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Messages - jevs

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311
Having 1 or 3 or 6 inputs will make no difference, when a limit is seen Mach will E-Stop. Really though you are still relying on software and if there is a possibility of damage being done if the software malfunctions and the axis hits the end of the screws then you should really have hardware limits, in other words these limits at the very least take the drives enable away.

 I have two largish machines, a 2Tonne (4400lbs) mill and 3Tonne (6600Lbs) Lathe and I just have the limits wired to Mach in a single input That was the way the limits were wired on the previous controls on my machnes (Heidenhain 145 and GE 1050) but also there are hard stops (metal blocks) and large ballscrews so the drives would trip with over current before damage was done if  the software didnt act properly.

E-Stop however is another matter, you should never rely solely on a signal to the software to E-Stop, I have a signal from E-Stop button going to Mach but also the second contact on the E-Stop cuts the E-Stop string on all contactors and drops out the power to the drives etc.



Hood

My machine also has some large blocks that would bang stop the machine on the X and Y if it did get past the limit switches. The Z axis would just bottom or top out and be metal on metal as well. It is captured so it could not go farther.

As for my E-stop, the limit switches will kill the drives, through the I/O board, but if you hit the actual E-stop button, it will kick off the 50 amp contactor and kill power to all drives and the VFD. So, that is about as safe as I know to do it and what machmotion recommends.

312
Attached is the schematic I have drawn up for my machine. As you can see I have it drawn with just the limit switches going to the I/O board (Machmotion).

I was thinking to do it this way and just forget about the homeing switches on the X and Y. What do you think?

As you can see at the bottom left, those are all the switches currently not designated to go anywhere. Can I use more than 3 inputs? If so which other switches will I need to get my tool changer working?

I am not sure that I like having all the limit switches on one input, is this a normal practice? According to the Mach3 directions and Machmotions directions for their I/O board I should hook all three axis seperatly. This machine is 4500 pounds and there is a lot of mass moving around on that bed mill (not sure this makes a difference). Mach gives different instructions based on the size and speed of the machine.  In part 4.6 of the manual.

313
General Mach Discussion / Best way to wire my home and limit switches?
« on: January 16, 2011, 07:20:19 PM »
My machine has a limit switch on the X and Y axis that is hit by a dog at each end of the table. There is also what I guess is a home switch that is slightly in from one of the limit dogs.
Should I uses the home switches at all? This is a VMC bed mill with tool changer.

My Z-axis is a whole other issue. There are two switches in series for the Z limits, but the top one is after the tool changing operation. The Z axis also has a home switch that designates the top of the "machining area". Above this tool changing occurs.
So, how should I wire this? Should I just rely on Mach 3 and a soft home limit for this home position, or try to use the switch somehow?

There are also 2 other switches above the home position and before the top limit switch as follows:
-A N/O switch that gets closed anytime the Z axis goes above the home and into the tool change area.
-An N/C switch that opens when the Z has gone up far enought to change the tool.

Here is a visualization of what occurs on the Z axis.
--- Over travel limit switch
|
--- Tool Change Zero switch (should never really go past this)
|
| Rotate To next tool
|                              Tool change occurs in this zone of z-axis movement
| Drop Turret          
|                                
| Release draw bar
|
--- Tool change area switch is closed above this and stay closed until it comes back down past
--- Home limit switch
|
|
|
|
| Machining area of Z axis
|
|
|
|
---Over travel limit switch

I realize I am going to have to do some sort of macro for the tool change, but how should I wire this and which switches should I actually use? There are a couple risks. One is that you don't want the spindle motor to be on during the tool change area. Also, I am not positive yet, but damage may occur to the tool change rod that rotates the the turret if you go past the tool change zero switch.

I am drawing the schematics for the machine now, and the last thing I need to figure out is the wiring of all these switches.

See attachment for a visualization of the switches. You can also read my post on determining if I needed a PLC or not here:

http://www.machsupport.com/forum/index.php/topic,17091.0.html

I have determined that a macro should do, but I  don't know how to do it yet. Right now I just want to get it wired correctly.

Thanks

314
General Mach Discussion / Re: Tool changer questions
« on: January 08, 2011, 11:09:40 PM »
Seems like there are conflicting opinions on the need for a PLC. This machine is from 1978, it had a bunch of giant propriatary Fanuc boards in it, not really a PLC like we see now. The programs were loaded from a roll of paper :) Keep in mind the whole tool change happens on it's own just by the z axis going up and coming back down. I assume the switches did nothing more than tell the old controls where the z-axis was positioned and what it should or shouldnt be doing at that time? I am sure it had to make sure the spindle was off during the tool change etc. For whatever reason the position of the Z axis alone was not used. Maybe it wasn't smart enough, or maybe once it got to the home switch it didnt even use the encoder and just used the switches to do it's thing? I do know that the switch dogs are adjustable, s maybe you had to time it by sliding the dogs to the exact spot. These adjustments and lack of technology may be why the Z axis position couldn't really be relied on. Maybe it had to be timed to each machine rather than a set coordinate or something. If you make a mechanical adjustment or something wears, maybe it won't "hit" exactly right? Or, maybe they are just in there for safety if it lost position data or something. I would think you could easily just time it all up electronically by position, but is this safe and would it be off as things wear? The only safety concerns seem to be that the spindle motor is off when it's trying to tool change and that it does not go up too far when it's rotating the turret. If you go to far it can damage the rod that rotates the turret, so I think that "tool change zero" limit switch was important.
 
Think of the Z axis like this as far as what occurs:

--- Over travel limit switch
|
--- Tool Change Zero switch (should never really go past this)
|
| Rotate To next tool
|                              Tool change occurs in this zone of z-axis movement
| Drop Turret             There is a long dog that keeps a limit switch on
|                               as shown in the pictures in my first post
| Release draw bar
|
--- Home limit switch
|
|
|
|
| Machining area of Z axis
|
|
|
|
---Over travel limit switch


"As for the tool #, you can add a User DRO to the screen to keep track of the tool, and Mach3 will remember it when you shut it down and restart it."

This is good, I was hoping it would.

"I'd spens a little time getting familiar with macro's, then ask more specific questions on the Mach Yahoo group.[/QUOTE]

I will, I have not been sleeping this week as it is just trying to figure out what components to buy all over again. There are a couple used PLC's I found and that is why I need to know if I am going to even need one.

315
General Mach Discussion / Tool changer questions
« on: January 08, 2011, 04:56:48 PM »
I am retrofitting a Pratt & Whitney Tapemate C with a 7 tool tool changer. I am trying to determing if I need a PLC or if Mach 3 can do this without one. The changer is purely mechanical and does it by moving the Z axis up past the home switch (machining area) where a few things happen mechanically. Once the Z axis gets passed the home switch, there is then another long dog that hits another switch to tell the old controls that it is in the tool changing area. As this goes through this area, an arbor release hits on a cam and release the ball on the end of the BT-30 tool. Next there is a stationary rod that catches on what we call the turret assembly. This assembly is on a slide attached to the z-axis. When the stationary rod hits this portion, then the z-axis continues to travel up while the turret stays put. This basically pulls the tooling out of the arbor and clears it for rotation. After this is clear, then there is a rod that catches and pulls the turret assembly making it rotate one tool position. At the point that the rotation is complete another dog hits a micro switch that signifies to the machine that it is at the zero point of the tool change. At this point the machine would reverse the z-axis travel and the tool/turret would go back up into the arbor, and then the arm at the top would release tension and trap the BT 30 Tool and pull it tight in the arbor. The machine would continue down and then the tool change long dog would realease the micro switch and it would know the tool change operation is done. Then it would continue down until it hit the Z axis home position switch. Then it is ready to go with that tool.

So, basically there are 5 roller tipped micro switches and dogs that can make contact during a full travel of the Z axis.
2 of them are over travel limit switches. One at the bottom of the machining area and one if the machine should happen to get past the "zero point of tool change" dog.
1 is the z axis home position for the machining area of the z axis
1 is activated while the machine is in the tool changing area north of the home switch
1 is the zero point of the tool change telling the machine to reverse and come back down.

So, this is all done just by moving the z axis with some switches to let the old controls know where it's at. The dogs are adjustable as well as rod position on the turret assembly so you could fine tune the operation on the old controls.

My questions are as follows:
1) Do I need a PLC ?
2) Do I just you Z-axis coordinates to make this happen, or do I incorporate the switches (which may be safer?)
3) How will it keep track of what tool it is on and will it know after a power down and power up?
4) Can Mach take inputs from the switches and do anything with it, or will this be where I need a PLC to handle things?
5) I have not used Mach 3 yet and this is my first retrofit. I also have not had a CNC Machine before this one although I do have a manual mill and lathe.

This all may make no sense as it is hard to verbalize, so please ask questions. It is actually a very simple tool changer.

Here are pictures to help visualize all of this:
http://img831.imageshack.us/img831/6035/img0645o.jpg
http://img440.imageshack.us/img440/5930/img2668b.jpg
http://img291.imageshack.us/img291/6362/img2669f.jpg
http://img545.imageshack.us/img545/3009/img2674p.jpg
http://img146.imageshack.us/img146/4060/toolchangeoperation.jpg
http://img255.imageshack.us/img255/7342/zaxisdogs.jpg

Extra Info not related to tool changer that you may like to know:
This machine was never used in production, it came out of Kansas University and they used it for training programming, so it is in very nice shape as you can see.
I am going to use AC servo motors and drives from Machmotion and their breakout board etc. to make everything easy.
I am using a VFD on the spindle motor.
I was going to use the stock Fanuc DC servo motors, Rutex drives, Bob Campell breakout board, Bob Campell spindle motor controller, A custom wound transformer with an input of 220 VAC single phase and outputs of 80VAC and 40VAC going into rectifiers and large caps (Z axis has different motor specs than the X,Y) and a +/-5VDC +/-12VDC 24VDC power supply. I actually already have all this stuff mounted in the machine, but due to ease of making this project quick I am just going to go with the new proven Machmotion stuff to make my life easier. This will make it easier to single source support if I run into any issues. They are also only 50 miles from me if I should need something ASAP in the future. All of these other parts will be for sale if your interested.

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