`
`63
`
`997B2
`
`US0074
`
`a2) United States Patent
`Pasolini et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,463,997 B2
`Dec. 9, 2008
`
`(54) PEDOMETER DEVICE AND STEP
`DETECTION METHOD USING AN
`ALGORITHMFOR SELF-ADAPTIVE
`COMPUTATION OF ACCELERATION
`THRESHOLDS
`
`(75)
`
`Inventors: Fabio Pasolini, S. Martino Siccomario
`(IT); Ive Binda, Voghera (IT)
`
`(73) Assignee: STMicroelectronics S.r.l., Agrate
`Brianza (IT)
`
`(*) Notice:
`
`Subject to anydisclaimer, the termof this
`patent is extended or adjusted under 35
`USS.C. 154(b) by3 days.
`
`(21) Appl. No.: 11/537,933
`
`(22)
`
`Filed:
`
`Oct. 2, 2006
`
`(65)
`
`(30)
`
`Prior Publication Data
`US 2007/0143068 Al
`Jun. 21, 2007
`
`Foreign Application Priority Data
`
`Oct. 3, 2005
`
`(EP)
`
`cicsecsecscseeesseseseeesseseeees 05425683
`
`(51)
`
`Int. Cl.
`(2006.01)
`GOIC 22/00
`(52) US. C1. cece cece cccteeeecsssesseeseteseeeeeeneeeees 702/160
`
`(58) Field of Classification Search ..
`702/141,
`702/150-154, 158, 160; 600/595; 73/490,
`73/510
`See applicationfile for complete searchhistory.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`.....esessees 702/160
`4/2000 Gaudet et al.
`6,052,654 A
`10/2000 Richardson etal.
`......... 600/300
`6,135,951 A
`6,826,477 B2* 11/2004 Ladetto etal.
`.............. 7FOL/217
`6,898,550 BL
`5/2005 Blackadar et al.
`........... 702/182
`2006/0020177 Al*
`1/2006 Seo etal. c.cccccessessessees 600/300
`
`2007/0073514 AL*
`2007/0143069 Al*
`2007/0198187 Al*
`
`........... 702/160
`3/2007 Nogimori etal.
`
`6/2007 Pasolini etal. vec... 702/160
`8/2007 Pasolini et al. ..........0 701/220
`
`FOREIGN PATENT DOCUMENTS
`
`GB
`
`2 359 890
`
`9/2001
`
`* cited by examiner
`
`Primary Examiner—Michael P Nghiem
`(74) Attorney, Agent, or Firm—Lisa K.Jorgenson; Dennis M.
`de Guzman; Seed IP Law Group PLLC
`
`(57)
`
`ABSTRACT
`
`In a pedometer device for detecting and counting steps ofa
`user onfoot, an accelerometer sensordetects a vertical accel-
`eration generated during the step. A processing unit, con-
`nected to the accelerometersensor, processes an acceleration
`signal relatingto the acceleration in order to detect the occur-
`rence of a step, and in particular compares the acceleration
`signal with a first reference threshold. The processing unit
`automatically adapts the first reference threshold as a func-
`tion of the acceleration signal. In particular, the processing
`unit modifies the first reference threshold as a function of an
`envelope of the amplitude of the accelerationsignal.
`
`5,583,776 A
`
`12/1996 Levi etal. woe 364/450
`
`30 Claims, 5 Drawing Sheets
`
`yo!
`
`PROCESSING UNIT
`
`SETTING
`
`FIRST COMPARATOR
`
`DISTANCE-CALCULATION
`
`THRESHOLD-ADAPTATION
`
`SECOND COMPARATOR
`
`DISPLAY MEAN-VALUE CALCULATION
`
`ENVELOPE CALCULATION
`
`LENGTH-ESTIMATION
`
`AXIS—DETERMINATION
`
`INTERFACE
`
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`LGEv. Uniloc USA
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`Page 1 of 12
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`LGE Exhibit 1005
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`

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`U.S. Patent
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`Dec. 9, 2008
`
`Sheet 1 of 5
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`US 7,463,997 B2
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`vo!
`
`PROCESSING UNIT
`
`SETTING
`
`FIRST COMPARATOR
`
`DISTANCE—CALCULATION
`
`THRESHOLD-ADAPTATION
`
`SECOND COMPARATOR
`
`INTERFACE
`
`ENVELOPE CALCULATION
`
`MEAN-VALUE CALCULATION
`
`LENGTH-ESTIMATION
`
`AXIS—DETERMINATION
`
`DISPLAY
`
`FIG. 1
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`LGEv. Uniloc USA
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`Page 2 of 12
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`LGE Exhibit 1005
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`

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`U.S. Patent
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`Dec. 9, 2008
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`Sheet 2 of 5
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`US 7,463,997 B2
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`U.S. Patent
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`Dec. 9, 2008
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`Sheet 3 of 5
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`US 7,463,997 B2
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`
`
`
`
`POSITIVE PHASE
`DETECTION
`CalAcc > S*
`
`
`
`
`
` NEGATIVE PHASE BEEN
`DETECTED?
`
`STEP
`INCREMENT
`
`STEP LENGTH
`
`ADAPTATION
`
`MASK INCREMENT
`
`DISTANCE
`INCREMENT
`
`2
`|
`DETERMINATION OF ACCELERATION DATUMTTTINCREMENT OF CALOR
`
`
`
`
`:
`
`CalAccANDTHRESHOLDADAPTATION
`
`SPEEDCOMPUTATION
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`Fig.3
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`U.S. Patent
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`Dec. 9, 2008
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`Sheet 4 of 5
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`US 7,463,997 B2
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`DETERMINATION OF ACCELERATION DATUM
`CalAcc AND THRESHOLD ADAPTATION
`
`11.18
`’
`
`ACQUISITION OF
`AGCELERATION SAMPLE Acc
`
`ELIMINATION OF D.C. COMPONENT
`AND DETERMINATION OF CalAcc
`
`30
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`34
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`34
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`32
`
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`Env* = o.,*Env*
`(a, < 1)
`
`+=
`
`Cad,
`.
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`35
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`CalAcc < Env-
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`NO<>YES
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`37 nv-=CalAcc(<1)
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`S*= B* Env*
`(<1).
`38
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`39
`40
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`ae+ = S,
`
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`$= 6* Env
`(B <1)
`
`42
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`43
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`U.S. Patent
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`Dec. 9, 2008
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`Sheet 5 of 5
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`US 7,463,997 B2
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`CalAcc
`
`i
`]
`|
`|
`HHHI,
`HHnaMtTAMtHE
`$ Mthaaataeen
`$+ ETHIEEEREREEETA
`nraeFHT
`
`Nog
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`+
`
`Fig.6
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`START
`
`PARAMETER
`INITIALIZATION
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`SPEED COMPUTATION
`Fig./
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`DETERMINATION OF ACCELERATION DATUM
`CalAcc AND THRESHOLD ADAPTATION
`
`POSITIVE PHASE DETECTION
`CalAcc > St
`
`HAS A
`POSITIVE PHASE BEEN
`DETECTED?
`
`
`
`

`

`
`
`US 7,463,997 B2
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`
`
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`1
`PEDOMETER DEVICE AND STEP
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`DETECTION METHOD USING AN
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`ALGORITHM FOR SELF-ADAPTIVE
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`COMPUTATION OF ACCELERATION
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`THRESHOLDS
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`2
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`counted as steps; on the other hand, if the threshold is too
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`high, some steps may notbe detected.
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`BRIEF SUMMARY OF THE INVENTION
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`BACKGROUND OF THE INVENTION
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`BRIEF DESCRIPTION OF THE SEVERAL
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`VIEWS OF THE DRAWINGS
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`For a better understanding of the present invention, pre-
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`ferred embodiments thereof are now described, purely by
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`way of non-limiting example and with reference to the
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`attached drawings, wherein:
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`FIG. 1 showsa block diagram of a pedometer device;
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`FIG. 2 shows a graph corresponding to the pattern of an
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`acceleration signal during a step;
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`FIG. 3 shows a flowchart corresponding to operations of
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`detection and counting of steps, executed by a processing unit
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`of the pedometer device of FIG. 1;
`FIG. 4 shows a flowchart corresponding to operations of
`self-adaptive modification of acceleration thresholds,
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`executed by the processing unit of the pedometer device of
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`FIG.1;
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`FIGS. 5-6 are graphs corresponding to the pattern of an
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`acceleration signal during a step and of reference thresholds
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`associated to the algorithm of FIG.3;
`FIG. 7 showsa possible variant of the flowchart of FIG.3;
`and
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`FIG. 8 is a partially exploded schematic view ofa portable
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`in particular a mobile phone,
`incorporating the
`device,
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`pedometer device of FIG. 1.
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`invention provides a
`One embodiment of the present
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`pedometer device and a method for detecting and counting
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`steps which will enable the aforesaid disadvantages and prob-
`1. Field of the Invention
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`lems to be overcome.
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`Thepresent invention relates to a pedometer device and to
`One embodimentofthe invention is a pedometer device for
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`a step detection method using an algorithm for self-adaptive
`detecting and counting the steps ofa user. The device includes
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`computation of acceleration thresholds.
`an accelerometer sensor configured to detect an acceleration
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`2. Description of the Related Art
`generated during a step; and a processing unit connected to
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`the accelerometer sensor, and configured to process an accel-
`Step-counting devices (referred to in general as pedom-
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`eration signal relating to the acceleration to detect the occur-
`eters) are known, which, being carried by a user, enable
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`rence of a step. The processing unit includesafirst compara-
`measurementofthe numberof steps made, and calculation of
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`tor configured to compare the acceleration signal with a first
`the distancetraveled, as well as supplying of additionalinfor-
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`reference threshold, and a threshold-adaptation circuit con-
`mation, such as, for example, the average speed, or the con-
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`figured to modify thefirst reference threshold as a function of
`sumption of calories.
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`the acceleration signal.
`Pedometers are advantageously used in inertial navigation
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`systems (the so-called dead-reckoning systems) applied to
`One embodiment of the invention is a step detection
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`human beings. Such systemstrace the movements ofa user,
`method for detecting steps in the gait of a user. The method
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`by identifying and measuring his/her displacements starting
`includes producing an acceleration signal relating to an accel-
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`from a knownstarting point, without resorting to the use of a
`eration generated during a step; and processing the accelera-
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`Global Positioning System (GPS), or by acting as aid to a
`tion signal to detect the occurrenceofthe step. The processing
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`GPS. In said systems, a compass supplies the information step includes comparing the acceleration signal withafirst
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`linked to the direction of displacement, and the pedometer
`reference threshold, and modifyingthe first reference thresh-
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`supplies the information linked to the amount of said dis-
`old as a function of the acceleration signal.
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`placement. Pedometersare also used in a wide range of appli-
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`cations in the clinical sector (for example, in rehabilitation),
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`and in general in the field of fitness (for example, as instru-
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`ments for monitoring a physical activity).
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`In particular, pedometers are known that use integrated
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`accelerometers of a MEMS (micro-electromechanical sys-
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`tem) type for step detection. In particular, such pedometers
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`have particularly compact dimensions, and can be advanta-
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`geously integrated within portable devices, such as mobile
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`phones, Mp3 readers, camcorders, etc.
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`The aforesaid pedometers implement a step detection
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`method based upon the analysis of the pattern of a vertical
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`acceleration, which is generated during the various phases of
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`the step by the contact of the foot to the ground, and which is
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`detected by an accelerometerfixed to the body of the user. In
`this connection, it is emphasized that “vertical acceleration”
`meansherein an acceleration directed along the vertical ofthe
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`user’s body. In particular, the occurrence of a step is deter-
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`mined by identifying acceleration peaks that appear in the
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`acceleration signal, and said peaksare detected by comparing
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`the acceleration signal with a given reference threshold, hav-
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`ing a pre-set value.
`However, even thoughthe acceleration signal hasa profile
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`that is repeatableat eachstep, its pattern (and, in particular,its
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`amplitude and temporal extension) has a wide variability
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`according to a numberoffactors that affect the gait, such as
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`the resting surface, the type of shoe worn (rigid sole or flex-
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`ible sole, etc.), and the speed of the gait (slow walking, fast
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`walking, running,etc.). Furthermore, each individualuser has
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`given characteristics and peculiarities that affect the gait,
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`differentiating it from that of other users.
`FIG. 1 is a schematic illustration of a pedometer device 1,
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`It follows that a step detection based upon the comparison
`comprising an accelerometer2, of a linear type and having a
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`ofthe value ofthe acceleration signal with a reference thresh-
`vertical detection axis z, and a processing unit 3, connected to
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`old having a pre-set value for the detection of acceleration
`the accelerometer 2. Advantageously, the accelerometer 2
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`peaks, involves the occurrence of errors that may even be
`and the processing unit 3 are mounted on the sameprinted
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`considerable in counting ofthe steps, and in the measurement
`circuit, housed inside a casing of the pedometer device 1 (not
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`of the distance traveled. In particular, if the threshold is too
`illustrated). The pedometer device 1 is carried by a user, for
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`low, spurious signals, rebounds, or noise in general, may be
`example on his belt or on his shoulder, so asto be fixed to the
`Page 7 of 12
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`DETAILED DESCRIPTION OF THE INVENTION
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`rence of a step), counting ofthe steps and measurementofthe
`body of the user and be able to sense vertical accelerations
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`total distance traveled are updated; otherwise, the algorithm
`that occur during the step, caused by the impactof the feet on
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`returns to the initial condition of looking for a new positive
`the ground.
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`phaseofthe step. In particular, the positive acceleration peaks
`The pedometer device 1 further comprises a display screen
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`that occur within the pre-set time interval are ignored by the
`4, connected at an output of the processing unit 3, and an
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`algorithm (in so far as they can be ascribed to phenomena of
`interface 5, connected at an input ofthe processing unit 3. The
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`noise, such as impact, anomalous rebounds, etc.).
`display screen 4 displays information at output from the
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`In detail, the algorithm starts with initialization, block 10,
`pedometer device 1, such as the numberofsteps, the distance
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`ofthe values ofthe positive and negative reference thresholds
`traveled, etc. The interface 5, for example, including push-
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`Stand S", respectively, at a positive minimum value S, and at
`buttons, an alphanumeric keypad, communicationports, etc.,
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`a negative minimum value S,, the latter being smaller, in
`allows the user to communicate with the processing unit 3 (for
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`absolute value, than the positive minimum value S,. As will
`example, by entering data).
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`be clarified, said minimum values represent limit values
`The accelerometer 2 is advantageously an integrated sen-
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`below which the reference thresholds are not allowedto drop.
`sor of semiconductor material, made using the MEMStech-
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`In addition, the values of a positive envelope Env* and of a
`nology, of a known type and thus not described in detail
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`negative envelope Env” of the acceleration signal A (which
`herein. In use, the accelerometer 2 detects the component
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`will subsequently be used for modification of the reference
`along the detection axis z of the vertical acceleration gener-
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`thresholds)are initialized, respectively, at the positive mini-
`ated during the step, and produces a corresponding accelera-
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`mum value S, andat the negative minimum value S,.
`tion signal A.
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`As shownin FIG.2,the pattern ofthe acceleration signal A Next, block 11, the processing unit 3 determinesafirst
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`(with the d.c. componentfiltered out) in time t has a given
`acceleration datum CalAcc, and consequently modifies the
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`acceleration profile which repeats at each step (indicated by
`values of the reference thresholds (as will be described in
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`the dashed rectangle). In detail, the acceleration profile com-
`detail hereinafter with reference to FIGS. 4 and 5).
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`prises in succession: a positive phase, in which a positive-
`The algorithm then proceeds, block 12, with the search for
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`acceleration peak occurs(i.e., directed upwards), due to con-
`the positive phase of the step, by comparing the value of the
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`tact and consequent impactof the foot with the ground; and a
`acceleration datum CalAcc with thepositive reference thresh-
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`old S*, to detect a positive acceleration peak of the accelera-
`negative phase in which a negative-acceleration peak occurs
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`(i.e., directed downwards) due to rebound, having an absolute
`tion signal A.
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`value smaller than that of the positive-acceleration peak.
`Until a positive phase of the step is found, block 13, the
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`The processing unit 3, comprising a microprocessorcircuit
`algorithm proceeds with acquisition of a new acceleration
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`(for example, a microcontroller or DSP), acquires at pre-set
`datum CalAcc in block 11 (and corresponding modification
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`intervals samples of the acceleration signal A generated by
`of the reference thresholds), and with the comparisonof said
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`the accelerometer 2, and executes appropriate processing
`new acceleration datum with the positive reference threshold
`s*.
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`operations for counting the numberof steps and measuring
`the distance traveled. As will be described in detail hereinaf-
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`Thepositive phase is detected whenthe acceleration datum
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`exceeds the positive reference threshold S* and then drops
`ter, the processing unit 3 compares the value ofthe accelera-
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`tion signal A (with the d.c. componentfiltered out) with a
`below the positive reference threshold, the instant of detec-
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`positive reference threshold S* and with a negative reference
`tion of the positive phase corresponding to the instant in
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`threshold S-, for identifying, respectively, the positive phase
`whichthe acceleration datum drops again below the positive
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`(positive acceleration peak) and the negative phase (negative
`reference threshold S*. At this instant, the processing unit 3
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`acceleration peak) of the step.
`stores the value assumedby the positive reference threshold
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`S*, which is a maximum value S*,,,_...
`According to one embodimentofthe present invention, the
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`values ofthe positive and negative reference thresholds S*, S~
`After the positive phase detection, the algorithm proceeds
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`are not fixed and equal to a given pre-set value, but are
`with the search for the negative phase of the step, block 14,
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`calculated in a self-adaptive way(i.e., in a way that adapts
`i.e., of a negative acceleration peak, by comparing the value
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`without any external intervention from a user) by the process-
`ofthe acceleration datum CalAcc with the negative reference
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`ing unit 3, based on the values assumed by the detected
`threshold S~. In particular, the search for the negative phase of
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`acceleration.In particular, as will be clarified hereinafter, the
`the step is executed within a certain time interval Mask, the
`value of which must be lower than a maximum interval Max-
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`values ofthe positive and negative reference thresholds St, S~
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`are modified at each acquisition of a new sample of the
`_Maskfrom detection ofthe positive phase (corresponding to
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`acceleration signal A, as a function of the value ofa positive
`acertain numberof samples, the value ofwhich is determined
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`and negative amplitude envelopeofthe acceleration signal, in
`also as a function of the sampling rate of the acceleration
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`such a mannerthat the reference thresholds vary with time
`data).
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`approximately following said envelopes. The pedometer
`Until a negative acceleration peak is detected, block 15,
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`device 1 thus adapts to variations in the detection conditions
`and as long as the time interval Mask is shorter than the
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`(and, in particular, to different profiles of the acceleration
`maximum interval Max_Mask, block 16, the algorithm pro-
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`signal, in terms of amplitude and duration), due, for example,
`ceeds with the search for the negative phase ofthe step. In
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`detail, the time interval Mask is incremented, block 17, a new
`to a different type ofterrain, or to an increase in the speed of
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`the gait.
`acceleration datum CalAcc is acquired (and the values of the
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`The algorithm implemented by the processing unit 3 for
`reference thresholds are modified accordingly), block 18
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`performing, amongotherthings, the operations of step count-
`(which is equivalent to block 11), and the algorithm returnsto
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`ing andoftraveled distance measurementis now described,
`block 14. Ifno negative phase of the step has been identified
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`with reference to FIG. 3. Said algorithm envisages the analy-
`after expiry of the maximum interval Max_Mask,block 16,
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`sis of the acceleration signal A in orderto look for a positive
`the algorithm returns to block 11 in order to look for a new
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`phase ofthe step followed by anegative phase within a pre-set
`potential positive phase ofthe step.
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`time interval from the occurrenceof the positive phase. In the
`On the contrary, if the negative phase is identified within
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`case where said sequence occurs (which indicates the occur-
`the maximum interval Max_Mask (ie.,
`the acceleration
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`5
`datum drops below the negative reference threshold S-), the
`processing unit 3 determines the occurrenceof a step, and,
`block 20, increments the count of the detected steps. Further-
`more, the estimate of the distance traveled is updated by
`adding to the previous value an estimate of the length of the
`current step LPS.
`In detail, according to one embodiment of the present
`invention, block 21, the processing unit 3 calculates the esti-
`mate of the length of the current step LPS as a function of the
`maximum value S*,,,,, reached by the positive reference
`threshold S* during the positive phase of the step, which is
`indicatory of the valueofthe positive acceleration peak. The
`actual length ofthe step varies with respect to a standard value
`determined on the basis of the physical characteristics of the
`user, according to the speedofthe step, or, equivalently, to the
`amplitude of the generated acceleration. Consequently, the
`estimate ofthe length ofthe current step LPSis calculated via
`the formula:
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`EPS=LPf(S"pax)
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`where LPis a standard length ofthe step, correspondingto 0.4
`to 0.5 timesthe heightof the user, and f(S*,,,,,) is a corrective
`function, for example a linear one, based upon the maximum
`value S*,,,... Lhe corrective function f(S",,,,,.) can be tabulated
`on the basis ofexperimentaltests, which enable association to
`a given maximum value S”*,,,,.. of an appropriate correction to
`be madeto the standard length ofthe step LP. In particular, the
`function f(S",,,,,.) is conveniently stored in the processing unit
`3.
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`The algorithm then proceeds, block 22, by increasing the
`distance traveled on the basis of the estimate of the length of
`the current step LPS, previously calculated. Furthermore,
`block 23, further variables supplied at output from the
`pedometer device 1 can be updated, such as the number of
`calories (also in this case, the previous count is updated by
`adding an average consumption ofcalories per step), and the
`average and instantaneous speed of travel, which are calcu-
`lated in a known way notdescribed in detail herein.
`Next, the algorithm returns to block 11 in order to detect a
`new acceleration profile indicating occurrenceofa step.
`There will now be described in detail, with reference to
`FIG.4, the algorithm implemented by the processing unit 3
`for determination of a new acceleration datum CalAcc and
`consequent updating ofthe valuesofthe positive and negative
`reference thresholds St and S~, in such a manner that the
`aforesaid values will follow approximately the positive and
`negative envelope of the acceleration signal.
`In brief, said algorithm envisages calculation, for each new
`acceleration datum CalAcc, ofthe values ofthe positive enve-
`lope Env* and negative envelope Env’, and modification of
`the value of the positive and negative reference thresholds St
`and S~ as a function of the positive envelope Env* and nega-
`tive envelope Env’, respectively.
`In detail,
`in an initial block 30, the processing unit 3
`acquires from the accelerometer 2 a new acceleration sample
`Accofthe acceleration A. Then, block 31, the d.c. component
`of said acceleration value (due substantially to the accelera-
`tion of gravity) is eliminated so as to determinethe accelera-
`tion datum CalAcc, with zero mean value, which will be used
`subsequentlyin the algorithm.In detail, the mean value Accm
`of the acceleration sample Accis calculated with the expres-
`sion:
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`Accm=y:Accm+(1-y):CalAce
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`mean value andof the acceleration datum, which were cal-
`culated at the previous acquisition. The new acceleration
`datum CalAccis calculated by applyingtherelation:
`CalAcc=Acc-Accm
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`Then,the algorithm proceeds with the determination ofthe
`new valuesofthe positive and negative envelopes Env*, Env”.
`In detail, block 32, if the value of the acceleration datum
`CalAccis higher than the value ofthe positive envelope Env*
`(as calculated at the previous acquisition), the new value of
`the positive envelope Env* is set equal to the value of the
`acceleration datum CalAcc, block 33. Otherwise, block 34,
`the valueofthe positive envelope Env*is set equalto a proper
`fraction of the previous value; i.e., the previous value is mul-
`tiplied by a first constant a,<1, for example, a,=0.9458. In
`this way, the value of the envelope coincides substantially
`with the value of the acceleration datum,if the acceleration
`datum is greater than the previous value of the envelope, and
`otherwise decreases(in particular, almost exponentially) with
`respectto the previous value.
`Likewise, block 35, if the value of the acceleration datum
`CalAccis smaller than the negative envelope Env” (as calcu-
`lated at the previous acquisition), the new value of the nega-
`tive envelope Env”is set equal to the value of the acceleration
`datum CalAcc, block 36. Otherwise, block 37, the value ofthe
`negative envelope Env” is set equal to a properfraction ofthe
`previous value of the envelope; i.e., it is multiplied by a
`second constant a,<1, for example, a,=0.9438. Note, in par-
`ticular, that the different value of the first and second con-
`stants ©, 21s due to the different value ofthe positive and
`negative accelerations, said negative accelerations being of
`smaller intensity, since the negative phase of the step is a
`reboundofthe positive phase.
`The algorithm then proceeds with updating ofthe values of
`the reference thresholds as a function of the envelope values
`previously calculated. In detail, block 38, the value of the
`positive reference threshold S* is set equal to a certain proper
`fraction of the positive envelope Env‘; in particular, it is set
`equalto the value of the positive envelope Env* multiplied by
`a third constant B<1, for example, B=0.65. However, if the
`value thus calculatedis less than the positive minimum value
`S,, block 39, the value ofthe positive reference threshold S*
`is set at said positive minimum valueS,, block 40.
`Likewise, block 41, the value of the negative reference
`threshold S~ is set equal to a certain proper fraction of the
`negative envelope; in particular, also this value is multiplied
`by thethird constant §. However, once again,ifthe value thus
`calculated is less than the negative minimum value S,, block
`42,the value ofthe negative reference threshold S~ is set at the
`negative minimum value S,, block 43.
`The values of the new reference thresholds thus calculated
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`are then usedfor detection of the positive and negative phases
`of the step, as described previously.
`FIGS. 5 and 6 show the curves of the positive and negative
`reference thresholds S*, S~, and of the positive and negative
`envelopes Env*, Env’, calculated using the algorithm
`described previously, and the pattern of the acceleration sig-
`nal CalAcc (constituted by the sequence of the acceleration
`data CalAcc). It is evident that the reference thresholds sub-
`stantially follow the envelopes of the acceleration signal
`(which, in turn, follow the peaks of the acceleration signal).
`In detail, the value ofthe positive acceleration threshold S*
`is initially equal to the positive minimum value S, (see, in
`particular, FIG. 6), and remains constantas long as the accel-
`eration datum CalAcc remains less than the positive accel-
`eration threshold S*. Starting from the instant at which the
`wherey is a constant between 0 and 1, for example equal to
`0.95, andAccm and CalAccarethe values, respectively, ofthe
`acceleration datum CalAcc exceedsthe positive acceleration
`Page 9 of 12
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`positive acceleration peak). In this case, the algorithm uses a
`threshold S:, and as long as the acceleration datum CalAcc
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`single reference threshold, in particular the positive reference
`increases,the positive acceleration threshold S* follows, ina
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`threshold S*, which is modified as a function of the value of
`“damped”way,the increase ofthe acceleration datum CalAcc
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`the positive envelope Env*, in a way altogether similar to
`in particular, FIG. 5). Next, the acceleration datum
`(see,
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`what has been described previously. Said simplified algo-
`CalAcc starts to decrease, and, along with it, the positive
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`acceleration threshold S*, which, as long as the acceleration
`rithm, although computationally less burdensomeforthe pro-
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`cessing unit 3, has, however, the disadvantage of being more
`datum CalAcc decreases, assumesa decreasing pattern (with-
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`sensitive to noise. In fact, the lack of check on the presence of
`out, however, dropping below the positive minimum value
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`S,). In particular, at the end of the positive phase of the step,
`the negative phase, after the positive phase, renders false
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`the maximum value S*,,,,,, is stored. The positive reference
`detection and counting errors more likely.
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`threshold S* returns to the positive minimum value S, when
`The accelerometer 2 could be equipped with a number of
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