Abstract:
A dispensing system comprising: a main body having an electrically driven SMA actuator; a container for a medium to be dispensed, the container being separate from, but connectable to, the main body; a dispenser, a portion of which is, in use, to be located within the container and moveable relative thereto so as to selectively dispense a portion of the medium, the dispenser also being arranged to be connected in use to the actuator of the main body: wherein the actuator is arranged to cause relative movement between the container and the dispenser in order to dispense a predetermined portion of the medium.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a dispensing system and, in particular, to a dispensing system which can be utilised to dispense controlled volumes of fluid from a disposable container. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known to have dispensing mechanisms which use a simple reciprocating action to induce linear motion in a single direction. Such as an actuator is shown in WO03/103758, in which a shape memory alloy (SMA) actuator is used to generate a reciprocating motion by having the SMA element acting between two movable parts. 
         [0003]    In its rest state, the spring or other biassing means applies its sufficient force to extend the SMA element, pushing the two sliding parts apart. When energised, the SMA element contracts, thereby providing sufficient force to both compress the spring and to pull the two sliding parts together. These parts (the combination of which will be described later as the “pusher”) move together and translate linearly, for example, along a tube. In this way, a reciprocating motion is set up. 
         [0004]    SMA actuators are energised by heating the SMA element above a critical heating temperature, usually achieved through resistive heating of the element by passing an electric current through it. On cooling back below the critical cooling temperature (typically lower than the heating temperature), the system returns to its rest state. 
         [0005]    In order to convert the reciprocating motion to linear motion, the two sliding parts are made to slide preferentially in one direction. In this way, the “lead” end slides when the actuator extends and the “back” end slides when the actuator contracts, thereby resulting in a caterpillar style linear movement (see  FIG. 1 ). 
         [0006]    Such devices however have two key limitations. Firstly, unless a facility is provided to return the pusher to the start of travel, the device can only provide a maximum travel which is equal to the length of the tube or structure that the SMA actuator is moving along. The whole assembly must then be discarded and this can be costly, given that the expensive part of the dispensing system is the SMA actuator itself. Secondly, electrical contact must be made to the pusher which is continually translating away from its start position and this can lead to difficult wiring and hence potential and more frequent failures of the electrical system. 
         [0007]    The second of these disadvantages can be addressed by an alternative configuration which can be seen in, for example, U.S. Pat. No. 5,919,167. In this example, the SMA acts between a static and a movable part, with a return spring in series with the SMA actuator. The movable part reciprocates and its motion is converted to continuous travel via a uni-directional coupling. However, such devices still require the disposal of the SMA and associated parts after all of the fluid has been dispensed as they cannot be reused (see  FIG. 2 ). Furthermore, the devices use the SMA to expel the fluid and the spring to return the SMA to its unenergised length, and this necessitates either rapid fluid expulsion (and hence large viscous loss within the device) to ensure a short (and therefore efficient) SMA heating cycle or, alternatively, a long inefficient heating cycle to minimise viscous loss. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention aims to solve the two drawbacks identified above without introducing further disadvantages. 
         [0009]    According to the present invention, there is provided a dispensing system comprising: 
         [0010]    a main body having an electrically driven SMA actuator; 
         [0011]    a container for a medium to be dispensed, the container being separate from, but connectable to, the main body; 
         [0012]    a dispenser, a portion of which is, in use, to be located within the container and movable relative thereto so as to selectively dispense a portion of the medium, the dispenser also being arranged to be connected in use to the actuator of the main body; 
         [0013]    wherein the actuator is arranged to cause relative movement between the dispenser and the container in order to dispense a predetermined portion of the medium. 
         [0014]    Thus, by having a main body which contains the SMA actuator connected to a dispenser, with a separate and disposable container for the medium to be dispensed, the present invention provides a solution which ensures that the disposable part is of little or negligible cost when compared to the remaining cost of the main body of the dispensing system which contains the relatively expensive SMA part. 
         [0015]    The actuator may also comprise at least one spring or other biasing means for assisting in the generation of the reciprocating motion. 
         [0016]    The SMA and the spring may be configured such that, when the SMA is energised, the spring is compressed and may also be configured such that medium is dispensed after the SMA is de-energised. In this way, the invention provides a configuration in which energy is stored in a spring during a rapid heating cycle and which is caused to expel the fluid at a low rate to reduce a viscous loss by the expansion of the spring. 
         [0017]    The spring is preferably arranged to move the dispenser relative to the container after the SMA has been de-energised. 
         [0018]    The SMA actuator may be configured to produce either an oscillating linear motion or alternatively it may produce an oscillating rotary motion. Whichever is generated, the oscillating motion is preferably converted into step-wise incremental motion of the dispenser, typically via a one-way ratchet mechanism. 
         [0019]    In a different example, the actuator may, rather than an SMA actuator, be a piezoelectric actuator which is preferably connected to a bending beam such that, when the piezoelectric actuator is driven, the beam is caused to deflect. In this arrangement, the bending beam is preferably arranged so as to move the dispenser relative to the container after the bending beam is de-energised. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Examples of the present invention will now be described with reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  illustrates the caterpillar style linear movement of the prior art; 
           [0022]      FIG. 2  illustrates the static and moveable configuration of the prior art; 
           [0023]      FIGS. 3 and 4  each show a schematic representation of an embodiment of the present invention; and 
           [0024]      FIG. 5  shows a schematic representation of an example of a similar device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    In  FIG. 1 , a dispensing tube  10  having an inlet and  10   a  and an outlet end  10   b  and holding a medium  11  therein for dispensing is provided, the tube having means, for preferentially allowing movement in one direction, in this case to the right of the drawings, whilst hindering or preventing movement in the opposite direction, i.e. to the left of the drawings. The means may include a series of sloped teeth as a ratchet mechanism, but in this embodiment, an inclined element  12  is provided on each movable element  13 ,  14  which achieves the same functionality. The element  12  is preferably positioned at inclined angle to the side wall and with a pre-load (e.g. by virtue of bending) so that there exits a contact force between its tip  12   a  and the side wall of the tube  10 . Such a configuration will reduce said contact force if the movable element is moved parallel to the side wall from left to right and will increase said contact force if the movable element is moved parallel to the side wall from right to left. Hence, this results in preferential (and in the limit case, one way) movement of the movable element from left to right. Element  12  may include a series of projections around each movable element or may be formed as a continuous collar. Movable elements  13  and  14 , placed at different axial locations within tube  10 , are connected by means of a shape memory alloy (SMA) element  15  and a spring  16 . An electrical connection  17  extends away from the shape memory alloy  15  to a power source (not shown). 
         [0026]    Movable elements  13 ,  14  form a dispenser which is moveable within the tube  10  so as to dispense the fluid medium  11  from the outlet  10   b  of the tube. The shape memory alloy  15  and the spring  16  form the actuator which causes linear motion of the dispenser along the tube, in this case to the right in the figures. 
         [0027]    Movement along the tube  10  is achieved with reference to  FIGS. 1   b  and  1   c . As shown in  FIG. 1   b , the SMA  15  is contracted (shown by a thicker line) thus causing moveable element  14  to slide to the right. Element  14  is caused to move preferentially to element  13 , as the slope of element  12  permits movement preferentially to the right. When the SMA  15  is de-energised, the spring  16 , which was compressed when the SMA  15  was energised, causes moveable element  13  to move to the right. Again element  13  is preferentially moved due to the shaped nature of element  12 . 
         [0028]    In this way, the dispenser is caused to move in small increments along tube  10 , thereby dispensing fluid from outlet  10   b.    
         [0029]    A second known example is shown in  FIGS. 2   a  to  c  in which a dispensing tube  20  is moveable relative to a static element  21  and a moveable element  22  of the dispenser. In this example the dispensing tube  20  is caused to move and its motion causes a plunger to be moved within a container having medium to be dispensed. 
         [0030]    Operation of this system occurs as follows: a spring  23  is mounted between a fixed surface  24  and one side of the moveable element  22 , with a shaped memory alloy element  25  connecting the moveable  22  and static  21  element. Upon energising the shaped memory alloy element  25  and hence contracting it, the moveable element  22  is drawn towards the static element  21  and, due to the shape and arrangement of the sloped element  26 , the dispensing tube is also caused to move to the right in  FIG. 2   a . This is shown in  FIG. 2   b  with the SMA actuator in the energised state and the spring  23  extended. When the SMA is de-energised, the spring returns to its at rest position, i.e. contracts, thereby pulling the moveable element  22  to the left as shown in  FIG. 2   c . By this movement, the dispensing tube  20  is translated to the right in a stepwise motion. 
         [0031]    The example shown in  FIGS. 3 to 5  show the details of solutions to the problems of the prior art. 
         [0032]    In  FIGS. 3 and 4 , a shape memory alloy plus spring actuator is provided that reciprocates, but does not translate and this leads to a simple low cost disposable components containing the medium to be dispensed which contains a means, typically in the form of a ratchet or the like, which converts the reciprocating motion into linear motion. This also is a configuration in which energy is stored in a low force spring during a rapid heating cycle and is caused to expel fluid at a low rate to reduce viscous loss when the SMA is de-energised. 
         [0033]    This is shown in  FIGS. 3   a  to  d  and  4   a  to  d , in which a static element  31 , to be mounted on the main body (not shown) of the dispensing system, and a moveable element  32  are arranged relative to a translating element  30  such that the translating element, which forms part of the disposable container for the medium to be dispensed can be easily removed from the static and moveable elements  31 ,  32 , as well as from the remainder of the dispensing system. 
         [0034]    The translating element  30  is, for example, a plunger in a static container of medium to be dispensed, such that movement of the element  30  by the SMA  35  and spring  33  combination causes liquid to be expelled from the container. 
         [0035]    In this example, a spring  33  is connected between a static element  34  and one side of the moveable element  32 , as was the situation in  FIG. 2   a . However, in this example, the SMA  35  is also connected between a static surface  34  and the moveable element  32 . The translating element  30  is provided, in  FIG. 3 , with a sloped element  37  similar to that described with reference to  FIGS. 1 and 2 , and in  FIG. 4 , with a series of teeth  36 . Each mechanism preferentially allow movement to the left in the figures, whilst preferentially preventing movement to the right. 
         [0036]    Thus, in operation, the SMA is energised and contracts, thereby drawing the moveable element  32  to the left in the drawings. This is the rapid heating cycle and is an efficient way of storing energy in the low force spring  33 . When the SMA is de-energised, the spring starts to extend back to its at rest position, thereby forcing moveable element  32  to the right and hence moving the translating element  30  also to the right. This expansion of the spring is done at a slower rate than the compression of the spring, and thereby ensures that this stage produces less viscous loss than known configurations, as the fluid is dispensed. In order to be able to reuse the dispenser which is formed by the SMA  35 , the spring  33 , the static part  31  and the moveable part  32 , a user simply has to disengage the translating tube from the static  31  and moveable  32  element as shown in  FIGS. 3   d  and  4   d . Thus, in this embodiment, the SMA and spring actuator is reusable, since both the SMA element and the spring are capable of withstanding thousands of use cycles. This is highly beneficial from a cost and a waste point of view. Furthermore, the electrical contacts to the SMA do not undergo a continuous translation, but rather only oscillate between two positions, thereby providing easier design and more reliable connection. 
         [0037]    The low cost of the disposable part enables the invention to be used in cost sensitive application areas such as consumer products. The compact nature of the invention allows it to be packaged within other systems, e.g. within the handle of a toothbrush. 
         [0038]    The disposable parts could, for example, include a fluid reservoir for the dispensing of liquids, gels, creams, powders or tablets and may include the dispensing of, for example, food stuffs in liquid, powder or tablet form, personal care products such as cosmetics e.g. lipsticks or creams, hand cleaners and sanatisers or toothpaste or even shaving products, pet care such as pet food on a timer, cleaning products, air fresheners, medicinal tablets or stationary. The reciprocating motion can be converted into quasi-continuous linear motion using a variety of methods. These include the toothed ratchet and pawls as shown in  FIG. 3 , in which one pawl is held static whilst the other is oscillated back and forth. Alternatively, this could be achieved using friction and a pawl, whereby the static pawl in the examples of  FIG. 3  or  4  could be replaced by a simple frictional engagement. A third alternative is that the reciprocating motion could be used to drive the rotation of, for example, a threaded rod causing a nut on the rod which is constrained from rotating to translate along its length. This can equally be configured such that the nut is rotated and the rod, which is constrained from rotation, translates. In any event, a reciprocating motion is translated into quasi-continuous linear motion. 
         [0039]    All of the above systems can be made through simple low cost manufacturing methods such as injection molded plastic. The reciprocation could alternatively be rectified directly by using a diaphragm type pump and this part can still be configured to be separable from the main actuator. 
         [0040]    In a different example shown in  FIG. 5 , a piezoelectric actuator  40  is connected to a bending beam  41  mounted on the main body  46 , the beam being activated to cause movement of the beam in one direction and deactivated to cause the beam to return to its at rest position. This can be configured to provide the necessary reciprocating motion shown by arrow  42  in order to drive the oscillating part  43 . A static part  44 , in conjunction with a dispensing tube  45  is also provided and this mechanism operates much in the same way as that of  FIGS. 3 and 4  and further description of that operation is unnecessary.