US3775684A

US3775684A - Accelerometer

Info

Publication number: US3775684A
Application number: US00003302A
Authority: US
Inventors: L Hoodwin
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-01-16
Filing date: 1970-01-16
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27

Abstract

This invention describes an accelerometer of the electromagnetic, self-generating, non-seismic type having a simplified design that permits construction at low cost.

Description

United States Patent 1191 UNITED STATES PATENTS 3/1932 Hewlett 324/162 Hoodwin Nov. 27, 1973 ACCELEROMETER 2,090,521 8/1937 Sen-ell 310/168 [76] Inventor: Louis s. 1:2 1:31; 13151:. 1,Box 246, I FOREIGN PATENTS 0R APPLICATIONS I Sawyer 1 1,147,787 4/1963 Germany 324/1 4 [22] Filed: Jan. 16, 1970 [21] Appi. No.: 3,302 Primary Examiner-Michael J. Lynch 52 us. c1. 324/162, 310/154 ['57] ABSTRACT 51 Int. Cl. G0lp 3/42 [58] Field of Search 324/162, 164; Tim mvemw" descflbes acceleromeer of the elec- 3 5 168 tromagnetic, self-generating, non-seismic type having r a simplified design that permits construction at low [56] References Citd cost- I 2 Elaims, 5 Drawing Figures PATENIEUNIIYZ'IIQH FIG.

FIG.3.

7 INVENTOR,

.FIG.5.

The object of this invention is to provide an accelerometer of simplified design that may be manufactured at low cost.

- When a piece of electrically conductive material is moved so as to cut the lines of flux of a magnetic field that is not uniform in the direction in which the con ductive material is moved, circulating electrical currents are generated in the conductor that are proportional to the-rate with which the conductor cuts the lines of magnetic flux. In accordance with this principle, accelerometers have been built in which a discshaped or tubular electrically conductive armature is rotated in a primary magnetic field. The induced annature currents produce secondary magnetic fields that are coupled to a pickup coil. The voltage output of the pickup coil is proportional to the rate of change of the secondary magnetic field which in turnjis proportional to the rate of change "of the armature current'which in turn is proportional to the rate of change of the velocity of the armature. Therefore, the vo'ltageoutput isproportional to the acceleration of the armature. In these previous designs, the magnetic flux paths for the primary and secondary fields have been separated.

An accelerometer built according to this invention utilizes a common structure for'both the primary and the secondary magnetic flux.

The details and thefunctioning of this invention will be described with the aid of the accompanying drawing in which the figures are as follows:

FIGS. 1 and 2 are schematic views of an acceleromet er in accordance with this invention;

FIG. 3 is a schematic sectional view of another accelerometer in accordance with this invention;

FIG. 4 is a schematic sectional view along the line 4-4 of FIG. 3;

FIG. 5 is a schematic view of a variation in magnetic structure in accordance withthe invention.

Referringto FIGS. v1 and 2, a disc armature is mounted on and turned by a shaft2. The armature 1 passes through a magnetic air gap-created'by a magnet 3 and a U-shapedaferromagnetic core4. Apickup coil 5 encircles the magnetic core4. The magnet 3 is magnetized so as to havetwo poles-6 of opposite sense on the side facing the armature 1. These poles 6 are indicated by theletters Niand S. Thepoles-6 arepositioned so that a line joining their centers isparallel tothe-instantaneous directionof motion of apoint on'the armature l midway between the;poles "6. *With optimum magnetization, there will'be poles of opposite sense on the side of the magnet3 in contact with the magnetic core 4. A large portion of 'theflux produced bythe magnet 3 will passthrough-the air gap. The flux emerging from either half-magnet pole 6 facing the airgap willreturn to the opposite pole contacting the magnetic core 4 by a-path 7 through the length of the core 4 and by a shorterpath across-the part of the core 4 across the airgap from themagnet 3, through the airgap and the other half of the magnet 3. The amount of flux following each path will depend on the relative reluc the primary flux therebycreating an electric currentin the armature '1 indicated by the path 8. This current is proportional to the velocity of the armature 1. The armature current produces a secondary magnetic flux 'which follows approximately the path 9. This flux is coupled to the pickup coil 5 the voltage output of which is proportional to the acceleration of the armature 1.

' Thepaths 7, 8, and 9 as shown on the drawing are intended to show only the approximate areas through which the current and fluxes flow. For example, the armature current will flow to some extent throughout the entire volume of the armature l; but the center of circulation of the current will be within the path 8.

Many variations are possible in the design described above whilestill utilizing thenovel features of the invention. For example, electromagnets consisting on one coilfor each pole maybe used in place of the permanent magnet 3' shown. If the electromagnet coils have equal turns and the magnetic structure is symmetrical, there will-be virtually no effective coupling between the magnet coils and the pickup coil 5.

For increasedoutput, the magnetic core 4 can be made of a single piece of stamped or cast iron or steel.

The pickup coil 5 may be'mounted anywhere around the magnetic core 4, as long as it is coupled to the secondary flux. Itmay even be wound directly on the magnet 3 obviating the need for a separate winding bobbin.

The accelerometer shown in FIGS. 1 and 2 is an angular accelerometer with which the angular acceleration' is measured between the shaft 2 and the assembly of the magnet 3 and the magnetic core 4. A linear accelerometermay be made by substituting a strip armature for the disc armature l and moving the strip arma- =ture linearly through the air gap.

For higher sensitivity, the number of magnets and pickup coils may beincreased. FIGS. 3 and 4 show a schematic presentation of an angular accelerometer with four magnets and coils arranged for high sensitivity. The disc armature 10 is turned by the shaft 11 in air gaps created by a ferromagnetic cup 12, a ferromagnetic plate 13, and four magnets 14. Pickup coils 15 are wound around the magnets 14 and are connected in se- -riesfor maximumvoltage output. The magnets 14 are magnetized'so that each has a north pole and a south pole, indicated bythe letters N and S,facing the armature in a manner similar to the magnet 3 of FIGS. 1 and '2. The'magnets 14 are shaped to cause the magnetic flux to passthrough the greatest possible area of the armature '10.

The principles described in the invention may be used-to construct an-angular accelerometer with a tubular armature. The armature may enclose either a magnetorone leg of the magnetic core.

"With'the construction shown in FIGS. 1 and 2, the flux density may vary across the air gap perpendicular totheface of the magnet 3. If the armature 1 wobbles toward and away from the magnet 3, a false acceleration signal will be generated even if the armature 1 is movingthrough'the gap at a constant velocity. FIG. 5 shows a'schematic view of a magnetic assembly which will provide moreuniform flux density in the air gap. This assembly consists of a magnetic core 16 and two double pole magnets 17 of similar size mounted symmetrically with respect to each other on opposite sides 3 of the air gap. The magnets 17 are magnetized similarly to the magnet 3 in FIGS. 1 and 2 with the added requirement that the poles on directly opposite sides of the armature must be of opposite polarity.

Magnetic structures do not have to be made of separate cores and magnets. An entire magnetic structure may be made in one'piece of permanent magnet material. A magnetic structure made of ductile permanent magnet material may be inserted through a pickup coil and then bent to form an air gap. If the magnetic structure is made of a brittle material and the air gap is too small to permit using a large coil by inserting it through the gap, a coil may be wound on the magnetic structure by using equipment designed for winding toroidal transformer coils.

I claim:

1. An accelerometer which utilizes the. secondary magnetic flux generated when an electrically conductive armature moves through a primary magnetic field, such an accelerometer having an electrically conductive armature the motion of which is to be monitored; a core of ferromagnetic material which conducts both primary and secondary magnetic flux and is shaped to reach from one side of the armature around the edge of the armature to the other side of the armature thereby creating an air gap through which the armature moves;

a source of magnetic flux on the end of the core at the air gap, between the core and the armature, such source providing a pair of opposite poles facing toward the armature, said poles positioned so the a line joining their centers is essentially parallel to the instantaneous direction of motion of a point on the armature midway between the poles;

a pickup coil mounted encircling the magnetic structure, each structure consisting ,of the source of magnetic flux and the ferromagnetic core, the mounting such that the secondary flux is coupled to the coil. 7

2. An accelerometer according to claim 1 in which the source of magnetic flux consists of magnetsofsimilar shape'symmetrically assembled to the core on both sides of the air gap.

Claims

1. An accelerometer which utilizes the secondary magnetic flux generated when an electrically conductive armature moves through a primary magnetic field, such an accelerometer having an electrically conductive armature the motion of which is to be monitored; a core of ferromagnetic material which conducts both primary and secondary magnetic flux and is shaped to reach from one side of the armature around the edge of the armature to the other side of the armature thereby creating an air gap through which the armature moves; a source of magnetic flux on the end of the core at the air gap, between the core and the armature, such source providing a pair of opposite poles facing toward the armature, said poles positioned so the a line joining their centers is essentially parallel to the instantaneous direction of motion of a point on the armature midway between the poles; a pickup coil mounted encircling the magnetic structure, each structure consisting of the source of magnetic flux and the ferromagnetic core, the mounting such that the secondary flux is coupled to the coil.

2. An accelerometer according to claim 1 in which the source of magnetic flux consists of magnets of similar shape symmetrically assembled to the core on both sides of the air gap.