Method and device for detecting the use of a belt of an occupant protection system for a vehicle and device for redirecting a belt

Abstract

Method for detecting the use of a belt (104) of an occupant protection system for a vehicle (100), wherein the method comprises the following steps: Reading (631) a first characteristic of a first reflected light ray, wherein the first reflected light ray represents a light ray (514) that reflects at a first time on a section of a surface of the belt (104) located within a detection area (512); Reading (633) at least one further characteristic of another reflected light ray, wherein the one further reflected light ray represents a light ray (514) that reflects at another time on a section of the surface of the belt (104) located within the detection area (512); Determining (635) a movement of the belt (104) within the detection range (512) using the first characteristic and at least one further characteristic, wherein the movement is an absolute amount of a belt extension relative to a previously determined initial value over time; and Comparing a course of movement of the belt (104) with a reference course to determine a state of a person using the belt (104), wherein the state is identified as the person's breathing processes.

Description

State of the art

[0001] The invention relates to a device or a method according to the preamble of the independent claims. The present invention also relates to a computer program.

[0002] By using a seat belt correctly, optimal protection from the seat belt can be achieved.

[0003] DE 10 2008 042 399 A1 describes a restraint system for a vehicle with a belt system for a vehicle occupant and at least one arrangement for detecting a belt that is not effectively fastened.

[0004] German patent DE 10 2007 030 575 A1 deals with a deflection fitting for a safety belt. An optical method allows the determination of the currently issued belt extension length, the direction (retraction or extension), and the speed of the belt movement.

[0005] From application DE 10 2011 018 710 A1, an optical sensor is known which comprises a light source, a circuit arrangement, and a detector. Light reflected from an object creates speckle patterns on the detector. The circuit arrangement evaluates changes in the speckle patterns between at least two signals, thereby providing information about a change in the object's position in space.

[0006] DE 10 2005 039 029 A1 discloses a sensor for detecting the position of a belt guide.

[0007] DE 10 2007 008 602 A1 discloses a rotation sensor, for example designed as an optical sensor, for determining a relative extension length of a safety belt by counting the revolutions of the roller. Disclosure of the invention

[0008] Against this background, the approach presented here introduces a method and a device for detecting the use of a seat belt in an occupant protection system for a vehicle, a device for redirecting a seat belt, and finally a corresponding computer program according to the main claims. Advantageous further developments and improvements of the device specified in the independent claim are possible through the measures listed in the dependent claims.

[0009] The described approach enables the detection of a vehicle occupant's correct seatbelt fastening, including the detection of misuse of the seatbelt system. Belt misuse detection is achieved through optical measurement, for example, at a belt guide.

[0010] Advantageously, embodiments of the described approach allow for the detection of different types of seatbelt misuse, such as the use of a dummy belt tongue, deactivation of the seatbelt warning light, sitting on the belt, deactivation in a workshop, belt routing behind the seat back, insertion of an unused belt, or a belt extension jam. To be able to detect these deactivation possibilities, it may be advantageous to prevent software-based deactivation of the function described here.

[0011] A procedure for detecting the use of a seat belt in a vehicle occupant restraint system includes the following steps: Reading a first characteristic of a first reflected light ray, wherein the first reflected light ray represents a light ray reflecting at a first time on a section of a surface of the belt located within a detection area; Reading at least one further characteristic of another reflected light beam, wherein the one further reflected light beam represents a light beam reflecting at a further time on a section of the belt's surface located within the detection range; and Determining movement of the belt within the detection range using the first characteristic and at least one further characteristic.

[0012] In an additional comparison step, the movement pattern of the belt is compared to a reference pattern. This determines the state of the person using the belt, with the person's breathing being recognized as part of this state. The movement pattern can be a temporal progression. For example, it can depict the speed or acceleration of the belt within the detection range. Essentially, the pattern can be understood as any movement of the belt, including displacement. The use of the belt can be understood as, for example, its proper or improper use.To compare different uses and / or states, the movement pattern can be compared with multiple reference patterns, each of which can be assigned a specific use and / or state. Using at least one reference pattern, a very precise statement can be made about the handling and use of the belt.

[0013] The occupant protection system can be a restraint system in which a vehicle occupant is restrained using a seat belt in the event of a collision with an obstacle. A characteristic of a light beam can be understood, for example, as its intensity or distribution. The movement of the belt can cause the characteristic of the light beam to change over time. This change can provide information about the movement and its nature.

[0014] According to one embodiment, a speckle pattern can be read as a characteristic in each step of the reading process. A speckle pattern can be caused by roughness in the surface of the belt. Movement of the belt leads to a change in the speckle pattern and thus to a change in the characteristics of the reflected light beam. In this way, an existing property of the belt's surface can be used to determine belt movement.

[0015] The reading process can be triggered by a signal indicating that a vehicle door is opened. Alternatively, or in addition, the reading process can be triggered by a signal indicating that the vehicle is moving. This allows for verification that the seatbelt is correctly fastened before the journey begins. If the reading process is performed while driving, it can, for example, verify the correct use of the seatbelt. This allows for monitoring the passenger's condition, and especially their breathing, during the journey.

[0016] The method can comprise a step of detecting the first characteristic and at least one further characteristic using an optical sensor that has a detection range. The detection range can be located at least near a belt guide for the seatbelt. Advantageously, known sensors can be used. By arranging the detection range near the belt guide, it can be ensured that movements of the belt that lead to an extension or shortening of the belt length are detected. Such an optical sensor can, for example, be attached to a belt guide or to the vehicle body.

[0017] A suitable device for detecting the use of a seatbelt in a vehicle's occupant protection system is configured to execute the aforementioned method. The approach presented here thus creates a device designed to perform, control, and implement the steps of a variant of the method presented here in appropriate facilities. This embodiment of the invention, in the form of a device, also allows the underlying problem to be solved quickly and efficiently.

[0018] In this context, a device can be understood as an electrical device that processes sensor signals and outputs control and / or data signals accordingly. The device may have an interface, which can be implemented in hardware and / or software. In the case of a hardware-based interface, the interfaces can, for example, be part of a so-called system ASIC, which incorporates various functions of the device. However, it is also possible that the interfaces are separate integrated circuits or consist at least partially of discrete components. In the case of a software-based interface, the interfaces can be software modules, which, for example, are present on a microcontroller alongside other software modules.

[0019] A device for redirecting a belt of an occupant protection system for a vehicle has the following features: a deflector for redirecting the belt; and an optical sensor having a detection area arranged at least near the deflector and configured to detect a characteristic of a reflected light beam, wherein the reflected light beam represents a section of a surface of the belt located within the detection area.

[0020] In this way, a known occupant protection system, such as a three-point seat belt system, can be extended to include the functionality described here. The deflector can be attached to, or be attached to, a seat or a body panel of the vehicle. The deflector can have an edge for redirecting the belt. The deflector can be located completely or partially within the detection range. Furthermore, the detection range can be located adjacent to, for example, at a distance of less than 10 cm from, the deflector or the edge.

[0021] The deflection device can also include a light source to illuminate the detection area. This allows the described approach to be implemented even in low ambient light conditions.

[0022] The deflection device may further include a device for detecting the use of a seat belt of an occupant protection system for a vehicle. The device may be connected to the optical sensor via an interface. The optical sensor may be configured to detect the first characteristic of the first reflected light beam at the first time point and to detect at least one further characteristic of the subsequent reflected light beam at at least one further time point.

[0023] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular if the program product or program is executed on a computer, a mobile device or a device.

[0024] Exemplary embodiments of the invention are shown in the drawings and explained in more detail in the following description. It shows: Fig. 1 a vehicle with a belt guided over a deflector as part of an occupant protection system of the vehicle; Fig. 2 a device for redirecting a belt of an occupant protection system for a vehicle according to an embodiment; Fig. 3 an installation position of an optical sensor for a device for deflecting a belt according to an embodiment; Fig. 4 an installation position of an optical sensor for a device for deflecting a belt according to an embodiment; Fig. 5 a device for detecting the use of a belt of an occupant protection system for a vehicle according to an embodiment; Fig. 6 a flowchart of a method for detecting the use of a seat belt of an occupant protection system for a vehicle according to an embodiment; Fig. 7. A description of the movement of a belt according to an exemplary embodiment; Fig. 8 a progression of the movement of a belt according to an exemplary embodiment; Fig. 9 a flowchart of a method for detecting the use of a seat belt of an occupant protection system for a vehicle according to an embodiment; and Fig. 10 an occupant protection system for a vehicle according to an embodiment.

[0025] In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and acting similarly, without repeating these elements.

[0026] Fig. Figure 1 shows a section of a vehicle 100 with a seat belt 104 guided over a guide 102 as part of an occupant restraint system of the vehicle 100. The guide 102 is attached to a pillar of the vehicle 100's body adjacent to a seat 106 of the vehicle 100. The seat belt 104 can be used by a person seated in the seat 106 to fasten their seatbelt. The person can fasten the belt by pulling on the guide 102. Fig. Pull one visible section of the strap 104 to extend the strap 104. To extend the strap further, another section can be used, in Fig. One non-visible, further section of the belt 104 is unwound from a retractor, also called a belt retractor unit. During the extension of the belt 104, it is pulled over the deflector 102. After the seatbelt has been fastened, for example, by inserting a buckle tongue 108 into a buckle, a slack section of belt can be removed from the retractor. In this process, the belt 104 is pulled over the deflector in a movement opposite to its extension. The belt 104 can also be moved past a deflection edge or point of the deflector at a later time, for example, due to the person's breathing or due to a movement caused by acceleration acting upon the person.

[0027] In other words, it shows Fig. 1. Thus, the position and design of a seat belt guide point in the vehicle 100. The position in and / or at the seat belt guide point is particularly suitable for the installation of an optical unit for detecting the seat belt fastening status, because, firstly, integration into an existing component is easily possible and, secondly, a defined scanning capability for the seat belt 104 is provided. This point is typically located at the B-pillar or is integrated into the seat, for example in convertibles and / or new vehicle concepts / interior concepts.

[0028] Fig. Figure 2 shows a device 200 for redirecting a belt of an occupant protection system for a vehicle 100 according to an exemplary embodiment. This can be the device based on Fig. The occupant protection system described in Figure 1 is supplemented by an optical sensor 210 in this embodiment. The optical sensor 210 has a detection area arranged to encompass a section of the belt 104 guided over the deflection edge of the deflector 102. The detection area can be considered a focal plane of the optical sensor 210. The optical sensor 210 is designed to detect a characteristic of a light beam reflected from a section of a surface of the belt 104 located within the detection area.

[0029] According to one embodiment, the optical sensor 210 is part of an optical detection unit. This optical detection unit is used at the belt guide point and belt guide deflection point of the belt system to unambiguously detect whether a vehicle occupant has correctly fastened their seatbelt, including detecting any misuse of the belt system. The optical detection unit is an essential component of this unit. The optical sensor 210 determines the movement of the belt from a sequence of images of an area of ​​the belt 104 illuminated, for example, by laser light or LED, or optionally only by ambient light. According to another embodiment, a logic based on a dynamic measurement and evaluation method is also used for detection.

[0030] In Fig. 2 are forces F acting at the belt deflection point of the deflector 102 A , F G and F UThe belt force angle α typically changes depending on the size of the occupant, the seating position and / or the height setting of the deflection fitting 102, where F A The belt force is that which is applied to the belt retractor unit, F G the belt force acting on the occupant, and F U the resulting force at the deflection fitting 102. The relationship is in Fig. 2 shown in more detail. It is essential that the applied belt forces F A , F G and F U as well as the associated angle having no influence on the evaluable guidance of the belt 104 necessary for a dynamic measurement.

[0031] According to one embodiment, the optical unit utilizes a laser unit. For example, a relatively weak laser can be used, so that it poses no danger to the human eye (infrared light in the wavelength range of approximately 832 nm to 865 nm). The contact surface, in this case the surface of belt 104, is illuminated by this laser unit. The proven technology used in laser mice in computer technology can be employed. These types of computer mice, in interaction with the surface, generate a speckled pattern. By utilizing the coherent light waves of a laser source, diffraction patterns that can be analyzed become visible based on the reflections at the surface. The detection rate is increased because any irregularity of the surface causes individual waves to be reflected in different directions than their neighbors.The resulting superposition, amplification, and cancellation lead to a distinct interference pattern in a given area. This is especially true when the irregularities are larger than the wavelength of the laser light. Even paint, glass, or polished metal usually exhibit roughness at this scale, thus altering the speckle pattern.

[0032] In contrast to the procedure with a computer mouse, the optical measuring device does not move, but is held fixed in one position (permanently installed in the vehicle), whereas the belt 104 moves in a defined direction (forward or backward).

[0033] Fig. Figure 3 shows a possible installation position 315 of an optical sensor or optical detection unit for a device for deflecting a belt 104 according to one embodiment. The installation position 315 is arranged on a surface of the belt 104 below the deflector 102 for the belt 104. According to an alternative embodiment, the installation position is arranged on the deflector 102.

[0034] According to an alternative embodiment, position 315 can represent the detection range of an optical sensor.

[0035] Fig. Figure 4 shows another possible installation position 315 of an optical sensor or optical detection unit for a belt deflection device according to an exemplary embodiment. The installation position 315 is located on a pillar of the vehicle body 100, below a mounting point, a so-called belt anchor point, for the belt deflection device.

[0036] Fig. Figure 5 shows a device 500 for detecting the use of a belt 104 of an occupant protection system for a vehicle according to an exemplary embodiment. This occupant protection system can include the belt 104, a deflector 102 for the belt 104, and an optical unit consisting of an optical sensor 210 and a light source 510.

[0037] The light source 510, for example a light-emitting diode or a laser source, is configured to illuminate a section of the belt 104 located within a detection range 512 of the optical sensor 210. The optical sensor 210 is configured to detect a characteristic of a light beam 514 reflected from a surface of the belt 104. For example, the optical sensor 210 is configured to detect as the characteristic an intensity or intensity distribution of the light beam 514 at successive time points. According to one embodiment, the characteristic represents a speckle pattern. The optical sensor 210 is configured to provide information 516 about the characteristic, for example an electrical signal representing the characteristic, to the device 500 via an interface for detecting use of the belt 104.Information provided at successive time points 516 differs if the belt 104 has moved between the time points. The light source 510 and the optical sensor 210 can form a single unit or be implemented as separate elements.

[0038] The device 500 has a reading device 520 configured to read in the information 516 about the characteristics at successive time points. Furthermore, the device 500 has a determination device 522 configured to determine a movement or a progression of the movement of the belt using the information 516 about the characteristics of the reflected light beam 514 detected at successive time points. This can be an absolute or a relative progression of the belt movement, for example, an absolute or relative belt extension over time. The determination device 522 is configured to provide information about the movement or the progression of the movement. According to one embodiment, the determination device 522 is configured to provide the information about the progression of the movement to an output interface of the device 500.

[0039] According to a further embodiment, the determining device 522 is configured to provide information about the movement pattern to a comparison device 524 of the device 500. The comparison device 524 is configured to compare the movement pattern of the belt 104, detected using the optical sensor 210, with at least one threshold value and additionally or alternatively with at least one predetermined reference pattern. Using the comparison result, the comparison device 524 is configured to determine information about the type of use of the belt 104 and additionally or alternatively about the condition of a person using the belt 104, and to provide this information to an interface, for example, an output interface of the device 500. The reference pattern can represent a threshold value or a reference pattern.

[0040] Fig. Figure 6 shows a flowchart of a method for detecting the use of a seat belt in an occupant protection system for a vehicle according to an exemplary embodiment. The method can be implemented, for example, using the information provided by Fig. The 5 facilities described will be implemented.

[0041] In step 631, a first characteristic of a first reflected light beam is read in, and in step 633, a second characteristic of a second reflected light beam is read in. For example, the characteristics can be read in by determining the values ​​based on… Fig. 5. Information about a characteristic provided by the optical sensor is read in at different times as described.

[0042] In step 635, a movement of the belt is determined using the first characteristic and the second characteristic.

[0043] In further reading steps, additional characteristics can be read in, representing the characteristics of light rays reflected from the belt's surface at other times. These additional characteristics can be used in step 635 to determine the belt's movement more precisely or over a longer period.

[0044] Fig. Figure 7 shows the motion of a belt according to an exemplary embodiment. The motion pattern can be determined as described with reference to the preceding figures.

[0045] The abscissa represents time in seconds, and the ordinate represents the belt extension. The first movement sequence, 741, represents a sequence for an incorrectly belted occupant. The second movement sequence, 743, represents a sequence for a correctly belted occupant.

[0046] Fig. Figure 8 shows the motion of a belt according to an exemplary embodiment. The motion pattern can be determined as described with reference to the preceding figures.

[0047] The abscissa represents time in seconds, and the ordinate represents the relative belt extension. A first motion profile 841 represents a profile for an incorrectly belted occupant. A second motion profile 843 represents a profile for a correctly belted occupant. Furthermore, a threshold value 845 is shown, which, according to this embodiment, represents a threshold value > 3. The time axis depends on the sampling rate, so the time span shown is merely exemplary. According to an embodiment of a system according to the invention, a significantly shorter period than that shown is possible. Fig. As shown in Figure 8, an evaluable result can be determined.

[0048] The Fig. 7 and Fig. Figure 8 represents a sample comparison for the belt extension.

[0049] The in the Fig. 7 and Fig. The eight schematic measurements shown demonstrate a differentiation method using a simple threshold comparison with the threshold value 845. One possible evaluation involves calculating the difference to a previously determined initial value, determining its absolute value, and querying it against the threshold value 845. This occurs whenever the threshold is exceeded. A counter is incremented, which is then subsequently checked against another threshold, generating a corresponding status flag. In this example, the threshold was set to 3. As can be seen, immediate evaluation is not possible, but only after several measurement cycles. However, the differentiation is unambiguous, allowing for a reliable distinction between the use cases "object" and "person." The influence of different sampling variations, particularly with low sampling rates, can be addressed through additional weighting.

[0050] According to one embodiment (not shown), an advantage over a winding sensor integrated into the seatbelt mechanism is the significantly finer resolution and thus more detailed resolution of the dynamics. Based on this, the breathing patterns of a buckled occupant can be precisely detected. This allows for the development of new functions in the area of ​​individual safety. A clear advantage is that impending accidents caused by pre-existing conditions or physical causes, such as a heart attack, can also be detected, enabling appropriate responses. Furthermore, the mechanical requirements for the system are kept very low, as only minor modifications to the actual design are necessary. For example, the webbing can remain unchanged, and the guide buckle can be designed with an integrated sensor.The measurement is also virtually contactless, which contributes to excellent durability and reliability. Another advantage is that the optical unit represents a very cost-effective sensor. Thus, the device according to the invention is a very cost-effective method for detecting misuse of the seatbelt. It is also advantageous that, depending on the device's design, further sensor information can be acquired or estimated from the optical measurement, such as height, respiration rate, etc. This sensor therefore enables further steps towards personalized safety. Furthermore, it is advantageous that the misuse cases already described can be reliably identified.

[0051] In an initial implementation variant, the system detects whether the seatbelt fastening process is plausible for a vehicle occupant, e.g., before the ignition is started but after the vehicle is unlocked. The value supplied by the seat-integrated sensor system during initialization, i.e., after power-on, is, for example, 1000. All subsequent values ​​refer to this reference value. In modern vehicles, initialization no longer occurs after ignition; instead, (partial) power is applied as soon as the vehicle is unlocked. For a possible initial implementation, assuming that the seat-integrated or seat-near sensors can be powered and provide a force, current, or other value, the following relationship emerges: During the process of getting into a vehicle, each occupant experiences a pattern specific to them, which also depends on the seat's position relative to the instrument panel and on the individual (body proportions). A corresponding pattern can be applied to rear seats. This case differs significantly from the exemplary use case of a seat being loaded with an object, as described in the Fig. 7 and Fig. 8 is shown as progressions 741, 841.

[0052] Fig. Figure 9 shows a flowchart of a method for detecting the use of a seat belt of an occupant protection system for a vehicle according to an exemplary embodiment.

[0053] The process starts at a time t = t i with step 901. In step 903, a difference of a currently determined belt extension length I is calculated. GA value is formed from an initial value. A value 905, representing the belt extension length, and a value 907, representing an initial value, are supplied. In step 909, the absolute value of the difference is calculated. In step 911, a threshold check is performed, specifying a threshold value 913. In step 915, the calculation n = n + 1 is performed. In step 917, a threshold check is performed, specifying a threshold value 919. In step 921, a detection result is output, for example, by means of a status flag. In step 923, the time t is determined. i incremented: t i = t i + 1. The procedure can then be restarted with step 901.

[0054] According to one embodiment, Fig. 9. A flowchart in which no vehicle dynamics information such as speed or longitudinal deceleration ax is used. It should be noted that a simple threshold query according to this embodiment is not sufficient. The separation in the range around two values ​​is considered measurement noise and tolerance. Therefore, a dynamic evaluation is required that allows for the observation of the relative quantity, for example, the in Fig. The 8 shown progressions 841, 843 are made possible. For this reason, the one in Fig. The process shown in section 9 was carried out several times within a defined time period.

[0055] According to another embodiment, additional vehicle dynamics information, such as speed or acceleration data, or other derived parameters, is taken into account. A corresponding algorithm, for example, the steps of the described procedure, is executed when the vehicle speed exceeds or falls below a defined threshold. According to another embodiment, only situation-adaptive evaluations are performed, particularly in situations where high occupant dynamics are expected, such as during acceleration and / or braking or cornering. This can increase the stability of the solution. For this purpose, the vehicle dynamics information already available on the CAN bus is evaluated as additional input. The vehicle speed and, if available, the longitudinal acceleration (ax) are used as the baseline information. This enables dynamic monitoring.In another embodiment, the lateral acceleration (ay) is used and, in comparison to the dynamic behavior of the belt extension, is employed to increase robustness.

[0056] According to one embodiment, the sensor's dynamic values ​​can also be used to further improve passive safety (not just to increase robustness). In another embodiment, the vehicle dynamics values ​​and measured sensor responses allow conclusions to be drawn about the sensor's size and weight. In yet another embodiment, the crash process can also be observed (forward displacement, force limiter activation, etc.).

[0057] According to another embodiment, the seat belt is appropriately coded so that, in addition to relative evaluation, absolute values ​​can also be determined. This offers the advantage that current does not necessarily have to be applied before the occupant gets into the seat. Furthermore, if the seat belt is used correctly, other derived occupant measurements can be recorded and taken into account by the restraint system.

[0058] Depending on whether the use of the seatbelt or a missed buckling procedure has been detected, visual, acoustic or haptic feedback can be given to the occupant.

[0059] Fig. Figure 10 shows an occupant protection system for a vehicle according to an exemplary embodiment. This can be the occupant protection system described with reference to the preceding figures, which includes the belt 104 with which a vehicle occupant can fasten their seatbelt. Fig. Figure 10 shows a winding device 1000, such as those used in connection with Fig. is called 1.

[0060] If an embodiment includes an “and / or” connection between a first feature and a second feature, this is to be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature, and according to another embodiment either only the first feature or only the second feature.

Claims

[1] Method for detecting the use of a belt (104) of an occupant protection system for a vehicle (100), the method comprising the following steps: Reading (631) a first characteristic of a first reflected light ray, wherein the first reflected light ray represents a light ray (514) that reflects at a first time on a section of a surface of the belt (104) located within a detection area (512); Reading (633) at least one further characteristic of another reflected light ray, wherein the one further reflected light ray represents a light ray (514) that reflects at another time on a section of the surface of the belt (104) located within the detection area (512); Determining (635) a movement of the belt (104) within the detection range (512) using the first characteristic and at least one further characteristic, wherein the movement is an absolute amount of a belt extension relative to a previously determined initial value over time; and Comparing a course of movement of the belt (104) with a reference course to determine a state of a person using the belt (104), wherein the state is identified as the person's breathing processes. [2] Method according to claim 1, wherein in the reading steps (631, 633) a speckle pattern is read in as a characteristic. [3] Method according to one of the preceding claims, wherein the reading steps are performed in response to a signal indicating an opening of a door of the vehicle (100) and / or in response to a signal indicating a movement of the vehicle (100). [4] Method according to one of the preceding claims, comprising a step of detecting the first characteristic and the at least one further characteristic using an optical sensor (210) having the detection area (512), wherein the detection area (512) is arranged at least in the vicinity of a belt deflection for the belt (104). [5] Device (500) for detecting the use of a belt (104) of an occupant protection system for a vehicle (100), which is configured to perform the method according to one of the preceding claims. [6] Device for redirecting a belt (104) of an occupant protection system for a vehicle (100), comprising the following features: a deflector (102) for deflecting the belt (104); an optical sensor (210) having a detection area (512) arranged at least near the deflector (102) and configured to detect a characteristic of a reflected light beam, wherein the reflected light beam represents a section of a surface of the belt (104) located within the detection area (512); and a device (500) according to claim 5, which is connected to the optical sensor (210) via an interface, wherein the optical sensor (210) is configured to detect the first characteristic of the first reflected light ray at the first time point and to detect at least one further characteristic of the further reflected light ray at at least one further time point. [7] Device for deflecting according to claim 6, comprising a light source (510) for illuminating the detection area (512). [8] Computer program configured to perform the method according to any of the preceding claims. [9] Machine-readable storage medium on which the computer program according to claim 8 is stored.

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