|||||||||||||||||||||||l|||||||||||||llll|||||||||||||||||||||||||||||||l||||||||||||||||l
`US 20060084879A1
`
`MOTION CANCELLATION 0F OPTICAL
`INPUT SIGNALS FOR PHYSIOLOGICAL
`PULSE MEASUREMENT
`
`lnvcnmrs: Richard A. .Valarian. Excelsior. MN
`(US); Lori E. [.uckc. Pagan. MN (US):
`Susan S. Allini. (‘hamplim MN (US):
`Mark .I. Bina. Shoreview. MN (US):
`Don W. E. Evans. St. Paul. MN (US):
`Paul Harris. |)c1m((.‘A): Michael w.
`Geatz. Maple (imvc, MN (US)
`
`v
`v
`I
`Ciirrespnndcnce‘.AddI:ess: ‘
`OPPLMII‘JIMLR WOLPl‘ & DONNELLY LLP
`45 SOUTH SEVENTH STREEI‘, SUITE 3300
`MIXNEAPOLIS‘ MN 55402 (US)
`
`ASS-19w: Pulse—fracer ‘l-echlwlugies Inch Vancmh
`W3]. (CA)
`
`App1_Nu_;
`
`1]}2501011
`
`liilcd:
`
`Oct. 13. 2005
`
`Related [1,8, Application Data
`
`Provisional application No. 60/61925l lilcd on ()c1.
`15. 2004. Provisional applicalion No. 601681.397.
`filed on May 16. 2005. I’mvisiuual appliculion No.
`fiOI’fi‘JfiBSS. filed on 11.11 6. 2005.
`
`Publication Classification
`
`(5|)
`
`Int- Cl-
`(20061“)
`A613 5/02
`(52) U.S. Cl.
`............................................................ .. 6001500
`
`(57)
`
`ABSII‘RMZ-T
`.
`.
`Includes an accelerometer lair
`A pulsc rate sensor that
`measuring periodic moucn and a piano sensor for detecting
`crmlic lnnlinn is capable of more accurately dctcnnining
`
`pulse rate by accounting for these types ofmotiou The pulse
`rate sensor in accordance with the presenl invention dimin—
`ishes pulse r2111: signal degradation din: In crralic nmlinn
`through a combinalion 01' algorithms that control signal
`boosting. wavcl'cnu refiucinenl and signal noise suppres-
`sinIL
`
`
`
`CONDITIONED OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`E
`
`PIEZOELECTRIC
`SENSOR
`
`E
`
`ACCELEROMETER
`ANDIOR DC
`COMPENSATION
`E
`
`[19) United States
`“2) Patent Application Publication (10) Pub. No.: US 2006/0084879 A1
`
`Nazariau et al. Apr. 20, 2006 (43) Pub. Date:
`
`
`US. Patent No. 8,923,941
`
`TIME DOMAIN FILTER
`
`fl
`
`-
`
`FREQUENCY DOMA‘IN -
`FOURIER TRANSFORM
`fl:
`
`FREQUENCY DOMAIN -
`FOURIER TRANSFORM
`E;
`
`BAND
`REJECT
`
`FILTER
`
`506
`
`PULSE RATE @—
`
`Apple Inc.
`APL1046
`
`Apple Inc.
`APL1046
`U.S. Patent No. 8,923,941
`
`001
`
`FITBIT, Ex. 1046
`
`

`

`US 2006/0084879 A]
`
`SAMPLE '#
`
`FIG. 1A
`
`NOISE
`
`Patent Application Publication Apr. 20, 2006 Sheet 1 of 6
`
`FIG. 1C
`
`SAMPLE #
`
`FIG. 1B
`
`SIGNAL + NOISE
`
`SAMPLE #
`
`002
`
`FITBIT, Ex. 1046
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 2 of 6
`
`US 2006/0084879 A1
`
`003
`
`FITBIT, Ex. 1046
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 3 of 6
`
`US 2006/0084879 A1
`
`004
`
`FITBIT, Ex. 1046
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 4 of 6
`
`US 2006/0084879 A1
`
`005
`
`FITBIT, Ex. 1046
`
`

`

`Patent Appiication Publication Apr. 20, 2006 Sheet 5 of 6
`
`US 2006/0084879 A1
`
`PIEZOELECTRIC
`SENSOR
`
`.50_2
`
`ACCELEROMETER
`ANDIOR DC
`COMPENSATION
`fl
`
`CONDITIONED OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`5_m.
`
`FIG. 4
`
`TIME DOMAIN FILTER
`fl
`
`'
`
`FREQUENCY DOMAIN —
`
`FOURIER TRANSFORM
`fli
`
`FREQUENCY DOMAIN —
`FOURIER TRANSFORM
`fiffi
`
`BAND
`
`REJECT
`
`FILTER
`
`PULSE RATE fl
`
`006
`
`FITBIT, Ex. 1046
`
`

`

`US 2006/0084879 A1
`
`ANALYZE DC
`
`COMPENSATION
`
`SIGNAL
`
`404
`
`'8
`
`MOTION
`
`DETECTED?
`E,
`
`USE FREQUENCY
`
`ANALYSIS
`
`.
`
`ALGORITHMS
`
`N8
`
`Patent Application Publication Apr. 20, 2006 Sheet 6 of 6
`
`412_.-o
`
`USE PEAK DETECTION
`
`ALGORITHMS
`
`410
`
`CALCULATE
`
`PULSE
`
`RATE
`
`007
`
`FITBIT, Ex. 1046
`
`

`

`US 20060084879 A1
`
`Apr. 20, 2006
`
`008
`
`[0005] Signals of interest are generated by transmitting a
`light source in the near infrared region into the tissue and
`measuring the retumed signal
`intensity. Typically two or
`four light emitting diodes (LEDS) are employed with vary-
`ing intensity to establish the optimum optical window. The
`return signal strength will be modulated by the capillary
`blood flow in the tissue and will vary with the physiologic
`pulse of the subject. This is a well understood and estab-
`lished principal that has been applied to pulse monitoring
`equipment for years. Pulse rate sensing taken at locations
`other than 131058 to the heart. has not been sunccsslttl because
`of the relatively low signal strength and relativeiy high
`“liaise” content. The low signal strength can be attributed to
`a number of factors including variations in skin and hair
`density. variations in vasculanzation. and optical alignment.
`Further. the received signal
`includes several components
`which can be generally classified as "noise" when attempt-
`ing to sense pulse rate. These high “noise” levels are in
`addition to classical noise sources present within almost all
`electrical systems and primarily include inherent optical
`noise sources. interfering light sources. and motion artifact.
`
`an accelerometer for detecting body motion during physical
`activity. The instrument further includes a processor for
`subtracting the body movement component front the signal.
`thus yielding the true heart beat signal.
`
`[0009] US. Pat. No. 5.431.170 to Mathews discloses a
`device which may be worn on the wrist or hand during
`physical activity. The device contains a light sensor to
`measure pulse and light sensor or accelerometer for mea-
`suring movement. Mathews discloses that a noise cancellaw
`tion circuit takes the values from these sensors to give a true
`pulse signal that is free of pedomctry vibration or noise.
`
`[0010] US. Pat. No. 5.801267 to Bryars et al. discloses an
`apparatus which can be combined in a single unit with a
`wrist watch to display the user‘s heart pulse rate during
`physical exercise. A primary piezo sensor detects the heart
`rate pulse of a user and a background piezo sensor detects
`the noise from local body motion. Signals from this back—
`ground sensor are digitally subtracted from the primary
`pulse sensor thus allegedly reducing the effects of random
`body itoise.
`
`[0011] US. Pat. No. 6.099.478 to Aoshima et a]. diselosse
`a pulse wave detecting means comprising an LIED. photo
`transistor. or piezoelectric microphone. Body motion detect-
`ing means detect body motion using an acceleration sensor.
`Aoshima et a]. disclose that pulse wave extracting means
`subtract the ontpttt of the two sensors to give an accurate
`pulse rate. Assignee related U.S. Pat. No. 5.776.070 pro-
`vides similar disclosures.
`
`[0012] US. Pat. No. 6.129.67'6 to Odagiri et al. discloses
`a pulse rate tnonitor that can be assembled into a wrist
`watchband and used during activities, such as mnning. The
`wrist watchband contains an acceleration sensor to detect
`action noise and a piezoelectric microphone to detect pulse.
`When constant motion such as running is detected.
`the
`action noise spectrum is subtracted ti‘om the pulse wave
`spectrum. which is depicted in FIGS. 6A—C. Running speed
`and distance may also be obtained. U.S. Pat. Nos. 5.697.374
`and 6.023.662 provide similar thSclostnL-s.
`
`[0013] US. Pat. No. 6.361.50l B1 to Amano et at. dis-
`closes a pulse wave diagnosing device formed of device
`main body having a wristwatch structure. and pulse wave
`detection sensor unit. A body motion component remover
`subtracts corrected body motion data li'om corrected pulse
`wave data. Body motion waves are detected by an accol-
`eration sensor. This device may be incorporated into a
`pedometer.
`
`to
`[0014] US. Patent Appln. Publn. 200510116820 A]
`Goldreich discloses a wrist mounted device that detects
`pulse rates. The vibration sensor is a pieao ceramic sensor
`that measures movement of the wrist and may include an
`accelerometer. A physiologic sensor detects the blood pres—
`sure pnlse rate. and may be fiber optic. Ambient sensors may
`also be present.
`
`[0015] Whatever the precise merits. features. and advan-
`tages of the above cited references. none of them achieves
`or fulfills the purposes of the present invention. For these
`reasons it would be desirable to provide an improved device
`and method for accurately measuring pulse rate during
`physical exercise and other activities.
`
`MOTION CANCELLATION 0F OPTICAL INPUT
`SIGNALS FOR PHYSIOLOGICAL PULSE
`MEASUREMENT
`
`BACKGROUND OF ‘I'l-lli INVI'EN‘I‘ION
`
`1. Field of the Invention
`[0001]
`[0002] The present invention relates generally to the field
`oi‘signa} processing. More specifically. the presettt inventiott
`is related to pulse rate monitors capable of providing accu-
`rate measurement and display ofa user’s pulse rate during
`times of physical exercise or other activity.
`
`[0003]
`
`2. Background of the Related Art
`
`[0004] The accurate measurement of an active person‘s
`pulse rate at the wrist
`is complicated due to [lie artifacts
`produced by body motion such as when the person is
`running or otherwise engaging in physical activity or exer—
`cise. Therefore. pulse rate monitors presently in the market
`utilize chest bands that are Worn close to the bean to
`minimize the etfect of motion produced by exercise. Arti-
`facts produced by body motion are detected by pulse rate
`sensors as “noise” that masks the heart rate pulse signal
`being measured. In order to mitigate the effects of these
`artifacts. it is necessary to filter out and cancel as much of
`the noise signal occurring in the pulse rate frequency band
`as possible while retaining the desired pulse signal.
`
`To illustrate. FIG. 1A depicts a signal of interest.
`[0006]
`FIG. 18 depicts noise caused by motion artifact. interfering
`lights sources. randont noise and the like. FIG. 1C illustrates
`how the signal of interest is masked by noise due to tow
`signal strength. as an example.
`
`[0007] While conventional signal processing techniques
`may be able to reduce “out of band" noise: that is. noise not
`found within the frequency of interest, they are challenged
`to address noise that mimics the signal of interest and that is
`non~random. the most common of which is motion.
`
`[0008] Various pulse rate detection systems are known in
`the art. U.S. Pat. No. 4.338.950 to Barlow. Jr. et al. discloses
`an instrument comprised ol‘wrist-mountcd unit. which con-
`tains a piezoelectric transducer for detecting pulse rate and
`
`008
`
`FITBIT, Ex. 1046
`
`

`

`in
`[0029] FIG. 2A illustrates a pulse rate sensor 10]
`accordance with the present invention. Emitters 102 (eg.
`LED. light emitting diodes) transmit a light source in the
`near infrared (IR) region into body tissue and a photo
`detector such as a reflective infra-red sensor 104 that
`receives the reflected light from the tissue. Pulse rate sensor
`.10] uses the inli'ared optical processes from which body
`volume displacement is analyzed to detect and store pulse
`rate data. which is indicative oi‘heart rate. Pulse rate sensor
`101 also comprises an accelerometer 108, preferably a
`two-dimensional accelerometer and optionally a three-di-
`mensional accelerometer. that detects periodic or constant
`motion ol‘the user. and a contact type motion sensor 106 that
`measures inconsistent or erratic motion ol‘thc user. and other
`movement related sources that effect the optical pulse. The
`contact type motion sensor can be a piezo sensor or other
`types of sensors capable of measuring erratic motion such as
`vibration. The accelerometer or optical sensor output may
`also be used as input for step counter or pedometer 114.
`Microprocessor 110 performs signal conditioning functions
`on the pulse signals received from the photo detector 104.
`and also samples and filters signals from accelerometer 108
`and piezo sensor 106. Pulse rate detector 112 calculates the
`pulse rate of a user by using conditioned optical pulse
`signals received by micmprocessor 110, filtered signals from
`accelerometer 108. and piano sensor 106. While pulse rate
`detector 112 is shown as being part of microprocessor 110.
`it is understood that these could also be separate compo—
`nents.
`
`009
`
`SUMMARY OF THE INVENTION
`
`It is therefore an object of the present invention to
`[0016]
`provide a device and method for accurately monitoring and
`detecting pulse rate.
`
`is an object of the present
`it
`[0017] More particularly.
`invention to provide a solution to that allows for adequate
`removal of inherent optical noise sources. interfering ambi-
`ent
`light sources and motion artifact
`in optical signals
`especially under intense physical activity.
`
`It is yet another object of the present invention to
`[0018]
`provide a pulse rate monitor that can distinguish between
`noise artifact and an individual's true pulse from a signal
`representing a composite of pulse and noise artifact as
`illustrated in FIG. 1C.
`
`[0019] These and other objects are accomplished in accor-
`dance with the present invention. a system and method for
`measuring a user’s pulse rate during physical exercise or
`activity. that includes a pulse rate sensor having one or more
`emitters capable of transmitting a light source into body
`tissue. a photo detector for receiving reflected light front the
`body tissue and producing a photo detector output signal
`indicative of the reflected light: an accelerometer for mea-
`suring regular motion of the individual and producing an
`accelerometer output signal indicative ofthe regular motion:
`a contact type motion sensor for measuring erratic motion of
`the individual and producing a piezo sensor output signal
`indicative of the erratic motion; and a microprocessor for
`receiving the photo detector output signal. the accelerometer
`output signal. and the contact type motion sensor output
`signal. and detennining the pulse rate of the individual.
`where the pulse rate is determined by conditioning the photo
`detector output signal and removing portions of the condi—
`tioned photo detector output caused by regular motion and
`erratic motion of the individual.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0020] FIG. 1A illustrates a desired optical signal to be
`measured.
`
`[0021] FIG. 13 illustrate noise typically caused by
`motion.
`
`[0022] FIG. 1C illustrates the combined optical signal and
`noise.
`
`[0023] FIG. 2A diagrammatically illustrates a pulse rate
`sensor in accordance with the present invention.
`
`[0024] FIG. 2|! illustrates a pulse rate sensor encapsulated
`in a watch module in accordance with the present invention.
`
`[0025] FIG. 3 illustrates the signal conditioning process
`for an optical signal in accordance with the present inven—
`tion.
`
`[0026] FIG. 4 illustrates a flowchart depicting the motion
`discrimination process in accordance with the present inven-
`tion.
`
`[0027] FIG. 5 illustrates a Flowchart depicting steps fol-
`lowed to calculate pulse rate in accordance with the present
`invention.
`DESCRIPTION OF THE PREFERRED
`[EMBODIMENTS
`
`[0028] While this invention is illustrated and described in
`a preferred embodiment. the device may be produced in
`
`US 20060084879 Al
`
`Apr. 20, 2006
`
`many dili‘erent configurations, forms and materials. There is
`depicted in the drawings. and will hereinafler be described
`in detail. a preferred embodiment of the invention. with the
`understanding that the present disclosure is to be considered
`as an exemplilication of the principles oftl'ic invention and
`the associated functional specifications for its construction
`and is not intended to limit the invention to the embodiment
`illustrated. Those skilled in the art will envision many other
`possible variations within the scope of the present invention.
`
`[0030] Pulse rate sensor 101 may be encapsulated in a
`watch module 120 as shown in FIG. 2|} Willi an optional
`rechargeable battery in one embodiment of the present
`invention. However. other carriersfmodules are envisioned
`as usable with the present
`invention such as pendants.
`jewelry. bracelets. patches. music players. etc. which may
`also contain standard watch ftmctions to include timei'date
`
`and a stopwatchfiimer. These other carriers may be posi-
`tioned anywhere on the arm ofan individual or in the case
`of a pendants around the neck of an individual. The pulse
`rate sensor in accordance with the present invention may
`also include capabilities for firmware updates through the
`implementation of a software boot loader. Other additions
`may include a communication module such as universal
`serial bus (1158) p011 or an RF receiven'transmitter to
`automatically upload data to a web portal. Additionally, the
`pulse rate sensor may include radio frequency identification
`(RFID) to uniquely identify each watch sold to the web
`portal.
`
`[003]] The pulse rate sensor in accordance with the pre-
`ferred embodiment of the present invention consists of an
`optical emitter including of one or more light emitting
`diodes. an optical receiver. active signal conditioning. an
`accelerometer and a piezo sensor. and a microprocessor. The
`microprocessor controls the active signal conditioning
`
`009
`
`FITBIT, Ex. 1046
`
`

`

`US 20060084879 A1
`
`Apr. 20, 2006
`
`applied to the optical sensor by automatically adjusting the
`light emitting diode otttpttt to maintain the optimal signal
`strength. controlling the amplification ofthe received signal.
`and automatically removing the direct current bias of the
`received signal. The conditioned optical sensor output and
`the accelerometer and piezo sensor outputs are sampled as
`input to two different pulse rate calculators. one used when
`there is no motion present and the other used when there is
`motion present. The piezo sensor is used to detect erratic
`motion while the accelerometer is used to detect periodic
`motion.
`
`[0032] As further described below. pulse rate signal deg-
`radation due to arm motion and skin vibrations is diminished
`through a combination of algoritluns that control signal
`boosting. waveliarm refinement and signal noise suppres-
`ston.
`
`provded from filter 12. Amplifier 28 has a fixed gain and is
`output to the microprocessor 110 at 2. The amplification and
`DC adjustment provided by amplifier 28 moves the signal
`level of its outpttt to the midrange of second operational
`amplifier 31! and allow-s for a second stage of amplification.
`The amplification gain 32 associated with second amplifier
`30 is programmable to allow for adjust necessary to deal
`with varying pulse strengths. The gain 32 is periodically
`adjusted by the microprocessor 110 to maintain signal
`integrity. A programmable direct current compensation sig—
`nal from output 6 is also applied to second amplifier 30 by
`mimprocessor 110.
`It is during this second stage that the
`sensor signal is significantly amplified. The programmable
`direct current cotnpensation at output 6 is adjusted with
`every sample of the first stage gain signal or input 2 of the
`analog to digital convertor. The microprocessor calculates
`the direct current value of the optical pulse signal. and
`applies that valuc using output 6 as the reference at the input
`ofthc amplifier stage 30. This is a line adjusLment and allUWS
`[or the quick recovery of the pulse signal during and after
`motion. As significant amplification is applied to the input
`singal at second amplifier 32.
`the programmable direct
`current compensation further helps to center the signal at the
`amplifier input. and prevents second amplifier 32 front
`saturating during periods of motion by the user. "thus. the
`pulse can be more accurately tracked during periods of
`motion.
`
`[0035] Referring again to FIG. 4. the steps used to control
`the direct current compensation signal 6 and the optical
`emitter supply signal 8 are described below.
`
`l)Thc optical sensor output signal. first atnplifcr
`[0036]
`output signal. and second amplifcr output signal are all
`oversampled at inputs 1. 2. and 3 as shown in FIG. 2
`to generate samples x10). x2(f). x30) where i repre-
`sents the i”‘ sample.
`filtered to produce a
`[0037]
`2) The signals are all
`smoother signal at a lower sample rate. More specifi-
`cally. the oversampled signals are processed as follows:
`
`A.
`
`F:
`.nnootluu’ljl = tltXt: thlll'l‘. X = number of points
`
`:‘l.
`1'
`i
`somatic-2U] = [UK t a Lflttl‘. X = number of points
`\
`
`j-i
`.rtitaotlrdtj] = [l]Xl¢-Z.t_i{fl'. X = number 01‘ points
`
`decrease output at signal 8.
`
`[0033] Referring to FIG. 3. the process to achieve signal
`conditioning of the pulse signal output from photo detector
`10 in accordance with the present invention is illustrated. A
`pulse signal output from photodetector 10. which may be a
`reflective infra-red sensor. is filtered through low pass filter
`12 and is provided to inpttt l of the microprocessor 110.
`which includes an intemal analog to digital convertor l4.
`Naturally. analog to digital converter [4 could also be a
`component separate from microprocessor Ill}. Through this
`connection. microprocessor 110 is able to monitor the output
`from photo detector 10 and to determine the appropriate
`intensity for an infra-red light emitting diode 16. which
`transmits optical signals into body tissue. The intensity of
`infra-red light emitting diode 16 is programmable using an
`output 8 from a digital
`to analog converter 18 within
`microprocessor 110 (again. digital to analog converter 18
`could also be a component separate from microprocessor
`110). As further discussed below. an internal closed loop
`control function within the microprocessor 110 maintains
`the proper intensity of the infra-red light emitting diode 16
`rising the feedback from the photodector 10 at input 1 to
`control output 8. Using this control function. the otitpttt
`signal from photodctoctor 10 is in an appropriate range for
`direct current compensation and other related functions.
`Further. this intensity control allows the microprocessor 110
`to periodically adjust the system to account for diil'erent
`environmental and physiolog'cal conditions. including vary—
`ing ambient light levels. long term blood flow changes and
`varying responses from user to user. The pulse signal
`transmitted from photodetector 10 is filtered through a
`lowpass filter 12 ofapproximatcly 10 [In to reduce inherent
`notse.
`
`[0034] The pulse signal from photodetector 10 generally
`includes a large direct current component that represents
`gross blood flow. and a small alternating current component
`that represents true pulse. Because it is desirable to accu—
`rately measure true pulse. active signal conditioning includ—
`ing additional amplification of the alternating current com—
`ponent and compensation of the direct current component is
`necessary. Compensation of the direct current component
`occurs in two stages. The first stage is accomplished using
`an amplifier 28 to achieve a fixed signal gain. The output
`from this first stage is provided to microprocessor 110 at
`input 2. The second stage is the programmable gain stage
`utilzing a second amplifier 30 with output to microprocessor
`110 shown at 3. A fixed direct current compensation voltage.
`shown at output 7. is subtracted from the filtered pulse signal
`
`[0038] The filtered sample signal (smootlixlm) is used
`for the automatic optical emitter control at signal 8. The
`filtered first amplifier output signal {smoothxlflin and
`the
`filtered
`second
`amplifier
`output
`signal
`(smoothx3(i)) are used for automatic direct current
`compensation at signal 6 and for pulse detection.
`respectively.
`
`3) Automatic control of optical emitter [6 is
`[0039]
`based on the filtered second amplifier output signal at
`input 1_. and is applied as follows on a periodic basis.
`[0040]
`a)
`If
`sniootlil(j)>expected
`range.
`then
`
`010
`
`FITBIT, Ex. 1046
`
`

`

`US 20060084879 A1
`
`Apr. 20, 2006
`
`smoothltjkexpected range.
`if
`b)
`[0041]
`increase output at signal 8.
`
`then
`
`where a non-zero value indicates a peak in the
`[0055]
`filtered signal and a zero indicates no peak.
`
`the pulse detection
`[0057] Referring back to FIG. 3.
`system also includes an accelerometer 20 attd piezo sensor
`22. Signals from accelerometer 20 and piezo sensor 22 are
`filtered through lowpass filters 24, 26 at analog to digital
`inputs 5 and 4. respectively before being sampled.
`'lhe
`accelerometer 20 is used in the motion mitigation fast
`fourier transform (FFT) algorilluus and the piano sensor is
`an indicator oferratic motion as shown in FIG. 4. Generally
`speaking. the accelerometer 20 and piezo sensor 22 are used
`to remove the motion artifacts from the optical sensor output
`present during motion of the user. When substantial erratic
`or momentary motion is detected using the piano sensor 22.
`the information is used to filter the optical sensor output in
`the time domain so that the signal is not used for pulse rate
`calculations during the erratic motion 504. Additional lil-
`tering may also be applied to the instantaneous pulse rate to
`provide a more stable pulse rate output. Periodic motion is
`detected by analyzing the accelerometer output signal in the
`frequency domain 505 and this information is used to
`generate a band reject filter which is applied to the optical
`sensor output in the frequency domain 506.
`
`smoothxz and smoothx3 at step 506;
`
`4) Direct current compensation is applied at
`[0042]
`output 6 as follows at the update rate of the smoothing
`filters as follows.
`
`a) ll" smooth3(j)>(max value of smooth3{j)—
`[0043]
`threshold).
`then Direct current compensations)-
`5111000120)
`
`smooth3(j)<(miu who of
`if
`lilsc
`b)
`[0044]
`smootltSfi)+threshold). then Direct current compen—
`sations)-=smooth2(i)
`
`c) Else direct current cotupettsatiottG)-direct
`[0045]
`current compensationfi- l ).
`
`[0046] During periods of motion. the signal applied for
`direct current compensation at output 6 by the microproces-
`sor is correlated to the motion of the user. As as result. the
`direct current compensation can also be used as an indicator
`of motion as shown in FIG. 5. The direct current compen-
`sation signal is first analyzed in step 404: and this analysis
`is ttsed to detect motion in step 406. If the direct current
`compensation is stable or lacks change this indicates a lack
`of motion and then the peak detection algorithm 410
`described below is used to calculate the pulse rate 412. This
`allows for a fast recovery of the pulse rate after periods of
`motion If the direct current compensation is correcting the
`signal. this indicates that motion is present and tlte frtxluency
`based algorithm 408 described below is used to calculate the
`pulse rate 412.
`
`[0047] The direct current compensationfli) signal is used
`for motion discrimination in block 406 and determines
`whether peak detection algorithms can be used. for example
`during periods of no motion. or if frequency analysis is
`necessary for example during periods of motion. Stated
`alternatively, the direct current compensationfi) signal
`is
`used to determine whether to apply peak detectiott algo-
`rithms in block 408 or frequency analysis in block 410 to
`determine the pulse rate More specifically. if direct current
`compensationfi) has not changed for the past 3x(l/pulse
`rate) seconds during which pulse rate is being measured.
`then the peak detection algorithm described below is used.
`If direct current compensations) has changed during the past
`3x(ltpulse rate) seconds during which pulse rate is being
`measured the frequency analysis algoritth described below
`is usnzd.
`Peak detection is calculated as follows:
`
`1) A first derivative calculated as difi‘l(i)-
`[0048]
`smoothx2(i)-smoothx2(i-1) is taken over the filtered
`signal.
`
`2) A second derivative. di02(i)=di[ll(i)-difll(i-
`[0049]
`l), is calculated or computed from the first derivative.
`
`3) Peak detection is analymd using the first and
`[0050]
`second derivatives to fittd the peaks within the filtered
`signal
`
`[0051]
`
`If difl‘l (i)-0 and dill‘Zti]<0 then
`
`[0052]
`
`peak(i)=i
`
`[0053]
`
`If difil (i) does not=0 and difl2(i)>0 then
`
`[0054]
`
`peak(i)=0
`
`4) The instantaneous pulse rate is calculated in
`[0056]
`block 412 as the difference between peaks in the filtered
`signal.
`lttstantuteous pulse nttct’iHsample rate tilt lterPeriod-
`(pesktiI-pmvious non-zeroipenktilil'fill sec-*minule.
`
`If it is determined that motion is present. a fre-
`[0058]
`quency algorithm as shown in FIG. 4 is used The signals
`that undergo frequency analysis are the smoothed first
`amplifier output signal (sniootltxZ) and the smoothed second
`amplifier output signal (smoothx3) itt step 501. Signals from
`the accelerometer 20 and direct current compensation are
`also provided in step 503 so that further frequency analysis
`can be done. Frequency analysis may include all or a subset
`of the foregoing signals The frequency bills will be ana-
`lyzed to determine whether motion frequencies are present.
`Again. motion frequencies are determined by the acceler—
`ometer output or the direct current compensation signal, The
`motion frequencies are then removed front the sensor sig-
`nals, smootth and smoothx3 to allow for discrimination of
`the pulse rate as follows:
`
`to
`second window filter
`tort
`21) Apply a
`[0059]
`smoothxz. smoothx3. accelerometer. and direct current
`compensation
`
`1)) Remove data as necessary ii'erratic motion is
`[0060]
`detected in the time domain at step 504
`
`c) Apply frequency translation to all or a subset
`[0061]
`of windowed smootth smoothxfi. accelerometer. and
`direct current compensation in step 505;
`
`01) Band pass filter all signals ill the range of0.5
`[0062]
`Hz to 4 Hz at step 506;
`
`smoothxl
`in
`Identify frequency peaks
`e)
`[0063]
`smoothxfi. accelerometer. and DC compensation:
`
`i) Using the frequency peaks from the accelers
`[0064]
`ometer of direct current compensation to deterntitte the
`frequencies to rejch using hand reject
`tiller.
`from
`
`011
`
`FITBIT, Ex. 1046
`
`

`

`US 20060084879 A1
`
`Apr. 20, 2006
`
`O12
`
`a microprocessor for receiving the pltoto detector output
`signal. the accelerometer output signal. and the contact
`type motion sensor output signal. and determining the
`pulse rate of the individual. wherein the pulse rate is
`determined by conditioning the photo detector output
`signal and removing portions of the conditioned photo
`detector output caused by regular motion and erratic
`motion of the individual.
`2. The pulse rate sensor of claim 1 wherein said trans-
`mitted light source lies in the near infrared region.
`3. The pulse rate sensor of claim 1 wherein said emitter
`comprises a plurality of light emitting diodes.
`4. The pulse rate sensor of claim 1 wherein said photo
`detector is a reflective infra—red sensor.
`5. The pulse rate sensor of claim 1 wherein said acceler-
`ometer is a two-dimensional accelerometer.
`
`3) Remove peaks from smootth that are not
`[0065]
`common with those in smoothx2.‘ and
`
`h) Pulse rate equals the lowest frequency peak in
`[0066]
`smoothx3 (block 507)
`
`If no peaks are remaining. the pulse rate is not updated.
`[0067]
`It is anticipated that the present invention may also
`be used as a pedometer. To use the pulse rate monitor wrist
`watch as a pedometer. the data from the two-axis acceler-
`ometer is filtered. If the motion detected is a “step.” i.e. loot
`motion. the filter applied to the Y—axis accelerometer data
`should be one-half that applied to the X»axis accelerometer
`data. Peak detection, ire. detecting the intervals between the
`peaks of the signals from the X and Y accelerometers. is
`used to determine the fundamental frequencies of motion.
`Peaks are detected using the first and second derivative
`methods described above
`
`[0068] The pulse rate is output using a digital signal which
`transitions at the rate of the pulse rate. The pedometer is
`output using a digital signal which transitions once for each
`step detected.
`
`[0069] A system and method for the effective implemen-
`tation of motion cancellation of optical
`input signals for
`physiological pulse measurement
`in accordance with the
`present invention has been disclosed herein. While various
`preferred embodiments have been shown and described,
`it
`will be understood that
`there is no intent
`to limit
`the
`invention by such disclosure. but rather.
`it
`is intended to
`cover all modifications and alternate constructions falling
`within the spirit and scope of the invention. as defined in the
`appended claims.
`We claim:
`
`1. A pulse rate sensor for measuring a physiological
`parameter of an individual comprising:
`
`an emitter for transmitting a light source into body tissue:
`a photo detector for receiving reflected light from said
`body tissue and producing a photo detector output
`signal indicative of reflected light;
`
`an accelerometer for measuring regular motion of the
`individual and producing an accelerometer output sig-
`nal indicative of the regular motion:
`a contact type motion sensor for measuring. erratic motion
`of the user and producing a contact type motion sensor
`output signal indicative Ui‘tllc erratic motion; and
`
`6. The pulse rate sensor of claim ] wherein said sensor is
`encapsulated in a watch module for wrist-based sensing.
`7. The pulse rate sensor of claim 6 wherein said watch
`module includes a universal serial bus port to automatically
`upload data, a radio frequency identification tag to uniquely
`identify said watch module. wherein said watch module is
`further capable of receiving finnware updates.
`8. The pulse rate sensor of claim 1 wherein said contact
`type motion sensor comprises a piezo sensor and said
`contact type motion sensor output signal comprises a piezo
`sensor output signal.
`9. A method of measuring a user pulse rate during
`physical exercise or activity. said method comprising:
`
`transmitting a light source into body tissue:
`
`the
`from said body tissue.
`receiving re