stepper motor problem

Your motor was designed to run at one speed with a built in time span to copletet the given task. This is a realtion ship of timing. If you slow down the speed rate, the time span will increase to complet the task as well. This is a gear driven event. As the speed of the motor increases, the time to complete the task is increased as well.

Any direct drive system will be varied by the amount of rotation speed ascerted.

Now, my question to you, is why do you want to increase the rate? Your motor is designed and rated to perform a function at "X" rate with a time constant of "Y".

If you increase the "X", then you will adversly loose the longevity of your motor. It's usable life span will decrease by 1/2 the rated time.

Now, if you want to increase the rate of this motor and keep the same duration rate of the function, you will need to increase the gear size of the "Y" function. This will also change the mounting position of your system. You will be required to re-design the actual placement of the final drive gear. You would be better off buying a new assembly with the built in abilities to afford your changes, or design a new mounting assembly with an adjustable meshing property for gear changes.

Good luck.

Maximo

My apologies to Lord Maximo, but his answer makes no sense! How can increasing speed make it take longer to complete a task? Stepper motors may have one or more most efficient speed, but they are hardly single-speed motors.

In motors, the word 'moment' is synonymous with 'torque". Torque is force multiplied by a perpendicular distance. Stepper motors have many poles, commonly 200. Rotation is caused by switching from one pole to the next (in microstepping, one field is diminished in steps, while the adjacent field is augmented in steps). At higher speeds, the rotor pole is already approaching the stator pole by the time the magnetic field reaches maximum. This means that the direction of the magnetic field is significantly NOT perpendicular to the radius, which is equivalent to having a smaller radius, and therefore a reduced torque, or moment.

Hi javad_maleki88,

I can't get you exactly; your requirement is to increase the speed of the stepper motor when the stepper motor's load decreases (load carried by the motor i.e, moment) its correct?

If my observation is correct what I got from your words, the solution for your problem is, you need to measure the current (amp) consumed by your stepper motor. Because, when the moment of the motor increases the consumed amps rate of the stepper motor will also increased and vice versa. So, you can correlate the moment and load, that is you can increase the speed of the motor when the consumed amps of the motor decreases (moment decreases). Try this...

karmegakannan

The problem with speeding up stepper motors has to do with the LR time constant of the windings. Typically a motor is rated at a certain max step rate at a certain maximum constant voltage. Usually you can make the motor go much faster by either of two ways. If you quadruple the voltage but insert resistors so that you limit the winding current to the rated value, since the inductive time constant t=1/LR, what now happens is you develop the rated winding current in less time, thereby pumping more power into the winding sooner and enabling it to respond more quickly. Using resistors is very inefficient and you can use a switching regulator to limit current while operating from a higher voltage to achieve the same effect more efficiently. I have run large motors rated at 200sps up to 2000sps by using 5 volt motors at 48 volts or more and there is no degrading of life expectancy since you never exceed the motors max current spec.

a good read from just one source; http://www.designnews.com/article/CA632573.html

There are resonant frequencies in stepper motors where the torque almost disappears. A good explanation was once found in Sigma's publication, "Stepper Motor Handbook." Resonances occur because the windings which cause a motor to move in one direction appear behind the salient pole when the pole is roughly half way to its destination, and there are harmonic frequencies which cause this too.