Abstract:
As system for clamping an rotary tool accessory disc or blade to an output shaft of a rotary tool comprising a cam clamping mechanism and a clutch assembly wherein the cam clamping mechanism comprises: a head element threadably engageable with the output shaft at a location axially outward of the accessory disc; a cam rotatably connected to the head element and rotatable between a clamped and unclamped position, wherein the clamped position the cam exerts a compression force axially inward against the accessory disc or blade; and wherein the clutch assembly comprises: at least one first type of disc located coaxially on and keyed to the output shaft; at least one second type of disc located coaxially on the output shaft and in planar parallel contact with the first type disc; and an inner washer having an internal bore, the inner washer located coaxially on the output shaft, axially outward of and surrounding the first type disc and the second type disc, the inner washer keyed at the internal bore to the second type of disc such that rotation of the second type of disc imparts rotation to the inner washer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to the field of rotary power tools. In particular the present invention relates to a tool-free mechanism for gripping interchangeable rotary tool accessories, such as circular saw blades and grinding wheels.  
         [0003]     2. Discussion  
         [0004]     Various types of rotary power tools require a user to selectively attach a tool accessory, such as a circular saw blade or grinding wheel. Over the course of a particular project or work period it may be necessary to employ a variety of such accessories and to replace worn or broken ones. Convenient removal and replacement of the interchangeable tool accessories is therefore desirable.  
         [0005]     Various methods are employed for gripping such accessory discs. For example, in current circular saw designs a blade has a center hole. The hole may be circular or a shape with sides and corners. A diamond shaped hole is well known for some applications. The hole in the blade fits over the end of the saw&#39;s output shaft or an extension thereof, with the plane of the blade transverse to the axis of the shaft. For some radial distance the axially inward facing surface of the blade rests against a flat shoulder of the shaft or an inner washer connected to the shaft.  
         [0006]     Conventionally, the blade is clamped in place against the shoulder or inner washer with a retaining-nut threaded down over a threaded end of the drive spindle. An outer washer may be placed between the nut and the blade. When changing blades, the nut must be loosened and removed. The tightening and loosening of the nut may be partially performed by hand, but the size and shape of the nut make it difficult and/or uncomfortable to properly tighten and then initially loosen using hands alone. Therefore, it is necessary to use a hand wrench or similar tool in order to apply sufficient torque to the retaining nut.  
         [0007]     Additionally, when tightening or loosening the nut, the shaft/spindle must be prevented from rotating or else it would be difficult to achieve relative motion between the nut and the rotatable spindle. Formerly, the loosening and tightening process required that the operator simultaneously grip both the shaft/spindle and the nut with two separate hand wrenches or the like. Then a torque was applied to the nut while the shaft was held in place. This was an awkward process and made even more so by the necessity to support the weight of the tool itself.  
         [0008]     More recently, tools have been designed that incorporate a locking mechanism that locks the shaft/spindle relative to the tool housing. Thus, the rotation of the shaft can be prevented, simply by employing the built in shaft lock. For such a power tool, only one hand wrench is required to loosen or tighten the nut.  
         [0009]     The need to use even one hand tool to change saw blades or grinding wheels, however, is still inconvenient. For example, when a blade replacement is required, the tool operator has to stop what he is doing to find a wrench, which may not be readily at hand.  
       SUMMARY OF THE INVENTION  
       [0010]     It is, therefore, one object of the invention to provide a tool with a means for gripping that allows the user to conveniently install or remove a tool accessory disc, such as a circular saw blade, without the use of any hand tools.  
         [0011]     It is another object of the invention to clamp the tool disc with a predetermined and reproducible amount of compression force and to thereby control the tool&#39;s slip torque.  
         [0012]     It is still another object of the invention to provide adequate drive torque to the tool disc, for the given compression force, without nuisance slippage.  
         [0013]     These and other objects of the invention are attained by a tool-free accessory clamping system employing a cam shaped clamp mechanism and/or a force multiplying clutch assembly.  
         [0014]     The cam clamping mechanism has a head element that is threadably engageable with the saw&#39;s output spindle or shaft. The head element may take the form of a bolt that threads into an axial bore in the spindle or it may take the form of a nut that threads over an externally threaded end portion of the spindle.  
         [0015]     Mounted by a pivot to the head element is a clamping element having a lever arm portion and a cam portion. The cam portion is in proximity to the pivot and has an irregular perimeter that is cam-shaped. The cam-shaped perimeter has a first portion of greater radius corresponding to the clamped position and a second portion of lesser radius corresponding to the unclamped position.  
         [0016]     The lever arm portion of the clamping element extends approximately radially outward from the pivot and provides a graspable appendage for rotating the cam from the unclamped position to the clamped position. In order that the lever arm not project from the center of a spinning blade, the lever arm portion may be connected to the cam portion such that when in the clamped position the long axis of the lever arm is essentially planar parallel to the saw blade and when in the unclamped position the long axis of the lever arm projects at an angle from the plane of the saw blade.  
         [0017]     The cam may act directly on the blade or a clamping washer may be interposed between the cam and the blade. Such a clamping washer may be coaxially and movably connected to the head of the blade clamp assembly. The clamping washer is located inwardly from the pivot pin and is engageable by the cam. When the clamping lever is rotated from the unclamped to the clamped position, the first portion of the cam shaped perimeter rolls into contact with the exterior face of the clamping washer and exerts an axially inward force against the clamping washer. Thus, the blade is clamped between the interior face of the clamping washer and the exterior face of the inner washer or end face of the spindle.  
         [0018]     The clamping washer may be a Belleville spring washer or such a spring washer may be interposed between the clamping washer and the axially exterior blade face. Belleville spring washers have a slightly convex profile, as viewed from the outside and exhibit a characteristically flat force versus deflection profile as they are pressed flat. By selection of the particular Belleville washer employed the tool designer or operator can effectively and reproducibly set the compression force which the saw blade will experience. In such an embodiment, as the clamping washer moves axially inward under the force exerted by the cam, the Belleville washer flattens and transmits the predetermined force onto the saw blade.  
         [0019]     Due to practical limitations, such as the stack height of the mechanism, an operator can only exert limited compression force with the mechanical advantage conferred by small finger gripped components. Similarly, the radius of the clamping components is limited by the smaller elements of the drive train. Thus, the drive torque transmitted to the blade is limited according to the formula Torque=F×μ×r (where F=the clamping or compression force, μ=the coefficient of friction and r=the radius of the clamped components). When forces under load exceed this value, slippage between the clamped surfaces can occur.  
         [0020]     Our work indicates that a common location for slippage to occur is at the contact surface between the inner washer and the inner race of the ball bearing, where the radius of the contacting parts is necessarily small. In order to increase the torque transmitted from the shaft to the blade while avoiding slippage, a force-multiplying clutch with multiple compression discs may be added to the blade clamping assembly described above. Alternatively, such a force-multiplying clutch may be employed with alternative clamping means; for example a simple finger tightened retaining nut.  
         [0021]     A clutch assembly may include a plurality of alternating discs located near the axially outer end of the drive shaft. For example, a first group of discs may be stacked over the end of and keyed to the drive shaft or spindle, for example with a so-called “Double-D” shaped key cutout in their center. A second group of discs are also stacked over the end of the drive shaft alternating with the discs of the first group, but are not keyed to the shaft. The discs of the second group may have a slightly larger diameter than those of the first group and on their perimeter each is provided with a plurality of radially outward projecting splines.  
         [0022]     Over the end of the drive shaft and over the alternating stack of discs is fitted an inner washer with an axial bore. The inner washer has an internal bore portion of increased diameter towards its axially inner end that has radially inward projecting splines. The inner splines of the inner washer interlock with the outer splines of the second group discs.  
         [0023]     Thus, the rotating shaft directly turns the first group discs keyed to it at their center. The first group discs transmit drive torque to the second group discs by friction contact at their alternating faces. In turn, the second group of discs directly drives the inner washer through the interlocked splines. The inner washer transfers the torque to the rotary tool accessory. By this clutch assembly, the available torque can be multiplied in accordance with the formula—Torque=F×μ×n×r (where F=the clamping or compression force, μ=the coefficient of friction, n=the number of disc friction-surface pairs and r=the radius of the discs).  
         [0024]     The axially outward facing head of the inner washer may serve as the contact surface for the interior face of the saw blade. The saw blade may be clamped to the inner washer as described above. The clamping force F will be transmitted through the alternating discs of the clutch assembly. Where the clutch assembly is employed the blade may be keyed to the inner washer with a diamond shape or the like, as previously mentioned. By providing such a positive torque-transmitting interface between the blade and inner washer, any slippage must occur at the multiple disc clutch surfaces.  
         [0025]     Thus, the cam clamp mechanism and the clutch assembly may be employed separately or together to provide a means for holding a rotary tool accessory, such as a circular saw blade, without the need for hand tools. Where torque requirements are lower the cam clamp mechanism or the clutch assembly individually may be sufficient. Where the rotary torque requirements are higher, the compression force provided by the cam clamp mechanism may be combined with the force-multiplying clutch assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiments that make reference to the drawings of which:  
         [0027]      FIG. 1  is a cross-section view of a cam clamping mechanism according to the present invention;  
         [0028]      FIG. 2  is a top plan of the cam clamping mechanism of  FIG. 1 ;  
         [0029]      FIG. 3  is an elevational cross section view of the cam clamping mechanism of  FIG. 1  further including a clutch assembly according to the present invention;  
         [0030]      FIG. 4  is a top plan view of a representative first group disc of the clutch assembly of  FIG. 3 ;  
         [0031]      FIG. 5  is a top plan view of a representative second group disc of the clutch assembly of  FIG. 3 ;  
         [0032]      FIG. 6  is a cross section along line  6 - 6  of  FIG. 3 ;  
         [0033]      FIG. 7  is an elevational cross-section view of an alternative embodiment of a cam clamping mechanism according to the present invention;  
         [0034]      FIG. 8  is a side elevational schematic of a circular saw incorporating the present invention; and  
         [0035]      FIG. 9  is a perspective schematic view of a circular saw incorporating the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0036]     The present invention provides a wrenchless accessory retention system for rotary power tools employing rotating accessories such as circular saw blades and grinding wheels. While shown through the drawings in various embodiments of a portable circular saw, those skilled in the art will appreciate that the invention is not so limited in scope. In this regard, the teachings of the present invention will be understood to be readily adaptable for use in any tool presently incorporating a threaded bolt or nut and washer clamping arrangement for holding a rotating tool accessory (e.g. framing saw, grinder, etc.). Furthermore, although described throughout as a blade or disc, it is contemplated that the present invention is adaptable to any interchangeable tool accessory designed to rotate around a central hub.  
         [0037]     Turning generally to the drawings in which identical or equivalent elements have been denoted with like reference numerals, and particularly to  FIGS. 1 and 2 , a cam shaped clamping mechanism is illustrated and designated with the reference numeral  10 . Clamping mechanism  10  cooperates with a rotary power tool, designated generally with the reference numeral  40 , to clamp and hold a disc shaped power tool accessory, here a circular saw blade  60 .  FIGS. 8 and 9  depict the rotary power tool  40  as a circular saw tool having a motor  41  with a shaft  44  and incorporating the clamp mechanism  10  and the clutch assembly  80  (described below) of the present invention.  
         [0038]     The particular clamp assembly shown is in the form of a bolt including a threaded shaft  12  and a head  14 . Shaft  12  threads down into the bore  42  of the power tool output spindle or shaft  44 . Head  14  is coaxial with the shaft  12  and projects perpendicular to the plane of the blade  60 . Head  14  is pierced by a pivot pin  16  transverse to the axis of the shaft  12  and includes a flange portion  15  perpendicular to the plane of the blade  60  and axially below the pivot pin.  
         [0039]     Pivotably mounted to the pivot pin  16  is a cam  18 . The peripheral surface  19  of cam  18  has two portions. First portion  21  has a first radius r 1  and corresponds to the clamped position of cam  18 . Second portion  22  has a second radius r 2 , smaller than r 1 , and corresponds to the unclamped position of cam  18 . A cam lever  20  is connected to cam  18  and projects from it in a line transverse to the pivot pin  16 . By means of cam lever  20 , the operator may rotate cam  18  from the clamped to the unclamped position.  
         [0040]     Arranged on the head  14  with limited axial mobility and arranged substantially planar parallel to the blade  60  is a cup-shaped clamp washer  24 . Clamp washer  24  is captured between the cam  18 , which can contact the axially outer surface  26  of the clamp washer  24 , and flange  15  of the head  14 .  
         [0041]     As can be seen in  FIG. 2 , the cam may be in two parts  18   a  and  18   b,  on either side of the head  14 . The cam lever  20  may be a U shaped piece connected to both cam parts  18   a  and  18   b.  The clamping mechanism may also include a cam release lever  30 . Release lever  30  is pivotally connected to pivot pin  16  and has two end portions. First end portion  32  lies underneath cam lever  20  and second end portion  34  is located at the other extremity of release lever  30 . Release lever  30  is bent approximately in the location where it connects to pivot pin  16 , so that ends  32  and  34  do not lie in the same plane.  
         [0042]     To install a saw blade  60  on a rotary tool  40 , the blade is installed with a central opening  62  coaxial with the bore  42  of the output spindle  44 . Shaft  12  is inserted through opening  62  and threaded into bore  42 , until finger tight. Cam  18  should be in the unclamped position and clamp washer  24  is loosely retained between the cam  18  and head flange  15 .  
         [0043]     To clamp the saw blade, the operator presses down (axially inward) on cam lever  20 . The movement of cam lever  20  causes cam  18  to rotate into the clamped position and moves first portion  21  of peripheral surface  19  into contact against the outer face  26  of the clamp washer  24 . As cam  18  rotates it exerts an increasing compression force onto clamp washer  24 , which in turn exerts increasing force onto blade  60 . When cam lever  20  is substantially parallel to the plane of blade  60 , cam  18  will be positioned so that first portion  21  with radius r 1  is exerting the maximum compressive force on blade  60 .  
         [0044]     Simultaneously, as cam lever  20  moves down it drives down first end portion  32  of cam release lever  30  and drives up second end portion  34 .  
         [0045]     To unlock blade  60 , the operator may press down on second end portion  34  of cam release lever  30 . The cam release lever  30  will pivot around pivot pin  16  and first end portion  32  will move up, thus pushing up against the underside of cam lever  20 . As cam lever  20  rotates upward, it will rotate the cam  18 . Peripheral surface  19  will rotate from first portion  21  to second portion  22  in contact with surface  26  of clamp washer  24 , thus releasing the force exerted against the clamp washer. This arrangement eliminates the need for an operator to get a finger underneath cam lever  20 , which might be difficult given the size of the components and clearances between them.  
         [0046]     To complete removal of the saw blade  60 , the operator unthreads the shaft  12  from the bore  42  with his fingers.  
         [0047]     In order to increase and control the compression force exerted on the saw blade  60 , and thus the torque that may be transmitted to the blade before slippage occurs in the drive train, elements depicted in  FIG. 3  (from which some details of the clamping mechanism  10  have been omitted) may also be incorporated into the current invention. For example, a spring washer or, more specifically, a Belleville washer  71  may be inserted between the clamp washer  24  and the saw blade  60 . The characteristically flat force versus deflection profile of a Belleville washer allows the tool designer to effectively and reproducibly set the compression force which the saw blade  60  will experience, relatively independent of the exact amount of rotation by the cam  18 . Here, as the clamping washer  24  moves axially inward under the force exerted by the cam  18 , the Belleville washer  71  flattens but the compression force transmitted through it onto the saw blade  60  remains relatively constants.  
         [0048]     Also as depicted in  FIG. 3 , the present invention may incorporate a clutch assembly  80 , which will transmit more torque to the blade  60  before the onset of slippage. In clutch assembly  80 , a plurality of alternating stacked discs  82  transmit torque between the drive spindle  92  and an inner washer  94 .  
         [0049]     Referring now to  FIGS. 4 and 5 , the stacked discs  82  consists of at least one each of two types. The first type of disc  84  is a generally circular washer keyed to the axially outer end  96  of the spindle  92  at a central opening  85 , here shown in the well known “double-D” shape. The second type of disc  86  is not keyed to the spindle end  96 . Second type discs  86  have a central opening  87 , here circular, that is freely rotatable around the spindle. The outer periphery  88  of the second type discs  86  has radially outward projecting splines  89  with a radius greater than that of the first type discs  84 .  
         [0050]     Referring now to  FIGS. 3 and 6 , the first type discs  84  and second type discs  86  are alternately stacked on the spindle  92 . The axially outward end  96  of the spindle  92  has a shape that fits into the keyed opening  85  of the first type discs  84 . The splines  89  of the second type discs  86  are aligned together.  
         [0051]     Over the axially outer end  96  of the drive shaft  92  and over the alternating stack of discs  82  is fitted an inner washer  94 . The inner washer  94  has an internal bore  98  on its axially inner end  100 : The internal bore  98  has radially inward projecting splines  102 . The inner splines  102  of the inner washer  94  interlock with the outer splines  89  of the second group discs  86 .  
         [0052]     Thus, the rotating shaft end  96  directly turns the first group discs  84  keyed to it at their center hole  85 . The first group discs  84  transmit drive torque to the second group discs  86  by friction contact at their alternating faces. In turn, the second group discs  86  directly drive the inner washer  94  through their interlocked splines  89  and  102 . The saw blade  60  is clamped to the axially outer face  95  of the inner washer  94 , as previously described, and thus the drive torque is transmitted to it from the inner washer. By this clutch assembly, the available torque is multiplied in accordance with the formula—Torque=F×μ×n×r (where F=the clamping or compression force, μ=the coefficient of friction, n=the number of disc friction-surface pairs and r=the radius of the discs). With the advantage of force multiplication the operator manipulated component, be it a cam clamping mechanism  10  or a conventional nut, can be smaller and yet avoid the need for a tool to give added mechanical advantage.  
         [0053]     In higher torque applications, in order to provide for direct torque transmission between the outer face  95  and the saw blade  60 , a raised geometric shape  97  (for example a diamond, shown only in cross section) in outer face  95  may be keyed to a matching hole  62  in the saw blade  60 . In such an arrangement, slippage must occur at the multiple disc clutch surfaces.  
         [0054]     Alternatively, as depicted in  FIG. 7 , the clamping assembly  10  may take the general form of a nut, instead of a bolt. In such an embodiment, head  114  has a threaded bore  142  and threads down over a threaded portion  112  of the power tool output spindle  144 . Head  114  is coaxial with the threaded portion  112  and projects perpendicular to the plane of the blade  60 . Head  114  is pierced by a pivot pin  116  transverse to the axis of the extension  112  and head  114 .  
         [0055]     Pivotably mounted to the pivot pin  116  is a cam  118 . The peripheral surface  119  of cam  118  has two portions. First portion  121  has a first radius r 1  and corresponds to the clamped position of cam  18 . Second portion  122  has a second radius r 2 , smaller than r 1 , and corresponds to the unclamped position of cam  118 . A cam lever  120  is connected to cam  118  and projects from it in a line transverse to the pivot pin  116 . By means of cam lever  120 , the operator may rotate cam  118  from the unclamped to the clamped position.  
         [0056]     Connected to the head  114  with limited axial mobility and arranged substantially planar parallel to the blade  60  is a clamp washer  124 . Clamp washer  124  is captured between the cam  118 , which can contact the axially outer surface  126  of the clamp washer  124 , and the saw blade  60 .  
         [0057]     In the  FIG. 7  embodiment, to install a saw blade  60  on a rotary tool  40 , the blade is installed with a central opening  62  coaxial over the shaft extension  112 . Head  114  is then threaded onto shaft extension  112 , till finger tight. Cam  118  should be in the unclamped position and clamp washer  124  is loosely retained between the cam  118  and head flange  113 .  
         [0058]     To clamp the saw blade  60 , the operator presses down on cam lever  120 . The movement of cam lever  120  causes cam  118  to rotate into the clamped position and moves portion  121  of peripheral surface  119  into contact against the outer face  126  of the clamp washer  124 . As cam  118  rotates it exerts an increasing force onto clamp washer  124 , which in turn exerts increasing force onto blade  60 . When cam lever  120  is substantially parallel to the plane of blade  60 , cam  118  will be positioned so that first portion  121  with diameter d 1  is exerting the maximum compressive force on blade  60 .  
         [0059]     Simultaneously, as cam lever  120  moves down it drives down first end portion  132  of cam release lever  130  and second end portion  134  up.  
         [0060]     To unlock blade  60 , the operator may press down on end portion  134  of cam release lever  130 . The cam release lever  130  will pivot around pivot pin  116  and first end portion  132  will move up, thus pushing up against the underside of cam lever  120 . As cam lever  120  rotates upward, it will rotate the cam  118 . Peripheral surface  119  will rotate from first portion  121  to second portion  122  in contact with surface  126  of clamp washer  124 , thus releasing the force exerted against the clamp washer.  
         [0061]     To complete removal of the saw blade  60 , the operator unthreads the head  114  from the shaft extension  112  with his fingers.  
         [0062]     While the above description constitutes three preferred embodiments of the invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the accompanying claims. In particular and as discussed above, the cam clamping mechanism and clutch assembly may be used individually or together depending on the torque requirements of the particular tool.