GB1596544A - Apparatus for determining the position of a remote object - Google Patents
Apparatus for determining the position of a remote object Download PDFInfo
- Publication number
- GB1596544A GB1596544A GB50204/77A GB5020477A GB1596544A GB 1596544 A GB1596544 A GB 1596544A GB 50204/77 A GB50204/77 A GB 50204/77A GB 5020477 A GB5020477 A GB 5020477A GB 1596544 A GB1596544 A GB 1596544A
- Authority
- GB
- United Kingdom
- Prior art keywords
- sector
- mask
- radiation
- view
- field
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000005855 radiation Effects 0.000 claims abstract description 47
- 238000005259 measurement Methods 0.000 claims abstract description 19
- 230000007423 decrease Effects 0.000 claims description 4
- 230000003287 optical effect Effects 0.000 abstract description 5
- 238000003384 imaging method Methods 0.000 abstract 2
- 238000011156 evaluation Methods 0.000 abstract 1
- 230000035945 sensitivity Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000010408 sweeping Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
- G01S3/78—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using electromagnetic waves other than radio waves
- G01S3/782—Systems for determining direction or deviation from predetermined direction
- G01S3/787—Systems for determining direction or deviation from predetermined direction using rotating reticles producing a direction-dependent modulation characteristic
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41G—WEAPON SIGHTS; AIMING
- F41G7/00—Direction control systems for self-propelled missiles
- F41G7/20—Direction control systems for self-propelled missiles based on continuous observation of target position
- F41G7/30—Command link guidance systems
- F41G7/301—Details
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Electromagnetism (AREA)
- Combustion & Propulsion (AREA)
- General Engineering & Computer Science (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)
- Position Input By Displaying (AREA)
- Numerical Control (AREA)
Abstract
In order to increase the measurement accuracy in the case of determining the offset of an object from a reference line which is defined by an optical measuring device, a rotatable shutter (12) is arranged in the imaging plane of the objective (11) of said measuring device. The shutter (12) has an opening (21) which is bounded on one side by a straight line and by a logarithmic spiral on the other side. The radiation pulses which strike a photosensor (15) during rotation of this shutter have a different length, depending on the distance of the image in the imaging plane from the centre, and have a different phase angle with respect to the shutter rotation, depending on the angular position of said image. The position coordinates of the imaged target object with respect to the reference line can be determined by means of evaluation electronics (17) in this manner, the measurement accuracy being linear with respect to the distance of the image from the centre of the shutter, that is to say being small close to the centre. <IMAGE>
Description
(54) APPARATUS FOR DETERMINING THE POSITION OF A
REMOTE OBJECT
(71) We, AKTIEBOLAGET BOFORS, of S690 20 Bofors, Sweden, a Swedish joint stock company, acting under the laws of Sweden, 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: The present invention relates to apparatus for determining the coordinates representing the position of a remote object, for instance a guided missile or a target to be tracked.
The invention is particularly intended for use in determining the position of an object which emits radiation generated by a source disposed in the object, or emits infra-red radiation. The object may have a reflector which reflects radiation emitted by a radiation source positioned at the location of the apparatus. Since the distance between the apparatus and the object varies the apparatus must have a wide field of view when the target is close and the requirements of sensitivity are moderate, and a narrow field of view when the object is at a distance when greater sensitivity is required.It is known to provide a measuring device having narrow clearly-defined, fan-shaped beams sweeping alternately in elevation and azimuth over the field of view of the measuring device, whereby the times when the beams scan the object constitute a measure of the position of the object relative to the device. In order to cover the the wide field of view when the object is close it is necessary to use a comparatively high scanning velocity. The resulting fast scan of the object requires the detector of the measuring device to react rapidly which is often difficult to attain. A further limit appears if the radiation source is modulated with a comparatively low frequency, which is often the case when the radiation source consists of a pulsating laser source.
In order to avoid these difficulties it is common to increase the width of the fanshaped beams thereby effectively increasing the scan time. This however, results in a corresponding decrease in the accuracy of measurement. In order to attain a sufficient accuracy of measurement when the object is located far from the measuring device, zoom optics can be used to increase the accuracy of measurement and restrict the field of view.
Another alternative is to use two measuring devices, one having a wide field of view and a low accuracy of measurement and the other having a narrow field of view and a high accuracy of measurement. A third alternative is to use interchangeable fixed optical systems having different magnifications.
In order to attain a good accuracy of measurement for small signals, a large aperture optical system is desired which makes zoom optics very expensive as well as bulky.
The same thing applies to interchangeable optical systems, in addition to which there is a serious functional cut-off when changing the optical systems. Devices for generating the fan-shaped scanning beams are, as a rule, very complicated and delicate because of their high manufacturing precision which makes this part of the measuring device expensive. Also the alternative including two separate measuring devices is expensive and complicated.
The main objective of the present invention is therefore to provide an improved measuring apparatus.
In accordance with this invention we provide apparatus which in use measures the coordinates of an object with respect to a reference point within a predetermined field of view by scanning radiation passing between the object and the apparatus within the field of view, the apparatus comprising means defining said field of view, means for rotating at a reference frequency a sector bounded by a logarithmic spiral at one side and a straight line at the other side to scan said field of view, the spiral and straight line meeting at a point which is coincident with the axis of rotation and forms said reference point, means for generating at least one electrical signal when said sector scans said object and intercepts said radiation, said signal defining a time duration represented by the radial distance of the object of from said reference point and shifted in phase with respect to said reference frequency by an amount represented by the angular position of said object.
A preferred embodiment of the invention will be described in more detail with reference to the accompanying drawings in which:
Figure 1 shows one embodiement of measuring apparatus according to the invention;
Figure 2 shows a mask for determing the shape of the beam:
Figure 3 is an enlarged view of the central portion of Figure 2:
Figure 4 illustrates another form of mask for determing the shape of the beam; and
Figure 5 is an enlarged view of the central portion of the mask illustrated in Figure 4.
The measuring apparatus shown in Figure 1 comprises an objective lens 11 which forms an image of the radiation emitted by an object on a mask 12 located in the image plane of the objective lens. The mask 12 is concentrically mounted on a bearing 14 and arranged to be rotated by an electric motor 13. In connection with the rotating mask there is provided mask position sensor means 16 of a type known in the art, and therefore not described in detail. An electrical signal is generated by the sensor means 16 which signal is an unambiguous function of the instantaneous angular position of the mask.
A photodetector 15 is provided adjacent the mask and the output signal provided by the detector is applied to a signal processing circuit 17, of a type known in the art together with the output signal from the sensor means 16.
The objective lens 11 and the mask 12 are mounted inside a cylindrical housing 18 which is aimed at the object whose position coordinates are to be determined. The measuring device is preferably mounted inside a larger sight unit for facilitating sighting the object.
Figure 2 illustrates one embodiment of the rotating mask 12. As seen in the figure the mask consists of two sector, one sector 21, for instance an opening, through which radiation can pass to the photo detector 15, and a second sector 22 which is opaque to radiation emitted by the radiation source.
When the mask is rotating the transparent sector 21 generates a beam rotating about the rotation centre 23 of the mask, which centre in this case coincides with the centre of the field of view. The form of the beaih is determined by the form of the sector 21 and from the figure it will be apparent that the boundary with the opaque portion of the mask consists of a logarithmic spiral 26 and a straight line 25, joined at the rotation centre 23 of the mask.
In Figure 3, which is an enlarged view of the region around the rotation centre 23 of the mask, the transition between the logarithmic spiral 36 and the straight line 35 is more clearly illustrated. Close to the centre the logarithmic spiral merges into a linear spiral 34, which joins the straight line at the rotation centre 33, or so that the rotation centre is located just beside the point at which the lines join. The reason why the transparent sector 21, 31 has been given this form will be explained below.
Radiation emitted by an object is projected by the lens 11 to a point on the mask 12, which does not coincide with the rotation centre. The point will describe a circle on the surface 22 of the rotating mask with the centre of the circle located at the rotation centre 23, 33 of the mask. During that part of the rotation when the point is passing the transparent sector 21, 31 of the mask an output pulse is generated by the detector, if the radiation emitted by the radiation source is continuous, or a pulse train if the radiation source is pulse modulated. The pulse or pulse train is repeated each revolution when the mask is rotating and because of the shape of the transparent sector, the length of the pulse or pulse train is directly related to the distance from the point to the rotation centre.
The phase of the pulse or pulse train relative to the rotation of the mask is a measure of the position of the point relative to the rotation centre. In this way an indication of the position of the point in polar coordinates is determined as well as a corresponding indication of the direction of the object from the device.
The length of the pulse or pulse train and the phase is determined by means of the signal processing circuit 17, the signal required for the phase comparison is derived from the sensor means 16. The signal processing circuit 17 may include a micro computer which besides signal processing performs, by means of a known computational program, a conversion between polar coordinates and cartesian coordinates, if desired.
The length of the pulse or pulse train is proportional to the logarithm of the reciprocal value of the distance between the point and the rotation centre of the mask due to the shape of the open sector of the mask. From this it follows that uncertainty of measurement in the radial direction decreases linearly with the distance between the point and the centre. As the direction towards the point is derived from the time of passage of the straight line 25, 35 also the uncertainty of measurement in the tangential direction decreases with the distance from the centre. In this way it is possible to combine a good accuracy of measurement in the central portion of the field of view with a wide field of view.Said relationship between the uncertainty of measurement and the distance to the centre is true when the response time of the photodetector or the pulse frequency of the radiation source limits the resolution.
Said relationship is not true very close to the centre where said conditions provide such good resolution that other conditions, such as limited image sharpness, provides a limitation. Therefore it is appropriate to design the boundary line of the mask as a linear spiral 34 close to the centre so that the dynamic range of the measuring device does not provide a higher resolution than can be utilised.
In the following some examples of other embodiments within the scope of the invention will be described. It is possible, by means of different designs of the transparent sector of the mask, to adjust the accuracy of measurement for different applications. One example of another embodiment is shown in
Figure 4, in which the entire mask is illustrated and in Figure 5, which is an enlarged view of the central portion of the mask. In both of these figures the opaque portion of the mask is indicated by the numerals 41, 43 and 51, 53 respectively, while two transparent sub-sectors are indicated by 42, 44 and 52, 54 respectively.With such sub-sectors two pulses having a constant length are obtained from the photo detector 15 at each revolution of the mask, but in which the interval between the pulses provides an unambiguous measurement of the distance between the projected point and the rotation centre of the mask. The constant length of the pulses enables the signal processing circuit 17 to suppress any noise pulses that may occur. From this it follows that this embodiment is specifically usable for such applications in which disturbances may occur. In order to avoid confusion between both pulse trains the regions 42, 52 and 44, 54 have different widths.
Another embodiment within the scope of the invention is the one in which the rotating mask is replaced by a rotating photo detector having a radiation sensitive area of the same shape as the transparent sector of the mask previously described and in which the electrical output signal is derived from the photo detector via, for instance, slip rings. A further embodiment is one in which a radiation source is located in the apparatus instead of a photo detector and a photo detector is located on the object instead of the radiation source.
This embodiment is of interest when it is desired to receive information regarding the position of the object at the object instead of at the apparatus. Information regarding the angular position of the rotating part of the apparatus is, in this case, transmitted telemetrically to the object by modulating the radiation source in a manner known in the art.
WHAT WE CLAIM IS:
1. Apparatus which in use measures the coordinates of an object with respect to a reference point within a predetermined field of view by scanning radiation passing between the object and the apparatus within the field of view, the apparatus comprising means defining said field of view, means for rotating at a reference frequency a sector bounded by a logarithmic spiral at one side and a straight line at the other side to scan said field of view, the spiral and straight line meeting at a point which is coincident with the axis of rotation and forms said reference point, means for generating at least one electrical signal when said sector scans said object and intercepts said radiation, said signal defining a time duration represented by the radial distance of the object from said reference point and shifted in phase with respect to said reference frequency by an amount represented by the angular position of said object.
2. Apparatus as claimed in Claim 1 wherein said sector forms part of a rotatable disc which is opaque to said radiation outside the area of said sector.
3. Apparatus as claimed in Claim 2 wherein said generating means includes a radiation sensitive detector, said disc being located between said detector and said field of view defining means.
4. Apparatus as claimed in Claim 1 wherein said generating means includes a detector and said sector comprises a radiation sensitive area of said detector, said rotating means rotating said detector at said reference frequency.
5. Apparatus as claimed in Claim 2 including a source of radiation, said object having a radiation sensitive detector and said disc is located between said source of radiation and said field of view defining means.
6. Apparatus as claimed in any one of the preceding claims wherein said sector includes first and second sub-sectors, the first being bounded by straight lines and the second which is circumferentially spaced from the first being bounded by logarithmic spirals.
7. Apparatus as claimed in Claim 6 wherein said generating means produces a first pulse as said first sub-sector intercepts said radiation for each rotation of said sector and a second pulse as said second sub-sector intercepts said radiation for each rotation of said sector, the time interval between the first
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (10)
1. Apparatus which in use measures the coordinates of an object with respect to a reference point within a predetermined field of view by scanning radiation passing between the object and the apparatus within the field of view, the apparatus comprising means defining said field of view, means for rotating at a reference frequency a sector bounded by a logarithmic spiral at one side and a straight line at the other side to scan said field of view, the spiral and straight line meeting at a point which is coincident with the axis of rotation and forms said reference point, means for generating at least one electrical signal when said sector scans said object and intercepts said radiation, said signal defining a time duration represented by the radial distance of the object from said reference point and shifted in phase with respect to said reference frequency by an amount represented by the angular position of said object.
2. Apparatus as claimed in Claim 1 wherein said sector forms part of a rotatable disc which is opaque to said radiation outside the area of said sector.
3. Apparatus as claimed in Claim 2 wherein said generating means includes a radiation sensitive detector, said disc being located between said detector and said field of view defining means.
4. Apparatus as claimed in Claim 1 wherein said generating means includes a detector and said sector comprises a radiation sensitive area of said detector, said rotating means rotating said detector at said reference frequency.
5. Apparatus as claimed in Claim 2 including a source of radiation, said object having a radiation sensitive detector and said disc is located between said source of radiation and said field of view defining means.
6. Apparatus as claimed in any one of the preceding claims wherein said sector includes first and second sub-sectors, the first being bounded by straight lines and the second which is circumferentially spaced from the first being bounded by logarithmic spirals.
7. Apparatus as claimed in Claim 6 wherein said generating means produces a first pulse as said first sub-sector intercepts said radiation for each rotation of said sector and a second pulse as said second sub-sector intercepts said radiation for each rotation of said sector, the time interval between the first
and second pulses representing the radial distance of said object from said reference points.
8. Apparatus as claimed in any one of the preceding claims wherein logarithmic boundary curve(s) includes a linear spiral adjacent said reference point terminating at said reference point.
9. Apparatus as claimed in Claim 3 wherein said field of view defining means comprises an objective lens located in front of said disc, said detector being mounted behind the disc in the image plane of the objective lens. said apparatus including an electric motor to rotate said disc at said reference frequency sensing means to determine the angular position of the mask, and signal processing means to derive the position coordinates of said object from the signals supplied by the generating means and said sensing means with reference to said reference frequency.
10. Apparatus for measuring the coordinates of an object with respect to a reference point substantially as described herein with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7613514A SE416234B (en) | 1976-12-02 | 1976-12-02 | DEVICE FOR SEATING THE DIRECTIONAL COORDINATES TO A RELATED OBJECT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1596544A true GB1596544A (en) | 1981-08-26 |
Family
ID=20329636
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB50204/77A Expired GB1596544A (en) | 1976-12-02 | 1977-12-01 | Apparatus for determining the position of a remote object |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5374063A (en) |
| CH (1) | CH629297A5 (en) |
| DE (1) | DE2753782A1 (en) |
| FR (1) | FR2373031A1 (en) |
| GB (1) | GB1596544A (en) |
| IT (1) | IT1090718B (en) |
| NL (1) | NL189878C (en) |
| NO (1) | NO149402C (en) |
| SE (1) | SE416234B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2156622A (en) * | 1984-03-22 | 1985-10-09 | Eltro Gmbh | Target location method and apparatus |
| US4840490A (en) * | 1984-12-10 | 1989-06-20 | Lasercheck Limited | Laser position measurement and alignment |
| GB2350248A (en) * | 1982-07-09 | 2000-11-22 | Short Brothers Ltd | Furnishing information to determine the position of a body |
| GB2350889A (en) * | 1999-06-09 | 2000-12-13 | Rover Group | Optical position target |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE445074B (en) * | 1980-10-31 | 1986-05-26 | Bofors Ab | DEVICE BY A CHOPPER |
| DE3602456A1 (en) * | 1986-01-28 | 1987-07-30 | Diehl Gmbh & Co | TARGETING DEVICE |
| JPH0161975U (en) * | 1987-10-15 | 1989-04-20 |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE977909C (en) * | 1959-12-18 | 1972-11-02 | Eltro Gmbh | Device for coordinate measurement |
-
1976
- 1976-12-02 SE SE7613514A patent/SE416234B/en not_active IP Right Cessation
-
1977
- 1977-11-29 JP JP14378177A patent/JPS5374063A/en active Granted
- 1977-11-30 NL NLAANVRAGE7713210,A patent/NL189878C/en not_active IP Right Cessation
- 1977-12-01 IT IT52022/77A patent/IT1090718B/en active
- 1977-12-01 FR FR7736237A patent/FR2373031A1/en active Granted
- 1977-12-01 GB GB50204/77A patent/GB1596544A/en not_active Expired
- 1977-12-01 NO NO774115A patent/NO149402C/en unknown
- 1977-12-01 CH CH1472777A patent/CH629297A5/en not_active IP Right Cessation
- 1977-12-02 DE DE19772753782 patent/DE2753782A1/en active Granted
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2350248A (en) * | 1982-07-09 | 2000-11-22 | Short Brothers Ltd | Furnishing information to determine the position of a body |
| GB2350248B (en) * | 1982-07-09 | 2001-04-04 | Short Brothers Ltd | A method of, and apparatus for. furnishing information to determine the position of a body |
| GB2156622A (en) * | 1984-03-22 | 1985-10-09 | Eltro Gmbh | Target location method and apparatus |
| US4840490A (en) * | 1984-12-10 | 1989-06-20 | Lasercheck Limited | Laser position measurement and alignment |
| GB2350889A (en) * | 1999-06-09 | 2000-12-13 | Rover Group | Optical position target |
Also Published As
| Publication number | Publication date |
|---|---|
| NO149402B (en) | 1984-01-02 |
| DE2753782C2 (en) | 1988-01-07 |
| IT1090718B (en) | 1985-06-26 |
| NL189878C (en) | 1993-08-16 |
| SE7613514L (en) | 1978-06-03 |
| NO149402C (en) | 1984-04-11 |
| FR2373031B1 (en) | 1984-07-20 |
| JPS5374063A (en) | 1978-07-01 |
| CH629297A5 (en) | 1982-04-15 |
| NL189878B (en) | 1993-03-16 |
| NL7713210A (en) | 1978-06-06 |
| SE416234B (en) | 1980-12-08 |
| NO774115L (en) | 1978-06-05 |
| JPS6161070B2 (en) | 1986-12-24 |
| FR2373031A1 (en) | 1978-06-30 |
| DE2753782A1 (en) | 1978-06-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed [section 19, patents act 1949] | ||
| PE20 | Patent expired after termination of 20 years |
Effective date: 19971130 |