FR2551556A1 - Device for the threshold detection or measurement of a quantity on a rotating object - Google Patents

Abstract

The device provides for the threshold detection or measurement of a quantity on an object rotating about an axis. The aim is to make a reliable measurement for any speed of rotation without material transmission of energy (friction) and without any material rotating energy source (batteries, accumulators). The device comprises two electric circuits, one fixed 1, the other mobile 2, each placed on a supporting surface. The two supporting surfaces have a similar shape with a symmetry axis corresponding to the rotation axis of the mobile object and are placed opposite each other. The fixed electric circuit 1 is supplied with a high frequency current. The quantity in question is detected by a sensor 4 affecting the impedance of the mobile electric circuit 2. The fixed electric circuit 1 has a detector 5 for detecting the variation in the impedance of the mobile electric circuit 2.

Description

"Device for detecting a threshold or measuring a quantity on a rotating mobile object".

 The present invention relates to a device for detecting a threshold or measuring a quantity on an object which is moving in rotation, without contact with said object and regardless of its speed of rotation.

 When 1 one wishes to monitor or measure a quantity 5u1- an object moving in rotation, one generally uses sliding contacts to transmit information from a sensor placed on said object Or, this transmission by contact is unreliable because generally operating conditions are difficult; these contacts must, for example, work in humid atmospheres at high temperatures and the high speed of the rotating moving object may cause disturbances in the transmission of the measurement.

 The invention applies, for example, to monitoring the tires of a road vehicle. Indeed, it is important that the designer of a road vehicle can be warned, for example, of insufficient pressure in one of its tires, so as to avoid accidents due to a burst. On the other hand, the failure of a failure such as a lack of pressure in the tire of an aircraft landing gear can allow the pilot to compensate for this failure during landing and avoid also an addict.

 The invention can be applied in many other fields where it is desired to monitor or measure a quantity from a distance on a rotating object. For example, the invention can be applied to the measurement of different quantities on a rotary kiln.

 The device according to the invention makes it possible to carry out this monitoring or this measurement of a quantity without contact with the moving object and independently of the speed of the latter, this speed possibly being zero, that is to say that the object is at I stop.

 The device according to the invention comprises two electrical circuits, one fixed and the other mobile, each arranged on a support surface, the two support surfaces being of similar shape, having a common axis of symmetry corresponding to the axis of rotation of the movable object and being arranged opposite one another; the fixed electric circuit is supplied with high frequency current, the quantity is entered by a sensor acting on the impedance of the mobile electric circuit and the fixed electric circuit is provided with means for detecting the variation in impedance of the mobile electric circuit.

 In other words, the invention consists in coupling between two circuits, one of which is fixed and receives a high frequency current, any variation in impedance of the mobile circuit being detectable on the fixed circuit.

 In a first embodiment of the invention intended to detect the passage of a quantity through a determined threshold, the mobile electrical circuit is tuned to the supply frequency of the fixed circuit and it comprises a switch actuated by the above-mentioned sensor and the closing or opening of which controls the detachment of the mobile circuit.

 In this embodiment, the passage of the quantity to be monitored by the predetermined aezlil causes the closing or opening of the switch, and consequently an abrupt variation in the impedance of the mobile circuit, this variation in impedance being translated by a variation of the current of the fixed circuit.

 Advantageously, one can have a low consumption indicator such as a light-emitting diode in the mobile circuit which is then arranged to excite said diode when the threshold has been exceeded.

 In another embodiment of the invention which is intended for measuring a quantity, the mobile electrical circuit includes a variable impedance controlled by the sensor such as a resistive sensor.

 Advantageously, in this case, the mobile electrical circuit includes a relaxer or oscillator whose frequency is controlled by the variation of the aforementioned variable impedance. The fixed circuit then comprises an element carrying out a frequency demodulation with a view to providing a signal proportional to the quantity to be measured.

 According to another embodiment of the invention, the mobile and fixed circuits are constituted by printed circuits on the opposite faces of two coaxial discs arranged at a short distance from each other. Advantageously, the two printed circuits are in the form of a spiral.

 The use of printed circuits makes it possible to obtain wide turns, which increases the high frequency coupling effect.

Other characteristics and advantages of the invention rsr + will go from the description which follows, given by way of illustration with reference to the above drawings in which
- Fig.1 is a diagram illustrating the principle of the invention
- Fig.2 shows an example of a circuit used in the present invention
- Fig.3 shows a sensor for detecting a drop in tire pressure
- Fig.4 is a diagram showing an embodiment of a threshold detector according to the present invention
- Fig.5 is a diagram showing an embodiment of a measuring device according to the present invention
- Figs. 6 to 8 show embodiments of the mobile circuit for a measurement of magnitude
- Fig.9 is the diagram of a fixed circuit intended for the measurement of a quantity; and
- Fig.10 shows a fixed disc for simultaneously measuring the speed or the angular position of the movable part.

 - Fig.11 shows an integrated circuit.

Fig. 1 illustrates the principle of the device according to
the present invention. It basically comprises two cir
electric cookers which are arranged one opposite the other
on two surfaces of similar shape, symmetrical with respect to
to the axis of rotation of the moving object on which we have to
monitor or measure a quantity and arranged opposite one
the other. One of these surfaces is linked to the moving object and
the other remains fixed. In Fig. 1 a diagrammatic representation has been made
the fixed circuit 1 and the mobile circuit 2; the circuit
stationary 1 is powered by a generator 3 providing current
at high frequency. The mobile circuit 2 has an impedance
variable 4 controlled by a magnitude sensor to be monitored
ler or to measure. Due to the coupling of the two circuits 1 and
2, any variation in impedance of the mobile circuit 2 can be
detected across fixed circuit 1, for example by varia
tion of the load of this circuit. For this purpose, a detector 5
is arranged in the fixed circuit 1 in order to detect or measure
the variation of the impedance 4.

The use of high frequency current for
supplying power to the fixed circuit optimizes coupling
between the two circuits, i.e. the transmission of energy
between the two fixed and mobile circuits, this high fre
quence is advantageously between 400 KHz and 600 KHZ but
depends above all on the size of the facing surfaces; in one embodiment of the invention it is around 600 KHz.

To increase the coupling of the two circuits, we
places them on two similar surfaces which are symmetrical
relative to the axis of rotation of the moving object, both
circuits being arranged face to face at a relatively distance
low.

The support surfaces can be surfaces of
revolution such as coaxial cylinders; in a fashion
shown in fig. 2, these surfaces are cons
titled by two discs arranged opposite.

 Advantageously, the fixed and mobile circuits consist of printed circuits in the support surfaces, the "turns" of these circuits thus having a large width and being comparable to a flat wire or conductor which improves spreading to the electromagnetic field. and therefore the coupling effect between the two circuits.

 In example e shown in fig.2, each ci-cuit consists of a spiral 11 printed on a support disc; this spiral can be arranged in a crown delimited by two coaxial circles but it can also extend to the center of the support disc when possible. In the example shown, it is a disc used for trausmission. the pressure of a tire and the central part which must remain free corresponds to the passage of the wheel hub.

In the airlock for application to the monitoring of a vehicle tire, the fixed disc can for example be fixed to the brake support such as the caliper support in the case of a disc brake ut the movable disc can be carried by the hub cRe the wheel It is also possible to provide for the movable disc to be directly printed on the rim of the wheel, which has the advantage that 1 assembly of the sensor and of the circuit can be secured to the wheel, which then avoids having to make disconnections and circuit connections when changing the wheel
The distance between the two fixed and mobile electrical circuits must be fairly small; however, if the choice of frequency is optimized and if lares "turns" are used as indicated above, it has been found in an exemplary embodiment that the device according to the invention can function correctly for a distance ranging up to 7 ') at between the two printed circuits.

 Fig. 3 shows an example of a sensor in the case of the application of the invention to a device for detecting a drop in pressure of a tire of a vehicle.

 This sensor is essentially constituted by a kind of hollow plug 21 which is screwed in place of the normal valve plug; it is provided with a circular seal 22 arranged inside and fixed on an internal shoulder 23. The position of this seal 22 when the 7th plug 21 is screwed in fully is such that the plug 22 pushes back the l shell of the valve of the air chamber 2 by means of the part 24 and this seal 22 is walled with an orifice therefore transmitting the pressure of the air chamber to the whole of the interior of the plug 21.

 In the plug 21 is fixed an elastic membrane 25 which acts on a movable piston 26 which can move in translation in a tubular element 27 fixed to the end of the plug 21. An adjustable hollow plug 28 is screwed onto the cylindrical part 27 and carries in its bottom 29 an elastic conductive strip 31 which is pushed back by the end of the piston 26 so as to close or open the contact of a switch carried by a printed circuit 32 on which the strip 31 is fixed and which can be seen the two terminals 33 and 34.

It is understood that the pressure cropping inside the air chamber acts on the elastic membrane 25 which itself moves the piston 26 and thus controls the opening or closing of the switch 32. It can therefore be seen that in the case where it is desired simply to detect a threshold of a quantity, the sensor acts on a switch arranged in the mobile circuit as represented in FIG. 4, which is the electrical diagram of an embodiment of a pressure monitoring device for a vehicle tire. The threshold value can be adjusted by screwing or unscrewing the adjustment cap 28.

Fixed circuit 1 is supplied with high current
frequency by a relaxer circuit of the
Charcoal maker essentially consisting of two scales of
Schmitt 41 and 42 and an inductor 43 in parallel on the first rocker 41. This relaxer makes it possible to obtain a fixed frequency and a high power level.

 In accordance with the invention, the two primary and secondary circuits are tuned to the frequency of the high frequency generator by means of capacitors 44 and 45 and the switch 46 placed in the secondary circuit 2 and controlled by the sensor of the quantity to be monitored by its closing or by its opening the detuning of the secondary circuit 2.

 In the example shown, the secondary circuit includes a low-consumption indicator such as a light-emitting diode 47 which is connected in parallel to the capacitor 45 and the switch 46 is normally closed until the pressure has dropped at a predetermined threshold value for which the switch 46 is open.

 In the example shown, when the quantity to be monitored exceeds a predetermined threshold, the switch 46 opens and the mobile circuit is then tuned; the diode 47 connected in parallel to the capacitor 45 is supplied and lights up. We can therefore see that the mobile object is provided with a warning light which lights up when the quantity to be monitored has exceeded a certain threshold. Furthermore, this sudden variation of l0 <m- impedance of the mobile circuit affects the fixed circuit and it is detected by means of a circuit essentially constituted by a Zener diode 48 and two Schmitt flip-flops 49 and 51 connected in series and controlling a transistor 52 whose ccladuction causes the excitation of another light namely in the example shown a light-emitting diode 53.

 The exceeding of the threshold value is therefore signaled both on the fixed part and on the mobile part.

 Also seen in fig.4 two stabilized power supplies 54 and 55 supplied for example by the vehicle battery, the power supply 54 providing a power voltage of 12 volts and the power supply 55 a logic voltage of 5 volts.

 In the example which has just been described, the passage of the quantity to be monitored beyond the threshold value results in the tuning of the mobile circuit. The reverse can also be achieved, that is to say that, in normal period, the switch 46 is open and it is closed by the sensor when the threshold value is reached. The solution chosen in the example shown makes it possible to have an indicator in the mobile circuit.

The example which has just been described in application to the monitoring of the pressure of the tires of a vehicle relates to the detection of passage by m threshold of a quantity and the detection circuit of the fixed circuit simply comprises a threshold detector essentially constituted by the diode
Zener 48 in the example shown.

 However, the invention also makes it possible to measure a quantity on a mobile object. In this case, the sensor of the quantity considered acts continuously on the impedance of the mobile circuit and the fixed circuit includes a device for detecting variations in this impedance.

 Fig.5 shows the electrical diagram of such a remote measuring device. There are printed circuits 1 and 2, tuning capacitors 44 and 45 and the high frequency generator 3. According to the invention, the sensor of the quantity to be measured acts continuously on a variable impedance such as the resistance 56; this sensor can be a resistive type sensor. In the example shown, this variable resistor is connected between the emitter and the base of a transistor 57 which is connected to a diode rectifier bridge 58, the other two terminals of which are connected to the two terminals of the capacitor 45 so as to constitute a variable impedance across this capacitor 45.

 The fixed circuit comprises a level detector device constituted by a diode 59 connected in parallel to the printed circuit 1 via a resistor 61 and a capacitor 62 in parallel; the voltage collected at point 63 varies according to the value of the resistor 56.

The Applicant has produced a device of this type for which, with a high frequency supply of 10 V at 66 kHz, a voltage difference at point 63 equal to approximately 20 V can be noted when the resistance 50 varies from zero to infinity, the space separating the two printed circuits
and 2 being 3 mm.

 However, the signal detected in the fixed circuit varies substantially over the distance of the two fixed and mobile circuits and, to overcome these variations, in accordance with the invention, the mobile circuit is provided with a rela xor or oscillator whose frequency is controlled by the ariation of the variable impedance and one carries out in the fixed circuit a detection of frequency or frequency modulation. This makes it possible to obtain a signal in the fixed circuit in response to the variation of the variable impedance of the mobile circuit, a signal which is little influenced by the geometric variations in the spacing of the two circuits. FIGS. 6 to 8 show exemplary embodiments of such mobi circuits comprising a relasiatel-r or an oscillator.

 In the embodiment of FIG. 6, the relaxer is essentially constituted by a unijunction transistor 65 controlled by a variable resistor 66 connected between the gate and to drain of this unijunction transistor.

7 shows an exemplary embodiment in which the relaxer circuit is constituted by an integrated circuit known under the reference 7400 N and essentially peddling four AND gates in series 67, 68, 69 and 71; this relaxer circuit is controlled by a magneto-inductance 70, that is to say a variable inductance under the effect of an external magnetic field which is connected between the input of the first and third circuits
AND on the one hand and 1 the input of the second circuit AND on the other hand.

In this case, the put sensor, for example, consists of a movable magnet.

 In the third embodiment shown in FIG. 8, the relaxer consists of an integrated circuit 72 known under the reference 555 and controlled by a variable resistor 73. This integrated circuit 72 is associated with a chemical capacitor 74 which constitutes a reservoir . This embodiment makes it possible to overcome variations in the voltage of the mobile circuit.

 The integrated circuit 555 is universally known for its qualities as a programmer, astable relaxer, bi-stable etc ... Its rising and falling edges in astable multivibrator are of the order of ss, 1sss. It delivers a square signal of excellent quality up to frequencies of 100 KHz and its frequency can be easily controlled by means of a variable resistance (possible resistive sensor) and a capacity.

 Circuit 555 (TA555 at Siemens, SN555 at Texas ... etc ...) is a circuit universally known to specialists.

By a very clever internal organization, this circuit produces very stable oscillations and time delays including a double comparison of voltages at 1/3 of Vcc and 2/3 of
Vcc and a reset logic (RES) are the main culprits.

 As shown in fig. 11, there is mainly a cellar with three equal resistances, R r and R ", which constitute two floating points with the supply voltage (Vcc), at 1/3 and 2/3 of its value; two comparators 101 and 102 which arc a bi-stable flip-flop (Flip / Flop) 103, one of the outputs of which activates a transistor 104 which discharges the delay capacitor 105 which is normally connected to terminal 7. An external reset enables the same transistor to be actuated.With this circuit, one can build monostable or astable circuits in quantity of high performance variants.

 In addition, one of the interesting properties of this circuit, taken advantage of in the present invention, resides in that, even under a low energy supply, the relaxation frequency delivered, in the astable relaxer configuration, is largely independent of the voltage. due to the fact that its tilting is based on a voltage ratio (1/3 and 2/3) and not on its value. The drift due to variations in supply voltage is only 5.10 5 to 10 4 / Volt.

 On the other hand, its temperature stability is excellent, which is appreciable in certain applications. Drifts due to temperature variations between 100 and 150 ppm / OC. Terminals 1 to 8 are earth, trip, output, reset, control, threshold, discharge and power terminals, respectively.

 ta fig.9 shows an embodiment of the fixed circuit comprising frequency demodulation means, this embodiment can for example be used in association with the mobile circuit described in fig.8. We find there the generator 33, the fixed circuit 1 and the tuning capacitor 44. The voltage of this capacitor is demodulated in frequency, then sent to an amplifier 75 then to a shaping circuit 76 before reaching a device of 'display 77.

In the case where the invention is applied to the monitoring of quantities on moving objects, such as pneumatic pressure, it is advantageous that all the fixed circuits 1 are connected to the detection circuit, which allows th achieve significant savings. In this case, as soon as a quantity to be overshooted exceeds the predetermined threshold1 this is detected by the detector which sends an alarm signal such as the ignition of a steering wheel. In the case of road vehicles, the driver can then stop and if the mobile circuits are not fitted with this indicator light, it suffices to go around the tires to detect which one is faulty We can also provide halayag devices for the various mobile circuits --- c- 'determine what is lacking. In this case, this determination can be made without stopping the vehicle, which is interesting for the case of airplanes
According to a variant of the invention, the support surfaces can be used to measure the speed of the mobile object or to identify its angular position. Fig.10 shows an embodiment of a fixed disc intended for such use. We see that the spiral 11 is surrounded by a plurality of peripheral spirals! & which will also be powered by the same high frequency generator. The mobile disc can either have a spiral of the same dimension tuned to the frequency of the high frequency generator, or a metal sector which, due to the eddy currents, will cause a reaction in each of the peripheral spirals 81 when it scrolls past them. . In both cases, there will be an induced modification of the fixed peripheral spirals 81 when the spiral or the metal sector of the secondary circuit passes in front of them.

 It can be seen that the invention makes it possible to carry out, without any contact, the measurement or monitoring of a quantity on a rotating mobile object and that this detection or measurement is done independently of the speed of rotation of this mobile object and also when this object is stopped.

 In the case of the application to monitoring the tires of a vehicle, the invention makes it possible to produce an economical and reliable device which clearly increases the safety of road vehicles.

Claims (12)

 1) Device for detecting a threshold or measuring a quantity on an object which is rotating around an ae, without contact with said object and independently of the latter's speed of rotation, characterized in that it comprises two electrical circuits, one fixed (1) and the other mobile (2), each arranged on a support surface, the two support surfaces being of similar shape, having an axis of symmetry corresponding to 1 axis of rotation of the mobile object and being arranged opposite one another, in that the fixed electrical circuit (1) is supplied with high frequency current, in that said quantity is captured by a sensor (4,21 -34.46) acting on the impedance of the mobile electrical circuit (2), and eri that the fixed electrical circuit (1) is provided with detection means (5, 48, 53, 59-63, 75-76) for detecting the variation in impedance of the mobile electrical circuit (2)  20, Device according to claim 1, intended to detect the exceeding of a threshold by a quantity, character-ized in that the mobile electrical circuit (2) is tuned to the supply frequency of the fixed circuit (1) and comprises a switch (32,46) actuated by said sensor and the setting or opening of which controls the detuning of the mobile circuit (2)  3) device according to claim 1, intended for the measurement of a quantity, characterized in that the mobile electrical circuit (2) comprises a variable impedance (56-58) controlled by the sensor, such as a resistive sensor.  40) Device according to claim 3, characterized e that the mobile electrical circuit (2) comprises a relaxer or oscillator (65-66, 67-71, 72-74) whose frequency is corninandé by the variation of the above impedance .  50) Device according to any one of claims 1 to 4, characterized in that the two support surfaces are constituted by two discs arranged one opposite the other.  60) Device according to claim 2 used for monitoring tire pressure, characterized in that the sensor is constituted by a special plug (21) disposed in place of the valve cap of the air chamber and comprising a switch ( 32) controlled by the pressure of the air chamber.  70) Device according to claim 6, characterized in that the plug (21) is provided with a second plug (28) which is screwed onto the plug (21) so as to allow adjustment of the threshold value.  80) Device according to any one of the preceding claims, characterized in that the high frequency generator (3) supplying the fixed circuit comprises two Schmitt rockers (41,42) and an inductor (43) placed in parallel on the first rocker by Schmitt (41).  9 i Device according to claim 2, characterized in that the primary circuit and / or the secondary circuit are provided with low consumption indicators (47,53) which are excited when the threshold of the quantity to be monitored is reached.  100) Device according to claim 4, characterized in that the mobile circuit comprises an oscillator constituted by a unijunction transistor (65) controlled by a variable resistor (66).  110) Device according to claim 4, characterized in that the mobile circuit comprises a relaxer constituted by four active doors iT (67,68,69,71) in series and controlled by a magneto-inductance (70).  120) Device according to claim 4, characterized in that the mobile circuit comprises an integrated circuit  130) Device according to any one of claims 1 to 12, characterized in that it comprises a device for detecting the speed and / or the angular position of the movable jet.  140) Device according to claim 2, intended for monitoring quantities on several moving objects, characterized in that the different fixed circuits are connected to a single detector.