Automatic board feeding and locking module for PCB flying probe test

Abstract

The invention relates to the field of circuit board detection, and relates to an automatic board feeding and locking module for a PCB flying probe test. The conveying belt is mounted on the inner side walls of the two sides of the mounting frame; the electric push rod is vertically arranged on the inner side wall of the mounting frame between the conveyor belt gaps; the top block is mounted on a movable rod of the electric push rod; the bearing frame is arranged at the top of the mounting frame; the multiple groups of clamping blocks are arranged in pairs, and each group of clamping blocks is movably hinged to the two sides of the bearing frame through two rotating rods; the first gear set takes two gears as one group, and the two gears are respectively arranged on the rotating rod in a sleeving manner and are meshed with each other; the self-locking driving device is installed on the bearing frame and used for driving the first gear set to rotate. The circuit board is conveyed to the range of the mounting frame through the conveying belt and then lifted through the electric push rod, and after the circuit board is lifted to the fixed height, the clamping blocks on the bearing frame are driven by the self-locking driving device to clamp and fix the side edge of the circuit board, so that automatic board feeding and fixing operation during detection of the circuit board is completed.

Description

Technical Field

[0001] The invention relates to the field of circuit board detection, and in particular to an automatic board locking module for PCB flying probe testing. Background Art

[0002] Flying probe test is mainly used to check the electrical function of PCB board, by using multiple independent probes to check the short circuit, open circuit and component value of PCB board. The flying probe test of PCB board is carried out on the flying probe machine. During the test, the PCB board to be tested needs to be fixed on the rack manually. After the PCB board is fixed, it is necessary to wait for the PCB board on the rack to be tested, and then remove the PCB board and replace the next board to be tested. In this way, someone needs to supervise and observe at all times during the test process, and complete the corresponding material replacement work. In the continuous production environment, this way of replacing board materials is inefficient and wastes human resources. Summary of the invention

[0003] The present invention aims to solve the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an automatic board locking module for PCB flying probe testing.

[0004] To achieve the above-mentioned purpose, the present invention provides such an automatic upper board locking module for PCB flying probe test, comprising: a mounting frame with positioning holes; a plurality of conveyor belts, which are installed at intervals on the inner side walls of both sides of the mounting frame; the transmission is completed by connecting synchronous wheel sets between the conveyor belts arranged at intervals; an electric push rod, which is vertically arranged on the inner side wall of the mounting frame between the gaps of the conveyor belts; a top block, which is installed on the movable rod of the electric push rod, and the gap between the conveyor belts allows the top block to be lifted and lowered; a bearing frame, which is arranged on the top of the mounting frame; extended protruding feet are symmetrically arranged at intervals on both sides of the bearing frame to leave a gap between the bearing frame and the mounting frame; a clamping block, which is provided with a plurality of groups in a group of two, and each group is movably hinged on both sides of the bearing frame through two rotating rods; the clamping block swings within the gap between the bearing frame and the mounting frame; a first gear set, which is provided with a plurality of groups with two gears as a group, and each group is respectively sleeved on the rotating rod and meshed with each other to keep the rotating rods rotating synchronously with each other; a self-locking drive device, which is installed on the bearing frame to drive the first gear set to rotate.

[0005] As a further improvement of the scheme, the self-locking drive device includes: a worm gear, rotatably arranged on the supporting frame and meshing with the gear in the first gear set; a second gear set, connected to the worm gear through a shaft; a protective cover, installed on the supporting frame to cover the second gear set; a first motor, installed on the protective cover and driving the second gear set to rotate.

[0006] As a further improvement of the solution, it also includes: a buffer block, which is movably installed on the clamping block through an adjusting bolt.

[0007] As a further improvement of the solution, the clamping blocks arranged in groups of two are provided with straight edges that can abut against each other after they are rotated to a state of being parallel to each other.

[0008] As a further improvement of the scheme, it also includes: a reinforcement plate installed on both sides of the installation frame; a bidirectional screw rod arranged on the reinforcement plate; a disconnection and separation limiting portion is provided in the middle of the bidirectional screw rod; a reduction drive member drivingly connected to one side of the bidirectional screw rod; a moving block installed on both sides of the bidirectional screw rod; a support rod, one end of which is hinged to the moving block; a connecting plate, both sides of which are respectively hinged to the support rods on both sides; a second motor installed on the connecting plate, and its output shaft is fixedly connected to the middle of the bearing frame.

[0009] As a further improvement of the solution, it also includes: an L-shaped block, which is added between the support rod and the connecting plate; one end of the L-shaped block is connected to the support rod, and the other end is hinged to the connecting plate.

[0010] As a further improvement of the solution, the support rod is an electric telescopic push rod.

[0011] As a further improvement of the solution, it also includes: a positioning column, which is arranged on the installation frame according to the position of the protruding foot, and the protruding foot is provided with a hole matching the positioning column.

[0012] As a further improvement of the solution, an extension plate is provided on the installation frame extending outwardly along the conveyor belt; height-limiting rollers are evenly installed on the extension plate at intervals and leave a gap between them and the conveyor belt.

[0013] As a further improvement of the scheme, it also includes: strip openings, which are evenly installed on the extension plate; a slider, which is slidably set in the strip openings; a limit frame, which is arranged on the extension plate according to the number of the strip openings, and a part of the slider is slidably placed in the limit frame; a guide rod, which is installed in the limit frame and slides through the slider; a spring, which is mounted between the sliders; and the height limiting roller is rotatably connected to the slider.

[0014] The present invention brings at least the following effects:

[0015] 1. The present invention uses a conveyor belt to transport the circuit board to the range of the installation frame and then lifts the circuit board through an electric push rod. After lifting it to a fixed height, a self-locking drive device drives the clamping block on the supporting frame to clamp and fix the side edge of the circuit board, thereby completing the automatic board loading and fixing operation of the circuit board during inspection. After the inspection is completed, the clamping block is released, and the circuit board moves down and falls on the conveyor belt and is sent out of the installation frame.

[0016] 2. The self-locking drive device is set up to drive the rotating rod to rotate so that the clamping block can clamp the circuit board. During the clamping process, the worm in the self-locking drive device can play a self-locking role. During the flying probe test of the circuit board, the clamping block will not suddenly expand and can firmly clamp the circuit board.

[0017] 3. The present invention can lift and rotate the supporting frame through the cooperation of the bidirectional screw rod, the support rod and the second motor, so that the circuit board that needs to be tested on both sides can be automatically turned over without human intervention, and can be freely switched between the two usage states.

[0018] 4. The positioning posts provided on the mounting frame of the present invention can keep the movable bearing frame at a fixed position on the mounting frame at all times, and will not cause the bearing frame to shift due to vibrations generated by the test, thereby avoiding the problem of inaccurate probe landing points.

[0019] 5. The height-limiting roller provided in the present invention can limit the circuit boards on the conveyor belt to prevent the circuit boards from pressing against each other and causing the circuit boards to arch on the conveyor belt. At the same time, the cooperation of the slider and the spring can make the height-limiting roller adapt to circuit boards of different thicknesses. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a complete schematic diagram of the present invention.

[0021] Figure 2 This is a schematic diagram of the clamping block of the present invention clamping a circuit board.

[0022] Figure 3 It is a partial schematic diagram of the present invention.

[0023] Figure 4 It is a schematic diagram of the specific position of the height limiting roller of the present invention.

[0024] Figure 5 The figure is a schematic diagram of the specific relationship between the synchronous wheel set and the conveyor belt of the present invention.

[0025] Figure 6 It is a partial cross-sectional schematic diagram of the carrying frame of the present invention.

[0026] Figure 7 For the present invention Figure 6 A partial schematic diagram after the carrier frame is hidden.

[0027] Figure 8 It is a schematic diagram of the clamping block, the buffer pad and the adjusting bolt of the present invention.

[0028] Fig. 9 It is a schematic diagram of disassembling the bidirectional screw rod, support rod, connecting plate and second motor of the present invention.

[0029] Fig.10 It is a schematic diagram of the slider, limit frame, guide rod and spring of the present invention.

[0030] The corresponding relationship between the reference numerals and the names of the components in the accompanying drawings is as follows:

[0031] 1-installation frame, 2-conveyor belt, 21-synchronous wheel set, 3-electric push rod, 31-top block, 4-carrying frame, 41-protruding foot, 42-clamping block, 43-rotating rod, 44-first gear set;

[0032] 45-worm, 46-second gear set, 47-protection cover, 48-first motor;

[0033] 421-buffer block, 422-adjusting bolt, 423-straight edge;

[0034] 5-reinforcement plate, 6-bidirectional screw rod, 61-reduction driving member, 62-limiting part, 7-moving block, 8-support rod, 81-L-shaped block, 9-connecting plate, 10-second motor;

[0035] 101- positioning column;

[0036] 102- extension plate, 11- height limiting roller;

[0037] 111 - strip opening, 112 - slider, 113 - limit frame, 114 - guide rod, 115 - spring. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It will be appreciated that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some but not all structures related to the present application are shown in the drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the art without making creative work are within the scope of protection of the present application.

[0039] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0040] The present invention specifically discloses an automatic board locking module for PCB flying probe testing, such as Figure 1-Figure 8 As shown, it includes: a mounting frame 1 with positioning holes, the positioning holes are arranged around the mounting frame 1, and the mounting frame 1 is fixedly mounted on the flying probe tester through the positioning holes when in use, and conveyor belts 2 are fixedly mounted on the inner side walls opposite to each other on both sides of the mounting frame 1, and the conveyor belts 2 are installed on the inner side walls in a manner of multiple groups of intervals, and the transmission is completed by connecting the synchronous wheel set 21 between the spaced conveyor belts 2, and the conveyor belt 2 is a synchronous belt with high running accuracy. The circuit board to be tested is transported by holding the edges of both sides of the circuit board through the conveyor belt 2, and the circuit board is sent to the inner area of ​​the mounting frame 1, and an electric push rod 3 is vertically mounted on the inner side wall of the mounting frame 1, and the electric push rod 3 is between the gaps of the conveyor belt 2. A top block 31 is fixedly connected to the movable rod of the electric push rod 3, and the top block 31 can be lifted up and down through the gaps between the conveyor belts 2 and is not restricted by the conveyor belt 2, so after the circuit board moves into the mounting frame 1 through the conveyor belt 2, the top block 31 is lifted up by the action of the electric push rod 3 and lifts the circuit board up, and a cushion is also provided on the top end surface of the top block 31, which can prevent the top block 31 from rubbing against the circuit board;

[0041] The top of the mounting frame 1 is provided with a bearing frame 4. Figure 3 and Figure 6 As shown, the two sides of the carrying frame 4 are symmetrically provided with extended protruding feet 41 at intervals. The function of the protruding feet 41 is to separate the carrying frame 4 from the installation frame 1, so that a gap is left between the carrying frame 4 and the installation frame 1. Two rotating rods 43 are respectively rotatably provided on the two sides of the carrying frame 4. The two rotating rods 43 on the same side are evenly fixedly connected with clamping blocks 42. The clamping blocks 42 are grouped in two groups, and multiple groups are provided. The two clamping blocks 42 in each group are respectively installed on the two rotating rods 43; the clamping blocks 42 rotate and swing on the carrying frame 4 through the rotating rods 43, and the reserved gap between the carrying frame 4 and the installation frame 1 will not hinder the swing of the clamping blocks 42; in order to maintain the two When the clamping blocks 42 are closed and clamped, they are kept in a fixed position. The rotating rod 43 is driven by a first gear set 44 composed of two gears. Gears are sleeved on the two rotating rods 43, and the two gears are meshed with each other. In this way, when one rotating rod 43 rotates, the other rotating rod 43 can also rotate synchronously. After the clamping blocks 42 are closed, they can maintain a fixed position, so that the circuit board can be kept in a horizontal state when being clamped. At the same time, in order to prevent the clamping blocks 42 from loosening themselves when clamping the circuit board, a self-locking driving device is installed on the carrier frame 4 to drive the first gear set 44 to rotate with the rotating rod 43, so that the clamping blocks 42 can still maintain a stable clamping state after closing.

[0042] Among them, according to Figure 6 and Figure 7As shown, the self-locking drive device includes: a worm 45 rotatably mounted on the carrier frame 4, the worm 45 meshes with the gear in the first gear set 44, and as the worm 45 rotates, the gear is rotated with it, so that the clamping block 42 can maintain a stable and non-deflected state after closing, two worms 45 are provided for the two gears of the first gear set 44, and are respectively meshed with the two gears, so that the rotation of the rotating rod 43 can be more stable, and the two worms 45 can rotate simultaneously through the second gear set 46, the second gear set 46 is composed of three gears, two of which are connected to the two worms 45 through an axis, and the third gear is located between the two gears, and the three gears are meshed with each other, and a protective cover 47 is fixedly installed on the carrier frame 4, and the protective cover 47 covers the second gear set 46 to prevent foreign objects from getting stuck in the gear, and a first motor 48 is installed on the protective cover 47, and the output shaft of the first motor 48 passes through the protective cover 47 and is connected to the middle gear of the second gear set 46, and drives the middle gear to rotate, thereby rotating the two worms 45;

[0043] Among them, according to Figure 8 As shown, the clamping block 42 is also movably connected with a buffer pad 421 through an adjusting bolt 422. When the clamping block 42 clamps the edge of the circuit board, the buffer pad 421 can play a buffering role. At the same time, when dealing with circuit boards of different thicknesses, in order to avoid clamping and damaging the circuit board, the buffer pad 421 can be adjusted by adjusting the bolt 422 to adapt to circuit boards of different thicknesses; wherein, two mutually cooperating clamping blocks 42 are provided with straight edges 423, and the straight edges 423 can abut against each other after the two clamping blocks 42 are rotated to a state parallel to each other. After the two straight edges 423 abut against each other, the rotating rod 43 cannot continue to rotate, and the clamping angle of the clamping block 42 also reaches the limit and cannot continue to clamp. In this way, The clamping block 42 has a minimum clamping angle when clamping the circuit board, which can prevent the clamping block 42 from damaging the circuit board; specifically, when in use, the circuit board is first transported to the installation frame 1 by the conveyor belt 2, and then the circuit board is lifted by the electric push rod 3. After the circuit board is lifted to a fixed height, the self-locking drive device drives the clamping block 42 to close, and the circuit board is clamped and kept in a horizontal state by the clamping block 42. After the clamping is firm, the circuit board is inspected by the probe on the flying probe tester. After the inspection is completed, the clamping block 42 is released by the self-locking drive device, and the circuit board follows the electric push rod 3 to move down and fall back on the conveyor belt 2. Finally, the conveyor belt 2 sends the tested circuit board out from the other side of the installation frame 1, and the circuit board inspection is completed.

[0044] Based on the previous specific implementation method, according to Figure 1 , Figure 2 , Figure 4 and Fig. 9As shown, it also includes: a reinforcing plate 5 fixedly installed on both sides of the mounting frame 1, a bidirectional screw rod 6 fixedly installed on the reinforcing plate 5, a reduction drive 61 is installed on one side of the bidirectional screw rod 6, the reduction drive 61 is a reduction motor, used to drive the bidirectional screw rod 6 to rotate, a disconnection limiting portion 62 is provided in the middle of the bidirectional screw rod 6, and moving blocks 7 are threadedly connected on both sides of the bidirectional screw rod 6. The moving blocks 7 on both sides approach or move away from each other under the rotation of the bidirectional screw rod 6. Support rods 8 are hinged on the moving blocks 7 on both sides, one end of the support rod 8 is hinged to the moving block 7, and the other ends of the two support rods 8 are hinged to both sides of the connecting plate 9. Therefore, when the moving blocks 7 approach each other, the support rod 8 pushes the connecting plate 9 to rise, and when the moving blocks 7 move away from each other, the connecting plate 9 drops, and The limiting portion 62 provided in the middle of the bidirectional lead screw 6 can prevent the moving blocks 7 from contacting each other, and prevent the bottom ends of the two support rods 8 from approaching each other while the top ends are restricted and cannot rotate, resulting in the rod body being bent. A second motor 10 is installed on the connecting plate 9, and the output shaft of the second motor 10 passes through the connecting plate 9 and is fixedly connected to the middle of the bearing frame 4, so the bearing frame 4 can rise together with the connecting plate 9, and after rising, the bearing frame 4 is rotated by the second motor 10; specifically, some circuit boards have components on both sides, so both sides need to be tested. At this time, after the detection of one side of the circuit board is completed, by lifting the bearing frame 4, and then using the second motor 10 to drive the bearing frame 4 to rotate half a circle to turn the circuit board over and then put it down, the other side of the circuit board can be tested;

[0045] Among them, according to Fig.10 As shown, an L-shaped block 81 is added between the support rod 8 and the connecting plate 9, one end of the L-shaped block 81 is connected to the support rod 8, and the other end is hinged to the connecting plate 9. When the supporting frame 4 is in contact with the mounting frame 1, the L-shaped block 81 can make the support rod 8 in an inclined state, so that the moving block 7 is more likely to arch the connecting plate 9 when they are close to each other, and at the same time, when the bottom ends of the support rods 8 are close to each other to the limit position, the top of the support rods 8 still has a large movable range, and it is not easy for the rod body to bend; wherein, the support rod 8 is an electric telescopic push rod. When the support rod 8 is an electric telescopic push rod, the connecting plate 9 can continue to be lifted by the electric telescopic push rod after it is lifted, so that it can be ensured that the supporting frame 4 will not be interfered with by other components on the mounting frame 1 when it rotates; wherein, according to Figure 4 As shown, a positioning column 101 is provided on the mounting frame 1 according to the position of the protruding foot 41 of the carrier frame 4, and a hole matching the positioning column 101 is opened on the protruding foot 41. Since the carrier frame 4 can move up and down, and the equipment is prone to vibration when the probe works at high speed, after the positioning column 101 enters the hole on the protruding foot 41, the carrier frame 4 will not be shifted on the mounting frame 1 due to vibration, so that the probe can be ensured to accurately fall on the test point on the circuit board to complete the inspection.

[0046] Based on the previous specific implementation method, according to Figure 1 , Figure 4 and Fig.10 As shown, the side wall of the installation frame 1 is extended outward along the conveyor belt 2 to set an extension plate 102, and strip openings 111 are evenly spaced on the extension plate 102. Slide blocks 112 are slidably installed in the strip openings 111. A limit frame 113 is fixedly provided on the back of the extension plate 102. The limit frames 113 are arranged in the same number according to the number of strip openings 111. Part of the slide block 112 is slidably placed in the limit frame 113. A guide rod 114 is fixedly installed in the limit frame 113. The guide rod 114 slides through the slide block 112. The slide block 112 can slide up and down on the guide rod 114, and springs 115 are sleeved on both the upper and lower sides of the guide rod 114. The slider 112 is placed between two springs 115, and the slider 112 is kept in the center position by the spring 115. The slider 112 is rotatably connected to the limited height roller 11, and a gap is left between the limited height roller 11 and the conveyor belt 2, and the gap is used to allow the circuit board to pass under the limited height roller 11; by setting the limited height roller 11, the circuit board can be kept from being offset and skewed when the conveyor belt 2 transports the circuit board, and the circuit boards can be prevented from colliding with each other and arching when they are piled up; at the same time, under the action of the spring 115 and the slider 112, the limited height roller 11 can adapt to the passage of circuit boards of different thicknesses and make the circuit boards close to the surface of the conveyor belt 2.

[0047] The above-mentioned embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. An automatic board locking module for PCB flying probe testing, comprising: A mounting frame (1) with positioning holes; a plurality of conveyor belts (2) are installed at intervals on the inner side walls of both sides of the mounting frame (1); the characteristic is that the transmission is completed by connecting a synchronous wheel set (21) between the conveyor belts (2) arranged at intervals; an electric push rod (3) is vertically arranged on the inner side wall of the mounting frame (1) between the gaps of the conveyor belts (2); a top block (31) is installed on the movable rod of the electric push rod (3), and the gaps between the conveyor belts (2) allow the top block (31) to be raised and lowered; A support frame (4) is arranged on the top of the installation frame (1); extended protruding feet (41) are symmetrically arranged at intervals on both sides of the support frame (4) so ​​that a gap is left between the support frame (4) and the installation frame (1); a plurality of clamping blocks (42) are provided in groups of two, and each group is movably hinged to the two sides of the support frame (4) through two rotating rods (43); the clamping blocks (42) swing within the gap between the support frame (4) and the installation frame (1); a first gear set (44) is provided in a plurality of groups with two gears as a group, and each group is respectively sleeved on the rotating rod (43) and meshed with each other to keep the rotating rods (43) rotating synchronously with each other; a self-locking drive device is installed on the support frame (4) and is used to drive the first gear set (44) to rotate.

2. The automatic board locking module for PCB flying probe testing according to claim 1, characterized in that: The self-locking drive device comprises: a worm (45) rotatably arranged on the bearing frame (4) and meshing with a gear in the first gear set (44); a second gear set (46) connected to the worm (45) via a shaft; a protective cover (47) mounted on the bearing frame (4) to cover the second gear set (46); and a first motor (48) mounted on the protective cover (47) to drive the second gear set (46) to rotate.

3. The automatic board locking module for PCB flying probe testing according to claim 1, characterized in that: Also includes: A buffer block (421) is movably mounted on the clamping block (42) via an adjusting bolt (422).

4. The automatic board locking module for PCB flying probe testing according to claim 3 is characterized in that: The clamping blocks (42) arranged in groups of two are provided with straight edges (423) that can abut against each other after they are rotated to a state where they are parallel to each other.

5. The automatic board locking module for PCB flying probe testing according to any one of claims 1 to 4, characterized in that: Also includes: A reinforcing plate (5) is mounted on both sides of the mounting frame (1); a bidirectional screw rod (6) is arranged on the reinforcing plate (5); a disconnection limiting portion (62) is provided in the middle of the bidirectional screw rod (6); a reduction drive member (61) is drivingly connected to one side of the bidirectional screw rod (6); a moving block (7) is mounted on both sides of the bidirectional screw rod (6); a support rod (8) has one end hinged to the moving block (7); a connecting plate (9) has two sides hinged to the support rods (8) on both sides respectively; a second motor (10) is mounted on the connecting plate (9), and its output shaft is fixedly connected to the middle of the supporting frame (4).

6. The automatic board locking module for PCB flying probe testing according to claim 5, characterized in that: Also includes: An L-shaped block (81) is additionally arranged between the support rod (8) and the connecting plate (9); one end of the L-shaped block (81) is connected to the support rod (8), and the other end is hinged to the connecting plate (9).

7. The automatic board locking module for PCB flying probe testing according to claim 6, characterized in that: The support rod (8) is an electric telescopic push rod.

8. The automatic board locking module for PCB flying probe testing according to claim 7, characterized in that: Also includes: A positioning column (101) is arranged on the installation frame (1) according to the position of the protruding foot (41), and a hole matching the positioning column (101) is opened on the protruding foot (41).

9. The automatic board locking module for PCB flying probe testing according to claim 8, characterized in that: An extension plate (102) is provided on the installation frame (1) and extends outwardly along the conveyor belt (2); height-limiting rollers (11) are evenly installed on the extension plate (102) and have a gap between them and the conveyor belt (2).

10. The automatic board locking module for PCB flying probe testing according to claim 9, characterized in that: Also includes: The strip openings (111) are evenly spaced and installed on the extension plate (102); the slider (112) is slidably arranged in the strip openings (111); the limit frame (113) is arranged on the extension plate (102) according to the number of the strip openings (111), and a part of the slider (112) is slidably placed in the limit frame (113); the guide rod (114) is installed in the limit frame (113) and slides through the slider (112); the spring (115) is sleeved between the sliders (112); and the height limiting roller (11) is rotatably connected to the slider (112).

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