AU654777B2 - Profiling gauge and method for measuring a profile - Google Patents

Description

AUSTRALIA

Patents Act 1990 654777 COMPLETE SPECIFICATION FOR A STANDARD PATENT PROFILING GAUGE AND METHOD FOR MEASURING A PROFILE THE FOLLOWING STATEMENT IS A FULL DESCRIPTION OF THIS INVENTION, INCLUDING THE BEST METHOD OF PERFORMING IT KNOWN TO ME:- The present invention relates to a gauge for profiling the shape of a member and a method for measuring a profile. The member may be solid or hollow and the gauge may be used for profiling the external or internal shape of such member.

Though the invention will be described with particular reference to the profiling of a rail head, it is to be understood that the invention has application to profiling other solid or hollow members.

1 In railways or tramways it is often necessary to measure wear of the rail and several methods for measuring rail profiles are known including the Seiki gauge, the "Lite-Slice" and the Head Gauge.

The Seiki gauge is a purely mechanical method whereby a scribing point is traced around the rail head and by a connected gearing arrangement an image of the point being traced is drawn on a piece of sensitized paper by a special stylus. "Lite-Slice" is a trade mark of a system whereby a laser scans the rail, the system being mounted on a vehicle travelling along the rail.

The "Lite-Slice" system has the disadvantage that it does not cover the full head of the rail. The head of the rail refers to that part with which the wheel flange of the vehicle is in contact. The Head gauge is a device which plots the shape of the top of the rail based only on two linear measurements made of the -2rail over a fixed interval.

The Seiki gauge is slow and inaccurate whereas the "Lite-Slice" and Head gauge methods do not cover the full rail profile.

Therefore the present invention seeks to provide an alternative to the types of gauge in existence.

According to a first aspect of the present invention there is provided an apparatus for measuring the profile of an object comprising a probe having a free end with a wheel movable over the object to be profiled and a fixed end attached to sensor means having outputs which are a function of the motion of said wheel in polar co-ordinates, said fixed and free ends of said probe being joined by a bridge piece not co-linear with said ends.

20 Preferably, the invention includes a gauge which can provide a complete 360 degree profile of a member.

Embodiments of the invention will now be described with respect to the following figures in which: 25Figure 1 shows a schematic of the components of the profile gauge according to the invention; oO o eeeo Figure 2 shows a schematic illustrating the method of measurement; and •Figure 3a and Figure 3b show the method of generation of the profile of the test piece measured in Figure 2.

The components of the apparatus are shown in Figure 1 and comprise a sensing unit 10 and computer 14 interconnected by cable 12. The sensing unit communicates with the host computer 14 over the data cable 12 using a standard RS232 serial port. The computer 14 can be any digital computer and is not limited to a laptop personal computer as illustrated.

In Figure 1, the computer 14 is also shown as portable to allow for ease of operation of the apparatus but need not be. For example, the computer may be remotely located or the data may be recorded on site for later processing.

The sensing unit 10 includes a measuring head 20 of C-shape, having at the end of one arm 22 a measuring wheel 24 and at the end of the other arm 26 a shaft 52 connected to the linear displacement transducer 28 which measures movement of the head 20 in the direction of the arrows 30. Transducer 28 can be any suitable linear displacement transducer known in the art.

The axis 32 of an angular displacement or rotary transducer 34 is connected at the midpoint of the linear displacement transducer 28. Transducer 34 measures the rotation of the axis 32 and thus the rotation of the linear displacement transducer 28 in the direction of the arrows 36 and converts it into a signal in a manner well known in the art. The output of transducer 34 can be either a digital or analogue 9*signal but in the embodiment described herewith is a binary encoded signal. The angular displacement transducer 34 can be for example a shaft encoder.

Thus, motion of the measuring head 20 involves the combined motion of the linear displacement transducer 28 in the direction of the arrows 30 and 36, the forr*.er measured by transducer 28 and the latter measured by the transducer 34. The output from the -4sensing unit 10 is a set of polar co-ordinates.

The linear displacement transducer 28 and the angular displacement transducer 34 are supported by a housing 38 with legs 40, 42. The legs 40, 42 are placed about the member to be measured, for example a rail or as in Figure 2, a rectangular test piece 50. The clamping screw 44 is then adjusted to hold part of the member free of the legs 40, 42 but within reach of the measuring head Referring to Figure 2, the measuring head 20 is moved manually over the surface of the test piece 50 with the wheel 24 in contact therewith. Test piece 50 is a regular rectangular solid. The movements of the wheel 24 are transmitted to the body of transducer 28 by shaft 52.

It is not necessary for the apparatus to be accurately positioned on the test piece 50. It is sufficient that it is secured to prevent movement of the apparatus while a measurement is made.

The transducers 28, 34 are mounted on a pedestal or 25 housing 38 in order to provide a suitable distance from the member being measured (here test piece 50) to allow the wheel 24 to run around the surface thereof.

The measuring head 20 can be rotated through 180 degrees (about shaft 52) as illustrated by arrow 53 to 30 enable a member to be covered in two halves.

The variable being measured is the position of the axis 60 of the measuring wheel 24. The position of this axis is determined relative to the axis 32 of the angular displacement transducer 34 by the fixed linear displacement or offset 56 and the variable linear displacement 54. Rotation of the shaft 52 does not change this displacement. That is, if the wheel 24 is placed on top of the test piece 50 as shown in Figure 2, and the head 20 rotated so that the wheel 24 remains in the same position, the total linear displacement does not change.

The angular displacement of the linear displacement transducer 28 is determined relative to some reference angle by the angular displacement transducer 34. In Figure 2, this reference angle is shown as being perpendicular to the test piece 50 as indicated by the dotted line 62, but in practice this angle may be any reference angle of choice.

The result in polar co-ordinates that is displacement plus angle of the axis 60 of the measuring wheel 24 is then uniquely determined.

As the wheel 24 runs along the surface of the test 20 piece 50, successive readings are taken at intervals determined by the computer 14. These readings represent a series of points corresponding to the path 66 traced by the axis 60 of the measuring wheel 24 as illustrated in Figure 3a. The traverse of the test :25 piece 50 can cover a full 360 degrees.

The computer 14 requests data from the sensing unit with the sensing unit 10 transmitting serially three successive bytes to the computer 14. The successive 30 bytes are separated by a small time delay to allow the S* computer 14 time to clear its receiver buffer before the next byte is loaded. Each successive reading (3 bytes) is processed and displayed on the screen before the next reading is requested.

If a reading has the same angular and linear values as the previous reading then it is ignored so as to avoid -6excessively long data files.

The linear and angular data is unpacked from each of the three bytes and converted into integer values.

The values are then converted to X-Y co-ordinate values. The X-Y cc-ordinates define the centre of a circle which has the approximate diameter of the measuring wheel 24. As the data points are received and plotted circles appear on the screen analogous to the wheel itself rolling over the surface of the test piece. The inner perimeter of the image thus created is a good representation of the profile of the test piece. A VGA graphics screen is used for the display and the data is modified so that it can be represented as pixels on the VGA graphics screen.

In addition to the linear and angular data encoded in i ~each three byte representation, two bits of one of these data bytes are used as control bits. The 20 computer's program examines these two bits and directs data as follows.

.:o0 i. When the control bits are both zero the data is processed as the profile co-ordinates.

2. When either control bit is non-zero, the data is treated as a special measurement point and stored in the data file header. This enables two special points on the profile to be recorded.

'E"o 3. When both control bits are non-zero the computer program discards the current profile readings and resets the display to a fresh screen. This latter feature enables the operator to abort a faulty measurement without having to return to the computer which may be some distance away.

When the profile measurement is complete the data is stored in a data file and in addition the computer program will prompt the operator for additional information such as location and test piece details.

This information is stored as a header in the data file. The file name is generated from time and date derived from the computer's internal clock so that each file has a unique identification.

When storing information the program looks at the most positive and the most negative angular co-ordinates and applies a correction so that the image is centred on the screen. However, the image may not yet be orientated correctly and the program contains another segment which allows the stored file to be displayed on the screen where, by means of horizontal and vertical cursor lines, the image can be rotated to the correct orientation chosen by the operator. The image file is then recalculated and overwritten. The 20 reference point created by the cursor lines is also stored and used as a basis for comparing other profiles of the same type of test piece.

When the stored file has been correctly orientated and 25 the reference point stored the interface software task is complete. The file is an ASCII file.

The stored data is then processed to regenerate the shape of the member in X-Y co-ordinates.

For the situation of the test piece 50, as shown in Figure 3b, this comprises the step of first taking a series of successive points and drawing a line 68 (equivalent to path 66) between each stored data point. At each stored data point, the required image point is then determined by projecting a line 70, 72 at 90 degrees to the line 68 (or path 66) for a -8distance equal to the radius of the measuring wheel 24. The image points 74, 76, 78 thus formed are joined to produce the image 80 of the test piece which is then displayed on the computer screen.

The test piece 50 being a regular solid is relatively simple to "regenerate" in this manner.

To understand in general the procedure whereby the stored data is processed to regenerate the shape of the member in X-Y co-ordinates a further embodiment will now be described with respect to determining the profile of a rail.

The profile is measured and the data stored as described above. The data file includes a header line, which specifies parameters such as kilometer ~reading, rail size, contact bands if appropriate and (due to the naming of files) time and date of 20 collection, The remainder of the file comprises a series of polar co-ordinates referenced relative to the centre of rotation (axis 60) of the measuring wheel 24.

e 25 The data is read in from the file and converted to rectangular co-ordinates relative to the axis 60. The data is ordered so that the points are in an anticlockwise direction starting at the bottom right hand side of the rail.

o The data is first processed to delete any points which are not needed to describe the profile in the following manner.

A first point (called the hook) is selected and a line is drawn from the hook to the third data point in an anticlockwise sense. A calculation is performed to -9determine if there are any points between the hook and the chosen point more than a specified distance from the constructed line. If there is not then the next point in the data sequence is chosen and the procedure repeated. Once a point is found beyond the specified distance from the constructed line then all points between the hook and this point are deleted. This new point then becomes the new hook and the process is repeated along the whole profile.

The data is next modified to account for the radius of the measuring wheel 24. Lines are drawn between successive of the remaining points. At each of the data points the angle formed between such lines is bisected by a respective vector which is projected to a distance equivalent to the radius of the measuring wheel 24. The end points of each of the vectors then represent the required profile.

20 Besides accurately describing the profile being measured the invention can include other software to compare and to calculate the departure of the profile from a reference profile, for example, to determine wear in a rail profile and to allow calculation of S: 25 grinding distance and grinding area necessary to reshape the rail.

One method of doing this will now be described. A number of standard shapes are stored in an ASCII file 30 called "profiles". These shapes consist of a number connected lines and curves. The program allows the user to call up the template of one of these standard shapes and to display it over the top of the calculated profile. The user is able to adjust the position of the template with respect to the profile by the use of the cursor keys. Once the user settles upon the positioning of the template the computer will calculate the maximum perpendicular distance from the template to the calculated profile. The grinding area is then calculated numerically by representing the area to be shaped as two hundred rectangular strips.

The program also allows the comparison of the currently displayed profile with other measured profiles which have been stored. Normally once a profile has been viewed and the necessary calculations performed the simplified profile is stored on the computer's hard disc or other storage medium well known in the art of computers. Any previous profile can be called up to be displayed and shown at the same scale as the currently displayed profile. Again, the cursor keys can be moved to enable the profiles to be more accurately overlain for comparison.

do Scaling factors are used to ensure accurate comparisons can be made between images for example to 20 compare wear patterns in railway rails.

Other applications exist for the invention apart from the profiling of a rail. For example, it can be used to measure the internal surface of a pipe to determine too.

25 wear, corrosion or uniformity of manufacture.

0In some situations, it may be necessary to position 0 00 the axis 60 of the wheel 24 perpendicular to that as shown in the above Figures in order to allow the 99: 30 measuring head 20 to follow the required shape, for example of a hollow body. The regeneration of the profile may then require projecting the bisecting line outwardly rather than inwardly of the path 66 of the axis 60 of the wheel 24 as described above. This can be done without departing from the principle of operation of the invention as herein described.

-11- Though the invention has been described above with respect to embodiments thereof, variations are contemplated within the knowledge of a person skilled in the art.

C

Claims (10)

1. An apparatus for measuring the profile of an object comprising a probe having a free end with a wheal movable over the object to be profiled and a fixed end attached to sensor means having outputs which are a function of the motion of said wheel in polar co-ordinates, said fixed and free ends of said probe being joined by a bridge piece not co-linear with said ends.

2. An apparatus for determining the profile of an object as claimed in claim 1 wherein said sensor means comprises a linear displacement transducer attached to said fixed end and a rotary transducer fixed to said linear transducer.

3. An apparatus for determining the profile of an obj3ct as claimed in claim 1 or claim 2 wherein said 20 bridge piece is substantially C-shaped.

4. An apparatus as claimed in any one of the :previous claims whereij.n said fixed end is rotatably S•connected to said sensor means.

An apparatus as claimed in any one of the previous claims further including means for converting the outputs of said sensor means into numerical data and calculating means for processing said numerical data S 30 to display the measured profile of the object.

6. An apparatus for determining the profile of an object as claimed in claim 5 wherein said calculating means comprises an electronic computer and a program converting said polar co-ordinates into rectilinear co-ordinates while compensating for the diameter of -13- said wheel to enable the display of said object's profile.

7. An apparatus for determining the profile of an object as claimed in any one of the previous claims, further including stationary support means securable to said object while supporting said sensor means in a manner allowing said wheel to move freely over the object.

8. An apparatus as claimed in any one of the previous claims wherein said object is a rail.

9. An apparatus as claimed in claim 7 wherein said object is a wheel.

10. An apparatus for determining the profile of an object substantially as herein beforedescribed with reference to the accompanying Figures. Dated this 18th day of June 1993. o TYLER YOUNG PARROTT PTY. LTD. Patent Attorneys for the Applicant HALFORD CO. e• oo:.* I -14- ABSTRACT (Fig.l) The apparatus comprises sensing unit 10 connected by cable 12 to computer 14. Sensing unit 10 includes measuring head 20 of C-shape, having a measuring wheel 24 on arm 22 and a shaft 52 on arm 26 connected to displacement transducer 28 to measure movement in the direction of arrows 30. Axis 32 of rotary transducer 34 is connected to the midpoint of transducer 28 t3 measure rotation in the direction of arrows 36. The sensing unit 10 outputs a set of polar co-ordinates. Transducers 28,34 are supported by housing 38 with legs 40, 42 which are placed about the member (not shown) to be measured and held thereto by clamping screw 44. 20 The measuring head 20 is moved manually over the member with the wheel 24 in contact therewith. The computer 14 requests data with the sensing unit responding. Prc.esfsing converts the data from polar co-ordinates into an image of the member which is then displayed on the computer screen adjusting for the radius of the *measuring wheel 24.