Photoelectric position indicator for control system

(74) Mandataireis): Cabinet Regimbeau, Cône, Martin, Schrimpf, Warcoin and Ahner.

(54) Photoelectric position indicator, working without contact.

(57) The invention relates to a position indicator working without contact.

In this position indicator constituted by a radiation barrier provided with a transmitter 1 and a radiation receiver 4 and in the radiation path of which is located a medium influencing the radiation flux and an operating circuit 10, two polarization elements 2, 3 are arranged in the path of the radiation so that a relative displacement can be produced between these elements, and the center of rotation of the rotation or tilting movement of the polarization plane of the first polarization element 2 can take any position relative to the center of rotation of the rotation or tilting movement of the plane of polarization of the second polarization element 3.

Application in particular to the adjustment circuits of analog regulation devices.

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FR 2 556 089

D

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The present invention relates to a photoelectric position indicator working without contact and aims to create such a device which can preferably be used to achieve regulation in connection with very fast analo g servo motors or correcting members. Furthermore, the position indicator is suitable for use as an adjustment resistor working without contact and allowing manual or other action to be taken on analog electrical adjustment quantities such as current and voltage.

In the solutions known from the prior art, variable photoresistor illumination is carried out using diaphragms or light corners (sensitometric corners), which makes it possible to influence the radiation flux of the radiation barrier ( photoelectric relay. The photoresistors however have a certain slowness so that they are not suitable for rapid cycles of displacement. The diaphragms and the light corners cannot be adjusted precisely without an expensive mechanical device and they are also suitable only for photoelectric cells of larger size, such as for example relatively slow photoresistors. Furthermore, such devices have no fixed fundamental attenuation. The radiation receiver receives light, through the diaphragms, on a variable surface, and therefore the photoelectric current does not depend on the incident illumination intensity, but is a function of the geometry of the illuminated surface. Such a device is described in the patent application filed in the United States of America No. 3,358,150. The output quantity however depends on a large number of technical parameters. Adjusting and maintaining, in operation, the output variable at a constant value is therefore very difficult and expensive.

The present invention aims to provide an economical and simple solution from the technical point of view for a position indicator working without contact and comprising usual commercial components, in order to guarantee multiple employment possibilities for the position indicator. .

The object of the present invention is to develop a photoelectric position indicator working without contact and in which on the radiation path between 1¹The radiation emitter and the radiation receiver are arranged with diaphragm elements which deliver the precise reproducible output quantities and have a low mass, so as to thus provide great speed in the case of adjustment operations.

This problem is solved in accordance with the invention thanks to the fact that a first and a second polarization element are located on the path of the radiation from the radiation barrier. A relative displacement can be obtained between the first and second polarization elements . The center of rotation of the rotation or tilting movement of the plane of polarization of the first polarization element can be in any position relative to the center of rotation of the rotation or tilting movement of the plane of polarization of the second polarization element. The two polarization elements can be arranged so that they can rotate and / or tilt. However, it is also possible to produce a fixed polarization element and the other polarization element capable of being able to rotate and / or tilt. The centers of rotation or tilting of the polarization elements can be located at the center or outside the center of the radiation path. The radiation barrier and the polarization elements are surrounded by a light opaque housing. The polarization planes of the polarization elements form an angle of 45 ° between them, in the middle position of the adjustment range of the position indicator.

The radiation emitter and the radiation receiver can also be arranged side by side and be separated from each other by a strip made of a material opaque to light. In this case a trihedral reflector is arranged opposite the radiation emitter and the radiation receiver. The first polarization element is located on the path of radiation in front of the radiation emitter and the second polarization element is located on the path of radiation in front of the radiation receiver. As a radiation emitter, a conventional light source can be used. Preferably, a GaP emitting diode emitting in the green is used. As a radiation receiver, a silicon cell forming a sensor is used. for this purpose it is preferable to use a silicon planar npn phototransistor.

The polarization elements are formed by polarization filters, which are preferably constituted by polarization strips, and by housings for these polarization strips. The polarization lamellae have a quasi-crystalline structure. They are preferably made with the same shape and have a recess or a spout and the recess or the spout is arranged in the direction of the polarization planes. To accommodate the polarization strip in the polarization elements, it is provided at the level of the housings, nozzles or recesses which form an angle of 45 ° between them, in the middle position of the range of adjustment of the position indicator. .

An operating circuit, which consists of an operational amplifier whose inverting control input and output are connected by a parallel resistor, is connected, at the inverting control input of the operational amplifier to the voltage positive service via the radiation receiver. This positive operating voltage also supplies the radiation emitter on the anode side. The cathode of the latter is connected to ground via a current limiting resistor.

The usual light sources and also the light from a luminescent diode emit natural light which is polarized in all possible planes. The polarization planes of different wave trains are distributed uniformly on average in all directions in space. Due to polarization, only the fraction, whose light vector (the amplitude of the transverse wave) is located in a preferential plane, is transmitted. We speak in this case of a linearly polarized light. Polarization filters are used in the field of photography to suppress parasitic reflections (Brewster's law) and in liquid crystal ICD elements to identify the polarization of liquid crystals. If, in accordance with the invention, for a position indicator working without contact, two polarization elements are placed one behind the other in the radiation flux of a radiation barrier, there is an attenuation of the light , which is the lowest when the polarization planes of the two polarization elements are oriented in the same way. Otherwise, the weakening of the light is maximum when the planes of the polarization elements form an angle of 90 ° between them. The intensity of illumination E, which is captured behind two filters whose polarization planes are turned by the angle, is E = C.cos²&lt;X ·

The maximum variation in brightness for a rotation of appears for 45 ° and this is why it is necessary to place in this location the center of the adjustment range of the position indicator. If at least one of the two polarization filters is then rotated relative to the other, a corresponding photoelectric current can flow in the radiation receiver, depending on the angle set between the polarization planes of the two filters . If, for reasons of space, the position indicator is placed on movable members which effect only slight angular displacements, the second strip can be arranged, according to the invention, on a movable member which, at during its angular displacement, first moves in the opposite direction, which doubles the relative angle. The evaluation of relative angular displacements and only of such displacements brings about notable advantages for the adjustment of the position indicator: the angular displacement of a lever is identical at all points, in the center of the position crcrrroe at its end. Transversal displacements, of the type such as those appearing in the case of crank drives as a function of the arc arrow, are not detected and therefore distort the result of the position measurement.

The possibilities of adaptation to the construction data, from which the position indicator must perform its measurement task, are extraordinarily great thanks to the chosen principle of the photoelectric position indicator using two polarization filters. Thus one can freely choose the positions of the centers of tilting and rotation of the polarization elements. When choosing the components for the radiation barrier, it is important to match the range of the maximum spectral emission of the radiation receiver. With a GaP emitting diode emitting in the green, for example VQA 25 serving as an emitter and with a silicon cell forming a sensor, for example SP 105, serving as a receiver, the radiation barrier is adapted as well from the point of view of the photoelectric current obtained only from spectral sensitivity. The use of a conventional incandescent lamp is in principle possible, but does not provide an advantageous solution because of its size and its short service life. Likewise it is not recommended to use infrared light since the polarization filters to be manufactured for this wavelength are much more expensive.

For polarization filters, preferably use lamellae forming polarization filters in the position indicator. Thanks to the insertion of herapathite crystals into the cellulose film, these lamellae are oriented, during the subsequent rolling, in a direction such that they receive a quasi-crystalline structure. One can easily think of also using the polarizing lenses used in photography. However, these glasses are very large and cannot be easily shaped to the position indicator. The polarization filter plates, of the type used to display numbers and characters on LCD elements or elements of liquid crystal display devices, are remarkably suitable for the position indicator. These strips can be cut in any shape and can be inserted, in a manner preventing any reversal, in the housings of the polarization elements of the indicator, which fixes the relative position of the polarization planes of the polarization elements.

The radiation flux, which is then correspondingly attenuated by the relative angular position of the polarization planes of the polarization elements, is converted in the operating circuit into a voltage proportional to the radiation flux and therefore the radiation barrier is decoupled from the downstream circuit, for example from the adjustment circuit.

The photoelectric position indicator according to the invention does not require, as indicated above, any kind of development of a special photosensitive laminate material. The use of components from mass production keeps the price at an extremely low value. The attenuation provided by the polarization filters, which is always constant at least in the case of a charge, guarantees a constant dependence of the radiation flux on the relative angular position of the polarization planes of the polarization filters and consequently also vis-à-vis the secure position me2556089 of a mobile mechanical device connected to the position indicator.

Other characteristics and advantages of the present invention will emerge from the description given below taken with reference to the appended drawings, in which:

- Figure 1 is the representation of the principle of an exemplary embodiment showing an arrangement of the polarization elements;

- Figure 2 shows an assembly of the photoelectric position indicator according to the invention;

- Figure 3 shows the position of the center of rotation or tilting of a polarization element, located outside the center of the radiation path;

- Figure 4 shows the position of the centers of rotation or tilting of the two polarization elements, outside the center of the radiation path;

- Figure 5 shows an angular offset between the polarization planes of the polarization elements;

FIG. 6 represents an exemplary embodiment of the photoelectric position indicator, in which the two centers of rotation of the polarization planes are located outside the center of the path of the radiation;

- Figure 7 shows a. exemplary embodiment of a photoelectric position indicator comprising a fixed polarization element and a mobile polarization element;

- Figure 8 shows a diagrammereproducing the measurement curve between the angular offset and the output voltage ü_QÜT for the photoelectric position indicator according to the invention j

- Figure 9 shows embodiments, according to the invention, of polarization elements; and

- Figure 10 shows an embodiment of a photoelectric polarization indicator, in which emitters and receivers of radiation are arranged side by side.

The operating principle of the photoelectric position indicator will first of all be better canary using representations of FIGS. 1 and 2. It consists in that the photosensitive radiation receiver 4 is irradiated by a flux of variable radiation, which causes the appearance of a photoelectric current proportional to the incident radiation flux. This photoelectric current is then transformed into an output voltage via an evaluation circuit 10, by means of an operational amplifier 7. Simultaneously this circuit ensures electrical decoupling from the downstream circuit.

In the case of the photoelectric position indicator according to the invention, represented in FIG. 1, the polarization elements 2 and 3 are arranged so as to be orientable relative to each other on the path 5 of the radiation between the radiation emitter 1 and the radiation receiver 4. The centers of rotation of the polarization planes of the polarization elements 2, 3 are located, in the case of this exemplary embodiment at the center of the path 5 of the radiation, which is indicated by the axis xx.

In Figure 2 there is shown an assembly of the photoelectric indicator position according to the invention. In this arrangement, the operating circuit 10, which is constituted by the operational amplifier 7, whose inverting input is connected by a resistor 6 to the output of the operational amplifier and whose non-inverting input is connected to the ground, is connected via the inverting input of the operational amplifier, to the anode side of the radiation receiver 4, the cathode of the radiation receiver being connected to the positive operating voltage.

In FIG. 2, the polarization elements 2 and 3 are arranged, from the point of view of the principle, between the radiation receiver 4 and the radiation emitter 1. The anode of the radiation emitter 1 is placed at a voltage positive service and its cathode is connected to the resistor 4 of current limitation, which for its part is connected to ground.

The figure. 3 shows an exemplary embodiment in which the polarizing element 2 is mounted, so as to be orientable, around the center of rotation on the y / y axis, that is to say that it is located in- outside the center of the x / x axis and therefore outside the radiation path 5, in which the polarization element 3 is mounted fixed.

Another embodiment shown in FIG. 4 shows that the center of rotation of the polarization element 2 is mounted so that it can rotate on the y / y axis and that the center of rotation of the polarization element 3 is arranged so that it can rotate on the z / z axis, outside the x / x axis and therefore outside the center of the path of the radiation.

In FIG. 5 the polarization element 2 is mounted so that it can rotate on the y / y axis and the polarization element 3 is mounted so that it can rotate on the z / z axis. On the polarization elements 2, 3, the polarization planes 11, 12 are indicated by hatching. When the polarization elements 2, 3 rotate around the y / y and z / z axes, the polarization planes 11, 12 assume the reciprocal angular position corresponding to the mechanical position, which causes the appearance of a flux of radiation, obtained as a function of the angle of the polarization planes 11, 12, on the radiation receiver.

In the embodiment of FIG. 6, the centers of rotation of the two polarization elements 2, 3 are arranged on the axis z / z and on the axis Y / y, outside the path 5 of radiation. The polarization element 2 is connected to the shaft 16. The polarization element 3 is also rigidly mounted on the shaft 15. The shafts 15 st 16 are journalled in the housing 17 and are coupled to each other by the inter2556089 median of toothed sectors 13 and 14. Therefore, during the adjustment movement of the polarization element 2 by means of the shaft 16, to which the toothed sector 14 is rigidly fixed, the polarization element 3 is also moved through the toothed sector 13. Depending on the choice of transmission between the toothed sectors 13 and 14, it is possible to detect and evaluate different adjustment angles or different adjustment channels using the photoelectric position indicator according to the invention.

In the embodiment of FIG. 7, the polarization element 2, which is fixed by a bar 19 to the shaft 20, is mounted iwhilp at the center of the path 5 of the radiation. The polarization element 3 is fixedly mounted on the housing 18. In the case of this arrangement, the adjustment angle is determined as a function of the shaft 20 and is transmitted by the intermediary of the bar 19 to the polarizing element 2. In the case of the device of FIGS. 6 and 7, the angular positions of the two polarization elements 2, are evaluated respectively by means of a circuit which is shown in FIG. 2, and it follows that a voltage is available at the output of the operational amplifier 7. A preferred embodiment variant of the photoelectric indicator is obtained in this position when a GaP emitting diode emitting in the green is used as radiation emitter 1. For this purpose, it is particularly well suited to use as a radiation receiver 4 a silicon cell forming an SP 105 sensor. It is within the scope of the invention to use, in place of the described combined assembly of components of the radiation barrier, also a light emitting diode emitting in the red as a radiation emitter and a phototransistor for the visible range, for example SP 212. In the case of this combined assembly, the incident intensity of the radiation flux is even much higher, and therefore the dependence on the temperature is also much higher.

Furthermore, the photoelectric current is a non-linear function of the illumination intensity, as operational amplifier 7 it is advantageous to use, in both cases, types of transistors designated under the term of BiFet, since in the case of these transistors, the residual input currents are significantly lower than in the case of other operational amplifiers. In the case of the use of the preferred components and of a corresponding coating (not shown) of the housing for the radiation barrier devices according to alternative embodiments, there are optimal conditions for obtaining a photoelectric position sensor conforming to the invention having high sensitivity. The variant embodiment indicated last can be carried out in a very advantageous manner in the case of the practical application of the idea of ​​the invention.

FIG. 9 shows polarization elements 2, 3 in accordance with the invention. Since the recess or the spout is provided on the edge, there can be no reversal during the insertion of these elements in the housing of the position indicator. The housings of the polarizing elements 2, 3 are shaped so that in the middle position of the photoelectric position indicator, an angular offset of 45 ° is provided between the two nozzles or the two recesses.

FIG. 10 represents a device in which the radiation emitter 1 and the radiation receiver 4 are arranged side by side. If a trihedron reflector 22 is used, the optical refractive index of which does not, in accordance with Brewster's law, rotate or polarize the incident light in the plane of polarization, this device can advantageously be used to many applications. To form a screen between the radiation emitter 1 and the radiation receiver 4, a strip 21 made of a material opaque to light is used. This arrangement provides a very flat form of construction of the photoelectric position indicator.

It is within the scope of the present invention that the mechanical construction of the photoelectric position indicator can differ from the embodiments shown and can take any form.

In FIG. 8 is represented by a diagram the relationship between the angular position of the polarization planes of the polarization elements and the intensity of illumination on the radiation receiver. It is a part of the function in square cosine, which represents the dependence of the intensity of illumination or of the output voltage delivered Uq_üt with respect to the relative angle oi between the planes of polarization of the polarization elements. This curve 9 can be considered as approximately linear in wide domains.

On the basis of FIG. 5, it can clearly be seen that for the angular position X = 0 °, the polarization planes are parallel, which means that the output voltage has its maximum value since a maximum flux of radiation can cross the polarization elements 2, 3. For the angular offset of 90 ° between the polarization elements 2, 3, there is an extinction of the light. No radiation flux can circulate and the output voltage takes its minimum value. Obviously, the middle position of the position indicator should be set to = 45 °.