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Hybrid Digital-Analog Control of Stepper Motor Pedestal Voltage

IP.com Disclosure Number: IPCOM000046811D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Cavill, BR: AUTHOR [+3]

Abstract

In certain stepper motor drive systems, "pedestal" voltages (high voltages for limited time periods) are applied in a regulatory manner. Such voltages may be controlled using either all analog or all digital techniques. In known all analog schemes, a level of current in a given commutation winding of the motor is sensed, and the pedestal voltage to that winding is turned on when the current drops below a specified low level and turned off when the current reaches a specified high level. Such analog techniques are susceptible to noise and crosstalk effects capable of inducing "false" triggering of pedestal functions. Known all digital schemes operate in an "open-loop" manner to turn the pedestal on and off at fixed time intervals.

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Hybrid Digital-Analog Control of Stepper Motor Pedestal Voltage

In certain stepper motor drive systems, "pedestal" voltages (high voltages for limited time periods) are applied in a regulatory manner. Such voltages may be controlled using either all analog or all digital techniques. In known all analog schemes, a level of current in a given commutation winding of the motor is sensed, and the pedestal voltage to that winding is turned on when the current drops below a specified low level and turned off when the current reaches a specified high level. Such analog techniques are susceptible to noise and crosstalk effects capable of inducing "false" triggering of pedestal functions. Known all digital schemes operate in an "open-loop" manner to turn the pedestal on and off at fixed time intervals. These schemes are insensitive to the noise effects of analog systems, but cannot respond to variations in circuit and motor parameters. The hybrid control scheme described next provides the advantages of both types of control schemes without the disadvantages of either type. In this scheme, pedestal turn-on is controlled digitally and turn-off is controlled by analog means. Furthermore, a digital override is provided which permits overriding digital control of pedestal turn-off. In the present system (Fig. 1), a single-chip microprocessor 1, which provides phase commutation signals to the stepper motor via lines 2, also directs the turn-on of the pedestal function and exerts over- riding control over the turn-off of the same function. The commutation signals provide four phases of excitation concurrently to four stepper motor windings which control motion, namely, phases A, Not A, B and Not B as shown. Threshold latches 3 and 4, respectively associated with the pedestal function relative to commutation phases A and B, receive setting excitation from the microprocessor and resetting stimulation from sources 5 and 6 associated with analog current sensing networks (not shown) linked to the A and B phase motor drives. Outputs from these latches are passed through drive gating circuits 7 and 8, respectively, under the direction of the over-riding "pedestal enable" function provided by the microprocessor. As shown in Fig. 2, the A and B pedestal functions respectively control pedestal power transistors 10 and 11 which operate in parallel wit...