Navigation aid system for determining the direction and / or speed of a moving object

Abstract

The invention relates to a navigation aid system (100) for determining the direction of movement and / or speed of a moving object. The navigation aid system (100) has at least two ultrasonic sensors (110, 112) mounted on the moving object (200), wherein the ultrasonic sensors (110, 112) are each configured to transmit an ultrasonic signal at a transmission frequency and to receive the ultrasonic signal again after reflection at a reception frequency, and wherein the at least two ultrasonic sensors (110, 112) have a known relative spatial relationship to each other, but are oriented in different directions.The navigation aid system (100) further includes an evaluation device which is designed to determine the direction of movement and / or speed of the moving object based on the at least two received frequencies and the relative spatial reference of the ultrasonic sensors (110, 112).

Description

Technical area

[0001] The invention relates to a navigation aid system for determining the direction of movement and / or speed of a moving object, a measuring system, a vehicle or robot comprising the navigation aid system, and a use of an ultrasonic sensor for determining a direction of movement and / or speed of a vehicle. State of the art

[0002] Odometry methods use various measurement signals, such as a wheel speed signal, to estimate a relative position. This is primarily required to create an environment model and generate a trajectory that can then be followed in a controlled manner. For this purpose, "classic" sensors are primarily used to determine speed and distance traveled, or acceleration sensors, whose measured values ​​are included in the calculation of the vehicle odometry. To stabilize the odometry and minimize odometry drift, additional sensor data from camera, radar, or lidar sensors can be used. The evaluation of these sensors is often cost-intensive and requires a lot of computing power. A certain speed must also be reached for motion estimation to function robustly using the aforementioned methods and sensors.Starting off or frequent changes of direction are particularly problematic, even for robust wheel speed sensors. The error or low resolution in the wheel speed measurement leads to a significantly increased relative error at low speeds. Furthermore, many signals are filtered or have unknown dead times, which makes merging multiple signal sources difficult.

[0003] From GB 2 523 096 A a vehicle is known which has a wheel speed detection system with wheel speed sensors, a ground speed detection system and a processor to determine wheel slip or loss of traction.

[0004] JPH06230122A describes a method for detecting vehicle conditions, excluding vehicle speed, using ultrasonic waves.

[0005] US20130226508A1 relates to a speed determination device for determining a speed of an object. Summary

[0006] One object of the invention could be to improve existing odometry.

[0007] The object is achieved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0008] The described embodiments similarly relate to the navigation aid system for determining the direction of movement and / or speed of a moving object, the measuring system, the vehicle, or the robot comprising the navigation aid system, and the use of an ultrasonic sensor for determining the direction of movement and / or speed of a vehicle. Synergy effects may arise from various combinations of the embodiments, although they may not be described in detail.

[0009] Furthermore, it should be noted that all embodiments of the present invention relating to a method may be carried out in the described order of steps, but this need not be the sole and essential order of steps in the method. The methods presented herein may be carried out with a different order of the disclosed steps without deviating from the respective method embodiment, unless expressly stated otherwise below.

[0010] According to a first aspect, a navigation aid system for determining the direction of movement and / or speed of a moving object is provided. The navigation aid system has at least two ultrasonic sensors mounted on the moving object, wherein the ultrasonic sensors are each configured to transmit an ultrasonic signal at a transmission frequency and to receive the ultrasonic signal again after reflection at a reception frequency, and wherein the at least two ultrasonic sensors have a known, relative spatial relationship to one another but are oriented in different directions. The navigation aid system further comprises an evaluation device configured to determine the direction of movement and / or speed of the moving object based on the at least two reception frequencies and the relative spatial relationship of the ultrasonic sensors.

[0011] "Based on the at least two receive frequencies" can mean that, as described later, the evaluation is performed directly using the receive frequencies, or indirectly, e.g., via an assigned voltage or a determined speed. It is understood that the transmit frequency is known and the receive frequency may differ from the transmit frequency. Depending on the evaluation method, the evaluation may also be based on the transmit frequency.

[0012] The ultrasonic sensors are arranged or mounted "on" the moving object. "On" is to be understood broadly and can also mean "in," "on," "under," etc. In any case, the ultrasonic sensors are firmly connected to the moving object.

[0013] The ultrasonic sensors are thus firmly connected to the object and have a known relative spatial relationship to each other. It goes without saying that the spatial relationship concerns the position and orientation, so that an absolute relationship between the orientation of the ultrasonic sensors and the moving object is also known.

[0014] The term navigation "assistance" system was chosen to distinguish it from well-known vehicle navigation systems based on maps and satellite navigation, as well as from assistance systems such as lane departure warning systems for vehicles. Nevertheless, the navigation assistance system can be used as an assistance system such as a parking aid. Another use is to support odometry at low speeds, e.g. at traffic lights. This particularly applies to traffic light situations where it is desirable to drive close to the vehicle in front, but also to classic parking scenarios, including changes of direction, which are very challenging for odometry. The navigation assistance system refers in particular to the immediate surroundings, not to navigation from location A to a distant location B. "Navigation" here also includes a targeted, predetermined movement to be carried out, i.e.a movement that is to be carried out along a trajectory, which in principle can take place in free space.

[0015] A “moving object” is understood to be, for example, a moving or flying object, or, for example, a stationary object that performs a movement, such as the movement of a robot arm.

[0016] Ultrasonic sensors monitor the immediate surroundings of the moving object and have a range of a few millimeters to well over 5 meters or more. Compared to other sensors, the evaluation of ultrasonic data requires few resources. The ultrasonic sensors are mounted on the moving object and have a fixed spatial relationship to each other. This means that in a local coordinate system of the moving object, they have a fixed position and constant orientation in the coordinates of the moving object, at least during their deployment.

[0017] When the object moves, the receiving frequency changes relative to the transmitting frequency. That is, according to embodiments, the receiving frequency is a Doppler-shifted frequency, and the ultrasonic sensors are configured to determine a speed of the sensor in the direction of its orientation from the receiving frequency Doppler-shifted relative to the transmitting frequency.

[0018] The sensor is designed to cover the range of Doppler shift with positive and negative sign, where the range corresponds to a predefined maximum amount of velocity.

[0019] The evaluation device thus determines the speed of the sensors in their orientation. Since the orientation is known, the evaluation device can calculate speed vectors and from them the composite speed vector. The speed vector is valid for the area of ​​the moving object in which the ultrasonic sensors are positioned. If two ultrasonic sensors assigned to a specific area are referred to as sensor pairs, several such sensor pairs can be arranged on the moving object to determine the vectorial movement, or the direction and magnitude of the movement, of these areas of the moving object, and thus comprehensively determine the movement of the object.

[0020] Ultrasonic sensors are already present in many vehicles, making this additional use very cost-effective. Furthermore, ultrasonic sensors are less susceptible to environmental interference such as lighting, fog, etc. than optical sensors.

[0021] According to the invention, the direction of movement and / or speed to be determined has a predefined minimum accuracy and the at least two ultrasonic sensors are spaced apart from each other at a maximum distance such that the predefined minimum accuracy is maintained.

[0022] This is primarily a mechanical requirement. For example, different parts of a vehicle have different directional speeds when maneuvering. If a driver steers a vehicle to the right while moving forward, for example, the right front area will move faster to the right than the right middle or even the rear area. Therefore, the ratio of the Doppler of a signal emitted forward to the Doppler of a signal emitted to the right by a rear ultrasonic sensor cannot be used to determine direction. Ideally, two ultrasonic sensors are positioned at the same location. However, it is often sufficient to use existing sensors at the front and on the sides, for example.

[0023] According to one embodiment, the evaluation device is configured to determine values ​​of the at least two reception frequencies and to determine the direction of movement and / or speed from the relation of the values ​​of the at least two reception frequencies.

[0024] This means that the ultrasonic sensors convert the acoustic signal into an electrical signal, which, after an analog-to-digital conversion, is then subjected to a Fourier transformation by the evaluation device, allowing the frequency to be determined. However, other methods can also be used. For example, the input signal can be mixed with the transmitted frequency to obtain a beat signal corresponding to the Doppler frequency. The beat signal can then also be Fourier transformed or converted into a voltage.

[0025] According to one embodiment, the navigation aid system further comprises a frequency tracking circuit for each of the at least two ultrasonic sensors, and the evaluation device is configured to determine voltage values ​​of the at least two frequency tracking circuits and to determine the direction of movement and / or speed from the voltage values.

[0026] In other words, the frequency does not need to be explicitly determined. For example, a control voltage or tracking voltage of a PLL can be used, so that the evaluation device uses the relationship between two control voltages or tracking voltages for the vector velocity. Predefined voltage-velocity curves can also be used.

[0027] According to one embodiment, the received ultrasonic signal is a multiply reflected signal.

[0028] In the case of multiple reflections, the signal can, for example, first hit the ground and then be reflected off a wall or various objects. Different angles that the ultrasonic signal passes through on its path may need to be taken into account. The angles can, for example, be determined from the environment model. The evaluation device can, for example, improve the estimation of Doppler velocities through the multiple reflections and the associated independent or partially independent multiple measurements. Advantageously, the surfaces between which the signal travels are designed in such a way that they reflect the ultrasonic signal well. This can be achieved, for example, by using a metallic material or suitable wall structures. This is the case, for example, when maneuvering in tight spaces, such as when parking or driving into a garage.

[0029] According to one embodiment, the ultrasonic sensors are each configured to additionally receive an ultrasonic signal from another ultrasonic sensor of the at least two ultrasonic sensors.

[0030] This also makes additional measurements possible to verify or improve the speed measurements.

[0031] According to one embodiment, the navigation aid system has a memory in which an ultrasonic environment model is stored, and wherein the evaluation device is configured to check the plausibility of and / or improve the ultrasonic environment model.

[0032] The ultrasonic environment model contains, for example, reflective structures and their geometry in the vicinity of the sensor. For example, the environment could be a garage or a parking garage. The ultrasonic environment model can be continuously adjusted based on the ultrasonic measurements and / or measurements from other sensors, such as radar sensors or cameras, so that changing objects, such as parked vehicles or obstacles on the ground, are included in the model and kept up to date.

[0033] According to one embodiment, at least one of the ultrasonic sensors is directed towards the ground at a defined angle.

[0034] The ultrasonic sensor(s) can be positioned at an angle downwards, allowing echoes from the ground to be measured. The ground could be, for example, a road surface or the floor of a hall. The Doppler shift of these echo signals can then be used to determine the speed or movement of the vehicle. The advantage of this variant is that no walls or other objects within the detection range of the ultrasonic sensors are required for speed measurement. The echoes from the road surface are available in almost all situations.

[0035] According to one embodiment, at least one of the at least two ultrasonic sensors or a third is configured to additionally or temporarily carry out a transit time measurement for speed determination and / or distance measurement.

[0036] The signals received from the sensors can be evaluated simultaneously with the frequency determination and the time-of-flight signal, i.e. the travel time. Particularly in the case of large static obstacles, the temporal change in the time-of-flight signal, i.e. the signal travel time from the sensor to the obstacle and back to the sensor, can be used to determine the vehicle speed. This is particularly possible in the front / rear area where several ultrasonic sensors overlap. Since the echoes originate from the same target, this design is particularly suitable for parking maneuvers. By measuring the time of flight, the distance to an object can first be determined and a speed can be determined from two consecutive measurements from the same sensor to the same object. In this way, the speed determined via Doppler can be checked for plausibility or this can be supported.Especially at low speeds, a measurement using the Doppler effect can achieve greater accuracy and is also available virtually instantaneously. The distance measurement allows for the creation of a precise model of the environment. By combining the determined direction, vector velocity, and distance, a vehicle can be navigated, or a robot or, for example, a robot component can be guided to the desired position and three-dimensional orientation.

[0037] According to one embodiment, the movable object is a vehicle, a robot or a part thereof.

[0038] The moving object could be, for example, a self-driving car or a vehicle that can perform autonomous movements, such as parking. It could also be a robot or a part of a robot, such as a hand, an arm, or a leg, etc.

[0039] According to a further aspect, a measuring system for determining the speed of a vehicle is provided, comprising speed sensors for measuring the speed of the moving object, and a navigation aid system according to one of the claims. The navigation aid system is configured to determine a speed component in the direction of travel, and the measuring system is configured to support a speed measured by means of the speed sensors with the speed component determined by the navigation aid system.

[0040] According to another aspect, a vehicle or robot is provided having a navigation assistance system as described herein.

[0041] According to a further aspect, an ultrasonic sensor is used to determine a direction of movement and / or speed of a vehicle, a robot or a part thereof.

[0042] The application takes place in a navigation aid system described here. The ultrasonic sensor is one of at least two sensors in the navigation aid system.

[0043] According to a further aspect, a method for determining the direction of movement and / or speed of a moving object is provided, which method is implemented by a navigation aid system comprising at least two ultrasonic sensors and an evaluation device. The at least two ultrasonic sensors have a fixed spatial relationship to one another but are oriented in different directions. The method comprises the following steps: transmitting, by the ultrasonic sensors, an ultrasonic signal at a transmit frequency, receiving the ultrasonic signal by the ultrasonic sensors after a reflection of the ultrasonic signal at a receive frequency, and determining, by the evaluation device, a respective direction of movement and / or speed of the ultrasonic sensors in the respective directions of movement based on the at least two receive frequencies.

[0044] The steps performed by the evaluation device may be implemented as a computer program which, when executed by a processor, causes the processor to perform the steps.

[0045] The computer program may be stored on a computer-readable medium. The computer-readable medium may be considered a storage medium or storage device, such as a USB flash drive, a CD, a DVD, a data storage device, a hard disk, or any other medium on which a program element can be stored as described above. In the embodiments described herein, a storage medium may include, but is not limited to, a non-transitory computer-readable medium, such as flash memory, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM).As used herein, the term “non-transitory computer-readable media” means any tangible computer-readable media, including non-transitory computer storage devices, including volatile and non-volatile media, as well as removable and non-removable media, such as firmware, physical and virtual memory, CD-ROMs, DVDs, and any other digital source, such as a network or the Internet, as well as digital means yet to be developed, with the sole exception of a transitory propagating signal. Alternatively, a floppy disk, a compact disc - read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), or any other computer-based device embodied by any method or technology for the short- and long-term storage of information, such ascomputer-readable instructions, data structures, program modules and sub-modules, or other data. Therefore, the methods described herein may be encoded as executable instructions, e.g., "software" and "firmware," embodied in a non-transitory, computer-readable medium. As used herein, the terms "software" and "firmware" are interchangeable and include any computer program stored in memory for execution by personal computers, workstations, clients, and servers. When executed by a processor, such instructions cause the processor to perform at least some of the methods described herein.

[0046] Thus, Doppler velocities can be measured using ultrasonic sensors to determine the direction of travel and the speed of the vehicle or, in general, of the moving object. This information can be merged with other sensor information in the odometry, or a plausibility check of the odometry can be performed. The calculation of the ultrasonic environment model can also be checked for plausibility / stabilized, as odometry information is often required here as well. Multiple reflections can be used to improve the estimation of Doppler velocities. The navigation aid system or method thus offers support, particularly when maneuvering in tight spaces, such as parking or entering a garage.

[0047] The navigation assistance system presented here improves odometry. As a result, localization and the environment model also benefit. Due to the short sensor range, the method is particularly suitable for areas with low vehicle speeds or where maneuvering is required in confined spaces, such as garages or parking garages. When used for mobile or moving robots, such as robot arms, odometry is also an important component for controlling robots. These also generally operate at low speeds, so the navigation assistance system can also be used in these areas. Short description of the characters

[0048] Embodiments of the invention are described below with reference to the figures. Fig. 1 shows a block diagram of a measuring system and a navigation aid system. Fig. 2 shows a sketch of a vehicle. Fig. 3 a sketch of an example scenario. Fig. 4 shows a flowchart of a method for determining the direction of movement and / or speed of a moving object. Examples of implementation

[0049] Corresponding parts are provided with the same reference numerals in all figures.

[0050] Fig. 1 shows a block diagram of a measuring system 130 and a navigation aid system 100 for determining the direction of movement and / or speed of a moving object and Fig. 2 shows a vehicle 200 as an example of a moving object 200, on which two ultrasonic sensors 110, 112 are mounted, and which has the navigation aid system 100 and the measuring system 130, respectively. The navigation aid system 100 has Fig. 1 includes a first 110 and a second 112 ultrasonic sensor, each configured to transmit an ultrasonic signal at a transmission frequency and, after reflection, to receive the ultrasonic signal again at a reception frequency. Preferably, however, several such sensor pairs are present. The at least two ultrasonic sensors 110, 112 have a fixed spatial relationship to one another, but are oriented in different directions. The navigation aid system 100 also has an evaluation device 120 configured to determine a respective direction of movement and / or speed of the ultrasonic sensors 110, 112 based on the at least two reception frequencies and to determine the direction of movement and / or speed of the moving object 200 from the respective directions of movement and / or speeds.The evaluation device 120 has a processor 122 for carrying out steps of the method, including processing the measurement data from the sensors and generating navigation data and / or control signals for navigation. Furthermore, the evaluation device 120 has at least one memory 124, to which the processor 122 has read and write access. The memory 124 can contain program elements for carrying out the method and for storing or temporarily storing data such as measurement data or calculation data. In particular, the at least one memory 124 has an environment model that either already exists or has been created by the processor 122. The processor 122 is configured to improve and verify the plausibility of the environment model.The evaluation device can optionally further comprise a communication unit 126 for a wired and / or wireless communication connection to a server outside the moving object. For example, parts or results of the calculation can be outsourced to the server 136, or measurement data from external sensors can be received via it. Results can, for example, be transmitted and displayed on a screen 138 arranged on a garage wall. The measuring system 130 thus comprises, in addition to the navigation aid system 100, additional sensors, for example speed sensors such as a sensor 132 for measuring wheel speed or optical sensors such as a camera attached to the vehicle or an external camera 134, as well as optionally the aforementioned external server 136 or an external display device 138, each of which can be wirelessly connected to the evaluation device 120. "External" here means outside the moving object.

[0051] Fig. 3 shows a sketch of an example scenario. The vehicle 200 enters a garage 300 with walls 302, 304, 306 at a speed characterized by the speed components 114. The ultrasonic sensors 110, 112 each transmit an ultrasonic signal 310 or 312, respectively, with a known transmission frequency, which is received again by the ultrasonic sensors 110, 112 at a respective reception frequency. The respective reception frequency can then be Doppler-shifted relative to the transmission frequency depending on the speed vector 114: f_e = f_s (1+(v / c)), where f_e is the reception frequency, f_s is the transmission frequency, v is the vehicle's speed component in the direction of transmission or reception, and c is the speed of sound of the ultrasonic signal. Thus, the speed components and thus the amount, angle and direction in which the vehicle 200 is moving can be determined from the received frequency.However, direction can also be determined without determining the speed. For example, due to the linearity of the Doppler with the offset of the transmit frequency, the receive frequencies can be directly related to each other. Furthermore, the direction and / or speed can be determined, for example, from the tracking voltage of a PLL, so the receive frequency itself does not need to be determined.

[0052] Strictly speaking, the velocity components 114 of the vehicle 200 are location-dependent due to the rotational movement of the vehicle 200 relative to the vehicle 200. Therefore, the velocity components 114 are, strictly speaking, the velocity components at the location where the ultrasonic sensors 110, 112 are located on the vehicle 200. However, due to known vehicle geometries and the known position of the sensors 110, 112 in the vehicle coordinates, the velocity components at other locations can be determined mathematically. In addition to the speed and direction, the distance to the walls 302, 304, 306 can also be determined by a time-of-flight measurement. This allows a model of the environment to be created, if one does not already exist, and thus the vehicle 200 can be navigated. The walls 302, 304, 306 are preferably made of a highly reflective material. This can then also allow multiple reflections.In a multiple reflection, the signal may, for example, first hit the ground and then be reflected off a wall or various objects. Different angles that the ultrasonic signal passes through on its path may need to be taken into account. These angles can, for example, be stored in the environment model. Instead of pointing at the walls 302, 304, 306, the ultrasonic sensors can also be directed diagonally downwards, e.g., at the ground or road surface, so that the signal reflected from the ground is received as an echo. Thus, the Doppler shift of these echo signals can be used to determine the speed or movement of the vehicle.

[0053] By performing two consecutive time-of-flight measurements, the Doppler measurement can be checked for plausibility or the correct frequency can be selected in the case of multiple receptions due to different reflections. As already mentioned Fig. 1, additional sensors can be integrated into the navigation aid system 100 to provide support, or can form a system 130, referred to herein as a measuring system 130, together with the described navigation aid system 100. This means that the navigation aid system 100 can itself have such additional sensors or be part of a larger measuring system 130. These sensors include, for example, cameras on the vehicle or in the garage, or wheel sensors 132 that measure the speed of the wheels. Additional sensors such as gyrometers or acceleration sensors can also be integrated into the measuring and / or navigation aid system 130, 100. Depending on the type of sensor, the additional sensors can be arranged in the vehicle or outside the vehicle. The evaluation device 120 can also be located outside the vehicle.In these cases, a wireless communication connection can be used to transmit sensor data, control data, evaluation data, environmental model data, navigation data, etc. In particular, the evaluation device 120 can also be integrated into a server 136, e.g., a cloud server.

[0054] Fig.4 shows a flowchart of the method 400 for determining the direction of movement and / or speed of a moving object 200, which is carried out by the navigation aid system provided with at least two ultrasonic sensors and an evaluation device. The at least two ultrasonic sensors have a fixed spatial relationship to one another but are oriented in different directions. The method comprises the following steps: transmitting, by the ultrasonic sensors, an ultrasonic signal at a transmit frequency; receiving the ultrasonic signal, by the ultrasonic sensors, after a reflection of the ultrasonic signal at a receive frequency; and determining, by the evaluation device, a respective direction of movement and / or speed of the ultrasonic sensors in the respective directions of movement based on the at least two receive frequencies. List of reference symbols 100 Navigation aid system 110 first ultrasonic sensor 112 second ultrasonic sensor 114 velocity components 120 Evaluation device 122 processor 124 memory 126 Communication unit 130 measuring system 132 Speed ​​sensor, wheel sensor 134 external sensor 136 servers 138 external screen display 200 moving object, e.g. vehicle or robot 300 Garage 302, 304, 306 Walls of a garage 310 Signal of the first ultrasonic sensor 312 Signal from the second ultrasonic sensor 400 procedures 402 - 406 Procedural steps

Claims

[1] Navigation aid system (100) for determining the direction of movement and / or speed of a moving object (200), comprising at least two ultrasonic sensors (110, 112) mounted on the movable object (200), wherein the at least two ultrasonic sensors (110, 112) are each configured to transmit an ultrasonic signal at a transmission frequency and to receive the ultrasonic signal again after reflection at a reception frequency; and wherein the at least two ultrasonic sensors (110, 112) have a known relative spatial relationship to each other, but are oriented in different directions; and an evaluation device which is configured to determine the direction of movement and / or speed of the movable object (200) based on the at least two reception frequencies and the relative spatial reference of the ultrasonic sensors (110, 112), wherein the direction of movement and / or speed has a predefined minimum accuracy and the at least two ultrasonic sensors (110, 112) are spaced apart from one another to a maximum extent such that the predefined minimum accuracy is maintained. [2] Navigation aid system (100) according to claim 1, wherein the receive frequency is a Doppler-shifted frequency and the ultrasonic sensors (110, 112) are each configured to determine a speed in their respective orientation from the Doppler-shifted frequency. [3] Navigation aid system (100) according to one of the preceding claims, wherein the evaluation device is configured to determine values ​​of the at least two reception frequencies and to determine the direction of movement and / or speed from the relation of the values ​​of the at least two reception frequencies. [4] Navigation aid system (100) according to one of the preceding claims, wherein the navigation aid system (100) further comprises a frequency tracking circuit for each of the at least two ultrasonic sensors (110, 112); wherein the evaluation device is configured to determine voltage values ​​of the at least two frequency tracking circuits and to determine the direction of movement and / or speed from the voltage values. [5] Navigation aid system (100) according to one of the preceding claims, wherein the received ultrasonic signal is a multiply reflected signal. [6] Navigation aid system (100) according to one of the preceding claims, wherein the ultrasonic sensors (110, 112) are each configured to additionally receive an ultrasonic signal from another ultrasonic sensor of the at least two ultrasonic sensors (110, 112). [7] Navigation aid system (100) according to one of the preceding claims, further comprising a memory (136) in which an ultrasonic environment model is stored, and wherein the evaluation device (120) is configured to check the plausibility of and / or improve the ultrasonic environment model. [8] Navigation aid system (100) according to one of the preceding claims, wherein at least one of the ultrasonic sensors (110, 112) is directed towards the ground at a defined angle. [9] Navigation aid system (100) according to one of the preceding claims, wherein at least one of the at least two ultrasonic sensors (110, 112) or a third is configured to additionally or temporarily carry out a transit time measurement for speed determination and / or distance measurement. [10] Navigation aid system (100) according to one of the preceding claims, wherein the movable object (200) is a vehicle, a robot or a part thereof. [11] Measuring system for determining the speed of a vehicle comprising speed sensors for measuring the speed of the moving object and a navigation aid system (100) according to one of the preceding claims; wherein the navigation aid system (100) is configured to determine a speed component in the direction of travel; and wherein the measuring system is configured to support a speed measured by means of the speed sensors with the speed component determined by the navigation aid system (100). [12] A vehicle, robot or part thereof comprising a navigation aid system (100) according to any one of claims 1-10. [13] Use of an ultrasonic sensor in a navigation system according to one of claims 1 to 10 for determining a direction of movement and / or speed of a vehicle, robot or part thereof by determining the reception frequency. [14] Method (400) for determining the direction of movement and / or speed of a moving object, which is carried out by a navigation aid system (100) which at least two ultrasonic sensors (110, 112) mounted on the movable object (200) and an evaluation device, wherein the at least two ultrasonic sensors (110, 112) have a known fixed spatial relationship to each other, but are oriented in different directions; and the method comprising the steps of: transmitting (402), by the ultrasonic sensors (110, 112), an ultrasonic signal having a transmission frequency; Receiving (404) the ultrasonic signal by the ultrasonic sensors (110, 112) after a reflection of the ultrasonic signal at a reception frequency; Determining (406), by the evaluation device, a respective direction of movement and / or speed of the ultrasonic sensors (110, 112) in the respective directions of movement based on the at least two reception frequencies and the relative spatial reference of the ultrasonic sensors (110, 112), wherein the direction of movement and / or speed has a predefined minimum accuracy and the at least two ultrasonic sensors (110, 112) are spaced apart from each other at a maximum distance such that the predefined minimum accuracy is maintained.

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