Production and measurement of workpieces

Abstract

A method of producing a workpiece is disclosed, wherein the workpiece is successively loaded onto two or more machine tools, and wherein one or more machining operations are performed to produce one or more features of the workpiece on each machine tool. After the machining operations on all of the machine tools, the workpiece is transferred to a common dimension inspection station. At the common dimension inspection station, dimensions of the features of the workpiece produced by the machining operations on the two or more machine tools are measured. Based on the results of measuring the dimensions of the features, two or more output signals are generated, which are respectively related to the performance of the two or more machine tools performing the machining operations. Each of the output signals is fed back to the machine tool performing the corresponding operation to adjust the production process of each corresponding machine tool.

Description

[0001] This application is a divisional application. The original application is a PCT application with application number PCT / GB2018 / 053605, filed on December 12, 2018, which entered the Chinese national phase on June 19, 2020, with national application number 201880082620.0 and invention title "Production and Measurement of Workpieces". Technical Field

[0002] This invention relates to the production and measurement of workpieces or parts, and also to methods and manufacturing systems for such production and measurement. In this specification, the terms "workpiece" and "part" are used interchangeably. Background Technology

[0003] An automated factory manufacturing system may include one or more production machines (such as machine tools) for producing workpieces. Typically, these workpieces may be produced as a series of nominally identical workpieces. The manufacturing system may also include one or more inspection stations for inspecting the produced workpieces. Inspection stations may include routine measurements, such as stationary measuring instruments or even manual measuring instruments (such as height measuring instruments or calipers). Alternatively, the inspection station may include a coordinate measuring machine (CMM) for measuring the workpiece, or a comparative measuring machine for comparing the workpiece to a master reference. These production and inspection machines may each have digital controls or computer controls linked via a network to one or more server computers. See U.S. Patent No. 5,189,624 (Barlow et al.) for an example.

[0004] A portion (or even all) of the workpieces produced on the production machines can be inspected at the inspection station. The server can schedule the workpieces to be transferred to the inspection station and control the transfer robots or conveyors for this purpose.

[0005] In some prior art examples, the inspection result can simply be a pass or a failure decision. In the case of a failure decision (rejection), the inspection result can be fed back to allow adjustments to the production machine, thereby controlling and improving subsequent production processes. In the example of U.S. Patent No. 5,189,624, this control over the production process is performed manually. Alternatively, even in the case of a pass decision, if the size of a single workpiece has exceeded the control limits, it may be possible to provide automatic feedback to adjust the production machine, for example, updating the cutting tool offset by an appropriate percentage of the dimensional error. In this case, the control limits can be set at a level lower than the tolerance limit at which the workpiece will be rejected. Alternatively, the control limits can be set at the level at which the workpiece is rejected.

[0006] It is known to perform more refined analyses on the inspection results of multiple workpieces within a series of nominally identical workpieces. For example, a series of measurements of a specific dimension of consecutive workpieces can be filtered to remove outliers. Alternatively, the series of measurements can be analyzed to detect trends. For instance, if the production machine is a machine tool with cutting tools that have worn or suffered thermal drift during use, there may be a gradual trend in the characteristic dimensions of the produced workpieces, increasing or decreasing over time. This analysis can be performed in a quality control room or laboratory after the workpieces have been inspected and separated from the production machine. Subsequently, manual corrections can be applied to the production process by a skilled machine operator, but this will have no beneficial effect on the workpieces already produced during this period.

[0007] U.S. Patent Application Publication No. 2003 / 0040830 (Parikh et al. / Applied Materials) discloses a multi-step semiconductor processing system. Individual features of a workpiece are processed sequentially by independently operating multiple processing tools, each performing a different type of manufacturing operation on the relevant feature. Between or after each manufacturing operation, the workpiece is removed and placed in metrology stations (multiple stations) where it is measured to identify whether the workpiece's features are within certain parameters. A metrology data analyzer can use the collected data to feed forward or feedback control signals to adjust the processing tools.

[0008] U.S. Patent Application Publication No. 2003 / 0040830 (Cameron / Rolls-Royce) discloses a processing unit with multiple processing tools that can perform operations on a workpiece. The unit also includes a measuring device for measuring the workpiece after the operations have been performed.

[0009] U.S. Patent No. 6,571,145 (Matsumiya et al. / Mitutoyo, Japan) discloses a manufacturing system with multiple machine tools. These machine tools process identical parts of workpieces. A measuring device measures the workpiece produced by each machine tool, thereby generating a calibration data file for the relevant machine tool, which contains calibration values ​​for multiple dimensions of the workpiece. This calibration data file is fed back to adjust the machine tool.

[0010] The applicant's unpublished UK patent application GB 1708730.5 describes a manufacturing system with multiple machine tools and multiple inspection stations. Workpieces produced by one of these machine tools can be measured at any of these inspection stations, and the results can be fed back to adjust the relevant machine tools.

[0011] What might be more efficient is to arrange the manufacturing system so that multiple machine tools continuously perform machining operations on a single workpiece, in order to balance the workload between the machine tools and to machine different workpiece features that might not be easily machined using the same setup on a single machine tool. However, measuring these different individual features after each machining operation performed on consecutive machine tools reduces overall efficiency. Summary of the Invention

[0012] This invention provides a method for producing a workpiece, comprising:

[0013] The workpiece is continuously loaded onto two or more machine tools, and one or more machining operations are performed to produce one or more features of the workpiece on each machine tool;

[0014] After all these machining operations on the machine tools, the workpiece is transferred to a common dimensional inspection station;

[0015] At the common dimensional inspection station, the dimensions of the features of the workpiece produced by these machining operations on the two or more machine tools are measured;

[0016] Based on the results of measuring the dimensions of these features, two or more output signals are generated, each of which is related to the performance of the two or more machine tools performing these machining operations; and

[0017] Each of these output signals is fed back to the machine tool that performs the corresponding operation to adjust the production process of each corresponding machine tool.

[0018] At least in a preferred embodiment of the invention, measuring features at a common dimensional inspection station after machining operations on all machine tools improves the overall cost-effectiveness and efficiency of the manufacturing system. Besides demonstrating that the final part has been manufactured within its design specifications (quality assurance), the common inspection station can also improve quality control by providing feedback on output signals relevant to the respective machine tools. This then allows for appropriate corrections to the machining process, even with few or no intermediate inspection stations between machine tools.

[0019] Preferably, the workpiece is one of a plurality of nominally similar workpieces, on which the machining operations are performed consecutively using two or more corresponding machine tools, and each of the workpieces is measured at a common inspection station. The method may include analyzing the results of measuring corresponding features of the workpieces, and generating output signals based on the analysis, which are respectively correlated with the performance of the two or more machine tools and fed back to those machine tools. Analysis of the results may include detecting trends in the measurement results of consecutive workpieces.

[0020] The output signals fed back to the machine tool can update the tool offset values ​​and / or the position of machining features and / or the workpiece coordinate system. This can correct for future workpiece production.

[0021] In a preferred embodiment, the method includes: calculating the second output signal based on a first output signal among the output signals before feeding the second output signal of the output signals back to the corresponding machine tool. The first output signal may be generated by measuring a reference feature of the workpiece, and the machine tool to which the second output signal is fed back may perform an operation relative to this reference feature.

[0022] In the context of this application, machine tools should be understood as a type of production machine, and therefore references to multiple machine tools herein refer to multiple production machines (each of which is a machine tool), rather than to multiple tools (e.g., different types of cutting tools) that can be used in a single production machine.

[0023] The present invention also provides a manufacturing system comprising two or more machine tools, at least one dimensional inspection station, and a server and / or one or more controllers configured to control the machine tools and inspection station to perform any of the methods described above.

[0024] The present invention further provides one or more software programs that, when run on a server and / or one or more controllers of such a manufacturing system, cause the manufacturing system to perform any of the methods described above. The software programs, including computer code, may be recorded on a non-transitory machine-readable medium such as an optical disc or storage device, or stored on a remote server for download. Attached Figure Description

[0025] Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0026] Figure 1 It is a schematic diagram of the manufacturing system layout in the factory, including production machines and inspection machines;

[0027] Figure 2 This is a flowchart of a method according to a preferred embodiment of the present invention;

[0028] Figure 3 An example of a workpiece that can be manufactured using this method is shown;

[0029] Figure 4 Is Figure 3 A schematic diagram illustrating the updating of tool offsets during the manufacturing of a workpiece;

[0030] Figure 5An example of another workpiece that can be manufactured using this method is shown; and

[0031] Figure 6 and Figure 7 It is a graph illustrating possible process control analyses that can be performed in a preferred embodiment of the invention. Detailed Implementation

[0032] Figure 1 The manufacturing setup comprises multiple production stations, each including 10, 12, 14, and 16 computer numerical control (CNC) production machines for producing parts (workpieces). These production machines can utilize any manufacturing technology. These machines can be machine tools such as milling machines, lathes, milling centers, etc., or machines used for grinding, drilling, laser cutting, lapping, honing, polishing, etc. Alternatively, these machines can be coating machines, forging machines, presses, or additive manufacturing machines (3D printing). The exact number of these machines is not important; two or more can exist. Any combination of different types of production machines can exist, or the production machines can all be identical.

[0033] Each production machine is controlled by a corresponding controller 11, 13, 15, 17, which may include a conventional CNC control unit. Optionally, any or all of these controllers may include a separate computer that communicates with the CNC control unit.

[0034] The manufacturing arrangement also includes one or more inspection stations, each comprising an inspection machine, preferably a CNC measuring machine 20, 22, 24, for inspecting parts (workpieces) produced by the production machines. Suitable flexible comparison measuring machines are sold by the applicant, Renishaw plc, under the trademark EQUATOR. As described in our earlier International Patent Application No. WO 2013 / 021157, which is incorporated herein by reference, the measuring machine has a motorized structure with a non-Cartesian geometry. The measuring machine moves probes in three dimensions relative to the production workpiece to compare the production workpiece with a master reference workpiece. Each measuring machine is controlled by a corresponding computer or controller 21, 23, 25, which also acquires the measurement results from the machine. Optionally, the computer or controller may also process the measurement results, for example, to determine whether the workpiece dimensions are within tolerances.

[0035] In addition to these measuring machines, the inspection station may also include other dimensional measuring devices, such as computer-controlled coordinate measuring machines (CMMs) or inspection robots. Alternatively, the inspection station may include measuring fixtures or jigs, wherein measuring machines with LYDTs or other transducers are specifically designed to measure specific dimensions of workpieces. The measurement results from these measuring instruments can be fed automatically or manually to the corresponding computers or controllers 21, 23, 25. There may also be inspection stations that use conventional handheld measuring instruments (such as height measuring instruments or calipers) to manually measure workpieces. Where computer motion control is not required, the computers or controllers 21, 23, 25 may be replaced by one or more terminals of a common server 28 (discussed below). The measurement results are then manually fed to the server via these one or more terminals.

[0036] The manufacturing arrangement further includes a transport system 26 for transferring parts (workpieces) from any of machine tools 10, 12, 14, 16 to any of measuring instruments 20, 22, 24. Here, these parts can be inspected for conformity to specified dimensional tolerances. The transport system may include a computer-controlled robot, carrier, or conveyor, or may simply involve the manual transfer of workpieces or pallets of workpieces. The transport system may be part of a larger transport system that also supplies unworked blanks or castings to the machine tools for machining, and / or removes workpieces after manufacturing or inspection. If necessary, the transport system may return workpieces to the machine tools for rework after inspection.

[0037] A server 28 is also provided. The program or software modules in this server 28 are responsible for scheduling workpiece production and are connected to the CNC controllers of the machine tools and measuring machines via one or more data buses 30. When needed, the server 28 also controls, for example, a transport system 26 for transferring workpieces between the machine tools and the measuring machines. For example, the server 28 may take the form of a programmable logic controller conventionally used to control production units with multiple machine tools, but with different programming as described below.

[0038] Server 28 can provide the necessary CNC part programs to the machine tools and measuring machines as needed to process and inspect each specific design of the parts (workpieces) to be produced. Alternatively, these part programs can be stored in the controllers of the machine tools and measuring machines and selected for use based on instructions received from server 28.

[0039] Typically, server 28 can be scheduled to produce a series of nominally identical parts (workpieces) of a specific design on machine tools 10, 12, 14, and 16. The server can then instruct each of these workpieces to be sent to one of the measuring machines (e.g., measuring machine 20) and can schedule its inspection on that machine. Alternatively, the server can be scheduled to inspect a sample of workpieces at certain intervals (e.g., inspecting every 10th workpiece; or inspecting workpieces after a given time period, such as inspecting one workpiece per hour).

[0040] Inspection of each workpiece at inspection stations 20, 22, and 24 generates multiple dimensional measurements, which are transmitted back to server 28 and stored on bus 30. If these measurements are processed by the computers or controllers 21, 23, and 25 at the inspection stations, for example, to determine whether the workpiece dimensions are within tolerance, the results are also transmitted back to server 28. If server 28, or the computers or controllers 21, 23, and 25 at the inspection stations, determine that a workpiece is out of tolerance, the server can schedule rejection or rework of the workpiece (as appropriate). Alternatively, computers / controllers 21, 23, and 25 can directly instruct the transport system 26 to send the workpiece to a "pass" or "fail" box or pallet.

[0041] The various functions of server 28 can be shared between two or more servers, as described in our unpublished co-pending UK patent application GB 1708730.5. As described in this application, one or more servers may also perform additional process control and quality control functions. Alternatively, in a simpler system, production scheduling, the use of various machines, and the transfer of workpieces between machines can be decided and executed by a human operator.

[0042] Figure 2 The flowchart of a preferred method of the present invention is shown, which produces a series of nominally identical workpieces 90, each of which may, for example, have the following characteristics: Figure 3 The features shown are illustrated.

[0043] In this example, the first machine tool 10 processes a first feature of the workpiece in the form of a shoulder 92. Based on the workpiece's design document, the machine tool 10 can be programmed to position the shoulder 92 at a distance d1 from a first reference plane 96 relative to the rear of the workpiece. The design document can be drawings or design files from a computer-aided design (CAD) system. The reference plane 96 can be defined by the original surface of the workpiece before machining or by the adjacent surface of the fixture to which it is mounted.

[0044] Next, the transport system 26 transfers the workpiece to the second machine tool 12, which is programmed to process another feature of the workpiece, such as two holes 98. The design document may specify that the centerlines of these holes should be spaced apart by a distance d2 from the second reference plane 100 defined by the shoulder 92.

[0045] Figure 3 Examples of additional features are shown, which can be machined by successive machine tools 14 and 16 programmed according to a workpiece design document. Machine tool 14 can machine additional holes 102, which may have a different size than hole 98. The design document may specify the spacing d3 between these holes and hole 98. Machine tool 16 can machine additional features, such as flanges 106 spaced apart on the underside of the workpiece.

[0046] While some of these features can be machined on the same machine tool, it is advantageous to machine them on different machine tools to balance the workload among all available machine tools in the factory. For example, since the different sizes of holes 98 and 102 require different cutters, it may be more efficient to machine them on different machines. Additionally, it may be impossible to produce flange 106 on the underside without changing the way the workpiece is mounted, which can be most efficiently achieved by transferring the workpiece to another machine.

[0047] After all processing is complete, transport system 26 then transfers some or all of the completed workpieces to common measuring machine 20 for inspection as instructed by server 28. The server can be scheduled to inspect all workpieces or only a sample (e.g., one-tenth of the workpieces). The sampling frequency can be pre-programmed or determined by the server according to a programming algorithm. For example, if a significant difference is found in the inspection results, the sampling frequency can be increased; conversely, if no significant difference is found, the sampling frequency can be decreased.

[0048] Measuring machine 20 is programmed to measure each of dimensions d1, d2, d3, and any other dimensions specified in the design documents (such as some or all of the diameters of holes 98, 102, and the width and spacing of flanges 106). Depending on the need for efficient scheduling of machine usage in the factory, one of the other measuring machines 22, 24 may alternatively serve as a common measuring machine for workpieces passed through after all machining processes. That is, one measuring machine 20 collectively measures all desired characteristics of a given workpiece 90, but other workpieces 90 in the same series may be measured on other measuring machines 22 or 24.

[0049] All measured dimensions are transmitted to server 28. The server performs this step if the measured dimensions have not yet been compared with design values ​​from the design document in the computer or controller 21 as discussed above. As an alternative to the pass / fail / rework decision made by the computer / controller 21, server 28 can determine whether the difference between the measured dimensions or coordinate system positions (such as the diameter of one or more holes 98, 102, or the location where a feature was machined) and the design value is greater than the predetermined tolerance specified in the design document. If so, the server schedules rework or rejects (scraps) the workpiece.

[0050] If a discrepancy exists between the measured and design values, server 28 also calculates an offset value and feeds it back to the controller of the machine tool that produced the measured feature, adjusting the machining process for subsequent workpieces. This can update the tool offset table in the machine tool's controller or correct the workpiece coordinate system in the machine tool's controller. This ensures that subsequent workpieces in the series are produced within tolerances. The server can also determine, for example, whether the measured dimension is only close to the design value and does not exceed it by comparing it to the control limits set in the design document. In this case, rejection or rework is not required, but the server again calculates an offset value and feeds it back to the controller of the machine tool that produced the feature. Again, this adjusts the machining process to ensure that subsequent workpieces continue to be produced within tolerances.

[0051] Therefore, for example, such as Figure 4 As shown, when measuring the position (dimension d1) of shoulder 92 relative to datum plane 96, the server can provide offset values ​​if necessary to update the positioning of the relevant cutting tool T1 in machine tool 10 for subsequent workpieces. If the correct design value of dimension d1 is 10mm (e.g., ...), ... Figure 4 As shown in (a), but the measurement results on measuring machine 20 indicate that the dimension is 10.1 mm (as shown in (b)), then the cutter offset of the diameter of cutting tool T1 can be increased by 0.1 mm. Alternatively, if the reference plane 96 defines the origin of the workpiece coordinate system, the position offset of tool T1 in that coordinate system can be reduced by 0.1 mm, or the origin of the workpiece coordinate system itself can be corrected.

[0052] When measuring the position (dimension d2) of the centerline of hole 98 relative to datum plane 100, the server feeds back an offset value if necessary to update the position of the relevant cutting tool T2 in machine tool 12. However, in this case, the server considers any offset already fed back to machine 10 for correcting the position of shoulder 92. The same offset will also affect the position of hole 98 when machining subsequent workpieces.

[0053] Figure 4 This demonstrates a design value of 15mm for dimension d2. Figure 4 In (b), the measurement result of d2 indicates that the dimension is too small, for example, 14.9 mm instead of 15 mm. However, after the offset of tool T1 in machine tool 10 has already been corrected by 0.1 mm, no further adjustment of the offset of tool T2 in machine tool 12 relative to the datum plane 96 or the workpiece coordinate system is required. The update of the tool T1 offset will automatically correct the measurement result of dimension d2 in subsequent workpieces.

[0054] If the measurement results of d2 indicate that the dimension is surface-corrected to 15 mm (as shown in (c)), then updating the offset of tool T1 will result in this dimension being incorrect in subsequent workpieces. Therefore, the position of the centerline of hole 98 should also be adjusted. This can be done by updating the position offset of tool T2 relative to datum plane 96 or the workpiece coordinate system by 0.1 mm in the opposite direction to the update of tool T1.

[0055] If the measurement result of d2 indicates that the dimension is too large, for example, 15.1 mm (as shown in (d)), then additional adjustments are required relative to the datum plane 96 or the workpiece coordinate system. This will take into account the feedback offset of tool T1 and correct for this oversized value. The offset of tool T2 in machine tool 12 will be updated accordingly.

[0056] Similarly, dimension d3 (the position of the centerline of hole 102 relative to the centerline of hole 98) takes into account both the previous dimensions d1 and d2. The relevant offset of machine tool 14 is updated accordingly.

[0057] Server 28 can also feed back tool offset values ​​to the controllers of the relevant machine tools 12, 14, and 16 to correct the diameters of holes 98 and 102 as well as the width and spacing of flanges 106.

[0058] like Figure 3 The workpiece shown is suitable for manufacture using a machining center or milling machine as machine tool 10 to 16. Figure 5 Alternative workpieces are shown, some or all of which can be machined using a turning machine or lathe as machine tool 10 to 16.

[0059] Figure 5 The workpiece has an end face 110, an inner face 112, an outer machined surface 118, and an inner machined surface 120 perpendicular to the centerline 108 of the turning machine or lathe. An annular groove 116 (e.g., to receive an O-ring) is provided in the inner machined surface 120. A flat-bottomed groove 114 is machined in a portion of the periphery of the outer machined surface 118.

[0060] like Figure 2These various features can be machined on different machine tools 10 to 16 to balance the workload between the machine tools. Specifically, the flat bottom groove 114 is most conveniently machined on a milling machine rather than a turning machine or lathe.

[0061] After all machining processes, dimensions d4 to d10 are measured on measuring machine 20, and the offsets are fed back to update the appropriate tool offsets in the corresponding machine tools. This is in accordance with... Figure 3 and Figure 4 The described method corrects the machining of subsequent workpieces.

[0062] The end face 110 can be considered, for example, as a reference surface, and the offset of the tool used to machine the inner face 112 can be updated based on the measured dimension d8.

[0063] Then, with Figure 4 In the same manner described, the offset of the tool used for machining the side of the annular groove 116 is updated based on the measured dimensions d9 and d10, while also taking into account any updates based on dimension d8. Similarly, the offset of the tool used for machining the other side of the groove 114 is updated while taking into account any updates based on the position of one side of the groove (dimensional d11).

[0064] Dimensions d4 and d5 are related to the positions of the inner turning surface 120 and the outer turning surface 118 relative to the centerline 108. The offset of the tool used to produce the bottom surfaces of the grooves 116 and 114 is updated based on dimensions d6 and d7, while also taking into account updates based on dimensions d4 and d5.

[0065] In any of the above examples, server 28 is pre-programmed to feed back the corresponding offset value to which of the machine tools 10 to 16, depending on which machine tool machined the relevant feature. The server is also pre-programmed to specify which measured dimensions and feature measurements should be used when calculating the offset value, and which offsets should be updated on that machine tool depending on the measured dimensions and which cutting tool was used. This is possible because measurements are performed together after machining operations on different machine tools. This is even true in the case where groove 114 is produced not only on a different machine tool than inner surface 120 but also on a machine tool of a different type.

[0066] For example, in manufacturing Figure 3When machining a workpiece, the positional offset related to the measured dimension d2 can be fed back to machine 12, as well as the cutting tool offset related to the measured diameter of one of the holes 98. It is not necessary to feed back the cutting tool offset for the diameter of the other hole 98 unless there is a significant error, such as due to chips or tool breakage. If both holes are machined by the same cutting tool, it can generally be assumed that any necessary corrections will be identical. In fact, it may not even be necessary to measure the other hole 98.

[0067] Alternatively, instead of pre-programming server 28, the program can accept input from the machine operator specifying which offsets should be updated. For example, if the operator has specified which cutting tool should be used for a particular machining operation on the machine, he / she can also specify that the corresponding offset value should be applied to that cutting tool.

[0068] In addition to feedback based on measurements of individual workpieces, server 28 also has a software module programmed to perform process control. As successive workpieces are inspected, this software module examines trends in the inspection measurements from these consecutive workpieces. For example, as successive workpieces are produced, a trend of gradual increase in the size of a particular dimension can be identified. This could be caused by wear of associated cutting tools in the relevant machine tools 10 to 16, or by gradual thermal growth of the machine tool or the raw material inventory, billets, or castings from which the workpieces are machined. Server 28 can then feed back the updated offset values ​​for the corresponding cutting tools to the CNC controller of the machine tool via bus 30. This corrects the machining process to ensure that future workpieces in the series remain within tolerances.

[0069] Of course, if it is more convenient, this process control can be performed on a different server that communicates with server 28.

[0070] To determine a trend in the measurement results, all parts (workpieces) can be delivered to the same measuring machine 20 in the same order produced by machine tools 10 to 16. However, to improve the overall production flexibility in the factory, all parts (workpieces) can be delivered to different measuring machines 20 to 24. In this case, the parts can be labeled according to their production order to help determine any trends, for example, by sorting the measurement results according to the production order performed by machine tools 10 to 16. This can be described as in our co-pending UK patent application number GB 1708730.5. The process control module can maintain a historical record of the inspection results of all parts processed within the desired time period.

[0071] A suitable form of process control is to sequentially analyze the results from successive parts in a series to generate an ordered history of the performance of the relevant cutting tools or tool turrets for the machining features of production machines 10 to 16. This is accomplished according to preset rules that depend on the manufacturing process and the tolerance requirements of the relevant parts. Suitable rules are known to those skilled in the art. Figure 6 The diagram illustrates some possible rules.

[0072] exist Figure 6 In the diagram, the dashed line T represents the maximum tolerance limit for the measured dimensions or coordinate points. Continuous measurements show a trend toward increasing tolerance limit T. This could be a trend in the overall performance of the machine tool 10 or other production machinery, for example, due to thermal drift, or a trend in the performance of the machine tool's tool-holding turret. Alternatively, there could be a trend caused by gradual wear, which affects the performance of the individual cutting tools used to machine the parts. The dashed line L represents a predetermined lower control limit, which is selected to allow for correction of the production process before exceeding the tolerance limit, thereby enabling uninterrupted production of parts within the tolerance.

[0073] One possible preset rule could be to simply assess whether the measured dimensions or point coordinates have exceeded the control limit L. Figure 6 In the example, the fifth measurement result has exceeded the control limit. A more refined rule could be to statistically analyze the continuous measurement results, for example, using least squares analysis. This could examine the results to obtain a trend as indicated by line 78. Depending on appropriately chosen criteria (such as detecting when the slope of line 78 exceeds a predetermined value), a rule might be triggered when such a trend is detected. Alternatively, another possibility is that the rule could assess whether and when a trend will exceed the control limit L. Figure 6 In the example, the sixth measurement result exceeds the control limits, but this could be predicted from earlier measurements. Other possible rules could detect a downward trend in measurements before reaching the minimum tolerance level, or detect whether a downward trend (or a single measurement result) will exceed a predetermined control limit in the negative direction and when it will exceed it. Other possible rules could filter a series of measurements to smooth the results or remove outliers that do not contribute to the overall trend. This could be done before determining whether the filtered series of measurements exceeds the control limits or before the filtered series of measurements exhibits a trend.

[0074] If a rule has been triggered, corrective action is required. For example, server 28 can generate control signals or values, such as calculating a new tool offset. This new tool offset could be, for example, a percentage of the error in the measured dimension, arranged to counteract the detected trend in some sense. This offset is fed back to the controller of the corresponding machine tool in machine tools 10 to 16. In this case, the new tool offset adjusts the cutting tools of machine tools 10 to 16, which are responsible for cutting the part features whose dimensions have been analyzed. In this way, server 28 generates control signals or values ​​to adjust the production process of the machine tools to ensure that the machine tools continue to produce good parts within the tolerance limit T.

[0075] Other feedback mechanisms are also possible. For example, if analysis indicates that the tolerance limit T has been suddenly and unexpectedly exceeded (indicating that the cutting tool has been damaged), the corresponding machine tools 10 to 16 can be instructed to replace the cutting tool with a replacement for future production. The server 28 then schedules rejection or rework of the out-of-tolerance workpiece. Alternatively, the process control module may simply generate an alarm or send a message requesting a human operator to take action to investigate the machine tool problem.

[0076] It is also possible to perform statistical analysis to automatically conduct statistical process control on the factory floor in real time, rather than relying on subsequent analysis performed in a quality control room or laboratory. Such statistical process control can determine the process capability of a production machine, or the tools or tool turret of that machine, i.e., the ability to produce parts within predetermined expected tolerances, such as C. pk C p or P pk This is in relation to known process capability indices. This can simply be output as a management report, or it can be used as feedback to adjust the production process, as discussed above. Alternatively, it's possible that the production machine is perfectly capable of producing parts within the required tolerances but deviating from the required nominal dimensional values. In this case, feedback corrections will be made to adjust the production machine, thereby eliminating the offset.

[0077] Figure 6 Measurement result bars 70, 72, and 74 are shown, simply arranged according to the production sequence on machine tools 10 to 16, thus they are evenly spaced. This can be suitable, for example, in cases where tool wear is anticipated and needs to be monitored. Alternatively, trends can be monitored while taking into account the actual recorded production time and the time interval between the production times of each part on machine tools 10 to 16. In this case, the spacing between the measurement result bars will be non-uniform. This can be suitable, for example, in cases where changes caused by gradual temperature drift need to be monitored.

[0078] Figure 7Another example of uneven spacing in the measurement result bars is shown, where gaps 75 exist between the measurement results. One reason for uneven spacing is that the process control module may include initial steps for detecting outliers in the measurement results (such as unconsidered outlier 76). Other reasons for gaps 75 include that the machine tool may have experienced some downtime, or that parts may not be selected for inspection at a fixed frequency. And / or some inspection results may not be available due to one of the inspection stations being busy and some inspection results being delayed. However, the analysis continues, trends can be detected, and other analysis rules can be executed based on the available measurement results. Of course, the gaps could also simply be due to unevenness in the time intervals between the actual recorded production times of the workpiece.

[0079] Will realize, Figures 6 to 7 A set of measurements relating to only one dimension or point among the nominally identical workpiece dimensions or points. In practice, multiple dimensions or coordinate points of multiple features of a workpiece can be measured, resulting in multiple sets of such measurements. Each set of measurements can be evaluated in the same manner and (depending on the case) fed back to the corresponding machine tool controller. However, it may not be necessary to provide feedback based on all sets of measurements. For example, if the variability in the machine tool production process is caused by tool wear, this can be evaluated, and corrective feedback can be provided based on only one set of measurements from the multiple sets that are affected by the corresponding worn tool. If the variability is caused by thermal growth, this can be evaluated, and corrective feedback can be provided based on only one or a few sets of measurements from the multiple sets (corresponding to only one or a few of the nominally identical features being measured).

Claims

1. A method for producing a workpiece, comprising: The workpiece is continuously loaded onto two or more machine tools, which are controlled to perform two or more different corresponding machining operations on the workpiece in turn based on two or more different corresponding production processes to produce two or more different corresponding features of the workpiece; After machining operations that produce two or more features of the workpiece on the two or more machine tools, the workpiece is transferred to a common dimensional inspection station; At the common dimensional inspection station, the dimensions of two or more features of the workpiece produced by the machining operations on the two or more machine tools are measured; Two or more output signals are generated based on the results of measuring the dimensions of the two or more features, and the two or more output signals are respectively related to the performance of the two or more machine tools performing the machining operation; as well as Each of the output signals is fed back to the machine tool that performs the corresponding operation in order to adjust the production process of each corresponding machine tool.

2. The method according to claim 1, comprising: Before feeding the second output signal from the output signals back to the corresponding machine tool, the second output signal is calculated based on the first output signal from the output signals.

3. The method according to claim 2, wherein, The first output signal is generated by measuring a reference feature of the workpiece, and the second output signal is fed back to the machine tool to perform an operation relative to this reference feature.

4. The method according to any one of claims 1 to 3, wherein, The workpiece is one of a plurality of nominally similar workpieces, on each of the workpieces, the machining operation is performed continuously using the two or more corresponding machine tools, and each of the workpieces is measured at a common inspection station. The method includes analyzing the measurement results of corresponding features of the workpieces and generating the output signal based on the analysis, the output signal being correlated with the performance of the two or more machine tools and fed back to the machine tools.

5. The method according to claim 4, wherein, There are two or more dimensional inspection stations, and each workpiece is measured at one of the dimensional inspection stations.

6. The method according to claim 4, wherein, The analysis of the results includes detecting trends in the measurement results for consecutive workpieces.

7. The method according to claim 5, wherein, The analysis of the results includes detecting trends in the measurement results for consecutive workpieces.

8. The method according to any one of claims 1 to 3, wherein, The output signal fed back to the machine tool will update the tool offset value.

9. The method according to claim 8, wherein, The tool offset value to be updated has been pre-programmed to correspond to the cutting tool in the machine tool performing the corresponding operation.

10. The method according to any one of claims 1 to 3, wherein, The output signals fed back to the machine tool will update the position of the machining features and / or the workpiece coordinate system.

11. A manufacturing system comprising two or more machine tools, at least one dimensional inspection station, and a server and / or one or more controllers, the server and / or the one or more controllers being configured to control the machine tools and the inspection station to perform the method according to any one of claims 1 to 10.

12. A non-transitory computer-readable medium having stored software program instructions thereon, which, when executed by a server and / or one or more controllers of the manufacturing system according to claim 11, cause the manufacturing system to perform the method according to any one of claims 1 to 10.

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