Patent ID: 6155139
Filing Date: 2000-12-05
Classification: B25B

Abstract:
A pneumatically operable screw driver comprising:a housing with an intake port connected to a compression air source supplying compression air;an air motor provided in said housing and driven by the compression air introduced from said intake port;an anvil having a rear end accommodated in said housing and a front end protruding out of said housing;a transmission mechanism provided between said air motor and said anvil for transmitting the rotation of said air motor to said anvil;a driver bit securely held at a front end of said anvil so as to be shiftable together with said anvil relative to said housing;a resilient means for resiliently urging said driver bit and said anvil in a protrusile direction and also allowing said driver bit and said anvil to shift in a retractile direction relative to said housing when said driver bit receives a reaction force from a screw inserted into a board member;an air passage connecting said intake port to said air motor;an intake valve responsive to an retractile shift movement of said driver bit to open said air passage and supplying the compression air from said intake port to said air motor so as to rotate said air motor, and closing said air passage in response to a protrusile shift movement of said driver bit returning to its original position so as to stop said air motor; andan assist mean for applying a pressure of the compression air to a rear end surface of said anvil in response to the rotation of said air motor,wherein the compression air is introduced into an inside space of said housing to apply the pressure of the compression air to said rear end surface of said anvil in response to the rotation of said air motor, and the compression air is discharged in response to the stop of said air motor.