US2596423A - Planimeter - Google Patents

Description

May 13, 1952 c. o. MILLER Erm. 2,596,423

PLANIMETER Filed Oct. 27, 1948 Patented May 13, 1952 UNITED STATES PATENT -OiF FICE Behrner, St. Paul, Minn.; said Bchmer assigner of one-tenth to Walter C. Manthey, St. Paul,

Minn.

Application ctober 27, 1948, Serial No. 56,702

3 Claims. l

invention relates to planimeters.

it `isa .general object of the invention to provide a -planiiiieter which is compact in structure .so that it can be conveniently carried in the pocket irl a fully assembled condition and which is .qi a'leht in function to a larger .and more cumbersome type of instrument.

Another object is to provide a planimeter with a fulcr-um and computing point determining device wherein relative movement is produced between the two elements but an extremely accurate relative positioning of these elements is maintained.

`A further object is to provide convenient and simple means for computing area from a pair of spaced .points secured with the instrument.

Still another object is to `provide an improved handle structure for the planimeter.

`The above and other objects and advantages of the invention will more fully appear from the following description made in connection with the accompanying drawing wherein like reference characters refer to the same parts `throughout the views, and, in which:

vFigure is a plan view of the instrument;

`Figure 2 is a side elevational view with portions Vthereof in full and dotted lines in alternate position;

Figure 3 is a bottom plan view with the handle in alternate positions in dotted and full lines;

Figure 4 is a fragmentary sectional view taken approximately on the line 4-4 of Figure 2; and

Figure 5 is a fragmentary perspective view of a modified form of fulcrum.

There is illustrated a body member 6 which is arched vertically, although this particular shape is not critical. This body is preferably straight and relatively ilat and thin. The left hand end of the body, as viewed in Figures 1 through 3, is provided with a downwardly extending post l having a contour following point 8 extending downwardly from it.

The post 'I has a laterally open recess 9 formed therein and in it lies a shank I of a handle member II. The shank I is pivotally connected with the post 'l by means of a pin I2 which bridges the recess 9, and the handle is adapted to swing from a folded inoperative position to an outwardly extending operative position as shown in dotted and full lines, respectively, in Figures 2 and 3.

The opposite end of the body 6 is flattened on its lower side and has a at spring metal strip I3 secured thereto by means of a screw I4. The strip has a slot I through which the screw eX- 2 tends to facilitate proper positioning thereof lengthwise of the body, `for a reason tobe brought out below.

The spring metal strip I3 is shown with its right hand end secured fiat and rigidly against the under side of the end of the body 6. This end of the strip has a computing or marker point I6 extending downwardly therefrom. The other end of the strip I3 extends beneath the arch of the body and consequently is `spaced therefrom and can swing `yieldably and vertically relative to the body. This free end of the strip I3 has a portion I'I which is turned down as shown and preferably is provided with a sharp edge I8 which is adapted to contact the `supporting `surface on which the instrument is used.

It should be noted that the spring metal strip I3 has Vsufficient strength to support the body 6 `with `the point marker IB in an elevated position, .but that pressure on the right 'hand end of the body will ex the strip I3 so the point marker will penetrate or prick the paper on which the instrument is being used.

`The intermediate arched portion of the body 6 has a beveled surface I9 which is provided with graduations 20 and 2|. These graduations are so correlated with the follower point 8, fulcrum I'I and computing point marker I6 that results can be read on the graduated scale in terms of area.

In Figure 5 there is illustrated another form of fulcrum. It is a small, relatively sharply edged wheel 22 carried by a flexible strip 23, the latter corresponding to the flexible strip I3 shown in Figures 2 and 3.

The operation of the device is, in general, the same as any conventional planimeter. Preferably, the follower point 8 is placed on a point which is approximately the center of a designated area to be measured. The follower is then moved over the paper on which the area is outlined until the perimeter of the area is reached.. Then the follower is moved along the perimeter until a complete circuit has been made. The follower is then moved into the area to the original starting point. When the follower is rst placed at the starting point, the right hand end of the body is pressed down, causing the marker point I6 to make a small mark in the paper. After the follower has made its circuit and is returned to the starting point, the marker point is again pressed into the paper. The scale on the body is then used to measure the distance between the two marks on the paper .made by the marker point and the reading will be the area of the gure or shape being measured.

It may be cased in the manner of an ordinary pocket comb, and it will take about as much space as a comb. While it may be susceptible of error, such is true of any planimeter. As in the case of larger and more cumbersome instruments, several measurements may be made and the average will be a very accurate determination of the area.

It is of considerable advantage to mount the marker point I6 rigidly relative to the body of the device. Some planimeters are constructed with the marker point vertically slidable against spring pressure relative to the body, but in instruments of this type and size, the slight degree of play which is present in a slidable pin or marker will greatly reduce the possible accuracy of the results.

The pivoted handle, which is adapted to be held between the thumb and forenger while guiding the follower about the outline of the figure to be measured, facilitates handling of the instrument. This handle can be swung to an inoperatvie position within the limits of length of the body and also within the lateral connes thereof, so that the bulk of the device is maintained at a minimum.

It will, of course, be understood, that various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scope of the invention.

What We claim is:

1. A planimeter comprising a body member, a computing point fixed at one end of said body member in depending relation thereto, a perimeter follower mounted in xed depending relation at the other end of said body member, a resilient arm mounted to the end of said portion of said body adjacent said computing point and 4 extending inwardly along said body toward said perimeter follower, a fulcrum fixed in depending relation at the inner end of said resilient arm for normally supporting said computing point in an elevated. position and said body having a recess under said spring arm to permit upward swinging movement thereof and thereby permitting said marker point to be pressed downwardly into marking relation.

2. The structure set forth in claim 1 and said fulcrum carrying resilient arm being mounted for longitudinal adjustment on said body member.

3. The structure set forth in claim 1 and a gripping handle swivelly mounted for swinging movement on a vertical axis on said body inember at the end thereto adjacent said follower, said gripping handle having the lower edge thereof adapted to slidably ride on the supporting Y surface at the same elevation as said follower to stabilize the tracing movement of said follower around the perimeter of an area to be measured, said body having a recess formed therein to permit retraction of said gripping handle thereinto and said gripping handle having a cooperating recess adjacent said body recess to permit complete retraction of said gripping handle into said body and thereby provide a compact, easily carried unit.

CLIFFORD O. MILLER.

EUGENE A. BEHMER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 500,202 Goodman June 27, 1893 752,470 Schierbeck Feb. 16, 1904 1,988,357 Hounsfield Jan. 15, 1935 FOREIGN PATENTS Number Country Date 407 Great Britain 1891 74,288 Germany Apr. 14, 1894 238,500 Germany Sept. 26, 1911 653,354 Germany Nov. 20, 1937

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