GB1562599A - Space scanning arrangements - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO SPACE SCANNING ARRANGEMENTS (71) We, THE MARCONI COM PANY LIMITED, a British Company of Marconi House, New Street, Chelmsford, Essex, CM1 1PL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to space scanning arrangements.

It is often required to scan space with either a receiving beam path for electromagnetic energy or a transmitted beam path of electromagnetic energy. One example is the scanning of space for the purposes of detecting infra-red energy from, for example, a forest fire.

Apparatus for carrying out such scanning commonly consists of an energy detector, or energy source, located at or near the focal point of an objective lens system, contained with some form of scanner for sweeping the energy path over the field of view of the objective lens.

The space between the energy detector or energy source and the objective lens system will hereinafter be referred to as the "image space", and the space beyond the objective lens will be referred to as the "object space", irrespective of whether the system is for transmission or reception.

One common form of scanner utilised in known space-scanning arrangements consists of an oscillating mirror in the object space. However, in such cases the oscillating mirror tends to be large, and any but very slow scan rates are difficult to obtain.

The present invention seeks to provide an improved space-scanning arrangement in which the use of an oscillating mirror in the object space may be avoided.

According to this invention, a space scanning arrangement (in which either a receiving beam path for electromagnetic energy or a transmitting beam path of electromagnetic energy is scanned in space) comprises, positioned in the beam path: a scanning lens system consistency essentially of a first lens element with a concave surface, a second lens element with a convex surface substantially complementary and in juxta position to said first element, and driving means for relatively moving said two lens elements so that said two surfaces move one across the other in a scanning manner, the whole arrangement being such that said receiving or transmitting path is subject to refraction through an angle which varies with relative position of said two elements.

Said concave and convex surfaces may be in contact, one provided to ride over the other, or closely spaced.

Preferably, said two elements are planoconcave and plano-convex.

Said concave and convex surfaces may be cylindrical if scanning is required to be effected by said scanning lens system in one plane only. Preferably, however, whether scanning is required on one plane only or in more than one plane, said concave and convex surfaces are spherical in view of the relative ease with which spherical lens surfaces may be produced compared with cylindrical lens surfaces.

One or other or both of said lens elements may be arranged to be drivably movable (by means known per se), and said scanning lens system may be positioned either in the image space or in the object space (preferably the latter) as hereinbefore defined.

Where said scanning lens system is positioned in the image space, and one or other element has a plane surface, prefer ably that plane surface is fixed, and provided as the window of a housing enclosing the elements of the scanning system, and the other of said lens elements is arranged to be movable.

The order in which the lens elements appear in the receiving or transmitting path is not material.

Where convenient, one of said lens elements may form part of the objective lens system of said scanning arrangement.

The invention is particularly useful where said scanning arrangement is a receiving system, especially such a system which is an infra-red scanning system with a detector element positioned at or near the focal point of an objective lens system.

The material of the scanning lens elements will naturally be chosen in dependence upon the wavelengths of electromagnetic energy to be received or transmitted and may, for example, be glass, silicon or germanium as appropriate.

The two elements of the scanning system may be of materials of different dispersions in order to achromatise the scanning lens system.

In one embodiment of the invention said scanning lens system is positioned in the object space, one of said scanning lens elements is arranged to move relative to the other to provide scanning in one plane only, and a movable mirror is provided in the image space to provide scanning in an orthogonal plane whereby a volume of space may be scanned.

Preferably, the degree of scan provided by said movable mirror is less than the degree of scan provided by said scanning lens system.

The invention is illustrated in and further described with reference to the drawings accompanying the Provisional Specification, in which drawings: Figure 1 is a schematic diagram illustrating the present invention as applied to an infra-red energy detecting arrangement in accordance with the present invention; and Figures 2 and 3 are views in plan and elevation respectively of one practical infra-red energy detecting arrangement in accordance with the present invention.

Referring to Figure 1, an infra-red detector 1 is positioned to receive input energy via an objective lens system represented at 2. The space 3i between the detector 1 and the objective lens system 2 is termed the "image space", whilst the space 3O beyond the objective lens system 2, towards a target source (not shown) of infra-red energy, is termed the "object space".

It is required to cause the receiving beam path for energy to scan across the object space in the plane of the drawing, and in order to achieve this a scanning lens system 4 is provided in the object space 3O and on the optical axis 5 of the objective lens system 2.

The scanning lens system 4 consists of two relatively-movable lens elements 6 and 7.

Lens element 6 is a plano-concave element, whilst lens element 7 is a plano-convex element. The concave and convex surfaces of the lens elements 6 and 7 are complementary, in contact, and (in this embodiment) spherical.

The material used for the lens elements both of the scanning lens system 4 and the objective lens system 2 is germanium (in view of the fact that it is infra-red energy which is of concern). The materials of the lens elements 6 and 7 are of different dispersions, however, in order to achromatise the scanning lens system 4, as knownper se.

Lens element 6 is fixed relative to objective lens system 2, and its plane surface forms the outer window of a sealed housing (not represented) for the whole detector arrangement.

Lens element 7 is arranged to be rotated over a limited arc, in the directions represented by the double-headed arrow 8, about a centre of rotation 9, As shown, the lens element 7 is in one extreme position of scan; the dotted outline 7' shows the lens element 7 in its other extreme position of scan.

The scanning lens system 4 in effect forms a prism of variable angle, and in the extreme position of scan shown the receiving beam path lies at an angle 0 in the plane of the drawing to the optical axis of the objective lens system 2. Thus, with the arrangement described, by moving lens element 7 from one extreme position of scan to the other the receiving beam path is caused to scan over an angle 20.

The concave and convex surfaces of the lens elements 6 and 7 are, as has already been mentioned, spherical (although to per- form the scanning function so far described cylindrical surfaces would suffice). However, lens elements with spherical surfaces are more readily manufactured, and, in addition, scanning in a direction orthogonal to that described (i.e. scanning in a plane at right angles to the plane of the paper), may be provided separately for so that the receiving beam path can be scanned in an "x, y" fashion through a volume of space, rather than merely linearly as described.

In the practical embodiment of the invention now to be described with reference to Figures 2 and 3, in which like references are used for parts in Figure 1, scanning in "x, y" fashion through a volume of space is provided for whilst, at the same time, and to avoid undue mechanical complexity, the scanning lens system 4 is utilised to provide linear scan in one plane (the horizontal plane) only.

In view of the description which has already been given with reference to Figure 1, Figures 2 and 3 will be largely selfexplanatory. The infra-red detector element 1 is provided in a Dewar chamber 10 on an optical axis 11 (Figure 3) which is at right angles to the optical axis 5 of the objective lens system 2. The rear and front lens elements of the objective lens system are represented at 12 and 13 respectively, whilst the objective principal planes are shown at 14.

Energy is transmitted to the infra-red detector 1 from the objective lens system 2 via a mirror 15 in the image space, which mirror can be oscillated in the vertical plane (i.e. about the axis 16 in Figure 2) to provide vertical scanning of the receiving beam path.

Scanning in the horizontal plane is provided for by the scanning lens system 4 in the object space, as described with reference to Figure 1.

Thus, the major scanning, i.e. azimuth scanning in the horizontal plane is provided for by the scanning lens system 4, whilst limited scanning, i.e. elevation scanning in the vertical plane, is provided for by the rocking mirror 15.

In this particular embodiment, rocking mirror 15 is controlled to scan in steps over an arc of 2.3 degrees in elevation, whilst scanning lens system 4 is limited to a maximum (26) of 10 in azimuth. The radius of curvature of the spherical concave and convex surfaces of the lens elements 6 and 7 is 25 cm. The objective lens system is of focal length 10 cm (F1.45).

WHAT WE CLAIM IS: 1. A space scanning arrangement (in which either a receiving beam path for electromagnetic energy or a transmitting beam path of electromagnetic energy is scanned in space) comprising, positioned in the beam path: a scanning lens system consisting essentially of a first lens element with a concave surface, a second lens element with a convex surface substantially complementary and in juxta position to said first lens element, and driving means for relatively moving said two lens elements so that said two surfaces move one across the other in a scaning manner; the whole arrangement being such that said receiving or transmitting path is subject to refraction through an angle which varies with the relative position of said two elements.

2. An arrangement as claimed in claim 1 and wherein said concave and convex surfaces are in contact, one provided to ride over the other.

3. An arrangement as claimed in claim 1 and wherein said concave and convex surfaces are closely spaced.

4. An arrangement as claimed in any of the above claims and wherein said two elements are plano-concave and plano-convex.

5. An arrangement as claimed in any of the above claims and wherein said concave and convex surfaces are cylindrical.

6. An arrangement as claimed in any of claims 1 to 4 and wherein said concave and convex surfaces are spherical.

7. An arrangement as claimed in any of the above claims and wherein one only of said lens elements is arranged to be desirably movable.

8. An arrangement as claimed in any of claims 1 to 6 and wherein both of said lens elements are arranged to be drivably movable.

9. An arrangement as claimed in any of the above claims and wherein said scanning lens system is positioned in the object space as hereinbefore defined.

10. An arrangement as claimed in any of claims 1 to 8 and wherein said scanning lens system is positioned in the image space and one of said lens elements has a plane surface, that plane surface is fixed, and is provided as the window of a housing enclosing the elements of the scanning system, and the other of said lens elements is arranged to be movable.

11. An arrangement as claimed in any of the above claims and wherein one of said lens elements forms part of the objective lens system of said scanning arrangement.

12. An arrangement as claimed in any of the above claims and wherein said scanning arrangement is a receiving system.

13. An arrangement as claimed in claim 12 and wherein said scanning system is an infra-red scanning system with a detector element positioned at or near the focal point of an objective lens system.

14. An arrangement as claimed in any of the above claims and wherein the two elements of the scanning system are of materials of different dispersions in order to achromatise the scanning lens system.

15. An arrangement as claimed in claim 9 or in any of claims 11 to 14 as dependent upon claim 1 and wherein one of said scanning lens elements is arranged to move relative to the other to provide scanning in one plane only and a movable mirror is provided in the image space to provide scanning in an orthogonal plane whereby a volume of space may be scanned.

16. An arrangement as claimed in claim 15 and wherein the degree of scan provided by said movable mirror is less than the degree of scan provided by said scanning lens system.

17. A space scanning arrangement substantially as herein described with reference to Figure 1 of the drawings accompanying the Provisional specification.

18. A space scanning arrangement substantially as herein described with reference to Figures 2 and 3 of the drawings accompanying the Provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. optical axis 11 (Figure 3) which is at right angles to the optical axis 5 of the objective lens system 2. The rear and front lens elements of the objective lens system are represented at 12 and 13 respectively, whilst the objective principal planes are shown at 14. Energy is transmitted to the infra-red detector 1 from the objective lens system 2 via a mirror 15 in the image space, which mirror can be oscillated in the vertical plane (i.e. about the axis 16 in Figure 2) to provide vertical scanning of the receiving beam path. Scanning in the horizontal plane is provided for by the scanning lens system 4 in the object space, as described with reference to Figure 1. Thus, the major scanning, i.e. azimuth scanning in the horizontal plane is provided for by the scanning lens system 4, whilst limited scanning, i.e. elevation scanning in the vertical plane, is provided for by the rocking mirror 15. In this particular embodiment, rocking mirror 15 is controlled to scan in steps over an arc of 2.3 degrees in elevation, whilst scanning lens system 4 is limited to a maximum (26) of 10 in azimuth. The radius of curvature of the spherical concave and convex surfaces of the lens elements 6 and 7 is 25 cm. The objective lens system is of focal length 10 cm (F1.45). WHAT WE CLAIM IS:

1. A space scanning arrangement (in which either a receiving beam path for electromagnetic energy or a transmitting beam path of electromagnetic energy is scanned in space) comprising, positioned in the beam path: a scanning lens system consisting essentially of a first lens element with a concave surface, a second lens element with a convex surface substantially complementary and in juxta position to said first lens element, and driving means for relatively moving said two lens elements so that said two surfaces move one across the other in a scaning manner; the whole arrangement being such that said receiving or transmitting path is subject to refraction through an angle which varies with the relative position of said two elements.

2. An arrangement as claimed in claim 1 and wherein said concave and convex surfaces are in contact, one provided to ride over the other.

3. An arrangement as claimed in claim 1 and wherein said concave and convex surfaces are closely spaced.

4. An arrangement as claimed in any of the above claims and wherein said two elements are plano-concave and plano-convex.

5. An arrangement as claimed in any of the above claims and wherein said concave and convex surfaces are cylindrical.

6. An arrangement as claimed in any of claims 1 to 4 and wherein said concave and convex surfaces are spherical.

7. An arrangement as claimed in any of the above claims and wherein one only of said lens elements is arranged to be desirably movable.

8. An arrangement as claimed in any of claims 1 to 6 and wherein both of said lens elements are arranged to be drivably movable.

9. An arrangement as claimed in any of the above claims and wherein said scanning lens system is positioned in the object space as hereinbefore defined.

10. An arrangement as claimed in any of claims 1 to 8 and wherein said scanning lens system is positioned in the image space and one of said lens elements has a plane surface, that plane surface is fixed, and is provided as the window of a housing enclosing the elements of the scanning system, and the other of said lens elements is arranged to be movable.

11. An arrangement as claimed in any of the above claims and wherein one of said lens elements forms part of the objective lens system of said scanning arrangement.

12. An arrangement as claimed in any of the above claims and wherein said scanning arrangement is a receiving system.

13. An arrangement as claimed in claim 12 and wherein said scanning system is an infra-red scanning system with a detector element positioned at or near the focal point of an objective lens system.

14. An arrangement as claimed in any of the above claims and wherein the two elements of the scanning system are of materials of different dispersions in order to achromatise the scanning lens system.

15. An arrangement as claimed in claim 9 or in any of claims 11 to 14 as dependent upon claim 1 and wherein one of said scanning lens elements is arranged to move relative to the other to provide scanning in one plane only and a movable mirror is provided in the image space to provide scanning in an orthogonal plane whereby a volume of space may be scanned.

16. An arrangement as claimed in claim 15 and wherein the degree of scan provided by said movable mirror is less than the degree of scan provided by said scanning lens system.

17. A space scanning arrangement substantially as herein described with reference to Figure 1 of the drawings accompanying the Provisional specification.

18. A space scanning arrangement substantially as herein described with reference to Figures 2 and 3 of the drawings accompanying the Provisional specification.