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Smooth Step Motor Current Shift

IP.com Disclosure Number: IPCOM000037955D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Goodwin, JG: AUTHOR [+2]

Abstract

Disclosed is a simplified technique for smooth power transfer between ramping and constant sequencing of a stepping motor.

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Smooth Step Motor Current Shift

Disclosed is a simplified technique for smooth power transfer between ramping and constant sequencing of a stepping motor.

When stepping motors are run in an open loop manner to speeds above their pull in torque curve, a predetermined set of timings by which stepping is sequenced are required. In order to overcome inertial loading and minimize the total time required to achieve the max/min step rate, it is typical to apply greater motor power during ramping. This is commonly done by allowing a larger current in the motor. Once the max/min speed is achieved, power/current is decreased to a minimum level to contain the temperature rise of the motor and drive electronics. The transition between ramping and constant sequencing is critical in order that synchronization be maintained and minimal velocity ripple is incurred. Previous techniques switch directly from one current level to another as shown in Fig. 1. This is usually done via an electronic gate which nearly instantly switches a reference voltage from a high/low state to a low/high state, as shown in Fig. 2. The technique introduced here allows the current to change in a smooth fashion as depicted in Fig. 3. This is accomplished by placing a capacitor in circuit as indicated in Fig. 4. V3(t), the motor current reference, is related to the circuit components via equation 1. Thus, the circuit timing can be computed for the desired charge or discharge response.

Implementation of t...