FR2582401A1 - ROTARY BODY WITH NON-UNIFORM MASSIVE DISTRIBUTION - Google Patents

Abstract

THE DENSITY OF AT LEAST ONE REGION 12, 13 OF THE SURFACE OF A ROTATING BODY IS INCREASED BY THE IMPLEMENTATION IN THIS REGION OF IONS OF APPROPRIATE ELEMENTARY MATERIAL SO THAT A SLIGHT MODIFICATION OF THE MASS DISTRIBUTION OF THE BODY. THE DESCRIPTION RELATES TO A MODIFICATION IN THE MASS DISTRIBUTION OF THE SPHERICAL ROTOR 10 OF AN ELECTROSTATIC SUSPENSION GYROSCOPE WHICH IS MADE OF BERYLLIUM AND RECEIVES SILVER IONS. USE TO MODIFY THE MASS DISTRIBUTION OF ROTARY BODIES.

Description

- I -

  The present invention relates to a rotating body with non-uniform mass distribution, and a method for producing such a body. It concerns in particular, but

  not exclusively, the manufacture of a mass rotor

  balanced for an electrostatic suspension gyro.

  The technique could be used for the equi-

precise liberation of a rotating body.

  There are many examples where the deliberate balancing or unbalancing of a rotating body can be done without much difficulty. Commonly used techniques involve adding material to the body or removing material from that body

  in selected points. To obtain a great deal

  this is usually removed from the material, for example

  by piercing material on the edge of a gyroscope rotor.

  However, the accuracy of this technique depends on

  factors, including the size of the rotor, and the precision with which the drilling operation is controlled.

  The rotor of a gyro with electrostatic suspension

  ticking poses a particular problem. In such a gyroscope the rotor is a hollow or solid sphere, supported by electric fields. The sphere is located in a vacuum chamber, with a very small space between the rotor and the enclosure. The enclosure is made of insulating material, but it contains a number of pairs of electrodes on its inner face. It is the electric field produced between these electrodes and the rotor which allows the suspension of the rotor. The rotor is rotated by magnetic fields generated by coils, usually external to the vacuum enclosure. Due to the electrostatic suspension and the vacuum chamber, the rotor is subjected to a very low drag, and once it has reached the desired rotational speed, the rotating field can be cut. As a result, the axis of rotation of the rotor - 2 -

  tends to remain fixed in the inertial space, even if the

  girdle rotates. So, to use the instrument for

  measuring a rotation, it is necessary to have means of determining

  the angle between the axis of rotation and the axis of the

  girded. One technique to achieve this requires a small modification of the mass distribution of the rotor, causing the separation of its center of gravity and its geometric center. Provided that the control system

  the suspension reacts slowly with respect to the period

  of rotor rotation, the rotor will rotate around its

  center of gravity, and not of its geometrical center,

  for a sinusoidal variation of the space between the rotor and any point of the enclosure, at the rotor rotation frequency, and with an amplitude and a phase depending on the angle between the axis of rotation and the axis of the enclosure. If the suspension system is equipped with a

  circuit diagram, this frequency can be detected

  for each pair of electrodes in the enclosure and

  can deduce the angle of the axis of rotation.

  For this technique to succeed, it is necessary that the axis of rotation of the rotor, as it would be seen by an imaginary observer on the rotor, is stable. In general, when such a rotor is rotated, it does not turn first around a stable axis. In fact, the

  only really stable axis is the axis of greater iner-

  tie. It is preferable that the mass distribution of the rotor be such that the axis of greatest inertia is perpendicular to the line joining the center of gravity and the geometric center, and such that it is possible, with external fields, to bring the axis of rotation

  to coincide with the axis of greater inertia.

  Several techniques are known to produce this change in the mass distribution. One is to form one or more flat areas on the surface - 3 -

  of the rotor while another consists of forming a coating-

  on certain parts of the surface, by placing

  cage or other techniques. These techniques are difficult to implement, in particular because a very high dimensional accuracy is required for a regular size rotor. In addition, rotors are usually

  beryllium, because of its high stiffness / density ratio

  site. However, beryllium is a dangerous material

  to machine, and this complicates the problems. Another technique

  Another problem is to form a beryllium billet with one or more wires of heavier material incorporated therein. The billet is extruded into a rod and the spherical rotor is machined from a piece of

  this rod. This is obviously a common technique

plex and expensive.

  One of the aims of the invention is to propose a rotating body in which the mass distribution of the body has been adjusted using a non-linear technique.

  affected by the problems mentioned above.

  Another object of the invention is to propose

  a method of manufacturing such a rotating body.

  According to the present invention, there is provided a rotating body with non-uniform mass distribution, in which the density of at least one region of its surface has been increased by the implantation in this region of ions of a suitable elementary material of to produce a desired modification of the mass distribution of the body. Still according to the invention, there is provided a method of manufacturing a non-uniform mass distribution rotating body which comprises increasing the density of at least one region of the body surface by implantation in that region of the surface of the body. ions of a suitable elementary material, so as to produce a desired change in the mass distribution of the body. The invention will now be described with reference to the accompanying drawings, which relate to an electrostatically suspended gyroscope rotor. Figures 1 and 2 are perpendicular elevational views of a rotor showing the implanted areas. In FIGS. 1 and 2, the rotor 10 of an electrostatic suspension gyroscope comprises a hollow or solid sphere made of beryllium supported in an enclosure under

  vacuum (not shown) by electric fields. The in-

  encircle includes a number of electrodes for

  to draw the electric fields and to detect movements of the sphere due to its imbalance. Coils produce magnetic fields that rotate the rotor around

of its axis of rotation 11.

  The change in the mass distribution that causes the separation of the center of gravity

  of the sphere and its geometric center is obtained by

  both silver ions in well-defined regions of its surface. These regions, referenced 12 and 13, are hatched in FIGS. 1 and 2. The particular pattern of implantation depends on the relationship that is desired between the center of gravity, the geometric center and the axes.

main inertia of the body.

  The process of ion implantation involves directing a high energy ion beam onto the body surface. The ions penetrate to a very small depth in the surface of the body and are held there, increasing the density of this part of the surface. Only a very small increase in density is possible by this means, because the incident ion beam can erode the

  surface, tearing off superficial atoms of the body.

  Previously implanted ions are also vulnerable to pulling out, and this means that there is a limit to the number of ions that can be implanted. To obtain the greatest density change possible by this technique, it is necessary to evaluate the mass of implanted ions and the number of ions that can be implanted per unit.

2582401D

  -5 area before reaching the tear-off limit. This

  is the reason for the choice of silver ions for the implan-

in a beryllium body.

  The ion implantation process has been known for a long time and is used for the doping of semiconductor materials. It is implemented in a room

  under vacuum, and requires the production of a beam of

  trons from an electron source. The beam of electricity

  trons is used to bombard a gas or vapor containing the elementary material to be ionized, and the produced ions are accelerated and used to bombard the target, in this case the rotating body. The implantation of a body over an entire region requires the body to be mobile with respect to the beam. In some equipment

  It is possible to electrostatically scan the

  ion in at least one direction. An alternative is to move the body forming the target, or to use both techniques. In the case of the sphere illustrated in Figures 1 and 2 the preferred method is to scan the beam in a plane and rotate the body in an orthogonal plane. A mask can be used to define the regions to be exposed to the ion beam, unless the control of the position of the point of impact of the beam on the body is sufficiently accurate

  so that we can do without a mask.

  Although the above description relates to a

  rotor for gyro with electrostatic suspension, the

  same invention can be used to modify the distribution of

  mass release of other rotating bodies. The body may not be designed for electrostatic support, and may be of any shape. The same invention can also be used to achieve a perfect balance rather than a deliberate imbalance. It is obvious that the possible differences between the center of gravity of the body and its geometric center are in principle very small, as are the modifications to the principal axes of inertia,

  and it is this aspect which will limit the applications of the invention

tion. - 6 -

Claims (6)

  Rotating body with non-uniform mass distribution, characterized in that the density of at least one region (12, 13) of its surface has been increased by the implantation in this region of ions of a suitable elementary material, to produce a modification   desired mass distribution of the body.   2. Body according to claim 1, characterized in that the body forms the spherical rotor (10) of a   electrostatic suspension gyroscope.   3. Body according to claim 2, characterized   in that the body is beryllium.   4. Body according to one of claims 2 or 3, characterized in that the elementary material is money.   5. A method of manufacturing a non-uniform mass distribution rotary body, characterized in that it includes increasing the density of at least one region of the body surface by implantation in this region of the surface of the body. ions of a suitable elementary material so as to produce a desired modification   the mass distribution of the body.   6. Process according to claim 5, characterized   performed by the steps of directing an ion beam of said elementary material toward the surface of the body, and producing a relative movement between the impact region of the beam and the body so that the ion implantation   occur on the desired area of the body surface.