Electrical power tool having a motor control circuit for increasing the effective torque output of the power tool

A method of controlling a power tool having a tool holder, gear means for coupling power to said tool holder, and an electric motor for driving said tool holder via said gear means, said gear means having associated therewith a degree of looseness which must be taken up before torque from said motor is transferred to said tool holder and which further causes said gear means to relax after power to said motor is reduced;

• the method comprising the steps of:
• applying power to said motor,
• monitoring an operating parameter of said motor,
• detecting a predetermined occurrence in said operating parameter, and
• thereupon cyclically reducing power to said motor for a first interval of sufficient duration to enable said gear means to at least partially relax and thereafter increasing power to said motor for a second interval to enable said motor to build up potential energy as the looseness in said gear means is taken up to thereby cause substantial repetitive variations in the torque applied to the tool holder.

A power tool having a tool holder, gear means for coupling power to said tool holder, operator actuable input means, and an electric motor for driving said tool holder via said gear means, said gear means having associated therewith a degree of looseness that must be taken up before torque from said motor is transferred to said tool holder and which further results in said gear means relaxing after power to said motor is substantially reduced;

• the improvement comprising:
• current sensing means for sensing a current flow through the motor of the power tool;
• and
• control means responsive to actuation of said input means for controlling the power supplied to the motor, and further responsive to said current sensing means for detecting when the current through the motor has exceeded a predetermined current level and thereupon, with said input means actuated, repetitively cycling the power to the motor by substantially reducing and increasing power to the motor such that the reduced power intervals are of sufficient duration and of sufficient magnitude to enable the gear means to at least partially relax.

A method for controlling a motor of an electric power tool such that said motor is caused to repetitively generate substantial variations in torque output once a predetermined current flow through said motor is reached, said method comprising the steps of:

• applying power to the motor in accordance with an operator actuable switch means;
• providing a current threshold level;
• sensing the current flow through said motor of said power tool;
• comparing said sensed current flow through said motor against said current threshold level;
• and
• with said switch means actuated, repetitively cycling power to the motor by substantially reducing and increasing power to the motor when said current flow through said motor exceeds said current threshold level such that current flow through said motor is alternatively reduced for a predetermined first interval sufficient to allow a gear train associated with said motor to at least partially relax, and after said predetermined first interval has expired, current flow through said motor is increased for a predetermined second interval.