| 摘要 |
The preferred embodiment of the invention disclosed herein relates to a method of and a tightening system for tightening a joint assembly including a fastener system to a yield point of one of the members in the assembly. According to the method torque is applied and rotation is imparted to a fastener member and the instantaneous slope of the Torque-Rotation curve which could be plotted is determined between successive increments of rotation of the fastener member. Each instantaneous slope is compared with the preceding instantaneous slope to determine the change in the slope of the curve. When the instantaneous slope of the curve decreases a predetermined consecutive number of times equal to a predetermined span of rotation divided by the interval between successive increments of rotation, tightening is discontinued. The tightening system includes a wrench and a control system associated with the wrench including gradient calculating means for determining the instantaneous slope between successive increments of rotation of the Torque-Rotation curve and for determining an instantaneous gradient signal representative thereof. Comparator means responsive to the instantaneous gradient signal determines the change in successive instantaneous gradient signals and develops signals indicating that the slope has increased or decreased. The indicating signals are fed to resettable counter means which counts each decrease signal, and resets to zero each time it receives an increase signal. When the counter means detects a predetermined successive number of decrease signals, it outputs a control signal that discontinues operation of the wrench.
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