GB2334127A

GB2334127A - Alertness monitor

Info

Publication number: GB2334127A
Application number: GB9802517A
Authority: GB
Inventors: Nigel Robert Oakley; Gary Steven Ungless
Original assignee: Cambridge Neurotechnology Ltd
Current assignee: Cambridge Neurotechnology Ltd
Priority date: 1998-02-05
Filing date: 1998-02-05
Publication date: 1999-08-11
Also published as: JPH11332856A; GB9802517D0

Abstract

An alertness monitor for maintaining the alertness of a user is implemented as a wrist-worn device. The monitor incorporates a movement sensor 20 for generating signals dependent on the movements of the user. The movement-dependent signals are input to a processor 26 which generates an alarm signal if the movement-dependent signals do not exceed a predetermined threshold during a predetermined time interval. The alarm signal drives an alarm buzzer 12. When the user is roused by the buzzer, he or she presses a switch 8 to cancel the alarm signal and the buzzer. In a second aspect, the processor generates alarm signals at random time intervals, independently of the user's movement. The user's alertness is maintained by the need to cancel each alarm signal by operating the switch.

Description

Alertness Monitor The invention relates to an alertness monitor. n many instances it is important to monitor the alertness of individuals and to ensure that they remain alert. Cne example is a pilot of an aeroplane. Often, a pilot neecs to remain alert through long periods of inactivity, such as during a long flight in a commercial airliner. It is known that there is a risk under such circumstances of a pilot becoming drowsy or even falling asleep.

The invention provides an alertness monitor as defined -n the appendant independent claims. Advantageous or preferred features of the invention are defined dependent subclaims.

In a first aspect the invention thus advantageously provides an alertness monitor in which a movement deter is coupled to an alarm. The alertness monitor may then worn by an individual, such as a pilot, to monitor his her) movements. If no movements above a predetermined movement threshold are detected during a predetermined time it is assumed that the individual has become drowsy, or even allen asleep, and an alarm is raised. The threshold used to assess the alertness of the individual cn the basis of sensed movements may be a fixed threshold eve or may be variable to a limited extent. example, an alarm may be raised even if movements sensed which exceed a preset fixed threshold but when such movements are infrequent. Any threshold parameters required to assess alertness in such ways may advantageously be preset.

The type ci alarm may vary depending on the application f ne alertness monitor. For exemple in the cockpit of an aeroplane it may be appropriate to sound an audible alarm to rouse or waken the pilot or to alert others in the cockpit that the pilot's level of alertness has dropped.

The alarm in a cockpit should preferably not, of course, oe confusable with any other audible signals used in the cockpit. In other circumstances, other types of alarm might be appropriate, such as a visual alarm or a buzzer which may be silent but be felt by the wearer of the alertness monitor.

The alertness monitor is advantageously a wrist-worn device, similar to a wristwatch, and incorporates the movement monitor ant te alarm in a single housing. This makes it simple and unobtrusive to use.

Advantageously the movement threshold ray be preset, by the user or otherwise. For example the threshold may be low, medium, high or none. A medium threshold is preferably about 0.05g acceleration, which is about 0.5ms-2. The optimum threshold may advantageously be chosen according to the environment in which the alertness monitor is to be used. For example, in an environment where there is little v vibration or background movement, a low ow threshold may be set in order to avoid false alarms if the user is still but not drowsy, while in an environment where there is much vibration or background movement, a high threshold may be set to filter out movements of the user which may be caused by the environnement even if the user is asleep.

The monitor preferably filters, by frequency, signals derived from movements to try to isolate deliberate movements by the user from movements derived from the environment. For example, if the monitor is wrist-worn it may advantageously sense movements of the wrist within a frequency range of about 1 to 20 Hz, or preferably 2 to Hz.

The frequency range is advantageously varied if the monitor is arranged to detect other body movements. n addition, the preset movement threshold advantageously suffers to reflect the different accelerations typical ci other body movements.

Advantageously the predetermined time period, after w-hn an a arm is raised if insufficient movement has been sensed, may be preset either by the user or otherwise. time period may preferably be 1, 2, 5 or 10 minutes, -- any other suitable time depending on the application or the alertness monitor.

The alertness monitor may be self-contained, with adjustments sch as those discussed above being mace via controls on the monitor itself, or it may be provided with means to interface to a PC, or other computer. The functionality of the monitor may then be set up in software using controls entered into the PC. in either case, the alertness monitor advantageously has a button or the like to allow a user to turn the monitor on and off, and to cancel the alarm if it stunts. For example a button may be pressed for 2 seconds, or other suitable time, to turn the alarm function on or off and pressed for only a short time to cancel an aarm.

The functionality of the alertness monitor may advantageously include an ability to log movements cf tne user within an internal memory even if no alarm is ra Any alarms may also be logged, as well as the time taken b the user to cancel any alarms. These tat ma be downloaded later on to a PC, or other computer, for analysis. For example the data may be displayed in actogram form. Thus the continuous level of alertness and movement or the user may be studied, including the response time of the user to cancel any alarms.

Experiments indicate that if a user has fallen asleep, the response time is long, whereas if a user is merely drowsy, the response time is quicker; false alarms when the user is alert may be cancelled very quickly. Preferably, the monitor records the response time to a resolution of about 30ms.

Post-use data analysis of this kind may advantageously allow the monitor te be preset for mote effective alertness monitoring in future, by tailoring its performance to a user and his or her environment.

Preferably, if an alarm-cancel button is pressed when no alarm is present, a marker is inserted in the memory.

The alertness monitor unit preferably has an @ED which flashes to show when the unit is operational (alarm unction on). Tc save power, the -D ma flash only after about four seconds with no movement If the alarm function is enabled.

In a second aspect, the invention provides an alertness monitor in which a unit worn by a user raises an alarm at various time intervals, and requires the user to cancel the alarm, for example by pressing a button as described above. The alarm may be independent or the user's movement. For example, this arrangement may be implemeted in the movement-sensing alertness monitor described above by setting the movement threshold to none.

Alternatively it may be implemented in combination with a movement-sensing alertness function.

The alarm may be of any type, as described above, and an alarm may be raised, or sounded, at random or pseudo- random time intervals, for example between 1 minute and 15 minutes with an average interval of 5 minutes.

This function may advantageously be used both to maintain the user's alertness and to monitor his alertness ovetime. or example, i response times to turn cff the alarm are logged and downloaded later on, an variations response times may be noted.

If the alarm on the alertness monitor according to the invention is audible, the maximum alarm Level i is preferably about 84dbA at 30 cm and 95dbA at 10 cm.

Advantageously different aiar levels, such as high and normal, may be set.

Advantageously the alertness monitor is wrist-worn, having a body size of about 32mm by 28mm by 9mm and a weight of about 19g (about 23g including a strap to fasten the unit to the wrist).

Preferably the alertness monitor's memory can store up to about 16300 activity samples, alarms or marKers. certain applications the alertness monitor unit preferably comprises a means for implementing a radio link with a remote supervisory station. The supervisory station may then advantageously receive an alarm signal from the monitor unit and raise an alarm to alert another person, for example in case the user o the alertness monitor has not been roused by the alarm on the alertness monitor unit. Suitable applications for this embodiment may be for patients in a hospital or nursing home, or workers in hazardous environments. In each case, a patient or worKer may become unconscious or be Inured and need assistance. The alertness monitor would then sense the lack of motion of the user, or the failure of the user to cancel an alarm, and transmit a signal to a supervisory station in order to summon outside assistance.

Specific embodiments of the invention ill now be described by way of example, with reference to the drawings in which; Figure 1 is a perspective view of a wrist-worn alertness monitor according to a first embodiment of the invention; Figure 2 is a schematic block diagram of the circuitry of the alertness monitor of Figure 1; Figures 3 and 4 show a circuit diagram of the circuitry of the alertness monitor of Figure 1; Figure 5 is a plan view of the layout of components on the upper side of a circuit board of the alertness monitor or Figure 1; Figure 6 is a flow chart illustrating the main interrupt routine of of the alertness monitor of Figure 1; and Figure 7 is a flow chart illustrating the main control loop or one alertness monitor of Figure 1.

Figure 1 shows a perspective view of an alertness monitor according to a first embodiment of the invention. The monitor comprises 2 casing 2, containing the operative components or one monitor, and a strap with a buckle S to allow the monitor to be worn on a user's wrist.

Mounted in the upper surface of the casing are a push button 8, an LED light emitting diode, 10 and an alarm buzze- 12. A hole 14 above the buzzer allows the stun the alarm to be heard mote clearly.

The monitor functions by sensing movements of the user's wrist and sounding an alarm if no movements above a predetermined threshold are detected within a predetermined time. The push button, or switch, and the LED allow the user to control the monitor. The monitor also logs the user's movements and can be interfaced to a PC for downloading stored data and for setting the operating parameters of the monitor.

Figure 2 is a block diagram of the circutor or the monitor. An accelerometer 20 senses the user's movements and outputs an acceleration signal. The accelerometer output is connected via an amplifier 22 and a band-pass filter 24 to a microprocessor 26. The microprocessor als has an input from the push button, or switch, 8. The microprocessor nas outputs coupled to the LED 10 and the alarm 12. The microprocessor is also coupled for two-way communication with a PC interface 28 and a memory 30. A reference clock (not shown) is the basis cf the timing the microprocessor.

The accelerometer 20 is a piezo-ceramic device oriented within the casing 2 of the monitor to sense movements o the wrist. The acceleration signal generated by one accelerometer is amplified by the amplifier filtered by the band-pass filter to remove frequencies outside the range from 2Hz to ilHz. These frequency limits may be varied to some extent but experiment indicates that this range of frequencies reflects the normal range of movements of the wrist. The filtered signal is then processed by software within the microprocessor.

The microprocessor incorporates an analog-to-digital converter which samples the filtered acceleration signal at 32Hz. The sampling frequency is controlled by the reference clcck. The digitised signa then passes through a slow DC filter to remove any DC component. In practice, the DC component arises because the accelerometer output is amplified by an amplifier, which generates a DC output voltage component. The DC component may also vary with temperature, so the microprocessor runs the slow DC filter to track and remove the slowly changing DC component caused by temperature changes.

The microprocessor then rectifies the DC filtered signal. so that all movements cc the user are registered as positive, regardless of direction to produce a movement evel signal.

To assess whether to sound an alarm, the movement level signal generated every 1/32 seconds is compared with the predetermined movement threshold. If the movement level signal does not exceed the movement threshold for a continuous time interval equal to the predetermined time, the microprocessor outputs a signal t sound the alarm. ne movement threshold (corresponding to a sensed level of acceleration of the wrist) and the corresponding time period are preset via the PC interface and stored in the memory. net the alarm sounds, one user can switch off the alarm using the switch, or push button.

The switch is also used to turn the monitor on or off. To do this, the switch must be pressed for 2 seconds or more.

The LED is used to show whether the monitor is switched on. The microprocessor can cause the LED to flash when the monitor is initially turned on by means to the switch.

It also causes the LED to flash if the monitor is switched on but detects no movement for a period of 4 seconds. The reason for this is in case the user takes cf the monitor without switching it off. If the monitor is oaken off and placed on a stationary surface, after 4 seconds the LED flashes to remind the user to turn it off. It is desirable to save power by turning the mor tor off when it is not required, particularly If it is batter powered.

During use, the microprocessor logs the movement level signal it the memory as follows. This data is sampled during successive sampling periods (or data-logging intervals or epochs), rather than stored continuously, it order to reduce required storage capacity. Specifically, each time the movement level signal generated at 32Hz exceeds the predetermined movement threshold during a sampling period, an accumulator is incremented. The ength of the sampling period is preset, cot example vie the PC interface, and may be, for example, between 15 seconds and 15 minutes, or may be as sort as 1 second.

The accumulator value is stored in the memory at the end o each sampling period, and the accumulator is reset to zero before the start of the next sampling period.

The microprocessor also logs certain other events in memory. Whet the alarm sounds, the microprocessor logs the time taken or the user to cancel the alarm by pressing the switch. This is termed the user's response time and Will vary depending on the state of alertness the user. The microprocessor also records it memory occasions when the user presses the switch he to alarm has beet sounded. This allows the user to retort one of external events in the logged data stream from the accelerometer. These are termed time-stamped events. For example, a pilot may wish to record the beginning and end or a flight.

The microprocessor also carries out z regular test for alertness by sounding the alarm at pseudo-random intervals. Each time, the alarm sounds until the user presses the switch. The response time of the user to each alarm is recorded in the memor to a resolution of about 30ms (this corresponds to the 32Hz clock frequency).

The PC interface permits the monitor to be coupled to a for the transfer of data and control signals. In the embodiment, one interface is a short-range radio link which operates whet the monitor is docked it a corresponding holder coupled via a 9-pin RS232 port to a PC, but alternatively may be implemented in any convenient manner. The PC runs software for receiving data output from the monitor, in the form of activity-rest patterns, records of alarm soundings and corresponding reaction times, and time-stamped events, and for transmitting data to the monitor, such as the various predetermined thresholds described above. Data is transferred it ASCTT format.

The microprocessor is also coupled to a transponder 31 for transmitting radio signals to a remote supervisory station. The transponder is preferably contained within the housing 2, but could be a separate unit connected to the alertness monitor. The microprocessor drives the transponder t transmit a radio signal if the user of the alertness monitor fails to cancel an alarm within a predetermined time after the alarm is raised. This is because the user may then be unable to help themselves, for example because they are unconscious or injured. The supervisory station, on receiving the signal from the monitor, alerts a third party to bring assistance to the user of the alertness monitor.

Figures 3 and 4 show a more detailed circuit diagram of the monitor of Figure 1. The circuit portions or components corresponding to the blocks in Figure 2 are numbered accordingly.

The voltage signal output by the piezo-ceramic accelerometer 20 is amplified by amplifier 22. The amplification has some high-frequency roll-off due to capacitors CS and C6. The piezo-ceramic accelerometer is a charge device and therefore the low-frequency roll-off is determined by the resistor R9. The values of CS, C6 and R9 produce a band-pass range of approximately 2Hz to 11Hz. The signal is bi-polar around a 1.2 volt DC reference voltage.

The monitor is powered by a 3 volt battery 32.

A second amplifier 34 is used to detect the presence of a carrier signal in a tuned circuit 29 which forms the PC interface 28. This is an inductor/capacitor tuned circuit comprising an inductor L1 and a capacitor Cl. It is tunec to 104kHz.

To interface with a PC, the alertness monitor is docked in a recess tn an interface unit. When so docked, the tuned circuit @ 29 in the monitor is positioned case t a corresponding tuned circuit, tuned to 104kHz, withIn the interface unit, which is coupled via signalling circuitry to a RS232 9-pin serial port of the PC.

To transmit data and control signals to the alertness monitor, the signalling circuitry drives the tuned circuit in the interface unit, generating an interface carrier signal which Induces the tuned circuit 29 of the monitor to resonate. The tuned circuit 29 is connected vie a diode 37 to an input of the amplifier 34, which therefore generates a "high" signal at its cutout when the tuned circuit 29 resonates. The amplifier output is "low" when the tuned circuit 29 does not resonate. The amplifier output is coupled to the microprocessor 26. The signalling circuitry in the interface unit therefore switches the tuned circuit it one interface unit on and off in accordance with a serial data stream received from the PC, which gives rise to a corresponding "high" and "low" data stream being received by the microprocessor in the monitor. Data and control signals, including movement thresholds and other operating parameters required by the alertness monitor, can thus be entered by a user into the PC using appropriate software, and, after a hadshake procedure iniated when the microprocessor first detects a "high" signal on the output of the amplifier 34, can be downloaded by the PC into the monitor. A data rate of CC baud is used.

The interface unit also permits data to be transmitted bv the monitor to the PC. To do this, the microprocessor loads the tuned circuit 29 via a resistor 39, which is coupled to the microprocessor, in accordance with the data to be transmitted. Meanwhile, the signalling circuitry drives the tuned circuit in the interface unit, and thus excited the tuned circuit 29 in the monitor. The power required to do this varies with the load applied to the tuned circuit 23 In one monitor, which can be detected the signalling circuity and converted into a corresponding data stream to be input to the PC. A data rate of 1200 baud is used to transmit data from the monitor to the PC.

This data includes the logged movement and alarm data stored in the memory of the monitor during use, which can be displayed and analysed by the PC using appropriate scftware.

The memory 30 iS implemented as two serial -POM non- volatile memories U3 and U4 for recording movement levels 2nd response ttmes, as well as the preset movement ant time thresholds.

The alarm 12 is driven by a buzzer drive circuit 33 and en associated voltage booster circuit 41 to too so the volume produced. The driving waveform for the alarm is produced bv the microprocessor in software.

The microprocessor 25 checks the switch 8 and operates the LED 10. A clock 35 provides a clock signal to the microprocessor.

The components of the circuit in Figures 3 and 4 are mounted on both sides of a circuit board 36, which is shaped to cit within the casing 2. The layout or components on the upper side of the circuit board is shown in Figure 5. Of note is the position of the piezo-ceramic accelerometer 20. This comprises a piezo-ceramic cantilever carrying a weight 42 at one end and supported near its cther end on a limb 40 extending from the circuit board 36. The cantilever is aligned transversely to the wrist when the monitor is worn.

Figures 6 and ' are flow charts Illustrating the o the microprocessor during operation of the alertness monitor.

Figure 6 slows, as a flow diagram, the functions of the microprocessor 26 while it monitors the movement of a user. The microprocessor samples the signal from one accelerometer (after it is amplified and filtered) once every 1/32 seconds. Each such sample is handled as follows (and as described above). After the microprocessor's clock has been increment by 1/32 seconds (step 50) the filtered and amplified signal from the accelerometer is analogue-to-digital converted, passed through a slow DC filter and rectified stet 52; . The microprocessor onet compares the digitized movement signa with the predetermined movement threshold also step 52'.

The microprocessor then repeats this process (steps 50, 52: until 1 second has passed (step 54; . fter 1 second has passed, tc a movement was detected above the preset threshold during that 1-second period (step 56), the microprocessor resets a no-movement counter step 58) and continues processing the signal from the accelerometer or a further second in the same way.

If n movement above the preset threshold is detected during 1 second of sampling (step 56), the no-movement counter is increment by 1 (step 60). The no-movement counter is then compared with the preset time period (step 62) after which at a alarm is to be raised if no movement above the movement threshold has bee detected. The preset time period may therefore be set at any integer number of seconds. the no-movement counter is below the preset time limit, the microprocessor samples the accelerometer signal for a further second. If the no- movement counter is equal to cr cove one reset me limit, then the microprocessor sets a flat for an alarm to be generated (step 64). If a alarm flag Is set, then a separate control routine is entered to handle subsequent operation.

It should be noted that figure 6 does not include the procedure for logging movement data (described above), which is not essential for the alertness monitoring function.

Figure 7 is a flow diagram or the control sequence of the microprocessor handling the generation and cancelling of alarms, interfacing with an external PC, and logging sampled mouvement data.

If an interface carrier signal is detected (step 70@ In the resonant circuit 29 of the PC interface 28, i.e. if t alertness monitor has bee docked i its corresponding interface unit for interfacing with a PC ant as received a carrier signal rom the PC, then it enters into ocmmunication with indicates that a sampling period has ended, then the value in the accumulator is saved in the EEPROM memory (step 82) and the accumulator and the data-logger timeout are reset.

Normal monitoring of the accelerometer signal is then continued.

Claims

CLAIMS 1. An alertness monitor to be worn by cr secured to a user, comprising; a sensor for sensing movement of one user and generating a movement-dependent signal; an aiarm; and a processor coupled to the sensor and the alarm; in which the processor generates an alarm signal drive the alarm if the movement-dependent signal does not exceed a predetermined threshold during a predetermined time interval.
2. An alertness monitor according to claim 1, which is housed in a casing having a strap for securing the monitor, in use, to the user's wrist.
3. Ar. alertness monitor according to claim - or 2, in which one senscr is sensitive, in use, to movements of the user's wrist.
An alertness monitor according to any preceding claim, in which the sensor generates a signal which is filtered by a band-pass filter to generate the movement- dependent signal.
5. An alertness monitor according to ary preceding claim, further comprising a user-operable swtocn for cancelling the alarm signal.
An alertness monitor according to any preceding claim, further comprising a memory, coupiec to the processor, for logging the movement-dependent signal, and@ or the response time taken for a user to cancel an alarm signal.
7. An aletness monitor according to any preceding claim, further comprising an interface coupled to the processor for interfacting the monitor, when desired, to an external computer.
8. An alertness monitor according to claim 7, in which the predeterminate movement threshold and/or the predetermined time interval can be preset via the external computer.
9. An alertness monitor according to any preceding claim, in which the processor genrates an alarm signal to drive the alarm attime intervals, independently of the movement-dependent signal, to be cancelled by the user.
19. An alertness monitor according to claim 9, in which one time intervals are random cr pseudo-random time intervals.
11. An alertness monitor according to any preceding claim, comprising a transmitter for transmitting an alarm signal to a remote supervisory station.
2. A R method for maintaining the alertness of a user, comprising providing an alertness monitor to be worn by or secured to the user, the alertness monitor carrying out the steps of; sensing movements of one user ant generating a movement-dependent signal; and monitoring the movement-dependent signal and generating an alarm signal to drive an alarm if the movement-dependent signal does not exceed a predetermined threshold during a predetermined time interval.
13. A method according to claim 12, in which the alertness monitor s wrist-worn.
14. A method according to claim 12 or 13, further comprising a step in which the user operates a switch to cancel an alarm signal
15. A method according to claim 12, 13 or 14, further comprising the step of generating an alarm signal, independently of the user's movement, to drIve an alarm to ce cancelled by the user.
16. A method according to claim 15, in which the movement-independent alarm signals are generated at random or pseudo-random time intervals.
:-. An alertness monitor to be worn by or secured to a user, comprising; at alarm; a switch; and a processor coupled to the alarm and the switch; in which the processor generates at alarm signal to drive the alarm at time intervals, and the user operates the switch to cancel the alarm signal each time after the alarm is driven.
18. An alertness monitor according to claim 17, it which the time intervals are random or pseudo-random time intervals.
19. An alertness monitor according to claim 17 or 18, in which the time intervals between the generation of successive alarm signals fall within a predetermined range.
20. An alertness monitor according to claim 17, 18 or 19, comprising a memory for storing the response time taken by user t cancel an alarm signal after the generation cc the alarm signal.
21. An alertness monitor according to any of claims 17 to 20, comprising a transmitter for transmitting an alarm signal to a remote supervisory station.
22. A method of maintaining the alertness of a user, comprising providing an alertness monitor to be worn by or secured to the user, in which; the alertness monitor generates an alarm signal to drive an alarm at time intervals; and the user operates a switch to cancel the alarm signal each time after the alarm is driven.
23. A method according to claim 22, in which the time intervals are random or pseudo-random time intervals.
24. An alertness monitor substantially as described herein with reference to the drawings.
25. A method fcr maintaining the alertness cf a user, substantially as described herein with reference to the drawings.