Improvement of electrical tomography measuring device

Abstract

Providing an electrical process tomography measurement device for solid substrates [Solution] The device 10 of the present invention comprises a current or voltage source 12, a plurality of electrodes 22 configured to be connected to a solid substrate 24 to be measured, and an AD converter 26 having two measurement inputs +, - and a reference input r, and configured to output a digital signal corresponding to a voltage difference between the two measurement inputs +, -, which is proportional to a voltage level determined by the reference input r. The connection of the current or voltage source to any pair of electrodes among the plurality of electrodes can be controlled so that a current from the current or voltage source flows to the substrate to be measured according to a specified current supply sequence, and the two measurement inputs +, - of the AD converter can each be connected to one electrode of any pair of electrodes selected according to the current supply sequence among the plurality of electrodes. This device is characterized in that the current or voltage source is connected to the reference input of the AD converter.

Description

[Technical field]

[0001] The present invention relates to the field of Electrical Process Tomography (EPT). [Background technology]

[0002] Electrical process tomography includes electrical capacitance tomography (ECT), electrical impedance tomography (EIT) and electrical resistance tomography (ERT), depending on which specific material properties each technique focuses on. -EIT is useful for processes with a continuous conductive phase. - Electrical Resistance Tomography (ERT) is a specific case of EIT where the real component of the electrical impedance is the dominant property of the material; and -ECT detects the dielectric constant distribution of a material distributed in a process having a continuous non-conductive phase.

[0003] Known applications of EPT are fluid measurements, especially in industrial processes. The sensor in EPT consists of several electrodes arranged around the periphery of the inner wall of a tank or pipe of the process, in contact with the process fluid but without intervening in said fluid. An alternating current is applied to some of the electrodes and voltages from the remaining electrodes are measured according to a given detection strategy. These voltage measurements are then used to reconstruct the impedance distribution inside the tank by means of a specific inverse algorithm.

[0004] There has been less development when the substrate being measured is solid (i.e., neither liquid nor gas). When EIT is applied to a solid substrate, it reconstructs the electric field at conductive parts of the substrate. This non-invasive technique is used in medical imaging to detect the inside of the body by applying electrodes to the surface of the patient's skin and measuring the changes in the electric field.

[0005] In addition to the medical field, a known application of EIT to solid substrates is pressure detection. That is, tactile sensors (pressure sensors) using EIT are proposed in papers such as Kato et al. ("Tactile sensor without wire and sensing element in the tactile region based on eit method", IEEE Sensors, pages 792-795, 2007) (Non-Patent Document 1) and Yao and Soleimani ("A pressure mapping imaging device based on electrical impedance tomography of conductive fabric", Sensor Review, 32(4): 310-317, 2012) (Non-Patent Document 2).Nagakubo et al. ("A deformable and deformation sensitive tactile distribution sensor", IEEE International Conference on Robotics and Biomimetics, ROBIO, pages 1301-1308, 2007) (Non-Patent Document 3), Alirezaei et al. ("A highly stretchable tactile distribution sensor for smooth surfaced humanoids", 7th IEEE-RAS International Conference on Humanoid Robots, pages 167-173, 2007) (Non-Patent Document 4), Alirezaei et al. ("A tactile distribution sensor which enables stable measurement under high and dynamic stretch", IEEE Symposium on 3D User Interfaces (3DUI), pages 87-93, 2009) (Non-Patent Document 5), and Tawil et al. ("Improved image reconstruction for an eit-based sensitive skin with multiple internal electrodes", IEEE Transactions on Robotics, 27(3): 425-435, 2011) (Non-Patent Document 6) propose an "artificial skin" type tactile device for robots. Their approach involves injecting current and measuring voltage from electrodes connected to the edges of a conductive fabric, and applying inverse problem analysis to reconstruct the local change in resistivity due to pressure.Finally, Pugach et al. ("Electronic hardware design of a low cost tactile sensor device for physical human-robot interactions", IEEE XXXIII International Scientific Conference Electronics and Nanotechnology, ELNANO, pages 445-449, 2013) (Non-Patent Document 7), Pugach et al. ("Neural learning of the topographic tactile sensory information of an artificial skin through a self-organising map", Advanced Robotics, 29(21): 1393-1409, 2015) (Non-Patent Document 8) and Pugach et al. ("Touch-based admittance control of a robotic arm using neural learning of an artificial skin", in 2016 IEEE / RSJ International Conference on Intelligent Robots and Systems (IROS), pages 3374-3380, 2016) (Non-Patent Document 9) describes a technique for identifying pressure points by using a neural network to reconstruct the resistance distribution in a conductive film.

[0006] Further applications include the detection of structural defects in cement: articles by Milad Hallaji et al. ("Electrical impedance tomography-based sensing skin for quantitative imaging of damage in concrete" 2014 Smart Mater. Struct. 23 085001) (Non-Patent Document 10) and Kimmo Karhunen ("Electrical resistance tomography imaging of concrete", 2013, Publications of the University of Eastern Finland Dissertations in Forestry and Natural Sciences No. 122) (Non-Patent Document 11) show the limitations of such measurements along with a study of the extension of EIT to materials where the measurement of electrical conductivity is more complicated than tissue or skin. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Kato et al. “Tactile sensor without wire and sensing element in the tactile region based on eit method”, IEEE Sensors, pages 792-795, 2007 [Non-Patent Document 2] Yao and Soleimani “A pressure mapping imaging device based on electrical impedance tomography of conductive fabric”, Sensor Review, 32(4): 310-317, 2012 [Non-Patent Document 3] Nagakubo et al. “A deformable and deformation sensitive tactile distribution sensor”, IEEE International Conference on Robotics and Biomimetics, ROBIO, pages 1301-1308, 2007) [Non-Patent Document 4] Alirezaei et al. “A highly stretchable tactile distribution sensor for smooth surfaced humanoids”, 7th IEEE-RAS International Conference on Humanoid Robots, pages 167-173, 2007 [Non-Patent Document 5] Alirezaei et al. “A tactile distribution sensor which enables stable measurement under high and dynamic stretch”, IEEE Symposium on 3D User Interfaces (3DUI), pages 87-93, 2009 [Non-Patent Document 6] Tawil et al. “Improved image reconstruction for an eit-based sensitive skin with multiple internal electrodes”, IEEE Transactions on Robotics, 27(3): 425-435, 2011 [Non-Patent Document 7] Pugach et al. “Electronic hardware design of a low cost tactile sensor device for physical human-robot interactions”, IEEE XXXIII International Scientific Conference Electronics and Nanotechnology, ELNANO, pages 445-449, 2013

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Fashion 11

[0008] In other words, the solid substrate to which EIT is applied must be a conductive material with a sufficiently large impedance change to be observable, and must have good electrode connection capabilities for measurement. For materials with small impedance changes or materials with complicated electrode connections, it is complicated to obtain measurement data with sufficient resolution to obtain information, and EIT and EPT are generally not applicable. [Means for solving the problem]

[0009] The present invention improves this situation. To this end, the invention provides an electrical process tomography measuring device for solid substrates, comprising: a current or voltage source; A plurality of electrodes configured to be connected to a solid substrate to be measured; an analog-to-digital converter having two measurement inputs and a reference input, the analog-to-digital converter being arranged to output a digital signal corresponding to a voltage difference between the two measurement inputs, the voltage difference being proportional to a voltage level determined by the reference input; Equipped with A connection of the current source or voltage source to any pair of electrodes among the plurality of electrodes can be controlled so that a current from the current source or voltage source flows to the substrate to be measured according to a specified current flow sequence; In a device, the two measurement inputs of the AD converter can be respectively connected to one electrode in any electrode pair selected according to the energization sequence among the plurality of electrodes, The device is characterized in that the current or voltage source is connected to the reference input of the AD converter.

[0010] This device is extremely advantageous as it enables the application of EPT, and especially EIT, to applications such as human-machine interfaces, non-destructive testing, and structural monitoring, even in materials that are not normally suitable for EPT or EIT.

[0011] In fact, by using a signal derived from the current or voltage source as the reference signal for the ADC, the stimulus signal itself can cancel the noise in the measurement, allowing a very significant improvement in the measurement resolution and making EPT applicable in situations where it was not possible before.

[0012] In various embodiments, the present invention may include one or more of the following features: the device further comprising: a first multiplexer connected downstream of the current or voltage source and connected to the plurality of electrodes; a second multiplexer connected upstream of the current or voltage source and connected to the plurality of electrodes; The power supply sequence is realized by providing the power supply; the device further comprising: a third multiplexer connected to the measurement input of one of the AD converters and to the plurality of electrodes; a fourth multiplexer connected to the other measurement input of the AD converter and to the plurality of electrodes; enabling the selected connections to be formed in accordance with the energization sequence; the device further comprising: a buffer disposed between the current source or voltage source and the reference input of the A / D converter; Equipped with; the device further comprising: an operational amplifier having an output connected to the reference input of the AD converter and each input connected to each electrode of the electrode pairs corresponding to the energization sequence among the plurality of electrodes; Equipped with; the device further comprising: a fifth multiplexer connected between the output of the first multiplexer and one of the inputs of the operational amplifier; a sixth multiplexer connected between the output of the second multiplexer and the other input of the operational amplifier; Equipped with; - the current or voltage source is a direct current or voltage source; - the current or voltage source is an alternating current or voltage source; - the measurement device performs human-machine interface measurements; The measuring device performs structural health monitoring or non-destructive testing metrology.

[0013] Other characteristics and advantages of the invention will emerge more clearly from the following description, derived from non-limiting exemplary embodiments of the invention derived from the drawings, in which: [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an overview of an implementation method of an EPT device. [Diagram 2] FIG. 1 is a diagram showing a first embodiment of a measurement device according to the present invention. [Diagram 3] FIG. 2 is a diagram showing a second embodiment of a measuring device according to the present invention. [Figure 4] FIG. 13 is a diagram showing a third embodiment of the measuring device according to the present invention. [Diagram 5] FIG. 13 is a diagram showing a fourth embodiment of the measuring device according to the present invention. [Figure 6] FIG. 13 is a diagram showing a fifth embodiment of a measuring device according to the present invention. [Figure 7] FIG. 13 is a diagram showing a sixth embodiment of the measuring device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The drawings and the following description inherently include structures / components of a specific nature, i.e., they may not only aid in a better understanding of the invention, but also contribute to the definition of the invention, where appropriate.

[0016] The present invention relates to the application of EPT and EIT metrology to monitoring the condition of, for example, SHM structures, NDT structures, HMI structures, etc. Such systems are intended to monitor the changes of a particular physical element over time.

[0017] As shown in Figure 1, such a system typically comprises a stimulation subsystem 2, an element or substrate 4 to be monitored, a data acquisition subsystem 6 incorporating an A / D converter, and a data processing subsystem 8 for determining the change in said particular physical element over time. The data processing subsystem 8 is not the main object of the invention. Everything up to the acquisition subsystem 6, enabling the acquisition of the measurements, is the main object of the invention. Alternatively, the data acquisition subsystem 6 may include amplification and filtering prior to A / D conversion.

[0018] The stimulation subsystem 2 is intended to generate an electrical stimulation signal and apply this stimulation to a physical element or substrate 4, thereby allowing the acquisition subsystem 6 to measure an electrical signal, which is a response from the physical element or substrate 4. The stimulation signal can be of various types (i.e. voltage or current) and can be applied in the form of a constant value (DC) or a value that varies over time (AC), e.g. sine wave, square wave, pulse wave, etc. A linear relationship exists between the stimulation signal and the measurement signal most of the time, i.e. the measured response is proportional to the stimulation signal.

[0019] Fluctuations, or noise, present in the system can mask the target information that the system is trying to extract from the measurement signal, mainly when the level of the measurement signal is very small, e.g., less than a few microvolts. In fact, the data acquired by the system depends on the voltage or current sources provided by the entire electronic system. Although these sources are designed for maximum accuracy, maximum stability and minimum noise, they have inherent fluctuations and noise, which are then directly injected into any dependent variables and thus measured by the acquisition chain.

[0020] EIT measurements are based on measuring the electrical impedance at multiple locations by sequentially passing a stimulus source through various electrodes placed on a sample or substrate, and then processing the multiple measurements across all or some of the electrodes. In the simplest embodiment of such a system, the signal is passed through a multiplexer, which selects which electrodes to stimulate and which to measure. Finally, data processing is used to plot a map of the impedance of the sample. As mentioned above, this processing is not central to the invention.

[0021] The present invention solves the above problem by connecting the stimulation subsystem 2 and the data processing subsystem 6 as close as possible to the material. That is, the electrical process tomography measuring device 10, as shown in Fig. 2, comprises a current source 12, multiplexers 14, 16, 18, 20, eight electrodes 22 arranged on a substrate 24 to be measured, and an AD converter 26 that outputs a measurement signal 28 in digital form.

[0022] In the example described herein, the electrodes 22 are substantially uniformly distributed on the substrate 24. The substantially circular shape is highly suitable for reconfiguration by the system 8. Alternatively, the device 10 may comprise fewer electrodes, for example four or more, for example sixteen or more, and the electrodes may also be non-uniformly arranged according to another shape other than a circle, depending on the application.

[0023] The multiplexer 14 is connected downstream of the current source 12, and the multiplexer 16 is connected upstream of the current source 12, and both can be connected to the respective electrodes 22. Thus, each electrode pair connected to the multiplexers 14, 16 forms a stimulation circuit together with the current source 12. Similarly, the multiplexer 18 is connected to the input "+" of the AD converter 26, and the multiplexer 20 is connected to the input "-" of the AD converter 26. That is, each electrode pair connected to the multiplexers 18, 20 forms a circuit for measuring the stimulation, and the measurement is sent to the terminals "+" and "-" of the AD converter 26.

[0024] In the example described here, the A / D converter 26 is included as part of the control means arranged to control the multiplexers 14, 16, 18, 20. Alternatively, said control may be separate therefrom. The A / D converter 26 thus performs a conversion of the voltages measured at the terminals of each electrode connected to the multiplexers 16, 18 into a digital form, with the input r of the A / D converter 26 as a reference voltage.

[0025] In the present invention, this input r is connected downstream of the current source 12. Thus, it receives a signal substantially identical to the stimulus signal formed by the multiplexers 14, 16. This causes the A / D converter 26 to output a signal 28 that is independent of the noise affecting the current source 12.

[0026] The above approach is entirely novel in the field of EPT and especially in the field of EIT. It should also be distinguished from conventional instruments using ratiometric measurements. In fact, such instruments use a physical element that is an absolute strong reference for the ratiometric measurement. This reference, which is separate from the monitored element, is necessary to detect minimal changes in the system that are not susceptible to noise. The method and teaching of the above approach are in stark contrast to what is done in the present invention, which stimulates the monitored element and uses its effect on the monitored element, which is also the reference for the ratiometric measurement. Also, in conventional ratiometric measurements, the connection between the monitored element and the system is fixed over time. In contrast, the present invention extends the ratiometric measurement principle to systems suitable for EPT by using the monitored element as a reference and establishing connections with the monitored element sequentially with multiple electrodes.

[0027] To perform the measurements, multiplexers 14, 16, 18, and 20 sequentially energize the devices according to the EIT energization method. - Adjacent method, where a current is introduced between adjacent electrodes and the voltage drop is measured between the remaining electrodes, by sequentially energizing all the electrode pairs; - a counter method in which a current is introduced between diametrically opposed electrodes and the voltage is measured at the remaining electrodes in sequence, by sequentially passing current through all pairs of electrodes; and -Transverse method, where a current is introduced between two electrodes facing each other across a fixed axis, and the voltage is measured by the remaining electrodes, passing current through all the electrode pairs in sequence; It should be understood that the term refers to a method selected from the above.

[0028] Other energizing methods are also possible.

[0029] In the examples described herein, stimulation is performed using a direct current source, and a simultaneous measurement voltage is taken at the electrodes, and if the current source is an alternating current source, the amplitude or deviation of the voltage relative to the alternating current is measured.

[0030] The second embodiment is shown in Figure 3, and the differences will be described below. In this embodiment, the source 12 is a voltage source, which may be a DC voltage source or an AC voltage source.

[0031] This embodiment has the advantage that the input r and the terminals of the multiplexers 14, 16 are supplied with the same voltage.

[0032] A third embodiment is shown in Figure 4. This embodiment is similar to the embodiment of Figure 1, but the device 10 further includes a buffer 29. The buffer 29 is used to minimize the effect of the input r on the current source 12, keeping it as clean and stable as possible.

[0033] A fourth embodiment is shown in FIG. 5. In this embodiment, multiplexers 30 and 32 are provided to feed into the input r a voltage that corresponds as closely as possible to the voltage corresponding to the stimulus. These multiplexers are connected to the output of the multiplexer 14 and to the output of the multiplexer 16, respectively, and to the inputs of an operational amplifier 34. The operational amplifier 34 thereby ensures that the voltage applied to the input r is actually a voltage that is directly proportional to the stimulus voltage applied to the substrate 24. The multiplexer 30 is energized in correspondence with the multiplexer 16, and the multiplexer 32 is energized in correspondence with the multiplexer 14. This embodiment has the advantage that the effects of possible voltage drops in the multiplexers 14 and 16 due to the strong currents being fed into the substrate 24 are suppressed.

[0034] A fifth embodiment is shown in Fig. 6. In this embodiment, the multiplexers 30, 32 are directly connected to the electrodes 22 to which the multiplexers 16, 14 are connected. This has the advantage that the input r is supplied with a voltage incorporating not only the noise generated by the multiplexers 14, 16 but also the noise due to the interaction between the multiplexers 14, 16 and the substrate 24. This means that other variations, such as noise and voltage drops caused by the multiplexer 14 located between the current source 12 and the substrate 24, are also injected into the reference voltage of the A / D converter 26.

[0035] Finally, FIG. 7 shows a sixth embodiment. In this embodiment, each electrode 22 on the substrate 24 is duplicated by arranging an additional set of electrodes of the same configuration as each electrode 22, but slightly spaced from each electrode 22. That is, each electrode 22 is associated with one of the additional set of electrodes. In this embodiment, multiplexers 30, 32 are connected to the electrodes associated with the electrodes 22 connected to multiplexers 16, 14. This embodiment has the advantage that the actual voltage seen by the substrate 24 is supplied to the input r. By its nature, this embodiment eliminates noise that occurs when the stimulus signal passes through the multiplexers 14, 16, between the multiplexers 14, 16 and the substrate 24, and finally through the contact resistance between the electrodes 22 and the substrate 24.

[0036] It should be understood that the substrate 24 in the above description may include a human machine interface, a substrate on which it is desired to perform NDT, or a substrate for which structural health monitoring is being performed. Thus, although the illustrated example is directed to an EIT-based application, applications of the apparatus 10 include: any human machine interface HMI intended to stimulate a physical interface and measure changes in local impedance within said interface by measuring a correlated signal resulting from the stimulation of said physical interface, said human machine interface HMI comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; any HMI based on electrical impedance tomography intended to measure local impedance changes within a physical interface by stimulating said interface and measuring the correlated signal caused by said stimulation, comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; any HMI based on electrical resistance tomography intended to measure changes in the local impedance of a physical interface by stimulating said interface and measuring the correlated signal caused by said stimulation, comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; any HMI based on electrical capacitance tomography intended to measure changes in local impedance within a physical interface by stimulating said interface and measuring a correlated signal resulting from said stimulation, said HMI comprising a variable electrical stimulus source and an analog-to-digital converter; any Structural Health Monitoring (SHM) system intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of its physical components, comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; any SHM system based on electrical impedance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of its physical components, comprising a continuous or variable electrical stimulus source and an AD converter; any SHM system based on electrical resistance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of said physical elements, comprising a continuous or variable electrical stimulus source and an AD converter; any SHM system based on electrical capacitance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal caused by the stimulation of said physical elements, comprising a variable electrical stimulus source and an AD converter; any non-destructive testing (NDT) system intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of its physical components, comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; any NDT system based on electrical impedance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of its physical components, comprising a continuous or variable electrical stimulus source and an AD converter; any NDT system based on electrical resistance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of said physical elements, comprising a continuous or variable electrical stimulus source and an analog-to-digital converter; and any NDT system based on electrical capacitance tomography intended to measure local impedance changes within a physical sample by stimulating said sample and measuring the correlated signal resulting from the stimulation of said physical elements, comprising a variable electrical stimulus source and an AD converter; Examples include:

Claims

1. An electrical process tomography measurement device (10) for solid substrates, comprising: a current or voltage source (12); a plurality of electrodes (22) configured to be connected to a solid substrate (24) to be measured; an AD converter (26) having two measurement inputs (+, -) and a reference input (r), and configured to output a digital signal corresponding to a voltage difference between the two measurement inputs (+, -), which is proportional to a voltage level determined by the reference input (r); The connection of the current or voltage source (12) to any pair of electrodes among the plurality of electrodes (22) can be controlled so that current from the current or voltage source (12) flows to the substrate to be measured in a specified current flow sequence; In the device, the two measurement inputs (+, -) of the AD converter (26) can be connected to one electrode of any electrode pair selected in accordance with the energization order among the plurality of electrodes (22), respectively; The current or voltage source (12) is connected to the reference input (r) of the AD converter (26); The apparatus further comprises: a first multiplexer (14) connected downstream of the current or voltage source (12) and connected to the plurality of electrodes (22); a second multiplexer (16) connected upstream of the current or voltage source (12) and connected to the plurality of electrodes (22); By providing the above, the energization sequence is realized, The apparatus further comprises: an operational amplifier (34) whose output is connected to the reference input (r) of the AD converter (26) and whose inputs are connected to the electrodes of the electrode pairs corresponding to the energization order among the plurality of electrodes (22); The apparatus further comprises: a third multiplexer (30) connected between the output of the first multiplexer (14) and one of the inputs of the operational amplifier (34); a fourth multiplexer (32) connected between the output of the second multiplexer (16) and the other input of the operational amplifier (34); An apparatus comprising:

2. 10. The apparatus of claim 1 further comprising: a fifth multiplexer (18) connected to one of the measurement inputs (+) of the AD converter (26) and to the plurality of electrodes (22); a sixth multiplexer (20) connected to the other measurement input (-) of the AD converter (26) and to the plurality of electrodes (22); and enabling the selected connections to be formed in accordance with the energization sequence.

3. 3. The device according to claim 1 or 2, further comprising: a buffer (29) arranged between the current or voltage source (12) and the reference input (r) of the AD converter (26).

4. 4. The apparatus of claim 3, wherein the current or voltage source (12) is a DC current or voltage source.

5. 4. The apparatus of claim 3, wherein the current or voltage source (12) is an AC current or voltage source.

6. 10. The apparatus of claim 1, wherein the measurement device (10) performs human-machine interface measurements.

7. 10. The apparatus of claim 1, wherein the measurement device (10) performs structural health monitoring or non-destructive testing metrology.

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