Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of momentary closure switches, and more particularly to the field of such switches which are adaptable to keyboard use.
2. Description of the Prior Art
Prior art ribbon actuated keyboards have used mechanical decoding to determine which key was depressed. The common mechanical decoding systems require that one key be released before a subsequent key is depressed. If one key is depressed prior to the release of the preceding key, the decoding system will decode inaccurately. Therefore, interlocking systems are required to prevent depression of more than one key at a time. This requirement causes a skilled operator to work slower than he is capable of working.
Prior art momentary contact switches must be replaced as a unit upon failure of the actuator or the contacts because it has been common practice to build their structure and mechanism as a unit. Thus, the replacement of an actuator requires replacing the unit which is costly. Replacement of just the actuator, for example, would take considerably longer, if it were possible, and would be even costlier.
It is known in the prior art to have an elastic diaphragm switch held closed by a spring loaded actuator. Such switches are not useful for those keyboard applications which require momentary contact.
The prior art has no momentary actuator which controls the force sufficiently to preserve the elastic diaphragm switch.
For the purpose of this invention, a ribbon is an elongate member, which may be either rigid or flexible.
OBJECTS
The primary object of the invention is to actuate a momentary contact switch in an improved manner.
Another object is to actuate a momentary contact switch by an impulse impact force striking all of the switch members.
A further object is to construct an actuator and switch contacts of a momentary contact switch separately instead of as a unit so that they can be individually replaced.
Still another object is to control the striking force of an actuator on a weak momentary contact switch member so the force is not so great as to damage the switch member and yet is strong enough to obtain quick momentary contact response time.
SUMMARY OF THE INVENTION
The above objects are accomplished by providing a momentary closure switch having a housing in which an actuator is slidably mounted. One or more small hammers, each having a bearing surface, are attached to the housing by cantilever springs. The actuator comprises a ribbon which has a projection integral with it. The projection presses against the bearing surface of the hammer during actuation. The projection on the ribbon displaces the hammer, storing energy in a spring. After the hammer reaches maximum displacement it is released by the projection passing beyond the bearing surface. Upon being released the hammer overthrows its rest position, striking a membrane switch to momentarily close the switch. The force generated by the hammer is determined by the mass of the hammer, the length of displacement of the hammer, the length of the spring, the spring constant and the spacing of the switch member to be struck. During the return of the actuator the projection on the ribbon passes over the hammer without actuating the switch.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the actuator showing the switch in its rest position.
FIG. 2 is a perspective view of the actuator in partial section showing the switch immediately after momentary actuation.
FIG. 3 is a view showing the ribbon's projection in relation to the hammer's bearing surface while they are in rest position.
FIG. 4 is a view showing the ribbon's projection and the hammer in the hammer's position of maximum displacement, just prior to release.
FIG. 5 is a view showing the hammer striking the membrane switch during overthrow, after release of the hammer.
FIG. 6 is a view showing the projection of the ribbon passing over part of the hammer in returning to the switch's rest position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2 and particularly FIG. 2, a switch is generally shown at 100 and is comprised of actuator means 110, housing means 130, impulse impact means 150, and switch means 180.
Actuator means 110 is comprised of a depressable keystem 112 and ribbons 114 and 118. Keystem 112 is slidably mounted in housing means 130. Each of the ribbons has two projections near one end, 115 and 116.
Housing means 130 is comprised of a keystem guide 132 of guiding keystem 112, inclined ramps 134 and 136 for guiding the ribbons 114 and 118; keystem return spring 138 for biasing keystem 112 to its rest position, and return spring supports 140, 142 and 144 for supporting the return spring.
The impulse-impact means 150 is comprised of hammers 154, hammer support springs 164, which attach the hammers 154 to the housing 132 and support the hammers in their rest positions.
As shown in FIG. 3, hammer 154 has a bearing surface 172, against which projection 116 of ribbon 114 presses to move the hammer. Hammer 154 also has a projection 174 on its lower face which strikes switch means 180 during actuation.
Switch means 180 is comprised of four elastic diaphragm switches 184, which are momentarily closed when struck by hammers 154. There is an additional elastic diaphragm switch (EDS) 190 located under the lower end of keystem 112. EDS 190 is actuated when keystem 112 is fully depressed. Although an elastic diaphragm switch is used in the preferred embodiment, any small displacement switch operable by a small mechanical force can be used. Alternatively one of the contacts can be on the hammer and the other can be struck by the hammer. Any force transducer sensitive to the force applied by the hammer can be used as the switch means.
In the preferred embodiment the ribbons 114 and 118 are flexible and follow a curved path. The curved path is determined by inclined ramps 134 and 136 which guide the flexible ribbons. However, the ribbons may be straight and either rigid and self-supporting or flexible and supported by straight ramps. If straight ribbons are used they would move parallel to the length of the keystem 112 and deflect the hammers 154 in a direction substantially perpendicular to the keystem. Therefore, the elastic diaphragm switches would be mounted parallel to the keystem rather than perpendicular to it as in the preferred embodiment. The number of ribbons and hammers may be easily varied according to the number of elastic diaphragm switches to be actuated by the actuator.
The ribbons 114 and 118 can be pulled, rather than pushed, by the depression of the keystem 112. This is accomplished by repositioning the inclined ramps 134 and 136 and by attaching ribbons 114 and 118 to keystem 112 at its lower end, so that the ends of the ribbons with the projections are nearer the upper end of the keystem. In this configuration depression of the keystem pulls the ribbon downward. For this embodiment the hammers and the elastic diaphragm switches must be relocated so that the hammers are activated by the ribbons and strike the switches.
Alternatively, a slide switch, rather than a push button switch, can be used. In such an arrangement the ribbons would be activated by the slide switch movement in a fashion similar to that of the push button embodiment. The hammers and the elastic diaphragm switches would then be placed where the ribbons actuate the hammer.
The invention is not restricted to these embodiments, but is usable in any embodiment which provides for an impulse-impact to the elastic diaphragm switches.
The switch 100 is preferably formed of molded plastic parts. The switch 100 may be molded in sections and the sections then glued or welded together to form the final assembly 100.
The ribbons 114 and 118 and the keystem 112 are preferably made from the same plastic material and acetal resin is preferred because it has good wear characteristics. It is preferred to mold the ribbons as an integral part of the keystem. However, if desired, the ribbons may be formed separately and glued or attached to the keystem in any other acceptable manner.
OPERATION OF THE INVENTION
The operation of the preferred embodiment will be described with respect to FIGS. 2-6, and especially FIGS. 3-6. For clarity the operation of switch 100 will be described in terms of ribbon 114, projection 116 and just one hammer 154, although the description applies equally to both ribbons and to every hammer.
In FIGS. 4, 5 and 6 the lower end of ramp 134 and all of the ribbon 114, except for projection 116, have been left out of the drawing to simplify the drawings and emphasize the significant relationships. These drawings show the relationship between hammer projection 174 and bearing surface 172 and between hammer projection 174 and elastic diaphragm switch 184 at different points during an actuation cycle.
To actuate switch 100, keystem 112 is depressed. As keystem 112 is depressed, ribbon 114 moves down inclined ramp 134 and projection 116 on the ribbon engages bearing surface 172 of hammer 154. As keystem 112 is further depressed, hammer 154 is displaced from its rest position by projection 116 on ribbon 114 which is moving along and is supported by ramp 134. As keystem 112 is further depressed, but before it is fully depressed, projection 116 passes beyond bearing surface 172, releasing hammer 154 which is driven back toward its rest position by spring 164. Spring 164 develops sufficient momentum in hammer 154 to cause the hammer to overthrow its rest position and strike elastic diaphragm switch 184. The noise made by the contact of hammer 154 with EDS 184 provides audible feedback to the person depressing keystem 112 indicating that switch 100 has been activated. In addition, ribbon 114 moves more easily after projection 116 passes beyond bearing surface 172 because there is less resistance to the movement of the ribbon. This easier movement provides a mechanical or tactile feedback to the person pressing the keystem. Hammer 154 striking EDS 184 momentarily closes elastic diaphragm switch 184. The period for which switch 184 is closed depends on the mass of the hammer, the spring constant, and the length of spring 164, and on the characteristics of the elastic diaphragm switch 184. When keystem 112 is fully depressed, the lower end of the keystem presses on elastic diaphragm switch 190, closing switch 190 for as long as keystem 112 is fully depressed in order to indicate that the keystem is fully depressed.
On the return stroke of keystem 112, projection 116 on ribbon 114 passes over hammer 154, depressing the hammer slightly but not enough to cause the hammer to strike EDS 184. Therefore, switch 184 is activated only on the depression stroke of keystem 112. When keystem 112 has returned to its initial position, projection 116 has passed over hammer 154 and is again in a position to press on the bearing surface 172 when the keystem is depressed.
For situations in which it is considered desirable, the hammer's bearing surface may be reversed and the hammer may be actuated on the return stroke of keystem 112, rather than on the depression stroke as in the preferred embodiment. In a situation where it is desired to know that the switch has returned to an actuatable condition, some hammers may be actuated on the depression stroke and others actuated on the return stroke. This is best accomplished by providing two ribbons as in the preferred embodiment and having one ribbon activate its hammers on the depression stroke and the other ribbon activate its hammers on the return stroke. Some situations in which it would be desirable to know that the push button has returned to an actuatable condition are where the button sounds a warning alarm or is used to activate a security device of some variety.