DE102018108926B3 - Illumination for a photoflash camera and time of flight camera system and method of operating such illumination - Google Patents

Abstract

Method for operating a photoflash camera, in which the current to the illumination 12 is adjusted by means of a controllable voltage source, and the voltage value of the last modulation phase n-1 is used as the voltage starting value of a modulation phase n.

Description

The invention relates to a lighting for a Lichtlaufzeitkamera and method for operating such according to the class of the independent claims.

In particular, the invention relates to all the time of flight of light or 3D TOF camera systems which acquire transit time information from the phase shift of an emitted and received radiation. As a light transit time or 3D TOF cameras in particular PMD cameras with photonic mixer detectors (PMD) are suitable, as for example in the DE 197 04 496 A1 and can be obtained from the company 'ifm electronic GmbH' or 'PMD-Technologies GmbH' as frame grabber O3D or as CamCube. In particular, the PMD camera allows a flexible arrangement of the light source and the detector, which can be arranged both in a housing and separately. Of course, the term camera or camera system should also encompass cameras or devices with at least one receiving pixel, such as, for example, the distance measuring device O1D of the Applicant.

From the DE 197 04 496 A1 Furthermore, the determination of a distance or a corresponding phase shift of the reflected light from an object is known. In particular, it is disclosed to selectively shift the transmitter modulation by 0 °, 90 °, 180 ° or 270 ° in order to determine a phase shift and thus a distance from these four phase measurements via an arctan function.

From the DE 10 2017 206 672 A1 a circuit for operating a light source is known, in which the illumination is formed with a current and voltage regulation, wherein during the active modulation phase, a current regulation and during the pauses between the modulation phases, a voltage regulation takes place.

The object of the invention is to improve the distance measurement of a light transit time camera system.

The object is achieved in an advantageous manner by the inventive time of flight camera system and method according to the preamble of the independent claims.

• - bei dem die Lichtquelle in einer Modulationsphase mit mehreren Pulsen moduliert wird,
• - bei dem der Controller in den Modulationsphasen ausgehend von der Strommessung den zur Lichtquelle fließenden mittleren Strom durch Verändern der Versorgungsspannung auf einen mittleren Sollstrom einstellt,
• - bei dem die Stromregelung in den Modulationsphasen mit einer Start-Stellgröße beginnt, die als Spannungsendwert am Ende der Stromregelung der vorhergehenden Modulationsphase anlag.

Advantageously, a method for operating a lighting for a light runtime camera is provided, in which the lighting comprises at least one modulatable light source, a modulation signal source, a controllable voltage source, a voltage measurement, a current measurement and a controller,

• in which the light source is modulated in a modulation phase with a plurality of pulses,
• in which, in the modulation phases, the controller adjusts the average current flowing to the light source by varying the supply voltage to a mean desired current starting from the current measurement,
• - In which the current control begins in the modulation phases with a start command value, which applied as voltage end value at the end of the current control of the previous modulation phase.

This approach has the advantage that in particular electrical and thermal changes in the lighting can be dynamically compensated.

Likewise advantageously, a light cycle camera or light time camera system is provided, which is designed to carry out the aforementioned method.

The invention will be explained in more detail by means of embodiments with reference to the drawings.

• 1 schematisch ein Lichtlaufzeitkamerasystem,
• 2 eine modulierte Integration erzeugter Ladungsträger,
• 3 eine erfindungsgemäße Strom- / Spannungsregelung,
• 4 ein Zeitdiagramm der erfindungsgemäßen Regelung.

Show it:

• 1 schematically a light transit time camera system,
• 2 a modulated integration of generated charge carriers,
• 3 a current / voltage control according to the invention,
• 4 a timing diagram of the control according to the invention.

In the following description of the preferred embodiments, like reference characters designate like or similar components.

1 shows a measurement situation for an optical distance measurement with a light time camera, as for example from the DE 197 04 496 A1 is known.

The light transit time camera system 1 comprises a transmitting unit or a lighting module 10 with a lighting 12 and associated beam shaping optics 15 as well as a receiving unit or light runtime camera 20 with a receiving optics 25 and a light transit time sensor 22 ,

The light transit time sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is in particular a PMD sensor educated. The receiving optics 25 typically consists of improving the imaging characteristics of multiple optical elements. The beam shaping optics 15 the transmitting unit 10 may be formed for example as a reflector or lens optics. In a very simple embodiment, if necessary, optical elements can also be dispensed with both on the receiving side and on the transmitting side.

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

The light source transmits according to the set modulation signal 12 an intensity modulated signal S _p1 with the first phase position p1 or p1 = φ ₀ + φ _var . This signal S _p1 or the electromagnetic radiation is in the illustrated case of an object 40 reflected and hits due to the distance traveled accordingly phase-shifted Δφ (t _L ) with a second phase position p2 = φ ₀ + φ _var + Δφ (t _L ) as a received signal S _p2 on the light transit time sensor 22 , In the time of flight sensor 22 becomes the modulation signal M _o with the received signal S _p2 mixed, wherein from the resulting signal, the phase shift or the object distance d is determined.

Furthermore, the system has a modulation control unit 27 on, depending on the present measurement task, the phase position φ _var the modulation signal Mo changed and / or via a frequency oscillator 38 sets the modulation frequency.

As illumination source or light source 12 Infrared light-emitting diodes or laser diodes, for example VCSELs, are preferably suitable. Of course, other radiation sources in other frequency ranges are conceivable, in particular, light sources in the visible frequency range are also considered.

The basic principle of phase measurement according to DE 197 04 496 A1 to which reference is made is schematically in 2 shown. The upper curve shows the time course of the modulation signal Mo with the illumination 12 and the light transit time sensor 22 be controlled. The object 40 reflected light hits as received signal S _p2 according to its light-time t _L phase Δφ (t _L ) on the light transit time sensor 22 , The light transit time sensor 22 collects the photonically generated charges q over several modulation periods in the phase position of the modulation signal M ₀ in a first accumulation gate ga and in a 180 ° shifted phase position M ₀ + 180 ° in a second accumulation Gb. From the ratio of the charges qa, qb collected in the first and second gates Ga, Gb, the phase shift can be determined Δφ (t _L ) and thus a distance d of the object.

3 shows a structure for carrying out the method according to the invention. For power and voltage supply of the light source 12 is a controllable voltage source 130 provided on the basis of determined current and voltage values by a controller 140 is controlled. Cathode side of the light source 12 is a switch 120 provided, starting from the modulation signal of the modulation signal source or the modulator 30 or phase shifter 35 is controlled. The modulation signal source 30 . 35 also provides an envelope signal Pulse _H the modulation for the controller 140 to disposal.

The light source 12 flowing middle stream I _B is due to a voltage drop of a measuring resistor R determined and via a differential amplifier 110 the controller 140 as a current signal U _I fed. Depending on the size of the resistor R and the gain of the differential amplifier 110 results in an actual value with the unit amperes per volt [A / V].

The controller 140 also detects the output of the controllable voltage source 130 applied supply voltage U _V , The voltage U _V can be either before or after the resistance R be measured. The time window for current regulation is determined by the envelope Pulse _H certainly. Through the capacitor C is used for the measurement of the light source 12 flowing electricity I _B averaged or smoothed so that at the resistor R a medium current I _B by the light source 12 flowing electricity I _B can be tapped.

Starting from the envelope signal Pulse _H it is intended to switch between a current or voltage regulation.

In current control mode, the average current flow is provided I _B to the light source 12 to regulate. The controlled variable I _B is about the resistance R and differential amplifier 110 the controller 140 as current actual value I _{B_ist} or current signal actual value U _I (I _{B _is} ) [A / V] provided. The controller 140 serves as a controller and generates from the actual current value I _{B_ist} and one preferably in the controller 140 stored reference variable or setpoint I _{B_soll} a control variable ( U _PWM ) for the voltage regulator 130 to the middle stream I _B over the supply voltage U _V to be regulated as a manipulated variable.

In voltage control mode, it is provided that at the light source 12 applied supply voltage uv to keep constant. For regulation, the controller detects 140 the at the voltage source 130 or alternatively at the light source 12 applied supply voltage Uv as a controlled variable or voltage actual value U _{V_ist} , According to the invention, it is provided, as a reference variable or the desired value, the supply voltage applied at the end of the preceding current regulation U _{V_end, n} to use. The controller 140 generates a control variable from the existing setpoints and actual values ( U _PWM ) for the voltage regulator 130 to regulate the supply voltage Uv to the setpoint.

In 4 In three time diagrams, the aforementioned regulations are described in detail. As shown in the first diagram, starting from signals of the modulation signal source 30 . 35 the controller 140 a modulation envelope Pulse _H made available. The beginning of the modulation phase Mine and the end of the modulation phase Mice can be determined, for example, by the rising and falling edge of the modulation envelope Pulse _H be recognized.

In the second diagram is a time course of the average current I _B to the illumination source 12 shown. As described, the average current I _B during the modulation phases to its setpoint I _{B_soll} kept constant. Between the modulation phases n is the switch 120 open and no current flows. Basically, the beginning could be My and the end mouse of a modulation phase n also be determined on the flanks of the average current signal.

The third diagram shows a time course of the supply voltage uv shown. At an initial start the modulation is sent to the light source 12 preferably initially a voltage stored in the system U _{V_init} created.

In the first modulation phase n-1 uses the current control as the first manipulated variable or voltage starting value U _{V_start} the applied supply voltage U _{V_init.}

As described, the regulation of the average current takes place I _B by changing the supply voltage U _V , The changes in the manipulated variable due to the control interventions are shown schematically.

According to the invention, it is now provided for the supply voltage applied at the end of the current regulation U _{V_end, n-1} for the subsequent voltage regulation as a _reference variable U _{V_setpoint} = U _{V_end, n-1} and for the subsequent current regulation as start control variable U _{V_start, n} = U _{V_end, n-1} .

That is, after the end of the modulation phase mouse becomes the supply voltage uv as shown on the last in the current control supply voltage U _{V_end, n-1} kept constant. With this voltage, the current regulation of the subsequent modulation phase n then begins at the time M y.

The current and voltage controls thus always take place as a function of the voltage end value U _{V_end, n-1} which was in the last or previous current regulation.

This approach has the advantage that the operation of the lighting 12 dynamic on thermal and / or electrical changes of the lighting 12 can be adjusted.

LIST OF REFERENCE NUMBERS

1

Time of flight camera system

10

lighting module

12

lighting

20

Receiver, light time camera

22

Transit Time Sensor

27

control

30

modulator

35

Phase shifter, lighting phase shifter

38

frequency oscillator

40

object

110

Amplifier, differential amplifier

120

counter

130

adjustable voltage source

140

controller

φ, Δφ (t _L )

term-related phase shift

φ _var

phasing

φ ₀

base phase

R

resistance

C

capacitor

M ₀

modulation signal

H

envelope

p1

first phase

p2

second phase

Sp1

Transmission signal with first phase

sp2

Received signal with second phase

.DELTA.Q

charge difference

d

subject Distance

Claims (6)

Method for operating a lighting system (10) for a light-propagating time camera (20), in which the illumination (10) comprises at least one modulatable light source (12), a modulation signal source (30, 35), a controllable voltage source (130), a current measurement (110) and a controller (140), wherein the controller (140) also detects a supply voltage (Uv), - in which the light source (12) in a modulation phase (s) is modulated with a plurality of pulses, - in which the controller (140) in the modulation phase (s), starting from the current measurement (110), the average current flowing to the light source (12) ( I _B ) by changing the supply voltage (U _Vn ) to a mean nominal current ( I _{B_soll} ), in which the current regulation in the modulation _{phases (n} ) starts with a starting manipulated variable (U _{V_start, n} ) which is used as voltage end _value (U _{V_end, n-1} ) at the end of the current regulation of the preceding modulation _phase (n-1). anlag. Method according to Claim 1 in which, after completion of the modulation _phase (s), voltage regulation takes place on the voltage end _value (U _{V_end, n} ) which was present at the end of the modulation phase (s). Method according to one of the preceding claims, in which, depending on an on and off signal (My, mouse) is switched between current and voltage control. Method according to Claim 3 In which the inputs and turn-off (M _a, mouse), starting from a rising and descending switching edge of the envelope signal (pulse _H) are determined. Illumination for a time of flight camera system used to carry out the method according to Claim 1 is trained. Lichtlaufzeitkamerasystem with lighting according to Claim 5 ,

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