The invention relates to a radiator for illuminating an object and a distance measuring device with the radiator.

Distance values can be measured between a measuring device and an object without a physical contact between the device and the object by optical methods. In these methods, the object is illuminated by the device and the light back reflected from the object is then captured by a light detector of the device.

Distance values can for example be determined by periodically modulating the light intensity which is emitted from the device and by measuring the phase difference between the emitted light and the back reflected light arriving on the detector. However, due to the periodicity of the light intensity this method results in an ambiguous distance measurement. Unambiguous distance values can be determined by measuring the time of flight between the emission of light and the arrival of the back reflected light on the detector.

The intensity of the light for illuminating the object

necessary for the distance measurement depends in particular on the sensitivity of the detector, the distance between the object and the measuring device as well as the reflectivity of the object. But otherwise a maximum of the intensity that can be used for illuminating the object is given by safety

standards .

It is an object of the invention to provide a radiator for illuminating an object and a distance measuring device with the radiator, wherein the radiator has a simple design and the distance measuring device is uncritical for safety standards.

The radiator according to the invention for illuminating an object with a predetermined intensity comprises a plurality of radiation units with a high density of electromagnetic radiation, with each radiation unit having an optical axis and being adapted to emit the electromagnetic radiation in the shape of a diverging radiation cone arranged around its optical axis, wherein the radiation units are arranged with the optical axes being substantially parallel, the radiation cones oriented in the same direction and the radiation units being in a transversal direction to the optical axes adjacent to each other and adjacent radiation units are spaced such that they are thermally decoupled so that the radiation units are

unaffected due to heat emission of adjacent radiation units and the radiation units can be operated to simultaneously emit the electromagnetic radiation, and a window arranged such that all radiation cones can pass through the window and such that an illumination origin being the point closest to the radiation units of an illumination area formed by the overlap of all radiation cones is on the opposite side of the window to the radiation units, wherein the number of radiation units is such that the sum of all intensities of all radiation cones

corresponds to the predetermined intensity in the illumination area. The distance measuring device according to the invention comprises the radiator, a detector for detecting the

electromagnetic radiation back reflected from the object and an evaluation unit to determine a time of flight between the emission of the electromagnetic radiation and the arrival of the electromagnetic radiation on the detector.

With the radiator according to the invention it is

advantageously possible to provide as many radiation units as it is necessary to obtain the predetermined intensity in the illumination area. The predetermined intensity can be chosen such that it is sufficiently high for a precise distance measurement with the distance measuring device according to the invention. Since the radiator comprises radiation units with their optical axes being substantially parallel, the radiator is capable of emitting directed light and therefore the

radiator can concentrate its light to a restricted region where the distance measurement is required to be carried out. The radiation units have the disadvantage that they produce heat due to the high electrical current densities required for the generation of the electromagnetic radiation with the high density. Since the radiation units are spaced such that they are thermally decoupled, advantageously no complex cooling device needs to be provided for the radiator. Because the window is arranged between the radiation units and the

illumination origin the complete illumination area is

accessible for the illumination of the object. Furthermore, it is advantageously achieved that the points of the highest intensities are located between the window and the illumination area, where they are uncritical for safety standards.

Therefore, the number of the radiation units can be increased in principle indefinitely without a violation of the safety standards .

The adjacent radiation units according to the invention are spaced such that the points of maximum intensity between the window and the illumination area can be attributed to a single radiation unit. This means that the overlap of the radiation cones leads to intensities which are lower than the maximum intensity close to the window. Therefore, provided that the relative spacing of the laser units, and window are such that safety standards are observed, the radiator is uncritical with respect to the safety standards.

Since the window is provided between the radiation units and the illumination origin, only the side of the window facing away from the radiation units is relevant for the safety certification. Due to the fact that each intensity maximum located at the window can be attributed to the corresponding radiation unit advantageously only these intensity maxima need to be considered for the safety certification.

It is preferred that the radiation units are laser units or LED units. It is preferred that the window is an optical diffuser which increases the opening angle of the illumination cones. Increasing the opening angle reduces the intensity after the optical diffuser and therefore it can be advantageously more easily complied with the safety standards. Also, it is possible to adapt the size of the illumination area to the field of view of the detector of the distance measuring device by choosing the degree of diffusion of the optical diffuser. It is

preferred that the window is an optical homogenizer. The optical homogenizer is homogenizing the intensity distribution of the electromagnetic radiation in planes perpendicular to the optical axes. Consequently, a more uniform illumination of the object can advantageously be achieved. In case the radiation units emit the radiation cones with an oval shape, the

homogenizer also functions to form this shape to being more rotationally symmetric. The radiation units are preferably adapted to emit light pulses, in particular with a duration in the order of nanoseconds. With these short light pulses precise time of flight measurements for the determination of the distance can advantageously be carried out.

It is preferred that the radiation units are arranged in a row. Alternatively, the radiation units are preferably arranged in a shape of an array, in particular a two-dimensional array. In another alternative, it is preferred that at least a part of the radiation units are arranged on a circle. In a further embodiment it is preferred that at least a part of the

radiation units are arranged on at least two concentric

circles. One of the radiation units is preferably arranged in the centre of the circles. With the circular arrangements of the radiation units a circular illumination of the object can be achieved, which can advantageously be adapted to the field of view of the detector. In another preferred embodiment the radiation units are arranged in a honeycomb pattern. This means that the radiation units are arranged in a hexagonal pattern.

The window is preferably part of a housing in which the

radiation units are arranged and the window is the only part of the housing where the electromagnetic radiation can pass through. Therefore, the points of the highest intensities are encapsulated inside the housing, where they are not considered for safety standards. It is preferred that the radiation units are arranged in atmosphere. Therefore and because the radiation units are arranged such that they are thermally decoupled, it is

advantageously sufficient to use air cooling for cooling of the radiation units.

In the following the invention is explained on the basis of schematic drawings.

Figure 1 shows a cross section of a radiator according to the invention,

Figure 2 shows a diagram of an intensity distribution on a cross direction perpendicular to an optical axis of the

radiator and

Figures 3 and 4 show top views of two embodiments of the radiator .

Figure 1 shows a radiator 1 that comprises a first radiation unit 4, a second radiation unit 5 and a third radiation unit 6. It is conceivable that the radiation units 4, 5, 6 are

individually operatable or, as an alternative, the radiation units 4, 5, 6 are operatable together in cooperation. The first radiation unit 4 comprises a first optical axis 7, the second radiation unit 5 comprises a second optical axis 8 and the third radiation unit 6 comprises a third optical axis 9. Each radiation unit 4, 5, 6 is adapted to emit electromagnetic radiation in the shape of a diverging radiation cone being substantially rotationally symmetric around the respective optical axis 7, 8, 9, wherein a first radiation cone 10 is assigned to the first radiation unit 4, a second radiation cone 11 is assigned to the second radiation unit 5 and a third radiation cone 12 is assigned to the third radiation unit 6. Each radiation unit 4, 5, 6 comprises a pump source 16 for generating the electromagnetic radiation. The pump source 16 is the main cause for heat production in the radiation units 4, 5, 6. This is especially the case if laser units are used for the radiation units 4, 5, 6.

The radiation units 4, 5, 6 are arranged within a housing 2 such that their optical axes 7, 8, 9 are parallel and that the radiation units 4, 5, 6 are oriented in the same direction. The radiation units 4, 5, 6 are arranged in a transversal direction to the optical axes 7, 8, 9 adjacent to each other in a row and in the order of the first 4, the second 5 and the third 6 radiation unit. The housing 2 comprises a window 3 which is arranged such that all radiation cones 10, 11, 12 can pass through the window 3 and the window 3 has a distance 22 to the radiation units 4, 5, 6. The window 3 is arranged perpendicular to the optical axes 7, 8, 9 but other arrangements are also conceivable. It is preferred that the housing 2 encapsulates the radiation units 4, 5, 6 and the window 3 is the only part of the housing 2 where the electromagnetic radiation can pass through. The radiator 1 further comprises a trigger generator 15 which can be used to control the radiation units 4, 5, 6 such that they emit the electromagnetic radiation

simultaneously .

The distance 26 between adjacent radiation units 4, 5 and 5, 6 is chosen such that the adjacent radiation units 4, 5 and 5, 6 are thermally decoupled so that each radiation unit is

thermally unaffected due to heat emission by the adjacent units. This means that substantially no heat is transferred to each radiation unit from the adjacent radiation units. The radiation cones 10, 11, 12 define an illumination area 13 being the area where all the illumination cones 10, 11, 12 overlap. It is preferred that an object to be illuminated is arranged within the illumination area 13 since this is the area with the highest intensity. The illumination area 13 has the shape of a cone and comprises an illumination origin 17 being the tip of the cone and having a distance 24 to the window 3. The illumination origin 17 is the closest point of the

illumination area 13 to the radiation units 4, 5, 6 and according to the invention the window 3 is arranged between the radiation units 4, 5, 6 and the illumination origin 17. The exact location of the illumination origin 17 depends on the beam divergence of the radiation cones 10, 11, 12 and the distance 27 between the outermost radiation units. By

increasing the number of the radiation units the distance between the outermost radiation units 4, 6 increases and therefore the illumination origin 17 is moved away from the radiation units while increasing the intensity in the

illumination area 13. By increasing the number of the radiation units it is advantageously achieved that objects further away from the radiation units can be illuminated with a sufficient intensity for a precise distance measurement.

As it can be seen in Figure 1, a first intersection point 18 is formed where the first radiation cone 10 and the second

radiation cone 11 intersect and a second intersection point 19 is formed where the second radiation cone 11 and the third radiation cone 12 intersect. Since the window 3 is

perpendicular to the optical axes 7, 8, 9 both intersection points 18, 19 have the same distance 23 to the window 3. In Figure 1, the window 3 is arranged between the radiation units 4, 5, 6 and the intersection points 18, 19. Therefore, the intensity adjacent to the window 3 on the side facing away from the radiation units 4, 5, 6 can be attributed to the

corresponding radiation unit 4, 5 or 6 and the safety

certification can be performed with respect to a single

radiation unit. In another conceivable embodiment the window 3 is arranged between the intersection points 18, 19 and the illumination origin 17.

The window 3 according to Figure 1 is an optical diffuser which increases the opening angle of the radiation cones 10, 11, 12 such that the radiation cones 10, 11, 12 have an original beam divergence angle 20 immediately after emission and after passing the window 3 a modified beam divergence angle 21 which is larger than the original beam divergence angle 20. A

scattering disk can for example be used as the optical diffuser. The scattering disk can also function as a beam homogenizer .

Figure 2 shows a diagram of an intensity profile in which an intensity 28 in a cross section 36 perpendicular to the optical axes 7, 8, 9 is plotted versus a cross direction 29. The cross section 36 has such a distance 25 to the window 3 that it crosses the illumination area 13. The intensity profile is the sum of the individual intensity profiles of each radiation unit 4, 5, 6. Immediately after emission each individual intensity profile has substantially a Gaussian shape in a direction perpendicular to its optical axis. After passing through the homogenizer the Gaussian profiles are changed towards a

rectangular profile which is assumed for the individual

intensity profiles in Figure 2.

As it can be seen in Figure 2 the global maximum of the

intensity I ₃ 32 is located in the illumination area 13 which is located in the centre of the intensity profile and is the region where the three illumination cones 10, 11, 12 of Figure 1 overlap. The length over which the intensity 28 is constant I3 corresponds to the width 14 of the illumination area 13 in the cross section 36. The intensity decreases from the centre of the intensity profile to radial outside in a step like manner under the assumption that each radiation unit (4, 5, 6) has the rectangular intensity profile. First, the intensity 28 decreases to an intensity I ₂ 31 which either corresponds to an overlap of the first 10 and the second 11 radiation cone or to an overlap of the second 11 and the third 12 radiation cone. Then the intensity decreases to an intensity Ιχ 30 which corresponds to the first 10 or third 12 radiation cone. Ii is the intensity of the single radiation units 4, 5, 6,

respectively, in the cross section and under the assumption that all radiation units 4, 5, 6 emit the same amount of light, it is: I ₂ = 2*Ii and I ₃ = 3*Ii. The length over which the intensity 28 is constant Ιχ or I ₂ corresponds to the distance 26 between the adjacent radiation units 4, 5 and 5, 6. In the embodiment according to Figure 3, radiation units 35 are arranged in a first pattern 33 which has the shape of a two dimensional array. Vertically and horizontally adjacent

radiation units always have the same distance 26 to each other.

In the embodiment according to Figure 4, radiation units 35 are arranged in a second pattern 34 which comprises a circle on which six radiation units 35 are arranged on. In the centre of the circle another radiation unit 35 is arranged. The radius of the circle is the distance 26 between adjacent radiation units which is identical to the distance 26 between adjacent

radiation units arranged on the circle. It is also conceivable that the second pattern 34 comprises further circles arranged concentric to the circle. It is preferred that the further circles have the distance 26 to their adjacent circles and that the radiation units 35 arranged on the further circles have also the distance 26 to their adjacent radiation units.

The radiation units 4, 5, 6, 35 can for example be diode lasers which emit the electromagnetic radiation in the infrared wavelength region.

In the following, the invention is explained on the basis of an example .

An inventive radiator 1 for illuminating an object with a predetermined intensity comprises from six to 124 radiation units 4, 5, 6, 35 of the type triple stack, 75 W, 905 nm. The radiation units 4, 5, 6, 35 are capable of emitting

electromagnetic radiation in the shape of a diverging radiation cone 10, 11, 12 arranged around the optical axis 7, 8, 9 of each radiation unit 4, 5, 6, 35. The radiation units 4, 5, 6, 35 are arranged such that the optical axes 7, 8, 9 are

substantially parallel and the radiation cones 10, 11, 12 are oriented in the same direction. The radiation units 4, 5, 6, 35 are arranged transversal to the optical axes 7, 8, 9 in a honeycomb pattern, or equivalently in a hexagonal pattern, wherein each distance 26 of a radiation unit to an adjacent unit is equal and ranges from 5 mm to 30 mm. The radiation units 4, 5, 6, 35 can be operated to simultaneously emit the electromagnetic radiation, wherein the electromagnetic

radiation is emitted in light pulses with a duration in the order of nanoseconds. The radiation units 4, 5, 6, 35 are arranged in a housing 2 that comprises a window 3 being

transparent for the electromagnetic radiation and being the only part of the housing where the electromagnetic radiation can pass through. The window 3 is arranged such that all the radiation cones 10, 11, 12 can pass through. The distance 22 between the window 3 and the radiation units 4, 5, 6, 35 is from 5 mm to 30 mm. The pulse energy of each radiation unit 4, 5, 6, 35 on the opposite side of the window 3 to the laser units 4, 5, 6, 35 is between 100 nJ and 500 nJ. The window 3 is an optical diffuser which increases the beam divergence angle 21 after the window 3 to a value from 40 ° to 80 °. An object arranged in a distance between 0.5 m and 20 m can be

illuminated with the radiator 3 such that the intensity is sufficient for a precise distance measurement. It is

advantageously sufficient to use air cooling for the radiator 1.

In another conceivable example four of five radiation units 4, 5, 6, 35 can be used which are for example arranged on a rectangle or on a circle.

List of reference signs

1 radiator

2 housing

3 window

4 first radiation unit

5 second radiation unit

6 third radiation unit

7 first optical axis

8 second optical axis

9 third optical axis

10 first radiation cone

11 second radiation cone

12 third radiation cone

13 illumination area

14 width of illumination area at cross section 36

15 trigger generator

16 pump source

17 illumination origin

18 first intersection point

19 second intersection point

20 original beam divergence angle

21 modified beam divergence angle

22 distance radiation unit - window

23 distance window - first intersection point

24 distance window - illumination origin

25 distance window - cross section 36

26 distance between adjacent radiation units

27 distance between outermost radiation units 28 intensity

29 cross direction

30 intensity Ii

31 intensity I ₂

32 intensity I3

33 first pattern

34 second pattern radiation unit cross section