US 7,091,683 B1
Method of monitoring and controlling the seating of screws to the optimum point of grip independent of screw size and material densityGeneral
US 7,091,683 B1
Method of monitoring and controlling the seating of screws to the optimum point of grip independent of screw size and material density
Tech Center:
2800 Semiconductors/Memory, Circuits/Measuring and Testing, Optics/Photocopying, Printing/Measuring and Testing
Examiner:
Paul Ip
Art Unit:
2837 Electrical Circuits and Systems
Agent:
Inventors:
Joseph Whyte; Mark Smith
Assignee:
Priority:
10/24/03
Filed:
10/22/04
Granted:
08/15/06
Expiration:
10/24/23
Abstract
A method of controlling a motor (106) used to drive a screwdriver bit (105) such that screws (107) are seated to the optimum point of grip between the screw (107) and the work piece material. An electronic control circuit controls the speed and output torque of the motor (106). The control system utilizes pulse width modulation (PWM) to control motor (106) speed and torque. The PWM signal controls the duty cycle of the transistors that supply current to the motor (106). The amount of current flowing through the motor (106) coils is proportional to the amount of torque the motor (106) is producing. Motor (106) current is measured as voltage produced across a precision resistor that is in series with the motor (106) coils. As the current in the motor (106) increases, the voltage across the resistor increases (V=IR). To accurately measure the torque, as measured by the voltage across the precision resistor, a capacitor with a resistor and/or a diode is used to average the analog signal that is measured by the microprocessor. The microprocessor further filters the analog signal using an averaging formula to produce a stable value corresponding to motor (106) torque/current. When a decrease in current, corresponding to a drop in torque, is detected at the optimum point of grip, the controller (100) stops the motor (106).