GB2266377A - Instrument for measuring radius of cylindrical surface - Google Patents

Abstract

An instrument for measuring the radius of a concave or convex cylindrical surface or a related parameter such as diameter or cross-sectional area, comprises first and second members 15, 19 which are located against the surface and a central member 21 which is then adjusted by a screw to contact the surface. The displacement of member 21 from a position on a straight line joining the contact tips of members 15, 19 to a position against the surface is monitored by a linear potentiometer and indicated on a digital display in terms of the surface radius or other parameter. Members 15, 19 and 21 are mounted on an elongate bar 10, and members 15, 19 are adjustable to different separations along the bar. The separation is fed into the electronics by pressing an appropriate button or measured and fed in via a keyboard. Member 21 may be spring-biassed away from the surface. An extendable tape 28 may be mounted on the bar and separate the actual surface from members 15, 19 and 21. Bar 10 may be extended by adding a section 10a. The bar carries vertical and horizontal spirit levels 27, 26. <IMAGE>

Description

A MEASURING INSTRUMENT The invention relates to a measuring instrument and is particularly concerned with an instrument for providing a measurement from which radius of a cylindrical surface or a measurement related thereto can be determined.

Measurement of relatively small cylindrical surfaces such as those of metal bars can normally be carried out easily, for example with a micrometer or a vernier caliper. However, where very large diameter objects are involved such as cylindrical storage tanks or cooling towers, the measurement of radius is much less straightforward. Typically, a tape measure is used to determine the circumference of the object and the radius is then calculated. However, determination of radius in that way is time consuming and can be difficult where obstructions prevent all-round access to the object.

An object of the present invention is to provide an instrument which will enable radius of large diameter objects or a measurement related thereto to be determined more easily.

According to the invention there is provided a measuring instrument comprising first and second spaced apart contact members for placing against or closely adjacent a cylindrical surface, and an adjustable third contact member which can be brought into contact with or positioned closely adjacent the cylindrical surface to provide a measurement from which the radius of the cylindrical surface or a measurement related thereto can be determined.

By using such an instrument, it is necessary only to place the first and second contact members in position and then adjust the third contact member accordingly to provide the measurements from which the, radius can be determined.

Preferably, the third contact member is positioned between, and preferably mid way between, the first and second contact members.

The third contact member may be adjustable by fine adjustment means, e.g., a screw and/or may be resiliently biased outwardly so that it will tend to occupy a position with a contact end thereof outwardly of a notional plane containing contact ends of the first and second contact members.

In the preferred embodiment, the third contact member is operatively connected to display means for providing a visual indication of measurement, e.g., a dial or other suitable display.

Preferably the display means is remotely connected to the third contact member. The connection is preferably effected by means of an expanding cord and connector. A plurality of display means may be connected to the third contact member.

The third contact member may be movable to a position each side of said notional plane containing contact ends of the first and second contact members to enable convex and concave curves to be measured.

The instrument may comprise a beam having slots at regular intervals therein, in which first and second contact members may be located. One of the first and second members may be movable towards or away from the other and in the preferred embodiment both of the first and second contact members are movable towards or away from each other. To enable the or each contact member to be movable in that manner, the measuring instrument preferably comprises a beam on which the first and second contact members are movably mounted. Suitable means may be provided for fixing the or each of the first and second contact members into a selected position on the beam. The first and second contact members can be placed in selected positions on the beam which will correspond, for example, to a maximum given radius to be measured.

Where it is required to determine accurately a curvature measurement of extreme radius, a more accurate measurement may be obtained by providing the beam with at least one extension for increasing the spacing between the first and second contact members.

When placing the instrument against a cylindrical surface, accurate measurement of diameter will be achieved when a notional straight line extending between the first and second contact members is at right angles to the axis of curvature of the surface. To assist the user in arranging the instrument in that way, a length of flexible material such as a pre-tensioned strip or tape can be provided on the instrument so as to extend eg, between the first and second contact members. The strip will provide a visual "line" which the user can arrange so that it lies substantially at right angles to what the user can judge as the axis of curvature. The third contact member can also be arranged to make contact with the strip of material.

Correct positioning of the instrument in relation to the surface can be assisted alternatively, or additionally, by means of one or more levels, e.g., spirit levels, incorporated in the instrument. One such level may be arranged transverse to the other.

A measuring device in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: - Fig.l is an elevation of a preferred form of device in accordance with the invention, Fig.2 is an end view of the device of Fig.l looking in the direction of arrow II in Fig.1, Fig. 3 is an elevation of an alternative device in accordance with the invention, Fig. 4 is a cross section of the device shown in Fig. 3 on line IV - IV in Fig. 3, Fig. 5 is a plan view of the device shown in Fig.

3, Fig 6 is an underplan view of the beam of the device shown in Fig 3.

Fig. 7 is a block diagrammatic representation of the electronics of the device of Figs. 3 to 5 and Fig. 8 is a block diagrammatic representation of the signal processor of Fig. 6.

The instrument of Figures 1 and 2 comprises a beam 10 of I-shaped cross section having upper and lower flanges 12, 13 respectively and an intermediate web 14. In Fig.l, the beam is shown broken away and, in practice, would be of a length between 500mm and 1000mm.

The beam 10 carries a first contact member 15 having a contact end 15a. The contact member 15 is formed with a slot 17 which has an internal contour corresponding to the cross sectional shape of the lower flange 13 and the web 14. In that way, the contact member 15 can be slidably mounted on the beam 10. A clamp bolt 18 is provided which can either pass through suitably spaced apertures in the web 14 to hold the contact member in selected positions on the beam 10 or can simply be screwed against the web 14 so as to hold the contact member 15 in place on the beam 10 frictionally.

The beam is also provided with a second contact member 19 having a contact end 19a and which is of identical construction to the first contact member 15. The second contact member 19 is arranged on the beam 10 so that the two contact members 15, 19 appear as mirror images of each other.

A third contact member 20 is positioned on the beam 10 precisely mid-way between the contact ends 15a, 19a of first and second contact members 15, 19. The third contact member 20 is arranged at right angles to the beam and is in the form of a cylindrical rod 21 having a domed contact end 21a.

The rod 21 is slidably mounted in a bore 23 extending through the flanges 12, 13 and web 14 at right angles to the beam 10 and threadedly engages a knurled adjustment nut 22. The nut 22 is arranged in a transverse clearance slot 14a in the web 14. The rod 21 is movable axially between upper and lower positions shown in broken lines in Fig.1 by means of the knurled adjustment 22.

Alternatively or additionally the rod 21 can be biased downwardly as viewed in Fig.1 by means of a spring The rod 21 is operatively connected to a linear potentiometer (not shown) forming part of circuitry (also not shown) of an electronic display unit 24 mounted on the web 14. he circuitry of the display unit 24 incorporates radii selector buttons 25a, 25b and 25c.

The beam 10 includes two horizontal spirit levels 26 and two vertical spirit levels 27. Also, a tape 28 may be provided fixed e.g. by screws 28a to opposite ends of the beam 10 and extends in a tensioned manner between the contact ends 15a, 19 of the contact members. The tape is preferably made of a plastics material.

To measure a convex curvature such as curve X1 as shown in Fig.1, the pin 21 is retracted into the bore 23 and the first and second contact members 15, 19 and tape 28 are placed against the curved surface X1. The tensioned tape 28 will stretch resiliently and extend around the curve to provide the user with an indication as to whether or not the device is substantially at right angles to the axis of curvature Y1. Where the surface X1 is formed on, say, an upright cylindrical tank or a horizontal large diameter pipe, the appropriate spirit levels 26, 27 can be used to position the instrument accurately.

After the first and second contact members 15, 19 are brought into contact with the surface X1 (such contact ends 15a, 19a via the tape 28 which positions the contact edges such that they lie closely adjacent the surface X1) the pin 21 is screwed outwardly until it makes contact with the tape 28. As the approximate radius of curve 1 can be assessed, the appropriate button 25a, 25b or 25c can then be selected so that with the first, second and third contact members and tape 28 against the surface X1, the display unit 24 will provide, in this case, a digital read-out of measurement.The required measurement can be the radius of the curve X1, the diameter or even the cross-sectional area of object being measured and the display unit can be programmed to provide any one or ail three of those measurements. Other curvature related measurements can also be provided by the display unit 24.

Where the pin 21 is spring biased, positioning of the instrument against the convex surface 1 will cause the pin 21 to be pushed inwardly by the surface against the bias of the spring If the instrument is to be used for measuring concave curves such as curve Z2 in Fig.1 having an axis of curvature Y2, the first and second contact members 15, 19 and the tape 28 are brought into contact with the surface C2. Where provided, the tape 28 and/or the spirit levels 26, 7 will again assist the user in correctly positioning the instrument. The pin 21 is then screwed outwardly so as to move the tape 28 adjacent pin 21 into contact with the surface X2. Once again, the appropriate button 25a, 25b or 25c is selected and the measurement will be provided by the display unit 24.

Where the pin 21 is spring biased, positioning of the instrument against the concave surface X2 will cause the pin to be pushed inwardly by the concave surface against the bias of the spring.

For a given distance e.g. Cb between the contact ends 15a, 19a and for a given movement r of the rod 21 from a notional straight line containing the contact edges 15a, 19a and the domed contact end 91 a, radius R of the curve X1 is given by the eauation: R = 1/2 ((Cb/2)2 + r) r Where extremely large diameters are to be measured accurately, the length of the beam 10 can be extended by means of extension units one of which is shown as 10a in Fig.1. Unless the third contact member 20 is mounted so as to be movable axially along the beam for centralising between the first and second contact members 15, 19, the extensions 10a will normally be used in pairs arranged one each end of the beam 10. The extensions 10a can carry the first and second contact members 15, 19 once fitted in position on the beam 10.The extensions 10a can be bolted or otherwise fixed to the beam 10 and can be of any suitable length.

Selector button 25a will be selected when measuring objects of, e.g., up to around 300mm in diameter and for that purpose, the first and second contact members 15, 19 will be positioned on the beam 10 as shown in broken lines so as to be spaced apart by dimension Ca with the third contact member 20 mid-way between them.

Selector button 25b will be used where the first and second contact members 15, 19 are positioned in full lines and spaced apart by dimension Cb where the radius of curvature is in excess of 300mm but less than, say, 1000mm.

Selector button 25c can be used with the extensions 10a in position to space the first and second contact members 15, 19 apart by dimension Cc for measuring curvatures in excess of 1000mm.

The tape 28 will be re-positioned to extend between the first and second contact members 15, 19 in their selected positions and will be of sufficient length to extend therebetween with the extensions 10a in position.

The instrument of figures 3 to 5 is similar in many respects to that shown in Figs. 1 and 2 and parts corresponding to parts in Figs. 1 and 2 carry the same reference numerals.

The instrument of Figs 3 to 5 comprises an I section beam 10 including upper and lower flanges 12 and 13 respectively connected by a web 14.

The beam 10 carries first and second contact members 15, 19 with contact ends 15a, 19a. The contact members 15,19 are located and suitably secured, eg by screws 13b in slots 13a in the lower flange 13. A plurality of slots are provided in the lower flange 13 along the length of the beam 10 so that the contact members 15,19 can be located at any of several predetermined distances apart depending upon the size of the object to be measured. The contact members 15,19 are arranged to appear as mirror images of each other.

The beam includes two horizontal spirit levels (not shown) and two vertical spirit levels 27.

A tensioned tape 28 extends between outer surfaces 29 of first and second contact members 15,19 and is fixed thereto by means of screws 28a.

A third contact member 20, positioned as in the previous embodiment, includes a cylindrical rod 21 of a linear potentiometer 30 having a domed contact end 21a. The rod 21 is normally biased by a spray (not shown) in the potentiometer housing such that its contact end 21a abuts the tape 28.

The linear potentiometer 30 is connected to an input/output port 32 (see Fig 6). The input/output port 32 is connected by means of an extendable connector wire 34 to the circuitry generally indicated at 36. The circuitry 36 includes a conditioning circuit 38 for powering the potentiometer 30, connected thereto via the output of the input/output port 32. The output of the input/output port 32 is connected to a signal processor 40 which in turn is conected to a microprocessor 42.

The potentiometer 30 produces an analogue signal which is processed by the signal processor 40.

The processor 40 (see Fig. 7) comprises an operational amplifier 46 and an analogue-todigital converter 48. The signal is amplified and converted into a digital signal for sending via bus 50 to the microprocesor 42. The microprocessor 42 then performs the appropriate calculations and displays the result on a display 46.

The instrument can be used to measure convex and concave surfaces in a similar way to that described for the embodiment of Figs. 1 and 2.

The beam can be extended for measurement of larger diameter objects. If the beam is extended or shortened then the distance Cb must be altered in the calculation and this alteration can be effected in the electronics either by pressing a selector button 25 as described above or by entering the exact distance, by means of a numeric keypad, for instance.

An instrument in accordance with the invention will enable the radii of large objects such as cooling towers and tanks to be determined far more easily than using tape measures. Where the height of the object is known, the instrument will enable surface areas of the objects to be calculated easily for estimating, for example, quantities of materials required for painting the surface of the object. It will also be appreciated that other quantities can be calculated from the results provided and that such calculations can be built into the electronics of the device, for instance, the uncoiled length of a bundle of steel strip coil can be calculated by measuring its radius and counting the number of turns. The weight of the bundle can subsequently be calculated provided mass per unit length of the strip is known. All of the above calculations can be incorporated into the electronics of the device.

It is envisaged that the tape 28 couid have one end wound on a rod which is resiliently torsionally biased to apply a tensile load to the tape but which will allow the tape to unwind and deflect when measuring a convex surface. The reel could conveniently be mounted on one end of the beam 10.

Claims (1)

1, A measuring instrument comprising first and second spaced apart contact members for placing against or closely adjacent a cylindrical surface and an adjustable third contact member which can be brought into contact with or positioned closely adjacent the cylindrical surface to provide a measurement from which the radius of the cylindrical surface or a measurement, related thereto can be determined.

2. A measuring instrument according to Claim 1 wherein the third contact member is positioned between the first and second contact members.

2. A measuring instrument according to Claim 2 wherein the third contact member is positioned mid-way between the first and second contact members.

4. A measuring instrument according to any preceding claim wherein the third contact member is adjustable by fine adjustment means.

5. A measuring instrument according to Claim 4 wherein the fine adjustment means is a screw threaded adjustment A A measuring instrument according to Claims 1, 2 or 3 wherein the third contact member is resiliently biased outwardly.

7. A measuring instrument according to Claim 6 wherein the third contact member is resiliently biased outwardly so that a contact end thereof tends to occupy a position outwardly of a notional plane containing contact ends of the first and second contact members.

8. A measuring instrument according to any preceding claim wherein the third contact member is associated with means for providing a visual display of measurement.

9. A measuring instrument according to Claim 8 wherein the means for providing the visual display is remotely connected to the measuring instrument.

10. A measuring instrument according to Claim 9 wherein the connection is effected by means of an expanding cord and connector.

11. A measuring instrument according to Claim 9 or 10 wherein a plurality of sand means for providing a visual display are connected to the measuring instrument.

12. A measuring instrument according to any preceding claim wherein the third contact member is movable to a position each side of a notional plane containing contact ends of the first and second contact members to enable convex and concave curves to be measured.

13 A measuring instrument according to any preceding claim in which the contact members are mounted on a beam.

14. A measuring instrument according to claim 13 wherein the beam has slots at regular intervals in which the first and second contact members are located.

15. A measuring instrument according to any preceding claim wherein one of the first and second members is movable towards or away from the other.

16. A measuring instrument according to any of Claims 1 to 14 wherein both of the first and second contact members are movable towards or away from each other.

17. A measuring instrument according to Claim 15 or 16 wherein suitable means is provided for fixing the or each of the first and second contact members into a selected position one relative to the other.

18. A measuring instrument according to any preceding claim wherein the first and second contact members can be placed in selected positions which correspond to a maximum given radius to be measured.

19. A measuring instrument according to any preceding claim wherein an extension is provided for increasing the spacing between first and second contact members where curvatures of extreme radii must be measured.

20. A measuring instrument according to any preceding claim wherein a length of flexible material extends between the first and second contact members.

21. A measuring instrument according to Claim 20 wherein the length of flexible material extends between contact ends of the contact members.

22. A measuring instrument according to Claim 20 or 21 wherein the third contact member is normally biased into engagement with the length of flexible material.

23. A measuring instrument according to claim 20, 21 or 22 wherein the flexible material, in use, has between the contact ends of the contact members and the cylindrical surface.

24. A measuring instrument according to any of Claims 20 to 23 in which the length of flexible material is normally under tension.

25. A measuring instrument according to any of Claims 20 to 24 wherein the flexible material is in the form of a tape.

26. A measuring instrument according to any preceding claim wherein at least one level is incorporated in the instrument to facilitate positioning.

27. A measuring instrument according to Claim 26 wherein a plurality of levels are incorporated.

28. A measuring instrument according to Claim 27 wherein one level is arranged transverse to another.

29. A measuring instrument according to any of Claims 26 to 28 wherein the levels are spirit levels.

30. A measuring instrument constructed and arranged substantially as described herein with reference to the accompanying drawings.