Patent ID: 6929184

Claim:
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.