Stylus

Abstract

This stylus is provided at a tip of a measurement probe, the stylus comprising: a stylus tip that makes contact, on an outer peripheral surface thereof, with an object being measured; and a stylus shaft one end of which is connected to the stylus tip. The stylus tip has a hard coating on the outer periphery thereof, and a 0.10 mm × 0.10 mm area having five or fewer coating protrusions is selectable from the outer peripheral surface of the stylus tip, where the coating protrusions are defined as protrusions of the hard coating that locally protrude from the outer peripheral surface and have a height of 1 μm or more.

Description

stylus

[0001] The present invention relates to a stylus to be attached to the tip of a measuring probe for a two-dimensional or three-dimensional measuring device, particularly a measuring probe suitable for scanning measurement.

[0002] Two-dimensional or three-dimensional measuring devices are used to measure precision mechanical parts such as gears. Measuring probes come into contact with the surface of these precision mechanical parts to measure the surface shape. Among these measurement methods, scanning measurement, which is a continuous measurement method, uses a much larger number of measurement points than point measurement, improving the reliability of the measurement results.

[0003] However, scanning measurements require an increased number of measurement points, resulting in increased measurement time and reduced measurement efficiency unless the measurement speed is increased. Increasing the measurement speed can lead to new problems, such as wear or breakage of the stylus tip, which constitutes the stylus attached to the tip of the measurement probe, tip damage, and scratches on the workpiece. If the stylus tip wears or breaks or is damaged during scanning measurements, the measurement must be repeated or the reliability of the acquired data may be compromised. Furthermore, using a wear-resistant superhard material for the stylus tip body to extend its lifespan due to wear not only increases the cost but also increases the risk of stylus tip breakage or tip damage. These problems are likely influenced by factors other than measurement pressure and measurement speed, such as the hardness, surface texture, and toughness of the stylus tip contact surface.

[0004] In this regard, for example, Patent Document 1 discloses a stylus whose tip ball has been treated to reduce friction with a DLC (diamond-like carbon) film that has high hardness and high wear resistance, with the aim of providing a three-dimensional measuring device and a probe used therein that are capable of realizing high-precision, high-speed, and stable scanning measurements. Patent Document 2 also discloses a method for manufacturing a stylus having such a low-friction treated tip ball.

[0005] JP 2006-201105 A JP 2019-190999 A

[0006] However, the present inventors have found that when a high-hardness coating treatment such as that described in Patent Documents 1 and 2 is applied to a stylus tip, while further increases in measurement speed are desirable to improve efficiency, it may not always be possible to simultaneously suppress peeling, wear, and breakage of the coating applied to the stylus tip and suppress scratches on the measurement workpiece, depending on conditions such as the object being measured and the measurement speed. In other words, the problem with conventionally disclosed styli is that they may be insufficient in terms of the durability of the stylus tip and the suppression of scratches on the measurement workpiece. The present invention has been made in consideration of these problems, and aims to provide a stylus that can suppress wear of the stylus tip at the tip of a measurement probe and scratches on the workpiece, thereby extending the durability and suppressing scratches on the measurement workpiece.

[0007] The present inventors conducted research to solve the above-mentioned problems and discovered that the presence of protrusions generated during the formation of a hard coating on the outer periphery of the stylus tip is a major factor in the problem. DLC coatings formed by chemical vapor deposition (CVD) using hydrocarbon gas as a raw material are generally characterized by the fact that they produce fewer protrusions due to the film formation method. However, they are inferior in wear resistance to DLC coatings formed by physical vapor deposition (PVD) using solid carbon as a raw material. Therefore, DLC coatings formed by PVD are suitable for components where wear and scratches are a problem. However, the present inventors discovered that DLC coatings formed by PVD produce more protrusions than DLC coatings formed by CVD, which causes the above-mentioned problems. After examining various conditions for forming a hard coating on the outer periphery of the stylus tip, the inventors discovered that the above problem could be solved by forming a hard coating that meets specific conditions on the outer periphery of the stylus tip, and thus completed the present invention.

[0008] The present invention relates to a stylus provided at the tip of a measurement probe, the stylus having a stylus tip that contacts an object to be measured on its outer circumferential surface, and a stylus shaft one end of which is connected to the stylus tip, the stylus tip having a hard coating on its outer periphery, and when a coating protrusion is defined as a hard coating protrusion having a height of 1 μm or more that occurs locally from the outer circumferential surface, the stylus can select a 0.10 mm x 0.10 mm area on the outer circumferential surface of the stylus tip in which the number of coating protrusions is 5 or less.

[0009] According to the present invention, it is possible to provide a stylus tip that can reduce wear and breakage of the stylus tip at the tip of the measurement probe in a two-dimensional or three-dimensional measuring device, extend the durability life, and reduce scratches on the workpiece being measured.

[0010] 1 is a schematic diagram showing an example of the configuration of a measurement probe; 2 is a cross-sectional schematic diagram showing the vicinity of the contact portion of the stylus tip; 3 (a) is an example when the shape of the stylus tip is spherical, and 4 (b) is an example when it is abacus-shaped; 5 is a photograph showing coating protrusions on a hard coating; and 6 is a photograph showing an inspection device for a wear test.

[0011] One embodiment of the present invention is a stylus provided at the tip of a measurement probe, the stylus having a stylus tip that contacts the object to be measured on its outer periphery and a stylus shaft one end of which is connected to the stylus tip, the stylus tip having a hard coating on its outer periphery, and where a coating protrusion is defined as a hard coating protrusion having a height of 1 μm or more that occurs locally from the outer periphery, the stylus is capable of selecting a 0.10 mm x 0.10 mm area on the outer periphery of the stylus tip in which the number of coating protrusions is 5 or less. Specific embodiments are described below. However, unless otherwise specified, the configurations described in the following embodiments are not intended to limit the technical scope of the invention to those configurations alone.

[0012] The stylus according to this embodiment can be attached to the tip of a measurement probe of a measuring device. The configurations of the measuring device and the measurement probe are not particularly limited, and the stylus can be applied to, for example, a three-dimensional measuring device for measuring precision mechanical parts such as gears and its measurement probe.

[0013] <Stylus> A measurement probe equipped with a stylus according to this embodiment will be described using FIG. 1. FIG. 1 is a schematic diagram showing an example of a measurement probe equipped with a stylus according to this embodiment. The stylus attached to the measurement probe is composed of a stylus shaft and a stylus tip. In FIG. 1, the up-down direction is the "radial direction" and the left-right direction is the "axial direction." The stylus 1 shown in FIG. 1 has a stylus shaft 10 and a stylus tip 11 provided on the tip side of the stylus shaft 10, and one end of the stylus shaft 10 is connected to the stylus tip 11. Measurement is performed by bringing the outer circumferential surface of the stylus tip 11 into contact with the object to be measured. The stylus tip 11 has a hard coating on its outer periphery.

[0014] In this specification, the term "contact portion" refers to the portion of the outer circumferential surface of the stylus tip 11 where the stylus tip 11 comes into contact with the object to be measured. Depending on the shape of the stylus tip 11 and the object to be measured, the entire outer circumferential surface of the stylus tip 11 can be the contact portion, but an example is the portion of the outer circumferential surface of the stylus tip 11 that is farthest from the central axis of the stylus shaft 10, as shown by reference numeral 12 in Figures 2(a) and 2(b).

[0015] In the example shown in Fig. 1, the shape of the stylus shaft 10 is cylindrical and the shape of the stylus tip 11 is abacus-shaped, but the shape of the stylus shaft 10 is not particularly limited and may be conical or rectangular. The shape of the stylus tip 11 may also be, for example, barrel-shaped, spherical, hemispherical, conical, cylindrical, or disk-shaped. Fig. 2(a) shows a spherical shape and (b) shows an abacus-shaped shape.

[0016] The material of the base material of the stylus shaft 10 and the stylus tip 11 is not particularly limited and may be a magnetic or non-magnetic material, such as, but not limited to, steel, ruby, cemented carbide, etc. Furthermore, a material with little thermal expansion and contraction is desirable.

[0017] <Hard coating> The stylus tip 11 has a hard coating on its outer periphery. The hard coating may cover at least a portion of the outer periphery of the stylus tip 11, including the contact portion, but from a manufacturing standpoint, it is preferable that the hard coating covers the entire outer periphery of the stylus tip 11. The hard coating may also cover at least a portion of the outer periphery of the stylus shaft 10. The stylus tip 11 may have a different coating or underlayer between the base material of the stylus tip 11 and the outermost hard coating. When the stylus tip 11 has multiple coatings, hereinafter, "hard coating" refers to the outermost hard coating, unless otherwise specified.

[0018] The composition of the hard coating is not particularly limited, but from the viewpoint of excellent wear resistance, it is preferably at least one selected from the group consisting of DLC coating, chromium nitride coating, and titanium nitride coating. Furthermore, a DLC coating is more preferable, and a so-called hydrogen-free DLC coating having a hydrogen content of 5.0 at% or less is even more preferable. The hydrogen content may be 2 at% or less, 1 at% or less, or 0.5 at% or less.

[0019] The inventors have discovered that the coating protrusions present on the surface of the hard coating are related to the balance between wear of the stylus tip 11 and suppression of scratches on the measurement workpiece. In this specification, coating protrusions refer to hard coating protrusions of 1 μm or more in height that arise locally from the outer surface of the stylus tip when the hard coating surface on the outer periphery of the stylus tip is measured under the following conditions:

[0020] The method for measuring the number of coating protrusions is described below. Figure 3 is a photograph of the coating protrusions on the surface of a hard coating observed under the following conditions: Hard coating: Hydrogen-free DLC coating, Hydrogen content: 0.3 at%, Film thickness: 4 μm, Measuring instrument: Keyence VK-X100 laser microscope, Measurement magnification: 50x objective lens, Measurement field of view: 0.20 mm x 0.27 mm. For example, φ1.7 x 1.6 in Figure 3 indicates that the major axis of the coating protrusions is 1.7 μm and the height of the coating protrusions is 1.6 μm. <Method for measuring the number of coating protrusions> The protrusions on the hard coating surface are measured using the following method. Using a Keyence VK-X100 laser microscope with a 50x objective lens, a microscopic image and three-dimensional data of the object surface are obtained. The measurement field of view is 0.20 mm x 0.27 mm. The measurement field of view may be changed as appropriate depending on the size and shape of the stylus tip being the object. After trimming the captured image to an arbitrary 0.10 mm x 0.10 mm field of view, the automatic noise removal function of the laser microscope analysis application is used to remove abnormal data values ​​during image acquisition, and the inclination of the outer peripheral surface during measurement is corrected to a flat surface using automatic surface tilt correction. A horizontal line is then drawn within the image on the profile screen, and protrusions with a height of 1 μm or more relative to the outer peripheral surface are counted, and this number is taken as the number of coated protrusions present in the 0.10 mm x 0.10 mm area. The diameter of the protrusions may also be measured when measuring the height.

[0021] In this embodiment, when the number of coated protrusions is measured using the above method, a 0.10 mm x 0.10 mm area with 5 or fewer coated protrusions can be selected. It is even more preferable to select a 0.10 mm x 0.10 mm area with 3 or fewer coated protrusions. Forming a hard coating that allows such a 0.10 mm x 0.10 mm area to be selected can reduce scratches during measurement.

[0022] Protrusions on the surface of a hard coating can occur when the hard coating is formed around the outer periphery of the stylus tip 11. These protrusions are formed when large molten particles called droplets, which are generated when raw materials are evaporated by plasma, adhere to the coating. The inventors have discovered that by setting the height and number of these protrusions within a specific range, it is possible to both suppress stylus wear and reduce scratches on the workpiece.

[0023] The maximum height of the coated protrusions is preferably 8 μm or less, more preferably 7 μm or less, and particularly preferably 5 μm or less. When the maximum height of the coated protrusions is 8 μm or less, deep scratches during measurement can be suppressed. The major axis of the coated protrusions is preferably 12 μm or less, more preferably 9 μm or less, and particularly preferably 7 μm or less. When the major axis of the coated protrusions is 12 μm or less, deep scratches during measurement can be suppressed.

[0024] The nanoindentation surface hardness of the hard coating is preferably 12 to 30 GPa. A surface hardness of 12 GPa or more of the hard coating suppresses wear of the stylus tip 11. Furthermore, a surface hardness of 30 GPa or less is preferable from the viewpoint of suppressing peeling of the hard coating and from the viewpoint of manufacturing. The surface hardness of the hard coating is more preferably 15 to 28 GPa. Generally, in consideration of wear resistance, a higher hardness of the hard coating is preferred, but if the hardness of the hard coating is too high, the hard coating tends to peel off easily, so it is preferable to keep it within the above range. The surface hardness of the hard coating can be adjusted by the material of the hard coating and the processing conditions during film formation.

[0025] The thickness of the hard coating in the 0.10 mm x 0.10 mm region is preferably 3 to 10 μm. On the other hand, if the thickness of the hard coating exceeds 10 μm, there is a risk of peeling of the hard coating and it may be difficult to control the height of the protrusions of the hard coating. The lower limit of the thickness may be 3 μm or more, or 5 μm or more. The upper limit of the thickness may be 8 μm or less, or 6 μm or less. A hard coating thickness of 3 μm or more is preferable because the wear suppression effect of the hard coating is easily exerted. Note that if other coatings or underlayers are present between the substrate of the stylus tip and the outermost hard coating, it is preferable that the total thickness including these is within the above range. The thickness of the hard coating can be appropriately adjusted depending on the conditions during film formation.

[0026] Furthermore, the inventors have found that when the object to be measured has a shape like a gear, the stylus intermittently hits the object during measurement, and the impact easily causes chipping (breakage) of the stylus. From the viewpoint of suppressing this, the hard coating is formed to have a plastic deformation work (W ｐｌａｓｔ ) is preferably 6.0 nJ or more.

[0027] Plastic deformation work (plastic deformation energy) (W ｐｌａｓｔ ) is the amount of work required for plastic deformation of the coating, which remains deformed even after the indenter is removed, out of the amount of work required for deformation of the coating by the indenter pressed into the coating surface in a nanoindentation test. Also, the amount of work required for elastic deformation (elastic deformation energy) (W ｅｌａｓｔ ) is the work released when the indenter is unloaded and the coating returns to its original shape. ｐｌａｓｔ The work of plastic deformation (W) measured at a load of 100 mN by a nanoindentation test is an index that characterizes a coating that is prone to plastic deformation when a foreign object is pressed into the coating surface. ｐｌａｓｔ ) is preferably 6.0 nJ or more, since it is possible to suppress peeling of the coating due to an impact load during measurement. ｐｌａｓｔ) is more preferably 6.4 nJ or more. ｐｌａｓｔ Although there is no particular upper limit for the value of ), if it is too large, it is not possible to maintain a hardness that satisfies the demand for wear resistance, so it is preferable that it is 10.5 nJ or less.

[0028] The nanoindentation test is performed using a Fisher Instruments nanoindentation measuring instrument, model HM-2000, with a Vickers indenter under the following conditions: an indentation load of 100 mN, a loading time of 30 seconds (seconds) until the maximum indentation load is reached, a holding time of 5 seconds (seconds), and an unloading time of 30 seconds (seconds). The plastic deformation work and elastic deformation work of the hard coating, as well as the nanoindentation hardness, are calculated using the load-indentation depth curve obtained in the nanoindentation test. The measured value is the average of measurements taken at three locations around the circumference of one stylus tip in the circumferential direction of the hard coating.

[0029] In addition, the total work load (also referred to as total deformation work load, W) calculated by the following formula (1) measured by the nanoindentation test ｔｏｔａｌ ) is preferably 18.0 nJ or more. There is no particular upper limit to the total work load, but it is preferably 24.0 nJ or less. By satisfying the above range, it is possible to achieve both good abrasion resistance and prevention of coating peeling due to impact load during measurement. W ｔｏｔａｌ = W ｐｌａｓｔ + W ｅｌａｓｔ (1)

[0030] Furthermore, the plastic deformation power (η ｐｌａｓｔ ) is preferably 32.4% or more, and the plastic deformation power is more preferably 33.0% or more, and even more preferably 34.0% or more. The upper limit of the plastic deformation power is not particularly limited, but it is preferably 45.0% or less. By satisfying the above range, it is possible to achieve both good abrasion resistance and suppression of coating peeling due to impact load during measurement. η ｐｌａｓｔ = (W ｐｌａｓｔ / W ｔｏｔａｌ ) × 100 (%) (2)

[0031] In addition, the nanoindentation hardness (HIT) and the plastic deformation work (W ｐｌａｓｔ ) ratio (HIT / W ｐｌａｓｔ ) is preferably 4.5 GPa / nJ or less, and more preferably 4.1 GPa / nJ or less. ｐｌａｓｔ ) ratio (HIT / W ｐｌａｓｔ Although the lower limit of the elastic modulus (A) is not particularly limited, it is preferably 1.5 GPa / nJ or more. By satisfying this range, it is possible to achieve both good abrasion resistance and prevention of coating peeling due to impact load during measurement.

[0032] Examples of film formation methods for forming a hard coating on the stylus tip 11 (film formation process) include physical vapor deposition (PVD) methods such as ion plating and sputtering. PVD is preferred from the viewpoint of providing the wear resistance of the DLC coating required for stylus measurement. PVD (physical vapor deposition) is a type of vapor deposition method in which particles emitted from a target are attached to a substrate to form a film on the surface of a material, and can also be called physical vapor deposition. PVD methods include ion plating, vacuum deposition, ion beam deposition, sputtering, and filtered cathodic vacuum arc (FCVA). Chemical vapor deposition (CVD) methods such as thermal CVD and plasma CVD can also be included.

[0033] The number and size of the protrusions in the hard coating can be adjusted to the desired value by adjusting the manufacturing method of the hard coating. More specifically, for example, by reducing the arc current value, which is one of the film formation parameters, the surface temperature of the melting point called the arc spot that occurs on the target surface during vacuum arc discharge can be reduced, thereby reducing the number of molten particles called droplets that cause protrusions in the coating. Furthermore, by reducing the diameter of the aperture, which is the path through which carbon ions emitted from the target adhere to the substrate, droplets that fly out from the target can be trapped within the path, thereby reducing the number of droplets in the coating.

[0034] The plastic deformation work measured by the nanoindentation test can be adjusted to a desired value by adjusting the manufacturing method of the hard coating. More specifically, when forming a hard coating using the FCVA method, the desired value can be achieved by adjusting the applied pulse bias voltage, the substrate temperature during hard coating formation, the chamber pressure (vacuum degree), the arc current, the target purity, etc.

[0035] When the hard coating includes a DLC coating, the DLC coating may be a hydrogen-containing DLC ​​coating or may be a so-called hydrogen-free DLC. For example, the hydrogen content may be 5.0 at% or less. A DLC coating with a high hydrogen content has lower wear resistance than a DLC coating that does not contain hydrogen. A known method can be used to form a hydrogen-free DLC coating, such as ion plating or sputtering.

[0036] The hard coating may contain other elements, such as, but not limited to, Si, Ti, W, Cr, Mo, Nb, V, etc. If these elements are contained, it is preferable that the total amount is 40 at% or less. Furthermore, a base layer containing Cr, Ti, Si, etc. may be provided on the stylus substrate. Providing a base layer can improve adhesion between the substrate of the stylus tip and the hard coating. The stylus according to this embodiment is completed through the above process, but surface processing such as buffing may be performed after film formation.

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0038] As shown in Table 1, the material of the stylus tip and the hard coating on the periphery were adjusted to produce styli according to Examples 1 and 2 and Comparative Examples 1 to 3. The amount of wear of each stylus tip shown in Table 2 was determined by carrying out the following wear test.

[0039] <Wear test> A probe was attached to the inspection device shown in Figure 4, brought into contact with a cylindrical workpiece under the following conditions, and the workpiece was rotated for the specified test time shown in Table 2. The part of the stylus tip that was in contact with the workpiece was observed under a microscope before and after the test, and the amount of wear was calculated. Test conditions Push-in amount (force): 150 μm (approximately 25 g) Stylus tip: abacus-shaped, φ1.5 mm Workpiece diameter: φ70 mm Workpiece material: alloy tool steel Workpiece surface roughness: Ra1.5 mm Workpiece rotation speed: 1.5 rpm (scanning speed 5.5 mm / sec)

[0040] <Evaluation of Workpiece Scratches> Scratches occurring on the workpiece due to contact with the stylus tip were tested using a reciprocating abrasion tester under the following conditions, which were stricter than those used in the above-mentioned abrasion test. Test Conditions: Pressing Load: 2.5 N, Stroke: 50 mm, Speed: 100 strokes / min, Lubricant: None (unlubricated = dry). Upper Test Piece: Stylus Tip. Lower Test Piece: Chromium Molybdenum Steel. Surface: Mirror Finish. Test Time: 30 seconds. The evaluation criteria were as follows: the depth and number of scratches occurring on the lower test piece after the test were measured. Scratches of 1.5 μm or more in depth were rated "NG," while none were rated "OK." Furthermore, five or more scratches of 0.5 μm to 1.5 μm in depth were rated "C," one to four scratches were rated "B," and none were rated "A." The results are shown in Table 3.

[0041] As is clear from the above examples, by providing the stylus tip according to this embodiment at the tip of the measurement probe, it is possible to perform measurement work while suppressing wear on the stylus tip and preventing scratches on the measurement workpiece. Note that although the present invention will be described in detail with reference to specific examples, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0042] 1 Stylus 10 Stylus shaft 11 Stylus tip 12 Contact portion 13 Probe

Claims

1. A stylus provided at the tip of a measurement probe, the stylus having a stylus tip that contacts an object to be measured on its outer circumferential surface, and a stylus shaft one end of which is connected to the stylus tip, the stylus tip having a hard coating on its outer periphery, and when a coating protrusion is defined as a hard coating protrusion having a height of 1 μm or more that occurs locally from the outer circumferential surface, a 0.10 mm x 0.10 mm area on the outer circumferential surface of the stylus tip in which the number of coating protrusions is 5 or less can be selected.

2. The stylus according to claim 1, wherein the thickness of the hard coating in the 0.10 mm x 0.10 mm area is 3 μm or more and less than 10 μm.

3. The stylus according to claim 1, wherein the nanoindentation hardness of the hard coating is 12 GPa or more and 30 GPa or less.

4. The stylus according to claim 1, wherein the hard coating is a DLC hard coating having a hydrogen content of 5.0 at % or less.

5. The hard coating has a plastic deformation work (W ｐｌａｓｔ 2. The stylus of claim 1 , wherein the force (f) is 6.0 nJ or greater.

6. The hard coating has a total work load (W) calculated by the following formula (1) measured at a load of 100 mN by the nanoindentation test. ｔｏｔａｌ 2. The stylus of claim 1, wherein W is 18.0 nJ or more. ｔｏｔａｌ = W ｐｌａｓｔ + W ｅｌａｓｔ (1) 7. The hard coating has a plastic deformation power (η ｐｌａｓｔ ) is 32.4% or more. ｐｌａｓｔ = (W ｐｌａｓｔ / W ｔｏｔａｌ ) × 100 (%) (2) 8. A stylus according to any one of claims 1 to 7, wherein the ratio (HIT / Wplast) of the nanoindentation hardness (HIT) of the hard coating to the plastic deformation work (Wplast) measured at a load of 100 mN by the nanoindentation test is 4.5 GPa / nJ or less.

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