Abstract:
There is disclosed a membrane-type keyboard comprising a support member, a pair of spaced-apart sheets of flexible insulating material having designated key portions positioned adjacent to and spaced from said support member and a pair of electrical conductors each attached to adjacent inner surfaces of said key portions. The depression of a key portion of the top sheet forces the adjacent electrical conductors into contact. Further depression of the key portion of the top sheet moves both electrical conductors and the key portions of the spaced-apart sheets a distance sufficient to provide a positive degree of tactile feedback to the operator.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a printed circuit keyboard, and more particularly, to a low-cost keyboard for use in a data terminal device. Data terminal devices are presently used in supermarket or fast food establishments which require fast checkout operations. With the introduction of low-cost printed circuit keyboards for use with data terminal devices employed in the above-cited operating conditions, problems have arisen in using such keyboards in that most keyboards have relatively flat contact surface portions which comprise key positions. Depression of a key position of this type keyboard provides very little tactile feedback to the operator. The use of this keyboard requires the operater to observe the required key position on the keyboard before depressing such key position. Because of this construction, the overall speed of operation of the keyboard is reduced as compared to a mechanical type keyboard wherein the operator, by the feel of each key, knows the location of the key required to be depressed without looking at the keyboard. In order to overcome this drawback, printed circuit keyboards have been constructed with raised portions or spherical proturbances corresponding to each key location on the keyboard. Examples of this type of construction may be found in U.S. Pat. Nos. 3,898,421, 3,988,551, 4,059,737 and 4,060,703. While this type of construction increases the tactile feedback of the raised portions, none produce fully the tactile feedback of a mechanical key operation. Other types of keyboards developed to solve the problem of tactile feedback include U.S. Pat. No. 3,898,421 which provides a keyboard construction in which a dimple portion is forced into engagement with a pair of fixed contacts to provide a switch closing operation intermediate the stroke of the dimple portion, the construction allowing the central portion of the dimple to move between the fixed contacts into engagement with a support member to eliminate excessive wear of the contact area. While this construction reduces the wear of the contact area of the dimple portion, it does not produce any greater tactile feedback other than the use of the raised dimple construction. It is therefore a principal object of this invention to provide a printed circuit keyboard construction which produces a tactile feedback to the operator similar to that of a mechanical key switch operation. It is a further object of this invention to provide such a keyboard which is simple in construction and low in cost. 
     SUMMARY OF THE INVENTION 
     In order to fulfill these objects, there is provided in one embodiment a printed circuit keyboard comprising a flexible cover sheet of insulating material having a plurality of raised proturbances or bubble portions each having a first electrical conductor secured to its lower surface, a flexible support sheet spaced from said cover sheet and having correspondingly aligned bubble portions, a second electrical conductor secured to the upper surface of the support sheet and spaced from the first electrical conductor, a spacer sheet and a support member each having a recessed area aligned with the bubble portions in said cover and support sheets. The depression of a bubble portion in the cover sheet results in the initial contact between adjacent first and second electrical conductors followed by the further movement of both the bubble portions in the cover and the support sheet together with said first and second electrical conductors a predetermined distance to provide a positive tactile feedback to the operator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Additional advantages and features of the present invention will become apparent and fully understood from a reading of the following description taken together with the annexed drawing, in which; 
     FIG. 1 is an exploded view of one embodiment of the keyboard construction in accordance with the present invention. 
     FIG. 2 is a cross-section view illustrating the keyboard construction of the embodiment shown in FIG. 1. 
     FIG. 3 is a cross-section view illustrating the keyboard construction of a second embodiment of the present invention. 
     FIG. 4 is a cross-section illustrating the keyboard construction of a third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown an exploded view of one embodiment of a printed circuit keyboard indicated by the numeral 20 and constructed in accordance with the present invention. The keyboard 20 includes a cover sheet 22 of insulating material composed preferably of a flexible plastic sheet material such as Mylar having a plurality of spherical proturbances or bubble portions 24 formed in a predetermined arrangement in said cover sheet 22 in any well-known manner such as molding. Other examples of flexible plastic sheet material that may be used in the present embodiment includes polypropylene, polycarbonate, fluorplastics, ABS and polyvinyl chlorides. The cover sheet 22 being composed preferably of a sufficiently resilient material provides that after depression, the bubble portions 24 will spring back to their raised position shown more clearly in FIG. 2. Each bubble portion 24 may have printed or affixed to its upper surface in a manner that is well-known in the art, an indicia representing the key designation as is conventional in the art. 
     Secured to the lower surface of each of the bubble portions 24 is a flexible electrical conductor 26 which may take the form of a coating composed of electrically conductive particles such as silver in a resilient plastic binder such as Versalon 1140 by General Electric. As shown in FIG. 1, the conductor 26 is common to each of the bubble portions 24 and extends from the sheet 22 to an appropriate electrical source located within the data terminal (not shown). It is obvious that other electrical conductors 26 such as flexible strips of conducting material may also be used in place of the coating 26. 
     Positioned adjacent the sheet 22 is a spacer sheet 28 preferably composed of an insulator material such as Mylar having a plurality of apertures 30, each in registration with one of the bubble portions 24. As shown more clearly in FIG. 2, the apertures 30 have a diameter preferably equal to or larger than the diameter of the bubble portions 24. 
     Located adjacent and below the spacer sheet 28 is a flexible support sheet 32 having a plurality of bubble portions 34 each located in registration with one of said apertures 30 in sheet 28 and an associated bubble portion 24 in sheet 22. The support sheet 32 is preferably composed of the same flexible insulating material as that of sheet 22 and has secured to the top surface of each of the bubble portions 24 an individual electrical conductor 36 which, as shown in FIG. 1, extends through a neck portion 38 of the sheet 32 for connection to the terminal in which the keyboard 20 is located in a manner that is well-known in the art. The conductor 36 may be composed of the same material as that of electrical conductor coating 26. The bubble portions 24 and 34 are preferably formed with the same radius of curvature in order for the electrical conductors 26 and 36 to be in a spaced-apart position (FIG. 2) prior to depression of the bubble portion 24 by the operator. The conductor 36 may cover only a portion of the upper surface of the bubble portion 34 or may be fabricated to conform to the total upper surface of the bubble portion 34 to insure a more complete contact with the conductor strip 26. 
     The sheets 22, 28 and 32 are mounted on a printed circuit board 40 (FIGS. 1 and 2) or any other type of supporting member in any conventional manner such as bonding, which circuit board 40 includes a plurality of recessed portions 42 in registration with the bubble portions 24 and 34 and the apertures 30. 
     In operation, the finger portion 44 (FIGS. 2 and 4) of an operator engages and depresses a selected bubble portion 24 in the sheet 22 until the electrical conductor 26 makes contact with the electrical conductor 36 secured to sheet 32, thereby generating an electrical signal over conductor 36 identifying the bubble portion 24 depressed in a manner that is well-known in the art. Further movement of the bubble portion 24 results in the electrical conductors 26 and 36, together with the bubble portion 34 moving downward into the recessed portion 42 of the printed circuit board 40 to provide an overthrow movement, which overthrow movement increases the tactile feedback to the operator when depressing the bubble portions 24. Since this construction produces a tactile feedback similar to that of a mechanical key switch operation, the operator can learn the locations of each of the bubble portions 24 by the feel of the location of the bubble portions therefore allowing her to operate the keyboard without looking at the specific bubble portion required to be depressed. 
     A second embodiment of the invention is shown in FIG. 3 in which parts similar to or corresponding to parts shown in FIGS. 1 and 2 are numbered similarly. With reference to FIG. 3, the keyboard 20 includes the printed circuit board 40, fabricated without the recessed portions 42 as shown in FIG. 2. It will be obvious that this construction limits the overthrow movement of the bubble portions 24 and 34. This construction may be used in those situations where the resilient characteristics of the sheets 22 and 32 (FIG. 1) are much stiffer than the corresponding sheets of the embodiment shown in FIGS. 1 and 2, thereby requiring less movement of the bubble portions 24 and 34 to provide the required tactile feedback. 
     A third embodiment of the invention is shown in FIG. 4 in which parts similar to or corresponding to parts shown in FIGS. 1 and 2 are numbered similarly. The keyboard 20 disclosed in FIG. 4 provides the sheets 22 and 32 without the bubble portions 24 and 34 shown in FIG. 2. Otherwise, the construction is the same. It is obvious from FIG. 4 that the keyboard construction shown therein will provide the overthrow movement and therefore the tactile feedback in those applications where the keyboard does not require a bubble-type construction, that is, where the application requires a flat keyboard having a large number of key position, such as 150 key positions. In this situation, the operator is required to look at the keyboard for the specific key designation before depressing the selected key position. The present invention will provide a tactile feedback to the operator indicating that the key contacts have been closed, thereby eliminating keyboard mis-operations due to the failure of the operator to depress the key position in the cover sheet 22 a sufficient distance to close the electrical conductors 26 and 36 (FIG. 4). 
     While the principles of the invention have now been made clear in an illustrated embodiment, it will be obvious that those skilled in the art that many modifications of structure, arrangements, elements and components can be made which are particularly adapted for specific environments without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications within the limits only of the true spirit and scope of the invention.