GB2095405A - Dual axis level device - Google Patents

Abstract

A level device comprises two inclinometers 12, 13 which detect inclination of e.g. mutually perpendicular axes and are mounted on a rigid triangular base 10 which may be replaceable, or provided with wear-resistant, low- friction feet (14, 15, 16) whose relative positions may be adjusted so that the grid length of measuring (see Figure 4) can be altered. The device is placed at a series of locations on a surface whose flatness is to be analysed, and measurements in two axes are taken simultaneously, thus saving time. The outputs of the inclinometers are supplied to a computer which may produce a visual representation of the surface and/or a value indicative of its flatness. The device may also be used to monitor two components of the motion of a surface simultaneously. <IMAGE>

Description

SPECIFICATION Dual axis level device The present invention relates to a dual axis level device which comprises two inclinometers, thus speeding up the measurement of inclinations and the assessment of the flatness of datum surfaces, for example those of surface tables and machine tables extensively used in engineering.

Previous techniques of checking surfaces have involved the use of inclinometers, levels or optically viewed "straightness transducers" which allow the measurement of the inclination of the su bject sur- face along one generator line or axis at a time, in appropriate step increments. A sequence of step measurements taken along the full length of the surface being tested provides a record of "straightness" in the vertical plane of the surface along that line.Further series of inclination measurements are taken along other specific 'generator lines' described over the whole work piece to form a regular 'grid' pattern of readings recorded as an indication of the "topography" of the surface. (Local irregularities that might arise within the grid pattern spacings are largely controlled by methods of manufacture, and are checked by other means).

The repeated single step method described has several shortcomings. It is quite tedious, even when electronic means are used to record each measurement automatically, - and although "cross grid" lines are stepped it is often the case that datum is iost and extra cross checks have to be made, or the whole process repeated.

According to the present invention there is provided a dual axis level device comprising a base member on which are mounted first and second inclinometers, which are arranged to determine inclination in mutually-inclined respective first and second axes.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which; Figure l is a top view of a dual axis level device in accordance with the present invention with its protective cover removed; Figure 2 is a side view taken along the line 2-2 of Figure 1; Figure 3 is a bottom plan view ocf the device of Figure 1, and Figure 4 is a schematic diagram showing the device of Figure 1 in use.

Referring now to Figure 1, a dual axis level device in accordance with the present invention comprises a rigid base plate 10 of for example granite or reconstructed granite. Base plate 10 has the shape of an isosceles right-angled triangles with feet 14,15,16 at the corners of the undersurface. The surfaces of the feet which contact a work surface are accurately co-planar and are of a wear resistant material so that measurable wear does not take place within a long sequence of measurements. The surfaces of the feet preferably have a low coefficient of friction so that the level device can be easily moved from one measuring station or position to another. When the base plate is of reconstructed granite it may have integral feet of an anti-friction compound. Alternatively hardened or sintered metal feet may be used.

Securely mounted on base plate 10 are two electronic inclinometers 12,13 transducers of high resolution and stability with their sensitive axes mutually perpendicular. The sensitive axes of the inclinometers are parallel to the centre lines between respective pairs of feet 11. The length of each of the sides of the triangle between feet 14 and 15, and between feet 14 and 16 coincides with one of various "grid pattern" lengths. As shown lengths 'p'and 'q' are equal (since the triangle is isosceles) but they may be different.

In use the level device is placed on a cleaned table surface in a predetermined sequence of rectangular grid positions corresponding to the selected grid pattern lengths p and q see Figure 4. At each positioning of the level device a measurement of inclination is provided not only in longitudinal axis X, but also and, if desired, simultaneously in lateral axis Y. Thus a full series of stepped measurements taken on grid generator lines parallel with X axis will automatically provide the necessary Y axis readings.

The electrical output from the two inclinometers 12,13 is sampled at each grid station after a short stabilising cycle, and is electronically converted to provided visual indication of elevational differences, and, if required, angular inclinations. Controls are provided to allow for various grid spacings, magnification of the display, serialising counter etc. To determine the flatness error of a nominally plane surface, it is necessary to state the minimum separation of two parallel planes that will just contain all irregularities of that surface, and the calculation involved in establishing these planes from a large number of measured points is conveniently processed by a computer. Thus generally a computer and graphic display, with or without print plotter is used to process the full pattern of grid point measurements and output results responding to a variety of software programs.The computer outputs may range from a complete graphical display of the surface table irregularities through any formulated index of flatness to a simple indication of grading of a table to national standard. Digital and/or analogue techniques may be used.

The capacity of the computer may also be used to display before measurement, the outline grid patterns appropriate to the table to be measured, and to indicate, during measurement, any individual reading that falls outside a reasonable error of the grade of table being examined. Appropriate software programs are provided for specific requirements and enable use of the system by relatively inexperienced persons.

Because two measurements may be made simultaneously, the above arrangement permits much quicker completion of a grid surface, and may halve the time taken. Alternatively a work surface may be calibrated to a closer grid spacing than prior art methods, without lengthening the calibration process.

The facts of taking, at each step, two level readings referred to one base point not only saves time but reduces the likelihood of error due to loss of 'datum'.

The stability of the triangular foot pattern improves the "cross referencing" of grid point measurements to identify anomalous readings that may be due to dirt or malfunction, and enhances confidence in use of the equipment. Processed data feed back may be used to identify error.

Various modifications may be made to the device described above. The base plate may have feet with adjustable centre lengths p and q. Alternatively a set of interchangeable base plates may be provided having a range of standard foot spacings p and q; different members of the set may have feet with different shapes and sizes as desired. Base plates with smaller values of p and q enable work surfaces to be more accurately checked using smallertriangular increments.

The two axes of the device may be mutually inclined at an acute or obtuse angle.

The dual axis level device may be used for a variety of other purposes, static or dynamic, which call for a "differential inclinometer", - for example the testing of a machine table surface or table motion, where "roll" or "yaw" may be differentiated from "pitch", and consequently static and dynamic "twist" of the machine elements may be readily determined. To enable pitch, roll and yaw to be simultaneously detected a third inclinometer may be provided with its sensitive axis perpendicular to the sensitive axes of the first and second inclinometers.

For surface table and similar use, high resolution, stable level transducers enabiing the identification of changes of inclination of 0.1 second of arc would be utilised, but for less critical work, devices of lower sensitivity can be used. Typical values of grid lengthspandqare 100,150 or 200 mm.

Claims (12)

1. A dual axis level device comprising a base member on which are mounted first and second inclinometers, which are arranged to determine inclination in mutually-inclined respective first and second axes.

2. A device as claimed in claim 1 wherein the first and second axes are mutually perpendicular.

3. A device as claimed in claim 1 or 2, wherein the base member has first, second and third spaced feet, a straight line joining the centres of said first and second feet being parallel to the first axis and a straight line joining the centres of said first and third feet being parallel to the second axis.

4. A device as claimed in claim 3 wherein the two straight lines define the equal sides of an isosceles right-angled triangle.

5. A device as claimed in claim 3 or 4, wherein said feet are adjustable in position.

6. A device as claimed in any preceding claim wherein said base member is arranged to be replaceable.

7. A device as claimed in any preceding claim in combination with signal detecting and indicating and/or processing apparatus, wherein the inclinometers provide electrical signals indicative of the inclinations in their respective axes to said apparatus.

8. A dual axis level device substantially as herein described with reference to the accompanying drawings.

9. A method of analysing the flatness of a surface comprising placing a device in accordance with any preceding claim at a plurality of locations on said surface and detecting the outputs of the inclinometers at each location.

10. A method as claimed in claim 9 wherein at each location the outputs of the inclinometers are detected substanially simultaneously.

11. A method of analysing the flatness of a surface substantially as herein described with reference to the accompanying drawings.

12. A dual axis device for analysing the flatness of a surface substantially as herein described with reference to the accompanying drawings.

12. A method of analysing the dynamic characteristics of a moving surface of which the motion has rotary components comprising placing a device in accordance with any of claims 1 to 8 on said moving surface and periodically detecting the outputs of the inclinometers.

13. A method of anlaysing the dynamic characteristics of a moving member of which the motion has rotary components substantially as herein described with reference to the accompanying drawings.

New claims or amendments to claims filed on 29 March 1982 Superseded claims ALL New or amended claims: CLAIMS

1. A method of analysing the flatness of a surface comprising successively placing at spaced positions on said surface a dual axis level device, comprising a base member and first and second inclinometers mounted on the base member, the inclinometers being arranged to determine inclination in mutuallyinclined respective first and second axes, and generating at each said position electrical signals representing the inclinations of the inclinometers in their respective axes.

2. A method as claimed in claim 1 wherein at each position the outputs of the inclinometers are generated substantially simultaneously.

3. A method as claimed in claim 1 or 2 wherein the first and second axes are mutually perpendicular.

4. A method of analysing the flatness of a surface substantially as herein described with reference to the accompanying drawings.

5. A dual-axis device for analysing the flatness of a surface comprising a base member having feet for engaging the surface, first and second inclinometers mounted on the base member, the inclinometers being arranged to determine inclination in mutuallyinclined respective first and second axes, and means for providing electrical signals indicative of the inclinations of the inclinometers in their respective axes.

6. A device as claimed in claim 5 wherein the first and second axes are mutually perpendicular.

7. A device as claimed in claim 5 or 6, wherein the base member has first, second and third spaced feet for engaging the surface, a straight line joining the centres of said first and second feet being parallel to the first axis and a straight line joining the centres of said first and third feet being parallel to the second axis.

8. A device as claimed in claim 7 wherein the two straight lines define the equal sides of an isosceles right-angled triangle.

9. A device as claimed in claim 7 or 8, wherein said feet are adjustable in position.

10. A device as claimed in any of claims 5 to 9 wherein said base member is arranged to be replaceable.

11. A device as claimed in any of claims 5 to 10 in combination with signal detecting and indicating and/or processing apparatus, wherein the inclinometers provide electrical signals indicative of the inclinations in their respective axes to said apparatus.