GB2237638A

GB2237638A - A fluid rate sensor

Info

Publication number: GB2237638A
Application number: GB8915673A
Authority: GB
Inventors: Douglas Frank George Dwyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-07-07
Filing date: 1989-07-07
Publication date: 1991-05-08
Anticipated expiration: 2009-07-07
Also published as: WO1991001008A1; JPH04506571A; GB2237638B; EP0486503A4; EP0486503A1; GB8915673D0

Abstract

An angular rate sensor for measuring angular velocity about a cavity sensitive axis which includes a fluid filled cavity, means to cause rotation of the fluid in the cavity about an axis perpendicular to said sensitive axis, the fluid having parallel to said rotation axis a flow rate gradient, and means to sense a change in the flow rate grandient with rotation of the cavity about said sensitive axis. The means can be electrical, as by measuring the change in electrical potential or electrical resistance or electrical current across the flow path, or optical by measuring the change in distribution of a neutrally buoyant material in an optically transparent fluid.

Description

AN IMPROVED FLUID RATE SENSOR Inertial sensors are devices that measure and provide information on the forces acting due to movement. The information is generally used for navigational purposes where it is employed to calculate position without the use of an external reference.

One family of inertial sensors measures rotation and for this purpose a gyro is most commonly used.

A major factor limiting the wider use of inertial sensors is the cost resulting from their complexity and the precision necessary in their manufacture.

According to the present invention a cavity is filled with a fluid capable of substantially free or unimpeded movement. Some or all of the fluid is arranged to be in motion such that it follows a path around the cavity and as a consequence has angular momentum. Rotation of the cavity perpendicular to the effective axis of spin or rotation of the fluid will give rise to a force acting on the moving fluid.

The force acting on the moving fluid will give rise to a force in opposition to or at 90 degrees to the force acting which will be transferred to the cavity and may be detected directly. alternatively the force acting on the moving fluid may be detected by arranging for a gradient in fluid velocity to exist through one axis of the cavity and to establish suitable means to detect the change in the profile of the velocity gradient resulting from the force arising due to rotation of the cavity perpendicular to the effective axis of fluid spin or rotation.

Rotation of the cavity perpendicular to to the effective axis of spin will give rise to forces acting on each element of the moving fluid in proportion to the angular momentum of that element and rate of cavity rotation and therefore alter a gradient of velocity or velocity profile within the fluid.

Rotation of the cavity and the consequent change in the velocity profile may be sensed by making measurements at various points of an optical or electrical parameter or characteristic resulting from the velocity or movement of the rotating fluid with respect to the cavity.

The electrical characteristic used to provide information on the velocity of the fluid may be varying resistivity or the generation of an alternating or direct electrical potential resulting from the movement of a conducting fluid through a magnetic field developed by a permanent magnet or a solenoid energised with a direct or an alternating current and fixed to the cavity.

The optical characteristics may be varying transmission or reflection due to inhomogenities deliberately introduced into a transparent rotating fluid.

A specific embodyment of the invention will now be described by way of a non-limitative sxample with reference to the accompanying drawingsin which: Fig 1 Shows a container with an annular cavity filled with mercury and shaped to provide appropriate flow characteristics. The mercury is caused to flow round the cavity as a result of the field established by the permanent magnets and the current that passes through the mercury via electrodes. A second set of magnets and electrodes are used for the measurement of the potentials generated as a result of the flow of the conductive fluid.

Fig 2 shows the above cavity in section to show the rotating fluid and electrodes.

Fig 3 shows schematically typical electrical connections and an amplifier to increase the output from the sensor.

Referring to the drawings the rotation sensor comprises a container 10 that will be generally but not necessarily electrically insulating. Fixed to the container will be permanent magnets 11 and 12 with North and South poles as shown.

Within the cavity formed by the container a conductive fluid 13 rotates as a consequence of the electrical current passing through the fluid originating from electrodes 14 and within the field from magnets 11.

Inset graph 18 shows the symmetrical distribution, with no cavity rotation, of the fluid velocity around the centre line and along the axis of rotation of the fluid (continuous line) and the asymmetric distribution of velocity (dotted line) due to rotation of the cavity perpendicular to the axis of rotation of the fluid. The electrical potentials resulting from the movement of the conducting fluid through the field established by magnets 12 is conducted out of the cavity by means of electrodes 15 and 16.

The electrical connections in Fig 3. show the sensor arranged to provide a balanced output from electrodes 15 centre tapped to ground electrode 16. When the cavity is at rest the velocity gradient will be symmetrically disposed about the ground electrode 16 and the voltages appearing at electrodes 15 will be equal and opposite and therefore cancel, with the cavity rotating in the apropriate sensitive axis a torque will be applied to the rotating fluid which will be displaced in proportion to its velocity and will therefore unbalance the the output from electrodes 15 and provide an output in proportion to the rate of rotation of the cavity in the sensitive axis, amplifier 17 will raise the output to a useful level.

Claims

1 A rotation sensor with an electrical output resulting from a gyroscopic torque in opposition to or at 90 degrees to an applied rotation and comprising a cavity filled with a conductive fluid and equipped with electrically conductive probes immersed in the conductive fluid and magnets fixed to the cavity such that the conductive fluid may be caused to rotate following a closed path around the cavity.

2 A rotation sensor as claimed in Claim 1 with alternating current exitation and alternating magnetic field to cause rotation of the conductive fluid following a closed path around the cavity.

3 A rotation sensor as claimed in claim 2 where rotation of the conductive fluid is by means of alternating electromagnetic fields with a controlled phase relationship such as to generate eddy currents in the conductive fluid to cause rotation.

4. A rotation sensor as in claims 1 to 3 where a second set of permanent magnets and electrodes is employed to develop electrical potentials in proportion to the distribution of velocity of flow of conductive fluid through a magnetic field and equipped with external electrical circuitry to develop an electrical output in proportion to the changing velocity distribution through the fluid brought about by rotation of the container.

5 A rotation sensor as in Claims 1 to 4 where the cavity is cylindrical.

6 A rotation sensor as in Claims 1 to 4 where the cavity is an annulus.

7 A rotation sensor as in Claims 1 to 4 where the cavity shape is torroidal.

8 A rotation sensor as in Claims 1 to 4 where the cavity is spherical or is the space between an inner sphere and an outer sphere and may provide outputs for rotation in two axes.

9 A rotation sensor as in Claims 1 to 8 where the cavity shape is designed to provide a radius of flow for the rotating fluid which varies along the axis and or circumference of fluid rotation to optimise flow profile for a particular application.

10 A rotation sensor as in claims 1 to 9 where the permanent magnets used for gradient sensing are replaced by solenoids energised by an alternating current and the electrodes immersed in the conducting fluid replaced by coils arranged to sense the field generated by currents induced in the conducting fluid by the previously mentioned solenoids energised by an alternating current. The relative amplitude and phase of the currents in the sense coils providing information on relative fow velocity in the conducting fluid.

11 A rotation sensor as in claims 1 to 10 where the cavity is electrically conducting and potentials resulting from a rotating conducting fluid are measured on the surface of the conducting container.

12 A rotation sensor as in claims 1 to 9 where the rotating fluid is optically transparent and rotation is sensed by variation in optical reflection or transmission due to the presence of a neutrally buoyant opaque or reflecting material capable of rotation with and within the rotating fluid.

13 A rotation sensor as in claims 1 to 9 where the rotating fluid is electrically conducting and rotation is sensed by variation of electrical resistivity due to the presence of neutrally buoyant material of differing electrical resistivity capable of rotation with and wihin the rotating fluid.