Ball screw mechanism component and mechanism incorporating such component

Abstract

To increase the service life of a ball screw mechanism.SOLUTION: A helical track 28 having a first flank 32 includes an intermediate section 36 of a plurality of consecutive turns forming a helix of constant pitch, and a first recirculation section 38 at a first axial end 40 of the intermediate section 36. A first theoretical imaginary flank 56 is defined by an imaginary geometric extension of the first flank 32 of the helical track 28 at a constant pitch from the intermediate section 36 beyond the first axial end 40. In the first recirculation section 38, the first flank 32 of the helical track 28 is directed axially towards the intermediate section 36 and has an axial offset D11 relative to the first theoretical imaginary flank 56, such that the first flank 32 of the helical track 28 is further away from the intermediate section 36 than the first theoretical imaginary flank 56.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a ball screw mechanism and a component for such a mechanism, which can be either a nut or a screw. [Background technology]

[0002] JP 2017-106583(A2) describes a ball screw mechanism comprising a screw, a nut and balls. The screw forms a helical track of constant pitch P around a reference axis of the ball screw mechanism. The nut also forms a helical track of constant pitch equal to P around the reference axis, the track comprising at least one intermediate section of a plurality of successive turns, a first recirculation section at a first axial end of the intermediate section and a second recirculation section at a second axial end of the intermediate section. The nut also forms a recirculation channel connecting the first and second recirculation sections and opening into each of the first and second recirculation sections through a mouth. The balls are positioned to circulate in a closed circuit between the helical track of the nut and the helical track of the screw and in the recirculation channel. A deflector is positioned at the mouth of the recirculation channel to guide the balls between the helical track and the recirculation channel.

[0003] In this type of ball screw, despite the deflector, chipping of the balls is observed due to contact between the balls and the sharp edges formed at the mouth of the recirculation channel, which significantly reduces the service life of the ball screw. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-106583 A Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to overcome the shortcomings of the prior art and to provide a means for increasing the useful life of ball screw mechanisms. [Means for solving the problem]

[0006] According to a first aspect of the invention, a component of a ball screw mechanism is proposed which forms a helical track around a reference axis for guiding a ball, the helical track of the component having a track base and a first flank and a second flank facing each other on either side of the track base, the helical track of the component comprising at least one intermediate section of one or more successive turns forming a helix of constant pitch equal to P, a first recirculating section at a first axial end of the intermediate section and a second recirculating section at a second axial end of the intermediate section, a first theoretical imaginary flank being defined by an imaginary geometric extension of the first flank of the helical track of the component from the intermediate section beyond the first axial end and / or the second axial end with a constant pitch P. The component comprises: in the first recirculation section, a first flank of the helical trajectory of the component is oriented axially towards the intermediate section and has an axial offset D11 with respect to the first theoretical imaginary flank, the first flank of the helical trajectory of the component being further away from the intermediate section than the first theoretical imaginary flank; and / or in the second recirculation section, a first flank of the helical orbit of the component is directed axially away from the mid-section and has an axial offset D21 with respect to the first theoretical imaginary flank, the first flank of the helical orbit of the component being closer to the mid-section than the first theoretical imaginary flank.

[0007] The axial offset reduces the force applied to the balls rolling on the helical track and creates clearance in the first and / or second recirculation sections to facilitate ball recirculation.

[0008] According to one embodiment, the recirculation channel connects the first and second recirculation sections and opens into each of the first and second recirculation sections through a mouth. The mouths can be aligned in the same plane containing the reference axis. In particular, the mouth of the recirculation channel is where the axial offset ensures that the ball is no longer loaded. The axial offset required to avoid contact between the ball and the edge of the recirculation channel mouth is small. In practice, for example, the axial offset D11 measured in an axial plane tangential to the mouth of the recirculation channel opening into the first recirculation section may be greater than 1 μm in absolute value and / or less than 25 μm in absolute value.

[0009] In one embodiment, the axial offset D11 increases continuously in absolute value over an angular sector about the reference axis from a zero value at the first end of the mid-section to a maximum value.

[0010] In one embodiment, the axial offset D21 increases continuously in absolute value over an angular sector about the reference axis from a zero value at the second end of the mid-section to a maximum value.

[0011] Preferably, the maximum value of the axial offset D11 is achieved in an axial plane tangential or secant to the mouth of the recirculation channel which opens into the first recirculation section.

[0012] Preferably, the maximum value of the axial offset D21 is achieved in an axial plane tangential or secant to the mouth of the recirculation channel which opens into the second recirculation section.

[0013] Thus, the decrease or increase in force depending on the direction of rotation is gradual along the path of the ball.

[0014] In one embodiment, the first recirculation section extends over an angular sector greater than 10° and less than 360°, preferably greater than 30°, more preferably less than 180°, and most preferably less than 90°.

[0015] In one embodiment, the second recirculation section extends over an angular sector greater than 10° and less than 360°, preferably greater than 30°, more preferably less than 180°, and most preferably less than 90°.

[0016] Two objectives are therefore compatible: on the one hand, to maximise the useful portion provided by the intermediate section for the load transmitted between the screw and the nut, and on the other hand, to ensure good ball guidance in the transition portion provided by the recirculating section of the nut.

[0017] Offset D11 and offset D21 are useful when the axial component of the force exerted by the component on the ball points in one direction and may be sufficient in applications where the force is unidirectional.

[0018] Assuming that the component is likely to be subjected to forces whose axial component is bidirectional, advantageously a second theoretical virtual flank is provided, defined by a virtual geometric extension of the second flank of the helical trajectory of the component, at a constant pitch P, from the intermediate section beyond the first axial end and the second axial end. In one embodiment, the second flank of the helical trajectory of the component has, in the first recirculating section, an axial offset D12 relative to the second theoretical virtual flank, the axial offset D12 being less than or equal to the axial offset D11, measured in absolute value in any axial plane, and the second flank of the helical trajectory of the component being further away from the intermediate section than the second theoretical virtual flank. Preferably, the axial offset D12 is equal in absolute value to the axial offset D11.

[0019] Alternatively, in the first recirculation section, the second flank of the helical trajectory of the component may be made to coincide with a second theoretical imaginary flank.

[0020] In one embodiment, the second flank of the helical orbit of the component has, in the second recirculation section, an axial offset D22 relative to the second theoretical virtual flank, the axial offset D22 being less than or equal to the axial offset D21, measured in absolute value in any axial plane, and the second flank of the helical orbit of the component being closer to the mid-section than the second theoretical virtual flank. Preferably, the axial offset D22 has an absolute value equal to the axial offset D21.

[0021] Alternatively, in the second recirculation section, the second flank of the helical trajectory of the component may be made to coincide with a second theoretical virtual flank.

[0022] Another aspect of the invention relates to a ball screw mechanism comprising two components having a helical track, namely a screw and a nut, a first of the two components being as claimed in any one of the preceding claims and a second of the two components having a helical track around a reference axis of the ball screw mechanism, the helical track of the second component forming a helix of constant pitch equal to P around the reference axis, and a ball positioned to circulate in a closed circuit between the helical track of the first component and the helical track of the second component and in a recirculation channel.

[0023] According to one embodiment, the helical track of the second component has a track base and a first flank and a second flank facing each other on either side of the track base, the first flank of the helical track of the second component facing in the same first axial direction as the first flank of the helical track of the first component, and the second flank of the helical track of the second component facing in the same second axial direction as the second flank of the helical track of the first component, and in the intermediate section, when the ball is simultaneously in contact with the first flank and the second flank of the helical track of the second component and the first flank of the track of the first component, an axial structural clearance J exists between the ball and the second flank of the helical track of the first component.

[0024] It is advantageous to take this structural clearance into account when determining the magnitude of the offset. Preferably, the offset D11 is smaller than the axial clearance J. Preferably, the offset D21 is smaller than the axial clearance J. Preferably, the axial structural clearance J measured parallel to the axial direction is larger than 1 μm. Preferably, the axial structural clearance J measured parallel to the axial direction is smaller than 25 μm. [Brief description of the drawings]

[0025] [Figure 1] FIG. 2 is a perspective axial cross-sectional view of a ball screw mechanism, particularly showing the balls circulating on the raceways and / or recirculation channels of the nut and screw of the ball screw mechanism. [Diagram 2] 2 is an axial cross-sectional view of the ball screw mechanism shown in FIG. 1. [Diagram 3] FIG. 2 is a schematic diagram of the positioning of balls circulating on a raceway of a ball screw mechanism. [Figure 4] FIG. 2 is a detailed view of a first end section of a nut track according to a first embodiment of the present invention. [Diagram 5] FIG. 4 is a detailed view of a second end section of the nut track according to the first embodiment of the present invention. [Figure 6] FIG. 11 is a detailed view of a first end section of a nut track according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a detailed view of a second end section of a nut track according to a second embodiment of the present invention. [Figure 8] FIG. 11 is a detailed view of a first end section of a nut track according to a third embodiment of the present invention. [Figure 9] FIG. 13 is a detailed view of a second end section of a nut track according to a third embodiment of the present invention. [Figure 10] 4 is a schematic cross-sectional view of a ball screw mechanism showing a clearance formed between a ball and a raceway surface. FIG. [Figure 11] 11 is another schematic cross-sectional view of the ball screw mechanism for explaining the clearance formed between the ball and the raceway. FIG.

[0026] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

[0027] For greater clarity, identical or similar elements are identified by the same reference signs in all the figures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] 1 and 2 show a ball screw mechanism 10 comprising two threaded components, a screw 12 and a nut 14 , and a ball 16 .

[0029] The screw 12 is made of metal, e.g., steel, and forms a helical raceway 18 around a reference axis 100 of the ball screw mechanism 10, facing radially away from the reference axis 100. The helical raceway 18 has a helical envelope of constant pitch P around the reference axis 100, with a raceway base 20 and a first flank 22 and a second flank 24 facing each other on either side of the raceway base 20, the first flank 22 facing a first axial direction 110 of the reference axis 100 and the second flank 24 facing a second axial direction 120 of the reference axis 100. The flanks 22, 24 of the helical raceway 18 of the screw 12 preferably have a concave cross section, e.g., a circular arc, in a plane perpendicular to the generatrix of the helical raceway 18, and may form diagonal ribs extending to either side of the raceway base 20, or a continuous circular arc.

[0030] The nut 14 is made of metal, for example steel, forms a helical raceway 28 around and facing a reference axis 100, and has a raceway base 30 and a first flank 32 and a second flank 34 facing each other on either side of the raceway base 30, the first flank 32 facing a first axial direction 110 of the reference axis 100, and the second flank 34 facing a second axial direction 120 of the reference axis 100. The base 30 of the helical raceway 28 of the nut 14 is at a fixed distance from the reference axis 100.

[0031] The helical track 28 of the nut 14 includes an intermediate section 36 of a plurality of successive turns forming a helix of constant pitch equal to P, a first recirculating section 38 at a first axial end 40 of the intermediate section 36, and a second recirculating section 42 at a second axial end 44 of the intermediate section 36. At least in the intermediate section 36, the flanks 32, 34 of the helical track 28 of the nut 14 preferably have a concave cross section, e.g., a circular arc, in a plane perpendicular to the generatrix of the helical track 28 and may form diagonal ribs extending on either side of the track base 30.

[0032] The nut 14 also defines a recirculation channel 46, which connects the first recirculation section 38 to the second recirculation section 42 and opens into each of the first and second recirculation sections 38, 42 via a mouth 48, 50. The edges of each mouth 48, 50 may form sharp edges. Deflectors 52, 54, preferably as inserts, possibly made of plastic or metal, are disposed in the mouths 48, 50 to guide the ball 16 as it changes direction at the inlet or outlet of the recirculation channel 46.

[0033] The balls 16 may be made, for example, of steel or ceramic and are sized and positioned to circulate in a closed circuit between the helical raceway 28 of the nut 14 and the helical raceway of the screw 12, as well as within the recirculation channel 46, preferably without separators between the balls 16.

[0034] The raceway and ball 16 are preferably dimensioned such that, in the central section 36, an axial structural clearance J exists between the ball 16 and the second flank 34 of the helical raceway 28 of the nut 14 when the ball 16 is in simultaneous contact with the second flank 24 of the helical raceway of the screw 12 and the first flank 32 of the raceway 28 of the nut 14. This axial structural clearance J, measured parallel to the axial direction, is preferably greater than 1 μm and less than 25 μm, and is shown diagrammatically and exaggerated in FIG.

[0035] To describe the helical trajectory 28 of the nut 14 in the circulating section, a first theoretical imaginary flank 56 (dashed line in FIGS. 4-9 ) can be geometrically defined as an imaginary geometric extension of the first flank 32 of the helical trajectory 28 of the nut 14, with a constant pitch P, from the mid-section 36 beyond the first end 40 and the second end 44. Similarly, a second theoretical imaginary flank 58 (dashed line in FIGS. 4-9 ) can be geometrically defined as an imaginary geometric extension of the second flank 34 of the helical trajectory 28 of the nut 14, with a constant pitch P, from the mid-section 36 beyond the axial first end 40 and the second end 44.

[0036] In the first recirculation section 38, as shown in Fig. 4, the first flank 32 of the helical track 28 of the nut 14 faces axially towards the intermediate section 36 in a first direction 110 and has an axial offset D11 with respect to the first theoretical imaginary flank 56, the first flank 32 of the helical track 28 of the nut 14 being further away from the intermediate section 36 than the first theoretical imaginary flank 56. The first recirculation section 38 extends over an angular sector A shown in Figs. 10 and 11 which is greater than 10° and less than 360°, preferably greater than 30°, more preferably less than 180° and most preferably less than 90°. Preferably, the axial offset D11 increases continuously in absolute value from a zero value at the first end 40 of the intermediate section 36 to a maximum value over the angular sector around the reference axis 100, preferably with a continuous drift. The axial offset D11 reaches a maximum value in an axial plane tangential to or intersecting the mouth 48 of the recirculation channel 46 opening into the first recirculation section 38. The axial offset D11 measured in an axial plane tangential to the mouth 48 of the recirculation channel 46 opening into the first recirculation section 38 is greater than 1 μm in absolute value and preferably less than 25 μm in absolute value. It is preferably smaller than the axial structural clearance J.

[0037] Similarly, in the second recirculation section 42, as shown in FIG. 5, the first flank 32 of the helical track 28 of the nut 14 faces axially away from the intermediate section 36 and has an axial offset D21 with respect to the first theoretical imaginary flank 56, the first flank 32 of the helical track 28 of the nut 14 being closer to the intermediate section 36 than the first theoretical imaginary flank 56. The second recirculation section 42 extends over an angular sector greater than 10° and less than 360°, preferably greater than 30°, more preferably less than 180° and most preferably less than 90°. Preferably, the axial offset D21 increases continuously in absolute value and preferably drifts continuously over an angular sector around the reference axis 100 from a zero value at the second end 44 of the intermediate section 36 to a maximum value. The axial offset D21 reaches a maximum value in an axial plane tangential to or intersecting the mouth 50 of the recirculation channel 46 opening into the second recirculation section 42. The axial offset D21 measured in an axial plane tangential to the mouth 50 of the recirculation channel 46 opening into the second recirculation section 42 is greater than 1 μm in absolute value and preferably less than 25 μm in absolute value. It is preferably smaller than the axial structural clearance J.

[0038] The gradual offset of the first flank 32 allows the balls 16 circulating in the first recirculating section 38 and the second recirculating section 42 to be progressively unloaded when the ball screw mechanism is loaded such that a force is applied by the balls 16 to the first flank 32 of the nut 14, particularly in the intermediate section 36.

[0039] In the first recirculation section 38, the second flank 34 of the helical track 28 of the nut 14 may optionally have an axial offset D12 relative to the second theoretical imaginary flank 58, the axial offset D12 being less than or equal to the axial offset D11, measured in absolute value in any axial plane, the second flank 34 of the helical track 28 of the nut 14 being further away from the intermediate section 36 than the second theoretical imaginary flank 58. In the example shown in Figure 4, the axial offset D12 has an absolute value equal to the axial offset D11.

[0040] Similarly, the second flank 34 of the helical track 28 of the nut 14 may have an axial offset D22 relative to the second theoretical imaginary flank 58 in the second recirculation section 42, as shown in FIG. 5, where the axial offset D22, measured in absolute value in any axial plane, is less than or equal to the axial offset D21, and the second flank 34 of the helical track 28 of the nut 14 is closer to the intermediate section 36 than the second theoretical imaginary flank 58.

[0041] The gradual offset of the second flank 34 allows the balls 16 circulating in the first recirculating section 38 and the second recirculating section 42 to be progressively unloaded when the ball screw mechanism is loaded such that a force is applied by the balls 16 to the second flank 34 of the nut 14, particularly in the intermediate section 36. Thus, the gradual offset of the second flank 34 is useful in applications where the ball screw mechanism 10 may be subjected to bidirectional resultant axial forces.

[0042] In a second embodiment, particularly for applications where the force is unidirectional, the second flank 34 of the helical track 28 of the nut 14 can coincide with a second theoretical virtual flank 58 in the first and / or second recirculation sections 42, as shown in Figures 6 and 7.

[0043] According to another embodiment shown in figures 8 and 9, in the first recirculation section 38, the second flank 34 of the helical track 28 of the nut 14 has an axial offset D12 relative to the second theoretical imaginary flank 58, which axial offset D12, measured in absolute value in any axial plane, is less than or equal to the axial offset D11, the second flank 34 of the helical track 28 of the nut 14 being in turn closer to the intermediate section 36 than the second theoretical imaginary flank 58. In the example shown in figure 4, the axial offset D12 has an absolute value equal to the axial offset D11.

[0044] Similarly, the second flank 34 of the helical track 28 of the nut 14 may have an axial offset D22 relative to the second theoretical imaginary flank 58 in the second recirculation section 42, as shown in FIG. 5, where the axial offset D22, measured in absolute value in any axial plane, is less than or equal to the axial offset D21, and the second flank 34 of the helical track 28 of the nut 14 is further away from the intermediate section 36 than the second theoretical imaginary flank 58.

[0045] In one embodiment, the two thread components are reversed in the sense that a fixed pitch raceway is provided on the nut and a variable pitch raceway and a recirculating raceway is provided on the screw.

Claims

1. A component (14) of a ball screw mechanism (10) forming a helical track (28) around a reference axis (100) for guiding a ball (16), the helical track (28) of the component (14) having a track base and a first flank (32) and a second flank (34) facing each other on either side of the track base, the helical track (28) of the component (14) having at least one intermediate section (36) of one or more successive turns forming a helix of constant pitch equal to P, and a second flank (34) formed on the intermediate section (36) of one or more successive turns forming a helix of constant pitch equal to P. a first recirculation section (38) at a first axial end (40) of said intermediate section (36) and a second recirculation section (42) at a second axial end (44) of said intermediate section (36), wherein a first theoretical imaginary flank (56) is defined by an imaginary geometric extension of said first flank (32) of said helical track (28) of said component (14) from said intermediate section (36) beyond said first axial end (40) and / or said second axial end (44) with a constant pitch P; in the first recirculation section (38), the first flank (32) of the helical track (28) of the component (14) is oriented axially towards the intermediate section (36) and has an axial offset D11 with respect to the first theoretical imaginary flank (56), the first flank (32) of the helical track (28) of the component (14) being further away from the intermediate section (36) than the first theoretical imaginary flank (56); and / or a component (14), in which in the second recirculation section (42), the first flank (32) of the helical track (28) of the component (14) is directed axially away from the intermediate section (36) and has an axial offset D21 with respect to the first theoretical imaginary flank (56), the first flank (32) of the helical track (28) of the component (14) being closer to the intermediate section (36) than the first theoretical imaginary flank (56).

2. The component (14) of claim 1, wherein a recirculation channel (46) connects said first and second recirculation sections and opens into each of said first and second recirculation sections through a mouth.

3. 3. The component (14) according to claim 2, wherein the axial offset D11, measured in an axial plane tangential to the mouth of the recirculation channel (46) opening into the first recirculation section (38), is greater than 1 μm in absolute value and / or less than 25 μm in absolute value.

4. said axial offset D11 increases continuously in absolute value over an angular sector around said reference axis (100) from a zero value at said first end (40) of said intermediate section (36) to a maximum value; and / or The component (14) according to any one of claims 1 to 3, wherein the axial offset D21 increases continuously in absolute value over an angular sector around the reference axis (100) from a zero value at the second end (44) of the intermediate section (36) to a maximum value.

5. the maximum value of the axial offset D11 is achieved in an axial plane tangential or secant to the mouth of the recirculation channel (46) opening into the first recirculation section (38), and / or A component (14) according to claim 4 in combination with claim 2 or claim 3, wherein the maximum value of the axial offset D21 is achieved in an axial plane tangential or secant to the mouth of the recirculation channel (46) opening into the second recirculation section (42).

6. said first recirculation section (38) extends over an angular sector greater than 10° and less than 360°, preferably greater than 30°, preferably less than 180°, preferably less than 90°; and / or The component (14) according to any one of claims 1 to 5, wherein the second recirculation section (42) extends over an angular sector greater than 10° and less than 360°, preferably greater than 30°, preferably less than 180°, preferably less than 90°.

7. a second theoretical imaginary flank (58) is defined by an imaginary geometric extension of the second flank (34) of the helical track (28) of the component (14) from the intermediate section (36) beyond the first axial end (40) and the second axial end (44) at a constant pitch P; in the first recirculation section (38), the second flank (34) of the helical track (28) of the component (14) has an axial offset D12 relative to the second theoretical imaginary flank (58), the axial offset D12 being less than or equal to the axial offset D11, measured in absolute value in any axial plane, and the second flank (34) of the helical track (28) of the component (14) is further away from the intermediate section (36) than the second theoretical imaginary flank (58); and / or The component (14) according to any one of claims 1 to 6, wherein in the second recirculation section (42), the second flank (34) of the helical orbit (28) of the component (14) has an axial offset D22 relative to the second theoretical virtual flank (58), which axial offset D22, measured in absolute value in any axial plane, is less than or equal to the axial offset D21, and the second flank (34) of the helical orbit (28) of the component (14) is closer to the intermediate section (36) than the second theoretical virtual flank (58).

8. said axial offset D12 is equal in absolute value to said axial offset D11, and / or A component (14) according to claim 7, wherein said axial offset D22 is equal in absolute value to said axial offset D21.

9. a second theoretical imaginary flank (58) is defined by an imaginary geometric extension of the second flank (34) of the helical track (28) of the component (14) from the intermediate section (36) beyond the first and second axial ends (40, 44) at a constant pitch P; in said first recirculation section (38), said second flank (34) of said helical track (28) of said component (14) coincides with said second theoretical imaginary flank (58); and / or The component (14) according to any one of claims 1 to 6, wherein in the second recirculation section (42), the second flank (34) of the helical track (28) of the component (14) coincides with the second theoretical virtual flank (58).

10. A ball screw mechanism (10), - two components with a helical track, namely a screw and a nut, a first of the two components being a component according to any one of claims 1 to 9 and a second of the two components having a helical track (18) around a reference axis (100) of the ball screw mechanism (10), the helical track (18) of the second component (12) forming a helix of constant pitch equal to P around the reference axis (100); a ball (16) positioned to circulate in a closed circuit between the helical track (28) of the first component (14) and the helical track (18) of the second component (12) and in the recirculation channel (46); A ball screw mechanism (10).

11. The helical track (18) of the second component (12) has a track base and a first flank (22) and a second flank (24) facing each other on either side of the track base, the first flank (22) of the helical track (18) of the second component (12) facing the same first axial direction (110) as the first flank (32) of the helical track (28) of the first component (14), and the second flank (24) of the helical track (18) of the second component (12) facing the second flank (32) of the helical track (28) of the first component (14).

11. The ball screw mechanism (10) of claim 10, wherein an axial structural clearance J exists between the ball (16) and the second flank (34) of the helical raceway (28) of the first component (14) when the ball (16) is in contact with the first flank (22) and the second flank (24) of the helical raceway (18) of the second component (12) and the first flank (32) of the raceway (28) of the first component (14) simultaneously in the intermediate section (36).

12. said offset D11 is smaller than said axial structural clearance J, and / or said offset D21 is smaller than said axial structural clearance J, and / or the axial structural clearance J, measured parallel to the axial direction, is greater than 1 μm, and / or The ball screw mechanism (10) according to claim 11, wherein the axial structural clearance J, measured parallel to the axial direction, is less than 25 μm.

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