초록 ▼

A portable electric power tool having a DC motor for driving tool bit is controlled according to speed and torque by employing a zero displacement switch means which is coupled to the tool and operative to provide an output voltage porportional to the pressure applied to the switch means via the han

A portable electric power tool having a DC motor for driving tool bit is controlled according to speed and torque by employing a zero displacement switch means which is coupled to the tool and operative to provide an output voltage porportional to the pressure applied to the switch means via the hand of the user. The zero displacement switch interfaces with a piezoresistive array which produces a voltage output proportional to the pressure applied to the zero displacement switch. The voltage output of the array is applied to control circuit means which are coupled to the motor and which controls the speed of the motor according to the pressure applied to the switch. There is further included motor control circuitry which operates to monitor the current through the DC motor to control the speed of the motor according to the torque imparted upon the tool bit being accommodated by the portable electric tool.

대표청구항 ▼

In a portable electric tool having a DC motor for driving a tool bit and for controlling the speed and torque at which said tool bit rotates, the improvement comprising: a zero displacement switch means coupled to said tool and operative to provide an output voltage proportional to the pressure appl

In a portable electric tool having a DC motor for driving a tool bit and for controlling the speed and torque at which said tool bit rotates, the improvement comprising: a zero displacement switch means coupled to said tool and operative to provide an output voltage proportional to the pressure applied directly to said switch via the hand of the user, control means coupled to said motor and responsive to said output voltage to variably control the speed of said motor according to the pressure applied to said displacement switch means, said control means including a pulse modulator for converting said output voltage to a pulse width modulated signal at an output of said modulator and means for applying said pulse width modulated signal to said motor for varying the speed of said motor according to said applied pressure, and switching means having first and second output electrodes and a control electrode, with said first output electrode coupled to one terminal of said motor and with said second output electrode coupled to a point of reference potential with said control electrode operative to switch said first and second output electrodes according to a control voltage applied thereto and with said control electrode coupled to said output of said pulse width modulator to operate said switch according to said pulse width modulated signal to therefore control the current through said DC motor and therefore the speed of said motor according to said pulse width modulated signal.