Patent Application
20100096459
Moving laser beam readers or laser scanners, as well as solid-state imaging systems or imaging readers, have both been used to electro-optically read one-dimensional bar code symbols, particularly of the Universal Product Code (UPC) type, each having a row of bars and spaces spaced apart along one direction, and two-dimensional symbols, such as Code 49, which introduced the concept of vertically stacking a plurality of rows of bar and space patterns in a single symbol, as described in U.S. Pat. No. 4,794,239. Another two-dimensional code structure for increasing the amount of data that can be represented or stored on a given amount of surface area is known as PDF417 and is described in U.S. Pat. No. 5,304,786.
Moving laser beam readers generally include a laser for emitting a laser beam, a focusing lens assembly for focusing the laser beam to form a beam spot having a certain size at a focal plane in a range of working distances, a scan component for repetitively scanning the beam spot across a target symbol in a scan pattern, for example, a scan line or a series of scan lines, across the target symbol multiple times per second, e.g., forty times per second, a photodetector for detecting light reflected and/or scattered from the symbol and for converting the detected light into an analog electrical signal, and signal processing circuitry including a digitizer for digitizing the analog signal, and a microprocessor for decoding the digitized signal based upon a specific symbology used for the symbol.
The imaging reader includes a solid-state imager or sensor having an array of cells or photosensors, which correspond to image elements or pixels in a field of view of the imager, an illuminating light assembly for illuminating the field of view with illumination light from an illumination light source, e.g., a laser or one or more light emitting diodes (LEDs), and an imaging lens assembly for capturing return ambient and/or illumination light scattered and/or reflected from the symbol being imaged over a range of working distances. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing electronic signals corresponding to a one- or two-dimensional array of pixel information over the field of view.
It is therefore known to use the imager for capturing a monochrome image of the symbol as, for example, disclosed in U.S. Pat. No. 5,703,349. It is also known to use the imager with multiple buried channels for capturing a full color image of the symbol as, for example, disclosed in U.S. Pat. No. 4,613,895. It is common to provide a two-dimensional CCD with a 640×480 resolution commonly found in VGA monitors, although other resolution sizes are possible.
As advantageous as both types of readers are in reading symbols, it is desirable in many applications to increase the range of working distances at which symbols can be read. Increasing the intensity or brightness of the laser beam in the moving laser beam reader will increase the working distance range, because there will be correspondingly more return light to detect from symbols that are further away from the moving laser beam reader. However, increasing the laser beam intensity too much may violate human eye exposure laser safety standard limits. For example, a class 2 laser is limited to an output power of 1 mW over a base time interval of 250 msec, and a class 1 laser is limited to an output power of 0.39 mW over a base time interval of 10 sec. The laser beam intensity cannot exceed these limits.
Similarly, increasing the intensity or brightness of the laser or LED illumination light in the imaging reader will increase the working distance range, because there will be correspondingly more return light for the imager to detect from symbols that are further away from the imaging reader. LEDs, just like lasers, are subject to human eye exposure safety standard limits, which cannot be exceeded.
For increased safety, the art has proposed maintaining the output power level of the laser or LED such that the output power does not exceed these limits. For example, the output power level of the laser is kept constant and the same for each scan line in the moving laser beam reader. However, as noted above, this reduces the working distance range and degrades reader performance.
Accordingly, there is a need for a system for, and a method of, enhancing the working distance range of such readers, without violating human eye exposure safety limit standards.
One feature of this invention resides, briefly stated, in reader for electro-optically reading a target, such as one- and/or two-dimensional bar code symbols, as well as non-symbols, in an extended range of working distances. The reader includes a housing, preferably one having a handle for handheld operation; a data capture assembly supported by the housing and operative for directing light at a variable power level at the target in a plurality of successive scans, and for detecting return light from the target; and a controller for controlling the data capture assembly by increasing the power level of the light during at least one of the successive scans to enable detection of the target located at an increased working distance from the reader, and by decreasing the power level of the light during at least another of the successive scans to maintain an output power level within safety limits.
In one embodiment, the reader is a moving laser beam reader, which includes a laser for emitting the light as a laser beam, a scanner for sweeping the laser beam across the target as a plurality of scan lines for reflection and scattering as the return light, and a detector for detecting the return light. The controller is operative for driving the laser at an increased power level during the at least one scan, and at a decreased power level during the at least other scan. Preferably, the controller is operative for driving the laser to alternate between the increased power level and the decreased power level during the successive scans. Advantageously, the increased power level is a higher constant and the same during a first group of the alternate scans, and the decreased power level is a lower constant and the same during a second group of the alternate scans.
In another embodiment, the reader is an imaging reader, which includes an illuminator for emitting the light as illumination light that illuminates the target, and a solid-state imager, such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device, for detecting the return illumination light in successive exposures. The controller is operative for driving the illuminator at an increased power level during at least one exposure, and at a decreased power level during at least another exposure. Preferably, the controller is operative for driving the illuminator to alternate between the increased power level and the decreased power level during the successive exposures. Advantageously, the increased power level is a higher constant and the same during a first group of the alternate exposures, and the decreased power level is a lower constant and the same during a second group of the alternate exposures.
Hence, in accordance with this invention, the increased output power level of the laser or LED increases the working range, and the decreased output power level of the laser or LED insures that the output power does not exceed human eye exposure safety limit standards. Reader performance is enhanced.
Another feature of this invention resides, briefly stated, in a method of electro-optically reading a target in a range of working distances from a reader, the method being performed by directing light at a variable power level at the target in a plurality of successive scans, detecting return light from the target, increasing the power level of the light during at least one of the successive scans to enable detection of the target located at an increased working distance from the reader, and decreasing the power level of the light during at least another of the successive scans to maintain an output power level within safety limits. Advantageously, the increasing and decreasing steps are alternately performed.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
When the reader 50 is operated in low light or dark ambient environments, the imaging reader 50 includes an illuminator 32 for illuminating the target during the imaging with illumination light directed from an illumination light source through the window 46. Thus, the return light may be derived from the illumination light and/or ambient light. The illumination light source comprises one or more light emitting diodes (LEDs) or a laser. An aiming light generator 34 may also be provided for projecting an aiming light pattern or mark on the target prior to imaging.
In operation of the imaging reader 50, the controller 70 sends a command signal to drive the illuminator LEDs/laser 32 for a short time period, say 500 microseconds or less, and energizes the imager 30 during an exposure time period of a frame to collect light from the target during said time period. A typical array needs about 33 milliseconds to read the entire target image and operates at a frame rate of about 30 frames per second. The array may have on the order of one million addressable image sensors.
Turning to
In accordance with the present invention, as shown in
Preferably, the controller 70 is operative for driving the laser 64 or the illuminator LEDs/laser 32 to alternate between the increased power level “P1” and the decreased power level “P2” during the successive scans. Advantageously, the increased power level “P1” is a higher constant and the same during a first group of the alternate scans, i.e., the odd-numbered scans or exposures, and the decreased power level “P2” is a lower constant and the same during a second group of the alternate scans scans, i.e., the even-numbered scans or exposures. The area under the graph of
Hence, in accordance with this invention, the increased output power level “P1” of the laser 64 or the illuminator LEDs/laser 32 increases the working range, and the decreased output power level “P2” of the laser 64 or the illuminator LEDs/laser 32 insures that the output power does not exceed human eye exposure safety limit standards. Reader performance is enhanced.
It will be understood that each of the elements described above, or two or more together, also may find a useful application in other types of constructions differing from the types described above.
While the invention has been illustrated and described as embodied in electro-optical readers, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. For example, the pattern depicted in
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
