Method and apparatus for classifying batches of wood chips or the like

A method and apparatus for classifying batches of wood chips or the like according to light reflection characteristics; provide optimal use of darker wood chips in pulp and paper processes. According to a preferred embodiment, light produced by a set of illumination sources is evenly directed onto superficial wood chips of an inspected batch portion transported on a conveyor while being inspected by a camera disposed over the conveyor. The superficial wood chips presenting light reflection characteristics being substantially representative of the wood chips of the inspected batch, reflected light is sensed by the camera to produce electrical signals representing rejection intensity values for the wood chips of the batch portion. From the electrical signals produced, image processing is performed to provide global reflection intensity data for the inspected batch, which are then compared with reference reflection intensity data to provide classification of the inspected wood chips batch into proper wood chips grade according to its light reflection characteristics.

FIELD OF THE INVENTION
 The present invention relates to classification of batches of wood chips or
 the like, and more particularly to a method and apparatus for classifying
 batches of wood chips according to light reflection characteristics.
 BACKGROUND OF THE INVENTION
 In the past years, significant efforts have been devoted to develop
 processes for the production of pulp and paper products aimed at reducing
 manufacturing costs while improving product quality. Quality control of
 the raw materials entering in the production of pulp and paper products,
 particularly regarding wood chips used, has been identified as a key
 factor in process optimization.
 A known approach to control quality of wood chips consists in treating wood
 chips at the manufacturing stage. Such an approach is employed in the wood
 chips manufacturing method disclosed in U.S. Pat. No. 5,577,671 issued on
 Nov. 26, 1996 to Seppanen et al, which method consists of separating from
 ground whole-tree chips, bark and cellulose wood chips through a series of
 separation stages including pneumatic separation, vibration segregation
 with sieve and color difference sorting. The resulting low bark, pale wood
 chips can be then processed using a minimum quantity of bleaching agent.
 Although processing cost can be minimized accordingly, added manufacturing
 cost due to bark separation step may still maintain overall production
 cost high.
 Another known approach consists of sorting trees according to their types
 prior to wood chips manufacturing, to produce corresponding batches of
 wood chips presenting desired characteristics associated with these types.
 Typically, hardwood trees such as poplar, birch and maple are known to
 generally produce pale wood chips while conifers such as pine, fir and
 spruce are known to generally yield darker wood chips. In practice, wood
 chips batches can either be produced from trees of a same type or from a
 blend of wood chips made from trees of plural types, preferably of a
 common category, i.e., hardwood trees or conifers, to seek wood chips
 uniformity. However, chips characteristics basically depending on initial
 bark content of wood chips used, knowledge of the types of wood chips for
 a given batch does not necessarily give a reliable indication of the chips
 quality.
 SUMMARY OF INVENTION
 It is therefore an object of the present invention to provide a method and
 apparatus for classifying batches of wood chips or the like according to
 optical characteristics representative of chips quality or grade.
 According to the above object, from a broad aspect of the present
 invention, there is provided a method for classifying batches of wood
 chips or the like according to light reflection characteristics,
 comprising the steps of: a) directing light onto superficial wood chips
 included in at least a representative portion of an inspected one of said
 wood chips batches, said superficial wood chips presenting light
 reflection characteristics being substantially representative of the wood
 chips of the inspected batch; b) sensing light reflected on the
 superficial wood chips included in said batch portion to produce
 electrical signals representing reflection intensity values for the
 superficial wood chips included in said batch portion; c) deriving from
 the electrical signals global reflection intensity data characterizing the
 inspected batch of wood chips; and e) comparing the global reflection
 intensity data with reference reflection intensity data to provide
 classification of said inspected batch of wood chips according its light
 reflection characteristics.
 According to a further broad aspect of the present invention, the method
 comprises the steps of: a) directing light orto superficial wood chips
 included in at least a representative portion of an inspected one of said
 wood chips batches, said superficial wood chips presenting light
 reflection characteristics being substantially representative of the wood
 chips of the inspected batch; b)sensing light reflected on the superficial
 wood chips included in said batch portion to produce first electrical
 signals representing reflection intensity values for the superficial wood
 chips included in said batch portion; c) measuring moisture of said
 superficial wood chips to produce second electrical signals representing
 average moisture values for the superficial wood chips included in said
 batch portion; d) deriving from said first and second electrical signals
 global reflection intensity data characterizing the inspected batch of
 wood chips, said global reflection intensity data being normalized
 according to a predetermined moisture reference value; and e) comparing
 the global reflection intensity data with reference reflection intensity
 data to provide classification of said inspected batch of wood chips
 according its light reflection characteristics.
 According to a still further broad aspect of the present invention, there
 is provided an apparatus for classifying batches of wood chips or the like
 according to light reflection characteristics. The apparatus comprises
 illumination means for directing light onto superficial wood chips
 included in at least a representative portion of an inspected one of said
 wood chips batches, said superficial wood chips presenting light
 reflection characteristics being substantially representative of the wood
 chips of the inspected batch. The apparatus further comprises image
 creating means for sensing light reflected on the superficial wood chips
 included in said batch portion to produce image electrical signals
 representing reflection intensity values for the wood chips included in
 said batch portion. The apparatus further comprises means for deriving
 from the image electrical signals global reflection intensity data for the
 inspected batch; and means for comparing the global reflection intensity
 data with reference reflection intensity data to provide classification of
 said inspected batch of wood chips according its light reflection
 characteristics.
 According to a still further broad aspect of the present invention, the
 apparatus comprises illumination means for directing light onto
 superficial wood chips included in at least a representative portion of an
 inspected one of said wood chips batches, said superficial wood chips
 presenting light reflection characteristics being substantially
 representative of the wood chips of the inspected batch, image creating
 means for sensing light reflected on the superficial wood chips included
 in said batch portion to produce first electrical signals representing
 reflection intensity values for the wood chips included in said batch
 portion, and moisture detector means for producing second electrical
 signals representing average moisture values for the superficial wood
 chips included in said batch portion. The apparatus further comprises
 means for deriving from said first and second electrical signals global
 reflection intensity data for the inspected batch, said global reflection
 intensity data being normalized according to a predetermined moisture
 reference value and means for comparing the global reflection intensity
 data with reference reflection intensity data to provide classification of
 said inspected batch of wood chips according its light reflection
 characteristics.
 According to a preferred embodiment of the present invention, a method and
 apparatus for classifying batches of wood chips or the like according to
 optical characteristics is provided, which allow optimal use of darker
 wood chips in pulp and paper processes. Although hardwood wood chips
 generally require more bleaching agent when being processed, their
 cellulose fibers may exhibit better physical characteristics than fibers
 found in conifers for the purpose of producing products presenting
 particular structural characteristics. Therefore, mixing a relatively
 small batch of such darker wood chips with a large batch of pale wood
 chips can produce a blend presenting the quality required for optimal
 processing, provided the characteristics of the darker wood chips batch
 have been accurately determined, to adjust parameters of the process
 accordingly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring now to FIG. 1, an apparatus according to the preferred embodiment
 of the present invention is generally designated at 10, which includes an
 inspection station 12 comprising an enclosure 14 through which extends a
 powered conveyor 15 coupled to a drive motor 18. The conveyor 15 is
 preferably of a trough type having a belt 13 defining a pair of opposed
 lateral extensible guards 16, 16' of a known design, for keeping the
 material to be inspected on the conveyor 15. Adjacent an input end 29 of
 the conveyor 15 is an hopper 21 for receiving at an upper inlet thereof
 (not shown) a batch 24 of material to be inspected for classification
 purposes, which material essentially consists of wood chips 26 in the
 example shown. However, it is to be understood that batches of other
 similar wooden materials could be advantageously classified in accordance
 with the present invention, such as flakes, shavings, slivers, splinters
 and shredded wood. Typically, the wood chips 26 may be caused to flow
 under gravity and discharged through a controlled outlet (not shown)
 provided at the bottom part of the upper 21 for further processing.
 Radially extending through a pair of opposed openings 22 receiving rotary
 bearings 17 provided on the peripheral wall 23 of the hopper 21 is a
 sampling device 19 having an elongated cylindrical sleeve 27 of a circular
 cross-section adapted to receive for rotation therein a feeding screw 28
 of a known construction. The sleeve 27 has a lateral input opening 29
 allowing wood chips 26 to cyclically reach an input portion of the screw
 28 whenever the sleeve opening 29 passes through an upper position as
 shown in FIG. 1. The sleeve 27 further has one or more output openings 31
 generally disposed over the conveyer input end 29 to allow substantially
 uniform discharge of the sampled wood chips 26 on the conveyer belt 13.
 The feeding screw 28 has a base disk 30 being coupled to the driven end of
 a driving shaft 32 extending from a drive motor 34 mounted on a support
 frame 36, which motor 34 imparts rotation to the screw 28 at a given RPM.
 The driving shaft 32 is provided with a small driving gear 38 cooperating
 with a large gear 40 and a small gear 42 mounted on first idle shaft 44
 supported by base 36, to transmit driving couple at a lower RPM to a
 reversing gear 46 mounted on a second idle shaft 48 rotatably engaging a
 support member 50 rigidly secured to the outer surface of hopper 21. The
 sleeve 27 has a driven end 52 provided with an outer annular disk 54
 having radially extending gear teeth cooperating with the reversing gear
 46 to impart rotation to the sleeve in a direction opposed to clockwise
 rotation of screw 28 and at a lower RPM, as will be explained later in
 more detail.
 Turning now to FIGS. 2 and 3, internal components of the inspection station
 12 will be now described. The enclosure 14 is formed of a lower part 56
 for containing the conveyor 15 and being rigidly secured to a base 58 with
 bolt assemblies 57, and an upper part 60 for containing the optical
 components of the station 12 and being removably disposed on supporting
 flanges 62 rigidly secured to upper edge of the lower part 56 with bolted
 profile assemblies 64. At the folded ends of a pair of opposed inwardly
 extending flanged portions 66 and 66' of the upper part are secured
 through bolts 68 and 68' side walls 70 and 70' of a shield 72 further
 having top 74, front wall 76 and rear wall 76' to optically isolate the
 field of view 80 of a camera 82 for optically covering superficial wood
 chips 26' included in a representative portion of the inspected wood chips
 batch and being disposed within an inspection area. The camera 82 is
 located over the shield 72 and has an objective downwardly extending
 through an opening 84 provided on the shield top 74, as better shown in
 FIG. 2. Superficial wood chips 26' are distributed onto the conveyor belt
 13 to present light reflection characteristics which are substantially
 representative of the wood chips 26 of the inspected batch. The camera 82
 is used to sense light reflected on superficial wood chips 26' to produce
 electrical signals representing reflection intensity values for the
 superficial wood chips 26'. For the example described herein, although any
 appropriate monochrome camera could be used to provided detection of
 desired optical characteristics, a color RGB CCD video camera is
 preferably used to further provide color displaying capability for the
 operator. Diagonally disposed within shield 72 is a transparent glass
 sheet acting as a support for a calibrating reference support 88 as better
 shown in FIG. 3, whose function will be explained later in more detail. A
 shown in FIG. 2, the camera 82 is secured according to an appropriate
 vertical alignment on a central transverse member 90 supported at opposed
 end thereof to a pair of opposed vertical frame members 92 and 92' secured
 at lower ends thereof on flanged portions 66 and 66' as shown in FIG. 3.
 Also supported on the vertical frame members 92 and 92' are front and rear
 transverse members 94 and 94'. Transverse members 90, 94 and 94' are
 adapted to receive elongate electrical light units 96 which use standard
 fluorescent tubes 98 in the example shown, to direct light substantially
 evenly onto the inspected batch portion of superficial wood chips 26'. The
 camera 82 and light units 96 are powered via a dual output electrical
 power supply unit 98. Electrical image signal is generated by the camera
 82 through output line 100. When used in cold environment, the enclosure
 14 is preferably provided with a heating unit (not shown) to maintain the
 inner temperature at a level ensuring normal operation of the camera 82.
 Referring to FIG. 2, an optional moisture sensing unit 78 is shown which is
 preferably disposed near the inspection station 12. The sensing unit 78 is
 used to inspect batches of material exhibiting variations in the moisture
 content, either between the batches or within any specific batch, which
 variations may affect reflectance characteristics of the superficial wood
 chips 26', thereby affecting reflection intensity values as measured by
 the camera 82. The moisture sensing unit 78 is preferably a non-contact
 sensing device such as the near-infrared sensor MM55plus supplied by NDC
 Infrared Engineering, Irwindale Calif. The unit 78 generates at an output
 79 thereof electrical signals representing average moisture values for the
 superficial wood chips 26'.
 For example, while batches of wood chips stored in large containers before
 processing generally exhibit substantially uniform and stable moisture
 contents, chips batches stored in open sites may present moisture
 variations which may have a material effect on the reflectance
 measurements. In processes where high classification accuracy is required,
 consideration of the effect of moisture variations may be needed.
 Referring to FIG. 4, the overall inverse relationship between moisture
 level in percentage and luminance as periodically measured during drying
 of a sample of wood chips is illustrated, which relation may be roughly
 expressed by .DELTA.l.apprxeq.-k.DELTA.m, wherein .DELTA.m represents any
 deviation in moisture value, .DELTA.l represents a corresponding variation
 in luminance value, k being a scale constant having a positive real value.
 It can be seen that chips showing an initial moisture content of 54% as
 shown by curve M intersecting the left vertical axis, are roughly 27%
 brighter (passing from 54 to 68.5 in luminance as shown by curve L
 intersecting the right vertical axis) after their moisture was reduced to
 26% after drying. That shift in measured luminance may be compensated by
 normalizing the reflection intensity values according to corresponding
 moisture deviations from a predetermined reference moisture value, as will
 be later explained in more detail.
 Control and processing elements of the apparatus 10 will be now described
 with reference to FIG. 2. The apparatus 10 further comprises a computer
 unit 102 having an image acquisition module 104 coupled to line 100 for
 receiving image electrical signals from the camera 82, which module 104
 could be any appropriate RGB image data acquisition electronic card
 currently available on the marketplace. The computer 102 is provided with
 an external communication unit 103 being coupled for bi-directional
 communication through lines 106 and 106' to a conventional programmable
 logic controller (PLC) 107 for controlling operation of the sample screw
 drive 28 and conveyor drive 18 through lines 108 and 110 respectively
 according to a predetermined program. The PLC 107 receives from line 112
 batch data entered via an input device 114 by an operator in charge of
 batch registration and dumping operations, as will be explained later in
 more detail. The input device 114 is connected through a further line 116
 to an image processing and communication software module 118 outputting
 control data for PLC through line 119 while receiving acquired image data
 and PLC data through lines 120 and 122, respectively. The image processing
 and communication module 118 receives input data from a computer data
 input device 124, such as a computer keyboard, through an operator
 interface software module 126 and lines 128 and 130, while generating
 image output data toward a display device 132 through operator interface
 module 126 and lines 134 and 136. Where a moisture sensing unit 78 is
 provided, the module 118 also receives the moisture indicating electrical
 signals through a line 81.
 Turning now to FIG. 5, general relations between measured optical
 characteristics and dark wood chips contain associated with several
 samples are illustrated by the curves traced on the graph shown, whose
 first axis 138 represents dark chips contain by weight percentage
 characterizing the sample, and whose second axis 140 represents
 corresponding optical response index measured. In the example shown, four
 curves 142, 144, 146, and 148 have been fitted on the basis of average
 optical response measurements for four (4) groups of wood chips samples
 prepared to respectively present four (4) distinct dark chips contains by
 weight percentage, namely 0% (reference group), 5%, 10% and 20%.
 Measurements were made using a RGB color camera coupled to an image
 acquisition module connected with a computer, as described before. To
 obtain curves 142 and 146, luminance signal values derived from the RGB
 signals corresponding to all considered pixels were used to derive an
 optical response index which is indicative of the relative optical
 reflection characteristic of each sample. As to curve 142, mean optical
 response index was obtained according to the following ratio:
 ##EQU1##
 Wherein I is the optical response index, L.sub.R is a mean luminance value
 associated with the reference samples and L.sub.S is a mean luminance
 value based on all considered pixels associated with a given sample. Curve
 146 was obtained through computer image processing to attenuate chip
 border shaded area which may not be representative of actual optical
 characteristics of the whole chip surface. To obtain curves 144 and 148,
 reflection intensity of red component of RGB signal was compared to a
 predetermined threshold to derive the optical response index according the
 following relation:
 ##EQU2##
 wherein I is the optical response index, P.sub.D is the number of pixels
 whose associated red component intensity is found to be lower than the
 predetermined ratio (therefore indicating a dark pixel) and P.sub.T is the
 total number of pixels considered. As for curve 146, curve 148 was
 obtained through computer image processing to attenuate chip border shaded
 areas. It can be seen from all curves 142, 144, 146, and 148 that the
 optical response index grows as dark chip contains increases. Although
 curve 148 shows the best linear relationship, experience has shown that
 all of the above described calculation methods for the optical response
 index can be applied, provided reference reflection intensity data are
 properly determined, as will be explained later in more detail.
 Returning now to FIGS. 1, 2 and 5, operation of the method and apparatus
 according to the preferred embodiment of the present invention will be now
 explained. Referring to FIG. 2, before starting operation, the apparatus
 10 must be initialized through the operator interface module 126 by
 firstly setting system configuration. Camera related parameters can be
 then set through the image processing and communication module 118,
 according to the camera specifications. The initialization is completed by
 camera and image processing calibration through the operator interface
 module 126.
 System configuration provides initialization of parameters such as data
 storage allocation, image data rates, communication between computer unit
 102 and PLC 107, data file management, wood type identification and
 corresponding reference threshold levels setting. As to data storage
 allocation, images and related data can be selectively stored on a local
 memory support or any shared memory device available on a network to which
 the computer unit 102 is connected. Directory structure is provided for
 software modules, system status message file, current accepted batch data,
 current rejected batch data and recorded rejected batch data. Image rate
 data configuration allows to select total number of acquired images for
 each batch, number of images to be stored amongst the acquired images and
 acquisition rate, i.e. period of time between acquisition of two
 successive images. Therefore, to limit computer memory requirements, while
 a high number of images can be acquired for statistical purposes, only a
 part of these images, particularly regarding rejected batches, need to be
 stored. The PLC configuration relates to parameters governing
 communication between computer unit 102 and PLC 107, such as master-slave
 protocol setting (ex. DDE), memory addresses for a) batch data input
 synchronization for batch presence checking following dumping information;
 b) alarm set for indicating a rejected batch; and c) &lt;&lt;heart beat&gt;&gt; for
 indication of system interruption, &lt;&lt;heart beat&gt;&gt; rate and batch presence
 monitoring rate. Data file management configuration relates to parameters
 regarding batch input data, statistical data for inspected batches, data
 keeping period before deletion for acceptable batch and data keeping
 checking rate. Statistical data file can typically contain information
 relating to batch number, supplier contract number, wood type, mean
 intensity values for Red, Green and Blue (RGB) signals, mean luminance,
 date of acquisition, batch status (acceptable or rejected). Data being
 systematically updated on a cumulative basis, the statistical data file
 can be either deleted or recorded as desired by the operator to allow
 acquisition of new data.
 All desired wood types can be identified as well as associated reference
 threshold levels used as reference reflectance intensity data. For a given
 wood type, based on initial visual inspection by the operator of optical
 characteristics presented by several representative samples for that
 particular wood type, the operator sets a low threshold value under which
 an inspected batch shall be rejected as containing an unacceptable amount
 of dark chips for that type of wood. It is to be understood that batch
 containing chips blend of known wood types can be characterized in a same
 way. In addition to visual inspection, process parameters such as required
 quantity of bleaching agent, processing time or spent energy measured for
 prior inspected batches can be recorded to find out low threshold value
 associated with minimum processing yield required to qualify a batch
 acceptable. Preferably, reference reflection intensity data may include
 range threshold data delimiting a plurality of wood chips grades. In that
 case, the operator may also set a maximum threshold value above which an
 inspected batch could be considered more than acceptable for that
 particular grade, ex. grade 1, and therefore could be classified in a
 higher quality grade of wood chips, ex. grade 2. The current levels
 setting for a current batch can be modified, stored or deleted as desired
 by the operator. It is to be understood that specific values given to the
 classification thresholds are also dependent upon calibration performed.
 Once the camera 82 is being configured as specified, calibration of the
 camera and the image processing module can be carried out by the operator
 through the operator interface, to ensure substantially stable light
 reflection intensities measurements as a function of time even with
 undesired lightning variation due to temperature variation and/or light
 source aging, and to account for spatial irregularities inherent to CCD's
 forming the camera sensors. Calibration procedure first consists of
 acquiring &lt;&lt;dark &gt;&gt; image signals while obstructing with a cap the
 objective of the camera 82 for the purpose of providing offset
 calibration, and acquiring &lt;&lt;lighting &gt;&gt; image signals with a gray target
 presenting uniform reflection characteristics being disposed within the
 inspecting area on the conveyer belt 13 for the purpose of providing
 spatial calibration. Calibration procedure then follows by acquiring image
 signals with an absolute reference color target, such as a color chart
 supplied by Macbeth Inc., to permanently obtain a same measured intensity
 for substantially identically colored wood chips, while providing
 appropriate RGB balance for reliable color reproduction. Initial
 calibration ends with acquiring image signals with a relative reference
 color target permanently disposed on the calibrating reference support 88,
 to provide an initial calibration setting which account for current
 optical condition under which the camera 82 is required to operate. Such
 initial calibration setting will be used to perform calibration update
 during operation, as will be later explained in more detail.
 Where a moisture sensing unit 78 is provided, further calibration steps are
 carried out, using a chips sample which is subjected to a progressive
 drying process according to an experimental moisture range that is
 representative of the actual moisture range, to derive a reference
 moisture curve through standard measurement in laboratory, such as the
 curve M shown in FIG. 4. The moisture curve is then compared with a
 reference moisture curve obtained with the sensing unit 78, allowing an
 initial calibration thereof. While the chips sample is being dried,
 luminance values are also measured to derive a luminance curve associated
 with the obtained moisture curve, such as curve L shown in FIG.4. Then,
 luminance compensation values to be used for the normalization to the
 predetermined reference moisture value can be obtained through the
 relation .DELTA.l.apprxeq.-k.DELTA.m , with .DELTA.m=m.sub.c -m.sub.r,
 wherein m.sub.c is a current moisture value as measured by the unit 78 and
 m.sub.r is the predetermined reference moisture value.
 Initialization procedure being completed, the apparatus 10 is ready to
 operate, the computer unit 102 being in permanent communication with the
 PLC 107 to monitor the operation of the screw drive 28 indicating the
 presence of a new batch to be inspected. Whenever a new batch is detected,
 the following sequence of steps are performed: 1) end of PLC monitoring;
 2) batch data file reading (type of wood chips, batch identification
 number); 3) image acquisition and processing for wood chips batch
 classification according to the set threshold values; and 4) data and
 image recording after batch inspection.
 Image acquisition consists in sensing light reflected on the superficial
 wood chips 26' included in the present batch portion to produce electrical
 signals representing reflection intensity values for the superficial wood
 chips 26', forming an image thereof Although a single batch portion of
 superficial chips covered by camera field of view 80 may be considered to
 be representative of optical characteristics of a substantially
 homogeneous batch, wood chips batches being known to be generally
 heterogeneous, it is preferable to consider a plurality of batch portions
 by acquiring a plurality of corresponding image frames of electrical pixel
 signals. In that case, image acquisition step is repeatedly performed as
 the superficial wood chips of batch portions are successively transported
 through the inspection area defined by the camera field of view 80. Where
 a moisture sensing unit 78 is provided, superficial wood chips 26' are
 scanned by infrared beam generated by the unit 78 which analyze reflected
 radiation to generate the moisture indication signals. It is to be
 understood that while the moisture sensing unit 78 is disposed at the
 output of the inspection station 12 in the illustrated embodiment, other
 locations downstream or upstream to the inspection station 12 may be
 suitable.
 As to image processing, the image processing and communication unit 118 is
 used to derive from the acquired pixel signals global reflection intensity
 data for the inspected batch, designated before as optical response index
 with reference to FIG. 5. Calibration updating of the acquired pixel
 signals is performed considering pixels signals corresponding to the
 relative reference target as compared with the initial calibration
 setting, to account for any change affecting current optical condition.
 Then, image noise due to chip border shaded areas, snow and/or ice and
 visible belt areas are preferably filtered out of the image signals using
 known image processing techniques. Where a moisture sensing unit 78 is
 provided, the image processing and communication unit 118 applies
 compensation to the acquired pixel signals using the corresponding
 moisture indicating electrical signals.
 Global reflection intensity data may then be derived by averaging
 reflection intensity values represented by ether all or representative
 ones of the acquired pixel signals for the batch portions considered, to
 obtain mean reflection intensity data. Alternately, the global reflection
 intensity data may be derived by computing a ratio between the number of
 pixel signals representing reflection intensity values above a
 predetermined threshold value and the total number of pixel signals
 considered. Any other appropriate derivation method known in the art could
 be used to obtain the global reflection intensity data from the acquired
 signals. Optionally, the global reflection intensity data may include
 standard deviation data, obtained through well known statistical methods,
 variation of which may be monitored to detect any abnormal heterogeneity
 associated with an inspected batch.
 As to wood chips batch classification, the image processing and
 communication unit 118 compares the global reflection intensity data to
 reference reflection intensity data including range thresholds, to provide
 classification of the inspected wood chips batch into a proper wood chip
 grade according its light reflection characteristics. As mentioned before,
 reference reflection intensity data may comprise threshold data
 respectively corresponding to a plurality of wood chip types. In that
 case, batch data input device 114 sends to the image processing and
 communication an electrical signal indicating a specific one of wood types
 to which the wood chips of the current inspected batch correspond, and
 classification is performed by comparing the global reflection intensity
 data to the reference reflection intensity data corresponding to the
 specific wood chips type accordingly. Alternately, input device 114 can be
 in the form of an automated reading device capable of detecting machine
 readable code associated with the inspected batch, the code representing
 the corresponding one of chips wood type. In a case where the inspected
 batch is classified as being acceptable for a given grade, the computer
 unit 102 resumes PLC monitoring for a next batch to be inspected.
 Otherwise, whenever an unacceptable batch is detected and therefore
 rejected, the computer unit causes an alarm to be set by the PLC before
 resuming PLC monitoring. In operation, the computer unit 102 continuously
 sends a normal status signal in the form of a &lt;&lt;heart beat&gt;&gt; to the PLC
 through line 106'. The computer unit 102 also permanently monitors system
 operation in order to detect any software and/or hardware based error
 which could arise to command inspection interruption accordingly.
 Preferably, to save computer memory, the computer unit 102 does not keep
 all acquired images, so that alter a predetermined period of time, images
 of acceptable inspected batches are deleted while images of rejected
 batches are recorded for later use. The image processing and communication
 module 118 performs system status monitoring functions such as automatic
 interruption conditions, communication with PLC, batch image data file
 management, dumping monitoring and monitoring status. These functions
 result in messages generation addressed to the operator through display
 132 whenever appropriate action of the operator is required. For automatic
 interruption conditions, such a message may indicate that video (imaging)
 memory initialization failed, an illumination problem arose or a problem
 occurred with the camera 82 or the acquisition card. For PLC
 communication, the message may indicate a failure to establish
 communication with PLC 107, a faulty communication interruption,
 communication of a &lt;&lt;heart beat&gt;&gt; to the PLC 107, starting or interruption
 of the &lt;&lt;heart beat&gt;&gt;. As to batch data files management, the message may
 set forth that acquisition initialization failed, memory storing of image
 or data failed, a file transfer error occurred, monitoring of recorded is
 being started or ended. As to chips dumping monitoring, the message may
 alert the operator that batch data has not been properly read, dumping
 monitoring being started or ended. Finally, general operation status
 information is given to the operator through messages indicating that the
 apparatus is ready to operate, acquisition has started, acquisition is in
 progress, image acquisition is completed and alarm for rejected batch
 occurred.
 Referring now to FIG. 6, a typical data output report which can be obtained
 using the above described method and apparatus is illustrated, which
 reports presents statistics associated with a selected wood chips image
 shown, as well as statistics related to the corresponding batch of gray
 pine wood chips. It can be seen from image statistics shown that although
 status of the current image indicates that it has been rejected with a
 mean intensity value of 48 as compared to a low threshold value set to 50,
 the corresponding cumulative batch data in turn indicate with a mean
 intensity of 52 that the batch as whole is qualified as acceptable for
 grade 1, while being not qualified as grade 2 for being lower than the
 high threshold set to 70.
 It is within the ambit of the present invention to cover any obvious
 modification of the described embodiment of the method and apparatus
 according to the present invention, provided it falls within the scope of
 the appended claims.