Browse Prior Art Database

Stall Detection on Step Motor Using Back EMF Detection

IP.com Disclosure Number: IPCOM000036090D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Heink, PJ: AUTHOR

Abstract

This invention allows one to determine whether a step motor has stalled (is not running synchronously with the input pulses) by sensing the signals on one pair of the motor leads. As described, it will work in applications where a step motor is driven with two phases on, by a constant current bipolar driver.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 3

Stall Detection on Step Motor Using Back EMF Detection

This invention allows one to determine whether a step motor has stalled (is not running synchronously with the input pulses) by sensing the signals on one pair of the motor leads. As described, it will work in applications where a step motor is driven with two phases on, by a constant current bipolar driver.

The invention provides a means of sensing a motor stall condition, by comparing the zero crossing times of the back EMF signal in one of the windings of the motor, with the logic signal which is used to change the phase of that winding in the motor. To do this, the back EMF generated by one of the windings of the motor is measured. This voltage will be given as: Ub = V - iRm - Ldi/dt,

WhereUb is the back EMF voltage,

V is the voltage applied to the winding, it can be

measured as V2-V1 where V2 and V1 are voltages,

relative to ground, sensed on each of the two

leads of the motor winding.

i is the current through the motor winding

Rm is the motor winding resistance

L is the motor winding inductance

di/dt is the change in motor current with respect

to time.

The back EMF signal is constructed by measuring:

V2 - V1 # a Vref,

Where Vref is a reference voltage used by the motor

driver to set

the constant current level (usually by chopping

the voltage

on and off with some duty cycle),

a is chosen as IcRm/Vref,

the sign of the Vref term is chosen based on the

polarity of the current in the winding.

Note that when the constant current driver is regulating the current, the inductance term in the back EMF equation becomes unimportant, and #a Vref is an appropriate approximation for iRm . When the motor is turning against a load, the zero crossing of the generated back EMF (one half step before the two- phase-on stable detent point) will generally occur some time after the current rises to its constant level (Ic). It is not possible to resolve its crossing if it occurs while current is still rising, because of the effect of the Ldi/dt term; this makes it appear that the zero crossing has occurred as soon as the current becomes constant. In general, any system which uses a constant current driv...