GB2228584A

GB2228584A - Optical seeker.

Info

Publication number: GB2228584A
Application number: GB8514880A
Authority: GB
Inventors: Peter Giesenberg; Dirk Jansen
Original assignee: Bodenseewerk Geratetechnik GmbH
Current assignee: Bodenseewerk Geratetechnik GmbH
Priority date: 1984-06-28
Filing date: 1985-06-12
Publication date: 1990-08-29
Anticipated expiration: 2005-06-12
Also published as: DE3423792C1; FR2643724A1; GB2228584B

Description

Optical Seeker The invention relates to an optical seeker arranged to scan a field of view along a rosette type path, comprising (a) a rotor rotating about an axis of rotation, (b) a housing-fixed detector, (c) an optical system arranged on the rotor and being of the type of a Cassegrain system having , as primary mirror, a concave mirror facing the field of view and a secondary mirror facing the concave mirror and the detector, the optical system imaging the field of view by the concave mirror and the secondary mirror in the plane of the detector, and (d) means for providing a rosette type motion of each point of the field ot view image relative to the detector, said means including an inclination of the secondary mirror to the axis of rotation of the rotor and a gear transmission.

From European patent publication no. 79 684, an optical seeker for target seeking missiles is known, in which a field of view. is scanned along a rosette-shaped path . The seeker comprises an imaging optical system which is of the type of a Cassegrain system with an annular concave mirror and an opposite plane mirror. The optical system is located on a gyro rotor rotating about its geometrical axis and pivotable with its geometrical axis with two degrees of freedom, by a gimbal mounting. The field of view is imaged by the concave mirror and the plane mirror as well as by a further annular mirror opposite the plane mirror, a plane mirror and a lens system, in the plane of a detector which is arranged, housing-fixed, essentially in the central point.The plane mirror forming the secondary mirror of the Cassegrain system, rotates with the gyro rotor. The additional annular mirror with the optical system is held in a mounting, on which the gyro rotor is mounted rotatably about its geometrical axis, and which is connected to the gyro rotor through a planetary gear. The lens system is thus always aligned with the geometrical axis of the gyro rotor, when the gyro rotor is pivotably moved about said central point. The mounting of the lens system with the annular mirror makes, however, a faster rotational movement in an opposite direction of rotation of the gyro rotor, as compared to the rotational speed of the gyro rotor. The secondary mirror of the Cassegrain system is slightly inclined relative to the axis of rotation of the gyro rotor. Also the annular mirror is slightly inclined relative to the axis of rotation.

These two mirrors ensure that each point of the the field of view image follows a rosette-shaped path relative to the detector.

The seeker of the prior art is compicatea n construction. The imaging optical system comprises, beside the primary rl"rror, that is the annular concave m rror, and the secondary mirror, that is the plane mirror, two other mirrors, the annular mirror and the further plane mirror opposite thereto. This increases the expenditure. The additional mirrors rotatable relative to each other may cause angular errors due to play and tolerances. It has to be noted that angular errors are doubled with each reflection. Such angular errors result in modification of the scanned rosette and thus in the signals obtained at the detector being associated with the wrong picture elements of the field of view.The planetary gear of the known seeker arranged in the gimbals is extremely difficult to manufacture.

It is the object of the invention to construct an optical seeker of the above defined type with only two mirrors, and to simplify the mechanism for the rosette scanning.

According to the invention this object is achieved in that (e) the secondary mirror is mounted on a rotor through a bearing the axis of which forms an angle, with the axis of rotation, (f) the optical axis of the secondary mirror forms an angle with the axis of the bearing an-d (g) the secondary mirror is coupled to the rotor through the gear transmission.

In such an arrangement, the secondary mirror of the C as segrai n system does not rot ate with the rotor speed contrary to the arrangement of European patent publication 79 684. Rather, it makes a nutating motion by the rotation of the rotor, due to the inclined bearing. A second nutating motion is superposed to this nutating motion, the second nutating motion being caused by the fact that the secondary mirror forms with its optical axis (that is a normal to the plane mirror surface) an angle with the axis of the bearing, and that it is slowly rotated by the gear transmission. The rosette scanning is thus caused by one single mirror.

Modifications of the invention are subject matter of the sub-claims.

An embodiment of the invetion will now be described in greater detail with reference to the accompanying drawings: Fig. 1 is a schematic sectional view of an optical seeker.

Fig. 2 shows a rosette-type trajectory of a point of a field of view on the detector of the seeker of Fig.l while the secondary mirror is rotating.

Fig. 3 is a schematic sectional view of another embodiment of an optical seeker.

The optical seeker comprises a rotor 12 rotating about a rotational axis 10, a housing-fixed detector 14, an optical system arranged on the rotor 12 and means for providing a rosette type motion of each point of the field of view image relative to the detector 14. The optical system comprises, as primary mirror, a concave mirror 16 facing the field of view and a secondary mirror 18 facing the concave mirror 16 and the detector 14.

The optical system is thus of the type of a Cassegrain system. The field of view is imaged through the concave mirror 16, the secondary mirror 18 formed as plane mirror, and a lens 20, in the plane of the detector 14. The secondary mirror 18 is rotatably mounted through a bearing 22 on the rotor 12. The axis 24 of the bearing 22 forms with the axis 10 of rotation an angle a . The optical axis of the secondary mirror 18, that is practically a normal 26 to the plane surface 28 of the secondary mirror 18, forms, with the axis 24 of the bearing 22, an angle ss. The secondary mirror 18 is connected to the rotor 12 through a gear transmission 30. The rotor 12 is a gyro rotor which rotates about its geometrical axis as axis of rotation 10, and which is mounted in a housing, practically an airframe of a missile, in a way permitting angular motion of the geometrical axis about a central point 32. The detector 14 is arranged essentially in the central point 32. The signals of the detector 14 are applied to a signal evaluating circuit known per se and thus not described here, which is adapted for generating follow-up ' signals indicative of the target deviation of a detected target from the geometrical axis 10. The follow-up signals are applied to a follow-up device also known per se and thus not described here, for providing a precession movement to reduce the target deviation and to align the geometrical axis 1C with the target. Thus the detector is arranged housing-fixed.The gyro rotor is pivotable about the central point 32, where the detector 14 is located. Thus the field of view is always imaged onto the detector 14. Due to the gyroscopic effect, the seeker is decoupled from the motion of the missile. The seeker is aligned with the target by the follow-up signals and the follow-up device. Controlling signals for controlling the missile may f.ex. be derived from the torques acting on the gyro rotor in this follow-up loop. A reference pick-off (not shown) is provided for the signal evaluating circuit and provides a signal which is phase synchronous with the rotation of the rotor 12 and is applied to the signal evaluating circuit.

A hollow shaft extending along the axis of rotation toward the secondary mirror is attached to the rotor. The bearing forming with the axis of rotation an angle is attached to the hollow shaft, the secondary mirror being mounted with a mirror support 36 on the bearing. The reducing gear 30 is a planetary gear having a sun gear 38, a planet carrier 40, planet wheels 42,44 which are mounted on the planet carrier 44 and in engagement with the sun gear 38, and a ring gear 46 the internal gear of which is in engagement with the planet wheels 42,44. The planet carrier 40 is held non-rotatably by a retaining member 48 extending through the hollow shaft 34. The sun gear 38 is attached to on the hollow shaft 34. The ring gear 46 is connected to the secondary mirror 18. To this end, a connecting member 52 provided with a radial slot 50 is connected to the ring gear 46.A projection 54 attached to the mirror support 36 of the secondary mirror 18 is guided in the radial slot 50 in a way permitting swivelling motion of the secondary mirror 18. The gyro rotor 12 is mounted, rotatably about its geometrical axis, on a non-rotatable part 56. This non-rotatable part 56 is mounted pivotably with two degrees of freedom about said central point 32. The planet carrier is connected through the retaining member to the non-rotatable part.

The secondary mirror is covered on the side of the field of view by a secondary mirror. The secondary mirror screen is connected to the planet carrier such that they are both held non-rotatably but pivotably with the geometrical axis of the gyro rotor by the retaining member. This ensures, that the path of rays is not covered by the secondary mirror screen 58, also if the Secoflddry mirror screen 58 does not constitute a part of the gyro rotor 12, and th gyro rotor 12 is pivoted out of its central position. The retaining member 48 is a torque rod which is mounted, at its end adjacent the planet carrier 40 in a constriction 60 of the hollow shaft 34.

The optical system comprises a lens 20 arranged in a mounting 62 and arranged in a path of rays between the secondary mirror 18 and the detector 14. The mounting 62 is attached to an inner gimbal 64 which is mounted in bearings 66 (in an outer gimbal non-illustrated), pivotably about an axis 68 extending through the central point 32. The gyro rotor 12 is rotatably mounted on the mounting 62 of the lens 20. The torque rod 48 is held, at its end remote from the planet carrier 40, in the front face 70 of the lens 20. The gyro rotor 12 supports the primary mirror 1 6, which is an annular concave mirror. A peripheral portion 72 rotationally symmetric about the geometrical axis 10 extends from the inner edge of the concave mirror 16 in the direction of the secondary mirror 18.The peripheral portion 72 supports at its end facing the secondary mirror 18, a window 78 traversed by the imaging path of rays and having a central aperture 80, the hollow shaft 34 being fixed in the aperture 80 and the torque rod extending through the aperture 80.

The mode of operation of the described arrangement is as follows: It be assumed that the secondary mirror 18 is held in circumferential direction through the projection 54 and the radial slot 50, while the gyro rotor 12 is rotating. In this case, the secondary mirror 18 makes a swivelling mouvement with the rotational frequency of the gyro. rotor between an angle of inclination + ss and an angle of inclination - a + B = O, in the plane of the radial slot 50, that is, f.ex., in the- plane of the paper of Fig.l.

The field of view would then periodically be scanned in this plane. The secondary mirror 18 with the ring gear 46 ' is however rotated through the reducing- gear 30. A slower circulating motion is therefore superposed to the radial rocking motion.

Each point of the field of view image thus fbllows a rosette, as illustrated in Fig.2. If the step up or step down gear transmission ratio, respectively, are integers, the rosette is closed after one rotation of the slow circating scanning (in this case the rotation stepped-down in rotary speed of the secondary mirror). Preferably, the reduction gear ratio is not an integer, such that a complete cycle, after which the rosette is closed, includes a plurality of rotations of the ring gear 46 and of the secondary mirror 18. The rosette is closed, when the product of reduction gear ratio or gear transnission ratio x number of rotations becomes an integer, f.ex, 6,75 x 4 = 27 i x n = number of rosette leafs = number of gyro rotations.

In the embodiment of Fig.3, the rotary speed of the quick scanning is identical with that of the rotor 12 and of the concave mirror 16. The rotary speed of the slow scanning is derived from the rotary speed of the rotor 12 through the reducing gear. In the embodiment of Fig.3, the rotary speed of the slow scanning is equal to the rotary speed of the rotor 12. The rotary speed of the quick scanning is derived from this rotary speed of the rotor 12 through a stepping-up gear 82.

The construction of the seeker of Fig.3 is similar to that of Fig.l, and corresponding elements are designated in both Figures by the same numerals.

In the gear transmission 82 also formed as planetary gear, a ring gear is connected to a flange 86 at the end of the hollow shaft 34. The ring gear 84 is thus driven by the rotor 12. The planetary wheels 88 of the gear transmission 82 are mounted in an inner flange 90 of the secondary mirror screen 58 serving as planet carrier. This secondary mirror screen 58 is held vehicie-fixed by the retaining member 48, similarly to the arrangement of Fig.l, such that it does not rotate with the rotor 12. The sun gear 92 is rotatably mounted on the hollow shaft 34 and connected to the connecting member 52. The ring gear thus rotates with the rotary speed of the rotor 12, while the secondary mirror 18 is driven by the stepped-up rotary speed of the sun gear 92.

In the embodiment of Fig.3 a type of support of the retaining member 48 is provided different from that shown in Fig.1. The mounting 62 of the lens 20 supports a funnel-shaped projection 94 closed by a window 96. The retaining member is held centrally by this window 96. The window 96 may be formed, just like the window 78, as correcting lens, which corrects, among others, the deviations from the spherical form of the dome covering the seeker. In the window 96, the retaining member 48 can be fixed much easier than in the lens 20. As can be seen from the- illustrated path of rays, the fastening of the retaining member 34 is located in the window 96 outside the path of rays.

Due to an appropriate selection of the step-up or step-down ratio respectively, 82 or 30 of the gear transmission and of the angles of nuation and ss, a plurality of scanning patterns may be realized.

The angles of nutation need not to be equal, but may well be selected differently. If the mounting causing a nutating movement of the secondary mirror 18, on the hollow shaft 34 rotates with the rotary speed of the rotor 12, and the secondary mirror is driven through the gear transmission 82, with the same rotary speed but in opposite direction, this will result in linear scanning.

Claims

1. Optical seeker arranged to scan a field of view along a rosette type path, comprising (a) a motor /12) rotating about an axis (10) of rotation, (b) a housing-fixed detector (14), (c) an optical system arranged on the rotor (12) and being of the type of a Cassegrain system having, as primary mirror, a concave mirror (16) facing the field of view and a secondary mirror (18) facing the concave mirror (16) and the detector (14), the optival system imaging the field of view by the concave mirror and the secondary mirror in the plane of the detector and (d) means for providing a rosette type motion of .each point of the field of view image relative to the detector, said means .including an inclination of the secondary mirror to the axis of rotation of the rotor and a gear transmission, characterized in that (e) the secondary mirror (18) is mounted on a rotor (12) through a bearing (22) the axis (24) of which forms an angle ( ), with the axis (10) of rotation, (f) the optical axis (26) of the secondary mirror (18) forms an angle (ss) with the axis (24) of the bearing (22), and (g) the secondary mirror (18) is coupled to the rotor (12) through the gear transmission (30).

2. Optical seeker as set forth in claim 1, characterized in that (a) the rotor (12) is a gyro rotor which rotates about its geometrical axis as axis of rotation and which is mounted in a housing in a way permitting angular motion of the geometrical axis about a central point (32), and (b) the detector (14) is arranged essentially in the central point (32).

3. Optical seeker as set forth in claim 2, characterized by (a) a signal evaluating circuit to which the signals of the detector are applied and which is adapted for generating follow-up signals indicative of the target deviation of a detected target from the geometrical axis, and (b) a follow-up device to which the follow-up signals are applied, for providing a precession movement to reduce the target deviation and to align the geometrical axis with the target.

4. Optical seeker as set forth in claim 3, characterized by a reference pick-off which provides a signal, phase synchronous with the rotation of the rotor, and applied to the signal evaluating circuit.

5. Optical seeker as set forth in anyone of the claims 1 to 4, characterized in that (a) a hollow shaft (34) extending along the axis (10) of rotation toward the secondary mirror (18) is attached to the rotor (12), (b) the bearing (22) forming with the axis (10) of rotation an angle ( " ) is attached to the hollow shaft (34), the secondary mirror- (18) being mounted on the bearing, and (c) the gear transmission (30) is a planetary reducing gear, the plane carrier (40,90) of which is held non-rotating by a retaining inember (48) extending through the hollow shaft (34).

6. Optical seeker as set forth in claim 5, characterized in that the sun gear (38) of the planetary gear is connected to the hollow shaft (34), and the ring gear (46) is connected to the secondary mirror (18).

7. Optical seeker as set forth in claim 5, characterized in that the ring gear (84) is connected to the hollow shaft (34), and the sun wheel (38) is connected to the secondary mirror.

8. Optical seeker as set forth in claim 6 or 7, characterized in that a connecting member (52) provided with a radial slot (50) is connected to the wheel (46,92) on the driven side of the planetary gear, and a projection (54) attached to a mirror support (36) of the secondary mirror (18) is guided in this radial slot (50) in a way permitting swivelling motion of the secondary mirror (18).

9. Optical seeker as set forth in claims 2 and 5, characterized in that (a) the gyro rotor (12) is mounted, rotatably about its geometrical axis (10), on a non-rotatable part (56), and this non-rotatable part (56) is mounted pivotably with two degrees of freedom about said central point (32), and (b) the planet carrier (40) is connected through the retaining memhcr (48) to the non-rotatable part (56).

10. Optical seeker as set forth in claim 9, characterized in that (a) the secondary mirror (18) is covered on the side of the field of view by a secondary mirror screen (58), and (b) the secondary mirror screen (58) is connected to the planet carrier (40) such that they- are both held non-rotatably but pivotably with the geometrical axis (10) of the gyro rotor (12), by the retaining member (48).

11. Optical seeker as set forth in claim 10, characterized in that the retaining member (48) is a torque rod which is mounted at its end adjacent the planet carrier (40) in a constriction (60) of the hollow shaft (34).

12. Optical seeker as set forth in anyone of the claims 9 to 11, characterized in that (a) the optical system comprises a lens (20) arranged in a mounting (62) and arranged in a path of rays between the secondary mirror (18) and the detector (14), (b) the mounting (62) is attached to an inner gimbal (64) which is mounted pivotably about an axis (68) passing through the central point (32), (c) the gyro rotor (12) is rotatably mounted on the'mounting (62) of the lens (20), and (d) the torque rod (48) is held, at its end remote from the planet carrier (40), by the lens (20).

13. Optical seeker as set forth in claim 12, characterized in that (a) a funnel-shaped projection (74) closed by a window (96) is provided on the mounting (62) of the lens (20), and (b) the torque rod (48) is supported centrally by the window (96).

14. Optical seeker as set forth in claim 12 or 13, characterized in that (a) the gyro rotor (12) supports the primary mirror (16), which is an annular concave mirror, (b) a peripheral portion (72) rotationally symmetric about the geometrical axis (10) extends from the inner edge of the concave mirror (16) in the direction of the secondary mirror (18), (c) the peripheral portion (72) supports at its end facing the secondary mirror (18), a window t783 traversed by the imaging path of rays, and having a central aperture (80), the hollow shaft (34) being fixed in the aperture (80) and the torque rod extending through the aperture (80).

15. Seekers set forth in claim 14, characterized in that the window (78) Is formed as correcting lens.

16. Seeker as set forth in claim 13, characterized in that the window (96) in the projection (74) of the mounting (62) is formed as a correcting lens.

Amendments to the claims have been filed as follows i. An optical seeker arranged to scan a field of view along a rosette type path, comprising (a) a rotor rotating about an axis of rotation, (b) a housing-fixed detector, (c) an optical system arranged on the rotor and being of the type of a Cassegrain system having, as primary mirror, a concave mirror facing the field of view, and a secondary mirror facing the concave mirror and the detector, the optical system imaging the field of view in the plane of the detector, via the concave mirror and the secondary mirror, and (d) means for providing a rosette type motion of each point of the field of view image relative to the detector, said means including an inclination of the secondary mirror to the axis of rotation of the rotor and a gear transmission, wherein (e) the secondary mirror is mounted on the rotor through a bearing the axis of which forms a first angle, with the axis of rotation, (f) the optical axis of the secondary mirror forms a second angle with the axis of the bearing, and (g) the secondary mirror is coupled to the rotor through the gear transmission.

2. An optical seeker as claimed in Claim i, characterised in that (a) the rotor is a gyro rotor which rotates about its geometrical axis as axis of rotation and which is mounted in a housing in a way permitting angular motion of the geometrical asis about a central point, and (b) the detector is arranged essentially in the central point.

3. An optical seeker as claimed in Claim 2, characterised by (a) a signal evaluating circuit to which the signals of the detector are applied and which is adapted for generating follow-up signals indicative of the target deviation of a detected target from the geometrical axis, and (b) a follow-up device to which the follow-up signals are applied, for providing a precession movement to reduce the target deviation and to align the geometrical axis with the target.

4. An optical seeker as claimed in Claim 3, characterised by a reference pick-off which provides a signal, phase synchronous with the rotation of the rotor, and applied to the signal evaluating circuit.

5. An optical seeker as claimed in any one of the Claims 1 to 4, characterised in that (a) a hollow shaft extending along the axis of rotation toward the secondary mirror is attached to the rotor, (b) the bearing forming the first angle with the axis of rotations attached to the hollow shaft, the secondary mirror being mounted on the bearing, and (c) the gear transmission is a planetary reducing gear, the planet carrier of which is held non- z rotating by a retaining member extending through the hollow shaft.

6. An optical seeker as claimed in Claim 5, characterised in that the sun gear of the planetary gear is connected to the hollow shaft, and the ring gear is connected to the secondary mirror.

7. An optical seeker as claimed in Claim 5, characterised in that the ring gear is connected to the hollow shaft, and the sun wheel is connected to the secondary mirror.

8. Ali optical seeker as claimed in Claims 6 or 7, characterised in that a connecting member provided with a radial slot is connected to the wheel on the driven side of the planetary gear, and a projection attached to a mirror support of the secondary mirror is guided in this radial slot in a way permitting swivelling motion of the secondary mirror.

9. An optical seeker as claimed in Claims 2 and 5, characterised in that (a) the gyro rotor is mounted, rotatably about its geometrical axis, on a non-rotatable part, and this non-rotatable part is mounted pivotably with two degrees of freedom about said central point, and (b) the planet carrier is connected through the retaining member to the non-rotatable part.

10. An optical seeker as claimed in Claim 9, characterised in that (a) the secondary mirror is covered on the side of the field of view by a secondary mirror screen, and (b) the secondary mirror screen is connected to the planet carrier such that they are both held non-rotatably but pivotably with the geometrical axis of the gyro rotor, by the retaining member.

il. An optical seeker as claimed in Claim 10, characterised in that the retaining member is a torque rod which is mounted at its end adjacent the planet carrier in-a constriction of the hollow shaft.

12. An optical seeker as claimed in any one of the Claims 9 to il, characterised in that (a) the optical system comprises a lens arranged in a mounting and arranged in a path of rays between the secondary mirror and the detector, (b) the mounting is attached to an inner gimbal which is mounted pivotably about an axis passing through the central point, (c) the gyro rotor is rotatably mounted on the mounting of the lens, and (d) the torque rod is held, at its end remote from the planet carrier, by the lens.

13. An optical seeker as claimed in Claim 12, characterised in that (a) a funnel-shaped projection closed by a window is provided on the mounting of the lens, and (b) the torque rod is supported centrally by the window.

14. An optical seeker as claimed in Claims 12 or 13, characterised in that (a) the gyro rotor supports the primary mirror, which is an annular concave mirror, (b) a peripheral portion rotationally symmetric about the geometrical axis extends from the inner edge of the concave mirror in the direction of the secondary mirror, (c) the peripheral portion supports at its end facing the secondary mirror, a window traversed by the imaging path of rays, and having a central aperture, the hollow shaft being fixed in the aperture and the torque rod extending through the aperture.

15. An optical seeker as claimed in Claim 14, characterised in that the window is formed as a correcting lens.

16. An optical seeker as claimed in Claim 13, characterised in that the window in the projection of the mounting is formed as a correcting lens.

17. An optical seeker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.