Cutting Blade for a Robotic Work Tool

Abstract

A cutting blade (100) adapted to be carried by a tool holder (20) provided in a robotic work tool (10), the cutting blade (100) comprising a blade body (110) and a cutting edge (120, 121) extending along at least a portion of the periphery (111) of the blade body (110), and a slit (113) arranged to receive a pin (30) for attaching the cutting blade (100) to said tool holder (20), wherein the cutting blade (100) is movable such that the pin (30) may be displaced within the slit (113). The hardness of the cutting blade (100) decreases in direction from the cutting edge (120, 121) towards the center (125) of the blade body (110) such that the hardness of the cutting edge (120, 121) is higher than the hardness of at least a center portion (126) of the blade body (110). The present disclosure also relates to a method for manufacturing a cutting blade.

Claims

1. A cutting blade adapted to be carried by a tool holder provided in a robotic work tool, the cutting blade comprising a blade body and a cutting edge extending along at least a portion of a periphery of the blade body, and a slit arranged to receive a pin for attaching the cutting blade to said tool holder, wherein the cutting blade is movable such that the pin is displaceable within the slit, and wherein hardness of the cutting blade decreases in direction from the cutting edge towards a center of the blade body such that hardness of the cutting edge is higher than hardness of at least a center portion of the blade body.

2. The cutting blade according to claim 1, wherein the cutting blade is elongate and the cutting edge comprises a first cutting edge and a second cutting edge arranged opposite to each other and wherein the slit extends within the blade body and between the first cutting edge and the second cutting edge.

3. The cutting blade according to claim 1, wherein the cutting edge is a beveled cutting edge and the blade body extends adjacent the beveled cutting edge, and wherein the cutting edge is ground to form a bevel on both faces of the cutting blade.

4. (canceled)

5. The cutting blade according to claim 1, wherein the cutting edge is integral with the blade body, wherein the cutting edge has a hardness of 650-850 HV1 and at least the center portion of the blade body has a hardness of 450-600 HV1, and wherein the cutting blade is manufactured of spring steel.

6. (canceled)

7. (canceled)

8. The cutting blade according to claim 1, wherein the cutting blade is manufactured of a steel material comprising: C: 0.70-1.30 (wt %) Mn: 0.30-0.90 (wt %) Si: 0.15-0.35 (wt %) P: ≤0.025 (wt %) S: ≤0.025 (wt %) Cr: ≤0.40 (wt %) Mo: ≤0.10 (wt %) Ni: ≤0.40 (wt %) remainder Fe and unavoidable impurities.

9. The cutting blade according to claim 8, wherein the steel material comprises: C: 1.20-1.30 (wt %); Mn: 0.30-0.60 (wt %).

10. The cutting blade according to claim 1, wherein the cutting blade is manufactured of case hardening steel or nitriding steel.

11. The cutting blade according to claim 1, wherein the cutting edge comprises a first steel material and the blade body comprises a second steel material and wherein the cutting edge and the blade body are joined to each other, and wherein the cutting edge has a hardness of 750-1000 HV1 and the blade body has a hardness of 450-600 HV1.

12. (canceled)

13. The cutting blade according to claim 11, wherein the first steel material is a high speed steel.

14. The cutting blade according to claim 13, wherein the second steel material is carbon steel or alloyed carbon steel.

15. The cutting blade according to claim 11, wherein the first steel material comprises in weight %: C: 0.78-0.94 (wt %) Mn: ≤0.40 (wt %) Si: ≤0.45 (wt %) P: ≤0.03 (wt %) S: ≤0.03 (wt %) Cr: 3.75-4.50 (wt %) V: 1.75-2.20 (wt %) Mo: 4.50-5.50 (wt % W: 5.50-6.70 (wt %) remainder Fe and unavoidable impurities,

16. The cutting blade according to claim 11, wherein the second material is a steel material comprising: C: 0.29-0.33 (wt %) Mn: 0.90-1.1 (wt %) Si: 0.20-0.35 (wt %) P: ≤0.02 (wt %) S: ≤0.01 (wt %) Cr: 3.80-4.00 (wt %) V: 0.30-0.40 (wt %) Mo: 1.0-1.2 (wt % remainder Fe and unavoidable impurities.

17. The cutting blade according to claim 1, comprising a wear resistant coating comprising TiN and/or CrN and/or DLC, and wherein the cutting edge is through-hardened.

18. (canceled)

19. The cutting blade according claim 1, wherein the cutting edge comprises cemented carbide and the blade body comprises steel material and wherein the cutting edge and the blade body are joined to each other, and wherein the cutting edge is 2 mm wide.

20. (canceled)

21. A method for manufacturing a cutting blade, comprising the steps: providing a blade precursor (200) comprising hardenable steel material having an edge portion and a body portion; forming at least one individual slit in the body portion of the blade precursor; hardening at least the edge portion of the blade precursor by heating to austenitizing temperature followed by quenching; grinding a bevel on at least a portion of the edge portion of the blade precursor thereby forming a cutting edge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1: A schematic drawing of a robotic work tool comprising a cutting blade according to an embodiment of the present disclosure.

[0039] FIG. 2: A schematic drawing of a portion of a tool holder of the robotic work tool shown in FIG. 1.

[0040] FIG. 3a: A schematic front view drawing of a cutting blade for a robotic work tool according to an embodiment of the present disclosure.

[0041] FIG. 3b: A schematic drawing of a cutting blade for a robotic work tool according to an embodiment of the present disclosure in cross-section.

[0042] FIGS. 4a-4f: Schematic drawings illustrating steps of a method for manufacturing a cutting blade for a robotic work tool according to the present disclosure.

[0043] FIG. 5: A flowchart showing steps of a method for manufacturing a cutting blade for a robotic work tool according to the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0044] The cutting blade for a robotic work tool according to the present disclosure will now be described more fully hereinafter. The cutting blade for a robotic work tool according to the present disclosure may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those persons skilled in the art. Same reference numbers refer to same elements throughout the description. Wherein, hereinabove or hereinafter, reference is made to “cutting blade” this feature may be nominated “robotic lawnmower cutting blade”

[0045] FIG. 1 shows a robotic work tool 10 embodied as a robotic lawnmower having at least one cutting blade 100 according to the present disclosure, that is a robotic lawnmower cutting blade 100. The robotic work tool 10 is, apart from the cutting blade 100, identical to the robotic work tool disclosed in WO2016/150503. The robotic work tool 10 is therefore hereinafter only described with reference to features relating to the cutting blades 100. Thus, the robotic work tool 10 comprises a tool holder 20, which is embodied as a cutting blade holder and may be a circular disc. The tool holder 20 is rotationally attached to the robotic work tool 10 and driven in rotational movement around its center axis by a cutter motor 21. The tool holder 20 carries at least one cutting blade 100. However, typically the tool holder 20 carries multiple cutting blades 100 such as three cutting blades 100 as shown in FIG. 2 or more. The cutting blades 100 are attached along the periphery of the tool holder 20. FIG. 2 shows an enlarged view of the encircled portion of the tool holder 20 of FIG. 1 and an obstacle 40, such as a stone, in the cutting path of the blade 100. Thus, the tool holder 20 comprises at least one pin 30 that extends from the face of the tool holder 20. The pin 30 is arranged at or adjacent the periphery of the tool holder 20. The cutting blade 100, which will be described in detail hereinafter, comprises a slit 113 in which the pin 30 is received. The cutting blade 100 is thereby arranged to be able to rotate around the pin 30 and also able to move relative the pin 30 along a path defined by the extension of the slit 113. The cutting blade may perform one or both of these movements in response to hitting the object 40.

[0046] FIG. 3a shows a cutting blade 100 according to the present disclosure. The cutting blade 100 may be rectangular and comprises a blade body 110 which may be rectangular and comprises a periphery 111 which comprises opposite long-sides 111.1, 111.2 and opposite short-sides 111.3, 111.4. The cutting blade may be flat, i.e. it may extend in a single plane. The blade body 110 comprises a slit 113 which is configured to receive the pin 30 of the tool holder 20. In FIG. 3a, the slit 113 extends parallel with the long-sides of the blade body 110. However, other extension of the slit 113 is possible, such as a curved or diagonal extension. In some embodiments, the blade 100 may, instead of a slit 113, have a circular hole which configured to receive the pin 30. The cutting blade 100 further comprises a first cutting edge 120 and a second cutting edge 121 which respectively extend adjacent the long-sides 111.1, 111.2 of the blade body 110 on opposite sides of the blade body 110. FIG. 3b shows the cutting blade in cross-section. Thus, the blade body 110 forms the center of the cutting blade which may be of uniform cross section. The first and the second cutting edge 120, 121 extend respectively along the periphery 111 of the blade body 110 and on opposite sides of the blade body. The first and the second cutting edge 120, 121 may have a bevel 122. Thus, seen in cross-section of the cutting blade 110, the beginning of the bevel 122 may define the interface between the first and the second cutting edge 120, 121 and the blade body 110. Thus, the blade body 110 extends along the bevel 122 of the cutting edges 120, 121.

[0047] The cutting blade may be 35.5 mm long, 18.7 mm wide and 0.6 mm thick. The cutting edges may be 1-2 mm wide and the bevel is 30° on both faces of the blade.

[0048] Returning to FIG. 3a, the blade body 110 has a center 125 and may also have a center portion 126 which extends from the center 125 of the blade body towards the first and the second cutting edges 120, 121. The blade body 110 may further comprise at least one border portion 112 which may extend at least partially between the center portion 125 and one or both of the cutting edges 120,121. For reasons relating to the manufacturing of the cutting blade 100, the center portion 126 and the border portion 112 may have different material characteristics. For example, in the present disclosure, the cutting edges 120, 121 may be hardened. In the hardening process the cutting edges are heated which may lead to some heat dissipation to the border portion 126 of the blade body 110. The dissipated may lead to partial hardening of the border portion and a hardness increase thereof. However, when the body portion is unaffected the center portion 126 has the same extension as the body portion 110.

[0049] According to the present disclosure, the hardness of the cutting blade 100 decreases in direction from the cutting edges 120, 121 towards the center 125 of the blade body 110 such that the hardness of the cutting edges 120, 121 is higher than the hardness of the center portion 126 of the blade body 110.

[0050] According to a first embodiment of the cutting blade 100, the cutting edges 120, 121 are integral with the blade body 110. Thus, the cutting edges 120, 121 and the blade body form one single piece of material without, i.e. free of, any joints there between. The, cutting blade 100 may thereby consist of a hardenable steel material such as carbon steel, low-alloy carbon steel or spring steel.

[0051] Such steels may be hardened by heating the steel above a predetermined temperature, at which the microstructure of the steel becomes austenitic followed by rapid quenching in e.g. oil, water or gas. During quenching, the austenitic microstructure transform into martensite or bainite or a mixture thereof.

[0052] Typically, the cutting blade 100 is subjected to local hardening of the cutting edges 120, 121. The blade body 110 is not subjected to hardening and is therefore less hard than the cutting blades. Typically, at least the center portion 126 of the blade body 110 has an annealed structure of ferrite and perlite and/or cementite.

[0053] The cutting edges 120, 121 may therefore have a hardness of 650-850 HV1 and at least the center portion 126 of the blade body 110 may have a hardness of 450-600 HV1. The resulting hardness of the cutting edges 120 and 121 may be controlled by selection of the steel material for manufacturing the cutting blade. Typically, the cutting edges 120 and 121 are through-hardened

[0054] For example, the cutting blade may be manufactured of a steel material comprising (in weight %): [0055] C: 0.70-1.30; Mn: 0.30-0.90; Si: 0.15-0.35; P: ≤0.025; S: ≤0.025; Cr: ≤0.40; Mo: ≤0.10; Ni: ≤0.40. The remainder is constituted by Fe and unavoidable or natural occurring impurities.

[0056] Examples of such steel material are the steels C75S, C85S, C90S, C100S and C125S of the steel standard SS-EN10132-4

[0057] The hardenability increases with increased contents of carbon (C) and manganese (Mn). Therefore, the carbon content may be 1.20-1.30 wt % and the manganese content may be 0.3-0.6 wt %.

[0058] According to a second embodiment of the cutting blade, the cutting edges 120, 121 comprises a first steel material and the blade body 110 comprises a second steel material. The first and second steel materials are steels having different compositions. The cutting edges 120, 121 and the blade body 110 are thereby joined to each other by joints formed by e.g. welding or brazing. If the cutting edges 120, 121 and the blade body 110 are joined to each other by welding, a welded joint may be created. In some embodiments, this welded joint may be grinded down.

[0059] According to an example, the first steel material, which forms the cutting edges 120, 121, is a high speed steel (HHS). For example, the first steel material maybe a steel material comprising (in weight %): [0060] C: 0.78-0.94; Mn: ≤0.45; Si: ≤0.45; P: ≤0.03; S: ≤0.02; Cr: 3.75-4.50; V: 1.75-2.20; Mo: 4.70-4.5; W: 5.50-6.75; remainder Fe and unavoidable or naturally occurring impurities. Mn may be 0.15-0.40 wt %.

[0061] An example of such a steel material is ASTMI M2 steel, which is commercially available from the company OTAI Special Steel.

[0062] According to another example, the steel material comprises (in weight %): [0063] C: 1.05-1.15; Mn: 0.20-0.45; Si: ≤0.7; P: ≤0.03; S: ≤0.02; Cr: 3.50-4.50; V: 0.95-1.5; Mo: 9.0-10.0; W: 1.15-2.0; Co: 7.75-8.75; remainder Fe and unavoidable or naturally occurring impurities.

[0064] An example of such a steel material is AISI M42 steel, which is commercially available from the company Böhler-Uddeholm AB.

[0065] The second steel material, which forms the blade body 110, may be one of the steel materials described in the first embodiment of the cutting blade of the present disclosure.

[0066] Alternatively, the second steel material may be a steel comprising (in weight %): [0067] C: 0.29-0.33; Mn: 0.90-1.1; Si: 0.20-0.35; P: ≤0.02; S: ≤0.01; Cr: 3.80-4.00; V: 0.30-0.40; Mo: 1.0-1.2; remainder Fe and unavoidable or naturally occurring impurities.

[0068] Typically, the cutting edges 120, 121 are hardened and the blade body is in annealed condition. The cutting edges may be through-hardened.

[0069] The cutting edges 120, 121 may have a hardness of 750-1000 HV1 and at least the center portion 126 of the cutting body may have a hardness of 450-600 HV1.

[0070] According to a third embodiment, the cutting edges 120, 121 comprises cemented carbide and the blade body 110 comprises a steel material as disclosed under the first and the second embodiment of the cutting blade according to the present disclosure. Cemented carbide typically comprises particles of tungsten carbide (WC) in a binder of metal alloy, such as nickel-cobalt alloy. Cutting edges of cemented carbide may have a hardness of 1000-1350 HV1. An example of a suitable cemented carbide is HC40 which is commercially available from the company Ceratizit.

[0071] Optionally, the cutting blades of the three embodiments described hereinabove may comprise a wear resistant surface coating which is applied on at least the cutting edges 120, 121. The coating may for example consist or comprise titanium nitride (TiN) or chromium nitride (CrN) or diamond-like-carbon (DLC) or mixtures thereof.

[0072] Following is a description of methods for manufacturing the cutting blade according to the first and the second embodiment of the present disclosure. Reference is made to the drawings 4a-4f and to the flowchart of FIG. 5. Several steps of the methods for manufacturing the cutting blades according to the first, the second and the third embodiments are identical. Therefore, the method for manufacturing the cutting blade according to the first embodiment is described in detail hereinafter together with differentiating steps of the methods of manufacturing the cutting blade according to the second and the third embodiment where appropriate.

[0073] Thus, turning to FIG. 4a, in a first step 1000 (see FIG. 5), a blade precursor 200 is provided. For manufacturing the cutting blade of the first embodiment, the blade precursor may be provided as strip of hardenable steel material having a width and a thickness that equals the dimensions of the final cutting blade. In terms of length the strip, i.e. the blade precursor may have a length that equals the length of the final cutting blade.

[0074] However, for high productivity the length of the strip may equal the total length of multiple cutting blades. The steel material may be selected from the steels disclosed hereinabove. The cutting blade has an edge portion 210, 211 which is the portion of the precursor 200 that will form the cutting edge 120, 121 of the final cutting blade. The blade precursor 200 also has a body portion 220 which is the portion of the blade precursor 200 that will constitute the body portion 110 of the final cutting blade.

[0075] Turning to FIG. 4a″, showing the step 1000 of providing a blade precursor 200 for a cutting blade according to the second embodiment. In this case, in a step 2000, at least one strip 210 of a first steel material is provided and one strip 220 of a second steel material is provided. In FIG. 4a″ two strips 210, 211 of a first steel material are provided. In a subsequent step 3000, the at least one strip 200 of the first steel material and the strip 220 of the second steel material are joined to each other. One longitudinal edge of the at least one strip 210 of the first steel material is joined to one longitudinal edge of the strip 220 of the second steel material. In FIG. 4″ two strips 210, 211 of the first steel material are provided. One longitudinal edge of the first and the second strip 210, 211 of the first steel material are joined to a respective longitudinal edge of the strip 220 of the second steel material. Joining may be achieved by welding, such as laser welding or friction stir welding or by brazing. The welded joint that may be created when the two materials are joined, may according to some embodiments be grinded down. Thus, the surface of the cutting blade 100 may become completely smooth. This may reduce the risk of the cutting blade 100 to brake, or pieces of the cutting edge 120, 121 to fall off.

[0076] Turning to FIG. 4b, in a subsequent step 4000, at least one individual slit 113 is formed in the blade precursor 200, the slit is typically formed in the body portion 220 of the precursor. The slit 113 may be formed by punching or cutting or other metal cutting techniques. As discussed above, the blade precursor 200 may be of a length equal to the length of multiple cutting blades. In this case multiple 113 slits may be formed along the blade precursor 200. The slits 113 are spaced apart so that one individual slit 113 is located in a final cutting blade.

[0077] Turning to FIG. 4c, in a subsequent step 5000, the blade precursor 200 is hardened by heating at least an edge portion 210, 211 of the blade precursor 200 to austenitizing temperature followed by quenching. The austenitizing temperature is the temperature at which the microstructure of the steel material turns to austenitic. This temperature may be different for different steel compositions and may be found in public reference literature or may be determined by routine experiments. For the spring steels and carbon steels disclosed hereinabove, the austenitizing temperature is 780-840° C., preferably 780-810° C. The austenitizing temperature of the high speed steel is 1169-1180° C. for M42 type steel and 1200-1250° C. for M2 Type steel. Heating of the blade precursor is typically performed by induction heating apparatus 400, since induction heating allows for local heating of a predetermined edge portion. Quenching may be performed by ejecting or spraying fluid onto the heated edge portion of the blade precursor (not shown).

[0078] Turning to FIG. 4d, in a subsequent step 6000, at least a portion of the edge portion 210, 221 of the blade precursor 200 is ground to form a cutting edge 120, 121. The blade precursor 200 may thereby be ground to form a bevel on one face or on both faces of the blade precursor 200. Grinding may be performed by a grinding machine 500 having a rotating grinding disc. In a case where the dimensions of the blade precursor corresponds to one cutting blade, the blade precursor is now ready to be used as a robotic lawnmower cutting blade.

[0079] Turning to FIG. 4e, in an optional subsequent step 7000, a wear resistant coating 123 may be applied onto at least a portion of the cutting edges 210, 211 of the blade precursor 200. The wear resistant coating 123 may be TiN or CrN or Dimond-Like-Carbide and may be provided by Chemical Vapor Deposition (CVD) or Physical Vapor Deposition (PVD).

[0080] Turning to FIG. 4f, in a case wherein the blade precursor 200 have a length which corresponds to the total length of multiple cutting blades, the blade precursor 200, in a step 8000, is divided into individual cutting blades 100. The blade precursor 200 is thereby divided such that each individual cutting blade 100 comprises a slit 113 and a cutting edge 120, 121. Division of the blade precursor 200 may be performed by metal cutting tools, such as shears or scissors.

[0081] While the method steps hereinabove have been described in a certain order, it is obvious that some steps may be performed in another order. For example, it is possible to grind the cutting edges on the blade precursor prior to hardening the blade precursor. It is further possible to first divide the blade precursor into individual cutting blades and then apply a wear resistant coating.

[0082] It is further possible to include further steps of heat treating in the method for manufacturing the cutting blade according to the present disclosure. For example, after hardening, the steel precursor may be subjected to a tempering step to make the hardened edge portion less brittle. Tempering may be performed in a temperature range of 250-350° C. It is also possible to harden the entire blade precursor and then temper the body portion of the blade precursor in order to achieve a hardness difference between the edge portions and the body portions of the blade precursor and the final cutting blade.

[0083] It is further possible to use other hardening methods. For example the blade precursor may be manufactured from a nitriding steel and subjected to nitriding hardening. It is also possible to manufacture the blade precursor from a case hardening steel and subject the blade precursor to case hardening. It is possible to locally harden the edge portions of the blade precursor by masking the body portion such that nitrogen or carbon is prevented from diffusing into the body portion of the blade precursor.

[0084] Regarding the manufacturing the cutting blade according to the third embodiment of the present disclosure. The cutting blade according to the third embodiment comprises a blade body of carbon steel and a cutting edge of cemented carbide. The cutting blade may be formed by a method comprising the steps of:

[0085] Providing, a blade precursor 200 comprising a body portion 220 comprising a steel material and an edge portion 210, 211 comprising cemented carbide. Typically, the blade precursor is provided by the steps of: providing a strip of steel material and a strip of cemented carbide. In a following step the strip of steel material and the strip of cemented carbide are joined to each other. Joining may be achieved by brazing. Any suitable brazing material may be used, for example a silver-based brazing material.

[0086] In the method for manufacturing the cutting blade according to the third preferred embodiment, the steps of hardening the blade precursor 200 are omitted. However, the other manufacturing steps as disclosed under the first and the second embodiment may be applied for manufacturing the cutting blade according to the third embodiment.