FR2570490A1 - Image coincidence portable range finder - Google Patents

Abstract

Image coincidence portable range finder of the type comprising a reference base 1 on which there is a mounted a first optical means for observing an object along a line of sight 2, a second optical means for observing the said object along a second line of sight 3 and a focusing means allowing determination of the distance of the object. This range finder is original in that: - the first optical means comprises an input objective 4, a first 5 and a second 6 reflecting prism for brining the first line of sight into a vision optical path 7 delimited by two objectives 8, 9, - the second optical means comprises an input objective 11, a first optical square 10 and a second optical square 12 which interact with a reflecting prism 13 in order to bring the second line of sight into the same optical axis 7, - and the focusing means is constituted by means for moving one of the two optical squares in translation. Application for measuring distances of between 0 and 500 metres.

Description

PORTABLE TEMPLATE WITH IMAGE COINCIDENCE
The technical sector of the present invention is that of devices for measuring the distance of a target point, of the type comprising two observation channels and a mixing system of these two channels.

 It is well known to measure the distance of an object using a range finder device by coincidence of images coming from two observation channels. Thus, patent FR 2 234 548 describes a mixed-field range finder in which an object is observed using two brackets fixed on a base. The focus and therefore the telemetric measurement is obtained by maneuvering a diasporameter which acts on the two beams coming from the two squares. This makes it possible to apply the same correction of anamorphosis and chromatic aberrations.

The disadvantage of this device lies in the complexity of implementation since it must be arranged for the two beams to pass through the diasporameter and in that the coincidence of images is made by rotation.

 The object of the present invention is to provide a portable-type image coincidence range finder in which this coincidence is achieved by translation of an optical system.

The invention therefore relates to a portable image coincidence rangefinder of the type comprising a reference base on which is mounted a first optical means for observing an object according to a first line of sight, a second optical means for observing said object along a second line of sight and focusing means for detecting the distance of the object, characterized in that
the first optical means comprises an entry objective, a first and a second return prism for bringing the first line of sight along an optical axis delimited by two objectives,
the second optical means comprises an input lens a first optical bracket and a second optical bracket cooperating with a return prism to bring the second line of sight along the same optical axis,
- And the focusing means is constituted by translation means of one of the two optical brackets.

 The two deflection prisms can be placed one in the path of the incident beam and the other on the emergent beam with respect to an optical square.

 The translation means and the deflection prisms can be applied to the same optical bracket.

 A deflecting prism may be placed on the path of the incident beam relative to the entry objective along the first line of sight.

 The optical path delimited by the objectives can pass through the first return prism.

 An advantage of the range finder according to the invention lies in the extremely simple design. Indeed, the optical elements are reduced in number: 4 prisms, 2 objectives in particular, and their assembly does not present any particular difficulty.

 Another advantage lies in the exclusive use of total reflection prisms, which are optical invariants for rotation around a vertical axis.

 Another advantage is the very small footprint and the very low mass.

Other advantages of the present invention will be better understood on reading the description of a particular embodiment given in connection with a drawing in which
- Figure 1 shows a cross section of the rangefinder showing its internal organization.

 - Figure 2 shows a perspective view.

 - Figure 3 illustrates the theoretical principle of the rangefinder according to the invention.

 The rangefinder shown in FIG. 1 comprises a reference base 1 with respect to which are arranged all the optical and mechanical elements. Two lines of sight 2 and 3 are materialized by two optical means. The first optical means comprises an input objective 4, two prisms 5 and 6 making it possible to bring back a first light beam along the optical axis 7 delimited by the two objectives 8 and 9.

The prisms 5 and 6 are of the total reflection type and invariant for rotation about a vertical axis and are positioned such that the optical path 7 is parallel to the line of sight 2 for rotation about a horizontal axis .

The second optical means comprises two optical brackets 10 and 12 of pentagonal shape, arranged along the base 1, between which is placed an objective 11 of focusing or input. A prism 13 cooperates with the prism 6 to bring a second beam along the optical axis 7. Thus by translating the bracket 10 relative to the base 1, the coincidence of the two images is achieved, the bracket 12 being fixed. The prisms 6 and 13 are placed adjacently and the plane I of intersection or image comprises two parts, one reflective, and the other transparent, to ensure respectively the reflection of the first beam and the transmission of the second beam. We then obtain two congruent half-images. A rotation of the prism 5 around the optical axis 7 makes it possible to obtain two parallel half-images.

 Until plane I, the number of reflections of the first beam is 3; however, it may be superior and odd in order to obtain at objective level 9 a straight image. By cons, the number of reflections of the second beam is 5 and can be higher and odd to keep a straight image. Beyond the plane I the two beams are merged, and the optical and mechanical defects encountered on this path are transparent since they affect both beams simultaneously.

 This device can be completed by prisms deviators to correct the angular defects of different prisms and the cancellation of position errors during their mechanical assembly to complete the final setting of the rangefinder. Thus, a deviating prism 14 is placed in the path of the incident beam relative to the optical square 10, for example at its input face 10a. Another deflecting prism 15 is placed in the path of the emergent beam of this optical bracket, for example at the exit face 10b. These two prisms are rotatably mounted relative to the optical axis of the bracket 10 and each provide a deflection of the light beam of a given angle while requiring the beam to be in its plane of triangulation.

 However, 11 square 12 can be made slightly mobile in translation, so as to perfect the adjustment and expand the acceptable dimensional tolerances on the various optical elements.

 Likewise, a rotational prism 16 may be placed upstream of objective 4.

 To reduce the size of the rangefinder, it is arranged that the optical axis 7 passes through the prism 5 and opens at an eyepiece 21.

 In fig. 2, there is shown a practical embodiment of the rangefinder where the reference base is embodied by the strip 18 at one end of which is fixed the plate 17. This plate supports the prisms 5, 6 and 13, the optical bracket 12, the objectives 4, 8, 9 and 11 and the eyepiece 21. The rotator prism 16, placed in front of the lens 4, is mounted on a rotatable support 22. The objective 11 is mounted on a support 23. A plate 19 is mounted movably relative to the slide 18. This plate supports the bracket 10 and the rotational prisms 14 and 15. Under the action of a pushbutton the slider 20 slides on the slide with automatic adjustment of play with respect to the axis of the strip.

The emergent ray exits through the window 24. The plate 19 still carries a movable finger 25 in front of a double graduation 26 for locating the distance of the target object along a scale of 0 to 100 meters and 100 to 500 meters. The passage from one ladder to another is achieved by a rotation of 1800 of the prism 16 on its support 22 modifying the corresponding target.

Finally, the rangefinder can be equipped with either a 27 in cleaved handle and mounted directly on a tripod support in the case of use in fixed point.

 The telemetry principle applied in the invention is explained in FIG. 3 on which only the different optical axes have been represented.

 The observation of an object at a distance of 100 m or 500 m is made at a given angle, determined by the fixed directions of the two lines of sight.

 The angles B and J have the respective values of 2 and 3 milliradians.

Scale 8-lOOm: α 1 = 5 milliradians
Scale 100-500m: 2 = 1 milliradian
Given the low value of the angle 0 <in both cases, we have the relation
tg &alpha; 1 = 4,908878.10-3
and oil = 4,908874.10-3
As a result b / d = tg &alpha; 1 # &alpha; 1 which justifies the use of a linear graduation on the ruler.

Claims (11)

1 - An image coincidence portable rangefinder of the type comprising a reference base (1) on which is mounted a first optical means for observing an object along a first line of sight (2), a second optical means for observing said object along a second line of sight (3) and focusing means for detecting distance from the object, characterized in that  the first optical means comprises an entry objective (4), a first (5) and a second (6) return prism for bringing the first line of sight along an optical path (7) defined by two objectives ( 8,9)  the second optical means comprises an input lens (11), a first optical bracket (10) and a second optical bracket (12) cooperating with a deflection prism (13) to bring the second line of sight along the same axis optical (7),  - And the focusing means is constituted by translation means of one of the two optical brackets. 2 - portable rangefinder according to claim 1, characterized in that two deflection prisms (14, 15) are placed one (14) on the path of the incident beam and the other (15) on the emerging beam relative to a square optical (10). 3 - portable rangefinder according to claim 2, characterized in that the translation means and the deflection prisms (14, 15) are applied to the same optical bracket (10). 4 - optical rangefinder according to claim 1, 2 or 3, characterized in that a deviating prism (16) is placed in the path of the incident beam relative to the entry objective (4) according to the first line of sight . 5 - optical rangefinder according to any one of claims 1 to 4, characterized in that the optical axis delimited by the objectives (9,8) passes through the first prism (5) return. 6 - optical rangefinder according to any one of claims 1 to 5, characterized in that an entry lens (11) is placed on the optical path connecting the two brackets (10, 12) (to review). 7 - Optical rangefinder according to any one of claims 1 to 6, characterized in that the return prism (13) is adjacent to the return prism (6) so that the light rays are in total reflection. 8 - Portable rangefinder according to any one of claims 1 to 7, characterized in that the number of reflections according to the first line of sight (2) is odd and greater than or equal to 3 and that according to the second line of sight (3 ) is odd and greater than or equal to 5. 9 - Portable rangefinder according to any one of claims 1 to 8 characterized in that the first optical means (4,5,6,9,8,16), the second optical square (12) and the prism of send (13) are inserted in a plate (17) integral with a strip (18) materializing the reference base. 10 - Portable rangefinder according to claim 9, characterized in that the first optical bracket (11) and the rotational prisms (14, 15) are inserted in a plate (19) movable in translation relative to the strip (18) carrying a graduation (26) under the action of a slider (20) in focus. 11 - Portable rangefinder according to any one of the preceding claims, characterized in that the prisms are invariant in a rotation about a vertical axis.