GB2407168A

GB2407168A - A method and system for detecting the contact of a person with an electrically conductive surface

Info

Publication number: GB2407168A
Application number: GB0420929A
Authority: GB
Inventors: Roberto Zappa
Original assignee: Sematic SpA
Current assignee: Sematic SpA
Priority date: 2003-10-13
Filing date: 2004-09-21
Publication date: 2005-04-20
Also published as: GB0420929D0; DE102004049896A1; ITMI20031968A1

Abstract

The method comprises detecting a capacitive signal between an electrically conductive surface and earth. The signal with a predefined frequency is processed to give an impedance value and a variation of the impedance value is determined. Analysis of the rate of variation of the impedance indicates whether a person has contacted the electrically conductive surface and is seen as a relatively fast change in the impedance value. A slow change caused by thermal drift or humidity change does not indicate a contact. The system is applied to lift or elevator doors to prevent a person or person's hand being trapped in closing doors and a sensed contact signal may be used to stop or open the doors.

Description

24071 68 - 1

A METHOD OF AND A SYSTEM FOR DETECTING THE SKIN CONTACT

OF A PERSON WITH AN ELECTRICALLY CONDUCTIVE SURFACE

The present invention refers to a method of and a system for detecting skin contact of a person with an electrically conductive surface.

More particularly, the present invention refers to a method of and a system for detecting skin contact of a person with an electrically conductive surface and being particularly but not exclusively, suitable for use in the field of glazed automatic doors of a lift with an electrically conductive surface.

The use of automatic doors and particularly of glazed automatic doors is widespread; especially in the access doors of a lift cabin.

These doors, or their drive systems are equipped with safety devices such as light barriers or the like in order to prevent a user from being trapped between the two doors during their closing. In other words, these devices are able to detect the presence of a user crossing the path of the closing door and, in this case, to control the motion of the doors so as to reverse their motion.

Even though these automatic doors are widely used and appreciated, they are not free from drawbacks. One drawback is that a person and particularly a child, during the opening of the doors can put the hands on the door and be dragged towards the door frame with the danger that his/her hands and particularly his/her fingers will get into the gap which necessarily exists between said door and door frame with a serious danger for hands or fingers.

Therefore a method and a system to detect the contact of the skin of a person with a surface, particularly a lift door surface in order to remove the above- mentioned drawback is desirable.

The present invention seeks to provide a method of and a system for detecting skin contact of a person with an electrically conductive surface in order to remove the above-mentioned drawbacks connected with the prior art.

According to the present invention these and other purposes resulting from the following description are reached by the method of detect skin contact of a person with an electrically conductive surface as defined in general in claim 1 and from the system defined in general in claim 4.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 is a flow chart of the method to detect the skin contact of a person with an electrically conductive surface according to the present invention; Figure 2 is a block diagram of the system to carry out the method shown in Figure 1.

With reference to the attached Figure 1, the method for detecting skin contact of a person with an electrically conductive surface is indicated as a whole by reference numeral 1. The detection of the skin contact of a person with an electrically conductive surface starts with the activation of the device to which this surface belongs. A capacitive sensor constantly detects the capacitive signal existing between the electrically conductive surface and a connection forming an earth. The capacitive signal is sampled at a pre-defined frequency which can be, for example, between 40 and 80 Hz, preferably 60 Hz, in a block 2 and is processed in order to determine a corresponding impedance value. The thus- determined impedance value is, in its turn, used to determine an impedance variation. The impedance variation is analysed in a block 4 to check whether this variation is "slow". This check is essentially carried out to control slow variations of the impedance value which are due to trends of the environmental feature impedance. In fact, the impedance is influenced by environmental conditions such as temperature and humidity. If this impedance variation is slow, a request for a new detection will be released by block 4.

If the impedance variation is not slow, we are in presence of skin contact of a person with the electrically conductive surface and, from the block 4, an "existing contact" signal is issued to a block 6. The latter will intervene in the drive control of the device to which the electrically conductive surface belongs in order to trigger required countermeasures such as the reversal or the temporary motion interrupt of the same surface.

A system suitable for putting into practice the above-mentioned method, indicated as a whole by 20, is schematically represented in Figure 2.

A capacitive sensor 24 is associated with an electrically conductive surface 22. This capacitive sensor 24 regularly sends a capacitive signal to an oscillator 26 which in turn is associated with a voltage frequency converter 28.

By means of an analog to digital converter 30, a microprocessor 32 acquires the input impedance value. This acquisition occurs at a predefined frequency, for example 60 Hz, which is determined by a clock signal. The microprocessor 32 processes the impedance value and carries out the control operations of indicated by the method in the block 4. If the impedance variation value falls within the limits of a slow variation, the microprocessor 32 orders a new frequency sampling. On the contrary, if it does not fall within these limits, an existing contact signal is emitted and sent to the control of the device to which the electrically conductive surface belongs so that it can intervene and trigger the required countermeasures such as the reversal or the temporary motion interrupt of the same surface.

The electrically conductive surface can be advantageously one or both the surfaces of a glazed door, for example a pyrolytic glass door of a lift. In this case the capacitive sensor 24 is connected to the electrically conductive surfaces 22 and to an earth contact 34 which can be, for example, the bottom surface of the lift cabin.

As can be noticed from the above description, the method of and the system for detecting skin contact of a person with an electrically conductive surface of the present invention has turned out to be particularly functional and versatile and, moreover, can be easily manufactured and allows the achievement of the purpose and the overcome of the above mentioned drawbacks connected with

the prior art. - 4

Claims

CLAIMS: 1. A method of detecting skin contact of a person with an

electrically conductive surface comprising at least the following steps: a) detecting an existing capacitive signal between an electrically conductive surface and an earth connection with a predefined frequency; b) processing said capacitive signal in order to determine a corresponding impedance value; c) determine a variation of impedance; d) analysing variation of the impedance in order to check whether said variation is "slow" and to go back to a new detection; e) indicating a new contact of a person's skin with said electrically conductive surface for a non-slow impedance variation; f) emitting an "existing contact" signal to the control of the operation of the device to which said electrically conductive surface belongs.
2. The method according to claim 1, wherein the predefined frequency is between 40 and 80 Hz.
3. The method according to claim 2, wherein the predefined frequency is Hz.
4. A system for detecting contact of the skin of a person with an electrically conductive surface, comprising: a) a capacitive sensor associated with an electrically conductive surface; b) an oscillator associated with a voltage frequency converter c) an analog to digital converter by means of which a microprocessor acquires an input impedance value to determine an impedance variation value and carry out control operations necessitated by said impedance variation; d) a connection to a control of the device to which the electrically conductive surface belongs in such a way that the required countermeasures are triggered such as reversal or temporary motion interrupt.
5. The system according to claim 4 wherein the acquisition of the input impedance value occurs at a predefined frequency determined by a clock signal.
6. The system according to claim 5, wherein the acquisition of the input impedance value occurs at a frequency of 60Hz.
7. The system according to any one of claims 4 to 6, wherein the electrically conductive surface is one of both the surfaces of a glazed door.
8. The system according to claim 7, wherein the glazed door is a lift door.
9 The system according to any one of claims 4 to 8, wherein the capacitive sensor is connected to the electrically conductive surfaces and to an earth connection.
10. The system according to claim 9 wherein the earth connection is the bottom surface of a lift cabin.
11. A method of detecting skin contact of a person with an electrically conductive surface substantially as described herein with reference to the drawings.
12. A system for detecting contact of the skin of a person with an electrically conductive surface substantially as described herein with reference to the drawings.