Multiprobe eddy current flaw detection device with means to raise and lower the individual probes

Claim 1

In an eddy current flaw detection device for detecting defects in a workpiece as the workpiece travels along a work path; (a) energizing means for causing a current to circulate in the workpiece in an inspection station along the path; (b) a plurality of pickup arms each pivotally mounted for movement toward and away from the path between inspection and storage positions; (c) a plurality of sets of individual sensing coils with each set of coils mounted on and supported by a corresponding and different one of said pickup arms; (d) said sets of sensing coils substantially completely surround a circumference of a workpiece when the sets of sensing coils are in proximity with the workpiece and the arms are moved in their sensing positions; (e) the individual sensing coils in each set being rigidly secured in spaced relationship with respect to each other for sensing changes in the current over a circumferential area of the workpiece; (f) a plurality of actuators respectively coupled to a corresponding one of said plurality of pickup arms for moving the respective pickup arms to their storage positions for maintaining the sensing coils out of proximity with the workpiece path and to move the arms to their inspection positions for maintaining the sensing coils in proximity with the workpiece; (g) each of the sets having an edge which is a leading edge with respect to the direction of workpiece travel along the path; (h) resilient shield means projecting in front of the leading edge of at least one set; (i) spring means for urging the at least one set away from the path until the shield means is between said leading edge and the path to protect the sensing set from collision with a workpiece advancing along the path into the station; (j) a plurality of bridge circuit means coupled to a respective set of sensing coils, each bridge circuit means having an input circuit coupled to the corresponding set of sensing coils and an output circuit for developing a control signal having a value representative of a level of unbalance on the corresponding set of sensing coils; and, (k) a like plurality of indicator circuit means each of which are coupled to the output circuit of a corresponding bridge circuit means for receiving the value of said control signal and developing an output signal indicative of both the occurrence and location of a flaw in the workpiece when the value of the control signal exceeds a predetermined value.