CN112742002A

CN112742002A - Rhythm device

Info

Publication number: CN112742002A
Application number: CN201911073496.4A
Authority: CN
Inventors: 郑希杰
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-10-29
Filing date: 2019-11-05
Publication date: 2021-05-04
Anticipated expiration: 2039-11-05
Also published as: TWI702975B; CN112742002B; TW202116377A

Abstract

A rhythm device comprises a seat cushion, a base arranged below the seat cushion and a middle base arranged between the seat cushion and the base. The bottom surface of seatpad has two first spouts, the top surface of base has two second spouts, the first spout of seatpad and the second spout mutually perpendicular of base, the middle seat has two first gyro wheels and two second gyro wheels, the middle seat utilizes two first gyro wheels and two second gyro wheels to locate two first spouts of seatpad and two second spouts of base respectively in, make the seatpad on the one hand can alone move along the relative base of a first direction and middle seat, on the other hand then moves along the relative base of the second direction of a perpendicular first direction together with the middle seat. Therefore, the rhythm device can realize the effect of multidirectional rhythm.

Description

Rhythm device

Technical Field

The invention relates to fitness equipment, in particular to a rhythm device capable of performing multidirectional movement.

Background

Among the existing indoor sports equipment, the running machine, the stepping machine or the elliptical machine is common, and the sports equipment belongs to high-intensity training, and although the body-building effect can be achieved, the indoor sports equipment is not suitable for people with arthritis or heart diseases to use for body-building.

In order to solve the above problems, there is a rhythm device that allows a user to lie, sit or stand on the device and then give regular exercise to the body, which is very suitable for a user who is difficult to perform high-intensity exercise, because it has many advantages in promoting blood circulation, relaxing muscles, increasing joint mobility, etc. however, the conventional rhythm device has only one-way rhythm exercise, and the exercise effect that can be achieved is very limited.

Disclosure of Invention

The invention mainly aims to provide a rhythm device which can realize bidirectional rhythm so as to improve the training effect.

To achieve the above objective, the rhythm device of the present invention comprises a seat cushion, a base, and a middle seat. The bottom surface of the seat cushion is provided with two first sliding grooves which are parallel to each other, and each first sliding groove extends along a first direction; the base is arranged below the seat cushion, the top surface of the base is provided with two second sliding grooves which are parallel to each other, and each second sliding groove extends along a second direction which is vertical to the first direction; the middle seat is arranged between the seat cushion and the base and provided with two opposite first idler wheels and two opposite second idler wheels, the middle seat is arranged in a first sliding groove of the seat cushion by utilizing the first idler wheels, so that the seat cushion can move relative to the base and the middle seat along the first direction independently, and the middle seat is arranged in a second sliding groove of the base by utilizing the second idler wheels, so that the middle seat and the seat cushion move relative to the base along the second direction.

Therefore, the rhythm device of the invention can enable a user to select horizontal rhythm along the first direction or the second direction according to actual needs, and even the rhythm device can be matched with the first direction or the second direction to form rotary rhythm, so that the training effect can be effectively improved by the various operations.

Preferably, the seat cushion has a cushion body, a supporting seat and an upper press button. The bottom surface of this pad body is located to this supporting seat, and the top surface of this supporting seat has a appearance groove, and the diapire of this appearance groove has a first stop portion, should go up the button and have a head and a body portion, and this head is connected to the one end of this body portion, and the other end of this body portion has a first tooth portion, and the head protrusion of this last button is outside this pad body, and the body portion of this last button is located the appearance inslot of this supporting seat, and the bottom surface of this body portion of going up the button has a second stop portion, and this middle seat still has a carrier plate that sets up these two first gyro wheels and these two second gyro wheels, and a side of this carrier plate has a second tooth portion. Therefore, when the upper press button is located at a positioning position, the first tooth portion of the body of the upper press button is engaged with the second tooth portion of the carrier plate of the middle seat, and the second blocking portion of the body of the upper press button is engaged with the first blocking portion of the support seat, so that the seat cushion cannot move relative to the base and the middle seat along the first direction.

Preferably, the seat cushion further has a return spring, the return spring is disposed in the accommodating groove of the supporting seat and pushes the upper press button in a direction away from the middle seat, so as to keep the upper press button at the release position.

Preferably, the body of the upper press button has a through hole penetrating through the top and bottom surfaces, the seat cushion further has a bolt, a nut and a positioning spring, the bolt penetrates through the through hole from top to bottom, the nut is screwed in the bolt, and the positioning spring is sleeved on the bolt and pushes down the top surface of the body of the upper press button to keep the upper press button at the positioning position.

Preferably, the seat cushion further has two first rails, each first rail is disposed on the bottom surface of the support seat and has a first sliding slot, two ends of each first rail are respectively provided with a stop block, and the two stop blocks are used for stopping the first roller from separating from the first sliding slot.

Preferably, the base has a bottom plate and a stopper plate. The top surface of the bottom plate is provided with a guide groove positioned between the two second sliding grooves, the middle seat is also provided with a bearing plate provided with the two first rollers and the two second rollers, the bottom surface of the bearing plate is provided with a guide part, the guide part of the bearing plate can be arranged in the guide groove of the bottom plate along the second direction in a displacement manner, the bottom plate is also provided with a positioning groove communicated with the guide groove, the stop plate is arranged below the bottom plate and can horizontally displace relative to the bottom plate between a positioning position and a release position along the first direction, and the top surface of the stop plate is provided with a positioning convex part. Therefore, when the stop plate is located at the positioning position, the positioning convex part of the stop plate is embedded in the positioning groove of the base plate and interferes with the guide part of the bearing plate of the middle seat, so that the middle seat cannot move relative to the base along the second direction.

Preferably, two opposite sides of the bottom plate are respectively provided with an opening, each opening is adjacent to the second sliding groove, the stop plate is provided with a plate body, two arm parts and two pressing buttons, the top surface of the plate body is provided with the positioning convex part, one ends of the two arm parts are connected with the plate body, the other ends of the two arm parts are respectively connected with one pressing button, and each pressing button is located in one opening of the bottom plate. Thus, the movement of the stop plate from the release position to the detent position is facilitated when one of the lower buttons is pushed, and the movement of the stop plate from the detent position to the release position is facilitated when the other lower button is pushed.

Preferably, there are two positioning grooves of the bottom plate and two positioning protrusions of the stop plate, the two positioning grooves and the two positioning protrusions are located on two opposite sides of the guiding groove, and the distance between the two positioning grooves is smaller than the distance between the two positioning protrusions. Therefore, only one positioning convex part is embedded into the corresponding positioning groove, and the positioning effect can be provided for the middle seat.

The details of construction, features, assembly, or use of the rhythm devices provided herein are set forth in the detailed description of the embodiments which follows. However, it should be understood by those skilled in the art that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention as defined by the appended claims.

Drawings

FIG. 1 is a perspective view of a rhythm device according to embodiment 1 of the present invention;

fig. 2 is a partial exploded perspective view of a rhythm device according to embodiment 1 of the present invention;

FIG. 3 is another exploded perspective view of a rhythm device according to embodiment 1 of the present invention;

fig. 4 is a partial cross-sectional view of a rhythm device according to embodiment 1 of the present invention, with the primary upper push button in a release position;

FIG. 5 is a view similar to FIG. 4, and shows primarily the upper push button in the secured position;

fig. 6 is a cross-sectional view of a rhythm device according to embodiment 1 of the present invention, showing primarily the detent plate in the release position;

FIG. 7 is similar to FIG. 6 and is primarily shown with the stop plate in the detent position;

FIGS. 8 a-8 e are perspective views of a rhythm device according to embodiment 1 of the present invention in use;

fig. 9 is a partial exploded perspective view of a rhythm device according to embodiment 2 of the invention.

[ description of reference ]

10 rhythm device 20 seat cushion

22 pad 24 first elongated hole

26 supporting the seat 28 in the second elongated hole

30-slot 32 first stop part

34 first rail 35 third rail

36 first runner 37 third elongated hole

D1 first direction 38 stop

39 third chute 40 base

42 bottom plate 44 channel

46 opening 48 positioning groove

49 screw hole 50 second rail

52 second slide way D2 second direction

53 fourth rail 54 end cap

55 fourth chute 56 middle seat

58 carrier plate 60 guide

62 second tooth 64 first roller

65 third roller 66 second roller

67 fourth roller 68 Upper Press button

70 head 72 body

74 first tooth 76 second stop

78 perforating 80 return spring

82 positioning spring 84 bolt

86 nut P1 locating position

P2 Release position 88 stop plate

90 plate body 92 positioning convex part

94 arm 96 push button

P3 locate position P4 release position

98 long groove 99 screw

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

In the description, which follows, and in the claims which follow, reference will be made to directional terms, which will be used throughout the specification and claims, and which are included in the following description and claims. Next, in the embodiments and the drawings to be described below, the same element numbers denote the same or similar elements or structural features thereof.

Referring to fig. 1-3, a rhythm device 10 according to embodiment 1 of the present invention includes a seat 20, a base 40, and an intermediate seat 56.

The seat cushion 20 has a cushion body 22, a support base 26 and two first rails 34. The cushion body 22 is rectangular and made of a soft material such as foam; the supporting seat 26 is disposed below the cushion body 22 for providing a supporting effect to the cushion body 22; the two first rails 34 are fixedly disposed on the left and right sides of the bottom surface of the supporting seat 26, each first rail 34 has a first sliding slot 36 extending along a first direction D1, and a cylindrical stopper 38 is disposed at each of the front and rear ends of each first rail 34.

The base 40 is disposed under the seat cushion 20 and has a bottom plate 42 and two second rails 50. The base plate 42 is rectangular and made of a material such as plastic; the two second rails 50 are fixedly disposed on the front and rear sides of the top surface of the base 40 and respectively have a second sliding slot 52 extending along a second direction D2 perpendicular to the first direction D1. In addition, the top surface of the bottom plate 42 has a guide groove 44 at the center between the two second sliding grooves 52, and the left and right ends of the guide groove 44 are respectively provided with an end cap 54.

The middle seat 56 is disposed between the seat cushion 20 and the base 40 and has a rectangular supporting plate 58, the bottom surface of the supporting plate 58 has two pairs of guides 60 arranged left and right, and the two pairs of guides 60 of the supporting plate 58 are movably inserted into the guide slots 44 of the bottom plate 42 and blocked by the left and right end caps 54 without falling out of the guide slots 44. In addition, a first roller 64 and a second roller 66 are respectively disposed at four corners of the carrier plate 58, wherein the first roller 64 is disposed in the first sliding slot 36 of the seat cushion 20 and can be blocked by the front and rear stoppers 38 without separating from the first sliding slot 36, and the second roller 66 is disposed in the second sliding slot 52 of the base 40 and can be blocked by the two pairs of guide portions 60 of the carrier plate 58 by the left and right end caps 54 without separating from the second sliding slot 52. Therefore, the middle seat 56 moves along with the seat cushion 20 along the second direction D2 relative to the base 40, but only the seat cushion 20 moves along the first direction D1 relative to the base 40 and the middle seat 56 because the second rollers 66 are constrained by the second sliding slots 52.

Referring to fig. 2, the left and right sides of the cushion body 22 have a first long hole 24, the left and right sides of the support base 26 have two second long holes 28 and a containing slot 30 located between the two second long holes 28, the bottom wall of each containing slot 30 has four parallel first stoppers 32, each first rail 34 has a third long hole 37, and the left and right sides of the support plate 58 of the middle seat 56 have a second tooth 62. In addition, the seat cushion 20 also has two upper press buttons 68, four return springs 80, and two positioning springs 82, wherein:

the upper button 68 has a head 70 and a body 72, one end of the body 72 is connected to the head 70, the other end of the body 72 has a first tooth portion 74, as shown in fig. 4, the head 70 of the upper button 68 is disposed in the first elongated hole 24 of the cushion body 22 and one of the second elongated holes 28 of the support seat 26 and partially protrudes out of the cushion body 22, the body 72 of the upper button 68 is inserted between the other second elongated hole 28 of the support seat 26 and the third elongated hole 37 of the first rail 34 and is located in the receiving slot 30 of the support seat 26, and the size of the upper button 68 is slightly smaller than the sizes of the two second elongated holes 28 of the support seat 26. As shown in fig. 2 and 4, the body 72 of the upper knob 68 has four second blocking portions 76 parallel to each other on the bottom surface thereof, and the body 72 of the upper knob 68 has a through hole 78 penetrating both top and bottom surfaces thereof.

The four return springs 80 are provided in pairs. Each pair of return springs 80 is disposed in the receiving groove 30 of the supporting base 26 and located between two adjacent first stopping portions 32, for providing an elastic force to push the upper press button 68 away from the middle base 56.

The positioning spring 82 is sleeved on a bolt 84 and abuts against the body 72 of the upper press button 68 at the bottom end, the bolt 84 passes through the through hole 78 of the body 72 of the upper press button 68 from top to bottom and is screwed with a nut 86 embedded in the support seat 26, so that the positioning spring 82 provides elastic force to push the upper press button 68 downward.

As can be seen from the above description, when the head 70 of the upper button 68 is not pressed by an external force, the first tooth 74 of the body 72 of the upper button 68 and the second tooth 62 of the support plate 58 of the middle seat 56 are separated from each other, and the second stopping portion 76 of the body 72 of the upper button 68 and the first stopping portion 32 of the support seat 26 are separated from each other, at this time, the upper button 68 is held at the release position P2 shown in fig. 4 by the elastic force of the return spring 80, so that the seat cushion 20 can move along the first direction D1 relative to the base 40 and the middle seat 56; on the contrary, when the head 70 of the upper button 68 is pressed by an external force, the first tooth 74 of the body 72 of the upper button 68 and the second tooth 62 of the carrier plate 58 of the middle seat 56 are engaged with each other, so that the return spring 80 is pressed by the upper button 68 to accumulate the elastic restoring force, and the second stopping portion 76 of the body 72 of the upper button 68 and the first stopping portion 32 of the supporting seat 26 are engaged with each other, and at this time, the upper button 68 is held at the positioning position P1 shown in fig. 5 by the elastic force of the positioning spring 82, so that the seat cushion 20 cannot move relative to the base 40 and the middle seat 56 along the first direction D1, but only moves along the second direction D2 along with the middle seat 56.

Referring to fig. 3, the front and rear sides of the bottom plate 42 are respectively provided with an opening 46 adjacent to the second sliding groove 52, the bottom plate 42 is further provided with four positioning grooves 48 penetrating the top and bottom surfaces, and the four positioning grooves 48 are arranged on the front and rear sides of the guide groove 44 in pairs and are communicated with the guide groove 44. In addition, the base 30 further has a stop plate 88, the stop plate 88 is located below the bottom plate 42 and has a plate body 90, two arm portions 94 and two press buttons 96, the front and rear sides of the top surface of the plate body 90 respectively have two positioning protrusions 92 arranged at intervals, the distance between the two positioning protrusions 92 is greater than the distance between the two positioning grooves 48, one end of each of the two arm portions 94 is connected to the front and rear sides of the plate body 90, the other end of each of the two arm portions 94 is connected to one press button 96, and each of the press buttons 96 is located in the front and rear openings 46 of the bottom plate 42. The plate body 90 further has two elongated slots 98, and two screws 99 respectively pass through the two elongated slots 98 of the plate body 90 and are locked in the two screw holes 49 on the bottom surface of the bottom plate 42, so that the stop plate 88 can move horizontally along the first direction D1 relative to the bottom plate 40.

As can be seen from the above, when the stop plate 88 is located at the release position P4 shown in fig. 6, the front and rear pairs of positioning protrusions 92 of the stop plate 88 are located outside the positioning grooves 48 of the bottom plate 42 and do not interfere with the left and right guides 60 of the intermediate seat 56, so that the intermediate seat 56 can move along with the seat cushion 20 along the second direction D2 relative to the base 40; on the contrary, when one of the lower buttons 96 is pressed by an external force, the pair of positioning protrusions 92 of the stopping plate 88 are inserted into the corresponding positioning recesses 48 and interfere with the guiding portion 60 of the middle seat 56, and the stopping plate 88 is located at the positioning position P3 shown in fig. 7, such that the middle seat 56 cannot move relative to the base 40 along the second direction D2, but the seat cushion 20 is allowed to move back and forth along the first direction D1, and when the other lower button 96 is pressed, the stopping plate 88 returns to the releasing position P4 shown in fig. 6.

Therefore, if the upper push button 68 is located at the release position P2 shown in fig. 4 and the stopper plate 88 is located at the release position P4 shown in fig. 6, the seat cushion 20 can be reciprocally moved in the second direction D2 in addition to the first direction D1; if the upper push button 68 is located at the positioning position P1 shown in fig. 5 and the stop plate 88 is located at the releasing position P4 shown in fig. 6, the seat cushion 20 can only reciprocate along the second direction D2; if the upper push button 68 is located at the release position P2 shown in fig. 4 and the stopper plate 88 is located at the positioning position P3 shown in fig. 7, the seat cushion 20 can only reciprocate along the first direction D1; if the upper push button 68 is located at the positioning position P1 shown in fig. 5 and the stopper plate 88 is located at the positioning position P3 shown in fig. 7, the seat cushion 20 remains stationary.

In actual operation, the user can select different postures and different decoration positions to operate according to actual needs. For example, the user puts the musical movement device 10 on a chair in fig. 8a, then operates in a posture of sitting on the chair, puts the musical movement device 10 on the ground in fig. 8b, then operates in a posture of sitting on the ground with the buttocks on the seat cushion 20, puts the musical movement device 10 on the ground in fig. 8c, then operates in a posture of sitting on the ground with both feet stepping on the seat cushion 20, puts the musical movement device 10 on the ground in fig. 8d, then operates in a posture of lying with the buttocks on the seat cushion 20, as for the musical movement device 10 on the ground in fig. 8e, then operates in a posture of lying with the heels of both feet on the seat cushion 20. Regardless of the position or posture, the body can be given regular motion in the front-rear direction by the reciprocating movement of the seat cushion 20 in the first direction D1, or in the left-right direction by the reciprocating movement of the seat cushion 20 in the second direction D2, or even in the similar rotation-in-place rotation by the alternating reciprocating movement of the seat cushion 20 in the first direction D1 and the second direction D2.

Finally, it should be added that the structure of the present invention can be further adjusted according to actual needs. As shown in fig. 9, in the 2 nd embodiment of the present invention, a third rail 35 is further disposed on the bottom surface of the seat cushion 20, the third rail 35 has two third sliding grooves 39 parallel to the first sliding grooves 36, a fourth rail 53 is further disposed on the top surface of the bottom plate 42, and the fourth rail 53 has two fourth sliding grooves 55 parallel to the second sliding grooves 52. As for the supporting plate 58 provided by the middle seat 56, it is in a cross shape, the left and right ends of the supporting plate 58 are respectively provided with a first roller 64 and two fourth rollers 67, wherein the fourth rollers 67 are disposed in the fourth sliding slot 55, the front and rear ends of the supporting plate 58 are respectively provided with a second roller 66 and two third rollers 65, and the third rollers 65 are disposed in the third sliding slot 39. Therefore, the embodiment 2 of the present invention utilizes the additional arrangement of the third sliding slot 39, the third roller 65, the fourth sliding slot 55 and the fourth roller 67 to increase the stability and smoothness of the three elements of the seat cushion 20, the base 40 and the middle seat 56 during the operation process, and the seat cushion 20 can change the appearance into a more rounded shape due to the structural change, so that the two sides are not limited to the strip-shaped sliding slots.

In summary, the rhythm device 10 of the present invention enables the user to select horizontal rhythm only along the first direction D1 or the second direction D2 or rotary rhythm in cooperation with each other in both directions according to the actual needs, so as to effectively enhance the training effect and increase the interest of the user through such varied operations.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A rhythm device, comprising:

the bottom surface of the seat cushion is provided with two first sliding grooves which are parallel to each other, and each first sliding groove extends along a first direction;

the base is arranged below the seat cushion, the top surface of the base is provided with two second sliding grooves which are parallel to each other, and each second sliding groove extends along a second direction which is vertical to the first direction; and

the middle seat is arranged between the seat cushion and the base and provided with two opposite first idler wheels and two opposite second idler wheels, each first idler wheel is arranged in a first sliding groove of the seat cushion to enable the seat cushion to move relative to the base and the middle seat along the first direction, and each second idler wheel is arranged in a second sliding groove of the base to enable the seat cushion and the middle seat to move relative to the base along the second direction.

2. The rhythm device as claimed in claim 1, wherein the seat cushion has a cushion body, a supporting seat and an upper press button, the supporting seat is disposed on the bottom surface of the cushion body, the top surface of the supporting seat has a receiving groove, the bottom wall of the receiving groove has a first stopping portion, the upper press button has a head portion and a body portion, one end of the body portion is connected to the head portion, the other end of the body portion has a first tooth portion, the head portion of the upper press button protrudes out of the cushion body, the body portion of the upper press button is disposed in the receiving groove of the supporting seat, the bottom surface of the body portion of the upper press button has a second stopping portion, the middle seat further has a support plate on which the two first rollers and the two second rollers are disposed, one side of the support plate has a second tooth portion, when the upper press button is located at a certain position, the first tooth portion of the body portion of the upper press button and the second tooth portion of the support plate of the middle seat are connected to each other, and the second stopping part of the body part of the upper press button is mutually clamped with the first stopping part of the supporting seat, so that the seat cushion can not move relative to the base and the middle seat along the first direction.

3. A rhythmic device according to claim 2, wherein the seat cushion further includes a return spring disposed in the receiving groove of the support base and urging the upper button in a direction away from the middle base to maintain the upper button in the release position.

4. A rhythm device according to claim 2, wherein the body of the upper button has a through hole penetrating through both sides of the top and bottom, the seat further has a bolt passing through the through hole from top to bottom, a nut screwed on the bolt, and a positioning spring sleeved on the bolt and pushing down the top surface of the body of the upper button to keep the upper button at the positioning position.

5. The rhythm device as claimed in claim 2, wherein said seat further comprises two first rails, each of said first rails is disposed on the bottom surface of said support base and has a first sliding slot, and two ends of each of said first rails are respectively provided with a stop for stopping a first roller from separating from a first sliding slot.

6. A rhythm device according to claim 1, wherein the base has a bottom plate and a stop plate, the top surface of the bottom plate has a guide slot between the two second sliding slots, the middle seat further has a support plate on which the two first rollers and the two second rollers are disposed, the bottom surface of the support plate has a guide portion, the guide portion of the support plate is movably disposed in the guide slot of the bottom plate along the second direction, the bottom plate further has a positioning groove penetrating through both top and bottom surfaces and communicating with the guide slot, the stop plate is disposed below the bottom plate and horizontally movable relative to the bottom plate between a positioning position and a release position along the first direction, the top surface of the stop plate has a positioning protrusion, when the stop plate is at the positioning position, the positioning protrusion of the stop plate is embedded in the positioning groove of the bottom plate and interferes with the guide portion of the support plate of the middle seat, when the stop plate is located at the release position, the positioning convex part of the stop plate is separated from the positioning groove of the bottom plate and does not interfere with the guide part of the bearing plate of the middle seat, so that the middle seat can move relative to the base along the second direction.

7. A rhythm device according to claim 6, wherein each of the opposite sides of the base plate has an opening, each of the openings is adjacent to the second sliding slot, the stop plate has a plate body, two arms and two push buttons, the top surface of the plate body has the positioning protrusion, one end of each of the two arms is connected to the plate body, the other end of each of the two arms is connected to one of the push buttons, and each of the push buttons is located in one of the openings of the base plate.

8. The device of claim 6, wherein the base further comprises two second rails, each second rail being disposed on the top surface of the base plate and having a second slot.

9. A rhythmic device according to any one of claims 6 to 8, wherein the base plate has two positioning recesses, the stopper plate has two positioning protrusions on a top surface thereof, the two positioning recesses and the two positioning protrusions are located on opposite sides of the guide slot, and a distance between the two positioning recesses is smaller than a distance between the two positioning protrusions.

10. A rhythm device according to claim 1, wherein the bottom surface of the seat further has two parallel third sliding grooves, each of the third sliding grooves extends along the first direction, the top surface of the base further has two parallel fourth sliding grooves, each of the fourth sliding grooves extends along the second direction, the middle base further has two opposite third rollers and two opposite fourth rollers, each of the third rollers is disposed in one of the third sliding grooves of the seat, and each of the fourth rollers is disposed in one of the fourth sliding grooves of the base.