Suitable circuit for using stepper as power feed

[staffordshirech]

Hi, I would appreciate any guidance or suggestions for circuit(s) to build a pulse generator that will enable me to control a stepper motor used as a milling machine power feed.
My turret mill is a Cincinatti Toolmaster which has a fancy DC disc
motor power feed system. Great until one motor burnt out and they
want over 1000 GB Pounds for another! Anyway it is 30 year old
technology so I am updating with the largest stepper motor and driver
from www.arceurotrade.com.
In order to make the thing useful I need a circuit that will
generate the pulses to control the driver. Obviously for power feed
I need to run the motor at variable speeds depending on the job in
hand. This could be via a potentiometer control or even
keypad/switch entry.
The other feature I would like is a fast traverse option to run the
motor at top speed. However, I do not know what 'top speed' is for
this type of motor. The original disc motor went up to 3000rpm but I
don't think I will get that from a stepper (will I ?).
Any info or sources to consider would be very gratefully received.

Regards,
Les Riley

[gar]

051118-1233 EST USA

staffordshirech:

Consider a 555 timer in astable mode.

Go to www.national.com then search for LM555 and/or LMC555 and download the datasheet.

You can set a given pulse width, and by changing resistance change the repetition rate. Wider speed changes will require a capacitor change. The LMC CMOS version has lower output drive capability but voltage swing is nearly rail to rail.

The LM version is TTL output with high current capability.

.

[machining fool]

I am trying to do the same thing, to convert my steppers on my Bridgeport to power feed. Have you found out anything?

[Mariss Freimanis]

Is this a frequently needed feature? I ask because I have a circuit I designed while ago that does just that. A potentiometer sets the speed, a trimpot sets the rate of acceleration / deceleration. Close a switch and the motor accelerates to the potentiometer-set speed. Release the switch and the motor decelerates to a stop. Change the speed potentiometer while the motor is running and it accelerates / decelerates to the new set speed without stalling no matter how quickly you turn the pot.

I don't want to go to the trouble of drawing it up and posting it unless there interest. I'm lazy.:-)

Mariss

[Laser.Tech]

Mariss,
I ,for one, would be very grateful if you could post a drawing of your circuit. As the owner of a couple manual machines and several dozen steppers, power feed has been on my to-do list for years but I haven't ran across a simple pulse generator with accel/deaccel. And with even cheapo power feeds selling for a couple hundred dollars, I think there are a lot of other folks who would also be interested. And if your feeling too lazy for a print, maybe just a quick description of how it works...

Just don't spend too much time away from designing your GREAT products!

Brent

[keebler303]

Mariss

I don't need the circuit right now but it would be handy to have on file. I also like to see elegant designs, which most of yours seem to be.

Keep up the great work
Matt

[Mariss Freimanis]

Sorry. I didn't mean this as a primadonna thing. Evidently there is enough interest to have me go through the archives and drag this circuit up. For those who like designs, it uses a charge-balancing VCO which I thought was very cool and elegant. I cannot get to the circuit until tomorrow when I'm at work. Everything got transfered to the servers at the shop.

Mariss

[staffordshirech]

I tried several more technical solutions but whilst some worked OK on bench test, they didn't seem to like working on the actual machine and kept burning chips out. So I went back to absolute basics and used a 555. I put two x 6 way switches to select from 36 combinations of resistors on the 555. This arrangement is still working happily (3 years?) on.
However, I must say I like the sound of Mariss' circuit. My arrangement is a bit harsh when going from slow to rapid traverse.
I would be very interested in an upgrade!
My present control panel is pictured here:-
http://www.staffordshirechina.com/Pi...ol%20panel.jpg

The stepper being on the x axis only.

Regards,
Les

[skip20]

I would like to see this design also

[gld952]

I too have been looking for a stepper driver like you describe.

[wwendorf]

I might be able to use this for driving a machine i'm building. I'm currently using a geared motor that is 1 speed only. The ability to select variable speeds with good torque would be fantastic!!! Please post your circuit when you can!

I'm assuming that this circuit would support reverse too, wouldn't it?

Thanks!
Wade

[Mariss Freimanis]

OK. I found the circuit this morning. I designed it in 1979 when I was much younger and dumber. The circuit was overly complicated for what it does so I spent a few hours today and designed a completely new circuit. It should cost less than $1 or $2 in parts.

Note: The op-amp must be a rail-to-rail output type. Don't try to use an LM324 or the like.

The max speed is zero to 50kHz, the acceleration time to max speed 0.1 to 5 seconds. Closing a switch to ground on the RUN/STOP input causes the pulses to accelerate linearly at a rate set by the ACCEL/DECEL trimpot setting to a speed set by the SPEED potentiometer. It stays at that speed until the switch is released. The pulses then decelerate linearly down to zero speed and stop. The STEP outputs give true and inverted output pulses which are 10uS wide. The circuit runs on 5VDC and consumes about 2mA.

The 4.7uF capacitor sets the integrator ramp rate, the 10nF capacitor by the PN2222A sets the maximum oscillator frequency. Both can be changed if the ramp rate or max frequency has to be different than what's specified in the circuit design.

Mariss