CN210232178U

CN210232178U - Screw assembling machine

Info

Publication number: CN210232178U
Application number: CN201921328607.7U
Authority: CN
Inventors: Jiangwei Xu; 徐江炜; Jingliang Chen; 陈景亮; Linfeng He; 何林峰; Fan Yang; 杨帆; Shiwei Zhou; 周世伟
Original assignee: Yuhuan Secondary Vocational Technical School
Current assignee: Yuhuan Secondary Vocational Technical School
Priority date: 2019-08-15
Filing date: 2019-08-15
Publication date: 2020-04-03
Anticipated expiration: 2029-08-15

Abstract

The utility model provides a screw assembly machine belongs to processing equipment technical field. It has solved the poor scheduling problem of current screw kludge equipment quality. This screw kludge, including base and support, be equipped with the work piece platform on the base, be equipped with the elevating platform on the support, be fixed with screw export coupling head and lift cylinder on the elevating platform, the fixed plate has been linked firmly on the piston rod of lift cylinder, electric screwdriver has been linked firmly on the fixed plate, electric screwdriver's tool bit inserts in the screw export coupling head and can stretch out from the lower extreme of screw export coupling head, be equipped with horizontal planker on the base, be equipped with vertical planker on the horizontal planker, the work piece platform links firmly on vertical planker, the work piece bench has linked firmly the bracket, be provided with the mounting groove that is used for installing the work piece on the upper surface of bracket, the mounting groove runs through the leading flank and the trailing flank of bracket, both sides articulate respectively around the bracket on the work piece bench has the. This screw kludge has advantages such as equipment quality is good.

Description

Screw assembling machine

Technical Field

The utility model belongs to the technical field of the processing equipment, a screw assembly machine is related to.

Background

Screws are common fasteners, and two parts are connected and fixed by screws. The common assembling mode of the screw is manual assembling, and in the assembling process, the screw needs to be firstly placed at a preset connecting hole, then the cutter head of the screwdriver is aligned to the positioning groove of the screw, and then the screw is screwed tightly by force. The manual assembly efficiency is low, the tightening degree is unstable, and neglected installation is easily caused, so designers design a screw assembling machine to realize the mechanization and automation of screw assembling.

Chinese patent literature document discloses an automatic screw assembling machine [ application number: CN 200710066650.6; the notice number is: CN100464943C ], the automatic screw assembling machine is provided with a microcomputer control system, a screw feeding mechanism, a screw power mechanism, a screw fastening mechanism and an assembly line sliding plate, wherein the microcomputer control system is respectively connected with the screw feeding mechanism, the screw power mechanism and the screw fastening mechanism, the screw feeding mechanism is connected with the screw power mechanism, the screw power mechanism is connected with the screw fastening mechanism, the microcomputer control system is used for controlling the operation of the automatic screw assembling machine, the screw feeding mechanism is used for automatically feeding screws, the screw power mechanism is used for conveying screws in place, and the screw fastening mechanism is used for automatically assembling screws.

An automatic screw assembling machine is applied to the assembly of a combination switch and a screw. When the screw assembling machine works, a screw feeding mechanism sends screws to a screw outlet connecting head, a screw power mechanism conveys the screw outlet connecting head to the right position, a combined switch of the screws to be assembled is conveyed to the position below the screw outlet connecting head by an assembly line sliding plate, then a power cylinder in a screw fastening mechanism drives an electric screwdriver to move downwards to the right position, a tool bit of the electric screwdriver is abutted against the screws, then the electric screwdriver works to screw the screws into the combined switch and fasten the screws, after the screws are assembled, the power cylinder drives the electric screwdriver to move upwards to reset, the screw feeding mechanism sends the next screw to the screw outlet connecting head, and the screw power mechanism conveys the screw outlet connecting head to the other position for assembling the next screw.

When the automatic screw assembling machine works, the combined switch is not provided with the fixing device, and the combined switch is easy to displace in the assembling process, so that the assembling position of the screw is deviated, and the assembling quality of a workpiece is poor.

Disclosure of Invention

The utility model aims at the above-mentioned problem that prior art exists, provide a screw assembling machine, the technical problem of solution is how to improve the equipment quality.

The purpose of the utility model can be realized by the following technical proposal:

a screw assembling machine comprises a base and a support vertically fixed on the base, wherein a workpiece table is arranged on the base, a lifting table capable of lifting up and down is arranged on the support, a screw outlet connecting head and a vertically arranged lifting cylinder are fixed on the lifting table, a screw feeding mechanism capable of conveying screws into the screw outlet connecting head is connected onto the screw outlet connecting head, a fixed plate positioned above the screw outlet connecting head is fixedly connected onto a piston rod of the lifting cylinder, an electric screwdriver is fixedly connected onto the fixed plate, a tool bit of the electric screwdriver is inserted into the screw outlet connecting head and can extend out from the lower end of the screw outlet connecting head, the screw assembling machine is characterized in that a transverse dragging plate capable of moving left and right on the base is arranged on the base, a longitudinal dragging plate capable of moving back and forth on the transverse dragging plate is arranged on the transverse dragging plate, workpiece table fixed connection is on vertical planker, fixedly connected with is located the bracket of screw export coupling head below on workpiece table's the upper surface, be provided with the mounting groove that is used for installing the work piece on the upper surface of bracket, the mounting groove runs through the leading flank and the trailing flank of bracket, both sides articulate respectively around being located the bracket on workpiece table's the upper surface has the clamp plate, be provided with the extension spring between clamp plate and the bracket.

Before the screw assembling machine works, the two pressing plates are turned outwards, then the workpiece is embedded into the mounting groove, the front end and the rear end of the workpiece extend out of the mounting groove, then the two pressing plates are released, and under the action of the elastic force of the tension spring, the two pressing plates respectively abut against the front end and the rear end of the workpiece, so that the workpiece is clamped and fixed on the workpiece table. When the screw assembling machine works, a screw feeding mechanism conveys screws into a screw outlet connecting head, a transverse planker and a longitudinal planker move to drive a workpiece table to move, so that the position, to be assembled, of a workpiece is located right below the screw outlet connecting head, then a lifting table descends to enable the screw outlet connecting head to descend to the position, to be assembled, close to the workpiece, then a piston rod of a lifting cylinder extends to enable a tool bit of an electric screwdriver to abut against the tail portion of the screw, the head portion of the screw abuts against the position, to be assembled, and then the electric screwdriver rotates to screw the screws into the workpiece to complete the assembly of one screw. After one screw is assembled, the electric screwdriver stops working, the lifting cylinder drives the electric screwdriver to ascend, the lifting platform ascends and resets, the screw feeding mechanism conveys the next screw into the screw outlet connecting head, the transverse planker and the longitudinal planker move to move the next position to be assembled of the workpiece to be right below the screw outlet connecting head, and the next screw is assembled by repeated action until all the positions to be assembled on the workpiece are assembled. And after the workpieces are assembled, the two pressing plates are turned outwards, the workpieces are taken out of the mounting groove, and then the next workpiece is loaded for assembling the next workpiece. The workpiece is fixed through the pressing plate and the bracket, so that the workpiece cannot run in the screw assembling process, and the assembling quality is improved.

In the screw assembling machine, the screw outlet coupling head comprises a fixed part, the upper end of the fixed part is fixedly connected with the lifting platform, the upper end surface of the fixed part is provided with an insertion hole penetrating through the lower end surface of the fixed part, the tool bit of the electric screwdriver is inserted in the insertion hole, the outer side surface of the fixed part is obliquely provided with an air path connecting part, the air path connecting part is connected with the screw feeding mechanism, the air path connecting part is provided with a screw passing hole communicated with the insertion hole, the left side and the right side of the fixed part are respectively hinged with a left moving part and a right moving part, a left pressure spring is arranged between the upper end of the left moving part and the fixed part, a right pressure spring is arranged between the upper end of the right moving part and the fixed part, the lower end of the left moving part and the lower end of the right moving part abut against below the insertion hole, and a screw, the screw through hole is a step hole and comprises an inlet section and an outlet section, wherein the inlet section is positioned above the outlet section, and the aperture of the inlet section is larger than that of the outlet section.

The screw feeding mechanism conveys screws into the jack from the screw access hole of the air path connecting part, the screws fall into the screw access hole after entering the jack, the head of the screws is positioned at the outlet section, the tail of the screws is positioned at the inlet section, and the screws are clamped in the screw access hole. Then the lifting cylinder drives the electric screwdriver to move downwards, the tool bit of the electric screwdriver is inserted into the screw through hole downwards and abuts against the tail of the screw, the screw pushes the lower end of the left moving part and the lower end of the right moving part away under stress, the head of the screw abuts against the position, to be assembled, of the workpiece, and then the electric screwdriver works to screw the screw into the workpiece to complete assembly. After the assembly is completed, the electric screwdriver rises upwards under the action of the lifting cylinder, the left moving part and the right moving part are respectively under the elastic action of the left pressure spring and the right pressure spring, the lower end of the left moving part is propped against the lower end of the right moving part again, and then the next screw enters the screw through hole again after passing through the screw through hole to wait for the assembly. The screw outlet coupling head is structurally arranged, so that the assembling process of the screw is orderly carried out, and the assembling quality is improved.

In the screw assembling machine, the screw through hole further comprises a transition section located between the inlet section and the outlet section, and a hole wall surface of the transition section is conical. Therefore, the left movable piece and the right movable piece are pushed open by the screw when the screw is subjected to the downward acting force of the electric screwdriver, so that the screw is smoothly pushed out from the screw through hole, and the assembly process is smoothly carried out.

In the screw assembling machine, a guide rail which is vertically arranged is further fixed on the lifting platform, a guide block is fixed on the fixing plate, the guide block is sleeved on the guide rail and can slide along the guide rail, a return spring is sleeved on the guide rail, the upper end of the return spring abuts against the guide block, and the lower end of the return spring abuts against the lifting platform. The guided way has the guide effect, avoids electric screwdriver lift in-process to take place the skew, makes screw kludge job stabilization. The reset spring has buffering and resetting functions, so that the screw assembling machine is further stable in work.

In the screw assembling machine, the two guide rails are arranged and are respectively positioned on two sides of the lifting cylinder. Further make screw kludge job stabilization.

In the screw assembling machine, the pressing plate is hinged to the workpiece table through the hinge shaft, the lower end of the pressing plate is provided with the convex strip, the left side and the right side of the convex strip on the workpiece table are respectively provided with the left convex block and the right convex block, and the hinge shaft sequentially penetrates through the left convex block, the convex strip and the right convex block. The arrangement makes the pressing plate and the workpiece platform hinged stably, and the hinge shaft is convenient to install.

Compared with the prior art, the utility model has the advantages of it is following:

the horizontal dragging plate and the longitudinal dragging plate are arranged to realize the horizontal movement of the workpiece table, the bracket is fixed on the workpiece table, the mounting grooves penetrating through the front side and the rear side of the bracket are formed in the upper surface of the bracket, the pressing plates are hinged to the front side and the rear side of the bracket on the workpiece table, the tension springs are arranged between the pressing plates and the bracket, so that workpieces are fixed stably, and the assembly quality is improved. A guide post is arranged on the lifting platform, and a return spring is sleeved on the guide post, so that the screw assembling machine works stably. The screw outlet connecting head is structurally arranged to push out the screws in order, so that the assembling process is smoothly carried out.

Drawings

FIG. 1 is a perspective view of the screw assembling machine;

FIG. 2 is a perspective view of the screw assembling machine at a workpiece table;

FIG. 3 is a perspective view of a screw outlet coupling head in the screw assembling machine;

FIG. 4 is a sectional view of the screw outlet coupling head in the present screw assembling machine.

In the figure, 1, a base; 2. a support; 3. a workpiece stage; 3a, a left bump; 3b, a right bump; 4. a lifting platform; 5. a lifting cylinder; 6. a screw outlet coupling head; 6a, a fixing piece; 6a1, jack; 6a2, gas path connection part; 6a3, screw access hole; 6b, a left movable piece; 6c, a right movable piece; 6d, a left pressure spring; 6e, a right pressure spring; 6f, passing the screw through the hole; 6f1, inducer; 6f2, transition section; 6f3, outlet section; 7. a fixing plate; 8. an electric screwdriver; 9. a transverse carriage; 10. a longitudinal carriage; 11. a bracket; 11a, a mounting groove; 12. pressing a plate; 12a, convex strips; 13. a tension spring; 14. a guide rail; 15. a guide block; 16. a return spring; 17. hinging a shaft; 18. and (5) a workpiece.

Detailed Description

The following are specific embodiments of the present invention and the accompanying drawings are used to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

Example one

As shown in fig. 1-4, a screw assembling machine includes a base 1 and a bracket 2 vertically fixed on the base 1, wherein a workpiece table 3 is arranged on the base 1. The base 1 is provided with a transverse carriage 9 which can move left and right on the base 1, the base 1 is fixedly connected with a transverse motor, and a screw nut transmission mechanism is arranged between the transverse motor and the transverse carriage 9. A longitudinal carriage 10 capable of moving back and forth on the transverse carriage 9 is arranged on the transverse carriage 9, a longitudinal motor is fixedly connected on the transverse carriage 9, and a screw nut transmission mechanism is arranged between the longitudinal motor and the longitudinal carriage 10. The workpiece table 3 is fixedly connected to the longitudinal planker 10, the bracket 11 is fixedly connected to the upper surface of the workpiece table 3, an installation groove 11a for installing a workpiece 18 is formed in the upper surface of the bracket 11, the installation groove 11a penetrates through the front side surface and the rear side surface of the bracket 11, pressing plates 12 are hinged to the front side and the rear side of the bracket 11 on the upper surface of the workpiece table 3 respectively, and a tension spring 13 is arranged between the pressing plates 12 and the bracket 11. The pressing plate 12 is hinged to the workpiece table 3 through a hinge shaft 17, a convex strip 12a is arranged at the lower end of the pressing plate 12, a left convex block 3a and a right convex block 3b are respectively arranged on the left side and the right side of the convex strip 12a on the workpiece table 3, and the hinge shaft 17 is sequentially arranged on the left convex block 3a, the convex strip 12a and the right convex block 3b in a penetrating mode. Or a convex strip 12a is arranged on the workpiece table 3, a left convex block 3a and a right convex block 3b are arranged at the lower end of the pressing plate 12, and the articulated shaft 17 is sequentially arranged on the left convex block 3a, the convex strip 12a and the right convex block 3b in a penetrating way. The upper end of the pressure plate 12 has a tendency to approach the bracket 11 by the tension spring 13. The workpiece 18 is inserted into the mounting groove 11a, and the upper end of the pressing plate 12 abuts against the workpiece 18 to fix the workpiece 18 under the action of the tension spring 13. A plurality of mounting grooves 11a may be provided on the bracket 11, and the mounting grooves 11a may be sequentially arranged in the left-right direction, so that a plurality of workpieces 18 may be mounted at one time.

The lifting platform 4 capable of ascending and descending is arranged on the support 2, the upper end of the support 2 is fixedly connected with a lifting motor, and a screw nut transmission mechanism is arranged between the lifting motor and the lifting platform 4. A lifting cylinder 5 and a screw outlet coupling head 6 are fixed on the lifting table 4, a screw feeding mechanism [ not shown in the figure ] capable of conveying screws into the screw outlet coupling head 6 is connected to the screw outlet coupling head 6, and the structure of the screw feeding mechanism can refer to the patent document with the application number of CN 200710066650.6. The lifting cylinder 5 is vertically arranged, a fixing plate 7 is fixedly connected to a piston rod of the lifting cylinder 5, and the screw outlet connecting head 6 is located between the fixing plate 7 and the bracket 11. An electric screwdriver 8 is fixedly connected to the fixing plate 7, and the screwdriver head of the electric screwdriver 8 is inserted into the screw outlet coupling head 6 and can extend out of the lower end of the screw outlet coupling head 6. A guide rail 14 which is vertically arranged is further fixed on the lifting platform 4, a guide block 15 is fixed on the fixing plate 7, the guide block 15 is sleeved on the guide rail 14 and can slide along the guide rail 14, a return spring 16 is sleeved on the guide rail 14, the upper end of the return spring 16 abuts against the guide block 15, and the lower end of the return spring 16 abuts against the lifting platform 4. The guide rails 14 are provided in two numbers and are respectively located at both sides of the lifting cylinder 5.

The screw outlet coupling head 6 comprises a fixing piece 6a, the upper end of the fixing piece 6a is fixedly connected with the lifting platform 4, the upper end face of the fixing piece 6a is provided with an insertion hole 6a1 penetrating through the lower end face of the fixing piece 6a, and the bit of the electric screwdriver 8 is inserted into the insertion hole 6a 1. An air path connecting part 6a2 is obliquely arranged on the outer side surface of the fixing part 6a, the air path connecting part 6a2 is connected with the screw feeding mechanism, a screw passing hole 6a3 communicated with the insertion hole 6a1 is formed in the air path connecting part 6a2, and screws conveyed by the screw feeding mechanism enter the insertion hole 6a1 through the screw passing hole 6a 3. A left movable piece 6b and a right movable piece 6c are hinged to the left side and the right side of the fixed piece 6a respectively, a left pressure spring 6d is arranged between the upper end of the left movable piece 6b and the fixed piece 6a, a right pressure spring 6e is arranged between the upper end of the right movable piece 6c and the fixed piece 6a, the lower end of the left movable piece 6b and the lower end of the right movable piece 6c abut against the lower portion of the insertion hole 6a1, and a screw through hole 6f communicated with the insertion hole 6a1 is formed between the lower end of the left movable piece 6b and the lower end of the right movable piece 6c after the lower end of. The screw through hole 6f is a stepped hole, the screw through hole 6f comprises an inlet section 6f1 and an outlet section 6f3, the inlet section 6f1 is located above the outlet section 6f3, and the aperture of the inlet section 6f1 is larger than that of the outlet section 6f 3. The screw through bore 6f further comprises a transition section 6f2 between the inlet section 6f1 and the outlet section 6f3, the wall of the bore of the transition section 6f2 being tapered.

Before the screw assembling machine works, the two pressing plates 12 are turned outwards, the workpiece 18 is embedded into the mounting groove 11a, the front end and the rear end of the workpiece 18 extend out of the mounting groove 11a, then the two pressing plates 12 are released, and under the action of the elastic force of the tension spring 13, the two pressing plates 12 respectively abut against the front end and the rear end of the workpiece 18, so that the workpiece 18 is clamped and fixed on the workpiece table 3. When the screw assembling machine works, the screw feeding mechanism conveys screws into the insertion holes 6a1 of the screw outlet coupling head 6 through the screw inlet holes 6a3, the screws fall into the screw outlet holes 6f after entering the insertion holes 6a1, the heads of the screws are positioned at the outlet section 6f3, the tails of the screws are positioned at the inlet section 6f1, and the screws are temporarily clamped in the screw outlet holes 6 f. Then the transverse carriage 9 and the longitudinal carriage 10 move to drive the workpiece table 3 to move, so that the position of the workpiece 18 to be assembled is positioned right below the screw through hole 6 f. Then the lifting platform 4 descends to enable the screw outlet connecting head 6 to descend to a position to be assembled close to the workpiece 18, then the piston rod of the lifting air cylinder 5 extends downwards to drive the electric screwdriver 8 to move downwards, the tool bit of the electric screwdriver 8 is inserted downwards into the screw through hole 6f, the tool bit of the electric screwdriver 8 abuts against the tail of the screw, the screw is stressed to push the lower end of the left moving piece 6b and the lower end of the right moving piece 6c away, the screw is pushed out of the screw through hole 6f, the head of the screw abuts against the position to be assembled of the workpiece 18, and then the electric screwdriver 8 rotates to screw the screw into the workpiece 18 to complete the assembly of one screw. After one screw is assembled, the electric screwdriver 8 stops working, the lifting cylinder 5 drives the electric screwdriver 8 to ascend, the lifting platform 4 ascends and resets, the lower end of the left moving part 6b and the lower end of the right moving part 6c are abutted against and form a screw through hole 6f again under the action of the left pressure spring 6d and the right pressure spring 6e, a screw feeding mechanism conveys the next screw into the screw outlet connecting head 6, the transverse carriage 9 and the longitudinal carriage 10 move to move the next position to be assembled of the workpiece 18 to the position below the screw outlet connecting head 6, and the next screw is assembled by repeated action until all the positions to be assembled on the workpiece 18 are assembled. After the assembly of the work pieces 18 is completed, the two pressing plates 12 are turned outward, the work pieces 18 are taken out from the mounting grooves 11a, and the next work piece 18 is loaded to assemble the next work piece 18. The workpiece 18 is fixed through the pressure plate 12 and the bracket 11, so that the workpiece 18 cannot run in the screw assembling process, and the assembling quality is improved.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made or substituted in a similar manner to the specific embodiments described herein by those skilled in the art without departing from the spirit of the invention or exceeding the scope of the invention as defined in the appended claims.

Claims

1. A screw assembling machine comprises a base (1) and a support (2) vertically fixed on the base (1), wherein a workpiece table (3) is arranged on the base (1), a lifting table (4) capable of ascending and descending is arranged on the support (2), a screw outlet connecting head (6) and a vertically arranged lifting cylinder (5) are fixed on the lifting table (4), a screw feeding mechanism capable of conveying screws into the screw outlet connecting head (6) is connected onto the screw outlet connecting head (6), a fixing plate (7) positioned above the screw outlet connecting head (6) is fixedly connected onto a piston rod of the lifting cylinder (5), an electric screwdriver (8) is fixedly connected onto the fixing plate (7), a tool bit of the electric screwdriver (8) is inserted into the screw outlet connecting head (6) and can extend out from the lower end of the screw outlet connecting head (6), the automatic tool setting device is characterized in that a transverse planker (9) capable of moving left and right on the base (1) is arranged on the base (1), a longitudinal planker (10) capable of moving back and forth on the transverse planker (9) is arranged on the transverse planker (9), the workpiece table (3) is fixedly connected onto the longitudinal planker (10), a bracket (11) located below a screw outlet connecting head (6) is fixedly connected onto the upper surface of the workpiece table (3), a mounting groove (11a) used for mounting a workpiece (18) is formed in the upper surface of the bracket (11), the mounting groove (11a) penetrates through the front side face and the rear side face of the bracket (11), pressing plates (12) are hinged to the front side and the rear side of the bracket (11) on the upper surface of the workpiece table (3) respectively, and a tension spring (13) is arranged between the pressing plates (12) and the bracket (11).

2. The screw assembling machine according to claim 1, wherein the screw outlet coupling head (6) comprises a fixing member (6a), the upper end of the fixing member (6a) is fixedly connected with the lifting platform (4), an insertion hole (6a1) penetrating through the lower end surface of the fixing member (6a) is formed in the upper end surface of the fixing member (6a), the bit of the electric screw driver (8) is inserted into the insertion hole (6a1), an air passage connecting portion (6a2) is obliquely formed in the outer side surface of the fixing member (6a), the air passage connecting portion (6a2) is connected with a screw feeding mechanism, a screw passing hole (6a3) communicated with the insertion hole (6a1) is formed in the air passage connecting portion (6a2), a left moving member (6b) and a right moving member (356 c) are respectively hinged to the left and right sides of the fixing member (6a), a left compression spring (6d) is arranged between the upper end of the left moving member (6b) and the fixing member (6a), the improved bolt is characterized in that a right pressure spring (6e) is arranged between the upper end of the right moving piece (6c) and the fixed piece (6a), the lower end of the left moving piece (6b) abuts against the lower end of the right moving piece (6c) below the insertion hole (6a1), a bolt through hole (6f) communicated with the insertion hole (6a1) is formed between the lower end of the left moving piece (6b) and the lower end of the right moving piece (6c) after abutting against the lower end of the left moving piece, the bolt through hole (6f) is a step hole, the bolt through hole (6f) comprises an inlet section (6f1) and an outlet section (6f3), the inlet section (6f1) is located above the outlet section (6f3), and the aperture of the inlet section (6f1) is larger than that of the outlet section (6f 3).

3. The screw assembling machine according to claim 2, wherein the screw through hole (6f) further comprises a transition section (6f2) between the inlet section (6f1) and the outlet section (6f3), the wall surface of the transition section (6f2) being tapered.

4. The screw assembling machine according to any one of claims 1 to 3, wherein a vertically arranged guide rail (14) is further fixed on the lifting table (4), a guide block (15) is fixed on the fixing plate (7), the guide block (15) is sleeved on the guide rail (14) and can slide along the guide rail (14), a return spring (16) is sleeved on the guide rail (14), the upper end of the return spring (16) abuts against the guide block (15), and the lower end of the return spring (16) abuts against the lifting table (4).

5. Screw assembling machine according to claim 4, wherein said guide rails (14) are provided in two and are located on either side of the lifting cylinder (5).

6. The screw assembling machine according to any one of claims 1 to 3, wherein the pressing plate (12) is hinged to the work table (3) by a hinge shaft (17), the pressing plate (12) is provided with a protruding strip (12a) at a lower end thereof, the work table (3) is provided with a left protruding block (3a) and a right protruding block (3b) at left and right sides of the protruding strip (12a), respectively, and the hinge shaft (17) is sequentially inserted through the left protruding block (3a), the protruding strip (12a) and the right protruding block (3 b).