A positioning device for semiconductor chip production

Abstract

The application discloses a positioning device for semiconductor chip production and belongs to the technical field of chip processing. The positioning device comprises a first plate body and a detachable second plate body. The first plate body is provided with an electric push rod. The end of the electric push rod is fixedly connected with a first push rod. The side, away from the electric push rod, of the first push rod is fixedly connected with two springs. The end of each spring is fixedly connected with a second push rod. The two second push rods are aligned and have a gap. An inclined guide part is arranged between the first plate body and the second push rod, and the inclined guide part can make the two second push rods close to each other. An adjustable limiting plate is arranged on the second plate body. A bottom plate is arranged between the first plate body and the second plate body. The second push rod is attached to the upper surface of the bottom plate. The positioning device has the advantages of quick detachability, double working modes, self-buffered clamping and adaptation to straight pin chip processing.

Description

Technical Field

[0001] This invention belongs to the field of chip processing technology, and in particular relates to a positioning device for semiconductor chip production. Background Technology

[0002] In subsequent production processes such as packaging, pin trimming, and testing, semiconductor chips require precise clamping and positioning to ensure no chip shifting or shaking during processing, thus guaranteeing chip manufacturing accuracy. Currently, most commercially available chip positioning devices are limited in function, offering only single-sided horizontal clamping and positioning. They cannot meet the needs of different processing stations, exhibiting poor versatility. Multiple positioning devices are required to complete multiple chip processing steps, significantly increasing equipment investment costs and workshop space requirements in chip manufacturing.

[0003] Meanwhile, most existing chip positioning and clamping structures adopt a rigid direct clamping method. There is no buffer structure during the clamping process, and the rigid extrusion force can easily cause extrusion damage to the chip body. In addition, conventional dual-claw positioning structures cannot adaptively switch the opening and closing stroke and clamping angle of the claws, and cannot freely switch between the two modes of horizontal pressing positioning and vertical centering clamping. Furthermore, existing split positioning equipment is cumbersome to disassemble and assemble, and there is a lack of convenient and stable disassembly and assembly connection structure between the boards. Disassembly and assembly takes a long time when switching working conditions, which seriously affects the processing efficiency of the entire chip production line.

[0004] Given the numerous shortcomings of existing chip positioning devices, such as limited functionality, inconvenient assembly and disassembly, lack of buffer protection, and inability to switch operating conditions, it is essential to design a semiconductor chip production positioning device that can be quickly assembled and disassembled, has dual working modes, features built-in buffer clamping, and is compatible with straight pin chip processing. This design has significant practical production value. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a positioning device for semiconductor chip production, which has the advantages of quick assembly and disassembly, dual working modes, built-in buffer clamping, and compatibility with straight pin chip processing, thus solving the problems of the prior art.

[0006] This invention is implemented as follows: a positioning device for semiconductor chip production includes a first plate and a detachable second plate. The first plate is provided with an electric push rod, and a first push rod is fixedly connected to the end of the electric push rod. Two springs are fixedly connected to the side of the first push rod away from the electric push rod, and a second push rod is fixedly connected to one end of each spring. The two second push rods are aligned and have a gap. An inclined guide is also provided between the first plate and the second push rods to bring the two second push rods closer to each other. An adjustable limiting plate is provided on the second plate, and a base plate is provided between the first plate and the second plate. The second push rods are attached to the upper surface of the base plate.

[0007] In a preferred embodiment of the present invention, the first plate has a first channel, and the first push rod is slidably disposed in the first channel; the second plate has a second channel, and the limiting plate is slidably disposed in the second channel.

[0008] As a preferred embodiment of the present invention, a connecting strip is fixedly connected to one side of the second plate, and the other end of the connecting strip is fixedly connected to the first plate.

[0009] As a preferred embodiment of the present invention, the connecting strip is provided with a mounting hole, and the first plate is provided with an insertion hole; the base plate is inserted into the mounting hole, and an L-shaped insertion rod is fixedly connected to the base plate, the L-shaped insertion rod being inserted into the insertion hole.

[0010] As a preferred embodiment of the present invention, the base plate is provided with two second slide rails, the second slide rails are slidably connected to a second slider, the upper side of the second slider is fixedly connected to a second push rod; the end of the second slide rail is connected to a third slide rail.

[0011] As a preferred embodiment of the present invention, the inclined guide includes: an inclined plate, a guide plate, and an adjusting seat; the inclined plate is fixedly connected to the back side of the second push rod; the first plate body is provided with a guide hole, the guide plate is slidably inserted into the guide hole, and the adjusting seat is fixedly connected to the upper side of the guide plate for adjusting the position of the guide plate.

[0012] As a preferred embodiment of the present invention, the edge of the second push rod is provided with a plurality of first grooves arranged at equal intervals, and the edge of the limiting plate is provided with a plurality of second grooves arranged at equal intervals.

[0013] As a preferred embodiment of the present invention, a first strip groove is provided above the first groove, and a second strip groove is provided above the second groove.

[0014] As a preferred embodiment of the present invention, the connecting strip is provided with a first slide rail, a first slider is slidably connected in the first slide rail, a crossbar is fixedly connected to one side of the first slider, and the lower half of the crossbar is located in the first strip groove.

[0015] As a preferred embodiment of the present invention, an inclined spring sheet is fixedly connected to the limiting plate, and a vertically arranged pressure plate is fixedly connected to the spring sheet; a roller is provided on the upper side of the second plate, the roller is in contact with the lower surface of the spring sheet, and the pressure plate can be engaged in the second slot.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Enables free switching between dual modes, improves equipment versatility, and reduces production costs. This device can quickly switch between two working modes: horizontal clamping and positioning, and vertical centering clamping, through a detachable second plate. The horizontal mode is suitable for the pin trimming process of straight pin chips, while the vertical clamping mode after removing the second plate is suitable for other chip processing processes. One device can meet the positioning needs of two different chip processes without the need for multiple positioning fixtures, effectively reducing investment in production equipment and saving workshop space.

[0017] 2. A spring buffer structure is added to avoid chip compression damage and improve the yield rate. A spring is set between the first push rod and the second push rod as a buffer connection. Whether it is horizontal pressing or vertical clamping, the rigid thrust output by the electric push rod can be buffered and unloaded by the spring, avoiding the direct rigid compression of the chip by the push rod, which may cause chip cracking, pin breakage and other problems. This effectively protects the semiconductor chip body and improves the yield rate of chip production.

[0018] 3. The automatic gripper retraction is achieved by relying on the inclined guide component. The structure has strong linkage and does not require additional drive or power components. It only relies on a single power source of electric push rod. With the inclined guide component’s inclined plane guidance, the two push rods can automatically retract and clamp each other during the retraction of the second push rod. This simplifies the overall drive structure of the equipment, reduces the equipment failure rate and production energy consumption, and the structural linkage is precise and the clamping action responds quickly.

[0019] 4. The split-type detachable structure design makes disassembly and assembly convenient and the working mode switching efficiency is high. The second board adopts a detachable structure design, which can quickly complete the disassembly and assembly of the second board without complicated disassembly and assembly tools. The switching process between the two working modes is simple and time-saving, which can perfectly match the continuous and efficient processing rhythm of the chip production line and adapt to the automated production line scenario.

[0020] 5. Excellent positioning and clamping stability, suitable for processing scenarios of straight pin chips. With the adjustable limiting plate on the second plate, the chip can be limited and blocked on the other side, forming a bidirectional clamping limit with the second push rod. The chip is positioned without offset or shaking, accurately adapting to the pin trimming operation of straight pin semiconductor chips without bending, and specifically solving the pain point that existing tooling cannot be adapted to the positioning and processing of straight pin chips. Attached Figure Description

[0021] Figure 1This is a three-dimensional structural schematic diagram of the positioning device for semiconductor chip manufacturing provided in an embodiment of the present invention; Figure 2 This is provided by the embodiments of the present invention. Figure 1 A magnified structural diagram of part A in the middle; Figure 3 This is provided by the embodiments of the present invention. Figure 1 A magnified structural diagram of part B in the middle section; Figure 4 This is provided by the embodiments of the present invention. Figure 1 A magnified structural diagram of section C; Figure 5 This is provided by the embodiments of the present invention. Figure 1 A magnified structural diagram of section D in the middle; Figure 6 This is a top view of the positioning device for semiconductor chip manufacturing provided in an embodiment of the present invention; Figure 7 This is provided by the embodiments of the present invention. Figure 6 A cross-sectional view of the EE section; Figure 8 This is provided by the embodiments of the present invention. Figure 7 A magnified structural diagram of section F in the middle.

[0022] In the diagram: 1. First plate; 2. Second plate; 3. Electric push rod; 4. First push rod; 5. Spring; 6. Second push rod; 7. Limiting plate; 8. Base plate; 9. First channel; 10. Second channel; 11. Connecting strip; 12. Mounting hole; 13. Insertion hole; 14. L-shaped insert rod; 15. Second slide rail; 16. Second slider; 17. Third slide rail; 18. Inclined plate; 19. Guide plate; 20. Adjusting seat; 21. Guide hole; 22. First groove; 23. Second groove; 24. First strip groove; 25. Second strip groove; 26. First slide rail; 27. First slider; 28. Crossbar; 29. ​​Spring piece; 30. Pressure plate; 31. Roller. Detailed Implementation

[0023] To further understand the invention's content, features, and effects, the following embodiments are provided, and detailed descriptions are given in conjunction with the accompanying drawings.

[0024] The structure of the present invention will now be described in detail with reference to the accompanying drawings.

[0025] like Figures 1 to 8As shown in the figure, a positioning device for semiconductor chip production provided by an embodiment of the present invention includes a first plate 1 and a detachable second plate 2. The first plate 1 is provided with an electric push rod 3. A first push rod 4 is fixedly connected to the end of the electric push rod 3. Two springs 5 ​​are fixedly connected to the side of the first push rod 4 away from the electric push rod 3. A second push rod 6 is fixedly connected to one end of each spring 5. The two second push rods 6 are aligned and have a gap. An inclined guide is also provided between the first plate 1 and the second push rods 6 to bring the two second push rods 6 closer to each other. The second plate 2 is provided with an adjustable limiting plate 7, and a base plate 8 is provided between the first plate 1 and the second plate 2. The second push rod 6 is attached to the upper surface of the base plate 8.

[0026] This device relies on the first plate 1 and the detachable second plate 2 as the main support structure. Together with the electric push rod 3, the first push rod 4, the spring 5, the second push rod 6, and the tilting guide, it forms a linked execution structure. The detachable second plate 2 enables switching between two independent working modes. The overall working principle is divided into two conditions: horizontal clamping positioning and vertical clamping positioning, as detailed below: The first working condition is that the first plate 1 and the second plate 2 are placed horizontally (for straight pin chip pin trimming). The second working condition is that the second plate 2 is removed, and the first plate 1 is rotated 90° for vertical use (for general chip clamping). Overall, this device relies on the detachable second plate 2 to achieve working condition switching, the spring 5 for clamping buffering, and the tilting guide to achieve automatic jaw retraction. One set of equipment can complete two different positioning and clamping actions, adapting to different chip production processes.

[0027] Furthermore, the first plate 1 has a first channel 9, and the first push rod 4 is slidably disposed in the first channel 9; the second plate 2 has a second channel 10, and the limiting plate 7 is slidably disposed in the second channel 10. The first plate 1 has a horizontally penetrating first channel 9, and the first push rod 4 is slidably embedded inside the first channel 9. The inner diameter of the first channel 9 and the outer diameter of the first push rod 4 are clearance-fitted to achieve a purely linear reciprocating motion of the first push rod 4. The second plate 2 has a vertically penetrating second channel 10, and the limiting plate 7 is slidably assembled within the second channel 10. The left and right positions of the limiting plate 7 can be adjusted manually or electrically. The upper surface of the base plate 8 is flush with the lower surfaces of the first channel 9 and the second channel 10 to ensure that the inverted semiconductor chip is level and to prevent pin alignment failure due to chip tilt.

[0028] Specifically, a connecting strip 11 is fixedly connected to one side of the second plate 2, and the other end of the connecting strip 11 is fixedly connected to the first plate 1. The connecting strip 11 has a mounting hole 12, and the first plate 1 has an insertion hole 13. The base plate 8 is inserted into the mounting hole 12, and an L-shaped insertion rod 14 is fixedly connected to the base plate 8, which is inserted into the insertion hole 13. A square L-shaped insertion rod (not a round rod, but a square rod structure to prevent self-rotation and improve locking stability) is fixed to the side of the base plate 8. The base plate 8 is horizontally inserted into the mounting hole 12 of the connecting strip 11, and the square L-shaped insertion rod is simultaneously inserted into the insertion hole 13 of the first plate 1. The initial fixing of the first plate 1, the connecting strip 11, and the second plate 2 is achieved through the integrated structure of the base plate 8 and the square L-shaped insertion rod.

[0029] Furthermore, the base plate 8 is provided with two second slide rails 15, and the second slide rails 15 are slidably connected to second sliders 16. The upper side of the second sliders 16 is fixedly connected to the second push rod 6; the end of the second slide rails 15 is connected to a third slide rail 17. The upper surface of the base plate 8 is provided with interconnected second slide rails 15 and third slide rails 17, both of which are horizontal straight grooves; the bottom of the second push rod 6 is fixed to the second slider 16, and the second slider 16 is slidably engaged inside the second slide rails 15. The gap between the second slider 16 and the second slide rails 15 is matched, and it can only slide horizontally along the slide rails. A locking screw is installed on the outside of the first plate 1, and the locking screw is vertically aligned with the side wall of the square L-shaped plug inside the insertion hole 13. During normal operation, the second slider 16 is always inside the second slide rail 15. The slider will prevent the base plate 8 from being pulled outward, and the base plate 8 cannot be detached during processing to prevent accidental separation of the plate. Only when the electric push rod 3 extends further to the end and drives the second slider 16 to slide to the position of the connected third slide rail 17 can the base plate 8 be pulled out smoothly, forming a mechanical interlock to avoid accidental disassembly during equipment operation.

[0030] The double locking principle is as follows: The base plate 8 and the L-shaped plug are inserted to complete the first-level insertion and positioning. The locking screw on the first plate 1 is tightened, and the end of the screw directly presses against the outer wall of the square L-shaped plug, eliminating the assembly gap between the plug hole 13 and the plug, and between the mounting hole 12 and the base plate 8, thus completing the second-level mechanical locking; completely solving the problem of plate loosening caused by the reciprocating motion vibration of the equipment.

[0031] Furthermore, the tilting guide includes: a sloping plate 18, a guide plate 19, and an adjusting seat 20; the sloping plate 18 is fixedly connected to the back side of the second push rod 6; the first plate 1 is provided with a guide hole 21, the guide plate 19 is slidably inserted into the guide hole 21, and the adjusting seat 20 is fixedly connected to the upper side of the guide plate 19 for adjusting the position of the guide plate 19. The tilting guide consists of three parts: the sloping plate 18, the guide plate 19, and the adjusting seat 20; the sloping plate 18 is fixed to the back side of the second push rod 6 (the side away from the chip clamping end), with the sloping surface facing the guide plate 19; the first plate 1 has a vertical guide hole 21, the guide plate 19 is vertically slidably inserted into the guide hole 21, and the top exposed end of the guide plate 19 is fixed with the adjusting seat 20, which can be manually lifted / pressed down to change the vertical height of the guide plate 19.

[0032] Working principle under different working conditions: Condition 1 (Horizontal Combination Pin Adjustment): Adjust the adjusting seat 20 upward, causing the guide plate 19 to retract upward. The bottom of the guide plate 19 does not extend into the stroke range of the first channel 9 and does not contact the inclined plate 18. The two second push rods 6 maintain the original alignment gap and only perform horizontal straight push without any retraction action, ensuring that the chip is horizontally pressed and positioned without interference.

[0033] Working condition 2 (removal of the second plate 2 vertical clamping): Press down the adjusting seat 20, the guide plate 19 moves down and fits against the inclined surface of the inclined plate 18; when the electric push rod 3 retracts and drives the second push rod 6 to move backward, the inclined plate 18 slides along the inclined surface of the guide plate 19, and the component force of the inclined surface pushes the two second push rods 6 to automatically move towards each other, realizing automatic clamping without additional power.

[0034] Furthermore, the edge of the second push rod 6 is provided with several equidistant first grooves 22, and the edge of the limiting plate 7 is provided with several equidistant second grooves 23. A first strip groove 24 is provided above the first groove 22, and a second strip groove 25 is provided above the second groove 23. The connecting strip 11 is provided with a first slide rail 26, in which a first slider 27 is slidably connected. A crossbar 28 is fixedly connected to one side of the first slider 27, and the lower half of the crossbar 28 is located in the first strip groove 24.

[0035] The second push rod 6 has several first grooves 22 evenly spaced on its side, and a first strip groove 24 is formed above each first groove 22. The limiting plate 7 has several second grooves 23 evenly spaced on its side, and a second strip groove 25 is formed above each second groove 23. The first grooves 22 and second grooves 23 are aligned and are used to accommodate the straight pins on both sides of the chip. A curved first slide rail 26 is formed on the connecting strip 11. A first slider 27 is slidably assembled inside the first slide rail 26. A crossbar 28 is fixed to the side of the first slider 27. The upper half of the crossbar 28 is located inside the first slide rail 26, and the lower half extends into the first strip groove 24. In the initial state, the crossbar 28 does not contact the pins.

[0036] This device is compatible with straight pin chips that are placed upside down with the pins facing upwards. The straight pins on both sides of the chip are respectively placed in the first groove 22 and the second groove 23. When the electric push rod 3 pushes the second push rod 6 to move forward horizontally, the first slider 27 moves forward synchronously with the second push rod 6. At the same time, the horizontal bar 28 is constrained by the trajectory of the curved first slide rail 26 and moves downward synchronously during the forward movement. The lower half of the horizontal bar 28 presses down on the offset pins inside the first strip groove 24. While the chip is pressed and positioned, the device automatically completes the correction of the pins on one side of the chip.

[0037] Furthermore, an inclined spring piece 29 is fixedly connected to the limiting plate 7, and a vertically arranged pressure plate 30 is fixedly connected to the spring piece 29; a roller 31 is provided on the upper side of the second plate body 2, the roller 31 is in contact with the lower surface of the spring piece 29, and the pressure plate 30 can be engaged in the second strip groove 25.

[0038] When the second push rod 6 pushes the chip closer to the limiting plate 7 for pressing, the limiting plate 7 moves backward a certain distance, and the spring 29 drops accordingly, causing the lower pressure plate 30 to move vertically downward. The pressure plate 30 is inserted into the second strip groove 25, automatically pressing down the chip pins on the other side of the groove. No additional driving components are needed; the pressing force of the chip can be used to achieve synchronous correction of the pins on the other side. In conjunction with the crossbar 28, it completes the synchronous shaping of the straight pins on both sides of the chip. It is suitable for the processing of straight pin chips throughout the process, but cannot be used to position and correct bent pins.

[0039] Working principle of the invention: First working condition: The first plate 1 and the second plate 2 are placed horizontally (for straight pin chip pin trimming). The entire equipment is kept in a horizontal assembly state. The base plate 8 is assembled between the first plate 1 and the second plate 2, and the second push rod 6 is attached to the upper surface of the base plate 8. The straight pin semiconductor chip to be processed is placed above the base plate 8, and the chip is positioned between the limiting plate 7 and the second push rod 6, completing the initial placement and limiting of the chip. Then, the electric push rod 3 is activated. The electric push rod 3 extends and outputs thrust, which sequentially pushes the first push rod 4, the spring 5, and the two second push rods 6 towards the chip. The second push rods 6 smoothly compress the side of the chip, achieving overall chip clamping and positioning. In this working condition, the inclined guide does not participate in the guiding and retraction action. The two second push rods 6 maintain their original alignment gap and only perform horizontal straight pushing. Together with the limiting plate 7, they complete the bidirectional limiting of the chip, stably completing the pin trimming operation of the straight pin chip. The spring 5 can buffer the pushing and compressing force to avoid rigid compression damaging the chip.

[0040] The second working condition: The second plate 2 is removed, and the first plate 1 is rotated 90° for vertical use (general chip clamping condition). First, the connection between the first plate 1 and the second plate 2 is disconnected, and the second plate 2 is disassembled as a whole. Then, the first plate 1 is rotated 90° so that the two second push rods 6 are arranged vertically downwards. The semiconductor chip is placed between the two aligned second push rods 6 with a gap. Then, the electric push rod 3 is controlled to shorten and retract, driving the first push rod 4, spring 5, and the two second push rods 6 to move backwards synchronously. During the retraction of the second push rods 6, the tilting guide applies opposing guiding forces to the two second push rods 6, forcing them to move closer together during the retraction process. Finally, the two second push rods 6 are used to achieve centered clamping and positioning of the chip, meeting the clamping requirements of other chip processing steps.

[0041] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A positioning device for semiconductor chip manufacturing, characterized in that, The system includes a first plate (1) and a detachable second plate (2). The first plate (1) is provided with an electric push rod (3). The end of the electric push rod (3) is fixedly connected to a first push rod (4). Two springs (5) are fixedly connected to the side of the first push rod (4) away from the electric push rod (3). One end of each spring (5) is fixedly connected to a second push rod (6). The two second push rods (6) are aligned and have a gap. An inclined guide is also provided between the first plate (1) and the second push rods (6) to allow the two second push rods (6) to approach each other. The second plate (2) is provided with an adjustable limiting plate (7), and a base plate (8) is provided between the first plate (1) and the second plate (2). The second push rod (6) is attached to the upper surface of the base plate (8).

2. The positioning device for semiconductor chip manufacturing as described in claim 1, characterized in that: The first plate (1) is provided with a first channel (9), and the first push rod (4) is slidably disposed in the first channel (9); The second plate (2) is provided with a second channel (10), and the limiting plate (7) is slidably disposed in the second channel (10).

3. The positioning device for semiconductor chip manufacturing as described in claim 2, characterized in that: A connecting strip (11) is fixedly connected to one side of the second plate (2), and the other end of the connecting strip (11) is fixedly connected to the first plate (1).

4. The positioning device for semiconductor chip manufacturing as described in claim 3, characterized in that: The connecting strip (11) is provided with mounting holes (12), and the first plate (1) is provided with insertion holes (13). The base plate (8) is inserted into the mounting hole (12), and an L-shaped plug (14) is fixedly connected to the base plate (8), which is inserted into the plug hole (13).

5. The positioning device for semiconductor chip manufacturing as described in claim 1, characterized in that: The base plate (8) is provided with two second slide rails (15), and the second slide rails (15) are slidably connected to the second slider (16). The upper side of the second slider (16) is fixedly connected to the second push rod (6); the end of the second slide rail (15) is connected to the third slide rail (17).

6. The positioning device for semiconductor chip manufacturing as described in claim 5, characterized in that: The inclined guide includes: an inclined plate (18), a guide plate (19), and an adjusting seat (20); The inclined plate (18) is fixedly connected to the back side of the second push rod (6); The first plate (1) is provided with a guide hole (21), the guide plate (19) is slidably inserted into the guide hole (21), and the adjustment seat (20) is fixedly connected to the upper side of the guide plate (19) for adjusting the position of the guide plate (19).

7. The positioning device for semiconductor chip manufacturing as described in claim 6, characterized in that: The edge of the second push rod (6) is provided with several equidistant first grooves (22), and the edge of the limiting plate (7) is provided with several equidistant second grooves (23).

8. The positioning device for semiconductor chip manufacturing as described in claim 7, characterized in that: A first groove (24) is provided above the first groove (22), and a second groove (25) is provided above the second groove (23).

9. The positioning device for semiconductor chip manufacturing as described in claim 8, characterized in that: The connecting strip (11) is provided with a first slide rail (26), and a first slider (27) is slidably connected in the first slide rail (26). A crossbar (28) is fixedly connected to one side of the first slider (27), and the lower half of the crossbar (28) is located in the first strip groove (24).

10. A positioning device for semiconductor chip manufacturing as described in claim 9, characterized in that: An inclined spring sheet (29) is fixedly connected to the limiting plate (7), and a vertically arranged pressure plate (30) is fixedly connected to the spring sheet (29); a roller (31) is provided on the upper side of the second plate (2), the roller (31) is attached to the lower surface of the spring sheet (29), and the pressure plate (30) can be engaged in the second strip groove (25).

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