U.S. patent number 3,911,215 [Application Number 05/452,784] was granted by the patent office on 1975-10-07 for discriminating contact sensor.
This patent grant is currently assigned to Elographics, Inc.. Invention is credited to William C. Colwell, Jr., George S. Hurst.
United States Patent |
3,911,215 |
Hurst , et al. |
October 7, 1975 |
Discriminating contact sensor
Abstract
A sensor construction is described for normally maintaining two
juxtaposed electrical potential carrying sheets, at least one being
flexible, separated from each other but permitting contact
therebetween when an object of specified radius of curvature is
pressed against the flexible sheet. The separation of the sheets is
accomplished by producing discrete small buttons of insulation,
preferably on the flexible sheet, with the spacing and the height
of the buttons determining the largest radius of curvature to which
the sensor will respond. This construction is specifically applied
to a telescriber sensor or the like whereby contact is made only by
depression of the flexible sheet with a writing instrument and not
by any portion of a writer's hand.
Inventors: |
Hurst; George S. (Oak Ridge,
TN), Colwell, Jr.; William C. (Oak Ridge, TN) |
Assignee: |
Elographics, Inc. (Oak Ridge,
TN)
|
Family
ID: |
23797920 |
Appl.
No.: |
05/452,784 |
Filed: |
March 18, 1974 |
Current U.S.
Class: |
178/18.05;
200/86R |
Current CPC
Class: |
G06F
3/045 (20130101) |
Current International
Class: |
G06F
3/033 (20060101); H01H 043/08 (); H04N
001/00 () |
Field of
Search: |
;200/86R,153M,46,159
;178/18,19,20 ;33/1M ;340/272 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robinson; Thomas A.
Attorney, Agent or Firm: Skinner; Martin J.
Claims
I claim:
1. A discriminating contact sensor which will respond only to a
contacting object having a radius of curvature less than a specific
value, which comprises: a first sheet of a flexible material
capable of being energized to establish an electrical potential
thereon, a second sheet capable of being energized to establish an
electrical potential thereon in juxtaposition with the first sheet,
and a plurality of substantially uniform discrete insulating
buttons electrically separating the first and second sheets
throughout the sensor, the buttons having a height and an average
spacing whereby the maximum radius of curvature of the object to
which the sensor will respond is approximately equal to the square
of the average spacing between the buttons divided by eight times
the height of the buttons.
2. The sensor of claim 1 wherein the insulating buttons are
substantially circular in a section parallel to the first and
second sheets and have a diameter from about 0.001 to about 0.015
in., an average spacing between adjacent buttons of from about
0.025 to about 0.075 in. and a height in a direction perpendicular
to the first and second sheets of from about 0.0005 to about 0.015
in.
3. An improved electrographic sensor for writing thereon of the
type wherein a uniform resistive sheet having electrodes attached
thereto for the application of orthogonal electrical potentials is
overlaid with a flexible conductive sheet and spaced therefrom so
as to normally prevent contact therebetween but permit contact when
the flexible sheet is deformed by an object having a radius of
curvature less than a specific value, wherein the improvement
comprises: discrete insulator buttons of substantially uniform size
electrically separating the sheets throughout the sensor, the
buttons having a height and an average spacing whereby the maximum
radius of curvature of the object to which the sensor will respond
is approximately equal to the square of the average spacing between
the buttons divided by eight times the height of the buttons.
4. The sensor of claim 3 wherein the insulating buttons are
attached to the surface of the conductive sheet.
5. The sensor of claim 3 wherein the buttons have a diameter from
about 0.001 to about 0.015 in., the height thereof is from about
0.0005 to about 0.015 in., and the average spacing between the
buttons is from about 0.025 to about 0.075 in.
6. The sensor of claim 3 wherein the electrodes attached to the
resistive sheet are a plurality of spot electrodes equally spaced
along each edge of the resistive sheet; and further comprising a
plurality of discrete resistors each of which are connected between
adjacent of the spot electrodes whereby a series resistor network
is formed along each edge of the resistive sheet.
Description
BACKGROUND OF THE INVENTION
Our invention relates generally to the insulation of one electrical
potential carrying sheet from a second such sheet except when
contact therebetween is purposely desired, and more specifically to
insulation means whereby the sheets are brought into contact only
by an object having a radius of curvature less than a specific
value, the value being established by the arrangement of the
insulation. The invention is illustrated as applied to writing
sensors useful for the electrographic determination of coordinates
of a point or for the telemetry of drawings, signatures and the
like.
Typical of the prior art in this field is found in U.S. Pat. No.
3,632,874 issued to L. C. Malavard et al. In that patent, and
specifically FIG. 9, a conductive sheet of flexible material is
separated only by an air space from a second surface or sheet to
which is applied orthogonal electrical fields. A writing instrument
is used to bring the sheets together and thereby generate x- and
y-related signals as the writing instrument is moved. However, it
may be seen that finger tips, knuckles, the edge of the hand, or
other objects could deform the flexible sheet and give rise to
erroneous output signals.
In copending application Ser. No. 244,629, now U.S. Pat. No.
3,798,370, issued to G. S. Hurst on Mar. 19, 1974, a sensor is
described in which a "deformable" insulation is utilized between a
flexible conductive grounding sheet and a resistive sheet having
the orthogonal electric fields. In one embodiment a gel separates
the layers. Although the gel provides the necessary insulation
between the sheets, it is not a practical solution for production
units because of the care required to produce a reproducible
characteristic. A second embodiment, in the form of a nylon net or
the like, is amenable to the production of sensors and is
satisfactory for many applications of the sensor. However, when
handwriting is performed on the sensors fabricated using the net,
the nonuniform thickness (the threads versus the knots) of even the
finest available net material may be felt during the writing. Also,
movement of the net between the layers gives rise to gradual
deterioration of the materials in contact therewith.
SUMMARY OF THE INVENTION
Our invention in its simplest form utilizes a distribution of small
discrete insulating buttons of uniform height to normally separate
two electrical potential carrying sheets where at least one of the
sheets is flexible. The buttons may be either uniformly or randomly
distributed and are preferably affixed to the flexible sheet. The
spacing and height of the insulating buttons are chosen, assuming a
fixed diameter, so as to prevent contact of the layers by an object
having a radius of curvature greater than a selected value and
thereby discriminate between objects of different radii of
curvature. Specifically, the dimensions are chosen to permit
contact between the layers upon deformation by a conventional
writing instrument but prevent contact by any part of a hand
holding the writing instrument. In this structure we eliminate any
physical or psychological deterrents to normal handwriting.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a simplified circuit,
substantially as found in above-referenced copending application
(now U.S. Pat. No. 3,798,370), for the purpose of permitting a
description herein of one application of our invention;
FIG. 2 is an enlarged cross sectional drawing illustrating the most
general form of the subject matter of our invention;
FIG. 3 is an enlarged cross sectional view of our invention when
contacted by an object of less than a specified radius of curvature
for a given set of parameters for the insulation;
FIG. 4 is an enlarged cross sectional view of our invention when
contacted by an object of greater than a specified radius of
curvature; and
FIG. 5 is an enlarged cross section drawing of an electrographic
sensor embodying our invention for point coordinate determination,
written telemetry and the like.
DETAILED DESCRIPTION
The underlying principle of our invention may be explained through
the use of FIG. 2 which shows the essential components of the
sensor in an enlarged cross sectional view. Two substantially
planar and parallel sheets 23, 24 are assumed to have an electrical
potential applied thereto by any conventional means such as
described hereinafter. Sheet 23 is flexible, so as to be deformable
toward the second sheet 24 which may be rigid. Typical of the
flexible material is "Velostat," a conductive plastic distributed
by Customs Materials, Inc., of Chelmsford, Mass., or Mylar (E. I.
DuPont) with an aluminized surface as manufactured by numerous
companies. The second sheet may be a conductive metal plate or,
alternatively, a resistive paper supported on an appropriate
backing. If a resistive sheet is utilized, a typical material is
resistance paper Type L, manufactured by Knowlton Bros., Watertown,
N. Y., having a resistance of 1000 to 2000 ohms per square.
Separating the sheets 23 and 24 are a plurality of distributed
insulation buttons 25 preferably attached, as shown, to the
flexible sheet for most applications. These buttons are of
substantially equal diameter, D, and height, H, and may be randomly
or uniformly distributed with a spacing, S, being either an average
spacing (if random) or the actual center-to-center spacing (if
uniform). The diameter, D, is very much smaller than the spacing,
S. In general, a small diameter is desirable, and the height and
spacing are chosen for a particular application of the layered
structure. The insulating buttons 25 may be applied to sheet 23
using one of several standard techniques again depending upon the
dimensions. Typical application methods are air-jet spraying,
electrostatic spraying, rollers and silk screen techniques. The
material utilized to form the buttons may be, for example,
insulating printer's ink, epoxy paint or varnish.
With the construction shown in FIG. 2, we have determined that the
height and spacing (with a small fixed diameter) will affect the
manner of deforming sheet 23 so as to contact sheet 24. We have
developed a quantitative relationship for the condition that the
two sheets can be brought into contact by pressing the flexible
sheet with an object. This relationship can be expressed in terms
of the radius of curvature, R, of the pressing object using the
equation R .apprxeq. S.sup.2 /8H. An object having a radius of
curvature smaller than the value of S.sup.2 /8H will bring about
contact of the layers, as shown in FIG. 3. In contrast, an object
of radius of curvature greater than S.sup.2 /8H will not bring
about contact, as illustrated in FIG. 4.
This characteristic of discrimination by the structure as to the
radius of curvature may be used, for example, to determine the
number of particles of a given size range that impinge against the
flexible layer 23. Thus, the structure would be used as a switch in
a conventional electrical counting system. The use of several
sensors each having a discrimination corresponding to different
values of R would provide an electrical counting system capable of
counting the number of impinging particles having various radii of
curvature.
Our invention, however, is of particular value in telemetry sensors
and coordinate determining sensors. Typical of such sensors is that
described in the aforementioned copending patent application of G.
S. Hurst. This may be understood by referring to FIG. 1 which is a
schematic circuit diagram of that patent application, and to FIG. 5
which is an enlarged cross section of a sensor embodying our
present invention for use with the circuit of FIG. 1. Referring
first to FIG. 1, a uniform highly resistive sheet 10 is suitably
mounted by any conventional means to a support (not shown) so as to
form a plane. In each corner of sheet 10 are spot electrodes 11 as
at points A, B, C, and D. Spaced between the corner spot
electrodes, in a row-like manner, are edge spot electrodes 12 along
each edge of sheet 10. Three edge electrodes are shown along each
edge for illustration; an actual sensor may have more or less for a
particular size and application.
Connected between adjacent spopt electrodes 11 and 12 are
individual discrete high precision (e.g., 0.1 to 1.0%) resistors
13. These resistors 13, in series along each edge, form four
resistor networks joined to electrodes 11 at points A, B, C and D.
It will be recognized that this structure, using discrete
resistors, permits the choice of preferred precision resistive
elements to assist in the establishment of uniform electrical
gradients in the resistive paper 10.
The ends of each resistor network are connected, in an appropriate
sequence, to a voltage source 18 or 19 by appropriate switches such
as 14a, 14b, etc., in order to achieve orthogonal electric fields.
Although a single switch across each network would function in the
same manner, solid state switches required for rapid operation
(e.g., 10.sup.4 -10.sup.5 Hz) often exhibit ohmic resistance in the
closed position. However, the resistance of each of the contacts of
a chip of four switches is substantially equal and thus the circuit
as shown overcomes the effect of differing internal resistance.
Operation of the switches 14-17 is governed by the output signals
of oscillator 20.
Further details of the electrical circuit may be found in the cited
copending application (now U.S. Pat. No. 3,798,370). The operation
of the circuit results in uniform orthogonal electric fields being
generated in resistive sheet 10 during mutually exclusive time
periods. Accordingly, when any specific electrical potential (such
as an electrical ground) is applied at a point on the resistive
sheet, as by bringing sheet 23 into contact with sheet 10, output
signals are produced that are related to the x- and y-coordinates
of the point. The coordinates are sampled at the rate of the
oscillator; thus, the coordinates of a "moving point" may be
followed from the signals generated at the output of conventional
sample-and-hold circuits 21, 22. These sample-and-hold circuits
maintain the signal due to one coordinate while the other
coordinate signal is being measured and then update the signal with
new values.
In practice, the resistive sheet 10 is made a portion of a sensor
unit such as illustrated in FIG. 5. This shows the sheet 10 and an
electrode 12 mounted within a case 26. Spaced above resistive sheet
10, and parallel thereto, is the flexible conductive sheet 23 such
as formed from aluminzed Mylar or the like. The flexible layer 23
is normally separated by the insulator buttons 25 from the
resistive sheet 10 as described hereinabove. Placed upon the
flexible sheet 23 is a protective cover sheet 27. Any conventional
writing instrument 28, such as a ball-point pen or pencil, may be
moved over the surface of the cover sheet 27, or another sheet (not
shown) laid thereon, so as to depress the flexible sheet 23 to
bring about contact with the resistive sheet 10 thus initiating
electrical signals corresponding to the coordinates of the contact
point.
In order that the writing instrument 28, if moved continuously on
the sheet 27, will not be above an insulating button 25 more than
about 1% of the time, a maximum button size (diameter) of less than
0.005 in. (0.125 mm) is preferred. With this condition, the time of
interruption of electrical contact between sheets 10 and 23 during
continuous writing will be much less than 1%. The spacing between
buttons 25 should be much greater than the diameter of the buttons
and for this application may be in a range of about 0.025 to 0.075
in. (0.635 - 1.9 mm). The height of the buttons, if less than about
0.005 in. (0.125 mm) cannot be felt as writing occurs. In order to
provide reasonable discrimination between pressure of a writing
instrument and portions of a writer's hand, the above-cited
equation, R .apprxeq. S.sup.2 /8H, may be used to determine the
value of R for various values of separation, S, and height, H. For
example, if S = 0.030 in. (0.66 mm) and H = 0.001 in. (0.025 mm)
then R equals about 0.1 in. (2.54 mm). With S = 0.050 and H = 0.002
in. (1.27 and 0.05 mm, respectively), R becomes 0.15 in. (3.8 mm).
Either of these values are sufficiently small such that the
portions of a writer's hand will not cause contact between the
flexible sheet 23 and the resistive sheet 10. However, an
instrument like a ball-point pen with a radius of curvature of
about 0.025 in. (0.635 mm) will readily cause contact as it moves
across the surface except when over a button (1% or less of the
surface). Accordingly, continuous writing may be performed with
output signals being derived continuously that are proportional to
the writing instrument position.
The output signals of the circuit may be utilized in many ways. For
example, if the sensor is utilized for signature verification, the
signals may be transmitted to a remote station where a duplicate of
the signature may be produced using conventional equipment (e.g.,
an oscilloscope). Alternatively, the signals may be compared with
signals held in storage in a computer for verification of the
identity.
In another utilization, data points on graphs and the like may be
digitized, displayed, reproduced and/or stored. This would apply
also to storage of information related to sketches of proposed
design of an apparatus part, etc., until a final design is
completed. Furthermore, output signals derived from data may be
processed by a programmed calculator to compute desired
information.
Having described several applications for our invention, it will
become apparent to those versed in the art that the basic sensor
has many applications. We mean, by the term basic sensor, a
composite of a pair of sheets, each being capable of carrying an
electrical potential and at least one being flexible, separated by
small discrete buttons of insulating medium. The preferred
dimensions of the insulating buttons will vary according to the
utilization of our discriminating sensor. For most applications,
one of the layers will be a resistive sheet in which may be
established orthogonal electric fields. Although we prefer applying
the present invention to the sensor of the cited copending
application (now U.S. Pat. No. 3,798,370), it may be applied to
sensors such as those described in U.S. Pat. Nos. 3,632,874,
3,449,516, 3,670,103, etc.
* * * * *