[svenakela]

I bought this tool changer from a guy who slaughtered a VMC.


There is a vid here with the changer before he took it down.
Arboga Combimatic 640 provkör atc'n - YouTube

There is an end stop with a dampener in the TC position. The dampener is the clicking sound in the vid when the TC hits the end position. The arm bottoms the dampener and is sitting there until the change is done. On top of that the dampener pushes the arm away if no force is applied.


It has a pneumatic cylinder that locks the carousel when a TC occurs, but there's nothing that holds the arm itself. This leads me to believe that the motor that rotates the arm probably has some kind of holding current when a TC happens. Probably in the resting position too. To complicate it even further, the end stop switch (approx sensor) is triggered before the dampener even touches the arm, it is placed so it will trigger at least 20 mm before the dampener is engaging. I have an idea that the end switch tells the controller to go from moving voltage to holding voltage and the last centimetres are done with the moving energy of the arm itself.
Possible?
Either the end switch triggers a change to something like 24 V DC which will act like a brake, or it will trigger a change to 24 V AC (or similar voltage) which will keep the motor trying to rotate and pushes the arm to the end stop all the time.
I need some ideas here, before I test the motors and maybe burn them.

[Al_The_Man]

Without checking it out in person it is hard to deduce, but AC induction motors are virtually impossible to position, and then hold position, I would have thought that the pre position sensor may be used to trigger a mechanism that pins or positions the T.C. position and also releases the motor to free wheel at that point?
Just Guessing.
The motor control circuitry should shed a little more light on the subject, also if you can obtain the machine model it came from, you may be able to source prints?
Al.

[svenakela]

Nope, there is no such thing as a locking mechanism. There is only the motor, and according to the previous owner it held it's position rock steady in both ends.
The VMC it came from is totally slaughtered down to the bone. This tool changer, the servo's and the base were the only parts left when I picked it up. That's why I'm trying to figure it out the hard way - I have no manuals or schematics to read.

... but AC induction motors are virtually impossible to position, and then hold position ...

This statement surprises me a bit. How about AC motor spindles with positioned tools? I have one and it seems to work.
Holding position isn't that hard with a DC voltage, right? If the motor slams into the dampener, which brings the momentum down, while the DC is applied it should hold its position.
DC injection braking - Wikipedia, the free encyclopedia

[mike_Kilroy]

no amount of dc injection braking will hold anywhere near stiff, sorry. it more helps produce torque at slower speeds like 200rpm down to say 10-ish rpm then is near useless - try it yourself to see.

ac induction motors with feedback (encoder, resolver, etc) can be very similar to servos in holding torque at 0 speed - if you have a good vecotr drive; the cheap vfd's that add a simple enocoder probably wont get you there.

have you any idea what ac drive was on this? is there an encoder or resolver on it?

I use REFU vector drives and they will do exactly what you say and want, but you will pay $ 3000 for one instead of $ 300.00. they will make an induction motor with hi res feedback operator absolutely identically as any servo system - except for the fact that physics still reigns and the higher rotor inertia of the induction motor compared to the servo will cause slower accel rates & velocity loop gains due to T=jw/t still.

[Al_The_Man]

This statement surprises me a bit. How about AC motor spindles with positioned tools? I have one and it seems to work.
Holding position isn't that hard with a DC voltage, right? If the motor slams into the dampener, which brings the momentum down, while the DC is applied it should hold its position.
DC injection braking - Wikipedia, the free encyclopedia

Yes, Spindle controllers such as the Mitsubishi are capable of this kind of control, they not only have a pulse generator from motor to drive, but also have an encoder on the final spindle and are capable of very fine positioning.
The only place to inject DC in an induction motor is to the stator, but to a non-P.M., non-rotating rotor it has no effect?
Al.
.

[svenakela]

I can assure you there is nothing more than a motor, a proximity sensor in both ends and a normal power cord. There was no such thing as a driver.
The motor is pretty well geared down. Look at the picture, there is a bolt on reduction and a gearing like 40:250 that rotates the arm (you see the big cog under the left motor). So I still believe DC breaking would hold the arm even if it just a tiny holding torque, but if anything would move the arm or if it stops before the end position it will not center under the spindle. That could be solved by a 10-15 V AC though. If not the current generates too much heat in the motor when standing still.

[Al_The_Man]

Doesn't the spindle have to be oriented to pick up the tool? What is the tool standard, one of the CAT keyed style?
Al.

[svenakela]

Doesn't the spindle have to be oriented to pick up the tool? What is the tool standard, one of the CAT keyed style?
Al.

Yes? But what does that has to do with the tool changer arm?

[holbieone]

i'm guessing the reduction gears alone should keep the arm stationary

[Geof]

How does the motor drive the movement of the arm? On my machines it is a crank mechanism which simply rotates through 180 degrees. When it is at either end of its motion it holds simply because it is impossible to back-drive a crank at the extremes of its motion.