Electricity: circuit makers and breakers – Capacitive switch
Patent
1994-07-28
1997-03-11
Scott, J. R.
Electricity: circuit makers and breakers
Capacitive switch
341 33, H03K 17975
Patent
active
056103808
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates touch sensitive control panels of the kind comprising a front plate preferably of a dielectric material such as glass, and electrodes disposed on a reverse side thereof together with electronic circuits where the front plate carries markings that indicate touch areas so that touching by a finger completes an operative coupling to respective electrodes disposed on the reverse side so that the panel unit provides selective control signals from the electronic circuits.
2. Description of the Prior Art
Such control panels are increasingly used in various kinds of electrical and electronic equipment because they may advantageously replace panels with mechanical switches or rotary or pushbutton activated elements. A light touch upon a selected area controls the desired function such as a starting or stopping or an increasing or decreasing control function without use of mechanically completed switching action. Normally the aforementioned type of control panel functions by a capacitive coupling.
In particular because this kind of control panel is known it is not necessary to discuss the general advantages of their use in detail here. Control panels are predominantly manufactured by specialty manufacturers because their manufacture is not performed by mounting of ready-made special switches and controllers and requires the manufacture of both the panel plate and at least the necessary electronic circuitry.
It has, however, been possible to prepare an intermediate stage where the manufacture of the panel plate itself is a specialized task but the electronic circuitry may be placed on a conventional printed circuit board prepared with suitable contacts for establishing contact with specific electrode areas on the reverse side of the front plate. These defined areas are typically made as a coating of graphite powder which has been fixed reliably to the reverse side of the front plate so that the electrode areas are located at a well-defined position and are easily accessible for establishing contact with projecting contact elements on the printed circuit board since these elements require only that the coatings abut the contact elements in an uncritical fashion.
However considerable contact problems still exist because mechanical fitting of the relevant contact parts is used. Contamination may make the establishment of an effective connection difficult.
SUMMARY OF THE INVENTION
According to the present invention the printed circuit board is eliminated in that the electronic components are placed directly on the panel plate to which they are fixed by cement to the electrode areas.
The important thing is that by using the panel plate to carry both the electrode areas and the electronic components the circuit board is eliminated and a totally integrated solution is obtained so that the manufacturing facility may construct the control panels with a high precision in an optimized manner having a high degree of functional reliability.
The panel plate may have any desired size or shape, including an arched or vaulted shape. The control panel may have a minimal thickness. The electronic components may be fastened by surface mounting (soldering) or cementing to the electrode areas or to other conductive layers on the panel plate or by cementing or casting the electronic components to the support.
The panel plate may be used as a printed circuit board, i.e. with fixed conductive strips between different terminal areas. However, the panel plate may also be used with a shielding coating around and between the operative electrode areas to provide high quality EMC shielding. The shielding coating may be used for fixing electronic components which are not electrically connected to the shield.
The coating itself may be differentiated to create different components such as resistors in a coating paste which has been formed. The coating may play an active role in providing a desired temperature compensation.
While the control panels of the invention
REFERENCES:
patent: 4090092 (1978-05-01), Serrano
patent: 4250495 (1981-02-01), Beckerman et al.
patent: 4290052 (1981-09-01), Eichelberger et al.
patent: 4304976 (1981-12-01), Gottbreht et al.
patent: 4380040 (1983-04-01), Posset
patent: 4394643 (1983-07-01), Williams
patent: 4413252 (1983-11-01), Tyler et al.
patent: 4614937 (1986-09-01), Poujois
patent: 4876461 (1989-10-01), Gratke
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