REFLECTION TYPE CONTACTLESS TOUCH SWITCH HAVING HOUSING WITH LIGHT ENTRANCE AND EXIT APERTURES OPPOSITE AND FACING
This invention relates to a contactless touch switch wherein an electric pulse is produced by light impinging on a photosensitive cell due to the reflection of a ray of light.
In modern apparatus techniques there is the tendency to reduce the extent to which mechanical functional groups are used to a minimum by the extensive use of electronics, in order to substantially eliminate the need for servicing and to reduce the weight of the apparatus and lessen the noise it produces.
This trend has already led to proposals to design manual control elements, such as switches, press-button keys and/or complete banks of keys, on a mechanical basis but in the form of contactless touch switches or keys.
The constructions of this kind hitherto revealed operate on a capacity basis, as disclosed by the subject matter of the German Pat. No. 1,010,139 for example, in which a gas-filled cold cathode tube is used and whose ignition voltage is only reached when an earth connection to an auxiliary electrode is established by body contact achieved by touching a key button.
Touch switches based on this principle still call for a relatively large amount of circuit components. In addition, such switches are so bulky that it is not possible, for example, to form multiple key banks with the spacing normally employed in typewriter keyboards. Moreover, the overall height of such switches is too great for their use not to involve difficulties in many cases.
For this reason, there has been proposed in our copending U.S. application Ser. No. 782,656, filed Dec. 10, 1968; U.S. Pat. No. 3,526,775. a contactless touch switch wherein the principle of the light barrier is used such that the ray of light passes through a trough which is constructed in such a manner that the ray may be interrupted by the insertion of the hand or part thereof.
The necessary insertion of for example a finger into the trough of such a construction can, in some cases, be the cause of a certain amount of difficulty of operation.
This drawback is avoided in the touch switch of the present invention, which is characterized in that the ray of light normally emerges through an aperture in the touch switch housing, which is closed on all sides, and the screen-protected photosensitive cell may be affected substantially only by rays caused by reflection of the ray of light by an object covering said aperture.
The invention is described below with reference to embodiments illustrated in the accompanying drawings.
FIG. 1 is a diagrammatic cross-sectional view of a number of touch switches of the invention combined in a single unit;
FIG. 2 is a cross section of the top part of the touch switch housing shown in FIG. 1, showing a translucent covering for the aperture;
FIGS. 3 and 4 are cross sections of embodiments of the touch switch illustrated in FIG. 1, in which mirrors are used to increase the luminous efficiency of the system;
FIGS. 5 and 6 are cross sections of a modification of the touch switch illustrated in FIG. 1, in which a light filter located in the path of radiation greatly suppresses influence by the ambient light; and
FIG, 7 shows a touch switch based on the principle of that shown on FIG. 5 or FIG. 6.
The diagrammatic representation given in FIG. 1 illustrates the basic principle of the touch switch of the invention. The three touch switches which are combined in a single housing 1 to form a unit are functionally completely separate from each other. The housing 1 which surrounds each touch switch interior on all sides has an aperture in its underside in which a tube-shaped screen 2 is mounted. The oppositely located cover panel of the housing 1 is provided with an aperture 3 corresponding to the diameter of said tube. Beneath the screen 2 there is disposed a light source (not shown) which provides a concentrated parallel beam of light 6, which, in the
nonactuated state of the switch, passes unhindered through the housing 1 in the manner shown to emerge therefrom through the aperture 3. The photosensitive cells 7, hereinafter referred to as photoelectric cells, are each disposed in the 5 chamber behind the tube-shaped screen 2. In order to substantially suppress any interference which may arise from external radiation, for example from the ambient light falling through the aperture 3, the inside walls of the housing 1 are provided with a light-absorbent coating la. 10 If one of the apertures shown in FIG. 1 is covered for example by laying the hand or a part thereof, such as a finger 5, over the aperture, reflection of the ray of light 6 is caused thereby such that scattered reflected light 6a impinges on the j j photoelectric cells 7, disposed behind the screen 2, from above so as to excite them and thus cause a potential to be produced at the terminals 7a, which potential may be recognized, for example, as indicative of actuation of the touch switch by a series-connected evaluating electronic system (not 2q shown).
In order to prevent dirt and dust from reaching the interior of the touch switch, it is desirable to provide the apertures 3 with a translucent covering 4, as shown in FIG. 2, where it will be seen that the said covering is fitted in the cover panel of the
25 touch switch housing 1.
In order to increase the efficiency of the reflected radiation 6a, mirrors 8 are placed around the photoelectric cells 7 in the embodiments shown in FIGS. 3 and 4 with the cells 7 again being screened by the screen 2. In this way the scattered
30 reflected radiation 6a is concentrated on to the respective photoelectric cell 7.
The embodiments described above are based on the assumption that the ambient light passing through the aperture 3 and impinging on the cells in the nonactuated state of the
35 touch switch is so slight compared with the effective useful radiation that no unintentional actuation may be expected as a result of external radiation when the photoelectric cells 7 are of suitable response sensitivity. As an extra safeguard, there are provided, in the embodi
40 ments shown in FIGS. 5 to 7; light filters 9 which allow the passage of radiation of certain wavelengths only, in known manner. In such cases the source generating the useful radiation 1 must be such that the major portion of its radiation energy lies in that part of the spectrum for which the light
45 filter 9 is permeable.
FIGS. 5 and 6 show such a touch switch in cross section, a light filter 9 being provided above the photoelectric cells 7 and the screen 2, unlike the embodiment shown in FIG. 1. In _ accordance with the above, this filter is no obstacle to the main part of the radiation 6 so that the latter can pass through at approximately full strength, whereas the ambient light 10 penetrating from above through the aperture 3 and mostly of other wavelengths is so strongly absorbed or reflected that the
55 portion thereof reaching the photoelectric cells 7 no longer has any effective influence. If, however, the aperture 3 is covered, for example by laying a finger 5 across it, the radiation 6 is reflected in the manner described above and the scattered reflected light 6a can pass through the filter 9 unhin
60 dered to excite the photocells 7, which give indication of the actuated condition in a form which can be evaluated by the electronic system used.
FIG. 7 is a structural modification of the previous embodiment, also shown in cross section. In this case the photoelec
65 trie cells 7 are located laterally of the aperture 3 in the touch switch housing 1 and are screened from external light by a funnel-shaped screen lb extending inwardly from the aperture 3. Beneath this screen there is disposed a light filter 9, and mirrors 8 are provided in the space adjacent the screen 2. In this
70 case the screen 2 also serves as a mount for a concentrating lens 11 which focuses the radiation 6 on to the center-point of the aperture 3. Again, the major portion of the radiation 6 is of a wavelength which can pass through the filter 9. When the aperture 3 is covered for example by a finger 5,
75 the said reflection takes place. The scattered reflected radia