Power tool having control means for monitoring screw tightening operations

1. A power tool comprising:

a driving unit for performing screw tightening operations;

a motor for rotatably driving the driving unit;

a rechargeable battery pack;

a trigger switch for turning on and off the motor; and

a control circuit, accommodated in a main body of the power tool, for monitoring the screw tightening operations, wherein the control circuit has a screw tightening completion detection unit for detecting completion of a screw tightening operation; a screw tightening count unit for counting the number of completed screw tightening operations detected by the screw tightening completion detection unit; a screw tightening number setting unit for presetting the number of screws to be tightened; and a screw tightening completion notifying unit having a piezoelectric buzzer for notifying completion of the screw tightening operations when the number of completed screw tightening operations reaches the preset number of screws, and wherein the screw tightening number setting unit and the screw tightening completion notifying unit are disposed at a lower front portion of a grip portion in the main body of the power tool, for being held by a hand,

wherein the piezoelectric buzzer produces one of selectable alarm sounds having different pitches.

2. The power tool of claim 1 , wherein a protruded elastomer is installed around an outer periphery of the lower front portion of the grip portion.

3. The power tool of claim 1 , wherein the screw tightening number setting unit includes a “mode” button, a “+” button and a “−” button, and a sound setting mode is initiated by setting the “mode” button longer than a predetermined time.

4. The power tool of claim 1 , wherein the screw tightening number setting unit is provided with a hold function to prevent the preset number of screws to be fastened from being changed.

5. The power tool of claim 1 , wherein a body portion and the grip portion of the main body of the power tool are connected rotatably such that an angle therebetween is changed freely and the display of the number of tightening operations set by the screw tightening number setting unit provided at the lower front portion of the grip portion is displayed upside down.

6. The power tool of claim 3 , wherein the predetermined time is 2 seconds.

7. The power tool of claim 3 , wherein the pitches of the alarm sounds are changeable by pressing the “+” button or the “−” button in the sound setting mode and if the “mode” button is pressed while one of the alarm sounds having a specific pitch is produced, the alarm sound having that pitch is selected and stored.