Computer-implemented method for machining a workpiece on a machine tool, machine tool, computer program product, and computer-readable medium
Patent Information
- Application Number
- EP2023732334
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-18
- Filing Date
- 2023-05-17
- Publication Date
- 2025-03-26
AI Technical Summary
Existing machine tools require complex structures to detect contour errors in workpieces, making the process cumbersome and inefficient.
A computer-implemented method for machining workpieces that automatically adjusts machining depth based on a CAD model, using detection criteria such as spindle speed, vibrations, or force sensors to ensure precise engagement with the actual outer contour, allowing for simplified detection and compensation of clamping errors and tool wear.
Enables accurate machining depth and reduced production time by automatically adapting control commands to the actual workpiece contour, eliminating the need for pre-measurement and minimizing tool wear, while maintaining high precision and efficiency.
Smart Images
Figure 1.1
Abstract
Description
[0001] COMPUTER-IMPLEMENTED METHOD FOR PROCESSING A WORK
[0002] PIECE ON A MACHINE TOOL, AS WELL AS A MACHINE TOOL, A COMPUTER PROGRAM PRODUCT AND A COMPUTER-READABLE MEDIUM
[0003] The invention relates to a computer-implemented method for machining a workpiece on a machine tool, as well as a machine tool, a computer program product and a computer-readable medium.
[0004] DD232223A1 discloses a machine tool and a method for operating the machine tool and for detecting and analyzing contour errors of a workpiece. The position measuring systems of the feed axes involved in contour generation on the machine tool are additionally connected to a contour detection device via special adapters.
[0005] The machine tool disclosed in DD232223A1 has the disadvantage that a complex structure of the machine tool is required to detect the contour errors of the workpiece.
[0006] The object of the present invention was to overcome the disadvantages of the prior art and to provide a machine tool and a method by means of which a contour error of a workpiece can be detected in a simplified manner.
[0007] This object is achieved by a method and a device according to the claims.
[0008] According to the invention, a computer-implemented method for machining a workpiece on a machine tool with a tool mounted in a work spindle is provided. The method comprises the following steps:
[0009] - Executing control commands of a computing unit for moving the tool and / or the workpiece and for bringing the tool into machining engagement with the workpiece, wherein the control commands are configured to machine the workpiece at a machining depth relative to a target outer contour specified on the basis of a CAD model of the workpiece;
[0010] - Automated detection when the tool engages with an actual outer contour of the workpiece, whereby a detection criterion is queried; - Automated adjustment of the control commands in the processing unit for shifting the machining depth determined on the basis of the target outer contour of the workpiece with respect to the detected actual outer contour of the workpiece.
[0011] The method according to the invention has the advantage that the control commands in the computing unit are specified on the basis of a target outer contour derived from a CAD model, wherein the control commands are automatically adapted to the actual outer contour of the workpiece. In this way, an exact machining depth can be achieved starting from the actual outer contour. This means that pockets or holes in workpieces, for example, can have an exact depth with respect to the actual outer contour. This is particularly advantageous when not the entire outer contour of the workpiece is to be machined, but when only machining recesses are to be made in the existing outer contour of the workpiece. This can be the case, for example, with cast workpieces with a sufficiently precise outer contour. Furthermore, the provided measure can be used to compensate for a clamping error of the workpiece on a clamping device.Furthermore, this measure can also compensate for cutting edge wear. In some cases, it may even eliminate the need to measure the tool after it has been clamped in the work spindle.
[0012] Furthermore, it may be useful
[0013] - that the speed of the work spindle is detected and when the speed of the work spindle is reduced by a threshold value, contact of the tool with the actual outer contour of the workpiece is assumed, or
[0014] - that vibrations in the machine tool are recorded by means of an acceleration sensor and if the vibrations exceed a threshold value, contact of the tool with the actual outer contour of the workpiece is assumed, or
[0015] - that a force acting on the tool is detected by means of a force sensor and if the force is exceeded by a threshold value, contact of the tool with the actual outer contour of the workpiece is assumed, or
[0016] - that by measuring the motor current of a drive motor of the work spindle or a drive motor of an axis adjustment spindle, a force acting on the tool is detected and, if the motor current is exceeded by a threshold value, contact of the tool with the actual outer contour of the workpiece is assumed. With this type of query, the detection criterion can be determined as simply and as accurately as possible. Querying the speed of the work spindle is a simple measure that can be carried out using sensors already installed on a modern machine tool. A force sensor can also be installed as standard in a modern machine tool. A device for measuring the motor current of a drive motor of the work spindle can also be installed in the machine tool. A device for measuring the motor current of a drive motor of an axis adjustment spindle can also be installed as standard in the machine tool.Acceleration sensors are also simple and robust sensors that can be installed as standard in a machine tool. By using standard machine tool components to query the detection criterion, the process for machining the workpiece can be kept as simple as possible.
[0017] Furthermore, it can be provided that the threshold value is set when the control commands of the processing unit are generated. This has the advantage that the threshold value can be adapted to the respective processing situation.
[0018] The creation of control commands for the processing unit can be referred to as NC programming. This creation of control commands can be done, for example, by input from a programmer. Alternatively, the control commands can also be generated automatically directly from a CAD model, which can optionally be adapted by a programmer.
[0019] Furthermore, the threshold value can be set taking into account the tool used in the machining process and the tool's machining position. This has the advantage of allowing for precise detection of the actual outer contour of the workpiece.
[0020] The machining position of the tool in the sense of this document is understood as how the tool is brought into engagement with the workpiece.
[0021] A machining position could be, for example, one in which a circumferentially arranged cutting edge engages the workpiece. During machining, the tool can be moved relative to the workpiece in a plane normal to a rotational axis of the tool. Another machining position could be, for example, one in which a front-end cutting edge engages the workpiece. During machining, the tool can be moved longitudinally relative to a rotational axis of the tool.
[0022] In another machining position, it is also conceivable for both a circumferentially arranged cutting edge and a front-end cutting edge to engage the workpiece. This can result in a combined machining operation combining the two machining operations described above.
[0023] Another advantageous embodiment is one in which the threshold value for achieving the detection criterion for different tools and different machining positions of the tool can be determined using a training data set, in particular with the aid of a neural network. This has the advantage that this measure allows the threshold value for achieving the detection criterion to be defined or preset in the training data set in such a way that an exact determination of the actual outer contour of the workpiece can be achieved. In particular, it is conceivable that the neural network is trained using machine learning or deep learning. Furthermore, it is also conceivable that the neural network continuously adapts during operation or is further trained using the real data.In particular, it can be provided that an adaptation of the neural network is achieved by measuring the machined workpiece.
[0024] According to a further development, it is possible to save the various threshold values determined using the training data set in a selection table. This has the advantage that, during NC programming, the known parameters or the machining tool used can be selected from the selection table, and the threshold value for achieving the detection criterion can be determined using the underlying training data set. This allows the definition of the threshold value to be as error-prone as possible. The selection values in the selection table can be, for example, the machining position of the tool, a tool diameter or tool type, a spindle speed, or other values. The selection values can be selected, for example, by input from a programmer.Alternatively, the selection values can be selected automatically, for example if the NC program is created automatically based on a CAD model.
[0025] Furthermore, it may be expedient for automated detection when the tool engages with the actual outer contour of the workpiece to involve an incremental feed of the tool and / or the workpiece, with the detection criterion being queried after each increment. This has the advantage that this measure allows for precise determination of the actual outer contour of the workpiece.
[0026] Furthermore, it can be specified that the infeed of a subsequent increment only occurs once the query of the detection criterion of the previous increment has been completed. This has the advantage that this measure allows for precise detection of the actual outer contour of the workpiece.
[0027] Alternatively, it is also conceivable for a subsequent increment to be delivered even if the calculation of the detection criterion query for the previous increment has not yet been fully completed. This measure can increase the delivery speed. A complete calculation result can be available at a later time, and the control commands can be adjusted once the calculation result is available.
[0028] Furthermore, it can be provided that the infeed dimension of an increment is selected depending on the required manufacturing tolerance of the workpiece. This has the advantage that the infeed speed can be increased by this measure. Thus, the manufacturing time can be reduced by this measure. In particular, it can be provided that the infeed dimension of the increment is selected between 5% and 20% of the manufacturing tolerance of the workpiece.
[0029] According to a special embodiment, it is possible for the deviation between the target outer contour of the workpiece and the actual outer contour of the workpiece to be documented and saved. This has the advantage that the actual outer contour of the workpiece can be clearly documented for a workpiece for quality assurance purposes. According to an advantageous further development, it can be provided that in order to query the detection criterion based on the speed of the work spindle or based on the measurement of the motor current of the drive motor of the work spindle, the motor current of the drive motor of the work spindle is selected such that the set speed of the work spindle can be maintained exactly. This has the advantage that even a slight braking effect on the work spindle leads to a reduction in the speed, whereby the detection criterion can be met.The set speed of the work spindle can be reduced by contact between the tool and the workpiece due to the cutting forces that occur.
[0030] In particular, it can be advantageous if, after the detection criterion has been established, the motor current of the work spindle drive motor is increased so that a predetermined speed of the work spindle can be maintained during the machining operation of the tool. This has the advantage of enabling precise machining of the workpiece.
[0031] Furthermore, it can be provided that as the tool approaches the target outer contour of the workpiece by a tolerance allowance, the feed rate is reduced. This has the advantage of shortening the machining time because the feed rate can be increased. At the same time, this measure can increase the tool's service life. The tolerance allowance can be selected such that, by summing the tolerance limits of the target outer contour to the actual outer contour, it can be ruled out that the tool comes into contact with the workpiece before the feed rate is reduced.
[0032] In particular, it is conceivable, for example, for the tool to be approached to the workpiece at an increased infeed speed until the point of the target outer contour plus tolerance allowance is reached. The infeed speed can then be reduced. In this case, the infeed speed can be reduced directly to the feed rate when machining the workpiece. Alternatively, the infeed speed can be reduced to a reduced infeed speed, and only upon detection of contact between the tool and the workpiece can the infeed speed be further reduced to the feed rate when machining the workpiece. According to the invention, a machine tool is designed which has means suitable for carrying out the steps of the above method and for machining workpieces.
[0033] In particular, it can be provided that the machine tool comprises the following components:
[0034] - a base frame;
[0035] - a work spindle with a tool holder for holding a tool;
[0036] - a workpiece table for holding a workpiece;
[0037] - at least one NC axis with an axis adjustment spindle and a drive motor coupled to the axis adjustment spindle for moving the workpiece table or the work spindle;
[0038] - a computing unit.
[0039] Furthermore, a tool can be accommodated in the tool holder.
[0040] According to the invention, a computer program product is designed which comprises instructions which cause the machine tool to carry out the method steps according to one of the above features.
[0041] According to the invention, a computer-readable medium is formed on which the above computer program product is stored.
[0042] A computing unit within the meaning of this document can be an electronic data processing device. This could be, for example, a computer or an NC controller.
[0043] For a better understanding of the invention, it is explained in more detail using the following figures.
[0044] They show in a highly simplified, schematic representation:
[0045] Fig. 1 is a schematic representation of an embodiment of a machine tool;
[0046] Fig. 2 is a schematic representation of a tool and a machining intervention of the tool on an actual outer contour in comparison to a desired outer contour of the workpiece.
[0047] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position.
[0048] Fig. 1 shows a schematic representation of an embodiment of a machine tool 1. In the present embodiment of the machine tool 1, it is designed in the form of a milling machine.
[0049] The machine tool 1 can comprise a base frame 2.
[0050] The machine tool 1 may also include a machining head 3, on which a work spindle 4 is mounted. The machining head 3 may be coupled to the base frame 2.
[0051] A tool holder 5 can be formed in the work spindle 4, which serves to hold tools 6, such as milling tools. Furthermore, a workpiece table
[0052] 7 may be provided, on which a workpiece holder 8 for holding workpieces 9 to be machined may be arranged.
[0053] The machine tool 1 can have a first guide 10, which can be designed, for example, as a linear guide, whereby the machining head 3 can be adjusted along a Y-axis. Furthermore, a first drive motor 11 can be provided, which serves to move the machining head 3 along the first guide 10.
[0054] Furthermore, a second guide 12 can be formed, by means of which the machining head 3 can be displaced along a Z-axis. Furthermore, a second drive motor 13 can be provided for displacing the machining head 3 along the second guide 12.
[0055] Furthermore, a third guide 14 can be formed, by means of which the workpiece holder
[0056] 8 is displaceable along an X-axis relative to the machining head 3. Furthermore, a third drive motor 15 can be provided, which serves to displace the workpiece table 7 along the third guide 14. The interaction of the first guide 10 and the first drive motor 11 can also be referred to as an NC axis 16. In particular, it can be provided that the first drive motor 11 is coupled to an axis adjustment spindle 17, which serves to convert the rotary movement of the first drive motor 11 into a linear movement. Analogously, the remaining guides 12, 14 with the remaining drive motors 13, 15 can also be referred to as NC axes 16. The further NC axes 16 can also have axis adjustment spindles 17.
[0057] The first guide 10, the second guide 12 and the third guide 14 can all or partially be designed to linearly displaceably accommodate the machining head 3 or the workpiece holder 8.
[0058] Alternatively, it is also conceivable that the first guide 10, the second guide 12 and the third guide 14 are all or partially designed to rotatably pivot the machining head 3 or the workpiece holder 8.
[0059] In this case, it can be provided that the workpiece holder 8 is movable relative to the machining head 3 by means of the first guide 10, the second guide 12, and the third guide 14. The guides 10, 12, 14 can be designed as linear guides, as shown in Fig. 1. Alternatively, it is also conceivable for all or some of the guides 10, 12, 14 to be designed as rotary guides.
[0060] At this point, it should be noted that Fig. 1 is an exemplary representation of an embodiment of a machine tool 1. The machine tool 1 may have more or fewer NC axes 16 than those shown.
[0061] As can be seen from Fig. 1, it can be provided that the work spindle 4 is coupled to a drive motor 18.
[0062] As further shown in Fig. 1, the work spindle 4 can be coupled to a drive motor 18. The drive motor 18 serves to rotate the work spindle 4 or the tool 6 about a rotation axis 19.
[0063] As can also be seen from Fig. 1, it can be provided that a computing unit 20 is designed which serves to control the movement sequences of the machine tool 1. As can also be seen from Fig. 1, it can be provided that an acceleration sensor 21 is designed on the machine tool 1. The acceleration sensor 21 can serve, for example, to detect vibrations on the machine tool 1. In particular, it can be provided that the acceleration sensor 21 is designed to detect vibrations or to detect movements in different axes or also to detect vibrations and to detect movements about different axes of rotation. In a first embodiment, it can be provided that the different accelerations are detected in a single acceleration sensor 21. In a further embodiment, it can be provided that for each linear movement axis orA separate acceleration sensor is installed on each rotation axis. The individual acceleration sensors can be evaluated together.
[0064] In particular, it can be provided that the acceleration sensor 21 is arranged on the machining head 3. Of course, it is also conceivable that several of the acceleration sensors 21 are distributed at different locations on the machine tool 1.
[0065] As can also be seen from Fig. 1, it can be provided that the machine tool 1 has a force sensor 22. The force sensor 22 can serve to detect an axial force on the work spindle 4. Furthermore, it is also conceivable that the force sensor 22 can serve to detect a radial force on the work spindle 4. In particular, it can be provided that the force sensor 22 can serve as an axial force sensor and as a radial force sensor for detecting a radial force and for detecting an axial force on the work spindle 4. In particular, it can be provided that the force sensor 22 is designed in the form of several sensors which are formed at a first bearing point and at a second bearing point of the work spindle 4. By distributing the force sensors 22 between the first bearing point and the second bearing point of the work spindle 4, not only an axial force on the tool 6 but also a radial force on the tool 6 can be detected.
[0066] Fig. 2 shows a schematic representation of the workpiece 9 and the tool 6 intended for machining the workpiece 9. On the one hand, a desired outer contour 23 of the workpiece 9 and an actual outer contour 24 of the workpiece 9 are shown.
[0067] Furthermore, it is apparent from Fig. 2 that it can be provided that the tool 6, starting from the actual outer contour 24, carries out a machining operation at a machining depth 25 relative to this actual outer contour 24. Due to incorrect positioning when positioning the workpiece 9 on the workpiece holder 8 or due to deviations in the actual outer contour 24 of the workpiece 9 or due to deviations in the actual position of a cutting edge of the tool 6, it can happen that the actual point of engagement or impact point of the tool 6 on the surface of the workpiece 9 does not correspond to the expected point of engagement or impact point of the tool 6 on the surface of the workpiece 9. If the machining is now carried out purely on the basis of the target parameters, without prior measurement of the workpiece 9 ora previous measurement of the tool 6 is carried out, it can happen that the machining depth 25 in relation to the actual outer contour 24 is greater or smaller than desired due to the shifted actual parameters. In order to compensate for this error, it can be provided that the tool 6 and the workpiece 9 are moved towards one another in order to bring the tool 6 into machining engagement with the workpiece 9. A relative movement of the tool 6 to the workpiece 9 can occur through exclusive movement of the tool 6, through exclusive movement of the workpiece 9 or through a combined movement of the tool 6 and the workpiece 9. In particular, it can be provided that during this feed movement of the tool 6 and the workpiece 9 towards one another, the position at which the tool 6 contacts the actual outer contour 24 of the workpiece 9 is detected.This makes it possible to detect, independently of the deviations described above, when a cutting edge of the tool 6 actually engages with the actual outer contour 24 of the workpiece 9. In a subsequent process step, the control commands can now be issued in the computing unit 20 for shifting the desired machining depth 25 with regard to actual parameters, in particular to the actual outer contour 24 of the workpiece 9. This allows for adapted machining, with the machining depth 25 of the actual outer contour 24 having an exact depth analogous to the specification of the machining depth 25 relative to the target outer contour 23.
[0068] With the aforementioned method, it is not absolutely necessary for the workpiece 9 to be measured before starting machining or after clamping the workpiece 9 to the workpiece holder 8. Measurement of the tool 6 can also be omitted. The method is particularly advantageous when only parts of the actual outer contour 24 of the workpiece 9 are to be machined and an exact machining depth 25 relative to the unmachined actual outer contour 24 of the workpiece 9 is required.The embodiments show possible embodiments, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments with each other are also possible and this possibility of variation lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.
[0069] The scope of protection is determined by the claims. However, the description and drawings must be used to interpret the claims. Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying these independent inventive solutions can be derived from the description.
[0070] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.
[0071] For the sake of clarity, it should finally be pointed out that, in order to better understand the structure, some elements have been shown out of scale and / or enlarged and / or reduced in size.
[0072] Reference symbol list
[0073] machine tool
[0074] Base frame
[0075] Machining head
[0076] Working spindle
[0077] Tool holder
[0078] Tool
[0079] Workpiece table
[0080] Workpiece holder
[0081] Workpiece first guide first drive motor second guide second drive motor third guide third drive motor
[0082] NC axis
[0083] Axle adjustment spindle
[0084] Drive motor working spindle
[0085] axis of rotation
[0086] Computing unit
[0087] Accelerometer
[0088] force sensor
[0089] Target outer contour
[0090] Actual outer contour
[0091] Machining depth
Claims
Patent claims 1. Computer-implemented method for machining a workpiece (9) on a machine tool (1) with a tool (6) mounted in a work spindle (4), comprising the process steps: - Execution of control commands of a computing unit (20) to move the tool (6) and / or the workpiece (9) and to bring the tool (6) into machining engagement with the workpiece (9), wherein the control commands are configured to machine the workpiece (9) at a machining depth (25) relative to a target outer contour (23) specified on the basis of a CAD model of the workpiece (9); - Automated detection when the tool (6) engages with an actual outer contour (24) of the real workpiece (9), whereby a detection criterion is queried; - Automated adjustment of the control commands in the computing unit (20) to shift the machining depth (25) determined on the basis of the target outer contour (23) of the workpiece (9) with regard to the detected actual outer contour (24) of the workpiece (9).
2. Computer-implemented method according to claim 1, characterized in that the querying of the detection criterion is carried out by the fact that - a rotational speed of the working spindle (4) is detected and when the rotational speed of the working spindle (4) is reduced by a threshold value, contact of the tool (6) with the actual outer contour (24) of the workpiece (9) is assumed, or - that vibrations in the machine tool (1) are detected by means of an acceleration sensor (21) and, if the vibrations exceed a threshold value, contact of the tool (6) with the actual outer contour (24) of the workpiece (9) is assumed, or - that a force sensor (22) detects a force acting on the tool (6) and, if the force is exceeded by a threshold value, contact of the tool (6) with the actual outer contour (24) of the workpiece (9) is assumed, or - that by measuring the motor current of a drive motor (18) of the working spindle (4) or of a drive motor (11, 13, 15) of an axis adjustment spindle (17) a force acting on the tool (6) is detected and if the motor current is exceeded by a threshold value, contact of the tool (6) with the actual outer contour (24) of the workpiece (9) is assumed.
3. Computer-implemented method according to claim 2, characterized in that the threshold value is set when generating the control commands of the computing unit (20).
4. Computer-implemented method according to claim 2 or 3, characterized in that the threshold value is determined taking into account the tool (6) used in the machining and a machining position of the tool (6).
5. Computer-implemented method according to one of claims 2 to 4, characterized in that the threshold for reaching the detection criterion is determined for different tools (6) and different machining positions of the tool (6) by means of a training data set, in particular with the aid of a neural network.
6. Computer-implemented method according to claim 5, characterized in that the different threshold values determined using the training data set are stored in a selection table.
7. Computer-implemented method according to one of the preceding claims, characterized in that, for automated detection, when the tool (6) engages with an actual outer contour (24) of the workpiece (9), an incremental feed of the tool (6) and / or the workpiece (9) is carried out, wherein the detection criterion is queried after each feed.
8. Computer-implemented method according to claim 7, characterized in that a delivery of a subsequent increment only takes place when the query of the detection criterion of the preceding increment has been completed.
9. Computer-implemented method according to claim 7 or 8, characterized in that an increment feed dimension is selected depending on the necessary manufacturing tolerance of the workpiece (9).
10. Computer-implemented method according to one of the preceding claims, characterized in that the deviation between the target outer contour (23) of the workpiece (9) and the actual outer contour (24) of the workpiece (9) is documented and stored.
11. Computer-implemented method according to one of claims 2 to 10, characterized in that, in order to query the detection criterion based on the rotational speed of the working spindle (4) or based on the measurement of the motor current of the drive motor of the working spindle (4), the motor current of the drive motor of the working spindle (4) is selected such that the set rotational speed of the working spindle (4) can just be maintained.
12. Computer-implemented method according to claim 11, characterized in that after the detection criterion has been determined, the motor current of the drive motor of the working spindle (4) is increased so that a predetermined rotational speed of the working spindle (4) can be maintained during the machining operation of the tool (6).
13. Computer-implemented method according to one of the preceding claims, characterized in that the feed rate is reduced when the tool (6) approaches the target outer contour (23) of the workpiece (9) by a tolerance allowance.
14. Machine tool (1) with means suitable for carrying out the steps of the method according to any one of claims 1 to 13 and for machining workpieces (9).
15. Computer program product comprising instructions that cause the machine tool (1) of claim 14 to perform the method steps according to any one of claims 1 to 13.
16. Computer-readable medium on which the computer program product according to claim 15 is stored.