GB2198231A

GB2198231A - Rotational motion sensor

Info

Publication number: GB2198231A
Application number: GB08628507A
Authority: GB
Inventors: David William Satchell
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1986-11-28
Filing date: 1986-11-28
Publication date: 1988-06-08
Anticipated expiration: 2006-11-28
Also published as: GB8628507D0; GB2198231B

Abstract

A rotation sensor device 11 includes a laminar body 12 supported on a taut filament 13 and undergoing torsional oscillation about an axis Z coincident with the filament 13. Rotation of the device, about an axis X through the plane of the body 12, induces an oscillatory torque, about an axis Y mutually perpendicular to the other two axes, the magnitude of which corresponds to the rate of rotation. Positive feedback maintains body 12 in oscillation at the resonant frequency (with electrostatic coupling) and there is capacitative detection of the oscillations. Three rotation sensor devices are employed in an initial guidance system for a projectile. Device 11 is formed by selective etching from a body of single crystal silicon. <IMAGE>

Description

ROTATIONAL MOTION SENSOR This invention relates to devices for sensing rotational motion, e.g. for navigation or inertial applications.

The key element in any inertial guidance system is the device which senses angular movement. Conventionally, mechanical gyroscopes are used for this purpose, precession of the gyroscope providing a measure of angular movement.

A more recent development is the fibre optic gyroscope which employs the Sagnac effect to detect rotation. Both these devices are relatively costly. Further, their large bulk and their sensitivity to vibration renders them unsuitable for use in small vehicles, e.g. projectiles and guided weapons, which are subject to high shock conditions.

The object of the present invention is to minimise or to overcome these disadvantages.

According to the invention there is provided a device for sensing angular motion, the device including a laminar body supported on a taut fibre so as to permit torsional oscillation of the body about a first axis coincident with the fibre, and means for detecting a torque about a second axis perpendicular to the plane of the laminar body in response to rotation of the body about a third axis in the plane of the body and perpendicular to said first axis.

An embodiment of the invention will now be described with reference to the accompanying drawings in which:- Fig. 1 is a plan view of a rotation sensor transducer; Fig. 2 is a schematic diagram of a rotation sensor device incorporating the transducer of Fig. 1, and Fig. 3 is a block schematic diagram of an inertial guidance system using a plurality of rotation sensor devices.

Referring to Fig. 1, the transducer comprises a supporting frame 11 having an opening in which a laminar body 12 is supported on a filament 13. The filament is maintained in a state of tension. The body 12 is free to oscillate in a torsional mode about an axis coincident with the filament 13. Typically the body 12 is maintained in a state of oscillation by electrostatic coupling thereto of an oscilLator signal whose frequency is matched to the resonant frequency of the device.

The transducer may be formed by selective etching fro a bod cf single crystal silicon. Typically a 100 orentec silicon wafer is masked and then etched with an ar-sotropic enchant to define the device structure.

Preferably the etchant comprises a mixture of aqueous potassum hydroxide and iso-propyl-alcohol, or a mixture of ethylene diamine, catechol and water. Such materials etch preferent-a''y in the 100 direction with very little undercutting and can thus be used to define a particular silica structure.

If the device is rotated about an axis X through the plane of the body 12 and perpendicular to the axis Z whilst the body as is in a state of torsional oscillation, a corresponding oscillatory torque is generated about an axis Y mutually perpendicular to the other two axes. The amplitude of this oscillatory torque corresponds to the rate at which the device is rotated about the axis X. The torque is generated by the well known gyroscopic or Coriolis effect. The torque manifests itself as a torsional oscillation of the body 12 about the Y axis, the filament 13 being sufficiently flexible to permit this mode of oscillation. The device is insensitive to rotation in the X and Z axis.

Fig. 2 shows the manner in which the transducer of Fig. 1 may be employed to provide a device for sensing rotational movement. The transducer 21 is mounted adjacent an insulating plate (not shown), e.g. of glass or surface oxidised silicon, on which a pattern of electrodes is disposed. A first pair of electrodes 22 provides electrostatic coupling to the body 12 to maintain the body in a state of oscillation. A second pair of electrodes 23 disposed in register with one end of the body 12 provides capacitive detection of torsional oscillation of the body in the Y-plane resulting from rotation of the device in the X-plane. An earthed scree 24 reduces coupling between the electrodes 22 and 23. Positive feedback to maintain oscillation at the resonant frequency is provided via a further electrode 25 in register with the other end of the body 12.

The signal at the electrode 25 is amplified by amplifier 26 and then fed via limiter 27 to a phase splitter 28. The two (antiphase) outputs of the phase splitter are fed each via a respective amplifier 29a, 29b to a respective one of the electrodes 22 to maintain the body 12 in a state of oscillation at its natural or resonant frequency.

Output signals from the pair of electrodes 23 are fed to the inputs of a differential amplifier 30, the output of which is fed to the input of a synchronous amplifier 31. The synchronous amplifier receives a control signal comprising the input signal to the phase splitter 28. When the device is subjected to rotational movement in the Y plane the signals at the electrodes 23 become out of balance. The corresponding signal from the output O/P of the synchronous amplifier provides a measure of the rate of rotation of the device.

Typically the components of the rotation sensor device of Fig. 2 are mounted on a common substrate, e.g. of glass or silicon. As the structure is small and robust it is adapted to use in high shock applications such as are experienced in projectiles and guided weapons.

A typical inertial guidance system is shown in Fig. 3 of the accompanying drawings. In this arrangement three rotation sensor devices, RX, RY and RZ, are employed to sense rotation in the X, Y and Z planes respectively.

The outputs of these devices are fed to a control system 31 which in turn drives directional controls CX, CY and CZ to maintain a predetermined source. It will of course be appreciated that in some applications, e.g. marine navigation, only one rotation sensor device will be required to provide guidance information.

Claims

CLAIMS:-

1. A device for sensing angular motion, the device including a laminar body supported on a taut fibre so as to permit torsional oscillation of the body about a first axis coincident with the fibre, and means for detecting a torque about a second axis perpendicular to the plane of the laminar body in response to rotation of the body about a third axis in the plane of the body and perpendicular to said first axis.

2. A device as claimed in claim 1, wherein said torque detection means includes a pair of electrodes disposed adjacent one end of the body whereby torsional oscillation of the body in the plane of the body in response to said rotation induces a corresponding electrical signal on said electrodes.

3. A device for sensing angular motion, the device including an elongate laminar body supported at its transverse axis as a taut elastic fibre so as to permit torsional oscillation of the body in a first mode about a first axis coincident with the fibre, a first electrode structure disposed adjacent the body whereby, in use, electrical signals are coupled to the body to maintain the body in a state of torsional oscillation, a second electrode structure disposed adjacent one end of the body whereby, in response to rotation of the device in the plane of the body, torsional oscillation of the body in a further mode about an axis perpendicular to the plane of the body induces a corresponding electrical signal on said further electrode structure.

4. A device as claimed in claim 3, wherein feedback signals for maintaining the body in a state of oscillation at its resonant frequency are provided via a third electrode structure disposed adjacent the other end of the body.

5. A device as claimed in claim 3 or 4, wherein said electrode structures are disposed on an insulating plate adjacent which the laminar body is mounted.

6. A device as claimed in claim 2, 3, 4 or 5, wherein said signal is amplified by a first differential amplifier and a second synchronous amplifier.

7. A device as claimed in any one of claims 1 to 6, wherein the laminar body and fibre are formed as an integral structure from a body of single crystal silicon.

8. A rotational movement detection device substantially as described herein with reference to and as shown in Figs. 1 and 2 of the accompanying drawings.

9. An inertial guidance system incorporating one or more devices as claimed in any one of claims 1 to 8.