WO2009146709A2

WO2009146709A2 - Adjustable article of furniture

Info

Publication number: WO2009146709A2
Application number: PCT/DK2009/000137
Authority: WO
Inventors: Norbert Klinke; Søren LOLK
Original assignee: Linak A/S
Priority date: 2008-06-06
Filing date: 2009-06-08
Publication date: 2009-12-10
Also published as: EP2299870A2; WO2009146709A3; EP2299870B1

Abstract

An adjustable table into which a linear actuator (8) is incorporated, where a squeeze protection device (11) is arranged in connection with the table. The device for squeeze protection (11) is arranged in connection with a mounting bracket, which connects the adjustable column (1) to the table top (5). The device for squeeze protection is based on a piezo element (16, 28) incorporated in the mounting bracket (14, 22). The piezo element (16, 28) is equipped with cables (29, 38), so that the signal from the squeeze protection in a simple manner may be communicated to an operating and control device (6), which can stop the motor (10) or momentarily reverse the direction of movement thus releasing a trapped object.

Description

Adjustable article of furniture

The invention relates to an adjustable article of furniture as stated in the preamble of claim 1.

The explanation of the invention departs from an adjustable article of furniture in the shape of a height- adjustable table. In its basic form a height-adjustable table consists of a foot section, a telescopic column with a motor drive, which enables the height of the column to be adjusted, and a table top mounted thereon. Generally, the structure is also furnished with a transverse beam between the adjustable columns.

As motor drive in height-adjustable tables linear actuators are used, which exert large forces during the adjustment, for which reason the problem exists that the table may cause injuries due to squeezing as a result of an encounter with an object. First and foremost, personal injury, if a part of the body is caught above or below the table top, is considered. Another scenario is if the table top unintentionally hits a fixed object. This could e.g. be a windowsill or a computer or drawer arrangement located under the table . In the last examples the focus is on both the consideration for the trapped object but also protection of the motor drive in the height- adjustable table.

Solutions for squeeze protection for use in connection with tables are already known. WO 03/071897 Al discloses a device for squeeze protection based on a measurement of the motor current . When the motor current exceeds a predetermined threshold, indicating that the table top has hit an object, the motor is momentarily stopped or reversed. The squeezing which activates the squeeze protection is here so extensive that personal injuries or damage to objects should be expected.

US 5 495 811 to Ergoflex System likewise discloses two solutions for squeeze protection in connection with a table. The first solution describes how a table top is loosely suspended in its frame and rests on a switch. In the downwards direction, the table top will, if it meets an obstacle, be lifted from the switch and thus interrupt the motor. The table top with its entire weight thus rests on the trapped object. However, if the carrying frame hits an object in the downwards direction, the squeeze protection will not be activated. The same applies if the squeezing occurs in the upward direction between an object and the top side of the table top. The other outlined solution is the use of so-called tape switches adhered to the underside of the table . Logically, the squeeze protection only functions where the switches are placed and does therefore not provide a secure squeeze protection. It would not make sense to place these on the upper side of the table top, which means that the squeeze protection can only function in the downwards direction of the table top.

The present invention tends more towards SE 516 479 C2 to Artektron AB. Here, load cells in the form of strain gauges are used, which are incorporated in a U-shaped profile located between the motor drive and the table top, alternatively between the table leg and the foot. It is obvious that the load on the U-shaped profile and thus the signaling from the load cell will depend on where above or under the table top the squeezing occurs as a torque load will affect the load cell more than a load directly on top of the U-shaped profile or near the table leg. This means that a squeezing at the rear edge of the table top hardly would be indicated, as the torque load here is considerably smaller that a corresponding load at the front edge of the table top. A squeeze protection of the type as shown does therefore not solve the problem in an expedient manner, and does not contribute knowledge as to how a squeeze protection is carried out in praxis .

Another solution to the outlined problem is thus required, namely to construct a squeeze protection device in connection with an adjustable article of furniture, which is both simple and inexpensive, but is also more integrated with the actuator in the adjustable column, even though the device in so far in a simple manner may be retrofitted.

This is achieved according to the invention by designing the adjustable article of furniture as stated in claim 1, where the squeeze protection device comprises a piezo element incorporated in a bracket, which connects the table top to the adjustable part, so that dynamic deviations of the load on the table are reflected in the read-out from the piezo element. In that the squeeze protection device is located in the longitudinal axis of the spindle, the sensitivity towards torque loads has been moderated, so that the squeeze protection device will be able to register a squeezing irrespective of where under or above the table it occurs . This reduces the dynamic range of a squeezing signal, for which reason a squeezing may be determined with greater certainty, by means of which the number of cases with false squeezings is minimized.

In that the squeeze protection device itself is directly incorporated into a top flange for mounting the adjustable leg with the actuator to the table, a solution is provided, which is both simple and inexpensive, but is also more integrated with the actuator in the adjustable column even though the device in so far in a simple manner may be retrofitted.

The device for squeeze protection comprises a piezo element, which is particularly expedient, as a piezo element does not express a static state, but only a dynamic movement when the piezo element is mechanically activated. The activation is caused by the piezo element getting squeezed or bent, at which a brief voltage pulse is generated. Here it concerns a piezo element of the type, constituting the membrane in an acoustic generator device. This membrane is moved, when being used as an acoustic generator device, in that an electric voltage is applied between two points on the disc, causing the piezo crystals to expand or retract. A corresponding effect, which is used in the invention, is achieved when a piezo element is bent at which a voltage is generated and may be used as an expression for the deflection of the piezo element. If the piezo element is arranged in connection with a mechanical part, which is bent during squeezing of an object, the piezo element can thus indicate that an incident in the form of a squeezing occurs.

The mounting bracket, which connects the column to the table top, is designed as a two-piece structure, consisting of a mounting flange and a housing. The piezo element is located between these two parts. The flange is equipped with holes for mounting the bracket against the table top or the table frame with screws and further there are holes for oppositely directed screws for connecting the bracket to the column. The bracket may thus be wrenched or bent moderately over a distance between the two fixtures for the column and table top or table frame, respectively. The flange, which is typically of metal, is, over the distance between the fixture points mentioned above, equipped with punching in order to make the flange more flexible. This means that a squeezing will feed into the bracket and result in a slight bending of the flange.

The housing may be designed to receive the mounting flange and surround this on the surface, facing towards the table top. If the housing is equipped with flaps, functioning as snap locking means, the two parts may be held together as a unit before being mounted on the column and the table top. For that reason, the entire squeeze protection device, consisting of the mounting flange, the piezo element and the housing, may be assembled after the production and be shipped to the customer as an assembled unit. Hereby, the piezo element is protected against damage during transportation in that is it located in its position in the housing. The housing may further, as described above, be designed in such a way that the mounting flange is hidden herein, so that the unit appears as more elegant . When the mounting flange is mounted up against the table top by means of screws, penetrating through holes in the housing, the two units are clamped together, and consequently the housing will be bent in the same way as the flange during a squeezing.

In one of the parts of or between the two-piece structure a holding arrangement for a piezo element of the membrane type is placed, so that this may be positioned between the mounting flange and the housing.

The holding arrangement is designed to support the membrane- like piezo element on the outermost diameter, so that the centre point is not supported. The holding arrangement is further secured to one of the parts in the two-piece structure as a first fixed point. To the centre point of the piezo element is connected a spring, which is in connection with the second part of the two-piece structure . The spring performs a certain spring force on the piezo element thus creating a prestress on the piezo element . This both causes the piezo element to be retained in its position and results in that the piezo element to a certain degree is bent and located in an active area, where the spring may move proportional to a squeezing both on the underside and upper side of the table. Expediently, it will be possible to adjust this prestress of the spring and with it the piezo element e.g. by means of a pointed screw, which compresses the spring even more. A squeezing would thus cause the mounting bracket and the housing to be wrenched, at which the piezo element in its holding arrangement also would be affected. This stress on the piezo element is minimal, for which reason it will never be destructively deformed, but the stress is nevertheless enough for a positive indication of a squeezing. That the piezo element is affected by a spring is particularly appropriate as the spring will function both as a gearing and a protection from damage of the piezo element. Further, the spring functions as a filter and for scaling the dynamic range of the signal indicating a squeezing.

The structure is also expedient in that the frictional forces, which may occur internally in the column between the separate telescopic members, will not affect the piezo element as this is not located in the lines of forces between the column and the actuator. For that reason the piezo element will not be influenced significantly by the dynamic forces, exerted during start or stop of the motor in the actuator. The dynamic forces affecting the piezo element are therefore exclusively related to the wrenching of the table top which is caused in connection with a squeezing.

An adjustable article of furniture according to the invention will be described more fully below with reference to the accompanying drawing. In the drawing,

Fig. 1, shows a height-adjustable table where the table top is shown transparent and the actuators are shown separately in their retracted state,

Fig. 2, shows a squeeze protection device mounted on an adjustable table leg seen from the top side of the squeeze protection device,

Fig. 3, shows a squeeze protection device mounted on an adjustable table leg seen from the underside of the squeeze protection device,

Fig . 4 , shows the squeeze protection device seen separated in the mounting flange, the housing for the piezo element and the piezo element with cables,

Fig. 5, shows the housing for the piezo element shown with the holding arrangement for the piezo element and the spring element,

Fig. 6, shows a principle sketch, showing the squeeze protection device mounted in connection with a column,

Fig. 7, shows another embodiment of the squeeze protection device, which shows a flange mounted with a cup-shaped holding arrangement for a piezo element, where the flange is mounted on an adjustable column,

Fig. 8, shows the squeeze protection device shown as an exploded view,

Fig. 9, shows a cup- shaped holding arrangement for a piezo element, and

Fig. 10, shows a housing for mounting between mounting flange and a table top or table frame.

The table, shown in Fig. 1 comprises a lifting column 1 at each side. The lifting column 1 consists of three co- operative telescopic members 2a, 2b, 2c, where the lower member 2a is fixedly secured to a foot 3. Further it can be seen that the two columns 1 are interconnected with a transverse beam 4 , which is fixed to the lower telescopic member 2a of the first and the second column 1, respectively. The table top 5 is mounted on the upper telescopic member 2c, which is not shown in the drawing to avoid unnecessary details. The mounting of the table top 5 varies from one table to the other, but generally it applies that the table manufacturer uses brackets, which may be connected to the fixtures on the column 1 and the motor drive 8, where after the table top 5 is mounted on the lower frame 1, 3, 4 with the bracket. The movement of the column 1 and thus the adjustment of the height of the table 5 is performed by the motor drive 8, which is a linear actuator. To the actuator is connected a control device 6 and an operation device 7 for adjusting the actuator 8.

Without going into details, a linear actuator consists of an electric motor 10, which through a drive unit drives a spindle on which a rotationally fixed spindle nut is moved back or forth along the spindle.

The device for squeeze protection is practically inserted between the adjustable table leg and the table top. As it can be seen from Fig. 2, the device for squeeze protection 11 is mounted on an adjustable table leg 1 by means of screws 12. The holes 13 for insertion of screws for mounting of the table leg onto the table top can be seen in Fig. 3, where the adjustable table leg is shown so that the device for squeeze protection is seen from the underside. The device for squeeze protection is thus a compact unit, which is integrated with the bracket for mounting of the adjustable legs on the table top 5.

A more detailed view of the construction of the device for squeeze protection 11 is shown in Fig. 4, where both the mounting flange 14 and the housing 15, which receives and holds a piezo element 16 is shown. The holder 17 is designed so that it grips the edge of the piezo element 16, which is of the membrane- like circular type, so that the piezo element 16 in its centre is not supported by the holder 17. The piezo element 16 may thus be moved in the centre point, though limited, in the upwards or downwards direction. The piezo element 16 does not lie loose in the holder 17. A finger- like spring 18 in the housing 15 exerts a pressure on the piezo element 16 in the centre point. This pressure constitutes a prestress on the piezo element 16, which is thereby pressed slightly down in the centre. A potential squeezing under or above the table top 5 will cause the mounting bracket, which constitutes the squeeze protection device 11, to be wrenched. The centre area of the mounting flange 14, where the four screws 12 for securing the column 1 are mounted, will constitute an area which is at rest, where the part between this area and the holes 19, where the screws for mounting the table frame or the table top 5 are led through, may be bent slightly during a squeezing. This area is equipped with punchings 20, which increases the flexibility of the material. In that the mounting flange 14 with screws for securing the table frame or the table top is connected to the housing 15, the housing 15 will also be deformed when the mounting flange 14 is deformed. This means that the finger- like spring 18 will change its pressure on the piezo element 16 in either positive or negative direction. It is noted that it is the prestress on the piezo element 16 which enables the squeezing in both direction to be monitored, as the spring 18 otherwise merely would hover over the piezo element 16 without affecting it in the mechanical non- loaded state.

The principle of the structure is shown in Fig. 6, where a column 8 is shown having a mounting in the shape of a mounting bracket. The lower part of the mounting is a mounting flange 14. The mounting flange 14 is both connected to the column 8 by means of screws, penetrating through the leg- like pieces facing down towards the column. The mounting flange 14 is in the outermost holes screwed up against the table top. The mounting flange 14 is thus retained against wrenching in the central part, whereas the part of the mounting flange 14 which protrudes outside of the column may be wrenched. The mounting flange 14 also functions as a retainer for the piezo element 16 in such a way that the piezo element 16 is secured on the edge but is free to move in the upwards and downwards direction. A housing 15 with a holder for a spring 18, 36 is mounted between the mounting bracket and the table top/frame 5 and will thus be wrenched proportionally with a wrenching of the mounting bracket. The difference is, however, that the housing 15 is not secured in the centre point so this will, depending on the wrenching, move in upwards or downwards direction. The spring 18, 36 is mounted in the centre point of the housing 15 so that a squeezing would cause the spring 18, 36 to be loaded and presses on the centre point of the piezo element 16, which thus will be deflected slightly. The degree of the deflection will be the ratio between the spring constants of the spring 18, 36 and the piezo element 16, respectively, which will then appear as a gear, where only a small portion of the forces being released during a squeezing, will be transferred to the piezo element 16. The deflection of the piezo element 16 will thus be minimal during a squeezing, which ensures that the piezo element 16 will never be loaded in a destructive manner.

The signal, released from the piezo element 16 during mechanical stress in the form of a pressure on this, is a dynamic signal, which reflects a change in the load of the actuator 8. The control unit 6, shown in Fig. 1, which receives and processes the signals, must thus be fitted to respond to sudden changes, since they indicate a potential squeezing. On the other hand, scenarios must be foreseen, where an error in indication may occur, like e.g. during start-up of the motor 10 in the actuator 8, also even though the frictional forces, which should be overcome during start-up, do not run through the squeeze protection device 11 but stays internally in the adjustable column 1.

The realization of the invention is particularly simple in that a squeeze protection device 11 incorporated in a mounting bracket is used to connect an adjustable column 1 to the table top 5. The device may thus also be retrofitted on existing tables with adjustable columns in that an appropriate fixture having the device incorporated is designed.

In that the squeeze protection device 11 is also fitted with a cable 21, preferably having a plug connected, the signal from the piezo element 16 is transferred in a convenient manner to a printed circuit board mounted in the actuator 8, and forms a connection with the control unit 6 in that a cabled connection is led externally out of the actuator 8. A control unit 6 can in this way react to a signal from the squeeze protection device 11 and in case of a squeezing both stop the motor 10 and reverse the motor 10 so that a trapped object is released. When desired, this function may be constructed separately on the printed circuit board in the actuator 8 or as mentioned above be implemented in the control unit 6.

The plug on the cable may expediently be designed so that the plug forms a connecting link between a cable from the adjustable column and a cable from the control. Thus the squeeze protection device 11 may quickly and easily be incorporated in the column 1 for adjusting the table and the control device 6.

The squeeze protection device 11, as described above in Figs . 2 - 5 , has by experiment shown both advantages and disadvantages, depending on what the desired functions of the unit are. Especially if it is desired that torque affects the device, this is advantageous, as torque from a random angle will affect the piezo element 16. A torque load, which is not perpendicular to the finger- like spring element 18 will thus cause the finger- like spring element 18 to tilt, at which it still affects the piezo element 16. A torque load will therefore in this embodiment affect the piezo element 16 more than a load directly vertically down on the column 1, or a torque load having engagement point further in on the width of the table top 5. This means that the signal given by the piezo element 16 depends on the position of the squeezing. Further, this means that the dynamic range for indication of a squeezing should be expected to be large.

If it is desired that the dynamic range of the squeezing protection is smaller, where the omitted signal during a squeezing of an object, is fairly constant irrespective of where above or below the table top 5 the squeezing occurs, another embodiment of the invention, as shown in Fig. 7, has been devised. Again it is a mounting flange for mounting the table top in connection with the adjustable column. The flange plate 22 of metal is by means of four screws 23 fixedly connected to the adjustable column 1. Further, there are holes 24 for mounting the flange plate 22 against the table top 5. In that the flange plate 22 is equipped with longitudinal punchings 25 between the fixtures 23 for the adjustable column and the table top 5, it is possible to wrench the flange plate somewhat, which happens when a squeezing occurs. The flange plate 22 has, as shown in Fig. 8, a hole 26 in which a holding arrangement in the shape of a cup- like element 27 for a piezo element 28 may be inserted. The holding arrangement 27 is fixedly mounted in the flange plate 22 with two screws 29. It is noted that the holding arrangement 27 is thus mechanically at rest and is not directly affected by a wrenching of the flange plate 22. In the depth, the holding arrangement is equipped with an edge 30 on which the piezo element 28 may rest with the outer rim of the circular membrane- shape. This means that the piezo element 28 is not supported under the centre of the membrane, which thus may be affected in upwards and downwards direction, and give a proportionally dynamic signal in the form of a tension, which expresses the mechanical stress of the piezo element 28. For, in a convenient manner, to be able to lead cables from the piezo element 28, the holding arrangement has further a recess 31, at which cables may be led out for connection with a possible printed circuit board in the adjustable column 1, alternatively to a control device 6 in connection with the adjustment of the table.

Over the flange 22, a housing 32 is mounted, which surrounds the flange plate 22 on the edges and the top side, but not on the underside. The housing 32 is fixedly connected to both the flange plate 22 in the outermost screw holes and to the table top 5 in that screws are led through the flange plate 22 in the holes 24 and through holes 33 in the housing 32 and up into the table top 5 or alternatively the table frame. A wrenching of the flange plate 22 will thus mean that the housing 32 is wrenched correspondingly. Between the sides of the housing 32 there are transverse ribs 34, which connects the sides to the centre point 35 of the housing. If the housing 32 is wrenched, the centre point 35 will move in upwards or downwards direction. In that there, in the centre, is a hole 35 for insertion of a spring 36, which engages the centre point of the piezo element, and the hole subsequently is equipped with a locking means 37, the spring exerts a pressure on the piezo element, which prestresses this, so that the piezo element is in a mechanical state, where both a squeezing above or below the table top may be indicated. The locking arrangement 37 for the spring 36 may as shown in Fig. 8 be a pointed screw, so that the prestress may be adjusted. In a mass production, an adjustment would however be unwanted, at which a fixed locking arrangement in the form of a clip, screw or the like would be preferred. The fact that spring elements are used in the invention for transferring a movement to the piezo element 16, 28 is both due to a wish for avoiding transference of a destructive pressure onto the piezo element 16, 28 and a wish for being able to filter out unwanted signals. Further, the spring 18, 36 results in that the dynamic range of the indication of a squeezing may be scaled, so that the signal during a squeezing with a torque load is muted. It is possible to assemble the device for squeeze protection 11 before the mounting in that the housing is equipped with snap- locking means in the shape of locking tongues 39, for locking the mounting flange 14, 22 in connection with the housing 15, 32. Thus the piezo element 16, 28 and the spring 18, 36 are well-protected during transportation. In that the device for squeeze protection 11 is a separate unit, it is possible to install it on new tables but also to retrofit it on existing tables.

Even though the invention here is described in connection with height-adjustable tables it should be noted that the invention may also be realized in connection with height- adjustable beds, where the upper part of the bed is carried by lifting columns of the type which e.g. are known from WO2009/033486 Al to Linak A/S. The invention may naturally also be realized in connection with single actuators cf . WO 02/29284 Al to Linak A/S, which e.g. are used for adjusting the back and leg rest sections of beds and leisure chairs.

Claims

1. Adjustable article of furniture comprising: a stationary part (3) , a relative thereto adjustable part (5) , at least one linear actuator (8) , which at a first point is connected to the stationary part (3) and at another point is connected to the adjustable part (5) in order to adjust this, a control device (6) , an operating device (7) , a device for squeeze protection (11) located between the linear actuator (8) and the article of furniture, c h a r a c t e r i z e d in that the device for squeeze protection (11) comprises a piezo element (16, 28) incorporated in a bracket, which connects the actuator (8) to the adjustable or stationary part (5; 3) of the article of furniture, so that dynamic deviations of the load on the adjustable element (5) of the article of furniture is reflected in the read-out from the piezo element (16, 28) .

2. Adjustable article of furniture according to claim 1, c h a r a c t e r i z e d in that the device for squeeze protection (11) is designed as a module consisting of a first part constituting a mounting bracket (14, 22) , which between fixings (12, 23) for the linear actuator

(8) , preferably in the shape of a telescopic adjustable columns (1) and the fixings (13, 24) for the adjustable part (5) may be bent, and a second part constitution a housing (15, 32) , where there in the device (11) further is a piezo element (16, 28) , which is affected by the bending of the mounting bracket (14, 22) .

3. Adjustable article of furniture according to claim 2, c h a r a c t e r i z e d in that the piezo element (16, 28) , preferably of the membrane type, is positioned in a holding unit (17, 27) , which is fixedly mounted in connection with the mounting bracket (14, 22), where the holding unit (17, 27) supports the edge of the piezo element (16, 28) , so that the piezo element (16, 28) is not supported in the centre point of the membrane .

4. Adjustable article of furniture according to claim 2, c h a r a c t e r i z e d in that the piezo element (16, 28) is fixed in the housing (15, 32) in a slit-shaped opening (17) , which supports the edge of the piezo element (16, 28) , so that the piezo element (16, 28) is not supported in the centre point of the membrane.

5. Adjustable article of furniture according to one of the claims 3 - 4, c h a r a c t e r i z e d in that the centre point of the membrane of the piezo element (16, 28) is connected, preferably through a spring (18, 36), functioning as a gearing, to a part of the unit, which relative to the support of the edge of the piezo element

(16, 28) moves proportional to a deflection of the mounting bracket (14, 22) .

6. Adjustable article of furniture according to claim 5, c h a r a c t e r i z e d in that the spring connected to the piezo element (16, 28) , is designed as a leaf spring (18) constituting part of the housing (15, 32) , for which reason the spring (18) is also affected by the housing (15, 32) being wrenched and affecting the piezo element (16, 28) .

7. Adjustable article of furniture according to claim 5, c h a r a c t e r i z e d in that the spring (18, 36) engages the centre point of the piezo element (16, 28) and in unloaded state performs a prestressing in the form of a pressure on the piezo element (16, 28) .

8. Adjustable article of furniture according to claim 2, c h a r a c t e r i z e d in that the piezo element (16, 28) is equipped with a cable (21, 38) , which preferably has a plug connection for connecting the cable (21, 38) to a matching plug connection in connection with the actuator (8) or the control unit (6) .

9. Adjustable article of furniture according to claim 2, c h a r a c t e r i z e d in that punchings (20, 25) are made in the mounting bracket (14, 22) which reduces the rigidity of the mounting bracket (14, 22) , for which reason squeezing at a random part of the adjustable part (5) will cause the mounting bracket (14, 22) to be wrenched, and affect the piezo element (16, 28) .

10. Adjustable article of furniture according to claim 2, c h a r a c t e r i z e d in that the mounting bracket

(14, 22) and the housing (15, 32) is equipped with mutually functioning snap-locking means (39) , so that the parts (14, 22; 15, 32) are fixed in the correct position and held together around the piezo element (16, 28) when the bracket is not mounted in connection with the article of furniture (5) or the actuator (8) and thus forms a whole module, which protects the piezo element (16,28) before, under and after the mounting on the adjustable article of furniture.

11. Adjustable article of furniture according to one of the claims 1 - 10, c h a r a c t e r i z e d in that the linear actuator (8) comprises at least one spindle and at least one spindle nut and that the squeeze protection device (11) is located in the longitudinal axis of the spindle .

12. Mounting bracket for mounting of one end of a linear actuator (8) , including a telescopic column in an adjustable article of furniture, where the actuator is mounted between a stationary part (3) and a relative thereto adjustable part (5), c h a r a c t e r i z e d in that the mounting bracket is equipped with a squeeze protection device (11) comprising a piezo element (16, 28) incorporated in the bracket, which connects one end of the actuator (8) to the adjustable or stationary part (5; 3) of the article of furniture, so that dynamic deviations of the load on the adjustable element (5) of the article of furniture are reflected in the read-out from the piezo element (16, 28) .