GB2132354A

GB2132354A - Determining and/or measuring the shape of a workpiece

Info

Publication number: GB2132354A
Application number: GB08333169A
Authority: GB
Inventors: Gunther Wulff; Alfred Wahl
Original assignee: Alusuisse Holdings AG; Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1982-12-20
Filing date: 1983-12-13
Publication date: 1984-07-04
Also published as: IT8324230A0; GB8333169D0; IT1168743B; BE898493A; JPS59120906A; SE8307019D0; DE3247697A1; SE8307019L

Abstract

A device and method for determining and/or measuring the shape of a workpiece, in particular its thickness or surface form, comprises at least one measuring pin 4 the or each of which is to point towards the workpiece 2, is movably mounted in a housing 3 to which the workpiece 2 is relatively movable and has a central bore 7 through which the workpiece 2 is to be jetted with compressed gas in such a manner that a local pressure is created between the measuring pin 4 and the surface 1 of the workpiece 2, as a result of which the measuring pin 4 maintains a constant distance 's' from the surface 1 of the workpiece 2. <IMAGE>

Description

SPECIFICATION Determining and/or measuring the shape of a workpiece Mechanically operable tools are well known for measuring the shape of a workpiece by which is meant for example the thickness or surface form of the workpiece. These tools are known as callipers, gauges or slide gauges. Apart from their inherent inaccuracy these mechanical tools suffer the disadvantage that they cannot be employed for measuring moving workpieces. Furthermore, it is difficult to determine the shape of a surface or the flatness thereof as this requires a plurality of measurements. Also known are complicated electronic devices which feature a fixed feeler nozzle mounted in a housing and out of which nozzle compressed air flows.Depending on the distance of the workpiece from the outlet of the feeler nozzle a thrust is developed in the jet of compressed air, the value of which is measured via complicated electronic means and converted into units of dimension. The frequency of error with this instrument is relatively large as the thrust values obtained depend on constant air feed and also on the speed of the workpiece moving past the feeler nozzle. Furthermore, there is no linear relationship between distance and thrust.

The object of the present invention has been to develop a device of the above-mentioned kind which is much more simply constructed, is versatile in use, and also provides extremely accurate measurements which are, to a large extent, independent of fluctuations in the gas pressure.

According to a first aspect of the present invention, a method for determining and/or measuring the shape of a workpiece, in particular its thickness or surface form, comprises the use of at least one measuring pin the or each of which points towards the workpiece, is movably mounted in a housing to which the workpiece is relatively movable and has a central bore through which the workpiece is jetted with compressed gas in such a manner that a local negative pressure is created between the measuring pin and the surface of the workpiece, as a result of which the measuring pin maintains a constant distance from the surface of the workpiece.

According to a second aspect of the present invention, a device for determining and/or measuring the shape of a workpiece, in particular its thickness or surface form, comprises at least one measuring pin the or each of which is to point towards the workpiece, is movably mounted in a housing to which the workpiece is to be relatively movable and has a central bore through which the workpiece is to be jetted with compressed gas in such a manner that a local negative pressure is created between the measuring pin and the surface of the workpiece, as a result of which the measuring pin maintains a constant distance from the surface of the workpiece.

The invention makes use of the so-called hydrodynamic paradox whereby a stream of gas flowing out of a nozzle, instead of pushing apart two surfaces, at a specific distance from each other, actually draws them together. This means that the measuring pin foilows the surface of the workpiece, without making contract with it, such that even the smallest deviation from flatness is sensed. It has been found in practice that on feeding gas through the nozzle, the distance between the surface of the workpiece and the measuring pin can be reduced to a certain value by increasing the pressure. After reaching a certain limiting pressure, however, this distance cannot be altered any further. The gas pressure can be set such that the distance also remains independent of the speed at which the workpiece moves relatively to the measuring pin.Likewise, within a certain range, a change in the gas pressure acting on the device does not have a disadvantageous effect on the values obtained.

To improve the effect of the hydrodynamic paradox, the measuring pin may have a discshaped foot the diameter of which is in a specific ratio to the diameter of the central bore in the measuring pin. If this ratio is too small, there is too small a region between the two surfaces in which a local negative pressure can be produced. If the ratio is too high, the compressed gas escapes in the surface region so that the size of the local negative pressure becomes smaller.

It is preferred to have the central bore in the measuring pin connnected to an annular chamber in the housing via a transverse bore in the measuring pin. In that case a supply line for the compressed gas connects up with the annular chamber. This arrangement should in particular ensure that the central bore or the foot of the measuring pin is always supplied with the same amount of compressed gas. The annular chamber thus acts as a compensation or equalising chamber.

In order that actual measurements can be carried out, the relative movement between the movable measuring pin and the housing must be detected. To this end the invention embraces the use of both mechanical and electronic measuring facilities and, as required, display facilities which give visual or audible signals. Peferably, the measuring pin carries a magnetic core which is a component part of a linear transducer. This linear transducer enables the smallest change in position of the measuring pin to be registered, and transmits its signal to a display or recording facility which, if desired, can intensify this signal and make it visible or audible.

In order to extend the range of free movement of the measuring pin, the housing is preferably designed to have a recess into which the foot of the pin can be fitted. This also provides protection for the foot, the sole of which should be as smooth as possible so that the local negative pressure can be established uniformly without interference.

In order to provide access, for example to replace a damaged linear transducer, the housing or the annular chamber is preferably closed by a lid which is penetrated at or near its axis by an endpiece of the measuring pin arranged in a bearing in the lid. The endpiece projecting out of the housing has proved to be advantageous as it permits the pin to be advanced again to the surface of the workpiece if some kind of failure occurs and the hydrodynamic paradox breaks down. However, to prevent any unintentional external interference with the measuring pin, the lid preferably has seated thereon a further housing such as a cap or cylinder providing an inner space or a pressure chamber within which the endpiece can freely move.

The endpiece may be acted on by a rod subjected to pressure from an energy storage means. This rod is located in a sleeve which penetrates the cap and has an opening to receive a compression tool. The said compression tool can then be a simple mandril. The energy storage means, for example a simple helical spring, helps to prevent the measuring pin from exceeding the limiting value at which the hydrodynamic paradox breaks down.

Alternatively, an energy storage means may be provided for the endpiece without the provision of an additional rod to counter any excessive movement of the measuring pin away from the workpiece.

In another embodiment of the invention, the pressure chamber surrounding the endpiece is connected to a pressure source via a compensating chamber and least one valve. This makes remote control of the device possible. If for example the measuring pin exceeds the limiting conditions under which the hydrodynamic paradox applies, then it can be returned again to the surface to be measured by increasing the pressure of the compressed gas in the pressure chamber.

Any play in the bearing in the lid for the measuring pin may be penetrable by the compressed gas.

Particularly advantageous is that the whole device is of extremely simple construction. It is made up of relatively few individual parts, which furthermore suffer very little wear. The measuring pin can be moved on one or more simple bearings in the housing.

A single device of the kind described above is preferably used for determining the flatness of the surface of a workpiece. In practice however two particular modes of application have proved especially effective.

The first concerns the use of a plurality of the devices on the upper and lower sides of a metal strip continuously cast on a strip or caterpillar track type mould in order to determine the thickness of the cast metal strip directly at the end of the mould. This enables conclusions to be made about the area at which the metal begins to solidify, and therefore permits the cooling to be regulated. In spite of the relatively high temprature of the cast metal strip at the point of measurement the devices suffer no damage as the ends of the measuring pins do not contact the cast metal strip and, furthermore, are covered by the compressed gas. At the same time any damage to the cast metal strip is ruled out.

The other preferred mode of application of a plurality of the devices is for the continuous measurement of the profile of a roll during rolling.

The devices can among other things control the cooling and thus the shape of the roll over the whole length of the roll cylinder. The devices are therefore preferably mounted close to the cooling jets, and coupled to the controls for regulating the amount of cooling medium. This way it is possible to detect changes in roll cross-section, even in specific local zones, and to eliminate them by reducing or increasing the coolant supply.

Three devices, and methods of operation thereof, in accorance with the present invention, will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a first device for determining the shape of a workpiece.

Figure 2 is a cross-section through a second device similar to that of Figure 1; and Figure 3 is a cross-section through a third device also similar to that of Figure 1.

A device R, as shown in Figure 1 for determining and/or measuring the shape of a workpiece, for example the flatness of a surface 1 or a workpiece 2, features a cylindrical housing 3 inside which resides a measuring pin 4 that can be reciprocated in direction x.

Compressed air or the like is introduced via a supply line 5 to an annular chamber 6 in the housing 3 which is connected via a transverse bore 8 in the measuring pin 4 to a central, axial bore 7 in the measuring pin 4. On passing through the central bore 7 of the pin 4, the compressed air arrives at a disc-shaped foot 9 which is thickerwalled than the rest of the measuring pin 4. The compressed air then escapes outwards. When in use, the surface 1 of the workpiece 2 sweeps past the foot 9 which is at a distance s from the surface 1, namely the distance at which the so-called hydrodynamic paradox has prevailed so that the foot 9 has been drawn towards the surface 1 due to a local negative pressure created by the air flow conditions. This effect is favoured by the ratio of the diameter D1 of the axial bore 7 to the diameter D2 of the foot 9.The air path is indicated by arrows in Figure 1.

As the housing 3 is stationary, the measuring pin 4 reacts to all unevenness in the surface 1 in that it moves almost without force inside the housing 3 in the direction x. In order not to limit the freedom of movement of the foot 9, it can be arranged to slide back and forth in a recess 10 in the housing 3.

Situated in the housing 3, and separated from the annular chamber 6 by a seal 11, is a linear displacement transducer 12 with a magnetic core 14 carried by the measuring pin 4. Its position is communicated via transmission wiring 1 5 to a display or recording facility not shown here. A lid 16 covers the annualar chamber 6 at the end away from the transducer 1 2.

As the foot 9, after a specific air pressure is exceeded, always maintains the same distance s from the surface 1 of the workpiece 2, even the smallest unevenness in the surface 1 can be detected. It has also been found that a considerable increase in the air pressure above a particular limit does not case the foot 9 to be raised, but instead the distance s remains unchanged.

In the device R, shown in Figure 2, a cylinder 18 is seated on top of the lid 1 6 and connects up via aline 1 9 to a pressure source not shown here.

The compressed air reaches a compensating chamber 21 in the cylinder 1 8 via throttle valve 20 and reaches a pressure chamber 23 via a second valve 22. Projecting into this chamber 23 is an endpiece 24 of the measuring pin 4 situated at the end away from the foot 9. This endpiece 24 is subjected to forces arising from a helical spring 25 which is fixed at one end to a ring 26 and at the other end to the lid 1 6. This arrangement provides better stabilising of the measuring pin 4.

The force arising from the hydrodynamic paradox is usually sufficient to keep the foot 9 always the same distance s from the surface 1. However vibration, jarring or a sudden change in the surface 1 could cause the limit for the hydrodynamic paradox to be exceeded with the result that the measuring pin 4 would be pushed away from the surface 1. The arrangement according to Figure 2 counters this or the measuring pin 4 can be returned again to its operating position by increasing the pressure in the pressure chamber 23. The controls for regulating the pressure in the pressure chamber can be situated some distance away, which is of a great advantage especially is the device is situated in a place where access is difficult.

Furthermore, this arrangement makes it possible to employ a shorter distance for the spacing s -- if this is desired. Equilisation of pressure in the chambers 6 and 23 is produced due to the provision of a non-sealing bearing 27 around the endpiece 24 of the measuring pin 4.

This enables irregularities in the supply of compressed air to the chamber 6 to be further compensated. Any excess or negative pressure which may arise is corrected by controlling the valves 22 and 20.

In the device R2 shown in Figure 3, a cylindrical cap 30 is set on top of the lid 1 6. Projecting at least part way into inner space 31 of the cap 3 is an endpiece 32 of the measuring pin 4. This endpiece features on its end face 33 a rounded notch 34 in which a tip 35 of a rod 36 engages.

This rod 36 is subjected to the pressure created by a helical spring 37 which is braced at one end of a disc 38 near the tip 35 and at the other end against a surface 39 of the cap 30. The rod 36 has its bearings in a sleeve 40 passing through the cap 30. The sleeve 40 features an opening 41 which points upwards and into which, if desired, a compression tool can be inserted. This enables the measuring pin 4 to be returned manually to its operating position if ever a disturbance of the kind described in connection with Figure 2 should occur.

Claims

1. A method for determining and/or measuring the shape of a workpiece, in particular its thickness or surface form, comprising the use of at least one measuring pin the or each of which points towards the workpiece, is movably mounted in a housing to which the workpiece is relatively movable and has a central bore through which the workpiece is jetted with compressed gas in such a manner that a local negative pressure is created between the measuring pin and the surface of the workpiece, as a result of which the meauuring pin maintains a constant distance from the surface of the workpiece.

2. A method according to claim 1, in which the movement of the measuring pin is detected and recorded by a measuring facility.

3. A method according to claim 1 or claim 2, in which the movement of the measuring pin is influenced by energy storage means and/or gas pressure.

4. A method for determining and/or measuring the shape of a workpiece and substantially as hereinbefore described with reference to any one of the accompanying drawings.

5. A device for determining and/or measuring the shape of a workpiece, in particular its thickness or surface form, comprising at least one measuring pin the or each of which is to point towards the workpiece, is movably mounted in a housing to which the workpiece is to be relatively movable and has a central bore through which the workpiece is to be jetted with compressed gas in such a manner that a local negative pressure is created between the measuring pin and the surface of the workpiece, as a result of which the measuring pin maintains a constant distance from the surface of the workpiece.

6. A device according to claim 5, in which the measuring pin has a disc-shaped foot the diameter of which is in a specific ratio to the diameter of the central bore in the measuring pin.

7. A device according to claim 5 or claim 6, in which the central bore is connected via a transverse bore in the measuring pin to an annular chamber in the housing with the annular chamber being connected to a supply line for the compressed gas.

8. A device according to any one of claims 5 to 7, in which a facility for measuring the movement of the measuring pin is provided for the housing.

9. A device according to claim 8, in which the measuring pin carries a magnetic core which is a component part of a linear transducer.

10. A device according to claim 9, in which the linear transducer is connected via wiring to a display or recording facility.

11. A device according to any one of claims 5 to 10, in which the housing or the annular chamber is closed by a lid which, at or close to its axis, is penetrated by an endpiece of the measuring pin arranged in a bearing in the lid.

12. A device according to claim 11, in which a further housing is seated on the lid, such that an inner space or a pressure chamber surrounds the endpiece.

13. A device according to claim 12, in which the further housing is a cap and the endpiece is acted on by a rod subjected to pressure from an energy storage means, said rod being located in a sleeve which penetrates the cap and has an opening to receive a compression tool, and said rod having a tip which engages in a rounded notch in an adjacent face of the endpiece.

14. A device according to claim 12, in which an energy storage means is provided for the endpiece and counters any excessive movement of the measuring pin away from the workpiece.

15. A device according to claim 12, in which the further housing is a cylinder defining the pressure chamber which is connected to a source of pressure via a compensating chamber and at least one valve.

16. A device for determining and/or measuring the shape of a workpiece and substantially as hereinbefore described with reference to any one of the accompanying drawings.

17. A method according to any one of claims 1 to 4, comprising the use of a plurality of the devices according to any one of claims 5 to 16 arranged on each side of a metal strip continuously cast on a strip or caterpillar track type mould in order to measure the thickness and start of solidification of said cast metal strip.

18. A method according to any one of claims 1 to 4, comprising the use of a plurality of the devices according to any one of claims 5 to 16 arranged for continuous measurement of the profile of a roll during rolling.