Gear mechanisms and robots

Abstract

To ensure strength while realizing weight reduction, compared to conventional gear mechanisms.SOLUTION: A gear mechanism (21) comprises housings (22, 23), an input unit (26+27) to which a drive is input, a gear member (28) to which the drive from the input unit (26+27) is transmitted, and an output unit (31) to which the drive from the gear member (28) is output. The housings (22, 23) is made of a resin material. The output unit (31) is made of a material with higher strength than that of the housings (22, 23).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a gear mechanism having gears and a robot provided with the gear mechanism, and particularly to a gear mechanism and a robot that can be suitably used for a speed reducer of an industrial robot.

Background Art

[0002] In recent years, globally, efforts towards sustainable development goals (SDGs) and carbon neutrality have been expanding, and in the field of industrial robots, energy conservation is desired. The power consumption of industrial robots is particularly related to the large self-weight of the robots, and reducing the self-weight leads to energy conservation. In order to reduce the weight of robots, replacing what has been conventionally made of metal with lightweight non-metallic materials such as resin has been conventionally considered (see, for example, Non-Patent Documents 1 and 2).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] (Problems of the Prior Art) Industrial robots require specific payload capacities and strengths depending on their application. Therefore, as described in Non-Patent Documents 1 and 2, simply constructing the entire robot out of resin may result in weight reduction but compromise the required strength.

[0005] The technical challenge of this invention is to achieve weight reduction while ensuring strength compared to conventional gear mechanisms. [Means for solving the problem]

[0006] To solve the aforementioned technical problems, the gear mechanism of the invention described in claim 1 is: The casing and An input unit disposed inside the housing and to which drive is input, the input unit having an input shaft portion and an eccentric shaft portion rotatable together with the input shaft portion, A gear member disposed inside the housing and to which drive from the input section is transmitted, the gear member being composed of a planetary gear to which drive is transmitted from the eccentric shaft section, A sun gear portion is positioned in contact with the outer circumference of the planetary gear and fixed to the housing, Multiple output transmission units formed at intervals along the circumferential direction of the planetary gear, A plurality of output transmission members are arranged corresponding to each of the plurality of output transmission units and loosely fitted to the output transmission units, An output unit disposed inside the housing, from which the drive from the gear member is output, the output unit supports all of the output-receiving members and supports the output shaft, Equipped with, The housing is made of nylon resin containing carbon fiber, The output unit is made of an epoxy resin containing carbon fiber and is made of a material with higher rigidity than the housing. It is characterized by the following:

[0007] In this specification and claims, the term "resin material" is used to include resin-based composite materials that use resin material as a base material.

[0008] Claim 2 In the gear mechanism according to claim 1, the invention described the planetary gear having an outer peripheral shape based on an epitrochoid curve is characterized by comprising the same.

[0009] To solve the above technical problem, Claim 3 the robot of the invention described in a plurality of arm parts, a joint part which is a connecting part between two arm parts, arranged at the joint part and transmitting the drive for displacing one arm part with respect to the other arm part, claim 1 or 2 the gear mechanism described in is characterized by comprising the same.

Advantages of the Invention

[0010] According to the invention described in claim 1, 3 compared with the conventional gear mechanism, it is possible to ensure strength while achieving weight reduction. Also, according to the invention described in claim 1, 3 in a gear mechanism having a planetary gear and a sun gear, it is possible to ensure strength while achieving weight reduction. Furthermore, according to the invention described in claim 1, [[ID=X]] 3 compared with the case where the output support member is made of metal, weight reduction can be achieved. Claim 2 According to the invention described in [], when using a resin containing fibers, it is easier to ensure strength compared with an involute type planetary gear.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a schematic explanatory view of the robot of Example 1 of the present invention. [Figure 2] FIG. 2 is an exploded explanatory view of a speed reducer as an example of the gear mechanism of the present invention. [Figure 3] FIG. 3 is an explanatory view of the behavior of the planetary gear, sun gear, eccentric shaft, etc. of the speed reducer in FIG. 2. [Figure 4] It should be noted that there seems to be an error in the original text where the reference number in "に記載の発明によれば、インボリュート型の遊星歯車に比べて、繊維が含有された樹脂を使用する場合には、強度を確保し易い。" is not filled correctly. I translated it as "According to the invention described in [], when using a resin containing fibers, it is easier to ensure strength compared with an involute type planetary gear. " with a placeholder "[[]]" for the correct reference number.FIG. 4 is an explanatory diagram of the experimental results of the no-load running torque, and is a graph with the target angular velocity on the horizontal axis and the driving torque on the vertical axis. [Figure 5] FIG. 5 is an explanatory diagram of the experimental results of the torque-torsion angle characteristics, and is a graph with the output torque on the horizontal axis and the value corresponding to the torsion angle of the reduction gear on the vertical axis.

Embodiments for Carrying out the Invention

[0012] Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described while referring to the drawings, but the present invention is not limited to the following examples. In the description using the following drawings, illustrations other than the members necessary for the explanation are appropriately omitted for ease of understanding.

Example

[0013] FIG. 1 is a schematic explanatory diagram of the robot of Example 1 of the present invention. In FIG. 1, a robot arm system S of Example 1 as an example of the robot of the present invention has an arm member 1. The arm member 1 has a plurality of arm parts 2 and joint parts 3 that connect the arm parts 2 to each other. The arm member 1 of Example 1 has a first arm part 2a whose one end is supported by a pedestal part 4. A first joint part 3a is supported at the other end of the first arm part 2a. Similarly, the second arm part 2b, the second joint part 3b,..., the ninth joint part 3i, and the tenth arm part 2j are connected. A robot hand part 2k capable of gripping and releasing an object is formed at the other end (tip) of the tenth arm part 2j. Therefore, in the arm member 1 of Example 1, as a whole, one end part of the first arm part 2a serves as the base end part, and the other end part of the tenth arm part 2j serves as the free end part.

[0014] Note that in Example 1, a configuration having nine joint parts 3a to 3i and ten arm parts 2a to 2j is illustrated, but it is not limited thereto. Also, in Example 1, the joint type is an example of a configuration having only rotational joints, but a robot arm including linear joints may also be used. The number of arm sections 2 and joint sections 3 can be increased or decreased to any number depending on the application, design, specifications, etc., of the arm member 1.

[0015] The aforementioned joints 3 (3a to 3i) are configured to allow rotation (displacement) of one arm section 2a to 2i relative to the other arm section 2b to 2j around a rotation axis. Each joint 3 incorporates a motor (not shown) and a gearbox as an example of a gear mechanism, and is configured to allow control of the amount of rotation by controlling the rotation drive and rotation stop of the motor. In Embodiment 1, the motors of each joint 3 are driven by receiving control signals from a wireless communication chip (not shown), but are not limited to this. It is also possible to control the motors by sending and receiving control signals via a wired connection such as a communication cable. The wireless and wired communication methods can be any conventionally known communication method, such as mobile phone lines, Bluetooth®, or wireless LAN, or any wired communication method such as USB (Universal Serial Bus) or parallel.

[0016] The arm member 1 is controlled by a computer device 11, which is an example of an information processing device. In Embodiment 1, the arm member 1 is configured to enable wireless communication with the computer device 11. The computer device 11 includes a computer body 12, a display 13, which is an example of a display unit, and a keyboard 14 and a mouse 15, which are examples of input units. In Embodiment 1, a desktop computer device is used as an example of the computer device 11, but the embodiment is not limited to this, and a laptop computer device can also be used. Furthermore, the computer device 11 is not limited to a personal computer device, but can be any form such as a server type, microcomputer type, or chip type.

[0017] (Explanation of the gearbox) Figure 2 is an exploded view illustrating a gear reducer as an example of the gear mechanism of the present invention. Figure 3 is an explanatory diagram illustrating the behavior of the planetary gears, sun gear, eccentric shaft, etc., of the reduction gear shown in Figure 2. In Figure 2, the gear reducer 21, as an example of the gear mechanism of the present invention, has an upper case 22 and a lower case 23, which are examples of housings. The upper case 22 is formed in a hollow box shape, and an opening 22b is formed in the top surface 22a. The lower case 23 has a bottom plate 23a and a cylindrical tube 23b, and an opening 23c is formed that penetrates the inside of the tube 23b. A sun gear 24 is arranged between the upper case 22 and the lower case 23. Multiple sun gears 24 are arranged at intervals along the circumferential direction of the tube 23b. One end of the sun gear 24 is supported by the tube 23b, and the other end is supported by the upper case 22. The sun gear 24 can be configured with a rotatable bearing supported on its shaft, or it can be configured as a non-rotatable (fixed shaft).

[0018] In the central part of the upper case 22, an eccentric shaft 26 is positioned as an example of an eccentric shaft. The eccentric shaft 26 has a central axis 26a and a disc-shaped eccentric bearing 26b supported by the central axis 26a. The center of the disc of the eccentric bearing 26b is supported eccentrically with respect to the central axis 26a. In Embodiment 1, two eccentric bearings 26b are supported along the axial direction of the central axis 26a, and the first eccentric bearing 26b-1 and the second eccentric bearing 26b-2 are supported at different phases such that the major axis portion of the second eccentric bearing 26b-2 corresponds to the minor axis portion of the first eccentric bearing 26b-1. The lower end of the central shaft 26a is supported by the input shaft portion 27. The input shaft portion 27 in Embodiment 1 is formed in a disc shape, and a connecting portion (joint) extending from the output shaft of a motor (not shown) can be connected to it. The other end of the eccentric shaft 26 is rotatably supported at the center of the output flange 31 (described later) via a bearing. The input shaft portion 27 and the eccentric shaft portion 26, etc. constitute the input portion 26+27 of Embodiment 1.

[0019] A planetary gear 28, as an example of a gear member, is supported inside the sun gear section 24. The planetary gear 28 of Embodiment 1 has a first planetary gear 28-1 and a second planetary gear 28-2, corresponding to two eccentric bearings 26b-1 and 26b-2. In Figures 2 and 3, the planetary gear 28 has an input transmission hole 28a formed in its center, which is an example of an input transmission section. The eccentric shaft 26 passes through the input transmission hole 28a, and its inner surface contacts the outer surface of the eccentric bearing 26b, thereby transmitting the drive of the eccentric shaft 26. The planetary gear 28 also has an output transmission hole 28b formed radially outward from the input transmission hole 28a, which is an example of an output transmission section.

[0020] The outer circumference 28c of the planetary gear 28 is configured in a gear shape that contacts the sun gear portion 24. The outer circumference 28c of the planetary gear 28 in Embodiment 1 is formed in an external shape that follows an epitrochoid curve. Here, if the angle between the vertices of the teeth's protrusions is θ, the radius of the gear's pitch circle (the distance from the center of the planetary gear 28 to the center of the sun gear) is a, the number of teeth is n, and the module (eccentricity in the configuration of Embodiment 1) is b / n, then the epitrochoid curve is represented by the following equation 1.

number

[0021] In Figure 2, an output support end 29, which is an example of a second output support member, is positioned between the planetary gear 28 and the input shaft portion 27. The output support end 29 in Embodiment 1 is formed in a disc shape. A through hole 29a is formed in the center of the output support end 29, through which the central axis 26a passes. An output flange 31, as an example of an output support member, is positioned on the upper side of the planetary gear 28. The output flange 31 is formed in a disc shape. The output flange 31 has a bearing portion 31a that is rotatably supported in the opening 22b of the upper case 22, and an output shaft portion 31b to which the output shaft of a joint portion 3 (not shown) is connected.

[0022] An output pin 32, as an example of an output-transmitted member, is supported between the output flange 31 and the output support end 29. In Figure 3, the output pin 32 passes through the output transmission hole 28b of the planetary gear 28. The outer diameter of the output pin 32 is formed to be small relative to the inner diameter of the output transmission hole 28b so that there is sufficient clearance 34 (play), and the output pin 32 is fitted with the output transmission hole 28b with some play (i.e., loosely fitted). The output pin 32 is positioned to pass through the output transmission holes 28b of both planetary gears 28-1 and 28-2. The output pins 32, output flange 31, and output support end 29 constitute the output sections 29-32 of Embodiment 1. An output cover portion 33 is positioned above the output flange 31, which holds a bearing portion 31a that rotatably supports the output flange 31.

[0023] In Figure 3, when a drive in the direction of arrow Ya (clockwise in Figure 3) is input to the input shaft 27, the eccentric shaft 26 rotates in the direction of arrow Ya. As the eccentric shaft 26 rotates, the planetary gear 28 also rotates in the direction of arrow Ya. When the two planetary gears 28 rotate in the direction of arrow Ya, the outer circumference 28c of the planetary gears 28 rotates while in contact with the sun gear portion 24, causing the planetary gears 28 to periodically move over the sun gear portion 24, and thus move radially as well. As the planetary gears 28 rotate in the direction of arrow Ya and move radially, the output pin 32 is pushed by the output transmission hole 28b, and the output pin 32, output flange 31, and output support end 29 rotate in the direction of arrow Yb, which is the opposite direction to the planetary gears 28, etc. In the reduction gear 21 of Embodiment 1, the drive is reduced when it is transmitted from the eccentric shaft 26 to the planetary gear 28, and also when it is transmitted from the planetary gear 28 to the output pin 32. Therefore, the reducer 21 of Embodiment 1 is composed of a so-called trochoidal tooth profile internal planetary gear reducer, and the drive input from the input shaft 27 is reduced and output to the output flange 31.

[0024] In Example 1, the upper case 22 and the lower case 23 are made of a resin material. As an example of a resin material, it is preferable to use a nylon resin containing carbon fiber as the base. When manufacturing using a 3D printer with this nylon resin, the fiber length of the carbon fiber is preferably about 0.01 mm to 0.5 mm, although this varies depending on the size of the 3D printer nozzle, and the carbon fiber content is preferably about 8 to 12% by volume. It is also possible to adjust the strength and rigidity by adding continuous carbon fibers to the nylon resin, and the amount added can be adjusted according to the required strength, rigidity, etc. for the upper case 22 and the lower case 23.

[0025] Furthermore, the output flange 31 of Example 1 is made of a material with higher rigidity than the upper case 22 and the lower case 23. As an example of rigidity, the output flange 31 of Example 1 is preferably made of a resin material that has high tensile strength, tensile modulus, bending strength, and bending modulus. As an example, it is preferable to use an epoxy resin containing carbon fiber as the base. In this epoxy resin, the fiber length of the carbon fiber is preferably 20 mm or more, or continuous fibers are preferable, and the carbon fiber content is preferably about 30% to 60% by volume. Because this epoxy resin has high strength and rigidity, it can be machined, and the planetary gear 28 can be cut out and manufactured by machining.

[0026] In Example 1, the output support end 29 and the planetary gear 28 are also made of the same resin material as the output flange 31. Therefore, in Example 1, the upper case 22, the lower case 23, and the output flange 31 are all made of CFRP (Carbon Fiber Reinforced Plastics), but CFRP with different strengths is used. It should be noted that the material is not limited to CFRP, and any resin material such as GFRP (Glass Fiber Reinforced Plastics) or KFRP (Kevlar Fiber Reinforced Plastics) can be used. In Example 1, the sun gear section 24, eccentric shaft 26, and output pin 32 are made of stainless steel (SUS304), but are not limited to this. Depending on the required strength, they can be made of general steel, or even non-metallic material (resin).

[0027] (Effect of Example 1) In the reduction gear 21 of the robot arm system S of Embodiment 1, which has the above configuration, the cases 22 and 23 and the output flange 31 are made of non-metallic resin, resulting in a lighter weight compared to a system where everything is made of metal. Furthermore, in Embodiment 1, the output flange 31 and other components are made of a material with higher strength and rigidity than the materials used for the cases 22 and 23. The output flange 31 and other components are the parts that transmit and output the drive, and if they are made of a material with low strength and rigidity like the cases 22 and 23, they may be prone to breakage due to insufficient strength, or deform, leading to poor drive transmission and potentially shortening their lifespan. Therefore, in the reduction gear 21 of Embodiment 1, where the output flange 31 and other components are made of a material with higher strength and rigidity than the materials used for the cases 22 and 23, it is possible to ensure greater strength compared to a system where the output flange 31 and other components are made of the same material as the cases 22 and 23.

[0028] (Example of experiment) Next, we conducted an experiment to confirm the effects of Example 1. (Experimental Example 1) In Experimental Example 1, the planetary gear 28 was designed with a=30mm, b=11, and n=11, and from there r s The design was intended to displace by only 3.5 mm. The reduction ratio was set to 10. In Experimental Example 1, cases 22 and 23 were made of nylon resin containing carbon fiber, and the planetary gear 28, output support end 29, and output flange 31 were made of epoxy resin containing carbon fiber. The weight, no-load running torque, and torque-torque characteristics were measured for the reducer 21 with this configuration.

[0029] (Comparative Example 1) In Comparative Example 1, all constituent materials were made of metal. Specifically, cases 22 and 23 were made of aluminum alloy (A7075, super duralumin), while the output flange 31, planetary gear 28, output support end 29, etc., were made of stainless steel (SUS304). The rest of the configuration was the same as in Experimental Example 1. (Experimental Example 2) In Experimental Example 2, only cases 22 and 23 were changed to nylon resin containing carbon fiber compared to Comparative Example 1; all other aspects were the same as in Comparative Example 1. (Experimental Example 3) In Experimental Example 3, the cases 22 and 23, the planetary gear 28, and the output support end 29 were changed to nylon resin containing carbon fiber compared to Comparative Example 1, while the output flange 31 was made of stainless steel (SUS304), as in Comparative Example 1. All other aspects were the same as in Comparative Example 1.

[0030] (Experimental results regarding weight) The weight of Comparative Example 1 was 772g. In contrast, the weights were 383g for Experimental Example 1, 637g for Experimental Example 2, and 473g for Experimental Example 3. Therefore, it was confirmed that Experimental Examples 1-3 were lighter than Comparative Example 1.

[0031] (Experimental results of no-load running torque) Figure 4 is an explanatory diagram of the experimental results for no-load running torque, with the target angular velocity on the horizontal axis and the driving torque on the vertical axis. In Figure 4, the driving torque was measured when the target angular velocity of the motor attached to the input side of the reduction gear 21 was changed at a slope of 10 rpm / s. In Figure 4, the no-load torque of the reference motor alone was 0.03 N·m. In Comparative Example 1, the torque was 0.15 N·m, which was about five times that of the motor alone. In contrast, in Experimental Example 1, it was about 0.08 N·m, and in Experimental Examples 2 and 3, it was about 0.07 N·m. From the experimental results in Figure 4, it can be seen that in Comparative Example 1, which is composed only of metal materials, the forces acting between parts due to manufacturing and assembly errors are large, resulting in large friction. On the other hand, in Experimental Examples 1-3, which were replaced with resin parts, the force is mitigated when subjected to large forces by the deformation of the resin parts, resulting in reduced friction. Therefore, the no-load torque in Experimental Examples 1 and 3, which were replaced with resin, is thought to be reduced by about 50% compared to Comparative Example 1, which is made of metal. In other words, replacing cases 22 and 23 from metal to resin is expected to allow for part errors, contribute to weight reduction while smoothing the drive.

[0032] (Torque-torque characteristics) Figure 5 is an explanatory diagram of the experimental results of the torque-torque characteristic, where the horizontal axis represents the output torque and the vertical axis represents the value corresponding to the torsion angle of the gearbox. The results of measuring torque by installing a torque meter on the output shaft of the reduction gear 21 in Example 1 are plotted on the horizontal axis of Figure 5. The input torque is varied with a slope of 0.05 N·m / s, with the motor's rated torque of 1 N·m being the maximum input torque. The vertical axis represents the angle obtained by dividing the angle of the motor attached to the input side of the reduction gear 21 by the reduction ratio, which corresponds to the twist angle of the reduction gear 21. According to the experimental results in Figure 5, in Experimental Example 2, the maximum value of the twist angle increased 6.5 times compared to Comparative Example 1. In contrast, in Experimental Examples 1 and 3, the increase was approximately twice that of Comparative Example 1. Cases 22 and 23 are the largest volume components, but the increase in helix angle relative to them (comparison between Experimental Example 2 and Comparative Example 1) is small compared to the substitution of internal components (comparison between Experimental Examples 1 and 3 and Experimental Example 2). Specifically, when comparing the cases after changing Cases 22 and 23 to resin, and comparing the cases where the internal components, such as the planetary gear 28 and output support end 29, are made of metal (Experimental Example 2) with those made of resin (Experimental Examples 1 and 3), the helix angle in Experimental Example 3 increases significantly. On the other hand, when comparing the cases where the internal components, such as the planetary gear 28 and output support end 29, are made of metal (Comparative Example 1) with those made of resin (Experimental Example 2), the increase in helix angle is not so large. Therefore, the experimental results showed that replacing cases 22 and 23 from metal (Comparative Example 1) to resin (Experimental Examples 1-3) significantly contributes to weight reduction while minimizing the impact on torsional rigidity. Furthermore, replacing internal and output components from metal (Experimental Example 2) to resin (Experimental Example 1), which has higher rigidity than the cases, allows for weight reduction while maintaining rigidity equivalent to that of metal.

[0033] (Example of change) Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the gist of the present invention as described in the claims. Examples of modifications to the present invention (H01) to (H06) are shown below. (H01) In the above embodiment, the number of joints 3, the length and number of arms, their shape, etc., are not limited to the example form. Therefore, the number, length, shape, etc., can be arbitrarily changed depending on the application, design, specifications, etc., of the arm members.

[0034] (H02) In the above examples and experimental examples, it is preferable to use the material names and numerical values ​​as exemplified, but is not limited to these. For example, as in Experimental Example 2, it is also possible to construct cases 22 and 23 from resin material and the output flange 31 etc. from a metal material such as titanium alloy which has higher strength and rigidity than cases 22 and 23. (H03) In the above embodiment, the type of joint 3 consisted only of a rotational joint, but it is not limited to that form. In other words, it is also applicable when a linear joint is included.

[0035] (H04) In the above embodiment, an example was given in which the outer circumference 28c of the planetary gear 28 was shaped using an epitrochoid curve, but it is not limited to this. It is also possible to use an involute type outer shape, which is commonly used in gears. However, involute types have finer teeth and larger changes in the curve shape of the outer shape of the teeth compared to epitrochoid curves (epitrochoid curves have smoother curve shapes), and tend to experience larger forces when the teeth make contact. When the teeth are finer, the carbon fiber is more likely to break during manufacturing, which can reduce strength, rigidity, and lifespan. Therefore, when using fiber-reinforced plastic, a trochoid type is more preferable than an involute type. (H05) In the above embodiment, a reduction gear 21 was given as an example of a gear mechanism, but it is not limited to this and can also be applied to a speed increaser. (H06) In the above embodiment, a planetary gear mechanism was used as an example, but the invention is not limited to this and can be applied to general gear mechanisms as well. [Explanation of Symbols]

[0036] 2...Arm section, 3... Joint area, 21... Gear mechanism, 22, 23... cabinet, 24... Sun Gear Section, 26...Eccentric shaft part, 26+27...Input section, 27...Input shaft section, 28... Planetary gears, gear components, 28b...Output transmission section, 31…Output section, 32... Output transmission member, S...Robot.

Claims

1. The casing and An input unit disposed inside the housing and to which drive is input, the input unit having an input shaft portion and an eccentric shaft portion rotatable together with the input shaft portion, A gear member disposed inside the housing and to which drive from the input section is transmitted, the gear member being composed of a planetary gear to which drive is transmitted from the eccentric shaft section, A sun gear portion is positioned in contact with the outer circumference of the planetary gear and fixed to the housing, Multiple output transmission units formed at intervals along the circumferential direction of the planetary gear, A plurality of output transmission members are arranged corresponding to each of the plurality of output transmission units and loosely fitted to the output transmission units, An output unit disposed inside the housing, from which the drive from the gear member is output, the output unit supports all of the output-receiving members and supports the output shaft, Equipped with, The housing is made of nylon resin containing carbon fiber, The output unit is made of an epoxy resin containing carbon fiber and is made of a material with higher rigidity than the housing. A gear mechanism characterized by the following features.

2. The planetary gear having an outer circumference shape based on an epitrochoid curve, The gear mechanism according to claim 1, characterized by comprising the above.

3. Multiple arm sections, The joint is the connecting part between the two arm sections, A gear mechanism according to claim 1 or 2, which is arranged in the joint and transmits a drive to displace one arm portion relative to the other arm portion, A robot characterized by having the following features.

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