U.S. patent application number 11/766312 was filed with the patent office on 2008-08-28 for closed-loop power dissipation control for cardio-fitness equipment.
This patent application is currently assigned to Expresso Fitness Corporation. Invention is credited to Steve Anderes, John Fisher, Joel Jensen, Keith Thompson.
Application Number | 20080207402 11/766312 |
Document ID | / |
Family ID | 38846314 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080207402 |
Kind Code |
A1 |
Fisher; John ; et
al. |
August 28, 2008 |
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; (Sunnyvale,
CA) ; Anderes; Steve; (Sunnyvale, CA) ;
Thompson; Keith; (Sunnyvale, CA) ; Jensen; Joel;
(Sunnyvale, CA) |
Correspondence
Address: |
PERKINS COIE LLP
P.O. BOX 1208
SEATTLE
WA
98111-1208
US
|
Assignee: |
Expresso Fitness
Corporation
Sunnyvale
CA
|
Family ID: |
38846314 |
Appl. No.: |
11/766312 |
Filed: |
June 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60817657 |
Jun 28, 2006 |
|
|
|
Current U.S.
Class: |
482/5 |
Current CPC
Class: |
A63B 21/225 20130101;
A63B 2220/16 20130101; A63B 21/0051 20130101; A63B 2220/30
20130101; A63B 22/0605 20130101 |
Class at
Publication: |
482/5 |
International
Class: |
A63B 24/00 20060101
A63B024/00; A63B 21/005 20060101 A63B021/005 |
Claims
1 . A magnetic resistance device (MRD), comprising: a flywheel
having an ability to rotate around an axis; at least one
electromagnet; and means for measuring a torque exerted on the at
least one electromagnet around the axis.
2. The MRD of claim 1, further comprising: a tachometer for
measuring an angular velocity of the flywheel.
3. A magnetic resistance device, comprising: a flywheel having an
ability to rotate around an axis; at least one electromagnet having
an ability to rotate at least partially around the axis; and a
spring mechanically attached to the at least one electromagnet,
wherein the spring is being stretched when torque is exerted on the
at least one electromagnet around the axis.
4. The magnetic resistance device of claim 3, further comprising:
means for measuring a stretch of the spring.
5. The magnetic resistance device for claim 3, further comprising:
a shock absorber mechanically attached to the at least one
electromagnet.
6. A magnetic resistance device, comprising: a base; a flywheel
having an ability to rotate around an axis, wherein the axis is
stationary in respect to the base; at least one electromagnet
having an ability to rotate at least partially around the axis; and
a spring mechanically attached between the at least one
electromagnet and the base, wherein the spring is being stretched
when torque is exerted between the at least one electromagnet and
the base around the axis.
7. The magnetic resistance device of claim 6, further comprising:
means for measuring a stretch of the spring; and means for
measuring an angular velocity of the flywheel.
8. The magnetic resistance device of claim 6, further comprising: a
shock absorber mechanically attached between the at least one
electromagnet and the base.
9. A method for adjusting the torque in a magnetic resistance
device, comprising: providing a magnetic resistance device
including: a flywheel able to rotate around an axis; an
electromagnet being energized with an electric current and having a
parameter; means for measuring torque exerted on the electromagnet
around the axis; and means for measuring an angular velocity of the
flywheel; providing a first torque amplitude; providing an
amplitude of the electric current; repeating the subsequent steps
at least once; energizing the electromagnet with the electric
current of the amplitude; measuring the angular velocity of the
flywheel; measuring a second torque amplitude using the means for
measuring torque exerted on the electromagnet around the axis,
wherein the second torque amplitude is a measure of torque exerted
on the electromagnet around the axis; calculating a value for the
parameter from one or more of the second torque amplitude, the
amplitude of the electric current, and the angular velocity of the
flywheel; and calculating a new value for the amplitude of the
electric current from one or more of the first torque amplitude,
the angular velocity of the flywheel, and the parameter.
10. A stationary exercise equipment, comprising: a frame; a seat;
one or more handlebars; pedals; a magnetic resistance device
including a flywheel and an electromagnet, wherein the flywheel and
the electromagnet are cable to at least partially rotate around an
axis, and the magnetic resistance device provides resistance to
rotation of the pedals when the electromagnet is energized with an
electric current; and a torque-measuring device mechanically
attached to and between the electromagnet and the frame, wherein
the torque-measuring device provides a measure of torque exerted
between the electromagnet and the frame around the axis.
11. The station exercise equipment of claim 10, wherein: the
measure of torque exerted between the electromagnet and the frame
around the axis is used to adjust the electric current.
12. An apparatus, comprising: a flywheel formed of a conductive
material, wherein the flywheel is coupled to a pedal of a
stationary bicycle; an axle about which the flywheel is mounted; a
support panel mounted about the axle; a first magnet mounted on the
support panel, wherein the first magnet is mounted in proximity to
the flywheel; an electrical power supply coupled to the first
magnet; and a deflection measuring component coupled to the first
magnet.
13. The apparatus of claim 12, further comprising: a second magnet
mounted on the support panel, wherein the second magnet is mounted
in proximity to the flywheel.
14. The apparatus of claim 13, wherein: the second magnet is
mounted opposite to the first magnet on the support panel with the
axle therebetween.
15. The apparatus of claim 13, wherein: the second magnet is
mounted in proximity to the first magnet.
16. The apparatus of claim 12, wherein: the support panel is shaped
with a weighted portion opposite to where the first magnet is
mounted, wherein the weighted portion is sized and positioned to
rotatably counterbalance the first magnet.
17. The apparatus of claim 12, further comprising: a counterweight
mounted on the support panel opposite to the first magnet with the
axle therebetween, wherein the counterweight is sized and mounted
to rotatably counterbalance the first magnet.
18. The apparatus of claim 17, further comprising: a counterweight
mounted on the support panel opposite to the first magnet and the
second magnet with the axle therebetween, wherein the counterweight
is sized and mounted to collectively rotatably counterbalance the
first magnet and the second magnet.
19. The apparatus of claim 12, wherein: the deflection measuring
component is an optical component.
20. The apparatus of claim 12, wherein: the deflection measuring
component is a spring and tension measuring component.
21. The apparatus of claim 12, further comprising: means for
receiving signals from a computer.
22. The apparatus of claim 12, further comprising: a power
regulator coupled to the electrical power supply.
23. The apparatus of claim 22, further comprising: a control bus
included in the power supply.
24. The apparatus of claim 23, further comprising: a conversion
component to convert an output of the deflection measuring
component into a digital signal.
25. The apparatus of claim 24, further comprising: a data bus
coupled to the deflection measuring component.
26. A method, comprising: receiving power from a stationary
exercise equipment; transferring the power to a flywheel;
generating electric currents within the flywheel with an
electromagnet; resisting rotation of the flywheel with the electric
currents; measuring a magnitude of resisting rotation; comparing
the magnitude to a predetermined value; and adjusting the electric
currents responsive to a result from the comparing step.
27. The method of claim 26, further comprising: looking up the
predetermined value.
28. The method of claim 26, further comprising: slowing the
stationary exercise equipment in response to the resisting
rotation.
29. A stationary exercise equipment, comprising: a computer running
a computer program; a video monitor in communication with the
computer; a stationary bicycle including handlebars and pedals,
wherein the pedals being able to rotate; a flywheel formed of a
conductive material, wherein the flywheel is coupled to a pedal of
the stationary bicycle; an axle about which the flywheel is
mounted; a support panel mounted about the axle; a first magnet
mounted on the support panel, wherein the first magnet is mounted
in proximity to the flywheel; an electrical power supply coupled to
the first magnet, wherein the electrical power supply is controlled
by the computer program; a deflection measuring component coupled
to the first magnet; and a movable member mechanically coupled to a
first electrical sensor, wherein the first electrical sensor
provides a first electrical signal to the computer when the movable
member is set in motion, wherein the electrical signal provided by
the first electrical sensor to the computer is used to adjust the
force resisting pedal rotation mechanism.
30. The stationary exercise equipment of claim 29, wherein: the
stationary bicycle further includes a heart-rate monitor, wherein
the heart-rate monitor communicates electronically with the
computer.
31. The stationary exercise equipment of claim 29, wherein: the
handlebars is steered by the rider of the stationary exercise
equipment, wherein the handlebars is mechanically coupled to a
second electrical sensor and the second electrical sensor provides
a second electrical signal to the computer when the handlebars are
steered.
32. The stationary exercise equipment of claim 31, wherein: the
computer program, upon execution by the computer, simulates a
virtual bicycle riding through a predetermined landscape, wherein
forward motion of the virtual bicycle through the predetermined
landscape is controlled responsive to the rotation of the pedals
and the first electrical signal, and direction of the virtual
bicycle is determined responsive to the second electrical
signal.
33. The apparatus of claim 29, further comprising: a second magnet
mounted on the support panel, wherein the second magnet is mounted
in proximity to the flywheel.
34. The apparatus of claim 33, wherein: the second magnet is
mounted opposite to the first magnet on the support panel with the
axle therebetween.
35. The apparatus of claim 29, further comprising: a power
regulator coupled to the electrical power supply.
36. The apparatus of claim 35, further comprising: a control bus
included in the power supply.
37. The apparatus of claim 36, further comprising: a conversion
component to convert an output of the deflection measuring
component into a digital signal.
38. The apparatus of claim 37, further comprising: a data bus
coupled to the deflection measuring component.
39. A cardio-fitness station system comprising: a first stationary
exercise equipment, including: a first computer, running a first
computer program, wherein the first computer program simulates
moving images seen by a first rider of a first virtual bicycle
while riding through a predetermined landscape; a first video
monitor in communication with the first computer, wherein the first
video monitor displays the moving images seen by the first rider of
the first virtual bicycle while riding through the predetermined
landscape; and a first stationary bicycle including: first
steerable handlebars; first rotatable pedals; a first movable
gear-shifting member; and a first pedal rotation resistance
component including: a first flywheel formed of a conductive
material, wherein the first flywheel is coupled to the first
rotatable pedals; a first axle about which the first flywheel is
mounted; a first support panel mounted about the first axle; a
first magnet mounted on the first support panel, wherein the first
magnet is mounted in proximity to the first flywheel; a first
electrical power supply coupled to the first magnet; and a first
deflection measuring component coupled to the first magnet; a
second stationary exercise equipment, including: a second computer
running a second computer program, wherein the second computer
program simulates moving images seen by a second virtual rider of a
second virtual bicycle while riding through a predetermined
landscape; a second video monitor in communication with the second
computer, wherein the second video monitor displays the moving
images seen by a second rider of the second virtual bicycle while
riding through the predetermined landscape; and a second stationary
bicycle including: second steerable handlebars; second rotatable
pedals; a second movable gear-shifting member; a second pedal
rotation resistance component including: a second flywheel formed
of a conductive material, wherein the second flywheel is coupled to
the second rotatable pedals; a second axle about which the flywheel
is mounted; a second support panel mounted about the second axle; a
second magnet mounted on the second support panel, wherein the
second magnet is mounted in proximity to the second flywheel; a
second electrical power supply coupled to the second magnet; and a
second deflection measuring component coupled to the second magnet,
wherein a wireless communication is established between the first
computer and the second computer.
40. The cardio-fitness system of claim 39, further characterized by
the first virtual bicycle may be placed at any location in the
predetermined virtual landscape.
41. The cardio-fitness system of claim 39, wherein the first
virtual bicycle and the second virtual bicycle jointly ride in the
same predetermined landscape.
Description
RELATED APPLICATIONS
[0001] This application claims priority 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 is 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.
Background of the Invention
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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).
[0013] 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.
[0014] 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.
[0015] 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 prior art commercially available
stationary bicycles.
[0016] 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). 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.
SUMMARY OF INVENTION
[0017] 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
[0018] The present invention is illustrated by way of example in
the accompanying drawings. The drawings should be understood as
illustrative rather than limiting.
[0019] FIG. 1 illustrates an exemplary cardio-fitness station with
virtual-reality capability in accordance with one embodiment of the
present invention.
[0020] FIG. 2 illustrates an exemplary cardio-fitness station in
block diagram form in accordance with one embodiment of the present
invention.
[0021] FIG. 3 illustrates an exemplary pedal assembly function
diagram in accordance with one embodiment of the present
invention.
[0022] FIG. 4 illustrates an exemplary magnetic resistance device
in accordance with one embodiment of the present invention.
[0023] FIG. 5 further illustrates an exemplary magnetic resistance
device in accordance with one embodiment of the present
invention.
[0024] FIG. 6 illustrates power dissipated by an exemplary flywheel
under varying separation distances in accordance with one
embodiment of the present invention.
[0025] 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.
[0026] 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
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] Except for bicycles used for bicycling-science research and
research in human power, the control of pedaling resistance
described in prior art section 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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
[0036] 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 121 A, 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).
[0037] 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 n, 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.
[0038] 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.
[0039] 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
[0040] 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.
[0041] 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.
[0042] 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.)
[0043] 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
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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 6 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 w of the flywheel and the magnetic field squared 62. 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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
[0063] 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.sub.B.sup.max) 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).
[0064] 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 eff v B t ( 1 )
P B ( t ) = F B ( t ) v B ( t ) ( 2 ) ##EQU00001##
[0065] 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), CR 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.
[0066] 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
[0067] 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##
[0068] 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.
[0069] 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).
[0070] The power delivered to the stationary bicycle by the rider
is given by
P.sub.s(t)=N(t).OMEGA.(t)=N(t)G.omega. (4)
[0071] 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, 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).
[0072] 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.
[0073] 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.G(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.
[0074] 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.
[0075] 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.
[0076] 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
[0077] 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.
[0078] 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.
[0079] Starting at the bottom left part of the chart, the
instantaneous value of cadence .OMEGA.(t) (shown with 802) and the
gear number nG(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.
[0080] 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.
[0081] 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(j+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.
[0082] 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.
[0083] 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.
* * * * *