Rami Arieli: "The Laser Adventure" Chapter 9.4.5 page 10

Fixed Laser

1. Laser fixed in a table - similar to the "light pen", but in this system the product with its bar code is moved along the fixed laser beam.
2. Automatic scanning system.

A low power laser beam (from Helium-Neon laser or a diode laser pass through an optical system which contains lenses, mirrors and prisms which transfer the laser lights to a beam splitter.
An example of such system is described in figure 9.21. From the beam splitter, the laser arrives to a spinning or vibrating mirror. For every situation of the mirror, the incidence angel of the light is different and so is the reflection angel. More mirrors are used to direct the beam to the bar code and back from bar code to the beam splitter which transfer it to the detector.

Figure 9.21: Automatic scanning system for reading information of a bar code.

The new systems in use today have several beams scanning in different directions simultaneously. No beam splitters are used since the beams arrive to the bar code at an angle, and are reflected to the other side at the same angle.
Thus, even if the product face the beams in any direction, it can still be read. The computer analyze the signals received from several detectors, and only when a meaningful reading is registered it makes a sound that the code is accepted.

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