Abstract:
A band saw has a blade tension adjustment to permit the blade tension to be reduced during times when the saw will not be used for a time. A sensor is connected to the blade tension adjustment. The sensor inhibits saw operation if the tension adjustment is set to a reduced tension setting. The sensor enables the saw operation if the tension adjustment is set to a full operating tension setting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/684,198, filed Aug. 17, 2012, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a power tool and more particularly to a system and method to prevent operation of a band saw when the blade tension control has been set to a tension state that is less than full tension. 
         [0004]    2. Description of the Related Art 
         [0005]    A band saw is a power tool that includes a blade in the shape of a continuous loop that is typically formed of steel and provided with saw teeth along one edge. The loop or band of the band saw blade rides on two wheels that are mounted in the same plane. A drive motor is connected to rotate one of the wheels, causing the blade to move at relatively high speed. Cutting is performed by pressing a workpiece against the portion of the blade that extends between the two wheels. 
         [0006]    The blade is kept under tension during use of the saw. If the saw is not being used for some time, the blade can deform and cause vibration during use of the saw. The wheels of the band saw are commonly coated with rubber on their rims to reduce noise and slippage of the blade. The rubber coating on the wheels can deform is the blade is kept under tension during periods between usage of the band saw. 
         [0007]    Users of band saws, particularly infrequent users of the band saws, such as home hobbyists, are advised to release the tension from the saw blade if the saw will not be used for a time. The user must reapply tension to the blade prior to use to ensure that the blade does not slip from the wheels or otherwise cause an unsafe condition. The user must remember to tension the blade if the full tension has been released. 
         [0008]    U.S. Pat. No. 6,739,231 B2 discloses a quick release lever for a band saw that permits a user to release tension from the band saw blade or to reapply tension to the blade by movement of a lever. The user must remember to move the lever to the full tension position prior to use of the band saw. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a system and method by which a band saw is prevented from operating or starting when the tension apparatus has been set to a partial or full tension release. A sensor in the band saw detects the position of the tension release mechanism and if the tension release is not in the full tension position, the sensor prevents the user from operating the saw. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an example of a band saw; 
           [0011]      FIG. 2  is a view of a different band saw showing the upper and lower housings open to reveal the wheels on which the blade rides; 
           [0012]      FIG. 3  is an enlarged side view of an upper housing of a band saw showing a quick release tension lever; and 
           [0013]      FIG. 4  is an enlarged side view of an upper wheel of the band saw including a switch that senses a position of the quick release lever. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]      FIG. 1  shows a band saw  10  for cutting workpieces, such as wood or metal. The band saw  10  includes a lower housing  12  containing a motor and a lower wheel, an upper housing  14  containing an upper wheel, a work table  16  mounted on the lower housing  12  on which the workpieces are supported during cutting. The upper housing  14  is connected to the lower housing  12  by a vertical housing portion  18 , through which a rear portion of the blade  20  passes as it extends between the wheels. A blade guard  22  is in place over the front portion of the blade  20 . The blade guide  22  ends just above the top of the work table  16  to reveal a portion of the blade path that is exposed for cutting. A wheel  24  for raising and lowering the blade guard  22  is provided. A power switch  26  to turn on the saw  10  is provided at the vertical portion  18 . The table  16  is provided with an adjustable work piece guide  28 . Other adjustments and controls are provided as known. 
         [0015]      FIG. 2  shows the upper and lower housings  14  and  12  open to reveal the upper and lower wheels  30  and  32  that the band blade  20  rides on. The upper and lower wheels  30  and  32  are provided with a shaped rim, preferably provided with a rubber blade contact element  34  on the rim of each wheel. The wheels  30  and  32  with their rubber rims  34  are sometimes referred to as tires. The lower wheel  32  is driven by a motor  36  that is connected to the lower wheel by a belt and pulley arrangement  38 . The blade guard  22  is in the raised position to reveal a length of the blade  20  between the end of the blade guard  22  and the work table  16 . In this band saw, a blade tension adjustment control  40  is provided on the underside of the upper housing  14 . 
         [0016]      FIG. 3  shows a portion of the upper housing  14  of the band saw  10  from the opposite side of that shown in  FIG. 1 . Extending from the housing  14  is a rotatable control  42  that is connected to an elongated lever  44 . The lever  44  has a hand grip  46  at its free end. The lever  44  can be moved to three different positions in this illustrated embodiment. The first position A, as shown, with the lever  44  in a substantially horizontal position is a position that provides full tension on the band saw blade  20 . In the full tension position A, the saw  10  is ready for use. A second position B is indicated by a sign  48  or other indicator on the housing  14 . The second position B for the illustrated lever  44  is a position extending downward yet still to the front of the band saw. The second position B provides a partial release of the tension on the band saw blade  20 , such as by moving the upper wheel  30  toward the lower wheel  32  by a distance sufficient to relieve tension on the blade  20  and reduce deforming of the rubber rim  34  on the wheel. By moving the lever  44  to the second position B between uses of the band saw  10 , particularly if the band saw  10  will not be used for an extended time, the blade  20  and the rubber rim  34  on the wheels  30  and  32  are not subject to being deformed. Vibration and other operational issues are reduced. 
         [0017]    A third position C is indicated by the sign  48  on the housing  14 . The third position C is a full release position at which the tension on the blade  20  is release sufficiently that the blade  20  can be removed and a different blade installed on the band saw device  10 . The wheels  30  and  32  are moved toward one another sufficiently to place the blade  20  in a full slack state. The partial tension position B is between the full tension position A and the full release position C of the tension lever  44 . 
         [0018]    The band saw  10  shown in  FIG. 3  is a 15 inch band saw, in other words a saw using 15 inch diameter wheels  30  and  32 . The present invention is not limited to the size of the band saw with which it is used, and other sizes of band saw are within the scope of this invention. Also visible in the view of  FIG. 3  is a front access door latch  50 , visible at the far left in the figure above the hand wheel  24  on the front of the housing  14 . The hand wheel  24  at the left of the figure, also on the front of the housing  14 , is operated to raise and lower the blade guide and the associated blade guard  22 . On the side of the housing  14  is a knob  52 , to the left in the view of the figure, that locks the guide post for the blade  20 . To the right in the figure is a knob  54  that provides blade tracking adjustment, and next to the tracking adjustment knob  54  is a lever  56  that locks the desired tracking adjustment in place. 
         [0019]    Turning to  FIG. 4 , the upper housing  14  of the band saw  10  has been opened by opening the side opposite the side with the tension lever  44 . Within the upper housing  14  is the upper wheel  30  on which rides the band saw blade  20 . The wheel  30  includes a central axel  56  about which the wheel  30  rotates, and includes a rim  58  that is covered by a rubber covering  34  that is in contact with the blade  20 . The blade  20  can be seen extended from each side of the wheel  30  toward the lower wheel. Through an opening  60  in the wheel  30  is visible a micro-switch  62 , which is mounted on an interior wall of the upper housing. 
         [0020]    The micro-switch  62  is connected electrically to a coil circuit in the magnetic starter for the motor  36  of the band saw device  10 . If the micro-switch  62  is in an operated or closed position, the micro-switch  62  closes a circuit to provide electrical power to the coil to hold the line contacts for the motor  36 , enabling the motor  36  of the band saw  10  to start and enabling the motor  36  to continue operating. If the micro-switch  62  is in its non-operated or open position, power is not provided to the coil and a spring inside the coil opens contacts so that power to the motor  36  is interrupted. This interruption in the circuit prevents the motor  36  from starting. If the motor  36  is already running, the movement of the micro-switch  62  to the non-operated position interrupts power to the motor  36  to stop the motor and hence band saw. The micro-switch  62  is connected to the magnetic starter of the band saw and basically adds an interruptible circuit to the magnetic starter coil. 
         [0021]    The micro-switch  62  has a roller  64  at the top of the switch unit that is displacable between extended and non-extended positions. Movement of the roller  64  opens or closes the circuit in which the micro-switch  62  is connected. The roller  64  is in contact with an arm  66  that is connected to the tension adjustment lever  44  shown in  FIG. 3 . As the lever  44  is moved between the full tension position A, the partial tension position B, and the full release position C, the arm  66  inside the housing  14  moves. The arm  66  and micro-switch  62  are positioned so that the motor  36  of the band saw device can only be operated when the tension on the blade  20  is sufficient for safe operation. The switch element of the illustrated micro-switch  62  is biased to the open position by an internal spring. In this example, moving the tension lever  44  to the second position B, where tension is partially released from the blade  20 , moves the arm  66  within the housing  14  away from the body of the micro-switch  62 , allowing the switch element to move by spring force to an open contact position. The motor  36  cannot be started when the tension lever  44  is in the second position B. 
         [0022]    The motor  36  also cannot be started when the tension lever  44  is in the full release position C. In the preferred embodiment, the tension lever  44  must be at the full tension position A, or at least sufficiently close to the full tension position A that a safe operating position of the saw is possible. 
         [0023]    The micro-switch  62  is thereby positioned to detect the position of the tension lever  44 , either directly or indirectly. Other means of sensing the position of the tension lever  44  are possible within the scope of this invention. 
         [0024]    In a preferred embodiment, the arm  66  is always in contact with the roller  64  of the micro-switch  62 . For example, a mechanism may link the arm  66  to the tension lever  44  to enable the large angle movements of the tension lever  44  to be translated into small angle movements of the arm  66  or into linear or near linear movements, as tension is applied and released. 
         [0025]    Other means to interrupt power to the motor or to the starter or to otherwise prevent operation of the band saw when the tension lever is at a position other than full tension are possible and are within the scope of this invention. 
         [0026]    The user who attempts to start the saw  10  with the tension lever  44  in the wrong position is prevented from starting the saw by the present apparatus. The position of the lever  44  indicates to the user the reason for the saw not starting so that the user need only look to the tension lever to realize that it must be returned to the full tension position to enable saw starting. It is envisioned that an indicator, such as an indicator light or a message on a display panel, may be provided to indicate to the user the reason for the saw not starting. 
         [0027]    The apparatus as shown and described herein prevents a user who has moved the tension lever  44  to the full release or the partial release position, for example to prevent distortion of the blade and wheels between uses, from operating the saw until full tension is applied to the blade. A potentially dangerous condition is thereby avoided. 
         [0028]      FIG. 4  also shows a tension spring  68  which applies tension to the blade  20  by applying a spring force to the upper wheel  30 . The tension spring  68  is visible through the lower opening  70  in the wheel  30  in this view. The tension spring  68  is mounted on a spring shaft  72  that is part of the tension adjustment system. Also visible in this view is a tension indicator pointer  74 . The pointer  74  has a slot in which rides a pin  76  that extends from the spring and spring shaft  72 . The pointer  74  is pivotally mounted within the housing  14 . The opposite end of the pointer points to a gauge that indicates the correct tension for various conditions, blade types, etc. 
         [0029]    The blade guide and blade shield  22  are visible at the lower right in the image. 
         [0030]      FIG. 5  shows a functional block diagram of another embodiment of the present apparatus. A band saw blade  80  is mounted on blade support wheels  82  so that the blade  80  moves as the wheels  82  rotate. A blade drive motor  84  is connected to drive at least one of the wheels  82  which in turn moves the blade  80  so that a work piece is cut by the blade  80 . The motor operation  84  is controlled by a motor control device  86  which controls whether the motor  84  operates or not. The motor control device  86  may be a saw start control. The user operates the start control or motor control  86  to start the saw operation. 
         [0031]    The blade support wheels  82  are connected to a blade tension adjustment  88 . Any blade tension adjustment apparatus may be provided, including the tension adjustment lever or some other tension adjustment device. The tension adjustment device  88  is sensed by a sensor  90  to determine if the blade tension is at full operating tension or if the tension has been released to a lesser tension level. The sensor  90  may instead sense the position of the blade support wheels  82  or may even sense the blade  80  directly, in alternative embodiments. The sensor  90  may be replaced by an interlock that prevents operation of a mechanical or electrical component if the tension is set at the incorrect level. In the present example, the sensor is connected to the motor control or saw start control  86  to prevent the saw from operating when the blade tension is at an improper level. 
         [0032]    The sensor  90  can be a position sensor, such as the micro-switch sensor shown in  FIG. 4 , or can be a quantitative sensor that determines the magnitude of the tension applied to the blade. If the blade tension is determined to be below a desired threshold, the saw operation is inhibited. The tension sensor  90  may also sense excess tension applied to the blade and prevent operation of the saw if the tension exceeds a desired level, or may otherwise indicate excess tension to the user. The sensor  90  may operate to interrupt the electrical circuit from the motor start circuit or from the saw start switch or some other circuit that is required to operate the saw. If an interlock is provided to inhibit saw operation when the tension is set to an incorrect level, the interlock may act to prevent operation of the start switch, to prevent rotation of the motor, to prevent rotation of the wheels, to interrupt transmission of rotational power between the motor and the wheels such as via an interruptable transmission linkage between the motor and wheels, to prevent movement of the blade for example by a blade brake, or through some other system interrupt or operational inhibitor. 
         [0033]    The present invention also encompasses a method for preventing operation of a band saw  10  when tension on the blade  20  is set at less than full tension. The steps of the method, which are apparent from a review of this specification, may include sensing a position of a tension release lever  44 , and inhibiting operation of the saw when the tension release lever  44  is determined to be at a position other than a full tension position. If the sensing of the tension release lever  44  determines that the lever is at a full tension position, then the operation of the saw is enabled. The user can only cause the saw to operate when the operation of the saw is enabled. 
         [0034]    Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.