Long traveling button switch with enhanced user feedback

Abstract: A pushbutton switch including a keycap (11) having a keycap top (11a) and a keycap plunger (11b), a retaining bezel (13) for guiding the keycap plunger and limiting the displacement thereof, a deformable elastomeric switch button (17) supporting a contact pad, and a printed circuit contact pattern (23) engageable by the contact pad when the switch button is deformed by the downward displacement of the keycap plunger. The deformation of the button switch tactile feedback, while impact of the keycap top against the retaining bezel provides audible feedback. The pushbutton switch is configured to limit the downward displacement of the keycap plunger to avoid excessive force on the printed circuit board.

Description: The disclosed invention is directed generally to a keyboard pushbutton switch, and more specifically is directed to a keyboard pushbutton switch having a long travel, and enhanced tactile and audible feedback, and improved contact reliability. Pushbutton switches are utilized in keyboards for calculators, device control panels, and the like. A known pushbutton switch structure includes a dome-shaped metallic contact which contactively engages contacts on a printed circuit board when deformed by actuation of an associated keycap. The deformation of the metallic dome provides both tactile feedback and audible feedback. An important consideration with a pushbutton switch having a metallic dome contact is the relatively small contact area provided by the deformed dome, which makes such switches susceptible to non-closure due to dust and dirt contamination. In order to increase reliability, some metallic dome pushbutton switches are individually packaged for insertion in printed circuit boards. Such switches can be more expensive and bulkier. Another consideration with metallic dome pushbutton switches is transmission of the keypress force to the printed circuit board, which if excessive could cause damage. A further consideration with pushbutton switches having metallic dome contacts is a limitation on the amount of key travel imposed by the metallic dome. Relatively longer key travel provides for a more comfortable keypress. US-A-3 668 356 discloses a switch structure in which a manually depressible keytop has a stem for engaging an actuator assembly. The latter assembly includes a cantilever arrangement which deforms to provide tactile feedback. Also, the keytop contacts a base to provide audible feedback. The actuating assembly is used to operate a diaphragm switch. DE-U-8 105 649 discloses a dome switch according to the first part of claim 1. SUMMARY OF THE INVENTION It would therefore be an advantage to provide a keyboard pushbutton switch structure having a reliably large contact area. Another advantage would be to provide a keyboard pushbutton switch structure which reduces the amount of keypress force transmitted to the printed circuit board utilized therewith. A further advantage would be to provide a keyboard pushbutton switch structure which provides for sufficient key travel. The foregoing and other advantages are provided by the invention which is defined by Claim 1. The advantages and features of the disclosed invention will readily be appreciated by persons skilled in the art from the following detailed description when read in conjunction with the drawing wherein: FIG. 1 is a schematic exploded perspective illustration of a pushbutton switch in accordance with the invention. FIG. 2 is an elevational sectional view illustrating the pushbutton switch of FIG. 1 with the keycap plunger in the non-actuated position and exerting a slight preload on the switch dome. FIG. 3 is an elevational sectional view illustrating the pushbutton switch of FIG. 1 with the keycap plunger sufficiently displaced to cause deformation of the switch dome and contactive closure of the switching elements. FIG. 4 is an elevational sectional view illustrating the pushbutton switch of FIG. 1 with the keycap plunger sufficiently displaced to cause audible feedback from the impact of the keycap top on the retaining bezel. In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals. Referring now to FIG. 1, shown therein is a pushbutton switch assembly that includes a keycap 11 having a keycap top 11a and a keycap plunger 11b. The keycap plunger 11a is slidably engaged and retained in a guiding and retaining bezel 13 which, for example, is integrally formed with other bezels in a bezel structure 15. By way of example, the keycap plunger includes barb-like tabs for engaging the bottom portions of the bezel 13 to limit the upward displacement of the keycap. An elastomeric dome switch button 17 is located beneath the keycap 11. By way of example, the switch button 17 is integrally formed in an elastomeric sheet 19, comprising rubber, for example, with other switch buttons. The elastomeric sheet 19 rests on a printed circuit board 21 having a conductive pattern 23 aligned with the switch button 17. By way of example, the conductive pattern 23 can comprise interleaved conductive traces to provide redundant contact elements. The printed circuit board 21 is attached to the bezel structure 15 to prevent relative displacement thereof. The elastomeric dome switch button 17 comprises a conical side wall 17a secured to the elastomeric sheet 19 at its lower boundary. A horizontal top wall 17b is formed on the upper boundary of the conical side wall 17a, and a circular ridge 17c is formed on the top wall 17b. A cylindrical bump 17d of shorter height than the circular ridge 17c is formed in the center of the top wall 17b. The thicknesses of the top wall 17b, the circular ridge 17c, and the central bump 17d are greater than the thickness of the conical side wall so that the conical side wall resiliently deforms more easily than the thicker elements. A conductive pad 25, comprising, for example, a carbon impregnated elastomer, is attached to the underside of the top wall 17b generally in alignment with the bump 17c. The keycap 11, the bezel 13, and the bezel structure 15 are configured to provide a slight preload on the switch button 17 when the keycap 11 is not actuated, as shown in FIG. 2. Further, the keycap 11 and bezel 13 are configured so that the bottom of the keycap top is against the top of the bezel 13 when the switch button 17 is fully deformed, which transfers further force to the bezel 13. The pushbutton switch operates as follows. The user presses the top of the keycap top 11a to displace the keycap 11 downwardly. The conical side wall 17a collapses just before the contact pad 25 engages the conductive pattern 23 on the printed circuit board, which causes a distinct variation in the resistance felt by the user's finger. In particular, the sudden collapse of the conical side wall 17a reduces the resistance on the keycap which, pursuant to the keypress force, then travels quickly to impact the bezel 13 and produce an audible feedback click. FIG. 3 shows the contact pad 25 against the conductive pattern 23 just after the conical side wall has collapsed, and FIG. 4 shows the keycap at its downward travel limit against the bezel 13. As particularly shown in FIG. 4, when the keycap 11 is fully depressed against the bezel 13, the side wall 17a is collapsed, and the top wall 17b is slightly deformed around the contact pad 23, but does not touch the printed circuit board 19. Any keypress force applied to the keycap beyond that required to collapse the side wall 17a and deform the top wall as shown in FIG. 4 will be transmitted to the bezel 13 and not to the printed circuit board 19. In particular, the keycap 11, the bezel 13, and the switch button 17 are configured so that a limited amount of force is transmitted to the printed circuit board, for example, an amount determined to be sufficient to assure appropriate contact between the contact pad 25 and the conductive pattern 23. In this manner, contact is assured while preventing excessive forces on the printed circuit board 21. The keycap travel and the nature of the tactile feedback are selected to provide for a comfortable keypress that provides a distinct indication that contact has been made. The keycap travel is determined by the difference between (a) the top to bottom height of the retaining bezel 13, and (b) the distance on the keycap plunger 11b between the barb-like tabs and the underside of the keycap top 11a. In conjunction with selection of keycap travel, the distance between the contact pad 23 and the printed circuit conductive pattern should be selected so that appropriate contact is assured while avoiding the application of excessive force when the keycap is fully depressed. The nature of the tactile feedback, which is the force-to-displacement characteristic of the switch button 17, is determined by the thickness of the conical sidewall 17a, the thickness of the top wall 17b, the outside diameter of the top wall 17b, and the inside diameter of the lower boundary of the conical sidewall 17a. The foregoing has been a disclosure of a pushbutton switch assembly that advantageously utilizes elastomeric switch buttons and provides tactile feedback as well as mechanically produced audible feedback. Further, the disclosed pushbutton switch allows for implementation of an appropriate comfortable keycap travel. Although the foregoing has been a description and illustration of specific embodiments of the invention, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims: A switch structure for electrically connecting contacts (23) on a printed circuit board (21), the switch structure comprising: a manually depressible keycap (11) having a top (11a) and a plunger (11b); retaining means (13,15) in which the plunger (11b) is slidably mounted and retained, and in which the printed circuit board (21) can be received; an elastomeric dome switch (17) having a conical side wall (17a), a central wall (17b) formed on a periphery of the side wall (17a) and a circular ridge (17c) formed on the central wall (17b); the dome switch (17) also having a contact (25) for engaging with the printed circuit board contacts (23) when the keycap (11) is depressed; the circular ridge (17c) engaging the plunger (11b) so that, when the plunger (11b) is depressed, the dome switch (17) yields to resist manual depression of the keycap (11), and then deforms, with less resistance, to provide tactile feedback, before the dome switch contact (25) engages with the printed circuit board contacts (23); the central wall (17b) and the circular ridge (17c) of the dome switch (17) being substantially thicker than its conical side wall (17a) so that, when the keycap (11) is depressed, the conical side wall (17a) resiliently deforms more easily than the central wall (17b) and the circular ridge (17c), characterised in that a part of the retaining means (13) acts as a stop, which allows limited displacement of the plunger (11b) after the dome switch contact (25) engages with the printed circuit board contacts (23); and that the retaining means (13), the keycap (11) and the dome switch (17) are configured so that: (a) the keycap top (11a) impacts with the retaining means (13) after said limited displacement, to provide audible feedback audible feedback; (b) the central wall (17b) deforms and the conical side (17a) stretches without kinking during the limited displacement, and (c) only a limited force is transmitted to the engaged contacts (23,25), as a result of the limited displacement, which ensures electrical connections, but prevents excessive force from being transmitted to the printed circuit board (21). A switch structure according to Claim 1 in which the keycap (11) and the retaining means (13,15) are configured so that the dome switch (17) is pre-loaded when the keycap (11) is in a non-depressed state. A switch structure according to Claim 1 or 2 in which the central wall has an enlarged central bump (17d) extending in the same direction of the circular ridge (17c), the bump (17d) being shorter than the circular ridge (17c) and being positioned above the contact (25), in the dome switch (17), so that a portion of the central wall (17b) extends beyond the dome switch contact (25). A switch structure according to any of the preceding Claims in which the part of the retaining means (13) which acts as a stop, is in the form of an upstanding sleeve having an upper rim portion which impacts with the keycap top (11a). A switch structure according to Claim 4 wherein the plunger (11b) is slidably mounted in the sleeve and has barb-like tabs engaging a lower end of the sleeve so as to retain the plunger (11b), the tabs extending across the circular ridge (17c).

Inventors: SCHROEDER CHRISTOPHER KARL, TORGERSON CURT N, SCHROEDER, CHRISTOPHER KARL, TORGERSON, CURT N.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1990
Main classification: H01H13
IPC codes: H01H13, A01C1