Abstract:
A rotating head for a device for the nondestructive testing of metallic test specimens has probe carriers, stray flux or eddy current sensors, a coupling ring and elastic coupling elements. In this way, tandem-like, roughly forced coupling of the pivoting motions of the probe carriers is produced.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a rotating head for use in a device for nondestructive testing of test materials or test specimens, especially test material in the form of metal articles, for example, of bar-shaped rolled material. 
   2. Description of Related Art 
   A similar device is known from European Patent EP 0452433 and corresponding U.S. Pat. No. 5,187,435, which is hereby incorporated by reference to its full extent, for the sake of brevity. This invention is a rotating head for nondestructive eddy current testing of, for example, ferromagnetic pipes, bars and wires, including those which are covered. 
   SUMMARY OF THE INVENTION 
   A primary object of this invention is to improve the rotating head of a nondestructive testing device of the initially mentioned type such that economical operation is enabled and improved, and more versatility is achieved for conducting stray flux tests and eddy current tests. 
   This object is achieved by a rotating head which has elastically acting construction elements for tandem-like, roughly forced coupling of pivoting motions of probe carriers to which stray flux or eddy current sensors are attached, the pivoting motions deflecting the stray flux or eddy current sensors and probe carriers based on eccentric position changes of a specimen being tested. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view of the prior art device of European Patent EP 0452443 and corresponding U.S. Pat. No. 5,187,435. 
       FIG. 2 ; is a cross-sectional view of construction elements which pivotably move probe carriers and test sensors for use in comparing the prior art device of  FIG. 1  with that of the present invention. 
       FIG. 3  is a cross-sectional view corresponding to that of  FIG. 2 , but showing construction elements which pivotably move probe carriers and test sensors attached thereto in accordance with the present invention; and 
       FIG. 4  is schematic representation for explaining how movement of the sensors is elastically controlled based on eccentric position changes of the test specimen. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows the prior art from the European Patent EP 0452443 and corresponding U.S. Pat. No. 5,187,435. The rotating disk  50  is mounted to be able to rotate relative to the housing  10  together with probe levers  52  which are mounted there and which can be pivoted around pins  54  or the like. The probe levers as sensors which bear eddy current detectors  60  which are mounted here, for example, on probe beams  58  and deliver useful signals. 
   A rough approximation of the construction elements of the prior art, if constructed in a manner comparable to that of the present invention, is shown in  FIG. 2 , the yokes  82 ,  84  together with exciter coils  80 ,  90  providing for the test specimen  62  to be magnetized according to the known rotary eddy current test process so that the sensors  60  can detect the eddy current variation which is caused by a material defect of the test piece. Testing with the prior art device can also be performed with stray flux or stationary eddy current transducers in addition to the rotary eddy current transducers. 
   In accordance with the present invention, it is possible to move the eddy current sensors much closer to the test article than was possible in the past. The reason for this is that the pressure forces of the sensors acting against the test article can be kept much smaller than has been or could be provided in the past. Therefore, for this reason, there can also be an eddy current sensor which functions with a rather low contact force on the test article (instead of the previously necessary contactless sensors). As a result, higher signal frequencies can be detected, or what is equivalent, defects with smaller dimensions on the test specimen than was possible in the past. 
   The actual innovation in accordance with the invention is apparent from  FIGS. 3 &amp; 4 . 
   As is apparent from  FIG. 3 , the probe levers  152 ,  152 ′, which can be pivoted around the bearing elements (for example, pins)  54 ,  54 ′, have their motion coupled via a coupling ring  180  with interposition of elastic elements (not shown in  FIG. 3 ). For this purpose there are coupling elements  170 ,  172  which cause the desired elastic coupling of the probe levers  152 ,  152 ′ to the coupling ring  180 . In this way, for example, a pivoting motion of the probe lever  152 ′ to the left, caused by the eccentricity of the test article  62  acting on the contact-making sensor  60 ′, provides for the sensor  60  on the sensor lever  152  to follow this motion in the desired sense without pressure springs, an electromagnetic actuator or the like being necessary. The same applies to a pivoting motion of the probe lever  152  to the right which then applies a tension motion to the probe lever  152 ′ together with its sensor  60 ′ so that two of these sensors remain resting on the test article with a relatively light contact force, always located at least in the immediate vicinity of the test piece. It goes without saying that the inside diameter of the coupling ring  180  must be larger than the outside diameter of the test article  62 . The coupling ring  180  is preferably produced from a light, stable material, such as titanium or aluminum, optionally also from a carbon fiber composite. 
   The conditions illustrated in  FIG. 3  are shown in highly schematic form in  FIG. 4 . Deflection of the sensor S 1  (reference number  60 ) caused by the eccentric location of the test piece  62 , e.g., a rod or pipe that is not perfectly strait, and resulting contact force F 1  is transmitted almost directly to the coupling ring  180  via an elastically acting construction element D 1  which is implemented, for example, in the form of a rubber buffer. The ring acts, for its part, via a second, likewise elastically acting construction element D 2  on the sensor lever  152 ′ with a moment of inertia M 2 . In this way, the sensor lever  152 ′ together with the respective sensor S 2  (reference number  60 ′) can follow the receding motion of the test specimen “M” (reference number  62 ) without spring force. A comparable result applies if contact is made with the sensor S 2  and a contact force F 2  shifts the sensor S 2  so that by means of the elasticities D 1 , D 2  and the coupling ring  180  subsequent displacement of the sensor S 1  ( 60 ) takes place. Moreover, the elasticities D 1 , D 2  allow matching of the location of the sensors S 1 , S 2  to the test specimen if it should have deviations from its nominal diameter. 
   In accordance with the invention, it is advantageous to provide additional, possibly selectively acting elastic construction element pairs D 11 , D 12 , &amp; D 21 , D 22  which provide for zero positioning (angular position setpoint) of the sensors S 1 , S 2  together with the coupling ring  180  in the absence of the test piece  62 . 
   Altogether, with the innovations in accordance with the invention, it becomes possible with great advantage to be able to sense, i.e., test, the ends of the test piece immediately upon entry into the rotating head; this was not possible with existing methods. Moreover, likewise, with great advantage, an electronically acting distance compensation device which was needed in the past for eddy current sensors can be omitted. 
   The indicated elastic construction elements can be produced from a metal, or a high-quality rubber-like material, for example, fluorosilicone rubber.