Scanning arrangement

Abstract: High speed scanning arrangements in scanners for reading bar code symbols by oscillating a scanner component in single or multi-axis scan patterns.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally relates to a scanning arrangement in a scanner operative for repetitively scanning indicia having parts of different light reflectivity, for example, bar code symbols, and, more particularly, to operating such a scanning arrangement at high speeds in single or multi-axis scan patterns. 2. Description of the Related Art Various optical readers and optical scanners have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths and spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting properties. The readers and scanners electro-optically decoded the coded patterns to multiple digit representations descriptive of the objects. Scanners of this general type have been disclosed, for example, in U.S. Patent Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,808,804; 4,816,661; 4,816,660; and 4,871,904, all of said patents having been assigned to the same assignee as the instant invention. As disclosed in the above-identified patents and applications, a particularly advantageous embodiment of such a scanner resided, inter alia, in emitting a light beam, preferably a laser beam, emitted from a light source, preferably a gas laser or a laser diode, and in directing the laser beam to a symbol to be read. En route to the symbol, the laser beam was directed to, and reflected off, a light reflector of a scanning component. The scanning component moved the reflector in a cyclical fashion and caused the laser beam to repetitively scan the symbol. The symbol reflected the laser beam incident thereon. A portion of the incident light reflected off the symbol was collected and detected by a detector component, e.g. a photodiode, of the scanner. The photodiode had a field of view, and the detected light over the field of view was decoded by electrical decode circuitry into data descriptive of the symbol for subsequent processing. The cyclically movable reflector swept the laser beam across the symbol and/or swept the field of view during scanning. U.S. Patent Nos. 4,387,297 and 4,496,831 disclose a high-speed scanning component including an electric motor operative for reciprocatingly oscillating a reflector in opposite circumferential directions relative to an output shaft of the motor. Electrical power is continuously applied to the motor during scanning. The light beam which impinges on the light reflector is rapidly swept across a symbol to be scanned in a predetermined cyclical manner. The scanning component comprises at least one scan means for sweeping the symbol along a predetermined direction (X-axis) lengthwise thereof. The scanning component may also comprise another scan means for sweeping the symbol along a transverse direction (Y-axis) which is substantially orthogonal to the predetermined direction, to thereby generate a raster-type scan pattern over the symbol. In addition to a single scan line and the raster-type pattern, other types of scan patterns are also possible, such as, x-shaped, Lissajous, curvilinear (see U.S. Patent 4,871,904), etc. For example, if the X and Y axis scanning motors are both driven such that the light reflectors are driven at a sinusoidally-varying rate of speed, then the scan pattern at the reference plane will be a Lissajous-type pattern for omni-directional scanning of the symbols. The use of two separate scanning motors and control means to produce the multi-axis and omni-directional scanning pattern increases material and labor costs as well as the amount of electrical power needed to operate the scanner. In addition, the relatively complicated motor Shaft and bearing arrangements of the scanning components may result in a useful life that is inadequate for some applications. Furthermore, the scanning components disclosed in U.S. Patents 4,387,297 and 4,496,831 are designed for miniature light reflectors and are not well suited for large scale reflectors. With respect to the prior art further attention is drawn to WO-89/11113 which discloses a beam scanning system having a beam reflecting element which is pivotable about two perpendicular axes so as to provide for scanning a reflected beam in two dimensions. The first pivot axis may be provided by a spindle supporting a galvanometer mirror. The second axis which coincides will the path of an incident beam will be provided by a motor driven shaft. From EP-A-0 344 882 a resonant scanning unit is known which utilizes a "tuning fork" design with a mirror mounted on one arm of the tuning fork and a counterbalance mass mounted on the other arm. A voice coil electromagnetic motor mounted between the arms causes the arms to move in opposite directions. Light generated by a line of LEDs is reflected from the oscillating mirror to generate a raster-type display. US-A-4 230 393 discloses an optical scanner capable of scanning parallel to two intersecting axes. The scanner comprises a single electromechanical transducer and a compliant link interconnecting the transducer with an optical element to which the two-axis movement is to be imparted. GB-A-2 175 705 discloses a dirigible reflector in which the reflector and its mountings are formed integrally in a single crystal material, for example silicon, by selective etching. GB-A-2 097 148 discloses a laser ray apparatus comprising means arranged to impose onto the mirror an oscillatory motion which determines for each incident laser light beam a distribution of the corresponding reflected beam within a predetermined angular field. The means comprises: a tipping support to which the mirror is connected; a motor; and a motion conversion unit which converts the rotary motion of a shaft of the motor into an oscillatory motion of the tipping support. The present invention relates to an arrangement for scanning indicia as referred to in independent claim 1. Preferred embodiments of the present invention are disclosed in the dependent claims. SUMMARY OF THE INVENTION It is a general object of this invention to advance the state of the art of scanners for reading indicia of different light reflectivity, particularly laser scanners for reading bar code symbols. An additional object of this invention is to provide novel high-speed scanning elements and novel scanning methods of operation. Yet another object of this invention is to conveniently generate single line, multi-line or omni-directional scan patterns with the same scanning elements. A further object of this invention is to provide a scanning arrangement having an increased scan line amplitude. It is another object of this invention to minimize the number of elements comprising the scanning component. Another object of this invention is to increase the working lifetime of the scanning components. These objects are solved by a scanning arrangement as defined in claim 1. Further embodiments are defined in dependent claims 2 to 12. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front perspective view of hand-held head employed in a scanner; Figure 2 is a cross-sectional view of an embodiment of the scanning arrangement according to this invention; Figure 3 is a cross-sectional view of yet another embodiment of a scanning arrangement according to this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, as shown in Figure 1, reference numeral 10 generally identifies a hand-held, gun-shaped scanner head having a barrel 12 and a handle 14. The head need not be gun-shaped as any suitable configuration may be used, such as box-like. A manually-operable trigger 16 is situated below the barrel 12 on an upper, forwardly-facing part of the handle 14. As known from the above-identified patents and applications incorporated by reference herein, a light source component, typically, but not necessarily, a laser, is mounted inside the head 10. The light source emits a light beam along a transmission path which extends outwardly through a window 18 that faces indicia, e.g. bar code symbols, to be read. Also mounted within the head is a photodetector component, e.g. a photodiode, having a field of view, and operative for collecting reflected light returning through the window 14 along a return path from the symbol. A scanner component is mounted within the head 10, and is operative for scanning the symbol and/or the field of view of the photodetector. The scanner component includes at least one light reflector positioned in the transmission path and/or the return path. The reflector is driven by an electrically-operated drive to oscillate in alternate circumferential directions, preferably at the resonant frequency of the scanner component. The photodetector generates an electrical analog signal indicative of the variable intensity of the reflected light. This analog signal is converted into a digital signal by an analog-to-digital converter circuit. This digital signal is conducted, according to one embodiment, along an electrical cable 20 to a decode module 22 located exteriorly of the head 10. The decode module 22 decodes the digital signal into data descriptive of the symbol. An external host device 24, usually a computer, serves mainly as a data storage in which the data generated by the decode module 22 is stored for subsequent processing. In operation, each time a user wishes to have a symbol read, the user aims the head at the symbol and pulls the trigger 16 to initiate reading of the symbol. The trigger 16 is an electrical switch that actuates the drive means. The symbol is repetitively scanned a plurality of times per second, e.g. 40 times per second. As soon as the symbol has been successfully decoded and read, the scanning action is automatically terminated, thereby enabling the scanner to be directed to the next symbol to be read in its respective turn. In addition, the head need not be a portable hand held type as fixedly mounted heads are also contemplated in this invention. Furthermore, the heads may have manually operated triggers or may be continuously operated by direct connection to an electrical source. The oscillations need only last a second or so, since the multiple oscillations, rather than time, increase the probability of getting a successful decode for a symbol, even a poorly printed one. The resonating reflector has a predetermined, predictable, known, generally uniform, angular speec for increased system reliability. An embodiment of the invention having an asymmetrically dimensioned U-shaped spring is shown in Figure 2 in which the tuning fork 121 is constructed having a small dimensioned arm 123 and a large dimensioned arm 125 which results in the nodal point 127 of the spring being positioned on arm 125 rather than at the bottom of the U as with a symmetrically dimensioned spring. As shown in Figure 2, the component 129 is mounted to arm 123 and the actuatcr comprises an electromagnetic coil 131 having a passage 133 through which magnet 135 passes with clearance. The U-shaped spring 121 is secured to a support 137 by a planar spring 139. The spring 139 is secured to base section 141 and the coil 131 is mounted to wall section 143. Leads 145 are provided to apply the driving signal to the coil 131 to effect angular movement of the component 129. The asymmetrically dimensioned U-shaped spring 121 provides an increased angular amplitude of the scan resulting from light directed from a laser 147 and reflected from component 129. In addition to increasing the angular amplitude, which can be as much as a 100% increase over a symmetrically dimensioned spring, the asymmetrically dimensioned U-shaped spring provides a higher durability against metal fatigue and cracking since the nodal point is not at a curved portion of the spring. Also shown in Figure 2, is a section 149 of spring 139 that is substantially parallel to wall 143 and section 151 angled away from wall 143 while at rest. The angled section 151 results in a further increase in the angular amplitude of scan oscillations (as much as 200% higher) over a symmetrically dimensioned U-shaped spring. Another benefit is less vibration being transferred to the base since the U-shaped spring is held only at the magnet end and angular movement of the magnet can be four times lower than that of the scanning component. The arrangement of Figure 2 is an elevated view showing the U-shaped spring 121 and the planar spring 139 both positioned for vibration in the x-y plane resulting in a single scan line directed along the y direction. If the U-shaped and planar springs are positioned in orthogonal planes and an appropriate superimposed high and low frequency driving signal is applied to the coil, a raster-type scan pattern will be provided with an increased x direction angular amplitude. In certain applications, it may be desirable to scan a symbol with an omnidirectional scan pattern. One technique for obtaining an omnidirectional pattern is to position the arrangement of Figure 2 such that the U-shaped spring vibrates in the x-z plane. Hence, by viewing Figure 2 as the top view of the arrangement, it can be seen that the material mass of the elements on the right hand side of spring 139 (spring 121 and component 129) is substantially greater than the mass of the elements on the left hand side of spring 139 (magnet 131). This difference in mass provides a weight imbalance that results in a torsional bending of the spring 139 that imparts an angular oscillatory movement of the component 129 in the x-y plane for effecting a y direction scan. In addition, the movement of the spring 139 towards the coil 131 and away from the coil 131 causes the U-shaped spring 121 to vibrate in the x-z plane which imparts an angular oscillatory movement to the component 129 for effecting an x direction scan. Upon the application the superimposed driving signal, preferably comprised of a pair of sine waves having a frequency ratio in the range of 1.05:1 to 5:1, to leads 145, spring 139 torsionally vibrates at the lower frequency and the U-shaped spring 121 simultaneously vibrates at the higher frequency in such a manner that light will be reflected from the component 129 in a Lissajous scan pattern over the indicia. The Lissajous pattern is provided by the path of the light beam being oscillated in the x and y orthogonal directions in simple harmonic motions at a predetermined ratio of frequencies. Thus, an omnidirectional scan pattern is produced. Figure 3 shows another technique for producing an omnidirectional scan pattern namely, rotating the entire holder means about an axis. The arrangement shown in Figure 3 is similar to that of Figure 2 and like reference numerals are used to identify like parts and a description thereof is not repeated here for the sake of brevity. In order to rotate the entire scanning arrangement, means 180 is provided to rotate the arrangement about an axis 182. The means 180 shown in Figure X3 is illustrative only as any suitable means for rotating the scanning arrangement about an axis may be employed to effect an omnidirectional scan pattern. The means 180 includes a motor 182 having a shaft 184 for driving a transmission belt 186. Belt 186 is coupled to a shaft (not shown) connected to the support 137 for rotating the support 137 about ball bearing 188 which is attached to support beam 190. The rotation of a single axis direction scan arrangement will produce an omnidirectional scan pattern in the form of a Rosette. The rotation of a two-axis scan arrangement will produce various other omnidirectional patterns depending on the type of two-axis arrangement rotated.

Claims: A scanning arrangement for reading indicia having parts of different light reflectivity by directing light toward the indicia, and by collecting reflected light returning from the indicia, said arrangement for scanning the indicia, comprising: (a) a scanner component (129); (b) holder means for mounting the component (129) for angular oscillating movement in first and second scan directions between first and second pairs of scan end positions; and (c) a read-start means for simultaneously moving the component in the first and second scan directions to simultaneously angularly oscillate the component between said first and second pairs of scan end positions for directing light along said first and second scan directions to thereby effect a scan pattern over the indicia; characterised in that the holder means includes a first and second vibratory means (121;139) attached to one another, and in that the first vibratory means (121) includes a U-shaped spring means. The arrangement according to claim 1, wherein said U-shaped spring means has a pair of arms (123;125) on one of which is mounted the component (129). The arrangement according to claim 1 or 2, wherein said second vibratory means (139) includes a generally planar spring means having one end secured to a base (141) and a free end secured to the other arm of the U-shaped spring means. The arrangement according to any of claims 1 to 3, wherein the arms (123,125) of the U-shaped spring means vibrate in a first plane and the planar spring torsionally vibrates in a second plane, and wherein said second plane is orthogonal to said first plane. The arrangement according to any of claims 1 to 4, wherein the arms (123,125) of the U-shaped spring means are asymmetrically dimensioned. The arrangement according to any of claims 1 to 5, further including means (180) for rotating the holder means about an axis (182) to thereby effect an omnidirectional scan pattern. The arrangement according to any of claims 1 to 6, wherein the component (129) is a light reflector. The arrangement according to any off claim 1 to 7, wherein the scan pattern is two-dimensional. The arrangement for scanning the indicia, comprising: according to any of the preceding claims, wherein said holder means mount the component (129) for oscillating movement about an axis in alternative circumferential directions thereof between angularly spaced scan end positions, said U-shaped spring means (121) having a pair of arms on one of which is mounted the component (129), the arms of the U-shaped spring means (121) being asymmetrically dimensioned; and wherein said read-start means move the component (129) in the circumferential directions to oscillate the component between the angularly spaced scan end positions. The arrangement according to claim 9, further comprising: (d) means (180) for rotating the holder means about an axis (182) to thereby effect an omnidirectional scan pattern. The arrangement according to claim 9 or 10, wherein the read-start means include an electrically-operated actuator operative, when actuated, for vibrating the U-shaped spring means (121) and oscillating the component (129) between said scan end portions. The arrangement according to any of claims 9 to 11, wherein the actuator is an electromagnetic coil (133,158) having a passage (160), and a magnet (135,156) mounted on the holder means and movable towards and away from the passage (160) during actuation of the coil.

Inventors: BARD SIMON, BARKAN EDWARD, DVORKIS PAUL, KATZ JOSEPH, SHEPARD HOWARD M, BARD, SIMON, BARKAN, EDWARD, DVORKIS, PAUL, KATZ, JOSEPH, SHEPARD, HOWARD M.
Applicants: SYMBOL TECHNOLOGIES INC, SYMBOL TECHNOLOGIES, INC.
Application year: 1991
Main classification: G06K7
IPC codes: G02B26, G06K7