Keyboard for a portable data terminal

The portable terminal keyboard includes silicone rubber mixed with phosphorescent material used on the external exposed surface of the keyboard and conventional silicone rubber used for the moving parts, so that it is luminous for a certain duration by being irradiated for a while with a light source, thereby facilitating the user's entry operation and also enhancing the durability of the keyboard. The keyboard has its key mat made of a magnetic material so that it is attached by magnetism to the main frane, thereby faciliting replacement with a different key mat. The magnetic key mat structure allows the single access attachment and eliminates such conventional fixtures as lugs, whereby the key mat can be replaced more easily even in darkness and the lugs or the like are not present to be damaged as would be otherwise caused by frequent key mat replacement.

BACKGROUND OF THE INVENTION 
This invention relates to a keyboard of a portable terminal which is used 
in dark environments such as the night outdoors. 
FIG. 1 shows a portable terminal. The terminal includes a display panel 1 
which can be read in the dark owing to the adoption of light emitting 
display elements or to an illuminating device provided for the case of 
non-luminant display elements such as liquid crystal elements, and an 
input panel 2 having operation keys, with the result of each operation 
appearing on the display panel. However, in order for the above-mentioned 
conventional panel design to have a luminous input panel, it would be 
necessary to provide illumination for the wide input panel area, and 
adding such an illumination device to the portable apparatus is difficult 
because of a resulting excessive weight and increased manufacturing cost. 
A keyboard is known which is made of silicone rubber, however it does not 
have a luminant property and therefore the operator needs an external 
light source such a flashlight to recognize each key. Luminant pigments 
have been known, however, silicone rubber mixed with pigment spoils the 
working life of rubber in the stressed portion due to frequent operations 
or creates a disparity in its resilience. 
FIG. 2 shows a key mat fitting structure for a conventional portable data 
terminal. A terminal unit 3 includes a key mat 4 made of a resin or paper 
sheet, on which key names are labeled. Key functions can be altered by a 
program stored in the terminal unit, and any key 2 can be given variable 
roles depending on the purpose of the terminal unit, and therefore the key 
mat 4 with the label of key names needs to be replaceable. Conventionally, 
a transparent sheet 5 has been used to settle the key mat 4 for the 
convenience of replacement. The settling sheet 5 is attached by inserting 
its four lugs 5a into sockets 3a formed in main frame. 
FIG. 3 shows the foregoing structure in more detail. A key switch is turned 
"on" when a key 2 is pressed by a finger and an associated conductive 
contact 6 connects contacts 7 provided on a substrate 18. The key 2 has a 
name which is indicated by the label 11 printed on the key mat 10. The key 
mat 10 is settled in position by being placed between a main frame 9 and a 
transparent settling sheet 12 which is fitted as shown in FIG. 2. 
However, the foregoing conventional key mat fitting structure compels the 
user to remove the settling sheet 12 at each replacement of the key mat 
10, and it is unsuitable for applications which require frequent key mat 
replacements. The data terminal is occasionally used in the outdoors, and 
a key mat fitting structure which allows much easier replacement has been 
desired. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a keyboard structure in which the 
keyboard luminesces for a certain duration after it has been irradiated 
with a light source for a while, thereby allowing the user to perform a 
key entry in the dark while viewing the display panel. 
Another object of this invention is to provide a keyboard structure which 
enables the user to replace the key mat easily in the dark night outdoors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 4 shows a cross section of a portable terminal keyboard embodying the 
present invention. In the figure, indicated by 13 is a key top of a push 
switch and it is made of silicone rubber mixed with a phosphorescent 
mterial such as lead-cadmium sulfide, zinc sulfate (ZnSCu), etc. A portion 
15 formed integrally with the key top 13 is made of pure silicon rubber, 
with its contact skirt section 15a being bent resiliently when the key top 
13 is depressed. Indicated by 16 is a key contact affixed to the center of 
the silicone rubber key bottom 15 and it is made of silicone rubber mixed 
with carbon to provide conductivity. Indicated by 17 is a substrate with 
printed wirings 17a and 17b being formed on its surface. A pair of 
contacts 18 are provided at one end of the printed wiring leads 17a-17b, 
and these contacts are connected electrically when the key contact 16 
comes in contact with them by being pushed through actuation of the key 
top 13 and contact skirt section 15a. 
The keyboard of this embodiment is manufactured by the compression method. 
Initially, pieces of silicone rubber and phosphorescent material in 
porportion for making 15-20% phosphorescent material mixed in silicone 
rubber are placed on the key top side of a metal mold, and only pieces of 
silicone rubber are placed on the key bottom side of the mold. The mold is 
closed and pressed at 400 kg/m.sup.2 at 180.degree. C. for 7 minutes, and 
the keyboard is formed. 
Next, the operation of the inventive keyboard will be described. In the 
daytime, the keyboard is used for a portable data terminal by a bank's 
salesman or stock manager. The operator presses a key top 13, causing the 
contact skirt section 15a to bend, and the key contact 16 comes in contact 
with the contacts 18 on the substrate. Then, the printed wiring leads 17a 
and 17b are connected electrically through the key contact 16, and a 
signal is transmitted. 
At night, it is too dark to read the key label, and the operator irradiates 
the keyboard 13 with a prepared flashlight for a while. After that, the 
flashlight is turned off and returned back to a coat pocket or the like, 
then the operator holds the portable terminal unit by one hand and 
operates the keyboard 2 by another hand. Since the key tops 13 include a 
phosphorescent component, the labels on the keyboard 13 can be identified, 
allowing the operator to hold the portable terminal unit by one hand and 
operate the keyboard by another hand. By being irradiated by an external 
light source or by a temporarily reinforced illumination of the display 
panel for a few minutes, each of the phosphorescent key tops 13 
phosphoresces over a period several times the light-charging time length. 
In practice, the charging light source is available from among a 
flashlight and reflected light from the display panel, as in this 
embodiment. The phosphorescent keyboard is also effective when the 
apparatus is moved from a bright place to a dark place, or when the 
environment has become dark suddenly, as in the case of power failure. 
It should be noted that the contact skirt section 15a is preferably made of 
pure silicone rubber so as to avoid the adverse effect of phosphorescent 
material which is an impurity against silicon, in consideration of the 
tight coupling with the key contact 16, the working life under stress and 
the disparity of its spring action. 
As will be appreciated from the foregoing embodiment, the inventive 
portable terminal keyboard has its key tops formed of the mixture of 
silicone rubber and phosphorescent material, its key contacts formed of 
the mixture of silicone rubber and carbon, and its key top bottom and 
contact skirt section formed of pure silicon rubber, allowing the user to 
operate in the night dark after the phosphorescent component has been 
activated with a flashlight, whereby the apparatus is useful even in the 
night time and its reliability is retained. 
FIG. 5 shows the cross section of a key mat fitting structure according to 
an embodiment of this invention. A key 22 is pressed by a finger, causing 
a conductive contact 23 to connect contacts 25 provided on a substrate 24, 
thereby turning on the switch. The structure for this operation is 
identical to the conventional ones. In order to display the name of keys 
22, a key mat 26 made of a sheet magnetic material is laid, with labels 27 
being printed on the mat surface. For settling the key mat 26 on the 
keyboard, a sheet magnet 28 is attached to a main frame 30 by means of a 
double-sided adhesive tape 29. Sheet magnets with a thickness of 0.5 mm or 
less are available currently, and they can be printed on both sides. 
One of the sheet magnets 26 and 28 may be formed of a sheet of metal 
attractive to magnetism, and in this case the metallic sheet needs an 
additional means of grounding in order to prevent electrostatic influence. 
It is also possible to print another label on the sheet magnet 28 on its 
opposite side where the double-sided adhesive tape 29 is absent, so that 
it serves for a key mat. 
As will be appreciated from the above embodiments, the inventive terminal 
keyboard has its key mat attached or detached very simply by utilization 
of magnetism, and the reliability and working life of the key mat fixture 
can be enhanced. 
As described above, the inventive keyboard enables the user to use luminous 
keys on the keyboard in darkness for a duration of time after the keys are 
irradiated by a light source, while viewing the associated display screen. 
It also allows the user to replace the key mat easily in darkness.