Patent ID: 7334648
Filing Date: 2008-02-26
Classification: B25B

Abstract:
1. A rotary impact power tool comprising: a motor; a drive shaft configured to be driven to rotate by said motor; an output shaft configured to hold a tool bit, said output shaft being provided with an anvil, a hammer coupled to said drive shaft to be rotatable together with said drive shaft, said hammer configured to be engageable with said anvil to give a rotary impact to said output shaft as said drive shaft rotates; a trigger configured to be manipulated by a user to give a speed index indicative of an intended speed of said drive shaft in proportion to a manipulation amount of said trigger; a speed commander configured to generate a target speed based upon said speed index; a speed detector configured to detect a rotation speed of said drive shaft to give a detected speed; a speed controller configured to generate a control signal which drives said motor in order to match said detected speed with said target speed; wherein said speed controller is configured to set a detection time frame, and to use a predefined pseudo-detection speed as a substitute for said detected speed when said speed controller receives no detected speed from said speed detector within said detection time frame, said pseudo-detection speed being a minimum speed greater than zero and being set to vary depending upon the target speed.