US3866447A

US3866447A - Apparatus and method for straightening tubes

Info

Publication number: US3866447A
Application number: US359897A
Authority: US
Inventors: William Kerr Ritchie
Original assignee: Post Office
Current assignee: Post Office
Priority date: 1972-05-18
Filing date: 1973-05-14
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18
Also published as: CA989285A; GB1426870A; AU5554073A; JPS4967185A; JPS532146B2

Abstract

Apparatus for straightening a tube includes a measuring device which is located within the bore of the tube, and a tube straightening mechanism, the tube being moved relative to both the measuring device and the straightening mechanism. The measuring device generates a control signal representing lack of straightness in the tube and this is applied to the straightening mechanism and determines the straightening force applied to the tube. A second measuring device may be located within that portion of the tube on which the straightening mechanism acts, to generate a feedback signal.

Description

United States Patent [191 Ritchie [4 1 Feb. 18, 1975 1 APPARATUS AND METHOD FOR STRAIGHTENING TUBES [75] Inventor: William Kerr Ritchie, Woodbridge,

England [73] Assignee: The Post Office, London, England [22] Filed: May 14, 1973 [21] Appl. No.: 359,897

[30] Foreign Application Priority Data May 18, 1972 Great Britain 23372/72 [52] US. Cl. 72/9, 72/12 [51] Int. Cl B2ld 3/10 [58] Field of Search ..72/9,10,ll,l2,17,18, 72/31, 208, 209, 367, 370, 393; 33/302, 303, 312

[56] References Cited UNITED STATES PATENTS 1,783,797 12/1930 Klein 72/420 3,030,901 4/1962 McConnell 72/31 3,316,743 5/1967 Ovshinsky 72/10 3,335,587 8/1967 Blachut 72/10 3,460,028 8/1969 Beaver ct a1... 3,496,644 2/1970 Short 3,566,640 3/1971 Harringt0n..... 3,602,031 8/1971 Graff 72/393 Primary Examiner-C. W. Lanham Assistant ExaminerM. J. Keenan Attorney, Agent, or Firm-Hall & Houghton [57] ABSTRACT Apparatus for straightening a tube includes a measuring device which is located within the bore of the tube, and a tube straightening mechanism, the tube being moved relative to both the measuring device and the straightening mechanism. The measuring device generates a control signal representing lack of straightness in the tube and this is applied to the straightening mechanism and determines the straightening force applied to the tube. A second measuring device may be located within that portion of the tube on which the straightening mechanism acts, to generate a feedback signal.

16 Claims, 1 Drawing Figure APPARATUS AND METHOD FOR STRAIGHTENING TUBES This invention relates to the straightening of tubes,

and is particularly applicable to the straightening of 5 tubes for use as waveguides.

A high order of straightness is required in tubes for use as waveguides and it is often necessary to straighten imperfect tubes. Traditional methods of tube straightening aim to straighten the outside of the tube: one method relies on visual observation of curvature in the tube and the application of a correcting force at an appropriate number of points along the tube and in another method the tube is passed through a series of angled rollers which rotate the tube and apply to it a series of bending movements. In the case of a waveguide tube, however, it is the atraightness of the bore of the tube that is of importance so that the traditional methods are only applicable to tubes in which the wall thickness is uniform. Moreover the accuracy of traditional methods is poor.

The present invention provides apparatus for straightening a tube, including a measuring device locatable within the bore of the tube and operable to generate a control signal representativeof the deviation from straightness in the surrounding portion of the tube; a tube straightening mechanism connected to receive the control signal and operable to apply, to a portion of the tube, a straightening force dependent on the value of the control signal derived from that portion; and a mechanism operable to effect relative movement between the tube and both the measuring device and straightening mechanism.

In a preferred embodiment of the invention, the mechanism for effecting relative movement is operable to effect continuous relative movement between the tube and both the measuring device and straightening mechanism. In this embodiment, the measuring device is operable to generate a continuous control signal.

The apparatus may include a second measuring device which is locatable within the bore of the tube in that portion of the tube on which the straightening mechanism is operable, the second measuring device being operable to generate a feedback signal represen tative of the deviation from straightness in the surrounding portion of the tube, and the straightening mechanism also being connected to receive the feedback signal and to apply the straightening force in dependence on the relative values of the control and feedback signals. The straightening mechanism may, for example, include a differential amplifier connected to receive both the control signal and the feedback signal and operable to produce an error signal in dependence on the relative values of those signals. The differential amplifier may be connected to receive the control signal through a control amplifier the gain of which is adjustable and which has an adjustable input/output characteristic.

In an embodiment of the invention, the straightening mechanism is spaced apart from the measuring device in the direction of the relative movement of the tube and is connected to receive the control signal from the measuring device through a delay equal to the time required for a portion of the tube to reach the straightening mechanism from the measuring device when the apparatus is in use. The delay is preferably adjustable in response to variations in the speed of the relative movement.

The apparatus may include a third measuring device which is locatable within the bore of the tube in a portion of the tube on which, when the apparatus is in use, the straightening mechanism has operated, the third measuring device being operable to generate a signal representative of the deviation from straightness in the surrounding portion of the tube.

The apparatus may include recording means connected to receive and record the signals generated by the first, second and third measuring devices.

The straightening mechanism may include an adjustable die engageable with the tube to apply the straightening force thereto.

The present invention also provides a method of straightening a tube, including the steps of locating within the bore of the tube a measuring device operable to generate a control signal representative of the deviation from straightness in the surrounding portion of the tube; effecting relative movement between the tube and the measuring device so that the measuring device generates a control signal representative of the deviation from straightness along the length of the tube, and effecting relative movement between the tube and a tube straightening mechanism and applying the control signal to the straightening mechanism to operate the latter to apply a straightening force to the tube. The relative movement between the tube and the straightening mechanism may be effected simultaneously with the relative movement between the tube and the measuring device, in which case the control signal generated by the measuring device is applied to the straightening mechanism after a delay equal to the time required for a portion of the tube to reach the straightening mechanism from the measuring device. Alternatively, the relative movement between the tube and the straightening mechanism may be effected after the relative movement between the tube and the measuring device, in which case the control signal generated by the measuring device is recorded and subsequently applied to the straightening mechanism.

In a preferred method in accordance with the invention, the relative movement between the tube and the measuring device is continuous and the measuring device generates a continuous control signal. In this preferred method, the relative movement between the tube and the straightening mechanism is continuous, and the straightening mechanism applies a continuous straightening force to the tube. Alternatively, however, the straightening mechanism may be operated to apply a straightening force to the tube at points spaced apart along the tube.

The method may also include the step of generating a feedback signal representative of the deviation from straightness in the portion of the tube to which the straightening force is being applied and applying that feedback signal to the straightening mechanism.

The method may also include the step of measuring the deviation from straightness in a portion of the tube to which the straightening force has been applied.

By way of example, apparatus and methods in accordance with the invention will be described with reference to the accompanying drawing which is a diagram of apparatus for straightening waveguide tubes.

The drawing illustrates the apparatus in use, that is with a waveguide tube 1 in the process of being straightened. The apparatus includes three

straightness measuring heads

3, 5, 7 located within the bore of the tube 1, and a straightening mechanism which is indicated generally at 9 and through which the tube extends. The

measuring heads

3, 5, 7 and the straightening mechanism 9 are all fixed, while the tube 1 is either pushed or pulled lengthwise through the apparatus at an appropriate speed in the direction indicated by the arrow 11. The mechanism for moving the tube can be of any suitable type: it may, for example, include a pair of resiliently-mounted rollers 35 which have a high coefficient of friction with the tube and are positioned close to the straightening mechanism 9, on the approach side of the latter, to engage and push the tube through the straightening mechanism.

The straightening mechanism 9 comprises two fixed dies 13 between which is located an adjustable die 15 movable in one plane by hydraulic rams 17. The

measuring heads

3, 5, 7 are spaced apart lengthwise of the tube 1 with the head being positioned within the adjustable die and the heads 3 and 7 being positioned respectively before and after the straightening mechanism 9 (relative to the direction of movement of the tube 1).

Each of the

heads

3, 5, 7 measures the deviation from straightness (if any) in the bore of the surrounding portion of the tube 1, and may be of any suitable type. The measuring heads shown in the drawing are all of a known type and will, therefore, be described only briefly. Each head has a central portion 19 which is shown only diagramatically in the drawing but which comprises a pair of parallel beams (typically about 20 cms. long) from each of which a set of three

feet

21, 22 and 23 extends. The feet in each set are spaced apart lengthwise of the tube with the

outer feet

21 and 23, which are located near the ends of the beam, being fixed. The two sets of feet are diametrically-opposed and the beams are spring-loaded apart so that the

fixed feet

21 and 23 engage the inner surface of the tube 1. Each of the centre feet 22 is mounted on the core of a transformer, forming a displacement transducer, and is movable with the core relative to the respective beam. Each core is spring-loaded so that the centre feet 22 also engage the inner surface of the tube 1 and the transducers are arranged to give a linear relationship between core movement and the transducer output signal. Any lack of straightness in the bore of the tube 1 will be indicated by an electrical output signal from the transducers, caused by movement of the centre feet 22: output signals resulting from variations in the diameter of the bore, rather than lack of straightness, can be eliminated by subtracting the outputs of the diametrically-opposed transducers.

The

measuring heads

3, 5 and 7 are mounted within the tube 1 so that they will not move longitudinally or rotate while the tube is being moved through the apparatus, but so that they are capable of aligning with the bore of the tube. This may be achieved by using an assembly of rods and universal joints to connect the

measuring heads

3, 5 and 7 through the bore of the tube 1, to an external mounting.

The output of the first measuring head 3 is connected, through a variable delay 25, to a variable gain amplifier 27 which has a variable input/output characteristic. The output of the amplifier 27 is applied to a differential amplifier 29 which also has an input from the second measuring head 5. The output of the differential amplifier 29 is applied to a hydraulic system 31 which controls operation of the rams 17 in the straightening mechanism 9. The outputs of all three

measuring heads

3, 5, 7 are applied to respective pens (indicated by crosses 3', 5, 7') of a pen-and-paper recorder 33.

The tube 1, as mentioned above, is moved continuously through the apparatus at an appropriate speed and the variable delay 25 is adjusted to equal the time taken for a cross-sectional plane of the tube 1 to move from the centre feet 22 of the first measuring head 3 to those of the second head 5. The variable delay 25 may, for example, be introduced by a magnetic drum or tape with read-on and read-off heads and rotating or moving, as the case may be, at a speed which is related to the transit speed of the tube 1 so that variations in the transit speed are unimportant. The first measuring head 3 produces a continuous output signal which varies with the curvature in the bore of the tube 1 along the length of the tube but, due to the delay 25, the input signal to the variable gain amplifier 27 represents, at any moment of time, the curvature in that part of the tube which, at that time, is within the second measuring head 5.

The measuring head 5 also produces an output signal proportional to the curvature in the tube 1 and this is subtracted, in the differential amplifier 29, from the signal produced by the measuring head 3 for the same portion of the tube to produce an error signal which is applied to the hydraulic system to operate the rams 17 and thereby move the die 15 which, in association, with 'the fixed dies 13 impresses a correction curvature on the tube 1. It will be appreciated from this that the measuring head 5 actually measures the correction curvature impressed by the rams l7 and provides a feedback signal to the hydraulic system: with sufficient gain in the feedback loop, the impressed correction curvature can be controlled very accurately by the output signal of the first measuring head 3 and can be adjusted very precisely by-altering the gain of the variable gain amplifier 27. The variable input/output characteristic of the amplifier can be used to compensate for the non-linear nature of the impressed curvature/change-incurvature" characteristic of the tube 1. The term change-in-curvature means the change actually brought about by the correction process, which can be measured from the outputs of the first and third measuring heads 3 and 7, since the third head 7 produces an output signal proportional to the curvature of the tube 1 after passage through the straightening mechanism 9. Ideally, of course, the curvature after passage through the straightening mechanism should be zero. It will be appreciated that the curvatures to be measured by the first and third heads 3, 7 will be much less than those to be measured by the second head 5 since the latter measures impressed curvatures which, to straighten the tube, must reverse the existing curvatures. The range of the first and third heads 3, 7 need not, therefore, be as great as that of the second head 5.

As mentioned above, the outputs of the measuring heads 3, 5 and 7 are connected to the pens 3', 5' and 7 respectively of the recorder 33. The transit speed of the paper of the recorder is related to the transit speed of the tube 1 and the spacing between the pens 3', 5 and 5', 7 in the direction of movement of the paper is similarly related to the spacing between the measuring

heads

3, 5 and 5, 7 so that superimposed portions of the three traces produced on the paper relate to the same portion of the tube 1. By observing the traces, an indication can be obtained of the necessary adjustment to the gain and input/output characteristic of the amplifier 27 to obtain the best results from the apparatus.

It will be appreciated from the above that the third measuring head 7 is not an essential component in so far as straightening the tube 1 is concerned since it merely provides a check on the effectiveness of the straightening operation: if such a check is not required then the third head 7 can be omitted. Even if a check on the effectiveness of the operation is required, the third head 7 can still be omitted and the check obtained by passing the tube 1 through the apparatus for a second time.

If second measuring head 5 were omitted from the apparatus it would then be necessary to operate the apparatus in a predictive manner since the feedback signal utilized in the apparatus shown in the drawing would not be produced. It would also be necessary to control accurately the gain in the input circuit to the hydraulic system 31, and the accuracy of the straightening operation would be limited by play and wear in the dies 13, and also by variations in the wall thickness of the tube (bearing in mind that, although the first head 3 measures the curvature of the bore of the tube, the die 15 acts on the external surface of the tube).

Alternatively, the results achieved with the apparatus shown in the drawing (in which three measuring

heads

3, 5, 7 are used and the tube 1 makes only one passage through the apparatus) could also be achieved with apparatus using only one measuring head, by passing the tube three times through the apparatus. During the first pass of the tube, the measuring head would be used in the manner of the first head 3 in the drawing to measure the curvature of the tube and the output of the head would be recorded. During the second pass of the tube, the measuring head would be used in the manner of the second head 5 in the drawing to measure impressed curvature, and correction curvatures would be applied to the tube on the basis of error signals derived from the recorded information via the feedback loop. During the third pass of the tube, the measuring head would be used in the manner of the third head 7 in the drawing to check on the effectiveness of the straightening operation.

In the apparatus shown in the drawing, the straightening dies 15 act in one plane only although action in two orthogonal planes may be required to straighten the tube 1 completely. This can be achieved most easily by rotating the tube 1 through 90 following the first passage through the apparatus; interchanging the electrical connections of the first and third measuring heads 3 and 7, and then passing the tube back through the apparatus in the opposite direction. The feedback loop through the second measuring head 5 is not interrupted during the changeover of the electrical conec- -tions so that an unstable state will not be brought about but it is, of course, essential that the outer measuring heads 3 and 7 should have equal sensitivities and be separated by the same distance from the measuring head 5. As an alternative to reversing the tube and interchanging the electrical connections, the tube could be passed through the apparatus for a second time in the same directon although rotated through 90. A further possibility is to apply a straightening action to the tube in two orthogonal planes during a single pass through the apparatus although difficulties may arise as a result of the large number of electrical connections that would be required to the measuring heads within the tube.

In the apparatus shown in the drawing the correction curvature to be impressed on the tube 1 in a particular cross-sectional plane by the die 15 is derived from a measurement made by the head 3 in that plane only. Under some circumstances this may be insufficient to straighten the tube adequately and it may be necessary, in deriving the correction curvature, to take account also of the curvature of the tube on either side of that particular cross-sectional plane. This could be done by measuring and recording the curvature of the tube over its whole length before carrying out any part of the straightening operation, and then using the recorded information to calculate the correction curvatures to be applied along the whole length of the tube during a subsequent passage through the straightening mechanism 9.

Rollers could be used in the straightening mechanism 9 rather than the dies 13 and 15 described above, with the advantage of a possible reduction in frictional effects as the tube 1 passes through the straightening mechanism: there is, however, the disadvantage of a possible loss in accuracy in the straightening action of the apparatus.

The continuous action of the straightening mechanism 9 along the length of the tube 1 is not essential and can, under appropriate circumstances, be replaced by a straightening action at points spaced apart along the tube. These points must, however, be close enough to each other to ensure that any resulting waves in the tube can be ignored. It is also not essential that the relative movement between the tube and the measuring heads 3, 5, 7 and straightening mechanism 9 should be continuous and, subject to appropriate modifications being made to the apparatus, discontinuous movement of the tube could be employed.

Finally, it should be mentioned that although the apparatus described above makes use of measuring

heads

3, 5, 7 which generate electrical control signals it could, as an alternative, be modified to make use of hydraulic control signals.

I claim:

1. Apparatus for straightening a tube, including first and second measuring devices locatable within the bore of the tube and operable to generate, respectively, a control signal and a feed back signal, each of said signals being representative of the deviation from straight ness in the surrounding portion of the tube; a tube straightening mechanism connected to receive the control and feedback signals and operable to apply, to that portion of the tube in which the second measuring device is located, a straightening force dependent on the relative values of the control and feedback signals derived from that portion; and a mechanism operable to effect relative movement between the tube and both the measuring devices and straightening mechanism.

2. Apparatus as claimed in claim 1, in which the mechanism for effecting relative movement is operable to effect continuous relative movement between the tube and both the measuring device and straightening mechanism.

3. Apparatus as claimed in claim 2, in which the measuring device is operable to generate a continuous control signal.

4. Apparatus as claimed in claim 1, in which the straightening mechanism includes a differential amplifier connected to receive both the control signal and feedback signal and operable to produce an error signal in dependence on the relative values of those signals.

5. Apparatus as claimed in claim 4, including a control amplifier connected between the first-mentioned measuring device and the differential amplifer, the control amplifier having an adjustable gain and an adjustable input/output characteristic.

6. Apparatus as claimed in claim 1, including a third measuring device which is locatable within the bore of the tube in a portion of the tube on which, when the apparatus is in use, the straightening mechanism has operated, the third measuring device being operable to generate a signal representative of the deviation from straightness in the surrounding portion of the tube.

7. Apparatus as claimed in claim 6, including recording means connected to receive and record the signals generated by the first, second and third measuring devices.

8. Apparatus as claimed in claim 1, in which the straightening mechanism is spaced apart from the first mentioned measuring device in the direction of the relative movement of the tube and including delay means connected between the straightening mechanism and the measuring device, the delay means providing a delay equal to the time required for a portion of the tube to reach the straightening mechanism from the first mentioned measuring device when the apparatus is in use.

9. Apparatus as claimed in claim 8, in which the delay is adjustable in response to variations in the speed of the relative movement.

10. Apparatus as claimed in claim 1, in which the straightening mechanism includes an adjustable die engageable with the tube to apply the straightening force thereto.

11. A method of straightening a tube. including the steps of locating within the bore of the tube a measuring device operable to generate a control signal representative of the deviation from straightness in the surrounding portion of the tube; effecting relative movement between the tube and the measuring device so that the measuring device generates a control signal representative of the deviation from straightness along the length of the tube; effecting relative movement between the tube and a tube straightening mechanism and operating the latter to apply a straightening force to the tube; generating a feedback signal representative of the deviation from straightness in the portion of the tube to which the straightening force is being applied and applying that feedback signal and the control signal to the straightening mechanism to operate said mechanism.

12. A method as claimed in claim 11, in which the relative movement between the tube and the straightening mechanism is effected simultaneously with the relative movement between the tube and the measuring device, the control signal generated by the measuring device being applied to the straightening mechanism after a delay equal to the time required for a portion of the tube to reach the straightening mechanism from the measuring device.

13. A method as claimed in claim 11, in which the relative movement between the tube and the straightening mechanism is affected after the relative movement between the tube and the measuring device, the control signal generated by the measuring device being recorded and subsequently applied to the straightening mechanism.

14. A method as claimed in claim 11, in which the relative movement between the tube and the measuring device is continuous and the measuring device generates a continuous control signal.

15. A method as claimed in claim 14, in which the relative movement between the tube and straightening mechanism is continuous, and the straightening mechanism applies a continuous straightening force to the tube.

16. A method as claimed in claim 11, including the step of measuring the deviation from straightness in a portion of the tube to which the straightening force has been applied.

Claims

1. Apparatus for straightening a tube, including first and second measuring devices locatable within the bore of the tube and operable to generate, respectively, a control signal and a feed back signal, each of said signals being representative of the deviation from straightness in the surrounding portion of the tube; a tube straightening mechanism connected to receive the control and feedback signals and operable to apply, to that portion of the tube in which the second measuring device is located, a straightening force dependent on the relative values of the control and feedback signals derived from that portion; and a mechanism operable to effect relative movement between the tube and both the measuring devices and straightening mechanism.

11. A method of straightening a tube, including the steps of locating within the bore of the tube a measuring device operable to generate a control signal representative of the deviation from straightness in the surrounding portion of the tube; effecting relative movement between the tube and the measuring device so that the measuring device generates a control signal representative of the deviation from straightness along the length of the tube; effecting relative movement between the tube and a tube straightening mechanism and operating the latter to apply a straightening force to the tube; generating a feedback signal representative of the deviation from straightness in the portion of the tube to which the straightening force is being applied and applying that feedback signal and the control signal to the straightening mechanism to operate said mechanism.