CN112273016A

CN112273016A - Transplanting part transverse moving cylindrical cam structure of rice transplanter

Info

Publication number: CN112273016A
Application number: CN202011598988.8A
Authority: CN
Inventors: 童晓辉
Original assignee: Jingguan Agricultural Machinery Changzhou Co ltd
Current assignee: Jingguan Agricultural Machinery Changzhou Co ltd
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2021-01-29
Anticipated expiration: 2040-12-30
Also published as: CN112273016B

Abstract

The invention discloses a transverse moving cylindrical cam structure of an transplanting part of a rice transplanter, which is provided with a lining, a driving spiral shaft and a guide key positioned at the upper part of the driving spiral shaft, wherein the upper part of the guide key is connected with an auxiliary spring, the upper end of the auxiliary spring is provided with a movable ball, the upper part of the guide key is provided with a cylindrical boss, the cylindrical boss is contacted with a cylindrical hole on the lining, the lining is provided with two positioning pit points, the two positioning pit points are a positioning pit A point and a positioning pit B point respectively, and the movable ball can be movably switched between the positioning pit A point and the positioning pit B point. The transplanting part of the rice transplanter transversely-moving cylindrical cam structure ensures timely and accurate reversing and stable locking after reversing, prolongs the service life of a transversely-moving mechanism of the rice transplanter, and reduces the failure rate.

Description

Transplanting part transverse moving cylindrical cam structure of rice transplanter

Technical Field

The invention relates to the technical field of agricultural machinery, in particular to a transverse-moving cylindrical cam structure of a transplanting part of a rice transplanter.

Background

The existing rice transplanter, especially the riding type high speed rice transplanter, generally includes an engine part, a hydraulic stepless speed regulation system HST (hydraulic static transmission-HST), a gearbox assembly, a front axle, a rear axle, a main support, a rear transplanting part, a seedbed support on the transplanting part, and the like. The engine drives the HST through a belt, an output shaft of the HST is rigidly connected with an input shaft of a gear box of the rice transplanter, and an output shaft of the gear box is divided into a first output shaft driving four wheels to walk and a second output shaft driving a transplanting part of the rice transplanter. The transmission system transmits power to the walking device and the rice transplanting device, namely, the gear box needs to simultaneously provide power to the four driving wheels and the rice transplanting part, and the rice transplanting arms transplant rice while walking. Chinese patent application No. CN201410247564.5, application date 20140605, grant bulletin No. CN104025785B, grant bulletin date 20170517 disclose an inserting part assembly of a hand-held rice transplanter, which is a non-riding type hand-held rice transplanter, and also includes an inserting part therein.

Chinese patent application No. CN201911367203.3, No. 20191226, No. CN111003589A, No. 20200414 discloses a cylindrical cam type traverse device. Chinese patent application No. cn201911241748.x, application date 20191206, publication No. CN111005336A, publication date 20200414 discloses a sweeper for town roads based on rotation of a cylindrical cam. Chinese patent (application No. CN201110154950.6, application date 20110609, grant publication No. CN102229359B, grant publication date 20130417) discloses a cylindrical cam flapping wing driving mechanism. These three chinese patents all include the typical structure and use of cylindrical cams. When the seedling planting machine plants seedlings, the transplanting assembly firstly separates seedlings from a seedling blanket in sequence, the seedling blanket is installed on a seedbed support, the seedling planting machine longitudinally moves forwards, the seedbed support transversely moves to make linear reciprocating motion, the linear motion is usually obtained by converting a second output shaft of a gearbox after rotating through a cylindrical cam, and the cylindrical cam is quick in response and simple and compact in structure. The cylindrical cam driving rotating part is internally provided with a profile distributed in a spiral curve shape and provided with a driven piece guide key, a second output shaft of the gearbox drives a cam main spiral shaft to rotate in a single direction (similar to the situation that an engine in a traditional automobile can only rotate in the same direction, a reverse gear needs to be added for reverse rotation), the driven piece guide key drives the seedbed support to move linearly in the spiral track, after the seedbed support moves to a terminal point at one end, the driven piece guide key is reversed along the spiral track of the curve profile of the cam and moves towards the other end, and therefore the single rotation of the second output shaft of the gearbox is converted into linear reciprocating transverse swing (similar to simple pendulum periodic swing) of the seedbed support.

The cylindrical cam structure applied to the rice transplanter for transverse linear reciprocating motion has some disadvantages: 1. the cam and the driven piece are in point contact or line contact, so the cam is easy to wear and is only suitable for occasions with small force transmission; 2. the cam profile precision requirement is higher, needs to be processed with the digit control machine tool.

The cylindrical cam structure applied to the transverse linear reciprocating motion of the rice transplanter has the following possible problems after years of practical use: 1. the added lubricating oil is inferior or not replaced and deteriorated for a long time; or the outer sheath is damaged after being repeatedly stretched to cause lubricating oil leakage, and the running abrasion of the cam driving rotating part and the driven part guide key is intensified under severe environment; 2. or the spiral track is abraded due to the lack of processing precision at the turning points of part of the cams; the disassembly and inspection find that the track is a single track without a fork when the forward direction is changed into the forward direction and the reverse direction is changed smoothly; however, when the rail is switched from the critical point to the reverse rail, a fork is arranged at the junction, and if the junction of the fork is lack of oil or the rail processing technology is not over, the fork on the spiral rail is abraded and deformed, or the lower part of the moon bud of the guide key becomes thin, so that the deflection is inaccurate, the clamping failure can be caused, and the spiral shaft rotates but the guide key cannot move to further aggravate the abrasion. Then the second output shaft of the gearbox rotates clockwise in one way, the cam drives the rotating shaft to idle, the driven part guide key is stuck like a clamping stagnation, the seedbed does not move transversely any more, and the rice transplanting operation is terminated. This is likely to cause user complaints: (1) in the busy season, after-sale service personnel have to replace the driven part guide key or the driving screw shaft at the same time, and the farming season is greatly delayed in a remote area; (2) the cam mechanism and the guide key belong to precision parts, and the workload of installation and disassembly is large; (3) the field maintenance needs to drive the transplanter out, and the regularity of the next operation is influenced by part of the field.

Chinese patent (application No. CN202010999275.6, application No. 20200922, publication No. CN111903295A, publication No. 20201110) discloses a rice seedling transplanter which introduces optimization of non-uniform transmission characteristics through a phase-variable elliptic gear train, and can adapt to higher seedlings.

Chinese patent (application No. CN201911033640.1, application No. 20191028, publication No. CN110735903A, publication No. 20200131) discloses a transverse transfer box of a riding type rice transplanter, which introduces a power input shaft, a power transmission shaft, a transverse transfer box transmission shaft and a screw shaft which are rotatably arranged in a transverse transfer box shell through bearings, wherein a guide groove is arranged on the screw shaft, a slide block is arranged in the guide groove, the slide block reciprocates along with the rotation of the screw shaft, and a guide column is also arranged on the slide block.

The above patent does not relate to the device content of the reversing problem in the linear reciprocating mechanism (traverse box) of the rice transplanter, and does not describe the prevention solution of faults such as reversing jamming of the transplanting part driving mechanism.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in order to solve the problems existing in the prior art, the transverse moving cylindrical cam structure of the transplanting part of the rice transplanter is provided, so that timely and accurate reversing is ensured, stable locking is realized after reversing, the service life of a transverse moving mechanism of the rice transplanter is prolonged, and the failure rate is reduced.

The technical scheme adopted by the invention for solving the technical problems is as follows: a transverse moving cylindrical cam structure of an transplanting part of a rice transplanter comprises a lining, a driving spiral shaft and a guide key positioned on the upper part of the driving spiral shaft, wherein the upper part of the guide key is connected with an auxiliary spring, the upper end of the auxiliary spring is provided with a movable ball, the upper part of the guide key is provided with a cylindrical boss, the cylindrical boss is in contact with a cylindrical hole in the lining, the lining is provided with two positioning pit points, the two positioning pit points are a positioning pit A point and a positioning pit B point respectively, and the movable ball can be movably switched between the positioning pit A point and the positioning pit B point.

Further specifically, in the above technical solution, the positioning concave pit a and the positioning concave pit B are on the same circumference.

Further specifically, in the above technical solution, an arc track is provided between the positioning pit a point and the positioning pit B point, the arc track is disposed on the bushing, and the arc track, the positioning pit a point, and the positioning pit B point are smoothly connected.

Further specifically, in the above technical solution, the depth of the circular arc track is smaller than the depth of the point a of the positioning pit, and likewise, the depth of the circular arc track is smaller than the depth of the point B of the positioning pit.

Further specifically, in the above technical solution, the driving screw shaft has a spirally distributed screw track, the lower part of the guiding key has a crescent moving frame, and the moving frame is located at the upper part of the screw track.

Further specifically, in the above technical solution, the circumference is a segment of circular arc, the circular arc is on a circle using the center of the bushing as a circle center, and a central angle formed by the point a of the positioning pit and the point B of the positioning pit and the center of the bushing has a certain corresponding relationship with a spiral track curve on the driving spiral shaft.

Further specifically, in the above technical solution, the lower surface of the moving frame is arc-shaped matching with the spiral track.

Further specifically, in the above technical solution, the lower end of the auxiliary spring is connected to the upper portion of the guide key, and the axis of the auxiliary spring is parallel to the axis of the cylindrical boss.

Further specifically, in the above technical solution, the spiral track includes a forward spiral track and a reverse spiral track, and the forward spiral track and the reverse spiral track are distributed in a staggered manner.

Further specifically, in the above technical solution, one end of the driving screw shaft is a proximal end, the other end is a distal end, and the driving screw shaft further has forward and reverse critical positions distributed at the proximal end and the distal end of the driving screw shaft.

The invention has the beneficial effects that: the invention relates to a traversing cylindrical cam structure of an transplanting part of a rice transplanter, which increases two positioning pit points, an arc track, an auxiliary spring and a movable ball on a bush contacted with the upper part of a guide key, wherein the rolling resistance of the movable ball on the arc track is smaller relative to the friction force of a crescent moving frame at the lower part of the guide key and a spiral track on a driving spiral shaft, and the rotation action of the guide key promotes the movable ball to be in pit-off, energy storage and pit-in, so that the state switching of the guide key is easier to be promoted, the direction is not completely changed by the rotation inertia of the driving spiral shaft, the timely and accurate direction change is ensured, the movable ball is not popped up to be in a stable state after the direction change, the service life of a traversing mechanism of the rice transplanter is prolonged under the limiting condition that the manufacturing level is difficult to be improved and the maintenance loss is existed (each user cannot be seriously and, the failure rate is reduced.

Drawings

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

FIG. 1 is a schematic view of the structure of a driving screw shaft;

FIG. 2 is a schematic view of the structure of a guide key and an auxiliary spring and a movable ball mounted on the top of the guide key;

FIG. 3 is a schematic view of the distal movement of the guide key on the helical track of the drive screw shaft;

FIG. 4 is a schematic view of the structure of the bushing, the auxiliary spring and the movable ball;

FIG. 5 is a schematic view of the guide key, assist spring and movable ball at the location pocket B point of the bushing;

fig. 6 is a schematic view of the guide key, the auxiliary spring and the movable ball on the circular arc orbit of the bush.

The reference numbers in the drawings are: 1. a driving screw shaft; 101. a spiral track; 102. forward and reverse critical positions; 2. a guide key; 201. a cylindrical boss; 202. a movable frame; 3. an auxiliary spring; 4. a movable ball; 5. a bushing; 501. positioning a pit A point; 502. positioning a pit B point; 503. a circular arc orbit.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1, 2, 3, 4, 5 and 6, the traversing cylindrical cam structure of the transplanting part of the rice transplanter of the invention comprises a bushing 5, a driving screw shaft 1 and a guide key 2 positioned at the upper part of the driving screw shaft 1, wherein the upper part of the guide key 2 is connected with an auxiliary spring 3, the upper end of the auxiliary spring 3 is provided with a movable ball 4, the upper part of the guide key 2 is provided with a cylindrical boss 201, the cylindrical boss 201 is a part of the guide key 2, the cylindrical boss 201 is contacted with a cylindrical hole on the bushing 5, i.e. the cylindrical boss 201 is contacted with the bushing 5 in an 'inserted state', and can rotate. The bushing 5 is independent, the bushing 5 is fixed in other mounting components, such as mounting plates or screw washers.

The bush 5 is provided with two positioning pit points, the two positioning pit points are a positioning pit A point 501 and a positioning pit B point 502 respectively, the movable ball 4 can be moved and switched between the positioning pit A point 501 and the positioning pit B point 502, specifically, the upper half part of the movable ball 4 is in contact with one of the positioning pit points, and can be moved and switched to the other positioning pit point.

The positioning pit a point 501 and the positioning pit B point 502 are on the same circumference, the circumference is a circular arc, the circular arc is on a circle with the center of the liner 5 as the center, and the depth of the positioning pit a point 501 and the depth of the positioning pit B point 502 are both H1.

An arc track 503 is arranged between the positioning pit A point 501 and the positioning pit B point 502, the arc track 503 is arranged on the liner 5, the arc track 503, the positioning pit A point 501 and the positioning pit B point 502 are connected smoothly, and the depth of the arc track 503 is H2.

The depth of the circular arc track 503 is smaller than that of the location pit a spot 501, and likewise, the depth of the circular arc track 503 is smaller than that of the location pit B spot 502, i.e., H2 is smaller than H1.

The positioning pit a point 501, the positioning pit B point 502, and the circular arc track 503 are all part of the liner 5.

The central angle formed by the positioning pit a point 501, the positioning pit B point 502 and the center of the bushing 5 has a certain corresponding relationship with the curve of the spiral track 101 on the driving spiral shaft 1.

The corresponding relationship is: a circle formed by a positioning pit A point 501, a positioning pit B point 502 and the central point of the bushing 5 is connected with the circular arc track 503 to form a fan shape; the central point of the bushing 5 forms a central angle with a positioning pit A point 501 and a positioning pit B point 502; this central angle needs to correspond to the curve deviation angle of the spiral track 101. For example, the curve of the spiral track 101 is shifted by 30 degrees from the forward direction to the critical point and by-30 degrees from the critical point to the reverse direction, and this central angle is typically 60 degrees.

The driving screw shaft 1 is provided with a spiral track 101 in a spiral distribution, the spiral track 101 is a part of the driving screw shaft 1, and the spiral track 101 comprises a forward spiral track and a reverse spiral track, and the forward spiral track and the reverse spiral track are distributed in a staggered way. One end of the driving screw shaft 1 is a near end, the other end is a far end, the driving screw shaft 1 is further provided with forward and reverse critical positions 102, the forward and reverse critical positions 102 are a part of the driving screw shaft 1, and the forward and reverse critical positions 102 are distributed at the near end and the far end of the driving screw shaft 1. The guide key 2 has a crescent-shaped moving frame 202 at the lower part thereof, the moving frame 202 is a part of the guide key 2, the moving frame 202 is located at the upper part of the spiral track 101, the lower surface of the moving frame 202 is arc-shaped to match the spiral track 101, and lubricating oil is provided between the moving frame 202 and the spiral track 101.

The lower end of the auxiliary spring 3 is connected to the upper part of the guide key 2, the axis of the auxiliary spring 3 is parallel to the axis of the cylindrical boss 201, i.e. the auxiliary spring 3 and the cylindrical boss 201 are arranged in parallel, the movable ball 4 is located at the upper end of the auxiliary spring 3, and the lower half part of the movable ball 4 is immersed in the auxiliary spring 3.

On the basis of a common cylindrical cam structure, a positioning pit A point 501 and a positioning pit B point 502 with the depth of H1 are added on a bush 5, an arc track 503 with the depth of H2 is added, and an auxiliary spring 3 and a movable ball 4 are also added. By means of the guiding key 2 rotating while walking in a curve, the guiding key 2 actively rotates a certain angle along the spiral track 101 when reaching the far end or the near end because the bushing 5 provided with the positioning pit a 501 and the positioning pit B502 cannot rotate. Firstly, the auxiliary spring 3 is pulled by the guide key 2, and then the auxiliary spring 3 drives the movable ball 4 to separate from the point A501 of the positioning pit and move along the circular arc track 503; the depth of the arc track 503 becomes shallow, which is equivalent to the fact that the auxiliary spring 3 is compressed to store energy during moving; the object always tends to turn from a high-energy state to a low-energy state, and the auxiliary spring 3 needs to be released; the guide key 2 slightly rotates to be inclined from the middle state again, the depth of the circular arc track 503 is kept H2 unchanged, the guide key 2 slightly pulls the movable ball 4 to deviate from the middle point, and the movable ball 4 has the tendency to move towards the positioning concave B point 502; the depth of the B point 502 of the positioning pit is deeper, and the positioning pit is locked again and enters a stable state; the rolling resistance of the movable ball 4 is much smaller than the friction force of the moving frame 202 which solely depends on the guide key 2, and the moving direction of the ball 4 when released is the same as the moving direction of the guide key 2. In the whole change process, the ball 4 is pulled out passively, passes through the energy storage and then passes through the critical point, and then actively releases energy, so that the power assisting device has a certain power assisting effect.

The working principle of the transverse cylindrical cam structure of the transplanting part of the rice transplanter is as follows:

starting at time T1, when the drive screw shaft 1 rotates clockwise and the guide key 2 advances "obliquely, the inclination angle is not changed before the direction change, the guide key 2 itself does not rotate, and the movable ball 4 is in the detent depression point a 501, and the movable ball 4 is in the locked state because the guide key 2 does not rotate. The cylindrical boss 201 on the top of the guide key 2 drives the bushing 5 and other mounting components to move linearly and distally in a direction parallel to the driving screw shaft 1;

at time T2, the guiding key 2 reaches near the distal end of the driving screw shaft 1, the screw track 101 is switched to be perpendicular to the longitudinal direction of the driving screw shaft 1, and at this time, the moving frame 202 follows the screw track 101 to force the guiding key 2 to move along the curve of the screw track 101, and the guiding key 2 tends to rotate in the direction perpendicular to the driving screw shaft 1, the movable ball 4 is slightly delayed, but the movable ball 4 is immediately driven by the auxiliary spring 3 to disengage from the positioning pit a 501; because the depth H2 of the arc track 503 on the bushing 5 is shallower than the depth H1 of the point A501 of the positioning pit, the auxiliary spring 3 is compressed at the moment, and certain 'energy storage' is stored;

at time T3, the spiral track 101 reverses again, and the navigation key 2 rotates again in the "tilted" position, the rotation angle being identical to that at time T1, but with the opposite bias, in the dynamic change process, the movable ball 4 accumulating certain elastic potential energy tends to be released, in the rotation process of the guide key 2, the movable ball 4 is synchronously driven to rotate along the circular arc track 503, the guide key 2 drives the auxiliary spring 3 and the movable ball 4 to slightly deviate from the middle position, the movable ball 4 and the auxiliary spring 3 tend to enter a deeper positioning pit B point 502, the energy of the auxiliary spring 3 is released, so that the guide key 2 smoothly rotates in place, and because the depth of the positioning pit B point 502 is deeper, the auxiliary spring 3 and the movable ball 4 form locking, the guide key 2 is smoothly and firmly reversed, the whole reversing is successful, and the guide key 2, the bush 5 and other mounting components linearly move towards the near end in parallel with the driving screw shaft 1.

At time T4, the navigation key 2, bushing 5, and other mounting components reach the proximal boundary, and the T1-T3 action is repeated, except that the movable ball 4 exits the detent pocket B point 502 to detent pocket a point 501.

The invention relates to a traversing cylindrical cam structure of a transplanting part of a rice transplanter, aiming at the phenomena that the manufacturing and processing level and consistency defects of a driving spiral shaft 1 and a guide key 2 of the traversing cylindrical cam of the rice transplanter are poor, or the guide key 2 is worn in an oil-deficient environment due to insufficient maintenance of a user, so that the guide key 2 is induced to be failed in reversing or difficult in reversing, the driving spiral shaft 1 rotates and extrudes to aggravate the abrasion fault, and further the transverse seedling conveying operation is stopped, through adding two positioning pit points, an arc track 503, an auxiliary spring 3 and a movable ball 4 on a lining 5 contacted with the upper part of the guide key 2, the functions of energy storage by the auxiliary spring 3 and the power-assisted reversing and locking by the movable ball 4 are realized, compared with the friction force of a crescent-shaped moving frame 202 at the lower part of the guide key 2 and a spiral track 101 on the driving spiral shaft 1, the rolling resistance of the movable ball 4 at the upper part is smaller, the state switching of the guide keys 2 is facilitated more easily, the direction change is not completed by means of the rotation inertia of the driving spiral shaft 1, the timely and accurate direction change is ensured, the guide keys are not popped up to be in a stable state after the direction change, the mechanism is ensured to be more durable under the limiting condition that the manufacturing level is difficult to improve and maintenance is absent (the intensive maintenance of each user cannot be required, namely the extremely severe maintenance is absent, the stable locking is ensured after the direction change is timely and accurate), the service life of the transverse moving mechanism of the rice transplanter is prolonged, and the failure rate is reduced.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. The utility model provides a transplanter portion of planting sideslip cylinder cam structure, its characterized in that: the novel spiral shaft is provided with a lining (5), a driving spiral shaft (1) and a guide key (2) positioned on the upper portion of the driving spiral shaft (1), wherein the upper portion of the guide key (2) is connected with an auxiliary spring (3), the upper end of the auxiliary spring (3) is provided with a movable ball (4), the upper portion of the guide key (2) is provided with a cylindrical boss (201), the cylindrical boss (201) is in contact with a cylindrical hole in the lining (5), the lining (5) is provided with two positioning pit points, the two positioning pit points are a positioning pit A point (501) and a positioning pit B point (502), and the movable ball (4) can be movably switched between the positioning pit A point (501) and the positioning pit B point (502).

2. The transplanter planting part traversing cylindrical cam structure according to claim 1, wherein: the positioning pit A point (501) and the positioning pit B point (502) are on the same circumference.

3. The transplanter planting part traversing cylindrical cam structure according to claim 1 or 2, characterized in that: an arc track (503) is arranged between the positioning pit A point (501) and the positioning pit B point (502), the arc track (503) is arranged on the lining (5), and the arc track (503), the positioning pit A point (501) and the positioning pit B point (502) are connected smoothly.

4. The transplanter planting part traversing cylindrical cam structure according to claim 3, wherein: the depth of the circular arc track (503) is smaller than that of the positioning pit A point (501), and likewise, the depth of the circular arc track (503) is smaller than that of the positioning pit B point (502).

5. The transplanter planting part traversing cylindrical cam structure according to claim 1, wherein: the driving screw shaft (1) is provided with a screw track (101) which is spirally distributed, the lower part of the guide key (2) is provided with a crescent-shaped moving frame (202), and the moving frame (202) is positioned at the upper part of the screw track (101).

6. The transplanter planting part traversing cylindrical cam structure according to claim 2, wherein: the circumference is a section of circular arc, the circular arc is on a circle taking the center of the lining (5) as the center of a circle, and a central angle formed by a point A (501) of the positioning pit, a point B (502) of the positioning pit and the center of the lining (5) has a certain corresponding relation with the curve of the spiral track (101) on the driving spiral shaft (1).

7. The transplanter planting part traversing cylindrical cam structure of claim 5, wherein: the lower surface of the moving frame (202) is in an arc shape matched with the spiral track (101).

8. The transplanter planting part traversing cylindrical cam structure according to claim 1, wherein: the lower end of the auxiliary spring (3) is connected to the upper part of the guide key (2), and the axis of the auxiliary spring (3) is parallel to the axis of the cylindrical boss (201).

9. The transplanter planting part traversing cylindrical cam structure of claim 5, wherein: the spiral track (101) comprises a forward spiral track and a reverse spiral track, and the forward spiral track and the reverse spiral track are distributed in a staggered mode.

10. The transplanter planting part traversing cylindrical cam structure of claim 9, wherein: one end of the driving screw shaft (1) is a near end, the other end of the driving screw shaft is a far end, the driving screw shaft (1) is also provided with forward and reverse critical positions (102), and the forward and reverse critical positions (102) are distributed at the near end and the far end of the driving screw shaft (1).