Browse Prior Art Database

Error-Detection Circuit for Drive Circuit for Stepper Motor

IP.com Disclosure Number: IPCOM000039556D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Fleck, AE: AUTHOR [+2]

Abstract

An error-detection circuit detects a high current in the drive circuit for a stepper motor used, for example, in a printer and, on detection of the high current, switches off the drivers in the drive circuit and carries out reliability and servicing (RAS) tests. The error-detection circuit also senses when the current in one phase of the motor has reached a steady state during RAS tests and during slewing of the motor. The figure illustrates half of the drive circuit of a stepping motor incorporating the error-detection circuit. When drivers T1 and T2 are switched on, the current builds up exponentially through coil L1 until the voltage across R5 is equal to VREF1. This causes the output of the comparator C1 to reset latch LH1 and shut off driver T1.

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 52% of the total text.

Page 1 of 3

Error-Detection Circuit for Drive Circuit for Stepper Motor

An error-detection circuit detects a high current in the drive circuit for a stepper motor used, for example, in a printer and, on detection of the high current, switches off the drivers in the drive circuit and carries out reliability and servicing (RAS) tests. The error-detection circuit also senses when the current in one phase of the motor has reached a steady state during RAS tests and during slewing of the motor. The figure illustrates half of the drive circuit of a stepping motor incorporating the error-detection circuit. When drivers T1 and T2 are switched on, the current builds up exponentially through coil L1 until the voltage across R5 is equal to VREF1. This causes the output of the comparator C1 to reset latch LH1 and shut off driver T1. When driver T1 is switched off, the current in L1 drops to half value and a current equal to this flows up through L2 and through a diode in driver T3 which is tied to ground. Current flows in the this loop until the next 25 kHz pulse is received by latch LH1. The receipt of this pulse turns on T1 again. The error detection circuit has sensing arrangements with four outputs: OVERCURRENT SENSE, CURRENT SENSE, CHOPPERS ON and DRVS OFF.

The output logic circuit for each of these sensing arrangements, also, has an input from the other half of the drive circuit (not illustrated). The OVERCURRENT SENSE arrangement senses at the output of comparator C2 a high current through one of the phases of the motor. VREF2 is set higher than VREF1, so the voltage across R5 should never reach VREF2 unless something in the circuit fails. The OVERCURRENT SENSE arrangement output is monitored all the time. The CURRENT SENSE arrangement senses at the reset output of latch LH1 or latch LH2 (in the other, not illustrated, half of the drive circuit) that the current in a phase of the motor has reached its steady-state value. The CURRENT SENSE output is monitored when the motor is slewing and also during RAS tests. The CHOPPERS ON arrangement senses that two upper drivers T1 and T2 of the drive circuit are turned ON.

Node N1 switches between +32 volts and ground and the resistors R1 and R2 divide this voltage down to a logic level. The DRVS OFF arrangement senses the voltage levels at the collectors of the four lower drivers of the drive circuit. Nodes N2 and N3 are normally at 32 volts or ground in the static case, but the voltage can go above 100 volts when running. Resistors R3 and R4 are set to give logic levels for 32 volts and ground, and the diodes D1 and D2 are used to clamp the inputs to the AND circuit during the voltage transients when the motor is running. The outputs from the CHOPPERS ON and the DRVS OFF sensing arrangements are only checked during RAS tests. If there is an output from OVERCURRENT SENSE, this could indicate that the top driver (T1 or T2) has shorted on or that something in the feedback loop has failed, so all four lower dr...