Abstract: A tension contol method for a nutrunner performed by the use of a nutrunner and a controller associated with each other. In accordance with the present invention, the fastening torque T.sub.f of the torque transducer of the nutrunner at an intermediate position of a fixed first rotation angle .theta. included in a middle range from the seating of a controlled screw on a tightened object to the final fastening position of the screw is stored. The motor of the nutrunner is stopped at a position of a second rotation angle (.theta.+.alpha.) larger than the first rotation angle by a fixed value .alpha.. The motor of the nutrunner is reversed at the second rotation angle (.theta.+.alpha.). A return torque T.sub.r of the motor at the position of the first rotation angle .theta. is stored. The ratio of the fastening torque T.sub.f to a bolt tension F applied to the screw is calculated by the use of a difference between the fastening torque T.sub.f and the return torque T.sub.

Abstract: A method for yield tightening of screws by use of a wrench including a device for detecting a tightening torque in the actual tightening process, a device for detecting a tightening angle and an electric motor for applying a torque to each screw, a device for driving the wrench, and a controller including a device for communication with an external device. After the actual tightening torque reaches a certain value, an average torque rate is obtained by an integration using four or more pieces of torque data and is compared with a preset target torque rate, judging a yield point. The integration is performed for each minimum angle for which new torque data can be obtained. The tightening process is stopped when the judgement of the yield point has been given in succession a larger number of times than 1/2 of the number of torque data used for the integration.

Abstract: A method or system for measuring the top dead center for a reciprocating crank mechanism, in which a reversible counter performs the additive counting operation from an amount H of shift of the piston of the reciprocating crank mechanism to another amount H of the shift of the piston in a reverse driving direction of the crankshaft of the reciprocating crank mechanism at both sides of a minimum shift of the piston, for each predetermined unit rotational angle deviation of the crankshaft. The reversible counter performs the subtractive counting operation from said another amount H of the shift of the piston in one driving direction of the crankshaft for each one half the predetermined unit rotational angle deviation of the crankshaft. A position of the piston is decided as the top dead center when the counting state of the reversible counter reached zero in said one driving direction of the crankshaft.

Abstract: A nut runner for tightening screwed objects comprising: a driving motor, a driving shaft to be coupled to the screwed objects for driving the same, a reduction gear mechanism provided for transferring the revolution power of the driving motor to the driving shaft, a torque for detecting a torque applied to the driving shaft, and a control circuit for controlling the driving motor by the use of the detected output of the torque detector. In accordance with the present invention, a two-phase induction motor is employed as the driving motor.

Abstract: A nut runner control circuit which permits tightening of a screw in the plastic region with a normal torque without necessity of detecting the critical point from the elastic region to the plastic region. The ratio T.sub.0 /.theta..sub.2 of an increase T.sub.0 of torque from a value T.sub.1 to a value T.sub.2 during tightening to a corresponding rotational angle .theta..sub.2 (the rate of increase in the torque) and the torque T.sub.2 are stored in a peak memory circuit. After rotation of an angle .theta..sub.1 from the end point P.sub.0 of the rotational angle .theta..sub.2 the above-mentioned stored values are read out. The stored torque T.sub.2 is increased at the stored rate T.sub.0 /.theta..sub.2, so that at the intersection of the increased torque value to the actual tightening torque, the driving of the screw tightening tool is stopped.

Abstract: A single-phase, reversible induction motor, comprising two cylindrical rotors disposed side by side on the same axis of rotation, the rotors being composed of laminated iron cores and provided with grooves of the same number disposed in parallel with the shaft and on respective surfaces of the cylindrical rotors at regular intervals; two two-pole field systems respectively composed of laminated iron cores and surrounding the rotors, and coils for exciting the field systems, respectively, the field systems and the coils being arranged so that the directions of passage through the rotors of magnetic fluxes emanating therefrom be perpendicular to each other; and a switching circuit for reversing the phase of a single-phase alternating current supplied to one of the coils. Conductors of a magnetically permeable material are fixedly secured to all the grooves of one of the rotors but electrically isolated from the rotor iron core.

Abstract: A motor-driven clamping method characterized by a two-step control operation, in which when a torque applied to a member to be clamped reaches a first set value smaller than a reference set value, a drive motor is once decelerated and rapidly stopped; then the drive motor is re-started immediately and controlled so that the torque applied to the member to be clamped increases along a predetermined torque increasing characteristic; and when the torque applied to the member to be clamped reaches a second set value corresponding to the reference set value, the drive motor is braked to be rapidly stopped. A handy motor-driven clamping device of light weight can be prepared by embodying the above method.