Bathtub system and bath entry determination method

Abstract

To provide a bathtub system suppressing false detection that someone enters a bathtub and being simply installed, and a bathtub enter determination system.SOLUTION: A bathtub system 100 includes a bathtub 10 having a sill surface 10a, a water level sensor 20 provided in the bathtub 10 and capable of measuring a water level L, and a control device 30. The bathtub system 100 determines that someone enters a bathtub according to a relation among the water level L, a water level change amount equivalent to a standard human body volume, and a reference water level Lr lower than the sill surface 10a by the water level change amount equivalent to the standard human body volume. The bathtub system 100 inputs the water level L, the water level change amount equivalent to the standard human body volume, the reference water level Lr, a first threshold th1, and a second threshold th2, and outputs that someone enters the bathtub according to a relation among the water level L, the water level change amount equivalent to the standard human body volume, the reference water level Lr, a first threshold th1, a second threshold th2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a bathtub system and a bath entry determination method. [Background technology]

[0002] In recent years, drowning has become a common cause of death in residential accidents. In nursing care settings, whether in a facility or at home, care recipients are often monitored by humans while bathing. However, human monitoring is reaching its limits in terms of both time and effort. Therefore, systems that use sensors to monitor care recipients while bathing are being actively studied.

[0003] For example, Patent Document 1 proposes a bath oil supply device that detects the presence or absence of a person using a water level sensor that detects the water level from changes in pressure in the bathtub and a human presence sensor in the bathroom.

[0004] Furthermore, Patent Document 2 proposes a method of determining whether or not a person has entered a bathtub by installing a load meter under the bathtub.

[0005] Furthermore, Patent Document 3 proposes a sensor that calculates the bath volume based on the water level in the bathtub and the bather's vital signs, and determines whether to enter or exit the bath based on the amount of change. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-002643 [Patent Document 2] Japanese Patent Application Publication No. 2019-158289 [Patent Document 3] Japanese Patent Application Publication No. 2019-203621 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of Patent Document 1 or Patent Document 3, there is a risk of false detection when the water level in the bathtub changes due to adding hot water or hot water overflowing from the bathtub when it is full, so the presence or absence of people is detected by using an entry / exit detection sensor that detects entry and exit, etc., which requires the installation of multiple sensors. In the case of Patent Document 2, a water heater that can be connected to a sensor must be used, and if it is to be retrofitted, it may be necessary to change the water heater. Additionally, it is possible to detect entry and exit using pyroelectric sensors, but there is a risk of false detection due to the influence of temperature and steam.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a bathtub system and a bath entry determination method that can be easily installed and suppresses false detection of bath entry. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following aspects. (1) One aspect of the present invention is a bathtub system that includes a bathtub with a frame surface, a water level sensor installed in the bathtub that can measure the water level, and a control device, and determines whether a person has entered the bath based on the relationship between the water level, the amount of water level change equivalent to a reference human body volume, and a reference water level that is lower than the frame surface by the amount of water level change equivalent to the reference human body volume. (2) In (1) above, the water level, the amount of water level change equivalent to the reference human body volume, the reference water level, a first threshold value, and a second threshold value may be input, and the fact that a person has entered the bath may be output according to the relationship between the water level, the amount of water level change equivalent to the reference human body volume, the reference water level, the first threshold value, and the second threshold value. (3) In the above (2), the first threshold value may be greater than the second threshold value. (4) In the above (2) or (3), the first threshold value may be the amount of change in water level equivalent to the reference human body volume. (5) In any of (2) to (4) above, the first threshold value may be a threshold value when the water level is in a low water level state below the reference water level, and the second threshold value may be a threshold value when the water level is in a high water level state above the reference water level. (6) In (5) above, the control device may include a memory unit in which the first threshold value and the second threshold value are set, and a judgment unit that determines that water has entered the tank when the amount of water level change exceeds the first threshold value in a predetermined time from the low water level state, or when the amount of water level change exceeds the second threshold value in a predetermined time from the high water level state. (7) In the above (6), the control device may calculate the amount of change in water level from a first water level at a first point in time and a second water level at a second point in time after a predetermined time has elapsed since the first point in time. (8) In (6) or (7) above, the control device may calculate a first average water level by sampling and averaging the water level at multiple points in a first hour, and a second average water level by sampling and averaging the water level at multiple points in a second hour consecutive to the first hour, and calculate the amount of water level change from the first average water level and the second average water level. (9) In any of (6) to (8) above, the control device may be provided with an alarm unit that issues an alarm when a predetermined time has elapsed since the time of tank entry determination and the amount of water level change does not exceed a third threshold value. (10) In any of the above (1) to (9), the water level sensor may be disposed on the inner surface of the bathtub. (11) One aspect of the present invention is a method for determining whether a person has entered a bathtub having a frame surface, which inputs the water level, the amount of water level change equivalent to a reference human body volume, a reference water level that is lower than the frame surface by the amount of water level change equivalent to the reference human body volume, a first threshold value, and a second threshold value, and outputs the fact that a person has entered the bath based on the relationship between the water level, the amount of water level change equivalent to the reference human body volume, the reference water level, the first threshold value, and the second threshold value. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a bathtub system and a bath entry determination method that can suppress false detection of bath entry and can be easily installed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is an explanatory diagram of the bathtub system according to the embodiment in a low water level state, simulating a state before entering the bath. [Figure 2] FIG. 10 is an explanatory diagram of the bathtub system according to the embodiment when a bather enters the bath from a low water level state. [Figure 3] FIG. 10 is an explanatory diagram of a high water level state assumed before entering the bathtub in the bathtub system according to the embodiment. [Figure 4] FIG. 10 is an explanatory diagram of the bathtub system according to the embodiment when a bather enters the bathtub from a high water level state. [Figure 5] FIG. 10 is an explanatory diagram of a low water level state assumed before the bathtub is discharged in the bathtub system according to the embodiment. [Figure 6] FIG. 10 is an explanatory diagram of the bathtub system according to the embodiment when the water is discharged from the bathtub from a low water level state. [Figure 7] FIG. 10 is an explanatory diagram of a high water level state assumed before the bathtub is discharged in the bathtub system according to the embodiment. [Figure 8] FIG. 10 is an explanatory diagram of the bathtub system according to the embodiment when the water is discharged from the bathtub from a high water level state. [Figure 9] FIG. 10 is a flow chart of tank entry determination by the control device. [Figure 10] FIG. 10 is a flow chart of the tank discharge determination by the control device. DETAILED DESCRIPTION OF THE INVENTION

[0012] A bathtub system 100 according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram of a low water level state, simulating a state before entering the bath, in a bathtub system 100 according to an embodiment. Unless otherwise specified, the water level L is expressed as the position of the water surface on a vertical axis with the frame surface 10a of the bathtub 10 set as zero, and with the point above the frame surface 10a set as positive and the point below set as negative. For example, when the water surface is at the frame surface 10a, the water level L is zero, and when the water surface is 5 cm below the frame surface 10a, the water level L is minus 5 cm.

[0013] (bathtub system) As shown in Figure 1, a bathtub system 100 according to one embodiment includes a bathtub 10 having a frame surface 10a, a water level sensor 20 mounted on the bathtub 10 and capable of measuring the water level L, and a control device 30. The bathtub system 100 determines whether a person has entered the bath based on the relationship between the water level L, the amount of water level change corresponding to a reference human body volume, and a reference water level Lr that is lower than the frame surface 10a by the amount of water level change corresponding to the reference human body volume. This allows the system to determine whether a person has entered the bath, regardless of whether the initial water level L is low or high. Bathtub system 100 also receives the water level L, the amount of water level change corresponding to a reference human body volume, the reference water level Lr, a first threshold value th1, and a second threshold value th2 as inputs, and outputs a notification that someone has entered the bath based on the relationship between the water level L, the amount of water level change corresponding to a reference human body volume, the reference water level Lr, the first threshold value th1, and the second threshold value th2. This makes it possible to determine that someone has entered the bath, regardless of whether the initial water level L is low or high.

[0014] (bathtub) The bathtub 10 has an inner tub that forms a recessed space downward so that water can be stored in it. The inner tub has a bottom surface and an inner side surface that extends upward from the periphery of the bottom surface. The bathtub 10 has a frame surface 10a that is the same as the water surface when the bathtub 10 is filled with water.

[0015] (Water level sensor) The water level sensor 20 is a sensor capable of measuring the water level. The water level sensor 20 may be, for example, a pressure-type water level sensor that detects a voltage that changes in response to a change in water pressure.

[0016] The water level sensor 20 can be installed in the inner tub of the bathtub 10. The water level sensor 20 is preferably installed on the inner surface (the inner surface along the long side of the rectangle when the inner tub of the bathtub 10 is rectangular in plan view) excluding the backrest of the bathtub 10 (the inner surface along the short side of the rectangle when the inner tub of the bathtub 10 is rectangular in plan view) so as not to come into contact with the bather and impair their relaxation. The water level sensor 20 may also be installed on the bottom of the inner tub.

[0017] The pressure receiving portion of the water level sensor 20 is disposed at a position a predetermined distance below the frame surface 10a. The pressure receiving part of the water level sensor 20 is preferably located at a distance below the frame surface 10a that is smaller than the depth of the bathtub 10, i.e., at a position shallower than the depth of the bathtub 10. Specifically, the pressure receiving part of the water level sensor 20 is preferably located at a distance of 300 to 600 mm below the frame surface 10a. This allows detection even when the amount of hot water is as low as possible.

[0018] (Control device 30) The control device 30 includes a memory unit 31 that stores a first threshold value th1 for a low water level state where the water level L is below a reference water level Lr (water level at the frame surface 10a minus the reference human body volume Vm = reference water level Lr), which is a water level equivalent to the reference human body volume Vm, and a second threshold value th2 for a high water level state where the water level L is above the reference water level Lr. The reference human body volume Vm may be a value that is appropriately set in advance. The reference human body volume Vm may be a value that assumes, for example, a state in which the half body of a small woman is immersed in water, and can be set arbitrarily. Even if the reference human body volume Vm is a fixed value, the reference water level Lr varies depending on the horizontal cross-sectional area of ​​the portion of the inner tub where water collects. The threshold in this embodiment refers to the amount of change in water level. The thresholds in this embodiment have the relationship: water level change amount equivalent to reference human body volume ≧ first threshold th1 > second threshold th2. The water level change amount equivalent to reference human body volume is equal to or greater than the first threshold th1. The first threshold th1 is greater than the second threshold th2.

[0019] Here, the first threshold value th1 may be the amount of water level change equivalent to a reference human body volume. The amount of water level change equivalent to a reference human body volume Vm. The amount of water level change equivalent to a reference human body volume differs depending on the horizontal cross-sectional area of ​​the inner tub where water collects, and is therefore set for each shape of the bathtub 10. This makes it possible to detect when a person enters or leaves the bathtub 10.

[0020] The control device 30 also includes a determination unit 32 that determines whether a person has entered the bathtub if the amount of water level change ΔL exceeds a first threshold value th1 within a predetermined period of time from a low water level (see FIG. 2) or if the amount of water level change ΔL exceeds a second threshold value th2 within a predetermined period of time from a high water level (see FIG. 4). The amount of water level change ΔL may be the vertical distance from a first water level L1 at a first point in time to a second water level L2 at a second point in time that is later than the first point in time. This allows the detection of a person entering the bathtub, even if the initial water level L is high (close to full water) and water overflows from the frame surface 10a when a person enters the bathtub. Even if the amount of water level change ΔL, which is the distance from the initial water level L to the frame surface 10a, is less than the amount of water level change equivalent to the reference human body volume, this can be distinguished from a case where water is simply supplied to the bathtub 10 until the bathtub becomes full.

[0021] The control device 30 may include an alarm unit 33 that issues an alarm when the amount of water level change ΔL does not exceed the third threshold value th3 for a predetermined period of time from the time of bath entry determination. This allows the person or an outsider to be notified that a person has been in the bath for a long period of time. The alarm method may be, for example, sound or display. The alarm means may be, for example, a speaker or display via a communication means connected to the bathtub system 100.

[0022] (action) Next, the operation of the bathtub system 100 will be described together with the control flow of the control device 30. FIG. 1 is an explanatory diagram of a low water level state assumed before bathing in a bathtub system 100 according to an embodiment. FIG. 2 is an explanatory diagram of bathtub system 100 according to an embodiment when entering the bath from a low water level state. FIG. 3 is an explanatory diagram of bathtub system 100 according to an embodiment when entering the bath from a high water level state. FIG. 4 is an explanatory diagram of bathtub system 100 according to an embodiment when entering the bath from a high water level state. FIG. 5 is an explanatory diagram of a low water level state assumed before bathing in a bathtub system 100 according to an embodiment. FIG. 6 is an explanatory diagram of bathtub system 100 according to an embodiment when bathing from a low water level state. FIG. 7 is an explanatory diagram of a high water level state assumed before bathing in a bathtub system 100 according to an embodiment. FIG. 8 is an explanatory diagram of bathtub system 100 according to an embodiment when bathing from a high water level state. FIG. 9 is a flowchart of bath entry determination by the control device 30. FIG. 10 is a flowchart of bathing removal determination by the control device 30.

[0023] (Entry decision) A bath entry determination method using the bathtub system 100 will be described. The bath entry determination method is a method for determining whether a person has entered a bathtub 10 having a frame surface 10a. The bath entry determination method inputs the water level L, the amount of water level change corresponding to a reference human body volume, a reference water level Lr that is lower than the frame surface 10a by the amount of water level change corresponding to the reference human body volume, a first threshold value th1, and a second threshold value th2, and outputs information indicating that a person has entered the bath based on the relationship between the water level L, the amount of water level change corresponding to the reference human body volume, the reference water level Lr, the first threshold value th1, and the second threshold value th2. This makes it possible to detect whether a person has entered the bath whether the initial water level L is low or high. Specifically, the reference water level Lr is set in advance in the storage unit 31 of the control device 30. The reference water level Lr may be a water level that is lower than the frame surface 10a by an amount equivalent to the reference human body volume Vm. In addition, a first threshold value th1 for a low water level state in which the water level L is below a reference water level Lr that is lower than the frame surface 10a by the amount of water level change equivalent to the reference human body volume is set in advance in the memory unit 31 of the control device 30. Furthermore, if the bathtub system 100 has a notification function, the third threshold value th3 is set in the storage unit of the control device 30 in advance.

[0024] (A1) The control device 30 measures the water level L at predetermined time intervals (for example, every second) using the water level sensor 20 (water level measurement step S11).

[0025] The control device 30 may calculate the amount of water level change ΔL from the first water level L1 at the first time point t1 and the second water level L2 at the second time point t2 a predetermined time after the first time point t1. The predetermined time is, for example, two seconds. This allows the amount of water level change ΔL to be constantly acquired.

[0026] Here, the control device 30 may calculate a first average water level L1m by sampling and averaging the water level L at multiple points in time during a first time D1, and a second average water level L2m by sampling and averaging the water level L at multiple points in time during a second time D2 subsequent to the first time D1, and then calculate the water level change amount ΔL from the first average water level L1m and the second average water level L2m. Note that the first time D1 and the second time D2 are, for example, 5 seconds. This makes it possible to obtain the water level change amount ΔL useful for detecting tank entry and exit without detecting instantaneous water level changes unrelated to tank entry and exit.

[0027] In addition, the control device 30 may calculate the water level change amount ΔL by, for example, adopting the smaller of the results calculated from the first water level L1 at the first point in time t1 and the second water level L2 at the second point in time t2 a predetermined time after the first point in time t1, and the results calculated from the first average water level L1m obtained by sampling and averaging the water level L at multiple points in time during the first time D1, and the second average water level L2m obtained by sampling and averaging the water level L at multiple points in time during the second time D2 subsequent to the first time D1.

[0028] (A2) Next, thresholds are set according to the water level L. The first threshold th1 is set to a value that does not exceed the amount of water level change corresponding to the reference human body volume. The second threshold th2 is set to a value that does not exceed the first threshold th1. The first threshold th1 is larger than the second threshold th2. In detail, as shown in Figure 1, when the water level L measured by the water level sensor 20 is in a low water level state below the reference water level Lr, the threshold is set to a first threshold th1 (for example, 30 mV, which is the change in voltage detected by the water level sensor 20 when the water level rises by an amount equivalent to the reference human body volume). On the other hand, as shown in Figure 3, when the water level L measured by the water level sensor 20 is in a high water level state above the reference water level Lr, the threshold is set to a second threshold th2 (for example, 5mV, which is the value obtained by subtracting 45mV, which is the voltage detected by the water level sensor 20 at the current water level L, from 50mV, which is the voltage detected by the water level sensor 20 when the water level L is at the sill surface 10a).

[0029] (A3) When the water level L is low and a person enters the tank, the water surface rises by a water level change amount ΔL within a predetermined time, as shown in Figure 2. At this time, the determination unit 32 of the control device 30 compares the water level change amount ΔL with a first threshold value th1 (first comparison step S12). If the water level change amount ΔL exceeds the first threshold value th1, it is detected that a person has entered the tank.

[0030] (A4) On the other hand, if the water level L before the person enters the bath is high, when the person enters the bath, the water level rises by an amount of water level change ΔL within a predetermined time, as shown in FIG. 4. When the person enters the bath, the water accumulated in the bathtub 10 is displaced by the person's volume, and some of the water overflows and is discharged from the frame surface 10a of the bathtub 10. At this time, the determination unit 32 of the control device 30 compares the amount of water level change ΔL after the person enters with a second threshold value th2 (second comparison step S13). If the amount of water level change ΔL exceeds the second threshold value th2, it is detected that a person has entered the bath.

[0031] (A5) When entry into the tank is detected, the time point of entry into the tank is appropriately recorded in the memory unit 31, and a timer is started.

[0032] Here, the control device 30 issues a notification via the notification unit 33 if the amount of water level change does not exceed the third threshold th3 for a predetermined time from the time of bath entry determination (notification step S14). The predetermined time is, for example, 10 minutes. The third threshold th3 may be, for example, the amount of water level change equivalent to a reference human body volume. The third threshold th3 may be, for example, the same as the first threshold th1. This allows the person or an outside party to be notified that the person has been bathing for a long period of time. The notification method may be, for example, a method of emitting a sound, display, etc. in response to a command from the notification unit 33. The notification means may be, for example, hardware such as a speaker or display connected to the bathtub system 100 via communication means such as a communication cable, a wireless device, or a router.

[0033] Thus, the control device 30 includes a determination unit 32 that determines whether a person has entered the bathtub if the amount of water level change ΔL exceeds the first threshold th1 within a predetermined time from a low water level state, or if the amount of water level change ΔL exceeds the second threshold th2 within a predetermined time from a high water level state. This allows the detection of a person entering the bathtub, even if the initial water level L is high (close to full water) and water overflows from the frame surface 10a, and the amount of water level change ΔL, which is the distance from the initial water level L to the frame surface 10a, is less than the amount of water level change equivalent to the reference human body volume. This distinguishes this from a case where water continues to be supplied to the bathtub 10 until the bathtub becomes full. Therefore, whether the initial water level L is low or high, a person entering the bathtub can be detected.

[0034] (Delivery decision) Next, the bath discharge determination by the bathtub system 100 will be described. In the tank discharge determination, similar to the tank entry determination, a reference water level Lr is set in advance in the memory unit 31 of the control device 30. The reference water level Lr may be a water level L lower than the frame surface 10a by an amount equivalent to the reference human body volume Vm. Furthermore, a first threshold value th1 that is common to both the low water level state and the high water level state is set in advance in the memory unit 31 of the control device 30. Note that the control device 30 does not need to use the second threshold value th2 when determining whether to discharge the water from the tank. The determination of whether to discharge the product from the tank may be performed on the condition that the determination of whether to put the product into the tank has been performed. The determination of whether to discharge the product from the tank may be performed independently of the determination of whether to put the product into the tank.

[0035] (B1) The control device 30 measures the water level L at predetermined time intervals (for example, every second) using the water level sensor 20 (water level measurement step S21). Note that the details of the measurement of the water level L and the calculation of the water level change amount ΔL in the tank discharge determination are the same as those in the tank return determination.

[0036] (B2) Next, a threshold value is set. In detail, as shown in Figure 5, when the water level L measured by the water level sensor 20 is in a low water level state below the reference water level Lr, the threshold is set to a first threshold th1 (for example, 10 mV, which is the change in voltage detected by the water level sensor 20 when the water level rises by an amount equivalent to the reference human body volume). Also, as shown in Figure 7, when the water level L measured by the water level sensor 20 is in a high water level state above the reference water level Lr, the threshold is set to the first threshold th1 (for example, 10 mV, which is the change in voltage detected by the water level sensor 20 when the water level rises by an amount equivalent to the reference human body volume), as in the case of a low water level state.

[0037] (B3) When the water level L is low and a person leaves the bath, the water level drops by an amount of water level change ΔL within a predetermined time, as shown in Figure 6. At this time, the determination unit 32 of the control device 30 compares the amount of water level change ΔL with the first threshold value th1 (third comparison step S22). If the amount of water level change ΔL exceeds the first threshold value th1, it is detected that someone has left the bath.

[0038] (B4) Similarly, when the water level L is high and a person leaves the bath, the water level drops by an amount of water level change ΔL within a predetermined time, as shown in Figure 8. At this time, the determination unit 32 of the control device 30 compares the amount of water level change ΔL with the first threshold value th1 (third comparison step S22). If the amount of water level change ΔL exceeds the first threshold value th1, it is detected that someone has left the bath.

[0039] (B5) When a tank discharge is detected, the tank discharge determination time is appropriately recorded in the memory unit 31. When a tank discharge is detected, the timer that was started at the time of the tank entry determination may be reset.

[0040] In this way, the control device 30 is equipped with a determination unit 32 that determines that water has been discharged from the tank when the amount of water level change ΔL exceeds the first threshold value th1 within a predetermined time. This makes it possible to detect that water has been discharged from the tank whether the initial water level L is high or low.

[0041] The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0042] The bathtub system 100 according to this embodiment includes a bathtub 10 having a frame surface 10a, a water level sensor 20 attached to the bathtub 10 and capable of measuring the water level L, and a control device 30. The bathtub system 100 determines whether a person has entered the bath based on the relationship between the water level L, the amount of water level change corresponding to a reference human body volume, and a reference water level Lr that is lower than the frame surface 10a by the amount of water level change corresponding to the reference human body volume. This allows entry to be detected whether the initial water level L is low or high. The bath entry determination method according to this embodiment is a method for determining whether a person has entered a bathtub 10 having a frame surface 10a. The bath entry determination method inputs the water level L, the amount of water level change corresponding to a reference human body volume, a reference water level Lr that is lower than the frame surface 10a by the amount of water level change corresponding to the reference human body volume, a first threshold value th1, and a second threshold value th2, and outputs information indicating that a person has entered the bath based on the relationship between the water level L, the amount of water level change corresponding to the reference human body volume, the reference water level Lr, the first threshold value th1, and the second threshold value th2. This makes it possible to detect whether a person has entered the bath whether the initial water level L is low or high. [Explanation of symbols]

[0043] 100 Bathtub System 10 Bathtub 10a Frame surface 20 Water level sensor 30 Control device 31 Storage section 32 Judgment section 33 Information Department D1 1st period D2 2nd Hour L water level L1 1st water level L1m 1st average water level L2 2nd water level L2m 2nd average water level Lr reference water level S11 Water level measurement step S12 First comparison step S13 Second comparison step S14 Notification step S21 Water level measurement step S22 Third comparison step t1 Time 1 t2 Second time point th1 First threshold th2 Second threshold th3 Third threshold Vm Reference human body volume ΔL Water level change

Claims

1. A bathtub system including a bathtub having a frame surface, a water level sensor provided in the bathtub and capable of measuring the water level, and a control device, The control device includes a storage unit configured with a reference water level change amount corresponding to a reference human body volume, a reference water level that is lower than the frame surface by the reference water level change amount, a first threshold value for when the water level is in a low water level state below the reference water level, and a second threshold value for when the water level is in a high water level state above the reference water level; a determination unit that determines that water has entered the tank when the amount of water level change exceeds the first threshold value in a predetermined time from the low water level state, or when the amount of water level change exceeds the second threshold value in a predetermined time from the high water level state; A bathtub system comprising:

2. The bathtub system according to claim 1, wherein the control device calculates the amount of change in water level from a first water level at a first point in time and a second water level at a second point in time a predetermined time after the first point in time.

3. The bathtub system described in claim 1 or claim 2, wherein the control device calculates a first average water level by sampling and averaging the water level at multiple points in a first time period, and a second average water level by sampling and averaging the water level at multiple points in a second time period consecutive to the first time period, and calculates the amount of water level change from the first average water level and the second average water level.

4. The bathtub system described in any one of claims 1 to 3, wherein the control device is provided with an alarm unit that issues an alarm when the amount of water level change does not exceed the amount of water level change equivalent to the reference human body volume or a third threshold value that is the same as the first threshold value for a predetermined time from the time of bath entry determination.

5. The bathtub system according to any one of claims 1 to 4, wherein the water level sensor is arranged on the inner surface of the bathtub.

6. A method for determining whether a person has entered a bathtub having a frame surface, comprising: a water level change amount equivalent to a reference human body volume; a reference water level that is lower than the frame surface by the water level change amount equivalent to the reference human body volume; a first threshold value when the water level in the bathtub is in a low water level state below the reference water level; and a second threshold value when the water level is in a high water level state above the reference water level. A method for determining whether water has entered the tank, which determines that water has entered the tank if the amount of water level change exceeds the first threshold value in a predetermined time from the low water level state, or if the amount of water level change exceeds the second threshold value in a predetermined time from the high water level state.

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