Hello folks,

I am facing some issues regarding a stepper motor drive. The stepper
motor I have is a 20KG 12V DC L/R Full step driven one. I need it to
drive a Lead screw which eventually builds up pressures of the likes
of 400Kg cm in a cylinder.
I have attached a gear box of ratio 12:1 to the stepper and tried
boosting the torque. With the direct coupling the pressure used to
reach around 100-150 Kg cm but even with the gearbox which I presume
would boost the torque by a factor of 12 the pressure fails to rise
above 200.
And the stepper slips if I try to run it at high RPMs (15RPM ) even
without any load.
What can I do to find a solution to these 2 problems? What could be
going wrong in this whole exercise?
Thanking you in anticipation.
Regards,
Chetan.

chetanthegreat wrote:

> Hello folks,
>
> I am facing some issues regarding a stepper motor drive. The stepper
> motor I have is a 20KG 12V DC L/R Full step driven one. I need it to
> drive a Lead screw which eventually builds up pressures of the likes
> of 400Kg cm in a cylinder.
> I have attached a gear box of ratio 12:1 to the stepper and tried
> boosting the torque. With the direct coupling the pressure used to
> reach around 100-150 Kg cm but even with the gearbox which I presume
> would boost the torque by a factor of 12 the pressure fails to rise
> above 200.
> And the stepper slips if I try to run it at high RPMs (15RPM ) even
> without any load.
> What can I do to find a solution to these 2 problems? What could be
> going wrong in this whole exercise?
> Thanking you in anticipation.
> Regards,
> Chetan.
with out seeing the stepper driving circuit, it could be a lot of things.
is the stepper motor spec'ed out to operate at the desired RPM?

Is this driver circuit something you made? if so, have you scoped
out the actual signals ?
etc..
we need a little detail on the circuit driving the stepper motor.

P.S.
Steppers are generally not suited for high speed applications.

if you need indexing, maybe what you should do is use a DC motor with
some torque and a A/B,Z feed back encoder into a uC or a PLC..

Like I said, I don't know your application. maybe you could spill a
little more on the actual electronics here.




--
http://webpages.charter.net/jamie_5"

On Sun, 17 Feb 2008 11:23:59 -0800 (PST), chetanthegreat
<chaudhari.chetan@gmail.com> wrote:

>Hello folks,
>
>I am facing some issues regarding a stepper motor drive. The stepper
>motor I have is a 20KG 12V DC L/R Full step driven one. I need it to
>drive a Lead screw which eventually builds up pressures of the likes
>of 400Kg cm in a cylinder.
>I have attached a gear box of ratio 12:1 to the stepper and tried
>boosting the torque. With the direct coupling the pressure used to
>reach around 100-150 Kg cm but even with the gearbox which I presume
>would boost the torque by a factor of 12 the pressure fails to rise
>above 200.
>And the stepper slips if I try to run it at high RPMs (15RPM ) even
>without any load.
>What can I do to find a solution to these 2 problems? What could be
>going wrong in this whole exercise?
>Thanking you in anticipation.
>Regards,
>Chetan.

Try an elastic/spring coupling at the motor to the box? Something
that will add just a bit of looseness to the system. Steppers aren't
their best at high speed and under load (starting torque). If you
want to operate a positive displacement pump, for instance, you either
have to add some black magic to the coupling system or grossly
increase the size of the stepper, or both.

High speed of only 15 RPM? At the stepper, or the output of the gear
box?

Too much friction in the system will also cause both problems.

DC servo is the obvious choice for that application unless it is
expected to be essentially stalled just supplying pressure to a system
without moving.

Steppers can be hard to apply for high starting torques. The elastic
coupling lets the motor get to the next step while the drive pulse is
still there, and then returns energy back to the system while the
mechanical gears catch up.

Mechanical resonance's are something else to look out for . . .
--

chetanthegreat <chaudhari.chetan@gmail.com> wrote in news:badaae5a-4f32-
4af4-94f9-324d4b7e7323@e10g2000prf.googlegroups.com:

> Hello folks,
>
> I am facing some issues regarding a stepper motor drive. The stepper
> motor I have is a 20KG 12V DC L/R Full step driven one. I need it to
> drive a Lead screw which eventually builds up pressures of the likes
> of 400Kg cm in a cylinder.
> I have attached a gear box of ratio 12:1 to the stepper and tried
> boosting the torque. With the direct coupling the pressure used to
> reach around 100-150 Kg cm but even with the gearbox which I presume
> would boost the torque by a factor of 12 the pressure fails to rise
> above 200.
> And the stepper slips if I try to run it at high RPMs (15RPM ) even
> without any load.
> What can I do to find a solution to these 2 problems? What could be
> going wrong in this whole exercise?
> Thanking you in anticipation.
> Regards,
> Chetan.

do you really mean 400kg/cm? that's about 5500psi. That's scary pressure.
This must be a massive structure.

What's the stepper torque rating, whats the rated Amps and volts for the
stepper, do you have a manufacturers torque curves?

What's the lead of the leadscrew, what's the area of the piston or working
surface in the cylinder operated by the leadscrew. Do some math - almost
certainly the stepper doesn't have the power to produce the pressure you're
expecting, so it's stalling.

If the stepper 'slips' at 15rpm with no load that's another issue. A
Steppers 'high' speed can be 1000rpm or more, depending on the load. If
it's slipping at such a slow speed then you have driver issues. You need to
show us what drivers or schematics you're using.

What voltage are you supplying and at what current.? Steppers should be
current limited to thier plate rating but voltages from the driver can and
often should be up to ~20 times the rated voltage - *as long as the driver
is a current limiting device*. Without the high voltages the stepper will
not achive reasonable speeds or much power either.

On Sun, 17 Feb 2008 21:04:37 GMT, Jerry <jerry@b.com> wrote:

>
>do you really mean 400kg/cm? that's about 5500psi. That's scary pressure.
>This must be a massive structure.

Not necessarily. There's something called High Performance Liquid
Chromatography pump used in chemical compound analysis. A pump with a
sapphire/ruby piston supplies milliliters per hour at pressures from
1-10K PSI. Sits on a table and occupies a half cubic foot or less.
Just a little flow, at high pressure, through 1/16" SS tubing with a
..02" bore . . .

You are thinking in pounds per square inch and imagining lots of those
square inches - when the tubing is very small even plastic will work.

Not scary at all. It fails and the usual symptom is a dribble of
liquid. Liquid under pressure is actually a lot nicer than steam or
gas when it fails (as a general rule - there are exceptions).

My first guess was HPLC when he said stepper and pressure . . .
Chemists are always looking for a pump that won't cause pressure
pulses. One way is to just load a large thick cylinder with liquid
(lots of square inches) and just slowly squeeze it out at a ml/hr rate
- no pulses since there's only one stroke of the pump.
--