Author Topic: Stepper motor  (Read 689 times)

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Offline drinuTopic starter

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Stepper motor
« on: December 27, 2013, 02:58:22 AM »
Hi all,

I am new to stepper motors since I always used DC brushed motors in the past. Can someone please help me with the following:

1) If a stepper is rated at 5.4V, can I use it with a 12V supply? If yes, what difference will I notice?

http://www.stepperonline.com/nema-23-stepper-motor-54v-15a-116nm1643ozin-23hs221504s-p-68.html

2) Why the maximum speed of the stepper motor is never mentioned? How can I calculate it?

3) I am using the stepper motor to drive the x-axis of a CNC. The weight of the part to be driven is approx. 25Kg (not the load) and I am using a 2010 ballscrew as the linear mover. Is a stepper motor with a torque of approx. 1Nm enough for this application?

Any help will be appreciated.
Thanks in advance.
« Last Edit: December 27, 2013, 03:01:21 AM by drinu »

Offline waltr

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Re: Stepper motor
« Reply #1 on: December 27, 2013, 08:39:01 AM »
Here is a link to some articles on stepper motors:
http://www.micromo.com/technical-library.aspx

If you directly apply a higher Voltage than specs then the motor will over heat. Note that many on the newer stepper driver chips have current limiting built in so will allow a higher Voltage to be applied to the driver chip.

Max speed is dependent on a number of factors. One of which is the resonant frequency of the stepper. Look at some of the stepper in MicroMo's catalog and this is spec'ed.
http://www.micromo.com/stepper-motors-datasheets.aspx

As to what the stepper motor can move depends on the acceleration desired and the frictional losses in the drive system (ballscrew, table slides, bearings, etc) more than the mass (weight) of the object to be moved. You will need to measure the frictional losses yourself.

Offline jwatte

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Re: Stepper motor
« Reply #2 on: December 27, 2013, 01:19:49 PM »
The real property that matters in stepper motors is coil current. They have a rating for maximum coil current, which will generate the maximum heat that the motor can dissipate without failing. The voltage in question is the voltage that will, at steady state, generate that current (based on the winding resistance.)

However, when you step the motor, the inductance in the windings will prevent the current from immediately flowing. Thus, it is common to run the motors with higher voltage than "steady state" ratings, and have a controller that knows to chop the supply once the current has reached its desired target.

A 2010 single-start leadscrew will move 10 millimeters for one revolution, and the lever arm is 10 millimeters (half the diameter.) This means it will generate a force of (1 N.m / 10 mm) == 100 N. If the mass is 25 kg, it means you can accelerate at about 0.4g, which seems reasonable at first blush. You will need to tune the control curves for your stepper for this -- you cannot go from zero to full speed at once, as you need to take the inertia of the mass into account. Also, as waltr said, you need to allow for losses in the system.

Offline drinuTopic starter

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Re: Stepper motor
« Reply #3 on: January 05, 2014, 05:18:35 PM »
Thanks a lot for the reply. Can I apply 48V to the LMD18245T driver IC {using 2PCS} to drive the 23HS22-2804S stepper motor {2.8A, 2.5V} ??

I was told that ideally you apply the maximum voltage that the driver can take. This will increase the stepper speed. Is this true? Because if not, I prefer using a 12V power supply instead since I have other components that will require 12V.

Will re looking forward for a reply.

Thanks in advance. 

Offline bdeuell

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Re: Stepper motor
« Reply #4 on: January 05, 2014, 06:54:08 PM »
The higher voltage will increase the maximum load the motor can handle at a specified speed ... so depending on the load you have it may increase the maximum speed you can operate at without slip. In stepper motors the speed is directly controlled by the controller unlike brushed DC motors where it is dependent on voltage and load. Speed is also limited by the maximum frequency the motor and controller can operate at, resonance and switching frequency become concerns at higher speeds.

Offline jwatte

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Re: Stepper motor
« Reply #5 on: January 05, 2014, 07:06:40 PM »
Torque comes from current -- how much magnetic force is generated in the windings?
Speed comes from voltage -- how quickly can you achieve the desired torque each time you commute the windings?
As long as the controller can stand the voltage, and can regulate the current to not overheat the motor, higher voltage is better.

HOWEVER, it is generally a good idea to specify the controller as twice the voltage of your motor voltage. The reason is that, if you were to do a full reverse from one step to the next, there may temporarily be a voltage across the coils that is twice that of the voltage you supply -- the motor basically works as a small, temporary boost converter.

If the controller is rated at 48V max, then 24V seems ideal for the supply voltage.

Offline drinuTopic starter

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Re: Stepper motor
« Reply #6 on: January 06, 2014, 03:59:03 PM »
Thanks for replying. The information you provided was very helpful.
I was watching this video on stepper motors:
Stepper Motors - Application and Use Part 3


At 2.40 he mentioned that switching mode power supplies are not ideal for stepper motors. If this it true, why all kits on E-bay and other sites sell stepper motors with switching mode power supplies?

Also, are Chinese manufactured SMPS any good?

Offline jwatte

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Re: Stepper motor
« Reply #7 on: January 07, 2014, 11:19:57 AM »
The problem with switch-mode power supplies is that they have negative source impedance, so they can oscillate, and they have kind-of jittery transient response. If you add enough capacitors on the output of the supply (and perhaps a filtering inductor before those capacitors,) then you'll probably do fine.

Are Chinese X any good? Depends on the "X part," much more than on the "Chinese" part. The cheapest possible imports? Probably not very good.

 


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