Strange Behaviour of Stepper Motor

Almost anything could be wrong. I suspect first that your acceleration rate is too fast.

I also wonder about your claim that motor runs off a parallel port. The low voltage (5V) and low currents (<0.5A) produced by the IEEE 1284 parallel port standard are not practical for any stepping motor I'm familiar with. Thus I believe that your parallel port signals are communicating to a stepping motor drive which actually does the driving of the coil windings. So the communication protocol between parallel port and driver maybe getting confused due to sloppy wiring.

You may even have a phase miswires. Your step size implies a two phase stepping motor but you could have a three or even five phase wiring that could be wrong. You might even just have the driver settings set wrong.

I am sorry I was not precise in my statement. Yes the parallel port drives a driver circuit (ULN 2008) to drive the motor

Why and how will sloppy wiring affect motion in one direction only. Any way I rechecked the wiring and everything seems ok.

It is a Five wire unipolar motor.Since it runs OK in one direction sequencing should not be wrong

You claim CW is different from CCW. Yet, you claim not looking at the two codes. How come?

Same software generates both codes .I have no idea how to "look" at the code

Can you look at what the parallel port signals? This is what the code should be producing.

There is a good chance you are trying to operate the motor at a resonance point. I found out about this many years ago when trying to write some programs to operate a simple stepper-driven plotter. Above a certain steps/rev the motor would enter resonance and would lose steps. There are mechanical dampers that one can get to help the issue. Google "Lanchester damper". I don't know if there are electronic devices such as stepper driver chips that can accomodate resonance issues nowadays.

I understand that if you can get above the resonance point you can also run the stepper reliably. It is just in the resonance range that you have problems, so you need to get through the resonance range as quickly as possible.

Jon.

What software are you using to drive the stepper motor? Direction is controled by the phase relation of the signals. The driver device you are using implies you are generating the phase signels in the software and output them through the port.

However it may be the software is outputing a step and direction signel as is common using a stepper driver board that then generates the motor phase signels.

A steper motor can turn with one phase constant but lack any power. If you have a scope or logic analyzer check the signels and make they are correct on both directions.

I did my own micro stepper board a few years back. It worked great for a while. But the shop enviorment corroded my wire wrip or chip socket contacts causing it to fail and I got very simular results when one phase stoped working. I bought micro stepper boards to replace the one I designed. Mine was 16 micro steps per step. But the boards have curent control that can be set. and speed compasation. Not really worth my time when you can buy them for $100.00.

Have you tried another stepper motor? If so, does it do the same thing? Your motor could just be worn out. I have seen stepper motors run perfectly in one direction only to "bind" and make less than proper indexes in the other direction due to wear of the mechanics.

Most stepper drivers take the step and dir pulses. The dir input can be latched for the wanted direction, or an appropriate dir pulse is given on every step pulse. BUT, in case that both are pulses, both pulse durations must be within limits AND the dir pulse MUST be applied first, by a given minimum time (in ms) that depends on driver type (and possible termination and impedance mismatches). It's not uncommon that the signal you feed the driver is not time-symmetric for both directions at that context. If you can't use a scope, test like this: Disconnect dir input, give it an external stable voltage within driver specs (~5V on first run and input ground for a second run) and watch if problem is solved. If yes you nailed it. S.M.

You definitely need to slow down the stepper. Then you can observe the events. Short of that, attach a weight on the axle, to move the resonance.