A UAV nacelle rotary take-up and pay-off mechanism

Abstract

The application discloses a kind of unmanned plane nacelle rotary take-up mechanism, it is related to unmanned plane nacelle technical field.This kind of unmanned plane nacelle rotary take-up mechanism, including mounting bracket, the mounting bracket is rotatably connected with mounting shaft, one end of the mounting shaft is fixed with operating frame, the operating frame is connected with camera by driving element, the upper end of the mounting bracket is provided with rotating element for the rotation of mounting shaft, and the speed limiting assembly for the rotation limiting speed of mounting shaft is arranged on the mounting bracket.This kind of unmanned plane nacelle rotary take-up mechanism, when unmanned plane low-speed flight, by each speed limiting assembly to the resistance of mounting shaft Speed reduction effect, limit mounting shaft and camera with fast way rotation, ensure the stability and flight safety of unmanned plane, and unmanned plane gradually with fast way flight, by transmission, reduce the effect of mounting shaft resistance speed limiting, so that mounting shaft and camera can be faster Speed rotation adjustment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of unmanned aerial vehicle nacelle, in particular to a kind of unmanned aerial vehicle nacelle rotary retraction mechanism. BACKGROUND

[0002] The unmanned aerial vehicle nacelle is a kind of equipment loaded on unmanned aerial vehicle, can carry various sensors and equipment, for monitoring and observation to ground, ocean, air and different environments.Unmanned aerial vehicle nacelle is usually composed of nacelle body, holder, sensor, control system etc., with fast response, high flexibility, low cost and other advantages, is widely used in military, civilian, scientific research and other fields.Microwave imaging is a kind of imaging method using microwave radiation technology.Microwave imaging technology can obtain the image information of the internal structure and characteristics of object by analyzing the reflection or scattering characteristics of different materials and densities of object.Microwave imaging technology has strong penetration, strong anti-interference ability, high imaging resolution and other advantages, can play an important role in military, security, medical and other fields.Combining unmanned aerial vehicle nacelle and microwave imaging technology can realize high-precision, high-resolution monitoring and identification of ground, building, traffic facilities and other targets, has wide application prospect.For example, it can be used for monitoring and identification in the fields of city planning, mineral exploration, traffic management, disaster relief, etc.

[0003] When unmanned aerial vehicle nacelle is installed and used on unmanned aerial vehicle, the camera on unmanned aerial vehicle is rotated and controlled by rotary retraction mechanism, and when unmanned aerial vehicle is running at low speed, the rapid rotation drive of camera by rotary retraction mechanism will cause the attitude of unmanned aerial vehicle body out of control, thereby affecting the stability and flight safety of unmanned aerial vehicle. SUMMARY

[0004] The purpose of the present application is to provide a kind of unmanned aerial vehicle nacelle rotary retraction mechanism to solve the problems raised in the above background.

[0005] To achieve the above purpose, the present application provides the following technical scheme: a kind of unmanned aerial vehicle nacelle rotary retraction mechanism, including mounting bracket, the mounting bracket is rotatably connected with mounting shaft, one end of the mounting shaft is fixed with operating frame, the operating frame is connected with camera by driving element, the upper end of the mounting bracket is provided with rotating element for the rotation of mounting shaft, limiting speed component is arranged on the mounting bracket for limiting the rotation speed of mounting shaft;

[0006] The speed limiting assembly comprises a square slot formed on the mounting frame, a square plate slidably connected to the square slot, a first connecting assembly arranged on the upper end of the mounting frame for connecting the square plate, a speed limiting plate arranged on one side of the square plate, an arc-shaped slot formed on one side of the speed limiting plate, a pushing assembly arranged on one side of the square plate for pushing the speed limiting plate, and the arc-shaped slot on the speed limiting plate is arranged in abutment with the outer side of the mounting shaft under the pushing of the pushing assembly.

[0007] Preferably, the speed limiting assembly is arranged in multiple groups on the mounting frame, and the multiple speed limiting assemblies are arranged in an annular array around the mounting shaft.

[0008] Preferably, the pushing assembly comprises multiple first sleeves fixed on one side of the square plate, a first sliding rod slidably connected to each first sleeve, one end of each first sliding rod fixed to one side of the speed limiting plate, a first spring sleeved outside each first sleeve, and both ends of the first spring arranged in abutment with the square plate and the speed limiting plate, and the arc-shaped slot on the speed limiting plate is arranged in abutment with the mounting shaft under the elastic force of each first spring.

[0009] Preferably, the first connecting assembly comprises a support plate fixed on the upper end of the mounting frame, multiple second sleeves fixed on the support plate, a second sliding rod slidably connected to each second sleeve, one end of the second sliding rod fixed to one side of the square plate, and a second spring sleeved outside each second sleeve, both ends of the second spring connected with the support plate and the square plate.

[0010] Preferably, the moving assembly comprises a support frame fixed on the upper end of the mounting frame, a cylinder arranged above the support frame, a second connecting assembly arranged on the support frame for connecting the cylinder, and a transmission assembly arranged between the cylinder and the square plate for transmitting the square plate.

[0011] Preferably, the transmission assembly comprises a rectangular plate fixed on the upper end of the square plate, a connecting rod arranged between the rectangular plate and the outer side of the cylinder, both ends of the connecting rod rotatably connected with the outer side of the cylinder and the upper end of the rectangular plate, an identification assembly arranged on the support frame for identifying the flight speed, and a lifting assembly arranged on the support frame for lifting the cylinder.

[0012] Preferably, the second connecting assembly comprises a third sleeve fixed on the upper end of the support frame, a third sliding rod slidably connected to the third sleeve, one end of the third sliding rod fixed to the lower end of the cylinder, a third spring sleeved outside the third sleeve, and both ends of the third spring connected with the cylinder and the support frame.

[0013] Preferably, the recognition assembly comprises a rotating shaft rotatably connected to the support frame, the cylinder is sleeved outside the rotating shaft, and the upper end of the rotating shaft is fixed with the fan blade.

[0014] Preferably, the lifting assembly comprises an annular plate fixed to the upper end of the cylinder, the annular plate is sleeved outside the rotating shaft, the inner side of the annular plate is provided with a conical surface, and the rotating shaft is provided with a pressing assembly for abutting and pushing the conical surface.

[0015] Preferably, the pressing assembly is arranged in multiple groups in an annular array on the rotating shaft, the pressing assembly comprises a mounting cylinder fixed outside the rotating shaft, a round rod is slidably connected to the mounting cylinder, one end of the round rod is fixed with a ball pin for abutting and pushing the conical surface, and a connecting spring for connecting the round rod is arranged in the mounting cylinder.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] The unmanned aerial vehicle nacelle rotary take-up and pay-off mechanism can limit the rotation of the mounting shaft and the camera in a fast manner when the unmanned aerial vehicle flies at a low speed, so as to ensure the stability and flight safety of the unmanned aerial vehicle, and can make the mounting shaft and the camera rotate at a faster speed when the unmanned aerial vehicle gradually flies in a fast manner through transmission and reduction of the effect of abutting and speed limiting of the mounting shaft. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall shape structure of the present application;

[0019] Figure 2 It is a schematic diagram of the structure below the unmanned aerial vehicle nacelle of the present application;

[0020] Figure 3 It is a schematic diagram of the speed limiting assembly and the pushing assembly structure of the present application;

[0021] Figure 4 It is a schematic diagram of the first connecting assembly structure of the present application;

[0022] Figure 5 It is a schematic diagram of the moving assembly and the recognition assembly structure of the present application;

[0023] Figure 6 It is a schematic diagram of the lifting assembly and the pressing assembly structure of the present application;

[0024] Figure 7 It is a schematic diagram of the transmission assembly and the second connecting assembly structure of the present application;

[0025] Figure 8 It is Figure 7 It is an enlarged schematic diagram of position A in the above figure.

[0026] In the figure: 101, mounting frame; 102, mounting shaft; 103, operating frame; 104, driving piece; 105, camera; 2, speed limiting assembly; 201, square groove; 202, square plate; 203, speed limiting plate; 204, arc-shaped groove; 3, pushing assembly; 301, first sleeve; 302, first sliding rod; 303, first spring; 4, first connecting assembly; 401, support plate; 402, second sleeve; 403, second sliding rod; 404, second spring; 5, moving assembly; 501, support frame; 502, cylinder; 6, transmission assembly; 601, rectangular plate; 602, connecting rod; 7, second connecting assembly; 701, third sleeve; 702, third sliding rod; 703, third spring; 8, identification assembly; 801, rotating shaft; 802, fan blade; 9, lifting assembly; 901, annular plate; 902, conical surface; 10, extrusion assembly; 1001, mounting cylinder; 1002, round rod; 1003, ball pin; 1004, connecting spring. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0028] Please refer to Figures 1-8 The present application provides a technical solution: a unmanned aerial vehicle nacelle rotating take-up and pay-off mechanism, including mounting frame 101, the mounting frame 101 is rotatably connected with mounting shaft 102, one end of mounting shaft 102 is fixed with operating frame 103, operating frame 103 is connected with camera 105 through driving piece 104, the upper end of mounting frame 101 is provided with rotating piece for rotating mounting shaft 102, the speed limiting assembly 2 for limiting the rotation of mounting shaft 102 is arranged on mounting frame 101;

[0029] The speed limiting component 2 includes a square groove 201 formed on the mounting bracket 101, a square plate 202 slidably connected to the square groove 201, a first connecting component 4 for connecting the square plate 202 is provided at the upper end of the mounting bracket 101, a speed limiting plate 203 is provided on one side of the square plate 202, an arc-shaped groove 204 is formed on one side of the speed limiting plate 203, and a pushing component 3 for pushing the speed limiting plate 203 is provided on one side of the square plate 202, and the arc-shaped groove 204 on the speed limiting plate 203 is pushed by the pushing component 3 and is connected to the outer edge of the mounting shaft 102. The mounting bracket 101 has a side-mounted abutment mechanism, and a moving component 5 is provided above the mounting bracket 101 for moving the square plate 202. When the drone flies at low speed, the speed limiting components 2 reduce the speed of the mounting shaft 102 by resisting each other, thus limiting the rapid rotation of the mounting shaft 102 and the camera 105, ensuring the stability and flight safety of the drone. When the drone gradually flies at a faster speed, the transmission reduces the speed limiting effect on the mounting shaft 102, allowing the mounting shaft 102 and the camera 105 to rotate and adjust at a faster speed.

[0030] Preferably, multiple sets of speed limiting components 2 are provided on the mounting bracket 101, and the multiple speed limiting components 2 are arranged in a circular array around the mounting shaft 102; the speed limiting effect is improved by using multiple speed limiting components 2.

[0031] Preferably, the pushing component 3 includes a plurality of first sleeves 301 fixed to one side of the square plate 202. Each first sleeve 301 is slidably connected to a first slide rod 302. One end of each first slide rod 302 is fixed to one side of the speed limiting plate 203. A first spring 303 is sleeved on the outside of each first sleeve 301. The two ends of the first spring 303 are respectively abutted against the square plate 202 and the speed limiting plate 203. The arc groove 204 on the speed limiting plate 203 abuts against the mounting shaft 102 under the elastic force of each first spring 303. The first sleeves 301 and the first slide rods 302 guide the relative movement between the square plate 202 and the speed limiting plate 203 after being subjected to force. The first springs 303 push and reset the speed limiting plate 203 and the square plate 202 after relative movement.

[0032] Preferably, the first connecting assembly 4 includes a support plate 401 fixed to the upper end of the mounting bracket 101. A plurality of second sleeves 402 are fixed on the support plate 401. A second slide rod 403 is slidably connected to each second sleeve 402. One end of the second slide rod 403 is fixed to one side of the square plate 202. A second spring 404 is sleeved on the outside of each second sleeve 402. The two ends of the second spring 404 are respectively connected to the support plate 401 and the square plate 202. The movement of the square plate 202 after being subjected to force is guided by each second sleeve 402 and the second slide rod 403. The return movement of the square plate 202 after movement is facilitated by each second spring 404.

[0033] Preferably, the moving assembly 5 comprises a support frame 501 fixed on the upper end of the mounting frame 101, a cylinder 502 is arranged above the support frame 501, a second connecting assembly 7 for connecting the cylinder 502 is arranged on the support frame 501, and a transmission assembly 6 for driving the square plates 202 is arranged between the cylinder 502 and the square plates 202; through the transmission assembly 6, the square plates 202 move away from each other after being stressed, and in the movement process of the square plates 202, the speed limiting plates 203 are driven to move through the connecting action of each component on the pushing assembly 3.

[0034] Preferably, the transmission assembly 6 comprises a rectangular plate 601 fixed on the upper end of the square plate 202, a connecting rod 602 is arranged between the outer side of the cylinder 502 and the rectangular plate 601, both ends of the connecting rod 602 are rotatably connected to the outer side of the cylinder 502 and the upper end of the rectangular plate 601, and an identification assembly 8 for identifying the flight speed and a lifting assembly 9 for lifting the cylinder 502 are arranged on the support frame 501; through transmission, the cylinder 502 and the annular plate 901 move downward after being stressed, in the downward movement process of the cylinder 502, each square plate 202 is pushed through the connecting rod 602, and in the pushing process, each square plate 202 moves away from each other after being stressed through the sliding guide action of each second sleeve pipe 402 and the second slide rod 403 on the first connecting assembly 4.

[0035] Preferably, the second connecting assembly 7 comprises a third sleeve pipe 701 fixed on the upper end of the support frame 501, a third slide rod 702 is slidably connected to the third sleeve pipe 701, one end of the third slide rod 702 is fixed to the lower end of the cylinder 502, a third spring 703 is arranged outside the third sleeve pipe 701, and both ends of the third spring 703 are connected to the cylinder 502 and the support frame 501; the movement of the cylinder 502 after being stressed is guided through each third sleeve pipe 701 and the third slide rod 702, and the movement of the cylinder 502 after being stressed is reset and pushed through each third spring 703.

[0036] Preferably, the identification assembly 8 comprises a rotating shaft 801 rotatably connected to the support frame 501, the cylinder 502 is arranged outside the rotating shaft 801, and a fan blade 802 is fixed to the upper end of the rotating shaft 801; in the flight process of the unmanned aerial vehicle, the rotating shaft 801 is driven to rotate through the action of the wind force and the fan blade 802, and the faster the flight speed, the faster the rotating shaft 801 rotates.

[0037] Preferably, the lifting assembly 9 comprises an annular plate 901 fixed at the upper end of the cylinder 502, the annular plate 901 is sleeved outside the rotating shaft 801, the inner side of the annular plate 901 is provided with a conical surface 902, and the rotating shaft 801 is provided with a pressing assembly 10 for abutting and pushing the conical surface 902; through the pressing assembly 10, when the ball pin 1003 at one end of the circular rod 1002 abuts against the conical surface 902 on the inner side of the annular plate 901 during the movement of the circular rod 1002, the annular plate 901 and the cylinder 502 are driven to move through the abutting action of the ball pin 1003 and the conical surface 902.

[0038] Preferably, the pressing assembly 10 is arranged in multiple groups in an annular array on the rotating shaft 801, the pressing assembly 10 comprises a mounting cylinder 1001 fixed outside the rotating shaft 801, the mounting cylinder 1001 is slidably connected with a circular rod 1002, one end of the circular rod 1002 is fixed with a ball pin 1003 for abutting and pushing the conical surface 902, and the inside of the mounting cylinder 1001 is provided with a connecting spring 1004 for connecting the circular rod 1002; during the flight of the unmanned aerial vehicle, the rotating shaft 801 is driven to rotate under the action of wind and the fan blade 802, during the rotation of the rotating shaft 801, the circular rod 1002 on each mounting cylinder 1001 moves towards the outside of the mounting cylinder 1001 under the action of centrifugal force, so that the flight speed of the unmanned aerial vehicle increases, and through transmission, the circular rod 1002 is further driven to slide outward on the mounting cylinder 1001, when the ball pin 1003 at one end of the circular rod 1002 abuts against the conical surface 902 on the inner side of the annular plate 901 during the movement of the circular rod 1002, the annular plate 901 and the cylinder 502 are driven to move through the abutting action of the ball pin 1003 and the conical surface 902.

[0039] Working principle: when the unmanned aerial vehicle nacelle is used, the driving member 104 and the rotating member drive the operating frame 103 and the mounting shaft 102 to rotate, so that the camera 105 rotates to monitor and shoot at different angles, and through the rotation of the camera 105, the camera 105 is adjusted to different states, facilitating the folding and unfolding of the camera 105;

[0040] When the unmanned aerial vehicle nacelle is used, the pushing assembly 3 pushes the speed limiting plate 203 through the pushing action of each first spring 303 on the speed limiting plate 203, so that the arc-shaped groove 204 on the speed limiting plate 203 abuts against the outer side of the mounting shaft 102, and the arc-shaped groove 204 abuts against the outer side of the mounting shaft 102 to frictionally abut against the rotating mounting shaft 102, further playing a role in limiting the speed of the rotating mounting shaft 102, avoiding the rapid rotation of the camera 105 when the unmanned aerial vehicle is flying at low speed, causing the unmanned aerial vehicle body to lose control, thereby ensuring the stability and flight safety of the unmanned aerial vehicle;

[0041] The unmanned aerial vehicle flies in the process, through the action of wind and fan blade 802, drive rotating shaft 801 rotation, rotating shaft 801 rotation process, each installation cylinder 1001 on the round bar 1002 is affected by centrifugal force to the outside of the installation cylinder 1001 movement, thus the speed of unmanned aerial vehicle flight increases, through the transmission, drive round bar 1002 further in the installation cylinder 1001 outside sliding, in the process of round bar 1002 movement, when the ball pin 1003 of round bar 1002 one end and the conical surface 902 inside the ring plate 901 abut, through the abutting action of ball pin 1003 and conical surface 902, drive ring plate 901 and cylinder 502 movement, in the process of cylinder 502 and ring plate 901 movement, through the sliding guide action of the third sleeve 701 and the third slide bar 702, make the stressed cylinder 502 and ring plate 901 move downward, in the process of cylinder 502 downward movement, through the connecting rod 602, push each square plate 202, in the process of pushing, through the sliding guide action of each second sleeve 402 and second slide bar 403 on the first connecting assembly 4, make each square plate 202 stressed mutual movement, in the process of each square plate 202 movement, through the connection action of each component on the push assembly 3, drive speed limiting plate 203 movement, reduce the abutting pressure of arc groove 204 and the outside of installation shaft 102, make the installation shaft 102 can rotate at a faster speed, the whole control and adjustment process is simply said that when the unmanned aerial vehicle flies at low speed, through the abutting speed limiting effect of each speed limiting assembly 2 on installation shaft 102, limit installation shaft 102 and camera 105 rotate at a fast way, ensure the stability and flight safety of unmanned aerial vehicle, when the unmanned aerial vehicle flies at a fast way, through the transmission, reduce the effect of installation shaft 102 abutting speed limiting, make the installation shaft 102 and camera 105 can rotate at a faster speed, because of the high speed flight of unmanned aerial vehicle, the fast adjustment of camera 105 has little effect on the swing of unmanned aerial vehicle at this time, realize both can ensure the low speed rotation limitation of camera 105 when unmanned aerial vehicle flies at low speed, also can ensure the camera 105 can rotate at a high speed when unmanned aerial vehicle flies at high speed.

Claims

1. A rotating and deploying mechanism for a drone pod, comprising a mounting frame (101), wherein a mounting shaft (102) is rotatably connected to the mounting frame (101), one end of the mounting shaft (102) is fixedly connected to an operating frame (103), a camera (105) is connected to the operating frame (103) via a driving component (104), and a rotating component for rotating the mounting shaft (102) is provided at the upper end of the mounting frame (101), characterized in that: The speed limiting assembly (2) is arranged on the mounting frame (101) and is used for limiting the rotation speed of the mounting shaft (102); The speed limiting assembly (2) comprises a square slot (201) arranged on the mounting frame (101), a square plate (202) slidably connected to the square slot (201), a first connecting assembly (4) arranged at the upper end of the mounting frame (101) and used for connecting the square plate (202), a speed limiting plate (203) arranged on one side of the square plate (202), an arc-shaped slot (204) arranged on one side of the speed limiting plate (203), a pushing assembly (3) arranged on one side of the square plate (202) and used for pushing the speed limiting plate (203), the arc-shaped slot (204) on the speed limiting plate (203) is arranged in abutment with the outer side of the mounting shaft (102) under the pushing of the pushing assembly (3), and a moving assembly (5) is arranged above the mounting frame (101) and used for moving the square plate (202); the moving assembly (5) comprises a support frame (501) fixed to the upper end of the mounting frame (101), a cylinder (502) arranged above the support frame (501), a second connecting assembly (7) arranged on the support frame (501) and used for connecting the cylinder (502), and a transmission assembly (6) arranged between the cylinder (502) and the square plate (202) and used for transmitting the square plate (202); the transmission assembly (6) comprises a rectangular plate (601) fixed to the upper end of the square plate (202), a connecting rod (602) arranged on the outer side of the cylinder (502) and the rectangular plate (601), and both ends of the connecting rod (602) are rotatably connected to the outer side of the cylinder (502) and the upper end of the rectangular plate (601), respectively, an identification assembly (8) arranged on the support frame (501) and used for identifying the flight speed, and a lifting assembly (9) arranged on the support frame (501) and used for lifting the cylinder (502); the identification assembly (8) comprises a rotating shaft (801) rotatably connected to the support frame (501), the cylinder (502) is sleeved on the outer side of the rotating shaft (801), and a fan blade (802) is fixed to the upper end of the rotating shaft (801); the lifting assembly (9) comprises an annular plate (901) fixed to the upper end of the cylinder (502), the annular plate (901) is sleeved on the outer side of the rotating shaft (801), a conical surface (902) is arranged on the inner side of the annular plate (901), and an extrusion assembly (10) is arranged on the rotating shaft (801) and used for abutting and pushing the conical surface (902); a plurality of groups of the extrusion assembly (10) are arranged in an annular array on the rotating shaft (801), the extrusion assembly (10) comprises a mounting cylinder (1001) fixed to the outer side of the rotating shaft (801), a circular rod (1002) slidably connected to the mounting cylinder (1001), a ball pin (1003) fixed to one end of the circular rod (1002) and used for abutting and pushing the conical surface (902), and a connecting spring (1004) arranged in the mounting cylinder (1001) and used for connecting the circular rod (1002). 2.The unmanned aerial vehicle nacelle rotating stowing and releasing mechanism according to claim 1, characterized in that: The speed limiting assembly (2) is provided with multiple groups on the mounting frame (101), and multiple speed limiting assemblies (2) are arranged in a ring array around the mounting shaft (102).

3. The unmanned aerial vehicle nacelle rotating stowing and releasing mechanism according to claim 1, characterized in that: The pushing assembly (3) comprises multiple first sleeves (301) fixed on one side of the square plate (202), each first sleeve (301) is slidably connected with a first slide rod (302), one end of each first slide rod (302) is fixed with the one side of the speed limiting plate (203), the outer side of each first sleeve (301) is sleeved with a first spring (303), both ends of the first spring (303) are respectively arranged in abutment with the square plate (202) and the speed limiting plate (203), and the arc-shaped groove (204) on the speed limiting plate (203) is in abutment with the mounting shaft (102) under the elastic force of each first spring (303).

4. The unmanned aerial vehicle nacelle rotating stowing and releasing mechanism according to claim 1, characterized in that: The first connecting assembly (4) comprises a supporting plate (401) fixed on the upper end of the mounting frame (101), multiple second sleeves (402) are fixed on the supporting plate (401), each second sleeve (402) is slidably connected with a second slide rod (403), one end of the second slide rod (403) is fixed with one side of the square plate (202), the outer side of each second sleeve (402) is sleeved with a second spring (404), both ends of the second spring (404) are respectively connected with the supporting plate (401) and the square plate (202).

5. The unmanned aerial vehicle nacelle rotating stowing and releasing mechanism according to claim 1, characterized in that: The second connecting assembly (7) comprises a third sleeve (701) fixed on the upper end of the supporting frame (501), the third sleeve (701) is slidably connected with a third slide rod (702), one end of the third slide rod (702) is fixed with the lower end of the cylinder (502), the outer side of the third sleeve (701) is sleeved with a third spring (703), both ends of the third spring (703) are respectively connected with the cylinder (502) and the supporting frame (501).

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