Method for calibrating an fsr sensor and device for carrying out a cardiac resuscitation procedure
Patent Information
- Application Number
- EP2023706280
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-02-02
- Filing Date
- 2023-01-31
- Publication Date
- 2024-12-11
AI Technical Summary
FSR sensors used in cardiac resuscitation devices are not precise in detecting dynamic forces due to time-dependent changes in electrical resistance, as they are calibrated using static test forces on solid bases, which do not accurately represent the rapid force changes during resuscitation.
The method involves calibrating FSR sensors by applying a predetermined reference force and then relieving it, recording and adapting the maximum and minimum signal values to account for both loading and unloading phases, using a flexible base such as a CPR manikin to simulate thoracic compression, and adjusting signals based on average values or recent readings.
This method allows for precise and accurate detection of forces during cardiac resuscitation, ensuring correct force indication to users by accounting for both maximum compression and complete unloading phases, improving the accuracy of force feedback.
Smart Images
Figure 1.1
Abstract
Description
[0001] Method for calibrating an FSR sensor and device for
[0002] Carrying out cardiac resuscitation
[0003] Technical area
[0004] The invention relates to a method for calibrating an FSR sensor for use in detecting forces in a device for performing cardiac resuscitation. The described method achieves particularly accurate detection of forces exerted on a human body during cardiac resuscitation. Furthermore, the invention relates to a device for performing cardiac resuscitation using an FSR sensor calibrated according to a method according to the invention.
[0005] State of the art
[0006] From DE 10 2015 006 540 A1, the applicant discloses a device for assisting a user during cardiopulmonary resuscitation. The known device is designed in the form of a partially flexible mat that can be placed on the chest of a person to be resuscitated. It has an optical display unit that facilitates the user in applying the required force and frequency during the resuscitation procedure. The device has an FSR sensor in the area where the user's hands rest, which serves to detect the forces exerted by the user. Furthermore, such FSR sensors are known in various forms from the prior art (e.g., US 2006 / 0007172 A1 or US 8,026,906 B2).In the context of the invention, an FSR sensor is understood to be a sandwich-like sensor with a layer made of a coated, conductive ink, the electrical resistance of which changes or reduces when a force is applied, which can be implemented in circuitry, for example, in a corresponding voltage signal of the FSR sensor.
[0007] The use of such an FSR sensor in connection with the described device for carrying out a resuscitation measure is sensible, in addition to design-related advantages such as a relatively low weight, its flexibility and its relatively low power consumption, because such FSR sensors can be manufactured relatively inexpensively with sufficient precision or accuracy for detecting forces, and the spread of the device mentioned at the outset, for example as a component in a first aid kit in a motor vehicle, is all the greater the cheaper such devices can be manufactured.
[0008] A particular problem with such FSR sensors is the time-dependent change in their electrical resistance and thus in the forces they detect. Although FSR sensors are usually tested by the manufacturer during production or statically subjected to a reference or test force in order to check their actual signals against specified tolerance values, the FSR sensor is usually placed on a solid base for this purpose and the actual signal is recorded after a specified waiting time. This is due to the fact that, due to physical effects, the measurement signal typically initially decreases or drifts relatively sharply within the first tenths of a second of the test force being applied, and the decrease in electrical resistance then weakens, so that the signal then remains at least approximately constant, i.e. after the waiting time has elapsed.In view of the force that is typically applied to the human body within approximately 0.3 seconds during cardiac resuscitation, the applied force cannot be determined precisely or exactly with conventionally calibrated FSR sensors, so that the determined values are not suitable for giving a user indication of whether the force is too high or too low.
[0009] Disclosure of the invention
[0010] The method according to the invention for calibrating an FSR sensor for use in detecting forces in a device for carrying out a cardiac resuscitation measure with the features of claim 1 has the advantage that, in connection with the most accurate possible detection of forces during the loading phase and a relief phase following the loading phase, it enables the use of FSR sensors which have been calibrated by the manufacturer only with regard to an actual signal which has been determined in the course of tests which usually take place against solid surfaces with a predetermined static test force.
[0011] The invention takes advantage of the finding that signals from FSR sensors differ not only during a dynamic loading phase, but also during a subsequent unloading phase. In other words, there are FSR sensors that may generate the same signals during the loading phase, but different signals during a subsequent unloading phase. However, since, with regard to the intended use, for the correct display of forces applied by a user to a chest, not only the maximum forces that ensure the (correct) compression of the chest are important, but also the minimum forces that, in the best case, lead to complete unloading of the chest with a complete reduction of the force (to zero), it is essential to calibrate the FSR sensors for an unloading phase as well.
[0012] Against this background, it is therefore provided in a method according to the invention for calibrating an FSR sensor for use in detecting forces in a device for carrying out a cardiac resuscitation measure that the FSR sensor is first subjected to a predetermined reference force and then unloaded again, wherein during the loading and unloading a maximum value and a minimum value of a signal generated by the FSR sensor are recorded and compared with predetermined values, and wherein the signals of the maximum value and the minimum value are adapted to the predetermined values by circuitry or software.
[0013] Predefined values are signals that are expected when a specific force is applied to the FSR sensor.
[0014] Advantageous further developments of the method according to the invention for calibrating an FSR sensor for use in detecting forces in a device for carrying out a cardiac resuscitation measure are listed in the subclaims.
[0015] As stated above, for the use of the FSR sensor during resuscitation, it is essential that the forces detected by the FSR sensor are recorded very quickly (within a few tenths of a second) with high precision, whereby loading phases and unloading phases typically alternate over a longer period of time during the resuscitation measure. In order to enable, in particular, adaptation of the FSR sensor used with a view to such an application, a further, particularly preferred method for calibration in a first variant provides that repeated loading and unloading with the reference force takes place during a predetermined test time, preferably at a frequency of 100 loading and unloading cycles per minute, and that the signals are adapted based on an average value of the signals during the test time.
[0016] Alternatively, it may also be provided that repeated loading and unloading with the reference force takes place during a predetermined test time, preferably at a frequency of 100 loading and unloading cycles per minute, and that the signals are adjusted based on the most recently recorded signals during the test time.
[0017] With regard to the intended application for compression of a chest, it is furthermore intended to simulate such an application that the increase and decrease of the reference force takes place linearly or abruptly, wherein the reference force is preferably reduced completely, ie to zero, during the decrease.
[0018] Furthermore, it is preferably provided that a load phase immediately follows a load phase for the FSR sensor with the reference force.
[0019] In the simplest case, the methods according to the invention described so far are carried out using a rigid base that serves as a support for the FSR sensor and is arranged on the side facing away from the FSR sensor from which the reference force is to be applied. However, it is particularly preferred for the FSR sensor to rest on a flexible base during the application of the reference force.
[0020] Given the intended application, it is particularly advantageous if the flexible base is designed as a so-called CPR manikin. Such a CPR manikin is typically defined by standards with regard to its specific design, i.e., its flexible behavior to mimic a human body or chest, and therefore offers the best possible opportunity to adapt the FSR sensor to the real-world application.
[0021] In connection with the use of a CPR manikin, it is particularly preferred that the reference force is selected such that the chest of the CPR manikin is compressed by a defined stroke, in particular by 5 cm, during the load.
[0022] The invention further encompasses a device for performing cardiac resuscitation measures using an FSR sensor calibrated according to a method described above. Such a device is embodied, in particular, in the form of the device disclosed in DE 10 2015 006 540 A1, which, in this respect, is incorporated into this application.
[0023] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments of the invention and from the drawings.
[0024] Short description of the drawings
[0025] Shown are: Fig. 1 a device for carrying out a resuscitation measure in an application position on the chest area of a person,
[0026] Fig. 2 shows a cross section through the device according to Fig. 1 in the area of an FSR sensor,
[0027] Fig. 3a and
[0028] Fig. 3b shows, in simplified representation, different arrangements for carrying out a stress test on an FSR sensor,
[0029] Fig. 4 is a diagram explaining different curve progressions during loading and unloading of a reference FSR sensor and an FSR sensor to be calibrated with a reference force and
[0030] Fig. 5 is a diagram explaining the application of a device according to Fig. 1 in connection with signals from an FSR sensor.
[0031] Embodiments of the invention
[0032] Identical elements or elements with the same function are provided with the same reference numbers in the figures.
[0033] Figure 1 shows a highly simplified illustration of a device 100 for performing a resuscitation measure, in particular cardiopulmonary resuscitation. Such a device 100 is known from the applicant's DE 10 2015 006 540 A1, which is incorporated herein by reference. Particular reference is made to the description of the functioning of such a device 100 and individual elements of the device 100 in the cited document.
[0034] The device 100 has a region 102 in which the user, when placing the device 100 on the chest BK of the person P to be resuscitated, is to exert a force on the chest BK via his arms in order to compress the chest BK of the person P, in order to thereby start or support the cardiac function of the person P. Typically, a compression of the chest BK in a direction perpendicular to the plane of the device 100 by a travel amount or stroke h of 5 cm is provided. By rhythmically loading and unloading the device 100 in the region 102 at a frequency of also typically 100 loading and unloading cycles per minute, the resuscitation process of the person P is carried out or supported, as is known per se.
[0035] The device 100 has, in the region 102 between two plates 104, 106, which in turn are enclosed by two layers 108, 109 of the device 100, an FSR sensor 10, which is designed to detect the force F acting on it perpendicularly in the plane of the FSR sensor 10 and to feed it as an input variable to a control device 110 of the device 100. The control device 110 of the device 100 detects, on the one hand, the temporal progression of the magnitude or level of the signal from the FSR sensor 10, so that, with regard to the above-mentioned resuscitation measures, in conjunction with a display 112 (and possibly a corresponding acoustic actuator) of the user performing the measures, information is output as to whether the user is performing the resuscitation measure with the required (correct) force F and the required (correct) frequency f.
[0036] Fig. 3a shows a highly simplified illustration of a first test setup Ai for calibrating an FSR sensor 10. The first test setup Ai comprises a rigid base Us on which the FSR sensor 10 rests. The FSR sensor 10 can be subjected to a reference force FR running perpendicular to the base Us and the plane of the FSR sensor 10, which is generated by a device not shown. Signals generated by the FSR sensor 10 are received and evaluated by an evaluation device 16.
[0037] Fig. 3b shows a highly simplified representation of a second test arrangement A2 for calibrating an FSR sensor 10. The second test arrangement A2 has a flexible base UF on which the FSR sensor 10 rests. The FSR sensor 10 can be subjected to a reference force FR running perpendicular to the base UF and to the plane of the FSR sensor 10. The flexible base UF can be, for example, a rubber or foam plate. Preferably, however, the flexible base UF is a CPR (cardiopulmonary resuscitation) manikin 14. In this case, when the reference force FR is applied, the CPR manikin 14 is compressed by a stroke h, which serves to simulate the compression of the thorax BK. In particular, the reference force FR is selected such that a stroke h of approximately 5 cm is achieved. This value corresponds to the value that should be aimed for as a guideline during resuscitation measures.
[0038] To ensure that the signals of the FSR sensor 10 detected by the control device 110 are detected with sufficient precision, reference is first made to the illustration in Fig. 4 below: In Fig. 4, the electrical resistance R generated by two different FSR sensors 10, 10a when subjected to the reference force FR is shown in a highly simplified manner over time t with various curve profiles A, B, C, and D. The electrical resistance R serves as an input variable for generating, in particular, a voltage signal representing the reference force FR, as is known per se from the prior art.
[0039] While the curves A and B are assigned to the FSR sensor 10a, which serves as a reference FSR sensor 10a, for example, during the calibration of FSR sensors 10 in the manufacturer's factory of the FSR sensors 10, the curves C and D are assigned to an FSR sensor 10 to be calibrated, which is to be used in a device 100.
[0040] Furthermore, curves A and C for the FSR sensor 10, 10a are intended to correspond to a test situation in which the FSR sensor 10, 10a is arranged on a rigid base Us according to the first test arrangement Ai shown in Fig. 3a. In contrast, curves B and D represent the FSR sensor 10, 10a, in which it is arranged on a flexible base UF according to the second test arrangement A2, as shown in Fig. 3b.
[0041] Figure 4 shows a loading phase I and a release phase II. During loading phase I, the FSR sensor 10, 10a is subjected to the reference force FR. In contrast, the release phase II is characterized by the reference force FR being (again) reduced to zero.
[0042] With reference to Fig. 4, the basic behavior of an FSR sensor 10, 10a is explained in that the resistance R generated when subjected to a load with the reference force FR initially drops sharply during the loading phase I, remaining at least approximately constant from time t1, which is typically reached after approximately 200 s. In particular, it is explained that the reduction in resistance R up to time t1 can be up to approximately 10% (relative to resistance R at time t = 0), with resistance R already decreasing by up to 30% of its total reduction within the first second.
[0043] Furthermore, it can be seen that curves A and C of the FSR sensors 10, 10a exhibit higher resistance values R due to the rigid base Us than curves B and D, where the FSR sensor 10, 10a is arranged on the flexible base UF. It can also be seen that the increase in resistance R during the unloading phase II, which starts at time t2, can differ from the increase during the loading phase I, i.e., the rates of change can differ by up to 5%, for example.
[0044] During production of the FSR sensor 10, its resistance R is compared by the manufacturer with the resistance of the reference sensor 10a in the first test arrangement Ai, specifically at a time t at which there is no longer any significant change in the resistance R, i.e., for example, as explained above, from time t. The difference AR between the resistances R of the two FSR sensors 10, 10a is typically due to manufacturing tolerances. The manufacturer of the FSR sensor, knowing the difference AR, can compensate the FSR sensor 10, for example in terms of circuitry using a series resistor or similar, or in software using a suitable algorithm if the FSR sensor 10, for example, has its own evaluation logic. However, such an FSR sensor 10 is not suitable for use in the device 100: One reason is that with a dynamic load on the FSR sensor 10, in which the reference force FR changes in particular every approx.0.6 s (corresponding to a frequency of 100 loads per minute) between zero and a value that results in a compression of the chest BK by approximately 5 cm, curves C and D are located in the period before time t1 and after time t2, i.e., they exhibit high rates of change. Furthermore, the effect of the flexible support UF or the CPR manikin 16 was not taken into account by the manufacturer.
[0045] For this reason, in order to calibrate the FSR sensor 10 in connection with the use of the FSR sensor 10 in the device 100, it is provided according to the invention, as shown in Fig. 5, to provide a load test during a test time with a load profile of the FSR sensor 10 in a first test arrangement Ai, in which the FSR sensor 10 is alternately loaded with the reference force FR and completely unloaded every approximately 0.6 s. This results in immediately subsequent loading phases I and unloading phases II. During the respective time intervals of approximately 0.6 s, the minimum resistance value Rmin and the maximum resistance value Rmax are recorded as actual values of the FSR sensor 10. The reference force FR is then assigned to the minimum resistance value Rmin, and the value of zero force is assigned to the maximum resistance value Rmax.For resistances R that lie between the minimum resistance value Rmin and the maximum resistance value Rmax, linear interpolation is preferably performed to assign the corresponding force values F to the corresponding resistances R. This allows the force-dependent characteristic curve of the FSR sensor 10 to be calibrated or generated. If the calibration procedure just described is to be further improved, the load profile of the FSR sensor 10 described above can be implemented using a flexible base UF according to the second test setup A2.
[0046] The calibration methods described so far can be modified or altered in a variety of ways without deviating from the inventive concept. For example, it is conceivable to precisely determine the curve profiles C and D of the FSR sensor 10 according to Fig. 4, in particular in the time periods t=0 to t1 and from time t2 onwards. The signals or resistance values R acquired in this process can be corrected or adjusted, taking into account the known resistance value R from time t1 onwards, for any desired time t, so that the reference force FR can also be precisely determined in the time periods up to time t1 or from time t2 onwards when a test according to Fig. 5 is carried out.
[0047] Reference symbol
[0048] 10 FSR sensor
[0049] 14 CPR doll
[0050] 16 Evaluation device
[0051] 100 device
[0052] 102 Area
[0053] 104 plate
[0054] 106 plate
[0055] 108 Location
[0056] 109 Location
[0057] 110 Control device
[0058] 112 Display h stroke t time ti, t2 time
[0059] I Stress phase
[0060] 11 Relief phase
[0061] Ai, A2 test arrangement
[0062] Us rigid base
[0063] UF flexible underlay
[0064] BK chest
[0065] F Force
[0066] FR Reference force
[0067] P Person
[0068] AD curve progression
Claims
Claims 1. Method for calibrating an FSR sensor (10) for use in detecting forces in a device (100) for performing cardiac resuscitation, wherein the FSR sensor (10) is first subjected to a predetermined reference force (FR) and then unloaded, wherein during the loading and unloading at least a maximum value (Rmax) and a minimum value (Rmin) of a signal (R) generated by the FSR sensor (10) is detected and compared with predetermined values, and wherein the signals (R) of the maximum value (Rmax) and the minimum value (Rmin) are adjusted to the predetermined values by circuitry or software.
2. Method according to claim 1, characterized in that repeated loading and unloading with the reference force (FR) is carried out during a predetermined test time, preferably at a frequency of 100 loading and unloading cycles per minute, and that the adjustment of the signals (R) is carried out based on an average of the signals (R) during the test time.
3. Method according to claim 1, characterized in that repeated loading and unloading with the reference force (FR) is carried out during a predetermined test time, preferably at a frequency of 100 loading and unloading cycles per minute, and that the adjustment of the signals (R) is carried out based on last recorded signals (R) during the test time.
4. Method according to one of claims 1 to 3, characterized in that the increase and decrease of the reference force (FR) is linear or instantaneous, wherein the reference force (FR) is preferably completely reduced during the decrease.
5. Method according to one of claims 1 to 4, characterized in that a relief phase (II) of the FSR sensor (10) with the reference force (FR) immediately follows a loading phase (I).
6. Method according to one of claims 1 to 5, characterized in that the FSR sensor (10) rests on a rigid base (Us) during the loading by the reference force (FR).
7. Method according to one of claims 1 to 5, characterized in that the FSR sensor (10) rests on a flexible substrate (UF) during the load by the reference force (FR).
8. Method according to claim 7, characterized in that a CPR mannequin (14) is used as the flexible support (UF).
9. Method according to claim 8, characterized in that the reference force (FR) is selected such that the chest (BK) of the CPR mannequin (14) during the The load is compressed by a defined stroke (h), in particular by 5 cm. Device (100) for performing a cardiac resuscitation measure, in which an FSR sensor (10) is used which is calibrated according to one of claims 1 to 9.