Abstract:
Linear actuator comprising a housing ( 1 ), a reversible electric motor ( 7 ), a transmission ( 22 ), a spindle ( 5 ) driven by the electric motor through the transmission ( 22 ), a bearing ( 31 ) for embedding the spindle ( 5 ), a spindle nut ( 6 ) secured against rotation on the spindle, an outer tube ( 3 ) surrounding the spindle, an activation element ( 4 ) telescopically embedded in the outer tube ( 3 ) and connected to the spindle nut ( 6 ), a rear mounting ( 9 ) designed as a separate element and secured in the housing for mounting of the actuator. The rear mounting ( 9 ) is equipped with a seat ( 35 ) for the bearing ( 31 ) of the spindle. The seat ( 35 ) is connected to an opening ( 36 ), which is guided out on the side of the rear mounting ( 9 ), so that the bearing ( 31 ) of the spindle may be inserted sideways in the seat ( 35 ). Thus a linear actuator is provided having a rear mounting which is easier to mount and ensures an easier handling during the assembly of the linear actuator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a linear actuator. 
     2. The Prior Art 
     Linear actuators are widely used in structures where the linear movement can be used for adjusting a movable part of a structure. Thus, linear actuators are used in furniture, hospital and care beds, patient lifters, vehicles, ships and airplanes, machines and processing plants, buildings, etc. The actuator is typically secured to the structure by means of a rear mounting arranged at the back of the actuator and a front mounting on the activation element. The activation element is typically a tubular piston rod, but may also be a particular design of the spindle nut. 
     EP 0 531 247 B1 Linak A/S discloses an actuator where the rear mounting and the housing of the actuator is moulded as one unit. U.S. Pat. No. 4,858,481 Brunswick Valve &amp; Control, Inc. discloses an actuator where the rear mounting as a separate unit is screwed onto the rear of the housing of the actuator. U.S. Pat. No. 5,809,833, Dana Corp. discloses an actuator where the rear mounting likewise is a separate unit, but is screwed onto an element inside the actuator. The rear mounting is here open in the front, where a bearing at the end of the spindle is positioned in and retained by means of a screwed on plate piece having a through hole for the spindle. WO 02/29284 A1, Linak A/S discloses an actuator, where the rear mounting consists of two halves which are joined in the axial center plane of the rear mounting. The rear mounting is furnished with a seat for a bearing, which is secured to the end of the spindle. All of the above are as such quite good constructions, but somewhat troublesome in terms of manufacturing and assembly as well as expensive. 
     To be exact, the invention relates to the type of linear actuators where the bearing is positioned in the rear mounting, which provides the advantage that the axial forces from the load on the activation element of the actuator are led directly through the spindle to the bearing of the spindle. 
     The purpose of the invention is to provide a rear mounting, which is easier to mount and further enables an easier handling during the assembly of the actuator. 
     SUMMARY OF THE INVENTION 
     This is achieved according to the invention in that the actuator is constructed such that the seat is connected to an opening which leads out to the side of the rear mounting so that the bearing may be inserted sideways into the seat. This eases the assembly process as the rear mounting with the seat in only one operation is guided over the bearing of the spindle and thus is fixed without the use of tools. In relation to this, it is expedient that the opening is extended all the way to one end of the rear mounting so that the shaft end of the spindle with the attached bearing may be inserted sideways into the rear mounting. The spindle can thus be mounted with various parts including bearing, whereupon the rear mounting is finally led over the bearing. 
     To prevent the rear mounting from unintentionally falling out of the spindle bearing, the opening may in a further embodiment of the actuator be closed by means of a closing element. In a particularly expedient embodiment the closing element has a tongue at each side, which fits into a spline in the side of the opening. The closing element is thus fixed so that it does not unintentionally fall out during the handling in the assembly process of the actuator. 
     In a further embodiment of the actuator, a circular opening is constructed in the housing into which the rear mounting is placed. Inside the housing, on the area surrounding the rim along the opening, there is a row of teeth. On the rear mounting, at least over a section, there is a corresponding row of teeth cooperating with the teeth in the housing. Thus, the rear mounting is secured against unintentional rotation about its axial axis. In a further embodiment the rear mounting has two sections with teeth located opposite each other, which provides a sufficiently secure retention against rotation while it further simplifies the manufacturing process. In an embodiment one of the sections with teeth is constructed as a locking element. The teeth further ensure that the rear mounting may be positioned and held in a desired angular position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will be described more fully below with reference to the accompanying drawing, in which 
         FIG. 1  shows a perspective view of the actuator shown from the front, 
         FIG. 2  shows a perspective view of the actuator shown from the rear, 
         FIG. 3  shows an exploded view of the rear part of the actuator, 
         FIG. 4  shows a longitudinal section through the actuator shown from the side, 
         FIG. 5  shows a longitudinal section through the actuator shown from above, 
         FIG. 6  shows an exploded view of the actuator, shown from the front, 
         FIG. 7  shows a perspective view of the mounting console, shown from the rear from the opposite side, as shown in  FIG. 3 , 
         FIG. 8  shows the printed circuit board, shown from the opposite side and end as shown in  FIG. 3 , 
         FIG. 9  shows a perspective view of the rear mounting and the rear part of the housing, shown from the front of the actuator, 
         FIG. 10  shows a perspective view of the rear mounting, shown towards the rear end of the actuator, and 
         FIG. 11  shows a perspective view of the rear part of the housing, shown from the front of the actuator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The main components of the actuator shown on the drawings include a two-part outer housing  1 , a mounting console  2 , an outer tube  3  secured to the mounting console  2  with a rear end, and in which a telescopic tube-shaped activation element  4  (in technical terminology, an inner tube), a spindle  5  with a spindle nut  6  to which the activation element  4  is mounted with a rear end, a reversible low voltage DC motor  7 , a front mounting  8  secured to a free front end of the activation element  4  and a rear mounting  9  at a rear end of the outer housing  1 . 
     The two-part outer housing  1  comprises a front part  1   a  and a rear part  1   b  assembled around the mounting console  2 , having a cross wall  2   a  with a circumferential flange  2   b , and where the exterior of the flange corresponds to the outer contour of the housing  1 . Along the outer side of the circumferential flange  2   b  at each side groove  2   c  for a sealing is arranged. In the corners are through holes  10  for screws  11 . The two parts  1   a , 1   b  of the housing  1  are assembled around the mounting console  2  in each corner with the screws  1  at each corner which are inserted through the holes  10  in each corner of the mounting console  2 . The screws are inserted from the rear part  1   b  and are screwed into the front part is of the housing. 
     At one side of the cross wall  2   a  of the mounting console there is a recess  2  ( FIG. 4 ) for receiving the front part of the motor  7 . The motor shaft  13  (see  FIG. 3 ) of the motor extends through a corresponding hole  14  in the mounting console  2 . The motor  7  is mounted to the mounting console  2  with screws  15 . 
     On the opposite side of the mounting console  2   a  housing  6  with a first and a second end wall is mounted, where the one end wall is constituted by the cross wall  2   a  of the mounting console while the other end wall  17 , the free end wall, is an independent wall at a distance from the cross wall  2   a . Between the two end walls  2   a ,  17  is arranged a side wall  18 , comprising a half circular wall element  18   a  which at its one end is extended into a short rectilinear wall element  18   b  and at the other end is extended into another longer rectilinear wall element  18   c . In connection with the half circular wall element  18   a  in the free end wall is arranged a circular opening  19  which is connected to a circular opening  20  in the cross wall  2   a  of the mounting console. Likewise, the housing  16  has an opening  21  in the side wall between the two rectilinear wall elements  18   b ,  18   c.    
     A transmission  22  mounted in the housing  16  comprises a first worm gear, the worm  23  of which is secured to the motor shaft  13 . The free end of the worm is embedded in a hole  24  functioning as a slide bearing in the free end wail  17  of the housing. Crosswise of the worm  23  a gear unit with a through going axle  25  is arranged. The axle  25  is embedded with its ends in the two rectilinear wall elements  18   b ,  8   c  and inclined in the housing  16 . In one end, the gear unit is equipped with at worm wheel  26  brought into mesh with the worm  23  at the motor shaft  13 . The remaining part of the gear unit is constructed as a second worm  27  with a large thread. The gear unit is led into the housing  16  through the opening  21  in the side wall  18  of the housing. 
     A shaft end  5   a  of the spindle is shaped as a D-spline upon which a bushing  28  is arranged. On the bushing  28  is arranged a worm wheel  30  with a large thread brought into mesh with the worm  27  with the large thread on the gear unit by means of a spline connection  29 . Thus, the spindle  5  is driven by the motor  7  over a transmission with two worm gears  23 , 26 ; 27 , 30  where one of the worm gears  26  and one of the worms  27  are moulded as a plastic component in one piece. Furthermore, the worm wheel  30  on the spindle  5  is also made of plastic. In that way a large gearing in the transmission is achieved, likewise, it is self-locking and thus prevents or locks the spindle  5  against rotation when the load on the activation rod  4  attempts to rotate the spindle  5 . 
     On the outer end of the spindle  5  up against the worm wheel  30  a ball bearing  31  is located, which with one side is extended over a stepped down end  28   a  of the bushing  28 . On the other side, the free side of the bearing  31 , a disc  32  with a D-shaped opening which extends over the end of the spindle is located. The disc  32  is equipped with a hub protruding into the opening of the ball bearing and stabilizes it. The outer end of the spindle  5  is shaped as a rivet head for retaining the disc  32  and the bushing  28  on the D-shaped shaft end  5   a  of the spindle  5 . 
     The rear mounting  9  is furnished with a circular part  9   a  the outer end of which, the free end, is here equipped with a fork fitting  33  having a through hole  34  for a bolt or a shaft piece, but it might as well have been a flange with a through hole. On the opposite side, the inner side of the rear mounting  9 , protruding into the housing  1  a recess  35  which is shaped as a seat for the ball bearing  31  is located. This recess  35  is connected to an opening  36 , functioning as seat for a cylindrical collar  30   a  on the rear side of the worm wheel  30  ( FIG. 6 ). The recess  35  for the ball bearing  31  and the opening  36  for the cylindrical collar  30   a  on the worm wheel  30  are connected to an opening  37  on the side of the rear mounting  9 , providing a U-shaped channel, such that the rear mounting can be extended sideways over the ball bearing  31  and the collar  30   a  on the worm wheel  30 . The opening  37  may be closed by means of an arc-shaped closing element  38 , which with a tongue  38   a  at each side, fits into a spline  37   a  at the side of the opening  37 . The closing element  38  is designed as a section in the circular part  9   a  of the rear mounting  9 . The circular part  9   a  of the rear mounting fits into the circular opening  19  of the free end wall  17  of the housing  16  on the mounting console  2  and abuts the rim of the circular opening  19  with the edge of a circular collar  9   b , which moreover functions as a stop for how far the circular part  9   a  of the rear mounting  9  extends into the housing  16 . As the spindle  5  with the bail bearing  31  is embedded in the rear mounting  9 , the position of the spindle in proportion to the mounting console  2  is thus precisely determined. 
     At the back end of the rear part  1   b  of the housing  1  a circular hole  39  is located through which the rear mounting  9  with the fork fitting  33  extends. Internally in the housing on the rim along the opening  39 , a row of teeth  40  is arranged more precisely forty-eight teeth. At the rear mounting  9  in connection with the circular collar  9   b  is arranged a stepping with two steps, of which the first step  9   c  is extended through the opening  39  of the housing while at the other step  9   d  two mutually facing sections  41   a , 41   b  with teeth are arranged corresponding to the teeth  40  at the opening  39  of the housing. One of the sections with teeth  41  a is arranged at the closing element  38 . The arrangement of teeth allows the rear mounting and thus the fork fitting  33  can be rotated into a random angle position with intervals of 7.5°. 
     The outer tube  3  is composed of a an aluminum tube with an almost square cross section as two diametrically located edges  3   a  are shaped as a soft circular arc while the two other edges  3   b  are sharper i.e. with a smaller radius of curvature. In each of these two corners  3   b  a screw channel  42  is arranged. The inner end, the end of the tube  3  protruding farthest into the housing, is riding at the edge of a tube shaped socket  43  on the mounting console  2 . Basically, the tube shaped socket  43  is shaped in accordance with the shape of the outer tube  3 . The outer tube  3  is fastened to the mounting console  2  by means of screws which are screwed into the screw channels  42  of the outer tube  3  from the opposite side of the mounting console  2 . In order to be able to guide the outer tube during the mounting process, the outer side of the tube shaped socket  43  is equipped with a number of guide pins  43   a . The outer tube  3  extends with its outer end through an opening  44  in the front of the front part of the housing. In order to prevent penetration of water between the outer tube and the housing a sealing is arranged in the opening. 
     The activation element  4  comprises a tube section the inner end of which, i.e. the end located inside the housing comprises an inner threaded part by means of which it is screwed onto the spindle nut  6  the outer side of which for the purpose is equipped with a thread  6   a . The front mounting  8  is secured to an outer end of the activation element  4 , i.e. the end of the tube section which is extended out of the front part of  1  the housing  1 . The front mounting  8  is here equipped with a fork fitting  45  with a through hole comprising two bushings  46  for a mounting bolt or a shaft, it might as well be constructed as a butt strap with a through hole just like the rear mounting. The other end of the front mounting  8  is constructed as a threaded part  8   a  by which it is screwed onto the tube section  4  which for the purpose is equipped with an inner thread. The position of the fork fitting can be adjusted stepless by simply turning the tube section  4  in its thread on the spindle nut. The thread coupling between the front mounting  8  and the tube section  4  is sealed so that water cannot penetrate into the actuator this way. 
     For guidance of the inner end of the tube shaped activation element  4  in the outer tube  3 , the spindle nut  6  is partly furnished with a neck  47 , partly with guide surfaces  47   a  which are guiding against the inner side of the outer tube  3 , and partly with guide bosses  47   b  which are guiding in axially running guides  3   a , constructed for the purpose, inside the outer tube. Moreover, the guide bosses  47   b  function together with the guide surfaces  47   a  as rotation protection for the spindle nut  6  so this is secured against rotation and thus will be moved in and out on the spindle  5  dependent of the direction of rotation of the spindle. To prevent the spindle nut  6  from moving off the spindle  5 , i.e. over the front of the spindle a mechanical stop shaped as a secured circular disc  48  is mounted on the front of the spindle. At the front of the outer tube  3  an end plug  49  is fastened with screws which are screwed into the screw channels  42  in the outer tube  3 . The end plug  49 , which moreover is sealed against the end of the outer tube  3 , has a central opening  50  for the tube shaped activation element  4  which is functioning as a guide for it. The activation element  4  is thus guided in the outer tube  3  both at its rear end and at the front of the outer tube. The opening of the end plug  49  is equipped with sealings in the form of o-rings for the activation element  4  to prevent water to penetrate into the actuator. One of the soft curved corners  3   a  of the outer tube  3  has two guides  51  for a strip shaped activation rod  52  which has an opening  52   a  at the rear part and a dog  52   b  in the form of an embossing at the front part. When the activation element  4  is brought into its outermost position, a guide boss  47   b  on the spindle nut  6  will hit the dog  52   b  and pull the activation rod  52  along until the motor stops. 
     At the front of the mounting console  2  edgeways at the side of the outer tube  3 , a circuit board  53  with switches is arranged. The end of the circuit board rests against the tube shaped socket  43  on the mounting console  2 , and the front edge is fixed between its side and pins on the mounting console  2 . The circuit board  53  has a hole  53   a  for insertion over a pin  43   b  at the side of the tube shaped socket  43  such that the circuit board  53  is secured in the axial direction as well as in the sideways direction. On the circuit board  53  two end stop switches  54 ,  55  are arranged below a longitudinal displaceable housing  56  which with a leg  56   a  at each end reaches into the guide  53   b  in the circuit board  53 . The housing  56  is spring-loaded by a coil spring  57  to occupy a neutral position in which none of the end stop switches  54 , 55  are activated. The coil spring  57  is arranged in a groove in the circuit board. Each end of the groove is connected to a guide through which two tabs  56   b  are arranged on the housing between which the coil spring  57  is embedded. On one side of the housing  56  is an arm  58  which is extended into the hollow of the tube shaped socket  43  through an opening. The aforementioned strip shaped activation rod  52  in the outer tube  3  is attached to the arm  58  with the opening  52   a . When the activation element  4  reaches its outermost end position the displacement of the activation rod  52  will pull the housing  56  along and activate the corresponding end stop switch  55 . This happens in that the ceiling  56   a  of the housing is countersunk at the ends such that the contact on the end stop switch  55  is pressed down when it passes over the end stop switch  55 . By activating the end stop switch  55  the motor will be stopped by switching off the power for it by means of guide electronics (not shown). At the inner retracted end position of the activation element  4  a guide boss  47   a  on the spindle nut  6  hits the arm  58  and thus pulls the housing  56  along and activates the other end stop switch  54 . Again the power for the motor is switched off by the guide electronics. On the other side of the circuit board  53  two positions switches  57   a ,  57   b  are arranged which will be activated by the tab  56   b  on the housing  56 . These position switches signal to the control unit about which end position the activation element  4  is in. Note that the position switches  57   a ,  57   b  are expendable if it is not necessary to know which end position the activation element  4  are in. Also note that the end stop switches  54 ,  55  can function as power switches which cut off the current to the motor  7  in order to simplify the guide electronics. However, it is often a strong wish that the mains voltage is kept as far from the actuator as possible for safety reasons. 
     Further, it is noted that if necessary the spindle nut  6  may be equipped with a metal safety nut  59 , applied in a groove at the end of the spindle nut  6  which typically is made of plastic in order to dampen noise. When the actuator is only exposed to pressure load only one safety nut  59  at the rear end of the spindle nut  6  is required, and when the actuator is only exposed to tensile load, only a safety nut at the front of the spindle nut is required. When the actuator is exposed to both pressure load and tensile load a safety nut can be arranged at each end. 
     The determination of the position of the activation element  4  may, as mentioned above, be done in different ways, e.g. with a Hall-element arranged on the printed circuit board  53 . At a collar  30   b  at the front of the worm wheel  30  on the spindle  5  a magnet ring  60  with more poles is embedded, which triggers the Hall-element each time a pole passes it. The magnet ring  60  is retained in its position by a locking ring  61 . 
     For the sake of completeness it is noted that  62  is a plug from the control device which is connected to the socket of the circuit board  64  through a gateway  63  in the outer housing. The gateway  63  is arranged in a countersunk area on the housing. To prevent the plug  62  from unintentionally being pulled out it can be locked by a locking element  65  which constitutes part of the front part  1   a  of the housing. At a lower edge of the housing  1 , a groove shaped notch for a cable  66  for the plug  62 . The cable  66  is secured by a clamp  67  arranged in the corner of the mounting console. The cable thus lies within the circumscribed rectangle of the housing and is thus properly protected. 
     The invention thus provides a linear actuator which provides the possibility of low manufacturing costs while the actuator still maintains a high quality and strength as well as a high degree of flexibility in terms of accessories and mounting brackets (front and rear mounting).