WO2011101536A1

WO2011101536A1 - A method for detecting objects in a planar sensor system and a planar sensor system

Info

Publication number: WO2011101536A1
Application number: PCT/FI2011/050129
Authority: WO
Inventors: Hannu Nummela
Original assignee: Marimils Oy
Priority date: 2010-02-17
Filing date: 2011-02-10
Publication date: 2011-08-25
Also published as: FI20105155A0; FI20105155A

Abstract

A planar sensor system, which system comprises a sensor (101) based on capacitive detection and an electronic detection unit (102), which sensor comprises conductive sensor areas, by examining the capacitance in which areas the objects on a sensor are monitored, and which system uses a planar sensor that comprises crossing conductive sensor strips (111a-111c, 112a - 112c), of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner are earthing strips, and in which system crossing areas or crossing spots formed by superimposed strip parts insulated from each other are formed at the crossing points (113a-113i) of the strips in question, the capacitance of each crossing point is determined at the crossing points by controlling the earthing strips consecutively into connection with the ground potential, by measuring the capacitances and by controlling the received capacitance values to the control unit, and in which detection unit the capacitance values received at the crossing points are compared to the capacitance values received at the same crossing point at different moments of time and/or at different crossing points and based on the changes in capacitance values the presence and/or the state of the objects on the sensor is/are deduced.

Description

A method for detecting objects in a planar sensor system and a planar sensor system

FIELD OF INVENTION

The current invention relates generally to planar sensor systems. More particularly the invention relates to a method for detecting objects in a planar sensor system, to a planar sensor system and also to a planar sensor used in the system.

BACKGROUND OF THE INVENTION

Near-field imaging is used to monitor e.g. the movements of people in rooms. Planar sensors, for example, disposed in floor structures are used in near-field imaging systems, by means of which planar sensors information about the position and state of a person being monitored is obtained by measuring the impedance changes caused by a conductive object, e.g. a person. This type of arrangement can be used in a number of different applications, e.g. in nursing homes, et cetera, to monitor elderly people, at an airport to monitor the movements of people, or also in shops to observe the number and consumption of sales products, such as for instance of beverage cans, on a shelf (object identification).

Publications WO 2006/0023245 and WO2008068387A1 present some sensor structures wherein the sensors are in web form and comprise a number of consecutive electrically conductive areas on the same plane. The monitoring of an object, such as of a person, on a sensor is based on changes in capacitance between adjacent conductive areas that are on the same plane. Electrically conductive areas are typically metallic, and they can be formed on a substrate, e.g. as printed layers, laminated layers, etched layers, or films. The metal is typically aluminum or copper, and each conductive area is connected with a dedicated connection lead to an electronic control unit next to the sensor, which control unit controls the system, as is disclosed e.g. in publication WO2008068387A1. When there are a number of consecutive conductive areas, a corresponding number of parallel connection leads are also needed, in which case the number of parallel leads and the space taken by them in the lateral direction are relatively large. Another problem related to planar sensor systems of this type provided with adjacent conductive areas is their susceptibility to interference, particularly to ambient conditions and changes in them; the capacitance between the conductive areas is significantly affected by e.g. the temperature of the control unit and also the floor material below. In some cases, for example, if the floor is protected from so-called electrostatic discharge (ESD) and therefore comprises a metal layer, the outcoming measuring signal in the monitoring of objects, which monitoring is based on the capacitance between conductive areas, weakens or even disappears completely owing to the metal layer of the floor.

SUMMARY OF THE INVENTION

The aim of the present invention is to achieve a completely new type of method for detecting objects in planar sensor systems, a planar sensor system and also a planar sensor.

According to the invention, a sensor comprising crossing conductive sensor strips, of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner are earthing strips, is used in a planar sensor system. Crossing areas or crossing spots formed by superimposed strip parts that are insulated from each other are created at the crossing points of the strips.

According to the invention, for detecting objects the change in capacitance is monitored at the crossing points and it is deduced based on said change whether a change in capacitance that has occurred at the crossing point in question is such that an object to be detected is at the crossing point in question. In this way each crossing point of a sensor area can be examined. The capacitance can be monitored according to the invention e.g. with a voltage-controlled oscillator (VCO) to be connected to each signal strip of a planar sensor and with an analog gate to be connected to each earthing strip.

Digitally-shaped frequency signals, which are thus proportional to the capacitance of the crossing point in question, because the capacitance is known to be inversely proportional to the frequency, can be received from the oscillators as the output of the measuring.

The measuring signals in question can then be recorded in the memory e.g. in table format as digital signals, which present the capacitance of each crossing point at the sampling moment. A comparison table can then be formed from a number of recorded consecutive measuring signals, by comparing the measuring signals in which table deductions can be made about the object at the crossing point in question.

A relative comparison can be used in the table inspection where the frequency values of the whole table are compared, in which case a change at only one crossing point means detection of an object whereas a change at several nearby inspection points means a change in external conditions, which change can thus be taken into account in the detection of the object.

The characteristic features of the method, of the system and of the sensor according to the invention are described in detail in the independent claims and the preferred embodiments of them in the other claims.

By means of the invention the detection of objects, e.g. at senior citizens' homes, airports and corresponding, can be implemented very reliably and quickly, more particularly without the interference caused by external factors.

SHORT DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in more detail by the aid of some examples of its embodiments with reference to the attached drawings, wherein

Fig. 1 presents a planar sensor system according to the invention, Fig. 2 a detection unit and Fig. 3 presents a cross-section of a planar sensor according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The planar sensor system based on the measuring of capacitance according to the invention comprises a sensor 101 , which covers a pre-determined area subject to examination and can be fitted to a flat base, such as to the floor 103 of a room below the surface of the floor, or also to a shelf of a store, and an electronic control unit/detection unit 102 to be connected to the edge of said sensor, which unit detects an object 100, such as a person or an object of conductive substance on top of the sensor, its position or state and notifies thereof onwards to the monitoring system, e.g. to the monitoring system (not shown in the figures) of the products sold in a store.

The conductive object on top of a sensor in this case affects the capacitance and the system measures the changes in capacitance, based on which changes the presence, position, movement or state of the object on the sensor can be determined.

According to the invention, a rectangular planar sensor 101 is used in the planar sensor system, which sensor comprises transversely crossing conductive sensor strips 11 a-111c, 112a- 12c, of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner at a right angle are earthing strips. Between the crossing strips is an insulation 114 (Fig. 3) and capacitively conductive squares formed by superimposed strip parts that are insulated from each other are created at the crossing points 113a-113i of the strips in question, the surface area of which squares is the surface area of the superimposed areas and in which squares the strips thus form among themselves a capacitor, which has a measurable capacitance Cm_a-Cn^. The earthing strips are connected to the monitoring unit with connection leads 115a-115c.

According to Fig. 3 the sensor is fitted between the floor 103 and the floor covering 104 on top of it and the strips in the sensor are insulated from each other with an insulation layer or insulation layers 114 between them and from the floor with an insulation layer 116, 1 7 on top of and below the sensor.

According to the invention for detecting objects the change in capacitance ACii₃a-ACn₃i is monitored at each crossing point and based on it is deduced whether a change in capacitance that has occurred at the crossing point in question is such that an object to be detected is at the crossing point in question. Typically the presence of an object at the inspection point is seen as a dip in capacitance. In this way the whole sensor area or a desired part of it can be examined.

The system comprises voltage-controlled oscillators 121a-121c (VCO) to be connected to a signal strip and analog gates 122a-122c to be connected to each earthing strip.

The system operates such that each earthing strip is always controlled one at a time to be conductive to earth by means of a switch (analog gate, AG) and in this way the whole sensor area is scanned by switching consecutively each earthing strip on for a moment. The analog voltage signal received this way then controls each oscillator such that a high-frequency digital output signal fi i 3a-fi i 3if, typically of a frequency of 30 ... 1000 kilohertz, dependent on the capacitance, is received. These output signals are recorded in the memory 123, e.g. according to an Eccless-Jordan circuit 124, at set intervals in a controlled manner into tables, which comprise signals corresponding to each crossing point over an inspection interval. Comparison tables can then be formed from a number of consecutive recorded measuring signals, the measuring signals in which tables are compared in a digital signal processor (DSP) processing unit 125 provided with a microprocessor, which unit compares capacitance values at different spots and at different moments of time and deduces the presence and the state of an object at the crossing points.

A relative comparison can be used in the table inspection where the frequency values of the whole table are compared, in which case a change at only one crossing point means detection of an object whereas a change at several nearby inspection points means a change in external conditions, which change can thus be taken into account in the detection of an object. These different situations are presented in Tables 3-5, of which Table 3 thus presents the frequency values of a normal state, Table 4 a situation wherein the value of only one point has changed, in which case an object is at the point in question, and Table 5 a situation wherein the values of all the crossing points of the area have changed, in which case the object is not at any of the inspection points but instead the change is a result of a change in the ambient conditions (temperature, humidity, et cetera). The value can typically change in this type of floor-sensor case from a value 50 of kHz to a value of 47 kHz, in which case this type of change in frequency at one point indicates that an object 100 is at the point in question.

Table 3

Table 4

Table 5

In order to avoid an interference signal of 50 hertz mains frequency containing harmonics of said frequency from getting into the memory, either a band-pass filter 126 or a high-pass filter is connected in between. It is obvious to the person skilled in the art that the different embodiments of the invention are not limited solely to the examples described above, but that they may be varied within the scope of the claims presented below. The size of the sensor and also the number of the strips needed and their dimensions are, of course, dependent on the application. The sensor strips do not necessarily need to be at a right angle with respect to each other but instead they must only be at such an angle with respect to each other that crossing areas suited to the measurement of capacitance are formed.

Claims

1. Method for detecting objects in a planar sensor system, which system comprises a sensor (101) based on capacitive detection and an electronic detection unit (102), which sensor comprises conductive sensor areas, by examining the capacitance in which areas the objects on a sensor are monitored, characterized in that in the method a planar sensor is used, which comprises crossing conductive sensor strips (111 a-111c, 112a - 112c), of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner are earthing strips, and in which sensor crossing areas or crossing spots formed by superimposed strip parts that are insulated from each other are formed at the crossing points (113a-113i) of the strips in question, the capacitance of each crossing point is determined at the crossing points by controlling the earthing strips consecutively into connection with the ground potential, by measuring the capacitances and by controlling the received capacitance values to the detection unit, and in which detection unit the capacitance values received at the crossing points are compared to the capacitance values received at the same crossing point at different moments of time and/or at different crossing points and based on the changes in capacitance values the presence and/or the state of the objects on the sensor is/are deduced.

2. Method according to claim 1 , characterized in that the capacitance is measured according to the invention e.g. with a controllable converter (VCO) to be connected to each signal strip of a planar sensor and with a switch to be connected to each earthing strip, wherein signals that are proportional to the capacitance of the crossing point in question can be received from the converters as the output of the measurement.

3. Method according to claim 1 , characterized in that the measuring signals are recorded in the memory to present the capacitance of each crossing point at different sampling moments and at different points, in which case comparison table values can then be formed from the recorded measuring signals, by comparing which values deductions can be made about an object at the crossing points.

4. Method according to claim 3, characterized in that a relative comparison can be used in the inspection where the frequency values of different points are compared, in which case a change at only one crossing point means detection of an object whereas a change at several nearby inspection points means a change in external conditions, which change can thus be taken into account in the detection of an object.

5. Planar sensor system for detecting objects, which system comprises a sensor (101) based on capacitive detection and an electronic detection unit (102), which sensor comprises conductive sensor areas, by examining the capacitance in which areas the objects on a sensor are monitored, characterized in that it comprises a planar sensor, which comprises crossing conductive sensor strips (111a-111c, 112a - 112c), of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner are earthing strips, and in which planar sensor crossing areas or crossing spots formed by superimposed strip parts that are insulated from each other are formed at the crossing points (113a-113i) of the strips in question, means to determine the capacitance of each crossing point at the crossing points by controlling the earthing strips consecutively into connection with the ground potential, by measuring the capacitances and by controlling the received capacitance values to the detection unit, and comparison means to compare the capacitance values received at the crossing points to the capacitance values received at the same crossing point at different moments of time and/or at different crossing points, and based on the changes in capacitance values the presence and/or the state of the objects on the sensor is/are deduced.

6. System according to claim 5, characterized in that the capacitance can be monitored according to the invention with a voltage-controlled oscillator (121a-121c) to be connected to each signal strip and with an analog gate (122a-122c) to be connected to each earthing strip, in which frequency signals that are proportional to the capacitance of the crossing point in question can be received from the oscillators as the output of the measurement.

7. System according to claim 5, characterized in that it comprises a memory, in which case the measuring signals can be recorded in the memory to present the capacitance of each crossing point at different sampling moments and at different points, in which case comparison table values can then be formed from the recorded measuring signals, by comparing which values deductions can be made about an object at the crossing points.

8. System according to claim 7, characterized in that the detection unit is fitted in the inspection to use a relative comparison where the frequency values of different points are compared, in which case a change at only one crossing point means detection of an object whereas a change at several nearby inspection points means a change in external conditions, which change can thus be taken into account in the detection of an object.

9. System according to claim 5, characterized in that the voltage- controlled oscillators are fitted to operate in the range of 30 - 100 kilohertz.

10. System according to claim 9, characterized in that it comprises a band-pass filter (126) or a high-pass filter so that interference signals of the mains frequency and their harmonics can be filtered out.

11. A planar sensor to be used in a planar sensor system for detecting objects, which system comprises a sensor (101) based on capacitive detection, which sensor comprises conductive sensor areas, by examining the capacitance in which areas the objects on a sensor are monitored, characterized in that the sensor is a planar sensor which comprises crossing conductive sensor strips (111a-111c, 112a - 112c), of which parallel first sensor strips are signal electrode strips and second sensor strips crossing with them in an insulated manner are earthing strips, and in which planar sensor crossing areas or crossing spots formed by superimposed strip parts that are insulated from each other are formed at the crossing points (113a-113i) of the strips in question.