Patent Application
20070285035
The invention is directed to an electromotive linear drive for the adjustable components of an item of furniture, with a housing having spaced-apart housing walls with aligned openings for receiving the axle of a movable furniture component, and with a closing element which covers the openings and is secured on the corresponding edges of the housing walls for securing the axle, with a drive motor and a rotation speed reduction gear coupled to the drive motor and having at least one driven element for driving at least one linearly movable actuator which operates on an articulated lever attached to the axle for converting its linear motion into a rotary motion of the axle.
The aforedescribed electromotive linear drive is known in many variations. It represents a so-called single drive with a drive motor and an actuator. The electromotive linear drive can be used to adjust the stationery, but rotatably supported shaft of the backrest or the foot section of a slatted frame. These are mass-produced articles which should be offered that the lowest possible price. As many components as possible are therefore made of plastic by injection molding. Because the rotation speed reduction gear is typically a worm gear, the worm is made of steel or the driven shaft of the drive motor is implemented as a worm. The worm wheel engaging with the worm is made of plastic. The housing is typically also a plastic housing. In conventional linear drives, the worm wheel drives a spindle which is usually also fabricated of steel, because such spindles are commercially available as standard parts. A spindle nut, which is secured against rotation, is placed on the spindle and moves in the longitudinal direction of the spindle, when the spindle rotates, depending on the rotation direction. The spindle nut is made of plastic and presses against the articulated lever made of steel. The end positions of the spindle nut are typically preset by two limit switches. Such drives should be quite compact when used in conjunction with a slatted frame, because the manufacturer of a slatted frame already installs these linear drives on the slatted frame. Moreover, the height of a slatted frame should also be as small as possible to facilitate stacking, and provide space-saving storage and space-saving transport.
In conventional implementations with a spindle and an attached spindle nut, the linear drive is relatively long, whereby the length of the linear drive is defined as the distance between one end and the opposite end, wherein the contemplated connection extends transversely to the rotary shaft of the motor.
It is an object of the invention to design an electromotive linear drive of the aforedescribed type, so that full functionality is ensured with the smallest possible dimensions and the smallest possible number of components.
The object is solved in that the driven element of the rotation speed reduction gear is a toothed wheel or a worm wheel, which is provided with a central bore having an interior thread, and that the actuator is an adjusting spindle which is in engagement with the toothed wheel or a worm wheel and secured against rotation and only moveable along its longitudinal direction, wherein the adjusting spindle is operatively connected with the articulated lever.
Unlike with conventional embodiments, the toothed wheel or worm wheel of the rotation speed reduction gear is hereby provided with a central bore with an interior thread, which engages with the spindle forming the actuator. When the toothed wheel or worm wheel turns, the spindle moves relative to the toothed wheel or worm wheel in a direction that depends on the rotation direction of the toothed wheel or worm wheel. Because the actuating spindle is directly or indirectly operatively connected with the articulated lever, not only is the spindle nut eliminated, but the length of the housing is significantly reduced compared to conventional embodiments, because unlike with conventional embodiments, the actuating spindle is now located on both sides of the toothed wheel or worm wheel. The reduced dimensions of the housing also save material, thereby lowering the total manufacturing costs. The travel speed of the connected furniture component is not decreased, because the pitch of the threaded portion of the actuating spindle can be designed so that the spindle nut attains the same speed as with conventional drives.
According to another embodiment, the closing element is moveable in the longitudinal direction of the axle in guides of the housing walls and is formfittingly connected in the end position with the upper edges of the housing walls.
The closing element now moves transversely to the longitudinal axis of the housing, so that force transmission is more advantageous than with the conventional linear drives. In the aforedescribed linear drives, the forces act in the longitudinal direction of the housing due to the configuration of the drive arrangement and therefore transverse to the travel direction of the closing element. The closing element in conventional linear drives is always viewed as a critical element of the drive. In the linear drive of the invention, the forces applied to the closing element can be transferred via the contact faces between the closing element and the housing walls.
A formfitting connection between the closing element and the housing walls is achieved by providing at least two undercut grooves in each housing wall, whereby the undercut grooves in the housing walls are aligned with one another. These components are made of plastic and can be shaped by a suitable design of the injection mold or injection molds. To achieve adequate guiding and an acceptable surface pressure, two grooves are provided in each housing wall on both sides of the aligned recesses, wherein at least the groove facing the recess is undercut. The closing element has, for formfitting attachment, safety ribs which engage with grooves disposed in the housing walls. These safety ribs extend advantageously from one longitudinal side to the opposite longitudinal side, which facilitates insertion of the closing element from the side. The closing element can also be provided with safety elements along its outside edges which prevent accidental movement of the closing element. These safety elements may include integrally formed ribs, beads, components which are additionally joined with the closing element, or a combination of thereof, which extend for force transmission or formfittingly behind a housing edge or in a housing edge, after the closing element is placed in its final position. Advantageously, the closing element is stabilized by longitudinal ribs extending on the free outer surface in the longitudinal direction; the ribs may also may extent through the outside towards the inside. Because the closing element is mainly subjected to a bending load, longitudinal or transverse ribs of significant height are advantageous, which may extent over the entire height of the closing element. To prevent accidental movement of the closing element, the closing element may include integrally formed or attached sections which engage for force transmission and/or formfittingly in the housing or on the housing. In addition, the safety elements can also be housed inside the housing. Advantageously, the safety element may be held between the housing parts after the linear drive is installed, while a free end of the safety element engages springily with or snaps into a recess of the closing element, thereby securing the closing element against accidental movement.
The housing of the aforedescribed electromotive linear drive is conventionally fabricated of plastic and is made of two housing halves, with the contacting surfaces arranged transversely to the rotary shaft of the motor. This facilitates installation of the components arranged in the interior, because the housing halves are then oriented in the installation position so as to be open towards the top, thereby leaving adequate space for assembly robots. The components arranged inside the housing halves are preferably secured without mechanical connecting elements simply by a corresponding shape of the housing halves, thereby eliminating mechanical connecting elements. Because the generated forces are transferred via the housing halves, the contacting surfaces of the housing halves are profiled, toothed or have a similar shape, and mesh with one another. Alternatively, the screw domes can include ring-shaped pegs, ribs or recesses which are arranged repeatedly and concentrically about the mounting screws. Alternatively, the housing halves may include ring-shaped pegs, ribs or openings which are arranged concentrically with respect to one another and extend around fastening screws such that the housing halves nest with each other when the screws are tightened. When the two housing halves are mounted, these pegs, ribs or recesses engage with one another and are firmly pressed into each other when the respective screw is tightened, so that the housing halves are secured against each other formfittingly and immovably. This effectively prevents even a small displacement of the two housing halves relative to one another. To keep the wall thickness of the housing halves as small as possible, the wall thickness can be reduced through reinforcement with fibers, preferably glass fibers.
The electromotive linear drive can operate by having the spindle extend or protrude from the housing when the spindle is retracted, i.e., when the connected furniture component is lowered. However, the spindle would then be exposed to the environment, for example to contamination from dust. To this end, the housing includes a cover made of a rigid or elastic material and located on the side facing away from the articulated lever, with the spindle engaging with the cover in the retracted position. The cover may be snapped onto the housing or screwed together with the housing; advantageously, the housing together with the cover may be formed as a single molded piece. To prevent the housing or the electromotive linear drive from rotating when the drive motor that adjusts the connected furniture component is energized, the housing may include an opening or a recess on the side facing the drive motor for providing a torque support. Advantageously, the width of the opening of the torque support may be adjusted by a component or a closing mechanism, or the opening may be covered with an additional closing element. The cross-sectional shape of this opening or recess is adapted to the component, and is preferably either circular or semicircular. With the open design, the linear drive can advantageously be attached to the component forming the support.
To give the housing sufficient rigidity for force transmission, the housing may include intersecting reinforcing ribs. To give the housing an appealing shape, since it is preferably smooth on the outside, with the intersecting reinforcing ribs arranged in the interior of the housing.
At least the ribs adjacent to the recesses can be concentric with the recesses. The intersecting ribs or the ribs oriented towards the recesses extend initially parallel and are spaced from the upper edge of the housing, and thereafter at an acute angle. To prevent obstruction of the travel of the articulated lever that lifts the furniture component, reinforcing ribs are absent from the travel area. Advantageously, the outer wall of the housing may jut outward in the immediate vicinity of this housing region, may have an outward curvature, or may have a combination of these features. Accordingly, the ribbed structure on the interior side of the housing can be even more prominent, whereby the housing can be designed to be stiff in zones exposed to high loads.
Depending on the application of the electromotive linear drive, the spindle can be made of steel or plastic. If the spindle is made of plastic, a pressure block is fixedly placed on the end region of the spindle facing the articulated lever to prevent the end region from deforming. The pressure block is advantageously made of plastic, preferably forms a molded part together with the spindle, and is provided with a metallic reinforcing insert. The metallic reinforcing insert may be located inside the block, whereby the metallic reinforcing element can be manufactured by extrusion-coating. However, the metallic reinforcing insert can also be attached to the plastic block of the side facing the articulated lever or snapped together with the plastic block if the plastic block is suitably shaped. The metallic reinforcing insert can also be constructed as a clip. If the spindle is made of steel, a pressure block made of steel or plastic can be connected with the spindle formfittingly or by a material connection. The contact surface between the pressure block and the articulated lever can also be oriented at a right angle with respect to the longitudinal center axis of the spindle or can be inclined with a relatively small acute angle, whereby this angle can be for example between 5° and 20°. The articulated lever is typically made of steel. This combination of materials is generally disadvantageous, but may be practical in the present example, because the travel speed of the spindle is relatively low. The pressure block or the reinforcing insert can also be made, at least in certain sections, of hardened steel, which minimizes wear between this component and the articulated lever. At least the surface of the articulated lever may also be hardened in the region contacting the pressure block or the reinforcing insert. Moreover, another material potentially harder than steel could be used in lieu of the pressure block or the reinforcing insert made of steel, for example, hard metal alloys or ceramics.
In a preferred embodiment, the articulated lever made of metal has an angular shape and can be fabricated as a punched part of steel or as a cast steel part with parallel side faces. The material combination where steel frictionally engages with steel can produce disconcerting noise which can be eliminated by shaping the surface of the articulated lever facing the pressure block as an arc or as a semicircle. For keeping the parts count as low as possible, it is generally known to have an arcuate section of the articulated lever directly contact the driven element of the linear drive along a line, and to have the arcuate section of the articulated lever frictionally engage with the end phase of the linearly movable driven element. This line contact produces high contact forces, which may cause excessive wear. In another embodiment, a pressure plate similar to a sliding block is arranged between the arcuate section of the articulated lever and the friction surface of the linear driven element. The pressure plate has on the side facing the articulated lever a circular trough which cooperates with a circular arcuate section of the articulated lever. During operation of the linear drive, the arcuate section of the articulated lever frictionally engages with the trough in the pressure plate, and the flat surface of the pressure plate frictionally engages with the linear driven element in front of the contact surface. This additional component transforms the aforedescribed linear contact into an area contact, distributing the forces over a significantly larger area.
To simplify the installation of the electromotive linear drive, for example in an article furniture, it may be advantageous to secure the pressure plate on ribs disposed on the linear driven element. Alternatively, the pressure plate may also be connected to or firmly attached to the articulated lever, thereby providing a kind of articulated joint between the articulated lever and the pressure plate, for example through trough-shaped recesses.
The worm wheel is advantageously supported by a roller bearing which is inserted in a gear angle implemented as a molded or cast part and connected by screws with the housing of the drive motor. The gear angle is made of a sleeve and a mounting flange attached to the sleeve. The gear angle can be easily manufactured as a molded plastic part and can be reinforced with fibers, preferably glass fibers.
To optimize the frictionally engaging parts, on one hand, between the motor shaft and the worm gear and, on the other hand, between the worm gear and the spindle, the worm wheel is formed in two parts and includes an outer rim and a support sleeve engaging with the outer rim, wherein the support sleeve is provided with the interior thread and on the outside with a bearing seat for the roller bearing. The components are made of different materials, which in particular make it possible to use only a single roller bearing for supporting the worm gear and the spindle. Advantageously, the outer rim is formfittingly connected with the support sleeve, for example, through ribs engaging with grooves formed in the other component. Alternatively, the worm wheel with the interior thread and the outer bearing seat for the roller bearing may also be formed as a one-piece molded plastic part. This reduces the overall number of components.
Preferably, the aforedescribed linear drives are preferably self-locking through suitable design of the spindle and, in the present example, also the interior thread, meaning that the connected component remains in the respective position when the drive motor is switched off. However, an increase in the travel speed requires spindles with a greater pitch, so that the linear drives are no longer self-locking. According to another embodiment, the linear drive may include a brake element acting in a travel direction of the spindle which is mounted between a rotating component and a stationary component. In a preferred embodiment, this component is a spring brake element having several turns, whereby one end of the winding is secured in the sleeve of the gear angle, while the spring brake element is otherwise arranged on the bearing seat of the worm wheel. Alternatively, the free windings of the spring brake element may be wound around a cylindrical projection.
In an embodiment employing a spindle made of steel, the end of the spindle facing away from the drive motor, instead of the pressure block, could operate on a slide block which is movably guided in the housing and which operates on the articulated lever. In one embodiment, the sliding block could be made of plastic, so that the material combination between the movable articulated lever and the sliding block would match. The end face of the spindle could be oriented perpendicular to the longitudinal center axis of the spindle or at an angle, for example with respect to the vertical, which would optimize force transmission to the articulated lever. Because it is desirable to install the aforedescribed linear drives with assembly robots, which requires keeping the number of mechanical mounting elements as small as possible, the housing halves include mounting ribs oriented transversely to the longitudinal center axis of the spindle and supporting the end faces of the sleeve of the gear angle. When the electromotive linear drive adjusts the furniture component against gravity, this occurs in the major loading direction. The item of furniture can be returned to its original position by gravity, whereby the aforementioned stop edge may support the gear or a gear component against displacement. A pressure element of the spindle operating on the articulated lever may be designed to have steps, with the stepped surface located on the side facing the articulated lever, thereby providing an area contact between the side surface of the articulated lever and the stepped surface.
The housing is advantageously designed so that the drive motor with the flanged-on gear angle and the worm wheel as well as the roller bearing can be mounted in the housing as a unit, and that the contact surfaces with the housing or with the housing half can provide support without the use of mechanical elements, for example safety elements. The aforedescribed electromotive linear drive is preferably used to adjust furniture components. As little noise as possible, which also should not be objectionable, should be emitted with the linear drive switched on. For this reason, at least the region located between the gear angle and the housing is filled with a sound-absorbing material. This could be, for example, an inserted rubber element or an extrusion-cast resilient element disposed on the housing and/or the gear. In cross-section, the housing is rounded at least on the bottom side facing the openings for the axle. To facilitate stacking of those slatted frames during transport, which are already provided with one of several electromotive linear drives, two transport elements can be attached to the housing formfittingly and/or for force transmission. This prevents the slatted frames from tipping or sliding relative to one another. Advantageously, the free side of the transport elements, i.e. the side facing away from the housing, includes aligned semicircular tapers. However, these tapers can also be integrally formed on the housing halves of the electromotive linear drive.
A terminal for a power cable can be provided on the housing near the drive motor for supplying electric power to the drive motor. A printed circuit board can be arranged inside the housing or in a extended space of the housing, so that cables can be eliminated. Advantageously, the motor including the terminal are protected by a cover, which prevents interruption of the electric power. These items are particularly difficult to repair, because the electromotive linear drives of articles furniture are typically not easily accessible. Finally, the end positions of the spindle are limited by limit switches.
The pressure block can also be made of steel and welded with a steel spindle. To prevent abrasion caused by movement of the pressure block, the steel pressure block may be provided with an externally applied plastic guide, which in a preferred embodiment has two plastic caps which are, for example, placed on the sides of the pressure block, preferably formfittingly. The caps can also be screwed together.
Moreover, a control board with mounted electric components for controlling at least one electric motor can be arranged inside the housing, or a printed circuit board could be installed inside the housing as a current distribution board to separate and forward the electric signals to the control and the power supply.
In addition, ribs, pegs or rails may be formed on the housing for formfitting attachment of a control housing or a power distribution unit. The housing may include additional ribs and/or recesses for formfitting attachment of a power cable or a power distribution or a plug connector for transmitting electric power.
These as well as additional ribs or pegs can also be used for attaching power supply units, control units and mounting units, so that for example all devices, equipment, operating components and mounting means required for the operation may be attached to the housing during transport of the electromotive linear drive, thereby forming a compact unit. These include, for example, transformers, DC power supplies, manual switches of the closing elements, etc. To this end, suitably shaped pockets or ribs for receiving these components are provided on the housing. The elements or components attached to the housing can be detached from the housing after transport
Moreover, ribs may be formed on or integrated in the housing for securing a connecting cable. Radii or arcuate sections or molded sections are also provided for supporting a cable so as not to a low a bending radius smaller than a minimally allowable bending radius. To this end, ribs or pegs are formed on the housing or in the housing to secure a cable for stress relief. Arcuate projections or recesses may also be formed on the housing or in the housing for supporting a cable with a minimum allowable bending radius as an anti-kink protection for the cable.
In addition, the motor connection can be designed as a plug connection. To prevent the plug from being pulled out accidentally, ribs can be formed on the housing of the linear drive which hold the housing of the plug in force transmitting or formfitting engagement. Instead or in addition, safety elements can also be attached on the housing of the being a drive, which secure the plug or the cable leading from the plug on the housing of the linear drive. This can be implemented by forming ribs or pegs on the housing or in the housing, which connect at least one terminal, for example a motor terminal, with the housing for force transmission or formfittingly. Alternatively, a safety element which secures a motor terminal on the housing may be attached to the pegs or ribs.
According to another embodiment, the linear drive and the housing may be constructed so that the drive can be installed, for example in an article furniture, without tools and by simple manipulation or by a robot. The linear drive and the housing are constructed to allow installation by hand or by a machine without the use of tools.
Use of the linear drive is normally limited to dry environments. To expand the applications of the linear drive, a seal is provided to prevent moisture and dust from entering the drive. The contacting surfaces of the housing can be implemented as a labyrinth seal. Preferably, one or several sealing elements made, for example, of an elastic material are introduced between the contacting surfaces of the housing parts, between the contacting surfaces located between the closing element, the housing and the axle. For example, one or several sealing elements for sealing the linear drive can be provided between the housing parts, the cover, the closing element, the axle, and the motor connection. The sealing elements can be implemented as individual and elastic elements or can be integrally formed on the components of the linear drive.
The electromotive linear drive illustrated in FIGS. 1 to 5 is a so-called single drive, i.e., the drive is designed to adjust a furniture component, in particular the backrest or the footrest of a slatted frame. The gear components of the electromotive linear drive 10 are arranged in a generally closed housing 11, which is composed of two housing halves 11a and 11b. The gear components are driven by a conventional DC motor which also has an outer housing 11. The housing 11 and the housing halves 11a and 11b are made of plastic. The two housing halves 11a and 11b are connected with several screws 13 which are screwed into domes of the housings half 11b in a manner not described in detail. The domes are formfittingly connected with corresponding counter elements in the other housing half 11a, thereby effectively preventing displacement between the housing halves 11a and 11b under load.
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The outside of the housing 11 can also be provided with ribs or similar elements (not shown) for attaching a manual control unit. The manual control unit can thereby be secured during transport. In addition, pockets or webs for receiving batteries or rechargeable power sources can also be located in the housing 11 or on the housing 11 for supplying emergency power.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-023-245.8 | May 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/04065 | 4/16/2005 | WO | 7/23/2007 |
