Electronically-controlled mechanically-damped off-resonant light beam scanning mechanism and code symbol readers employing the same

摘要

Disclosed is laser beam scanning apparatus in the form of an electronically-controlled mechanically-damped off-resonant laser beam scanning mechanism. The scanning mechanism comprises an etched scanning element having a small flexible gap region of closely-controlled dimensions disposed between an anchored base portion and a laser beam deflecting portion The light beam deflecting portion supports a permanent magnet and a light beam deflecting element (e.g., mirror or hologram). A reversible magnetic force field producing device (e.g., an electromagnet) is placed in close proximity with the permanent magnet so that it may be forcibly driven into oscillation in response to electrical current flowing through the electromagnet. The resonant frequency of oscillation of the laser beam deflecting portion relative to the anchored base portion is determined by the closely controlled dimensions of the flexible gap region set during manufacture. The steady-state frequency of oscillation of the laser beam deflecting portion is determined by the frequency of polarity reversal of the electromagnet, which is electronically controlled by the polarity of electrical current supplied thereto. In the illustrative embodiments, the forcing frequency of the electromagnet is selected to be at least ten percent off (i.e., greater or less than) the natural resonant frequency of the laser beam deflecting portion of the scanning element. The steady-state frequency of oscillation can be set at the time of manufacture to be any one of a very large range of values (e.g., 25-127 Hz) for use in both low-speed and high-speed laser scanning systems.