Patent Publication Number: US-2022221035-A1

Title: Linear actuator

Description:
The invention relates to a linear actuator of the type mentioned in the preamble of claim  1 . 
     In hospital and care beds, the carrying surface for the mattress is divided into a back-rest section and a leg-rest section as well as typically also a fixed middle section. The back-rest and leg-rest sections are individually adjustable about a horizontal axis by means of a linear actuator each, cf. e.g. EP 0 498 111 A2 J. Nesbit Evans &amp; Company Ltd. 
     In certain situations, e.g. in case of heart failure, it is crucial to be able to immediately lower the back-rest section from a raised position to a horizontal position. The speed of a linear actuator is simply too low to be able to perform the required immediate lowering of the back-rest section to a horizontal position. To solve the problem, linear actuators with a so-called quick release have been developed, which disengages the spindle itself, which is of a non-self-locking type, from the motor or disengages a part of the transmission in driving connection with the spindle, where this part of the transmission and the spindle are non-self-locking. Examples of linear actuators of this type with quick release are known from e.g. EP 0 577 541 A1, EP 0 685 662 A2, WO 03/033946 A1 and WO 2006/039931 A1 all to LINAK A/S. As mentioned, it is noted that the spindle of the linear actuator is not self-locking, so that the load on the tubular adjustment element of the linear actuator, which is connected to the spindle nut, rotates the spindle. The spindle will accelerate as a result of the force from the load, such that the adjustment element with increasing speed will move towards the end position, and the back-rest section will be suddenly braked in a collision-like manner, when the back-rest section reaches its horizontal position. The acceleration towards the horizontal position is enhanced by the construction of the bed, where the load on the linear actuator is smallest when the back-rest section assumes its maximum raised position. The impact of the force is significantly increased the closer the section gets to its horizontal position, where the impact of the force is at a maximum. This collision-like braking can to a great extend be injurious to the patient, who already is traumatized, and further it is a tremendous overload of the bed structure and the linear actuator. As such, a traumatic situation on the whole is chaotic around the patient, as well as being a not insignificant risk that someone will get squeezed between the back-rest section and the upper frame in which the back-rest section is embedded, when the back-rest section uncontrolled rushes to a horizontal position. The problem is sought solved by incorporating gas springs in the bed structure to dampen the movement, but this complicates and adds costs to the construction, see e.g. DE202008001634 to DEWERT ANTRIEBS UND SYSTEMTECHNIK. This is owing to the fact that the bed structure comprises extra mountings or the like to which the gas springs can be secured. In addition to this, the mounting time increases and the gas springs are an added cost. Further, the bed will often be equipped with two gas springs to meet existing requirements. Thus, this solution does not intuitively appear to be the right solution to the problem. This problem is previously realized in EP 0 944 788 B1 to LINAK A/S, which concerns a linear actuator with quick release and brake means for controlling the speed of the spindle when the spindle is disengaged from the motor and transmission. The embodiment shown in EP 0 944 788 B1 deals with a screw spring functioning as a brake spring, which tightens against a fixed contact surface. By a controlled loosening of the engagement of the screw spring against the contact surface, the speed of the spindle can be controlled. The construction is fine but requires adroitness for the operator to be able to control the speed evenly. Moreover, the construction is complex. WO2011/066836 A1 to LINAK A/S discloses a construction where this problem of controlling the speed manually is sought solved by means of a centrifugal brake, but this construction is likewise rather complex and does not solve the problem completely. 
     In WO2016/026495 to LINAK a linear actuator has brake means constituted by a rotary damper of the fluid type comprising an internal body located in a liquid-filled hollow in an outer body, where one body is in driving connection with the spindle or the part of the transmission, which extends from the spindle to the quick release, and where a dampening effect, which dampens the speed of the spindle and thus the adjustment element, is generated when this body is rotated relative to the other body as a result of activation of the quick release. However, since the dampening is in response to the rotational speed of the spindle, the dampening will vary along the stroke length spindle. Lowering of the back-rest section may therefore take a while. 
     The purpose of the invention is to provide a different solution for a controlled lowering or retraction of an adjustment element when this is disengaged from the motor and the transmission. 
     The linear actuator according to the invention is characteristic in that it comprises a coupling connected to the brake means, where the brake means is configured to be in either 1) an active state, where the rotation of the spindle is braked, or 2) an inactive state, where the rotation of the spindle is not braked. The coupling being configured to be in a state of either 3) engaged, or 4) slipping or disengaged, and where the coupling will set the brake means in 1) the active state, when the coupling is 3) engaged, or 2) the inactive state, when the coupling is 4) slipping or disengaged. 
     Hereby, the brake means are not activated until the coupling is in its engaged state. This state of the coupling can be reached by using an automatic coupling or a manual coupling. 
     In an embodiment, the coupling is a centrifugal coupling acting in response to the rotational speed of the spindle. It is thus possible to provide a construction where the lowering speed is controlled in response to the rotational speed of the spindle when the quick release is activated. 
     In an embodiment, the coupling comprises a rotation holder, a spring, and a sliding element, where the rotation holder comprises a cavity for receiving the sliding element, and where the cavity comprises an opening through which at least a part of the sliding element can be displaced. The spring is arranged between the sliding element and the rotation holder such that the sliding element is spring-loaded relative to the rotation holder. The linear actuator comprises a stop prepared for engagement with the part of the spring-loaded sliding element extending out of the opening of the rotation holder, where the coupling is in 3) the engaged state, when the part of the spring-loaded sliding element extending out of the opening of the rotation holder fully engages the stop, and is in 4) the slipping or disengaged state, when the part of the spring-loaded sliding element extending out of the opening of the rotation holder is slipping or disengaged from the stop. If the rotational speed of the spindle passes a certain threshold, the centrifugal force exerted on the sliding element will cause it to be displaced out of the opening of the cavity. This threshold is only reached if the quick release unit is activated. Hence, during normal operation of the linear actuator, the brake means will not be worn. 
     In an embodiment, the linear actuator comprising a rear mounting for mounting of the linear actuator, where the rear mounting comprises a cavity adapted to receive at least a part of the centrifugal coupling, where the side wall of the cavity has an approximately circular cross section, and where a circular arc of the side wall is displaced radially outwards, and where the circular arc comprises the stop. By incorporating at least a part of the coupling into the rear mounting, the built-in dimensions of the linear actuator can be kept as small as possible. 
     In an embodiment, the brake means is a rotary damper or a wrap spring. 
     In an embodiment, the spring of the centrifugal coupling is a compression spring or extension spring. 
     In an embodiment of the linear actuator, the coupling is a manual coupling. Hereby, an operator can determine when to engage the coupling and thus active the brake means. 
     In an embodiment, the linear actuator comprises a rear mounting for mounting of the linear actuator and the manual coupling comprises a damper holder with a protrusion extending out from the side of the damper holder, and where the rear mounting comprises a cavity for receiving at least a part of the manual coupling, and further comprises a stop element, which can be moved in and out of the cavity by a manual operation. Where the manual coupling is in the engaged state when the stop element extends into the cavity, such that the protrusion engages the stop element, whereby the damper holder cannot rotate, and where the manual coupling is in the slipping or disengaged state when the stop element is fully or almost fully retracted from the cavity, such that the damper holder can rotate. 
     In another embodiment, the invention relates to a bed comprising an adjustable carrying surface for a mattress and where the carrying surface comprises an adjustable section. The bed comprises at least the one linear actuator of the type described above, configured to adjust the adjustable section of the bed. In a further embodiment, the adjustable section of the bed is a back-rest section. In yet a further embodiment, the bed is a hospital or care bed. In these embodiments, the coupling can be configured to lower or retract the adjustment element as fast as possible and at the same time duly consider the health and required treatment of a person or patient occupying the bed. In addition, the adjustable section can be lowered without damaging the bed. 
    
    
     
       A linear actuator according to the invention will be described more fully below under reference to the accompanying drawing. The drawing shows: 
         FIG. 1 , an outline of a hospital or care bed, 
         FIG. 2 , a perspective view of a linear actuator with quick release, brake means and a coupling for activating the brake means, 
         FIG. 3 , a longitudinal cross section of the linear actuator in  FIG. 2 , 
         FIG. 4 , an exploded perspective of a rear mounting, centrifugal coupling, and brake means, 
         FIG. 5 a - d   , different views of a damper holder of the centrifugal coupling, 
         FIG. 6 a - b   , two perspectives of a sliding element of the centrifugal coupling, 
         FIG. 7 a - b   , a top view and a perspective of the rear mounting, 
         FIG. 8 , a cross section of the linear actuator through the rear mounting, where the centrifugal coupling is in a slipping or disengaged state, 
         FIG. 9 , a cross section of the linear actuator through the rear mounting, where the centrifugal coupling is in an engaged state, 
         FIG. 10 a - b   , a side view and perspective of the centrifugal coupling and rotary damper, where the centrifugal coupling is in a slipping or disengaged state, 
         FIG. 11 a - b   , a side view and perspective of the centrifugal coupling and rotary damper, where the centrifugal coupling is in an engaged state, and 
         FIG. 12 a - b   , a schematic cross section of second embodiment of the coupling. 
     
    
    
     The hospital or care bed  1  shown in  FIG. 1  of the drawing comprises a lower frame  2  equipped with drive wheels  3  and an upper frame  4 . An adjustable carrying surface for the mattress is mounted to the upper frame  4 . The carrying surface comprises a back-rest section  5 , an articulated leg-rest section  6  and a fixed middle section  7  between these two sections  5 , 6 . The back-rest and leg-rest sections  5 , 6  can be adjusted with a linear actuator  8 , 9  each, such that the carrying surface can assume various contours, indicated by the arrow  10 . The upper frame  4  is connected to the lower frame  2  with a lever mechanism  11 , 12  at each end. The upper frame  4  can be raised and lowered by means of a pair of actuators  13 , 14  connected to the lever mechanism  11 , 12 . The actuators  8 , 9 ; 13 , 14  are connected to a control box  15  containing a power supply for connection to mains, optionally a rechargeable battery pack as well as a controller. Operating units such as hand controls  16  and fixed control panels in guard rails  17  are connected to the control box  15 . 
       FIG. 2  shows a linear actuator  8  which is arranged to move the back-rest section  5  of the hospital or care bed  1 . The linear actuator comprises a housing  18  with a reversible electric motor  19 , which through a worm gear  20  drives a spindle  21  with a spindle nut  22 , to which a tubular adjustment element  23 , also called an inner tube, surrounded by an outer tube  24 , is secured. A front mounting  25  is located at the end of the tubular adjustment element  23 , and a rear mounting  26  for mounting of the linear actuator  8  is located at the rear end of the linear actuator. The linear actuator  8  is equipped with a quick release unit  27  with a release mechanism. 
     Referring to  FIGS. 3-11 , the linear actuator  8  comprises a rotary damper  28  which is connected to the lower/rear end of the spindle  21 , i.e. the end closest to the rear mounting  26 . The rotary damper  28  comprises an inner body in the shape of a cylinder placed in a liquid-filled hollow in an outer body  29 . The liquid used in the hollow of the rotary damper  28  is preferably a silicone oil. The inner body is through a shaft end  30  in driving connection with the shaft end of the spindle  21 . 
     The rotary damper  28  can be connected directly to the spindle  21  or via one or more parts depending on the specific construction of a linear actuator. In the present embodiment ( FIGS. 2-11 ), the shaft end  30  of the rotary damper  28  is connected to a gear wheel  31 , which engages a position wheel  32 . The rear end of the spindle  21  is connected to an end nut  33 , which engages the position wheel  32 . 
     The outer body  29  of the rotary damper  28  is fixed to a centrifugal coupling  34 , which comprises a damper holder  35 , a spring  36 , and a sliding element  37 . The damper holder  35  is a circular element with two circular segments cut off. 
     Collars  38   a - c  for rotationally fixing the rotary damper  28  to the damper holder  35  extends from an upper side thereof. The damper holder  35  has a cavity  39  with two openings  40 , 41 . The opening  40  is open towards the upper end and the opening  41  is open to the side of the damper holder  35 . The cavity  39  is adapted to receive the sliding element  37 , which is shaped as an oblong rectangular block with a protrusion  42  at one end extending to the side of the sliding element  37 . The end of the sliding element  37  placed at the opening  41  is curved such that it levels with the circular outer surface of the damper holder  35 . A small part of the cavity  39  is adapted to receive a spring  36 , here a compression coil spring. One end of the spring  36  engages a wall piece  43  of the cavity  39 . The other end of the spring  36  engages the protrusion  42  of the sliding element  37 . To fit in the space between the wall piece  43  and the protrusion  42 , the spring  36  is compressed and therefore in a pre-stressed state. Hence, the sliding element  37  is spring-loaded. 
     The rear mounting  26  comprises a cavity  44  having a wall  45  with an approximately circular cross section. The cavity  44  is adapted to receive at least a part of the coupling  34  with a small distance of play between the coupling  34  and the wall  45 . A circular arc of the circumference of the wall  45  is displaced radially outwards, creating a small arc shaped track  46  relative to the circular cross section of the cavity  44 . The cavity  44  has a small hole  47  at its bottom adapted to receive a pin  48  extending from the underside of the damper holder  35  with a small distance or play between the two. In this embodiment, the underside of the damper holder  35  engages a part of the bottom of the cavity  44 . This serves among other things to keep the rotary damper  28  in place along the longitudinal axis of the spindle  21 . 
     Since the damper  28  and the coupling  34  ( 35 , 36 , 37 ) are directly and/or indirectly connected to the spindle  21 , both will rotate together with the spindle  21 . If the rotational speed of the spindle  21  passes a certain threshold, the centrifugal force exerted on the sliding element  37  will cause it to be displaced out of the opening  41  of the cavity  39 . This threshold can only be reached if the quick release unit  27  is activated. Hence, during normal operation, the linear actuator  8  will not reach such a high rotational speed. 
     Passing the threshold will cause the curved end of the sliding element  37  to engage the wall  45  of the cavity  44  of the rear mounting  26 . When the sliding element  37  reaches the circular arc of the circumference of the wall  45 , it will displace into the arc shaped track  46 . Once here, a side of the sliding element  37  will engage the end  49  of the track  46 , which functions as a stop. In this embodiment, the track end  49  is constituted by a hollow cylindric tube  50  with a longitudinal slit, in which a protrusion of the wall  45  is received. 
     The relation between the size of the centrifugal force and the impact of the engagement between the sliding element  37  and the track end  49 , determines whether the sliding element  37  remains in engagement with the track end  49  or is forced back into the cavity  39 . The latter constitutes a slipping state of the coupling  34 , which will cause the spindle  21 , the damper  28  and the coupling  34  to continue its rotation. The former constitutes an engaged state of the coupling  34 , which causes an activation of the rotary damper  28 . More precisely, the damper holder  35  and thereby the outer body  29  of the rotary damper  28  will be kept in a fixed non-rotating position. Only the shaft end  30  of the inner body of the rotary damper  28  will continue to rotate with the spindle  21 . Consequently, the rotary damper  28  will dampen the rotational speed of spindle  21 . Upon reduction of the rotational speed of the spindle  21 , the centrifugal force exerted on the sliding element  37  reduces, causing it to retract into the cavity  39 . This again will cause the complete rotary damper  35 , the coupling  34 , and the spindle  21  to rotate together. 
     The coupling  34  will normally be in a slipping state a number of times, before the rotational speed reaches the threshold causing the coupling  34  to be in an engaged state. For the sake of clarity, a disengaged and slipping state of the coupling will be regarded as one single state. The threshold can be set to a determined level depending on the bed or other construction in which the linear actuator is used. A range number of parameters can be used to reach the threshold. These could be, but are not limited to, the following, namely the thread pitch of the spindle  21 , geometry and material of the damper holder  35  and sliding element  37 , and the spring force of the spring  36 . The coupling  34  could also be embodied such that the spring  36  could be an extension spring rather than a compression spring. 
     In the present embodiment, the rotary damper  28  is rotationally fixed by the collars  38   a - c  and fixed along the longitudinal axis of the spindle by the engagement between the underside of the damper holder  35  and a part of the bottom of the cavity  44  of the rear mounting  26 . In an alternative embodiment, the collars  38   a - c  could be embodied as snap locks and thus extend along the full height of the outer body  29  and engage the top surface thereof. This would fix the rotary damper  28  both rotationally and in the longitudinal direction. Engagement between the underside of the damper holder  35  and the bottom of the cavity  44  would therefore not be needed. 
     Instead of a rotary damper, other types of brake means or dampers could be used, e.g. a wrap spring brake. 
       FIG. 12 a - b    shows schematic cross sections of a second embodiment of the invention, where the coupling is a manual coupling. In  FIGS. 12 a - b   , the rear mounting  50  of the linear actuator has a circular side wall forming a cavity  51  adapted for receiving at least a part of the manual coupling. The damper holder  52  comprises a protrusion  53  extending out from the side of damper holder  52 . The rear mounting  50  comprises a stop element  54 , which can be moved in and out of the cavity  51 . Collars  55   a - c  for rotationally fixing a brake means to the damper holder  52  extends from an upper side thereof. The brake means is connected to the spindle of the linear actuator in the same way as described in the first embodiment. At least the damper holder  52  and the stop element  54  constitutes the manual coupling of this embodiment. The manual coupling can be in either of two states as the centrifugal coupling  34  of the first embodiment. A slipping or disengaged state where the stop element  54  is fully or almost fully retracted from the cavity  51 , such that the damper holder  52  can rotate freely, or an engaged state where the stop element  54  is extended into the cavity  51 , such that the protrusion  53  engages the stop element  54 , whereby the damper holder  52  cannot rotate. In the latter situation, the brake means will be in an active state and thus dampen the rotational speed of the spindle. In the former situation, slipping or disengaged state, the brake means will be in an inactive state and thus not dampen the rotational speed of the spindle.