Patent Publication Number: US-7908950-B2

Title: Table saw with improved safety system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/079,836, filed Mar. 27, 2008, issuing as U.S. Pat. No. 7,640,837 on Jan. 5, 2010, which is a divisional continuation of U.S. patent application Ser. No. 09/929,235 filed Aug. 13, 2001, issued as U.S. Pat. No. 7,350,444 on Apr. 1, 2008, which in turn claimed the benefit of and priority from the following U.S. Provisional Patent Applications: Ser. No. 60/225,056, filed Aug. 14, 2000, Ser. No. 60/225,057, filed Aug. 14, 2000, Ser. No. 60/225,058, filed Aug. 14, 2000, Ser. No. 60/225,059, filed Aug. 14, 2000, Ser. No. 60/225,089, filed Aug. 14, 2000, Ser. No. 60/225,094, filed Aug. 14, 2000, Ser. No. 60/225,169, filed Aug. 14, 2000, Ser. No. 60/225,170, filed Aug. 14, 2000, Ser. No. 60/225,200, filed Aug. 14, 2000, Ser. No. 60/225,201, filed Aug. 14, 2000, Ser. No. 60/225,206, filed Aug. 14, 2000, Ser. No. 60/225,210, filed Aug. 14, 2000, Ser. No. 60/225,211, filed Aug. 14, 2000, and Ser. No. 60/225,212, filed Aug. 14, 2000. The disclosures of all these applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     The present invention relates to table saws and more particularly to a table saw with an improved safety system. 
     BACKGROUND 
     Table saws are a type of woodworking machinery used to cut workpieces of wood, plastic and other materials. Table saws include a flat surface or table with a circular saw blade extending up through a slot in the table. A user slides a workpiece on the table against and past the blade while the blade is spinning to cut the workpiece. 
     Of all the tools in a wood working shop, table saws present perhaps the greatest risk of injury. Table saws present a risk of injury to users because the spinning blade is often exposed when in use. The blade cuts very quickly and can sever a finger upon the slightest slip or misplacement. Accordingly, safety features or systems have been developed to minimize the risk of injury. Probably the most common safety feature is a blade guard that physically blocks a user from making contact with the spinning blade. In many cases, blade guards effectively reduce the risk of injury, however, there are many instances where the nature of the operations to be performed precludes using a guard that completely blocks access to the blade. There exists a need for a table saw with a safety system that significantly reduces the risk of serious injury from a user accidentally contacting the spinning blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a machine with a fast-acting safety system. 
         FIG. 2  is a schematic diagram of an exemplary safety system in the context of a machine having a circular blade. 
         FIG. 3  shows a table saw. 
         FIG. 4  is a schematic side view of one side of a table saw with an improved safety system. 
         FIG. 5  is a schematic side view of a second side of the table saw of  FIG. 4 . 
         FIG. 6  is a schematic bottom view of the table saw of  FIG. 4 . 
         FIG. 7  is a schematic perspective view of the table saw of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Machine  10  may be any of a variety of different table saws. Machine  10  includes an operative structure  12  having a cutting tool  14  and a motor assembly  16  adapted to drive the cutting tool. Machine  10  also includes a safety system  18  configured to minimize the potential of a serious injury to a person using machine  10 . Safety system  18  is adapted to detect the occurrence of one or more dangerous conditions during use of machine  10 . If such a dangerous condition is detected, safety system  18  is adapted to engage operative structure  12  to limit any injury to the user caused by the dangerous condition. 
     Machine  10  also includes a suitable power source  20  to provide power to operative structure  12  and safety system  18 . Power source  20  may be an external power source such as line current, or an internal power source such as a battery. Alternatively, power source  20  may include a combination of both external and internal power sources. Furthermore, power source  20  may include two or more separate power sources, each adapted to power different portions of machine  10 . 
     It will be appreciated that operative structure  12  may take any one of many different forms, depending on the type of machine  10 . For example, operative structure  12  may include a stationary housing configured to support motor assembly  16  in driving engagement with cutting tool  14 . Alternatively, operative structure  12  may include a movable structure configured to carry cutting tool  14  between multiple operating positions. As a further alternative, operative structure  12  may include one or more transport mechanisms adapted to convey a workpiece toward and/or away from cutting tool  14 . 
     Motor assembly  16  includes one or more motors adapted to drive cutting tool  14 . The motors may be either directly or indirectly coupled to the cutting tool, and may also be adapted to drive workpiece transport mechanisms. Cutting tool  14  typically includes one or more blades or other suitable cutting implements that are adapted to cut or remove portions from the workpieces. The particular form of cutting tool  14  will vary depending upon the various embodiments of machine  10 . For example, in table saws, miter saws, circular saws and radial arm saws, cutting tool  14  will typically include one or more circular rotating blades having a plurality of teeth disposed along the perimetrical edge of the blade. For a jointer or planer, the cutting tool typically includes a plurality of radially spaced-apart blades. For a band saw, the cutting tool includes an elongate, circuitous tooth-edged band. 
     Safety system  18  includes a detection subsystem  22 , a reaction subsystem  24  and a control subsystem  26 . Control subsystem  26  may be adapted to receive inputs from a variety of sources including detection subsystem  22 , reaction subsystem  24 , operative structure  12  and motor assembly  16 . The control subsystem may also include one or more sensors adapted to monitor selected parameters of machine  10 . In addition, control subsystem  26  typically includes one or more instruments operable by a user to control the machine. The control subsystem is configured to control machine  10  in response to the inputs it receives. 
     Detection subsystem  22  is configured to detect one or more dangerous, or triggering, conditions during use of machine  10 . For example, the detection subsystem may be configured to detect that a portion of the user&#39;s body is dangerously close to, or in contact with, a portion of cutting tool  14 . As another example, the detection subsystem may be configured to detect the rapid movement of a workpiece due to kickback by the cutting tool, as is described in U.S. Provisional Patent Application Ser. No. 60/182,866, the disclosure of which is herein incorporated by reference. In some embodiments, detection subsystem  22  may inform control subsystem  26  of the dangerous condition, which then activates reaction subsystem  24 . In other embodiments, the detection subsystem may be adapted to activate the reaction subsystem directly. 
     Once activated in response to a dangerous condition, reaction subsystem  24  is configured to engage operative structure  12  quickly to prevent serious injury to the user. It will be appreciated that the particular action to be taken by reaction subsystem  24  will vary depending on the type of machine  10  and/or the dangerous condition that is detected. For example, reaction subsystem  24  may be configured to do one or more of the following: stop the movement of cutting tool  14 , disconnect motor assembly  16  from power source  20 , place a barrier between the cutting tool and the user, or retract the cutting tool from its operating position, etc. The reaction subsystem may be configured to take a combination of steps to protect the user from serious injury. Placement of a barrier between the cutting tool and teeth is described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,206, entitled “Cutting Tool Safety System,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference. Retraction of the cutting tool from its operating position is described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,089, entitled “Retraction System For Use In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference. 
     The configuration of reaction subsystem  24  typically will vary depending on which action(s) are taken. In the exemplary embodiment depicted in  FIG. 1 , reaction subsystem  24  is configured to stop the movement of cutting tool  14  and includes a brake mechanism  28 , a biasing mechanism  30 , a restraining mechanism  32 , and a release mechanism  34 . Brake mechanism  28  is adapted to engage operative structure  12  under the urging of biasing mechanism  30 . During normal operation of machine  10 , restraining mechanism  32  holds the brake mechanism out of engagement with the operative structure. However, upon receipt of an activation signal by reaction subsystem  24 , the brake mechanism is released from the restraining mechanism by release mechanism  34 , whereupon, the brake mechanism quickly engages at least a portion of the operative structure to bring the cutting tool to a stop. 
     It will be appreciated by those of skill in the art that the exemplary embodiment depicted in  FIG. 1  and described above may be implemented in a variety of ways depending on the type and configuration of operative structure  12 . Turning attention to  FIG. 2 , one example of the many possible implementations of safety system  18  is shown. System  18  is configured to engage an operative structure having a cutting tool in the form of a circular blade  40  mounted on a rotating shaft or arbor  42 . Blade  40  includes a plurality of cutting teeth (not shown) disposed around the outer edge of the blade. As described in more detail below, braking mechanism  28  is adapted to engage the teeth of blade  40  and stop the rotation of the blade. U.S. Provisional Patent Application Ser. No. 60/225,210, entitled “Translation Stop For Use In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference, describes other systems for stopping the movement of the cutting tool. U.S. Provisional Patent Application Ser. No. 60/225,057, entitled “Miter Saw With Improved Safety System,” filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is herein incorporated by reference, describes safety system  18  in the context of particular types of machines  10 . 
     In the exemplary implementation, detection subsystem  22  is adapted to detect the dangerous condition of the user coming into contact with blade  40 . The detection subsystem includes a sensor assembly, such as contact detection plates  44  and  46 , capacitively coupled to blade  40  to detect any contact between the user&#39;s body and the blade. Typically, the blade, or some larger portion of cutting tool  14  is electrically isolated from the remainder of machine  10 . Alternatively, detection subsystem  22  may include a different sensor assembly configured to detect contact in other ways, such as optically, resistively, etc. In any event, the detection subsystem is adapted to transmit a signal to control subsystem  26  when contact between the user and the blade is detected. Various exemplary embodiments and implementations of detection subsystem  22  are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,200, entitled “Contact Detection System For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,211, entitled “Apparatus And Method For Detecting Dangerous Conditions In Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference. 
     Control subsystem  26  includes one or more instruments  48  that are operable by a user to control the motion of blade  40 . Instruments  48  may include start/stop switches, speed controls, direction controls, etc. Control subsystem  26  also includes a logic controller  50  connected to receive the user&#39;s inputs via instruments  48 . Logic controller  50  is also connected to receive a contact detection signal from detection subsystem  22 . Further, the logic controller may be configured to receive inputs from other sources (not shown) such as blade motion sensors, workpiece sensors, etc. In any event, the logic controller is configured to control operative structure  12  in response to the user&#39;s inputs through instruments  48 . However, upon receipt of a contact detection signal from detection subsystem  22 , the logic controller overrides the control inputs from the user and activates reaction subsystem  24  to stop the motion of the blade. Various exemplary embodiments and implementations of control subsystem  26  are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,059, entitled “Logic Control For Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,094, entitled “Motion Detecting System For Use In Safety System For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference. 
     In the exemplary implementation, brake mechanism  28  includes a pawl  60  mounted adjacent the edge of blade  40  and selectively moveable to engage and grip the teeth of the blade. Pawl  60  may be constructed of any suitable material adapted to engage and stop the blade. As one example, the pawl may be constructed of a relatively high strength thermoplastic material such as polycarbonate, ultrahigh molecular weight polyethylene (UHMW) or Acrylonitrile Butadiene Styrene (ABS), etc., or a metal such as aluminum, etc. It will be appreciated that the construction of pawl  60  will vary depending on the configuration of blade  40 . In any event, the pawl is urged into the blade by a biasing mechanism in the form of a spring  66 . In the illustrative embodiment shown in  FIG. 2 , pawl  60  is pivoted into the teeth of blade  40 . It should be understood that sliding or rotary movement of pawl  60  might also be used. The spring is adapted to urge pawl  60  into the teeth of the blade with sufficient force to grip the blade and quickly bring it to a stop. 
     The pawl is held away from the edge of the blade by a restraining mechanism the form of a fusible member  70 . The fusible member is constructed of a suitable material adapted to restrain the pawl against the bias of spring  66 , and also adapted to melt under a determined electrical current density. Examples of suitable materials for fusible member  70  include NiChrome wire, stainless steel wire, etc. The fusible member is connected between the pawl and a contact mount  72 . Preferably, fusible member  70  holds the pawl relatively close to the edge of the blade to reduce the distance the pawl must travel to engage the blade. Positioning the pawl relatively close to the edge of the blade reduces the time required for the pawl to engage and stop the blade. Typically, the pawl is held approximately 1/32-inch to ¼-inch from the edge of the blade by fusible member  70 , however other pawl-to-blade spacings may also be used within the scope of the invention. 
     Pawl  60  is released from its unactuated, or cocked, position to engage blade  40  by a release mechanism in the form of a firing subsystem  76 . The firing subsystem is coupled to contact mount  72 , and is configured to melt fusible member  70  by passing a surge of electrical current through the fusible member. Firing subsystem  76  is coupled to logic controller  50  and activated by a signal from the logic controller. When the logic controller receives a contact detection signal from detection subsystem  22 , the logic controller sends an activation signal to firing subsystem  76 , which melts fusible member  70 , thereby releasing the pawl to stop the blade. Various exemplary embodiments and implementations of reaction subsystem  24  are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,056, entitled “Firing Subsystem For Use In Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC, U.S. Provisional Patent Application Ser. No. 60/225,170, entitled “Spring-Biased Brake Mechanism for Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,169, entitled “Brake Mechanism For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference. 
     It will be appreciated that activation of the brake mechanism will require the replacement of one or more portions of safety system  18 . For example, pawl  60  and fusible member  70  typically must be replaced before the safety system is ready to be used again. Thus, it may be desirable to construct one or more portions of safety system  18  in a cartridge that can be easily replaced. For example, in the exemplary implementation depicted in  FIG. 2 , safety system  18  includes a replaceable cartridge  80  having a housing  82 . Pawl  60 , spring  66 , fusible member  70  and contact mount  72  are all mounted within housing  82 . Alternatively, other portions of safety system  18  may be mounted within the housing. In any event, after the reaction system has been activated, the safety system can be reset by replacing cartridge  80 . The portions of safety system  18  not mounted within the cartridge may be replaced separately or reused as appropriate. Various exemplary embodiments and implementations of a safety system using a replaceable cartridge are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,201, entitled “Replaceable Brake Mechanism For Power Equipment,” filed Aug. 14, 2000 by SD3, LLC, and U.S. Provisional Patent Application Ser. No. 60/225,212, entitled “Brake Positioning System,” filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are herein incorporated by reference. 
     While one particular implementation of safety system  18  has been described, it will be appreciated that many variations and modifications are possible within the scope of the invention. Many such variations and modifications are described in U.S. Provisional Patent Application Ser. Nos. 60/182,866 and 60/157,340, the disclosures of which are herein incorporated by reference. 
       FIG. 3  shows one type of a table saw  1400 , often called a contractor&#39;s saw. It includes a table  1401  through which a blade  1402  extends from beneath the table. The table and blade are supported by a housing  1403  and legs  1404 . Housing  1403  encloses the mechanics that support, position and drive the blade. A motor to drive the blade can be positioned in or outside of the housing. A switch  1405  turns the saw on and off, causing blade  1402  to spin. Handles, such as handle  1406 , are used to adjust the position of the blade relative to the table, for example, how far the blade extends above the table or how the blade tilts relative to the top of the table. Of course, table saws take many different configurations, from large saws sized for industrial use to small saws that can be placed on a bench top or counter, and table saws come with various types of tables and housings. Essentially, a table saw is a saw with a flat workspace or “table” and a cutting blade projecting up through the table. A user places a workpiece on the table and slides it into the blade to cut the workpiece. 
       FIGS. 4 and 5  show side elevation views of the internal mechanism one type of table saw configured with a safety system as described above.  FIG. 6  shows a bottom view of the same saw, and  FIG. 7  shows a perspective view. 
     In the saw, blade  1402  is mounted on an arbor  1407  by a nut (not shown). The arbor spins the blade in the direction of arrow  1409 . Table  1401  (not shown in  FIG. 5 ), which defines the work surface for the table saw, is adjacent the blade and the blade extends above the table. 
     An arbor block  1410  supports arbor  1407  and holds the arbor in bearings to allow the arbor to rotate. The arbor is connected to a motor (not shown), such as by belt extending around a pulley on the arbor and a pulley on the motor&#39;s drive shaft, and the motor drives or spins the arbor, as is known in the art. The motor may be mounted on motor plate  1411  shown in  FIG. 5 . 
     Arbor block  1410  is also mounted on a pin  1412  and may pivot around that pin. Pin  1412 , in turn, is mounted to a support member  1413  that, along with another support member  1414 , comprise at least part of the supporting frame of the table saw. The supporting frame is connected to the housing, legs, and/or table. 
     Blade  1402  is configured to pivot up and down so that a user can position the blade to extend above the table as needed. The blade pivots around pin  1412 . A user may pivot the blade to adjust its position by turning a shaft  1415  on which a worm gear  1416  is mounted. The worm gear is mounted on the shaft so that it turns with the shaft, but so that it may slide on the shaft when necessary, as explained below. Worm gear  1416  is mounted on shaft  1415  like a collar, with the shaft extending through a longitudinal hole in the worm gear. The worm gear is held in place during normal operation of the saw by a spring clip  1417 , which is positioned in a notch or channel on the worm gear and which also engages a detent or groove on shaft  1415  to hold the worm gear in place. The worm gear engages a rack or segment gear  1418  that is connected to or part of arbor block  1410 . Thus, when a user turns shaft  1415 , such as by turning a knob or handle attached to the shaft, like handle  1406  in  FIG. 3 , worm gear  1416  moves rack  1418  and the blade up and down, depending on the direction that the worm gear is turned. 
     Most table saws are also configured to allow blade  1402  to tilt from side to side relative to table  1401 . That is accomplished by a system similar to shaft  1415 , worm gear  1416 , and rack  1418 , but oriented generally perpendicularly to the plane of the blade. Support members  1413  and  1414  may be used as part of that system; for example, support member  1414  may comprise a segment gear or rack like rack  1418 . The support members include arcuate projections  1440  that fit into arcuate grooves or slides in mounting blocks (not shown) to allow the support members to pivot. The mounting blocks are secured to the table of the saw. 
     A brake cartridge  1419  is mounted in the saw adjacent blade  1402 . (The cartridge is shown open in  FIGS. 4 and 6 , and shown with a cover in  FIG. 7 .) The cartridge may be configured as described above and as described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,201, titled “Replaceable Brake Mechanism for Power Equipment,” and U.S. Provisional Patent Application Ser. No. 60/225,212, titled “Brake Positioning System,” both filed Aug. 14, 2000. The brake cartridge includes a pawl  1420  biased toward blade  1402  by a spring  1421 . Various pawls are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,169, titled “Brake Mechanism for Power Equipment,” filed Aug. 14, 2000. The pawl is held away from blade  1402  by a release mechanism  1422 , as described generally above and as described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,170, titled “Spring-Biased Brake Mechanism for Power Equipment,” filed Aug. 14, 2000. The cartridge is configured so that the release mechanism releases the pawl into the blade upon the receipt of a detection signal, as explained generally above and as explained in more detail in U.S. Provisional Patent Application Ser. No. 60/225,056, titled “Firing Subsystem for use in a Fast-Acting Safety System,” filed Aug. 14, 2000. The detection signal that causes the release of the pawl, and the system or systems to generate that signal, are explained in more detail in U.S. Provisional Patent Application Ser. No. 60/225,200, titled “Contact Detection System for Power Equipment,” and U.S. Provisional Patent Application Ser. No. 60/225,211, titled “Apparatus and Method for Detecting Dangerous Conditions in Power Equipment,” both filed Aug. 14, 2000. Electronics that form at least part of the system to detect contact between a user and the blade, and then to signal the release of the brake pawl, are enclosed in housing  1423  mounted on arbor block  1410 . The housing should be closed to prevent sawdust and other particles from entering the housing and potentially damaging the electronics housed therein. 
     When the pawl is released, the pawl quickly hits the teeth of the blade. The teeth bite into the pawl, stopping the blade. The saw described above can stop the blade in 2-10 milliseconds, thereby reducing the extent of injury caused by accidental contact with the blade. 
     Brake cartridge  1419  is positioned on the blade&#39;s pivot axis so that pawl  1420  can move around pin  1412 . Thus, when pawl  1420  hits the blade, the angular momentum of the blade is transferred to the arbor, and the blade, arbor, rack and cartridge tend to retract or move down in the direction of arrow  1424 . The blade will move down to the extent permitted by the contact between rack  1418  and worm gear  1416 . If the worm gear is fixed in place, the downward movement of the blade may strip teeth on the rack and/or worm gear, and may prevent the blade from moving down as far as desired. In the embodiment shown in  FIGS. 4 and 5 , the worm gear is adapted to snap free and move on shaft  1415  when the blade hits the pawl. 
     When the blade hits the pawl, the force of the impact causes spring clip  1417  to snap loose, allowing the worm gear to slide down shaft  1415  toward an end  1425  of the shaft. The spring clip snaps loose because the rack is urged down when the blade is stopped, and the rack contacts the worm gear and forces the worm gear to move. The force of the rack against the worm gear causes the spring clip to snap loose. The worm gear then moves into a receptacle  1426  formed around the end of the shaft. The worm gear is put back in place by simply raising arbor  1410  up, or by rotating shaft  1415  to pivot the blade up, which causes the rack to move up and the worm gear to slide back along shaft  1415  until the spring clip snaps into place on the shaft. 
     The table saw shown in  FIGS. 4 and 5  also includes a support  1427  configured with a seat or region  1428  in which is placed an impact-absorbing material  1429  (shown in  FIGS. 4 and 5 , but not in  FIG. 7 ). The support is positioned under the arbor and arbor block so that when the blade retracts, the arbor block strikes impact-absorbing material  1429 . Support  1427  and impact-absorbing material  1429  act as a barrier to stop the downward movement of the blade. The support is positioned so that blade  1402  may retract a sufficient distance. The impact-absorbing material can be any one of a number of cushioning materials, such as rubber, dense foam, plastic, etc. Alternatively, impact-absorbing material  1429  may be attached to the undersurface of the arbor block instead of on support  1427 . Additionally, support  1427  may take many forms. In fact, shaft  1415  may be configured and positioned so that it provides a surface to stop the downward movement of the blade. 
     In the construction described above, the angular momentum of the blade causes the blade, rack and cartridge to all pivot down when the pawl strikes the blade. Thus, the angular momentum of the blade causes the retraction. Blade  1402  is permitted to move downward a sufficient distant so that the blade is completely retracted. The ability of the blade to retract minimizes any injury from accidental contact with the blade and works simultaneously with the braking system described above. The ability of the blade to retract is in part because the point around which the blade pivots relative to the direction that the blade spins may be described as on what could be thought of as the “back side” of existing table saws. The brake cartridge is also mounted on this “back side,” and may be mounted to pivot with the blade as described above, or may be fixedly mounted to the frame of the saw so it does not pivot with the blade and so that the blade climbs down the pawl when the pawl engages the blade. Other configurations to cause the blade to retract, which can be used alone or in conjunction with the embodiment described herein, are described in U.S. Provisional Patent Application Ser. No. 60/225,089, titled “Retraction System for Use in Power Equipment,” filed Aug. 14, 2000. 
       FIG. 5  also shows a splitter  1430  that extends above table  1401  behind blade  1402  to prevent kickback. A blade guard may also substantially enclose blade  1402  and prevent accidental contact with the blade. 
     Table saws like those described above can include logic controls to test that the saw and its safety system are functioning properly. For example, the logic controls can verify that the brake pawl is in place adjacent the blade, and that the firing system is ready to release the pawl into the blade upon the detection of accidental contact between the blade and a user. The saws also may include various signals, lights, etc., to inform a user of the status of the saw and the features in operation. Self tests, logic controls and user interfaces are described in more detail in U.S. Provisional Patent Application Ser. No. 60/225,059, titled “Logic Control for Fast Acting Safety System,” and U.S. Provisional Patent Application Ser. No. 60/225,094, titled “Motion Detecting System for Use in Safety System for Power Equipment,” both filed Aug. 14, 2000. 
     The table saws described above are configured to absorb the impact of a brake pawl stopping a blade. However, on some table saws, small saws for example, it may be desirable to construct the saw knowing that if the brake pawl stops the blade, the saw would be damaged, perhaps by bending the arbor or other support structure. In fact, the saw may be constructed specifically to absorb the energy of stopping the blade by destroying or damaging part of the saw. Such saws may be thought of as disposable to the extent they are intended to be used only until an accident occurs requiring the brake pawl to stop the blade. A disposable saw may be less expensive to manufacture, and reduced injury to a user in the event of an accident would more than justify the entire cost of the saw. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to power equipment, and specifically to table saws. 
     It is believed that the disclosure set forth above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. No single feature, function, element or property of the disclosed embodiments is essential to all of the disclosed inventions. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. 
     It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.