Patent Publication Number: US-2021190352-A1

Title: Ventilator with a sensor device to avoid a collision between an object with the rotor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German patent application 10 2019 135 412.9, filed on Dec. 20, 2019, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates to a ventilator having a device to avoid a collision between an object with a rotor of the ventilator. 
     BACKGROUND OF THE INVENTION 
     Ventilators for room ventilation, air conditioners, PC fans, and the like typically include a protective screen. The protective screen is close-meshed so that vertebrates and in particular humans and human limbs cannot reach the rotor. The protective screen throttles a fluid conveyed by the ventilator, in particular air, at an inlet as well as at an outlet. Due to the throttling, the protective screen reduces the efficiency of the ventilator. The protective screen further causes swirling and turbulences in the fluid, which can cause disruptive noise emissions. For safety reasons, fans, for example fans in a passenger car or a PC, also generally include a protective screen even when they may be difficult to access. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a ventilator that prevents objects from colliding with a rotor in the ventilator without the use of an axial protective screen. 
     This object of the invention is solved by means of the independent claims. The subclaims represent further advantageous embodiments. The subclaims can be combined with one another in any technologically sensible manner. The description, in particular in connection with the exemplary embodiments, additionally characterizes and specifies the invention. 
     The present invention provides a ventilator having a rotor which is mounted in a rotatable manner around an axis of rotation. The rotor includes blade-like rotor blades. The ventilator includes:
         a sensor device for detecting an object approaching one of the rotor blades,   a control device, which is connected in a signal-transmitting manner to the sensor device and to the ventilator,   where the control device extrapolates a trajectory of the object from a position and a speed of the object,   and where the control device adjusts an angular position or rotational speed of the rotor in such a way that the object can continue to move along its trajectory without colliding with one of the rotor blades.       

     The rotor can be a rotor for a ventilator. As stated above, the ventilator can be a ventilator for room ventilation, PC ventilation, or similar ventilators. The ventilator can be a turbine which drives a generator, in which case the rotor with the rotor blades is a turbine wheel, an electro mechanical transducer is the generator, and the rotor is a turbine. The electro mechanical transducer can also be an electric motor which drives the rotor as a fan. 
     The sensor device can accurately detect an object approaching the rotor blade based on its current position, speed, and acceleration. The sensor device also may convert optical and/or acoustical signals into machine-readable analog or digital signals, which can be detected by the control device. The sensor device can detect the object independently of ambient conditions, such as darkness and fog. 
     The control device may include a microprocessor and memory, and a program may be stored on the memory. The control device detects the data collected by the sensor and uses the program to evaluate the data. The program calculates the position, speed, and acceleration of the object from the data, and correlates them with the current and future positions of the rotor. When the trajectory of the object remains constant, the control device is able to determine when and with which rotor blade a collision will take place if the speed of the rotor remains the same. In the case of an imminent collision, a signal-related, optical, or acoustic warning signal may be output. 
     The control device also can determine if the object will pass between the rotor blades, thus avoiding a collision. The system will unlikely react in this case. In another scenario, a collision can be prevented by accelerating the rotor. In this case, the control device prompts the electro mechanical transducer (the electric motor) to accelerate the rotor. However, acceleration of the rotor to avoid a collision preferably only occurs when a collision cannot be avoided by decelerating the rotor, for example in the case of very fast objects, such as birds and bats. In a further case, the control device recognizes that a collision can only be avoided by stopping the rotor. In that case, the control device will stop the rotor. 
     In one embodiment, the rotor can be decelerated via a braking device. The braking device can be embodied to slow the rotor down to a halt within less than two rotations of the rotor. The rotor is preferably decelerated before an object can enter into a protective region around the rotor. 
     The braking device can be separate or it can be integrated into the electro mechanical transducer. The braking device decelerates the rotor so quickly that the rotor stops before the object reaches its vicinity. For this purpose, the braking device can decelerate the rotor to varying degrees based on the time remaining before a collision. 
     In one embodiment, the braking device includes an annular surface arranged at an outer circumference of the rotor and a brake shoe cooperating therewith. The inner circumference of the annular surface is adjacent to the rotor blades. In case of an abrupt braking of the rotor blades, forces act on the rotor blades against the direction of rotation while the inertia of the rotor and rotor blades is in the direction of rotation. The outer circumferential annular surface supports the annular surface of the rotor blades, so that the forces cannot lead to an overloading of the rotor blades. The actuator and the brake shoe can be arranged at a massive wall ring which surrounds the rotor. The actuator can be electro mechanical and can actuate the brake shoe via an electrically controllable magnet. In one alternative, the actuator can also have a spring which biases the brake shoe in the closing or braking position during operation of the ventilator so that the brake shoe is applied to the annular surface by means of the spring in the event of a failure of the actuator to decelerate the rotor. In one embodiment, the annular surface is aligned with an outer circumference of the rotor blades. In other embodiments, the annular surface is arranged farther on the inside or farther on the outside in the radial direction with respect to the rotor blades. 
     In a further embodiment, the ventilator includes a pyrotechnically inflatable catch cushion, which has a slow-down effect and which is deployed before the rotor blade collides with the object to stop the rotor blade. 
     With larger fans, the pyrotechnically inflatable catch cushion, also referred to as an airbag, can be arranged at the rotor blades. With smaller rotors, the catch cushion can be arranged at a frame which supports the rotor. The catch cushion can engage between the rotor blades or can be arranged on the outer circumference so that the rotor blades strike against the catch cushion after the catch cushion is inflated, thus stopping the rotor blades. For torque support, that is, to prevent a breakdown torque acting on the rotor, two pyrotechnically inflatable catch cushions can be arranged offset from one another by 180°. The catch cushion preferably stops the rotor in less than 100 milliseconds, in particular less than 50 milliseconds, and particularly preferably less than 20 milliseconds. These specified times within which the catch cushion stops the rotor includes the time from triggering the pyrotechnical propelling charge until the rotor stops rotating. 
     In an alternative or additional embodiment, the ventilator has an outer circumferential pyrotechnically inflatable catch cushion that extends around the ventilator, in particular around one half of the ventilator, after inflation. 
     The outer circumferential pyrotechnically inflatable catch cushion may inflate around the ventilator hemispherically. 
     The outer circumferential pyrotechnically inflatable catch cushion that inflates around the ventilator can protect a surrounding area of the ventilator against flying parts when, for example, the rotor is slowed down so abruptly that its inertia leads to a mechanical destruction of the rotor. 
     The mechanical destruction can occur in particular when, according to a further embodiment, the ventilator has a mechanical stopping device which enters into a trajectory of the rotor blades, abruptly bringing the rotor to a halt and mechanically overloading the rotor blades. In this embodiment, the mechanical stopping device is actuated to avoid a collision. 
     In one embodiment, the stopping device can be formed by a stopping element which can be moved into a trajectory of the rotor blades via a corresponding actuator, which will likely cause damage to the rotor blades. The stopping element can be moved into the trajectory of the rotor blades in an angular position. In one embodiment, several stopping devices are distributed on the circumference of the rotor. In a further embodiment, the stopping devices are distributed evenly around the circumference of the rotor. In a further embodiment, the number of stopping devices corresponds to the number of rotor blades arranged on the rotor. In this case, the stopping device corresponding to the rotor blade that is expected to collide with the object can be activated in a very short time exactly when the object is expected to collide with the rotor blade, thus mechanically stopping the target rotor blade. 
     The actuator of the stopping device can be arranged at a massive wall ring which surrounds the rotor. The actuator can be electro mechanical and can actuate the stopping device via an electrically controllable magnet. In an alternative embodiment, the actuator can also have a spring, which is biased in the direction of the stopping position during operation of the ventilator, so that the stopping device is moved into the trajectory of the rotors by means of the spring in the event of a failure of the actuator or of the control device, respectively. 
     In one embodiment, the ventilator further has an axially covering pyrotechnically inflatable catch cushion, which forms a barrier between the object and the rotor, in order to prevent a collision between the object and the rotor. 
     The barrier fulfills two functions. On the one hand, it protects the surrounding area against flying parts. On the other hand, it completely prevents the object from entering the region of the rotor. 
     In one embodiment, the control device short-circuits conductor windings of a stator and/or electric rotor of the electro mechanical transducer in order to decelerate the rotor. 
     Depending on the construction of the electro mechanical transducer, either the electric rotor or the stator or both are alternatingly supplied with current in order to generate electricity or in order to provide mechanical drive power. The electro mechanical transducer can be a brushless direct current motor, in which case the stator is alternatingly energized in order to drive the rotor. When the stator is short-circuited, an induction in the stator has a braking effect on the rotor. However, the braking power, which can be attained in this way, is not as high as, for example, a braking power which can be generated by the braking device. The braking power, which can be attained by a separate brake, can be selected to be higher. In one embodiment, the stator is therefore initially short-circuited in response to small required delays of the rotor, for example when the object is still sufficiently far away. When the rotor is unexpectedly still not decelerating fast enough, the brake is additionally activated. When the brake also does not decelerate the rotor quickly enough, one of the pyrotechnically inflatable air cushions can be deployed. In the alternative or in addition, the above-described stopping device can additionally stop the rotor or individual rotor blades. 
     In one embodiment, the control device instructs the electro mechanical transducer to increase its rotational speed so that instead of the object colliding with a rotor blade, it passes through the rotor between two adjacent rotor blades. 
     This embodiment can be productive, for example, when the object is a bird, which, compared to the rotor, is so fast that the rotor could not be brought to a halt quickly enough. Instead of decelerating the rotor, an acceleration as described could be productive to avoid collision in this case. In the case of a driven ventilator, the increase of the rotational speed can take place by means of an increase of an electrical drive power. In the case of a driving ventilator, which is used as a turbine, the increase of rotational speed can be attained by decreasing (braking) the generator power. 
     In one embodiment, the sensor device has two sensors, where a first sensor detects a first measured variable, and where a second sensor detects a second measured variable which differs from the first measured variable. The first and second sensor may be selected from a non-exhaustive list, including: an infrared sensor, an infrared camera, an ultrasonic sensor, a lidar sensor, a radar sensor, and/or a camera operating under visible light. 
     With two sensors, the sensor device can validate the signals received from the sensors. In addition, having two sensors can increase the accuracy of detecting the object. Backup sensors may also be provided for the first and second sensors in case one of the sensors fails. 
     In at least one embodiment, the invention is directed to a method for a ventilator having a rotor with rotor blades, an electro mechanical transducer connected in a rotationally fixed manner to the rotor, and a sensor device, where the method includes the following steps:
         detecting an object approaching the rotor blade via the sensor device,   extrapolating a trajectory of the object from a position and a speed relative to the ventilator and the rotor blades considering an angular position and rotational speed of the rotor,   adjusting the rotor speed such that the object can continue to move along the trajectory without colliding with one of the rotor blades.       

     The rotor speed may be adjusted via an actuator, which actuates a brake shoe that acts on an annular surface arranged at the outer circumference of the rotor in order to decelerate the rotor. For this purpose, the control device is connected in a signal-transmitting manner to the actuator. 
     As mentioned above, the rotor speed may be adjusted by unfolding a pyrotechnically inflatable catch cushion, which has a slow-down effect and stops the rotor. The catch cushion preferably unfolds so that the rotor can be stopped in less than 100 milliseconds, in particular less than 50 milliseconds, and particularly preferably less than 30 milliseconds. 
     The present invention also is directed to a computer program product that includes program code stored on a computer-readable data carrier to carry out a process embodied as described above when the computer program product is executed on a computer, in particular on a control device for a ventilator. 
     For this purpose, the computer program can have encoded instructions which carry out the process when the computer program is executed on a computer, in particular a computer in a control device disclosed herein. 
     In terms of hardware and/or software, the process for detecting objects and for stopping or accelerating, respectively, a rotor in order to avoid a collision with an object, can be formed in a control device. The control device can include a digital processing unit, in particular a microprocessor unit (CPU), which is preferably data- or signal-connected, respectively, to a storage and/or bus system, and/or one or several programs or program modules. The CPU can be formed to process commands, which are implemented as a program stored in a storage system, to detect input signals from a data bus and/or to output signals to a data bus. A storage system can have one or several different storage media, in particular optical, magnetic solid bodies, and/or other non-volatile media. The program can be designed such that it represents or is able to carry out the processes described herein, respectively, so that the CPU can perform the steps of processes of this type, and can thus control, in particular regulate, the actuators for the brake and the stopping device, the pyrotechnically inflatable catch cushions, and the electro mechanical transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantages of the invention become clear on the basis of the exemplary embodiments, which are illustrated in the drawings, in which: 
         FIG. 1  schematically shows a ventilator comprising a control device and a sensor device; 
         FIG. 2  schematically shows a ventilator comprising a stopping device; 
         FIG. 3  schematically shows a ventilator comprising a braking device; 
         FIG. 4  schematically shows a ventilator comprising a pyrotechnically inflatable catch cushion, which has a slow-down effect and which stops the rotor; 
         FIG. 5  schematically shows a ventilator comprising an axially covering pyrotechnically inflatable catch cushion, which axially covers the rotor; 
         FIG. 6  schematically shows a ventilator comprising an outer circumferential pyrotechnically inflatable catch cushion, which protects a surrounding area against flying parts; and 
         FIG. 7  schematically shows three process steps, which can run in the control device in order to control the ventilator. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     The nature of the following description is only illustrative. For the sake of clarity, the same reference numerals are used in the drawings in order to identify similar elements. The devices illustrated in  FIGS. 2 to 6  can be provided individually or in combination with a ventilator according to claim  1 . For the sake of clarity, they are illustrated separately from one another. 
       FIG. 1  shows a ventilator  1  having a rotor  3  which is mounted in a rotatable manner around an axis of rotation  2 . Rotor blades  5  extend from a hub  4  at the rotor  3 . An electro mechanical transducer  6 , which is connected in a rotationally fixed manner to the rotor  3 , can be arranged in the hub  4 . 
     A sensor device  7 ,  7 ′ for detecting an object  8  which may be present is arranged close to the ventilator  1 , possibly connected to the ventilator  1  or in a higher-level, non-illustrated unit. The sensor device  7  detects the object  8 . The sensor device  7  detects a position x of the object  8  and generates a signal therefrom, which can be evaluated by a control device  9 . The control device  9  is connected in a signal-transmitting manner to the sensor devices  7 ,  7 ′ and to the ventilator  1 . Two sensor device  7 ,  7 ′ can be provided, as illustrated in  FIG. 2 , in order to be able to calculate a larger region around the ventilator  1 . The sensor device  7 ,  7 ′ can have sensors  10 ,  10 ′ for detecting the object  8 . 
     A computer program, which is able to calculate a speed v and an acceleration a of the object  8  from a temporal change of a position x of the object  8 , and to at least temporarily store this for processing purposes, runs in the control device  9  during operation of the ventilator  1 . The control device  9  can calculate a trajectory  11  of the object  8  from the position x, the speed v, and the acceleration a of the object  8 . The trajectory  11  thus reflects a position x of the object  8  in the next few seconds. An angular position p and a rotational speed n of the rotor  3  is further known to the control device  9 . From the trajectory  11  of the object  8  and from the angular position p and rotational speed n, with the knowledge of a geometry of the rotor  3  as well as a number and angular position of individual rotor blades  5 , the control device  9  can now recognize whether the trajectory  11  of the object  8  intersects a trajectory of the rotor blades  5 . If the trajectories of the rotor blades  5  and of the object  11  intersect, a collision could be imminent. The control device  9  adjusts the rotational speed n of the rotor  3  to prevent a collision. The rotational speed n may be adjusted, for example, by means of additional components or by means of a corresponding control of the electro mechanical transducer  6 . All of the embodiments discussed in connection with  FIGS. 2 to 6  can be applied individually or in combination with ventilator  1  according to  FIG. 1 . 
     The rotational speed n adjustment may accelerate the rotor  3 , thus increasing the rotational speed n, when a speed v and acceleration of the object  8  is high enough to be able to pass between two rotor blades  5  without making contact with the blades  5 . Contrary to the exemplary illustration, the object  8  can also be a very fast bird, the electro mechanical transducer  6  can be a generator, and the rotor  3  can be a turbine. The rotor  3  can also be stopped by short-circuiting a non-illustrated stator winding provided in the electro mechanical transducer  6  so that self-induced currents can generate a magnetic field, which has a slow-down effect. The stator can also be controlled by generating a torque, which decelerates the rotor  3 . 
     As illustrated in an exemplary and schematic manner in  FIG. 2 , the adjustment of the rotational speed n can also take place via a stopping device  12 ,  12 ′. As shown in the exemplary embodiment, two stopping device  12 ,  12 ′ are provided. Alternatively, the number of stopping devices  12 ,  12 ′ may correspond to the number of rotor blades  5 . The stopping device  12 ,  12 ′ has an actuator  13  and a stopping element  14 . The stopping element  14  can be a plastic block or the like. When the actuator  13  is triggered, the stopping element  14  enters into a trajectory  15  of the rotor blades  5  and prevents them directly from continuing to rotate. Due to the abrupt stop, the rotor blades  5  may be damaged as a result of an inertia i3 of the rotor  3 . So that flying shards do not lead to injuries to the object  8  or other non-illustrated objects, an airbag, which completely surrounds the ventilator  1 , can simultaneously be deployed when the stopping device  12 ,  12 ′ is triggered, as illustrated in  FIG. 6 . 
     As mentioned,  FIG. 6  shows a ventilator  1  comprising an airbag or an outer circumferential pyrotechnically inflatable catch cushion  16 , respectively, which is formed such that it extends around the ventilator  1  or the rotor  3 , respectively, when inflated. The pyrotechnically inflatable catch cushion  16  can in particular be hemispherical. In the exemplary embodiment shown in  FIG. 6 , an outer circumferential pyrotechnically inflatable catch cushion  16 ,  16 ′ is in each case arranged around one half  17 ,  17 ′ of the ventilator  1 . In an operational position, the outer circumferential catch cushions  16 ,  16 ′ are arranged in airbag modules  18 ,  18 ′. The outer circumferentially pyrotechnically inflatable catch cushion  16  is deployed when damage to the rotor  3  is expected, when damage has occurred to the rotor  3 , or when an object approaches close to the rotor. The airbag modules  18 ,  18 ′ receive a signal transmitted from the control device  9  to trigger a pyrotechnical or any other suitable propellant charge and deploy the catch cushion  16  when the control device  9  determines an imminent collision between the object  8  and the rotor  3  and/or when the control device  9  determines that the rotor  3  will be damaged by the stopping device  12  (see  FIG. 2 ). 
     The pyrotechnically inflatable catch cushion  16 ,  16 ′ illustrated in  FIG. 6  is one of three alternatives disclosed herein. A further alternative is stretched over the rotor  3  like a curtain, according to  FIG. 5 . A further alternative engages with a trajectory  15  of the rotor blades  5 , similar to the stopping device  12 ,  12 ′ to stop the rotor  3 . 
     According to the exemplary embodiment illustrated in  FIG. 3 , the rotor  3  can be stopped by means of a braking device  19 . For this purpose, the braking device  19  decelerates the rotor  3  to stop it in a short time or in a very short time. This takes place in particular before an object can enter into a protective region  20  around the rotor  3 . For this purpose, the braking device  19  may include a brake shoe  21 , which can be moved inwards via an actuator  22  opposite a radial direction R. The actuator  22  and the brake shoe  21  are fastened to a massive wall ring  28 , which surrounds the rotor  3 . The brake shoe  21  then frictionally engages an annular surface  23  arranged at the outer circumference of the rotor  3  to decelerate the rotor  3 . As illustrated in  FIG. 3 , several brake shoes  21 , 21 ′ and actuators  22 , 22 ′ can be arranged so as to be evenly distributed around the circumference. The braking device  19  can be actuated in order to stop the rotor  3  when stopping the electro mechanical transducer  6  by short-circuiting the stator winding or other mitigating measures does not stop the rotor  3  before the object collides with the rotor blade. 
     As already described above in connection with the hemispherically inflatable pyrotechnical catch cushion that protects the surrounding area against flying parts, the ventilator according to the exemplary embodiment illustrated in  FIG. 4  includes a pyrotechnically inflatable catch cushion  24  which has a slow-down effect and can be deployed before an imminent collision of a rotor blade  5  with the object  8  to stop the rotor blade  5  in less than 100 milliseconds, in particular less than 50 milliseconds, and particularly preferably less than 30 milliseconds. The pyrotechnically inflatable catch cushion  24  is arranged in an airbag module  25  in an appropriate position on the ventilator  1 . The airbag module  25  is arranged at a massive, that is, a mechanically durable wall ring  28  (see  FIG. 3 ). Several pyrotechnically inflatable catch cushions  24 ,  24 ′ can be arranged so as to be distributed around the circumference of the rotor  3 . The pyrotechnically inflatable cushion or cushions  24 ,  24 ′ can be deployed when the braking device  19  is unable to stop the rotor  3  in due time before a collision between the object  8  and the rotor  3 . The pyrotechnically inflatable catch cushions  24 ,  24 ′ are arranged in airbag modules  25 ,  25 ′ at the wall ring  28  in an appropriate operational position of the ventilator. The airbag modules  25 ,  25 ′ are connected in a signal-transmitting manner to the control device  9  (see  FIG. 1 ). If the control device  9  detects a collision of the object  8  with the rotor  3  or individual rotor blades  5  and an alternative slow-down embodiment would not bring the rotor  3  to a halt in due time before the collision, the control device  9  transmits a signal to the airbag modules  25 ,  25 ′ to trigger the pyrotechnically inflatable catch cushions  24 ,  24 ′. The catch cushions  24 ,  24 ′ also extend so far away from the rotor  3  in the axial direction A (away from an image plane in  FIG. 4 ) that an object  8  (animals or a body part, respectively) cannot get into the vicinity of the rotor  3 . 
     To attain an even slow-down, for torque support and/or to prevent a breakdown torque acting on the rotor  3 , two or more pyrotechnically inflatable catch cushions  24 ,  24 ′, stopping devices  12 ,  12 ′, or brake shoes  21 ,  21 ′, can be arranged offset from one another. 
       FIG. 5  shows a further alternative of a pyrotechnically inflatable catch cushion  26 , which stretches over the rotor  3  after deployment, thus forming a barrier between the object  8  and the rotor  3  before the object  8  can get into the protective region  20  opposite to an axial direction A. What is shown is an axially covering pyrotechnically inflatable catch cushion  26 . The axially covering, pyrotechnically inflatable catch cushion  26  is arranged in an airbag module  27  in an appropriate operational position of the ventilator  1 . The airbag module  27  is connected in a signal-transmitting manner to the control device  9  (see  FIG. 1 ). If the control device  9  detects a collision between the object  8  and the rotor  3  or individual rotor blades  5  and when alternative slow-down embodiments would not bring the rotor  3  to a halt in due time before a collision, the control device  9  triggers the pyrotechnically inflatable catch cushion  26  so that a barrier is formed between the object  8  and the rotor  3 . 
     As described above, the ventilator  1  can have two sensor devices  7 ,  7 ′, each comprising two sensors  10 ,  10 ′. A first sensor  10  can detect a first measured variable, for example electromagnetic waves. A second sensor  10 ′ can detect a second measured variable which differs from the first measured variable, for example electromagnetic waves in a different frequency range, or a completely different measured variable, for example ultrasonic waves. The sensors can be selected from a non-exhaustive list including: an infrared sensor, an infrared camera, an ultrasonic sensor, a lidar sensor, a radar sensor, and/or a camera operating under visible light. 
     Referring to  FIGS. 1 and 7 , the present invention is also directed to a process for controlling or regulating the ventilator  1 . In a first step  701 , the sensor device  7  detects an object  8  (see  FIG. 1 ). The object  8  does not need to be a rabbit, as illustrated. Any, in particular, living objects, can be detected. After the detection of an object  8  approaching the rotor blade  3 , in step  702  the process extrapolates a trajectory  11  of the object  8  using a position x and a speed v of the object  8  relative to the ventilator  1  and determines if the object  8  is on a collision course with the rotor blades  5 , taking into consideration an angular position p and rotational speed n of the rotor  3 . The sensor devices  7 ,  7 ′ detects a position x of the object  8  at several points in time. A speed v and an acceleration a can be calculated from the positions x at several points in time. A trajectory  11  resulting at constant speed v and acceleration can be calculated from these values. The trajectory  11  provides information about future positions x of the object  8 . The future position x of the object  8  and also its extension around the position x is considered in the extrapolation. Subsequently, in step  703 , the rotor speed n is adjusted so that the object  8  can continue to move along the trajectory  11  without colliding with one of the rotor blades  5 . 
     Several possible process sequences and time periods, in which different protective measures can be activated, will be described below in an exemplary manner. They shall in no way be presumed to be limiting, because the specified time periods are strongly dependent on the inertia i3 of the rotor  3 . 
     In case there is a very long time period (1 to 10 seconds) remaining before the collision, the rotor speed n may be adjusted by turning-off the rotor  3 . In case there is a long time period (1 to 5 seconds) remaining before the collision, the rotor speed n may be reduced by short-circuiting a stator winding. Otherwise, if the rotor  3  cannot be electro mechanically slowed down in due time (0.1 to 2 seconds), a braking device  19  may be used to reduce the rotor speed n (see  FIG. 3 ). 
     In case the braking device  19  cannot bring the rotor  3  to a halt before a collision with the object, a stopping device  12  can abruptly bring the rotor  3  to a halt, which may result in damage to the rotor blades  5 . Alternatively, or in addition to the use of the stopping device  12  to halt the rotor blades, the rotor speed n can be reduced by the deployment of three different, yet combinable, pyrotechnically inflatable catch cushions  16 ,  24 ,  26 . A catch cushion  24  not only decelerates and stops the rotor blades, but it also extends so far in the axial direction A and opposite to an axial direction A that it prevents the object  8  from engaging with the rotor  3 . 
     As discussed above, in case the braking device  19  is unable to stop the rotor  3  before it collides with the object, a stopping device  12  can be used to abruptly bring the rotor  3  to a halt, which will likely damage the rotor blades  5 . In case there is damage to the rotor blades  5 , the surrounding area can be protected against flying parts by deploying a catch cushion  16  arranged at an outer circumference, as shown in  FIG. 6 . This is the preferred embodiment when the ventilator  1  does not have an outer circumferential annular surface  23  or when this annular surface  23  is likewise destroyed. 
     If the stopping device  12  is used to reduce the rotor speed, the surrounding area can be protected from flying parts when a catch cushion  26  is deployed to axially cover the rotor  3 , as shown in  FIG. 5 . This is preferred when the ventilator  1  does not have an outer circumferential cage. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Ventilator 
           2  axis of rotation 
           3  Rotor 
           4  Hub 
           5  rotor blades 
           6  electro mechanical transducer 
           7 ,  7 ′ sensor device 
           8  Object 
           9  control device 
           10  first sensor 
           10 ′ second sensor 
           11  Trajectory 
           12 ,  12 ′ stopping device 
           13 ,  13 ′ Actuator 
           14  stopping element 
           15  Trajectory 
           16 ,  16 ′ catch cushion 
           17 ,  17 ′ Half 
           18 ,  18 ′ airbag module 
           19  braking device 
           20  protective region 
           21 ,  21 ′ brake shoe 
           22 ,  22 ′ Actuator 
           23  annular surface 
           24  catch cushion 
           25  airbag module 
           26  catch cushion 
           27  airbag module 
           28  wall ring 
         A acceleration 
         A axial direction 
         P angle 
         V speed 
         X position