RU2830703C1 - Calibration system and method of determining geometrical parameters of working elements for automation of construction equipment operation - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention relates to measurement of geometrical parameters of moving parts of construction equipment. System for calibrating geometric parameters of working elements for automation of construction equipment includes a machine chassis, a cabin, moving elements, working element with possibility of movement relative to chassis, sensors of cabin inclination, moving elements and working element with working point defined on it. System also includes a GPS positioning system receiver mounted on the cabin. System also includes a device for measuring the relative position of the working point, made in the form of a tape measure with a digital interface, which is attached by one end to the working point on the working member, and the other to an arbitrary point in the working area of construction equipment, and a processor for calculating the current position of the working point and geometric parameters of the moving parts of the excavator.

EFFECT: high accuracy, efficiency and reliability of calibration of an automatic control system for construction equipment, as well as reduced requirements for qualification of personnel performing calibration.

3 cl, 4 dwg, 1 tbl

Description

The invention relates to measuring the geometric parameters of moving parts of construction equipment, in particular, to a device and method necessary for automating the operation of construction equipment, as well as for the operational calibration of industrial automation systems for construction work.

There are various systems for measuring the geometric parameters of construction equipment, the most obvious of which is measuring the lengths of moving parts of construction equipment using mechanical tape measures, tilt angles with a level, rotation angles with an encoder or a protractor. However, the disadvantage of measurements with the listed tools is the impossibility of accurately determining the centers of the axes of large equipment, the technical inaccessibility of some parts on operating construction equipment as a result of the presence of a large number of hydraulic hoses and wires along the moving parts, which leads to errors in both measuring lengths and angles, which does not allow achieving the required accuracy of automatic operation of construction equipment.

The closest in technical solution adopted as a prototype is patent RU 2650857C1 "System for determining geometric parameters of three-dimensional objects" by authors Dubenko Yu.V., Timchenko N.N. This patent relates to the field of contactless measurements of contours or curves of three-dimensional objects in real time and is based on the use of stereometry, i.e. processing images from two high-resolution cameras. The technical result of this solution is to increase the speed of monitoring the geometric parameters of three-dimensional objects, but it is impossible to achieve the accuracy of measurements required for construction equipment, since the accuracy of measurements of geometric parameters depends on the accuracy of determining the angles and the size of the base between the cameras and, as a result, the accuracy decreases with the distance to the measured object, which is unacceptable within the framework of the solved problem of calibration of construction equipment.

The technical result of the proposed technical solution for the calibration system is an increase in the accuracy, efficiency and reliability of measuring the geometric parameters of moving parts of construction equipment.

The technical result is achieved using a simple and reliable device for measuring the relative distance of the working point of the working element from an arbitrary point in the working area of the construction equipment, unlike complex and expensive devices for measuring the absolute coordinates of the working point and a laser rangefinder, which require the involvement of qualified personnel. Such a device for measuring the relative distance with the ability to automatically read values in digital form is a mechanical tape measure with a digital interface - a digital tape measure, which is a flexible cable wound on a spring-loaded drum with an encoder, the flexibility of the cable allows it to bend towards the working point when moving the working element, and the encoder gives the values of the length of the wound cable, measuring the distance between the working point and an arbitrary point in the working area of the construction equipment in which the digital tape measure is fixed.

The drawings show the digital tape measure:

Fig. 1 - example of installation on construction equipment;

Fig. 2 - structure of the calibration system;

Fig. 3 - structure of the moving links of the excavator;

Fig. 4 - example of errors in installing tilt sensors.

In Fig. 1 and Fig. 2, the system for determining the geometric parameters of moving parts of construction equipment, for example an excavator, includes a cabin 1 installed on a chassis 2, a positioning system 3 is located in the area of the cabin, moving parts 4 of the working element are attached, on which tilt and rotation sensors 5 are located, and the working element 6 itself with a working point 7 designated on it for its positioning.

The digital tape measure 8 is fixed with one end at an arbitrary point of the working area (the zone of movement of the working element), with the other end to the working point 7 of the working element, the distance measured by the digital tape measure 8 between them is 9. The data obtained from the tilt and rotation sensors 5 simultaneously with the data from the digital tape measure 8 and the positioning system 3 are sent to the information processing unit 10, in which the calculations of the lengths of the moving parts 4, 6 and the displacement of the installation angles of the tilt and rotation sensors 5 are implemented. The values obtained as a result of calibration are stored in the processing unit 10 and used to calculate the coordinates of the working point 7 during the operation of the construction equipment.

The implementation of the proposed technical solution for installing a digital tape measure is carried out in the proposed method for measuring the geometric parameters of moving parts of construction equipment, necessary for the automation of the operation of construction equipment.

Automatic control systems of Topcon X-53x, X-63x, X33 for excavators are known, which support the calibration procedure, in which a set of marks is installed at points with known coordinates and height, after which the working element of the excavator (edge of the bucket) touches all the marks, which allows to correlate absolute coordinates WGS-84 and local coordinates (x, y, z).

The disadvantage of this method is the impossibility of specifying previously entered values of the lengths of moving parts and errors in determining angles during such calibration. High accuracy is achieved only in a narrow range of rotation angles and digging depths.

Similar automation and calibration systems have been developed by Leica Geosystems (Leica PowerDigger Lite iCON system), Trimble (GCSFlex system), MOBA Mobile Automation AG (Xsite PRO, Link system), Bridgin (iDig system), etc. None of the described systems allows automatic correction of errors in measuring the lengths of moving parts of construction equipment.

The calibration system of the LOADRITE™ company (X2650 system) is known, which uses measurements of the minimum and maximum angles of rotation of the moving parts of the excavator (boom, handle and bucket) to calibrate lengths and angles, as well as the installation of “zero”, that is, a known level, which is considered “zero” in the software package.

The closest prototype of the calibration algorithm is the patent US9644346B2 of Komatsu Ltd (authors Masanobu Seki, Masashi Ichihara). This patent describes a method for measuring the lengths of the working parts of an excavator based on recording the coordinates of the working element (bucket), obtained at different positions of the boom, handle and bucket (three positions for each moving part). The coordinates are determined by an external device (tape measure, theodolite and GPS receiver). The advantages of this method are the ability to correct errors in measuring the lengths of moving parts and angles and binding the obtained coordinates of the working element to absolute GPS coordinates, the disadvantages include the difficulty of accurately measuring the absolute coordinates of the bucket position, especially when the bucket is raised high above the ground, since all the coordinates of the working element used in calibration are measured by specialists using precise measuring equipment.

The technical result of the invention is to increase the accuracy, efficiency and reliability of the calibration of the automatic control system of construction equipment, as well as to reduce the requirements for the qualifications of the personnel performing the calibration.

The technical result is achieved by installing sensors for the tilt of the cabin, moving elements and the working body of the construction equipment, connecting a digital tape measure with one end at any convenient point in the operating area of the working body of the construction equipment (bucket), with the other end of the tape measure to the working point of the working body (the most important part of the working body, the coordinates of which must be calculated for the automation of the work), recording the values of the rotation angles of the moving parts of the construction equipment simultaneously with the readings of the digital tape measure, after which a system of nonlinear equations is solved to find such lengths of the moving parts and offset angles of the sensor installation, at which the system of equations converges with a minimum root-mean-square error. Thus, to calibrate the lengths of the moving parts and the offset angles of the sensors, it is sufficient to install a digital tape measure in an arbitrary place in the working area of the calibrated construction equipment, connect its other end to the working point on the working body (bucket), record the current data of the tilt angles and tape measure readings, and then calculate all the necessary parameters for calibration. This calibration can be carried out without special training of personnel, does not require technical training and time.

The essence of the invention

As an example of construction equipment, we will take an excavator as it is quite complex to operate and calibrate. A typical excavator has a rotating tower, boom, handle and bucket. To measure the tilt and rotation angles, it is necessary to install 3 inclinometers and a tower rotation sensor, which is shown in Figure 3 - the structure of the excavator's moving links. The accuracy of the sensor installation is not known in advance, and the value read from the inclinometer, in addition to the random error, contains a constant offset.

There are two known problems of positioning the moving links of an excavator: a direct problem, in which the position of the working element (bucket) is determined by the known values of the lengths of the moving parts and their rotation angles, and a reverse problem, in which the positions of the moving links must be determined by the given position of the working element (bucket).

For calibration, a mathematical model of the solution of the direct problem is constructed, data on the bucket position and signals from the tilt sensors are collected, after which the inverse problem is solved, as a result of which correction values for the lengths of the links and corrections for the rotation angles from the sensors are calculated. To solve the problem of rotation and transfer of the coordinate system of the link (i-1) to the (i) coordinate system, a transfer matrix can be used, presented in the following form [1], formula (1):

Where

θ is the angle of rotation around the z _i-1 axis such that the x _i-1 axis becomes parallel to the x _i axis;

d _i - the magnitude of the shift along the x _i axis until the x _i and x _i-1 axes are completely aligned;

a _i - distance between the origins of coordinates;

α _i is the angle of rotation around the x _i axis that results in the coincidence of the coordinate systems (i) and (i-1).

The parameters of the coordinate systems of the moving parts of the excavator required to solve the direct problem are given in Table 1.

Table 1. Parameters of coordinate systems of moving parts of the excavator

Link θ _i α _i a _i d _i 1 (base) Θ ₁ -π/2 L1 0 2 (arrow) Θ ₂ 0 L2 0 3 (handle) Θ ₃ 0 L3 0 4 (bucket) Θ ₄ 0 L4 0

The matrix connects the coordinates of an arbitrary point Pi (in the coordinate system i) with the corresponding coordinates of the same point in the coordinate system (i-1), formula (2) [4]:

Therefore, if point O ₄ is a point in the bucket coordinate system, then to recalculate the relative coordinates of the coordinate system (4) into the coordinate system of the base part of the excavator, it is necessary to perform the following operation according to formula (3) [4]:

But to solve the direct problem, it is necessary to know in advance the values of L ₁ , L ₂ , L ₃ , L ₄ and to know the angles of inclination of the links with high accuracy. As has already been said, it is technically either impossible to measure the lengths of the links between the centers of the rotation axes with a given accuracy, or it requires the use of complex additional equipment, similar to the comparison of the axes of the inclination sensors and the axes of the links.

An example of errors in installing sensors on the moving links of an excavator is shown in Figure 4.

Thus, if we represent the lengths of the boom, handle and bucket through L ₁ , L ₂ , L ₃ , angles (taking into account unknown displacements) θ ₀ + φ ₀ , θ ₁ + φ ₁ , θ ₂ + φ ₂ , θ ₃ + φ ₃ , θ ₄ + φ ₄ , then to describe the position of the bucket it is necessary to find the values of L ₁ , L ₂ , L ₃ , φ ₁ , φ ₂ , φ ₃ , φ ₄ . This problem can be solved analytically by solving a system of N equations to find N unknowns, but each measurement of the bucket position contains a random error, which leads to the presence of errors in determining the values of the lengths and angles. Therefore, to reduce the measurement error of the bucket position and the measurement errors of angles, we will use the accumulation of results, assuming that the variance of the estimate of the average value of a random variable decreases proportionally to the square of the number of experiments. For calibration, it is necessary to carry out significantly more measurements than the number of unknowns, and to calculate the values of the unknown parameters, we use the least squares method [2,3]. This method assumes that when finding the model parameters (coefficients L ₁ , L ₂ , L ₃ , φ ₁ , φ ₂ , φ ₃ , φ ₄ ) the error distribution law was close to normal (the central limit theorem in most problems allows using this assumption [4]).

The criterion of this method consists in finding such parameters L ₁ , L ₂ , L ₃ , φ ₁ , φ ₂ , φ ₃ , φ ₄ of the function F(x), at which the square of the positioning error is minimal, formula (4)

where y _i are the measured values of the coordinates, F(x) are the calculated values.

A necessary condition for the existence of a minimum of the error function is that its partial derivatives with respect to unknown variables are equal to zero [3]. As a result, we obtain the following system of equations, formula (5):

In our case, the function F(x) contains both powers and trigonometric functions, so obtaining an analytical expression for solving the system of equations is difficult. It is advisable to use numerical methods for finding the roots of nonlinear equations.

Thus, the method for measuring the geometric parameters of the moving parts of the working element (calibration procedure) consists in the fact that tilt and rotation angle sensors (inclinometers, encoders, protractors), as well as a positioning system, are installed on all moving parts of the working element of construction equipment; tilt and rotation sensors are necessary for calculating the position of the working element, but this requires preliminary measurement of the lengths of all moving parts and an offset of the installation angles of the tilt and rotation sensors from the axes of the moving parts; a digital tape measure is connected with one end to the working point of the working element of the equipment and to an arbitrary point in its working area of operation so that when the moving actuator parts of the equipment move, the digital tape measure allows measuring distances (does not catch on the moving parts and does not tear), as shown in Fig. 3; to increase the accuracy of calibration, the fixing point in the working area must be selected in the central part of this area; a control computer is connected that collects data from the positioning system, tilt and rotation sensors, as well as the values of the digital tape measure; turn on periodic recording of current values, ensure movement of all moving parts of the excavator with different speeds of movement and amplitudes, turn off recording; based on the data obtained, start the procedure for calibrating the lengths of the moving parts and angular displacements of the position of the equipment sensors (using numerical methods, select such values of the geometric parameters of the moving parts at which the calculated and measured values of the digital tape measure have a minimum standard deviation); record the obtained results in the model of the three-dimensional positioning system of the equipment for subsequent calculation of the position of the working point during operation.

Using the example of an excavator as a type of construction equipment, the proposed method for measuring the geometric parameters of the moving parts of the working element (calibration process) works when performing the following actions:

1. All moving parts of the excavator are pre-equipped with tilt and rotation angle sensors and a positioning system is installed;

2. Determine the location of the working point on the working element of the excavator, in our example the excavator bucket tooth;

3. Connect one end of the digital tape measure to the working point - the bucket tooth and to an arbitrary point in the working area of the excavator so that during movement the executive parts of the excavator do not interfere with the measurements, as shown in Fig. 3. To increase the accuracy of the calibration, the fixing point must be selected in the central part of the working area;

3. Connect the control computer, which receives data from the positioning system, tilt and rotation sensors, as well as the values of the digital tape measure;

4. Then they turn on the periodic recording of current values, during which they ensure the movement of all moving parts of the excavator at different speeds and amplitudes, and turn off the recording;

5. Based on the data obtained, a procedure is launched for software calibration of the lengths of the moving parts and angular displacements of the excavator sensor positions, in which numerical methods are used to select such values of the geometric parameters of the moving parts that the calculated and measured values of the digital tape measure have a minimum standard deviation;

6. After which, the obtained results are recorded in the model of the excavator’s three-dimensional positioning system and saved for subsequent calculation of the position of the working point during operation.

The result of the calibration method is a set of values L ₁ , L ₂ , L ₃ , φ ₁ , φ ₂ , φ ₃ , φ ₄ , necessary for the operation of the excavator model and subsequent control of the working element, i.e. the excavator bucket.

Calibration can also be carried out using absolute and relative coordinates.

Thus, when using a satellite positioning system and recalculating lengths and angles with reference to earth coordinates, absolute positioning is obtained, and calibration allows one to calculate the coordinates of the working point using any current coordinates of the receiver.

In the absence of a satellite positioning system, calibration is possible relative to the chassis or an arbitrary point on the construction equipment, which allows obtaining relative positioning of the working point.

The invention can be used to calibrate the geometric parameters of moving parts of construction equipment with any automatic control system, increasing the accuracy, reliability and validity of the results obtained, and also not requiring highly qualified personnel and complex equipment to perform the calibration.

List of references

1. Guanglong Du and Ping Zhang. Research ArticleIMU-Based Online Kinematic Calibration of Robot Manipulator // Hindawi Publishing Corporation. 2013.

2. R. Hook, T. A. Jeeves "Direct search for solutions to numerical and statistical problems", 212-219 p., 1961.

3. Linnik Yu. V. The method of least squares and the basics of the mathematical-statistical theory of observation processing. - 2nd ed. - M., 1962. 312 p.

4. Jorge Santolaria, Ana C. Majarena, David Samper, Agustín Brau, and Jesús Velázquez. Research Article Articulated Arm Coordinate Measuring Machine Calibration by Laser Tracker Multilateration. Hindawi Publishing Corporation. 2014.

Claims (3)

1. A system for calibrating the geometric parameters of working bodies for automating the operation of construction equipment, as applied to an excavator, including a machine chassis, a cabin, moving elements, a working body with the ability to move relative to the chassis, sensors for the tilt of the cabin, moving elements and the working body with a working point determined on it, a receiver of the GPS positioning system installed on the cabin, as well as a device for measuring the relative position of the working point, made in the form of a tape measure with a digital interface, which is attached at one end to the working point on the working body, and the other to an arbitrary point in the working area of the construction equipment, and a processor for calculating the current position of the working point and the geometric parameters of the moving parts of the excavator. 2. A method for determining the geometric parameters of working bodies for automating the operation of construction equipment, characterized in that all moving parts and the working body of the excavator are pre-equipped with angle and rotation sensors, a positioning system is placed, after which the location of the working point on the working body is assigned, then a tape measure with a digital interface is connected with one end to the working point, and the other to an arbitrarily selected point in the working area of the excavator, after which a control processor is connected to the input of which data are received from the positioning system, tilt and rotation angle sensors, as well as the tape measure, and periodic recording of their current readings is turned on, which are received at the input of the processor, are processed by it taking into account a mathematical model of the movement of the moving elements of the equipment, and, as a result, the actual lengths of the moving elements of the working body and the displacement of the tilt angles of the sensors from the axes of the moving elements are determined, the obtained data are stored in the processor memory and then used to determine the current position of the working point on the working body during the operation of the construction equipment. 3. The method according to item 2, characterized in that when installing a tape measure with a digital interface to increase the accuracy of measurements, its second end is secured in the central part of the working area of the excavator working element.