HK1220024B - Sequenced illumination in mark reading devices - Google Patents

Description

Sequential illumination in an identification reading device

Technical Field

The present invention relates to readers operable to read indicia, such as readers and scanners for reading security indicia or one or two dimensional bar codes attached to some sort of substrate. The invention also relates to a method of operating such an apparatus, and to a corresponding computer program and computer program product.

Background

It is common today to apply identification (e.g., one-or two-dimensional bar codes) to articles such as consumer products, food products, beverage packaging, cans and bottles, cigarette packaging and other tobacco products, documents, certificates, banknotes, and the like. The identification may then be used for the purpose of tracking, identifying, or authenticating the item in the area (i.e., in the marketplace), on a production or packaging line, at a retailer, during shipping, and so forth.

Once the identification is applied to the article, the encoded information may then be acquired by an identification (barcode) reading device. Such devices typically first obtain the image data, which is acquired using, for example, a digital camera. Other acquisition support may be provided by way of illumination means such as LEDs, lasers and other light sources. The reading device may then employ processing resources, for example in the form of a microprocessor (CPU) and associated memory, for processing the acquired image data. Typically, this processing involves isolating (identifying) the barcode in the image data and decoding the payload data. The decoded data may then be further processed, displayed, or transmitted to other entities.

The identification also occurs in various ways, two examples of which are shown in fig. 1A and 1B: the common one-dimensional barcode 10 ' of fig. 1A typically includes an arrangement of elements as, for example, black and white lines 1 ', 2 '. Information is encoded by a predetermined set of black and white lines 1 ', 2' connecting varying thicknesses and distances. These groups are typically associated to a particular character or meaning by some industry standard.

FIG. 1B illustrates a common two-dimensional barcode 10 "that generally encodes information by arranging first type elements 1" and second type elements 2 "(e.g., rectangles, dots, triangles, etc.) along two dimensions in an ordered grid. The example of fig. 1B follows an implementation according to the GS1 (trademark) DataMatrix ECC 200 standard (GS1 is the international association providing standards for two-dimensional barcodes). For example, the standard employs a so-called "L-seek pattern" 4 (also referred to as L-shaped solid line, L-line, solid line, etc.) and a so-called "clock trace" 3 (also referred to as clock line, L-shaped clock line, etc.) that surrounds data 5 carrying the actual payload data of the barcode.

In both the case of one-dimensional and two-dimensional barcodes, at least two distinguishable types of elements are used. For example, a white printed square as a first type element may represent information 0, and a black printed square as a second type element may represent information 1. However, in any case, the implementation by means of black and white lines or dots (elements) represents only one example.

In particular, barcodes may also be implemented well by using color and/or fluorescent dyes or inks, thermal printing on thermal paper, mechanical means (e.g. milling, embossing, grinding) or physical/chemical means (e.g. laser etching, acid etching, etc.). For example, any type of implementation is possible as long as the elements can distinguish them into the respective types in the image data that has been obtained from the two-dimensional barcode normally applied to an article (merchandise) of a certain type. For example, a digital camera may obtain digital image data of a bar code printed on a paper document or laser etched on a metal can.

Likewise, luminescent materials are also used for security markings provided on documents or articles (articles), or in bulk materials for documents or articles, as authenticity features. Luminescent materials typically convert the energy of excitation radiation of a given wavelength into emission light of another wavelength. The luminescent emission for identifying authenticity may be in the spectral range from Ultraviolet (UV) light (below 400 nm), visible light (400 + 700nm) or near mid-infrared light (NIR, MIR, IR) (700 + 2500 nm). In this case, the so-called "up-conversion" material emits radiation at a shorter wavelength than the excitation radiation. In contrast, a "down-converting" material emits radiation at a longer wavelength than the excitation radiation. Most luminescent materials may be excited at more than one wavelength, while some luminescent materials may emit at more than one wavelength simultaneously.

Luminescence can be divided into so-called "phosphorescence", which relates to a time-delayed radiation emission (typically having a decay lifetime of from about 1 to about 100 s) observable after removal of the excitation radiation, and so-called "fluorescence", which relates to a rapid radiation emission upon excitation (typically having a decay lifetime of below 1 s).

Thus, depending on the illumination of the excitation light with an excitation wavelength range, the luminescent material for marking typically emits illumination light in an emission wavelength range, which may (depending on the material used) be different from or overlap the excitation wavelength range. For example, a characteristic spectral characteristic of a luminescent material (e.g. its emission light intensity profile over time, or its characteristic decay time after excitation has ceased) may be employed as a signature of the material, and may therefore be further used as a security feature for detecting genuineness or counterfeiting (authenticity).

Thus, the luminescent material may be a component of a security ink or paint. For example, the following patents disclose luminescent substances (which may include pigment mixtures having different decay time characteristics) and security papers including the same: EP 0066854B1, US4,451,530, US4,452,843, US4,451,521. Methods and devices for detecting the luminescence and authenticity of marked items are also well known: see, e.g., US4,598,205 or US4,533,244 (which discloses the inductive decay behavior of luminescence emission). Luminescent code symbols are known from US 3,473,027, while optical readers for luminescent codes are disclosed in US 3,663,813. Patents US 6,996,252B2, US 7,213,757B2 and US 7,427,030B2 disclose the use of two luminescent materials with different decay time characteristics for verifying items.

The wide variety of possible implementations also results in widely different optical properties of the indicia. For example, barcodes may be printed using specific inks, such as fluorescent or phosphorescent inks that emit different wavelengths (compared to the wavelength used for illumination) and/or have delayed light. The specific characteristics of these specific inks can be employed for authenticating the identification.

However, the particular features that are required to be able to detect the markers also require appropriate illumination so that the appropriate illumination wavelength is available for which certain markers respond. Typically, a high-intensity broadband light source is employed to ensure that sufficient intensity is provided in all wavelengths under consideration. This privilege places high demands on the respective light sources used for illuminating the sign, wherein the emission power characteristics of a given light source are exploited to some maximum extent.

However, such an operation may lead to increased or even impermissible heat generation, so that additional tools for cooling the light source may become necessary. Furthermore, operating the light source close to or even beyond the maximum power rating can greatly reduce the lifetime of the components involved. Once the light source becomes too hot or even has deteriorated, the corresponding reading device will fail, because suitable illumination is no longer possible.

At the same time, handheld or even wireless reading devices featuring only a limited capacity (battery) power source are commonly used today. In this way, a short-term effect is also observed, in that an increased stop time of the device is caused by excessive power consumption of the light source, during which the battery has to be replaced or charged, and, conversely, the device is unusable. Furthermore, any additional measures for cooling the light source in the handheld device are clearly undesirable as they increase the weight, size and power consumption of the device again.

Conventional light sources for such readers include incandescent lamps (typically having wavelengths between about 400nm and about 2500nm), flash lamps (such as, for example, xenon high-pressure flash lamps), lasers or light emitting diodes (LEDs, which emit in the ultraviolet, visible or infrared regions, typically having wavelengths from about 250nm to about 1 micron). Conventional light sources are powered via a drive current, such as an LED, or via a drive voltage, such as a discharge lamp. As an example, composite light sources with multi LED modules (equipped with collimating and mixing structures) are disclosed in US patent application US 2009/0316393a1 (see also US 7,125,143B2 and european patent EP 1815534B 1).

In other words, the light source should deliver illumination to the marker such that the emitted light intensity is sufficient for the measuring operation. Due to the fact that only a part of the illumination light corresponds to the sub-bandwidth actually used for excitation, heat dissipation problems may arise for the light source. This may require controlling the heat within the light source to avoid damaging the source and/or reduce the life cycle. Such techniques include, for example, the specific design of the LEDs themselves and/or the arrangement on a suitable substrate, and also cooling systems.

Accordingly, there is a need for an improved identification reader device that avoids overheating of the light source, maximizes the life of the light source and identification device as a whole, and reduces overall size, weight, and power consumption.

Disclosure of Invention

The above mentioned problems are solved by the subject matter of the independent claims of the present invention. Preferred embodiments are described in the dependent claims.

According to an embodiment of the present invention, there is provided a reader operable to read an identification on a substrate, the reader including: a power supply operable to deliver a variable drive current or voltage; a light source operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage; a light sensor operable to measure an intensity of light received from the indicia and deliver a corresponding light intensity signal; and a control unit operable to control the power supply and light sensor to control the timing of the illumination light pulses according to a switching pattern and timing to acquire the light intensity signal for synchronizing the acquisition of the light intensity signal with the sequence of illumination light pulses, the control unit further operable to adjust a duty cycle of the switching pattern so as to maintain heat generation associated with each illumination light pulse below a given threshold.

According to another embodiment of the invention, a method of operating a reader operable to read indicia on a substrate, the reader comprising: a power supply operable to deliver a variable drive current or voltage; a light source operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage; a light sensor operable to measure an intensity of light received from the indicia and deliver a corresponding light intensity signal; the method comprises the following steps: controlling the timing of the illumination light pulses in accordance with a switching pattern and timing to acquire the light intensity signal for synchronizing the acquisition of the light intensity signal with the sequence of illumination light pulses, and adjusting a duty cycle of the switching pattern so as to maintain heat generation associated with each illumination light pulse below a given threshold.

According to further embodiments of the present invention, there are provided a computer program and a corresponding computer program product, the computer program comprising code which, when executed on a processing resource, implements a method embodiment of the present invention.

Drawings

Embodiments of the present invention will now be described with reference to the accompanying drawings, which are presented for a better understanding of the concepts of the invention and are not to be considered as limiting the invention, wherein:

FIGS. 1A and 1B show schematic diagrams of an exemplary conventional bar code;

2A-2C illustrate schematic views of an identification reader device according to further embodiments of the present invention;

FIG. 3 shows a schematic graph of pulse intensity versus time for a given plurality of component light sources, according to an embodiment of the invention;

FIG. 4 shows a schematic diagram of a circuit of an identification reader device according to a further embodiment of the invention;

FIGS. 5A and 5B show schematic graphs of current pulses versus time; and

fig. 6 shows a flow chart of a method embodiment of the invention.

Detailed Description

Fig. 2A shows a schematic view of an embodiment of the apparatus of the present invention. The apparatus 100 (e.g., a barcode or identification reader) includes a power source 102 and a light source 101, the power source 102 operable to deliver a variable drive current or voltage, the light source 101 operable to illuminate the identification 10 with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage. The device 100 also includes a light sensor 104, the light sensor 104 operable to measure the intensity of light received from the sign 10 and deliver a corresponding light intensity signal.

The device 100 further comprises a control unit 103, which control unit 103 for example comprises a microprocessor (CPU)131 and a storage unit 132. The control unit 103 is operable to control said power supply 102 and light sensor 104 to control the timing of said illumination light pulses according to a switching pattern and timing to acquire said light intensity signals for synchronizing the acquisition of said light intensity signals by said sequence of illumination light pulses. The control unit 103 is further operable to adjust the duty cycle of the switching pattern in order to maintain the heat generation associated with each illumination light pulse below a given threshold.

For example, a first light pulse has light of a first wavelength spectrum and a second light pulse has light of a second wavelength spectrum, wherein the second wavelength spectrum is different from the first wavelength spectrum. In the context of the present disclosure, the fact that the spectra are "different" is to be understood in the context of the present disclosure, in the sense that the spectra comprise at least one local maximum in emission intensity at different light wavelengths. In this way, the two spectra are different, although the spectra may be characterized by an overlap region in which the light intensities of the two spectra at certain given wavelengths are non-zero or even comparable or identical. In general, the timing may also be "different", in the sense that there is at least one point in time when there is illumination using only one of the two wavelength spectra. Preferably, the two wavelength spectra are used for different time sequences, so that there is only illumination with one spectrum at a time.

As a further option, the control unit 103 may comprise a communication unit 133 for communicating instructions related to the control of the emission of the light source 101. The instructions may be received from other entities such as a server, a controller, etc. The communication may be implemented via a network, such as a Local Area Network (LAN), wireless network (WLAN), the internet, etc. Further, bus systems such as CAN also be used for data exchange.

Further, the apparatus 100 may optionally also include integrated image capture means as the light sensor 104 for capturing image data identifying (and possibly also surrounding, e.g., a substrate in the form of an identification of an applied item, product, or item). In general, the light sensor and/or the image acquisition means may comprise or may consist of: one or more photodiodes (single or array), one or more phototransistors or photoresistive circuits, linear CMOS or CCD sensors, collection optics (lenses, etc.), and the like.

The image acquisition tool 104 may be coupled to the control unit 103 for the purpose of processing the acquired image data by the exemplary CPU 131 for recognizing and/or decoding the identification, for example in the form of a one-dimensional or two-dimensional barcode. In such embodiments, an optional communication unit 133 may be employed for communicating the identification, decoding and/or authentication results to the other entities described above.

Fig. 2B shows a schematic view of a further embodiment of the invention in the form of a handheld identification reader (scanner) 100'. For example, the apparatus 100' is configured to acquire an image of an identification on a product or item, and recognize and decode the image. The device 100 ' includes a window 101 ', through which window 101 ' the logo can be illuminated according to embodiments of the present invention, and a digital image can be acquired. In particular, the device 100' again comprises a light source according to an embodiment of the present invention. Images may also be acquired through the window 101 'by respective tools integrated in the device 100'.

Although window 101 'is shown as a useful means for protecting the light source, the light sensor and/or any imaging means from e.g. dust, water or humidity, this window 101' is optional, as the light source itself may already feature some sort of housing providing sufficient protection from the environment. For the purpose of controlling the light source and (optionally) also processing any acquired image data for decoding/authentication, the apparatus 100' may comprise integrated processing resources configured to operate in accordance with embodiments of the present invention.

Fig. 2C shows a schematic view of a fixed-type identification reader in accordance with another embodiment of the present invention. The apparatus 100 "comprises a light source 101" according to an embodiment of the invention. At the same time, the device 100 "may comprise an image acquisition means 102", which image acquisition means 102 "is used to image the identification illuminated with said light source 101". The illustrated embodiment contemplates a camera type image acquisition tool 102", for example in the form of a CCD camera (although related techniques such as those described in connection with tool 104 may also be employed). For purposes of controlling the light source and (optionally) also processing any acquired image data for decoding/authentication, the apparatus 100 "may further comprise integrated processing resources configured to operate in accordance with embodiments of the present invention.

As a further option, the devices 100' and 100 "may comprise a communication unit for communicating instructions or identification, decoding and/or authentication related to the control of the light source emission from and/or to the other entities mentioned above. Although the device 100' is shown as wired, communication may be accomplished wirelessly via any type of suitable network (e.g., a Local Area Network (LAN), a wireless network (WLAN), the internet, etc.). Further, for example, a CAN thermal bus system CAN also be used for data exchange. A power module for supplying power to the reader, a radio module for wireless communication (e.g., via Wi-Fi), a display module (e.g., a liquid crystal display LCD, or a kinescope display) for displaying measured data or scan parameters (decoding/authentication results), and a control interface for inputting scan conditions (including buttons with various functions and on/off switching buttons) are also contemplated.

To some extent, embodiments of the present invention relate to optical devices for reading and/or decoding indicia having a pattern (barcode, data matrix, etc.) applied to an object or substrate. It should be understood that in the context of the present disclosure, the terms article, item and product refer to the same entity, i.e., identify the article to which it is applied. For example, a light-emitting pattern and a logo, i.e., having a decay time characteristic of illumination light emitted by a patterned light-emitting material, and a non-light-emitting pattern imaged from light reflected by the pattern can be read.

Thus, embodiments of the present invention provide an imaging barcode reader (identification reader) that is also capable of imaging moving products, for example, on high speed production lines, and illuminating the target product identification with different types of illumination (e.g., different colors of light) by means of a composite light source. The illumination flash may be synchronized with the opening of the image aperture of the image capture tool employed. The illumination type, illumination intensity, and exposure time are programmable so that the reader can scan many different types of tags under different environmental conditions (e.g., ambient light intensity or type), where different illumination is required, while preventing the light source from overheating. In this manner, a handheld version of the scanner (see, e.g., the example apparatus 100' of fig. 2B) may also be considered in an advantageous manner.

According to an embodiment of the invention, the illumination light source delivers illumination light pulse components, each having its wavelength distribution (spectrum) within a wavelength sub-range of the overall wavelength range of the light source, the light pulse components being delivered by the light source according to an illumination sequence, i.e. according to the switched on/off timing of the pulse components.

As a result, the light source is adapted to deliver high illumination intensity to the target indicia while avoiding excessive power loss as heat, which would damage the light source and reduce its life cycle. Furthermore, by selecting the pulse components (spectra) and their timing (possibly, the light pulse components may overlap in time and/or may repeat during the overall illumination period), a given (standardized) light source may be adapted to various identification types. Possibly, the light intensity delivered by the light pulse component can be set, as well as the pulse duration and the sequence of light pulse components forming the global illumination light (in this sense, the intensity profile of one spectrum is globally changed by, for example, a scaling factor).

In response to illumination by the light source, a light sensor adapted to the type of identification may receive light from the identification and may collect light synchronized with the illumination sequence so that (over a measurement time sequence) only light intensities of certain specific illumination light pulse components primarily attributed to the illumination sequence are measured. Thus, the setting of the illumination sequence delivered by the light source and the related measurement of the light intensity operated by the light sensor allows to easily adapt the light illumination and light detection operation of high intensity to a plurality of identification types (having specific light reflection and/or light emission characteristics) while avoiding damages due to excessive power losses in the light source.

In a further embodiment of the invention, the device being configured to read, decode and/or authenticate may comprise an identification of the luminescent material based on illumination light emitted by said material (having decay time characteristics) in response to illumination from the light source having a specific sequence. Such "decay time scanners" include an illumination source for delivering excitation light to a lighted sign according to the present disclosure and a luminescence light sensor for measuring the intensity of the emitted light received from the sign in response to the excitation light.

In general, flash illumination light sources have an illumination light wavelength distribution within a wavelength spectrum bandwidth WS ═ λ min, λ max (with Δ λ S ═ λ max — λ min), and may be suitable for illuminating a marking comprising certain luminescent particles having a high intensity excitation light pulse during a target illumination period T (i.e., pulse duration). After the illumination has ceased, the luminescent light sensor is then operable to receive the attenuated luminescence light intensity (emitted from the marker after its luminescent particle has been excited by the illumination source) over a measurement time Δ t of about 100 μ s (e.g. a camera integration time). Typically, T is approximately within a range or magnitude of Δ T (e.g., T Δ T).

The marking may comprise a luminescent particle type i having a decay time value τ i. After having been excited by the respective excitation light component of the excitation light pulse delivered by the light source, the luminescent particles of type i in the marking emit luminescence light in a narrow luminescence bandwidth i centered around the luminescence emission wavelength λ (i), wherein the excitation wavelength sub-bandwidth of the light source is comprised within WS. In general, Δ t > > τ i can be assumed.

According to an embodiment of the invention, the light source is a compound light source, i.e. the illumination light source comprises a plurality of different illumination light sources s (j), j ═ 1. For example, a single Light Emitting Diode (LED) may be disposed on the support. Each individual light source module may then be made operable to deliver a respective excitation light pulse component having its own intensity profile ij (T) (elapsed time), duration T (j) (included within T), and wavelength bandwidth (i.e., illumination wavelength spectrum within the wavelength bandwidth).

Thus, the overall illumination light pulse delivered by the light source (corresponding to a given color) is composed of a plurality of (possibly partially overlapping in wavelength) excitation light pulse components j of wavelength bandwidth [ λ jmin, λ jmax ] around a wavelength λ j (corresponding to a different color), having respective spectral widths Δ λ j ═ λ jmax- λ jmin, each comprised within [ λ min, λ max ].

Furthermore, certain different excitation light pulse components may be delivered simultaneously or at different times and timing within the illumination period T (possibly, the time delay between the pulse components may be set) and may even partially overlap in time. For example, the composite light source may deliver various excitation light pulse components (temporal pulses) by a control unit switching sequence configured to switch on/off the individual light source modules j according to a set timing, so as to generate excitation light pulses having their characteristic values ij (t), t (j) and spectral distributions, and in turn so as to deliver a sequence for illuminating the indicia.

Thus, the excitation light pulse components delivered in time may form some kind of broadband illumination light delivered by the light sources, since a sequence of more than one illumination wavelength spectrum may compile more or less broadband spectra, although each composite light source provides only some spectral contributions. For example, a sequence of red, green, and blue light pulses may be assembled into a composite white light broadband light pulse.

When using a composite light source as described above, the luminescent light sensor (image acquisition means) may accordingly be adapted to measure in time the intensity of the emitted light of at least one type i from the identified luminescent particles, the emitted light of which is caused by excitation by at least one excitation light pulse component delivered by the light source.

According to a further embodiment, each illumination light pulse I may be set so as to excite a respective luminescent particle type I present in the marking. The luminescent light sensor (image acquisition means) may then be adapted to measure different luminescent emission light components i emitted by luminescent particles of respective types i. This may involve a specific emission sequence resulting from an illumination sequence with excitation light pulse components. For example, the luminescent sensor may be a composite one, comprising different luminescent sensors, which are more specifically adapted and controlled in order to measure the emission intensity of the different types of luminescent particles of the identification. For example, each individual component sensor has been designed for the detection characteristics of the respective wavelength spectrum.

According to embodiments of the invention, the reader may be effectively equipped with a broadband illumination light source operable to measure the luminescence intensity i (i) emitted by luminescent particles of type i in the indicia within a narrow luminescence bandwidth i centered on the luminescence emission wavelength λ (i) and in response to a high intensity illumination light pulse delivered by the light source to the indicia during the period T, said luminescence emission light component (i) being in fact the response of the indicia to at least one excitation light pulse component of a wavelength sub-bandwidth within the broadband illumination light.

The classical luminescence decay intensity curve (intensity profile over time) from a luminescent material can be modeled by the exponential law I (t) ═ I0exp (- α [ t-t0]), where time t is calculated from the instant t0 at which excitation light is removed. The pulsed light source illuminates the luminescent material of the marker with excitation light of a given intensity and within an excitation wavelength range only during an excitation time interval, then possibly with a time delay after the illumination has ceased, the light sensor images the marker from the received attenuated luminescence intensity within the emission wavelength range over a measurement time interval, and a corresponding digital image can be stored in a memory for further image processing (decoding/authentication). It is possible to set the excitation time interval and/or the time delay so as to avoid having the luminous intensity value below the detection threshold of the light sensor or above its saturation threshold.

According to one embodiment of the invention, the light source comprises a plurality of chip-on-board LED (COB LED) cells (an array of chip-on-board LED cells) bonded on an aluminum PCB, each COB LED cell comprising a set of three LEDs, a red light emitting diode (R LED), a green light emitting diode (G LED), and a Blue Light Emitting Diode (BLED), and collimating optics for the cells. The COB LED units are connected to circuitry that allows the controller to independently switch power to the R, G and B LEDs of the array. In this way, a light source is obtained comprising a plurality of individual component light sources operable to emit at least a first and a second light pulse having a first and a second wavelength spectrum, respectively.

Such a light source is operable to substantially uniformly illuminate the indicia with R, G, B light pulses of high light intensity according to a given sequence of switching times. These R, G, B light pulses form an illumination light pulse component of a global illumination light pulse delivered by the light source during the illumination time interval T. For example, in case the luminescent material is excited by light within the Near Infrared (NIR) portion of the wavelength range of the R illumination light pulse, i.e. 680-1000nm, the typical duration T (R) of the R illumination light pulse component may be about 100 μ s. An example of an illumination sequence may consist of only three consecutive illumination pulses: one R pulse (duration T (R)), intensity level i (R)), one G pulse (duration T (G)), intensity level (level) i (G)), and one B pulse (duration T (B)), intensity level i (B)) (see fig. 2), having, for example, T (R) ═ T (B) — 100 μ s (we have T (R) + T (G) + T (B) — 300 μ s). T (r) and i (r) are sufficient to "charge" the luminescent particles of the indicia sufficiently to receive sufficient luminescent emission intensity from the indicia.

Once the first R illumination pulse, which is an excitation pulse for the luminescent material, has been delivered, the light sensor of the imaging unit (image acquisition tool, camera) of the reader may start to receive luminescent emission light from the marker (by means of an adapted optical block). The light sensor integrates the received emitted light intensity signal over a measurement time interval Δ t, which in this example is about 100 μ s. In this manner, the imaging tool has acquired a digital image of the identification in the form of image data.

According to a further embodiment of the invention, one of the following parameters may be set or adjusted: pulse component duration, pulse component intensity level, start time of pulse component time, and measurement time interval (image acquisition interval). In addition, the timing of the turning on/off of the LEDs as the component light sources can be further set to complete the switching time sequence, and thus the illumination sequence, by the pulse component.

Fig. 3 shows a schematic graph of an exemplary such sequence of three light pulses. The light intensity 302 is plotted against time 301 for red light pulse 310, green light pulse 320 and blue light pulse 330 with respective pulse times t (r)311, t (g)312 and t (b) 313. The overall pulse in the sequence has a time T300.

In fig. 4 is shown an arrangement of a scanner/reader according to another embodiment. The controller 401 controls a camera 402 (image acquisition means comprising some suitable type of light/image sensor) equipped with an optics block 403, which in turn may comprise some kind of lens or optical system. The camera 402 may receive light from an identification 404 applied to a substrate/article 405 and focus the received light on a light sensor in the camera. An optical filter 406 may be added to filter the light received from the marker 404 for narrowing the wavelength band sent to the light sensor 402.

The illumination light source is operable to illuminate the indicia 404 with an illumination pulse light having red, green, and blue illumination light pulse components delivered by red LED 421, green LED 422, and blue LED 423, respectively. After excitation by the red pulse component emitted by the red type ("R") LED 421 of the light source, some (data matrix/barcode) pattern forming a logo 404 printed on the substrate 405 with luminescent ink emits luminescence, and is then imaged by the camera 402 through the filter 406 with the optics block 403.

According to this embodiment, the light source (or corresponding control unit) comprises a switched mode power supply 407(SMPS or switched power supply), which switched mode power supply 407 may be a buck converter or a boost converter depending on whether its output voltage is lower or higher than its input voltage, respectively; the SMPS407 is connected to the controller 401 for receiving an input voltage Vi 432 (a fixed value) and is operable to deliver a constant output voltage Vo 431 to a circuit that includes LEDs (e.g., Vi is 24V and Vo is 48V). A further controller 408 controls the illumination sequence of the LEDs 421 and 423 and is operable to receive synchronization signals from the controller 401 over a synchronization connection 410 for setting the illumination by the LEDs and for capturing by the camera 402 (via signals through the connection 411 and for controlling the emission of light pulses by the LEDs). A further controller 408 controls the drive current delivered in each of branches 412 and 413. Typically, the further controller 408 uses PWM (pulse width modulation) for creating the control signals for the illumination sequence.

R, G and a B LED 421-. Thus, the drive current in each of branches 412 and 413 can be controlled individually. The drive current control loop 409 is further operable to dissipate power generated by the voltage drop and drive current in the branch. Furthermore, the drive current control loop 409 has a connection 416 with an SMPS407 to send a setting signal for setting the (constant) value of the output voltage Vo 431 in order to deliver an appropriate drive current level in the branch in order to avoid excessive heat generation by the LEDs while having illumination of sufficient light intensity.

The camera 402 is connected to the controller 401 via an ethernet link 418 and a high speed link 417, the ethernet link 418 being used to receive the camera setting signal, the high speed link 417 being used to receive the set point signal (on/off) from the controller 401 and to deliver the digital image to the controller unit 401 for image processing (and further data matrix/barcode decoding in the programmable CPU unit of the controller). Thus, the camera 402 is operable to receive a set point signal from the controller 401 to open its shutter to capture images (image data) of the indicia 404 and at the same time send a synchronization signal to the controller 401 to initiate control of the illumination light pulses to be delivered by the light sources, which the controller transmits to further controllers of the light sources.

The drive current profile 511 is shown in fig. 5A as a plot of current 502 versus time 501. The profile 511 is controlled via the drive current control loop 409 at a constant output voltage Vo 431 delivered by the SMPS407 to R, G, B LED 421 and 423 in branches 412 and 413 of the light source. Due to the specific circuit arrangement in the drive current control loop 409, the edges of the current profile (when the LED has just been switched on or switched off) may be quite sharp and may show damped transient oscillations. In contrast, without precaution, the drive current profile in the LED would have the typical profile 512 shown in fig. 5B, i.e., the current would exhibit characteristic non-damped transient oscillations that would damage the LED. Fig. 5A and 5B are intended to show profiles 511 and 512 at the same scale for current 502 and time 501.

Furthermore, with a drive current profile 512, for a typical average current level of about 2A, the maximum amplitude of the corresponding transient drive current profile may be as high as about 1A, generating excessive heat (here, for a pulse duration of about 100p, the transient oscillation time is about 100 ns). Thus, the dissipation in the drive current control loop 409 together with the setting of the control loop via connection 416 by a convenient output voltage level Vo 431 delivered by the SMPS407 helps to maintain heat generation within the light source at an acceptable level, together with an appropriate illumination sequence, while allowing illumination of the identification with an appropriate light intensity level for accurate light intensity measurement of the light received by the light sensor from the identification (and further digital image processing by the processor of the camera). For example, with an input voltage Vi of about 24V, the output voltage level Vo can be set to any value between 30V and 48V.

The controller 401 sends a set point signal to the camera 402 so that the camera opens its shutter to acquire images of the indicia 404 (during the measurement time interval) and simultaneously sends a synchronization signal to the controller to initiate control of the illumination light pulses delivered by the light sources. After the red pulse component emitted by the R-type LED 421 has excited the marker and the measurement time interval has expired, the controller 401 sends a signal to the camera 402 that has acquired the marked digital image to close the shutter. The camera then sends the acquired digital image to the controller 401 for further image processing and decoding of the acquired digital image of the data matrix/barcode.

To further reduce heat generation at the light sources, the on/off switching sequence of LEDs may control a plurality of illuminations by at least one of the component light sources (e.g., red type LEDs 421), and corresponding digital image acquisition operations (over a measurement time interval) by the camera 402.

Fig. 6 shows a flow chart of a method embodiment of the invention. Method embodiments relate to operating a reader operable to read indicia on a substrate, the reader comprising a power source operable to deliver a variable drive current or voltage, a light source operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage, and a light sensor operable to measure the intensity of light received from the indicia and deliver a corresponding light intensity signal. A method embodiment comprises a step 601 ("control") and a step 602 ("adjust"), the step 601 ("control") controlling the timing of the illumination light pulses according to a switching pattern and timing to acquire the light intensity signal for synchronizing the acquisition of the light intensity signal with the sequence of illumination light pulses, and the step 602 ("adjust") adjusting the duty cycle of the switching pattern in order to maintain the heat generation associated with each illumination light pulse below a given threshold. Steps 601 and 602 may be performed sequentially, alternately, or simultaneously (e.g., by implementing parallel threads).

In general, embodiments comprising image acquisition tools allow for control of the calculation of the decay time of the identified luminescent material based on the image data and the time sequence. In particular, information about the wavelength spectrum and identifying the timing of the received light may be employed. For example, controlling the illumination timing and image acquisition time of light pulses of different illumination wavelength spectra allows the time response of any luminescence to be measured. For example, varying the distance (delay) between illumination with one wavelength and the corresponding image data acquisition may provide information about the emission decay of any particular (luminescent) component or material of the identification. The calculated decay time may then be a characteristic for a certain identification ink and may thus be used to authenticate the identification, in the sense that information is retrieved as to whether the identification consists of the correct (genuine) compound.

It is thus possible according to the present embodiment to use a (composite) light source to acquire a global profile of the emitted luminescence intensity i (t) from the marker in order to calculate the decay time value of the luminescent compound, while relying on power management by means of sequential illumination to avoid overheating. The decay time value is a physical property of the luminescent compound that can be used to validate the luminescent compound. Typically, for illuminated signs, a high excitation light intensity is required in order to have a sufficient intensity of luminescence emission measured (hence, heat generation may be a problem).

Thus, an advantage of the (composite) light source is that it can be used for different types of luminescent pigments (materials) because it is possible to flash LEDs with a suitable spectrum (in some cases, only a part of its spectrum is available for excitation), or even to use different LEDs whose spectra overlap in the excitation range. In the case of fluorescent pigments, we generally have a first excitation pulse, and then the emitted light intensity of luminescence (intensity decay over time) is collected from the marker and analyzed for calculating a decay time value (compared to a reference value), or compared to a reference intensity profile (possibly after normalization). This requires managing the illumination time and the subsequent light intensity acquisition time (the respective spectra are distinct). However, such decay time measurements (verification of the luminescent component of the identified material) may be combined with imaging of patterns such as barcodes (e.g. for decoding purposes).

According to a further embodiment of the invention, the identification reading device is a scanner for imaging the identification (M) from luminescence emitted by a luminescent material of the identification, which luminescence material emits said luminescence within an emission wavelength range, according to an illumination of a composite illumination light pulse delivered during an illumination time interval T and having an illumination light wavelength distribution within an illumination wavelength range WS ═ λ min, λ max ], the composite illumination light pulse being formed by a sequence of at least two different illumination light pulse components, each illumination light pulse component having a respective wavelength distribution within a sub-wavelength range WSj ═ λ jmin, λ jmax ] of said illumination wavelength range WS, said emission of luminescence due to excitation of the luminescent material by at least one of said two illumination light pulse components, the scanner comprising a power supply (P); a light source (S) connected to the power supply and operable to illuminate the luminescent material with the composite illumination light pulse within the illumination wavelength range WS when powered with a drive current or a drive voltage during an illumination time interval T; an imaging unit comprising a light sensor operable to measure the luminescence intensity received from the luminescent material in the emission wavelength range and deliver a corresponding luminescence intensity signal, the imaging unit operable to form a digital image of the identity from the intensity signal delivered by the light sensor; and a control unit operable to control the power supply, light source, light sensor and imaging unit to acquire a digital image of the identity from the luminous intensity signals delivered over the measurement time interval Δ t, wherein: the power supply (P) is operable to deliver a variable drive current or drive voltage; the light source (S) is operable to generate the composite illumination light pulse with an intensity that varies according to the delivered drive current or drive voltage; and said control unit is further operable to receive said luminous intensity signal and to control said power supply to switch on/off according to a switching waveform of said drive current or drive voltage delivered to the light source (S) so as to synchronously acquire said luminous intensity by means of a light sensor through the generation of at least one illumination (excitation) light pulse component by the light source (S), while adjusting the duty cycle of said switching waveform by means of a drive current control loop or a drive voltage control loop so as to maintain heat generation within the light source below a given threshold. In case the identification forms a coding pattern, like for example a data matrix, the above scanner may further comprise image processing means operable to decode a digital image acquired by the imaging unit.

According to a further embodiment of the invention, the marking reading device is a scanner for imaging the marking (M) from light reflected by a light-reflective material of the marking, said material reflecting said light in the reflected wavelength range under illumination with a composite illumination light pulse delivered during an illumination time interval T and having an illumination light wavelength distribution within an illumination wavelength range WS ═ λ min, λ max ], said composite illumination light pulse being formed by a sequence of at least two different illumination light pulse components, each illumination light pulse component having a respective wavelength distribution within a sub-wavelength range WSj ═ λ jmin, λ jmax ] of said illumination wavelength range WS, the scanner comprising a power supply (P) as a result of the reflection of the light by the marking by the material of at least one of said two illumination light pulse components; a light source (S) connected to said power supply and operable to illuminate said reflective material with said composite illumination light pulse within said illumination wavelength range WS when energized with a drive current or drive voltage during an illumination time interval T; an imaging unit comprising a light sensor operable to measure light intensity within the reflected wavelength range reflected and received from the reflective material and deliver a corresponding reflected light intensity signal, the imaging unit operable to form a digital image of the identity from the intensity signal delivered by the light sensor; and a control unit operable to control the power supply, light source, light sensor and imaging unit to acquire a digital image of an identity from reflected light intensity signals delivered over a measurement time interval Δ t, wherein the power supply (P) is operable to deliver a variable drive current or drive voltage; a light source (S) operable to produce the composite illumination light pulse with an intensity that varies according to the delivered drive current or drive voltage; and said control unit is further operable to receive said reflected light intensity signal and to control said power supply to switch on/off according to a switching waveform of said drive current or drive voltage delivered to the light source (S) so as to synchronously acquire said reflected light intensity by means of the light sensor by generation of at least one illumination light pulse component by the light source (S), while adjusting the duty cycle of said switching waveform by means of a drive current control loop or a drive voltage control loop to maintain heat generation within the light source below a given threshold.

According to a further embodiment of the invention, a scanner for imaging indicia on a substrate comprises a power supply, a light source, a light sensor and a control unit, the light source being connected to the power supply and operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra when powered with a drive current or a drive voltage; the light sensor is operable to measure light intensity within a range of wavelengths received from the identification in response to an illumination sequence and deliver a corresponding light intensity signal; and the control unit is operable to control the power supply, the light source and the light sensor to control the timing of the illumination light pulses and to collect a light intensity signal from the identification of received light, wherein the power supply is operable to deliver a variable drive current or drive voltage, the light source is operable to generate the illumination light pulses with an intensity that varies in accordance with the delivered drive current or drive voltage, and the control unit is further operable to receive the light intensity signal from the light sensor and to control the power supply to switch on/off in accordance with a switching waveform of the drive current or drive voltage delivered to the light source, so as to synchronously collect the light intensity by the light sensor through generation of a sequence of illumination light pulses by the light source and to adjust the duty cycle of the switching waveform by way of a drive current control loop or a drive voltage control loop, in order to maintain the heat generation associated with the generation of each illumination light pulse within the light source below a given threshold.

Still further, the disclosed embodiments may also be used as an aspect for implementing an apparatus for sequentially illuminating a plurality of markers having a common optical characteristic, the apparatus comprising a light source operable to illuminate the markers with a repeating pulse sequence comprising a plurality of light pulses of different wavelength spectra, wherein the pulse timing specifies the position and duration of each pulse in one pulse sequence, and a control unit configured to control said pulse timing for each pulse sequence for controlling heat generation in accordance with said common optical characteristic.

Although detailed embodiments have been described, these serve only to provide a better understanding of the invention as defined by the independent claims and should not be considered as limiting.

Claims (26)

1. A reader operable to read indicia on a substrate, the reader comprising:

a power source operable to deliver a variable drive current or voltage,

a light source operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage;

a light sensor operable to measure an intensity of light received from the indicia and deliver a corresponding light intensity signal; and

a control unit operable to control the power supply and the light sensor to control the timing of the pulses of illumination light according to a switching pattern and timing to acquire the light intensity signal for synchronizing the acquisition of the light intensity signal with the sequence of pulses of illumination light,

the control unit is further operable to adjust a duty cycle of the switching pattern so as to maintain heat generation associated with each illumination light pulse below a given threshold,

wherein the control unit is further configured to calculate a decay time of the identified luminescent material based on the light intensity signal.

2. The reader of claim 1, wherein the light source comprises at least two component light sources, a first component light source operable to illuminate the indicia with light pulses of a first wavelength spectrum, and a second component light source operable to illuminate the indicia with light pulses of a second wavelength spectrum.

3. The reader of claim 1, further comprising an image capture tool as the light sensor for capturing image data of the indicia.

4. The reader of claim 3, wherein the control unit is configured to control an acquisition time of the image acquisition tool for controlling the timing to acquire the light intensity signal.

5. The reader of claim 4, wherein the acquisition time is an aperture open time during which image data of the indicia is acquired.

6. The reader of any one of claims 1 to 5, wherein the decay time is also calculated based on wavelength spectrum information associated with light received from the identification.

7. The reader according to any one of claims 1 to 5, wherein the identification comprises a luminescent material and the control unit is configured to control the timing in accordance with an emission characteristic of the luminescent material.

8. The reader according to any one of claims 1 to 5, wherein the identification comprises a plurality of luminescent materials, each having a different emission characteristic, and the control unit is configured to control the timing in accordance with each emission characteristic of each luminescent material.

9. The reader according to any one of claims 1 to 5, wherein the control unit is configured to control any one of a delay between the timings, a position of one of the timings, and a duration of one of the light pulses.

10. The reader according to any one of claims 1 to 5, wherein the control unit adjusts the duty cycle of the switching pattern by means of a control loop.

11. The reader of any one of claims 1 to 5, wherein the switching pattern is a switching waveform defining switching on and off of the variable drive current or voltage.

12. The reader of any one of claims 1 to 5, wherein the identification is any one of a one-dimensional barcode, a two-dimensional barcode, a data matrix, and a security identification.

13. A method of operating a reader operable to read an identification on a substrate, the reader comprising:

a power source operable to deliver a variable drive current or voltage,

a light source operable to illuminate the indicia with a sequence of illumination light pulses of different wavelength spectra, the intensity of the illumination light pulses varying as a function of the delivered drive current or voltage;

a light sensor operable to measure an intensity of light received from the indicia and deliver a corresponding light intensity signal;

the method comprises the following steps:

controlling a timing of the illumination light pulses in accordance with a switching pattern and timing to acquire the light intensity signal for synchronizing the acquisition of the light intensity signal with the sequence of illumination light pulses,

adjusting a duty cycle of the switching pattern so as to maintain heat generation associated with each illumination light pulse below a given threshold, an

Calculating a decay time of the identified luminescent material based on the light intensity signal.

14. The method of claim 13, wherein the light source comprises at least two component light sources, a first component light source operable to illuminate the indicia with light pulses of a first wavelength spectrum, and a second component light source operable to illuminate the indicia with light pulses of a second wavelength spectrum.

15. The method of claim 13, further comprising acquiring image data of the identification.

16. The method of claim 15, further comprising: and controlling the acquisition time of the acquired image data, and controlling the time sequence to acquire the light intensity signal.

17. The method of claim 16, wherein the acquisition time is an aperture open time during which the identified image data is acquired.

18. The method of any of claims 13 to 17, wherein the decay time is also calculated based on wavelength spectrum information associated with light received from the identity.

19. A method according to any of claims 13 to 17, wherein the identification comprises a luminescent material and the control unit is configured to control the timing in accordance with an emission characteristic of the luminescent material.

20. A method according to any one of claims 13 to 17, wherein the indication comprises a plurality of luminescent materials, each having a different emission characteristic, and the control unit is configured to control the timing in accordance with each emission characteristic of each luminescent material.

21. A method according to any of claims 13 to 17, further comprising controlling any of a delay between the sequences, a position of one of the sequences and a duration of one of the light pulses.

22. A method according to any of claims 13 to 17, further comprising adjusting the duty cycle of the switching pattern by means of a control loop.

23. A method as claimed in any of claims 13 to 17, wherein the switching pattern is a switching waveform defining switching on and off of the variable drive current or voltage.

24. The method of any one of claims 13 to 17, wherein the identification is any one of a one-dimensional barcode, a two-dimensional barcode, a data matrix and a security identification.

25. A computer readable storage medium for storing a computer program comprising code which, when executed on a processing resource, implements the method of any of claims 13 to 24.

26. The computer readable storage medium of claim 25, wherein the computer readable storage medium comprises a tangible data carrier storing the computer program in a non-volatile manner.