Ultrasonic inspection apparatus for a spherical body

Abstract

A spherical body inspection apparatus including a support arrangement realized to support a spherical body during an inspection procedure; a probe arrangement comprising a plurality of ultrasonic testing probes arranged about the spherical body such that the ultrasonic testing probes target a common test point at the surface of the spherical body; and a displacer for effecting at least one relative rotational displacement between the spherical body and the probe arrangement. Also described is a method of inspecting a spherical body.

Claims

1. A spherical body inspection apparatus comprising: a support arrangement realized to support a spherical body during an inspection procedure; a probe arrangement comprising a plurality of ultrasonic testing probes arranged about the spherical body such that the ultrasonic testing probes simultaneously target a common test point at the surface of the spherical body and at least one of the plurality of ultrasonic testing probes is arranged to emit an ultrasonic pulse that enters and exits the spherical body at the common test point and passes as a longitudinal wave through the spherical body and at least one other of the plurality of ultrasonic testing probes is arranged to emit an ultrasonic pulse that, after refraction into the spherical body, passes as a transverse wave along a chord of the spherical body to the common test point; and a displacer for effecting at least one relative rotational displacement between the spherical body and the probe arrangement.

2. The inspection apparatus according to claim 1, wherein the displacer comprises a rotator realized to rotate the spherical body about a first axis of the spherical body and/or a probe displacer realized to rotate the probe arrangement about a second axis of the spherical body.

3. The inspection apparatus according to claim 2, wherein the first axis and the second axis are orthogonal axes passing through the centre of the spherical body such that successive test points describe a loxodrome on the spherical body.

4. The inspection apparatus according to claim 3, comprising a controller realized to control the rate of rotation of the spherical body and/or the rate of rotation of the probe displacer.

5. The inspection apparatus according to claim 1, wherein the at least one other of the plurality of ultrasonic testing probes is held to subtend a predetermined angle of incidence relative to a central axis of the spherical body to achieve a desired refraction angle.

6. The inspection apparatus according to claim 1, wherein an ultrasonic testing probe of the plurality of ultrasonic testing probes comprises a focused ultrasonic testing probe having a focal length, which ultrasonic testing probe is held at a distance from the spherical body corresponding essentially to the focal length of that ultrasonic testing probe.

7. The inspection apparatus according to claim 1, wherein the probe arrangement comprises a set of matched ultrasonic testing probes.

8. The inspection apparatus according to claim 1, further comprising an acquisition unit for recording reflected ultrasonic pulses detected by the ultrasonic testing probes.

9. The inspection apparatus according to claim 1, further comprising an analysis unit for analysing the recorded ultrasonic pulses to determine the presence of an anomaly in the spherical body.

10. The inspection apparatus according to claim 1, realized for use in an immersion tank.

11. A method of inspecting a spherical body, which method comprises: arranging a probe arrangement comprising a plurality of ultrasonic testing probes relative to the spherical body such that the ultrasonic testing probes simultaneously target a common test point at the surface of the spherical body with at least one ultrasonic pulse that enters and exits the spherical body at the common test point and passes as a longitudinal wave through the spherical body and at least one ultrasonic pulse that, after refraction into the spherical body, passes as a transverse wave through the spherical body along a chord to the common test point; and actuating the ultrasonic testing probes to emit the ultrasonic pulses while effecting at least one relative rotational displacement between the spherical body and the probe arrangement of the ultrasonic testing probes.

12. The method according to claim 11, wherein a rate of rotation of the spherical body and a rate of displacement of the probe arrangement are chosen to achieve an essentially complete coverage of the surface of the spherical body by a path described by a succession of test points on the surface of the spherical body.

13. The method according to claim 11, wherein, in a first relative rotational displacement, the spherical body is rotated through a plurality of complete revolutions about a first axis while, in a second relative rotational displacement, the probe arrangement is displaced at least through a space containing one hemisphere of the spherical body.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows an embodiment of an inspection apparatus;

(3) FIG. 2 shows a further view of the inspection apparatus of FIG. 1;

(4) FIG. 3 is a schematic drawing of a transverse ultrasonic wave through a spherical body;

(5) FIG. 4 shows a first path of targeted test points described on a spherical body during an inspection method;

(6) FIG. 5 shows a second path of targeted test points described on a spherical body during an inspection method;

(7) FIG. 6 shows a portion of an embodiment of an inspection apparatus;

(8) FIG. 7 shows a first instant during an inspection method;

(9) FIG. 8 shows a second instant during an inspection method;

(10) FIG. 9 shows exemplary anomalies in a steel bearing ball that may be detected by the inspection apparatus;

(11) FIG. 10 shows a known art bearing ball inspection setup.

(12) In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION

(13) FIGS. 1 and 2 show two views of an embodiment of an inspection apparatus 1 according to embodiments of the invention. A steel bearing ball 2 is supported in a support arrangement 10. Three UT probes 11A, 11B, 11C of a probe arrangement are held in a configuration to point at the bearing ball 2 such that they target a common test point on the surface of the ball 2. One probe 11C is a longitudinal UT probe 11C, i.e. it is held to emit an ultrasonic pulse that will travel through the ball 2 as a longitudinal pulse. The other two probes 11A, 11B are transverse UT probes 11A, 11B, i.e. these are held to emit an ultrasonic pulse that will be refracted upon entry into the ball 2 to result in a transverse wave. A probe holding arrangement comprises a wing 11 to which are mounted a number of jigs 112. Each jig 112 holds its probe 11A, 11B, 11C in a predefined attitude relative to the sphere 2 to maintain the desired configuration of the probe arrangement throughout the inspection procedure, for example by ensuring a specific angle of incidence of the ultrasonic pulse to achieve a desired angle of refraction of the resulting shear wave or transverse wave.

(14) The inspection apparatus 1 comprises a ball rotator 100, 101, which causes the ball 2 to rotate about a first axis X passing through the center of the ball 2. A probe displacement means or displacer 110 causes the wing 11 to rotate about a second axis Y that is orthogonal to the first axis X and also passes through the center of the ball 2.

(15) These elements of the inspection apparatus can be placed in an immersion tank 15, as indicated in FIG. 2, which can be filled with water to act as a couplant during the inspection procedure. A further element of the inspection apparatus 1 is a controller 12 for controlling the rate of rotation of the bearing ball 2, and the rate of rotation of the wing 11. An appropriate combination of rotation rates can be chosen to achieve the desired level of coverage of the ball surface. The controller 12 can send appropriate commands 120, 121 to the ball rotation means or rotator 100 and probe displacement means or displacer 110 respectively. The skilled person will be familiar with such a setup. A further element of the inspection apparatus 1 is a data acquisition unit 13 for collecting and recording the reflected ultrasonic waves detected at the working surfaces of the UT probes 11A, 11B, 11C. To this end, the probes 11A, 11B, 11C can transfer probe data 130, 131, 132 to the data acquisition unit, e.g. over a network or wireless connection, as will be known to the skilled person. The acquired data can be analyzed in real-time and/or can be stored for analysis at a later point. Preferably, the inspection apparatus 1 according to embodiments of the invention includes an analysis unit 14 for analyzing the recorded ultrasonic signals to determine the presence of an anomaly in the spherical body 2. Alternatively or in addition, the recorded ultrasonic signals can be rendered by an appropriate module of a graphical user interface to allow a visual interpretation of the information.

(16) FIG. 3 is a schematic drawing showing the path of a transverse ultrasonic wave W.sub.T through a spherical body 2 during an inspection method according to embodiments of the invention. The diagram shows a section through the sphere 2 in the plane containing one of two transverse probes of the probe arrangement 11A, 11B, 11C of FIGS. 1 and 2. This diagram also indicates a favorable distance F between the working surface of a probe and the surface of the ball 2. The distance F is the same as the focal length of a focused probe. All three UT probes 11A, 11B, 11C are preferably focused probes held at this distance F from the ball 2.

(17) In this exemplary arrangement, a transverse probe 11A is held such that the initially longitudinal ultrasonic wave W.sub.L subtends an angle of incidence .sub.1 to a normal N to the surface of the ball 2. This results in an angle of refraction .sub.2 of the ultrasonic wave on account of the difference in density at the boundary between the couplant and the bearing ball 2. An angle of refraction .sub.2 of 45 has been observed during tests to result in an optimum shear wave amplitude at the far boundary, i.e. at the targeted test point P. The shear wave W.sub.T is reflected at the test point P and travels back to the entry point, where it undergoes refraction once again and conversion to a longitudinal wave, and is subsequently detected at the working surface of the transverse probe 11A. Any flaw or anomaly in the vicinity of the targeted test point P will appear in the detected signal as a departure from the expected pulse arrival time and amplitude. During the inspection procedure, the ball 2 is rotated about an axis above while the probe arrangement is moved about the rotating ball 2. The arrow in the diagram indicates the rotational displacement of this probe 11A relative to the bearing ball 2.

(18) The diagram also shows an initial position and a final position of the transverse probe 11A (dotted lines) for targeted test points at initial and final poles P.sub.1, P.sub.2 of a spherical spiral or loxodrome traced by the test points during the inspection procedure. The angle of incidence .sub.1 of the transverse probe 11A remains the same throughout the inspection procedure. For the sake of clarity, the diagram does not show the longitudinal probe 11C and the other transverse probe 11B, since these do not lie in the plane of the page, and it may be assumed that pulses emitted by these other probes 11B, 11C meet at the targeted test point P. The other transverse probe 11B is also held at the desired angle of incidence .sub.1 as described above.

(19) A portion of a loxodrome L already traced by the targeted test points P (under rotation of the ball and probe arrangement) commencing at an initial pole P1 is indicated as a projection in the lower part of the diagram. The density of the loxodrome L is determined by the rotational speed of the ball and/or the displacement speed of the probe arrangement.

(20) In an alternative approach, the desired refraction angle could be achieved by holding a transverse probe 11A such that its long axis is parallel to a central axis K of the bearing ball 2, but offset from that axis K by a predefined distance K.sub.offset as indicated in the diagram. The angle of refraction will increase as the offset increases. For an offset of 0 mm, no refraction occurs. For a steel bearing ball 2 with a diameter D of 60 mm, an offset of 14 mm has been found to result in the favorable angle of refraction .sub.2 of 45.

(21) FIG. 4 shows a loxodrome L that might be described on a bearing ball by a succession of targeted test points during an inspection method according to embodiments of the invention. Here, the loxodrome L is relatively open, as might be achieved by a relatively rapid motion of the probe arrangement. FIG. 5 shows a loxodrome L which is tighter or more dense, indicating the effect of a slower displacement of the probe arrangement. Experiments have shown that a probe displacement of 0.5 for every complete rotation of the bearing ball 2 can achieve an essentially complete coverage of a bearing ball with a diameter in the range of 50-80 mm.

(22) FIG. 6 schematically indicates part of an inspection apparatus 1 according to embodiments of the invention. The diagram indicates a possible realization of the support arrangement and rotation means or rotator. Here, the ball 2 rests on two pins 101 which are synchronously turned by some suitable driving means or driver (FIG. 2 shows a drive belt arrangement). The pin rotation causes the bearing ball 2 to rotate in the opposite direction about its X axis. This diagram also shows all three axes X, Y, Z of a 3D Cartesian space with its origin at the centre of the sphere 2. During an inspection procedure, as the bearing ball 2 rotates about the X axis, a probe arrangement (not shown) can be displaced along a curved path as indicated by the arrow R.sub.11, such that the test point momentarily being targeted lies along a vertical semi circle (broken line) in the upper hemisphere of the ball 2. Since the ball 2 is being rotated relatively rapidly about the X axis as indicated by the arrow R.sub.2, the previously targeted test points describe a spherical spiral L as indicated in the diagram. The probe arrangement can be moved from 0 to 180 along a semi-circular path as indicated in the diagram. To ensure an even better coverage of the ball surface, the probe arrangement can be moved through 200, with an additional 10 at either end of the 180 arc shown in the diagram.

(23) FIG. 7 shows a first instant during an inspection method according to embodiments of the invention. The diagram shows a longitudinal probe 11C flanked by two transverse probes 11A, 11B in a symmetrical arrangement. Here, the position of each transverse probe 11A, 11B is fixed according to a predefined attitude such that the transverse waves W.sub.T arrive at the target point P defined by the point of entry/exit of the longitudinal wave W.sub.L emitted by the longitudinal UT probe 11C. The diagram shows the probe arrangement in a position to target a test point near a first pole P.sub.1 of a loxodrome or spherical spiral. The successive test points already targeted have traced a portion of a virtual loxodrome as indicated in the diagram. The rates of rotation of ball 2 and probe arrangement 11A, 11B, 11C have been set to achieve a fairly dense loxodrome, giving good coverage of the ball surface. FIG. 8 shows a later instant during the inspection procedure. Here, the probe arrangement 11A, 11B, 11C has been gradually displaced in the direction R.sub.11 while the bearing ball 2 has been rotated multiple times about its X axis as indicated by the arrow R.sub.2. The diagram shows the spherical spiral L traced by the targeted test points P and completed to a greater extent.

(24) FIG. 9 shows a cross-section through a steel bearing ball 2, showing exemplary anomalies or defects 20, 21, 22. One type of flaw 20 is a crack or tear at the surface. Another type of flaw is a pit 21 at the surface. These defects 20, 21 may be too small to be reliably detected by a visual inspection procedure, but can be large enough to have a detrimental effect on the performance of a bearing in which such a flawed ball 2 is used. A third type of flaw 22 is concealed below the surface and cannot be detected visually. If a ball with this kind of flaw 22 used in a bearing of a large machine, the flaw 22 can break open later on during operation of the machine, leading to poor performance or even seizure of the bearing. The inspection apparatus and method according to embodiments of the invention can reliably detect these and other similar kinds of defect, so that a high level of quality can be assured for any bearing that passes the inspection procedure.

(25) FIG. 10 shows a perspective view of a known art inspection setup 5 for performing UT inspection of a bearing ball. A single longitudinal UT probe 50 is mounted to point through the centre of the bearing ball 2. A support arrangement holds the bearing ball 2 underneath the probe 50. A number of rollers 51 underneath the bearing ball 2 are turned to effect a random rotation of the bearing ball 2 while the UT probe 50 emits successive ultrasonic pulses and detects their reflections. A controller 52 issues control signals to the rollers 51 to coordinate their actuation. A data acquisition unit 53 collects date from the UT probe 50. In this known art arrangement, it is difficult to achieve a full coverage of the bearing ball surface on account of the random rotations.

(26) Furthermore, the sensitivity of the single longitudinal probe 50 on its own is so low that only relatively large flaws can reliably be detected, and smaller but significant flaws of the type described in FIG. 9 can escape detection. Because only a longitudinal UT probe 50 is used, this prior art UT scanner arrangement cannot detect linear defects that are perpendicular, i.e. normal to the inspection surface. Small surface breaking cracks are defects that fall under this category, and would remain undetected, so that the prior art technique can only achieve an unfavorably low PoD. This kind of inspection arrangement is therefore associated with an unsatisfactory PoD level and is unsuited to the inspection of balls for a ball bearing intended to support a heavy machine such as a wind turbine generator.

(27) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(28) For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a module does not preclude the use of more than one unit or module.