GB2253053A

GB2253053A - Optical pick-up for gyroscope

Info

Publication number: GB2253053A
Application number: GB9203634A
Authority: GB
Inventors: Karl-Heinz Hauser
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1991-02-20
Filing date: 1992-02-19
Publication date: 1992-08-26
Also published as: FR2672985A1; GB9203634D0; DE4105204C1; FR2672985B1

Description

1 4.

2253053 AN OPTICAL GYRO PICK-UP The invention relates to an optical pick-up for a torquecompensated gyro, the gyro rotor of which is mounted in an inner frame rotatable around an axis oriented vertically to the gyro-rotor axis and which is mounted In a second frame firmly attached to the housing, the rotation of the inner frame being detected by means of an optical pick-up.

An example of a gyro pick-up of the aforementioned type Is known, from DEPS 38 04 766. The optical measuring pick-up of this known device comprises a light source, a two-part light-sensitive device and a passive construction element arranged in the beam path between the light source and the light-sensitive device. The current increases In one surface section of the light-sensitive device and decreases in the other surface section during an alignment of the gyro frame. The light-sensitive device is preferably a differential photo diode, in which respect the passive construction element can then be, for example, a slit diaphragm. Positional displacements of the slit diaphragm cause a respective displacement of the light beam hitting the differential photo diode, which beam displacement is detected and used as switch signal for a torque transmitter for compensating the frame alignment.

It Is an object of the present invention to increase by simple means the pick-up precision whilst maintaining the advantages of a contact-free pick-up.

The object is achieved by means of an optical pick-up for a torquecompensated gyro, the gyro rotor of which is mounted In an inner frame, rotatable around an axis oriented vertically to the gyro-rotor axis and which is mounted in a second frame firmly attached to the housing, the rotation of the inner frame being detected by means of an optical pick-up, Characterised in that the inner frame has, at a radial JSS120292 dústance from Its axús, an optúcally reflectúve surface havúng a normal surface which coincides with a motion component of the inner frame, a reflective surface in the beam path of an interferometer, which is firmly attached to the housing, is arranged so that the optical radiation reflected from the reflective surface interferes with a reference beam such that interference lines are detected by at least two photo diodes and the photo diodes are connected to an electrical circuit for determining the number and direction of interference linesmoving over the said photo diodes.

The interferometric gyro pick-up permits, dependent on the wavelength of the applied light and.theradial distance between the reflective surface and the frame axis, an angular resolution In the region of 10-30 with a construction volume of a few cubic centimetres. With such a high resolution the rotating mass of the gyro rotor can be considerably reduced, so that the bearings are also exposed to lesser loads and thus can be constructed to be of a reduced friction type.

The invention will now be described in more detail with reference to the accompanying drawing In which the single figure is a partly schematic illustration of an exemplary embodiment.

The exemplary embodiment in the figure is based on a torque-compensated gyro as illustrated in Figure 1 of the aforementioned DE-PS 38 04 766. In place of the slit diaphragm and the associated opto-electrical elements, a device according to an aspect of the invention will be used.

Attached to the gyro frame, which is not Illustrated, Is a beam 2 such that its longitudinal axis extends vertically to the rotary axis of the frame 1. A reflective surface 2.1 of the beam 2 extends in the plane of the rotary axis 1 and is oriented so that its normal surface approximately coincides with the movo-ment direction of the surface 2.1 during JSS120292 insignificant rotation of the beam 2 around the axis 1. Above the axis 1 and the beam 2 is a Michelson type interferometer, which substantially comprises a laser diode 3, a collimator 4, a prism 5 with semi-permeable surface 5.1, a first plane mirror 6, a second plane mirror 7 and a convex mirror 8.

Coherent light, which is transmitted by the laser diode 3, is bundled by the collimator 4 into a parallel beam 10.1 and initially hits the partially permeable surface 5.1 of the prism 5. A part of the beam passes through unhindered and hits the mirror 6, from which it is reflected, and again hits the rear of the partially permeable layer 5.1 (beam path 10.2). Another portion of light of the beam path 10.1 is deflected at the surface 5.1 through 900 parallel to the longitudinal axis of the beam 2 (beam path 10.3).

In the region above the reflective surface 2.1 of the beam 2 is a deflection mirror 7, which is firmly attached to the housing and which vertically deflects the portion of light following beam path 10.3 onto the reflective surface 2.1. The beam reflected therefrom is then directed via the deflection mirror 7 to the prism 5.1 acting as a beamsplitter where it interferes with the reference beam 10.2. The light beam 10.4 established after interference hits the convex deflection mirror 8 whilst being widened. The interference-line pattern, which forms in the plane 9 widens accordingly and is detected by two photo diodes 10 and 11.

If the distance between the deflection mirror 7, which is fixed to the housing, and the surface 2.1 of the beam 2 which is fixed to the frame, changes due to a rotation of the gyro frame, then the optical path length of the measuring beam path 10.3 changes, so that the interference lines move Into the one direction or the other, depending on the change In distance. Tilting of the surface 2.1 can be neglected with minor alignments of the beam. The two photo diodes 11 and 12, which are arranged at a distance which is smaller than that of two JSS120292 interference lines, serve to detect such movement of the interference lines. In this respect the associated electronics, which are connected to the photo diodes but are not illustrated in detail for clarity, measure the movement of the interference lines. The electronics substantially comprise a counter, which sums the number of Interference lines passing over the photo diodes with directional. sensitivity. The counter's position is constantly increased when the interference lines move in one direction, and decreased respectively when the interference lines move in the opposite direction. Thus, the counter position corresponds with the movement of the gyro frame. The counter position can then be used as a control signal for a torque compensation, which is generally known and not illustrated in detail, by means of which the beam 2 and, in consequence, the inner gyro frame is returned into its inoperative position.

1 The invention is not confined to the foregoing details and variations may be made thereto within the scope of the invention.

JSS120292

Claims

1. An optical pick-up for a torque-compensated gyro, the gyro rotor of which is mounted in an inner frame, rotatable around an axis oriented vertically to the gyro-rotor axis and which is mounted in a second frame firmly attached to the housing, the rotation of the inner frame being detected by means of an optical pick-up, characterised in that the inner frame has, at a radial distance from its axis, an optically reflective surface having a normal surface which coincides with a motion component of the inner frame, a reflective surface in the beam path of an interferometer, which is firmly attached to the housing, is arranged so that the optical radiation reflected from the reflective surface Interferes with a reference beam such that interference lines are detected by at least two photo diodes and the photo diodes are connected to an electrical circuit for determining the number and direction of interference lines moving over the said photo diodes.

2. An optical pick-up according to claim 1, characterised In that the interferometer is a Michelson type interferometer.

3. An optical pick-up according to claim 1 or 2, characterised in that the reference beam path of the interferometer extends parallel to the Inner frame's axis and the measuring beam path extends vertically to the inner frame's axis.

4. An optical pick-up substantially as hereinbefore described with reference to and as Illustrated in the accompanying #rawing.