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.

1) Do I need a PLC ?

No, personally I would but its not needed

2) Do I just you Z-axis coordinates to make this happen, or do I incorporate the switches (which may be safer?)

I would use the switches for the safety
 

3) How will it keep track of what tool it is on and will it know after a power down and power up?

Mach will keep note of tool number if "Tool Selections Persistent" are chosen on General Config page

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?

Yes you will need to write a M6 macro whether you have a PLC or just have the inputs via the parallel port but the macro would likely be simpler with a PLC.


Nice looking mill.
Hood

I don't think a PLC is needed. Its only a few switches and the PP is great for that. The logic is in the macro. The way you attack a problem like this is think how you would instruct a 3 year old to complete the task. Break it all down in its simplest form on what is done to make it work. Don't forget how you know what tool is the first one on startup. I can help you with the code at that point and I am sure other will chime in as well.

I would use a PLC as it probably had one originally. It can contain the changer logic AND the tool table. Your macro or plugin can then just handle the simple side. Load tools into the table and Initiate the Change based on requested tool  then restart the program when the Change is complete .

IF you contact Peter Holmann he uses his MODIO (Modbus) and creates a special hardcode for the modio to drive  TC's and talk to MACH.

Just a thought, (;-) TP

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.

You can do it all with simple io and macros.  Take a look a this thread.

http://www.machsupport.com/forum/index.php/topic,13365.msg106327.html#msg106327

JH