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Stepper Motor Current as a Measure of Break Away Torque

E

EdV

Jan 1, 1970
0
I am hoping to determine if a stepper motor driven flapper valve
assembly was properly built. The mechanical design guy says it should
open (break away) from it home position with 50 grams of mass applied
to one side of the flapper.

The electrical guy I am taking over for says that he cannot detect a
change in current between a "50 gram" and a "100 gram" assembly. He
said it may have something to do with the stepper motor driver's
"smart" PWM capabilities making it didficult to pick out something
conclusive on an oscilloscope trace of current.

Anybody in the group used current to characterize torque in a stepper
motor?

I am thinking maybe running the flapper full travel 10 times and
averaging the current.

Maybe use a non PWM driver and capture a "cleaner" current waveform.

Of course this is a last minute problem that has to be done without
spending any money in the next two weeks. ;-)

Thanks in advance for any advice,
Ed V.
 
L

Leo Marx

Jan 1, 1970
0
EdV said:
I am hoping to determine if a stepper motor driven flapper valve
assembly was properly built. The mechanical design guy says it should
open (break away) from it home position with 50 grams of mass applied
to one side of the flapper.

The electrical guy I am taking over for says that he cannot detect a
change in current between a "50 gram" and a "100 gram" assembly. He
said it may have something to do with the stepper motor driver's
"smart" PWM capabilities making it didficult to pick out something
conclusive on an oscilloscope trace of current.

Anybody in the group used current to characterize torque in a stepper
motor?

I am thinking maybe running the flapper full travel 10 times and
averaging the current.

Maybe use a non PWM driver and capture a "cleaner" current waveform.

Of course this is a last minute problem that has to be done without
spending any money in the next two weeks. ;-)

Thanks in advance for any advice,
Ed V.

Many of the better drivers will reduce the motor current after a time of
inactivity. This provides a holding torque without burning the power of
full current.

JAM
 
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