Multiplex measuring device with a plurality of sensors.

The present invention relates to a measuring device comprising two or more sensors for one or more measured variables, these sensors being arranged to be connected to a power source and to provide, on the output conductors, function of the signals quantity to be measured, the device comprising further transmission devices and processing sensor output signals.

The invention applies more particularly to an indication of the absolute angular position of a shaft device, having position sensors rotary member, the rotary member of a first sensor being mechanically coupled with said shaft, and the rotary bodies or other sensors being successively coupled with that of the first sensor via gears, these sensors being arranged to be fed by a sinusoidal or pulsed voltage, and for providing output signals depending on the angular position their rotary member.

In such devices, the sensors must be connected on the one hand, to a supply source and, on the other hand, at one of their output signals processing device. In the case of the use of inductive sensors, e.g. resolver type these output signals appear at the terminals of two phases and therefore require up to four wires for each sensor for transmission to the processing device usually located at a distance sensors. In the application to the measurement of the angular position of a shaft, the number of sensors used depends on the device of the working range, that is to say, the maximum number of revolutions of the input shaft than the device to specify, so that a large number of connecting conductors is often necessary, which is in practice a considerable drawback.

To limit in the latter case the number of necessary connecting conductors can be used between the various sensors of the high reduction ratio gear, to reduce the number of sensors required for a particular field of work. However, this solution requires sensors and high precision gears, and therefore results in relatively high cost of the entire device.

The invention aims to provide a device of the type mentioned at the outset, wherein the number of connecting conductors between the sensors and a signal processing device and a supply device can be significantly reduced, while allowing to reduce also, in some cases significantly, the cost of the entire device.

For this purpose, the device according to the invention comprises a feed assembly and multiplexing connected to said sensor and connected, moreover, on the one hand by means of a number of drivers at least approximately equal to that of said output conductors a single sensor, the signal processing device and, on the other hand, to a supply and multiplexing command device.

The number of connecting conductors thus becomes independent of the number of sensors. In the above particular case of the device for measuring the angular position of a shaft by means of inductive sensors, the number of the sensors can, for example, be increased in order to allow the use of lower reduction ratios, or more generally lower numbers of teeth, and therefore significantly less costly gears. On the other hand, only the first sensor coupled directly to the input shaft of which one wants to measure the angular position, generally requires, in this case, high accuracy, that is to say that desired for the indication of the angular position of a revolution of the shaft, the other sensors used to indicate the number of complete revolutions of the shaft between a starting position and a final position, needing only a sufficient precision to determine the number of revolutions, precision exigency that diminishes with the reduction ratio used. However, it turns out that very economical structure sensors may be constructed, for example according to the principle of variation of the coupling between a primary winding and secondary windings in phase quadrature using a movable passive sensors which are capable of providing the same size as output signals of inductive sensors of the type resolver significantly more expensive.

According to a particular embodiment of the device according to the invention, the addressing of different sensors for multiplexing is performed in an extremely simple manner by means of a coding at the supply voltage, requiring and the two power supply conductors for the transmission of the address control. Various preferred embodiments of this device are described in claims 2 to 6.

The objects, advantages and features of this device will emerge, moreover, more clearly from the following embodiment of a description, shown in the accompanying drawing in which<ul><li>Fig. 1 is an overall diagram of a device according to the invention for measuring the angular position of a shaft,</li><li>Fig. 2 is the diagram of the supply and multiplexing device control part of the apparatus of FIG. 1, and</li><li>Fig. 3 is the diagram of the feeding assembly and multiplexing part of the device of Fig. 1.</li></ul>

According to Fig. 1, an input shaft 1, which is meant to indicate the absolute angular position, that is to say the position from a starting position, including the number of complete revolutions made between these positions, is coupled mechanically C1 with a first position sensor which is constituted, in this case, by a resolver. This sensor C1 is supplied by two conductors indicated generally by MC1 and provides output signals on four conductors indicated generally by SC1.

Fig. 1 further shows, by way of non-limiting example, three other sensors C2, C3 and C4 which may be resolvers but are preferably constituted by inductive sensors passive movable member providing output signals the same format as a resolver and can therefore be treated with the same converter device. The rotatable members of these sensors C1 to C4, mounted on respective axes 2,3,4,5, are coupled successively, that is to say each with that of the previous sensor, by means of gears, for example of 'reduction gears such as 6.7 between C1 and C2, between C2 and C3 8.9, and 10.11 between C3 and C4. Their reduction ratio can be 16: 1, for example, which enables these gears in a very economical way compared to having gears, for example, ratios of 100: 1, as usually in qu'utilisés such a device. In the case of a coupling of the kind between Master-Vernier sensors, it is advantageous to use, similarly, the numbers of teeth lower than those of conventional devices of this type, for example by making Master-Vernier reports 4:17 p.m..

The supply conductors C2-C4 sensors and the conductors connecting their output terminals in a feed assembly and multiplexing 12 are designated, respectively, MC2, MC3, MC4 and SC2, SC3, SC4, similarly to those of the sensor C1.

The set of supply and multiplexing 12 is installed close to the sensors, for example on a machine such as an industrial robot, and is connected to a signal processing device shown schematically by the blocks 13,14, and that a feed device and multiplex control shown by blocks 15,16,17. As shown in Fig. 1, this connection is achieved, firstly, by four conductors S1, S2, S3, S4 and, on the other hand, by two conductors M1, M2, therefore by six conductors in total. The signals appearing on the conductors S1 to S4 are first processed in block 13, consisting essentially, in the case illustrated, by an analog-digital R / D converter to convert analog signals resolver format into digital signals, which will then be processed in an evaluating device 14 to determine the angular position of the input shaft and / or the speed of rotation of this shaft.

A supply current source for the sensor and the assembly 12 is indicated by the block 15. It provides, via two conductors R1, R2, a sinusoidal or pulsed voltage to a coding circuit 16 connected by drivers M1, M2 in all 12.

Selection of C1 to C4 sensors for transmitting corresponding output signals, multiplex, the device 13 is performed under control of address signals provided on conductors A1, A2, A3, A4, as shown schematically in Fig. 1, by a control device 17 also connected to the operating device 14.

Fig. 2 shows the diagram of the circuit 16 according to an exemplary embodiment, for superimposing the alimention voltage applied between R1 and R2 different offset voltages respectively defined by the level of DC voltages selectively applied to the conductors A1 to A4. The superimposed DC voltages determined, for example, by the choice of resistors R1 to R6 of FIG. 2 preferably have, a substantially smaller value than the supply voltage but must, of course, be sufficient to allow easy discrimination. It should also be noted that the potential of M1 and M2 are floating.

Fig. 3 is a simplified diagram of a feed assembly and multiplexing 12 used in the device of Fig. 1. The voltage applied via the conductors M1 and M2, firstly, rectified and filtered by circuits 18 to 21, to obtain a continuous supply voltage Vcc, in particular for feeding analog multiplexers represented by block 22.

The voltage on M1, M2 is additionally provided to the various sensors via MC1 to MC4 conductors, a filter being provided to remove the DC component by means of a high-pass filter 23 which, in this example can be mounted downstream of the first sensor C1 diet.

Furthermore, the voltage on M1, M2 is filtered by a low pass filter 24 for applying the offset voltage to a discriminator 25 levels shown schematically in Fig. 3. This discriminator provides addressing inputs A 1 ', A 2', A 3 ', A 4' a corresponding address signal, which shows the output signals from the respective sensor on the transmission conductors S1-S4 .

In the case of a sensor supply by a pulse current, the detection of the DC offset voltage is preferably effected in the interval between two consecutive pulses.

It should be noted that, generally, the multiplexing according to the invention hardly complicates the overall structure of this device, since it allows the use of a single analog-digital converter or other device signal processing. In contrast, the use of a minimum of connecting conductors, and in particular in the case described by way of example, the possibility of using simpler and more economical sensors, and gear relatively small number of teeth, provides decisive technical and economic advantages.