1. Field of the Invention
The present invention relates generally to automatic code symbol reading (i.e., recognition) systems, and more particularly to an automatic code symbol reading device having a control system which permits multiple modes of fully automated operation while conserving power and providing versatility in its method of use.
2. Brief Description of the Prior Art
Hitherto, a number of techniques have been proposed for reading bar code symbols using hand-held devices. Despite variety amongst prior art bar code symbol reading devices, the various techniques incorporated into prior art devices can be classified into two principally distinct classes, namely, manually operated or triggered bar code symbol reading devices, and automatic bar code symbol reading devices.
Representative of prior art manually operated bar code symbol reading devices are U.S. Pat. No. 4,387,297 to Swartz, et al., U.S. Pat. No. 4,575,625 to Knowles, and U.S. Pat. No. 4,845,349 to Cherry. While such prior art devices are capable of successful bar code symbol reading, they nevertheless suffer from several significant shortcomings and drawbacks. In particular, the user is required to manually pull a trigger or push a-button each time scanning and decoding is to be cyclically initiated and terminated. The requirement is most fatiguing on the user when large numbers of bar code symbols are to be read. Also, in certain symbol reading applications, such as warehouse inventory, pulling the trigger to initiate scanning of bar code symbols may be extremely difficult for the user due to the physical location of the objects bearing the bar code symbols.
An alternative to manually operated a bar code symbol reading devices is use of automatic bar code symbol readers, which incorporate techniques for automatically initiating and terminating scanning and decoding operations. Representative of prior art automatic bar code symbol devices are U.S. Pat. No. 4,639,606 to Boles, et al. and U.S. Pat. No. 4,933,538 to Heiman et al. While capable of automatically initiating scanning of bar code symbols, such prior art devices and incorporated techniques nevertheless also suffer from significant shortcomings and drawbacks.
In particular, U.S. Pat. No. 4,639,606 to Boles, et al. discloses laser emission control circuitry for use in implementing a hand-held triggerless bar code scanner. The laser is operated in a pulsed "find paper" mode until a reflected signal is obtained, indicating the presence of an object (e.g., paper) in the search field. Thereupon, the circuitry is changed to a "search mode" in which the power of the laser is increased to above the safety limits for a period of time, and the return signal is monitored for signal transitions corresponding to the black bars of the code. On detection of the first black bar, the circuitry is changed to an "in-code" (decode) mode as long as successive symbols are received within a given period of time. If the decode mode terminates within a predetermined time interval (e.g., one second after the beginning of the search mode), then the search mode is re-entered, otherwise the decode mode will change to find paper mode.
While the triggerless bar code symbol reader proposed in U.S. Pat. No. 4,639,606 possesses three modes of operation, this prior art bar code symbol reader nevertheless suffers from several significant shortcomings and drawbacks. In particular, this prior art bar code symbol reader requires continuous use of a pulsed laser beam to determine the presence of an object within the scan field, which, in hand-held portable battery power devices, undesirably drains limited power reserves, especially in extended time duration bar code reading applications. Furthermore, by its very design this prior art automatic bar code symbol reader, by its very design, will reread the same bar code symbol every 40 milliseconds provided the bar code symbol is decoded each time within a 1 millisecond or less time period. Consequently, when using this prior art bar code symbol reader, the user has no ability to manually control its operation in order to selectively read a bar code symbol one or more times as desired.
U.S. Pat. No. 4,933,538 discloses a bar code symbol scanning system, which in the "object sensor mode" the scanner is triggerless and the constantly on laser beam normally emits at a narrow angle and low power. When an indicia pattern indicative of a bar code symbol has been detected, the laser beam will widen, the power of the beam will increase, and the beam will read the entire symbol. While this prior art scanning technique permits detection of bar code symbols within the scan field in order that the power of the laser beam may be automatically increased to a higher level for collecting scan data for use in decoding operations, this prior art system nevertheless suffers from several significant shortcomings and drawbacks as well. In particular, this prior art system requires continuous use of laser emission to determine the presence of both objects and bar code symbols within the scan field, which necessarily results in drain of limited power reserves in portable battery power applications. Furthermore, when using this prior art bar code symbol reader, the user is incapable of manually controlling the reading of the same bar code symbol one ore more times, as desired or required in a particular bar code symbol reading application.
In general, prior art automatic bar code symbol reading devices also suffer from other shortcomings and drawbacks. For example, unlike manually operated devices which rely on the user to activate a trigger, once for each bar code to be read, prior art triggerless (i.e., automatic) bar code symbol reading devices also lack programmed intelligence capabilities which are necessary to prevent undesired multiple reading of bar code symbols, particularly when the scanning beam is permitted to dwell on a bar code symbol for extended periods of time.
Furthermore, prior art automatic bar code symbol reading devices have generally lacked control capabilities which permits diverse modes of programmable system-control operation which ensure power conservation, while preventing inadvertent or undesired multiple reads of the same bar code symbol.
Thus, there is a great need in the code symbol reading art for a fully automatic code symbol reading device which overcomes the above shortcomings and drawbacks of prior art devices and techniques.