GB2329243A

GB2329243A - Optical force sensor for forces applied to the body

Info

Publication number: GB2329243A
Application number: GB9718900A
Authority: GB
Inventors: Paul Strickland
Original assignee: PORTSMOUTH ENTERPRISE, University of
Current assignee: PORTSMOUTH ENTERPRISE, University of
Priority date: 1997-09-05
Filing date: 1997-09-05
Publication date: 1999-03-17
Also published as: WO1999013306A2; WO1999013306A3; AU8990998A; GB9718900D0

Abstract

A sensor (1) comprises light emitting means (3) and light receiving means (4) located at opposite ends of a flexible passage (2), filled with a material (6) which may be a solid, liquid, or gas (e.g. air). Bending or deformation of the passage alters the amount of light received by the light receiving means from the light emitting means, thereby providing an indication of the extent of deformation or bending of the passage. A plurality of such sensors may be arranged to define a matrix. Such a sensor or sensor matrix may be incorporated in an item of clothing such as, a shoulder pad, to monitor forces and/or bending stresses on the human body while performing a task. Such a pad could be utilised for enabling the forces exerted on the shoulder of a player during a rugby scrum to be monitored to facilitate correct training of players in scrummaging techniques.

Description

A SENSOR FOR MEASURING FORCES APPLIED TO A BODY AND ITEMS OF CLOTHING INCORPORATING SUCH SENSORS This invention relates to sensors for measuring forces applied to part of a body such as, for example, a human being and to items of clothing incorporating such sensors.

There are many sensors currently available for measuring applied forces such as pressure transducers or electronic pressure switches, LVDT position transducers, magnetostrictive transducers and load cells. These sensors tend, however, generally to be relatively expensive and can also be relatively heavy and even bulky.

In one aspect the present invention provides a sensor comprising a body defining a passage for guiding from a light emitting device to a light receiving device, the passage containing material allowing light from the light emitting device to reach the light receiving device. The walls of the passage are arranged so as not substantially to transmit light emitted by the light emitting device and may be, for example, opaque to or arranged to reflect light emitted by the light emitting device. The passage is formed so as to deform or bend in response to application of a force, which bending or deformation alters the amount of light emitted from the light receiving device that can be received by the light receiving device, so that the output of the light receiving device can be used to provide an indication of the force applied or the degree to which the passage has been bent.

In another aspect, the present invention provides a sensor comprising a light containing or retaining tubular body housing a light transmissive material for providing an optical path between a light emitting device and a light receiving device.

The passage may be defined between two sheet like members.

The material forming the walls of the passage and the material contained within the passage may be selected so as to tailor the response of the sensor to an applied deformation or bending force. For example, the body may be formed of silicone rubber and the material contained within the passage may comprise a gas such as air, nitrogen or argon which may be at atmospheric or greater pressure, and/or a liquid or gel-like material such as, for example, liquid paraffin, or water. As another possibility, the material may comprise a solid material such as a silicone or other glue.

A sensor for measuring bending forces may comprise a tube opaque to light containing optically transmissive spheres or beads of comparable cross-section to the tube.

The sensor may be circular or rectangular in crosssection. The cross-section may be uniform throughout its length or vary periodically along the length and the resistance of the passage to an applied force may be arranged to vary along its length by, for example, applying a shaped member to the outside of the passage.

The light emitting and light receiving devices may operate in the infrared range of the spectrum.

In another aspect, the present invention provides a sensor wherein changes in optical or electrical characteristics of a passageway defined by a body result from application of a force to the body.

The present invention also provides an item of clothing such as, for example, a shoulder pad, elbow pad, knee pad, thigh pad, strap, vest or other garment to be worn by a user which incorporates one or more sensors adapted to respond to bending of the part of the body or application of a force to the part of the body where the sensor is located. Such sensors may comprise, for example, a tubular member coupling a light emitting and light receiving device.

There is currently considerable concern about the neck and other serious spinal injuries which may arise during the game of rugby, in particular during the carrying out of scrummages. In another aspect, the present invention provides a training device which enables the forces exerted upon a player during a scrum to be monitored enabling, for example, a coach to determine whether players are adopting a correct scrummaging technique and to allow correction of any incorrect techniques. Such a system may also be used to provide a warning when the scrummaging technique is sufficiently incorrect that a collapse of the scrummage which may result in injury is likely to occur.

In another aspect, the present invention provides a shoulder pad adapted to be worn by a player during a rugby scrum, for example during coaching or training, to monitor the forces applied to the shoulder of the player during the scrummage. The shoulder pad may comprise a number of sensors each comprising a passage defining a light path between light emitting and light receiving devices, which passage deforms or bends in response to an applied force thereby altering the amount of light which can pass through the passage. Alternative forms of sensors may be used in the shoulder pads.

In another aspect, the present invention provides apparatus for monitoring forces applied to a body, which comprises means for processing signals from a garment such as, for example, a shoulder pad incorporating sensors responsive to forces applied to the body and means for providing an indication when the output of one or more of the sensors is such as to implicate that a particular condition, for example a critical condition which may result in injury to the wearer of the garment, is likely to occur.

In another aspect, the present invention provides means for calibrating a sensor responsive to applied forces by determining the outputs of the sensor when predetermined forces are applied to a body carrying the sensor and using those outputs to provide a reference.

In another aspect, the present invention provides means for providing a reference with which the output of a sensing device can be compared by converting signals from the sensor derived as a result of the application of predetermined forces to the sensor into the frequency spectrum to provide a reference frequency spectrum characteristic of the response of the sensor to those predetermined forces.

In another aspect, the present invention provides a rugby scrum monitoring system which comprises a plurality of shoulder pads adapted to be worn during a full scrummage or a half scrummage with a scrummaging machine and processing means for processing output signals from sensor incorporated into those shoulder pads to determine whether the players are performing the scrummaging technique correctly.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic part cross-sectional view of a first embodiment of a sensor in accordance with the present invention; Figure 2 shows an example of a circuit for deriving an output signal from a sensor embodying the present invention; Figure 3a illustrates very diagrammatically the application of a force to a sensor of the type shown in Figure 1 so as to deform the sensor; Figure 3b illustrates graphically the relationship between the output voltage from the circuit shown in Figure 2 and the force F applied to the sensor in the manner shown in Figure 3a; Figure 3c illustrates graphically the change in the voltage output of the circuit shown in Figure 2 with time when a given force or load is applied to the sensor and then removed; Figure 4a illustrates very diagrammatically bending of the sensor shown in Figure 1 so that each end of the sensor subtends an angle a with respect to a centre point of the sensor; Figure 4b illustrates graphically the relationship between the output in volts of the circuit shown in Figure 2 and the angle a shown in Figure 4a; Figures 5, 6 and 7a show schematically and partly in cross-section further embodiments of a sensor in accordance with the present invention while Figure 7b shows the effect of bending the sensor shown in Figure 7a; Figures 8 and 9 illustrate possible alternative cross-sectional shapes for a sensor embodying the present invention; Figure 10a shows a plan view during the formation of another embodiment of a sensor in accordance with the present invention while Figure lOb shows a part crosssectional view through the sensor when completed; Figures 11 and 12 are diagrammatic plan views for illustrating configurations of a sensor embodying the invention for enabling sensing of a load in a particular area; Figure 13 shows diagrammatically and in plan view a matrix of sensors embodying the invention; Figure 14 illustrates a force measuring device incorporating a sensor embodying the present invention; Figure 15 illustrates another example of a force measuring device incorporating a sensor embodying the present invention; Figures 16a and 16b show another example of a sensor embodying the invention; Figures 17a and 17b illustrate, respectively, a part cross-sectional view through part of an item of clothing incorporating a sensor and a circuit associated with the sensor for providing an alarm; Figure 18 illustrates processing apparatus for processing an output from the circuit shown in Figure 2; Figures 19 and 20 are flow charts for illustrating the operation of the processing apparatus shown in Figure 16; Figure 21 shows diagrammatically a portion of one of a rugby player wearing a shoulder pad embodying the present invention; Figure 22a shows schematically in plan view one example of a shoulder pad embodying the present invention and Figure 22b shows a part cross-sectional view through part of that shoulder pad; Figure 23 shows a block diagram of a processing circuit for processing signals output from a shoulder pad embodying the present invention; Figure 24 is a flow chart for illustrating ways in which signals output from a shoulder pad embodying the present invention may be processed; and Figure 25 shows a way of calibrating a shoulder pad embodying the invention.

Referring now to the drawings, Figure 1 shows a first embodiment of a sensor 1 for enabling measurement of applied forces and/or curvature or bending. The sensor 1 comprises a tube 2. The tube 2 of the sensor 1 is, in this example, 2mm in diameter with a O.5mm thick wall and has a length between the light emitting and receiving devices 3 and 4 of typically up to 7cm. The tube 2 is formed of a material which does not substantially transmit the emitted light. A light emitting device 3 is mounted in one end 2a of the tube for directing light into the tube while a light receiving device 4 is mounted in the other end 2b of the tube so as to receive light emitted by the light emitting device 3. The space between the light emitting and receiving devices 3 and 4 is filled with a material transmissive to light emitted by the light emitting device 3.

Generally, the tube 2 will be formed of an electrically insulative material. However electrically conductive materials may be used if the light emitting and receiving devices can be sufficiently electrically isolated from the tube, for example by potting or encapsulating them in epoxy resin. The light emitting and light receiving devices 3 and 4 may be secured to the tube 2 by use of adhesive 5 such as superglue, hot melt adhesive on even a lacing cord or tie rope, provided that the resulting seal does not allow the filling material to leak out which will, of course, depend on the nature of the filling material and the internal pressure in the tube.

In this particular example, the light emitting device 3 is a conventional infrared LED and the light receiving device is a conventional infrared responsive photodiode. The use of an infrared light source is advantageous in that outside light (ambient or artificial light) will not generally contaminate the emitted light even of the outside light does leak into the tube. Also, infrared light can, if desired, be easily modulated and the receiving device tuned to pick up the transmitted modulated light which should further cut down the possibility of interference from unwanted light. Of course, other light emitting devices such as phototransistors, photoresistors and the like may be used. In this example, the tube 2 is formed of a silicone rubber opaque to the emitted light, the light emitting and receiving devices are mounted to the tube by adhesive 5 and the material filling the space 6 is in this example liquid paraffin or paraffin jelly which are infrared transmissive.

As will be described below, the amount of light from the light emitting device 3 which reaches the light receiving device 4 is affected by deformation of the tube 2.

Figure 2 illustrates a simple circuit 60 for deriving an output signal from the sensor 1 shown in Figure 1.

As shown in Figure 2, the light emitting device 3 is coupled in series with a resistor R1 between a positive (generally 5 volts) voltage supply line 7 and an earth or ground line 8 with the cathode of the light emitting device 3 connected to the positive voltage supply line 7 and the anode to the resistor R1. The light receiving device 4 is coupled in series with a resistor R2 between the positive and earth voltage supply lines 7 and 8 with the cathode of the light receiving device being coupled to the earth line 8 and the anode to the resistor R2. Typically, the resistors Ri and R2 have values of 1 kilo-ohm and 100 kilo-ohms, respectively. The anode of the light receiving device 4 is also coupled via a resistor R4 to the negative input of an operational amplifier OA1 which has its positive input coupled to the ground line 8 via a, typically, 1 kilo-ohm resistor R3 and its output coupled by a feedback resistor R5 to its negative input. The output of the operational amplifier OA1 provides a voltage signal V representative of the light from the light emitting device 3 received by the light receiving device 4. The circuit may be powered by a conventional battery BT having its positive supply terminal coupled to the power supply line 7 by, for example, a pull-down resistor Rp to provide a 5 volt supply. If necessary, a Zener diode or other voltage regulation circuit may be provided between the positive and ground supply lines 7 and 8 to maintain a 5 volt supply.

The effect on the output voltage V of the application of a force F to the tube 2 of the sensor 1 has been tested. Initially, the sensor 1 was arranged so that the output voltage V was zero, that is so that the light receiving device 4 was saturated. A load was then applied to the centre of the tube 2 as shown in Figure 3a by means of a 3mm radius applicator 0 and the output voltage of the circuit shown in Figure 2 was measured. The load or force F applied via the applicator O was increased in increments of lOg and the output voltage V measured for each load.

As can be seen from Figure 3b, the output voltage does not change substantially until the load applied reaches about 80g. This is the stage at which the load applied causes the tube 2 to begin to deform so that its outside, and therefore internal, diameter decreases and the amount of light from the light emitting device which can be received by the light receiving device is reduced.

There is thus a marked increase in the output voltage V at a load of about 80g and thereafter the output voltage climbs relatively steadily with increase in load.

It can thus be seen from Figure 3b that the sensor 1 described above may be used as a digital force sensor having a threshold of about 80g. Alternatively, the sensor may be used as an analogue sensor providing a reading of the actual force applied, especially once the load exceeds 80g. It will, of course, be appreciated that the maximum force or load which can be measured using such a sensor is the force at which the tube 2 first completely collapses so that no light from the light emitting device can reach the light receiving device.

The response characteristics shown in Figure 3b are determined primarily by the mechanical resistance of the tube 2 in combination with the additional mechanical resistance provided by the filling material and the response characteristics may be tailored by, for example, altering the mechanical strength of the tube 2, in particular its resistance to deformation, by, for example, using tubing having a greater or lesser wall thickness or by using a material other than silicone rubber. Other suitable materials are for example PVC tubing or synthetic neoprene tubing.

The use of paraffin jelly or liquid paraffin as the filling material is particularly advantageous because it is homogenous and therefore acts to increase the mechanical resistance to an externally applied force without significantly detrimentally affecting the optical characteristics of the sensor. Other filling liquids or gels may be used provided that they are optically transmissive at the required wavelength, chemically relatively inert so as to avoid corrosion of the light emitting and light receiving devices and provide the required mechanical strength. Other suitable filling materials are polyurethane adhesives, cosmetic gels and creams which are transparent in the required wavelength range, silicone gels and sealants, glues such as UHU (trade mark), and double distilled water provided that care is taken to ensure that adequate sealing against leakage is achieved. Of course, the material used will be dependent upon the optical wavelengths desired to be used.

The materials used for forming the tubing and the filling material may also affect the speed of response to and recovery from the application of a force with, for example, a material of high viscosity slowing down the response of the tube to an applied force or load.

Figure 3b shows the output voltage for a given load once a steady state has been reached. However, it will in practice take a finite time for the steady state to be reached. Typically as shown schematically in Figure 3c, if a force F is applied to the tube 2 of the sensor 1 at a time to then a finite time Tmin will elapse before the sensor responds to the applied force. This time Tmin will be dependent on the mechanical resistance to the applied force of the sensor, that is mainly the mechanical resistance of the tube 2 and the filling material 6 to deformation under the applied force. A further time Ttask will elapse before the sensor reaches a stable state in response to a particular given applied force so that a total time T1 will elapse before the sensor reaches a steady state output voltage in response to a steady applied force or load. Assuming that the load is applied for a period T2 after the steady state has been reached, then a further time T3 will be required for the sensor to relax or return to its original state after removal of the load at the end of the period T2.

Each sensor will have an individual response time characteristic TR of the type shown in Figure 3 and, of course, the materials used to form the sensor tube and the filling material may be selected to achieve a required response time characteristic TR The output of the light receiving device 4 is also responsive to bending of the tubing 2. Figure 4a shows diagrammatically bending of the tube 2 so that the tube 2 forms a symmetrical arc about a centre line CL and at the point where the tube intersects the centre line CL subtends an angle a with either the end face of the light emitting device 3 or the light receiving device 4.

Figure 4b illustrates graphically the change in the output V of the circuit shown in Figure 2 for changes in the angle a. As can be seen from Figure 4b, the relationship between the angle a and the output voltage is almost linear showing that the sensor may be used to provide a signal indicating the amount to which the tubing 2 is bent and also may be used in a force displacement type sensor in which the amount by which the tube is bent is determined by a force applied to a structure in which the sensor 1 is incorporated.

Examples of such force displacement sensors will be described in greater detail below with reference to Figures 14 and 15.

Where it is desired for the sensor to be used to measure bending forces rather than deformation forces then the material forming the tube may be selected so as to inhibit deformation. Examples of suitable tubing include nylon or polyurethane ridged wall tubes although angles of no more than 45" may be achievable with ridged tubes. Also coaxial cabling, with the inner wire or cable removed or flexible metal housing may be used, provided care is taken to ensure appropriate electrical insulation of the light emitting and receiving devices.

Generally, the sensor 1 will be supplied as a package with the remainder of the circuit 60 shown in Figure 2 together with a data sheet showing the graphs of Figures 3b, 3c and 4b for that particular sensor so as to enable the end user to calibrate the output of the sensor.

The sensor shown in Figure 1 is simple and cheap to manufacture and may be easily mounted to a surface to enable the force applied to or the bending of that surface to be determined. For example, the sensor may be secured to the required surface such as an item of clothing by stitching or by use of an adhesive with generally only the ends being attached to the surface.

The filling material 6 used within the tube 2 need not necessarily be a liquid or gel. For example, where relatively small forces are to be measured, then the tube 2 may be filled with air or another inert gas such as nitrogen or argon. Generally, the gas will be at atmospheric pressure. However, it may be possible by selecting the material from the tube 2 or by use of appropriate reinforcement for the gas within the tube 2 to be at a pressure higher than atmospheric pressures so as to increase the mechanical resistance of the tube to deformation.

As another alternative to the use of a liquid filling material, the tube 2 may be filled with a suitably transparent solid material which is capable of flexing or deforming as required. As an example, the tube 2 may be filled with a silicon glue.

Figure 5 illustrates a further example of a sensor la embodying the invention in which the tube 2 is filled with spheres 6a which, in the example shown, are of similar diameter to the internal diameter of the tube 2.

The spheres 6a may be, for example, glass, plastics or soft silicon beads and the spaces between the beads may be filled with a further solid or liquid 6b of similar refractive index 2 of the glass beads, for example. The sensor shown in Figure 5 is in other respects similar to the sensor shown in Figure 1 and will be used in combination with a circuit similar to that shown in Figure 2. The spheres inhibit deformation of the tube 2 while still allowing curvature of the tube 2 so adapting this sensor for measuring curvature or for use in a force-displacement sensor such as those described below with reference to figures 14 and 15. Spheres of diameters smaller than that of the tube may also be used.

Solid objects of different shapes could also be used.

Figures 1 and 5 show a sensor 1 having a tube 2 of uniform cross-sectional area along its length. However, the shape of the tube 2 may be tailored so as to modify the output voltage V, for example, to provide a particularly high output signal in response to a particular degree of curvature or deformation. Figure 6 illustrates another example of a sensor 1b embodying the invention where the diameter of the tube 2 varies periodically along its length so as to control the response of the sensor to deformation or curvature and possibly provide localised areas which may enhance force measurement. This may be achieved by moulding the tube to the desired shape or by restricting the circumference of the tube at given positions by, for example, applying ties or bands around the tube. In other respects, the sensor 1b shown in Figure 6 is similar to that shown in Figure 1 and the filling material 6 may be any of those discussed above with reference to Figure 6.

The sensor 1 shown in Figure 1 may be modified as shown in Figure 7a by coupling it to a contact pad 2a which has, for example, a regular array of protuberances which cause the tube 2 to deform in a particular way when a bending or deformation force is applied to the tube so as to tailor the output signal of the sensor so that, for example with the arrangement shown in Figure 7a, jumps or steps occur in the output voltage V as the angle through which the sensor is bent changes or the applied force varies.

The sensors 1, la, Ib and ic may have a tube 2 which is of circular cross-section as shown in Figure 8 so that the sensor is of equal stiffness in all directions and is omni-directional responding to a given force in the same way no matter whereabouts around the circumference of the tube 2 the force is applied. As another possibility, however, the tube 2 may have a crosssectional shape designed so that the sensor responds differently to a given force dependent upon where around the circumference of the tube 2 to the force is applied.

For example, as shown in Figure 9, the tube 2 may be of rectangular cross-sections so as to present a different stiffness dependent upon where the forces are applied to the periphery of the tube 2.

In the examples described above, the sensor 1 has a unitary tube 2 which is filled with the filling material 6, be it liquid, gas or solid or even a combination thereof. Figures 10a and 10b illustrate another example of a sensor 1d embodying the invention.

The sensor 1d is formed from a substrate 20 on to which the light emitting and receiving devices 3 and 4 are mounted, for example, by means of a suitable epoxy adhesive. In this case, the filling material 6 is provided by applying a track of a suitable optically transmissive material on to the substrate 20 between the light emitting and light receiving faces 3a and 4a of the devices 3 and 4. For example, the track 6' may be formed by depositing a track of silicone glue on to the substrate 20 between the end faces of the devices 3 and 4. The track 6' is then covered, as shown in Figure 10b, by another substrate 21 formed of a material similar to the substrate 20. Suitable materials for forming the substrate 20 and 21 are rubbers, foams and the like.

Where it is desired to measure an average of a force applied over a relatively large area of a body B, then, as shown schematically in Figure 11, a sensor embodying the invention may be arranged so as to lie along a diagonal of the area A where the force is to be sensed.

Such an arrangement may, however, not be satisfactory if the contact area of the applied force is relatively small and falls outside the area occupied by the sensor.

Accordingly, as another possibility, the sensor may be shaped as shown schematically in Figure 12 so as to cover as much as possible of the area in which the force is to be detected. A sensor defining a sensing path such as that shown in Figure 12 may be achieved most easily by using a sensor of the type described with reference to Figures 10a and 10b. Alternatively, tubing which may be permanently shaped, for example, by heat treatment or moulding, may be used.

Where it is desired to measure the force applied at discrete regions within a relatively large area, then the relatively large area may be covered by a network or matrix of columns li, li+lr ...li+n, and rows lj, lj+l, . . .1 of sensors and a determination made that a force f(x) has been applied to a point D(i,j) representing the area where the ith column and jth row sensors intersect only when both the ith and jth sensors provide the requisite output by, for example, using conventional logic circuitry.

As discussed above, the relationship between the bending angle a and the output voltage of the circuit 2 may be used to provide a force-displacement sensor.

Figure 14 illustrates schematically one example of such a sensor FS1. This sensor consists of a pair of pivotally connected arms 22 and 23 whose free ends are coupled together by, for example, a compression spring 24. The sensor 1 is, in this example, arranged so that the light emitting device at one end 2a of the tube 2 is coupled by a conventional pivot mount P to one arm 22 at a given distance from the pivot point and the light receiving device at the other end 2b of the tube 2 is similarly coupled to other arm 23 at the same distance from the pivot point P so as to achieve a linear response. The sensor could alternatively be coupled to the arms by the ropes or other loose connections which would result in a non-linear response. Squeezing of the two arms 22 and 23 together against the force of the spring 24 will cause the tube 2 to bend enabling an output voltage to be obtained which is related to the angle a through which the tube bends, which voltage is also related to the force applied to compress the spring 24.

Figure 15 shows an alternative form of forcedisplacement sensor wherein one end 2a of the sensor is coupled to one end of a first arm 22a and the other end 2b of the sensor is coupled to the same end of a second arm 23a which arms are held apart by a compression spring 24a. Again, application of a force to one or other of the arms 22a and 23b will cause the tube of the sensor to bend to provide an output voltage related to the angle through which the tube bends and thus to the force applied to the arm or arms.

Figures 16a and 16b illustrate another example of a sensor le embodying the invention. In this example, the tube 2 is formed of a stretchable material such as latex and intended to be used where a force is applied along its length so as to stretch the tube, for example as a result of bending of an area of a body to where the sensor is fixed. Stretching of the tube causes a reduction in the cross-sectional area of a central section of the tube and thus a decrease in the amount of light received by the light receiving device 4. The reduction is cross-sectioned area and thus the reduction in the amount of length received will depend upon the degree of stretching. If the tubing is formed by electrically conductive latex, then the light emitting and receiving devices may be replaced by electrical contacts and the variation in electrical resistance due to stretching of the tube may be sensed.

The sensors described above are relatively simple and cheap to manufacture and may be incorporated into, for example, pressure pads to be used in robot grippers or the like to enable the robot to be provided with an indication of the force being applied to an object by the gripper. Another use of such sensors is for monitoring or checking the performance of the human body as it carries out a repetitive task or as it performs a sport, for example. Sensors embodying the invention can easily be incorporated into items of clothing. For example, the sensors shown in Figures 1 to 7a may be secured to an outer or inner layer of an item of clothing or may be sandwiched between layers forming the item of clothing.

The sensor described with reference to Figures 10a and lOb may be formed in situ in the item of clothing by depositing the light transmissive track on to one layer of the item of clothing before that layer is combined with a further layer of the item of clothing. Sensors embodying the invention may be used to determine the pressure or force being applied by or to a part of the body by incorporating them into, for example, the fingertips of gloves, into shoulder pads or into the soles of socks or shoes, for example or into bands or straps to be wound round and fixed in place (by Velcro (trademark) or the like)). Sensors to be used for measuring the degree of curvature of a part of the body may similarly be incorporated into items of clothing which extend along the spine or around the elbow or over the knee joint, for example. Where the area to be monitored is greater than about 7cm in length, then to avoid undue attenuation of the output signal, the length to be monitored may be covered by a number of sensors with their outputs V coupled in series via amplifier or repeater stations.

Figure 17a shows schematically the insertion of a sensor 1 embodying the invention and associated circuitry into a substrate such as a garment. The sensor may be any of those described above. In this example, the garment is formed of multiple layers 40, 41 of a material such as rubber or foam. The sensor 1 is received within a groove formed in an outer layer 40 of the garment.

although not shown, the sensor may be protected by an adhesively secured covering. The sensor is generally secured in the groove by adhesive. The output leads from the light emitting and light receiving devices 3 and 4 extend through the outer layer 40 to a space between the inner and outer layers where a printed circuit board PCB is loosely mounted. The printed circuit board in this example carries the components of the circuit shown in Figure 2 plus a comparator 50 which compares the output V of the operational amplifier OA1 with a voltage reference Vref. When the output voltage V exceeds the reference voltage indicating that an excessive load, stretching or bending force has been applied to the sensor, the output of the comparator goes high raising the control electrode voltage of a transistor T1, in this example a n-channel field effect transistor, and so coupling an alarm device such as an LED or electrically operated buzzer or the like between the power supplying lines 7 and 8 providing an alarm to indicate that a circuit board, stretching or bending force has been exceeded. The power supply for the circuit may be provided by a 5 volt battery BT which may be mounted to the garment in a similar manner to the sensor. Such an arrangement is very simple to manufacture.

As an alternative, the output of one or more sensors incorporated in a garment may be supplied to a conventional data logging system such as a chart recorder similar to that used for monitoring the performance of the heart, for example. The output V from each of the sensors 1 may be coupled to the data logger via an appropriate electrical cable. Alternatively, the outputs V of the various sensors may be, for example, supplied via an infra-red or radio transmitter to an appropriate receiver on the data logger so as to allow the person being monitored greater freedom of movement.

Sensors embodying the invention are relatively lightweight and can be easily incorporated into items of clothing in a manner such as not to interfere with the carrying out of their normal task or performance by the wearer of the items of clothing. Such sensors may be, for example, incorporated into gloves or straps to be bound around appropriate areas of the finger held in place by velcro or the like to enable the forces and bending stresses involved in repetitive manual tasks such as typing or assembly of components to be manufactured to determine whether repetitive strain injury is likely to occur and whether there are techniques which can be used to avoid excessive strains on areas such as the joints, or into shoulder, knee, elbow or thigh pads or larger straps to be applied to areas of the body such as the torso. A number of sensors of the type adapted to measure bending forces may be arranged in lines, each with their respective circuits 10, and coupled via amplifiers to enable the bending of a large area to be measured. One use for such a device is in measuring the bending of the human back during, for example, lifting of heavy loads and the sensors may, for example, be incorporated into a vest or body stocking type of garment in a manner similar to that described with reference to Figure 17a so as to lie along or parallel to the spine.

Items of clothing incorporating sensors embodying the present invention may also be used, for example, in teaching a person how to perform a task correctly so as, for example, to avoid injury or so as to ensure that a person recovering from injury correctly carries out remedial exercises without always requiring the detailed supervision of, for example, a physiotherapist. Items of clothing incorporating sensors embodying the present invention may also be used, for example, for sports training or coaching to ensure that an athlete or sportsman is carrying out the appropriate actions in the required manner without placing undue stresses or strains on joints or ligaments, for example. Thus, for example, the item of clothing may be a glove for use in training racket players, rowers and the like. Alto, items of clothing incorporating sensors embodying the invention may be used in virtual reality systems.

In each of the examples described above, it has been assumed that the outputs of the circuits shown in Figure 2 associated with the sensors embodying the invention are supplied simply either to a warning device or to data logging equipment which can provide a display or printout of the variation of the voltage V during the carrying out of a task. However, a simple warning may be insufficient and the output of a data logger may be difficult to interpret and may require operation by a person skilled and experienced with the equipment.

Figure 18 is a block diagram of processing apparatus 9 which may be used with any one of the sensors described above for enabling desired information to be obtained from the output signals V of the circuit shown in Figure 2.

The processing apparatus shown in Figure 18 comprises a main processing unit or mother board 10 which has associated random access memory (RAM) 11, read only memory (ROM) 12, a hard disk drive (HD) 13, a floppy disk drive or CD ROM drive 14 by which data can be input to the computer via a disk FD, a keyboard 15a and mouse 15b for enabling user input of information to the processing apparatus, a monitor 16 for displaying instructions to the user, data and processed data and a printer 17 for enabling a hard copy of data and processed data to be obtained by a user. A transceiver 18 such as a MODEM or IR port may be provided to enable communication with other computers. Where the output from only one sensor 1 is to be processed, then this output V is supplied by an operational amplifier OA2 to an analogue to digital (A/D) converter 16 which, under the control of the processing unit 10, provides digitised data which is stored in the RAM 11.

If the data from more than one sensor 1 is to be processed, then either separate A/D converters will be required for each sensor or the outputs V for each of the sensors may, as shown in Figure 16, be supplied first to a multiplexer MUX which provides a time multiplexed output to the operational amplifier OA2. Where a number of sensors are provided, then the outputs V from the sensors may be supplied to the multiplexer via a respective DC offset amplifier DCl to DCn of conventional form and a respective gain amplifier GA1 to GA, (only two of each being shown in Figure 18) so that each of the signals input to the multiplexer MUX lies within a predetermined voltage range, 0 to 5 volts, so as to enable the best use of the range of the multiplexer and also to allow sensors to be interchanged without difficulty.

The processing apparatus 9 may comprise a conventional personal computer such as a pentium computer with an associated printer. In such a case, the analogue to digital converter to be found on the sound card of the computer may be used as the analogue to digital converter 18.

In the example shown, the sensors 1 are coupled to the processing circuit 9 via appropriate flexible cables.

The DC offset amplifies DCi and gain amplifiers GAi may be housed adjacent the sensor for example on the same PCB as the circuit shown in Figure 2 and the flexible cable may connect the amplifiers GAi to the multiplexer MUX.

As an alternative a conventional remote telemetry link such as an infrared or radio link may be provided with the remote telemetry link preferably being between the multiplexer MUX and the operational amplifier OA2. In this case, the multiplexer MUX and the power source for the electrical components (which will generally be a battery) may be housed in a pack carried by the wearer of the garment, for example in a belt or harness or in a pocket specifically designed into the garment if the garment is large enough.

The processing apparatus shown in Figure 18 may be used to calibrate the sensors to which it is coupled.

For example, as illustrated by the flowchart shown in Figure 19, in response to an input from the user requesting a calibration mode, the processing unit 10 first requests the user to input a code identifying the sensor to be calibrated if more than one sensor is coupled to the processing means (step S1). Once this has been identified, the user is requested to input the force F(x) and time t(y) for which the force is to be applied to the sensor (step S2). Once this has been input, the user is instructed to apply the force F(x) for the required time to the tube of the appropriate sensor (step S3). The digitised output from the analogue to digital converter 18 for that sensor is logged for a time greater than the time t(y) for which the force is applied so that measurements of the output voltage V at time intervals ti for a period greater than that for which the force is applied are stored in the RAM ii (steps S4 and S5). This information will include the time response of the sensor to the applied force. In this example, the profile provided by the signals V (ti) is transformed to the frequency domain by using, for example, a conventional fast Fourier transform (FFT) process (step S6). In order to reduce the amount of data required to be stored, the resulting frequency spectrum may be sampled to provide a discrete frequency spectrum or pattern for that particular applied load (step S7).

The procedure may be repeated for different applied loads (step S8) and the loads may be varied within 2 calibration process so that frequency spectra representing the response of the sensor to a varying load may also be stored. Once all of the required characteristic spectra have been obtained for a given sensor, the process may be repeated for each of the other sensors coupled to the processing apparatus so that a plurality of frequency spectra characteristic of the response of each sensor to a given force is stored in the RAM 11. In practice, the processing apparatus will scan the channels for the various sensors to determine their current state on, for example, a differential basis with the processing unit reading the signal when it exceeds a given level. The force being measured may be bending or deformation (radial or longitudinal, i.e. stretching) forces, dependent upon the intended use and actual structure of the sensor. Where a sensor is to be used for measuring curvature rather than applied force, then a procedure similar to that shown in Figure 17 may be used with the applied force being replaced by a bending angle. The bending angle need not be symmetric throughout the length of the sensor but may vary along its length so that the characteristic spectra for different forms of bending of the sensor can be stored.

Where the sensors are provided in items of clothing to be worn by a particular person, then the sensors may be calibrated in situ on that person by, for example, a trainer or physiotherapist deliberately placing the appropriate body parts of the user into the required orientations and/or causing the required force to be applied to its body part to obtain the necessary characteristic signals. For example, the trainer or physiotherapist could cause the person being monitored to execute a task correctly and also to carry out the task incorrectly so that excessive strains are placed on joints or ligaments. Both sets of resulting frequency spectra would then be stored each in association with a reference indicating whether or not the body positions or force exerted by the user during the carrying out of a task were correct.

Once the sensors have been calibrated, then the processing apparatus may be used to monitor the output from each of the sensors coupled to the apparatus, for example in the manner illustrated by Figure 20. Thus, when the user instructs the processing unit 10 via the mouse 15b or keyboard 15a to commence a measurement cycle, the processor reads the digitised stored signals from each of the sensors at the interval ti (step S10 in Figure 20) and stores the resulting set of signals V(ti) (step S11). The processing unit then converts the stored signals V(ti) to the frequency domain using the same fast Fourier transform at step S11 and stores the frequency spectrum characteristics at step S13 in the RAM 11 in the same manner as described with reference to steps S6 and S7 of Figure 17.

The processing unit 10 then compares the measured spectrum with the previously stored calibrated spectra at step S14 and if a match is identified at step S15, outputs (step S16) the measured data to be displayed (or printed) together with, as indicated above, an appropriate indication such as an alarm sound when the output of the sensor indicates an optimum response or indicates that an excessively high strain has been placed on a particular joint or ligament. The output data for each of the sensors may be displayed on, for example, a representation of the human body showing the locations of the sensors and marking the locations in, for example, red if a joint or ligament is being overstressed or a person is bending incorrectly and in green if the force or bending measured by a particular sensor is within an acceptable range.

If the data for a particular sensor does not match any of the stored spectra, then the processing unit may simply cause the monitor to display the information and indicate that no match can be found (step S17). The user of the apparatus will then need to look at the particular output from the sensor in detail or may request the person being monitored to execute the desired task again until a match can be found.

As mentioned above, one area in which sensors embodying the invention may be used is in the monitoring of the stresses and strains arising during a sporting activity to reduce the risk of injury. One sport in which the risk of injury is of great concern is rugby.

In particular, there is great concern over the number of neck and other serious injuries which can occur when a scrum collapses and which can lead to tetraplegia.

In a rugby scrummage the players' torsos are nearly parallel to the ground, with their legs bent underneath and their heads tucked downwards. Players are bound together by interlinking the arms and applying pressure through the shoulders. A coach's primary aim in teaching players correct scrummaging technique is to ensure that the forces applied are along the shoulder rather than above or below with, in a perfect scrummage, all forces being slightly upwards and equally proportioned at the front of the scrummage. If the forces are above or below the line of the shoulder, rotational movement will occur and the scrum will collapse. If the force is directed too far upwardly, the scrum will collapse upwardly which may cause injury. If, however, the force is directed too far downwardly, a downwards collapse will occur which can result in serious, sometimes fatal, neck and spine injuries.

Conventionally, a coach trains players in scrummaging technique by using sufficient players to form a half scrummage and a scrummaging machine. The coach has, however, to rely on visual information to determine whether the players are adopting a correct scrummaging technique and it is difficult even for an expert coach to visually monitor the performance of each of the individual members of the path scrum. Furthermore, this arrangement provides no information whatsoever about the forces involved in the scrummage.

Figure 20 shows schematically part of one of the players P shown in the scrummage of Figure 19 wearing a shoulder pad 30 embodying the present invention.

Although not shown in Figure 20, the shoulder pad may be secured to the clothing of the player by velcro (trade mark), tapes or similar fastening means. Alternatively, the shoulder pads may be fitted in an upper body harness worn by the player so as to inhibit movement of the shoulder pad.

Figure 22a is a plan view of a shoulder pad 30 embodying the present invention while Figure 22b is a part-sectional view along the line X-x in figure 22a.

The shoulder pad may be a modified commercially available shoulder pad such as, for example, the rhinopad rugby shoulder pad supplied by Cartasport Leisure Ltd.

of Keighley, West Yorkshire, England, UK and, in this example, comprises outer layers 31a and 31c formed of, for example, foam rubber or plastic sandwiching an inner layer 31c formed of a hard plastics material. The layer 31a which is outermost in use is formed with a number (5 as shown) of elongate apertures 3ld extending generally parallel to a line SL which will lie along the top of the shoulder in use of the shoulder pad. Sensors 1 of the type described above with reference to Figure 1 are mounted to the inner layer 3lb so as to extend in the apertures 31d. The circuitry shown in Figure 2 which is associated with each sensor is mounted to a PCB board which can be attached to the underneath side of the inner layer 31b. The output lines V from each of the sensor circuit boards extend through the centre of the shoulder pad and are coupled to a ribbon cable 32 for connection to processing means which will be described below.

The shoulder can be modelled simply as a part of a cylinder of radius or with a length 1 along the shoulder enabling the contact area between binding players to be assessed. What is generally required in practice is that the binding force at shoulder level against the player in front should be upwards at an angle of about 380 upwards from the horizontal.

Experiments with load sensitive paper have also enabled the areas of force and where the important loads were placed during a scrum to be identified. The two points of maximum force during a scrum were determined to be at either side of the midline SL through the shoulder 1 on the acromion or point of the shoulder blade and one on the trapezius muscle. Other important areas are the centre ridge of the shoulder, the area past the clavicle at the front of the shoulder and the area past the spine of the scapula at the rear of the shoulder.

The shoulder pad shown in Figure 22a has five rows of sensors one extending parallel to the shoulder line SL. Each sensor is approximately 40mm long and the sensors are spaced apart by approximately 15mm (between their centre lines) with two sensors SE6 and SE7 being provided on the chest side of the shoulder pad and three sensors SE3 to SE5 on the back side of the shoulder pad.

The sensor SE6 is located at the optimum point for contact with the player in front, that is where, on the simple cylinder model, the angle between the horizontal and the radius of the cylinder extending through the sensor SE6 is approximately 38". The sensor SE7 indicates a position where the force is directed too far in an upwardly direction while the sensors SE5 to SE3 are arranged to indicate a progressively increasing downwards force which is too great. In addition to the sensors arranged parallel to the shoulder line further sensors SEl and SE2 are arranged to extend perpendicular to the shoulder line. These sensors SEl and SE2 may have their innermost ends spaced from the closest laterally arranged sensor by about 15mm. The sensor SEl may have a length of about 40mm and the sensor SE2 a length of about 30mm.

The sensor SE1 is located in the area where a contact force would cause a downward pressure to collapse the scrum and the sensor SE2 is indicated in the area where an upward force would cause an upward collapse of the scrum.

The sensors may have length longer or shorter than 40mm although if the length is greater than about, for example, 140mm, then the attenuation along the tube may result in significant loss of signal. This can be avoided by providing shorter sensors coupled together by amplifiers or repeater stations or by providing a reflective inner coating on the tube so as to reduce attenuation or absorption of light along the tube. In addition or alternatively a more intense light source or multiple light sources may be used.

Fewer than five rows of laterally arranged sensors may be provided although this will give a less accurate measurement of the contact angle. Alternatively of course, a larger number of lateral rows of sensors may be provided although a minimum separation of about 2-3mm will be required because of the size of the contact area between binding players. Also, the sensors SE1 and SE2 may be supplemented by further sensors arranged in parallel thereto so as to increase the area over which a dangerous contact force can be detected. In addition, each of the sensors 1 may be divided into a number of separate individual sensors so as to enable, for example, variations in force along the contact area to be determined so as to assess whether, for example, a turning force is being applied between the binding players.

Generally, the sensors SE1 and SE2 will be used as threshold sensors to provide a digital output giving a high signal when a contact force above a predetermined value is detected by that sensor. In this example the threshold voltage is selected to be that which results when a force of 3kg is applied over half the area of the sensor. The threshold detection may be achieved by, for example, using a circuit similar to that shown in Figure 17b. The buzzer or warning device shown in Figure 17b may be, for example, mounted on the shoulder pad so that the player is given an immediate warning that his position is potentially dangerous. A remote link, for example by radio or infrared, may be provided to the coach so as to ensure that the coach also receives a reliable warning that dangerous forces are being applied within the scrum.

The sensors SE3 to SE7 will generally be used to measure the actual force (i.e. the force magnitude) being applied at the contact area. However, these sensors could also simply be used as threshold sensors.

Outputs V from the circuits 60 of the sensors 1 are supplied to processing apparatus 9a shown schematically by the block diagram in Figure 23. Initially, each of the output signals V from the sensors being used to determine the actual force magnitude is supplied to a respective DC offset amplifier DC1 to DCN. The outputs of the respective DC offset amplifiers are supplied to conventional gain amplifiers GAl to GAN. This ensures that the output signals from the sensors to be processed all lie in the range 0-5 volts enabling, for example, changing of sensors.

Where a sensor 1 is being used just to determine whether or not a force is actually being applied to a particular area of the shoulder pad, then the output V is supplied to a respective threshold circuit TH1 to THN which provides a high output when the voltage V exceeds a predetermined value and a low output when the voltage V is below that value. The DC offset and gain amplifier for a given sensor may be provided on the same printed circuit board as the circuit 60 shown in Figure 2.

Similarly, the threshold circuit THI for a particular sensor may be provided on the circuit board carrying the circuit 60 associated with that sensor. In this example, the output leads Al to AN for a given shoulder pad and the digital signals D1 to D for the same shoulder pad are supplied to respective time multiplexing multiplexers MUX1 and MUX2 via the ribbon cable 32. Each of the shoulder pads would thus provide an analogue multiplexed output AM1 and a digital multiplexed output DM1. The analogue and digital multiplexed outputs AM1 and DM1 from each of the shoulder pads are supplied to a conventional personal computer which may be, for example, a pentium personal computer having, as noted with reference to Figure 18, a main processing unit or mother board 10, RAM 11, ROM 12, hard disc drive, a floppy disc or CD ROM drive 14, user input devices in the form of a keyboard 15a and a mouse 15b, a monitor 16 for displaying data and instructions to the coach and possibly optionally also a printer 17 for providing a hard copy of data. The computer may also have a remote communication device such as a modem or infrared port 18 for enabling data to be transferred to another personal computer, for example.

The analogue multiplexed signals AMX from each shoulder pad are supplied to an analogue input/output interface IN1 of the computer which includes an analogue-to-digital converter 18 for converting the analogue multiplex signals into digital signals. If, as in the present case, only one analogue-to-digital converter 18 is available, then the multiplexed analogue signals AM1 to AMi from the respective shoulder pads may be further multiplexed by an additional multiplexer MUX3 before supply to the A/D converter. Alternatively, separate A/D converters may be provided for the output from each of the multiplexers MUX1. This would, in the case of a half scrummage require, of course, sixteen analogue-to-digital converters 18, one for each shoulder pad of the eight players.

The analogue-to-digital converter used may, for example, be that provided by the sound card which is usually present in a personal computer.

The digital multiplex signals DM1 to DMn from each shoulder pad are supplied to a digital input/output interface IN2 of the computer. A thirty-two input interface card IN2 may be used allowing two digital inputs from each shoulder pad to be input in parallel to the input/output card IN2. If fewer inputs are available or greater than two digital signals from each shoulder pad are required, then a further multiplexer (not shown) may be provided to multiplex the outputs DM1 to DMM from each of the shoulder pads before supply to the interface card IN2. The outputs from the interface cards IN1 and IN2 are supplied to the computer RAM 11. All of the mutliplexers, the interface cards IN1 and IN2 and the RAM 11 are clocked under the control of the processing unit 10 with the interface cards operating on a conventional interrupt basis.

Data from each of the sensors and load cells associated with each shoulder pad may thus be stored in the RAM 11 of the processing unit 10.

In the example described above, the shoulder pads are connected via flexible cables to the computer with the multiplexers MUX1 and MUX2 and the multiplexer MUX3 if required being provided in, for example, a card within the computer or a separate box. As an alternative, a remote telemetry connection between the shoulder pads and the computer may be provided. In such a case, the multiplexers MUXl and MUX2 associated with each shoulder pad and an appropriate transmitter will be provided in a package which may be located in a belt worn by the player or, if space provides, within the actual shoulder pad itself. Suitable interface cards for receiving the remote telemetry signals would then be provided at the computer. The remote telemetry may be by way of, for example, radio or infrared communication.

The shoulder pads and associated processing apparatus described above may be used to assist a coach in training players in scrummaging techniques where either a full scrum is being trained or a half scrum is being trained using a scrummaging machine.

In use of the system, once the players wearing their shoulder pads have been coupled appropriately to the processing apparatus, the coach can then instruct the players to commence scrummaging practice. Figure 24 illustrates the operation of the processing apparatus during a scrummaging practice. Initially at the start (step S1) the coach instructs the computer to commence monitoring of the signals from the shoulder pads of the players involved in the scrum. The signals from the shoulder pads are read (step S20 in Figure 24) into the RAM 11 under control of the processing unit 10 as discussed above and the processing unit 10 then looks at the signals derived from each shoulder pad in turn to determine whether the correct force is being applied and whether the angle of the shoulder is correct at step S3 by determining which of the sensors SE1 to SE7 is sensing an applied force. The actual angle may be determined by means of a look-up angle which indicates a correct contact angle of approximately 380 if only the sensor SE6 is sensing a contact force and specified other contact angles if only the sensor SE7, SE3, SE4 or SE5 senses the applied force. If more than one of the sensors senses the applied force then the contact angle may be determined by extrapolation weighting the angle towards the angle represented by sensors which is sensing the higher force. The actual contact angle represented by a force applied to a given sensor will be dependent on the physique of the player with, on the simple cylinder model, the radius r varying for different individuals.

A shoulder pad may be specifically designed and tailored for an individual player and a look-up table generated using, for example, a simple cylinder model having a radius and length determined by measurements taken from the player. Alternatively, a range of different shoulder pads may be provided for various different physiques with each shoulder pad being associated with its own look-up table. The latter option would be cheaper but less accurate than the option of individually tailored shoulder pads. Another alternative which will be discussed below is a self-calibration technique which enables the shoulder pad to be calibrated to an individual player so as to allow the contact angles and forces for that individual player to be determined. If the processing unit determines at step S3 that the angle is correct, then the processing unit checks the outputs of the analogue force sensors at step S22 and displays the outputs of the analogue force sensors at step S23.

If the angle is not, however, correct then the processing unit displays the actual force angle at step S24 and will generate an alarm using, for example, the internal sound card of the computer to warn the coach that a dangerously incorrect angle of force has been detected if either of the sensors SE1 or SE2 is providing a signal.

The processing unit then determines at step S25 whether the signals from each of the shoulder pads of each of the players concerned have been read, that is if S equals Spmax. If the answer is yes at step S25, then the processing unit may display all the results for all of the players to the coach at step S26. If, however, the answer is no, then the computer increments a counter at step S27 and reads the signals for the next shoulder pad. This process is then repeated until the outputs from all of the shoulder pads of the players concerned have been read.

The coach may be in communication with each of the players by a radio link enabling him to tell them how to adjust their position to achieve the correct angle when he sees the displayed results.

Although in the examples described above, the outputs from the sensors may be combined in software to provide the force angle, it would also be possible to combine these electronically at the shoulder pad to provide a combined analogue signal. This would have the advantage of reducing the number of signals to be supplied from the shoulder pad to the processing apparatus 9a.

In the example described above, whether or not a player is adopting the correct scrummaging technique or whether there is a danger of the scrummage being collapsed is determined by the information already stored in the computers regarding the desired force angle during the scrummage. However, players vary in size and it may be desirable for the shoulder pads to be calibrated for each of the players involved in the scrummage practice.

Figure 25 illustrates one way in which this may be achieved using the processing unit. Thus, as shown in Figure 25, if the coach instructs the processing unit via the keyboard or mouse that a calibration process is to be executed, then the processing unit first of all at step S30 reads the signals for a first shoulder pad from the memory 11 and then displays those signals at step S31. For example, a graphical display may be provided which gives an indication of the force at each of the sensors and the perceived contact angle based on the look-up table described above. The coach may then physically check the position of the player concerned and determine whether the processing unit's assessment of the signals from the shoulder pad is correct at step S32.

If the information provided by the processing unit regarding the forces applied to the shoulder pad concurs with the coach's view of whether or not the player is performing correctly, then the coach will instruct the processing unit via the keyboard or mouse to accept the data and store it (step S33) as reference optimum data for that particular player. If, however, the coach considers that the processing unit's interpretation of the data provided is not correct, having determining that the player concerned is adopting the correct scrummaging posture, then the coach may adjust the results derived by the processing unit at step S34 and these adjusted results will then be stored at step S33. The processing unit then checks at step S35 whether the calibration procedure is required to be repeated for further shoulder pads and if so repeats the steps S30 to S34 for each further required shoulder pad.

Once all of the desired shoulder pads have been calibrated for the particular players concerned, the end results may be displayed to the coach at step S36.

Although the calibration procedure described above may simply be used to determine that the processing unit's assessment of the angle of the shoulder pad of a particular player is correct, it would also be possible to, once the coach has determined that a particular player is adopting a correct scrummaging technique, for a frequency spectrum characteristic for that player for that correct scrummaging technique to be derived and stored in memory as discussed above with reference to Figure 19. Similarly, other profiles identifying dangerous scrummaging techniques for that particular player may be obtained by appropriately positioning the player and storing the results in memory. Then, during an actual practice session, the results read by the processing unit could be converted to the frequency domain as described above with reference to Figure 20 and compared with the stored spectra to determine whether the player is achieving his optimum position during the scrummage or whether changes are required to avoid, for example, collapse of the scrummage.

As a further technique for calibrating a shoulder pad to an individual player's physique a further sensor 1 shown in dotted lines in Figure 22a may be provided which is responsive only to bending forces (for example it may have the form shown in Figure 5). This sensor may be used to determine the actual radius (on the simple cylinder model) of the particular player's shoulder to enable this to be taken into account when determining the contact angle. Such a sensor if also deformable could double up as a danger zone warning sensor.

The above described shoulder pad uses sensors 1 of the type shown in Figure 1. However, any of the sensors shown in Figures 6, 7, 8, 9, 10, 11, 12, 13 or even 14 or 15 may be used as digital or analogue force measurement devices within the shoulder pads.

Although the use of such sensors is advantageous because they are lightweight and cheap to manufacture, other ways of measuring the forces exerted on the shoulder pad may be used. For example, load cells such as those produced by DS Europe SRL of Milan, Italy may be used throughout the shoulder pad. Such sensors are, however, expensive. As other alternatives, piezoelectric force sensors may be used. Another method of sensing the forces exerted on the shoulder pad may be to use a resistive network using rectangles of resistive foam.

However, it is difficult to interpret from the resulting outputs the distribution of forces.

An alternative form of sensor comprises rows of conductive strips between which is located a conductive loaded rubber which, when sufficiently deformed makes connection between neighbouring conductive strips.

Although simpler to interpret, the cost and robustness of the sensor were not sufficient for the purpose required. Other forms of pressure sensitive devices including keyboard membranes have been tested but found not to be sufficiently rugged for the purpose required.

Although the rugby scrum training system described above provides a computer processing apparatus for processing and monitoring the output signals from the shoulder pads of the players involved in the scrum during coaching, it would be possible to provide a simple system which just provides a warning light or buzzer actually on the shoulder pad of the player or on a scrummaging machine when the player is adopting a dangerous posture.

Such an arrangement may be similar to that described above with reference to, for example, Figure 17b. As another possibility, the output signals from the shoulder pads of the players involved in the scrum may be output simply to a conventional data log for later interpretation by the coach.

Such shoulder pads may be used for training in other similar sports and, as noted above, sensors embodying the invention may be incorporated into other items of clothing such as gloves for using training racket players or rowers, for example. Vests and other similar items of clothing or bands or straps carrying sensors may be used for training athletes or other sports people to adopt a correct posture, especially, for example, to avoid injury to the back.

Straps or bands or the like incorporating sensors embodying the invention may be provided to be worn across joints of the body such as the ankles, wrists, elbows and across the back. Such items of clothing may be used in training systems similar to the one described above for monitoring and correcting the posture of a player during training. Particular sports where such training aids may be useful are, for example, golf, racket sports such as squash, tennis and other popular sports including, for example, martial arts where the particular posture adopted for stances is important. The items of clothing may incorporate, as discussed above with reference to Figure 17b, circuitry which provides an alarm by way of a buzzer or light when the sensor detects that an incorrect posture is adopted. This circuity may be made small enough to be incorporated in a pouch or integrated within the item of clothing. Such circuitry may be modified to enable signals to be given to the wearer when a correct posture is being adopted or to indicate to the wearer the direction in which the posture should be changed so as to correct it. This may be achieved by, for example, using different tone audio signals or different colour lights or an array of lights. Control of these lights may be by way of conventional logic circuitry or, for example, a digital signal processor.

Sensors embodying the invention may be applied directly to the body using, for example, microtape or a skin compatible glue. For example, sensors may be applied directly to the body to measure forces and bending of a sprinter's knee joint. Also, an item of clothing into which the sensors are incorporated may have other uses, for example the sensors may be incorporated into a support bandage such as, for example, an elastic knee wrap.

Sensors embodying the invention may, as noted above, be used in other areas than sport. For example, the sensors and items of clothing or substrates carrying such sensors may be used for rehabilitation to monitor patients during exercises so as to ensure correct posture. Such patients may be, for example, patients recovering from accident or injury or patients requiring corrective therapy to correct a naturally occurring posture defect. Sensors and items carrying sensors embodying the invention may also be used for monitoring for repetitive strain injury during the carrying out of repetitive tasks, for example repetitive tasks such as typing or assembly procedures in factories and also for health and safety monitoring to ensure correct posture such as correct back and knee posture when lifting heavy loads, when example.

Sensors embodying the invention and substrates carrying such sensors may also be used with animals in addition to human beings, for example during rehabilitation of an animal such as a racehorse or during training of competitive animals. Similarly, sensors embodying the invention may be applied to objects subject to applied forces and/or bending. For example, sensors embodying the invention may be applied, either directly or via a substrate, to equipment such as golf clubs and the like to measure the curvature of the club during use.

Claims

1. A sensor comprising: a light emitting device; a light receiving device responsive to light emitted by the light emitting device; and a body defining a passage extending between the light emitting and receiving devices and containing material allowing light emitted by the light emitting device to reach the light receiving device, the walls of the passage and the material within the passage allowing the passage to bend or deform in response to application of a force to the walls of the passage whereby, in use of the sensor, bending or deformation of the passage alters the amount of light emitted from the light emitting device that can be received by the light receiving device.

2. A sensor according to claim 1, wherein the body comprises a tubular member.

3. A sensor according to claim 1, wherein the passage is defined between two sheet-like members forming the body.

4. A sensor according to claim 1, 2 or 3, wherein the body is formed of silicon rubber.

5. A sensor according to claim 1, 2, 3 or 4, wherein the material contained within the passage comprises gas comprising at least one of air or an inert gas such as nitrogen or argon.

6. A sensor according to claim 5, wherein the gas is at a pressure greater than atmospheric pressure.

7. A sensor according to claim any one of claims 1 to 6, wherein the material comprises a liquid or a gel-like material.

8. A sensor according to claim 7, wherein the material comprises liquid paraffin.

9. A sensor according to any one of claims 1 to 8, wherein the material comprises a solid.

10. A sensor according to claim 9, wherein the solid comprises an adhesive such as silicon glue.

11. A sensor according to any one of claims 1 to 10, wherein the material comprises spheres or beads.

12. A sensor according to claim 11, wherein the spheres or beads are comparable in size to the cross-sectional area of the passage.

13. A sensor according to any one of the preceding claims, wherein the walls of the passage are opaque to light emitted by the light emitting device.

14. A sensor according to any one of claims 1 to 12, wherein the internal surface of the passage is light reflective.

15. A sensor according to any one of the preceding claims, wherein the passage is of circular or rectangular cross-section.

16. A sensor according to any one of the preceding claims, wherein the passage is of uniform cross-section throughout its length.

17. A sensor according to any one of claims 1 to 15, wherein the cross-sectional area of the passage varies periodically along its length.

18. A sensor according to any one of the preceding claims, wherein the resistance of the passageway to an applied force is arranged to vary along its length.

19. A sensor according to claim 18, wherein a shaped member is coupled to an outer surface of the passageway to cause the resistance of the passageway to an applied force to vary along its length.

20. A sensor according to any one of the preceding claims, wherein the light emitting device is an infra red light emitting diode and the light receiving device is an infra red photo sensor.

21. A sensor comprising: a hollow tube having first and second ends; a light emitting device received within the first end of the tube; a light receiving device responsive to light emitted by the light emitting device received in the second end of the tube, the tube containing material allowing light emitted by the light emitting device to reach the light receiving device, the tube and the material within the tube allowing the tube to bend or deform in response to application of a force to the tube whereby, in use of the sensor, bending or deformation of the passage alters the amount of light emitted from the light emitting device that can be received by the light receiving device.

22. A sensor comprising: a first substrate; a track of material deposited onto the first substrate; a second substrate provided on the first substrate so that the first and second substrates define a tube enclosing the track; a light emitting device and a light receiving device responsive to light emitted by the light emitting device mounted to one of the first and second substrates at opposite ends of the track, the track providing a passage allowing light emitted from a light emitting face of the light emitting device to be received by a light receiving face of the light receiving device, the substrates and passage being arranged to bend or deform in response to application of a force to the passage whereby, in use of the sensor, such bending or deformation alters the amount of light emitted from the light emitting device that can be received by the light receiving device.

23. A sensor according to any one of the preceding claims, further comprising means for deriving from the light receiving device a signal representing the force applied to the sensor or the bending of the passage between the light emitting and receiving devices.

24. A sensor comprising: a tubular body deformable by stretching along its length, at least a portion of a surface of the tubular body being electrically conductive with at least one electrical property of the electrically conductive portion changing with deformation of the body, thereby enabling a force resulting in stretching of the tube to be determined by measurement of said at least one electrical property.

25. A sensor comprising: a light emitting device; a light receiving device responsive to light emitted by the light emitting device; and a body defining a passage extending between the light emitting and receiving devices and containing material allowing light emitted by the light emitting device to reach the light receiving device, the walls of the passage and the material within the passage allowing the passage to bend or deform in response to application of a force to the walls of the passage, one end of the passageway being coupled to a first arm and the other end of the passageway being coupled to a second arm with the first and second arms being movable relative to one another so as to cause bending or deformation of the passage for altering the amount of light emitted from the light emitting device that can be received by the light receiving device.

26. A sensor matrix comprising a plurality of sensors in accordance with any one of the preceding claims arranged on a substrate.

27. A sensor matrix according to claim 26, wherein the sensors are arranged to define a regular matrix of rows and columns of sensors and means are provided for determining the location of the application of a force to the matrix from output signals provided by at least one row and one column sensor.

28. A sensing device comprising a substrate carrying at least one sensor in accordance with any one of claims 1 to 25 or a sensor matrix in accordance with claim 26 or 27, adapted to be fixed to a part of a body at which an applied force or degree of bending is to be measured.

29. An item of clothing incorporating at least one sensor in accordance with any one of claims 1 to 25 or a sensor matrix in accordance with claim 26 or 27 positioned so as to cause bending or deformation of the or at least one sensor during the carrying out of a task or performance of a given action by a wearer.

30. An item of clothing comprising: a first substrate; at least one passage defined on the first substrate by material deposited thereon; a second substrate provided on the first substrate so that the first and second substrates define a or a respective tube enclosing the or each passage; a respective light emitting device and an associated light receiving device responsive to light emitted by the light emitting device mounted to one of the first and second substrates at opposite ends of the or each passage to form a sensor, the passage being arranged to allow light from a light emitting face of the light emitting device to be received by a light receiving face of the light receiving device the substrates and passage being arranged so that when the item of clothing is worn by a user the passage bends or deforms during the carrying out of a task or performance of a given action by the user with such bending or deformation altering the amount of light emitted from the light emitting device that can be received by the light receiving device.

31. An item of clothing according to claim 29 or 30, further comprising means for providing an indication when an output of the sensor exceeds a predetermined level.

32. A device for measuring the forces applied to or bending of a body comprising a sensing device in accordance with claim 28 or an item of clothing in accordance with claim 29 or 30.

33. A device according to claim 32, wherein the item of clothing is a shoulder pad.

34. A device for sensing forces exerted in the shoulder area of a player during a rugby scrummage, comprising a substrate carrying one or more force-responsive sensors, the substrate being arranged to be secured to the shoulder of the player.

35. A device for sensing forces exerted in the shoulder area of a player during a rugby scrummage, comprising a substrate carrying a plurality of sensors arranged to lie transverse, for example substantially perpendicular, to a shoulder line of the substrate which shoulder line lies along the top of the shoulder during use of the device, with at least one of the plurality of sensors being provided at a first area of the substrate which would rest on a region of the back of the shoulder in use and at least one being provided at a second area of the substrate which would rest on a region of the front of the shoulder in use, the regions of the front and back of the shoulder area being regions where a contact force during a rugby scrum may cause collapse of the scrum.

36. A device according to claim 35, further comprising a further plurality of sensors arranged to lie substantially parallel to one another and to the shoulder line of the substrate, the sensors of the further plurality being spaced apart in a direction perpendicular to the shoulder line with at least one sensor being provided on each side of the shoulder line.

37. A device according to claim 34, 35 or 36, wherein the or at least some of the sensors are sensors as claimed in any one of claims 1 to 25.

38. A device according to any one of claims 34 to 37, wherein the substrate comprises a shoulder pad.

39. Apparatus for monitoring forces applied to a body for use with a device in accordance with any one of claims 32 to 38, comprising means for determining when an output signal of the or one of the sensors reaches a predetermined level or lies within a predetermined range and means for providing a warning signal or indication when the predetermined level or range is reached.

40. Apparatus according to claim 39, wherein the means for determining when a sensed force reaches a predetermined level or lies within a predetermined range comprises means for comparing the sensed force with a reference.

41. Apparatus according to claims 39 or 40, which comprises means for comparing signals derived from the sensor or sensors with information stored in a look-up table to determine information regarding the applied force.

42. Apparatus according to claim 41, further comprising means for obtaining the reference by calibrating the or each sensor by using the response of the sensor(s) to a predetermined applied force.

43. Apparatus according to claim 42, further comprising means for converting the reference signals to the frequency domain and storing the reference as a frequency spectrum and means for converting the sensed signal to the frequency domain to provide a sensed frequency spectrum, the comparing means being arranged to compare the sensed and reference frequency spectra.

44. Apparatus according to any one of claims 39 to 43 adapted to receive output signals from the sensors of a plurality of devices in accordance with any one of claims 32 to 38, for example devices worn by members of a rugby scrum during a scrum, and to provide output signals representing the forces sensed by the sensors of the devices and/or to provide an indication when a sensed force or forces reach(es) the predetermined level or lies within a predetermined range.

45. A rugby training system comprising a device for sensing the forces exerted on at least one player and means for processing a signal output by the device to determine whether the player is performing correctly or is susceptible to possible injuries.

46. Any combination of any of the features recited in any of the preceding claims.

47. A sensor substantially as hereinbefore described with reference to Figures 1 to 16b of the accompanying drawings.

48. An item of clothing substantially as hereinbefore described with reference to Figures 17a and 17b or Figures 21, 22a and 22b of the accompanying drawings.

49. A shoulder pad substantially as hereinbefore described with reference to Figures 20, 21a and 21b of the accompanying drawings.

50. A processing apparatus substantially as hereinbefore described with reference to Figures 18 to 20 or 23 to 26 of the accompanying drawings.