Method for fabricating a magnet structure

• US 6,692,676 B1
• Filed: 04/19/2001
• Issued: 02/17/2004
• Est. Priority Date: 03/08/1999
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Vig, Ravi, Pinelle, Sandra R., Bowman, Gregory R., Dwyer, Daniel S., Clapp, Terry R.
• Primary Examiner(s): ORTIZ, ANGELA Y
• Application Number:
  US09/837,991
• Time in Patent Office: 1,034 Days
• Field of Search: 264/250, 264/254, 264/255, 264/259, 264/271.1, 264/275, 264/104, 264/105, 264/272.19, 264/272.2, 264/272.15, 264/427, 264/429, 296/07, 296/08
• US Class Current: 264/255
• CPC Class Codes: G01B 7/001 Constructional details of gauge heads G01B7/012 takes precedence
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: H03K 17/9517 using galvanomagnetic devices

Abstract

A magnet structure including a magnet and an integral magnetically permeable concentrator and methods for making the same are provided. The concentrator is comprised of a plastic loaded with one or more magnetically permeable materials to a percentage suitable for providing desired magnetic field characteristics. The magnetic element may be comprised of a conventional magnetic material or a plastic loaded with one or more magnetic materials. An insert molding technique is described in which either the concentrator or magnetic element is prefabricated and inserted into a mold which is subsequently filled with a loaded plastic to provide the other component of the magnet structure. In an alternate fabrication technique, both the concentrator and magnet are sequentially formed by injection molding in the same mold. Also described is a magnet structure including a ring magnet having a central aperture in which a steel rod is disposed.

Claims

1. A method of fabricating a magnet structure, comprising the steps of:

inserting an element into a cavity of a mold; and

injecting a selected one of a magnetically permeable plastic compound and a magnetic plastic compound into the mold so as to contact at least a portion of said element, wherein said inserting step and said injecting step result in formation of a concentrator in contact with a magnet, so that an end of each of said concentrator and said magnet define a front face of said magnet structure, said concentrator presenting a magnetic field of one polarity at said front face and said magnet presenting a magnetic field of the opposite polarity at said front face.

2. The method of claim 1 wherein said element inserting step comprises inserting a magnet element into said cavity and said injecting step comprises injecting a magnetically permeable plastic compound into the mold.

3. The method of claim 2 further comprising the step of combining a magnetically permeable material and a plastic to form said magnetically permeable plastic compound.

4. The method of claim 3, wherein said combining step further comprises the step of selecting a percentage weight of said magnetically permeable material in response to a desired magnetic field pattern and desired strength characteristics.

5. The method of claim 4, wherein said plastic is selected from the group consisting of:

polyamide, polyphenylene sulfide (PPS), polyphthalamide (PPA), a themoset molding compound, and an epoxy molding compound.

6. The method of claim 4, wherein said magnetically permeable material is selected from the group consisting of:

iron, stainless steel, ferrite, and iron oxide.

7. The method of claim 1 wherein said element inserting step comprises inserting a concentrator element into said cavity and said injecting step comprises injecting a magnetic plastic compound into the mold.

8. The method of claim 7, further comprising the step of combining a magnetic material and a plastic to form said magnetic plastic compound.

9. The method of claim 8, wherein said step further comprises the step of selecting a percentage weight of said magnetic material in response to a desired magnetic field pattern and strength characteristics.

10. The method of claim 8, wherein said plastic is selected from the group consisting of:

polyamide, polyphenylene sulfide (PPS), polyphthalamide (PPA), and an epoxy molding compound.

11. The method of claim 8, wherein said magnetic material is selected from the group consisting of magnetic ferrite and SmCo.

12. The method of claim 1, further comprising the step of heating the magnet structure to provide a chemical bond between said element and said selected one of the magnetically permeable plastic compound and the magnetic plastic compound.

20. The method of claim 1, wherein the magnetic field of one polarity and the magnetic field of the opposite polarity cancel to provide an essentially zero magnetic field at said front face.

13. A method of fabricating a magnet structure, comprising the steps of:

injecting a selected one of a magnetically permeable plastic compound and a magnetic plastic compound into a first mold cavity formed by mold parts placed in a first position relative to one another;

moving said mold parts to a second position relative to one another to form a second mold cavity; and

injecting the previously non-selected one of a magnetically permeable plastic compound and a magnetic plastic compound into said second mold cavity, wherein said inserting step and said injecting step result in formation of a concentrator in contact with a magnet, so that an end of each of said concentrator and said magnet define a front face of said magnet structure, said concentrator presenting a magnetic field of one polarity at said front face and said magnet presenting a magnetic field of the opposite polarity at said front face.

14. The method of claim 13, wherein said injecting step further comprises the step of combining a selected percentage weight of magnetically permeable material and a plastic to form said magnetically permeable plastic compound in response to a desired magnetic field pattern and desired strength characteristics.

15. The method of claim 14, wherein said plastic is selected from the group consisting of polyamide, polyphenylene sulfide (PPS), polyphthalamide (PPA), a themoset molding compound, and an epoxy molding compound.

16. The method of claim 14, wherein said injecting step further comprises the step of combining a selected percentage weight of magnetic material and a plastic to form said magnetic plastic compound in response to a desired magnetic field pattern and desired strength characteristics.

21. The method of claim 13, wherein the magnetic field of one polarity and the magnetic field of the opposite polarity cancel to provide an essentially zero magnetic field at said front face.

17. A method of fabricating a magnet structure, comprising the steps of:

inserting a rod into a central region of a substantially cylindrical mold; and

injecting a magnetic plastic compound into said mold so as to form a ring-shaped magnet surrounding and in contact with said rod.

18. The method of claim 17, wherein the rod is comprised of steel.

19. The method of claim 17, said ring-shaped magnet has a height substantially equal to the length of said rod.