Abstract:
An automatic braking system for a pivoting power tool includes a cutting assembly, a cutting arm supporting the cutting assembly, a hinge supporting the cutting arm through a pivot, a primary braking system operably connected to the cutting assembly, a safety circuit configured to sense an unsafe condition and, in response to sensing the unsafe condition, control the primary braking system to oppose rotation of a blade supported by the cutting assembly, and a damper system operably connected to the cutting arm, the damper system configured to oppose rotation of the cutting arm when the primary braking system is controlled to oppose rotation of the blade.

Description:
This application claims the benefit of U.S. Provisional Application No. 61/781,749 filed Mar. 14, 2013, the entirety of which is incorporated herein by reference. 
    
    
     FIELD 
     This disclosure relates to machines such as miter saws which include protective systems configured to rapidly stop rotational movement of a shaping device. 
     BACKGROUND 
     A number of power tools have been produced to facilitate forming a work piece into a desired shape. One such power tool is a miter saw. Miter saws present a safety concern because the saw blade of the miter 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. A number of different safety systems have been developed for miter 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, a user&#39;s finger is nonetheless in proximity to the moving blade, particularly when attempting to secure a work piece as the miter saw is used to shape the work piece. 
     Miter saw safety systems have 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. In general, upon detection of a person in the vicinity of the blade, a signal is processed and sent to a brake mechanism to stop blade rotation within a short period of time. One such system is disclosed in U.S. Patent Publication No. 2011/0048197. In other systems, a mechanical or electrical brake is used. In all of these systems, however, the short stopping time of the blade generates a large angular momentum that will either swing the head up or down (depending on blade or motor rotation direction for miter saws) with a high force which is destructive to the structure of the tool. In addition to posing a danger to the tool, the high angular momentum forces pose an additional injury risk to the user. 
     What is needed therefore is a simple and reliable configuration which reduces the potential for transferring high angular momentum forces to a tool thereby causing movement of the tool. 
     SUMMARY 
     In one embodiment, an automatic braking system for a pivoting power tool includes a cutting assembly, a cutting arm supporting the cutting assembly, a hinge supporting the cutting arm through a pivot, a primary braking system operably connected to the cutting assembly, a safety circuit configured to sense an unsafe condition and, in response to sensing the unsafe condition, control the primary braking system to oppose rotation of a blade supported by the cutting assembly, and a damper system operably connected to the cutting arm, the damper system configured to oppose rotation of the cutting arm when the primary braking system is controlled to oppose rotation of the blade. 
     In another embodiment, a method of operating an automatic braking system for a pivoting power tool includes supporting a cutting assembly with a cutting arm, sensing an unsafe condition using a safety circuit, controlling with the safety circuit a primary braking system to oppose rotation of a blade supported by the cutting assembly in response to sensing the unsafe condition, and opposing with a damper system rotation of the cutting arm about a pivot when the primary braking system is controlled to oppose rotation of the blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a front right perspective view of a miter saw assembly; 
         FIG. 2  depicts a schematic diagram of the power transfer train between the motor and the blade including a clutch and a primary braking system; 
         FIG. 3  depicts a simplified plan view of the right side of the power transfer train; 
         FIG. 4  depicts a simplified left side plan view of a hydraulic torsional dampener located at the pivot between the cutter arm and bevel arm; and 
         FIG. 5  depicts a simplified left side plan view of a hydraulic linear dampener extending between the cutter arm and bevel arm. 
     
    
    
     DESCRIPTION 
     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 skilled in the art to which this disclosure pertains. 
     Referring now to  FIG. 1 , there is shown a miter saw assembly  100 . The miter saw assembly  100  includes a base  102  and a turntable  104  that is rotatable on the base  102 . The miter saw assembly  100  further includes a cutting head  106  mounted on a cutting head support assembly  108 . The cutting head  106  (which may also be referred to herein as a “cutting assembly”) includes a motor  110  that is operable to rotate a circular saw blade  112 . The cutting head support assembly  108  is attached to the turntable  104  and configured to support the cutting head  106  such that the cutting head  106  may move over the turntable  104  and perform cutting operations on a work piece supported by the turntable  104 . A rip fence  114  attached to the base  102  may be used to align a work piece thereon. 
     The cutting head support assembly  108  includes a bevel arm  116 , a cutting arm  118 , a first pivot mechanism  120 , and a second pivot mechanism  122 . The bevel arm  116  (also referred to herein as a “bevel post”) provides a bevel support structure for the miter saw assembly  100 . The bevel arm  116  is pivotally attached to the turntable  104  by the first pivot mechanism  120 . The first pivot mechanism  120  includes a hinge arrangement that enables the bevel arm  116  of the support assembly  108  to pivot with respect to the turntable  104  during a setup procedure. In particular, this arrangement is configured to enable the bevel arm  116  to pivot from a vertical position (as shown in  FIGS. 1-2 ) to an angle of 45° (not shown) or more in the leftward direction prior to a cutting operation. This pivoting allows the blade  112  of the cutting assembly  106  to approach the table  104  from a bevel angle and perform angled cuts on a work piece supported on the table  104 , as is well known in the art. 
     The cutting arm  118  of the support assembly  108  provides a support for the cutting assembly  106 . The cutting arm  118  is pivotably connected to the bevel arm  116  via the pivot mechanism  122 . The pivot mechanism  122  enables pivoting movement of the cutting assembly  106  in relation to the turntable  104  and the base  102  during a cutting operation. This pivoting allows the blade  112  of the cutting assembly  106  to move toward and away from the horizontal turntable  104  to perform a cutting operation. In some embodiments, the cutting arm may be configured to alternatively or additionally allow movement of the cutting assembly along the cutting arm. 
     The cutting assembly  106  includes a handle  126  connected to the cutting arm  118  to facilitate movement of the cutting assembly  106  in relation to the turntable  104 . The handle  126  is designed and dimensioned to be grasped by a human hand when performing a cutting operation. This allows the user to easily pivot the cutting assembly  106 . A switch (not shown) may be provided on the handle  126  to allow the user to easily energize and de-energize the electric motor  110  during a cutting operation. A blade guard  128  covers the top portion of the circular saw blade  112 . A lower blade guard  124 , shown in shadow for purpose of clarity, is rotatably mounted to the cutting head assembly  106 . The lower blade guard  124  is configured to rotate in a clockwise direction with respect to the cutting head assembly  106  when the cutting head assembly  106  is pivoted toward the turntable  104  thereby exposing the circular saw blade  112 . 
     The connection between the motor  110  and the saw blade  112  is further described with reference to  FIGS. 2 and 3 . The motor  110  has an output shaft  130  which drives a pinion gear  132 . The pinion gear  132  is operably connected to a gear  134  that drives a clutch assembly  136 . The output of the clutch assembly  136  is operably engaged with a primary braking assembly  138 . The primary braking assembly  138  in one embodiment is the braking assembly described in U.S. Patent Application Publication No. 2011/0048197, the entire contents of which are herein incorporated by reference. 
     The primary braking assembly  138  drives a pulley  140  which is operably connected to a pulley  142  by a belt  144 . In some embodiments, the pulley system is replaced by a geared drive system. The pulley  142  is operably connected to a gear  146  which drives a gear  148  operable connected to a drive shaft  150  on which the blade  112  is mounted. The motor  110 , along with the gears and pulleys, are configured such that the blade  112  rotates downwardly at a location farthest from the bevel arm  116 . 
       FIG. 2  further shows a safety circuit  152  that is operably connected to the clutch assembly  136 , the primary braking assembly  138 , and a blade sensor  154  (located adjacent to the drive shaft  150  in this embodiment). The safety circuit  152  includes a processor  156  and a memory  158 . Program instructions within the memory  158  are executed by the processor  156  to perform at least some of the actions ascribed to the safety circuit herein. The safety circuit  152  detects when a user too closely approaches or touches the blade  112  and issues a signal which disengages the clutch  136  and activates the primary braking assembly  138  to rapidly stop as discussed in more detail in the &#39;197 Publication. 
     The safety circuit  152  is further connected to a dampener which in this embodiment is a hydraulic torsional dampener  160  (see  FIG. 4 ). The torsional dampener  160  is located at the pivot  122  between the cutting arm  118  and the bevel arm  116  and is activated at about the same time as the primary braking assembly  138 . Accordingly, as the rotation of the blade  112  in the direction of the arrow  164  (see  FIG. 4 ) is terminated by the primary braking assembly  138 , a large angular momentum in the direction of the arrow  166  is generated which forces the cutting arm  118  to pivot about the pivot  122  in the direction of the arrow  166 . The hydraulic torsional dampener  160 , however, counters the large angular momentum, thereby reducing any movement of the cutting arm  118  in the direction of the arrow  166 . The active dampening system which includes the dampener  160  is thus configured to reduce the destructive force that could transfer to the structure of the tool or to the hand of the end user. This dampening system makes the braking of the blade in a short time possible for miter saws without undesired “kickback” of the cutting arm  118 . 
     In some embodiments, the torsional dampener is replaced with a linear dampener.  FIG. 5  depicts a linear dampener  170  with a first end  172  pivotably attached to the bevel arm  116  and a second end  174  positioned within a slot  176  in the cutting arm  118 . Accordingly, as the rotation of the blade  112  in the direction of the arrow is terminated by the primary braking assembly  138  in the manner described above, a large angular momentum in the direction of the arrow  180  is generated which forces the cutting arm  118  to pivot about the pivot  122  in the direction of the arrow  180 . The hydraulic linear dampener  170 , however, is activated and at the same time the end portion  174  is locked within the slot  176  by the safety circuit  152 . The linear dampener  170  thus counters the large angular momentum, thereby reducing any movement of the cutting arm  118  in the direction of the arrow  180 . 
     The incorporation of a dampener such as the hydraulic torsional dampener  160  or the linear dampener  170  reduces output force to the structure of a power tool to enable for braking within a predetermined time to mitigate potential injuries. The dampening system enables control of a power tool such as miter saw head assemblies. 
     The described system in different embodiments is configured as a torsional or linear form and can be configured between the bevel arm and cutting arm (as shown in above figures or in similar configurations). 
     The described dampening system in some embodiments is activated using the angular acceleration of the cutting arm through mechanisms similar to that of an automotive seatbelt or other mechanical means. In other embodiments, a dampening system is activated using an electromechanical system. In some embodiments, activation of the dampening system is accomplished by locking an end of the dampener which is free to move during normal saw operation. 
     The above described system in some embodiments is used with a mechanical brake similar to that described in the &#39;197 Application and is sized accordingly based on moment inertia of the blade and other rotation components the blade is connected to. 
     In some embodiments, the primary brake is a mechanical brake such as an aluminum block that makes contact with the blade teeth, or any friction material that makes contact with the blade walls, output shafts, or any drive mechanism. In some embodiments, the primary brake is an electronic brake generated within the motor assembly. 
     In different embodiments, the output force reduction occurs immediately after flesh detection or after flesh detection plus a predetermined time. 
     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.