Abstract:
The performance of scanning systems can be significantly enhanced by replacing the traditional power track with preferably just two wires or transmission channels for effecting communication between (i) the sensors on the mobile carriage of the scanning system and (ii) the controls, power sources, and related devices that are typically located in a compartment or module which is a significant distance away. This can be implemented by employing selected multiplexer and complementary de-multiplexer combinations in the scanner head and in the module. This technique reduces EMI noise, power loss, drag on the moving scanner heads carrying the sensors, and cost of construction.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to a scanning or moving system that is equipped with multiple sensors or other electronic devices requiring a large number of control and measurement wires and more particularly to a technique that reduces the number of wire interconnections linking the sensors to control devices that are located remotely from the moving sensors, which improves system reliability, efficiency and sensitivity and which reduces costs. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is often desirable to obtain measurements of selected characteristics of sheet materials during manufacture. Although various properties of sheet materials can be detected by off-line laboratory testing, such tests often are not practical because of the time required for sample acquisition and analysis. Also, laboratory testing has the shortcoming that samples obtained for testing may not accurately represent sheet material that has been produced. 
         [0003]    To overcome the drawbacks of laboratory testing of sheet materials, various sensor systems have been used for detecting sheet properties “on-line,” i.e., on a sheet-making machine while it is operating. Typically, on-line sensor devices are operated to periodically traverse, or “scan,” traveling webs of sheet material during manufacture. Scanning usually is done in the cross direction, i.e., in the direction perpendicular to the direction of sheet travel. Depending upon the sheet-making operation, cross-directional distances can range up to about ten meters or more. 
         [0004]    A wide variety of scanning sensor devices has been developed for on-line measurements of sheet materials. As illustrated in  FIGS. 4A and 4B , the scanning sensor system  100  typically includes a stationary frame  102 , having a pair of upright end members that stand on a factory floor for supporting a guide member  104  that extends horizontally across a traveling sheet (not shown). A motor driven carriage is mounted to travel on the guide member  104 . The carriage is connected to a drive system to be driven back and forth across sheet. The scanning sensor system also includes a scanning head  106  that is mounted on the carriage member. The scanning head  106  contains the detection components. For example, in the case of a spectrometric analyzer, the scanner head can include a source of infrared light, collimating and beam-splitting mirrors, and photosensitive detector. 
         [0005]    The scanner head  106  is electronically connected by a large number of wires  108  that are connected to the process controller  110 . The scanner head  106  travels back and forth along the cross direction adjacent the traveling sheet being analyzed. In  FIG. 4A , the scanner head  106  is at one side of the frame  102  and is moving toward the middle of the frame  102  as shown in  FIG. 4B . Wires  108  typically comprise a power chain or track that has either relatively flat or cylindrical, elongated structure that consists of a series of long, parallel conductors that are separated from one another by an insulating material. As the carriage moves back and forth, the wires are subject to fatigue as it undergoes cyclic motion, as well as by abrasion, impact or tension overload. In addition, the weight of the power chain causes the suspended wires  108  to sag because of the lack of adequate support. Consequently, the detection components, that are located in the scanner head, are subject to excessive vibrations. Moreover, the presence of the relatively heavy power chain makes it more difficult to drive the carriage and to control its speed. These phenomena combined reduce the reliability, efficiency and sensitivity of the detectors. The numerous wires in power chains are also subject to electromagnetic interference (EMI) and power losses. The art is in need of techniques for improving the operations of scanning systems by minimizing or eliminating the problems associated with power chains. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is based in part on the recognition that the reliability and performance of scanning systems can be significantly enhanced by replacing the traditional power track with preferably just two wires or transmission channels for effecting communication between (i) the sensors on the mobile carriage of the scanning system and (ii) the controls, power sources, and related devices that are typically located in a compartment or module which is a significant distance away. The signal update is in “real time,” enabling proper system operation. 
         [0007]    In one aspect, the invention is directed to a scanning system, for moving a first set of sensor electronic devices between a first end and a second end along a main scanning direction, which includes: 
         [0008]    a mobile carriage, onto which the first set of sensor electronic devices is secured wherein, for at least a plurality of the sensor electronic devices, each has a sensor input; 
         [0009]    a first set of control electronic devices that is located remotely from the mobile carriage, wherein for at least a plurality of the control electronic devices, each has a control output; 
         [0010]    a control multiplexer that is coupled to the plurality of control electronic devices and that receives input signals therefrom and that provides control signals for transmission through a first transmission channel; 
         [0011]    a sensor de-multiplexer that is coupled to the plurality of sensor electronic devices and that receives the control signals from the first transmission channel and that provides sensor signals to selected sensor electronic devices to which the sensor de-multiplexer is coupled; and 
         [0012]    means for driving a mobile carriage along the main scanning direction. 
         [0013]    In another aspect, the invention is directed to an on-line scanning sensor system capable of detecting multiple characteristics of a traveling sheet of paper product as it progresses through or exits from a papermaking machine that includes: 
         [0014]    (a) a support member spanning across the traveling sheet of paper product; 
         [0015]    (b) a mobile carriage, that is slidably attached to the support member, onto which a first set of sensor electronic devices is secured wherein, for at least a plurality of the sensor electronic devices, each has a sensor input; 
         [0016]    (c) a first set of control electronic devices that is located remotely from the mobile carriage, wherein for at least a plurality of the control electronic devices, each has a control output; 
         [0017]    (d) a control multiplexer that is coupled to the plurality of control electronic devices and that receives input signals therefrom and that provides control signals for transmission through a first transmission channel; 
         [0018]    (e) a sensor de-multiplexer that is coupled to the plurality of sensor electronic devices and that receives the control signals from the first transmission channel and that provides sensor signals to selected sensor electronic devices to which the sensor de-multiplexer is coupled; and 
         [0019]    (f) means for driving a mobile carriage between a first end and a second end along a main scanning direction such that the mobile carriage scans back and forth across at least a substantial portion of the paper product along a cross direction of the moving sheet, characterized in that the first set of sensor electronic devices is operated to detect a plurality of physical characteristics of the paper product. 
         [0020]    In a further aspect, the invention is directed to a method for transmitting signals between sensor electronic devices and control electronic devices that include the steps of: 
         [0021]    securing a first set of sensor electronic devices to the mobile carriage wherein, for at least a plurality of the sensor electronic devices, each has a sensor input; 
         [0022]    providing a first set of control electronic devices that is located remotely from the mobile carriage, wherein for at least a plurality of the control electronic devices, each has a control output; 
         [0023]    providing a control multiplexer that is coupled to the plurality of control electronic devices and that receives input signals therefrom and that provides control signals for transmission through a first transmission channel; 
         [0024]    providing a sensor de-multiplexer that is coupled to the plurality of sensor electronic devices and that receives the control signals from the first transmission channel and that provides sensor signals to selected sensor electronic devices to which the sensor de-multiplexer is coupled; 
         [0025]    moving the mobile carriage between a first end and a second end along a main scanning direction; and 
         [0026]    operating the first set of sensor electronic devices and the first set of control electronic devices. 
         [0027]    In preferred embodiments, the control multiplexer generates compressed signals through a transmission channel to the complementary sensor de-multiplexer and similarly the sensor multiplexer generates compressed signals through a transmission channel to the complementary control multiplexer. Each de-multiplexer decompresses the signals and provides output updates in “real time” which enables operation of the scanning system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a scanning system with mobile carriage sensors connected thereto; 
           [0029]      FIG. 2  is a top plan view of the scanning system; 
           [0030]      FIG. 3  is a schematic diagram of the sensor head and control module illustrating the multiplexer and de-multiplexer devices therein; and 
           [0031]      FIGS. 4A and 4B  illustrate a prior art scanning apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]      FIG. 1  illustrates an embodiment of the scanning system  10  of the present invention which includes a frame  14  that is constructed of steel or other material of sufficient structural strength. Typically, for scanning systems that are employed to scan in the cross direction of a moving sheet or web  12 , such as paper in a papermaking machine, the length of support member  16  of frame  14  is about the same as the width of the moving sheet  12  so that the scanner head  2  is able to traverse the entire width along the cross direction between pulleys  40  and  42 . This distance can be six to eight meters or more. In this arrangement, scanner head  2  is positioned underneath sheet  12  to be analyzed, however, it is understood that when only one scanner head is employed, it can be positioned directly above or, at an angle relative to the sheet in order to measure properties from the sheet surface facing the scanner head. 
         [0033]    Scanner head  2 , which is broadly defined as a light weight structure housing one or more electronic and/or optical devices, is in communication with controls, database and other devices, which are housed in process control compartment or module  8 , via transmission channels  4 . The present invention is particularly suited for scanner heads that include multiple sensors and electronic components that constitute many data sources that must be connected to control devices kept safely away from the harsh environment of the papermaking machine. As will be described further herein, a feature of the invention is that the number of wires required in the transmission channels  4  is significantly less than that required in prior art scanning systems thereby reducing the weight of the transmission channels. 
         [0034]    Preferably the scanning system  10  includes a wire take-up mechanism  6  which routs the moving transmission channels  4  through a path that is defined by pulleys and springs to minimize wear as the scanning head  2  travels back and forth. Suitable up-take mechanisms are described in US Patent Application 2006/0109519 to Beselt et al., which is incorporated herein by reference. 
         [0035]    In another embodiment, scanning systems are configured to measure radiation that is transmitted through the sheet. In this arrangement, the sensor comprises two components, a light source and a detector, which are positioned on opposite sides of the moving sheet. As illustrated in  FIG. 1 , in a dual scanner head arrangement, scanner head  2  can include a detector that monitors radiation that is transmitted through sheet  12  that is illuminated by a beam of radiation from a source located on scanner head  18  which is secured to support member  36  of frame  44 . Sensor head  18  is in communication with controls, database and other devices, which are housed in process control module  8 , via transmission channels  54 . Movement of scanner head  18  between pulleys  56  and  58  is facilitated by take-up mechanism  46 . 
         [0036]    The movements of the dual scanner heads  2 ,  18  are typically synchronized with respect to speed and direction so that they are aligned with each other. Scanning systems having sensor components on opposite sides of the sheet being analyzed are described, for example, in U.S. Pat. No. 5,773,714 to Shead and U.S. Pat. No. 5,166,748 to Dahlquist, which are incorporated herein by reference. It is understood however that the top scanner head  18  and bottom scanner head  2  can be designed to move independently of each other as the sensors attached thereon perform measurements of sheet  12 . For instance, each scanner head can feature sensors that measure radiation that is reflected from the sheet surface so that the top and bottom scanner heads can function independently. 
         [0037]    The scanner head  2  can be advanced back and forth along the cross direction by a number of transport mechanisms. In the embodiment illustrated in  FIG. 2 , the scanning system  20  includes a mobile carriage  22  which is slidably attached to rails  24  and  26  which function as low-friction guides for carriage  22  as it travels or slides back and forth. Carriage  22 , which can be a platform with rollers, supports scanner head  2  which is in communication with module  8  via transmission lines  4  which is routed by guide pulleys  40  and  42 . Carriage  22  is connected to a belt  28  that is wound around drive pulley  32  and driven pulley  30 , which is operatively connected to motor  34 . In operation, control of motor  34  regulates the speed and direction of the movement of the carriage  22  which can travel at the speed of 1 to 5 meters per second or higher. Where the scanning system includes two scanner heads, the second head is similarly maneuvered on a mobile carriage and associated mechanism as shown in  FIG. 2 . 
         [0038]      FIG. 3  illustrates the data link between sensor head  2  and process control module  8 . Electronic devices which are housed in the mobile sensor head  2  may be generally referred to as “sensor electronic devices” whereas electronic devices which are safely stored in the stationary process control module  8  may be generally referred to as “control electronic devices.” It is understood however that the terms are to differentiate the locations of the devices and not to limit their functions. In this example, the control compartment  8  includes output control devices  52 ( 1 ) through  52 ( j ), which represent any suitable electronic device with output signals, and input control devices  82 ( 1 ) through  82 ( m ), which represent any suitable electronic device that receives input signals. Similarly, sensor head  2  includes input sensor device  62 ( 1 ) through  62 ( k ), which represent any suitable electronic device that receives input signals, and output sensor device  92 ( 1 ) through  92 ( n ), which represent any suitable electronic device with output signals. Each of j, k, m, and n preferably ranges from 2 to 100 or more. Typically, j is equal to k and m is equal to n. 
         [0039]    Each input control device  52 ( 1 ) through  520 ( j ) is connected to an amplifier assembly  70  through a multiplexer  50  which samples and compresses all of the input control devices and transmits the compressed signals through a communication channel  94 . Signals from the output control devices are inputs to the multiplexer. At the receiving end of the communication data link, a complementary de-multiplexer  60  decompresses the data stream, which is amplified by amplifier assembly  72 , back down into the original streams. The de-multiplexer  60  selects one of the input sensor devices  62 ( k ) and connects the single input to the selected output line. Output signals from the demultiplexer are input signals to the input sensor devices. 
         [0040]    Similarly, each output sensor device  92 ( 1 ) through  92 ( n ) is connected to an amplifier assembly  76  through a multiplexer  90  which samples and compresses all of the output sensor devices and transmits the compressed signals through a communication channel  96 . Signals from the output sensor devices are inputs to the multiplexer. At the receiving end of the communication data link, a complementary de-multiplexer  80  decompresses the data stream, which is amplified by amplifier assembly  74 , back down into the original streams. The de-multiplexer  80  selects one of the input control devices  82 ( m ) and connects the single input to the selected output line. Output signals from the demultiplexer are input signals to the input control devices. 
         [0041]    Conventional high speed multiplexing and de-multiplexing techniques such as time division and frequency division multiplexing can be employed to achieve very fast “real time” communication along with bit compression and decompression techniques. 
         [0042]    As is apparent, in this example, only two wires are needed to effect electronics communication between multiple numbers of sensor devices and corresponding control devices. The invention can be readily implemented, for instance, by connecting multiplexer  50  and de-multiplexer  80  of module  8  to a first electronic circuit board and connecting de-multiplexer  60  and multiplexer  80  of sensor head  2  onto a second electronic circuit board. The two electronic circuit boards are interconnected by three communication wires, namely, the two transmission channels  94 ,  96  and, optionally, a ground wire  98 . Even when sensor head  2  and module  8  are separated by a distance of 50 to 100 meters or more, this arrangement provides real time signal updates and the signal update latency can be less than one microsecond. In addition, because the electronic circuit boards provide current locally, the wires do not have to carry large currents over long distance which minimizes power loss and EMI noise is reduced substantially. 
         [0043]    As noted above, the scanning system can employ two scanning heads that are attached to separate mobile carriages with each scanner head incorporating appropriate sensor devices. For example, a top scanner head can include multiplexer  90  and the associated electronic devices while a bottom scanner head can include de-multiplexer  60  and the associated electronic devices as illustrated in  FIG. 3 . In this case, an optional grounding wire can be used with each scanner head. In an embodiment of a more complex design, the scanner system has two scanning heads each with the circuitry shown in  FIG. 3 . 
         [0044]    The scanning system can be employed to measure a variety of web or sheet properties such as fibrous sheets of paper in a papermaking machine, however, it is understood that the scanning system can be employed to measure properties of other materials, including, for example, plastics. In the art of making paper with modern high-speed machines, sheet properties must be continually monitored and controlled. The sheet variables that are most often measured include basis weight, moisture content, fiber orientation, temperature, and caliper, i.e., thickness, of the sheets at various stages in the manufacturing process. Papermaking devices are well known in the art and are described, for example, in U.S. Pat. No. 5,539,634 to He, U.S. Pat. No. 5,022,966 to Hu, U.S. Pat. No. 4,982,334 to Balakrishnan, U.S. Pat. No. 4,786,817 to Boissevain et al., and U.S. Pat. No. 4,767,935 to Anderson et al. which are incorporated herein by reference. 
         [0045]    As is apparent, the choice of sensor devices in the scanner head and corresponding control devices in the control module of  FIG. 3  depends on the physical characteristics of the paper being monitored and/or the process control being implemented. Sensor devices to measure various properties of paper are described, for example, in US Patent Application 20060255300 to Shakespeare and US Patent Application 20060237156 to Shakespeare et al, U.S. Pat. Nos. 6,967,726 and 6,281,679 both to King et al., which are incorporated herein by reference. Process control techniques for papermaking machines are further described, for instance, in U.S. Pat. No. 6,149,770 to Hu et al., U.S. Pat. No. 6,092,003 to Hagart-Alexander et al, U.S. Pat. No. 6,080,278 to Heaven et al., U.S. Pat. No. 6,059,931 to Hu et al., U.S. Pat. No. 5,853,543 to Hu et al., and U.S. Pat. No. 5,892,679 to He, which are all incorporated herein by reference. 
         [0046]    The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.