Scan pattern generator for bar code symbol readers

Abstract: A light scanning system, for example for a bar code reader, provides a scan pattern of intersecting lines by means of a scanning system having at least one rotating mirror (176,210), and a plurality of fixed angled mirrors (180,182,184) which are spaced around the axis of rotation of the rotating mirror.

Description: This invention generally relates to light scanning systems for reading symbols and, more particularly, to scan pattern generators for generating scan patterns which extend across a symbol to be read. The invention may, without limitation, be used in laser bar-code scanners. The present application is divided out of EP-A-87309713.3 which relates to a light scanning system for producing parallel scan lines. Laser scanning systems and components of the type exemplified by US-A-4,251,798; US-A-4,360,798; US-A-4,369,361; US-A-4,387,297; US-A-4,593,186; US-A-4,496,831; US-A-4,409,470; US-A-4,460,120 and US-A-4,607,156 have generally been designed to read bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working or reading distance from a hand-held or stationary scanner, and with a reading spot of a certain size, the spot being scanned over each symbol to trace a scan line. It has previously been proposed to generate scan patterns of mutually parallel scan lines extending along one or two directions, as well as omni-directional scan patterns of intersecting scan lines, and even curve-linear scan patterns, for superposition over the symbol to be read to insure that, no matter what the angular orientation of a respective symbol might be within predetermined limits, at least one of the scan lines or part of the pattern will be scanned over the entire length of the respective symbol. Yet, the known patterns are generated by highly complex and expensive systems. Also, quite apart from the angular orientation of the symbols to be read, one symbol might be located close-in to the scanner, whereas another symbol might be located far-out from the scanner and, in short, successive symbols might be located at different working distances from the scanner. In the case of a scanner which has been designed to read symbols within a certain range of working distances, should it occur that a particular symbol falls outside this range, then the distance between the scanner and the symbol must be adjusted, and usually within a short time interval, for, otherwise, the symbol will not be read. In the case of a hand-held scanner, the scanner is usually manually moved toward or away from the symbol to adjust the distance between the scanner and the symbol. This can be a tiring procedure and require multiple reading attempts. It would be desirable, therefore, if the scan pattern generators also incorporated a so-called "zoom" characteristic in which the working distance is automatically changed during scanning. PCT document WO-A-84/00228 discloses those features set out in the preamble to Claims 1 and 8. US patent document US-A-4,560,862 discloses a system for optical scanning over a large depth of field incorporating a device which produces a scanning motion by means of a rotating polygonal hub. It is a general object of this invention to advance the state of the art of laser scanning systems for reading bar code symbols. It is another object of this invention to generate scan patterns of intersecting lines over the symbol with a relatively simple pattern generator system, with the option of simultaneously changing the working distance of the outgoing laser beam. According to the present invention there is provided a light scanning system characterised by the features in the characterising portion of Claim 1 and 8. The invention may be carried into practice in a number of ways and two specific embodiments will now be described by way of example, with reference to the figures, in which Figure 1 is a perspective view of a light scanning system in accordance with a first embodiment of this invention, and diagrammatically illustrating one scan pattern; Figure 1A is a diagrammatic illustration of another scan pattern; Figure 1B is a diagrammatic illustration of yet another scan pattern; Figure 1C is a diagrammatic illustration of still another scan pattern; Figure 1D is a diagrammatic illustration of a further scan pattern; Figure 2 is a perspective view of a further light scanning system in accordance with a second embodiment of this invention; and Figure 3 is a sectional view of the embodiment of Figure 2. Referring now to the drawings, Figures 1 to 3 generally identify an arrangement in a laser scanning system of the type generally described in the above-identified patents, for reading symbols, particularly UPC bar code symbols. As used in this specification and the following claims, the term "symbol" is intended to be broadly construed and to cover not only symbol patterns composed of alternating bars and spaces, but also other patterns, as well as alpha-numeric characters. The arrangement includes a housing 12 (Figure 3) which is intended to represent either hand-held, desk-top workstation, or stationary scanner, housings having an exit port 14 through which an outgoing laser light beam is directed to impinge on, and to be scanned across, symbols located exteriorly of the housing, each symbol to be scanned and read in its respective turn. A laser source, e.g. a gas later tube 16 or a semiconductor laser diode, is mounted in the housing 12 and, when energized, the source 16 generates a laser beam. An omni-directional scan line pattern generator (light scanning system) 170 is illustrated in Figure 1, and is operative for generating intersecting line patterns. The generator 170 is simple in construction and comprises a drive motor 172 having a vertical output shaft 174 on which a front surface planar mirror 176 is fixedly mounted for rotation in the circumferential direction of arrow 178. A plurality of inclined reflecting side mirrors 180,182,184 are equiangularly distributed about the vertical shaft 174. The side mirrors are positioned in the light path of a laser beam emitted from source 16 and directed by overhead folding mirror 186 to the centre mirror 176. Upon rotation of centre mirror 176, the laser beam is successively directed to mirrors 180,182,184 each in its turn, for reflection towards a symbol to be read. The resulting multiple line pattern 188 covers the symbol in the Figure 1 embodiment with three intersecting lines. If four, eight, six or five mirrors were equiangularly distributed about vertical shaft 174, then the patterns depicted in Figures 1A, 1B, 1C and 1D respectively, would be generated during each revolution of the centre mirror 176. A drive, such as a piston rod 181, reciprocally movable relative to a cylinder 183 along the directions of double-headed arrow 185, is connected to any one of the side mirrors, e.g. 180. As the side mirror 180 is moved radially toward and away from the axis of rotation of the centre mirror 176, the focused scan line associated with the side mirror 180 is located at different working distances, thereby achieving a zooming function. Another omni-directional scan line pattern generator 190 is illustrated in Figures 2 and 3 and generates not only intersecting scan line patterns, but also individual scan lines which are located at different working distances from the housing, thereby achieving a zooming function. As before, a drive motor 172 rotates a vertically oriented output shaft 174. A plurality of inclined side reflecting mirrors 180,182,184 are equiangularly arranged about the shaft 174. A housing 12 having exit aperture 14 also supports an overhead folding mirror 186 to which a laser beam from source 16 is directed. Rather than rotating a single mirror on shaft 174, as proposed by the previous embodiment, this embodiment proposes mounting a mirror assembly on the shaft 174. This mirror assembly includes elongated upper and lower bars 192,194 whose inner ends are fixed to shaft 174 and rotatable therewith in mutual parallelism. The bars 192, 194 are axially spaced apart by spacer 196. At the outer ends of bars 192,194 are respectively supported mirrors 198,200. Mirror 198 is stationarily mounted at the outer end of bar 192. Mirror 200 is mounted for rotation about axis 202 which is parallel to vertical axis 204 of the shaft 174. Mirror 200 is mounted at the outer end of bar 194 on a central shaft of a planetary gear 206 having exterior gear teeth which meshingly engage with exterior gear teeth of a stationary sun gear 208. Sun gear 208 coaxially surrounds the shaft 174 and is stationarily mounted on the housing of motor 172. Gears 206,208 are circular and sun gear 208 has a much larger diameter than that of planetary gear 206, so that mirror 200 is rotated at a high angular speed about its axis 202. Another mirror 210 is fixedly mounted at the inner end of bar 192, and is located in the optical path of light reflected from overhead mirror 186. The light reflected from mirror 210 is directed to stationary mirror 198, whereupon the reflected light is directed through a hole 212 in bar 192 to the rotary mirror 200 located underneath hole 212. In operation, light from source 16 is directed along an optical path by successive reflections off mirrors 186,210,198 and 200 prior to being directed to side mirrors 180,182,184. The relative positions of mirrors 210 and 198 are fixed relative to each other during rotation of the mirror assembly. At the same time that shaft 174 rotates, the mirror 200 experiences a dual movement. First, the mirror 200 rotates about its axis 202 with an angular speed proportional to the ratio of the diameters of gears 206,208. Second, the mirror 200 is moved along a circular annulus concentric with axis 204. Hence, the light reflected off mirror 200 will, for each revolution of mirror 200 about axis 202, sequentially impinge on side mirrors 180,182,184 which are inclined to direct successive scan beams out through port 14. Due to the diversion of light and the different optical paths between the rotary mirror 200 and the side mirrors 180, 182,184 at any one moment, at least some of the scan iines are positioned closer in to the housing 12 than other scan lines, thereby achieving a zooming action. Also, as the mirror 200 is also orbiting about the axis 204, the working distance generated by reflection from any one side mirror is always changing. A three-dimensional coverage of a symbol can thus be achieved with a very sophisticated pattern together with a zooming action. Of course, more than three side mirrors could have been used to obtain even more coverage. The exit port 14 need not be located above the generator 190, as shown in Figures 2 and 3 for use in a so-called "scan-above" system. Alternately, the port 14 could have been located so as to form a "scan-below" system or even a "scan-out" system. Although the preceding description has been rendered in terms of laser scanning systems and arrangements for optically modifying laser beams, it will be expressly understood that this invention is not intended to be so limited and, in fact, is intended to include non-laser light sources and beams, including non-coherent and coherent light sources such as light-emitting diode sources, incandescent light sources, gas discharge sources, etc. 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, different from the types described above. 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.

Claims: A light scanning system for reading symbols, comprising a housing (12) having an exit port (14), light means (16) in the housing for generating a light beam, and scanning means for scanning the light beam in scan lines across a symbol to be scanned located exteriorly of the housing; the scanning means comprising rotating drive means (172) arranged to drive a shaft (174), a rotating mirror (176,210) mounted with respect to the shaft for rotation by the drive (172), and a plurality of folding mirrors (180,182,184) mounted with respect to the housing (12), whereby as the shaft (174) rotates light from the light means (16) is directed to the exit port (14) along a plurality of optical paths, each path including the rotating mirror (176,210) and a respective one of the folding mirrors (180,182,184); characterised in that the rotating mirror (176,210) has a surface inclined with respect to a shaft axis (204), the scanning system further including means (181) for selectively moving at least one of the folding mirrors (180,182,184) to change the length of the respective optical path along which the light beam travels A light scanning system as claimed in Claim 1 in which the folding mirrors (180,182,184) are equiangularly spaced around the shaft (174). A light scanning system as claimed in Claim 1 or Claim 2 including means for radially moving at least one of the folding mirrors (180,182,184) towards and away from the shaft axis. A light scanning system as claimed in Claim 1 or Claim 2 in which the scanning means are arranged to focus each scan line at a predetermined distance from the exit port (14) of the housing (12), the scanning means further including means for changing the predetermined focusing distance of at least one of the scan lines during scanning. A light scanning system as claimed in any one of the preceding claims in which the scanning means generates a plurality of intersecting scan lines across the symbol to be scanned. A light scanning system as claimed in any one of the preceding claims in which the light beam is travelling along the shaft axis (204) when it impinges upon the rotating mirror (176,201). A light scanning system as claimed in Claim 6 in which the light means (16) are positioned off the shaft axis (204), the light beam being directed along the shaft axis by a further angled mirror (186). A light scanning system for reading symbols, comprising a housing (12) having an exit port (14), light means (16) in the housing for generating a light beam, and scanning means for scanning the light beam in scan lines across a symbol to be scanned located exteriorly of the housing; the scanning means comprising rotating drive means (172) arranged to drive a shaft (174), a first rotating mirror (176,210) mounted with respect to the shaft for rotation by the drive (172), and a plurality of folding mirrors (180,182,184) mounted with respect to the housing (12), whereby as the shaft (174) rotates light from the light means (16) is directed to the exit port (14) along a plurality of optical paths, each path including the first rotating mirror (176,210) and a respective one of the folding mirrors (180,182,184); characterised in that the first rotating mirror (176,210) has a surface inclined with respect to a shaft axis (204), the light beam further impinges upon a second rotating mirror (200), the second rotating mirror being mounted offset from the shaft axis (204) for rotation in a circular motion about the shaft axis (204), and being arranged in addition for rotation about its own second rotation axis (202) at an angular speed greater than that of said first rotating mirror so as to change the length of the respective optical path along which the light beam travels. A light scanning system as claimed in Claim 8 in which the light beam is directed from the rotating mirror (210) to the second rotating mirror (200) via an intermediate mirror (198) which is fixedly mounted with respect to the first rotating mirror (210). A light scanning system as claimed in Claim 8 or Claim 9 in which the second rotating mirror (200) is caused to rotate about the second rotation axis (202) by means of a planetary gear arrangement (206,208).

Inventors: KRICHEVER MARK J, METLITSKY BORIS, KRICHEVER, MARK J., METLITSKY, BORIS
Applicants: SYMBOL TECHNOLOGIES INC, SYMBOL TECHNOLOGIES, INC.
Application year: 1987
Main classification: G06K7
IPC codes: G06K7