Numerous commercial uses have been developed in recent years for devices capable of creating an optical scanning pattern and associated devices for collecting and interpreting reflected or transmitted light beams with respect to various objects. Devices of this nature include symbol recognition systems, position sensors and image reproduction equipment.
One of the most common commercial applications of symbol recognition systems is in the retail market, particularly grocery stores, in which universal product codes ("UPC") and other commonly used bar codes are utilized to designate specific products and brands. These bar codes are directly placed upon the products or the packaging thereof and are adapted to be scanned and analyzed by commercially available apparatus. Large grocery chains have made particular use of systems of this type.
Bar code reading systems fall into to two major categories, with one being a type of system in which the scanner is moved past the code while the other utilizes a movement of the scanned object through a scanning pattern created by a stationary system. Both types of systems have advantages and disadvantages but the stationary system is best adapted for large scale operations such as supermarkets and large grocery stores.
Numerous United States Patents have been issued regarding bar code reading systems of both types. Examples of hand held or portable scanning devices are found in U.S. Pat. No. 4,251,798, issued to J. Swartz, et al., U.S. Pat. No. 4,578,571, issued to R. E. Williams and U.S. Pat. No. 4,570,057, issued to G. E. Chadima, Jr., et al. These represent hand held devices which are held in a specific orientation and then moved past the bar code on the object. The devices are utilized to transmit information regarding the bar code to processing apparatus. With this sort of device the scanning pattern generated by the scanning device need not be complex and may in fact be a single beam in a constant position, since the device may be moved, thus creating its own scanning pattern by device movement, is held in close proximity to the bar code and need not scan a wide field.
In the case of stationary scanning systems, this is not the case. It is desirable to allow a fair amount of operator flexibility in placement of the bar code with respect to the scanning device. The desirability of a fairly broad and deep scanning zone for effective reading of the bar code makes it necessary for the system to include a device which generates a scanning pattern with a substantial effective spatial zone. Consequently, stationary scanning systems tend to be highly complex as compared to portable systems. Examples of United States Patents which have been issued on stationary bar code scanning systems are U.S. Pat. No. 4,057,784, issued to B. R. Tafoya, U.S. Pat. No. 4,093,895, issued to F. G. Nickl and U.S. Pat. No. 4,282,431, issued to J. D. Anthony, Jr., et al.
A necessary element of the stationary bar code scanning systems is an effective scanning pattern generator. These generators must include a method for taking a beam of coherent light, typically generated by a laser, and scattering it into a specific scan pattern. This is ordinarily accomplished, as shown in the stationary systems patents referred to above, by rotating multi-faceted mirrors or oscillating mirrors. The beam of light will be sequentially reflected off the moving facets and thus be directed into different pathways, depending on the angles of reflection. If the rotation or oscillation is undertaken at high speed an effective pattern may be created. An example of a U.S. Patent relating to a scanning apparatus utilizing this type of technology in a somewhat simplified manner is to be found in U.S. Pat. No. 4,450,350, issued to J. A. Hardy. Another pure pattern generator is disclosed in U.S. Pat. No. 4,041,322, issued to T. D. Hayosh, et al.
A common disadvantage of the prior art scanning pattern generators is that systems based on multi-faceted rotating mirrors are difficult and expensive to manufacture and result in complex and bulky systems. Typically, a stationary system such as utilized in a grocery store is a large under the counter installation weighing in excess of twenty kilograms and occupying a substantial volume. These sorts of devices also represent substantial capital investment which is beyond the means of many smaller operations.
Consequently, there has been a substantial need in the marketplace for a low cost compact combination optical scanning pattern generator and associated detector apparatus which is more appropriate for a small operation. It is particularly desirable that this be a fixed system since this is the manner in which most clerks handle items. It is much more efficient to keep the item moving in front of the fixed scanner that to move the scanner over the item in such applications as grocery stores where the bar codes are utilized. The need has also existed for an overhead mounted scanner since this will be easier for the clerk to utilize since the clerk will be able to optically observe the scan and the positioning of the bar codes during the scan process.