Patent Publication Number: US-6698566-B2

Title: Clutch type safety switch for power tools

Description:
FIELD OF THE INVENTION 
     The present invention relates to a clutch type switch for a chainsaw to prevent the chainsaw from being activated by touching the trigger unintentionally. 
     BACKGROUND OF THE INVENTION 
     A conventional switch device for a power tool generally includes a trigger which is engaged with a trigger assembly. When pulling the trigger, the circuit of the power tool is activated and the tool is operated. However, most of the triggers have no safety device to avoid the user to touch the trigger unintentionally so that it is possible that the trigger is pulled unintentionally and the chainsaw for example is running. This is extremely dangerous so that there is a need to develop a safety device to prevent the situation from happening. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a clutch safety switch for a power tool and the clutch safety switch comprises a casing having a slot for a safety member slidably engaged therewith. A lug extends from an underside of the safety member and a trigger is pivotally located in the casing and has a protrusion which is interfered by the lug of the safety member. A link has an end thereof connected to the safety member. A gear is received in the casing and connected to a power source. The gear is independently mounted to an output shaft and a plurality of engaging recesses are defined in the gear. A plurality of guide rods and guide members respectively extend from an inside of the casing. A clutch member is mounted to the output shaft and has a plurality of blades each of which has a guide slot in which respective one of a plurality of guide rods extends. Each blade has a tapered extension extending therefrom which is able to be movable along the guide member. An engaging member is movably mounted to the output shaft and has bosses extending from a side thereof. A cover is fixed on the clutch member end the engaging member is retained in a central hole in the clutch member by the cover. A link is connected between the safety member and one of the blades of the clutch member. 
     The primary object of the present invention is to provide a clutch safety switch for a power tool wherein the trigger cannot be squeezed if the safety member is not slid. The power is not transferred to the chainsaw when releasing the trigger. 
     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view to show a clutch safety device of a power chainsaw of the present invention; 
     FIG. 2 is a side view to show the clutch safety device of the present invention; 
     FIG. 3 is a side view to show the clutch safety device of the present invention wherein the trigger is squeezed; 
     FIG. 4A shows that the engaging member is not yet moved to engage with the clutch member of the clutch safety device of the present invention, and 
     FIG. 4B shows that the engaging member is moved to engage with the clutch member of the clutch safety device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, the clutch switch device of the present invention comprises a casing  1 , a trigger assembly  2  and a clutch device  3 . The casing  1  includes a handle  11  of the power chainsaw and a pin  12  for pivotally connecting the trigger assembly  2  extends from an inside of the casing  1 . An activation switch frame  13  is connected above the trigger assembly  2 . A rod  16  is located in the casing  1  and a spring  17  has one end thereof connected to the rod  16 . The trigger assembly  2  includes an activation switch  21  which is received in the activation switch frame  13  and a trigger  22  which has a protrusion  221  and is pivotally mounted to the pin  12 . A slot  14  is defined through the casing  1  so that a safety member  23  is slidably engaged with the slot  14  and a stop member  15  located at a closed end of the slot  14 . A thumb portion  231  extends from the safety member  23  and through the slot  14 , a lug  232  extending from an underside of the safety member  23  so that when the protrusion  221  contacts the lug  232 , the trigger  22  cannot be squeezed. The safety member  23  has a head  233  and a link  25  is connected to the head  233 . A spring  24  has one end connected to the head  233  and the other end of the spring  24  is connected to the stop member  15 . The clutch device  3  includes a first gear  32  which is connected to a power source such as a motor (not shown) and a clutch device casing  31  for an output shaft  34  extending therefrom. A second gear  33  is located in the clutch device casing  31  and engaging recesses  331  is defined in a central portion of the second gear  33 . The second gear  33  and the output shaft  34  are two independent members which are not connected with each other. A clutch member  35  has three blades  351  extending radially outward therefrom at equal intervals and the output shaft  34  extends through a central hole of the clutch member  35 . A guide slot  352  is defined in a remote end of each of the blades  351  and a tapered extension  353  extends from each of the blades  351 . Three guide rods  311  and three guide members  312  extend from the clutch device casing  31 . The guide rods  311  are received in the guide slots and the guide members  312  are shaped to cooperate with the tapered extensions  353 . A spring  355  has one end connected to a hole  354  defined in one of the three blades  351  and the other end of the spring  355  is connected to a guide rod  311  in one of the guide slots  352 . A pushing portion  357  is connected to a remote end of one of the blades  351  and has a hole  356  for being connected to the other end of the spring  17 . A plate  36  is connected to the pushing portion  357  and has a hole  361  for being connected to the other end of the link  25 . A support plate  362  is connected to the plate  36  so as to prevent the link  25  from dropping from the hole  361 . An engaging member  37  has bosses  371  on a side and is movably mounted to the output shaft  34 . A cover  38  is mounted to the output shaft  34  and fixed to the clutch member  35  so that the engaging member  37  is retained in the central hole of the clutch member  35 . When the bosses  371  are engaging with the engaging recesses  331  in a central portion of the second gear  33 , the output shaft  34  is driven by the second gear  33 . A plurality of rollers are embedded in the engaging member  37  so as to reduce the frictional wear between the cover  38  and the engaging member  37 . 
     As shown in FIGS. 3 and 4A, when the safety member  23  is not slid toward the chainsaw, the protrusion  221  contacts the lug  232  so that the trigger  22  cannot be squeezed. After the safety member  23  is pushed to remove the lug  232 , the trigger  22  can be squeezed to activate the activation switch  21  to operate the chainsaw. In the meanwhile, the spring  24  is compressed when the safety member  23  is pushed and the link  25  pushes the plate  36  so as to let the clutch member  35  rotate clockwise. The rotation of the clutch member  35  and its blades  351  make the tapered extensions  353  move along the guide members  312  to let the bosses  371  move and engage with the engaging recesses  331  as shown in FIG.  4 B. Therefore, the power can be transferred from the second gear  33  to the output shaft  34  to drive the chainsaw. 
     When releasing the trigger  22 , the activation switch  21  is released and the safety member  23  is moved back by the spring  24 . The springs  17  and  355  pull the clutch member  35  to rotate counter clockwise and the bosses  371  are disengaged from the engaging recesses  331 . The power is then not transferred to the output shaft  34  and the chainsaw stops. 
     While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.