Patent Publication Number: US-2005140516-A1

Title: Power tool

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a power tool having a power indicating device.  
      Conventional power tools are commonly provided with a rather long supply wire for convenient long range use. However, if there is motor damage or the power plug thereof is carelessly loosened or detached from the power jack, the power tool may stop working suddenly. In these circumstances, the operator determines whether the power is on or off by walking up to the remote power plug. This is a rather time-consuming exercise and may inconveniently prolong operating time.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to overcome certain disadvantages of the prior art by providing a power tool having a power indicating device positioned in visible proximity to an operator to indicate whether power is on or off.  
      A power tool comprises a supply wire, a power switch and a first electrical circuit including the power switch. The power tool further comprises a power indicating device which includes a power indicator which can emit light visible to indicate whether power is on or off and forming a second electrical circuit. The second electrical circuit and the first electrical circuit are connected in parallel to the supply wire.  
      Thus viewed from a first aspect the present invention provides a power tool comprising: 
          a power supply wire for supplying power;     a power switch electrically connected to the power supply wire;     a first electrical circuit including the power switch;     a power indicating device positioned in visible proximity to an operator, the power indicting device including:     a power indicator which is capable of emitting radiation visible to the operator when power is on; and     a second electrical circuit including the power indicating device, wherein the second electrical circuit and the first electrical circuit are connected in parallel to the power supply wire.        

      By virtue of the power indicating device, the power tool of the invention allows the operator to conveniently judge whether power is on or off when the power tool stops working. This is particularly advantageous when the power plug is far away from the operator.  
      The power indicating device may be located in a housing. The housing may be the operator handle of the power tool. The radiation may be visible to the operator from an open end of the housing. The radiation may be visible to the operator from a window or aperture in a wall of the housing.  
      Preferably the power indicating device further includes a circuit board electrically connected to the power supply wire.  
      Particularly preferably the power indicator is mounted on the circuit board.  
      In a preferred embodiment the power tool further comprises a housing for the power indicating device; and a transparent sheath located adjacent to the power indicator and partially exposed from the housing (e.g. from the proximal end of the housing).  
      In a particularly preferred embodiment the power tool further comprises a wire sheath surrounding the power supply wire, wherein the transparent sheath is mounted between the wire sheath and the housing.  
      Preferably the power indicator is electrically connected to the circuit board.  
      In a particularly preferred embodiment, the power tool further comprises a housing for the power indicating device, wherein the housing incorporates a through hole and the power indicator is visibly received in the through hole.  
      Preferably the power indicator is a light emitting diode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded perspective view of a part of a power tool of a first embodiment of the present invention;  
       FIG. 2  is an assembled perspective view of the embodiment of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view along A-A of  FIG. 4 ;  
       FIG. 4  is a cross-sectional view along C-C of  FIG. 3 ;  
       FIG. 5  is a cross-sectional view along B-B of  FIG. 4 ;  
       FIG. 6  is a schematic circuit diagram of an embodiment of the present invention;  
       FIG. 7  is an exploded perspective view of a part of a power tool of a second embodiment of the present invention; and  
       FIG. 8  is an assembled perspective view of the embodiment of  FIG. 7 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  illustrates an exploded perspective view of a part of a power tool according to a first embodiment of the present invention. The power tool includes generally a housing  7 , a supply wire  1  and a power switch  2 . A power indicating device  20  within the housing  7  is electrically connected to the supply wire  1 . A wire sheath  12  encloses the supply wire  1  and is partially embedded in the housing  7 . The wire sheath  12  forms a slot  22  and the housing  7  forms a projection  24  fitted in the slot  22 . A power plug  8  is connected remotely at a proximal end of the supply wire  1  to be inserted into a power jack (not shown).  
      With particular reference to FIGS.  2  to  5 , the power indicating device  20  includes a circuit board  21 , a power indicator  23  electrically connected to the circuit board  21  and a transparent sheath  27 . A pair of resistors  26  are positioned distal to the circuit board  21 . The power indicator  23  is a pair of light emitting diodes (LEDs— 23   a ,  23   b ) which are mounted proximally on the circuit board  21  and are electrically connected to the corresponding resistors  26 . The transparent sheath  27  is cylindrical and embedded between the wire sheath  12  and housing  7  so as to be partially exposed from the housing  7 . The transparent sheath  27  is adjacent to and aligned with the LEDs  23   a, b . A pair of latching rings  29  are formed externally on the transparent sheath  27  and engage the housing  1 .  
       FIG. 6  shows schematically a circuit diagram of the electrical connection between the power indicating device  20 , the power switch  2  and the power supply wire  1 . A first electric circuit  15  containing the power switch  2  and a second electrical circuit  16  containing the power indicating device  20  are connected in parallel to the power supply wire  1 .  
      Referring to  FIGS. 7 and 8 , a power tool according to a second embodiment of the present invention is shown. Wherever possible, the reference numerals used hereinbefore in respect of FIGS.  1  to  6  are used in describing hereinafter the second embodiment. The power tool of the second embodiment includes a housing  7 , a power supply wire  1 , a power switch  2  and a power indicating device  3 . The power indicating device  3  and power switch  2  are electrically connected to the supply wire  1 . In the second embodiment, the power indicating device  3  includes a power indicator  4  and a circuit board  5  electrically connected to the power indicator  4  by wires  120  and a retaining device  6  for retaining the circuit board  5  in the housing  7 . In this embodiment, the power indicator  4  such as an LED is positioned on a positioning plate  10  and is fixed to the housing  7  via a pair of screws  11 . The housing  7  defines a through hole  9  and the power indicator  4  is received in the through hole  9  so as to be visible therethrough.  
      In accordance with the first and second embodiment, the operator can quickly judge whether or not power has been interrupted via the power indicator  4  and does not need to walk to the power plug  8 .