Abstract:
A two directional traversing mechanism uses a ratchet bar moved by an actuator to oscillate. Notches in the ratchet bar engage a pawl pivotally mounted to a piece of equipment so that the pawl and equipment move in the first direction. When the direction of the ratchet bar is reversed either the pawl is moved forward to an adjacent notch, or the pawl swings due to a biasing force such that when the ratchet bar again reverses direction, the ratchet bar causes the bar to pivot the pawl in a direction opposite the first direction. When the ratchet bar again operates in the reverse direction the pawl now engages with a notch of the ratchet bar and moves the equipment in the reverse direction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to devices which cause linear motion of a machine component in general, and to devices employing a ratchet mechanism in particular.  
         [0002]     Papermaking is usually performed on a papermaking machine which manufactures a paper web many meters wide, typically 5-10 meters wide in a cross machine direction which is perpendicular to the direction defined by the motion of the paper web as it is being formed. Within the papermaking machine, for most processes, every effort is made to treat the entire width of the paper web uniformly to insure cross machine direction uniformity in the paper web being formed. However for some processes within the papermaking machine it is not necessary or cost-effective to perform a particular operation simultaneously on the entire cross machine direction width of the web. For example, when properties of the web are monitored in the cross machine direction it is often sufficient to have the monitoring instrument be moved from one edge of the paper web to the other, traversing back and forth across the web in a systematic manner. In addition, instruments which measure web caliper, web density, web moisture, web curl, etc. can be periodically scanned in the cross machine direction over the paper web. Cleaning operations which need not be continuous but which are necessary to maintain the functionality of a roll, an air knife, a fabric, a felt or a wire, can be performed with a cleaning unit which is moved back and forth in the cross machine direction.  
         [0003]     Because of the wide width of the papermaking machine, of up to around 10 m, the test instrument or cleaning unit will typically be positioned on machine ways, linear bearings, or wheels mounted to a cross machine direction bridge which provides the required stiffness and resistance to vibration necessary for accurate positioning of a scanning instrument or cleaning device. The remaining necessity is some means of driving the test instrument or cleaning unit back and forth in a cross machine direction. Known approaches are the use of a machine screw, a rack and pinon gear arrangement, or a belt or cable drive, however these approaches require expensive components, or suffer from a lack of reliability, require significant maintenance or utilize an excessive amount of space. What is needed is a mechanically simple, low-cost, compact, and reliable means for traversing a piece of equipment back and forth in the cross machine direction over the entire width of a paper web in a papermaking machine.  
       SUMMARY OF THE INVENTION  
       [0004]     The traversing mechanism of this invention employs a short stroke, double acting pneumatic or hydraulic actuator connected to oscillate a ratchet bar with a forward stroke and reverse stroke provided by the double action of the pneumatic or hydraulic actuator. A series of spaced apart notches or teeth are cut into the ratchet bar forming outwardly opening notches and outwardly protruding teeth between the notches. The stroke of the double acting pneumatic or hydraulic actuator is slightly greater than the distance between the notch center lines. Thus with each stroke of the double acting actuator the ratchet bar is moved forward or back slightly more than the distance between notch centers. A piece of equipment movable in the cross machine direction on a linear bearing has a pivotally mounted pawl which is biased by gravity or a spring to engage the spaced apart notches of the ratchet bar. When the pawl is engaged with a notch of the ratchet bar it moves with the ratchet bar, causing the piece of equipment to move along the linear bearing to which the piece of equipment is mounted. When the direction of the ratchet bar is reversed, one of two actions results. First, if a protruding portion of the bar follows the notch in a direction defined by the reversed movement of the ratchet bar, then the pawl is biased by the protruding portion further against the spring or gravity and the pawl slides over the ratchet bar until encountering another notch in the ratchet bar. Secondly, if no portion of the bar engages the pawl during the ratchet bar&#39;s motion in the reverse direction, the pawl swings until aligned with the force of gravity or by the spring. When the ratchet bar again reverses direction, the forward motion of the ratchet bar causes the bar to again engage the pawl but not move the attached equipment. Instead, the pawl is biased by the bar against the spring or gravity so that the pawl pivots in a direction opposite to that when the pawl and equipment are moving in the forward direction. When the ratchet bar again operates in the reverse direction the pawl now engages within the notch of the ratchet bar and the equipment moves in the reverse direction.  
         [0005]     The reversing action requires that at least one motion of the pawl and the equipment attached thereto moves less than the normal step either before the reversal or after the reversal of direction. The partial step allows the ratchet bar to disengage from the pawl and then reengage the pawl so the pawl acts in a reverse direction.  
         [0006]     It is a feature of the present invention to provide a self-reversing cross machine direction traversing mechanism of simplicity and low-cost.  
         [0007]     It is a further feature of the present invention to provide a reversible cross machine direction traversing mechanism in a papermaking machine of lower-cost.  
         [0008]     It is another feature of the present invention to provide a reversible cross machine direction traversing mechanism in a papermaking machine for conveying a cleaner or an instrument, the mechanism serving to repeatedly traverse the cleaner or instrument from the back to the front, and from front to the back, of the papermaking machine.  
         [0009]     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side elevational schematic view of a ratchet mechanism of this invention showing linear motion in a first direction.  
         [0011]      FIG. 2  is a side elevational schematic view of the racket mechanism of  FIG. 1  showing linear motion in a second direction opposite to the first direction.  
         [0012]      FIG. 3  is side elevational schematic view of an alternative embodiment of the ratchet mechanism of  FIG. 1   
         [0013]      FIG. 4  is side elevational schematic view showing the motion of a pawl on the ratchet mechanism of  FIG. 1 .  
         [0014]      FIG. 5  is an isometric view of a further alternative embodiment of the ratchet mechanism of  FIG. 1 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring more particularly to  FIGS. 1-5  wherein like numbers refer to similar parts,  FIG. 1  shows a ratchet bar  20  which is moved back and forth in an oscillating motion by a double acting pneumatic actuator  22 . A piece of equipment  24  is mounted to a linear bearing (not shown) which extends in a cross machine direction in a papermaking machine. A pawl  26  is pivotally mounted to the piece of equipment  24 . The pawl  26  engages with notches  28  or teeth  30  defined between the notches which are formed on the ratchet bar  20 . As shown in  FIG. 1 , the piece of equipment  24  is progressively moved in a first direction i.e., to the right as indicated by arrows  32 . The distance from the beginning or left-hand side  34  of one notch  28  to the beginning or left-hand side of an adjacent notch  40  is uniform and/or less than the stroke of the pneumatic actuator  22 .  
         [0016]     Thus, as shown in  FIG. 1 , when the ratchet bar  20  moves in a first direction, shown by arrow  36 , the pawl  26  pushes the pawl and the equipment  24  to the right by the distance between left-hand sides of adjacent notches  28 . When the pawl  26  is engaged with the beginning or left-hand side of a notch  28  it assumes a first position labeled  1  in  FIG. 4 . When the double acting pneumatic actuator  22  reverses direction the end or right-hand side  44  of the notch  28  engages the pawl  26  lifting it in to a second position labeled  2  in  FIG. 4  until the adjacent notch  40  is positioned below the pawl and the pawl pivots downwardly into engagement with the left-hand side of the adjacent notch  40 . By repeated action of the double acting pneumatic actuator  22 , acting first to the right and then to the left, the pawl and the equipment to which the pawl is mounted moves in steps to the right.  
         [0017]     The reversal of the motion of the pawl  26  and the piece of equipment  24  to which the pawl is engaged is explained by reference to  FIG. 4  and the right hand ends of  FIGS. 1 and 2 . Referring to position  1  of  FIG. 4 , the arrangement of the pawl  26  is such that although the pawl is pivotally mounted to the equipment  24  it is not free to pivot because the equipment  24  and the ratchet bar  20  are constrained by linear bearings such that they are movable only in a horizontal, and not in the vertical plane. Position  1  of the pawl  26  when moved as indicated by arrow  42  creates an upward thrust on the equipment  24  and a downward thrust on the ratchet bar  20  which are resisted by the linear bearing on which the equipment  24  is mounted, and on the linear bearing on which the ratchet bar  20  is mounted. The forward thrust of the pneumatic actuator  22  and the ratchet bar is transmitted through the pawl  26  to the equipment  24 . The entire force supplied by the ratchet bar  20  aside from any friction losses is transmitted through the pawl to the equipment  24  because the vertical forces on the equipment  24  and the ratchet bar  20  are opposite sign so, neglecting friction, the linear forces on the ratchet bar are identical to the linear forces applied to the equipment  24  through the pawl  26 . The end of the pawl which engages the notches  28 ,  48  is a pointed right angle as shown in  FIGS. 1, 2 ,  3 ,and  4 , which fits against the bottom and one side of the notches  28 ,  48 .  
         [0018]     In normal operation the position  1  is followed by lifting up of the pawl  26  by the interaction of the right-hand side  44  with the pawl, followed by the pawl engaging the left-hand side on the following or adjacent notch as described above. The orientation of the pawl  26  is reversed between  FIG. 1  and  FIG. 2  and the reversing of the pawl orientation is accomplished as shown in  FIG. 4 . Referring to position  3  of  FIG. 4 , as a first end  52  of the ratchet bar  20  is pulled past the pawl  26 , the pawl is released and allowed to assume a neutral position under the force of gravity. From this neutral position, as shown in position  3 , the forward motion of the ratchet bar  20  causes the pawl to swing to the right, position  4 , and engage the right hand side  44  a notch  48  so that, as shown in position  5  of  FIG. 4 , the pawl moves the equipment  24  to the left as the ratchet bar oscillates to the left.  
         [0019]     In order for the reversal of the pawl to occur it is necessary that the oscillation of the ratchet bar  20  to the left frees the pawl  26  to return to the neutral position  3  and that the oscillation of the ratchet bar to the right, as shown in position  4 , moves the notch  48  underneath the pawl  26  until the pawl drops into the notch  48  as shown in position  5 . For the same oscillatory motion on the ratchet bar  20  which moves the equipment  24  to cause a reversal of the pawl  26 , it is necessary that the motion of the pawl and the equipment be less in the final step before the pawl reversal. Referring to  FIGS. 1 and 2 , a notch  48  is longitudinally larger than normal such that the left-hand side of the notch  48  is spaced considerably less than the distance between notches  28 . Thus the pawl  26  and the equipment  24  are moved to the right only a fraction of the total stroke of the pneumatic actuator  22 . This partial stroke allows the last upstanding portion  50  at the right end  52  of the ratchet bar  20  to be drawn past the pawl  26  as shown in position  2  of  FIG. 4  by the normal leftward stroke of the actuator  22  and the ratchet bar  20 , and to pick up the pawl with the right hand side of the notch  48  the next time the ratchet bar  20  moves to the left as shown in position  5  in  FIG. 4 .  
         [0020]     The reversing of the motion of the equipment  24  on the left end  54  of the ratchet bar  20  is substantially identical to the series of steps shown in  FIG. 4  except the steps  1 - 5  are performed as in a mirror image, and the left end  54  of the ratchet bar  20  is the mirror image of the right end  52  of the ratchet bar  20 .  
         [0021]     An alternative embodiment ratchet mechanism which employs a first ratchet bar  120  and a second ratchet bar  121  is shown in  FIG. 3 . The first ratchet bar  120  is connected directly to a double acting pneumatic actuator  122  having a stroke length  119 . The second ratchet bar  121  is geared to the first ratchet bar  120  by a double rack and pinion arrangement consisting of the first rack  123  on the first ratchet bar  120 , and a second rack  125  mounted to the second ratchet bar  121 , with a pinion gear  127  mounted therebetween. The pinion gear mounted for rotation, but not for linear motion. The first rack  123  changes the linear motion supplied by the pneumatic actuator  122  into rotating motion of the pinion gear  127 . The second rack  125  changes the rotation of the pinion gear  127  back into linear motion which is 180° out of phase with the linear motion of the pneumatic actuator  122  and the first ratchet bar  120 . A piece of equipment or equipment carriage  124  is mounted for linear motion to a guide bar  128 . A first pawl  126  is pivotally mounted to the carriage  124  and interacts with the first ratchet bar  120 , and the notches  129 , and teeth  130  formed thereon. At the same time a second pawl  131  also pivotally mounted to the carriage  124  interacts with the second ratchet bar  121  and the notches  132 , and teeth  133  formed a thereon. Each time the pneumatic actuator  122  extends or retracts the first ratchet bar  120  moves the stroke length  119  in the same direction as the actuator  122 , and the second ratchet bar  121  moves the stroke length  119  in a direction opposite the actuator  122  and the first ratchet bar  120 . This arrangement allows the equipment carriage  124  to move linearly each time the actuator  122  is extended or retracted, substantially increasing the speed and uniformity of the equipment carriage  124  and any equipment mounted thereto. The two ratchet bars  120 ,  121  and the corresponding pawls  126 ,  131  as shown in  FIG. 3  perpetually reversed direction in concert causing the equipment carriage  24  to repeatedly traverse the guide bar  128  first in one direction and then the opposite direction.  
         [0022]     A further alternative embodiment ratchet bar  56  is shown in  FIG. 5  for the particular application of moving a cleaner along the an air knife (not shown). In certain circumstances it is desirable to apply a spray of materials such as coating to a dryer cylinder within a papermaking machine. In order to prevent the coating from escaping from an application chamber over which a dryer cylinder rotates, a jet of air from an air knife contacts the dryer cylinder, and prevents the sprayed material migrating across the air knife. If coating accumulates on the air knife and partly or completely blocks the flow of air, the air knife is rendered nonfunctional. Thus periodically a cleaning a blade  58  is moved along the air knife to clean the air knife nozzle opening. The air knife cleaning blade is supported on cleaning legs  60  which clean the sides of the air knife and may use additional edges  62  to provide some removal of material from exterior surfaces forming part of the air knife structure. The cleaning legs  60  are cantilevered to a platform  64  which in turn is mounted to a carriage  66 .  
         [0023]     The carriage  66  has a first inverted L-shaped guide  68  and a second inverted L-shaped guide  70  which are held in fixed relation by a spacer block  72  which has a portion (not shown) which extends between the L-shaped guides. The short legs  74 ,  76  of the L-shaped guides  68 ,  70  ride on upwardly facing surfaces  78 ,  80  of an inverted T-shaped guide bar  82  which extends in the cross machine direction and is attached to the front and back sides of the papermaking machine. The pawl is not located symmetrical to the T-shaped guide bar  82 . When the pawl is loaded, it imparts a torque on the carriage  66  about an axis that is approximately longitudinal to the T-shaped guide bar. The bearing surfaces  78 ,  96  are relatively larger than the bearing surface  80  to suit the offset location of the pawl. When the pawl is loaded, it causes vertically downward loading on the side of the carriage where the pawl is located adjacent the L-shaped guide  68 . When the cantilevered cleaning legs  60  are loaded due to friction which acts in the cross-machine direction, the cantilevered cleaning legs  60  impart a torque upon the carriage  66 . This torque is about an axis that is approximately perpendicular to the T-shaped guide bar and approximately parallel to the bearing surfaces  78  and  80 . To reduce frictional loading that occurs between the T-shaped guide bar  82  and the carriage  66  due to the various loadings, four wheels  97 , two of which are visible in  FIG. 5 , are mounted beneath the T-shaped guide bar  66 . The wheels  97  are mounted between the first and second L-shaped guides  68 ,  70  and portions of the spacer block  72  as shown in  FIG. 5 .  
         [0024]     The ratchet bar  56  is positioned between a lower bearing plate  88  and an upper bearing plate  86  fabricated of bearing bronze. The upper and lower bearing plates are spaced apart and mounted to the guide bar  82 . A double acting pneumatic actuator  90  is mounted over the upper bearing plate, and is connected by an arm  92  to the ratchet bar  56  through a slot  94  in the upper bearing plate  88 . Actuation of the pneumatic actuator  90  causes the ratchet bar  56  to oscillate back and forth while engaged between the upper and lower bearing plates. The ratchet bar  56  has a series of slots (not shown) through which guide pins (not shown) extend to connect the upper bearing plate to the lower bearing plate. The guide pins and the slots constrain the ratchet bar motion to a straight linear path that is parallel to the motion of the pneumatic actuator  90 .  
         [0025]     The ratchet bar  56  has evenly spaced notches  98  which are engaged by a counterweight pawl  100  mounted to the platform  64  and to the carriage  66 . The spacing of the notches  98  is slightly less than the stroke of the pneumatic actuator  90 . The pawl  100  extends upwardly to engage in the notches  98  and causes the carriage  66  to move progressively along the ratchet bar  56 . The pawl  100  has an end in the shape of a right angle notch and it engages the side and lower surface of the ratchet bar  56 . Reversal of the direction of the carriage  66  is accomplished in a way similar to that described above with respect to  FIGS. 1-4 . However, instead of having the notches closest to either end of the ratchet bar being longer than normal so that the equipment moves only one half step, a separate end notch  102  is closely spaced between the end  104  of the ratchet bar  56  and the last regularly spaced notch  106 . After the ratchet bar end  104  is a drawn past the pawl  100  allowing the pawl to move to a vertical position and to be reversed by the next movement of the ratchet bar, the pawl  100  is engaged by the end-notch  102 . The movement of the carriage  66  when the pawl is engaged with the end notch  102  is only sufficient to allow the pawl to engage with the last regularly spaced notch  106 . Once the pawl is engaged with the regularly spaced notch the carriage moves a distance equal to the regular spacing between notches with each complete cycle of the pneumatic actuator  90 .  
         [0026]     It should be understood that instead of a partial rightward or leftward movement at the ends of the bar, the pneumatic actuator may be allowed or controlled to make only a partial stroke. For example, the equipment&#39;s rightward or leftward movement could be constrained by a stop or, motion of the equipment beyond a rightward or leftward position could be arranged to vent the pneumatic actuators to prevent further motion. It is also possible that all movements towards the bar ends are uniform but the first step away from the bar end is only partial as shown with respect to  FIG. 5  wherein the first step away from the bar end results in moving the pawl to a closely spaced adjacent notch  106 .  
         [0027]     It should also be understood that were in two or more ratchet bars are used such as shown in  FIG. 3  various mechanisms, such as a pivoting arm, or a free-floating piston with twice the desired movement of the ratchet bars connected between the ratchet bars, and other similar mechanical arrangements could be you.  
         [0028]     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.