Abstract: In the present method for monitoring and controlling a screwing process in creating a screw connection, ultrasonic pulses are coupled into the screw using a pulse-echo method before and during the tightening of the screw. The time for the pulses to traverse the length of the screw, i.e., the propagation time, is measured. A dependency of the propagation time on the predetermined tension of the screw is calculated from the material specific characteristic values of the screw and the measured propagation time. By comparing the values of a change in propagation time dependent on a parameter of the screw with the values of a change in propagation time dependent on the predetermined tension of the screw, the screwing process can be monitored.

Abstract: The present invention relates to a method for monitoring and, if need be, controlling a screwing process in the creation of a screw connection using a screw, in which ultrasonic pulses are repeatedly coupled into the screw starting from the head of the screw using a pulse-echo method before and during the tightening process and the time it takes the ultrasonic pulses to traverse the length of the screw (propagation time) is measured. Before starting the tightening process, a dependency of the propagation time of the ultrasonic pulse on the predetermined tension of the screw is calculated from the material-specific characteristic values of the screw utilizing the measured propagation time through the load-free screw. Comparison of a change in propagation time dependent on a screw parameter with a calculated change in propagation time dependent on the predetermined tension of the screw permits drawing conclusions about the control of the screwing process.

Abstract: A device for measuring ultrasound transit times in workpieces disposed over an HF pulse generator which generates high-frequency wave trains with few oscillations periods and which is connected with an ultrasound transmitter/ultrasound receiver, whose output signal acts upon a comparator. The comparator generates pulses on zero crossings of the ultrasound echo. Between a gate circuit and a counter there is provided an AND-gate, whose second input is acted upon with the output signal of the comparator. The time gate of the gate circuit can be positioned, computer controlled, a quarter-wavelength of the ultrasound before the maximum of the envelope curve signal of the amplified ultrasound echo, so that it always equal-lying steepest zero crossing triggers the start or stop impulse of the counter.