Abstract:
The invention relates to a connector comprising a housing, a spring biased contact surface facing in a front direction of said connector for establishing a contact with a connector counterpart, said contact surface being movable within a working area against a spring force from a first rest position to a second connecting position by a force directed to the contact surface upon establishing a contact with the connector counterpart. In order to achieve a connector which makes it possible to keep the contact force at an appropriate and substantially constant level, said connector comprises a rolled spring with an outer end protruding in said front direction of said connector; said protruding end is attached to the housing of said connector, whereby said rolled spring is at least partly unrolled when said contact surface is moved against the spring force.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a connector with a spring biased contact surface, which is movable against the spring force when a force is directed to the contact surface upon establishing a contact with a connector counterpart. The phrase ‘spring biased contact surface’ refers in this application to a solution where the force of a spring is used to return the contact surface to a first rest position, when the contact surface is located somewhere else than in said rest position. 
   2. Description of the Prior Art 
   Previously there is known a connector with a helical spring arranged inside the connector body. One such prior art connector  1  is shown in  FIG. 1 . This connector  1  comprises a housing  2  and a contact part  3  which is movable in relation to the housing  2  in the direction shown by the arrow. The housing  2  contains a helical spring  4 , which presses a rear end of the contact part  3 . A force directed to the contact surface  5  of the contact part  3 , upon establishing a contact with a connector counterpart, will move the contact part  3  to the left in  FIG. 1 , against the spring force of the spring  4 . 
   A problem with the prior art connector shown in  FIG. 1  is that the spring force increases with the travel distance of the contact surface  5  from the rest position shown in  FIG. 1 . In other words, the spring force is at its lowest minimum when the contact surface  5  is located in the rest position, and the highest maximum is reached when the contact surface  5  has been moved to the left as much as possible in  FIG. 1 . This increase in the spring force has the disadvantage that the contact force between the contact surface  5  and the contact surface of a connector counterpart varies. Such a variation of the contact force is not acceptable because it affects the electrical performance of the connector. Another problem with a variation in the contact force is that the contact force may increase to a level where the plating of the contact surface  5  is damaged. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to solve the above mentioned drawback and to provide a connector with a construction that makes it possible to keep the contact force at an appropriate and substantially constant level over the entire working area. 
   Another object of the present invention is to provide a connector whose working area can be increased as compared with the working area of prior art connectors while the contact force is kept at an appropriate and substantially constant level. 
   The above mentioned and other objects of the present invention are achieved with the connector as defined in independent claim  1 . 
   The invention is based on the idea of utilizing a rolled spring in a connector. An outer end of this rolled spring is attached to the housing of the connector, while the remaining “roll” of the spring is allowed to move in the housing. Thus when the contact surface of the connector moves within the working area in a direction against the spring force of the rolled spring, the rolled spring is at least partly unrolled. The advantage obtained is that the spring force of the spring does not substantially increase with the distance, but instead the spring force remains substantially constant within the working area. A constant spring force ensures that the contact force and the electrical performance of the connector substantially remain constant, and that no such increase occurs in the spring force which could damage the plating of the contact surface. 
   The outer end of the rolled spring can be attached to the housing of the connector in different ways. One alternative is to bend the outer part such that it obtains a hooked shape, which can grip a suitable part of the housing. Alternatively the outer end of the rolled spring can be attached to the housing, for instance, by gluing or by ultrasonic welding. 
   Preferred embodiments of the connector are disclosed in the attached dependent claims  2  to  9 . 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the present invention will be described in closer detail by way of example and with reference to the attached drawings, in which 
       FIG. 1  illustrates a prior art connector, 
       FIG. 2  illustrates a first preferred embodiment of a connector, 
       FIG. 3  illustrates a second preferred embodiment of a connector, 
       FIG. 4  illustrates a third preferred embodiment of a connector, 
       FIG. 5  illustrates a fourth preferred embodiment of a connector, 
       FIG. 6  illustrates a fifth preferred embodiment of a connector, 
       FIGS. 7   a  and  7   b  illustrate a sixth preferred embodiment of a connector, 
       FIGS. 8   a  and  8   b  illustrate a seventh preferred embodiment of a connector, and 
       FIGS. 9   a  and  9   b  illustrate an eight preferred embodiment of a connector. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 2  illustrates a first preferred embodiment of a connector  11  according to the present invention. The connector  11  comprises a housing  12  wherein a rolled spring  14  is arranged. In this embodiment, the contact surface  15  of the connector consists of the surface of the spring. This contact surface can have a plating of a suitable material in order to improve the electrical connectivity of the connector. One alternative is to provide the contact surface with a coating including, for instance, copper (Cu), nickel (Ni) or gold (Au). 
   It is by way of example assumed that the connector shown in  FIG. 2  is a battery connector for a mobile telephone. The housing  12  of the connector  11  is open towards the front direction of the connector. This opening makes it possible to arrange a battery  16  in the connector  11  such that a connector counterpart of the battery is pushed towards the contact surface  15  of the connector  11 , against the spring force. An outer end  19  of the rolled spring  14  protrudes from the spring in the front direction of the connector  11 . This outer end  19  is attached to the housing  12  of the connector  11  such that it has been bent into a hooked shape, which grips an outer surface of the housing  12 . Thus, when the connector counterpart of the battery is pushed against the contact surface  15 , the rolled spring  14  rotates in the housing  12  such that it is at least partly unrolled. When the battery  16  is attached to the connector, a first end of it is supported by the housing  12  of the connector  11 , and a second end by a support  18 . The connector  11  and the support  18  are both attached to a circuit board. 
   In the example of  FIG. 2 , the protruding end  19  of the spring also forms a terminal T to be used for wiring the connector to the circuit board. In that case, the terminal T on the end  19  can, for instance, be soldered to the circuit board. The spring  14  thus provides the electrical path between the connector counterpart in the battery  16  and the circuit board. 
   The spring force needed in a practical implementation of a battery connector is typically within the range of 0.5N to 1.5N, preferably 0.7N to 1.0N. The needed working area, in other words the distance the contact surface  15  needs to move, is typically 5 to 10 mm at maximum. However, in many implementations less than 2 mm is sufficient. 
   An advantage of utilizing a rolled spring in the connector of  FIG. 2  is that the spring force remains substantially constant throughout the entire working area. Thus, the spring force is in practice the same when the roll of the rolled spring is located as much to the right as possible in the housing  12  (when the contact surface is located in its first rest position), as it is if the roll of the rolled spring is located as much to the left as possible in the housing. In  FIG. 2 , the spring is shown in a situation where the contact surface is located in its second contact position. 
   A rolled strip spring can be used as the spring in a connector according to the present invention. One alternative is also to use a so-called constant force spring in order to obtain a substantially constant spring force within the working area. Thus, the contact force can efficiently be kept at a controlled constant level, which ensures that the electrical performance of the connector  11  remain constant and that the plating on the contact surface  15  does not wear too much during use. One previously known type of a constant force spring, which can be used in the present invention, is rolled strip spring commercially available from Lesjöfors Stockholms Fjäder AB, Jämtlandsgatan 62, SE-162 20, Vällingby Sweden (www.lesioforsab.com). However, also other types of constant force springs can be used in the invention. 
   In  FIG. 2 , it is by way of example assumed that the rolled spring  14  is arranged in the connector housing  12  in such a position that the center axis of the roll is substantially parallel with the surface of the circuit board. However, it is also possible to construct the connector such that the center axis of the roll is not parallel with the circuit board, but instead it forms an angle with the surface of the circuit board. Such an angle can be even 90°. 
   Still another possibility is to provide the roll of the rolled spring with a center shaft around which the rolled strip is rolled. In such a case two grooves are formed within the opposite walls of the housing along with the travel of the rolled spring in order to allow the ends of the center shaft protruding from the opposite sides of the rolled spring to be guided within the housing. In this case it is also possible to utilize the surface of the shaft as the contact surface of the connector, in which case an electrical connection to a connector counterpart is established via the surface of the shaft. 
     FIG. 3  illustrates a second preferred embodiment of a connector. The embodiment of  FIG. 3  is very similar to the one explained in connection with  FIG. 2 . Therefore, the embodiment of  FIG. 3  will in the following be explained mainly by pointing out the differences between these embodiments. 
   In  FIG. 3 , the connector  21  includes a movable contact part  27 . The contact surface  25  consists of a front part of the contact part and the rolled spring  24  presses against a rear part of the contact part  27 . Similarly, as in  FIG. 2 , an outer end  29  of the rolled spring  24  protrudes in the front direction of the connector  21 , and this end  29  is attached to the housing  22  of the connector. The end  29  is bent to form a hook which grips the housing in order to accomplish the attachment. Thus, as the contact part  27  moves in relation to the housing  22  (direction of movement indicated by arrow A), the roll of the spring  24  rotates as indicated by arrow B. The terminal T which is used for connecting the connector to an electrical wire or to a circuit board is formed at the hooked-shaped end  29 . 
   The rear part of the contact part  27  is in the embodiment of  FIG. 3  inclined such that when the spring  24  presses the rear part, the rear part of the contact part presses sideways towards the connector housing  22 . This arrangement makes it possible to have a separate conductive path (as in  FIG. 5 ) along the inner wall of the connector housing (at the location towards which the contact part is pressed), and to ensure that a sufficient electrical contact is established between the contact part  27  and the electrical path. 
     FIG. 4  illustrates a third preferred embodiment of a connector. The embodiment of  FIG. 4  is very similar to the one explained in connection with  FIG. 3 . Therefore, the embodiment of  FIG. 4  will in the following be explained mainly by pointing out the differences between these embodiments. 
   The connector  31  of  FIG. 4  is by way of example assumed to be a battery connector for a mobile phone. Thus the contact surface  35  on the contact part  37  is in  FIG. 4  connected to the connector counterpart  30  of the battery  36 . The rolled spring presses against the rear part of the contact part  37 . In this embodiment, the rear part has a flat surface which forms a  900  angle with the surface of the circuit board. 
   The attachment between the protruding end  39  of the rolled spring and the housing  32  is also in  FIG. 4  accomplished by bending the end into a hooked-shape. The terminal T which is used for connecting the connector to an electrical wire or to a circuit board is formed at the hooked-shaped end  39 . 
     FIG. 5  illustrates a fourth preferred embodiment of a connector. The embodiment of  FIG. 5  is very similar to the one explained in connection with  FIG. 3 . Therefore, the embodiment of  FIG. 5  will in the following be explained mainly by pointing out the differences between these embodiments. 
   In  FIG. 5 , a separate conductive path  40  is arranged along an inner wall of the housing  42  in addition to the rolled spring  44 . The conductive path can, for instance, consist of a metallic strip. An end of the conductive path protrudes to the outside of the connector  41  and forms the terminal T to be used for connecting the connector to a circuit board or to a cable, for instance. Such a conductive path can also be used in any of the other embodiments. 
   The rear part of the contact part  47  is inclined such that when the spring  44  presses the rear part, the rear part of the contact part presses the conductive path  40 . Thus, the electrical connection between the contact surface  45  and the terminal T is provided through the contact part  47  and the conductive path  40 . 
   The use of the separate conductive path  40  means that it is not necessarily required to use the rolled spring  44  for establishing an electrical contact between the connector and the terminal T. This makes it possible to produce the rolled spring from materials which are not electrically conductive, or which have insufficient electrical properties. However, it is of course also possible to use a spring made of an electrically conductive material together with the separate conductive path. In that case the spring will further ensure a sufficient electrical contact between the contact part  47  and the conductive path  40 . 
   In the embodiment of  FIG. 5  the end  49  from the rolled spring is not bent into a hooked-shape as in previous embodiments. Instead the end is attached to the inner surface of the housing, for instance, by gluing or by ultrasonic welding. Such a solution can be used also in the other embodiments. 
     FIG. 6  illustrates a fifth preferred embodiment of a connector. The embodiment of  FIG. 6  is very similar to the one explained in connection with  FIG. 4 . Therefore, the embodiment of  FIG. 6  will in the following be explained mainly by pointing out the differences between these embodiments. 
   In  FIG. 6 , the housing  52  of the connector  51  has a cavity which is arranged to form an angle with the surface of the circuit board. Thus, the connecting part  57  and the rolled spring  54  do not move in parallel with the circuit board as in the previous embodiments. The advantage obtained by this embodiment is that a slight scraping is provided between contact surfaces  55  and  50  when a battery  56  is connected to the connector  51 . This scraping cleans the contact surfaces and ensures a sufficient electrical contact between the contact surfaces. 
   The attachment between the protruding end  59  of the rolled spring and the housing  52  is also in  FIG. 6  accomplished by bending the end into a hooked-shape. The terminal T which is used for connecting the connector to an electrical wire or to a circuit board is formed at the hooked-shaped end  59 . 
     FIGS. 7   a  and  7   b  illustrate a sixth preferred embodiment of a connector. In the embodiment of  FIGS. 7   a  and  7   b  the connector  61  has a contact part  67  which is provided with grooves in opposite sides. The connector  61  also includes an intermediate part  66  made of a conductive material and having two parallel protrusions which are arranged into the opposite grooves. The contact part thus travels along these protrusions. 
   The intermediate part  66  forms a conductive path between the contact part  67  and the terminal T. An advantage with the embodiment of  FIGS. 7   a  and  7   b  is that the conductive part has at least two contact points, one on each side (one at each groove). This ensures a sufficient conductive path in each situation between the contact surface  65  on the contact part  67  and the terminal T. The end  69  of the rolled spring  64  is bent into a hooked-shape in order to grip the housing of the connector. 
     FIGS. 8   a  and  8   b  illustrate a seventh preferred embodiment of a connector  71 . The embodiment of  FIGS. 8   a  and  8   b  also includes an intermediate part  76  of a conductive material. This intermediate part  76  forms a conductive path between the contact surface  75  of the contact part  77  and the terminal T. 
   The protruding end  79  of the rolled spring  74  is bent into a hooked-shape in order to grip the housing of the connector. 
   The intermediate part  76  is generally U shaped, and in the figures the upper inner part of the intermediate part  76  touches the upper side of the contact part  77 . The contact part  77  is shaped with an eave, which protrudes over the rolled spring  74 . Due to its shape the rolled spring  74  has a restoration force which presses the roll of the spring and the contact part upwards in the figures. Thus a sufficient and stable electrical contact is established between the contact part  77  and the intermediate part  76 . 
     FIGS. 9   a  and  9   b  illustrate an eight preferred embodiment of a connector. The connector  81  of this embodiment is similar as the one shown in  FIGS. 7   a  and  7   b , as it includes an intermediate part  86  having two parallel protrusions which are arranged into opposite grooves of the contact part  87 . The intermediate part  86  thus forms a conductive path between the contact surface  85  of the contact part and the terminal T. 
   In  FIGS. 9   a  and  9   b  the housing  82  is shown in cross-section. The bottom of the housing  82  is thicker to the left in the figures than it is to the right in the figures. The advantage obtained by this variation of thickness is that the rolled spring  84  touches the contact part  87  at the same height (same point) all the time. Thus, the reduction of the outer diameter of the rolled spring  84 , which occurs when the roll of the rolled spring is unrolled by moving it from the position of  FIG. 9   a  to the position of  FIG. 9   b , is compensated by the increased thickness of the bottom of the housing  82 . It is to be understood that the above description and the accompanying figures are only intended to illustrate the present invention. It will be obvious to those skilled in the art that the invention can be varied and modified also in other ways without departing from the scope and spirit of the invention disclosed in the attached claims.