WO2008015465A1

WO2008015465A1 - Exercise article

Info

Publication number: WO2008015465A1
Application number: PCT/GB2007/003006
Authority: WO
Inventors: Paramjit Singh Sangha
Original assignee: Paramjit Singh Sangha
Priority date: 2006-08-04
Filing date: 2007-08-06
Publication date: 2008-02-07
Also published as: GB0615564D0; GB2440510A

Abstract

An exercise article, such as a ball, comprising: one or more 3-axis accelerometers; a signal processor for analysing an output of the accelerometers to provide information about a motion of the exercise article; and a memory for storing said information about the motion of the exercise article. The exercise article can provide a read-out of exercise parameters, such as height of throw or frequency of bounces.

Description

EXERCISE ARTICLE

The present invention relates to a human-propelled projectile, such as a ball, for use in human exercise and play.

It is widely recognised that obesity and lack of exercise are growing health problems. The World Health Organisation has estimated that 60% of the world's population does not exercise enough, and that 2 million people die every year through inactivity. Furthermore, it is estimated that more than 10% of children, and more than 20% of young adults in the United Kingdom are clinically obese. Therefore, a need exists to promote physical exercise in the minds of children and young adults.

At present one of the major problems in getting this age group to exercise is the internet and internet based games as well as gaming consoles, such as X-Box,

Sony PlayStations, or Nintendo (all registered Trade Marks). These encourage children and young adults to sit and play at a screen each and every day with little or no movement into the outside world. Therefore there is a significantly reduction in the amount of exercise and this compounds the obesity issues with these age groups.

The gaming consoles are so popular because the games are so addictive and interesting to the young in that the games incorporate the user experience and the player is directly involved in the action.

US - A - 5779576 describes a throw-measuring American football having an ellipsoidal shape and a tail fin to stabilise the flight of the ball, A single-axis accelerometer is provided inside the football positioned at a specific angle, and the distance travelled by the ball is determined by measuring the initial velocity and the time of flight of the ball, the whole calculation being initiated by the release of a switch which is kept in a depressed position before the throw. The primary purpose of this ball is to assist the training of American football players. If a throw is of too steep a nature, it is then beyond the scope of use and provides a message of "LOB" back to the user. The mathematics used to calculate trajectory information of speed and distance is of a simple nature as the attachment of a fin reduces spin, which would confuse the output of the single- accelerometer and the input to the processor for calculation.

US - A - 4577865 describes an athletic ball containing a pressure sensor and a display 20 device. The sensor detects the pressure pulse inside the ball when it strikes a surface. The number of such impacts is displayed.

The present invention is concerned with providing a gaming instance where the player experiences the user involvement and is fully and directly involved in the playing instance.

The present invention provides a human propelled projectile in the form of an exercise article as claimed in claim 1.

Preferably, the motion detector is a 3-axis accelerometer.

The term "motion detector" as used herein refers to any detector capable of detecting any movement of an article including acceleration and deceleration and moment.

Preferably, the human-propelled projectile is a ball. The ball is preferably substantially spherical. The diameter of the ball is typically about 5cm to about

30cm. The weight of the projectile is typically from about 10Og to about 1kg.

Suitably, the 3-axis accelerometers and the system controller are enclosed in cushioned pockets inside the projectile. For example, the projectile may be filled with a fibrous or foam cushioning material. The projectile may be tethered by a string, but more usually it is free to be thrown or struck in any direction.

The three-axis accelerometers may suitably be micro-electro-mechanical (MEMS) accelerometers. These are solid-state devices that measure the changes in capacitance caused by the relative movement of moving and fixed structures created in a silicon substrate using wafer processing techniques. The accelerometers typically comprise an interface chip that generates a digital output, typically a serial digital output. The devices are commercially available, for example from STMicroelectronjcs.

Preferably, there are at least two of the three-axis accelerometers, positioned at different locations within the projectile. The optimum location for the accelerometers is directly opposite each other on a line through the centre of mass of the projectile. Suitably, the accelerometers in this configuration are equidistant from the centre of mass. It can be shown that, even with two 3-axis accelerometers positioned at two locations within the projectile it is not possible uniquely to determine the force and moment on the body. However, provided that the motion does not impart too much spin in relation to the sampling frequency of the accelerometers, it is possible to calculate the trajectory parameters with reasonable accuracy using just two accelerometers. A larger number of accelerometers, for example four or six accelerometers, can be used for greater accuracy.

The orientation of the accelerometers is not important but the initial moment of inertia tensor of the object should be symmetrical. To achieve this, small counterweights could be placed in the ball.

The sampling frequency is suitably from about 100Hz to about 2.5 kHz, which is the maximum frequency for the accelerometer's z-channel. Sampling accuracy is typically 16-bits over the full-scale deflection of the accelerometers.

Suitably, the information about the motion of the projectile comprises one or more of the following parameters in one or more combinations: maximum speed, attainment of minimum heights or distances thrown or number of throws during a given time period, mean speed, distance travelled (total distance and/or horizontal distance), position, maximum height attained, mean frequency of bounces, total number of bounces, spin frequency, kinetic energy expended, mean frequency of projections and total number of projections. The term "projections" refers to bounces, throws or strikes applied to the article. The use of 3-axis accelerometers allows all of these parameters to be calculated independently of the shape of the projectile or the path followed.

It will be appreciated that, for the calculation of these parameters, the signal processor must include a clock circuit so that acceleration can integrated over time to determine velocity and position values. Typically, the clock will be started and stopped (either automatically or by the user) at the start and end of an exercise program, and the parameters achieved can then be displayed.

Preferably, the projectile further comprises a display positioned to be visible from the exterior of the projectile. Typically, the display is adapted to display one or more of the said parameters of motion. The different parameters may displayed simultaneously, but more usually the different parameters are displayed individually in response to display commands entered through soft-key programming using one or more input keys associated with the display. In certain embodiments, the programming may be carried out wholly or in part by mechanical actuation of the projectile. For example, the user could scroll through a menu by flipping or tapping the projectile.

In certain embodiments, for example where it is expected that the projectile may be struck or bounced hard enough to damage a display on the outside thereof, the display may be located inside the projectile, at a protected or cushioned location accessible by opening the projectile (for example by opening a reclosable fastener on the projectile) after the exercise program. In yet other embodiments, there may be no display in the projectile but simply a data port for downloading the measured parameters to an external display device after the exercise program. The same or different data port can be used for uploading exercise parameter thresholds as discussed below. Alternatively, communication with the projectile can be by wireless connectivity such as Bluetooth (registered trade mark) for transferring data between the projectile and a computer or mobile phone.

In certain embodiments, the projectile further comprises an alarm which may be activated by the system controller in the course of an exercise program when one or more of the parameters of motion falls below a respective predetermined threshold. The alarm may for example comprise a light (typically a light-emitting diode), or an audible alarm produced by a sound emitter, or a prerecorded or computer generated synthetic voice. This enables the user to determine if they are achieving an exercise regime defined by the predetermined thresholds. For example, the alarm may be activated if the article is not being thrown high enough, or not being thrown, bounced or struck with sufficient frequency.

The predetermined thresholds may be fixed. However, preferably the user can define the threshold values of the parameters of motion so as to customise their exercise program. Accordingly, the projectile preferably further comprises an input device for inputting said predetermined threshold in respect of one or more of said parameters. The input device may, for example, comprise one or more keys associated with the display and programmable in conventional soft-key programming fashion to customise the thresholds. The input device may be mechanically actuated by flipping, shaking or tapping the projectile as hereinbefore described.

In certain embodiments, the article further comprises automatic turn-on means, which are sensitive to motion, for turning on or re-setting the system controller. For example, in certain embodiments the device is reset by shaking it a predetermined number of times.

In certain embodiments, the article further comprises automatic shut-off means for turning off the display after a predetermined period of immobility. An embodiment of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a top plan view of a preferred form of article in the form of a ball according to the present invention;

Figure 2 shows a schematic cross-section through the ball of Fig. 1;

Figure 3 is a block circuit diagram of the circuitry of the ball;

Figure 4 shows a block diagram of the operational features of article:

Figure 5A shows a diagram of the processor circuitry for the article; and

Figure 5B shows a circuit diagram of the article.

Referring to the drawings, the ball 1 has generally the appearance of a standard soccer ball. The outer diameter of the ball is about 15cm. On the outer surface of the ball is located a display (e.g. liquid crystal) 2 with input keys 3, 4, 5, 6, LED alarm light 7 and buzzer 8. (In alternative embodiments, some or all of the input keys could be omitted, and programming could be performed via the accelerometers by tapping, flipping or shaking the ball.)

Referring to Fig. 2, the interior of the ball 1 is filled with packing material (e.g. a closed-cell polymer foam) to provide cushioning. Two three-axis accelerometers

10, 11 , are located opposite each other on a line through the center of the ball and equidistant therefrom, each at a distance from the center of about 4.5cm. To validate the accuracy in this test projectile, two further three-axis accelerometers

12, 13 are located opposite each other on a perpendicular line through the center of the ball and equidistant therefrom. The accelerometers are mounted on respective, curved printed circuit boards 14,15,16,17. The accelerometers are

MEMS devices with serial digital output, available from STMicroelectronics under the designation LIS3LO2D. A rechargeable 9-volt battery 18 is located in a central pocket in the foam and can be recharged through a socket (not shown) in the side of the ball. A microprocessor based signal processor 19 is also embedded in the foam core of the ball, and is connected through suitable connectors (not shown) to the battery 18 and to the accelerometers.

In another embodiment (not shown in the drawings) the ball has a cushioned outer layer, typically of foam or other resilient material, and a rigid inner layer within which the electronics of the ball are housed.

In use, the ball may be activated by systematic shaking, or by pressing any of the soft keys or by making a connection between diodes (the same mechanism as with exercise machines when gripping the handle enables the heartbeat to be measured). This resets the display 2. The operator can then program a preselected exercise program or exercise thresholds into the ball with the keys 3, 4, 5, 6 using conventional soft-key programming techniques. For example, the display may prompt the user to select one or more of, for example, minimum number of projections, minimum frequency of projections, minimum height, distance, speed or number/frequency of throw, mean speed, distance travelled (total distance and/or horizontal distance), position, maximum height attained, mean frequency of bounces, total number of bounces, spin frequency, kinetic energy expended, mean frequency of projections and total number of projections, and so forth. When the program is complete, the display 2 prompts the user to start the exercise regime. If the user fails to achieve the programmed parameters during the exercise regime, then alarm light 7 and buzzer 8 will indicate failure. After exercise, the keys can again be manipulated to read out from the display parameters such as the average projection frequency achieved, average height achieved, or any of the other parameters identified above. A speaker emitting an audio alarm or digital speech may be provided as an alternative to or in addition to the buzzer 8.

Figure 3 shows a simple block circuit diagram of the electronics of the ball and includes a store 30 for storing information provided by the processor 19.

Normally, the processor 19 is programmed to power down the system when not in use in order to conserve battery power. However, this can equally be effected additionally or alternatively by suitable selection of an input key which, when pressed, causes the processor 19 to power down the system. In the absence of a power down signal from the input key, the processor 19 would normally be programmed to power the system down after a preset time during which no motion or motion below a preset limit is sensed by any of the accelerometers.

When used as an exercise article, when the ball is moved to impart an acceleration above a preselected limit, the processor 19 is programmed to power up the circuitry. Alternatively, this can be effected by pressing one of the soft keys. A main menu display is then shown on the display 2 and, as discussed above, the user then programs his desired exercise levels into the processor 19 and these are stored in the memory 30 for comparison with levels achieved during exercise movement of the ball.

For example, when the ball is bounced the acceleration and deceleration levels sensed by the accelerometers are monitored by the processor 19 and compared with prestored levels which enable the processor 19 to identify the fact that the ball is being bounced and store a count of the number of bounces. The processor 19 also includes a clock which allows the bounce rate to be calculated.

Thus, if the user is not achieving the preset bounce rate the processor 19 can trigger the alarm light 7 and/or buzzer 8 or voice activation.

The above applies equally to each of the other parameters which can be programmed as described above.

The menu options shown on the display 2 can be changed by suitable programmed movement of the ball, for example simply by raising and lowering the ball in the user's hand or twisting the ball about a horizontal axis, left and right. The accelerometers 10 to 13, will sense this movement and generate specific signals representative of the force applied to them during the movement. The processor 19 compares the signals produced by each of the accelerometers with preset values or value ranges which will indicate the force/moment and thus the action being applied to the ball. Thus the processor 19 detects that the user wishes to navigate through the display screens and changes the display accordingly, depending on movement of the ball. For example, raising the ball can move the menu display up through the menu or down through the menu whilst lowering the ball has the opposite effect.

It would also be possible to use this movement sensing to play games displayed on the display 2. For example, the display 2 may show a maze and the user navigates a ball shown on the screen through the maze by movement of the ball. This movement is detected by the accelerometers and processed by the processor 19 to move the screen ball through the maze. The processor can be programmed to allow the playing of a game only once a preprogrammed exercise routine had been completed.

Now referring to Figure 4 of the drawings there is shown a block diagram of the possible functional operations of the article including the diagnostic interfaces, Bluetooth interface, MEMS Devices, Flash Memory, Power supply and Data/OLED. This is just an example of the article and other interfaces and operational drivers may be added as the basic concept and system are developed.

Now referring to Figures 5A and 5B there is shown a complete circuit layout of the article. For ease of reference the diagram has been split into two sections. Figure 5A shows the basic circuit comprising the user interface with the device and Figure 5B shows the circuit arrangement for the processor control system. Both of the drawings are self explanatory and the operational characteristcs of the system are clearly evident to a man skilled in the art. No further specific description is needed or will be given here. The following is a discussion of the mathematical background for the signal processing program. Whilst this discussion is expressed in terms of the accelerometer configuration shown in the drawings, it will be appreciated that the principles of the method are applicable to different accelerometer configurations or projectile shapes.

Introduction

The equations of motion for a rigid body can be written

wx = F (1)

L = M (2)

L = RIR^τω (3) R = ΩR (4)

The variables are defined below. Equation 1 is the conservation of linear momentum and F = ]T. F₁ is the sum of all the forces acting on the ball. Equation 2

is the conservation of angular momentum and M = ^(Z_j -X) AF₁ is the total momenta acting on the body (z_; is the position force F₁ acts). The matrix Ω is a function of the vector ω defined by equation 23.

Equation 3 gives the relation between the angular velocity and angular momentum. The moment of inertia tensor is defined by:

There is a very important simplification if the ball is sufficiently symmetric so that / is proportional to the identity matrix. In this case RIR^T = 1 and / can be treated as a scalar rather than a vector. If this is not the case the ball will wobble in fight. The electronics within the ball may make the ball asymmetric, but this can easily be countered by the positioning of internal weights. This is a very important simplification to the equations which will henceforth assume is true. L can then be eliminated as a variable and equations 2 and 3 combined to give:

I ω = M (6)

The simplification is because equations of motion no longer depend on the orientation R , which evolves according to equation 4.

Suppose in the reference configuration that x = 0 and y is some other point in the ball. The position of this point later in time is given by x + Ry (7) and its velocity will be

d . . .

— (x + i?y) = x+ i?y = x+ Ωi?y (8) dt

Differentiating once more the acceleration is

An accelerometer at position y experiences the difference between the acceleration at this point and gravity. So that the measured acceleration will be

SL = R g F MΛ (i?y)

-Ω²Ry (10) m

The inertial guidance problem is then to estimate F and M from measurements of acceleration a_; at different location y_f and to use these to then integrate the equations of motion so as to know the position, and orientation of the ball at each moment in time. Suppose we have two sensors at y_j and y₂ measuring accelerations a._λ and a₂. After multiplying through by R and using RR^T =1 we have

*_{a2 =g}_i_M^&L_{Ω%2 (12)} m I

Subtracting the two equations and defining R(y₂ ~y_x) = b we get

i?(a₁ -a₂) + MΛ [i?(y₁ - y₂)]+Ω²i?(y₁ -y₂) = 0 (13)

This equation only has a solution if [(a₁ -a₂) + i?^rΩ²i?(y₁ -y₂)J-(y₁ -y₂) = 0.

This condition on the accelerations should always hold when the ball is behaving as a rigid body. This can be used to check correct functioning of the unit. During a tap or a bounce however when the body deforms and no longer behaves like a rigid body it may not be satisfied. However, this condition means that there are only five independent measurements of acceleration and it is impossible to determine all six unknown variables, 3 components each of F and M . This is clear in the general solution of equation 14 which is

where λ can be any number. This uncertainty cannot be eliminated without the measurement of at least one component of acceleration at another location. If this solution is substituted back into equation 11 F can then be solved for, but this solution will also be arbitrary unless y, is proportional to y₂ , that is they lie on the same line through the centre of the ball.

If we choose y, = y and y₂ = -y , that is opposite points on the sphere, when we add equations 11 and 12 we get

Λ(a, -a₂)/2 = g — (15) m

Thus the moment force and centrifugal term exactly cancel and we get the force as

F = mg -mR(a_l -a₂)/2 (16)

For our application the main requirement is an accurate estimation of F however and some uncertainty in M may not matter provided that the ball does not rotate too much in the throwing phase. That is provided we know R and we can assume it to be constant, we can estimate F accurately from this equation and centrifugal and moment forces cancel. The only errors coming from orientation changes during the throw. These can be partly compensated for and estimated since we can estimate M by using the minimum norm solution from equation 14 with λ = 0.

Trajectory Phases

The ball can be in different states that can be identified as follows. In each case the identification procedure operates by identifying a residual function e that must be small over a series of observations.

Stationary If the ball is stationary or only being moved slowly then F = O , M = O and ω = 0 , so that a_λ = R^τg and a₂ = R^τg . The residual function is then

e = a_λ -R^τg + a_z -R^Tg (17)

R is calculated by minimising e over the sequence thus the orientation of the ball is known.

Free motion

In free motion the ball moves along a ballistic trajectory and F = mg , M = 0 so that

Si₁ + a₂ = 0 and the residual test is

e = Ά_X + Ά₂ (18)

There is also a connection with the angular velocity

(a₁ -a₂) + 2i?Wi?y = 0 (19)

which is the centrifugal acceleration. If the angular velocity is known from the throw phase this can be used as an additional check. Since ω is constant in free motion for a symmetric ball then R^TΩR = Ω so this simplifies to

(a_j - a₂) + 2« Λ (ω Λ y) = 0 (20)

From this equation it is possible to calculate two components of ω and this can be used to check or improve the calculation of the total force and moment in the throw phase.

Rolling In the rolling phase there is only a small retarding force and small moment. So this is the same as the stationary phase except that there are centrifugal terms. Thus a_j +a_j =2iϋ^rg . However R is not constant and changes according to its equation of motion, and this must be included in calculating the residual.

e = |(a₁ +a₂)~2J?^rg|² +|(a_I -a₂) + 26)A (fi>A y)|² (21)

There is another possible phase of motion corresponding to rolling with slipping where there will be a significant retarding force and moment. This could also be detected if necessary.

Tapping

A tap is characterised by a rapid rise and fall in acceleration with total impulse zero ( ja._{dt = O ), after subtracting gravity. Precise characterisation is not possible in advance as it depends on how the ball deforms under impact. If the ball resonates this may provide a particularly easy way to detect taps using a filter tuned to the resonance frequency. This may be detected using equation 16, but rather than looking for small values of e a tap is identified with large values.

Bouncing

This is similar to tapping except there will be a large residual impulse ( ≠ O )

that should be compatible with the impact speed.

Throwing

This is the most important stage to accurately identify and track. For a motion to be identified as a throw it must follow the stationary phase and transition to the free motion phase. This distinguishes it from a bounce, which is between two free motion phases, or a tap, which is between to stationary phases. The phase is identified with large accelerations that do not match any of the other conditions. If the throwing motion is such that there is very little orientation change during the throw it is easy to integrate the accelerations directly, after removing gravity, to calculate the resultant linear velocity. If however the ball changes orientation during the throw, the evolution of the orientation must be integrated by estimating the moment and angular velocity. The resultant linear velocity will then be

Appendix

If we define

then Ω is an antisymmetric matrix such that ΩX = O ΛX for all x . Rotation matrices can be parameterised in different ways. The best for our purposes is in terms of unit quaternions q_x , q₂ , q₃ and q₄ such that

+q₃ +q] =1 . These require no trigonometric functions and do not suffer from gimbal lock. Then we write

2q₂q₃ +2q_xq₄ 2q₂q₄ ~2q_xq₃

•R(g) f +

2q₃q₄ + 2q_xq₂ ( 24)

2q,q, ~ 2q_λq₂

- q]

The equation of motion R(q) = Ω(ω)R(q) can then be written

For constant ω this can be integrated exactly as

To increase speed the trig functions can be approximate using ^sm^ ^ω — - «//2 ω and cos(tø/2) ∞ ^\-{t²ω² IA) . This preserves the normalisation of q . Various identities hold if ω is constant. Consider

—(R^τςϊR) = (R)ΩR + (R)^τΩR = R^τΩ^τΩR + R^τΩΩR = R^τ(Ω^τ +Ω)ΩR = O (27)

since Ω js antisymmetric. Thus R^TΩR = Ω that is R and Ω commute and Rω = ω

Table 1 - Definition of Terms x Centre of mass position

_* x Centre of mass velocity

x Centre of mass acceleration ω Angular velocity L Angular momentum vector

L Rate of change of angular momentum vector

R Rotation matrix specifying orientation of the ball

R Rate of change of rotation matrix

Ω Instantaneous rotation vector y General point within the ball

a Acceleration measured by a transducer

F Total force on the ball

M Total moment on the ball m Mass of the ball / Moment of inertia tensor of the ball g Gravity

q Quaternion coordinates parameterising R

The above embodiment has been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.

Claims

1 An exercise article comprising: a housing; at least one motion detector means in said housing for detecting an external force applied to said housing and generating an output signal representative of said force; a microprocessor for analyzing said output signal to provide information about the motion of the article; and a memory for storing said information about the motion of the projectile.

2 An exercise article according to claim 1 , further comprising input means for inputting a preselected exercise routine or exercise threshold into said microprocessor.

3 An exercise article according to claim 2, wherein said preselected exercise routine or threshold comprises at least one of the following: maximum or minimum speed, attainment of minimum heights or distances thrown or number/frequency of throws during a given time period, mean speed, distance travelled (total distance and/or horizontal distance), position, maximum height attained, mean frequency of bounces, total number of bounces, spin frequency, kinetic energy expended, mean frequency of projections and total number of projections.

4 An exercise article according to any preceding claim, comprising two said detector means situated opposite each other on a line through the centre of mass of the exercise article.

5 An exercise article according to any preceding claim, wherein the information about the motion of the exercise article comprises one or more of the following parameters: maximum speed, mean speed, distance travelled, position, maximum height attained, mean frequency of bounces, total number of bounces, spin frequency, kinetic energy expended, mean frequency of projections and total number of projections.

6 An exercise article according to any preceding claim, further comprising a display positioned to be visible from the exterior of the exercise article and adapted to display said information.

7 An exercise article according to claim 6, wherein the exercise article further comprises an alarm which is activated when one or more of the parameters of motion falls below a respective predetermined threshold.

8 An exercise article according to claim 7 further comprising a least one input device for inputting said predetermined threshold in respect of one or more of said parameters.

9 An exercise article according to claim 8, wherein the input device is actuated by shaking, tapping or flipping the exercise article.

10 An exercise article according to any preceding claim, further comprising automatic turn on means, which are sensitive to motion, for turning on the display.

11 An exercise article according to any preceding claim, further comprising automatic shut-off means for turning off the display after a predetermined period of immobility.

12 An exercise article according to any preceding claim, wherein the exercise article is a projectile.

13 An exercise article according to any preceding claim, wherein the exercise article is a substantially spherical ball.

14 An exercise article according to any preceding claim wherein each said motion detector is a 3-axis accelerometer.

15 An exercise article according to any preceding claim, wherein said processor is programmed with at least one game for display on said display, and is configured for navigating a user through the game in response to predefined movement of said article.

16 An exercise article according to claim 15, wherein said processor is configured to initiate said game only in response to completion of a preprogrammed exercise routine or threshold.