WO2016042352A1

WO2016042352A1 - System and method for avoiding a collision for a vehicle

Info

Publication number: WO2016042352A1
Application number: PCT/IB2014/002104
Authority: WO
Inventors: Cany IGNATIUS; Jean LE-BASTARD
Original assignee: Alstom Transport Technologies
Priority date: 2014-09-19
Filing date: 2014-09-19
Publication date: 2016-03-24
Also published as: AU2014406175A1; CN106715234A; EP3194242A1; BR112017005186A2; IL251109A0

Abstract

A safety system (10, 10') for avoiding a collision for a vehicle (12) comprises a calculation unit (14) that is adapted to calculate a plurality of ranges of zones, one or more radar sensors (16a, 16b, 16c, 16d) that are adapted to detect a relative position of an object to the vehicle (12), a determination unit (18) that is adapted to determine a zone at which the object is positioned, based on the relative position detected by the one or more radar sensors (16a, 16b, 16c, 16d) and a safety unit (20) that is adapted to take actions for avoiding a collision between the vehicle (12) and the object, based on the zone determined by the determination unit (18) and the speed of the vehicle.

Description

System and method for avoiding a collision for a vehicle

The present invention concerns an automatic collision detection system for railway vehicle (tramway).

Object detection is already provided in the automotive industry. For instance, US

2009/0002222 A1 discloses a collision avoidance system for reducing the number of false alerts caused by hyper-elevated objects such as overpasses, and hypo-elevated appurtenances such as railroad tracks. US 2009/0002222 A1 describes a system for estimating the elevation of at least one target utilizing conventional single-dimensional radar technology. The system includes short and long range scanning radar sensors having differing ranges and beam angles of inclination, and a digital processor for estimating the elevation of said each of said at least one target based on a relative signal value based on the first and second return signals.

However, the system merely warns a driver of a vehicle, therefore, it cannot surely avoid a collision of the vehicle with human/anything moving in front of the vehicle or side of the vehicle.

It is an object of the present invention to provide an improved safety system for detecting a collision-free path for a vehicle. This object is achieved by a safety system as claimed in claim 1 .

To this end, the invention relates to a safety system for avoiding a collision for a vehicle, the system comprising:

- one or more sensors that are adapted to detect a relative position of an object to the vehicle, characterized in that the system further comprises:

- a calculation unit that is adapted to calculate a plurality of ranges of zones and to obtain the speed of the vehicle;

- a determination unit that is adapted to determine a zone at which the object is positioned, based on the relative position detected by the one or more sensors; and

- a safety unit that is adapted to take actions for avoiding a collision between the vehicle and the object, based on the zone determined by the determination unit, and the speed of the vehicle.

Thanks to the invention, the system allows to automatically search for avoiding a collision for a vehicle such as a tram. That is, the system is able to execute actions without obstructing a driver of the vehicle according to the relative position of the obstacle to the vehicle in order to avoid the collision. According to other advantageous aspects of the invention, the system comprises one or more of the following features taken alone or according to all technically possible combinations:

- the sensor is one of the following group: radar, camera, lidar;

- the calculation unit is adapted to calculate the ranges of zones based on the speed of the vehicle;

- the calculation unit is adapted to calculate the ranges of zones based on outer condition and/or features of the vehicle;

- the calculation unit is adapted to calculate ranges of three zones comprising a first zone, a second zone and a third zone in the order closer to the vehicle;

- the radar sensors are two sensors placed at the front of the vehicle and two sensors placed at the front lateral side of the vehicle;

- detection angles of the radar sensors placed at the front lateral side of the vehicle are shorter than detection angles of the radar sensors placed at the front of the vehicle;

- the safety unit is adapted to send out alarm, when the object is detected within the third zone by the one or more sensors and the determination unit;

- the safety unit never release brakes of the vehicle, when the vehicle is not moving and the object is detected within any one of the zones by the one or more sensors and the determination unit;

- the safety unit is adapted to execute an emergency brake, when the object is detected within the first zone by the one or more sensors and the determination unit;

- the safety unit is adapted to slow down the speed of the vehicle, when the object is detected within the second zone by the one or more sensors and the determination unit;

- the calculation unit is adapted to divide each zone into rectilinear area along the straight line at the front of the vehicle and side area outside of the rectilinear area so that the side area is closer to the vehicle than the rectilinear area;

- the calculation unit is adapted to calculate the ranges of the zones based on the relative speed of the vehicle to the object;

- the determination unit is adapted to estimate the future relative positional relation between the vehicle and the object, and determines the future zones at which the object will be positioned, based on the future relative positional relation between the vehicle and the object;

- the safety system further comprises:

- an imaging unit that is adapted to capture an image of the front of the vehicle; and - an image processing unit that is adapted to obtain the track positioning information by processing the image captured by the imaging unit; wherein

- the determination unit is adapted to further determine whether the object is dangerous according to the track positioning information obtained by the image processing unit, and

- the safety unit is adapted to take actions for avoiding the collision only when the object is determined to be dangerous by the determination unit;

- the image processing unit is adapted to obtain the object positioning information by processing the image captured by the imaging unit, and

- the determination unit is adapted to further determine whether the object is dangerous according to the object positioning information obtained by the image processing unit.

The invention will be better understood upon reading of the following description, which is given solely by way of example and with reference to the appended drawings, in which:

- Figure 1 is a block diagram indicating a functional configuration example of a safety system 10;

- Figure 2 is a diagram showing a positional relationship of radar sensors and zones;

- Figure 3 is a block diagram indicating another functional configuration example of a safety system 10;

- Figure 4 is a conceptual drawing of the object/obstacle detection;

- Figure 5 is a flowchart of fixed object/obstacle detection;

- Figure 6 is a flowchart of moving object/obstacle detection.

Below, a first embodiment of a safety system 10 for detecting a collision-free path for a tram 12 pertaining to the present invention will be described using Fig. 1 and Fig. 2.

In Figure 1 , a safety system 10 for avoiding a collision for a tram 12 comprises a calculation unit 14, four sensors 16a, 16b, 16c and 16d, for example radar type or lidar type, a determination unit 18 and a safety unit 20. The calculation unit 14, the determination unit 18 and the safety unit 20 are incorporated in the onboard system of the tram 12.

The safety system 10 is adapted to include one or more radar sensors for detecting a relative position of at least an object to the tram 12. In this embodiment, the safety system 10 has four radar sensors 16a, 16b, 16c and 16d placed in front of the tram 12 for detecting a relative position of an object to the tram 12. The two radar sensors 16a and 16b are placed at the front of the tram 12 and monitor straight. The two radar sensors 16c and 16d may be placed at the front lateral side of the tram 12 and monitor the sides. The two radar sensors 16c and 16d are adapted to monitor only a short angle, and the side of the angle will depend on the tram size, so that the tram 12 can pass through with in the collision-free path. The radar sensors 16 c and 16d have an acute field of view which is between 30 and 60 degrees and preferably about 45 degrees. The other two radar sensors 16a and 16b placed in the center have an obtuse field of view, which is between 120 and 180 degrees and preferably about 150 degrees. That is, detection angles of the radar sensors 16c and 16d placed at the front lateral side of the tram 12 are shorter than detection angles of the radar sensors 16a and 16b placed at the front of the tram 12.

The determination unit 18 includes means to determine a zone at which the object is positioned, based on the relative positions detected by the one or more radar sensors, that is, the radar sensors 16a, 16b, 16c and 16d in this embodiment.

Figure 2 shows a positional relationship of radar sensors 16a to 16d and the zones. The system monitoring is divided into three zones EBZ (emergency brake zone), SDZ (slowdown zone) and AZ (alarm zone), each zone is monitored by different angles which include both the rectilinear and the sides.

The calculation unit 14 is adapted to calculate the ranges of the three zones based on the speed of the tram 12. Furthermore, in this embodiment, the calculation unit 14 divides each zone into rectilinear area along the line at the front of the tram 12 and side area outside of the rectilinear area so that the side area is closer to the tram 12 than the rectilinear area. As shown in Fig. 2, EBZ is divided into EBZR representing "emergency braking zone - rectilinear" and EBZS representing "emergency braking zone - side". SDZ is divided into SDZR representing "slowing down zone - rectilinear" and SDZS representing "slowing down zone - side". AZ is divided into AZR representing "alarm zone - rectilinear" and AZS representing "alarm zone - side". In other words, AZ (alarm zone area) is the area covered by both AZS and AZR. SDZ (slowdown zone area) is the area covered by both SDZS and SDZR. EBZ (emergency brake zone area) is the area covered by both EBZS and EBZR.

Therefore, EBZR, SDZR and AZR are the front zones identified at the front of the tram 12. EBZS, SDZS and AZS are the side front zones identified along the side. The radius of the EBZS is literally smaller than that of the EBZR. The sensing range of the EBZS shall be reduced based on the required detection area on the side. The radius of the SDZS is literally smaller than that of the SDZR. The sensing range of the SDZS shall be reduced based on the required detection area on the side. The radius of the AZS is literally smaller than that of the AZR. The sensing range of the AZS shall be reduced based on the required detection area on the side. The safety system 10 includes means to receive information concerning the current dynamic features of the tram 12, and environmental condition like dry and wet track and characteristics of the rolling stock.

The calculation unit 14 is connected to the tramway control system or to an independent odometry or a positioning system 20a to receive the position, the speed and the acceleration of the tram 12.

It is also connected to a moisture sensor 20b to determine the outer condition and to an inner database 20c containing the features of the tram 12 such as the weight and the braking capacity.

The calculation unit 14 includes control means to control the tram based on the information concerning the position of the object in one of the zone areas. The tramway movement (speed) can be provided by the Tramway control system or by an independent odometry or a positioning system 20a. For example, the calculation unit 14 is adapted to calculate ranges of three zones comprising a first zone, a second zone and a third zone in the order closer to the tram 12. In this case, the first zone is an emergency brake zone area, the second zone is a slowdown zone area, and the third zone is an alarm zone area.

The emergency brake zone is an area where the tram 12 shall automatically take the decision to stop by automatically applying the brakes to reduce the tram speed even if the tram driver has not observed if an object is present and must be considered as an obstacle within the region and if it is a collision path for the tram 12 to move ahead. The emergency zonal distance can be derived from the current speed of the tram 12, which extrapolate to emergency braking distance and a buffer distance of x meters.

The slowdown zone is an area where the tram 12 shall automatically slow down if an object is detected within the region and it is a collision path for the tram 12 if the tram 12 is moving with the same speed, the object being considered as an obstacle in this case. The slowdown zone distance can be calculated from the current speed of the tram 12, which extrapolate to the normal braking distance and a buffer distance of y meters.

The alarm zone is an area where the tram 12 shall automatically give an alarm (Horn) if an object is detected in this zone and therefore considered as an obstacle. The alarm zone shall be z meters from the slowdown zone end which shall be configurable.

Furthermore, the calculation unit 14 may calculate the zonal distances dynamically based on not only the tram speed but also the acceleration of the tram 12, characteristics of the rolling stock and environmental condition like dry and wet track. Based on the speed and acceleration it is possible to estimate the position that the tram 12 will reach in a given number of seconds (for example 3s). Therefore, in general, each range of the zones is broadened as the speed of the tram 12 is fast. In addition, the calculation unit 14 is able to be adapted to calculate the ranges of the zones based on the relative speed of the tram 12 to the object. In this case, the calculation unit 14 is connected to the radar sensors 16a to 16d. Here, if the object is moving, the distance covered by the tram 12 towards the object is not proportional to the speed of the tram 12. Therefore, the calculation unit 14 can recognize that the object is moving. Moreover the radar sensors normally output the relative speed. Therefore, it is easy to calculate the other object's speed if any. That is to say, the calculation unit 14 is able to calculate the ranges of the zones dynamically by extrapolating the future relative positional relation between the tram 12 and the object.

The safety unit 20 is adapted to take actions for avoiding a collision between the tram 12 and the object, based on the zone determined by the determination unit 18. When the object is detected in one zone, it's considered as an obstacle.

Specifically, the safety unit 20 sends out alarm (Horn), when the obstacle is detected within the third zone (alarm zone area) by the one or more radar sensors (the radar sensors 16a, 16b, 16c and 16d) and the determination unit 18. This alarm (Horn) is for warning the obstacle (human) that the tram 12 is approaching. The safety unit 20 never releases brakes of the tram 12, when the tram 12 is not moving and the obstacle is detected within any one of the zones by the one or more radar sensors (the radar sensors 16a, 16b, 16c and 16d) and the determination unit 18. Furthermore, the safety unit 20 is adapted to execute an emergency brake, when the obstacle is detected within the first zone (emergency brake zone area) by the one or more radar sensors (the radar sensors 16a, 16b, 16c and 16d) and the determination unit 18. In addition, the safety unit 20 is adapted to slow down the speed of the tram 12, when the obstacle is detected within the second zone (slowdown zone area) by the one or more radar sensors (the radar sensors 16a, 16b, 16c and 16d) and the determination unit 18. The safety unit 20 should not necessarily control the alarm and the speed (brake) of the tram 12 directly by itself. In other words, the safety unit 20 is able to provide inputs to a device which control or may be a part of a system which directly control the alarm (Horn of the tram 12) and brake controlling unit responsible for mechanical and electrical brake control and also responsible for emergency braking of the tram 12.

Next, the operations of the safety system 10 using an automatic collision detection algorithm will be described.

Firstly, the case that the tram 12 is stopped and ready to start will be described. The calculation unit 14 calculates the ranges of three zones (EBZ, SDZ and AZ) based on the speed of the tram 12. As stated above, emergency braking distance and normal braking distance are taken into account for calculating the ranges of EBZ and SDZ, respectively. Therefore, when the tram 12 is stopped, the ranges are relatively narrow. If one of the radar sensors 16a, 16b, 16c and 16d detects an object and the determination unit 18 determines that the object is positioned within one of the three zones and considered as an obstacle, then the safety unit 20 never releases brakes of the tram 12. This function is very advantageous because if the tram 12 starts and the obstacle is not moving soon it will enter in to the emergency zone distance and unnecessary braking has to be applied. Therefore, thanks to this function of the safety unit 20, the tram 12 having the safety system 10 can avoid the unnecessary braking. Furthermore, the safety unit 20 may send out an alarm (Horn) when the obstacle is detected within any one of the zones by the radar sensors 16a to 16d and the determination unit 18 without the intervention of the tram driver.

Secondly, the case that the tram 12 is moving with a constant speed will be described. The calculation unit 14 calculates the ranges of three zones (EBZ, SDZ and AZ) based on the speed of the tram 12. Specifically, the zonal distances shall be calculated dynamically based on the tram speed, characteristics of the rolling stock and environmental condition like dry and wet track. The emergency brake zone distance can be derived from the current speed of the tram 12, which extrapolates to emergency braking distance and a buffer distance of x meters (can be configured). The slowdown zone distance again can be calculated from the current speed of the tram 12, which extrapolates to the normal braking distance and a buffer distance of y meters (can be configured). The slowdown zone will start from the end of the emergency brake zone distance. The alarm zone shall be z meters from the slowdown zone end which shall be configurable.

The calculation unit 14 may calculate the ranges of three zones based on the speed of the tram 12 and the breaking distance required by the tram 12. So the zone range will be calculated dynamic based on the speed of the tram 12 and the breaking distance required by the tram 12 together with a distance x will be zonal area, so the zone distance will increase as the tram speed increases and the zone distance will be less when the tram speed is less.

The radar sensors 16a, 16b, 16c and 16d continuously monitor the three zones during the movement of the tram 12. If the radar sensors 16a to 16d detect an object and the determination unit 18 determines that the object is positioned within one of the three zones, then the object is considered as an obstacle and the tram status needs to be moved to slowdown zone, alarm zone or emergency brake zone.

When the determination unit 18 determines that the obstacle is positioned within the emergency zone area, the tram 12 needs to automatically apply emergency brake, so that the collision between the tram 12 and the obstacle is avoided without the intervention of the tram driver. Therefore, in this case, the safety unit 20 executes an emergency brake. During the emergency braking, in case if the sensors have detected a collision-free path, the brakes needs to be released and the tram 12 is allowed to take back the normal speed. Therefore, even if the safety unit 20 is executing the emergency brake, if the radar sensors 16a to 16d and the determination unit 18 do not detect any obstacles in the three zones, the safety unit 20 may release the brake and take back the normal speed.

When the determination unit 18 determines that the obstacle is positioned within the slowdown zone area, the tram 12 needs to automatically slowdown the speed of the tram 12 without the intervention of the tram driver. Therefore, in this case, the safety unit 20 slows down the speed of the tram 12. During the slowing down the speed, in case if the sensors have detected a collision-free path, the brakes needs to be released and the tram 12 is allowed to take back the normal speed. Therefore, even if the safety unit 20 is slowing down the speed of the tram 12, if the radar sensors 16a to 16d and the determination unit 18 do not detect any obstacles in the three zones, the safety unit 20 may release the brake and take back the normal speed.

When the determination unit 18 determines that the obstacle is positioned within the alarm zone area, the tram 12 needs to automatically send out an alarm (Horn). Therefore, in this case, the safety unit 20 sends out an alarm. If the same obstacle moves inside the slowdown zone area, then the safety unit 20 slows down the speed of the tram 12. If the same obstacle moves inside the emergency brake zone area, then the safety unit 20 executes an emergency brake.

The determination unit 18 may estimate the future relative positional relation between the tram 12 and the obstacle, and determine the future zones at which the obstacle will be positioned, based on the future relative positional relation between the tram 12 and the obstacle. In this case, the safety unit 20 takes different actions for avoiding the collision according to the future zones determined by the determination unit 18. Therefore, the safety system 10 can promptly cope with the case that the obstacle is moving.

Accordingly, the safety system 10 makes it possible to surely avoid a collision of the tram 12 with the obstacle (human/anything) moving in front of the tram 12 or side of the tram 12 by taking different actions according to the relative positional relation between the tram 12 and the obstacle. Moreover, the safety system 10 has the advantage that it requires only one or more radar sensors to be added to conventional tramway. In general, the radar sensor is less expensive than stereo camera, having moreover a good day and night "visibility". Next, a second embodiment of the safety system 10' for avoiding a collision for a tram 12 pertaining to the present invention will be described using Fig. 3 to Fig. 6. It will be noted that the same numbers will be given to components that are the same as those of the preceding first embodiment and that description of those same components will be omitted.

Fig. 3 shows an embodiment of another functional configuration of a safety system 10'. The safety system 10' comprises all the components of the safety system 10 described in Fig. 1 , for which the same reference numeral are used.

In addition, the safety system 10' comprises an imaging unit 21 and an image processing unit 22 operationally connected to the imaging unit 21 and the determination unit 18. The imaging unit 21 captures an image of the front of the tram 12. The image processing unit 22 obtains the track positioning information by processing the image captured by the imaging unit 21 . The imaging unit 21 may be a front tramway video camera. In this case, the image processing unit 22 may obtain the track positioning information through analysis of the video provided by the imaging unit 21 . In another embodiment not represented, the track positioning information is obtained using an independent localization device, GPS type for example, and track cartography in a local or remote database.

Next, the operations of the safety system 10' using an automatic collision detection algorithm will be described. Figure 4 shows a conceptual drawing of the obstacle detection. Video coverage 30 is an imaging range of the imaging unit 21 . The image processing unit 22 recognizes the track 38 by obtaining the track positioning information. Radar coverage 36 is a range of the radar sensors. Object circles 42 are ranges of concentric circles, centering on an object 34. As shown in Fig. 4, in this embodiment, the calculation unit 14 does not divide each zone into the rectilinear area and the side area as described in the first embodiment.

Basically, the safety system 10' avoids the collision by using three pieces of information. The first item of the information is the tramway movement, more precisely the speed and the acceleration of the tram 12. Based on the speed and acceleration it is possible to estimate the position that the tram 12 will reach in a given number of seconds (for example 3s). As stated above, the calculation unit 14 can obtain the speed and the acceleration of the tram 12 from the tramway control system, an independent odometry or the positioning system. The second item of the information is the radar information, providing a given number (for example 32) of objects positions and/or objects movements (speed and/or acceleration) in front of the tram 12. The information can be obtained by the radar sensors 16a to 16d. In Fig. 4, the object 34 is located within the area of radar coverage 36. The third item of the information is the track positioning information, providing information on track position and track profile, such as the information about whether the track turns right or left with which radius, or the track is passing a point machine and divided in two tracks. As shown in Fig. 4, the track position integrates the danger zone 40 on the track 38 i.e. the zone on and around the track 38 where the tramway body will be.

Figure 5 shows a flowchart of fixed obstacle detection, and Figure 6 shows a flowchart of moving objects detection. The difference between the flowcharts is that a front image captured by the imaging unit 21 is used for identifying intersection of objects circles 42 and danger circles 32 in the case of the moving objects detection. The calculation unit 14 calculates a plurality of ranges of zones (danger circles 32) based on the speed of the tram 12. At that time, the calculation unit 14 may use not only the speed but also the acceleration of the tram 12.

The safety system 10' may include one or more radar sensors or lidar sensors for detecting a relative position of an object to the tram 12. In this embodiment, the safety system 10' has four radar sensors 16a, 16b, 16c and 16d placed in front of the tram 12 for the monitoring purpose. The radar sensors 16a, 16b, 16c and 16d continuously monitor the zones during the movement of the tram 12, and identify objects (objects or not).

On the other hands, the imaging unit 21 captures an image of the front of the tram 12. The image processing unit 22 obtains the track positioning information by processing the image captured by the imaging unit 21 . Furthermore, the image processing unit 22 obtains the object positioning information by analyzing the captured image. That is to say, the image processing unit 22 identifies the objects (obstacles) in the captured image.

The determination unit 18 determines a zone at which the object is positioned, based on the relative position detected by the radar sensors 16a, 16b, 16c and 16d. In other words, the determination unit 18 identifies objects in the danger circles 44. At that time, the determination unit 18 may also use, in combination or not, the object positioning information obtained by the image processing unit 22. This is beneficial for the moving object detection. For example, the radar sensors 16a, 16b, 16c and 16d may detect objects in the track which are not obstacle such as signaling objects or zebra crossing. Those objects are filtered to avoid wrong detection thanks to image analysis done by the camera (the image processing unit 22).

The determination unit 18 may follow the movement of objects and estimate the object position at different period of time (for example after 0,5s, 1 s, 1 ,5s...). The movement identification can integrate the speed and the acceleration of the object. The speed and acceleration could be provided by the radar sensors, but a better estimation could be done using the image analysis correlated with the radar information. The determination unit 18 may estimate if in which danger circle 32 the object will be in a predetermined time, e.g. 3s.

The determination unit 18 determines whether the object is dangerous and must be considered as an obstacle according to the track positioning information. That is to say, the track positioning information allows the determination unit 18 to filter objects in the danger circles 32 and "on the track". The determination unit 18 may determine that the object is not dangerous if the object is out of the track danger zone 40.

The safety unit 20 takes different actions such as a simple horning or emergency braking for avoiding a collision between the tram 12 and the obstacle, based on the zone determined by the determination unit 18. The safety unit 20 may take the actions for avoiding the collision only when the object is determined to be dangerous and considered as an obstacle by the determination unit 18.

Accordingly, the safe system 10' makes it possible to surely avoid a collision of the tram 12 with the obstacle (human/anything) by taking different actions according to the relative positional relation between the tram 12 and the obstacle. Moreover, the safety system 10' can make more exact decisions by analyzing the image captured by the imaging unit 21 .

Claims

1 . A safety system (10, 10') for avoiding collision for a vehicle (12), the system (10, 10') comprising:

one or more sensors (16a, 16b, 16c, 16d) that are adapted to detect a relative position of an object to the vehicle (12), characterized in that the system (10, 10') further comprises:

a calculation unit (14) that is adapted to calculate a plurality of ranges of zones and to obtain the speed of the vehicle;

a determination unit (18) that is adapted to determine a zone at which the object is positioned, based on the relative position detected by the one or more sensors (16a, 16b, 16c, 16d); and

a safety unit (20) that is adapted to take actions for avoiding a collision between the vehicle (12) and the object, based on the zone determined by the determination unit (18), and the speed of the vehicle.

2. The safety system (10, 10') according to Claim 1 , wherein the sensor is one of the following group: radar, camera, lidar.

3. The safety system (10, 10') according to one of Claims 1 and 2, wherein the calculation unit (14) is adapted to calculate the ranges of zones based on the speed of the vehicle (12).

4. The safety system (10, 10') according to Claim 3, wherein the calculation unit (14) is adapted to calculate the ranges of zones based on outer condition and/or features of the vehicle.

5. The safety system (10, 10') according to one of Claims 1 to 4, wherein the calculation unit (14) is adapted to calculate ranges of three zones comprising a first zone, a second zone and a third zone in the order closer to the vehicle (12).

6. The safety system (10, 10') according to one of Claims 1 to 5, wherein the radar sensors (16a, 16b, 16c, 16d) are two sensors (16a, 16b) placed at the front of the vehicle (12) and two sensors (16c, 16d) placed at the front lateral side of the vehicle (12).

7. The safety system (10, 10') according to Claim 6, wherein detection angles of the radar sensors (16c, 16d) placed at the front lateral side of the vehicle (12) are shorter than detection angles of the radar sensors (16a, 16b) placed at the front of the vehicle (12).

8. The safety system (10, 10') according to one of Claims 5 to 7, wherein the safety unit (20) is adapted to send out alarm, when the object is detected within the third zone by the one or more sensors (16a, 16b, 16c, 16d) and the determination unit (18).

9. The safety system (10, 10') according to one of Claims 1 to 8, wherein the safety unit (20) never releases brakes of the vehicle (12), when the vehicle (12) is not moving and the object is detected within any one of the zones by the one or more sensors (16a, 16b, 16c, 16d) and the determination unit (18). 10. The safety system (10,

10') according to one of Claims 5 to 9, wherein the safety unit (20) is adapted to execute an emergency brake, when the object is detected within the first zone by the one or more sensors (16a, 16b, 16c, 16d) and the determination unit (18).

1 1 . The safety system (10, 10') according to one of Claims 5 to 10, wherein the safety unit (20) is adapted to slow down the speed of the vehicle (12), when the object is detected within the second zone by the one or more sensors (16a, 16b, 16c, 16d) and the determination unit (18).

12. The safety system (10, 10') according to one of Claims 1 to 1 1 , wherein the calculation unit (14) is adapted to divide each zone into rectilinear area along the straight line at the front of the vehicle (12) and side area outside of the rectilinear area so that the side area is closer to the vehicle (12) than the rectilinear area.

13. The safety system (10, 10') according to one of Claims 1 to 12, wherein the calculation unit (14) is adapted to calculate the ranges of the zones based on the relative speed of the vehicle (12) to the object.

14. The safety system (10, 10') according to one of Claims 1 to 13, wherein the determination unit (18) is adapted to estimate the future relative positional relation between the vehicle (12) and the object, and determines the future zones at which the object will be positioned, based on the future relative positional relation between the vehicle (12) and the object.

15. The safety system (10, 10') according to one of Claims 1 to 14, wherein the safety system (10, 10') further comprises:

an imaging unit (21 ) that is adapted to capture an image of the front of the vehicle (12); and

an image processing unit (22) that is adapted to obtain the track positioning information by processing the image captured by the imaging unit (21 ); wherein

the determination unit (18) is adapted to further determine whether the object is dangerous according to the track positioning information obtained by the image processing unit (22), and

the safety unit (20) is adapted to take actions for avoiding the collision only when the object is determined to be dangerous by the determination unit (18).

16. The safety system (10, 10') according to Claim 15, wherein the image processing unit (22) is adapted to obtain the object positioning information by processing the image captured by the imaging unit (21 ), and

the determination unit (18) is adapted to further determine whether the object is dangerous according to the object positioning information obtained by the image processing unit (22).

17. A safety method for detecting a collision-free path for a vehicle, the method comprising:

calculating a plurality of ranges of zones;

detecting a relative position of an obstacle to the vehicle;

determining a zone at which the obstacle is positioned, based on the relative position of the obstacle to the vehicle; and

taking actions for avoiding a collision between the vehicle and the obstacle, based on the zone at which the obstacle is positioned.