JP2010203531A - Spring mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce friction resistance smaller than ever before in a spring mechanism S without using a transverse slider and achieve a satisfactory equal repulsive force characteristic without causing a cost rise. <P>SOLUTION: The spring mechanism includes a first link 1 having an upper end pivotally supported by a supported side (A) and extending obliquely downward from there, a second link 2 having an upper end pivotally supported by a lower end of the first link (B, C), extending obliquely downward from there to form a [dog leg] shape along with the first link and having a lower end (D) pivotally supported by a supporting side member 5, and a compression coil spring 3 having an upper end coupled to a pin 4 connecting the first and second links 1, 2, extending obliquely downward from there and having a lower end (E, F) coupled to the supporting side member 5. The compression coil spring 3 is put in a pre-compressed state and, as the upper end (A) of the first link 1 receiving the load of a supported body displaces downward, arises while being compressed further. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spring mechanism that supports a supported body by a repulsive force of a spring, and particularly relates to a spring mechanism that has a so-called iso-repulsive force characteristic in which a change in the repulsive force accompanying displacement is very small.

  Conventionally, in a welfare such as a chair for standing up, a medical device or a lift for unloading, so-called iso-repulsive force characteristics with a very small change in repulsive force in order to reduce the burden on the person who uses it. There is a need for a mechanism having For example, in the case of a stand-up auxiliary chair, it has already been proposed to raise and lower the seat of the chair so that even a person with weak legs can sit and stand up easily. A gear, an air bag or the like is used.

  Specifically, when using a spring, the seat of the chair is supported from below by a coil spring or the like, and the human movement is assisted by the repulsive force of the spring. In such a case, in the process of getting up from the chair, As the amount of compression of the spring decreases, the repulsive force decreases, and the repulsive force necessary to stand up may not be obtained.

  On the other hand, when an electric gear, air bag, or the like is used, a gear mechanism, a motor, a control device, an air pump, etc. are required, which increases the weight and becomes expensive. Must be installed or an external power supply must be secured.

In order to solve such problems, the present inventors have proposed a spring mechanism that exhibits a uniform repulsive force characteristic by combining a link mechanism and a slider with a coil spring, and previously filed a patent application (see Patent Document 1). ). In this structure, a main coil spring (primary spring) that receives the load of the supported body is disposed between the upper frame and the lower frame, and a coil spring that applies an upward force to the upper frame via a link and a slider (two The secondary spring has a negative spring characteristic in which the repulsive force decreases as the upper frame descends, so that the change in the total repulsive force combined with the primary spring becomes very small. I am doing so.
JP 2006-55494 A

  However, in the spring mechanism of the conventional example (Patent Document 1), since a support load in the vertical direction is applied to the slider that slides horizontally through the link, there is a problem that the frictional resistance tends to increase. there were.

  In addition to a positive spring characteristic coil spring that receives the load of the supported body, a coil spring that exhibits a negative spring characteristic must be provided, resulting in a slightly complicated structure and an increase in cost. Concerned.

  In view of these points, an object of the present invention is to provide a spring mechanism capable of realizing a constant repulsive force characteristic without causing an increase in cost while reducing a frictional resistance by a new structure that does not use a lateral slider. Is to provide.

  In order to achieve the above object, in the present invention, in particular, the layout of the compression coil spring is devised so that both positive and negative spring characteristics appear by a single coil spring. That is, the invention of claim 1 is a spring mechanism that supports the supported body by the repulsive force of the spring, and includes the first and second two links and the compression coil spring.

  The first link has a load receiving portion at an upper end thereof pivotally supported on the supported side, and is guided to move in the vertical direction, and extends obliquely downward therefrom. The upper end of the second link is pivotally supported by the lower end of the first link, and extends obliquely downward therefrom to form a “<” shape with the first link. The lower end is pivotally supported by the support side. ing.

  The compression coil spring has an upper end portion connected to the lower end side of the first link, while a lower end portion is connected to the support side and is laid out so as to tilt obliquely from above and below. When the load receiving portion of one link is at the upper limit of the movable range, it is in a pre-compressed state that has already been compressed, so that the first link collapses as the load receiving portion is displaced downward therefrom. When it rotates, it gets up while being further compressed.

  With the above configuration, when the load receiving portion at the upper end of the first link is displaced downward as the supported body moves up and down, the first link moves around the lower end so that it falls down as a whole. Similarly, the second link also rotates around the lower end so as to fall while moving downward as a whole, and both are deformed so as to be folded up and down. At this time, the compression coil spring rises around the lower end while being compressed from above with the operation of the first link.

  As a result of the compression, the repulsive force (axial direction) of the coil spring increases, and when it rises, the ratio of the repulsive force in the vertical direction also increases, and the force that lifts the supported body via the first link Will increase. On the other hand, the horizontal ratio of the repulsive force is reduced by waking up in this way, and the lifting force that the horizontal component acts on the supported body via the first link is reduced.

  In other words, the force acting to lift the supported body is a positive spring characteristic that is increased by an increase in the amount of compression, while the repulsive force is generated by the vertical component of the repulsive force of the compression coil spring. Due to the horizontal component force, the negative spring characteristic that decreases as the amount of compression increases, and the uniform repulsive force characteristic can be easily obtained by a single coil spring.

More specifically, when the upper end of the compression coil spring is connected to a support shaft that connects the lower end of the first link and the upper end of the second link, the length of the arm of the second link is L, When the load receiving portion of the first link is at the lower limit of the movable range, if the angle formed by the second link with respect to the horizontal direction is θ _min , the compression coil spring is connected to the lower end portion and the second portion. The layout may be such that the horizontal distance from the lower end of the link is larger than L × cos θ _min and smaller than L × tan θ _min .

  In this way, the compression coil spring always rises while being compressed when the load receiving portion is displaced downward from the upper limit to the lower limit in the movable range, and the action of the invention of claim 1 is achieved. Is obtained.

  Preferably, the first and second links and the compression coil spring are arranged side by side so as to form a symmetrical pair, and the load receiving portions of the first link forming the pair are supported by a common support shaft. (Claim 3). Note that left and right means left and right when viewed in the axial direction of the support shaft connecting the links. In this way, the operation of the spring mechanism is stabilized, and the pair of first links are biased upward by the repulsive forces of the left and right compression coil springs. The force which approaches is applied, and the moving direction becomes a substantially up-down direction.

  In this case, it is more preferable that at least one of the first and second links is connected to the first and second links of the mating counterpart by a tension coil spring (Claim 4). The repulsive force characteristic is improved by the tensile force of the tension coil spring.

  Further, in the above configuration, a restriction link for restricting the operation of the first link is provided, and when the second link rotates around the lower end portion, the load receiving portion at the upper end of the first link is only in the vertical direction. It can also be guided to move (claim 5). Note that the load receiving portion may be guided in the vertical direction by, for example, a slider, and this does not increase the frictional resistance as in the conventional example (Patent Document 1).

  As described above, according to the spring mechanism according to the present invention, since both positive and negative spring characteristics appear by a single compression coil spring, there is no concern about cost increase and a relatively simple structure, and there is no repulsion. A spring mechanism having force characteristics can be realized. There is no need for a horizontal slider, and there is no fear of increased frictional resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the following description of preferable embodiment is only an illustration essentially, and is not intending restrict | limiting this invention, its application thing, or its use.

  FIG. 1 shows a configuration of a spring mechanism S according to the present invention. This is to support the load W of a supported body (not shown) acting from above as indicated by the white arrow in the figure by the repulsive force of the spring (shown as a black arrow P), as will be described later. For example, if it is used as a lifting device (see FIG. 9), a heavy object can be lifted and lowered with a relatively small force. Another possible use of the spring mechanism S is as a pantograph (see FIG. 10).

  The spring mechanism S according to the present invention has a so-called iso-repulsive force characteristic in which the change of the spring force due to the displacement is very small as in the above-described Patent Document 1. As an ideal example, as shown in FIG. 2, the absolute value of the spring constant is the same as the negative value with respect to the normal (positive) spring characteristic in which the spring force increases proportionally with the increase of the displacement x. By combining the spring mechanisms having negative characteristics in parallel with each other in parallel, the total spring force obtained by combining both is made substantially constant regardless of the displacement x.

  As shown in FIG. 1, the spring mechanism S of this embodiment combines four links 1, 1, 2 and 2 in a rhombus shape, and urges the left and right corners upward by compression coil springs 3 and 3, respectively. Yes. The upper two links 1 and 1 (hereinafter referred to as the first link) have their upper ends shared by a common pin 4 (support shaft, which is also a load receiving portion in this example, hereinafter also referred to as point A). It is pivotally supported by a member (not shown) on the supported side, and receives a load W of the supported body via its pin 4.

  The two first links 1 and 1 extend obliquely downward (the left side is the lower left and the right side is the lower right) so as to be gradually separated downward, and the lower two links 2 are provided at the lower ends thereof. , 2 (hereinafter referred to as second link) are pivotally connected by pins 4 (support shafts: point B, point C). The second links 2 and 2 extend obliquely downward so as to gradually approach each other (the left side is the lower right side and the right side is the lower left side), and the lower ends thereof are based on a common pin 4 (support shaft: point D). A side (support side) member 5 is rotatably connected.

  In the example shown in the figure, the upper ends of the compression coil springs 3 and 3 are connected to the pins 4 and 4 (points B and C) at the left and right corners, respectively, so that the first and second links 1 and 2 are rotated. It is possible to move. Each of the compression coil springs 3 and 3 extends obliquely downward (the left side is the lower left and the right side is the lower right) on the side opposite to the second links 2 and 2, and the lower ends thereof are respectively pin 4 ( It is rotatably connected to the foundation side member 5 by a support shaft (E point, F point).

  Furthermore, in this example, when the four links 1, 1, 2 and 2 are substantially square as shown in FIG. When the rhombus links 1, 1, 2 and 2 are folded so as to be crushed from this state, the left and right compression coil springs 3 and 3 are raised while being compressed. The lowest position of the spring mechanism S is when the compression coil spring 3 rises most as shown in FIG.

  The left and right compression coil springs 3 and 3 are assembled in a pre-compressed state so that they are already compressed at the highest position. It is pressing and biasing in the direction. As a result, the pin 4 (point A) that connects the upper ends of the first links 1 and 1 is also subjected to a force that lifts upward and moves toward the center of the left and right. Guided to move in the direction.

  Although not shown, when actually used, it is preferable to provide a stopper mechanism to limit the operation of the spring mechanism S to the range from the highest position to the lowest position. 4 corresponds to the upper limit of the movable range, and the height of point A at the lowest position corresponds to the lower limit.

  As is apparent from the figure, the spring mechanism S is symmetrical with respect to a line segment AD connecting the upper and lower corners of the rhombus link, and the first link 1, the second link 2 and the compression coil spring 3 are paired symmetrically. Is provided. Therefore, it is sufficient to examine the left or right half of the mechanical behavior of the spring mechanism S, and only the left half will be described below with reference to FIGS.

  As shown in FIG. 3, in the left half of the spring mechanism S, the first and second links 1 and 2 are formed in a “<” shape, and the point A is moved up and down by spreading or folding up and down. It is designed to be displaced in the direction. When the point A is at the upper limit (maximum position) of the movable range as shown in FIG. 5A, the compression coil spring 3 has already been compressed by a predetermined amount, and as the point A is displaced downward therefrom, It gets up while being further compressed. As a result, the spring mechanism S exhibits both positive and negative spring characteristics.

Specifically, if the displacement x of point A is positive in the downward direction and x = 0 at the highest position in FIG. 3A, the compression coil spring 3 is already compressed at this highest position. At the point, an initial repulsive force P ₀ is generated in the axial direction of the compression coil spring 3. This initial repulsive force P ₀ can be decomposed into the vertical direction and the horizontal direction as shown in the figure, and they are further decomposed into a force in the axial direction of the first link 1 and a force in a direction perpendicular thereto. The

That is, as shown in FIG. 4 with only the first link 1 taken out, the vertical component force can be decomposed into a force in the link axial direction and a force in the horizontal direction, from the balance of the force in the first link 1 to the point A. Generates a lifting force _F1,0 . Similarly, the horizontal component force can be broken down into a link axial force and a vertical force (shown in FIG. 5), thereby generating a lifting force of F _{2,0 at} point A. The lifting force at point A is expressed as F (x) = F ₁ (x) + F ₂ (x) as a function of the displacement x.

  As the point A moves downward from the highest position and the displacement x increases, the first link 1 rotates around the connecting pin 4 (point B) with the second link 2 in the clockwise direction in the figure, The second link 1 rotates around the connecting pin 4 (point D) with the base member 5 in the counterclockwise direction of the figure, and both are folded while moving downward as a whole (see FIG. 1 (b)). ). At this time, the point B moves diagonally downward to the left on the circumference centering on the point D, and the compression coil spring 3 is compressed, and the counterclockwise direction of the drawing is centered on the lower end (point E). Rotate to get up.

The repulsive force (axial direction) P of the coil spring 3 thus compressed becomes larger than the initial repulsive force P ₀ , and the angle formed with the first link 1 changes as shown in FIG. As shown, the component force in the vertical direction of the repulsive force P increases, and the lifting force F ₁ acting on the supported body via the first link ₁ also increases. As shown in FIG. 5B, the lifting force F ₁ becomes the maximum value F _{1, max} at the lowest position (x = x _max ) of the spring mechanism S.

On the other hand, since the component force in the horizontal direction of the repulsive force P is reduced by raising the compression coil spring 3 in this way, the force F ₂ that lifts the supported body through the first link 1 by this horizontal component force. Becomes smaller and becomes the minimum value F2 _{, min} at the lowest position shown in FIG. 5 (b). At this lowest position, the compression coil spring 3 is in the most raised state, and its axial center is completely in the up-down direction or slightly tilted. When fully up and down, the lifting force F _{2, min} = 0 by the horizontal component force becomes zero.

As described above, the repulsive force of the compression coil spring 3 acting on the supported body via the first link 1 exhibits a positive spring characteristic in which the lifting force F ₁ due to the vertical component force increases with the displacement x, The lifting force F ₂ due to the horizontal component force exhibits a negative spring characteristic that decreases as the displacement increases. In other words, both positive and negative spring characteristics appear in the lifting force to the supported body based on the repulsive force of the single compression coil spring 3, thereby obtaining an equal repulsive force characteristic with a simple structure. Is.

-Layout of compression coil spring-
As described above, in the spring mechanism S, in order to cause the compression coil spring 3 to rise as the point A falls within the movable range, the arm of the second link 2 is schematically shown in FIG. The lower end of the compression coil spring 3 is L, where the angle formed by the second link 2 with respect to the horizontal direction in the state where the point A is the lowest position (x = x _max ) at the lower limit of the movable range is θ _min. It is preferable that the portion (point E) be separated from the lower end portion (point D) of the second link 2 in the horizontal direction by at least L × cos θ _min and at an interval shorter than L × tan θ _min .

If the interval between the point D and the point E is smaller than L × cos θ _min , the upright compression coil spring 3 will fall to the opposite side while the point A is displaced downward. This is because if the distance is more than L × tan θ _min, the compression coil spring 3 that has risen while the point A is displaced downward will fall back to the same side again.

-Optimal example-
FIG. 7 shows an example of the spring mechanism S according to this embodiment, which is optimized so that the variation of the lifting force of the supported body due to the displacement of the point A is minimized. That is, as shown, the angle formed by the second link 2 with respect to the horizontal direction is θ ₁ , the angle formed by the compression coil spring 3 with respect to the horizontal direction is θ _2, and the repulsive force (axial direction) of the compression coil spring 3 is ) Is P, and the weights of the first and second links 1 and 2 are both m, detailed explanation is omitted, but the gravitational acceleration is g and the lifting force F by the spring mechanism S is
F = P (tan θ ₁ cos θ ₂ + sin θ ₂ ) −2 mg (1)

In the spring mechanism S of the present invention, it is desirable that the variation in the magnitude is as small as possible with respect to the displacement at the point A while exhibiting a required lifting force. The variation rate of the lifting force F with respect to changes in ₁ and θ ₂ and the repulsive force P is defined by an average value of deviations from the target value of the lifting force, and this value (average variation rate) is minimized. Just design.

More specifically, the design parameters of the spring mechanism S are, as shown in the figure, the horizontal distance b between the points E and F determined by the heights h _max and h _{min of} the point A at the highest and lowest positions and the dimensions on the foundation side. (basic unit length), the horizontal distance lambda (rotational allowance length of the second link 2) of the point B point E at the lowest position, the spring constant k of the compression coil spring 3, be six of its initial repulsive force P ₀₁ By determining these, the lifting force F at an arbitrary position is determined.

If the required lifting force F, that is, the target value is F ₀ , the average fluctuation rate shown in the following formula (2) as an index representing the fluctuation of the actual lifting force F with respect to the target value F ₀ is shown. δ can be used.

The smaller the average fluctuation rate δ, the smaller the fluctuation of the lifting force F due to the displacement of the point A, and a substantially constant lifting force can be obtained regardless of the displacement. Here, the lifting force F is obtained by the above equation (1), and detailed description thereof is omitted. However, the calculation of the average variation rate δ of the equation (2) is performed by the six design parameters h _max , h _min , In addition to b, λ, k, and P ₀₁ , a lift force target value F ₀ is required. However, since the target value F ₀ , the stroke s (h _max −h _min ) of the point A and the length b of the foundation are often given as design conditions, if these values are fixed, the parameters to be set _Are three points: A point minimum height h _min , rotation allowance length λ, and spring constant k.

For example, given the target value 500N of the lifting force F, the stroke s = 60 mm at point A, and the base part length b = 300 mm, the result of searching for the values of h _min , λ, k so that the average fluctuation rate δ is minimized. The obtained optimum solution is the embodiment shown in the figure. When the relationship between the displacement x of the point A and the lifting force F is obtained by calculation for the spring mechanism S of this embodiment, it becomes as shown in the graph of FIG. 8, and good isotropic force characteristics can be obtained by optimal parameter setting. I understand.

  Therefore, according to the spring mechanism S according to this embodiment, as described mainly with reference to FIGS. 3 to 5, both the positive and negative spring characteristics appear by the single compression coil spring 3. With a relatively simple structure, there is no worry of an increase in cost, and an excellent design such as a good repulsive force characteristic can be obtained by optimal design.

  Further, since a horizontal slider as in the conventional example (Patent Document 1) is not used, even if the load W of the supported body is received in the vertical direction, the frictional resistance is not so large. Moreover, as is clear from FIG. 1 and the like, the repulsive force of the compression coil spring 3 is transmitted to the first link 1 so as to be directed obliquely upward, and the spring repulsive force P is effectively converted to produce a large lifting force F. Can be obtained.

-Application example-
FIG. 9 shows an example in which the spring mechanism S of the above embodiment is applied to an elevating device, in which a substantially constant lifting force is applied to a top plate 10 (a member on the supported side) on which a heavy object is mounted. Since it can be moved up and down with a relatively small force, the height of the top board 10 on which a TV, a personal computer, a water tank or the like is mounted can be easily adjusted. Moreover, if it applies to a care bed or an auxiliary chair, the burden on the caregiver or the user can be reduced.

  Specifically, in the example shown in the figure, the left and right halves of the spring mechanism S of FIG. 1 are shifted in the front-rear direction to give depth. Further, the left half part and the right half part are arranged so as to overlap each other when viewed in the front-rear direction, thereby achieving compactness. In such a case, it is necessary to guide the upper end (point A) of the first link 1 so as to move in the vertical direction. For this purpose, a restriction link 6 that restricts the operation of the first link 1 is provided in the illustrated example.

  The lower end portion of the restriction link 6 is pivotally supported by the base side member 5 by the pin 4, and the upper end portion is pivotally supported by the pin 4 on the extending portion 1 a extending further downward from the lower end portion of the first link 1. Thereby, when the 2nd link 2 rotates around the lower end part (D point), the upper end part (A point) of the 1st link 1 comes to move only to an up-down direction.

  FIG. 10 shows an application example to a pantograph, which is a current collector for a train. In general, in the pantograph, the contact force with the overhead line fluctuates due to a change in height due to a change in the tension between the node position and the abdominal position of the overhead line or the running vibration of the train. When such a line-separation phenomenon occurs, a spark is generated between the overhead wire and the hull, causing problems such as wear, disconnection, noise, etc., and stable current collection becomes difficult, which may adversely affect the running of the train. There is also.

  Therefore, if the spring mechanism S of this embodiment is applied to a pantograph so that the boat body 20 (supported member) is attached to the upper end of the first link 1 as shown in the figure, the height of the boat body 20 is increased. Regardless of the change, the contact force with the overhead wire 30 can be kept substantially constant, and the above-mentioned problems can be prevented in advance. In addition, the code | symbol 31 of illustration is a roof of a train, and the foundation | substrate side member 5 is arrange | positioned on it.

-Other embodiments-
The spring mechanism according to the present invention is not limited to the structure of the above-described embodiment, but includes various other structures. That is, for example, in the spring mechanism S as shown in FIGS. 9 and 10, the operation of the first link 1 is restricted by the restriction link 6, and the upper end portion (point A) is guided so as to move only in the vertical direction. For example, the point A may be guided by a vertical slider. Since the load of the supported body acts in the vertical direction, the frictional resistance does not increase so much even if the vertical slider is provided.

  Further, when the first and second links 1 and 2 are provided in a rhombus shape as shown in FIG. 1, when the vertical stroke at point A increases, the relationship between the displacement x and the lifting force F deviates from linearity, As shown schematically in FIG. 11 (b) by a broken line graph, it has been found that the characteristic is a quadratic function that is convex downward. Conventionally, when the left and right corners of the rhombus link are connected to each other by a lateral tension spring, the lifting force due to the repulsive force of this spring is a quadratic function that protrudes upward as shown by the dashed-dotted line graph in FIG. It is known to show typical characteristics.

  Therefore, the pins 4 and 4 (points B and C) at the left and right corners of the rhombus formed by the first and second links 1 and 2 of the spring mechanism S are connected by the tension coil spring 7 as shown in FIG. Then, as shown by the solid line graph, the two characteristics cancel each other, and the fluctuation of the lifting force accompanying the displacement of the point A in the spring mechanism S is further reduced. As shown in the drawing, the tension coil spring 7 does not need to connect the pins 4 and 4 (points B and C) at the left and right corners, and may connect the first links 1 and 1 to each other. In addition, at least one of the second links 1 and 2 may be connected to the counterpart first to second links 1 and 2 that form a pair.

  In the embodiment described above, the pair of first and second links 1 and 2 and the compression coil spring 3 are provided as the spring mechanism S in a bilaterally symmetrical manner. Only one half may be provided, or a plurality of pairs may be provided. Further, as shown in FIG. 1, it is not necessary to pivotally support the upper ends of the first links 1 and 1 that make a pair with each other on the supported side by the common pin 4. It may be.

  Further, the first and second links 1 and 2 may not be the same, and may be different in length, thickness, weight, or the like. The upper end of the compression coil spring 3 does not have to be connected to the pin 4 and may be connected to the first link 1 or the second link 2.

  As described above, the spring mechanism of the present invention has a relatively simple structure and is capable of obtaining a repulsive force characteristic, and there is no fear of increasing the frictional resistance or increasing the cost. It is suitable for.

It is a schematic block diagram of the spring mechanism which concerns on embodiment. It is explanatory drawing of an ideal iso-repulsive force characteristic. It is a figure explaining the dynamic behavior of a spring mechanism about the left half part. It is explanatory drawing of the lifting force by the up-down direction component of the repulsive force of a spring. It is explanatory drawing of the lifting force by the horizontal direction component of the repulsive force of a spring. It is explanatory drawing of the layout of a compression coil spring. FIG. 2 is a view corresponding to FIG. 1 according to an optimized embodiment of a spring mechanism. It is a graph which shows the relationship between the displacement and lifting force of the Example. It is a schematic block diagram of the example applied to the raising / lowering apparatus. It is a schematic block diagram of the example applied to the pantograph. It is the FIG. 1 equivalent view which concerns on other embodiment which provided the tension coil spring of horizontal orientation.

S spring mechanism 1 first link 2 second link 3 compression coil spring 4 pin (support shaft)
5 Foundation side (support side) member 6 Restriction link 7 Tension coil spring 10 Top plate (supported side member)
20 Hull (member on the supported side)

Claims (5)

A spring mechanism for supporting a supported body by a repulsive force of a spring;
A first link that is pivotally supported on the supported side at the upper end and guided so as to move in the vertical direction, and extends obliquely downward therefrom;
A second link whose upper end is pivotally supported by the lower end of the first link and extends obliquely downward from the first link to form a "<" shape with the first link, and the lower end is pivotally supported on the support side. When,
A compression coil spring having an upper end connected to the lower end side of the first link, extending obliquely downward therefrom, and a lower end connected to the support side;
The compression coil spring is in a pre-compressed state that is already compressed when the load receiving portion of the first link is at the upper limit of its movable range, and the first link is moved in accordance with the downward displacement of the load receiving portion. As it falls down, it is laid out to get up while being further compressed,
A spring mechanism characterized by that. The upper end of the compression coil spring is connected to a support shaft that connects the lower end of the first link and the upper end of the second link,
The length of the arm of the second link is L,
When the load receiving portion of the first link is at the lower limit of the movable range, the angle formed by the second link with respect to the horizontal direction is θ _min ,
The compression coil spring is laid out so that a horizontal interval between a lower end portion thereof and a lower end portion of the second link is larger than L × cos θ _min and smaller than L × tan θ _min. 2. The spring mechanism according to 1. The first and second links and the compression coil spring are provided in pairs symmetrically side by side,
3. The spring mechanism according to claim 1, wherein the load receiving portions of the first links that are paired with each other are pivotally supported on the supported side by a common spindle.   4. The spring mechanism according to claim 3, wherein at least one of the first and second links is connected to a mating first or second link and a tension coil spring. 5.   When the second link rotates around its lower end, a restriction link is provided to restrict the operation of the first link so that the load receiving portion at the upper end of the first link moves only in the vertical direction. The spring mechanism according to any one of claims 1 to 4.

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