Acorn Carousel Tool Changer

[mick41zxr]

Fredrik,
There is a way to to operate the carousel without using the 4th axis, however I have not tested this yet. The Ether1616 will help greatly in this area.
It can be done with 4 bit grey code, or you could use a Clearpath MCPV Servo in Move to Absolute position mode.
https://www.youtube.com/watch?v=-LubKmpB5-8
I am leaning towards this in my build as it will free the 4th axis & eliminate the need for a 3rd party controller to drive the stepper for the carousel.
Your machine looks like a great little mill.
The spindle motor you have is a CTB Servo Spindle which is very similar to mine.
This should have an indexing feature built into the driver. You will need to check your manual for exactly how. But on my servo driver there was an input for indexing. It was a matter of connecting one acorn output to two 24v relays. One set the servo driver to positioning mode & the other activated the position command.
The position was done by setting an absolute encoder position set in the servo driver. I may have a copy of your manual somewhere, I can check later.
Regards,
Michael

[mick41zxr]

Marty / Fredrik,
You should be able to use the FI (0-10v) input as opposed to the FV (+/- 0-10v) input to use the driver directly with Acorn.
Then use the I1 & I2 terminals to control direction (I1 CW, I1& I2 for CCW). I1 & I3 should enable positioning mode.
Manuals scraped off the net attached, but appear to be very similar to mine (look at page 36).

CTB GH Manual.pdf

(3.39 MiB) Downloaded 151 times

Regards,
Michael

[martyscncgarage]

What is a CTB GH?
The original DM4400 cam with a Servo Dynamics SD3060 servo amplifier and the spindle motor was bascially a large SEM DC Brush Servo.

[mick41zxr]

That is the spindle servo driver in Fredriks photo's.

[fredrik]

Marty

Yes i did change out the spindle motor, it just seemed like to much of a hassle to work with the old one and with this new motor it will run with 6000rpm at 1:1. Than's for the tip of the lube line i will double check this, i didn't see this when i checked the Y ball screw.

When it comes to the swing arm i was planing on using the limit switches that was on the machine from start. Do i need sensors in the pneumatic cylinder as well? I do not have switches for the drawbar. I was trying to figure out a solution to this. What do you think of mounting a magnet to the pushrod from the cylinder, that could be used as a reference for a sensor?


Michael

You are a rock! than's for the manual. The manual that came with the spindle and drive was in Chinese
And my Chinese is pretty rusty. And after many emails and a couple of hours chatting with the engineers at CTB i gave up, and they could not provide a manual in english for me. I am running the spindle with 0-10v signal to FI and controlling the direction with I1 and I2. My issue is that it wont spin CCW. The instructions that i got was to connect it like in my pictures. FI to V-out on acorn and FC to common on Acorn. But when it came to the direction signal i only got the spindle to move if I1 is connected to PV while I2 is connected to SC. And if i reverse the connection the spindle runs the same as before. I guess i'm doing something wrong.

https://ibb.co/XSx9xCd
https://ibb.co/y47WRqR

Regarding the encoder in the spindle. I have though of this, and this might be a good option. But at the moment the pulleys on the motor and spindle is not 100% that same size. I had to modify them on my manual lathe to be 1:1. I think that it's a difference of 0.05mm on the radius and after spinning a couple of thousand revolutions the spindle will be off alignment to the motor and encoder. Thats why i was thinking if it is possible to have some type of sensor that could reference to a magnet on the spindle. But i will look into utilizing the encoder on the spindle. I want to wire it to the acorn anyway.

That Clearpath servo looks awesome. I will have to wait until you have this figured out I guess i will be running with the stepper in the beginning, the 4th axis is a project after the ATC anyway.

Many Thanx
Fredrik

[martyscncgarage]

https://goo.gl/photos/neSAL3iVeFEAtjTRA
Pictures of my mill for reference.
Had no problem using the original spindle motor.
Do you still have the original spindle motor and drive? Where are you located?

Marty

[fredrik]

Thank you! Very nice build.

I am located in Sweden

Fredrik

[mick41zxr]

Fredrik,
I1 is the enable circuit, I2 is reverse direction. So to reverse you need to enable both inputs.
With regards to pulley size, the driver has a function for drift compensation. You may be able to cheat & try & compensate that way or move to a toothed belt pulley.
You should be able to wire from the DB9 on the driver into the DB9 of Acorn for spindle encoder through port T4 on driver.
Pay close attention to your shielding with this cable as it makes a difference.
Regards,
Michael

[kyanite]

Marty,
Here you go, finished the reduction ratio 3:1 with 3Nm closed loop stepper. I loaded carousel up will all the tool holders I currently have (7). It performs a lot better.
Regards,
Michael

Michael awesome machine!

Did the reduction ratio fix the problem of the 4th axis limiting rapid speeds of the other axes?
Not sure if you had to lower rapids because of the Inertia and stalling or because of the driver not keeping up.
I'm also useing dmm servos and have a 4th. But that sounds like a lot of reduction.

[mick41zxr]

I used the reduction ratio to increase torque of the stepper. This reduced the jerk in start stop motion.
As you can imagine the moment of inertia of a full carousel is significant. I have since upgraded to a larger frame stepper.
I would imagine that with a DMM servo you will need to step down significantly as the speeds achieved by a servo are
far higher than a stepper. I think in this instance with the relatively slow speeds required by a carousel you may be better served
with a closed loop stepper motor as it has high torque at slower speeds.