Calibration method and method of obtaining workpiece information

Abstract

A method comprising: a) causing a tool mounted on a machine tool to process a workpiece, and at least one sensor configured to measure one or more aspects of the tool and / or the machine tool to collect sensor data during the processing; b) inspecting the portion of the workpiece processed in step a) with a measuring device to obtain measurement data; and c) calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

Description

[0001] The present invention relates to obtaining calibration information for a sensor configured to monitor various aspects of the machine and / or tool during tool processing so that information about a workpiece processed by a tool mounted on a machine tool can be inferred from data obtained by the sensor.

[0002] It is known to embed sensors into the body of a tool, in close proximity to the tool body, tool insert, or cutting edge; for example, to monitor properties / aspects of the tool or cutting process, such as deflection, temperature, load, and / or vibration, while the tool is machining a workpiece. Such tools are referred to in the industry as "smart tools." It is also known to embed sensors into components of a machine tool, such as a spindle, to monitor various aspects of the machine tool during machining operations. The outputs of these sensors can be monitored to assist in tool setup, to assess whether there are problems with the machining operation and to take action (e.g., to stop the machining operation if the sensor output indicates an unfavorable condition), and also to attempt to provide some general prediction of the surface finish of the workpiece.

[0003] The present invention relates to a method for using this data in a novel way, whereby measurement data of a processed portion (e.g., a surface) of a workpiece can be inferred from these sensors. In particular, as described in more detail below, the method can include determining calibration information that, for example, correlates measurement data about the portion of the workpiece processed by the tool (measurement data obtained by inspecting the portion of the workpiece by a measuring device) with sensor data obtained while the tool is processing the portion of the workpiece. This calibration information can then be used to infer measurement data about the processed portion of the workpiece from this sensor data obtained during other (e.g., subsequent) machining steps / operations.

[0004] According to a first aspect of the present invention, a method is provided, comprising: a) causing a tool mounted on a machine tool to process (in other words, "machine") a workpiece, and at least one sensor configured to measure (e.g., monitor) one or more aspects / attributes of the tool and / or the machine tool to collect sensor data during said processing ("machining"); b) a measuring device to inspect the portion of the workpiece processed ("machined") in step a) to obtain measurement data; and c) calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

[0005] A benefit of the present invention is that sensor-to-workpiece data calibration information ("calibration information") can be used to (automatically) infer information (e.g., measurement data) about a portion of a workpiece that is processed (e.g., machined) at a different (e.g., subsequent or earlier) time based on sensor data obtained during such processing / machining. Accordingly, in other words, step c) can be said to be determining "sensor data-to-workpiece data conversion information" (instead of "sensor-to-workpiece data calibration information"). Optionally, the sensor-to-workpiece data calibration information can be simply referred to as "sensor calibration information". This can provide a variety of different advantages. For example, this can significantly reduce production cycle time. For example, instead of directly measuring all relevant aspects of a workpiece processed by a smart tool using a dedicated measurement tool (such as a contact measurement probe), the present invention can use sensor-to-workpiece data calibration information to infer information about the workpiece (e.g., measurement data) with a high degree of confidence based on sensor data obtained by a sensor configured to measure (e.g., monitor) one or more aspects of the tool and / or machine tool during workpiece processing. In other words, inferred information about a workpiece based on sensor data (e.g., measurement data) can be used / output in the same way as actual information (e.g., measurement data) obtained by inspecting the processed portion of the workpiece using a dedicated measurement probe. This can save significant time, particularly when manufacturing a series of nominally identical products. For example, using sensor-to-workpiece data calibration information obtained by measuring only some or even just one workpiece, information about an entire series of nominally identical workpieces can be inferred from sensor data obtained during workpiece processing / machining.

[0006] Furthermore, sensor-to-workpiece data calibration information can be used to infer information about portions of a workpiece that are difficult or impossible to measure directly using specialized measurement equipment. For example, it can be difficult to accurately measure features located toward the far end of a long hole. For example, some holes may be multiple meters deep (e.g., at least 1 meter, such as at least 2 meters, and, for example, at least 3 meters), and the bottom of the hole may be difficult to access. Accordingly, the present invention can be used to infer measurement information about these features based on sensor data obtained during processing of these features.

[0007] In other words, the method may include using the sensor-to-workpiece data calibration information to infer information (e.g., measurement data) about different portions of the workpiece based on sensor data obtained during processing of the different portions of the workpiece (by at least one sensor configured to measure one or more aspects of the tool and / or machine tool). The different portions may be located towards the bottom end of the hole, for example, towards the closed end of the hole. The hole may be at least 2 meters long (or "deep"), for example, at least 3 meters long. The method may include using the sensor-to-workpiece data calibration information to infer information about a portion of the hole, the portion being located at least 1 meter from a first end of the hole (e.g., an open end, or an end where machining of the hole is performed), optionally at least 1.5 meters from the first end of the hole, for example, at least 2 meters or even 3 meters from the first end of the hole.

[0008] The length of the tool (e.g., the distance between i) the point at which the tool is held in the tool holder and ii) the tool insert) can be at least 1 m, such as at least 2 m, such as at least 3 m. The method can include inferring information (e.g., measurement data) about the workpiece (e.g., an identical or nominally identical workpiece) based on sensor-to-workpiece data calibration information and sensor data related to one or more aspects / attributes of the tool and / or machine collected during processing of the workpiece (via at least one sensor configured to measure one or more aspects of the tool and / or machine). As described above, the present invention can be particularly advantageous when the workpiece is processed ("machined") by a long tool, because features formed by the long tool can be difficult for a measurement device to access.

[0009] As will be appreciated, step c) may calculate sensor-to-workpiece data calibration information based on multiple sets of sensor data and measurement data (e.g., from multiple different executions or repetitions of steps a) and b)), which may or may not be obtained from the same workpiece. For example, calibration information may be obtained from sensor data and measurement data obtained from multiple (e.g., identical) machining operations performed on the same workpiece and / or from (e.g., identical) machining operations performed on different workpieces.

[0010] As will be appreciated, the method may include first performing steps a) through c), then performing subsequent processing (machining) of the workpiece, and thereafter inferring information about at least one portion of the subsequent processing of the workpiece using sensor-to-workpiece data calibration information and sensor data related to one or more aspects / attributes of the tool and / or machine collected during the subsequent processing of the workpiece (via at least one sensor configured to measure one or more aspects of the tool and / or machine). Optionally, the method may include performing multiple machining operations on a workpiece (or multiple nominally identical workpieces), then measuring only one machined portion (or only some of the multiple portions) (or, for example, only one of the workpieces), thereby determining calibration information, and then using this calibration information to infer information about other machined portions of the workpiece (or about other workpieces). Accordingly, for example, it is not necessary to determine the calibration information prior to processing / machining the portion from which information inference is to be made.

[0011] The tool, machine, and / or sensor used during processing of the workpiece from which information (e.g., measurement data) is inferred may be the same tool, machine, and / or sensor used during step a). Of course, it can be assumed that, for workpieces processed by nominally identical tools and machines, the same sensor calibration information can be used to infer information (e.g., measurement data) based on sensor data obtained by the nominally identical sensors. As will be understood, nominally identical sensors, tools, and machines may be those having substantially identical specifications (e.g., configured to have the same performance / function and formed from substantially identical components). For example, nominally identical may mean that they are sourced from the same manufacturer and have the same model / part number. Accordingly, for example, if the tool is replaced with a (nominally) identical tool, the need to repeat steps a), b), and c) can be avoided. However, it may be preferred that steps a), b), and c) be repeated even if the tool is replaced with a (nominally) identical tool and / or even if the tool or nominally identical tools are used to machine nominally identical workpieces on different machines. Such repetition of steps a) to c) may help provide the most accurate inferred information (eg, measurement data). Accordingly, the method may include repeating steps a) to c) with the tool or a portion thereof (eg, a tool insert) being replaced.

[0012] Optionally, steps a) to c) may be repeated even if the tool is not changed / replaced. For example, steps a) to c) may be repeated at regular and / or predetermined time intervals. For example, steps a) to c) may be repeated after a predetermined amount of time (e.g., machining time using the tool) and / or after a predetermined number of machining operations have been performed using the tool.

[0013] Optionally, if a significant change in the environmental factor is detected, steps a) to c) are repeated. For example, the method may include repeating steps a) to c) if the temperature change of the operating environment exceeds a predetermined threshold.

[0014] The workpiece of step a) may be one of a series of nominally identical workpieces to be processed (e.g., to form a series of nominally identical articles). Accordingly, for at least one other workpiece in the series, information about it may be inferred based on sensor-to-workpiece data calibration information and sensor data obtained during its processing. For example, the method may further include processing a series of nominally identical workpieces to form a series of nominally identical articles (e.g., nominally identical to the workpiece / articles of step a)). For at least some of the workpieces, information (e.g., measurement data) may be inferred based on sensor-to-workpiece data calibration information and sensor data related to one or more aspects / attributes of the tool and / or machine tool obtained during the processing of the workpiece (by at least one sensor configured to measure one or more aspects of the tool and / or machine tool).

[0015] For example, the method may include: d) processing the same or nominally the same workpiece as in step a). This processing may be performed using the same or nominally the same tool and / or the same or nominally the same machine tool as used in step a). The method may include: e) using sensor-to-workpiece data calibration information to infer information about the workpiece (e.g., measurement data) based on sensor data collected during the processing by (e.g., the same or nominally the same) sensor (configured to measure one or more aspects of the tool and / or machine tool). Step d) may be performed after or before step b) and / or step c).

[0016] As will be understood, a nominally identical workpiece may be a workpiece comprising the same material as the workpiece of step a). A nominally identical workpiece may be a workpiece having substantially the same dimensions as the workpiece of step a). A nominally identical workpiece may be a workpiece formed or to be formed to the same design specifications (e.g., the same computer-aided design (CAD) specifications). For example, a nominally identical workpiece may be a workpiece machined or to be machined according to the same machining instructions as the workpiece of step a).

[0017] The inferred information may include measurement data (e.g., absolute / quantitative). For example, the measurement data may include dimensional measurements, such as pore size. The measurement data may include error measurements. The measurement data may include surface roughness and / or surface waviness measurements.

[0018] Optionally, the inferred information may include information regarding whether a processed portion of a workpiece is acceptable, such as whether it conforms to a predetermined tolerance. For example, rather than determining absolute measurement data regarding surface roughness, the method may include using sensor-to-workpiece data calibration information and sensor data obtained by at least one sensor (configured to measure / monitor one or more aspects / attributes of a tool and / or machine tool) during (e.g., subsequent) machining of the workpiece to make decisions regarding the workpiece and / or subsequent machining operations. For example, the sensor-to-workpiece data calibration information and such sensor data may be used to automatically determine whether a machining process of a workpiece (e.g., a workpiece or a nominally identical workpiece) was performed correctly and / or whether a portion of the workpiece may be out of tolerance. This information may be used as part of an automated feedback control loop, for example, to enable adjustments to the machining of the workpiece in real time and / or to enable adjustments to subsequent machining steps of the same or nominally identical workpiece. This may be based on, for example, a threshold value generated / determined based on the sensor-to-workpiece data calibration information.

[0019] The tool may comprise a fixed tool or a mobile (eg rotating) tool. For example, the tool may be at least one of a boring bar, a milling tool, a grinding tool, a reaming tool, a polishing tool or a drilling tool.

[0020] As will be appreciated, calibration information may include functions, models, lookup tables, and / or data.As explained above, sensor-to-workpiece data calibration information may be referred to as sensor-to-workpiece data conversion information (or simply sensor calibration information).

[0021] Said aspect / property of the tool and / or machine tool may include (in other words, the sensor data may include) at least one of: vibration, deflection, temperature and / or load.

[0022] Accordingly, the at least one sensor may include any sensor configured to measure at least one of vibration, deflection, temperature, and / or load. For example, the at least one sensor may include at least one of the following: an accelerometer, a temperature sensor, and / or a strain gauge (e.g., a force sensor).

[0023] The measured data and / or inferred measured data may include at least one of: a position, a dimension, a surface roughness, a surface waviness of the workpiece.

[0024] Processing the workpiece (in other words "machining") may include at least one of: cutting, drilling, grinding, polishing, turning, reaming and milling.

[0025] The machine tool may include at least one sensor. For example, the tool holder and / or the spindle of the machine tool may include at least one sensor. Advantageously, the tool may include at least one sensor. This may provide more accurate and repeatable sensor data. The tool may include a tool insert (or cutting edge) configured to interact with the workpiece to process the workpiece. The tool may include a tool body for holding the tool insert. Accordingly, the tool insert may be mounted on the machine tool via the tool body. The tool body may include at least one sensor. Preferably, the at least one sensor is positioned toward the end of the tool body close to the tool insert.

[0026] Step b) can be performed by a measuring device installed on a machine tool. Alternatively, step b) can be performed by a measuring device installed on a different positioning device (eg, a coordinate measuring machine (CMM)).

[0027] The measuring device may include a measuring probe. The probe may be configured to measure dimensional properties of a workpiece. For example, the probe may be configured to measure the position (e.g., coordinates) of a specific point in a three-dimensional measurement volume. Optionally, the probe may be configured to measure surface roughness and / or waviness of a surface. The measuring probe may include a contact measuring probe. The probe may include a deflectable stylus. The probe may be configured to determine and output the degree of stylus deflection. Such probes are typically referred to as scanning probes or analog probes. Such probes are distinguished from contact trigger probes, which are configured to provide a "trigger" signal in response to stylus deflection exceeding a specific / threshold amount. As will be understood, the measuring device is separate from the tool. Accordingly, the method may include transferring the tool and the measuring device to and / or from the tool holder (e.g., automatically from a storage rack / carousel). This may be particularly the case if the machine tool has only one tool holder.

[0028] The method may further include using the inferred information (e.g., measurement data) to adjust subsequent processing of the workpiece or subsequent nominally identical workpieces using the inferred information (e.g., measurement data). Such adjustments may include using the inferred information (e.g., measurement data) to automatically adjust subsequent processing of the workpiece or subsequent nominally identical workpieces.

[0029] Step c) may include adjusting previously determined sensor-to-workpiece data calibration information based on the sensor data and the measurement data (e.g., to make it specific to the current workpiece / series of workpieces and / or to compensate for changes in the tool, machine tool, and / or operating environment). For example, such adjustment may include compensating for previously determined sensor-to-workpiece data calibration information. Such previously determined sensor-to-workpiece data calibration information may be general sensor-to-workpiece data calibration information, e.g., general for a tool (and optionally a machine tool, e.g., a tool / machine tool combination), but not specific to a workpiece. Accordingly, step c) may include adjusting / updating the general sensor-to-workpiece data calibration information (based on the sensor data and the measurement data) to determine sensor-to-workpiece data calibration information that is specific / dedicated to a particular workpiece, tool, and machine tool combination. Accordingly, the method may include determining general sensor-to-workpiece data calibration information for a particular tool (and optionally, machine tool) combination, and then performing steps a) to c) to update / adjust the general calibration information.

[0030] Step a) may include causing the tool to process the workpiece in such a manner that the tool experiences different machining properties (e.g., different loads, different amounts of vibration) at different points in space and / or time. Step b) may include inspecting, with a measuring device, the portion(s) of the workpiece that has been subjected to the different machining properties. Accordingly, step c) may include calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data associated with the different machining properties.

[0031] In other words, step a) may include i) causing a tool mounted on a machine tool to process a workpiece according to first machining parameters and collecting sensor data obtained by at least one sensor during the processing according to the first machining parameters, and ii) causing the tool mounted on the machine tool to process the workpiece according to second machining parameters (different from the first machining parameters) and collecting sensor data obtained by at least one sensor during the processing according to the second machining parameters. The first machining parameters and the second machining parameters may be configured differently so that the tool experiences different properties (e.g., different loads, different amounts of vibration) during processing of the workpiece. Step b) may include inspecting (e.g., using at least one measuring device) the portion / surface of the workpiece that has been formed by steps i) and ii). Step c) may include calculating sensor-to-workpiece data calibration information based on the sensor data obtained in steps i) and ii) and the measurement data obtained in step b). As will be understood, step b) may be performed once after both steps i) and ii) have been performed (in which case steps i) and ii) may be performed at different locations on the workpiece). Optionally, step i) and step ii) may be performed on the same portion of the workpiece, wherein step b) is performed after step i) and before step ii) to inspect the portion / surface of the workpiece formed by step i), and then step b) is repeated again after step ii) to inspect the portion / surface of the workpiece formed by step ii).

[0032] The sensor-to-workpiece data calibration information can be workpiece-specific. In other words, the sensor-to-workpiece data calibration information can be determined for the workpiece processed in step a) and for nominally identical workpieces (i.e., workpieces in a series of nominally identical workpieces). Accordingly, different sensor calibration information can be determined for different / non-nominal identical workpieces. The sensor-to-workpiece data calibration information can be determined for (e.g., potentially specific to) a specific tool and machine combination. In particular, the sensor-to-workpiece data calibration information can be determined for (e.g., potentially specific to) a specific workpiece, tool, and machine combination.

[0033] This application describes a method for inferring information about a workpiece processed by a tool mounted on a machine tool apparatus based on sensor data related to one or more aspects / attributes of the machine tool and / or the tool mounted thereon. The method may include (in any suitable order): a) determining sensor calibration information based on: i) actual measurement data of a portion of the workpiece that has been processed by the tool, and ii) sensor data related to one or more attributes of the machine tool and / or the tool mounted thereon, obtained during processing of the portion measured in i) by the tool. The method may further include: b) acquiring sensor data related to one or more attributes of the machine tool and / or the tool mounted thereon, obtained while processing the workpiece by the tool mounted thereon. The method may further include: c) using the sensor calibration information to derive inferred information (e.g., measurement data) about the workpiece based on the sensor data obtained during step b).

[0034] According to another aspect of the present invention, a method of inferring measurement data about a workpiece processed by a tool mounted on a machine tool is provided, the method comprising, in any suitable order: a) acquiring sensor data obtained by at least one sensor, the at least one sensor being configured to measure one or more aspects of the tool and / or the machine tool as the tool processes the workpiece; and b) inferring information about the workpiece based on the sensor data using sensor calibration information configured for a specific tool and workpiece combination.

[0035] As will be appreciated, any of the above methods may be computer-implemented. Accordingly, according to another aspect of the present invention, there is provided a computer program product comprising computer program code that, when executed by a computer, causes the computer to perform any of the above methods. According to another aspect of the present invention, there is provided a computer-readable medium carrying the computer program code as described above.

[0036] According to another aspect of the present invention, a machine tool device is provided, which includes a tool for processing a workpiece, at least one sensor configured to measure one or more aspects of the tool and / or the machine tool during said processing of the workpiece, and a controller configured (for example using computer program code) to cause the machine tool device to perform any of the above-mentioned methods.

[0037] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

[0038] Figure 1 A machine tool apparatus is schematically shown, on which a tool for processing a workpiece is mounted;

[0039] Figure 2 Schematically shows Figure 1A machine tool device, but in which a measuring probe is installed on the machine tool instead of a tool;

[0040] Figure 3 is a flow chart of an example process according to the present invention; and

[0041] Figures 4a to 4c is a graph showing possible calibration models.

[0042] Reference Figure 1 , shows a machine tool apparatus 2 including a machine tool 4, a numerical controller (NC) 6 (e.g., a computer numerical controller or "CNC"), a PC 8, and a transmitter / receiver interface 10. The machine tool 4 includes a tool holder 12 that holds a tool 20 and moves it relative to a workpiece 16 mounted in a spindle 18. The NC 6 controls the rotation of the spindle 18 and the x, y, and z motion of the tool holder 12 within the machine tool's working area using, for example, a motor and an encoder (not shown). The NC 6 can be programmed with machining operations, for example, via the PC 8.

[0043] In the depicted embodiment, the tool 20 is a boring bar and includes a tool body 22 and a tool insert 24 (e.g., a cutting insert configured to interact with (e.g., cut) a workpiece to machine the workpiece. The boring bar 20 (and particularly the tool body 22) includes at least one sensor 26 for measuring / monitoring one or more aspects / properties of the tool during workpiece processing. For example, in this embodiment, the tool body includes an accelerometer (for measuring / monitoring vibration), a temperature sensor, and a strain gauge, collectively illustrated in the figure by box 26. As shown, the sensor 26 is located at an end of the tool body 22 proximate the tool insert 24. In alternative embodiments, one or more sensors for measuring / monitoring one or more aspects / properties of the machine tool during workpiece processing may be provided, for example, in the toolholder 12 and / or the spindle 18 (in addition to or in place of sensors in the tool 20).

[0044] The tool 20 processes the workpiece 16 by moving the tool insert 24 into the workpiece while the workpiece 16 is rotated by the spindle 18. Simultaneously, data can be obtained from at least one sensor 26 in the tool body 22. For example, data related to at least one of the tool's temperature, vibration, load, and deflection can be obtained. This data can be transmitted to an external device, such as the NC 6 and / or PC 8, via a wireless link and the interface unit 10, for example. For example, the at least one sensor 26 can communicate with the interface unit 10 via the Bluetooth wireless technology standard. In the depicted embodiment, data is streamed instantaneously and continuously. However, as will be appreciated, this need not necessarily be the case. For example, data can be transmitted at intervals (regular or irregular) or only upon request, for example. In other exemplary embodiments, data from the at least one sensor 26 can be stored locally in memory in the tool 20 and downloaded to the NC 6 and / or PC 8 at a later time, such as after the tool has been processed, for example, via a wired or wireless link.

[0045] Figure 2 It shows that the measuring probe 30 can replace the tool 20 ( Figure 1 ) is loaded into a tool holder 12 of a machine tool 4. In this embodiment, the probe 30 is a contact probe comprising a body 32 mounted to the tool holder 12, a stylus 34 extending from the body 32, and a stylus tip 36 at the end of the stylus 34 remote from the body 32. In the depicted embodiment, the stylus 34 can be deflected relative to the body 32 (e.g. when the stylus tip 36 contacts a surface), and such deflection can be detected by a sensor in the body 32. In particular, in the depicted embodiment, the probe is a scanning probe (also known in the art as an analog probe) because the probe 30 can sense and report the extent / amount / degree of deflection of the stylus from a rest position (in contrast to a touch trigger probe which only reports when the stylus has been deflected, e.g., by a predetermined threshold amount). Such scanning probes for machine tools are known; for example, there is the SPRINT probe available from Renishaw plc. TM As will be appreciated, other probes and other technologies may be used.

[0046] Accordingly, by bringing the stylus tip 36 into contact with the surface of the workpiece 16, the processed portion of the workpiece can be measured. The stylus deflection data from the probe 30 can be streamed instantaneously and continuously to the NC 6 and / or PC 8 via the interface 10 (e.g., wirelessly). Depending on the tool described above, this can be achieved via a Bluetooth connection. As will be appreciated, other technologies can be used to transmit the stylus deflection data. For example, the data can be transmitted at time intervals (regular or irregular) or only when requested, for example. In other exemplary embodiments, the stylus deflection data can be stored locally in a memory in the probe 30 and downloaded to the NC 6 and / or PC 8 at a later time, for example, via a wired link or a wireless link.

[0047] If desired, the data from the probe 30 can be combined with machine tool position data; for example, data regarding the relative positions of the probe 30 and the workpiece 16. For example, the data from the probe 30 can be combined with toolholder 12 position data obtained from encoders (not shown) that monitor the position of the toolholder 12 in any or all of the x-, y-, and z-axes.

[0048] Accordingly, as will be understood, the measurement data regarding the processed portion of the workpiece may be raw data obtained / output by the probe 30, or may be data obtained by processing the raw data obtained / output by the probe 30 (e.g., by combining it with other data, such as data regarding the position of the tool holder 12).

[0049] As will be appreciated, measurement probes other than scanning stylus deflection probes may be used. For example, a touch trigger measurement probe or a surface finish probe may be used. Alternatively, a non-contact probe may be used. Alternatively, the part need not be measured on the same machine. For example, the part may be removed from the machine tool and measured on a coordinate measuring machine (CMM) or the like.

[0050] Figure 3 An exemplary process 100 according to the present invention is shown.

[0051] The exemplary process 100 begins at step 102, where a workpiece 16 is processed by a tool 20 and data is obtained from at least one sensor 26 of the tool 20 during processing of the workpiece. Figure 3 As schematically shown in FIG, tool sensor data may be stored in memory (e.g., in PC 8) for subsequent use. As will be appreciated, data may be stored elsewhere, such as in NC 6, interface 10, or elsewhere, such as in network storage or cloud storage.

[0052] At step 104, the portion of the workpiece 16 processed by the tool 20 is then measured using the measurement probe 30 to obtain measurement data (eg, dimensional data and / or surface roughness / waviness data) about the portion. Figure 3 As schematically shown in FIG, the measurement data can be stored in a memory for subsequent use.

[0053] At step 106, the tool sensor data and measurement data obtained in steps 102 and 104 are used to determine sensor-to-workpiece data calibration information. This can be accomplished in a variety of different ways. For example, a model can be determined based on one or more test cuts and measurements of the workpiece that models the relationship between i) a specific property of the tool (such as the load on the tool, as measured by a strain gauge, for example) and ii) a dimensional error of the part (e.g., a hole diameter). For example, such a model can be in the form of a function or a lookup table. Figure 4a is a graph showing the model determined based on two different test hole cuts made at two different loads and the diameter errors of the holes formed by these two test cuts. These results are shown plotted on Figure 4a As shown in the figure, a model (e.g., a function) can be determined that fits a straight line through the results of the two test cuts. This model can be (or form the basis for) a calibration model of the workpiece. Accordingly, for subsequent cuts of the workpiece (or a nominally identical workpiece), the error in the hole diameter (and therefore the actual size of the hole) can be inferred based on the load measured during the cutting process.

[0054] In this embodiment, two test cuts are obtained. However, as will be appreciated, more or fewer test cuts may be obtained. For example, if more than two test cuts are obtained, the calibration model may be based on a line (straight or curved) of best fit through the measurements obtained from the different test cuts.

[0055] In alternative embodiments, generic sensor-to-workpiece data calibration information may already be available for the tool (and optionally the machine, e.g., for the tool / machine combination). Figure 4b As shown by the solid line in , a general model of the relationship between load and machining error may have been determined for a tool (and optionally a machine tool, e.g., for a tool / machine tool combination). However, the inventors have found that using such a general model does not necessarily provide accurate measurements for any given workpiece.

[0056] Accordingly, the inventors have discovered that performing one or more test cuts on a workpiece (or on nominally identical workpieces), measuring the cut portion(s), and determining a calibration model / function for that workpiece (and for subsequent workpieces in a series of nominally identical workpieces) can have significant benefits. Accordingly, the sensor-to-workpiece data calibration information can be workpiece-specific. For example, this can include performing only one test cut, based on which a general model is adapted. For example, Figure 4b As shown, it can be determined that for a load "x" measured during machining of the hole, the actual error in the diameter of the hole is e2, not e1 as predicted by the general model. This error difference can be assumed to be constant, and thus Figure 4b As shown by the dashed line in the graph of , the adapted calibration model can be determined by offsetting the generic model by the difference between e2 and e1. As will be appreciated, more than one test cut and its measurement can be performed if desired, which can provide more accurate deviation information.

[0057] Likewise, Figure 4c As shown, the same approach can be applied to properties other than load. For example, a general model of measured vibration and surface roughness (Ra) can be adapted based on actual readings of surface roughness experienced at a specific measured vibration level "y".

[0058] The calibration information (eg, function, model, data, or other suitable information) may then be stored in a memory (eg, in a PC) for subsequent use.

[0059] At some subsequent point in time, the workpiece (or, for example, a nominally identical workpiece) is again processed by the tool (or, for example, a nominally identical tool), as represented by step 108 in process 100. Figure 3 As shown, tool sensor data from at least one sensor 26 of the tool 20 is acquired during workpiece processing and stored in memory (eg, in a PC) for subsequent use.

[0060] At step 110, the calibration information obtained at step 106 and the tool sensor data obtained at step 108 are used to infer measurement data about the portion of the workpiece processed at step 108. For example, in the case of forming a hole, in combination with Figure 4a and Figure 4b , which may include using the model determined at step 106 to look up an inferred diameter error based on the load applied to the tool as measured by the sensor 26 during the machining process at step 108. Alternatively or additionally, in combination Figure 4c, which may include using the model determined at step 106 to determine the surface roughness of the part based on the vibrations measured by the sensor 26 during the machining process, as at step 108. Once determined, the inferred measurement data may be stored in a memory (e.g., in a PC) for subsequent use, such as at step 112. For example, such use of the inferred measurement data may include determining at least one of: whether to accept or reject the workpiece; how to adjust subsequent processing of the workpiece, either in real time or during subsequent machining steps; and / or stopping the process.

[0061] Accordingly, using the techniques of the present invention, measurement data about a processed portion of a workpiece may be determined without actually directly measuring the portion using a measurement tool.

[0062] As will be appreciated, the method may include using the calibration information determined at step 106 to determine process control parameters for controlling subsequent machining steps (of the same or nominally the same workpiece), rather than inferring measurement data of the machined surface. For example, the method may include determining a threshold vibration level above which corrective action should be taken.

[0063] As will be understood, references herein to storing data in a memory device may include storing the data in permanent storage and / or temporary storage, such as random access memory (RAM). Furthermore, the aforementioned storage step may be optional. For example, the inferred measurement data may be transmitted to an external device and / or used immediately (e.g., by the NC 6 for decision making) without being stored in a memory device.

[0064] As will be appreciated, although the NC 6 and PC 8 are shown sharing one interface 10, they may each have their own separate interface 10. Furthermore, such interfaces may be embedded in the NC 6 and / or PC 8, rather than separate, as depicted in the figures.

[0065] In the above embodiment, the measuring probe 30 is mounted in the tool holder 12 instead of the tool 20. However, as will be appreciated, in alternative embodiments, the measuring probe may be mounted on a separate tool holder or other part of the machine tool. In this case, there is no need to replace the tool with the measuring probe.

[0066] In the above-described embodiment, the same parts, the same tools, and the same machines are used in all steps. However, this need not necessarily be the case. For example, the workpiece, tool, and / or machine tool used in steps 102 and 104 may be different (although nominally the same) than the workpiece, tool, and / or machine tool used in step 108. For example, in one embodiment, calibration information may be obtained on different machine tools. For example, steps 102 and 104 may be performed on a different machine tool than step 108. In another exemplary embodiment, steps 102 and 108 may be performed on the same machine tool, but step 104 may be obtained on a different device, for example, a different machine tool or a specialized measuring device such as a coordinate measuring machine (CMM).

[0067] As will be appreciated, in alternative embodiments, tools other than boring bars may be used. For example, the tool may comprise a drill, a grinding wheel, or a milling, reaming or milling tool.

[0068] As will be appreciated, in alternative embodiments, relative motion in any or all of the x, y, and z dimensions may be provided by motion of the spindle 18 in place of motion of the toolholder 12, or by motion of the spindle and the toolholder. In addition, motion may be limited to fewer dimensions, such as only x, and / or y. In addition, the described embodiments include Cartesian machine tools, however, as will be appreciated, this need not necessarily be the case and non-Cartesian machine tools may be examples. In addition, as will be appreciated, although the present invention is shown in conjunction with a lathe, the present invention may be used with many other types of machine tool equipment and machining centers, such as milling machine equipment (for example, in which the tool is held in a spindle that can move). Accordingly, the present invention may be used with embodiments in which the tool rotates while the part remains fixed.

[0069] As will be appreciated, steps 102 and 104 may be repeated, for example, on a different (eg, nominally identical) workpiece, with calibration information being obtained from the workpiece at step 106 .

[0070] In the above-described embodiment, the method includes performing an initial test cut and measurement to determine calibration information before subsequent machining is performed. However, as will be appreciated, this need not necessarily be the case, and machining operations from which information is inferred may have already been performed before calibration information is determined. For example, the method may include performing multiple machining operations on a workpiece (or multiple nominal workpieces), measuring only one (or only some) of the machined portions (or, for example, measuring only one or some of the workpieces) to thereby determine calibration information, and then using the calibration information to infer information about other portions of the workpiece (or other workpieces) that have been machined.

Claims

1. A method comprising: a) causing a tool mounted on a machine tool to process a workpiece for a first time, wherein at least one sensor configured to measure one or more aspects of the tool and / or the machine tool collects sensor data during the processing; b) inspecting the portion of the workpiece processed in step a) with a measuring device to obtain measurement data; c) calculating calibration information from the sensor data and the measurement data, the calibration information then being usable to infer measurement data about the same workpiece or nominally the same workpiece processed at different times from sensor data obtained during processing of the same workpiece or nominally the same workpiece at different times; and d) using the calibration information and sensor data collected during a second, different-than-first, processing of the same workpiece or a nominally identical workpiece to infer measurement data about the same workpiece or the nominally identical workpiece, Wherein, step d) comprises: d1) processing the same workpiece or nominally the same workpiece as processed in step a) using the same tool or nominally the same tool and the same machine tool or nominally the same machine tool as used in step a), and d2) using said calibration information to infer measurement data about the same workpiece or nominally the same workpiece from sensor data collected during step d1) by the same sensor or nominally the same sensor as used in step a). 2 . The method of claim 1 , further comprising using the extrapolated measurement data about the same workpiece or the extrapolated measurement data about the nominally identical workpiece to adjust subsequent processing of the workpiece or a subsequent nominally identical workpiece.

3. A method as claimed in any preceding claim, wherein The sensor data includes at least one of: vibration, deflection and / or load.

4. The method according to claim 1, wherein The measurement data includes at least one of the following: position, size, surface roughness, and surface waviness of the workpiece.

5. The method according to claim 1, wherein The processing of the workpiece includes at least one of the following: cutting, drilling, grinding, polishing, turning, reaming and milling.

6. The method of claim 1, wherein: The tool comprises the at least one sensor.

7. The method according to claim 6, wherein: The tool comprises a tool insert and a tool body, the tool insert being mounted to the machine tool via the tool body, and wherein the tool body comprises the at least one sensor.

8. The method of claim 7, wherein: The at least one sensor is positioned toward an end of the toolholder proximate the tool insert.

9. The method of claim 1, wherein: Step b) is performed by a measuring device installed on the machine tool.

10. The method of claim 1, wherein: The measuring device comprises a measuring probe, such as a contact measuring probe, for measuring dimensional properties of the workpiece.

11. The method of claim 1, wherein: Step c) comprises adjusting previously determined calibration information based on said sensor data and said measurement data.

12. A method of inferring measurement data relating to a workpiece processed by a tool mounted on a machine tool, the method comprising, in any suitable order: a) acquiring sensor data obtained by at least one sensor, the sensor data relating to one or more properties of the tool and / or the machine tool when the workpiece is processed by the tool for the first time; as well as b) inferring measurement data about the workpiece processed for the first time from the sensor data of step a) using calibration information configured for the tool and workpiece and machine tool combination, wherein the calibration information is determined according to: i. sensor data collected using the same or nominally the same sensor as used in step a) during a second, different from the first, processing of the same or nominally the same workpiece as in step a) using the same or nominally the same tool and the same or nominally the same machine tool as used in step a), and ii. Measurement data obtained by a measuring device inspecting the portion of the same or nominally the same workpiece processed in step i.

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