WO1992014991A1

WO1992014991A1 - Optical displacement or deformation measurement process and device

Info

Publication number: WO1992014991A1
Application number: PCT/DE1992/000118
Authority: WO
Inventors: Humberto Chaves Salamanca; Gerd E. A. Meier; Boleslaw Stasicki
Original assignee: MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 1991-02-20
Filing date: 1992-02-19
Publication date: 1992-09-03
Also published as: DE4105270A1

Abstract

An optical process and device for measuring displacement or deformation is disclosed, in which a light beam is emitted by a light emitter (1) having a time-constant luminous power. By coupling the object to be measured to the light emitter (1), to an optical system (2, 4 to 13) or to an optical light receiver (3), the size of a cross-section of the light beam that coincides with a predetermined optical cross-sectional plane of the light beam located in the path of the light beam determined by the optical system (2, 4 to 13) changes with the displacement or deformation of the object to be measured. The luminous power, that also changes when the cross-section of the light beam changes, is measured by the optical light receiver (3) only in a partial cross-section of the light beam having predetermined constant dimensions that lies in said optical cross-sectional plane. The thus measured luminous power is evaluated to determine the displacement or deformation of the object to be measured. This measurement principle allows a high measurement resolution in time to be achieved.

Description

Optical displacement or deformation measuring method and optical displacement or deformation meter

The invention relates to an optical method for measuring the path or the deformation of a measurement object as well as an optical path or deformation meter with optical elements comprising a light transmitter, a light receiver and an optical system determining the beam path of the light beam emitted by the light transmitter.

From US-PS 4 865 443 and DE-OS 36 19 923 optical odometers are known, based on the unaffected drop in the intensity of a radiation source with the square of

Distance based. In this case, however, the light receiver must not be in the vicinity of the point at which the light transmitter is imaged by the imaging optical system, because then the drop in radiation intensity described above with the square of the distance is no longer valid.

The object of the invention is to provide an optical method for measuring the path or the deformation of a measurement object and an optical path or deformation meter and to design such that a high temporal resolution of the measurements can be achieved.

According to the invention, in the optical method, a light beam is emitted from a light transmitter with a light output that is constant or kept constant during the measurement, in the beam path of the light beam the size of the light beam cross-section that falls on a predetermined optical cross-sectional plane of the light beam is changed with the path or the deformation of the measurement object and the light output only over a predetermined constant area size, lying in the optical cross-sectional plane, different from the total cross-section lying in the optical cross-sectional plane Partial cross-section of the light beam measured and evaluated to determine the respective path or the respective deformation of the measurement object.

The optical path or deformation meter according to the invention has optical elements from a light emitter that emits a light beam with light output that is constant or kept constant during the measurement, an optical system that determines the beam path of the light beam, and a light receiver arranged in the beam path, at least one of which is optical Elements is coupled to the measurement object or is formed by the latter in such a way that the area size of the light beam cross-section which falls on a predetermined optical cross-sectional plane of the light beam is changed as a function of a change in the location or the degree of deformation of the measurement object, and the light receiver for measuring the light output is arranged and / or designed only over a partial cross-section of the light bundle which has a predetermined constant size and lies in the optical cross-sectional plane and which is different from its total cross-section in the optical cross-sectional plane is different.

Preferred embodiments of the invention are the subject of the dependent claims.

According to the invention, the displacement or deformation meter thus consists of a light transmitter of limited extent emitting a light bundle (e.g. a light-emitting diode (LED) or of the end of a light guide fed in with light) and light output emitted at a constant time, an imaging optical system (e.g. concave mirror or Lens) and a light receiver with a limited sensitive area (e.g. photodiode). The operating principle is based on the change in light output, which is detected with the limited sensitive area of the light receiver. To change the light output, the test object is rigid with one of the optical elements mentioned coupled or trained on this. The light receiver or the entrance surface of a light guide connected to it is located in a convergent or divergent light beam path, the opening angle of which changes due to the coupling of the measurement object during its movement, so that the cross section of the light beam and thus the light intensity above it and thus also the light intensity above change the partial cross-sectional area detected by the light receiver, which remains constant in size, and the light intensity measured by the light receiver and converted into an electrical signal (the quotient of light output and area) depends on the distance of the measurement object or its degree of deformation. This dependency can be verified by calibrating the displacement or deformation meter by appropriately assigning mechanically measured length measurements to the

Output variables of the receiver can be determined. The limitation of the sensitive area of the light receiver exposed to the light to the detection of only a partial cross section of the light beam, which differs from the entire light beam cross section, can be achieved by the

Geometry of the light receiver itself, through a light guide or through an aperture or the like.

From GB-OS 20 77 421 it is known to optically measure the path of a measurement object by emitting a light bundle from a light transmitter with light output that is constant over time during the measurement, in the beam path of the light bundle the size of the light beam to a predetermined cross-sectional plane omitted light beam cross-section is changed with the path of the measurement object and the light output is measured over a partial cross-section of the light beam lying in the optical cross-sectional plane and is evaluated to determine the respective distance of the measurement object. Here, however, a measuring principle different from the measuring principle according to the invention is implemented. It is namely the chromatic aberration of an optical lens for changing the difference or the ratio of the proportions of light components of clearly different wavelengths, for example red and blue Light components are used, which are emitted onto an annular entrance surface of a receiver light guide by a reflector forming the measurement object through the lens and are therefore detected by two assigned receivers. Since the partial cross-section of the light beam, which overlaps more or less with the entry surface of the receiver light guide depending on the size of the respective deviation of the reflector from its zero position, must change as intended, in contrast to the invention, this partial cross-section of the light beam is not constant, but changeable with the path of the measurement object.

The time resolution of the optical path and deformation meter according to the invention is not limited by the measuring principle, but solely by the rate of change of the

Light receiver (e.g. light intensity / current conversion for the photodiode). Due to the high time resolution, the speed or acceleration can be determined by differentiation according to time.

The principle is explained in more detail with reference to FIG. 1. A light source 1 is imaged with the lens 2 on a plane in front of or behind the light receiver 3. The light receiver 3 thus detects only part of the light beam emitted by the light source 1. If the position of one of the elements 1, 2 or 3 is changed along the optical axis of the system, the proportion of the light beam detected by the light receiver 3 also changes. Depending on the design, the measurement object is therefore also one of the three optical elements or the object to be examined is rigidly connected to one of the three optical elements, so that the movement of this object can also be detected. If the light receiver is located near the point where the light transmitter 1 is imaged by the imaging system 2, the highest sensitivity can be achieved. In this case, a significant part of the total light output that is emitted by the light transmitter is also detected by the light receiver. The signal level is therefore significantly higher than that of optical ones State-of-the-art odometers.

A variant of the measuring method is shown in Fig. 2. Here the imaging element is a concave mirror 4, from which the light emitted by the light transmitter 1 is reflected to the light receiver 3 located in the vicinity of the light transmitter 1. The mode of operation is as described above, but this variant has the advantage of being compact. Furthermore, the light transmitter 1 and the light receiver 3 can be integrated into one unit. In this case, the distance of the

Concave mirror 4 measured by the transceiver 1, 3. An odometer according to GB-OS 2 160 310 uses a similar configuration as in this case, however the known odometer focuses the light on a reflector with a lens, i.e. the beam path is convergent. In contrast, in the case of the invention, the light is not focused on the concave mirror, but on the contrary, the beam path of the light beam incident on the mirror (reflector) is divergent. The arrangement according to the invention is not so sensitive to the tilting of the mirror. In addition, a simpler and more compact structure is achieved.

The light can be guided directly or, as can be seen from FIGS. 3 and 4, via light guides 5, 6 connected to the light transmitter 1 or the light receiver 3. In this

In this case, the light transmitter 1 and / or the light receiver 3 can be placed in a more suitable environment. 3 and 4, the partial cross section of the light bundle detected by the light receiver 3 is determined by the end face of the light guide 6 facing away from the receiver 3, to which the light receiver 3 is connected.

In the case of a combined transmitter and receiver unit with an optical fiber, various arrangements are possible. Fig. 5 shows the structure of a transceiver with

The light emitted by the light transmitter is bundled by the converging lens 9 onto one end face of the light guide 7 and from the other end face onto the Hollow mirror 4 emitted, from which the light is reflected back to the light guide 7. The feed and the reflected light are divided by means of a beam splitter 8 formed here from prisms. The lens 10 collects and focuses the light reflected on the beam splitter 8 onto the light receiver 3. The limitation of the light receiver area required for the measuring principle to a partial cross-section of that at the concave mirror 4 reflected light beam also takes place here on the end face of the light guide 7 facing the concave mirror 4 and not on the light receiver 3 itself.

6 shows a distribution of the light with a fork light guide 11, from which the light fed into one branch of the light guide 11 by the light transmitter 1 is emitted onto the concave mirror 4, which reflects the light bundle back to the light guide 11, from which a limited part of the light beam is directed to the light receiver 3 connected to the other branch of the light guide 11. The limitation of the light detected by the light receiver to one

Partial cross section of the reflected light bundle takes place at the entry end of the fork light guide 11 facing the concave mirror.

7, the division of the

Reached light with the optical fiber bundle 12, which from the bundle section facing the concave mirror 4, on the front side facing the concave mirror, the limitation of the cross-sectional part of the reflected light bundle detected by the receiver 3, to the transmitter 1 and the receiver 4 in the form of Partial fiber bundles branched. Here, several variants of the distribution of the transmit / receive optical fibers over the cross section of the optical fiber bundle are possible: concentric, divided, stochastic, etc.

If the imaging element 2 or 4 deforms and thereby changes its imaging properties, the deformation becomes for fixed components of the system. 8 shows the arrangement of the optical elements for the detection of the deformation of a flexible reflecting membrane 13. In this case the imaging element consists of the lens 2 and the membrane 13 itself, since in general the deformation of the membrane alone would not be sufficient, to do the illustration. The light transmitter and the light receiver, which are not shown in FIG. 8, are coupled via the light guide 12, for example in accordance with FIG. 7.

In general, the output signal I of the light receiver 3 will not be proportional to the path x or to the deformation of the measurement object (see FIG. 9). However, since a certain part of the light bundle is detected by the light receiver for each position of the measurement object, the characteristic curve of the light receiver can be linearized by dimming certain parts of the light bundle. The dimming is done by inserting an optical filter 14 into the optical imaging system. This filter can be attached directly to the lens or on the reflective element or separately in the

Beam path can be inserted. The transmission T of the filter 14 is not constant on its surface (Fig. 10); Rather, it is designed so that both the non-linearity of the characteristic curve and the inhomogeneous light intensity of the light transmitter 1 are compensated for over the beam surface. The optical filter 14 can be designed with discrete covering segments 15 (FIG. 10a) or by a continuous or discontinuous gray value distribution.

So far it has been assumed that there is a sufficient ratio of useful signal to interference signal. If this is not the case, an amplitude modulation of the light transmitter signal and a synchronous demodulation of the light receiver signal (e.g. phase-sensitive rectification) can significantly reduce the interference level, the bandwidth of the system being determined at high frequencies by the modulation frequency. The aging processes of the electronic components as well as wear and soiling of the optical elements can lead to misalignment of the system and thus have a negative impact on the reproducibility of the measurements. In applications where the reproducibility of the measurement is important (calibrated sensors such as pressure transducers, microphones or absolute displacement sensors), these effects can be largely compensated for by regulating the power fed into the light transmitter 1.

This can be done in the following way (Fig. 11):

If the system is in the rest position, the power fed into the light transmitter 1 is adjusted by a control element 16 in such a way that the difference between the signal obtained by the light receiver 3 and a reference signal (setpoint) is minimized. This power is then kept constant during the measurement.

12 shows the schematic structure of an injector with an integrated needle position sensor according to the invention. The typical structure of an injector consists of a divided nozzle body 17a, 17b and a nozzle needle 18 which is axially movable in 17a. The nozzle needle 18 is pressed by the spring 19 onto the needle seat 21 via the intermediate piece 18a. If the pressure of the fuel in the fuel supply 22 is increased beyond a threshold value determined by the spring 19, the nozzle needle 18 lifts off the needle seat 21 and the fuel flows out of the nozzle 23.

Broadly speaking, this is how a typical injector works. The amount of fuel flowing out through the nozzle 23 per unit of time is determined by the respective nozzle needle positions. Knowing the respective current position of the nozzle needle with high time resolution therefore allows an exact metering of the fuel and the

Optimization of the combustion process in the engine. In order to obtain knowledge of the respective current needle position, the injector can be supplemented with the following elements according to the invention become. A concave mirror 4 is attached or formed on the end face of the intermediate piece 18a facing away from the needle seat 21. In the exemplary embodiment, a light guide 12 is passed through the nozzle body part 17b and fixed coaxially to the concave mirror 4 by means of a light guide 20, so that the outlet end of the light guide 12 is axially aligned with the concave mirror 4. However, several light guides can also be used. The light guide coupling at the other end to light transmitter 1 and light receiver 3 takes place as already described. The measuring arrangement preferably corresponds to that from FIGS. 4 to 7. The light receiver 3 supplies a signal which corresponds to the current nozzle needle position with high temporal resolution.

The conventional needle stroke transmitters (BOSCH) work with an inductive measuring bridge, which requires a carrier frequency amplifier to evaluate the signal. Due to the required carrier frequency, the bandwidth is limited to a maximum of half. The carrier frequency in turn is due to the

Construction and the magnetic properties of the encoder are limited (approx. 50 kHz). The effort to install tiny coils in the injector body is not insignificant. Such sensors have so far only been used for laboratory measurements, since the evaluation electronics are probably too expensive, sensitive and unreliable for use in the motor vehicle.

A known optical embodiment of a needle stroke encoder according to DE-OS 35 15 476 is based on the light barrier principle. The optical structure requires two light guides and two

Deflecting mirrors or prisms and an optical diaphragm that is moved by the needle. This structure is more complicated than that according to the invention and requires precise positioning of the light guide and deflecting mirror.

When the system is used as a microphone, the reproducibility of the direct component of the light receiver signal is generally not important, but only the alternating components on. In this case, the control can also be carried out during operation by constantly comparing the reference signal with the time average of the light receiver signal and minimizing the difference thus obtained by readjusting the power fed into the light transmitter.

Advantages of the invention:

a) The temporal resolution of the signal is only by the speed of the conversion of light intensity into that

Limited useful signal and not by the measuring principle itself.

b) Since the optical components of a sensor according to the invention can be designed temperature-resistant with an optical fiber, e.g. Mineral glass light guides, quartz glass lenses, metallic mirrors, the sensor can be used at very high temperatures, because the temperature-sensitive elements (light transmitter, light receiver and possibly evaluation electronics) can be placed coupled outside the high temperature range via the light guide. The same applies to other adverse conditions, such as high pressures, aggressive environment, electromagnetic interference fields, etc. The sensor is also advantageous in systems that do not allow electrical currents (e.g. explosion hazard, in medicine), or in

Systems that require freedom from metal. Here, a mirror can also be made only from non-metallic reflective material (e.g. glass or plastic) or the sensor version according to FIG. 1 can be used.

c) The optical fiber coupling is also advantageous if the distance from the measuring point to the evaluation point is to be large. Signal transmission by means of fiber optics prevents transmission interference and bandwidth limitation.

d) Depending on the application, the sensor can be manufactured in any practical size. In particular are Miniature versions of interest that can be used in hard-to-reach places (needle lift sensors, subminiature microphones or pressure transducers).

e) Due to the inexpensive and simple design, the sensor is well suited for series production.

Claims

1. Optical method for measuring the path or the deformation of a measurement object, in which a light beam is emitted by a light transmitter with the light output constant or constant during the measurement, in the beam path of the light beam the size of the light beam cross-section due to a predetermined optical cross-sectional plane of the light beam with the way or the

Deformation of the measurement object is changed and the light output is measured only over a partial cross-section of the light beam that has a predetermined constant size and lies in the optical cross-sectional plane and is evaluated to determine the respective path or the respective deformation of the measurement object.

2. Optical path or deformation meter with optical elements consisting of a light emitter (1) emitting a light beam (1) with constant light output over time, an optical system (2, 4 to 13) determining the beam path of the light beam and a light receiver (3) arranged in the beam path, whereby at least one of these optical elements is coupled to or is formed by the measurement object in such a way that the size of the cross section of the light beam which is to be accounted for at a predetermined optical cross-sectional plane of the light beam is changed as a function of a change in the location or the degree of deformation of the measurement object, and the light receiver (3) for measuring the light output is arranged and / or designed only over a predetermined constant size on an iron partial cross-section of the light bundle lying in the optical cross-sectional plane.

3. Optical displacement or deformation meter according to claim 2, wherein the optical system has an optical filter (14), the transmission of which is so different locally that a linearization of the measurement characteristic of the light receiver takes place. (Fig. 10, 10a)

4. Optical displacement or deformation meter according to claim 2, wherein the measurement object is a concave mirror (4), which is also the optical system.

5. Optical displacement or deformation meter according to claim 2, wherein the optical system for measuring the deformation of a reflective measurement object (13) is formed by this and a lens (2). (Fig. 8)

6. Optical displacement or deformation meter according to claim 2, wherein the size of the partial cross-section of the light beam detected by the light receiver (3) is determined by means of an aperture or by the geometry of the light receiver itself.

7. An optical displacement or deformation meter according to claim 2, wherein the optical system couples a coupling to the light transmitter (1) and the light receiver (3), sorted towards these branched optical fiber bundles (12) or one of the light transmitter (1) and the light receiver (3 ) Coupling fork light guide (11), from the end face facing away from the light transmitter and the light receiver, the size of the partial cross section of the light beam detected by the light receiver (3) is determined. (Fig.7, 6)

8. Optical displacement or deformation meter according to claim 2, wherein the light transmitter (1) and the light receiver (3) are each coupled via a light guide (5, 6) and the size of the partial cross-section of the light beam detected by the light receiver (3) Input face of the light guide (6) is determined, which is connected to the light receiver (3). (Fig. 3, 4)

9. Optical displacement or deformation meter according to claim 5, wherein the reflective measurement object (13) is the membrane of a microphone or a pressure transducer.

10. Optical path or deformation meter according to claim 4, wherein the concave mirror (4) the calotte, membrane or the Dust protection cap of a loudspeaker is.

11. Optical displacement or deformation meter according to claim 4, wherein for measuring the respective current position of the nozzle needle (18) of an injection nozzle, the concave mirror (4) is formed on the nozzle needle (18). (Fig.12)

12. Optical displacement or deformation meter according to claim 2, wherein the light transmitter (1) is amplitude modulated and the signal of the light receiver (3) is subjected to phase-sensitive demodulation.

13. Optical displacement or deformation meter according to claim 2, wherein for calibration the power fed into the light transmitter (1) is readjusted by the light receiver signal.