||||l|IllllllllllllllllllllIllllllllllllllllllllllllllllllllllllllIllllllll
`U8005197489A
`
`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,197,489
`
`Conlan
`
`[45] Date of Patent: Mar. 30, 1993
`
`[54]
`
`[75]
`
`ACTIVITY MONITORING APPARATUS
`WITH CONFIGURABLE FILTERS
`
`Inventor: Robert W. Conlan, Niceville, Fla.
`
`[73]
`
`Assignee:
`
`Precision Control Design, Inc., Fort
`Walton Beach, Fla.
`
`[21]
`
`[22]
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Appl. No.: 716,853
`
`Filed:
`
`Jun. 17, 1991
`
`Int. 01.5 .............................................. A613 5/103
`U.s. Cl. .................................... 128/782; 128/670;
`128/671; 128/690; 128/721
`Field of Search ............... 128/782, 774, 690, 721,
`128/722, 670, 671, 687, 713, 714, 419 PG, 419
`PT; 340/573
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,807,388 4/1974 Orr et a1. ............................. 128/690
`4,088,139
`5/1978 Auerbach ..................... 128/419PT
`4,117,834 10/1978 McPartland et a].
`.
`128/782
`
`5/1980 Walton ..................
`4,202,350
`128/690
`
`....... 128/782
`4,353,375 10/1982 Colburn et a].
`
`.......... 128/690
`4,425,921
`1/1984 Fujisaki et a].
`
`4,428,378
`1/1984 Anderson et a].
`128/419 PG
`
`4,819,652 4/1989 Micco ..................... l28/661.09
`
`4,830,021
`5/1989 Thornton ......
`128/707
`
`
`8/1990 Krctschmer et a .
`4,945,916
`128/671
`2/1991 Fore .................................... 128/721
`4,989,612
`5,010,887
`4/1991 Thomander ..
`........... 128/696
`
`4/1991 Sholder .................... 128/782
`5,010,893
`
`6/1991 Niwa ........................ 128/670
`5,025,791
`
`7/1991 Alt ...................... 128/419 OPG
`5,031,614
`8/1991» Thornton ..................... 128/670
`5,036,856
`
`5,044,365
`9/1991 Webb et a1.
`128/419 PG
`5,074,303 12/1991 Hauck .......................... 128/419 PG
`
`OTHER PUBLICATIONS
`
`Experimental Prototype (AM—16) Block Diagram.
`Redmond, D. and Hegge, F., Observations on the de-
`sign and specification of a wrist-wom human activity
`monitoring system Behavior Res. Methods, Instruments
`& Computer 1985 17(6), 659—669.
`
`Primary Examiner—Max Hindenburg
`Assistant Examiner—Guy V. Tucker
`Attorney, Agent, or Firm—Lockwood, Alex, Fitzgibbon
`& Cummings
`
`[57]
`
`ABSTRACT
`
`An activity monitor adapted to be worn on the non-
`dominant wrist of a subject includes a bimorphous beam
`motion sensor. The output signal of the sensor is ampli-
`fied in an amplifier circuit having a selectable amplifica-
`tion factor, and filtered by highpass and lowpass filter
`circuits having individually selectable cut-off frequen-
`cies to obtain an analog signal for- processing having a
`bandpass and amplitude characteristic corresponding to
`a particular body activity under observation. A control
`and processing circuit within the monitor includes a
`microprocessor which responds to either resident inter-
`nal operating instructions or to externally supplied op-
`erating instructions, or to designated data signal param-
`eters, to provide configuration control signals to the
`amplifier and filter circuits, and processing of the col-
`lected data, appropriate to the particular activity being
`monitored. The processed data is digitally stored in an
`internal memory for subsequent transfer through a data
`port to an associated computer for display or further
`processing.
`
`33 Claims, 8 Drawing Sheets
`
`
`
`|PR2018-00564
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`US. Patent
`
`Mar. 30, 1993
`
`Sheet 1 of 8
`
`5,197,489
`
`-/i'iill
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`|PR2018—OO564
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`US. Patent
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`Mar. 30, 1993
`
`Sheet 2 of 8
`
`5,197,489
`
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`|PR2018—00564
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`US. Patent
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`Mar. 30, 1993
`
`Sheet 3 of s
`
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`5,197,489
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`
`
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`US. Patent
`
`Mar. 30, 1993
`
`Sheet 6 of 8
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`5,197,489
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`
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`WITH COMPENSATION
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`WITHOUT COMPENSATION
`
`|PR2018—OO564
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`US. Patent
`
`Mar. 30, 1993
`
`Sheet 7 of 8
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`5,197,489
`
`BREATHING
`
`l‘
`
`' HI GAIN
`
`HEART
`
`FIG.14
`
`= Signal Amplitude .
`= Threshold Amplitude
`= Time Above Threshold
`= EpocH
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`
`where:
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`US. Patent
`
`Mar. 30, 1993
`
`Sheet 8 of 8
`
`5,197,489
`
`
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`|PR2018—00564
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`

`1
`
`5,197,489
`
`ACI‘IVITY MONITORING APPARATUS WITH
`CONFIGURABLE FILTERS
`
`BACKGROUND OF THE INVENTION
`
`5
`
`The subject invention relates to apparatus and meth-
`ods for monitoring activity of the human body. More
`particularly, the invention relates to apparatus, systems
`and methods by which the occurrence and length of
`certain types of body movements which form activity 10
`phenomenon can be selectively observed and accu-
`rately quantified.
`A human subject engages in a wide range of body
`' movements. Such movements can range from the vol-
`untary and visually perceptible—such as the movement 15
`of legs, arms and head, to the involuntary and visually
`imperceptible, such as the slight changes in elevation of
`skin caused by the rhythmic pulsations of blood and
`breathing.
`The observation of body movement can provide 20
`much information useful to physicians and researchers.
`For example, by observing a subject’s movements, the
`occurrence and length of natural phenomenon, such as
`wakefulness, rest and sleep can be determined. By ob-
`serving the nature of a subject’s movement, the occur- 25
`rence and severity of disorders and the effects of drugs
`or other therapy can be assessed. In many cases quantifi-
`cation of the subject’s movement is preferred so that the
`movement pattern of one subject can be compared with
`the movement pattern of others.
`-
`Direct visual observations of body movement are
`labor intensive, time consuming and tedious. Moreover,
`direct visual observations provide only a limited range
`of qualitative information, such as subjective descrip=
`tions of a subject’s visually perceptible movements. 35
`Little, if any, quantification in readily comparable val-
`ues, such as degree, strength, and/or violence of a sub-
`ject’s activity, and no information, either qualitative or
`quantitative, of a subject’s visually imperceptible move-
`ments is obtained. Furthermore, the value of qualitative 40
`information obtained by directly observing a subject is
`subject to question as such observations themselves may
`cause the subject to become conscious of and thereby
`alter his or her movements.
`
`30
`
`Activity monitors have been developed for observing 45
`and quantifying certain aspects of movement without
`the involvement of an observer. However, such moni-
`tors had disadvantages which limited their usefulness.
`For example, such prior monitors were typically of a
`size which interfered with free movement of the sub- 50
`ject, and typically had either little or no internal mem-
`ory and/or little or no data processing capabilities. In
`order that data produced by many of these activity
`monitors could be stored and/or processed it was neces-
`sary to connect the monitors through cables to external 55
`data storage and processing devices. Tethering the
`monitor in this way to an external device also tethered
`the subject to the device, thereby restricting the sub-
`ject’s movement and biasing the results.
`In those prior activity monitors which had internal 60
`memory, saturation of the memory occurred when the
`subject engaged in activity which produced a volume of
`data that, for the period of time over which the subject
`was being monitored, exceeded the capacity of the
`memory.
`This problem was aggravated because prior activity
`monitors were not selectively configurable to collect
`data only for a particular activity, so that unusable or
`
`65
`
`2
`irrelevant data was often allowed to occupy memory
`space along with usable data. Prior monitors did not
`have the capability to be reconfigured according to
`preset instructions and/or in response to the data col-
`lected by the monitor.
`Prior monitors typically utilized sensors to detect
`body movement which, because of the need to suppress
`harmonics and other artifacts from the limited memory,
`lacked the sensitivity to detect small .scale, visually
`imperceptible movements such as those caused by
`breathing, the beat of the heart, and the flow of blood.
`A demand therefore exists for an activity monitor and
`method by which the activity of a subject, even that
`activity which includes movements that are not neces-
`sarily visually perceptible, can be selectively observed
`and accurately quantified. The present inVention satis-
`fies this demand.
`
`is a general object of the present
`it
`Accordingly,
`invention to provide an improved apparatus, system and
`methods for selectively observing and accurately quan-
`tifying certain aspects of the motion of a subject.
`An object of the present invention is to provide an
`activity monitor having a size and construction such
`that
`the monitor may be conveniently worn on the
`subject.
`Another object of the present invention is to provide
`an activity monitor which can collect data regarding a
`subject’s activity automatically and according to in-
`structions initialized in the monitor.
`
`Another object of the present invention is to provide
`an activity monitor having a memory in which operat-
`ing instructions and collected data are stored.
`Another object of the present invention is to provide
`an activity monitor with which data regarding a sub-
`ject’s movement can be processed automatically and
`according to instructions initialized in the monitor.
`Another object of the preSent invention is to provide
`an activity monitor wherein the type of data collected
`and the processing of the data by the monitor can be
`automatically changed.
`SUMMARY OF THE INVENTION
`
`The present invention is directed to an activity moni—
`tor and methods by which both visually perceptible and
`visually imperceptible movement can be selectively
`observed and accurately quantified.
`The apparatus includes an activity monitor, or acti-
`graph, having a size, shape and construction that allows
`the monitor to be worn on the surface of the skin of a
`subject and which functions reliably and without re-
`striction of the subject’s movement. One preferred em-
`bodiment of the monitor of the present invention is
`configured for wearing on a subject’s non-dominant
`wrist. The monitor may be configured to be worn on
`other parts of a subject’s body as well.
`In particular, the activity monitor of the present in-
`vention includes a movement sensor by which the full
`range of a subject’s movement, even that which is visu-
`ally imperceptible, can be detected. A preferred sensor
`is a cantilever piezoelectric bimorph beam. The use of a
`bimorph beam as a sensor is advantageous in that it
`provides high sensitivity and operates without requiring
`any'operating power, such as from a battery, thereby
`conserving this generally limited resource. Further-
`more, such a sensor operates in the absence of a gravita-
`tional field thereby expanding the applications in which
`the monitor can be utilized.
`
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`5,197,489
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`4
`which the system normally generates so that counts
`generated by the detector are caused by variations in
`the motion detector output signal and not by monitor
`noise.
`'
`
`3
`The bimorph beam in response to an applied force
`produces a signal whose frequency varies according to
`the movement to which the monitor is subjected. When
`the monitor is secured adjacent to the surface of the skin
`of a subject, such as on the subject’s non-dominant
`wrist, the monitor produces signals having frequencies
`ranging from approximately 0.16 hertz to 9 hertz.
`Within this frequency range, certain activities of the
`subject produce frequencies falling within certain spe-
`cific narrow frequency ranges. For example, breathing
`produces a signal having a frequency range of 0.2 to 1
`hertz, the beat of the heart produces a signal having a
`range of 2 to 3 hertz, and the typical night time activity
`of a subject produces a signal having a range between
`0.2 and 3 hertz. Disorders, such as tremor activity,
`typically produce a signal having a range of 2 to 9 hertz.
`So that such specific frequency ranges among the
`wide range of frequencies which a subject’s many
`movements produce can be selectively observed and
`quantified, the activity monitor includes signal process-
`ing means which amplify, shape and filter the signal
`produced by the sensor.
`In particular, so that a low amplitude signal, such as
`those produced by breathing and heart beats, can be
`isolated for later processing, the activity monitor in,
`cludes signal conditioning means in the form of a mo-
`tion signal amplifier having an amplification factor se-
`lectable by an applied configuration control signal, and
`a highpass filter circuit having a threshold selectable by
`another applied configuration signal below which mo-
`tion sensor signals are greatly attenuated. This is advan-
`tageous in that it allows observations to be made of a
`subject both during a high activity period, when a rela-
`tively high amplitude high frequency signal is produced
`by the sensor, and during a low activity period, such as
`during the night, when the subject is typically produc»
`ing a relatively low amplitude and low frequency signal.
`To eliminate DC drift in the motion signal amplifier
`the signal processing means preferably include a drift
`compensation circuit which compares the dc level of
`the amplified motion signal developed by the amplifier
`with a fixed dc reference voltage to develop a drift
`corrected voltage at the motion detector which nulls
`out any drift.
`To eliminate artifacts present in the sensor output
`signal, such as those caused by the natural resonance of
`the motion sensor, and to obtain in conjunction with the
`highpass filter a desired frequency spectrum for analysis
`and quantification, the activity monitor includes a low
`pass filter circuit having a threshold frequency select-
`able by applied configuration signals.
`The activity monitor further includes an analog-to-
`digital converter which samples the analog signal devel-
`oped by the motion sensor, after processing by the am-
`plifier, high-pass filter and low-pass filter, and passes the
`resultant digital values to internal memory means in the
`monitor for storage and later retrieval.
`The activity monitor also includes a window detector
`which compares the voltage level of the processed
`motion signal to upper and lower voltage thresholds
`selectable by an applied configuration signal, and pro-
`vides an activity count each time the signal voltage
`level crosses the thresholds. Preferably, the signal volt-
`age level is compared to both a high threshold voltage
`level and a low threshold voltage level which are sym-
`metrically positioned opposite the regulated reference
`voltage. Preferably, the amount by which the upper and
`lower thresholds differ exceeds the amount of noise
`
`The activity monitor further includes a temporary
`internal memory for recording the activity counts gen-
`erated by the activity detector over a selectable obser-
`vation period, or epoch. At the end of the epoch, the
`total number of events occurring during the epoch is
`stored, and the temporary memory is erased for use
`during the next epoch. Advantageously, the epoch time
`period is selected according to the type of activity to
`which the observation is directed. For example, because
`a subject engages in generally less movement while
`asleep, the epoch used during such an observation per-
`iod can be generally of greater duration than that, for
`example, used when a subject
`is monitored while
`awake. A selectable epoch period avoids the memory
`saturation problem that prior monitors had in collecting
`data for periods of time inappropriate to a particular
`type of movement.
`The activity monitor also includes an internal micro-
`processor having resident software by which the con-
`figuration of the various circuits of the monitor are
`controlled. The microprocessor is preferably capable of
`powering up and shutting down the processing circuits
`at selected times to conserve battery power.
`The microprocessor has associated with it memory in
`which software to control the monitor components is
`resident and in which data obtained from the operation
`of the monitor is stored. Specifically, the memory in-
`cludes a read-only memory (ROM) which contains
`instructions to operate the monitor. Preferably,
`the
`ROM includes an operating system by which the moni-
`tor’s signal processing components can be initially con-
`figured so that, for example, certain aspects of a sub-
`ject’s movement can be initially observed, from which
`the monitor’s signal processing components can be
`reconfigured so that other aspects of a subject’s move-
`ment can be observed, and by which/ the data that is
`collected is stored.
`
`to provide an activity monitor
`Advantageously,
`which is fully adaptable and which can be altered to
`collect data regarding activity patterns not
`initially
`envisioned, the monitor memory includes a random-ac-
`cess memory (RAM) for storing instructions, for exam-
`ple, different from those stored in the ROM. Advanta-
`geously, the monitor can operate off either, or a combi-
`nation of those instructions stored in the ROM or in the
`RAM.
`
`Communication between the activity monitor and,
`for example, a personal computer, with which the data
`obtained by the monitor be stored, evaluated, and fur-
`ther processed, and from which new instructions to be
`stored in the monitor RAM can. be prepared, is facili-
`tated 'by an interface unit providing electrical connec-
`tions between the monitor and the computer. To this
`end, the interface unit preferably includes a receptacle
`for receiving the monitor, and the monitor is provided
`with an electrical connector on the surface of its hous-
`ing which engages a complementary connector in the
`receptacle.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features of the present invention which are be-
`lieved to be novel are set forth with particularity in the
`appended claims. The invention, together with the fur-
`ther objects and advantages thereof, may best be under-
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`5
`stood by reference to the following description taken in
`conjunction with the accompanying drawings, in the
`several figures of which like reference numerals identify
`like elements, and in which:
`FIG. 1 is a perspective view of a wrist-mounted ac-
`tivity monitor constructed in accordance with the in-
`vention as worn on the wrist of a subject.
`FIG. 2 is an activity monitoring system including a
`computer, interface and wrist-mounted activity monitor
`constructed in accordance with the invention.
`FIG. 3 is an enlarged perspective view of a portion of
`the interface unit shown in FIG. 2 showing the position-
`ing of the wrist-mounted activity monitor therein.
`FIG. 4 is a functional block diagram showing the
`principal components of the activity monitoring system
`of FIG. 2.
`
`FIG. 5 is an enlarged plan view of the control panel
`of the wrist-mounted activity monitor of FIGS. 1—3.
`.FIG. 6 is an exploded perSpective view of the wrist-
`mounted activity monitor showing certain principal
`components thereof.
`FIG. 7 is an enlarged perspective view of the piezo-
`electric bimorph beam motion detector .utilized in the
`activity monitor of FIGS. 1-3.
`FIG. 8 is a functional block diagram showing the
`principal components and circuits of the activity moni-
`tor of FIGS. 1—3.
`
`FIG. 9 is a simplified schematic diagram of the activ-
`ity monitor described in FIG. 8.
`FIG. 10 is an illustrative plot of the frequency spec-
`trum of five different activities of the human body.
`FIG. 11 is a simplified depiction of the frequency
`spectrum and signal characteristics of five specific ac-
`tivities of the human body.
`FIG. 12 is a simplified schematic diagram and plot
`illustrating the characteristics of the piezoelectric bi-
`morph beam sensor utilized in the activity monitor of
`the invention.
`
`FIG. 13 is a graphical depiction of certain voltage
`relationships associated with the window detector uti—
`lized in the activity monitor of the invention.
`FIG. 14 is a graphical depiction of certain bandpass
`characteristics associated with the high-pass filter uti-
`lized in the activity monitor shown in FIGS. 8 and 9.
`FIG. 15 is a depiction of a sinusoidal waveform illus-
`trating certain parameters thereof.
`FIG. 16 is a depiction of a repetitive waveform show-
`ing certain zero-crossing parameters thereof.
`FIG. 17 is a three-dimensional depiction of certain
`axes useful in analyzing activity of the human body.
`FIG. 18 is a 3-dimensional depiction of certain activi-
`ties of the human body viewed along the axes of FIG.
`14.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Referring to the Figures, and particularly to FIGS. 1
`and 2, a wrist-mounted activity monitor or actigraph 10
`constructed in accordance with the invention may be
`similarly shaped and sized to a wrist—watch, having a
`flexible band 11 securing a generally rectangular hous-
`ing 12 against the skin surface of a subject being moni-
`tored. Typically, in this form the monitor is mounted on
`the non-dominant wrist, the activity of which has been
`found to correlate with body activity, muscle move-
`ment and brain waves.
`
`In use, the activity monitor 10 is worn by the subject
`for a predetermined collection period which may ex-
`
`10
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`15
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`25
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`5,197,489
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`tend over one or more days. Data collected by the
`monitor over the collection period is downloaded at the
`end of the period to a personal computer 13 which,
`except for containing necessary software for accom-
`plishing the down-loading of data from the monitor and
`the uploading of operating instructions to the monitor,
`may be entirely conventional in construction and opera-
`tion. Communication between the activity monitor 10
`and computer 13 is facilitated by an interface unit 14,
`which is connected to a data port of computer 13 by
`means of a conventional RS-232 cable 15 or the like.
`
`The interface unit 14 preferably includes a receptacle 16
`(FIG. 3) on its top surface dimensioned to receive the
`monitor housing 12. An electrical connector 17 located
`along one side of receptacle 16 engages a connector 18
`on housing 12 when the monitor is seated within the
`receptacle. With this arrangement the monitor can be
`quickly and conveniently installed and removed from
`interface unit 14. A plurality of controls 20 on the top
`surface of interface unit 14 assist the operator in accom-
`plishing the downloading and uploading functions.
`Activity monitor 10, personal computer 13 and inter-
`face unit 14 together comprise a system for collecting
`and analyzing human activity data. Depending on the
`particular software resident in personal computer 13 a
`wide variety of written reports and displays may be
`- generated from the data collected by the monitor.
`In this regard, and with reference to FIG. 4, data is
`exchanged between personal computer 13 and interface
`unit 14 in both directions, and between interface unit 14
`and activity monitor 10 in both directions. This pro?
`vides complete flexibility in that necessary operating
`instructions may be provided to monitor 10 through
`interface unit 14 from personal computer 13. When the
`monitor is removed from interface unit 14, these resi-
`dent instructions control the operation of the monitor in
`a subsequent data collection assignment. As will be
`seen, a number of operating parameters in the monitor
`can be configured for either an entire data collection
`period, or for portions of a data collection period, or for
`single epochs, providing activity data and an activity
`monitor of optimum utility.
`Referring to FIG. '5, the top surface of activity moni-
`tor 10 includes a pair of user-input pushbutton switches
`22 and 23. These switches, which are preferably mem-
`brane type switches, allow the subject to indicate the
`occurrence of a particular event. For example, upon the
`occurrence of dizziness or pain, the subject may be
`instructed to depress one of the push button switches to
`cause that occurrence to be recorded in the internal
`memory of the monitor. To enable these switches to be
`readily identified, the right switch may be one color,
`such as red, may be provided with a single raised dimple
`for tactile feedback, and may be accompanied by a
`single audible beep. The left pushbutton switch 23 may
`be provided with two raised dimples, may be another
`color, such as green, and may cause two audible beeps
`when actuated.
`
`Referring to FIG. 6, the housing 12 of activity moni-
`tor 10 is seen to include a side panel 24 on which electri-
`cal connector 18 is positioned for engaging the electri-
`cal connector 17 of receptacle 16. The other side of
`housing 12 includes a sliding tray assembly 25 within
`which a coin-type battery cell 26 is mounted for inser-
`tion into housing 12. Within housing 12 a first circuit
`board 27 and a second parallel-Spaced circuit board 28
`provide mounting and connection means for a major
`portion of the circuitry of the monitor, and also provide
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`mounting means for motion sensing means in the form
`of a cantilever piezoelectric bimorph beam motion sen-
`sor 30.
`
`Referring to FIG. 7, motion sensor 30 is seen to com-
`prise a bimorph beam 31 fixedly positioned relative to
`circuit board 27 at one end by a metallic clamp 32 and
`compression contact 33. The compression contact 33
`forces one face of beam 31 against clamp 32, completing
`one electrical connection to the beam through a con-
`ductor 34. The other electrical connection to beam 31 is
`established through compression contact 33, which
`bears against the other face of the beam and a metallic
`pad 35 on circuit board 27 to which a conductor 36 is
`connected. Thus, the bimorph beam is electrically con-
`nected on opposite faces to the circuitry of the monitor
`by mounting means which fixedly position the con-
`nected end relative to circuit board 27. The distal end of
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`8
`activity monitor to analyze very low level motion sig-
`nals, such as those associated with sleep.
`The output of conditioning amplifier 42 (v1+Vg) is
`applied to a low pass amplifier 44 and to a dc drift cor—
`rection circuit 45. Within drift correction circuit 45 the
`
`amplifier output is compared with a fixed reference
`voltage Vgo, which comprises a virtual ground for the
`amplifier and filter circuitry, to generate the drift com-
`pensated signal Vg for application to sensor circuit 40.
`In this way, the DC output level of conditioning ampli-
`fier 42 is continuously compared with a fixed reference
`voltage, and the voltage applied to the motion sensor is
`varied to prevent any deviation between the DC output
`level of the amplifier and the reference voltage. Conse-
`quently, any DC drift within the high gain conditioning
`amplifier circuit is eliminated. This makes it possible for
`the conditioning amplifier to operate at the high gains
`required for successful low level body activity detec-
`tion and analysis.
`The output of conditioning amplifier 42 is applied to
`a low pass filter 44 wherein high frequency components
`of the signal, such as produced by the natural resonance
`of the bimorph beam sensor, are attenuated. Low pass
`filter 44, in accordance with one aspect of the invention, '
`can be configured by configuration signals applied on
`configuration control lines 30D, 40D and HCF by pro-
`cessor circuit 43 to obtain three different high fre-
`quency cutoff frequencies. In a preferred embodiment
`of the invention, filter 44 is configurable for thresholds
`of 1, 3 or 9 hertz.
`Since the high pass filter of conditioning amplifier 42
`can be configured with a threshold of either 0.2‘or 2
`hertz, and filter 44 can be configured with a threshold of
`either 1, 3 or 9 hertz, the monitor is advantageously able
`to collect information within a selected one of five dis-'
`
`tinct frequency ranges: 0.16 to l hertz; 0.16 to 3 hertz;
`0.16 to 9 hertz; 2 to 3 hertz; and 2 to 9 hertz. This is
`illustrated in FIG. 10. As previously stated, and as illus-
`trated in FIG. 11, the motion sensor when exposed to
`certain specific types of body movement produces sig-
`nals which generally fall
`into these distinct ranges.
`Nighttime activity, such as sleep, produces a signal
`between 0.2 and 3 hertz. Breathing produces a signal
`between 0.2 and l hertz. Heart beats produce a signal
`between 2 and 3 hertz. Tremor activity produces a
`signal between 2 and 9 hertz. Accordingly, by configur-
`ing filters 42 and 44 to pass signals above a selected
`threshold and below another selected threshold,
`the
`activity monitor 10 can be configured in accordance
`with the invention to collect data only for certain spe-
`cific types of activities of a subject.
`The output of low pass filter 44, designated ANO, is
`applied to an analog-to-digital sampling converter 45
`within processor 43. This circuit samples the analog
`ANO signal at a predetermined rate, for example, 10
`samples per second, for application to an analog-to-digi-
`ta] (A/D) converter 47 within the sampling circuit. The
`signals are also applied to a comparator 46, wherein
`their voltage level is compared with one or more se-
`lected reference signals appropriate to the measurement
`being made. In particular,
`the reference signal may
`comprise either a low level reference for recognizing
`excessively low activity signals, such as might occur
`with negative'saturation of the conditioning amplifier, a
`high level reference signal for recognizing excessively
`high activity signals, such as might occur with positive
`saturation of the conditioning amplifier, a reference
`signal proportional to repetition rate, as determined by
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`beam 31 may be fitted with a proof mass 37 to impart
`desired electro-mechanical characteristics to the bi-
`morph beam assembly 30. This method of making con- 20
`nections to the bimorph beam has the advantage of
`avoiding solder connections to the beam, and their at-
`tendant cracking or deterioration with time.
`Referring to FIG. 8, within activity monitor 10 the
`bimorph beam assembly 30 is incorporated in a sensor
`circuit 40. Within this circuit the motion signal v devel-
`oped by the bimorph beam is added to a voltage Vg
`provided by a drift correction circuit 41.
`Since the motion signal v generated by the beam
`contains harmonics at the beam resonant frequency, has
`relatively poor low frequency response and is of low
`amplitude, it is necessary that the motion signal be con-
`ditioned prior to analysis and storage. To this end, the
`resulting sensor output signal V+Vg is applied to a con—
`ditioning circuit 42 comprising a configurable threshold
`high pass filter and configurable gain signal amplifier.
`Within conditioning circuit 42 the signal is AC and DC
`amplified, typically by AC factors of from 5-25 and a
`DC factor of 75—375 provide a signal of sufficient ampli-
`tude that even visually imperceptible movements can be
`recognized and quantified without corruption due to
`DC drift. Undesired low frequency components result-
`ing from other than body activity to be monitored,
`which are typically below 0.16 hertz, are attenuated.
`Since virtually all movement of a subject produces
`signals having frequencies that are above 0.16 hertz,
`valid data is not affected. Low level signals, such as
`result from heart beats or blood flow, are both above
`0.16 hertz and are amplified for subsequent processing.
`In accordance with one aspect of the invention, the
`low frequency threshold' of the high pass filter amplifier
`40 is configurable to either 0.16 hertz or 2 hertz to per-
`mit selective attenuation of low frequency signals asso-
`ciated with body activities such as breathing, which
`typically produce a signal between 0.2 and l hertz.
`Selection of the desired threshold is accomplished over
`a configuration control line LCF which receives an
`appropri