GB2175087A - Laser gyrosystem - Google Patents

Abstract

A compact laser gyrosystem comprises a main gyrostructure 1 of cylindrical configuration and having an internally reflecting surface 1a. Entrance and exit planes 1b and 1 c are defined in the gyrostructure and a beam splitter 2 is positioned therebetween. Light from laser source 3 is split by the beam splitter and follows two polygonal paths within the gyrostructure in opposite directions, emerging to respective detectors 4 and 5. Rotation of the gyrostructure about its axis results in the movement of interference fringes which are detected by the detectors, and arithmetic logic unit 6 calculates the angular velocity. The number of turns made by both laser beams inside the gyrostructure 1 can be altered by changing the angle of incidence of the laser beam on the gyrostructure. <IMAGE>

Description

SPECIFICATION Laser gyrosystem BACKGROUND OF THE INVENTION The present invention relates to a laser gyrosystem.

Laser gyrosystems of a plurality of types have conventionally been proposed based on the Sagnac effect.

A plan view of a laser gyrosystem built in accordance with the ring laser system is shown in Fig. 1. Four gas tubes 11 through 14 are arranged to form a square whose side measures one meter.

The optical path of the square is established by gas tubes 11, 12, 13, 14, planar mirrors 16 and 17, curved mirror 18 and output mirror 19. A coupling mirror is identified by number 20 and a detector by number 22, The laser gyrosystem constitutes a Sagnac interferometer as shown in Fig. 2. Part of the light beam emitted from light source A passes through mirror C and travels along the optical path consisting of mirrors C, D3, D2 and D1 which turns clockwise; and the remainder of the light beam emitted from light source A is reflected from C and travels along the optical path consisting of C, D1, D2 and D3 which turns counterclockwise. When the laser gyrosystem revolves clockwise or counterclockwise, an optical phase difference between these two routes can occur corresponding to the angular velocity of revolution.

The interference fringes which occur due to the phase difference between these two optical routes move to enable the angular velocity to be detected.

Fig. 3 shows a plan view of another example of the laser gyrosystem wherein an optical fiber and a laser oscillator are used. The optical fiber is wound on a drum two turns or more to improve the detection efficiency.

The more the number of turns increases, the more the detection sensitivity increases. Thus, the drum whereon the optical fiber is wound two turns or more is used to form a gyrosystem.

The gyrosystem built in accordance with the conventional techniques, however, is massive and inappropriate for use to control the motion of a high speed machine.

The objective of this invention is therefore to present a new type of light-weight, small-size laser gyrosystem.

SUMMARY OF THE INVENTION The laser gyrosystem built in accordance with the present invention consists of a laser gyrosystem comprising a main gyrostructure consisting of a block of transparent optical material and having a cylindrical internally reflecting surface, a laser oscillator, a beam splitter arranged to receive light from the laser oscillator and to split it into two beams which enter the main gyrostructure and rotate through multiple internal reflection in opposite directions within the gyrostructure, and detector means for detecting the difference in the phase shift in the two beams whereby the angular velocity of the gyrosystem may be determined.

Certain embodiments of the invention will now be described by way of example and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a laser gyrosystem of a square type.

Figure 2 shows the principle of operation of the Sagnac interferometer.

Figure 3 is a schematic diagram of an optical fiber gyrosystem.

Figure 4 is a perspective view of an embodiment of a laser gyrosystem built in accordance with the present invention.

Figure 5 is a plan view of the optical path within the main gyrostructure of Fig. 4.

Figure 6 shows the relation between the incident angle and the optical path.

Figure 7 is a schematic diagram illustrating the incident and reflection angles of the light beam.

Referring to Fig. 4, main gyrostructure 1 is made of transparent quartz, and reflector film la made of evaporated aluminium is formed on the outside of the cylinder so as to effectively reflect the light beam.

Main gyrostructure 1 provides an entrance plane 1 b for a light beam revolving clockwise, which can also be used as an exit plane for a light beam revolving counterclockwise, and another entrance plane 1c for the light beam revolving counterclockwise, which can also be used as an exit plane for the light beam revolving clockwise.

Beam splitter 2 is arranged on the plane which bisects the angle between the planes 1 b and 1c of the main gyrostructure. The light beam emitted from laser source 3 is incident on the main gyrostructure 1.

A light beam is incident on entrance plane 1b for revolving clockwise and goes out of plane 1 c after the light beam revolves clockwise with multiple reflections from reflector 1 a. This light beam can be detected in detector 4 for sensing the light beam which turns clockwise.

Another light beam is incident on entrance plane 1 c for revolving counterclockwise and goes out of plane 1 b after the light beam revolves counterclockwise with multiple reflections from reflector 1a. This light beam can be detected in detector 5 for sensing the light beam which turns counterclockwise.

Data detected in detectors 4 and 5 are compared by arithmetic logic unit 6 so as to calculate the acceleration applied to the gyrosystem.

Fig. 5 shows an example of the optical path within the main gyrostructure.

The light beam travelling along the circular path which turns clockwise in Fig. 5 has route razz (reflectedì .1b ,M3 ,M4 ... M111c.

The light beam travelling along the circular path which turns counterclockwise in Fig. 5 has route a .2 (transparentì~M1,... M3 1 b.

If the gyrosystem is located within a quiescent system, no optical phase difference can occur in main gyrostructure 1 between the light beam travelling along the circular paths which turn clockwise and counterclockwise, respectively.

If main gyrostructure 1 is located within a revolving system whose axis agrees with the cylinder axis of the main gyrostructure 1, some optical phase differences can occur in main gyrostructure 1 due to the Sagnac effect.

The phase difference in the optical path for the laser beam can be used to detect the angular velocity of revolution in the revolving system.

Fig. 6 shows an example of the gyrosystem wherein the angle of incidence can be varied depending on the location of the incident light beam.

Tangential lines to what would be the circumference of the cylinder at the entrance and exit points have angles of a and y with respect to the directions of incidence of the beams d and c and angles of ss and os with respect to the directions of exit. If the tangential angle is gradually changed from angle a to y, the light beam at the entrance point travels along a different optical path with a certain number of multiple reflections and turns by a certain number of cycles.

The properties of the light beams travelling along different optical paths will be summarized hereinafter.

DEG M N DIS ADIS 45" 1 4 1.41 5.66 46" 11 45 1.39 62.52 47" 43 180 1.36 245.52 48" 6 30 1.34 40.15 DEG: Angle of the incident light beam with respect to the normal to the surface of the assumptive cylinder at the incident point M: Number of cycles by which the light beam travelling along the circular path turns while the light beam goes from the entrance plane to the exit plane N: Total number of multiple reflections plus one, i.e. the number of straight-line paths within the cylinder DIS: Optical path length between adjacent reflection points on the circumference when the radius is assumed unity ADIS: Total distance of the optical path from the entrance plane to the exit plane of the light beam Fig. 7 shows an example of the optical path at an incident angle of 48 degrees.

The light beam incident at 43 degrees (90"-47") with respect to the tangential line of a disk with a radius of 100 mm in a quiescent system is reflected 179 times (=N-1) and revolved by 43 turns (=M). The light beam then returns to a location of +0.05 mm or less far from the incident point. The returning point is 1/1000 or less of the radius far from the incident point.

The light beam within the gyrosystem can travel a distance of approximately 24550 mm.

If the incident angle is properly set, the number of multiple reflections or the number of cycles within a disk can be increased. This implies realization of a high sensitivity laser gyrosystem. As indicated in Fig. 6, the incident angle can be selected by moving the laser beam sideways of the beam direction.

If the laser beam is incident on the plane perpendicular to the central axis of the cylinder with a small amount of inclination, the light beam can travel helically along the revolving path around the circumference of main gyrostructure 1. Thus, the light beam appears at an exit point which is different from the entrance point in the direction of height.

This is the reason why the optical axis of the detector is inclined from that of the laser beam in Fig. 4.

As described above, the laser gyrosystem built in accordance with the present invention has an optical system which is simple, stable and of light weight; and it has such a high sensitivity as the optical fiber gyrosystem.

The laser gyrosystem of cylinder type built in accordance with the present invention can be used to control the speed of the wheels in a vehicle, robot arm motion, and to control the attitude of robots.

Claims (4)

1. A laser gyrosystem comprising a main gyrostructure consisting of a block of transparent optical material and having a cylindrical internally reflecting surface, a laser oscillator, a beam splitter arranged to receive light from the laser oscillator and to split it into two beams which enter the main gyrostructure and rotate through multiple internal reflection in opposite directions within the gyrostructure, and detector means for detecting the difference in the phase shift in the two beams whereby the angular velocity of the gyrosystem may be determined.

2. A laser gyrosystem as claimed in claim 1 wherein the main gyrostructure is formed in its edge with reentrant entrance and exit planes for the laser beam and the beam splitter is disposed between the entrance and exit planes.

3. A laser gyrosystem as claimed in claim 1 or 2 wherein the laser beam is incident at a small angle on the plane perpendicular to the axis of the cylindrical surface, whereby the light follows a generally helical path between the beam splitter and the detector means.

4. A laser gyrosystem substantially as hereinbefore described with reference to the accom panying drawings.