Abstract:
Electronic device for reading and setting angles. An electronic angle or position sensing mechanism is mounted together with appropriate circuitry, controls and a digital readout in a small housing having a base and at least one side, and preferably two sides, oriented at right angles to the base. A relatively powerful permanent magnet, such as a rare earth magnet, is fixed in each housing side so that the entire device can be temporarily attached to a ferromagnetic metal surface with one of the magnet-containing housing walls in firm contact with that metal surface, such as the side of a circular saw blade or a machine fence.

Description:
REFERENCE DATA  
       [0001]     This patent claims priority to U.S. Provisional patent application Ser. No. 60/718,423 filed Sep. 19, 2005, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to protractors, angle gauges and other devices for determining the angle between two surfaces, such as a table saw blade and the table surface, or for establishing a specific desired such angle between two surfaces.  
       BACKGROUND OF THE INVENTION  
       [0003]     Accurate determination of the angle between two surfaces is frequently important in a wide variety of endeavors, including woodworking, among many others. For instance, in the course of woodworking, it is frequently important to establish one work piece surface at a particular angle relative to another surface of the same work piece. The desired angle is often  90  degrees, which typically is fairly easy to do because woodworking machinery usually is configured to repeatedly cut or form such work piece surfaces at rights angles. Establishing other work piece surface angles is more difficult, particularly with accurate repeatability. This is because, among other reasons, the scales provided on woodworking tools such as table saws and jointers often cannot be read accurately, and usually no stops are available to facilitate setting non-typical angles, such as angles that are not 45 or 90 degrees.  
         [0004]     such other angles are needed, for instance, when a picture frame, glued-segment bowl blank or other such multi-component assembly utilizes five or more segments.  
         [0005]     As a result there is a need for a more accurate, easier to use, repeatable means for setting and reading angles on woodworking tools like table saws, jointers and other tools and machinery.  
       SUMMARY OF THE INVENTION  
       [0006]     This invention is a small, convenient, easily used, inexpensive electronic device for reading and setting angles. An electronic angle or position sensing mechanism is mounted together with appropriate circuitry, controls and a digital readout in a small housing having a base and at least one side, and preferably two sides, oriented at right angles to the base. A relatively powerful permanent magnet, such as a rare earth magnet, is fixed in each housing side so that the entire device can be temporarily attached to a ferromagnetic metal surface with one of the magnet-containing housing walls in firm contact with that metal surface, such as the side of a circular saw blade or a machine fence.  
         [0007]     The mechanism can be used, for instance, by positioning it upright on a table saw table top, horizontal surface. After turning it “on” with the “on/off” button, pushing the “zero” button “zeros” the unit, making it read “0” degrees. The unit can then be attached to the saw blade using one of the magnets. At this point it will read the angle of the saw blade (or that angle plus or minus  90  degrees) relative to the table top by reference to which it was “zeroed,” providing that angle without regard to whether the saw table top was actually level. The saw blade angle can be adjusted using the table saw tilt mechanism in the normal way while reading the angle showing on the LED readout. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is an front view of an exemplary embodiment of the angle reading and setting apparatus of this invention.  
         [0009]      FIG. 2  is a side view of the apparatus shown in  FIG. 1 .  
         [0010]      FIGS. 3A and 3B  are schematic diagrams of an exemplary circuit for use in practicing this invention.  
         [0011]      FIG. 4  is a functional block diagram of an exemplary position sensing device usable in the apparatus of this invention.  
         [0012]      FIG. 5  is an alternative embodiment of this invention using a cruciform housing.  
         [0013]      FIGS. 6 and 7  are schematic front views of a table saw with the angle reading and setting apparatus of this invention positioned on the table top in  FIG. 6  and attached to the blade in  FIG. 7 . 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  is an enlarged front view of one embodiment of the angle reading and setting apparatus  10  of this invention. Positioned on the front  11  of housing  13 , the on/off button  12 , “zero” button  14 , and the window  16  through which numerals  18  may be seen on an LED display.  
         [0015]      FIG. 2  is a side view of the apparatus  10  showing side  20  of housing  13  with a round rare earth magnet  22  fixed (for instance with glue or liquid thread locker such as Locktite brand thread locker) in the side  20  and flush with its surface. Alternatively, the magnets  22  can be mounted slightly below the surface of each side  20  to insure that side  20  will seat solidly against any ferromagnetic surface it contacts. As is apparent from  FIG. 1 , the sides  20  and  24  of housing  13  are “square” to its bottom  26  (i.e., sides  20  and  24  form a 90° angle with bottom  26 ). In the embodiment of this invention illustrated in the Figures, the front  13  is square to both the sides  20  and  24  and the bottom  26 . This arrangement works well but is not required. The front  13  could slope back from the bottom, which would facilitate viewing the readout in certain situations, and the front  13  could also form other than a ninety degree angle with the sides  20  and  24 . Moreover, the front  13  need not be flat. Other configurations could also be used, including ones in which one or both of the readout opening  16  and the controls  12  and  14  could be mounted on the top or back of the apparatus  10 . It is desirable, however, for the apparatus  10  to have a bottom that will register with a horizontal surface to make position readings relative to that surface. It is likewise desirable for the apparatus  10  to have at least one magnet-containing side surface that is square to the bottom (forms a ninety degree angle with the bottom) and that will register with a planar ferromagnetic surface to which the apparatus can be attached with the magnet.  
         [0016]     Mounted inside housing  13  is sensitive position-sensing circuitry and a battery to power the circuitry. Numerous devices and circuitry could be used to provide the needed position-sensing functionality for this invention. In the embodiment illustrated in the figures, an ADXL213 Dual Axis Accelerometer with Duty Cycle Modulated Outputs is utilized, which has the functional block diagram shown in  FIG. 4 .  
         [0017]     This dual axis accelerometer  28  (in  FIG. 3 ) may be used as shown with a MSP430F42 integrated circuit and LCD readout  32  (or with other suitable components) to provide the described functionality.  
         [0018]     Housing  13  should be a suitably sturdy material to maintain its shape and the square relationship between the bottom  26  and sides  20  and  24 . Various plastics could be used, as can suitable metals, including aluminum, steel and metal alloys (provided that magnets mounted in such material can function as described temporarily to secure the housing  13  to a ferromagnetic surface). While housing  13  can be various sizes and shapes, certain ranges of sizes and shapes are preferable.  
         [0019]     One of the more common uses of the apparatus of this invention will be in setting the angle of a table saw blade relative to the saw table top. Many such saws utilize blades ten inches in diameter, providing a maximum distance of less than 5 inches between the blade teeth and the blade arbor. A full one-half of the blade does not however, project through the table saw table top, and the unobstructed area of blade plate may be further reduced by the blade teeth and a disk-shaped blade stabilizer positioned on the saw arbor beside the blade. Because it is desirable for the apparatus  10  to mount, using one of the magnets  22 , squarely against the blade plate, the size of the sides  20  and  24  needs to be relatively small in width and height. The side  20  and  24  height should be at most about four inches, preferable no more than three inches and most preferable no more than about two and one-quarter inches. Smaller sizes are also possible in the exemplary embodiment illustrated in the drawings, the dimensions “x” and “y” (width and height) can be about two and one-forth inches, and the depth “z” can be about one and one-fourth inch.  
         [0020]     Angle reading and setting apparatus  10  is used by positioning it at a desired “zero” position such as resting on a table saw  50  horizontal table top  52  ( FIG. 6 ) or on a jointer table. After turning apparatus  10  “on” by pressing the “on/off” button  12 , the “zero” button  14  is pushed to “zero” the unit, making it read “0” degrees in display window  16 . The unit can then be attached to the saw blade  54  ( FIGS. 6 and 7 ) or other reference surface such as a jointer fence using one of the magnets (or, if it is already so attached, that surface can be tilted) and the angle of tilt will be displayed in display window  16 . The “angle of tilt” displayed on the readout may actually be the deviation from 90° relative to the table top because, by convention, a blade square to the table top is said to have “0° tilt.” 
         [0021]     As will be understood by those skilled in the art, the angle device  7  of this invention can also be used in a variety of other situations to determine the relative angles of reference surfaces or to set such surfaces at desired angles. It can be used, for example, in setting the tilt angle of a motorized miter box or “chop” saw or of a jointer fence.  
         [0022]     As will also be understood by those skilled in the art, numerous variations and modifications of the components described above and of the described configurations of components, can be used without departing from the scope or spirit of this invention or the claims set forth below. For instance, magnets  22  could also be mounted in the top and bottom of the housing  13  to make it possible to position the device  10  more solidly on horizontal ferromagnetic support surfaces (like cast iron woodworking machinery) tables and, if desired, against the underside of horizontal ferromagnetic surfaces. Similarly, other position sensing devices and other switch configurations and apparatus circuitry could also be used. Indeed, some or all of the circuitry, including the controls and readout, could be positioned in a housing separate from (but electronically linked to) a position-sensing unit containing the accelerometer (or its functional equivalent) and one or more magnets for securing the position-sensing unit against ferromagnetic surfaces in order to make angle readings.  
         [0023]     Furthermore, the sides  20  and  24  of housing  13  in the embodiment depicted in the drawings are rectangular and flat; however, other shapes are also usable provided that an appropriate registration surface is provided for contact with a ferromagnetic surface when securing the housing  13  to that surface during use. As an example, housing  113  for apparatus  100  illustrated in  FIG. 5  has a cruciform shape but still has a side registration surface  124  that is square or orthogonal to bottom  126 .