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# Increased Speed and Torque Capability from a Stepper Motor

IP.com Disclosure Number: IPCOM000074177D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 33K

IBM

## Related People

Barcomb, JG: AUTHOR

## Abstract

As the speed of a stepper motor increases, its available torque decreases because of: 1) Back Electromotive Force increases with speed; and 2) The L/R Time Constant of the motor limits the motor current at higher speeds.

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Increased Speed and Torque Capability from a Stepper Motor

As the speed of a stepper motor increases, its available torque decreases because of: 1) Back Electromotive Force increases with speed; and 2) The L/R Time Constant of the motor limits the motor current at higher speeds.

Usually a stepper motor drive system is limited by the drive capability of its driver and by the voltage available. Once the motor has started to move, its current is limited by (1) and (2) and the torque is thus limited.

As shown in A, two additional resistors R3 and R4 are provided in addition to the usual current limiting resistors R1 and R2 in series with the phase windings, A, A and B, B and their associated A and B switching means. The resistors R3 and R4 may be connected in parallel with their associated resistors R1 and R2 after the motor is up to speed. This increases the time constants of the winding circuits, but results in the motor currents reaching higher values because of the reduction in total resistance in the circuit. The curves in B show that at a specific time period, for example, L over R, the current I is greater for each decrease of
R. By controlling the value of R so that the current capabilities of the motor drivers are not exceeded, an increase in motor performance can be realized.

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