GB2380331A

GB2380331A - Eddy current load unit for an exercise machine

Info

Publication number: GB2380331A
Application number: GB0123545A
Authority: GB
Inventors: Karl Drage
Original assignee: EXERTRIS Ltd
Current assignee: EXERTRIS Ltd
Priority date: 2001-10-01
Filing date: 2001-10-01
Publication date: 2003-04-02
Also published as: GB0123545D0; WO2003030337A1

Abstract

The rotating disk or ring 2 of a compact axial air gap eddy current brake defines the outer diameter of the brake unit and wherein the electromagnetic assembly 4 does not extend radially beyond that diameter, step-up gearing 3 being located radially within the diameter and the drive shaft is coaxial with the rotor axis. The rotor operates in a gap (5mm) between the actuate array of coils 4 and a ferrite ring A reflecting beam tachometer, associated with markings (pits) on the rotor, supplies data to a computerised control incorporating a programmable integrated circuit (PIC). The processing machine may be a home computer or games machine.

Description

LOAD APPLYING UNIT The present invention relates to a unit or system for applying a load and, thus, a braking effect in exercise apparatus or sports apparatus.

In many exercise machines, the user performs some form of activity, over a period of time, against the resistance of the machine. For example, a user may pedal an exercise cycle, perform a stepping motion on a stepper machine, a rowing motion on a rowing machine, etc.

Many exercise machines have adjustable resistance levels, thus allowing the user to increase the level of exercise as their fitness increases. This resistance is provided by means of a load applying device. Such devices are typically belt-friction brakes, using a band around a large flywheel, or electromagnetic eddy current brakes.

Typically, the human body exercises at a relatively low number of cycles per minute, generally in the region of 40-100 cycles per minute. Commonly used systems for offering resistance against an exerciser, in exercise machines, are only effective at a high number of revolutions per minute, e. g. in the range of 500 to 6000, or, torque needs to be amplified in order for the brake to be effective. Thus, for these systems to be useful in practice, the mechanism directly driven by the user, e. g. the rotation of pedals, the movement of steps, etc. causes rotation of a shaft, and this rotation is then stepped up to the higher rotation required to operate the braking mechanism by means of a gear mechanism using, for example, a chain or belt drive connecting the driven shaft with appropriate gear wheels.

Whilst such mechanisms are effective in operating the braking mechanism to provide the required resistance, the large belt or chain gearing mechanism is cumbersome and also requires a high level of maintenance in, for example, tensioning, greasing or re-fitting of various components. This high level maintenance is costly in terms of parts and time and means that the exercise machine is out of use during maintenance, which is clearly undesirable.

The present invention aims to solve the problems of the prior art by producing a braking unit which is small and compact and leads to exercise equipment that is simple to maintain.

According to one aspect, the present invention provides an eddy current brake unit comprising a rotatable disk or ring, at least part of which is formed from an electrically conductive material; and an electromagnetic assembly arranged to introduce eddy currents into the disk or ring as it rotates; characterised in that the electromagnetic assembly and the rotatable disk or ring are arranged relative to each other such that the diameter of the disk or ring defines the outer diameter of the brake unit and the electromagnetic assembly does not extend axially beyond that diameter.

Preferably, the rotatable disk or ring is rotated by means of a drive shaft connected to the rotatable disk or ring by means of a gear mechanism to cause the rotatable disk or ring to rotate at a rate greater than the rate of rotation of the drive shaft, wherein the drive shaft, the gear mechanism, the rotatable disk and the electromagnetic assembly are all arranged in a unit having a maximum diameter corresponding to the diameter of the rotatable disk or ring.

In the most preferred embodiment, the drive shaft rotates around the same axis as the axis of rotation of the rotatable disk or ring. However, the drive shaft and rotatable disk or ring may also rotate about different axes, both being within the radial range defined by the outer circumference of the rotatable disk, and such an arrangement would still achieve the advantages of the present invention.

Different types of step-up or gearing mechanisms may, of course, be used, including, for example, a number of rotatable gear wheels connected by chains or belts.

Again, all of these components are arranged such that they fit within a radially defined area defined by the outer circumference of the rotatable disk or ring.

The electromagnetic assembly preferably comprises one or more electromagnetic coils arranged, in an axial direction, on one side of the rotatable disk or ring and a ferric plate or ring arranged on the opposite side of the rotatable disk or ring such that magnetic flux is generated which is cut by rotation of the conductive disk or ring.

Preferably several coils are used and these are arranged around an arch of a circle, preferably in a semicircle, having a radius smaller than that of the rotatable disk or ring.

The entire brake unit is preferably arranged in a housing slightly larger than the diameter of the brake unit, i. e. slightly larger than the diameter of the conductive disk or ring. is self-contained unit within the housing can then be easily attached and removed from, for example, the exercise machine in which it finds application.

In accordance with another aspect of the invention, there is provided an exercise machine comprising a driven mechanism operated by the user and a brake unit as described above, wherein the rotatable disk or ring is caused to rotate in response to operation of the driven mechanism, and wherein the electromagnetic assembly introduces eddy currents into the disk which exert a braking force on the disk, the braking-force being conveyed to the driven mechanism operated by the user to provide resistance to driving by the user.

The brake unit of the present invention finds application in a large range of leisure and exercise machines, in particular exercise cycles, stepping machines, rowing machines, skiing machines and the like.

The braking unit itself, incorporated into a housing, could be merely provided with pedals connected to a drive shaft for causing rotation of the rotatable disk or ring and can be connected, via control circuitry, into, for example, a home computer or games console, such that rotation of the pedals by a user interacts with software in the computer or games console.

In another aspect of the invention, there is provided a single interface control circuit between a data processing machine and the brake unit, comprising a programable integrated circuit located between a microprocessor serial port and a load circuit of the brake system. Rotation of the rotatable disk or ring generates a tachometer signal which is communicated, via the PIC to a computer. A load command is then provided by the computer, in response to the tachometer signal received, which is then communicated, via the PIC to the control circuitry for applying current to the electromagnetic assembly, and thus, to control the

braking effect on the rotatable disk or ring.

As a safety feature, to prevent over-heating of the coils, the system can be arranged such that no current is supplied to the electromagnetic assembly when no motion is applied to the pedals, etc. to drive the rotatable disk or ring.

Preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings.

Figure 1 shows a simple schematic view of a braking unit according to the present invention ; Figure 2 is a side sectional view of the braking unit; and Figure 3 is an exploded view of the unit, but not showing the gears and shafts.

The drive unit comprises a driven axle 1 driven by the user, via e. g. pedals or by a rowing or stepping motion etc. The unit also comprises a conductive disk 2 or ring caused to rotate with the driven axle around the same axis. This conductive disk 2 or ring is preferably made of conductive aluminium but may also be made of copper, some other conductive alloy or a complex conductive configuration for example.

The driven axle 1 causes the disk 2 or ring to rotate via a gear mechanism. The gear mechanism preferably comprises a number of different sized gear wheels 3 positioned on different axles or a plurality of step-up stages connected by small belts. In the preferred embodiment, the gear ratio is approximately 1: 45. The ratio is preferably between 1 : 40 and 1 : 60 although other

ratios may be used, according to the particular application and requirements of the apparatus.

A plurality, preferably six, magnetic coils 4 are located inside the outer circumference of the disk or ring, but spaced from its inner circumference. The axes of the coils 4 are normal to the plane of the disk 2.

These coils are arranged around half of the inner circumference of the disk 2, in such a way that their pole faces adjacent the inner surface of the disk or ring alternate from coil to coil, i. e. the first coil may have a north face adjacent the ring; the next coil its south face; the next coil its north face, etc.

On the other side of the disk is provided a ferric ring.

This ring, together with the alternating north, south, north etc. faces of the coils 4 on the opposite side of the conductive disk 2 forms a complete magnetic circuit.

The gap between the ferric ring and the faces of the coils is approximately 5mm, in a preferred arrangement and the conductive disk ring rotates within this gap.

Because the coils 4 are spaced around the circumference of a semi-circle, thus describing part of a ring having an outer diameter just slightly smaller than the diameter of the conductive disk or ring 2, the conductive disk cuts the magnetic flux generated by the electromagnets at the largest possible diameter within this compact arrangement.

The remaining space within the area defined by the circumference of the conductive disk is taken up by the gearing arrangement 3 described above.

The fact that all of the components are arranged within

the area of the conductive disk 2 means that the brake unit is as compact as possible.

In the preferred arrangement, the unit has a 20cm diameter and is in the form of a 10cm high cylinder.

As mentioned above, the preferred gear ratio is between 1: 40 and 1: 60, i. e. one revolution of the pedal crank or crank driven by the rowing or stepping motion, etc. produces up to 60 revolutions of the conductive disk.

This can be achieved with a number of step-up stages or gear components such as 1 ; 4,1 : 4, 1: 2 and 1 : 2. Such a configuration would give a total step-up of 1: 64. In one preferred construction, the ratios selected are 1: 4, 1 : 4,1 : 1,94 and 1: 2, giving an overall step-up of 1: 62.1.

In the preferred embodiment, the step-up stages are fixed steel gears 3. However, other types of gear mechanism can also be used, for example toothed belts or chains and a combination of steel gears and toothed belts or chains. In one embodiment, a combination of steel gears and toothed belts is used, providing an overall step-up ratio of 1 : 45.

In the preferred example, where the braking unit is used in combination with an exercise bicycle, pedalling at say, 60 revolutions per minute turns the pedal cranks and this causes the conductive disk or ring to spin at 3726 revolutions per minute, with the preferred step-up ratio.

Preferably, the conductive disk is 200mm in diameter.

The centre line of the ring or disk apparent to the pole faces of the electromagnetic coils is of radius 85mm.

The conductive disk, apparent to the centre line of the magnetic field generated in the coils, therefore travels

at an equivalent linear speed of approximately 33m/s.

Preferably, the coils contain 7000 turns of copper wire around a soft iron core (relative permeability mu 7000). This will allow a current of approximately 100mA per coil.

Eddy currents are induced in the conductive disk as it cuts the perpendicular magnetic field. According to Lenz's law, which states that an induced emf will tend to cause a current to flow in such a direction as to oppose the cause of the induced emf, a force is apparent on the disk to oppose the generation of the eddy currents, i. e. a braking force.

In the particular example described herein, when the user pedals at 60 revolutions per minute, the brake will sink approximately 500 Watts of input power. This power is converted to heat in the aluminium disk through joule heating by the eddy currents. The heat is dissipated away from the disk by airflow stimulated by detailing on the aluminium disk.

The electromagnetic coils are driven by a circuit which may apply a fixed current level or a number of fixed current levels, for example zero, medium and high. A control circuit then switches these current levels on and off in order to achieve the appropriate average current. In this way, the system can be programmed to control the level of braking since changing the average current level across the coils changes the magnetic field generated by the coils, which changes the power sunk by the brake.

In a preferred embodiment, the brake unit contains a fixed position tachometer which generates a signal related to disk speed by reflecting a beam, preferably

an infrared beam onto the disk and detecting reflection of the beam from the disk. The disk is provided with markings or pits etc. which interrupt the reflection of the beam and the reflection pattern is converted into an electronic signal used by the control circuitry of the system.

The brake unit is particularly reliable because of the design of the fixed gear box which contains a number of highly reliable individual components, assembled to precision engineering standards in factory conditions, with appropriate life-wear characteristics on each of these components and, where necessary, lubrication sealed in appropriate places.

As the brake unit is comprised in a single compact unit, maintenance is greatly simplified since the unit can be removed in its entirety and replaced with a new unit without affecting the rest of the exercise machine, and thus minimising downtime of the machine.

The control electronics and remaining structure of the machine are not integrated with the brake unit and are thus not affected by removal of the unit.

As mentioned above, a tachometer can be incorporated into the brake unit and the control circuitry for the brake, in the preferred embodiment, is also novel.

In this particular preferred arrangement, the brake unit is controlled by means of a Programmable Integrated Circuit (PIC) chip located between a microprocessor serial port and the circuit which delivers the current supply to the coils in the brake unit. The PIC reads the tachometer signal and sends it to a controlling computer. The PIC acts as a serial interface and receives a load word from the computer and applies an

appropriate pulse width modulated signal to the circuit which applies current to the coils.

Preferably, in order to prevent the coil control circuit from overheating and burning out, the load current is only applied if there is rotary motion indicated from the tachometer.

Claims

Claims 1. An eddy current brake unit comprising a rotatable disk or ring, at least part of which is formed from an electrically conductive material; and an electromagnetic assembly arranged to introduce eddy currents into the disk or ring as it rotates; characterised in that the electromagnetic assembly and the rotatable disk or ring are arranged relative to each other such that the diameter of the disk or ring defines the outer diameter of the brake unit and the electromagnetic assembly does not extend radially beyond that diameter.
2. An eddy current brake unit as claimed in claim 1 further comprising a drive shaft and a gear mechanism connected to the rotatable disk or ring configured so as to cause the rotatable disk or ring to rotate at a rate greater than the rate of rotation of the drive shaft.
3. An eddy current brake unit as claimed in claim 2 wherein the drive shaft, the gear mechanism, the rotatable disk, and the electromagnetic assembly are all arranged in said unit, said unit having a maximum diameter corresponding to the diameter of the rotatable disk or ring.
4. An eddy current brake unit as claimed in claims 2 or 3, wherein said drive shaft rotates around the same axis as the axis of rotation of the rotatable disk or ring.
5. An eddy current brake unit as claimed in any preceding claim wherein said electromagnetic assembly comprises one or more electromagnetic coils on one side of the rotatable disk or ring and further comprising a ferric plate or ring arranged on the opposite side of

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the rotatable disk or ring.
6. An eddy current brake as claimed in claim 5 wherein said electromagnetic coils are arranged in an arch of a circle having a radius smaller than that of the rotatable disk or ring.
7. An eddy current brake unit as claimed in any preceding claim further comprising means for connection to control circuitry, said control circuitry adapted for connection to a data processing machine such that rotation of the rotatable disk or ring interacts with software in the data processing machine.
8. An eddy current brake unit as claimed in claim 7, wherein said data processing machine is a home computer or games console.
9. An eddy current brake unit as claimed in any preceding claim wherein said brake unit further comprises a tachometer arranged to provide a signal representative of the rotational speed of the rotatable disk or ring and; a load control circuit configured to control the load applied by the electromagnetic assembly in response to a load control signal.
10. An eddy current brake unit as claimed in claim 9, wherein said load control circuit is configured to control the load applied by said electromagnetic assembly in response to said load control signal which has been pulse width modulated.
11. An exercise machine comprising a driven mechanism operated by the user and an eddy current brake unit as claimed in any preceding claim, wherein the rotatable

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disk or ring is caused to rotate in response to operation of the driven mechanism, and wherein the electromagnetic assembly introduces eddy currents into the disk which exert a braking force on the disk, the braking force being conveyed to the driven mechanism operated by the user to provide resistance to driving by the user.
12. An exercise machine as claimed in claim 11 wherein said driven mechanism is a cardiovascular exercise machine mechanism.
13. An apparatus comprising an eddy current brake unit as claimed in any of claims 1 to 10, a data processing machine and an interface control unit connected between said eddy current brake and said data processing machine, wherein said interface control unit comprises a programmable integrated circuit connected between a microprocessor serial port and a load control circuit of the eddy current brake unit.
14. An apparatus as claimed in claim 13, wherein rotation of the rotatable disk or ring generates a tachometer signal which is communicated to the data processing machine via said programmable integrated circuit; and a load control signal is generated by said data processing machine in response to the tachometer signal and is communicated via said programmable integrated circuit to said load control circuit for applying current to the electromagnetic assembly so as to control the braking effect on the rotatable disk or ring.
15. An apparatus as claimed in claim 14, wherein said load control circuit is configured to control the load applied by said electromagnetic assembly in response to

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said load control signal which has been pulse width modulated.
16. An apparatus as claimed in claim 13 or 14 wherein said data processing machine is a home computer or games console.
17. An eddy current brake unit as hereinbefore described with reference to the drawings.