spindles have 2 choices - filter the VFD or adopt a Mach3 always switched on procedure.
For all people, a kill-switch before changing cutters will keep all fingers attached.
But, on a broad theoretical level, can the handshaking be better, using only one port? ..... The "charge" signal of the charge pump is 12.5kHz and I presume it is a very steady frequency because that is what the Mach engine is good at doing....putting out steady, known frequencies. Can a "receiver" be put on the breakout board (or plugged onto the header pins) that recognises this pure frequency when it is present? |
Gerald_D
Registered
Username: Gerald_d
Post Number: 421
Registered: 11-2005
| | Posted on Friday, November 10, 2006 - 08:08 am: |
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Last night, Steve Stallings echoed the proposal to fit a 1k resistor, saying that if it worked then all future PMDX122's would have such a resistor. This morning I fitted a temporary resistor (on JP4, across "normal" and "OK" and it does work - the false signal is drained away. Now I have a pluggable resistor and a facilty for chasing the source of the interference.
If I can kill interference enough to go without this resistor, then the system should be clean. The resistor will go back on after the cleanup.
Thanks for all the suggestions Mike  , but I must admit that most of them were way over my head  |
Gerald_D
Registered
Username: Gerald_d
Post Number: 425
Registered: 11-2005
| | Posted on Friday, November 10, 2006 - 01:37 pm: |
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Before I disappear for a weekend away, I just want to mention that I have fitted a smallish ferrite ring (only one available today) to the VFD's input side and the fault situation is a lot better. I can nearly do without the 1k resistor on the board. Will find the right size, as suggested by the VFD supplier, and try this in due course.
Enjoy the weekend! |
fabrica
Registered
Username: Daya
Post Number: 186
Registered: 10-2006
| | Posted on Thursday, January 18, 2007 - 05:45 am: |
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Gerald, The Wiring of the control box is almost complete. Can please explain to me in simple lannguage as to how the (PMDX) breakout card and the stepper drivers are to be wired. Specially I need to know as to how the two steppers on the x axis are made to rotate in opposite directions and also as to how the two motors are to be synchronised. |
fabrica
Registered
Username: Daya
Post Number: 187
Registered: 10-2006
| | Posted on Thursday, January 18, 2007 - 05:50 am: |
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In the picture of the PMDX card I see only three wires going from the card to the drivers. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 723
Registered: 11-2005
| | Posted on Thursday, January 18, 2007 - 07:25 am: |
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The picture above is correct - there are only 3 wires each. (one place (pin 7) on the Gecko is not connected). Put the jumpers in the right places. Give power to the PMDX. To be safe, read and understand the documentation for
the PMDX and Gecko.
If you need to reverse the direction of rotation of a stepper motor, you need to reverse one coil only. The easiest way to do this is to reverse a pair of connections (swap) at the Gecko. (Only do this if the Gecko is dead, or else you might kill it). I suggest you swap pins 5 and 6.
Remember to install the correct resistor across pins 11 and 12.
The synchronising of the two x-motors is done in Mach. The name of the second X-motor in Mach is the A-axis. Look in the Mach documentation on how to "slave" the a-xis to the x-axis. On the screen you will see this:
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70. Control Systems