Abstract:
The invention relates to a backrest assembly for a wheelchair with a backrest frame pivotally connected to a seat or seat frame, a carrying means provided by or attached to the backrest frame, a rotating means rotatable secured to the carrier means, a first sliding means slidable connected to the backrest frame on the rear side of the backrest assembly and connected to the rotating means via a first mechanical link, a second sliding means slidable secured to the backrest frame on the front of the backrest assembly and connected to the rotating means via a second mechanical link, and an actuator for adjusting the backrest assembly between an upright and reclined position with the actuator being connected to the first sliding means for driving the second sliding means via the rotating means to perform a sinusoidal movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the National Phase of International Application PCT/IB2015/053651 filed May 18, 2015 which designated the U.S. and that International Application was published in English under PCT Article 21(2) on Nov. 26, 2015 as International Publication Number WO 2015/177709 A1. PCT/IB2015/053651 claims priority to European Patent Application No. 14168876.2, filed May 19, 2014. Thus, the subject nonprovisional application claims priority to European Patent Application No. 14168876.2, filed May 19, 2014. The disclosures of both applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention refers to a backrest assembly for a wheelchair with a reclining seat. 
         [0003]    A wheelchair having a primary articulated member, at least one secondary articulated member, a primary sensor for detecting the position of the primary member, a secondary sensor for detecting the position of the secondary member, and a controller capable of articulating the secondary articulated member as a function of the movement of the primary articulated member, is known from US 2004/094936. 
         [0004]    US 2005/0088024 discloses a reclining seat which includes a base, a back frame and back support connected to the back frame for translation relative to the back frame. In a first embodiment, a mechanism is described to couple the back frame to the back support such that rotation of the back frame relative to the base automatically translates the back support relative to the back frame. In a second embodiment, a mechanism is described to allow a user to control movement of the back support independently of back frame rotation. Said reclining seat can be incorporated into a wheelchair. 
         [0005]    A backrest assembly for a wheelchair is known from US 2012/0080919 (EP 2 621 445 A1) which includes a support plate pivotally connected to a seat, wherein the support plate is configured to be pivotally adjusted between upright and reclined positions with respect to the seat; a slide plate slidably secured on a front surface of the support plate; and a backrest adjustment assembly operatively connected to the support plate and the slide plate. The backrest adjustment assembly includes a link configured to adjust the support plate. The slide plate slides over the support plate through the link. 
         [0006]    In general a backrest assembly of a wheelchair has a pivot point of a rotational movement of a backrest frame relative to a seat frame during adjustment of the backrest assembly between an upright position and a reclined position. In case said pivot point is not concentric with the hip rotation point of a user of the wheelchair, shear forces will be caused during said adjustment between the backrest assembly, in particular a cushion of the backrest assembly, and the back of the user. In order to compensate said shear forces backrest assemblies have been developed with a support plate pivotally connected to a seat and a slide plate slidably secured on a front surface of the support plate, as described in US 2012/0080919 (EP 2 621 445 A1). In the prior art the link between the slide plate and the support plate is configured to adjust the slide plate with respect to the support plate by connecting a post to a drive bar on a rear surface of the support plate, with the drive bar operatively connecting to a pivot arm on the front surface of the support plate, and the pivot arm operatively connecting to the slide plate via a knob sliding through a slot within the slide plate such that movement of the pivot arm causes the slide plate to slide over the support plate. A recline angle between the backrest and the seat of the known wheelchair thus is determining the rotation of the pivot arm which in turn causes the sliding of the sliding plate via the knob. The effect of the recline angle of the known backrest assembly on the movement of the slide plate is not adjustable. 
         [0007]    Thus it would be desirable to provide a backrest assembly for a wheelchair with a reclining seat overcoming the disadvantages known in the state of the art, especially allowing an adjustable compensation of shear forces. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention provides a backrest assembly for a wheelchair with a backrest frame pivotally connected to a seat or seat frame, a carrying means provided by or attached to the backrest frame, a rotating means rotatable secured to the carrier means, a first sliding means slidable connected to the backrest frame on the rear side of the backrest assembly and connected to the rotating means via a first mechanical link, a second sliding means slidable secured to the backrest frame on the front of the backrest assembly and connected to the rotating means via a second mechanical link, and an actuator for adjusting the backrest assembly between an upright and reclined position with a recline angle, with the actuator being connected to the first sliding means for driving the second sliding means via the rotating means to perform a sinusoidal movement. 
         [0009]    A preferred embodiment is characterized in that the first mechanical link comprises a first driving cam sliding within at least one first control slot, and/or second mechanical link comprises a second driving cam sliding within at least one second control slot. 
         [0010]    It is proposed that the first and/or second driving cam is attachable at different positions, and/or the first and/or second control slot has a predefined path, preferably with a slope and/or a curvature. 
         [0011]    With the invention it is also proposed that the sinusoidal movement is adjusted or adjustable via the position of the first and/or second driving cam and/or the path of the first and/or second control slot. 
         [0012]    It is advantageous that the backrest frame comprises at least a first rail for slidable engagement of the first sliding means and at least a second rail for slidable engagement of the second sliding means, and/or the backrest frame comprises two parallel first bars, preferably each being provided with one first and one second rail, in particular by having a T shaped cross section or two opposing recesses at each of two opposite edges, and/or two parallel second bars between the two first bars. 
         [0013]    It is preferred that the carrying means is provided within the space defined by the backrest frame, and/or the carrying means is arranged between the two first bars, preferably extending between the two second bars, or the carrying means comprises at least a first rail for slidable engagement of the first sliding means and at least a second rail for slidable engagement of the second sliding means. 
         [0014]    Some embodiments of the invention are characterized in that the rotating means is arranged on the rear side of the backrest frame, and the rotating means has a first section provided with the first control slot and a second section provided with the second driving cam, preferably the two sections having a relative angular displacement of at least 90°, and/or the rotating means provides the first slot extending substantially radially, and/or the rotating means provides a plurality of positions for the attachment of the second driving cam. 
         [0015]    Alternative embodiments of the invention are characterized in that the rotating means is arranged on the front side of the backrest frame, and the carrying means leaves free space relative to the backrest frame or is provided with a first first control slot, preferably the first first slot extending substantially vertical in the upright position of the backrest assembly, and the rotating means has a first section provided with a first second control slot and a second section provided with the second driving cam, preferably the two sections having a relative angular displacement of at least 90°, and/or the rotating means provides the first second slot extending substantially radially, and/or the rotating means provides a plurality of positions for the attachment of the second driving cam. 
         [0016]    Still further it is preferred that the first sliding means houses at least a part of the actuator, and/or the first sliding means moves together with the actuator, and/or the first sliding means is pivotally connected to at least one push rod being fixedly connected to the seat or seat frame, and/or the first sliding means is provided with the first driving cam. 
         [0017]    Embodiments of the invention are characterized in that the actuator driving the sliding movement of the first sliding means, which is pivotally connected to the push rod being fixedly connected to the seat or seat frame, causes the reclining movement of the backrest frame relative to the seat or seat frame. 
         [0018]    It is proposed in line with the invention that the second sliding means has a plate form, and/or the second sliding means is provided with the second control slot, the second control slot preferably extending parallel to or at least partly sloped and/or curved relative to a horizontal line in the upright position of the backrest assembly, and/or the second sliding means carries at least one cushion and/or accessory on the front of the backrest assembly. 
         [0019]    Also proposed is that the actuator extends at least partly between the first sliding means and the rotating means or the backrest frame, and/or the actuator comprises a linear drive. 
         [0020]    In line with the invention it is advantageous that a radial displacement of the second driving cam affects the total stroke applied to the second sliding means, and/or an angular displacement of the second driving cam affects the starting point of the sinusoidal movement. 
         [0021]    With the invention it is also proposed that a negative slope of the second control slot relative to a horizontal line in the upright position of the backrest assembly amplifies the sinusoidal movement, and/or a positive slope of the second control slot relative to a horizontal line in the upright position of the backrest assembly levels the sinusoidal movement. 
         [0022]    It is preferred that the rotating means, the first sliding means and/or the second sliding means, preferably the second sliding means, is selectable from a plurality of such means for selecting the movement of the second sliding means during an adjustment of the backrest assembly between the upright and the reclined position. 
         [0023]    The invention also refers to a wheelchair comprising a seat, at least two drive wheels and a backrest assembly according to the invention, with the recline angle being controllable from at least 90° to 180°, preferably from 85° to 180°. 
         [0024]    Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1 a    shows a front perspective view of a first embodiment of a backrest assembly of the invention; 
           [0026]      FIG. 1 b    shows a rear perspective view of the backrest assembly of  FIG. 1   a;    
           [0027]      FIG. 2  shows a part view of the front side of the backrest assembly of  FIG. 1   a;    
           [0028]      FIG. 3 a    shows a front view of an alternative rotating means of the backrest assembly of  FIG. 1   a;    
           [0029]      FIG. 3 b    shows 5 graphs explaining a force transmission depending on a recline angle and the placement of a driving cam of the rotating means of  FIG. 3   a;    
           [0030]      FIG. 3 c    shows a front view of a second sliding means of the backrest assembly of  FIG. 1   a;    
           [0031]      FIG. 3 d    shows 5 graphs explaining a force transmission depending on the recline angle and the slope of a control slot of the second sliding means of  FIG. 3   c;    
           [0032]      FIG. 4 a    shows an exploded view of the parts of a backrest assembly according to a second embodiment of the invention, from the front side thereof; 
           [0033]      FIG. 4 b    shows an exploded view of the parts of the backrest assembly of  FIG. 4   a,  from the rear side thereof; 
           [0034]      FIG. 5 a    shows an exploded view of the parts of a backrest assembly according to a third embodiment of the invention, from the front side thereof; and 
           [0035]      FIG. 5 b    shows an exploded view of the parts of the backrest assembly of  FIG. 5   a,  from the rear side thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]      FIGS. 1 a  and 1 b    depict a backrest assembly according to a first embodiment of the invention. Such a backrest assembly  1  comprises a seat frame  10  with a pivot point  11  and in connection with two arm rests  12  connected via an armrest axle  13 . A backrest frame  20  is connected to the seat frame  10  such that it can be rotated or rather pivoted around the pivot point  11  to adjust the backrest assembly  1  between and upright position and a reclined position. In the upright position the recline angle between the seat frame  10  and the backrest frame  20  is around 90°, but can also be 85°, whereas in the reclined position the recline angle is around 180°. 
         [0037]    The backrest frame  20  is connected with a carrying means  30  having first rails  31  attached to its rear side and second rails  32  attached to its front side. A rotating means  40  is rotatably connected to the carrying means  30  on the front side thereof. A first sliding means  50  is slidably attached to the carrying means  30  via the first rails  31  and a second sliding means  60  is attached to the carrying means  30  via the second rails  32 , with the rotating means  40  being arranged between the second sliding means  60  and the carrying means  30 . An actuator  70  is arranged between the first sliding means  50  and the carrying means  30 , with the actuator  70  comprising a linear drive like a linear motor and being fixedly secured to the first sliding means  50  in order to slide the first sliding means  50  relative to the carrying means  30  as well as the backrest frame  20 . The first sliding means  50  has the form of a bridge. Push rods  80  are connected at one end thereof with the first sliding means  50  and at the other end thereof to the seat frame  10  such that the actuator  70  affects a rotation of the backrest frame  20  relative to the seat frame  10  around the pivot point  11 , with the first sliding means  50  sliding up during reclining of the backrest frame  10  and the second sliding means  60  slide down during such a reclining 
         [0038]    The force transmission between the first sliding means  50  and the second sliding means  60  is achieved via two links, with a first link between the first sliding means  50  and the rotating means  40  and a second link between the rotating means  40  and the second sliding means  60 . With respect to  FIG. 2  the first and second links are explained in further detail. The first link comprises a first driving cam  51  secured to the first sliding means  50 , said first driving cam  51  passing through a first first control slot  33  within the carrying means  30  as well as a first second control slot  42  within the rotating means  40  in order to slide within the respective control slots  33 ,  42 . This first link converts a sliding movement of the first sliding means  50  into a rotational movement of the rotating means  40  rotating around a pivot point  41 . As can be seen in  FIG. 2  the first first control slot  33  extends substantially parallel to the rails  31 ,  32 , whereas the first second control slot  42  extends radially. 
         [0039]    The second link can be best understood with reference to  FIG. 2 . It comprises a second driving cam  43  fixedly attached to the rotating means  40  and passing through a second control slot  61  provided within the second sliding means  60  for travelling within said second control slot  61 . Accordingly, a rotation of the rotating means  40  is converted into a sliding movement of the second sliding means  60  within the second rails  32  relative to the carrying means  30  and the backrest frame  20 . 
         [0040]    The movement of the second sliding means  60  is a function of the movement of the first sliding means  50  driven by the actuator  70 . The recline angle between the seat frame  10  and the backrest frame  20  is also a function of the first sliding means  50  driven by the actuator. The movement is a sinusoidal movement due to the conversion of the sliding movement of the first sliding means  50  via the rotational movement of the rotating means  40  into the sliding movement of the second sliding means  60 . The actuator stroke as a function of the recline angle as well as the rotation angle of the rotating means  40  as function of the recline angle are depicted in  FIGS. 3 b    and  3   d.    
         [0041]    By a displacement of at least one of the two driving cams and the arrangement as well as shape of at least one of the control slots the sinusoidal movement is adjustable. 
         [0042]    In fact, a radial displacement of the second driving cam  43  affects the total stroke applied to the second sliding means  60  and an angular displacement of the second driving cam  43  affects the starting point of the sinusoidal movement of the second sliding means  60 . This is explained in further detail with respect to  FIGS. 3 a    and  3   b.    FIG. 3 a    shows an alternative rotating means  40 ′ with its pivot point  41 ′, first second control slot  42 ′ and a plurality of attachment positions  44 ,  44 ′,  44 ″,  44 ′″. The first second control slot  42 ′ is extending radially. In the following the effect of the position of the second driving cam (not shown) in one of the three attachment positions  44 ′,  44 ″ and  44 ′″, being angularly displaced with respect to each other, is explained with respect to  FIG. 3   b.  Said  FIG. 3 b    shows the actuator stroke as a function of the backrest angle or better recline angle, the cam disk angle being the rotation angle of the rotating means  40 ′ as a function of the recline angle and the plate travel being the sinusoidal movement of the second sliding means for an attachment of the second driving cam for each one of the three different attachment positions  44 ′,  44 ″,  44 ′″ as a function of the recline angle. A clockwise angular displacement from the attachment position  44 ′ to the attachment position  44 ″ leads to a shift of the starting point of the sinusoidal movement to higher recline angles; whereas a counterclockwise angular displacement from the attachment position  44 ′ to the attachment position  44 ′″ leads to a shift of the sinusoidal movement to smaller recline angles. 
         [0043]    With respect to  FIGS. 3 c  and 3 d    the effect of a slope of the second sliding means is explained.  FIG. 3 c    shows an alternative second sliding means  60 ′ with its second control slot  61 ′ and two alternative second control slots, one second control slot  61 ″ with a negative slope and another second control slot  61 ′″ with a positive slope. In case the second control slot has a negative slope relative to a horizontal line in the upright position of the backrest assembly  1 , see second control slot  61 ″ in  FIG. 3   c,  the sinusoidal movement of the second sliding means  60 ′ is amplified, whereas a positive slope as depicted as second control slot  61 ′″ in  FIG. 3 c    leads to a leveling of the sinusoidal movement of the second sliding means  60 ′. This is reflected by the three respective curves in  FIG. 3   d,  corresponding to the three arrangements of the second control slot  61 ′,  61 ″,  61 ′″ as depicted in  FIG. 3   c.  In addition,  FIG. 3 d    again depicts the actuator stroke as a function of the recline angle and the cam disk angle as a function of the recline angle. 
         [0044]    Accordingly, a backrest assembly of the invention provides a high degree of flexibility due to the fact that the movement of the second sliding means  60 ,  60 ′ as a function of the actuator stroke can be adjusted to the special needs of a user of a wheelchair provided with said backrest assembly  1 . 
         [0045]    In order to increase the flexibility a set of rotating means  40 ,  40 ′ and second sliding means  60 ,  60 ′ in form of a construction kit can be provided. This enables a selection of the different components of the backrest assembly  1  adapted to the user of the wheelchair. 
         [0046]      FIGS. 4 a  and 4 b    refer to a second embodiment of the backrest assembly  100  of the invention. The backrest assembly  100  comprises a backrest frame  120  connected to a seat frame (not shown) in order to be pivotable around a pivot point  110 . The backrest frame  120  is provide with first rails  121  and second rails  122  for a slideable attachment of a first sliding means  150  on the rear side thereof and a second sliding means  60  on the front side thereof. The first sliding means  150  is fixed to an actuator  170 . The actuator  170  is also carried by a carrying means  130  extending substantially parallel to two parallel first bars  123  of the backrest frame  120  and attached to two parallel second bars  124  of the backrest frame  120 , with said second bars  124  running substantially perpendicular to the first bars  123 . The carrying means  130  does not extend within the complete space defined by the first and second bars  123  and  124 , rather leaves enough space for a first driving cam  151  fixedly secured to the first sliding means  150  to pass there through, in order to slide within a first control slot  142  provided by a rotating means  140  rotably attached to the carrying means  130  via a pivot pin  131  passing through a pivot point  141 . The rotating means  140  has the form of a propeller with two blades, the first control slot  142  being provided within one of said blades and the other blade carrying a second driving cam  143 . The two blades are arranged substantially opposing each other. The second driving cam  143  is attached to the rotating means  140  at one of a plurality of attachment positions  144 . By selecting one of said attachment positions  144  for the attachment of the second driving cam  143  the total stroke as well as the starting point of the sinusoidal movement of the second sliding means  160  is adjustable. The second driving cam  143  passes through a second control slot  161  provided by the second sliding means  160 . Said second control slot  161  has a curved shape in order to selectively amplify and/or level the sinusoidal movement of the second sliding means  160  as a function of the recline angle or rather stroke of the actuator  170 . 
         [0047]    A backrest assembly  200  according to a third embodiment of the invention is depicted of  FIGS. 5 a    and  5   b.  The third embodiment differs from the second embodiment with respect to the arrangement of the rotating means. Whereas the rotating means  140  of the second embodiment is arranged between the carrying means  130  and the second sliding means  160 , and thus on the front side of the frame  10 , a rotating means  240  of the third embodiment is arranged between a first sliding means  250  and a carrying means  230  and thus on the rear side of a frame  220 . The first sliding means  250  is provided with a first driving cam  251  and is securely attached to an actuator  270  which is also attached to the carrying means  230  at attachment points  232 , leaving enough space there between for the rotating means  240  attached to the carrying means  230  via a pivot pin  231  at a pivot point  241 . The rotating means  240  is provided with a first control slot  242  extending substantially radially and a second driving cam  243  attached to one of a plurality of attachment positions  244 . The backrest frame  220  is comprised of first bars  223  and second bars  224 , with the first bars  223  carrying first rails  221  on its rear side and second rails  222  on its front side. Within the first rails  221  the first sliding means  250  can slide, whereas within the second rails  222  the second sliding means  260  can slide. The second bars  224  extend between the first bars  223  and carry the carrying means  230  by providing attachment means with the attachment points. The second sliding means  260  is provided with the second control slot  261  having the shape of a curve. 
         [0048]    The functioning of the second and third embodiment with respect to the transfer of forces from the actuator  170 ,  270  to the second sliding means  160 ,  260  via the first sliding means  150 ,  250  and the rotating means  140 ,  240  correspond to that of the first embodiment. In all three cases two links, each in form of a driving cam and at least the control slot within which the driving cam can move, are provided to convert a first sliding movement into a rotational movement and said rotational movement into a second sliding movement such that an actuator stroke is converted into a sinusoidal movement of a second sliding means on which the back of the user rests, either directly or indirectly in case a cushion is provided on the front side of the second sliding means. The important feature of the invention is the adjustability of the sinusoidal movement of the second sliding means  60 ,  160 ,  260  via the links. This avoids the application of shear forces to the back of the user during a rotation of the backrest frame  20 ,  120 ,  220  relative to the seat frame  10  of a wheelchair in order to switch from a more or less upright seating position of the user to a more or less reclined lying position of the user on the wheelchair. 
         [0049]    The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.