Patent ID: 9114542
Filing Date: 2015-08-25
Classification: B26B

Abstract:
1. A method of indicating to a user that an electrically driven cutting tool that is driven by an electric motor in a back and forth motion has become dirty, comprising: measuring a parameter that corresponds to the motion of the cutting tool, and that is used to control the electric motor, wherein said parameter is selected from the group consisting of voltage applied to a coil of the electric motor, current flowing through said coil, the change of current flowing through said coil as a function of time, and combinations thereof; measuring changes in the parameter; registering a change in the parameter as a dirtying event if the amount of the change is greater than a threshold value; counting dirtying events; comparing the number of dirtying events to a reference number; and activating an indicator if the number of dirtying events meets or exceeds the reference number; further comprising: defining a first and a second threshold value; comparing negative changes in the parameter with the first threshold value; and comparing positive changes of the parameter with the second threshold value, and providing a counter for counting dirtying events; and weighting negative changes in the parameter higher than positive changes of the parameter during the counting.