JP5432645B2 - Self-weight compensation mechanism - Google Patents

Description

  The present invention relates to a technique for offsetting or reducing the influence of the weight of an object in a mechanism for holding, moving, and the like of the object having a weight.

  In a working robot, an imaging device fixture, and the like, a self-weight compensation mechanism that can cancel the self-weight of an object to be operated by a mechanical configuration is used. By providing such a self-weight compensation mechanism, the power for maintaining the object in a stationary state can be unnecessary or reduced.

  In Patent Document 1 and Patent Document 2, one end of the wire is connected to a tension spring, and the other end is fixed to a predetermined fixing member via a pulley, and the weight of the object and the arm member is compensated by the elastic force of the tension spring. A mechanism is disclosed.

  In Patent Document 3, a cam member that is displaced according to the rotation of an arm member, a cam follower that abuts on the cam surface of the cam member, and an elastic force that presses the cam follower against the cam surface side and is stored in a storage member. There is disclosed an armrest characterized in that the cam surface has a shape that generates torque that repels rotation of the arm member in a predetermined direction.

  In Patent Document 4, Patent Document 5, and Patent Document 6, other self-weight compensation mechanisms are exemplified.

JP 2007-119249 A JP 2003-181789 A JP 2007-190162 A JP-T-2004-520558 JP 2004-1000074 A JP 2006-282300 A

  The mechanisms disclosed in Patent Document 1 and Patent Document 2 require mechanisms such as the wire and the pulley. These mechanisms have a problem that it is difficult to improve durability and are not suitable for use in a high load state. Further, the mechanism disclosed in Patent Document 3 assumes an armrest, and is uneasy about operational stability and the like when used in a high load state.

  In view of the above problems, an object of the present invention is to provide a self-weight compensation mechanism that is excellent in durability, operational stability, and the like.

One embodiment of the present invention includes an arm member that holds an object and rotates around a rotation axis, and is displaced according to the rotation of the arm member, and a distance from the rotation axis changes according to the displacement. A cam member having a cam surface formed thereon, a driven member that is in contact with the cam surface and is displaced in accordance with the displacement of the cam member, and an elasticity having an elastic force in a direction in which the driven member is pressed against the cam surface. a member, a pinion coupled to the arm member, meshing with the pinion, and a rack member coupled to the cam member, that converts the rotation of the arm member into linear motion of the cam member itself It is a heavy compensation mechanism.

According to another aspect of the present invention, there is provided an arm member that holds an object and rotates around a rotation axis, and is displaced according to the rotation of the arm member, and from the rotation axis according to the displacement. A cam member having a cam surface with a variable distance ; a driven member that is in contact with the cam surface and is displaced according to the displacement of the cam member; and an elastic force in a direction in which the driven member is pressed against the cam surface. and an elastic member which causes indirectly caused, and a link member for transmitting before SL driven member the elastic force of the elastic member, the driven member to one end of said link member is connected, the other of said link members One end of the elastic member is connected to the link member between the rotation shaft and the driven member, and the link member is parallel to the rotation surface of the arm member. From a member that rotates on a flat surface That is a weight compensation mechanism.

  According to the above aspect, when the object and the arm member are displaced in the direction of gravity, a torque is generated that prevents the cam member from being displaced. This torque can be set as appropriate depending on the shape of the cam surface, the structure of the link member, and the like, and this can correspond to the weight of the object and the arm member. As a result, the arm member can be operated only by a pure torque applied by an actuator, an operator, or the like. Further, according to the above aspect, the operation of the mechanism can be stabilized.

In the above other embodiments, the have a load member fixed to the link member, that this by the weight of the load member, the driven member is Ru is increased pressure in contact with the cam surface, those Is preferred. As a result, the operation can be further stabilized.

The cam member may include at least two cam surfaces. In such an aspect, it is preferable that the cam member has a line-symmetric or point-symmetric shape. Furthermore, the first and second driven members that are in contact with the first and second cam surfaces, respectively, and a mechanism that pressurizes the first and second driven members toward the rotation shaft of the cam member, respectively. Are preferably provided. By such an aspect, further stabilization of the operation can be achieved. Further, since the elastic force of the elastic member is applied to the cam member from both sides substantially evenly, the load on the member such as the rotating shaft is greatly reduced. This makes it possible to improve durability and life, use a small and inexpensive bearing, and the like.

  According to another aspect of the present invention, there is provided an arm member that holds an object and rotates around a rotation axis, and is displaced according to the rotation of the arm member, and from the rotation axis according to the displacement. A cam member having a cam surface with a variable distance; a driven member that is in contact with the cam surface and is displaced according to the displacement of the cam member; and an elastic force in a direction in which the driven member is pressed against the cam surface. And a link member that transmits the elastic force of the elastic member to the driven member, and the link member is L-shaped, and the L-shaped bent portion. Is a self-weight compensation mechanism composed of a member rotating on a plane parallel to the rotation surface of the arm member, with the driven member connected to one end and the elastic member connected to the other end.

  According to the present invention, it is possible to provide a self-weight compensation mechanism that does not require a wire, a pulley, or the like. This makes it possible to provide a self-weight compensation mechanism that is excellent in durability, operational stability, and the like.

It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the cam member which concerns on the said Embodiment 2. FIG. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 3 of this invention. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 4 of this invention. It is a figure which shows the structure of the self-weight compensation mechanism which concerns on Embodiment 5 of this invention. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 6 of this invention. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 7 of this invention. It is a figure which shows the structure of the dead weight compensation mechanism which concerns on Embodiment 8 of this invention. It is a figure which shows the structure of the self-weight compensation mechanism which concerns on Embodiment 9 of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that, in different embodiments, portions having the same or similar operational effects are denoted by the same reference numerals and description thereof is omitted.

Embodiment 1
FIG. 1 shows the configuration of a self-weight compensation mechanism 1 according to Embodiment 1 of the present invention. The self-weight compensation mechanism 1 includes an arm member 2, a cam member 3, a driven member 4, and an elastic member 5.

  The arm member 2 is provided with a mechanism capable of holding an arbitrary object 10 at the tip thereof, and the rear end thereof is pivotally supported by a predetermined fixing member by a rotation shaft 11. The arm member 2 according to the present embodiment is a rod-shaped member having no joint mechanism. The object 10 has a predetermined mass M and generates a weight Mg in the vertical direction (downward in the figure). The arm member 2 according to the present embodiment is fixed to a pinion 12 that can rotate around the rotating shaft 11. As a result, the pinion 12 rotates together with the arm member 2.

  The cam member 3 has a cam surface 15 and is fixed to a rack 16. The rack 16 meshes with the pinion 12 and slides in the arrow A direction according to the rotation of the pinion 12. With this configuration, the cam member 3 slides in the direction of arrow A on the same plane as the pinion 12 rotates (displacement of the arm member 2 and the object 10). The cam surface 15 is formed of a smooth curved surface, and in the present embodiment, the cam surface 15 has a shape in which the height y gradually increases in the direction of the arrow x.

  The driven member 4 abuts on the cam surface 15 and is displaced along the shape of the cam surface 15. As the driven member 4, for example, a mechanism such as a wheel can be applied.

  The elastic member 5 has an elastic force in a direction (indicated by an arrow F in the drawing) in which the driven member 4 is pressed against the cam surface 15. As the elastic member 5, for example, a coil spring or the like can be applied.

  According to the present embodiment, when the object 10 and the arm member 2 are displaced downward in the figure, the arm member 2 and the pinion 12 are rotated in the direction in which the rotation angle θ increases (the direction of the arrow). Then, the rack 16 and the cam member 3 slide to the right side in the drawing. At this time, the height y of the cam surface 15 where the passive member 4 contacts gradually increases, the amount of deflection of the elastic member 5 increases, and the pressure in the arrow F direction increases. This prevents the cam member 3 and the rack 16 from sliding to the right in the figure, the pinion 12 and the arm member 2 from rotating in the increasing direction of the rotation angle θ, and the object 10 from being lowered.

  In the above configuration, the shape of the cam surface 15, the spring constant of the elastic member 5, the pinion 12 and the rack 16 correspond to the weight of the object 10 and the arm member 2, the length of the arm member 2, and the like. By appropriately setting the gear ratio and the like, it is possible to construct a mechanism that can effectively compensate (cancel) the dead weights of the object 10 and the arm member 2.

Embodiment 2
FIG. 2 shows the configuration of the self-weight compensation mechanism 21 according to Embodiment 2 of the present invention. The self-weight compensation mechanism 21 is different from the self-weight compensation mechanism 1 according to the first embodiment in the shape of the cam member 23 and the connection structure between the arm member 2 and the cam member 23.

  The arm member 2 according to the present embodiment is fixed to a rotating plate 22. The rotating plate 22 is pivotally supported so as to be rotatable about the rotating shaft 11. The cam member 23 is directly fixed to the rotating plate 22.

  FIG. 3 shows the shape of the cam member 23 according to the present embodiment. The cam member 23 has a cam surface 25 and a flat surface 26. The cam surface 25 is a portion with which the driven member 4 comes into contact, and is composed of smooth curved surfaces with different curvatures. The curvature decreases as the rotation angle α increases (in the direction of the arrow). A rotation center portion 27 is formed on the flat surface 26. The rotation center portion 27 is a portion fixed to the rotation shaft 11 and is formed at a position shifted to the right side in the drawing from the center portion of the flat surface 26. The distance r indicates the distance from the rotation center portion 27 to the cam surface 25. The distance r increases as the rotation angle α increases.

  According to the present embodiment, when the object 10 and the arm member 2 are displaced downward in the drawing, the arm member 2, the rotating plate 22, and the cam member 23 are in the direction in which the rotation angle θ increases. To turn. At this time, the portion of the cam surface 25 that is in contact with the passive member 4 moves in the direction in which the rotation angle α increases. That is, the distance r gradually increases, the amount of deflection of the elastic member 5 increases, and the pressure in the arrow F direction increases. Thereby, the dead weights of the object 10 and the arm member 2 are compensated.

Embodiment 3
FIG. 4 shows the configuration of the self-weight compensation mechanism 31 according to Embodiment 3 of the present invention. The self-weight compensation mechanism 31 is different from the self-weight compensation mechanism 21 according to the second embodiment in that a link member 32 is provided.

  The link member 32 indirectly transmits the elastic force of the elastic member 35 to the driven member 4. The link member 32 according to the present embodiment is a rod-shaped member, and one end portion thereof is pivotally supported by the rotation shaft 33 so as to be rotatable in the direction of arrow C. The driven member 4 is fixed to the other end portion of the link member 32. One end of the elastic member 35 is fixed to a predetermined immovable portion 36, and the other end is fixed to an intermediate portion (between the one end and the other end) of the link member 32. The elastic member 35 has an elastic force in the arrow D direction.

  According to the present embodiment, when the object 10 and the arm member 2 are displaced downward in the drawing, the tensile amount of the elastic member 35 increases and the pressure in the direction of the arrow F increases. As described above, by interposing the link member 32 between the driven member 4 and the elastic member 35, the operation of the driven member 4 and the like can be stabilized.

Embodiment 4
FIG. 5 shows the configuration of the self-weight compensation mechanism 41 according to Embodiment 4 of the present invention. The self-weight compensation mechanism 41 differs from the self-weight compensation mechanism 31 according to the third embodiment in the shape of the cam member 43, the connection structure between the link member 32 and the elastic member 35, and the like.

  The cam member 43 is a disk-like member having a perforated portion 44. The drilling portion 44 has a cam surface 45 and a flat surface 46. The cam surface 45 corresponds to the cam surface 25 according to the second and third embodiments. The curvature of the cam surface 45 according to the present embodiment becomes smaller toward the right side in the figure. On the flat surface 46, a rotation center portion 47 corresponding to the rotation center portion 27 (see FIG. 3) according to the second embodiment is formed. The rotation center portion 47 is formed at a position shifted to the left in the drawing from the center portion of the flat surface 46. The cam member 43 is directly fixed to the arm member 2 and rotates together with the arm member 2 about the rotation shaft 11. The driven member 4 abuts on the cam surface 45 in the drilling portion 44. The elastic member 35 is connected to an intermediate portion of the link member 32 and has an elastic force in the direction of arrow E.

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the figure, the cam member 43 rotates in a direction in which the rotation angle θ increases. At this time, the curvature of the portion of the cam surface 45 where the passive member 4 contacts gradually increases, the amount of tension of the elastic member 35 increases, and the pressure in the arrow G direction increases. Thereby, the dead weights of the object 10 and the arm member 2 are compensated.

Embodiment 5
FIG. 6 shows the configuration of the self-weight compensation mechanism 51 according to the fifth embodiment of the present invention. The self-weight compensation mechanism 51 is different from the self-weight compensation mechanism 41 according to the fourth embodiment in that the cam member 53 has a shape, a weight member 58, and the like.

  The cam member 53 has a shape in which the cam member 23 shown in FIG. 3 is integrated by reversing the flat surface 26 with a symmetrical line. The cam member 53 includes the cam surfaces 25 at the top and bottom in the drawing, and the curvatures of both the cam surfaces 25 are both larger toward the right side and smaller toward the left side in the diagram. The cam member 53 is formed with a rotation center portion 57 corresponding to the rotation center portion 27. The cam member 53 is directly fixed to the arm member 2 and rotates together with the arm member 2 about the rotation shaft 11.

  As in the third or fourth embodiment, one end of the link member 32 is pivotally supported by the rotating shaft 33 and the other end is fixed to the driven member 4. The elastic member 35 is connected to an intermediate portion of the link member 32 and the load member 58 is fixed. The elastic member 35 has an elastic force in the arrow H direction. The load member 58 has a mass m and generates a weight mg in the vertical direction.

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the figure, the amount of deflection of the elastic member 35 increases due to the shape of the cam surface 25, and the pressure in the direction of the arrow F increases. Further, the weight mg of the load member 58 is applied to the cam surface 25. As a result, the weight of the object 10 and the arm member 2 can be compensated for using the elastic member 35 having a smaller spring constant than the other embodiments.

Embodiment 6
FIG. 7 shows a configuration of a self-weight compensation mechanism 61 according to the sixth embodiment of the present invention. The notable points of the self-weight compensation mechanism 61 are the shape of the cam member 63, the arrangement of the driven member 64 and the elastic member 65, and the like.

  The cam member 63 has a shape obtained by rotating the cam member 23 according to the second embodiment shown in FIG. 3 by 180 ° with the rotation center portion 27 as a symmetry point. The cam members 63 are arranged such that the cam surfaces 25 are positioned on the upper and lower sides in the drawing. The curvature of the upper cam surface 25 decreases as it goes to the left in the figure, and the curvature of the lower cam surface 25 decreases as it goes to the right in the figure. The cam member 63 is directly fixed to the arm member 2 and rotates together with the arm member 2 about the rotation shaft 11.

  The driven member 64, the elastic member 65, the guide member 67, and the base member 68 are provided corresponding to the two cam surfaces 25, respectively. The driven member 64 is constituted by wheels or the like and is pivotally supported by the guide member 67. One end of the elastic member 65 is fixed to the guide member 67, and the other end is fixed to the base member 68. The base member 68 is a stationary member that is fixed to a casing or the like of the apparatus main body. In the present embodiment, the two elastic members 65 are disposed between the pair of guide members 67 and the base member 68. The elastic member 65 has an elastic force in the direction of arrow I. In addition, it is preferable that the said structure is designed so that the practical movable range of the said cam member 63 may be about rotation angle (beta).

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the drawing, the amount of deflection of each elastic member 65 increases due to the shape of the cam surface 25, and the pressure in the direction of arrow J increases. To do. Thereby, the dead weights of the object 10 and the arm member 2 are compensated. Thus, in the present embodiment, the cam member 63 has a point-symmetric shape, and the elastic force of the elastic member 65 acts from the vertical direction of the cam member 63. As a result, the operation can be stabilized. Further, since the elastic force of the elastic member 65 is applied to the cam member 63 from the vertical direction substantially evenly, the load on the members such as the rotating shaft 11 is greatly reduced. As a result, it is possible to realize improvement in durability and life, cost reduction by using a small and inexpensive bearing, and the like.

Embodiment 7
FIG. 8 shows the configuration of the self-weight compensation mechanism 71 according to Embodiment 7 of the present invention. The self-weight compensation mechanism 71 differs from the self-weight compensation mechanism 61 according to the sixth embodiment in the arrangement of the cam member 63, the elastic member 75, the guide member 76, and the like.

  The cam member 63 is arranged so that the cam surfaces 25 are positioned on the left and right sides in the figure. The cam member 63 is fixed to the arm member 2 and rotates together with the arm member 2. The driven member 64 is pivotally supported by the guide member 76 and abuts on the cam surfaces 25. The two guide members 76 are arranged such that their longitudinal directions are along the vertical direction in the drawing. The elastic member 75 is disposed between the two guide members 76. Both end portions of the elastic member 75 are fixed to opposite end portions of the both guide members 76. The elastic member 75 has an elastic force in the arrow K direction.

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the figure, the tensile amount of each elastic member 75 increases due to the shape of the cam surface 25, and the pressure in the direction of the arrow L increases. To do. Thereby, the dead weights of the object 10 and the arm member 2 are compensated. Even with such a configuration, the elastic force of the elastic member 75 can be applied from both sides of the cam member 63, so that the operation can be stabilized. In the present embodiment, since the elastic member 75 is disposed between the guide members 76, a member corresponding to the pedestal member 68 according to the sixth embodiment can be eliminated. Thereby, in addition to the effects described in the sixth embodiment, it is possible to reduce the mechanism and reduce the weight.

Embodiment 8
FIG. 9 shows a configuration of a self-weight compensation mechanism 81 according to Embodiment 8 of the present invention. The self-weight compensation mechanism 81 differs from the self-weight compensation mechanism 71 according to the seventh embodiment in the structure of the link member 86 and the elastic member 85.

  The link member 86 has an L shape. The bent portion of the link member 86 is pivotally supported by a rotation shaft 82 so as to be rotatable. The driven member 64 is pivotally supported at one end of the link member 86, and one end of the elastic member 85 is fixed to the other end 83. The other end 84 of the elastic member 85 is fixed to a stationary part such as a casing. The elastic member 85 has an elastic force in the arrow M direction.

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the figure, the tensile amount of the elastic member 86 is increased due to the shape of the cam surface 25 and the pressure in the direction of the arrow L is increased. . Thereby, the dead weights of the object 10 and the arm member 2 are compensated. Even with such a configuration, the elastic force of the elastic member 85 can be applied from both sides of the cam member 63, so that the operation is stabilized, the burden on the rotary shaft 11 and the like is reduced, and the durability / lifetime is improved. Improvement and cost reduction can be achieved. Further, according to the present embodiment, it is not necessary to use a plurality of the elastic members 85.

Embodiment 9
FIG. 10 shows the configuration of the self-weight compensation mechanism 91 according to Embodiment 9 of the present invention. The self-weight compensation mechanism 91 is different from the self-weight compensation mechanism 81 according to the eighth embodiment in the structure of the link member 96 and the elastic member 95.

  One end of the link member 96 is pivotally supported by a rotating shaft 92. The other end portion 93 of the link member 96 is swingable. One end of the elastic member 95 is fixed to the rotating shaft 92. The other end of the elastic member 95 is fixed to the other end 93 of the link member 96. The elastic member 95 has an elastic force in the arrow N direction. The driven member 64 is pivotally supported at an intermediate portion of the link member 96 and abuts on the cam surface 25.

  According to the above configuration, when the object 10 and the arm member 2 are displaced downward in the figure, the tensile amount of the elastic member 95 is increased due to the shape of the cam surface 25 and the pressure in the direction of the arrow L is increased. . Thereby, the dead weights of the object 10 and the arm member 2 are compensated. Even with such a configuration, the elastic force of the elastic member 95 can be applied from both sides of the cam member 63, so that the operation is stabilized, the burden on the rotary shaft 11 and the like is reduced, and the durability and life span are improved. Improvement and cost reduction can be achieved.

  Note that the present invention is not limited to the above-described embodiment, and can be appropriately changed, replaced, combined, and the like without departing from the spirit of the present invention.

1, 11, 21, 31, 41, 51, 61, 71, 81, 91 Self-weight compensation mechanism 2 Arm member 3, 23, 43, 53, 63 Cam member 4, 64 Drive member 5, 35, 65, 75, 85 , 95 Elastic member 15, 25, 45 Cam surface 32, 86, 96 Link member 58 Load member 67, 76 Guide member

Claims (8)

Holding the object, and the arm member you rotate about an axis of rotation,
A pinion connected to the arm member;
A rack member that meshes with the pinion and linearly moves by rotation of the arm member ;
The rack member is connected to the rack member and linearly moves with the linear motion of the rack member , and the linear motion of the rack member is converted into a linear motion in the y direction that is orthogonal to the linear motion direction of the rack member. A cam member having a cam surface for
A driven member that contacts the cam surface and linearly moves in the y direction in response to the linear motion displacement of the cam member;
And an elastic member having an elastic force in a direction for pressing the driven member to the cam surface,
The cam surface is
A shape in which the distance from the rack member in the y direction gradually increases so as to gradually push the driven member against the elastic force as the arm member rotates in the direction in which the object moves downward. Is
A self-weight compensation mechanism characterized by that . Holding the object, and the arm member you rotate about an axis of rotation,
The cam member is connected to the arm member and rotates with the rotation of the arm member, and has a cam surface for converting the rotation of the arm member into a linear motion in a direction perpendicular to the rotation axis of the arm member. A cam member;
A driven member for linear movement displaced the cam surface contact, depending on the rotational movement of the cam member,
An elastic member that indirectly generates an elastic force in a direction in which the driven member is pressed against the cam surface;
A link member that transmits the elastic force of the elastic member to the driven member;
The driven member is connected to one end of the link member, and the rotation shaft of the link member is connected to the other end of the link member,
One end of the elastic member is connected to the link member between the rotation shaft of the link member and the driven member,
The link member is Ri Do a member which rotates on a plane parallel to the rotation plane of the arm member,
The cam surface is
A shape in which the distance of the arm member from the rotation axis gradually changes so that the driven member is gradually pushed against the elastic force as the arm member rotates in the direction in which the object moves downward. Is
Self weight compensation mechanism, characterized in that. In the self-weight compensation mechanism according to claim 2,
A load member is fixed to the link member, and the weight of the load member increases the pressure with which the driven member abuts the cam surface.
Self weight compensation mechanism, characterized in that. In the self-weight compensation mechanism according to claim 2 or claim 3,
The cam member includes at least two cam surfaces.
Self weight compensation mechanism, characterized in that. In the self-weight compensation mechanism according to claim 4,
The cam member, that have a shape of a line symmetry
Self weight compensation mechanism, characterized in that. In the self-weight compensation mechanism according to claim 4,
The cam member, that have a shape of point symmetry
Self weight compensation mechanism, characterized in that. In the self-weight compensation mechanism according to claim 5 or 6,
The first and second driven members abutting on the first and second cam surfaces, respectively;
And a mechanism for pressurizing toward the axis of rotation of the first and second driven members respectively said cam member
Self weight compensation mechanism, characterized in that. Holding the object, and the arm member you rotate about an axis of rotation,
The cam member is connected to the arm member and rotates with the rotation of the arm member, and has a cam surface for converting the rotation of the arm member into a linear motion in a direction perpendicular to the rotation axis of the arm member. A cam member;
A driven member that comes into contact with the cam surface and linearly moves in accordance with the rotational movement of the cam member;
An elastic member that indirectly generates an elastic force in a direction in which the driven member is pressed against the cam surface;
A link member that transmits the elastic force of the elastic member to the driven member;
The link member is L-shaped, the L-shaped bent portion is a rotation axis, the driven member is connected to one end, the elastic member is connected to the other end, and the rotation surface of the arm member Do a member which rotates on a plane parallel to the Ri,
The cam surface is
A shape in which the distance from the rotation shaft of the arm member gradually increases so that the driven member is gradually pushed against the elastic force as the arm member rotates in the direction in which the object moves downward. Is
Self weight compensation mechanism, characterized in that.

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