Patent Publication Number: US-6670566-B1

Title: Tact switch

Description:
FIELD OF THE INVENTION 
     The present invention relates to an improved tact switch and particularly a tact switch adopted for use in computers, light pens, mouse devices or remote controllers. 
     BACKGROUND OF THE INVENTION 
     Tact switches have been widely used in computers, light pens, mouse devices or remote controllers. A tact switch generally consists of a seat body with an open surface and a reed dome and a pushbutton located in the seat body from a lower portion to an upper portion thereof. There is a closure body mounted onto the seat body to cover all other elements. When the pushbutton receives an external force, the pushbutton presses the metallic reed dome which in turn connects the electrodes located therebelow to output a signal. 
     Conventional tact switches can be classified in two types. The first type has a rubber pushbutton and a reed dome made of Be—Cu or Pb—Cu. The pliable rubber pushbutton forms a soft contact with the reed dome when in use, thus may has a longer life span. However, the surface of the rubber pushbutton is prone to wear or chip off after being used for a long period of time. And the surface becomes damp and rough. Another type of tact switch has the pushbutton made from plastics. While the plastic pushbutton can maintain a smooth and tidy surface for a long period of time, its bottom end forms a hard contact with the reed dome, thus the life span of the reed dome is shorter. 
     In view of the aforesaid disadvantages, applicant has developed an improved tact switch which was granted in U.S. Pat. No. 6,140,596, entitled: “Tact Switch”. That patent aims to remedy the shortcomings of conventional pushbuttons. It mainly includes a press set formed by coupling a hat body and a second elastic element. The hat body is made from plastics while the second elastic element is made from rubber. The hat body and the second elastic element are matched and coupled tightly, and has a longer durability. However, in order to form a tight coupling to prevent the hat body and the second elastic element from shaking or affecting the downward stroke when depressed, the coupling of the two must be very tight. As they are made from different materials that have different friction, coupling the two becomes difficult and troublesome. Hence although it can resolve some of the problems occurred to the conventional tact switches, there is still room for improvement, especially on the coupling and assembly of the elements. 
     SUMMARY OF THE INVENTION 
     Therefore the primary object of the invention is to resolve the aforesaid disadvantages. The invention mainly includes a hat body which has a coupling section and a directing section formed on the periphery of an opening of the hat body with an inner diameter greater than the coupling section. There is a chamfered edge formed at the juncture of the directing section and the coupling section so that a second elastic element may be inserted into the coupling section easily, and the press stroke may be maintained steadily without skew to enable electrodes to deliver signals even deformation occurred to the second elastic element when the pushbutton is depressed. 
    
    
     The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the invention. 
     FIGS. 2 and 3 are exploded views of the invention. 
     FIGS. 4A and 4B are sectional views of the invention in operating conditions. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1,  2 , and  3 , the tact switch of the invention consists of a seat body  1  which has a housing compartment  11  for accommodating a first conductive electrode  12  and a second conductive electrode  13 , a first elastic element  2  located in the housing compartment  11  above the first and the second conductive electrodes  12  and  13 , a press set  3  located in the housing compartment  11  above the fist elastic element  2 , and a closure body  4  fastened to the seat body  1  to cover the housing compartment  11 . The press set  3  further includes a hat body  31  which has a coupling section  311  and a second elastic element  32  coupled with the coupling section  311 . The coupling section  311  has an opening. The periphery of the opening forms a directing section  312  with an inner diameter greater than the coupling section  311 . The juncture of the directing section  312  and the coupling section  311  forms a chamfered edge  313  to facilitate insertion and assembly of the second elastic element  32  in the coupling section  311 . 
     For assembly, first dispose the first conductive electrode  12  and the second conductive electrode  13  in the housing compartment  11  of the seat body  1 . Then place the first elastic element  2  in the housing compartment  11 . The first elastic element  2  is made from an elastic blade with a dome top and has a flat peripheral rim  21  to press constantly the second conductive electrode  13  and a center bulged portion  22  spaced from the first conductive electrode  12  at a selected gap. Hence no conduction occurs when the first elastic element  2  is initially mounted. Next, couple the second elastic element  32  with the hat body  31 . The second elastic element  32  is integrally formed and includes a connecting section  321  to engage with the coupling section  311 , a balance section  322  to be contained in the housing compartment  11 , and a compression section  323  to press the first elastic element  1 . The connecting section  321  has a top end formed a tapered edge  324  with a smaller diameter than the connecting section  321 . Thus when the second elastic element  32  is disposed in the coupling section  311 , the tapered edge  324  of the connection section  321  may be coupled with the chamfered edge  313  to make insertion of the connecting section  321  of the second elastic element  32  into the coupling section  311  of the hat body  31  smoothly and snugly even though the second elastic element  32  is made from a pliable material such as rubber or plastics. Then the assembled second elastic element  32  and the hat body  31  is placed into the housing compartment  11  of the seat body  1 . The housing compartment  11  of the seat body  1  and the hat body  31  have respectively retaining slots  14  and anchor lugs  314  formed on opposing sides thereof to couple with each other to facilitate positioning. The housing compartment  11  further has side walls formed a coupling surface  15  to allow the assembly of the second elastic element  32  and the hat body  31  to slip into and position accurately without skewing. The seat body  1  also has anchor struts  16  located on the periphery to engage with retaining holes  42  formed on the closure body  4  corresponding to the anchor struts  16  to enable the closure body  4  to couple and cover the seat body  1 . The hat body  31  has a press head  315  on the top end which runs through an opening  41  formed on the closure body  4  and exposes outside the closure body  4  to receive external forces. 
     Referring to FIGS. 4A and 4B, when the tact switch of the invention is in use, an external force is exerted on the press head  315 . The outer diameter of the press head  315  coincides with the inner diameter of the closure body  4  so that the tact switch may be moved downwards in a balanced manner for the first stage. As the hat body  31  is coupled closely with the second elastic element  32 , when the hat body  31  is moved downwards under the external force, the second elastic element  32  is also moved downwards. The retaining slots  14  of the seat body  1  and the anchor lugs  314  of the hat body  31  enable the tact switch to generate a second stage downward movement in a balanced manner. The coupling surface  15  on the side wall of the housing compartment  11  may couple with the balance section  322  of the second elastic element  32  so that the second elastic element  32  may be moved linearly downwards to compress the first elastic element  2 . As a result, the center bulged portion  22  of the first elastic element  2  receives the force in a balanced manner and makes the first conductive electrode  12  and the second conductive electrode  13  to form a conductive connection. As the second elastic element  32  is made from rubber or plastics, a deformation occurs when it is subject to compression. The housing compartment  11  has a hollow recess corresponding to the balance section  322  and the compression head  323  that presses the first elastic element  2  to absorb the deformation occurred. In the event that the external force exceeds the desired compression stroke, deformation occurs to the entire second elastic element  32 . However due to the connecting section  321  has a selected height which is not fully housed in the coupling section  311  of the hat body  31 , the connecting section  321  has a lower portion exposed outside the coupling section  311  to absorb the deformation mentioned above. In addition, as the connecting section  321  of the second elastic element  32  is coupled tightly with the hat body  31 , no skew will happen when they are being depressed downwards. Thus the invention can simultaneously resolve the problems of difficult assembly, unsteady downward compression and excessive deformation that happen to the conventional tact switches. 
     While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.