Method for determining a compensated angle

Abstract

The invention relates to a method for determining a compensated angle (αcomp) of a component (2) of a work machine which can be pivoted relative to a reference component (4) between a first and a second end position, wherein there is a known end position angle difference between the first and the second end position, wherein an angle sensor (8) is provided which is coupled to the component (2) and the reference component (4) and which is designed to measure sensor angle values of the component relative to the reference component.The method comprises a calibration phase, including pivoting (110, 16) of the component (2) into the first end position and detecting a first sensor angle value (αSens(αmin)) in the first end position, pivoting (120, 18) of the component (2) into the second end position and detecting a second sensor angle value (αSens(αmin)) in the second end position, and determining (130) a hysteresis angle value from the sensor angle difference between the first and the second sensor angle value and from the end position angle difference, and an application phase, including detecting (140) a sensor angle value for a determination time, determining (150) whether a positive or a negative pivot direction of the component is present at the determination time, and determining (160) the compensated angle (αcomp) by correcting the sensor angle value at the determination time. by an angle correction depending on the hysteresis angle value and the swivel direction.

Description

The present invention relates to a method for determining a compensated angle, to a computing unit and to a computer program for carrying it out, and to a work machine.BACKGROUND OF THE INVENTIONIn mobile work machines, e.g. an excavator, a wheel loader, a telescopic handler or a crane, it is often of interest to determine the position of an element (e.g. of the superstructure of an excavator relative to a world coordinate system) or the position of individual joints (e.g. boom, arm, bucket joint). Knowing these variables is useful, for example, in order to give the operator an accurate feedback about the position of the working tool or also for the realization of control or regulation algorithms, such as, for example, for delimiting the working space or for coordinate control. For determining the position of an element, methods for measuring the stroke (e.g. magnetostrictive) on a cylinder, for measuring the joint angle (e.g. by means of a potentiometer or an optical or magnetic encoder) or by means of inertial sensor systems can be used, for example.Disclosure of the InventionAccording to the invention, a method for determining a compensated angle, a computing unit and a computer program for carrying it out, and a working machine 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 makes use of the measure of determining a compensated angle of a component of a working machine that can be pivoted relative to a reference component between a first and a second end position by means of a calibration phase and an application phase, wherein sensor angle values are measured or detected with an angle sensor that is coupled to the component and the reference component. In the calibration phase, the component is successively pivoted into the first and the second end position and corresponding sensor angle values are detected, from which a hysteresis angle value is determined. In the use phase, a sensor angle value and a swivel direction are detected or determined for a determination time and the compensated angle is determined by correcting the sensor angle value by an angle correction dependent on the hysteresis angle value and the swivel direction. By means of the procedure according to the invention, i.e. in particular taking into account the hysteresis angle value and the pivot direction during the angle correction, consistent values for the compensated angle can be determined in which errors are compensated which are caused by a play of the mechanical coupling of the angle sensor to the component and the reference component. In particular, the compensated angle is independent of the pivot direction.According to one embodiment, in the case of a positive swivel direction, a first fraction of the hysteresis angle value is added to the sensor angle value at the determination time and, in the case of a negative swivel direction, a second fraction of the hysteresis angle value is subtracted from the sensor angle value at the determination time. In particular, the sum of the first and second fractions of the hysteresis angle value is equal to the hysteresis angle value. The first and second fractions of the hysteresis angle value may be equal to half the hysteresis angle value. According to this embodiment, the compensated angle is within a band determined by hysteresis, for example, at the center thereof.According to one embodiment, the pivot direction is determined based on sensor angle values at successive points in time. Here, the swing direction is determined to be positive when the sensor angle values increase between successive times, and determined to be negative when the sensor angle values decrease between successive times. If the sensor angle values change in the direction of larger angles, a positive pivot direction is thus assumed. If the sensor angle values change in the direction of smaller angles, a negative pivot direction is correspondingly assumed. This configuration is simple to implement, since it is based on already present variables (sensor angle values).According to one configuration, the pivot direction is determined on the basis of measurement by a sensor different from the angle sensor, in particular an inertial sensor. This is expedient since this method is independent of measurements of the angle sensor; in particular, measurement errors do not affect both in the sensor angle and in the pivot direction.According to one embodiment, the steps of the use phase are repeated without the calibration phase being carried out in the meantime. This repeated execution of the steps of the use phase can be carried out continuously, in particular, so that newly present sensor angle values are compensated for in each case.According to one embodiment, the calibration phase is performed again to update the hysteresis angle value. In particular, the calibration phase is carried out again at at least one specific point in time and / or in response to at least one specific event and / or in response to a corresponding input by an operator of the work machine. Possible changes in the hysteresis angle, for example due to wear, can thus be taken into account.A computing unit according to the invention, e.g. a control unit of a mobile work machine, is configured, in particular by programming, to carry out a method according to the invention.A working machine according to the invention has a component which can be pivoted relative to a reference component between a first and a second end position, wherein a known end position angle difference exists between the first and the second end position, wherein an angle sensor is provided which is (mechanically) coupled to the component and the reference component and which is configured to measure sensor angles of the component relative to the reference component. Furthermore, the working machine has a computing unit according to the invention. The (mechanical) coupling may have a play that leads to hysteresis in the measured sensor angle values. This hysteresis is taken into account by the method according to the invention in order to achieve a consistent angle determination.According to one configuration, the angle sensor has a detection element which is arranged fixedly on the reference component and an arm element which is rotatably mounted on the reference component and is in engagement with a entrainment element which is arranged fixedly on the component. A play can be present here between the arm element and the entrainment element.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 illustrates rotational movements of a component relative to a reference component and an associated angle measurement with an angle sensor. FIG. 2 shows a flow chart according to an embodiment of the invention.Detailed Description of the DrawingsFIG. 1 illustrates rotational movements or pivoting movements 16, 18 of a rotatable component 2 relative to a reference component 4 and an associated angle measurement with an angle sensor 8, The component 2 is attached to the reference component 4 by means of a pivot joint 6, such that the component 2 is pivotable or rotatable relative to the reference component 4. The component 2 can be, for example, a boom of an excavator, wherein the reference component 4 is the superstructure of the excavator or is fixedly attached to the superstructure. The rotational movement or pivoting movement of the component is effected by an actuator, for example a hydraulic cylinder or the like (not illustrated). The angle measurement is intended to determine an angle of rotation about an axis of the rotary joint 6 of the (rotatable) component 2 relative to the reference component 4. The rotatable component 2 is also referred to simply as component 2.The component 2 is rotatably movable (rotatable) or pivotable between a first end position corresponding to an (actual) minimum angle α min and a second end position corresponding to an (actual) maximum angle α max respectively. The first end position is assumed, for example, when the hydraulic cylinder is retracted to the greatest possible extent, and the second end position is assumed, for example, when the hydraulic cylinder is extended to the greatest possible extent. Since the kinematics or the geometry of the structure comprising the component 2, the reference component 4, the rotary joint 6 and the actuator are known, the minimum angle α min and the maximum angle α max are known per se or since the direction which corresponds to the zero angle (i.e. the orientation of the corresponding coordinate system) can be arbitrarily defined, at least the actual angle difference α max- α min of these two angles is known. This angle difference is also referred to as the final position angle difference.An angle sensor 8 is provided, which has, for example, an element fixedly arranged on the reference component 4, referred to as a detection element, and an element rotatably arranged on the reference component 4, referred to as an arm element 10. The arm member 8 is rotatable, for example, about an axis which coincides with the axis of the pivot 6. Furthermore, the arm element 8 is in engagement with an element, referred to as a entrainment element 12, which is arranged fixedly on the pivotable component 4, so that the arm element 8 is rotated or carried along by the component 2. The entrainment element 12 is, for example, a pin or pin. The angle sensor 8 measures an angle, referred to as a sensor angle α Sens of the arm member 10 relative to the sensing member. For example, the arm element 10, the detection element, together with further elements of the angle sensor, can form a potentiometer, the variable resistance of which corresponds to the angle value. The angle sensor is configured in particular to determine current sensor angle values (i.e. current values for the sensor angle) continuously or at certain time intervals which are regularly or irregularly spaced, for example on a time grid or with a certain measurement frequency. The angle sensor can furthermore be configured to transmit measured or determined current sensor angle values to an electronic controller (computing unit), for example to the working machine which has the pivotable component and the reference component (not illustrated).There is a clearance between the arm member 10 and the follower member 12 which results in hysteresis in the angle measurement by the angle sensor 8. The resulting hysteresis curve is shown below in FIG. 1 in a graph in which the sensor angle value α Sens is plotted against the actual angle α act. More generally, there is a play which is caused by the mechanical coupling of the angle sensor 8 to the component 2 and the reference component 4. This play can lead to hysteresis.For example, a first pivoting movement 16 takes place in the direction of smaller angles (negative pivoting direction), i.e. in the clockwise direction in the figure, until the first end position or the actual minimum angle α min is reached. In this case, a minimum angle measured by the angle sensor, i.e. a minimum sensor angle value α Sens( α min), is likewise achieved. During the first pivoting movement 16, the pin, i.e. the entrainment element 12, bears against a part of the fork-shaped end of the arm element 10 which is situated in the clockwise direction.After the movement reversal, a second pivoting movement 18 takes place in the direction of larger angles (positive pivoting direction), i.e. in the counter-clockwise direction in the figure, until the second end position or the actual maximum angle α max is reached. After a transition phase, the pin, i.e. the entrainment element 12, abuts a part of the fork-shaped end of the arm element 10 which is situated counter to the clockwise direction during the second pivoting movement 18. This transition between the parts against which the entrainment element abuts, i.e. this play, leads to the angle measured by the angle sensor 8, i.e. the sensor angle value, initially remaining at the minimum sensor angle value α Sens( α min) immediately after the movement reversal. The sensor angle value thus initially remains unchanged, although a change of the actual angle α act already takes place. When the actual maximum angle α max is reached, a maximum angle measured by the angle sensor, i.e. a maximum sensor angle value α Sens( α max), is likewise reached.If a new movement takes place subsequently in the direction of smaller angles, i.e. clockwise, a phase occurs here too, because of the play immediately after movement reversal, in which the sensor angle value initially remains at the maximum sensor angle value α Sens( α max) even though the actual angle α act already decreases.This hysteresis leads to a measured sensor angle value not being able to be assigned a unique value for the actual angle, or to the sensor angle value being a defective value for the actual angle. This problem is solved by the method according to the invention, in which a compensated angle α comp is determined.FIG. 2 shows a flow chart according to one embodiment of the invention, i.e. a method for determining a compensated angle of a component of a working machine that can be pivoted relative to a reference component between a first and a second end position. It is assumed that an angle sensor is provided which is configured to determine or measure sensor angle values. This corresponds to the arrangement shown in FIG. 1. The method can be implemented, for example, by an electronic controller (or computing unit) of the work machine by executing a corresponding computer program (angle compensation program). The electronic controller is also configured, in particular, to control an actuator which brings about the relative pivoting movement of the component with respect to the reference component (for example by executing a corresponding actuator control program). The angle sensor transmits measured current sensor angle values to the electronic control, as explained above. Compensated angles determined by the electronic control using the method can be used further by the electronic control for control tasks.The method comprises a calibration phase (steps 110 to 130) and a deployment phase (steps 140 to 160).In step 110, the first end position is first approached (by appropriate actuation of the actuator), which corresponds to the actual minimum angle α min for example. This corresponds approximately to the first pivoting movement 16 in FIG. 1. the associated sensor angle value determined by the angle sensor in the first end position is detected and referred to as the first or minimum sensor angle value α Sens( α min) respectively. The following applies:The deviation of the first or minimum sensor angle value from the actual minimum angle is referred to as the first offset angle α down. The first offset angle, which is generally different from zero, is caused by the play, as explained. Furthermore, the offset angle can include a systematic deviation (in particular due to the establishment of the zero angle).Subsequently, in step 120, the second end position is approached (by corresponding actuation of the actuator), which corresponds e.g. to the actual maximum angle α max (obviously the procedure could likewise be reversed, i.e. the maximum angle could be approached first and the minimum angle could be approached subsequently). The associated sensor angle value determined by the angle sensor is detected and referred to as the second or maximum sensor angle value α Sens( α max) respectively. The following applies:The deviation of the minimum sensor angle value from the actual maximum angle is referred to as the second offset angle α up. The second offset angle, which is generally different from zero, is caused by the aforementioned play (and possibly by the systematic deviation).In step 130, a hysteresis angle value α hyst is determined. Specifically, the hysteresis angle value α hyst is determined as the difference (referred to as a sensor angle difference) between the first and second offset angles using the above equations:This can be reformulated as:In this equation for the hysteresis angle value α hyst the first expression (sensor angle difference) can be determined from measured sensor angle values and the second expression (end position angle difference) is known from the kinematics of the components under consideration. The hysteresis angle value is determined accordingly as a sensor angle difference minus end position angle difference. The systematic deviation that may be present is reflected from the second expression because of the difference. The hysteresis angle value α hyst is used for angle compensation in the subsequent use phase.In step 140, a sensor angle value α Sens( t B) is detected for a determination time t B. An angle measurement value of the angle sensor is therefore detected. The determination time point t B may be a current time point, for example.In step 150, a sweep direction of the component is determined at the determination time t B. Thus, it is determined whether the component rotates in the direction of larger angles or in the direction of smaller angles. The rotation in the direction of larger angles is referred to as the positive pivot direction. The rotation in the direction of smaller angles is referred to as the negative swing direction.The pivot direction may be determined, for example, by comparing successive sensor angle values (measured by the angle sensor). For example, sensor angle values α sens( t k) are detected at successive points in time t k wherein k is an integer and wherein the points in time are, for example, regularly spaced (t k+1= t k+ Δt, with constant Δt). It is then true that a positive pivoting direction exists if the following applies:A negative pivot direction is present if the following applies:The determination time t B is in particular one of the successive times t k.In addition to the comparison of successive sensor angle values, other methods are also conceivable for determining the pivot direction. For example, an evaluation of measured values of one or more other sensors, e.g. inertial sensors. Control signals, for example for the actuator, can also be evaluated for this purpose.In step 160, the compensated angle α comp is determined. Here, the sensor angle value α Sens( t B) is corrected at the determination time t B by an angle correction α korr, which is dependent on the hysteresis angle value α hyst and the swivel direction S, i.e. α korr= α korr( α hyst, S) applies, wherein S can assume the values "pos" for the positive swivel direction and "neg" for the negative swivel direction, for example. The angle correction is added to the sensor angle value, in particular:In particular, provision is made for the sensor angle value α Sens( t B) to be corrected at the determination time t B by adding half the hysteresis angle value α hyst to the sensor angle value α Sens( t B) in the case of a positive swivel direction and by subtracting half the hysteresis angle value α hyst from the sensor angle value α Sens( t B) in the case of a negative swivel direction in order to obtain the compensated angle α comp. The compensated angle α comp then moves midway between the hysteresis branches as shown in FIG. 1.With this correction, in which half the hysteresis angle value is added or subtracted, the following applies when the swivel direction is positive:In the case of a negative pivot direction, the following applies:More generally, a correction other than addition / subtraction of the half hysteresis angle value may be selected. For example, furthermore starting from α comp( t B) = α Sens( t B) + α korr( α hyst, S), the angle correction can be given as the product of the hysteresis angle value α hyst and a factor r(S) dependent on the pivot direction:In this case, for example, the factor r(S) is equal to a constant g (i.e. r(pos)=g) in the case of a positive pivot direction and is equal to one minus the constant g (i.e. r(neg)=1-g) in the case of a negative pivot direction. The constant g is in particular between zero and one (i.e. g ∈[0,1]). The constant g is a (first) fraction of the hysteresis angle value, which is added to the sensor angle value in the case of a positive swivel direction. One minus the constant g (i.e. 1-g) is a (second) fraction of the hysteresis angle value, which is subtracted from the sensor angle value in the case of a negative pivot direction.The compensated angle α comp may be used to implement control functions of the work machine (e.g., in suitable control algorithms). Display or notification functions, for example, in which information about the angle is output on a display of the work machine, can also be implemented in order to facilitate the operation of the work machine.Steps 140 to 160 of the deployment phase can be carried out repeatedly, in particular continuously, for different determination times, i.e. a jump is made from step 160 to step 140. In this case, the same hysteresis angle value can be used in each case, i.e. steps 140 to 160 of the use phase are repeated without a calibration phase being carried out between the repetitions.Optionally, the calibration phase can be re-performed in step 170 (i.e. the method jumps to step 110) in order to update the hysteresis angle value. Step 170 may be performed at certain times (e.g., regularly) and / or in response to certain events (e.g., start of the work machine) and / or in response to a corresponding input from an operator of the work machine. A redetermination of the hysteresis angle value is expedient since the play of the mechanical coupling of the angle sensor to the component and the reference component can change over time (e.g. due to wear) or else with temperature.Furthermore, it can be provided to check whether the hysteresis angle value is above a predetermined maximum angle, such a check can be carried out, for example, following step 130. If it is determined that the hysteresis angle value is above a predetermined maximum angle, an error message can be generated and output, for example, on a display of the work machine. Such an error message may also be communicated to control algorithms that use the compensated angle (such as to implement automatic control functions) such that they implement only limited functionality in response thereto.

Claims

Method for determining a compensated angle (α comp) of a component (2) of a working machine that can be pivoted relative to a reference component (4) between a first and a second end position, wherein a known end position angle difference exists between the first and the second end position, wherein an angle sensor (8) is provided which is coupled to the component (2) and the reference component (4) and which is configured to measure sensor angle values of the component relative to the reference component, comprising a calibration phase including pivoting (110, 16) the component (2) into the first end position and detecting a first sensor angle value (α Sens( α min)) in the first end position; Pivoting (120, 18) the component (2) into the second end position and detecting a second sensor angle value (α Sens( α min)) in the second end position; determining (130) a hysteresis angle value from the sensor angle difference between the first and second sensor angle values and from the end position angle difference; and an employment phase including detecting (140) a sensor angle value for a determination time point; determining (150) whether a positive or a negative pivoting direction of the component is present at the determination time point; and determining (160) the compensated angle (α comp) by correcting the sensor angle value at the determination time point by an angle correction dependent on the hysteresis angle value and the pivoting direction.The method of claim 1, wherein, in the case of a positive sweep direction, a first fraction of the hysteresis angle value is added to the sensor angle value at the determination time and, in the case of a negative sweep direction, a second fraction of the hysteresis angle value is subtracted from the sensor angle value at the determination time to determine (160) the compensated angle (α comp).The method of claim 2, wherein the sum of the first and second fractions of the hysteresis angle value is equal to the hysteresis angle value.The method of claim 2 or 3, wherein the first and second fractions of the hysteresis angle value are equal to half the hysteresis angle value.Method according to one of the preceding claims, wherein the hysteresis angle value is determined as a sensor angle difference minus end position angle difference.The method of any preceding claim, wherein the sweep direction is determined (150) based on sensor angle values at successive times; wherein the sweep direction is determined to be positive when the sensor angle values increase between successive times and determined to be negative when the sensor angle values decrease between successive times.Method according to one of the preceding claims, wherein the pivot direction is determined (150) on the basis of a measurement by a sensor different from the angle sensor (8), in particular an inertial sensor.The method of any preceding claim, wherein the steps of the deployment phase are performed repeatedly without intermediate performance of the calibration phase.Method according to one of the preceding claims, wherein the calibration phase is carried out again in order to update the hysteresis angle value; wherein in particular the re-execution of the calibration phase takes place at at least one specific point in time and / or in response to at least one specific event and / or in response to a corresponding input of an operator of the working machine.A computing unit comprising a processor configured to perform the method of any preceding claim.A working machine comprising a component (2) pivotable relative to a reference component (4) between a first and a second end position, wherein a known end position angle difference exists between the first and the second end position, wherein an angle sensor (8) is provided which is coupled to the component (2) and the reference component (4) and which is configured to measure sensor angle values of the component relative to the reference component; further comprising a computing unit according to claim 10.Working machine according to claim 11, wherein the angle sensor (8) has a detection element arranged fixedly on the reference component (4) and an arm element (10), which is rotatably mounted on the reference component and is in engagement with a entrainment element (12) arranged fixedly on the component (2).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 9.Computer-readable data medium on which the computer program according to Claim 13 is stored.

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