U.S. patent application number 11/935080 was filed with the patent office on 2009-05-07 for closed-loop power dissipation control for cardio-fitness equipment.
Invention is credited to Steve Anderes, John Fisher, Joel Jensen, Keith Thompson.
Application Number | 20090118099 11/935080 |
Document ID | / |
Family ID | 40588726 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090118099 |
Kind Code |
A1 |
Fisher; John ; et
al. |
May 7, 2009 |
CLOSED-LOOP POWER DISSIPATION CONTROL FOR CARDIO-FITNESS
EQUIPMENT
Abstract
Various embodiments of the present invention provide (a) an
inexpensive apparatus enabling the measurement of power dissipated
by the rider of a cardio-fitness station (or any other stationary
bicycle) that does not depend on manufacturing tolerances or
machine condition variations, and (b) a method of using the data
measured by such an apparatus to improve the accuracy of exercise
condition settings by implementing the invented apparatus into a
closed-loop control system which improves the quality of the
exercise experience and enhances the adoption of exercise on a
cardio-fitness station employing this as a community activity.
Inventors: |
Fisher; John; (Los Gatos,
CA) ; Anderes; Steve; (Cupertino, CA) ;
Thompson; Keith; (Mountain View, CA) ; Jensen;
Joel; (Redwood City, CA) |
Correspondence
Address: |
PERKINS COIE LLP
P.O. BOX 1208
SEATTLE
WA
98111-1208
US
|
Family ID: |
40588726 |
Appl. No.: |
11/935080 |
Filed: |
November 5, 2007 |
Current U.S.
Class: |
482/5 |
Current CPC
Class: |
A63B 21/0052 20130101;
A63B 2024/009 20130101; A63B 2071/0644 20130101; A63B 2220/54
20130101; A63B 22/0605 20130101; A63B 21/00069 20130101; A63B
2230/06 20130101 |
Class at
Publication: |
482/5 |
International
Class: |
A63B 21/005 20060101
A63B021/005 |
Claims
1. A system, comprising: a computer running a computer program; a
video monitor in communication with the computer; a stationary
exercise equipment including steerable handlebars and pedals,
wherein the pedals are able to rotate around a first axis, the
rotation of the pedals providing a first electrical signal to the
computer; a flywheel comprising conductive material, the flywheel
able to rotate around a second axis, wherein the flywheel is
mechanically coupled to the pedals such that pedal rotation causes
flywheel rotation; a first electromagnet mounted in proximity to
the flywheel, the first electromagnet fixed to the stationary
bicycle; an electrical power supply coupled to the first
electromagnet, the electrical power supply configured to deliver
electric current to the electromagnet, wherein the magnitude of the
electric current is controlled by the computer program; and a
torque-measuring module mechanically coupled to the pedals, the
torque-measuring module measuring the torque exerted by pedals
around the first axis, the torque-measuring module providing a
second electrical signal to the computer; wherein the first and the
second electrical signals are used by the computer program to
adjust the electrical current to the first electromagnet.
2. The system of claim 1, wherein: the stationary bicycle further
includes a heart-rate monitor, wherein the heart-rate monitor
communicates electronically with the computer.
3. The system of claim 1, wherein: the steerable handlebars are
steered by the rider of the stationary exercise equipment, wherein
the steerable handlebars are mechanically coupled to a third
electrical sensor and the third electrical sensor provides a third
electrical signal to the computer when the steerable handlebars are
steered.
4. The system of claim 1, wherein: the computer program, upon
execution by the computer, simulates a virtual bicycle riding
through a computer simulated virtual landscape, wherein forward
motion of the virtual bicycle through the computer simulated
virtual landscape is controlled responsive to at least the first
electrical signal, and the direction of the virtual bicycle within
the computer simulated virtual landscape is determined responsive
to the third electrical signal.
5. The system of claim 1, further comprising: a second
electromagnet mounted in the proximity of the flywheel, wherein the
second electromagnet is fixed to the stationary exercise
equipment.
6. The system of claim 1, further comprising: a gear-shifting
member fixed to the stationary bicycle, the motion of the
gear-shifting member providing a fourth electrical signal to the
computer; and the first, the second, and the fourth electrical
signals are used by the computer to adjust the magnitude of the
electric current.
7. The system of claim 6, further wherein: the first, the second,
and the fourth electrical signals are used by the computer to
adjust the magnitude of torque exerted by the pedals around the
first axis; and the magnitude of torque exerted by the pedals
around the first axis is adjusted to a value determined by the
computer depending on the motion of a virtual bicycle riding
through a computer simulated virtual landscape.
8. The system of claim 1, wherein the torque-measuring module
comprises a strain gauge.
9. A method of power level control, the method comprising:
receiving a request indicating a a target power level; determining
a current power level based on identifying one or more of torque
exerted on a flywheel and an angular velocity of the flywheel; and
adjusting an electric current to change a resistance to movement of
the flywheel; wherein the electric current is adjusted based on a
difference between the target power level and the current power
level; and recomputing an updated current power level and adjusting
the electric current such that the updated current power level
substantially approaches the target power level.
10. A machine-readable medium embodying instructions, the
instructions, which when executed, causing a machine to perform a
method comprising: receiving a request indicating a a target power
level; determining a current power level based on identifying one
or more of torque exerted on a flywheel and an angular velocity of
the flywheel; adjusting an electric current to change a resistance
to movement of the flywheel; wherein the electric current to be
adjusted based on a difference between the target power level and
the current power level; and recomputing an updated current power
level and adjusting the electric current such that the updated
current power level substantially approaches the target power
level.
11. A stationary exercise equipment, comprising: a frame; a seat;
pedals, the pedals being able to rotate around an axis; a magnetic
resistance device including an electromagnet, the magnetic
resistance device providing resistance to rotation of the pedals
around the axis when the electromagnet is energized with an
electric current; and a torque-measuring device mechanically
attached to and between the pedals and the magnetic resistance
device, wherein the torque-measuring device provides a measure of
torque exerted by the pedals around the axis.
12. The stationary exercise equipment of claim 11, wherein: the
measure of torque exerted on the pedals around the axis is used to
adjust the electric current.
13. The stationary exercise equipment of claim 11, wherein: the
torque-measuring device comprises a magnetoelastic torque
sensor.
14. The stationary exercise equipment of claim 12, wherein: the
torque-measuring device comprises a piezo-electric transducer.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Utility patent
application Ser. No. 11/766,312, filed Jun. 21, 2007, and entitled
"Closed-Loop Power Dissipation Control For Cardio-Fitness Equipment
and to U.S. Provisional Patent Application No. 60/817,657, filed
Jun. 28, 2006, and entitled "Closed-Loop Power Dissipation Control
For Cardio-Fitness Equipment," by John Fisher et al., and are
hereby incorporated herein by reference.
[0002] This application is related to and cross-references U.S.
application Ser. No. 11/433,778, filed May 11, 2006, and entitled
"Cardio-Fitness Station With Virtual-Reality Capability," by John
Fisher et al., the contents of which application are hereby
incorporated by reference.
BACKGROUND
[0003] 1. Field of Invention
[0004] This invention relates to stationary exercise equipment and
power dissipation control used by such equipment. More
specifically, the invention relates to closed-loop power
dissipation control for cardio-fitness equipment.
[0005] 2. Background of the Invention
[0006] A major sports equipment industry has developed over the
last decades round providing fitness equipment for home and indoors
exercises based on so-called stationary exercise equipments, which
can be but are not limited to stationary exercise bicycles, in
which the action of pedaling is used to dissipate power by the
person (rider) exercising. The resistance to pedal rotation is
allowed for power dissipation, which is an integral part of the
exercise. State of the art exercise equipments often feature
heart-rate monitoring, entertainment, and a varying degree of
pedaling resistance, which is used to control the amount of power
the rider dissipates while pedaling.
[0007] On many stationary exercise equipments, the power necessary
to pedal can be set directly to a predetermined level by the rider,
yet on some, the power can be set in terms of real-world
parameters, such as slope of a hill, to give the rider the
impression that he or she is riding a real bicycle up a hill.
Cardio-fitness stations, the most advanced exercise tools, offer
virtual reality capabilities in which the rider interacts with a
virtual environment shown on a video monitor and experiences a
virtual bicycle ride through a predetermined landscape with hills,
valleys, and road obstacles. Such feature has given rise to
competition between riders exercising on two cardio-fitness
stations, i.e., the riders can operate separate cardio-fitness
stations to ride jointly in a race through the same predetermined
virtual landscape. Furthermore, with the advance of exercise
equipments, many riders have increased their demands for accurate
monitoring of their performance and performance history.
[0008] A fact not immediately apparent to an average rider of
stationary equipments is that their performance, i.e., the
resistance to pedal these cardio-fitness stations under a specified
setting or virtual terrain slope, is not always consistent among
the stations. This is noticeable when one rider is racing another
rider riding another unit and the other rider may have an easier
time making it to the finish line. Furthermore, for a given
constant cadence and same resistance setting, stationary equipment
will deliver pedal resistance that depends on the history of the
cadence and torque in a practically unpredictable manner due to the
cumulative effect of machine temperature and wear.
[0009] All these problems arise from the fact that
pedal-rotation-resistance mechanism implemented in present-day
exercise equipments is not intended for such precise setting and
repeatability of pedal torque, which has been the choice of the
manufacturers for cost reasons and the fact that it was not
required by the riders. The source of the drift and unit-to-unit
variation in the relationship between the setting of pedal
resistance and the actual value of resistance experienced by the
rider comes from the drift in the performance of mechanical and
electrical elements, for non-limiting examples, manufacturing
tolerance, mechanical wear, and heating effects on the equipment.
Such variation ultimately yields unsatisfactory accuracy of power
dissipation and an incorrect assessment of total amount of work
that rider has performed during his or her exercise session, which
makes it next to impossible to execute a fair race between riders
on two separate cardio-fitness stations.
SUMMARY OF INVENTION
[0010] One embodiment of the present invention provides an
inexpensive apparatus enabling measurement of power dissipated by
the rider of a cardiofitness station (or any other stationary
exercise equipment) that does not depend on the manufacturer,
manufacturing tolerances, or machine condition. In addition, a
method of using the data measured by such an apparatus to improve
the quality of the exercise experience is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention is illustrated by way of example in
the accompanying drawings. The drawings should be understood as
illustrative rather than limiting.
[0012] FIG. 1 illustrates an exemplary cardio-fitness station with
virtual-reality capability in accordance with one embodiment of the
present invention.
[0013] FIG. 2 illustrates an exemplary cardio-fitness station in
block diagram form in accordance with one embodiment of the present
invention.
[0014] FIG. 3 illustrates an exemplary pedal assembly function
diagram in accordance with one embodiment of the present
invention.
[0015] FIG. 4 illustrates an exemplary magnetic resistance device
in accordance with one embodiment of the present invention.
[0016] FIG. 5 further illustrates an exemplary magnetic resistance
device in accordance with one embodiment of the present
invention.
[0017] FIG. 6 illustrates power dissipated by an exemplary flywheel
under varying separation distances in accordance with one
embodiment of the present invention.
[0018] FIG. 7 illustrates measured flywheel torque as a function of
electromagnetic current for varying separations distances in
accordance with one embodiment of the present invention.
[0019] FIG. 8 illustrates an exemplary process for control of
pedaling resistance in accordance with one embodiment of the
present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0020] A system, method and apparatus are provided for closed-loop
power dissipation control for cardio-fitness equipment. The
specific embodiments described in this document represent examples
(e.g., stationary exercise bicycles) or embodiments of the present
invention, and are illustrative in nature rather than restrictive.
In the following description, for purposes of explanation, numerous
specific details are set forth in order to provide a thorough
understanding of the invention. It will be apparent, however, to
one skilled in the art that the invention can be practiced without
these specific details. In other instances, structures and devices
are shown in block diagram form in order to avoid obscuring the
invention.
[0021] Reference in the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure, or
characteristic described in connection with the embodiment is
included in at least one embodiment of the invention. The
appearances of the phrase "in one embodiment" in various places in
the specification are not necessarily all referring to the same
embodiment, nor are separate or alternative embodiments mutually
exclusive of other embodiments. Features and aspects of various
embodiments may be integrated into other embodiments, and
embodiments illustrated in this document may be implemented without
all of the features or aspects illustrated or described.
[0022] Some embodiments of the present invention provide (a) an
inexpensive apparatus enabling the measurement of power dissipated
by the rider of a cardio-fitness station (or any other stationary
exercise equipment) that does not depend on manufacturing
tolerances or machine condition variations, and (b) a method of
using the data measured by such an apparatus to improve the
accuracy of exercise condition settings by implementing the
invented apparatus into a closed-loop control system which improves
the quality of the exercise experience and enhances the adoption of
exercise on a cardio-fitness station employing this as a community
activity.
[0023] Some embodiments of the present invention provide (a) a
device for measuring the output power of a stationary exercise
equipment (b) use of the device to calibrate the resistive force
applied to the pedals of a stationary exercise equipment according
to a present or programmed value, and (c) use of the device to
enhance the quality of exercise experience on cardio-fitness
stations with virtual-reality capability. There are several ways
known in the industry that enable the stationary exercise
equipments to provide and control resistance to pedaling. For a
non-limiting example, the rotational pedal motion may be
transferred to a rotating flywheel whose rotation is slowed down by
mechanical friction. The rotation of the flywheel may be converted
to electrical energy using an alternator, and then the generated
power is dissipated on an electrical load. Finally, the resistance
to the rotation of the flywheel may be provided by a
magneto-resistive device in which the eddy currents induced by an
electromagnet give rise to magnetic fields that oppose the flywheel
rotation, thereby slowing the flywheel down. The type of control of
pedaling resistance may include discrete levels of resistance
settings available as a switch or a level accessible to the rider,
or is controlled by a computer program which is guiding the rider
(person exercising) or is being guided by the rider, as in an
exercise session on a cardio-fitness station with virtual reality
capability. In order to determine the power output by the rider,
one has to determine the product of the torque applied on the
pedals and the angular velocity of the pedals, from now on referred
to as cadence. Neither the torque exerted on the pedals nor the
cadence is uniform in time--both depend on the pedal position
(angle) with respect to the rider's legs (or ground) and/or the
condition and the performance of the rider. The total energy (kcal)
dissipated can be found by integrating (calculating the integral
of) the torque and the instantaneous cadence. There are a number of
ways of dissipating the rotational power delivered by the pedals
practiced in the industry. Most of the ways offer options for
adjusting the amount of resistance to pedal rotation. Three common
ways for dissipating pedal power and the associated mechanisms for
adjustment of resistance are presented here. The first example is
by dissipating the pedal power on a flywheel which is being slowed
down by a belt, wherein the resistance to rotation is adjusted by
tightening or loosening the belt placed around the flywheel.
Although options for adjusting the resistance are provided, there
is no precise measurement of the torque induced with the belt, and
hence no attempt is made to correct the tightness of the belt to
meet the setting. The second and third examples of ways to
dissipate pedal power commonly practiced today involve conversion
of pedal rotational energy into electricity and then adjusting the
dissipation of the electrical power. The second example is involved
in stationary fitness bicycles that use an alternator to convert
mechanical energy into electrical energy, and then dissipate this
electrical energy on an electrical (resistive) load. The adjustment
of dissipated power is achieved via adjustment of the magnitude of
the electrical current through the resistive load where the
generated electrical power is converted to heat. The third example
of a way to dissipate power, recently more commonly used, is to use
a metallic flywheel and adjust the strength of a magnetic field
through which at least one part of the flywheel is passing as it
rotates. The magnetic field established by an electromagnet induces
eddy currents in the flywheel and the induced currents dissipate
energy on the electrical resistance in the flywheel. The power
dissipation heats the flywheel, while the eddy currents establish a
magnetic field which opposes the rotation of the flywheel, thereby
exerting resistance to rotation experienced (caused) by the rider.
The adjustment of the pedal resistance (torque) is performed by
adjusting the current flowing into the electromagnets. Fitness
equipment that uses this type of power dissipation method is
commonly referred to as equipment with a magnetic resistance device
(MRD). The way above approaches are generally implemented is that
for a particular design, the pedal resistance is experimentally
evaluated in advance for every cadence and resistance setting, and
used in the form of a look-up table or a formula based on a fit to
the experimental data. This is generally done for every design,
namely, an identical formula or look-up table for a specific model,
but is not cost effective to evaluate on every unit a company
ships. Even if this were done for every unit, the systematic
variation and wear on the equipment could not be predicted, and
therefore the look-up table would not be solving the entire
problem--it would drift out of sync over time. In the case of an
MRD, the variation in the size of the gap between the flywheel and
the electromagnet produces most dramatic changes in the
relationship between the electromagnet current and the resistive
force. This is because the gap, which is air filled, dramatically
impacts the magnetic circuit made up from the electromagnet and the
flywheel. The gap between the magnet and the flywheel changes due
to manufacturing tolerances and the temperature of the flywheel. As
the temperature of the flywheel rises, it expands and closes the
gap between the flywheel and the magnets, thereby increasing the
strength of the resistance to rotation for a given current. The
value of the flywheel resistance affects the rate of heating and
varies from flywheel to flywheel. Due to the large thermal capacity
of the flywheel, the temperature depends on a long history of
pedaling at any time. These factors make the relationship between
the pedaling resistance and the current energizing the
electromagnets very difficult to predict and repeat. Consequently,
the tracking between the pedal resistance setting and the actual
value of pedal resistance is insufficient to produce consistent
exercise results and/or fair competition done on two cardio-fitness
stations of the same design. In all of the above methods for
providing pedal resistance, the value of the resistance is set by
the rider or a computer program, but it is not measured to check
the accurate value of the resistance and no attempt is made to make
correction to the quantity that controls the resistance (electrical
current of the electromagnets in the MRD, for a non-limiting
example). This is a potential disadvantage of all commercially
available stationary bicycles. Today, there are many options for
measuring power and torque accurately and researchers have gone
through development of experiments and tools to provide such
experiments. See, for a non-limiting example, Bicycle Science by
David Gordon Wilson (3rd edition, The MIT Press, Cambridge, Mass.,
2004), which is incorporated herein by reference. However, these
tools are used in research environments for monitoring and have not
been manufactured in a form suitable for commercial products. The
primary reasons for this are cost and complexity needed to
implement a sophisticated power monitoring system. In addition, it
has never become apparent that an accurate calibration of exercise
equipment would be needed.
[0024] Except for bicycles used for bicycling-science research and
research in human power, the control of pedaling resistance
described is typically done in so-called open-loop control.
Open-loop control is a control architecture that involves setting a
process parameter to a particular predetermined value depending on
another process parameter without asking or taking into account the
result. A control mechanism that does exactly the same, but also
takes into account the result to make fine adjustment of the
parameter set is called closed-loop control. A non-limiting example
of open-loop control is night lights that come on when the sky
darkens. In the case of a pedaling resistance, it means that a
setting may be applied for a predetermined amount of resistance
torque, but the torque that is actually experienced is not measured
in real time and no correction to the setting is available. What
distinguishes the open-loop control from closed-loop control is the
presence of feedback in closed-loop control. Open-loop control is
used because of its simplicity and lower cost of implementation. It
is a practical solution for applications in which output accuracy
is not important and where the system can function well without the
guarantee that the output will track the input. Simple commercially
available stationary bicycles typically satisfy these two
conditions. Open-loop control implemented in present-day exercise
bicycles cannot correct for the uncertainties in the performance of
mechanical and electrical elements, such as, manufacturing
tolerance and heating effects on the equipment. This variation
results in unsatisfactory accuracy of power dissipation.
[0025] The approach presented in the present invention is to
implement closed-loop control of power dissipation on any type of
stationary exercise equipment and more specifically on
cardio-fitness stations with virtual reality capability, and to
disclose an apparatus that provides an inexpensive component that
measures the power dissipated by the rider during exercise.
[0026] In some embodiments, one can implement closed loop control
in stationary exercise equipments by measuring the torque and the
angular velocity of the flywheel (or at the pedals). A common way
to measure the torque is to use strain gauges and angular velocity
via markers on the flywheel or the pedal wheel, and then use this
information in an electronic (or software) feedback loop to correct
the variable that sets the resistance and to make the measured
resistance equal to the set value. In one embodiment, a strain
gauge and a tachometer are placed on the pedal gear. A tachometer
is a device for indicating speed of rotation. In another
embodiment, the deflection of a mechanical spring caused by the
torque exerted on the flywheel is used to measure the torque
exerted on the electromagnets and a counter is used to measure the
angular velocity of the flywheel.
[0027] In one embodiment, the information gathered can then be used
to determine the power dissipation at any time the rider is
dissipating power. In another embodiment, the same information is
used to correct the original electrical current setting until the
power dissipation becomes arbitrarily close to the power setting.
The power dissipation setting may be either independently set by
the rider or by a computer program running a virtual reality
program and the power setting may be dependent on the rider's
virtual position in the predetermined landscape and the rider's
virtual ground velocity.
[0028] By using closed-loop control, the tolerance variations as
well as systematic uncertainties present by design, the temperature
changes, and gap variations are all eliminated from the
relationship between the dissipation setting and the actual power
dissipated by the rider of the cardio-fitness station.
Introduction
[0029] FIG. 1 shows a photograph of an embodiment of an exemplary
cardio-fitness station with virtual reality capability and employs
a magnetic resistance component. The illustrated cardio-fitness
station is modeled after a real outdoor bicycle, but has elements
of stationary exercise equipment. The cardio-fitness station 100
includes handlebars 141, a gear-shifting lever 142, a pedal
assembly 130, a seat 121A, a computer 160, and a video monitor 150,
all mechanically connected or attached to a frame assembly 110. The
rider, desiring to exercise, sits on the seat 121 as one would on a
real bicycle and turns pedals 131 while holding the handlebars 141.
The video monitor 150 is positioned in the plain view of the rider
while the rider is seated on the seat 121. The rider may watch the
images on the video monitor 150, listen to sounds coming from the
headphones (not shown), and optionally speak into a microphone (not
shown).
[0030] In some embodiments, the computer 160 runs a virtual reality
program and accepts input from the rider exercising via the
position of the handlebars 141, the momentary gear number via the
motion of the gear-shifting lever 142, and the rotation of the
pedals 131. The listed input parameters are used to determine the
motion of the rider's own virtual bicycle in the virtual landscape.
Exercise parameters used to follow the rider's actions include (a)
angular velocity of pedal rotation .OMEGA., also referred to as
cadence, (b) angular position of the handlebars, (c) gear number,
and (d) the history of all of those parameters. Turning the
stationary bicycle pedals 131 by the rider results in forward
motion of the rider's own virtual bicycle in the virtual
environment tracked by the computer running a virtual reality
program. Steering the handlebars 141 on the cardio-fitness station
results in rider's own virtual bicycle turning left or right in the
predetermined virtual landscape. (Angular velocity is the rate of
rotation around an axis usually expressed in radians per second
(rad/sec) or revolutions per minute (RPM)). The predetermined
landscape displayed on the video monitor is computer-generated or
is a real reconstructed landscape.
[0031] In some embodiments, the rider steers through a path y(x)
with predetermined length and elevation profile, z(x, y), where x
and y are horizontal coordinates used to define the location of the
rider's own virtual bicycle in the predetermined landscape tracked
by the virtual-reality program running on the computer. Such a path
with predetermined length is referred to as virtual exercise route
(VER). The VER exhibits upward or downward slopes. The slope at a
position x, y is determined by taking gradient of the elevation
profile .gradient.z(x, y) and is expressed as s.ident.sin .theta.,
where tan .theta.=|.gradient.z(x, y)|. If the elevation of the path
in the virtual environment increases as the virtual bicycle is
moving forward, the slope is said to be positive or upward (s>0)
and the torque resisting pedal rotation is increased proportionally
to the slope. If the elevation of the path in the virtual
environment decreases as the virtual bicycle moves forward, the
slope is said to be negative or downward (s<0) and the
slope-related contribution to the resistance to pedal rotation is
set to zero.
[0032] As the rider's own virtual bicycle rides along this VER, the
virtual reality program communicates to the pedal assembly to set a
specific level of pedaling resistance. Accelerating a real bicycle
requires additional power from the rider to exert on the pedal to
add kinetic energy to the bicycle and rotational energy to the
wheels. This power is proportional to the acceleration and is
appropriately modeled by the virtual-reality computer program and
suitable increased torque exerted on the pedals. Additionally, when
the rider rides very fast (tens of miles per hour) most of the
resistance comes from the aerodynamic drag, and the pedal
resistance must reflect that power loss. The listed variables:
terrain slope, aerodynamic drag, and acceleration are variables
that influence the pedal resistance. A realistic implementation of
these variables on a cardiofitness station involves sophisticated
control. The request (or command) for a specific pedaling
resistance (or torque) results in an approximate value of the
resistance in the controlled device (bicycle). Measurement of
torque performed by a magnetic resistance device can enable the
computer program to correct the setting and establish correct value
of the resistance.
Hardware Description
[0033] The hardware concept of some embodiments is intended for use
in conjunction with a cardio-fitness station with virtual reality
capability, but may be applied to any regular stationary exercise
equipment. The functional schematic of a cardio-fitness station
with virtual-reality capability is illustrated in FIG. 2. It
includes at least the following components and assemblies: a frame
assembly 210, a seat 221, a pedal assembly 230, a steering assembly
240, a video monitor 250, and a computer 260. The components and
assemblies 221, 230, 240, 250, and 260 are mechanically connected
to the frame assembly 210. The purpose of the frame assembly 210 is
to support the rider and all of the associated components and
assemblies of the cardio-fitness system.
[0034] For the purpose of some embodiments, the handlebars 241
provide the rider a facility to steer the direction of the virtual
rider bicycle, the gear-shifting lever 242 allows the rider to
optimize between pedaling speed (cadence) and pedaling resistance
in according to his or her exercise level and ability. Its purpose
is identical to the purpose of gear shifting on real bicycles with
multiple speeds, for a non-limiting example. The gear-shifting
lever includes a movable lever (or handle) that is internally
coupled to an electrical switch. The electrical switch is, in turn,
sensed by the computer 260 and interpreted as a directive to
increment or decrement the gear number to next value up or down,
depending whether the lever was moved up or down.
[0035] In some embodiments, the computer 260 communicates with the
steering assembly 240 via a link 246 and with the video monitor 250
via a link 256. The computer 260 runs a virtual reality program,
which sends sensory stimuli to the rider by one or more of: (a)
sending images and information to the video monitor 250 via link
256, (b) sending sound to the rider's headphones (not shown) that
are plugged into the steering assembly 240 via link 246, and (c)
controlling the resistance of the pedal rotation in the pedal
assembly 230 via links 243 and 246. Furthermore, the computer 260
acquires exercise parameters by receiving information about the
pedal 231 rotation via links 243 and 246, position of the
handlebars 241, gear number, and rider program selection from the
steering assembly 240 via link 246. (The listed exercise parameters
need not be all the exercise parameters that the computer may
acquire, the listed parameters are relevant to this
description.)
[0036] The purpose of the pedal assembly 230 is to provide the
rider of the cardio-fitness system a device to exercise leg muscles
and dissipate energy while exercising. The pedals 231 are rotated
in the same manner as one would when riding a road bicycle. The
pedal assembly 230 may include the magnetic resistance device, and
will be described in more detail in the next section.
Pedal Assembly
[0037] A pedal is a foot lever or treadle by which a part is
activated in a mechanism. In case of a road bicycle there are two
pedals, the rotation of the pedals sets the bicycle in motion. On a
stationary exercise equipment (bicycle), there also two pedals and
their rotation is used to provide exercise to the rider of the
stationary bicycle in the same sense as rotation of the pedals,
i.e., pedaling, the pedals on a real bicycle. The pedals are
rotatable, i.e. they can be rotated by the action of feet as on a
typical road bicycle or a typical stationary bicycle.
[0038] The pedal assembly 300 is explained using FIG. 3. The rider
rotates the pedals 301 while exercising. The resistance to rotation
of the pedals 301, also referred to as pedaling difficulty, is
varied in a controlled manner, thereby delivering to the rider a
varying degree of exercise difficulty.
[0039] In some embodiments, the pedals 301 are mechanically coupled
to pedal pulley 302 and are able to rotate as indicated with arrow
316. The arrow points only in one direction, but the pedals can
rotate in either direction. The pedals 301 are mechanically coupled
to a magnetic resistance device 303 via a pedal pulley 302 and a
belt 304. The cadence sensor 313 is mechanically attached (not
shown) to the bicycle frame 314. The frame 314 is a part of the
frame assembly 210 shown in FIG. 2.
[0040] In some embodiments, the cadence sensor is a tachometer and
may be implemented in a number of ways. In one embodiment, the
cadence sensor is a counter that counts the number of impulses
produced by the passing cadence pulley. In another embodiment, the
cadence may be measured on another pulley in the belt system.
[0041] An embodiment of the magnetic resistance device 303 includes
a flywheel 305, a flywheel pulley 306, a flywheel shaft with clutch
307, at least one electromagnet 308, a spring 310, a shock absorber
311, a deflection measuring assembly 309, a magnet counterweight
320, a magnet support panel 321, and a flywheel rotation sensor
312. FIG. 4 shows a mechanical drawing of an implementation of the
embodiment of an exemplary magnetic resistance device and FIG. 5
shows a photograph of the same embodiment of the exemplary magnetic
resistance device.
[0042] In some embodiments, the flywheel 305, the flywheel pulley
306, and the magnet support panel 321 all are able to rotate around
the same rotational axis as the flywheel shaft 307. The magnet
support panel 321 rotates independently from the flywheel 305 and
the flywheel pulley 306. The flywheel shaft 307 contains a clutch
which allows relative rotation between the flywheel 305 and the
flywheel pulley 306 only in one direction. When the pedals 301
rotate in the direction indicated by arrows 316, the clutch in the
flywheel shaft 307 is engaged and the flywheel pulley 307 and the
flywheel 305 rotate accordingly as indicated with arrow 318. When
the pedal rotation direction is opposite from the one indicated by
arrow 316 or the flywheel rotates faster than the flywheel pulley
306 in the same direction, the clutch in the flywheel shaft 307 is
disengaged and the pulley 306 rotates accordingly with the pedals,
but the flywheel 305 rotates independently. This ensures that when
the pedal rotation 316 suddenly ceases or reduces, the flywheel can
continue to rotate due to its inertia.
[0043] In some embodiments, both the pedal pulley 302 and the
flywheel shaft 307 (together with the flywheel 305 and flywheel
pulley 306) rotate around axes that are mechanically attached (not
shown) and fixed relative to the bicycle frame 314. The
electromagnet 308 and the electromagnet counterweight 320 are
mechanically attached to the magnet support panel 321. The weight
of the magnet counterweight 320 is approximately equal to the
weight of the electromagnet 308. The electromagnet 308 is mounted
in the proximity of the flywheel 305 so when the electromagnet 308
is energized (electric current flows through it) the magnetic field
from the electromagnet 308 penetrates the flywheel 305 as
illustrated with magnetic field lines 319.
[0044] In some embodiments, the flywheel 305 is made out of a
material that is electrically conductive, most commonly metal. When
the flywheel 305 rotates and the magnetic field 319 is present,
electrical currents are induced inside the metal flywheel (so
called eddy currents). These currents in turn produce a magnetic
field that opposes the rotation of the flywheel according to well
known laws of physics. The resistance of the metal flywheel 305 is
finite. Electrical power is lost in the flywheel (converted into
heat) and this manifests itself as resistance to the rotation of
the flywheel 305, i.e., slowing down the flywheel rotation. The
torque slowing down the flywheel 305 is exerted by the
electromagnet 308, which is mounted on the magnet support panel 321
and can rotate around the same axis as the flywheel 305.
[0045] In some embodiments, the magnet support panel can partially
rotate around the same axis as the flywheel, e.g., it can rotate
around the same axis over a limited range. In one embodiment this
limited range is 18.degree.. This limited freedom in rotation of
the magnet support panel is used to quantify the torque resisting
the flywheel rotation. The deflection of the magnet support panel
321 is constrained with the spring 310, which is attached to the
bicycle frame 314. Any amount of torque resisting the rotation of
the flywheel 305 will stretch or compress the spring 310
proportionally to the magnitude of torque. A deflection sensor 309
is used to quantify the stretching (or compression) 315 of the
spring 310. In one embodiment, the deflection sensor is realized as
an optical sensor that senses the passing of a perforated screen
attached to the electromagnet support panel by counting pulses of
light generated by a light-emitting diode on the opposite side of
the perforated screen. In another embodiment, there is one
deflection measuring spring. In yet another embodiment, more than
one spring is used. Both compression and tension springs may be
used to accomplish the same function.
[0046] In some embodiments, the magnet counterweight 320 ensures
that the deflection of the spring 310 does not depend on the
angular position of the electromagnet in respect to the axis of
rotation. Namely, the torque resulting from the weight of the
magnet changes with the angle at which the magnet is
positioned--this dependency can be removed by adding a counter
weight. The counterweight may be replaced by another (one or more)
electromagnets of the same weight to accomplish the same function.
Additionally, a single magnet may be used in the device--additional
magnets allow for greater effects, but are not necessary to simply
achieve the desired magnetic resistance. Moreover, just as the
counterweight may be replaced by one or more magnets, the overall
system of magnets and the component on which the magnets are
mounted may be sized as desired for other design constraints, as
long as the center of mass of the system of magnets and mounting
component coincides with the axis of rotation of the flywheel.
[0047] In some embodiments, the torque experienced by the
electromagnet (and the support panel) varies in time. The shock
absorber 311 is used to dampen any mechanical oscillations of the
magnet support panel (with the electromagnet and the magnet
counterweight). A shock absorber is any of several devices for
absorbing the energy of sudden impulses or shocks in machinery or
structures, and dampens oscillations. Another common word used for
shock absorber is damper.
[0048] In some embodiments, the described deflection sensor 309 and
the spring 310 provide a torque-measuring device. There are
numerous ways to realize a torque-measuring devices. In one
embodiment, the electromagnet support panel 321 is stationary in
respect to the frame 314 and the torque exerted on the
electromagnets 308 is quantified by a torque-measuring device
including a semiconductor strain gauge disposed between the
electromagnet 308 and the frame 314 or the electromagnet support
panel 321 and the frame 314. In another embodiment, the
torque-measuring device is disposed between at least one pedal and
the pedal pulley, thereby directly measuring the torque on the
pedals.
[0049] In some embodiments, the number of pulleys and belts in FIG.
3 may vary, and the arrangement shown in FIG. 3 involving three
pulleys--302, 306, and the tightening pulley. For a non-limiting
example, two belts each with two pulleys and one tightening pulley
may be used to increase the torque capability of the cardio-fitness
station. The ratio of the flywheel angular velocity 318 to the
cadence 316 is fixed by the ratio of the perimeters of the pulleys.
The typical value of this ratio ranges from 25:1 to 35:1 with the
flywheel 305 rotating faster than the pedal pulley 302 (and thus
the pedals 301) in some embodiments.
[0050] In some embodiments, the power delivered by the person
exercising is quantified by measuring the torque exerted onto the
electromagnet 308 (i.e., the magnet support panel 321 on the same
axis as the flywheel 305) and the angular velocity of the flywheel
measured by sensor 312. The flywheel angular velocity sensor 312
measures electrical, optical, or magnetic impulses generated by the
passing flywheel and converts the rate of the pulses into angular
velocity. There is more than one way that the flywheel angular
velocity can be measured. In one embodiment the sensor uses a hall
effect sensor and senses the rotation of at least one magnetic disk
attached to the flywheel (shown in FIG. 4), where the number of
pulses per flywheel revolution is 12. The torque resisting rotation
depends on the strength and the distribution of the magnetic field
in the flywheel 305, the electrical resistance of the metal
flywheel 305, and the diameter and cross-sectional shape of the
flywheel.
[0051] Exact calculations of the relationship between the torque,
the applied magnetic field, and the electrical current that
generates the magnetic field are complex and difficult, and are
also not necessary to operate the magnetic resistance device
effectively. Empirical data, obtained from measurements, even data
that is not very accurate can be used efficiently because
closed-loop control is available. Generally, the magnetic field
density is proportional to the electromagnet current I and
inversely proportional to the gap h between the magnet pole and the
flywheel. The torque N.sub.MRD is proportional to the angular
velocity .omega. of the flywheel and the magnetic field squared
This means that increasing the electromagnet current I will
increase the torque N.sub.MRD. Adjusting the amount of current
flowing into the electromagnet results in the adjustment of the
resistance to rotation of the flywheel 305, and consequently the
resistance to rotation of the pedals 301. If one applies a weak
electric current to the electromagnet, the pedals 301 rotate
easily. If one applies a large current to the electromagnet, high
resistance to rotation of the pedals 301 will be experienced by the
rider.
[0052] If the gap h between the electromagnet pole and the flywheel
changes due to manufacturing tolerance or temperature, the torque
N.sub.MRD will not be precisely known. Because of this inherent
uncertainly, all magneto-resistive devices used in stationary
bicycles exhibit imprecise magnitude of the torque N.sub.MRD for
any given electromagnet current.
[0053] This device provides a system for measurement of the torque
exerted on the electromagnet and the angular velocity of the
flywheel, and thereby determining the power delivered by the person
exercising. This measured power enables calibration of the
cardio-fitness machines independent of the manufacturing tolerances
and temperature of the flywheel, the electromagnets, and
independent of any other variables that can fluctuate from machine
to machine or from one magnetic resistance device to another.
[0054] The described system for monitoring the torque exerted on
the flywheel and the flywheel angular frequency may be used to
determine the power dissipated by the rider exercising. This system
may be used to either monitor the power or as a signal to correct
the value of the electromagnet current to adjust the torque on the
flywheel to match the value requested or commanded by the
pedal-resistance setting set by the rider or set by a computer
program.
[0055] Also described in this document is a method for using this
feature of the cardio-fitness station in conjunction with the
virtual-reality capability.
Analysis of Power Dissipation in a Real Bicycle
[0056] In a read road bicycle, the gear is characterized by a
predetermined transmission ratio G.sub.B between the cadence
.OMEGA..sub.B and the rear wheel rotation .omega..sub.B:
G.sub.B=.omega..sub.B/.OMEGA..sub.B. A real road bicycle will have
an integer number of gear values--typically between 1 and 15 gears,
i.e., G.sub.B is an array of discrete rational values: G.sub.B
(n.sub.B), with n.sub.B being the gear number (an integer varying
between 1 and the maximum number of gears n.sup.max.sub.B) Together
with the radius of the rear wheel r.sub.B, the velocity of a real
bicycle v.sub.B is given by
v.sub.B=2.pi.r.sub.BG.sub.B(n.sub.B).OMEGA..sub.B. The bicycle
rider controls .OMEGA..sub.B and n.sub.B, while the bicycle
manufacturer defines r.sub.B and the discrete vales of the
G.sub.B(N.sub.B) array for every n.sub.B. The instantaneous value
of torque N.sub.B(t) applied to the pedals multiplied by the
instantaneous value of cadence .OMEGA..sub.B(t) gives the
instantaneous power P.sub.B(t) delivered by the biker to move
forward with ground velocity v.sub.B(t).
[0057] In some embodiments, the relationship between the power
P.sub.B(t), cadence .OMEGA..sub.B(t), and gear-number changes in
time n.sub.B(t) depends on the bicycle design, the weather (wind
speed), the road conditions, the terrain (hills and valleys), and
the style of riding (constant or accelerating). The terrain profile
is expressed as elevation profile z(x, y) defined for every
location with coordinate in a horizontal plane x, y measured
against a reference. The force resisting the movement of the
bicycle forward and the power needed to move the bicycle with
ground velocity v.sub.B(t) is approximately expressed as:
F ( t ) = K A ( v B + v w ) 2 + mg ( s + C R ) + m rff v B r ( 1 )
P B ( t ) = F B ( t ) v B ( t ) ( 2 ) ##EQU00001##
[0058] This relationship is referred to as the physical model of
the bicycle motion. Its interpretation and development is well
known, and can be found in widely available literatures, for a
non-limiting example, Bicycle Science, by David Gordon Wilson (3rd
edition, The MIT Press, Cambridge, Mass., 2004). The
time-dependency of the velocity, force, and power is explicitly
shown in equation (1) and (2). The first term in equation (1)
models the aerodynamic drag, where v.sub.B and v.sub.W are ground
velocities of the bicycle and headwind (SI units m/s),
respectively, and K.sub.A is the coefficient of aerodynamic drag
(SI units in Ns.sup.2/m.sup.2). The second term models the change
in potential energy due to a slope in the terrain and the road
resistance/tire friction, where m is the mass of the bicycle and
biker together (SI units kg), g is the gravitational acceleration
(9.81 m/s.sup.2), C.sub.R is the rolling resistance coefficient
(dimensionless), and s is the slope in the terrain with level z(x,
y) at location x, y given with s.ident.sin .theta., where tan
.theta.=|.gradient.z(x, y)| (s is dimensionless). The third term
accounts for the force required to accelerate the bicycle and the
third term includes both the increase in kinetic energy of the
biker-bicycle body as well as the increase in energy stored in the
rotation of the wheels and gears on the bicycle. Since a majority
of the rotational energy is contained in the rotation of the wheels
and the angular velocity of the wheels directly related to the
ground velocity of the bicycle, these linear and rotational
energies are jointly expressed in terms of an effective mass
m.sub.eff. Naturally, m.sub.eff>m, and this last term makes the
temporal variation in the ground velocity of the bicycle to exhibit
significantly smaller variation in amplitude than the torque
exerted on the pedals.
[0059] In some embodiments, the instantaneous power required to
move a real bicycle is given by equation (2), where the time
dependency is explicitly shown. The torque on the pedals is given
by N.sub.B(t)=F.sub.B(t)v.sub.B(t)/.OMEGA..sub.B(t).
Analysis of a Power Dissipation in a Stationary Exercise
Bicycle
[0060] In some embodiments, the rider (person exercising), has
control over the cadence .OMEGA.(t), gear number n.sub.G, and the
torque N(t) applied to the pedals in a cardio-fitness station. The
transfer ratio between the stationary-bicycle pedal
angular-velocity .OMEGA. and the angular velocity of the flywheel
.omega., G.sub.s=.OMEGA./.omega., is typically fixed by the size of
the pulleys (or gears), but may be implemented as variable, such as
an automatic gear shifting mechanism. In one embodiment, this ratio
equals 12, but may be higher or lower in other embodiments.
Rotating pedals delivers rotational energy to a flywheel (and any
other wheels or gears in the assembly) with a moment of inertia
equal to I.sub.FW (all other inertia included). The torque N(t)
that needs to be provided by the stationary bicycle is thus given
by,
N ( t ) = I FW .omega. t + C F ( .omega. ) + N MRD ( .omega. , I )
( 3 ) ##EQU00002##
[0061] Here C.sub.F(.omega.) represents the friction coming from
gears, belts, and bearings involved in the mechanical assembly. The
effect of friction depends on the angular velocities of the gears
and shafts, and has here been normalized to the angular velocity of
the flywheel. This factor contributes to the natural mechanical
power loss. The last term in equation (3) is the torque N.sub.MRD
(t) exerted by a device that produces controlled resistance to the
pedal rotation. This device may be any device used for this purpose
(for a non-limiting example, mechanical friction or alternator
powering an electrical load). In one embodiment, the resistance
producing device is an MRD.
[0062] In some embodiments, the torque of an MRD depends primarily
on the strength of the magnetic field overlapping the flywheel and
the angular velocity of the flywheel. The magnetic field is
controlled by the value of direct electric current flowing through
the at least one electromagnet used to produce the magnetic field.
The exact relationship between the torque, the angular frequency of
the flywheel, and the electric current flowing through the magnets
is determined by size and shape of the flywheel, its electrical
resistance, and the specific properties of the magnetic circuit
that is formed by the electromagnets, the flywheel, and the air gap
present between the flywheel and the electromagnet core. Energizing
at least one electromagnet provides a magnetic field in the
flywheel. Due to the motion of the flywheel, this magnetic field
induces the eddy currents in the flywheel and these currents give
rise to a magnetic field that opposes, i.e., resists the flywheel
motion. This phenomenon is well known in the electrical engineering
field. The torque resulting from current I at angular velocity w of
the flywheel is denoted with N.sub.MRD(.omega., I).
[0063] The power delivered to the stationary bicycle by the rider
is given by
Ps(t)=N(t).OMEGA.(t)=N(t)G.omega. (4)
[0064] In some embodiments, a rider familiar with riding through a
real countryside with elevation profile z(x,y) under known
atmospheric and bicycle conditions may prefer to sit down on a
stationary bicycle, look at the computer screen, follow a bike ride
though a virtual landscape with the same z(x,y) elevation profile,
and have the stationary bicycle deliver approximately the same
cadence, gear number, and torque (.OMEGA., n.sub.G, N) in a similar
manner. This means that ideally on the same landscape profile
z(x,y), a rider riding a real bicycle and a rider riding the
cardio-fitness station with virtual reality capability along the
same path y(x) should exhibit equal cadence
.OMEGA.(t)=.OMEGA..sub.B(t) and change the gear number at the same
time n.sub.G(t)=n.sub.B(t). The velocity v.sub.B(t) of the real
bicycle and the velocity v(t) of the rider's own virtual bicycle in
the predetermined virtual landscape will be equal, v(t)=v.sub.B(t),
and hence the powers dissipated by the two riders will also be
equal P.sub.B(t)=P(t).
[0065] Naturally, meeting equality in the above relations exactly
is practically impossible, but it is not necessary to create a
perception and entertainment value to the rider riding the
cardio-fitness station with virtual reality capability. What is
more important is that the approximate relationship between the
above relations remains consistent for repeated use and between
cardio-fitness equipments. An approximation is established by
assuming values of the following variables: the weight of the rider
and the rider's own virtual bicycle, the landscape elevation
profile corresponding to an actual geographic location, weather and
road conditions corresponding to an actual time and place, and
bicycle of a specific design. In one embodiment, the virtual
bicycle weight is entered by the rider exercising and the virtual
reality accounts for the fact that bicycle riders with different
weights may experience different levels of power loss when going
uphill.
[0066] In order to accomplish an approximate modeling of real
biking experience, the current I controlling the resistance on the
MRD in equation (3) is programmed so that it compensates for the
physical phenomena modeled with equation (1). The target current
that accomplishes this is given implicitly by combining equations
(1) through (4). The velocity of the virtual bicycle is given by
v=2.pi.rG(n.sub.G).OMEGA., r is the assumed wheel size of the
virtual bicycle, and G(n.sub.G) is assumed gear ratios of the
virtual bicycle. Besides providing the pedaling resistance when
cadence is constant, the MRD also provides the increased resistance
due to inertia when the cadence increases just as it would on a
real bicycle. This is described by equation (5):
N MRD ( .omega. , I ) = K A ( v + v w ) 2 v + mg ( s + C R ) v + m
eff v v t G S .OMEGA. - I FW G S .OMEGA. t - C F ( G S .OMEGA. ) (
5 ) ##EQU00003##
The effective mass of a real bicycle determines how much more pedal
torque is necessary to increase the speed of the real bicycle
v.sub.B, while the moment of inertia I.sub.FW of the flywheel
determines the amount of extra torque needed to increase the
angular velocity of the flywheel on the stationary bicycle.
Generally, these two effects are not equal because I.sub.FW is
fixed by the stationary bicycle design, while m.sub.eff depends on
the rider's mass and the type of real bicycle design. The intent of
the cardio-fitness station is to approximate the behavior of a real
bicycle and hence the inertial behavior of the real bicycle, e.g.,
the response to temporal changes in cadence, d.OMEGA.(t)/dt, is
approximated by the resistance provided jointly by the MRD and the
inertia of the stationary bicycle I.sub.FW.
[0067] In some embodiments, the implementation of this model on a
stationary bicycle involves a number of assumptions and
simplifications while still maintaining the principle of the
stationary bicycle mimicking the actions of real bicycle. The
dominant effect difficult to predict is that of the efficiency of
the magnetic circuit: The strength of the magnetic field in the
flywheel is dependent on the size of the air gap between the
flywheel and the electromagnet. A typical variation in the size of
this gap due to manufacturing variations and thermal expansion of
the flywheel and the magnets may vary from 0.1 mm to 1 mm, which
produces greater than 25% change in the pedaling resistance. This
level of variance is noticeable by the rider and is unacceptable
for a state-of-the-art cardio-fitness station. FIG. 6 illustrates
power dissipated by the flywheel under various air gap sizes. FIG.
7 shows measured flywheel torque for flywheel angular velocity 600
RPM illustrating the variation of torque with electromagnet current
and gap between the electromagnet and the flywheel.
[0068] In some embodiments, the size of the gap is estimated from
the known physical properties of the flywheel (size and thermal
expansion coefficient) and the flywheel temperature. The
temperature of the flywheel is measured using a thermostat or
thermocouple located on or in the close proximity of the flywheel.
Based on the temperature of the flywheel as additional information
about the MRD, the relationship between the electromagnet current
and the torque is characterized for a range of angular frequencies,
torques exerted on the fly wheel, and temperatures of the flywheel.
The obtained data is used to create a formula or a lookup table,
which is then used by the computer to set the current through the
electromagnets depending on the temporal variation of the cadence.
The input variables to the formula are the flywheel angular
frequency, gap between the electromagnet and the flywheel, and the
required torque (resistance). Accounting for the temperature
variation of the gap improves the MRD performance, but it does not
eliminate the manufacturing variation in dimensions.
[0069] In order to improve this pedaling force uncertainty further,
one may attempt to measure the gap size in real time and/or specify
a tighter manufacturing tolerances. However, these approaches are
potentially impractical as they increase the complexity and the
price of the cardio-fitness station to an unacceptable level.
Another approach described herein is to use the measurement of
torque as a feedback to make a correction to the assumed
relationship between the current, angular velocity, and the torque.
The method by which this is implemented in a cardio-fitness station
with virtual reality is described with reference to FIG. 8.
Method of Use
[0070] In some embodiments, the rider sitting on the cardio-fitness
station (such as the station shown in FIG. 1) watches the images on
the video monitor 150 and listens to the sounds coming from the
headphones (not shown) while rotating the pedals 131, steering the
handlebars 141, and occasionally changing the gear using the
gear-shifting lever 142. The computer 160 runs a virtual reality
program and accepts inputs from the rider exercising via the
position of the handlebars 141, the momentary gear number via the
history of all gear changes applied to the gear-shifting lever 142,
and the rotation of the pedals 131. The listed input parameters are
used to determine the motion of the rider's own virtual bicycle in
a predetermined virtual landscape.
[0071] FIG. 8 is used to describe an exemplary process for control
of pedaling resistance in accordance with one embodiment of the
present invention. The control system is implemented in discrete
time steps because computers operate by calculating quantities at
discrete time instances. The time increments of this physical model
are denoted with .DELTA.t.sub.PM and are typically 1/60 of a
second, but can be smaller. Here subscript PM refers to Physical
Model. The method of FIG. 8 and other methods of this document are
composed of modules which may be rearranged into parallel or serial
configurations, and may be subdivided or combined. The method may
include additional or different modules, and the modules may be
reorganized to achieve the same result, too.
[0072] Starting at the bottom left part of the chart, the
instantaneous value of cadence .OMEGA.(t) (shown with 802) and the
gear number n.sub.G(t) (shown with 801) are captured by the
computer. The computer calculates in block 803 the velocity v(t) of
the virtual bicycle from these two variables and the assumed
virtual bicycle wheel size r and gear ratio G(n.sub.G), as
illustrated with block 804. In block 805, the location x,y of the
rider's own virtual bicycle in the virtual landscape (or position
along a VER y(x)) with elevation profile z(x, y) is used to
determine the slope virtual s(x, y). The computer has previously
stored a set of constants needed to completely define the bicycle
power dissipation model: the assumed mass of the rider (constant or
entered by the rider externally prior to exercise), and aerodynamic
and rolling resistance factors (block 806). The virtual bicycle
velocity calculated in the previous step v(t-.DELTA.t.sub.PM) and
cadence .OMEGA.(t=.DELTA.t.sub.PM) have also been stored. In block
807, all these parameters are used to calculate the power P(t) that
a real road bicycle would be dissipating using equations (1) and
(2), and the power is converted to torque N.sub.s(t) that needs to
be exerted by the MRD using equation (4). Here, subscript s refers
to a set value (e.g. a predetermined value), and the torque is
given by N.sub.S(t)/G.sub.SP(t)/.OMEGA.. The value of the torque on
the flywheel required by the physical model 808 is now applied to
the MRD torque control loop 809.
[0073] An efficient use of the MRD involves a computer predicting
the MRD operation from its input variables. The implicit
relationship between the relevant variables at steady state is
expressed as
M(N,.omega.,I,h)=0. (6)
This equation will in upcoming text be referred to as MRD master
equation. The input to the MRD are the electric current I (into the
electromagnets) and the flywheel angular velocity .omega.. The
current, flywheel angular velocity and the resulting torque
N.sub.MRD are fast-changing MRD parameters, i.e., they can change
significantly between the turns of the pedals of the cardio-fitness
station. The MRD performance is also affected by slow-varying
parameters such as temperature, which affects the
flywheel-electromagnet gap and the electrical resistance, and also
by unknown starting values of the resistance and
flywheel-electromagnet gap. The flywheel-electromagnet gap and its
variation have the strongest affect on the accuracy of the MRD
performance prediction and for this reason all of the slow-varying
parameters (including the gap) are combined in one parameter h,
referred to as the gap parameter.
[0074] In some embodiments, the time steps .DELTA.t.sub.TC, through
the MRD torque-control loop may be equal to the physical model
times step .DELTA.t.sub.PM, but may be faster if smoother variable
changes are necessary. The discrete time steps are numbered with
integer j. At the time when the torque N.sub.s required by the MRD
is set and delivered to the torque-control loop 809, the
measurement of the angular velocity .omega..sub.m(j) and the gap
parameter h(j) are available and the value of electromagnet current
I(j) that would give the requested torque:
M(N.sub.s,.omega..sub.m(j),I(j),h(j))=0 is solved in block 810.
Although the MRD master equation (6) is written implicitly, the
current I(j) is obtained from an explicit formula or a look-up
table based on the MRD master equation (6). The calculated current
I(j) is applied to the electromagnets in the MRD 811. A measurement
of torque N.sub.m(j+1) 812 and flywheel angular velocity
.omega..sub.m(j+1) 813 are performed using the preferred embodiment
of the MRD described above. The new torque value N.sub.m(j+1)
includes the contribution from both the MRD and the inertia of the
flywheel, as shown in equation (7):
N m ( j + 1 ) = I FW .omega. ( j + 1 ) - .omega. ( j ) .DELTA. t +
N MRD ( j + 1 ) ( 7 ) ##EQU00004##
This ignores the friction of the stationary bicycle
C.sub.F(.omega.), but it can be added in a straight forward way.
Block 814 solves the torque delivered by the MRD N.sub.MRD(j+1)
using equation (7) with known flywheel moment of inertia I.sub.FW.
Even without acceleration of the flywheel, the set N.sub.s value
and the N.sub.MRD value are seldom equal and a correction should be
performed. This correction is necessary because the previous (or
the first) guess (provided by a temperature measurement 816) for
the gap parameter was not correct. The values N.sub.MRD(j+1),
.omega..sub.m(j+1) and I(j+1) are now used with the MRD master
equation in block 815 to determine a corrected value of the gap
parameter h(j+1) (Namely, solving
M(N.sub.s,.omega..sub.m(j+1),I(j+1),h(j+1))=0 for the new,
corrected value of the gap parameter to get a corrected value for
the gap parameter h(j+1)). This is again done using a formula or a
look-up table. The corrected value of the gap parameter h(j+1), the
current flywheel angular velocity .omega..sub.m(i+1), and MRD
torque N.sub.s required by the physical model are now again used to
set the MRD current in block 810, i.e., the torque-control loop now
repeats.
[0075] In some embodiments, the variation in the gap parameter is
slow in comparison with the time variation in the angular velocity
and torque, and in this arrangement the approach converges
efficiently and provides satisfactorily small errors (rider
un-noticeable) within very few loops of the torque-control
algorithm.
[0076] It will be understood that other embodiments of the
torque-loop algorithm are possible within the context of the
systems and methods of this document. The time steps
.DELTA.t.sub.PM for the physical model may be equal to slower than
the torque-control loop time steps .DELTA.t.sub.TC. A typical range
for .DELTA.t.sub.PM may be between about 1/60 and about 1/200 of a
second. Moreover, many embodiments have been specifically described
as including components from one or more figures in combination.
However, other components may be substituted. Similarly, components
may be grouped or subdivided in various ways. Thus, embodiments may
be formed using some of the components and offering some of the
features described, and may include components not described or
offer features not described in this document. Moreover, features
of one embodiment may be incorporated into other embodiments, even
where those features are not described together in a single
embodiment within the present document.
* * * * *