Pushgate® Design Description

Duraswitch's PushGate push-button electronic switch is truly unique in that it incorporates all the best features of both discrete and membrane technology, thus giving the customer the best of both worlds at a competitive price. The patented magnetic armature design provides crisp, tease-proof and reliable tactile feedback as each switch is actuated without the "spongy" feel of typical tactile membrane switches.

The advantages of this next generation technology go far beyond merely providing a second-to-none feel. By design, each switch is shielded against EMI/RFI interference as well as static discharge. Actuation force is uniform over the face of each switch while still providing the travel so coveted by the user to give him a feeling that he has "done something" when he actuates a switch.  All of this is provided while still maintaining the long life and sealed washable surface of a typical membrane switch.

The basic PushGate is shown in figure #1. It is composed of a membrane, a steel plate, a magnetic sheet, an armature, a spacer and a substrate with either plated etched copper or silver contacts on its upper surface. The armature is held in place against the magnetic sheet by the magnetic field.  As shown in the figure, the armature has a pivot point mechanically formed into it. An actuating button is also mechanically formed into the armature. This actuating button protrudes up through the magnetic sheet material and is exposed on the top side of the switch. An overlay or label may or may not be placed over the top side of the switch to provide a seal against dust, dirt and spilled liquids as well as providing a surface for graphics to be printed. It is recommended that the overlay be embossed to provide space for the actuating button and also to provide material movement.

During actuation, pre-travel is achieved when the overlay is first deformed to come into contact with the actuating button. As the overay is further deformed, the armature abruptly breaks away from the magnetic sheet material, thus providing a very crisp tactile sensation. The switch is actuated when the armature contacts the second pad on the top surface of the substrate.  Improved tactile feel can be achieved by placing a ferro-magnetic material on the top surface of the magnetic sheet material. This material has the effect of directing the magnetic field downward toward the armature. The material further enhances the tactile sensation by providing rigidity to the magnetic sheet material. One example of this material would be thin, soft steel sheet.

PUSHGATE® FORCE TRAVEL CURVES

For as long as mechanical push-button switches have been in existence the user has been accustomed to feeling a tactile sensation when the switch is depressed. This sensation can take the form of a smooth linear increasing force or it can provide a crisp reduction in force at the actuation point. A typical force/travel curve for a mechanical switch is shown graphically in figure #2. 

With the advent of membrane touch switches, this tactile feel was lost and many users found themselves out of touch or disoriented. Frequently they were inclined to push the switch excessively hard or, out of frustration they would use a sharp object thus destroying the switch. Although this situation was typically related to the user's familiarity with the equipment at hand, the membrane switch manufacturers were nevertheless forced to find a way of providing tactile feel for their switches.

PUSHGATE® FORCE TRAVEL CURVES, II

For years, the membrane switch manufacturer has toiled with the problem with reasonable success in the marketplace. The logical first approach was to place a metal dome under the membrane. The dome was similar to the one used in mechanical switches; however, the mechanics of the finger coming into virtually direct contact with the dome caused the switch to feel somewhat like an oil can. In addition to the oil can feel, there were also problems with the switch actuation point not being at the point of the tactile force reduction which led to further problems with "teasability".  This gave the user the feeling that he had actuated the switch when he had in fact not done so.

Many attempts, such as the Polydome, have been made at providing alternatives to the metal domes; however, they have been directed primarily toward reducing cost. The rubber switch, on the other hand, provides a reasonable alternative at a lower cost; however, by its very nature it provides a somewhat spongy feel and does not provide a high quality image.

PUSHGATE® FORCE TRAVEL CURVES, III

This push-button represents a state of the art alternative to the mechanical push-button switch in every respect for the first time since membrane switches were first developed. This product provides the user with a very crisp tactile sensation directly at the switch actuation point (figure #4). Additionally, there is no "spongy" feel since there is no dome.

Unlike mechanical switches inserted under the membrane, the unique patented design has no flexing metal parts to fatigue and fracture, thus providing the ultra long life typically associated with membrane switches in general.  This product has been repeatedly tested in excess of ten million cycles without failure. 

There are many other advantages with the push-button switch as stated earlier, and these will be expanded as the technology is further refined in applications. The designer can be assured that when he incorporates this technology into his product, he is using the most current technology available today. He can be further assured that the customer is the driving force, and his best interest will be incorporated in any future refinements.