Apparatus for controlling a fastener driving tool, with user-adjustable torque limiting control
View Patent ↗An improved hand-held fastener driving tool is provided with an adjustable torque limiting control. The tool is portable, and is electrically powered using either a battery pack or a power cord as a power source. The tool drives collated fasteners (e.g., screws) into solid objects. The motor current is measured to determine the amount of torque being applied to a screw by the motor and mechanical drive components. As the screw bottoms out, the motor torque increases to a point where it exceeds the user-adjusted torque limiting control. The motor is automatically turned off at that point, thereby preventing the screw from being stripped.
1. 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.
2. A portable fastener-driving tool, comprising:
(a) a housing containing an electric motor, said housing having a guide rail portion that receives a collated strip of fasteners and directs them toward a driving end of the housing, said driving end of the housing having a fastener driving mechanism proximal thereto that receives said collated strip of fasteners from said guide rail portion and moves a fastener of the collated strip of fasteners to a driving position, said motor providing power to said fastener driving mechanism;
(b) an adjustable torque-limiting control device, said torque-limiting control device being set to a predetermined state by a user; and
(c) a controller circuit that is configured to compare an amount of torque being generated by said motor to said predetermined state of the torque-limiting control device, and to turn off said motor when amount of torque is greater than or equal to said predetermined state of the torque-limiting control device;
(d) wherein said controller circuit is further configured:
(i) to calculate a derivative of an electrical current flowing through said motor, versus time; and
(ii) to determine if said derivative of the motor electrical current is greater in absolute magnitude than a predetermined False Reading Setting.
3. A portable fastener-driving tool as recited in claim 2 , wherein:
(a) said guide rail portion is positioned on an upper surface of said housing; and
(b) said guide rail portion comprises a longitudinal pathway having an entry area along said housing upper surface and an exit area proximal to said housing driving end, said collated strip of fasteners being received at said entry area and then directed through said pathway toward said exit area, said collated strip of fasteners being directed from said exit area toward said fastener driving mechanism.
4. The portable fastener-driving tool as recited in claim 2 , wherein said controller circuit comprises:
(a) a current sensing circuit for determining a magnitude of said electrical current flowing through said motor;
(b) an input stage that detects a state of said user-adjustable torque-limiting control device;
(c) an output stage for controlling the magnitude of said current flowing through said motor; and
(d) a processing circuit that is configured to interface to said input stage and said current sensing circuit, and is configured to drive a gating signal to said output stage.
5. The portable fastener-driving tool as recited in claim 4 , wherein said controller circuit further comprises:
(e) a peak-to-peak detector circuit to determine an AC magnitude of said current flowing through said motor; and
(f) a zero voltage crossing detector to determine appropriate starting and stopping times for driving said gating signal.
6. A portable fastener-driving tool, comprising:
(a) a housing containing an electric motor, said housing having a first end and a second end, said housing including a first intermediate drive device that translates movement from said motor toward said second end;
(b) a detachable nose sub-assembly having a third end and a fourth end, in which said third end is positioned proximal to said second end of the housing when attached thereto, said third end including a second intermediate drive device that in is mechanical communication with said first intermediate drive device when said housing is attached to said detachable nose sub-assembly, said fourth end of the nose sub-assembly including a fastener driving mechanism that is in mechanical communication with said second intermediate drive device, used for driving a fastener into an object;
(c) an adjustable torque-limiting control device, said torque-limiting control device being set to a predetermined state by a user; and
(d) a controller circuit that is configured to compare an amount of torque being generated by said motor to said predetermined state of the torque-limiting control device, and to turn off said motor when amount of torque is greater than or equal to said predetermined state of the torque-limiting control device;
wherein said comparison between said amount of torque generated by the motor and said predetermined 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, 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 predetermined 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, de-energizing said motor.