U.S. patent application number 11/843204 was filed with the patent office on 2008-01-24 for monitoring sports and swimming.
This patent application is currently assigned to SPORTZCO PTY LTD. Invention is credited to Neil Davey, Ronald Grenfell, Daniel James, Colin Mackintosh, Kefei Zhang.
Application Number | 20080018532 11/843204 |
Document ID | / |
Family ID | 32231628 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080018532 |
Kind Code |
A1 |
Mackintosh; Colin ; et
al. |
January 24, 2008 |
MONITORING SPORTS AND SWIMMING
Abstract
A data logger for a swimmer which includes an accelerometer, and
a GPS unit to sense position and velocity, a heart rate monitor, a
controller programmed to manipulate the data and provide a display
of the heart rate, lap times, stroke rate etc. The data can be
stored or transmitted to a remote computer for use by the coach.
The device can also be adapted for other sports.
Inventors: |
Mackintosh; Colin; (Bruce,
AU) ; James; Daniel; (Nathan, AU) ; Davey;
Neil; (Nathan, AU) ; Grenfell; Ronald;
(Melbourne, AU) ; Zhang; Kefei; (Melbourne,
AU) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W.
SUITE 1100
WASHINGTON
DC
20036
US
|
Assignee: |
SPORTZCO PTY LTD
Hawthorn
AU
|
Family ID: |
32231628 |
Appl. No.: |
11/843204 |
Filed: |
August 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10531263 |
Apr 13, 2005 |
7272499 |
|
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PCT/AU03/01430 |
Oct 31, 2003 |
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11843204 |
Aug 22, 2007 |
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Current U.S.
Class: |
342/357.57 ;
342/176; 600/500 |
Current CPC
Class: |
A63B 2220/12 20130101;
A63B 2024/0025 20130101; A63B 24/0021 20130101; G01C 22/00
20130101; A63B 71/06 20130101; A63B 2230/42 20130101; A63B 2220/40
20130101; A63B 2230/06 20130101; A63B 2225/50 20130101; A63B
2220/30 20130101; A63B 2225/60 20130101; A63B 69/06 20130101; B63H
16/00 20130101; A63B 2230/207 20130101; B63B 49/00 20130101 |
Class at
Publication: |
342/357.12 ;
342/176; 600/500 |
International
Class: |
G01S 1/00 20060101
G01S001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2002 |
AU |
2002952407 |
Jun 23, 2003 |
AU |
2003903123 |
Sep 28, 2006 |
AU |
20062232730 |
Claims
1. A data acquisition system for use in swimming events which
incorporates a) a global position sensor to derive three
dimensional positioning data relative to time elapse b) at least
one accelerometer to derive acceleration and velocity data in three
dimensions c) a microcontroller with a clock to interrogate the
global position sensor and to collect the accelerometer data d) a
power supply e) communication means for transmission of global
position and accelerometer data from the microcontroller to a
computer device f) the computer device being programmed to use the
global position and accelerometer data to provide accurate and
continuous output of parameters such as velocity acceleration and
distance traveled.
2. A data acquisition system as claimed in claim 1 in which
velocity is derived from the global position sensor and the
accelerometer data is sampled to obtain movement characteristics in
swimming
3. A data acquisition system as claimed in claim 1 wherein the
accelerometer data is integrated to derive velocity related
movement characteristics and drift is be checked every second using
the output from the global position sensor.
4. A data acquisition system as claimed in claim 1 wherein an
inertial navigation system based on the accelerometer data is used
to determine position when the GPS system is unable to receive
data.
5. A data acquisition system as claimed in claim 1 which includes a
display screen.
6. A data acquisition system as claimed in claim 5 in which the
global position sensor is located in a separate unit to the micro
controller and the display.
7. A data acquisition system as claimed in claim 6 in which the
global position sensor is adapted to be mounted on the swimmers
head and the display unit is adapted to be mounted on the swimmers
wrist
8. A data acquisition system as claimed in claim 1 which also
includes a physiological sensor.
9. A data acquisition system as claimed in claim 6 in the
physiological sensor is a heart rate monitor.
Description
[0001] This invention relates to a method and system for monitoring
performance characteristics of swimmers and in particular the
particular movements which contribute to enhanced performance.
BACKGROUND TO THE INVENTION
[0002] Monitoring of athletes performance both in training and in
competition, is important in the development and implementation of
new approaches aimed at improving sporting performance.
[0003] The ability to measure and record athlete physiological
information and positional information associated with athlete
movement in real-time is critical in the process of athlete
training and coaching. Blood oxygen, respiration, heart rates,
velocity, acceleration/force, changes in direction, and position
and many other factors are required in elite athlete training and
coaching. The position, movement and force information plays an
important role in effective analysis of the athlete performance,
especially for rowers. For example, the stroke frequency, force and
synchronization of athletes are critical for the performance of the
rowers in a competition. Currently the stroke information can only
be measured in either dedicated sports laboratories or using
simulated devices. Reliable analysis of the stroke rate and stroke
distance in rowing has been a challenge for a long time due to the
availability of the real scenario data, in particular a high
precision of position, velocity and acceleration data. Existing
technologies used for this purpose include theoretical studies,
video-footage procedure, indoor tank procedure, computer modeling
and ergometer studies. Much of the equipment is either too heavy,
expensive, obtrusive or less reliable. Therefore, smart real-time
monitoring during training and competition to help elite athletes
to improve their performance and avoid injuries is critical for
both athletes and coaches. Any methodology that would improve the
situation would not only bring benefits to the rower practice, but
also to many other sports related application including both team
sports and individual athlete.
[0004] U.S. Pat. Nos. 4,984,986 and 5,099,689 disclose measuring
systems for off water rowing apparatus which measure the number of
strokes or the force applied to the machine.
[0005] U.S. Pat. No. 6,308,649 discloses a monitoring system for
sail boat racing which provides feedback to the crew of such
parameters as wind speed and direction boat speed, sail boat
comfort parameters, sail shape, line tensions, rudder angle
etc.
[0006] Some development of monitoring systems has occurred in non
water sports. U.S. Pat. No. 6,148,262 discloses a bike mounted
sports computer including a GPS receiver to provide a mapping
facility.
[0007] U.S. Pat. No. 5,685,722 discloses swimmers goggles which
incorporate a timer and a display. An accelerometer senses the
tumble turns to count laps and the goggles include a strap to sense
the pulse of the swimmer. Such head-mounted systems make it
difficult to discriminate between the movements of the head and the
rest of the body of the swimmer.
[0008] Wrist watch type sensors for swimmers have also been
proposed as in U.S. Pat. No. 5,864,518 and application
2004/0020856.
[0009] Recently proposed swimming loggers prefer a display in the
goggles.
[0010] U.S. Pat. No. 6,033,228 discloses a device attached to a
swimmers waist. The device includes an impeller magnetic device
which is able to signal changes in speed to a visual display worn
by the swimmer.
[0011] U.S. Pat. No. 5,685,722 discloses a goggle mounted
accelerometer and display.
[0012] WO/03061779 suggests displaying real time data visually in
the goggles but does not suggest aural display. This disclosure
favors separation of the display from the motion sensor which is
located preferably on the back with RF transmission to the display.
There is a suggestion of monitoring pulse rate using a temporal
artery and to integrate the whole device into one unit on the
goggles.
[0013] Accelerometers are able to detect changes in acceleration
but do not provide a meaningful measure of velocity.
[0014] It is an object of this invention to provide a device for
real time monitoring of swimmers that is useful during a training
session and also for coaches to carry out detailed analysis after
the training session.
BRIEF DESCRIPTION OF THE INVENTION
[0015] To this end the present invention provides a data
acquisition system for use in swimming which incorporates [0016] a)
a global position sensor to derive 3 dimensional positioning data
relative to time elapse [0017] b) at least one accelerometer to
derive acceleration and velocity data in 3 dimensions [0018] c) a
microcontroller with a clock to interrogate the global position
sensor preferably at a frequency of at least 1 Hz and to measure
the accelerometer data [0019] d) a power supply [0020] e)
communication means for transmission of global position and
accelerometer data from the microcontroller to a remote computer
device [0021] f) the remote computer device being programmed to use
the global position and accelerometer data to provide accurate and
continuous output of parameters such as velocity acceleration and
distance traveled.
[0022] This device will provide positional data from the training
and competition environment and provide both athlete physiological
data and performance data related to the sport.
[0023] The movement sensor is an accelerometer combined with a GPS
unit to sense instantaneous position and velocity. A GPS receiver
transmitter is included in the device to derive location and speed
parameters.
[0024] Preferably physiological sensors are also attached to the
athlete and integrated with the sensor system. Heart rate is the
prime parameter to be measured and this may be sensed using
electrical sensors or microphones. Respiratory rate is also
important and may be measured by sensing the stretching of a chest
band or using a microphone and signal recognition software. Another
parameter is arterial oxygen saturation which may be measured non
invasively by a sensor, placed on an earlobe or finger tip, using
pulse oximetry employing an infra red absorption technique.
Infra-red spectroscopy may be used for non invasive measurement of
blood lactate concentrations.
[0025] Preferably velocity is derived from the global position
sensor and the accelerometer data is sampled to obtain movement
characteristics of the sport being monitored. Preferably the
accelerometer data is integrated to derive velocity related
movement characteristics and drift is checked every second using
the output from the global position sensor.
[0026] This system provides a platform device which can be used for
a wide range of sports simply by providing appropriate software to
derive from the accelerometer and GPS data, the desired sport
parameters such as stride frequency velocity stride length,
vertical acceleration, time off the ground for long jumping and
events such as aerial skiing. The system of this invention can be
used in swimming to identify stroke type, turns, and with turns the
number of laps and the stroke rate per lap as well as lap times.
Careful analysis of each stroke can show the efficiency and power
by comparing the acceleration and deceleration cycles and the
effect of breathing cycles. In open water swimming the GPS can also
be used to provide an indication of location, direction, and speed
relative to the course.
[0027] The device of this invention may also include an
accelerometer so that tri-athletes who run and swim can obtain
accelerometer (pedometer) based speed and distance data for the
land portion of their activities. Similarly GPS devices may also be
included to derive similar distance and speed data. By adding a
magnetometer to the unit on the cyclist pedal cadence can be
sensed.
[0028] Alternatively pedal cadence can be sensed by a unit on the
bike and transferred to the unit on the cyclist using a radio
frequency pickup unit.
[0029] The accelerometer information may also be used to determine
stroke type, stroke count, turns, lap count, lap times and speed in
swimming and stride count, stride length and speed in running and
cadence and power in cycling.
[0030] In another embodiment the present invention provides a wrist
mounted sensor with a large display screen able to communicate with
a second unit mounted on the swimmers head. Because GPS may not
receive signals when the device is submerged the GPS unit may be
mounted in the unit on the head and communicates wirelessly with
the device on the wrist when the wrist is out of the water.
Alternatively it is within the scope of this invention to modify
the GPS polling routine to ensure that basic location information
can be received within the time interval that the wrist is clear of
the water.
[0031] This means that the display unit can receive and process the
sensor data for display when required. It is preferred for open
water swimming to combine a GPS sensor with triaxial accelerometers
to provide the essential velocity, distance, direction and stroke
information. The accelerometers in combination with the processor
clock provide information relating to stroke type, number of
strokes per lap, lap times, turn efficiency and velocity off the
wall. The velocity measurements from accelerometers tend to drift
and the GPS signals are used to correct the velocity measurements
in open water. The GPS can also be used to provide directional and
distance information in open water as well as the same information
in running and cycling. For tri athletes the accelerometers can
also provide stride information and for the bicycle leg cadence
information on the number of pedal revolutions. The central
processor can also be in communication with a physiological sensor
such as a heart rate monitor mounted on the athletes chest.
[0032] The quality of the display is an important issue
particularly for swimmers. In a preferred aspect the wrist mounted
display provides different coloured screens for preprogrammed
functions. For example if the athlete is attempting to maintain a
heart rate within a certain band a first colour indicates that the
rate is within the band and a second colour indicates that it is
too low and a third colour that it is too high. In open water
swimming one colour may indicate that the swimmer is on course
while a second colour may indicate that the swimmer needs to bear
to the right and the third colour that the swimmer needs to bear to
the left. In the pool tumble turns provide an opportunity for the
swimmer to view a wrist display. As accelerometers allow the turn
to be identified and also indicate the conclusion of a lap, the
processor may be programmed to display on the wrist basic
information such the lap number and the last lap time. Other
information that could be displayed are heart rate and the number
of strokes. Such a display is preferably for a short time as the
swimmer comes off the wall. The display may be brightly lit for
this period and be relatively large. The display can also be
oriented for easy viewing on the wrist when the arms are extended
in front of the swimmer which is the usual orientation coming out
of a turn.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Particular embodiments of the invention will be
described.
[0034] FIG. 1 is a schematic layout of a data logger used for a
rower and a rowing shell;
[0035] FIG. 2 shows the software output flow diagram for a rowing
data logger;
[0036] FIG. 3 is a graphical illustration of stroke determined by
using GPS data;
[0037] FIG. 4 illustrates the display for a computer screen;
[0038] FIG. 5 illustrates the deviation between code and carrier
derived velocity measurements;
[0039] FIG. 6 is a video frame and triaxial accelerometer readings
for a swimmer;
[0040] FIG. 7 is the core circuit diagram for monitor mounted on a
swimmer;
[0041] FIG. 8 is the radio transceiver circuit for the monitor of
FIG. 7;
[0042] FIG. 9 is the sensor circuits for the monitor of FIG. 7.
[0043] Recent developments in micro-electromechanical systems
(MEMS) technology have opened new avenues for the use of high
precision lightweight accelerometers and gyroscopes for new and
challenging sports applications (eg. characterize rate and length
of rowing stroke and stride). MEMS integrate both electrical and
mechanical components on a single chip through extensive research
into integrated circuit processing technologies. As MEMS
accelerometers originated from monitoring vehicle safety and
electronic stabilization, they only provided very low accuracy
measurements. However, as micromechanical devices are inherently
smaller, lighter, and usually more precise than their macroscopic
counterparts, more and more reliable sensors are becoming
available. Accelerometers measure linear acceleration and
gyroscopes measure angular acceleration (pitch, yaw and roll).
[0044] Most accelerometers are used concurrently with gyroscopes to
form an inertial navigation or "dead reckoning" system. That is
where the deviation from position of a known reference (or starting
point) is determined by integration of acceleration in each axis
over time.
[0045] Inertial sensors errors include initial system heading
errors, accelerometer scale factor and bias errors. These drifts
and biases inherent in the inertial sensors will cause a
misalignment of the platform and errors in the sensed
accelerations, which subsequently results in errors in computed
velocities and positions.
[0046] The advent of the advanced global navigation satellite
systems (GNSS), GPS in particular, has revolutionized conventional
precise positioning techniques. GPS has been made more amenable to
a wide range of applications through the evolution of rapid static
and kinematic methods, and now even more so with the advent of the
On-The-Fly (OTF) technique and most recently network-based RTK
techniques such as the Trimble virtual reference station system and
Geo++ surface correction parameter method. Real-time Kinematic
(RTK) or single epoch positioning allows for the determination of
the integer ambiguities in real-time. It is therefore not necessary
to carry out any static initialization before performing the
survey. Due to the small wavelengths of the carrier phase
frequencies (eL1.sub.iO19 cm and eL2.sub.iO24 cm), the
determination of position within a specific cycle to a millimetre
level by utilizing differential carrier phase measurements (i.e.
differential techniques) is possible. Most systems statistically
determine the most likely solution for the position of the roving
receiver. Virtually, all carrier phase processing algorithms that
utilize an OTF technique, rely on the double difference carrier
phase observables as the primary measurement. A search box is
determined within which the position must lie. All possible
solutions are then assessed and the statistically most-likely
candidate is selected. This procedure is extremely computing
intensive, particularly with a large number of satellites.
[0047] Regardless of whether the system is for real-time or
post-mission use, the algorithm is generally treated the same.
Clearly, with real-time implementations, data outages, unfavourable
observation environments, multipath and cycle slips can severely
limit the performance of the system. The time for ambiguity
resolution can range from a few seconds to several minutes
depending on some of the following considerations: [0048] Use of L1
versus L1-L2 (widelane, L2.sub.iO86 cm) observable [0049] Distance
between reference and roaming receivers [0050] Number and geometry
of satellites [0051] Ambiguity search method used and differential
atmospheric conditions [0052] Quality of the received signal
(multipath effects, code and carrier phase noise etc.)
[0053] Precise detection and removal of cycle slips is essential
for the successful use of the OTF kinematic GPS technique. Various
cycle slip detection techniques have been developed in the past
decade. Included are double and triple differencing techniques,
comparing the difference between adjacent carrier phase and code
values (range residual), comparing the adjacent four observables
equation, comparing adjacent ionospheric residual, the
least-squares ambiguity decorrelation adjustment, carrier phase
curve fitting, using redundant satellites and using the raw Doppler
values. These methods typically assume a known stochastic behaviour
for un-modeled errors (e.g. noise, multipath, differential
atmospheric effects), which if present, will adversely affect the
performance of the algorithm. None of these techniques can "cure
all" kinematic positioning problems. Sometimes a cycle slip may be
detected, but not accurately corrected for. Such instances include
a loss of lock, large multipath effects and lower signal-to-noise
ratio. This necessitates the combination of two or more of these
techniques for a more robust solution.
[0054] FIG. 1 illustrates the basic components of a system to
monitor boat speed and an oarsman's heart rate.
[0055] The accelerometer provides a PWM output where the duty cycle
is related to the acceleration. On the rising edge and falling edge
of the PWM output, a timer value is captured and used to calculate
the accelerometers duty cycle. The firmware also includes an
algorithm to adjust for jitter in the PWM period, and for a small
amount of drift. A more detailed algorithm that compensates for
temperature drift over time has been looked at, and will be
implemented at a later date.
[0056] The impeller pickup uses a Melexis MLX90215 Hall Effect
sensor to detect the rotations of the NK impeller. The MLX90215 is
programmed with a sensitivity of 100 mV/mT. Output from the sensor
is amplified by 100 to increase the signal amplitude to a usable
range. This signal is then sampled using an A/D at 1200 Hz and
processed using DSP techniques within the firmware to calculate
rotations. Instead of using an impeller to detect boat speed a
water flow sensor may be used. One preferred sensor is a micro PCB
or silicon based micro fluid flow sensor that uses a heater in
combination with a heat sensor that measures the change in
temperature of fluid flowing past the heater and sensor to
determine the fluid flow rate which in this case is the water
flowing past a fixed point on the boat hull. This can then be used
to measure boat speed.
[0057] For competition and race profile analysis it is preferred
not to use impellers or water flow sensors but rely on GPS and
accelerometers.
[0058] The display device is a handheld Compaq iPAQ.TM. computer
programmed to present the data in a form that is useful to a coach
or rower.
[0059] It is preferred that the device have data logging and IrDA
transfer capabilities which makes data storage on the unit of
slightly less importance. However storing data on the unit makes
sense as the raw data can be streamed into the device and the
greater processing power of the unit chip allows for flexible
software and display development.
[0060] The microprocessor is a Hitachi HD64F3672FP which stems from
the H8/300H family. Its main features are: [0061] eight 32-bit
registers OR sixteen 16-bit or sixteen 8-bit [0062] Serial
communication Interface (SCI) [0063] 10-bit ADC (4 channels) [0064]
2 k bytes of RAM
[0065] The accelerometer unit is powered from a 9 Volt battery,
which is regulated down to 5 volts internally. The dimensions of
the accelerometer unit are 25 mm.times.30 mm.times.9 mm (smaller
that the average matchbox). The cover needs to be splash proof but
importantly the on/off buttons and start/stop buttons etc must be
able to be accessed even when the rowers are wearing gloves.
[0066] All the chips that have been selected are amongst the
smallest available in their range, the Hitachi HD64F3672FP measures
on 12 mm.times.12 mm, this incorporates a 64 pin architecture and
the ADXL202 measuring only 5 mm.times.5 mm.
[0067] FIG. 2 illustrates the output flow from the various sensors
namely impeller, heart rate monitor, clock, GPS sensor and 3 D
accelerometer. Stroke rate and stroke drive to recovery ratio are
most conveniently derived from the accelerometer data while intra
stroke velocity, distance per stroke and velocity per stroke are
derived from the accelerometer, GPS and time clock data.
[0068] The data for 1 block (by 3 or 4 channels) will be packaged
and transmitted in a single frame. The sampling time for a frame (1
block at 150 samples/sec) will be equivalent to 6.6 ms. This data
will be combined with block and channel information.
[0069] A total of eight bytes is required to transmit one block of
data this includes the header, two 16-bit channels, Impeller
Rotation count and Heart Rate count. The Heart Rate count is only
transmitted once a second, or one in every 150 frames. Heart rate
is an output indicating the millisecond value from the previous
beat or the millisecond of the beat that occurred during that
packet of information. This is used to calculate instantaneous HR
on a beat to beat basis. Alternately the number of beats in 15 secs
is totalled and then multiplied by 4 to get the HR. The algorithm
then runs on a 5 sec rolling average to smooth the data. Given that
maximum HR will never exceed 250 bpm this means that at most a beat
will occur every 240 ms which is approximately 1 pulse every 2
packets of information. Table 1 shows a block of data excluding the
framing and network information data. TABLE-US-00001 TABLE 1 Byte 1
Frame header(xEE) 2 Number of Blocks(4 bits) Number of channels (4
bits) 3 ACC "Y" bits 1-8 4 ACC "Y" bits 9-16 5 ACC "X" bits 1-8 6
ACC "X" bits 9-16 7 Impeller rotation count (8 bits) 8 Heart rate
count (8 bits)
[0070] Table 2 illustrates an example of the bit stream for 2
frames. The first frame containing two 16-bit channels and Impeller
Rotation count, and the second frame containing two 16-bit
channels, Impeller Rotation count and Heart Rate count
TABLE-US-00002 TABLE 2 Data Stream Meaning 0xEE Header Byte 0x13
One Block, eg. 3Channels 0xA9 Acc Y Lower Byte 0xEA Acc Y Upper
Byte 0x46 Acc X Lower Byte 0xC9 Acc X Upper Byte 0x01 Impeller
Rotation Count 0xEE Header Byte 0x14 One Block, eg. 4Channels 0xA9
Acc Y Lower Byte 0xEA Acc Y Upper Byte 0x46 Acc X Lower Byte 0xC9
Acc X Upper Byte 0x01 Impeller Rotation Count 0x02 Heart Rate
Count
[0071] A single unit may be used for each crew member or the heart
rate lines for each crew member can be included with the
accelerometer and speed data to provide a composite set of data. In
a multi crew boat each crew member has a receiver within 2 feet
that picks up the heart rate signal from the polar heart rate
monitor strapped to each crew member. Each heart rate monitor
transmits a uniquely coded signal that is assigned to each crew
member the boat data logger receives the heart rate signals for all
crew members by cable from the heart rate receivers
[0072] A GPS unit may be integrated with the data logger system.
This could comprise two units, basic unit plus a second unit for
GPS. The units would share the same serial line and communicate
using a network protocol. Alternatively the GPS unit could be
connected to the basic unit and additional firmware code added to
receive and retransmit data.
[0073] Inertial navigation systems (INS) may be used to cover the
information gaps of the GPS outages. When the INS approach is used
in rowing, the required sensors need to be small, lightweight,
unobtrusive and inexpensive. These requirements can be met when the
sensors are manufactured with MEMS technology. However, due to
inherent biases and drift errors of accelerometers and gyroscopes,
the accuracy of the current state-of-the-art MEMS sensors must be
accounted for in high precision rowing tracking. The basic
procedure in INS positioning systems is to process the inertial
sensor data. The double integration of acceleration measurements,
cannot be applied due to the lower accuracy of MEMS sensors. This
is because in the double integration, errors accumulate quickly,
which soon result in velocity errors comparable to typical rowing
speeds. However, the advantages of the INS system include its low
cost and high output rate of the movement information.
[0074] The high precision GPS system can provide high precision
velocity and acceleration information (acceleration is the first
derivative of velocity and second derivative of displacement).
However the GPS system is normally bulky, expensive and provides a
low output rate and high power consumption. To solve these
problems, an integrated system takes advantage of both low-cost GPS
and MEMS sensors to provide high performance capabilities. MEMS
sensors are used to provide precise, high rate (say 200 Hz), low
cost, low volume, low power, rugged, and reliable geo-positioning
while low-cost GPS is used for high frequency system calibration
(say 5-20 Hz) a lower frequency (1 Hz) is preferred for calibrating
the inertial sensors to conserve battery power. It combines
measurements from a GPS OEM board and subsequently GPS chip with
inertial measurement units from a combination of three MEMS
gyroscopes and accelerometers (say Analog Devices).
[0075] A 1 Hz GPS receiver is the minimum frequency that is
practical and ideally a 2-5 Hz system is preferred. With a 1 Hz
receiver accurate velocity and distance measurements can be
obtained but sampling the accelerometer data is needed to obtain
stroke rate and intra-stroke characteristics. The accelerometer
data could be integrated to get intra-stroke velocity but drift
would need to be checked every second using the output from the GPS
receiver.
[0076] The carrier smoothing procedure will be used to improve the
accuracy of the low-cost GPS pseudo range measurements. Carrier
phase smoothing is a process that the absolute but noisy pseudo
range measurements are combined with the accurate but ambiguous
carrier phase measurements to obtain a good solution without the
noise inherent in pseudo range tracking through a weighted
averaging process. A Kalman filtering system will be designed to
integrate the two system measurements.
[0077] FIG. 3 presents the stroke signals captured using geodetic
type GPS receivers and post-processing with the kinematic
differential GPS technique. It is demonstrated that the signals
captured provide a clear picture of the rowing stroke phases as
described above. In this particular stroke, the graph indicates
that the rower has problem in harmonizing his stroke cycle by using
too much time in the catch instead of the driver.
[0078] The software can display the derived information on a
computer screen and combine it with video data of the same event as
illustrated in FIG. 4. The screen may display time and distance
information as well as velocity and stroke rate and can also
display the graphical signals derived from accelerometer and GPS
signals.
[0079] To evaluate the accuracy of the GPS carrier phase receiver,
two GPS receivers were mounted on the same rowing boat
simultaneously. The base station is located on the bank of a river
which is about 1.about.2 km away from the course of the boat trial.
The baseline solutions from each of the rowing antennas were
processed independently from the base station using the PPK
technique. The independent baseline length between the two roving
receivers was then calculated and compared with the result measured
using a surveying tape. This baseline length is considered as a
"ground truth" (3.57 m in our case).
[0080] RTK GPS has been proved to be able to provide high precision
positioning in river environment. However, there are a number of
factors that need to be taken into consideration: [0081] Multipath
effects: The antenna being positioned near the water surface could
potentially be prone to large multipath error. This effect can be
up to 5 cm for carrier and 5 m for code measurements respectively.
[0082] Signal obstruction/satellite visibility: The GPS antenna is
installed in a constricted space in a racing boat, it is therefore
unavoidable that the movement of the athlete will block the GPS
signals at some time to an elevation angle of approximately 70
degrees. This may potentially cause severe signal obstruction
problems and loss of GPS solutions. [0083] Obtrusion: Ideally the
presence of any instrument should not cause direct visual or
physical impact on the athlete, therefore, the size and height of
the antenna is a primary consideration.
[0084] The "fixed baseline length" and external check methods are
used. Reliable mounting of the GPS receiver is required. If we
assume that the accuracy of the position to one GPS rover is the
same as to the other, then, from the simple (Least Squares
Adjustment) error propagation law, the accuracy of the position of
the kinematic GPS measurement (for a single baseline) can be
estimated as 0.0027 m (0.0038 m/sqrt(2)). A few millimetre accuracy
of the river height was achieved in a three (consecutive) day
trial. Given the closeness of the antenna and the reflective nature
of the water surface, the performance of the PPK GPS presents
consistent results.
[0085] The velocity determined from the GPS position and time
information uses the following first-order central difference
procedure. Velocity .function. ( .upsilon. T ) = P .function. ( T +
.DELTA. .times. .times. T ) - P .function. ( T - .DELTA. .times.
.times. T ) 2 .times. .times. .DELTA. .times. .times. T = .DELTA.
.times. .times. P 2 .times. .times. .DELTA. .times. .times. T
##EQU1##
[0086] where .nu..sub.T is the velocity of the boat (at time T)
determined from PPK GPS solution,
.DELTA.P=P(T+.DELTA.T)-P(T-.DELTA.T) is the plane distance
travelled between time T.sub.1 and T.sub.2 and
.DELTA.T=T.sub.2-T.sub.1. .DELTA. .times. .times. P = ( N 2 - N 1 )
2 + ( E 2 - E 1 ) 2 , ##EQU2## where E and N are the Easting and
Northing coordinates of the GPS units. The subscripts "1" and "2"
indicate that position derived from unit 2 and unit 1 respectively.
The accuracy of the velocity (.sigma..sub..nu.), can then be
roughly estimated through the following formula (using the error
propagation law): .sigma. .upsilon. = 1 2 .times. .DELTA. .times.
.times. T .times. .sigma. P = 1 2 .times. 0.1 0.0027 .apprxeq. 0.02
.times. .times. m .times. / .times. s ##EQU3##
[0087] Where .sigma..sub.P is the positional accuracy and
.sigma..sub.P=0.0027 m as determined previously.
[0088] FIG. 5 shows the differences in velocity determined
simultaneously from the code and the carrier measurements. Assuming
the carrier velocity to be accurate (ie ground truth), the code
derived velocity has an average accuracy in the order of
.about.0.03 m/s. The results confirm that the accuracy of 0.1 m/sec
claimed by the manufacturer is correct for more than 95% of
observations.
[0089] The data logger assembly is fitted to a rowing shell in a
stable location with a relatively clear view of the sky. Relative
motion of the athlete or boat is measured using three dimensional
accelerometer at 100 hHz and position and velocity using GPS at 10
Hz. The device supplies timing information with the measured
signals using an internal crystal corrected clock and a GPS derived
1 Hz pulse. The timing is accurate to 0.1 sec per hour. An internal
heat rate monitor pickup receives pulses from a coded polar heart
rate monitor/transmitter and stores these with a resolution of 1
beat a minute within a range of 0 to 250 beats/minute updated at 1
Hz. The device is powered by a battery sealed into the unit and is
rechargeable via an RS232 port. Recording battery life is 6 hours
and 1 month in sleep mode. The single universal port allows
recharging, connecting an RF module, connecting an external GPS
antenna, connecting the external heart rate receiver and to connect
a serial cable to send data to the hand held computer device. The
device can be fitted into a flexible package of a size
approximately 100 mm.times.70 mm.times.50 mm and weighs less than
250 g and is buoyant and water resistant. The package is coloured
to reduce heating from incident sunlight.
[0090] The device can be adapted to detect strokes and turns in
swimming as shown in FIG. 6. Analysis of the signals from the 3
axes of the accelerometer allows coaches to derive information as
detailed as stroke formation and turn efficiency.
[0091] FIGS. 7 to 9 illustrate the circuitry used in further
embodiment of the invention.
[0092] FIG. 7 shows the core circuitry centred on the micro
controller 20. The micro controller is preferably an 8 bit Atmel AT
mega 128 micro controller. The micro controller can be programmed
and can store data and is provided with a 256 megabyte flash memory
27. The USB port 22 is preferably a Silicon Technologies USB to
UART data transfer CP 2101 and allows data to be down loaded to a
personal computer for further analysis and storage and also allow
the battery to be charged by way of the battery charger 31 which in
turn is connected to the power supply 32. The microcontroller
functions are actuated by the tactile switches 23 which allows the
user to navigate through the device menu. The microcontroller
displays outputs on the LCD display 35 and also provides a
backlight display 36. As shown in FIG. 8 the monitor includes a 2.4
GHz transmitter and receiver 40 so that data can be transmitted and
received. The transmitter and receiver 40 is preferably a GFSK
transceiver nRF2401 sold by Nordic Semiconductor. The output power
and frequency channels are programmable using a 3 wire serial
interface. The GPS unit is an iTRAX 03 by Fastrax with 12 channels
and an update rate below 5 Hz with a 1 Hz default rate.
[0093] The sensor circuits shown in FIG. 9 are the core components
of the real time clock 41 the three axis accelerometer 43. A single
external transistor may be used to lower the scale factor and an
external capacitor is used to set the bandwidth.
[0094] The micro controller in the swimming monitor is programmed
with a set of algorithms to process the raw data from the sensors.
The algorithms filter the raw data with a low pass filter. The aim
is to use slower changing orientation information from the
accelerometers rather than quickly changing real accelerations. The
algorithm looks for peaks and troughs on each filtered sensor
trace. Strokes are defined as combinations of peaks and
troughs--each stroke type has a specific combination with a
specific set of rules. Once locked on to a particular stroke type
then look first for that stroke type next. Initially looks for
freestyle first.
[0095] Freestyle [0096] ignores small peaks/troughs [0097] requires
up/down accelerometer>0 [0098] requires a sideways accelerometer
peak followed by a trough--each peak/trough is a stroke [0099]
looks for several strokes in a row to lock on
[0100] Backstroke [0101] ignores small peaks/troughs [0102]
requires up/down accelerometer to be less than 0 [0103] requires a
sideways accelerometer peak followed by a trough--each peak/trough
is a stroke [0104] looks for several strokes in a row to lock
on
[0105] Butterfly [0106] consists of two peaks--one higher than the
other [0107] looks for several fwd/back peaks in a row to lock
on--first must be high, next low, next high etc [0108] peaks must
be spaced appropriately [0109] high peaks should be equally spaced,
low peaks likewise [0110] high peaks should be equal magnitude, low
peaks likewise [0111] highest up/down acc peak in the area must be
large enough [0112] lowest up/down acc peak in area must be
significantly less than highest
[0113] Breaststroke [0114] uses troughs in fwd/back acceleration
[0115] two quick troughs and a gap [0116] looks for several troughs
to lock on [0117] sufficient trough spacing [0118] time between
troughs 1/2 and 3/4 should be close [0119] time between toughs 2/3
and 4/5 should be close [0120] up acc must be >0
[0121] There is a fourth type of stroke which is the dolphin
kick.
[0122] Starts/turns/Finishes
[0123] A state variable keeps track of the current lap state. There
are 3 possible states: [0124] Waiting for a start [0125] Progress
during the lap [0126] Possible end of lap
[0127] Waiting for Start
[0128] When a stroke is detected in this state look backwards for
the start. Since stroke detection requires several strokes in a row
(depending on the stroke type) then we are likely to be a fair way
down the pool at this stage, particularly after a block start and a
few dolphin kicks (these are ignored for start purposes--there has
to be several of the regular stroke types in a row before checking
for a start). [0129] After the first stroke look at rate-of-change
peaks. If there is only one, or the highest is large enough, then
we have a start at the highest point. [0130] If the above didn't
succeed then look for a large swing in z (up/down acc) in the time
before the first stroke--this is defined as a peak >0 g preceded
by a trough <0 g and with sufficient difference between the two.
The start is then the low fwd/back trough which is close to the
highest rate-of-change in the region. [0131] If neither of the
above get a result then the start is a fixed time before the start
of the first stroke.
[0132] State then changes to . . .
[0133] Progress During the Lap
[0134] After being in this state for sufficient time, watch for
turns or end of lap [0135] First look for low fwd/back acc readings
either side of the end of the last stroke. If the lowest trough
before the end of the last stroke is sufficiently greater than the
lowest trough after then change state to "Possible end of lap"
[0136] If above wasn't successful then look for a large vertical
accelerometer swing. Again look either side of the end of the last
stroke. This time search for a z-axis high to low change to change
state to "Possible end of lap"
[0137] Within the time it is also possible to change state but only
if enough time has elapsed with no sign of a new stroke.
[0138] End of Lap Detection
[0139] At next stroke look back from the start of the last stroke
for the end of lap: [0140] A large swing in z (as above) [0141] Or
a large rate-of-change (as above) [0142] Or the lowest fwd/back acc
reading [0143] Or a point a fixed time period back
[0144] Also look for the finish of a set of laps.
[0145] This is done by looking for the first point with "zero"
rate-of-change which is defined as a short period with all
rate-of-change results (ie for every point) sufficiently low. If
this is found and there are no strokes for a while then end of set
is assumed to be at the beginning of the "zero" rate-of-change
period.
[0146] A display is mounted in a water proof enclosure in a visible
location so that the athlete can view summary information such as
stroke rate distance and heart rate. An easily accessible button on
the display unit starts the data recording. As soon as the device
is switched on recording begins. The coach may take the device
after the event and load the data into a personal computer to view
the data graphically or combine it synchronously with video
footage.
[0147] The device may be attached near the small of the back. An
extension GPS aerial runs from the device to the shoulders, but
mounting on the wrist or head is also possible. A separate GPS unit
may be mounted on the head to improve reception and the
microcontroller, accelerometers and display may be mounted on the
wrist or arm.
[0148] The RF module enables the real time data to be transmitted
to the Coach's wireless enabled PC via a blue tooth connection.
Alternatively the data may simply be uploaded after the event.
[0149] The advantages of the swim monitor of this invention are:
[0150] The device can give feedback both in real-time and
post-training. [0151] The real-time feedback to the swimmer may be
via a variety of methods: [0152] Aural via an ear-piece [0153]
Visual via a `heads-up` display on the goggle [0154] Visual via an
LCD panel on the device [0155] Visual via a remote display panel
either in the pool or adjacent to it. [0156] If the preferred
real-time feedback is used, some additional circuitry incorporating
an FM receiver may be used to allow a coach to talk to the swimmer
via the device. [0157] The real-time feedback would likely be
delivered at the start of a new lap and would give key results
about the previous lap. The results may include: [0158] Average
velocity [0159] Number of strokes [0160] Number of laps completed
[0161] A further enhancement of the system would be to add an MP3
player or FM receiver to the device so the swimmer may be
entertained. [0162] The device may also include pulse counters
taking advantage of the temple mounting for deriving heart rate
[0163] For tri-athletes the device may include accelerometers or
GPS units to derive speed and distance and stride length data for
the land based activities [0164] The post-training display may be
on a standard PC. It would show summary graphs such as `velocity vs
time` and `stroke-rate vs time` for the entire session. It would
also be able to calculate bio-metric efficiencies such as distance
per stoke. The user is able to zoom into a section of the graph to
obtain information about each stroke, enabling the swimmer to gain
information about how bio-metric improvements may be made.
[0165] Those skilled in the art will realize that the invention may
be implemented in a variety of embodiments. A variety of sensors
may also be used to gather data applicable to the event. It will
also be appreciated that the logger unit is small and adaptable
enough to be fitted to any athlete or sporting equipment where
accelerometer data provides useful performance information for
coaches and athletes.
* * * * *