FR2544545A1 - Operating keypad for electrical or electronic devices - Google Patents

Abstract

Operating keypad for electrical or electronic devices of the type including keys returned by spring 3, arranged on a steel or aluminium stamped metal grid 5. The grid 5 is stamped so as to create by pushing back the concave lateral guidance walls for the plungers 3 the keys, and undergoes a finishing treatment by anodisation, in order to control this same guidance. In their lower part the keys receive a diaphragm 4 providing for the contact with the circuit 6 whilst enhancing the tactile sensation at the end of the stroke.

Description

 The invention generally relates to a keyboard for controlling an electrical or electronic device, of the type comprising a stamped grid or plate with numerous orifices receiving sliding keys intended to establish one or more electrical contacts when they are actuated.

 The techniques for manufacturing keyboards often call for the use of a support grid receiving clipped molded plastic keys. These keys generally comprise several parts including a spring or any other elastic return device.

 The present invention specifically aims to simplify the implementation of such a keyboard by limiting the number of parts making it up, so as to lower the production cost while obtaining high reliability.

 The invention therefore provides a keyboard for controlling an electrical or electronic device comprising a metal grid (aluminum or steel) stamped from a modular tool, punch and die. The originality comes from the fact that said grid is formed in a single stamping operation, so as to create the barrels directly guiding the attached rods or plungers.

 The plungers comprise, at their lower part, a diaphragm of conical added shape coming to establish, by pressure, one or more contacts on a flexible or rigid printed circuit. In the case of a flexible circuit, a rigid counter plate enables contact to be established.

 The invention will be better understood, and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, made with reference to the appended schematic drawings given by way of example illustrating a embodiments of the invention.

 Figure 1 shows an exploded view of the grid and the key in perspective.

 Figure 2 shows an exploded view of a key.

 Figure 3 shows a sectional view, the grid and button assembly placed above the contact assembly.

 Figure 4 shows in section the plunger housed in the guide plate.

 The grid or guide plate 5 is stamped and cut from an aluminum or steel sheet of thickness given in relation to the diameter of the orifices and the stroke to be obtained, generally 3.6 to 4 rrpn. The orifices in said grid are of square section with concave inner flanks, with rounded angles.

 This same grid, after forming undergoes a definition surface treatment by anodic deposition which conditions the fatty and precise guidance of the plunger 3 molded in polyacetal resin of complementary shape to the orifice in the anodized grid 5 of square section whose sides include a undercut with respect to the rounded angles which alone are in contact with the walls of said grid, thereby limiting friction.

 The plunger 3 transmits the pressure of the finger through a cabochon 1 and an optional adapter 2 at its upper part and a viscoelastic frustoconical diaphragm 4 molded in polyethylene plastic at its lower part, portfolio of flexible polyester films screen printed 6 with conductive ink; said wallet 6 resting on a rigid counter-plate. The visco-elastic characteristic of this diaphragm 4 has the effect of limiting, by deformation of the edges of the clone, the forces exerted at the end of the stroke when contact is established.

 The return spring 7 calibrated between 3 N and 6 N standardizes the tactile sensation of several keys of the same keyboard and returns, as soon as the key is released, the latter to the initial rest position.

 It is only intended by this technology to establish closing contacts therefore normally open initially between two conductive pads.

 The realization of the waterproof portfolio of polyester films, comprising the contact matrix, generally used in the keyboard industry, does not require any particular implementation.

 The service life of the mechanical assembly, guide plate / plunger / diaphragm / spring, under normal conditions of use is 108 operations.

Claims (5)

 1. Keyboard for controlling electrical or electronic devices of the type comprising keys recalled by spring, (7) disposed on a stamped metal grid, (5) of steel or aluminum, characterized in that said grid (5) is stamped with pushing the material laterally to the walls of the orifices, so as to define without intermediate parts, guide surfaces for the plunger element (3) of the keys. Said surfaces having undergone an anodization treatment.  2. Keyboard according to claim 1 characterized in that the plungers (3) are equipped at their lower part with a frustoconical diaphragm, (4) ensuring both pressure contact on a film portfolio screen printed with conductive ink ( 6) resting on a rigid counter plate, (8) (8) as well as the damping of the whole of the key at the end of the stroke.  3. Keyboard according to claim 2 characterized in that the orifices and the square section defined by the concave guide surfaces with rounded corners form a complementary surface with the edges of the plungers. (3)  4. Keyboard according to claim 3 characterized in that the molded plungers, (3) of section complementary to that of the orifices of the grid (5) have rounded bearing surfaces on the four edges as well as undercuts limiting the friction at these four edges.  5. - Keyboard according to claim 4 characterized in that the square section plungers with rounded edges and undercut sides are molded in polyacetal resin having the best characteristics complementary to the orifices of the anodized grid.