DE102023108014A1 - Inspection device and method for optically detecting properties of an object transported on a conveyor in a transport direction by means of fluorescence excitation - Google Patents

Abstract

The present invention discloses an inspection device for optically detecting properties of an object (06) moved in a relative movement direction relative to the inspection device by means of fluorescence excitation and measurement of the fluorescence decay time of object segments, wherein the inspection device has an illumination unit (04) for illuminating the object (06), a detection unit (05) for measuring the fluorescence signal emitted by an object segment and a measuring unit.
The detection unit (05) comprises a plurality of detectors (D1, D2, ..., Dn) arranged one behind the other in the direction of relative movement, and the measuring unit is designed to determine the fluorescence decay time of an object segment from the fluorescence intensities measured one after the other by the detectors (D1, D2, ..., Dn) arranged one behind the other, each corresponding to the arrangement in the direction of relative movement.

Description

The invention relates to an inspection device for optically detecting properties of an object moved in a relative movement direction relative to the inspection device by means of fluorescence excitation and measurement of the fluorescence decay time of object segments, wherein the inspection device has an illumination unit for illuminating the object, a detection unit for measuring the fluorescence signal emitted by an object segment and a measuring unit.

The invention further relates to a method for optically detecting properties of an object moving in a direction of movement relative to an inspection device by means of fluorescence excitation by illuminating the object, measuring the fluorescence signal emitted by an object segment and determining the fluorescence decay time of the object segment from the measured fluorescence signal.

The further development of production processes to fully automated production lines is very attractive for most companies that offer goods to the end consumer. Not only can larger quantities be produced efficiently and without additional effort by automating the production line, but the sales achieved and thus the profit are also increased. The great advantages of automated production lines are offset by the fact that they are prone to errors. This can affect the quality of the products manufactured or foreign bodies can even creep into the end product, which can damage the company's image or even lead to the closure of production facilities. The further development of inspection systems is therefore of great importance for companies that develop (automated) production lines.

When it comes to visual inspection of consumer products, the limited recognition ability of the human eye represents a limitation and fatigue in monotonous production processes also represents an uncertainty factor.

Currently, many studies are being conducted in the field of imaging vibration spectroscopy in order to carry out possible quality control in real time. However, the possibilities are very limited because the vibration spectra of the materials produced and to be inspected sometimes appear very similar to the vibration spectra of the contamination to be detected, which makes reliable detection of the contamination difficult.

WO 2021/160309 A1 discloses a method for checking a sample by determining a deviation of the decay time distribution of an autofluorescence of the sample excited by electromagnetic radiation from an expected decay time distribution. This allows plastic contamination of a food sample to be detected. During the fluorescence decay time, the sample must not move relative to the detector in order to avoid falsifying the decay time behavior.

The fluorescence decay time can generally be determined by two types of measurements: by measuring the fluorescence decay time in the time domain and in the frequency domain.

The method of measuring fluorescence decay time in the time domain is an integrative method according to the state of the art. It is described, for example, in A. Bouchard, J. Fréchette, M. Vernon, J-F. Cormier, R. Beaulieu: Optical characterization of Pseudomonas fluorescens on meat surfaces using time-resolved fluorescence, in: Journal of Biomedical Optics 11(1), January/February 2006, 014011-1 to -7.

After fluorescence excitation with a short pulse from a light source, the histogram of the fluorescence signal decaying exponentially over time is reconstructed by measuring the fluorescence intensity at different points in time. At each of these points in time, the photons are integrated, usually via a photomultiplier and a photodiode (photodiode array). According to theory, at least three integration points in time or a photon counting algorithm are necessary for reconstruction in order to reconstruct the exponentially decaying fluorescence signal and calculate the fluorescence decay time according to equation (1). $$I\left(t\right)=I_0\ast \text{exp}\left(-\frac{t}{\tau }\right)$$

After excitation of the sample with a short laser pulse at time t _{0 ,} the fluorescence intensity decays exponentially over time t. At time τ the fluorescence intensity is $\frac{1}{e}{\mathrm{<figure-callout\; id="0"\; label="I"\; filenames="DE102023108014A1\_0008.png"\; state="\{\{state\}\}">I</figure-callout>}}_0.$

The fluorescence decay time can be measured in the time domain using a photon counting algorithm. A clock is started at time t ₀ and stopped as soon as the first photon hits the detector. The counter for the time when the photon hits the detector, e.g. between t ₁ and t ₂ , is increased by 1. The clock is then started again at time t ₀ and the process is repeated until a previously defined The final value of counting steps (I ₀ ) is reached. The counting histogram can be used to reconstruct the exponentially decreasing fluorescence emission and thus calculate the fluorescence decay time.

Another approach is to reconstruct the exponentially decaying fluorescence signal by integrating all photons over three defined time periods (S1, S2 and S3). For this, the fluorescence is also excited with a short laser pulse. The clock then starts at time t ₁ and integrates all photons up to time t ₂ . The integration is then carried out for two further time periods from t ₂ to t ₃ and t ₃ to t ₄ . The time periods can be of equal length. The three integrations can be used to reconstruct the exponentially decaying fluorescence signal and to calculate the fluorescence decay time using equation (1). In today's fluorescence decay time measuring devices, the photon counting method described above is often used for measurement technology, as the measurement becomes more accurate when several support points are recorded.

The method of measuring fluorescence decay time in the frequency domain is also an integrating method according to the state of the art. However, the fluorescence decay times can be measured much faster than using the previously described fluorescence decay time measurement in the time domain, since a shorter integration time is required.

In general, to measure the fluorescence decay time in the frequency domain, a modulated light signal (e.g. sine or square) is used for fluorescence excitation, which has a defined modulation frequency ω, a defined amplitude B and a defined equivalent A. The fluorescence excitation is followed by a phase- and equivalent-shifted and amplitude-damped fluorescence signal, which has the same frequency ω or wavelength λ as the fluorescence excitation. If the phase shift ϕ is measured, the phase-dependent fluorescence decay time can be calculated according to equation (2): $${\tau }_{Ph}=\frac{\text{tan}\left(\varphi \right)}{\omega }$$

In addition, the modulation index M can be calculated from the amplitude attenuation and the equivalence shift according to equation (3): $$M=\frac{b/a}{B/A}$$

The calculated modulation index M can then be used to calculate the modulation-dependent fluorescence decay time according to equation (4): $${\tau }_M=\frac{1}{\omega }\cdot \sqrt{\frac{1}{M^2}-1}$$

The radiative process of fluorescence decays within a few nanoseconds, which means that the modulation frequencies ω are usually in the range of several tens of MHz.

For imaging fluorescence decay time measurement, also called Frequency Domain Fluorescence Lifetime Imaging Microscopy, cameras are available that can measure this fluorescence oscillation statically.

H. Chen, G. Holst, E. Gratton: Using of a modulated CMOS camera for fluorescence lifetime microscopy, in: Microsc. Res. Tech. 2015 December; 78(12): 1075-1081 describe a CMOS camera that provides a series of modulated images at its output. The non-uniform system response across the image sensor is calibrated at the pixel level. This pixel calibration is required for e.g. the modulation frequency and the exposure time. There is a significant dependence of the modulation signal on the intensity, so an additional calibration is carried out for each pixel depending on the pixel intensity.

The camera consists of 1008x1008 pixels, with two taps (Tap A and Tap B) in each pixel. Tap A integrates the incoming fluorescence photons from 0 to π and Tap B from π to 2π. However, the sinusoidal fluorescence oscillation cannot be reconstructed using two integrations. For this reason, the integration windows must be shifted by a defined period of time (phase angle). Depending on the accuracy, four integrations at two different phase angles, eight integrations at four different phase angles, or sixteen integrations at eight different phase angles can be used to reconstruct the sinusoidal fluorescence signal. For example, an integration measurement can be carried out with sixteen photon integrations at eight different phase angles. Tap A is active in the period from 0 to π and Tap B from π to 2π. The start time is then shifted to π/8, resulting in two new periods in which Tap A and Tap B are active: Tap A from π/8 to 5π/8 and Tap B from 5π/8 to 9π/8. Shifting the phase angle a further six times by π/8 each leads to sixteen integration points from which the fluorescence oscillation is reconstructed. The sixteen integrations always take place one after the other in this measurement. The user has to set an exposure time. By defining the exposure time determines how often these integration cycles are run through. This allows the phase shift and the modulation index to be measured and the phase-dependent and modulation-dependent fluorescence decay time to be determined for each pixel.

It is important for the measurements that the sample to be measured by the camera remains stationary and is not moved relative to the camera during the exposure period, which makes it impossible to use the camera for near-real-time processes.

The object of the present invention is therefore to provide an inspection device and a method for optically detecting properties of an object moving in a relative movement direction relative to the inspection device by means of fluorescence excitation in order to carry out an automated, real-time, sensitive and selective identification of quality features of a moving object.

The object is achieved with the inspection device having the features of claim 1 and by the method having the features of claim 11. Advantageous embodiments are described in the subclaims.

In the generic inspection device for optically detecting properties of an object moved in the relative movement direction relative to the inspection device by means of fluorescence excitation and measurement of the fluorescence decay time of object segments, it is proposed that the detection unit comprises several detectors arranged one behind the other in the relative movement direction and that the measuring unit is set up to determine the fluorescence decay time of an object segment from the fluorescence intensities measured one after the other with the detectors arranged one behind the other in accordance with the arrangement in the relative movement direction.

• - Beleuchtung des Objektes,
• - Messung des von einem Objektsegment des Objektes emittierten Fluoreszenzsignals und
• - Ermittlung der Fluoreszenzabklingzeit des Objektsegmentes aus dem gemessenen Fluoreszenzsignal

durchgeführt. Dabei erfolgt die Ermittlung der Fluoreszenzabklingzeit eines Objektsegmentes aus den mit einer Anzahl von in Relativbewegungsrichtung hintereinander angeordneten Detektoren jeweils entsprechend der Anordnung in Relativbewegungsrichtung nacheinander gemessenen Fluoreszenzintensitäten.The optical detection of properties of an object moving in the direction of relative movement relative to the inspection device by means of fluorescence excitation is carried out by the following process steps:

• - lighting of the object,
• - Measurement of the fluorescence signal emitted by an object segment of the object and
• - Determination of the fluorescence decay time of the object segment from the measured fluorescence signal

The fluorescence decay time of an object segment is determined from the fluorescence intensities measured one after the other with a number of detectors arranged one behind the other in the direction of relative movement, each according to the arrangement in the direction of relative movement.

The relative movement can be achieved by transporting the object on a conveyor, with the detectors arranged in a fixed position relative to the conveyor. The object is then moved past the detectors relative to the inspection device. However, the relative movement can also be achieved with a stationary object by moving the inspection device or its detectors past the object. A relative movement is also conceivable, in which both the object and the inspection device with its detectors are moved relative to one another during the optical recording of the properties using fluorescence excitation.

A respective integration period can be specified for each detector. The integration periods of the detectors arranged one behind the other can begin one after the other starting from a fluorescence excitation according to their spatial arrangement in order to realize different integration intervals. The inspection device can be set up for repeated fluorescence excitation and measurement of a summed fluorescence intensity by summing the fluorescence intensities measured after a respective fluorescence excitation with one detector in each case in the respective integration period in order to obtain a summed fluorescence intensity for each detector for the integration period of the detector.

By repeatedly exciting the fluorescence and measuring a summed fluorescence intensity by summing the fluorescence intensities measured after each fluorescence excitation with one detector in each integration period in order to obtain a summed fluorescence intensity for each detector for the integration period of the detector, even individually weak fluorescence intensities can be reliably detected.

The respective integration periods can be specified for each detector in such a way that the integration periods of the detectors arranged one behind the other start one after the other in accordance with their spatial arrangement, starting from a fluorescence excitation. This means that each detector records a section of the fluorescence decay curve that is determined specifically for each detector in order to obtain an integrated (summed) measurement value for the fluorescence intensity at this specified measurement time or measurement period. The detectors arranged one behind the other, each of which is assigned measurement times or integration periods that follow one another in time in accordance with the spatial arrangement, allow several integrated measurement values for the fluorescence intensity to be determined at different support points of the fluorescence decay curve in order to determine the fluorescence decay curve or the fluorescence decay behavior with the fluorescence decay time. A relative movement of the object in the relative movement direction, ie in the direction of the detectors arranged one behind the other, can be compensated in this way and is harmless.

A measurement can be carried out by repeated fluorescence excitation and summation of the fluorescence intensities measured in an integration period in a measurement time interval in which an object segment is located in the detection range of a detector during its relative movement.

The fluorescence intensities measured by the detectors can form measured values at support points of the fluorescence decay behavior of an object segment. The measuring unit can be set up to determine the fluorescence decay time from the fluorescence decay behavior measured with the measured values at the support points.

In one variant, the fluorescence decay time for an object segment can be determined, for example, in the time domain from the fluorescence intensities measured one after the other after pulsed fluorescence excitations from the detectors arranged one behind the other. For this purpose, a detector can record a fluorescence intensity at a specific point in time or over a specific time interval. The fluorescence decay time can then be determined from the fluorescence intensities for the different time ranges that are shifted relative to one another.

In another variant, the fluorescence decay time for an object segment can be determined, for example in the frequency domain, from the fluorescence intensities measured by the detectors arranged one behind the other after a frequency-modulated fluorescence excitation for successive integration periods. For this purpose, a detector can record a fluorescence intensity for a given oscillation phase range of the oscillation of the frequency-modulated fluorescence excitation. The fluorescence decay time can then be determined from the fluorescence intensities for the various oscillation phase ranges that are shifted relative to one another.

In this case, a number of detectors arranged directly one behind the other in the direction of relative movement can be present, whereby each detector detects the fluorescence intensity in a predetermined temporally successive oscillation phase range according to its spatial positioning in the sequence of the arrangement of the detectors one behind the other.

The inspection device can have several groups, each with a number of detectors arranged directly one behind the other. The groups can be arranged one behind the other in the direction of relative movement. The measuring unit is then set up to add up the fluorescence intensities recorded by the detectors of the groups for the same oscillation phase ranges for an object segment in order to obtain summed fluorescence intensities for time ranges of a fluorescence decay phase that correspond to the respective oscillation phase range.

The inspection device can have several detection lines arranged next to one another in the width direction transverse to the direction of relative movement, which in the case of an object being moved on a conveyor belt in a transport direction corresponds to the longitudinal extent of the conveyor belt or the transport direction, each with a number of detectors arranged directly one behind the other in a sequence in the relative movement direction. The measuring unit is then set up to determine the fluorescence decay times of object segments lying next to one another in the width direction transverse to the direction of relative movement with the detection lines.

The inspection device and the method can be used advantageously to inspect (cut) slices of food products which, after being cut, are separated on a conveyor belt and fed to a packaging machine. These objects move at a high speed on the conveyor belt. The defined movement is then used to measure the fluorescence intensity for an object segment at the time when the object segment is in the detection range of the detector, or at a time or integration period of the fluorescence decay phase assigned to the detector, using the detectors arranged one behind the other in the transport direction, i.e. the relative movement direction, and to combine these with the fluorescence intensities for these support points, which were measured one after the other with the detectors, in order to calculate the fluorescence fluorescence decay curve or the associated fluorescence decay time.

However, the inspection device and the method can also be used for other applications, such as for inspecting the quality of wood materials conveyed in the production process, fluid media, in the manufacture of strip-shaped semi-finished products, yarns and the like.

In addition, the inspection device can also be designed in such a way that it moves itself over a static object, for example to inspect pipes (both inside the pipe and on the outside of the pipe) for contamination. The relative direction of movement is determined by the inspection direction in which the inspection device is moved along the object. Depending on the intended use, the detectors can be arranged one behind the other in the direction of extension of the static object to be examined.

The inspection device can be installed in a measuring tunnel to reduce disruptive influences from extraneous light and improve the signal-to-noise ratio. It can, for example, be combined with an X-ray scanner that has a shielded measuring tunnel.

When carrying out the method, a repeated fluorescence pulse excitation and measurement of a summed fluorescence intensity can be carried out by summing the fluorescence intensities measured after a respective fluorescence excitation with a respective detector in a respective integration period in order to obtain a summed fluorescence intensity for the integration period of the detector for each detector. The respective integration periods for each detector are specified in such a way that the integration periods of the detectors arranged one behind the other start one after the other in time, starting from a fluorescence pulse excitation, in accordance with their spatial arrangement.

A repeated fluorescence pulse excitation and summation of the fluorescence intensities measured in an integration period can be carried out in a measurement time interval in which an object segment is in the detection range of a detector during its relative movement in the direction of relative movement. This means that even weak fluorescence signals can be processed by integration into measurement signals that have a sufficient signal-to-noise ratio.

When carrying out the method, the fluorescence decay time can be determined from the fluorescence decay behavior measured with measured values at support points, whereby the fluorescence intensities measured by the detectors form the measured values at support points of a fluorescence decay phase of an object segment.

The determination of the fluorescence decay time for an object segment can be carried out in the time domain from the fluorescence intensities measured one after the other for each object segment by the detectors arranged one behind the other after a pulsed fluorescence excitation.

However, it is also advantageous to determine the fluorescence decay time for an object segment in the frequency range from the fluorescence intensities measured by the detectors arranged one behind the other after a frequency-modulated fluorescence excitation for successive integration periods. For this purpose, a detector records a fluorescence intensity for a predetermined oscillation phase range of the oscillation of the frequency-modulated fluorescence excitation and the fluorescence decay time is determined from the fluorescence intensities for the various oscillation phase ranges shifted relative to one another.

The relative movement can be used to detect the fluorescence intensity by a detector according to its spatial positioning in the sequence of the arrangement of the detectors one behind the other in a predetermined consecutive oscillation phase range. In this case, a number of detectors are arranged directly one behind the other in the direction of relative movement.

When carrying out the method, the fluorescence intensities recorded by the detectors of the groups for the same time ranges of the fluorescence decay phase or the same oscillation phase ranges for an object segment can be summed up in order to obtain summed fluorescence intensities for integration time ranges of a fluorescence decay phase. In this case, several groups, each with a number of detectors arranged directly behind one another, can be present, with the groups being arranged one behind the other in the direction of relative movement.

• 1 - Schematische Darstellung der Messung von Fluoreszenzabklingzeiten im Zeitbereich;
• 2 - Schematische Darstellung der Messung von Fluoreszenzabklingzeiten im Frequenzbereich;
• 3 - Schematische Darstellung einer FD-FLIM Messung mit Photonenintegrationsfenstern zu zwei verschiedenen Zeitpunkten der Fluoreszenzschwingung;
• 4 - Schematische Seitenansicht einer Inspektionsvorrichtung mit einem Transportband, einer Beleuchtungseinheit und einer Detektionseinheit, die mehrere in Transportrichtung hintereinander angeordnete Detektoren aufweist;
• 5 - Schematische Frontansicht der Inspektionsvorrichtung aus 4;
• 6 - Skizze einer Detektionseinheit mit einem Detektor, einem Objektiv und einem optischen Filter zum Blocken von Reflexionen, Streulicht oder ähnlichem;
• 7 - Diagramm eines beispielhaften zeitlichen Verlaufs des Fluoreszenzsignals mit den Integrationszeiträumen von verschiedenen Detektoren für die Ermittlung der Fluoreszenzabklingzeit im Zeitbereich;
• 8 - Skizze der Größe eines Detektors mit dem Zeitintervall, in dem ein Objektpunkt den Erfassungsbereich des Detektors überstreicht;
• 9 - Diagramm eines beispielhaften zeitlichen Verlaufs des Fluoreszenzsignals mit den Integrationszeiträumen von verschiedenen Detektoren für die Ermittlung der Fluoreszenzabklingzeit im Frequenzbereich.

The invention is explained in more detail below with reference to the accompanying drawings with exemplary embodiments. They show:

• 1 - Schematic representation of the measurement of fluorescence decay times in the time domain;
• 2 - Schematic representation of the measurement of fluorescence decay times in the frequency domain;
• 3 - Schematic representation of an FD-FLIM measurement with photon integration windows at two different times of the fluorescence oscillation;
• 4 - Schematic side view of an inspection device with a conveyor belt, a lighting unit and a detection unit having several detectors arranged one behind the other in the transport direction;
• 5 - Schematic front view of the inspection device from 4 ;
• 6 - Sketch of a detection unit with a detector, a lens and an optical filter to block reflections, scattered light or similar;
• 7 - Diagram of an exemplary temporal course of the fluorescence signal with the integration periods of different detectors for the determination of the fluorescence decay time in the time domain;
• 8 - Sketch of the size of a detector with the time interval in which an object point passes over the detection area of the detector;
• 9 - Diagram of an exemplary temporal course of the fluorescence signal with the integration periods of different detectors for the determination of the fluorescence decay time in the frequency domain.

1 shows a schematic representation of the measurement of fluorescence decay times in the time domain. In diagram a) it can be seen that at time t ₀ a fluorescence excitation of an object occurs by an electromagnetic excitation pulse with an intensity I _0. This causes fluorescence to be emitted from the object, the fluorescence intensity of which decreases exponentially over time t according to the equation (1) mentioned at the beginning.

At the time of the time constant τ the fluorescence intensity is $I\left(\tau \right)=\frac{1}{\mathrm{<figure-callout\; id="0"\; label="e\; I"\; filenames="DE102023108014A1\_0008.png"\; state="\{\{state\}\}">e</figure-callout>}}{I}_{}{}_0.$

This basic principle assumes that the object does not move relative to the detector during the decay phase of the fluorescence.

The photons of the emitted fluorescence of the object that hit a detector can now be measured in the time domain using a photon counting method.

This is outlined in diagram b). For this, a clock is started at the excitation time t ₀ and the time at which the first photon hits the detector is determined. The counter for the time at which a photon hits the detector, e.g. in the time interval t ₁ to t _2, is then incremented and the measurement is repeated by re-excitation and restarting the clock at the excitation time t _0. This process is repeated until a predetermined final value of counts is reached.

As shown in diagram c), the detected fluorescence intensities can also be integrated over integration periods (e.g. S1 in the period t1 to t2, S2 in the period t2 to t3, S3 in the period t3 to t4). These three integrations, for example, measure the values for the different support points of the fluorescence decay curve, from which the exponentially decreasing fluorescence signal can be reconstructed and the fluorescence decay time can be calculated using equation (1).

2 shows a schematic representation of the measurement of fluorescence decay times in the frequency range. The fluorescence excitation is carried out with a modulated light signal 01, such as a sinusoidal signal (as shown) or a square wave signal (not shown), which has a predetermined modulation frequency ω, a defined amplitude B and a defined equivalent A. In response to the fluorescence excitation, the object emits a fluorescence signal 02 that is phase- and equivalent-shifted and attenuated in amplitude and has the same modulation frequency ω as the fluorescence excitation, ie the light signal 01. By measuring the phase shift Φ, the phase-dependent fluorescence decay time τ _Ph can be calculated according to the equation (2) mentioned at the beginning.

In addition, the modulation index M can be calculated from the amplitude attenuation and the equivalence shift according to the equation (3) mentioned above.

The calculated modulation index M can then be used to calculate the modulation-dependent fluorescence decay time according to equation (4).

The radiative process of fluorescence decays within a few nanoseconds, which means that the modulation frequencies ω are usually in the range of several tens of MHz.

3 shows a schematic representation of an FD-FLIM measurement with photon integration windows at two different times of the fluorescence oscillation. The fluorescence intensity The images are detected pixel by pixel in a spatially resolved manner by the photons that hit the respective pixels. Here, too, it is initially assumed that the object does not move relative to the camera during the exposure time.

There are two taps in each pixel (Tap A and Tap B). Tap A integrates the incident fluorescence photons in the phase angle from 0 to π and Tap B in the phase angle from π to 2π of the full wave of the fluorescence signal 02. The integration windows are shifted by a defined period of time (phase angle). Depending on the accuracy, four integrations at two different phase angles, eight integrations at four different phase angles or sixteen integrations at eight different phase angles can be used to reconstruct the sinusoidal fluorescence signal.

For example, an integration measurement can be carried out with sixteen integrations at eight different phase angles. Tap A is active in the period from 0 to π and Tap B from π to 2π. The start time is then shifted to π/8 and two new periods are created in which Tap A and Tap B are active: Tap A from π/8 to 5π/8 and Tap B from 5π/8 to 9π/8. Shifting the phase angle a further six times by π/8 leads to sixteen integration points from which the fluorescence oscillation is reconstructed. The sixteen integrations always take place one after the other in this measurement. The user has to set an exposure time. Defining the exposure time determines how often these integration cycles are run through. This allows the phase shift and the modulation index to be measured and the phase-dependent and modulation-dependent fluorescence decay time to be determined for each pixel.

The measurement methods explained above in the basic principle assume that the object is at rest and does not move relative to the camera during the exposure period.

Based on these basic principles, improved inspection methods are described below in which the object can move in a relative direction of movement relative to the inspection device. For this purpose, the object can be moved on a conveyor in a transport direction relative to detectors arranged in a fixed position relative to the conveyor.

4 shows a schematic side view of an inspection device with a conveyor device 03 (e.g. conveyor belt 03), a lighting unit 04 and a detection unit 05, which has several detectors D1, D2, ..., Dn arranged one behind the other in the transport direction TR. The transport direction TR is identified with an arrow with the transport speed v. The conveyor belt 03 with the objects 06 positioned on it moves from left to right at the transport speed v.

The lighting unit 04 is arranged schematically above the conveyor belt 03 and is variably adapted to the number of detectors D1, D2, ..., Dn of the detection unit 05 in order to ensure the illumination of the section of the measuring setup to be inspected. The length of the entire measuring setup depends on the selected transport speed v, the selected detector size U and the number of detectors n*05. The more precise the resolution of the measuring method has to be, the more detectors D1, D2, ..., Dn are connected in succession. The detectors D1, D2, ..., Dn are used either for detection in the time domain or in the frequency domain.

The lighting unit 04 can, for example, comprise a light panel, a diode laser, an LED array or the like.

The detectors D1, D2, ..., Dn are arranged one behind the other in the transport direction TR. The distance x between the detectors D1, D2, ..., Dn can be selected depending on the resolution of the detection unit 05. The number of detectors D1, D2, ..., Dn can be selected depending on the exposure time required for the measurements at the times t ₁ , t ₂ , ..., t _n .

The detectors D1, D2, ...., Dn can be, for example, photodiodes, photodiode arrays or photosensitive pixels of a camera sensor. The detectors D1, D2, ..., Dn arranged one behind the other in the transport direction TR form a group of detectors.

5 shows a schematic front view of the inspection device from 4 . The conveyor device 03 moves the objects 06 positioned thereon in the transport direction TR (ie in the relative movement direction), which runs in the viewing direction into or out of the representation. It can be seen that in this embodiment, several detectors of the detection unit 05 are arranged next to one another in the direction of the width of the conveyor device 03, ie transversely to the transport direction TR, in order to be able to inspect object segments of one or more objects 06 across the width of the conveyor device 03 through a restricted detection area.

It can be seen that the objects 06 to be inspected for quality assurance are located on the conveyor device 03 (e.g. conveyor belt 03). A lighting unit 04, which can consist of light panels, diode lasers, LEDs, LED arrays or similar, irradiates the objects 06 located on the conveyor belt 03 with pulsed light during inspection in the time domain or with modulated light during inspection in the frequency domain. The pulse duration, the frequency of the pulses and/or the measurement time (integration interval) can be specified by the user for the measurement in the time domain depending on the application.

The modulation of the light for the measurement in the frequency range can, for example, be rectangular or sinusoidal with a modulation frequency determined by the user and the application. Depending on the application, the lighting unit 04 can provide one or more wavelengths from the electromagnetic spectrum (UV, VIS, NIR, MIR,...) to excite the fluorescence.

The lighting unit 04 is arranged and designed such that it illuminates the entire conveyor belt 03 at a defined angle of incidence. The position of the lighting unit 04 is only shown schematically and can also be selected differently relative to the conveyor belt 03. When measuring the fluorescence signal in the time domain, the object segments of an object 06 to be examined emit an exponentially decaying fluorescence signal of a few nanoseconds. In the frequency domain, the objects 06 emit a fluorescence signal that has the same frequency as the excitation signal that emanates from the lighting unit 04. The fluorescence signal is detected by the detection units 05 both in the case of the measurement in the time domain and in the case of the measurement in the frequency domain.

6 shows a sketch of a detection unit 05 with a detector 07, a lens 08 and a filter 09.

In general, a detection unit 05 for fluorescence measurements is made up of several units, although not all of them have to be present. For fluorescence measurement, the signal detected by the detector 07 should be free of any reflection and scattered light. A detector 07 can be a photodiode, a photodiode array or a photosensitive area of a camera sensor. This photosensitive element is generally referred to as a detector 07. The exposure time, the recording delay and the start of the recording can be set on the detection unit 05 or triggered by external signals. Optical filters 09 are normally used for this. However, these can also be neglected if the lighting unit 04 and the detection unit 05 are positioned at an angle to one another at which no reflection or scattering hits the detector 07. In addition, a lens or lenses 08 are normally used for detectors 07 in order to allow the light to be detected to fall onto the detector 07 in a collimated manner.

7 shows a diagram of an exemplary temporal course of the fluorescence signal with the integration periods of different detectors D1, D2, D3 for the determination of the fluorescence decay time in the time domain.

A schematic representation of how the detection process and the reconstruction of the fluorescence signal in the time domain are carried out via the individual detectors D1, D2, D3 arranged one after the other in the transport direction TR is shown in the 7 to be recognized. At time t ₀ , a laser is pulsed to excite fluorescence. The first detector D1 then integrates all photons in the period from t ₁ to t ₂ . After the integration is complete and the fluorescence has died down (a period of nanoseconds), the laser is pulsed again and the second detector D2 integrates the photons in the period from t ₂ to t ₃ . The renewed pulsing and integration is repeated with the third detector D3 from t ₃ to t _4. The exponentially decaying fluorescence signal can be reconstructed from the three integrations and the fluorescence decay time can be calculated according to theory.

Of course, four or more integration periods per fluorescence signal can be selected for greater accuracy. For example, if sixteen detectors are used to reconstruct the fluorescence oscillation, sixteen integration periods result and the accuracy of the method increases. At least three detectors must be used, as only then is the reconstruction of the exponentially decaying fluorescence signal possible with the three support points.

In order to determine the fluorescence decay time for an object segment, the decay curve resulting from a single excitation is determined at at least three support points or in at least three integration periods. If the object segment to be examined is only in the detection range of a single detector during an excitation, the inspection is carried out in such a way that the movement of the object at a relative speed along the detectors arranged one behind the other is used to assign a support point of the fluorescence decay curve, which in principle remains the same for each excitation, to each detector. and to use the detectors to detect the fluorescence intensities at the respective support points for all object segments that are in the detection range of a detector D1, D2, ..., Dn at that time when several object segments are excited. After the advance, at a later detection time the object segment that was previously inspected by an upstream detector, e.g. detector D1, with regard to a support point, e.g. the first support point, is in the detection range of a downstream detector, e.g. detector D2. The object segment is then inspected by this detector (e.g. D2) with regard to the next support point, e.g. the second support point. The fluorescence intensities for the support points recorded in this way for an object segment with the detectors D1, D2, ..., Dn one after the other can then be assigned to a common object segment depending on the known transport speed or relative speed in order to determine the fluorescence decay curve or the fluorescence decay time for the selected object segment from these measured values.

The determination of the fluorescence decay time in the time domain is illustrated below using an example.

The fluorescence decay time measurement in the time domain can be used, for example, on a production line in the food industry to inspect sliced salami. After the cutting process, the individual salami slices (objects 06) run at a belt speed of 0.5 m/s (0.5 nm/ns). Salami has a fluorescence decay time of 2 - 2.5 ns. This results in a time of around 12 ns until the fluorescence intensity value has dropped to <0.01. If four detectors D1, D2, D3, D4 are used for integration, the selected detector D1, D2, D3, D4 must be able to achieve an integration time of 12 ns/4 = 3 ns.

A photodiode is selected as detector D1, D2, D3, D4, each of which has a length of 1 mm in the direction of the tape travel. When measuring a distance of 1 mm, an offset of 6 nm during the decay of the salami's fluorescence can be neglected. In this example, the movement of object 06 over the distance of 1 mm at a tape speed of 0.5 m/s takes about 2 ms (period Δxt).

This is from the 8 which shows a sketch of the local detection range Δx of a detector D in relation to the time interval Δt in which an object point enters and exits the detection range of the detector D, i.e. sweeps over the detection range. The time xt1 represents the first measurement on an object segment and the time interval Δxt the time that passes until the spot on the object segment leaves the photosensitive surface of the detector D. The edge length of the detector D represents, for example, the photosensitive detection size or the detection length Δx of the detector D.

Within an integration period, additional fluorescence intensities can be induced and measured by repeated fluorescence excitation, ie by pulsing the illumination unit 04. Thus, in a first integration period t ₁ to t ₂ of 2 ms with a fluorescence decay time of 12 ns, a number of 166,667 additional photon integrations can be carried out by repeated pulsing (2 ms / 12 ns = 166,667). These individual photon integrations are summed and represent the first integration in the period t ₁ to t ₂ . The integrations are repeated for the second detector D2, the third detector D3 and the fourth detector D4, but after the pulse the period t ₁ to t ₂ , t ₂ to t ₃ and t ₃ to t ₄ is waited for and the photons are only integrated in the period t ₂ to t ₃ , t ₃ to t ₄ and t ₄ to t _5. The selected parameters result in a total exposure time of 2 ms per photodiode and the length of the measuring section of 4 mm.

If 128 photodiode arrays are connected in series to repeat and sum the measurements for the four integration windows (ie four support points) from t ₁ to t ₂ , t ₂ to t ₃ , t ₃ to t ₄ and t ₄ to t ₅ 32 times each, this results in a total exposure time of 64 ms per photodiode array and a length of 12.8 cm.

Using a suitable algorithm, the individual integrations are calculated with each other so that a reconstruction of the fluorescence oscillation is possible and the fluorescence decay time can be calculated.

If a larger signal is required, especially to improve the signal-to-noise ratio, even longer exposure times can be selected and/or additional detectors can be added.

9 shows a diagram of an exemplary temporal course of the fluorescence signal with the integration periods of different detectors for the determination of the fluorescence decay time in the frequency domain.

A schematic representation of how the detection process and the reconstruction of the fluorescence signal in the frequency domain via the individual detectors is carried out is shown in 9 The first detector D1 assigned to time t ₁ integrates over half a period of the modul The excitation and the detector D2 assigned to time t ₂ also integrates over half a period, but is phase-shifted by π/2 (i.e. offset in time). The integration window of the third detector D3 at time t ₃ is shifted by a defined phase (e.g. π/8) and integrates the photons over a half-oscillation - but phase-shifted. The fourth detector D4 at time t ₄ integrates the fluorescence photons exactly π out of phase with the third detector D3.

The measurement is therefore carried out at different starting phases of the phase angles over a portion of the period (e.g. half a period) in order to detect a whole period of the fluorescence signal at different phase starting angles. The number of detectors D1, D2, ..., Dn used to completely reconstruct the fluorescence signal depends on the reconstruction accuracy.

If sixteen detectors are connected in series, the oscillating fluorescence signal can be reconstructed with sixteen support points. The n = 16 detectors D1, D2, ..., D16 are connected in series. The minimum number of detectors is n = 3, since at least three support points are required for reconstruction.

The higher the modulation frequency of the excitation oscillation, the lower the integration time of the detectors D1, D2, ..., Dn must be set.

For both measuring methods (time and frequency domain), the number of detectors D1, D2, ..., Dn depends on the fluorescence intensity emitted by the object 06 as a result of irradiation with the illumination unit 04.

If the fluorescence intensity is low and the exponentially falling fluorescence signal (time domain) or the fluorescence oscillation (frequency domain) is to be determined from the measurements of e.g. For example, if sixteen detectors are to be reconstructed, a further sixteen detectors can be installed behind the first sixteen detectors, which have exactly the same measurement sequence: The detector D17 of the second group of sixteen detectors then integrates from time t ₁ to t ₂ (time domain) or from 0 to π (frequency domain) of the fluorescence decay phase, the detector D18 from t ₂ to t ₃ (time domain) or from π to 2π (frequency domain), the detector D19 from t ₃ to t ₄ (time domain) or from π/8 to 5π/8 (frequency domain) and the detector D20 from t ₄ to t ₅ (time domain) or from 5π/8 to 9π/8 (frequency domain).

This series connection of detector groups can be repeated as often as desired and can also be defined in advance by laboratory tests, as the optimal exposure time for individual objects can be determined here. To classify the quality, the integrations of the respective detectors are then summed and the exponentially decreasing fluorescence signal (time domain) or the fluorescence oscillation (frequency domain) is reconstructed. Using the theory, the fluorescence decay time (time domain) or the phase-dependent and modulation-dependent fluorescence decay time (frequency domain) can then be calculated.

The determination of the fluorescence decay time in the frequency domain is illustrated below using an example.

The measuring method explained is to be used on a production line in the food sector to inspect sliced salami (object 06). After the cutting process, the individual salami slices run at a belt speed of 0.5 m/s (0.5 nm/ns). Since salami has a fluorescence decay time in the range of 2 - 2.5 ns, a modulation frequency of 25 MHz is provided for the excitation oscillation. With the modulation frequency of 25 MHz, a time of 40 ns is created, which lasts for one oscillation period of the excitation oscillation and fluorescence oscillation (0 to 2π). The duration of the half-oscillation from 0 to π then corresponds to 20 ns. According to these specifications, the selected detector D must therefore be able to manage an integration time of 20 ns.

By defining the band speed and modulation frequency of the excitation signal and thus the frequency of the fluorescence signal emitted by the object, a measurement point offset of 10 nm per integration of the half period can be set. This means that the object moves by 10 nm during the photon integration over 20 ns at a band speed of 0.5 nm/ns in the first half period.

A photodiode is selected as detector D, which has a detection length of 1 mm in the relative direction of movement. In relation to the measurement of the entire detection length of 1 mm, the offset of 10 nm occurring during a half period is small and can be neglected for integration. In addition, with a high modulation frequency of e.g. 25 MHz, a large number of photon integrations of a half oscillation can be carried out in the period Δxt. The period Δxt describes the time in which a point on an object (ie an object segment) covers the detection length Δx of the detector D (see 8 ).

In this example, the object segment moves 1 mm in 2 ms at a belt speed of 0.5 m/s. In the period of 2 ms, 50,000 individual photon integrations can be carried out (50,000 x 40 ns = 2 ms). These are summed and represent the first integration at time t ₁ (from 0 to π). At time t ₂ , the same is repeated, but only the second half-oscillation from π to 2π is considered.

For example, to reconstruct the fluorescence oscillation, sixteen detectors are used to reach sixteen support points. The third detector D3 then integrates the photons in the range from π/8 to 5π/8, the fourth detector D4 in the range from 5π/8 to 9π/8, the fifth detector D5 in the range from π/4 to 3π/4, the sixth detector D6 in the range from 3π/4 to 5π/4 and the remaining detectors Dn are each shifted by π/8. With the selected parameters, a maximum exposure time of 32 ms can be set and the length of the measuring section is a minimum of 16 mm.

Since 32 milliseconds are often not enough to reconstruct the fluorescence oscillation in the case of weak fluorescence signals, the number of detectors can be increased to 128, for example. The number 128 is eight times sixteen and thus the individual photon integrations can be repeated eight times. The detectors D1, D2, D3, D4, ..., Dn arranged one after the other are described in accordance with this arrangement by consecutive numbers 1, 2, 3, 4, ...., n in the order of the arrangement in the transport direction. The detectors Di with the serial numbers i = 1, 17, 33, 49, 65, 81, 97 and 113 then integrate the photons over the period 0 to π, the detectors with the serial numbers 2, 18, 34, 50, 66, 82, 98 and 114 from π to 2π, the detectors with the serial numbers 3, 19, 35, 51, 67, 83, 99 and 115 from π/8 to 5π/8, the detectors with the serial numbers 4, 20, 36, 52, 68, 84, 100 and 116 from 5π/8 to 9π/8, the detectors with the serial numbers 5, 21, 37, 53, 69, 85, 101 and 117 from π/4 to 3π/4, the detectors with the consecutive numbers 6, 22, 38, 54, 70, 86, 102 and 118 from 3π/4 to 5π/4. The other detectors integrate analogously, each shifted by π/8. The measuring section then has a minimum length of 12.8 cm. By expanding to 128 detectors, a total exposure time of 256 ms can be achieved. The individual integrations are offset against one another using a suitable algorithm, so that a reconstruction of the fluorescence oscillation is possible and the fluorescence decay time can be calculated.

If even longer exposure times are required, additional detectors can be added.

To reference the photodiode arrays, a sample standard can be placed on the conveyor belt at defined time intervals if possible, or the conveyor belt can be used directly if the fluorescence decay time of the conveyor belt is known.

Fluorescence can also be detected over a certain penetration depth. With thin panes, this can lead to the problem that the conveyor belts cause a measurement effect because they "shine through" individual panes or through part of the bottom pane of a portion shingle. Therefore, in the case of so-called "shine through", the transport media should be made of a material that does not contain the foreign bodies to be detected or generally does not show any measurable fluorescence in the area to be assessed. Alternatively or additionally, the constant and known fluorescence effect of the conveyor belt could also be calculated out by calibration.

1. a) Es befindet sich neben dem Objekt auf der Fördereinrichtung eine Anordnung, die eine oder mehrere Bezugsproben enthält, die geeignet sind, die Systemparameter zu prüfen bzw. passend zu justieren. Diese Bezugsproben, die durch eine Abdeckung gegen Verschmutzung geschützt sind, werden zum entsprechenden Zeitpunkt freigegeben und in den Aufnahmebereich gefahren.
2. b) Es gibt einen Sensorausleger, der nur den Bereich mit den Bezugsproben im Blickfeld hat bzw. das Sichtfeld der gesamten Messanordnung kann den Bereich der Bezugsproben einsehen, wie bspw. einen Randbereich eines Transportbandes, auf dem die Bezugsproben platziert werden.
3. c) In einfachen Fällen, wo ein „Durchschimmern“ ausgeschlossen werden kann, kann das Förderband - sofern es eine bekannte Fluoreszenzabklingzeit besitzt - zum Abgleich des Fluoreszenzmesssystems herangezogen werden und auch in den Fällen, in denen klar ist, dass kein Fremdstoff mit der Abklingzeit vom Objekt auftreten kann.

The fluorescence measurement can be calibrated using a sample standard, for example. This makes it even more reliable to ensure that the fluorescence measurement system can be automatically and repeatedly adjusted to the measurement task. The following solutions are conceivable:

1. a) Next to the object on the conveyor there is an arrangement containing one or more reference samples that are suitable for checking the system parameters or for adjusting them accordingly. These reference samples, which are protected against contamination by a cover, are released at the appropriate time and moved to the receiving area.
2. b) There is a sensor boom that only has the area with the reference samples in its field of view or the field of view of the entire measuring arrangement can see the area of the reference samples, such as an edge area of a conveyor belt on which the reference samples are placed.
3. c) In simple cases where “show-through” can be excluded, the conveyor belt - provided it has a known fluorescence decay time - can be used to calibrate the fluorescence measuring system and also in cases where it is clear that no foreign substance can appear with the decay time of the object.

The procedure for detecting properties of the inspected object segments, such as in particular for detecting foreign bodies and defects in food, can be usefully supplemented, e.g. by a method for measuring the spatial dimensions (ie the 3D data) of the objects to be tested 06. This allows the measured fluorescence intensities to be assigned to the measured geometric data.

This allows phase shifts due to the influence of pure time of flight differences due to the distance to an object point to be corrected. This is of interest in the case of relatively short fluorescence decay times and in the case of large differences in the height of the objects 06. In addition, the combination with height data, with appropriate calibration of the elements involved, also enables partial views of camera images to be combined to form a complete image of the surface of the object. The camera images can, for example, be images of the fluorescence signals taken by detector cameras. Knowing the viewing direction of a relevant sensor field element to the object surface enables a more precise determination of the error size that a detected foreign body has under the viewing angle, since the projection angle under which the object location and any foreign body are seen is known through the combination with a 3D surface measurement.

A further advantage of coupling with a 3D surface measurement arises with changing object heights (individual panes, flat shingle portions, high shingle portions, stacks of panes, individual pieces) through an automatic optimal adaptation of the evaluation parameters as well as the recording parameters to the respective conditions, i.e. to the surface area to be checked.

One adjustment could be, for example, to move the measuring equipment to the optimal distance range.

One or more light section sensors, e.g. with triangulation methods, can preferably be used here, since these only use the light that is scattered back from the surface of the object. Since only the light that is directly scattered back from the object surface is used, the light color that is used for fluorescence excitation can also be used, for example. Depending on the application, the light color of such a light section sensor can also be specifically selected.

Depending on the application, another 3D surface detection method with light can also be used, which only uses the light scattered and reflected directly on the object surface and, for example, works according to a triangulation principle and uses the light components reflected directly on the object surface. It is irrelevant whether structured light or the surface structure of the object itself is used.

In principle, depending on the requirements, a pure distance measurement to the object can also be used using another method that works independently of the fluorescence excitation (such as ultrasound or point-by-point, local triangulation without 3D surface detection).

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2021/160309 A1 [0006]

Claims (18)

Inspection device for optically detecting properties of an object (06) moved in a relative movement direction relative to the inspection device by means of fluorescence excitation and measurement of the fluorescence decay time of object segments, wherein the inspection device has an illumination unit (04) for illuminating the object (06), a detection unit (05) for measuring the fluorescence signal emitted by an object segment and a measuring unit, characterized in that the detection unit (05) comprises a plurality of detectors (D1, D2, ..., Dn) arranged one behind the other in the relative movement direction and the measuring unit is set up to determine the fluorescence decay time of an object segment from the fluorescence intensities measured one after the other with the detectors (D1, D2, ..., Dn) arranged one behind the other in each case according to the arrangement in the relative movement direction. inspection device according to Claim 1 , characterized in that a respective integration period is predetermined for each detector (D1, D2, ..., Dn), the integration periods of the detectors (D1, D2, ..., Dn) arranged one behind the other starting one after the other from a fluorescence excitation in accordance with their spatial arrangement, and in that the inspection device is set up for repeated fluorescence excitation and measurement of a summed fluorescence intensity by summing up the fluorescence intensities measured after a respective fluorescence excitation with a respective detector (D1, D2, ..., Dn) in the respective integration period in order to obtain a summed fluorescence intensity for the integration period of the detector (D1, D2, ..., Dn) for each detector (D1, D2, ..., Dn). inspection device according to claim 2 , characterized in that the inspection device is set up for measurement by repeated fluorescence excitation and summation of the fluorescence intensities measured in an integration period in a measuring time interval in which an object segment is located in the detection range of a detector (D1, D2, ..., Dn) during the relative movement. Inspection device according to one of the preceding claims, characterized in that the fluorescence intensities measured by the detectors (D1, D2, ..., Dn) form measured values at support points of the fluorescence decay behavior of an object segment and that the measuring unit is set up to determine the fluorescence decay time from the fluorescence decay behavior measured with the measured values at the support points. Inspection device according to one of the Claims 1 until 3 , characterized in that the measuring unit is set up to determine the fluorescence decay time for an object segment in the time domain from the pulsed fluorescence excitations from the detectors (D1, D2, ..., Dn) arranged one behind the other for fluorescence intensities measured one after the other. Inspection device according to one of the preceding claims, characterized in that the measuring unit is designed to determine the fluorescence decay time for an object segment in the frequency range from the fluorescence intensities measured by the detectors (D1, D2, ..., Dn) arranged one behind the other after a fluorescence excitation with a frequency (ω) for integration periods lying one after the other, wherein a detector (D1, D2, ..., Dn) detects a fluorescence intensity for a predetermined oscillation phase range of the oscillation of the fluorescence excitation and the measuring unit is designed to determine the fluorescence decay time from the fluorescence intensities for the various oscillation phase ranges shifted relative to one another. inspection device according to claim 6 , characterized in that a number of detectors (D1, D2, ..., Dn) are arranged directly one behind the other in the direction of relative movement, wherein a detector (D1, D2, ..., Dn) detects the fluorescence intensity in a predetermined successive oscillation phase range in each case according to its spatial positioning in the sequence of the arrangement of the detectors (D1, D2, ..., Dn) one behind the other. Inspection device according to one of the preceding claims, characterized in that the inspection device has a plurality of groups, each with a number of detectors (D1, D2, ..., Dn) arranged directly one behind the other, and the groups are arranged one behind the other in the direction of relative movement, wherein the measuring unit is set up to add up the fluorescence intensities detected by the detectors (D1, D2, ..., Dn) of the groups for the same oscillation phase ranges for an object segment in order to obtain summed fluorescence intensities for the respective oscillation phase range, and wherein the measuring unit is set up to use the oscillation phase ranges as support points for reconstructing the fluorescence oscillation and for calculating the phase shift, amplitude attenuation and/or equivalent shift with respect to the excitation. supply oscillation is set up using the support points. Inspection device according to one of the preceding claims, characterized in that the inspection device has a plurality of detection lines arranged next to one another in the width direction transverse to the direction of relative movement, each with a number of detectors (D1, D2, ..., Dn) arranged directly one behind the other in a sequence in the direction of relative movement, wherein the measuring unit is set up to determine the fluorescence decay times of object segments lying next to one another in the width direction transverse to the direction of relative movement with the detection lines. Inspection device according to one of the preceding claims, characterized in that the inspection device is arranged in a measuring tunnel, preferably in a measuring tunnel together with an X-ray scanner. Method for optically detecting properties of an object (06) moved in a relative movement direction relative to an inspection device by means of fluorescence excitation by illuminating the object (06), measuring the fluorescence signal emitted by an object segment and determining the fluorescence decay time of the object segment from the measured fluorescence signal, characterized by determining the fluorescence decay time of an object segment from the fluorescence intensities measured one after the other by a number of detectors (D1, D2, ..., Dn) arranged one behind the other in the relative movement direction, each corresponding to the arrangement in the relative movement direction. procedure according to claim 11 , characterized by repeated fluorescence pulse excitation and measurement of a summed fluorescence intensity by summing the fluorescence intensities measured after a respective fluorescence excitation with a respective detector (D1, D2, ..., Dn) in a respective integration period in order to obtain a summed fluorescence intensity for the integration period of the detector (D1, D2, ..., Dn) for each detector (D1, D2, ..., Dn), wherein the respective integration periods for each detector (D1, D2, ..., Dn) are predetermined such that the integration periods of the detectors (D1, D2, ..., Dn) arranged one behind the other begin one after the other in time starting from a fluorescence pulse excitation in accordance with their spatial arrangement. procedure according to claim 12 , characterized by repeated fluorescence pulse excitation and summation of the fluorescence intensities measured in an integration period in a measuring time interval in which an object segment is located in the detection range of a detector (D1, D2, ..., Dn) during its relative movement in the direction of relative movement. Method according to one of the Claims 11 until 13 , characterized by determining the fluorescence decay time from the fluorescence decay behavior measured with measured values at support points, wherein the fluorescence intensities measured by the detectors (D1, D2, ..., Dn) form the measured values at support points of a fluorescence decay phase of an object segment. Method according to one of the Claims 11 until 14 , characterized by determining the fluorescence decay time for an object segment in the time domain from the fluorescence intensities measured successively for one object segment at a time by the detectors (D1, D2, ..., Dn) arranged one behind the other after a pulsed fluorescence excitation. Method according to one of the Claims 11 until 15 , characterized by determining the fluorescence decay time for an object segment in the frequency domain from the fluorescence intensities measured by the detectors (D1, D2, ..., Dn) arranged one behind the other after a frequency-modulated fluorescence excitation for successive integration periods, wherein a detector (D1, D2, ..., Dn) detects a fluorescence intensity for a predetermined oscillation phase range of the oscillation of the frequency-modulated fluorescence excitation and a determination of the fluorescence decay time is carried out from the fluorescence intensities for the various oscillation phase ranges shifted relative to one another. procedure according to claim 16 , characterized by detecting the fluorescence intensity by a detector (D1, D2, ..., Dn) in each case according to its spatial positioning in the sequence of the arrangement of the detectors (D1, D2, ..., Dn) one behind the other in a predetermined successive oscillation phase range, wherein a number of detectors (D1, D2, ..., Dn) arranged directly behind the other in the direction of relative movement are present. Method according to one of the Claims 11 until 17 , characterized by summing the fluorescence intensities detected by the detectors (D1, D2, ..., Dn) of the groups for the same time ranges of the fluorescence decay phase or the same oscillation phase ranges for an object segment to obtain summed fluorescence intensities for integration time ranges of a fluorescence decay phase, wherein several groups each with a number of detectors (D1, D2, ..., Dn) arranged directly one behind the other and the groups are arranged one behind the other in the direction of relative movement.

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