UNITED STATES PATENT OFFICE.
Edward J. Willis, of Richmond, Virginia.
PLANIMETER.
Specification forming part of Reissued Letters Patent No. 11,568,
dated September 22, 1896;
Original No. 529,008, dated November 13, 1894.
Application for reissue filed March 20, 1896.
To all whom it may concern:
Be it known that I, Edward J. Willis, a citizen of the
United States, residing at Richmond, in the county of Henrico and State of
Virginia, have invented certain new and useful Improvements in Planimeters;
and I do hereby declare the following to be a full, clear, and correct
description thereof, such as will enable others skilled in the art to which it
appertains to make and use the same, reference being had to the accompanying
drawings, and to the figures of reference marked thereon, which form a part of
this specification.
My invention relates to certain improvements in polar planimeters
for ascertaining areas and determining the mean effective pressure and
horse-power of
steam-indicator
diagrams.
It is the aim of my invention to simplify and improve the
construction and operation of apparatus of this type in such manner as to
enable the user to read the mean effective steam-pressure or
horse-power direct from the scale attached to the instrument without
calculation of any kind and without application of measurements to the
diagram.
It is my purpose also to provide means whereby the instrument may
be used to determine mean effective pressures, horse-powers, or irregular areas
upon different scales of measurement; and my invention consists in the novel
features of construction and new combination of parts hereinafter fully
described, and then particularly pointed out and defined in the claims.
To enable those skilled in the art to which my said invention
pertains to fully understand the same, I will describe said invention in
detail, reference being had for this purpose to the accompanying drawings, in
which-
Figure
1 is a
plan view showing a planimeter constructed in accordance with my invention and
applied to a steam-indicator diagram to ascertain the mean effective
pressure indicated, the dotted lines indicating a second position of the parts.
Figure
2
is a partial sectional view of the parts shown in Fig.
1,
taken in the line of the tracer-bar; and Fig.
3
is a detail view showing different interchangeable scales constructed for
application to the planimeter to adapt it to be used upon diagrams
taken with springs of different scale.
The reference-numeral 1 in said drawings indicates the
frame of the instrument, consisting, substantially, of a plain rectangular
housing having a longitudinal opening which receives the tracer-bar
2. A set-screw 3 fastens the latter at any
point to which it may be adjusted in the frame, the latter being open at both
ends to allow the maximum longitudinal movement of the tracer-bar. In a boss
dropped from the lower side of the frame 1 is a pivoted
axis 1a for the end of the fulcrum-bar
4, the other extremity of the latter being provided with a sharp
point 5,, of steel or other suitable metal, the body of
which is extended through and rises above the end of the bar. Projecting from
the upper side of the frame 1 is a small conical
point 6, having its apex in the same straight line with the
axis upon which the end of the fulcrum-bar 4 is mounted.
The reference numeral 7 indicates a fixed shaft which
extends from the side of the frame 1, opposite that upon
which the fulcrum-bar 4 lies, the axis of the shaft being
at an angle of ninety degrees with the longitudinal line of the frame and
tracer-bar. Upon this shaft is placed the measuring wheel 8,
accurately fitting the shaft, but capable of turning freely and moving
longitudinally from end to end thereof, the end of the shaft being provided
with a slight enlargement 9, which prevents the wheel from
passing off. The periphery of the latter is beveled off to an edge not keen
enough to cut, but having such a sharp definition that it may readily be
placed in exact coincidence with the graduations of a linear scale.
An attachable scale 10 is mounted upon the
upper side of the frame 1, to which it is rigidly secured
by a thumb-screw 12, passing through an opening in its end
and tapped into the metal of the frame. A dowel or nipple 13,
rising from the frame near the thumb-screw, enters a small aperture in the
scale and determines the exact position of the same, its graduated edge lying
in parallelism with the axis of the shaft 7 and in close
proximity to, but just removed from actual contact with, the edge of the
measuring wheel 8.
I provide a series of different scales, two of which are shown in
Fig.
3
of the drawings. These scales differ from each other only in
graduation, this being varied to correspond with the various measurements for
which the instrument is adapted. For example, one series may be graduated to
correspond to the different scales of springs with which
indicator-diagrams are taken, others may be so graduated as to read
directly the horse-power of certain engines when running at a given speed
and the indicator-card taken with a specified spring, thus saving the usual
tedious calculation of horse-power, while other scales may be graduated to
conform to the cubic measurement, or, if desired, to the metric and other
systems used abroad.
The end of the tracer-bar is supplied with a
tracing-point 14, projecting from its lower surface.
Upon the upper face of the same bar is a nipple 15, used
in guiding the tracer-point. The end of this nipple is tapered to a point
which lies in the same axial line with the tracing-point and which
serves, in conjunction with the conical point 6,
to fix the adjustment of the tracer-bar in the frame 1.
When the planimeter is used for determining the mean effective
pressure of an indicator-diagram, the scale corresponding the spring used
in taking the diagram is attached to the instrument. Thus supposing the
indicator-card to have been taken with a thirty-pound scale, then the scale
with thirty graduations to the inch is attached to the instrument. The
tracer-bar is then moved longitudinally in the frame 1
until the point of the nipple 15 and the conical
point 6 are brought into coincidence with the length of the
diagram to be measured. The fulcrum-bar 4 being then
extended and at its point 5 caused to pierce the surface
on which the instrument rests, the measuring-wheel 8 is
moved along the shaft 7 until its edge coincides with the
zero-mark on the graduated scale, which is preferably arranged in or near the
central part of the graduated edge. The tracing-point is then caused to
follow the diagram accurately, beginning at any point, care being taken to see
that the measuring-wheel remains in contact with the surface over which
it moves. This contact communicates rotary movement to the wheel and causes it
to traverse the shaft 7 longitudinally in both directions,
its edge moving as it recedes from or approaches the frame 1
over the scale 10. When the tracing-point
14 returns to its point of departure on the diagram, the edge of
the wheel will coincide with a graduation of the scale, indicating in pounds
the mean effective pressure. The fractions of a pound may be denoted by a
vernier.
Prior to my invention planimeter have employed
measuring-wheels having a rotary movement, the indications given thereby
being merely the height of the line denoting the mean effective pressure on
the diagram. So far as I am aware there has been no provision made heretofore
for reading the mean effective pressure in pounds and fractions of a pound
direct from the scale of the instrument. Neither am I aware of any instance
in which the instrument has been so organized as to permit the use of
interchangeable scales or the reading of horse-powers directly from the
instrument. As the indicator-scales are obtainable at a small cost and
are readily fitted, the expense of manufacture is not materially increased and
the usefulness of the instrument is largely increased, while its accuracy is
strictly preserved.
This planimeter differs primarily from all previously-formed
planimeters in having the axis of the measuring-wheel perpendicular or at
right angles to the tracer-arm and the wheel rotatable on the axis parallel to
the tracer-arm and longitudinally movable thereon perpendicular to the said arm,
and, furthermore, in having the reading-scale arranged parallel with the axis
of the measuring-wheel, so that the wheel may move along the scale
parallel therewith and enable the reading to be made direct from the scale, as
indicated thereon by the measuring-wheel.
The equation upon which the instrument is organized according to
my invention is substantially as follows: If A be taken to represent
the superficial area of a diagram, M denoting the movement of the
measuring-wheel, and L the length of the tracer-arm, (which is
adjusted to the length of the diagram,) then
A=MxL, and the mean effective pressure will be
equal to A/L. Representing this pressure by the
letters M.E.P., the equation will read M.E.P.=A/L,
or, clearing the denominator, A=(M.E.P.)L. Substituting
(M.E.P.)L=MxL, whence
M.E.P.=M; that is to say, the mean effective pressure is equal
to the movement of the measuring-wheel, which is read in pounds per
square inch by the same scale as that of the spring with which the card is
taken. Thus, if the card be taken with a fifty-pound spring, then the mean
effective pressure (M) is measured in pounds per square inch by a
scale with fifty graduations to the inch.
When used for measuring areas, the points 6 and 15
are set apart the distance corresponding to the scale which is attached to the
instrument. Thus, if a scale with thirty graduations to the inch be on the
planimeter, the points 6 and 15 are set three inches apart
and the areas read in square inches. If the scale with one hundred graduations
to the inch be attached, then the points 6 and 15 should be ten
inches apart, and reading will be in square inches. Similarly for foreign
measures, and if a centimeter-scale were attached with ten graduations
per centimeter and points 6 and 15 be ten centimeters apart
it would read in square centimeters.
To obtain horse-power direct from the scales it is necessary to
have a scale or set of scales so graduated as to read the horse-powers of
the engine or engines from which the cards are taken with a specified spring.
Thus if we had a card taken with a fifty-pound spring from a twelve-inch by
eighteen-inch engine running at one hundred and forty-eight revolutions per
minute, and we were to use a scale with seventy-five graduations per inch, the
reading of the instrument would be the horse-power of the engine, for the
constant by which we would multiply its mean effective pressure to obtain its
horse-power is 1.5, and since, as per previous paragraphs, a scale with fifty
graduations to the inch would read the mean effective pressure, a scale with
seventy-five graduations to the inch would read 1.5 times the mean effective
pressure, which is the horse-power.
I am not confined to the particular form of the scale employed
nor to the manner in which the scales are secured in place nor in which they
are rendered interchangeable or replaceable, as various forms may be employed
in which will be embodied the feature of replaceability or interchangeability
of scales.
By the statement in the
specification
and
claims
that the measuring-wheel axis, or the shaft on which the
measuring-wheel moves, shall be perpendicular or at right angles to the
tracer-bar is meant that the wheel-axis shall be perpendicular to the line
joining the guide-point and the tracer-point of the tracer arm or
bar.
Having described my invention and set forth its merits, what I
claim is -
1. A polar planimeter comprising a measuring-wheel whose
axis is perpendicular to the tracer-bar and having rotary and longitudinal
movement on a fixed shaft, a fulcrum-bar, and a graduated scale over the
straight edge of which the periphery of the wheel moves, substantially as and
for the purposes set forth.
2. A polar planimeter comprising a measuring-wheel having
rotary and longitudinal movement on a fixed shaft, a fulcrum-bar, and a scale
replaceably attached to the frame to permit an interchange of scales and over
the straight edge of which the periphery of the wheel moves, substantially as
and for the purposes set forth.
3. A polar planimeter having a measuring-wheel loosely
mounted on a fixed shaft at right angles to the tracer-bar, and a replaceable
scale adapted to be mounted on the frame in parallelism with said fixed shaft,
and to be replaced by a different scale, substantially as and for the purposes
set forth.
4. In a polar planimeter, the combination with a frame, of a
pivotally-attached fulcrum-bar, a longitudinally-adjustable
tracer-bar, a measuring-wheel turning and moving longitudinally upon a
shaft at right angles to the tracer-bar, and an attachable and detachable
scale mounted on the frame with its straight graduated edge lying in close
proximity to the edge of the measuring-wheel and in parallelism with its
shaft, substantially as and for the purposes set forth.
5. A planimeter comprising a tracer-bar, a measuring-wheel
axis perpendicular to the tracer-bar, a measuring-wheel having a
rotatable movement on its axis parallel to the tracer-bar and a longitudinal
movement thereon perpendicular to the tracer-bar, and a scale along which the
wheel moves, substantially as and for the purposes set forth.
6. A planimeter comprising a tracer-bar, a shaft perpendicular to
said bar, a replaceable or interchangeable scale extending longitudinally of
said shaft, and a measuring-wheel having a rotatable movement on said
shaft and a longitudinal movement along the same and parallel to said scale,
substantially as and for the purposes described.
7. A planimeter comprising an adjustable tracer-bar, a
measuring-wheel axis perpendicular to the tracer-bar, a
measuring-wheel having a rotatable movement on its axis parallel to the
tracer-bar and a longitudinal movement thereon perpendicular to the tracer-bar,
and a scale along which the wheel moves, substantially as and for the purposes
set forth.
In testimony whereof I affix my signature in presence of two
witnesses.
Edward J. Willis.
- Witnesses
- Nathan H. Robbins,
- Alfred T. Gage.
Figures 1,
2,
3,
all.
Notes:
- A steam-indicator is a device for plotting the pressure in the cylinder
of a steam engine as a function of the phase of the engine's working cycle.
The shape of this diagram reveals possible faults of the machine. With a
planimeter one can determine the mean effective steam pressure in the engine
or, when the stroke and diameter of the cylinder and the number of revolutions
per minute are known, the power of the engine.
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- This planimeter patent was HTML'ized by
Andries de Man from a microfilm copy.
Andries de Man
11/29/1998