FR2890762A1 - Force sensing resistor`s linear position determining device for motor vehicle, has unit calculating position relative to support on semiconductor support based on measured voltage if resistor output is coupled to ground and supply potential - Google Patents

Abstract

The device has a commutation unit (15) for connecting an output (16) of a reference resistor alternatively and sequentially to ground and to a supply potential. A measuring unit (8) measures a voltage between an input (9) of the reference resistor and the ground. A calculating unit (21) calculates the position relative to a support on a semiconductor support based on the measured voltage when the resistor output is connected to the ground and the supply potential. An independent claim is also included for a method of determining a linear position for a force sensing resistor.

Description

Device for determining a relative position for force sensors

sensitive

  The present invention relates to a device for determining a relative position for pressure-sensitive force sensors and a method implemented by the device.

  In the field of touch sensors, a technology using pressure sensitive resistors (also known as the FSR sensor for Force Sensing Resistor) is ahead of more and more other equivalent technologies, such as for example capacitive technologies. still optical thanks to its ease of implementation and its robustness.

  Such sensors are for example known under the name of digitizing tablet ("Digitizer pad") and are cited as prior art the following documents: US 4,810,992, US 5,008,497, FR 2683649 or EP 0 541 102.

  These sensors comprise semiconductor layers sandwiched between, for example, a conductive layer and a resistive layer. By exerting pressure on the FSR layer, its ohmic resistance decreases allowing, by applying a suitable voltage, to measure the pressure applied and / or the location of the place where the pressure is exerted.

  US 5,008,497 and EP 0 541 102 each provide a method for determining the bearing position on the sensor. These methods are based on the principle of the divider bridge.

  However, the methods specified above require highly accurate electronic components having a high cost.

  The object of the present invention is to propose a method for determining a relative position for pressure-sensitive force sensors which is both robust for use in the automobile field for example and simple so that electronic components can be used. low end can be used for the determination of the support position.

  Independently, according to another aspect, the present invention aims to propose a solution to the problem of transients occurring when there is a change of state, that is to say, support or not, during a sample of measurement.

  For this purpose, the subject of the invention is a device for determining a linear position for pressure-sensitive force sensors, comprising a resistive component defining a linear resistor according to a control dimension, one terminal of which is connected to ground. and whose other terminal is connected to a supply potential, E an associated semiconductor layer sensitive to pressure so as to reduce its ohmic resistivity locally at the point where pressure is exerted on this layer, this layer being placed with one face against the resistive component and the other surface being connected to an input of a reference resistor so that pressing on the semiconductor layer connects the reference resistor to a specific point of the resistor linear circuit so as to form a circuit equivalent to a potentiometer, characterized in that it further comprises E switching means allows both to connect the output of the reference resistance alternately and sequentially to the ground and the supply potential, É means for measuring a voltage between the input of the reference resistance and the ground, and É means of calculating a relative position of the support as a function of the voltages measured between the input of the reference resistance and the ground when the output of the reference resistance is connected firstly to ground and secondly to the ground. supply potential.

  SFR5045 25 Moreover, the subject of the invention is a control module for a motor vehicle, in particular for the control of electric windows, mirrors, the position of the headlights, an air conditioning system, a mechanism electric roof opening device, an electric curtain, an audio system or a navigation system, characterized in that it comprises at least one aforementioned device according to the invention.

  Finally, the subject of the invention is a method for determining a linear position for pressure-sensitive force sensors, wherein a resistive component defining a linear resistance according to a control dimension is connected to a ground terminal and with the other terminal at a supply potential, an associated semiconductor layer sensitive to pressure so as to reduce its ohmic resistivity locally at the point where pressure is exerted on that layer, is placed with one face against the resistive component and the other surface is connected to an input of a reference resistor so that pressing on the semiconductor layer connects the reference resistor to a specific point of the linear resistor so as to form a resistor. circuit equivalent to a potentiometer, characterized in that it comprises the following steps E is connected the output of the reference resistor to the mas A first voltage is measured between the input of the reference resistor and the ground. The output of the reference resistor is connected to the supply potential. A second voltage is measured between the input of the resistor of the resistor. reference and mass, the position of the support is calculated as a function of the first and second measured voltages. SFR5045 Other features and advantages of the invention will emerge from the following description, given by way of example, without being limiting in nature. FIG. 1 shows a block diagram of a circuit of a device according to the invention, and FIG. 2 presents three diagrams as a function of time of two measurement voltages and of the support force. on the device.

  An exemplary non-limiting embodiment of the invention will be described later in connection with the accompanying figures.

  FIG. 1 schematically represents the electrical circuit of a device 1 for determining a linear position for pressure-sensitive force sensors.

  In more detail, this device 1 comprises a resistive component defining in a control dimension a linear resistor R of which one terminal 3 is connected to ground and the other terminal 5 is connected to a supply potential. The supply potential has a value of about 5V and is referred to as a resistor. This resistive component may have any structural shape as long as between the two aforementioned connection terminals a linear control dimension equivalent to a linear resistance is defined.

  By linear resistance is understood a conductive material which has a certain ohmic resistance and whose general shape is elongated. In the present example, there is shown a rectangular shape, various elongate shapes, for example arc or serpentine are possible without departing from the spirit of the present invention.

  The device further comprises a pressure-sensitive FSR semiconductor associated layer so as to decrease its ohmic resistivity locally at the location where pressure is exerted on that layer. Preferably, this FSR layer has approximately the same dimensions as the resistive component R. In a manner known for sensors of the FSR type and not shown in the figure, the FSR layer is placed with one face against the resistive component and the another surface being connected, for example via a conductive film deposited on this face with an input of a reference resistor Rref.

  SF R5045 Preferably, the value of the reference resistor is chosen according to the following relationship: 0.25 R Rref where R is the total resistance over its entire control length of the resistive component, and Rref is the resistance of the reference resistor .

  The FSR layer is represented with a double arrow on the circuit to illustrate that its ohmic resistance varies as a function of the support or not on this layer.

  Thus, a support, for example with a finger, significantly reduces the ohmic resistance of the FSR layer at the support zone and the linear layer FSR connects the reference resistance Rref to a specific point 7 of the resistive component R, that is to say at the point of support, so as to form a circuit equivalent to a potentiometer.

  Means 8 for measuring a voltage between the input of the reference resistor Rref and the ground are connected to point 9 of the circuit.

  These means 8 can be made by any suitable circuit. In this case, they are made by an operational amplifier 11 connected in follower mode followed by a control and processing unit 13 ensuring, among other things, the analog-digital conversion of the measured voltage. This unit can be implemented in the form of a microcontroller, an ASIC or an analog / digital converter.

  According to an advantageous aspect of the invention, the device 1 comprises switching means 15 for connecting the output of the reference resistance Rref alternately and sequentially (represented by the arrows 17) to the ground and to the supply voltage Valim.

  The switching of the means 15 is controlled by the unit 13 (see arrow 19 in dashed line) so as to connect during a predefined sampling interval alternately and sequentially the output 16 of the reference resistance to the ground then to the voltage of Vatim power supply.

  The duration of the sampling interval is chosen between 200ps and 1 ms, preferably between 400ps and 600ps, in particular around 500ps. This duration is SFR5045 chosen in agreement with the ergonomic gestures defined for the control of this device and depends on the temporal reactivity that one wishes to obtain.

  The output of the unit 13 is connected to the input of means 21 for calculating the relative position of the support as a function of the voltages measured between the input of the reference resistor Rfef and the ground, when the output of the reference resistance is connected on the one hand to ground and on the other hand to the supply potential.

  For the definition, it is considered that VI is the voltage between the input 9 of the reference resistor Rfef and the ground when the output thereof is connected to the ground, and V2 is the voltage measured between the input 9 of the reference resistor Rfef and the ground mass when the output thereof is connected to the supply voltage Valim.

  The time course of the measurement will be detailed below in relation to FIG. 2.

  Taking therefore the above definitions, the relative bearing position X is determined by the calculation means 21 using the following formula: X = V, Valim (V2 V)] This bearing position is of course a position relative having a value of 1 at the end of the resistive component connected to supply voltage Vaiim and 0 to the end of the resistive component connected to ground.

  In fact, it can be seen in the assembly of FIG. 1 that the resistance between the mass and the fulcrum 7 has the value X * R, whereas the resistance between the fulcrum 7 and the terminal 5 possesses the value (1X) * R.

  Of course, the absolute position can be inferred by multiplying X with the total control length of the resistive component.

  As can be seen, the determination of the support position is advantageously independent of the pressure exerted by a user.

  In order to prevent any unwanted control, the calculation means 21 are adapted so as to calculate only a position if for a predefined number of samples (between 1 to 5 samples), the following condition is fulfilled: Va lin> (V2 VI) SFR5045 By this condition, it is imposed that there is indeed a voluntary support by a user on the FSR layer.

  Optionally, particularly if it is desired to define non-sensitive dead zones at the ends of the resistive component, it may be added as additional conditions to perform the calculation that the voltage between the input of the reference resistor Rfef and the ground is greater than a first threshold value Viseu when the reference resistance is connected to ground and the voltage between the input of the reference resistor Rfef and the ground is less than a second threshold value V2threshold when the reference resistor is connected to the voltage of d The operation of the device according to the invention will now be described with reference to FIG. 2.

  FIG. 2 presents three time diagrams 30, 31, 32 whose time scale on the abscissa is divided into periods of 500ps corresponding to the duration of a measurement sample.

  To facilitate the description, the successive time intervals have been called lj 1j + 1, lj + 2, where j is simply any natural number.

  Diagram 30 has the ordinate force F support on the measuring device. According to the example chosen, the force F is zero during the intervals Ij to Ij + 4, then, there is a support with a certain force during the interval Ii + S and this support force remains constant during the intervals following Ij + 6 to lj + g.

  Diagram 31 shows in full line the voltage V1 between the input of the reference resistor Rfef and the ground when the output thereof is connected to ground and dashed line the fact that the output of Rref is connected to the supply voltage Vai; m for the measurement of V2 [therefore, V1 is not measurable during this period]. The circles 35 with a checker pattern represent the moments of measurement of V1. It can therefore be seen that V1 is measured every millisecond and that the output of Rref is connected to the ground approximately 300 to 100ps before the measuring point 35 allowing the voltage to be measured to be stabilized beforehand.

  It can be seen that up to the moment of support during the period Ij + 5, the voltage V1 is lower than the predefined threshold voltage V1 threshold so that no calculation is performed by SFR5045 the calculation means 21. Then, one can measure a certain value higher than V, threshold at the beginning of the intervals Ij + 6 and Ij + 8.

  Diagram 32 shows in full line the voltage V2 between the input of the reference resistor (Rref) and the ground when the output thereof is connected to the supply voltage Valim and dotted line the fact that the output of Rref is connected to ground for VI measurement [therefore, V2 is not measurable during this period]. This diagram is read in the same way as the diagram 31 and the circles 37 represent the measurement instants of V2.

  Thus, in these diagrams 31 and 32, the alternating connection of ro the output of Rref to ground and to the supply voltage Valim is well observed, as well as an alternation of the measurements VI and V2 which can advantageously be achieved by the same means. measuring 8.

  In addition, until the moment of support during the period Ii + 5, the voltage V2 is greater than the predetermined threshold voltage V2threshold so that no calculation is performed by the calculation means 21. Then, can measure a certain value less than V2 threshold at the beginning of the intervals lj + 7 and lj + 9.

  Advantageously, the device further comprises means 40 (see FIG. 1) for detecting a transient during a measurement sample and means inhibiting, when calculating the position of the support, the taking into account of the measurement values. voltages measured when a transient has been detected during a measurement sample.

  Indeed, the elimination of such transients is important, because in the calculation of the relative position X, taking into account in the calculation of a transient would lead to an erratic position and therefore not desired by the user.

  These means 40 for detecting a transient in a measurement sample and inhibiting means are incorporated in the processing unit 13.

  These means 40 comprise means for comparing the measured voltage between at least two successive samples having the same switching state, that is to say either a switching state connecting the output of the reference resistance to the ground (intervals li + 2k (k being a natural number)), ie a switching state connecting the output of the reference resistor to the supply voltage SFR5045 (intervals Ij + 2k + 1 (where k is a natural number)). A sample is considered to have a transient when the voltage difference with the preceding samples exceeds a predefined difference threshold value.

  According to the example, the voltage V1 measured at the beginning of the interval Ij + 6 is compared with that measured at the beginning of the interval 1 + 4 and since the difference between the two measured voltages is large, the means 40 conclude that there has been a transient in the meantime.

  Similarly, the voltage V2 measured at the beginning of the interval 1 + 7 is compared with that measured at the beginning of the interval 1 + 5 and since the difference between the two measured voltages is large, the means 40 conclude that there was a transient meanwhile.

  Under these conditions the device keeps an output signal corresponding to the previous output signal.

  On the other hand, the voltage V1 measured at the beginning of the interval I1 + 8 is close to or equal to that measured at the beginning of the interval I1 + 6 and the voltage V2 measured at the beginning of the interval lj + 9 is equal to that measured at the beginning of the interval I1 + 7 so that the means 21 calculate the relative position X of support and can repecute it during the interval Ij + 9.

  Thus, a bearing signal is repercussion with a slight delay.

  It is thus clear that this device makes it possible with limited and simple electronic means to make an accurate measurement of the position of a sensor of the FSR type.

  This device is well suited to be used in a control module for a motor vehicle, in particular for the control of power windows, mirrors, the position of the headlights, an air conditioning system, a control mechanism. electric roof opening.

  According to another advantageous development of the present invention, it is envisaged to apply the same measurement method and a similar arrangement to a two-dimensional resistive component, for example of square shape by respectively applying 2 terminals for connection to the supply voltage. and to the mass at the opposite sides of the square. For a measurement of the relative position in X and proceed as described above by supplying the terminals of the resistive component defining this linear control dimension.

  SFR5045 io Then, for the measurement of a relative position in Y, preferably orthogonal to the linear dimension in X, and one proceeds also as described above, but by supplying the terminals of the resistive component defining this linear dimension of control in Y. In this case, it is envisaged to increase the sampling frequency.

  It is further seen that such a solution is very inexpensive, since the entire electrical circuit for measurement, processing and calculation can remain unchanged.

SFR5045 15

Claims (12)

  Apparatus (1) for determining a linear position for pressure-sensitive force sensors, comprising a resistive component defining a linear resistance (R) having a terminal (3) connected to the terminal in accordance with a control dimension. the other terminal (5) is connected to a supply potential (Vaiim), E a pressure-sensitive semiconductor associated layer (FSR) so as to reduce its ohmic resistivity locally to the location where a pressure is exerted on this layer, this layer (FSR) being placed with one face against the resistive component (R) and the other surface being connected to an input of a reference resistance (Rref) so that a support on the semiconductor layer (FSR) connects the reference resistor (Rref) to a specific point (7) of the linear resistor (R) so as to form a circuit equivalent to a potentiometer, characterized in that it comprises further E switching means (15) for connecting the output (16) of the reference resistance alternately and sequentially to ground and to the supply potential (Vaiim), E means (8) for measuring a voltage between input (9) of the reference resistance (Rref) and the mass, and E means of calculation (21) of a relative position of the support as a function of the voltages measured between the input of the reference resistor ( Rref) and the mass when the output (16) of the reference resistance is connected on the one hand to ground and on the other hand to the supply potential (Valim).   SFR5045 2. Device according to claim 1, characterized in that the relative bearing position X is determined by the calculation means (21) using the following formula: X = V 'l Valim (V2 r or - X is the position relative value having a value of 1 at the end of the resistive component connected to the supply voltage Vaiim and 0 at the end of the resistive component connected to ground, - Valim is the supply voltage, - VI is the measured voltage between the input and the reference resistance and the ground when the output of the reference resistor is connected to ground, and - V2 is the voltage measured between the input of the reference resistor and the ground when the output the reference resistance is connected to the supply voltage Valim.   3. Device according to claim 2, characterized in that the means (15) of is switching are configured to connect during a predefined sampling interval alternately and sequentially the output (16) of the reference resistance to the mass and at the supply voltage (Vaiim) 4. Device according to claim 3, characterized in that it further comprises means (40) for detecting a transient during a measurement sample and means inhibiting, when calculating the position of the support, the taking measured voltage measurement values into account when a transient has been detected during a measurement sample.   5. Device according to claim 4, characterized in that the means (40) for detecting a transient comprise means for comparing the measured voltage between at least two successive samples having the same switching state, that is to say either a switching state connecting the output of the reference resistor to ground, or a switching state connecting the output of the reference resistor to the supply voltage (Valim) and in that a sample is considered to comprise a transient when the difference of SFR5045 voltage with the preceding samples exceeds a predefined difference threshold value.   6. Device according to any one of claims 1 to 5, characterized in that the calculation means (21) are adapted to calculate only a position if for a predefined number of samples, the following condition is met: Valim i V2 VI1 - Valim is the supply voltage, - VI is the voltage measured between the input and the reference resistance and the ground when the output of the reference resistor is connected to ground, and - V2 is the voltage measured between the input of the reference resistor and the ground when the output of the reference resistor is connected to the supply voltage Valim.   7. Device according to any one of claims 1 to 6, characterized in that the value of the reference resistor is chosen according to the following relationship: 0.25 R Rref where - R is the total resistance over its entire length of resistive component control, and Rref is the resistance of the reference resistor.   8. Control device according to any one of claims 1 to 7, characterized in that the duration of the sampling interval is chosen between 200ps and 1 ms, preferably between 400ps and 600ps, in particular about 500ps .   9. Control module for a motor vehicle, in particular for the control of power windows, mirrors, position of the headlights, an air conditioning system, an electric roof opening mechanism, a electric curtain, an audio system or a navigation system, characterized in that it comprises at least one device according to any one of claims 1 to 8.   SFR5045 20 A method for determining a linear position for pressure-sensitive force sensors, wherein a resistive component defining a linear resistance (R) in one control dimension is connected to a ground terminal and to the other terminal to a supply potential (Vaiim), a pressure-sensitive semiconductor-associated layer (FSR) so as to reduce its ohmic resistivity locally at the point where pressure is exerted on this layer, is placed with one face against the resistive component and the other surface is connected to an input of a reference resistor so that pressing on the semiconductor layer connects the reference resistor to a specific point of the linear resistor so as to form a resistor. circuit equivalent to a potentiometer, characterized in that it comprises the following steps E is connected the output of the reference resistance to the mass E is measured e a first voltage between the input of the reference resistor (Rref) and the ground, E one connects the output of the reference resistor to the supply potential, E is measured a second voltage between the input of the resistor of reference (Rfef) and the mass, É one calculates the position of the support according to the first and second measured voltages.   Method according to claim 10, characterized in that the relative bearing position X is calculated using the following formula: X = Valim (V2 VI)] or - X is the relative position having a value of 1 to the end of the resistive component connected to supply voltage Valim and 0 to the end of the resistive component connected to ground, SFR5045 - Valim is the supply voltage, - VI is the measured voltage between the input and the reference resistance and the mass when the output of the reference resistor is connected to ground, and - V2 is the voltage measured between the reference resistor input and the ground when the reference resistor output is connected at the supply voltage Valim.   12. Method according to claim 11, characterized in that a transient is detected during a measurement sample and the calculation of the position of the support is inhibited when taking into account the voltage measurement values. measured when a transient looper was detected during a measurement sample. SFR5045