Patent ID: 7331406

Claim:
A portable fastener-driving tool, comprising: (a) a housing containing an electric motor, said housing having a driving end that has a fastener driving mechanism proximal thereto, for receiving a collated strip of fasteners and moving a fastener of the collated strip of fasteners to a driving position, said motor providing power to said fastener driving mechanism; (b) a user-adjustable torque-limiting control device; and (c) a controller circuit that is configured: (i) to determine an amount of torque being generated by said motor, while actuating one of the fasteners in said driving position; (ii) to determine a state of said user-adjustable torque-limiting control device; and (iii) to compare said determined amount of torque generated by the motor with said determined state of the user-adjustable torque-limiting control device, and to turn off said motor when said determined amount of torque generated by said motor indicates that said fastener being driven has been sufficiently tightened, based on said determined state of the user-adjustable torque-limiting control device; thereby terminating a fastener driving event; wherein said comparison between said determined amount of torque generated by the motor and said determined state of the user-adjustable torque-limiting control device further comprises: (e) calculating a derivative of an electrical current flowing through said motor, versus time; (f) determining if said derivative of the motor electrical current is greater in absolute magnitude than a predetermined False Reading Setting, and: (i) if not, terminating said fastener driving event by de-energizing said motor; or (ii) if so, waiting for a predetermined time interval, and then determining if said derivative of the motor electrical current has become a negative value, and: (A) if so, continuing said fastener driving event; or (B) if not, determining if the motor current now has a magnitude greater than or equal to a current corresponding to said determined state of the user-adjustable torque-limiting control device times an End of Cycle Factor, and: (1) if not, continuing said fastener driving event; or (2) if so, terminating said fastener driving event by de-energizing said motor.