Power Tools

Abstract

A typically battery-operated power tool, such as a chainsaw or hedge trimmer, comprising a working element ( 4 ), a motor ( 6 ) arranged to drive the working element ( 4 ) and a controller ( 9 ) arranged to control the speed at which the motor drives the working element ( 4 ), in which there is provided a sensor ( 12 ) for at least one factor indicative of the efficiency with which the power tool is being operated, the controller ( 9 ) being arranged to vary the speed at which the motor ( 6 ) drives the working element ( 4 ) should the factor indicate that the power tool is being operated in a sub-optimal manner. Typically, the factor is the pressure which the user is applying the power tool, and the sensor ( 12 ) is a sensor for the current flowing through the motor ( 6 ).

1 . A power tool comprising a working element, a motor arranged to drive the working element and a controller arranged to control the speed at which the motor drives the working element, in which there is provided a sensor for at least one factor indicative of the efficiency with which the power tool is being operated, the controller being arranged to vary the speed at which the motor drives the working element, so as to provide feedback through said speed to the user, should the factor indicate that the power tool is being operated in a sub-optimal manner. 
     
     
         2 . The power tool of  claim 1 , in which the controller is arranged to reduce the speed at which the motor drives the working element in the event of the power tool being used in a sub-optimal manner. 
     
     
         3 . The power tool of  claim 1 , in which the controller is arranged to cyclically vary the speed, so as to provide vibrations to the user, in the event of the power tool being used in a sub-optimal manner. 
     
     
         4 . The power tool of  claim 1 , in which the at least one factor comprises the pressure which the user applies the working element to a subject to be worked. 
     
     
         5 . The power tool of  claim 1 , in which the tool is an electric power tool and the motor is an electric motor and in which the sensor comprises a current sensor arranged to measure the current flowing through the motor. 
     
     
         6 . The power tool of  claim 5 , in which the controller is arranged to reduce the speed at which the motor drives the working element when the current measured by the current sensor exceeds a limit. 
     
     
         7 . The power tool of  claim 1 , being an electric power tool where the motor is an electric motor, in which the controller comprises a variable power control element having an input and an output, in which the controller is arranged so that, if the factor as measured by the sensor is indicative of a sub-optimal operation of the power tool, the power control element reduces the power that is transmitted from the input to the output. 
     
     
         8 . The power tool of  claim 7 , in which the power tool comprises a source of electric power, a speed selector operable by a user of the power tool and operative to take electric power from the source and output an electric signal indicative of a speed at which the user desires to operate the power tool, the output of the speed selector being coupled to the input of the power control element. 
     
     
         9 . A method of operating a power tool comprising a working element, a motor arranged to drive the working element and a control element via which a user indicates a desired speed, the method comprising sensing at least one factor indicative of the efficiency with which the power tool is being operated, the power tool varying the speed at which the motor drives the working element from the desired speed should the factor indicate that the power tool is being operated in a sub-optimal manner, thereby providing feedback to the user through the speed at which the working element is being driven. 
     
     
         10 . The method of  claim 9 , in which the step of varying the speed comprises reducing the speed at which the motor drives the working element. 
     
     
         11 . The method of  claim 9 , in which the at least one factor comprises the pressure which the user applies the working element to a subject to be worked, the load on the working element as it works the subject to be worked or the speed at which the motor or the working element is working; the temperature of a battery of the tool; the temperature of the motor; the current drawn by the motor, the integral of the current drawn by the motor, or the power consumed by the motor.