 |
Description  |
|
|
The invention is directed to a keyboard with a printed circuit board and
which carries keys, and a housing therefor.
BACKGROUND OF THE INVENTION
It is expected of keyboards, particularly those which, as autonomous units,
constitute an auxiliary component, so to speak, of data processing
systems, that they function reliably, can be exchanged at any time and
integrated in an existing device configuration and that they be
inexpensive.
Such conditions compel a standardization of the keyboards with the goal of
achieving high production numbers and providing the prerequisites for
large-scale production and mechanical assembly with as few work steps as
possible and structural component parts which are simple in terms of
functional design.
However, as a rule, a reduction in the quantity of structural component
parts and in costs in manufacturing and assembly and manufacturing
tolerances, which allows largescale manufacturing, impairs the stability
and accordingly also the operating reliability, particularly where parts
which are relatively large in dimension and are produced by means of
injection molding are involved.
In contrast with efforts toward economical manufacturing is the fact that a
high quality must also be demanded with respect to the external appearance
for use of such keyboards in office environments which have constant
climatic conditions and where the risk of soiling is relatively low, in
the teller window of banks and the like, and that, when used in the area
of manufacturing, in filling stations, in storage spaces and on
construction sites, where negative environmental influences predominate,
the functions of the keyboards must be designed for conditions of use
which are severe under certain circumstances and must not be destroyed by
environmental influences.
Keyboards used in trade generally correspond to the demands for quality in
aesthetic and functional respects in the office environment. Under more
severe conditions of use and operation, these keyboards are often
unsatisfactory as a result of temperature-dependent expansions. These are
essentially caused by the classical construction of the keyboards with a
plurality of structural component parts which are screwed together. To
this extent, the construction of the known keyboards can also not meet the
requirements of a large-scale production with subsequent mechanical
assembly.
SUMMARY OF THE INVENTION
The object of the present invention accordingly consists in optimizing the
construction of keyboards in such a way that it meets the requirements
with respect to economical manufacturing on the one hand and the different
conditions of use of the keyboards on the other hand.
To achieve this and other objects, the invention provides a housing
comprising a front frame and a base part, having latch or locking
elements, which cooperate with one another, formed at the front frame and
the base part, with the front frame and base part constructed in such a
way that the assembly of the front frame with the base part and the
engagement or interlocking of the latch elements holds an intermediately
located printed circuit board so as to be substantially free of play.
The advantages of the invention, which have been found also for
alphanumeric keyboards with considerable dimensions, consists in that the
keyboard comprises only a front frame, a base part and a preassembled
component, namely a printed circuit board which is directly equipped with
keys, and these structural component parts are connected with one another
exclusively by means of the latch connections. In so doing, the printed
circuit board is held between the front frame and base part in a floating
manner, so to speak, when the latter are locked with one another, i.e. the
housing formed from the front frame and base part can expand, e.g. because
of temperature, relative to the printed circuit board without stresses
occurring in the printed circuit board because of such expansion. In other
words, the printed circuit board is not, itself, directly fastened to the
front frame or base part. Moreover, with the construction according to the
invention, vertical tolerance additions relative to the key plane are
reduced and the manufacturing tolerances in the key plane, which must be
designed in a relatively rough manner when the housing structural
component parts are produced by means of injection molding, have no
influence to a great extent with respect to the assembly of the keyboard.
This effect is achieved in that an aligning element is formed on or at a
central location of the front frame, e.g. at a rib or web dividing the
keyboard into individual key fields, which aligning element cooperates
with an opening in the printed circuit board and provides a relatively
exact central fixing of the two structural component parts at least in the
direction of the maximum dimension of the keyboard. This requires that
relatively exacting tolerances are provided for this connection. At least
one additional aligning element constructed at the front frame and an
additional opening in the printed circuit board, which opening cooperates
with the additional aligning element, are provided in order to form a
safeguard against twisting, so to speak, between the front frame and
printed circuit board and in order to form a fixing of the parts in a
second dimension, wherein the additional opening is constructed as an
elongated hole in order to enable expansions relative to the central
fixing.
The amount of expansion of the housing structural component parts is halved
by means of the central fixing and the provided degrees of freedom.
Changes in the gap widths between the dividing ribs or webs of the front
frame and the rows of key heads, which changes are caused by tolerances
and temperature, are less visible or not at all noticeable, as a result of
these steps. On the other hand, the ability of the housing structural
component parts to expand relative to one another and relative to the
printed circuit board and the adaptability to dimensions changing within
the given rough tolerances, prevent operating disturbances.
In addition, it is advantageous that an alignment of the front frame and
base part be effected, so to speak, along only one line, specifically
along the greatest dimension of the keyboard, so that the reliable
engagement of the latch elements which are effective on this line in
particular is ensured. Another advantage of the invention is that the
alignment elements and latch elements are constructed in such a way that
both can be associated with one and the same opening in the printed
circuit board. Otherwise, the front frame is constructed in such a way
that it overlaps the rim of the base part on all sides at a certain
distance, the base part being constructed in the manner of a trough. In
the same way, sufficient lateral free space is also associated with every
latch connection. It is noted, in addition, that the front frame and base
part are constructed as relatively simple parts so that the costs of
molding is small.
The preconditions for a particularly uncomplicated and preferably
mechanical assembly are accordingly provided, in which the front frame is
held by means of a suitable jig or receptacle, the printed circuit board
provided with the keys is supplied, placed on the front frame and brought
into engagement with the aligning elements, and the base part is
subsequently locked with the front frame.
SUMMARY OF DRAWINGS
The invention is now explained in more detail with the aid of the attached
drawings which show an exemplary embodiment of a keyboard constructed
according to the invention, wherein:
FIG. 1 is a perspective overall view of the keyboard;
FIG. 2 is an exploded view, staggered in perspective, of bottom views of
the structural component parts of the keyboard which are assembled
corresponding to the assembly sequence;
FIG. 3 is a cross-sectional view of the keyboard;
FIG. 4 is a partial section of the keyboard in the area of a latch
connection;
FIG. 5 is a perspective partial view of the aligning and latch elements
constructed at a web of the front frame of the keyboard.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The perspective overall view of FIG. 1 shows an alphanumeric keyboard 1
with letter, number, function and so-called cursor key fields 2, 3, 4 and
5, respectively. Webs or ribs 7, 8 and 9 are formed on or at a front frame
6 and delimit the individual key fields 2, 3, 4 and 5 relative to one
another. A base part which, together with the front frame 6, forms the
housing of the keyboard 1 is designated by 10.
In a perspective staggered or exploded arrangement, FIG. 2 shows the rear
and bottom views of the structural component parts forming the keyboard 1,
namely the front frame 6, the base part 10 shaped in a trough-like manner,
and a printed circuit board 12 carrying the keys, one of which is
designated by 11 in FIG. 1. For the sake of completeness, it is noted that
conductor paths, not designated in more detail, are applied to the printed
circuit board 12, which conductor paths intersect on both sides and,
together with a bore hole in the printed circuit board in each instance,
form inductance coils at the intersecting points. That is, the signaling
is effected inductively in the chosen embodiment example. The invention is
not limited to this specific technology.
For reasons relating to some extent to injection molding techniques, the
individual sides of the front frame 6, which are not designated in more
detail, and the webs 7, 8 and 9 have a U-shaped profile, as can be seen
from FIG. 2, so that a circumferentially extending outer wall 13 and inner
wall parts, one of which is designated by 14, are formed. The inner wall
parts 14 of the webs 7, 8 and 9 and the side of the front frame 6 form the
support for the printed circuit board 12. The end faces of the wall parts
14 are preferably formed so as not to lie in one and the same plane and a
point support or limited line support of the printed circuit board 12 is
accordingly achieved.
In a substantially central area of the front frame 6, tongues 15 and 16,
which constitute aligning elements, are formed at the web 7. When the
printed circuit board 12 is placed on the frame 6, these tongues 15 and 16
engage through an elongated opening 17 located in the printed circuit
board 12 and effect an exact mutual positioning of the printed circuit
board 12 and front frame 6 with respect to the larger dimension or
longitudinal direction of the keyboard 1. Together with a rib 19 which is
constructed transversely relative to the web 7, a latch hook 18, which is
likewise formed on or at the web 7, forms an additional aligning element
which, together with an elongated hole 20 provided in the printed circuit
board 12 through which latch 18 passes, effects an exact fixing of the
front frame 6 and printed circuit board 12 exclusively in the shorter
dimension of the keyboard 1. Since the opening 17 is likewise constructed
as an elongated hole, specifically in the direction of the short
dimension, additional aligning and latch elements and an elongated hole
corresponding to the aligning and latch elements 18, 19 and the elongated
hole 20 can be provided, preferably so as to be symmetrical relative to
the opening 17. In other words, additional elements similar to elements
18, 19, and 20 (not shown in FIG. 2) can be provided on ribs 7 but on the
opposite side relative to opening 17. The smaller horizontal width of hole
17, cooperating with tongues 15, 16 fix the board position in the long
dimension (horizontal in FIG. 2), whereas the 90 degree rotated smaller
vertical height of hole 20 fixes the board position in the shorter
dimension (vertical in FIG. 2). Yet, that same hole 20 orientation permits
play in the long dimension. The construction of the aligning and latch
elements can be seen in detail more clearly from FIG. 5. The rib 19
connects the walls 14 of the web 7, as shown by FIG. 5, and accordingly
serves additionally as stabilization. The lines L1 and L2, which are drawn
in dash-dot lines, symbolize the position of the bottom edge of the right
angle oriented elongated holes 17 and 20 in the printed circuit board 12
when the latter is positioned on the respective front frame.
Cavities 21, in which the latch hooks 18 engage, are formed in the base
part 10. The opening 22 is for the tongues 15 and 16, so that a mutual
positioning of the base part 10 and the front frame 6 is effected on a
line predetermined by means of the central web 7, since the aligning
elements 18, 19 are constructed in such a way that they also engage in the
pockets, 21., Two or three latch elements 23, 24 are formed on or at the
base part 10 and engage with openings 25 and 26 in the wall parts 14 of
the front frame 6 when the housing is assembled. By so doing, sufficient
lateral free space is provided for all the latch connections in the
longitudinal direction (horizontal) of the keyboard 1. For the sake of
completeness, it is noted that supports 27, with which a recessed grip 28
is associated in each instance, are swivelably supported in the base part
10 and serve to adjust the inclination of the keyboard 1 in use. In
addition, a bulge 29 is formed in the base part 10; added units can, if
necessary, be assigned to the keyboard 1 via this bulge 29.
It can be seen from the sectional view of FIG. 3 that ribs 30, upon which
the printed circuit board 12 lies when the housing structural component
parts 6, 10 are locked together, are constructed in the base part 10, and
that the printed circuit board 12 is secured and supported only between
the wall parts 14 of the front frame 6 and the ribs 30. In addition, FIG.
3 shows that the front frame 6 engages around the trough-shaped base part
10 so as to be at a distance on all sides. The keys 11 are fastened
directly on the printed circuit board 12, i.e. the respective key base 31
is locked with the printed circuit board 12, for example, and the key head
32 is supported in a resilient, spring-mounted manner on the key base by
means of suitable column guiding in a manner known per se.
The sectional view of FIG. 4 clearly shows the integrated manner of
construction of the aligning and latch elements 18, 19 which are
constructed at the web 7 and engage the opening 20 in the printed circuit
board 12 and the pocket 21 in the base part 10. As will be evident, during
assembly, when the base 10 is placed over the assembled front frame 6 and
board 12, pressing of the base 10 causes the latches 18, 23, and 24 to
engage, respectively, the cavities 21, and the holes 25 and 26 and the
latch hook ends lock the assembly together. Note that the hooks of the
respective latches 18, and 23, 24 face in opposite directions. While only
one latch 18, 19 is shown in FIG. 2, it will be understood that additional
latches of the same type can be provided along the central rib 7. The
assembly is readily disassembled by pushing back the hook ends of latches
18, 23, and 24 to release them.
While the invention has been described in connection with preferred
embodiments, it will be understood that modifications thereof within the
principles outlined above will be evident to those skilled in the art and
thus the invention is not limited to the preferred embodiments but is
intended to encompass such modifications.
* * * * *
|
|
 |
|
 |
Description |
|
