Lockout mechanism for power tool

Information

  • Patent Grant
  • 6512188
  • Patent Number
    6,512,188
  • Date Filed
    Friday, September 7, 2001
    23 years ago
  • Date Issued
    Tuesday, January 28, 2003
    21 years ago
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




STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT




Not applicable.




FIELD OF INVENTION




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




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'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.




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's hand gripping the handle.




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.




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.




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.




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.




Therefore, a lockout mechanism is needed which will overcome the problems with the prior art lockout mechanisms discussed above.




SUMMARY OF THE INVENTION




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.




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.




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's thumb to slide easily and quickly to a normal gripping orientation about the power tool handle.




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.




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.




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.




Another object of the present invention is to provide a lockout mechanism utilizing a spring member that subjects an operator's thumb to generally consistent force during operation.




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'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'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.




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.




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.




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




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:





FIG. 1

is a top perspective view of a circular saw with a lockout mechanism embodying the principles of this invention;





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;





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;





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;





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;





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;





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;





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;





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





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




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.




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.




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


.




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


.




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.




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.




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


.




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.




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


.




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


.




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'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'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.




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


.




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.




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.



Claims
  • 1. A power tool comprising:a housing having a motor disposed therein, the housing including a handle with a gripping portion for gripping by a power tool operator and at least two apertures, the apertures being spaced apart from one another and being located adjacent the gripping portion; a switch coupled with the housing and movable between an “off” position and an “on” position for operating the motor; a locking member at least partially received in the housing and movable between a first position, wherein the locking member prevents the switch from being moved from the “off” position, and a second position, wherein the locking member permits the switch to be moved to the “on” position by the power tool operator; and wherein a first portion of the locking member is accessible to the power tool operator through one of the apertures, wherein a second portion of the locking member is accessible to the power tool operator through another of the apertures, and whereby the power tool operator can operate the locking member by engaging either of the first and second portions of the locking member and thereby move the locking member to the second position to permit activation of the power tool.
  • 2. A power tool with an ambidextrous switch lockout mechanism, the tool comprising:a housing having a motor disposed therein and a handle for gripping by a power tool operator, the handle having first, second and third apertures formed therein; a switch at least partially received in the first aperture of the handle and movable by a finger of the power tool operator when the handle is gripped by the operator between an “off” position and an “on” position; a locking member at least partially received in the handle and movable between a rest position, wherein the locking member prevents the switch from being moved from the “off” position, and a tension position, wherein the locking member permits the switch to be moved to the “on” position by the power tool operator; wherein a first portion of the locking member extends outwardly from within the handle through the second aperture in the handle and is engagable by a thumb of the power tool operator when the handle is gripped by a right hand of the operator; and wherein a second portion of the locking member extends outwardly from within the handle through the third aperture in the handle and is engagable by a thumb of the power tool operator when the handle is gripped by a left hand of the operator, whereby the operator can move the locking member to the tension position with their thumb whether they operate the power tool with their right hand gripping the handle or their left hand.
CROSS REFERENCE TO RELATED APPLICATIONS

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, 1998, now U.S. Pat. No. 6,091,035, both entitled “Lockout Mechanism for Power Tool” and both by the same inventors.

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Continuations (2)
Number Date Country
Parent 09/617306 Jul 2000 US
Child 09/949167 US
Parent 09/134321 Aug 1998 US
Child 09/617306 US