Magnetic flux leakage inspection apparatus with surface-responsive sensor mounting

• US 5,614,825 A
• Filed: 11/28/1994
• Issued: 03/25/1997
• Est. Priority Date: 11/28/1994
• Status: Expired due to Fees

• Current Assignee: Industrial Sensors and Actuators
• Original Assignee: Industrial Sensors and Actuators
• Inventors: Maxfield, Bruce W., Fitzgerald, Pamela C.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/345,901
• Time in Patent Office: 848 Days
• Field of Search: 324/235, 324/238-243, 324/262
• US Class Current: 324/242
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws

Abstract

Magnetic flux leakage inspection apparatus systems with independently suspended magnetic sensor blocks. The apparatus includes a magnet and a sensor assembly. The magnet is disposed over a surface of a magnetizable material under inspection for inducing magnetic flux in the material, and the sensor assembly is disposed in a predetermined inspection position over the surface for detecting magnetic flux leakage from the material that may indicate a magnetic anomaly in the material. The magnet and sensor assembly are moved along over the surface while the sensor assembly scans for magnetic leakage flux. The sensor assembly is formed with one or more independently suspended sensor blocks, each block including a plurality of sensors rigidly held in the block for detecting magnetic flux leakage. Each sensor block is independently mounted to permit the block to move perpendicular to the surface under inspection during the course of measurement as the sensor assembly and the surface are moved in scanning relation to one another. To avoid contamination of the measurement results by the normally present parallel flux leakage components, each block is subject to stringent constraints on the permitted departures of the perpendicular movement from perpendicularity, that is, on the amount by which the block may tilt as it undergoes its perpendicular movement. Each of the one or more blocks may be disposed to ride on the surface of the material under inspection, and each block may then undergo perpendicular movement independent of any other block in response to variations of the surface encountered in the course of inspection without causing undesirable magnetic field measurements to be mixed into the detected signal that would otherwise mask the much weaker desired signal indicative of magnetic anomalies.

Claims

1. Magnetic flux leakage inspection apparatus for precision inspection of a magnetizable material for magnetic anomalies, said apparatus including magnetizing means disposed over a surface of said material for inducing magnetic flux in said material for inspection thereof, and a sensor assembly disposed in a predetermined inspection position for detecting magnetic flux leakage from said material indicative of magnetic anomalies in the material, wherein said magnetizing means, said sensor assembly, and said material are disposed for relative movement of said magnetizing means and said sensor assembly in said predetermined inspection position along said surface for inspection of said material, said apparatus being characterized in that said sensor assembly comprises:

a sensor block including a plurality of sensors rigidly held therein for detecting

said magnetic flux leakage,

said sensor block being disposed in said inspection position to ride substantially on said surface, and

said sensor block being mounted for movement perpendicular to said surface in response to variations of said surface encountered in the course of inspection, wherein said sensor block is mounted to undergo said perpendicular movement through a distance of at least twice a characteristic size of said variations, and wherein said block is constrained to tilt at most 0.02 radians during said perpendicular movement;

whereby said sensor block undergoes perpendicular movement in response to said variations without causing a significant contribution to be mixed in from a magnetic field component parallel to the surface under inspection.

2. The apparatus of claim 1, further comprising at least one supporting member fixed to said sensor block and presenting a bearing surface for facilitating said perpendicular movement, and a receiving member formed to receive said supporting member and engage said bearing surface to permit said perpendicular movement.

3. The apparatus of claim 2 wherein said supporting member comprises a first elongate post secured at one end to said sensor block and having a bearing surface, and said receiving means defines a first elongate bore formed to receive said first post and engage said bearing surface to permit longitudinal movement of said first post therein and thereby to effect said perpendicular movement.

4. The apparatus of claim 3 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in adjacent rows are in line with one another.

5. The apparatus of claim 3 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in at least two adjacent rows are offset from one another.

6. The apparatus of claim 3, further comprising a second said post secured to said sensor block and parallel to said first post, and said receiving means defines a second elongate bore parallel to said first bore and formed to receive said second post to permit longitudinal movement of said second post therein.

7. The apparatus of claim 2 wherein said sensor block further comprises means defining a sacrificial wear surface formed for engaging the surface of the material under inspection.

8. The apparatus of claim 1 wherein said plurality of sensors are disposed in a line with said sensors being spaced apart from one another by a separation no greater than 0.40 inch.

9. The apparatus of claim 1 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in adjacent rows are in line with one another.

10. The apparatus of claim 1 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in at least two adjacent rows are offset from one another.

11. The apparatus of claim 1, further comprising means for urging said sensor block against the surface of said magnetizable material under inspection.

12. Magnetic flux leakage inspection apparatus for precision inspection of a magnetizable material for magnetic anomalies, said apparatus including magnetizing means disposed over a surface of said material for inducing magnetic flux in said material for inspection thereof, and a sensor assembly disposed in a predetermined inspection position for detecting magnetic flux leakage from said material indicative of magnetic anomalies in the material, wherein said magnetizing means, said sensor assembly, and said material are disposed for relative movement of said magnetizing means and said sensor assembly in said predetermined inspection position along said surface for inspection of said material, said apparatus being characterized in that said sensor assembly comprises:

a plurality of independently suspended sensor blocks, each said sensor block including a plurality of sensors rigidly held therein for detecting said magnetic flux leakage,

each said sensor block being disposed in said inspection position to ride on said surface, and

each said sensor block being mounted for movement perpendicular to said surface in response to variations of said surface encountered in the course of inspection independently of the other sensor blocks of said plurality, wherein each said sensor block is mounted to undergo said perpendicular movement through a distance of at least twice a characteristic size of said variations, and wherein each said block is constrained to tilt at most 0.02 radians during said perpendicular movement;

whereby said sensor blocks undergo independent perpendicular movement in response to said variations without causing a significant contribution to be mixed in from a magnetic field component parallel to the surface under inspection.

13. The apparatus of claim 12 wherein said plurality of sensor blocks are disposed in a line side by side with one another.

14. The apparatus of claim 13, further comprising at least one supporting member for each said sensor block, each said supporting member being fixed to a respective said sensor block and presenting a bearing surface for facilitating perpendicular movement of said respective sensor block, and a receiving member formed to receive said supporting members and engage said bearing surfaces to permit said perpendicular movement.

15. The apparatus of claim 14 wherein each said supporting member comprises a first elongate post secured at one end to said respective sensor block and having a bearing surface, and said receiving means defines a first plurality of bores formed to receive the first posts of said supporting members and engage said bearing surfaces to permit longitudinal movement of said first posts therein and thereby to effect said perpendicular movement.

16. The apparatus of claim 15 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in adjacent rows are in line with one another.

17. The apparatus of claim 15 wherein said plurality of sensors are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in at least two adjacent rows are offset from one another.

18. The apparatus of claim 15, further comprising a second said elongate post for each said sensor block, each said second post being secured to a respective said sensor block and parallel to said first post, and said receiving means defines a second plurality of elongate bores parallel to said first plurality of bores and formed to receive said second posts to permit longitudinal movement of said second post therein.

19. The apparatus of claim 13 wherein said sensor block further comprises means defining a sacrificial wear surface formed for engaging the surface of the material under inspection.

20. The apparatus of claim 12 wherein the plurality of sensors in each said sensor block are disposed in a line with said sensors being spaced apart from one another by a separation no greater than 0.40 inch.

21. The apparatus of claim 12 wherein said plurality of sensors of each said sensor block are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in adjacent rows are in line with one another.

22. The apparatus of claim 12 wherein said plurality of sensors of each said sensor block are disposed in a two-dimensional array comprising a plurality of parallel rows of sensors wherein the sensors in at least two adjacent rows are offset from one another.

23. A sensor block for use with magnetic flux leakage inspection apparatus for precision inspection of a magnetizable material for magnetic anomalies, said inspection apparatus including magnetizing means disposed over a surface of said material for inducing magnetic flux in said material for inspection thereof, and a sensor assembly for detecting magnetic flux leakage from said material indicative of magnetic anomalies in the material, said sensor assembly including sensor block mounting means for mounting said sensor block, wherein said sensor block comprises:

a housing;

a plurality of sensors rigidly held in said housing for detecting said magnetic flux leakage; and

first and second elongate posts, each said post being secured at one end to said housing and being formed with a bearing surface to be received in said sensor block mounting means to permit longitudinal movement of said first and second posts in said sensor block mounting means, wherein said first and second posts are parallel to one another to within 0.02 radians for facilitating movement of said housing with respect to said sensor block mounting means in a direction perpendicular to said surface.

24. The apparatus of claim 23, further comprising a spring disposed for urging said sensor block toward said surface when said sensor block is received in said sensor block mounting means.