Head tracking system

Abstract

 The present invention relates to a method for tracking a head of an occupant (41) of a vehicle (40). According to the method, a reference signal (46) is sent from a predetermined location with respect to the vehicle (40). The reference signal (46) is received at a headphone (20) worn by the occupant (41). A receive direction of the reference signal (46) is determined with respect to the headphone (20). A direction, in which the head of the occupant (41) is directed, is determined based on the receive direction and the predetermined location. The predetermined location, from where the reference signal (46) is sent, is a passenger compartment illumination device of the vehicle (40).

Description

[0001] The present application relates to a method for tracking ahead of an occupant of a vehicle, to a head tracking system for a vehicle, and to an audio reproduction system generating a virtual surround sound for a user using the head tracking system.

Related art

[0002] Head tracking systems are used to detect different types of movements of the head. For example, a gyroscope may be used to detect a turning of the head around the longitudinal axis of the head, i.e., in a horizontal plane of the head. The gyroscope may detect an angular acceleration.

[0003] Furthermore, EP 2012170 A1 discloses a method for operating a head tracking system, in which a stationary reference point is detected and a position of a head equipped with the head tracking system is determined based on the detected reference point. According to an embodiment, light is emitted from the reference point and the stationary reference point is detected by detecting the emitted light. The stationary reference point based detection may be used to calibrate detecting means for detecting a position of the head or may be used exclusively for detecting the position of the head. However, when such a head tracking is used in a vehicle, a stationary reference point is needed at an appropriate position for users sitting on front seats, as well as on back seats of the vehicle. Furthermore, a power supply at the position of the stationary reference point is needed for emitting a signal or light from the reference point.

[0004] Accordingly, there is a need to provide a head tracking system for a vehicle which can easily be installed at low cost and which is usable by users on front seats as well as on back seats of the vehicle.

Summary of the invention

[0005] According to the present invention, a method for tracking ahead of an occupant of a vehicle is provided. According to the method, a reference signal is sent from a predetermined location with respect to the vehicle, and the reference signal is received at a headphone worn by the occupant. A receive direction of the received reference signal is determined with respect to the headphone, and a direction in which the head of the occupant is directed is determined based on the receive direction and the predetermined location. The predetermined location, from where the reference signal is sent, is a passenger compartment illumination device of the vehicle. By sending the reference signal from the passenger compartment illumination device which may be arranged at a ceiling of the vehicle, the reference signal may be receive at headphones worn by occupants sitting on front or rear seats of the vehicle. Furthermore, a power supply for the compartment illumination device is usually present which may be used to generate the reference signal. Therefore, no additional power supply and corresponding cables have to be provided for generating and sending the reference signal. The sent reference signal may comprise an infrared signal, a radio frequency signal, or a magnetic field. These kinds of reference signal may be easily detectable by a corresponding unit arranged at the headphones worn by the occupant and will not disturb or annoy a driver of the vehicle.

[0006] According to an embodiment, the sent reference signal is an infrared signal emitted by an infrared diode mounted on the passenger compartment illumination device. An infrared signal is not visible to occupants, and will therefore not be considered to be annoying. Furthermore, an infrared diode is a small device which may be easily mounted on or be comprised in the passenger compartment illumination device. A direction sensitive receiver receiving the reference signal at the headphone based on infrared light is for example known from EP 2102170 A1. The infrared diode may be powered with electrical energy provided at the passenger compartment illumination device of the vehicle. Therefore, no additional cabling for providing electrical energy to the infrared diode is needed. As especially in optical head tracking systems no synchronisation between the sender and the receiver is necessary, the sender may be provided with electrical energy provided at the passenger compartment illumination device and no additional cabling for a synchronisation is necessary. However, other methods utilising, e.g., radio frequency signals or a magnetic field may also be used and a corresponding sender may also be integrated in or may be mounted on the passenger compartment illumination device and may be powered by electrical energy provided to the passenger compartment illumination device.

[0007] According to the presentation invention, a method for reproducing audio data via a headset to an occupant of a vehicle is provided. According to the method, a head of the occupant is tracked according to the above described method for tracking a head of an occupant of a vehicle. The audio data to be reproduced is adapted based on the direction in which the head of the occupant is directed. The adapted audio data is output via the headphones to the occupant. Such a method for reproducing audio data via the headset allows to provide stereo or surround audio data to the occupant whereby the occupant gets the impression that the audio data, especially the stereo and surround effects, have a fixed special relation to the interior of the vehicle, even when the occupant is moving the head.

[0008] According to the present invention, a head tracking system for a vehicle is provided. The system comprises a sender, a direction sensitive receiver, and a processing unit. The sender is configured to send a reference signal from a predetermined location with respect to the vehicle to a headphone to be worn by an occupant of the vehicle. The direction sensitive receiver is mounted on the headphone and configured to receive the reference signal and to determine a receive direction from which the reference signal is received. The processing unit is configured to determine a direction in which the head of the occupant is directed with respect to the vehicle. The direction is determined based on the receive direction of the direction sensitive receiver and the predetermined location where the sender is located. The sender is mounted on the passenger compartment illumination device of the vehicle. By mounting the sender on the passenger compartment illumination device, which is usually arranged at a ceiling of a vehicle, an appropriate coverage of the interior of the vehicle can be reached to send the reference signal to direction sensitive receivers of headphones worn by occupants sitting on rear and front seats of the vehicle. Furthermore, as at a passenger compartment illumination device a power supply is available, no additional wiring for providing electrical power to the sender is needed.

[0009] According to an embodiment, the sender comprises an infrared light emitter, a radio frequency sender or a magnetic field generator. Depending on the kind of direction sensitive receiver, a corresponding sender may be selected and mounted on the passenger compartment illumination device. The sender may comprise an infra-red light emitter diode which may be easily integrated into the passenger compartment illumination device due to its small form factor. The infra-red light emitter diode may be coupled to a power supply of the passenger compartment illumination device and therefore no additional cabling for operating the infra-red light emitter diode is needed.

[0010] According to the present invention, an audio reproduction system is provided. The audio reproduction system comprises a head tracking system as described above, an audio input for receiving audio date to be output to the occupant, and a processing unit configured to adapt the audio data based on the direction in which the head of the occupant is directed. The audio data may comprise especially stereo or surround sound and may be adapted such that dependent from an orientation of the head of the occupant, the occupant gets the impression that the stereo or surround sound is reproduced by loudspeakers arranged at fixed positions in the vehicle.

[0011] According to another aspect of the present invention, a vehicle is provided comprising a head tracking system and an audio reproduction system as defined above. Occupants of the vehicle may listen to audio data, especially stereo or surround audio data, in such a way that independent from a location where the occupant is sitting and the direction in which the occupants moves the head, the occupant gets the impression that the audio data is emitted from a plurality of loudspeakers which are arranged at fixed locations with respect to the vehicle.

[0012] Although specific features described in the above summary and the following detailed description are described in connection with specific embodiments, it is to be understood that the features of the embodiment described may be combined with each other unless it is noted otherwise.

Brief description of the drawings

[0013] In the following, the head tracking system will be described in more detail with reference to the accompanying drawings.

Figure 1 shows a schematic view of a head tracking system according to an embodiment of the present invention.

Figure 2 shows a schematic view explaining the generation of a virtual surround sound using headphones.

Figure 3 shows a direction sensitive receiver which may be used in the head tracking system of figure 1.

Figure 4 shows a diagram explaining the functioning of the direction sensitive receiver of figure 3.

Figure 5 shows a schematic view of a vehicle comprising a head tracking system and an audio reproduction system according to an embodiment of the present invention.

Figure 6 shows a flow chart describing steps for generating a virtual surround sound for a user.

Detailed description

[0014] In the following, exemplary embodiments of the present invention will be described in detail. It is to be understood that the following description is given only for the purpose of illustrating the principles of the invention and is not to be taking in a limited sense. Rather, the scope of the invention is defined only by the appended claims and not intended to be limited by exemplary embodiments hereinafter.

[0015] It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other unless specifically noted otherwise. Same reference signs in the various instances of the drawings referred to similar or identical components.

[0016] It is also to be understood that in the following detailed description of the exemplary embodiments, any direct connection or coupling between functional blocks, devices, components or other physical or functional units shown in the drawings or described herein could also be implemented by an indirect connection or coupling.

[0017] Figure 1 shows schematically a head tracking system comprising one or more reference signal senders, e.g., light sources 10, emitting light to a direction sensitive receiver 100 mounted on headphones 20. The sender 10 can be a light emitting diode LED, emitting light in a predetermined frequency range, e.g., infrared light. In the following description, the sender will be assumed as a light source. However, the present application is not restricted to senders based on light, and the methods and systems described herein may also utilise instead of a light source a radio frequency sender or a magnetic field generator and corresponding direction sensitive receivers. The infrared frequency range of the light source 10 may be used in order not to disturbed a user wearing the headphones 20. As will be explained with reference to figures 2-4 in the following, the light emitted by the LED 10 generates a light spot on the direction sensitive receiver 100. The position of the light spot on the direction sensitive receiver 100 is used to determine the head position of the user wearing the headphones 20. The LED 10 may be mounted on a passenger compartment illumination device of the vehicle as will be shown in connection with figure 5, and may transmit the light in direction of the user wearing the headphones 20. The system shown in figure 1 may be part of a rear seat vehicle entertainment system in which a user sitting on the back seat of a vehicle hears music or watches a film, the audio signals of which are consumed using the headphones 20. With the present disclosure, it is possible to generate virtual surround sound for the user wearing the headphones as will be explained with reference to figure 2.

[0018] Determination of the head position is necessary for generation of a virtual surround sound. In a virtual surround sound using headphones, a listening impression is generated as if the user used a five or seven loudspeaker sound system as shown in figure 2 showing a system of five loudspeakers 50. The virtual surround sound field gives the listener the impression as if the sound source is stable localised in a virtual room, even if the user is turning the head. This phenomenon is known as acoustical room-constancy allows the user using headphones to stable determine the direction from where the sound is coming. The user also experiences an interactive listening process with the system when turning the head, corresponding to the real world situation, since it is possible to localise the sound source stable outside of the head with correct front and back position.

[0019] A room-constant localisation of audio data when listening through a standard headphone 20 becomes possible by tracking the position of the head and by determining filters for the determined head position which are used for adapting the audio signal, e.g., by convolution of the audio signal with the filters.

[0020] These filters can be generated in the following way using a dummy head with microphones in each ear and measuring binaural room impulse responses. To this end, the dummy head is positioned in the location, e.g., in the vehicle, where the system should be used. Different positions of the dummy head, e.g. different rotations, are used and for each head position the loudspeakers 50 as shown in figure 2 output the sound that is detected by the microphones in the dummy head. This may be repeated for different head rotations. The audio signals are detected for each of the loudspeakers 50 and for the different head positions generating a plurality of impulse responses. Based on the impulse responses a filter element is determined for each head position. When a stereo sound system is then filtered using a filter for a determined head position by determining a real-time convolution of the audio signal with the filter, the virtual surround sound can be obtained in which the user using the headphones has the impression as if the audio signal came from a sound system as shown in figure 2.

[0021] The head tracking system used to generate the virtual surround sound will now be explained in more detail with reference to figures 3 and 4.

[0022] Figure 3 shows a direction sensitive receiver 100 as it is known from EP 2012170 A1. Light emitted by a light source, such as the LED 10 is focused on the direction sensitive receiver 100 using a lens (not shown). The direction sensitive receiver which is positioned in the focal plane of the lens receives the light emitted by the light source 10 and a light spot is generated on the direction sensitive receiver 100. Depending on an arrangement of the light source 10 with respect to the direction sensitive receiver 100, the light spot is located at an X-Y-position as shown in figure 3. An implementation of the direction sensitive receiver 100 will be explained in more detail with reference to figure 4.

[0023] In the upper part of figure 4 a cross-sectional view of the direction sensitive receiver 100 is shown. The receiver 100 comprises a PIN structure, P indicating a P-doped semiconductor layer, I designating a nominally undoped or low-doped (insulating) semiconductor layer, and N designating an N-doped semiconductor layer. A back contact ko is coupled with the N-doped layer of the structure approximately in the middle thereof. At opposite sides contacts k₁ and k₂, contact the P-doped layer. In order to provide a two-dimensional sensing, additional contacts (not shown) are provided in a direction perpendicular to the contacts shown.

[0024] Such a receiver uses the so-called lateral photo effect for position sensing. A total current is supplied via contact ko. An arrow label Φ indicates a position where light falls on the receiver 100. At the area where the light falls on the receiver, the device becomes conducting in a traverse direction (up-down-direction in figure 4). In the p-axis in the middle of figure 4, this location is designated p₁.

[0025] Assuming that the resistance of the N-doped layer is low, the resistance from k ₀ to k₁ (Rq1 and Rq2), respectively, as shown in the lower part of figure 4) are determined by the position p₁ where light falls on the sensor. Currents I₁, I₂ detected at k₁, k₂, respectively, are indicative of the position. In particular, in the dimension shown in the position p₁ relative to the middle of the sensor is proportional to (I₁-I₂) / (I₁+I₂).

[0026] Similar considerations hold true for the two-dimensional receiver. With the above-described direction sensitive receiver, the above give ratio of currents does not depend on the light-intensity received by the receiver, such that the distance from the light source 10 to the direction sensitive receiver does not influence the result.

[0027] Referring back to figure 3, this means that a light spot in the active area of the receiver 100 having a length L describes the head rotation alone (in a one-dimensional case) or the head rotation and the "nodding position" of the head in case of a two-dimensional receiver.

[0028] As can be seen from the descriptions above, the head tracking system needs a lightsource 10 arranged apart from the headset at a fixed location with respect to the vehicle. Furthermore, the light source 10 should be arranged such that light from the light source can be reliably received by the direction sensitive receiver 100 mounted at a headphone worn by an occupant of the vehicle.

[0029] Figure 5 shows such an arrangement of the light source 10. The light source 10 is mounted on or comprises in a passenger compartment illumination device of a vehicle 40. By arranging the light source 10 near or in the passenger compartment illumination device at a ceiling of passenger compartment wiring and installation space may be saved. A power supply comprising, e.g. a 12 volt DC current is usually provided at the compartment illumination device and may be used to power the light source. Furthermore, due to the small form factor of the light source, e.g. an LED, the light source can be easily integrated in an illumination device or mounted near the illumination device, e.g. in a console carrying the illumination device. Traditionally, the light source may be installed near a video monitor arranged on a dashboard or in headrests of the vehicle 40.

[0030] However, this requires additional installation space and a wiring for providing a power supply to the light source. By arranging the light source in combination with a passenger compartment illumination, e.g. in a front seat area or a back seat area of the vehicle 40, installation space in the dashboard and the headrests can be saved and therefore a larger video monitor may be used. Furthermore, additional cost for wiring a power supply to the light source can be saved.

[0031] Figure 5 furthermore shows schematically components of an audio reproduction system 42 of the vehicle 40. The audio reproduction system 42 comprises a head tracking system comprising the light sender 10, the direction sensitive receiver 100 and a processing unit 44. The light sender 10 is arranged at a passenger compartment illumination device at the ceiling of the vehicle 40 and configured to send a reference signal 46 to a headphone 20 worn by an occupant 41 of the vehicle 40. The direction sensitive receiver 100 is mounted on the headphone 20 and is configured to receive the reference signal 46 and to determine the receive direction of the reference signal 46 as described above in connection to figures 1, 3 and 4. The processing unit 44 is configured to determine a direction in which the head of the occupant 41 is directed based on the receive direction and the known location of the light sender 10. The audio reproduction system 42 comprises an audio input for receiving audio data to be output to the occupant 41. The audio input may comprise, e.g., a multi-media player or a CD player 45 providing e.g. music or speech to be output to the occupant 41. The audio re-production system 42 comprises furthermore a processing unit 43 configured to adapt the audio data based on the direction in which the head of the occupant 41 is directed. Adapting the audio data has been described above in connection with figure 2.

[0032] In figure 6, method steps carried out for determining the natural surround sound for the occupant 41 wearing headphones 20 are summarised. In step 61, a reference signal 46 is sent from a predetermined location of the vehicle 40. The predetermined location is the passenger compartment illumination device comprising, e.g. a light source emitting the reference signal. In step 62 the reference signal 46 is received at the direction sensitive receiver 100 mounted on the headphone 20 worn by the occupant 41. In step 63, a receive direction of the reference signal 46 is determined by the direction sensitive receiver 100 with respect to the headphone 20 and thus with respect to the head of the occupant 41. In step 64, a direction in which the head of the occupant 41 is directed is determined based on the receive direction and the predetermined location of the light source 10. In step 65, audio data to be output to the occupant 41 is adapted based on the determined head direction. Finally, the audio data is output in step 66 via the headset 20 to the occupant 41.

[0033] While exemplary embodiments have been described above, various modifications may be implemented in other embodiments. For example, the light source 10 may be arranged in a compartment illumination device which is arranged above front seats of the vehicle or above backseats of the vehicle. Furthermore, the compartment illumination device may be arranged centred with respect to a lateral direction of the vehicle or may be arranged near doors of the vehicle. Furthermore, a plurality of light sources 10 may be arranged at a plurality of passenger compartment illumination devices. The plurality of light sources may emit light at different wave lengths to be distinguishable by the direction sensitive receivers. Furthermore, the plurality of light sources may emit pulsed reference signals with different pulse patterns.

[0034] Finally, it is to be understood that all the embodiments described above are considered to be comprised by the present invention as it is defined by the appended claims.

Claims

1. A method for tracking a head of an occupant of a vehicle, the method comprising:

- sending (61) a reference signal (46) from a predetermined location with respect to the vehicle (40),

- receiving (62) the reference signal (46) at a headphone (20) worn by the occupant (41),

- determining (63) a receive direction of the received reference signal (46) with respect to the headphone (20), and

- determining (64) a direction in which the head of the occupant (41) is directed based on the receive direction and the predetermined location, Wherein the predetermined location, from where the reference signal (46) is sent, is a passenger compartment illumination device of the vehicle (40).

2. The method according to claim 1, wherein the sent reference signal (46) is an infrared signal, a radio frequency signal or a magnetic field.

3. The method according to claim 1 or 2, wherein the sent reference signal (46) is an infrared signal emitted by an infrared diode mounted on the passenger compartment illumination device.

4. The method according to claim 3, wherein the method further comprises:

- powering the infrared diode with electrical energy provided at the passenger compartment illumination device of the vehicle (40).

5. A method for reproducing audio data via a headset to an occupant of a vehicle, the method comprising:

- tracking a head of the occupant (41) according to any one of the preceding claims,

- adapting (65) the audio data based on the direction in which the head of the occupant (41) is directed, and

- outputting (66) the adapted audio data via the headphone (20) to the occupant (41).

6. A head tracking system for a vehicle, the system comprising:

- a sender (10) configured to send a reference signal (46) from a predetermined location with respect to the vehicle (40) to a headphone (20) to be worn by an occupant (41) of the vehicle (40),

- a direction sensitive receiver (100) configured to receive the reference signal (46) and to determine a receive direction of the reference signal (46), wherein the direction sensitive receiver (100) is mounted on the headphone (20), and

- a processing unit (43) configured to determine a direction in which the head of the occupant (41) is directed based on the receive direction and the predetermined location,
wherein the sender (10) is mounted on a passenger compartment illumination device of the vehicle.

7. The head tracking system according to claim 6, wherein the sender (10) comprises an infrared light emitter, a radio frequency sender or a magnetic field generator.

8. The head tracking system according to claim 6 or 7, wherein the sender (10) comprises an infrared light emitter diode comprised in the passenger compartment illumination device.

9. The head tracking system according to claim 8, wherein the infrared light emitter diode is coupled to a power supply of the passenger compartment illumination device.

10. An audio reproduction system, comprising:

- a head tracking system according to any one of claims 6-9,

- an audio input (45) for receiving audio data to be output to the occupant (41), and

- a processing unit (44) configured to adapt the audio data based on the direction in which the head of the occupant (41) is directed.

11. A vehicle, comprising a head tracking system according to any one of claims 6-9 or comprising an audio reproduction system (42) according to claim 10.

Drawing