SENSOR APPARATUS FOR A COMPRESSION GARMENT

Abstract

A sensor apparatus includes a sensor device (2), for attaching to an outer surface of a compression garment (1), and a controller. The sensor device (2) comprises a first mounting point (70), attached to a first point on the garment (1), and a second mounting point (45), attached to a second point on the garment (1). The sensor device (2) senses displacement between the first (70) and second mounting points (45). The controller processes information representative of the sensed displacement to estimate a pressure exerted by the compression garment (1) on a wearer of the garment (1).

Claims

1. A sensor apparatus comprising a sensor device, for attaching to an outer surface of a compression garment, and a controller, wherein the sensor device comprises: a first mounting point for attaching to a first point on the outer surface of the compression garment; and a second mounting point for attaching to a second point on the outer surface of the compression garment, wherein the sensor device is arranged to sense displacement between the first and second mounting points; and wherein the controller is configured to process information representative of the sensed displacement to estimate a pressure exerted by the compression garment on a wearer of the compression garment.

2. The sensor apparatus of claim 1, wherein the sensor device is arranged for non-destructively detachable attachment to the compression garment.

3. The sensor apparatus of claim 1, wherein the sensor device further comprises a first part and a second part, wherein the first part is moveable relative to the second part, and wherein the first mounting point is on the first part and the second mounting point is on the second part.

4. The sensor apparatus of claim 1, wherein the sensor device is arranged to generate an analogue or digital electronic signal representative of displacement between the first and second mounting points.

5. The sensor apparatus of claim 1, wherein the sensor device further comprises a light-emitting component and a light-receiving transducer.

6. The sensor apparatus of claim 5, wherein the sensor device is configured so that increased displacement between the first and second mounting points causes less light to strike the light-receiving transducer, resulting in a lower output signal from the transducer.

7. The sensor apparatus of claim 5, wherein the sensor device comprises a light-interrupting element configured to progressively occlude an optical path between the light-emitting component and light-receiving transducer in dependence on the displacement between the first and second mounting points.

8. The sensor apparatus of claim 5, wherein the sensor device further comprises an optical fibre extending at least partly between the light-emitting component and the light-receiving transducer.

9. The sensor apparatus of claim 8, wherein the second mounting point is coupled to a point on the optical fibre such that the movement of the second mounting point relative to the first mounting point causes the optical fibre to bend so that opposite ends of the optical fibre are drawn closer together or are pushed further apart.

10. The sensor apparatus of claim 8 wherein the sensor device comprises a first optical fibre and a second optical fibre, wherein the first optical fibre is arranged to receive light emitted from the light-emitting component and to transmit the light to the second optical fibre, and wherein the sensor device is configured so that increased displacement between the first and second mounting points causes a relative lateral movement between a light-emitting end of the first optical fibre and a light-receiving end of the second optical fibre such that less light is transmitted from the first optical fibre to the second optical fibre.

11. The sensor apparatus of claim 1, wherein the sensor device further comprises a first capacitor plate coupled to the first point, and a second capacitor plate coupled to the second point, for providing a variable capacitance between the first and second capacitor plates, wherein the sensor device is configured to use the variable capacitance between the first and second capacitor plates to sense displacement between the first and second mounting points.

12. The sensor apparatus of claim 1, wherein the sensor device is configured to use a variable resistance, or a variable magnetic field, or a variable electric field, to sense displacement between the first and second mounting points.

13. The sensor apparatus of claim 1, comprising a biasing member arranged to resist a displacement between the first mounting point and the second mounting point.

14. The sensor apparatus of claim 1, wherein the controller is configured to use the information representative of displacement to determine a tension force in the compression garment.

15. (canceled)

16. The sensor apparatus of claim 1, wherein the controller is configured to calculate an estimated pressure exerted by the compression garment on a wearer of the compression garment by: determining a relative or absolute displacement value from the information representative of the sensed displacement; determining a relative or absolute tension force value from the information representative of the sensed displacement; calculating the estimated pressure by dividing the determined tension force value by a linear function of the determined displacement value.

17. The sensor apparatus of claim 16, wherein the linear function is the sum of a first constant and a product, wherein the product is the product of a second constant and the determined displacement value, and wherein the first constant is equal to the circumference of the compression garment in an un-stretched state.

18. (canceled)

19. The sensor apparatus of claim 1, wherein the controller comprises a microcontroller for executing software instructions and/or comprises dedicated hardware circuitry, and is configured to use the microcontroller or dedicated hardware circuitry to process the information representative of the displacement to estimate the pressure exerted by the compression garment on a wearer of the compression garment.

20. (canceled)

21. The sensor apparatus of claim 1, wherein the controller is configured to log data representative of the displacement and/or pressure exerted on a wearer of the compression garment over time.

22. A compression garment apparatus comprising a compression garment and a sensor apparatus as claimed in claim 1, wherein the sensor device of the sensor apparatus is attached to an outer surface of the compression garment.

23. The compression garment apparatus of claim 22, wherein the first mounting point and the second mounting point of the sensor device are attached to the compression garment using a mechanical fastener, such as one or more hook-and-loop pads.

24. (canceled)

25. The compression garment apparatus of claim 22, comprising one or more further sensor devices, each further sensor device comprising: a respective first mounting point for attaching to a respective first point on the outer surface of the compression garment; and a respective second mounting point for attaching to a respective second point on the outer surface of the compression garment, wherein each further sensor device is arranged to sense displacement between the respective first and second mounting points; and wherein the controller is configured to determine a rate of blood flow or a change in muscle volume from the respective sensed displacements.

26. A method comprising applying a compression garment and a sensor device of a compression garment apparatus to a person or animal, wherein: the compression garment apparatus comprises the compression garment and a sensor apparatus, wherein the sensor apparatus comprises a sensor device attached to an outer surface of the compression garment, and a controller; the sensor device comprises a first mounting point, attached to a first point on the outer surface of the compression garment, and a second mounting point attached to a second point on the outer surface of the compression garment; the sensor device is arranged to sense displacement between the first and second mounting points; and the controller is configured to process information representative of the sensed displacement to estimate a pressure exerted by the compression garment on the person or animal.

27. The method of claim 26, comprising using the sensor device to sense displacement between the first and second mounting points, and comprising the controller processing information representative of the sensed displacement, received by the controller from the sensor device, to estimate a pressure exerted by the compression garment on the person or animal

28. The method of claim 26, further comprising using the sensor device to sense a first displacement before the compression garment is applied to the person or animal, and using the sensor device to sense a second displacement after the compression garment has been applied to the person or animal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0100] FIG. 1 is a perspective view of a pressure sensor device according to an embodiment of the present invention;

[0101] FIGS. 2a-d are cross-sectional front and plan views of the pressure sensor device of FIG. 1;

[0102] FIG. 3 is a schematic cross section showing the change in circumference of a garment when stretched;

[0103] FIGS. 4a-d are cross-sectional front and plan views of a pressure sensor device according to a further embodiment of the present invention, in un-stretched and stretched states;

[0104] FIGS. 5a and 5b are plan views of a pressure sensor device according to a further embodiment of the present invention, in un-stretched and stretched states;

[0105] FIGS. 6a and 6b are plan views of a pressure sensor device according to a further embodiment of the present invention, in un-stretched and stretched states;

[0106] FIG. 7 is a schematic view of a pressure sensor device according to a further embodiment of the present invention;

[0107] FIG. 8 is a semi-schematic side perspective view of an exemplary arrangement of sensor devices according to an embodiment of the present invention on a compression stocking worn by a human;

[0108] FIG. 9 is a semi-schematic perspective view of a further exemplary arrangement of sensor devices according to an embodiment of the present invention on a compression sleeve in order to determine the volume of blood flow into a human organ;

[0109] FIG. 10 is a perspective view of an electronic control and power supply unit for use with embodiments of the invention;

[0110] FIG. 11 is a rear view of a further exemplary arrangement of a sensor device according to an embodiment of the present invention on a nappy in order to determine an indication of the fullness of the nappy; and

[0111] FIGS. 12a-d are cross-sectional front and plan views of a pressure sensor device according to a further embodiment of the present invention, in un-stretched and stretched states.

DETAILED DESCRIPTION

[0112] FIG. 1 shows a compression garment apparatus according to an embodiment of the present invention. The apparatus comprises a compression garment 1 and a sensor device 2. The sensor device 2 comprises a plastic housing 70 and a stud 45. The plastic housing 70 and the stud 45 are affixed to different respective points (i.e. a first mounting point and a second mounting point respectively) on the outer surface of the compression garment 1 (i.e. the surface that faces away from the wearer when the garment is worn). The fastening may be achieved using hook-and-loop fastening pads, adhesive, stitching, riveting, or any other suitable mechanism.

[0113] The apparatus also comprises an electronic controller (not shown), such as the electronic control and power supply unit described below with reference to FIG. 10, which may be at least partly contained within the housing 70, or which may be separate from the housing 70 and stud 45 (e.g. connected by an electrical cable).

[0114] A light-emitting diode (LED) 6 is mounted on the plastic housing 70, opposite a photodetector 140, which is also mounted on the plastic housing 70. A first rigid tube 10 and a second rigid tube 100 are mounted rigidly on the plastic housing 70, along respective portions of a path between the LED 6 and the photodetector 140.

[0115] An optical fibre 50 extends through the first and second tubes 10, 100, with a first end adjacent the LED 6 and a second end adjacent the photodetector 140, so as to direct light produced by the LED 6 to the photodetector 140. The optical fibre has an outer diameter in the region of 0.25 mm-1 mm. The first 10 and second tubes 100 each have an outer diameter of up to 2 mm and an inner diameter very slightly (e.g. between 0.05 mm and 0.2 mm) larger than the outer diameter of the optical fibre 50. The first 10 and second tubes 100 may be constructed from metal, ceramic, glass or plastic. The photodetector 140 is arranged to generate an electrical output signal corresponding to the amount of light it receives from the LED 6, through the optical fibre 50.

[0116] The first end of the optical fibre 50 is fixed to the front of the LED 6 (e.g. to a lens of the LED 6), while the second end of the optical fibre 50 is located at a distance 120 from the front of the photodetector 140 (e.g. spaced around 2 mm away). The second end of the optical fibre 50 is not fixed and is free to move longitudinally through the second tube 100. In other embodiments, the first end of the optical fibre 50 may instead be fixed adjacent the front of the photodetector 140 and the second end of the optical fibre 50 may be located adjacent the LED 6 but free to move longitudinally within the first tube 10.

[0117] A central portion of the optical fibre 50 is not contained within either the first tube 10 or the second tube 100. This exposed central region is approximately 10 mm in length. The first 10 and second tubes 100 are used to encase the optical fibre 50 and restrain it from lateral movement, apart from in the exposed central portion of the optical fibre 50.

[0118] A thread 56 comprises a first end and a second end. The first end of the thread 56 is attached to the stud 45 and the second end of the thread 56 is attached to the central portion of the optical fibre 50 that is not covered by either the first tube 10 or the second tube 100, approximately centrally between the first and second tubes 10, 100.

[0119] A device 2 further comprises a spring 65 having a first end and a second end. The first and second ends of the spring 65 are attached to the housing 70 adjacent the LED 6 and the photodetector 140 respectively, such that the spring 65 extends parallel to the optical fibre 50. The spring 65 is linked to the central portion of the optical fibre 50 by the second end of the thread 56.

[0120] The housing 70 further comprises locator studs 35, 82 for connecting a protective casing (not shown) around the optical fibre 50, LED 6, spring 65 and photodetector 140.

[0121] FIGS. 2a and 2b respectively show cross-sectional front and plan views of the device 2 of FIG. 1 when the compression garment 1 is in a slack state—i.e. before stretching of the garment 1 over a patient's body.

[0122] In use, the stud 45 and housing 70 of the sensor device 2 are attached to the compression garment 1, with the thread 56 minimally taut, before the assembled compression garment apparatus is put on the wearer. In this state, the wire spring 65 is also minimally taut and thus exerts a zero or minimal biasing force on the thread 56 and the optical fibre 50. Typically, the stud 45 will be circumferentially displaced from the housing 70, so that the sensor measures circumferential displacement (e.g. displacement around a limb of the wearer). Before the garment 1 is applied, power is supplied to the device 2 (from an internal or external power supply such as a battery), causing light from the LED to pass through the optical fibre 50 to the photodetector 140, with the optical fibre 50 following a straight path. The photodetector 140 produces an output signal that corresponds to an un-stretched state of the garment 1. The garment 1 is then applied to the wearer.

[0123] The garment 1 is stretched once it is put on the wearer, and so the distance between the stud 45 and the housing 70 increases, causing the thread 56 to pull the exposed central portion of the optical fibre 50 in the direction of the stud 45. This causes the distance 120 between the second end of the optical fibre 50 and the photodetector 140 to increase. This increase in distance 120 reduces the amount of light received by the photodetector 140 from the LED 6 via the optical fibre 50. The proportion of the emitted light that strikes the photodetector 140 reduces with increasing distance. Therefore, the electrical output signal produced by the photodetector 140 is lower once the garment 1 is fitted than when it was slack.

[0124] The movement of the stud 45 away from the housing 70 also causes the thread 56 to pull the central portion of the spring 65 in the direction of the stud 45, thus causing the spring 65 to extend. As a result of this extension, the spring 65 exerts a biasing force on the optical fibre 50 and the stud 45 via the thread 56. This biasing force acts against the tension in the thread 56, tending to restore the position of the stud 45 and the optical fibre 50 to the initial “un-stretched” position shown in FIGS. 2a and 2b. This biasing force helps to reduce the effects of hysteresis in the fibre when the garment is stretched and un-stretched repeatedly—e.g. when the garment 1 is repeatedly taken on and off.

[0125] If the stretch in the garment 1 is reduced, the separation between the stud 45 and the housing decreases, allowing the optical fibre 50 to extend towards the photodetector 140, thus reducing the distance 120 between the second end of the optical fibre 50 and the photodetector 140. This increases the amount of light received by the photodetector 140 from the LED 6 via the optical fibre. Therefore, the output signal produced by the photodetector 140 increases in this situation.

[0126] FIGS. 2c and 2d respectively show cross-sectional front and plan views of the device 2 with the garment 1 in a stretched state. As can be seen, the increase in the distance between the stud 45 and the housing 70 causes the thread 56 to pull on the exposed central portion of the optical fibre 50 and the central portion of the spring 65 such that the optical fibre 50 and the spring 65 deflect. The initial (un-stretched) position of the optical fibre 50 is shown by a semi-dashed line in FIG. 2d. This deflection in the optical fibre 50 results in a change in the distance 120 between the second end of the optical fibre 50 and the photodetector 140, from d.sub.1 in a slack state, to a larger value, d.sub.2, in the stretched state. As described above, while in the stretched state shown in FIGS. 2c and 2d, the spring 65 exerts a biasing force on the fibre 50 and the thread 56 that helps to restore the stud 45 and the fibre 50 to their original (un-stretched) positions once stretching of the garment is relaxed.

[0127] The change in distance 120 depends on the properties of the material from which the compression garment 1 is made, and on the properties of the optical fibre 50. The deflection of the optical fibre 50 in the exposed region in the direction of stretch is expressed analytically by the following equation:

[00001] $\begin{matrix} δ_{\max} = \frac{(F L^{3})}{48 EI} & (1) \end{matrix}$

[0128] in which δ.sub.max is the deflection of the fibre 50 in the direction of the stretch, F is the pulling force in the thread 56, L is the length of the exposed central region of the optical fibre 50, E is the Young's Modulus of the material of the optical fibre 50, and I is the moment of inertia of the optical fibre 50.

[0129] When the garment 1 is stretched, the force F (where the force of the spring 65 is considered in the force F) exerted on the optical fibre 50 by the thread 56 increases, thus increasing the deflection δ.sub.max of the fibre 50 according to equation (1). This deflection results in an increase in the distance d.sub.2 between the second end of the optical fibre 50 and the photodetector 140. As the intensity of the light received by the photodetector 140 is proportional to

[00002] $\frac{1}{d_{2}^{2}},$

the electrical output signal produced by the photodetector 140 decreases. Therefore, the electrical output of the photodetector 140 is proportional to the stretch distance δ.sub.max of the garment 1.

[0130] The electronic controller of the device 2 may, in some embodiments, accordingly map the output of the photodetector 140 to a value of stretch distance δ.sub.max, e.g. using a lookup table of empirically determined data stored in a memory of the controller.

[0131] The stretch distance δ.sub.max of the garment 1 is equal to the difference between the initial distance of the stud from the housing x.sub.1 and the distance from the stud to the housing after the garment 1 has been stretched x.sub.2. This difference is also proportional to the change in circumference of the garment 1 from an initial (un-stretched) circumference C.sub.1 to a final (stretched) circumference C.sub.2, and to the tension T in the garment 1 (as shown by the factor F in equation (1) above and by T in equation (2) below).

[0132] The pressure exerted by the compression garment 1 on the body is determined by the well-known Laplace Law:

P=T/r (2)

in which P is the pressure, T is the tension in the garment 1 material, and r is the radius of curvature of the garment. However, the circumference of the garment 1 may be used instead of the radius of curvature. As the tension T is proportional to the stretch distance of the garment 1, the tension T may be determined from the output of the photodetector 140.

[0133] The controller connected to the device 2 may, in some embodiments, map the output of the photodetector 140 to a value of tension T, e.g. using a lookup table of empirically determined data.

[0134] The method for determining an accurate value of compression pressure from the measurements obtained by the sensor device is explained below with reference to FIG. 3.

[0135] The pressure can be calculated by the electronic controller—e.g. using software executed by a processor, or using custom hardware logic such as an FPGA or ASIC. A data logger (not shown) can then record the values of the pressure at intervals. Data may be logged as frequently as required and either displayed in real-time or retrieved via a USB port 1500 (shown in FIG. 10).

[0136] FIG. 3 schematically represents the change in circumference of the compression garment when stretched. The un-stretched garment is represented by a circle 28 and the stretched garment is represented by a larger circle 41. The initial and final circumferences of the garment, before stretching and after stretching, are C.sub.1 and C.sub.2 respectively. The initial circumference C.sub.1 of the garment is typically specified by the manufacturer of the garment. It can be stored as a constant by the controller.

[0137] The circumference C.sub.1, C.sub.2 of each circle 28, 41 has been equally divided into eight arcs. The difference between the length x.sub.1 of an arc 33 of the circle 28 prior to stretching and the length x.sub.2 of the same arc 33 of the circle 41 after stretching is given by Δx=x.sub.2−x.sub.1. Thus, the arc 33 corresponds to a respective displacement between the stud 45 and the plastic housing 70. It will be appreciated that Δx may correspond to an increase or a reduction in distance, depending on whether the amount of stretching of the garment is increasing or decreasing.

[0138] If N.sub.1=C.sub.1/x.sub.1, where N.sub.1 is the number of arcs, and N.sub.1=N.sub.2=C.sub.2/x.sub.2, then C.sub.1/x.sub.1=C.sub.2/x.sub.2. This may be rearranged to

[00003] $C_{2} = \frac{C_{1} x_{2}}{x_{1}} .$

[0139] Furthermore, Δx=x.sub.2−x.sub.1 may be rearranged to give x.sub.2=Δx+x.sub.1.

[0140] Thus:

[00004] $C_{2} = \frac{C_{1} (Δ x + x_{1})}{x_{1}}$ $C_{2} = \frac{C_{1} Δ x}{x_{1}} + C_{1}$ $C_{2} = C_{1} + \frac{C_{1}}{x_{1}} Δ x$ $C_{2} = C_{1} + \frac{C_{1}}{x_{1}} Δ x$ $C_{2} = C_{1} + A Δ x,$

where A is a constant defined by

[00005] $A = \frac{C_{1}}{x_{1}},$

which may be pre-stored in a memory of the controller.

[0141] Consequently, the pressure applied by the garment when stretched is given by the following equation:

[00006] $\begin{matrix} P = \frac{T}{C_{1} + A Δ x} & (3) \end{matrix}$

[0142] Both T and Δx are proportional to the amount of stretch and may be determined from the change in the output signal produced by the photodetector 140 when the garment is stretched. As the change in change in arc length Δx is likely to be very small in comparison to the radius of the garment, Δx may be assumed to be equal to the linear displacement δ.sub.max of the stud from the housing, as discussed above.

[0143] Thus, in order to calculate the pressure P applied by the garment, the controller may calculate a value of tension Tin the garment, and a value of the linear displacement δ.sub.max=Δx of the stud 45 from the housing 70, from the change in the output signal produced by the photodetector 140, e.g. using a lookup table. The controller then calculates the pressure P as the determined tension T divided by a linear function of the determined displacement Δx. It preferably does this by numerically evaluating a function of T and Δx (e.g. using floating point arithmetic operations), but it could determine an approximate pressure estimate by using a multi-dimensional look-up table of pre-calculated pressures for sets of possible values for T and Δx.

[0144] In some embodiments the apparatus may determine a qualitative measure (e.g. a binary determination of whether the garment is sufficiently stretched or not). The controller may compare the calculated pressure estimate against a threshold value, or it could directly compare the voltage output of the photodetector 140 with a predetermined threshold value, to detect when it passes below the threshold, as being indicative of having sufficient tension in the garment. This may be used to provide an indication of whether or not the garment is being (or has been) worn. In other embodiments, (instead of, or as well as, a voltage input), a capacitance, resistance, magnetic field strength or other electrical or optical signal as appropriate may be compared to a predetermined threshold value to determine whether there is sufficient tension in the garment.

[0145] FIGS. 4a and 4b respectively show cross-sectional front and plan views of a sensor device 102 in accordance with an alternative embodiment of the present invention, in which an obscuring element 31 is moved by the stretching of a compression garment (not shown) to interrupt an optical beam.

[0146] In this embodiment, a housing 36 retains a first optical fibre 45, which receives light at a first end from an LED 106, and a second optical fibre 44, arranged coaxially with the first optical fibre 45 such that it receives light, at first end, from a second end of the first optical fibre 45 and outputs the light from a second end to a photodetector 51. An elongate arm 27 is arranged between the second end of the first optical fibre 45 and the first end of the second optical fibre 44. The arm 27 is perpendicular to the shared axis of the first 45 and second optical fibres 44. The arm 27 is arranged to move longitudinally relative to the housing 36. The arm 27 comprises an obscuring element 31, which has a substantially triangular, wedge-shaped cross-section, an end-stop 58 and an extended portion 77. The distal end of the extended portion 77 is fixedly mounted on an anchor block 66.

[0147] The anchor block 66 and the housing 36 are affixed to respective points of the outer surface of a garment, around a circumference of the garment. Prior to the stretching of the garment, they are separated by a distance x.sub.1.

[0148] The housing 36 further comprises a void 41 through which light from the first optical fibre 45 is directed into the second optical fibre 44. The arm 31 is movable relative to the housing 36 between an un-stretched position (shown in FIGS. 4a and 4b) and a stretched position (shown in FIGS. 4c and 4d).

[0149] In the un-stretched position, the obscuring element 31 is arranged to interrupt the beam of light as it passes through the void 41 between the first 45 and second optical fibres 44 to small degree, or not at all. Thus, in this position, the photodetector 51 receives a maximum amount of light from the LED 106.

[0150] FIGS. 4c and 4d respectively show cross-sectional front and plan views respectively of the device 102 of FIGS. 4a and 4b with the garment in the stretched position. The stretch in the garment causes the anchor block 66 and the housing 36 to move apart by a distance δ.sub.max=x.sub.2−x.sub.1 such that the anchor block 66 and the housing 36 are separated by a distance x.sub.2, as shown in FIGS. 4c and 4d.

[0151] In the stretched state, the obscuring element 31 is arranged to interrupt the beam of light between the first 45 and second optical fibres 44 to a greater extent, due to its wedge shape. Thus, in this position, the photodetector 51 receives a lesser amount of light from the LED 106. The photodetector 51 is arranged to produce an electrical output signal that is proportional to the amount of light received from the LED 106.

[0152] A high resolution analogue signal is produced by the photodetector 51. This signal may optionally be converted to a digital signal by an analogue-to-digital converter for display and/or data logging purposes.

[0153] The change in output signal from the photodetector 51 corresponds to the change in circumference of the garment. Therefore, the compression pressure may be determined, and optionally logged by an electronic controller, in a similar way to that described above.

[0154] FIGS. 5a and 5b show cross-sectional views of a pressure sensor device 202 according to an alternative embodiment of the present invention in which an organic photodetector 345 is arranged to detect light emitted from an organic LED 240.

[0155] Organic devices have a very low profile, which is convenient for applications where the devices are arranged on a garment. Furthermore, such devices are inexpensive to manufacture in large quantities.

[0156] In this embodiment, a first end 235 of an elongate organic LED 240 can be fixed to a first region of a compression garment (not shown), and a first end 460 of an elongate organic photodetector 345 can be fixed to a second region of the compression garment, such that the LED 240 and the photodetector 345 are in a side-by-side overlapping arrangement, both oriented parallel with a circumferential direction of the compression garment, and with first ends 235, 460 distal from each other. Stretching of the compression garment thus causes the first end 235 of the organic LED 240 and the first end 460 of the organic photodetector 345 to move apart, reducing the length of overlap.

[0157] The LED 240 is arranged such that an elongate light-emitting portion of the LED 240 is alongside an elongate light-detecting portion of the photodetector 345. Thus, light emitted from this portion of the LED 240 can be received by the photodetector 345. Light emitted from portions of the LED 240 that are not overlapping the light-detecting portion of the photodetector 345 is not detected by the photodetector 345.

[0158] The photodetector 345 is arranged to produce an output signal that is proportional to the amount of light received by the photodetector 345 from the LED 240. As with the other embodiments herein, the sensor device may comprising a casing (not shown) which may shield the photodetector 345 from ambient light.

[0159] FIG. 5a shows the arrangement of the device 202 before the garment is stretched. As can be seen, a region of the LED 240 of initial length x.sub.1 is opposite the photodetector 345. Thus, in FIG. 5a, the photodetector 345 receives incident light from this portion of the LED 240 alone and produces a corresponding output signal.

[0160] FIG. 5b shows the arrangement of the device 202 during stretching of the garment. As can be seen, the region of the LED 240 that is opposite the photodetector 345 has decreased in length to x.sub.2. Thus, the amount of light received by the photodetector 345 from the LED 240 is reduced, in proportion with the displacement of the two ends 235, 460, which means that the photodetector 345 produces a lower output signal.

[0161] Thus, the change in output signal corresponds to a change in circumference of the garment and may therefore be used to determine a compression pressure, as disclosed above.

[0162] In alternative embodiments, the optical elements may be replaced by an inductive or magnetic sensor having appropriate fixed and movable parts where the inductive and magnetic sensing elements may be of a small footprint MEMS (micro electromechanical systems) type.

[0163] FIGS. 6a and 6b show plan views of a pressure sensor device 302 according to an alternative embodiment of the present invention in which a variable capacitor is used to determine the change in circumference of a compression garment after stretching.

[0164] FIG. 6a shows a capacitor comprising a first plate 1250 and a second plate 1470. The capacitor may be a thin film MEMS-type micro-fabricated capacitor. As can be seen in FIG. 6a, the first 1250 and second capacitor plates 1470 comprise a number of interdigitated ‘fingers’, which may be up to 0.2 mm wide. The capacitor plates 1250, 1470 may be around 0.1 mm in thickness and are separated by an initial (un-stretched) distance x.sub.1 of up to 0.1 mm.

[0165] Capacitor plates 1250, 1470 are connected to electronic circuitry (not shown) via arms 235, 1655 that terminate at mounting pads 115, 1757. The electronic circuitry is configured to measure the capacitance of the capacitor. The mounting pads 115, 1757 may be constructed from thin films (which may be deposited, screen printed etc.). Each of the mounting pads 115, 1757 is mounted on a structure (not shown) that can be affixed to the outer surface of a compression garment, e.g. by a detachable hook-and-loop connecting mechanism.

[0166] FIG. 6b shows the device 302 of FIG. 6a after stretching of the garment. As can be seen, the stretching of the garment causes the mounting pads 115, 1757 to move apart, thus causing the capacitor plates 1250, 1470 to move apart such that the distance between the capacitor plates 1250, 1470 increases to x.sub.2.

[0167] The increase in distance between the capacitor plates 1250, 1470 reduces the capacitance of the capacitor that is measured by the electronic circuitry. The capacitance will change in some proportion to the change in circumference of the garment caused by stretching. Therefore, a correlation may be determined between the change in capacitance and the change in circumference of the garment during stretching. Thus, Equation 2 may be used to calculate a compression pressure from a determined change in circumference of the garment, if required.

[0168] FIG. 7 is a schematic view of a sensor device 402 according to an alternative embodiment of the present invention in which a variable resistor 1120 is used to determine the change in circumference of a compression garment.

[0169] The device 402 comprises a first 1155 and second mounting pad 1130 that can be affixed to the outer surface of a compression garment, typically along a circumferential path. The device 402 further comprises a variable resistor 1120, the resistance of which is arranged to vary according to the application of a mechanical load. The variable resistor 1120 may be a strain gauge, conductive polymer, piezoresistive element or similar. The variable resistor 1120 is fixedly connected to the first 1155 and second 1130 mounting pads by a first 1121 and second wire 1119 respectively.

[0170] The variable resistor 1120 is electrically connected to an electronic circuit (e.g. comprising a Wheatstone-Bridge circuit) (not shown) that is arranged to measure the resistance of the variable resistor 1120. The variable resistor 1120 may comprise an inductor, piezoelectric element or similar, that is connected to the electronic circuit such that the strain on the sensing element during stretching of the garment produces a change in the output signal.

[0171] During stretching of the garment, the first mounting pad 1155 is moved away from the second mounting pad 1130. As a result, the first 1121 and second wires 1130 exert a tension on the variable resistor 1120 such that the resistance of the variable resistor 1120 changes. The change in resistance of the variable resistor 1120 is proportional to the tension exerted by the first 1121 and second wires 1130 and is therefore proportional to the amount by which the garment is stretched. Consequently, a change in circumference of the garment may be determined and subsequently used to calculate a compression pressure according to Equation 2.

[0172] FIG. 8 shows an exemplary arrangement of three sensor devices, each embodying the invention, positioned on a compression stocking 815 worn on a leg 800 of a patient. These may communicate with one or more controllers in one or more of the sensor devices, or with a controller that is remote from the sensor devices. The sensor devices and controller(s) may embody a sensor apparatus as disclosed herein.

[0173] Compression stockings 815 have several uses including the management of venous leg ulcers. The compression applied to the leg 800 may be ‘graduated’, meaning that the compression pressure is higher (e.g. 40 mm Hg) at the ankle and is gradually decreased towards the knee (e.g. to 15 mm Hg). If the compression pressure is too high, it may cause problems with the patient's skin. On the other hand, if the compression pressure is too low, the effectiveness of the compression treatment is reduced. Correct application of compression allows faster healing. Therefore, it is important for clinicians to know the amount of compression applied.

[0174] In this example, before the compression stocking 815 is put on the leg 800 of the patient, sensor devices 1120, 1130, 1140 are positioned on the outer surface of the compression stocking 815 at various locations along the length of the stocking 815. The first sensor device 1120 is positioned just above the ankle 806. The second sensor device 1130 is positioned at the mid-calf 820 area. The third sensor device 1140 is positioned just below the knee 840.

[0175] The sensor devices 1120, 1130, 1140 may be used to determine the distribution of pressure over the compression garment 815. The data generated by the sensor devices 1120, 1130, 1140 may then be analysed to establish whether then compression garment is performing as required.

[0176] FIG. 9 shows an exemplary arrangement of sensor devices according to any embodiment of the present invention when positioned on a compression sleeve 720.

[0177] In some circumstances, it may be desirable to measure the swelling of a part of the body. For example, this is required in case of patients suffering from lymphedema. Compression sleeves are used after a surgical procedure to remove trapped fluid from the lymphatic system and reduce swelling. The decrease in swelling in the affected area is used as an indication of the patient's improvement.

[0178] As a further example, athletes may wish to measure the volume change in a body part when performing certain exercises, e.g. to determine muscle growth. The volume change may be related to a change in blood flow to or from the body part or a change in muscle volume.

[0179] FIG. 9 shows an exemplary compression garment 720 that may be worn on, for example, an arm or leg. The compression garment 720 has an upper radius r.sub.1, measured at a distal end of the compression garment 720, a lower radius r.sub.2, measured at a proximal end of the compression garment 720, and a height h.

[0180] The volume (V) contained within the compression garment 720 may be determined according to the equation:

[00007] $\begin{matrix} V = \frac{π}{3} (r_{1}^{2} + r_{1} r_{2} + r_{2}^{2}) h & (4) \end{matrix}$

[0181] A first sensor device 710 is located on the surface of the distal end of the compression garment 720 (e.g. located just below the knee of the wearer). A second sensor device 700 is located on the surface of the proximal end of the compression garment 720 (e.g. located around the ankle of the wearer).

[0182] A change in the lower radius r.sub.2 and the upper radius r.sub.1 caused by a stretching of the compression garment 720 may be determined according to any of the methods discussed above. Thus, Equation 4 may be used to determine a change in volume of the compression garment 720 that corresponds to a change in volume of the body part around which the compression garment 720 is worn.

[0183] For higher accuracy, additional sensor devices may be located at an intermediate locations (e.g. at the mid-calf area). In this case, the above equation would be used multiple times and the results summed to determine the total volume.

[0184] Where multiple sensor devices are used (e.g. between two and twenty) on a single compression garment, the sensor devices may be linked electronically to facilitate the construction of a map of the pressure distribution. The sensor devices may be distributed linearly along the length of the compression garment or around a circumference. Each sensor device may be accessed individually or simultaneously to detect pressure distribution.

[0185] In the case of a muscular volume change, it may also be possible to determine a blood flow rate from the change in volume of the muscle, as the change in volume of a muscle is related to the rate of blood flow in the leg.

[0186] FIG. 10 shows an electronic control and power supply unit 1520 (i.e. a controller) that may be used with any embodiment of the invention. The control and power supply unit 1520 may comprise signal amplifiers, an analogue-to-digital converter, a microcontroller or other processor, memory, a data logger, a wireless transmission (e.g. Bluetooth™) system, discrete or integrated electronic components, FPGAs, DSPs, ASICs, etc. It may have a digital display 1530 which is configured to display instantaneous pressure readings. The electronic control and power supply unit may comprise an audio indicator—e.g. for signalling an alert if the pressure applied by the compression garment is outside a target range—e.g. if the garment is pressing too loosely and/or is pressing too tightly. The entire electronic control and power supply may be contained within a housing of the unit 1520.

[0187] Measurements determined by the sensor device can be captured at intervals and stored in the data logger prior to processing in the microprocessor. Measurements may be taken and recorded in the data logger as frequently as desired—e.g. every minute or every hour. Data from the data logger or the microprocessor may be transmitted by the transmission system to a remote device or server. This may be a smartphone, laptop, pager or other device. The remote device can keep a record of pressure data that can be used for clinical evaluation or performance assessment by athletes.

[0188] This data logging may be used by clinicians to monitor the healing response of an individual under different compression conditions. However, such logging is not essential, and the control unit 1530 may simply provide an instantaneous indication of displacement of the compression garment.

[0189] The control and power supply unit 1520 further comprises a rechargeable coin cell for supplying electrical power to the claimed pressure sensor device and the electrical components of the control and power supply unit 1520. The power supply unit 1520 supplies a voltage of 5V or less. The control and power supply unit 1520 further comprises a USB port 1500 by which data may be retrieved from the data logger.

[0190] The control and power supply unit 1520 may be attached to a garment via adhesive pads, a hook-and-loop connecting mechanism or similar, or it may be integrated into a housing or casing of the sensor device, or it could be connected by a cable and located remotely—e.g. in a pocket of clothing worn by the wearer, or on a bedside trolley.

[0191] Although the above embodiments describe the sensor device of the present invention with regard to uses on a compression garment, where compression forces are relevant, any features of the above-described embodiments can also be applied to embodiments that deduce the expansion of a garment more generally, e.g. expansion of a nappy.

[0192] FIG. 11 shows a sensor device 1602 in accordance with an embodiment of the present invention, attached to the outer surface of a nappy 1600 (diaper) that is being worn by a baby 1604. It will be appreciated that the nappy could instead be worn by an adult.

[0193] The first and second mounting points (not shown) of the sensor device 1602 are attached to respective first and second points on an outer surface of the nappy 1600. These points may be any appropriate distance apart—e.g. around 2 cm apart when the nappy is dry and unsoiled.

[0194] A first displacement between the first and second mounting points is measured before or soon after the nappy 1600 has been put onto the baby 1604, or is preconfigured. This first displacement is representative of the state or stretch in the nappy 1600 when the nappy 1600 is in an unsoiled ‘empty’ state.

[0195] Subsequently, the sensor device 1602 records, at intervals, further measurements of the displacement between the first and second mounting points of the sensor device 1602. Each further measurement of displacement can be compared with the first displacement. If the device 1602 records a displacement measurement that is greater than the first displacement by a predetermined threshold, indicating a significant expansion of the nappy 1602, the device 1602 determines that the nappy 1602 has been filled, e.g. by urine or faeces. Consequently, the device 1602 may be arranged to issue an alert to the parent or guardian of the baby 1604 that the nappy 1600 has been soiled and therefore requires changing—e.g. by sending a radio message to a baby monitor device, or to an app on a phone belonging to the parent or guardian. In some embodiments, more complex processing of the displacement measurement may be performed, e.g. to filter out changes arising due to movement of the baby (e.g. crawling).

[0196] FIGS. 12a and 12b respectively show cross-sectional front and plan views of a sensor device 2002 in accordance with an alternative embodiment of the present invention, in which a light emitting diode (LED) 2041 is connected to a first optical fibre 2051, and a photodetector 2022, connected to a second optical fibre 2030, is arranged to detect light emitted from the LED 2041 through the first optical fibre 2051.

[0197] In this embodiment, the sensor device 2002 comprises a first anchor block 2062 and a second anchor block 2096 that are attached to respective first and second mounting points on an outer surface of a garment 2085, such as a compression stocking or a nappy (diaper), around a circumference of the garment 2085. A rigid elongate arm 2010 is arranged to connect the second anchor block 2096 to a third anchor block 2073 so as to maintain a fixed displacement between the second anchor block 2096 and the third anchor block 2073. The third anchor block 2073 lies adjacent the outer surface of the garment 2085 such that the third anchor block 2073 and the first anchor block 2062 are adjacent. The third anchor block 2073 is not fixedly mounted on the garment 2085. Thus, displacement of the second anchor block 2096 relative to the first anchor block 2062 (e.g. owing to stretching the garment 2085) results in a corresponding displacement of the third anchor block 2073 relative to the first anchor block 2062.

[0198] The first anchor block 2062 defines a first through-bore 2063 that extends from an LED 2041, mounted on the first anchor block 2062, through the first anchor block 2062. The third anchor block 2073 defines a second through-bore 2074 that extends from a photodetector 2022, mounted on the third anchor block, through the third anchor block 2073. The first anchor block 2062 and the third anchor block 2073 are mounted adjacent one another on the garment 2085 such that, prior to stretching of the garment 2085, the first through-bore 2063 and the second through-bore 2074 are coaxial (i.e. they extend along the same axis).

[0199] The sensor device 2002 comprises a first optical fibre 2051, retained within the first through-bore 2063, and a second optical fibre 2030, retained within the second through-bore so as to be in alignment with the first optical fibre 2051 in an un-stretched state of the garment 2085. A first end of the first optical fibre 2051 receives light from the LED 2041. A first end of the second optical fibre 2030 is arranged to receive light (from the LED 2041) from a second end of the first optical fibre 2051. The photodetector 2022 is arranged to detect light transmitted through the second optical fibre 2030. Thus, the photodetector 2022 is arranged to detect, via the first optical fibre 2051 and the second optical fibre 2030, the light emitted by the LED 2041.

[0200] Prior to stretching of the garment 2085, the first anchor block 2062 and the second anchor block 2096 are separated by a distance 2107 (x.sub.1), in a direction perpendicular to the axis along which the first optical fibre 2051 extends through the first anchor block 2062. When the garment 2085 is stretched (e.g. when it is being worn), the distance 2107 between the first anchor block 2062 and the second anchor block 2096 increases from x.sub.1 to x.sub.2. This is shown in FIGS. 12c and 12d.

[0201] The displacement between the first anchor block 2062 and the second anchor block 2096 results in a corresponding displacement between the first anchor block 2062 and the third anchor block 2073 and, thus, a misalignment of the first optical fibre 2051 and the second optical fibre 2030. The misalignment in the fibres 2051, 2030 means that cross-sectional area of the second optical fibre 2030 that is exposed to the cross-sectional area of the first optical fibre 2051 (and, thus, the light transmitted through the first optical fibre 2051 to the second optical fibre 2030) is reduced. As a result, the photodetector 2022 measures a decrease in the received light intensity.

[0202] The photodetector 2022 is arranged to produce an electrical output signal that is proportional to the amount of light received from the LED 2041. A high resolution analogue signal is produced by the photodetector 2022. This signal may optionally be converted to a digital signal by an analogue-to-digital converter for processing by a controller as disclosed herein. In particular, the change in output signal from the photodetector 2022 corresponds to the change in circumference of the garment 2085; therefore, the compression pressure exerted by the garment 2085 can be determined, and optionally logged by an electronic controller, in ways described herein.

[0203] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible, within the scope of the accompanying claims.

SENSOR APPARATUS FOR A COMPRESSION GARMENT

Inventors

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G01L1/12

PHYSICS

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G01L1/142

PHYSICS

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A61F13/00051

HUMAN NECESSITIES

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G01L1/22

PHYSICS

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G01L1/242

PHYSICS

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A61F13/08

HUMAN NECESSITIES

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A61F2013/423

HUMAN NECESSITIES

International classification

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G01L1/24

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A61F13/08

HUMAN NECESSITIES

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G01L1/12

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G01L1/14

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G01L1/22

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Abstract

Claims

Description