A FAST cable detection robot simulation test device

Abstract

The application discloses a FAST feed support cable detection robot simulation test device, which comprises a feed cabin simulation tower, a simulation support tower and a FAST cable driving main cable arranged between the two towers; the FAST cable driving main cable is hung with all kinds of original fixed pulleys, movable pulleys and cable optical cables and other components of the FAST main cable at the 240-meter section of the feed cabin end; the distance between the feed cabin simulation tower and the simulation support tower is greater than 37 meters, the length of the main cable is greater than 58 meters, the height of the high point of the main cable from the ground is greater than 50 meters, and the high point of the main cable simulates the inclination angle of the FAST main cable at the 240-meter section of the feed cabin end. The feed cabin simulation tower simulates the position and connection relationship among the FAST original equipment feed cabin, the cabin parking platform and the FAST cable driving main cable. Meanwhile, a pulley hanging track on the top of the FAST feed support tower is simulated on the simulation support tower, which is used for installing a fixed pulley of a traction robot. The environment of the robot walking detection on the main cable of the simulation test device is the same as that of the FAST telescope equipment, and the simulation of the FAST actual object is completely realized.

Description

Technical Field

[0001] The present invention relates to a FAST cable inspection robot simulation test device, which is used to fully simulate the FAST cabin docking platform, feed cabin, 240-meter-long main cable of the feed cabin section, and cable entry mechanism components, cables and optical cables, FAST feed support tower, and tower top hand chain hoist guide rails installed on this main cable section. At the FAST cable drive main cable hanging point of the simulated feed support tower, the inclination angle of the main cable simulates the inclination angle of the 240-meter-long FAST cable drive main cable of the FAST feed cabin section. The FAST cable inspection robot conducts robot adaptability, structural rationality, and material durability tests for the specific task of FAST cable inspection on this simulation test device, completing all links from functional verification to performance improvement, and ultimately achieving a series of verifications of the cable inspection robot's indicators. Finally, the verified final prototype is used to complete a full-system inspection operation demonstration application on the FAST cable. Background Art

[0002] The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the world's largest single-aperture radio telescope, with three independent innovations: using Guizhou's natural karst depression as the site; actively deforming the reflecting surface; using a flexible and lightweight six-cable parallel mechanism to drag the feed cabin to achieve primary cable drive, and using the AB rotating shaft mechanism and Stewart parallel mechanism in the feed cabin to achieve secondary fine-tuning of the feed position, thereby achieving high-precision positioning of the feed.

[0003] The FAST reflecting surface can achieve active deformation of the 300-meter aperture reflecting surface, from a spherical surface to a parabola, ensuring that the parabola always points to the celestial body to be observed and focusing the radio wave signals from the celestial body. This process is continuous.

[0004] Six feed support towers, each over 100 meters tall, are evenly distributed along a 600-meter diameter circle around the outer edge of the reflector. Each tower supports a 46mm diameter steel cable, driven by a drive winch at the base of each tower. The cables are securely connected to the feed cabin via a ground-based guide pulley, a cable channel in the tower's center, and a guide pulley mechanism at the top of the tower. This six-cable feed cabin towing system is called the FAST cable drive system. The cable drive system is a 600-meter-long parallel cable mechanism that tows the feed cabin at altitudes of 140 to 177 meters, within a 207-meter circumference, for astronomical tracking observations. This system leverages the cable's advantages, such as its cost-effectiveness and low weight-to-span ratio. Consequently, the primary factor affecting FAST's safety is now focused on the cables.

[0005] During FAST's operation, various factors can cause premature damage or breakage of the cables. Prompt detection of cable defects can effectively minimize the damage caused by cable breakage. Timely, comprehensive, and accurate inspection of the six cable drive cables is crucial for predicting their service life and enabling timely replacement, ensuring the healthy and economical operation of FAST. A 240-meter-long section of FAST's cable drive cables at the feed module is located outdoors for extended periods, over long distances, at high altitudes, and with steep slopes. The cables are entangled with obstacles such as pulleys, cable clamps, and electrical and optical cables. Located above FAST's reflector, these obstacles are inaccessible to humans, pose numerous blind spots for telescopic inspection, and are difficult to inspect with a remotely controlled aircraft. To date, the use of cable inspection robots has proven to be an effective means of comprehensive cable inspection. These robots must perform nondestructive testing for damage such as broken wires and wear, detect faults in pulleys, cables, and optical cables, and provide visual and directional awareness of obstacles. Inspection requires navigating obstacles such as pulleys on the cables. Summary of the Invention

[0006] The inventor believes that the 240-meter-long cable section at the end of the FAST feed cabin has a cable entry mechanism for the FAST electric and optical cables hanging on the main cable. In order to reduce the damage to the steel cable caused by the cable entry mechanism, the pulley sheaves and cable clamps hanging on the cable are made of oil-containing nylon, and the pulley bodies are made of aluminum alloy to reduce the wear and damage that the pulley may cause to the steel cable. However, the risk of defects in the steel cable during use still exists, and the 240-meter cable section needs to be inspected. However, most of the current cable inspection robots are developed for the inspection and maintenance of high-altitude power transmission line cables. There is no robot suitable for FAST cable-driven steel cable inspection. It is necessary to develop a special robot suitable for FAST cable-driven steel cable inspection to solve the current problem that FAST cable-driven steel cables cannot be inspected online. The development of the FAST cable inspection robot directly targets the key technical difficulties in the types and scales of obstacles on the steel cable and the field of cable inspection robots.

[0007] In order to ensure the safety of FAST and reduce interference with FAST's normal observations, it is necessary to design a dedicated robot simulation test device to carry out testing of the cable detection robot prototype. Once it is verified that the robot's function and safety meet the FAST cable drive cable detection requirements, the robot will be transported to the FAST site for testing and inspection on the FAST cable drive main cable.

[0008] When the cable inspection robot is working, FAST is shut down, and the feed cabin enters the port and docks on the cabin docking platform at the bottom of the FAST reflector surface, and is in a stationary state. In this way, the main cable at the top of the feed support tower passes through the pulley to the feed cabin section. The main cable is about 400 meters long, and the robot only needs to inspect the 240-meter-long main cable at the feed cabin end. In this working condition, the main cable is relatively stable, which is conducive to the safety of the robot's cable up and down and main cable inspection. The inclination angle of the main cable is the largest at 240 meters at the feed cabin end, and the traction force required for the cable inspection robot to crawl on the cable at this point is also the largest, and the climbing difficulty increases simultaneously. The cable inspection robot's cable up and down devices are installed on the pulley support device of the cabin docking platform, and the robot can be installed and down at the original FAST cabin docking platform.

[0009] The purpose of the present invention is to provide a FAST cable detection robot simulation test device which has a novel and unique structure, is easy to use, and can perform testing and verification experiments on the FAST cable detection robot; the specific technical solution is:

[0010] A FAST cable detection robot simulation test device includes a feed cabin simulation tower and a simulation support tower; a FAST cable drive main cable is set up between the feed cabin simulation tower and the simulation support tower; the simulated drive main cable is hung with cables, optical cables, fixed pulleys, movable pulleys and other cable entry mechanism parts (components) that are the same as the original FAST components; the length of the simulated drive main cable between the feed cabin simulation tower and the simulation support tower is greater than 57 meters; the distance between the feed cabin simulation tower and the simulation support tower is greater than 37 meters; and the highest point of the simulated drive main cable is greater than 50 meters from the ground.

[0011] Furthermore, the upper end of the FAST driving main cable of the simulated support tower is provided with an adapter connecting plate for adjusting the length of the FAST cable driving main cable, so as to adjust the inclination angle of the upper end of the main cable and accurately simulate the inclination angle of the main cable at 240 meters at the feed cabin end of the FAST prototype equipment.

[0012] Furthermore, the top of the simulated support tower is provided with a hand-pulled hoist track identical to that of the FAST feed support tower top, which is used to fix the fixed pulley of the traction device on the robot.

[0013] Furthermore, the simulated FAST drive main cable is equipped with cable entry mechanism components such as optical cables, fixed pulleys and movable pulleys that are the same as the original FAST components; the length of the simulated drive main cable between the feed cabin simulation tower and the simulated support tower is between 57 and 59 meters; the distance between the feed cabin simulation tower and the simulated support tower is 37 meters; the highest point of the simulated FAST cable drive main cable is 50 meters from the ground.

[0014] Furthermore, the feed module simulation tower simulates the FAST prototype feed module, its docking platform, and the connection between the feed module and the FAST cable drive main cable. This location is where the robot's cable assembly and disassembly mechanism is installed. The polyhedron on the upper portion of the feed module simulation tower simulates the structure near the cable anchor head of the original FAST feed module. Its lower surface provides the movement limits for the robot's cable assembly and disassembly mechanism, as well as the robot and operator.

[0015] Furthermore, the embedded parts of the feed cabin simulation tower foundation simulate the two columns of the cabin docking platform equipment pulley support device. The upper surfaces of the two columns at the same height are the main installation planes of the robot's upper and lower cable devices. There are two M56 lifting threaded holes on each of the two columns. All four M56 lifting threaded holes are used for fixed connection of the robot's upper and lower cable devices.

[0016] The FAST cable detection robot simulation test device of the present invention designs a feed cabin simulation tower, a simulation support tower, and hangs a 48-meter-long FAST cable drive main cable and a main cable length adjustment mechanism on two base towers, and installs all kinds of pulleys, other components and optical cables hung on the 240-meter-long main cable of the FAST prototype equipment on the 48-meter-long main cable, so as to simulate the main cable on the 240-meter cable length that the robot needs to detect, all kinds of hanging parts on the main cable, and simulate the inclination of the main cable at 240 meters. It can realize the obstacle crossing capability of the full-scale detection robot, the ability to walk at a large inclination angle on the main cable, and the ability to detect the main cable and all the hanging parts installed on it, and fully simulate the test verification environment; it can basically ensure that the qualified detection robot can be successfully installed and operated on site once, and minimize the interference with the normal operation of FAST. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the cable drive cable of the FAST prototype device;

[0018] Figure 2 This is the main view of the FAST feed module entering the port;

[0019] Figure 3 This is a front view of the FAST cable detection robot simulation test device provided by the present invention;

[0020] Figure 4 A top view of the FAST cable detection robot simulation test device provided by the present invention;

[0021] Figure 5 The FAST main cable detection robot simulation test device provided by the present invention simulates the top main view of the support tower;

[0022] Figure 6 This is a bird's-eye view of the FAST feed module entering the port;

[0023] Figure 7 Figure 6 is a top view of a pulley support device for a FAST cabin docking platform;

[0024] Figure 8 Figure 1 is a front view of a feed source cabin simulation tower provided by the present application;

[0025] Figure 9 Figure 6 is a top view of a pulley support device for a FAST cabin docking platform;

[0026] Figure 1 is a front view of a feed source cabin simulation tower provided by the present application; Figure 2 is a front view of a lower main cable anchoring seat; Figure 3 is a front view of a lifting ring; Figure 4 is a front view of a simulation driving main cable; Figure 5 is a front view of a nylon hanging component; Figure 6 is a front view of a heavy fixed pulley; Figure 7 is a front view of a movable pulley; Figure 8 is a front view of a traction steel wire rope; Figure 9 is a front view of a cable; Figure 10 is a front view of an optical cable; Figure 11 is a front view of a traction pulley; Figure 12 is a front view of an angle adaptive connecting plate; Figure 13 is a front view of a pulley steel wire rope anchoring seat; Figure 14 is a front view of an upper main cable anchoring seat; Figure 17 is a front view of a second traction fixed pulley; Figure 18 is a front view of a simulation support tower; Figure 20 is a front view of a machine room; Figure 22 is a front view of a φ8mm traction steel wire rope; Figure 23 is a front view of a cabin end fixed pulley; Figure 24 is a front view of a main cable connecting piece; Figure 25 is a front view of a robot cable ascending and descending device interface; Figure 26 is a front view of a tower 1 polyhedral seat; Figure 27 is a front view of a feed source cabin; Figure 28 is a front view of a ring beam platform; Figure 29 is a front view of a pulley support device; Figure 30 is a front view of a left driving main cable; Figure 31 is a front view of a right driving main cable; Figure 32 is a front view of a FAST reflecting surface center main cable; Figure 33 is a front view of a lifting stand; Figure 34 is a front view of a cabin cable anchoring head; Figure 35 is a front view of an M56 nut; Figure 36 is a front view of a robot cable ascending and descending device; Figure 42 is a front view of a support tower; Figure 43 is a front view of a FAST reflecting surface; and Figure 44 is a front view of a hardened pavement. DETAILED DESCRIPTION

[0027] The application is hereinafter more fully described with reference to the examples. The application can be embodied in many different forms and should not be construed as limited to the examples set forth herein.

[0028] For ease of explanation, spatially relative terms such as "upper", "lower", "left", "right", and the like can be used herein for describing an element's or feature's relationship to another element or feature as illustrated in the figures. It is to be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device is inverted, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative explanations herein interpreted accordingly.

[0029] As Figure 1As shown, the FAST field hangs the feed cabin 27 above the FAST reflector 43 by the driving main cable provided on the 6 support towers 42 (only 2 of which are shown in the figure). The height difference between the top of the support tower of the FAST prototype device and the feed cabin 27 is about 270 meters, and the horizontal distance from the feed cabin 27 is 300 meters; copying the size of the original device not only has high cost, but also has great difficulty in construction. If a model is made by scaling down, the detection robot needs to be scaled down by the same ratio; since the detection robot is already a small device, after scaling down, it is obviously impossible to achieve its intended function. After analysis, the inventor believes that only the heavy fixed trolley 6 of the FAST cable driving main cable and the moving trolley 7 and other accessories above it need to be configured according to the field, and the types of the hanging parts of the optical cable and the cable below the fixed trolley 6 need to be configured with the minimum number, optimized in quantity, for the detection robot to identify and train.

[0030] Now when the main cable leakage detection is performed, the detection personnel and equipment detect the cable at the top of the tower, and only the driving main cable needs to be tightened from the longest to the shortest, and the other driving main cables are loosened, leaving only 240 meters suspended in the air that cannot be detected; the cable detection robot only needs to detect the remaining 240 meters of the driving main cable. When the cable detection robot detects the driving main cable, the feed cabin enters the port and docks.

[0031] As shown in Figure 2 , the bottom center of the FAST reflector 43 is provided with a regular pentagonal hole, and the reflector panels forming the regular pentagonal hole are supported by the main cable 32 at the center of the FAST reflector to provide a docking space for the feed cabin 27. During field detection, the feed cabin 27 is fixed on the 3 sets of lifting columns 33 on the upper part of the ring beam platform 28, and the robot up and down cable device 36 is provided to hoist the robot onto the driving main cable or lower the driving main cable; although this station has the defect of a high elevation angle that needs to be climbed by the robot, it can keep the driving main cable relatively stable, adapt to the strong wind environment on site, ensure the safety of the robot work, and avoid the robot falling off the driving main cable to cause damage to the FAST. The robot up and down cable device 36 is fixed by the M56 nut 35 and the column of the pulley support device 29.

[0032] In order to reduce the elevation angle of the top end of the driving main cable during detection and reduce the difficulty of climbing for the robot; the driving main cable can be tightened; the elevation angle of the driving main cable at a distance of 240 meters from the bottom end is the maximum climbing elevation angle for the robot.

[0033] As shown in Figure 3 , Figure 4As shown, the FAST cable detection robot simulation test device in the embodiment comprises a feed source cabin simulation tower 1 and a simulation support tower 18; the feed source cabin simulation tower 1 is provided with a lower main cable anchoring seat 2; the hole shaft center distance of the lower main cable anchoring seat 2 from the ground only needs to be consistent with the height of the lower main cable anchoring seat 2 of the field feed source cabin from the ring beam platform 28; taking the ring beam platform 28 as a reference, the verification experiment will not have adverse effects, and it is beneficial to reduce the height of the feed source cabin simulation tower 1 and save costs. The horizontal distance A of the shaft center of the lower main cable anchoring seat 2 from the vertical surface of the feed source cabin simulation tower 1 is also set to be consistent with the vertical surface distance of the center of the main cable anchoring seat of the FAST original equipment feed source cabin from the cabin berthing platform lifting column 33, so as to verify whether the up and down cable operation of the detection robot will cause interference.

[0034] The simulation support tower 18 is installed on the tower foundation, the periphery of which is provided with a hardened pavement 44, which is convenient for equipment transportation and personnel passage; a machine room 20 can also be arranged to provide a working site for the test personnel and a placing site for the control equipment.

[0035] Through analysis, it is found that for the robot climbing, the span difficulty of the stacked moving trolleys above the fixed trolley is the largest; it should belong to a necessary verification link; the main cable parts below the fixed trolley have few accessories and can be appropriately shortened; the spacing between the moving trolleys above the stacked part is large, and the span difficulty is small; the number of moving trolleys can be reduced, and the influence on the climbing ability detection is small; however, it is beneficial to shorten the length of the test cable; in the embodiment, 7 moving trolleys above the stacked part are reserved; which is convenient for training the robot.

[0036] The same as the field, the fixed trolley 6 to the feed source cabin section, hangs the nylon hanging piece on the simulation driving main cable 4, hangs the traction steel wire rope 22, the cable and the optical cable and the like. The fixed trolley 6 to the FAST cable driving main cable 240 meters, the fixed trolley 6, 12 to 18 moving trolleys 7 are installed on the simulation driving main cable 4, wherein, the stacked moving trolleys 7 are consistent with the number of moving trolleys stacked on the FAST driving main cable in the state. Figure 5 The traction steel wire rope 8 is connected between every 2 trolleys, the cable 9 and the optical cable 10 are fixed on the trolley saddle beam. The cabin end fixed trolley 23 is fixedly arranged at the lowermost end; the uppermost end is the traction trolley 11; it is connected with the tower top trolley steel wire rope anchoring seat 13 through the steel wire rope; the robot detects the working condition, the feed source cabin enters the port and is berthed, and all the trolleys are relatively stationary. The base of the feed source cabin simulation tower 1 is provided with a robot up and down cable mechanism interface 25.

[0037] The distance and height between the simulated support tower 18 and the feed module simulated tower 1 are fixed. The cable length is adjusted using the angle adapter connecting plate 12 installed in the simulated test apparatus. The inclination angle of the main cable at the top of the simulated support tower 18 can be adjusted to align with the inclination angle of the FAST prototype's main cable at 240 meters, the endpoint of the robotic inspection. The simulated drive main cable between the feed module simulated tower 1 and the simulated support tower 18 is approximately 58 meters long; the distance between the feed module simulated tower 1 and the simulated support tower 18 is 37 meters; and the highest point of the simulated drive main cable is 50 meters above the ground.

[0038] The lower end of the simulated driving main cable 4 is fixedly connected to the lower main cable anchoring seat 2 through the main cable connecting member 24 ; the upper end of the simulated driving main cable 4 is fixedly connected to the upper main cable anchoring seat 14 .

[0039] like Figure 5 As shown, in order to accurately simulate the maximum inclination angle of the driving main cable, an angle adaptation connecting plate 12 is provided between the upper end of the simulated driving main cable 4 and the upper main cable anchor seat 14; the maximum inclination angle of the simulated driving main cable 4 erected between the feed cabin simulation tower 1 and the simulated support tower 18 is changed by the angle adaptation connecting plate 12, and fine-tuned so that it is greater than the maximum climbing elevation angle within 2°; for example, 65 degrees.

[0040] The angle adaptor plates 12 come in a set of three. The shortest plate is 200 mm long, with the others increasing in length by 200 mm. Each plate has connection holes at both ends, connecting to the simulated drive main cable 4 and the upper main cable anchor 14, respectively. Using fixed-length angle adaptor plates 12 ensures a simple structure and a low failure rate.

[0041] The upper traction cable fixed pulley 15 is fixed on the top steel beam 16 above the upper main cable anchor seat 14.

[0042] During use, the inspection robot is mounted on a simulated main drive cable 4; the upper and lower traction units cooperate to pull the inspection robot upward or downward. This simulates on-site use, inspecting the positional relationships of cables, optical cables, pulleys, and other components suspended from various sections of the main drive cable, as well as overcoming obstacles and the maximum tilt state of the main cable while crawling.

[0043] A robot cable access interface 25 is also located at the base of the feed module simulation tower 1. This interface is rectangular, with threaded positioning holes at the corners. The holes are spaced 3280 mm in length and 1080 mm in width. These dimensions match those of the robot cable access interface installed atop the pulley support 29 of the FAST docking platform.

[0044] like Figure 6 、 Figure 7As shown, the driving main cables led out from the two support towers 42 on site are respectively connected to the two holes of the same cabin cable anchoring head support 2 of the feed cabin 27 through the cabin cable anchoring head 34; the angle between the long side of each group of left driving main cables 30 and right driving main cables 31 and the pulley support device 29 is fixed and the same at 58°.

[0045] like Figure 8 As shown, the horizontal distance A between the axis center of the lower main cable anchor seat 2 and the elevation of the feed cabin simulation tower 1 is also set to be consistent with the elevation distance between the center of the main cable anchor seat of the original FAST equipment feed cabin and the cabin docking platform lifting column 33; the height B between the axis center of the lower main cable anchor seat 2 and the ground is consistent with the height of the main cable anchor seat of the on-site feed cabin from the ring beam platform; in order to verify whether the upper and lower cable operations of the detection robot will cause interference.

[0046] The angle α between the inclined surface below the lower main cable anchor seat 2 and the horizontal plane is consistent with the angle between the inclined surface below the lower main cable anchor seat 2 of the on-site feed cabin and the horizontal plane; this is to verify whether the upper and lower cable operations of the detection robot will cause interference.

[0047] like Figure 9 As shown, the embedded parts at the foundation of the feed cabin simulation tower simulate the two sets of columns of the pulley support device 29 of the original FAST equipment. The four lifting screw holes on the upper part of the two sets of columns are used to connect with the robot up and down cable device. The upper part of the columns is used as the main support surface of the robot up and down cable device. The two robot up and down cable device interfaces 25a and 25b are used to simulate the on-site pulley support device 29 respectively. Using one main cable can simulate each set of left drive main cable 30 and right drive main cable 31 respectively; in this way, Figure 8 The feed cabin simulation tower 1 and the interfaces 25a, 25b and the simulated driving main rope 4 shown simulate the feed cabin 27, the pulley support device 29, the main rope 30 and the main rope 31 on site in full proportion.

[0048] The above examples are only used to illustrate the present invention. In addition, there are many different implementation methods. These implementation methods are all conceivable by those skilled in the art after understanding the concept of the present invention. Therefore, they are not listed here one by one.

Claims

1. A FAST cable detection robot simulation test device, characterized in that: It includes a feed cabin simulation tower and a simulation support tower; a FAST cable drive main cable is set up between the feed cabin simulation tower and the simulation support tower; the FAST cable drive main cable is hung with the same cables, optical cables, fixed pulleys and movable pulley components as the original FAST components; the length of the FAST cable drive main cable between the feed cabin simulation tower and the simulation support tower is greater than 57 meters; the distance between the feed cabin simulation tower and the simulation support tower is greater than 37 meters; The highest point of the simulated driving main cable is greater than 50 meters from the ground; The feed cabin simulation tower simulates the feed cabin, cabin docking platform equipment and the connection relationship between the FAST cable drive main cable and the feed cabin of the original FAST equipment; the embedded parts at the foundation of the feed cabin simulation tower simulate the two sets of columns of the pulley support device of the original FAST equipment. The four lifting screw holes on the upper part of the two sets of columns are used to connect with the robot's upper and lower cable devices, and the top of the columns is used as the main support surface of the robot's upper and lower cable devices.

2. The FAST cable detection robot simulation test device according to claim 1, characterized in that: The polyhedron seat at the upper part of the feed cabin simulation tower simulates the structure near the cabin cable anchoring head seat of the feed cabin of the original FAST equipment, and its lower surface is the activity limit of the robot's upper and lower cable devices, the robot and the operator.

3. The FAST cable detection robot simulation test device according to claim 1, characterized in that: An adapter connecting plate for adjusting the length of the FAST cable-driven main cable is provided at the upper end of the simulated support tower. Its function is to adjust the inclination angle at the connection point at the upper end of the main cable to simulate the maximum inclination angle of the cable segment that the FAST prototype equipment robot needs to detect.

4. The FAST cable detection robot simulation test device according to claim 1, characterized in that: The length of the FAST cable-driven main cable between the feed cabin simulation tower and the simulation support tower is less than 59 meters.

Images