simple count up stepper controller ?

[D.D.Machine]

I need a simple way to count encoder pulses and then give out a pulse to a stepper driver.

What I`m doing is trying to time a dividing head with a cutter spindle.

( I`m working on making a horizontal mill into a gear hobber, so I need to keep the cutter hob in time with the dividing head. my max spindle speed well be about 120 RPM on the hob and the gear blank well be in the 5 rpm range. I`m looking at gearing up the encoder and the indexing head to about 8,000 steps per rev.)

I`m thinking a simple PLC might work but can they take encoder pulses as a input?
Thanks

[pastera]

As the direction will not change, you only need to watch one of the quadrature signals. This simplifies the control to be a pulse rate converter -
simple job for a small micro.

I don't have enough experience with ladder logic to say if a PLC could easily keep up AND be flexible enough to support different ratios (different gears)

Aaron

[D.D.Machine]

thanks thats been my hold up, I don`t know if a plc well do it or not.
I can make about and cnc software that well thread do it but would like to not have to deal with a PC.

[kreutz]

I don't think it is difficult to do with a PIC or AVR, as Pastera said, it is only a programmed divider, but there is also a need to program the cutter head's feed rate . How do you move the cutter head?

[pastera]

Please give some more details of the setup.

My assumptions:
Rotary axis linked to spindle rotation
vertical axis programmed feed rate per revolution of hobbed gear
linear axis (along rotary axis) feed rate per revolution of hobbed gear

Programming a small microcontroller to do this would be easy if you use step&direction controls. You might even be able to use the threading module in EMC with a little tweaking.

Aaron
BTW: gearig down the rotary axis may limit the size gear you can cut - a small, low module gear may need to spin faster than the rotary table can!

[D.D.Machine]

the setup is simple.
universal horizontal mill with a dividing head, stepper drive the dividing head with the same # steps as the spindle encoder and then its just divide by the # of teeth you want to cut to get your step count.

[D.D.Machine]

The feed of the cutter thrue the part has no bearing on the setup. I could hand feed it and it would still work. the only trick to make it work is angle the table at the same angle as the lead on the hob and get the timing in sink with the hob and the gear blank.

all I need is to make the gear blank turn one tooth for every turn on the hob.

so lets say I want to make a gear with 16 teeth. I take the spindle encoder with 8,000 steps per rev and divide that by the 16 teeth ( 8,000 * 16 = 500)
so for every 500 steps the encoder moves it sends 1 step to the stepper motor

( a hob is a helix cutter like a tap)

its the same as threading on a cnc , spindle goes one rev the X axis moves the lead of the thread, only thang is rather than one thread lead I need to move one gear tooth.

[pastera]

If you are looking for a semi-automated interface that will only sync the part and hobb then it's quite easy.

How simple of an interface do you want?
Would a simple text LCD and up/down knob be good?
Would you also want other functions on the rotary axis (indexing, dividing)?
Built in stepper driver or external step&direction controller?

Aaron

[kreutz]

You are talking about 8000 pulses/ rev. Is your encoder a 2000 ppr encoder 4x decoded or a pure 8000 ppr? Do you always rotate the blank in the same direction? Do you already have the stepper driver? What is the maximum number of teeth you want it to cut on one blank. What should it do when the total number of teeth are cut, continue rotation in sync with the spindle as before or turn off the spindle motor?

[D.D.Machine]

as for the encoder I might just use a 2000 ppr and belt it 4 to 1

as for the indexing thats all I need to to do is keep the hob and the gear blank in time,

I well just start the spindle and get it in time with the gear blank then use the power feed on the mill to feed it thrue the blank and just use the mill feed stops to stop the table feed, as for the indexing head and the hob it can just keep going.

All it needs to do is keep the hob and the gear blank in time, I don`t need to to control any other part of the machine.

* its going to be used for a production runs and it well only need about 8 programs to run all the gear counts*

[pastera]

I would not add any gearing to the encoder - not when you can do a 4x decode on the encoder to get the resolution you need.

At 120RPM and 8000 counts/rev, that's only a 16kHz pulse rate - something the average microcontroller can do in spare time. It would start to get interesting if you go 10x the spingle speed, but just barely!

The problem is going to be spinning a rotary table fast enough - the input shaft on a 60:1 table would need to spin at 7200/(number_of_teeth) to keep up. As you can see this would get a little fast for small gears.

If you want something that will read the spindle encoder (with/without index) and run a switch selected timing PM me.

Aaron

[NC Cams]

Investigate the use of a 4029 IC or it's TTL/low power CMOS replacements.

The chip is a resettable, up or down, daisy chain able counter/divider that is programable to dividing at any quantity you want.

You might also want to look into Red Lion Controls. They have bidirectional counters that might serve your needs and bolt on to your equipment. Lots easier to bolt stufff together that is already industrial strength than to develop stuff anew.