Method and system for identifying the position of a point on a surface

Abstract

The present invention relates to a machining system (100) and method for identifying the position of a point on a machined surface of a workpiece (130). The machining system comprises a machine tool (102), a cutting tool (104) provided with a tool body (105) arranged on the machine tool and including at least one sensor (115), and a control system (150) adapted to control and monitor the position of the tool body. The method includes a step (206) of machining the workpiece using the cutting tool (104), and a step of measuring the workpiece using a measuring instrument (104, 600) having a tool body (105) and a first tip. The step of measuring the workpiece includes moving the measuring instrument towards the workpiece while measuring a parameter using the sensor (208), and identifying a first position of the first tip where the tip contacts a point on the machined surface based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor, thereby identifying the first position of the first tip indicating the position of the point on the machined surface, and includes a step of measuring the workpiece (130).

Description

Technical Field

[0001] The present disclosure generally relates to methods and systems for identifying the position of a point on a surface, and more particularly, to methods and systems for identifying a point on the surface of a workpiece in a machining system.

Background Art

[0002] In manufacturing, a workpiece is machined in a machining system to produce a finished product. The finished product needs to not deviate excessively from its intended dimensions in order to perform its function. Depending on the type of article being manufactured, the degree of deviation (also called tolerance) of the article from its intended dimensions that is acceptable can vary.

[0003] In a machining system equipped with various tools, an article is machined. After the article has been machined, a measurement system is used to determine whether the requirements regarding tolerance are met. Usually, in order to perform the measurement, it is necessary to replace the tool and / or move the article to another location. This consumes both time and resources, especially when it is determined that the article deviates excessively from the required tolerance and further machining is required to complete it.

[0004] Improving the current system would be beneficial in order to shorten the time required to inspect an article machined in a machining system and, if necessary, perform further operations after measurement.

[0005] In conclusion, there is a need for improvement, particularly with respect to machining systems for measuring and evaluating articles.

Summary of the Invention

[0006] The object of the present invention is to address at least some of the problems and issues outlined above. An object of an embodiment of the present invention is to shorten the time required for inspecting a machined workpiece. Another object of an embodiment of the present invention is to improve the accuracy of such inspection.

[0007] According to one aspect, the present invention relates to a method for specifying the position of a point on a machined surface of a workpiece in a machining system. The machining system includes a machine tool, a cutting tool including a tool body disposed on the machine tool and having at least one sensor, and a control system adapted to control and monitor the position of the tool body. The method includes machining the workpiece with the cutting tool, and then measuring the workpiece using a measuring instrument including the tool body and a first tip, the step of measuring the workpiece including moving the measuring instrument toward the workpiece while measuring a parameter using the sensor (208), and specifying a first position of the first tip at which the first tip contacts a point on the machined surface based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor, thereby indicating the position of the point on the machined surface, specifying the first position of the first tip including the step of measuring the workpiece, and including.

[0008] By using the same sensor-equipped tool body that is used in machining also during the measurement of the machined workpiece, an efficient and accurate method for identifying the position of points on the machined surface can be obtained. Preferably, the sensor used for measuring the machined workpiece can also be utilized during the measurement in the machining process. Thus, according to the present disclosure, the sensor embedded in the tool body can be used not only for monitoring cutting process-related parameters such as deflection during machining, but also for measuring the workpiece after machining.

[0009] By using the method according to the present invention, the workpiece can be measured without the need to use a separate dedicated measuring probe or to move the workpiece to a separate machine, such as a coordinate measuring machine, for inspection. The measurement is performed using the same tool body that is also used when machining the surface, so the accuracy is improved.

[0010] Machining of the workpiece refers to a cutting process in which a cutting tool and the workpiece engage while they are in relative rotational motion, and as a result, the cutting edge of the cutting tool separates material from the surface of the workpiece.

[0011] As already mentioned, the sensor can also be used for measurement during machining. However, the step of measuring the workpiece as defined in the present disclosure is performed after machining, i.e., when there is no relative rotational motion between the measuring instrument and the workpiece.

[0012] The body of the cutting tool is more rigid compared to a conventional measuring probe and is thus less affected by vibrations and other disturbances. Therefore, for example, when measuring the inner surface deep inside a machined hole, a conventional measuring probe may lack sufficient rigidity, but the cutting tool itself has the ability to machine the hole and thus has the rigidity required for performing a reliable measurement.

[0013] The movement of the tool body, i.e., the start and stop of the movement of the cutting tool and the measuring instrument, is performed via a control system.

[0014] The machine tool may be a computer or a computerized numerical control (CNC) machine tool, and in particular, may be a machine tool that can be used for turning operations, such as a CNC lathe, a multitasking machine, a turn-mill machine, or a sliding head machine. The machining may be an internal turning process, in which case material is removed from the inner surface of the workpiece, for example, from within a hole in a rotating workpiece. Internal turning is sometimes also referred to as boring. It is also contemplated that the method may be used in connection with other machining operations such as milling.

[0015] As used herein, when referring to the "tip", this refers to the point of the portion of the measuring instrument that is intended to engage the workpiece, i.e., the most distal point in the direction of movement of the measuring instrument when it is moved towards a point on its surface for measuring the workpiece. In other words, the tip is the point of the measuring instrument that first contacts a point on the surface of the workpiece when the measuring instrument is moved towards its surface for measuring the workpiece.

[0016] The tip may be located on a head disposed at the end of the tool body.

[0017] A mechanical interface may be disposed at the end of the tool body opposite the end where the head is disposed to facilitate the placement of the tool body in the machine tool.

[0018] Preferably, the parameter is measured continuously or intermittently during the measurement of the workpiece.

[0019] According to some embodiments, identifying the first position of the first tip of the measuring instrument includes: detecting, based on the measured value of the parameter, that the first tip has contacted a point on the machined surface of the workpiece; stopping the movement of the measuring instrument; Obtaining the position of the first tip based on the position of the tool body monitored by the control system, Identifying the deflection of the measuring instrument based on the measured value of the parameter, and Identifying the first position of the tip based on the identified deflection and the obtained position of the tip.

[0020] By identifying the deflection of the measuring instrument caused by the contact of the tip with the machined surface of the workpiece, it is possible to accurately identify the position of a point on the machined surface. This is done by using the identified deflection of the measuring instrument to adjust the position monitored by the control system and obtained from the control system. In this case, the position of the point on the machined surface can be identified by correcting the position obtained and monitored by the control system based on the identified deflection.

[0021] For the non-deflected state of the measuring instrument, the displacement of a point on the tool body caused by the deflection of the measuring instrument will clearly depend on the position of the point along the longitudinal extension of the measuring instrument. However, as used in this specification, the amount of deflection of the measuring instrument should be understood as the displacement of the tip of the measuring instrument from the position it would have had if there were no deflection of the measuring instrument.

[0022] Preferably, the parameter is measured continuously or intermittently during the measurement of the workpiece, at least until the movement of the measuring instrument stops, so that the deflection of the measuring instrument can be identified based on the value of the parameter measured when the measuring instrument is in the stop position.

[0023] According to some embodiments, the point on the machined surface of the workpiece is a point on the inner circumference of the hole.

[0024] As used herein, when referring to a workpiece, a "hole" should be understood as a cavity that is circular or substantially circular in any cross-section taken perpendicular to the extent of the hole, but does not necessarily have a constant diameter. In other words, the hole may be a perfect cylindrical shape, or for example, may comprise a plurality of sections with different diameters.

[0025] According to some embodiments, the cutting tool comprises a cutting head including a cutting edge for machining a workpiece.

[0026] The cutting head may be an integral part of the cutting tool, i.e., integrated with or non-removably attached to the end of the tool body. Alternatively, the cutting head is a part that is detachably arranged at the end of the tool body so that the cutting head can be replaced and different heads can be selectively used together with the tool body.

[0027] The cutting edge may be integral with the cutting head, or the cutting edge may be part of a replaceable cutting insert that is detachably arranged in an insert seat of the cutting head.

[0028] According to some embodiments, the measuring instrument is the same as the cutting tool, and the first tip is located on the cutting edge of the cutting tool. Thus, in such embodiments, the tip refers to a point on the cutting edge, i.e., the point on the cutting edge that first contacts a point on the surface when the measuring instrument (corresponding to the cutting tool in such embodiments) is moved towards the surface for measuring the workpiece.

[0029] According to other embodiments, the method further includes attaching a probing head to the tool body such that the measuring instrument includes the tool body and the probing head after machining the workpiece and before measuring the workpiece, and the first tip is located on the probing head. Thereby, while still using the same tool body and sensor for measurement, a tip specifically adapted for probing can be utilized. The method may include first removing the cutting head used when machining the workpiece from the tool body and then attaching the probing head in its place. In other words, the probing head and the cutting head can be replaced. Since only the cutting head is removed and the probing head is attached in its place, the measuring instrument comprises the same tool body as that used for machining during the step of measuring the workpiece.

[0030] According to some embodiments, a point on the machined surface of the workpiece is a first point at a first location along the extent of a hole on the inner circumference of a hole in the workpiece, the measuring instrument further comprising a second tip located at a known distance from the first tip, the first and second tips being arranged to face the first and second points on the machined surface respectively, the second point being located on the inner diameter of the hole opposite the first point, and the step of measuring the workpiece comprises identifying a second position of the first tip at which the second tip contacts the second point based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor; identifying the inner diameter of the hole based on the identified first and second positions of the first tip and the known distance between the first tip and the second tip; and further includes.

[0031] The extension of the hole referred to in this specification should be understood as the longitudinal extension along the axis of the hole, which corresponds to the axis of the spindle, i.e., the axis of rotation of the workpiece, in the case of a workpiece arranged on a lathe or other machine tool suitable for turning. Therefore, the first and second points on the machining surface are points on the inner circumference of the hole at a first location along the axis of the hole.

[0032] Referring to the probing head, the first and second tip portions may be diametrically opposed points on a rim, such as a disk-shaped or ring-shaped rim, extending around the periphery of the probing head. Alternatively, the two tip portions may be separate distinguishable protrusions located on opposite sides of the periphery of the probing head. Therefore, when used in this specification with respect to the probing head, the tip portions should be understood as the points of the probing head that first come into contact with the surface to be measured when the measuring instrument is used to measure the workpiece.

[0033] The inner diameter of the hole can be determined by adding the known distance between the first tip portion and the second tip portion to the difference between the first position and the second position of the first tip portion.

[0034] Thus, since the difference between the two specified positions is used as the reference for determining the inner diameter, the determination is not affected by any error in the position of the first tip portion obtained based on the position of the tool body monitored by the control device, and the inner diameter of the machined hole can be easily and accurately determined.

[0035] To determine the second position of the first tip portion, the same method as when determining the first position of the first tip portion can be used. Accordingly, the step of determining the second position of the first tip portion may include the following: Moving the measuring instrument towards the second point, Detecting that the second tip portion has contacted the second point based on the measured value of the parameter, Stopping the movement of the measuring instrument, Obtaining the position of the first tip based on the position of the tool body monitored by the control system, Identifying the deflection of the measuring instrument based on the measured value of the parameter, and Identifying the second position of the first tip based on the identified deflection and the obtained position of the first tip.

[0036] According to some embodiments, the method further includes repeating, along the extent of the hole, the step of measuring the workpiece and identifying the diameter of the hole at one or more additional locations spaced from the first location with respect to the inner circumference of the hole in the workpiece, and then identifying the deviation from the cylindrical shape of the hole based on the diameters identified at the first location and the one or more additional locations.

[0037] When machining a true circular cylindrical hole in a workpiece, the resulting hole may in some cases be slightly conical, such as tapering towards the innermost end of the hole, or the machined hole may deviate from the desired cylindrical shape in other ways. By repeating the measurement of the inner diameter at one or more additional locations along the extent of the hole, the magnitude of the deviation from the cylindrical shape can be identified. As a simple example, assuming a linear and uniform diameter change along the extent of the hole, measurements at two different locations can provide a rough estimate of the conicity of the hole. If the machined hole is expected to have a more complex deviation from the desired cylindrical shape, preferably the measurement should be repeated at further locations along the hole.

[0038] Instead of using a probing head having two tip portions for measuring the diameter of the hole, it is also contemplated that a cutting head having additional tip portions other than the tip portion of the cutting edge may be used to identify the diameter in a corresponding manner. For this reason, considering a point on the machined surface of the workpiece as a first point at a first location along the extent of the hole on the inner circumference of the hole in the workpiece, and considering the tip portion located on the cutting edge as the first tip portion, the cutting head may include a second tip portion located at a known distance from the first tip portion, and the first and second tip portions are arranged to face the first point and the second point on the machined surface, respectively. The second point is located on the inner diameter of the hole on the opposite side of the first point, and the step of measuring the workpiece includes, identifying a second position of the first tip portion where the second tip portion contacts the second point based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor; identifying the inner diameter of the hole based on the identified first and second positions of the first tip portion and the known distance between the first tip portion and the second tip portion; and further includes.

[0039] If the measuring instrument and the tip portion are not fully aligned at a known position in the coordinate system of the machine tool, i.e., with respect to the zero reference point of the machine tool, a more accurate determination of the position of the point on the machined surface can be achieved by first calibrating the machining system.

[0040] In this case, according to some embodiments, the following steps may precede the step of machining and measuring the workpiece: moving the measuring instrument towards a reference point having a known spatial location; identifying a reference position of the first tip portion where the first tip portion contacts the reference point based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor; identifying an offset error based on a known spatial location and a specified reference position of a first tip, and calibrating a machining system based on the identified offset error.

[0041] The deviation between the specified reference position of the first tip and the true known spatial location of the reference point is the result of the offset error of the machining system. Accordingly, when the specified reference position of the first tip is compared with the known spatial location of the reference point, the offset error can be easily identified therefrom and used for calibrating the machining system. Thus, the machining system is calibrated based on the identified offset error, so that the offset error is taken into account for the positions of the tool body and the first tip subsequently monitored by the control system.

[0042] As a result, since the offset error is taken into account for the position of the first tip obtained based on the position of the tool body monitored by the control system, subsequent measurements for identifying the position of a point on the machining surface of the workpiece become more accurate.

[0043] For example, such an offset error can be caused by random deviations associated with the attachment of the tool body to the machine tool, or the joint between the head and the tool body, or the joint between the cutting head and the cutting insert. The offset error can also be caused, for example, by temperature changes.

[0044] The offset error can be defined as the difference between the specified reference position of the first tip where the first tip contacts the reference point and the known spatial location of the reference point.

[0045] Unless otherwise indicated, when used in the specification, "offset" or "offset error" may, in order to distinguish from other types of offsets such as axial offset, be referred to as "radial offset" and "radial offset error" respectively, and is measured in the direction of movement experienced by the measuring instrument when specifying the position of a point on the machined surface. This direction of movement, in the case of turning operations, corresponds to the radial direction with respect to the axis of rotation of the workpiece being machined, more precisely, it may correspond to the x-axis in the conventional lathe coordinate system. The offset may refer to the distance in the above direction from the zero reference point of the machine tool to the reference point of the joint where the tool body is attached to the machine tool when the first tip is at the reference position. Therefore, depending on the machining system used, the offset before calibration may be defined by a certain distance that is preferably stored in the machining system and is utilized when controlling and monitoring the position of the tool body (and thus the cutting tool and the measuring instrument) in the x-axis direction. The offset error specified according to the present invention is then added to this previously stored offset, resulting in an updated or calibrated offset being obtained. Accordingly, calibration may in that case correspond to storing this updated offset and / or offset error in the machining system for later use when controlling and monitoring the position of the tool body.

[0046] The offset and / or offset error may be stored in a memory or other storage medium that is part of or communicatively coupled to the control system and may be read from and utilized by the control system in the process of controlling and monitoring the position of the tool body.

[0047] One approach for specifying the reference position of the first tip that contacts the reference point is to use a method similar to that for specifying the position of a point on the machined surface of the workpiece as described above. Accordingly, the method for specifying the reference position of the first tip that contacts the reference point may include the following steps: Detecting that the first tip has contacted the reference point based on the measured value of the parameter; Stopping the movement of the measuring instrument; Obtaining the position of the first tip based on the position of the tool body monitored by the control system; Specifying the deflection of the measuring instrument based on the measured value of the parameter, and Specifying the reference position of the first tip based on the specified deflection and the obtained position of the first tip.

[0048] To identify the offset error, it is necessary to know the true spatial location of the reference point in the machine coordinates of the machine tool. The reference point can be located on a surface that is not part of the workpiece but is at a known fixed position relative to the machine tool, and the measuring instrument can be positioned such that it can move towards such a reference point.

[0049] According to another embodiment, the reference point is a point on the inner circumference of a hole in the workpiece to be machined, and the spatial location of the reference point is identified in a probing procedure that utilizes a measuring instrument having a first tip and a second tip with a known distance therebetween. The probing procedure includes: Positioning the measuring instrument such that the first tip and the second tip face the reference point and the auxiliary point on the inner circumference of the hole, respectively, where the auxiliary point is located on the inner diameter of the hole on the opposite side of the reference point; Measuring the workpiece by specifying the reference position of the first tip when the first tip contacts the reference point and specifying the auxiliary position of the first tip when the second tip contacts the auxiliary point, and Identifying the spatial location of the reference point based on the specified reference position and auxiliary position of the first tip, and the known distance between the first tip and the second tip.

[0050] Referring to an embodiment that utilizes a probing head for such a probing procedure, the measuring instrument comprises the same tool body as used in machining, but at its end, instead of a cutting head, a probing head having, in this case, first and second tips is attached.

[0051] Such a probing head used to identify the spatial location of the reference point is preferably the same probing head that can also be used to measure the workpiece and determine the diameter of the hole after machining.

[0052] The diameter of the hole can be determined by adding the known distance between the first tip and the second tip to the difference between the reference position and the auxiliary position. Assuming that the hole is centered with respect to the central axis of the spindle and the position of the central axis of the spindle in the coordinate system of the machine tool is clearly defined, the radius of the hole, i.e., the value obtained by dividing the specified diameter by 2, reflects the spatial location of the reference point in the coordinate system of the machine tool along the movement direction of the probe when measuring the workpiece.

[0053] To identify the reference position and the auxiliary position of the first tip, the same method as when identifying the position of a point on the machined surface of the workpiece can be used. Accordingly, the step of identifying the reference position may include the following: Moving the measuring instrument towards the reference point, Detecting that the first tip has contacted the reference point based on the measured value of the parameter, Stopping the movement of the measuring instrument, Obtaining the position of the first tip based on the position of the tool body monitored by the control system, Identifying the deflection of the measuring instrument based on the measured value of the parameter, and Identifying a reference position based on the identified deflection and the obtained position of the first tip.

[0054] Similarly, the step of identifying the auxiliary position may include the following: Moving the measuring instrument towards the auxiliary point, Detecting that the second tip has contacted the auxiliary point based on the measured value of the parameter, Stopping the movement of the measuring instrument, Obtaining the position of the first tip based on the position of the tool body monitored by the control system, Identifying the deflection of the measuring instrument based on the measured value of the parameter, and Identifying the auxiliary position based on the identified deflection and the obtained position of the first tip.

[0055] When attaching a new workpiece having a pre-formed circular hole to the spindle of a machine tool, such a hole may not always be perfectly aligned with the central axis of the spindle, and the hole may not always be a perfect circular cylinder. Thus, according to some embodiments, a machining step of machining the inner surface of the hole may precede the probing procedure. In this way, the hole that will subsequently undergo the probing procedure will have a circular cross-section and will be centered with respect to the central axis of the spindle. As a result, the true spatial location of the reference point in the coordinate system of the machine tool along the movement direction of the measuring instrument when measuring the workpiece will be reflected with high accuracy in the radius of the hole identified using the probing procedure.

[0056] Depending on the machine tool, it may have a dedicated probing surface configured as an inherent part of the machine tool, and this probing surface can be moved to the working position, which, as described above, will be used as a reference point when calibrating the machining system. However, nevertheless, it may be beneficial to first perform a probing procedure similar to the above-described procedure on the hole in the workpiece and use the results of such a probing procedure to confirm or update the true spatial position of the probing surface. In this case, for example, the difference between the radius of the hole specified using a measuring instrument equipped with a probing head as considered above and the specified reference position of the first tip can be regarded as the offset error of the machining system at that time. Subsequently, when measuring the position of the reference point on the probing surface using a measuring instrument equipped with a probing head as well, the true spatial location of this reference point can be specified simply by adding the offset error to the specified position of the tip when contacting such a reference point. Subsequently, the probing surface can be used as a reference point in any subsequent calibration, for example, when the measuring instrument corresponds to a cutting tool, that is, when the tool body is equipped with a cutting head instead of a probing head and the first tip is located on the cutting edge, in a subsequent calibration.

[0057] According to some embodiments, the parameter to be measured is strain, that is, the sensor disposed on the tool body is a strain sensor.

[0058] Strain can be easily measured using an affordable sensor and can be utilized to identify the deflection of the measuring instrument and also to determine that the tip has come into contact with the workpiece.

[0059] According to some embodiments, the method further includes identifying the applied force of the measuring instrument when it is detected that the tip has contacted a point on the machined surface of the workpiece based on the measured parameter. For example, the applied force can be identified based on the strain measured in the tool body, but it is also necessary to identify the relationship between the measured strain and the applied force of the measuring instrument.

[0060] According to some embodiments, the relationship between the measured strain and the applied force can be pre-identified in a separate procedure, for example, by applying a known force to the measuring instrument, measuring the resulting strain, and defining the coefficient characterizing the relationship as the measured strain divided by the known force. Such a coefficient may be stored in a memory or other storage medium and read therefrom to be used to identify the applied force when the method is executed.

[0061] By detecting the applied force, it is possible to detect how firmly the tip is pressed against the surface of the workpiece. If the applied force is too high, especially when the measurement is performed using a cutting head instead of a probing head, i.e., when the tip is located on the cutting edge, the tip may damage the surface. On the other hand, if the applied force is too low, it may become difficult to obtain accurate measurement values that are not affected by noise and vibration in the machining system.

[0062] Accordingly, according to some embodiments, the step of detecting that the first tip has contacted a point on the machined surface of the workpiece and / or the step of stopping the movement of the measuring instrument includes moving the measuring instrument towards the workpiece and continuing until a predetermined amount of applied force of the measuring instrument is specified, and then stopping the movement. The predetermined amount of applied force may correspond to a threshold value at which contact between the first tip and the point on the machined surface is considered to be detected. Contact between the first tip and the point on the machined surface may actually be detected earlier or at least made detectable with a smaller magnitude of applied force, however, the measuring instrument can still be further moved towards the workpiece until a predetermined magnitude of applied force is specified in order to perform a stable measurement that is less affected by vibrations and other disturbances.

[0063] The applied force of a predetermined amount should be large enough so that the influence of the vibration and signal noise of the machine tool is eliminated or at least reduced. This is particularly important when the tool body is long, that is, when the distance between the tip and the position where the tool body is attached to the machine tool is large. Such a long tool body is usually required, for example, when machining a deep hole machined in a workpiece and measuring its inner diameter. However, the applied force of a predetermined amount should not be so large as to damage the surface when the tip is pressed against the surface of the workpiece. By appropriately selecting the amount of the predetermined applied force, the position of the first tip obtained from the control system represents a position where the tip is firmly pressed against the surface so that stable measurement can be performed without damaging the surface. To achieve this, based on the characteristics of the tool body in use, a predetermined amount of applied force can be selected. According to some embodiments, the applied force of a predetermined amount can be in the range of 5N to 100N, for example, in the range of 10N to 50N, or in the range of 15N to 30N, etc. As an example, the amount of the applied force of a predetermined amount can be 20N, or substantially 20N, which may be suitable for a tool body with a diameter of 60mm and a length of 720mm. For a tool body with a diameter of 40mm to 100mm and a length 8 to 16 times the diameter, a predetermined amount of applied force in the range of 5N to 100N may be suitable, but this may also be used for other dimensions. In the case of a very large (i.e., rigid) tool, it may be beneficial to use a predetermined amount of applied force greater than 100N.

[0064] As discussed, a predetermined amount of applied force may represent a threshold at which a stop command is sent to the control system. Depending on the system's latency, the measuring instrument may continue to move a short distance before actually stopping, after which the resulting position of the tip is obtained from the control system. Thus, the predetermined amount of applied force does not necessarily represent the actual applied force when the measuring instrument stops. Accordingly, the deflection of the measuring instrument does not necessarily correspond to a predetermined amount of applied force, and is determined when the measuring instrument actually stops such that the true deflection of the measuring instrument is used as a basis for specifying the position of the surface point.

[0065] According to some embodiments, the deflection of the measuring instrument is determined based on the strain measured in the measuring instrument, but it is also necessary to specify the relationship between the measured strain and the deflection of the measuring instrument.

[0066] As discussed, the sensor disposed on the tool body may be a strain sensor, whereby the strain of the measuring instrument can be measured. The relationship between the measured strain and the deflection of the measuring instrument can be specified in advance in a separate procedure, for example, by deflecting the measuring instrument by a known distance, measuring the resulting strain, and defining the coefficient characterizing the relationship as the measured strain divided by the known deflected distance. Such a coefficient may be stored in a memory or other storage medium and retrieved therefrom for use in determining the deflection of the measuring instrument based on the measured strain. The relationship between strain and deflection may depend not only on that particular tool body but also on various other parameters of the machining system. Accordingly, each time the tool body is installed in a new machine, the specific relationship between the measured strain and the deflection may be specified.

[0067] As described above, according to some embodiments, the step of identifying the deflection and / or applied force of the measuring instrument may include measuring the strain in the measuring instrument. However, it is also contemplated that some of the parameters used in the method may be identified by other means. For example, the deflection of the measuring instrument may be measured using an optical sensor.

[0068] For example, by using strain sensors with different orientations arranged on the tool body, it may be possible to measure strains, deflections, and / or forces in various directions with respect to the measuring instrument. However, unless explicitly stated otherwise, any reference to strain, deflection, and / or force made herein is in relation to such parameters in the direction of movement of the measuring instrument towards the workpiece during measurement of the workpiece. Thus, by way of example, when identifying the position of a point on the inner circumference of a hole, the deflection identified refers to the radial deflection with respect to the hole, more precisely, the radial deflection in the direction in which the measuring instrument moves during measurement of the workpiece.

[0069] When the cutting edge is part of a replaceable cutting insert disposed in the cutting head, such a cutting insert may be subject to wear caused by machining and may need to be replaced periodically. In that case, when replacing the cutting insert, the machining system can be recalibrated simply by identifying a new offset based on the assumption that a point on the surface of the workpiece that was recently machined and measured (using the old cutting insert) represents a reference point having a known spatial location.

[0070] Correspondingly, when replacing a machined workpiece with a new workpiece to be machined without changing the tool body, cutting head, or cutting insert, the previously used offset remains valid and the cutting tool can be used for both machining and measuring the new workpiece without the need for a new probing procedure.

[0071] However, nonetheless, recalibrating the machining system and / or repeating the probing procedure at regular intervals may be beneficial to ensure that the machining system is properly calibrated.

[0072] According to a second aspect, the present invention is a machining system operable to identify the position of a point on a machined surface of a workpiece, a machine tool, a cutting tool comprising a tool body disposed on the machine tool and having at least one sensor, and a control system adapted to control and monitor the position of the tool body and comprising, whereby the machining system is configured to perform a method according to any of the method steps described herein.

[0073] The machining system preferably comprises a processing circuit configuration and a storage medium such as a memory.

[0074] The processing circuit configuration and the storage medium may be an integral part of the machine tool and the control system, or may be arranged connected thereto. Alternatively, the processing circuit configuration and / or the storage medium may be located in a computer or server remote from the machine tool and the control system, but can be communicatively coupled to the control system, for example via a communication interface, such that control instructions to be executed by the control system, such as control instructions to stop the movement of a measuring instrument, can be sent to the control system, or coefficients and sensor data necessary to perform the method can be received and transmitted. Accordingly, the processing circuit configuration may be configured to execute a computer program stored in the storage medium that triggers at least some of the method steps to be performed. The storage medium can also store, if necessary, the output from the sensors, and the measurement results, and other parameters necessary to perform the method.

[0075] Thus, according to a third aspect, the present invention relates to a computer program comprising computer-readable instructions executable in a machining system according to the second aspect of the present invention, the computer-readable instructions causing the machining system to execute a method according to any of the method steps described herein.

[0076] In this case, the method described herein may be embodied by one computer program or a plurality of computer programs that may exist in various forms. For example, they may exist as a software program composed of program instructions for executing some of the method steps, and may also be embodied on a computer-readable medium.

[0077] According to some embodiments, a processing circuit configuration configured to execute a computer program that causes a machining system to execute a method is located in an external computer communicatively coupled to a control system, and execution of the computer program may trigger execution of other computer programs stored in the control system, for example, a program for controlling the position of a tool body and machining a workpiece, and a program for reading data from the control system, in order to execute the method. Thus, the external computer may be configured to receive signals from at least one sensor disposed on the machine tool and / or on the tool body, analyze the signals, detect that the tip has contacted the surface, send instructions to the control system to stop the measuring instrument based on such signals, identify the deflection of the measuring instrument, and be used to identify the position of points on the machined surface.

[0078] As already discussed, the sensor disposed on the tool body may be a strain sensor. The strain sensor may be any type of sensor capable of detecting strain, such as a sensor based on a strain gauge resistor, such as a resistance foil strain gauge. Alternatively, the strain sensor may be, for example, a piezoelectric sensor, a force transducer, an optical strain gauge, or a surface acoustic wave (SAW) strain sensor. The strain sensor may be disposed, for example, along the tool body (or integrated with the tool body), such as inside the tool body, so as to be protected from chips of the material cut from the workpiece during machining. Alternatively, the strain sensor may be disposed on the outer surface of the tool body.

[0079] The output from the strain sensor may be transmitted, for example, wirelessly or via a wire, to a processing circuit configuration where the sensor output is processed and utilized to perform the method according to the present disclosure.

[0080] Accordingly, the tool body may further comprise a strain sensor and means for transmitting the sensor output, as well as a battery or some other power source for powering any other electronic components disposed on the tool body. For example, a memory and / or a processor may be locally disposed on the tool body, for example, in the form of one or more microcontrollers, where the sensor output may be read and collected before being wirelessly transmitted to an external computer.

[0081] According to some embodiments, the tool body further comprises a damper. A measuring instrument including a damper is particularly suitable for achieving reliable measurement results when using the method according to the present invention. The reason is that vibrations in the machining system that may be present during measurement and that may interfere with the measurement are reduced.

[0082] Further possible features and advantages of this solution will become apparent from the following detailed description.

[0083] Here, with reference to the following attached drawings, the solution will be described in more detail by way of exemplary embodiments.

Brief Description of the Drawings

[0084]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figures 6a - 6c

Modes for Carrying Out the Invention

[0085] All the figures are schematic and are not necessarily drawn to an exact scale. Generally, only the parts necessary to detail each embodiment are shown, and the other parts are omitted or merely suggested. Unless otherwise indicated, like reference numerals refer to like parts in different figures.

[0086] Briefly described, the present solution relates to a method and system for measuring a workpiece by using the same sensor-equipped tool body as that used for machining the workpiece after machining the workpiece. According to the embodiments described below, measuring the workpiece includes moving a measuring instrument towards the workpiece and stopping the movement of the instrument when the tip of the measuring instrument hits a point on the surface being measured. Measuring further includes identifying the deflection of the measuring instrument and then identifying the position of the point on the surface based on the identified deflection and the position of the tip obtained from the control system. In some embodiments, the offset value of the machining system can be obtained before machining the workpiece, which makes the method even more efficient and accurate.

[0087] One insight related to such embodiments is that there will be a small delay between when the tip contacts the workpiece and when the system detects such contact and stops the measuring instrument, so the measuring instrument will deflect to some extent. By measuring this deflection together with the position of the tip obtained from the control system, an accurate determination of the spatial location of the point on the surface can be achieved.

[0088] In some embodiments, to further simplify the method, a strain sensor can be used in the tool body and the relationship between the strain and the deflection of the measuring instrument can also be used by using the strain as a measure of the deflection. To further simplify the method, in particular, the relationship between the applied force and the strain can also be used to control the amount of force applied so that the contact between the tip and the workpiece is accurately detected.

[0089] Referring now to FIG. 1, a system according to the present disclosure is described in which the method described herein can be implemented.

[0090] System 100 includes a machine tool 102 to which a cutting tool 104 is connected, and a control system 150 adapted to control and monitor the position of the cutting tool.

[0091] The cutting tool 104 includes a tool body 105 and a cutting head 106 disposed at an end of the tool body 105. The cutting head 106 includes a cutting edge 107 adapted to engage a workpiece to separate material (e.g., metal) from the workpiece. According to this embodiment, the cutting edge 107 is part of a replaceable cutting insert disposed within an insert seat of the cutting head.

[0092] The control system 150 schematically shown in FIG. 1 is shown as an integral part of the machine tool 102 and may include, for example, a programmable logic controller (PLC) and a numerical control device (NC).

[0093] The machining system 100 further includes a processing circuit configuration and a memory. The processing circuit configuration and the memory may be an inherent part of the control system 150 of the machine tool. In the embodiment shown in FIG. 1, an external computer 155 communicatively coupled to the control system 150 via a communication interface 145 includes a memory and a processing circuit configuration configured to execute the methods described herein.

[0094] The processing circuit configuration may include one or more programmable processors, application specific integrated circuits, field programmable gate arrays, or combinations thereof (not shown) adapted to execute instructions. The memory includes instructions executable by the processing circuit configuration, whereby the machining system 100 is operable to execute the methods described herein.

[0095] Parts of the machining system 100 that execute the method, such as the control system 150 and / or the external computer 155, may be a group of devices, in which case the functionality for executing the method is distributed among various physical or virtual devices of the system. In other words, the part of the machining system 100 that executes the method may be a cloud solution, i.e., may be deployed as cloud computing resources that can be distributed within the machining system 100.

[0096] The instructions executable by the above processing circuit configuration may be configured as a computer program, for example, stored in a memory. The processing circuit configuration and the memory may be configured as a lower-level configuration. The lower-level configuration may be a microprocessor and appropriate software and storage therefor, a programmable logic device, a PLD, or other electronic components / processing circuits configured to execute the methods described herein.

[0097] When executed on the machining system 100, the computer program may comprise computer-readable code means for causing the machining system 100 to execute the method steps described in any of the embodiments described herein. The computer program may be carried by a computer program product connectable to the processing circuit configuration. The computer program product may be a memory. The memory may be realized, for example, as RAM (Random Access Memory), ROM (Read Only Memory), or EEPROM (Electrically Erasable Programmable ROM). Further, the computer program may be carried by a separate computer-readable medium such as a CD, DVD, or flash memory, from which the program can be downloaded to the memory. Alternatively, the computer program may be stored, for example, in a connected server or other entity accessible to the machining system 100 via the communication interface 145. The computer program may then be downloaded from the server to the memory.

[0098] The tool body 105 is an elongated element or an elongated member. In this embodiment, the tool body 105 is a cylindrical element extending along the axis 111.

[0099] At the end of the tool body 105, a mechanical interface 140 is arranged for attaching the tool body and thus the cutting tool 104 into the machine tool 102. In the embodiment shown in FIG. 1, the cutting tool 104 is used for internal diameter turning in which material is removed from the inner surface of the workpiece 130, for example, from within the hole 131 of the workpiece. Internal diameter turning is sometimes also called boring.

[0100] The tool body 105 further comprises a sensor 115. In this embodiment, the sensor is a strain sensor arranged on the outer part of the tool body 105, and the cutting tool 104 further comprises a damper 118 arranged inside the tool body 105. The damper may be used to suppress vibrations when machining deep inside the hole, thus improving the machining result. Such a damper also contributes to the realization of accurate measurement according to the present invention because the vibrations of the tool body that could normally impede measurement are reduced.

[0101] The machine tool 102 further comprises a spindle 120 for rotating the workpiece 130 about the central axis C of the spindle. The cutting tool 104 is attached via the mechanical interface 140 so as to be movable towards the workpiece 130 to separate material from the workpiece 130 as the workpiece 130 rotates. In this embodiment, the workpiece 130 has a hole 131, and within this hole 131, the cutting tool 104 can separate material to enlarge the hole 131.

[0102] As already described, the machine tool may comprise a communication interface 145 for communicating with an external computer 155, for example to send data from the control system 150 to the external computer 155 and / or to receive control instructions from the external computer 155 in the control system. The communication interface 145 may also be used, for example, to send sensor output from the sensor 115 to the external computer 155. However, in other embodiments, such sensor output is sent directly from a separate communication interface disposed on the cutting tool to the external computer 155.

[0103] The signaling provided by the communication interface 145 within the machine tool and / or the communication interface disposed on the cutting tool may be provided via a wired signal or a wireless signal, such as Bluetooth(R). The external computer 155 may have a user interface, for example, for showing the results of the measurement to a human operator using the machine tool 102. The computer 155 may be, for example, a personal computer or a handheld device such as a mobile phone or a tablet computer.

[0104] Referring now to FIG. 2, the steps of a method for identifying the location of a point on the surface of a workpiece in a machining system according to an embodiment are described next. The surface of the workpiece is typically a machined surface that requires measurement to determine whether the workpiece or a part of the workpiece is within the required tolerances.

[0105] Optionally, the method includes obtaining 202 the spatial location of a reference point and / or obtaining an offset error based on such a reference point or based on other reference points having known spatial locations, and calibrating 204 the machining system based on such offset error.

[0106] The method includes machining a workpiece 206 using a cutting edge of a cutting tool. The machining can be any type of machining using a cutting tool, such as turning or boring. According to some embodiments, machining the workpiece 206 includes enlarging a hole in the workpiece. The machining may include machining the entire workpiece until it is finished, or may include finishing one or more features of the workpiece.

[0107] The method further includes measuring the workpiece using a measuring instrument having a tool body and a first tip after machining the workpiece. The measuring can be performed using the same cutting edge that is used for machining the workpiece, i.e., the tip utilized for measuring is located on the cutting edge. In other words, the cutting tool used to machine the workpiece can also be utilized as a measuring instrument for measuring the workpiece.

[0108] Measuring first includes moving the measuring instrument towards the workpiece while measuring a parameter using a sensor disposed on the tool body 208. The movement of the measuring instrument is performed in a controlled manner via a control system and is generally relatively slow so as not to hit the workpiece too hard.

[0109] Second, measuring includes identifying 209 a first position of a first tip of the measuring instrument where the first tip contacts a point on the machining surface, thereby identifying 209 the first position of the first tip of the measuring instrument that indicates the position of the point on the machining surface. According to the embodiment shown in FIG. 2, identifying 209 the position of a point on the surface may include several steps 210-218 described below.

[0110] Optionally, the method includes measuring 210 the applied force of the measuring instrument. Such measurement can be based on the strain in the measuring instrument, which is measured using a strain sensor disposed on the tool body.

[0111] According to the illustrated embodiment, measuring includes detecting 212 that the first tip of the measuring instrument has contacted a point on the surface of the workpiece. Detecting 212 can be performed using any type of sensor for detecting an interaction. In this embodiment, detecting 212 is performed by a strain sensor that measures the strain in the measuring instrument. The measured strain can be converted into an applied force using a pre-specified relationship between strain and force. Accordingly, the step 212 of detecting that the tip has contacted a point on the surface of the workpiece can correspond to measuring 210 a force that reaches or exceeds a predetermined force threshold.

[0112] According to the illustrated embodiment, measuring further includes stopping 214 the movement of the measuring instrument after detecting that the tip is in contact with the workpiece. Depending on the system and implementation, there may be a slight delay between the detection of the contact between the tip and the workpiece and the actual stopping of the movement of the measuring instrument.

[0113] According to the embodiment shown, measuring further includes obtaining the position of the tip 216 based on the position of the tool body monitored by the control system after the measuring instrument has stopped. Since the control system does not take into account the deflection of the tool, the obtained position of the tip may not be appropriate. This is schematically shown in FIG. 4 where the measuring instrument is shown as a cutting tool, i.e., the tip is located on the cutting edge 107 of the cutting tool. The cutting tool is shown in the state during measurement immediately after the tool has stopped and is thus deflected to the maximum extent. For the purpose of explanation, in FIG. 4, the deflection of the cutting tool due to the cutting edge being pressed against the surface of the workpiece 130 is greatly exaggerated. The non-deflected tool body 105' at the time when the tip of the cutting edge 107 first contacts the workpiece is shown by the dashed line. According to this embodiment, the position of the tip of the cutting edge 107 in the moving direction of the cutting tool when measuring the workpiece, which is controlled and monitored by the control system 150, i.e., in the direction along the x-axis according to the conventional coordinate system of the lathe in this embodiment (see FIG. 5), depends on the distance L between the position of the tool body in such a direction, more precisely, the zero reference point 401 of the machine tool and the mechanical interface reference point 402 corresponding to a point on the tool body or a point on the tool holder to which the tool body is attached to the machine tool. x The position of the tip on the cutting edge along the x-axis monitored by the control system will in that case be equal to the sum of the distance L x and the known distance D along the x-axis between the mechanical interface reference point 402 and the tip on the non-deflected cutting edge 107 of the cutting tool.

[0114] Referring again to FIG. 2, according to the illustrated embodiment, measuring further includes identifying the deflection 218 of the measuring instrument. By identifying how the position of the tip is affected by the deflection of the tool, the position of the point on the workpiece can be more accurately identified. In some embodiments, identifying the deflection 218 is performed by a processing circuit configuration, e.g., a processor of an external computer 155, based on the measurement signals it receives.

[0115] Next, based on the identified deflection and the position of the tip obtained from the control system, the position of the point on the surface, i.e., the position of the tip where the tip contacts the point on the surface, is identified.

[0116] In this embodiment, identifying the deflection includes measuring the strain in the measuring instrument and converting the measured strain into the deflection of the measuring instrument. Referring to FIG. 1, the strain can be measured by the sensor 115, and the sensor output can be received by the external computer 155. Further, by using a pre-identified relationship between the measured strain and the applied force, the force can be continuously monitored based on the strain sensor signal. As soon as the force reaches a predetermined threshold, i.e., a predetermined amount of applied force, a stop command is triggered and sent from the external computer 155 to the control system 150 via the communication interface 145. When this command is received, the control system stops the movement of the measuring instrument. The strain at the measuring instrument at the stop position, measured by the strain sensor 115 and received by the external computer 155, is then used to identify the deflection of the measuring instrument by utilizing the pre-identified relationship between the measured strain and the deflection of the measuring instrument. Next, the external computer 155 identifies the position of the point on the machining surface based on the identified deflection and the position of the tip obtained from the control system via the communication interface 145. As discussed, the position obtained from the control system is based on the position of the tool body monitored by the control system and the known position of the tip relative to the tool body, but does not take into account the deflection of the measuring instrument.

[0117] According to some embodiments, the step of identifying the position of a point on the surface includes subtracting the deflection of the measuring instrument from the position of the obtained tip. Accordingly, referring to the example shown in FIG. 4 where the deflection of the cutting tool is ΔX, the position of the tip on the cutting edge 107 by the control system is L x +D, but the true position of the tip, and thus the position of the point on the workpiece surface, is L x +D - ΔX.

[0118] For a non-deflected measuring instrument, when the exact position of the tip of the measuring instrument in the coordinate system of the machine tool (e.g., relative to the central axis of the spindle of the machine tool) is unknown or uncertain, it may be preferable to calibrate the machining system by identifying the offset error before using the above-described method for identifying the position of a point on the machined surface of the workpiece.

[0119] FIG. 5 schematically shows a machining system 100 including a machine tool 102 as viewed from above, and the cutting tool is shown at a reference position where the tip on the cutting edge 107 is located on the central axis C of the spindle. At this reference position, the distance in the x direction between the machine tool zero reference point 401 and the machine interface reference point 402 corresponds to the radial offset RO. The position of the tip on the cutting edge 107 in the coordinates of the machine tool along the corresponding direction (i.e., along the x-axis) is defined in this case as the sum of the radial offset RO and the distance in the corresponding direction between the tip on the cutting edge 107 and the central axis C of the spindle. The radial offset RO may be stored in a memory and utilized by the control system when controlling and monitoring the position of the cutting tool. However, as already mentioned, due to inaccuracies caused, for example, by random deviations associated with the attachment of the cutting tool to the machine tool, or the joint between the cutting head and the tool body, or the joint between the cutting head and the cutting insert, the stored radial offset may not be appropriate, i.e., this offset does not represent the actual distance in the x-axis direction between the machine tool zero reference portion 401 and the machine interface reference point 402 when the tip on the cutting edge 107 is located on the central axis C of the spindle, and thus the position of the cutting edge 107 monitored by the control system may become inappropriate.

[0120] Accordingly, referring to FIG. 3, the spatial location of the reference point is obtained 202, the offset error of the measuring instrument, or the updated offset, is obtained based on such a reference point, and the machining system is calibrated 204 based on such an offset error or updated offset. Optional steps will be further described below.

[0121] According to some embodiments, the reference point is a point on the inner circumference of a hole in the workpiece to be machined. In that case, a method for obtaining the spatial location of such a reference point may include an initial machining step 302 of machining the workpiece 130 or a part of the workpiece to ensure that the hole 131 containing the reference point is a perfect circle and is centered about the central axis C of the spindle.

[0122] If there is an offset error not only in the radial direction but also in the axial direction of the cutting tool, i.e., along the longitudinal axis 111 of the tool body, such an axial offset error can also be identified during this initial machining step. For example, according to some embodiments in which a strain sensor is used to detect the deflection of the cutting tool, the axial offset error can be identified by detecting the change in the measured strain caused by engaging the workpiece when the cutting tool is moved axially to machine the inner surface of the hole in the workpiece. Accordingly, the axial position of the tip on the cutting edge when an increase in strain is detected can indicate the true axial offset AO (shown in FIG. 5) with respect to the machine interface reference point 402.

[0123] After the initial machining step 302, a probing procedure can be performed to identify the true spatial position of the reference point.

[0124] The probing procedure may include replacing the cutting head with a probing head 606 shown in FIGS. 6a - 6c, which has a first tip 601 and a second tip 602 arranged to face a reference point 603 and an auxiliary point 604, respectively, located on opposite sides of the inner diameter of the hole 131, and the distance PD between the first tip and the second tip is known. Thus, the same tool body 105 is used, and the probing head 606 is attached to the tool body 105 instead of the cutting head 106. In this state, the measuring instrument corresponds to a probe 600 comprising the tool body 105 and the probing head 606.

[0125] As shown in FIG. 6b, the probing procedure may further include measuring the workpiece by identifying a reference position P1 of the first tip 601 where the first tip 601 contacts the reference point 603, and identifying an auxiliary position P2 of the first tip 601 where the second tip 602 contacts the auxiliary point 604, as shown in FIG. 6c. According to some embodiments, each of these measurements can be performed in a manner similar to using the tip to identify the position of a point on the machined surface of the workpiece as described above.

[0126] Accordingly, the probing procedure may include moving the probe 600 towards the workpiece such that the first tip 601 approaches the reference point 603 or the second tip 602 approaches the auxiliary point 604 306.

[0127] Next, the probing procedure may include detecting a contact between the first tip and the reference point or between the second tip and the auxiliary point 308.

[0128] Next, the probing procedure may include stopping the movement of the probe 600 310.

[0129] Next, the probing procedure may include obtaining the position of the first tip 601 monitored by the control system after the probe 600 has stopped 312.

[0130] Next, the probing procedure may include identifying the deflection of the probe 600 314.

[0131] Next, the probing procedure may include identifying the position of the first tip 601 based on the identified deflection and the obtained position of the first tip 601 monitored by the control system 316.

[0132] As already described, when using a strain sensor disposed on the tool body 105 to detect the deflection of the measuring instrument, it is necessary to establish the relationship between strain and deflection for a certain tool configuration. Such a relationship may be specified in a separate procedure, but it can also be specified as an optional step during the probing procedure. In that case, the control system may be instructed to further move the probe 600 from the reference position where the probe is stopped towards the workpiece by a predetermined distance to a secondary position. In this regard, it should be noted that the further movement towards the workpiece does not result in actual movement of the tip (since the tip is already in contact with the surface of the workpiece), but only further deflects the probe 600 by the corresponding distance. Therefore, the relationship between strain and deflection can be obtained from the ratio between the difference between the respective strain measurement values obtained at the reference position and the secondary position and the distance by which the probe is instructed to move.

[0133] Thereafter, as shown in FIG. 3, steps 306 to 316 can be repeated 317 for points that have not yet been measured such that the reference position P1 and the auxiliary position P2 of the first tip 601 are specified by the location where the first tip 601 contacts the reference point 603 and the location where the second tip 602 contacts the auxiliary point 604, respectively.

[0134] The method further includes specifying 318 the spatial location of the reference point based on the specified reference position P1 and auxiliary position P2 of the first tip 601 and the known distance PD between the first tip and the second tip.

[0135] According to the embodiment shown, the spatial location of the reference point along the x-axis direction corresponds to the radius of the hole. In this case, since the sum of the known distance PD and the distance between the reference position P1 and the auxiliary position P2 corresponds to the diameter of the hole, the spatial location of the reference point can be specified as (P1 - P2 + PD) / 2.

[0136] As further shown in FIG. 3, when the spatial location of the reference point is known, it is possible to identify the offset error and calibrate the machining system based thereon, as described below at 204.

[0137] First, when calibrating the cutting tool used in subsequent machining, the probing head currently attached to the tool body is removed, a cutting head 106 having a cutting edge 107 is attached to the tool body 105, the measuring tool is made to correspond to the cutting tool 104, and a first tip arranged to contact the workpiece for measuring the workpiece is positioned on the cutting edge 107.

[0138] Next, according to some embodiments, the offset error can be identified using measurements performed in a manner similar to that for identifying the position of points on the machined surface of the workpiece as described above.

[0139] Correspondingly, a method for identifying the offset error may include moving the measuring instrument towards the reference point 320.

[0140] Next, based on the position of the tool body monitored by the control system, the position of the first tip whose tip contacts the reference point is identified. This may include, for example, the following steps: Step 321 of detecting that the first tip has contacted the reference point, Step 322 of stopping the movement of the measuring instrument, Step 323 of obtaining the position of the tip based on the position of the tool body monitored by the control system, Step 324 of identifying the deflection of the measuring instrument, and Step 325 of identifying the position of the tip based on the identified deflection and the obtained position of the tip.

[0141] Next, the method may include identifying an offset error of the measuring instrument based on a known spatial location of a reference point and a specified position of the tip. According to some embodiments, the offset error is simply the difference between the specified position of the tip and the known location of the reference point.

[0142] Next, the machining system may be calibrated based on the identified offset error. For example, an updated offset corresponding to a previously stored offset adjusted by the offset error may be stored. Such an updated or calibrated offset is then used in place of the previously stored offset when controlling and monitoring the position of the tip of the measuring instrument.

[0143] After machining a hole in the workpiece, the diameter of the finished hole can be identified using a method similar to that described above with reference to FIGS. 6a - 6c (and preferably using the same or a similar probing head), i.e., when the first and second tips of the probing head are arranged to contact first and second points on opposite sides of the inner diameter on the inner circumference of the machined hole. This enables very accurate measurement of the diameter of the machined hole.

[0144] Although the foregoing description contains a number of specific items, they are not to be construed as limiting the scope of the concepts described herein, but rather as merely providing an explanation of some exemplary embodiments of the described concepts. It will be understood that the scope of the concepts described herein fully encompasses other embodiments that may be obvious to those skilled in the art, and thus the scope of the concepts described herein is not limited. References to elements in the singular are not intended to mean "one and only one" unless explicitly stated otherwise, but rather are intended to mean "one or more." All structural and functional equivalents of the elements of the above-described embodiments known to those skilled in the art are expressly incorporated herein by reference, and they are intended to be included herein. Further, in including an apparatus or method herein, it need not address every possible problem that the concepts described herein attempt to solve. In the figures used as examples, dashed lines generally mean that the features within the dashed lines are optional.

Claims

1. 1. A method for locating a point on a machined surface of a workpiece in a machining system, the method comprising: A machine tool (102); a cutting tool (104) disposed on the machine tool (102) and comprising a tool body (105) having at least one sensor (115); a control system (150) adapted to control and monitor the position of said tool body (105); Equipped with The method comprises: Machining (206) the workpiece with the cutting tool (104), and then measuring the workpiece (130) using a measuring instrument (104, 600) comprising the tool body (105) and a first tip, moving (208) the measurement tool toward the workpiece (130) while measuring a parameter using the sensor (115); and and determining (209) a first position of the first tip where the first tip contacts the point on the machined surface based on the position of the tool body (105) monitored by the control system (150) and the value of the parameter measured by the sensor (115), thereby determining (209) the first position of the first tip, which indicates the position of the point on the machined surface. measuring the workpiece (130), A method comprising:

2. Identifying the first position of the first tip of the measurement tool comprises: Detecting (212) when the first tip contacts the point on the machined surface of the workpiece based on the measured value of the parameter; stopping the movement of the measuring instrument (214); obtaining (216) a position of the first tip based on the position of the tool body monitored by the control system; determining (218) a deflection of the measurement tool based on the measured value of the parameter; determining the first position of the first tip based on the determined deflection and the obtained position of the first tip; The method of claim 1 , comprising:

3. The method of claim 1, wherein the point on the machined surface of the workpiece is a point on the inner periphery of a hole (131) in the workpiece.

4. The method of claim 1 , wherein the measuring tool is the same as the cutting tool and the first tip is located on a cutting edge (107) of the cutting tool.

5. 2. The method of claim 1, wherein after machining the workpiece and before measuring the workpiece, the method further comprises attaching the probing head to the tool body such that the measuring instrument comprises the tool body and a probing head, and wherein the first tip is located on the probing head.

6. the point on the machined surface of the workpiece is a first point on an inner periphery of a hole in the workpiece at a first location along the extension of the hole, the measuring tool further comprising a second tip located a known distance from the first tip, the first and second tips being positioned opposite the first and second points on the machined surface, respectively, the second point being located opposite the first point on the inner diameter of the hole, and the step of measuring the workpiece includes: determining a second position of the first tip where the second tip contacts the second point based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor; and determining the inner diameter of the hole at the first location based on the determined first and second positions of the first tip and the known distance between the first tip and the second tip; The method of claim 1 further comprising:

7. repeating the step of measuring the workpiece and determining the inner diameter of the hole for an inner periphery of the hole in the workpiece at one or more additional locations along the extension of the hole, the additional locations being spaced from the first location; determining a deviation from a cylindrical shape of the hole based on the determined inner diameter at the first location and the one or more additional locations; and The method of claim 6 further comprising:

8. prior to the steps of machining and measuring the workpiece; moving (320) the measuring instrument towards a reference point having a known spatial location; determining a reference position of the first tip portion where the first tip portion contacts the reference point based on the position of the tool body monitored by the control system and the value of the parameter measured by the sensor (321-325); determining (326) an offset error based on the known spatial location and the determined reference position of the first tip; calibrating (327) the machining system based on the determined offset error; The method of claim 1 , preceded by

9. The reference point having a known spatial location is a point on the inner periphery of a hole in the workpiece, the known spatial location being identified in a probing procedure preceding the steps of claim 8, the measuring tool comprising a second tip (602) located a known distance (PD) from the first tip (601), and the probing procedure comprising: positioning the measuring tool such that the first tip (601) and the second tip (602) face the reference point (603) and an auxiliary point (604) on the inner circumference of the hole, respectively, the auxiliary point (604) being located opposite the reference point (603) on the inner diameter of the hole; measuring (306-316) the workpiece by determining a reference position (P1) of the first tip (601) where the first tip (601) contacts the reference point (603) and determining an auxiliary position (P2) of the first tip (601) where the second tip (602) contacts the auxiliary point (604); determining (318) the spatial location of the reference point based on the determined reference position (P1) and auxiliary position (P2) of the first tip (601) and the known distance (PD) between the first tip (601) and the second tip (602); The method of claim 8, comprising:

10. 10. The method of claim 9, wherein the probing procedure is preceded by a machining step (302) in which the inner surface of the hole is machined.

11. The method of claim 1 , wherein the measured parameter is strain.

12. 3. The method of claim 2, further comprising determining an applied force of the measuring tool when it detects that the tip has contacted the point on the machined surface of the workpiece based on the measured parameter.

13. The method of claim 12 , wherein the applied force of the measuring instrument is determined based on a predetermined relationship between strain and applied force of the measuring instrument.

14. 13. The method of claim 12, wherein detecting when the tip has contacted the point on the machined surface of the workpiece and stopping the movement of the measuring tool comprises continuing to move the measuring tool toward the workpiece until a predetermined amount of applied force of the measuring tool is determined, and then stopping the movement.

15. The method of claim 14, wherein the predetermined amount of applied force is in the range of 5N to 100N.

16. The method of claim 2 , wherein the deflection of the measuring instrument is determined based on a predetermined relationship between strain and deflection of the measuring instrument.

17. A machining system (100) operable to identify a location of a point on a machined surface of a workpiece (130), comprising: A machine tool (102); a cutting tool (104) disposed on the machine tool (102) and comprising a tool body (105) having at least one sensor (115); a control system (150) adapted to control and monitor the position of the tool body (105); a processing circuit configuration; Memory and Equipped with A machining system (100) whereby said machining system (100) is configured to carry out the method according to any one of claims 1 to 16.

18. The machining system of claim 17, wherein the sensor (115) is a strain sensor.

19. 18. A computer program comprising computer readable instructions for execution on a machining system according to claim 17, said computer readable instructions, when executed on said machining system, causing said machining system to perform the method of claim 1.

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