Abstract:
A sensor head-transporting roller carriage has four pairs of wheels acting around pivot points at the four corners of the carriage, which is advanced along tracks that are supported by vertical structures. The lateral wheel spacing is chosen in correlation with the track support interval distances such that the vertical travel of all the wheels together is averaged, to be zero. As a result, variations in displacement alignment of the sensor are minimized. In addition, the pivot mechanism results in a fifty percent reduction in the effect of random vertical deflections caused by track debris or wheel concentricity etc. versus standard non-pivoting wheel sets. The roller carriage moves the sensor head along the cross direction to monitoring physical characteristics of a web of material that is moving in the machine direction.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a scanning sensor that employs a roller carriage that transports the sensor on tracks that are supported by vertical structures that are mounted at intervals along the length of the tracks. The wheel spacing for the rocker wheel system in the carriage is chosen in correlation with the track support structure interval distances such that variations in displacement alignment of the sensor are minimized. 
       BACKBROUND 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, this procedure is often 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 developed 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 twelve meters or more. 
         [0004]    Sensors for continuous flat sheet production processes typically employ single or double sided packages which traverse the width of the sheet, guided on rail systems affixed to stiff beam structures. Often the accuracy of the sensor system is related to the relative x, y, z displacement alignment between upper and lower sensor halves, therefore it is of particular interest to designers of such mechanisms to be able to reduce alignment errors. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is based in part on the recognition that the gap between sensors in scanning systems can be easily influenced by conditions such as initial track alignment, track material straightness, track deflection caused by sensor payload in unsupported areas between mounting points, wheel concentricity, material buildup on wheels, material buildup on track surfaces, and track wear. Vertical deflection of track material between adjustment supports can cause sinusoidal alignment errors in sensor profiles. By using a pair of wheels acting around a pivot point at the four corners of the roller carriage, wheel spacing can be chosen in correlation with track support interval distances such that the vertical travel of all the wheels together is averaged to be zero. Other benefits of the present invention include a fifty percent reduction in the effect of random vertical deflections caused by track debris or wheel concentricity etc. versus standard non-pivoting wheel sets, and automatic load sharing of wheels thereby enabling the use of stiff/hard mating materials. 
         [0006]    In one aspect, the invention is directed to a transport carriage that includes: 
         [0007]    a frame having a longitudinal axis, an upper surface, a lower surface, a front end and a rear end; 
         [0008]    a first pair of wheels positioned in tandem, wherein the first pair of wheels are secured to a first rigid member that is pivotally mounted to the frame such that the first pair of wheels are located on a first opposing side of the frame toward the front end; 
         [0009]    a second pair of wheels positioned in tandem, wherein the second pair of wheels are secured to a second rigid member that is pivotally mounted to the frame such that the second pair of wheels are located on a second opposing side of the frame toward the front end; 
         [0010]    a third pair of wheels positioned in tandem, wherein the third pair of wheels are secured. to a third rigid member that is pivotally mounted to the frame such that the third pair of wheels are located on a first opposing side of the frame toward the rear end; and 
         [0011]    a fourth pair of wheels positioned in tandem, wherein the fourth pair of wheels are secured to a fourth rigid member that is pivotally mounted to the frame such that the fourth pair of wheels are located on a second opposing side of the frame toward the rear end. 
         [0012]    In another aspect, the invention is directed to a carriage system for a moving mobile device between a first end and a second end along a main scanning direction that includes: 
         [0013]    a track means that extends along a first direction that is parallel to the main scanning direction; and 
         [0014]    a carriage assembly that comprises: 
         [0015]    (i) a frame having a longitudinal axis, an upper surface, a lower surface, a front end and a rear end; 
         [0016]    (ii) a first pair of wheels positioned in tandem that engage the track means, wherein the first pair of wheels are secured to a first rigid member that is pivotally mounted to the frame such that the first pair of wheels are located on a first opposing side of the frame toward the front end; 
         [0017]    (iii) a second pair of wheels positioned in tandem that engage the track means, wherein the second pair of wheels are secured to a second rigid member that is pivotally mounted to the frame such that the second pair of wheels are located on a second opposing side of the frame toward the front end; 
         [0018]    (iv) a third pair of wheels positioned in tandem that engage the track means, wherein the third pair of wheels are secured to a third rigid member that is pivotally mounted to the frame such that the third pair of wheels are located on a first opposing side of the frame toward the rear end; and 
         [0019]    (v) a fourth pair of wheels positioned in tandem that engage the track means, wherein the fourth pair of wheels are secured to a fourth rigid member that is pivotally mounted to the frame such that the fourth pair of wheels are located on a second opposing side of the frame toward the rear end. 
         [0020]    In a further aspect, the invention is directed to a method of moving a mobile scanning device hack and forth along a main scanning path on a track means that extends along a first direction that is parallel to the main scanning direction so as to reduce vertical misalignment of the scanning device profile, which includes the steps of: 
         [0021]    (a) providing a carriage assembly that includes:
       (i) a frame having a longitudinal axis, an upper surface, a lower surface, a front end and a rear end;   (ii) a first pair of wheels positioned in tandem that engage the track means, wherein the first pair of wheels are secured to a first rigid member that is pivotally mounted to the frame such that the first pair of wheels are located on a first opposing side of the frame toward the front end;   (iii) a second pair of wheels positioned in tandem that engage the track means, wherein the second pair of wheels are secured to a second rigid member that is pivotally mounted to the frame such that the second pair of wheels are located on a second opposing side of the frame toward the front end;   (iv) a third pair of wheels positioned in tandem that engage the track means, wherein the third pair of wheels are secured to a third rigid member that is pivotally mounted to the frame such that the third pair of wheels are located on a first opposing side of the frame toward the rear end; and   (v) a fourth pair of wheels positioned in tandem that engage the track means, wherein the fourth pair of wheels are secured to a fourth rigid member that is pivotally mounted to the frame such that the fourth pair of wheels are located on a second opposing side of the frame toward the rear end, wherein each rigid member has a pivot point at the middle as to allow for upward vertical motion of the first wheel that is secured to the rigid member and for simultaneous reciprocating downward vertical motion of the second wheel that is secured to the rigid member; and       
 
         [0027]    (b) driving the carriage assembly back and forth along the main scanning path. 
     
    
     
       BREIF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a perspective view of a roller carriage; 
           [0029]      FIG. 2  shows the roller carriage positioned on a set of tracks and from which a sensor head is suspended; 
           [0030]      FIG. 3  is a front view of the roller carriage and track; 
           [0031]      FIG. 4  is a side view of a supporting beam structure with the roller carriage being supported on the track; 
           [0032]      FIGS. 5A and 5B  show the independent movements of the wheels on the roller carriage in relationship to mounting points of the track support; 
           [0033]      FIG. 6  depicts movement of the roller carriage along the track and operations of the rocker or pivoting mechanism; and 
           [0034]      FIG. 7  is a side view of upper and lower structural beams of a scanning system with each beam supporting a roller carriage that supports one of the dual sensor heads. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0035]      FIG. 1  shows a roller carriage  2  that has an elongated frame or panel  32  with lateral members  4  and  6  secured to its sides. Lateral member  4  defines two slots or gaps into which pivot bars  8  and  10  are positioned. Bar  8  is secured to the middle of the slot by a flexible spring mechanism  9  while bar  10  is secured by a flexible spring mechanism  11  to the middle of the slot. Similarly, lateral member  6  defines two slots or gaps into which pivot bars  12  and  14  are positioned. Bars  12  and  14  are secured to the middle of slots with flexible spring mechanism  13  and  15 , respectively. Each spring mechanism is connected to a pivot bar at its midpoint and serves as a pivot point. Alternatively, a pivot ball assembly can be used. Pinned joint or live hinge devices can be employed as pivot connections. 
         [0036]    Each pivot bar supports a pair of wheels that are arranged in tandem and are mounted equal distance from the pivot point. Thus, on one side of roller carriage  2 , dual wheels  16 ,  18  are secured at opposite ends of the pivot bar  8  and dual wheels  20 ,  22  are secured at opposite ends of the pivot bar  10 . Similarly, on the other side of roller carriage  2 , dual wheels  24 ,  26  are secured at opposite ends of pivot bar  12  and dual wheels  28 ,  30  are secured at opposite ends of pivot bar  14 . Preferably, the diameters of the wheels are all the same and the distance between each dual set of wheels is preferably the same for all four sets. The distance between inner wheels  18  and  20  (and between wheels  26  and  28 ) does not need to be the same as that between the dual wheels, that is, the spacing between the pairs of wheels is arbitrary; however, in a preferred embodiment, the distance is the same as that between the wheels the dual wheels. Panel  32  includes apertures  34  through which bolts are employed to secure a device that is to be transported by the roller carriage. 
         [0037]    The roller carriage of the present invention is particularly suited for transporting articles along a suspended track system, that is, one that is positioned above the ground. In this fashion, the roller carriage can transport a detection device travel over a sheet or other material being monitored. For example,  FIG. 2  depicts a set of suspended tracks  44  and  46  dimensioned to accommodate the wheels of a roller carriage that is transporting a sensor head  40  that is attached to the underside of the carriage via support assembly  42 . Tracks  44 ,  46  define a fixed path in the main scanner direction through which the carriage transports the suspended sensor head  40 . A single sensor head  40  can be employed to measure physical properties of a material when the sensor is operating in the reflection mode. For example, if infrared radiation detection is employed, sensor head  40  will house both the source of the infrared radiation as well as the detector that captures radiation reflected from the material of interest. 
         [0038]    As shown in  FIG. 3 , tracks  58 ,  60  are situated on opposite sides of a transverse, rigid member  52  that is supported by vertical track supports  62 ,  63  that are secured to an elevated support beam (not shown). Lateral members  56  and  54 , which are connected to the outer perimeter of panel  32  of the roller carriage, flank tracks  58  and  60 , respectively. As further described herein, the pivot mechanisms of wheels  16  and  24 , which are mounted to pivot bars (not shown) on the roller carriage, permit each wheel to independently respond to discontinuities on the otherwise flat, low-friction track surfaces. 
         [0039]    The roller carriage can be incorporated into a scanning system that is used, for instance, to monitor physical characteristics of a web of paper in an industrial papermaking machine. As shown in  FIG. 4 , the scanning system includes an upper support beam  70  that has a lower surface  66  to which a plurality of rigid support structures  76 ,  78 ,  80  and  82  are mounted. These elongated, vertical structures are typically spaced laterally apart at a distance “d” as they support track  64 . Wheels  24 ,  26 ,  28  and  30  of roller carriage $ 4  engage track  64  as the carriage advances along the cross direction to a moving sheet (not shown). Controlled movement of the carriage is facilitated with a drive mechanism that includes an endless drive belt  72 ,  74  that is coupled to a linkage assembly  68  that is connected to roller carriage  84 . 
         [0040]    Because track  64  is supported by a series of individual vertical support structures, the track tends to sag along the intervals between the structures such that the track exhibits a sinusoidal pattern along its length. Specifically, if the distance between the track supports is “d” then the largely sinusoidal deflection period of the track is also equal to “d.” In order to compensate fbr the sinusoidal nature of track  64 , the roller carriage is designed so that all the wheels have the same diameter; in addition, for each pair of wheels, the distance between the two wheels is equal to (n×d)+d/2 where n is equal to 0, 1, 2, . . . While n can be any whole number, in practice, n is preferably equal to zero so that the distance between the two wheels is equal to d/2, which is the design used for roller carriage shown in  FIG. 4 . In addition, the distance between inners wheels  26  and  28  is also equal to d/2. The effect of employing a roller carriage where the wheels are so configured is that the plane of the frame of the roller carriage remains horizontal as the carriages moves despite the sinusoidal nature of the track. 
         [0041]      FIGS. 5A and 5B  simulate the path of a roller carriage in the case where the track supports are separated by a distance d and the spacing between wheels on the pivoting rocker arms is set to d/2. Although not critical, in this example, the distance between the inner wheels and is also equal to d/2.  FIG. 5A  shows the position of the wheels when the mid point of the frame (main carriage structure) is at one of the track support locations. As shown, the pivot bars are both parallel to the track at this position. As the roller carriage moves a distance of d/2 on the track as illustrated in  FIG. 5B , one wheel of a dual wheel sits at the track height maximum while the other is located at a minima. As is apparent, as the roller carriage moves along the deflection pattern, one wheel of a dual wheel set will be arising as the other fills such that the pivot point largely maintains an average distance between the two wheel heights. In this fashion, the frame of the roller carriage travels along a linear path, i.e., the “filtered” carriage path. 
         [0042]    Other benefits of using the roller carriage is its ability to reduce the effect of random vertical deflections that are caused by track debris or wheel concentricity vs. standard non-pivoting wheels and the automatic load sharing of the wheels which enable the use of stiff/hard mating materials. As shown in  FIG. 6 , as a first wheel encounters debris of size “h,” it is raised a distance h, while the pivoting mechanism causes the pivot point to elevate a distance of h/2, and the middle of the frame to elevate a distance of only h/4. In contrast, without the pivot mechanism, the middle of the frame of a similar size roller carriage would be elevated a distance of h/2. In this fashion, the pivot mechanism reduces the effect of vertical deflection by fifty percent. 
         [0043]      FIG. 7  shows a scanning system with scanner sensor heads  98  and  102  that eniploy roller carriages of the present invention. This configuration, which employs dual sensor heads, is typically employed when the sensor is operating in the transmission mode. For example, upper sensor head  98  may house a source of infrared radiation while the lower sensor head  102  houses an infrared detector that measures the radiation that is transmitted through the material being monitored. The upper scanner head  98 , as described previously, is supported by an upper support beam  70  that has a lower surface to which a series of laterally spaced apart rigid support structures is mounted. These vertical structures support track  64 . The wheels of roller carriage  84  engage track  64  as the carriage advances along the cross direction to a moving sheet  106 . The lower scanner head  102  is supported by a lower support beam  90  that has a lower surface on which a plurality of laterally spaced apart rigid support structures is mounted. Movement of the roller carriage is facilitated by a drive mechanism similar to that of the upper scanner head. Vertical structures also support track  104  onto which the wheels of carriage  94  are engage. A power chain supplies  92  electricity and electrical signal to lower scanner head  102 . Upper sensor head  102  is mounted on a member  96  that extends from roller carriage  94  so as to position lower sensor head  102  adjacent to upper scanner head  98 . The operative faces of the lower and upper scanner heads  102 ,  98  define a gap with an entry  108  and exit  110  through which a web of material  106 , that is moving in the machine direction, passes. The movements of the dual scanner heads  102 ,  118  are 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. Each of the roller carriages in the dual scanner system of  FIG. 7  is able to maintain a smoother, linear filtered carriage path because of the pivot mechanism of each carriage. 
         [0044]    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.