Chatter detection device, processing machine, and chatter detection method

Abstract

To effectively detect chatter. [Solution] The chatter detection device 5 has a strain sensor 7 that measures the strain of a holding member (e.g., a tool holder 105) that directly or indirectly holds the tool 101 in a detachable manner.

Description

Technical Field

[0001] The present disclosure relates to a chatter detection device that detects chatter occurring during machining (e.g., cutting), a machine tool having the chatter detection device, and a chatter detection method.

Background Art

[0002] It is known that vibrations called chatter can occur during machining (e.g., cutting). Examples of chatter include regenerative chatter, forced chatter, friction chatter, and system chatter, etc., and generally have a relatively high frequency. In the following Patent Documents 1 and 2, techniques for detecting chatter are disclosed.

[0003] Specifically, in Patent Document 1, chatter is detected based on the output signal of a force sensor that detects machining reaction force. The force sensor has a strain gauge, is integrated with the tool, and is provided on the tool rest. That is, although not specified in Patent Document 1, the force sensor detects the strain of the tool. In Patent Document 2, chatter is detected based on the vibration detected by a vibration sensor arranged on the spindle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a need for a chatter detection device, a machine tool, and a chatter detection method that can suitably detect chatter.

Means for Solving the Problems

[0006] A chatter detection device according to one aspect of the present disclosure includes a strain sensor for measuring the strain of a holding member that directly or indirectly holds a tool in a detachable manner.

[0007] A machining center according to one aspect of this disclosure comprises the chatter detection device and a machining center body that processes a workpiece with the tool.

[0008] A chatter detection method according to one aspect of this disclosure measures the strain of a holding member that directly or indirectly holds a tool detachably when machining is performed with the tool. [Effects of the Invention]

[0009] According to the above configuration and procedure, chatter can be effectively detected. [Brief explanation of the drawing]

[0010] [Figure 1] A perspective view showing a processing machine according to an embodiment. [Figure 2] Figure 1 shows a perspective view of the tool and its surrounding area in a machining center. [Figure 3] Cross-sectional view along line III-III in Figure 2. [Figure 4] A diagram illustrating an example. [Modes for carrying out the invention]

[0011] The diagrams used in the following explanation are schematic. Therefore, for example, the dimensional ratios on the drawings do not necessarily match those of reality. Furthermore, dimensional ratios may not match between drawings. Certain shapes and / or dimensions may be exaggerated, or details may be omitted. However, the above does not negate the possibility that the actual shape and / or dimensions may be as shown in the drawings, or that the characteristics of the shape and / or dimensions may be extracted from the drawings.

[0012] In the description of the embodiments, the term "shape" may or may not include dimensions. Either interpretation is acceptable as long as it does not create any inconsistencies. When referring to a rectangle or rectangular shape, for example, the corners may be chamfered. The same applies to other polygons. Furthermore, when referring to a rectangle or rectangular shape, relatively small recesses or protrusions (intentional, not errors) may be formed. The same applies to other shapes.

[0013] In relation to machining equipment, the term "axis" can refer to an axis defining a coordinate system (or, from another perspective, a virtual line), or to a drive mechanism that enables movement along such an axis. Furthermore, the term "axis" in relation to machining equipment can refer not only to axes related to linear movement (translational movement) (sometimes called "linear axes"), but also to axes related to rotational movement (sometimes called "rotational axes"). Here, rotation does not necessarily require rotation within a 360° angular range (i.e., includes tilting).

[0014] The tools, workpieces, and parts of the machining center may be arranged in any orientation. However, for convenience, in the description of the embodiments, the positive side of the Y-axis, as described later, may be considered the upper side, and terms such as upper surface and lower surface may be used.

[0015] In the description of the embodiments, for convenience, strain and deformation, signal, or charge that correlates with strain may not be distinguished. These terms may be substituted for each other in the description of the embodiments, as long as no inconsistencies arise.

[0016] (Summary of the embodiment) Figure 1 is a perspective view showing a machining center 1 according to an embodiment. The machining center 1 processes (e.g., cuts) a workpiece 103 (e.g., a material to be cut) by bringing a tool 101 (e.g., a cutting tool) into contact with the workpiece 103 (e.g., a material to be cut) that is rotating around an axis parallel to the Z-axis. The machining center 1 comprises a machining center body 3 that performs the machining and a chatter detection device 5 (hereinafter, for convenience, may be simply referred to as "detection device 5") that detects chatter during machining.

[0017] FIG. 2 is a perspective view showing the tool 101 and its peripheral part of the processing machine 1. The tool 101 is detachably held by a tool holder 105 (which may also be referred to as a tool rest, an example of a holding member). The detection device 5 has a strain sensor 7 for detecting strain. For the sake of description, the strain can be, for example, the degree of deformation (rate of change) of an object, and can also be, for example, the ratio of the amount of deformation to a reference amount (for example, the length before deformation) (amount of deformation / reference amount).

[0018] In the illustrated example, the strain sensor 7 measures the strain of the tool holder 105 that directly holds the tool 101. Different from the illustrated example, the strain sensor 7 may measure the strain of a member that holds the tool holder 105 (that is, a member that indirectly holds the tool 101). In the description of the embodiment, for the sake of convenience, the description may be based on the illustrated example without special notice.

[0019] The measured value (dynamic strain) of the strain sensor 7 is acquired, for example, as time-series data. This time-series data is displayed by an oscilloscope 9, for example, as shown in FIG. 1. The user can determine the presence or absence of chatter based on the change over time (waveform) of the strain displayed on the oscilloscope 9. And / or, the arithmetic unit 11 (processor 11a from another perspective) can determine the presence or absence of chatter based on the time-series data (for example, without performing the following Fourier transform and / or by performing it).

[0020] And / or, for example, the time-series data of the strain sensor 7 is subjected to a Fourier transform (for example, FFT) by the arithmetic unit 11. Thereby, data SD of the frequency spectrum is obtained. The user and / or the arithmetic unit 11 can determine the presence or absence of chatter based on the frequency spectrum (for example, the magnitude of the amplitude spectrum).

[0021] Such a strain detection device 5 has various advantageous effects. Examples are given below.

[0022] Since the strain sensor 7 measures the strain of a holding member (e.g., a tool holder 105) that directly or indirectly holds the tool 101 in a detachable manner, rather than measuring the strain of the tool 101 itself, it can be positioned away from the machining area. As a result, chatter can be detected even in equipment and / or situations where the machining area is relatively small (e.g., equipment and / or situations where precision machining is performed).

[0023] Strain is a rate of change of an object (or, from another perspective, a dimensionless quantity), and is not a physical quantity with absolute units like acceleration. Therefore, unlike, for example, measuring acceleration, the distance from the machining point has little effect on the measurement result. As a result, even if, for example, the machining area is small and the strain sensor 7 is placed far from the machining point, it is easy to maintain the accuracy of chatter detection.

[0024] Furthermore, the fact that chatter can be detected by measuring the strain of the holding member (e.g., the tool holder 105) rather than the strain of the tool 101 is a finding obtained through the inventor's diligent research. The fact that chatter can be detected by measuring the strain of the holding member will be explained later in the description of the examples.

[0025] The tool 101, including the shank 101b (Figure 2), is made of a relatively high-strength metal (e.g., tool steel). Therefore, it is difficult to provide a sensor integrated with the tool 101 to detect strain in the tool 101. When detecting strain in a retaining member that directly or indirectly holds the tool 101 in a detachable manner, it is easy to avoid such inconveniences.

[0026] It should be noted that the effects exemplified above do not necessarily have to be achieved. Furthermore, technical ideas from perspectives different from those described above may be extracted from this disclosure. In this case, for example, the strain sensor 7 may be provided on a member other than the holding member (e.g., the tool 101), or another sensor may be provided in place of the strain sensor 7.

[0027] The above is an overview of the embodiment. Below, the embodiment will be described in general terms as follows. 1. Processing machine body 2. Tools and workpieces 3. Holding member (tool holder, etc.) 4. Vibration detection device 5. Examples 6. Summary of Embodiments

[0028] (1. Processing machine body) The configuration of the processing machine body 3 shown in Figure 1 can be various, as long as it can be combined with the detection device 5, and may be a known configuration, for example. The configuration of the processing machine body 3 shown in Figure 1 is merely one example.

[0029] For example, the machining operations that the machining center body 3 can perform can be varied. For example, the machining may involve contact between the tool 101 and the workpiece 103. Specifically, examples include cutting (as shown in the illustration), grinding, and polishing. Furthermore, the machining may be performed by rotating the workpiece 103 (e.g., turning), by rotating the tool 101 (e.g., milling), by rotating both the tool 101 and the workpiece 103, or by moving both the workpiece 103 and the tool 101 in parallel without rotating either (e.g., shaping).

[0030] In the description of the embodiments, for convenience, explanations may be given based on the illustrated example (turning) without further explanation. However, the description of the embodiments may be applied to configurations and methods related to examples other than the illustrated example (other processing), as long as no inconsistencies arise. For example, the explanation of the part where strain is measured by the strain sensor 7, the type of strain measured (e.g., expansion and contraction), and the direction of the strain (all described later) may be applied to configurations and methods related to processing other than turning.

[0031] The processing machine body 3 includes, for example, a mechanical unit 13 that performs mechanical operations and a controller 15 that controls the mechanical unit 13. As can be understood from the above description, the structure of the mechanical unit 13 and the hardware and software of the controller 15 may be of various types, including those known to the public.

[0032] For example, the configuration of the mechanical part 13 may be a configuration commonly used in the mechanical parts of machine tools (as shown in the illustration), a configuration commonly used in the mechanical parts of industrial robots, or it may not be possible to categorize them in any way. Furthermore, the mechanical part 13 may have a spindle 17 for rotating the workpiece 103 (as shown in the illustration), a spindle for rotating the tool, both, or neither.

[0033] Taking the machine part of a machine tool as an example, the machine part 13 may have linear axes and rotary axes (drive mechanisms) in any direction. For example, the machine part 13 may have three linear axes corresponding to the X, Y, and Z axes, or it may have fewer or more linear axes. The machine part 13 may also have a rotary axis (excluding the spindle 17), or it may not have one. Examples of rotary axes include the A axis (axis around the X axis), the B axis (axis around the Y axis), and the C axis (axis around the Z axis). Relative movement of each axis (linear axis or rotary axis) may be realized by either the movement of the tool 101 in the absolute coordinate system or the movement of the workpiece 103 in the absolute coordinate system.

[0034] The configuration of the drive source for each axis (including the spindle 17) is arbitrary and may be, for example, an electric motor, hydraulic equipment, or pneumatic equipment. The electric motor may be a rotary motor or a linear motor. The range of possible rotational speeds for the spindle 17, as well as the movable range, possible speed range, and positioning accuracy for the linear and rotary axes (excluding the spindle 17), are arbitrary. The machine unit 13 (machining machine body 3) may or may not be configured to enable precision machining.

[0035] The configuration of the linear guides on each axis (including the main shaft 17) is arbitrary and may be, for example, sliding guides, rolling guides, or hydrostatic guides, or a combination of two or more of these. Similarly, the bearings (e.g., the bearings on the main shaft 17) may be sliding bearings, rolling bearings, or hydrostatic bearings, or a combination of two or more of these. The fluid used in the hydrostatic guides or hydrostatic bearings may be a gas (e.g., air) or a liquid (e.g., oil).

[0036] As previously mentioned, the mechanical unit 13 shown in Figure 1 is merely an example. However, for reference, the configuration of the illustrated mechanical unit 13 will be briefly explained.

[0037] As previously described, the machine unit 13 performs machining by rotating the workpiece 103. That is, the machine unit 13 has a spindle 17 that rotates the workpiece 103. Furthermore, the machine unit 13 is configured to allow relative movement of the tool 101 and the workpiece 103 along the X, Y, Z, and B axes.

[0038] More specifically, the mechanical unit 13 has, for example, the following components: • Base 19: Installed on the factory floor or similar surface, and is basically immobile. • Z-axis movable part 21Z: Supported by the base 19, it is movable in the Z-axis direction. Column 23: Supported by the Z-axis movable part 21Z. • Y-axis movable part 21Y: Supported by column 23, it is movable in the Y-axis direction. It also supports the main shaft 17. • X-axis movable part 21X: Supported by the base 19, it is movable in the X-axis direction. • B-axis movable part 21B: Supported by the X-axis movable part 21X, it is movable (rotatable) in the B-axis direction. It is also capable of (indirectly) holding the tool 101.

[0039] As can be understood from the above, in the illustrated example, the workpiece 103 is movable in the Z-axis and Y-axis directions in the absolute coordinate system, and is also rotatable around the axis of the spindle 17. The tool 101 (spindle 17) is movable in the X-axis and B-axis directions in the absolute coordinate system. The shape of each movable part is arbitrary; for example, the X-axis movable part 21X, Y-axis movable part 21Y, Z-axis movable part 21Z, and B-axis movable part 21B are table-shaped.

[0040] The controller 15 may, for example, perform control based on an NC program, perform control based on teaching, or perform other types of control. From another perspective, the processing machine body 3 may be classified as a machine tool, a robot, or may not be classifiable in any way from a control standpoint. Figure 1 illustrates an embodiment in which the controller 15 includes an NC device 15a.

[0041] (2. Tools and Workpieces) As can be understood from the description of the machine body 3, the tool 101 may be a cutting tool or a grinding wheel. Also, the tool 101 may be one that does not rotate (e.g., a turning tool (cutting tool)) as shown in the example in Figure 2, or one that is rotated by the spindle (e.g., a milling tool (rotary tool)).

[0042] The specific configuration of the cutting tool is also arbitrary. For example, the cutting tool may be a throwaway cutting tool (as shown in the illustration), a solid cutting tool, or a cutting tool with an attached edge. Alternatively, the cutting tool may be a sword cutting tool, a beveled sword cutting tool, a single-edged cutting tool, a boring tool, a parting tool, a male thread cutting tool, a female thread cutting tool, a roughing tool, or a finishing tool. From another perspective, the machining with the cutting tool may target either the outside (e.g., the outer circumference and end faces) or the inside (e.g., the inner circumference and bottom faces of a hole) of the workpiece 103, and any machined shape or surface texture may be targeted. Right-handed and left-handed cutting are also not particularly limited.

[0043] In any type of cutting tool, it typically has a shank 101b and a cutting edge 101a located at its tip. The shank 101b has, for example, a portion that extends linearly with a certain cross-sectional shape. This cross-sectional shape is, for example, rectangular (square or rectangular). Unlike the illustrated example, the shank 101b may have a circular cross-sectional shape or the like. It should be noted that, although this is essentially a repetition of the precautions already mentioned, the descriptions of the shank 101b itself and the retaining member that holds the shank 101b (e.g., tool holder 105) described above or below may also apply to cutting tools and tools other than those shown in the illustration.

[0044] The tool 101 illustrated in Figure 2 is a throwaway type (also called an insert type) cutting tool in which the cutting edge 101a, made of a tip, can be attached to and detached from the shank 101b. Details such as the mechanism for attaching and detaching the cutting edge 101a are not shown in the illustration. The shank 101b in this embodiment is sometimes referred to as a holder. However, in this disclosure, the term tool holder does not refer to the shank 101b.

[0045] As can be understood from the description of tool 101 above, the material and shape (before and after processing) of the workpiece 103 are arbitrary. For the sake of clarity, let me give a brief example. For example, the material of the workpiece 103 may be metal, glass, resin, ceramic, or wood. The shape (before or after processing) of the workpiece 103 may be roughly axial (example in Figure 1), block-shaped, or plate-shaped. An axial workpiece 103 may be processed (e.g., cut) on the outside and / or inside. The chuck 107 (e.g., collet and faceplate, etc.) located at the tip of the spindle 17 and holding the workpiece 103 may be replaced depending on the shape of the workpiece 103, etc.

[0046] (3. Holding members (tool holders, etc.)) The holding member (tool holder 105 in the illustrated example) that directly or indirectly holds the tool 101 and whose strain is detected by the strain sensor 7 may be of various types.

[0047] For example, in the example shown in Figure 1, the tool 101 is held by a tool holder 105, the tool holder 105 is held by a jig 109, and the jig 109 is held by a B-axis movable part 21B. Therefore, for example, the holding member from which strain is detected may be the jig 109 and / or the B-axis movable part 21B instead of, or in addition to, the tool holder 105.

[0048] As can be seen from the above example, the holding member may be detachable from the machine body 3 (machine part 13) (for example, a tool holder 105 and a jig 109), or it may be a part of the machine body 3 (for example, the B-axis movable part 21B). Also, as already mentioned, the holding member may directly hold the tool 101 (for example, a tool holder 105), or it may indirectly hold the tool 101 (for example, a jig 109 and the B-axis movable part 21B).

[0049] The B-axis movable part 21B is held by the X-axis movable part 21X, and the X-axis movable part 21X is held by the base 19. Therefore, the X-axis movable part 21X and the base 19 are also holding members that indirectly hold the tool 101. However, if parts that move relative to each other are interposed between the part that causes chatter and the part that detects strain, the deformation caused by chatter is absorbed by the relative moving part. As a result, depending on the type of chatter, it becomes difficult to detect the strain caused by chatter. For example, strain caused by self-excited chatter is unlikely to occur or will be small in the X-axis movable part 21X or the base 19. Therefore, the holding members may be limited to those that hold the tool 101 so that it cannot move relative to themselves (for example, the tool holder 105, the jig 109 and the B-axis movable part 21B) (but may not be limited).

[0050] Figure 3 is a cross-sectional view taken along the line III-III in Figure 2.

[0051] The tool holder 105 illustrated in Figures 2 and 3 is generally a U-shaped member. In other words, the tool holder 105 has a groove 15r extending in a direction intersecting the Y axis on its side (the surface along the Y axis), an upper part 105a located above the groove 15r (+Y side), a lower part 105b located below the groove 15r, and a part (not shown) that fixes the upper part 105a and the lower part 105b. Multiple (four in the illustrated example) female threads 105f (screw grooves not shown) penetrate the upper part 105a in the Y direction, into which set screws 111 can be screwed.

[0052] The tool 101 (shank 101b) is positioned in the groove 15r. When the set screw 111 is screwed in downward, the lower end of the set screw 111 contacts the upper surface of the shank 101b, and furthermore, the shank 101b is pressed against the lower part 105b. This holds the tool 101 in the tool holder 105. Unlike the illustrated example, a spacer may be placed between the set screw 111 and the shank 101b. That is, the set screw 111 may indirectly press against the shank 101b without making contact with it.

[0053] The more detailed shape of the tool holder 105 is arbitrary. For example, the overall shape of the tool holder 105 is roughly a rectangular parallelepiped, ignoring the groove 15r. The cross-sectional shape of the groove 15r is, for example, rectangular. Its width and height are, for example, slightly larger than the width and height of the shank 101b. The upper part 105a and the lower part 105b are flat plates. Although not specifically shown, the tool holder 105 may have a part for attachment to a jig 109, etc., and therefore may have a shape that deviates from a rectangular parallelepiped.

[0054] The tool holder 105 is, for example, integrally constructed from metal. However, the tool holder 105 may be constructed from a combination of multiple components. The specific material of the metal is arbitrary. The Young's modulus of the material of the tool holder 105 may be lower, equal to, or higher than the Young's modulus of the material of the shank 101b. When the Young's modulus of the tool holder 105 is lower than that of the shank 101b, strain in the tool holder 105 becomes easier to detect.

[0055] Multiple female threads 105f have, for example, the same configuration as each other. Specifically, for example, multiple female threads 105f have the same root diameter, outer diameter, pitch, lead, thread shape, and thread direction (right-hand or left-hand thread), etc. In other words, multiple female threads 105f can be fitted with set screws 111 of the same configuration. However, some or all of the female threads 105f may have a different configuration from the other female threads 105f. In this case, the differences may not affect, or have little effect on, the ability to fit set screws 111 of the same configuration (for example, thread length in the Y direction), or they may not.

[0056] Multiple female threads 105f are arranged in a straight line, for example. The spacing between the multiple female threads 105f is arbitrary; for example, they do not have to be equally spaced (as shown in the example), or they may be equally spaced.

[0057] The number of female threads 105f is also arbitrary; it may be 4 (as shown in the illustration), 2, 3, or 5 or more. As will be described later, when multiple female threads 105f are used to fix the strain sensor 7, the number of female threads 105f may be, for example, the number of female threads 105f used to fix the strain sensor 7 (1 in the illustration) + 2 or more.

[0058] The number of female threads 105f actually used to fix the tool 101 is also arbitrary. For example, all female threads 105f may be used to fix the tool 101, or all female threads 105f except for the female thread 105f used to fix the strain sensor 7 may be used to fix the tool 101 (example in Figure 3), or there may be female threads 105f that are not used to fix the tool 101 or the strain sensor 7.

[0059] The type of set screw 111 is arbitrary. In the illustrated example, all set screws 111 are so-called grub screws, which do not have screw heads. Furthermore, the entire set screw 111 is located below the upper surface of the upper part 105a (the entrance to the female thread 105f). This reduces the likelihood, for example, that the set screw 111 may obstruct the attachment of the strain sensor 7 to the upper part 105a. However, if such an effect is not desired, and / or for set screws 111 for which such an effect is not desired, a set screw with a screw head may be used. The specific shape of the set screw 111 is also arbitrary. For example, the shape of the hole for applying rotational force to the set screw 111 or the outer shape of the screw head is arbitrary.

[0060] The configuration of the jig 109 shown in Figure 1 is arbitrary. For example, although the jig 109 is schematically shown as a single block-shaped component in Figure 1, the jig 109 may be constructed by combining two or more components. The tool holder 105 and the jig 109, and the jig 109 and the B-axis movable part 21B may be fixed using bolts or the like (not shown) as appropriate.

[0061] As previously stated, the configuration of the tool 101 can vary, and consequently, the configuration of the holding member that directly or indirectly holds the tool 101 can also vary. Examples are given below. It should be noted that, although this is essentially a repetition of the precautions already mentioned, the following examples may be applied not only to turning tools but also to various other tools (for example, milling tools and grinding wheels), as long as no inconsistencies arise.

[0062] As shown in Figures 2 and 3, the tool holder that secures the cutting tool, which is positioned in a groove, with a set screw may have grooves on two or more sides. The tool holder may also tighten the shank 101b with a collet, utilize a force that pulls the shank 101b toward the rear end, or press a member that fits into recesses and / or protrusions provided on the side of the shank 101b from the side.

[0063] Furthermore, the tool holder described above may be held by other tool holders, and the manner of holding may be any of the above-described manners. The distinction between tool holder, jig, and tool post is not necessarily clear. The movable part of the machine unit 13 that holds the tool holder (which directly holds the tool 101, or which holds the tool holder that directly holds the tool 101) or the jig 109 (the B-axis movable part 21B in the example of Figure 1) is not limited to a table shape, but may be a turret or a drum, or a spindle.

[0064] (4. Vibration detection device) The detection device 5 shown in Figure 1 may, for example, be an option for the processing machine body 3. From another perspective, the entire processing machine body 3 and the entire detection device 5 may be able to circulate independently of each other. And / or, the processing machine body 3 and the detection device 5 may be able to be processed independently of each other.

[0065] However, at least a part of the detection device 5 may be integrally and inseparably integrated with a part of the processing machine body 3. And / or, at least one of the detection device 5 and the processing machine body 3 may utilize signals from the other. For example, the strain sensor 7 may be inattachably attached to the machine part 13. Also, as shown by the dotted line in Figure 1 indicating a virtual signal path, a part of the processing unit that processes the detection signal from the strain sensor 7 may be included in the controller 15. In the description of the embodiment, the example will basically be one in which the detection device 5 is optional.

[0066] As previously described, the detection device 5 includes, for example, a strain sensor 7, and may also include an oscilloscope 9 and / or a computing device 11 as optional additional elements.

[0067] The strain sensor 7 may consist only of a transducer that converts a physical quantity correlated with strain into an electrical signal, or it may have a processing unit that performs predetermined processing (amplification, calculation, and control, etc.) in addition to the transducer. Figure 1 illustrates the former or a similar configuration, where the signal generated by the strain sensor 7 is output to the oscilloscope 9 and / or calculation unit 11 via a charge amplifier 25 that amplifies the signal. The charge that can be obtained by the strain sensor 7 is often very small, so amplification by the charge amplifier 25 is effective. The specific division of roles between the strain sensor 7 and the charge amplifier 25, and the specific division of roles between the charge amplifier 25 and the oscilloscope 9 and / or calculation unit 11 are arbitrary.

[0068] The type of strain sensor 7 (or, from another perspective, the principle of strain detection) is arbitrary. For example, the following may be used. • Strain gauge type: The electrical resistance value of the gauge changes according to the deformation of the gauge. • Piezoelectric type: Generates an electric charge in response to the deformation of a piezoelectric material (e.g., quartz). • Optical fiber type: The parameters of the light passing through the optical fiber (intensity, frequency, etc.) are changed according to the deformation of the optical fiber. • Capacitive type: Changes capacitance in response to relative movement between electrodes due to deformation.

[0069] The strain sensor 7, for example, contacts the surface (measured surface) of the object to be measured (a tool holder 105 in the illustrated example) and measures the expansion and contraction of the measured surface in a direction along the measured surface. However, the strain sensor 7 may be installed inside the object to be measured to measure internal deformation, or it may be configured to measure shear or bending. In the description of the embodiments, unless otherwise specified, examples may be given of devices that detect the expansion and contraction of the measured surface.

[0070] The strain sensor 7 may have an appropriate external and / or internal configuration to increase its sensitivity to deformation (e.g., stretching) in a predetermined measurement direction. Furthermore, the strain sensor 7 may be configured to output only signals corresponding to deformation in the measurement direction. Contrary to the above, the strain sensor 7 does not need to have high sensitivity in a particular measurement direction.

[0071] The performance of the strain sensor 7 is arbitrary. For example, the measurable range may be -600 με to +600 με or a wider range (or conversely, a narrower range). The minimum measurable value may be 1 με or less, 0.5 με or less, 0.1 με or less, or 0.05 με or less. In the case of a piezoelectric type, the charge (absolute value) generated by a strain of 1 με may be 50 pC or more. The responsiveness (measurable frequency) may be 10 kHz or more (the sampling frequency may be twice that or more).

[0072] In the illustrated example, the strain sensor 7 has an overall shape that is roughly block-like (for example, rectangular parallelepiped). The strain sensor 7 has a roughly planar detection surface 7a (the bottom surface in the illustrated example) that contacts the object to be measured (tool holder 105) where strain is detected. The detection surface 7a (more precisely, a portion of a certain thickness including the detection surface 7a) deforms in accordance with the deformation of the object to be measured (for example, expansion and contraction in the direction along the detection surface 7a). A signal corresponding to this deformation is output from the strain sensor 7.

[0073] More specifically, as shown in Figure 3, the detection surface 7a has two contact portions 7b that are separated from each other in a predetermined measurement direction DD (in the illustrated example, the longitudinal direction of the strain sensor 7). The two contact portions 7b protrude downward and contact the planar surface of the object to be measured (the surface to be measured). The strain sensor 7 then outputs a signal corresponding to the expansion and contraction of the portion between the two contact portions 7b. The distance between the two contact portions 7b, as well as the shape and dimensions of each contact portion 7b (for example, the length in the longitudinal and transverse directions of the strain sensor 7, etc.), are arbitrary. Furthermore, the contact portions 7b or their lower surfaces may be made of a material that reduces the likelihood of sliding against the surface of the object to be measured.

[0074] Unlike the illustrated example, the strain sensor 7 may be, for example, in the form of a film or a thin plate. Furthermore, its entire thickness may be configured to deform in accordance with the deformation of the surface to be measured (for example, expansion and contraction along the surface to be measured). In this case, the surface that contacts the surface to be measured may be one of the two surfaces of the thin strain sensor 7, or it may not be. In any case, as in the illustrated example, the strain sensor 7 can be considered to have a detection surface 7a.

[0075] The strain sensor 7 may measure strain (e.g., strain related to expansion and contraction) in any direction at any position on the holding member (e.g., tool holder 105). In the examples of Figures 2 and 3, the strain sensor 7 is positioned to measure the strain related to the axial expansion and contraction of the tool 101 on the upper surface of the tool holder 105 (an example of a surface intersecting the direction of the main force component). That is, the detection surface 7a is in contact with the upper surface of the tool holder 105, and the measurement direction DD is parallel to the longitudinal direction of the tool 101.

[0076] The method of attaching the strain sensor 7 to the holding member is arbitrary. For example, the strain sensor 7 may be attached to the holding member detachably by screws (and nuts if necessary), the detection surface 7a etc. may be bonded to the holding member, or it may be attached to the holding member by a dedicated device.

[0077] In the examples shown in Figures 2 and 3, the strain sensor 7 has a through hole 7h that penetrates the strain sensor 7 in a direction intersecting (e.g., perpendicular to) the detection surface 7a. The strain sensor 7 is fixed to the tool holder 105 by screwing a male screw 113 inserted through the through hole 7h into one of the multiple female screws 105f of the tool holder 105.

[0078] In the illustrated example, the female thread 105f into which the male thread 113 is screwed does not have the set screw 111 screwed into it. However, if the length of the female thread 105f in the through direction is relatively long, it is possible to screw both the male thread 113 and the set screw 111 into the same female thread 105f.

[0079] The number and position of the through-holes 7h are arbitrary. In the illustrated example, one through-hole 7h is provided in the center of the detection surface 7a (midway between the two contact portions 7b). Unlike the illustrated example, for example, a total of two through-holes 7h may be provided on both sides of the detection surface 7a in the measurement direction DD. In this case, the strain sensor 7 may (or may not) be configured to output a signal corresponding to the expansion and contraction of the portion between the through-holes 7h without having contact portions 7b (and even the detection surface 7a).

[0080] The shape and dimensions of the male thread 113 are arbitrary, as long as they can be screwed into the female thread 105f. In the illustrated example, the head of the male thread 113 is conical and engages with the upper conical portion of the through hole 7h. Unlike the illustrated example, the head may engage with the upper surface of the strain sensor 7 (the area around the through hole 7h). Also, in the illustrated example, the head has a hole into which a spanner can be inserted. Unlike the illustrated example, the head may have a shape on its outer surface into which a spanner or wrench can be fitted.

[0081] The strain sensor 7 may be attached to any of the multiple female threads 105f, as long as it can detect the strain of the tool holder 105. For example, in the example in Figure 3, the tool holder 105 can be attached to either of the two female threads 105f on the left side of the figure (towards the tip of the tool 101). In the example in Figure 3, the two female threads 105f (all or their centers) are located to the left of the groove 105r (towards the tip of the tool 101) than the center in the left-right direction of the figure (towards the axial direction of the tool 101).

[0082] Unlike the illustrated example, depending on the configuration of the tool holder 105, the strain sensor 7 may be attached to the female thread 105f located in the center of the groove 105r in the left-right direction of the diagram, or to the right of the center (towards the rear end of the tool 101). The tool holder 105 may or may not be designed with the attachment of the strain sensor 7 in mind.

[0083] The oscilloscope 9 shown in Figure 1 displays the waveform of the electrical signal from the strain sensor 7 (more precisely, the charge amplifier 25 in the illustrated example). For example, as schematically shown, the screen of the oscilloscope 9 shows time on the horizontal axis and voltage on the vertical axis, with the change in voltage over time shown as a waveform. This waveform moves in the direction of the horizontal axis as time progresses. The scales of the horizontal and vertical axes are variable.

[0084] The arithmetic unit 11 is comprised of, for example, a computer (e.g., a PC). The computer includes a processor 11a (e.g., a CPU), RAM, ROM, and an external storage device. The processor 11a executes programs stored in the ROM and / or external storage device to construct a functional unit that performs Fourier transforms and the like. The arithmetic unit 11 may include a display device (not shown) that displays the frequency spectrum of the strain.

[0085] Unlike the illustrated example, at least two of the oscilloscope 9, the arithmetic unit 11, and the controller 15 may be integrated. For example, the controller 15 may include at least a part of the oscilloscope 9 and display waveforms on a touch panel (not shown) of the controller 15, and / or include at least a part of the arithmetic unit 11 and display frequency spectra on the touch panel. Alternatively, a separate device integrating the oscilloscope 9 and the arithmetic unit 11 may be provided to display waveforms, Fourier transforms, and frequency spectra.

[0086] The detection of chatter by the detection device 5 may be performed during a trial to set the machining conditions, and / or during the actual machining (e.g., mass production of products) in accordance with the set machining conditions. If strain detection is performed only during the former machining, the strain sensor 7 may remain attached to the holding member (tool holder 105) or may be removed from the holding member during the latter machining.

[0087] If the strain sensor 7 is removed during the actual machining process, a dummy sensor (component) may be installed in its place. This brings the vibration conditions of the holding member closer to those of the trial. If a dummy sensor is not installed, the female thread 105f used for mounting the strain sensor 7 may or may not be used to press the tool 101 with the set screw 111 during the actual machining process.

[0088] (5. Examples) The inventor performed the same machining process as illustrated in Figure 1 using a configuration substantially identical to that illustrated in Figures 1 to 3, and measured the strain of the holding member (more specifically, the tool holder 105). As a result, it was confirmed that chatter (more specifically, self-excited chatter) could be detected by measuring the strain of the holding member, rather than the strain of the tool 101. The experiment was conducted under various conditions, some of which are described below.

[0089] As illustrated in Figure 1, a straight cutting tool (tool 101) was brought into contact with the outer circumferential surface of a shaft-shaped workpiece (workpiece 103) at an oblique angle to the rotation axis of the spindle 17, and the outer circumferential surface of the workpiece was cut. The workpiece was a brass base material with electroless Ni-P plating. The plated portion was then cut so that the shape after processing had a diameter of 8.0 mm. The cutting edge 101a was a single-crystal diamond (nose radius 2.0 mm). The cutting was performed in an oil mist environment. Turning was then performed under the following three processing conditions. In all processing conditions, the depth of cut was 0.008 mm. ·Processing conditions (1) ·Cutting speed: 37.7m / min Feed rate: 0.007 mm / rev. ·Processing conditions (2) ·Cutting speed: 25.1m / min Feed rate: 0.010 mm / rev. ·Processing conditions (3) ·Cutting speed: 12.6m / min Feed rate: 0.020 mm / rev.

[0090] As illustrated in Figures 2 and 3, the strain sensor 7 was attached to the second female thread 105f from the front of the four female threads 105f of the tool holder 105. A piezoelectric strain sensor using a quartz crystal was used as the strain sensor 7. Its measurable range is -600 με to +600 με. Its sensitivity is approximately -60 pC / με. Its response time is approximately 10 kHz.

[0091] The presence or absence of chatter was determined by methods other than strain measurement, and the results of this determination were compared with the strain measurement results to confirm that chatter was reflected in the strain measurement results. The following methods were used as alternatives: • Processed sound: The presence or absence of high-frequency sounds associated with processing (buzzing) was determined by the human ear. • Machined surface: The presence or absence of irregularities (chafing-induced surface) due to chatter was determined by visual inspection of magnified images of the machined surface.

[0092] Figures 4(a) to 4(c) show the frequency spectra of strain obtained under processing conditions (1) to (3), respectively. Under processing conditions (1) and (2), the amplitude is large (a peak appears) around 4.0 kHz. On the other hand, under processing condition (3), no such peak appears, and the amplitude is uniformly low.

[0093] The results of the chatter assessment using other methods when machining was performed under each machining condition are as follows: ·Processing conditions (1) • High-pitched processed sound: Yes Machined surface: Chatter-machined surface ·Processing conditions (2) • High-pitched processing sound: None Machined surface: Chatter-machined surface ·Processing conditions (3) • High-pitched processing sound: None ...Processed surface: normal surface

[0094] The observed chatter on the machined surface was presumed to be self-excited chatter (particularly regenerative chatter) based on its shape and periodicity. The inventor also investigated the natural frequencies of the tool 101 and tool holder 105 used in the above experiment by conducting a hammering test using an acceleration pickup. The result showed that the natural frequency was approximately 4.4 kHz, which is close to the frequency at which the strain peak appeared. From the above, it was determined that the chatter that occurred in the above experiment was self-excited chatter.

[0095] As can be understood from the above, there is a correlation between the occurrence of self-excited (regenerative) chatter and the occurrence of a strain peak in the tool holder 105, and it was confirmed that self-excited (regenerative) chatter can be detected by measuring the strain of the tool holder 105 (holding member) rather than the tool 101. Furthermore, as can be understood from the processing conditions (2), it was found that chatter detection by measuring the strain of the tool holder 105 can detect chatter that may not be detectable by the operator's ear.

[0096] Unlike the experiment described above, the inventor also conducted a similar experiment when the strain sensor 7 was attached to the leftmost female thread 105f (the tip end of the tool 101) in Figure 3. As a result, in this case as well, roughly the same strain was measured. However, under the tool 101 and tool holder 105 used in the experiment, and other conditions, the strain peak was slightly clearer in the example in Figure 3 (the second position from the left).

[0097] Furthermore, the inventor also conducted experiments measuring acceleration using an acceleration pickup attached to the tool holder 105 during machining under machining conditions (1) to (3). As a result, the frequency spectrum of acceleration did not show a clear peak around 4.0 kHz, unlike the peak for strain.

[0098] In the experiment using the acceleration pickup described above, the acceleration pickup was positioned to the side of the strain sensor 7 (towards the back of the page in Figure 3) and at the right end of the tool holder 105 in Figure 3 (towards the rear end of the tool 101). The acceleration detected at the latter position had a less pronounced peak than the acceleration detected at the former position. In other words, it was confirmed that the position has a significant effect on acceleration.

[0099] (6. Summary of Embodiments) Below, we will extract the configuration of the detection device 5 and other components according to the embodiment and describe examples of their effects. Note that the extracted configuration does not necessarily have to produce the effects exemplified below.

[0100] The chatter detection device 5 according to this embodiment includes a strain sensor 7 that measures the strain of a holding member (e.g., a tool holder 105) that directly or indirectly holds the tool 101 in a detachable manner.

[0101] From another perspective, the processing machine 1 according to the embodiment includes the detection device 5 according to the embodiment described above, and the processing machine body 3 that processes the workpiece 103 with the tool 101.

[0102] From yet another perspective, the chatter detection method according to the embodiment measures the strain of a holding member (e.g., a tool holder 105) that directly or indirectly holds the tool 101 in a detachable manner when machining is performed with the tool 101.

[0103] Therefore, as described in the overview of the embodiment, for example, strain caused by regeneration strain, etc., can be measured even when the processing area is small.

[0104] The holding member (e.g., a tool holder 105) into which strain is detected by the strain sensor 7 may have a plurality of female threads 105f into which a set screw 111 for fixing a tool 101 can be screwed. In the detection device 5 according to the embodiment, the strain sensor 7 may be mounted on the holding member by having a through hole 7h through which a male thread 113 that can be screwed into the female threads 105f is inserted. In another view, in the detection method according to the embodiment, the strain sensor 7 may be mounted on the holding member by the male thread 113 inserted through the through hole 7h being screwed into one of the plurality of female threads 105f.

[0105] In this case, for example, the female thread 105f is also used for mounting the strain sensor 7, thus simplifying the configuration. Furthermore, since the strain sensor 7 can be selectively attached to multiple female threads 105f, a mounting position that improves sensitivity can be selected.

[0106] The detection device 5 may have an oscilloscope 9 that displays the output of the strain sensor 7.

[0107] In this case, for example, the user can determine the presence or absence of chatter in real time. Therefore, it becomes easier to infer the cause of chatter by comparing, for example, the processing conditions or processing sound with the occurrence of chatter in real time.

[0108] The detection device 5 may have a processor 11a that performs a Fourier transform on the output of the strain sensor 7.

[0109] In this case, for example, it becomes easier to determine the frequency at which the chatter occurs. As a result, for example, it becomes easier to infer the cause of the chatter.

[0110] The strain sensor 7 may have a measurable range that includes the range of -600 με to +600 με, and may also have a response time of 10 kHz or higher.

[0111] With this level of performance, it is possible to detect strain in the retaining member caused by chatter, as demonstrated in the examples.

[0112] The machining center body 3 may be configured to perform machining by bringing the tool 101 into contact with the workpiece 103 which is being rotated by the spindle 17.

[0113] In this case, for example, the detection device 5 can be applied to machining processes that are prone to regenerative chatter (e.g., turning).

[0114] The holding member (for example, the tool holder 105) may hold the tool 101 so that it cannot move relative to the holding member.

[0115] In this case, as already mentioned, the likelihood of strain being absorbed by the intervening part between the tool 101 and the strain sensor 7 is reduced. As a result, the sensitivity of chatter detection is improved.

[0116] In the chatter detection method, when machining is performed by bringing the tool 101 into contact with the workpiece 103 which is being rotated by the spindle 17, the strain related to the expansion and contraction of the tool 101 in the axial direction may be measured on a surface of the holding member that intersects the direction of the main force component (for example, the upper surface of the tool holder 105).

[0117] In this case, for example, the deflection of the tool holder 105 in the direction of the main force component can be detected. Since the tool 101 and the tool holder 105 are generally prone to deflection in the direction of the main force component, it is expected that the sensitivity of chatter detection will improve.

[0118] The technology relating to this disclosure is not limited to the embodiments described above and may be implemented in various forms. For example, in addition to, or instead of, a strain sensor for measuring the strain of a holding member that holds a tool may be provided for measuring the strain of a tool, a workpiece, or a holding member that holds a workpiece, or a sensor for detecting other chatter (e.g., an acceleration pickup) may be provided. The description of the embodiments may be used in reference to the extent that it does not lead to inconsistencies with the measurement of tool strain. [Explanation of Symbols]

[0119] 1... Machining machine, 3... Machining machine body, 5... Chatter detection device, 7... Strain sensor, 101... Tool, 103... Workpiece, 105... Tool holder (holding member).

Claims

1. It has a strain sensor that measures the strain of a retaining member that directly or indirectly holds a tool in a detachable manner. Vibration detection device.

2. The retaining member has multiple female threads into which a set screw for fixing the tool can be screwed. The strain sensor can be attached to the retaining member by having a through hole through which a male screw that can be screwed into the female screw is inserted. The vibration detection device according to claim 1.

3. The system includes an oscilloscope that displays the output of the strain sensor. The vibration detection device according to claim 1.

4. The system includes a processor that performs a Fourier transform on the output of the strain sensor. The vibration detection device according to claim 1.

5. The strain sensor has a measurable range that includes -600 με to +600 με and a response time of 10 kHz or higher. The vibration detection device according to claim 1.

6. A vibration detection device according to any one of claims 1 to 5, A machining center body for machining a workpiece using the aforementioned tool, A processing machine that has the following features.

7. The machining center body is configured to perform machining by bringing the tool into contact with the workpiece, which is being rotated by the spindle. The processing machine according to claim 6.

8. When machining is performed using a tool, the strain of a holding member that directly or indirectly holds the tool in a detachable manner is measured. A method for detecting chatter.

9. The holding member holds the tool so that it cannot be moved relative to the holding member. The method for detecting chatter according to claim 8.

10. The retaining member has multiple female threads into which a set screw for fixing the tool can be screwed. The strain sensor is attached to the retaining member by a male screw inserted through a through hole in the strain sensor being screwed into one of the plurality of female screws. The method for detecting chatter according to claim 8.

11. When machining is performed by bringing the tool into contact with a workpiece being rotated by the spindle, the strain related to the expansion and contraction of the tool in the axial direction of the surface of the holding member that intersects the direction of the main force component is measured. The method for detecting chatter according to claim 8.

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