Machine for the working of tubes provided with a device for detecting any slippage of the tube being worked

Abstract

The machine comprises a working apparatus arranged to carry out the working operation on a tube, or a similar blank, and a tube feeding device arranged to feed the tube towards the working apparatus. The working apparatus and the tube feeding device comprise respective clamping members for clamping the tube being worked. According to the invention, at least one of the clamping members of the working apparatus or of the tube feeding device is provided with a displacement sensor arranged to detect and measure any movements of the tube relative to said clamping member while the tube is clamped by said clamping member during the working operation.

Claims

1. A machine for the working of elongated blanks, comprising a working apparatus arranged to carry out one or more working operations on an elongated blank, and a blank feeding device arranged to feed the elongated blank towards the working apparatus, wherein the working apparatus and the blank feeding device comprise respective clamping members for clamping the elongated blank during the working operation, wherein at least one of the clamping members of the working apparatus and of the blank feeding device is provided with a displacement sensor arranged to detect and measure in a contactless manner any movements of the elongated blank relative to said clamping member while the elongated blank is clamped by said clamping member during the working operation.

2. The machine of claim 1, wherein the displacement sensor is an optical sensor arranged to detect and measure any movements of the elongated blank relative to said clamping member on the basis of the digital processing of images of a surface portion of the elongated blank acquired by the displacement sensor in successive time instants.

3. The machine of claim 2, wherein the displacement sensor comprises a light source for illuminating said surface portion of the elongated blank, a camera for acquiring images of said surface portion of the elongated blank, and a digital processing unit for determining at each time instant, based on the comparison between the image of said surface portion of the elongated blank acquired by the camera in that time instant with the image acquired at the preceding time instant, any movements of the elongated blank relative to said clamping member.

4. The machine of claim 1, further comprising a programmable controller for managing the working operation on the elongated blank by controlling the movements of the elongated blank feeding device, as well as of movable parts of the working apparatus, wherein the controller is connected to the displacement sensor for receiving therefrom data relating to any movements of the elongated blank relative to said clamping member during the working operation.

5. The machine of claim 4, wherein the controller is programmed to vary the forces acting on the elongated blank during the working operation and/or to interrupt the working operation in case the displacement sensor detects a movement of the elongated blank relative to said clamping member exceeding a given threshold.

6. The machine of claim 1, wherein the machine is arranged to carry out bending operations on the elongated blank.

7. The machine of claim 6, wherein the working apparatus comprises a die suitably shaped, around which during the bending operation a section of elongated blank to be bent is deformed, and a pair of said clamping members arranged to clamp the elongated blank near said section of elongated blank to be bent, and wherein the displacement sensor is mounted on either of the clamping members.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention will become more apparent from the following detailed description, given purely by way of non-limiting example with reference to the accompanying drawings, wherein:

(2) FIGS. 1A and 1B schematically show a tube bending apparatus arranged to operate according to the draw bending method, at the beginning and at the end of the bending operation, respectively;

(3) FIGS. 2A and 2B schematically show a tube bending apparatus arranged to operate according to the compression bending method, at the beginning and at the end of the bending operation, respectively;

(4) FIG. 3 is a perspective view of a tube bending machine according to an embodiment of the present invention;

(5) FIGS. 4A and 4B schematically show the bending apparatus of the tube bending machine of FIG. 3, at the beginning and at the end of the bending operation, respectively; and

(6) FIG. 5 shows, on an enlarged scale, the detail A of FIG. 4A.

DETAILED DESCRIPTION OF THE INVENTION

(7) With reference to FIG. 3, wherein parts and elements identical or corresponding to those of FIGS. 1A and 1B are indicated with the same reference numbers, a tube working machine according to an embodiment of the present invention is generally indicated at 100.

(8) The machine 100 shown in FIG. 3 is arranged to bend tubes, in particular according to the draw bending method (i.e. according to the bending method described above with reference to FIGS. 1A and 1B). As will be clear from the following description, the present invention is not however limited to a tube bending machine. Moreover, in the case of application to a tube bending machine, the present invention is not limited to a tube bending machine operating according to the draw bending method but is applicable to tube bending machines operating according to other bending methods, for example according to the compression bending method.

(9) The structure and operation of the machine 100 are known per se (and have been, at least in part, already illustrated in the introductory part of the present description with reference to FIGS. 1A and 1B) and will therefore not be described in detail here.

(10) The machine 100 basically comprises a working apparatus, which in the embodiment proposed herein is a bending apparatus arranged to carry out the bending of the tube T according to the draw method and therefore comprises a die 10 having a shaped groove 12, a pair of front clamping blocks 14 for clamping the tube T to be bent, and a rear pressure block 16. More specifically, in the illustrated embodiment one of the two clamping blocks is made in a single piece with the die 10. The die 10 and clamping blocks 14 are carried by an arm 18, which is rotatably mounted on a machine base 20 (only partially visible in FIG. 3) for rotation about an axis of rotation z, which in the illustrated example is oriented vertically. The machine 100 further comprises a tube feeding device 22 for gripping the tube T to be bent by means of suitable clamping members (known per se and thus not illustrated in detail) and feeding it in the direction of its longitudinal axis (indicated at x) towards the working apparatus, as well as (optionally) rotating it about its longitudinal axis x.

(11) FIGS. 4A and 4B schematically show the bending apparatus of the machine 100 at the beginning and at the end of the bending operation, respectively. As already explained in the introductory part of the description, the bending operation is carried out first by clamping the tube T between the two clamping blocks 14 and then, with the tube T held between the two clamping blocks 14, by rotating the arm 18 (and, therefore, both the die 10 and the clamping blocks 14 therewith) about the axis of rotation z, while the pressure block 16 is moved forward in the direction of the longitudinal axis x to accompany the forward movement of the tube T and counteract, by applying a counter force perpendicular to the longitudinal axis x, the deformation of the free portion of the tube T that is not to be subjected to bending.

(12) The machine 100 also comprises, as is well known, a control unit that is suitably programmed to manage the movements of the components of the bending apparatus (die 10, clamping blocks 14 and pressure block 16), as well as the tube feeding device 22, according to the number, the bending radius and the orientation of the curves to be made on the tube T, as well as according to the distance between each curve and the subsequent one.

(13) As explained above, for the correct operation of a machine of this type, it is advantageous to avoid, or in any case limit, during the bending operation any slippage of the tube T with respect to the clamping members of the machine, for example with respect to the clamping blocks 14 between which the tube T is held clamped, near the tube section to be bent.

(14) In order to provide the control unit of the machine, in real time during the bending operation, with information regarding any slippage of the tube T with respect to the clamping blocks 14, the bending apparatus is equipped with a displacement sensor 24, in particular a contactless displacement sensor, which is mounted on one of the clamping blocks 14 and is arranged to detect and measure any relative movements of the tube T with respect to the clamping blocks 14.

(15) As an alternative, or in addition, to a displacement sensor for detecting and measuring any relative movements of the tube T with respect to the clamping blocks 14 of the bending apparatus, it is possible to provide (according to a further embodiment of the invention, not shown in the drawings) a displacement sensor for detecting and measuring any relative movements of the tube T with respect to the clamping members of the tube feeding device 22.

(16) As shown in FIG. 3, as well as in FIGS. 4A and 4B, in the illustrated embodiment, which as mentioned above refers to the case of a tube bending machine arranged to bend tubes according to the draw bending method, the displacement sensor 24 is advantageously mounted on a front face 14a of one of the two clamping blocks 14. Depending on the bending method used by the machine, however, other arrangements of the displacement sensor 24 may be envisaged. In general, the displacement sensor 24 will be mounted on an element of the bending apparatus that is arranged to clamp the tube T during the bending operation and will be placed near the lateral surface of the tube T.

(17) Preferably, the displacement sensor 24 is an optical sensor for measuring any relative movement of the tube T with respect to the clamping member on which the sensor is mounted on the basis of an appropriate processing of images of a surface portion of the tube acquired in subsequent instants by the sensor, as will be explained in detail below.

(18) With reference to FIG. 5, in case of a displacement sensor 24 made as an optical sensor, it essentially comprises a light source 26 (for example a laser or LED source) for illuminating a surface portion S of the tube T, a camera 28 for high-frequency acquisition of images of the surface portion S, and a processing unit 30 arranged to determine at any given instant, on the basis of the comparison between the image of the surface portion S acquired in that instant by the camera 28 and the image acquired at the previous instant, a possible movement of the tube T with respect to the clamping member on which the sensor 24 is mounted (in this case with respect to the clamping block 14), determining in particular both the extent and the direction of this movement.

(19) The images acquired by the camera 28 are very small, for example fifteen pixels per side, but contain tiny details and imperfections of the surface portion S of the tube T in front of which the displacement sensor 24 is placed. The images acquired by the camera 28 are processed in pairs by the processing unit 30 and each pair of consecutive images is used to calculate the displacement (if any) of the tube T with respect to the clamping block 14 in the time interval between the two instants at which these images have been acquired.

(20) For example, the displacement between two consecutive images is determined by cross-correlation. Indicating with I.sub.A(i,j) the grey intensity (the images are, in fact, acquired in grey scale) of each pixel of coordinates i, j of the first image, with I.sub.B(i,j) the grey intensity of the same pixel of the second image, and with m and n the displacement (in pixels) of the second image with respect to the first one in the two perpendicular directions, the correlation function Φ(m,n) is equal to the total sum of the products of the grey intensities of each pixel of the two images, according to the following equation:

(21) $\Phi \left(m,n\right)=\underset{i,j}{.Math.}{I}_A\left(i,j\right)I_B\left(i+m,j+n\right)$

(22) The correlation function Φ takes its maximum value when the two images are perfectly superimposed. In order to determine the displacement between two consecutive images, displacement values m and n in the two directions that maximize the function are calculated. On the basis of these displacement values between consecutive pairs of images, the amount and direction of displacement of the surface portion S of the tube T facing the displacement sensor 24 with respect to the clamping block 14 are determined instant by instant.

(23) If, during the bending operation, the displacement sensor 24 detects a displacement of the tube T with respect to the clamping block 14, the control unit of the machine may, depending for example on the amount of this displacement, immediately interrupt the working process or vary the forces exerted on the tube T (for example, by increasing the clamping force exerted by the clamping block 14 on the tube T to avoid further slippage of the tube relative to the clamping block).

(24) As is clear from the preceding description, providing a tube working machine, such as for example a tube bending machine, with a displacement sensor, such as, in particular, an optical sensor, that is able to detect any movements (slippage) of the tube with respect to a clamping member of the machine (irrespective of whether it is a clamping member of the working apparatus and/or a clamping member of the tube feeding device) during the working process, ensures a more reliable operation of the machine, as it allows, for example, to avoid damage or breakage of components of the working apparatus resulting from the formation of wrinkles on the tube caused by the slippage of the tube. Such a displacement sensor, especially if it is made as an optical sensor, is inexpensive, easy to install (even on existing machines), very accurate and reliable.

(25) Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.