Patent Description:
Pruritus, or itch, is a common symptom of many dermatological diseases, such as atopic dermatitis and senile xerosis, and usually results in the act of scratching. For patients with certain conditions, such as patients with atopic dermatitis and patients with both Alzheimer's disease and senile xerosis, itching may also result in the patient experiencing a vicious itch-scratch cycle, where the patient exhibits the act of near-constant scratching to relieve the itching, which often significantly impairs a patient's quality of life.

Often, the severity of itchiness experienced by a patient is determined through self-assessment and reporting by the patient (e.g., through the use of a visual analogue scale). However, in some cases, the patient is unable to verbalize the amount of itching being experienced. Whether a given patient is experiencing itching and the severity of that itching is difficult to objectively evaluate.

A device and a method for detecting scratching is disclosed by <NPL>.

One method for estimating the severity of itching is through the use of an actigraph device. An actigraph device is worn by a patient and measures the motor activity produced by the patient due to the act of scratching. The device may then estimate the severity of itching experienced by the patient by quantifying the amount of scratching measured. However, this method requires a specially-developed device that measures the amount of scratching as a lump sum (e.g., the cumulative amount of hours during a given time period, such as during sleep, that the patient scratches) and provides the data after the fact, rather than in real time. In addition, in order to estimate the amount of scratching exhibited by the patient, the movement data collected by the device must be thereafter analyzed in view of a recorded scratching video in order to distinguish motor activity due to scratching from motor activity due to other types of movements.

Smart devices, such as mobile smart phones, smart tablets, or the like, are multifunctional devices that are capable of wirelessly communicating with peripheral wearable devices, such as watches or bracelets. The wearable devices are often capable of performing similar functions as the central smart device. In certain cases, the wearable device also includes one or more sensors, such as an actigraph sensor capable of capturing movements of a wearer.

By providing an actigraph sensor on a wearable device, the wearable device can measure the amount of scratching in real time and the duration and frequency of the scratching can be accurately captured to the second. With the real time detection of scratching, the wearable device can alert the user with a distraction (by, for example, deploying a signal such as a vibration) to break the itch-scratch cycle. Based on scientific evidence, it has been established that the itch-scratch cycle can be broken with a distraction.

A system in accordance with the invention is defined in claim <NUM>. A method in accordance with the invention is defined in claim <NUM>.

According to an exemplary embodiment of the present disclosure, a system for monitoring and measuring itch of a patient includes a wearable device including an actigraph sensor; and a controller electrically connected to the wearable device and including a processor and a memory. The wearable device is configured to measure, via the actigraph sensor, a movement of the patient; and send data indicative of the measured movement of the patient to the controller. The controller is configured to receive, via the processor, the data indicative of the measured movement; and determine, via the processor, a scratching movement of the patient based on the data indicative of the measured movement.

According to one aspect of the system, the controller is also configured to measure an amplitude and a frequency of the data indicative of the measured movement, and the controller is also configured to determine whether the measured movement is a scratching movement based on the measured amplitude and the measured frequency.

According to another aspect of the system, the controller is also configured to determine whether the measured amplitude exceeds a predetermined amplitude and whether the measured frequency exceeds a predetermined frequency, and, if the measured amplitude exceeds the predetermined amplitude and the measured frequency exceeds the predetermined frequency, the controller is configured to determine that the measured movement is a scratching movement.

According to another aspect of the system, the wearable device is configured to alert the patient when the controller determines that the measured movement is a scratching movement.

According to another aspect of the system, the wearable device is configured to alert the patient with at least one of an auditory signal, a visual signal, and a tactile signal.

According to another aspect of the system, the wearable device also includes a heart rate sensor, the heart rate sensor is configured to measure a heart rate of the patient, and the controller is configured to determine a depth of sleep of the patient based on the measured heart rate.

According to another aspect of the system, a first time period is defined as a period between a first time, which is a time when an acceleration measured by the actigraph sensor is zero, and a second time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero, and a second time period is defined as a period between the second time and a third time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero, and the controller is configured to determine, via the processor, a scratching movement of the patient by determining that all of the following conditions are met: (<NUM>) a difference in a maximum absolute value of acceleration during the first time period and a maximum absolute value of acceleration during the second time period does not exceed a predetermined upper limit; (<NUM>) a difference in a length of time of the first time period and a length of time of the second time period does not exceed a predetermined upper limit; (<NUM>) a maximum absolute value of acceleration during the first time period is not less than a predetermined lower limit; (<NUM>) a length of time of the first time period does not exceed a predetermined upper limit; and (<NUM>) an error rate does not exceed a predetermined upper limit, the error rate being defined as a percentage of time periods among a predetermined number of previous time periods that fail to meet conditions (<NUM>) through (<NUM>).

According to another aspect of the system, the wearable device is a wrist-worn device.

According to another aspect of the system, the controller is located in an external device that is separate from the wearable device.

According to another aspect of the system, the external device is a mobile phone.

According to another aspect of the system, the wearable device is integral with the controller.

According to another exemplary embodiment of the present disclosure, a method for monitoring and measuring itch of a patient includes the steps of measuring, via a wearable device, a movement of the patient; sending, via the wearable device, data indicative of the measured movement of the patient to a controller; and determining, via the controller, a scratching movement of the patient based on the data indicative of the measured movement.

According to one aspect of the method, the step of measuring the data indicative of the measured movement includes measuring, via the controller, an amplitude of the data indicative of the measured movement; and measuring, via the controller, a frequency of the data indicative of the measured movement. The step of determining the scratching movement of the patient based on the data indicative of the measured movement includes determining the scratching movement of the patient based on the measured amplitude and the measured movement.

According to another aspect of the method, the step of determining the scratching movement of the patient based on the data indicative of the measured movement also includes determining, via the controller, whether the measured amplitude exceeds a predetermined amplitude; and determining, via the controller, whether the measured frequency exceeds a predetermined frequency. If the measured amplitude exceeds the predetermined amplitude and the measured frequency exceeds the predetermined frequency, the controller determines that the measured movement is a scratching movement.

According to another aspect, the method also includes alerting the patient, via the wearable device, when the controller determines that the measured movement is a scratching movement.

According to another aspect of the method, the wearable device alerts the controller via at least one of an auditory signal, a visual signal, and a tactile signal.

According to another aspect of the method, a first time period is defined as a period between a first time, which is a time when an acceleration measured by the actigraph sensor is zero, and a second time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero, and a second time period is defined as a period between the second time and a third time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero, and determining, via the controller, a scratching movement of the patient based on the data indicative of the measured movement includes determining that all of the following conditions are met: (<NUM>) a difference in a maximum absolute value of acceleration during the first time period and a maximum absolute value of acceleration during the second time period does not exceed a predetermined upper limit; (<NUM>) a difference in a length of time of the first time period and a length of time of the second time period does not exceed a predetermined upper limit; (<NUM>) a maximum absolute value of the acceleration during the first time period is not less than a predetermined lower limit; (<NUM>) a length of time of the first time period does not exceed a predetermined upper limit; and (<NUM>) an error rate does not exceed a predetermined upper limit, the error rate being defined as a percentage of time periods among a predetermined number of previous time periods that fail to meet conditions (<NUM>) through (<NUM>).

According to another aspect of the method, the wearable device is a wrist-worn device.

According to another aspect of the method, the controller is located in an external device that is separate from the wearable device.

According to another aspect of the method, the external device is a mobile phone.

<FIG> shows a system <NUM> for itch monitoring and measurement according to one embodiment. As shown in <FIG>, system <NUM> includes a wearable device <NUM> and a controller <NUM>. The wearable device <NUM> is electrically connected with the controller <NUM> such that the wearable device <NUM> can receive and/or send signals to the controller <NUM>. In certain embodiments, the wearable device <NUM> is wirelessly connected with the controller <NUM>. For example, the wearable device <NUM> includes a transceiver (not shown) configured to allow wireless communication between the wearable device <NUM> and the controller <NUM> and/or an external device. As one example, the transceiver is configured to operate using a frequency-hopping technique. According to one specific example, the transceiver is Bluetooth®-enabled and communicates with the controller <NUM> over a Bluetooth® link.

The wearable device <NUM> is configured to be worn by a user of the system <NUM>, such as a patient (for example, a patient suffering from an itching condition). In certain embodiments, the wearable device <NUM> is a wrist-worn device. For example, the wearable device <NUM> is a smart watch, such as an Apple Watch, or a smart bracelet or the like. In certain embodiments, an external device includes the controller <NUM> such that the controller <NUM> is physically separate from the wearable device <NUM>. For example, the controller <NUM> is a mobile communication device, such as a mobile phone, a tablet, a laptop computer, or the like. In other embodiments, however, the controller <NUM> is integrally provided with the wearable device <NUM>.

As shown in <FIG>, according to one aspect, the wearable device <NUM> includes one or more sensors <NUM>, a processor <NUM>, a memory <NUM>, a device interface <NUM>, and a display <NUM>. The one or more sensors <NUM> include an actigraph sensor configured to detect a movement of the user or patient. In addition, in some embodiments, the one or more sensors <NUM> may also include additional sensors such as a heart rate sensor, which is configured to detect a heart rate, or pulse rate, of the user or patient. The memory <NUM> is configured to store machine instructions that, when executed by the processor <NUM>, cause the processor <NUM> to perform operations to monitor and measure scratching movement and itch experienced by the user or patient, as will be described in further detail below. The memory <NUM> may also store data to effect presentation of one or more resources, content items, measurements, etc., via the display <NUM>. The processor <NUM> may include a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc., or combinations thereof. The memory <NUM> may include, but is not limited to, electronic, optical, magnetic, or any other storage or transmission device capable of providing the processor <NUM> with program or machine instructions. The memory <NUM> may include a floppy disk, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), magnetic disk, memory chip, read-only memory (ROM), random-access memory (RAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), erasable programmable read only memory (EPROM), flash memory, optical media, or any other suitable memory from which the processor <NUM> can read instructions. The instructions may include code from any suitable computer programming language such as, but not limited to, ActionScript®, C, C++, C#, HTML, Java®, JavaScript®, Perl®, Python®, Visual Basic®, and XML.

As also shown in <FIG>, the controller <NUM> includes a processor <NUM>, a memory <NUM>, a device interface <NUM>, and a display <NUM>. The memory <NUM> is configured to store machine instructions that, when executed by the processor <NUM>, cause the processor <NUM> to perform operations to monitor and measure scratching movement and itch experienced by the user or patient, as will be described in further detail below. The memory <NUM> may also store data to effect presentation of one or more resources, content items, measurements, etc., via the display <NUM>. The processor <NUM> may include a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc., or combinations thereof. The memory <NUM> may include, but is not limited to, electronic, optical, magnetic, or any other storage or transmission device capable of providing the processor <NUM> with program or machine instructions. The memory <NUM> may include a floppy disk, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), magnetic disk, memory chip, read-only memory (ROM), random-access memory (RAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), erasable programmable read only memory (EPROM), flash memory, optical media, or any other suitable memory from which the processor <NUM> can read instructions. The instructions may include code from any suitable computer programming language such as, but not limited to, ActionScript®, C, C++, C#, HTML, Java®, JavaScript®, Perl®, Python®, Visual Basic®, and XML.

<FIG> shows a flow diagram of a method used to measure and monitor itch according to one embodiment. As noted above, the wearable device <NUM> includes an actigraph sensor <NUM> that is configured to detect a movement of the user or patient. As shown in <FIG>, in a step S100, movement of the user or patient is measured using the actigraph sensor <NUM> of the wearable device <NUM>. Data indicative of the movement detected by the actigraph sensor <NUM> may be stored in the memory <NUM> and sent via the device interface <NUM> to the controller <NUM> in a step S200. In certain embodiments, the wearable device <NUM> is configured to continuously send, in real time (e.g., on a second-by-second basis), the data indicative of the movement detected by the actigraph sensor <NUM> to the controller <NUM> via the device interface <NUM>. In certain other embodiments, the wearable device <NUM> is configured to store the data indicative of the movement detected by the actigraph sensor <NUM> in the memory <NUM> and send the data indicative of the movement to the controller <NUM> after an entire body of data indicative of the movement has been measured and stored in the memory <NUM>. After a predetermined amount of time (for example, a period corresponding to a user or patient's entire sleep session), the wearable device <NUM> is configured to send the data indicative of the movement detected by the actigraph sensor <NUM> to the controller <NUM>.

In a step S300, the controller <NUM>, via the device interface <NUM>, receives the data indicative of the measured movement and determines, via the processor <NUM>, whether the movement constitutes a scratching movement based on the received data. For example, <FIG> show examples of data indicative of measured movement received by the controller <NUM>. As shown in <FIG>, the data includes the relative movement of the wearable device <NUM> as moved by the user or patient. In certain embodiments, the relative movement is measured in a three-coordinate system (e.g., X, Y, and Z coordinates, as shown in <FIG>). The controller <NUM>, via the processor <NUM>, may be configured to measure an amplitude of the relative movement of the wearable device <NUM> in one or more of the three coordinates and determine whether the amplitude exceeds a predetermined amplitude in one or more of the three coordinates. In addition, the controller <NUM> may be also configured to measure a frequency of the amplitude of the relative movement that exceeds the predetermined amplitude and determine whether the frequency exceeds a predetermined frequency in one or more of the three coordinates. If the measured amplitude does not exceed the predetermined amplitude and/or if the measured frequency does not exceed the predetermined frequency (i.e., NO at step S300), the controller <NUM> may be configured to determine that the user or patient is exhibiting non-scratching behavior (e.g., non-scratching movement), such as shown in <FIG>. As shown in <FIG>, the method proceeds to step S100 and continues to measure movement of the user or patient via the wearable device <NUM>. If the measured amplitude exceeds the predetermined amplitude and the measured frequency exceeds the predetermined frequency (i.e., YES at step S300), the controller <NUM> may be configured to determine that the user or patient is exhibiting scratching movement, such as shown in <FIG>. As shown in <FIG>, the method proceeds to a step S400, in which the system <NUM> alerts the user or patient to the scratching behavior, as described in more detail below. The method then proceeds to step S100 and continues to measure movement of the user or patient via the wearable device <NUM>. In the embodiments in which the wearable device <NUM> is configured to send the data indicative of the movement detected by the actigraph sensor <NUM> to the controller <NUM> after a predetermined period of time has elapsed, the controller <NUM> is configured to determine that the user or patient is exhibiting scratching movement after the predetermined period of time has elapsed and the data indicative of the movement detected by the actigraph sensor <NUM> has been received by the controller. Accordingly, in such embodiments, the controller <NUM> is configured to determine a timing and duration of the scratching movement after the predetermined period of time has elapsed.

<FIG> graphically illustrates an algorithm used to determine if the user or patient is engaged in scratching. The data indicative of the measured movement (for example, accelerometer data in three dimensional space) are the independent variables on which the algorithm bases calculations. The controller computes a time-course of acceleration based on a number of consecutive time periods. A first time period, such as time period t<NUM> shown in <FIG>, is defined as a period between a first time, which is a time when an acceleration measured by the actigraph sensor is zero, and a second time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero. A second time period, such as time period t<NUM> shown in <FIG>, is defined as a period between the second time and a third time, which is a next subsequent time when the acceleration measured by the actigraph sensor is zero. According to the algorithm, scratching is considered to be ongoing if all of the following predetermined conditions are met: (<NUM>) a difference in a maximum absolute value of acceleration during a time period and an immediately subsequent time period (shown as the difference between h<NUM> and h<NUM> in <FIG>) does not exceed a predetermined upper limit; (<NUM>) a difference in a length of a time period and an immediately subsequent time period (shown as the difference between l<NUM> and l<NUM> in <FIG>) does not exceed a predetermined upper limit; (<NUM>) a maximum absolute value of acceleration during a time period is not under a predetermined lower limit (shown as hmin in <FIG>); (<NUM>) a length of a time period does not exceed a predetermined upper limit; and (<NUM>) an error rate, defined as a percentage of time periods among a predetermined number of previous time periods (for example, time periods t<NUM>, t<NUM>, t<NUM>, and t<NUM> shown in <FIG>) that fail to meet conditions (<NUM>) through (<NUM>). Additionally, the algorithm relies on two additional predetermined conditions to determine when a scratching begins and when the scratching ends. Scratching is considered to have started if the acceleration values continuously meet all of the conditions (<NUM>) through (<NUM>) beyond a predetermined minimum time duration. Scratching is considered to have ended if the acceleration values do not meet any of the conditions (<NUM>) through (<NUM>) during a predetermined minimum number of consecutive time periods.

The algorithm accordingly allows for a highly reliable, real time detection of scratching by a user or patient. Combined with stimulation features (as described herein), the real-time detection of scratching provides to the user or patient an immediate response to distract the user or patient from scratching.

In certain embodiments, if scratching movement is determined by the controller <NUM>, the controller <NUM> may be also configured to determine the amount of scratching movement performed over a period of time. For example, the controller <NUM> may be configured to determine the amount of time the user or patient exhibits scratching behavior from a point in time in which scratching behavior was exhibited to first begin (e.g., at a given point in time, the controller <NUM> determines that the user or patient has scratched for a certain amount of time). Based on the movement determined by the controller <NUM> (e.g., whether the controller <NUM> determines that the user or patient is exhibiting non-scratching movement or scratching movement), the controller <NUM> may determine whether the movement indicates that the user or patient is experiencing itching. In some embodiments, the controller <NUM> is also configured to determine a severity of a scratching movement performed by the user or patient (e.g., minimal scratching, moderate scratching, severe scratching) based on the measured amplitude and the measured frequency of the scratch. Based on the determination of the severity of the scratch, the controller <NUM> may be configured to determine the severity of itching that the user or patient is experiencing.

As noted above, the one or more sensors <NUM> of the wearable device <NUM>, for example, also includes a heart rate sensor <NUM> configured to detect a heart rate of the user or patient. Data indicative of the heart rate detected by the heart rate sensor <NUM> may be stored in the memory <NUM> and sent via the device interface <NUM> to the controller <NUM>. In certain embodiments, the wearable device <NUM> is configured to continuously send, in real time, the data indicative of the heart rate detected by the heart rate sensor <NUM> to the controller <NUM> via the device interface <NUM>.

In certain embodiments, the controller <NUM>, via the device interface <NUM>, receives the data indicative of the measured heart rate and determines, via the processor <NUM>, whether the heart rate indicates that the user or patient is sleeping (e.g., whether the heart rate indicates a sleep depth of the user or patient). In this case, the controller <NUM> can monitor the amount of scratching (as determined by the received data indicative of the movement detected by the actigraph sensor <NUM> of the wearable device <NUM>) performed by the user or patient during a period of sleep. The controller <NUM> may be also configured to store the data indicative of the movement detected by the actigraph sensor <NUM> during the period of sleep as determined by the data indicative of the measured heart rate, in which the user or patient may later view via the display <NUM>.

In some embodiments, the wearable device <NUM> is configured to provide a signal to the user or patient to indicate that the user or patient is engaging in scratching behavior (e.g., step S400 as shown in <FIG>). According to one aspect, the signal is configured to distract the user or patient such that the user or patient stops engaging in scratching behavior. The signal is, for example, at least one of an auditory signal, a visual signal, and/or a tactile signal. For example, if the controller <NUM> determines that the user or patient is engaging in scratching movement, the controller <NUM> sends a signal, via the device interface <NUM>, to the wearable device <NUM> to alert the user or patient by emitting a sound, a light, and/or a vibration. For example, upon receiving a signal from the controller <NUM> to alert the user or patient, the wearable device <NUM> may alert the user or patient with a graphical display via the display <NUM> and/or a sound or alarm. By providing such alerts to the user or patient, the user's attention is lessened on the itch, thereby reducing the amount of scratching and breaking the itch-scratch cycle.

In certain embodiments, and as also shown in <FIG>, the controller <NUM>, via the device interface <NUM>, is configured to communicate with a central server <NUM> via a network, such as the Internet. The controller <NUM>, via the device interface <NUM>, may be configured to send movement data that may be stored on the central server <NUM>. The central server <NUM> may be accessed to view scratching behavior over more time periods. For example, a physician may access the central server <NUM> to view scratching behavior to determine, monitor, and/or alter treatment for itching.

The controller <NUM> may be also configured to provide a user interface, via the display <NUM>, which may be configured to allow the user or patient to enter, view, and/or change data relating to the system <NUM>. For example, the user interface may allow the user or patient to enter profile data regarding the user or patient. The profile data may include information relevant to the user's current conditions relevant to itch. For example, the user or patient may enter profile data that indicates the user's demographic information (e.g., age, gender, race, etc.), medical history, dermatological conditions (e.g., whether the user or patient has atopic dermatitis), levels of itching experienced, skin care routine (e.g., extent of use of moisturizer), current skin conditions (e.g., scar evaluation, extent of dry skin), and other relevant medical information (e.g., whether the user or patient has Alzheimer's disease, medications). In addition, the user interface may also allow the user or patient to monitor progress of treatment of itch. For example, the user interface may allow the user or patient to view scratching behavior over a select period of time (e.g., over a day, a month, a year, etc.) to view patterns in scratching during the time period. The user interface may also allow the user or patient to control (e.g., start and/or stop) when the wearable device <NUM> measures the user's movement. For example, the user interface allows the user or patient to indicate when the user or patient is going to sleep, allowing the system <NUM> to begin measuring the movement of the user or patient for scratching behavior.

The system and methods described herein allow for the measurement and monitoring itch by providing for real-time measurement of scratching movement. By measuring and analyzing scratching movement of a user or patient, itching experienced by the user or patient can be objectively evaluated and treated in real-time. This allows for the treatment of itching in a user or patient having conditions that cause severe itch-scratch cycles and/or conditions that prevent the user or patient from verbalizing the extent of itching experienced. In addition, the system <NUM> is useable in combination with other treatment methods. For example, the system <NUM> is useable in conjunction with anti-itch drugs and can thereby improve the efficacy of such drugs. The system <NUM> also allows the user or patient and/or the user's physician to objectively monitor the progress and/or efficacy of the drug treatment.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination.

Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated in a single software product or packaged into multiple software products embodied on tangible media.

References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms.

Thus, particular implementations of the subject matter have been described. In certain implementations, multitasking and parallel processing may be advantageous.

Claim 1:
A system for monitoring and measuring itch of a patient, comprising:
a wearable device (<NUM>) comprising an actigraph sensor (<NUM>); and
a controller (<NUM>) electrically connected to the wearable device (<NUM>) and comprising a processor (<NUM>) and a memory (<NUM>), characterized in that
the wearable device (<NUM>) is configured to:
measure, via the actigraph sensor (<NUM>), a movement of the patient; and
send data indicative of the measured movement of the patient to the controller (<NUM>); and the controller (<NUM>) is configured to:
receive, via the processor (<NUM>), the data indicative of the measured movement; and
determine, via the processor (<NUM>), a scratching movement of the patient based on the data indicative of the measured movement,
the controller (<NUM>) being further configured to determine occurrence of the scratching movement when conditions (<NUM>)-(<NUM>) are met:
(<NUM>) a difference in a maximum absolute value of acceleration during the first time period and a maximum absolute value of acceleration during the second time period does not exceed a predetermined upper limit, in which (i) the first time period is a period between a first time, which is a time when acceleration measured by the actigraph sensor (<NUM>) is zero, and a second time, which is a next subsequent time when the acceleration measured by the actigraph sensor (<NUM>) is zero, and (ii) the second time period is a period between the second time and a third time, which is a next subsequent time when the acceleration measured by the actigraph sensor (<NUM>) is zero;
(<NUM>) a difference in a length of time of the first time period and a length of time of the second time period does not exceed a predetermined upper limit;
(<NUM>) a maximum absolute value of acceleration during the first time period is not less than a predetermined lower limit;
(<NUM>) a length of time of the first time period does not exceed a predetermined upper limit; and
(<NUM>) an error rate does not exceed a predetermined upper limit, the error rate being defined as a percentage of time periods among a predetermined number of previous time periods that fail to meet conditions (<NUM>) through (<NUM>).