Method of Calibration and Method of Obtaining Workpiece Information

Abstract

A method comprising: a) processing a workpiece with a tool attached to a machine tool, wherein at least one sensor configured to measure one or more aspects of the tool and / or machine tool collects sensor data during processing; b) inspecting a 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

[Technical field]

[0001] The present invention relates to obtaining sensor calibration information so that information about a workpiece being processed by a tool attached to a machine tool can be inferred based on data obtained by sensors configured to monitor the state of the machine and / or the tool during processing by the tool. [Background technology]

[0002] For example, it is known to embed sensors in the body of a tool, in close proximity to the tool body, tool insert, or cutting edge, to monitor tool characteristics / conditions or the cutting process, such as deflection, temperature, load, and / or vibration, while the tool is machining a workpiece. Such tools are known in the industry as "intelligent tools." It is also known to embed sensors in machine tool parts, such as the spindle, to monitor machine tool conditions during machining operations. The output of such sensors may be monitored to assist in setting up the tool, to assess whether there are problems with the machining run and to take action (e.g., stopping the machining run if the sensor output indicates adverse conditions), and also to provide a general prediction of the surface finish of the workpiece. Summary of the Invention

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

[0004] According to a first aspect of the present invention, there is provided a method comprising the steps of: a) causing a tool attached to a machine tool to process (in other words "machine") a workpiece, wherein at least one sensor measuring (e.g. monitoring) one or more aspects / characteristics of the tool and / or machine tool collects sensor data during said process ("machining"); b) inspecting with a measurement device a 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] An advantage of the present invention is that the sensor-to-workpiece data calibration information ("calibration information") can be used to (automatically) infer information (e.g. measurement data) about a part of a workpiece being processed (e.g. machined) at a different (e.g. subsequent or earlier) time than the sensor data acquired during such processing / machining. As a result, in other words, step c) can be said to be a step of defining "sensor data to workpiece data conversion information" (instead of "sensor-to-workpiece calibration information"). Optionally, the sensor-to-workpiece data calibration information can be simply referred to as "sensor calibration information". This can result in a variety of different advantages. For example, production cycle times can be significantly reduced. Instead of directly measuring all relevant aspects of the workpiece processed by the intelligent tool using a dedicated measuring tool, such as a contact measuring probe, the present invention allows for reliable inference of information (e.g., measurement data) about the workpiece based on sensor data acquired by a sensor configured to measure (e.g., monitor) one or more aspects of the tool and / or machine during processing of the workpiece using sensor-to-workpiece data calibration information. That is, the workpiece-related information (e.g., measurement data) estimated based on the sensor data can be used / output as if it were actual information (e.g., measurement data) obtained by inspecting a portion of the processed workpiece with a dedicated measuring probe. This allows for significant time savings, especially when producing a series of nominally identical workpieces. For example, information about a large number of nominally identical workpieces can be inferred based on sensor data acquired during processing / machining by using sensor-to-workpiece data calibration information acquired by measuring only a portion or one workpiece.

[0006] Furthermore, the sensor-to-workpiece data calibration information can be used to infer information about portions of the workpiece that are difficult or impossible to measure directly using a dedicated measurement device. For example, it may be difficult to accurately directly measure features located facing the distal end of a long hole. For example, some holes may be several meters deep (e.g., at least one meter (1 m), e.g., at least 2 m, e.g., at least 3 m), and it may be difficult to approach the bottom end of the hole. Thus, by using the present invention, measurement information about such features can be inferred based on sensor data obtained during processing of such features.

[0007] In other words, the method can include using the sensor-to-workpiece data calibration information (e.g., measurement data) to infer information (e.g., measurement data) about a different portion of the workpiece based on sensor data obtained (by at least one sensor configured to measure one or more aspects of the tool and / or machine) during processing of the different portion. The different portion can be located at a bottom end of the hole, e.g., facing a closed end of the hole. The hole can be at least 2 m long (or "deep"), e.g., at least 3 m long. The method can include using the sensor-to-workpiece data calibration information to infer information about a portion of the hole that is at least 1 m from a first end of the hole (e.g., an open end, or an end at which machining of the hole begins), optionally at least 1.5 m from the first end of the hole, e.g., at least 2 m or even 3 m 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 by the tool holder and ii) the tool insert) may be at least 1 m, e.g., at least 2 m, e.g., at least 3 m. The method may include inferring information (e.g., measurement data) about the workpiece (e.g., the same or nominally the same workpiece) based on the sensor-to-workpiece data calibration information and sensor data related to one or more conditions / characteristics of the tool and / or machine tool collected during processing of the workpiece (by at least one sensor configured to measure one or more conditions of the tool and / or machine tool). As discussed above, the present invention may be particularly advantageous when the workpiece is processed ("machined") by a long tool, since features formed by the long tool may be difficult for a measurement device to access.

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

[0010] As is clear, the method may first perform steps a) to c), then perform subsequent processing (machining) on ​​the workpiece, and then use the sensor-to-workpiece data calibration information and the sensor data related to one or more conditions / characteristics of the tool and / or machine tool collected (by at least one sensor configured to measure one or more conditions of the tool and / or machine tool) during the subsequent processing on the workpiece to infer information about at least one portion of the workpiece to be subsequently processed. Optionally, the method may perform multiple machining operations on one workpiece (or multiple nominal workpieces), then measure only one machined portion (or only a few portions) (or for example measure only one of the workpieces), determine calibration information based thereon, and then use the calibration information to infer information about other portions of the workpiece (or other workpieces) already machined. As a result, for example, the calibration information does not necessarily have to be determined before the portion for which the information is to be inferred is processed / machined.

[0011] The tools, machine tools and / or sensors used during processing for the workpieces for which information (e.g., measurement data) is inferred can be the same tools, machine tools and / or sensors used during step a). Of course, it can be assumed that the same sensor-to-workpiece data calibration information can be used to infer information (e.g., measurement data) based on sensor data acquired by the nominally same sensors for workpieces processed by the nominally same tools and machine tools. As is evident, the nominally same sensors, tools and machine tools can be sensors, tools and machine tools having substantially the same specifications, for example, configured to have the same performance / function and formed from substantially the same components. For example, nominally the same can mean that they are from the same manufacturer and have the same model / part number. As a result, for example, if a tool is replaced with a (nominally) the same tool, the need to repeat steps a), b) and c) can be avoided. Nevertheless, it may be preferable to repeat steps a), b) and c) when the tool is replaced with a (nominally) the same tool and / or when the tool or the nominally the same tool is used to machine the nominally the same workpiece on a different machine tool. In such cases, repeating steps a)-c) helps to provide the most accurate estimated information (e.g., measurement data). Accordingly, the method may include repeating steps a)-c) when the tool or a part thereof (e.g., a tool insert) is replaced.

[0012] Optionally, steps a)-c) are repeated even if the tool has not been changed / replaced. For example, steps a)-c) can be repeated periodically and / or at predetermined intervals. For example, steps a)-c) can be repeated after a predetermined time (e.g., machining time with the tool) and / or after a predetermined number of machining operations have been performed with the tool.

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

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

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

[0016] As will be apparent, a nominally identical workpiece may be a workpiece comprising the same material as the workpiece in step a). A nominally identical workpiece may be a workpiece having substantially the same dimensions as the workpiece in step a). A nominally identical workpiece may be a workpiece that is 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 one that has been or is to be machined according to the same machining instructions as the workpiece in step a).

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

[0018] Optionally, the inferred information may include information regarding whether a portion of the processed workpiece is acceptable, e.g., conforms to a predetermined tolerance. For example, the method may include using the sensor-to-workpiece data calibration information and sensor data acquired by at least one sensor (configured to measure / monitor one or more aspects / characteristics of the tool and / or machine tool) during (e.g., subsequent) processing to determine for 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 for a workpiece (e.g., the workpiece or a nominally identical workpiece) whether the machining process is operating correctly and / or whether a portion of the workpiece is out of tolerance. This information may be used as part of an automatic feedback control loop, whereby, for example, adjustments to the machining of the workpiece may be made in real time and / or adjustments to subsequent machining operations of the same or nominally identical workpiece may be made. This may be possible based on thresholds generated / determined from the sensor-to-workpiece data calibration information.

[0019] The tool may include a stationary tool or a moving (e.g., rotating) tool. For example, the tool may be at least one of a boring bar, a milling tool, a grinding tool, a reaming tool, an abrasive tool, or a drilling tool.

[0020] As will be apparent, the calibration information may include functions, models, lookup tables, and / or data. As noted above, the sensor-to-workpiece data calibration information may also be referred to as sensor-to-workpiece data transformation information (or simply sensor calibration information).

[0021] The conditions / characteristics of the tool and / or machine may include at least one of vibration, deflection, temperature, and / or load (i.e., may include sensor data).

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

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

[0024] The processing performed on the workpiece (or "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, a tool holder and / or a spindle of the machine tool may include at least one sensor. Advantageously, the tool may include at least one sensor. This results in more accurate and reproducible sensor data. The tool may include a tool insert (or cutting edge) configured to interact with a workpiece to process the workpiece. The tool may include a tool body for holding the tool insert. As a result, the tool insert may be attached to the machine tool via the tool body. The tool body may comprise at least one sensor. Preferably, the at least one sensor is arranged towards an end of the tool body proximal to the tool insert.

[0026] Step b) may be performed by a measuring device mounted on the machine tool. Optionally, step b) is performed by a measuring device mounted on a different positioning device, for example a coordinate measuring machine (CMM).

[0027] The measurement device may include a measurement probe. The probe may be configured to measure a dimensional characteristic of the workpiece. For example, the probe may be configured to measure the position (e.g., coordinates) of a particular point in a three-dimensional measurement volume. Optionally, the probe is configured to measure surface roughness and / or surface waviness. The measurement probe may include a contact measurement probe. The probe may include a deflectable stylus. The probe may be configured to determine and output a degree of deflection of the stylus. Such probes are commonly known as scanning probes or analogue probes. Such probes are to be contrasted with touch-trigger probes, which are configured to generate a "trigger" signal in response to the stylus being deflected beyond a particular / threshold value. As will be apparent, the measurement device is separate from the tool. As a result, the method may include exchanging (e.g., automatically from a storage rack / carousel) the tool and the measurement device to and / or from the tool holder. This is particularly true when the machine tool has only one tool holder.

[0028] The method can further include using the inferred information (e.g., the measured data), which can include adjusting processing on subsequent or subsequent nominally-similar workpieces using the inferred information (e.g., the measured data), which can include automatically adjusting processing on subsequent or subsequent nominally-similar workpieces using the inferred information (e.g., the measured data).

[0029] Step c) may include adjusting the pre-determined sensor-to-workpiece data calibration information based on the sensor data and the measurement data (e.g., making the information specific to the current workpiece / series of workpieces and / or compensating for changes in the tool, machine tool and / or operating environment). For example, such adjustments may include supplementing the pre-determined sensor-to-workpiece data calibration information. Such pre-determined sensor-to-workpiece data calibration information may be generic sensor-to-workpiece data calibration information, e.g., information that is generic to the tool (and optionally the machine tool, e.g., the tool / machine tool combination), but not specific to the workpiece. As a result, step c) may include adjusting / updating the generic sensor-to-workpiece data calibration information (based on the sensor and measurement data) to determine sensor-to-workpiece data calibration information that is specific / unique to a particular workpiece, tool and machine tool combination. As a result, the method can 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 processing the workpiece with the tool in a manner that causes the tool to sense different machining characteristics (e.g., different loads, different vibration amounts) at different points in space and / or time. Step b) may include a measurement device inspecting portions of the workpiece that are subject to such different machining characteristics. As a result, step c) may include calculating sensor-to-workpiece data calibration information based on sensor data and measurement data related to the different machining characteristics.

[0031] In other words, step a) may include: i) causing a tool attached to the machine tool to process a workpiece according to first processing parameters and collecting sensor data obtained by at least one sensor during said processing according to the first processing parameters; and ii) causing a tool attached to the machine tool to process a workpiece according to second processing parameters (different from the first processing parameters) and collecting sensor data obtained by at least one sensor during said processing according to the second processing parameters. The first and second processing parameters may be configured differently such that the tool senses different characteristics (e.g., different loads, different vibration amounts) during processing of the workpiece. Step b) may include inspecting the portion / surface of the workpiece formed by steps i) and ii) (e.g., by at least one measuring device). 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 apparent, 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, steps i) and ii) may be performed on the same part of the workpiece, in which case 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 may be workpiece-specific. In other words, the sensor-to-workpiece data calibration information may be determined for the workpiece processed in step a) and the nominally identical workpiece (i.e., a workpiece in a series of nominally identical workpieces). As a result, different sensor calibration information may be determined for different / not nominally identical workpieces. The sensor-to-workpiece data calibration information may be determined for a (e.g., unique) specific tool and machine combination. In particular, the sensor-to-workpiece data calibration information may be determined for a (e.g., unique) specific workpiece, tool, and machine combination.

[0033] The present application describes a method for inferring information about a workpiece being processed by a tool attached to a machine tool system based on sensor data related to one or more aspects / characteristics of the machine tool and / or the tool attached thereto. The method may include (in any suitable order) determining sensor calibration information based on i) actual measurement data of a portion of the workpiece processed by the tool, and ii) sensor data related to one or more characteristics of the machine tool and / or the tool attached thereto, obtained during processing of the portion measured in i) by the tool. The method may also include b) acquiring sensor data related to one or more characteristics of the machine tool and / or the tool attached thereto, obtained while the workpiece is being processed by the tool attached to the machine tool system. The method may also include using the sensor calibration information to c) acquire inferred information (e.g., measurement data) about the workpiece based on the sensor data acquired during step b).

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

[0035] As will be apparent, any of the above methods may be implemented on a computer. Thus, according to another aspect of the invention, there is provided a computer program product comprising computer program code which, when executed by a computer, causes the computer to perform any of the above methods. According to another aspect of the invention, there is provided a computer readable medium carrying the above mentioned computer program code.

[0036] According to another aspect of the invention, there is provided a machine tool apparatus comprising 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 processing of the workpiece, and a controller configured (e.g. using computer program code) to cause the machine tool apparatus to perform any of the methods described above. [Brief description of the drawings]

[0037] Embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which: [Figure 1] FIG. 1 shows diagrammatically a machine tool device equipped with tools for processing a workpiece. [Diagram 2] FIG. 2 shows diagrammatically the machine tool arrangement of FIG. 1, but with a measurement probe attached to the machine tool instead of the tool. [Diagram 3]FIG. 3 is a flow chart of an exemplary process in accordance with the present invention. [Figure 4a] FIG. 4a is a graph illustrating a possible calibration model. [Figure 4b] FIG. 4b is a graph illustrating a possible calibration model. [Figure 4c] FIG. 4c is a graph illustrating a possible calibration model. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Referring to Figure 1, there is shown a machine tool system 2 including a machine tool 4, a numerical control device 6 (NC) (e.g., a computer numerical control or "CNC"), a PC 8, and a transceiver interface 10. The machine tool 4 includes a tool holder 12 that holds and moves a tool 20 relative to a workpiece 16 mounted on a spindle 18. The NC 6 controls the rotation of the spindle 18 and the x, y, and z movement of the tool holder 12 within the working volume of the machine tool, such as by means of motors and encoders (not shown). The NC 6 can be programmed, for example via the PC 8, for machining operations.

[0039] In the described embodiment, the tool 20 is a boring bar and comprises a tool body 22 and a tool insert 24 (such as a cutting insert configured to interact with (e.g., cut) a workpiece to process the workpiece). The boring bar 20, and in particular the tool body 22, comprises at least one sensor 26 for measuring / monitoring one or more aspects / characteristics of the tool during processing on the workpiece. For example, in the present embodiment, the tool body comprises an accelerometer (for measuring / monitoring vibrations), a temperature sensor, and a strain gauge, which are collectively indicated in the figure by a box 26. As shown, the sensor 26 is located at an end of the tool body 22 proximal to the tool insert 24. In alternative embodiments, one or more sensors can be provided (in addition to or instead of the sensors of the tool 20) on, for example, the tool holder 12 and / or the spindle 18 for measuring / monitoring one or more aspects / characteristics of the machine tool during processing on the workpiece.

[0040] The workpiece 16 can be machined by the tool 20 by moving the tool insert 24 into the workpiece 16 while being rotated by the spindle 18. At the same time, data from at least one sensor 26 of the tool body 22 can be acquired. For example, data related to at least one of the tool temperature, vibration, load and deflection can be acquired. Such data can be transmitted to an external device, e.g., the NC6 and / or the PC8, e.g., via a wireless link and the interface unit 10. For example, the at least one sensor 26 can communicate with the interface unit 10 by the Bluetooth wireless technology standard. In the described embodiment, the data is streamed instantaneously and continuously. However, as will be appreciated, this need not necessarily be the case. For example, the data can be transmitted at intervals (regular or irregular) or only when requested. In other exemplary embodiments, the data from the at least one sensor 26 can be stored locally in the memory of the tool 20 and downloaded later, e.g., after processing by the tool, to the NC6 and / or the PC8, e.g., via a wired or wireless link.

[0041] FIG. 2 shows that a measurement probe 30 may be loaded into the tool holder 12 of a machine tool 4 in place of the tool 20 (FIG. 1). In this embodiment, the probe 30 is a contact probe including a body 32 attached 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 distal to the body 32. In the described embodiment, the stylus 34 may be deflected relative to the body 32 (e.g., when the stylus tip 36 contacts a surface), and such deflection may be detected by a sensor in the body 32. In particular, in the described embodiment, the probe is a scanning probe (also known in the art as an analogue probe) in that the extent / quantity / degree of deflection of the stylus from a rest position may be sensed and reported by the probe 30 (as opposed to a touch-trigger probe, which only reports when the stylus has been deflected, for example, by a predetermined threshold amount). Such scanning probes for machine tools are known, for example, as the OSP60 probe with SPRINT™ technology available from the applicant. Obviously, other probes and other techniques may be used.

[0042] As a result, by contacting the stylus tip 36 with the surface of the workpiece 16, a machined portion of the workpiece can be measured. Stylus deflection data from the probe 30 can be instantaneously and continuously streamed to the NC 6 and / or PC 8 via the interface 10, for example wirelessly. As with the tools described above, this can be via a Bluetooth connection. As will be apparent, other techniques can also be used to transfer the stylus deflection data. For example, data can be sent at intervals (regular or irregular) or only when requested. In other exemplary embodiments, the stylus deflection data can be stored locally in the memory of the probe 30 and later downloaded to the NC 6 and / or PC 8, for example via a wired or wireless link.

[0043] If desired, the data from the probe 30 can be combined with machine tool position data, for example data relating to the relative position of the probe 30 and the workpiece 16. For example, the data from the probe 30 can be combined with tool holder 12 position data, which may be obtained from an encoder (not shown) that monitors the position of the tool holder 12 in any or all of the x, y and z axes.

[0044] As a result, as will be apparent, the measurement data relating to the portion of the workpiece being processed may be raw data acquired / output by the probe 30, or data obtained by processing the raw data acquired / output by the probe 30 (e.g. combining it with other data, such as data relating to the position of the tool holder 12).

[0045] 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 finishing probe may be used. Optionally, a non-contact probe may be used. Optionally, the part of the workpiece need not be measured on the same machine tool. For example, the part may be removed from the machine tool and measured on a coordinate measuring machine (CMM) or the like. An exemplary process 100 in accordance with the present invention is shown in FIG. 3.

[0046] The exemplary process 100 begins at step 102 where a workpiece 16 is processed by a tool 20, and data from the tool 20 of at least one sensor 26 is acquired during processing of the workpiece. As shown diagrammatically in FIG. 3, the tool sensor data is stored in memory (such as in the PC 8) for later use. As will be apparent, the data can be stored elsewhere, e.g., in the NC 6, the interface 10, or elsewhere, e.g., in network storage or the cloud. Next, in step 104, the portion of the workpiece 16 processed by the tool 20 is measured using a measurement probe 30 to obtain measurement data (e.g., dimensional and / or surface roughness / waviness data) for the portion. As shown diagrammatically in FIG. 3, the measurement data is stored in memory for later use.

[0047] In step 106, the tool sensor data and the measurement data obtained in steps 102 and 104 are used to determine sensor-to-workpiece data calibration information. This determination can be achieved in various ways. For example, a model that relates i) a particular characteristic of the tool (e.g., tool load as measured by a strain gauge) to ii) the dimensional error of the part (e.g., hole diameter) can be determined from one or more test cuts and measurements of the workpiece. Such a model can be in the form of, for example, a function or a look-up table. Figure 4a is a graph showing a model determined from two different test hole cuts performed at two different loads and from the error in the diameter of the holes formed by those two test cuts. These results are shown plotted in the graph of Figure 4a. As shown, a model (e.g., a function) that fits a straight line can be determined from the results of the two test cuts. This model can be (or form the basis of) a calibration model of the workpiece. As a result, in subsequent cutting of the workpiece (or a nominally identical workpiece), the hole diameter error (and therefore the actual size of the hole) can be inferred from the loads measured during the cutting process.

[0048] In this embodiment, two test cuts were obtained, although 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 best fit line (straight or curved) through measurements obtained from the different test cuts.

[0049] In an alternative embodiment, sensor-to-workpiece data calibration information may already be available that is generic to the tool (and optionally the machine tool, e.g., the tool / machine tool combination). For example, as shown by the solid line in FIG. 4b, a generic model of the relationship between load and machining error may already be determined for the tool (and optionally the machine tool, e.g., the tool / machine tool combination). Nevertheless, the inventors have found that using such a generic model does not necessarily result in accurate measurements for a given workpiece. As a result, the inventors have found that there may be a significant advantage to performing one or more test cuts on a workpiece (or a nominally identical one), measuring the cut parts, and determining a calibration model / function for that workpiece (and subsequent workpieces in a series of nominally identical workpieces). As a result, the sensor-to-workpiece data calibration information may be specific to the workpiece. For example, this may include performing only one test cut and adapting the generic model based thereon. For example, as shown in Figure 4b, for a load of "x" measured during machining of a hole, it can be determined that the actual error in the hole diameter is e2, not e1 as predicted by the generic model. This difference in error can be considered constant, and a fitted calibration model can be determined by offsetting the generic model by the difference between e2 and e1, as shown by the dashed line in the graph in Figure 4b. Obviously, multiple test cuts and their measurements can be performed, if desired, which can result in more accurate offset information.

[0050] Similarly, the same approach can be taken for properties other than load, as shown in Figure 4c. For example, a generic model of measured surface roughness (Ra) versus vibration can be adapted based on the actual reading of the surface roughness perceived at a particular measured vibration level “y”.

[0051] The calibration information (eg, features, models, data or other suitable information) is stored in a memory (eg, a PC) for later use.

[0052] At some point thereafter, the workpiece (or, e.g., the nominally same workpiece) is again processed by the tool (or, e.g., the nominally same tool), as represented by step 108 of process 100. As shown in Figure 3, tool sensor data from the tool 20 at the at least one sensor 26 is acquired during the processing of the workpiece and stored in memory (e.g., a PC) for subsequent use.

[0053] In step 110, the calibration information obtained in step 106 and the tool sensor data obtained in step 108 are used to infer measurement data for the portion of the workpiece processed in step 108. For example, in the case of forming a hole, and with reference to Figures 4a and 4b, this inference process may include using the model determined in step 106 to look up an estimated diameter error based on the load acting on the tool, measured by sensor 26 during the machining process of step 108. Alternatively, or in addition, with reference to Figure 4c, this inference process may include using the model determined in step 106 to determine a surface roughness of the portion based on vibrations measured by sensor 26 during the machining process of step 108. Once a determination is made, the inferred measurement data is stored in memory (e.g., a PC) for subsequent use, such as for use in step 112. For example, such uses of the inferred measurement data may include at least one of: deciding whether to accept or reject the workpiece, deciding how to adjust subsequent processing of the workpiece, either in real time or during a subsequent processing step, and / or deciding to stop processing.

[0054] As a result, the techniques of the present invention can be used to determine measurement data about a portion of a processed workpiece without actually directly measuring the portion with a measurement tool.

[0055] As will be apparent, the method may include using the calibration information determined in step 106 to determine process control parameters for use in 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.

[0056] As will be apparent, references herein to storing data in memory may include storing data in a permanent storage medium and / or in a temporary memory (e.g., random access memory “RAM”). Furthermore, the above-mentioned storage steps may be optional. For example, the inferred measurement data may be transmitted to an external device and / or used immediately (e.g., by NC6 to make decisions) without being stored in a memory device.

[0057] As will be apparent, although a common interface 10 is shown for NC6 and PC8, they may each have their own separate interface 10. Furthermore, such interfaces may be incorporated within NC6 and / or PC8 rather than being separate as shown.

[0058] In the embodiment described above, the measurement probe 30 is mounted to the tool holder 12 in place of the tool 20. However, it will be apparent that in alternative embodiments the measurement probe could be mounted to a different tool holder or other part of the machine tool, thereby avoiding the need to exchange the tool for the measurement probe.

[0059] In the above-described embodiment, the same part, the same tool, and the same machine are used in all steps. However, this is not necessarily the case. For example, the workpiece, tool, and / or machine used in steps 102 and 104 may be different (albeit nominally the same) than the workpiece, tool, and / or machine used in step 108. For example, in one embodiment, the calibration information may be obtained on a different machine. For example, steps 102 and 104 may be performed on a different machine than step 108. In another exemplary embodiment, steps 102 and 108 may be performed on the same machine, but step 104 may be obtained on a different device, for example, a different machine tool or a dedicated measurement device such as a coordinate measuring machine (CMM).

[0060] As will be appreciated, in alternative embodiments, tools other than boring bars may be used, for example the tools may include drills, grinding wheels, or milling cutters, reamers, or milling machine tools.

[0061] As will be apparent, in alternative embodiments, relative motion in any or all of the x, y and z dimensions can be provided by movement of the spindle 18 instead of or together with the tool holder 12. Furthermore, motion may be limited to fewer dimensions, e.g., only x and / or y. Furthermore, while the described embodiments include Cartesian machine tools, it will be understood that this is not necessarily the case and could, for example, be a non-Cartesian machine tool. Furthermore, as will be apparent, although the invention is shown in conjunction with a lathe machine tool, the invention can be used in many other types of machine tool systems, such as milling machine tool systems (e.g., the tool is held on a movable spindle) and machining centers. As a result, the invention can be used in embodiments in which the tool rotates and the part is held stationary.

[0062] As will be apparent, steps 102 and 104 may be repeated, for example, for a different (eg, nominally the same) workpiece, thereby obtaining calibration information in step 106.

[0063] In the above-described embodiment, the method includes performing an initial test cut and measurement to determine the calibration information before any subsequent machining is performed. Nevertheless, as will be apparent, this need not necessarily be the case and it is also possible that the machining operation from which information is inferred is performed before the calibration information is determined. For example, the method includes performing multiple machining operations on a workpiece (or multiple nominally identical workpieces), measuring only one (or only a few) machined portion (or measuring only one or a few of the workpieces, for example), determining the calibration information from the results, and then using the calibration information to infer information about other portions of the workpiece (or other workpieces) that have already been machined.

Claims

1. a) at a first time processing a workpiece with a tool attached to a machine tool, wherein at least one sensor configured to measure one or more aspects of the tool and / or the machine tool collects sensor data during said processing; b) inspecting the portion of the workpiece processed in step a) with a metrology device to obtain metrology data; c) calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data; d) at a second time, processing the same or nominally the same workpiece as used in step a) with the same or nominally the same tool as used in step a) mounted on the same or nominally the same machine tool as used in step a), sensor data relating to one or more aspects of the same or nominally same tool and / or the same or nominally same machine tool are collected at said second time by the same or nominally identical sensors as used in step a); e) using the sensor-to-workpiece data calibration information determined in step c) and the sensor data collected in step d) to infer measurement data for the same or nominally the same workpiece processed in step d); The method according to claim 1, further comprising:

2. 10. The method of claim 1, further comprising using the inferred information about a workpiece to adjust processing of the workpiece or a nominally identical workpiece.

3. 3. The method of claim 1, wherein the sensor data comprises at least one of vibration, deflection and / or load.

4. 3. A method according to any of claims 1 to 2, wherein the measured data and / or inferred information comprises at least one of the following: position, dimensions, surface roughness, and surface waviness of the workpiece.

5. 5. The method of claim 1, wherein the processing of the workpiece comprises at least one of cutting, drilling, grinding, polishing, turning, reaming, and milling.

6. 6. The method according to any one of the preceding claims, characterized in that the tool comprises at least one sensor.

7. 7. The method of claim 6, wherein the tool includes a tool insert and a tool body via which the tool insert is attached to a machine tool, the tool body comprising at least one sensor.

8. 8. The method of claim 7, wherein the at least one sensor is positioned facing an end of the tool holder proximal to the tool insert.

9. 9. A method according to any one of the preceding claims, characterized in that step b) is performed by means of a measuring device attached to the machine tool.

10. 10. A method according to any preceding claim, wherein the measurement device comprises a measurement probe for measuring a dimensional characteristic of the workpiece.

11. 11. The method of claim 1, wherein step c) comprises adjusting predetermined sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

12. 1. A method for estimating measurement data relating to a workpiece processed by a tool attached to a machine tool, comprising the steps of: a) acquiring, at a first time, sensor data obtained by at least one sensor, the sensor data relating to one or more characteristics of a tool and / or machine tool while a workpiece is being processed by the tool; b) obtaining sensor-to-workpiece data calibration information from the sensor data obtained in step a) and the measurement data relating to the workpiece processed in step a); and c) at a second time, processing the same or nominally the same workpiece as used in step a) with the same or nominally the same tool as used in step a) mounted on the same or nominally the same machine tool as used in step a), wherein sensor data relating to one or more aspects of the same or nominally the same tool and / or the same or nominally the same machine tool are collected at said second time by the same or nominally the same sensor as used in step a); d) using the sensor-to-workpiece data calibration information determined in step b) and the sensor data collected in step c) to infer measurement data for the same or nominally the same workpiece processed in step c); The method according to claim 1, further comprising:

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