Method for monitoring and / or carrying out a movement of a work device, as well as work device and computer program product

Description

[0001] The present invention relates to a method for monitoring and / or carrying out a movement of a work device, a work device which is designed to carry out the method according to the invention, and a computer program product. When earth excavation work or digging processes are carried out using excavators, forces are generated which act on the tool (e.g. excavator bucket). The excavator must overcome these forces in order to be able to continue the digging process. If the digging is too deep or if there is an obstacle in the digging trajectory, the forces which arise may no longer be able to be overcome. The same applies to other earth excavation devices or material handling devices which have a tool for picking up or gripping material and which may also encounter obstacles.The underlying problem is described below using excavators carrying out excavation work, whereby the following statements apply analogously to other earth excavation or material handling equipment.

[0002] Traditionally, excavators are controlled manually, requiring the operator to independently assess the condition of the machine and the excavation process. In manual operation, the excavator can provide the operator with feedback regarding the forces acting during the excavation process.

[0003] Excavator operations have been increasingly automated in recent years, for example, through assistance functions such as the Tool Center Point control, which assist the operator but do not fully automate the process. For autonomous or semi-autonomous excavator operation, it is necessary to adapt the planned excavation trajectory based on the forces acting and the forces that the excavator can apply, thus ensuring smooth operation. For automated operation, the (digging) forces occurring during the excavation process must therefore be taken into account in order to react to the respective environmental influences and avoid deviations in the movement sequence or even damage.

[0004] EP3351689A1 discloses a method for the semi-automatic control of an excavator, wherein a force actually acting on a working device is determined based on a comparison of measured external loads and calculated reference values.

[0005] The present invention is therefore based on the object of enabling or improving the automation of such work processes of earth excavation or material handling equipment.

[0006] According to the invention, this object is achieved by a method having the features of claim 1, a working device having the features of claim 17, and a computer program product having the features of claim 19. Advantageous embodiments of the invention emerge from the subclaims and the following description.

[0007] Accordingly, according to one aspect of the present invention, a method is provided for monitoring and / or executing a movement of a work device, preferably a material handling or earthmoving device, and in particular an excavator. The work device has a movement device with a tool for picking up material, which comprises at least two components, each of which is movable via at least one actuator. Furthermore, the work device comprises a controller by means of which the actuators of the movement device can be controlled and / or regulated.

[0008] The movement device can be a boom, in particular an excavator boom. The tool can be, for example, an excavator bucket or clamshell bucket. The tool can be regarded as one of the at least two components of the movement device, although this does not necessarily have to be the case. Of course, more than two components, each with associated actuators, can be provided, one of which can represent the tool. The other components can be, for example, a boom and a stick. The actuators can be hydraulic cylinders and / or motors (for example a slewing gear motor). An uppercarriage or a slewing gear of the work equipment can also be considered components of the movement device.

[0009] The method according to the invention comprises the following steps: 1) Recording status information relating to at least one current position and / or a current speed and / or a current acceleration of at least two components of the movement device, 2) Calculating torques which act on components due to a current configuration of the work device (i.e. model-based or theoretical torques), taking into account the said status information and component information of the components, 3) Recording torques actually acting on components, 4) Comparing the torques calculated in step 2) and the torques recorded in step 3) and determining a force vector actually acting on a defined point of application of the work device based on the said comparison, and 5) Carrying out an action depending on the force vector calculated in step 4).

[0010] These steps do not necessarily have to be performed consecutively or in the order given.

[0011] When we talk about the detection of a torque in this case, this also includes the case where the actual measurement concerns another quantity (e.g. a pressure or a force) and a suitable conversion into a torque takes place (e.g. a measured force can be converted into a torque via the cross product with a position vector, whereby the position vector can be known as component information or as information derived from it).

[0012] The method according to the invention takes into account the forces actually acting on the moving device during the execution of a work process in the form of a force vector, which is related to a defined point of application. The latter can ideally be definable and is preferably located on the tool or an end effector. In the case of an excavator performing a digging operation, said calculated force vector is, in particular, a currently actually acting digging force.

[0013] The calculation of the theoretical torques in step 2) and the recording of the actual torques in step 3) refer to the same components, allowing a direct comparison to be made and the actual force vector to be determined. To characterize the latter as accurately as possible, the torques of at least two different components must be compared so that at least two non-parallel components of the force vector can be determined. The more components of the motion device are included in the comparison, the more accurately the force vector can be determined.

[0014] However, in principle, even with components aligned parallel to each other (or the associated position vectors), a sufficient estimation of the actually acting force could work, since the unobserved force component would be absorbed by the structure of the work tool and the actuators would therefore only have to overcome the observable (or determinable by the comparison mentioned) part of the force vector.

[0015] The term "comparison" should be interpreted broadly. The comparison can therefore include any method that allows the actual acting force to be determined or estimated from the calculated torques and the determined torques. Thus, the comparison can include determining the actual acting force using the least squares method or using another estimation method, particularly a recursive estimation method.

[0016] Taking the digging force into account enables automation of the digging process, for example, by adapting a planned trajectory for a movement during the digging process (i.e., a digging trajectory) to the digging force and / or by issuing a warning to the operator of the implement if a limit is exceeded. An adjustment can, for example, take the form of replanning the digging trajectory or terminating the digging process.

[0017] Adjusting the digging trajectory and issuing a hint are merely examples of the aforementioned action, which is performed depending on the calculated force vector. Other actions are, of course, conceivable, such as adjusting machine parameters. Furthermore, adjusting the digging trajectory can depend on other conditions, such as exceeding a time threshold and / or the presence of a minimal trajectory tracking error.

[0018] The method according to the invention can be used not only in digging processes, but generally in all work processes in which external forces act on the tool (or the movement device) of the work device, which may require consideration such as an adaptation of a predetermined trajectory within the framework of automatic movement sequences. One such work process can be, for example, the picking up of material with the gripping tool of a material handling device. Here, for example, the jamming of material to be moved could lead to the occurrence of increased forces, which must be taken into account for an automatic handling process. In the present case, external forces are understood to mean in particular all forces which can arise due to the work process of the work device, for example when digging, when lifting or moving material, when picking up material, etc.

[0019] In one possible embodiment, the component information relates to a mass, a moment of inertia, and / or a center of gravity of the respective components. Ideally, geometric information or dimensions of the components are provided as component information. Data-driven models that only require the state information and torque measurements would also be conceivable here. The component information is required to determine model-based torques that act on the individual components solely based on the configuration (or setup status) and the current position of the work tool or movement device—without taking into account external forces or forces arising from the work process.

[0020] The component information can be stored in a memory of the implement, which can be, for example, part of the controller or an external component connected to the controller. The component information can also be stored in an external computer unit, such as a cloud, that is in communication with the controller, particularly wirelessly, and can be retrieved by the controller. Alternatively or additionally, the component information can be generated by a modeling tool of the controller based on a static or dynamic model of the implement or the motion device.

[0021] In another possible embodiment, the defined point of application is located on the tool, in particular on an end effector (i.e., the tool center point or TCP) of the movement device. The point of application can be fixed or variable, e.g., by the operator of the work tool.

[0022] In a further possible embodiment, it is provided that the calculated (model-based or theoretical) and the measured (actual) torques are each referenced to the same reference points of the movement device. This makes it possible to infer the presence of an additional external force, such as a digging force, by comparing the torques predicted solely on the basis of the configuration and position of the movement device and the actually measured torques. The reference points are preferably joints or swivel joints of the movement device, via which the components are rotatably connected to one another (or to the tool, whereby the latter can also be regarded as a component of the movement device).

[0023] The joints of the components of the motion device forming a kinematic chain define, in particular, position vectors, which are used to characterize the current positions or movements of the components and to calculate the torques. For example, a boom articulated to an uppercarriage of the work equipment via a first joint and pivotally connected to a stick via a second joint can be represented by a position vector running from the first to the second joint. A torque acting on the boom at the location of the first joint is then the cross product of said position vector and a force acting on the boom at the location of the second joint. The same applies to the other articulated components, such as the stick, tool, etc.

[0024] According to the example described above, a further possible embodiment provides that the reference points for the calculated torques, starting from a joint of a component on an upper carriage of the implement, define position vectors which are not parallel to one another when the torques are recorded. The torque at a rotary joint due to the external force (e.g. digging force) is the cross product of the position vector and the said force. Thus, only the portion of the force vector orthogonal to the position vector influences the torque. Therefore, at least two torque measurements are required to estimate the force vector in the plane, whose position vectors are not parallel to one another.

[0025] In another possible embodiment, the status information is acquired by means of sensors arranged on the movement device. For example, a combination of position and / or speed and / or acceleration sensors can be provided.

[0026] The working device can generally include a number of sensors for detecting different quantities.

[0027] The work device can have at least one pressure sensor for measuring the hydraulic pressure applied to an actuator. The movement device can have one or more hydraulic cylinders as actuators to move the individual components. Preferably, at least one pressure sensor is provided per hydraulic cylinder, which measures the prevailing or applied hydraulic pressure. Ideally, two pressure sensors are used per hydraulic cylinder, with both the rod and the base side of each hydraulic cylinder being equipped with a pressure sensor each. The pressure determined in this way can be used to calculate the force acting on the actuator, which can then be defined as a vector based on the known spatial position of the actuator or hydraulic cylinder.The force vectors of the actuators calculated from the geometric actuator parameters and the measured pressures are also referred to as pressure vectors for the sake of simplicity.

[0028] From the pressure vector of an actuator, taking into account the corresponding component information of the component moved by the actuator and its current position or orientation, a force acting on one of the component's joints, and thus the corresponding torque, can be calculated. The component information of the motion device preferably also includes information on the respective actuators, such as the articulation points of the cylinder and rod on the respective components, the piston areas, friction values, the masses of the actuators, etc., in order to be able to determine the corresponding forces from the pressure measurements.

[0029] Alternatively or additionally, the work tool can include at least one torque sensor for measuring the applied torque. It is conceivable that at least one torque sensor is provided per actuator to measure the torque acting on the respective components.

[0030] Alternatively or additionally, the work device can comprise at least one angle sensor for measuring the current angle of a component. The measured angle can be the angle of a component relative to another component, to an upper carriage of the work device, or to the tool. The angle sensor is ideally arranged in the area of ​​a swivel joint of a component. Preferably, one angle sensor is provided for each swivel joint in order to fully record the positions of the individual components of the kinematic chain. Alternatively or additionally, at least one sensor can be provided which measures the extension length of at least one hydraulic cylinder. The defined geometry of the movable component results in a corresponding angular position.

[0031] Alternatively or additionally, the implement can have at least one position sensor for measuring the current position of a component. The detected position can be an absolute position, which is measured, for example, using a GPS module attached to the corresponding component or a GNSS antenna (including receiver). A GPS module / GNSS antenna can also be provided at another location on the implement, such as on an upper carriage, for example to record the position of the implement. The attitude and position of the implement can also be estimated using a combination of GNSS antennas and IMUs (e.g., an IMU can be installed on an upper carriage of the implement for this purpose). This can make it possible to incorporate terrain information, which can be useful, for example, for autonomous operation of the implement and / or for tipping protection.For example, if the digging forces are too high, intelligent trajectories could be generated to continue an autonomous digging process.

[0032] Alternatively or additionally, the implement can have at least one inertial sensor for measuring the current speed and / or acceleration of a component, for example, an acceleration sensor and / or a yaw rate sensor. The inertial sensor can be an inertial measurement unit (IMU). Preferably, an inertial sensor or an IMU is provided on several components, in particular on each component of the movement device used to detect the actually acting force; in the case of an excavator boom, this means in particular on the boom and stick, and possibly on the tool. To determine the position of the implement, an IMU can also be installed on a rotatable upper carriage of the implement.

[0033] Alternatively or additionally, the work tool can have at least one sensor for detecting the current fill level and / or fill weight of the tool. This makes it possible, for example, to detect the current fill level of an excavator bucket. It can be provided that a current, automatic digging process is terminated when a maximum fill level is reached, for example, to empty the bucket at a specific unloading position. Alternatively, the fill weight could be determined by a suitable algorithm that uses information from various sources such as position and attitude estimation, terrain information, trajectory travel, etc.

[0034] Alternatively or additionally, the implement can have at least one acoustic sensor for detecting a noise from the implement during operation. The signals from this sensor are preferably evaluated using an analysis tool to determine the current operating state of the implement, such as whether a performance limit has been reached. A machine learning method or artificial neural network can be used to analyze the sensor signals in order to reliably identify different machine states based on the recorded noises and, if necessary, execute appropriate actions.

[0035] In a further possible embodiment, it is provided that the actually acting force vector is determined by means of a recursive method, for example a "Recursive Least Squares" algorithm or by means of an observer such as a Kalman filter.

[0036] Alternatively or additionally, the actually acting force vector can be multiplied by a weighting factor. This allows uncertainties in the model underlying the determination of the theoretical torques to be taken into account, thus ensuring that the maximum load limit of the motion device can be reliably maintained. The weighting factor can depend on the current state of the motion device or the work tool, or on the determined actually acting force vector.

[0037] In another possible embodiment, the executed action includes issuing a warning or notification, particularly visually and / or acoustically. This can, for example, alert the operator of the implement that a maximum force (e.g., digging force) has been exceeded, that the tool has reached its maximum filling level, that a safety range regarding the implement's tipping safety has been exceeded, or that a trajectory has been adjusted. Furthermore, it can be provided that a message or signal is sent to an external device or a cloud.

[0038] In another possible embodiment, the controller is configured to automatically control the actuators such that the tool moves along a trajectory. The controller is thus designed for autonomous or semi-autonomous control of the implement and can perform movements along predetermined trajectories. The action, depending on the calculated force vector, can include a change in the trajectory and / or an intervention in the automatic movement along the trajectory.

[0039] The trajectory can be a digging trajectory, i.e., a predefined trajectory along which the tool moves during a digging process. The work process can be divided into several work steps or phases, with one or more trajectories being predefined for each phase.

[0040] For example, an automatically executed excavation process can be divided into three phases: a first phase involves the actual excavation, in which material is picked up with an excavator bucket, and the resulting excavation forces are taken into account using the method according to the invention; a second phase involves unloading the material, for example, onto a truck; and a third phase involves moving the excavator bucket from the unloading point to the next excavation position. Of course, a division into more or fewer phases is possible, with one or more trajectories per phase.

[0041] The method according to the invention can be applied not only during the excavation itself, but also in other phases. For example, during unloading, a force can also act on the tool or the movement device, which, if appropriately taken into account, can lead to an adaptation of the trajectory.

[0042] In another possible embodiment, the determined force vector is compared with at least one reference force vector, and the action is executed based on said comparison. The at least one reference force vector preferably corresponds to a maximum possible force (e.g., a maximum possible digging force). If, for example, the magnitude of the determined force vector exceeds the magnitude of the reference force vector, a trajectory can be adjusted or recalculated, or the current work process can even be terminated. Outputting a notification is also conceivable.

[0043] The reference force vector can be stored in a memory or calculated by a modeling tool during the work process using a static or dynamic model, taking into account the current position of the work tool or the movement device.

[0044] In another possible embodiment, at least one force vector calculated based on the maximum possible pressure on an actuator is projected onto a reference vector to obtain the reference force vector. For each actuator of the movement device, a corresponding force vector can be determined and projected onto the reference vector, thus calculating several reference force vectors. For each of these reference force vectors, a comparison can be made with the actually applied force, and a specific action can be performed if necessary.

[0045] The reference vector can be the determined actual acting force vector, a velocity vector representing a trajectory followed by the motion device, or another definable or defined vector. If the reference vector does not correspond to the determined actual acting force vector, the latter is preferably also projected onto the reference vector so that the projections of the force vectors determined from the actuator pressures and the projection of the actual acting force vector can be meaningfully compared.

[0046] To obtain the force vectors for comparison with the determined actual applied force, it may be necessary to convert the force or pressure vectors applicable to the individual actuators into corresponding force vectors that are referenced to specific reference points of the components moved by the actuators, for example, to rotary joints or to a reference point on the tool or end effector. Since the components are determined by design, the pressure or force vectors can be converted into the force vectors at the reference point(s) using the available component information.

[0047] In another possible embodiment, the action is performed if the magnitude of the determined force vector exceeds the magnitude of the comparison force vector and / or a trajectory tracking error exceeds a preferably definable limit. These criteria, either individually or in combination, can lead to an action such as adjusting or recalculating the trajectory, issuing a notification, or terminating the current work process. Of course, other criteria can be used. These can either be fixed or depend on the current position of the implement and / or environmental influences.

[0048] In a further possible embodiment, the trajectory is traversed at a reference speed, wherein the action comprises a reduction in the reference speed. The reduction can be made either to a lower reference speed or to a speed of zero in order to end the current work process. The reduction can be made step by step, i.e. the reference speed is first reduced to a lower value and then the actually acting force, determined again in a subsequent step, is again compared with the comparison force vector. If the value is exceeded again, the reference speed can either be reduced again to a lower value or the current work process can be aborted directly or ended in a controlled manner.

[0049] In a further possible embodiment, the action comprises terminating the automatic movement along the trajectory, wherein a previously reached position of the tool, in particular a maximum depth and / or distance of the tool from an upper carriage of the work device, is preferably recorded and stored in the controller (or a memory connected to the controller). These values ​​can be used when planning the next work operation. In other words, when the trajectory is continued, it is preferably planned and / or executed starting from the aforementioned stored position.

[0050] In a further possible embodiment, it is provided that a parameter representing the tipping behavior of the implement is determined on the basis of the actually acting force vector and a current position of the implement or the movement device, wherein the said action is preferably carried out if the parameter exceeds or falls below a limit value. For example, a digging force determined by the method according to the invention can be used to monitor the tipping behavior of the implement. For example, if a safety range with regard to tipping safety is exceeded, an automatic work process can be aborted and the implement can be put into a safe state. This can, for example, also relate to the mere moving or setting down of a load or material. For the analysis or monitoring of the tipping behavior of the implement, the position orPosition of the work equipment is determined, for example via an IMU installed on the upper carriage of the work equipment.

[0051] In a further possible embodiment, the movement device is an excavator boom, wherein a first component is a boom articulated to an upper carriage of the work device and a second component is a stick articulated to the first component. Preferably, a third component is the tool itself. The tool can be articulated to the stick directly or via one or more further components. The various components of the excavator boom are preferably connected to one another via hydraulic cylinders and can be pivoted relative to one another. One of the components of the movement device can be the slewing gear of said upper carriage. This can be the first link in a kinematic chain formed by the movement device. Alternatively, the boom articulated to the upper carriage can represent the first link in the kinematic chain.

[0052] Not all movable components of the excavator boom necessarily have to be considered components of the movement device within the meaning of the present invention. For example, the excavator boom can have one or more bell cranks for moving an excavator bucket, to which a bucket cylinder is connected. However, it is not necessary to separately calculate model-based torques for such bell cranks and to record the actual torques. The kinematic chain of such an excavator arm is defined in particular by the swivel joint between the excavator bucket and the stick or the boom component connected to the excavator bucket.

[0053] The calculations and / or control commands can refer to actuator coordinates or Cartesian coordinates (e.g., TCP coordinates or world coordinates). However, the choice of the precise coordinate system has no influence on the subject matter of the invention. The various coordinate systems can be easily converted into one another using appropriate transformations, if necessary.

[0054] The present invention further relates to a working device, preferably a material handling or earthmoving device and in particular an excavator, comprising a movement device with a tool for picking up material, which comprises at least two components which can each be moved via at least one actuator, and a control by means of which the actuators can be controlled and / or regulated.

[0055] The implement is designed to carry out the method according to the invention, i.e., it has appropriate means for performing the method steps according to the invention. The implement can be designed according to one or more of the embodiments presented above, which were discussed in the context of the method according to the invention. This obviously results in the same advantages and properties as for the method according to the invention, which is why a repeated description is omitted here.

[0056] It is conceivable that the respective process steps, in particular steps 2), 4), and 5 described above, can be carried out by the controller or entirely or partially by means associated with the controller. Some of the process steps can be carried out outside the implement, for example, by an external computer unit or cloud, and the corresponding data can be transmitted to the implement. It is also conceivable that a separate electronic component or a separate computer unit on the implement is available for carrying out certain process steps, such as estimating digging force.

[0057] In one possible embodiment, the work tool comprises an upper carriage rotatably mounted on a mobile undercarriage, the movement device being an excavator boom, with a first component being a boom articulated to the upper carriage and a second component being a stick articulated to the first component. Preferably, a third component is the tool itself. The tool can be articulated to the stick directly or via one or more additional components. The various components of the excavator boom are preferably connected to one another via hydraulic cylinders and can be pivoted relative to one another.

[0058] The present invention further relates to a computer program product comprising instructions which, when the program is executed, cause the work device according to the invention to carry out the steps of the method according to the invention. The method steps can all be carried out by means of the work device. Alternatively, it is conceivable for one or more steps to be outsourced and carried out by a (computer) unit connected to the work device, with a corresponding data exchange taking place. The latter feature is also understood here to mean that the respective steps are carried out by the work device, since the work device provides at least the data required to carry out these steps and / or receives the externally generated data in order to carry out a corresponding action if necessary.

[0059] It may be intended that all steps requiring calculation, modeling, comparison, or other data processing be performed by the control system of the implement itself. However, as mentioned above, one or more of these steps can be performed by external modules or computers connected to the control system.

[0060] Further features, details and advantages of the invention will become apparent from the exemplary embodiments explained below.

[0061] To illustrate the method according to the invention, the following assumes a hydraulic excavator with a superstructure that can be rotated by means of a slewing gear and an excavator boom articulated thereto as the movement device. The excavator boom comprises a boom pivotally connected to the superstructure about a pivot joint, a stick or dipper stick connected to the boom at the other end of the boom and pivotally connected to the boom about another pivot joint, and an excavator bucket as the tool connected to the boom at the other end of the stick and pivotally connected to the boom about another pivot joint.

[0062] The boom, stick, and bucket are each movable or pivotable by means of at least one hydraulic cylinder, while at least one hydraulic motor drives the slewing gear of the superstructure. Each of the movable components (superstructure, boom, stick, and bucket) is thus assigned at least one actuator (slewing gear, hydraulic cylinder). For example, extending one or two boom cylinders arranged between the superstructure and boom causes the boom to pivot about the pivot joint on the superstructure, causing the end spaced apart from the superstructure to move upwards. A stick cylinder, which is articulated to the boom and stick, pivots the stick relative to the boom. A bucket cylinder is also provided, which pivots the bucket relative to the stick, possibly via one or more bellcranks. An energy recovery cylinder can also be provided between the superstructure and boom.In this case, the influence of the energy recovery cylinder (e.g. the force exerted by it during a boom support movement) must also be taken into account for the kinematic model of the implement.

[0063] The various components can be moved independently of one another using the different actuators, forming a kinematic chain. For the following discussion, it is irrelevant whether the superstructure itself is considered a component of the motion system (although the center of gravity and the mass of the superstructure are relevant for the issue of tipping prevention).

[0064] The implement includes a controller that controls the individual actuators and thus regulates its movement. The overall movement of the implement is comprised of the individual movements of the components moved by the various actuators. The controller is configured to move the implement or excavator arm automatically. For example, the controller is capable of performing an autonomous digging process in which, for example, earth is excavated and deposited at a dumping location in several consecutive and coordinated steps.

[0065] The number of moving components, their exact design, and the type and number of associated actuators are shown here only as examples. However, the method according to the invention functions independently of the exact number and design of the components and actuators, particularly with a larger number of components or degrees of freedom of movement. Likewise, the work process does not have to involve an excavation process, and the work tool does not have to be a hydraulic excavator.

[0066] The following section describes possible algorithms for automatic excavation using the method according to the invention in a hydraulic excavator. These include, among other things, the determination of the current excavation force, static and dynamic models of the excavator, and trajectory generation methods for time-indexing a reference path.

[0067] Based on a current terrain model and a target profile, the necessary work steps are planned. The result of this work planning are the individual work steps, which include, among other things, the position of the excavator, the local paths for excavating material, and the local paths for unloading the material (e.g., onto a truck).

[0068] For automated excavation, these individual work steps are linked sequentially and time-indexed using a suitable trajectory generation method. These reference trajectories can be planned in Cartesian coordinates or in the joint or actuator coordinates, among other things. If the trajectories are planned in Cartesian coordinates, they are transformed into joint or actuator coordinates using a suitable algorithm. The actual control usually takes place in the coordinates of the actuators. The task of actuator control is to ensure that the measured states of the actuators follow the reference states with minimal errors. Reference states can be, among other things, the position or the speed of an actuator.

[0069] Based on the work plan and the associated local paths, these paths are time-indexed for automated excavation. A distinction is made between three phases. The first phase involves the actual excavation, during which material is picked up with a bucket or excavator bucket (alternatively, another tool, such as a clamshell or multi-shell grab, could be used). The second phase involves unloading the material, for example, onto a truck. In the third phase, the excavator moves from the unloading point to the next excavation position.

[0070] When digging in the ground, it is possible that the actuators cannot generate enough power to overcome the digging forces acting on the tool (e.g., bucket). If this happens, the movement will stop.

[0071] During a manual movement, the operator detects this and initiates new steps. For an automated excavation process, this situation must be taken into account in the trajectory generation. Failure to do so would result in significant trajectory errors.

[0072] Various approaches are conceivable for accounting for digging forces during the digging process. One possibility is to consider the current digging forces in conjunction with the maximum possible digging force and incorporate this into the trajectory generation. A concrete example of determining the current digging force according to the present invention is described below.

[0073] To calculate the maximum possible digging force, a combination of different pressure vectors of the individual actuators is used, depending on the current position of the excavator and a static or dynamic model, to calculate a model-based digging force.

[0074] This matrix of various force vectors on the tool is then projected. The projection vector can be, among other things, the current digging force (filtered if necessary), the current speed (filtered if necessary), the reference direction, or various heuristic vectors. Furthermore, the current digging force vector is projected onto this vector. To account for uncertainties in the model, a factor is introduced that is multiplied by the projected maximum possible digging force.

[0075] The trajectory is then replanned based on various criteria. These criteria can include: A current projected digging force exceeds the maximum possible projected digging force and in addition the trajectory following error exceeds another threshold value. The trajectory following error exceeds a threshold value.

[0076] If one of these criteria is met, the reference speed of the trajectory is reduced in a first step. This reduction occurs gradually depending on further criteria such as exceeding a time threshold. If one of the above-mentioned criteria is not met again during this measure, the reference speed is increased again depending on criteria such as exceeding a time threshold. However, if the above-mentioned criteria are active for another time threshold, a further reduction of the reference speed to an even lower value or to zero is planned. If any further criteria are met, the digging process is ended and the material is unloaded. Among other things, the maximum depth reached and / or the position of the tool in the longitudinal axis is saved and used when planning the next digging process.Thus, the further planning of the trajectory is carried out adaptively from previous digging operations and the positions reached by the tool.

[0077] Further aspects for replanning an excavation trajectory can include environmental influences. For example, sensor configurations can detect the surroundings and plan based on the current terrain. This can also be repeated after each excavation. Additionally, these or other sensors can be used during the excavation process, for example, to detect the current bucket fill level and thus replan the trajectory. This replanning can, for example, terminate the current excavation process when the bucket has reached its maximum fill level.

[0078] Other sensors for determining machine conditions can include acoustic sensors, for example. These can signal, for example, when the performance limit and thus the maximum possible digging force have been reached, using suitable evaluation mechanisms. Machine learning methods, among others, can be used for this purpose.

[0079] The estimated digging force can also be used to assess tipping safety. This can also be implemented in the automated digging process. For example, if a tipping safety safety zone is exceeded, the automatic digging process can be aborted and the implement can be put into a safe state. A safe state can depend on the current position and the digging process, among other things, and can result in stopping the entire movement, for example.

[0080] In the second phase, the trajectory is planned from the last position during the digging process to the unloading position. This can be done either in Cartesian coordinates, joint coordinates, or the coordinates of the actuators. The final unloading position can be varied depending on external influences, such as the current material distribution on a truck.

[0081] In the third phase, the trajectory from the final unloading position to the next starting position is planned. This can, for example, be the movements of individual actuators (e.g., slewing gear, boom, stick, and bucket), a combination of these, or a combination of the excavator's movement with the movement of the other actuators.

[0082] The following describes a method for calculating or estimating the current digging force.

[0083] To estimate the digging force, a model-based torque is required to obtain the necessary information on the digging force based on the difference between the measured torques and the model-based torques. The calculation of the unloaded torque can take any form. In this example, a rigid body system is assumed, for which the calculation of the torques / forces applied to the joints t m e.g. in regressor form using the relation τ m = H b q q ˙ q ¨ β can be carried out. The vector β Contains parameters such as the mass, center of gravity, and moment of inertia of the components (= component information), which can occur in linear combinations. The matrix H describes the influence of the parameter vector β on the joints of the excavator depending on the current positions q, Speeds q̇ and accelerations q̈the degrees of freedom or components. These can be measured, for example, using angle sensors and IMUs arranged on the components of the excavator boom.

[0084] To estimate the instantaneous digging force, a model with high quality should be available, ie in the unloaded case, approximately τ m , mess ≈ τ m with the measured torque τ m,mess The high quality of the model is necessary to obtain information about the external force(s) and thus the digging force F-grab above τ grab = τ m , mess − τ m The differential torque the grab enables the reconstruction of the actually acting force vector or the digging force vector, assuming an attack point.

[0085] The torque at a pivot joint due to the digging force is the cross product of the position vector and the applied force. Thus, only the part of the digging force vector orthogonal to the position vector influences the torque. grab it. Therefore, at least two torque measurements are required to estimate the force vector in the plane, whose position vectors are not parallel to each other (orthogonal position vectors would be ideal).

[0086] The relationship between the force acting on the end effector F-grab and the corresponding torques at the joints the grab is τ grab = J T q F grab , with the geometric Jacobian matrix J ( q ) . The latter is the Jacobian matrix of the forward kinematics p TCP = f q , ie it applies J q = ∂ f q ∂ q .

[0087] In summary, equations (1), (3) and (4) show the relationship J T q F grab = τ m , mess − H b q q ˙ q ¨ β , which can be used with recursive estimation methods such as a "Recursive Least Squares" algorithm or with observers such as a Kalman filter to estimate the digging force F-grabIt should be explicitly noted that the point of attack is predefined by function (5) at the end effector or TCP.

[0088] The digging force estimated using the method described above can be used for several purposes. Firstly, it can be used to check whether the maximum force of the manipulator or the movement device is reached (this can be determined by the maximum force that can be absorbed by one of the actuators). If this is the case, the operator can either be given a warning or, in automated operation, the planned trajectory can be adjusted to continue the digging process. Secondly, the estimated acting force can be used to assess the excavator's tipping stability. To minimize the risk of tipping, a sufficient counter-torque must be ensured by a counterweight. This counter-torque must be greater than the torque caused by the dynamics of the equipment and the external forces acting on it.

Claims

1. Method for monitoring and / or performing a movement of an item of machinery, in particular an excavator, wherein the item of machinery comprises the following: - a movement device with a tool for picking up material, which comprises at least two components, each of which is movable via at least one actuator, and - a control system by means of which the actuators can be controlled by way of open-loop and / or closed-loop control, wherein the method comprises the following steps: 1) detecting status information concerning at least one current position and / or current speed and / or current acceleration of at least two components, 2) calculating model-based torques on the basis of a static or dynamic model of the item of machinery or the movement device, that are applied to components due to a current configuration of the item of machinery, in consideration of the detected status information and in consideration of component information of the components, 3) detecting torques actually applied to components, 4) comparing the calculated and detected torques and determining a force vector actually applied at a defined application point of the item of machinery on the basis of said comparison, and 5) executing an action depending on the calculated force vector.

2. Method according to claim 1, wherein the component information concerns a mass, a moment of inertia and / or a centre of gravity of the components, wherein the component information is preferably stored on a memory of the item of machinery or on an external computer unit connected communicatively, in particular wirelessly, to the control system and / or is generated by a modelling means of the control system on the basis of a static or dynamic model of the item of machinery.

3. Method according to claim 1 or 2, wherein the defined application point is located at the tool, in particular at an end effector of the movement device and is preferably fixable.

4. Method according to any one of the preceding claims, wherein the calculated and the detected torques are each related to the same reference points of the movement device, wherein the reference points are preferably joints via which the components are rotatably connected to each other.

5. Method according to the preceding claim, wherein the reference points, starting from a joint of a component on a superstructure of the item of machinery, define position vectors which are not parallel to each other when the torques are detected.

6. Method according to any one of the preceding claims, wherein the status information is detected by means of sensors arranged on the movement device, wherein the item of machinery preferably has one or more of the following sensors: - at least one pressure sensor for measuring a hydraulic pressure applied to an actuator, - at least one torque transducer, - at least one angle sensor for measuring a current angle of a component, - at least one position sensor, in particular a GPS module, for measuring a current position of a component, - at least one inertial sensor, in particular an inertial measurement unit, for measuring a current speed and / or acceleration of a component, - at least one sensor for detecting a current fill level and / or fill weight of the tool, - at least one acoustic sensor for detecting a noise of the item of machinery during operation, the signals of said sensor being preferably evaluated by means of an analysis means, in order to conclude a current operating state of the item of machinery.

7. Method according to any one of the preceding claims, wherein the force vector is determined by means of a recursive method and / or is multiplied by a weighting factor.

8. Method according to any one of the preceding claims, wherein the action comprises the in particular visual and / or acoustic issuance of a warning.

9. Method according to any one of the preceding claims, wherein the control system is configured to automatically actuate the actuator in such a way that the tool moves along a trajectory, wherein the action preferably includes a change of the trajectory and / or an intervention in the automatic movement along the trajectory.

10. Method according to any one of the preceding claims, wherein the determined force vector is compared with at least one comparison force vector and the action is executed on the basis of said comparison, wherein the at least one comparison force vector preferably corresponds to a maximum possible force.

11. Method according to the preceding claim, wherein at least one force vector calculated on the basis of a maximum possible pressure at an actuator is projected onto a reference vector in order to obtain the comparison force vector, wherein the reference vector is preferably the determined force vector, a speed vector that represents a trajectory travelled by the movement device, or a definable vector.

12. Method according to claim 9 and one of claims 10 to 11, wherein the action is executed when the absolute value of the determined force vector exceeds the absolute value of the comparison force vector and / or a trajectory following error exceeds a preferably definable limit value.

13. Method according to claim 9 and one of claims 10 to 12, wherein the trajectory is travelled at a reference speed, wherein the action comprises a reduction of the reference speed.

14. Method according to claim 9 and one of claims 10 to 13, wherein the action comprises a termination of the automatic movement along the trajectory, wherein preferably a position of the tool reached so far, in particular a maximum depth and / or distance from a superstructure of the item of machinery, is detected and stored in the control system, wherein more preferably, when continuing the trajectory, this is planned and / or performed starting from the stored position.

15. Method according to any one of the preceding claims, wherein a parameter representing the tilting behaviour of the item of machinery is concluded on the basis of the determined force vector and a current position of the item of machinery, wherein preferably said action is performed if the parameter exceeds or falls below a limit value.

16. Method according to any one of the preceding claims, wherein the movement device is an excavator boom, wherein a first component is a boom articulated to a superstructure of the item of machinery and a second component is an arm articulated to the first component, wherein preferably a third component of the movement device is the tool, which is articulated to the arm or to a further component.

17. Item of machinery, in particular an excavator, comprising a movement device with a tool for picking up material, which comprises at least two components each movable via at least one actuator, a control system by means of which the actuators can be controlled by way of open-loop and / or closed-loop control, wherein the item of machinery is configured to perform the method according to one of the preceding claims and wherein the control system comprises a modelling means for calculating the model-based torques.

18. Item of machinery according to the preceding claim, comprising a superstructure rotatably mounted on a mobile undercarriage, wherein the movement device is an excavator boom, wherein a first component is a boom articulated to the superstructure and a second component is an arm articulated to the first component, wherein preferably a third component of the movement device is the tool, which is articulated to the arm or to a further component.

19. Computer program product comprising commands which, when the program is executed, cause the item of machinery according to claim 17 or 18 to execute the steps of the method according to one of claims 1 to 16.