SENSING APPARATUS FOR SENSING A MOVEMENT

FIELD OF THE INVENTION

The invention relates to a sensing apparatus, a sensing method and a computer program for sensing movements of at least two parts of an object. The invention further relates to a vehicle comprising the sensing apparatus for sensing movements of at least two parts of an object.

BACKGROUND OF THE INVENTION

US 2007/0181810 Al discloses an apparatus for a vehicle light detection and ranging system (LIDAR system) for sensing a region close to a vehicle. The apparatus comprises a plurality of semiconductor lasers and an optical element mounted with respect to the plurality of lasers so that at least two of the plurality of lasers produce beams that emanate from the optical element in different directions. A control circuitry is coupled to the plurality of semiconductor lasers and configured to sequentially and separately activate at least two of the plurality of lasers. Light from the produced emanated beams is reflected by objects in the environment of the vehicle and the reflected light is detected so as to provide information about the objects to vehicle operators and/or passengers.

This apparatus for a vehicle LIDAR system has the drawback that it cannot distinguish whether an object in the environment of the vehicle is a living object like an animal or a human being, for example, a child playing around the vehicle or a burglar approaching the vehicle, or a non-living object like another vehicle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sensing apparatus, a sensing method and a computer program for sensing movements of at least two parts of an object, which allows to determine whether a living object like a human being or an

animal or a non-living object like a vehicle is moving. It is a further object of the present invention to provide a corresponding vehicle, which comprises the sensing apparatus.

In an aspect of the present invention a sensing apparatus for sensing movements of at least two parts of an object is presented, wherein the sensing apparatus comprises:

- a movement determination unit for determining whether the at least two parts belong to the same object and for determining the movements of the at least two parts,

- a movement comparison unit for comparing the movements of the at least two parts, wherein the movement comparison unit is adapted for applying a similarity measure to the movements of the at least two parts and for determining whether the movements of the at least two parts are similar with respect to the similarity measure.

The invention is based on the idea that, generally, different parts of a living object, for example, an arm and a breast of a human being, move differently with respect to each other, whereas, generally, different parts of a non-living object, for example, of a car approaching the sensing apparatus, move in the same manner. Thus, by determining the movements of at least two parts of the same object and by comparing the determined movements of the at least two parts, in particular, by determining if these movements are similar movements or different movements, it can be determined whether the object is a living object like a burglar or a playing child or a non-living object like a vehicle.

In an embodiment, the movement determination unit is adapted to determine the movements of the at least two parts, only if the at least two parts belong to the same object, and the movement comparison unit is adapted to compare the movements of the at least two parts, only if the at least two parts belong to the same object.

It is preferred that the movement determination unit is adapted to determine whether the at least two parts belong to the same object by determining a first distance between a first part of the at least two parts and the sensing apparatus and by determining a second distance between a second part of the at least two parts and the sensing apparatus, wherein the movement determination unit is adapted to determine that

the movements of the at least two parts belong to the same object, if an absolute difference between the first distance and the second distance is smaller than a predefined value. Since elements which belong to the same object generally exhibit an absolute difference between the first distance and the second distance which is smaller than a predefined value, by determining these distances and by comparing these distances, it can easily be determined whether the at least two elements belong to the same object or not. Preferably, the predefined value is defined by the smallest geometric dimension, i.e. size, of the object whose movement is expected to be sensed and which is preferably a human being, wherein, in this case, the predefined value is preferably equal to the width between shoulders. The predefined value is therefore preferably smaller than 100 cm, more preferably smaller than 50 cm and even more preferably smaller than 25 cm. In an embodiment, the predefined value is 50 cm, in particular, if the object is expected to be an adult, e.g. a burglar, and in another embodiment, the predefined value is 20 cm, in particular, if the object is expected to be a child. At first, generally, it is not known whether the at least two parts of an object belong to the same object or to different objects. The movement determination unit determines therefore whether the at least two parts belong to the same object, because if the at least two parts belong to the same object, it can be determined whether the object is a living or a non-living object, depending on the comparison of the movements of the at least two parts of the object. The at least two parts can also be denoted as at least two elements, wherein the at least two elements can be portions of, for example, a human being or of a component of a car.

In a preferred embodiment, the movement determination unit is adapted for determining the movements of the at least two parts by determining at least two velocities of the at least two parts, wherein the movement comparison unit is adapted for applying the similarity measure by determining a velocity difference between the at least two velocities and wherein the movement comparison unit is adapted for determining whether the movements of the at least two parts are similar with respect to the similarity measure by determining whether the determined velocity difference is within a predetermined velocity range. Thus, in this embodiment, the movements of the at least two parts of the object are determined as the velocities of these parts and these velocities are regarded as being similar if the difference between them is within a predefined

velocity range. Since, in general, the velocity of a first part of a living object differs from the velocity of a second part of the object, by comparing these two velocities it can be determined whether the object is a living object or a non-living object. The velocity range is preferably predetermined such that, if the determined velocity difference is outside of the predetermined velocity range, this determined velocity difference cannot be caused by errors of measurement only. In particular, two velocities are regarded as being similar if the absolute value of the corresponding velocity difference is smaller than 5 percent, preferably smaller than 3 percent and more preferably smaller than 1 percent of the absolute value of the average velocity of the at least two velocities. It is further preferred that the movement determination unit is further adapted for determining at least two locations of the at least two parts of the object at different points in time and for determining distances between the at least two parts from the determined at least two locations of the at least two parts at different points in time, wherein the movement comparison unit is further adapted for applying a similarity measure by determining whether differences between the distances, which have been determined at different points in time, are within a predetermined distance range. Thus, the movements of the at least two parts of the object are determined as the change of the relative distance between these at least two parts in a certain time interval, wherein the movements of the at least two parts are regarded as being similar if the absolute changes of the relative distance between these at least two parts are smaller than a predetermined difference value, i.e. are within a predetermined distance range, or if this relative distance does not change at all with respect to a certain period of time. Since the relative distance of at least two parts of a living object like a human being or animal generally changes in time and this distance does not generally change in time for a non-living object like a vehicle, it can be determined whether an object is a living object or a non-living object by determining whether the determined differences are within a predetermined difference range or not. Preferably, the predetermined difference range is chosen in such a way that a difference between the distances, which have been determined at different points in time, which is outside of the predetermined difference range, cannot be caused by errors of measurement only. Preferably, distances between the at least two parts of the object are regarded as being similar if the difference is smaller than 5 percent, preferably smaller than 3 percent and more preferably smaller than 1 percent of the absolute value of the

distance between the two parts of the object, in particular of the two measurement points at which the distances are measured.

It is further preferred that the movement determination unit is adapted for determining the movements of the at least two parts by determining at least two velocities of the at least two parts, by determining at least two locations of the at least two parts of the object at different points in time and by determining the distances between the at least two parts from the determined at least two locations of the at least two parts at different points in time, wherein the movement comparison unit is further adapted for applying a similarity measure by determining whether the determined velocity difference is within a predetermined velocity range and whether differences between the distances, which have been determined at different points in time, are within a predetermined distance range. This means that it can be decided whether an object is a living object or a non-living object, based on the result of the application of the similarity measure, which determines whether the determined velocity difference is within the predetermined velocity range and whether the distances, which have been determined at different points in time, are within a predetermined difference range. Thus, the velocities and the distances are considered, thereby improving the quality of a decision concerning living or non-living objects, based on the comparison by the movement comparison unit.

In a preferred embodiment, the movement determination unit is adapted for determining the movements of the at least two parts by determining at least two velocities of the at least two parts, wherein the movement determination unit is further adapted for determining at least two locations of the at least two parts of the object for determining distances between the at least two parts, and wherein the movement determination unit is adapted for measuring the at least two velocities and the at least two locations simultaneously. Thus, in this embodiment the movement is determined by determining the velocities of the at least two parts and the locations of the at least two parts simultaneously. This allows to determine simultaneously, or at least shortly after one another, whether the determined velocity differences are within a predetermined velocity range and whether differences between distances determined at different points in time are within a predetermined distance range , thereby increasing the quality of the decision whether an object is a living object or a non-living object, if the decision is based on velocity differences and changes in the distance between the at least two parts

of the object in a certain time interval.

It is preferred that the movement determination unit is adapted for determining the movements of the at least two parts within a predefined sensitivity distance from the sensing apparatus. This allows to limit the area, in which objects can be sensed, to a predefined area which is defined by the sensitivity distance. Objects which are outside of this sensing region are not considered and do not influence or disturb the sensing of the sensing region.

It is further preferred that the sensing apparatus comprises a signal generation unit for generating a signal if the movement determination unit determines that the at least two parts belong to the same object and the movement comparison unit determines that the movements of the at least two parts are not similar with respect to the similarity measure. This allows to output a warning if it is likely that the movement of a living object, in particular of a human being or an animal, is sensed by the sensing apparatus. For example, a signal can be generated if a burglar approaches a vehicle or if a child is playing around the vehicle. The generated signal is, for example, an acoustic and/or optical signal.

In a preferred embodiment, the sensing apparatus further comprises an object presence determination unit for determining whether an object is present within a predefined area and a control unit for controlling the movement determination unit and/or the movement comparison unit, wherein the control unit is adapted for activating the movement determination unit and/or the movement comparison unit if the object presence determination unit determines the presence of an object within the predefined area. The object presence determination unit can be any unit which allows to determine whether an object is present within a predefined area. The object presence determination unit is, for example, a motion detector, which can comprise a passive infrared sensor, an active ultrasonic sensor or a microwave sensor. This allows to activate the movement determination unit and/or the movement comparison unit and, optionally, further units of the sensing apparatus only if they are needed, i.e. only if an object is present within a predefined area. It is further preferred that the sensing apparatus further comprises an imaging unit for imaging the object and a control unit for controlling the imaging unit, wherein the control unit is adapted for activating the imaging unit if the movement

comparison unit determines that the movements of the at least two different parts are not similar with respect to the similarity measure. The imaging unit is, for example, a camera, in particular a video camera. This allows to generate an image of the object if this object is likely to be a living object like a human being or an animal. If, for example, a burglar approaches a vehicle comprising the sensing apparatus and if the sensing apparatus determines that the movements of the at least two different parts of the burglar are not similar with respect to the similarity measure, the imaging unit is activated for imaging the burglar. This can be used to identify the burglar.

In a preferred embodiment, the movement determination unit comprises self-mixing interference sensors for determining the movements of the at least two parts. It is further preferred that the movement determination unit comprises at least two VCSEL-based self-mixing interference sensors. This allows the velocity and the distance of at least two different parts of an object to be determined simultaneously and very fast. Furthermore, the determination of the velocity and the distance of the at least two different parts of the object are based on the determination of a frequency output by the sensors, which can be measured very accurately. Thus, the velocity and the distance of the at least two parts of the object, which is based on the frequency of the sensors, can also be determined very accurately.

In a further aspect of the present invention a vehicle comprising the sensing apparatus for sensing movements of at least two parts of an object as defined in claim 1 is presented.

In a further aspect of the present invention a sensing method for sensing movements of at least two parts of an object is presented, wherein the sensing method comprises the following steps: - determining whether the at least two parts belong to the same object,

- determining movements of the at least two parts,

- comparing the movements of the at least two parts, wherein a similarity measure is applied to the movements of the at least two parts and wherein it is determined whether the movements of the at least two parts are similar with respect to the similarity measure.

In a further aspect of the present invention a computer program for sensing movements of at least two parts of an object is presented, wherein the computer

program comprises program code means for causing a sensing apparatus as defined in claim 1 to carry out the steps of the sensing method as claimed in claim 14, when the computer program is run on a computer controlling the sensing apparatus.

It will be understood that the sensing apparatus of claim 1 , the vehicle of claim 13, the sensing method of claim 14 and the computer program of claim 15 have similar and/or identical preferred embodiments as defined in the dependent claims.

It will be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the following drawings

Fig. 1 shows exemplarily and schematically a sensing apparatus for sensing movements of at least two parts of an object,

Fig. 2 shows exemplarily and schematically an arrangement for reading out a sensor for determining a movement of an object, and Fig. 3 shows exemplarily a flow chart illustrating a sensing method for sensing movements of at least two parts of an object.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows schematically and exemplarily a vehicle 15, in this embodiment a car, comprising a sensing apparatus 1 for sensing movements of at least two parts of an object. The sensing apparatus 1 comprises a movement determination unit 10 for determining whether at least two elements 5, 6 belong to the same object 7 and for determining movements of the at least two elements 5, 6, preferably if it has been determined that the at least two elements 5, 6 belong to the same object 7. In this embodiment, the object 7 is a burglar who approaches the vehicle 15. The at least two parts of the object 2 are, for example, an arm 6 and a stomach 5 of the burglar. The movement determination unit 10 is adapted to determine whether the at least two parts belong to the same object by determining a first distance between a first part 5 of the at least two parts and the sensing apparatus and a second distance

between a second part 6 of the at least two parts and the sensing apparatus, wherein the movement determination unit 10 is adapted to determine that the movements of the at least two parts belong to the same object if an absolute difference between the first distance and the second distance is smaller than a predefined value. The sensing apparatus 1 further comprises a movement comparison unit 9 for comparing the movements of the at least two parts 5, 6, preferably if it has been determined that the at least two parts belong to the same object. The movement comparison unit is adapted for applying a similarity measure to the movements of the at least two parts 5, 6 and for determining whether the movements of the at least two parts 5, 6 are similar with respect to the similarity measure.

The movement determination unit 10 comprises two vertical-cavity surface-emitting laser (VCSEL)-based self-mixing interference sensors 3, 4 and a velocity and relative distance-determination unit 8. The sensors 3, 4 emit laser light, which is reflected by the object 7 and the reflected laser light is sensed by the sensors 3, 4, in particular, the reflected laser light interferes with the laser light within the cavity of the laser and the resulting change in the output power of the laser of the respective sensor 3, 4 is detected. The sensors 3, 4 preferably comprise a photodiode for measuring this change in the output power. The sensors 3, 4 can be driven and the photodiode of the respective sensor 3, 4 analyzed such that the velocity of the at least two parts 5, 6 of the object and the distance of the respective part of the object can be determined from a frequency of the photodiode signal. In order to analyze the frequencies of the photodiode signal, a FFT analysis of the photodiode signal can be performed. In this embodiment, as exemplarily and schematically shown in Fig. 2, the photodiode signal of a sensor 3 is mixed with a frequency modulation signal generated by a frequency- modulated signal generator 16 by an operational amplifier 17, which is preferably an analogue operational amplifier, in order to analyze the frequencies of the photodiode signal. The driving of the sensors, the frequency analysis of the photodiode signal and the determination of the velocity and of the distance based on the frequency analysis are described in more detail in, for example, "A miniaturized multidirectional optical motion sensor and input device based on laser self-mixing", M. Leiss et ah, Meas. Sci. Technol. 13 (2002) 2001-2006 and "A scanning range finder using the self-mixing effect inside a laser diode for 3-D vision", T. Bosch et al, IEEE Instrumentation and Measurement

Technology Conference Brussels, Belgium, June 4-6, 1996, which are herewith incorporated by reference.

The velocity and relative distance determination unit 8 determines the velocities of the two parts 5, 6 of the object 7 and the distance of these two parts 5, 6 from the respective sensor 3, 4 from the output signals of the sensors 3, 4 as described in, for example, the above mentioned articles. In addition, the velocity and relative distance determination unit 8 determines distances between the at least two parts 5, 6 at different points in time from the determined distances between the at least two parts 5, 6 and the respective sensors 3, 4. The movement comparison unit 9 is adapted for applying a similarity measure to the determined velocities by determining a velocity difference between the at least two velocities and by determining whether the determined velocity difference is within a predetermined velocity range. If the velocity is within the predetermined velocity range, i.e. if the absolute value of the velocity difference is smaller than a predetermined velocity value, the two velocities are regarded as being similar. In an embodiment, the movements of the at least two parts 5, 6 are regarded as being similar if the velocities of these parts are regarded as being similar.

Preferably, the movement comparison unit 9 is further adapted for applying a similarity measure by determining whether differences between distances between the at least two parts 5, 6, which have been determined for different points in time, are within a predetermined distance range. In an embodiment, the movements of the at least two parts 5, 6 are regarded as being similar if these differences are regarded as being similar at different points in time. For example, if the absolute value of a difference between these distances, which have been determined at different points in time, is smaller than a predetermined distance value, the movements of the at least two parts 5, 6 are regarded as being similar. In another embodiment, the movements are regarded as being similar if the velocities of the at least two parts 5, 6 are regarded as being similar and if the differences between the distances, which have been determined at different points in time, are within the predetermined distance range. Preferably, the VCSEL-based self-mixing interference sensors 3, 4 are used for measuring the velocities of the at least two parts 5, 6 and at least two locations of the at least two parts with respect to the locations of the sensors 3, 4 simultaneously.

The measured locations of the at least two parts 5, 6 are used for determining the distance between the at least two parts 5, 6 by the velocity and relative distance determination unit 8.

The sensing apparatus 1 is preferably adapted such that the movements of the at least two parts 5, 6 are determined only if the at least two locations of the at least two parts 5, 6 are within a predefined sensitivity distance from the sensing apparatus 1, in particular, from the sensors 3, 4.

The sensing apparatus 1 further comprises a signal generation unit 11 for generating a signal if the movement comparison unit 9 determines that the movements of the at least two parts 5, 6 are not similar with respect to the similarity measure. This signal is, for example, an acoustic and/or optical signal for a person within the vehicle 15, which warns the person that a living object like a child playing around the vehicle could be present. Furthermore, the signal could be an acoustic and/or optical signal, i.e. an alarm signal, which can preferably be noticed outside of the vehicle 15 and which is generated, if a living object like a burglar approaches the vehicle 15. Thus, if movements of two different parts of an object within a region located in the environment of the vehicle 15 are determined as being not similar with respect to the above described similarity measure, it is likely that a burglar approaches the car and a warning signal is generated by the signal generation unit 11. In this embodiment, the sensing apparatus 1 further comprises an object presence determination unit 12 for determining whether an object 7 is present within a predefined area 20 or not. The object presence determination unit 12 is preferably a motion detector, which is preferably based on a passive near-infrared sensor, an active ultrasound sensor and/or an active microwave sensor. The object presence determination unit 12 is arranged such that it can determine whether an object 7 is present within a predefined area 2 or not. The sensing apparatus 1 further comprises a control unit 13 for controlling the movement determination unit 10, the movement comparison unit 9 and optionally also the signal generation unit 11. The control unit 13 is adapted to activate the movement determination unit 10 and/or the movement comparison unit 9 and optionally the signal generation unit 11, if the object presence determination unit 12 determines a presence of an object 7 within the predefined area 2. The sensing apparatus 1 further comprises, in this embodiment, an imaging unit 14 for imaging the object,

which is preferably also controlled by the control unit 13. The imaging unit is, in this embodiment, a camera, for example a video camera, for imaging the predefined area 2, in particular, an object 7, which is in this predefined area 2. The control unit 13 is adapted for activating the imaging unit 14 if the movement comparison unit 9 determines that the movements of the at least two different parts 5, 6 are not similar with respect to the similarity measure. If the movement comparison unit 9 has determined that the movements of the at least two parts 5, 6 of the object 7 are not similar with respect to the similarity measure, it is likely that the object 7 is a living object like a burglar approaching the vehicle 15 or a child playing around the vehicle 15. In this case the imaging unit 14 is activated for imaging the object 7, for example, a burglar or a child. The sensing apparatus is preferably used as a security system against car burglaries in the absence of the car owners and/or as a safety system to prevent collisions with other traffic participants, especially persons.

A burglar is a human being who moves differently in comparison with automobiles, bicycles and other obstacles that can be found in traffic. If the car is parked, the burglar may approach the car and may attempt to break in. But, in order to park another car next to this car, also the other car may approach the car in question. Furthermore, a bicycle may pass the car. The sensing apparatus can identify the burglar and his movement from a distance. When a car moves relatively slowly, for example with the speed of walking or running persons, and in the situation where a car starts moving or is about to stop, it is sometimes the case that a human being is near the car, for instance, a child playing on the ground or people walking around. It is important to recognize the presence of human beings in the surroundings of the car to prevent accidents from occurring. It is usually the case that apart from human beings, other cars, obstacles, houses, walls, etc. are located in the periphery of the car. The sensing apparatus allows to identify a human being and to give a warning signal to this human being and/or to a person driving the car to prevent an accident from occurring. Preferably, the VCSEL- based self-mixing interference sensors 3, 4 comprise a laser cavity, which is exposed to a feedback being the laser light reflected from the at least two parts 5, 6 of the object 7. The laser, i.e. the VCSEL-based self-mixing interference sensors 3, 4, reacts with a change ofthe output power. The VCSEL-based self-mixing interference sensors 3, 4

each comprise a photodiode for measuring this change in output power. The VCSEL- based self-mixing interference sensors can be driven and the signal of the photodiode analyzed such that the velocity of the at least two parts 5, 6 of the object 7 and the distance of the at least two parts to the sensors 3, 4 can be determined from the photodiode signal. As already mentioned above, this determination of the velocities and of the distances is described in more detail in the above mentioned articles by M. Leiss et al. and T. Bosch et al..

While the parts of automobiles, bicycles or other solid obstacles in traffic move with the same velocity and with unchanged relative distance, the parts of a moving human body move with different velocities and positions relative to each other. For instance, small wrinkles and pleats of the clothes move differently when a person walks or runs. A measurement of the velocity and the distance by the self-mixing interference sensors 3, 4 allows to detect a moving body at the position where the laser beam of the sensors is reflected. If at least the velocities and/or the locations of at least two different parts of a moving body in question are measured, in particular, simultaneously, these measurements are used for determining information about the moving object itself. If the moving object is solid, for example, a car, a wall, a house, etc., the two locations, in particular the two different parts of the object, have an identical velocity and a relative distance which does not change in time. On the other hand, if the moving object is a moving human being, two different parts of the human being move differently because of the elastic movement of the human being . Thus, the two measured parts of the object have different velocities and the relative distance between these two parts may change in time. If the moving comparison unit 9 determines that the movements of the at least two parts are not similar to each other, i.e. that the object is likely to be a living object like a human being or an animal, the sensing apparatus can be adapted such that it sends a signal to a control unit of the vehicle 15, thereby causing the vehicle 15 to be automatically decelerated or stopped. The imaging unit 14 of the sensing apparatus 1 can be used for recording or photographing an approaching object if the movement comparison unit 9 has determined that the movements of the at least two parts are not similar.

The laser light beams of the sensors are preferably parallel to each other and are preferably at a distance from each other which is smaller than, for example, the average value of the distance between the shoulders of a child, for example, smaller than 20 cm, preferably smaller than 15 cm and more preferably smaller than 10 cm. In the following, a sensing method for sensing movements of at least two parts of an object will be exemplarily described with reference to a flow chart shown in Fig. 3.

In step 101, the object presence determination unit 12 determines whether an object 7 is present within a predefined area 2. If an object is present within the predefined area 2, the next step 102 is performed, and if this is not the case, step 101 is repeated.

In step 102, the movement determination unit 10 determines whether at least two parts 5, 6 belong to the same object 7. Furthermore, the movement determination unit 10 determines movements of the at least two parts 5, 6 of the object 7. In this embodiment, the velocities of the at least two parts 5, 6 of the object 7 with respect to the sensors 3, 4 and the distances of the at least two parts 5, 6 to the sensors 3, 4 are measured simultaneously and for different points in time the relative distance between these at least two parts 5, 6 of the object 7 is determined.

Preferably, the movement determination unit 10 determines whether the at least two parts 5, 6 belong to the same object by determining a first distance between a first part 5 of the at least two parts 5, 6 and the sensing apparatus, in particular, between a first part 5 of the at least two parts 5, 6 and the sensors 3 or 4, by determining a second distance between a second part 6 of the at least two parts 5, 6 and the sensing apparatus, in particular, between a second part 6 of the at least two parts 5, 6 and the sensors 3 or 4, wherein the movement determination unit 10 determines that the movements of the at least two parts 5, 6 belong to the same object if an absolute difference between the first distance and the second distance is smaller than a predefined value.

In step 103, the movements of the at least two parts 5, 6 are compared by the movement comparison unit 9, wherein a similarity measure is applied to the movements of the at least two parts 5, 6 and it is determined whether the movements of the at least two parts 5, 6 are similar with respect to the similarity measure. In this

embodiment, the velocities of the at least two parts 5, 6 and the relative distance between these two parts is determined for different points in time and it is determined whether these determined velocities are similar and whether the relative distances between the at least two parts, which have been determined for different points in time, are similar, i.e. whether this relative distance is constant in time. If the movements of the at least two different parts 5, 6 are not similar, the next step 104 is performed, and if these movements are similar, the method continues with step 101.

In step 104, the signal generation unit 11 generates a signal and in step 105 the imaging unit 14 is activated for generating an image of the object 7. Step 101 can be omitted. Steps 104 and 105 can be performed simultaneously and in an embodiment at least one of these steps is omitted. If, in step 102, it has been determined that the at least two parts do not belong to the same object, the determination of the movements and/or the comparison of the movements can be omitted. In this case, the determination whether at least two parts belong to the same object is preferably repeated, wherein, for example, because of a movement of an object, now movements of at least two parts of the same object can be determined and the movement comparison can be performed.

Although in the above described embodiment the sensing apparatus 1 comprises two self-mixing interference sensors 3, 4 only, in other embodiments, the sensing apparatus can comprise more than two self-mixing interference sensors, in particular an array of self-mixing interference sensors. Furthermore, although in the above described embodiment the self-mixing interference sensors point in the same direction, in other embodiments several self-mixing interference sensors can be provided which point in different directions, wherein preferably a pair of two self-mixing interference sensors point in the same direction, i.e., for example, a first pair or array of self-mixing interference sensors can point to the front of the car, a second pair or a second array of self-mixing interference sensors can point to the back of the car and two more pairs or arrays of self-mixing interference sensors can be directed to the sides of the car. The sensing apparatus can be used in place of or in addition to existing sensors and/or video systems, which may already be present on the vehicle. The sensing apparatus preferably does not generate a signal if the velocities of the at least two parts of the object are similar and if the relative distance between these at least two parts is

constant in time, because it is concluded that in this case the object is solid, for example, a vehicle. If the two velocities are not similar or if the relative distance between the at least two parts is not constant in time, the sensing apparatus preferably generates a signal, because in this case it is concluded that the object is a living object like a human being or an animal.

Although in the above described embodiment the sensing apparatus is arranged in a vehicle, in other embodiments the sensing apparatus can be a standalone system or can be arranged in another object. For example, the sensing apparatus can be integrated in a building or another object for detecting whether a person or a solid inelastic object approaches the building or the other object.

Although in the above described embodiment the sensors are VCSEL- based self-mixing interference sensors, in other embodiments other sensors can be used which are based on self-mixing interference sensors. Any coherent light source, like a solid-state laser, gas laser, monochromatic light source for distance vision (sodium lamps) et cetera, can be used in combination with an interferometric system.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Determinations, calculations et cetera by one or several units or devices can be performed by any other number of units or devices. For example, steps 101 to 103 can be performed by a single unit or by any other number of different units. The control of the sensing apparatus in accordance with the sensing method can be implemented as program code means of a computer program and/or as dedicated hardware.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as

part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Any reference signs in the claims should not be construed as limiting the scope.