Positioning clamp for glass processing

Abstract

The utility model belongs to the technical field of automobile part processing, and particularly discloses a positioning clamp for glass processing, which comprises a placing table, a suction cup group arranged on the upper surface of the placing table, first air bags positioned on two sides of the suction cup group and an elastic pressing plate arranged right above the suction cup group, the top of the cavity is communicated with the bottom of the suction cup set, the bottom of the cavity is communicated with the first air bag, a transverse push plate is arranged above the elastic pressing plate, at least two springs are arranged between the push plate and the elastic pressing plate, a second air bag is arranged between the push plate and the elastic pressing plate, and the second air bag is communicated with the bottom of the cavity. The push plate is connected with a control mechanism for controlling the push plate to move up and down and is connected with the partition plate through a push rod. By the adoption of the technical scheme, the suction cups are combined with the elastic pressing plate and other components, and clamping and positioning of glass with different bending radians are achieved.

Description

Technical Field

[0001] The utility model belongs to the technical field of automobile component processing and relates to a positioning fixture for glass processing. Background Art

[0002] The car sunroof is installed on the roof and is a very important part of the car body accessories. It can effectively circulate the air in the car and increase the intake of fresh air. At the same time, the car sunroof can also broaden the field of vision and meet the needs of mobile photography and video shooting. Car sunroofs can be roughly divided into: sliding type, internal type, internal type, external type, panoramic type and curtain type, etc., and are mainly installed on commercial SUVs, sedans and other models. Opening the sunroof in a traffic jam can prevent exhaust gas from entering the car, because in a traffic jam, all vehicles are stagnant and the car exhaust will inevitably spread in the air. At this time, opening the car sunroof and closing the side windows will discharge the exhaust gas in the car and filter it through the car air conditioner to complete the exchange of fresh air.

[0003] During the processing of automobile sunroof glass, it is generally necessary to fix it with a clamp. However, due to the different models of automobile glass, the arc angle of its surface is also different. The existing fixtures are currently adjusted by replacing the clamping parts. The adjustment process is time-consuming and inconvenient, which affects the processing efficiency of the product. At the same time, therefore, the traditional fixtures are basically mechanically rigid, the clamping force is difficult to control, the stability is poor, and it is easy to scratch the glass, affecting the processing effect of the sunroof glass. Utility Model Content

[0004] The utility model aims to provide a positioning fixture for glass processing, which can realize the clamping and positioning of glass with different curvatures.

[0005] In order to achieve the above-mentioned purpose, the basic scheme of the utility model is: a positioning fixture for glass processing, comprising a placement table, a suction cup group arranged on the upper surface of the placement table, a first air bag located on both sides of the suction cup group and an elastic pressure plate arranged just above the suction cup group;

[0006] The placement table is provided with a cavity, a transverse partition is sealed and slidably connected in the cavity, the top of the cavity is connected to the bottom of the suction cup group, the bottom of the cavity is connected to the first airbag, and the cavity below the partition contains gas;

[0007] A horizontal push plate is provided above the elastic pressure plate, and at least two springs are provided between the push plate and the elastic pressure plate, one end of the spring is fixedly connected to the top of the elastic pressure plate, and the other end of the spring is fixedly connected to the bottom of the push plate, and the springs are symmetrically arranged along the center line of the elastic pressure plate;

[0008] A second airbag is provided between the push plate and the elastic pressure plate, one end of the second airbag is fixedly connected to the bottom of the push plate, the second airbag is communicated with the bottom of the cavity, the push plate is connected to a control mechanism for controlling its up and down movement, the control mechanism can be self-locking, a vertical push rod is fixedly connected to the push plate, one end of the push rod away from the push plate extends into the cavity and is fixedly connected to the partition.

[0009] The working principle and beneficial effects of this basic solution are as follows: the glass to be processed is placed on the placement table, and the center position of the arc-shaped convex side of the glass to be processed is placed on the suction cup group. The control mechanism can control the push plate to move downward, and the push plate moves downward to drive the elastic pressure plate connected to it to move downward synchronously. The elastic pressure plate moves downward to contact the upper surface of the glass and gradually press against the glass. At the same time, the elastic pressure plate has elastic deformation ability. During the downward pressing process, it can change its own shape and fit with the glass under the pressure of the push plate and the pressing effect of the glass, thereby applying pressure to the glass and positioning the glass.

[0010] The push plate drives the partition to move synchronously through the push rod. When the partition moves down, the space above the partition in the cavity increases, and negative pressure is formed in the space, which absorbs the air between the suction cup group and the glass, making the suction cup group and the glass fit more closely. At the same time, the negative pressure applies suction to the glass to position the glass.

[0011] During the downward movement of the partition, the gas in the cavity below the partition is pushed by the partition and enters the first airbag and the second airbag, causing the first airbag and the second airbag to expand. The expansion of the first airbag provides support for the lower surface of the glass that is not in contact with the suction cup group, preventing the two sides of the curved surface of the glass from being pressed by the elastic pressure plate and being excessively stressed and broken, and the first airbag has a specific elastic buffering effect, which will not scratch the glass. When the second airbag expands, the push plate transmits the pushing force to the elastic pressure plate through the second airbag. At the same time, the second airbag has an elastic buffering force, which can prevent the push plate from directly pushing the elastic pressure plate and causing damage to the elastic pressure plate. According to the different curved surface angles of different types of glass, the curvature of the glass can limit the expansion degree of the first airbag. When the expansion degree of the first airbag is limited, more gas that cannot enter the first airbag is discharged into the second airbag, and the expansion degree of the second airbag is enhanced. In this way, the downward movement degree of the push plate can be judged according to the expansion degree of the second airbag, so as to control the control mechanism to stop.

[0012] Furthermore, the control mechanism includes a rotating wheel, a threaded rod and a motor. The end face of the rotating wheel is parallel to the push plate. The rotating wheel is fixedly connected to the top of the push plate through a connecting rod. The rotating wheel is provided with a threaded hole threadedly connected to the threaded rod. The threaded rod is vertically arranged. The top of the threaded rod is fixedly connected to the output end of the motor. The motor is suspended above the placing table through a frame. The frame is provided with a vertical limit groove. The side wall of the rotating wheel is fixedly connected to a limit block, and the limit block is slidably connected to the limit groove.

[0013] The motor controls the rotation of the threaded rod, and the motor is fixed on the frame, so the position of the threaded rod is fixed to the motor. The rotating wheel is connected to the threaded rod through the threaded hole, and the rotating wheel is restricted by the limiting groove and the limiting block, and can only slide vertically in the limiting groove but cannot rotate. When the threaded rod rotates, a threaded transmission is generated between the rotating wheel and the threaded rod, and the rotating wheel moves up or down along the limiting groove. The rotating wheel is fixedly connected to the push plate, and the movement of the rotating wheel can drive the push plate to move up or down synchronously, and the threaded transmission itself can achieve self-locking, ensuring that the rotating wheel can still maintain a stable connection in its position when the motor stops.

[0014] Furthermore, it also includes a limiting mechanism, which is arranged at the feed end of the placement table. The limiting mechanism includes two telescopic rods. The upper surface of the telescopic rod is tangent to the upper surface of the placement table. One ends of the two telescopic rods are opposite to each other. The other ends of the two telescopic rods are fixedly connected with a baffle. The two telescopic rods are symmetrically arranged with the suction cup group as the center, and a scale is provided on the side of the telescopic rod.

[0015] According to the width of the glass to be processed, compare with the scale and adjust the extended length of the telescopic rods to ensure that the extended lengths of the two telescopic rods are equal. This ensures that when the glass is placed on the placement table, it is in the center position between the telescopic rods, so that the arc-shaped protrusion at the bottom of the glass is directly opposite to the suction cup group, which is convenient for subsequent positioning.

[0016] Furthermore, a cylindrical hole is provided on the opposite side of the telescopic rods, an internal thread is provided on the inner wall of the cylindrical hole, a rotating rod is provided between the telescopic rods, and symmetrical external threads are provided on the rod body of the rotating rod near its two ends, and the two ends of the rotating rod are respectively connected to the internal threads in the cylindrical hole of the telescopic rod through the external threads, an annular groove is provided in the middle of the rod body of the rotating rod, a connecting piece is fixedly provided on the placement table and is slidably connected to the annular groove, a sliding block is fixedly connected to the outer wall of the telescopic rod, and a sliding groove slidably connected to the sliding block is provided on the placement table.

[0017] The connecting piece limits the movement of the rotating rod, and a slider is provided on the telescopic rod, and the slider is provided in the slide groove. The telescopic rod is limited by the slider and can only slide along the slide groove. Therefore, when the rotating rod is controlled to rotate, a thread transmission is generated between the rotating rod and the telescopic rod. The threads at both ends of the rotating rod are symmetrically arranged. When the rotating rod and the two telescopic rods are threaded, the two telescopic rods can slide outward or inward synchronously along the slide groove to adjust the position of the upper baffle of the telescopic rod. It is only necessary to symmetrically set the position where the two telescopic rods are initially connected to the rotating rod, so that the position of the telescopic rod after the movement of the rotating rod can always be symmetrically set relative to the suction cup group.

[0018] Furthermore, a gear or a hexagonal nut is fixedly sleeved on the middle part of the shaft of the rotating rod.

[0019] The user uses tools such as a rack or a wrench to control the rotation of the gear or the hexagonal nut, and the rotation of the gear or the hexagonal nut drives the rotating rod to rotate. The rack or the wrench is convenient for the user to hold and grasp, making it easier to control the rotating rod.

[0020] Furthermore, the outer surfaces of the first airbag and the second airbag are both provided with anti-slip protrusions.

[0021] The anti-skid protrusions prevent the first airbag from sliding when in contact with the glass, thereby causing unstable positioning of the glass. At the same time, they prevent accidental sliding between the push plate, the second airbag and the elastic pressure plate, thereby preventing the glass from being pressed too tightly and causing erroneous movement of the glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a front cross-sectional view of the positioning fixture for glass processing of the utility model;

[0023] Figure 2 The utility model is a structural schematic diagram of a limiting mechanism of a positioning fixture for glass processing.

[0024] The figure marks in the drawings of the specification include: a placement table 1, a first airbag 2, an elastic pressure plate 3, a push plate 4, a second airbag 5, a spring 6, a push rod 7, a partition 8, a cavity 9, a rotating wheel 10, a threaded rod 11, a motor 12, a frame 13, a limit groove 14, a limit block 15, a suction cup group 16, a telescopic rod 17, a rotating rod 18, and a baffle 19. DETAILED DESCRIPTION

[0025] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0026] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0027] In the description of the present utility model, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection of two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0028] like Figure 1 As shown, the utility model discloses a positioning fixture for glass processing, comprising a placement table 1, a suction cup group 16 arranged on the upper surface of the placement table 1, a first air bag 2 located on both sides of the suction cup group 16 and an elastic pressure plate 3 arranged directly above the suction cup group 16.

[0029] The placing table 1 is preferably a square table, and a cavity 9 is provided in the placing table 1, and the cavity 9 can be set to be square or cylindrical. A transverse partition 8 is sealed and slidably connected in the cavity 9, and the partition 8 divides the cavity 9 into two layers, upper and lower. The top of the cavity 9 is connected to the bottom of the suction cup group 16, and the bottom of the cavity 9 is connected to the first air bag 2 through a soft air tube. The soft air tube moves and extends into the cavity 9, and the other end of the soft air tube extends into the first air bag 2. The cavity 9 below the partition 8 contains gas. According to needs, the area of ​​the end face of the placing table 1 can be adjusted during manufacturing so that the placing table 1 can place glass of a larger range of sizes. For example, when the width of the placing table 1 is increased, the height of the placing table 1 can be reduced, which increases the placement area. At the same time, the center of gravity of the placing table 1 is lowered, and the stability when placed is stronger.

[0030] The manufacturing material of the elastic pressure plate 3 can be selected from plastic or rubber, etc. When not in use, the gap between the elastic pressure plate 3 and the placement table 1 is large enough to accommodate the conveyed glass. A horizontal push plate 4 is provided above the elastic pressure plate 3, and at least two springs 6 are provided between the push plate 4 and the elastic pressure plate 3. One end of the spring 6 is welded to the top of the elastic pressure plate 3, and the other end of the spring 6 is welded to the bottom of the push plate 4. The spring 6 is symmetrically arranged along the center line of the elastic pressure plate 3. A second air bag 5 is provided between the push plate 4 and the elastic pressure plate 3, and one end of the second air bag 5 is welded to the bottom of the push plate 4, and the second air bag 5 is connected to the bottom of the cavity 9. The push plate 4 is connected to a control mechanism that controls its up and down movement, and the control mechanism can be self-locking. A vertical push rod 7 is welded on the push plate 4, and one end of the push rod 7 away from the push plate 4 extends into the cavity 9 and is fixedly connected to the partition 8. According to the need for pushing stability, two or more push rods 7 can be set to connect with the push plate 4 and the partition 8. At the same time, the push rod 7 can also be set on the side or front end of the push plate 4 as needed to avoid the push rod 7 limiting the size of the glass placed on the placement table 1. In a preferred mode of this embodiment, the outer surfaces of the first airbag 2 and the second airbag 5 are both provided with anti-skid protrusions (not shown in the figure), and the anti-skid protrusions are integrally forged or welded and bonded to the outer surfaces of the corresponding airbags.

[0031] The control mechanism includes a rotating wheel 10, a threaded rod 11 and a motor 12. The end face of the rotating wheel 10 is parallel to the push plate 4. The rotating wheel 10 is fixedly connected to the top of the push plate 4 through a connecting rod. The connecting rod is vertically arranged. The top of the connecting rod is welded to the bottom of the rotating wheel 10, and the bottom of the connecting rod is welded to the top of the push plate 4. The rotating wheel 10 is provided with a threaded hole threadedly connected to the threaded rod 11. The threaded rod 11 is vertically arranged. The top of the threaded rod 11 is fixedly connected to the output end of the motor 12 (such as the output end of the conventional motor 12 is connected by a connecting key). The motor 12 is suspended above the placing table 1 through a frame 13, and the motor 12 is welded to the frame 13. A vertical limiting groove 14 is provided on the frame 13, and the top of the limiting groove 14 is welded to the frame 13. A limiting block 15 is welded to the side wall of the rotating wheel 10, and the limiting block 15 is slidably connected to the limiting groove 14. The frame 13 is provided with supporting feet for positioning, and the gaps between the push rods, between the frame 13 and the placement table 1, and between different supporting feet of the frame 13 are large enough to ensure the operation of other equipment for conveying glass and processing glass.

[0032] In a preferred embodiment of the present invention, the positioning fixture for glass processing further includes a limiting mechanism, such as Figure 2 As shown, the limiting mechanism is arranged at the feeding end of the placing table 1, and the limiting mechanism includes two telescopic rods 17, and the upper surface of the rod body of the telescopic rod 17 is tangent to the upper surface of the placing table 1. One end of the two telescopic rods 17 is directly opposite to each other, and the other end of the two telescopic rods 17 is welded with a baffle 19, preferably the baffle 19 is perpendicular to the telescopic rod 17, and the baffle 19 is located on the upper surface of the telescopic rod 17. The two telescopic rods 17 are symmetrically arranged with the suction cup group 16 as the center, and the side of the telescopic rod 17 is provided with a scale (not shown in the figure), and the scale is fixedly arranged (such as inlaid, welded or bonded, etc.) on the placing table 1.

[0033] The telescopic rods 17 are provided with cylindrical holes on the opposite sides thereof, and the inner wall of the cylindrical holes is provided with internal threads. A rotating rod 18 is provided between the telescopic rods 17, and the rotating rod 18 is provided with symmetrical external threads on the rod body near the two ends thereof, and the two ends of the rotating rod 18 are respectively connected with the internal threads in the cylindrical holes of the telescopic rod 17 through the external threads. A slider (not shown in the figure) is welded on the outer wall of the telescopic rod 17, and the slider is preferably a square block. The placement table 1 is provided with a slide groove that is slidably connected to the slider, and the side wall of the slide groove fits the slider, and the slide groove is arranged horizontally. An annular groove is provided in the middle of the rod body of the rotating rod 18, and a connecting piece is fixedly provided on the placement table 1 to be slidably connected to the annular groove. The connecting rod is preferably an annular clamping block, and the annular clamping block is clamped in the annular groove, and the end of the annular clamping block away from the annular groove is welded to the placement table 1. A gear or a hexagonal nut (not shown) is fixedly sleeved in the middle of the shaft of the rotating rod 18, and the inner ring of the gear or the hexagonal nut is welded to the rotating rod 18. The gear can be controlled to rotate by a rack or other tools, and the hexagonal nut can be turned by a wrench.

[0034] Specific operation process: first, place the glass to be processed on the placement table 1, then rotate the rotating rod 18, the rotating rod 18 rotates but cannot move, the telescopic rod 17 can move along the slide slot but cannot rotate, and the rotating rod 18 and the telescopic rod 17 are connected by threads to generate thread transmission. Control the movement of the two telescopic rods 17 so that the distance between the baffles 19 on the telescopic rods 17 is relative to the vertical projection width of the glass, then determine whether the position of the glass is correctly placed, and adjust the position of the glass so that the center of the convex side of the glass is placed on the suction cup group 16.

[0035] Start the motor 12, the motor 12 rotates forward, and controls the threaded rod 11 to rotate. The motor 12 is fixed on the frame 13, so the threaded rod 11 is fixed with the motor 12, and the threaded rod 11 can only rotate but not move. The rotating wheel 10 is fixedly connected to the limiting block 15, and the limiting block 15 can only slide along the limiting groove 14, so that the rotating wheel 10 can only slide along the limiting groove 14 but cannot rotate. The threaded rod 11 is threadedly connected to the rotating wheel 10. The threaded rod 11 rotates, and a threaded transmission is generated between the rotating wheel 10 and the threaded rod 11, and the rotating wheel 10 moves downward along the limiting groove 14. The rotating wheel 10 drives the push plate 4 to move downward synchronously, and the push plate 4 drives the elastic pressure plate 3 to move downward through the spring 6. The elastic pressure plate 3 gradually moves downward and contacts the concave arc surface of the glass, exerting pressure on the glass to position it.

[0036] During the downward movement of the push plate 4, the push plate 4 drives the partition plate 8 to move downward synchronously through the push rod 7. When the partition plate 8 moves downward, the volume of the space above the partition plate 8 in the cavity 9 increases, forming a negative pressure. In addition, since the top of the cavity 9 is connected to the suction cup, the negative pressure space can absorb the air between the suction cup group 16 and the glass, and at the same time, the suction cup applies suction to the glass to further position the glass.

[0037] During the downward movement of the partition 8, the gas in the cavity 9 below the partition 8 is pushed by the partition 8 and enters the first airbag 2 and the second airbag 5. The first airbag 2 expands until its top abuts against the glass, exerting a supporting force on the glass, which is equivalent to the clamping force on the glass. The second airbag 5 expands to fill the space between the push plate 4 and the elastic pressure plate 3. The push plate 4 exerts a pushing force on the elastic pressure plate 3 through the second airbag 5. At the same time, the shape of the second airbag 5 can be changed by the pushing action of the push plate 4. During the expansion of the second airbag 5, the push plate 4 pushes the second airbag 5 so that the second airbag 5 fits with the top of the elastic pressure plate 3, ensuring that the elastic pressure plate 3 fits tightly with the glass. The running time of the motor 12 can be controlled as needed to control the downward movement distance of the push plate 4. When the elastic pressure plate 3 moves down a certain distance and clamps with the glass, the motor 12 is stopped to stop the push plate 4 from moving down and keep it at a certain position until the glass processing is completed. When resetting is required, the motor 12 is controlled to rotate in the reverse direction, thereby controlling the rotating wheel 10 to move upward, driving the push plate 4 to reset, and the push plate 4 drives other components to reset.

[0038] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0039] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate 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 claims and their equivalents.

Claims

1. A positioning fixture for glass processing, characterized in that: It includes a placing table, a suction cup group arranged on the upper surface of the placing table, a first air bag located on both sides of the suction cup group, and an elastic pressing plate arranged just above the suction cup group; The placement table is provided with a cavity, a transverse partition is sealed and slidably connected in the cavity, the top of the cavity is connected to the bottom of the suction cup group, the bottom of the cavity is connected to the first airbag, and the cavity below the partition contains gas; A horizontal push plate is provided above the elastic pressure plate, and at least two springs are provided between the push plate and the elastic pressure plate, one end of the spring is fixedly connected to the top of the elastic pressure plate, and the other end of the spring is fixedly connected to the bottom of the push plate, and the springs are symmetrically arranged along the center line of the elastic pressure plate; A second airbag is provided between the push plate and the elastic pressure plate, one end of the second airbag is fixedly connected to the bottom of the push plate, the second airbag is communicated with the bottom of the cavity, the push plate is connected to a control mechanism for controlling its up and down movement, the control mechanism can be self-locking, a vertical push rod is fixedly connected to the push plate, one end of the push rod away from the push plate extends into the cavity and is fixedly connected to the partition.

2. The glass processing positioning fixture according to claim 1, characterized in that: The control mechanism includes a rotating wheel, a threaded rod and a motor. The end face of the rotating wheel is parallel to the push plate. The rotating wheel is fixedly connected to the top of the push plate through a connecting rod. The rotating wheel is provided with a threaded hole threadedly connected to the threaded rod. The threaded rod is vertically arranged. The top of the threaded rod is fixedly connected to the output end of the motor. The motor is suspended above the placement table through a frame. The frame is provided with a vertical limit groove. The side wall of the rotating wheel is fixedly connected to the limit block, and the limit block is slidably connected to the limit groove.

3. The glass processing positioning fixture according to claim 1, characterized in that: It also includes a limiting mechanism, which is arranged at the feeding end of the placement table. The limiting mechanism includes two telescopic rods. The upper surface of the telescopic rod is tangent to the upper surface of the placement table. One ends of the two telescopic rods are opposite to each other. The other ends of the two telescopic rods are fixedly connected with a baffle. The two telescopic rods are symmetrically arranged with the suction cup group as the center, and a scale is provided on the side of the telescopic rod.

4. The glass processing positioning fixture according to claim 3, characterized in that: The telescopic rods are provided with cylindrical holes on the opposite sides thereof, and internal threads are provided on the inner walls of the cylindrical holes. A rotating rod is provided between the telescopic rods, and symmetrical external threads are provided on the shafts of the rotating rods near the two ends thereof. The two ends of the rotating rods are respectively connected with the internal threads in the cylindrical holes of the telescopic rods through the external threads. An annular groove is provided in the middle of the shaft of the rotating rod, and a connecting piece is fixedly provided on the placement table and is slidably connected with the annular groove. A sliding block is fixedly connected to the outer wall of the telescopic rod, and a sliding groove slidably connected with the sliding block is provided on the placement table.

5. The glass processing positioning fixture according to claim 4, characterized in that: A gear is fixedly sleeved on the middle part of the shaft of the rotating rod, and a rack is meshed with the gear, and the rack is slidably arranged on the placement platform.

6. The glass processing positioning fixture according to claim 1, characterized in that: The outer surfaces of the first airbag and the second airbag are both provided with anti-slip protrusions.

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