DE102020133599A1 - Time-of-flight camera system with switchable diffuser - Google Patents

Abstract

Time-of-flight camera system with an illumination module 10 for emitting an intensity-modulated light and with a receiving unit (20) for receiving the light emitted and reflected by a scene, the time-of-flight camera system being designed to determine distance based on a phase shift of the emitted and received light, the illumination module (10 ) has a diffuser (18) whose scattering behavior can be adjusted, so that the light from a light source (12) of the lighting module (10) can be emitted with different scattering angles.

Description

The invention relates to a time-of-flight camera system according to claim 1.

Time-of-flight camera systems of this type relate in particular to all time-of-flight or 3D-TOF camera systems that obtain transit-time information from the phase shift of an emitted and received radiation. PMD cameras with photomixing detectors (PMD) are particularly suitable as time-of-flight or 3D-TOF cameras, as they are used, for example, in DE 197 04 496 C2 are described. In particular, the PMD camera allows a flexible arrangement of the light source and the detector, which can be arranged either in one housing or separately. Of course, the term camera or camera system should also include cameras or devices with at least one receiving pixel.

Furthermore, from the WO 2017/041167 A1 a liquid crystal beam shaper is known, which provides different scattering angles by changing the applied voltage.

The object of the invention is to improve a time-of-flight camera system for use in different distance ranges.

The object is advantageously achieved by the time-of-flight camera system according to the invention of the independent claim.

The invention is explained in more detail below using exemplary embodiments with reference to the drawings.

• 1 ein Lichtlaufzeitkamerasystem,
• 2 eine modulierte Integration fotogenerierter Ladungsträger,
• 3 ein erfindungsgemäßes Lichtlaufzeitkamerasystem.

They show schematically:

• 1 a time-of-flight camera system,
• 2 a modulated integration of photogenerated charge carriers,
• 3 a time-of-flight camera system according to the invention.

In the following description of the preferred embodiments, the same reference symbols designate the same or comparable components.

1 shows a measurement situation for an optical distance measurement with a time-of-flight camera, such as that from DE 197 04 496 A1 is known.

The time-of-flight camera system 1 comprises a transmission unit or an illumination module 10 with a light source 12 and associated beam-shaping optics 15 and a receiving unit or time-of-flight camera 20 with receiving optics 25 and a time-of-flight sensor 22.

The time-of-flight sensor 22 has at least one transit-time pixel, preferably also a pixel array, and is designed in particular as a PMD sensor. The receiving optics 25 typically consist of several optical elements to improve the imaging properties. The beam-shaping optics or light shaper 15 of the transmission unit 10 can be designed, for example, as a reflector or lens optics.

The measuring principle of this arrangement is essentially based on the fact that the propagation time and thus the distance covered by the received light can be determined based on the phase shift of the emitted and received light. For this purpose, the light source 12 and the time-of-flight sensor 22 are acted upon by a modulator 30 together with a specific modulation signal M _o with a basic phase position φ ₀ . In the example shown, a phase shifter 35 is also provided between the modulator 30 and the light source 12, with which the base phase φ ₀ of the modulation signal Mo of the light source 12 can be shifted by defined phase positions φ _var . For typical phase measurements, phase positions of φ _var =0°, 90°, 180°, 270° are preferably used.

According to the set modulation signal, the light source 12 emits an intensity-modulated signal S _p1 with the first phase position p1 or p1=φ ₀ +φ _var . In the case shown, this signal S _p1 or the electromagnetic radiation is reflected by an object 40 and, due to the distance covered, arrives as a received signal with a phase shift Δφ(t _L ) with a second phase position p2=φ ₀ +φ _var +Δφ(t _L ). S _p2 to the time-of-flight sensor 22. In the time-of-flight sensor 22, the modulation signal M _o is mixed with the received signal S _p2 , the phase shift or the object distance d being determined from the resulting signal.

Infrared light-emitting diodes/VCSELs are preferably suitable as light sources 12 . Of course, other radiation sources and in particular also in other frequency ranges are also conceivable; in particular, light sources in the visible frequency range can also be considered.

The basic principle of phase measurement is shown schematically in 2 shown. The upper curve shows the course over time of the modulation signal M ₀ with which the light source 12 and the time-of-flight sensor 22 are controlled. The light reflected by the object 40 strikes as received signal S _p2 phase-shifted according to its light propagation time t _L Δφ(t _L ) to the time-of-flight sensor 22. The time-of-flight sensor 22 collects the photonically generated charges q over several modulation periods in the phase position of the modulation signal Mo in a first accumulation gate Ga and in a phase position M ₀ +180° shifted by 180° in a second accumulation gate GB The phase shift Δφ(t _L ) and thus a distance d of the object can be determined from the ratio of the charges qa, qb collected in the first and second gates Ga, Gb.

According to the invention, as in 3 outlined, a switchable diffuser 18 for dynamic lighting control of a time-of-flight camera or time-of-flight camera system is proposed.

LEDs or VCSELs are typically used as light sources 12 in order to illuminate a scene for an active 3D measuring method. CPCs are mostly used as light shapers 15 for LEDs and DOEs for VCSELs.

1. a) Nahbereichsausleuchtung: gleichmäßige Ausleuchtung, verteilt in einen möglichst großen Winkelbereich, (auf kurze Entfernungen ist mehr als genug Signal vorhanden, Überbelichtung ist ein größeres Problem).
2. b) Mitteldistanz: homogene Ausleuchtung im Winkelbereich.
3. c) Mittenzentriertes Fernfeld: Nur ein innerer Bereich wird ausgeleuchtet, um maximale Reichweite in der Mitte zu ermöglichen.

The light distribution in the scene directly influences the sensitivity and range of the measurement. Depending on the application, different illumination is desired. When there are many possible applications, the choice of illumination is a compromise. Desirable illuminations according to measurement distance and application would be:

1. a) Close-range illumination: uniform illumination distributed over as wide an angular range as possible (there is more than enough signal at short distances, overexposure is a bigger problem).
2. b) middle distance: homogeneous illumination in the angular range.
3. c) Centre-centered far field: Only an inner area is illuminated to allow maximum range in the centre.

In order to make this possible, a switchable diffuser 18 is proposed, which is connected downstream of the light source 12 and the beam-shaping optics 15 . According to the invention, the diffuser 18 is controlled in such a way and is constructed in such a way that a scattering angle can be set between non-scattering and scattering in the complete half-space (2π).

For example, it would be possible to illuminate a long-distance area according to variant c) with a deactivated diffuser, so that the complete optical power is emitted in a small angular area.

For the near-field illumination according to variant a), the diffuser 18 is activated to the maximum, so that the emitted light preferably illuminates the entire half-space (2π).

Depending on the requirements, intermediate levels can also be set for the medium distance range. In particular, the spread of the diffuser can be adjusted to the field of view FOV of the camera. Depending on the design, this can be combined with a second engineered diffuser, which provides basic illumination and enables a change/smearing by switching a diffuser.

The main advantage is the redistribution of the light by the switchable diffuser 18, no mechanical moving parts required. The redistribution also improves the luminous efficacy, so that only a small amount of optical power is lost as useful light. The redistribution or the scattering angle of the diffuser 18 can be set statically or dynamically in software. This can, for example, be dynamically controlled as a function of a recognized scene or statically specified for a specific application.

Such a diffuser 18 is advantageously designed as an electrically switchable liquid crystal diffuser. A Liquid Crystals are typically long-chain polar molecules that align in an electric field. Depending on the voltage applied, the properties of the liquid crystals can be changed. In particular, the phases and diffusion properties of the liquid crystal arrangement can be changed. The effect of the liquid crystal typically correlates with the order or orientation of the liquid crystal molecules.

In a further configuration, a plurality of light sources 12 and/or further lighting modules 10 can also be provided, which each have their own diffusers 18 . Such an arrangement allows an individual adjustment of the scattering angles of the individual light sources 12 and thus also an individual adjustment of the light profile or scattering angle profile emitted by the light sources 12 in their entirety.

Reference List

1

time-of-flight camera system

10

lighting module

12

lighting

15

light shaper,

18

switchable diffuser

20

Receiver, time-of-flight camera

22

time-of-flight sensor

30

modulator

35

Phase shifter, lighting phase shifter

40

object

φ, Δφ(tL)

runtime-related phase shift

φvar

phasing

φ0

base phase

Mon

modulation signal

p1

first phase

p2

second phase

Sp1

First phase transmit signal

Sp2

Receive signal with second phase

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited 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.

Patent Literature Cited

• DE 19704496 C2 [0002]
• WO 2017/041167 A1 [0003]
• DE 19704496 A1 [0009]

Claims (6)

Time-of-flight camera system with an illumination module 10 for emitting an intensity-modulated light and with a receiving unit (20) for receiving the light emitted and reflected by a scene, the time-of-flight camera system being designed to determine the distance based on a phase shift of the emitted and received light, the illumination module (10 ) has a diffuser (18) whose scattering behavior can be adjusted, so that the light from a light source (12) of the lighting module (10) can be emitted with different scattering angles. Time-of-flight camera system claim 1 , which is designed in such a way that the scattering angle is automatically adjusted based on depth information of a detected scene. Time-of-flight camera system according to one of the preceding claims, in which the scattering angle of the diffuser is set to a maximum for a close range and to a minimum for a far range. Time-of-flight camera system according to one of the preceding claims, in which the light source (12) has beam-shaping optics (15). Time-of-flight camera system according to one of the preceding claims, with a plurality of light sources (12), each light source (12) having its own diffuser (18) which can be controlled individually. Time-of-flight camera system according to one of the preceding claims, which is designed in such a way that different beam or scattering angle profiles can be set by individually controlling the diffusers (18).

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