Patent Publication Number: US-2023150077-A1

Title: Log Cutting Saw With Automatic Blade Changer and Method of Using Same

Description:
The present application claims priority benefit of U.S. provisional application Ser. No. 63/280872, filed Nov. 18, 2021, the disclosure of which is incorporated by reference herein. 
    
    
     SUMMARY 
     The present disclosure is directed to a log cutting saw, for instance, a tissue log cutting saw. The log cutting saw is adapted and configured to cut logs axially into rolls for consumer use. The log cutting saw may include a saw house. Within an interior of the saw house, the saw may be provided with an arm that orbitally moves while a saw blade rotates for cutting one or more tissue logs introduced into the saw house. The logs may be conveyed on a conveyor that moves through the interior of the saw house. The saw may include an arm with one or more blades for cutting the logs in the interior of the saw house. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a saw including a saw house and a blade array storage unit mounted on a slide of the saw house. 
         FIG.  2    is a top partial view of an interior of the saw house showing a tool change actuator mounted to a structure of the saw and a spindle assembly mounted on an arm of the saw. 
         FIG.  3    is a partial perspective view of the interior of the saw house showing the arm and the spindle assembly and the tool change actuator. 
         FIG.  4    is another partial perspective view of the interior of the saw house showing the arm and the spindle assembly and the tool change actuator. 
         FIG.  5    is a perspective view of the tool change actuator. 
         FIG.  6    is a top view of the tool change actuator. 
         FIG.  7    is a side view of the tool change actuator. 
         FIG.  8    is a perspective view of the arm and spindle assembly. 
         FIG.  9    is a top view of the arm and spindle assembly. 
         FIG.  10 A  is a front view of the arm and spindle assembly. 
         FIG.  10 B  is another front view of the arm and spindle assembly with a blade grinding unit and a blade guard assembly covering a saw blade; 
         FIG.  10 C  is a view of the blade grinding unit of  FIG.  10 B . 
         FIG.  11    is a cross-sectional side view of the spindle assembly taken along lines  11 - 11  of  FIG.  10 A . 
         FIG.  12    is a cross-sectional side view of the spindle assembly of  FIG.  11    with a tool holder of the saw blade removed from the end of the spindle. 
         FIG.  13    is a cross-sectional side view of the spindle. 
         FIG.  14    is a perspective view of a blade array. 
         FIG.  15    is another perspective view of the blade array. 
         FIG.  16    is a side view of the blade array with a storage unit of the blade array in the extended position. 
         FIG.  17    is cross-sectional front view of the blade array taken along lines  17 - 17  of  FIG.  16   . 
         FIG.  18    is a representation of the orientation of the saw blades stored coaxially aligned in the blade array. 
         FIG.  19    is a front view of a saw blade mounted on a tool holder. 
         FIG.  20    is a rear view of the saw blade mounted on the tool holder. 
         FIG.  21    is a front view of the tool holder. 
         FIG.  22    is a rear view of the tool holder. 
     
    
    
     DESCRIPTION 
       FIG.  1    shows an exemplary saw  30  and saw house  32 . The saw house  32  comprises a rectangular structure with a support frame  34 , panels  34   a  and a viewing window(s)  34   b . Typically, the material to be cut in the saw house, for instance, logs of convolutely wound web material are passed through an interior  34   c  of the saw house  32  on a conveyor with an arm  36  of the saw  30  moving orbitally as one or more saw blades  38  rotate and cut the logs into rolls for consumer end use within the interior of the saw house. The conveyor may be in accordance with U.S. Pat. No. 10,272,585, the disclosure of which is incorporated by reference. The logs may be held during cutting by clamps in accordance with pending U.S. Pat. No. 11,447,362, the disclosure of which is incorporated by reference. The arm  36  may include a spindle assembly  40  mounted on the arm. 
     The spindle assembly  40  may include a spindle housing  42  and a spindle  44  rotatably disposed in the housing. The spindle  44  may be adapted and configured to rotate one or more saw blades  38 , each of which may be mounted to the spindle  44  in a tool holder  46  at an end of the spindle. Multiple conveyor lanes may be provided through the interior of the saw house  32  to cut the logs as the logs are advanced to the saw blade  38 . One or more spindle assemblies  40  may be mounted on the arm, each with the functionality described below. Thus, multiple saw blades  38  may be disposed on the arm, although not shown in the drawings. A blade guard assembly  48  in accordance with U.S. Pat. No. 11,305,394, the disclosure of which is incorporated by reference, may be provided. 
     The exemplary saw  30  further includes a storage unit  50  that is adapted and configured to store the saw blade  38  mounted on the tool holder  46 . Accordingly, the saw  30  is adapted and configured to exchange the saw blade  38  between the spindle  40  and the storage unit  50 . In one aspect, the storage unit  50  is adapted and configured to move between an extended position in which the storage unit is disposed in the interior  34   c  of the saw house  32  adjacent the spindle  44  and a retracted position in which the storage unit  50  is moved away from the spindle, which may be within the interior of the saw house or to a location exterior to the saw house. In another example, the storage unit may be withdrawn from the interior  34   c  of the saw house  32  in the retracted position. In another example, the storage unit  50  may be detachably connected to the structure  34  of the saw house. In another example, the storage unit  50  may be provided as one of a plurality of like storage units as a blade array or storage system  52 . In another example, the blade array or storage system  52  may be in accordance with U.S. Pat. No. 10,946,546, the disclosure of which is incorporated by reference herein. In another example, the blade array or storage system  52  may be movable in the direction of the log travel relative to the structure  34  of the saw  30  so that each storage unit  50  in the blade array may be positioned adjacent the spindle  44  to allow exchange of the saw blade  38  between the spindle and the respective storage unit. For instance, each storage unit may be configured in the blade array to store a saw blade  38  such that the center axes of rotation of the saw blades in the blade array is aligned coaxially. The blade array  52  may be mounted to a horizontal slide  54  on the structure  34  of the saw house  32  that moves the blade array in a direction parallel to the center axis of rotation of the saw blade and parallel to the direction of log advancement through the saw house. Accordingly, the slide  54  may position the blade array  52  such that each storage unit  50  of the blade array may be moved in a direction parallel to the direction of advancement of the log, and then perpendicular to the direction of advancement of the log from the blade array into the interior of the saw house and adjacent the spindle  44  to allow exchange of the saw blade  38  between the spindle and the respective storage unit when the respective storage unit is in the extended position. A vertical slide  55  on the structure  34  of the saw house  32  may also be provided to allow for adjustment of the vertical position of the blade array  52  to facilitate exchange of the saw blade  38  between the spindle and the respective storage unit when the respective storage unit is in the extended position. 
     The saw  30  may have a human machine interface HMI  56  to allow an operator to control operation of the saw. The HMI  56  may have a control associated with the saw, the blade array  52 , the storage unit  50 , and/or the conveyor. The HMI  56  may allow the operator to enable the saw for cutting a log. When the saw  30  is enabled for cutting operations, the saw moves the arm  36  orbitally within the interior  34   c  of the saw house  32  which causes the spindle assembly  40  (e.g., the spindle and spindle housing) to move orbitally as the arm moves orbitally. The saw  30  may be configured to rotate the spindle  44  so as to rotate the saw blade  38  releasably attached at an end of the spindle with the tool holder  46  within the interior of the saw house. The HMI  56  may also allow the operator to disable the saw from cutting a log as desired including disabling the saw from cutting to perform a tool change as will be described in greater detail below. The tool change may be manually controlled by an operator at the HMI, or may be automatic, for instance, based upon saw blade wear or cycle time, or may be a combination of both depending upon the level of intervention desired. The tool change itself may also be performed manually without any hindrance from the automatic tool change system using the same procedures as in a saw without an automatic tool change system, for example if an appropriate blade is not available in storage unit  50 , or if the automatic tool change system is not operational. 
     To periodically change the saw blade  38 , the saw  30  may be disabled from cutting operations, a blade grinding unit  58 , for instance, as shown in  FIGS.  10 B and  10 C , may be automatically moved to a retracted position, the saw blade may be removed from the spindle  44  and exchanged with a saw blade provided in the storage unit  50 , and the blade grinding unit  58  may be automatically moved to an engaged position based on the location of the edge of the newly mounted blade detected by a blade edge detector  59 . The saw  30  may be provided with a tool change actuator  60  adapted and configured to work with the spindle  44  to facilitate exchange of the saw blade between the spindle and the storage unit  50 . The tool change actuator  60  may be positioned in the saw house interior  34   c . The tool change actuator  60  may be mounted to a structure  34  within the interior of the saw house that is separate and apart from the arm  36 . In one example, the tool change actuator  60  may be mounted to a stationary structure  34  within the saw house that is sufficiently spaced from the arm  36 , the spindle assembly  40  and the saw blade  38  so as to allow the arm and spindle assembly to rotate orbitally and cut a log during cutting operations as needed. In one example, the tool change actuator  60  is positioned on an upstream side (e.g., relative to the direction of log advancement) of the spindle assembly  40  and spaced from the saw blade  38 . As shown in the drawings, the tool change actuator is arranged generally at the driven end  44   b  of the spindle  44 , that is, the saw blade  38  is engaged with the spindle  44  at an end  44   a  opposite of the driven end. In a configuration of multiple spindle assemblies on an arm, there may be one tool change actuator arranged to work with each of the spindles to facilitate tool change between the spindle and the storage unit. Alternatively, there may be multiple tool change actuators positioned within the interior of the saw house to work with one or more spindles to facilitate tool change between the spindle and the storage unit. The tool change actuator  60  may include a servomotor  62  that drives a gearbox  64 . The gearbox  64  may be operatively connected to a shaft  66 , and the output shaft may be operatively connected to an end effector  68 . The servomotor  62  may operatively rotate the end effector  68  at the distal end of the tool change actuator via the gear box  64  and the shaft  66 . The shaft  66  may be operatively connected to the end effector  68  with a flex coupling  70 . The servomotor  62  and gearbox  64  may be mounted to a subplate  72 . The servomotor  62 , the gearbox  64 , the shaft  66 , and the end effector  68  may move relative to the subplate  72  via a linear actuator  74 . In another embodiment, the motions of the servo motor  62  and linear actuator  74  may be provided by a linear rotary servo motor. The shaft  66  may extend through a hole in the subplate  72  so that the end effector  68  is on one side of the subplate and the servomotor  62  and the gear box  64  are on the opposite side of the subplate. The linear actuator  74  may allow the servomotor  62  and the gear box  64  to reciprocate in a linear fashion relative to the driven end  44   b  of the spindle. For instance, the linear actuator  74  may be a pneumatic cylinder, and two linear actuators may be placed on opposite sides of the servomotor and gear box. Through the linear actuator  74 , the tool change actuator  60  may be enabled to position the end effector  68  in (i) a retracted position where the end effector is spaced from the driven end  44   b  of the spindle, (ii) an engagement position where the end effector  68  is in initial engagement with a tool holder clamp  76  of the spindle, and (iii) an actuation position where the end effector  68  is in full engagement with the tool holder clamp  76  of the spindle. In one aspect, when the tool change actuator  60  moves the end effector  68  to the retracted position, the end effector is at a first distance from the subplate  72  and spaced from the driven end  44   b  of the spindle; when the tool change actuator  60  moves the end effector  68  to the engagement position, the end effector moves away from the subplate  72  to a second distance which is greater than the first distance, and engages the tool holder clamp  76  of the spindle  44 , and when the tool change actuator  60  moves the end effector  68  to the actuation position, the end effector moves away from the subplate  72  to a third distance which is greater than the second distance while maintaining engagement with the tool holder clamp  76  of the spindle  44 . 
     The tool change actuator  60  may include an end effector drive sensor  78 . The end effect drive sensor  78  may be adapted and configured to sense when the end effector  68  has moved between the retracted position and the engagement position. The end effector drive sensor  78  may be a position transmitter disposed adjacent the linear actuator  74  so as to measure the displacement of the end effector  68  via the movement of the linear actuator  74 . Feedback from the servomotor  68  and signals from the end effector drive sensor  78  may be used to provide an indication of movement of the end effector between the engagement position and the actuation position, as will be discussed below. 
     The spindle assembly  40  may include the spindle  44  rotatably disposed in the spindle housing  42 . As stated before, the spindle housing  44  is mounted to the arm  36  so the spindle assembly moves with the arm. The spindle  44  has a driven end  44   b  for rotating the spindle. For instance, a spindle drive chain  80  may rotate the spindle  44  via a toothed belt (not shown) and toothed gear  82  provided at the driven end  44 B of the spindle. The spindle  44  may be supported in the spindle housing  42  with bearings  84  and a sleeve assembly  86 . The spindle  44  may have the tool holder clamp  76  disposed in the center of the spindle extending along a center axis of rotation of the spindle. The tool holder clamp  76  may releasably engage the tool holder  46  of the saw blade  38  at the end  44   a  of the spindle, which is opposite the driven end  44   b  of the spindle. The tool holder clamp  76  may have an operator  88  that is accessible at the driven end  44   b  of the spindle. 
     The operator  88  may be configured to allow movement of the clamp  76  between a hold position in which the clamp  76  secures the tool holder  46  to the first end  44   a  of the spindle and a release position in which the clamp  76  moves to a position relative to the spindle  44  to allow the tool holder  46  to be removed from the first end  44   a  of the spindle. The clamp  76  may include a drawbar  90  that extends through the spindle center and allows operation of the clamp at the first end  44   a  of the spindle with the operator  88  at the driven end  44   b  of the spindle. The drawbar  90  may act against spring pressure when the clamp  76  is moved from the hold position to the release position. One or more springs or a spring stack  92  acting on the drawbar may urge the clamp to the hold position. The driven end  44   b  of the spindle may be configured with a threaded region  94 , and the operator  88  may be provided as a screw threaded member. For instance, the operator  88  may be an Acme threaded screw member that engages the threaded region  94  of the spindle. Thus, in moving the clamp  76  from the hold position to the release position, the threaded screw member of the operator  88  may be rotated within the threaded region  94  of the spindle so the threaded screw member of the operator  88  rotates and moves linearly along the center axis of the spindle. A thrust bearing  96  may be disposed between the threaded member of the operator  88  and the drawbar  90  so as to allow the operator to engage the drawbar and move the drawbar against spring pressure as the operator rotates and moves linearly to move the clamp from the hold position to the release position. The threaded region  94  of the spindle may be provided via a locking nut that is secured at the axial end of the driven end of the spindle. The locking nut may receive the threaded member of the operator  88 . 
     The operator  88  may include a releasable drive connection that cooperates with the end effector  68 , so as the end effector  68  rotates, the operator  88  may rotate and thread through the threaded region  94  of the spindle to move the drawbar  90  as needed. In one aspect, the end effector  68  and the operator  88  have a hexalobe type configuration. To allow for slight misalignment between the end effector  68  and the operator  88 , the flexible coupling  70  may be provided on the shaft connection to end effector. The end effector drive sensor  78  may be configured to sense when the end effector  68  abuts the operator  88  and when the end effector is fully engaged with the operator, and based on the end effector drive sensor signals, the linear actuator  74  and servomotor  62  of the tool change actuator may be operated in a manner to rotate the end effector  68  and axially displace the end effector from a position in which the end effector abuts the operator and then moves to the engagement position. In one aspect, the tool change actuator  60  may rotate the end effector  68  incrementally while pressing the end effector against the operator  88  under light pressure from the linear actuator  74  until the end effector  68  moves axially and fully engages the operator  88  of the tool holder clamp  76 . To prevent rotation of the spindle  44  while the end effector  68  rotates and axially displaces the operator/threaded member  88 , the toothed belt acting on the toothed drive pulley  82  on the driven end  44   b  of the spindle, and the spindle drive  80  holding position for the spindle servomotor provide sufficient inertia and counter torque against the rotation of the spindle. 
     The first end  44   a  of the spindle may be configured in a manner to receive the tool holder  46  of the saw blade. For instance, in one configuration, the first end  44   a  of the spindle includes a tapered bore  100  which receives the tool holder  46 . The clamp  76  extends into the tapered bore and has fingers  102  that are adapted and configured to engage the tool holder  46 . In one aspect, the fingers  102  of the clamp  76  may cooperate with the tool holder  46  to hold the tool holder in the tapered bore  100  of the spindle when the clamp is in the hold position thereby securing the tool holder with the spindle  44  as an integral unit allowing the spindle to rotate the saw blade  38  mounted to the tool holder  46  to cut a log. When the clamp  76  is moved to the release position, the fingers  102  of the clamp may cooperate with the tool holder  46  to disengage the tool holder from the tapered bore  100  on the spindle to allow the saw blade and the tool holder to be removed from the spindle. 
     The exemplary blade array  52  comprises a frame with a plurality of drawers or storage units  50  that are each adapted and configured to move from a retracted position in which the storage unit is contained within the blade array and an extended position in which the storage unit moves in a linear fashion outward from the blade array into the interior of the saw house. The blade array frame may include telescoping rails and guides  101  for each storage unit that allow the storage unit to move linearly between the retracted and extended positions. Each storage unit may have a tab  102  extending from the frame. The tab  102  may cooperate with a pull bar  104  ( FIG.  1   ) of the saw so when the blade array  52  is connected with the saw  30 , the pull bar  104  may engage the tab  102  of the respective storage unit  50  and move the storage unit from the retracted position in the blade array to the interior of the saw house adjacent the first end of the spindle, and vice versa. As described previously, the blade array  52  may be mounted on a slide  54  extending from the structure  34  of the saw house  32 . The slide  54  may move the blade array in the direction of advancement of the logs, so the saw  30  may move a respective storage unit  50  adjacent the spindle  44 . Preferably, the saw  30  is provided with one pull bar  104 , and the motion of the slide  54  is configured to move the tab  102  of the respective storage unit  50  into register with the pull bar  104  when a specific storage unit is called for by the control of the saw  30 . 
     The blade array  52  may be detachably connected with the structure  34  of the saw house  30 , for instance, detachably connected with the slide  54  of the saw house. One blade array may be serviced off line, for instance, to replace worn blades, and another blade array may be moved into position and connected with the saw house. The blade array may include casters  106  that allow the blade array to be moved as desired in the facility and adjacent to the saw, and to allow one blade array to be changed with another blade array to facilitate saw operations. The blade array frame may also include fork tubes  108  that enable the blade array to be moved with a forklift and/or strap openings  110  for connection with lifting straps and a crane or other overhead lifting devices. The blade array frame may also be provided with hand grips  111  to enable the blade array to be moved manually as desired. The blade array may also be provided with releasable connections  112  to enable the blade array frame to be detachably mounted on the slide(s)  54 , 55  of the saw house  32 . 
     At the center of each storage unit or drawer of the blade array, the storage unit may be provided with a hub structure  120  that allows the tool holder with the saw blade to releasably engaged with the storage unit. The storage unit hub structure  120  has features allowing the tool holder  46  with the saw blade  38  to be removed from the storage unit with the clamp  76  of the spindle  44  and allowing the clamp of the spindle to mount the tool holder with the saw blade on the hub structure in the storage unit. When the storage unit  50  is moved to the extended position, the storage unit may be positioned sufficiently adjacent the first end  44   a  of the spindle so as to allow the clamp  76  to engage the tool holder and move the tool holder  46  and the saw blade  38  from the hub structure  120  of the storage unit to the first end of the spindle, and to move the tool holder with the saw blade from the spindle to the hub structure of the storage unit. 
     The tool holder  46  may have a first side  132  and a second side  134 . The first side  132  of the tool holder  46  may be adapted and configured to releasably engage the hub structure  120  of the storage unit  50 . The second side  134  of the tool holder  46  may be adapted and configured to releasably engage the clamp  76  at the first end  44   a  of the spindle. In one aspect, the tool holder may be formed as a two piece assembly with a blade holder  136  supporting the saw blade  38  and a blade clamp  138  that secures the saw blade to the blade holder. The blade holder  136  may be adapted and configured to releasably connect with the first end  44   a  of the spindle and also releasably connect with the hub structure  120  of the storage unit  50 . The blade clamp  138  may be secured to the blade holder  138  with mechanical fasteners  140  that pass through the blade clamp, matching holes in the saw blade, and secured in place in threaded holes  142  in the blade holder  136 . 
     In one aspect, the blade holder  136  may have features that form first and second sides  132 , 134  of the tool holder. For instance, the blade holder  136  may have an annular wall  144  that extends from one side of the tool holder. The annular wall  144  may have an outer diameter surface that provides a locator for the blade clamp. The outer diameter surface of the annular wall  144  may also fit within a recess  146  ( FIG.  16   ) of the hub structure  120  on the storage unit to allow the recess support a portion of the tool holder  46  and saw blade  38  within the storage unit  50 . The annular wall may also have an inner diameter surface. The inner diameter surface may have a groove  148  ( FIG.  12   ), which may be a discontinuous groove, that may be adapted to receive a spring loaded pawl  150  ( FIG.  17   ) on the hub structure  120 . For instance, the hub structure  120  of the storage unit  50  may be provided with four spring loaded pawls  150  that engage the groove  148  on the inner diameter surface of the annular wall  144 . In the alternative, the hub structure may be provided with canted coil springs, a pneumatic spring/bladder, elastomeric springs or elastomer material to engage the groove  148  on the inner diameter of the annular wall. The tool holder  46  may also have a center locator hub  152  that extends from the tool holder. The center locator hub  152  may be connected to the blade holder  136 . The center locator hub  152  may fit within a hole  154  ( FIG.  16   ) of the hub structure to further support and align the tool holder  46  in the storage unit  50 , as will be described in greater detail below. 
     The blade holder  136  may also be formed with features that form the second side  134  of the tool holder  46 . For instance, the blade holder  136  may be formed with an annular extension  156 . The annular extension  156  may have an outer diameter surface which is tapered and cooperates with the tapered bore  100  at the first end  44   a  of the spindle. The annular extension  156  may also include a bore with a center axis that is aligned with the tapered outer surface of the annular extension. The bore may be defined by an interior surface. The interior surface may include an enlarged interior radius area  158  so that the interior surface has two regions  160 , 162  that cooperate with the fingers  102  of the clamp  76 . The first region  160  of the interior surface  158  may be shaped in a manner so that the fingers  102  of the clamp  76  engage the first region  160  of the interior surface  158  when the clamp  76  moves from the release position to the hold position. The interior surface  158  may also have a second region  162  that is adapted and configured to be engaged by the fingers  102  of the clamp  76  when the clamp moves from the hold position to the release position. The second region  162  of the interior surface  158  of the bore may also be configured and shaped with a shoulder  163  to receive a plunger  164  of the clamp  76 . The plunger  164  of the clamp  74  may bear against the shoulder  163  of the second region  162  of the interior surface  158  of the bore to facilitate removing the tool holder  46  from the first end  44   a  of the spindle. 
     To ensure alignment of the end effector  68  with the operator  88  of the clamp  76  of the spindle  44 , the tool change actuator  60  may be configured to slowly rotate the end effector  68  until the end effector fully engages the operator with a correct alignment. The end effector drive sensor  78  may be provided on the linear actuator  74  of the tool change actuator  60  to sense when the end effector  68  moves sufficiently in the direction of the center axis of the spindle  44  to properly engage the operator  88 . The end effector drive sensor  78  is configured and adapted to sense when the end effector  68  has moved from the retracted position to the engagement position relative to the operator  88  and the driven end  44   b  of the spindle. In moving the end effector  68  from the engagement position to the actuation position, the servomotor  62  of the tool change actuator  60  rotates the end effector  68  while the linear actuator  74  moves the tool change actuator  60  and thus end effector  68  axially thereby threadably engaging the operator  88  with the threaded region  94  of the spindle  44  to drive the operator  88  along the center axis of the spindle. The pitch of the screw threading and the rotation of the tool change actuator servomotor  62  for each tool change cycle may be stored in a memory of the control and used to determine the distance that the clamp  76  has moved from the hold position to the release position as the tool change actuator  60  moves the end effector  68  from the engagement position to the actuation position, and from the release position to the hold position as the tool change actuator moves the end effector from the actuation position to the engagement position. The rotation of the tool change actuator servomotor  62  for each tool change cycle may be stored in a memory of the control and used to determine the angular relation of the end effector  68  to the operator  88 , and the angular relation of the spindle  44  to the tool holder  46 . 
     To further facilitate alignment between the end effector  68  and the operator  88  and to facilitate alignment of the tool holder  46  with the spindle  44 , the driven end  44   b  of the spindle may be provided with a flag  170  and the tool change actuator  60  may be provided with a proximity sensor  172 . The flag  170  and the proximity sensor  172  may work together as a spindle rotation sensor that is adapted and configured to determine the angular position of the spindle  44 . The spindle rotation sensor  170 , 172  may generate a signal to the control to rotate the spindle drive servomotor as needed to provide any necessary alignment. The first end  44   a  of the spindle may be provided with plurality of guide pins  174  projecting outward from the first end of the spindle. The guide pins  174  may cooperate with guide holes  176  formed in the tool holder  46  and guide holes  178  formed in the hub structure  120  of the storage unit  50 . The guide pins  174  aid in aligning the tool holder  46  on the spindle  44  when the saw blade  38  with the tool holder is moved from the storage unit  50  to the spindle, and to ensure the tool holder  46  is properly oriented on the hub structure  120  when the saw blade  38  with the tool holder  46  is moved from the spindle  44  to the storage unit  50 . The spindle rotation sensor  170 , 172  may send a signal to the control to the spindle drive servomotor to rotate the spindle  44  as necessary to provide the alignment so the guide pins  174  come into register with the guide holes  176  formed in the tool holder  46  and the guide holes  178  formed in the hub structure  120  of the storage unit  50 . Further, to aid in alignment of the tool holder  46  and the saw blade  38  on the spindle  44 , a tool holder engagement sensor  180  may be provided on the spindle housing  42 . The tool holder engagement sensor  180  may be a proximity sensor that is adapted and configured to determine the distance between the tool holder  46  and the spindle  44 , for instance, the rear axial face of the blade holder  136  and the spindle  44 . In operation, after the saw blade  38  with the tool holder  46  is moved from the storage unit  50  to the spindle  44 , the spindle may be slowly rotated prior to commencing of the cutting of the log to sense any distance variation between the tool holder  46  and the tool holder engagement sensor  180  around the tool holder. To the extent the tool holder engagement sensor  180  senses any excessive variation of the distance between the tool holder  46  and the proximity sensor  180 , for instance, circular run-out of the tool holder, the control of the saw  30  can provide an alert or alarm if the variation is excessive, and/or adjust the pressure of the clamp  76  to reseat the tool holder  46  in the spindle  44 . 
     To provide further alignment between the storage unit  50  and the spindle  44  during a tool change, the arm  36  may be provided with a storage unit alignment sensor  184 . The storage unit alignment sensor  184  may be adapted to sense the position of the storage unit  50  relative to the spindle  44  when the storage unit is in the extended position in the interior of the saw house  32  adjacent the first end  44   a  of the spindle. The storage unit  50  may be provided with a triangular cut out  186  at a distal end of the storage unit. The triangular cut out  186  may cooperate with the storage unit alignment sensor  184  to enable the storage unit alignment sensor to sense the position of the storage unit, and in particular, in a plane which is arranged perpendicular to the center axis of the spindle. The triangular cut-out  186  provides a graduated indication with an apex or maximum spacing that can be sensed by the storage unit alignment sensor  184  to enable the control to determine the position of the storage unit  50  in the extended position. The storage unit alignment sensor may provide signals to the control that enable the pull bar  104  on the saw house  32  to be operated as necessary to provide alignment of the storage unit  50  in the cross machine direction. The storage unit alignment sensor  184  may also provide signals to the control enabling the control to provide signals to the vertical slide  55  to adjust the height of the array  52  and/or storage unit  50 . The desired storage unit alignment position may be associated with a position in which the storage unit alignment sensor  184  is located with a known relationship relative to the center of the blade spindle  44 . The geometric center of the triangular cut out  186  in the storage unit may also have a known relationship with the center of the hub for the tool holder in the blade storage unit  120 . With these relationships known, an alignment correction can be derived by evaluating the fraction of the motion of the blade storage unit extension that the alignment sensor  184  is influenced by the triangular cut out  186  and relating it to what is expected given ideal alignment. For example, consider  186  to be an isosceles triangular cut out with angles of 45°,45°, and 90° and an arbitrary cartesian coordinate system with the origin defined to be at the axis of rotation of the blade spindle  44  and coplanar with the blade  38 . During extension of the blade storage unit  50  towards the blade spindle, the position is decreasing as the blade storage unit  50  approaches the blade spindle  44 . The triangle  186  will pass the storage unit alignment sensor  184  during this motion. The extension positions of the blade storage unit associated with the leading and trailing edges of the triangular cut out will be captured as X_Leading, and X_Trailing respectively. Given this information, the detected position of the triangle position can be evaluated in relation to the desired position. To continue, consider the point (X_Target,Y_Target) to be the geometric center of the triangle that would correspond to the blade storage unit positioned ideally relative to the measurement sensor and blade spindle. TargetWidth is the width of the triangle at this point. 
     These incremental corrections can be used to adjust the position of the blade storage unit to provide ideal alignment of the blade spindle ( 44 ) and the blade tool holder ( 46 ). Given the description, it should be obvious that the geometric shape used for this system does not have to be limited to a triangle. Any shape with an edge that is not perpendicular to the axis of motion of the blade storage unit as it enters the saw house could work. The triangle, as described, provides a simple and concise geometry that provides good resolution relative to the expected magnitude of the alignment errors in both axes and is also easily added to the described blade storage unit during manufacturing. 
     In the description above, the principle and embodiments of the present application are illustrated herein by specific examples. The description of the above embodiments is only intended to facilitate the understanding of the method and the concept of the present application. For those skilled in the art, changes can be made to specific embodiments and an application scope of the present application, according to the concepts of the application. In conclusion, contents of the specification should not be construed as limitation to the present application.