DE102013014282A1 - Position measuring system and method for determining position - Google Patents

Abstract

A position measuring system (1), in which a plurality of sensors (9) are arranged in a fixed positional relationship to one another and a measurement object (3) is movable along a defined path relative to the sensors (9), is characterized in that for each sensor (9 ) a measuring cell is provided and the sensors (9) can be coupled sequentially to at least one output bus, wherein for the sensor (9) within its measuring cell, a logic circuit for coupling at least one output of the sensor (9) is provided to the associated output bus. The invention further relates to a method for determining position with such a position measuring system (1).

Description

The invention relates to a position measuring system in which a plurality of sensors are arranged in a fixed positional relationship to each other and a measurement object along a defined path is movable relative to the sensors, and a method for determining position with such a position measuring system.

In practice, in many applications there is a requirement to determine the position of one object relative to another. For example, there is a desire in hydraulics to detect the changing position of the piston rod in a piston rod-cylinder unit. For this purpose, various solutions have been proposed in the past, for example, consist in attaching a scale on the piston rod, which is detected and evaluated either by an operator or by an optical system.

For automated position determination and reed contacts are used, which are arranged in a "chain". Reed contacts are electrical components in which electrical contact tongues are welded in a glass bulb. Under the influence of a magnetic field, the contact tongues approach and close a circuit. With a plurality of reed contacts arranged in a row or chain, a relatively coarse position measurement is thus possible.

In addition, the rights holder sells a linear displacement sensor called "HLT 1000", which works according to the physical principle of magnetostriction. According to this measuring principle, a path or a speed is detected based on a transit time measurement. In this way, a high-precision determination of a position is made possible. The sensor operates without contact and wear and is available in one embodiment in a pressure-resistant stainless steel housing, which is completely integrated in a piston rod. The measuring signals can then be evaluated with various systems that are freely available on the market.

Another linear displacement sensor in rod design is offered under the name "HLT 2100" by the owner of the protective rights. Here, a ring magnet is slidably mounted on a pipe section. The position of the ring magnet relative to a sensor located in the tube is detected and evaluated.

Many or most magnetic-based position measuring systems currently available have been found to provide an improved compromise between accuracy and cost.

The invention is therefore based on the object to show a position measuring system and a method for determining position with such a position measuring system, which allow high accuracy in the position measurement at low cost.

A solution of the objective part of this task consists in a position measuring system having the features of claim 1. Advantageous embodiments of the position measuring system are apparent from the dependent claims 2 to 14. A solution of the procedural part of the object consists in a position determination method with the method steps of claim 15.

According to the invention, a measuring cell is provided for each sensor and the sensors can be coupled sequentially to at least one output bus line, wherein a logical circuit for coupling at least one output of the sensor to the associated output bus line is provided for the sensor within its measuring cell.

The solution according to the invention has the advantage that due to the sequential coupling of the sensor to the output bus line and thus to the downstream unit, an output bus line used in common with the other sensors can be used. This brings a considerable simplification of the structure of the sensor and thus a great savings with it. It is no longer necessary to provide a separate data line for each sensor to the downstream evaluation unit. This saves space and material and reduces the system's susceptibility to errors. This allows any number of sensors to be strung together. The effort required to connect the sensors is very small and independent of the number of sensors. Another advantage is that due to the simplification of the structure more sensors can be used to detect the position of the measurement object. In this way, an optimum of the ratio of accuracy to number of sensors can be achieved or selected depending on the intended use.

Particularly advantageous with the logic circuit both outputs of the associated sensor can be coupled simultaneously to the output bus lines. This allows a complete decoupling of the sensor from the output bus lines, so that the signals transmitted on the output bus line of another sensor can not be adversely affected.

In addition, at least one input of the assigned sensor can be coupled to an input bus line with the logic circuit. This makes it possible to detect and evaluate not only the output voltage but also the input voltage at the respective sensor. In this way, the accuracy of the position measurement is again significantly increased. It was advantageously recognized that due to the fact that there are hardly any parasitic capacitances, the source is low-impedance and the measurement is high-impedance, the time from the coupling to the input voltage until the sensor generates a stable output signal is very short, ie towards zero preferably less than 5 milliseconds, more preferably less than 1 millisecond. Therefore, it is advantageous in this case, not to energize all sensors evenly, but only the one that is currently being evaluated. This, in addition to improving precision, results in significant energy savings.

Advantageously, with the logic circuit both inputs of the sensor can be coupled simultaneously to the input bus lines. Again, it has been found to be advantageous to decouple the sensor from the input bus lines in order not to risk falsification of the measurement results by currently not activated sensors.

With the logic circuit, the at least one input and the at least one output of the associated sensor can be coupled to the respective bus lines at the same time. The complete decoupling of the sensor from the bus lines represents the optimum in precision and energy efficiency.

The measuring cells can be arranged in a row spaced from each other, wherein advantageously individual measuring cells are separable starting from a free end, without affecting the functionality of the measuring system. In this way, the position measuring system can advantageously be shortened and thus adapted to an installation situation in a region to be monitored. The position measuring system can therefore be offered with a uniform length and cut to length as required, i. H. sawn off, cut off or otherwise separated, without the need for further measures. This brings considerable savings in the production and distribution of the position measuring system, since only one embodiment has to be designed, manufactured, stored and delivered.

The logic circuit may advantageously be a flip-flop. A flip-flop is a fundamental circuit of digital technology that has proven itself over the decades. The flip-flops of the individual measuring cells can be switched as a shift register. This makes it possible to connect the measuring cells sequentially one after the other to the respective bus lines. The circuit of the individual flip-flops is ensured by a uniform clock signal, which is forwarded via a common clock line to the flip-flops.

A measuring cell, which includes a sensor cell and a logic circuit for coupling the sensor to the output bus lines and optionally input bus lines, may be arranged on a microchip. In this way, a high degree of integration of components in a small space is achieved. In addition, the assembly effort can be reduced because fewer components must be installed. Advantageously, a plurality of measuring cells can be arranged on a microchip spaced from each other.

Furthermore, an evaluation unit for evaluating the signals transmitted on the output bus lines can be present. This evaluation unit can advantageously be used for evaluating the signals of the output bus lines and the input bus lines. In this way, the output voltage and the input voltage of a sensor, or their amplitudes, can be set in relation to each other to determine the most accurate position possible.

At least one of the input bus lines may have a series resistor or an adjustable current sink for current limitation. The internal resistance of the sensor may vary depending on temperature and aging and in particular be too low to have taken in itself a sufficient current limit. Thus, overloads of the sensors are avoided by the series resistor.

The input bus lines are advantageously connected to one another via a current source or via a voltage source, wherein the polarity of the current source or the voltage source can be switched. This makes it possible to compensate for any offset errors emanating from the source or a downstream unit. Thus, low cost components can be used without adversely affecting accuracy, or higher accuracy can be achieved with higher quality components.

The sensors may be advantageous Hall sensors. In addition, other magnetic field sensors can be used within the scope of the present invention.

The measuring object is preferably a magnet. The magnet is preferably in the form of a Ring magnet executed, since this has a magnetic field, which changes in coaxial sensors significantly only in one dimension.

• • Einlesen der Sensorsignale;
• • Korrigieren der Sensorsignale;
• • Auswerten von primären Merkmalen zur groben Positionsbestimmung;
• • Auswerten von sekundären Merkmalen zur Feinabstimmung der Positionsbestimmung;
• • vorzugsweise, Korrigieren von Nichtlinearitäten;
• • Auswählen einer aktiven Zone; und
• • Bestimmen der Position des Messobjektes.

The position determination method according to the invention has the following seven steps:

• • reading the sensor signals;
• • correct the sensor signals;
• • evaluation of primary features for coarse positioning;
• • Evaluate secondary features to fine-tune position determination;
• Preferably, correcting nonlinearities;
• • selecting an active zone; and
• • Determining the position of the measurement object.

The sensor signals must first be determined and corrected for an offset and a sensitivity in a subsequent step. The following steps of evaluating primary and secondary features and correcting non-linearities can be done in several ways.

The primary features are understood to be those properties of a magnetic field that can be uniquely identified with the aid of sensors, for example the maximum or minimum field strength or a maximum or minimum gradient. From the primary features, rough position information can always be derived.

• • Sie spiegeln die Bewegung des Messobjektes um das identifizierte primäre Merkmal herum wieder.
• • Sie sind zwischen zwei primären Merkmalen skalierbar.
• • Sie haben einen stetigen und streng monotonen Verlauf zwischen zwei primären Merkmalen.
• • Sie sind tolerant gegenüber Störeinflüssen (beispielsweise durch Relativierung).
• • Sie sind in der Nähe eines primären Merkmals linear abhängig von der Position des Messobjektes, wobei etwaige Nichtlinearitäten entweder vernachlässigt oder korrigiert werden können.

Secondary features are unique, especially in the environment of a primary feature. They are used to interpolate the position of the measurement object, in particular when the measurement object is located between two sensors. The secondary properties have the following properties:

• • They reflect the movement of the measurement object around the identified primary feature.
• • They are scalable between two primary features.
• • They have a steady and strictly monotonous course between two primary features.
• • They are tolerant of interference (for example, by relativization).
• • They are linearly dependent on the position of the measurement object in the vicinity of a primary feature, whereby any nonlinearities can either be neglected or corrected.

On the basis of the evaluation of the primary and secondary features, the position of the measurement object can then be determined with high accuracy.

The invention is explained in more detail with reference to exemplary embodiments illustrated in the figures. Show it:

1 a perspective view of the position measuring system according to the invention;

2 a plan view of the position measuring system of 1 ;

3 a cross section along the line AA in 2 ;

4 a block diagram of a sensor cell;

5 a block diagram of a measuring cell;

6 a block diagram of an interconnection of the measuring cells; and

7 a block diagram of an alternative, advantageous embodiment of the measuring cell.

In the 1 to 3 is the position measuring system according to the invention 1 shown in total in several views. A measurement object 3 in the form of a ring magnet is on a tubular element 5 arranged axially displaceable. In the tubular element 5 is a circuit board 7 with spaced-apart sensors 9 inserted. The sensors 9 thus form a row-like sensor chain 11 out. The number of sensors 9 in the sensor chain 11 is in principle arbitrary. The sensors 9 are arranged in a row, with individual sensors 9 starting from a free end 13 can be separated without the functionality of the position measuring system 1 in general. At the other free end 15 the board 7 there is a control unit 17 in the form of a microprocessor with an evaluation unit 19 via appropriate connections 21 can be coupled. In principle, it is also conceivable to use the evaluation unit 19 on the board 7 to arrange. About the connections 21 can also be the PWM, the current signal and / or the voltage signal to downstream, not shown units are transmitted. Thus, a position measuring system 1 shown in which several sensors 9 are arranged in a fixed positional relationship to each other and a measurement object 3 along a through the rohrformige element 5 defined path relative to the sensors 9 is movable.

In 4 is a sensor cell 23 shown. The sensor cell 23 forms the smallest unit of the position measuring system 1 , In the sensor cell 23 is a sensor 25 , which is designed as a Hall sensor, arranged. In principle, however, it is also possible to use other magnetoresistive sensors, for example sensors using the anisotropic magnetoresistive effect (AMR), the giant magnetoresistive effect (GMR), the tunnel magnetoresistive effect (TMR) or the colossal magnetoresistive effect (CMR). In addition, come Switching elements based on these technologies into consideration. The two entrances 27 . 29 and the two outputs 31 . 33 of the sensor 25 are each via analog switches 35 - 41 at entrance bus lines 43 . 45 and output bus lines 47 . 49 coupled.

The sensor cell 23 forms the heart of a measuring cell 51 , in the 5 is shown. A measuring cell 51 includes next to the sensor cell 23 a logic circuit 53 for coupling the sensor 25 to the bus lines. The signal to toggle the analog switches 35 - 41 comes from the logic circuit 53 in the form of a flip-flop. The flip flop 53 controls over its exit 55 the analog switches 35 - 41 via control lines 57 at. According to the timing of the flip-flop, all analog switches 35 - 41 the sensor cell 23 closed or opened at the same time. The flip flop 53 saves the state and thus the coupling of the sensor cell 23 during detection of the sensor signals of the selected measuring cell 51 ,

As 6 shows are arranged in a row measuring cells 51 about the logical circuits 53 interconnected with each other. It's an interconnection of flip-flops 53 to a shift register 59 intended. For this purpose are each an output 55 of the flip-flop 53 the analog switches 35 - 41 the sensor cell 23 and an entrance 61 of the flip-flop 53 the following measuring cell 51 connected. All flip flops 53 are in parallel with another entrance 63 to a line 65 connected, on which a system clock is transmitted, whose frequency can be up to a few megahertz (MHz). This is how the sensors become 25 the measuring cells 51 at a very high speed sequentially sequentially to the input bus lines 43 . 45 and the output bus lines 47 . 49 coupled. The entire sensor chain 11 can thus be recorded and evaluated. Due to the special connection via the shift register 59 is the number of measuring cells 51 any. The speed of the measurement is limited only by how fast the sensor signals can be evaluated.

The operation of the Hall sensor 25 is electrically similar to a Wheatstone bridge circuit. To the entrances 27 . 29 becomes one of the input bus lines 43 . 45 coming operating voltage applied and at the outputs 31 . 33 the signal voltage is tapped. As with the Wheatstone bridge circuit, the signal voltage is dependent on the operating voltage. Among other things, this depends on the internal resistance of the Hall sensor 25 from. Because the internal resistance of the Hall sensor 25 and the internal resistances of the analog switches 35 - 41 are in the same order of magnitude and both types of internal resistances are very undefined and highly temperature-dependent, the operating voltage of the Hall sensor 25 but so can not be determined.

To also the operating voltage of the Hall sensor 25 To be able to detect a modified signal tap is required in the embodiment of the sensor cell 67 of the 7 is shown. The sensor 25 is at an entrance 29 with an input bus 43 firmly connected. Thus, in principle, a coupling of the Hall sensor 25 to the input bus lines 43 . 45 and the output bus lines 47 . 49 with only three analog switches 35 . 39 . 41 possible because no voltage drop occurs even with this connection. To the remaining entrance 27 with an analog switch 39 becomes parallel a second analog switch 69 connected to the operating voltage U _b at the Hall sensor 25 via a signal bus line 71 to be able to tap. Since the operating voltage U _{b is} measured with high impedance, plays in relation to the low internal resistance of the analog switch 69 a negligible role. Even with the high-impedance measurement of the signal voltage U _s , the low-resistance internal resistance of the analog switch 35 . 39 . 41 . 69 now be neglected. From the values of the measurement of the operating voltage U _b and the signal voltage U _s , the measurement result is formed.

Thus, it is possible with this embodiment, the individual sensor cells 25 individually to the input bus lines 43 . 45 and the output bus lines 47 . 49 coupled and in addition the operating voltage U _{b of} the respective Hall sensor 25 to eat.

The sensor cell 25 is from a source 73 supplied with a voltage U _q , where it is in principle arbitrary, whether a current source or a voltage source 73 is connected. Because the internal resistance of the Hall sensor 25 Temperature can be very small, is a series resistor R _v or a controllable current sink in one of the input lines 45 intended. According to the invention, the supply of the sensors 25 not regulated, but measured. In this way, the speed of the measurement and its accuracy can be improved. The temperature response of the analog switch 35 - 41 . 69 is also negligible here.

The precision of the measurement result can be further improved if the polarity of the source can be switched over and the voltages U _b , U _s are measured in both polarities. In this way, statistical offset errors can be eliminated, which occur, for example, in the measuring amplifiers, which are used to evaluate the measurement. This has the advantage that less expensive components can be used. In addition, when digital signals are used, a particularly easy switchable voltage source can be used 73 realize.

It is the evaluation unit 19 (see. 1 ) for the evaluation of the on the output bus lines 47 . 49 and the input bus lines 43 . 45 provided signals. The evaluation unit 19 has a display unit 75 on.

• • Einlesen der Sensorsignale;
• • Korrigieren der Sensorsignale;
• • Auswerten von primären Merkmalen zur groben Positionsbestimmung;
• • Auswerten von sekundären Merkmalen zur Feinabstimmung der Positionsbestimmung;
• • vorzugsweise, Korrigieren von Nichtlinearitäten;
• • Auswählen einer aktiven Zone; und
• • Bestimmen der Position des Messobjektes.

The sensor signals can be in the evaluation unit 19 be processed in a seven-step process of a position determination method. The individual process steps are:

• • reading the sensor signals;
• • correct the sensor signals;
• • evaluation of primary features for coarse positioning;
• • Evaluate secondary features to fine-tune position determination;
• Preferably, correcting nonlinearities;
• • selecting an active zone; and
• • Determining the position of the measurement object.

The flip-flops are used to read in the sensor signals 53 set to zero as part of an initialization. In this way, all analog switches 35 - 41 . 69 disabled. Then the shift register becomes 59 triggered the individual measuring cells 51 . 67 successively to activate and to the input bus lines 43 . 45 and the output bus lines 47 . 49 to couple these with the evaluation unit 19 connect to. For every sensor 9 . 25 With the index i, the amplitudes A _{i + of} the output signals in the form of the signal voltage U _s or the ratio U _s / U _{b of} the signal voltage U _s to the operating voltage U _{b of} each sensor i are detected in succession. The detected amplitudes A _{i +} are stored in a memory array as A _i .

For correction of offset errors, such as a digital-to-analog converter or a measuring amplifier, the source 73 then reversed polarity and the measurement of the amplitude A _i- across all sensors 9 . 25 be performed. In this case, the averaged amplitudes A _{i, avg are stored} as A _i in the memory _array : A _i = A _{i, avg} = (A _{i +} + A _i- ) / 2 (1)

In the method step of correcting the sensor signals, the amplitudes A _{i are} multiplied by a constant, sensor-dependent factor a _i determined by calibration in order to correct the sensitivity of the individual sensors. Subsequently, the zero position (offset) is corrected by subtracting a constant sensor-dependent factor b _i also determined by calibration: A _{i, corr} = a _i * A _i -b _i (2)

In the subsequent step of selecting the active sensor, the index j of the sensor becomes 9 . 25 determined where A _{i, corr is} maximum. The sensor j is then the active sensor and already roughly describes the position of the measurement object 3 , For more precise determination of the position, the sensor signals A _{j-1, corr} , A _{j, corr} and A _{j + 1, corr of} the sensor j and its immediate neighbors with the indices j-1 and j + 1 are used in particular.

The sensor signals _{Aj-1, corr} , _{Aj + 1, corr} and _{Aj + 1, corr} are scaled in the next step to the interval [0, 1]. The finally calculated value x ("weighting") serves to determine the exact position of the measurement object and results from subtraction of the minimum of the three sensor signals from the sensor signals and subsequent division by the new maximum of the three specific values: y _j-1 = A _{j-1, corr} minimum (A _{j-1, corr} ; A _{j, corr} ; A _{j + 1, corr} ) (3) y _j = A _{j, corr} - minimum (A _{j-1, corr} ; A _{j, corr} ; A _{j + 1, corr} ) (4) j + 1 = A _{j + 1, corr} - minimum (A _{j-1, corr} ; A _{j, corr} ; A _{j + 1, corr} ) (5) k = index (medium (y _j-1 ; y _i ; y _{j + 1} )) (6) x = medium ( _yj-1 ; _yj ; _{yj + 1} ) / maximum ( _yj-1 ; _yj ; _{yj + 1} ) (7)

In this way, for. B. the temperature variations of the sensors and the measurement object compensated by the relativization. The comparison and the scaling ensure that the weighting x, in particular at the transition between two active sensors, has a continuous progression between 0 and 1 (or 0% and 100%).

Optionally, a possibly existing non-linearity can be corrected in a further method step. In the described determination of the position by means of weighting, a non-linearity or positional nonlinearity remains in the case of a non-linear spatial course of the signal from the measurement object. This can be corrected in the case of knowledge or acceptance of a functional relationship via an adaptation. Alternatively, the position of the DUT can be adjusted.

In the next step, the active zone is selected. The measuring object is displaced in the direction of the sensor with the index k in relation to the active sensor. Accordingly, a zone Z _u , when k is less than j, or a zone Z _o , when k is greater than j, is defined.

In the final step, the position of the measurement object is determined. The sensors either have a fixed distance or their positions are stored as values p _i in the memory after a calibration. Relative displacements p _u and p _{o are} defined: p _u = (p _i -p _j-1 ) / 2 (8) p _o = (p _{j + 1} -p _i ) / 2 (9)

In the case of fixed distances, p _u = p _o .

Depending on the zone, the position of the object to be measured results in: Z _u : p _abs = _pj - x · p _u (10) Z _o : p _abs = p _j + x · p ₀ (11)

The position measuring system according to the invention 1 has the advantage that due to the sequential coupling of the sensors 9 . 25 to the output bus 47 . 49 and thus to the downstream unit 19 one with the other sensors 9 . 25 shared output bus 47 . 49 can be used. This brings a considerable simplification of the structure of the position measuring system 1 and therefore a big saving. It no longer has to be for every sensor 9 . 25 a separate data line to the downstream unit 19 to be provided. This saves space and material and the error rate of the position measuring system 1 reduced. Another advantage is that due to the simplification of the structure more sensors 9 . 25 can be used to determine the position of the measurement object 3 capture. In this way, an optimum of the ratio of accuracy to number of sensors can be achieved or selected depending on the intended use.

With the position determination method according to the invention, those with the sensors 9 . 25 determined data can be easily and quickly converted into a position value. In this way it is possible to specify the position of the measurement object 3 several hundred times a second with the position measuring system 1 to update. A position determination with this accuracy and timeliness can be used in a variety of devices to control even complex processes with high accuracy.

Claims (15)

Position measuring system in which several sensors ( 9 . 25 ) are arranged in a fixed positional relationship to one another and a measurement object ( 3 ) along a defined path relative to the sensors ( 9 . 25 ) is movable, characterized in that for each sensor ( 9 . 25 ) a measuring cell ( 51 ) and the sensors ( 9 . 25 ) sequentially to at least one output bus ( 47 . 49 ), whereby for the sensor ( 9 . 25 ) within its measuring cell ( 51 ) a logic circuit ( 53 ) for coupling at least one output ( 31 . 33 ) of the sensor ( 9 . 25 ) to the assigned output bus ( 47 . 49 ) is provided. Position measuring system according to claim 1, characterized in that with the logic circuit ( 53 ) both outputs ( 31 . 33 ) of the associated sensor ( 9 . 25 ) simultaneously to the output bus lines ( 47 . 49 ) can be coupled. Position measuring system according to one of the preceding claims, characterized in that with the logic circuit ( 53 ) additionally at least one input ( 27 . 29 ) of the associated sensor ( 9 . 25 ) to an input bus ( 43 . 45 ) can be coupled. Position measuring system according to claim 3, characterized in that with the logic circuit ( 53 ) both inputs ( 27 . 29 ) of the sensor ( 25 ) at the same time to the input bus lines ( 43 . 45 ) can be coupled. Position measuring system according to one of the preceding claims, characterized in that with the logic circuit ( 53 ) at least one input ( 27 . 29 ) and the at least one output ( 31 . 33 ) of the associated sensor ( 25 ) to the respective bus lines ( 43 - 49 ) can be coupled. Position measuring system according to one of the preceding claims, characterized in that via a signal bus line ( 71 ) at the entrances ( 27 . 29 ) of the sensors ( 25 ) applied operating voltage (U _b ) can be detected. Position measuring system according to one of the preceding claims, characterized in that the measuring cells ( 51 ) are arranged in a row spaced from each other, wherein individual measuring cells ( 51 ) starting from a free end ( 13 ) are separable without the functionality of the position measuring system ( 1 ). Position measuring system according to one of the preceding claims, characterized in that the logic circuit ( 53 ) is a flip-flop. Position measuring system according to claim 7, characterized in that the flip-flops ( 53 ) of the individual measuring cells ( 51 ) as a shift register ( 59 ) are switched. Position measuring system according to one of the preceding claims, characterized in that an evaluation unit ( 19 ) for the evaluation of the on the output bus lines ( 47 . 49 ) transmitted signals is present. Position measuring system according to one of the preceding claims, characterized in that at least one of the input bus lines ( 45 ) has a series resistor (R _v ) or a controllable current sink for current limiting. Position measuring system according to one of the preceding claims, characterized in that the input bus lines ( 43 . 45 ) via a power source or a voltage source ( 73 ), whereby the polarity of the current source or the voltage source ( 73 ) is switchable. Position measuring system according to one of the preceding claims, characterized in that the sensors ( 9 . 25 ) Hall sensors are. Position measuring system according to one of the preceding claims, characterized in that the measuring object ( 3 ) is a magnet. Positioning method with a position measuring system according to one of Claims 1 to 14, characterized by the following steps: • reading the sensor signals; • correct the sensor signals; • evaluation of primary features for coarse positioning; • Evaluate secondary features to fine-tune position determination; Preferably, correcting nonlinearities; • selecting the active zone; and • Determine the position.

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