GB2238872A - Range and direction finding system for robots - Google Patents

Abstract

A set of corner reflectors (8) which reflect sound substantially back in the incident direction are provided e.g. on walls (3), by means of which range and direction information is acquired through an acoustic transmitter/receiver on the robot (1). <IMAGE>

Description

ROBOTIC RANGE AND DIRECTION FINDING The invention relates to range and direction finding for robotic machines. There is a requirement to direct robots along controllable paths in an environment in order that they may move between locations to effect different tasks or to convey items. One arrangement provides tracks embedded in the floor which the robot follows. This is inflexible in that the robot cannot depart from the track in order, for example, to go to a new location or to circumvent objects on the track. Efforts have been made, therefore, to provide robots with sensors whereby they may detect the range and position of objects in their neighbourhood.In this way not only can collisions be avoided but also a map of the environment may be built up against which the sensor outputs may be compared as a reference so that the robot may determine its own position for use in flexible route control.

The high speed of transmission of electromagnetic radiation, including light and radio waves, makes it an expensive and impractical medium for this purpose. A better medium is acoustic waves, either of audio or preferably ultrasonic frequencies.

A difficulty with acoustic transducers is that they are relatively poor direc-tionally and this means that in a standard environment they are not accurate enough for practical purposes.

Reference is made to Figures 1 and 2 of the accompanying drawings, of which: Figure 1 is a diagram illustrating the acoustic beam coverage of a transducer facing a wall; and Figure 2 is a diagram illustrating the effect of directing the beam obliquely with respect to the wall.

In Figure 1 the acoustic transducer is shown at 1 and has a transmission/reception acoustic beam pattern 2. As shown, the beam is directed orthogonally with respect to a wall 3 and sound is reflected directly from the wall back to the transducer. In known manner the time delay between transmission and reception of the sound is measured to give an output according to the distance of the wall.

The direction of the wall is taken to be the direction of the principal axis 4 of the beam.

In Figure 2 the beam is directed obliquely with respect to the wall. Nevertheless, the orthogonal from the wall lies within the beam width and sound is transmitted and received directly as indicated by the arrows. As far as distance is concerned, therefore, the interpretation of the transducer signals will give the orthogonal distance to the wall, namely the same as in the arrangement of Figure 1. As far as direction is concerned, it will be taken that the wall is in the new direction of the principal axis 4 of the beam. The effect will be that the signal interpretation will be that the nearest point of the wall is shifted from position 5 to position 6. This is clearly an error. It is to be noted that the component of sound from the transducer directed along the major axis 4 is specularly reflected from the wall as indicated at 7 and is not returned to the transducer.

The invention seeks to provide an improvement whereby the accuracy of a sonic direction and rangefinding arrangement may be enhanced.

Accordingly to the invention there is provided an acoustic direction and range-finding system including an acoustic transmitter/receiver transducer arrangement having means to transmit sound in particular directions and determine distance by measurement of delays between transmissions and reflections and a set of corner reflectors in the neighbourhood of the transducer arrangement, the corner reflectors being arranged to present rightangled corners into which sound may enter to be reflected towards its source regardless of its angle of incidence.

Normally, a mobile robot will carry the transducer arrangement and the corner reflectors will be distributed in the environment. However, the converse arrangement is possible where the robot carries the corner reflectors, which may be constituted by one or more multiple reflector units, and one or more acoustic transducer arrangements are mounted in the environment and linked to determine the position of the robot.

In many situations the corner reflectors may be disposed at a specific height or height range above the floor which corresponds to the height of the acoustic transducers. Then the corner reflector may be two-sided, being constituted by two plane surfaces at right angles. Generally the plane surfaces will be vertical.

In other situations it may be desirable that the corner reflectors should reflect back sound from different vertical directions as well as different horizontal directions. Then the reflectors will have three orthogonal plane surfaces intersecting at a corner point.

In one embodiment of the invention the corner reflectors are provided by small cubes fixed to walls and/or floors and/or ceilings of the environment. The corners presented by the sides of the cubes and the adjacent surface provide the required reflective properties. Being two-plane reflectors the cubes need to be fixed in a particular height range corresponding to the transducer height, with limits determined by the beam spread. The cubes may be individually fixed to the walls, for example, or may be moun-ted at predetermined intervals on a band or strip of material which itself is attached to the wall, floor or ceiling.

The invention will further be described with reference to Figures 3 to 7 of the accompanying drawings, of which: Figure 3 is a diagram illustrating the effect of a corner reflector on reflection of a beam; Figure 4 is a plan of an environment modified in accordance with the invention; and Figures 5 to 7 are two-part diagrams showing maps produced with and without the use of the invention.

Referring to Figure 3 there is shown an arrangement similar to Figure 2 except that a corner reflector 8 is provided on the wall. The corner reflector comprises a block of wood about lcm cube fixed to the wall at the height of the transducer. As shown, sound is efficiently returned to the transducer from the corner reflector despite the oblique angle of the beam with respect to the wall. Thus, the main reflection is now derived along the principal beam axis and determination of the range and position of that part of the wall on which the reflector is situated is accurate.

Figure 4 shows a plan view of an L-shaped corridor from which lead rooms. There are five walls 20; three double doors 21 and two single doors 22.

Figure 5(a) shows a map of this environment produced from the outpu-t of an acoustic range and direction finding transducer arrangement situated at a point Pl.

Then a set of corner reflectors 23 of the kind described with reference to Figure 3 was positioned along the walls, the blocks being spaced apart some 20cm. Figure 5(b) shows the map produced by the same transducer arrangement positioned at Pl.

Figure 6(a) and 6(b) are maps produced respectively without and with the corner reflectors from position P2. Figures 7(a) and 7(b) are maps produced respectively without and with the corner reflectors from position P3. The improvement of accuracy of the maps by the use of the corner reflectors is evident.

It may be found that blocks protruding from the walls are obtrusive. By placing such blocks on the floor at the base of the walls advantage can be taken of the fact that the floor will constitute part of a three-plane reflector and redirect sound to the transducer in spite of the discrepancy in elevation.

Satisfactory results are obtainable with this arrangement.

Claims (6)

1 An acoustic direction and range-finding system including an acoustic transmitter/receiver transducer arrangement having means to transmit sound in particular directions and determine distance by measurement of delays between transmissions and reflections and a set of corner reflectors in the neighbourhood of the transducer arrangement, the corner reflectors being arranged to present rightangled corners into which sound may enter to be reflected towards its source regardless of its angle of incidence.

2. A system as claimed in claim l wherein the corner reflectors are distributed on or in plane surfaces in the environment and the transducer arrangement is mounted on a mobile robot.

3. A system as claimed in claim 1 or claim 2 wherein the corner reflectors are constituted by two plane surfaces at right angles.

4. A system as claimed in claim 3 wherein one of the plane surfaces is a wall, a floor or a ceiling.

5. A system as claimed in any of the preceding claims wherein the corner reflectors are provided by small cubes fixed to walls and/or floors and/or ceilings of the environment.

6. A system as claimed in claim 5 wherein the cubes are mounted on a band or strip of material.