A deep soil sampling device for environmental testing

Abstract

The present invention belongs to the technical field of soil sampling, and discloses a deep soil sampling device for environmental detection, including a main board, a plurality of support columns fixedly connected to the edge of the main board, a plurality of fixed rods fixedly connected to the upper surface of the main board, a support ring fixedly connected to the middle of the fixed rods, and a motor sleeve movably sleeved on the upper parts of the plurality of fixed rods. The present invention discloses that the sampling mechanism at the target soil depth performs a rotational motion by driving the motor to work and driving the rotating sleeve to rotate through a small driving gear, and at the same time, the telescopic rod works and slowly extends outward, so that the arc-shaped piece protrudes from the curved surface of the annular sleeve, and the arc-shaped piece rotating clockwise will dig the soil at the target depth into the top of the bottom plate, and when the inside of the bottom plate is sufficient to take a proper amount of sample, the telescopic rod is reset, so that the arc-shaped piece is reset, and the soil at the target depth is preserved, thereby solving the problem that when the existing drilling sampling is performed, soil at other depths falls at the bottom of the borehole, thereby reducing the accuracy of the sampled sample.

Description

Technical Field

[0001] The invention belongs to the technical field of soil sampling, in particular to a deep soil sampling device for environmental detection. Background Art

[0002] With the continuous development of human society and the continuous improvement of science and technology, people are destroying the natural environment more and more seriously, especially soil resources. Soil resources are vital to human beings, so it is necessary to monitor the soil environment at all times and take samples for testing. Deep soil sampling for environmental use is an important part of environmental monitoring and assessment. It aims to obtain information about deep soil layers for analysis of pollutant distribution, geological structure, nutrients, groundwater pollution or soil health. This process involves a variety of technologies, equipment and methods to ensure that the samples are representative and accurate.

[0003] The existing deep soil sampling is to drill to the target depth of soil with a drill bit, and then take samples through a sampling tube. After drilling to the target depth in this way, soil from other depths will fall to the bottom of the borehole, thereby reducing the accuracy of the sample. Moreover, when the soil at the bottom of the borehole is relatively soft, it is difficult to press the soil at the bottom of the borehole into the sampling tube. During the drilling process of taking out the sample, the soil will scatter at the bottom of the borehole, making the sampling efficiency low and further affecting the sampling accuracy. Summary of the invention

[0004] The purpose of the present invention is to provide a deep soil sampling device for environmental detection to solve the problems raised in the above background technology.

[0005] In order to achieve the above-mentioned purpose, the present invention provides the following technical solutions: a deep soil sampling device for environmental detection, comprising a main board, a plurality of support columns are fixedly connected to the edge of the main board, a plurality of fixed rods are fixedly connected to the upper surface of the main board, a support ring is fixedly connected to the middle of the fixed rod, a motor sleeve is movably sleeved on the upper parts of the plurality of fixed rods, a fixing ring is threadedly connected to the top of the fixed rod, a driving motor is fixedly installed in the middle of the motor sleeve, a large driving gear and a small driving gear are fixedly installed on the output shaft of the driving motor, a mounting through hole is opened in the middle of the main board, a threaded sleeve and a rotating sleeve are rotatably installed in the middle of the mounting through hole, a plurality of mounting grooves are opened on the outer curved surfaces of the threaded sleeve and the rotating sleeve, an electromagnet is fixedly installed on the inner wall of the mounting groove, a permanent magnet is slidably connected to the inside of the mounting groove, an upper gear, an upper gear is rotatably sleeved on the curved surface of the threaded sleeve, a lower gear is rotatably sleeved on the curved surface of the rotating sleeve, a lifting rod is threadedly connected to the inside of the threaded sleeve, a connecting rod is movably connected to the bottom end of the lifting rod, and a sampling mechanism is movably connected to the bottom end of the connecting rod.

[0006] Preferably, the sampling mechanism includes a connecting column movably connected to the connecting rod, the curved surface of the connecting column is fixedly connected to a plurality of spiral sheets, the bottom end of the spiral sheet is fixedly connected to a bottom plate, the side of the bottom plate away from the spiral sheet is fixedly connected to a side plate, the upper surface of the bottom plate is fixedly connected to a telescopic rod, the telescopic end of the telescopic rod is fixedly connected to an extension rod, the outer side of the extension rod is fixedly connected to a connecting sheet, the middle part of the connecting sheet is fixedly connected to a connecting pin, the edges of the plurality of spiral sheets are fixedly connected to annular sleeves, the inside of the annular sleeve is fixedly connected to a plurality of fixing columns, the lower end of the fixing column is rotatably mounted with an arc sheet, and the lower end of the annular sleeve is fixedly connected to a serrated ring.

[0007] Preferably, the large driving gear is meshed with the upper gear, the small driving gear is meshed with the lower gear, and the upper gear and the lower gear are both rotatably connected to the main board.

[0008] Preferably, the inner walls of the upper gear and the lower gear are provided with slots whose number is equal to the installation slots, the slots are adapted to the permanent magnets, and the depth of the slots is less than the length between the inner side and the outer side of the permanent magnet.

[0009] Preferably, a plurality of sliding grooves are provided on the outer surface of the lifting rod, the rotating sleeve and the sliding grooves are slidably connected, and the rotating sleeve is adapted to the lifting rod.

[0010] Preferably, the inner sides of the bottom plate and the side plates are fixedly connected to the connecting columns, the outer side of the bottom plate is fixedly connected to the serrated ring, the upper end of the side plate is fixedly connected to the spiral sheet, and the outer side of the side plate is fixedly connected to the annular sleeve.

[0011] Preferably, a rotation groove is provided on the inner side of the arc-shaped piece, and the arc-shaped piece is rotationally connected to the upper and lower ends of the connecting piece.

[0012] The beneficial effects of the present invention are as follows:

[0013] 1. The present invention works by driving a motor, and drives the rotating sleeve to rotate through a small driving gear, so that the sampling mechanism at the target soil depth performs a rotating motion. At the same time, the telescopic rod works and slowly extends outward, so that the arc-shaped piece protrudes from the curved surface of the annular sleeve. The arc-shaped piece rotating clockwise will dig the soil at the target depth into the top of the bottom plate. After a proper amount of sample is taken inside the bottom plate, the telescopic rod is reset to reset the arc-shaped piece and preserve the soil at the target depth, thereby solving the problem that soil at other depths falls at the bottom of the borehole during existing drilling sampling, thereby reducing the accuracy of the sampling sample.

[0014] 2. The present invention rotates downward to the target depth soil through the closed arc-shaped piece and the bottom plate with an empty interior, and then opens the arc-shaped piece, rotates to dig out the soil at the target depth, and then closes. Each sampling can stably take out a certain amount of soil at the target depth. After the sampling is completed, the soil sample at the target depth is isolated and taken out to avoid contact with the target soil, which solves the problem that the existing sampling tube is difficult to sample soft soil, improves the sampling efficiency, and further ensures the sampling accuracy.

[0015] 3. Secondly, the existing sampling method mainly takes out all the soil above the target depth. After the sampling is completed at the target depth, the soil needs to be backfilled. However, the present invention, through the setting of the spiral blade, only loosens the soil above the target depth when going deep into the soil, and guides it to the top of the sampling mechanism. After the sampling is completed at the target depth, the soil above is guided to the bottom of the sampling mechanism. After the sampling is completed, there is no need to backfill the soil, which greatly saves the sampling time and sampling cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall appearance of the present invention;

[0017] Figure 2 A half-section schematic diagram of the motherboard of the present invention;

[0018] Figure 3 This is a schematic diagram of the appearance of the sampling mechanism of the present invention;

[0019] Figure 4 This is a schematic diagram of the bottom plate structure of the present invention;

[0020] Figure 5 For the present invention Figure 4 The enlarged schematic diagram at A in the middle;

[0021] Figure 6 A half-section schematic diagram of a threaded sleeve of the present invention;

[0022] Figure 7 It is a half-section schematic diagram of the rotary sleeve of the present invention;

[0023] Figure 8 This is a schematic diagram of the explosion of the lower gear of the present invention;

[0024] Fig. 9 It is a schematic diagram of the structure of the arc-shaped sheet of the present invention.

[0025] In the figure: 1, main board; 2, support column; 3, fixing rod; 4, support ring; 5, motor sleeve; 6, fixing ring; 7, drive motor; 8, large drive gear; 9, small drive gear; 10, mounting through hole; 11, threaded sleeve; 12, rotating sleeve; 13, mounting groove; 14, electromagnet; 15, permanent magnet; 16, upper gear; 17, lower gear; 18, lifting rod; 19, connecting rod; 20, sampling mechanism; 201, connecting column; 202, spiral sheet; 203, bottom plate; 204, side plate; 205, telescopic rod; 206, extension rod; 207, connecting sheet; 208, connecting pin; 209, annular sleeve; 2010, fixing column; 2011, arc sheet; 2012, serrated ring. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figures 1 to 9As shown, an embodiment of the present invention provides a deep soil sampling device for environmental detection, including a main board 1, a plurality of support columns 2 are fixedly connected to the edge of the main board 1, a plurality of fixing rods 3 are fixedly connected to the upper surface of the main board 1, a support ring 4 is fixedly connected to the middle of the fixing rods 3, a motor sleeve 5 is movably sleeved on the upper parts of the plurality of fixing rods 3, a fixing ring 6 is threadedly connected to the top of the fixing rods 3, a driving motor 7 is fixedly installed in the middle of the motor sleeve 5, a large driving gear 8 and a small driving gear 9 are fixedly installed on the output shaft of the driving motor 7, a mounting through hole 10 is opened in the middle of the main board 1, a threaded sleeve 11 and a rotating sleeve 12 are rotatably installed in the middle of the mounting through hole 10, a plurality of mounting grooves 13 are opened on the outer curved surfaces of the threaded sleeve 11 and the rotating sleeve 12, and a plurality of mounting grooves 13 are installed. The inner wall of the groove 13 is fixedly installed with an electromagnet 14, the interior of the installation groove 13 is slidably connected with a permanent magnet 15, an upper gear 16, the curved surface of the threaded sleeve 11 is rotatably sleeved with the upper gear 16, the curved surface of the rotating sleeve 12 is rotatably sleeved with the lower gear 17, the internal thread of the threaded sleeve 11 is connected with a lifting rod 18, the bottom end of the lifting rod 18 is movably connected with a connecting rod 19, the bottom end of the connecting rod 19 is movably connected with a sampling mechanism 20, the sampling mechanism 20 includes a connecting column 201 movably connected to the connecting rod 19, the curved surface of the connecting column 201 is fixedly connected with a plurality of spiral sheets 202, the bottom end of the spiral sheet 202 is fixedly connected with a bottom plate 203, the side of the bottom plate 203 away from the spiral sheet 202 is fixedly connected with a side plate 204, the upper surface of the bottom plate 203 The surface is fixedly connected with a telescopic rod 205, the telescopic end of the telescopic rod 205 is fixedly connected with an extension rod 206, the outer side of the extension rod 206 is fixedly connected with a connecting piece 207, the middle part of the connecting piece 207 is fixedly connected with a connecting pin 208, the edges of multiple spiral pieces 202 are fixedly connected with an annular sleeve 209, the inside of the annular sleeve 209 is fixedly connected with multiple fixed columns 2010, the lower end of the fixed column 2010 is rotatably installed with an arc piece 2011, and the lower end of the annular sleeve 209 is fixedly connected with a sawtooth ring 2012, which functions to drive the rotating sleeve 12 to rotate through the small driving gear 9 through the driving motor 7, so that the sampling mechanism 20 at the target soil depth rotates, and at the same time, the telescopic rod 205 works and slowly extends outward. , so that the arc piece 2011 protrudes from the curved surface of the annular sleeve 209, and the arc piece 2011 rotating clockwise will dig the soil of the target depth into the top of the bottom plate 203. When a proper amount of sample is taken inside the bottom plate 203, the telescopic rod 205 is reset to reset the arc piece 2011 and preserve the soil of the target depth, thereby solving the problem that soil from other depths falls at the bottom of the borehole during the existing drilling sampling, thereby reducing the accuracy of the sampled sample; through the setting of the spiral piece 202, when going deep into the soil, only the soil above the target depth is loosened and guided to the top of the sampling mechanism 20. After the sampling is completed at the target depth, the soil above is guided to the bottom of the sampling mechanism 20, and there is no need to backfill the soil after the sampling is completed.

[0028] Among them, the large driving gear 8 is meshed with the upper gear 16, the small driving gear 9 is meshed with the lower gear 17, the upper gear 16 and the lower gear 17 are both rotatably connected to the main board 1, the inner walls of the upper gear 16 and the lower gear 17 are provided with a number of slots equal to the mounting slot 13, the slots are adapted to the permanent magnet 15, the depth of the slots is less than the length between the inner and outer sides of the permanent magnet 15, the outer surface of the lifting rod 18 is provided with a plurality of slide grooves, the rotating sleeve 12 is slidably connected to the slide grooves, the rotating sleeve 12 is adapted to the lifting rod 18, and its function is , the upper and lower electromagnets 14 work to generate a magnetic field that repels the permanent magnet 15, so that the permanent magnet 15 moves outward until the outside moves to the inside of the slot, and then stops working, the drive motor 7 works to drive the large drive gear 8 and the small drive gear 9 on the output shaft to rotate, the large drive gear 8 drives the meshing upper gear 16 to rotate clockwise, because the upper permanent magnet 15 is located between the slot and the mounting slot 13, the upper gear 16 drives the threaded sleeve 11 to rotate clockwise, and the small drive gear 9 drives the meshing lower gear 17 to rotate clockwise. The lower gear 17 drives the rotating sleeve 12 to rotate clockwise, because the permanent magnet 15 below is located between the card slot and the installation slot 13. Since the rotation speed of the rotating sleeve 12 is slower than that of the threaded sleeve 11 and there is a speed difference, the rotating sleeve 12 will limit the lifting rod 18 relative to the threaded sleeve 11, thereby driving the lifting rod 18 to move downward. Since the rotating sleeve 12 drives the lifting rod 18 to rotate clockwise, the connecting rod 19 and the sampling mechanism 20 rotate clockwise and move downward at the same time; The electromagnet 14 works to generate a magnetic field that attracts the permanent magnet 15, thereby moving the permanent magnet 15 inward until it is completely moved to the inside of the mounting groove 13, and the lower electromagnet 14 stops, and the drive motor 7 works in the reverse direction, driving the threaded sleeve 11 to rotate counterclockwise, and the lower gear 17 rotates idly without driving the rotating sleeve 12 to rotate; the upper electromagnet 14 works to attract the upper permanent magnet 15 to be completely located inside the mounting groove 13, and the drive motor 7 works. At this time, only the lower gear 17 drives the rotating sleeve 12 to rotate, and the upper gear 16 is in an idling state.

[0029] Among them, the inner sides of the bottom plate 203 and the side plate 204 are fixedly connected to the connecting column 201, the outer side of the bottom plate 203 is fixedly connected to the sawtooth ring 2012, the upper end of the side plate 204 is fixedly connected to the spiral sheet 202, the outer side of the side plate 204 is fixedly connected to the annular sleeve 209, and a rotation groove is provided on the inner side of the arc-shaped sheet 2011. The arc-shaped sheet 2011 is rotatably connected to the upper and lower ends of the connecting sheet 207. Its function is that when the annular sleeve 209 is located at the target soil depth, the driving motor 7 stops working, the upper electromagnet 14 works to attract the upper permanent magnet 15 to be completely located inside the mounting groove 13, and the driving motor 7 works. At this time, only the lower gear 17 drives the rotating sleeve 12 to rotate, and the upper gear 16 is in an idling state, so that the sampling mechanism 20 at the target soil depth rotates. At the same time, the telescopic rod 205 works and slowly extends outward, driving the extension rod 206, the connecting piece 207 and the connecting pin 208 to move outward, so that the arc piece 2011 protrudes from the curved surface of the annular sleeve 209. The arc piece 2011 rotating clockwise will dig the soil of the target depth into the top of the bottom plate 203. When a proper amount of sample is taken inside the bottom plate 203, the telescopic rod 205 is reset, so that the arc piece 2011 is reset, and the soil at the target depth is preserved.

[0030] Working principle:

[0031] Before use, select the location where sampling is required and level the surface nearby, and place the device directly above it so that the center of the sampling mechanism 20 is aligned with the center of the sampling location;

[0032] When in use, the upper and lower electromagnets 14 both work to generate a magnetic field that repels the permanent magnet 15, thereby causing the permanent magnet 15 to move outward until the outside moves to the inside of the slot, and then stops working, and the drive motor 7 works to drive the large drive gear 8 and the small drive gear 9 on the output shaft to rotate, and the large drive gear 8 drives the meshing upper gear 16 to rotate clockwise. Since the upper permanent magnet 15 is located between the slot and the mounting slot 13, the upper gear 16 drives the threaded sleeve 11 to rotate clockwise, and the small drive gear 9 drives the meshing lower gear 17 to rotate clockwise. Since the lower permanent magnet 15 is located between the slot and the mounting slot 13, the lower gear 17 drives the rotating sleeve 12 to rotate clockwise. Since the rotation speed of the rotating sleeve 12 is slower than that of the threaded sleeve 11 and there is a speed difference, the rotating sleeve 12 will limit the lifting rod 18 relative to the threaded sleeve 11, thereby driving the lifting rod 18 to move downward. Since the rotating sleeve 12 will drive the lifting rod 18 to rotate clockwise, the connection The rod 19 and the sampling mechanism 20 rotate clockwise and move downward, and the sawtooth ring 2012 and the spiral piece 202 will destroy the soil structure and go deep. When the bottom end of the lifting rod 18 is about to touch the ground, the drive motor 7 stops working, disconnects the connection between the bottom of the lifting rod 18 and the connecting rod 19, and the lower electromagnet 14 works to generate a magnetic field that attracts the permanent magnet 15, so that the permanent magnet 15 moves inward until it is completely moved to the inside of the installation groove 13. The lower electromagnet 14 stops, and the drive motor 7 works in the reverse direction to drive the threaded sleeve 11 to rotate counterclockwise. The lower gear 17 rotates idly without driving the rotating sleeve 12 to rotate. The speed difference between the threaded sleeve 11 and the rotating sleeve 12 reaches the maximum, thereby quickly driving the lifting rod 18 to move downward, and the drive motor 7 stops working. After moving to a suitable distance, the remaining connecting rods 19 are connected, and the lower electromagnet 14 works to push out the permanent magnet 15. The drive motor 7 works to continue to drive the sawtooth ring 2012 and the spiral piece 202 clockwise to go deep underground.

[0033] When the annular sleeve 209 is located at the target soil depth, the driving motor 7 stops working, the upper electromagnet 14 works, attracting the upper permanent magnet 15 to be completely located inside the mounting groove 13, and the driving motor 7 works. At this time, only the lower gear 17 drives the rotating sleeve 12 to rotate, and the upper gear 16 is in an idling state, so that the sampling mechanism 20 at the target soil depth performs a rotational motion. At the same time, the telescopic rod 205 works and slowly extends outward, driving the extension rod 206, the connecting piece 207 and the connecting pin 208 to move outward, so that the arc piece 2011 protrudes from the curved surface of the annular sleeve 209, and the clockwise rotating arc piece 2011 digs the soil of the target depth into the top of the bottom plate 203. When a proper amount of sample is taken inside the bottom plate 203, the telescopic rod 205 is reset, so that the arc piece 2011 is reset, and the soil at the target depth is preserved;

[0034] The upper and lower permanent magnets 15 are both at the outermost sides, and the driving motor 7 works in the reverse direction to remove a section of the connecting rod 19 until the sampling mechanism 20 with the target soil sample in the soil is driven to emerge from the ground, and the telescopic rod 205 works to open the arc-shaped piece 2011 to take out the sample inside the bottom plate 203.

[0035] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0036] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A deep soil sampling device for environmental detection, comprising a main board (1), wherein the edge of the main board (1) is fixedly connected to a plurality of support columns (2), Features: A plurality of fixing rods (3) are fixedly connected to the upper surface of the main board (1), a support ring (4) is fixedly connected to the middle of the fixing rods (3), a motor sleeve (5) is movably sleeved on the upper parts of the plurality of fixing rods (3), a fixing ring (6) is threadedly connected to the top of the fixing rods (3), a driving motor (7) is fixedly mounted on the middle part of the motor sleeve (5), a large driving gear (8) and a small driving gear (9) are fixedly mounted on the output shaft of the driving motor (7), a mounting through hole (10) is opened in the middle part of the main board (1), and the middle part of the mounting through hole (10) is rotated. A threaded sleeve (11) and a rotating sleeve (12) are movably mounted thereon, the outer curved surfaces of the threaded sleeve (11) and the rotating sleeve (12) are each provided with a plurality of mounting grooves (13), an electromagnet (14) is fixedly mounted on the inner wall of the mounting groove (13), a permanent magnet (15) is slidably connected inside the mounting groove (13), an upper gear (16) is rotatably mounted on the curved surface of the threaded sleeve (11), a lower gear (17) is rotatably mounted on the curved surface of the rotating sleeve (12), a lifting rod (18) is rotatably connected to the inner thread of the threaded sleeve (11), and the bottom end of the lifting rod (18) is movably mounted thereon. The connecting rod (19) is connected to the bottom end of the connecting rod (19) and is movably connected to a sampling mechanism (20). The sampling mechanism (20) comprises a connecting column (201) movably connected to the connecting rod (19). A plurality of spiral sheets (202) are fixedly connected to the curved surface of the connecting column (201). The bottom ends of the spiral sheets (202) are fixedly connected to a bottom plate (203). A side of the bottom plate (203) away from the spiral sheets (202) is fixedly connected to a side plate (204). The upper surface of the bottom plate (203) is fixedly connected to a telescopic rod (205). The telescopic end of the rod (205) is fixedly connected to an extension rod (206), the outer side of the extension rod (206) is fixedly connected to a connecting piece (207), the middle part of the connecting piece (207) is fixedly connected to a connecting pin (208), the edges of the plurality of spiral pieces (202) are fixedly connected to an annular sleeve (209), the interior of the annular sleeve (209) is fixedly connected to a plurality of fixing columns (2010), the lower end of the fixing column (2010) is rotatably mounted with an arc-shaped piece (211), and the lower end of the annular sleeve (209) is fixedly connected to a sawtooth ring (2012).

2. A deep soil sampling device for environmental testing according to claim 1, Features: The large driving gear (8) meshes with the upper gear (16), the small driving gear (9) meshes with the lower gear (17), and the upper gear (16) and the lower gear (17) are both rotatably connected to the main board (1).

3. A deep soil sampling device for environmental testing according to claim 2, Features: The inner walls of the upper gear (16) and the lower gear (17) are each provided with a number of slots equal to the number of the mounting slots (13); the slots are adapted to fit the permanent magnets (15); and the depth of the slots is less than the length between the inner side and the outer side of the permanent magnet (15).

4. A deep soil sampling device for environmental testing according to claim 3, Features: The outer surface of the lifting rod (18) is provided with a plurality of sliding grooves, the rotating sleeve (12) and the sliding grooves are slidably connected, and the rotating sleeve (12) is adapted to the lifting rod (18).

5. A deep soil sampling device for environmental testing according to claim 4, Features: The inner sides of the bottom plate (203) and the side plate (204) are fixedly connected to the connecting column (201), the outer side of the bottom plate (203) is fixedly connected to the sawtooth ring (2012), the upper end of the side plate (204) is fixedly connected to the spiral sheet (202), and the outer side of the side plate (204) is fixedly connected to the annular sleeve (209).

6. A deep soil sampling device for environmental testing according to claim 5, Features: A rotation groove is provided on the inner side of the arc-shaped piece (2011), and the arc-shaped piece (2011) is rotationally connected to the connecting piece (207) at both upper and lower ends.

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