Science/Engineering/Technical forums

With the other thread on gear hobbing and servos going I started to think about my 10ee that I retrofitted to servo a couple years ago. I never had mounted the drives or tidied up the wiring so I figured it was time. Also figured that while I was at it I would install a 5kw Mitsubishi servo and drive I has lying around. I tested it out the other night and the thing worked so I went ahead and built a support structure for the drives and its supporting components. I also figured it would be a good time to install the VFD for the coolant pump too.

I had some polypropylene sheet that I had pulled from an old semiconductor was station. Cut it up at work and then welded it together with my Leister hot air plastic welder. Here are a couple pics of the rack sitting in the area in the base of the lathe where the motor-generator used to be:


End cover by macona, on Flickr


Side cover by macona, on Flickr

Last night I mounted the drives and the support parts, terminal blocks, din rail, 24v power supply for logic, main breaker, vfd breaker, main contactor, and 240-120v control transformer. In the event of a alarm output on the servo drive the main contactor opens and kill the bus power. The control transformer is for the contactor. I only had a contactor in that size in 110v coil. It took about three hours to get it wired up to this point:


Drive unit by macona, on Flickr


Drive unit by macona, on Flickr

Today I made a little adapter to bring out the wired needed off the Mini-D Ribbon/Mini Centronics connector that Mitsubishi loves so dearly. Use a piece of delrin to support a PC mount connector end and soldered and heat shrinked flying leads off of that to the terminal blocks. You can see it in the above picture below the transformer. Finally the wiring was finished so I yanked the old servo and control from the lathe. Of course the bellow coupling on the motor shaft was stuck to that slowed things down. Popped the new motor in place, it fit perfectly. I slid the tray in and connected the motor cables and power leads to the input terminal blocks. Hit the power button.

BOOM!

All the lights in the house went out. I blew the main breaker and the one the lathe was on. Flip them and the lathe breaker blows again. Found the main contactors contacts had welded together. I managed to get them apart though. I did some testing and found that the lines to the electronics tray were showing a dead short across the terminal blocks, What the heck? They feed right into the main breaker which was off. Then I notice a little cover on the terminal strip, pull it off, yep, shorting bar connecting the poles together. Remove it and reconnect. No booms! Had my phasing a little wrong and had forgot to wire in a couple things like the control relay and power to the control transformer. So far so good.

Grabbed the pendant for the servo drive and jogged it. Everything sounded good, Finished wiring in the control pot and fwd/rev lever, changed a couple parameters to enable speed mode and she runs! Wired up the VFD for the coolant and thats working too.

That took another 3 hours tonight. Still need to do some tuning on the Servo as well as the VFD, but that shouldnt be a big deal. This drive has continuos auto-tuning which seems to work pretty well, even with my big 8" 3 jaw on there. I also need to drop the decel time on the VFD down. Its set at something like 3 seconds from when it was on the old Gorton I used to have.

Ill take some video when I get it tuned.

-Jerry


Drive electronics by macona, on Flickr


Drives by macona, on Flickr

Got the parameters worked out. Handles much better than the old servo.

Niiice. I'd love to have that super slow speed for some coil winding I do here. I'm looking into how to make a machine/jig/cam arrangement to do "universal" windings for high frequency work, where the wire guide oscillates back and forth along the "pie" at a particular (non integer) rate to accomplish this - somewhere in the library there is a chapter that shows how to decide what ratio to use in a given circumstance, to have the resulting winding "lay right" with a phase shift per roundy round about 1 wire thickness. I suppose to do that I'll first have to rig a drive off the main spindle, or at least come up with something like a rotary encoder on it to control that.

Doing it mechanically sounds like threading via changing gears all the time, yuck. I'd suppose with numeric control it'd be a whole lot better. Since most "pies" are on the narrow side, one could probably make something that clamped into the tool post for this -- I have a passive one now for straight windings, an active one would be killer-cool.

A servo is really perfect for an application like that. You can set up the servo drive in torque mode where it will keep a specific tension on the feed spool as the coil takes up the wire. Another servo controls the mandrel in speed mode and is electronically geared to another servo that controls the laydown of the wire. You would use a pulse output of the drives encoder out trigger the step input on the layout motor which would be in position mode. Adjustable limit switches at the ends of the travel would flip-flop the direction input reversing the direction at the end of the pass. The laydown motor's built in electronic gearing function would control the pitch of the laydown. The index pulse out of the mandrel motor could be connected to a count down to stop at a pre-determined wind count. Other than the electronic gearing control the only other control you would need is a pot connected to the analog input on the mandrel motor and two more pots on the the reel motor to control torque and max speed. I bet you could reliably wind up to a couple thousand RPM even with very fine wire.

This could all be done with either 50 or 100watt motors off ebay. I would recommend the Mitsubishi MR-J2S-10A1 drives with 50 or 100 watt KFS series motors. They have 131,072 count encoders on the motors. They are going pretty cheap on ebay. The newest J3 motors have 262144 count encoders.

Back to the lathe:

The idea of adding constant surface speed is crossing my mind. Maybe using a quadrature to step/dir IC fed into a digital potentiometer IC to an op-amp might do what I want. Not sure.

Or maybe do all of it in an arduino. Use the analog out to control the drive. Its only 10 bits out but that is still about 2-1/2 rpm resolution. Stick a little control panel/readout on the DRO.

Finished the last part of the puzzle tonight. When the spindle stops it says servo locked, that is you can turn the chuck by hand and any attempt will be countered with resistance, it pushes back. This isn't too big of a deal but it sucks when you are trying to get to the chuck key socket.

On the drive there is a "Servo On" input. This is pulled low to activate the servo. I used two Omron H3FA time delay relays to turn off this input when the fwd/rev handle is in neutral. The reset of each relay is tied to the forward and reverse terminals through a small signal diode to prevent the relay itself from activating the drives forward and reverse optoisolators. The two NC contacts on the relays are in parallel and in series with the servo on input to ground.

When power is turned on the reset lines of the relays float and the timer's relay closes disabling the servo. When forward or reverse is selected the reset line is pulled closes as well as the direction input of the drive, the relay closes activating the servo and the motor runs in that direction. When the control is returned to off the reset line goes high and the timer kicks in and holds the contact closed for 1 second while the drive decelerates to a stop and then opens disabling the drive. You can plug reverse without any problems since the relay's outputs are in parallel.

I also found the drive's fans were not operating. Looks like the internal 24v power supply is dead. Looks to have always been that way as there is zero dust in the fan blades or on the heat sink. I routed 24v to the fans to keep the heat sink and breaking resistor cool.


Servo lock time out board by macona, on Flickr