Abstract:
Embodiments of the present invention are directed to a power compound miter saw having miter angle as well as bevel angle adjustment capabilities, with sensing units that can measure the angular position of the miter table relative to the base as well as the bevel angle of the blade relative to the table. Such sensing units generate position signals that can be used to provide a digital display of the miter and bevel angles to a high degree of accuracy. Moreover, the embodiments utilize mechanisms which enable a user to tighten the pivot connections of the table and the base as well as the pivot connection between the table and the bevel pivot support housing without damaging the sensing units. The sensing units are configured and mounted in such a way as to not interfere with access to the nut which can be rotated to vary the amount of friction between the adjacent components.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to power tools.  
         [0002]     Power miter saws that are used by trim carpenters, artisans and woodworkers are becoming ever more sophisticated as a result of continuing research and development efforts on the part of commercial manufacturers. Relatively recent developments include compound miter saws having extremely large blades that can cut miter and bevel angles on large pieces of stock, such as relatively wide crown and other types of molding. Still more recent developments include sliding compound miter saws which have a blade and engine assembly which can slide on rails toward the user after engaging the work piece, which enables large size stock to be cut at various miter and bevel angles using the well known conventionally sized smaller blades. Such sliding compound miter saws are extremely useful and convenient for performing accurate cuts on large sized trim pieces and other stock, particularly in the home building business sector.  
         [0003]     Regardless of whether sliding compound or regular miter saws are used, the more recent compound miter saw designs typically include detents for common settings that are required for miter angles for various types of trim and other carpentry work. Specific bevel and miter angles are commonly used for cutting trim pieces for inside and outside corners in either a vertical or horizontal orientation, as well as to cut trim pieces for inside and outside corners of crown molding, for example.  
         [0004]     It is also known by experienced and competent artisans that small variations in the resulting angles of a 90° inside or outside corners can occur during construction, which require some angular compensation in order for the trim pieces to mate in a tight seam. This is usually effectively accomplished only by those individuals who have solid knowledge and experience. Such knowledgeable artisans may often wish to adjust either a miter angle or a bevel angle or both to produce a desirable result and such adjustments may be less than a single degree from the known or expected angles. While conventional miter saws typically have such angular markings for setting miter as well as bevel angles, it is not always easy to lock in desired settings or to accurately differentiate such small angles.  
       SUMMARY OF THE INVENTION  
       [0005]     Embodiments of the present invention are directed to a power compound miter saw having miter angle as well as bevel angle adjustment capabilities, with sensing units that can measure the angular position of the miter table relative to the base as well as the bevel angle of the blade relative to the table. Such sensing units generate position signals that can be used to provide a digital display of the miter and bevel angles to a high degree of accuracy. Moreover, the embodiments utilize mechanisms which enable a user to tighten the pivot connections of the table and the base as well as the pivot connection between the table and the bevel pivot support housing without damaging the sensing units. The sensing units are configured and mounted in such a way as to not interfere with access to the nut which can be rotated to vary the amount of friction between the adjacent components. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view from a lower left side of a compound miter saw embodying the present invention;  
         [0007]      FIG. 2  is a perspective view from beneath the left side of a portion of the apparatus shown in  FIG. 1 ;  
         [0008]      FIG. 3  is an enlarged side view of the miter angle sensor structure of the embodiment shown in  FIG. 1 ;  
         [0009]      FIG. 4  is another enlarged section of a portion of the miter angle sensor structure shown without the base or table of the embodiment shown in  FIG. 1 ;  
         [0010]      FIG. 5  is a bottom view of a portion of the embodiment shown in  FIG. 1  and particularly illustrating the miter angle sensor structure;  
         [0011]      FIG. 6  is a side view of a portion of the embodiment shown in  FIG. 1  and illustrating the bevel angle sensor structure;  
         [0012]      FIG. 7  is a rear view of the embodiment shown in  FIG. 1 , particularly illustrating the bevel pivot support housing and the bevel angle transducer structure;  
         [0013]      FIG. 8  is an enlarged perspective side view illustrating the main components of the bevel angle sensor structure of the embodiment shown in  FIG. 1 ;  
         [0014]      FIG. 9  is a cross section of a portion of the preferred embodiment of the miter saw and illustrating an  0 -ring connection between a shaft and a shaft encoder  
         [0015]      FIG. 10  is a partial perspective of a portion of an alternative embodiment of the miter saw, particularly illustrating a tolerance ring that can be used to connect a shaft and a shaft encoder;  
         [0016]      FIG. 11  is a cross section portion of an alternative embodiment of the miter saw particularly illustrating a spline or key connection of a shaft and a shaft encoder;  
         [0017]      FIG. 12  is a cross section of a portion of an alternative embodiment, particularly illustrating a keyed washer and a grooved shaft;  
         [0018]      FIG. 13  is a cross section portion of an alternative embodiment of the miter saw particularly illustrating a flat surface to flat surface connection of a shaft and a shaft encoder;  
         [0019]      FIG. 14  is a bottom view of a portion of an alternative embodiment particularly illustrating a string potentiometer or string driven transducer implementation for determining the miter angle;  
         [0020]      FIGS. 15A and 15B  are side and top views, respectively, of an alternative embodiment of a pin and fork connection; and,  
         [0021]      FIGS. 16A and 16B  are side and top views, respectively, of another alternative embodiment of a pin and fork connection. 
     
    
     DETAILED DESCRIPTION  
       [0022]     The preferred embodiment of the present invention is shown in  FIGS. 1-9  of the drawings and comprises a power sliding compound miter saw that has the capability of adjusting both the miter and bevel angles. It should be understood that the present invention may also be implemented in a miter saw that does not have the compound sliding capability. For that matter, the sensing unit structure may be useful in other applications where the angular position of one component relative to another is to be determined and where the two components may be required to be tightened relative to one another by the use of a nut on a shaft, which thereby necessitates the ability of the sensing unit to be axially moved along a shaft. The two sensing unit structures that will be illustrated and described herein are not identical to one another, but share some functional commonality. The differences between the bevel and miter sensing unit structures may lend themselves to be used for different applications. Both sensing unit structures can produce highly accurate measurements of the miter and bevel angles, i.e., to at least 0.1 degrees which are displayed on a digital display located on the miter saw.  
         [0023]     Turning now to  FIGS. 1 and 2 , a compound miter saw indicated generally at  10 , is shown in perspective and includes a saw base  12  that is preferably generally circular in its overall shape and which has downwardly extending legs for supporting the saw on a surface. The saw  10  has a rotatable table, indicated generally at  14 , which pivots around a central generally vertical shaft  16 . The table  14  can be positioned at different bevel angles by using a handle assembly, indicated generally at  18 , that preferably includes a detent and release mechanism as well as a locking mechanism for setting the bevel angle of the saw. The detent and release mechanism and the locking mechanism are not in and of themselves a necessary part of the present invention except insofar as some type of such mechanisms are required for such a compound miter saw  10 .  
         [0024]     The table  14  includes a bevel base portion  20  located at the rear thereof and has a generally horizontal shaft  22  that defines the horizontal axis for adjusting the bevel angle. The shaft  22  supports a bevel pivot support housing, indicated generally at  24 , that pivots relative to the bevel base portion  20 . The bevel pivot support housing  24  has openings in which a slideable carriage  26  is located with the carriage  26  supporting a saw blade and motor assembly, indicated generally at  28 . The blade and motor assembly  28  has a motor  30 , a saw blade  32 , a guard structure  34  and a handle  36 . The blade and motor assembly also pivots about a shaft  38  for bringing the saw blade downwardly into a cutting position. The saw  10  has a fence  40  that is operatively connected to the base  12  for holding a work piece (not shown) in position to be cut.  
         [0025]     The miter angle is measured by a miter angle sensing structure, indicated generally at  42 , and the bevel angle is measured by a bevel angle sensing structure, indicated generally at  44 . With regard to the miter angle sensing unit structure  42 , and referring particularly to  FIGS. 2, 3  and  4 , the table  14  is carried by the base  12  and the table  14  is rotatable about the shaft  16  which is tightly secured to the table by bolts  46  that are preferably screwed into threaded apertures of the base  12 . The shaft  16  extends through the base  12  which is preferably an aluminum die casting and has a flat annular boss  48  formed therein. The shaft  16  also extends through the base  12  and has a threaded end portion which a threaded nut  50  is applied screwed onto. The nut  50  controls the amount of friction that exists between the table  14  and the base  12  so that when it is tightened, it is more difficult to rotate the table relative to the base.  
         [0026]     It should be understood that over the life of the saw  10 , it may be necessary to tighten the nut  50  because of normal wear to maintain the desired amount of friction between the base  12  and the table  14 . The sensing structure  42  is located between the base casting  12  and the nut  50  and comprises a thrust bearing  52 , an angular position transducer, indicated generally at  54 , which has an inner hollow cylinder  56 , an outer cylindrical housing  58  and an anti-rotation keyed washer  60 , which is located on the shaft  16  between the hollow cylinder  56  and the nut  50 .  
         [0027]     As shown in  FIGS. 3, 4 , and  5 , an anti-rotation pin  62  is preferably press-fit into a complimentary sized and shaped opening in the base casting  12  and its axis is preferably substantially parallel to the axis of the shaft  16 . An anti-rotation bracket  64  has a forked outer end portion that contacts the anti-rotation pin on opposite sides thereof and the bracket  64  is attached to the cylindrical housing  58  of the angular position transducer  54 . Since the pin is secured to the base  12 , the cylindrical housing  58  of the angular position transducer  54  is immobilized relative to the base  12 . The inner hollow shaft  56  is secured to the shaft  16  so that when the table is rotated relative to the base, the shaft  16  as well as the inner hollow cylinder  56  rotates relative to the cylindrical housing  58  of the angular position transducer and the angular position transducer  54  thereby generates signals that are indicative of the angular position of the table  14  relative to the base  12  of the saw. An alternative embodiment of the pin and fork connection is shown in  FIGS. 15A and 15B  where the fork  64 ′ has curved faces  51  so that there is only point contact on opposite sides of the pin  62 . Similarly, another alternative embodiment is shown in  FIGS. 16A and 16B  wherein the pin  62 ′ has a smaller diameter base portion and an enlarged spherical end portion  53  that also ensures point contact on opposite sides of the spherical end portion  53  and the sides of the fork  64 . Both of these embodiments allow for relative angular misalignment between the pin and the fork which may occur during the manufacture of the saw  10 . However, regardless of the misalignment, there are no resulting errors because point contact on opposite sides of the pin with the fork is maintained.  
         [0028]     An alternative embodiment of the sensing structure  42  is shown in  FIG. 14  which comprises a string potentiometer or string driven transducer  43  mounted to the base  12  which has a string or flexible wire  45  that is wound around a string guide  47  and has its outer end attached to the string guide  47  by a screw  49  or the like. As is known to those of ordinary skill in the art, the string is biased to retract the string and provides an electrical signal that is indicative of the length of the extended string. Therefore, as the string guide is rotated, electrical signals are generated that are proportional to the angular position of the table  14 .  
         [0029]     As can be appreciated from  FIG. 3 , when the nut  50  is tightened on the shaft  16 , there will be a compressive force applied to the keyed washer  60 , the hollow cylinder  56  and the thrust bearing  52  against the boss  48  of the base. As the nut is tightened, this compressive force will increase the friction of the table relative to the base and therefore increase the amount of force that is required to rotate the table relative to the base. It should also be appreciated that as the nut  50  is rotated, it will cause the angular position transducer  54  to move in an axial direction. Since the shaft encoder  54  is a unitary item, it is necessary that the inner hollow cylinder  56  and cylindrical base  58  move in unison. While the inner hollow cylinder  56  needs to be able to move in the axial direction, it is also necessary that the cylinder  56  not have any angular movement with respect to the shaft  16  for the reason that this would result in an inaccurate angular position signal being generated by the shaft encoder  54 .  
         [0030]     One of several configuration or mechanisms can be used to permit axial movement while resisting relative rotational movement between the inner hollow cylinder and the shaft  16 . It is preferable that a rubber or rubber-like O-ring  65  be positioned between the inside diameter of the inner hollow cylinder  56  and the shaft  16  as shown in  FIG. 9 . The O-ring  65  should be sized so that it is placed in sufficient compression to insure that rotation of the shaft will result in rotation of the hollow cylinder  56  but also permit the limited axial movement that is necessary as a result of the tightening of the nut  50 . While the use of the O-ring  65  is preferred, a tolerance ring as shown in  FIG. 10  may also be employed. As is known to those skilled in the art, a tolerance Ring is a precision-engineered device made from a thin spring steel strip of material into which waves, corrugations or bumps are formed. The strips are cut to length and curled into the ring shape. The waves are either facing inward or outward to accommodate different applications. For the purpose of this alternative embodiment, the waveforms are designed to preferably exert a rotational holding force while permitting axial movement.  
         [0031]     A key or spline arrangement may also be used as shown in  FIG. 11 . In this alternative embodiment, a groove is cut or formed on the inside surface of the inner hollow cylinder  56  and in the outside of the shaft  16 , and a key or spline  67  is placed in the grooves to prevent relative angular movement between them while permitting axial movement of the cylinder  56  along the shaft  16 .  
         [0032]     A principal consideration of these embodiments is the capability of maintaining angular nonslipping contact while permitting axial movement so that the angular position transducer  54  is not damaged by the axial movement of it when the nut is rotated to increase the friction between the base  12  and table  14 .  
         [0033]     It is also important that rotation of the nut relative to the shaft does not damage the angular position transducer, and it is for that reason that the keyed washer  60  is provided to prevent any rotating force being applied to the inner hollow cylinder  56 . As shown in  FIG. 12 , the keyed washer  60  has an inwardly directed tang  64  that engages a groove  66  in the shaft  16 . Another embodiment shown in  FIG. 13  employs adjacent flats  69 A and  69 B which prevent relative rotation of the hollow cylinder  56 ,  72  and shaft  16 ,  22  while permitting sliding movement.  FIG. 13  shows a gap between the two components which in practice would not exist to the extent that any appreciable play would occur between these components.  
         [0034]     The angular position transducer  54  is preferably a single rotation potentiometer that will actually rotate less than a full revolution as applied to the embodiment illustrated. As is typical for miter saws, the table is generally limited in its rotation from a left 45° position to a right 45° position. Thus, only approximately 90° of rotation is used to generate the angular position signals that are sent to a display unit  68  that preferably has an internal microprocessor that is configured to receive the position signals from the sensing unit  42  and thereby generate a digital display of the angular position of the table.  
         [0035]     The user can zero the display unit  68  by putting the miter saw into a detent zero position and pressing the zero button. In this zero position, the blade  32  is preferably exactly perpendicular to the plane of the fence  40 . The user can also press a store button and store the current position.  
         [0036]     The angle display unit  68  should be mounted on the saw table near the front for easy viewing, and may conveniently be located on the handle  18 . While not discussed in detail, the bevel sensing structure  42  also produces signals that result in a digital display. It is preferred that the display unit  68  be able to display both the miter angle and the bevel angle, and have a button that allows switching between viewing the miter or bevel angle. Alternatively, there could be two displays units, i.e., one mounted near the front of the saw table that would display the miter angle and another display mounted near or on the bevel pivot support housing that would display the bevel angle. The display unit(s) will preferably show two numbers for each of the bevel and miter angles. One of these numbers preferably indicates the actual angle measurement and the other number preferably indicates a stored value or a calculated value that the user can use to adjust either the miter angle or the bevel angle until the two numbers are identical.  
         [0037]     With regard to the bevel angle transducer structure  44  and referring to  FIGS. 2, 6  and  8 , it comprises an angular position transducer  70  that includes an inner hollow cylinder  72  and a cylindrical housing  74  that is rotatable relative to the inner hollow cylinder and the shaft. The angle position transducer v  70  generates signals indicating the angular position of the two cylinders relative to one another, and is mounted on the threaded shaft  22  and is held by an end nut  76  threaded onto the threaded shaft  22 . A keyed washer  78  is also provided between the inner hollow shaft  72  and the nut  76 . The keyed washer  78  and shaft  22  has substantially the same configuration as the keyed washer  60  shown in  FIG. 12  and performs the same function of preventing any rotational force being applied to the hollow cylinder  72  as a result of rotating the nut  76  to tighten the connection between the bevel pivot support housing  24  and the bevel base portion  20  of the table  14 . In this sensing unit, the hollow cylinder  72  is held in place relative to the shaft  22  in a similar manner as the outer cylinder  56  is operatively connected to the vertical shaft  16 . Thus, an O-ring, spline or tolerance ring is used to prohibit relative rotational movement between the hollow cylinder  72  and the shaft  22 , while permitting limited axial movement that may be necessary when the nut  76  is tightened on the shaft  22  for the purpose of increasing the amount of friction that exists during rotation of the bevel pivot support housing  24  and the bevel base portion  20 .  
         [0038]     The cylindrical housing  74  is operatively connected to the bevel pivot support housing  24  which causes the cylindrical housing  24  to move in unison with the bevel pivot support housing. This is achieved by a bracket  80  that is similar to the bracket  63  on the miter sensing unit structure. In this regard, it has a forked end portion that contacts both sides of a pin  82  that is secured to the bevel base portion  20  of the table. By virtue of the sliding relationship of the bracket  80  and the pin  82 , limited axial movement of the shaft encoder is permitted as may result from tightening of the nut  78  on the shaft  22 .  
         [0039]     The angle position transducer  70  generates signals that are fed to the display  82  by connectors and conductors, not shown, and the display  82  may be located on the saw  10  at a convenient location that is visible to a user as previously described. As is the case with the display  68 , if the display  82  is separate from the display  68 , it would similarly have processing means incorporated into its design so that the position signals from the bevel sensing structure  44  can be converted to a digital display for viewing by an operator.  
         [0040]     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.  
         [0041]     Various features of the invention are set forth in the appended claims.