Method for yield tightening of screws

Claim 1

A method for yield tightening of screws by use of a wrench including a device for detecting a tightening torque, a device for converting a tightening angle and an electric motor for generating a screwing torque, and a controller including a device for receiving electric signals corresponding to the tightening torque and the tightening angle, a device for driving the electric motor, a read only memory for storing sequences necessary for a tightening process, a calculating step and a judgement step, a random access memory for storing present data necessary for the tightening process and data obtained during the tightening process, a microprocessor for performing calculations and judgements necessary for the tightening process, a device for displaying the various data and a device for transmission and reception of a judgement signal and various data between the controller and external systems, the method comprising: a step wherein after an actual tightening torque passes a certain preset torque limit, "n" (equal to or more than 4) pieces of actual torque data stored in a preset means are integrated by two integration stages and an average torque rate is calculated on the basis of a difference between the respective integrated values by the two stages; a step wherein it is recognized that an actual torque curve has reached a yield area when it is determined that the average torque rate is smaller than a preset target torque rate; a step wherein the tightening process is stopped immediately when the said recognition has been given in succession a plurality of times greater in number than 1/2 of the number "n"; a step wherein when the tightening process proceeds to a condition in which the next new data is provided, the oldest piece of data is removed from a routine of calculating the average torque rate and a new piece of data is added to the routine, the calculation being performed in succession updating the data to be calculated until the tightening process is stopped; and a step wherein after the actual tightening torque reaches the torque limit, an integrated value is calculated by subtracting the torque limit from the actual tightening torque, the area of a right triangle inscribed in the area of the integrated value is calculated, a difference value between the integrated value and the area of the right triangle is calculated, and when the difference value is larger than an area calculated by the use of a present target angle limit, the tightening process is immediately stopped.

Claim 2

A method for yield tightening of screws by use of a wrench including a device for detecting a tightening torque, a device for converting a tightening angle and an electric motor for generating a screwing torque, and a controller including a device for receiving electric signals corresponding to the tightening torque and the tightening angle, a device for driving the electric motor, a read only memory for storing sequences necessary for a tightening process, a calculating step and a judgement step, a random access memory for storing present data necessary for the tightening process and data obtained during the tightening process, a microprocessor for performing calculations and judgements necessary for the tightening process, a device for displaying the various data and a device for transmission and reception of a judgement signal and various data between the controller and external systems, the method comprising: a step wherein after an actual tightening torque passes a certain preset torque limit, "n" (equal to or more than 4) pieces of actual torque data stored in a preset means are integrated by two integration stages and an average torque rate is calculated on the basis of a difference between the respective integrated values by the two stages; a step wherein it is recognized that an actual torque curve has reached a yield area when it is determined that the average torque rate is smaller than a preset target torque rate; a step wherein the tightening process is stopped immediately when the said recognition has been given in succession a plurality of times greater in number than 1/2 of the number "n"; a step wherein when the tightening process proceeds to a condition in which the next new data is provided, the oldest piece of data is removed from a routine of calculating the average torque rate and a new piece of data is added to the routine, the calculation being performed in succession updating the data to be calculated until the tightening process is stopped; and a step wherein after the actual tightening torque reaches the torque limit, an integrated value is calculated by subtracting the torque limit from the actual tightening torque, the area of a right triangle inscribed in the area of the integrated value is calculated, a difference value between the integrated value and the area of the right triangle is calculated, and when the difference value is larger than an area calculated by the use of a present target angle limit, the tightening process is immediately stopped.