Abstract:
A table saw includes a safety system to protect a user from injury. The safety system detects a sensed condition and rapidly moves a saw blade away from the user. The safety system includes a dual ratchet mechanism to prevent the blade from rebounding back above a work surface after an initial rapid retraction of the blade. The table saw has a swing arm that rotates to move the blade below the work surface. A first ratchet engages a first contact surface of the swing arm after rotation of the swing arm over a first range of angular displacements to prevent counter rotation of the swing arm. A second ratchet engages a second contact surface of the swing arm after rotation of the swing arm over a second range of angular displacements to prevent counter rotation of the swing arm.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to power tools and more particularly to power tools with exposed shaping devices. 
       BACKGROUND 
       [0002]    A number of power tools have been produced to facilitate forming a work piece into a desired shape. One such power tool is a table saw. A wide range of table saws are available for a variety of uses. Some table saws are very heavy and relatively immobile. Other table saws, sometimes referred to as job site table saws, are relatively light and portable so that a user can easily transport and position the table saw at a job site. All table saws, including cabinet table saws and job site table saws, present a safety concern because the saw blade of the table saw is typically very sharp and moving at a high rate of speed. Accordingly, severe injury such as severed digits and deep lacerations can occur almost instantaneously. 
         [0003]    Various types of safety systems have been developed for table saws in response to the dangers inherent in an exposed blade moving at high speed. One such safety system is a blade guard. Blade guards movably enclose the saw blade, thereby providing a physical barrier that must be moved before the rotating blade is exposed. While blade guards are effective to prevent some injuries, the blade guards can be removed by a user either for convenience of using the table saw or because the blade guard is not compatible for use with a particular shaping device. 
         [0004]    Table saw safety systems have also been developed which are intended to stop the blade when a user&#39;s hand approaches or touches the blade. Various stopping devices have been developed including braking devices which are physically inserted into the teeth of the blade. Such approaches are extremely effective. Upon actuation of this type of braking device, however, the blade is typically ruined because of the braking member. Additionally, the braking member is typically destroyed. Accordingly, the user must replace the blade and the braking member, often at considerable expense, after actuation of the safety device. Another shortcoming of this type of safety device is that the shaping device must be toothed. Moreover, if a spare blade and braking member are not on hand, a user must travel to a store to obtain replacements. Thus, while effective, this type of safety system can be expensive and inconvenient. 
         [0005]    Some table saw safety systems, including some systems that incorporate blade braking devices, also move the blade below the surface of the table saw to prevent further contact with the user once the safety system detects an initial contact.  FIGS. 1 and 2  depict a known table saw  100  that includes a safety system that moves the blade below the table saw surface in response to blade contact with the user. The table saw  100  includes a base housing  102  and a work-piece support surface  104 . A riving knife or splitter  106  is positioned adjacent to a blade  108  which extends from within the base housing  102  to above the work-piece support surface  104 . A blade guard (not shown) may be attached to the splitter  106 . An angle indicator  110  indicates the angle of the blade  108  relative to the work-piece support surface  104 . A bevel adjust turn-wheel  112  may be used to establish the angle of the blade  108  with respect to the work-piece support surface  104  by pivoting a frame  114  ( FIG. 2 ) within the base housing  102 . 
         [0006]    A motor  116 , which is powered through a switch  118  located on the base housing  102 , is supported by a carriage assembly  120 . The carriage assembly  120  and a stop pad  122  are supported by the frame  114 . The carriage assembly  120  includes a carriage  124  to which the motor  116  is mounted and two guiderails  126 / 128 . The position of the carriage  124  along the guiderails  126 / 128  is controlled by a blade height turn-wheel  130  through a gearing assembly  132  and a height adjustment rod  134 . The carriage  124  fixedly supports a latch assembly  140  and supports a swing arm assembly  142 . 
         [0007]    The swing arm assembly  142  is pivotally coupled to the carriage  124  for movement between a latched position in which the blade is held above the support surface  104  and a de-latched position in which the blade is allowed to rotate into the base housing  102 . As shown in  FIG. 3 , the swing arm assembly  142  includes a housing  144 . The housing  144  encloses a power wheel (not shown) that is driven by an output shaft  152  of the motor  116 . The output shaft  152  may be directly driven by the motor  116  or by a reduction gear. A belt (not shown) transfers rotational movement from the power wheel  150  to a blade wheel  156 . A nut  158  is used to affix the blade  108  (not shown in  FIG. 3  for purpose of clarity) to the blade wheel  156 . Additionally, as shown in  FIG. 3 , the swing arm assembly  142  may also include a strike plate  146  and a rebound plate  148  mounted on the housing  144 . 
         [0008]    In operation, the swing arm assembly  142  is initially maintained in a latched position with the blade wheel  156  positioned sufficiently close to the work-piece support surface  104  such that the blade  108  extends above the work-piece support surface  104  as shown in  FIG. 1 . A user operates the bevel adjust turn wheel  112  to pivot the frame  114  with respect to the work-piece support surface  104  to establish a desired angle between the blade  108  and the work-piece support surface  104 . The user further operates the blade height adjustment turn-wheel  130  to move the carriage  124  along the guiderails  126 / 128  to establish a desired height of the blade  108  above the work-piece support surface  104 . Using the switch  118 , power is then applied to the motor  116  causing the output shaft  152  and the power wheel to rotate. Rotation of the power wheel  150  causes the belt to rotate the blade wheel  156  and the blade  108  which is mounted on the blade wheel  156 . A work-piece may then be shaped by moving the work-piece into contact with the blade  108 . 
         [0009]    The table saw  100  includes a sensing and control circuit (not shown) which activates an actuator, such as a solenoid or a pyrotechnic cartridge, in response to a sensed condition. Any desired sensing and control circuit may be used for this purpose. One known sensing and control circuit is described in U.S. Pat. No. 6,922,153, the entire contents of which are herein incorporated by reference. The safety detection and protection system described in the &#39;153 patent senses an unsafe condition and provides a control signal which, in the table saw  100 , is used to activate the actuator. 
         [0010]    Upon activation of the actuator, an actuator pin is forced outwardly from the actuator. When the swing arm assembly  142  is maintained in a latched position, the strike plate  146  is aligned with the solenoid. Accordingly, as the actuator pin is forced out of the actuator, the actuator pin contacts the strike plate  146 , which releases the latch assembly  140  and imparts an impact force on the swing arm assembly  142 . Consequently, the swing arm assembly  142  pivots about the output shaft  152  such that the blade wheel  156  moves away from the work-piece support surface  104 . Accordingly, the blade  108  is pulled by the swing arm assembly  142  in a direction away from the work-piece support surface  104 . 
         [0011]    The swing arm assembly  142  continues to pivot about the output shaft  152  until the swing arm assembly  142  contacts the stop pad  122 . Accordingly, further rotation of the swing arm assembly  142  is impeded by the stop pad  122 . At this position, the blade  108  is completely located below the work-piece support surface  104 . Therefore, an operator above the work-piece support surface  104  cannot be injured by the blade  108 . 
         [0012]    The stop pad  122  can be formed from microcellular polyurethane elastomer (MPE). MPEs form a material with numerous randomly oriented air chambers. Some of the air chambers are closed and some are linked. Additionally, the linked air chambers have varying degrees of communication between the chambers and the orientation of the linked chambers varies. Accordingly, when the MPE structure is compressed, air in the chambers is compressed. As the air is compressed, some of the air remains within various chambers, some of the air migrates between other chambers, and some of the air is expelled from the structure. One such MPE is MH 24-65, commercially available from Elastogran GmbH under the trade name CELLASTO®. 
         [0013]    Use of an MPE or other appropriate material in the stop pad  122  stops rotation of the swing arm assembly  142  without damaging the swing arm assembly  142 . However, prior to impacting the stop pad  122 , the swing arm assembly  142  may be moving with sufficient force to cause the swing arm assembly to rebound off of the stop pad  122 . For instance, in some table saw safety systems, a pyrotechnic device is detonated in order to generate the high-energy actuating force on the swing arm assembly  142  needed to rapidly move the blade  108  below the support surface  104  when the safety system detects contact with the user. The energy applied to rotate the swing arm assembly  142  can be partially absorbed by the material of the stop pad  122 , but due to the high energy displacement of the swing arm assembly  142 , some rebound is still possible. In such a circumstance, the swing arm assembly  142  will rotate about the power shaft  152  in a counterclockwise direction. Thus, the blade  108  moves toward the work-piece support surface  104 . 
         [0014]    In view of the foregoing, it would be advantageous to provide a power tool with a safety system that prevents a rotating blade from rebounding toward a user after the blade is moved away from the user in response to contact between the user and the blade. A safety system that decreases the activation time to prevent such rebounding of the blade would be further advantageous. A further advantage would be realized by a safety system that could be reset without the need for disassembly of the power tool. 
       SUMMARY 
       [0015]    A table saw in one embodiment includes a frame that supports a work surface, a swing arm that cooperates with the frame via a pivot, the swing arm defining first and second contact surfaces disposed concentrically about and proximate to the pivot, a blade rotatably attached to the swing arm at a position spaced from the pivot, the blade having an operating position in which the blade extends above the work surface and a retracted position in which an uppermost extent of the blade is positioned below the work surface, the swing arm rotatable about the pivot to move the blade from the operating position to the retracted position in response to a sensed condition, a first ratchet configured to cooperate with the first contact surface so as to maintain the blade in the retracted position after the swing arm rotates over any one of a first range of angular displacements from the operating position, and a second ratchet configured to cooperate with the second contact surface so as to maintain the blade in the retracted position after the swing arm rotates over any one of a second range of angular displacements from the operating position, the second range of angular displacements including angular displacements that are greater than angular displacements of the first range of angular displacements. 
         [0016]    A table saw in another embodiment includes a frame that supports a work surface, a swing arm that cooperates with the frame via a pivot, the swing arm defining a contact surface disposed concentrically about and proximate to the pivot, a blade rotatably attached to the swing arm at a position spaced from the pivot, the blade having an operating position in which the blade extends above the work surface and a retracted position in which an uppermost extent of the blade is positioned below the work surface, the swing arm rotatable about the pivot to move the blade from the operating position to the retracted position in response to a sensed condition, and a ratchet configured to cooperate with the contact surface so as to maintain the blade in the retracted position after the swing arm rotates over any one of a range of angular displacements from the operating position. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  depicts a top perspective view of a prior art table saw incorporating a safety system that that moves a blade below a work-piece support surface in response to blade contact with a user; 
           [0018]      FIG. 2  depicts a bottom perspective view of the table saw of  FIG. 1  with a housing of the table saw removed showing a movable carriage mounted on a pivoting frame beneath the work-piece support surface; 
           [0019]      FIG. 3  depicts a perspective view of a swing arm assembly of the table saw of  FIG. 1 ; 
           [0020]      FIG. 4  shows a table illustrating the change in angular displacement of a swing arm in accordance with the principles of the disclosure as the height of a blade attached to the swing is moved between its operating range; 
           [0021]      FIG. 5  depicts a bottom perspective view of a table saw with a safety system incorporating a dual ratchet mechanism to prevent a swing arm of the table saw from rebounding toward a work-piece support surface after the swing has been moved away from the user in response to blade contact with a user; 
           [0022]      FIG. 6  depicts a top perspective view of the table saw of  FIG. 5  showing a first pawl of the dual ratchet mechanism in an first active position in a first groove formed about the pivot of the pivot of the swing arm; 
           [0023]      FIG. 7  shows a top perspective view of the table saw of  FIG. 5  showing a second pawl of the dual ratchet mechanism in an active position in a second groove formed about the pivot of the swing arm; 
           [0024]      FIG. 8  shows a side plan view of the dual ratchet mechanism with the first pawl and the second pawl in a ready position along respective concentric surfaces of the swing arm; 
           [0025]      FIG. 9  depicts a top plan view of the table saw of  FIG. 5  with the throat plate removed to show the dual ratchet mechanism in a release position; 
           [0026]      FIG. 10  shows a top perspective view of the table saw of  FIG. 9  further illustrating the dual ratchet mechanism in the release position; 
           [0027]      FIG. 11  shows a side perspective view of the table saw of  FIG. 9  illustrating the dual ratchet mechanism in the release position and resting against a stop pin formed on the carriage assembly of the table saw; 
           [0028]      FIG. 12  depict another side perspective view of the table saw of  FIG. 9  showing the dual ratchet mechanism in the release position and resting against the stop pin; and 
           [0029]      FIG. 13  and  FIG. 14  show an embodiment of a table saw in which a single ratchet mechanism can be incorporated to prevent a swing arm of the table saw from rebounding toward a work-piece support surface after the swing arm has been moved away from the user in response to blade contact with a user. 
           [0030]      FIG. 15  shows a table illustrating angular displacements of the swing arm assembly in which the first pawl is in the first active position, but the second pawl is not yet in the second active position. 
       
    
    
     DESCRIPTION 
       [0031]    For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one of ordinary skill in the art to which this disclosure pertains. 
         [0032]      FIG. 5  shows a dual ratchet system  200  for a table saw  202  that includes a safety system for moving a rotating saw blade  108  ( FIG. 1 ) below a work-piece table support surface  104  in response to certain conditions, such as blade contact with a user. Elements of the table saw  202  that are substantially similar to elements of the table saw  100  described above are identified with the same reference numerals used in  FIGS. 1-3 , while new or modified elements of the table saw  202  are identified with new reference numerals. 
         [0033]    The dual ratchet system  200  includes a first ratchet  204  and a second ratchet  206  pivotally mounted to the carriage  124  of the table saw  202 . In the embodiment shown, the first ratchet  204  and the second ratchet  206  rotate about a common axis defined by a ratchet bolt  208 . The first ratchet  204  has first tip portion  210  ( FIG. 6 ) at one end and a first retention portion  212  at an opposed end with the ratchet bolt  208  passing through the first ratchet  204  at a location generally between the first tip portion  210  and the first retention portion  212 . The second ratchet  206  has a second tip portion  214  ( FIG. 6 ) at one end and a second retention portion  216  at an opposed end with the ratchet bolt  208  passing through the second ratchet  206  at a location generally between the second tip portion  214  and the second retention portion  216 . 
         [0034]    The table saw  202  includes a swing arm assembly  218  that is rotatably mounted to the carriage  124 . Similar to the swing arm assembly  142  discussed above with reference to  FIGS. 1-3 , the swing arm assembly  218  rotates about a pivot  220  of the carriage  124  in response to an actuation force triggered by the sensing and control circuit of the table saw safety system. 
         [0035]    Referring now to  FIG. 5  and  FIG. 6 , the swing arm assembly  218  has a first contact surface  222  and a second contact surface  224  disposed substantially concentrically about the pivot  220 . The first ratchet  204  and the second ratchet  206  are biased via respective first and second biasing forces such that the first tip portion  210  of the first ratchet  204  contacts the first contact surface  222  and the second tip portion  214  of the second ratchet  206  contacts the second contact surface  224 . In the embodiment shown, the first and the second biasing forces are generated by a first extension spring  226  and a second extension spring  228 , respectively. The first extension spring  226  extends between the first retention portion  212  of the first ratchet  204  and a spring bolt  230 . The second extension spring  228  extends between the second retention portion  216  of the second ratchet  206  and the spring bolt  230 . In some embodiments, the first and second biasing forces can be generated by torsional springs (not shown) instead of the first ( 226 ) and second ( 228 ) extension springs. In yet further embodiments, the first and the second biasing forces can be generated by compressible material disposed between the carriage  124  and the first ( 212 ) and the second ( 216 ) retention portions of the first ( 204 ) and the second ( 206 ) ratchets. 
         [0036]    With reference now to  FIGS. 5-7 , the first contact surface  222  of the swing arm assembly  218  includes a first ready surface  232  disposed at a first radial distance from the pivot  220  and a first active surface  234  disposed at a second radial distance from the pivot  220 . In the embodiment shown, the first radial distance is greater than the second radial distance such that the first ready surface  232  is disposed farther from the pivot  220  than the first active surface  234 . The second contact surface  224  of the swing arm assembly  218  includes a second ready surface  236  disposed at a third radial distance from the pivot  220  and a second active surface  238  disposed at a fourth radial distance from the pivot  220 . In the embodiment shown, the third radial distance is greater than the fourth radial distance such that the second ready surface  236  is disposed farther from the pivot  220  than the second active surface  238 . In some embodiments, the first radial distance and the third radial distance are the same, while in other embodiments the first radial distance and the third radial distance are different. Similarly, in some embodiments, the second radial distance and the fourth radial distance are the same, while in other embodiments the second radial distance and the fourth radial distance are different. 
         [0037]    A first stop face  240  is formed along the first contact surface  222  at the intersection of the first ready surface  232  and the first active surface  234 . The first stop face  240  is formed due to the differing radial distances of the first ready surface  232  and the first active surface  234  from the pivot  220 . A second stop face  242  is formed along the second contact surface  224  at the intersection of the second ready surface  236  and the second active surface  238 . The second stop face  242  is formed due to the differing radial distances of the second ready surface  236  and the second active surface  238  from the pivot  220 . As will be described in more detail below, the positioning of the first ( 204 ) and the second ( 206 ) ratchets relative to the swing arm assembly  218  enables the ratchets to engage the stop faces ( 240  and  242 ) and prevent counter rotation or rebound of the swing arm assembly  218  once the swing arm assembly is moved away from the support surface in response to a sensed condition. 
         [0038]      FIG. 4  shows a table that illustrates the total angular travel of the swing arm assembly  218  as a function of the height of the saw blade  108  above the work-piece support surface  104 . For instance, the swing arm assembly  218  rotates approximately 63.7 degrees to its stop position when the blade is positioned 83 millimeters above the work-piece support surface  104 . In contrast, the swing arm assembly  218  rotates approximately 39.7 degrees to its stop position when the blade is positioned 3 millimeters above work-piece support surface  104 . Thus, the difference in total rotation of the swing arm assembly  218  from a blade height of 83 millimeters to a blade height of 3 millimeters is approximately 24 degrees. As shown in  FIG. 4 , the starting angle of 8.7 degrees for the swing arm assembly  218  is the same for each height increment depicted in the table. The dual ratchet assembly  200  disclosed herein takes into account the variances in total angular travel of the swing arm assembly  218  by staggering the position of the first stop face  240  and the second stop face  242  along the first contact surface  222  and the second contact surface  224 , respectively. 
         [0039]    The operation of the dual ratchet system  200  is now described with reference to  FIGS. 5-7 . Similar to the operation of the table saw  100  of  FIG. 1 , the swing arm assembly  218  of the table saw  202  is initially maintained in a latched position with the blade wheel  156  ( FIG. 3 ) positioned sufficiently close to the work-piece support surface  104  such that the blade  108  extends above the work-piece support surface  104 . With the swing arm assembly  218  in the latched position, the first tip portion  210  of the first ratchet  204  rests on the first ready surface  232  of the first contact surface  222 , and the second tip portion  214  of the second ratchet  206  rests on the second ready surface  236  of the second contact surface  224 . In the embodiment shown, the first ready surface  232  and the first active surface  234  of the first contact surface  222  are concentric about the pivot  220 . Similarly, the second ready surface  236  and the second active surface  238  of the second contact surface  224  are concentric about the pivot  220 .  FIG. 8  best depicts the concentricity (depicted as dashed line  244  for clarity) of the second ready surface  236  about the pivot  220 . Once the first ratchet  204  and the second ratchet are in contact with the first contact surface  222  and the second contact surface  224 , respectively, the concentricity of the contact surfaces  222  and  224  ensures that the ratchets  204  and  206  remain in contact with the contact surfaces for any rotational speed of the swing arm assembly. 
         [0040]    Referring again to  FIG. 6 , the dual ratchet system  200  is shown after the swing arm assembly  218  rotates from a common start position to a first angular displacement. As shown in  FIG. 6 , the first ratchet  204  now rests on the first active surface  234  of the swing arm assembly  218 . This position of the first ratchet  204  results because, as the swing arm assembly  218  is rotated through the first angular displacement, the first active surface  234  is rotated under the first ratchet  204  and the bias of the first extension spring  226  pulls the first tip portion  210  of the first ratchet  204  against the first active surface  234 . In this embodiment, the first stop face  240  is shown spaced from the first tip portion  210 . Any counter rotation or rebound of the swing arm assembly  218  after the first ratchet  204  contacts the first active surface  234  will be impeded by contact between the first tip portion  210  of the first ratchet  204  and the first stop face  240  of the swing arm assembly  218 . As shown in  FIG. 6 , the second ratchet lever  206  remains resting on the second ready surface  236  after the swing arm assembly rotates through the first angular displacement. In some embodiments, a steel wear plate  250  ( FIG. 7  and  FIG. 8 ) is added to second stop face  242  to protect the material of the swing arm assembly  218  from deformation since the second stop face  242  is typically subject to the highest percentage of impact hits from the dual ratchet system  200 . 
         [0041]    Referring again to  FIG. 7 , the dual ratchet system  200  is shown after the swing arm assembly  218  rotates from the common start position to a second angular displacement, which is larger than the first angular displacement. As shown in  FIG. 6 , the first ratchet  204  remains resting on the first active surface  234  of the swing arm assembly  218 . In addition, the second ratchet  206  now rests on the second active surface  238  of the swing arm assembly  218 . This position of the second ratchet  206  results because, as the swing arm assembly  218  is rotated through the second angular displacement, the second active surface  238  is rotated under the second ratchet  206  and the bias of the second extension spring  228  pulls the second tip portion  214  of the second ratchet  206  against the second active surface  238 . In this embodiment, the second stop face  242  is shown spaced from the second tip portion  214 . Any counter rotation or rebound of the swing arm assembly  218  after the second ratchet  206  contacts the second active surface  238  will be impeded by contact between the second tip portion  214  of the second ratchet  206  and the second stop face  242  of the swing arm assembly  218 . 
         [0042]      FIG. 6  and  FIG. 7  best illustrate the staggered arrangement of the first stop face  240  and the second stop face  242  about the pivot  220  of the swing arm assembly  218 . In operation, the staggered arrangement of the stop faces  240  and  242  enables the dual ratchet system  200  to account for the variances in total angular displacement of the swing arm assembly  218  and ensure the blade cannot rebound back above the work-piece support surface  104 . In the embodiment shown, the first ratchet  204  is configured to release onto the first active surface  234  first. Shortly thereafter, depending on the elevation of the blade  108  against the work-piece support surface  104 , and upon continued rotation of the swing arm assembly  218 , the second ratchet  206  is configured to release onto the second active surface  238 . As best shown in  FIG. 6 , there are some angular displacements in which the first ratchet  204  is in contact with the first active surface  234 , but the second ratchet  206  is still in contact with the second ready surface  236  and, therefore, is not in position to prevent counter rotation of the swing arm assembly  218 . However, even if the second ratchet  206  does not release onto the second active surface  238 , the first ratchet  204  is already in position to engage the first stop face  240  and prevent counter rotation of the swing arm assembly  218 .  FIG. 15  shows a table that identifies angular displacements of the swing arm assembly  218  in which the first ratchet  204  is positioned to engage the first stop face  240 , but the second ratchet  206  is not yet in position to engage the second stop face  242 . 
         [0043]    In some instances, there can be angular displacements in which the second ratchet  206  begins to release towards the second active surface  238 , but the second ratchet  206  does not fully release onto the second active surface  238  before the swing arm assembly  218  rebounds and counter rotates towards the support surface  104 . This partial release of the second ratchet  206  results in the second ratchet  206  impacting only a tip portion of the second stop face  242  near the second ready surface  236 . The wear plate  250  ( FIG. 7  and  FIG. 8 ) added to the second stop face  242  ensures there is no deformation in the impact area between the second ratchet  206  and the second stop face  242 , even if the impact occurs at the tip portion of the second stop face  242 . 
         [0044]    Referring still to  FIG. 6  and  FIG. 7 , the first tip portion  210  of the first ratchet  204  has a first angled face  246 . The first stop face  240  is angled such that contact between the first stop face  240  and the first angled face  246 , even partial contact, causes the first ratchet  204  to ramp closed and fully engage the first stop face  240 . Similarly, the second tip portion  214  of the second ratchet  206  has a second angled face  248 . The second stop face  242  is angled such that contact between the second stop face  242  and the second angled face  248 , even partial contact, causes the second ratchet  206  to ramp closed and fully engage the second stop face  242 . The angles on the first and the second stop faces  240  and  242  and the first and the second ratchets  204  and  206  are also configured to absorb the remaining energy left in the swing arm assembly  218  after it has hit the stop pad  122 . The energy is then transferred thru the first and the second ratchets  204  and  206  and into the ratchet bolt  208 , which is solidly mounted into carriage  124 . 
         [0045]    Referring now to  FIGS. 9-12 , the dual ratchet system  200  is shown with the first ratchet  204  and the second ratchet  206  in a released position. The released position allows the swing arm assembly  218  to rotate back into the latched position once the condition that caused activation of the table saw safety system is cleared. In the embodiment shown, the first ratchet  204  includes a release portion  252  that extends away from the ratchet bolt  208 . The release portion  252  has an end with a contact portion  254  extending therefrom in a direction parallel with the common axis defined by the ratchet bolt  208 . The contact portion  254  has a generally planar surface that is configured to be contacted by the user to release the first ratchet  204 . 
         [0046]    The first ratchet  204  further includes an engaging portion  256  that extends from the first retention portion  212  in a direction generally parallel with the common axis and towards the second retention portion  216  of the second ratchet  206 . The engaging portion  256  contacts an abutment surface  258  of the second ratchet  204  such that rotation of the first ratchet  204  towards the released position also rotates the second ratchet  206  towards the released position. As used herein, rotation of the first ratchet  204  towards the released position means rotation of the first ratchet  204  such that the first tip portion  210  is rotated away from and out of contact with the first contact surface  222  of the swing arm assembly  218 . Accordingly, rotation of the first ratchet  204  also rotates the second tip portion  214  of the second ratchet  206  away from and out of contact with the second contact surface  224  of the swing arm assembly  218 . The arrow  260  ( FIGS. 9-11 ) indicates generally the direction of force that the user imparts on the contact portion  254  of the first ratchet  204  to rotate the first and the second ratchets  204  and  206  into the released position. 
         [0047]    In the embodiment shown in  FIGS. 10-12 , a stop  262  is formed on the carriage  124 . The stop  262  is positioned between the release portion  252  and the tip portion  210  of the first ratchet  204 . The stop  262  contacts the tip portion  210  when the first ratchet  204  has been rotated to the released position. The stop  262  prevents damage to the first and the second extension springs  226  and  228  from over rotation of the first and the second ratchets  204  and  206  during release of the swing arm assembly  218 . As best shown in  FIG. 9  and  FIG. 10 , the contact portion  254  of the first ratchet  204  is positioned generally proximate to the work-piece support surface  104  such that upon removal of the throat plate (not shown) of the table saw  202 , the user can easily access the contact portion  254  and release the swing arm assembly  218 . 
         [0048]    The configuration of the dual ratchet system  200  is configured to not only stop the swing arm assembly  218  and blade  108  from rebounding back above the work-piece support surface  104 , but also to minimize reaction time for the first ratchet  204  and the second ratchet  206  to drop and get into their stopping positions. This minimized reaction time is accomplished by allowing the swing arm assembly  218  to rotate freely (concentrically) thru the contact areas between the ratchets  204  and  206  and swing arm  218  itself, thereby eliminating any radially outward force that could throw the ratchets off, or away from the swing arm assembly  218  (due to the high speed nature of the device). Also, because of the need to minimize the area of the undercarriage compartment of the table saw, the dual ratchet system  200  ensures there is always at least one ratchet in position to prevent the blade from rebounding back above the plane of the support surface, at any blade elevation, once the safety system has been activated. 
         [0049]    Referring now to  FIG. 13  and  FIG. 14 , the table saw  302  in another embodiment incorporates a single ratchet system  300  to prevent the swing arm assembly  318  from counter rotating above the work-piece support surface. The single ratchet system  300  is similar to the dual ratchet system  200  described above except that the swing arm assembly  318  has only a single contact surface  322  and the single ratchet system  300  includes only a single ratchet  304 . Similar to the first contact surface  222  of the dual ratchet system  200 , the single contact surface  322  is disposed substantially concentrically about the pivot  320  of the swing arm assembly  313 . Similar to the first ratchet  204  of the dual ratchet system  200 , the single ratchet  304  is rotatable about a pivot  308  and has a tip portion  310  that is biased towards the single contact surface  322 . To implement the single ratchet system  300 , the angular displacement of the swing arm assembly  318  should be constant or less restricted, the blade should be allowed to go below the carriage, or the carriage should be much lower to accommodate such displacement. 
         [0050]    With reference now to  FIG. 14 , the swing arm assembly  318  has a plurality of teeth  350  disposed along a portion of the single contact surface  322 . The teeth define respective stop faces  352  that can engage the tip portion  310  of the single ratchet to prevent counter rotation of the swing arm assembly from different blade heights. The embodiment shown in  FIG. 14  illustrates the swing arm assembly  318  after rotating through a given angular displacement in a clockwise direction as viewed parallel to the rotation axis of the swing arm assembly  318 . Since the tip portion  310  is biased toward the single contact surface  322 , any counter rotation in the counter clockwise direction will be impeded by contact between the tip portion  310  and any one of the successive stop faces  352 . Although the single ratchet  304  is shown having only one tip portion configured to impede the counter rotation of the swing arm assembly, the single ratchet in other embodiments may be formed with multiple tip portions that interact with one or more of the stop faces formed in the swing arm assembly  318 . 
         [0051]    In yet further embodiments, a ratchet system includes three or more ratchets configured to interact with any number of stop faces on any number of contact surfaces on a swing arm assembly in order to prevent counter rotation of the swing arm assembly above the support surface. 
         [0052]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.