Abstract:
A switch lockout mechanism for a power tool includes a handle housing for gripping by a power tool operator. The handle housing is generally elongated in a direction corresponding to the gripping axis of a power tool operator. A switch is attached to the housing and is actuatable between an “on” position and an “off” position. A locking member is rotatably or pivotally attached to the housing. The locking member is rotatable about an axis that generally extends in the same direction as the handle housing in an elongated direction. The locking member has a first rotatable position wherein the switch is locked in its “off” position, and a second rotatable position wherein the switch is actuated to its “on” position. An actuating member allows a tool operator to move the locking member between its first and second positions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of Ser. No. 09/617,306, filed Jul. 17, 2000, now U.S. Pat. No. 6,288,350, which itself was a continuation of Ser. No. 09/134,321, filed Aug. 14, 998, now U.S. Pat. No. 6,091,035, both entitled “Lockout Mechanism for Power Tool” and both by the same inventors. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a switch lockout mechanism for a power tool, and, more particularly, to a mechanism that locks the power switch in an “off” position and requires an operator to actuate a separate lever to orient the switch to its “on” position.  
         BACKGROUND OF THE INVENTION  
         [0003]    Power tools, such as circular saws, typically have a handle molded into the body of the tool. Such a handle is grasped by the power tool operator to guide and propel the tool through the workpiece. Usually, in a circular saw there is a rear handle and a forward handle. The rear handle oftentimes resembles a pistol-type grip. The handle extends upwardly and forwardly and is separated from the body of the saw so that the operator can easily grasp an elongated handle section that fits easily within the hand of the operator. This handle section typically extends in a direction that is generally parallel to and along the line of travel of the saw. As is apparent, it is extremely desirable to have the on/off switch for the saw located so that it can be actuated by at least the index and middle fingers of the operator&#39;s hand engaging the handle. Such an arrangement allows an operator to selectively start and stop the cutting operation of the saw while having his/her hand gripping the handle.  
           [0004]    Many prior power tool constructions have a lockout mechanism also associated with the handle structure which holds the switch on the handle in a locked position and requires the operator to actuate the mechanism prior to turning the power tool to the “on” position utilizing the switch. In particular, many of these prior structures require an operator to actuate a separate button or lever with his/her thumb prior to or simultaneously with actuation of the switch by the index and middle finger of the operator&#39;s hand gripping the handle.  
           [0005]    Prior lockout mechanisms or latches typically are of two main types, a pivoting type and a sliding type. In a pivot type arrangement, the latch is pivotally mounted within the handle structure about an axis which is transverse or perpendicular to the elongated direction of the handle. In the case of a circular saw, the latch is pivotally mounted about an axis that is parallel to the axis of rotation of the saw blade. These latches operate by pivoting between an engaged position wherein the handle switch contacts the latch member and is prevented from movement to its “on” position, and a disengaged position wherein the operator is allowed to actuate the switch to the “on” position. Examples of these transverse pivotal lockout mechanisms can be found in U.S. Pat. No. 3,873,796 and U.S. Pat. No. 5,577,600. In each of these references, the latch mechanism is actuated by a button located on the top surface of the handle. In particular, they require either the pushing of the button or the rotating of the button rearwardly to allow actuation of the switch. These structures are disadvantageous for various reasons. In particular, the location of the lockout mechanism button on the top surface of the handle requires the positioning of the thumb in an awkward position. More specifically, it is natural when gripping a handle for the thumb to be along the side of the handle with the cross section of the handle received between the thumb and index finger. As is apparent, to actuate the mechanisms in these references, the thumb must first be positioned on the top of the handle, thus resulting in a less secure grip on the handle. Such loose gripping can result in misalignment of the saw during its initial cutting actions. Still further, in these prior references, for the thumb to reach the normal gripping position on the side of the handle, the thumb must slide off the button and over the side of the handle. The friction associated with the thumb passing over the top of the handle and the awkward sideward movement of the thumb can result in operator discomfort during the initial cutting action of the saw.  
           [0006]    A still further disadvantage of these references is the location of the lockout mechanism actuating button above or behind the on/off switch with respect to the longitudinal axis of the handle. More specifically, when a person typically grabs a handle, the tendency is for the thumb to be forward of the index and middle fingers. To actuate the lockout mechanism buttons of these references, the thumb must be moved rearwardly to push the actuating button, thus presenting a potential awkward position for the saw operator, and, further, possibly resulting in unnecessary reorientation of the thumb along the side of the handle to the normal gripping position.  
           [0007]    The second type of lockout mechanism includes a latch member which, when actuated, slides within the handle housing to allow actuation of the on/off switch by the operator. An example of this type of sliding latch member is disclosed in U.S. Pat. No. 5,638,945. These sliding lockout mechanisms are oftentimes relatively complicated and do not allow ergonomic positioning of the thumb during the beginning power tool operation. More specifically, the structure of the above reference, again, has the actuating switch positioned on the top surface of a handle housing and at a location that is above the actuating switch for the power tool. Thus, an operator, to operate the power tool, is required to position his or her thumb on the top of the handle instead of along the side, and to push the lockout mechanism button forward on the upper surface while pushing upward on the switch, and thereafter to slide the thumb of the hand positioned on the handle to the side of the handle to the normal comfortable gripping position. As with the pivoting latch mechanisms discussed above, this sliding-type mechanism is highly disadvantageous because it requires the operator to utilize significant effort to reposition his or her thumb in a normal gripping operation, and also has the sliding actuating switch or button located directly above the on/off switch which is typically not a normal position for a hand gripping the handle.  
           [0008]    A still further disadvantage of all the above lockout mechanisms is the structure used to bias the lockout mechanism back to its original locked position. In particular, the prior mechanisms tend to utilize leaf springs or deformable arms to supply the biasing force. These types of biasing structures are disadvantageous because the spring force of the structure increases generally from zero along a generally linear type path with further deformation of the spring or arm. In other words, as these springs become more deformed, they offer more resistance. As is apparent, this is disadvantageous to an operator because his/her thumb must increase force with further actuation of the lockout button or lever, thus again causing more uncertainty, and less stability during initial cutting operations. Some prior art structures also utilize coil springs compressed along their central axis. These coil springs compressed in this way also have a generally linear spring force curve and are disadvantageous for the same reasons as the other biasing structures.  
           [0009]    Therefore, a lockout mechanism is needed which will overcome the problems with the prior art lockout mechanisms discussed above.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an object of the present invention to provide a lockout mechanism which can be easily accessed by the thumb of a power tool operator at a location which allows the operator to obtain a normal gripping position as soon as possible after actuating the mechanism.  
           [0011]    Another object of the present invention is to provide a lockout mechanism for a power tool wherein an advantageous lockout mechanism actuating lever is accessible equally to both left-handed and right-handed power tool operators.  
           [0012]    A still further object of the present invention is to provide a lockout mechanism for a power tool, wherein the actuating lever allows an operator&#39;s thumb to slide easily and quickly to a normal gripping orientation about the power tool handle.  
           [0013]    A further object of the present invention is to provide a lockout mechanism for a power tool, wherein the actuating lever of the lockout mechanism is located at a more natural longitudinal location on the handle with respect to the on/off switch of the power tool so as to allow easier operation.  
           [0014]    Yet another object of the present invention is to provide a lockout mechanism of a power tool that is easily assembled and has a minimum number of parts.  
           [0015]    A still further object of the present invention is to provide a lockout mechanism utilizing a spring member that does not require precompressing or stretching during the assembly of the lockout mechanism.  
           [0016]    Another object of the present invention is to provide a lockout mechanism utilizing a spring member that subjects an operator&#39;s thumb to generally consistent force during operation.  
           [0017]    Accordingly, the present invention provides for a switch lockout mechanism for a power tool, including a handle housing, for gripping by a power tool operator. The handle housing is generally elongated in a direction corresponding to the gripping axis of a power tool operator&#39;s hand. A switch is disposed in the housing and is actuatable between an “on” position and an “off” position. A locking member is rotatably attached to the housing. The locking member is rotatable about an axis that generally extends in the same direction as the handle housing&#39;s elongated direction. The locking member has a first rotatable position wherein the switch is locked in its “off” position, and a second rotatable position wherein said switch is actuated to its “on” position. An actuating member is coupled to the locking member and allows the power tool operator to move the locking member between the first and second rotatable positions.  
           [0018]    The invention further includes a lockout mechanism for a power tool wherein the locking member has a third rotatable position that is in a rotational direction opposite to the direction that said locking member is rotated in from its first position to its second position. The third position also allows the switch to be actuated to its “on” position.  
           [0019]    The present invention is further directed to the structure as described above, including a biasing element for urging the locking member toward its first rotatable position from both the second and third rotatable positions.  
           [0020]    Additional objects, advantages and novel features of the invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In the accompanying drawings which form a part of this specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:  
         [0022]    [0022]FIG. 1 is a top perspective view of a circular saw with a lockout mechanism embodying the principles of this invention;  
         [0023]    [0023]FIG. 2 is an enlarged, side elevational view of the lockout mechanism shown in FIG. 1 positioned in the handle housing of the circular saw;  
         [0024]    [0024]FIG. 3 is a cross-sectional view taken generally along line  3 - 3  of FIG. 1 and showing the structure of the lockout mechanism and switch with the lockout mechanism in its locked position which prevents actuation of the power switch to its “on” position;  
         [0025]    [0025]FIG. 4 is a cross-sectional view taken generally along line  4 - 4  of FIG. 3 and showing the opposing actuating levers of the lockout mechanism, the levers in their “locked” position shown in solid lines, and the levers in the various unlocked positions shown in phantom lines and the rotation indicated by arrows;  
         [0026]    [0026]FIG. 5 is a cross-sectional view taken generally along line  5 - 5  of FIG. 3 and showing the lockout mechanism in its locked position wherein the locking fin of the lockout mechanism engages an abutment projection on the power switch;  
         [0027]    [0027]FIG. 6 is a view similar to FIG. 5 showing the lockout fin in its disengaged position and actuation of the power switch, an alternative disengaged position shown in phantom lines;  
         [0028]    [0028]FIG. 7 is an enlarged view of the area designated by the numeral “ 7 ” in FIG. 3, with parts broken away and shown in cross section to reveal details of construction, and showing the biasing coil spring of the present invention and its attachment to the lockout shaft;  
         [0029]    [0029]FIG. 8 is a cross-sectional view taken generally along line  8 - 8  of FIG. 7 and showing the deformation of the coil spring when the lockout mechanism is rotated in one particular direction to its disengaged position to allow actuation of the power switch;  
         [0030]    [0030]FIG. 9 is a view similar to FIG. 8, but showing the lockout mechanism rotated in a direction opposite to that shown in FIG. 8 with the opposite deformation of the coil spring; and  
         [0031]    [0031]FIG. 10 is a cross-sectional view taken generally along line  10 - 10  of FIG. 7, and showing the locking fin of the present invention in its engaged position so as to prevent actuation of the power switch. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    Referring to the drawings in greater detail, and initially to FIGS. 1 and 2, a power circular saw designated generally by the numeral  20  is shown. Saw  20  has a housing assembly  22  in which is disposed a motor for powering a blade  24 . Blade  24  is generally surrounded by an upper stationary guard  26  and a lower movable guard  28 . Saw  20  also has a generally planar base or shoe  30  attached to stationary guard  26 . Base  30  rests on the upper surface of the workpiece as the saw passes therethrough and is used to gauge the depth to which blade  24  cuts.  
         [0033]    Saw  20  further includes a rear trigger handle  32  and a forward brace handle  34 . The trigger handle  32  has a power switch  36  mounted therein for operation by one hand of the saw user. The other hand of the saw user is positioned on brace handle  34  which allows the user to further control the saw as it passes through a workpiece.  
         [0034]    Trigger handle  32  has a generally hollow housing  38  which is formed in a clamshell fashion by two half sections  39 . Housing  38  has a gripping portion  40  which fits within the palm of an operator during operation, and generally extends in an elongated direction along an axis  42 , as best shown in FIGS. 2 and 3. Axis  42  is generally at an angle to the plane of base  30  and slopes downwardly in a direction from a forward end of the saw toward a rearward end of the saw. Power switch  36  is received within a generally rectangular mounting section or boss  44  of each of the clamshell halves  39  of housing  38 . Switch  36  has a trigger  46  extending through an aperture  48  within housing  38  that allows actuation by the index and middle finger of an operator in a generally upwardly direction such that electrical connections can be made within switch  36  to connect the power supply of the saw with the saw motor resulting in rotation of the blade. Trigger  46  is generally internally biased toward its disengaged or “off” position. Trigger  46  generally is of a solid construction, as shown in FIG. 5, but has a pair of hollow chambers  50  formed adjacent a forward end, which are separated by a locking abutment or ridge  52 . As will be more fully explained below, the upper surface  54  of ridge  52  serves as the engaging surface with a lockout mechanism  56 , also disposed within housing  38 . As will be further explained, the hollowed portions of chamber  50  on each side of ridge  52  act as clearance areas to allow actuation of trigger  46 , as is shown in FIG. 6.  
         [0035]    Lockout mechanism  56  includes an elongated cylindrical locking shaft  58  and a biasing coil spring  60 . Lockout shaft  58 , as best shown in FIGS. 3, 5,  6  and  7 , includes a locking fin  62  positioned and integrally formed on one end, and an oversized actuating cylinder  64  formed on an opposite end. Cylinder  64  and shaft  58  are rotatably or pivotally received within the clamshell halves  39  of housing  38  via appropriate generally semicircular shaped bosses formed in each housing half  39 . In particular, the end of shaft  58  located adjacent fin  62  is received in a pivotally/rotatably supporting boss  66 . Still further, the entire actuating cylinder  64  is received in a generally semicircular boss  68 . Boss  68  almost completely surrounds cylinder  64  when the clamshell halves  39  of housing  38  are put together, thus allowing rotation of shaft  58  and cylinder  64  about an axis  70  which is generally aligned with and parallel to the axis  42  of gripping portion  40 .  
         [0036]    As best shown in FIGS. 5 and 6, locking fin  62  has a lower surface  72  which engages surface  54  or ridge  52  when trigger  46  is in its locked-out position. Still further, fin  62  is received within either of chambers  50  of trigger  46  to allow actuation of the trigger to its “on” position, as will be more fully described below.  
         [0037]    Actuating cylinder  64  has positioned on its peripheral surface  74  actuating levers  76  at diametrically opposed locations. As best shown in FIG. 4, each lever  76  extends through an aperture  78  formed in each of the clamshell halves  39  of housing  38 . Apertures  78  are generally rectangular in shape and allow movement of levers  76  therein in both generally upwardly and downwardly rotations, as indicated by the arrows and phantom line locations in FIG. 4. Therefore, rotation of either lever  76  within aperture  78  will result in rotation of shaft  58  and thus fin  62 . This rotating action results in mechanism  56  obtaining its disengaged or unlocked position, as will be more fully described below.  
         [0038]    Coil spring  60  is also received within housing  38  via generally semicircular bosses  80  formed in clamshell halves  39 , as best shown in FIGS. 3 and 7. In particular, the lower half portion  82  of spring  60  is snugly received in a generally cylindrical chamber formed by bosses  80 . However, a suitable chamber  84  is formed in housing  38  which allows the top half  86  of spring  60  to be deformed in a left or right direction with respect to axes  42  and  70 , as best shown in FIGS. 8 and 9. Upper half  86  of spring  60  is coupled to shaft  58  via circumferential protrusion  88  having a generally spherical coupling end  90 . End  90  is received within the hollow interior of spring  60 , as best shown in FIG. 7. Spherical end  90  allows a smooth rotating action of protrusion  88  with respect to spring  60  when shaft  58  is rotated so as to deform spring  60 . In addition to protrusion  88 , spring  60  has an upwardly extending leg  92  which is received in an aperture  94  formed in an end planar surface  65  of actuating cylinder  64 . Leg  92  serves as an additional attachment to shaft  58  and cylinder  64 . As is apparent, spring  60 , through its protrusion  88  and leg  92 , serves to bias fin  62  to its locked position from its disengaged/unlocked positions resulting from rotation of shaft  58  in either direction via lever  76 .  
         [0039]    With reference to FIGS. 2, 5,  7  and  10 , the lockout mechanism  56  is shown in its locked position which will prevent an operator from actuating trigger  46  upwardly to result in rotation of blade  24 . More specifically, locking fin  62  of locking shaft  58  engages ridge  52  of trigger  46 , as best shown in FIG. 5, and prevents upward movement of trigger  46 . Additionally, in this position, spring  60  is in its natural unbiased state and is not exerting any biasing pressure on shaft  58  or actuating cylinder  64 . Therefore, in this position if an operator grips portion  40  of housing  38  and attempts to actuate trigger  46  with his or her index and middle finger, such actuation will be prevented so that the saw cannot be turned to its “on” position.  
         [0040]    If an operator wishes to position trigger  46  in its depressed or “on” position, the operator must first position his or her thumb on one of the actuating levers  76  extending through the apertures  78  in housing  38 . More specifically, an operator can grip portion  40  easily within his or her hand and position the index and middle fingers on trigger  46 . Portion  40  can rest easily within the palm of the operator and the thumb of the hand gripping portion  40  can be positioned along the side surface of housing  38  forwardly of the index and middle finger in the natural and stable gripping configuration. The thumb engages the top surface of the lever  76  on the side the thumb is on, and can exert downward pressure on the lever so as to rotate cylinder  64  and shaft  58 . This rotation of shaft  58  will result in rotation of locking fin  62 , as best shown in FIG. 6, such that fin  62  is no longer positioned directly above ridge  52 . With pressure applied via the index and middle fingers of the operator to trigger  46 , the trigger can be depressed to its “on” position, and in this position fin  62  will be disposed in one of the chambers  50 , as best shown in FIG. 6. After the switch has been depressed, the lever  76  will be in a downwardly sloped orientation (shown in phantom in FIG. 4) such that the thumb can easily slide off of the actuating lever and resume a more normal position along the side of handle housing  38 .  
         [0041]    With reference to FIG. 8, during a rotation of shaft  58  from its locked to unlocked position, coil spring  60  will be deformed sidewardly. As is apparent, spring  60  will want to regain its natural state from this deformed state, and thus will tend to bias shaft  58  to its locked position. Therefore, during operation of the saw, shaft  58  will remain in an unlocked position, and spring  60  will remain in its deformed position, because fin  62  will be disposed in a one of chambers  50 , thus preventing the shaft from rotating to its locked position. However, once an operator releases trigger  46 , which is typically biased to its “off” position, ridge  52  will no longer prevent rotation of fin  62 , and thus the bias of spring  60  will return shaft  58  and fin  62  to their locked positions. Therefore, if the operator again desires to actuate trigger  46 , he or she must first push downwardly on lever  76 .  
         [0042]    As best shown in FIGS. 4, 6,  8  and  9 , an advantage of the present invention is the feature that rotation of the locking mechanism in any direction results in the locking mechanism moving from its locked to unlocked position. This allows levers on either side of housing  38 , and thus allows easy accommodation of both left-handed and right-handed saw operators. In particular, levers  76  located on either side of housing  38  provide comfortable positions for either a left-handed or right-handed saw operator&#39;s thumbs during the initial cutting operations and easy transition from the initial operations requiring actuation of mechanism  56  to a full grip about handle portion  40 . In particular, as the thumb of a user pushes down on lever  76 , the top surface of lever  76  becomes slanted downwardly and easily allows the user&#39;s thumb to slide off of lever  76  and go to its natural position. As this is done, the bias of the mechanism attempts to return lever  76  to its locked position. Still further, the rotation or orientation of shaft  58  generally along the longitudinal orientation of handle portion  40  allows flexibility, in that an operator can even, if so desired, push upwardly along one of levers  76  which will still result in the mechanism obtaining its disengaged unlocked position. A still further advantage found in the present invention is the location of actuating lever  76  ahead of trigger  46 , such as to allow the thumb of an operator to obtain a more natural position and to quickly obtain a gripping position after actuating the mechanism. In prior art mechanisms, it was oftentimes necessary to locate the structure of the lockout mechanism as close as possible to the switch in order to obtain mechanical advantages, or to utilize sliding or camming surfaces. Because of the provision of rotating shaft  58 , generally along the axis of the handle, lever  76  can be positioned at any desirable point ahead of the trigger, and all that is necessary is that access or space be available within the handle for the shaft and fin  62 . Thus, the provision of shaft  58  rotating generally along the axis of the handle allows flexibility in deciding where to put the actuating levers and biasing structures.  
         [0043]    As is apparent, mechanism  56  also provides a very easily assembled, simple lockout mechanism for a power switch. In particular, mechanism  56  can be comprised essentially of two parts. Fin  62 , shaft  58 , cylinder  64 , and levers  76  can all be molded as a one-piece part, which can be easily dropped into the relevant bosses formed in the clamshell structure of housing  38 . Coil spring  60  can easily be assembled with such part and also dropped within the relevant bosses of housing  38  during manufacture. It is also a noticeable advantage that spring  60  does not require any precompressing or pretensioning during assembly. Such precompressing or pretensioning of a spring during assembly oftentimes requires certain skill and patience when putting parts together. An additional advantage of the present invention is the sideward deformation of coil spring  60 . In particular, it has been found that deforming a coil spring not along its axis, but sidewardly, as shown in FIGS. 8 and 9, allows the spring to have a substantially constant force curve. In particular, once a threshold force is reached, the coil spring will start to deflect outwardly without offering increasing resistance. This is advantageous to the saw user when actuating the lockout mechanism, because lever  76  will not begin to rotate until the threshold force level is reached, and as the lever  76  is rotated, the force the operator is required to apply will not increase. Thus, the provision of the sideward deformation of the coil spring provides for ease and stability in actuating lockout mechanism  56 .  
         [0044]    Thus, the present lockout mechanism provides an easily assembled simple mechanism which is ergonomically advantageous to an operator and which allows the operator to easily assume the normal gripping orientation as quickly as possible after actuating the lockout mechanism.  
         [0045]    From the foregoing, it will be seen that this invention is one well-adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matters herein set forth or shown in the accompanying drawings are to be interpreted as illustrative and not in a limiting sense.