A touch-sensitive pushbutton switch includes an optical sensor, in particular an infrared sensor, and an evaluation circuit. The evaluation circuit is able, through the use of a reference device, to set a sensitivity of the optical sensor in dependence on a detected basic level of an evaluation signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2006 004 979.9, filed Feb. 1, 2006; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a touch-sensitive pushbutton switch including an optical sensor, which contains an electromagnetic-radiation-emitting transmitter and an electro-magnetic-radiation-receiving receiver and which is disposed behind a covering that is at least partly transmissive to the electromagnetic radiation. An evaluation circuit evaluates a measurement signal which is generated by the receiver of the optical sensor and generates an evaluation signal. Such a pushbutton switch is intended to be used, in particular, in a control device for a domestic appliance.

The basic construction and the basic principle of such a touch-sensitive pushbutton switch are known from German Published, Non-Prosecuted Patent Application DE 40 07 971 A1, for example. That touch-sensitive pushbutton switch has an electromagnetic-radiation-emitting transmitter and an electromagnetic-radiation-receiving receiver, which are disposed behind a covering that is at least partly transmissive to the electromagnetic radiation. Furthermore, provision is generally made for an evaluation circuit for evaluating a measurement signal generated by the receiver and generating an evaluation signal for further processing. One advantageous application of such touch-sensitive pushbutton switches is, for example, use in control devices for domestic appliances, such as ranges or cookers, glass ceramic cool top platforms or cook tops or hobs, microwave ovens and the like, in which the pushbutton switch is accommodated behind a covering, such as a glass plate or glass ceramic plate, for example, for simple operation and cleaning.

In conventional pushbutton switches of that type, one problem is that different pushbutton switches in a control panel generally do not always react identically to one another, nor do they react in an unchanged manner over a relatively long period of time. That is due to various ambient influences and tolerance faults of its components, which may make it more difficult for a user to operate a control panel and may reduce the service life of the control panel.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a touch-sensitive pushbutton switch, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which, in particular, a well-defined operability can be ensured even over a long period of time.

With the foregoing and other objects in view there is provided, in accordance with the invention, a touch-sensitive pushbutton switch, comprising a covering being at least partly transmissive to electromagnetic radiation. An optical sensor is disposed behind the covering and has an electromagnetic-radiation-emitting transmitter and an electromagnetic-radiation-receiving receiver. An evaluation circuit is provided for evaluating a measurement signal generated by the receiver and for generating an evaluation signal. A reference device is provided for conducting part of the electromagnetic radiation emitted by the transmitter to the receiver even without actuation of the pushbutton switch, and generating a basic level of the evaluation signal. The evaluation circuit sets a sensitivity of the optical sensor in dependence on a detection of the basic level of the evaluation signal.

By virtue of the above-described construction of the pushbutton switch, the receiver receives a small quantity of radiation even without the actuation of the pushbutton switch and thus generates a corresponding measurement signal from which a basic level of the evaluation signal is determined. The evaluation circuit then in each case sets a sensitivity of the optical sensor in dependence on the basic level of the evaluation signal thus detected. In this way, it is possible to ensure, for example, that all of the pushbutton switches in a control panel on one hand always have an identical sensitivity with respect to one another and on the other hand over a long period of time. It is possible, therefore, to eliminate temperature influences on the optical sensors of the pushbutton switches, to compensate for relatively large tolerances of the components of the optical sensor, to continuously adjust the pushbutton switches, and the like.

In accordance with another feature of the invention, the evaluation circuit sets a minimum swing of the evaluation signal necessary for identifying an actuation of the pushbutton switch, in dependence on the detected basic level of the evaluation signal, for example to a predetermined factor of a reference swing corresponding to the detected basic level.

In accordance with a further feature of the invention, the reference device has an at least partly transmissive passage opening in a partition of a diaphragm frame between the transmitter and the receiver. Therefore, part of the radiation emitted by the transmitter always passes directly through the passage opening to the receiver, independently of an actuation of the pushbutton switch.

In accordance with an added feature of the invention, alternatively, the covering for the reference device is formed in such a way that part of the radiation emitted by the transmitter is reflected at the front and/or the rear surface of the covering in the direction of the receiver. This may be achieved, for example, by the choice of a specific refractive index of the material of the covering, by a specific constitution of surfaces or by a specific coating of the surfaces of the covering.

In accordance with an additional feature of the invention, the reference device has both an at least partly transmissive passage opening in a partition of a diaphragm frame between the transmitter and the receiver and the covering which reflects part of the radiation emitted by the transmitter at its front and/or rear surface in the direction of the receiver.

In accordance with a concomitant feature of the invention, the radiation is infrared radiation.

Although the invention is illustrated and described herein as embodied in a touch-sensitive pushbutton switch, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawings in detail and first, particularly, toFIG. 1thereof, there is initially seen a mechanical construction of a touch-sensitive pushbutton switch10according to the invention. The touch-sensitive pushbutton switch of the invention is, for example, an infrared pushbutton switch for a domestic appliance such as a range, a microwave oven, a cool top platform or cook top, a washing machine, a tumble dryer, a dishwasher or the like, without the invention being restricted to electromagnetic radiation in any particular wavelength range or to these specific applications.

The touch-sensitive pushbutton switch10has an optical sensor with an infrared transmitter14and an infrared receiver16, on a printed circuit board12. The transmitter14and the receiver16are surrounded by a diaphragm frame18having two openings20and22at its top side19. The diaphragm frame18is formed from an IR-opaque material and has feet24which are inserted through holes in the printed circuit board12and thus fixed to the latter.

The transmitter14and the receiver16are positioned in the diaphragm frame18in such a way that they are disposed within respective cavities26and28beneath the diaphragm openings20and22. In this case, the two cavities26and28are separated from one another by an IR-opaque partition30. A covering32made of a material that is at least partly transmissive to IR radiation, for example a glass ceramic plate of a domestic range, lies directly on the top side19of the diaphragm frame18.

The radiation emitted by the transmitter14passes along an optical path36to a top side34of the covering32. When the touch-sensitive pushbutton switch10is actuated by a finger37placed onto the surface of the covering32, the radiation of the transmitter14is diffusely and multiply scattered, so that enough scattered radiation is reflected onto the receiver16and the latter transmits a corresponding measurement signal VEto an evaluation circuit40in order to initiate a corresponding switching function.

The evaluation circuit40, which corresponds in principle to an evaluation circuit of a conventional pushbutton switch, is illustrated inFIG. 2. A voltage divider circuit, to which a supply voltage Vdd is applied, is constructed from a first resister R1and a first transistor Q1. The measurement signal VEof the receiver16switches the first transistor Q1. An evaluation signal VINis tapped off between the first resister R1and the first transistor Q1and fed to an input IN of a microprocessor42for further processing.

In the case of a functional pushbutton switch10, without actuation of the pushbutton switch10, the first transistor Q1is at high impedance, so that the evaluation signal VINhas a high signal level. When the pushbutton switch10is actuated, the first transistor Q1is switched to a low impedance by the measurement signal VEof the receiver16, so that the signal level of the evaluation signal VINfalls correspondingly, which the microprocessor42interprets as an actuation of the pushbutton switch10.

Referring toFIG. 1again, the partition30of the diaphragm frame18has a passage opening38that is at least partly transmissive to the electromagnetic radiation emitted by the transmitter14. In addition or as an alternative, the top side34and/or an underside35of the covering32may be constituted or coated in such a way that at least part of the electromagnetic radiation of the transmitter14is reflected in the direction of the receiver16. Therefore, the covering32and the passage opening38together form a reference device. What is achieved in this way is that, even without an actuation of the pushbutton switch10by a user, the receiver16receives a certain quantity of radiation from the transmitter14and generates a corresponding measurement signal VEfor the evaluation circuit40.

A signal profile of the evaluation signal VINof the pushbutton switch10according to the invention will now firstly be described with reference toFIG. 3.

As is illustrated inFIG. 3, the pushbutton switch10is evaluated in multiplex operation in a time window tAto tB. Within that time window tA-tBthere exists a transmission clock cycle ta-tbin which the transmitter14emits radiation. Outside the time window tA-tB, the multiplex operation is switched to other pushbutton switches in the control panel.

FIG. 3shows, through the use of a solid line, the signal profile of an evaluation signal VINwithout actuation of the pushbutton switch10(and without overshoot radiation of the pushbutton switch10). As a reaction to the radiation emitted by the transmitter14, the receiver16generates a measurement signal VEwhich, even without the actuation of the pushbutton switch10, during the transmission clock cycle ta-tb, leads to a slight lowering (by a reference swing HREF) of the evaluation signal VINto a basic level VREF. The basic level VREFis defined, for example, by a defined slot width of the passage opening38or through the use of a reflectivity of the top side34of the covering32.

This lowering of the evaluation signal VINis significantly more greatly pronounced in the case of a pushbutton switch actuation, as is indicated by a dashed signal profile inFIG. 3. A signal swing HEFFis significantly greater than the reference swing HREF.

As is illustrated inFIG. 4, the signal swing HEFFgenerally depends proportionally on the present sensitivity of the pushbutton switch10. In the case of a weak pushbutton switch10(on the left inFIG. 4), the signal swing HEFFin the event of an actuation of the pushbutton switch10is correspondingly smaller than in the case of a strong/sensitive pushbutton switch10(on the right inFIG. 4). This behavior equally holds true for the reference swing HREFof the evaluation signal VIN, which is utilized as follows according to the invention.

In order to ensure that the microprocessor42identifies the actuation of the pushbutton switch10, the signal swing HEFFof the evaluation signal VINduring the transmission clock cycle ta-tbof the transmitter14of the optical sensor must exceed a specific minimum swing HMIN. While the minimum swing HMINis fixedly predetermined in the case of a conventional pushbutton switch, in the case of the present invention the minimum swing HMINis presently adapted in each case, as is illustrated inFIG. 4.

In particular, the minimum swing HMINnecessary for identifying a pushbutton switch actuation is set in a manner dependent on the basic level VREFof the evaluation signal VINthat is detected according to the invention. In one exemplary embodiment, the minimum swing HMINmay be set to a specific factor (e.g. approximately a factor of 2 inFIG. 4) of the reference swing HREFcorresponding to the basic level VREF. As can be discerned inFIG. 4, in the case of a more sensitive pushbutton switch10it is therefore necessary to detect a larger signal swing HEFF, in order to ensure that the microprocessor42identifies an actuation of the pushbutton switch10, than in the case of a less sensitive pushbutton switch10. In other words, despite properties that are actually different, the two pushbutton switches10react identically due to the adapted threshold HMINfor identification of button touching.

Such setting of the sensitivity of the optical sensor, more precisely of the minimum swing HMINrequired for identifying a pushbutton switch actuation, through the use of software in the microprocessor42, makes it possible, in a simple and reliable manner, to have the effect that all of the pushbutton switches in a control panel react identically for a user, which simplifies operability. Moreover, temperature influences and sensitivity tolerances or tolerance faults of the optical sensor can be eliminated or at least minimized since the pushbutton switch is continuously readjusted to a good button touching behavior.

Whereas the invention has been described above on the basis of a preferred exemplary embodiment with reference to the accompanying drawings, it is self-evident to the person skilled in the art that further variants and modifications thereof can also be implemented without departing from the scope of protection of the invention as defined by the appended claims.

By way of example, in the diagrams shown inFIGS. 2 to 4, the polarities can be interchanged without impairing the effects and advantages of the invention.