JP2002370896A - Lift for projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lift for a projector capable of miniaturizing a device, and capable of taking a lifting stroke large. SOLUTION: One end side of a chain 28 is connected to a support 3 for installing and supporting the projector 1, and the other end side of the chain 28 is meshed with a sprocket 25 provided in the ceiling. An electric motor M is arranged for rotatably driving a rotary shaft 24 of the sprocket 25. The projector 1 is constituted so as to be freely liftable to a housing attitude housed in the ceiling and a using attitude lowered below a ceiling surface by using driving force of the electric motor M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is constructed such that it can be stored in a ceiling when not in use, and can be lowered from the ceiling when used. The present invention relates to a lifting device for a projector.

[0002]

2. Description of the Related Art As an elevating device for a projector, for example, the one shown in FIG. 12 has been proposed. This engages with guide rollers 51, 51 (only the right side is shown in the figure) provided at two places on the left and right of the elevating plate 50 on which the projector is mounted on the lower surface, and stands on the support 52 to move the projector vertically by rotation. A pair of left and right ball screws 53, 53 (only the left ball screw is shown at the upper end in the figure), and rotating rollers 54, which are rotatably attached to the upper ends of the ball screws 53, 53, respectively.
54, two timing gears 55, 55 for synchronizing the rotations of the ball screws 53, 53, two tension rollers 56, 56, a drive roller 59 that is rotatably attached to a drive shaft 58 of the electric motor 57, and These rollers 5
4, 55, 59, and the like, a timing belt 60 and the like for transmitting power are provided to constitute a projector elevating device.

[0003]

According to the above construction, the roller 5 is provided over almost the entire area of the upper plate 61 of the support 52.
In addition to the arrangement of the members constituting the belt transmission mechanism such as 4, 55, 59, etc., the electric motor 57 must be arranged in a vertical position, so that the lifting / lowering device can be moved not only in the horizontal direction but also in the vertical direction. Space is required, and the whole apparatus becomes large. Also, the ball screw 53
The projector can only be moved up and down by the effective length of the projector.In order to increase the elevation of the projector, not only a large vertical space is required inside the ceiling, but also it is difficult to install it inside the ceiling. There was room for improvement.

An object of the present invention, in view of the above-mentioned circumstances, is to provide a lifting device for a projector that can reduce the size of the device and can take a large lifting stroke.

[0005]

In order to solve the above-mentioned problems, according to the present invention, one end of a chain is connected to a support for mounting and supporting a projector, and the other end of the chain is connected to a ceiling. An electric motor for rotating the rotating shaft of the sprocket is provided, and the projector is housed in the ceiling using the driving force of the electric motor. It is configured to be able to move up and down to the use posture lowered downward. Therefore, only by changing the length of the chain, it is possible to raise and lower the support by the length of the chain and change the posture between the storage posture and the use posture. That is, when the support is raised, the chain is wound up by rotating the sprocket, and the other end of the chain is lowered. Because of this, long chains can be used as long as there is space for the chains to go down and loosen. Further, since it is only necessary to provide a single sprocket for winding the chain, it is sufficient to drive the drive shaft of this sprocket, so that it is wound around a number of rotating bodies (pulleys and the like). Since the timing belt can be dispensed with, the components required for driving the electric motor or the like for driving the drive shaft of the sprocket can be concentrated and arranged at a specific location. By connecting and fixing the other end of the chain to the fixed side, there is an advantage that the chain can be stably (smoothly) engaged with the sprocket, but the chain may be free without being connected. .

[0006] The sprocket is integrally rotatably attached to the left and right ends of a drive shaft extending linearly in the left-right direction, and one end of each of the chains meshing with the two sprockets is connected to the support to form a single sprocket. Ascent and descent can be performed smoothly and stably as compared with those that are raised and lowered by a chain.

[0007] By providing a blocking means at a predetermined location on the outer peripheral side of the sprocket for preventing the engaged chain from moving toward the disengagement side, the chain does not come off the sprocket.

The electric motor is arranged at a position overlapping the drive shaft in the front-rear direction in such a manner that its operation shaft is substantially parallel to the drive shaft, and the electric motor and the drive shaft are connected by a gear mechanism. By interlocking, the drive shaft and the electric motor can be arranged in the most compact state.

[0009] The support is formed with an upper plate portion having a substantially rectangular shape in plan view to which one end of the chain is connected, and a lower surface of a projector attached to a lower surface of the upper plate portion to form a ceiling surface; A top plate suspended from four corners of the upper plate and supported by a support bar, so that the projector can be stably supported, but the upper plate and the top The four support rods can function as guard members that can prevent other objects from coming into contact with the projector.

[0010] By providing a guide means for preventing the support from swinging in the front-rear direction and the left-right direction when the support is raised and lowered, the projector swings (sways) not only at the time of lifting and lowering but also due to wind of a blower or the like. Can be reliably prevented.

[0011] The guide means includes: a fixed guide rail;
A movable member that slides with respect to the guide rail, and the movable member includes a plurality of movable portions that can be extended and retracted. In addition, it is possible to prevent the projector from swaying (swaying) due to the wind or the like, and it is possible to further increase the amount of elevation of the projector by the stretchable guide means.

By disposing the guide means and the sprocket at different positions in the horizontal direction so that the guide means does not interfere with the sprocket as the support moves up and down, the support is moved by the guide means. Lifting and lowering while being guided can be performed without being restricted by the sprocket, and the amount of lifting and lowering of the support can be increased accordingly.

[0013]

1 to 3 show a projector 1 according to the present invention.
Lifting device for raising and lowering the projector (hereinafter referred to as
(Referred to as a lifting device). The lifting device includes a fixed support 2 fixed in a ceiling, and a movable support 3 attached to the fixed support 2 so as to be able to move up and down, and for mounting and supporting the projector 1.
And a chain-type drive mechanism 4 for raising and lowering the movable support 3. Reference numeral 5 shown in FIG. 3 is a cover for substantially covering the entire lifting device, and may not be provided. H shown in FIGS. 1 and 2 is a ceiling. In addition, S shown in FIG. 3 is a control box, which is provided so as to protrude outward in the horizontal direction from the cover 5.

As shown in FIGS. 1 to 3 and 5, the fixed side support 2 has a pair of right and left vertical frames 6 and 6 having a substantially U-shape in plan view, and an upper side of the vertical frames 6 and 6. The front ends or the upper rear ends are connected and fixed in the left-right direction by bolts (or welding) B1 or the like.
And a pair of front and rear horizontal frames 7, 7 and a drive shaft 2 described later.
4 and a substantially U-shaped intermediate frame 8 for attaching an electric motor M described later. By connecting the left and right intermediate portions of the horizontal frames 7, 7 with the intermediate frame 8 as described above, there is an advantage that the strength of the support 2 itself can be increased, but the intermediate frame 8 is omitted. May be implemented.

As shown in FIGS. 5 and 6, guide means are provided for preventing the movable body 3 from swinging back and forth and left and right when the movable body 3 is raised and lowered. The guide means is a fixed-side guide rail (which may be attached by welding) attached to each of the inner surfaces of the vertical frames 6 and 6 by using a bolt B2 and a nut N1 (a core whose inside is open in plan view). , Any shape may be used.) 9 and a pair of front and rear vertical walls 9A, 9A of the guide rails 9 are respectively in contact with the inner and outer surfaces of the respective vertical rails 9A to sandwich the vertical wall 9A. A pair of upper and lower rotating rollers 10 and 10 and a lifting member 11 as a substantially T-shaped movable member in a side view fixed to the movable-side support 3 with bolts or the like. , Movable side support 3 The projector 1 is supported by the movable supporting member 3 so that never swing (swinging) in the longitudinal direction and lateral direction by the wind lift or when the air conditioner. One of the pair of left and right guide rails 9, 9 may be omitted, or may be implemented without any guide rails 9, 9. If the operation is performed in a state where the guide rails 9 and 9 are not provided at all, it is disadvantageous in terms of swinging (swaying), but the range in which the movable support 3 can be lowered is not restricted by the guiding means. There is an advantage that the length of a chain 28 described later can be used substantially effectively.

The guide rail 9 on the fixed side is connected to a sprocket 25 attached to a vertical frame 6 described later in FIG.
, The upper end of the guide rail 9 is located below the sprocket 25, and the elevation of the movable-side support 3 is restricted by the sprocket 25. For this reason, as shown in FIG. 10, the upper end of the guide rail 9 is arranged by disposing the guide rail 9 in a position different from the sprocket 25 in the horizontal direction, that is, by distributing the sprocket 25 and the guide rail 9 before and after the vertical frame 6. Can be positioned up to the upper end of the vertical frame 6, and there is an advantage that the amount of elevation of the movable support 3 can be increased accordingly. The other configuration shown in FIG.
Although there are some shapes slightly different from those shown in FIG. 6,
The members are substantially the same, and are denoted by the same reference numerals. FIG.
In this case, the elevating member 11 and the upper plate portion 19 are formed of the same member, and there is an advantage that the number of parts and the number of assembling steps can be reduced. Also, R1 and R2 shown in FIG. 10 are upper and lower limit switches for regulating the elevation position of the projector 1, and a lower limit switch R2 located below is provided so as to adjust the vertical position.

The control box S is connected to the cover 5 in FIG.
However, as shown in FIG. 11, by arranging the position of the electric motor M rationally as shown in FIG. 11, the control box S can be arranged inside the elevating device, The size of the apparatus in the horizontal direction can be reduced. As a result, as shown in FIG. 9, the horizontal width of the lifting device, that is, the horizontal width of the vertical frames 6, 6 can be made smaller than the opening K of the ceiling. In the lifting device of FIG. This is disadvantageous in terms of a mounting work surface in which the lifting device must be mounted before turning the ceiling up or the ceiling H must be turned up again after the ceiling H has been turned up. After the H is lifted, the lifting device can be attached via the opening K of the ceiling H, which is advantageous in terms of attachment work. The other components not described in FIGS. 9 and 11 are the same as those described above, and thus are denoted by the same reference numerals and description thereof will be omitted.

As shown in FIGS. 7 and 8, the movable member 11 is constituted by a plurality of movable parts which can be extended and contracted, so that the range of lowering of the movable support 3 can be enlarged. In other words, a first movable rail 12 having a substantially U-shape in plan view, constituting a first movable portion including a plurality of rollers 13 for supporting the guide rail 9 in a vertically movable manner,
The movable member 11 is formed from a substantially U-shaped second movable rail 15 in a plan view constituting a second movable portion having a plurality of rollers 14 for vertically supporting the first movable rail 12 inside the first movable rail 12. The movable support 3 is fixed to the lower end of the second movable rail 15 by screws or welding. Pins 1 protruding from the first movable rail 12 are provided on both sides (only one is shown in the figure) of the second movable rail 15.
A long hole 15A is formed in the vertical direction, which fits into the shaft of No. 6 so that the second movable rail 15 can descend to the first movable rail 12 via the long hole 15A. ing. Therefore, by lowering the movable-side support 3, first, the second movable rail 15 is lowered, and
A from the time when the upper end of A contacts the shaft of the pin 16
The movable rail 12 is lowered, and a contact-type limit switch (a non-contact sensor may be used) detects the position of the movable-side support 3 and stops the movable-side support 3 from descending. (The state of FIG. 8).
By raising the movable-side support 3, the second movable rail 15 is also raised, and the first movable rail 1 is moved from the time when the lower end of the elongated hole 15A contacts the shaft of the pin 16.
2 is raised, and a contact-type limit switch (a non-contact-type sensor may be used) detects the position of the movable-side support 3 and stops the movement of the movable-side support 3 by detecting the position of the movable-side support 3. (State of FIG. 7). As described above, the operation of the electric motor M described later is controlled by the detection means such as the limit switch to move the movable support 3 up and down, and the electric motor M described later is set by contacting the contact portion. Alternatively, the operation of the electric motor M may be controlled to detect the application of the load, and the movable support 3 may be moved up and down.

The movable support 3 is a projector 1
A mounting plate 17 whose upper end is fixed by a screw or the like, and an angle adjusting bracket (which can adjust the angle of the projector 1 in the left-right direction and the front-back direction) on the mounting plate 17.
And an upper plate portion 19 in a plan view in which the elevating members 12, 12 slidably engaged with the guide rails 9, 9 are attached, and a lower surface of the projector 1 are covered. Four ceilings are formed and are suspended from four corners of the upper plate portion 19 (any number is acceptable if it is two or more, but the greater the number, the more advantageous in terms of strength) And a ceiling cover 21 which is a top plate suspended and supported by the lower end of the bolt 20 of FIG. The upper end of the bolt 20, the lower end of the upper plate 19 and the lower end of the bolt 20, and the mounting brackets 22 of the ceiling cover 21 are fixed in a state of being positioned by a pair of upper and lower nuts 23, but are welded. Or other fixing methods.

The angle adjusting bracket 18 is formed of a substantially rectangular plate-like frame material in a plan view, and is pivotally connected to a suspending bracket 33 provided on the lower surface of the upper plate 19 via a pin 34 to support the angle adjusting bracket 18. A pair of left and right long holes 33 formed in the bracket 33
A, 33A, can be fixed by a pair of bolts 35, 35 screwed and fixed to the front and rear plates of the angle adjusting bracket 18, and the angle adjusting bracket 18 is turned around the axis of the pin 34 in the elongated holes 33A, 33A. By moving the projector 1, the angle of the projector 1 can be adjusted in the left-right direction.
Further, a bracket 37 having a hook portion 37A formed on a vertical plate portion for suspending and supporting the mounting plate portion 17 by being engaged with pin bodies 36, 36 protruding from the left and right plate portions of the angle adjusting bracket 18, respectively. Are welded to the mounting plate 17. A pair of front and rear long holes 37B formed in the vertical plate portion of the bracket 37,
The bracket 37 can be fixed to the angle-adjusting bracket 18 by a pair of bolts 38, 38 screwed and fixed to the left and right plate portions of the angle-adjusting bracket 18 through the 37B, and the elongated holes 33A, 33A. By rotating the bracket 37 around the axis of the pin 36 inside the projector 1,
Can be adjusted in the front-rear direction. Here, the angle of the projector 1 is adjusted, but the angle of the projector 1 may not be adjusted.

As shown in FIGS. 3 and 6, the drive mechanism 4 rotates through the electric motor M as a drive source, the left vertical frame 6, the intermediate frame 8, and the right vertical frame 6 in this order. A drive shaft 24 that is freely supported, sprockets 25 and 25 that are externally rotatably fitted at two locations at both ends in the longitudinal direction of the drive shaft 24, and a sprocket 25 that is integrally rotatably mounted substantially at the center in the longitudinal direction of the drive shaft 24. A driven gear 27 which is fitted and meshes with a drive gear 26 which is externally rotatably fitted to an operation shaft (not shown) of the electric motor M;
1, one end is connected and fixed via a roller chain bolt B3, and the other end is engaged with the sprockets 25, 25 and the other end is connected and fixed to the vertical frames 6, 6 via a roller chain bolt B3. It consists of a long chain 28,28. Accordingly, by rotating the operation shaft of the electric motor M to one side, the chain 2 is rotated.
By winding up the upper and lower ends 8 and 28, the movable support 3 on which the projector 1 is mounted and supported is raised until the upper limit switch (or a non-contact sensor or the like) R1 shown in FIG. As shown in FIG. 1, the projector 1 can be positioned in a storage posture stored in a ceiling, and from this state, the electric motor M is driven and rotated in a direction opposite to the direction, whereby the chain 2 is rotated.
The lower limit switch (which may be a non-contact type sensor or the like) R2 shown in FIG.
The movable-side support 3 is lowered until is detected, so that the projector 1 can be positioned in the use posture lowered below the ceiling surface as shown in FIG. As shown in FIG. 1, the electric motor M is driven by arranging the electric motor M in a state where its operation shaft m is substantially parallel to the drive shaft 24 and overlapping the drive shaft 24 in the front-rear direction. Although there is an advantage that the shaft 24 and the electric motor M can be arranged in the most compact state,
It is not limited to the arrangement shown in the figure.

By arranging the chains 28, 28 so as to draw a U-shape as shown in FIG. 6, the optimal engagement direction with the sprocket 25 is achieved, and the engagement can be performed smoothly. The length of the chains 28, 28 is set to be equal to or slightly longer than the guide length guided by the guide rails 9, 9. However, when the guide rails 9, 9 are omitted, The amount of elevation of the projector 1 can be changed according to the set lengths of the chains 28. By connecting and fixing the other end of the chain 28 to the vertical frame 6 as described above, the meshing direction of the chain 28 with the sprocket 25 is not changed as described above, and the same direction can always be maintained. Although there is an advantage that the meshing can be performed well, it is not always necessary to connect them.

As shown in FIGS. 3 and 6, a pair of front and rear bolts 30, 30 penetrating the vertical frame 6 through plate-like cover members 29, 29 for covering the inner sides of the sprockets 25, 25. They are attached by nuts 31 to be screwed together. Then, the cylindrical members 32, 32 are externally fitted to the bolts 30, 30, and the sprocket 25,
Blocking means for preventing the chain 28 meshing with the chain 25 from moving to the meshing releasing side is configured. The positions of the cylindrical members 32, 32 are located on the outer peripheral side of the sprockets 25, 25 and the chains 28, 28.
Any position may be used as long as it does not come into contact with and does not cause the chains 28, 28 to come off. Further, the shape and number of the blocking means are not limited to those shown in the drawings.

[0024]

According to the first aspect of the invention, since the other end of the chain is engaged with the sprocket, the projector can be moved up and down according to the length of the chain. By using such a chain type, it is possible to greatly increase (spread) compared to the lifting stroke using a ball screw as shown in
The size of the apparatus can be reduced accordingly. In addition, even if installation is not possible due to the size of the space inside the ceiling, it is not only possible to install it, but it is also advantageous in terms of handling, especially for useful projectors that are easy to install in the ceiling An elevating device can be provided. In addition, since a timing belt for winding around a number of rotating bodies (such as pulleys) is not required, the electric motor for driving the sprocket can be centrally arranged at a specific location, and the size of the apparatus can be further reduced. Can be. Further, since the chain and the sprocket are meshed with each other, an error due to a slip or the like, such as a string or a rope, does not occur, and a complicated configuration for performing elevation control can be eliminated. Further, if the other end of the chain is fixedly connected to the fixed side, there is an advantage that the engagement with the sprocket can be performed smoothly.

According to the second aspect of the present invention, a sprocket is attached to each of the left and right ends of a drive shaft extending linearly in the left-right direction so as to be integrally rotatable, and one end of each of the chains meshing with the two sprockets is attached to the support. By connecting, the lifting and lowering can be performed smoothly and stably as compared with the lifting and lowering with one chain, which is advantageous in durability.

According to the third aspect of the present invention, a chain is disengaged from the sprocket by providing a predetermined portion on the outer peripheral side of the sprocket with a blocking means for preventing the engaged chain from moving toward the disengagement side. Thus, it is possible to provide a projector elevating device that can be used favorably for a long period of time.

According to the fourth aspect of the present invention, the electric motor is disposed at a position overlapping the drive shaft in the front-rear direction in such a manner that the drive shaft is substantially parallel to the drive shaft. Are linked by a gear mechanism, the drive shaft and the electric motor can be arranged in the most compact state, and a more compact elevating device can be obtained.

According to the fifth aspect of the present invention, the support is provided so as to cover an upper plate having a substantially rectangular shape in plan view to which one end of the chain is connected, and a lower surface of the projector attached to a lower surface of the upper plate. The projector can be stably supported by forming a surface and having a top plate portion suspended and supported by support rods hanging down from four corners of the upper plate portion. Plate part, top plate part,
The four support rods can function as guard members that can prevent other objects from coming into contact with the projector, and can have a preferable configuration for the lifting device.

According to the sixth aspect of the present invention, by providing the guide means for preventing the support from oscillating in the front-rear direction and the left-right direction when the support is raised and lowered, it is ensured that the projector vibrates during the vertical movement. The lifting and lowering can be performed in a favorable state without operation failure during lifting and lowering and detachment of the chain.

According to the seventh aspect of the present invention, the guide means comprises a fixed-side guide rail and a movable member which slides with respect to the guide rail, and the movable member comprises a plurality of movable portions which can extend and contract. By doing so, it is possible to raise and lower the projector in a stable state without vibration as described above, but it is possible to avoid that the elevation of the projector is limited by the guide means, and a projector elevating device that is advantageous in terms of use. can do.

According to the eighth aspect of the present invention, the guide means and the sprocket are arranged at different positions in the horizontal direction so that the guide means does not interfere with the sprocket as the support moves up and down. Can be lifted and lowered while being guided by the guide means, without being restricted by the sprocket, so that not only the amount of lifting and lowering can be increased by that amount, but also the lifting device can be made more compact. It is possible to provide an elevating device in which the elevating device can be mounted even in a narrow space above the ceiling, which has been difficult to mount, and the elevating device can be spread.

[Brief description of the drawings]

FIG. 1 is a partially sectional front view of an elevating device in which a projector is in a storage position.

FIG. 2 is a partially sectional front view of the elevating device in which the projector is in a use posture.

FIG. 3 is a plan view of the lifting device.

FIG. 4 is an exploded perspective view showing a structure in which the angle of the projector can be adjusted.

FIG. 5 is an exploded perspective view showing a configuration of a guide unit.

FIG. 6 is a perspective view of a main part showing a meshing portion between the chain and the sprocket.

FIG. 7 is a perspective view showing another guide means.

FIG. 8 is a perspective view showing a state in which the guide means of FIG. 7 is at the lowest position.

FIG. 9 is a partially sectional front view showing another elevating device.

FIG. 10 is a partially sectional side view showing the lifting device shown in FIG. 9;

11 is a plan view showing the elevating device shown in FIG.

FIG. 12 is a perspective view showing a conventional elevating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Projector 2 Fixed-side support body 3 Movable-side support body 4 Drive device 5 Cover 6 Vertical frame 7 Horizontal frame 8 Intermediate frame 9 Guide rail 9A Vertical wall 10 Rotary roller 11 Lifting member (movable member) 12 First movable rail 13, 14 Roller 15 Second movable rail 16 Pin 17 Mounting plate 18 Angle adjusting bracket 19 Upper plate 20 Bolt 21 Top cover 22 Mounting bracket 23 Nut 24 Drive shaft 25 Sprocket 26 Drive gear 27 Follower gear 28 Chain 29 Cover member 30 Bolt 31 Nut 32 Cylindrical member (blocking means) 33 Suspension bracket 33A Long hole 34 Pin 35 Bolt 36 Pin body 37 Bracket 38 Bolt 50 Lifting plate 51 Guide roller 52 Supporting body 53 Ball screw 54 Rotating roller 55 Timing gear 56 Tension roller 57 Electricity Motor 58 operating shaft 59 driving roller 60 a timing belt 61 the upper plate portion B1, B2 bolts B3 roller chain bolts H ceiling K opening N1 nut M electric motor P pins R1, R2 limit switch S control box

Claims (8)

[Claims] An end of a chain is connected to a support for mounting and supporting a projector, the other end of the chain is engaged with a sprocket provided in a ceiling, and a rotating shaft of the sprocket is rotationally driven. A projector lifting / lowering device provided with an electric motor and configured to be able to move up and down between a storage position in which the projector is stored in a ceiling and a use position lowered below a ceiling surface by using a driving force of the electric motor. 2. The drive system according to claim 1, wherein said sprocket is integrally rotatably mounted on each of left and right ends of a drive shaft extending linearly in the left-right direction, and one end of each of said chains meshing with said two sprockets is connected to said support. 2. The lifting device for a projector according to 1. 3. The projector elevating device according to claim 1, further comprising a blocking means provided at a predetermined position on an outer peripheral side of the sprocket to prevent the chain in the engaged state from moving to the unengaged side. . 4. The electric motor is disposed at a position overlapping the drive shaft in the front-rear direction in such a manner that an operation shaft thereof is substantially parallel to the drive shaft, and the electric motor and the drive shaft are geared. The lifting device for a projector according to claim 1 or 2, wherein the lifting device is linked with a mechanism. 5. A ceiling, which is formed by covering an upper plate having a substantially rectangular shape in plan view to which one end of the chain is connected, and a lower surface of a projector attached to a lower surface of the upper plate. 2. The projector as claimed in claim 1, further comprising a top plate suspended and supported by support rods hanging down from four corners of the upper plate. 6. The projector as claimed in claim 1, further comprising guide means for preventing the support from oscillating in the front-rear direction and the left-right direction when the support is raised and lowered. 7. The projector according to claim 6, wherein the guide means comprises a fixed-side guide rail and a movable member that slides with respect to the guide rail, and the movable member comprises a plurality of movable portions that can expand and contract. Lifting device. 8. The sprockets are arranged at different positions in the horizontal direction so that the guides do not interfere with the sprockets when the support is moved up and down. Or the lifting device for projector according to 7.