Variable-force coil spring and pull rope control device

Abstract

The utility model provides a variable force coil spring which comprises a center hole and a belt body wound outwards from the center hole, the belt body comprises an inner end located in the center hole, an outer end, an outer end section, a first force lowering section, a second force lowering section and a force maintaining section, and the outer end section, the first force lowering section and the second force lowering section are sequentially and continuously arranged from the outer end to the inner end. The outer end section generates a first length from the outer end to a first length, the first force descending section generates a gradually-descending elastic restoring force from the first length to a second length, and the second force descending section generates a gradually-descending elastic restoring force from the second length to a third length. The force maintaining section generates maintaining elastic restoring force from the third length to the fourth length. The utility model further provides a pull rope control device comprising the variable force coil spring. The utility model is suitable for curtains, and enables a user to conveniently and easily fold the curtains smoothly.

Description

Technical Field

[0001] The utility model relates to the technical field of coil springs, in particular to a pull rope control device for a variable force coil spring. Background Art

[0002] Please refer to US Patent No. US11193328B2. A commonly used curtain has a pull cord control device on its upper beam. The pull cord control device includes an outer frame, and two winding wheels and two coil spring winding wheels arranged in the outer frame. The coil spring winding wheels mesh with each other and provide a coil spring for winding together. The winding wheels mesh with the coil spring winding wheels and provide a pull cord for winding respectively. The pull cord passes through the two sides of the outer frame and the upper beam and the blades of the curtain and then connects to the lower beam of the curtain. Through the action of the pull cord control device, the user can control the opening and closing of the curtain by pulling the lower beam of the curtain, and the lower beam can be stopped at any position between the uppermost position (i.e., the position where the curtain is fully folded) and the lowermost position (i.e., the position where the curtain is fully unfolded).

[0003] To be more specific, the coil spring in the above-mentioned pull-cord control device usually has different torques at different positions due to its width, thickness or other structural designs, thereby providing corresponding elastic restoring forces in response to the opening and closing conditions of the curtains, so that the lower beam of the curtain can stay at any position between the uppermost position and the lowermost position when being pulled down, and when the lower beam of the curtain is at the lowermost position, the user only needs to push the lower beam slightly upwards to allow the elastic restoring force of the coil spring to pull the lower beam upwards, thereby achieving a convenient and labor-saving effect.

[0004] However, the commonly used coil spring design is prone to a problem, that is, when the lower beam is at the lowest position, the elastic restoring force of the coil spring is too small to avoid the friction of the pull cord, resulting in the curtain not being able to be retracted smoothly and requiring the user to try multiple times to achieve the desired effect, or even malfunctioning and being unable to be retracted, or the elastic restoring force is too large to cause rebound (similar to a constant force spring). Utility Model Content

[0005] In view of the above problems, the main purpose of the utility model is to provide a variable force coil spring suitable for a curtain pull cord control device, and allowing users to conveniently and easily pull up the curtain smoothly.

[0006] In view of the above problems, another object of the present invention is to provide a pull cord control device, which allows users to smoothly and easily pull up the curtain.

[0007] To achieve the above-mentioned purpose, the variable force coil spring provided by the utility model includes a center hole and a belt body wound outward from the center hole, the belt body includes an inner end located in the center hole, an outer end, and a plurality of sections arranged successively from the outer end to the inner end, the plurality of sections include an outer end section, a first force reduction section, a second force reduction section, and a force retention section in sequence from the outer end to the inner end, the outer end section is from the outer end to a first length, the first force reduction section generates a gradually decreasing elastic restoring force from the first length to a second length, the second force reduction section generates a gradually decreasing elastic restoring force from the second length to a third length, and the force retention section generates a maintained elastic restoring force from the third length to a fourth length.

[0008] To achieve the above-mentioned object, the rope control device provided by the utility model includes a housing, at least one winding wheel and a spring winding wheel rotatably disposed in the housing, and a variable force coil spring. The variable force coil spring includes a center hole and a belt body wound outward from the center hole, the belt body includes an inner end located in the center hole, an outer end, and a plurality of sections arranged successively from the outer end toward the inner end, the variable force coil spring is used to be wound to the coil spring winding wheel under the action of an external force from an initial installation state, when the variable force coil spring is in the initial installation state, the outer end of the belt body is arranged on the coil spring winding wheel, the section of the belt body wound from the initial installation state to the coil spring winding wheel includes a first force reduction section, a second force reduction section and a force maintaining section in sequence, the first force reduction section generates a gradually decreasing elastic restoring force from a first length to a second length, the second force reduction section generates a gradually decreasing elastic restoring force from the second length to a third length, and the force maintaining section generates a maintained elastic restoring force from the third length to a fourth length.

[0009] Furthermore, the maintained elastic restoring force described in the present invention means that the elastic restoring force remains consistent or slightly increases. More specifically, the force maintaining section generates a consistent elastic restoring force from the third length to the fourth length, or the force maintaining section generates a gradually increasing elastic restoring force from the third length to the fourth length, and the increase rate of the elastic restoring force of the force maintaining section is less than the decrease rate of the elastic restoring force of the first and second force decreasing sections.

[0010] Therefore, when the variable force coil spring of the present invention is applied to the cord control device of the curtain, when the curtain is in a fully folded state, that is, when the lower beam is at the uppermost position, the lower beam carries all the blades. At this time, the force to pull the lower beam needs to be the largest. Accordingly, the variable force coil spring can generate the largest elastic restoring force at the first length, which is used to pull the lower beam at the uppermost position, so that the curtain is maintained in a fully folded state. In the process of the lower beam being pulled down, the number of blades carried by the lower beam gradually decreases, so the force required to pull the lower beam also gradually decreases. Accordingly, the elastic restoring force of the variable force coil spring in the first and second force reduction sections gradually decreases, so that the total weight of the lower beam and the blades it carries, the friction force of the cord and the elastic restoring force of the variable force coil spring are balanced as much as possible, and then the lower beam can stay at any position in the process of being pulled down. The fourth length of the variable force coil spring is used to correspond to the lowest position of the lower beam, and the third length is used to correspond to the position adjacent to the lowest position. The elastic restoring force of the variable force coil spring of the utility model does not continue to decrease from the third length to the fourth length, but remains consistent or slightly increases, so that the lower beam can not only still stay at the lowest position, but also, when the user wants to retract the curtain and slightly pushes the lower beam located at the lowest position upwards, the elastic restoring force of the variable force coil spring of the utility model can ensure that the curtain is pulled upward, so that the user can conveniently and easily retract the curtain smoothly.

[0011] The detailed structure, features, assembly or use of the variable force coil spring and pull rope control device provided by the utility model will be described in the detailed description of the implementation mode in the following. However, ordinary technicians in the field of the utility model should understand that these detailed descriptions and specific embodiments listed for implementing the utility model are only used to illustrate the utility model, and are not used to limit the scope of the patent application of the utility model. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A front view schematic diagram of a variable force coil spring provided in a preferred embodiment of the utility model.

[0013] Figure 2 It is a bottom view schematically showing the variable force coil spring.

[0014] Figure 3 It is a plan view of a belt body used for winding into the variable force coil spring.

[0015] Figure 4 It is a curve graph of the elastic restoring force of the variable force coil spring versus length.

[0016] Figure 5 The figure is a side view of a curtain using the variable force coil spring.

[0017] Figures 6 to 10This is a curve diagram of the elastic restoring force versus length of the variable force coil spring provided in other preferred embodiments of the utility model.

[0018] Fig.11 The utility model is a cross-sectional schematic diagram of a pull rope control device provided by the utility model.

[0019] Reference numerals

[0020] 10: Variable force coil spring

[0021] 12: Center hole

[0022] 20: belt body

[0023] 21: Inner end

[0024] 22: Outer end

[0025] 23: Straight part

[0026] 30: Curtains

[0027] 31: Beam

[0028] 32: Lower beam

[0029] 33:Leaf

[0030] 40: Pull rope control device

[0031] 41: Shell

[0032] 42: Winding wheel

[0033] 43: Coil spring set wheel

[0034] 44: Spring winding wheel

[0035] L1: First length

[0036] L2: Second length

[0037] L3: The third length

[0038] L4: Fourth length

[0039] P1: Top position

[0040] P2: First middle position

[0041] P3: Second middle position

[0042] P4: The lowest position

[0043] S1: Outer segment

[0044] S2: First force descent section

[0045] S3: Second strength decline section

[0046] S4: Power maintenance section

[0047] S: Initial installation status DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0049] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "include", "comprises", etc. used herein indicate the existence of features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0050] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0051] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0052] The applicant first explains that in the embodiments and drawings to be introduced below, the same reference numbers represent the same or similar components or their structural features. It should be noted that the components and structures in the drawings are for illustration purposes only and are not drawn according to the actual proportions and quantities, and if possible in practice, the features of different embodiments can be applied interchangeably.

[0053] Please read first Figure 1 and Figure 2 A variable force coil spring 10 provided in a preferred embodiment of the utility model includes a central hole 12 and a belt body 20 wound outward from the central hole 12.

[0054] like Figure 3As shown, the strip 20 is originally in a planar strip shape, and its two opposite ends are defined as an inner end 21 and an outer end 22. Then, the strip 20 is wound into a variable force coil spring 10, at which time the inner end 21 is located inside the variable force coil spring 10, that is, located at the center hole 12, and the outer end 22 is located outside the variable force coil spring 10. When manufacturing the strip 20, its width or thickness can be changed in a specific way to form multiple sections with different torsions. Alternatively, when winding the strip 20, its curvature can be changed in a specific way to form multiple sections with different torsions.

[0055] like Figure 3 As shown, the belt body 20 includes an outer end section S1, a first force reduction section S2, a second force reduction section S3, and a force retention section S4 which are sequentially arranged from the outer end 22 to the inner end 21, corresponding to Figure 4 In the present invention, any point of the belt body 20 has a corresponding length, which is measured from the outer end 22, that is, the distance between any point of the belt body 20 and the outer end 22 in the length direction. Figure 4 The point where the length is 0 is the outer end 22. Figure 1 and Figure 2 As shown, the belt body 20 in this embodiment includes a straight portion 23 adjacent to the outer end 22, and the straight portion 23 is a part of the outer end section S1. In the process of the belt body 20 being wound into the variable force coil spring 10, the straight portion 23 is not wound and remains in a straight state, so the straight portion 23 does not generate elastic restoring force, and is mainly used for the installation of the variable force coil spring 10. However, the variable force coil spring 10 of the present invention may not include the straight portion 23. In this way, when the variable force coil spring 10 is not stressed, the outer end section S1 of the belt body 20 is entirely wound around other parts of the belt body 20. Such an outer end section S1 can also be stressed and elastically deformed into a straight shape for the installation of the variable force coil spring 10. Once the belt body 20 begins to be stressed and elastically deformed, it will begin to generate elastic restoring force.

[0056] The variable force coil spring 10 of the utility model is mainly used in a pull rope control device 40 (such as Fig.11As shown in the figure, the pull rope control device 40 includes a housing 41, and the housing 41 is mainly provided with at least one winding wheel 42, a coil spring sleeve wheel 43, a coil spring winding wheel 44, and a variable force coil spring 10. The winding wheel 42, the coil spring sleeve wheel 43 and the coil spring winding wheel 4 in this embodiment are arranged on different axes and are connected to each other by mutual engagement to generate a connection relationship that can rotate with each other. However, the pull rope control device 40 of the utility model can also be designed that the winding wheel 42 is respectively arranged on the same axis as the coil spring sleeve wheel 43 and the coil spring winding wheel 44, as long as the winding wheel 42, the coil spring sleeve wheel 43 and the coil spring winding wheel 44 can rotate with each other. The variable force coil spring 10 is sleeved on the coil spring sleeve wheel 43, that is, the coil spring sleeve wheel 43 is located in the center hole 12 of the variable force coil spring 10. Fig.11 The variable force coil spring 10 is shown in an initial installation state S, at which the outer end 22 of the belt body 20 is disposed on the coil spring winding wheel 44, and the belt body 20 is wound around the coil spring winding wheel 44 by an external force from the initial installation state S. However, the pull cord control device 40 does not necessarily have to have a coil spring sleeve wheel 43, and the variable force coil spring 10 can be sleeved on a shaft or movably disposed in the housing 41, but the design of the variable force coil spring 10 being sleeved on the coil spring sleeve wheel 43 can make the variable force coil spring 10 more stable and more smoothly retracted and released.

[0057] like Figure 4 As shown, the outer end section S1 generates a gradually increasing elastic restoring force from the outer end 22 to a first length L1. In this embodiment, the elastic restoring force of the outer end section S1 increases at a roughly constant rate from the outer end 22 to the first length L1, and its increasing rate is large. Figure 4 The length from 0 to the first length L1 corresponds to an upwardly inclined straight line with a large slope. As can be seen from the above content, the outer end section S1 is mainly used to install the variable force coil spring 10 as follows Fig.11 In the initial installation state S shown, during the installation process, the variable force coil spring 10 is initially in a state of no force, and then is subjected to an external force so that a portion of it is wound onto the coil spring winding wheel 44. Therefore, when the variable force coil spring 10 is installed on the testing machine for testing, the elastic restoring force of the variable force coil spring 10 is measured to increase rapidly from 0. In other words, regardless of whether the variable force coil spring 10 has a straight portion 23, Figure 4 The elastic restoring force corresponding to the point where the length is 0 is 0, which means that the variable force coil spring 10 is not yet subjected to force. Figure 4 The elastic restoring force that rises rapidly from the middle length 0 to the first length L1 is generated during the installation process of the variable force coil spring 10. In addition, if the pull cord control device 40 is tested, the variable force coil spring 10 is in the initial installation state S at the beginning, so only the section where the belt body 20 is wound from the initial installation state S to the coil spring winding wheel 44 is measured, that is, the first force reduction section S2, the second force reduction section S3, and the force retention section S4 in sequence, as described in detail below.

[0058] The first force drop section S2 generates a gradually decreasing elastic restoring force from the first length L1 to the second length L2. In this embodiment, the elastic restoring force of the first force drop section S2 decreases at a roughly constant rate from the first length L1 to the second length L2, and its decreasing rate is less than the increasing rate of the outer end section S1. Figure 4 The middle length from the first length L1 to the second length L2 corresponds to a downward slope line with a smaller slope. The second force reduction section S3 from the second length L2 to a third length L3 will also produce a gradually decreasing elastic recovery force. The elastic recovery force of the second force reduction section S3 decreases at a roughly constant rate from the second length L2 to the third length L3, and its decrease rate is slightly smaller than the decrease rate of the first force reduction section S2. Therefore Figure 4 The middle length from the second length L2 to the third length L3 corresponds to a downwardly inclined straight line with a slightly smaller slope. The force retention section S4 from the third length L3 to a fourth length L4 will generate a maintained elastic restoring force. In this embodiment, the maintained elastic restoring force is maintained consistent, that is, the force retention section S4 generates a consistent elastic restoring force from the third length L3 to the fourth length L4, so Figure 4 The middle length from the third length L3 to the fourth length L4 corresponds to a horizontal straight line. The fourth length L4 is not necessarily the inner end 21 of the belt body 20. Usually, there are other sections between the fourth length L4 and the inner end 21. This part is not the technical feature of the utility model, so the curve diagram in the utility model does not show the part after the fourth length L4.

[0059] The elastic restoring force described in the present invention increases or decreases at an approximately constant rate means that the elastic restoring force presents an approximately fixed increase rate or decrease rate from a macroscopic perspective, and the curve graph generated by actual testing usually has slight fluctuations rather than being a perfect straight line.

[0060] Figure 5The side view of a curtain 30 using a pull cord control device 40 is shown. The pull cord control device 40 can be disposed in an upper beam 31 or a lower beam 32 of the curtain 30. The user can control the opening and closing of the curtain 30 by controlling the height of the lower beam 32 of the curtain 30. When the curtain 30 is in a fully folded state, that is, when the lower beam 32 is at the uppermost position P1, all blades 33 are carried on the lower beam 32. At this time, the force to pull the lower beam 32 is the largest. Accordingly, the variable force coil spring 10 can generate the largest elastic restoring force at the first length L1, which is used to pull the lower beam 32 at the uppermost position P1, so that the curtain 30 is maintained in a fully folded state. During the process of the lower beam 32 being pulled downward, the number of blades 33 carried by the lower beam 32 gradually decreases, and thus the force required to hold the lower beam 32 also gradually decreases. Correspondingly, the elastic restoring force of the variable force coil spring 10 in the first and second force reduction sections S2 and S3 gradually decreases, so that the total weight of the lower beam 32 and the blades 33 it carries, the friction force of the pull rope and the elastic restoring force of the variable force coil spring 10 are balanced as much as possible, thereby allowing the lower beam 32 to stay at any position during the process of being pulled downward, wherein the second length L2 and the third length L3 of the variable force coil spring 10 correspond to a first middle position P2 and a second middle position P3 of the lower beam 32, respectively. The fourth length L4 of the variable force coil spring 10 corresponds to the lowest position P4 of the lower beam 32, and the second intermediate position P3 corresponding to the third length L3 is adjacent to the lowest position P4. The elastic restoring force of the variable force coil spring 10 does not continue to decrease from the third length L3 to the fourth length L4, but remains consistent, so that the lower beam 32 can not only still stay at the lowest position P4, but also, when the user wants to retract the curtain 30 and slightly pushes the lower beam 32 located at the lowest position P4 upward, the elastic restoring force of the variable force coil spring 10 can ensure that the curtain 30 is pulled upward, so that the user can conveniently and easily retract the curtain 30 smoothly.

[0061] In other embodiments, the elastic restoring force generated by the force maintaining section S4 may not be maintained uniformly, but may be slightly increased, such as Figure 6 , Figure 8 and Fig.10 As shown, the force retention section S4 generates a gradually increasing elastic restoring force from the third length L3 to the fourth length L4, and the increasing rate of the elastic restoring force of the force retention section S4 is less than the increasing rate of the elastic restoring force of the outer end section S1 and the decreasing rate of the elastic restoring force of the first and second force decreasing sections S2 and S3. Figure 6 , Figure 8 and Fig.10 The middle length from the third length L3 to the fourth length L4 corresponds to an upward inclined straight line with a minimum slope. Such a design can also ensure that the elastic restoring force of the variable force coil spring 10 can pull the curtain 30 upward, so that the user can conveniently and easily retract the curtain 30 smoothly.

[0062] In other embodiments, Figures 7 to 10 As shown, the decreasing rate of the elastic restoring force in the first force decreasing section S2 may be smaller than the decreasing rate of the elastic restoring force in the second force decreasing section S3. Figure 7 and Figure 8 In the figure, the elastic restoring force of the first force drop section S2 is nonlinear and drops quickly at first and then slowly. Therefore, the length from the first length L1 to the second length L2 corresponds to an arc with a downward trend. It can be seen that the drop rate of the elastic restoring force of the first force drop section S2 described in the utility model is smaller than the drop rate of the elastic restoring force of the second force drop section S3. It is not to compare each point of the first force drop section S2 with the second force drop section S3, but to compare the overall drop rates of the two. Fig. 9 and Fig.10 In the figure, the elastic recovery force of the first force drop section S2 decreases at an approximately constant rate from the first length L1 to the second length L2, so the length from the first length L1 to the second length L2 corresponds to a downward inclined straight line, and the slope of this downward inclined straight line is smaller than the slope of the downward inclined straight line corresponding to the second length L2 to the third length L3.

[0063] If the curtain 30 has a large tolerance during manufacturing, it may produce a poor cushioning effect, causing the user to feel that the lower beam 32 will suddenly drop and be difficult to control when the user pulls the lower beam 32 downward. By designing that the reduction rate of the elastic restoring force of the first force reduction section S2 is smaller than the reduction rate of the elastic restoring force of the second force reduction section S3 as described above, the cushioning effect of the curtain 30 can be improved, thereby avoiding the problem that the lower beam 32 suddenly drops and is difficult to control when being pulled downward.

[0064] The embodiments of the present invention are described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, a person skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A variable force coil spring, characterized in that: The invention comprises a central hole and a belt body wound outward from the central hole, wherein the belt body comprises an inner end located at the central hole, an outer end, and a plurality of sections arranged successively from the outer end toward the inner end, wherein the plurality of sections sequentially comprise: an outer end section extending from the outer end to a first length; a first force decreasing section, generating a gradually decreasing elastic restoring force from the first length to a second length; a second force reduction section, generating a gradually decreasing elastic restoring force from the second length to a third length; and A force maintaining section generates a maintained elastic restoring force from the third length to a fourth length.

2. The variable force coil spring according to claim 1, characterized in that: The force maintaining section generates a consistent elastic restoring force from the third length to the fourth length.

3. The variable force coil spring according to claim 1, characterized in that: The force maintaining section generates a gradually increasing elastic restoring force from the third length to the fourth length, and the increasing rate of the elastic restoring force of the force maintaining section is smaller than the decreasing rate of the elastic restoring force of the first force reduction section and the decreasing rate of the elastic restoring force of the second force reduction section.

4. The variable force coil spring according to any one of claims 1 to 3, characterized in that: The decreasing rate of the elastic restoring force in the first force reduction section is greater than the decreasing rate of the elastic restoring force in the second force reduction section.

5. The variable force coil spring according to any one of claims 1 to 3, characterized in that: The decreasing rate of the elastic restoring force in the first force reduction section is smaller than the decreasing rate of the elastic restoring force in the second force reduction section.

6. The variable force coil spring according to claim 5, characterized in that: The elastic restoring force of the first force reduction section decreases nonlinearly from the first length to the second length and decreases quickly at first and then slowly.

7. A pull rope control device, characterized in that: Contains: a housing; At least one winding wheel and a coil spring winding wheel are rotatably disposed in the housing; and A variable force coil spring includes a center hole and a belt body wound outward from the center hole, wherein the belt body includes an inner end located in the center hole, an outer end, and a plurality of sections arranged successively from the outer end toward the inner end, wherein the variable force coil spring is used to be wound to the coil spring winding wheel under the action of an external force from an initial installation state, wherein when the variable force coil spring is in the initial installation state, the outer end of the belt body is arranged on the coil spring winding wheel, and the sections of the belt body wound from the initial installation state to the coil spring winding wheel sequentially include: a first force decreasing section, generating a gradually decreasing elastic restoring force from a first length to a second length; a second force reduction section, generating a gradually decreasing elastic restoring force from the second length to a third length; and A force maintaining section generates a maintained elastic restoring force from the third length to a fourth length.

8. The pull rope control device according to claim 7, characterized in that: It also includes a coil spring sleeve wheel. The at least one winding wheel, the coil spring winding wheel and the coil spring sleeve wheel are rotatably arranged in the shell, and the variable force coil spring is sleeved on the coil spring sleeve wheel.

9. The pull rope control device according to claim 7, characterized in that: The force maintaining section of the variable force coil spring generates a consistent elastic restoring force from the third length to the fourth length.

10. The pull rope control device according to claim 7, characterized in that: The force maintaining section of the variable force coil spring generates a gradually increasing elastic restoring force from the third length to the fourth length, and the increasing rate of the elastic restoring force of the force maintaining section is smaller than the decreasing rate of the elastic restoring force of the first force reduction section and the decreasing rate of the elastic restoring force of the second force reduction section.

11. The pull rope control device according to any one of claims 7 to 10, characterized in that: The decreasing rate of the elastic restoring force of the first force decreasing section of the variable force coil spring is greater than the decreasing rate of the elastic restoring force of the second force decreasing section.

12. The pull rope control device according to any one of claims 7 to 10, characterized in that: The decreasing rate of the elastic restoring force of the first force decreasing section of the variable force coil spring is smaller than the decreasing rate of the elastic restoring force of the second force decreasing section.

13. The pull rope control device according to claim 12, characterized in that: The elastic restoring force of the first force reduction section of the variable force coil spring decreases nonlinearly from the first length to the second length and first quickly and then slowly.

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