Structure and Working Principle of membrane switch of electronic scale
The membrane switch of electronic scale is composed of panel, upper circuit, insulating layer and lower circuit, which belongs to the light touch on normally open switch. Under normal circumstances, the two contacts of the membrane switch are open. When an external force is applied to the contacts of the membrane switch of the electronic scale, the two normally open contacts are momentarily closed. After the external force disappears, the switch contacts return to the normally open state. Generally, the circuit contacts are bulged or added with pot chips (good hand feeling). Press the film switch of the electronic scale, the contact of the upper circuit is deformed downward, and the contact with the electrode plate of the lower circuit is conductive. When the finger is released, the contact of the upper circuit bounces back, the circuit is disconnected, and the circuit triggers a signal.
As we all know, silver or carbon are conductive substances, whose physical properties determine that they can be used only in solid form. First, they are ground into powder form, and then infiltrated into special resin adhesive to dissolve into liquid. High precision screen printing is used to print on PET or other insulating materials. After drying and aging, conductive lines are formed. The circuit under the film switch of electronic scale is usually made into a semicircle or non intersecting labyrinth net contact with a larger area, which can be used as a switch if the metal sheet or conductive rubber is used on it.
The structure of this membrane switch for the electronic scale determines that its working voltage is low (< 50V), its carrying DC current is small (< 300mA), and it has no self-locking function, so it can not be directly connected to the 220 V circuit, and it can not directly control the load circuit, so it can not be used for alternate switching or interlocking. In use, it needs to cooperate with the auxiliary circuit. The trigger signal (weak current) derived from the film switch of the electronic scale controls the auxiliary circuit, and the auxiliary circuit controls the main circuit (strong current), so as to realize the function of weak current controlling strong current.
Main concerns of design
In the design of the membrane switch of the electronic scale, the designer must be familiar with the plate making and printing process, as well as the subsequent assembly technology, and confirm that the design of the switch meets the requirements of these processes and technologies. For the design of normal membrane switch, it is required to be simple, bright and suitable for printing; for some high-grade products with special design requirements, special personnel must be organized to tackle key problems when assembling after printing.
Because the printing process and materials of the electronic scale film switch are totally different from those of the general books and periodicals. Therefore, in the design of screen printing, it is necessary to fully consider the characteristics of the materials and printing process of the electronic scale film switch. Screen printing is often met with the need for hollowing and inlay process. Especially if the manuscript needs bright colors or gold and silver, the printing plate must be made into a hollow inlay plate, otherwise it is easy to cause problems such as color darkening, lack of gold and silver ink.
The operation of the electronic scale membrane switch only needs the elastic membrane to flick slightly in a vertical direction. Therefore, it can guarantee a long use time and a lot of use times.
Shanben focuses on the selection of material and process that ensure the vertical action can be done over one million times. And the whole testing procedure is complete simulation of the actual use, and even more stringent, i.e. continuous wearing actions of the switch clicking which won’t happen in real practice.
Criteria of finished product
1. Good appearance, flat appearance, common luster, free of mechanical operation, scratches, inclusion and stain.
2. Excellent weather resistance, free of deformation, cracking, aging and discoloration under certain natural environment conditions. Strong chemical resistance against different common chemicals such as alcohol, ether and mineral oil.