MONITORING BI-DIRECTIONAL MOTOR DRIVE FAILURE IN ELECTRO-OPTICAL READER

• US 20050092841A1
• Filed: 11/05/2003
• Published: 05/05/2005
• Est. Priority Date: 11/05/2003
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Barkan, Edward
• Granted Patent: US 6,929,184 B2
• Time in Patent Office: Days
• US Class Current: 235/462.25
• CPC Class Codes: G06K 7/10633 by oscillation

Abstract

Malfunction of a bi-directional resonant motor drive in an electro-optical reader is detected without new hardware by monitoring the frequency of a start-of-scan signal, and by determining whether the monitored frequency lies within a predetermined frequency range.

Claims

1. An arrangement for detecting a malfunction of a bi-directional motor drive in a reader for electro-optically reading indicia, the arrangement comprising:

a) a resonant motor having a rotor oscillatable about an axis;

b) a permanent magnet jointly oscillatable with the rotor;

c) a scanning element jointly oscillatable with the rotor, and operative for directing a light beam at the indicia to be electro-optically read;

d) a drive coil in operational proximity with the magnet, and operative for generating a drive signal to drive the rotor, the magnet and the scanning element in opposite directions about the axis over the indicia at a resonant frequency;

e) a feedback winding in operational proximity with the magnet, and operative for generating a feedback signal having a feedback frequency corresponding to the resonant frequency during oscillation of the magnet;

f) a zero crossing detector for detecting zero crossings of the feedback signal to generate a start of scan (SOS) signal having an SOS frequency; and

g) a control processor for monitoring the SOS frequency, and for sensing the malfunction when the SOS frequency is outside a predetermined range of SOS frequencies.

2. The arrangement of claim 1, wherein the scanning element is a light reflector.

3. The arrangement of claim 1, wherein the zero crossing detector is a comparator having one input connected to a reference voltage, another input to which the feedback signal is conveyed, and an output from which the SOS signal is conveyed to the processor.

4. The arrangement of claim 1, wherein the processor generates a laser shut-off signal when the malfunction is sensed.

5. The arrangement of claim 1, wherein the predetermined range of SOS frequencies is ±

20% of the resonant frequency.

6. A method of detecting a malfunction of a bi-directional motor drive in a reader for electro-optically reading indicia, the method comprising the steps of:

a) mounting a rotor of a resonant motor for oscillation about an axis;

b) mounting a permanent magnet for joint oscillation with the rotor;

c) mounting a scanning element for joint oscillation with the rotor;

d) directing a light beam at the indicia to be electro-optically read;

e) generating a drive signal to drive the rotor, the magnet and the scanning element in opposite directions about the axis over the indicia at a resonant frequency;

f) generating a feedback signal having a feedback frequency corresponding to the resonant frequency during oscillation of the magnet;

g) detecting zero crossings of the feedback signal to generate a start of scan (SOS) signal having an SOS frequency; and

h) monitoring the SOS frequency, and sensing the malfunction when the SOS frequency is outside a predetermined range of SOS frequencies.

7. The method of claim 6, wherein the scanning element is a light reflector.

8. The method of claim 6, wherein the zero crossing detecting is performed by a comparator.

9. The method of claim 6, and the step of generating a laser shut-off signal when the malfunction is sensed.

10. The method of claim 6, wherein the predetermined range of SOS frequencies is ±

20% of the resonant frequency.