Display push switch

Abstract: A display push switch has a switch housing having an open upper end and an open lower end. A key top member made of substantially transparent material is disposed within the open upper end of the switch housing. The key top member is operable by an operator to be pushed into the switch housing. A lens is disposed within the switch housing. A lower end surface of the lens confronts a surface structure of a display device through the open lower end of the switch housing. An upper end surface confronts the key top member and is spaced from the switch housing to permit a stroke movement of the key top member when the key top member is pushed by the operator. The lens includes a plurality of lens elements each having a longitudinal axis in a vertical direction and operable to form an image by itself. The lens elements are arranged in juxtaposed relationship with each other.

Description: The present invention relates to a display push switch according to the preamble of claim 1 adapted to be mounted on a display device for transmitting an image displayed on the display device to a key top member so as to display the image on the key top member. Such a display push switch is described for example in GB-A-95 90 77. Japanese Laid-Open Patent Publication No. 6-44857 (Application No. 4-239938) in the name of the same applicant as the present application discloses a display push switch which is adapted to be mounted on a display device such as an LCD (liquid crystal display) and an ELD (electroluminescent display) for transmitting an image displayed on the display device to a push button or a key top member so as to display the image on the key top member. The key top member is made of transparent material and is disposed above an image plane of the display device, so that the image can be recognized by an operator through the key top member. This prior art has proposed various constructions to provide an improved recognizability of the image through the key top member. One proposed construction is characterized in the provision of a image guide which is made of a plurality of optical fibers and which is disposed between the image plane and the key top member at a position adjacent the image plane. Another proposed construction is characterized in the provision of a lens disposed between the image plane and the key top member. Still another proposed construction is characterized in the provision of an image guide and a lens disposed between the image plane and the key top member. The lens is positioned between the image plane and the image guide. The image guide is made of a plurality of optical fibers and is positioned below the key top member. Here, a display device normally includes a surface plate structure which is disposed on an image plane and is composed of one or more glass plates or transparent plastic plates, a protection plate, and a deflection or polarizer plate. The image guide of the first-proposed construction is operable to transmit an image formed on one end of the image guide to the other end of the same. The image guide however has the following characteristics: If a substantial distance exists between the image plane of the display device and one end of the image guide, an image which is out of focus is received by the one end of the image guide and is transmitted to the other end. Further, as the distance between the image plane and the one end of the image guide increases, an angle of view field of the transmitted image becomes smaller at the other end of the image guide. Therefore, strictly speaking, the display push switch of the first-proposed construction incorporating the image guide can display only an image which is out of focus and of smaller angle of field of view. If an image guide is placed on a display device such as an LCD and an ELD having a relatively thin surface structure above an image plane, a shorter distance may be provided between the image plane and an upper surface of the surface structure, so that a commercially acceptable image may be obtained on an upper end of the image guide. However, very limited types of display devices can successfully be used to provide an acceptable image, even if the image guide is placed on their surface structures such that it closely contacts upper surfaces of the surface structures. More specifically, a CRT, a POP (plasma display) and a VFD (fluorescent display), etc. cannot be used with a display push switch because of a substantial distance between an image plane and a surface structure. On the other hand, with this kind of display push switch having a key top member, a predetermined space corresponding to a distance of stroke movement of the key top member is provided between the key top member and an upper end of the image guide so as to prevent the key top member from abutting on the upper end of the image guide when the key top member is pushed by an operator. Thus, with the display push switch incorporating the image guide, the image information is not displayed on the key top member itself but is displayed on the upper end of the image guide which is positioned below the key top member by the predetermined distance. This means that the operator must recognize, through the key top member, the image displayed on the upper end of the image guide which is positioned below the key top member by the predetermined distance. Therefore, the first-proposed construction has a disadvantage in visibility to some extent. The second-proposed construction incorporating the lens is also disadvantageous for the following reason: In general, in order to obtain a shorter focal distance of a lens having a spherical surface, a radius of curvature of the spherical surface is determined to be smaller. This means that the diameter of the lens becomes smaller, resulting in that field of view of the lens (scope of mapping) becomes smaller and that distortion of the mapped image increases. Therefore, a lens having a shorter focal distance for use with a display push switch inevitably has a smaller radius of curvature and provides a smaller field of view. If a satisfactorily field of view is to be obtained by the display push switch of the second-proposed construction, the lens must have a larger radius of curvature, and therefore, the focal distance and the diameter of the lens increases. Consequently, the size of the display push switch in length, width and height becomes larger. Additionally, this display push switch incorporating the lens has a disadvantage that the image is moved as an observing point is moved. The third-proposed construction of the display push switch incorporating both the image guide and the lens involves the following disadvantages: The display push switch must naturally be large in size than the first-proposed construction as well as the second-proposed construction. Additionally, with the third-proposed construction, in order to form an image on the lower end of the image guide to cover a broader area of the image plane, a longer focal distance of the lens as well as a larger size of the lens (radius of curvature) is required. Further, the distance between the surface structure of the display device and the lens as well as the distance between the lens and the lower end of the image guide must be determined to be longer. For this reason, the size of the display push switch becomes further larger. Further, with the third-proposed construction, the image formed on the lower end of the image guide and then transmitted to the upper end of the image guide is an inverted image of an image displayed on the display device. It is, accordingly, an object of the present invention to provide a display push switch in which a key top member displays an erecting image corresponding to an image displayed on an image plane of a display device. It is another object of the present invention to provide a display push switch in which an image displayed on a key top member does not become out of focus even if the display switch is positioned away from the display surface, so that the display push switch can be applied to various kinds of display devices. It is a further object of the present invention to provide a display push switch which is smaller in size. According to the present invention, there is provided a display push switch adapted for mounting on a surface structure of a display device, comprising: a switch housing having an open upper end and an open lower end; a key top member made of substantially transparent material and disposed within the open upper end of the switch housing, the key top member being operable by an operator to be pushed into the switch housing; and lens means disposed within said switch housing and having a lower end surface and an upper end surface, said lower end surface confronting the surface structure of the display device through said open lower end of said switch housing, and said upper end surface confronting said key top member and being spaced from said switch housing to permit stroke movement of said key top member when said key top member is pushed by the operator; characterised in that said lens means is a self-focusing lens comprising a plurality of vertically elongate lens elements each having a longitudinal axis in a vertical direction and operable to form an image by itself, said elements being arranged in juxtaposed relationship with each other so as to form a single image of the display device. With the present invention, by appropriately determining the length and the vertical position of the lens elements relative to the key top member, an image displayed on the display device is formed on an upper or a lower surface of the key top member as an erecting real image through the lens. The operator can therefore operate the key top member to turn on or off the switch device while he visually recognizes the image formed on the key top member. The invention will be further understood from the following description, when taken together with the accompanying drawings, which are given by way of example only and in which: FIG. 1 is a plan view of a display push switch according to an embodiment of the present invention; and FIG. 2 is a sectional view taken along line II-II in FIG. 1. An embodiment of the present invention will now be explained with reference to the accompanying drawings. Referring to FIGS. 1 and 2, there is shown a display push switch 3 having a housing 10. The housing 10 has an open upper end and an open lower end. A square frame-like bottom plate 11 is disposed within the housing 10 at the open lower end thereof. A push button or key top member 5 made of transparent material is disposed at the open upper end of the housing 10 and is supported by the bottom plate 11 via coil springs 12. Vertical support pins 13 are fixedly mounted on the bottom plate 11 and are inserted into the coil springs 12 so as to keep the vertical position of the coil springs 12. A self-focusing lens 4 is disposed within the housing 10 and has a lower flat end supported by the bottom plate 11 at its peripheral portion. The self-focusing lens 4 has an upper flat end spaced from the key top member 5 by a predetermined distance. The lower flat end is positioned above the lower open end of the housing 10. The upper flat end and the lower flat end are parallel with each other. The self-focusing lens 4 is composed of a plurality of lens elements each having a longitudinal axis in a vertical direction and arranged in juxtaposed relationship with each other. Each of the lens elements is circular in section and has a refractive index distribution such that it is symmetrical with respect to the central axis in section. More specifically, the refractive index distribution has a parabolic distribution in which the refractive index increases toward the central axis of the lens element. With such a refractive index distribution, when an incident light from an image enters one end of the lens element, the light moves in a zigzag fashion within the lens element and then outgoes from the other end. Practically, by determining the length of the lens element as 3/4 times the period of the zigzag movement, an equimultiple erecting real image can be formed by the outgoing light. Thus, the lens element serves to form an image by itself and functions in a similar way as a convex lens having a shorter focal distance. The lens element however provides an erecting real image and is different from the convex lens which provides an inverted real image. The display push switch 3 thus constructed is disposed on a display device 8 such as a CRT, an LCD, an ELD, a PDP and a VFD. The display device 8 has a face glass 2 disposed above an image plane 1 which may be a flat surface or a curved surface. For example, the image plane 1 is a curved surface if the display device 8 is a CRT. The lower open end of the housing 10 of the display push switch 3 is positioned in contact relationship with the face glass 2 or is positioned above the same by a predetermined distance. The vertical length of the self-focusing lens 4 and the position of the key top member 5 is determined such that an image displayed on the image plane 1 is mapped on an inner surface 6 or on an outer surface 7 of the key top member 5 as an erecting real image by the self-focusing lens 4 as described above. Here, the inner surface 6 or the outer surface 7 of the key top member 5 on which the erecting real image is formed is ground to provide a mat surface (ground surface). With this construction, the view field of the image (mapping area) displayed on the image plane 1 of the display device 8 becomes broader as the number of the lens elements of the self-focusing lens 4 increases. Therefore, the field of view of the image can be selectively determined in response to the number of the lens elements in lengthwise and widthwise directions of the self focusing lens 4. Thus, the view field of the image can be broadened without varying the length of the lens elements or without varying the focal distance, so that the self-focusing lens 4 may be small in size and that the display push switch 3 may be small in size. Further, with this embodiment, as shown in FIG. 1, a switching device 14 is mounted on the housing 10. The switching device 14 is operable to be turned on and off in response to shifting of the key top member 5. Such a switching device may be constructed by a microswitch, a lead switch or the like and is well known in the art. Although not shown in the drawings, a plural number of the display push switches 3 each having the key top member 5 and the housing 10 can be provided. In such a case, the display device 8 displays different images corresponding to the key top members 5. With the present invention, the following effects can therefore be obtained. With the self-focusing lens 4 being spaced from the image plane 1 of the display device 8, an image displayed on the image plane 1 can be formed on the inner surface 6 or the outer surface 7 of the key top member 5 as an erecting real image which is not out of focus and has a broader angle of field of view, so that the display push switch can be adapted to various kinds of display devices. Additionally, the display push switch of the present invention may be small in size than the prior art display push switch which incorporates a convex lens or which incorporates a convex lens and an image guide.

Claims: A display push switch (3) adapted for mounting on a surface structure of a display device, comprising: a switch housing (10) having an open upper end and an open lower end; a key top member (5) made of substantially transparent material and disposed within said open upper end of said switch housing (10), said key top member (5) being operable by an operator to be pushed into said switch housing (10); and lens means (4) disposed within said switch housing (10) and having a lower end surface and an upper end surface, said lower end surface confronting the surface structure of the display device through said open lower end of said switch housing (10), and said upper end surface confronting said key top member (5) and being spaced from said switch housing (10) to permit stroke movement of said key top member (5) when said key top member (5) is pushed by the operator; characterised in that said lens means (4) is a self-focusing lens comprising a plurality of vertically elongate lens elements each having a longitudinal axis in a vertical direction and operable to form an image by itself, said elements being arranged in juxtaposed relationship with each other so as to form a single image of the display device. The display push switch as defined in claim 1 wherein said upper end surface and said lower end surface of said lens means (4) are formed as flat surfaces extending in parallel with each other. The display push switch as defined in claim 1 wherein each of said lens elements has a substantially circular section and has a refractive index distribution in section such that the refractive index increases towards the center of the circular section. The display push switch as defined in claim 1 wherein said key top member (5) has an outer surface and an inner surface, said outer surface being exposed to the outside, said inner surface confronting said upper surface of said lens means (4), and one of said outer and inner surfaces being formed as a matt surface on which the image displayed on the display device and transmitted by said lens means (4) is formed as a non-inverted real image. The display push switch as defined in claim 4 wherein said non-inverted real image is formed on said matt surface when said key top member (5) is not pushed into said housing (10).

Inventors: FUKATSU HIROKAZU, FUKATSU, HIROKAZU, FUKATSU, HIROKAZU, C/O TIETECH CORP.
Applicants: TIETECH CORP, TIETECH CORPORATION
Application year: 1995
Main classification: H01H13
IPC codes: H01H13, H01H9