Method for calibrating an orientation / position sensor

Abstract

The invention relates to a method for calibrating an orientation / position sensor with which the orientation / position of a component of an equipment of a mobile working machine can be detected, with the following method steps: - at least two orientations / positions of the equipment component are selected and the distance of the at least two orientations / positions from one another is predetermined; - the at least two orientations / positions of the equipment component are identified independently of the orientation / position sensor; - a calibration parameter for the orientation / position sensor is determined from the signals emitted by the orientation / position sensor in the at least two orientations / positions of the equipment component and the predetermined distance of the at least two orientations / positions.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for calibrating an orientation / position sensor with which the orientation / position of a component of an equipment of a mobile working machine can be detected. BACKGROUND

[0002] It is known from US 9 347 763 B2 that, in order to determine the angular position of individual equipment components, such as a boom, a stick and a bucket, relative to one another or relative to the superstructure, in an excavator, position sensors for the piston rod are provided for the hydraulic cylinders with which the individual parts are moved relative to one another. It is also conceivable to detect the orientation of the bucket relative to the stick, the orientation of the stick relative to the boom and the orientation of the boom relative to the superstructure of the excavator with angle sensors. In US 9 347 763, incremental angle sensors with reference signals are provided.

[0003] It is known that sensors for orientation / position detection provided at the equipment of a mobile working machine can be calibrated to some extent offline with the aid of external reference signals (GPS, level) in terms of their installation position. Associated with this is a high application outlay and a high time outlay. This outlay can be reduced when the sensors can be calibrated online at the start of operation and during operation of the mobile working machine. According to US 9 347 763, such an online calibration of the position sensors is provided. To this end, the equipment of the excavator is provided with rotary sensors for the angular orientation of the boom relative to the superstructure and for the angular orientation of the stick relative to the boom and a magnetic sensor at the bucket cylinder, with the aid of which the reference position of the hydraulic cylinders is detected. The calibration then comprises assigning the output signals emitted by the position sensors in the reference position to the reference position. The position sensors or stroke sensors are designed in such a way that they convert the linear movement of the piston rod of the hydraulic cylinder into rotary movement. To this end, the stroke sensors comprise a roller which is placed on the surface of the piston rod and performs a rotary movement when the piston rod is moved. The rotary movement of the roller is transmitted to a magnet which opposes a Hall sensor, the change in the magnetic flux during the rotary movement of the roller being detected by the Hall sensor and a corresponding signal being emitted. The number of rotations of the roller and the stroke of the piston rod of the hydraulic cylinder can thus be determined.

[0004] It is also stated in US 9 347 763 B2 how a hydraulic cylinder of an implement can be identified to have reached a stroke end position. For this purpose, three conditions must be met according to US 9 347 763 B2. Firstly, a lever of a handle must be deflected depending on the actuation of the hydraulic cylinder. Furthermore, a stroke position detected by a position sensor must be within a distance of, for example, 3 mm from the stroke position. And finally, the movement speed of a piston and a piston rod of the hydraulic cylinder must be less than or equal to a speed of, for example, 3 mm / s. As an alternative to calibration in a reference position detected by means of an additional sensor, the position sensor detecting the stroke length can also be calibrated in the stroke end position. SUMMARY

[0005] The task of the present application is to develop a method for online calibration of an orientation / position sensor at an implement of a mobile working machine, with which method the orientation / position sensor can be online calibrated extremely precisely and reliably over the entire service life of the orientation / position sensor.

[0006] The task is solved by a method with the following method steps:

[0007] - at least two orientations / positions of an implement component are selected and the distance of the at least two orientations / positions from one another is predetermined;

[0008] - at least two orientations / positions of an implement component are identified independently of the orientation / position sensor;

[0009] - a calibration parameter for the orientation / position sensor is determined from the signals emitted by the orientation / position sensor at the at least two orientations / positions of the implement component and the predetermined distance of the at least two orientations / positions. The distance can be the distance of two points in space or also an angular distance.

[0010] According to the method according to the application, the position of the equipment component is identified independently of the position sensor not only in one reference position, but also in at least two reference positions. In this way, it is possible to balance not only changes in the position of the sensor or slip of the roller, but also changes over the duration of operation by means of calibration. Changes in the radius of the roller can be balanced, for example, in a position sensor according to US 9 347 763 B2. In a rope pull sensor with a potentiometer, changes in the generality and thus changes in the elongation of the rope can be balanced. In general, changes in the slope of the analog signal or changes in the number of digital signals occurring over a certain stroke length or over a certain angle can be taken into account in the calibration. The parameters determined by means of calibration thus include parameters relating to the installed state of the sensor, such as the exact position and inclination of an inertial measurement unit on a boom, but also parameters for describing the input-output behavior, such as the angle-to-voltage conversion.

[0011] The advantages of the application first of all lie in the fact that the costly sensor calibration in the factory can be dispensed with, the time until the work machine is put into operation is reduced, and the effects of imprecision and aging when the sensor is installed are compensated for. The compensation for the effects of aging is advantageous in particular in mobile work machines that are partially or highly automated, since the operator as a corrective factor is dispensed with.

[0012] The calibration method according to the application can be designed in an advantageous manner.

[0013] The position of the equipment component relative to another equipment component or relative to the work machine or in space can be detected by means of the position sensor.

[0014] The signal emitted by the position sensor is advantageously filtered.

[0015] In order to keep the influence of noise and outliers in the detected values small, it is advantageous to detect the signals emitted in the at least two positions for calibrating the position sensor over a certain time and to average them.

[0016] The at least two positions of the equipment component can be distinguished by means of the current state of the work machine. This advantageously takes place without additional sensors. In principle, however, the current machine state can also be determined using signals of additional sensors.

[0017] If the equipment component can be moved between two end positions, it is expedient for the first position identified independently of the position sensor to be one end position of the equipment component and the second position identified independently of the position sensor to be the second end position, and for the end positions to be detected by means of a control signal for controlling the equipment component.

[0018] The final position of the equipment component can be detected by means of the duration, size and direction of the actuating signal.

[0019] A particularly simple implementation consists in detecting the final position of the equipment component by means of an actuating signal which is greater than 50% of the maximum size of the actuating signal for a duration of more than 5 seconds. It is possible here for the equipment components to be moved one after the other in the calibration run from one final position directly into another final position. But the calibration can also take place during normal operation, since the final positions are also approached repeatedly during operation. For example a rope-pulling sensor with potentiometer for detecting the stroke of a hydraulic cylinder provides an analog output signal in the form of a voltage which is related to the stroke. From the voltage the stroke is calculated according to the formula

[0020] stroke = m * voltage + c

[0021] The stroke can be calculated. When the minimum cylinder stroke and the maximum cylinder stroke are approached, then there is a linear equation system of two equations and two unknowns m and c which can be solved in terms of the unknowns. The equation system is over-determined due to the above-mentioned measurement over a longer period of time. The parameters which minimize the mean variance (least squares) can then be calculated numerically. Abnormal measurement values caused by measurement noise are thus avoided from having a strong influence on the parameters.

[0022] The orientation / position sensor can be an angle sensor or a travel sensor or an inertial measurement unit. If the sensor to be calibrated is an inertial measurement unit, then an inertial measurement unit can be provided at the superstructure, at the boom, at the stick and at the bucket and the angles to be measured between the superstructure and the boom, between the boom and the stick and between the stick and the bucket are based on the orientation difference of the two inertial measurement units. It is characteristic of the calibration method that the inertial measurement units can be calibrated in sequence from the superstructure. However there is no reference for the first inertial measurement unit at the superstructure. Since in most cases only the relative angles between the parts are important, the inertial measurement unit at the superstructure is assumed to be correct in the measurement. The inertial measurement units at the boom, at the stick and at the bucket are then calibrated in sequence according to the method of the application.

[0023] Existing signals, for example the signals of sensors which detect the cylinder stroke or the signals of inertial measurement units, the actuating signals emitted by the electronic sensors according to the wishes of the operator and certain basic knowledge about the kinematics and / or dynamics of the working machine can also be combined algorithmically. Values according to a computer- statistical method known as Kalman filtering can for example be combined on the basis of a model and the calibration parameters are then output as evaluation parameters.

[0024] The integrated solution allows the integration of additional sensor devices with more or less known transmission characteristics. Additional sensors that can be considered include pressure sensors, load cells, laser sensors, radar, ultrasound, camera systems.

[0025] A flow chart of the method according to the application is shown in the drawings. The application will now be explained in more detail with the aid of these drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] In the drawings:

[0027] Figure 1 A backhoe is shown; and

[0028] Figure 2 A method for calibrating a sensor is schematically shown. DETAILED DESCRIPTION

[0029] According to Figure 1 The backhoe has a lower structure 10 with a crawler track undercarriage and an upper structure 11 which can be pivoted relative to the lower structure 10 about an axis which is perpendicular to the bearing surface of the lower structure. The working equipment of the backhoe is a backhoe arm which is composed of several parts and which has, as equipment components, a boom 12, a stick 13 and a bucket 14. The boom 12 is fixed in a pivotable manner at the upper structure 11 and can be actuated by two parallel to each other arranged hydraulic boom cylinders 15 which are fixed in a pivotable manner about a first common axis with their cylinder housings 16 at the upper structure and in a pivotable manner about a second common axis with their piston rods 17 at the boom. The common axes of the two boom cylinders at the upper structure are parallel to the axis of the boom and are spaced apart parallel to the axis of the boom.

[0030] The stick 13 is fixed in a pivotable manner at the distal end of the boom 12, where the pivot axis between the stick and the boom is parallel to the pivot axis between the boom and the upper structure. The stick can be swiveled relative to the boom by means of a stick cylinder 18 which is fixed in a pivotable manner at the boom with its cylinder housing 19 and in a pivotable manner at the stick with its piston rod 20 spaced apart from the pivot axis between the stick and the boom.

[0031] The bucket 14 is fixed in a rotatable manner at one end of the stick 13 and is pivotable relative to the stick 13 by means of a bucket cylinder 21, which is rotatably fixed at the stick 13 with its cylinder housing 22. The piston rod 23 of the bucket cylinder 22 is hingedly connected to a four- bar linkage, which comprises an element formed by a section of the stick 13, an element formed by a section of the bucket 14, an element 24 hinged at the stick, and an element 25 hinged at the bucket. The piston rod 23 of the bucket cylinder is hingedly connected to the four-bar linkage at the hinge between the two last-mentioned elements 24 and 25. All the axes of rotation between the bucket and the stick are parallel to one another and to the other axes of rotation of the equipment.

[0032] According to Figure 1 , the excavator is equipped with a series of orientation / position sensors, which are intended to be used to detect the movements of the equipment and in particular the position of the bucket 14 relative to the lower structure 10. Not necessarily all the sensors mentioned in Figure 1 are present in the specific case. Rather, the type and number of the sensors present depend on the wishes of the user and the requirements of the use case.

[0033] An encoder 30 can be present, with which the angular position between the lower structure 10 and the upper structure 11 can be detected. An encoder 31 can be present, with which the angular position between the upper structure 11 and the boom 12 can be detected. An encoder 32 can be present, with which the angular position between the upper structure 11 and the boom cylinder 15 can be detected. An encoder 33 can be present, with which the angular position between the stick 13 and the boom 12 can be detected. An encoder 34 can be present, with which the angular position between the bucket 14 and the stick 13 can be detected. This encoder 34 can be provided either to detect the angular position in the hinge between the bucket 14 and the stick 13 or to detect the angular position between the hinge element 24 and the stick.

[0034] A stroke sensor 37 can be present, with which the stroke of the boom cylinder 15 can be detected. A stroke sensor 38 can be present, with which the stroke of the stick cylinder 18 can be detected. A stroke sensor 39 can be present, with which the stroke of the bucket cylinder 21 can be detected. The stroke sensors can be configured as rope-pull sensors, which contain a sensor element, for example a potentiometer or an encoder, which converts the travel change into a proportional or incremental or absolute digital electrical signal.

[0035] An inertial measurement unit (IMU) 44 may be mounted on the superstructure 11 to detect the acceleration and angular velocity of the superstructure. An inertial measurement unit (IMU) 45 may be mounted on the boom 12 to detect the acceleration and angular velocity of the boom 12. An inertial measurement unit 46 may be mounted on the arm 13 to detect the acceleration and angular velocity of the arm 13. An inertial measurement unit 47 may be mounted on the hinge element 24 to detect the acceleration and angular velocity of the bucket 14.

[0036] according to Figure 2 The calibration of the sensors is carried out in a correspondingly programmed computer 50. The raw output data of a large number of sensors 1 to N are input to this computer. In addition, the computer receives signals from different human-machine interfaces HMI 1 to HMI M, which contain specific drive requirements 1 to M for different drives of the equipment components and superstructures and are Figure 2 The human-machine interface can be realized, for example, by two electronic handles, the joysticks of which can control two Figure 2 Excavators have hydraulic drives for equipment and superstructures.

[0037] In addition, known machine parameters such as kinematics, maximum cylinder stroke, mass and moment of inertia are input into the computer 50. Figure 2 This is symbolically represented by block 51 and an arrow from this block to computer 50. Within computer 50, the signals from sensors 1 to N are filtered and processed in subfunction 52. In subfunction 53, the current machine state, such as "at rest" or "boom raised," is determined from the signals, namely, the drive requests 1 to M from human-machine interfaces HMI 1 to HMI M. The sensors are then calibrated in algorithm 54 in computer 50. This algorithm utilizes previously known machine parameters, filtered and processed sensor raw data, the drive requests output by the human-machine interface, and the current machine state to determine the values ​​for the sensor parameters to be set or adjusted and thereby calibrate the sensors.

[0038] A simple practical approach to determining whether one of the hydraulic cylinders 15 , 18 or 21 has reached the minimum cylinder stroke or the maximum cylinder stroke is provided by the following provisions:

[0039] If the handle for the corresponding hydraulic cylinder is deflected by more than 50% for more than 5 seconds, the hydraulic cylinder is at the minimum or maximum cylinder stroke, depending on the deflection direction of the handle. A duration of 5 seconds and a 50% deflection are undoubtedly applicable to a wide range of machines. However, these values ​​are merely examples and are machine-specific.

[0040] The output signals of the calibrated sensors, shown by arrows 55, for example, the information about the sensor fixation, shown by arrows 56, and the information about the sensor status, shown by arrows 57, are transmitted by the computer 50 to an electronic control system 60, which comprises partial functions 61 for process control, partial functions 62 for machine control and partial functions 63 for component control.

[0041] List of reference signs

[0042] 10 lower structure

[0043] 11 upper structure

[0044] 12 boom

[0045] 13 stick

[0046] 14 bucket

[0047] 15 boom cylinder

[0048] 16 cylinder housing of 15

[0049] 17 piston rod of 15

[0050] 18 stick cylinder

[0051] 19 cylinder housing of 18

[0052] 20 piston rod of 18

[0053] 21 bucket cylinder

[0054] 22 cylinder housing of 21

[0055] 23 piston rod of 21

[0056] 24 hinge element

[0057] 25 hinge element

[0058] 30 encoder

[0059] 31 encoder

[0060] 32 encoder

[0061] 33 encoder

[0062] 37 stroke sensor

[0063] 38 stroke sensor

[0064] 39 stroke sensor

[0065] 44 inertial measurement unit

[0066] 45 inertial measurement unit

[0067] 46 inertial measurement unit

[0068] 47 inertial measurement unit

[0069] 50 computer

[0070] 51 block

[0071] 52 partial functionality in 50

[0072] 53 partial functionality in 50

[0073] 54 algorithm in 50

[0074] 55 arrow as a symbol for transmitted data

[0075] 56 arrow as a symbol for transmitted data

[0076] 57 arrow as a symbol for transmitted data

[0077] 60 electronic control system

[0078] 61 partial functionality of 60

[0079] 62 partial functionality of 60

[0080] 63 partial functionality of 60

Claims

1. A method for calibrating an orientation / position sensor (30, 31, 32, 33, 34, 37, 38, 39, 45, 46, 47) for detecting the orientation / position of an equipment component (12, 13, 14) of a mobile working machine, wherein: The method comprises the following steps of detecting the position / location of the equipment component (12, 13, 14) relative to another equipment component or relative to the work machine by means of the position / location sensor: - selecting at least two positions / locations of the equipment components (12, 13, 14) and predetermining the distances between the at least two positions / locations of the equipment components (12, 13, 14); - identifying at least two positions / locations of an equipment component (12, 13, 14) independently of position / location sensors (30, 31, 32, 33, 34, 37, 38, 39, 45, 46, 47); - determining calibration parameters for a position / position sensor (30, 31, 32, 33, 34, 37, 38, 39, 45, 46, 47) from signals emitted by the position / position sensor in at least two positions / positions of the equipment component (12, 13, 14) and a predetermined distance between the at least two positions / positions.

2. The method according to claim 1, wherein The signals emitted by the position / location sensors (30, 31, 32, 33, 34, 37, 38, 39, 45, 46, 47) are filtered.

3. The method according to claim 1 or 2, wherein: The signals emitted by the position / location sensors (30, 31, 32, 33, 34, 37, 38, 39, 45, 46, 47) in at least two positions / locations are averaged over a specific time.

4. The method according to claim 1 or 2, wherein: At least two positions / locations of the equipment component (12, 13, 14) are distinguished using the current state of the work machine.

5. The method according to claim 4, wherein The equipment component (12, 13, 14) is movable between two end positions, wherein the first position / position is a first end position of the equipment component (12, 13, 14) and the second position / position is a second end position, and wherein the end positions are detected by means of an actuation signal for actuating the equipment component (12, 13, 14).

6. The method according to claim 5, wherein: The final position of the equipment component (12, 13, 14) is detected by means of the duration, magnitude and direction identification of the actuation signal.

7. The method according to claim 6, wherein The final position of the equipment component (12, 13, 14) is detected by means of an actuation signal which is greater than 50% of the maximum magnitude of the actuation signal for a duration of greater than 5 seconds.

8. The method according to claim 1 or 2, wherein: The orientation / position sensor is an angle sensor (30, 31, 32, 33, 34) or a travel sensor (37, 38, 39) or an inertial measurement unit (45, 46, 47).

9. The method according to claim 1 or 2, wherein: To calibrate the signals emitted by the sensors, the control signals are algorithmically combined with basic knowledge about the kinematics and / or dynamics of the work machine.

10. The method according to claim 9, wherein The algorithmic combination occurs via a Kalman filter, which combines the values ​​for the calibration parameters in a model-based manner and outputs them as evaluation variables.

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