Method for determining the weight of a load carried by a boom of a work machine

Abstract

The invention relates to a method for determining the weight of a load picked up by a boom of a work machine (1), wherein the boom forms a kinematic chain with a plurality of links (5, 2, 4) which are coupled to one another by at least one pivoting device, wherein the at least one pivoting device includes a rotary joint (6) and a hydraulic actuator (8, 10), wherein a weighing function is provided in order to determine the weight of picked up loads, wherein the weighing function includes friction terms for the at least one pivoting device; wherein a movement value (24) for the actuator of the at least one pivoting device is determined from an operating signal value (22) for the actuator of the at least one pivoting device, which movement value corresponds to a size of a movement orRotational movement of the links of the kinematic chain relative to one another, which are coupled by the at least one pivoting device, corresponds to and / or indicates this; wherein an amount of the movement value (24) for the actuator of the at least one pivoting device is determined; and wherein a weight value (30) of the load is determined by the weighing function taking into account the amount of the movement value (130), wherein the amount of the movement value is used in the consideration to select suitable times for determining the face value of the load, so that the weight value can be determined with high accuracy.

Description

The present invention relates to a method for determining a weight of a load absorbed by a boom of a work machine, and to a computing unit and a computer program.BACKGROUND OF THE INVENTIONCertain working machines, e.g. construction machines such as excavators or wheel loaders, have a movable boom or working arm with a plurality of boom elements, at the end of which loads can be picked up by means of one of the boom elements, e.g. a bucket or fork, in order to move these. The boom elements are movable by means of actuators, in particular hydraulic cylinders. Such work machines can have a weighing function which determines forces and / or torques acting on the actuators by means of sensors in order to determine the load weight.Disclosure of the InventionAccording to the invention, a method for determining a weight of a load absorbed by a boom of a work machine, and a computing unit and a computer program having the features of the independent patent claims are proposed. Advantageous embodiments are the subject matter of the dependent claims and of the following description.The invention relates to a working machine comprising a boom formed by a kinematic chain having a plurality of links, the links being coupled to each other by at least one pivot device including a pivot joint and a hydraulic actuator. In this case, a weighing function is provided which is configured to determine the weight of loads absorbed, wherein the weighing function includes one or more friction terms for the at least one pivoting device. The invention makes use of the measure of taking into account an amount of a movement value for the actuator of at least one pivot device, which movement value is determined from an operating signal value, when determining a weight value of the load by the weighing function, wherein the amount of the movement value is used in the taking into account to select suitable points in time for determining the face value of the load, so that the weight value can be determined with high accuracy.Taking into account the movement value or the amount of the movement value is advantageous since it is possible to infer friction states present in the pivoting device from the latter and it is thus possible to select points in time at which specific friction states are present, which are taken into account in the weighing function. Furthermore, friction terms suitable for the respective friction state can be used in the weighing function.According to one embodiment, the movement value is the operating signal value or a control signal value determined from the operating signal value for the actuator of the at least one pivoting device. The control signal or the control signal value can be, for example, a control signal (value) for a valve which controls the flow of pressure medium to and / or from chambers of a hydraulic cylinder (actuator).According to one embodiment, the movement value is a speed of the actuator of the at least one pivot device or an angular speed between the links which are coupled by at least one pivot device. Such speeds or angular speeds allow, for example, a statement as to whether a specific minimum speed (first threshold value) sufficient for the evaluation of the weighing function is exceeded. The speeds or angular speeds can be determined from the operating signal value, for example, by means of simple models or by means of characteristic maps, non-linearities being taken into account, for example.According to one embodiment, the movement value is determined from the operating signal value by means of a model of the work machine. This can be, in particular, a model of a hydraulic system of the working machine, which includes the actuator of the at least one pivot device, and / or of the boom. This configuration allows the accuracy and / or robustness of the method to be further improved. In particular, sizes and information known from design data of the hydraulic components used can be taken into account in the model. Such and further information can already be implemented in the control software when the machine is controlled electrohydraulically. Examples of this information are: valve edge geometries, properties of the valve springs and thus, for example, a relationship between control pressure and valve travel, customary system pressures (tank prestress etc.), valve settings (of pressure-reducing valves, pressure-limiting valves etc.), special actuator connections which are provided, for example, for gravity sinks, hydraulic vibration elimination or the like.According to one embodiment, the operating signal value is detected by means of an operating device of the working machine. The operating device can be, in particular, a joystick, wherein the operating signal value is approximately proportional to the deflection of the joystick or is obtained from the operating signal value by a (monotone) function and / or preprocessing (e.g. filtering). For example, the control signal value may increase progressively with the joystick deflection.According to one embodiment, a sign of the operating signal value and / or of the movement value for the actuator of the at least one pivot device is evaluated in order to determine a direction of the rotation effected by the actuator of the at least one pivot device, wherein the one or more friction terms for the at least one pivot device are dependent on the direction of the rotation. By this configuration, the accuracy of the determined weight value can be improved because the frictional force acts in or opposite to the direction of force caused by the load depending on the direction of movement.According to one configuration, the amount of the movement value for the actuator of the at least one pivot device is compared with a first threshold value which is greater than zero, and if at least one condition is fulfilled which includes the determination during the comparison that the amount of the movement value for the actuator of the at least one pivot device is above the first threshold value, the weight value of the load is determined by the weighing function. The suitable points in time for determining the face value are determined accordingly by the at least one condition being fulfilled. Those points in time are therefore selected as suitable points in time for the determination of the face value for which the at least one condition is fulfilled. In particular, points in time at which a standstill is present are avoided and thus friction values or other force values cannot be determined exactly. At the same time, relatively little computing power is necessary to check the at least one condition, since the condition can be evaluated without determining the exact pose of the boom or of the kinematic chain for successive points in time in order to detect a relative movement of links.According to one embodiment, the at least one condition includes that the amount of a kinematic speed of the actuator of the at least one pivot device, determined or estimated by means of sensor measurements, or kinematic angular speed between the links coupled by at least one pivot device, is greater than a second threshold value, which is greater than zero. By combining two conditions, the robustness of the method with respect to faults can be improved. Calculations or models used, if appropriate, for determining the movement value and / or the kinematic (angular) speed can also be designed relatively easily.According to one configuration, if the at least one condition is not fulfilled, no weight value is determined and / or the execution of the weight function is not permitted. Thus, the determination of likely incorrect weight values and their possible further use can be avoided.According to one embodiment, points in time are selected as suitable points in time for determining the face value of the load for which the at least one condition was fulfilled at one or more points in time within a previous period of time, which is a time length equal to a certain period of time T.According to one configuration, at least one friction term of the one or more friction terms of the weighing function is activated or deactivated as a function of the movement value or the amount of the movement value. For example, starting from a certain cylinder or joint speed (as movement value), a friction term describing a viscous friction component can be used, since it gains relevance.According to one embodiment, the at least one friction term is activated and / or deactivated by means of a weighting that can be continuously changed between 0 and 1, wherein the weighting is dependent on the movement value or the amount of the movement value. In this way, sudden curves of the weight value can be avoided. Examples of such weights or weighting functions are polynomials, hysteresis functions (in particular in the case of very slow movements), and the like. A further example is 0.5*(tanh(a*v cyl- b)+1), wherein a and b are constants and v cyl is a cylinder speed which represents the movement value or is obtained from it. This achieves a behavior similar to that in the case of a threshold value comparison, the profile being continuous.According to one embodiment, the weighting is time-dependent. This is expedient since the onset of static friction is a time-dependent process. For example, after the cylinders have stopped, the weight values are further determined over a specific time period T (e.g. as above in connection with the at least one condition). T is selected such that the error occurring in the beginning static friction in this time interval is still tolerable. This is particularly expedient since disturbing accelerations in the vehicle are reduced to a minimum when the cylinders are stationary.A computing unit according to the invention, e.g. a control unit of a mobile working machine or of a hydraulic system of a working machine, is configured, in particular by program technology, to carry out a method according to the invention.The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous since this causes particularly low costs, in particular if an executing control device is also used for further tasks and is therefore present in any case. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, among others. Download of a program via computer networks (Internet, intranet, etc.) is also possible.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.The invention is schematically illustrated in the drawing on the basis of exemplary embodiments and is described in detail below with reference to the drawing.DESCRIPTION OF THE FIGURESFIG. 1 shows a wheel loader as an example of a working machine having a boom. FIG. 2 shows a flow chart of a method for determining a weight of a load absorbed by a boom of a work machine according to one embodiment of the invention. FIG. 3 illustrates the determination of the movement value by means of modeling. FIG. 4 illustrates the consideration of a second condition for the determination of the weight value.Detailed Description of the DrawingsFIG. 1 shows a wheel loader 1 as an example of a work machine. 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 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 boom 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 machine components or machine elements shown, namely the boom support 5, the lifting arm 2 and the bucket 4, form links of a kinematic chain, wherein a load can be absorbed by a link (here the bucket) which is located at a free end of the kinematic chain in the example shown. The link at the other end of the kinematic chain (here chassis) serves as a carrier. This can be movable, e.g. in the case of a mobile working machine, or else fixed. The links of the kinematic chain are connected to one another by means of rotary joints, in FIG. 1, for example the axles 6 and axle slide bearings (not shown), by means of which the links are rotatable or pivotable relative to one another as a result of the actuators. The rotary joints together with the actuators form pivoting devices, wherein two successive links are coupled to one another by one pivoting device each.The actuators 8, 10 can be controlled by an electronic controller 18, wherein in the case of hydraulic cylinders 12, 14 one or more valves (in particular directional valves, e.g. in a valve block, not shown) are provided, which control the flow of pressure medium (i.e. hydraulic fluid, typically hydraulic oil) to the hydraulic cylinders. A hydraulic pump (not shown) is provided for supplying pressure medium. Overall, a hydraulic system or drive system for the pivot devices is thus formed, wherein the actuators are part of the hydraulic system.Sensors are provided (not shown in FIG. 1 ) which acquire force data and angle and / or position data. Force data are data or measurement data which characterize or indicate forces applied by the actuators. Pressure sensors can be used in particular for this purpose. For example, the pressure on both sides of the piston can be measured at the hydraulic cylinders, wherein the force applied by the hydraulic cylinder is then characterized by the pressure difference. Angle and / or position data are data or measurement data which characterize or indicate the position (e.g. angle) of the cantilever elements, in particular their relative position or their position relative to the cantilever carrier and / or relative to the environment (or relative to the gravitational field), in particular also relative angles in each case. For this purpose, angle sensors, in particular, can be provided, or (position) sensors, which determine the deflection of the hydraulic cylinders. Furthermore or additionally, acceleration sensors can be provided, from the data of which e.g. the orientations of the cantilever elements relative to the gravitational field can be determined. In particular, the pose of the kinematic chain can be determined from angle and / or position data. Examples of state data or sensors are mentioned above; in general, additionally or alternatively state data can also be detected by other sensors (not shown in detail), for example in order to detect pressure data, torque data, speed data, acceleration data and / or tension data (which, as noted, can in principle also be understood as force and / or angle and / or position data).Since the geometric relationships of the cantilever elements and their weights or masses are known, the weight or mass of a load recorded can be calculated or estimated from the state data. For this purpose, a so-called weighing function is used, which is based on a model of the work machine. The implementation of weighing functions is known per se to the person skilled in the art. The state data can be acquired continuously, for example at regularly or irregularly spaced points in time. The load or mass received can be calculated by the weighing function on the basis of the (current) state data acquired last, which are present at a (weighing) time or within a (weighing) time period. The mass obtained by the weighing function is referred to as the weighing value. The weighing function is evaluated repeatedly, for example, so that a continuous time series of weighing values can be obtained overall.In order to obtain accurate weighing values, the weighing function for the swivel devices, in particular for the swivel joints, includes friction terms, by means of which the friction force occurring in the swivel devices is taken into account in the determination of the weight of the load absorbed. In this case, it is assumed, in particular on account of the relatively low rotational speeds, that, despite lubrication, no purely viscous friction is present, but mixed friction is present or, for example, in the case of poor lubrication, solid-state friction is present. The frictional force at a pivot joint is accordingly approximately dependent on the radial force applied to it (effected by the weight of the links of the kinematic chain and the load) and / or on the direction of rotation. In addition to friction terms for the pivot joint, the friction terms of the pivot devices can also include friction terms for friction occurring at the actuators, e.g. hydraulic cylinders, or at their bearings.For physical reasons, it is problematic to estimate the friction during standstill of the actuators. The system is in static friction. The magnitude of the static frictional forces typically cannot be detected with the sensor system customary on the vehicle. Furthermore, typically in a state in which a hydraulic cylinder is located at an end stop, which likewise corresponds to a standstill, the force which causes the rotation of the members cannot be calculated from a measured pressure. In order to overcome this problem, it is provided to trigger the weighing function or to evaluate or use the results thereof only when a rotational movement of the links of the kinematic chain relative to one another is present. The corresponding method is described below with reference to exemplary embodiments.FIG. 2 shows a flow diagram of a method for determining a weight of a load absorbed by a boom of a work machine (as described, for example, in connection with FIG. 1 ) according to one embodiment of the invention. A working machine is thus assumed whose boom forms a kinematic chain with a plurality of links, wherein the links are coupled to one another in pairs by at least one pivot device. A link of the kinematic chain is configured to receive the load. This can expediently be the link at a free end of the kinematic chain. The at least one pivot device has a rotary joint about which the members coupled by the pivot device are rotatable relative to one another, and a hydraulic actuator which brings about this rotation. A weighing function is provided, which is configured to determine the weight of loads absorbed by the link at the free end of the kinematic chain. This weighing function includes one or more friction terms for the at least one pivot. The method can be implemented by an electronic controller (control unit or computing unit) of the work machine.In step 100, an operating signal value 22 for the actuator of the at least one pivot device is detected. The operating signal value is determined in particular by an operating device (e.g. joystick) based on an input of an operator of the work machine. In this case, preprocessing of the signal detected by the operator control device (e.g. joystick deflection) or the like can be carried out in order to obtain the operator control signal value.In step 110, a movement value 24 for the actuator of the at least one pivot device is determined from the operating signal value 22. The motion value 24 is a value corresponding to or indicative of a magnitude (and optionally direction) of movement or rotational motion of the links of the kinematic chain relative to each other coupled by the at least one pivot device. In the simplest case, the movement value 24 can be the operating signal value 22 itself (step 110 is then trivial). The movement value 24 can also be a control signal for the actuator of the at least one pivot device, e.g. a control signal for a valve which controls volume flows of pressure medium to and from the actuator, for example a hydraulic cylinder. Furthermore, a model of the working machine or of the hydraulic system included therein or the like (e.g. a characteristic map) can also be used in order to obtain the movement value 24 from the operating signal value 22.In step 120, the amount of the motion value 24 is compared to a first threshold 26 that is greater than zero. The first threshold 26 may be adjustable. Based on a maximum possible value range (e.g. from no joystick deflection to maximum joystick deflection) of the movement value 24, the first threshold value can be, for example, between 1% and 5% of the (amount of) maximum possible value range. Of course, corresponding absolute values can also be used as the first threshold value. If the amount of the movement value 24 is above (or equal to) the first threshold value 26, the weighing function is called up or permitted to execute, for example by means of a weighing signal 28, for example by setting a register to a specific value. On the other hand, if the amount of the motion value 24 is below the first threshold value 26, execution of the weighing function is not permitted.The amount of the motion value 24 being above (or equal to) the first threshold 26 may be considered a condition where the weighing function is invoked or permitted to execute when satisfied. Optionally, further conditions can be provided; cf. FIG. 4.In step 130, the weighing function is executed to determine or calculate a weight value 30 for the load. Step 120 represents a consideration of the amount of the motion value in determining the weight value. Thus, the weight value 30 for the load is determined when the condition that the amount of the motion value 24 is above (or equal to) the first threshold 26 is satisfied. The determined weight value 30 may be used by other functionalities of the work machine. For example, when loading a truck with bulk material, weight values for respective shovel loads may be added up in succession in order to determine a loaded total weight. The determined weight value 30 or optionally the added total weight can also be displayed on a display of the working machine for the operator.In optional step 140, a sign of the operating signal value 22 and / or of the movement value (not shown) can be evaluated in order to determine a movement direction 32 of the rotary joint of the at least one pivot device. The direction of movement 32 corresponds to a direction of movement or rotation of the links coupled by the pivoting device relative to one another. The operating signal value 22 can be additionally taken into account by the weighing function in step 130.FIG. 3 illustrates the determination of the movement value 24 from the operating signal value 22 by means of modeling or a model. The modeling in steps 112, 114 and 116 represents a configuration of step 110 of FIG. 2, so that the description of other steps, in particular the comparison of the amount of the operating signal value 22 with the first threshold value 26, is not repeated, but rather is referred to in this regard the description of FIG. 2.The model includes multiple sub-models. In step 112, a transformation into a control pressure 24 for a valve or a valve block takes place, with which volumetric flows of pressure medium to and from the actuator are controlled. The valve or the valve block is actuated, for example, in an electromagnetically pilot-controlled manner, i.e. the valve or the valve block is hydraulically adjusted, wherein the control pressure of the pressure medium for this adjustment is generated by an electromagnetic proportional valve. The transformation in step 112 describes the relationship of the control pressure with the operating signal value.In step 114, a valve block model is implemented, which determines a cross-sectional area 36 of the valve block adjusted therewith from the control pressure 34. This includes, for example, information about valve edge geometries.In step 114, a hydraulic system model including the actuator is implemented that determines a speed 28 of the actuator (e.g., piston speed of a hydraulic cylinder) from the cross-sectional area 36. Alternatively, instead of the speed 28 of the actuator, a rotational speed or angular speed of the rotary joint of the at least one pivot device can also be determined. The actuator speed 28 (or angular speed) is used as the motion value 24 and compared to the corresponding first threshold 26 in the comparison in step 120.The modeling in steps 112, 114 and 116 enables a precise determination of the movement value 24, which is not easily susceptible to disturbances, so that the evaluation of the weighing function takes place accordingly at suitable points in time.FIG. 4 illustrates the consideration of a second condition for the determination of the weight value.The first condition, which is based on the operating signal value 22, and the check thereof in step 120 has already been explained in conjunction with FIGS. 1 and 2, so that reference is made substantially to the description thereof for this purpose. In FIG. 4, the determination of the motion value 24 from the operation signal value 22 is implemented by step 118 (which is a specific configuration of step 110 of FIG. 2 ). In this case, in step 118, a simplified model (for example compared to the model of FIG. 3 ) of the system (of the working machine or of the hydraulic system) is used in order to map the operating signal value 22 to the movement value 24. The model can also be given, for example, by a characteristic diagram. A simple model is associated with relatively little computational effort.In addition, a second condition is evaluated in FIG. 4. In this case, sensor measurements 52 are recorded and a kinematic speed 54 of the actuator or a kinematic angular speed between the links is determined therefrom in step 150 by means of a simple kinematic model. The magnitude of the determined kinematic speed 54 or angular speed is compared to a second threshold value 56 that is greater than zero in step 160.In step 170, which is essentially an AND operation, if both conditions are fulfilled, the weighing function is called up or permitted to execute, for example, as explained by means of the weighing signal 28. If at least one of the two conditions is not fulfilled, no weight value is determined, i.e. the weighing function is not called up or its execution is not permitted.It is understood that further conditions may be provided which must be fulfilled in order to determine the weight value. Such further conditions are selected in particular such that they correspond to favorable weighing times. The approach of taking two (or more) conditions into account is expedient since a high accuracy or a high robustness with respect to faults can be achieved, although each of the conditions is associated with a relatively low amount of computing effort.

Claims

Method for determining a weight of a load absorbed by a boom of a working machine (1), wherein a kinematic chain having a plurality of links (5, 2, 4) which are coupled to one another by at least one pivot device is formed by the boom, wherein a link (4) which is situated in particular at a free end of the kinematic chain is configured to absorb the load, wherein the at least one pivot device includes a pivot joint (6) about which the links coupled by the pivot device are rotatable relative to one another and a hydraulic actuator (8, 10) which brings about the rotation, and wherein a weighing function is provided which is configured to determine the weight of loads absorbed by the link (4), wherein the weighing function includes one or more friction terms for the at least one pivot device; wherein a movement value (24) for the actuator of the at least one pivot device is determined (110) from an operating signal value (22) for the actuator (8, 10) of the at least one pivot device, said movement value corresponding to a magnitude of a movement or rotary movement of the links of the kinematic chain, which are coupled by the at least one pivot device, relative to one another and / or indicating said movement value; wherein an amount of the movement value (24) for the actuator of the at least one pivot device is determined; and wherein a weight value (30) of the load is determined (130) by the weighing function taking into account the amount of the movement value, wherein the amount of the movement value is used in the taking into account to select suitable points in time for the determination of the weight value of the load, such that the weight value can be determined with high accuracy.Method according to Claim 1, wherein the movement value (24) is the operating signal value (22) or is a control signal value for the actuator (8, 10) of the at least one pivoting device, said control signal value being determined from the operating signal value.The method of claim 1, wherein the motion value (24) is a speed (38) of the actuator of the at least one pivot or an angular speed between the links coupled by the at least one pivot.Method according to one of the preceding claims, wherein the movement value (24) is determined (112, 114, 116; 118) from the operating signal value by means of a model of the working machine, in particular a model of a hydraulic system of the working machine which includes the actuator of the at least one pivot device, and / or of the boom.Method according to one of the preceding claims, wherein the operating signal value (22) is detected by means of an operating device of the working machine (1).Method according to one of the preceding claims, wherein a sign of the operating signal value and / or of the movement value for the actuator of the at least one pivot device is evaluated (140) in order to determine a direction (32) of the rotation effected by the actuator of the at least one pivot device; and wherein the one or more friction terms for the at least one pivot device are dependent on the direction of the rotation.The method of any preceding claim, wherein the amount of the motion value (24) for the actuator of the at least one swing is compared (120) to a first threshold value (26) greater than zero; and wherein if at least one condition is met that includes determining upon the comparison that the amount of the motion value (24) for the actuator of the at least one swing is above the first threshold value (26), the weight value (30) of the load is determined (130) by the weighing function.The method of claim 7, wherein the at least one condition includes the amount of a kinematic speed (54) of the actuator of the at least one pivot determined (150) or estimated by sensor measurements or kinematic angular speed between the links coupled by the at least one pivot being greater than a second threshold value (160) that is greater than zero.Method according to claim 7 or 8, wherein if the at least one condition is not fulfilled, no weight value is determined and / or the execution of the weight function is not permitted.A computing unit (18) comprising a processor configured to perform the method of any preceding claim.A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claims 1 to 8.Computer-readable data medium on which the computer program according to Claim 10 is stored.

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