GB2152320A

GB2152320A - Position location system

Info

Publication number: GB2152320A
Application number: GB08431007A
Authority: GB
Inventors: Robert James Siddall
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-12-07
Filing date: 1984-12-07
Publication date: 1985-07-31
Also published as: GB8431007D0

Abstract

In a position location system for enabling an object 3 equipped with a receiver and microprocessor to locate its position, two base stations 1, 2, situated a known distance apart, transmit laser beams rotating about vertical axes. One station 1 transmits two contra- rotating laser beams (A, B) and the other station 2 transmits at least one laser beam C; all the beams rotate at the same angular velocity and are capable of individual identification by each being transmitted on a unique (but parallel) plane of rotation. The receiver and microprocessor on the object 3 calculate the angular bearing and thus the position of the object from the differences between the times at which the signals from the different rotating laser beams are detected at the receiver. <IMAGE>

Description

SPECIFICATION Position Location System The invention relates to a position location system for enabling an object (which expression includes a person) equipped with a suitable receiver and microprocessor to locate its position at any instant relative to two or more base stations from which beams of energy are transmitted wherein at least three beams of energy, preferably lasers, rotating about parallel, generally vertical, axes are transmitted from said base stations, all the beams rotating at known angular velocities and being capable of individual identification, and wherein the receiver and microprocessor on the object calculate the instantaneous position of the object from the time differences between the time at which the signals from the different rotating beams of energy are detected at the receiver.

According to one embodiment, the location system comprises two base stations, situated a known distance apart, from which beams of energy, preferably lasers, rotating about parallel, generally vertical, axes are transmitted, at least one of the stations transmitting two contra-rotating beams, all the beams rotating at the same angular velocity and being capable of individual identification, for example by being transmitted in unique planes of rotation, and a receiver and microprocessor on the object which calculates the instantaneous position of the object from the time differences between the signals detected at the receiver from the rotating beams of energy at the base stations.

An embodiment according to the invention will now be described with reference to the accompanying drawings in which Figures 1 to 6 are diagrams showing the positions of the various beams of energy at various elapsed times.

The system comprises two base stations 1 and 2 a known fixed distance apart. Conveniently the two base stations are identical, each providing a pair of contra-rotating lasers although it is only necessary for a calculation for one of the stations to provide a pair of contra-rotating lasers. These are shown as lasers A and B transmitted from station 1; only one laser C is shown at station 2, the second laser D having been omitted. All the lasers should have the same angular velocity R in degrees per second. Each laser has a unique plane of rotation so that a detector on the object 3, which requires to locate its position, can differentiate between the lasers merely by their height above a common datum.

One laser at each station would be shielded for 180 of its rotation and the shields are so orientated that only three lasers would be visible from one side or the other of the base line running between the two stations 1 and 2.

The detector on the object may comprise four separate photo-electric cells or the like, arranged one above the other so that each coincides with the plane of rotation of one of the lasers respectively.

At elapsed time To all lasers are preferably parallel to the base line as shown in Figure 1.

As shown in Figure 2, at the shown position of the object 3, the laser A will strike the detector before the laser C, namely when laser A has turned through angle a which equals the elapsed time Tax R. That is a T,=--.

R When the lasers have turned through angle ss (Fig.

3) laser C will strike the detector at elapsed time p T,=--.

R As shown in Figure 4, laser B will strike the detector after rotation through an angle of (360-a)" at elapsed time (360-a) TB= R After a complete revolution of the lasers they will again be parallel with the base line at elapsed time 360 T,=--- R (Figure 5), whereafter laser A will again strike the detector (Figure 6) at elapsed time (360+a) TA R The time difference tBA between laser B striking the detector and the next striking by the laser A is therefore (360+a) (360-a) tE3A= R R (2a) R tBAXB hence a= 2 Also the time difference tce between the laser C striking the detector and laser B striking it is (360-a) ss (360-a-P) to=Ts-Te = - R R R and substituting the above value for awe have (3=360-R (tce±21 tuba) It is thus easy to calculate, e.g. by the microcomputer, the position of the object from the two time differences given that R is known and so are the positions of the base stations.

It would be desirable if another timer could check R by noting consecutive passes of any of the lasers in orderto check that the base stations were operating correctly.

Laser D (not shown) at station 2 is brought into use with two other lasers, e.g. B and C, if the object 3 is positioned on the opposite side of the base line so that the position of the object relative to the base line can be readily identified.

The system according to the invention is simple, should be relatively cheap, and can be self-checking.

The use of lasers should make the system free from almost any form of external interference.

It could be used, either as the basis for an automated surveying system orto enable a freeranging "intelligent" machine to find its position and hence navigate, within a predetermined area, without needing any form of inertia guiding system.

There is no limit to the number of objects which could use the same pair of base stations to fix their positions, provided that their microprocessors could make allowance for occasional obstruction by one of the other objects.

While a particular embodiment has been described, it will be understood that various modifications may be made without departing from the scope of the invention. For example, it is possible to produce similar geometric expressions to calculate the position of the detector relative to almost any number of base stations using almost any number and combinations of lasers and detectors. However the increasing complexity offers little if any benefit over the basic concept.

There may be significant benefit in increasing the complexity of the detector so that it could differentiate between the lasers by means of either their wavelength or frequency or the shape of the beams ratherthan bytheir height above the datum, as this might make the devices more flexible.

If a device carried two or more detectors, it could navigate its way around a complete plant, provided that suitable base stations were conveniently sited throughout the area and its electronic "intelligence" was iarge enough to cope with the problem.

Instead of rotating the two beams at one base station in opposite directions, they could be rotated in the same direction but at different speeds.

Claims

1.A A position location system for enabling an object (which expression includes a person) equipped with a suitable receiver and microprocessor to locate its position at any instant relative to two or more base stations from which beams of energy are transmitted, wherein at least three beams of energy, preferably lasers, rotating about parallel, generally vertical, axes are transmitted from said base stations, all the beams rotating at known angular velocities and being capable of individual identification, and wherein the receiver and microprocessor on the object calculate the instantaneous position of the object from the time differences between the time at which the signals from the different rotating beams of energy are detected at the receiver.

2. A system according to claim 1, wherein at least one of the base stations transmits two contrarotating beams.

3. A system according to claim 1 or 2, wherein all the beams rotate at the same angular velocity.

4. A system according to claim 1, 2 or 3, wherein the beams are capable of individual identification by each being transmitted in a unique plane of rotation.

5. A system according to any preceding claim, comprising two base stations each of which transmits a pair of contra-rotating lasers, each laser rotating at the same angular speed and one laser at each station being shielded for 1800 of its rotation, the shields being so oriented that only three lasers are visible from one side and from the other side of a base line running between the two base stations.

6. A system according to any preceding claim, wherein the microcomputer calculates the position of the object from its bearing angles a and ss made with the base line at the first and second stations respectively from the expressions tBAXR a 2 and 13=360-B (tub+2 teA) in which tBA is the time difference in seconds between the time at which the two beams at the first station are detected at the receiver; tas is the time difference in seconds between the times at which the beam at the second station and the beam at the first station which rotates in the same direction are detected at the receiver; and R is the common angular velocity of the beams in degrees per second.

7. A system according to any preceding claim, wherein the objects is a free-ranging machine, the output from the microcomputer being used as a control to navigate the machine within a predetermined area.

8. A position location system substantially as described with reference to the drawing.