EP0970348A1

EP0970348A1 - Apparatus for measuring the diameter of a workpiece

Info

Publication number: EP0970348A1
Application number: EP98910762A
Authority: EP
Inventors: Kimmo KÖLIÖ; Seppo LÖYTYNOJA; Heikki Jussila; Sami Jussila
Original assignee: R-Met Oy
Current assignee: R-Met Oy
Priority date: 1997-03-27
Filing date: 1998-03-23
Publication date: 2000-01-12
Also published as: FI971296A0; FI103214B1; WO1998044310A1; AU6501898A; FI103214B; FI971296A

Abstract

The invention relates to an apparatus for measuring the diameter of a workpiece, which apparatus (2) includes a body (10) and a measuring head (12) attached to it, which is positioned between them with an operating device (6). In addition, the apparatus (2) includes a measuring roller (13) adapted to the measuring head (12), one sensor (14) for determining the rotational movement of the measuring roller (13) and another sensor (7) for measuring that of the workpiece being measured, and equipment for processing the values from the aforesaid sensors (7, 14). According to the invention, the measuring roller (13) comprises a two-part construction, in which there is a hard-metal ring (18) on top of an inner disc (17).

Description

APPARATUS FOR MEASURING THE DIAMETER OF A WORKPIECE

The present invention relates to an apparatus for measuring the diameter of a workpiece, which apparatus comprises a frame and a measuring head attached to it, for the positioning of which there is an operating device between them, a measuring roll adapted to the measuring head, and a second sensor for determining the rotation of the workpiece being measured, as well as equipment for processing the values from the aforementioned sensors.

SU patent publication number 1460597 for determining a diameter using an auxiliary roll, so that the number of revolutions of the auxiliary roll, the diameter of which is known precisely, is determined for a single revolution of the piece being measured. From this, the circumference of the rcll is obtained and in turn the calculatory diameter. Several calculation components, however, make this system complicated.

A similar system is known from DE publication 2C48 682. In the publication, it is proposed that the measuring roll should be of the same material as the piece being measured, when thermal expansion will be as great in both. Unfortunately, large pieces, for example, long rolls, often do no: have an even temperature. Corundum can be used as a surfacing to increase friction, while the measuring roll can have an outer ring of hard plastic. A corundum surface may make the diameter of the measuring roll imprecise. A general property of plastics is that they recover slowly from compression, which will alter the diameter of the measurement roll in subsequent revolutions.

SU patent publication number 675302 presents a device for measuring the diameter and shape of a workpiece. The measuring device in question applies two rolls connected to one another, which are attached to an operating device with an articulated joint. The rolls are considerably smaller that the piece being

CORRECTED measured. At the moment of measurement, the piece rotates. When the rolls then rotate, the sensors connected to them send sine-wave signals to separate calculation equipment. On the basis of the signals, the diameter of the piece and its deviation from a cylindrical form are determined. The measurement arrangement described, based on sine-waves, is inaccurate .

The known solutions applying an auxiliary roll are extremely sensitive to possible slipping in the auxiliary roll, which will immediately cause a large error in the measurement. In addition, the dirtying of the rolling surfaces, and particularly of the auxiliary roll, will cause a measurement error, both directly and secondarily in the form of increasing slip.

The purpose of the invention is to create a precise and versatile apparatus for measuring the diameter of a roll or other round workpiece. The measuring apparatus according to the invention is more reliable and precise than previous devices and is independent of ambient conditions. The characteristics of this invention appear in the accompanying Claims. The coefficient of friction of hard metal against steel is great, which primarily prevents slipping. A hard-metal ring permits quite vigourous mechanical cleaning.

The invention is described in detail in the following text with reference to the accompanying drawings depicting one application of the invention, in which

Figure 1 shows a measuring apparatus according to the invention installed in a machining device, Figure 2 shows the measuring device in Figure 1 in a side view, Figure 3 shows the measuring device in Figure 1 in a front view and in partial cross-section. Figure 1 shows a measurement apparatus 2 according to the invention installed in a machine tool 1. The piece to be measured, i.e. in this application, a large roll 3 has been placed on the support blocks of the machine tool 1, in which there are bearings for the axle 4 of the roll 3. The measuring device 2 is moved along the longitudinal axis of the roll 3 with the aid of horizontal guides 5. The measuring device 2 is set in a normal tool-holder of the machine tool 1 and follows with the aid of the machine tool's own following system. To determine precisely the rotation of roll 3, the machine tool 1 has an optical sensor 7, which detects the mark 8 on the end of the roll 3. If the drive mechanism of the roll 3 includes devices to determine a complete revolution, such a device is used in place of the optical sensor 7. Flexible electrical and pneumatic leads (not shown) are connected to the measuring device 2, to drive it and permit the diameter to be measured over the entire length of the roll 3.

The measuring device includes a measuring head 12 attached to its body 10 by means of guides 11. The actual measurement of the diameter is based on the rotation of the measurement roller 13 and the roll 3 and its measurement. For this purpose, in measuring head 12 there is a measurement roller 13 with a pulse sensor 14 attached to it. The diameter of roll 3 can be determined precisely using the sensors 7 and 14 referred to above with the measured values of the rotation of the roll 3 and the measuring roller 13 and the known characteristics of the measuring roller 13. For the calculations, the values of the sensors 7 and 14 are led to a separate device, advanta- geously a computer (not shown) , in which case it is possible to use sensors that transmit precise, frequent pulses. During the testing of the measuring device 2, a pulse sensor was used, one revolution of which corresponds to 10 000 pulses.

Figure 2 shows the structural components of measuring device 2 in greater detail. The aforementioned guides 11 allow the measuring head 12 to be moved longitudinally on frame 10. This movement is carried out by pneumatic cylinder 6, which receives compressed air through connection 16. Measuring roller 13 is attached with bearings to measuring head 12. The measuring roller 13 in question consists of a two-part construction, with a carbon-fibre inner ring 17, on top of which there is a hard- metal ring 18. This is economically obtained from a hard-metal seal blank. Because hard-metal and steel have a good coefficient of friction between them and permit considerable pressure, this construction can eliminate slip between the measuring roller 13 and the roll 3. In addition, the ratio of carbon fibre to resin is the aforementioned ring 13 can be adjusted so that the coefficient of thermal expansion of the inner disc 17 is the same as that of the ring 18. In that case, coefficient of thermal expansion of both is advantageously 6.5*10^"6 1/K, when a two-part construction is possible. The compatibility of the coefficients is also affected by the orientation of the carbon fibres.

The construction of a measuring roller according to the invention permits a manufacturing method, in which the axle and the blank comprising the measuring roller are ground together, in which case the bearing and rolling surfaces can be made concentric.

A scraper 20 is also arranged in the guard 19 in the measuring head to press against the measuring roller 13 to keep ring 18 clean. The flexible blade 21 of the two-part scraper 20 presses continuously against the surface of ring 18. Blade 21 is set against the direction of rotation of measuring roller 13. In addition, blade 21 is pressed by a rigid support 22, which prevents the blade from leaving ring 18. A scraper 20 can also be installed on each side of the measuring roller 13, when it is possible for the measuring roller 13 to rotate in either direction. The cleaning effect of blade 21 is increased by a flow of air led to the measuring roller, which blows impurities off the roll 3 and the measuring roller 13. The aforesaid flow of air to the measuring head is brought through hose 23.

Besides cleaning, the air flow has another purpose. By arranging an adjustable air heater (not shown) on the compressed air line, the temperature of measuring roller 13 can be kept constant. In addition, temperature variations in the axial direction of the piece being measured can be taken into account. A change of 2°C over the length of a long, large- diameter roll will affect the diameter by 0.05 mm. In order to measure the temperature, there are sensors (not shown) in both the measuring head 12 and the compressed air line. IR sensors can be advantageously used to measure the temperature of the roll.

Figure 3 shows the measuring device 2 in partial cross-section, with the guard 19 of the measuring roller 13 removed. The figure also shows that the ring 18 of the measuring roller 13 is narrower than the inner disc 17, advantageously 25 - 75% of the width of inner disc 17. In one measuring roller with a diameter of 100 mm, there was a hard-metal ring with a cross- section of 6 mm x 6 mm around a 12 mm-wide inner disc. The box shown by broken lines to the right of measuring roller 13 is a turbine 24 driven by compressed air. This assists the rotation of measuring roller 13, so that the contact of measuring roller 13 with roll 3 does not cause wear in the surfaces. Using turbine 24, the speed of measuring roller 13 can be made in advance to match the speed of the rotating roll 3. Rotation assist reduces the possibility of slip and also overcomes the bearing friction in the measuring head 12.

The pulse sensor 14, which measures the rotation of the measuring roller 13, the turbine 24, and the measuring roller 13 are placed on the same axis, which is shown by a broken line. Thus, there is no free play while the rotating masses are small, which makes the measuring device 2 sensitive. Here, this means that measuring device 2 rapidly adapts to conditions and that measuring roller 13 rotates evenly. The composite construction of measuring roller 13 also reinforces this property, because the mass of measuring roller 13 is concentrated in ring 18. In addition, Figure 3 shows the electrical connection 26 from the pulse sensor 14 to the computer.

On both sides of body 10 there are linear guides 11 for the positioning of measuring head 12. It is advantageous to use guides operating on the recirculating ball principle. Such guides 11 have very low static friction, so that measuring head 12 moves lightly. In addition, free play can be eliminated from the guides 11. Measuring apparatus 2 also includes, insides its body 10, a pneumatic single-acting cylinder 6 with a return spring. To maintain a constant contact pressure by the measuring roller 13 on the piece being measured, the pressure feed line to cylinder 6 has an operating pressure regulator

(not shown). The aforementioned regulator, i.e. pressure equalizer, also uses a constant pressure to compensate for movement due to eccentricity in the piece being measured. The propulsive force of cylinder β is typically about 70 N, if the diameter of the measuring roller is 100 mm. This creates a knife-edge contact between the measuring roller and the workpiece, unlike a plastic ring.

Due to its construction, a measuring apparatus 2 according to the invention has a short installation length, but an excellent ability to conform. It is then possible to also measure a workpiece that rotates eccentrically. The hard-metal ring 18 of the measuring roller 13 can be machined to high dimensional precision and does not wear in use. In addition, measuring apparatus 2 can be programmatically calibrated.

Tests have shown measuring apparatus 2 to be independent of the temperature of the piece being measured in the range 15 - 45°C and of variations in ambient temperature. Measuring apparatus 2 also operates under production conditions independently of dust, dirt, and thermal currents. It is also possible to carry out measurements during machining. A single measuring apparatus 2 covers a broad range of external and internal measurements. A light, measuring apparatus 2 can also be easily installed in, for example, a machine tool 1, while measuring apparatus 2 can be used to make several measurements at several different points. Measuring apparatus 2 can be adapted to different kinds of holders, by simply bolting a suitable attachment to body 10. As measurement is automatic, it can be carried out by a single person. On the other hand, the measurement result from a calibrated measuring apparatus 2 does not depend on the person making the measurement.

Linear guide 11 advantageously includes a linear movement measurement sensor 27. The apparatus is arranged to combine the data from this sensor with the data from the measurement roller, to measure the shape of the workpiece. Measurement can also be started and/or stopped with the aid of the linear measurement data.

A measuring apparatus 2 according to the invention can also be adapted with the aid of different kinds of sensor. The number of sensors can also vary. Advantageously, the measuring roller is set in bearings on only one side and the measuring apparatus is adapted otherwise to be brought very close to the face area. Unlike the construction according to Figure 3, not only is the left-hand bearing removed, but also the left-hand linear guide must be located more in the centre.

Claims

PATENT CLAIMS

1. An apparatus for measuring the diameter of a workpiece, which apparatus (2) includes a body (10) and a measuring head (12) attached to it, which is positioned between them with an operating device (6), a measuring roller (13) adapted to the measuring head (12), one sensor (14) for determining the rotational movement of the measuring roller (13) and another sensor (7) for measuring that of the workpiece being measured, and equipment for processing the values from the aforesaid sensors (7, 14), characterized in that the measuring roller

(13) comprises a two-part construction, in which there is a hard-metal ring (18) on top of an inner disc (17).

2. An apparatus according to Claim 1, characterized in that the inner disc (17) is of composite-structure carbon fibre, in which structure the ratio of the carbon fibre to the resin and the orientation of the fibres are arranged to that the coefficient of thermal expansion of the inner disc (17) is essentially the same as that of the ring (18).

3. An apparatus according to Claims 1 or 2, characterized in that a rotation device (24) is arranged in the measuring head (12), to match the speed of the measuring roller (13) with that of the rotating workpiece (3) beforehand.

4. An apparatus according to any of Claims 1 - 3, characterized in that a cleaner (20) is arranged in the measuring head (12) against the measuring roller (13), to keep the ring (18) clean.

5. An apparatus according to any of Claims 1 - 4, characterized in that there are connections (23) and control devices in the apparatus (2) to connect a flow of air with an adjustable temperature to the measuring roller (13) .

6. An apparatus according to Claim 5, characterized in that, to adjust the flow of air, they arrange that the control devices operated in conjunction with a temperature sensor connected to the measuring roller (13) .

5

7. An apparatus according to any of Claims 1 - 6, characterized in that the operating device (6) includes an operating pressure regulator to maintain a constant contact pressure by the measuring roller (13) on the workpiece (3)

10 being measured.

8. An apparatus according to any of Claims 1 - 7, characterized in that the measuring head (12) is attached to the body (10) by means of linear guides (11), which advanta-

15 geously operate on the recirculating ball principle.

9. An apparatus according to any of Claims 1 - 8, characterized in that the aforementioned first sensor (14), the rotation device (24), and the measuring roller (13) are

20 arranged on the same axis (25) .

10. An apparatus according to any of Claims 1 - 9, characterized in that the operating device (6) and the rotation device (24) are driven by compressed air.

25

11. An apparatus according to Claim 8, characterized in that the linear guide (11) includes a sensor (27) for measuring linear movement.

30 12. An apparatus according to any of Claims 1 - 11, characterized in that the width of the ring (18) of the measuring roller (13) is 25 - 75% of the width of the inner disc (17) .