the embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing embodiments of the invention . upon reading the following description in light of the accompanying figures , those skilled in the art will understand the concepts of the invention and recognize applications of these concepts not particularly addressed herein . it should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims . the preferred embodiment of the invention will now be described with reference to the accompanying drawings . the invention may , however , be embodied in many different forms and should not be construed as limited to the embodiment set forth herein ; rather , this embodiment is provided so that this disclosure will be thorough and complete , and will fully convey the scope of the invention to those skilled in the art . the terminology used in the detailed description of the particular embodiment illustrated in the accompanying drawings is not intended to be limiting of the invention . in the drawings , like numbers refer to like elements . the following description handily refers to the references ( x , y , z ), comprising : the longitudinal x - axis defining the longitudinal x - direction extending from the front toward the rear of the sofa , and established according to the greatest length of the bed base ( the term “ front ” referring to the front of the sofa ( the seat side ) and the term “ rear ” referring to the rear of the sofa ( the backrest side )); the transverse y - axis defining the transverse y - direction extending from the right to the left of the sofa , and established according to the width of the sofa from the left to the right , the axes x and y defining the horizontal plane when the sofa rests on a horizontal ground ; and the vertical z - axis defining the vertical z - direction extending upwardly from below , and established according to the height of the sofa when the sofa is typically situated , that is to say , resting on a horizontal ground . with reference to the drawings , a sofa 1 as in the invention comprises a fixed structure 2 which is composed of a frame of an outer width ls ( in the y - direction ) provided with : two lateral beams 20 , right and left , respectively , extending in the x direction ; two transverse beams 21 , front and rear , respectively , extending in the y direction and connecting the two lateral beams 20 ; and four feet 22 at the front and rear ends of the lateral beams 20 . the lateral beams 20 each have a substantially planar upper surface ( the tops of the lateral beams 20 ), which form contact surfaces . the fixed structure 2 comprises also two front supports 25 , right and left respectively , fixed onto the respective lateral beams 20 . each front support 25 is fixed onto the front end of the corresponding lateral beam 20 , and each front support 25 is fixed onto the outer side of the corresponding lateral beam 20 , that is to say , opposite to the interior of the frame of the fixed structure . the front supports 25 each have an upper surface , which form contact surfaces . as illustrated in fig9 a to 9 d , each front support 25 is formed to be a rigid plate , in particular steel , which creates a central , flat board 251 parallel to the upper surface of the corresponding lateral beam 20 , the central board 251 being , for example , coplanar with ( that is to say , on the same level as ) the upper surface of the corresponding lateral beam 20 . for each front support 25 , the board 251 is framed by two ramps , respectively a front ramp 250 ( or guide ramp ) and rear ramp 252 ( or lock ramp ), which descend relative to the board 251 ; in other words , the board 251 represents the peak of the ramps 250 , 252 . the sofa 1 also comprises a foldable structure 3 comprising articulated panels , namely , a front panel 4 , a central panel 5 , and a rear panel 6 . the central panel 5 has two opposite transverse sides ( parallel to the transverse beams 21 ) respectively articulated on the front panel 4 and on the rear panel 6 along parallel joint axes a , b . the front panel 4 is formed so as to be a frame of an inner width la ( in the y - direction ), provided with : two lateral beams 40 , left and right , respectively , extending in the x direction ; and two transverse beams 41 , front and rear , respectively , extending in the y - direction and connecting the two lateral beams 40 . the front panel 4 is also provided with four feet 42 , terminating in wheels 420 or sliding pads , the feet being disposed at the front and rear ends of the lateral beams 40 and provided so as to be ( rollingly or slidingly ) supported by the ground when moving in longitudinal translation toward the front and rear during the phases of unfolding and folding , respectively . the inner width la is substantially greater than the outer width ls of the frame of the fixed structure 2 plus twice the width of the front supports 25 ( the two supports having the same width ). thus , as illustrated in fig6 , the frame of the front panel 4 can come to fit onto the fixed structure 2 ( with the mounting kits nearby ) in the sofa configuration . the front panel 4 also incorporates two front wheels 43 and two rear wheels 44 , in particular of a roller pad type , which are rotatably mounted onto the lateral beams 40 , and more specifically rotatably mounted onto the inner or lower sides of the lateral beams 40 , with one front wheel 43 and one rear wheel 44 per lateral beam 40 . the right front wheel 43 is mounted onto the lateral beam 40 opposite to ( or symmetrically to ) the left front wheel 43 , which is mounted onto the left lateral beam 40 , and the right rear wheel 44 is mounted onto the lateral beam 40 opposite to ( or symmetrically to ) the left rear wheel 43 , which is mounted onto the left lateral beam 40 . the wheels 43 , 44 do not protrude beyond above the frame of the front panel 4 , so as not to interfere with receiving a mattress . the wheels 43 , 44 are directed toward the inside of the frame of the front panel 4 , with the rear wheels 44 more shifted in the y - direction from the respective lateral beams 40 thereof than the front wheels 43 ; in other words , each of the front wheels 43 is closer to the lateral beam 40 thereof than the rear wheel 44 , the front wheel 43 being substantially pressed against the lateral beam 40 ( with the near fitting clearance necessary for the front wheel 43 to rotate properly ), whereas the rear wheel 44 is offset transversely from the lateral beam 40 at a distance substantially corresponding to the width of the front supports 25 . the rear wheels 44 are located closer to the rear ends of the respective lateral beams 40 , whereas the front wheels 43 are located closer to the front ends of the respective lateral beams 40 . however , each of the rear wheels 44 is disposed at a predetermined distance from the rear end of the corresponding lateral beam 40 , to facilitate the driving forward of the front panel 4 when the foldable structure 3 is being unfolded . in addition , the front wheels 43 have a larger diameter than that of the rear wheels 44 , and the axes of rotation of the front wheels 43 are downwardly shifted with respect to the rear wheels 44 . thus , the front wheels 43 provide rolling support surfaces located beneath with respect to the rolling support surfaces provided by the rear wheels 44 . the central panel 5 is in the form of a frame of an inner width la , provided with two lateral beams 50 , left and right , respectively , extending along the x - axis and connected by a front transverse beam 51 extending along the y - axis . the central panel 5 also comprises a central beam 52 parallel to the lateral beams 50 . alternatively , the central panel 5 does not comprise such a central beam 52 , but rather comprises a rear transverse beam extending along the y - axis and connecting the two lateral beams 50 . the front panel 4 is articulated on the central panel 5 along an axis of rotation a ( parallel to the y - axis ), by means of two hinges or articulations 53 provided between the rear ends of the lateral beams 40 of the front panel 4 and the front ends of the lateral beams 50 of the central panel 5 . the rear panel 6 is formed so as to be a frame of an inner width la , provided with : two lateral beams 60 , left and right , respectively , extending along the x - axis ; two transverse beams 61 , front and rear , respectively , extending along the y - axis and connecting the two lateral beams 60 . optionally , the rear panel 6 also comprises a central beam 62 parallel to the lateral beams 60 and extending between the two transverse beams 61 , or even a plurality of inner beams extending along the y - axis and connecting the two transverse beams 61 . the front panel 6 is articulated on the central panel 5 along an axis of rotation b ( parallel to the y - axis ), by means of two hinges or articulations 54 provided between the front ends of the lateral beams 60 of the rear panel 6 and the rear ends of the lateral beams 50 of the central panel 5 . in the embodiment with the central beams 52 , 62 , a third hinge or articulation 54 may also be provided between the front end of the central beam 62 and the rear end of the central beam 52 . the rear panel 6 is also articulated on the fixed structure 2 along an axis of rotation c ( parallel to the y - axis ). more specifically , the rear panel 6 is articulated on the rear of the fixed structure 2 , by means of at least one arm 63 secured to the rear transverse beam 61 of the rear panel 6 and articulated on the fixed structure 2 , e . g ., on the lateral beams 20 . preferably , for the sake of stability , the rear panel 6 is articulated onto the fixed structure 2 by means of a plurality of arms 63 secured to the rear transverse beam 61 of the rear panel 6 and articulated onto the fixed structure 2 , e . g ., on the two lateral beams 20 . the arm 63 or plurality of arms 63 each have an end fixed onto the rear transverse beam 61 of the rear panel 6 and an opposite end articulated onto the fixed structure 2 . the sofa 1 also comprises a motorized , electric actuator 7 comprising a body 70 within which a rod 71 is movable in translation . the body 70 is articulated on the fixed structure 2 along an axis of rotation d ( parallel to the y - axis ), and is , for example , positioned in the middle of the sofa 1 , so that the body 70 can be articulated on the middle of the front transverse beam 20 of the fixed structure 2 . the body 70 is thus positioned on the front of the fixed structure 2 , on the front transverse beam 21 . the rod 71 has one end articulated on the rear panel 6 along an axis of rotation e ( parallel to the y - axis ), in order to rotatingly move the rear panel 6 about the axis of rotation c , and consequently fold / unfold the foldable structure 3 . more specifically , the rod 71 on the rear panel 6 is articulated on a lever arm 64 secured to the frame of the rear panel 6 , and more specifically secured to the rear transverse beam 61 . the lever arm 64 has one end secured to the rear transverse beam 61 and an opposite end rotatingly articulated on the end of the rod 71 . the lever arm 64 extends substantially at a right angle to the rear transverse beam 61 as well as to the central beam 62 . the lever arm 64 is located in the middle of the sofa 1 , and is continuous with and at a right angle to the central beam 62 . the following description relates to the operation of the sofa 1 . the fixed structure 2 is stabilized on the ground , whereas the foldable structure 3 can be folded and unfolded between : a sofa configuration ( fig5 and 6 ) in which the front panel 4 forms a seat , the central panel 5 forms a backrest , and the rear panel 6 is folded over the central panel 5 , with the rear panel 6 behind the central panel 6 ; and a sleeping configuration ( fig1 and 2 ) in which the three panels 4 , 5 , 6 are substantially coplanar , parallel to the horizontal plane ( x , y ), to form a bed base . the sleeping configuration , the rod 71 is extended out of the body 70 of the actuator 7 , whereas in the sofa configuration , the rod 71 is retracted to inside the body 70 . in the sleeping configuration , the front panel 4 rests on the feet 42 thereof , the central beam 52 of the central panel 5 rests on the transverse beam 21 of the fixed structure 2 , and the front transverse beam 61 of the rear panel 6 rests on the lateral beams 20 and central beam 23 of the fixed structure 2 . therefore , the transition from the sleeping configuration ( fig2 ) to the sofa configuration ( fig5 ) is achieved , according to a folding movement , by controlling the actuator 7 in the direction of retraction of the rod 71 , with the subsequent rolling out , with reference to fig2 to 5 and 9 a to 9 d : at the start of the movement ( fig3 and 4 ), the retraction of the rod 71 concomitantly causes pivoting toward the rear of the rear panel 6 about the c - axis ( the steering of the folding of the foldable structure 3 occurring at the level of this c - axis ), rotating movement about the b - axis between the panels 5 , 6 , which corresponds to a folding movement in the direction of reunification between the two panels 5 , 6 , and rotating movement about the a - axis between the panels 4 , 5 , which leads to translation of the front panel 4 towards the rear ( facilitated by the wheels 420 ); then ( fig9 a ), the rear wheels 44 roll over the top of the lateral beams 20 of the fixed structure 2 ( the height and width positioning of the rear wheels 44 being provided to establish this rolling support of the rear wheels 44 on the lateral beams 20 , in order to apply a force aimed at pressing the fixed structure 2 to the ground ); then ( fig9 b ) the front wheels 43 ride on the front ramps 250 of the front supports 25 ( the height and width positioning of the front wheels 43 being provided to establish this rolling support of the front wheels 43 on the front supports 25 , in order to apply a force aimed at pressing the fixed structure 2 to the ground ), and the rear wheels 44 may be released opposite to the lateral beams 20 , as a result of the folding / unfolding mechanism , which in no way negatively affects the transfer of weight , because the front wheels 43 are well supported on the fixed structure 2 ; then ( fig9 c ) the front wheels 43 roll on the boards 251 of the front supports 25 , thus maintaining the force aimed at pressing the fixed structure 2 to the ground ; and finally ( fig9 d and 5 ) the front wheels 43 go down the rear ramps 252 of the front supports 25 and stop on the rear ramps 252 , the rear wheels 44 being again supported on the lateral beams 20 . in the sofa configuration , the front wheels 43 are dimensioned and arranged so that , despite the lowering of the support point as a result of the rear ramps 252 , the front wheels 43 lift up the front of the front panel 4 which forms the seat ; in other words , the lateral beams 40 are no longer horizontal , but are rather inclined with the front ends thereof higher than the rear ends thereof , thus providing an improved seating comfort . it shall be readily understood that the invention is not limited to the specific embodiment , and that variations can be considered , such as , for example , the following variations . in one variation , the fixed structure comprises two lateral armrests , right and left , respectively , optionally connected at the rear by a transverse bar . for the embodying of the invention , the armrests have lateral beams on the respective internal faces thereof . in such a case , the front supports are provided on the inner sides of the lateral beams , and the front and rear wheels of the front panel are directed to the outside of the frame so as to cooperate with the lateral beams . in one variation , the body of the actuator is fixed to other points of the fixed structure , and a variation with at least two synchronized actuators is conceivable . unless otherwise stated , use of the word “ substantially ” may be construed to include a precise relationship , condition , arrangement , orientation , and / or other characteristic , and deviations thereof as understood by one of ordinary skill in the art , to the extent that such deviations do not materially affect the disclosed methods and systems . throughout the entirety of the present disclosure , use of the articles “ a ” or “ an ” to modify a noun may be understood to be used for convenience and to include one , or more than one of the modified noun , unless otherwise specifically stated . elements , components , modules , and / or parts thereof that are described and / or otherwise portrayed through the figures to communicate with , be associated with , and / or be based on , something else , may be understood to so communicate , be associated with , and or be based on in a direct and / or indirect manner , unless otherwise stipulated herein . although the methods and systems have been described relative to a specific embodiment thereof , they are not so limited . obviously many modifications and variations may become apparent in light of the above teachings . many additional changes in the details , materials , and arrangement of parts , herein described and illustrated , may be made by those skilled in the art . having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used . accordingly , it is submitted that that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims .
a convertible sofa of the perpendicular - sleeping type , comprising a fixed structure supporting a foldable structure which comprises three articulated panels and a system of actuation of folding / unfolding of the foldable structure between a sofa configuration and a sleeping configuration and vice versa , which comprises at least one motorized actuator comprising a body within which a rod is movable in translation , where the body is mounted on one of either the fixed or foldable structure and the end of the rod is articulated on the other of the fixed or foldable structure , the movement of the rod causing the foldable structure to fold / unfold .