Abstract:
A saw includes a surface defining an opening therein, a plate structure configured to be attached to the saw below the surface, and an arm attached to the plate structure about a first shaft. A blade is configured to be engaged with the arm at a location spaced from the first shaft. The blade extends through the opening when the saw is in a normal operating position. The saw includes a firing mechanism including a barrel end portion having a bore defined therein and an extendable piston at least partially positioned within the bore. The barrel end portion is attached to the plate structure. The extendable piston engages the arm during its extension and causes the arm to pivot about the first shaft when the firing mechanism is activated by an activation signal. The pivoting of the arm causes the blade to be moved downwardly below the surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and hereby claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 12/623,694, filed Nov. 23, 2009, U.S. Pat. No. 8,074,546 by William R. Knapp et al., entitled PYROTECHNIC DROP MECHANISM FOR POWER TOOLS, which is a continuation of, and claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 11/589,344, filed Oct. 30, 2006, now U.S. Pat. No. 7,628,101 by William R. Knapp et al., entitled PYROTECHNIC DROP MECHANISM FOR POWER TOOLS, which is a continuation of and claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 11/374,319, filed Mar. 13, 2006, now abandoned by William R. Knapp et al., entitled PYROTECHNIC DROP MECHANISM FOR POWER TOOLS, which claims priority under 35 U.S.C. §119(e) to, U.S. Provisional Patent Application Ser. No. 60/660,788, filed Mar. 11, 2005, by William R. Knapp et al., entitled PYROTECHNIC DROP MECHANISM FOR POWER TOOLS. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to power tools and to blade dropping systems for such power tools. 
     Systems have been developed and are described in a plurality of patent applications that are assigned to SD2, LLC which include various mechanisms that have a detection system for detecting contact between a human and a blade The detection system triggers a brake mechanism that typically includes a pawl structure that is urged into the blade by a biasing mechanism that is retained by a fusible member and is melted by a high energy electrical current. Severing the fusible member releases the pawl to stop the blade or to retract it below the work surface of a table saw, for example. The systems have disadvantages; for example they are expensive and inconvenient to use since they require the replacement of expensive modules after they have been fired, which is time-consuming and difficult. An additional disadvantage is the variability of the system based on the blade design. 
     SUMMARY OF THE INVENTION 
     Embodiments of a saw are disclosed of the type which has a top with an opening in the top through which a saw blade can extend, the height and angular orientation of which can be adjusted, and also configured to be retracted in response to an activation signal being applied, the saw comprising a plate structure configured to be mounted to the saw below the top, an arm pivotally mounted to the plate structure about a first shaft, a rotatable circular blade having an arbor mounted to the arm at a location spaced from the first shaft, and being configured so that at least a portion of the blade can extend through the top opening and be in position to cut a work piece when the blade is in its normal operating position, a drive motor with an output shaft operatively connected to power the saw blade, a firing mechanism having a barrel end portion with a cylindrical bore mounted to the plate structure and an extendable piston positioned in the bore, the piston engaging the arm during its extension and causing the arm to pivot about the first shaft when the firing mechanism is activated by the activation signal being applied, the pivoting of the arm causing the blade to be moved downwardly below the saw top toward its retracted position. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a preferred embodiment of the blade retracting mechanism, showing the blade in the normal operating position; 
         FIG. 2  is a cross section of a portion of the apparatus shown in  FIG. 1 , particularly illustrating the pyrotechnic firing mechanism; 
         FIG. 3  is a side view of the apparatus shown in  FIG. 1 , but illustrating the saw blade in a partially retracted position; 
         FIG. 4  is a view similar to  FIG. 2 , but showing the firing mechanism immediately after firing when the piston is at the extent of its travel; 
         FIG. 5  is a side view of the apparatus shown in  FIG. 1 , but illustrating the saw blade in a fully retracted position; 
         FIG. 6  is a view similar to  FIG. 2 , but showing the firing mechanism after firing but with the piston reacting back to its post firing resetting position; 
         FIG. 7  is a side view of a portion of a second embodiment of the blade retracting mechanism and is shown with the blade in a normal operating position; 
         FIG. 8  is a view of the apparatus shown in  FIG. 7 , but illustrating the blade in a fully retracted position; 
         FIG. 9  is an idealized perspective view of a portion of the apparatus shown in  FIG. 8 , with the blade in its normal operating position; and 
         FIG. 10  is a similar perspective view of a portion of the apparatus shown in  FIG. 9  illustrating portions of the mechanism that were hidden from view in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     The preferred embodiments of the blade retracting mechanism that are shown and described herein are operable with a detection system that is designed and configured to be able to detect the presence of a person either by use of a mechanism that detects the proximity of a person&#39;s hand or possibly by virtue of detection of contact of a person&#39;s body with a portion of the saw or other tool that is designed to be a sensor. The most likely component to be used as a sensor is the saw blade, which would be used to detect the person&#39;s proximity or contact with a saw blade. If contact with a saw blade is necessary for detection, there would necessarily be at least some injury to a user depending upon the speed of approach and the speed in which the entire system operates. 
     The preferred embodiment of the present invention is shown in  FIGS. 1-6 , with  FIG. 1  showing a side view of a blade retracting mechanism indicated generally at  10 , with the blade  12  being in a normal operating position, where the blade is near a riving knife  14 . In  FIG. 3 , the blade  12  is shown to be partially retracted as would occur during operation of the mechanism  10  and in  FIG. 5 , the blade  12  is fully retracted below the surface of the table saw top which is approximately at the elevation shown by the dotted line T of  FIGS. 1 ,  3  and  5 . The blade  12  rotates on a shaft  16  that is journaled in a generally triangularly shaped arm  18  that has a curved lower surface  20 . The arm  18  rotates around another shaft  22  that is attached to a large plate  24  that is mounted to the saw by mounting brackets  26  and  28  located on opposite ends of the plate  24 . The plate  24  carries a motor base  30  that is mounted above the elevation of the plate  24  and carries a motor  32  for driving the saw blade  12 . 
     The output shaft of the motor  32  is not shown, but it carries a pulley which drives a belt  34  and a pulley  36 , with the pulley  36  being connected to another pulley or having an extension for driving a belt  38  and in turn drives a pulley  40  that is operatively connected by the shaft  16  to an arbor (not shown), but which drives the blade  12 . Since the arm  18  is pivotable about the shaft  22 , it should be understood that the motor  32  is configured to be able to drive the belts  34  and  38  via the motor pulley and pulley  36  regardless of the vertical position of the blade  12 . Stated in other words, the distance between pulleys  36  and  40  remains constant as does the distance between pulley  36  and the motor drive shaft regardless of the vertical position of the blade  12 . 
     When the blade is in the normal operating position as shown in  FIG. 1 , the top right surface of the arm  18  abuts against a stop member  41  that is mounted to the plate  24  by a mounting bracket  42  with bolts  44 . The arm  18  is held in the upper position as shown in  FIG. 1  by a detent assembly, indicated generally at  46 , that comprises a main bracket  48  that is bolted to the plate  24  by bolts  50  and wherein a detent rod  52  engages a V-shaped recess  54 . The rod  52  is biased into engagement with the recess  54  by a spring  56  that is seated on a bolt  58  and which is adjustable to vary the biasing force that is applied to the rod  52 . The detent assembly  46  is therefore designed and configured to maintain the arm  18  in its normal operating position unless it is rotated downwardly with sufficient force to depress the detent rod  52  away from the V-shaped recess  54  and release the arm  18  for rotation. 
     The force that is necessary to overcome the detent assembly  46  is provided by a firing mechanism that is indicated generally at  60 . A cross-section of the mechanism is shown in  FIGS. 2 ,  4  and  6 , and comprises a cylindrical barrel structure  62  having a cylindrical bore  64  in which a piston  66  is positioned. The mechanism  60  has a replaceable cartridge  68  that is placed in a smaller bore  70  with the cartridge  68  being retained by an end cap structure  72  through which a metal pin  74  is located with the pin extending to the cartridge  68  so that it can be fired. The pin  74  is connected to a wire  76  which in turn is connected to a capacitor  78 . 
     During operation, the capacitor  78  is switched to release its electrical charge which travels through wire  76  to heat the pin  74  to a temperature that fires the cartridge  68  and this causes high pressure gases to be produced and cause the piston  66  to be moved to the left out of the bore  64 . The piston  66  is guided by a support  80  having a cylindrical opening therein sized to receive the cylindrical piston  66 . As it is driven in the leftward direction, i.e., away from the barrel  62 , a hammer  82  is driven toward a hammer damper  84  that is mounted to a skid  86  that also has a mounting structure, indicated generally at  88 , which holds the damper  84  and cushions the hammer  82 . During its travel the hammer  82  drives the arm  18  in the clockwise direction around the shaft  22 . The piston  66  has an enlarged end portion  90  that defines a shoulder  92  that engages the support member  80  at the end of its travel. It should also be understood that the skid  86  and support member  80  are effectively connected together. An end bracket  94  has a narrow center portion  96  that extends rearwardly and it is retained by a pair of support members  98  ( FIG. 1 ) located on opposite sides of the center portion  96 . The support members  98  are bolted to the plate  24  by bolts  100 . 
     An anvil  102  is connected to the arm  18  by a pair of pins  104  and a pair of bolts  106  as well as by a strap  108  that is bolted on opposite ends to the anvil  102  and the arm  18 . It should be apparent that the front surface of the hammer  82  is in contact with the adjoining surface of the anvil  102  so that when the firing mechanism  60  is activated, the piston  66  will cause the hammer  82  to move the anvil  102  and arm  18  in a clockwise direction so as to retract the blade  12  below the surface T before the user is seriously injured. 
     When the microprocessor triggers the pyrotechnic device, a high amperage current is sent through the wire  76  to the electrode or pin  74 , which directs the current to the back of the cartridge  68 . The cartridge  68  fires causing a rapid pressure rise in the barrel  62  behind the piston  66  that produces approximately 10,000 pounds of force that propels it toward the anvil  102 . The piston  66  is forced to move along the barrel axis pushing the anvil  102  as it does so. This pushing force overrides the detent assembly  46  and the arm  18  rotates in a clockwise direction. When the arm  18  moves to its position of maximum travel as shown in  FIG. 5 , the hammer  82  fully compresses the hammer damper  84 . In this position, the barrel  62  vents the combustion gases because the piston  66  moves past the end of the barrel  62  thus relieving the barrel pressure in preparation to stopping the piston  66 . Since the arm  18  and hammer  82  are not physically connecting, i.e., they only touch, the arm  18  is free to continue rotating even though the piston  66  stops. The arm  18  continues to rotate until it contacts a mechanical stop that is not shown, at which time its movement ends. The hammer damper  84  then relaxes and pushes the hammer  82  and piston  66  back into the barrel  62 . The cartridge  68  is a commonly available  22  caliber nail gun cartridge that is used in construction and costs about $0.05. An advantage of the preferred embodiments of the present invention is that once the cartridge  68  is fired, the end cap  72  can be removed enabling the spent cartridge shell to be removed. The firing mechanism  60  can be rearmed by placing another cartridge  68  in the bore  70 , inserting another pin  74  in the end cap  72 , connecting the wire  76  to the pin and recharging the capacitor  78 . 
     In a second preferred embodiment shown in  FIGS. 7-10 , reference numbers that have been given to the first preferred embodiment shown in  FIGS. 1-6  are used where the components are similar. In the embodiment shown in  FIG. 7 , the arm  18  has structure that interacts with a detent assembly  46  in a slightly different manner, i.e., the V-shape recess  54  is not directly contacted by the detent rod  52 , but contains an extension piece  112  that extends beyond the curved surface  20  of the arm  18  and contacts the end of the detent rod  52  as shown. 
     This extension is necessary because of a slight modification to the placement of the detent assembly  46  to accommodate the addition of an anti-bounce mechanism, indicated generally at  114  that is located below the anvil  102 . The outer surface  20  of the arm  18  has a number of serrated teeth  116  along a portion of the surface which are positioned to engage a ratchet assembly  118  that pivots about a shaft  120  that is operatively connected to the plate  24 . A compression spring  122  has one end engaging an extension  124  of the ratchet assembly and the opposite end bearing against a bracket  126  so that a pawl  128  of the ratchet assembly  118  is biased toward the arm  18 . 
     As shown in  FIG. 8 , the saw blade  12  is mounted to the arm  18  through an aperture in the plate  24  by the shaft  16 . The aperture in the plate comprises an arcuately-shaped track  21  such that when the arm  18  rotates clockwise about the shaft  22 , the shaft  16  moves downwardly along the arcuately-shaped track  21 . After the firing mechanism  60  rotates the arm  18  in a clockwise direction, its left surface  130  will contact a stop or damper  132 . Because of the tremendous force having been applied to the arm  18 , the arm  18  is moving rapidly and bounces off the stop  132 . As show in  FIG. 8 , as the arm  18  bounces off of the stop  132 , the pawl  128  will engage one of the teeth  116  and stop the counterclockwise movement of the arm  18  and prevent the blade  12  from moving upwardly above the tabletop to potentially strike the user. While not shown, a pull lever is preferably provided to release the pawl  128  from the teeth  116  as the arm  18  is returned to its normal operation position. While adjustable, it is preferred that the amount of force needed to release the pawl  128  be in the range of about 10 to about 20 pounds. The amount of force needed to lift the arm  18  to its normal operation position is within the range of about 10 to about 20 pounds and the amount of force to overcome the spring  56  in the detent assembly  46  to latch the arm  18  in the normal operating position is preferably within the range of about 15 to about 25 pounds. 
     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.