Temperature compensation of machine tools

Abstract

This invention relates to temperature compensation for machine tools. The machine tool includes a base for positioning a workpiece thereon, at least one machining device for machining the workpiece, one or more actuators for moving the machining device relative to the base, and a control unit for controlling the actuators. The control unit includes a data storage unit for storing nominal data providing nominal dimensions of the workpiece at a predefined machining temperature, and at least one temperature sensor configured to determine one or more actual temperature values ​​of the workpiece. The at least one temperature sensor is configured to generate temperature data based on the determined actual temperature values ​​and provide the temperature data to the control unit. The control unit is configured to calculate the actual dimensions of the workpiece based on the nominal dimensions and the provided temperature data, and control the actuators to machine the workpiece according to the calculated actual dimensions. The machine tool includes one or more fixing devices for fixing the position and orientation of the workpiece on the base.

Description

Technical Field

[0001] This invention generally relates to a system for machining or manufacturing workpieces. The system includes, for example, a machine tool embodied as a CNC machine, one or more temperature sensors for determining the temperature of the workpiece, and thermal compensation functionality that allows compensation for deformation caused by the temperature of the machined and measured object and / or prediction of the dimensions of the same object at a predefined temperature. Background Technology

[0002] Various types of machine tools, including CNC (Computerized Numerical Control) machines, can be used to process and manufacture a wide variety of parts. During production, the temperature distribution of the workpiece may be uneven, and this temperature distribution may differ significantly from the temperature distribution of the machine tool and its surrounding environment. Moreover, the temperature distribution changes over time and also depends on the type of fixture. For example, essentially identical workpieces to be machined may have different temperature distributions due to different storage or transportation conditions, or different process influences at the machine tool or during previous machining steps. Furthermore, these temperature distributions often differ from the nominal conditions of the workpiece design. In most cases, the design envisions a uniform temperature distribution with, for example, a "standard temperature" of 20°C.

[0003] Due to temperature variations, deviations from a uniform standard temperature can affect workpiece dimensions, including localized or overall deformation (e.g., expansion). Typically, to eliminate this effect, the workpiece is tempered to a predefined standard temperature. This eliminates localized workpiece expansion caused by temperature variations during machining or manufacturing. However, a drawback of this conventional method is the long waiting time required for the workpiece temperature to equalize with the standard temperature. This settling time is particularly dependent on the initial temperature of the workpiece and its thermal inertia—or the different thermal inertia resulting from the use of different materials in different parts of the workpiece. Since tempering the workpiece can therefore take a considerable amount of time before measurement or machining steps can be performed, it is desirable to reduce this waiting time and thus the total time required to produce the workpiece.

[0004] If the temperature expansion state of the workpiece is known, tempering is not necessary. Then, during production, temperature expansion can be considered and compensated for at various points on the workpiece, i.e., temperature-dependent expansion relative to the standard temperature can be taken into account.

[0005] Some machine tools employ different methods, where the workpiece is clamped to the machine and a temperature sensor is attached to the workpiece at a specified point, or a temperature sensor controlled by the machine tool is used to measure at various points. These sensor values ​​are then used to form an average value for a specific point in time. The main drawback of this method stems from the "uniform view" of the workpiece—especially if the workpiece is composed of more than one material—which rarely matches reality. Furthermore, the effects of localized heat outflow (or inflow) are ignored. Therefore, this form of compensation is only suitable for low-precision applications. A solution is desired that avoids these drawbacks and can be used to produce workpieces with high precision.

[0006] An example of a thermal imaging temperature sensor for determining the temperature of a workpiece is disclosed in EP 546 784 A2.

[0007] CN 108 296 877 A generally discloses the application of the coefficient of thermal expansion in machine tools. The temperature of the workpiece is monitored during machining, and the actual coefficient of thermal expansion is calculated by combining theoretical values ​​and the actual measured workpiece dimensions. However, this method does not include internal or residual stresses in the workpiece caused by its fixation.

[0008] US 9,739,606 B2 discloses a CMM for inspecting numerous workpieces by correcting for temperature variations by measuring the temperature of a master piece. A drawback of this method is that, for it to work, the machining of each workpiece must be identical, and all workpieces must have exactly the same characteristics regarding temperature distribution. Summary of the Invention

[0009] Therefore, one object of the present invention is to provide an improved machine tool and an improved method for machining workpieces having a temperature deviating from a predefined machining temperature.

[0010] Another objective is to provide a machine tool and method for workpieces with non-uniform temperature distribution.

[0011] Another objective is to provide a machine tool and method that allows for the determination of deformation caused by temperature deviations with high precision.

[0012] Another objective is to provide a machine tool and method that allows for the machining of workpieces with high precision—particularly based on determined deformation.

[0013] Another objective is to provide a machine tool and method that allows the coefficient of thermal expansion of the workpiece to be taken into account.

[0014] At least one of these objectives is achieved by a machine tool according to the invention, a method according to the invention, and / or other aspects of the invention.

[0015] A first aspect of the invention relates to a machine tool for machining a workpiece having a temperature deviating from a predefined machining temperature. The machine tool includes:

[0016] - A base on which the workpiece is positioned;

[0017] - At least one processing device for processing the workpiece;

[0018] - One or more actuators for moving the processing device relative to the base;

[0019] - A control unit for controlling the actuator, the control unit including a data storage unit for storing machine parameters of the machine tool and nominal data of the workpiece, the nominal data including nominal dimension data providing the nominal dimensions of the workpiece at the predefined processing temperature; and

[0020] - At least one temperature sensor, the at least one temperature sensor being configured to determine one or more actual temperature values ​​of the workpiece, for example, the actual temperature distribution on at least a portion of the workpiece.

[0021] The at least one temperature sensor of the machine tool is configured to generate temperature data based on a determined actual temperature value and provide the temperature data to the control unit. The control unit of the machine tool is configured to calculate the actual dimensions of the workpiece based on the nominal dimension data and the provided temperature data, and is configured to control the actuator to process the workpiece according to the calculated actual dimensions.

[0022] A machine tool can be represented as a CNC machine. A machining device can be represented as a tool or include one or more tools for machining a workpiece. For example, a tool can include a drill bit, a milling cutter, a cutting tool, etc.

[0023] The machine tool includes one or more fixing devices configured to fix the position and orientation of the workpiece on the base, and the machine parameters include information about the fixing devices. The nominal data includes one or more coefficients of thermal expansion of the workpiece, and the control unit is configured to further calculate the actual dimensions of the workpiece based on the coefficients of thermal expansion of the workpiece and the information about the fixing devices.

[0024] According to one embodiment of the machine tool, the control unit is configured to determine the deformation or internal stress in the workpiece caused by the fixed position and orientation of the workpiece on the base. In this case, the control unit may also be configured to calculate the actual dimensions of the workpiece based on the determined deformation or internal stress.

[0025] According to some embodiments of the machine tool, the control unit is configured to further calculate the actual dimensions of the workpiece based on machine temperature data generated based on one or more determined actual temperature values ​​of one or more components of the machine tool. The one or more components of the machine tool may, for example, include the one or more fixtures or include one or more specific points located at or near the one or more fixtures. In one embodiment, the at least one temperature sensor is configured to determine the one or more actual temperature values ​​of the one or more components of the machine tool to generate the machine temperature data and provide the machine temperature data to the control unit. In another embodiment, the machine tool includes at least one additional temperature sensor, wherein the at least one additional temperature sensor is configured to determine the one or more actual temperature values ​​of the one or more components of the machine tool to generate the machine temperature data and provide the machine temperature data to the control unit.

[0026] According to another embodiment of the machine tool, information about the fixing device includes one or more expansion coefficients of the fixing device, and the control unit is configured to also calculate the actual size of the workpiece based on the expansion coefficients of the fixing device.

[0027] According to another embodiment of the machine tool, calculating the actual dimensions of the workpiece includes:

[0028] - Obtain the coordinates of one or more machining points on the workpiece to be approached and machined by the machining device;

[0029] - In the numerical simulation model of the workpiece, identify one or more adjacent nodes of each of the one or more machining points;

[0030] - Determine the node-based displacement vectors of each adjacent node; and

[0031] - Apply the node-based displacement vector of an adjacent node (e.g., the adjacent node with the shortest distance from the processing point) or an interpolated displacement vector calculated from the node-based displacement vectors of multiple adjacent nodes to each of the one or more processing points to generate temperature correction information for each of the one or more processing points (21) - the temperature correction information includes, for example, temperature-corrected 3D coordinates.

[0032] In one embodiment, controlling the actuator to process the workpiece according to the calculated actual dimensions includes: correcting the 3D coordinates of the one or more processing points.

[0033] In another embodiment, determining the node-based displacement vector includes using numerical temperature simulation to calculate the thermal expansion values ​​for the difference between the predefined temperature and one or more actual temperatures, for example, using Nastran analysis.

[0034] In another embodiment, identifying adjacent nodes of each of the one or more processing points is based on the plurality of actual temperature values ​​of the workpiece, for example, based on the actual temperature distribution over at least a portion of the workpiece.

[0035] According to another embodiment of the machine tool, controlling the actuator to process the workpiece includes: controlling the actuator to move the processing device along a processing path according to the nominal data, the control unit being configured to generate a modified processing path for the processing device based on the calculated actual size of the workpiece, and controlling the actuator to process the workpiece according to the calculated actual size includes: controlling the actuator to move the processing device along the modified processing path.

[0036] According to some embodiments of the machine tool, the at least one temperature sensor is a thermal imaging temperature sensor configured to point towards the object or towards the working volume of the machine tool, and to generate the temperature data in the form of one or more thermal images. In this case, the control unit can be configured to generate the modified machining path based on the thermal images.

[0037] In one embodiment, the thermal imaging temperature sensor is movable relative to the base. In another embodiment, the thermal imaging temperature sensor is configured to continuously determine the actual temperature value and generate multiple sets of temperature data based on the continuously determined actual temperature value, wherein each set of temperature data is referenced to the position of the processing device.

[0038] According to another embodiment of the machine tool, the at least one temperature sensor is configured to continuously determine the actual temperature value and generate multiple sets of temperature data based on the continuously determined actual temperature value, wherein each set of temperature data is provided to a computing device in real time and / or together with a timestamp. For example, each set of temperature data may include one or more thermal images, and each set of temperature data may be provided to the computing device with reference to the position of the processing device.

[0039] According to another embodiment of the machine tool, the at least one temperature sensor is configured to determine the actual temperature value synchronously with the machining of the workpiece, for example, wherein the modified machining path is dynamically generated while the machining device moves along the modified machining path.

[0040] According to some embodiments, the machine tool includes a contact temperature sensor configured to approach and contact a surface point of the workpiece to measure the temperature at each of the surface points and generate a contact temperature value for each of the surface points.

[0041] In one embodiment, the control unit is configured to use the contact temperature value to adjust temperature data from the at least one temperature sensor. In another embodiment, the contact temperature sensor is included in a stylus. In yet another embodiment, the plurality of processing points comprises the plurality of surface points.

[0042] According to another embodiment, the machine tool includes at least one attachable temperature sensor configured to attach to a surface point on the workpiece to measure the temperature at the surface point and generate a contact temperature value for the surface point. In this case, the control unit can be configured to adjust temperature data from at least one temperature sensor using the contact temperature value. For example, the attachable temperature sensor can be connected to the control unit via a cable or a wireless data connection.

[0043] According to one embodiment, the at least one temperature sensor is configured to determine one or more actual temperature values ​​of the workpiece by means of infrared measurement, for example, if the at least one temperature sensor is a thermal imaging temperature sensor. The contact temperature values ​​of the surface points can then be used to calibrate or correct the one or more actual temperature values ​​of the workpiece measured by the at least one temperature sensor.

[0044] In one embodiment, the surface points are defined for determining the emissivity of the relevant surfaces, wherein defining the surface points includes: detecting reflective surfaces on the workpiece using the nominal size data, the material information of the workpiece, and / or temperature data from the one or more thermal imaging temperature sensors.

[0045] In another embodiment, the at least one temperature sensor is configured to move relative to the workpiece while determining one or more actual temperature values ​​of the same surface of the workpiece by means of infrared measurement, and the computing device is configured to determine the emissivity and / or reflectivity of the surface and use the contact temperature values ​​based on the determined emissivity and / or reflectivity to correct one or more actual temperature values ​​on the surface.

[0046] A second aspect of the invention relates to a computer-implemented method for machining a workpiece using a machine tool (e.g., a machine tool according to the first aspect of the invention), the workpiece having a temperature deviating from a predefined machining temperature. The method includes the following steps:

[0047] - Obtain the nominal data of the workpiece, the nominal data including nominal dimension data that provides the nominal dimensions of the workpiece at the predefined processing temperature;

[0048] - Determine one or more actual temperature values ​​of the workpiece, for example, the actual temperature distribution over at least a portion of the workpiece;

[0049] - Calculate the actual dimensions of the workpiece based on the nominal dimension data and the provided temperature data; and

[0050] - The workpiece is machined according to the calculated actual dimensions.

[0051] The position and orientation of the workpiece are fixed on the base of the machine tool by means of one or more fixing devices. The nominal data includes one or more coefficients of thermal expansion of the workpiece, and the actual size of the workpiece is calculated based on the coefficients of thermal expansion of the workpiece and information about the fixing devices.

[0052] According to one embodiment, the method further includes: determining deformation or internal stress in the workpiece caused by the fixed position and orientation of the workpiece on the base, wherein the actual dimensions of the workpiece are calculated based on the determined deformation and / or internal stress.

[0053] According to another embodiment of the method, information about the fixing device includes one or more expansion coefficients of the fixing device, and the actual size of the workpiece is also calculated based on the expansion coefficients of the fixing device.

[0054] According to another embodiment of the method, the step of calculating the actual dimensions of the workpiece includes:

[0055] - Obtain the coordinates of one or more machining points on the workpiece to be approached and machined by the machining device of the machine tool;

[0056] - In the numerical simulation model of the workpiece, identify one or more adjacent nodes of each of the one or more machining points;

[0057] - Determine the node-based displacement vectors of each adjacent node; and

[0058] - Apply the node-based displacement vector of a neighboring node (e.g., the neighboring node with the shortest distance from the processing point) or an interpolated displacement vector calculated from the node-based displacement vectors of multiple neighboring nodes to each of the one or more processing points to generate temperature correction information for each of the one or more processing points—the temperature correction information including, for example, temperature-corrected 3D coordinates.

[0059] In one embodiment, the step of calculating the actual dimensions of the workpiece includes: correcting the 3D coordinates of the one or more machining points;

[0060] In another embodiment, the step of determining the node-based displacement vector includes: using numerical temperature simulation to calculate the thermal expansion values ​​for the difference between the predefined temperature and one or more actual temperatures, for example, using Nastran analysis.

[0061] In one embodiment, the neighboring nodes of each of the one or more processing points are identified based on the plurality of actual temperature values ​​of the workpiece, for example, based on the actual temperature distribution over at least a portion of the workpiece.

[0062] The third aspect of the invention relates to a computer program product comprising program code stored on a machine-readable medium, or the computer program product being embodied by an electromagnetic wave including program code segments, and having computer-executable instructions for performing a method according to a second aspect of the invention, particularly when executed on a control unit of a machine tool according to a first aspect. Attached Figure Description

[0063] The invention will now be described in detail with reference to exemplary embodiments accompanied by the accompanying drawings, in which:

[0064] Figure 1a An exemplary workpiece machined by a tool is shown, which has a uniform temperature at a predefined temperature.

[0065] Figure 1b This shows temperatures that deviate from a predefined temperature and the deformation caused by the deviation. Figure 2 The workpiece;

[0066] Figure 2 This illustrates two thermal imaging temperature sensors measuring the temperature of a workpiece while it is being machined.

[0067] Figure 3 It shows the fixed to the machine. Figure 2 Two thermal imaging temperature sensors are used to measure the temperature of the workpiece.

[0068] Figure 4 It shows Figure 3 Exemplary thermal images of the workpiece;

[0069] Figure 5 The nominal dimensions of the workpiece are shown;

[0070] Figure 6a and Figure 6bThe workpiece is shown to be composed of different materials, each with a different coefficient of thermal expansion;

[0071] Figure 7 A flowchart illustrating a method known in the art is shown; and

[0072] Figure 8 A flowchart illustrating an exemplary embodiment of the method according to the present invention is shown. Detailed Implementation

[0073] Figure 1a and Figure 1b The workpiece 2 is shown to be fixed to the base of the machine by means of three fixing devices 19 and processed by means of the machine's tools attached to the working part 17 of the machine.

[0074] The working part 17 is movable relative to the workpiece 2 to approach tooling points on the workpiece 2, where machining operations will be performed using the tool 18. In the example shown, the tool is a drill bit used to drill two holes into the workpiece 2 at locations 22, 23 predefined by nominal data of the workpiece. The claimed invention can be used in conjunction with any machining machine and tooling method (e.g., CNC machines and methods) that utilize the nominal 3D coordinates of an object.

[0075] This fixing device improves machining accuracy and is advantageous in situations requiring high-precision production. However, depending on the type and material of the fixing device, these can significantly affect the temperature development of workpiece 2, particularly the temperature development of the section or component to which the workpiece is fixed.

[0076] exist Figure 1a In this process, workpiece 2 is measured at a first temperature 51, which is a "standard temperature" predefined by the workpiece's nominal data, at which workpiece 2 has defined nominal dimensions. The standard temperature can be room temperature, for example, defined as 20°C. When workpiece 2 is processed at this standard temperature 51, the nominal dimensions of workpiece 2 can be directly used to guide tool 18 to the coordinates of positions 22, 23 so that holes can be drilled into the workpiece at these coordinates.

[0077] exist Figure 1b In this context, the same workpiece 2 is processed by the same machine, but this workpiece 2 has a second temperature 52 (e.g., a second non-uniform temperature field) that deviates from the defined "standard temperature" 51. For example, workpiece 2 from previous processing steps is still hot. Due to the different coefficients of thermal expansion of the workpiece materials, the dimensions of workpiece 2 may be significantly different from the dimensions of the same workpiece at standard temperature 51. Moreover, the temperature distribution may be irregular and inconsistent, as some parts may cool faster than others. It should be noted that, for clarity, the temperature distribution is depicted in an exaggerated manner. Figure 2The deformation of workpiece 2 is shown. Due to these deformations, the actual positions 22”, 23” on workpiece 2 deviate from their predefined coordinates 22', 23'. Therefore, the 3D coordinates of the nominal data cannot be directly used to perform operations... Figure 1a The same processing steps are used because once workpiece 2 cools down, the resulting drill hole will be in the wrong position.

[0078] exist Figure 2 In the middle, two temperature sensors 5A and 5B are located on workpiece 2. Figure 1a and Figure 1b The temperature of workpiece 2 is measured simultaneously during machine processing. The temperature and its distribution on workpiece 2 are continuously and simultaneously measured at multiple points on the workpiece.

[0079] Alternatively, the machine may include a temperature sensor disposed on a movable component (leg 12) of the machine and thus movable relative to the base and the workpiece 2 positioned thereon.

[0080] Temperature sensors 5A and 5B are implemented as thermal imaging temperature sensors, for example, configured as thermal imagers to create thermal images using infrared (IR) radiation. For example, temperature sensors 5A and 5B may be sensitive to wavelengths from about 1 μm to about 14 μm.

[0081] Using computer-aided engineering (CAE) (e.g., finite element method (FEM)), a virtual mesh is created for the known workpiece 2, and a virtual model, such as an FEM model, is generated. This model contains all relevant physical information, such as temperature distribution (whether uniform or discontinuous), material information (coefficient of thermal expansion, mass), and other information about loads, such as through clamps or other fixing devices. Users can additionally define relevant material parameters, such as the coefficient of thermal expansion of the workpiece. Alternatively, information about the materials in workpiece 2 and their 3D distribution can be provided along with the workpiece's CAD data (or other 3D model data).

[0082] The manner in which the workpiece is fixed to the machine, as well as the temperature conditions (e.g., coefficient of thermal expansion) of the fixture 19 and the base for fixing the workpiece, can also be known. The fixture 19 and its heat dissipation or heat addition are defined and determined accordingly. The type and location of the fixture 19 can be determined automatically or provided as user input. The machine base and other related parts can also be modeled. The initial temperature distribution of the workpiece and, optionally, the initial temperature distribution of the base can be defined in the virtual model.

[0083] The deformation state of workpiece 2 due to non-uniform temperature distribution is determined by transferring the temperature distribution at the measurement points to a virtual model. The temperature distribution on workpiece 2 is then determined through appropriate spatial interpolation at all nodes of the model. Subsequently, the deformation state can be determined using an FEM model and a corresponding solver (e.g., Nastran). The average temperature of the coordinate measuring device or its surrounding environment can be used as a reference temperature. Alternatively, the reference temperature can be a standard temperature defined in the nominal data according to the standards or specifications of the workpiece or manufacturing process.

[0084] Optionally, the initial deformation of the base on which workpiece 2 is positioned can be determined in the same manner. Taking the fasteners 19 into account includes: setting corresponding nodes in the model or connecting them to the base. If the base is part of the model, it is assumed that its deformation state defines the nodes of the fasteners or imprints these nodes onto the workpiece.

[0085] During the machining of workpiece 2, the temperature state of the workpiece (and optionally the base) is continuously recorded at several points. These conditions are transferred to the FEM model. The temperature distribution at each node on workpiece 2 and optionally the base is estimated by spatial interpolation.

[0086] Since the fixing device 19 is taken into account, the change in the initial state (i.e., before or shortly after fixing) is determined. The deformation state due to the initial temperature change and the fixing device 19 is subtracted from the initial deformation state, and then the result is returned to the average machine state or according to standards and specifications.

[0087] This specific and virtual deformation state can then be used to compensate for machining errors. Thus, relevant points on workpiece 2 can be used for machining. Spatial interpolation of the deformation state is performed at these points, and the deformation state is subtracted accordingly before machining. Therefore, the machining of the workpiece is calculated back to the standard temperature.

[0088] If the temperature varies over time, some or all of the measurements can be repeated periodically. Alternatively, similar measurements can be performed at similar locations. This information, along with the temperature values ​​over time and the specific deformation state, allows the simulation to be optimized. Parameters (e.g., details of the modeling of the coefficient of thermal expansion of the fixture) can be adjusted so that the estimated altered deformation state better matches the estimated machining state.

[0089] Ideally, the improved simulation model can now be used to redefine all deformation states (including the initial state) and correct for machining. If this is not possible, the corrected model is used from the corresponding time point. The model can then be continuously improved.

[0090] The more temperature measurement points that exist and can be transferred to the model as input, the closer the estimated deformation will be to reality. To increase the number of temperature measurement points, it is advantageous to use non-contact temperature measurement methods such as thermal imagers. However, this depends on the corresponding workpiece characteristics (i.e., emissivity in the infrared range) and environmental influences (e.g., reflections on the surface of workpiece 2).

[0091] Therefore, non-contact temperature measurement can be inaccurate and negatively impact the quality of deformation conditions. However, non-contact temperature measurement can be improved autonomously by measuring the temperature at certain points on the workpiece using standard contact methods and by performing non-contact temperature measurements at the same or similar locations on the workpiece. In this way, the parameters of the non-contact measurement can be adjusted to take into account the aforementioned influences from the workpiece itself or the environment, resulting in more accurate measurements. For example, the effective emissivity of the workpiece can be determined. The emissivity of a surface depends on its properties and its material. For example, rough surfaces have higher emissivity.

[0092] Workpiece surfaces that are prone to temperature reflection due to their reflective properties and / or their orientation relative to an external heat source can be automatically identified. Contact temperature measurements can then be focused on these surfaces. For example, the metallic surface of workpiece 2 can be detected using nominal 3D data and material information of workpiece 2, and workpiece surfaces oriented at a critical angle relative to an external heat source can be identified using the orientation of workpiece 2 and the known position of the heat source relative to the machine. Emission, absorption, and reflection are interrelated properties of a surface; therefore, the surface's emissivity can be derived from the detected temperature reflection, and vice versa.

[0093] Therefore, the emissivity of a surface can be determined using contact temperature measurement. The determined emissivity can then be used to improve (e.g., correct) infrared temperature measurements, especially when the determined emissivity exceeds a predefined value (typically around 0.6). If this value is small (e.g., <0.6), there is often a risk of measuring the ambient temperature rather than the object's temperature due to temperature reflection from the surrounding environment. In such cases, the surface temperature measured by an infrared sensor can be ignored rather than corrected.

[0094] For example, such temperature reflections can be identified by moving temperature sensors 5A and 5B relative to workpiece 2 and capturing more than one thermal image of the same surface. If the temperature image changes as the thermal image sensors move relative to the surface, it indicates the presence of reflection. Therefore, this relative motion and post-processing steps can be used to detect and filter out reflections, which can also be achieved using AI technology.

[0095] Optional contact temperature measurement can be performed by a special stylus attached to the working part 17 of the machine, for example, by means of a magnet. Alternatively, an attachable temperature sensor can be used.

[0096] Alternatively or additionally, utilizing artificial intelligence (AI) methods can help quickly consider temperature states deviating from a given state. Local temperature assignment can be performed using AI-based thermal image assessment. This can include adjusting local emissivity or eliminating reflections in the image. The obtained local temperature information is then transferred to a finite element model. The AI ​​system can be trained using simulation results (thermal expansion) of discrete temperature distributions that provide the data basis. The AI ​​can then predict simulation results of temperature states deviating from the trained baseline data.

[0097] A complete thermal image of workpiece 2 can be generated using temperature simulation (see...). Figure 3 This yields a temperature-dependent displacement image. Machining points on the workpiece can be mapped precisely or approximately. Finally, the temperature-dependent displacement vector can be used for all machining points on the workpiece.

[0098] For all the machining points measured, the temperature-related displacement vectors are stored in the machine's software and can be automatically taken into account (i.e., compensated) during machining.

[0099] In some implementations, only a thermal imaging temperature sensor may be provided. In this case, some parts of the workpiece 2 cannot be imaged in the thermal image of the thermal imaging temperature sensor. This problem can be overcome by placing one or more mirrors with known shapes, positions, and orientations to capture other hidden parts of the workpiece 2.

[0100] Alternatively or additionally, gaps in the temperature distribution data of the workpiece surface can be filled in a calculated manner. For example, this may include one or more of the following:

[0101] - Use classic interpolation and extrapolation techniques, such as linear, bilinear, or cubic;

[0102] - Use a lookup table, for example, generated from a previously performed full measurement;

[0103] - Use an AI model that allows the generation of a complete image from reduced input;

[0104] - Use a complex FEM model from which the distribution is derived during the optimization step of the model; or

[0105] - Combine AI and FEM models, i.e., use sophisticated FEM simulations to simulate a dataset with a hypothetical temperature distribution and train an AI model that can estimate the complete distribution from an incomplete distribution.

[0106] Non-contact temperature measurement can be improved by measuring the temperature at certain points on a workpiece using standard contact methods, and by performing non-contact temperature measurements at the same or similar locations on the workpiece. For example, workpiece surfaces that readily reflect temperature due to their reflective properties and / or their orientation relative to external heat sources can be equipped with contact temperature sensors. Alternatively, contact temperature measurement can also be performed using a temperature sensor integrated into or located on tool 18.

[0107] Figure 3 It shows the result of Figure 2 An exemplary thermal image 25 of workpiece 2 is captured by one of temperature sensors 5A and 5B, which are implemented as thermal imagers. Each color (pattern) in the thermal image 25 represents a different temperature. In this example, the measured temperature range is from 42°C to 30°C, causing different parts of the workpiece to deform in different ways. The higher the resolution of the thermal image 25, the better the deformation can be calculated.

[0108] Figure 4 The nominal dimensional data 26 of the workpiece is shown, such as computer-aided design (CAD) data. The nominal dimensional data 26 describes the nominal dimensions of the workpiece at standard temperatures, i.e., the nominal dimensions of the workpiece after tempering.

[0109] According to some embodiments of the present invention, the nominal data also includes information about the coefficient of thermal expansion of the workpiece. Figure 5 In the example, the workpiece comprises two different materials, each with a known coefficient of thermal expansion provided in the nominal data. Therefore, at least for the possible temperature span, the degree to which the various parts of the workpiece expand at a given temperature is known. This is combined with measured temperatures (e.g., from...) Figure 3 The thermal image 25) can be used to calculate the workpiece relative to (e.g., thermal expansion coefficient) the workpiece. Figure 5 (The nominal dimensions provided in data 26) are variations of its nominal dimensions.

[0110] Figure 6a and Figure 6b An example is shown using finite element temperature simulation to calculate the elongation value for any temperature difference DT between the actual temperature 52 and the predefined standard temperature 51. Other numerical temperature simulations can be used instead of the finite element temperature simulation shown. A machining point 21 on the workpiece is shown; this point is where the machine is expected to perform a tooling action, such as milling a notch into the workpiece surface, and therefore the machine must move the corresponding tool toward the coordinates of machining point 21.

[0111] exist Figure 6aIn the model, workpiece 2 has a standard temperature 51. Machining point 21 reflects the coordinates relative to the standard temperature 51. The FEM model includes multiple FE nodes, with FE node 29 being closest to machining point 21. Preferably, the number of nodes in the FEM model is high enough that the positional difference between FE node 29 and machining point 21 is negligible. Each FE node can be assigned a displacement vector relative to multiple temperatures or temperature differences DT, where the displacement vector relative to zero temperature difference DT (i.e., standard temperature 51) is zero. These displacement vectors can be provided as a lookup table.

[0112] Figure 6b The same workpiece 2 is shown, having the same machining point 21 and the same FE node 29. However, workpiece 2 has an actual temperature 52 (T+DT) that differs from the predefined standard temperature 51. This temperature difference DT generates a displacement vector (d) at FE node 29. x d y d z Under the assumption that the positional difference between FE node 29 and machining point 21 is negligible, the same displacement vector is valid for machining point 21 and can be used to compensate for tool positioning. Under the condition of T+DT (i.e., temperature 52), the displacement vector caused by DT can be subtracted from the nominal value at machining point 21 to obtain machining results applicable to standard temperature 51.

[0113] Figure 7 A flowchart illustrating a prior art method 100' for machining a workpiece is shown. The method begins by tempering the workpiece 101 to bring it to a predetermined "standard temperature," thereby eliminating workpiece deformation due to temperature effects. Tempering the workpiece may include storing it in a tempering chamber (e.g., an air-conditioned room) with exactly the desired standard temperature and waiting until the workpiece reaches ambient temperature.

[0114] After the workpiece has been tempered, it is positioned in a machine—which can also be positioned in the tempering chamber—and the workpiece's nominal data 102 is obtained. The workpiece can then be machined 103 according to the nominal data.

[0115] The drawback of this conventional method is the long waiting time until the temperature in the workpiece equals the standard temperature. This settling time is particularly dependent on the initial temperature in the workpiece and its thermal inertia. Since tempering the workpiece can thus take a long time before it can be further processed, it is desirable to reduce the waiting time.

[0116] Figure 8A flowchart illustrating an exemplary embodiment of a computer-implemented method 100 according to the invention is shown, wherein the step of tempering the workpiece is not required. Instead, in a first step of the method, nominal data 110 of the workpiece is obtained, including the coordinates of the workpiece and the coordinates of the tooling positions—that is, those positions where the machine's tool should perform tooling actions on the workpiece. Since the object may deform, these coordinates cannot be used directly. Therefore, multiple temperatures 120 of the untempered object are measured by means of one or more thermal imaging temperature sensors. Preferably, these temperature measurements 120 include continuous monitoring of the temperature distribution on the surface of the workpiece.

[0117] Based on the known coefficient of thermal expansion of the workpiece (e.g., provided with nominal data) and the measured temperature of 120, the deformation of the untempered workpiece at 130 can be determined, that is, the deformation relative to the shape that the same workpiece would have if it had been tempered.

[0118] Based on the obtained 3D coordinates and the determined deformation (or alternatively, directly based on measured temperature and coefficient of thermal expansion), the 3D coordinates of the tooling position are adjusted 140. The workpiece can then be machined 150 according to the design using the adjusted coordinates. Therefore, steps 130 and 140 may include calculating the actual dimensions of the workpiece that can be calculated.

[0119] Steps 130 and 140 can be executed by an algorithm that uses at least the initial measured temperature of the object and the expansion coefficient distribution in the measured object as input, wherein the expansion coefficient distribution can be obtained from information on the material distribution in the measured object and the properties of these materials (including the expansion coefficient).

[0120] In one implementation, computer-aided engineering (CAE), such as the finite element method (FEM), is used to virtually mesh the known workpiece, where the user additionally defines relevant material parameters, such as the workpiece's coefficient of thermal expansion. The fixture and its heat dissipation or heat addition are defined and determined accordingly. The machine base and other relevant parts can also be modeled. The initial temperature state of the workpiece is defined—optionally, the initial temperature state of the base can also be defined.

[0121] Optionally, calculating the actual dimensions of the workpiece may include obtaining the coordinates of machining points on the workpiece (i.e., points on the workpiece that will be approached by a machine tool to machine the workpiece), identifying one or more adjacent nodes of each machining point in the numerical simulation model of the workpiece, and determining the displacement vector of each adjacent node. Then, to generate temperature correction information for each machining point, the displacement vector is applied to each of these machining points. This displacement vector may be the displacement vector of adjacent nodes (e.g., the adjacent node with the shortest distance to the machining point). Alternatively, the displacement vector may be an interpolated displacement vector calculated from the displacement vectors of multiple adjacent nodes.

[0122] Machining 150 of a workpiece includes controlling the actuators of a machine tool to machine the workpiece according to calculated actual dimensions. Optionally, controlling the actuators may include correcting the 3D coordinates of the machining points.

[0123] Controlling the actuator to machine a workpiece typically involves moving the machine tool's machining apparatus along a machining path based on nominal data. Optionally, in these cases, the control unit can generate a modified machining path for the machining apparatus based on the calculated actual dimensions of the workpiece, such that controlling the actuator to machine the workpiece according to the calculated actual dimensions will involve controlling the actuator to move the machining apparatus along the modified machining path.

[0124] Modifying the machining path can be achieved in several ways. For example, volume compensation for kinematic defects can be adjusted together with temperature compensation, causing the axis to be actuated to move the machining device along the modified machining path. Furthermore, workpiece offset can be adjusted according to the program flow (e.g., in 6DOF). Alternatively, the workpiece's CAD information, used as input variables to obtain the machine tool program flow, can be adjusted accordingly. Moreover, if the relevant features and their parameters are known, the machine's program flow code (e.g., G-code) can be customized accordingly. Alternatively, setpoint modification can be used to adjust the path sequence; this may involve intercepting the setpoint from the controller to the axis and adjusting it based on temperature information or determined deformation.

[0125] Although the invention has been described above with reference to some preferred embodiments, it must be understood that various modifications and combinations of different features of the embodiments are possible. All such modifications are within the scope of the appended claims.

Claims

1. A machine tool for machining a workpiece having a temperature deviating from a predefined machining temperature, the machine tool comprising: - A base on which the workpiece is positioned; - At least one processing device for processing the workpiece; - One or more actuators for moving the processing device relative to the base; - A control unit for controlling the actuator, the control unit including a data storage unit for storing machine parameters of the machine tool and nominal data of the workpiece, the nominal data including nominal dimension data providing the nominal dimensions of the workpiece at the predefined processing temperature; and - At least one temperature sensor, said at least one temperature sensor being configured to determine one or more actual temperature values ​​of the workpiece. in, - The at least one temperature sensor is configured to generate temperature data based on a determined actual temperature value and provide the temperature data to the control unit; - The control unit is configured to calculate the actual dimensions of the workpiece based on the nominal dimension data and the provided temperature data; and The control unit is configured to control the actuator to process the workpiece according to the calculated actual dimensions. Its features are: - The machine tool includes one or more fixing devices configured to fix the position and orientation of the workpiece on the base; - The machine parameters include information about the fixing device; - The nominal data includes one or more coefficients of thermal expansion of the workpiece; and The control unit is configured to also calculate the actual dimensions of the workpiece based on the workpiece's coefficient of thermal expansion and information about the fixing device. The control unit is configured to determine the deformation and / or internal stress in the workpiece caused by the fixed position and orientation of the workpiece on the base, and to calculate the actual size of the workpiece based on the determined deformation and / or internal stress.

2. The machine tool according to claim 1, wherein, The control unit is configured to also calculate the actual dimensions of the workpiece based on machine temperature data, which is generated based on one or more determined actual temperature values ​​of one or more components of the machine tool. - The at least one temperature sensor is configured to determine the one or more actual temperature values ​​of the one or more components of the machine tool to generate the machine temperature data and provide the machine temperature data to the control unit; and / or - The machine tool includes at least one additional temperature sensor, wherein the at least one additional temperature sensor is configured to determine the one or more actual temperature values ​​of the one or more components of the machine tool to generate machine temperature data and provide the machine temperature data to the control unit.

3. The machine tool according to claim 1, wherein, Information about the fixing device includes one or more expansion coefficients of the fixing device, and the control unit is configured to also calculate the actual size of the workpiece based on the expansion coefficients of the fixing device.

4. The machine tool according to claim 1, wherein, Calculating the actual dimensions of the workpiece includes: - Obtain the coordinates of one or more machining points on the workpiece to be approached and machined by the machining device; - In the numerical simulation model of the workpiece, identify one or more adjacent nodes of each of the one or more machining points; - Determine the node-based displacement vectors of each adjacent node; and - Apply to each of the one or more processing points: - A node-based displacement vector of a neighboring node, or - An interpolated displacement vector calculated from the node-based displacement vectors of multiple neighboring nodes. To generate temperature correction information for each of the one or more processing points.

5. The machine tool according to claim 4, wherein, - Controlling the actuator to process the workpiece according to the calculated actual dimensions includes: correcting the three-dimensional coordinates of one or more processing points; - Determining node-based displacement vectors includes: using numerical temperature simulation to calculate the thermal expansion values ​​for the difference between the predefined processing temperature and one or more actual temperatures; and / or - Identifying adjacent nodes of each of the one or more processing points is based on multiple actual temperature values ​​of the workpiece.

6. The machine tool according to claim 1, wherein, - Controlling the actuator to process the workpiece includes: controlling the actuator to move the processing device along a processing path according to the nominal data; - The control unit is configured to generate a modified machining path for the machining device based on the calculated actual dimensions of the workpiece; and Controlling the actuator to process the workpiece according to the calculated actual dimensions includes: controlling the actuator to move the processing device along the modified processing path.

7. The machine tool according to claim 6, wherein, The at least one temperature sensor is a thermal imaging temperature sensor, and the thermal imaging temperature sensor is configured to: - The working volume pointing to the workpiece or the machine tool, and - Generate the temperature data in the form of one or more thermal images. The control unit is configured to generate the modified processing path based on the thermal image.

8. The machine tool according to claim 1, wherein, The at least one temperature sensor is configured to: - Continuously determine the actual temperature values ​​and generate multiple sets of temperature data based on the continuously determined actual temperature values, wherein each set of temperature data is provided to a computing device in real time and / or along with a timestamp; and / or - The actual temperature value is determined synchronously with the processing of the workpiece.

9. The machine tool of claim 8, the machine tool comprising a contact temperature sensor configured to approach and contact a surface point of the workpiece to measure the temperature at each of the surface points and generate a contact temperature value for each of the surface points.

10. The machine tool according to claim 9, wherein, - The at least one temperature sensor is configured to determine the one or more actual temperature values ​​of the workpiece by means of infrared measurement; and - The contact temperature value of the surface point is used to calibrate or correct the one or more actual temperature values ​​of the workpiece measured by the at least one temperature sensor.

11. The machine tool according to claim 1, wherein, The one or more actual temperature values ​​are the actual temperature distribution over at least a portion of the workpiece.

12. The machine tool according to claim 2, wherein, The one or more components of the machine tool include the one or more fixing devices and / or include one or more specific points located at or near the one or more fixing devices.

13. The machine tool according to claim 4, wherein, The adjacent node is the adjacent node with the shortest distance from the processing point.

14. The machine tool according to claim 4, wherein, The temperature correction information includes temperature-corrected three-dimensional coordinates.

15. The machine tool according to claim 5, wherein, Nastran analysis is used to calculate the thermal expansion values ​​for the difference between the predefined processing temperature and one or more actual temperatures.

16. The machine tool according to claim 5, wherein, Identifying adjacent nodes of each of the one or more processing points is based on the actual temperature distribution on at least a portion of the workpiece.

17. The machine tool according to claim 7, wherein, The thermal imaging temperature sensor: - Capable of moving relative to the base; and / or - Configured to continuously determine the actual temperature value and generate multiple sets of temperature data based on the continuously determined actual temperature value, wherein each set of temperature data is referenced to the position of the processing device.

18. The machine tool according to claim 8, wherein, Each set of temperature data includes one or more thermal images, and / or each set of temperature data is provided to the computing device with reference to the location of the processing device.

19. The machine tool according to claim 8, wherein, The modified processing path is dynamically generated as the processing device moves along it.

20. The machine tool according to claim 9, wherein, - The control unit is configured to use the contact temperature value to adjust temperature data from the at least one temperature sensor; - The contact temperature sensor is included in the stylus; and / or - One or more processing points include multiple surface points.

21. The machine tool according to claim 10, wherein, The at least one temperature sensor is a thermal imaging temperature sensor.

22. The machine tool according to claim 10, wherein, - Define the surface points to determine the emissivity of the relevant surfaces, wherein defining the surface points includes: detecting reflective surfaces on the workpiece using the nominal size data, the material information of the workpiece, and / or temperature data from the one or more thermal imaging temperature sensors; and / or - The at least one temperature sensor is configured to move relative to the workpiece while determining one or more actual temperature values ​​of the same surface of the workpiece by means of infrared measurement, and the computing device is configured to determine the emissivity and / or reflectivity of the surface and use the contact temperature value based on the determined emissivity and / or reflectivity to correct one or more actual temperature values ​​on the surface.

23. A computer-implemented method for machining a workpiece using a machine tool, the workpiece having a temperature deviating from a predefined machining temperature, the machine tool being a machine tool according to any one of the preceding claims, the method comprising the following steps: - Obtain the nominal data of the workpiece, the nominal data including nominal dimension data that provides the nominal dimensions of the workpiece at the predefined processing temperature; - Determine one or more actual temperature values ​​for the workpiece; - Calculate the actual dimensions of the workpiece based on the nominal dimension data and the provided temperature data; as well as - The workpiece is machined according to the calculated actual dimensions. Its features are: - The position and orientation of the workpiece are fixed on the base of the machine tool by means of one or more fixing devices; - The nominal data includes one or more coefficients of thermal expansion of the workpiece; and - The actual dimensions of the workpiece are also calculated based on the workpiece's coefficient of thermal expansion and information about the fixing device.

24. The method according to claim 23, wherein, Information about the fixing device includes one or more expansion coefficients of the fixing device, wherein the actual size of the workpiece is calculated based on the expansion coefficients of the fixing device.

25. The method according to claim 23 or claim 24, wherein, The steps for calculating the actual dimensions of the workpiece include: - Obtain the coordinates of one or more machining points on the workpiece to be approached and machined by the machining device of the machine tool; - In the numerical simulation model of the workpiece, identify one or more adjacent nodes of each of the one or more machining points; - Determine the node-based displacement vectors of each adjacent node; and - Apply to each of the one or more processing points: - A node-based displacement vector of a neighboring node, or - An interpolated displacement vector calculated from the node-based displacement vectors of multiple neighboring nodes. To generate temperature correction information for each of the one or more processing points.

26. The method according to claim 23, wherein, The one or more actual temperature values ​​are the actual temperature distribution over at least a portion of the workpiece.

27. The method according to claim 25, wherein, The adjacent node is the adjacent node with the shortest distance from the processing point.

28. The method according to claim 25, wherein, - The temperature correction information includes temperature-corrected three-dimensional coordinates; - The step of calculating the actual dimensions of the workpiece includes: correcting the three-dimensional coordinates of the one or more machining points; - The steps for determining node-based displacement vectors include: using numerical temperature simulation to calculate the thermal expansion values ​​for the difference between the predefined processing temperature and one or more actual temperatures; and / or - Identifying adjacent nodes of each of the one or more processing points is based on the multiple actual temperature values ​​of the workpiece.

29. The method according to claim 28, wherein, Nastran analysis is used to calculate the thermal expansion values ​​for the difference between the predefined processing temperature and one or more actual temperatures.

30. The method according to claim 28, wherein, Identifying adjacent nodes of each of the one or more processing points is based on the actual temperature distribution on at least a portion of the workpiece.

31. A computer program product comprising program code stored on a machine-readable medium, or the computer program product being embodied by an electromagnetic wave including program code segments, and having computer-executable instructions for performing the method according to any one of claims 23 to 30 when executed on a control unit of a machine tool according to any one of claims 1 to 22.

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