Method of calibrating a robot

Abstract

The invention relates to a method for calibrating a robot (2), wherein a work space (AR) of the robot (2) at least partially overlaps a work space (AW) of a machine tool and / or production machine (4), wherein the robot (2) is moved in such a way that a reference point of the robot is located at a first position within the work space (AW) of the machine tool and / or production machine (4), wherein a first position value of the robot (2) at the first position is compared with a first position value of the machine tool and / or production machine (4) at this position, wherein, when the first position value of the robot (2) and the first position value of the machine tool and / or production machine (4) are not identical, the first position value of the robot (2) is corrected or the first position value in the machine tool and / or production machine (4) is corrected, so that the first position value of the robot (2) and the first position value of the machine tool and / or production machine (4) are identical.

Description

Technical Field

[0001] This invention relates to a method for calibrating a robot. Background Technology

[0002] Collaboration between robots and machine tools and / or production machinery is advantageous, for example, in the processing of workpieces. For instance, with the help of robots, processes on machine tools and / or production machinery that would otherwise have to be done manually can be automated. This sometimes includes loading and unloading processes.

[0003] However, due to this collaboration, work steps that are not well-suited to by the machine tool and / or production machinery itself, especially when the workpiece needs to be held in a clamped state, can also be successfully performed. For example, these are post-processing steps, such as deburring.

[0004] However, the low mechanical precision of robots related to design makes such collaboration difficult.

[0005] WO 2005 / 084895 A1 relates to a method for measuring the operating point of a tool in an industrial robot. EP1152 212B1 describes a calibration method. A drawback of this method is the need for an optical measuring device to perform the measurement.

[0006] JP 2011048467 A discloses a machining system having a machine tool controlled by a machine tool controller and a robot controlled by a robot controller to perform work on the machine tool. The machining system includes a data acquisition device with a data acquisition unit for acquiring a nominal value P on a specified movable part of the robot set in a robot coordinate system. The machining system further includes: a measuring device for measuring the position of the nominal point P in the machine tool coordinate system; and a relative relationship derivation device for deriving the relative relationship between the robot coordinate system and the machine tool coordinate system based on the data acquired by the data acquisition device and the position data measured by the measuring device.

[0007] EP 3418 838A1 discloses an electrical discharge machining system, comprising: an electrode movement control unit for moving a wire electrode while keeping the wire electrode parallel to the Z1 axis so that the wire electrode contacts a reference workpiece, and simultaneously moving the wire electrode at an inclination relative to the Z1 axis; an electrode position detection unit for detecting the position of the wire electrode in the X1Y1Z1 rectangular coordinate system when the wire electrode contacts the reference workpiece; a position detection unit for detecting the position of the reference workpiece in the orthogonal X2Y2Z2 coordinate system when the wire electrode contacts the reference workpiece; and a relative position relationship calculator for calculating the relative position relationship between the coordinate systems based on the detected positions.

[0008] DE 102016 011 653A1 discloses a low-cost robot system capable of easily measuring the position of a target point. When the target is located at a known first target position in the robot coordinate system, the system stores the feature dimensions of the target image included in the captured image as reference data, and stores the first target position relative to the end of the robot arm as the tool center of the position. When the target is located at a second target position, the system compares the feature dimensions obtained from the captured image with the feature dimensions of the reference data to induce end-of-arm movement, and the feature dimensions of the reference data induce end-of-arm movement. The system then calculates the second target position in the robot coordinate system based on the second robot position corresponding to the moved end-of-arm position and the position of the tool center.

[0009] DE 102015 015 094A1 discloses a collaborative system consisting of a robot and a machine tool, aiming to obtain a high-precision, simple coordinate transformation device for converting the robot coordinate system to the machine coordinate system. A preliminary coordinate system is defined by the coordinate values ​​of three calibration marks in a base coordinate system obtained by translating the machine coordinate system. A coordinate transformation matrix is ​​calculated based on the preliminary and base coordinate systems. The positions of the marks in the robot coordinate system are recorded using a camera. The coordinate transformation matrix from the robot coordinate system to the preliminary coordinate system is calculated based on the three coordinate values ​​in the robot coordinate system. The coordinate transformation matrix from the robot coordinate system to the base coordinate system is based on the aforementioned second matrix. Summary of the Invention

[0010] This invention is based on the aim of improving the collaboration between robots and machine tools and / or production machines.

[0011] This objective is achieved by the present invention, namely, a method for calibrating a robot, wherein the robot's workspace at least partially overlaps with the workspace of a machine tool and / or production machine, wherein the robot is moved such that a reference point of the robot is located at a first position within the workspace of the machine tool and / or production machine, wherein a first position value of the robot at the first position is compared with a first position value of the machine tool and / or production machine at that position, wherein, when the first position value of the robot differs from the first position value of the machine tool and / or production machine, the first position value of the robot is calibrated or the first position value of the machine tool and / or production machine is calibrated such that the first position value of the robot is the same as the first position value of the machine tool and / or production machine.

[0012] In a preferred embodiment, the robot's first position value is corrected.

[0013] This is advantageous because machine tools and / or production machines typically have higher precision than robots. For robots, especially industrial robots, the typical order of magnitude of absolute static precision achievable is about 1 mm, while for machine tools and / or production machines it is about 10 μm.

[0014] The advantage provided by this invention is that time-consuming and expensive calibrations of robots, particularly robotic mechanisms, using 3D measuring devices, such as those capable of detecting the position of a robotic arm (advantageously having a tool center point, abbreviated as TCP), are unnecessary. Calibration can be performed quickly and inexpensively using this invention.

[0015] Another advantage of this invention is that it can be repeatedly calibrated during use.

[0016] This is a major advantage compared to current standard calibrations, which are typically performed only during commissioning.

[0017] In this way, errors that accumulate over time can be corrected.

[0018] One advantageous design is one where the location values ​​have a first coordinate, a second coordinate, and a third coordinate.

[0019] It is preferable to use a coordinate system with three axes (x-axis, y-axis, z-axis).

[0020] Typical, but not mandatory, use of orthogonal coordinate systems, especially Cartesian coordinate systems.

[0021] One advantageous design is a mobile robot whose reference point is located at a second position within the workspace of the machine tool and / or production machine, wherein a second position value of the robot at the second position is compared with a second position value of the machine tool and / or production machine at that position, wherein when the robot's second position value differs from the second position value of the machine tool and / or production machine, the robot's second position value is corrected, or the second position value of the machine tool and / or production machine is corrected so that the robot's second position value is the same as the second position value of the machine tool and / or production machine.

[0022] In the preferred design, the robot's initial position value is corrected.

[0023] One advantageous design approach is to determine a third position value using interpolation or extrapolation based on a calibrated first position value in the robot or machine tool and / or production machine, and a calibrated second position value in the robot or machine tool.

[0024] This makes it possible to make good estimates for points that have not been individually calibrated.

[0025] This invention can significantly improve the accuracy of robots within the machine tool workspace, particularly the relative accuracy between the robot and the machine tool and / or production machinery. Any slight decrease in robot accuracy outside the machine tool workspace is acceptable.

[0026] Therefore, more precise machine tools and / or production machines can be used as measurement standards for less precise robots.

[0027] One advantageous design is a mobile robot, in which the robot's reference point is located at multiple locations within the workspace of the machine tool and / or production machine.

[0028] The reference point is advantageously located at multiple positions in chronological order.

[0029] In other words, this advantageously means: first approach point A, then approach point B. Then, for example, it is possible to approach point C.

[0030] Two or more positions are advantageous.

[0031] An advantageous design is to arrange multiple locations in a grid and / or array shape, or to arrange multiple locations such that these locations are at or near critical points of the workpiece to be processed.

[0032] Examples of key points include: corners and / or edges.

[0033] Corners and edges are advantageous because they are easy to measure.

[0034] The reference point is advantageously located where the correspondence between the robot and the machine tool and / or production machine is particularly important.

[0035] One example is that measuring the edge is advantageous when the robot is deburring the edge.

[0036] Another example involves the assembly of components: if a robot is inserting one component into another, it is advantageous to measure the grooves, fits, etc. provided for this purpose.

[0037] The advantage of doing this is that it allows for precise handling of key points.

[0038] It is advantageous to arrange the robot's reference point on the robot's end effector.

[0039] The tool center point is advantageously located at the end effector of the robot.

[0040] Machine tools and / or production machines also advantageously have a reference point. This reference point can also be called the tool center point. It is advantageously located at the penetration point of the tool, which is arranged on the spindle of the machine tool and / or production machine.

[0041] One advantageous design is a mobile robot whose reference point is located on the worktable of the machine tool and / or production machine, for example, at a corner of the worktable.

[0042] The advantage here is that there are a large number of points with known locations within the workspace of the machine tool and / or production machinery. These include, for example, the surface of the worktable and the location of the tool tip.

[0043] This tool can also be a particularly precise measuring tool or sensor probe.

[0044] Robots can approach a location or point by, for example, guiding sensor probes or distance measuring devices themselves, or by establishing mechanical contact (this is achieved, for example, by deflecting sensor probes of tools and / or products, or by moving the machine to a fixed stop point), and record their TCP position values ​​in space at these points (specifically using three coordinates x, y, z).

[0045] Differences in the spatial position values ​​measured by machine tools and / or production machines for these points are advantageously considered as errors in the robotic mechanism that need to be compensated for at these points. Therefore, machine tools and / or production machines can be used as measuring devices.

[0046] Errors in the machine tool and / or production machine itself compared to an ideal, error-free machine tool and / or production machine have no effect, because the collaboration between the robot and the machine tool and / or production machine essentially depends on the relative accuracy of both.

[0047] One advantageous design is a mobile robot in which the robot's reference point is located on the spindle of the machine tool and / or production machine.

[0048] One advantageous design approach is to detect contact with the worktable and / or spindle via sensor probes located on and / or within the robot's end effectors.

[0049] The robot can move to the worktable until contact, preferably mechanical contact, occurs. The worktable surface serves as a reference for comparing the two coordinate systems. After the initial adjustment, geometric errors in the robot's mechanics can be corrected by moving to a further known point on the machine tool and / or production line.

[0050] One advantageous design approach is to detect contact with the spindle using sensor probes present on and / or within the spindle.

[0051] The sensor probes can also be placed in the tool holder of machine tools and / or production machines.

[0052] For this purpose, the spindle of the machine tool and / or production machine advantageously has at least one sensor probe. A robot approaches it. The sensor probe advantageously detects contact. The deflection of a dial indicator serves as a reference for comparing the two coordinate systems of the robot and the machine tool and / or production machine.

[0053] Following this first comparison, the spindle of the machine tool and / or production machine is advantageously moved to at least one other position, and the described process is repeated.

[0054] If these points sufficiently cover the common workspace, as described above, these support points can be used to address errors at other unmeasured points in the workspace using interpolation or extrapolation methods. The resulting characteristic map is advantageously used to feed compensation values ​​into the robot's movement within the workspace of the machine tool and / or production machine, making the robot more capable of reaching the desired position from the machine tool and / or production machine's perspective. This means, for example, that the contour executed by the robot during machining is maintained more accurately on the workpiece.

[0055] Another calculation of the measured position values ​​involves correcting for the geometric features of the robot's mechanics, particularly the precise position of the joints relative to each other, the size of the robot arm segments between the joints, and / or load-dependent deflections.

[0056] For example, this can be achieved by establishing an overdetermined system of equations based on the robot's kinematic transformation equations. For example, the solution can be achieved using the least squares method. Particularly advantageous is that if the robot manufacturer has not corrected (as described above) mechanical errors (especially deviations from the ideal geometry) at the factory, and the workspace of the machine tool and / or production machine is large enough to allow for sufficient joint deflection, then the errors become visible.

[0057] This allows for improved robot precision even outside the workspace of machine tools and / or production machines.

[0058] If the positional error at the measurement location in the workspace does not become zero, a second pass can be performed after the alternative calculation of the measurement values ​​to compensate for this. For example, this can be done by moving the robot to all measurement locations using geometrically corrected robot mechanics and eliminating the remaining error using the compensation method mentioned above.

[0059] Comparisons between machine tools and / or production machines and robots are not limited to Cartesian coordinate (x, y, z) evaluations.

[0060] In another advantageous embodiment of the invention, it is also possible to determine the angular position of the computer bed and / or production machine and robot relative to each other. This means that not only positioning can be agreed upon, but orientation can also be agreed upon.

[0061] The solution to the above objective can also be achieved by the present invention, namely a system for performing the method, comprising a robot and a machine tool and / or production machine, the system being arranged such that the workspace of the robot at least partially overlaps with the workspace of the machine tool and / or production machine.

[0062] The solution to the above objective can also be achieved by the present invention, namely by using a machine tool and / or production machine as a measuring tool, which has a sensor probe preferably on and / or in the spindle. Attached Figure Description

[0063] The invention will now be described and explained in more detail with reference to the embodiments shown in the accompanying drawings. The drawings show:

[0064] Figure 1 The system shown includes robots and machine tools and / or production machines.

[0065] Figure 2 The first possible embodiment is shown.

[0066] Figure 3 A second possible embodiment is shown.

[0067] Figure 4 The method according to the invention is shown.

[0068] Figure 5 Examples of robot workspaces and machine tool and / or production machine workspaces are shown.

[0069] Figure 6 and Figure 7 An example of digital control assignment is shown. Detailed Implementation

[0070] Figure 1 The system 10 is shown, which has a robot 2 and machine tools and / or production machines 4.

[0071] Robot 2 and machine tools and / or production machines 4 are arranged to make the robot's workspace AR (see Figure 5 The workspace of the machine tool and / or production machine (AW) at least partially overlaps with the workspace of the machine tool and / or production machine (see Figure 5 ).

[0072] The figure also shows workpiece 6 and the robot's tool center point (TCP) 12.

[0073] The tool position of robot 2 is described by its end effector. This is a hypothetical reference point located at a suitable point on the tool. The reference point according to the invention is advantageously TCP 12.

[0074] The figure also shows the display 16 of the machine tool and / or production machine 4. The figure shows that workpiece 6 has been processed in area 18.

[0075] The machining of workpiece 6 is achieved through collaboration between machine tools and / or production machines 4 and robot 2. For example, machine tools and / or production machines 4 can be used to machine and join workpiece 6.

[0076] Robot 2 can, for example, place workpiece 6. Robot 2 can also be used for cleaning, deburring, and / or polishing. Robot 2 can also perform other tasks.

[0077] Workpiece 6 can be processed simultaneously by machine tools and / or production machines 4 and robots 2.

[0078] However, so-called combined processing is advantageous, in which workpiece 6 is processed alternately by machine tools and / or production machines 4 and robots 2. However, simultaneous processing is also feasible.

[0079] The machine tool and / or production machine 4 has a higher precision than the robot 2. The machine tool and / or production machine 4 is typically at least an order of magnitude more accurate.

[0080] For example, robot 2 has an accuracy of about 1 mm, especially static accuracy, while machine tool and / or production machine 4 has an accuracy of about 10 μm.

[0081] The advantage provided by this invention is that it can improve the accuracy of the robot 2 in the workspace of the machine tool and / or production machine 4, and in particular, the relative accuracy of the robot 2 with respect to the machine tool and / or production machine 4 can be significantly increased.

[0082] Here, slight degradation of the accuracy of robot 2 that may occur outside the overlapping workspace of machine tool and / or production machine 4 and robot 2 is fully acceptable.

[0083] More precise machine tools and / or production machines 4 are advantageously used as measurement standards for less precise robots 2.

[0084] The system 10 shown in the figure illustrates a feasible arrangement of machine tool and / or production machine 4 and robot 2. Here, robot 2 is arranged relative to machine tool and / or production machine 4 such that the two workspaces at least partially overlap.

[0085] However, it is also feasible to use robots 2 and machine tools and / or production machines 4 outside of this public workspace.

[0086] Within the workspace of the machine tool and / or production machine 4, multiple points whose positions are precisely known can be obtained. These include, for example, the surface of the worktable and the positions of the tool tip 14 and / or the spindle of the machine tool and / or production machine 4.

[0087] The tool center point of the machine tool and / or production machine 4 is advantageously located at the tool tip 14.

[0088] Robot 2 is able to approach these points, for example, by having its own sensor probes and / or using distance measuring devices. For example, by establishing mechanical contact between the tool center point 12 and the worktable, the position value of the tool center point 12 in space can be determined.

[0089] The position value advantageously includes three coordinates. The first coordinate advantageously defines the position value on the x-axis, the second coordinate preferably defines the position on the y-axis, and the third coordinate preferably specifies the position on the z-axis.

[0090] The difference in position values ​​measured at a point by the machine tool and / or production machine 4, for example, using its own sensor probes, is considered to be an error of the robotic mechanical device to be compensated at that point.

[0091] For this purpose, the machine tool and / or production machine 4 can be used as a measuring mechanism. Here, the error of the machine tool and / or production machine 4 itself compared to an ideal or error-free machine tool and / or production machine 4 has no effect, because the cooperation of the robot 2 and / or the machine tool and / or production machine 4 only requires the relative accuracy of the two devices relative to each other.

[0092] Figure 2 A first feasible embodiment is shown.

[0093] The figure shows system 10, which has robot 2 and machine tools and / or production machines 4.

[0094] The figure also shows the workbench 20, the robot's zero point 0R, and the machine tool and / or production machine's zero point 0W. The tool center point 12 of the robot 2 and the tool tip 14 of the machine tool and / or production machine 4 are also identified.

[0095] In this embodiment, robot 2 is moved until it advantageously makes mechanical contact with worktable 20. Here, the surface of worktable 20 can be used when comparing two coordinate systems. Robot 2 advantageously approaches multiple locations on the surface of worktable 20.

[0096] The coordinate system of robot 2 can be different from the coordinate system of machine tool and / or production machine 4. Therefore, it is advantageous to transform position values ​​from one coordinate system to another.

[0097] Figure 3 A second feasible embodiment is shown.

[0098] The figure shows a machine tool and / or production machine 4 with a sensor probe 141. A robot 2 approaches the sensor probe 141, causing contact to be made between the tool center point 12 and the sensor probe 141.

[0099] Here, the deflection of the dial indicator on the sensor probe 141 is used as a reference for comparing the two coordinate systems.

[0100] The tool tip 14 of the machine tool and / or production machine 4 is advantageously moved to a different position in order to perform a second comparison.

[0101] Here, the robot 2 is moved such that the tool center point 12 makes advantageous contact with the sensor probe 141. The first contact generates a first position value for the robot 2 at the first position and a first position value for the machine tool and / or production machine 4 at that position.

[0102] The difference can be identified by comparing the two values. If the two values ​​are different, the first position value of robot 2 can be advantageously corrected so that the two position values ​​are the same. Alternatively, the position value of machine tool and / or production machine 4 can be corrected.

[0103] Similarly, a second position value, particularly a second corrected position value, can be determined. Points located between or outside these position values ​​can be determined using interpolation or extrapolation methods.

[0104] Robot 2 advantageously has a numerical control device 98 (see Figure 6 ).

[0105] Machine tools and / or production machines 4 also advantageously have numerical control devices 99 (see Figure 6 ).

[0106] Alternatively, it is conceivable to provide a more advanced numerical control device 100 in system 10 (see Figure 7 It has two channels 101 and 102 (see...) Figure 7 ).

[0107] Here, the first channel 101 is advantageously assigned to the robot 2. Here, the second channel 102 is advantageously assigned to the machine tool and / or production machine 4.

[0108] Figure 4 The method according to the present invention is shown.

[0109] In method step S1, the robot 2 is moved such that the robot's reference point is located at a first position within the workspace of the machine tool and / or production machine 4.

[0110] In method step S2, the first position value of robot 2 at the first position is compared with the first position value of machine tool and / or production machine 4 at the same position.

[0111] If the first position value of robot 2 is different from the first position value of machine tool and / or production machine 4 (identified by decision E2, and query identified by E), then the first position value of robot 2 is corrected in method step S4.

[0112] If these values ​​are not different, no correction is performed in method step S3.

[0113] Alternatively, the first position value of the machine tool and / or production machine 4 can also be corrected (see method step S4). However, it is preferred to correct the first position value of the robot 2 because the machine tool and / or production machine 4 has higher accuracy.

[0114] Perform a correction so that the first position value of robot 2 is the same as the first position value of machine tool and / or production machine 4.

[0115] Figure 5 The robot's workspace AR and the machine tool and / or production machine 4's workspace AW are shown purely as examples. The overlapping area is identified as AW+R.

Claims

1. A method for calibrating a robot (2), wherein, The workspace (AR) of the robot (2) at least partially overlaps with the workspace (AW) of the machine tool and / or production machine (4). - Wherein, the robot (2) is moved such that the reference point of the robot is located at a first position within the workspace (AW) of the machine tool and / or production machine (4). - Wherein, the first position value of the robot (2) at the first position is compared with the first position value of the machine tool and / or production machine (4) at that position. - Wherein, when the first position value of the robot (2) is different from the first position value of the machine tool and / or production machine (4), the first position value of the robot (2) is corrected or - Correct the first position value of the machine tool and / or production machine (4), - Make the first position value of the robot (2) the same as the first position value of the machine tool and / or production machine (4), wherein the first position value of the robot (2) and the first position value of the machine tool and / or production machine (4) are measured, wherein the measured position values ​​are calculated to correct the geometric features of the robot mechanics, the geometric features including the precise position of the joints relative to each other, the size of the robot arm segments between the joints and / or the deflection depending on the load.

2. The method according to claim 1, wherein, The position value has a first coordinate (x), a second coordinate (y), and a third coordinate (z).

3. The method according to claim 1 or 2, wherein, Move the robot (2) such that the reference point (12) of the robot (2) is located at a second position within the workspace (AW) of the machine tool and / or production machine (4). - Wherein, the second position value of the robot (2) at the second position is compared with the second position value of the machine tool and / or production machine (4) at the second position. - Wherein, when the second position value of the robot (2) is different from the second position value of the machine tool and / or production machine (4), the second position value of the robot (2) is corrected or - Correct the second position value of the machine tool and / or production machine (4), - Make the second position value of the robot (2) the same as the second position value of the machine tool and / or production machine (4).

4. The method according to claim 3, wherein, A third position value is determined by interpolation or extrapolation based on a first position value of the robot (2) or the machine tool and / or production machine (4) and a second position value of the robot (2) or the machine tool and / or production machine (4).

5. The method according to claim 1 or 2, wherein, Move the robot (2) such that the reference point (12) of the robot (2) is located at multiple locations within the workspace (AW) of the machine tool and / or production machine (4).

6. The method according to claim 5, wherein, The plurality of locations are arranged in a grid shape and / or an array shape, or the plurality of locations are arranged such that they are at or near critical points of the workpiece to be processed.

7. The method according to claim 1 or 2, wherein, The reference point (12) of the robot (2) is arranged on the end effector of the robot.

8. The method according to claim 1 or 2, wherein, Move the robot (2) so that the reference point (12) of the robot (2) is located on the worktable (20) of the machine tool and / or production machine (4).

9. The method according to claim 8, wherein, Move the robot (2) such that the reference point (12) of the robot (2) is located at the corner (50) of the worktable (20) of the machine tool and / or production machine (4).

10. The method according to claim 1 or 2, wherein, Move the robot (2) so that the reference point (12) of the robot (2) is located at the spindle (51) of the machine tool and / or production machine (4).

11. The method according to claim 10, wherein, Contact with the worktable (20) and / or the spindle (51) is detected by sensor probes located on and / or within the end effector of the robot (2).

12. The method according to claim 10, wherein, Contact with the spindle (51) is detected by a sensor probe (141) present on and / or in the spindle.

13. A system (10) for performing the method according to any one of claims 1 to 12, the system having a robot (2) and a machine tool and / or production machine (4), the system being arranged such that the workspace (AR) of the robot (2) at least partially overlaps with the workspace (AW) of the machine tool and / or production machine (4).

14. An application of a machine tool and / or production machine (4) as a measuring instrument in a system (10) according to claim 13 for performing the method according to any one of claims 1 to 12, wherein, The machine tool and / or production machine (4) has a sensor probe (141) on and / or inside the spindle (51).

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