Abstract: Apparatus and method for tightening assemblies held together by threaded fasteners. The desired tightened condition is achieved by turning the threaded fastener through a precise tightening angle required to induce a predetermined preload in the threaded fastener and calculated from input parameters characteristic of the assembly being tightened and the predetermined preload. The tightening angle is measured from the onset of linearity of the preload-rotation curve for the assembly by sensing the onset of the substantially linear tightening portion of the torque-rotation curve through which the assembly is taken as it is being tightened.

Abstract: A tightening system for tightening a fastener is disclosed herein and includes a wrench for tightening the fastener, a control system for shutting off the wrench when the fastener has been tightened to a predetermined condition and a quality control system including apparatus for determining the condition of the fastener at the predetermined condition and for also checking the operation of the system during the tightening cycle. Accordingly, an easily discernible and meaningful signal can be provided indicating that the tool has functioned properly and that the joint has been tightened to the predetermined condition.

Abstract: A sequential tightening system is disclosed in this application for tightening a plurality of fasteners to a final predetermined condition and includes a plurality of wrenches for tightening the fasteners and a control system operatively associated with each of said wrenches for tightening the fasteners to a first predetermined condition, preferably their seated condition and at a relatively high output speed of the wrenches, and temporarily discontinuing the tightening procedure. When the tightening procedure of all of the wrenches has been temporarily discontinued, the control means restarts the tightening procedure of each wrench simultaneously or, if desired, sequentially, and, preferably at a lower output speed of the wrenches. As each wrench tightens its operatively engaged fastener to the final predetermined condition, the control means discontinues the tightening procedure of that wrench.