Method of producing an omnidirectional scan pattern

Abstract: A method of optimizing the reading ability of an omnidirectional optical scanner for various bar code label aspect ratios which can effectively double the angular coverage of an ordinary scan module is provided. For high aspect ratio bar code labels, the method involves increasing the speed ratio between a first scanner motor (20) within a scan module (12) for providing a first multi-line scan pattern, and a second scanner motor (36) within a tilted mirror assembly (48) for rotating said first multiline scan pattern about the axi of rotation of said second scanner motor (36), by decreasing the speed of the second scanner motor (36) by a predetermined amount. For other bar code labels, the method involves decreasing the speed ratio between the first scanner motor (20) and the second scanner motor (36) by increasing the speed of the second scanner motor (36) by the predetermined amount. The method also includes the steps of decreasing the swipe speed of articles having high aspect ratio bar code labels and increasing the swipe speed of other articles.

Description: This invention relates to optimising the reading ability of omnidirectional optical scanners for reading bar code labels. Optical scanners are well-known for their usefulness in retail checkout and inventory control. Optical scanners generally employ a laser diode, the light from which is focussed and collimated to produce a scanning beam. The beam is reflected by mirrors and produces a multi-directional scan pattern covering a bar code label. A detector receives the returning beam reflected from the bar code label and signals generated by the detector are then decoded and transmitted to a remote processing member. EP-A-0323026 discloses a multi-directional optical scanner including a laser/detector unit which generates a light beam directed along an optical path with first and second mirrors each inclined at a tilt angle and each rotated about an axis at an angular speed. The size and shape of the scan pattern may be controlled by adjusting the tilt angles and the angular speeds. This European specification provides no teaching as to how to optimise the reading ability of the scanner for various bar code label aspect ratios. According to the invention there is provided a method for optimising the reading ability of an omnidirectional optical scanner for various bar code label aspect ratios, the scanner comprising a laser source, first and second mirror assemblies and a detector, to provide a scan pattern having a plurality of first scan lines intersecting a respective plurality of second scan lines, the first mirror assembly being part of a scan module having a plurality of stationary pattern mirrors and an optical transceiver rotated by a first, fixed speed scanner motor for directing a laser beam towards the pattern mirrors, for producing a plurality of scan lines and collecting light from articles having bar code labels to be scanned the second tilted mirror assembly having a second scanner motor for turning a drive shaft and a mirror mounted at an angle to the drive shaft for reflecting the scan lines from the first mirror assembly for scanning an article having a bar code label which is swiped past the scanner at a predetermined swipe speed, the method comprising the following steps: (a) if the bar code label is a high aspect bar code label, increasing the speed ratio between the first scanner motor and the second scanner motor, including the sub-step of decreasing the speed of the second scanner motor by a first predetermined amount to increase the angle of intersection of the first of second scan lines; (b) decreasing the swipe speed of the high aspect bar code label (30) past the scanner; and (c) collecting and decoding light reflected from the high aspect ratio bar code label; or (d) if the bar code label has any other aspect ratio, decreasing the speed ratio between the first scanner motor and the second scanner motor, including the sub-step of increasing the speed of the second scanner motor by a second predetermined amount to decrease the angle of intersection of the first and second scan lines; (e) increasing the swipe speed of the other bar code label past the scanner; and (f) collecting and decoding light reflected from the other bar code label. Summarising, we have found that optimisation may be achieved by using as a component of a multi-directional optical scanner as set forth in EP-A-0323026 a scan module as disclosed in US-A-4971410, and by varying the relative speeds of the scanner motor in the module and a second scanner motor rotating the second mirror in the manner set forth in claim 1. Put very briefly, to optimise the reading ability of an omnidirectional optical scanner for high aspect ratio bar code labels, the speed ratio between the first scanner motor within the scan module and the second scanner motor with a tilted mirror assembly is increased by decreasing the speed of the second scanner motor by a predetermined amount. For other non-high aspect ratio bar code labels, the speed ratio between the first scanner motor and the second scanner motor is decreased by increasing the speed of the second scanner motor by a predetermined amount. In an enhancement of the method, programming tags and speed control circuitry are used to change the speed of the second motor. It is particularly advantageous in the present invention that the speed of the first motor within the scan module remains fixed providing simplicity of operation and structure and accordingly reducing costs. The invention is described further hereinafter by way of example only with reference to the accompanying drawings in which: Figure 1 is a detailed schematic representation of an optical scanner used in implementing a method embodying the present invention; Figure 2 is a plan view of a scan pattern generated by the scan module of Figure 1; Figure 3 is a plan view of a scan pattern generated by a tilted reflecting mirror; Fig. 4A is a plan view of a part of a first scan pattern produced by the optical scanner at a first tilted mirror speed; Fig. 4B is a plan view of a part of a second scan pattern produced by the optical scanner at a second tilted mirror speed; and Fig. 5 is a flow chart of the method of the present invention. Referring now to Fig. 1, optical scanner 10 includes scan module 12, tilted mirror assembly 14, and printed circuit board (PCB) 16. Scan module 12 produces a first scan pattern 17 (Fig. 2) and includes laser 18, motor 20 for driving a hollow shaft 22, transceiver 24 mounted to the end of shaft 22, stationary pattern generating mirrors 26, and photodetector 28. Laser 18 projects a laser beam through hollow drive shaft 22 to be deflected by transceiver 24 towards pattern generating mirrors 26. Mirrors 26 deflect the first pattern towards tilted mirror assembly 14. Light reflected from bar code label 30 is redirected towards pattern generating mirrors 26. Pattern generating mirrors 26 direct the light at transceiver 24 which directs the light to photodetector 28. The construction of scan module 12 is disclosed in U.S. Patent No. 4,971,410. A PCB 16 contains processing circuitry, including a controller 31, for decoding signals generated by photodetector 28 and transmitting the decoded signals over coiled cable 32 to remote processing member 34. Power is supplied to laser 18, motor 20, tilted mirror assembly motor 36, and photodetector 28 through electrical plug 38 and cable 32. Motor 36 is coupled to speed control circuitry 39. Printed circuit board 16 additionally contains circuitry for operating speaker 40, and green and red indicator lights 42 and 44, which represent valid and invalid reading operations, respectively. Tilted mirror assembly 14 includes motor 36 having drive shaft 46 and rotating reflecting mirror 48, which is offset-mounted to drive shaft 46. Preferably, motor 36 and motor 20 rotate in opposite directions. Motor shaft 46 is oriented at an angle to drive shaft 22, which preferably is forty-five degrees. In the preferred embodiment, bar code label 30 may also be a programming tag for programming the speed of motor 36. A feature of scanner 10 is that the speed ratio of motor 20 to motor 36 is selectable. Preferably, the speed of motor 36 is one-twentieth the speed of motor 20, which in the preferred embodiment is forty-eight hundred rpm. Although integer values for the motor speed ratio are preferred, non-integer values are also envisaged, especially to compensate for motor speed ratio drift. Referring now to Fig. 2, scan pattern 17 is a star pattern. The points of the star subtend an angle 52, which in the preferred embodiment is about twenty-six degrees. Referring now to Fig. 3, tilted mirror assembly 14 uses first pattern 17 generated by scan module 12 to produce a highly-dense, second scan pattern 53. First scan pattern 17 is projected onto rotating reflecting mirror 48, which rotates scan pattern 17 about the tilted axis of drive shaft 46 to form scan pattern 53. Advantageously, tilted mirror assembly 14 improves the reading efficiency of scanner 10, irrespective of the size or orientation of bar code label 30. Turning now to Fig. 4A, the rotation and tilt of mirror 48 create a raster effect. During the first half-cycle of mirror 48, motor 20 completes a predetermined number of revolutions, each revolution producing a complete scan pattern 17. Since mirror 48 is tilted with respect to shaft 46, mirror 48 presents an increasing angle of incidence during one half-cycle and a decreasing angle of incidence during the other half-cycle. The increase and decrease in angle of incidence cause lines from scan pattern 17 to be spread out in the scanning reference plane above scanner 10. It is a feature of scanner 10 that the angle of an individual scan line changes as it rasters up or rasters down to enhance the angular coverage of the first scan pattern. The method of the present invention optimizes this effect by properly selecting the speed ratio of the first motor to the tilted mirror assembly motor to effectively double the angular coverage of the scan module and thereby doubles the aspect ratio for which the pattern of the scanner is omnidirectional. Reflected lines 56 originate from one line of scan pattern 17 and follow one after the other in one direction to describe a raster down effect. Reflected lines 58 also originate from the one scan line and follow one after the other in an opposite direction to describe a raster up effect. Combining the raster lines of all of the scan lines of scan pattern 17 produces scan pattern 53. A feature of this combination is the angular multiplication effect. The angle 60 between crossing raster up and raster down lines 56 and 58 is approximately twice the angle of one of either of these lines with respect to a scanned article. Angle 60 varies with the distance or raster width D separating the raster lines from each other, which is a function of the speed ratio of motors 20 and 36. High speed ratios produce more lines separated by less distance and therefore subtended by smaller angles. Turning now to Fig. 4B, a part of a second scan pattern from scanner 10 has a larger raster width D', a larger angle 60', and a lower number of scan lines 56 and 58 than the scan pattern of Fig. 4A. This scan pattern is suited for reading high aspect bar code labels and is produced by increasing the speed ratio between motors 20 and 36. The method of the present invention involves altering the speed ratio of motors 20 and 36 to optimize scanning efficiency for different aspect ratio bar code labels. Increasing the speed ratio of motor 20 to motor 36 optimizes scanning efficiency for high aspect ratio bar code labels, but requires slower article swiping speeds. Here, high aspect ratio bar code labels are those having a length to width ratio between three and six. Decreasing the speed ratio optimizes scanning efficiency for other aspect ratio bar code labels and permits faster article swiping speeds. In the preferred embodiment, the speed of motor 20 is fixed to match the processing resolution of the controller 31; therefore, the speed of motor 36 is altered to match the aspect ratio of the label to be scanned. The speed of motor 36 may be altered using programming tags, which are bar code labels containing programming information, and motor speed control circuitry 39. Turning now to Fig. 5, method 70 of the present invention begins at "START" 72. In block 74, method 70 awaits programming instructions from programming tags. If programming instructions have not been read by scanner 10, then method 70 returns to the main program for operating scanner 10 in block 76. If programming instructions have been read, then method 70 determines the type of programming instructions read in block 78. If the programming instructions are not related to raster width, then method 70 performs non-raster programming in block 80 and then returns to the main program in block 76. If the programming instructions are related to raster width, then method 70 determines whether the programming instructions call for a decrease in raster width in block 82. If the programming instructions call for a decrease in raster width, then method 70 decreases the speed ratio of motor 20 to motor 36. In the preferred embodiment, the speed of motor 20 is fixed and the speed of motor 36 is increased by a predetermined speed increment in block 84. Method 70 then returns to the main program in block 76. In the preferred embodiment, the predetermined increment is one twentieth of the speed of motor 20. If the speed of motor 20 is forty-eight hundred rpm, then the increment is two-hundred-and-forty rpm. If the programming instructions are not related to decreasing the raster width, then the programming instructions call for an increase in raster width. Method 70 increases the speed ratio, as represented in block 86, and then returns to the main program in block 76. In the preferred embodiment, the speed of motor 20 is fixed and the speed of motor 36 is decreased by a predetermined increment. In the preferred embodiment, the predetermined increment is one twentieth of the speed of motor 20. Advantageously, the method of the present invention effectively doubles the angular coverage of the scan module and thereby doubles the aspect ratio for which the pattern of the scanner is omnidirectional. It is a feature of the omnidirectional scanner that the angle of an individual scan line changes as it rasters up or rasters down to enhance the angular coverage of the first scan pattern. The method of the present invention optimizes this effect by properly selecting the speed ratio of the first motor to the tilted mirror assembly motor to effectively double the angular coverage of the scan module and thereby double the aspect ratio for which the pattern of the scanner is omnidirectional.

Claims: A method for optimising the reading ability of an omnidirectional optical scanner for various bar code label aspect ratios, the scanner comprising a laser source (18), first and second mirror assemblies (26, 48) and a detector (28), to provide a scan pattern having a plurality of first scan lines intersecting a respective plurality of second scan lines, the first mirror assembly being part of a scan module (16) having a plurality of stationary pattern mirrors (26) and an optical transceiver (24) rotated by a first, fixed speed scanner motor (20) for directing a laser beam (18) towards the pattern mirrors (26), for producing a plurality of scan lines and collecting light from articles having bar code labels to be scanned, the second tilted mirror assembly (48) having a second scanner motor (36) for turning a drive shaft (46) and a mirror (48) mounted at an angle to the drive shaft for reflecting the scan lines from the first mirror assembly for scanning an article having a bar code label (30) which is swiped past the scanner at a predetermined swipe speed, the method comprising the following steps: (a) if the bar code label (30) is a high aspect bar code label, increasing the speed ratio between the first scanner motor (20) and the second scanner motor (36), including the sub-step of decreasing the speed of the second scanner motor (36) by a first predetermined amount to increase the angle of intersection of the first of second scan lines; (b) decreasing the swipe speed of the high aspect bar code label (30) past the scanner; and (c) collecting and decoding light reflected from the high aspect ratio bar code label; or (d) if the bar code label has any other aspect ratio, decreasing the speed ratio between the first scanner motor (20) and the second scanner motor (36), including the sub-step of increasing the speed of the second scanner motor (36) by a second predetermined amount to decrease the angle of intersection of the first and second scan lines; (e) increasing the swipe speed of the other bar code label (30) past the scanner; and (f) collecting and decoding light reflected from the other bar code label. A method for optimising the reading ability of an omnidirectional scanner according to Claim 1, wherein the sub-step in step (a) comprises the following sub-sub-steps: (i) scanning a programming tag having program instructions for a controller (31) to decrease the speed of the second scanner motor (36) by the first predetermined amount; and (ii) sending controller instructions to decrease the speed of the second scanner motor (36) to speed control circuitry (39) coupled between the controller (31) and the second scanner motor (36). A method for optimising the reading ability of an omnidirectional scanner according to Claim 1 wherein the sub-step in step (d) comprises the following sub-sub-steps: (i) scanning a programming tag having program instructions for a controller (31) to increase the speed of the second scanner motor (36) by the second predetermined amount; and (ii) sending controller instructions to increase the speed of the second scanner motor (36) to speed control circuitry (39) coupled between the controller (31) and the second scanner motor (36).

Inventors: COLLINS DONALD ALEXANDER JR, LINDACHER JOSEPH MICHAEL, WIKE CHARLES KENNETH JR, COLLINS, DONALD ALEXANDER, JR., LINDACHER, JOSEPH MICHAEL, WIKE, CHARLES KENNETH, JR.
Applicants: NCR INT INC, NCR INTERNATIONAL, INC.
Application year: 1992
Main classification: G06K7
IPC codes: G06K7