FORCE SENSORS

FIELD OF THE INVENTION

This invention relates to a conductive pressure sensitive layer structure, force sensors and in particularly force sensors for use in robotics.

STATEMENT OF PRIOR ART

The most relevant prior art is typically as set out in US Patent Nos. 6,291,568, 6,495,069, 6,646,540 and 7,186,356, all granted in the name Peratech Limited, of Darlington, Great Britain, and US Patent No. 7,145,432 (Baudendistel).

^• SUMMARY OF THE INVENTION

In one embodiment of the invention, a pressure sensitive layer structure for a force sensor is provided. The pressure sensitive layer structure comprising: a conformable support structure; and a first conductive layer adhered to the conformable support structure.

In another embodiment of the invention, the first conductive layer is adhered to a first surface of the conformable support structure, and the pressure sensitive layer structure further comprises: a second conductive layer adhered to a second surface of the conformable support structure opposite to the first surface of the conformable support structure, wherein the first and second conductive layers are in electrical contact.

In another embodiment of the invention, the first and second conductive layers are in electrical contact through the conformable support structure. In another embodiment of the invention, the conformable support structure comprises a mesh structure. In another embodiment of the invention, the conformable support structure comprises a steel mesh. In

another embodiment of the invention, the conformable support structure has a thickness of 0.2 mm. In another embodiment of the invention, the conformable support structure comprises a stretchable structure. In another embodiment of the invention, the conformable support structure is electrically conductive.

In another embodiment of the invention, the conductive layer comprises a pressure sensitive conductive layer. In another embodiment of the invention, the conductive layer comprises a polymeric material. In another embodiment of the invention, the conductive layer comprises a natural polymer. In another embodiment of the invention, the conductive layer comprises a rubber incorporating conductive particles. In another embodiment of the invention, the conductive layer comprises a quantum tunnelling composite (QTC). In another embodiment of the invention, the first conductive layer comprises two first conductive layers. In another embodiment of the invention, the second conductive layer comprises two second conductive layers. ^J >■

In another embodiment of the invention, a first surface of the first conductive layer is adhered to the conformable support structure, and the pressure sensitive layer structure further comprises: an underlayer adhered to a second surface of the first conductive layer opposite to the first surface of the first conductive layer.

In another embodiment of the invention, the underlayer comprises a fabric. In another embodiment of the invention, the underlayer comprises a stretchable structure. In another embodiment of the invention, the underlayer comprises a non-woven cotton material. In another embodiment of the invention, the underlayer comprises a natural or synthetic material. In another embodiment of the invention, the underlayer has a thickness of 0.1 mm.

In one embodiment of the invention, a force sensor for a robotic limb and/or appendage, comprising the pressure sensitive layer structure is provided.

In one embodiment of the invention, a method of manufacturing a pressure sensitive layer structure is provided. The method comprising: adhering together a conformable support structure and a first layer of conductive material.

In another embodiment of the invention, a first surface of the conformable support structure is adhered to the first layer of conductive material, and the method further comprises: adhering together a second layer of conductive material and a second surface of the conformable support structure, opposite to the first surface of the conformable support structure.

In another embodiment of the invention, the conformable support structure is adhered to a first surface of the first layer of conductive material, and the method further comprises: adhering together an underlayer and a second surface of the first layer of conductive material, opposite to the first surface of the first layer of conductive material.

In one embodiment of the invention, a force sensor, comprising: an electrode layer; and a pressure sensitive layer structure provided adjacent to the electrode layer is provided.

In one embodiment of the invention, a force sensor for a robotic part is provided. The force sensor comprising: an electrode layer configured into a shape of at least a portion of a robotic part; and a conductive layer provided adjacent to and conforming to the shape of the electrode layer.

In another embodiment of the invention, the electrode layer comprises: an insulating substrate; and at least two electrically conductive elements provided on the insulating substrate, wherein the electrically conductive elements are in electrical contact with the conductive layer.

In another embodiment of the invention, the insulating substrate is configured into the shape of at least a portion of the robotic part. In another embodiment of the invention, the

insulating substrate comprises a substantially rigid substrate. In another embodiment of the invention, the insulating substrate comprises a flexible substrate. In another embodiment of the invention, the at least two electrically conductive elements comprises a matrix of electrically conductive elements.

In another embodiment of the invention, the force sensor further comprises: a protective layer provided adjacent the conductive layer. In another embodiment of the invention, the protective layer comprises polyurethane. In another embodiment of the invention, the protective layer comprises a Shore A Hardness of 30. In another embodiment of the invention, the protective layer has a thickness of 2 mm. In another embodiment of the invention, the protective layer has a thickness of 1 mm.

In another embodiment of the invention, the force sensor further comprises: a barrier layer provided between the conductive layer and the protective layer. In another embodiment of the invention, the barrier layer comprises polyvinyl chloride. In another embodiment of the invention, the barrier layer has a thickness of between 0.007 mm to 0.015 mm.

In another embodiment of the invention, the force sensor further comprises: a lubricant layer provided between the conductive layer and the barrier layer. In another embodiment of the invention, the lubricant layer comprises chalk. In another embodiment of the invention, the conductive layer comprises the pressure sensitive layer structure.

In another embodiment of the invention, the electrode layer has a curvature about at least one axis. In another embodiment of the invention, the electrode layer has a curvature about at least two axes. In another embodiment of the invention, the electrode layer has a curvature about three axes.

In another embodiment of the invention, the robotic part comprises: one or more of: a finger-tip; a thumb; a hand.

In one embodiment of the invention, a robotic limb and/or appendage comprising the force sensor is provided. In another embodiment of the invention, the robotic appendage comprises a finger-tip. In another embodiment of the invention, the robotic appendage comprise a thumb-tip.

In one embodiment of the invention, a force sensor for sensing the position and magnitude of force exerted locally at each of a multiplicity of positions, or any of them, lying within a certain area is provided. The force sensor comprises: a resiliently compressible first layer variable locally in electrical conductance under such pressure as may be exerted on said layer at any site within the area thereof, the magnitude of the electrical conductance developed locally across said first layer at said site under such a force being a function of such pressure as may, for the time being, be acting on said layer at said site; a resiliently compressible second layer, being a protective outer covering layer for said first layer, having one of its faces in confronting relationship with a face of said first layer, said one face of said second layer conforming in shape to said confronting face of said first layer; a substantially rigid third layer having a face confronting the other face of said first layer, said third layer face presenting to said confronting first layer face an electrically conductive grid, being a grid which comprises: a first set of electrically conductive, strip elements extending in one direction with respect to said face of said third layer; and, a second set of electrically conductive strip elements, insulated from the strip elements of said first set, the strip elements of said second set overlying the strip elements of said first set such as to extend in a direction orthogonal to said first set, the strip elements of said second set each having openings located therealong at positions corresponding, respectively, to the locations at which the orthogonal strip elements of said sets intersect with one another, such as to leave the electrically conductive strip elements of said first set exposed to contact with said locally pressure responsive electrically conductive first layer through said openings of the strip elements of said second set; and, between said first and second layers, a permanent barrier layer, being a membrane composed of a limp sheet material.

In another embodiment, said third layer face is singly curved, that is to say, has a curvature

about one axis. In another embodiment, said third layer is doubly curved, that is to say, has a curvature about two orthogonal axes. In another embodiment, said limp sheet material is substantially impervious to fluids. In another embodiment, said membrane comprises a plastic film having a thickness of between about 0.007 to 0.015. In another embodiment, said plastic film is of PVC sheet material. In another embodiment, said first layer comprises a polymeric material. In another embodiment, said polymeric material is a rubber incorporating conductive particles. In another embodiment, said polymeric material comprises a quantum tunnelling composite (QTC). In another embodiment, said second layer is composed of a polyurethane. In another embodiment, the force sensor has, between said first and third layers, a dusting of an inert non-abrasive powdery dry lubricant said dusting being such as not substantially to interfere with the electrical interaction between the pressure responsive electrically conductive first surface and the electrically conductive grid of the third layer.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made by way of example only to the accompanying drawings:

Figure 1 illustrates schematically a conductive pressure sensitive layer structure of one embodiment of the invention;

Figure 2 illustrates a process flow diagram for making a conductive pressure sensitive layer structure of one embodiment of the invention;

Figure 3 illustrates schematically a force sensor of one embodiment of the invention;

Figures 4A to 4C illustrate schematically an electrode layer of one embodiment of the invention;

Figure 5 illustrates a process flow diagram for making an electrode layer of one embodiment of the invention;

Figures 6A and 6B illustrate a robotic finger-tip comprising a force sensor of one embodiment of the invention;

Figures 7A and 7B illustrate ^' a robotic thumb-tip comprising a force sensor of one

embodiment of the invention;

Figure 8 illustrates a block diagram of an electronic circuit for a force sensor of one embodiment of the invention;

Figure 9A illustrates schematically a force sensor of one embodiment of the invention; and

Figure 9B illustrates schematically an electrode layer of one embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

Figure 1 illustrates schematically a conductive pressure sensitive layer structure 10 of one embodiment of the invention. The conductive pressure sensitive layer structure 10 illustrated in figure 1 comprises: an underlayer 11, a layer of conductive material 13, a conformable support structure 15, and a second layer of conductive material 17.

In one embodiment, a conductive pressure sensitive layer structure 10 comprises a layer of conductive material 13 and a conformable support structure 15. In another embodiment, a conductive pressure sensitive layer structure 10 comprises a layer of conductive material 13, and a conformable support structure 15, and a second layer of conductive material 17.

In one embodiment, the layer of conductive material 13 and the second layer of conductive material 17 are in electrical contact. In one embodiment, the layer of conductive material 13 and the second layer of conductive material 17 are in electrical contact via the conformable support structure 15. In one embodiment, the layer of conductive material 13 and the second layer of conductive, material 17 are in electrical contact through the conformable support structure 15.

In one embodiment, the underlayer 11 comprises a layer of fabric. In one embodiment, the underlayer 11 comprises a stretchable material. In one embodiment, the underlayer 11

comprises a non-woven cotton. In one embodiment, the underlayer 11 comprises a natural or synthetic material. In one embodiment, the underlayer 11 is 0.1 mm thick.

In one embodiment, the conductive material 13, 17 comprises a conductive pressure sensitive material. A conductive pressure sensitive material in the present context is a material having conductive properties when a pressure (force) is applied to the material, the conductive properties varying as a result of the magnitude of the force applied to the material.

In one embodiment, the conductive material 13, 17 comprises a polymeric material. In one embodiment, the conductive material 13, 17 comprises a natural polymer. In one embodiment, the conductive material 13, 17 comprises a rubber incorporating conductive particles. In one embodiment, the conductive material 13, 17 comprises a quantum tunnelling composite (QTC). In one embodiment, the QTC comprises the QTC described and claimed in International Patent Publication No. WO 9938173.

In one embodiment, the conductive material 13 comprises two layers of conductive material. The two layers of conductive material 13 are separated with a dotted line as illustrated in figure 1. In one embodiment, the second conductive material 17 comprises two layers of conductive material. The two layers of second conductive material 17 are separated with a dotted line as illustrated in figure 1.

In one embodiment, the conformable support structure 15 comprises a mesh. A mesh may be any structure, such as a lattice, grid or matrix. In one embodiment, the mesh is not required to have identically shaped or sized sections. In one embodiment, the conformable support structure 15 comprises a steel mesh. In one embodiment, the conformable support structure 15 is electrically conductive. In one embodiment, the conformable support structure 15 is 0.2 mm thick.

The conformable support structure 15 provides extra strength and stability to the conductive

pressure sensitive layer structure 10, in particular when the conductive pressure sensitive layer structure 10 is to be applied to a curved structure. The conformable support structure 15 is capable to conforming to the shape of any object to which it is applied.

Figure 2 illustrates the steps involved in manufacturing a conductive pressure sensitive layer structure 10. The conductive pressure sensitive layer structure 10 is formed on a mould.. In one embodiment; the mould is ceramic, although other materials can also be used. Ceramic is advantageous since it creates a roughness on the underside of conductive pressure sensitive layer structure 10 (the side in contact with the mould), which prevents the conductive pressure sensitive layer structure 10 from bonding to the electrode layer described in detail below. The mould is formed using conventional techniques known in the art. In one embodiment, the mould is a flat sheet. In another embodiment, the mould is the shape of a robotic part, such as a robotic arm, hand, finger, finger-tip or thumb-tip etc.

In one embodiment, the underlayer 11 is applied to the mould (step S200) so that the underlayer 11 conforms to the contours of the mould. For example, if the mould is curved, such as finger-tip or thumb-tip shaped, then the underlayer 11 is stretched over the mould so that the are no wrinkles in the underlayer 11.

A first layer of conductive material 13 is then applied to the underlayer 11 (step S210), such that the layer of conductive material 13 conforms to the contours of the underlayer 11 and the mould. In one embodiment, the layer of conductive material 13 is painted onto the underlayer 11. In one embodiment, the layer of conductive material 13 is applied to the underlayer 11 and dried at room temperature. In another embodiment, the layer of conductive material 13 is applied to the underlayer 11 and dried at temperatures up to about 120 "C.

The conformable support structure 15 is then applied to the conductive material 13 (step S220). The conformable support structure 15 is applied such that it conforms to the contours of the first layer of conductive material 13, the underlayer 11 and the mould. In

one .embodiment, .the conformable support structure 15 is applied to the conductive material 13 prior to the conductive material 13 being completely dry. Consequently, the conformable support structure 15 adheres to the conductive material 13 as the conductive material 13 dries. In one embodiment, the conformable support structure 15 is applied to the conductive material 13 approximately 10 minutes after application of the conductive material 13. In one embodiment, the conformable support structure 15 is adhered to the conductive material 13, using known adhesives. Other method of adhering, as known in the art, could also be used.

A second layer of conductive material 17 is then applied to the conformable support structure 15 (step S230). The second layer of conductive material 17 is applied such that it conforms to the contours of conformable support structure 15, the first layer of conductive material 13, the underlayer 11 and the mould. The conformable support structure 15 is thus affixed between the first and second layers of conductive material 13, 17. In one embodiment, the first and second layers of conductive material 13, 17 are in direct contact through the mesh of the conformable support structure 15. In one embodiment, the first and second layers of conductive material 13, 17 are left for eight hours to dry completely.

In one embodiment, it is necessary to leave the conductive pressure sensitive layer structure 10 two to three days before use, such that any residual moisture has been removed.

In another embodiment, the conductive material 13 is applied directly to the mould, no underlayer 11 is required. Consequently, step S200 is illustrated with a dotted line.

In another embodiment, the first layer of conductive material 13 comprises two constituent layers of conductive material 13. In this embodiment, the first constituent layer of the first layer of conductive material 13 is applied to the underlayer 11 or mould (as appropriate), the second constituent layer of the first layer of conductive material 13 is then applied to the first constituent layer of the first layer of conductive material 13, after the first constituent layer of the first layer of conductive material 13 has dried. In one embodiment, the second

constituent layer of the first layer of conductive material 13 is applied to the first constituent layer of the first layer of conductive material 13, after 10 minutes.

In another embodiment, the second layer of conductive material 17 comprises two constituent layers of conductive material 17. In this embodiment, the first constituent layer of the second layer of conductive material 17 is applied to the conformable support structure 15, the second constituent layer of the second layer of conductive material 17 is then applied to the first constituent layer of the second layer of conductive material 17, after the first constituent layer of the second layer of conductive material 13 has dried. In one embodiment, the second constituent layer of the second layer of conductive material 17 is applied to the first constituent layer of the second layer of conductive material 17, after 10 minutes.

Following manufacture of the conductive pressure sensitive layer structure 10, the conductive pressure sensitive layer structure 10 is removed from the mould. In one embodiment, conductive pressure sensitive layer structure 10 has a curvature about at least one axis. In one embodiment, conductive pressure sensitive layer structure 10 has a curvature about at least two axes. In one embodiment, conductive pressure sensitive layer structure 10 has a curvature about three axes.

Figure 3 illustrates schematically a force sensor 30 of the invention. The force sensor 30 comprises: an electrode layer 31; a conductive layer 33, provided adjacent to the electrode layer 31; a lubricant layer 35, provided adjacent to the conductive pressure sensitive layer 33; a barrier layer 37, provided adjacent to the lubricant layer 35; and a protective layer 39, provided adjacent to the barrier layer 37.

In another embodiment, a force sensor 30 of the invention comprises an electrode layer 31 and a conductive layer 33, provided adjacent to the electrode layer 31. In another embodiment, a force sensor 30 of the invention comprises an electrode layer 31; a conductive layer 33, provided adjacent to the electrode layer 31; and a protective layer 39,

provided adjacent to the conductive layer 33. In another embodiment, a force sensor 30 of the invention comprises an electrode layer 31; a conductive layer 33, provided adjacent to the electrode layer 31; a barrier layer 37, provided adjacent to the conductive layer 33; and a protective layer 39, provided adjacent the barrier layer 37.

In one embodiment, the lubricant layer 35 comprises chalk. The lubricant layer 35 prevents the barrier layer 37 from adhering to the conductive pressure sensitive layer 33. In one embodiment, the barrier layer comprises polyvinyl chloride (PVC). In one embodiment, the barrier layer 37 is substantially impervious to fluids in order to prevent the transfusion of gases and liquids through the barrier layer 37. In one embodiment, the barrier layer 37 has a thickness of about 0.007 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.008 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.009 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.010 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.011 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.012 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.013 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.014 mm. In one embodiment, the barrier layer 37 has a thickness of about 0.015 mm.

In one embodiment, the protective layer 39 comprises polyurethane. In one embodiment, the protective layer 39 comprises a Shore A Hardness of 30. In one embodiment, the protective layer 39 has a thickness of about 2 mm. In another embodiment, the protective layer 39 has a thickness of about 1 mm.

In one embodiment, a force sensor 30 is assembled comprising an electrode layer 31, a conductive layer 33, a lubricant layer 35 and a barrier layer 37. The assembled force sensor 30 is then screwed into a two-part mould. The mould is then clamped together and the protective layer 39 is injected into the mould, such that it surrounds the assembled force sensor 30. This is then left for a day before being removed and trimmed.

In one embodiment, the conductive layer 33 comprises the conductive pressure sensitive layer structure 10 described above with reference to figure 1. When the conductive layer 33 comprises the conductive pressure sensitive layer structure 10, the underlayer 11 is provided adjacent to the electrode layer 31 and provides a relatively rough surface which prevents adhesion of the conductive pressure sensitive layer structure 10 to the electrode layer 31.

In another embodiment, the conductive layer 33 comprises conductive rubber. In one embodiment, the conductive layer 33 comprises a quantum tunnelling composite (QTC). In one embodiment, the conductive layer 33 comprises a QTC as described and claimed in International Patent Publication No. W09938173.

Figures 4A and 4B illustrate schematically the electrode layer 31. The electrode layer 31 comprises an insulating substrate 42 and electrically conductive elements 4OA to 4OG. The invention is not limited to the number of electrically conductive elements illustrated, and any number of electrically conductive elements can be used. However, a minimum of two electrically conductive elements is required. In one embodiment, the substrate 42 is substantially rigid. In another embodiment, the substrate 42 is flexible.

In one embodiment, the substrate 42 is formed into the shape of a robotic part, such as a robotic arm, hand, finger, finger-tip or thumb-tip etc. The electrically conductive elements 4OA to 4OG are provided on the shaped substrate 42.

With reference to figure 4C, the conductive layer 33 is provided adjacent to the electrode layer 31. The conductive layer 33 is provided in contact with the electrode layer 31, such that the conductive layer 33 is in constant, even contact with the electrode layer 31 at all times.

In order to detect that a force F has been applied to the conductive layer 33, and the magnitude of the force F, a known voltage, for example 5 V, is applied to one of the electrically conductive elements 40, for example, element 4OC. The conductive layer 33,

having a known resistance, is in contact with the electrically conductive elements 40 and creates an electrical connection between the electrically conductive elements 40. Consequently, when no force is applied, a "base" value voltage can be detected in the electrically conductive element 4OD (to which no voltage is applied).

If there is a gap between the conductive layer 33 and the electrode layer 31, when a force F is applied to the conductive layer 33, then the resistance of the conductive layer 33 will rise before dropping. Constant, even contact between the conductive layer 33 and the electrode layer 31 gives a linear response from the first application of the force F.

The resistance provided by the conductive layer 33 changes in proportion to the magnitude of the force F applied to the conductive layer 33. Consequently, the magnitude of the force F can be determined based on the detected value of the voltage in the electrically conductive element 4OD, the known value of the voltage applied to the electrically conductive element 4OC and the known properties of the conductive layer 33. In one embodiment, the voltage detected in the electrically conductive element 4OD rises in response to the force applied to the conductive layer 33.

In one embodiment, a matrix of electrically conductive elements 40 may be provided such that a more precise indication of the position of the force F can be determined.

Figure 5 illustrates the steps involved in manufacturing an electrode layer 31. The substrate 42 is formed at step S500. The substrate 42 is formed using conventional techniques known in the art. In one embodiment, the substrate 42 is formed into a flat sheet. In another embodiment, the substrate 42 is formed into the shape of finger-tip or thumb-tip. In one embodiment, the substrate 42 comprises a ceramic material, although other materials can also be used.

In order to manufacture the electrically conductive elements 40, a layer of copper is applied to the substrate 42 using techniques known in the art (step S510). A photoresist layer is

then applied to the layer of copper at step S520, and a laser is used to draw a pattern of the electrically conductive elements 40 onto the photoresist layer (step S530). The copper is then etched following the pattern to form the electrically conductive elements 40 (step S540). The copper is etched using a laser. In one embodiment, the laser is a pin point focused ultraviolet unit mounted in a 5 axis milling machine. The electrically conductive elements 40 are then coated with nickel (step S550) and gold (step S560).

The nickel and gold coatings are applied in order to stop the copper from oxidising.

In one embodiment, the electrode layer comprises a matrix of electrically conductive elements, as illustrated in figure 9B. In one embodiment, a matrix of electrically conductive elements comprises a first array of electrically conductive elements 97A, and a second array of electrically conductive elements 97B, orthogonal to the first array of electrically conductive elements 97A, as conventionally known in the art. A sensing region is formed at the intersections between the two arrays of elements.

In one embodiment, a first array of electrically conductive elements 40 is provided on a first (outer surface) of the substrate 42 and a second array of electrically conductive elements 40 is provided on a second (inner surface) of the substrate 42. In this embodiment, before the substrate is copper plated at step S520, a plurality of holes are drilled through the substrate 42, a hole at each sensing region. In one embodiment, the holes are 0.6 mm in diameter. When the layer of copper is applied at step S520, the copper is applied through the holes and connects the inner and outer surfaces of the substrate 42. The copper is then etched (at step S540) to form the electrically conductive elements, 40 on both the inner and outer surfaces of the substrate 42.

In one embodiment, an etch resist layer is applied to the layer of copper at step S520, and a laser is used to draw a pattern of the electrically conductive elements 40 onto the etch resist layer (step S530). The copper is then etched following the pattern to form the electrically conductive elements 40 (step S540).

Although etching has been described, the electrically conductive elements 40 could also be formed using other method known in the art of manufacturing PCBs.

Figures 6A and 6B, and 7A and 7B illustrate the force sensor of the invention applied to a robotic finger-tip (figures 6A and 6B) and a robotic thumb-tip (7A and 7B). Figure 6B and 7B illustrate the arrangement of 34 tactile sensors over each tip. The tactile sensors are formed by a matrix of electrically conductive elements. As can be seen clearly from figures 6B and 7B, the matrix does not need to form square or rectangular tactile sensors. In the embodiments illustrated, the shape of the tactile sensors have been optimised to provide maximum coverage over the tip with no dead spots, in other words spots without sensor coverage. Although 34 tactile sensors are illustrated, the invention is not limited to 34 tactile sensors and any number of tactile sensors may be utilised depending on the application. In one embodiment, the tactile sensors are distributed evenly over the surface. However, different arrangements are possible depending on the application of the force sensor.

In one embodiment, each tactile sensor is sensitive to loads ranging from 0.1 N to 25 N, although other sensitivities are possible.

Figure 8 illustrates a block diagram of one embodiment of an electronic circuit for sensing forces applied to a force sensor of the invention. The tactile sensors 81 are arranged in a grid pattern, and scanned row by row. To sample one tactile sensor, the control logic 83 switches the row on which the one tactile sensor is positioned to 5 V, and all the other rows to high impedance. It then measures the voltage on the column on which the one tactile sensor is positioned. When no pressure is applied to the tactile sensor, the voltage measured will be that produced by the digital to analogue converter (DAC) 85 together with the rest voltage due to the standing conductivity in the conductive layer. As the pressure increases, so does the conductance of the tactile sensor, and the voltage on the column on which the one tactile sensor to be sampled is positioned rises towards 5 V. The voltage is

amplified by a programmable gate amplifier (PGA) 87, before it is sampled by the analogue to digital converter (ADC) 89.

Figures 9A and 9B illustrate one embodiment of the invention. The force sensor 90 comprises a conductive layer 91, a protective layer 93, an electrode layer 95, an electrically conductive grid 97 and a barrier layer 98.

In one embodiment, the conductive layer 91 comprises a resiliently compressible material. The magnitude of the electrical conductance of the conductive layer 91 is a function of a pressure exerted on the conductive layer 91. The protective layer 93 is a protective outer covering layer for the conductive layer 91, having a first surface 93A adjacent to a first surface 91A of the conductive layer 91. The shape of the protective layer 93 conforms to the shape of the conductive layer 91.

In one embodiment, the electrode layer 95 is substantially rigid. The electrode layer 95 has a first surface 95A adjacent a second surface 91B of the conductive layer 91, the first surface 95A of the electrode layer 95 is provided with an electrically conductive grid 97, such that the electrically conductive grid 97 is provided adjacent to the second surface 91B of the conductive layer 91.

The electrically conductive grid 97 comprises a first set of electrically conductive strip elements 97A extending in one direction with respect to the first surface 95A of the electrode layer 95, and a second set of electrically conductive strip elements 97B, insulated from the first set of strip elements 97A, the second set of strip elements 97b overlying the first set of electrically conductive strip elements 97A extending in a direction orthogonal to the first set of electrically conductive strip elements 97A. However, as illustrated above, with reference to figures 6B and 7B, the first and second sets of electrically conductive strip elements 97A, 97B do not have to be orthogonal to one another. The second set of electrically conductive strip elements 97B each have an opening 99 located at a position corresponding to the location at which the first set of strip elements 97A intersect the

second set of strip elements 97B. This results in the first set of electrically conductive strip elements 97A being exposed to contact the conductive layer 91, when pressure is applied to the conductive layer 91, through the openings 99 of the second set of strip elements 97B.

•

In one embodiment, a barrier layer 98 is provided between the conductive layer 91 and the protective layer 93. In one embodiment, the barrier layer 98 is a membrane composed of a limp sheet material.

In one embodiment, the barrier layer 98 is substantially impervious to fluids in order to prevent the transfusion of gases and liquids through the barrier layer 98, which may have a detrimental effect on the performance of the force sensor 90. In one embodiment, the barrier layer 98 comprises PVC. In one embodiment, the barrier layer 98 has a thickness of between about 0.007 mm to 0.015 mm.

In one embodiment, the barrier layer 98 prevents the protective layer 93 from adhering to the conductive layer 91 of the force sensor 90. If the protective layer 93 does bond to the conductive layer 91, then the sensitivity to pressure of conductive layer 91 may be reduced. ^•

In one embodiment, the barrier layer 98 provides frictional resistance against shear movement between the conductive layer 91 and the protective layer 93.

In one embodiment, the conductive layer 91 is composed of a polymeric material. In one embodiment, the conductive layer 91 comprises a natural polymer. In one embodiment, the conductive layer 91 comprises a rubber incorporating conductive particles. In one embodiment, the conductive layer 901 comprises a quantum tunnelling composite (QTC). In one embodiment, the conductive layer 91 comprises a QTC as described and claimed in International Patent Publication No. W09938173.

In one embodiment, the protective layer 93, has physical characteristics approximating to those exhibited by human flesh, such as, for example may be encountered at the pads of

flesh at the finger-tips. In one embodiment, the protective 93 comprises a polyurethane.

In one embodiment, the force sensor 90 is provided with a lubricant (not illustrated) between the conductive layer 91 and the electrode layer 95. In one embodiment, the lubricant is a dusting of an inert non-abrasive powdery dry lubricant such as, for example, chalk, in one embodiment, the lubricant comprises a material, and has a thickness, which does not substantially interfere with the connection between the electrically conductive strip elements 97A and 97B and the conductive layer 91.

The invention has been described with particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the scope of the invention.