GB2030700A

GB2030700A - Spherometer

Info

Publication number: GB2030700A
Application number: GB7929705A
Authority: GB
Original assignee: HOEKSTRA O
Current assignee: HOEKSTRA O
Priority date: 1978-08-31
Filing date: 1979-08-28
Publication date: 1980-04-10
Also published as: NL7808975A; DE2934243A1; JPS5535300A

Abstract

A spherometer for determining the radius of a basically circular cylindrical object such as a tube comprises first means defining a chord between two points of the circumference of a circle belonging to the cross-section of the object in the plane perpendicular to the axis of the part of the object whose basic geometrical form is a circular cylinder, second means for measuring the sagitta of the chord, and third means for rendering the measure of the sagitta or of the correlative measurement of the radius perceptible. <IMAGE>

Description

SPECIFICATION Radius meter This invention relates to a meter suitable for determining the radius of a part of an object, whose basic geometrical form is a circular cylinder.

In practice, a meter having the possibility described in the preceding paragraph has great utility, in particular in those cases in which only a portion of the object concerned is available or accessible, for example, only the top portion of a subterraneous tube. However, such a meter will lose much of its value if, while being on the one hand applicable in a flexible manner, it is not based on a measuring method in which the sense of measurement of the operator of the meter is fully, or substantially, eliminated, in order that the results of the measurements are not affected by the degree of skillfulness of the operator.

It is accordingly an object of the invention to provide a meter having the above properties.

According to the present invention, there is provided a meter which is characterized by first means for defining, during the performance of the measurement, a chord between two points of the circumference of a circle belonging to the crosssection of the object in the plane perpendicular to the axis of the portion of the object which has a circular cylinder for its basic geometric form, second means for measuring the sagitta of the chord, and third means for rendering perceptible the size of the sagitta or of the correlative radius.

The invention will now be described in greater detail with reference to the accompanying diagrammatic drawings, which illustrate, by way of example, a preferred embodiment of the meter according to the invention. In said drawings, Fig. 1 shows a front-elevational view of an embodiment of the meter according to the invention; and Fig. 2 shows a preferred embodiment of a chord defining means pertaining to the meter.

Referring to the drawings, reference numeral 1 designates a part of the outer circumference of a tube whose radius r has to be determined.

Reference numeral 2 designates a meter according to the present invention, which comprises a clock indicator having a dial 3 with two sets of graduations, relating to both measurement of the external radius, represented by graduation 4, and measurement of the internal radius, represented by graduation 5, of the tube, and a pointer 6 rotatable via a central shaft 7.The meterfurthercomprisesa carrying beam 8 having a square cross-section, to which chord defining means are secured in the form of congruent flat beams 9 and 10, extending at right angles to beam 8, and having wedge-shaped ends 11 and 12 with sharp edges 13 and 1 4. In a preferred embodiment, the chord defining means is a beam whose wedge-shaped end has been produced by beveling the end of the beam to produce two surfaces intersecting each other at an angle cc of approximately 1200 and to form a sharp edge 23 (Fig. 2).

Beams 9 and 10 are connected to beam 8 by means of removable clamps 1 5 and 1 6 which clamp the beam against the end surfaces of beam 8, and which enables accurate adjustment of the position of beams 9 and 10 by shifting them in the longitudinal direction thereof. Edges 13 and 14 are accurately parallel to each other, and the distance between these edges, when the meter is placed on the basis to be measured, represents the length of the defined chord AB. This distance k may be, for example, 10 cm. This is not essential, however, and the distance is selected partly in dependence on the range of radii to be measured.

The device further comprises a feeler 1 7 with a feeler tip 18. The form of tip 18 can be varied, and can be adapted to suit the requirements of accuracy of the measurement.

Feeler 17 is axially resiliently displaceable within extreme limits in a manner known per se Uend not shown in the drawings, with the movement of the feeler being transmitted to pointer 6 for rotating the latter. For this purpose feeler 1 7 engages via a rack-and-pinion system with the central shaft 7. After the measurement, the feeler is returned into its starting position (position of rest) by means of a spring system, which spring system also ensures that the feeler tip 1 8 exercises a substantially constant pressure on the surface of the object.

The axial length of displacement of feeler 17 is selected so that the pointer can rotate at least twice through an angle of 3600 from its arrestable zero position. When the arrestable zero position of the pointer is then selected to be the position reached after one rotation through 3600, the meter is suitable for measuring both the internal and the external radius of the tube.

Although not essential, it is preferable, partly from considerations of symmetry, for the position of feeler 17 to be so selected relative to the chord defining means 9 and 10 that the axis of the feeler intersects the line connecting the midpoints of edges 13 and 14 in the midpoint, with the feeler axis being naturally perpendicular to the plane passing through the edges 1 3 and 14.

When the ends 11 and 12 of the chord defining means are given the shape of two parallel edges 13 and 14, which have a certain length of, for example, 1 cm, elimination of the influence of the operator of the meter on the results of the measurement is promoted. Owing to the interaction of the curved surface of the object on the straight edges, the edges have a self-centering effect on the finding of the correct position of the meter on the surface of the object, which is reached if the edges 13 and 14 coincide with the generating straight lines of the circular-cylinder surface.

In addition to being suitable for the direct measurement of the radius of curved surfaces having a circular cross-sectional configuration, the meter according to the invention is also suitable for use in making comparative measurements of analogously formed surfaces whose basic geometrical form is not a circular cylinder. Thus the meter could be used for transferring an aircraft wing form, determined in a test model in a windtunnel, to the actual wing being constructed.

The embodiment of the meter shown in the drawing is that of a radius meter with direct indication. When the meter is placed on the outer surface of the tube 1, the feeler will be depressed relative to the plane passing through the edges 13, 14 by a distance equal to the sagitta p of the chord AB. For the direct reading of the radius, the graduation 4 is based on the formula p = r - r2 - (+k)2, in which formula p, as stated, is practicaliy determined, and k, as the defined chord, is a fixed meter constant.

During measurement of the internal radius of tube 1, the feeler will be driven outwards beyond the plane containing the edges 1 3, 14, under the influence of the spring tension. The radius can then be directly read from the graduation 5, which of course is also based on the above formula.

Although the embodiment of the meter described above is extremely practical and handy in practice, the present invention is not so limited.

Thus it is possible for the meter to be provided with a graduation directly showing the measurement of the sagitta, in which case the corresponding measurement of the radius can be found in an appropriate table.

Other important embodiments that can be mentioned are those in which the measurement of the radius is directly readable in digital form, using known per se mechanical or electronic means.

Claims

1. A meter suitable for determining the radius of a part of an object, whose basic geometrical form is a circular cylinder, characterized by first means with which, during the performance of the measurement, a chord can be defined between two points of the circumference of a circle belonging to the cross-section of the object in the plane perpendicularto the axis of the part of the object whose basic geometrical form is a circular cylinder, second means for measuring the sagitta of the chord, and third means for rendering the measurement of the sagitta or of the correlative measurement of the radius perceptible.

2. A meter according to claim 1 , characterized by a dimensionally stable, rigid carrying beam, provided with two laterally extending, rigid chord defining members to be placed on the object to be measured, of which chord defining members the end to be placed on the object is beveled to form a sharp edge, the two sharp edges being mutually parallel, and by a feeler which within the area between the sharp edges or the prolongations thereof, and in the midpoint of the distance between the sharp edges is passed through said carrying beam to extend at right angles to the plane containing said sharp edges and so as tc be axially movable under the action of spring means, the displacement of the feeler being perceptible as a measure for the sagitta through a coupling of the feeler with the third means.

3. A meter as claimed in claim 2, characterized in that the chord defining members are two separate congruent members in the form of flat beams of rectangular cross-sectional configuration, and whose ends to be placed on the object to be measured are analogously beveled, and which chord defining members are slidably connected with, and at right angles to, the carrying beam by clamping means, and the feeler axis, along which the feeler can be displaced, intersects the line connecting the midpoints of the sharp edges of the chord defining members in the midpoint.

4. A meter as claimed in claims 2-3, characterized in that the meter comprises a clock meter for direct clock reading of the measurement of the sagitta or the correlative measurement of the radius, said feeler being connected according to the rack-and-pinion principle to the central shaft of a pointer movable along a graduated dial, in known perse manner.

5. A meter substantially as hereinbefore described with reference to the accompanying drawings.