Abstract:
Actuator comprising of a quick release unit and a means for determining the position of an activation element. With the quick release unit it is possible to release the activation element from the actuator&#39;s electric motor and the transmission or, at least part of it, to make a rapid adjustment to the activation element without the motor and transmission. The means typically used for determining the position of the activation element comprises of a potentiometer, an optical or magnetic encoder indirectly driven by the motor. By connecting the instrument for position determination ( 33 ) to the spindle ( 2 ) or the part of the transmission between the quick release and the spindle ( 2 ), the position of the activation element remains known regardless of whether it is released or connected, or has been released.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an actuator which includes a quick release unit on a transmission between an activation element and a reversible motor. 
     2. The Prior Art 
     The description of the invention departs from a linear actuator, comprising an electric motor which operates a spindle through a transmission. On the spindle there is a spindle nut with a piece of tubing attached at one end; this serves as the activation element. The other end of the piece of tubing is attached to the movable element in the construction where the actuator is built-in, while the other part of the actuator is attached with a rear fixture to the stationary part of the construction. By keeping the spindle nut from rotating, the nut is moved either outwards or inwards on the spindle, depending on the direction of rotation, and the piece of tubing is either moved axially outward or retracts in a manner similar to a piston rod in a telescopic cylinder. 
     The registration of the position of the tubing is typically performed by counting the number of revolutions made by the spindle from its initial position. The number of revolutions multiplied by the thread pitch determines the position of the tubing. An absolute determination of the position can be made using a potentiometer operated by the motor through a gearing. When the transmission ratios are known, the revolutions of the spindle can be calculated. A more common way of determining the position is by use of a magnetic or optical decoder. A magnetic encoder comprises a magnetic ring with a number of poles which activate a read-switch or Hall-element each time one of the poles passes the switch, thereby producing an electrical signal. Typically, with four poles, the position is determined by each quarter revolution of the spindle. An optical encoder works in the same way using a rotating disc with perforations and a light source. When a perforation passes the light source, light passes through to a photocell producing an electrical signal. Based on the signals, the position is calculated by a microprocessor in the control. 
     A quick release in an actuator is used for temporary release of the activation element for manual setting. An example of use of the quick release is in hospital beds, fire doors and other constructions where it is important or even essential to be able to spontaneously set the activation element. 
     Actuators with quick release function are known from, amongst others, EP 685 662 B1, WO 03/033946 A1 and WO 03/033946 A1 and EP 577 541 B1 all in the name of Linak A/S. The first three documents relates to a quick release construction based on a releasable clutch spring around a cylinder part on the activation element and a matching cylinder element from the exit of the motor/transmission. The last document EP 577 541 relates to a quick release construction using an angular gear where the pinion from the output of the motor/transmission may be displaced to release the grip with the pinion on the activation element. 
     A problem with the known actuators with quick release function is that the position determination is lost at release of the quick release, and it is necessary to reset the system. This is not normally a problem as the system is set up to reset the actuator by driving it to an outer position, and release of the quick release usually results in the actuator being brought to an outer position. 
     In some situations it may also be desirable to know the position after the quick release has been activated without the need to bring the actuator to an end position. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to provide a solution to the problem described. 
     This is, according to the invention, provided by designing the actuator to include a means of position determination connected to the spindle or the part of the transmission between the quick release and spindle, so that the position of the activation element is continuously determined, regardless of whether the spindle is coupled in or out. 
     The invention has the advantage that the instrument used for position determination can be a well known one based on magnetic or optical encoders or a potentiometer. In a magnetic encoder, the magnetic ring may be directly or indirectly attached to the spindle and the same applies for the disc with perforations in an optical encoder. The rotary potentiometer may be operated directly or indirectly by the spindle. The sensors mentioned may, of course, also be connected to the part of the quick release that is attached to the spindle. For position determination it is appropriate to use two Hall-elements angularly displaced to each other. 
    
    
     
       A linear actuator as defined in the invention will be specified below with reference to the attached drawings. 
         FIG. 1 , a bed 
         FIG. 2 , an exploded illustration of the actuator. 
         FIG. 3 , a detailed illustration of the quick release unit 
         FIG. 4 , a longitudinal section through another actuator, 
         FIG. 5 , the actuator in  FIG. 5  seen from the side 
         FIG. 6 , an exploded illustration of the quick release unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a hospital bed equipped with an actuator system comprising four actuators  101 - 104 , a control box  105  containing a power supply  105   a  and a control  105   b ; and there is a hand control  106  and an operations panel (ACP)  107  at the end of the bed (operation unit). The power supply consists of a low voltage unit, typically transformer-based, and a rechargeable battery pack. Two of the actuators  101 ,  102  are for adjustment (profiling) of the base  108  carrying the mattress, while the two other  103 ,  104  are for height adjustment of the upper frame  109  on which the base is mounted. The two actuators last mentioned also allow for tilting of the base frame over a transverse axis (Trendelenburg/Anti-Trendelenburg position). 
     In  FIG. 2  is shown an actuator with a quick release construction of the type mentioned in WO 2006/039931, more precisely  FIGS. 1-7  therein. The main element of the actuator is a cabinet in two parts  1   a ,  1   b  with a reversible electric motor, which through a worm gear drives a spindle  2  with a spindle nut  3 , on which an activation rod  4  (inner tube) surrounded by a protective tube  5  (outer tube) is attached. Note that the motor is not shown on the drawing, but this is located in the perpendicular section  1   c  of the cabinet. The motor shaft extends into a worm gear  6 . The spindle  2  is seated in the cabinet with a ball bearing  7 . 
     The quick release construction, which includes inner and outer couplings parts  8 , 9 , where the inner coupling part  8  is mounted at the end of spindle  2 , while the outer coupling part  9  is mounted in the worm wheel  6 . On the side facing the front end of the actuator, this worm wheel is designed with a hollow cylindrical part that accommodates the outer coupling part  9  for torque transfer with a spline connection. 
     In the back of the worm wheel is a circular disc  11  with three legs  12  protruding through the openings in the worm wheel into the hollow cylindrical part and guided there. In the upper part  1   b  of the cabinet is a release mechanism  13  in a housing  14  with an entry for a cable (not shown), leading to an operating handle (not shown either). The release mechanism comprises an axle unit  15 , led down behind the circular disc  11 . At the end of the axle unit is a cam  16  which, by turning the axle unit, is brought into contact with the disc  11  and presses this forward towards the worm wheel. The axle unit is spring loaded with a spring  17 , to an inactive position, i.e., a position where the cam  16  is not in contact with the disc  11 . A ring  18  is attached at the upper end of the axle, to which the end of the cable leading to the operating handle is attached. 
     The outer coupling part  9 , connected to the worm wheel, has an internal torque transfer spline connection  21   a  in the front. On the outer side of the coupling part  9  at the front end, in front of the spline connection to the worm wheel, there is a flange  22   
     The inner coupling part  8  has a narrow part  23  in the front so that it can pass through the opening in the part of the spline connection  21   a  placed in the outer coupling part  9 . The other part of the spline connection is part of the step between the narrow end  23  and the outer side of the coupling part. In the narrow part  23  there is a groove for a disc  24 , creating a flange. 
     The quick release is activated by operation of the release mechanism, which turns the cam  16  on the axle unit  15  into contact with disc  11 , which is then pushed forward. The spline connection  21   a ,  21   b  between the outer coupling part  9  and the inner coupling part  8  will thus be interrupted and the spline will rotate freely, independent of motor and transmission. The activation rod  4  of the actuator and hence the element attached to it, will then be manually adjustable. 
     An electrical contact in the form of a micro switch is placed next to the turning axle  15 , and a cam opposite cam  16  activates the micro switch at the same time as the quick release is activated. This sends an electrical signal through the cable connection to the control unit, which is brought from sleep mode, the power supply for the control is activated; more precisely that part of the power supply comprising the rechargeable battery pack. By keeping the battery pack switched off until it is required, i.e. use ‘on demand’, means a substantial saving of battery pack power. When the bed is connected to mains power, the low voltage unit is active. Placing the switch in the actuator itself has the advantage that further cabling is avoided as only the cable for the actuator is required. 
     When the bed is without mains power and the back section  110  must be moved rapidly to the horizontal position, such as in the case of a patient with cardiac arrest, this is achieved by activating the quick release. Simultaneously the control is brought from sleep mode and the bed becomes fully operational. The leg section  111  may be moved to the horizontal position and, if required, the bed may be brought into the Trendelenburg position. 
     In  FIGS. 4-5 , the actuator shown is the same type as specified in WO 2006/039931 Linak A/S, specifically in  FIGS. 8-15  therein and this is referred to as part of the present application. The quick release construction is shown in  FIG. 4 . Elements  2 ′,  6 ′,  8 ′,  9 ′ and  14 ′ correspond to elements  2 ,  6 ,  8 ,  9  and  14  in the  FIG. 2  embodiment. As seen in  FIG. 6 , the release mechanism includes a tilting element  27  that takes an inclined resting position. An axially sliding element  28  with a hook at the end grabs the tilting element and is connected to the operating handle with a cable. By operating the handle, element  28  is pulled upwards and brings the tilting element  27  to a vertical position, releasing the quick release as previously described. 
     To the tilting element  27  is connected a micro switch  30  activated by turning it. This supplies an electrical signal to the control unit through a cable and terminal  29 , and consequently the control is brought from sleep mode. The tilting element  27  turns around an axle  27   a , on the axle is an arm  27   b  which activates the micro switch  30 . 
     The inner coupling part  8  is equipped with a magnetic ring  31  with four poles for position determination of the activation rod  4 . Two Hall elements, or sensors,  33   a ,  33   b  on a small printed circuit board  32 , work in conjunction with this. The elements  31 ,  33   a  and  33   b  constitute a magnetic encoder. The Hall-elements are activated when a pole passes these on rotation of the magnetic ring, thereby sending a signal to the control unit which, by means of a microprocessor, computes the position of the activation rod  4  based on the rotation, its direction and the thread pitch of the spindle. Because the two Hall- elements are angularly displaced in relation to the magnetic ring  31 , the rotation direction of the spindle can be detected (quadrature detection) and determines whether signals must be added or subtracted depending on whether the activation rod  4  is extended or retracted. As the magnetic ring  31  is mounted on the inner coupling part  8 , the ring  31  always rotates with the spindle; this will also be the case when the spindle is released from motor/transmission. Therefore, the position of the activation rod is known at all times, including after release of the quick release. The exact design of the controls is dependent on the circumstances; for example, it may be presumed that the spindle rotates in one direction and uses one Hall-element to register movement in the other direction, and the second Hall element to register the number of rotations. Both Hall-elements may of course be used to register rotation direction and number of rotations. 
     The actuator illustrated in  FIG. 2  may be similarly equipped with a magnetic ring on the inner coupling and Hall-elements, so that the position of the activation rod is known regardless of whether the quick release has been activated or not. 
     The position of the bed is known, even after a quick release, through the position of the actuators. The position is used to control movement of the bed and to set various movement patterns.