Method and arrangement for compensating non-geometric error effects on a robot absolute accuracy by means of a laser sensor system

Abstract

The invention relates to a method for compensating non-geometric error effects on an absolute accuracy of a robot (110) by means of a laser sensor system. The method according to the invention is characterised in that at least one radiation pattern is radiated through the working space (200) and measurement configurations are chosen, such that for at least one elasticity element (111, 112, 113, 114, 115, 116, 117, 120), there is at least one pair of measurement configurations (I, II, III, IV) for which the absolute magnitude of the difference in the torques of the at least one pair of measurement configurations on the at least one elasticity element (111, 112, 113, 114, 115, 116, 117, 120) is greater than a target value, in that on a light-sensitive surface of the at least one sensor (130) a deviation from a straight line and / or plane implicitly predetermined by the at least one radiation pattern and its beam direction as well as its radiation pattern orientation is taken into account, by the projection detected by the at least one sensor (130) for the measurement configurations (I, II, III, IV) being implicitly mathematically compared with a position of the projection determined on the basis of the erroneous robot structure information and in that corrected robot structure information is generated from the deviation to compensate for the non-geometric error effects.

Description

[0001] Method and arrangement for compensating non-geometric error influences on a robot absolute accuracy by means of a laser sensor system

[0002] The invention relates to a method for compensating non-geometric error influences on a robot's absolute accuracy by means of a laser sensor system according to the preamble of claim 1 and a corresponding arrangement.

[0003] In the current state of the art, the term "mechanism" encompasses various types of robots, particularly industrial robots. These mechanisms are generally universally programmable machines that operate largely autonomously within a given framework, for example, for handling, assembling, or processing workpieces. With appropriate programming, a mechanism is capable of consistently and autonomously repeating a given workflow.

[0004] For a detailed explanation of the prior art and in particular for the definition of the terms used below, reference is made to the applicant's DE 10 2023 105 674.3, the complete content of which is also intended to be incorporated into the present patent application by this reference.

[0005] In addition to the definition of the terms in DE 10 2023 105 674.3, the definition of “effector” (point 2 of the definitions in DE 10 2023 105 674.3) is to be expanded for the present application as follows:

[0006] An effector is any one of a number of clearly defined segments or rigid bodies of the robot. An effector can be, in particular, a possibly complex, rigid or inherently movable element of a robot to which a tool (e.g. a gripper for gripping a workpiece, a milling cutter, a drill, a sensor such as a camera, etc.) can be arranged to carry out a predefined activity. The so-called TCP (tool center point) is a freely determined point of action of a tool or workpiece arranged on the effector, for example the focus of a picked-up laser or the center of a held object. The effector is occasionally referred to in the literature as the “robot hand.” In serial kinematics, i.e. open kinematic chains, the effector does not necessarily have to be the last element in the kinematic chain; rather, it is conceivable that further elements such as joints or rigid bodies follow the effector.

[0007] In principle, it is also conceivable that a robot has more than one effector.

[0008] In the specific configurations of the comparatively inexpensive, locally measuring systems used to date, some non-geometric robot parameters or robot structural information cannot be identified with sufficient precision due to conceptual, unavoidable, algebraic dependencies. These algebraic dependencies are fundamentally due to the existing local measurement principles, not to a lack of measurement accuracy or deficiencies in artificial intelligence or mathematical parameter identification.

[0009] Elastic deformations, in particular, have not yet been consistently captured by robot manufacturers and taken into account in robot controllers, and are usually only modeled very simply. Elasticities are a significant source of error in robots. If they are not identified and taken into account in the controller, the achievable absolute accuracy of the robot is significantly compromised.

[0010] If non-geometric parameters are nevertheless determined using a local measurement method in the prior art, as described, for example, in WO29 / 175 A1, it is not only necessary to perform numerous measurements in different joint configurations and under different loads on a large number of effector objects and reference objects. Furthermore, it is a mandatory requirement that the precise position of the reference objects and the effector objects relative to each other be precisely measured in advance, so that in this case, too, a global measuring system must be used at least once. However, such laser trackers or theodolite systems are associated with high acquisition costs.

[0011] It is an object of the present invention to propose a comparatively cost-effective and locally measuring method by means of which, in particular, non-geometric parameters of a robot can be precisely identified. This object is achieved according to the invention by the method for compensating non-geometric error influences on the absolute accuracy of a robot by means of a laser sensor system according to claim 1. Advantageous embodiments and further developments of the invention emerge from the dependent claims. The invention relates to a method for compensating non-geometric error influences on the absolute accuracy of a robot by means of a laser sensor system, wherein the robot comprises a plurality of elastic elements and a control unit, wherein an elastic element is a rigid body or a joint or an effector or a robot base,wherein at least one radiation pattern generator is arranged stationary in an environment of the robot within a workspace or outside the workspace, wherein at least one radiation pattern is radiated through the workspace of the robot by means of the at least one radiation pattern generator, wherein the at least one radiation pattern comprises at least one laser light beam and / or at least one laser light plane, wherein at least one sensor with at least one light-sensitive surface is arranged on the effector of the robot, wherein the robot is controlled by means of the control unit successively into a plurality of measuring configurations in which the at least one radiation pattern impinges on the at least one light-sensitive surface, wherein the robot is controlled in accordance with robot structural information stored electronically in the control unit,wherein a position of a projection of the at least one radiation pattern onto the light-sensitive surface is detected by the at least one sensor, and measurement information describing the position is forwarded from the at least one sensor to a computing unit, wherein torques act on the elastic elements due to an external force depending on a respective joint configuration, and wherein the robot structural information is subject to errors due to the non-geometric error influences.

[0012] The method according to the invention is thus implemented as a so-called laser sensor calibration, in which all measurement information required for calibration is recorded and processed locally by sensors on light-sensitive sensor surfaces. The robot to be calibrated has, in addition to a robot base that is stationary in the workspace, a plurality of joints and rigid bodies, at least one effector, and a control unit. Typically, the robot has exactly one effector, but the method according to the invention is not limited to robots with only one effector.

[0013] The joints can take different forms, for example, as rotary, sliding, or screw joints. Furthermore, the joints preferably have electric actuators for moving the joints and the rigid bodies attached to them.

[0014] The rigid bodies represent rigid and inherently immobile connecting bodies in the sense of arm segments between two joints.

[0015] The at least one effector is preferably arranged via a joint on the outermost rigid body, i.e., the rigid body furthest from the robot base, and can, for example, pick up or operate a tool, a gripper, or even a workpiece, in particular, pick up a workpiece using the gripper. As already described, however, it is also conceivable and preferred for the at least one effector not to be the last element of the kinematic chain, but for further elements to follow the effector.

[0016] Since the joints, the rigid bodies, the robot base and the effector have an inherent, unavoidable elasticity, they are summarized under the generic term “elasticity elements” in the sense of the invention.

[0017] Finally, the control unit can be connected to the remaining components of the robot exclusively at the data level, for example, via one or more data cables or wirelessly. A more extensive connection is possible, but not required. The control unit includes an electronic processing unit that enables real-time control of the robot by converting movement requests to the robot into corresponding joint control commands.

[0018] At least one radiation pattern generator is arranged in the robot's workspace, spaced apart from the robot base or spaced apart from the robot, and additionally or alternatively outside the robot's workspace. The at least one radiation pattern generator is stationary, i.e., fixed and immobile at least for the duration of the implementation of the method according to the invention. In contrast to the known generic methods, however, the invention does not require the exact position of the associated radiation pattern generator relative to the robot base, i.e., advantageously, no laser tracker or theodolite system is required to determine this position.

[0019] The at least one radiation pattern generator is advantageously designed as a laser, for example, a semiconductor laser diode or a gas laser, in particular a HeNe laser, with upstream optics for generating a specific radiation pattern. The optics can consist of one or more optical lenses or optical gratings.

[0020] The light emitted by the at least one radiation pattern generator then represents the generated and emitted radiation pattern. Within the meaning of the invention, it is not necessary for the radiation pattern to have a wavelength perceptible to the human eye. The wavelength can also be in the infrared or ultraviolet range.

[0021] At least one sensor with at least one light-sensitive surface is arranged on the effector. The at least one sensor is therefore an optical sensor and can, for example, be a so-called CCD sensor or CMOS sensor, with the at least one light-sensitive surface advantageously representing the associated light-sensitive sensor array. The light-sensitive surface of the at least one sensor preferably has a matrix structure that not only detects the impact of the radiation pattern but also allows the shape and position of the projection of the radiation pattern to be determined.

[0022] Alternatively, the at least one sensor can preferably also comprise, for example, a housing, a diffuser disk, and a matrix camera. The diffuser disk represents a surface section of the housing in which the matrix camera is arranged. The matrix camera can be aligned with the diffuser disk and capture one or more incident radiation patterns. In this case, too, the matrix camera can enable the shape and position of the projection of the radiation pattern to be determined. However, the light-sensitive surface can also be an essentially one-dimensional line. The sensor would then be designed as a so-called line sensor. In this case, the radiation pattern is preferably a light plane.

[0023] The at least one sensor is configured to detect the position of the projection of the at least one radiation pattern when it strikes the at least one light-sensitive surface. Accordingly, the at least one light-sensitive surface is configured to detect all wavelengths of all radiation pattern generators used.

[0024] The position of a projection on the light-sensitive surface is detected by the at least one sensor. Within the meaning of the invention, the "position of the projection" refers to the shape, orientation, and precise position of the at least one radiation pattern on the at least one light-sensitive surface. With a non-point cross-section of the radiation pattern, the shape and orientation of the at least one radiation pattern on the at least one light-sensitive surface contain not only the position but also information about the orientation of the at least one sensor relative to the at least one radiation pattern generator. The orientation information can advantageously be used for calibration.Instead of having a continuous cross-section, such as the square or circular cross-section mentioned above, the radiation pattern can also consist of two or more spaced-apart individual beams, which can increase the information yield of a measurement.

[0025] Measurement information from the at least one sensor, which describes the position of the projection on the light-sensitive surface, is then forwarded to an advantageously external processing unit. The measurement information preferably includes a position of the projection on the light-sensitive surface, a shape of the projection on the light-sensitive surface, and an orientation of the projection on the light-sensitive surface.

[0026] The at least one radiation pattern comprises at least one laser light beam with, for example, a circular, rectangular, or oval cross-section. Any other cross-sectional geometries are also conceivable. The radiation pattern can be generated, for example, by a so-called diffractive optical element. The diffractive optical element can split a single beam into several separate, unconnected laser light beams, which, within the meaning of the invention, are understood as independent and distinct laser light beams. The laser light beam then preferably consists of individual light beams with no or only a very small expansion angle.

[0027] When implementing the method according to the invention, the robot is controlled by the control unit into a plurality of joint configurations in which the at least one radiation pattern is detected by the at least one sensor, i.e., in which the at least one radiation pattern impinges on the light-sensitive surface. Such joint configurations are referred to as measurement configurations within the meaning of the invention.

[0028] Due to unavoidable external forces, such as gravity, all elastic elements of the robot are subject to varying or equal torques. Since the elastic elements exhibit a certain degree of elasticity, they react to the torques caused by the external force with slight elastic deformation, which leads to inaccuracies in the robot's operation. These elastic deformations are considered non-geometric errors. Accordingly, the uncorrected robot structural information is subject to errors due to ignored or incorrect non-geometric geometric errors.

[0029] The method according to the invention is characterized in that the at least one radiation pattern is radiated through the working space in such a way and the plurality of measuring configurations is selected in such a way that for at least one elasticity element from the plurality of elasticity elements there is at least one pair of measuring configurations for which the absolute value of the difference in the torques of the at least one pair of measuring configurations on the at least one elasticity element is greater than a target value, that on the light-sensitive surface of the at least one sensor a deviation from a straight line and / or plane implicitly predetermined by the at least one radiation pattern and its beam direction as well as its radiation pattern orientation is taken into account,By implicitly comparing the projection position detected by at least one sensor for each of the multiple measurement configurations with a projection position determined from the erroneous robot structural information, and by generating corrected robot structural information to compensate for the non-geometric error influences from the deviation. The aforementioned target value is not a fixed value, but advantageously a flexibly adjustable value.

[0030] Furthermore, according to the invention, the deviation is determined by comparing the recorded projection position for the measurement configurations with a projection position determined based on the erroneous robot structural information. The deviations thus determined include the error influence of the elasticity of the elastic elements as well as, in general, the non-geometric and geometric parameter values ​​during robot operation when the robot is controlled according to the erroneous robot structural information.

[0031] Finally, to compensate for the non-geometric and, advantageously, also the geometric error influences, corrected robot structural information is calculated from the totality of the deviations. This corrected robot structural information is used for future robot control.

[0032] Thus, the invention describes a method which, without the need for a costly laser tracker or a theodolite system or similar costly global measuring devices, makes it possible to directly identify the non-geometric parameters such as the elasticities of joints or rigid bodies of the robot on the basis of the obtained measured values ​​and to take them into account accordingly during a calibration of the robot or to eliminate the error influences in the corrected robot structural information, so that the working accuracy of the robot can be significantly improved compared to generic, locally measuring methods.

[0033] According to a preferred embodiment of the invention, it is provided that a model-based parameter identification is carried out, wherein the corrected global structural information is corrected model parameters of a mathematical model of the robot as well as of the at least one radiation pattern generator and of the at least one sensor, wherein the model parameters comprise robot parameters describing the robot as well as calibration object parameters describing the at least one radiation pattern generator and the at least one sensor, wherein the plurality of measurement configurations consists of at least one measurement series, wherein a measurement series comprises all measurement configurations that are recorded with a selected calibration object pair.

[0034] To calculate the corrected robot structural information, a mathematical model or a mathematical description of the robot's kinematic structure as well as the non-geometric and geometric error influences is implemented in the computing unit. In model-based robot calibration, the robot structural information is referred to as the model's robot parameters. The calibration object parameters describe the position of at least one sensor relative to the effector and of at least one radiation pattern generator relative to the robot base. The mathematical model describes the position of the effector and thus of at least one sensor for each given joint configuration. Once the position of the radiation pattern generator is known, the position of the projection on the sensor in the sensor coordinate system can be calculated based on the mathematical model.

[0035] According to a particularly preferred embodiment of the invention, the corrected robot parameters are calculated iteratively by the computing unit. The goal of the iterative calculation method is, in particular, to minimize the residual, or the average residual error, or the deviation between the calculated positions of the respective projection and the positions detected by the sensor.

[0036] The iterative process generates improved model parameters in each iteration step, which are increasingly closer to the real or finally corrected model parameters, but are still subject to errors.

[0037] According to another particularly preferred embodiment of the invention, the corrected robot parameters are calculated by the computing unit using a characteristic system of equations, which can also be represented in the form of a characteristic matrix equation. The characteristic system of equations is derived from a general kinematic system of equations and additionally includes the position of calibration objects. In contrast to the kinematic system of equations, the characteristic kinematic calibration equation system—characteristic equation(s) for short—also takes into account the calibration method used, along with the associated calibration objects and their arrangement. The characteristic system of equations can be represented as a characteristic (matrix) equation using homogeneous matrices.Preferably, each side of the characteristic equation describes the position of the radiation pattern on the light-sensitive sensor surface, which is explained in more detail below.

[0038] According to a particularly preferred embodiment of the invention, the characteristic system of equations is formulated as P * L = Go * Gi * ... G n * S, where P describes a position of the at least one radiation pattern generator relative to the robot, where L describes a beam direction of the at least one radiation pattern, where Go * Gi * ... G nstarting from the robot base, describes a spatial transition from the robot base to the effector and the G, describe a transition from one rigid body of the robot to a next rigid body including the joint belonging to the respective transition or from one joint to a next joint including the intermediate rigid body, where n denotes the number of joints of the robot and where S describes a spatial transition from the effector of the robot to an arbitrary but fixed coordinate system on the light-sensitive surface of the at least one sensor.

[0039] The characteristic equation is obtained by successively mathematically describing and linking the transformations or transitions from the robot base to the first joint, then from joint to joint and finally from the last joint to the sensor as well as to the predicted position of the radiation pattern on the sensor or by suitably concatenating the transformations and then comparing the result with the measured position of at least one radiation pattern on the sensor.

[0040] According to a particularly preferred embodiment of the invention, the computing unit creates a Jacobian matrix based on the characteristic system of equations, which mathematically relates an infinitesimal change in the deviations to an infinitesimal change in the robot parameters. The use of the Jacobian matrix for iterative parameter identification has proven to be a suitable method for determining optimal approximate solutions for overdetermined nonlinear systems of equations.

[0041] According to a further preferred embodiment of the invention, it is provided that the computing unit forms a pseudo-inverse of the Jacobian matrix.

[0042] The pseudoinverse of a matrix is ​​a generalization of the inverse matrix to non-square matrices, which is why it is often called a generalized inverse.

[0043] According to a further particularly preferred embodiment of the invention, it is provided that the corrected robot parameters are calculated by the computing unit by means of model-based mathematical parameter identification and that this comprises at least one calculation step carried out as a non-linear optimization.

[0044] The nonlinear optimization methods advantageously used for this purpose have proven to be suitable for identifying precise values ​​of the robot parameters of the characteristic system of equations.

[0045] Methods suitable for carrying out the at least one calculation step carried out as a non-linear optimization within the meaning of the invention are, for example, the Gauss-Newton method and the Levenberg-Marquardt method.

[0046] According to an alternative preferred embodiment of the invention, it is provided that the corrected robot structural information is contained in weighting matrices, wherein the weighting matrices are created and / or parameterized using a machine learning method and / or artificial intelligence. In this case, the method according to the invention is therefore not carried out in a model-based manner. The weighting matrices contain the information of the mathematical model without the model parameters explicitly appearing in the matrices. According to a further preferred embodiment of the invention, it is provided that the at least one radiation pattern generator is arranged such that an angle of between 30° and 150° exists between the propagation direction of the at least one radiation pattern and a direction of action of the force of gravity.

[0047] If the angle is 90°, the radiation pattern is projected horizontally through the room. This ensures that high torques act on the robot's elastic elements in many of the measurement configurations. The higher the torques acting during the measurements, the more pronounced the errors resulting from incorrect values ​​of the elasticity parameters or missing parameters become in the laser beam deviations.

[0048] According to a further preferred embodiment of the invention, the at least one radiation pattern comprises at least two rigidly connected laser beams with an angle of less than 5 degrees or at least two crossed light planes. The spacing of the parallel laser beams should be sufficiently close in this case so that both can strike the light-sensitive surface of the sensor simultaneously in suitable measurement configurations.

[0049] According to a further preferred embodiment of the invention, it is provided that the target value is 5% of the mathematically maximum possible absolute value of all pairwise differences of the torques which any pairs of practically or theoretically measurable measuring configurations have on at least one elasticity element.

[0050] According to a further preferred embodiment of the invention, the external force is a gravitational force, a compressive force, or a torsional force. These are the external forces typically acting on the robot. Gravity acts constantly on the robot in any joint configuration, with the torque resulting from gravity acting on one or more elastic elements being significantly determined by the orientation of the respective elastic element(s). The compressive force acts on the robot or its elastic elements when the robot presses a workpiece or, in general, the effector against another body, for example, against a tool or workpiece, so that the elastic elements are compressed. This can also result in an acting torque.The torsional force acts, for example, when the robot rotates a workpiece against resistance, such as screwing a screw into a thread with a specific torque. The identical torque then acts on the robot's elastic elements.

[0051] According to a further preferred embodiment of the invention, it is provided that the robot is repeatedly controlled with different additional weights or payloads into the plurality of measuring configurations and / or in subsets thereof.

[0052] The different payloads can, for example, correspond to the full weight or half the weight that the robot lifts or moves in production. Another important special case is that no additional payload is carried.

[0053] According to a further preferred embodiment of the invention, it is provided that the corrected robot structural information is generated for a predeterminable subset of elastic elements of the robot.

[0054] This provides additional information that can be used to determine the corrected robot structural information.

[0055] The invention also relates to an arrangement for compensating for non-geometric error influences on the absolute accuracy of a robot by means of a laser sensor system, comprising a robot with a plurality of elastic elements and with a control unit, at least one radiation pattern generator, at least one sensor with at least one light-sensitive surface, wherein an elastic element is a rigid body or a joint or an effector or a robot base, wherein at least one radiation pattern generator is arranged stationary in an environment of the robot within a workspace or outside the workspace, wherein the at least one radiation pattern generator is designed to radiate at least one radiation pattern through the workspace of the robot, wherein the at least one radiation pattern comprises at least one laser light beam and / or at least one laser light plane,wherein at least one sensor with at least one light-sensitive surface is arranged on the effector of the robot, wherein the control unit is designed to control the robot in accordance with robot structural information electronically stored in the control unit successively into a plurality of measurement configurations in which the at least one radiation pattern impinges on the at least one light-sensitive surface, and wherein the sensor is further designed to detect a position of a projection of the at least one radiation pattern onto the at least one light-sensitive surface and to forward measurement information describing the position to a computing unit.

[0056] According to the invention, the arrangement is designed to carry out the method according to the invention. This results in the advantages already described in connection with the method according to the invention also being applicable to the arrangement according to the invention.

[0057] According to a preferred embodiment of the invention, the computing unit is functionally and structurally integrated into the control unit. This results in the advantage that the method according to the invention can be executed by the robot without an additional, external computing unit.

[0058] According to a further preferred embodiment of the invention, it is provided that the at least one sensor comprises a housing, a diffuser disk, and a matrix camera, wherein the diffuser disk is a surface section of the housing and the matrix camera is housed by the housing, wherein a light refraction of the diffuser disk is designed such that an incident light beam at an angle of 45° causes an offset of a light spot of less than 0.3 mm between the front and back of the disk, wherein the matrix camera is arranged such that it can capture an image of the diffuser disk, and wherein the matrix camera is designed to output information about the captured image. This embodiment of the at least one sensor is comparatively cost-effective, but nevertheless allows reliable detection and recognition of the shape and position of the projection of the radiation pattern.

[0059] The information to be output is preferably pixel information of the matrix camera, i.e., information about which pixels of the matrix camera capture the radiation pattern and are passed on to the computing unit already described.

[0060] The matrix camera is advantageously designed or adjusted such that, for a predetermined maximum intensity of the ambient light and a predetermined light intensity of the radiation pattern, the contrast between an incident radiation pattern and the unirradiated surface of the diffuser disc is always sufficient to detect the radiation pattern reliably and without loss by the matrix camera, or that at least a threshold value for the radiation intensity can be specified, beyond which it is ensured that detected radiation originates from the radiation pattern.

[0061] The invention is explained below by way of example with reference to embodiments shown in the figures.

[0062] They show:

[0063] Fig. 1 shows, by way of example and schematically, a possible embodiment of an arrangement according to the invention for compensating non-geometric error influences on the absolute accuracy of a robot by means of a laser sensor system,

[0064] Fig. 2 shows an example and schematic view of the robot in two different measuring configurations,

[0065] Fig. 3 shows an example and schematic representation of the robot of Fig. 2 in two further, different measuring configurations and

[0066] Fig. 4 shows, by way of example and schematically, another possible embodiment of an arrangement according to the invention.

[0067] Identical objects, functional units, and comparable components are designated by the same reference symbols throughout the figures. These objects, functional units, and comparable components are identical in terms of their technical features, unless explicitly or implicitly stated otherwise in the description.

[0068] Fig. 1 shows, by way of example and schematically, a possible embodiment of an arrangement 100 according to the invention for compensating for non-geometric error influences on the absolute accuracy of a robot 110 using a laser sensor system. The arrangement 100 comprises, for example, the robot 110 and the laser sensor system.

[0069] The robot 110 is designed, for example, as an industrial robot 110 which is intended for machining workpieces (not shown in Fig. 1 ) in a productive operation.

[0070] The robot 110 comprises, for example, a plurality of elastic elements 111, 112, 113, 114, 115, 116, 117, 120 as well as further elastic elements not explicitly shown in Fig. 1, from which the ball joints 114, 115 and 116 are composed, among other things.

[0071] The robot 110 is arranged stationary in the workspace 200 with its robot base 120, which is also elastically deformable under the action of force and is thus an elastic element 120.

[0072] The further elastic elements 111, 112, 113, 114, 115, 116, 117 are partly designed as rigid bodies 111, 112, 113 and partly as joints 114, 115, 116.

[0073] The rigid bodies 111, 112, 113 represent, for example, arm segments 111, 112, 113 of the robot 110, which connect the joints 114, 115, 116 to one another. The joints 114, 115, 116 are, for example, ball joints 114, 115, 116. Another elastic element 117 is the effector 117, on which an optical sensor 130 with, for example, a light-sensitive surface is arranged. The arrangement 100 according to the invention also comprises, for example, a control unit 140, which is connected to the robot 110 via a wired data connection and is arranged outside the workspace 200. The control unit 140 is designed as a computer device 140 which, by means of suitable control software, is designed to control the robot 110 or to specify joint configurations of the robot 110 and to read out joint positions.The control unit 140 further comprises a human-machine interface via which a human operator can make various inputs, such as for controlling or maintaining the robot 110.

[0074] The arrangement 100 according to the invention further comprises the already mentioned optical sensor 130 with the light-sensitive surfaces as well as two radiation pattern generators 131, 132.

[0075] In the example of Fig. 1, the two radiation pattern generators 131, 132 are arranged stationary and with a fixed orientation in the working space 200.

[0076] The arrangement of the radiation pattern generators 131, 132 in the work space 200 is such that a first radiation pattern of a first radiation pattern generator 131 is emitted at an angle of 30° against the direction of gravity (illustrated by an arrow 160) and a second radiation pattern of a second radiation pattern generator 132 is emitted at an angle of 25° against gravity.

[0077] The control unit 140 is configured to successively control the robot 110 into a plurality of measurement configurations based on robot structural information stored electronically in the control unit 140. For this purpose, the control unit 140 uses a mathematical model of the robot, which mathematically describes the robot 140 via its robot parameters. The mathematical model contains the robot structural information as so-called robot parameters, with the robot parameters describing the non-geometric and geometric properties of the robot 110. The robot parameters, like the calibration object parameters, are part of the model parameters, with the calibration object parameters describing the positions and orientations of the radiation pattern generators 131, 132 relative to the robot base 120.When a radiation pattern strikes a light-sensitive surface of sensor 130, sensor 130 detects the precise position of the radiation pattern on the light-sensitive surface. In other words, sensor 130 detects the projection of the radiation pattern striking the light-sensitive surface. Sensor 130 then wirelessly transmits measurement information describing the position of the projection to a computing unit 150, for example. Likewise, control unit 140 transmits information describing the measurement configuration to computing unit 150.

[0078] However, since the robot structural information stored in the control unit 140 and used for the mathematical model has not yet been corrected, as is the case, it is erroneous and leads to a deviation between a desired position of the projection of the radiation pattern on the sensor 130 at the effector 117 and an actually measured position of the projection of the radiation pattern on the sensor 130 at the effector 117. This deviation is characterized, for example, by a gravitational force acting on the exemplary elasticity elements 111, 112, 113, 114, 115, 116, 117, 120, which leads to an elastic deformation of the elasticity elements 111, 112, 113, 114, 115, 116, 117, 120 that depends on the respective joint configuration.

[0079] The two radiation patterns are now radiated through the work space 200 in such a way that a plurality of measuring configurations is enabled, in which for each elasticity element 111, 112, 113, 114, 115, 116, 117, 120 to be identified, at least one pair is to be included in the totality of all measuring configurations for which the absolute value of the difference between the torques caused by gravity on at least one elasticity element 111, 112, 113, 114, 115, 116, 117, 120 is greater than a target value.

[0080] The computing unit 150 then calculates the corrected robot structural information or the corrected model parameters from the deviations between the detected positions of the projection on the light-sensitive surface of the sensor 130 and the respective calculated impact points in an iterative process. The corrected model parameters are calculated, for example, based on a characteristic system of equations. According to a further exemplary embodiment, also shown in Fig. 1, the computing unit 150 and the control unit 140 are designed as a neural network that generates the corrected robot structural information using artificial intelligence. In this case, the robot structural information is contained in weighting matrices, which the computing unit 150 and the control unit 140 generate from as much measurement data as possible.The weighting matrices therefore contain the information of the mathematical model without the model parameters appearing explicitly in the matrices.

[0081] Fig. 2 shows an example and schematically the robot 110 in two different measuring configurations I, II. The measuring configuration I is shown in dashed lines, while the measuring configuration II is shown with solid lines. In both measuring configurations I, II, a torque caused by gravity acts on the elastic elements 111, 112, 113, 114, 115, 116, 117, 120. The special thing here is that the joints 115 and 116 in the two measuring configurations I, II shown are each subjected to opposite maximum loads and the absolute value of the difference between the two torques is maximum, since the rigid body 113, the joint 116 and the effector 117 are held perpendicular to the force of gravity 160 in both measuring configurations I, II. These torques act on the individual elastic elements 111, 112, 113, 114, 115, 116, 117, 120 differently and depending on the respective measurement configuration I, II.

[0082] For example, in the measurement configuration I, a torque acting on the joint 114 rotates to the left in the illustration in Fig. 2, which is caused by the weight force of the elastic elements 112, 113, 115, 116, 117 following the joint 114 being held by the joint 114.

[0083] In measurement configuration I, joint 115 also experiences a counterclockwise torque, which is caused by the weight of the elastic elements 113, 116, 117 following joint 115. Joint 116 also experiences a maximum torque in measurement configuration I.

[0084] If the robot 110 is brought into the measuring configuration II, which, for example, corresponds to the measuring configuration I mirrored on a vertical axis, the torques from the measuring configuration I act on the joints 114, 115 and 116, but with the opposite sign.

[0085] The resulting absolute value of the difference in the torques acting on joints 115 and 116 in measurement configurations I and II is therefore, as shown in the example, maximum. In contrast, the absolute value of the difference in the torques at joint 114 is not maximum for measurement configurations I and II in Fig. 2. Fig. 3 shows, by way of example and schematically, robot 110 from Fig. 2 in two further, different measurement configurations III, IV. Measurement configuration III is shown in dashed lines, while measurement configuration IV is shown in solid lines. In contrast to Fig. 2, according to Fig. 3, joint 114 is also subjected to opposite maximum loads in the two measurement configurations III, IV shown. In the measurement configuration III shown in dashed lines, the elastic elements 112, 113, 115, 116, 117 following the joint 114 are stretched perpendicular to the force of gravity, so that a maximum torque acting downwards to the left results at the joint 114.

[0086] In the measurement configuration IV, the maximum torque also acts on the joint 114, since here too the elastic elements 112, 113, 115, 116, 117 following the joint 114 are stretched perpendicular to the force of gravity, whereby in this case the torque is opposite in its direction of action to the torque at the joint 114 of the measurement configuration III.

[0087] Measurement configuration IV corresponds to measurement configuration III mirrored on a vertical axis.

[0088] Therefore, the absolute value of the difference between the torques at joint 114 is maximum for the measurement configurations III and IV according to the embodiment of Fig. 3. The torques on joints 115 and 116 in both measurement configurations III, IV are identical to the torques already described in Fig. 2.

[0089] Fig. 4 shows, by way of example and schematically, another possible embodiment of an arrangement 100 according to the invention. According to the example, the arrangement 100 comprises the robot 110 and the radiation pattern generator 131, which are arranged at a distance from one another in the work space 200.

[0090] Fig. 4 illustrates the representation of robot 110 and radiation pattern generator 131 in the mathematical model or in the characteristic equation system. Robot 110, for example, again comprises the three ball joints 114, 115, and 116. The corresponding joint transitions are each described as homogeneous 4 x 4 matrices and designated G1 to G6. The origin of the robot base coordinate system is, for example, in the upper left corner of the pedestal-shaped robot base 120. The transition from this upper left corner to the rigid segment 111 is represented, for example, via the transfer matrix G0.

[0091] The radiation pattern generator 131 emits a radiation pattern. The exit point of the radiation pattern from the radiation pattern generator 131 relative to the upper left corner of the robot base 120 is given by the vector p or the transition matrix P. The radiation pattern generator 131 radiates in the direction 7. The radiation pattern strikes the optical sensor 130 at a point that is given relative to a local sensor coordinate system on the light-sensitive surface of the sensor 130 by two plane coordinates or a transition matrix S. The distance between the exit point of the radiation pattern and the point of incidence of the radiation pattern is a distance |7|. The transition matrix from the exit point of the radiation pattern to the point of incidence of the radiation pattern at the distance |7| is denoted by the transition matrix L. Using these notations, the characteristic system of equations can be written, for example, as follows:

[0092] The straightness of the radiation pattern, which is a laser beam and thus completely straight, is specified, for example, by the transition matrix L in the model, which specifies a straight propagation with a constant direction vector 7 and a scalar variable. The straightness of the radiation pattern is thus integrated into the mathematical model, as is the special arrangement of the calibration objects 130, 131. Together with the elasticities of the elasticity elements 111, 112, 113, 114, 115, 116, 117, 120, which are also described in the mathematical model, the mathematical model, together with corresponding measurements, can now be subjected to a nonlinear optimization or a suitable iterative calculation method in order to, among other things, determine the elasticities or correct erroneous model parameters.

[0093] List of reference symbols

[0094] 100 arrangement

[0095] 110 robots, industrial robots

[0096] 111 , 112, 113 Elastic element, rigid body

[0097] 114, 115, 116 Elastic element, joint

[0098] 117 Elasticity element, effector

[0099] 120 robot base

[0100] 130 Optical Sensor

[0101] 131 radiation pattern generator, semiconductor laser diode

[0102] 132 radiation pattern generator, semiconductor laser diode

[0103] 140 Control unit

[0104] 150 computing units

[0105] 160 Gravity

[0106] 200 Working space r direction vector

[0107] 7 Distance

[0108] Go,Gi, G2, G3, G4, Gs, transition matrix

[0109] G6.S,P,L

[0110] I, II, III, IV measurement configuration

Claims

Patent claims 1. A method for compensating non-geometric error influences on an absolute accuracy of a robot (110) by means of a laser sensor system, wherein the robot (110) comprises a plurality of elastic elements (111, 112, 113, 114, 115, 116, 117) and a control unit (140), wherein an elastic element (111, 112, 113, 114, 115, 116, 117) is a rigid body (111, 112, 113) or a joint (114, 115, 116) or an effector (117) or a robot base (120), wherein at least one radiation pattern generator (131, 132) is arranged stationary in an environment of the robot (110) within a workspace (200) or outside the workspace (200), wherein by means of the at least one radiation pattern generator (131, 132) at least one radiation pattern is radiated through the workspace (200) of the robot (110), wherein the at least one radiation pattern comprises at least one laser light beam and / or at least one laser light plane, wherein at least one sensor (130) with at least one light-sensitive surface is arranged on the effector (117) of the robot (110), wherein the robot (110) is controlled by means of the control unit (140) successively into a plurality of measuring configurations in which the at least one Radiation pattern that hits at least one light-sensitive surface,wherein the robot (110) is controlled in accordance with robot structural information electronically stored in the control unit (140), wherein a position of a projection of the at least one radiation pattern onto the at least one light-sensitive surface is detected by the at least one sensor (130) and measurement information describing the position is forwarded from the at least one sensor (130) to a computing unit (150), wherein, due to an external force and depending on a respective joint configuration, torques are applied to the elastic elements (111, 112, 113, 114, 115, 116, 117, 120) and wherein the robot structural information is faulty due to the non-geometric error influences, characterized in that that the at least one radiation pattern is radiated through the working space (200) in such a way and the plurality of measuring configurations (I, II, III, IV) is selected in such a way that for at least one elasticity element (111, 112, 113, 114, 115, 116, 117, 120) from the plurality of elasticity elements (111, 112, 113, 114, 115, 116, 117, 120) there is at least one pair of measuring configurations (I, II, III, IV), for which the absolute value of the difference of the torques of the at least one pair of measuring configurations on the at least one elasticity element (111, 112, 113, 114, 115, 116, 117, 120) is greater than a desired value, that on the light-sensitive surface of the at least one Sensor (130) a deviation from a straight line and / or plane implicitly predetermined by the at least one radiation pattern and its beam direction as well as its radiation pattern orientation is taken into account by for the plurality of measurement configurations (I, II, III,IV) the position of the projection detected by the at least one sensor (130) is implicitly compared with a position of the projection determined on the basis of the erroneous robot structural information, and corrected robot structural information is generated to compensate for the non-geometric error influences from the deviation.

2. The method according to claim 1, characterized in that a model-based parameter identification is carried out, wherein the corrected global structural information is corrected model parameters of a mathematical model of the robot (110) and of the at least one radiation pattern generator (131, 132) and of the at least one sensor (130), wherein the model parameters comprise robot parameters describing the robot (110) and calibration object parameters describing the at least one radiation pattern generator (131, 132) and the at least one sensor (130), wherein the plurality of measurement configurations consists of at least one measurement series, wherein a measurement series comprises all measurement configurations recorded with a selected calibration object pair (130, 131, 132).

3. Method according to claim 2, characterized in that the corrected robot parameters are calculated iteratively by the computing unit (150).

4. Method according to at least one of claims 2 and 3, characterized in that the corrected robot parameters are calculated by the computing unit with the aid of a characteristic system of equations, which can also be represented in the form of a characteristic matrix equation, wherein the characteristic system of equations is derived from a general kinematic system of equations and additionally includes the position of calibration objects.

5. Method according to claim 4, characterized in that the characteristic system of equations is in the formulation P * L = Go * Gi * ... G n * S, where P describes a position of the at least one radiation pattern generator relative to the robot (110), where L describes a beam direction of the at least one radiation pattern, where Go * Gi * ... G nstarting from the robot base, describes a spatial transition from the robot base to the effector (117) and the Gi describe a transition from one rigid body of the robot to a next rigid body including the joint belonging to the respective transition or from one joint to a next joint including the intermediate rigid body, where n denotes the number of joints of the robot and where S describes a spatial transition from the effector of the robot to an arbitrary but fixed coordinate system on the light-sensitive surface of the at least one sensor.

6. Method according to at least one of claims 4 and 5, characterized in that that the computing unit creates a Jacobi matrix based on the characteristic system of equations, which mathematically relates an infinitesimal change in the deviations to an infinitesimal change in the robot parameters.

7. The method according to claim 6, characterized in that the computing unit (150) forms a pseudoinverse of the Jacobian matrix.

8. Method according to at least one of claims 2 to 7, characterized in that the corrected robot parameters are calculated by the computing unit (150) by means of model-based mathematical parameter identification and this comprises at least one computing step carried out as a non-linear optimization.

9. The method according to claim 1, characterized in that the corrected robot structural information is contained in weighting matrices, wherein the weighting matrices are created and / or parameterized by means of a machine learning method and / or by artificial intelligence.

10. Method according to at least one of claims 1 to 9, characterized in that the at least one radiation pattern generator is arranged such that an angle exists between the propagation direction of the at least one radiation pattern and a direction of action of the force of gravity, the angle being between 30° and 150°.

11. Method according to at least one of claims 1 to 10, characterized in that the at least one radiation pattern comprises at least two rigidly connected laser beams with an included angle of less than 5 degrees or at least two crossed light planes.

12. Method according to at least one of claims 1 to 11, characterized in that the target value is 5% of the mathematically maximum possible absolute value of all pairwise differences of the torques which any pairs of practically or theoretically measurable measuring configurations have on at least one elasticity element.

13. Method according to at least one of claims 1 to 12, characterized in that the external force is a gravitational force, a compressive force or a torsional force.

14. Method according to at least one of claims 1 to 13, characterized in that the robot (110) is repeatedly controlled with different additional weights or payloads into the plurality of measuring configurations and / or in subsets thereof.

15. Arrangement (100) for compensating non-geometric error influences on an absolute accuracy of a robot (110) by means of a laser sensor system, comprising a robot (110) with a plurality of elastic elements (111, 112, 113, 114, 115, 116, 117, 120) and with a control unit (140), at least one radiation pattern generator (131, 132), at least one sensor (130) with at least one light-sensitive surface, wherein an elastic element (111, 112, 113, 114, 115, 116, 117) is a rigid body (111, 112, 113) or a joint (114, 115, 116) or an effector (117) or a robot base (120), wherein at least one radiation pattern generator (131, 132) is arranged stationary in an environment of the robot (110) within a workspace (200) or outside the workspace (200), wherein the at least one radiation pattern generator (131, 132) is designed toto radiate at least one radiation pattern through the working space (200) of the robot (110), wherein the at least one radiation pattern comprises at least one laser light beam and / or at least one laser light plane, wherein at least one sensor (130) with at least one light-sensitive surface is arranged on the effector (117) of the robot (110), wherein the control unit (140) is designed to control the robot (110) in accordance with robot structural information stored electronically in the control unit (140) one after the other into a plurality of measurement configurations (I, II, III, IV), in which the at least one radiation pattern impinges on the at least one light-sensitive surface, and wherein the sensor (130) is further designed to detect a position of a projection of the at least one radiation pattern onto the at least one light-sensitive surface and to forward measurement information describing the position to a computing unit (150), characterized in that the arrangement (100) is designed to carry out a method according to at least one of claims 1 to 14.

16. Arrangement according to claim 15, characterized in that the at least one sensor comprises a housing, a diffuser disk and a matrix camera, wherein the diffuser disk is a surface section of the housing and the matrix camera is housed by the housing, wherein a light refraction of the diffuser disk is designed such that an incident light beam at an angle of 45 ° causes an offset of a light spot of less than 0.3 mm between the front and back of the disk, wherein the matrix camera is arranged such that it can capture an image of the diffuser disk and wherein the matrix camera is designed to output information about the captured image.

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