Patent ID: 7419013
Filing Date: 2008-09-02
Classification: B25B

Abstract:
1. A rotary impact tool comprising: a rotary driving mechanism including a driving source that rotates a driving shaft; a rotation sensor that senses rotation of a shaft of the driving source; a hammer fixed on the driving shaft; an output shaft to which a driving force is applied by impact blow of the hammer; a torque setting unit that sets a fastening torque; a processor that calculates fastening torque from impact blow of the hammer; a rotation speed setting unit that sets rotation speed of the driving shaft; a controller that rotates the driving shaft of the rotary driving mechanism in a rotation speed set in the rotation speed setting unit and stops rotation of the driving shaft of the rotary driving mechanism when the fastening torque calculated in the processor becomes equal to or larger than a reference value of fastening torque previously set in the torque setting unit; an input side rotation speed sensor that is connected to the rotation sensor and senses rotation speed of the driving shaft of the rotary driving mechanism from a rotation angle of the driving shaft from an impact blow to a next impact blow of the hammer; an impact sensor that senses occurrence of the impact blow of the hammer with the output shaft; and an output side rotation angle sensor that is connected to the rotation sensor and calculates the rotation angle of the output shaft from an impact blow to a next impact blow of the hammer using a rotation angle of the driving shaft of the driving source obtained from an output of the rotation sensor; wherein the processor calculates the fastening torque by dividing the impact energy, which is calculated using a mean rotation speed of the output shaft between the impact blows of the hammer sensed by the rotation angle sensor and the rotation speed sensor, by a rotation angle between the impact blows of the hammer which is sensed by the rotation angle sensor; and the controller drives the rotary driving mechanism at a rotation speed lower than a rotation speed set in the rotation speed setting unit, when a value of the fastening torque set in the torque setting unit is smaller than a predetermined reference value.