System and method for improved collision avoidance

Abstract

The invention relates to a method for avoiding a collision of the mobile machine with an external object (99), wherein the mobile machine comprises at least one first environment sensor (S1) which is positioned on a mobile machine (1) and which is used for the function for avoiding a collision of the mobile machine with an external object (99), wherein the method comprises the following steps: a. Determination of a relative position between the mobile machine and the object (99) b. Determination of a relative movement between the mobile machine and the object (99) and c. Calculating a target deceleration of the mobile machine based on the relative position determined in step a. and the relative movement determined in step b.; d. controlling or regulating the deceleration of the mobile machine based on the target deceleration calculated in step c.; e. Recording an actual value of at least one physical quantity which has changed due to the control or regulation of step d.; f. Adjusting the control of the mobile machine or the regulation of the mobile machine based on the actual value recorded in step e.

Description

Collisions of mobile work machines with other objects pose a serious risk both to the people they are serving and to the machines themselves. Particularly in situations with limited visibility, for example when a wheel loader with a loaded bucket or a dumper with a filled bucket is in the way, there is the risk of serious accidents. There are already known systems which aim to avoid such collisions or to minimize their effects. These systems include backup cameras, bird eye view cameras for enhanced surround view, and various warning and avoidance systems based on camera, ultrasound, radar, or lidar technology. They act as assistance systems to increase the safety during operation of these machines.If systems are concerned which are based on surroundings sensor systems such as radar, the sensors detect obstacles such as persons, other vehicles or walls. These known systems then calculate a time-to-collision and a critical distance, at which a warning should be issued if undershot--in this case there remains enough time for the driver to brake manually, on the basis of the transmitted data, such as the distance and relative speed of the detected object. Likewise, a distance is determined at which an automatic braking or deceleration intervention is to be triggered when the distance falls below.Similar systems are already established in the automotive sector and can also be used with adapted configurations in mobile work machines. The implementation of these systems generally includes one or more sensors, such as radar, inertial sensors for transmitting their own movements (yaw rates) to the corresponding radar sensors, as well as a control unit for evaluating the objects detected by the sensor and for calculating the relevant variables which are relevant for triggering warnings or interventions.These systems are an important step in improving safety in the operation of mobile work machines and help avoid accidents or at least reduce their severity.In systems for preventing collisions with active intervention in the traction drive, a targeted deceleration of the vehicle is initiated in order to ensure that the vehicle comes to a standstill in front of the detected obstacle. This delay can be implemented by various mechanisms, such as, for example, by using the hydrostatic travel drive (by pivoting the pump and / or motor) or by using the service brake. In developing the collision avoidance algorithm, it is necessary to make assumptions about the deceleration behavior in order to trigger the intervention in good time.The assumptions about the deceleration behavior are based on a large number of factors, including the distance from the obstacle, the relative speed between obstacle and vehicle, and the condition of the roadway. The calculation of the time at which the deceleration or braking must be initiated is decisive in order to ensure that the vehicle comes to a standstill in good time. The challenge is that the real deceleration may deviate from the deceleration used in the calculation, especially when simplified models are used, such as constant deceleration over the entire brake path.An additional problem is present in practice, where unknown interference variables can occur. For example, unknown road grade, additional load due to skid, or varying friction characteristics between wheels and ground may affect the actual deceleration. Therefore, in the development of collision avoidance systems, measures must be taken to ensure that the vehicle is stopped in good time despite such disturbances.The sub-problems that arise in this context include: I. ensuring a timely deceleration: it is to be ensured that even with simplified assumptions about the vehicle deceleration, the vehicle stops in good time in front of the obstacle. This requires precise calculations and adjustments in real time. Compensation for disturbances and unknown model parameters: In order to take into account unpredictable factors such as road gradient, loading and friction, mechanisms must be implemented that recognize and compensate for these disturbances in order to ensure the timely stopping of the vehicle.The main object is thus to find a solution to the two described sub-problems.SUMMARYAccording to one specific embodiment of the present invention, a method for avoiding a collision of the mobile machine with an external object (99) is claimed, the mobile machine including at least one first surroundings sensor (S 1) which is positioned on a mobile machine (1) and which is applied for the function for avoiding a collision of the mobile machine with an external object (99), the method including the following steps: a. ascertaining a relative position between the mobile machine and the object (99), b. ascertaining a relative movement between the mobile machine and the object (99), and c. calculating a setpoint deceleration of the mobile machine on the basis of the relative position ascertained in step a. and the relative movement ascertained in step b; d. controlling the deceleration of the mobile machine on the basis of the desired deceleration calculated in step c.; e. detecting an actual value of at least one physical variable which has changed because of the control or regulation from step d.; f. adapting the control of the mobile machine or the regulation of the mobile machine on the basis of the actual value detected in step e.It is understood that steps c. to f. are preferably performed after it is determined that intervention in the control of the mobile machine is to take place in order to avoid a collision (i.e. the function for preventing collision directly intervenes in the travel drive of the mobile machine). It is not relevant to the invention whether control of the deceleration will take place. The core idea is that an actual value of at least one physical quantity, which has changed because of the control or regulation of step d., is detected. By this detection, either feedback control of the delay or adjustment of the control can be carried out (with a similar result).BRIEF DESCRIPTION OF THE FIGURESThe present invention will be described with reference to the accompanying figures, wherein like reference numerals refer to like parts and / or to like parts and / or to corresponding parts of the system. Regarding the figures: FIG. 1 shows a wheel loader as an example of a mobile machine; FIG. 2 shows a schematic illustration of a mobile machine with environment sensors; FIG. 3 shows a method for avoiding a collision of the mobile machine with an external object according to the prior art; FIG. 4 shows a method for avoiding a collision of the mobile machine with an external object according to a first embodiment of the present invention; FIG. 5 is a block diagram for a collision avoidance function of a mobile machine according to the first embodiment of the present invention; FIG. 6 is a block diagram for a collision avoidance function of a mobile machine according to a second embodiment of the present invention.DETAILED DESCRIPTIONThe present invention will now be described with reference to specific embodiments as shown in the accompanying figures. Nevertheless, the present invention is not limited to the particular embodiments described in the following detailed description and shown in the figures, but the described embodiments are merely illustrative of some aspects of the present invention, the scope of which is defined by the claims.Other modifications and variations of the present invention will be apparent to those skilled in the art. The present description thus includes all modifications and / or variations of the present invention, the scope of which is defined by the claims.FIG. 1 shows a wheel loader 1 as an example of a work machine. However, it is worth noting that the present invention can also be applied in other fields, such as in the automotive field, and therefore cannot be applied exclusively to a mobile work machine. Moreover, the wheel loader is only an example of a mobile work machine. It is not necessary for the mobile work machine to comprise a working kinematics, as in the wheel loader.The wheel loader 1 has a boom which in turn has a plurality of boom elements for receiving loads. The boom elements are here, by way of example, a lifting arm 2 (also known as a "boom arm") and a bucket 4, which are connected to one another or to a boom carrier 5 (e.g. chassis) of the wheel loader 1 by means of axles 6 in a rotatable or pivotable manner. The cantilever elements 2, 4 are movable by means of actuators 8, 10, i.e. the rotational or pivoting movement about the axes is effected by a movement of the actuators.A first actuator 8 is provided for the lifting arm 2, which brings about the movement or rotation of the lifting arm 2 relative to the boom support 5. Likewise, a second actuator 10 is provided for the blade 4, which moves or rotates (tilts) the blade 4. The actuators comprise in particular hydraulic cylinders 12, 14, i.e. a first hydraulic cylinder 12 of the first actuator 8 and a second hydraulic cylinder 14 of the second actuator 10.The actuators 8, 10 can be controlled by a controller 18, wherein in the case of hydraulic cylinders 12, 14 directional valves are provided which control the flow of hydraulic fluid to the hydraulic cylinders.The mobile work machine 1 includes a plurality of wheels that allow movement of the mobile work machine. The movement may result in collisions between the mobile work machine and external objects (such as another mobile work machine or a tree). Such collisions pose a serious risk both to the people they are serving and to the machines themselves. In order to avoid such a risk, collision avoidance functions are generally used.In such a function, environment sensors (radar sensors, ultrasonic sensors, cameras and lidar) will generally detect their environment and recognize obstacles, other vehicles or persons in the vicinity. The acquired data is then analyzed by a control system to detect potential collisions. Once potential collision hazards are detected, the machine may trigger warnings or alarms. These can be done visually via screens or LED displays, acoustically via warning tones or by vibrations in the interior of the vehicle in order to alert the driver or the operators. Advanced systems may activate automatic emergency brakes or reduce speed to avoid collisions. These systems may be capable of acting independently to stop or slow the machine when there is a risk of a collision. Some mobile machines are equipped with driver assistance systems that help the driver avoid collisions. These systems may include steering assist, lane keeping assist, adaptive cruise control, and other functions to ensure that the engine is operated safely and without collisions. By establishing zones or areas in which the machine can operate safely and implementing zone detection systems, the machine can be programmed to perform certain actions or adjust its speed in certain areas.The exact implementation of these measures depends on the type of machine, its intended uses and the safety standards. A combination of different technologies and systems typically provides the most reliable collision avoidance for mobile machines.Detailed description of a collision avoidance function will be omitted in this description because the method of the present invention can be applied to any collision avoidance function.For this reason, the mobile work machine (as shown in FIG. 2 ) comprises a first environment sensor S 1 and preferably a second environment sensor S 2 in order to expand the field of view. The environment sensors are part of an environment sensor system of the mobile machine. The environment sensors need not necessarily be of the same type of environment sensors. Known types of environment sensors are, for example, camera-, radar-, ultrasonic- or lidar-based sensors. For example, the first environment sensor S 1 could be a camera and the second environment sensor could be a radar.Referring now to Fig. 3, the prior art problem which has already been roughly explained in the introduction of the present invention will be described in detail.Both FIG. 3 and FIG. 4 are divided into three sections. In the upper section, a time profile v(t) of the actual speed (continuous line) and the setpoint speed (dashed line) of the mobile machine is shown. In the central section, a time profile a(t) of the actual deceleration (continuous line) and the desired deceleration (dashed line) of the mobile machine is shown. In the lower section, only the time profile of a control variable (e.g. activation brake) according to the setpoint deceleration of the mobile machine is shown.As shown in FIG. 3, it is determined at time t 0 that the mobile machine is to be decelerated to avoid collision. In particular, a desired delay is calculated shortly before time t 0 and from time t 0 is to be delayed by an automatic intervention in the delay of the mobile machine based on the predicted desired delay.As shown in the central portion of Figure 3, there is in many cases a deviation between the desired delay and the actual delay of the mobile machine: i.e. the system predicted desired delay deviates from the actual occurring delay. This is because changing previously unpredictable conditions, such as road grade or loading, results in a reduced delay from prediction. By the arrow in the upper portion of Fig. 3 is meant the additional time required for the mobile machine to stop against prediction, which will of course also cause a correspondingly longer distance.It could also happen that the mobile machine stops earlier than predicted. Such behavior should also be prevented, since unnecessary deceleration of the mobile machine would take place. This would be the case if in FIG. 3 the dashed line were to represent the actual behavior and the continuous line was to represent the desired behavior (i.e. the lines of FIG. 3 were reversed). For this reason, a method according to a first embodiment of the present invention is illustrated in FIG. 4. The main difference compared to the prior art is that a regulation of the deceleration additionally takes place. This control actually enables a safe deceleration of the mobile machine to take place.As can be seen in FIG. 4, it will be possible by the control to follow the setpoint profile of the travel speed (upper section of FIG. 4 ).It is noted that it is not necessary that a continuous control of the deceleration of the mobile machine actually takes place. As will be more clearly understood from the description of the second embodiment of the present invention, the gist of the invention resides in that an actual value of at least one physical quantity that has changed due to the deceleration is detected, and the braking performance is further carried out based on the detected actual value.Referring now to Figs. 5 and 6, the logics of the two main embodiments of the present invention will be explained.FIG. 5 is a block diagram illustrating a method for avoiding collision of the mobile machine with an external object according to the first embodiment of the present invention.In a first step 100, a position and preferably a speed of the external object is determined by the environment sensors S 1 and S 2. In step 102, a relative movement between the mobile machine and the external object 99 is also determined using the information about the own movement of the mobile machine.In a further step 103, it is then determined whether the mobile machine should actually be delayed on the basis of the function for preventing collisions. This means that in this step 103, it is determined when the time t0 is from FIGS. 3 and 4 and the target deceleration of the mobile machine is calculated on the basis of the determined relative position and the determined relative movement. The information is then passed on to the regulation of the delay.In the event that it is determined in step 103 that the time t0has come and therefore the collision avoidance function is to intervene, an output is preferably generated, for example by a human machine interface 104, that the function for the collision avoidance has intervened in the deceleration of the mobile machine.In step 105 and step 106, the deceleration control will actually take place. In particular, the setpoint deceleration is taken as the reference variable and is controlled on the basis of a manipulated variable which can lead to a deceleration of the mobile machine.The intended deceleration of the mobile machine may be achieved by various methods. Therefore, the present invention is not limited to a specific type of delay. One possibility is to use hydrostatic deceleration, in which a resistance acting on the hydraulic components is generated. Alternatively, a brake engagement can also take place, as a result of which the kinetic energy of the vehicle is converted into heat. Another possibility is electromotive deceleration, which also offers the option of recuperation. In this method, the kinetic energy of the vehicle is converted into electrical energy and stored in an energy store, which can lead to improved energy efficiency. Therefore, the control variable can represent a brake pedal value or can also be a pivot angle of a hydrostatic component of a hydrostatic drive.The control is intended to take account of manipulated variable restrictions or a maximum deceleration defined by the vehicle and brake system. Methods known from the literature ("anti-windup") can be used to prevent windup effects. The control is executed as a software algorithm, e.g. in the form of a proportional (P) or proportional-integral (PI) or proportional-integral-derivative controller (PID). Also conceivable are more complex, model-based regulations, such as, for example, model predictive regulations, optimum or robust regulations, as are known from the technical regulation literature and practice.It is pointed out that for the regulation, the actual acceleration can be detected in various ways: I. Direct measurement by means of inertial or acceleration sensor systems, also known as IMU (Inertial Measurement Unit) or accelerometer. If necessary, a corresponding low-pass filtering 106 of the signal is required in order to compensate for noise effects. The direct detection of the longitudinal acceleration of the vehicle compensates for the influence of wheel slip. Numerical Derivation of an Already Present Speed Signal. The longitudinal speed is often already present in the vehicle bus system, for example by measuring the output rotational speed at the wheel, the drive shaft or the hydraulic motor in hydrostatic travel drives. However, this approach does not take into account any possible slip at the wheel. III. Detection of Vehicle Movement by Means of (Differential) PM. This also enables a reduction of the slip effects on the wheel.In order to avoid unnecessary fluctuations, the control is preferably only executed if the deviation between the actual and the desired deceleration exceeds a certain threshold value.One embodiment integrates the regulation with a pilot control, which is also referred to as a so-called 2-degree-of-freedom regulation. In this approach, the control signal is modified by the feedback control according to the pilot control by being decreased or increased. This enables the application of the regulation, for example a PI controller, to a system behavior linearized by the pilot control. As a result, the precision and dynamics of the control are improved.A second embodiment will now be illustrated with reference. Since the second embodiment is very similar to the first embodiment, detailed description of the second embodiment is omitted to avoid repetition.The main difference from the first embodiment is that in this second embodiment control of the deceleration of the mobile machine takes place instead of regulation. Specifically, in step 107, the control of the deceleration is executed. To achieve the objective of this invention, after a certain time (e.g., at least one second), the target deceleration is recomputed 108 based on the environment sensor data and based on the own motion, and then control is performed based on this new calculated target deceleration.Alternatively to this embodiment, control may be performed such that the actual deceleration is continuously determined to compare the actual behavior with the target behavior, but without actively regulating something. After a certain time, the differences are then added and it is then determined whether and how an adjustment of the control of the delay, i.e. an adjustment of the desired delay, is to take place.All these ideas have in common that there is always a determination (e.g. detection) of an actual value of at least one physical variable.The described method is stored in a memory unit and is executed by the control unit 18. The present invention furthermore comprises a computer program which causes a computing unit to carry out the described method when it is executed on the computing unit. Moreover, a machine-readable storage medium having the computer program stored thereon is disclosed.While the present invention has been described with reference to the above-described embodiments, it will be apparent to those skilled in the art that it is possible to realize various modifications, variations and improvements of the present invention in the light of the above-described teaching and within the scope of the appended claims without departing from the scope of the invention.Moreover, the areas of skill in the art would not be described herein to unnecessarily obscure the described invention. Accordingly, the invention is not to be limited by the specific illustrative embodiments, but by the scope of the appended claims.

Claims

Method for avoiding a collision of the mobile machine with an external object (99), wherein the mobile machine comprises at least one first environment sensor (S1), which is positioned on a mobile machine (1) and which is applied for the function for avoiding a collision of the mobile machine with an external object (99), wherein the method comprises the following steps: a. determining a relative position between the mobile machine and the object (99) at least from information from the first environment sensor (1); b. determining a relative movement between the mobile machine and the object (99); c. determining on the basis of the determinations from steps a. and b. that the function for avoiding a collision is to intervene in the control of the movement of the mobile machine; d. calculating a target deceleration of the mobile machine on the basis of the relative position determined in step a. and the relative movement determined in step b. ; e. controlling or regulating the deceleration of the mobile machine on the basis of the target deceleration calculated in step d. ; f. detecting an actual value of at least one physical variable which has changed from step e. on account of the control or regulation; g. adapting the control of the mobile machine or the regulation of the mobile machine on the basis of the actual value detected in step f.Method according to claim 1, wherein in step e. a regulation of the target deceleration of the mobile machine takes place and as a consequence in step e. the physical quantity is an actual deceleration.Method according to claim 2, wherein the adaptation of step f. is carried out only if the deviation between actual and desired deceleration exceeds a certain threshold value.Method according to one of claims 2 or 3, wherein the control of step e. is executed as a software algorithm, wherein the software algorithm preferably takes the form of a proportional (P) or proportional-integral (Pl) or proportional-integral-derivative controller (PID).Method according to one of Claims 2 to 4, wherein said control is combined with a pilot control, such that the control modifies the actuating signal according to the pilot control in order to enable control for a route behavior linearized by the pilot control.The method of claim 1, wherein a time interval is provided between step e. and step f., wherein the time interval is at least one second.Method according to claim 6, wherein, in the adjustment of the control of the mobile machine, a new desired deceleration is calculated on the basis of the actual value detected in step e., which is then applied in the control of the deceleration of the mobile machine.Method according to claim 7, wherein the actual value represents a relative position between the mobile machine and the object (99) and / or relative movement between the mobile machine and the object (99) and / or a current deceleration of the mobile machine.Method according to one of Claims 1 to 8, wherein the control or regulation of the deceleration of the mobile machine can be effected by a hydrostatic deceleration and / or a mechanical brake intervention and / or an electromotive deceleration.Computing unit which is configured to carry out a method according to one of the preceding claims.Mobile working machine (1) configured to absorb loads, environment sensors being provided which are set up to observe an environment of the mobile working machine; having a computing unit according to Claim 10.A computer program that causes a computing unit to perform a method according to any one of claims 1 to 9 when executed on the computing unit.A machine readable storage medium having stored thereon a computer program according to claim 12.

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