Tightening system

Abstract

The invention disclosed herein relates to a tightening system including a wrench for applying torque and imparting rotation to a fastener system. Associated with the wrench is a control system including measuring systems for developing a first signal representative of the torque applied to the fastener being tightened and a second signal representative of the rotation of the fastener, both of which are fed to a gradient calculating system for developing a signal representative of the slope of a Torque-Rotation curve which can be plotted for the particular fastener being tightened. The gradient signal is used to develop a signal representative of a theoretical curve which is processed with one of the previously developed signals to develop a control signal when the fastener has been tightened to its yield point or some similarly significant point. In one embodiment of the invention, the theoretical curve signal is representative of a curve which ultimately becomes parallel to the linear portion of the Torque-Rotation curve and whose linearity is maintained when the Torque-Rotation curve deviates. The difference between the theoretical torque signal and the instantaneous torque signal, which is referred to as a decision-making signal, is determined and the difference between successive decision-making signals over a fixed increment of rotation is compared to the maximum gradient of the Torque-Rotation curve in its linear region. When the compared signals have a predetermined relationship, the control signal is developed. In another embodiment of the invention, the theoretical curve signal is representative of a curve superimposed on the Torque-Rotation curve through its linear region and whose linearity is maintained when the Torque-Rotation curve deviates. A ratio of the instantaneous torque signal to the theoretical torque signal is determined, and when this ratio is approximately equal to a predetermined ratio, the control signal is developed. In yet another embodiment of the invention, the theoretical curve signal is representative of a curve offset from the Torque-Rotation curve through its linear region by a predetermined constant and whose linearity is also maintained when the Torque-Rotation curve deviates. The theoretical torque signal is compared to the instantaneous torque signal and when the compared signals are approximately equal, the control signal is developed.