Abstract:
Linear actuator comprising a housing ( 1 ) consisting of at least two parts ( 1   a   , 1   b ) a mounting console ( 2 ) a reversible motor ( 7 ) with a transmission ( 22 ), a spindle ( 5 ) which over the transmission is driven by the motor, a bearing ( 16 ) for embedding the spindle ( 5 ), a spindle nut ( 6 ) secured against rotation on the spindle, an outer tube ( 3 ) which surrounds the spindle, an activation element ( 4 ) telescopically mounted in the outer tube ( 3 ) and connected to the spindle nut ( 6 ), a front mounting ( 8 ) on the outer end of the activation element ( 4 ), a rear mounting ( 9 ) arranged in the housing. In the rear mounting ( 9 ) is a seat for the bearing ( 31 ) of the spindle. The motor ( 7 ), the transmission ( 22 ) and the outer tube ( 3 ) is secured to the console ( 2 ). The mounting console ( 2 ) is constructed as a separate element around which the two parts ( 1   a   , 1   b ) of the housing is assembled and the mounting console ( 2 ) constitutes alone the bearing chassis of the actuator. Thus a possibility for a compact actuator with low manufacturing costs together with high performance and quality properties is achieved.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a linear actuator. 
     2. The Prior Art 
     Actuators of this type are known i.e. from EP 531 247 A1, EP 586 326 A1, EP 647 799 and EP 662 573 A1 all of them to Linak NS. The forces of the spindle are transmitted to a compression/tension bearing embedded in a plastic housing. The forces between the bearing and the rear mounting are transmitted through the plastic housing which has to be dimensioned and shaped accordingly. Such a plastic housing represents a significant portion of the total cost of the actuator. WO 98/30816 to Linak NS discloses an example of a sophisticated actuator with very high performance in which the forces between the bearing and the rear mounting are transmitted via a metal chassis. The actuators are used for i.e. incorporation in furniture, e.g. hospital and nursing beds for which it is required that the actuators can withstand moisture and water. As for instance mentioned in EP 488 552 A1 Huntleigh Technology plc concerning a hospital bed. Since the actuators are fully or partly exposed it is an additional requirement that the actuators have a minimum of design with smooth and filth-repelling surfaces. 
     A non-design heavy-duty actuator without a housing for industrial purposes is based on a bearing metal housing with an integrated rear mounting from which the forces are transmitted. 
     An actuator of this type is known from DE GM 94 04 383.3 U1 with the housing being of die-cast zinc is equipped with a cylindrical portion in which the motor is located, said cylindrical portion being closed by means of a cover. Furthermore, the actuator is waterproof, if it is provided with appropriate sealing which makes it suitable for beds in the hospital and care sector. The die-cast zinc housing being relatively large as the motor has to be build in it, makes the solution relatively expensive. 
     EP 0 831 250 A2 Dana Corp discloses an actuator with a housing, having a shell which surrounds the motor and the transmission. The shell being open in the rear i.e. towards the rear mounting of the actuator is closed with a cover. In front, i.e. towards the spindle, the shell is equipped with a mounting for the outer tube which serves as guide for the spindle nut and as guide for the outer end of the tube shaped activation element being secured to the spindle nut. The lateral load which after all appear on the activation element and thus on the spindle are transmitted through the outer tube to the housing. However, it is also stated that the housing and the outer tube are made from a rigid material and as an example is stated i.e. aluminium, zinc alloys and stainless steel, i.e. the stated plastic materials: nylon containing glass fibre, polyvinylchloride and polyethylene all having a corresponding rigidness. All things considered a rather expensive solution. 
     WO 02/29284 A1 Linak A/S discloses an actuator in which a console is secured to the front part of the motor such that the electric motor and the console appear to be the bearing chassis of the motor while the housing is functioning as a dust and watertight cover, however, forces as such are not transmitted through the housing. 
     The object of the invention is to provide a compact actuator of the first mentioned type which is inexpensive to manufacture, but meets the requirements of these when it comes to output and quality. 
     SUMMARY OF THE INVENTION 
     This is achieved according to the invention in that the actuator includes a mounting console constructed as a separate element around which the two parts of the housing are mounted and the mounting console alone constitutes the bearing chassis of the actuator. The mounting console can be constructed with the sole purpose of being able to withstand and/or transmit the forces occurring in consequence of the parts which are mounted on the mounting console and besides be constructed as compact as possible. Therefore, there are no particular strength demands on the housing, which means that no particular considerations have to be taken as far as manufacturing and the shaping concerns. As a consequence of this, the material thickness can be made thin and strengthening ribs are not strictly necessary resulting in a simpler mould as well as a simplified manufacturing process. Furthermore, plastic materials with lower strength can be chosen which is cheaper and also an advantage in the manufacturing process. 
     A particular compact embodiment of the actuator can be achieved by positioning the motor parallel to the spindle and particularly along a shaft end of the spindle. 
     The housing may of course be constructed of more parts; however, it is appropriate in terms of assembly and logistics if the housing is made of two parts only. The mounting plane may be positioned in the axial direction, but it is attractive that mounting planes are located perpendicular on the longitudinal axis of the spindle. It provides the possibility for shaping the two parts of the housing as half shells which can be assembled around the mounting console. This differs from the construction in U.S. Pat. No. 5,809,833 Dana Corp, where the housing is made of only one cup-shaped shell to be closed with a cover. 
     In a particular expedient embodiment, the mounting console is equipped with a rigid wall element around which and upon which the housing of the actuator, the electric motor, the transmission and the outer tube are mounted. This makes it possible to mount the individual components on each side of the wall element and a fairly balanced force and weight distribution on the wall element is achieved. 
     By constructing the outer outline of the mounting console consistent with or basically consistent with the outer shape of the cross section of the housing it is possible to make the mounting console coincide with the outer side of the housing, which provides an attractive design as well as a smooth and cleaning-friendly surface. 
     Dependent of the chosen type of transmission it can be secured on the mounting console in different ways. In case of a toothed belt drive, a belt pulley on the motor shaft and at the end of the spindle will be sufficient. When using a gear with parallel axles, the gear wheels may also be secured directly to the mounting console. However, if the transmission is a little more complicated it would be suitable to construct a housing for the transmission on the mounting console. 
     The outer tube can be secured to the console in different ways, for example it can be secured directly with screws to the mounting console or be led into a tube shaped socket constructed on the mounting console and retained by snap locking means. In a particular embodiment the mounting console is equipped with a tube shaped socket, of which the inner and outer shape are consistent with, or basically are consistent with, the inner and outer shape of the outer tube causing this to be positioned on a free edge of the tube shaped socket. The tube shaped socket will then function as an extension of the outer tube into the console. This is particularly important for axially running guides in the outer tube. In this embodiment it is suitable to secure the outer tube in the mounting console with screws as the outer tube is furnished with screw channels for this purpose. 
     The actuator can be stopped in the outer position of the activation element in different ways i.e. by means of mechanical end stops in connection with detecting of an overcurrent, detecting of the position of the activation element by means of potentiometers, Hall elements, magnetic or optical encoders, but typically, end stop switches are preferred for safety reasons. In an embodiment the actuator comprises a circuit board with end stop switches mounted on the side of the tube shaped socket and on the circuit board is mounted a slider with an arm for activation of the end stop switches, where the spindle nut in an inner end position affects the arm on the slider and that in the outer tube there is an axially displaceable embedded rod which is mounted to the arm at the one end, while the other end has a stop collar affected by the spindle nut in the other end position. The possibility for a compact structure in combination with the possibility for a relative large circuit board is provided when the circuit board is being mounted edgewise on the side of the actuator. 
     The rear mounting could be constructed as an integrated part of the housing; however, it has proven to be most expedient to construct it as a separate part which makes the spindle with the gear, the bearing and the rear mounting appear as one unit, ready to be mounted in the actuator. An attractive construction is designed in such a way that a seat for the bearing of the spindle is connected to an opening on the side of the rear mounting. Thus, the rear mounting can be extended sideways over the bearing of the spindle and is thus secured. In order to prevent the rear mounting from unintentionally falling off, the opening could be constructed slightly narrowed so that the rear mounting has to be pressed over the bearing. Another possibility is to block the opening with a closing element. 
     The rear mounting can be mounted in the housing in different ways, e.g., incorporated between shaped wall elements in the housing. In a particularly simple construction, the rear mounting is fixed between the housing on the mounting console and an end wall on the rear part of the housing. It should be remembered that when the bearing of the spindle is located in the rear mounting the axial forces are led directly through the rear mounting to the construction in which the actuator is mounted. Thus, the rear mounting is not particularly exposed to transverse forces in the housing. However, the transverse forces which may occur are directly transmitted to the mounting console. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment according to the invention will be explained more fully below with reference to the accompanying drawing. 
         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 a exploded view of the actuator shown from the rear, 
         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 a 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 , and 
         FIG. 8  shows the circuit board shown from the opposite side and end as shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The main components of the actuator shown on the drawing comprise a two-part outer housing  1 , a mounting console  2 , an outer tube  3  secured to 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 la 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 a grove  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  11  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  1   a  of the housing. 
     At one side of the cross wall  2   a  of the mounting console there is a recess  12  ( FIG. 4 ) for receiving the front part of the motor  7 . The motor shaft  13  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  16  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, the free end wall  17 , 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 wail 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 wall  17  of the housing. Crosswise of the worm  23  a gear unit with a through going axle  25  is arranged. Said axle  25  is embedded with its ends in the two rectilinear wall elements  18   b , 18   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 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 stabilises 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 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 is located. This recess  35  is connected to an opening  36  functioning as a seat for a cylindrical collar on the rear side of the worm wheel  30  ( FIG. 6 ), The recess  35  for the ball bearing  31   31  and the opening  36  for the cylindrical collar  30   a  on the worm wheel  30  is connected to an opening  37  on the side of the rear mounting  9  such that it can be extended sidewards over the ball bearing  31  and the collar  30   a  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  of 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 ball 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 aluminium tube with an almost square cross section as two diametrically located edges  3   a  are shaped as a as a soft circular arc while the two other edges  3   b  are sharper i.e. with a 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   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  tube  3  is fastened to the mounting console  2  by means of screws which are 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 shaped socket  43  is equipped with a number of guide pins  43   a . The outer 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 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 seals 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 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 position 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 positions 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).