Scanning arrangement

Abstract: An optical scanner (30) has a scanner component mounted to a leaf spring (34) for oscillatory motion about an axis. An electromagnetic coil (58) and permanent magnet (56) cause a force to be applied to the scanner component away from a central, neutral, position. Bending of the leaf spring provides a restoring force biasing the scanner component back towards the neutral position.

Description: 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. 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 and being hereby incorporated herein by reference. 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), et. 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 labour 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. SUMMARY OF THE INVENTION 1. Objects 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. Prior publication GB-A-2175705 discloses those features set out in the preamble to Claim 1. In addition, US-A-4,578,571, although different in detail, discloses the same features. According to the present invention there is provided an optical scanner characterised by those features set out in the characterising portion of Claim 1. 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. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front perspective view of hand-held head employed in a scanner; and Figure 2 is a top plan view of an 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 18 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 speed for increased system reliability. As shown in Figure 2, one embodiment 30 of a high speed scanning arrangement of the present invention, includes a flexible beam, e.g. a generally planar leaf spring 34. Leaf spring 34 has one end 36 fixedly mounted to an upright of an L-shaped bracket 38 which is anchored to a base support 40. Spring 34 has an opposite end 42 fixedly mounted to an upright of another L-shaped bracket 44 which is anchored to the base support 40. The uprights are oriented at 90° relative to each other. A central portion of the spring 34 is guided around a cylindrical clamping pin 46. The central portion of the spring 34 is clamped between the clamping pin 46 and a bearing surface of a V-block 48 by means of a set screw 50. The clamping pin 46 imparts a 90° bend to the leaf spring at the central portion. A scanner component, e.g. a light reflector 52, is fixedly mounted to a rear support 54 which, in turn, is fixedly secured to the V-block. The rear support 54 has a permanent magnet 56 mounted at one of its ends. An electromagnetic coil 58 is mounted adjacent the magnet 56 on an upright of another L-shaped bracket 60 which, in turn, is mounted on the base support 40. The coil 58 has a central passage 62 through which the magnet enters with clearance each time a momentary, periodic energizing pulse is applied to input leads 64. The frequency of the energizing pulse is preferably selected at the resonant frequency of 1 2π k, I where k equals the spring constant of leaf spring 34, and where I equals the moment of inertia of the magnet/reflector assembly suspended from the leaf spring. The assembly is oscillated about the axis 66. The spring is advantageously constituted of plastic or metal material. Non-metal materials would be more rugged. In operation, each time the energizing pulse is applied to the coil 58, the magnet 56 is drawn into the passage 62, thereby pulling the reflector 52, the rear support 54, the V-block 48, the clamping pin 46, the set screw 50 therealong. At the same time, the leaf spring is bent. In the illustrated rest position, each arm of the leaf spring is generally planar. Upon being displaced, each arm of the leaf spring is bent, thereby storing energy therein. An L-shaped stop 68 mounted on the base support 40 is located behind the clamping pin 46 to prevent movement of the same past the stop. The pin 46 does not normally engage the stop; it is intended as a safety feature in the event that the arrangement is subjected to external shock forces. The flexible support near the centre of rotation of the component provides an excellent shock absorber. Once bent, the leaf spring 34 releases its stored energy, thereby displacing the magnet/reflector assembly back to and past the rest position. The entire assembly oscillates in a damped manner, until eventually coming to a halt in the rest position. Each arm of the leaf spring alternately assumes a concave and then a convex shape during such oscillation. Light directed from a source, e.g. a laser 70, onto the reflector 52 is swept in one direction in a scan across indicia to be read. The assembly undergoes constant amplitude excitation, with continuous oscillation. The driving signal is a continuously applied AC signal that causes the magnet 56 to be cyclically drawn into the passage 62 and forced out of the passage 62. The spring 34 vibrates to oscillate the reflector 40 between scan end positions. By providing a well defined centre of rotation at axis 66 that is close to the scan component, image translation is minimized. In addition, in this configuration the scan pattern stays centred regardless of the scan position. 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.

Claims: An optical scanner (30) comprising a scanner component mounted to a leaf spring (34) for oscillatory motion about an axis, the scanner component being biased by the leaf-spring towards a neutral position which is intermediate first and second scan end positions, and read-start means supplied with an AC signal and arranged to apply a force to the scanner component to move it from the neutral position towards one of the scan end positions, characterised in that the scanner component is mounted to a bent central portion of the leaf spring (34). An optical scanner as claimed in claim 1 in which the leaf spring comprises a first planar portion connected to a second planar portion via the bent central portion, the first and second planar portions lying at 90° to one another. An optical scanner as claimed in claim 1 or claim 2 in which the scanner component is mounted to the leaf spring (34) by means of a cylindrical mounting pin (46) around which the bent central portion of the spring is guided. An optical scanner as claimed in any one of the preceding claims including a stop (68) arranged to prevent unwanted movement of the scanner component in the event of jarring. An optical scanner as claimed in any one of the preceding claims in which the read-start means comprises an electrically-driven actuator. An optical scanner as claimed in claim 5 in which the actuator comprises an electromagnetic assembly. An optical scanner as claimed in claim 6 in which the electromagnetic assembly is arranged to oscillate the scanner component continuously. An optical scanner as claimed in claim 6 or claim 7 in which the electromagnetic assembly includes an electromagnet coil (58) and a permanent magnet (56), the permanent magnet being moved towards and away from the coil during oscillation of the scanner component. An optical scanner as claimed in any one of claims 5 to 8 in which the actuator is energised at a resonant frequency of the scanner component oscillation. An optical scanner as claimed in any one of the preceding claims in which the scanner component includes a light reflector (52). A hand-held scanner head comprising a housing and, within the housing, an optical scanner as claimed in any one of the preceding claims. An optical scanner according to Claim 1, comprising a light source (70), a reflector (52) mounted on said leaf spring (34) in a position to reflect light from the light source on the object to be scanned, and an AC driven electromagnetic oscillator (56,58) connected to the reflector (52) and operable to oscillate the reflector about its neutral position against the bias of said spring (34) and between its end scan positions, thereby to effect multiple passes of the reflected light beam across the object to be scanned. An optical scanner according to Claim 12, incorporating a trigger switch (16) controlling the power supply to the electromagnetic oscillator. An optical scanner according to Claim 13, wherein, following the operation of the trigger switch (16) to supply power to the electromagnetic oscillator, the power supply to the electromagnetic oscillator is terminated automatically after a preset period. An optical scanner according to Claim 12, which is designed for continuous operation by direct connection to a source of AC power. An optical scanner according to any one of Claims 12 to 15, wherein the light source (70) is a laser. An optical scanner according to any one of Claims 12 to 16, wherein the electromagnetic oscillator operates to oscillate the reflector (52) at substantially the resonance frequency of the movable scanner components. An optical scanner according to any one of Claims 12 to 17, wherein the electromagnetic oscillator comprises an electromagnetic coil (58) mounted in the scanner at a fixed position and a magnetic core (56) coupled to the reflector(52) and aligned for reciprocal movement along the axis of the coil when the coil is energised. An optical scanner according to Claim 18, wherein the frequency of the energising pulse supplied to the electromagnetic coil is equal to 1/2π √(k/I), where k is the spring constant of the leaf spring (34) and I is the moment of inertia of the reflector (52) and the moving parts associated with it, other than the spring itself. An optical scanner according to any one of claims 12 to 19, wherein the leaf spring (34) is a spring having two substantially planar arms at right angles one to the other and interconnected at the midpoint of the spring by an integrally formed curved section, the two arms being anchored at their respective distal ends (36, 42) to anchoring blocks (38,44), and the reflector (52) being mounted to the spring substantially at its mid point at the intersection of the two arms. An optical scanner according to Claim 20, wherein at its midpoint, the leaf spring is curved around a pin (46). An optical scanner according to Claim 21, wherein at its midpoint the leaf spring is clamped between the said pin (46) and a mounting block (48) for the reflector (52). An optical scanner according to Claim 22, wherein the mounting block (48) has a V-shaped configuration, having two arms substantially at right angles one to the other, and the leaf spring (34) is clamped between the pin (46) and the internal angle between the two arms. An optical scanner according to any one of Claims 21 to 23, wherein a fixed stop (68) is provided inwardly of the pin (46) in the internal angle of the arms of the leaf spring (34) to limit inward movement of the pin due to inward flexing of the spring. An optical scanner as claimed in any one of claims 12 to 24, wherein the leaf spring (34) is a metal spring. An optical scanner according to Claim 1, wherein the leaf spring (34) is a spring having two substantially planar arms at right angles one to the other and interconnected at the midpoint of the spring by an integrally formed curved section, the said arms being anchored at their respective distal ends (36, 42) to anchoring blocks (38,44), and the reflector (52) being mounted to the spring substantially at its mid point at the intersection of the two arms. An optical scanner according to Claim 26, wherein at its midpoint, the leaf spring is curved around a pin (46). An optical scanner according to Claim 27, wherein at its midpoint the leaf spring is clamped between the said pin (46) and a mounting block (48) for the reflector (52). An optical scanner according to Claim 28, wherein the mounting block (48) has a V-shaped configuration, having two arms substantially at right angles one to the other, and the leaf spring (34) is clamped between the pin (46) and the internal angle between the two arms. An optical scanner according to any one of Claims 27 to 29, wherein a fixed stop (68) is provided inwardly of the pin (46) in the internal angle of the arms of the leaf spring (34) to limit inward movement of the pin due to inward flexing of the spring. An optical scanner as claimed in any one of claims 26 to 30, wherein the leaf spring (34) is a metal spring. An optical scanner according to any one of Claims 26 to 31, incorporating a trigger switch (16) controlling the power supply to the electromagnetic oscillator. An optical scanner according to Claim 32, wherein, following the operation of the trigger switch (16) to supply power to the electromagnetic oscillator, the power supply to the electromagnetic oscillator is terminated automatically after a preset period. An optical scanner according to any one of Claims 26 to 31, which is designed for continuous operation by direct connection to a source of AC power. An optical scanner according to any one of Claims 26 to 34, wherein the light source (70) is a laser. An optical scanner according to Claim 1, in the form of a hand held bar code scanner comprising a laser light source (70) mounted in a hand held housing (12), a leaf spring (34) having two arms substantially at right angles to each other and anchored in the housing at their respective distal ends (36,42) to anchoring blocks secured within the housing, said spring, at its mid point, passing in a smooth curve through a 90" angle around a pin (46), a reflector (52) mounted to the said spring at its mid point opposite the said pin and in a position to reflect light from the laser (70) externally of the housing onto the bar code to be scanned, an electromagnetic coil (58) mounted at a fixed position in the housing (12), a magnetic core (56) coupled to the reflector(52) and aligned for reciprocal movement along the axis of the coil, said electromagnetic coil and core serving, when the coil is energised with an AC current, to oscillate the reflector about its neutral position against the bias of said spring (34) and between its end scan positions, thereby to effect multiple passes of the reflected light beam across the object to be scanned, and a photodetector element disposed in the housing in a position to receive to light reflected back to the scanner by the bar code and being operable to pass a signal representing that bar code to an external decoder (22). An optical scanner according to Claim 36, wherein the electromagnetic coil is effective to oscillate the reflector about its neutral point at a frequency substantially equal to the resonance frequency of the movable scanner components. An optical scanner according to Claim 36 or 37 the operation of which is controlled by a trigger switch (16). An optical scanner according to Claim 1, in the form of a bar code scanner comprising a laser light source (70) mounted in a housing (12), a leaf spring (34) having two arms substantially at right angles to each other and anchored in the housing at their respective distal ends (36,42) to anchoring blocks secured within the housing, said spring, at its mid point, passing in a smooth curve through a 90° angle around a pin (46), a reflector (52) mounted to the said spring at its mid point opposite the said pin and in a position to reflect light from the laser (70) externally of the housing onto the bar code to be scanned, an electromagnetic coil (58) mounted at a fixed position in the housing (12), a magnetic core (56) coupled to the reflector (52) and aligned for reciprocal movement along the axis of the coil, said electromagnetic coil and core serving, when the coil is energised with an AC current, to oscillate the reflector about its neutral position against the bias of said spring (34) and between its end scan positions, thereby to effect multiple passes of the reflected light beam across the object to be scanned, and a photodetector element disposed in the housing in a position to receive to light reflected back to the scanner by the bar code and being operable to pass a signal representing that bar code to a decoder (22). An optical scanner according to Claim 39, wherein the electromagnetic coil is effective to oscillate the reflector about its neutral point at a frequency substantially equal to the resonance frequency of the movable scanner components. An optical scanner according to Claim 39 or 40, which is designed for continuous operation by direct connection to a source of AC power.

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: G06K7