A center of gravity support for unmanned aerial vehicle operations

Abstract

The utility model discloses a keep unmanned aerial vehicle operation gravity center support, including fixed seat and organism, the bottom surface fixed landing gear of fixed seat has, and the both sides center position of fixed seat is installed with the hanging arm, and the hanging arm is U shape, and the hanging arm opening end is located at the bottom, and the front support and the external hanging support are equipped respectively in the front position of hanging arm, and the back position of hanging arm is equipped with the servo support, and servo support, front support and external hanging support all with the corresponding position of the shaft joint of hanging arm end, and the bottom end of hanging arm is connected with the guide rod, and the inside surface of guide rod is equipped with the guide rail, and the front link, rear link and sliding block are equipped respectively between front support and servo support, when unmanned aerial vehicle needs to carry out the contact type operation, servo motor accurate control wire retraction, drive servo support and counterweight box lifting, and then through sliding block and link drive front support synchronous movement, make external hanging equipment flexible adjustment operation height and angle, through the linkage mechanism of rigid link and adjustable structure composition.

Description

Technical Field

[0001] This utility model relates to the field of unmanned aerial vehicle (UAV) technology, specifically to a support for maintaining the center of gravity of an UAV during operation. Background Technology

[0002] With the development of drones, drone operations are facing increasingly diverse scenario requirements. The center of gravity of most single-rotor drones is designed on the rotor's rotation axis, while that of most dual-rotor drones is at the midpoint of the line connecting the two rotor axes. For multi-rotor drones, the center of gravity is at the focal point of the lines connecting the rotation axes of the diagonal rotors. Drones are merely flight platforms; different operational equipment is attached according to mission and operational requirements to give them operational capabilities. Conventional methods for external load-bearing include attaching a single device near the center of gravity axis with lift compensation algorithms or attaching it to opposite sides of the center of gravity axis to reduce the drone's roll performance. However, attaching operational equipment outside the rotor surface projection significantly exceeds the lift surface. If the flight control program incorporates a center of gravity adaptation algorithm, prolonged center of gravity deviation during flight can lead to power compensation fatigue, i.e., overheating of the power compensation power source or interference of the lift compensation equipment with other lift-generating equipment during flight. If the center of gravity exceeds its extreme limits, it can result in the drone being damaged upon takeoff.

[0003] The external load racks used in existing multi-rotor drones all adopt the fixed-point hanging method, which cannot exceed the projection range of the rotor's rotation surface. If the horizontal volume of the mounted equipment is too large, it will affect the lift area, thus causing lift loss. If the vertical volume of the mounted equipment is too large, it will cause the drone to be unable to land, or the external equipment to touch the ground first during landing. Utility Model Content

[0004] The purpose of this invention is to provide a support for maintaining the center of gravity of a drone during operation, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, this utility model provides the following technical solution: This application provides a support for maintaining the center of gravity of a drone, including a fixed base and a body. A landing gear is fixed to the bottom surface of the fixed base. Hanging arms are installed at the center positions of both sides of the fixed base. The hanging arms are U-shaped, with the open end of the hanging arm located at the bottom. A front bracket and an external bracket are respectively provided on the front position of the hanging arm. A servo bracket is provided on the back position of the hanging arm. The servo bracket, the front bracket, and the external bracket are all axially connected to the corresponding positions at the ends of the hanging arms. A guide rod is connected to the bottom end of the hanging arm. A guide rail is opened on the inner side of the guide rod. A front connecting rod, a rear connecting rod, and a slide are respectively provided between the front bracket and the servo bracket.

[0006] In one possible implementation, the fixed seat is a rectangular frame, and the top end of the hanging arm is sleeved on the surface of the fixed seat, and the two are fixed together by screws.

[0007] In one possible implementation, the front bracket is axially connected to the outer portion of the end of the hanging arm, the external bracket is axially connected to the inner portion of the end of the hanging arm, and the connection position of the servo bracket is symmetrical to the connection position of the front bracket.

[0008] In one possible implementation, the front end portion of the front bracket is provided with a support guide wheel assembly, which includes a sleeve and a limiting wheel, and a portion of the external bracket contacts and engages with the surface of the limiting wheel.

[0009] In one possible implementation, the sleeve is fitted onto the front end surface of the front bracket and the two are fixed together, with the limiting wheel located on the sleeve in a V-shape.

[0010] In one possible implementation, one end of both the front link and the rear link is located on the slider, and the two are staggered from left to right. The front link is connected to the front bracket, and the rear link is connected to the servo bracket.

[0011] In one possible implementation, the slider is located inside the guide rail, the slider cooperates with the guide rail, and the slider and the guide rail are slidably connected.

[0012] In one possible implementation, a mounting box is fixed to one end of the servo bracket, and servo motors are provided on both sides of one end of the servo bracket. Pullers are respectively installed on the rotating end of the servo motor and on the outer part of the bottom end of the hanging arm.

[0013] Compared with the prior art, the beneficial effects of this utility model are: 1. When the drone needs to perform contact operations, the servo motor precisely controls the extension and retraction of the steel wire, driving the servo bracket and counterweight box to rise and fall. In turn, the slider and connecting rod drive the front bracket to move synchronously, allowing the external equipment to flexibly adjust the working height and angle. Through the linkage mechanism composed of rigid connecting rods and adjustable structures, physical dynamic center of gravity matching between the external equipment and the drone body is achieved. Regardless of whether the external equipment is stationary, moving, or in contact with the drone, it can automatically adjust. Without relying on complex flight control algorithms, it can fundamentally ensure the attitude stability of the drone in various flight stages, including takeoff, operation, and landing.

[0014] 2. Both the front support and the servo support are connected to the slider via front and rear linkages. The slider is strictly confined to the guide rail, effectively suppressing the disturbance of flight vibration and sway to the attached equipment and preventing its accidental deviation. Secondly, when the shape changes, it provides rigid motion constraints and guidance for the entire mechanism, ensuring the stability and predictability of the center of gravity axis during dynamic adjustment. At the same time, the support guide wheel assembly installed at the front end of the front support supports most of the weight of the attached support and the equipment on the support in a rolling contact manner. While providing reliable support, it greatly reduces frictional resistance. This gives the attached support a low-resistance floating degree of freedom in the working direction, which can not only prevent position deviation caused by external disturbances, but also ensure the flexibility and smoothness when the working equipment contacts the target. Attached Figure Description

[0015] Figure 1 This is a perspective view of the present utility model; Figure 2 This is an overall structural diagram of the present invention; Figure 3 This is a side view of the present invention; Figure 4 This is a diagram of the hanging arm connection structure of this utility model; Figure 5 This is a structural diagram of the guide rod of this utility model; Figure 6 This is a structural diagram of the support guide wheel assembly of this utility model.

[0016] In the diagram: 1. Fixed base; 2. Landing gear; 3. Hanging arm; 4. Front support; 5. Support guide wheel assembly; 51. Sleeve; 52. Limit wheel; 6. External bracket; 7. Servo bracket; 8. Front connecting rod; 9. Rear connecting rod; 10. Slider; 11. Guide rod; 12. Guide rail; 13. Mounting box; 14. Servo motor; 15. Body; 16. Pulley. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this application, unless otherwise stated, "multiple" means two or more.

[0019] Example 1: refer to Figure 1-6 A support for maintaining the center of gravity of a drone provided in this application embodiment includes a fixed base 1 and a body 15. A landing gear 2 is fixed to the bottom surface of the fixed base 1. Hanging arms 3 are installed at the center positions of both sides of the fixed base 1. The hanging arms 3 are U-shaped, and the open end of the hanging arms 3 is located at the bottom. A front support 4 and an external support 6 are respectively provided on the front position of the hanging arms 3. A servo support 7 is provided on the back position of the hanging arms 3. The servo support 7, the front support 4, and the external support 6 are all axially connected to the corresponding positions at the ends of the hanging arms 3. A guide rod 11 is connected to the bottom end of the hanging arms 3. A guide rail 12 is opened on the inner side of the guide rod 11. A front connecting rod 8, a rear connecting rod 9, and a slider 10 are respectively provided between the front support 4 and the servo support 7.

[0020] Specifically, the external support bracket 6 can mount a variety of work equipment, and the center of gravity of the electronic equipment mounting box 13 and the external work equipment is kept in the same position through the center of gravity keeping linkage mechanism. During the take-off, landing, flight path and work flight of the UAV, the center of gravity of the external work equipment and the lift center of gravity of the UAV can be kept on the same axis. For UAVs without a flight control program with an adaptive algorithm for center of gravity change, the matching problem between the external equipment and the UAV flight control program can be solved from the outside through physical structure.

[0021] In one possible implementation, the fixed base 1 is a rectangular frame, and the top end of the hanging arm 3 is sleeved on the surface of the fixed base 1, and the two are fixed by screws. The front bracket 4 is axially connected to the outer part of the end of the hanging arm 3, the outer bracket 6 is axially connected to the inner part of the end of the hanging arm 3, and the connection position of the servo bracket 7 is symmetrical to the connection position of the front bracket 4.

[0022] Specifically, the body 15 is a schematic entity of the UAV. A fixed base 1 is added to the bottom of the body 15, and the front bracket 4, external bracket 6 and servo bracket 7 are connected by the hanging arm 3. The fixed base 1 is a rectangular frame that fits with the surface of the body 15 so that the body 15 can be placed on the fixed base 1. The added center of gravity bracket is assembled and connected to the body 15 by bolts and other components. The landing gear 2 is directly connected and fixed to the bottom surface of the fixed base 1. The bottom part of the landing gear 2 can directly contact the ground, so that the landing gear 2 can make stable contact with the ground during landing, thereby allowing the body 15 to land smoothly.

[0023] Specifically, the hanging arm 3 has a U-shaped structure, with one end sleeved on the surface of the fixed base 1 and fixed to the fixed base 1 by bolts. The bottom end is a U-shaped open end. The front bracket 4, the external bracket 6, and the servo bracket 7 are all connected to the corresponding parts of the bottom end of the hanging arm 3. To further explain, the connecting end of the front bracket 4 is axially connected to the outer side of the bottom end of the hanging arm 3, and the connecting end of the external bracket 6 is axially connected to the inner side of the bottom end of the hanging arm 3. The connecting ends of the external bracket 6 and the front bracket 4 are horizontally aligned and are located on the outer and inner sides of the hanging arm 3, respectively. The position of the servo bracket 7 is symmetrical to the position of the front bracket 4 and is also axially connected to the bottom part of the hanging arm 3.

[0024] In one possible implementation, the front end of the front support 4 is provided with a support guide wheel assembly 5, which includes a sleeve 51 and a limiting wheel 52. Part of the external support 6 is in contact with the surface of the limiting wheel 52. The sleeve 51 is sleeved on the front end surface of the front support 4 and the two are fixed. The limiting wheel 52 is located on the sleeve 51 to form a V-shape. The main purpose of the external support 6 is to install and connect the tools required for the operation, so that the aircraft 15 can carry the tools with it during flight and place the tools in the working position to achieve the operation. The front support 4 provides support for the external support 6, and the two are in gravity contact.

[0025] Specifically, the front end of the front support 4 is equipped with a support guide wheel assembly 5, which consists of a sleeve 51 and a limiting wheel 52. The limiting wheel 52 forms a V-shape on the sleeve 51. After the sleeve 51 is fitted onto the front end of the front support 4 and fixed, the external support 6 rests on the limiting wheel 52. It supports the weight of the working equipment and the external support 6 and has a position control function for the external equipment and the external support 6. This prevents the external equipment mounting bracket from deviating due to external disturbances during flight and operation. The external support 6 can obtain one degree of freedom in the Z-axis during operation, which can better ensure the contact flexibility between the working equipment and the working target.

[0026] In one possible implementation, one end of the front link 8 and the rear link 9 are both located on the slider 10, and the two are staggered. The front link 8 is connected to the front bracket 4, and the rear link 9 is connected to the servo bracket 7. The slider 10 is located inside the guide rail 12, and the slider 10 and the guide rail 12 cooperate with each other and are slidably connected. The guide rod 11 is located on the bottom surface of the hanging arm 3 and is bolted to the hanging arm 3. The guide rail 12 is provided on the inner side of the guide rod 11, and the slider 10 is located at the position of the guide rail 12. The two cooperate to allow the slider 10 to slide linearly along the guide rail 12.

[0027] Specifically, the slider 10 includes a front connecting rod 8 and a rear connecting rod 9. Both the front rod and the rear connecting rod 9 are directly connected to the front bracket 4 and the servo bracket 7. It is worth noting that when the positional motion energy component on the servo bracket 7 is working, the position of the servo bracket 7 changes. At this time, when the servo bracket 7 moves up or down, the corresponding slider 10 slides in the guide rail 12. The front bracket 4 moves in conjunction with the slider 10, thereby achieving the linkage adjustment between the front bracket 4 and the external bracket 6.

[0028] In one possible implementation, a mounting box 13 is fixed to one end of the servo bracket 7, and servo motors 14 are provided on both sides of one end of the servo bracket 7. A pulley 16 is installed on the rotating end of the servo motor 14 and the outer part of the bottom end of the hanging arm 3, respectively. The pulley 16, the servo motor 14, the mounting box 13 and the lead screw are used as a positional energy component.

[0029] Specifically, the positional energy component is mainly located on one end of the servo bracket 7, including components such as mounting box 13, servo motor 14, pulleys 16 and winding steel wire. The servo motor 14 control circuit system and power supply are installed in the mounting box 13. The power supply, as an indispensable energy source, also plays the role of an important counterweight. At the same time, counterweights can be added inside the box as needed. The power supply provides power to the servo motor 14, enabling the servo motor 14 to work. One set of pulleys 16 is connected to the servo motor 14, and the other set of pulleys 16 is mainly located on the outer side of the end of the hanging arm 3. The two sets of pulleys 16 are flush with each other and are connected by steel wire.

[0030] It is necessary to explain that when the servo motor 14 drives the connected pulley 16 to rotate, the steel wire is wound up. At this time, the servo bracket 7 moves upward under the winding force of the steel wire, and the front bracket 4 moves upward synchronously under the action of the slider 10, the front connecting rod 8 and the rear connecting rod 9. Similarly, when the servo motor 14 reverses to control the steel wire on the pulley 16 to relax, the servo bracket 7 moves downward under the influence of the gravity of the mounting box 13. Similarly, the front bracket 4 moves downward synchronously, thereby completing the adjustment of the external bracket 6, so that the external bracket 6 and the connected external working equipment can be freely adjusted along the Z-axis.

[0031] The working principle is as follows: The fuselage 15 is a schematic representation of the UAV. A fixed base 1 is added below the fuselage 15, and the front support 4, external support 6, and servo support 7 are connected by the mounting arm 3. The fixed base 1 is a rectangular frame that fits with the surface of the fuselage 15, allowing the fuselage 15 to be placed on the fixed base 1. The added center of gravity support is assembled and connected to the fuselage 15 by bolts and other components. The landing gear 2 is directly connected and fixed to the bottom surface of the fixed base 1, and the bottom part of the landing gear 2 can directly contact the ground, allowing the landing gear 2 to make a smooth contact with the ground during landing, thus enabling the fuselage 15 to land smoothly. The landing arm 3 has a U-shaped structure, with one end sleeved on the surface of the fixed base 1 and fixed to the fixed base 1 by bolts. The bottom end is a U-shaped open end. The front bracket 4, the external bracket 6, and the servo bracket 7 are all connected to the corresponding parts of the bottom end of the hanging arm 3. Specifically, the connecting end of the front bracket 4 is axially connected to the outer side of the bottom end of the hanging arm 3, and the connecting end of the external bracket 6 is axially connected to the inner side of the bottom end of the hanging arm 3. The connecting ends of the external bracket 6 and the front bracket 4 are horizontally aligned and are located on the outer and inner sides of the hanging arm 3, respectively. The position of the servo bracket 7 is symmetrical to the position of the front bracket 4 and is also axially connected to the bottom part of the hanging arm 3.

[0032] The guide rod 11 is located on the bottom surface of the hanging arm 3 and is bolted to the hanging arm 3. A guide rail 12 is provided on the inner side of the guide rod 11. The slider 10 is located at the position of the guide rail 12. The two cooperate to allow the slider 10 to slide linearly along the guide rail 12. The slider 10 includes a front connecting rod 8 and a rear connecting rod 9. The front upright and the rear connecting rod 9 are directly connected to the front bracket 4 and the servo bracket 7. It is worth noting that when the positional motion energy component on the servo bracket 7 is working, the position of the servo bracket 7 changes. At this time, when the servo bracket 7 moves up or down, the corresponding slider 10 slides in the guide rail 12. The front bracket 4 moves in conjunction with the slider 10, thereby achieving the linkage adjustment of the front bracket 4 and the external bracket 6.

[0033] Specifically, the main purpose of the external mounting bracket 6 is to install and connect the tools required for the operation, so that the aircraft 15 can carry the tools with it during flight and position them in the working position to perform the operation. The front bracket 4 provides support for the external mounting bracket 6, and the two are in gravity contact. The front end of the front bracket 4 is equipped with a support guide wheel assembly 5, which is composed of a sleeve 51 and a limiting wheel 52. The limiting wheel 52 forms a V-shape on the sleeve 51. After the sleeve 51 is fitted onto the front end of the front bracket 4 and fixed, the part of the external mounting bracket 6 is on the limiting wheel 52, which supports the weight of the working equipment and the external mounting bracket 6, and has the function of position control of the external equipment and the external mounting bracket 6, preventing the external equipment mounting bracket from deviating due to external disturbances during flight and operation. The external mounting bracket 6 can obtain one degree of freedom in the Z-axis during operation, which can better ensure the contact flexibility between the working equipment and the working target.

[0034] The positional energy component is mainly located at one end of the servo bracket 7, including a mounting box 13, a servo motor 14, pulleys 16, and winding steel wire. Further, the mounting box 13 houses the servo motor 14 control circuit system and power supply. The power supply, as an indispensable energy source, also plays an important role as a counterweight. Additional counterweights can be added to the box as needed. The power supply provides power to the servo motor 14, enabling it to operate. One set of pulleys 16 is connected to the servo motor 14, while another set of pulleys 16 is mainly located on the outer side of the end of the hanging arm 3. The two sets of pulleys 16 are flush with each other and are connected by steel wire. When connecting 16, it is necessary to explain that when the servo motor 14 drives the connected pulley 16 to rotate, the steel wire is wound up. At this time, the servo bracket 7 moves upward under the winding force of the steel wire, and the front bracket 4 moves upward synchronously under the action of the slider 10, the front connecting rod 8 and the rear connecting rod 9. Similarly, when the servo motor 14 reverses to control the steel wire on the pulley 16 to loosen, the servo bracket 7 moves downward under the influence of the gravity of the mounting box 13. Similarly, the front bracket 4 moves downward synchronously, thereby completing the adjustment of the external bracket 6, so that the external bracket 6 and the connected external working equipment can be freely adjusted along the Z-axis.

[0035] When slider 10 is at the top of guide rail 12, external support 6, front support 4, and servo support 7 are all positioned close to the bottom surface of the fuselage 15, i.e., above it. At this time, when the fuselage 15 lands, it does not affect the lift surface of the fuselage 15 rotor, the stability of the external equipment's center of gravity axis, or the support performance of the landing gear 2 due to the size of the external equipment. By utilizing the force of the wire winding or unwinding, the position of servo support 7 can be dynamically adjusted, allowing slider 10 to be in different positions on guide rail 12. This enables external support 6, front support 4, and servo support 7 to freely adjust the set angle of the Z-axis. Slider 10 moves within the limits of guide rail 12, effectively controlling the weight matching of external support 6 and servo support 7. This allows the external equipment to contact the target work area at different angles. This function is suitable for scenarios in UAV operations where contact with external objects is required. When the external equipment contacts an object, the weight of the external equipment is supported by the external object, while the counterweight on servo support 7 has shifted from outside the UAV's center of gravity range back into the center of gravity range, ensuring that changes in the center of gravity range do not alter the flight center of gravity and cause control failure.

[0036] The beneficial effects of using the embodiments of this application are as follows: During the takeoff, landing, and cruise phases of the UAV, the servo motor 14 tightens the steel wire to raise the servo bracket 7, including the counterweight mounting box 13, to a high position. Simultaneously, the slider 10 and connecting rod drive the front bracket 4 and the external bracket 6 to retract synchronously, ensuring that the entire set of operating equipment is close to the body 15. This ensures the overall center of gravity of the UAV is stable and does not interfere with the landing gear 2's grounding. When the UAV arrives at the work point and the external equipment needs to contact the target, the servo motor 14 reverses and releases the steel wire. The servo bracket 7 naturally droops under the action of the counterweight. Through the linkage mechanism, the front bracket 4 and the external bracket 6 extend downward, allowing the operating equipment to contact the target and bear its weight. At this time, the counterweight position of the servo bracket 7 swings back to the UAV's center of gravity range, thereby balancing the torque changes caused by the equipment extension in real time during the operation, ensuring the stability of the flight control system. After the operation is completed, the servo motor 14 tightens the steel wire again, retracts and locks the external equipment, and restores the flight state, realizing the adaptive switching of center of gravity compensation and operating attitude.

[0037] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. This application is not limited to the exact structures described above and illustrated in the accompanying drawings, and it should not be considered that the specific implementation of this application is limited to these descriptions. For those skilled in the art, various changes and modifications made without departing from the concept of this application should be considered to fall within the protection scope of this application.

Claims

1. A support for maintaining the center of gravity of a drone during operation, characterized in that: The device includes a fixed base (1) and a body (15). The bottom surface of the fixed base (1) is fixed with a landing gear (2). Hanging arms (3) are installed at the center positions on both sides of the fixed base (1). The hanging arms (3) are U-shaped and the open end of the hanging arms (3) is located at the bottom. A front bracket (4) and an external bracket (6) are respectively provided on the front position of the hanging arms (3). A servo bracket (7) is provided on the back position of the hanging arms (3). The servo bracket (7), the front bracket (4) and the external bracket (6) are all axially connected to the corresponding positions at the end of the hanging arms (3). A guide rod (11) is connected to the bottom end of the hanging arms (3). A guide rail (12) is opened on the inner side of the guide rod (11). A front connecting rod (8), a rear connecting rod (9) and a slider (10) are respectively provided between the front bracket (4) and the servo bracket (7).

2. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: The fixed seat (1) is a rectangular frame, and the top of the hanging arm (3) is sleeved on the surface of the fixed seat (1), and the two are fixed by screws.

3. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: The front bracket (4) is axially connected to the outer part of the end of the hanging arm (3), the external bracket (6) is axially connected to the inner part of the end of the hanging arm (3), and the connection position of the servo bracket (7) is symmetrical to the connection position of the front bracket (4).

4. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: The front end of the front bracket (4) is provided with a support guide wheel assembly (5), which includes a sleeve (51) and a limiting wheel (52). Part of the external bracket (6) is in contact with the surface of the limiting wheel (52).

5. A support for maintaining the center of gravity of a drone during operation according to claim 4, characterized in that: The sleeve (51) is fitted onto the front end surface of the front bracket (4) and the two are fixed together. The limiting wheel (52) is located on the sleeve (51) to form a V shape.

6. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: One end of the front link (8) and the rear link (9) are both located on the slider (10), and the two are staggered. The front link (8) is connected to the front bracket (4), and the rear link (9) is connected to the servo bracket (7).

7. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: The slider (10) is located inside the guide rail (12), the slider (10) and the guide rail (12) cooperate with each other, and the slider (10) and the guide rail (12) are slidably connected.

8. The support for maintaining the center of gravity of a drone during operation according to claim 1, characterized in that: A mounting box (13) is fixed on one end of the servo bracket (7). Servo motors (14) are provided on both sides of one end of the servo bracket (7). Pulleys (16) are installed on the rotating end of the servo motor (14) and the outer part of the bottom end of the hanging arm (3).

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