US3838372A

US3838372A - Magnetic pickup assembly

Info

Publication number: US3838372A
Application number: US00406589A
Authority: US
Inventors: A Damijonaitis
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1971-10-29
Filing date: 1973-10-15
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24

Abstract

A magnetic pickup assembly includes a one-piece mounting member having a bobbin portion with a coil thereon and a support portion with a pair of apertures having conducting rods extending therethrough. The bobbin portion further has a bore therethrough which receives a magnetic pole piece which extends through the coil. The support portion of the mounting member has a counterbore which receives a magnet; said magnet is inserted through the counterbore and held in engagement with the pole piece.

Description

United States Patent 1191 1111 3,838,372 Damijonaitis Sept. 24, 1974 MAGNETIC PICKUP ASSEMBLY 2905913 9/1959 Leigh 336/96 x 3,223,954 12 1965 M 336 107 lnvemori Algis Damijfinaitis, Chicago 3,237,079 2/1966 .1 336/l9 2 x 3,307,164 2/1967 Zimmer 324/34 D [73] Asslgnee' Motorola Franklin Park 3,355,687 1/1967 Adams 336/208 x [22] Filed: Oct. 15, 1973 3,546,647 12/1970 Roddy et al. 336/I98 X [21] Appl' No; 406589 Primary Examiner-Thomas J. Kozma Related US. Application Data Attorney, Agent, or Firm-Mueller, Aichele & Ptak [63] Continuation of Ser. No. 193,838, Oct. 29, 1971,

bandmcd [57] ABSTRACT U S R A magnetic assembly includes a one-piece u 336/192 336/198 mounting member having a bobbin portion with a coil [51] Int Cl b 27/28 thereon and a support portion with a pair of apertures [58] Field 336/96 having conducting rods extending therethrough. The 6/1'92 I98 6 92 1 6 bobbin portion further has a bore therethrough which 3 receives a magnetic pole piece which extends through [56] References Cited the coil. The support portion of the mounting member has a counterbore which receives a magnet; said mag- UNITED STATES PATENTS net is inserted through the counterbore and held in en 1,763,114 6/1930 Wermme 336/208 X gagement i h h l i 2,662,996 12/1953 Martin r. 324/34 R 6 Claims, 3 Drawing Figures MAGNETIC PICKUP ASSEMBLY This is a continuation, of application Ser. No. 193,838, filed Oct. 29, I971, now abandoned.

BACKGROUND OF THE INVENTION Constructing magnetic pickups used with tachometers has involved a number of problems. There has been no very successful method for precisely aligning individual parts of the pickup while encapsulating the same.

One of the most significant problems encountered in producing a low cost magnetic pickup has been breakage of the thin coil output wires connected to the terminal conductors. When encapsulating the assembled parts, the conductor wires twist and the thin coil wires sometimes break. This twisting of conductors and coil and magnet movement have made it difficult to maintain precise alignment of the parts for injection molding and have required special and expensive apparatus including retractor and positioning pins which must be retracted at the proper time during the encapsulation step.

SUMMARY OF THE INVENTION It is an object of this invention to provide a rigid structure for a magnetic pickup which can be easily encapsulated.

It is yet another object of this invention to provide a structure for a magnetic pickup which may be easily handled prior to and during encapsulation without breakage of parts.

It is still another object of this invention to provide a method for constructing a magnetic pickup utilizing fewer parts.

In one embodiment of this invention, a coil is wound on a mounting member comprising a nonmagnetic, nonconducting material such as nylon. Another embodiment utilizes a pre-woundt coil secured to the mounting member. A core piece for the coil is inserted into a cavity in the mounting member that extends through the coil. The core piece includes a pole piece of soft iron extending through the coil and a magnet which is connected to the pole piece by cementing with epoxy or by silver soldering. Rigid brass conductor rods are then inserted into support portions of the mounting member, each rod having a terminal at one end, a portion with a small cross-section at the other end, and having knurls positioned along its length for providing a tight fit in the holes of the support portion, and for press fitting to each terminal. Each output wire of the coil is wrapped around a portion of the conductor rod having a smaller cross-section than the rest of the rod, and then soldered thereto. A pole piece adapter which acts as an extension of the pole piece may then be attached to the end portion of the pole piece. The assembled structure is positioned in an aluminum casing in one embodiment and encapsulated by pressure injection molding with a molding compound. In another embodiment the molded compound forms the outer cas- BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view in partial cross-section of the encapsulated magnetic pickup of this invention;

FIG. 2 is a perspective view of the encapsulated magnetic pick up of FIG. 1; and

FIG. 3 is an exploded view in partial cross-section of the structure of the magnetic pickup of another embodiment of this invention.

DETAILED DESCRIPTION Referring to the drawings, a coil 12 with

output wires

14 and 16 is wound on a mounting member 10 (FIG. 1). The coil may either be wound directly on the bobbin portion I8 (FIG. 1) of the one-piece mounting member 10 (FIG. 1), or prewound and mounted directly as a unit on the bobbin 18 as with the embodiment of FIG. 3. When the coil is mounted as a unit, it must be cemented or otherwise secured to the mounting member to prevent it from being broken away therefrom. Like parts are given like numbers in the figures of the drawings. The mounting member 10 is constructed of a nonmagnetic, non-conducting material such as nylon and provides a rigid support for the various parts of the magnetic pickup.

A core piece comprising the pole piece 20 and the magnet 22 are then inserted in respective receiving

portions

24 and 26 of the mounting member. Pole piece 20 extends through the receiving portion 24 and acts as a core for the coil 12. The pole piece is constructed of a soft iron because of the magnetic qualities of high permeability and low retentivity, and may have an end portion 28 formed for staking a pole piece adapter 30, which acts as an extension of the pole piece, to the pole piece 20 for picking up and conducting changes in the magnetic flux normal to the center line of the core piece (FIGS. 1 and 2). In the embodiment shown in FIG. 3 there is no adapter, and changes in magnetic flux are sensed'directly by the pole piece 20. The magnet 22 is constructed of a metallic alloy which has permanent magnet properties. The pole piece 20 and magnet portion 22 are connected together by epoxy or silver solder and inserted into the mounting member.

The magnet portion 22 may be a permanent magnet in a magnetized state, but because of handling in construction of the pickup such magnets can lose some strength. Handling the magnets in the construction stage may also be a problem in and of itself. As a solution the magnet portion 22 may be magnetized after the pickup has been assembled and encapsulated. A magnetizer may be used to obtain a magnetic strength which is uniform in comparison with other magnetic pickups.

Rigid brass conductor rod 32 has knurled

portions

36 and 38 and rod 34 has knurled

portions

40 and 42.

Rods

32 and 34 are inserted through

holes

44 and 46 in

support portions

48 and 50 respectively of the mounting member 10. The

knurls

36 and 40 provide tight fits for the rods in the support portions of the mounting member.

A rigid structure is provided by the rigid brass conductors, the mounting member 10 and the parts therein, including the coil 12, pole piece 20 and magnet portion 22 of the magnetic pickup. The

output wires

14 and 16 of the coil 12 may then be wrapped around the

end portions

52 and 54 of the

rods

32 and 34 respectively and soldered thereto. The reduced cross-section of each end portion, 52 and 54, of each rigid brass conductor, 32 and 34, facilitates soldering of the output coil wires to the brass conductors. This connection is between the coil 12 which is rigid with respect to the mounting member and the

rods

32 and 34 which are rigidly mounted with the support portions of the mounting member. Consequently, the possibility of breakage of the

output wires

14 and 16 after connection to rigid conducting rods is greatly reduced. The rigid rods are press fitted to the

terminal portions

56 and 58 respectively at the knurled

portions

38 and 42 respectively. The

terminal portions

56 and 58 are thus in precise rigid alignment with the rigid mounting structure 10 of the magnetic pickup, along with the other assembled parts including the coil, pole piece and magnet portion.

The completed structure is rigid and may be easily handled without breakage of coil output wires and without misalignment of the various parts of the rigid structure. The ease with which the structure may be handled facilitates encapsulation during the final step of constructing the magnetic pickup. The rigid structure may be tested and handled prior to encapsulation with reasonable certainty that the structure will, if found to operate according to specification, perform properly after encapsulation. When assembled, the mounting member 10 positions the coil, core piece and conductor rods within the aluminum casing 68 for encapsulation. Positioning pins and retractible pins are unnecessary during the step of injecting the molding compound such as a phenolic into the aluminum casing by pressure injection molding. In the embodiment shown in FIG. 1 the aluminum casing is eliminated, and the molding compound itself forms the outer casing 60. The mounting member 10 is positioned directly in a pressure injection mold in this latter embodiment and encapsulated. The casing of the pickup in either embodiment may include a section of molding compound forming a flange portion 62 to provide means for connecting the magnetic pickup to a particular apparatus.

Holes

64 and 66 may be molded or drilled through the flange portion to provide indexing means for fasteners (FIG. 2).

What has been described therefore is a rigid structure for a magnetic pickup which is relatively inexpensive to make and which can be easily encapsulated.

I claim:

1. A magnetic pickup assembly including in combination, a coil having output wires, a core for said coil comprising a pole piece of magnetic conducting material and a magnet connected thereto, a pair of elongated rigid electrical conductor rods, a one-piece mounting member having a bobbin portion for mounting said coil thereon and having a support portion with apair of apertures extending therethrough, said bobbin portion of said mounting member further having a bore therethrough for receiving said core, with said pole piece being inserted through said bore and extending through said coil, said support portion of said mounting member further having a counterbore therethrough for receiving said magnet, with said magnet being inserted through said counterbore and held in engagement with said pole piece, each said electrical conductor rod being inserted through a respective one of said apertures in said support portion and each having a portion thereon for tightly fitting said conductor rods to said support portion, said output wires of said coil being electrically connected to the ends of said respective conductor rods, and said rods, coil pole piece, magnet and mounting member cooperating to form a rigid structure for encapsulation.

2. The magnetic pickup assembly according to claim 1 wherein said mounting member comprises nonmagnetic material.

3. The magnetic pickup assembly according to claim 1 wherein said mounting member comprises nonconducting material.

4. The magnetic pickup assembly according to claim 1 wherein said mounting member comprises nylon.

5. The magnetic pickup assembly according to claim 1 wherein said rigid electrical conductor rods comprises brass. I

6. Apparatus for assembling the parts of a magnetic pickup for encapsulation, including in combination, a one-piece mounting member having a bore and a counterbore therethrough and including a bobbin portion at one end thereof and a support portion at the other end thereof, a coil having output wires, a core comprising a cylindrical pole piece of magnetic conducting material having a flange portion at one end and a cylindrical magnet magnetically connected at said flange portion, said coil positioned about said bobbin portion of said mounting member, and said pole piece positioned in the bore of said mounting member with said flange portion and said magnet fitted into the counterbore thereby positioning said pole piece in a spaced relation relative to said coil, and a pair of elongated rigid electrical conductor rods, said support portion of said mounting member further having a pair of apertures for receiving said conductor rods, said conductor rods each including means for tightly securing said conductor rods in the wall of the apertures with the same being inserted therethrough to fix said rods in a spaced relation relative to said coil, said coil output wires being connected to respective ones of said conductor rods whereby said rods, coil, pole piece, magnet and mounting member cooperate to form a rigid structure for encapsulation.

Claims

1. A magnetic pickup assembly including in combination, a coil having output wires, a core for said coil comprising a pole piece of magnetic conducting material and a magnet connected thereto, a pair of elongated rigid electrical conductor rods, a one-piece mounting member having a bobbin portion for mounting said coil thereon and having a support portion with a pair of apertures extending therethrough, said bobbin portion of said mounting member further having a bore therethrough for receiving said core, with said pole piece being inserted through said bore and extending through said coil, said support portion of said mounting member further having a counterbore therethrough for receiving said magnet, with said magnet being inserted through said counterbore and held in engagement with said pole piece, each said electrical conductor rod being inserted through a respective one of said apertures in said support portion and each having a portion thereon for tightly fitting said conductor rods to said support portion, said output wires of said coil being electrically connected to the ends of said respective conductor rods, and said rods, coil pole piece, magnet and mounting member cooperating to form a rigid structure for encapsulation.

5. The magnetic pickup assembly according to claim 1 wherein said rigid electrical conductor rods comprises brass.