System for adjusting a magnetic sensor to detect the presence of ferrous objects

• US 6,127,821 A
• Filed: 12/18/1997
• Issued: 10/03/2000
• Est. Priority Date: 06/02/1997
• Status: Expired due to Fees

• Current Assignee: ZF Friedrichshafen AG (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: Cherry Corporation (ZF Electronics Corp.)
• Inventors: Ramsden, Edward A., Beiermann, Bradley S.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US08/993,723
• Time in Patent Office: 1,020 Days
• Field of Search: 324/202, 324/207.12, 324/207.2, 324/207.21, 324/207.26, 324/235, 338/32 H, 338/32 R, 335/205, 335/207, 361/147, 361/148
• US Class Current: 324/202
• CPC Class Codes: G01D 5/147 influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12
• CPC Class Codes: H03K 17/9517 using galvanomagnetic devices

Abstract

A proximity detector that employs a Hall-effect flux sensor disposed between the like poles of two magnets. The opposing fields of the magnets define a null flux field at a sensing plane of the Hall-effect sensor. A proximate ferrous object will deflect the null point and will therefore apply flux to the sensor. The sensor generates a signal indicative of the presence or absence of the ferrous object. In manufacturing a preferred spatial position of the null point with respect to the Hall-effect sensor is defined by adjusting the field strength of at least one of the opposed magnets.

Claims

1. A system for adjusting a magnetic flux detector to detect the presence of ferrous objects, comprising:

a magnetic flux sensor disposed at one position;

at least two magnets having like poles disposed on opposite sides of said sensor, the opposing fields of said magnets defining in the absence of a proximate ferrous object, a null flux point at a position that does not coincide with said one position of the flux sensor; and

means for inducing a permanent adjusted field in at least one of said magnets in the absence of a proximate ferrous object, so that the null flux point is moved to coincide with the one position of the flux sensor so that the sensor is not activated.

2. The magnetic flux detector of claim 1, wherein each of said magnets is an AlNiCo magnet.

3. The magnetic flux detector of claim 1, wherein one of said magnets is an AlNiCo magnet and the other of said magnets is a rare earth magnet.

4. The magnetic flux detector of claim 1, wherein said magnets are rectangular in shape.

5. The magnetic flux detector of claim 1, wherein said magnets are cylindrical in shape.

6. The magnetic flux detector of claim 1, wherein at least one of said magnets is rectangular in shape.

7. The magnetic flux detector of claim 1, wherein at least one of said magnets is cylindrical in shape.

8. The magnetic flux detector of claim 1, wherein said flux sensor is a Hall-effect sensor.

9. The magnetic flux detector of claim 1, wherein said flux sensor is a magneto-resistor.

10. The magnetic flux detector of claim 1, including an electrical circuit that generates a first electrical signal when the sensed flux intensity is above a predefined maximum level and a second electrical signal when the sensed flux intensity is below a predefined minimum level.

11. The magnetic flux detector of claim 10, wherein said first signal is a predefined maximum current and said second signal is a predefined minimum current.

12. The magnetic flux detector of claim 10, wherein said first signal is a predefined maximum voltage and said second signal is a predefined minimum voltage.

13. The magnetic flux detector of claim 1, wherein said magnets are rectangular in shape and are disposed adjacent to opposite corners of said magnetic flux sensor, whereby the concentrated flux from the corners of the magnets defines a null flux field adjacent to said at least one flux sensitive portion of the flux sensor.

14. The magnetic flux detector of claim 1, further including a mechanism having a ferrous latch for engaging and disengaging from said mechanism, said latch moving adjacent to one of said magnets of said flux detector when the latch is engaged, said circuit generating an electrical signal indicative of the presence of said latch and the latched condition of said mechanism.

15. The magnetic flux detector of claim 1, wherein said means for inducing further includes means for adjusting the field strength of at least one of said magnets, thereby defining a spacial position of said null flux point with respect to said flux sensor at which the sensed flux is below a release point (Brp) for said flux sensor.

16. The magnetic flux detector of claim 1, including two pairs of magnets, the magnets of each pair having like poles disposed on opposite sides of said sensor.

17. A method for manufacturing a proximity detector, comprising the steps of:

applying at least two opposing magnetic flux fields of like polarity from permanent magnets positioned on opposite sides of a flux sensor, the opposing magnetic fields defining in the absence of a proximate ferrous object, a null flux point at a first position that does not coincide with the position of the flux sensor;

applying a magnetic inducing field which permanently alters the magnetic field of at least one of said at least two magnets in the absence of a proximate ferrous object, so that the null flux point is moved to a second position that coincides with the position of the flux sensor so that the sensor is not activated;

removing the magnetic inducing field; and

detecting a null flux field with said flux sensor in the absence of a proximate ferrous object and detecting the presence of flux when a ferrous object is present.

18. The method of claim 17, further including the step of detecting a flux field with the flux detector in the presence of a proximate ferrous object.

19. The method of claim 17, further including the step of using a Hall-effect device as a flux sensor.

20. The method of claim 17, further including the step of using a magneto-resistor as a flux sensor.