WO2008038279A2

WO2008038279A2 - Force transducer and method

Info

Publication number: WO2008038279A2
Application number: PCT/IL2007/001183
Authority: WO
Inventors: Kfir Nissan; Moshe Nissan
Original assignee: Kfir Nissan; Moshe Nissan
Priority date: 2006-09-25
Filing date: 2007-09-25
Publication date: 2008-04-03
Also published as: WO2008038279A3

Abstract

The present invention provides an optical force transducer (200) and method for use thereof. The optical force transducer (200) comprises a light source (2) attached to a first base (3) and a light sensor (4) attached to a second base (5) The light sensor (4) detects characteristics of an illuminated area created by the light source (2), the characteristics corresponding to forces applied on at least one of the first (3) and second (5) bases The relative positions of the first (3) and second (5) bases are changeable in accordance with the force applied thereto. The method comprises sensing the characteristics of the illuminated area and changes in these characteristics due to force applied to the optical force transducer (200) and calculating three dimensional vectors of forces and/or moments of the applied force base on the sensed characteristics and changes in these characteristics.

Description

FORCE TRANSDUCER AND METHOD

BACKGROUND OF THE INVENTION

Different kinds of dynamometers are well known and used heavily in industrial and research environments. They are made, in most cases, of one or more strain gauges, piezoelectric materials, capacitance or resistive transducers.

Three-dimensional force transducers are usually made of a combination of strain- gauges or piezoelectric systems, attached to highly complicate mechanical structures. As a result, these three-dimensional transducers are bounded to sizes which prevent them from being used in some applications. Additionally, they are difficult to calibrate and too expansive for many potential uses.

There are two primary types of known force transducer plates, for example for foot pressure analysis. The first kind usually includes a plate of about four or five columns, each including three-dimensional piezoelectric or strain gauge transducers. The data detected by the gauges is translated to forces and moments.

The second major kind of force transducer plates usually includes a plate made of a matrix of elements including in most cases capacitance or resistive transducers. Each transducer measures the vertical force applied to its respective part as applied to it by the foot while walking on the plate. Known force transducer plates usually do not enable calculation of three- dimensional forces on each plate part. These plates may provide a single resultant three- dimensional force values or distribution of pressures across a two-dimensional plane.

BRIEF DESCRIPTION OF THE DRAWINGS The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: Figs. IA and IB are schematic illustrations of two views of a basic force transducer device for sensing three-dimensional vectors of forces according to some embodiments of the present invention;

Figs. 2A, 2B₅ 2C and 2D are exemplary schematic illustrations of different views of a force transducer device according to one embodiment of the invention, in which Figs. 2B and 2D are illustrations of a dismantled device and Figs. 2A and 2C are illustrations of an assembled device;

Fig. 3 is a cross-sectional schematic Three-dimensional illustration of a force transducer matrix according to some embodiments of the present invention; and Fig. 4 is a flow chart representing a method according to some embodiments of the present invention.

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

Embodiments of the present invention may provide force transducer units for sensing three-dimensional vectors of forces. These force transducer units may be relatively simple in structure and therefore, for example, may be easily reduced to small sizes of units and may be relatively inexpensive. Force transducer units and arrays or matrices of these units according to embodiments of the present invention may provide sensitive high-resolution pressure sensor surfaces.

Reference is made to Figs. IA and IB, which are schematic illustrations of two views of a basic force transducer device 100 for sensing three-dimensional vectors of forces according to some embodiments of the present invention. Device 100 may include a light source 2, a light source base 3, a light sensor 4 and a light sensor base 5. Light sensor 4 may include, for example, CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) or any other suitable light sensor. Light source 2 may create a beam of light 6 which may illuminate an area 7 on sensing area 4a of light sensor 4. Changes may occur in the position of light source base 3 relative to light sensor base 5, for example, as a result of forces applied on light source base 3 and/or light sensor base 5, which may cause complex relative movement between them. The relative movement may be due to coaxial forces along the X axis of Fig. IA, forces acting parallel to the Y-Z plane of Fig. IA or combinations thereof. The changes in relative position may cause changes in characteristics of the illuminated area 7, such as, for example, position, shape, size and/or brightness of the illuminated area 7 on sensing area 4a. The characteristics of illuminated area 7 and the changes in these characteristics may imply on the forces applied to light source base 3 and/or light sensor base 5 and the changes in these forces.

Light sensor 4 may communicate sensed illumination data to a processor 11 which may calculate the three dimensional vectors of the forces applied on light source base 3 and/or light sensor base 5 and the changes in these forces, for example, based on changes in characteristics of illuminated area 7. Changes in position of illuminated area 7, for example, may be translated by processor 11 to forces acting parallel to the Y-Z plane of Fig. IA. Changes in size and/or brightness of illuminated area 7, for example, may be translated by processor 11 to forces acting parallel to the X axis of Fig. IA. Preferably, one of light source base 3 and light sensor base 5 may be fixed, for example, to a firm platform or floor, and the other one may be movable and change its position in response to applied pressure and/or forces. For example, the movable base may be attached to an elastic substrate (such as substrate 12 shown in Figs. 2A-2D) which may be distorted in response to applied pressure. The position of the movable base may change by moving in the directions of the X, Y and Z axes and/or by rotation about these axes.

Light source base 3 and/or light sensor base 5 may enable conduction of power to light source 2 and/or light sensor 4, respectively. Light sensor base 5 may enable conduction of data signals from light sensor 4 to processor 11. Light source base 3 and/or light sensor base 5 may include, for example, circuit boards, conductive wires or any other suitable conduction means.

The basic principle of operation described above with reference to Figs. IA and IB may be implemented in various embodiments. Reference is now made to Figs. 2A₅ 2B, 2C and 2D, which are exemplary schematic illustrations of different views of a force transducer device 200 according to one embodiment of the invention. Figs. 2B and 2D are illustrations of dismantled device 200 and Figs. 2A and 2C are illustrations of assembled device 200. Device 200 may include a frame 10, for example, to hold light source 2, light source base 3, light sensor 4 and light sensor base 5 which were described with detail above with reference to Figs. IA and IB. Device 200 may also include an elastic substrate 12. Light source base 3 may be held in a groove 15 in substrate 12. The shape of groove 15 may conform to the shape of light source base 3, thus, for example, light source base 3 may fit and be held tightly in groove 15. Substrate 12 may include a terrace 13 which may facilitate installation of substrate 12 in frame 10. The external contour of terrace 13 may fit tightly with the inner contour of frame 10 where substrate 12 may be assembled.

The required maximal modulus of elasticity (Young's modulus) of substrate 12 may depend in the specific application of a device according to the present invention. The modulus of elasticity is the momentary ratio of stress to strain. The maximal modulus of elasticity may depend on the elastic material itself and on the shape, thickness and size of elastic substrate 12, on the design of the assembly of light source base 3 or light sensor base 5 with substrate 12 and other parameters related to design considerations.

For some applications, for example, the required maximal vertical stress which may be applied on elastic substrate 12 may be about 150 Newton on an area of about 10 mm , i.e., vertical stress of 15 MPa. The required maximal vertical strain which may be applied on elastic substrate 12 for the same applications may be about 0.15 mm for an initial material length of about 3 mm in the lateral walls of substrate 12, i.e., strain of 5% of the material length. Therefore the required maximal modulus of elasticity of vertical forces may be about 300 MPa.

In some applications, the required maximal shear stress which may be applied on elastic substrate 12 may be about 100 Newton on an area of about 2 mm², i.e., shear stress of 50 MPa. The required maximal shear strain which may be applied on elastic substrate 12 in some applications may be about 0.5 mm for an initial material length of about 10 mm, i.e., shear strain of 5% of the material length. Therefore the required maximal modulus of elasticity for shear forces may be about 1 GPa.

Elastic substrate 12 may therefore include suitable materials with the required characteristics. For example, Polypropylene may fit for certain applications which may require modulus of elasticity of about 0.1-2.5 GPa. In other applications, for example, Polyethylene with modulus of elasticity of about 1.5-3.5 GPa may be used.

Substrate 12 may include an opening 14 through which light source 2 may illuminate the sensing area 4a. In some embodiments, light source 2 may protrude from light source base 3. In such cases opening 14 may fit to receive light source 2 when light source base 3 is installed in groove 15.

Light sensor base 5 and light sensor 4 may be assembled in frame 10 opposite to the substrate 12. In some embodiments, light sensor base 5 and light sensor 4 may be integral with frame 10. In the embodiment shown in Figs. 2A-2D light source base 3 and light source 2 may be installed in elastic substrate 12 and therefore, for example, their position and orientation with respect to each other may change as result of pressure applied on light source base 3 and/or on elastic substrate 12. In this embodiment, light sensor base 5 and light sensor 4 may be stationary and may be connected for example, directly to frame 10. Therefore, for example, light source 2 may change its position and orientation relative to light sensor 4 and three dimensional vectors of forces applied on light source base 3 and/or on substrate 12 may be calculated based on the characteristics of the illuminated area 7 and changes in those characteristics. It will be appreciated that the same principle of operation and results may be obtained in other equivalent embodiments. For example, light sensor base 5 and light sensor 4 may be installed in an elastic substrate and light source base 3 and light source 2 may be stationary, so that, for example, the position of light sensor 4 may change relative to light source 2 and three dimensional vectors of forces and/or moments applied on the elastic substrate may be calculated based on the characteristics of the illuminated area created by light source 2 on sensing area 4a and changes in those characteristics. In order that the changes in illumination from light source 2 may be sensed by light sensor 4, the illuminated area should be smaller than sensing area 4a and its perimeter should not exceed the boundary of area 4a. In order to limit the illumination to an area smaller than sensing area 4a, frame 10 may include a screen 8 with an aperture 9, with or without a lens or another optic device, so that, for example, only the light passing through aperture 9 may reach light sensor 4.

The embodiment of Figs. 2A-2D and equivalent embodiments may have various implementations. Device 200 may constitute a very small force transducer unit. Therefore, systems including arrays or matrices of these units may form high-resolution force sensitive surfaces. This may be used, for example, to create a robotic sense of touch. Additionally, the force transducer units according to embodiments of the present invention and/or arrays and/or matrices of these units may enable detection and analysis of three-dimensional vectors of forces and moments applied, for example, by a foot on the ground when standing, walking, running, or in any other activity that has foot-ground interaction. This may be done, for example, by installing force transducer units according to embodiments of the present invention in a sole of a shoe in places corresponding to points-of-interest of the foot. Additionally, matrices of force transducer units according to embodiments of the present invention may constitute flat sensitive surfaces, which may be used for detecting and analyzing three-dimensional vectors of forces and moments applied on a surface by an object such as foot, wheel or any other suitable object.

Reference is now made to Fig. 3, which is a cross-sectional schematic illustration of a force transducer matrix 300 according to some embodiments of the present invention. Matrix 300 may include numerous force transducer units 310, each unit 310 may be substantially similar to device 200 described with reference to Figs. 2A-2D. The frontal units 310 are shown cut at the middle, to illustrate the components of each unit 310. Matrix 300 may include frames 30, for example, to hold light sources 22, light source bases 34, light sensors 20 and light sensor bases 26 which their assembly and operation may be substantially similar to the assembly and operation of the components of devices 100 and 200 described with detail above with reference to Figs. IA and IB and Figs. 2A-2D. Device 300 may also include an elastic substrate 32. Light source bases 34 may be held in grooves 36 in substrate 32 similarly to the holding of light source base 3 in groove 15 as described with reference to Figs. 2A-2D. Frames 30 may include screens 24 with apertures 28, for example, to limit the illumination substantially similarly to the operation of screen 8 and aperture 9 described with reference to Figs. 2A-2D.

Frames 30 may be substantially immovable relative to each other. Frames 30 may form one integral frame. Light sensors 20 may be immovable relative to each other and to frames 30. Light sensor bases 26 may be connected to each other or form one integral base, for example, in the bottom of frames 30. Additionally or alternatively, light sensor bases 26 may be integral with frames 30. The walls of frames 30 may be opaque so that each force transducer unit 310 may be isolated from the other units 310.

Light source bases 34 may move substantially independently from each other in elastic substrate 32. Thus, for example, when matrix 300 includes many small force transducer units 310 according to embodiments of the present invention, it may constitute a high-resolution force-transducer plate.

As explained above with reference to Figs 2A-2D, it will be appreciated that the same principle of operation and results may be obtained in other equivalent embodiments. For example, light sensor bases 26 and light sensors 20 may be installed in elastic substrate 32 and light source base 34 and light source 22 may be stationary and may be fixed in the bottom of frames 30.

I addition to calculation of forces applied to each unit 310, matrix 300 may enable calculation of moments applied to it by an object by mapping the distribution of forces applied to units 310 by the obj ect.

Matrix 300 may be used, for example, for gait analysis. Such gait analysis may be done by walking over a force-transducer plate including one or more matrices similar to matrix 300 described above. The three-dimensional vectors of forces applied on each of units 310 may be calculated. The three-dimensional vectors of moments applied a foot may be calculated using units 310 under the foot area. By reducing the size of each unit 310 up to thousands of units 310 may cover an area corresponding to area of one foot. This may facilitate very high resolution of gait analysis.

Reference is now made to Fig. 4, which is a flow chart representing a method according to some embodiments of the present invention. As indicated in block 510, the method may include sensing characteristics of illuminated area and changes in these characteristics. As indicated in block 520, the method may include calculating three dimensional vectors of forces and/or moments based on the sensed characteristics and changes in these characteristics.

While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMSWhat is claimed is:

1. A device comprising: a light source attached to a first base; and a light sensor attached to a second base, the relative positions of said first and second bases are changeable, wherein said light sensor is to detect characteristics of illuminated area created by said light source, said characteristics correspond to forces applied on at least one of the first and second bases which cause change in position of said first and second bases relative to each other.

2. A device according to claim 1, wherein said light sensor comprising a light sensing area and wherein said illuminated area is illuminated by said light source on said light sensing area.

3. A device according to claim 1, further comprising a processor to calculate three dimensional vectors of forces applied on at least one of the first and second bases, based on said detected characteristics.

4. A device according to claim 3, wherein said light sensor is further to communicate data of the detected characteristics to said processor.

5. A device according to claim 1, wherein said detected characteristics are one or more from a list comprising: position, shape, size and brightness of the illuminated area.

6. A device according to claim 1, wherein one of said first and second bases is fixed and the other base is movable relative to the fixed base.

7. A device according to claim 6, wherein the position of the movable base is changeable in response to applied force.

8. A device according to claim 6, wherein the movable base is attached to an elastic substrate distortable in response to applied force.

9. A device according to claim 6, wherein the position of the movable base is changeable by moving in directions of at least one of three orthogonal axes and by rotation about at least one of these axes.

10. A device according to claim 1, wherein at least one of said first and second bases enable conduction of at least one of power and data signals.

11. A device according to claim 1, further including a frame to hold at least one of a list comprising said light source, light sensor, the first and second bases and

• 5 an elastic substrate distortable in response to applied force to hold one of said first and second bases.

12. A device according to claim 11, wherein said elastic substrate is configured to hold one of said first and second bases and assembled in the frame opposite to the other base which is not held by said elastic substrate. 0

13. A device according to claim 12, wherein the base which is not held by said elastic substrate is immovable relative to the frame or integral with the frame.

14. A device according to claim 11, wherein said frame further including a screen with an aperture to limit the illumination from the light source to an area smaller than a sensing area of said light sensor. 5

15. A plurality of devices according to claim 1 arranged side by side to form a row and further arranged row by row to form a matrix, said plurality of devices further comprising a plurality of frames to hold at least some of a list comprising light sources, light sensors, light source bases and light sensor bases. 0

16. A plurality of devices according to claim 1, wherein said frames are identical to each other and arranged in the same direction and immovable relative to each other.

17. A plurality of devices according to claim 15, further comprising an elastic substrate to hold said light source bases or said light sensor bases assembled on5 said plurality of frames, said elastic substrate distortable in response to applied forces and.

18. A plurality of devices according to claim 17, wherein the bases which are not held by the elastic substrate are immovable relative to the frame and to each other or integral with the frames.

19. A plurality of devices according to claim 15, wherein walls of said frames which separate between the devices are opaque.

20. A plurality of devices according to claim 17, wherein the bases which are held by the elastic substrate are movable substantially independently relative to each other.

21. A method comprising: sensing characteristics of illuminated area and changes in these characteristics due to force applied to a force sensing device; and calculating three dimensional vectors of forces and/or moments of said applied force based on the sensed characteristics and changes in these characteristics.

22. A method according to claim 21, wherein said force is applied on at least one of a light source base and a light sensor base, wherein said applied force causes change in position of said light source base and light sensor base relative to each other, the change in position affecting said sensed characteristics.

23. A method according to claim 21, further comprising illuminating an area on a light sensing area of a light sensor.

24. A method according to claim 21, wherein said sensed characteristics are from a list comprising: position, shape, size and brightness of the illuminated area.