CN112631059A

CN112631059A - Laser projection television capable of electrically adjusting projection picture size

Info

Publication number: CN112631059A
Application number: CN202011582123.2A
Authority: CN
Inventors: 尹炜; 葛君廷; 王婷; 孔维成; 杜健; 杨思文; 廖明慧
Original assignee: China Hualu Group Co Ltd
Current assignee: China Hualu Group Co Ltd
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-04-09
Anticipated expiration: 2040-12-28
Also published as: CN112631059B

Abstract

The invention discloses a laser projection television capable of electrically adjusting the size of a projection picture, which comprises: the projection device comprises a projection host and a screen, and further comprises a host tray, a screen hanging rack, a base, a host horizontal movement assembly and a screen lifting movement assembly; the projection host is arranged on the host tray; the screen is arranged on the screen hanging frame; the base is arranged below the host tray and the screen hanging rack; the base is connected with the host tray through the host horizontal movement component, and the host horizontal movement component drives the host tray to horizontally move relative to the screen; the screen is connected with the screen hanging rack through the screen lifting motion assembly, and the screen lifting motion assembly drives the screen to do lifting motion on the screen hanging rack; the host horizontal movement component and the screen lifting movement component drive the host tray and the screen to synchronously move through a gear linkage structure. The invention can improve the regulation efficiency and precision of the size of the projection picture, and has reliable performance and lower manufacturing cost.

Description

Laser projection television capable of electrically adjusting projection picture size

Technical Field

The invention relates to the technical field of laser televisions, in particular to a laser projection television capable of electrically adjusting the size of a projection picture.

Background

Users of laser projection televisions sometimes have a need to adjust the size of a projection picture, and adjusting the size of the projection picture needs to adjust the depth position of a laser television host in the horizontal direction and the height position of a screen in the vertical direction. The former is lack of the function and cannot meet the requirements of users; the latter requires that the user rises from the watching place and moves to the vicinity of the laser projection television and the screen, and manually adjusts the positions of the host and the screen, respectively, in order to achieve a better watching effect, the host position and the screen position need to be matched with each other, and this process may need to be repeated many times, which wastes time and labor, and the adjustment precision is not high, which may cause the user experience to be greatly reduced.

In the prior art, there is also a projection television capable of automatically adjusting the size of a projection picture, angle data is acquired by an angular displacement sensor, and a control unit controls a host horizontal adjusting mechanism and a screen lifting table to move according to the calculated projection angle, so that the purpose of automatically adjusting the size of the projection picture is achieved. However, the high manufacturing cost and maintenance cost of the projection television lead to the over-price of the projection television, which is difficult to be received by the public.

Disclosure of Invention

The invention provides a laser projection television capable of electrically adjusting the size of a projection picture, which aims to overcome the technical problem.

The invention relates to a laser projection television capable of electrically adjusting the size of a projection picture, which comprises: projection host computer and screen still include: the device comprises a host tray, a screen hanging frame, a base, a host horizontal movement assembly and a screen lifting movement assembly; the projection host is arranged on the host tray; the screen is arranged on the screen hanging rack; the base is arranged below the host tray and the screen hanging rack; the base is connected with the host tray through the host horizontal movement component, and the host horizontal movement component drives the host tray to horizontally move relative to the screen; the screen is connected with the screen hanging rack through the screen lifting motion assembly, and the screen lifting motion assembly drives the screen to perform lifting motion on the screen hanging rack; and a linkage structure is arranged between the host horizontal movement assembly and the screen lifting movement assembly, so that the host tray and the screen can move synchronously.

Further, the host horizontal movement assembly comprises: the host tray horizontal movement component and the base horizontal movement component; host computer tray horizontal movement subassembly set up in the host computer tray is equipped with the opposite face of projection host computer, include: the tray main rack, the tray auxiliary rack, the two tray main shaft sliding blocks and the two tray auxiliary shaft sliding blocks; the tray main rack and the tray auxiliary rack are arranged on two sides of the host tray in parallel; the two tray main shaft sliding blocks and the two tray auxiliary shaft sliding blocks are arranged on the host tray at the same side of the tray main rack and the tray auxiliary rack respectively; the base horizontal motion assembly comprises: the tray main shaft, the tray auxiliary shaft, the driving motor, the worm, the driving gear linkage mechanism, the driven gear linkage mechanism and the gear shaft are arranged on the tray main shaft; the tray main shaft and the tray auxiliary shaft are arranged on two sides of the base in parallel and are respectively connected with the host tray through the tray main shaft sliding block and the tray auxiliary shaft sliding block; the driving gear linkage mechanism and the driven gear linkage mechanism are respectively arranged on the base at the same side as the tray main shaft and the tray auxiliary shaft; the gear shaft connects the driving gear linkage mechanism and the driven gear linkage mechanism; the driving motor is arranged on the base and is connected with the driving gear linkage mechanism through the worm; the driving gear linkage mechanism and the driven gear linkage mechanism are respectively meshed with the tray main rack and the tray auxiliary rack.

Further, the screen lifting motion assembly comprises: the screen main rack and the screen auxiliary rack are arranged on the back surface of the screen, the two screen main shaft sliding blocks and the two screen auxiliary shaft sliding blocks are arranged on the screen hanging rack, and the screen main shaft and the screen auxiliary shaft are arranged on the screen hanging rack; the screen main rack and the screen auxiliary rack are respectively and longitudinally fixedly connected to the lower part of the back of the screen and are respectively meshed with the driving gear linkage mechanism and the driven gear linkage mechanism; the screen main shaft sliding block and the screen auxiliary shaft sliding block are respectively arranged on two sides of the back surface of the screen; the screen main shaft and the screen auxiliary shaft are respectively arranged on two sides of the screen hanging rack; the screen main shaft and the screen auxiliary shaft are respectively connected with the screen main shaft sliding block and the screen auxiliary shaft sliding block.

Further, the driving gear linkage is a triple gear, including: the first tooth body, the second tooth body and the third tooth body of the driving gear are arranged on the base; the tray main rack is meshed with the first tooth body of the driving gear; the screen main rack is meshed with the driving gear second rack; the worm is meshed with the third tooth body of the driving gear; the driven gear linkage is a dual gear comprising: the driven gear first tooth body and the driven gear second tooth body; the tray auxiliary rack is meshed with the first tooth body of the driven gear; the screen auxiliary rack is meshed with the driven gear second gear body.

Further, the gear ratio of the first gear body of the driving gear to the second gear body of the driving gear is 50: 22; the first tooth body of the driving gear and the second tooth body of the driving gear are respectively the same as the first tooth body of the driven gear and the second tooth body of the driven gear in specification.

Furthermore, the worm and the third tooth body of the driving gear are meshed in a mode that the third tooth body of the driving gear is driven to rotate by the worm.

The projection host is supported by the host tray, the screen hanging frame supports the screen, the base supports the host tray and the screen hanging frame, the host horizontal movement component is arranged between the host tray and the base and drives the host tray to horizontally move relative to the screen, and therefore the relative distance between the projection host and the screen is adjusted; the screen lifting motion assembly is arranged between the screen hanging frame and the screen, the screen lifting can be achieved, the host tray and the screen can move synchronously through the gear linkage structure between the host horizontal motion assembly and the screen lifting motion assembly, therefore, the projection picture size of the laser projection television can be adjusted synchronously by adjusting the relative distance and the position between the projection host and the screen, the adjusting efficiency and the adjusting precision are high, and the user experience is improved. The invention can ensure lower manufacturing cost and reliable performance, thereby reducing the overall price and being more beneficial to market promotion.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic perspective view of the present invention;

FIG. 2 is a schematic view of the structure of the host tray horizontal motion assembly of the present invention;

FIG. 3 is a schematic diagram of the base horizontal motion assembly of the present invention;

FIG. 4 is a schematic structural diagram of a screen lifting motion assembly provided on a screen according to the present invention;

FIG. 5 is a schematic structural view of a screen lifting assembly provided on the screen hanger according to the present invention;

FIG. 6 is a schematic structural view of the mating relationship of the driving and driven gear linkages with the tray and the screen rack of the present invention;

FIG. 7 is a schematic structural view of a driving gear linkage mechanism according to the present invention;

FIG. 8 is a schematic structural view of a driven gear linkage mechanism of the present invention;

FIG. 9 is a schematic diagram of the host and screen displacement changes before and after adjustment and the corresponding projection size changes according to the present invention;

FIG. 10 is a schematic perspective view of the present invention showing the variation of the size of the projected image before and after adjustment.

The reference numbers illustrate:

1. a projection host; 2. a screen; 3. a host tray; 4. a screen hanger; 5. a base; 6. a host horizontal motion assembly; 7. a screen lifting motion assembly; 8. a screen spindle slider; 9. a screen auxiliary shaft slider; 10. a tray main rack; 11. a tray auxiliary rack; 12. a tray spindle slide block; 13. a tray countershaft slide block; 15. a screen spindle; 16. a screen countershaft; 18. a tray main shaft; 19. a tray countershaft; 20. a drive motor; 21. a worm; 22. a driving gear linkage mechanism; 23. a driven gear linkage mechanism; 24. a gear shaft; 25. a first tooth body of the driving gear; 26. a second tooth body of the driving gear; 27. a third tooth body of the driving gear; 28. a driven gear first tooth body; 29. a driven gear second tooth body; 36. a screen main rack; 37. and a screen auxiliary rack.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the present embodiment provides a laser projection television for electrically adjusting the size of a projection screen, comprising: the projection system comprises a projection host 1 and a screen 2, and further comprises a host tray 3, a screen hanging frame 4, a base 5, a host horizontal movement assembly 6 and a screen lifting movement assembly 7; the screen lifting motion assembly 7 and the host horizontal motion assembly 6 are fixed components, and the screen 2 and the host tray 3 are respectively movable components. The specific connection structure is as follows: the projection host 1 is arranged on a host tray 3 in the horizontal direction; the screen 2 is arranged on a screen hanging frame 4 in the vertical direction; the base 5 is arranged below the host tray 3 and the screen hanging rack 4; the base 5 is fixedly connected with the host tray 3 through the host horizontal movement component 6, and the host horizontal movement component 6 drives the host tray 3 to horizontally move relative to the screen 2; the screen 2 is fixedly connected with the screen hanging frame 4 through the screen lifting motion assembly 7, and the screen lifting motion assembly 7 drives the screen 2 to do lifting motion on the screen hanging frame 4; the host horizontal movement component 6 and the screen lifting movement component 7 are connected through a gear linkage structure, so that the screen 2 correspondingly moves in the vertical direction while the projection host 1 moves in the horizontal direction, and therefore, as shown in fig. 9, the adjustment of the size of a projected picture is realized through the synchronous change of the displacement of the projection host 1 and the displacement of the screen 2.

The specific structure of the main unit horizontal movement assembly 6 and the screen lifting movement assembly 7, and the gear linkage structure are described in the following embodiments.

In this embodiment, the main unit horizontal movement assembly 6 includes two parts: the device comprises a host tray horizontal movement component and a base horizontal movement component, wherein the host tray horizontal movement component is fixed on a host tray 3, and the base horizontal movement component is fixed on a base 5; as shown in fig. 2, a tray main rack 10, a tray auxiliary rack 11, two tray main shaft sliders 12 and two tray auxiliary shaft sliders 13 are fixed on the back surface of the host tray 3; the tray main rack 10 and the tray auxiliary rack 11 are arranged at the edges of two sides of the host tray 3 in parallel; the two tray main shaft sliding blocks 12 and the two tray auxiliary shaft sliding blocks 13 are respectively arranged on the host tray 3 at the same side as the tray main rack 10 and the tray auxiliary rack 11; as shown in fig. 3, a tray main shaft 18, a tray auxiliary shaft 19, a driving motor 20, a worm 21, a driving gear linkage mechanism 22, a driven gear linkage mechanism 23 and a gear shaft 24 are fixed on the base 5; the tray main shaft 18 and the tray auxiliary shaft 19 are arranged on two sides of the base 5 in parallel and are respectively connected with the host tray 3 through a tray main shaft sliding block 12 and a tray auxiliary shaft sliding block 13; the driving gear linkage mechanism 22 and the driven gear linkage mechanism 23 are respectively arranged on the base 5 at the same side of the tray main shaft 18 and the tray auxiliary shaft 19; the gear shaft 24 connects the driving gear linkage 22 and the driven gear linkage 23; the driving motor 20 is arranged on the base 5 and is connected with the driving gear linkage mechanism 22 through a worm 21; the driving gear linkage 22 and the driven gear linkage 23 are respectively engaged with the tray main rack 10 and the tray auxiliary rack 11, so that the main tray 3 can perform axial reciprocating motion on the tray main shaft 18 and the tray auxiliary shaft 19 of the base 5.

The screen lifting motion assembly 7 comprises a screen main rack 36 and a screen auxiliary rack 37 which are arranged on the back surface of the screen 2, two screen main shaft sliders 8 and two screen auxiliary shaft sliders 9, and a screen main shaft 15 and a screen auxiliary shaft 16 which are arranged on the screen hanging rack 4, as shown in FIG. 4; the screen main rack 36 and the screen auxiliary rack 37 are respectively and longitudinally fixedly connected to the lower part of the back surface of the screen 2, and are respectively meshed with the driving gear linkage mechanism 22 and the driven gear linkage mechanism 23 as shown in fig. 6; the screen main shaft sliding block 8 and the screen auxiliary shaft sliding block 9 are respectively arranged at two sides of the back surface of the screen 2; the screen main shaft 15 and the screen auxiliary shaft 16 are respectively arranged at two sides of the screen hanging rack 4; the screen main shaft 15 and the screen auxiliary shaft 16 are respectively connected with the screen main shaft slide block 8 and the screen auxiliary shaft slide block 9, so that the screen 2 can axially reciprocate on the screen main shaft 15 and the screen auxiliary shaft 16 of the screen hanging frame 4.

As shown in fig. 7, the driving gear linkage mechanism 22 is a triple gear, and includes a driving gear first tooth 25, a driving gear second tooth 26 and a driving gear third tooth 27; the tray main rack 10 is meshed with a first tooth body 25 of the driving gear; the screen main rack 36 is meshed with the second gear body 26 of the driving gear; the worm 21 is meshed with a third gear body 27 of the driving gear; as shown in fig. 8, the driven gear linkage 23 is a dual gear including a driven gear first tooth body 28 and a driven gear second tooth body 29; the tray auxiliary rack 11 is meshed with a first tooth body 28 of the driven gear; the screen auxiliary rack 37 is meshed with the driven gear second tooth body 29.

Based on the above embodiment, the specific working method is as follows:

when the driving motor 20 is powered on to start working, the worm 21 mounted on the rotating shaft of the motor rotates along with the worm, and since the driving gear third tooth body 27 is meshed with the worm 21, because the three tooth bodies are positioned on the same gear, the driving gear first tooth body 25 and the driving gear second tooth body 26 are driven simultaneously, and meanwhile, the gear shaft 24 transmits power to the driven gear linkage mechanism 23 on the other side, and the driven gear linkage mechanism 23 starts to rotate synchronously. Since the driving gear second tooth 26 and the driven side gear second tooth 29 are engaged with the screen main rack 36 and the screen auxiliary rack 37, respectively, the screen 2 is subjected to the driving force of the screen main rack 36 and the screen auxiliary rack 37, so that the screen 2 moves longitudinally on the screen main shaft 15 and the screen auxiliary shaft 16. Meanwhile, since the driving gear first tooth 25 and the driven gear first tooth 28 are engaged with the tray main rack 10 and the tray sub rack 11, respectively, the host tray 3 on which the laser projection tv host is placed is also synchronously driven to move in the horizontal direction. When the driving motor 20 is powered off and stops working, the driving gear linkage 22 and the driven gear linkage 23 stop rotating, and the movement of the screen 2 and the host tray 3 also stops. As shown in fig. 9, since the host projector 1 and the screen 2 change in displacement amount, the size of the projection screen of the host projector 1 changes on the screen 2 as shown in fig. 10, and adjustment of the size of the projection screen is realized.

In this embodiment, the gear ratio between the driving gear first gear 25 and the driving gear second gear 26 is 50: 22; the driving gear first tooth 25 and the driving gear second tooth 26 are the same in specification as the driven gear first tooth 28 and the driven gear second tooth 29, respectively.

Specifically, the gear ratio of the driving gear first gear 25 and the driving gear second gear 26 can be designed according to the ratio relationship between the displacement of the projection host 1 and the corresponding displacement of the screen 2, and the optimal gear ratio is 50: 22; the sizes, the numbers of teeth and other specifications of the first driving gear tooth 25 and the second driving gear tooth 26 are the same as those of the first driven gear tooth 28 and the second driven gear tooth 29, so that the positions of the corresponding screen 2 in the vertical direction of the projection host 1 at any position in the horizontal direction are all suitable.

In this embodiment, the worm 21 and the third gear 27 of the driving gear are engaged in such a manner that the worm 21 drives the third gear 27 of the driving gear to rotate.

In particular, in order to ensure that the screen 2 does not move uncontrollably due to its own weight when the drive motor 20 stops operating, the worm 20 and the third toothed rack 27 of the driving gear meshing therewith are designed to be self-locking, so that the third toothed rack 27 of the driving gear can only be driven by the worm 20 to rotate, and the third toothed rack 27 of the driving gear cannot in turn drive the worm 20 to move.

The whole beneficial effects are as follows:

1. compared with a laser projection television without the function of adjusting the size of the projection picture, the invention provides more choices of the size of the projection picture for users.

2. Compared with a laser projection television capable of manually adjusting the size of a projection picture, the laser projection television adopts a motor driving mode, so that a user does not need to stand up to manually adjust the positions of a host and a screen, and can control the host and the screen only by using a remote controller at a watching position; in addition, the adjustment of the position of the host computer and the adjustment of the position of the screen are synchronous, and the parameters of a transmission system can be designed according to requirements, so that the adjustment of the position of the host computer and the adjustment of the position of the screen can be automatically adapted under various specifications and picture sizes, the adjustment action is simple and accurate, and the situations that the manual adjustment mode needs to adjust the positions of the host computer and the screen step by step and repeatedly and the adjustment precision is poor are avoided. Therefore, the invention has great advantages in the aspects of adjusting efficiency and adjusting precision compared with a manual adjusting mode.

3. The invention can realize the movement of the laser projection television host and the screen in two directions respectively only by the drive of one motor and the transmission of a few pairs of gears, does not need additional mechanical structure or electrical control, and can realize the self-locking function only by the design of the parameters of a transmission system, thereby having less types and numbers of parts, simple product structure and manufacturing process, lower cost and reliable performance.

In conclusion, the invention has obvious advantages in the aspects of functional diversity, working efficiency, action precision, product cost, reliability and the like, and the experience of the user is obviously improved.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser projection television for electrically adjusting the size of a projected picture, comprising: projection host computer (1) and screen (2), its characterized in that still includes:

the screen lifting device comprises a host tray (3), a screen hanging frame (4), a base (5), a host horizontal movement assembly (6) and a screen lifting movement assembly (7);

the projection host (1) is arranged on the host tray (3); the screen (2) is arranged on the screen hanging rack (4); the base (5) is arranged below the host tray (3) and the screen hanging rack (4); the base (5) is connected with the host tray (3) through the host horizontal movement component (6), and the host horizontal movement component (6) drives the host tray (3) to horizontally move relative to the screen (2); the screen (2) is connected with the screen hanging rack (4) through the screen lifting motion assembly (7), and the screen lifting motion assembly (7) drives the screen (2) to move up and down on the screen hanging rack (4);

a linkage structure is arranged between the host horizontal movement assembly (6) and the screen lifting movement assembly (7), so that the host tray (3) and the screen (2) can move synchronously.

2. The laser projection television for electrically adjusting the size of a projected picture according to claim 1, wherein the main body horizontal movement assembly (6) comprises:

the host tray horizontal movement component and the base horizontal movement component;

host computer tray horizontal movement subassembly set up in host computer tray (3) are equipped with the opposite face of projection host computer (1), include: the tray comprises a tray main rack (10), a tray auxiliary rack (11), two tray main shaft sliding blocks (12) and two tray auxiliary shaft sliding blocks (13); the tray main rack (10) and the tray auxiliary rack (11) are arranged on two sides of the host tray (3) in parallel; two tray main shaft sliding blocks (12) and two tray auxiliary shaft sliding blocks (13) are arranged on the host tray (3) at the same side of the tray main rack (10) and the tray auxiliary rack (11) respectively;

the base horizontal motion assembly comprises: the tray comprises a tray main shaft (18), a tray auxiliary shaft (19), a driving motor (20), a worm (21), a driving gear linkage mechanism (22), a driven gear linkage mechanism (23) and a gear shaft (24); the tray main shaft (18) and the tray auxiliary shaft (19) are arranged on two sides of the base (5) in parallel and are respectively connected with the host tray (3) through the tray main shaft sliding block (12) and the tray auxiliary shaft sliding block (13); the driving gear linkage mechanism (22) and the driven gear linkage mechanism (23) are respectively arranged on the base (5) at the same side as the tray main shaft (18) and the tray auxiliary shaft (19); the gear shaft (24) connects the driving gear linkage mechanism (22) and the driven gear linkage mechanism (23); the driving motor (20) is arranged on the base (5) and is connected with the driving gear linkage mechanism (22) through the worm (21); the driving gear linkage mechanism (22) and the driven gear linkage mechanism (23) are respectively meshed with the tray main rack (10) and the tray auxiliary rack (11).

3. The laser projection television for electrically adjusting the size of a projected picture according to claim 2, wherein the screen lifting motion assembly (7) comprises:

the screen main rack (36) and the screen auxiliary rack (37) are arranged on the back surface of the screen (2), the two screen main shaft sliding blocks (8) and the two screen auxiliary shaft sliding blocks (9) are arranged, and the screen main shaft (15) and the screen auxiliary shaft (16) are arranged on the screen hanging rack (4);

the screen main rack (36) and the screen auxiliary rack (37) are respectively and longitudinally fixedly connected to the lower part of the back of the screen (2) and are respectively meshed with the driving gear linkage mechanism (22) and the driven gear linkage mechanism (23); the screen main shaft sliding block (8) and the screen auxiliary shaft sliding block (9) are respectively arranged on two sides of the back surface of the screen (2); the screen main shaft (15) and the screen auxiliary shaft (16) are respectively arranged at two sides of the screen hanging rack (4); the screen main shaft (15) and the screen auxiliary shaft (16) are respectively connected with the screen main shaft sliding block (8) and the screen auxiliary shaft sliding block (9).

4. The laser projection television of claim 3, wherein the driving gear linkage (22) is a triple gear comprising: a first driving gear tooth body (25), a second driving gear tooth body (26) and a third driving gear tooth body (27);

the tray main rack (10) is meshed with the first tooth body (25) of the driving gear; the screen main rack (36) is meshed with the second gear body (26) of the driving gear; the worm (21) is meshed with the third gear body (27) of the driving gear;

the driven gear linkage mechanism (23) is a dual gear, comprising: a driven gear first tooth body (28) and a driven gear second tooth body (29);

the tray auxiliary rack (11) is meshed with the driven gear first tooth body (28); the screen auxiliary rack (37) is meshed with the driven gear second tooth body (29).

5. The laser projection television for electrically adjusting the size of a projected picture according to claim 4, wherein the gear ratio of the first gear (25) of the driving gear to the second gear (26) of the driving gear is 50: 22; the specifications of the first driving gear tooth body (25) and the second driving gear tooth body (26) are the same as the specifications of the first driven gear tooth body (28) and the second driven gear tooth body (29), respectively.

6. The laser projection television for electrically adjusting the size of the projection picture according to claim 5, wherein the worm (21) is engaged with the third gear body (27) of the driving gear in a manner that the worm (21) drives the third gear body (27) of the driving gear to rotate.