GB2333920A

GB2333920A - Optical distance measuring apparatus

Info

Publication number: GB2333920A
Application number: GB9900300A
Authority: GB
Inventors: Dierk Schmidt; Juergen Luginsland; Joerg Stierle; Peter Wolf; Gunter Flinspach
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-02-03
Filing date: 1999-01-07
Publication date: 1999-08-04
Anticipated expiration: 2019-01-07
Also published as: DE19804059A1; DE19804059B4; GB2333920B; GB9900300D0; FR2774475A1

Abstract

An apparatus for optical distance measurement by signal propagation timing, has a transmitting optical system (23) for emitting a concentrated measuring signal (which may be produced by a laser diode) and receiving optical system for picking up a measuring signal fraction reflected by a remote subject (27). Disposed downstream of the receiving optical system (28) is an optoelectronic transducer (29), which is connected to an evaluation device (31). The receiving optical system (28) comprises at least one Fresnel lens (32) which, by virtue of its segment-like composition, both serves as a convergent lens for long subject distances and by diffuse scattering ensures that, even in the case of short subject distances, measuring signals fractions of adequate intensity reach the transducer (29).

Description

2333920 1 012tical distance-measuring apparatus The invention proceeds

from an optical distance-measuring apparatus according to the preamble of claim 1. An optical distance-measuning apparatus is already known (DE-A-43 16 348), which has a transmitting device for emitting a concentrated measuring signal and a receiving optical system for picking up measuring signal fractions reflected by a remote subject. By means of the receiving optical system reflected measuring signals are directed towards an optoelectronic transducer. In order with the aid of the receiving optical system always to direct an adequate intensity of reflected measuring signals towards the transducer both in the case of small and large subject distances, with the known distance-measuring apparatus it is proposed to provide in the beam path of the reflected signal, besides an - in terms of optical imaging - correct convergent lens for longer subject distances, additional means which ensure that even in the case of short object distances reflected measuring signal beams of adequate intensity reach the optoelectronic transducer. Alternatively, it is proposed to support a signal entry surface for the transducer in.an adjustable manner. For this, however, a light guide is additionally required.

The optical distance-measuring apparatus accordmig to the invention has the advantage of having a receiving optical system which, while being of a simple design and a low weight, guarantees the measurement of the distance of both close and very remote subjects.

Advantageous developments and improvements of the optical distancemeasuring apparatus according to the invention are possible by virtue of the measures outlined in the dependent claims.

An embodiment of the invention is illustrated in the drawings and explained in detail in the following description. Figure 1 shows a perspective view of an optical distance-measuring apparatus, Figure 2 a perspective paitial

1) front view of the apparatus and Figure 3 a view of the basic construction of the apparatus of Figure 1.

In Figure 1, 10 denotes an optical distance-measunng apparatus, described in shorCas a distance-measur-ing unit. The distance-measuring unit 10 has a housing 11, on the top 12 of which function keys 13 for the connection/disconnection and retrieval of various measuring programs as well as a key 14 for the initiation of a measuring operation are disposed. Also situated on the top 12 is a display 15 for displaying, for example, a deternimied measured value and information about tile selected measuring program.

A front end 16 (Figure 2) of the distance-measuring unit 10 has a windowlike opening 17, firom which an exit channel 18 for an optical measuring signal projects. The opening 17 is covered by a transparent protective screen 19.

In Figure 3, 23 denotes a transmitting device, which comprises an electrically controllable laser diode 25 as a measuring signal source. Situated adjacent to the laser diode 25 in the direction of emission of the measuring signal (direction of an arrow 22) is a collimator lens 26, which deflects the measuring signal produced by the laser diode 25 into a virtually parallel beam cluster.

Situated axially adjacent to the collimator lens 26 is a tubular exit channel 18 which, with an exit opening 33-) remote from the laser diode 25, projects through the screen 19.

The measuring signal exiting in the direction of the arrow 22 encounters a subject 27, the distance of which from the apparatus 10 is to be measured. At the subject 27 the measuring signal is scattered to a greater or lesser extent and, in a manner which is not shown, is reflected back into the half-space. Fractions of the reflected measuring signal arrive back at the distance-measunng unit 10 and are picked up there by the receiving optical system 28.

Disposed downstream of the receiving optical system 28 is an optoelectronic transducer 29 which, in the present example, is formed by an 1 3 avalanche photodiode 3 W. Electrical connections 44, 45 of the photodiode 30 are connected in an electrically conductive manner to an evaluation device -3) 1 which, by measuring the propagation delay between the emitted and received measuring signal, determines the distance from the subject 27 and shows the determined measured value on the display 15.

In the embodiment shown mi Figure 3, there is situated in the exit channel 18 a deflection flap 39, which is part of a device for reference measurement of a previously known distance between laser diode 25 and photodiode 3 W. A reference measurement is described, for example, also mi DE A-43 16 348, to which express reference is made here for the purpose of disclosure. In Figure 3, the reversing flap 39 is swivelled in such a way mito the beam path of the measuring signal that measuring signal fractions are guided directly through an opening 40 to the transducer 30. No measuring beams then pass out of the exit opening 33.

For measuring the distance from the subject 27, the deflection flap 3-) 9 is hinged upwards so that the opening 40 in the exit channel 18 is closed and an ummpeded exit of the measuring signal in the direction of the arrow 22 through the exit opening 33 is guaranteed.

The receiving optical system 28 has the task of picking up measuring beams reflected by the subject 27 and directing them towards the transducer 29. The receiving optical system 28 comprises a lens body 32, which is disposed in a protected manner behind the screen 19. The lens body 32 has, e.g. on its side 38 facing the subiect 27, the structure of a Fresnel lens. The Fresnel structure may however alternatively be provided on a reverse side 50 of the lens body 32 remote from the subject 27 or on both sides of the lens body 32. Such lenses are subdivided into concentric circular zones of similar thickness so as to produce a stepped lens construction at their surface. The Fresnel lens takes the form of an 4 integral lens having a single optical axis 35. The structure of the Fresnel lens appears to the observer as a superficially disposed, annular nibbing.

The Fresnel structure allows the lens body J32 to be made relatively thin even in the case of a high aperture ratio. The lens body 32 is preferably manufactured from plastic material by injection mouldmig. This enables inexpensive manufacture combined with a low weight and small dimensions.

The Fresnel lens, although formed integrally on the lens body 32, combmies two optical properties. Firstly, the Fresnel lens serves as a conventional convergent lens which, given long distances, collects the reflected measuring beams at its focal point F. The distance of the lens body 32 from the photodiode 30 is, in the present case, so selected that the latter lies, say, at the focal point F of the Fresnel lens 32.

The second property of the Fresnel lens 32, which is required for short distance measurements, is diffuse scattering at segment edges of its optical structure so that an adequate intensity of reflected measuring signal beams unpm'ge upon the photodiode 30 even Mi the case of subject distances outside of the actual range of focus. By virtue of said property, distance measurement is possible even in cases where the subject is a very short distance away.

The lens body 32 is designed, say, as a rectangular plate. Close to its edges the lens body 3)2 is provided at its side facing the photodiode 30 with dome-shaped bumps 3)4, of which one is situated close to a top edge and two are situated on either side of the side edges substantially at the level of the optical axis of the Fresnel lens 32. The Fresnel lens 32 at its underside J36 has an open edged slot 37, which is substantially U-shaped and through which the exit channel 18 projects. The optical axis 3)5 of the Fresnel lens in the present case is disposed eccentrically, close to the slot 37. This means that the Fresnel lens is designed, not as a rotationally symmetric, fully circular lens, but as a segmental lens.

1 1 The exit channel 18 is mounted on an optical system carrier 4 1, which comprises a base plate 41 a and a frame 42 projecting substantially vertically from said base plate. Formed on the frame 42 are a total of 3 limb pairs 43, which between them form a self-centring prismatic holder for the bumps 3 A of the Fresnel lens '32. To said end, the end faces of the limb pairs 433 directed towards the bumps 34 are provided with outwardly widening oblique surfaces 46, which allow in each case a displacement in one direction (degree of freedom). The degree of freedom in the present case is always at right angles to the respective edge surface of the lens body 3)2 in order to enable an unimpeded expansion of the lens. Thus, even in the case of e.g. thermal expansion, a stress-free support of the lens body 32 is always provided. Substantially U-shaped clasps 48, which take the form of resilient clamps, engage on the one hand behind the frame 42 and on the other hand behind the lens body J3)2, which in said manner is secured on the optical system carrier 4 1.

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Claims

1. Apparatus for optical distance measurement by virtue of propagation delay measurement having a transmitting device (23) for emitting a concentrated measuring signal, having a receiving optical system (28) for picking up measuring signal fractions reflected by a remote subject (27) and having an optoelectronic transducer (29) disposed downstream of the receiving optical system (28), characterized in that the receiving optical system (28) comprises at least one lens body (32), which has the structure of a Fresnel lens.

2. Apparatus according to claim 1, characterized in that the lens body 2) is of a plate-like design and is provided at its side (3 8) facing the subject (2 7) with the Fresnel structure.

3. Apparatus according to claim 1 or 2, characterized in that the Fresnel lens takes the form of an integral lens having a single optical axis (35).

4. Apparatus according to claim 3, characterized in that the lens body is made of plastic material.

5. Apparatus according to one of the preceding claims, characterized in that the lens body (32) is held by means of dome-shaped bumps (34) on an optical system cam er (4 1).

6. Apparatus according to claim 5, characterized in that the optical system carrier (41) comprises parallel limbs (43), between which the bumps (3)4) engage.

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7 7. Apparatus according to claim 6, characterized in that the limbs (43) at their end face form in each case inclinations (46) of a prismatic holder having a degree of fireedom.

8. Apparatus according to one of the preceding claims, charactenized m that the lens body (32) is of a substantially rectangular basic shape and has a U shaped slot (37), which is open-edged towards an underside (36) and through which an exit channel (18) for the measuring signal engages.

9. Apparatus according to claim 8, characterized 'm that the Fresnel structure of the lens body (32) has an optical amis (35) which is disposed eccentrically, close to the open-edged slot (37).

10. Apparatus accordmig to one of the preceding claims, characterized m that the Fresnel structure is disposed in a segment-like manner on the lens body (32).

11. An apparatus for optical distance measurement substantially as herein described with reference to the accompanying drawings.