WO2000075690A1

WO2000075690A1 - Method for calibrationless distance determination and equipment for realization of the method

Info

Publication number: WO2000075690A1
Application number: PCT/SK1999/000008
Authority: WO
Inventors: Eduard Burian
Original assignee: Eduard Burian
Priority date: 1999-06-02
Filing date: 1999-06-02
Publication date: 2000-12-14
Also published as: AU3963899A

Abstract

Distance to a surface with unknown reflection and scattering characteristics is determined (the) so that surface is irradiated by the system of sequentially (activated) switched radiation sources (6), and reflected radiation intensity is measured by system of radiation detectors (1), which enable the microcomputer system (4) with implemented generic surface reflectivity model to estimate the distance to unknown surface.

Description

Method for calibrationless distance determination and equipment for realization of the method

The Field of Technics

Invention is related to equipment for small distance determination by contactless optical method, particularly surface distances of objects with vague specification of optical reflection and scattering characteristics.

Present State of Technics

Nowadays, the commercial available optical switches consisting of light-emitting diode radiating in infrared electromagnetic spectrum domain and of photodetector on basis of a fototransistor or photodiode integrated in one, generally in three-pole housing comprising also infrared radiation filters, are regularly used for terminal positior. sensing by electric linear drives or as incremental revolution sensing components. In a certain range, it is possible to exploit these sensors also for distance measurement to specific surfaces. In such case, an amplified photocurrent is converted to digital form and by usage of inverse functional dependence of normalized photocurrent to surface distance, supplied by manufacturer, estimated surface distances are calculated. The disadvantage of this method is that optical switch photocurrent is strongly dependent on reflectance and scattering of the reflective surface, so the information about surface type to which the distance is estimated has to be known in advance. In practice however, it may be encountered a necessity of distance estimation to beforehand not known surfaces (for example, surface clear span, wall distance or to accidentally occurring objects etc.), which excludes an employment of such system. The known technical solutions are based then on echo-location, radar or exploit expensive stereoscopic image processing systems .

The Essence of Invention

Fundamentals of the method for calibrationless surface distance determination consist in the fact that intensity distribution of reflected light, which is function of reflectivity, scattering and distance to the surface, is sensed at more points by system of photodetectors . Information from photodetectors is then compared with generic reflection model implemented in software of a microprocesor system, which finds out the distance to the given surface as a component of the solution to the system of equations

1\I(X)- F = 0 ,

where M is generic surface model with parameters X = (reflectivity, scattering, distance} and F is vector of sensed photocurrents . The generic surface model has to include at the same time also properties of the radiation emitter. For the best surface distance estimation, the suggested method reckons on with exploitation of a set of sequentially activated radiation emitters (light-emitting

? diodes), irradiating surface from various points and eliminating thereby influence of possible non-uniformity or unknown surface structure.

Equipment in a form of integrated circuit for realization of the method can comprise of two semiconductor dies placed in one transparent housing, which are consisting of linearly aligned light-emitting diodes and photodetectors together with analog and logic circuits controlling activation of diodes and evaluating the intensities of incident light. To avoid parasitic influence between emitters and detectors of light, the space between the dies is filled by non-transparent material, which can be with an advantage realized by suitable forming of metallic prime material that serves as a common electrical contact of both dies. Because the parasitic light reflection can arise also on inner interface of the optical active surface, it is desirable to minimize their influence by suitable forming of this surface in such a way that between optical shielding of dies created by forming of the metallic primer material and housing top surface will remain only minimal gap, given by used housing technology.

Survey of Pictures on Scetches

The principal scheme of electronic circuit for realization of the method according the invention is shown in Fig. 1. In Fig. 2, geometrical parameters of the exemplar system of irradiation emitters and detectors, utilized in algorithm. for distance estimation, are shown. Fig. 3 illustrates exemplar method of activation of emitters and cumulation of values of illumination. The electrical scheme of one part of a system of photodetectors with inherent cumulation of measured values of incident irradiation is in Fig. 4a. Fig. 4b illustrates principal scheme of an electronic circuit of the system of light-emitting diodes and photodetectors for the device with inherent cumulation of measured values of incident irradiation. The device according to the invention is shown in front view in Fig. 5a and in side view in Fig. 5b.

Realization of Invention and its Examples

An example of principal connection of electronic circuit for realization of the invention is in Fig. 1. The system of photodetectors 1 by means of analog multiplexer 2 and analog-to-digital converter _3 and the system of light- emitting diodes 6 by means of demultiplexer 5 are connected to the managing microcomputer 4 that controls the activation of individual light-emitting diodes and evaluates the data from individual photodetectors, which serve then for estimation of the distance to the unknown surface .

An algorithm for activation of light-emitting diodes and measurement of values of irradiation at individual photodetectors in notation of language C shown in Tab. i creates a symmetric data file in a field with length 2N-1 ciphers in floating-point representation, where A^r is the number of implemented light-emitting diodes, or implemented photodetectors, respectively, so, that the measured data void acquisition (int N, float* data)

{ int i,j,iter[2*N-l] ; /* variable declarations */ float f; for (i=0 ;i<2*N-l ;i++) /* data fields initialization */ { data[i]=0; iter[i]=0; } for (i=0;i<N;i++) /* acquisition loop */ { setLED(i) ; /* LED switch-on * , for(j=0;j<N;j++) { f=aquireFD (j) ; /* fotodetector acquisition */ data[j-i+N-l]+=f; /* data field actualization */ iter[j-i+N-l]++; /* iteration field incrementation

resLED (i) ; /*" LED swizch-off * ■^■' } for (i=0;i<2*N-l ;i++) /* data normali∑azicr. */ data [i] /-iter[i] ; /* intensity per one iteration */ }

Table 1. corresponds to illumination of the surface from a point, measured by a system of 2N-1 linearly aligned photodetectors .

Fig. 3 illustrates operation of the algorithm by system of eight light-emitting diodes and eight photodetectors. In eight steps, individual light-emitting diodes are activated step-by-step from left to right and values read from all the photodetectors, whereas actual values are added to values read in previous steps with offset of one cell as so as is indicated by the punctuated lines connecting individual photodetectors in Fig. 3, and at last, they are put to data field of 15 elements. Because the mid of the data field cumulates more values than the margins, it is necessary to normalize the individual cells of the data field for the number of cumulated values of illumination at individual photodetectors.

Rather than generally applicable method of solving of system of equations, the explicit algorithm of data evaluation, shown in Tab. 2, is more suitable for microcomputer implementation. The algorithm first normalizes the measured values, then evaluates the ean value and the dispersion, and at least by exoression

estimates distance to the generic surface, where h is estimated distance, e and d are geometrical parameters of the systems of light-emitting diodes and photodetectors according to Fig. 2, D is evaluated dispersion and the constant k is related with an effective emission angle φ_LΕX) of a light-emitting diode given by

1 + ∞sφ_LED k

1-cos u-_D

which but can be obtained experimentally.

Proposed electronic circuit with extensive connection of photodetectors to the analog-to-digital converter by means of analog multiplexer may be disadvantageous by larger number of sensing elements, not only because of more expensive housing of the sensor with several analog outputs connected to the individual photodetectors or because of extensive circuit structure, if the multiplexer were integrated on the chip of the sensor, but mainly because of quadratical grooving time needed for completing the illumination and measurement algorithm. These lacks are solved by serial connection of photodetectors with inherent analog cumulation of photocurents, principally illustrated in Fig 4b. Individual light-emitting diodes are connected to outputs of a N-stage digital shift register formed by flip-flops DC to DC _-_. with input signals of serial data LSI and clock impulses LCK and with output signal of serial data LSO. The photodetectors are equipped with and electronic circuit according to the Fig. 4a, which integrates photodetector current, proportional to incident irradiation, and at the same time, cumulates the values measured in preceding elements of the system, whereas the integrated values of photocurrent can be reset at the start of the cycle. The serial connection of such cells AC to AC---, can be viewed as an analog shift register with an input of analog serial data FSI, clock impulses FCK and float evaluatio (int N, float* data , float e, float d, float k) ! int i; /* varaihle declarations */ float s=0,M=0,D=0,h; for(i=0;i<2*N-l;i++) /* data field normalization */ s+=data [i] ; for(i=0;i<2*N-l;i++) data [i] /=s ; for (i=0 ;i<2*N-l ;i++) /* enumeration of mean value */

M+=data[i]*i; for (i=0;i<2*N-l ;i++) /* enumeration of dispersion */

D+=data [i]* (i-mO) * (i -mO) ; h=sqrt (e*e*k*D-d*d) /2; /* enumeration of surface distance */ return h; }

reset input RES, and with output of analog serial data FSC. Activation of individual light-emitting diodes, controlled by serial impulses LCK and shifting of integrated analog values of photocurents by impulses FCK is simultaneous, which enables to use unique periodic source of impulses for both clock imputs . So is the time needed for completing the measurement proportional only to the number of used elements in the system of light-emitting diodes, or photodetectors, respectively, and to the integration time, i.e. to the period of control clock frequency. At the same time, by changing of the period of the control clock impulses, the dynamic range of measurement can be advantageously changed through an interval of several decades, multiplying in such a way the dynamic range of the analog-to-digital converter, and eliminating so the necessity of usage of amplifiers with selectable amplification. Sensors, integrating systems of light- emitting diodes and photodetectors, can be easily chained so that the serial digital and analog outputs are connected to corresponding serial inputs, of the next sensor; in such a way, the range of measured distance can be multiplied without necessity of structural changes in the additional hardware or software. An another alternative is a usage of charge-coupled structure (CCD) instead of cells of photodetectors and integrators, which can eventually further lower the costs for sensor fabrication.

The device comprising of two semiconductor optoelectronic systems of emitters and detectors of infrared radiation, integrated to a common transparent housing 1_1 for surface mounting is shown in Figure 5a, b. Set of light emitting diodes 7 created in conjunction with current drivers and logical circuits on semiconductor die 8 and set of photodetectors 9 created along with analog photocurrent amplifiers and logical circuits on semiconductor die 10 are placed on metal priming material .13, which creates therewithal common electrical contact _14_ for both semiconductor dies 2, 4. Forming L2 of metallic basic material _13 prevents to direct optical influence of the two optoelectronic systems. Optimization of equipment's optical characteristics including directivity correction, sensitivity increase and decimation of other mutual impacts is obtained by forming of optical active surface L5 of the transparent housing 11.

Industrial Utilization

Method for calibrationless surface distance determination according to the invention and equipment for realization of this method are exploitable for example in automated traffic systems for distance determination from barriers and room walls, in positioning systems as a feedback element, in a human-machine interface, as an universal proximity sensor etc.

Claims

P A T E N T C L A I M S

1. Method for calibrationless surface distance determination characterized in that radiation sequentially transmitted by system of emitters (6), reflected from the surface with unknown radiation reflectivity and scattering characteristics, is sensed by system of detectors (1), the picked-up values of intensity of radiation incident to individual detectors are consequently processed by microcomputer system (4), which at the same time activates emitters (6) of radiation, and which by means of implemented generic model of reflection characteristics estimates the distance to the unknown surface.

2. Equipment for realization of method according to the item 1 characterized in that it consists of system of radiation emitters in the form of linearly aligned light- emitting diodes (7) created on semiconductor die (8) with integrated current drives and logical circuits and of system of linearly aligned photodetectors (9,ι created or. semiconductor die (10) with integrated analog photocurrent amplifiers and logical circuits, the semiconductor dies (8, 10) of light-emitting diodes (7) and photodetectors (9) are optically shielded.

3. Equipment according to the item 2 characterized in that semiconductor dies (8, 10) of light-emitting diodes

(7) and photodetectors (9) are integrated into one transparent housing (11) , optical shielding of system of photodetectors (9) from system of light-emitting diodes

(7) is realized by forming (12) of the metallic primer