| 摘要 |
<p>A laser scanning system for reading a bar code includes a motor (116), a movable scanning element (120) driven by said motor (116), laser beam generating means (122) for producing a laser beam arranged to be deflected by said scanning element (120) so as to scan the bar code, and motor drive circuitry (318, 332). Three Hall sensors (336, 340, 344) are arranged to produce output signals in response to the sensing of movement of the rotor of said motor (116), these output signals being applied to a microprocessor (332) forming part of said motor drive circuitry (318, 332). The microprocessor (332) is arranged to determine the speed of movement of said rotor in response to receipt of said output signals from said sensors (336, 340, 344). For the purpose of avoiding ocular health hazards, the microprocessor (332) is arranged to shut down the operation of the laser beam generating means (122) if it determines that the speed of movement of the rotor is below a predetermined threshold.</p> |
