CA1233865A - Tactile sensors for robotic gripper and the like - Google Patents

Tactile sensors for robotic gripper and the like

Info

Publication number
CA1233865A
CA1233865A CA000445327A CA445327A CA1233865A CA 1233865 A CA1233865 A CA 1233865A CA 000445327 A CA000445327 A CA 000445327A CA 445327 A CA445327 A CA 445327A CA 1233865 A CA1233865 A CA 1233865A
Authority
CA
Canada
Prior art keywords
conductive rods
conductive
rods
electrically
layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000445327A
Other languages
French (fr)
Inventor
Robert R. Peterson
Dale W. Schubert
Peter N. Cholakis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hutchinson Aerospace and Industry Inc
Original Assignee
Barry Wright Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Barry Wright Corp filed Critical Barry Wright Corp
Application granted granted Critical
Publication of CA1233865A publication Critical patent/CA1233865A/en
Expired legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H13/00Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch
    • H01H13/70Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard
    • H01H13/78Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard characterised by the contacts or the contact sites
    • H01H13/785Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard characterised by the contacts or the contact sites characterised by the material of the contacts, e.g. conductive polymers
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B25HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25JMANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J13/00Controls for manipulators
    • B25J13/08Controls for manipulators by means of sensing devices, e.g. viewing or touching devices
    • B25J13/081Touching devices, e.g. pressure-sensitive
    • B25J13/084Tactile sensors
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00Measuring force or stress, in general
    • G01L1/18Measuring force or stress, in general using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00Measuring force or stress, in general
    • G01L1/20Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G01L1/205Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress using distributed sensing elements
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01LMEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/22Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers
    • G01L5/226Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping
    • G01L5/228Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for measuring the force applied to control members, e.g. control members of vehicles, triggers to manipulators, e.g. the force due to gripping using tactile array force sensors
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H13/00Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch
    • H01H13/70Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard
    • H01H13/702Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H13/00Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch
    • H01H13/70Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard
    • H01H13/702Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
    • H01H13/703Switches having rectilinearly-movable operating part or parts adapted for pushing or pulling in one direction only, e.g. push-button switch having a plurality of operating members associated with different sets of contacts, e.g. keyboard with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches characterised by spacers between contact carrying layers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2201/00Contacts
    • H01H2201/022Material
    • H01H2201/032Conductive polymer; Rubber
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2203/00Form of contacts
    • H01H2203/002Raised edge
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2203/00Form of contacts
    • H01H2203/008Wires
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2205/00Movable contacts
    • H01H2205/006Movable contacts mounted on spacer
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2207/00Connections
    • H01H2207/01Connections from bottom to top layer
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2209/00Layers
    • H01H2209/002Materials
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2209/00Layers
    • H01H2209/024Properties of the substrate
    • H01H2209/032Properties of the substrate non elastomeric
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2209/00Layers
    • H01H2209/046Properties of the spacer
    • H01H2209/056Conductive rubber
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2209/00Layers
    • H01H2209/068Properties of the membrane
    • H01H2209/074Properties of the membrane elastomeric
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2211/00Spacers
    • H01H2211/026Spacers without separate element
    • H01H2211/032Pressure sensitive layer on contacts
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2227/00Dimensions; Characteristics
    • H01H2227/03Hardness
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2231/00Applications
    • H01H2231/04Robot
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01HELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H2239/00Miscellaneous
    • H01H2239/078Variable resistance by variable contact area or point

Abstract

Abstract A tactile sensor for sensing an object in contact therewith. In its preferred form, the sensor compri-ses a plurality of layers disposed in a sandwich arrangement. A top layer is comprised of a flexible, electrically-insulating material and a plurality of parallel flexible conductive rods. A bottom layer is comprised of an electrically-insulating material and a plurality of parallel conductive rods that extend at right angles to the conductive rods of the top layer, thus forming a sensory array comprising a plurality of superimposed intersection points arranged in a grid pattern. An intermediate layer is comprised of a resilient, electrically-insulating material in which is disposed a plurality of parallel conductive posts that extend perpendicular to the plane of the three layers. These posts are comprised of a resilient con-ducting material. Each conductive post is disposed at one of the sensor's aforementioned intersection points so as to electrically couple one of the conductive rods of the top layer to one of the conductive rods of the bottom layer. The conductive rods are formed with a selected cross-section, in order that changes in the amount of pressure exerted on the sensor will produce corresponding logarithmic changes in the contact sur-face area, and hence electrical contact resistance, established between the conductive rods and those con-ductive posts disposed beneath the points of pressure.

Description

' ~ ~

TACTILÆ SENSORS POR ROBOTIC ~g ~2~D THE LIl;

Field Of The Invention This invention relates to industrial robots in general, and more particularly to tactile sensors for~J
use in such robots.

i Backqround Of The Invention Industrial robots are well known in the art. Such robots are intended to replace human workers in a variety of assembly tasksq It has been recognized that in order for such robots to e~fectively replace;
human workers in increasingly more delicate and de-tailed tasks, it will be necessary to provide sensory apparatus for the robots which is functionally equiva-lent to the various senses with which human workers are naturally endowed, e.g. sight, hearing, etc.
Of particular importance for delicate and detailed assembly tasks is the sense of touch. To~ch can be important for close-up assembly work where vision may be obscured by arms or other objects, and touch can be important for providing the sensory feedback necessary for grasping delicate objects firmly without causing damage to them. Touch can also provide a useful means for discriminating between objects having different sizes, shapes or weights. Accordingly, various tac-tile sensors have been developed for use with industrial robots.
One such tactile sensor, developed by William D.
Hillis and John Hollerback, is disclosed in the article, "How Smart Robots Are Becoming Smarter", by Paul Kunnucan, High Technology Magazine, Sept./Oct.
issue, pp. 32,36, Technology Publishing Company. This tactile sensor comprises 256 pre~sure-sensitive ,,. ~.., ~s ,,'~
~ .

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~ ~.

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electrical switches arranged in a 16 x 16 grid pat-tern. When an object is brought into contact with the sensor, appropriate swi~ches are triggered so as to produce a pattern of electrical signals which correspond to the "feel" of the object contacting the sensor. Hillis and Hollerback constructed their tac-tile sensor by sandwiching a piece of ordinary pan-tyhose between a top layer comprised of a piece of non-conductive silicon rubber impregnated with conduc-tive graphite along 16 parallel lines and a bottom layer comprised of a printed circuit board having 16 parallel conducting lines disposed therein. Hillis and Hollerback oriented their top and bottom layers relative to one another so that the 16 parallel con-ducting lines in the top layer were disposed at right angles to the 16 parallel conducting lines in the bot-tom layer, thereby orming a sensory array comprising 256 superimposed intersection points arranged in a 16 x 16 grid pattern. The conducting lines of the top layer are normally separated from the conducting lines of the bottom layer by the pantyhose. However, when an object comes into contact with the sensor and exerts a requisite minimum pres~ure on the sensor, the conducting lines make contact with one another through the meshes of the pantyhose at those intersection points disposed beneath the points o~ pressure, thereby allowing current to flow between the top and bottom layers at selected locations so as to produce a pattern of electrical signals which corresponds to the "feel" of the~object contacting the sensor.

'`' ' . .. ..

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This same concept is believed disclosed in another publication, "Active Touch Sensing" by William Daniel Hillis, distributed by the MIt~ Artificial Intelligence Laboratory as A.I. Memo 629 n In this second publica-tion, Hillis also describes replacing the intermediate layer of pantyhose with an alternative separator layer comprised of non-conductive paint. This non- -conductive paint is sprayed directly onto the bottom side of the top layer as a fine mist so that it adheres thereto as a collection of spaced, non-conductive dots. The conducting lines of the top layer are normally separated from the conducting lines of the bottom layer by the misted layer oE non-conductive paint. When an object comes into contact with the sensor and exerts a requisite minimum pressure on the sensor, the conducting lines of the top layer ~ake contact with the conducting lines of the bottom layer through the gaps existing between adjacent dots of non-conductive paint at those inter-section points disposed beneath the points of pressure, thereby allowing current to flo~ between the top and bottom layers at selected locations so as to produce a pattern of electrical...signals which corresponds to the "feel" of the object contacting the sensor.
U.S. Patent No. 4208648 discloses another tactile sensor which comprises 256 pressure-sensitive electri-cal switches arranged in a 16 x 16 grid pattern, such that when an object is brought into contact with the sensor, appropriate switches are triggered so as to , ~t~
:

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produce a pattern of electrical signals corresponding to the "feel" of the object contacting the sensor.
The tactile sensor disclosed in U.S. Patent No.
4208648 differs significantly from the aforementioned sensors in many of the particulars of its construction and operation. More particularly, the sensor disclosed in U.S. Patent ~o. 4208648 comprises three distinct layers disposed in a sandwich arrangement.
The top layer is comprised of a resilient, electrically-insulating material in which is disposed a first set o~ 16 parallel conducting lines. The bot-tom layer is comprised of a resilient, electrically-insulating material in which is disposed a second set of 16 parallel conducting lines. The bottom layer is disposed relative to the top layer so that the second set of conducting lines extend at right angles to the first set of conducting lines, thus forming a sensory array comprising 256 superimposed intersection points arranged in a 16 x 16 grid pattern. The intermediate layer is comprised of a synthetic resin mater;al which is electrically conductive to some extent in its natural, unstressed state, and whose conductivity is increased by compression. When an object exerts a requisite minimum pressure on the sensor, the conduc-tivity of the intermediate layer is altered at those locations disposed beneath the points of pressure. As a resùlt, the current flowing between thé first and second sets of conducting lines is also altered at the locations affected by pressure, and a pattern of electrica~ signals is produced which .

, ~331~65 corresponds to the 'tfeel" of the object contacting the sensor.
Unortunately, the tactile sensors described above are believed to suffer from one or more of the following limitations: (1) poor reliability, (2) poor durability, (3~ high cost of manufacture, (4) signifi-cant complexity of manufacture, (5) limited sen-sitivity~ (6) complicating signal "cross-talk" (where-the current signal travels through the intermediate layer at locations other than those disposed at the points of pressure) and (7) a pressure/current rela-tionship of limited utility.

Ob1ects_Of The Invention Accordingly, the principal object of the present invention is to provide an improved form of tactile sensor which overcomes or reduces the limitations set forth above.

Summary O~ The Invention These and other objects of the present invention are attained in a preferred embodiment by providing a tactile sensor which comprises three distinct layers disposed in a sandwich arrangement. The top layer is comprised of a flexible, electrically-insulating material and a plurality of parallel flexible conduc-tive rods. The bottom layer is comprised of an electrically-insulating material and a plurality of parallel conductive rods that extend at right angles to the conductive rods of the top layer, thus forming .

~33~365 a sensory array comprising a plurality o~ superimposed intersection points arranged in a grid pattern. The intermediate layer is comprised of a resilient, electrically-insulating material in which is disposed a plurality of parallel conductive posts that extend perpendicular to the planes of the three layersD
These posts are comprised of a resilient conducting materialO Each conductive post is disposed at one of the sensor's aforementioned intersection points so as to electrically couple one of the conductive rods of the top layer to one of the conductive rods of the bottom layer. The conductive rods are formed with a selected cross-section, in order that changes in the amount of pressure exerted on the sensor will produce corresponding changes in the contact surface area, and hence a change in the electrical contact resistance, between the conductive rods and those conductive posts disposed beneath the points of pressure. As a result of this construction, the sensor i5 capable of better providing a pattern of electrical signals which, through use of an appropriate computer and computer software, will provide a determination better approxi-mating the "feel" of an object contacting the sensor.

Brief Descri~ion Of The Drawings Tllese and other objects and features of the present inyention will be more clearly described or rendered obvious in the following detailed description of the preferred embodiment, which is to be considered ' together with the accompanying drawings wherein like .

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numbers refer to like parts and further wherein:
Fig. 1 is a fragmentary perspective view with por-tions broken away of the preferred embodiment of the present invention;
FigO 2 is a sectional view taken along line 2-2 of Fig. l;
Fig. 3 is a scaled illustration of the cross sectional shape of the conductive rods used in the ~
preferred embodiment shown in Figs~ 1 and 2;
Fig. 4 is a block diagram of an electronic control circuit integrating the present invention; and Figs. 5-8 are alternative embodiments of the pre-sent invention.

Detailed Description Of The Preferred Embodiment Looking irst to Figs. 1 and 2, the tactile sensor
2 generally comprises three distinct layers disposed in a sandwich arrangement: a top layer 4r an inter-mediate layer 6, and a bottom layer 8.
Top layer 4 is comprised o~ a flexible, electrically-insulating material which is abrasion-resistant. Preferably top layer 4 is formed out o~
a polymeric material such as an elastomer,~ for example, a blend of polybutadiene and natural rubberr and has a hardness of between about 50 and 60 duro-meter on the Shore A 2 scale. Layer 4 has a planar ; ~ top surface 10 and a planar bottom surface 12 provided with a plurality of parallel grooves 14. In the pre-ferred embodiment there are 16 grooves 14.
Each of the grooves 14 has a conductive rod 18A, ;

., .
.

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18B, 18C, etc., secured therein by an adhesive or equivalent meansO Rods I8A, 18B~ 18C, etc., are formed out of a flexible cond~ctive material.
Preferably rods 18A, 18B, 18C, etc. are made of a polymeric'elastorner, e.g., chloroprene, which is doped with a suitable conducting material, e.g., carbon black. Rods 18A~ 18B, 18C, etc. are formed so that they have a hardness of between about 70 and 80 duro`
meter on the Shore A 2 scale.
Conductive rods 18A, 18B, 18C, etc., are shaped so that at their intermediate portions (i.e. those por-tions of the rods which extend adjacent intermediate layer 6) each has a cross-sectional profile generally similar to the cross-sectional profile of a "hull" of a ship. The cross-sectional prof'ile of the inter-mediate portions of rods 18A, 18B, 18C, etc., is shown iQ greater detail in Fig~ 3. As seen in Fig. 3, the intermediate portions of'the conductive rods are formed with a double curvature of a selected func-'tional character and have a projecting nose portion 19~ Grooves 14 and conductive rods 18A, 18B, 18C~
etc., are sized relative to one another so that the projecting nose portions l9 of ~onductive rods 18A, 18B, 18C, etc., extend below the bottom surface 1~ of top layer 4 (see Fig. 2~. As will hereinafter be discussed in qreater detail, cond~ctive rods i8A, 18B, 18C, etc. are shaped at their end portions (i.e. those portions of the rods which project out beyond the ~' region of intermediate layer 6, so that each has a substantially rectangular cross-section, as indicated .

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in Fig. 1 at 18lD, 18'E, 18'F, etc.
Bottom layer 8 is comprised of a rigid, electrically-insulating material such as a non-conducting polymer or the sort of material typically used to fabricate circuit board substrates, e.g., resin-impregnated fiberglass sheets. Layer 8 has a planar top surface 20 and a planar bottom surface 22, and is provided with a plurality of flat conductive copper buses 26A, 26B, 26C, etc. In the preferred embodiment there are 16 buses 26A, 26B, 26C, etc.
Buses 26A, 26B, 26C, etc., are preferably fixed in place on the top surface 20 of bottom layer 8 by bonding or other equivalent means. Buses 26A, 26B, 26C, etc., are sized relative to bottom layer 8 so that an end portion of each bus extends out beyond the end of bottom layer 8, as shown in Figs. 1 and 2.
Bottom layer 8 also has a plurality of conductive rods 28A, 28B, 28C, etc., disposed thereon.
Conductive rods 28A, 28B, 28C, etc., are preferably identical to conductive rods 18A, 18B, 18C, etc.
described above, except that they lack any flat pro-jecting end portions corresponding to the projecting end portions 18~D, 18'E, 18'F, etc. noted above. In the preferred embodiment there are 16 rods 28A, 28B, 28C, etc. Rods 28A, 28B, 28C, etc., are preferably fixed in place as shown in Figs. 1 and 2 by an adhe-sive or other equivalent means so that rods 28A, 28B, 28C, etc., make good conductive contact with buses 26A~ 26B, 26C, etc~
Bottom layer 8 is disposed relative to top layer 4 , . .

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so that conductive rods 28A, 28B, 28C, etc., extend at right angles to conductive rods 18A, 18B, 18C, etc., thereby forming a sensory array comprising 256 superimposed intersection points arranged in a 16 x 16 grid pattern. Preferably conductive rods 18A, 18B, 18C, etc. are uniformly spaced from one another, and the same is true for conductive rods 28A, 28Bt 28C, etc.
Intermediate layer 6 is comprised of a pad 30 formed out of a non-conducting elastomeric material such as polyurethane and has a hardness of between ahout 40 and 60 durometer on the Shore A-2 scale. Pad 30 has planar top and bottom surfaces 32 and 34.
Intermediate layer 6 also comprises a plurality of transversely-extending conductive posts 36. Posts 36 extend perpendicular to the major plane of pad 30 and run between and intersect the pad's top and bottom sur-faces 32 and 34. Conductive posts 36 are formed from an elastomeric material which is electrically-conductive. Posts 36 are preferably formed out of a ; material of selected conductivity, e.g., a polymer such as chloroprene compounded ~ith carbon black so as to be conductive, and have a hardness of between about 50 and 60 durometer on the Shore A-2 scale. As seen in Figs. 1 and 2, one conductive post 36 is disposed at each of the sensor's aforementioned intersection points so as to electrically couple one of the conduc-tive rods 18A, 18B, 18C, etc., of top layer 4 to one of the conductive rods 28A, 28B, 28C, etc., of bottom layer 8.
As seen in Fig. 2, when no force is applied to the :~:

~233~365 top surface 10 of thè sensor, only the projecting nose portions of conductive rods 18A, ]8B, 18C, etc., con-tact the conductive posts 36, and only the projecting nose portions of conductive rods 28A, 28B, 28C, etc., contact the conductive posts 36. However, when an object comes into contact with the top surface 10 of the sensor and exerts a certain requisite minimum pressure on the sensor, layers 4, 6 and 8 are forced together so that conductive rods 18A, 18B, l~C; etc., and conductive rods 28A, 28B, 28C, etc., approach one another at the points of pressure. As the conductive rods 18A, 18B, 18C, etc., and the conductive rods 28A, 28B, 28C, etc., are forced together at the points of pressure, the conductive rods tend to press into the softer intermediate layer 6 so as to increase their effective surface area contact with those conductive posts 36 disposed about the points of pressure. As a result, the electrical contact resistance established between the conductive rods and those conductive posts disposed beneath the points of pressure tends to decrease correspondingly, whereby for a given vltage applied between rods 18~, 18B, 18C, etc. and rods 28A, 28B, 28C, etc. the current flow will increase in inverse relation to the changes in contact resistance.
On account of the foregoing construction, it will be seen that a pressure-sensitive switch is formed at each of the sensor's intersection points. When coupled to an appropriate electric circuit, these switches are together capable of producing a pattern of electrical signals corresponding to the n feel" of , i ; BAR-75 .

lZ33~

.
an object contacting the sensor.
It will be appreciated that the conductive rods 18A, 18B, 18C, etc~ must be sufficiently flexible along their length so that the localized application of pressure at an intersec'ion point will not register significantly at adjacent intersection points. At the same time, however, the conductive rods 18A, 18B, 18C, ete. must have a suffieient hardness vis-a-vis the components in intermediate layer 6 so that it is the layer 6, and not the conductive rods, which deforms under the application of pressure. The cross-sectional geometry chosen for conductive rods 18A, 18B, 18C, etc., and conductive rods 28A, 28B, 28C, etc. (shown in detail in Fig. 3), is such that the pressure/current relationship of sensor 2 tends to have a non-linear response of substantially logarith-mie form which enables it to aeeurately reflect minute variances of pressure under very light loads as well as great variances of pressure under very heavy loads.
It is to be noted that the cross-sectional shape of rods 18A, 18B, 18C, etc. and rods 28A, 28B, 28C, etc.
are si~ilar to the cross-sectional profile of the hole of a ship having symmetrical double curvatures which work with the nose portions 19 to give the desired effect. It will also be appreciated that the precise pressure/current relationship of the sensor 2 will depend also on a number of other factors s~ch as layer thieknesses, layer eompositions, and also the relative ~ hardnesses of eonductive rods 18A, 18B, 18C, ete., and ; 28A, 2aB, 28C, ete., and conductive posts 36. By '~, ~, ~ ' ~
~, ' .

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.

selectively adjusting the aforementioned factors, it is possible to build a tactile sensor having the desired sensitivity.
In order to render the tactile sensor 2 substan-tially impervious to the effects of certain inhospi-table climates, e.g., water or oil, it is preferred that the edges of top layer 4 and bottom layer 8 extend out beyond the edges of intermediate layer 6, so that the two may be brought together and joined to form a sealed environment. More particularly, it is preferred that top layer 4 be folded do~7n and bonded to bottom layer 8 in the manner shown in Fig. 2. At the same time, in order to allow the sensor to be coupled into an appropriate electric circuit, the pro-jecting end portions 18'A, 18'B, 18'C, etc. of conduc-tive rods 18A, 18B, 18Cr are turned down as shown in Fig. 1 so that they run along the top surface 20 of bottom layer 8 towards the perime~er of the sensor, and these projecting end portions (formed with a substantially rectangular cross-section, as noted above) and buses 26A, 26B, 26C, etc. extend out beyond the sealed side edges of the sensor, ready to be coupled to an appropriate electric circuit.
Fig. 4 shows how the preferred form of tactile sensor 2 may be coupled into an electric circuit for use with an industrial robot. This circuit generally comprises a computer 50 which is coupled to the input line of a 16-line demultiplexer 52. Computer 50 is also coupled to demultiplexer 52 by a control line (shown in phantom). The 16 output lines of :;
; ' :
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, . .

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~3~

demultiplexer 52 are respectively attached to the 16 projecting end portions of conductive rods 18A, 18B, 18C7 etc. of sensor 2. The 15 projecting end portions o~ buses 26A, 26B, 26C, etc., of sensor 2 are respec~
tively attached to the 16 input lines of a current-to-voltage converter 54. ~he 16 output lines of the converter 54 are respectively attached to the 16 input lines of a multiplexer 56. The output line of multiplexer 56 is coupled to an analog-to-digital con-verter 58 and the control line of multiplexer 56 (shown in phantom) is coupled to the computer 50. The output fro~ converter 58 is fed to computer SOr The output of computer 50 is coupled to a robot computer 60, ~hich is itself attached to robot manipulation controls 62. Robot manipulation controls 62 control an arm or other robot appendage working in cooperation with tactile sensor 2. It is to be appreciated that computer 50, demultiplexer 52, current-to-voltage converter 54, multiplexer 56, analog-to-digital con-verter 58, robot computer 60, and robot manipulation controls 62 are all of the sort well known in the art.
In a typical case, the sensor 2 is mounted to a robot appendage so that the rigid bottom layer 8 faces and is fixed to the appendage and the flexible top layer 4 faces outwardly in position to engage an object to be handled.
During operation of the robo~, the presence of an object on sensor 2 is determined by the control circuit in the following manner. The computer 50 sends a signal to demultiplexer 52 to energize conductive rod "

.

~33~65 18A. Since conductive rod 18A is coupled to each of the conductive rods 28At 28B, 28C, etc.t by conductive posts 36 at the sensor's superimposed intersection pointsr energizing conductive rod 18A produces a current in each of the conductive rods 28A, 28B, 28Ct etc. However, as previously described, the current flowing in each of the lines 28A, 28B, 28Ct etc. will vary from one another in accordance with the amount of pressure being applied to the sensor at the intersec-tions of conductive rod 18A with conductive rods 28At 28B t 28C, etc. Converter 54 receives the current pre-sent in each of the conductive rods 28At 28B, 28C, etc. by virtue of its connections to buses 26At 268t 26Ct etc.t and converts the current flowing in each of -the conductive rods 28At 28Br 28C, etc., to a corresponding voltage. The output from converter 54 is then passed along to multiplexer 56. Computer 50 uses multiplexer 56 as a gating mechanism so as to allow it to sequentially sample the output from each of tne conductive rods 28A, 28B, 28C, etc., and to feed the outputs to converter 58. The latter converts these analog voltage outputs to digital signals which are automatically fed to compu~r 50. Then the com-puter orders demultiplexer 52 to deenergize conductive rod 18A and energize conductive rod 18B~ Since con-ductive rod 18B is coupled to èach of the conductive rods 28A, 28B, 28C, . etc., by conductive rods 36 at the sensor's superimposed intersection points, energizing conductive rod 18B raises a current in e~ch of the conductive rods 28A, 28B, 28C, etc. However, as pre-.' , ~233~

viously described, the current flowing in each of the lines 2BA, 28B, 28C, etc., will vary from one another in accordance with the amount of pressure being applied to the sensor at the intersections of conduc-tive rod 18B with conductive rods 28A, 28B, 28C, etc.
The computer then uses the circuitry as outlined above to sequentially sample the output derived from conduc-tive rods 28A, 28B, 28C, etc., and to apply the out- -puts to converter 58~ This process is repeated over and over, until the computer 50 has sampled the electricaL signals from all 256 intersection points on the sensor and has coordinated the digital data so as to form a conclusion resarding the presence of any object on the tactile sensor. The computer 50 then relays this digital information to the robot cornputer 60 which automatically adjusts the robot manipulation controls 62 as needed.

Advantaqes_Of The Present Invention The preferred embodiment of the present invention described and illustrated herein is believed to have numerous advantages over the prior art.
First, the tactile sensor disclosed herein has a wide range o~ sensitivity~ The unique geometry of conductive rods 18A, 18B, 18C, etc., and 28A, 28B, 28C, etc., ensures that the sensor's signal output will vary logarithmically with contact pressures, in order that the sensor will be capable of determining minute YarianCeS in pressure under very light loads as well as great variances of pressure under very heavy : ~ .

BsA2R807~DN
., ~

~.~Z33~

loads.
Second, the tactile sensor disclosed herein is relatively reliable, durable, inexpensive to make, and simple to produce.
Third, the tactile sensor disclosed herein has an intermediate layer which is conductive only at the sensor's superimposed intersection points, so that signals can pass between the conductive rods of the top and bottom layers only at the intersection points.
Fourth, the tactile sensor is completely sealed from its environment so as to render it operational under a variety of threatening conditions.

Modifications Of The Preferred Embodiment It is, of course, possible to modify the preferred embodiment of the present invention without departing from the scope of the invention.
Thus, for example, the tactile sensor 2 may be formed with more or less than 16 conductive rods 18A~ r 18Br 18C, etc., and more or less than 16 conduct ve rods 28A, 28B, 28C, etc. Or the conductive rods 18Ar 18B, 18C, etc., and conductive rods 28A, 28B, 28C, etc., may extend at some angle other than a right angle to each other.
Optionally, conductive posts 36 may be formed with a cross-sectional shape different than the circular one shcwn on Figs. 1 and 2, e.g., sqLIare or other arbitrary shape; similarly, conductive rods 18A, l~B, 18C, etc., and 28A, 28B, 28C, etc., may be formed with a cross-sectional shape different than the one shown s-280-CDN
.~

~3~3~6~ïi in Figs. 1-3, e.g., triangular.
Furthermore, the sensor's bottom layer ~ need not be stiff or rigid but may be formed of a flexible material, such as that commonly used to form flexible circuit boards, or a material the same or similar to the material of which top layer 4 is made.
Obviously, the way in which the tactile sensor 2 is coùpled into the electric circuit shown in Fig. 4 may also be varied. Thus, for example, the output lines from demultiplexer 52 may ~e coupled to buses 26A, 26B, 26C, etc., and the input lines to converter 54 may be coupled to conductive rods 18A, 18B, 18C, etc. Also, computer 50 may be programmed to sample the current flowing through the sensor's intersection points in a sequence other than that disclosed.
Alternatively, sensor 2 may be used with a circuit entirely different from that shown in Fig. ~.
Referring to Fig. 5, the intergroove material in top layer 4 may be extended in length as shown at 100 so that the conduc~ive rods 18A, 18B, 18C, etc~ do not normally contact the posts 36 disposed in intermediate member 6~ This construction results in the sensor requiring some non-zero pressure threshold before an electrical signal can pass between the conductive rods 18A, 18B, 18C, etc. of the top layer 4 and the conduc-tive rods 28A, 28B, 28C, etc. o~ the bottom layer 8.
Alternatively, as shown in Fig. 6, the inter-mediate layer 6 shown in Figs. 1 and 2 may be replaced with a new intermediate layer 6' comprising a uniform sheet of an elastomeric material which is conductive, - - .

~33~

e g., a silicone rubber layer impregnated with con-ductive particles such as particles of carbon, silver, copper and the like (see V.S. Patent No. 4208648).
Also, as shown in Fig. 7, the conductive rods 18A, 18B, 18C, etc. and conductive rods 28A, 28B, 28C, etc.
may be formed so that they have substantially rec-tangular or square cross-sections throughout their length, and the conductiye posts :36 may be formed so that their projecting ends have cross-sectional pro-files similar to the hull of a ship as previously described in connection withn rods 18A, 18B, 18C, etc.
and rods 28A, 28Br 28C, etc. Of course, in th;s arrangement the rods 18A~ 18~, 18C, etc. and 28A, 28B, 28C, etc. will have a hardness less than the hardness of conductive posts 36, in order that rods 18A, 18B, 18C, etc. and 28A, 28B, 28C, etc. will deform under the application of pressure to the face of sensor 2 while posts 36 wiil remain substantially undeformed.
It is also envisioned, as shown in Fig. 8, that the intermediate layer 6 could be omitted entirely.
In this case the conductive rods 18A, 18B, 18C, etc.
would contact conductive rods 28A, 2~B, 28C~ etc.
directly, and by forming one or both sets of rods from relatively soft compositions, the requisite pressure variations of surface area contact (and hence electri-cal contact resistance) could be achieved at the affected intersection points.
Furthermore, the sensor may be formed SG that only the cond~ctive rods of the top layer have a hardness greater than the intermediate layer, or so that only the conductive rods of the bottom layer have a hard-ness greater than the lntermediate layer.

.
' ' ,, ~. .

~3~

It is also envisioned that the top surface 10 of top layer 4 can be textured or have a tread-like con-tour so as to improve traction. Furthermore, the sen sor need not be planar along its surfaces but rather each of the surfaces and their associated structure can be se~ments of a sphere or cylinder.
These and other similar modifications are be~ieved obvious to one skilled in the art, and are within the scope of the present invention.

,

Claims (12)

What We Claim Is:
1. A tactile sensor for sensing the pressure impressed by an object in contact therewith, said sen-sor comprising a sandwich having:
(a) a top layer comprised of a flexible, electrically-insulating material and a first plurality of flexible conductive rods extending parallel to one another;
(b) a bottom layer comprised of an electrically-insulating material and a second plurality of con-ducting rods extending parallel to one another, said bottom layer being disposed relative to said top layer so that the rods of said first plurality of rods extend at an angle to the rods of said second plura-lity of rods so as to form a sensory array comprising a plurality of superimposed intersection points arranged in a grid pattern; and (c) an intermediate layer comprised of a resi-lient, electrically-insulating material and a plura-lity of conductive posts extending transversely to said top, bottom, and intermediate layers, said con-ductive posts being made of a resilient material and being disposed so that one of said conductive posts is disposed at each of said intersection points so as to electrically couple one of said conductive rods of said top layer to one of said conductive rods of said bottom layer.
2. A tactile sensor according to claim 1 wherein the said conductive rods of said top and bottom layers all have a cross-sectional profile substantially the same as the cross-sectional profile shown in Fig. 3.
3. A tactile sensor according to claim 2 wherein all of said conductive rods are formed of a flexible material.
4. A tactile sensor according to claim 3 wherein the said conductive rods of at least one of said top and bottom layers have a hardness greater than the hardness of said intermediate layer.
5. A tactile sensor according to claim 4 wherein said flexible, electrically-insulating material of said top layer is comprised of a polymer, said electrically-insulating material of said bottom layer is comprised of a polymer, said resilient, electrically-insulating material of said intermediate layer is comprised of a polymer, and said conductive posts are comprised of a polymer compounded with a conducting material.
6. A tactile sensor according to claim 3 wherein said conductive rods are comprised of polymers.
7. A tactile sensor according to claim 6 having 16 conductive rods in said top layer and 16 conductive rods in said bottom layer.
8. A tactile sensor for sensing an object in con-tact therewith, said sensor comprising:

(a) a top layer made of a flexible, electrically-insulating material and including a plurality of first conductive rods extending parallel to one another, said first conductive rods being flexible along their length and having a cross-sectional profile substan-tially the same as the profile illustrated in Fig. 3;
(b) a bottom layer made of an electrically-insulating material and including a plurality of second conductive rods extending parallel to one another, said second conductive rods having a cross-sectional profile substantially the same as the pro-file shown in Fig. 3, said bottom layer also being disposed relative to said top layer so that said second conductive rods extend at an angle to said first conductive rods, thus forming a sensory array comprising a plurality of superimposed intersection points arranged in a grid pattern; and (c) an intermediate layer made of a resilient material which is electrically-conductive.
9. A tactile sensor according to claim 8 wherein said first conductive rods and said second conductive rods are formed of the same material
10. A tactile sensor according to claim 9 wherein said first conductive rods and said second conductive rods have a hardness greater than the hardness of said intermediate layer.
11. A tactile sensor according to claim 10 wherein said flexible, electrically-insulating material of said top layer is made of a polymer, said electrically-insulating material of said bottom layer is made of a polymer, and said intermediate layer is made of a polymer compounded with a conducting material.
12. A tactile sensor according to claim 11 having 16 conductive rods in said top layer and 16 conductive rods in said bottom layer.
CA000445327A 1983-03-18 1984-01-16 Tactile sensors for robotic gripper and the like Expired CA1233865A (en)

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US06/476,685 US4492949A (en) 1983-03-18 1983-03-18 Tactile sensors for robotic gripper and the like
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GB8404628D0 (en) 1984-03-28
GB2137022A (en) 1984-09-26
US4492949A (en) 1985-01-08
FR2542659A1 (en) 1984-09-21
GB2137022B (en) 1987-06-17
FR2542659B1 (en) 1989-08-25
DE3406093A1 (en) 1984-09-20
NL8400708A (en) 1984-10-16
IT1177555B (en) 1987-08-26
IT8447679A0 (en) 1984-02-13
JPS59175992A (en) 1984-10-05

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