Machining apparatus

Abstract

To provide a machining apparatus capable of highly accurately evaluating a burn state during machining using an eddy-current sensor regardless of a shape of a workpiece.SOLUTION: A machining apparatus 1 comprises: a workpiece rotation device which rotates a workpiece W; an eddy-current sensor 20 which is disposed to face a portion to be machined of the workpiece W, induces an eddy current inside the workpiece W by an excitation current, and outputs an alternating current output signal corresponding to a magnetic field generated by the eddy current; a feature information acquisition unit 43 which acquires, for each predetermined rotation angle of a workpiece rotation shaft, feature information obtained by associating imaginary-axis values and real-axis values when an output signal of the eddy-current sensor 20 is represented on a complex plane, with machining times of the workpiece W; a burn boundary reference storage unit 45 which stores a burn boundary reference indicating a boundary between a burn state and a non-burn state of the portion to be machined; and a burn state evaluation unit 48 which evaluates a burn state of the portion to be machined of the workpiece W during machining on the basis of the feature information and the burn boundary reference for each rotation angle.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a processing device. [Background technology]

[0002] Conventionally, when grinding a workpiece using a processing device, the temperature of the processed part of the workpiece tends to become high, which can cause grinding burns on the surface of the workpiece depending on the processing conditions. Grinding burns are undesirable because they can cause a decrease in the mechanical strength of the workpiece. One method for detecting such grinding burns is to evaluate the presence or absence of grinding burns and their depth by utilizing the fact that changes in the magnetic field caused by eddy currents generated in the workpiece by an excitation current differ depending on the presence or absence of grinding burns.

[0003] For example, in the configuration disclosed in Patent Document 1, the presence or absence of grinding burn is detected with high accuracy by comparing the output signals of eddy currents generated by two types of excitation currents with different frequencies using an eddy current sensor. Furthermore, in the configuration disclosed in Patent Document 2, the output signals of eddy currents generated by two types of excitation currents with different frequencies using an eddy current sensor are corrected to remove components of residual magnetic flux density remaining in the workpiece, thereby improving the accuracy of determining the presence or absence of grinding burn. In addition to these methods, the grinding burn condition on the workpiece surface is also evaluated by etching the workpiece after grinding with a corrosive solution such as nital and observing the surface condition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-106932 [Patent Document 2] Japanese Patent Application Publication No. 2018-189603 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the configurations and etching-based evaluations disclosed in Patent Documents 1 and 2 evaluate the grinding burn condition after the grinding process is completed, which requires waiting for the grinding process to finish before obtaining the grinding burn condition evaluation results, which takes time. Therefore, it has been considered to apply an excitation current to the workpiece during grinding and evaluate the grinding burn condition during processing based on the signal acquired by an eddy current sensor. In this case, when the workpiece has a cylindrical or planar shape, the contact state between the tool and the workpiece and the contact state between the eddy current sensor and the workpiece are stable, resulting in a stable output from the eddy current sensor. However, when the workpiece has a non-cylindrical shape, such as a cam-shaped one, the curvature of the processing point changes depending on the phase of the cam, which changes the contact state between the tool and the workpiece and the position of the processing point. This causes large variations in the eddy current sensor output, making it unstable and significantly reducing the accuracy of the grinding burn evaluation. Therefore, a configuration that can accurately evaluate grinding burn condition during processing using an eddy current sensor, regardless of the shape of the workpiece, has not yet been realized.

[0006] The present invention provides a processing apparatus that can evaluate the burn state with high accuracy during processing using an eddy current sensor, regardless of the shape of the workpiece. [Means for solving the problem]

[0007] One aspect of the present invention is A processing device that processes the surface of a workpiece multiple times with a tool to form it into a final target shape, a workpiece rotation device that rotates the workpiece around a workpiece rotation axis; an eddy current sensor disposed opposite to a portion to be machined of the workpiece, which induces an eddy current inside the workpiece by an excitation current and outputs an AC output signal corresponding to a magnetic field generated by the eddy current; a characteristic information acquiring unit that acquires characteristic information, which associates an imaginary axis value and a real axis value when an output signal output by the eddy current sensor is represented on a complex plane in a Cartesian coordinate system with a time when the workpiece is machined, for each predetermined rotation angle of the workpiece rotation axis; a burnt boundary reference storage unit configured to store, for each of the predetermined rotation angles, a burnt boundary reference corresponding to a burnt boundary signal that is an output signal of the eddy current sensor indicating a boundary between a burnt state and a non-burnt state of the workpiece portion displayed on the complex plane; and a burnt state evaluation unit that evaluates the burnt state of the processed portion of the workpiece being processed based on the characteristic information and the burnt boundary criterion for each rotation angle. [Effects of the Invention]

[0008] According to the above aspect, an eddy current sensor detects eddy currents generated inside a workpiece during machining due to an excitation current, and characteristic information, in which imaginary and real axis values ​​when the output signal from the eddy current sensor is represented on a complex plane in Cartesian coordinate system and time information are linked, is acquired for each predetermined rotation angle of the workpiece rotation axis, and a burn boundary criterion indicating the boundary between a burnt state and a non-burnt state of the machined portion for each rotation angle is stored. Then, for each rotation angle, the burnt state of the machined portion of the workpiece during machining is evaluated based on the characteristic information and the burnt boundary criterion. This allows for highly accurate evaluation of the burnt state of the machined portion during machining, regardless of the shape of the workpiece, whether it is circular or non-cylindrical.

[0009] As described above, according to the above aspect, it is possible to provide a machining apparatus that can evaluate the burn state during machining with high accuracy using an eddy current sensor, regardless of the shape of the workpiece. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a conceptual diagram showing the configuration of a processing device in the first embodiment. [Figure 2] FIG. 1 is a functional block diagram showing the configuration of a burnt state evaluation device according to a first embodiment. [Figure 3] 4 is a conceptual diagram showing a first positional relationship between a tool, a workpiece, and an eddy current sensor during machining in the first embodiment. FIG. [Figure 4] FIG. 2 is a diagram for explaining an outline of synchronous detection in the eddy current sensor according to the first embodiment. [Figure 5] 6 is a conceptual diagram showing a second positional relationship between the tool, workpiece, and eddy current sensor during machining in the first embodiment. FIG. [Figure 6] 10 is a conceptual diagram showing a third positional relationship among the tool, workpiece, and eddy current sensor during machining in the first embodiment. FIG. [Figure 7] FIG. 3 is a conceptual diagram showing the relationship between the grinding load and the change in the output signal of the eddy current sensor on a complex plane when a cylindrical workpiece is ground in the first embodiment. [Figure 8] FIG. 10 is a conceptual diagram showing the relationship between the grinding load and the change in the output signal of the eddy current sensor on the complex plane when no grinding burn occurs in the rough machining process when grinding a cylindrical workpiece in the first embodiment. [Figure 9] FIG. 3 is a conceptual diagram showing feature information for each rotation angle of a workpiece on a complex plane in the first embodiment. [Figure 10] FIG. 3 is a partially enlarged view of a conceptual diagram showing feature information for each rotation angle of a workpiece on a complex plane in the first embodiment. [Figure 11] FIG. 3 is a partially enlarged view of a conceptual diagram showing feature information for each rotation angle of a workpiece on a complex plane in the first embodiment. [Figure 12] FIG. 2 is a flowchart of a grinding process in the first embodiment. [Figure 13] FIG. 3 is a flowchart of a burnt state evaluation process according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Embodiment 1) The burnt condition evaluation device 30 of the first embodiment evaluates the burnt condition of the workpiece W that is ground by the processing device. Each component will be described in detail below.

[0012] 1. Configuration of processing device 1 In the first embodiment, the processing apparatus 1 includes a machine tool 2 and a processing unit 3. The machine tool 2 is not limited to a specific one and can be a grinding machine, a lathe, or the like. In this embodiment, the grinding machine 2 will be described. As shown in FIG. 1 , the grinding machine 2 has a grinding wheel 16 as a tool, which is a rotating body. The grinding machine 2 rotates the workpiece W around a workpiece rotation axis (C-axis), rotates the grinding wheel 16 around a grinding wheel rotation axis 16c of the grinding wheel 16, and moves the grinding wheel 16 relatively close to the workpiece W in a direction intersecting the axis of the workpiece W, thereby grinding the outer or inner peripheral surface of the workpiece W. The grinding machine 2 can be a table traverse type grinding machine, a wheelhead traverse type grinding machine, or the like. The grinding machine 2 can also be a cylindrical grinding machine, a cam grinding machine, or the like. In this embodiment, a cam grinding machine is used as the grinding machine 2.

[0013] In this embodiment, as shown in FIG. 1, the workpiece W is a member constituting a camshaft having a shaft Wa equipped with multiple cams Wb. The outer peripheral surfaces of the cams Wb serve as the processed portion. Each cam Wb is formed radially eccentrically relative to the shaft Wa. The shape of the workpiece W is not limited to a camshaft, and may be any shape, such as an eccentric shaft used in a reducer or a cylindrical shape with an inner peripheral surface. If the workpiece W is cylindrical, the inner peripheral surface of the workpiece W may serve as the processed portion.

[0014] In this embodiment, the workpiece W is supported by workpiece support members at both ends of the shaft Wa. However, the workpiece W shown in Fig. 1 is just an example, and the grinding machine 2 can grind workpieces having various shapes.

[0015] 1, the processing unit 3 includes a burn condition evaluation device 30 and a control device 31 that controls the grinding machine 2. As will be described later, the burn condition evaluation device 30 evaluates the burn condition caused by grinding on the workpiece W, and adjusts the grinding conditions for the workpiece W based on the evaluation results. The control device 31 controls the grinding machine 2, thereby controlling the grinding process.

[0016] The burn condition evaluation device 30 can function as a simulation device independent of the grinding machine 2 and the control device 31, or as a simulation device that operates in conjunction with the grinding machine 2 and the control device 31. In the former case, the burn condition evaluation device 30 can, for example, determine optimal grinding conditions without actually grinding the workpiece W. In the latter case, the burn condition evaluation device 30 can, for example, determine the presence or absence of grinding burn, adjust grinding conditions, or operate to affect various controls by processing in parallel with the grinding process of the workpiece W by the grinding machine 2. The burn condition evaluation device 30 can also be an embedded system in the grinding machine 2 and the control device 31.

[0017] 2. Configuration of the grinding machine 2 and the control device 31 The configuration of the grinding machine 2 will be described with reference to Fig. 1. In this embodiment 1, the grinding machine 2 is a wheelhead traverse type, for example. However, a table traverse type can also be used for the grinding machine 2. The grinding machine 2 mainly includes a bed 11, a headstock 12, a tailstock 13, a traverse base 14, a wheelhead 15, a grinding wheel 16, a sizing device 17, a coolant device 18, and an eddy current sensor 20.

[0018] The bed 11 is fixed on a mounting surface. The headstock 12 is provided on the upper surface of the bed 11, on the near side in the X-axis direction (the lower side in FIG. 1) and on one end side in the Z-axis direction (the left side in FIG. 1). The headstock 12 supports the workpiece W rotatably around the Z-axis with the center line C of the workpiece W as the center. The workpiece W is rotated by driving a motor 12a that constitutes a workpiece rotation device provided on the headstock 12. The tailstock 13 is provided on the upper surface of the bed 11, in a position facing the headstock 12 in the Z-axis direction, i.e., on the near side in the X-axis direction (the lower side in FIG. 1) and on the other end side in the Z-axis direction (the right side in FIG. 1). In other words, the headstock 12 and the tailstock 13 rotatably support both ends of the workpiece W.

[0019] The traverse base 14 is provided on the upper surface of the bed 11 so as to be movable in the Z-axis direction. The traverse base 14 is moved by driving a motor 14a provided on the bed 11. The grinding wheel head 15 is provided on the upper surface of the traverse base 14 so as to be movable in the X-axis direction. The grinding wheel head 15 is moved by driving a motor 15a provided on the traverse base 14. The grinding wheel 16 is rotatably supported on the grinding wheel head 15. The grinding wheel 16 is rotated by driving a motor 16a provided on the grinding wheel head 15. The grinding wheel 16 is composed of a plurality of abrasive grains fixed together with a bond material.

[0020] The sizing device 17 functions as a detector that measures the dimension (diameter) of the workpiece W. However, the detector is not limited to the sizing device 17, and may be a contact sensor having a single probe or a non-contact sensor such as a laser displacement meter. The sizing device 17 is provided so as to be movable in the Z-axis direction in synchronization with the traverse base 14 via a mechanism not shown.

[0021] 2-1. Eddy current sensor 20 The eddy current sensor 20 is provided so that its sensor head faces the processed portion of the workpiece W. The eddy current sensor 20 constitutes part of a burn condition evaluation device 30, which will be described later. In this embodiment 1, as shown in FIG. 3, the eddy current sensor 20 is located on the opposite side of the workpiece W from the grinding wheel 16. In FIGS. 1 and 3, the reference numeral 20 indicates the position of the sensor head, and the sensor body is not shown. Also, as shown in FIG. 3, the sensor head of the eddy current sensor 20 is biased toward the grinding wheel 16 via a spring 20b. As a result, the tip 20a of the sensor head of the eddy current sensor 20 is kept in contact with the workpiece W, and the portion of the workpiece W where the tip 20a contacts is the measurement point.

[0022] The eddy current sensor 20 induces an eddy current inside the workpiece W using an excitation current and outputs an AC signal corresponding to the magnetic field generated by the eddy current. The eddy current sensor 20 may be configured to be able to change the phase of the output signal. In this embodiment, as shown in FIG. 2 , the eddy current sensor 20 has a coil serving as an oscillator 21, and by supplying an excitation current to the coil, an output signal is applied to a probe 22 provided at the tip of the sensor head of the eddy current sensor 20, thereby applying a magnetic field to the workpiece W and inducing an eddy current inside the workpiece W. The eddy current sensor 20 then amplifies the change in impedance acquired via the probe 22 in an amplifier 23 and inputs it to a detector 24, extracts only the frequency component of the oscillator 21, and processes the signal in a signal processor 25.

[0023] The detection unit 24 detects the signal by synchronous detection. As shown in Fig. 4, the input signal v(t) to the detection unit 24 is a signal obtained by amplifying the output of the probe 22 in the amplifier unit 23, and v(t) is defined by the following equation (1). Here, t is time, A is amplitude, f is the frequency of the oscillator 21 inside the eddy current sensor 20, and θ is the phase difference with respect to the oscillator 21 inside the eddy current sensor 20.

[0024]

number

[0025] Then, in detection unit 24, v(t) that has passed through amplifier unit 23 is multiplied by a sine wave sin2πft, which has the same frequency as frequency f of oscillator 21. This is called x(t). Similarly, the result of multiplying by cos2πft is called y(t). x(t) and y(t) can be expressed as the following equations (2) and (3).

[0026]

number

[0027]

number

[0028] Next, x(t) and y(t) are passed through a low-pass filter having a sufficiently low cut-off frequency fc. Generally, the relationship fc << f holds. The first terms in equations (2) and (3) are AC because they contain t, while the second terms are DC because they do not contain t. Therefore, after passing through the low-pass filter, equations (2) and (3) become the real-axis signal X and the imaginary-axis signal Y shown in the following equations (4) and (5), respectively.

[0029]

Number

[0030]

Number

[0031] Then, as shown in the following equations (6) and (7), A and θ of v(t) can be obtained from equations (4) and (5).

[0032]

Number

[0033]

Number

[0034] ​​​​​The eddy current sensor 20 is configured to supply multiple excitation currents with different frequencies to the coil. In this first embodiment, the frequency of the excitation current can be set by a frequency setting unit (not shown). Since the penetration depth of the eddy current varies depending on the frequency of the excitation current, the frequency of the excitation current can be set according to the target penetration depth of the eddy current. The target penetration depth of the eddy current is set to match the surface layer where grinding burn may occur, and can be, for example, 1 to 100 μm from the processed surface, preferably 1 to 50 μm, and more preferably 10 to 30 μm. If the penetration depth is shallow, the sensitivity of the eddy current sensor becomes too high, resulting in a lower signal-to-noise ratio and reduced detection accuracy. On the other hand, if the penetration depth is deep, the detection level of the magnetic property change characteristic decreases in areas shallow from the processed surface, resulting in reduced detection accuracy.

[0036] The frequency of the excitation current according to the penetration depth can be set in the frequency band of 20 kHz to 200 MHz, preferably 100 kHz to 200 MHz, and more preferably 250 to 2500 kHz. In this embodiment, the frequency of the excitation current is set to 250 kHz so that the penetration depth of the eddy current is 30 μm.

[0037] The coolant device 18 supplies coolant from a coolant nozzle to the point where the workpiece W is ground by the grinding wheel 16. The coolant device 18 cools the collected coolant to a predetermined temperature and supplies it again to the grinding point. The coolant device 18 is capable of adjusting the flow rate and supply timing of the coolant. Note that in FIG. 1, reference numeral 18 indicates the position of the coolant nozzle. Although not shown, a temperature sensor may be provided as a detector to acquire the temperature of the collected coolant.

[0038] 2-2.Control device 31 The control device 31 grinds the workpiece W by controlling the driving of the grinding wheel 16, the coolant device 18, etc. in the grinding machine 2 based on an NC program generated based on operation command data such as the shape of the workpiece W, the grinding conditions, the shape of the grinding wheel 16, and coolant flow rate or supply timing information. In particular, the control device 31 grinds the workpiece W until it reaches the finished shape (target shape) based on the grinding conditions created by the processing condition adjustment unit 50 (described later) and the diameter of the workpiece W measured by the sizing device 17. Furthermore, the control device 31 performs correction (truing and dressing) of the grinding wheel 16 by controlling a grinding wheel correction device (not shown) etc. at the timing to correct the grinding wheel 16.

[0039] 3. Configuration of the burnt condition evaluation device 30 As shown in FIG. 2, the burn condition evaluation device 30 includes an eddy current sensor 20, a workpiece rotation angle acquisition unit 40, a rotation angle conversion unit 41, a signal acquisition unit 42, a feature information acquisition unit 43, a time acquisition unit 44, The burnt condition evaluation device 30 includes a burnt boundary reference storage unit 45, a phase angle calculation unit 46, a distance calculation unit 47, a burnt condition evaluation unit 48, a burnt depth estimation unit 49, a processing condition adjustment unit 50, and a margin calculation unit 51, which are configured by a storage device or a computing device. The burnt condition evaluation device 30 also includes a burnt condition display unit 52 and a complex plane display unit 53, which are configured by a predetermined display device.

[0040] The workpiece rotation angle acquisition unit 40 acquires the rotation angle of the workpiece rotation device (workpiece motor) 12a. Then, the rotation angle conversion unit 41 converts the rotation angle so that the measurement position of the eddy current sensor 20 corresponds to the machining position of the tool 16.

[0041] Specifically, as shown in FIG. 3, the measurement position M1 where the tip 20a of the eddy current sensor 20 contacts the workpiece W is located on the imaginary line X0 connecting the rotation centers of the workpiece W and the tool 16. However, the machining position Q1, which is the position where the tool 16 contacts the workpiece W, changes depending on the rotation angle of the workpiece W. For example, in the example shown in FIG. 3, the machining position Q1 is not on the imaginary line X0. As shown in FIG. 5, it takes a rotation angle θ1 for the machining position Q1 to reach the measurement position Q1'. That is, the signal measured by the eddy current sensor 20 is information about the position machined a rotation of the rotation angle θ1 before. On the other hand, in the example shown in FIG. 6, it takes a rotation angle θ2 for the machining position Q2 to reach the measurement position Q2'. Therefore, the signal measured by the eddy current sensor 20 is information about the position machined a rotation of the rotation angle θ2 before. The rotation angle θ2 is different from the rotation angle θ1.

[0042] As described above, the correspondence between the measurement positions measured by the eddy current sensor 20 and the machining positions changes depending on the rotation angle of the workpiece W. Based on the rotation angle of the workpiece W acquired by the workpiece rotation angle acquisition unit 40, the rotation angle conversion unit 41 calculates the difference between the machining position rotation angle, which is the rotation angle of the machining positions Q1, Q2, and the measurement position rotation angle, which is the rotation angle of the measurement positions Q1', Q2' on the workpiece W, and converts the rotation angle of the workpiece W based on this difference so that the measurement positions Q1', Q2' become the machining positions Q1, Q2.

[0043] The signal acquiring unit 42 acquires the output signal P output from the eddy current sensor 20. The characteristic information acquiring unit 43 acquires the characteristic information. The characteristic information is information that links the imaginary axis value and real axis value when the output signal P acquired by the signal acquiring unit 42 is represented on a complex plane in a Cartesian coordinate system with time information that is the time when the workpiece W is ground. Then, the characteristic information acquiring unit 43 acquires the characteristic information for each predetermined rotation angle of the workpiece rotation axis (C-axis) after conversion by the rotation angle conversion unit 41.

[0044] For example, as shown in Fig. 9, the feature information at predetermined rotation angles R1 to Rn is displayed such that both the imaginary axis value and the real axis value of the output signal P expressed on the complex plane are linked to the elapsed time acquired by the time acquisition unit 44 (described later), and the start of the rough machining process is the origin. In this embodiment, feature information at the start and end of the rough machining process is plotted for each rotation angle in the rough machining process, and feature information for each rotation at each rotation angle in the finish machining process is plotted. The number of rotation angles R1 to Rn for which feature information is acquired and the rotation angles can be set as appropriate.

[0045] The time acquisition unit 44 acquires the elapsed time from the start time T0 of the rough machining step. In this embodiment, the grinding process S1 of the workpiece W is made up of a rough machining step S1a and a finish machining step S1b, as shown in Fig. 12. The rough machining step S1a includes a rough grinding step S11, and the finish machining step S1b includes a fine grinding step S12, a fine grinding step S13, and a spark-out step S14. Each step will be described later.

[0046] 2 stores the burnt boundary criterion. The burnt boundary criterion is a criterion corresponding to the burnt boundary signal, which is the output signal P of the eddy current sensor 20, indicating the boundary between the burnt state and the non-burnt state of the workpiece W expressed on the complex plane for each predetermined rotation angle of the workpiece W. In this embodiment, the burnt boundary criterion includes a reference phase angle φg, which is the phase angle of the burnt boundary signal relative to the output signal at the start of the rough machining process on the complex plane, and a reference distance Rw, which is a reference value of the distance from the start output signal to the burnt boundary signal.

[0047] The boundary between the burnt and non-burnt states of the workpiece, which defines the burnt boundary signal, will now be described in detail. Burnt refers to a significant change in mechanical properties due to the transformation of the base material of the workpiece by heat. A burnt state refers to a state in which burnt occurs, and a non-burnt state refers to a state in which no burnt occurs. The presence or absence of burnt can be determined based on whether a softened layer is formed due to thermal changes in the base material of the workpiece. Therefore, a burnt state can be determined when a softened layer is formed in the workpiece. A non-burnt state, in which grinding burn does not occur, can be determined when the base material of the workpiece remains or when a retained austenite-reduced layer, whose mechanical properties are closer to those of the base material than the softened layer, is formed. Based on this, in this embodiment, the boundary between the burnt and non-burnt states of the workpiece is defined as the boundary between the softened layer and the retained austenite-reduced layer.

[0048] When the output signal of the eddy current sensor 20 is plotted on a complex plane, the softened layer and the retained austenite-reduced layer are plotted at different positions due to the different magnetic properties. Figure 7 shows the relationship between the grinding load (grinding efficiency) and the change in the output signal P on the complex plane when a cylindrical workpiece W is ground using a grinding machine 2. First, the grinding load is successively increased from 0 to a, b, and c. The 0-a region shown in Figure 7 is a region where the retained austenite-reduced layer is formed because the grinding load is small and the amount of heat generated is small. Meanwhile, the a-b region shown in Figure 7 is a region where the softened layer is formed because the grinding load is larger and the amount of heat generated is greater than in the 0-a region. Furthermore, the b-c region shown in Figure 7 is a region where the grinding load is even larger and the amount of heat generated is even greater than in the a-b region, so a white layer is formed beyond the softened layer.

[0049] As shown in Figure 7, in the 0-a region (retained austenite reduced layer) where no burn occurs, the phase φ of the output signal on the complex plane is nearly constant, and the radius Rw (distance from the origin 0) increases as the grinding load increases. The phase in the 0-a region is taken as the reference phase angle φg. On the other hand, in the a-b region (softened layer) and the b-c region (white layer) where burn occurs, the phase φ increases as the grinding load increases (the burn becomes larger), but the radius R (distance from the origin 0) does not tend to gradually increase or decrease. From this, it can be determined that burn has occurred when the phase angle during the rough machining process is greater than the reference phase angle φg, with the start of the rough machining process being the reference (origin 0 on the complex plane).

[0050] Furthermore, when grinding a cylindrical workpiece W, if grinding burn does not occur during the rough cutting process and the base material remains (the grinding load is small), the output signal of the eddy current sensor 20 will have the relationship shown in Figure 8 on the complex plane. As shown in Figure 8, the distance from the origin 0 to the total output signal is smaller than in Figure 7, where grinding burn occurs, and the output signal is located within a circle of radius Rw near the origin 0. While there is no structural alteration due to grinding heat within this range, the output signal changes due to changes in mechanical properties due to the base material depth and drift of the eddy current sensor, which can cause variations in the value of phase φ even when grinding burn does not occur. For this reason, the area below radius Rw is considered to be in a non-burn state regardless of the phase φ, and this radius Rw is used as the reference distance.

[0051] The phase angle calculation unit 46 shown in Fig. 2 calculates the phase angle of the feature information acquired by the feature information acquisition unit 43 with respect to the start output signal, which is the output signal at the start of machining on the complex plane. For example, in the case of the rotation angle R1 shown in Fig. 9, the angle formed by the vector connecting the start time A1 of the rough machining process and the end time Ae of the rough machining process and the vector of the real axis of the complex plane is acquired as the phase angle φm.

[0052] The distance calculation unit 47 shown in FIG. 2 calculates the distance from the start output signal to the feature information on the complex plane. For example, in the case of the rotation angle R1 shown in FIG. 9, the length of the vector connecting A1 at the start of the rough machining process and Ae at the end of the rough machining process is obtained.

[0053] 2 evaluates the burn state of the processed portion of the workpiece W during processing based on the feature information and the burn boundary criterion for each rotation angle of the workpiece W. In this embodiment, it is evaluated that a burn has occurred at the processing position (rotation angle) corresponding to the time of the feature information when the phase angle φm calculated by the phase angle calculation unit 46 is equal to or greater than the reference phase angle φg and the distance Rm calculated by the distance calculation unit 47 is equal to or greater than the reference distance Rw.

[0054] The burn depth estimation unit 49 estimates the burn depth when the burn state evaluation unit 48 evaluates that there is a burn. The burn depth estimation unit 49 estimates the burn depth for each predetermined rotation angle of the workpiece W. The burn depth estimation method first extracts a group of characteristic information consisting of multiple pieces of characteristic information having the same rotation angle from the characteristic information in the finishing process. In this embodiment, the characteristic information having the rotation angle R1 shown in FIG. 9 is extracted as a group of characteristic information.

[0055] Next, on the complex plane, a first vector is derived, starting from first feature information having a first time included in the above feature information group and ending from second feature information having a second time which is one rotation after the first feature information, and a second vector is derived, starting from the above feature information and ending from third feature information having a third time which is one rotation after the second feature information.When the difference between the phase angle of the first vector and the phase angle of the second vector becomes less than a predetermined value, it is estimated that the depth removed from the workpiece from the start of the finishing process to the first time corresponds to the depth of the burn that had occurred at the end of the roughing process.

[0056] 9, for example, the first feature information having a first time point is defined as first feature information Bk at k rotations, the second feature information having a second time point is defined as second feature information Bk+1 at k+1 rotations, and the third feature information having a third time point is defined as third feature information Bk+2 at k+2 rotations. Then, as shown in Fig. 10, a first vector K1 is derived with the first feature information Bk as its start point and the second feature information Bk+1 as its end point, and a second vector K2 is derived with the first feature information Bk as its start point and the third feature information Bk+2 as its end point.

[0057] Next, when the difference between the phase angle φK1 of the first vector K1 and the phase angle φK2 of the second vector K2 becomes equal to or less than a predetermined value, it is estimated that the depth removed from the workpiece from the start of the finish machining process to the first time corresponds to the depth of the burn that occurred at the end of the rough machining process. In this embodiment, since the difference between the phase angle φK1 of the first vector K1 and the phase angle φK2 of the second vector K2 is approximately zero, it is estimated that the burn is removed during K rotations, and the depth removed from the workpiece from the start B1 of the finish machining process to the Kth rotation corresponds to the depth of the burn that occurred at the end of the rough machining process. In other words, it is estimated that the tool 16 has reached the burn boundary at the Kth rotation. The depth removed from the workpiece from the start B1 of the finish machining process to the Kth rotation is estimated to be the value obtained by multiplying the cutting depth of the workpiece W per rotation by the rotation speed K. Furthermore, from the second characteristic information Bk+1 and the third characteristic information Bk+2 onwards, since the second vector K2 is almost the same as the reference phase angle φg-180°, it can be estimated that the retained austenite reduced layer is being removed by grinding.

[0058] On the other hand, in the example of feature information having a rotation angle R1 shown in Fig. 9, for example, if the first feature information having a first time is the first feature information BL at L rotations, the second feature information having a second time is the second feature information BL+1 at L+1 rotations, and the third feature information having a third time is the third feature information BL+2 at L+2 rotations, then a first vector L1 is derived starting from the first feature information BL and ending at the second feature information BL+1, and a second vector L2 is derived starting from the first feature information BL and ending at the third feature information BL+2, as shown in Fig. 11. However, because the difference between the phase angle φL1 of the first vector L1 and the phase angle φL2 of the second vector L2 is not substantially zero, the burn remains after L rotations, and it is estimated that the depth of the burn that occurred at the end of the rough machining process is at least equal to or greater than the value obtained by multiplying the cutting depth of the workpiece W during one rotation by L.

[0059] The method for estimating the burn depth in the burn depth estimating unit 49 is not limited to the method of calculating the vector described above. For example, an approximation line may be created using three points on a complex plane, namely, the first feature information Bk, the second feature information Bk+1, and the third feature information Bk+2, and the slope of the approximation line may be set as φm and compared with the reference phase angle φg. The burn depth estimating unit 49 may estimate the burn depth for each full rotation angle of the workpiece W, but may also estimate the burn depth only for a rotation angle at which it is determined that a burn has occurred.

[0060] The processing condition adjustment unit 50 shown in Fig. 2 adjusts the grinding conditions for the workpiece based on the evaluation result of the burn depth estimation unit 49. For example, if the evaluation result indicates that grinding burn remains, the grinding efficiency in the rough grinding step S11 can be reduced so that no grinding burn remains, and the grinding burn (softened layer) generated in the rough grinding step S11 can be removed in the subsequent fine grinding step S12. Also, if the evaluation result indicates that no grinding burn remains, the grinding efficiency can be increased within a range in which no grinding burn remains, with reference to the margin described below.

[0061] The margin calculation unit 51 calculates the grinding margin of the workpiece W based on the evaluation result of the burn depth estimation unit 49. In the example of the rotation angle R1 shown in Fig. 9, the residual austenite reduced layer, which is not grinding burn, is ground after Bk, so no burn occurs after Bk. Therefore, the cutting depth after Bk is the margin.

[0062] The burnt state display unit 52 displays the evaluation result of the burnt state, and the complex plane display unit 53 displays the locus of the output signal P expressed on a complex plane.

[0063] 4. Grinding Process S1 Description The grinding process S1 will be described with reference to Fig. 12. As described above, the grinding process S1 is made up of a rough processing step S1a and a finish processing step S1b, with the rough processing step S1a including a rough grinding step S11, and the finish processing step S1b including a fine grinding step S12, a fine grinding step S13, and a spark-out step S14.

[0064] In the rough grinding step S11, the control device 31 rotates the grinding wheel 16 at a predetermined speed based on operation command data such as the shape of the workpiece W, grinding conditions, the shape of the grinding wheel 16, and coolant flow rate or supply timing information, to grind the workpiece W with a first depth of cut. In this embodiment, the workpiece W is non-cylindrical, and a camshaft with a cam is used. Note that the workpiece W may be cylindrical or columnar instead of non-cylindrical.

[0065] In the fine grinding step S12, the control device 31 grinds the workpiece W with a second cutting depth that is smaller than the first cutting depth. In the fine grinding step S13, the control device 31 grinds the workpiece W with a third cutting depth that is smaller than the second cutting depth. In the spark-out step S14, the workpiece W is rotated at a preset rotation speed to grind away the portion left unground in the fine grinding step S13, thereby achieving a target cross-sectional shape. The cutting depth in the spark-out step S14 can be set to zero.

[0066] The cutting depth can be adjusted by controlling the cutting position of the grinding wheel 16 with the control device 31. The first to third cutting depths in each of the steps S11 to S13 are appropriately set within a range that satisfies the above-mentioned relationship, and the actual cutting depth in the spark-out step S14 is substantially zero. The first cutting depth in the rough grinding step S11 is the largest, and the rough grinding step S11 has the highest grinding efficiency among the steps S11 to S14. Therefore, grinding burn occurs substantially only in the rough grinding step S11 (rough machining step S1a).

[0067] 5. Burn condition evaluation process S2 Next, the burnt state evaluation process S2 performed by the burnt state evaluation device 30 will be described with reference to the flow chart of Fig. 13. The burnt state evaluation process S2 is performed in parallel with the grinding process S1.

[0068] In the evaluation S2 of the grinding burn state, first, a first parallel process S21, S22 and a second parallel process S23, S24 are performed. In the first parallel process, after setting the frequency of the excitation current in the eddy current sensor 20 in step S21, an eddy current is generated in the workpiece W by the eddy current sensor 20 in step S22, and an output signal P, which is the output signal of the eddy current sensor 20, is acquired by the signal acquisition unit 42.

[0069] Meanwhile, in the second parallel processing, in step S24, the workpiece rotation angle acquisition unit 40 acquires the rotation angle of the measurement position of the workpiece W on the workpiece rotation device 12a. Then, in step S24, the rotation angle conversion unit 41 converts the rotation angle of the measurement position into the rotation angle of the processing position.

[0070] After the first and second parallel processes are completed, in step S25, the characteristic information acquisition unit 43 acquires characteristic information for each rotation angle of the processing position, the characteristic information being formed by linking the imaginary axis value and real axis value when the output signal P is represented on a complex plane in Cartesian coordinate format with time information elapsed since the processing start time. The acquired characteristic information can be displayed on the complex plane display unit 53 as a characteristic information group for each rotation angle. The time information is acquired by the time acquisition unit 44.

[0071] Then, in step S26, the phase angle calculation unit 46 calculates the phase angle φm on the complex plane in the feature information for each rotation angle in the rough machining process S1a, and the distance calculation unit 47 calculates the distance Rm from the origin on the complex plane in the feature information for each rotation angle in the rough machining process S1a. Note that the origin on the complex plane is the feature information at the start of the rough machining process S1a.

[0072] Thereafter, in step S27, the burn state evaluation unit 48 determines whether the distance Rm is greater than the reference distance Rw stored in the burn boundary reference storage unit 45. If it is determined that the distance Rm is not greater than the reference distance Rw, the process proceeds to No in step S27, and in step S28, it is determined that no burn has occurred, and the flow ends.

[0073] On the other hand, if it is determined that the distance Rm is greater than the reference distance Rw, the process proceeds to Yes in step S27 and then to step S29. Then, in step S29, the burn state evaluation unit 48 determines whether the phase angle φm is greater than the reference phase angle φg. If it is determined that the phase angle φm is not greater than the reference phase angle φg, the process proceeds to No in step S29, and in step S28, it is determined that no burn has occurred, and the flow ends.

[0074] On the other hand, if it is determined that the phase angle φm is greater than the reference phase angle φg, the process proceeds to Yes in step S29 and then to step S30. Then, in step S30, it is determined that grinding burn has occurred. After that, in step S31, the burn depth estimation unit 49 estimates the burn depth at the end of the rough machining process.

[0075] The burn depth at the end of the rough machining process in step S31 is calculated by calculating, for each rotation angle, the difference between the phase angle φK1 of the first vector K1 from a point on the complex plane rotated K times from the start of the finish machining process to a point on the complex plane rotated K+1 times, and the phase angle φK2 of the second vector K2 from a point on the complex plane rotated K times to a point on the complex plane rotated K+2 times.If this difference is less than a predetermined value (in this embodiment, when the difference is approximately 0), it is estimated that the depth removed from the machined part from the start of the finish machining process through K rotations corresponds to the burn depth that occurred at the end of the rough machining process.If the difference is not less than the predetermined value, it is estimated that a burn depth greater than the depth removed from the machined part through K rotations from the start of the finish machining process.

[0076] Furthermore, in step S32, the margin calculation unit 51 calculates the margin. The margin is calculated as the depth removed by the end of machining after K rotations when the difference between the phase angle φK1 of the first vector K1 and the phase angle φK2 of the second vector K2 becomes equal to or less than a predetermined value (in this embodiment, when the difference becomes approximately 0) in the finish machining step S1b. Note that if the difference between the phase angle φK1 of the first vector K1 and the phase angle φK2 of the second vector K2 does not become equal to or less than the predetermined value, the margin is set to 0, indicating that there is a burnt residue.

[0077] Thereafter, in step S33, the machining condition adjusting unit 50 adjusts the grinding conditions for grinding the next workpiece W based on the calculated margin, and the flow ends. That is, in this embodiment, the burn depth is estimated and the grinding conditions are adjusted before the next machining.

[0078] 6. Action and Effects According to the machining device 1 of this embodiment, an eddy current sensor detects eddy currents generated inside the workpiece during machining due to the excitation current. The output signal from the eddy current sensor is represented on a complex plane in Cartesian coordinate system. Characteristic information, which associates imaginary and real axis values ​​with time information, is acquired for each predetermined rotation angle of the workpiece rotation axis (C-axis). A burn boundary criterion indicating the boundary between a burnt and non-burnt state of the machined portion for each rotation angle is also stored. Then, for each rotation angle, the burnt state of the machined portion of the workpiece W during machining is evaluated based on the characteristic information and the burnt boundary criterion. This allows the burnt state of the machined portion to be evaluated with high accuracy during machining, regardless of whether the workpiece W is circular or non-cylindrical.

[0079] Furthermore, in this embodiment, the workpiece W is non-cylindrical, and includes a workpiece rotation angle acquisition unit 40 that acquires the rotation angle of the workpiece W, and a rotation angle conversion unit 41 that calculates the difference between the machining position rotation angle, which is the rotation angle of the machining position on the workpiece W that comes into contact with the tool 16, and the measurement position rotation angle, which is the rotation angle of the measurement position on the workpiece W that faces the eddy current sensor 20, based on the rotation angle of the workpiece W acquired by the workpiece rotation angle acquisition unit 40, and converts the rotation angle based on this difference so that the measurement position becomes the machining position. As a result, even when machining a non-cylindrical workpiece W, it is possible to acquire measurement results of the machining position with high accuracy using the eddy current sensor 20.

[0080] This embodiment also includes a phase angle calculation unit 46 that calculates the phase angle φm of the feature information relative to the start output signal, which is an output signal at the start of processing on the complex plane, and a distance calculation unit 47 that calculates the distance Rm from the start output signal to the feature information on the complex plane. The burn boundary criteria include a reference phase angle φg, which is the phase angle of the burn boundary signal relative to the start output signal on the complex plane, and a reference distance Rw, which is a reference value of the distance from the start output signal to the burn boundary signal. Furthermore, the burn state evaluation unit 48 evaluates that a burn has occurred at a processing position corresponding to the time of the feature information when the phase angle φm calculated by the phase angle calculation unit 46 is greater than the reference phase angle φg and the distance Rm calculated by the distance calculation unit 47 is longer than the reference distance Rw. This allows the location of the burn to be estimated with high accuracy.

[0081] Furthermore, this embodiment includes a processing condition adjustment unit 50 that adjusts the processing conditions of the processing device 1 based on the evaluation result of the burn state evaluation unit 48. This makes it easy to adjust the processing conditions to reduce the occurrence of burns on the processed part.

[0082] In addition, in this embodiment, the burn condition evaluation unit 48 evaluates the burn condition in the current machining of the workpiece W before machining the next workpiece W. This makes it possible to shorten the cycle time and improve productivity.

[0083] In this embodiment, the machining of the workpiece W by the tool 16 includes a rough machining step S1a in which machining is performed at a first machining efficiency, and a finish machining step S1b in which machining is performed at a machining efficiency lower than the first machining efficiency after the rough machining step S1a. The burn condition evaluation unit 48 evaluates the burn condition based on the output signal P in the rough machining step S1a. This allows the burn condition to be evaluated during the current machining, which can contribute to shortening the cycle time.

[0084] This embodiment also includes a burn depth estimation unit 49 that estimates the burn depth when the burn state evaluation unit 48 evaluates that the workpiece W has burned. The burn depth estimation unit 49 extracts a group of feature information from the feature information in the finishing process S1b, including multiple pieces of feature information for which the rotation angle of the workpiece W is the same. The burn depth estimation unit 49 derives, on a complex plane, a first vector whose origin is first feature information having a first time included in the group of feature information and whose end point is second feature information having a second time one rotation after the first feature information, and a second vector whose origin is the first feature information and whose end point is third feature information having a third time one rotation after the second feature information. Then, when the difference between the phase angle of the first vector and the phase angle of the second vector becomes equal to or less than a predetermined value, the burn depth estimation unit 49 estimates that the depth removed from the workpiece W from the start of the finishing process S1b to the first time corresponds to the burn depth occurring at the end of the rough machining process. This allows the burn depth to be estimated with high accuracy.

[0085] In addition, in this embodiment, the burn depth estimation unit 49 estimates the burn depth at a rotation angle at which the burn state evaluation unit 48 evaluates that a burn has occurred among the predetermined rotation angles of the workpiece W. This reduces the amount of calculation and allows the calculation of the estimation result to be performed earlier, which contributes to shortening the cycle time.

[0086] Furthermore, this embodiment includes a processing condition adjusting unit 50 that adjusts the processing conditions of the processing device 1 based on the estimation result of the burn depth estimating unit 49. This makes it easy to adjust the processing conditions to reduce the occurrence of burns on the processed part.

[0087] In this embodiment, the burn depth estimation unit 49 estimates the burn depth in the current machining of the workpiece W before machining the next workpiece W. This allows the current machining result to be reflected in the next machining, thereby improving productivity.

[0088] As described above, according to the above-described embodiment, it is possible to provide a machining apparatus 1 that can evaluate the burn state of the workpiece W with high accuracy using the eddy current sensor 20 during machining, regardless of the shape of the workpiece W.

[0089] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments within the scope of the present invention. [Explanation of symbols]

[0090] 1 Processing equipment 2 Grinding machines 3 Processing section 17 Sizing device 20 Eddy current sensor 12a Workpiece rotation device (workpiece motor) 18 Coolant unit 20 Eddy current sensor 40 Workpiece rotation angle acquisition unit 41 Rotation angle conversion unit 42 Signal acquisition unit 43 Feature information acquisition unit 44 Time acquisition part 45 Burn boundary reference memory section 46 Phase angle calculation section 47 Distance calculation unit 48 Burn condition evaluation section 49 Burn depth estimation unit 50 Machining condition adjustment section 51 Margin calculation section

Claims

1. A processing device that processes the surface of a workpiece multiple times with a tool to form it into a final target shape, a workpiece rotation device that rotates the workpiece around a workpiece rotation axis; an eddy current sensor disposed opposite to a portion to be machined of the workpiece, which induces an eddy current inside the workpiece by an excitation current and outputs an AC output signal corresponding to a magnetic field generated by the eddy current; a characteristic information acquiring unit that acquires characteristic information, which associates an imaginary axis value and a real axis value when an output signal output by the eddy current sensor is represented on a complex plane in a Cartesian coordinate system with a time when the workpiece is machined, for each predetermined rotation angle of the workpiece rotation axis; a burnt boundary reference storage unit configured to store, for each of the predetermined rotation angles, a burnt boundary reference corresponding to a burnt boundary signal that is an output signal of the eddy current sensor indicating a boundary between a burnt state and a non-burnt state of the workpiece portion displayed on the complex plane; a burnt state evaluation unit that evaluates the burnt state of the processed portion of the workpiece being processed based on the characteristic information and the burnt boundary criterion for each rotation angle.

2. the workpiece is non-cylindrical; a workpiece rotation angle acquisition unit that acquires a rotation angle of the workpiece; 2. The machining apparatus according to claim 1, further comprising a rotation angle conversion unit that calculates a difference between a machining position rotation angle, which is the rotation angle of a machining position on the workpiece that comes into contact with the tool, and a measurement position rotation angle, which is the rotation angle of a measurement position on the workpiece that faces the eddy current sensor, based on the rotation angle of the workpiece acquired by the workpiece rotation angle acquisition unit, and converts the rotation angle based on the difference so that the measurement position becomes the machining position.

3. a phase angle calculation unit that calculates a phase angle of the feature information with respect to a start output signal, which is the output signal at the start of processing on the complex plane; a distance calculation unit that calculates a distance from the initial output signal to the feature information on the complex plane; Equipped with the burnt boundary criterion includes a reference phase angle, which is a phase angle of the burnt boundary signal with respect to the start output signal on the complex plane, and a reference distance, which is a reference value of a distance from the start output signal to the burnt boundary signal; 3. The processing device according to claim 1, wherein the burn state evaluation unit evaluates that a burn has occurred at a processing position corresponding to a time in the feature information when the phase angle calculated by the phase angle calculation unit is greater than the reference phase angle and the distance calculated by the distance calculation unit is longer than the reference distance.

4. The processing device according to claim 3 , further comprising a processing condition adjusting unit that adjusts processing conditions of the processing device based on the evaluation result of the burnt state evaluating unit.

5. The processing device according to claim 3 , wherein the burnt state evaluation unit evaluates the burnt state in the current workpiece processing before the next workpiece processing.

6. The machining of the workpiece by the tool includes a rough machining step in which machining is performed at a first machining efficiency, and a finish machining step in which machining is performed at a machining efficiency lower than the first machining efficiency after the rough machining step, The processing device according to claim 1 or 2, wherein the burnt state evaluation unit evaluates the burnt state based on the output signal in the rough processing step.

7. a burn depth estimation unit that estimates the burn depth when the burn state evaluation unit evaluates that there is a burn, The burn depth estimation unit extracting a group of characteristic information consisting of a plurality of pieces of characteristic information having the same rotation angle of the workpiece from the characteristic information in the finishing process; deriving, on the complex plane, a first vector having a first feature information element having a first time instant included in the feature information group as a starting point and a second feature information element having a second time instant that is one rotation after the first feature information element has rotated one revolution, and a second vector having a first feature information element as a starting point and a third feature information element having a third time instant that is one rotation after the second feature information element has rotated one revolution, 7. The processing device according to claim 6, wherein when a difference between the phase angle of the first vector and the phase angle of the second vector becomes equal to or less than a predetermined value, it is estimated that the depth removed from the workpiece from the start of the finish processing step to the first time point corresponds to the burn depth that occurred at the end of the rough processing step.

8. The processing device according to claim 7 , wherein the burn depth estimation unit estimates the burn depth at a rotation angle at which the burn state evaluation unit evaluates that a burn has occurred, among the predetermined rotation angles.

9. The processing device according to claim 7 , further comprising a processing condition adjusting unit that adjusts processing conditions of the processing device based on the estimation result of the burn depth estimating unit.

10. The machining device according to claim 7 , wherein the burn depth estimating unit estimates the burn depth in machining of the current workpiece before machining of the next workpiece.

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