Pressure-sensitive pad with calibration unit

Abstract

A pressure sensitive pad configured to be placed under a mattress and configured to identify the presence or absence of a threshold weight on the mattress. The pressure sensitive pad comprises a signal generator, a sensing area, at least one variable matching resistor, and a microcontroller unit (MCU). The signal generator is configured to generate an electrical signal. The sensing area has a sensing resistor having a first resistance that varies in response to pressure on the sensing area. The variable matching resistor is disposed in series with the sensing resistor and the signal generator and has a second resistance. The MCU has an analog-to-digital converter (CAN) configured to receive and measure a portion of the signal at an electrical junction between the sensing resistor and the at least one variable matching resistor, and the MCU is configured to control the second resistance of the at least one variable matching resistor.

Description

Technical Field

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[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Application No. 63 / 216,600, filed Jun. 30, 2021, the entire content of which is incorporated herein by reference.

[0002] In some embodiments, the present invention relates to a pressure - sensitive pad under a mattress, and more particularly (but not limited to) to the calibration of a pressure - sensitive pad under a mattress for use with various mattresses.

Background Art

[0003] A pressure - sensitive pad under a mattress is a pad that is placed under a mattress to detect the presence of an object (such as a person) on the mattress. This pad is used with various mattresses having various shapes and weights and is configured to always detect the presence of an object having a specific weight on the mattress. An example of such a pad is described in U.S. Patent No. 10,357,197 to Smith, Jr. et al.

[0004] A pressure - sensitive pad under a mattress includes a sensing zone disposed under the mattress. The sensing zone includes a conductive material such as a wire and has a resistance that decreases when pressure is applied. Thereby, a resistance measurement circuit such as a voltage divider, used together with an analog - to - digital converter (ADC) of a microcontroller (MCU), can detect the presence of an object on the mattress. The variable - resistance material may include one or more of a conductive film (e.g., a film called Velostat, manufactured by 3M, or any similar material), a conductive foam, a strain gauge that generates a variable resistance when deformed, and a conductive ink.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Figure 1 shows an electrical diagram of a pad 100 known in the prior art. The pad 100 has a sensing zone equipped with a variable resistor (hereinafter referred to as the "sensing resistor") which has a resistance RSENSE that decreases as the pressure to the sensing zone increases.

[0007] Pad 100 further comprises a microcontroller unit (MCU) 104 having a signal generator 102, a resistor with a fixed resistor RPOT, and an analog-to-digital converter (ADC) 106. The sensing zone has one end connected to an electrical junction 108 and the other end connected to ground 100. The resistor with the RPOT has one end connected to the signal generator 102 and the other end connected to the electrical junction 108. Finally, the electrical junction 108 is also connected to the ADC 106 of the MCU 104. Thus, the circuit forms a voltage divider, and the voltage from the signal generator 102 is applied in series to two resistors (a resistor with a fixed resistor RPOT and a variable sensing resistor with a resistor RSENSE), and this voltage is measured by the MCU at the junction 108 between the two resistors.

[0008] Thus, once a signal is generated by the signal generator, the signal travels to the junction 108 through a resistor equipped with a fixed resistor RPOT. From the junction 108, the signal travels to the ground 110 through the sensing zone (RSENSE) and also to the ADC 106.

[0009] The voltage portion of the signal that reaches the ADC and is measured by the ADC depends on the RSENSE. The RSENSE, in turn, depends on the pressure applied to the sensing zone. Therefore, the voltage measured by the ADC indicates the pressure on the sensing zone and can be processed to determine the presence or absence of an object on the sensing zone.

[0010] In a sample of 10 ink-based pads randomly selected from a population of 400 manufactured by the inventors, no-load resistance values ​​(resistance of the sensing zone with no weight applied to the top) were found to range from 10 k ohms to 98 k ohms. This variation becomes problematic when a voltage divider with a matching resistor (RPOT in Figure 1) is used to measure the resistance of the pressure-sensing material within the sensing zone. The value of this matching resistor must be selected to complement the resistance of the sensing material within the sensing zone in order to provide the system's optimal operating range. Because the resistance RPOT of the matching resistor must match the resistance value of the sensing zone, substantial variations in the resistance of the sensing zone pose problems for the mass production of pressure-sensitive pads under mattresses. Since the resistance of the sensing zone changes substantially, the selection of the resistance RPOT of the matching resistor may not allow for an optimal operating range for all sensing zones.

[0011] To illustrate this issue, Figure 2 shows sample response curves for two worst-case scenarios for pads from a sample of pads. The orange horizontal line 120 represents the maximum ADC voltage reading that the microcontroller can reach. Curves 122 and 124 are the response curves for a low-resistance pad (50k ohm unloaded resistance) and a high-resistance pad (120k ohm unloaded resistance), respectively. As seen below, the voltage of the portion of the signal that reaches the ADC decreases as the weight placed on the sensing zone increases and the RSENSE decreases. The further the response curve deviates from this line, the less sensitive the pad becomes. In this case, the low-resistance pad (curve 122) is approximately 50% less sensitive than the high-resistance pad (curve 124).

[0012] A challenge in using voltage dividers in sensing circuits is the inherent behavior of signals that shift away from the ADC's maximum (or Vref) value. In the voltage divider equation, as shown in Figure 1, it is desirable that Vout (voltage measured by the ADC) be as close as possible to Vin (voltage of the signal generated by the signal generator) during calibration time in order to maintain the maximum operating range of the ADC reading. Unfortunately, in a standard ADC setting, Vref = Vin. This means that the maximum Vout that can be obtained for any value of RSENSE is also determined by RPOT.

[0013]

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[0014] As the value of RSENSE (sensor material) decreases relative to a given RPOT, Vout begins to approach zero. This can be observed in Figure 2, where the response curve 122 for the low-resistance pad is shifted lower in the graph than the response curve 124 for the high-resistance pad.

[0015] Lowering the RPOT helps to bring the response curve back up, but this can only be adjusted down to a certain extent. As the RPOT approaches zero ohms, the battery drain of the pads increases during normal operation, and if the RPOT is chosen to be zero, the effect of the voltage divider is completely canceled out.

[0016] To solve the above-mentioned problems identified by the inventors of the present invention, in some embodiments of the present invention, the matching resistor RPOT in the voltage divider is a variable potentiometer controlled by an MCU. This makes it possible to adjust the matching resistor to select a desired value that complements the actual resistor in the sensing zone during pad calibration. This helps to mitigate changes in the sensing material of the pad by creating an adaptive circuit.

[0017] In addition, in some embodiments of the present invention, Vref is set to a desired voltage. This shifts the “ADC Max” line, as seen in Figure 1, downward toward the pad response curve. As further shown below, this shift allows the adaptive circuit to have a larger operating range and to dynamically adjust the pad response curve.

[0018] Therefore, one aspect of several embodiments of the present invention relates to a pressure-sensitive pad configured to be placed under a mattress and to identify the presence or absence of a threshold weight on the mattress. The pressure-sensitive pad comprises a signal generator, a sensing zone, at least one variable matching resistor, and a microcontroller unit (MCU). The signal generator is configured to generate an electrical signal. The sensing zone has a sensing resistor having a first resistance that changes in response to pressure applied to the sensing zone. At least one variable matching resistor is in series with the sensing resistor and the signal generator and has a second resistance. The MCU has an analog-to-digital converter (ADC) configured to receive and measure a portion of the signal at an electrical junction between the sensing resistor and at least one variable matching resistor. The MCU is configured to control the second resistance of at least one variable matching resistor. The sensing zone is configured to be connected to an electrical ground. The pressure-sensitive pad is configured to be calibrated for any mattress by placing a sensing zone under the mattress without adding weight to the mattress, generating an electrical signal via a signal generator, automatically measuring the portion of the electrical signal that reaches the ADC using the ADC, and automatically changing the second resistance of at least one variable matching resistor via a microcontroller unit until a desired value of the second resistance is found such that the portion of the signal that reaches the ADC is within a predetermined range of a desired predetermined voltage. In post-calibration operation, the microcontroller unit is configured to set the second resistance to a desired value, the signal generator is configured to generate an electrical signal regularly, the electrical signal is configured to travel via at least one variable matching resistor to an electrical junction, from the electrical junction to the ADC, and from the electrical junction to electrical ground via the sensing resistor, such that the portion of the signal that reaches the ADC relies on the first resistance of the sensing resistor, and the portion of the signal that reaches the ADC can be processed to identify the presence or absence of threshold weight on the sensing zone.

[0019] In a modified configuration, at least one variable matching resistor comprises two variable matching resistors in series, each of which has a corresponding second resistor independently controlled by a microcontroller unit. The MCU is configured to automatically change the second resistor of at least one variable matching resistor by changing a first portion of the second resistor to reach a first desired value, thereby changing the portion of the signal reaching the ADC to have a voltage within a predetermined coarse range of the desired voltage, while keeping the second portion of the first resistor fixed; or by changing a second portion of the second resistor to reach a second desired value, thereby changing the portion of the signal reaching the ADC to have a voltage within a predetermined range of the desired voltage, where the predetermined range is smaller than a predetermined coarse range. In operation, the microcontroller unit is configured to set the first portion of the second resistor to a first desired value and the second portion of the second resistor to a second desired value.

[0020] In another variant, the pressure-sensitive pad further comprises a third resistor in series with at least one variable resistor, the third matching resistor having a fixed resistance.

[0021] In yet another variant, the MCU is further configured to determine whether the calibration is valid by (i) starting a period, (ii) performing a first check at the end of the period to determine whether the measured voltage at the ADC during the post-calibration period was always well above a predetermined desirable voltage, (iii) if the check in step (ii) is positive, increasing the first desirable value and repeating all steps from step (i), (iv) if the check in step (iii) is negative, performing a second check at the end of the period to determine whether the measured voltage at the ADC during the post-calibration period was always well close to 0V, (v) if the check in step (iv) is positive, decreasing the first desirable value and repeating all steps from step (i), and (vi) if the check in step (iv) is negative, determining that the calibration was accurate.

[0022] The MCU may be further configured to repeat all steps from step (i) after executing step (vi).

[0023] Another aspect of some embodiments of the present invention relates to a method for calibrating a pressure-sensitive pad configured to be placed beneath a mattress and to detect the presence or absence of a threshold weight on the mattress. The method includes (i) providing a sensing zone having a signal generator configured to generate an electrical signal, a sensing resistor having a first resistance that changes in response to pressure applied to the sensing zone, at least one variable matching resistor in series with the sensing resistor and the signal generator and having a second resistance, and an analog-to-digital converter (MCU) configured to receive and measure a portion of the signal at an electrical junction between the sensing resistor and at least one variable matching resistor, wherein the MCU is configured to control the second resistance of at least one variable matching resistor; (ii) connecting the sensing zone to an electrical ground; (iii) positioning the sensing zone under a mattress without adding any additional weight to the mattress; (iv) generating an electrical signal via the signal generator; (v) automatically measuring the portion of the electrical signal that reaches the ADC using the ADC; and (vi) automatically changing the second resistance of at least one variable matching resistor via the microcontroller unit until a desirable value for the second resistance is found such that the portion of the signal that reaches the ADC is within a predetermined range of a desired predetermined voltage.

[0024] In a variant form, the step of providing at least one variable matching resistor includes providing two variable matching resistors in series, each of the two variable matching resistors having a corresponding second resistor that is independently controlled by a microcontroller unit. The step of automatically changing the second resistor of at least one variable matching resistor is to change a first portion of the second resistor so as to reach a first desired value, whereby the portion of the signal reaching the ADC has a voltage within a predetermined coarse range of the desired voltage while the second portion of the first resistor remains fixed, changing; fixing and maintaining the first portion of the second resistor at the first desired value and changing a second portion of the second resistor so as to reach a second desired value, whereby the portion of the signal reaching the ADC has a voltage within a predetermined range of the desired voltage, the predetermined range being smaller than the predetermined coarse range, including changing.

[0025] Yet another aspect of some embodiments of the present invention relates to a method for operating a pressure-sensitive pad configured to be disposed under a mattress and configured to identify the presence or absence of a threshold weight on the mattress. The method includes, as described above, the step of calibrating the pressure-sensitive pad, the step of setting a second resistor to a desired value via a microcontroller unit, and generating an electrical signal configured to move from an electrical junction through at least one variable matching resistor, from the electrical junction to the ADC, and from the electrical junction to an electrical ground through a sensing resistor such that the portion of the signal reaching the ADC depends on the first resistor of the sensing resistor, and processing the portion of the signal reaching the ADC to identify the presence or absence of a threshold weight on the sensing zone.

[0026] In a modified form, the step of providing at least one variable matching resistor includes providing two variable matching resistors in series, each of the two variable matching resistors having a corresponding second resistor independently controlled by a microcontroller unit. The step of automatically changing the second resistor of at least one variable matching resistor includes changing a first portion of the second resistor to reach a first desired value such that the portion of the signal reaching the ADC has a voltage within a predetermined rough range of the desired voltage, while keeping the second portion of the first resistor fixed; changing a second portion of the second resistor to reach a second desired value, while keeping the first portion of the second resistor fixed at the first desired value, such that the portion of the signal reaching the ADC has a voltage within a predetermined range of the desired voltage, where the predetermined range is smaller than a predetermined rough range; and the step of setting the second resistor to a desired value via a microcontroller unit includes setting the first portion of the second resistor to the first desired value and setting the second portion of the second resistor to the second desired value.

[0027] In another variation, the method further includes the steps of determining whether the calibration is effective by (a) starting a period; (b) at the end of the period, performing a first check to determine whether the measured voltage at the ADC during the post-calibration period was always well above a predetermined desirable voltage; (c) if the check in step (b) is positive, increasing the first value and repeating all steps from step (a); (d) if the check in step (c) is negative, performing a second check at the end of the period to determine whether the measured voltage at the ADC during the post-calibration period was always well close to 0V; (e) if the check in step (d) is positive, decreasing the desirable value and repeating all steps from step (a); and (f) if the check in step (d) is negative, determining that the calibration was accurate.

[0028] In the modified form, the method further includes repeating all steps from step (a) after step (f).

Brief Description of the Drawings

[0029] [Figure 1] FIG. 1 is a circuit diagram of a pressure-sensitive pad under a mattress known in the prior art. [Figure 2] FIG. 2 is a graph of the response curves of pressure-sensitive pads under mattresses of the prior art having various no-load resistance values, discovered by the inventor of the present invention. [Figure 3] FIG. 3 is a circuit diagram of a pressure-sensitive pad under a mattress provided with an adaptive voltage divider having at least one variable resistor controlled by an MCU, according to some embodiments of the present invention. [Figure 4] FIG. 4 is a graph of the response curves of pressure-sensitive pads under mattresses having various no-load resistance values and an adaptive voltage divider, according to some embodiments of the present invention. [Figure 5] FIG. 5 is a graph showing a binary search for a predetermined desired voltage in an ADC using a single variable resistor, according to some embodiments of the present invention. [Figure 6] FIG. 6 is a graph showing a binary search for a predetermined desired voltage in an ADC using two variable resistors, according to some embodiments of the present invention. [Figure 7] FIG. 7 is a flowchart of a method for calibrating and using a pressure-sensitive pad under a mattress having an adaptive voltage divider, according to some embodiments of the present invention. [Figure 8] FIG. 8 is a flowchart of a method for adjusting an inaccurate calibration of a pressure-sensitive pad under a mattress, according to some embodiments of the present invention.

Modes for Carrying Out the Invention

[0030] The present invention is often described herein in terms of exemplary environments. These descriptions of environments are provided to enable the various features and embodiments of the invention to be depicted in the context of exemplary applications. After reading this description, it will be clear to those skilled in the art how the invention may be implemented in different and alternative environments.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as they would ordinarily be understood by those skilled in the art in which the present invention pertains. All patents, applications, published applications and other publications referenced herein are incorporated by reference in their entirety. If any definition set forth in this section contradicts or otherwise conflicts with any definition set forth in any application, published application and other publication incorporated by reference herein, the definition set forth in this document shall prevail over the definition set forth in any application, published application and other publication incorporated by reference herein.

[0032] Figure 3 is a circuit diagram of a pressure-sensitive pad 200 under a mattress that forms an adaptive voltage divider having at least one variable resistor controlled by an MCU, according to some embodiments of the present invention.

[0033] The pressure-sensitive pad 200 comprises a signal generator 202, a sensing zone, at least one variable matching resistor, and a microcontroller unit (MCU) 204 having an analog-to-digital converter (ADC) 206.

[0034] The signal generator 202 is configured to generate an electrical signal having a predetermined voltage (Vin). The sensing zone has a sensing resistor with a first resistance RSENSE that changes in response to the pressure applied to the sensing zone. More specifically, the resistance RSENSE decreases as the pressure on the sensing zone increases.

[0035] The variable matching resistors are in series with the sensing resistor and the signal generator 202. Each variable matching resistor is controlled by the MCU 204. In embodiments where there is one variable matching resistor, the variable matching resistor has a second resistor Rwiper0. In some embodiments of the present invention, there are multiple variable matching resistors. In a non-limiting example, there are two variable matching resistors, each having a second resistor Rwiper0 and Rwiper1, respectively. In some embodiments of the present invention, there is also a fixed resistor with resistor R1. In other words, the matching resistor device 203 is arranged in series with the sensing resistor having a first resistor RSENSE. The matching resistor device 203 comprises one or more variable matching resistors controlled by the MCU, and optionally one or more fixed resistors.

[0036] In a non-limiting example, for a signal generated by a signal generator with a voltage of approximately 3.3V, two variable matching resistors were selected to be 100k ohm potentiometer chips, allowing for an adjustment range of 0 to 200k ohms in 512 steps. A fixed resistor with resistor R1 was selected to be small (1k ohm) so as to allow the potentiometer to have the greatest effect on the circuit. The number, type, and resistance values ​​of the variable and fixed matching resistors in the matching resistor device 203, as well as the voltage of the signal generated by the signal generator 202, can be changed according to different requirements of the pad without departing from the spirit of the present invention.

[0037] The potentiometer chip was connected to the MCU via an SPI data bus. This allows the microcontroller to adjust both potentiometers to any available increment with a single data command, thereby speeding up the discovery of the exact value. This could also be achieved using up / down potentiometer chips, but this would increase the logic required to bring the potentiometers to a known good state, resulting in longer search times to determine the exact value.

[0038] The microcontroller unit (MCU) 204 has an analog-to-digital converter (ADC) 206 configured to receive and measure a portion of the signal at an electrical junction 208 between the sensing resistor and the matching resistor device 203. The MCU 204 is configured to control the second resistance of at least one variable matching resistor.

[0039] Referring now to Figure 7, a flowchart 700 is shown of a method for calibrating and using a pressure-sensitive pad under a mattress having the adaptive voltage divider of Figure 1, according to some embodiments of the present invention.

[0040] In 702, a signal generator, a sensing zone, an MCU having an ADC, and a matching resistor device are provided as described above.

[0041] In model 704, the sensing zone is located under the mattress.

[0042] In the 706, the sensing zone is electrically connected to the electrical grounding point.

[0043] In 708, an electrical signal having a predetermined voltage is generated via a signal generator.

[0044] In the 710, the ADC automatically measures the portion of the electrical signal that reaches the ADC.

[0045] In 712, all resistances in the matching resistor device are automatically adjusted by the MCU until the desired value of the matching resistor device is found so that the portion of the signal reaching the ADC is within a predetermined range of the desired voltage.

[0046] In some embodiments of the present invention, the matching resistor device comprises a single variable resistor. In these embodiments, the resistance of the variable matching resistor is changed to bring the signal voltage in the ADC to a predetermined desired voltage within a desired range.

[0047] In some embodiments of the present invention, the matching resistor device includes two variable resistors in series: one having resistor Rwiper0 and the other having resistor Rwiper1 (see Figure 3). In such embodiments, both Rwiper0 and Rwiper1 are modified independently of each other by the MCU to bring the signal voltage at the ADC to a predetermined desired voltage within a desired range. In some embodiments of the present invention, Rwiper0 is modified until a value is found such that the signal voltage at the ADC is within a coarse range of a predetermined desired voltage, while Rwiper1 is fixed and maintained at an initial resistance value. Rwiper0 is then maintained at the previously found value, and Rwiper1 is fine-tuned to bring the voltage at the ADC closer to the predetermined desired voltage within a fine range. The fine range is smaller than the coarse range. This allows for better control of the matching voltage and the final value of Vout (voltage measured at the ADC) which is closer to the desired value.

[0048] In 714, after calibration is complete, the microcontroller unit is configured to set the second resistor of the matching resistor device 203 (Figure 3) to the value found during calibration.

[0049] In 716, the signal generator is configured to regularly generate an electrical signal that travels to the electrical junction via a matching resistor device, from the electrical junction to the ADC, and from the electrical junction to the electrical ground via a sensing resistor, such that the portion of the signal that reaches the ADC depends on the first resistance of the sensing resistor.

[0050] In 718, the portion of the signal that reaches the ADC is processed to identify the presence or absence of a threshold weight on the sensing zone.

[0051] In some embodiments of the present invention, in 720, the microcontroller unit is configured to check whether the calibration was performed correctly or is valid after a period in which the sensing zone pad may have deteriorated. This check may be performed periodically or continuously during the initial period of the pad's operation. If several conditions indicating that the calibration was performed incorrectly are met (see Figure 8, further described below), the MCU is configured to change the second resistance of the matching resistor device 203 (Figure 3) over time during the use of the pad in order to correct the calibration.

[0052] Figure 4 is a graph of response curves for pressure-sensitive pads under a mattress having different no-load resistance values ​​and adaptive voltage dividers, according to several embodiments of the present invention.

[0053] The matching resistors within the voltage divider allow the matching resistance to be adjusted during the pad calibration phase to select the desired ideal value. This helps mitigate variations in the sensor material of the sensing zone by creating an adaptive circuit. This is applied to the same two pads used in Figure 2, resulting in the response curves found in Figure 4.

[0054] In Figure 4, it is readily apparent that response curves 122 and 124 are nearly identical. Furthermore, both curves 122 and 124 are pulled up to approach the ADC maximum reading line 120. This vertical shift is partly due to the dynamic resistance calibration described above.

[0055] Vertical shifting is also aided by reducing the MCU's reference voltage (ADC maximum voltage) to a desired level. For example, if the voltage of the signal generated by the signal generator is 3.3V, the selected reference voltage can be reduced to approximately 1V. Thus, the ADC maximum line is shifted downwards.

[0056] While this alone does not solve the problem, the dynamic resistance calibration of the adaptive voltage divider allows for a wider operating range, enabling dynamic adjustment of the response curve.

[0057] For example, referring to the values ​​in Table 1, the voltage at the ADC is measured for different combinations of unloaded RSENSE and Rwiper0 (in embodiments where a single matching resistor is present). If the goal is to achieve a Vref of 3.3V, which is the maximum voltage at the ADC when RSENSE is much higher than the matching resistor, then these Vref values ​​are all concentrated in the upper left part of the table. Therefore, when RSENSE is above 30k ohms, Rwiper0 can only be changed between 1k ohms and 2k ohms in order for the response curve to rise to Vref and increase the sensitivity of the pad. Higher values ​​of Rwiper0 cannot compensate for lower values ​​of unloaded RSENSE and shift the response curve to reach approximately 3.3V.

[0058] Alternatively, when the target Vref is approximately 1V, the table shows that the 1V value runs through the center of the inventors' table, providing a better opportunity to reach the target voltage. Therefore, even if the RSENSE falls below 30k ohms (down to 500 ohms), the Rwiper0 can be increased up to 100k ohms to raise the response curve closer to Vref, and thus maintain higher sensitivity.

[0059] [Table 1]

[0060] Figures 5 and 6 refer to binary search for a predetermined desired voltage in an ADC. Figure 5 is a graph showing binary search for a predetermined desired voltage in an ADC using a single variable resistor, according to some embodiments of the present invention. Figure 6 is a graph showing binary search for a predetermined desired voltage in an ADC using two variable resistors, according to some embodiments of the present invention.

[0061] In some embodiments, one or more variable matching resistors are modified via a binary search technique to find a predetermined desired voltage in the ADC during calibration.

[0062] A binary search begins by comparing the middle element of the array with the target value. If the target value matches the element, its position in the array is returned. If the target value is less than the element, the search continues in the lower half of the array. If the target value is greater than the element, the search continues in the upper half of the array. By doing this, the binary search technique eliminates the half in each iteration where the target value cannot exist.

[0063] The above description of binary search is applicable to the search for a desired voltage in the ADC of the present invention, except that a potentiometer step is used instead of a sorted array and the "target value" is the voltage returned by the ADC.

[0064] At the start of the calibration cycle, all variable matching resistors are set to their midpoints to establish a known good state and in preparation for the next step. The MCU then begins a binary search to establish a target ADC value of approximately 1V, or within a specific range of 1V (e.g., ±0.1V).

[0065] This process is performed on the first variable matching resistor to determine its desired resistance. Once this process is complete, any additional variable matching resistors present in the circuit are iterated over to find their respective desired values.

[0066] A simpler implementation of a single potentiometer can be seen in Figure 5. At the start of the calibration cycle (specified by marker A1), the potentiometer is set to its intermediate value (100k ohms). Next, a binary search is performed by modifying Rwiper0 in 8 steps to narrow down the voltage measured by the ADC to a desired value of (0.9±0.1)V (i.e., within 0.1V from the desired value of 1V). In this case, the binary search was completed in approximately 12ms.

[0067] For comparison, Figure 6 shows the signals from the MCU to the potentiometers during potentiometer calibration performed using dual variable matching resistors. Each signal pulse is the result of instructing each potentiometer to increase or decrease its resistance according to the binary search technique described above. A single signal is started when the sensor circuit is energized and rises sharply from 0V, reaching a positive value and then flattening out at the positive value, at which point the calibration logic obtains its reading for binary search. The sensor circuit is then de-energized, and the signal drops sharply from the positive value to 0V, but the potentiometers are adjusted for the next step in the calibration process.

[0068] Again, the midpoints of both matching resistors are set, and using the timescale at the top of the diagram, the Rwiper0 binary search starts at 6.085 seconds and finishes at 6.094 seconds (total 9 ms). Then, Rwiper0 is kept at the value found in the first binary search, and then the Rwiper1 binary search starts at 6.095 seconds and finishes at 6.105 seconds (another total of 10 ms).

[0069] At the end of this double potentiometer calibration search, the voltage in the ADC voltage is 0.9947V over a period of 20ms, just below the target of 1V. Compared to a single potentiometer search, it is found that implementing this system as a dual potentiometer configuration yields a more accurate final voltage at the expense of a longer calibration time. This time is still too small for the end user to observe, so the trade-off is very good. In addition, by including a second potentiometer, the circuit can be tuned to a much wider range of pressure response curves, accommodating a greater tolerance for variations generated during the pad manufacturing process.

[0070] In preliminary tests conducted by the inventors, progressively increasing weights were placed directly on the pressure-sensitive ink. When these tests were performed without using the variable matching resistor of the present invention and without setting the ADC voltage to a desired target, the minimum weight that had to be added before a measurable difference in the pad's response could be observed was 100 grams.

[0071] By repeating this precise test using a new dual potentiometer circuit with a 1V target, the inventors found that the minimum weight that had to be added before confirming a measurable difference in the pad's response was 1 gram.

[0072] This test measured the material of the pads and the weight response of the pad circuits. This test demonstrated that the circuit of the present invention has much better fidelity than previously used pad circuits.

[0073] Figure 8 is a flowchart of a method for correcting inaccurate calibration of a pressure-sensitive pad under a mattress, according to some embodiments of the present invention.

[0074] The pad is intended to be calibrated before use with only the mattress in place over the sensing zone. However, field tests conducted by the inventors concluded that the pad may not be properly calibrated before use, or that users may forget to calibrate the pad before use.

[0075] For example, if staff calibrate the pad with the patient on the mattress before use, during use the pad may detect an extremely heavy mattress and miss the patient getting out of bed. Conversely, if staff calibrate the pad without a mattress before use, during use the pad may detect the weight of the mattress as the weight of the person relative to the pad, and the pad may detect the patient getting out of bed even when the patient is still on the bed.

[0076] The new potentiometer-based calibration system allows for post-calibration determination of whether the initial calibration was accurate through a new check.

[0077] In the pad of the present invention, a mattress without a patient must generate a signal of a predetermined voltage (e.g., 1V) in the ADC to the pad, while a mattress with a patient must generate a signal close to 0V (but not 0V) in the ADC to the pad.

[0078] This means that if readings above 1V are consistently measured in the ADC over a period of time, excess weight has been removed from the pad. This likely indicates a pad that was miscalibrated due to a person being on the mattress during calibration.

[0079] On the other hand, if the ADC consistently measures approximately 0V over a period of time, it indicates that excessive weight is being applied to the pad. This likely indicates a pad that has been incorrectly calibrated due to the mattress not being placed over the sensing zone during calibration.

[0080] Since both of the above scenarios (voltages of approximately 1V or 0V) can legitimately occur in the short term, it is undesirable to adjust the variable matching resistor too large or too quickly after detecting the aforementioned potential miscalibration. For example, when the mattress is lifted while the sheets are being changed, the voltage at the ADC may briefly exceed approximately 1V. Alternatively, if there is weight on the mattress in addition to the patient, such as another person sitting on the bed, the voltage at the ADC may be 0.

[0081] To address this, in some embodiments of the present invention, if the above scenario occurs after calibration is complete, the voltage of the variable matching resistor device is changed by one step every few minutes to change the voltage of the ADC and bring the voltage in the ADC within the desired range. In our tests, as a result, the miscalibrated pads were typically corrected within 30 minutes after pressure was applied to or removed from the pads (based on the type of miscalibration that occurred).

[0082] Therefore, in the 800, after calibration, the voltage in the ADC is measured several times over a certain period. This period can be several minutes, for example, 2 minutes, 3 minutes, 5 minutes, or 6 minutes. Note that any length of the period is within the scope of the present invention.

[0083] In step 802, a check is performed to determine whether the measured voltage at the ADC during the period is sustainably well above a predetermined desired voltage (e.g., above 1V and above 0.1V). "Sustainably" can be defined as any selected percentage of the a priori selected measured value, such as 40% or more, 50% or more. In this case, the resistance of the matching resistor increases in step 804, and a new period begins.

[0084] If the measured voltage at the ADC during the period does not consistently exceed a predetermined desirable value in 802, a new check is performed in 806 to determine whether the measured voltage at the ADC is consistently close to 0V (e.g., less than 0.1V) during the period. "Consistently" can be defined as any selected percentage of the a priori selected measured value, such as 40% or more, 50% or more, etc. In this case, the resistance of the matching resistor decreases in 808, and a new period begins.

[0085] If the measured voltage at the ADC during the period is not consistently close enough to 0V, then the calibration is determined to be accurate in 810.

[0086] It should be noted that the use of the lower method 720 may not be limited to periods after calibration or when user activity is detected. In fact, over time, the variable resistance material in the sensing zone of the pad degrades, reducing its sensitivity to pressure and resulting in measurements indicating the absence of a person from the mattress, even when a person is on the mattress. Therefore, the lower method 720 may be used periodically or continuously to assess the validity of the initial calibration and to compensate for the degradation of the material in the sensing zone of the pad. The dotted arrows returning from step 810 to step 800 indicate embodiments in which the lower method 720 is performed periodically or continuously, even after the calibration has been deemed accurate in the previous cycle.

[0087] While the present invention has been described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects, time measures, and functionalities described in one or more of the individual embodiments are not limited to the specific embodiment in which they are described, but rather can be applied individually or in various combinations to one or more other embodiments of the present invention, regardless of whether such embodiments are described or whether such features are presented as part of the described embodiment. Therefore, the breadth and scope of the present invention should not be limited by any of the exemplary embodiments described above.

Claims

1. A pressure-sensitive pad configured to be placed under a mattress and to identify the presence or absence of a threshold weight on the mattress, A signal generator configured to generate electrical signals, A sensing zone having a sensing resistor with a first resistance that changes in response to the pressure applied to the sensing zone, At least one variable matching resistor having a second resistance, which is in series with the sensing resistor and the signal generator. A microcontroller unit (MCU) having an analog-to-digital converter (ADC) configured to receive and measure a portion of the electrical signal at an electrical junction between the sensing resistor and the at least one variable matching resistor, comprising an MCU configured to control the second resistance of the at least one variable matching resistor, The sensing zone is configured to be connected to the electrical grounding section. The pressure-sensitive pad is To position the sensing zone beneath the mattress without adding any additional weight to the mattress, To generate an electrical signal via the aforementioned signal generator, The portion of the aforementioned electrical signal that reaches the ADC is automatically measured by the ADC. The microcontroller unit automatically changes the second resistance of the at least one variable matching resistor until a desirable value for the second resistance is found such that the portion of the electrical signal reaching the ADC is within a predetermined range of a desired voltage. It is configured to be calibrated for any mattress, In operation after calibration, The microcontroller unit is configured to set the second resistor to the desired value, A pressure-sensitive pad, wherein the signal generator is configured to regularly generate an electrical signal that moves to the electrical junction via the at least one variable matching resistor, from the electrical junction to the ADC, and from the electrical junction to the electrical ground via the sensing resistor, such that the portion of the electrical signal that reaches the ADC relies on the first resistance of the sensing resistor, and the portion of the electrical signal that reaches the ADC can be processed to identify the presence or absence of a threshold weight on the sensing zone.

2. The at least one variable matching resistor comprises two variable matching resistors in series, each of the two variable matching resistors having a corresponding second resistor independently controlled by the microcontroller unit. The MCU controls the second resistor of the at least one variable matching resistor, Modifying the first portion of the second resistor to reach a first desired value, thereby changing the portion of the electrical signal that reaches the ADC to have a voltage within a predetermined rough range of the desired voltage, while keeping the second portion of the first resistor fixed. The first portion of the second resistor is fixed and maintained at the first desired value, and the second portion of the second resistor is modified to reach the second desired value, thereby the portion of the electrical signal reaching the ADC has a voltage within a predetermined range of the desired voltage, and the predetermined range is smaller than the predetermined coarse range. It is configured to change automatically, The pressure-sensitive pad according to claim 1, wherein in operation, the microcontroller unit is configured to set the first portion of the second resistor to a first desired value and the second portion of the second resistor to a second desired value.

3. The pressure-sensitive pad according to claim 1, further comprising a third matching resistor in series with the at least one variable matching resistor, the third matching resistor having a fixed resistance.

4. In operation, the MCU determines whether the calibration is effective. (i) Commence the period, (ii) At the end of the period, perform the first check to determine whether the measured voltage of the ADC during the calibrated period was always sufficiently above a predetermined desirable voltage. (iii) If the check in step (ii) is positive, increase the first desired value and repeat all steps from step (i). (iv) If the check in step (iii) is negative, at the end of the period, a second check is performed to determine whether the measured voltage of the ADC during the calibrated period was always sufficiently close to 0V. (v) If the check in step (iv) is positive, decrease the first desired value and repeat all steps from step (i). (vi) If the check in step (iv) is negative, determine that the calibration was accurate. A pressure-sensitive pad according to claim 1, further configured to determine by

5. The pressure-sensitive pad according to claim 4, wherein the MCU is configured to repeat all steps from step (i) after performing step (vi).

6. A method for calibrating a pressure-sensitive pad configured to be placed under a mattress and to identify the presence or absence of a threshold weight on the mattress, (i) A signal generator configured to generate electrical signals, A sensing zone having a sensing resistor with a first resistance that changes in response to the pressure applied to the sensing zone, At least one variable matching resistor having a second resistance, which is in series with the sensing resistor and the signal generator. A microcontroller unit (MCU) having an analog-to-digital converter (ADC) configured to receive and measure a portion of the electrical signal at an electrical junction between the sensing resistor and the at least one variable matching resistor, wherein the MCU is configured to control the second resistance of the at least one variable matching resistor. The process of providing (ii) A step of connecting the sensing zone to the electrical grounding section, (iii) The step of placing the sensing zone under the mattress without adding any additional weight to the mattress, (iv) A step of generating an electrical signal via the signal generator, (v) A step of automatically measuring the portion of the electrical signal that reaches the ADC using the ADC, (vi) The process of automatically changing the second resistance of the at least one variable matching resistor via the microcontroller unit until a desirable value for the second resistance is found such that the portion of the electrical signal reaching the ADC is within a predetermined range of a desired predetermined voltage. A method that includes this.

7. The step of providing at least one variable matching resistor includes providing two variable matching resistors in series, each of the two variable matching resistors having a corresponding second resistor independently controlled by the microcontroller unit. The step of automatically changing the second resistance of the at least one variable matching resistor is: Modifying the first portion of the second resistor to reach a first desired value, thereby changing the portion of the electrical signal that reaches the ADC to have a voltage within a predetermined rough range of the desired voltage, while keeping the second portion of the first resistor fixed. The first portion of the second resistor is fixed and maintained at the first desired value, and the second portion of the second resistor is modified to reach the second desired value, thereby such that the portion of the electrical signal reaching the ADC has a voltage within a predetermined range of the desired voltage, and the predetermined range is smaller than the predetermined coarse range. The method according to claim 6, including the method described in claim 6.

8. A method for calibrating a pressure-sensitive pad configured to be placed under a mattress and to detect the presence or absence of a threshold weight on the mattress, A step of calibrating the pressure-sensitive pad according to the method of claim 6, A step of setting the second resistor to a desired value via the microcontroller unit, A step of generating an electrical signal, configured such that the portion of the electrical signal that reaches the ADC depends on the first resistance of the sensing resistor, and that the signal moves to the electrical junction via the at least one variable matching resistor, from the electrical junction to the ADC, and from the electrical junction to the electrical ground via the sensing resistor. A step of processing the portion of the electrical signal that reaches the ADC so as to identify the presence or absence of a threshold weight on the sensing zone. A method that includes this.

9. The step of providing at least one variable matching resistor includes providing two variable matching resistors in series, each of the two variable matching resistors having a corresponding second resistor independently controlled by the microcontroller unit. The step of automatically changing the second resistance of the at least one variable matching resistor is: Modifying the first portion of the second resistor to reach a first desired value, thereby changing the portion of the electrical signal that reaches the ADC to have a voltage within a predetermined rough range of the desired voltage, while keeping the second portion of the first resistor fixed. The modification involves fixing and maintaining a first portion of the second resistor at a first desired value, and changing a second portion of the second resistor to reach a second desired value, wherein the portion of the electrical signal reaching the ADC has a voltage within a predetermined range of the desired voltage, and the predetermined range is smaller than the predetermined coarse range. The method according to claim 8, wherein the step of setting the second resistor to a desired value via the microcontroller unit includes setting a first portion of the second resistor to a first desired value and setting a second portion of the second resistor to a second desired value.

10. Whether the calibration is effective, (a) Commence the period, (b) At the end of the period, perform the first check to determine whether the measured voltage of the ADC during the calibrated period was always sufficiently above a predetermined desirable voltage. (c) If the check in step (b) is positive, increase the first value and repeat all steps from step (a). (d) If the check in step (c) is negative, at the end of the period, a second check is performed to determine whether the measured voltage of the ADC during the calibrated period was always sufficiently close to 0V. (e) If the check in step (d) is positive, decrease the desired value and repeat all steps from step (a). (f) If the check in step (d) is negative, determine that the calibration was accurate. The method according to claim 8, further comprising the step of determining by

11. The method according to claim 10, further comprising the step of repeating all steps from step (a) after step (f).

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