JP4489097B2 - Seismic isolation device - Google Patents

Description

  The present invention relates to a seismic isolation bearing device that is displaced in the vertical direction at the time of displacement or deformation isolation (specifically, a seismic isolation ball bearing device or a laminated rubber bearing device using a conical or mortar-shaped rolling plate). Further, the present invention relates to a device for preventing the seismic isolation from rising, which is provided in the seismic isolation bearing device that performs horizontal displacement.

  In the conventional technology for horizontal sliding base isolation bearings and horizontal rolling base isolation bearings, the upper and lower linear guide rails can be easily constrained vertically by, for example, slidably engaging each other in the horizontal direction. In addition, various types of seismic isolation floating prevention devices of the horizontal sliding bite type are widely used.

  However, in a base-isolated ball bearing device using a conical or mortar-shaped rolling plate, the base-isolating ball repeatedly rolls up and down along the surface of the rolling plate and displaces at the time of rolling isolation. For this reason, it is not possible to use a lift prevention device that is slidably bitten in the horizontal direction. Further, in the laminated rubber bearing device, when the laminated rubber is deformed horizontally during a horizontal earthquake, the seismic isolation rubber sinks downward, so that the horizontal sliding bite type anti-lifting device cannot be used.

  In the above-mentioned conventional horizontal sliding bite type various seismic isolation object lifting prevention devices such as sliding between the upper straight guide rail and the lower straight guide rail in the horizontal direction, the biting portion The sliding friction resistance is large because it is necessary to precisely bite the two without gaps.

  In the seismic isolation bearing device that is displaced in the vertical direction at the time of displacement or deformation isolation, the configuration can follow the vertical displacement of the seismic isolation bearing continuously and continuously to prevent lifting. There is no simple and inexpensive conventional anti-seismic object floating prevention device.

  The present invention relates to a seismic isolated object lifting prevention device having a simple structure and a seismic isolation bearing that is horizontally displaced, which can be used in combination with a seismic isolation bearing device that is displaced in the vertical direction during displacement or deformation isolation. It is an object of the present invention to provide a seismic isolated object lifting prevention device with a simple structure and a small frictional resistance that can be used in combination with the device at low cost.

  According to the first aspect of the present invention, in the space portion between the base plate on which the seismic isolation bearing device that is displaced in the vertical direction at the time of displacement or deformation isolation is disposed, and the base of the seismic isolation object, the space portion is placed at an appropriate position. , Made of a rigid body with a predetermined effective length and a predetermined shape, with the base plate side roller body on the upper side and the base lower roller body on the lower side, horizontally in the center of each length It is allowed to rotate freely and orthogonally crossed, the rotating shafts protrude from the center of both ends of both roller bodies, and support pedestals with rotating bearings are arranged and supported at both ends of each rotating shaft, Seismically isolated with vertical displacement at the time of seismic isolation displacement, with the support base of the base plate side roller body firmly screwed to the base plate and the support base of the lower base roller body under the base. It is the structure of the seismic isolation object floating prevention apparatus attached to a support apparatus.

  The appropriate place of the space portion is a space portion that has no trouble during the base isolation operation of the base isolation bearing device or the laminated rubber bearing device using a conical rolling board.

  The predetermined effective length of the base plate side and base lower roller body is the amount of earthquake design horizontal displacement or twice the required horizontal displacement to the diameter of the base plate side roller body and base lower roller body. It is the length obtained by adding (total amplitude).

  The predetermined shape of the base plate side and the base lower roller body is a seismic isolation device using a conical rolling plate, and is required when a conical rolling plate is used for the lower rolling plate. Both sides of the frustoconical roller rolling surface are widened from the entire circumference of both ends of the base plate side roller body having a diameter toward the center point of the length using the inclination angle of the conical rolling plate. The shape is formed by combining the bottom surfaces of both cones at the center point of the length. Further, the inclination angle of the conical rolling plate is used in an expanded form from the entire circumference of the center point of the base lower roller body having the required diameter toward both ends of the roller body. Thus, a truncated cone-shaped roller rolling surface having both ends of the roller body as conical bottom surfaces is formed on both sides.

  In the case of a seismic isolation bearing device using a conical rolling plate, when the conical rolling plate is used as the upper rolling plate, the entire circumference of the center point of the base plate side roller body having the required diameter Using the inclination angle of the conical rolling disc in a widening direction from the line toward the both ends of the roller body, both sides of the frustoconical roller rolling surface with both ends of the roller body as a conical bottom surface It is the formed shape. In addition, the cone-bottom shape is formed by using the inclination angle of the conical rolling plate in a widened form from the entire circumference of both ends of the lower roller body having the required diameter toward the center point of the length. The roller rolling surface is formed from both sides, and the conical bottom surfaces of both sides are combined at the center point in the length.

  When using a laminated rubber bearing device, the horizontal displacement of the earthquake design or the required horizontal displacement is the amount of subsidence when the laminated rubber bearing is deformed. The both end diameters of the roller body are added to the radius of the roller body on the side, and the both ends of the roller body are conically widened toward the both ends of the roller body from the entire circumference of the central point of the length. It is the shape which formed the truncated cone-shaped roller rolling surface made into the bottom on both sides. Further, by adding the sinking amount to the radius of the roller body at the center of the length of the base lower roller body having the required diameter, the center diameter of the roller body is obtained. In this shape, the roller rolling surfaces having a truncated cone shape are formed from both sides so as to expand toward the central diameter, and the bottom surfaces of both cones are combined at the center point in the length.

  Both of the rollers having a shape in which the inclination angle of the conical rolling disk used or the sinking amount of the laminated rubber bearing device is used for the base board side roller body and the base lower roller body as described above. When the body is in contact with each other in a horizontal manner and rotated at the center, it is synchronized with the rolling motion of the seismic isolation ball on the conical rolling plate during horizontal earthquake motion, and the laminated rubber bearing is deformed horizontally. In contact with the ring, the contact rolling continuously without interruption. During vertical earthquake motion, the base plate side roller body and the base lower roller body cross each other, so it resists vertical tension and prevents the seismic isolation object from rising. Both the roller bodies having the length of the total amplitude of the seismic design horizontal displacement or the required horizontal displacement do not interfere with the seismic isolation displacement or deformation of the seismic isolation bearing device.

  According to the invention of claim 2, in a space portion between the base plate on which the seismic isolation bearing device using the horizontal base isolation plate is disposed and the base of the base isolation object, a predetermined effective length is provided at an appropriate position of the space portion. The base plate side roller body is on the upper side and the base lower roller body is on the lower side. The rotating shafts protrude from the center of both ends to the outside of the roller bodies, and support pedestals with rotating bearings are arranged and supported at both ends of the respective rotating shafts. The structure of the seismic isolation object lifting prevention device, which is attached to the base isolation device using the horizontal base isolation board, which firmly and firmly screws the support base of the base lower roller body under the base. is there.

  The appropriate place of the space portion is a space portion that does not interfere with the seismic isolation operation of the seismic isolation bearing device using a horizontal seismic isolation panel.

  The predetermined effective length of the base plate side and the base lower roller body is the diameter of the roller body in the case of using a single base plate side roller body and base base roller body, and a plurality of base plates. In the case of using the side roller body and the lower roller body of the base, add the seismic design horizontal displacement amount or double the required horizontal displacement amount (total amplitude) to the sum of the diameters of the roller bodies. Is the length. The minimum length required.

  Following the start of seismic isolation when a horizontal seismic isolator is used for horizontal seismic motion, it rolls in contact with less frictional resistance, and during vertical seismic motion, the base plate side roller body and the base lower roller body Because of the crossing, it resists the vertical pulling force and prevents the seismic isolation object from floating up. Both the roller bodies having the length of the total amplitude of the seismic design horizontal displacement or the required horizontal displacement do not interfere with the seismic isolation displacement or deformation of the seismic isolation bearing device.

  The invention of claim 1 uses the shape of the base plate side and the base lower roller body in accordance with the inclination angle of the conical rolling plate and the amount of subsidence of the laminated rubber bearing device, During horizontal seismic motion, the base plate side and the base lower roller body follow the vertical displacement of the seismic isolation bearing device and follow the base plate side roller body and the base lower roller body continuously without interruption. The base plate side roller body and the base lower roller body are in cross contact with each other at the time of vertical earthquake motion. As described above, the base plate side roller body and the base lower roller body can prevent the seismic isolation object from rising while the cross contact rolling. Both the roller bodies having the length of the total amplitude of the seismic design horizontal displacement or the required horizontal displacement do not interfere with the seismic isolation displacement or deformation of the seismic isolation bearing device.

In the invention of claim 2, the base plate side and the base lower roller body follow the displacement of the base isolation bearing device during horizontal seismic motion and contact rolling with less frictional resistance. Since the lower roller body is always in cross contact with the upper and lower tensile forces, it prevents floating up, and when the vertical horizontal and horizontal earthquake motions, the base board side roller body and the base lower roller body are the same as above. It is possible to prevent the seismic isolation object from floating while crossing and rolling. Both the roller bodies having the length of the total amplitude of the seismic design horizontal displacement or the required horizontal displacement do not interfere with the seismic isolation displacement or deformation of the seismic isolation bearing device.

I will explain below.

  FIG. 1 (a) shows a rolling seismic isolation bearing using a conical rolling plate 10 as a lower rolling plate, which is disposed between the base plate and the base of the seismic isolation object according to claim 1. Arrangement sectional drawing which shows the state which equipped the apparatus A with the seismic isolation object floating prevention apparatus 12. FIG. FIG.1 (b) is a whole perspective view of the seismic isolation object rising prevention apparatus 12 used for Fig.1 (a). FIG. 2A is an arrangement cross-sectional view showing a displacement state during the horizontal earthquake motion of FIG. FIG. 2B is a plan view of the seismic isolation object lifting prevention device 12 as viewed from the AA portion in FIG. FIG. 3 (a) shows that the seismic isolation object lifting prevention device 22 is added to the laminated rubber bearing device B arranged between the foundation board and the base of the seismic isolation object according to claim 1. Arrangement sectional drawing which shows a state. FIG. 3B is a plan view of the seismic isolation object lifting prevention device 22 as seen from the BB part in FIG. FIG. 4A is an arrangement cross-sectional view showing the deformation and displacement state during the seismic isolation of FIG. FIG.4 (b) is a top view of the seismic isolation object floating prevention apparatus seen from CC section of Fig.4 (a). The black dot in the figure indicates the elastic cushioning material, and the white arrow indicates the horizontal seismic motion direction.

  A first embodiment of the present invention will be described below with reference to FIGS. 1 (a) to 2 (b).

  A rolling seismic isolation device A is installed between the base 1 and the base plate 2 of the seismic isolation object, and other parts that do not interfere with the rolling isolation of the rolling seismic isolation device A. An appropriate number of seismic isolation object lifting prevention devices 12 described below are provided in appropriate spaces.

  The base lower roller body 3 and the base board side roller body 4 are formed of a metal material made of a rigid body such as a steel material because it is necessary to resist the tensile force in the vertical direction. The rotating shaft 5 is protruded from the center of both ends of the roller bodies 3 and 4. The rotating shaft 5 may be formed integrally with the two roller bodies 3 and 4 by introducing the rotating shaft 5 through the cylindrical shaft hole 6 through the longitudinal center of the two roller bodies 3 and 4. .

  A support receiving base 7 with a rotary bearing is fitted and disposed at both ends of the rotating shaft 5 projecting out of the two roller bodies 3 and 4, and the base lower roller body 3 is placed on the lower side of the base lower roller body 3. 4 in the upper part, and in a horizontal manner at each center so as to be freely rotatable and orthogonal to each other, the support base 7 with the rotary bearing of the base lower roller body 3 is placed under the base 1 of the base to be quake-absorbed. A support pedestal 7 with a rotary bearing of the board side roller body 4 is firmly and screwed to the base board 2.

  In addition, the rotation support part 7 with a rotary bearing is separated into a rotary bearing part and a support base, and a rotary bearing part is provided in the shaft hole 6 of both the roller bodies 3 and 4 so as not to rotate through the rotary bearing part. The shaft 5 can be used by being supported by a support cradle. The shape and support method of the support pedestal 7 with a rotary bearing can be appropriately used as long as they can rotate and can withstand the seismic isolation load and the vertical tensile force.

  Appropriate elastic cushioning material 8 is appropriately attached to the side surfaces of the support pedestal 7 with rotary bearings facing both ends of the roller bodies 3 and 4 so that the roller bodies 3 and 4 should not collide. Impact can be reduced.

  An elastic buffer silencer plate 9 made of a rubber body or the like can be attached to the outer surfaces of the roller bodies 3 and 4 with an appropriate thickness to mute the contact rolling noise.

  In addition, the base lower roller body 3 and the base board side roller body 4 are not limited to being formed of a metal material made of a rigid body such as a steel material, but also impact resistance, load resistance, wear resistance, durability, etc. Can be configured using a synthetic resin material or the like that is excellent.

  As the predetermined effective length of the base lower roller body 3 and the base board side roller body 4, for example, when 25 mm is used as the seismic design horizontal displacement amount or the required horizontal displacement amount, it is twice the amount of 25 mm. The diameter value of the roller bodies 3 and 4 (assumed to be 10 mm) is added to 50 mm (total amplitude), and the required effective length of 60 mm is the minimum necessary length.

  The predetermined shapes of the base lower roller body 3 and the base board side roller body 4 will be described below using appropriate numbers.

  The radius of the conical rolling disk 10 of the rolling seismic isolation device A is 30 mm, and the height difference between the center and the circumferential edge is 2 mm (corresponding to the inclination angle). The roller bodies 3 and 4 have a diameter value of 10 mm, and 30 mm from the center point to both ends. If the diameter of both ends is 10 mm, and the height difference of 2 mm between the center of the conical rolling disk 10 and the circumference of the circle is added to the radius 5 mm of the center diameter of the base plate side roller body 4, the center dot diameter is 14 mm. (Radius 7 mm). Therefore, when a straight line is drawn from both ends toward the central point diameter in an extended angle, two frustum-shaped roller rolling surfaces can be formed.

  Furthermore, the center point diameter of the base lower roller body 3 is 10 mm, and both end diameters are 14 mm (radius 7 mm). Therefore, similarly, two conical truncated cone roller rolling surfaces can be formed from both sides from the central point diameter to the both end diameters.

  With the base plate side roller body 4 on the upper side and the base lower side roller body 3 on the lower side, they are brought into horizontal contact with each other at the center of each length so as to be orthogonal to each other. When the seismic support device A horizontally displaces 25 mm, the lower roller body 3 of the base is located at the center point of the roller body 4 of the foundation board in synchronization with the rolling ball rising on the conical rolling plate 10 by about 2 mm. The roller rolls so as to rise from the diameter (radius 7 mm) to the end diameter (radius 5 mm) of the roller body 4. While the rolling ball repeatedly rolls in all directions on the conical rolling platen 10, the base lower roller body 3 and the base plate side roller body 4 cross-roll in synchrony with each other, and during vertical earthquake motion The crossed roller bodies 3 and 4 resist the tensile force in the vertical direction and prevent the seismic isolation object from rising.

  It should be noted that the surface angle shape of a mortar-shaped rolling disk other than the conical rolling disk 10 of the rolling seismic isolation device A or other hemispherical rolling disk is set to the roller rolling of the roller bodies 3 and 4 as described above. By forming it on the moving surface, the roller bodies 3 and 4 roll over in synchronization, and the crossed roller bodies 3 and 4 resist the tensile force in the vertical direction during the vertical earthquake motion, and the seismic isolation object rises. To prevent damage. Further, when the sliding seismic isolation hemisphere plate other than the rolling isolation ball is used for the rolling isolation bearing device A, the lifting prevention device 12 can be similarly used.

  Next, a second embodiment of the present invention will be described with reference to FIGS. 3 (a) to 4 (b). Constituent elements common to those in the first embodiment described below are denoted by the same reference numerals and description thereof is omitted.

  Place the laminated rubber bearing device B between the base 1 and the base plate 2 of the seismic isolation object, and other suitable locations between them that do not interfere with the deformation isolation of the laminated rubber seismic isolation device B A number of seismic isolation object floating prevention devices 22 described below are provided as appropriate in the space.

  As in the first embodiment, the predetermined effective length of the base lower roller body 3 and the base board side roller body 4 is 50 mm (total amplitude), and the diameter value of the roller bodies 3 and 4 (assuming 10 mm) 60 liters) to which is added) is used.

  The predetermined shapes of the base lower roller body 3 and the base board side roller body 4 will be described below by applying appropriate numbers.

  The amount of sinking when the laminated rubber seismic isolation device B horizontally deforms 25 mm during horizontal earthquake motion is 2 mm, the diameter of the roller bodies 3 and 4 is 10 mm, and 30 mm from the center point to both ends. And If the sinking amount is added to the radius 5 mm of the both end diameters, the diameter of both ends becomes 14 mm (radius 7 mm). The center point diameter is 10 mm. Therefore, when a straight line is drawn from both ends toward the central point diameter in an extended angle, two frustum-shaped roller rolling surfaces can be formed.

  Further, the central point diameter of the base lower roller body 3 is 14 mm (radius 7 mm), and both end diameters are 10 mm. Therefore, when a straight line is drawn from both sides toward the both end diameters in an enlarged angle shape, two frustoconical roller rolling surfaces can be formed.

  With the base plate side roller body 4 on the upper side and the base lower side roller body 3 on the lower side, they are brought into horizontal contact with each other at the center of each length so as to be orthogonal to each other. In synchronization with the seismic isolation bearing device B being horizontally deformed 25 mm and gradually sinking 2 mm, the base lower roller body 3 starts from the center point diameter (radius 5 mm) of the base plate side roller body 4. The roller body 4 rolls so as to descend about 2 mm to the end diameter (radius 7 mm). While the laminated rubber seismic isolation device B deforms and sinks in all directions, the base lower roller body 3 and the base plate side roller body 4 roll over in synchronism with each other at all times. The roller bodies 3 and 4 resist the tensile force in the vertical direction and prevent the seismic isolation object from rising.

  In addition, in the seismic isolation bearing device A using the conical rolling plate 10, when the conical rolling plate 10 is used as the upper rolling plate, when the anti-seismic object lifting prevention device 22 is provided, Similarly, the base lower roller body 3 has a shape that descends from the center point diameter (radius 5 mm) of the base board side roller body 4 to both end diameters (radius 7 mm), and the rolling sphere under the conical rolling disk 10 The roller bodies 3 and 4 that intersect with each other resist the tensile force in the vertical direction and prevent the seismic isolation object from rising.

  FIG. 5 (a) shows that the seismic isolation object floats on the seismic isolation support device C using the horizontal base isolation board, which is arranged between the base plate and the base of the base isolation object according to claim 2. The arrangement | positioning sectional drawing which shows the state which provided the prevention device 32 side by side. FIG.5 (b) is the top view of the seismic isolation object floating prevention apparatus 32 seen from the DD section of Fig.5 (a). FIG.5 (c) is a top view which shows the displacement state at the time of the horizontal earthquake motion of FIG.5 (b).

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  A seismic isolation device C using a horizontal seismic isolation plate is arranged between the base 1 and the base plate 2 of the seismic isolation object so that the seismic isolation device C does not interfere with slip isolation. An appropriate number of seismic isolation object floating prevention devices 32 are provided in appropriate spaces in the meantime.

  Constituent elements common to those in the first embodiment described below are denoted by the same reference numerals and description thereof is omitted.

  The predetermined effective lengths of the base lower roller body 3 and the base board side 4 are the diameters of the roller bodies 3 and 4 and a plurality of the roller bodies when a single roller body 3 and 4 are used. When 3 and 4 are used, the length is the sum of the diameters of the plurality of roller bodies plus the seismic design horizontal displacement or twice the required horizontal displacement (total amplitude). The minimum length required.

  In this embodiment, similarly to the first embodiment, the single lower roller body 3 and 4 are used as 50 mm (total amplitude) as the predetermined effective length of the base lower roller body 3 and the base board side roller body 4. Then, 60 mm is added to the diameter value (assumed to be 10 mm).

  With the base plate side roller body 4 on the upper side and the base lower side roller body 3 on the lower side, the base plate side roller body 3 is in contact with each other at the center of each length so as to be able to rotate in a horizontal manner and perpendicular to each other. Synchronously with the horizontal seismic isolation plate 11 of the seismic bearing device C sliding and moving 25 mm, the lower roller body 3 of the base horizontally extends 25 mm from the center point of the base plate side roller body 4 toward the roller end. Roll. Although the horizontal seismic isolator 11 repeatedly slides and displaces in all directions, the base lower roller body 3 and the base board side roller body 4 roll with less frictional resistance because of the rotational cross rolling. . During the vertical earthquake motion, the intersecting roller bodies 3 and 4 resist the tensile force in the vertical direction and prevent the seismic isolation object from rising.

  In addition, even when a rolling ball is used between the upper and lower horizontal seismic isolation plates 11 of the seismic isolation device C using a horizontal seismic isolation plate, the lift prevention device 32 can be used in the same manner.

  As described above, since the lengths of the base lower roller body 3 and the base board side roller body 4 are relatively long, in this embodiment, 10 mm is used for the diameters of the roller bodies 3 and 4. As described above, since a strong vertical tensile force is applied to the roller bodies 3 and 4 and the rotating shaft 5, the diameters of the roller bodies 3 and 4 and the rotating shaft 5 are the types of seismic isolation objects, high Select appropriately from the weight, seismic design horizontal displacement used, etc.

  Other than the above, the configurations of the base lower roller body 3 and the base plate side roller body 4 and the support configuration of the rotary shaft 5 and the support pedestal 7 with the rotary bearing may be within the scope of the present invention. Any configuration may be used.

(A) Arrangement sectional drawing which shows the state where the seismic isolation object rising prevention apparatus 12 was attached to the rolling seismic isolation apparatus A using a conical rolling board. (B) Whole perspective view of seismic isolation object rising prevention apparatus 12. FIG. (A) Arrangement sectional drawing which shows the time of seismic isolation rolling displacement of (a) of FIG. (B) The top view of the seismic isolation object rising prevention apparatus 12 seen from the AA part of Fig.2 (a). (A) Arrangement cross-sectional view showing a state in which the seismic isolation object lifting prevention device 22 is provided alongside the laminated rubber seismic isolation device B. (B) The top view of the seismic isolation object lifting prevention apparatus 22 seen from the BB part of Fig.3 (a). (A) Arrangement | sequence sectional drawing which shows the deformation | transformation and displacement state at the time of seismic isolation of (a) of FIG. (B) The top view of the seismic isolation object lifting prevention apparatus 22 seen from CC section of Fig.4 (a). (A) Arrangement sectional drawing which shows the state where the seismic isolation object rising prevention apparatus 32 was added to the sliding seismic isolation apparatus C. (B) The top view of the seismic isolation object floating prevention apparatus 32 seen from the DD section of Fig.5 (a). (C) Arrangement cross-sectional view showing the seismic isolation rolling displacement of FIG. 5 (b).

Explanation of symbols

A Rolling seismic isolation device using a conical rolling plate B Laminated rubber seismic isolation device C Sliding seismic isolation device 1 Under the base of the seismic isolation object 2 Base plate 3 Base lower roller body 4 Base plate side Roller body 5 Rotating shaft 6 Shaft hole 7 Support pedestal with rotating bearing 8 Elastic shock absorbing material 9 Elastic buffer silencer 10 Conical rolling plate 11 Horizontal seismic isolator 12, 22, 32 Anti-seismic object lifting prevention device

Claims (2)

  In the space between the base plate where the seismic isolation bearing device that is displaced in the vertical direction at the time of displacement or deformation isolation is arranged and under the base of the seismic isolation object, a predetermined effective length and a predetermined The base plate side roller body is on the upper side and the base lower side roller body is on the lower side, and is in contact with each other at the center of each length so that it can rotate horizontally. The rotating shafts protrude from the center of both ends of the two roller bodies to the outside of the two roller bodies, and support pedestals with rotating bearings are arranged and supported at both ends of the respective rotating shafts. A base-isolated bearing device that is displaced in the vertical direction during base-isolated displacement, characterized in that the base of the support base is rigidly screwed to the base under the base and the base is under the base. A seismic isolation device that prevents the object from being lifted.   In the space between the base plate where the seismic isolation bearing device using a horizontal seismic isolation panel is arranged and the base of the seismic isolation object, a singular or more that has a predetermined effective length at an appropriate place in the space Made of rigid body, with the base plate side roller body on the upper side and the base lower roller body on the lower side, in a horizontal and freely rotating manner, they are perpendicular to each other. Protruding out of the two roller bodies, disposing and supporting support pedestals with rotary bearings at both ends of the respective rotation shafts, and supporting the base board side roller body on the base board, the base lower roller body The seismic isolation object lifting prevention apparatus which is attached to the seismic isolation bearing apparatus using a horizontal seismic isolation board, characterized in that the support cradle is firmly screwed under the base.

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