FIELD OF THE INVENTION

The present invention relates to a machine and to polishing bent pipes and to a method of its operation.

BACKGROUND OF THE INVENTION

For polishing pipe sections it is customary to manually guide the pipe through a belt polishing machine, in which an arrangement of two polishing belts are moving on op posite sides of the pipe while the arrangement is rotating about the central axis of the pipe in order to polish the pipe around the circumference from all sides.

In order to facilitate polishing, automatic pipe polishing machines are used, which, how ever, involve some technical challenges to get proper results after polishing.

Chinese patent application CN106826479A discloses an automated pipe polishing ma chine in which a bent pipe section is held by two holders at opposite ends for stabiliza tion of the pipe section during polishing. Due to the two holders, the machine it is com plicated to load and unload either manually or by robot. The end with the lose pivoting rods 811 812 must be secured for precise loading the rotating belt wheel 611 also risks being able to hit these unsecured rods. The sliding base 811 must during work always be numeric controlled by three movements. First two linear in X and Y, and also rota tional by 823 /rotational block.

In order to increase flexibility with respect to pipe lengths in automatic pipe elbow pol ishing machines, systems have been proposed in CN 103042460A and CN 106041690A, in which the pipe is held at one end only and where the belt polishing machine is moved and rotated along the pipe section. Although, this serves the purpose of automatic pol ishing of pipe sections, the constructions are complex and relatively large and heavy because the heaviest part, namely the polishing unit, is moved and not the pipe section. Automatic movement of a bent pipe section through a polishing machine is disclosed in CN103302582A. However, in this construction, the driving mechanism of the horizon tally oriented polishing machine is located under the table, which limits the polishing machine to polish only very short pipe elbows.

US3146646 discloses a apparatus for machining arcuate bodies of round cross-section. The machine provides improvements over disclosed prior art, but still lacks efficiency in automated processing of differing curvatures of workpieces. It would be desirable to provide an improved automated pipe elbow polishing machine, which is flexible with respect to pipe length and curvature, but also light weight.

DESCRIPTION / SUMMARY OF THE INVENTION

It is therefore an objective of the invention to provide an improvement in the art. It is also an objective to provide an improved automated pipe elbow polishing machine, in particular lightweight and flexible. This objective and further advantages are achieved with a pipe polishing machine as described below and, in the claims, as well as the following method of its operation.

The polishing machine comprises a holder for holding a workpiece. Although the ma chine is configured for also polishing straight pipes as workpieces, it is especially useful for bent pipes, also called pipe elbows, especially when bent at right angles. However, the disclosed polishing machine is also suited to be used with pipe elbows being at any angle between 0-92 degrees. Such workpiece has a front end and a rear end and a bent portion in between. The bent portion has a radius of curvature and a centre of curvature. A centre line extends longitudinally through and along the centre of the pipe. In some embodiments, the pipe has a straight section in extension of the bent portion. The polishing machine is also suited for polishing welding fittings.

The polishing machine comprises a polishing station for polishing the workpiece. A rotational unit is rotating in a rotational plane about a rotation axis and carrying a pol ishing device arranged at a central area of the rotational unit for polishing the workpiece around its circumference by the polishing device when the workpiece is inserted into the central area and the rotational unit is rotating. For example, the polishing device comprises two polishing belts arranged on opposite sides of the central area. Alterna tively, the polishing device comprises a sandblasting head having one or more sand blasting nozzles which are rotating around the workpiece in order to sandblast the pipe all around its circumference.

A swivelling mechanism provides a swivelling motion of the holder in a swivel plane about centre of circular motion and, correspondingly, along a circular curve. The swivel plane is oriented perpendicular to the rotational plane of the rotational unit for feeding the bent portion of the workpiece through the central area by the swivelling motion when the bent portion of the workpiece shall be polished by the polishing device. In order to polish the entire bent portion of the workpiece, the polishing is done during the swivelling motion through the central area. Herein, for simplicity, directions will be described relatively to an X-Y coordinate sys tem. The Y direction is parallel to the rotation axis, and the X-direction is perpendicular thereto and within the swivel plane.

A main support structure is carrying the swivelling mechanism, and thus also carrying the workpiece in the holder. A linear driving mechanism moves the main support struc ture together with the swivelling mechanism and the workpiece in the holder by a mo torised straight linear translation, for example controlled by a PLC (programmable logic controller). The linear motion is in a direction that is only parallel with the rotation axis, the Y-direction, in order to move the bent portion of the workpiece to the central area by the linear translation. This linear translation is also used for moving straight parts through the central area for polishing the straight parts (end-sections).

For example, the linear driving mechanism of the main support structure comprises straight rails that are parallel with the rotation axis (Y direction). On the rails, the main support structure is arranged for moving the main support structure along the straight rails in the Y-direction parallel to the rotation axis. A linear actuator system, for exam ple a belt drive, is arranged for moving the main support structure along the rails in combination with the swivelling mechanism, the holder, and the workpiece. However, for a circular bent portion of the workpiece, when moved through the central area for polishing, the straight translation is stopped, as the movement of the circular bent part, for example 90 degrees bent portion, is done only by the swivelling mecha nism that follows the curve corresponding to the radius of curvature and centre of cur- vature of the circular bent portion of the workpiece.

Although, more complex, it is also possible, in principle to polish circular or non-circu lar bent portions other than 90 degrees in the central area. In such cases the swivelling of the swivelling mechanism must be combined with both the linear translation of the main support structure and with the radius adjustment mech anism.

By programming these translations in combination bents from 0-92 degrees will be pos sible to polish together with various non-circular variants. However, non-circular bent sections is not the typical case.

An adjustment mechanism is mechanically connecting the main support structure with the holder. The adjustment mechanism is configured for adjusting the position of the holder relatively to the main support structure prior to polishing of the workpiece. The adjustment is an important step, as the position of the workpiece needs to be adjusted so that the centre line of the workpiece is guided correctly through the central area for polishing. In particular, the curved centre line of a bent workpiece should follow the rotation axis during feeding of the workpiece through the polishing station. This adjustment prior to polishing comprises a number of steps, typically performed when a bent workpiece is held at its rear end by the holder. For example, the holder comprises a clamp for holding the workpiece. Advantageously, the clamp fixes the workpiece only on the inner side of the pipe, as the complete outer surface is then avail able for polishing.

Prior to polishing, the adjustment mechanism is used for adjusting the swivelling mech anism to swivel the workpiece about the centre of curvature of the circular bent portion of the workpiece. When the workpiece is swivelled from a first to a second orientation, the workpiece follows the curve of a circle, relatively to the main support structure, about the centre of curvature of the circular bent portion of the workpiece. If the main support structure is standing still, the motion of the workpiece is a circular motion through the central area. The angular distance from the first to the second orientation corresponds to the angle of bending of the bent part, typically 90 degrees.

In a preferred embodiment, , the swivelling mechanism comprises a circular curved rail and a swivelling- support arranged movable on the rail for by movement on the rail to follow a circular motion. In order for the holder to be swivelled, the swivelling support advantageously carries the holder.

For example, the swivelling support is mounted on the curved rail by means of rollers, optionally the rollers following edges of the curved rail. In this case, the polishing of the bent portion of the workpiece in the central is done while the swivelling support is rolling on the curved rail from the first orientation to the second orientation, causing the workpiece to be swivelled through the central area. Advantageously, a motorised actu ator is functionally connected to the swivelling support for automatically actuating the swivelling support along the curved rail by the actuator from the first orientation to the second orientation.

For example, the swivelling mechanism is fixed to a first base, and the first base is provided on the main support structure for the straight translation. This way, an auto mated straight translation by the linear driving mechanism and a circular swivelling motion by the swivelling mechanism can be combined. Only if at the same time of the swivelling by the swivelling mechanism, the straight driving mechanism is moving the main support structure, the motion of the workpiece through the central area is not cir cular, as the motion is a combination of a circular motion and a straight motion. For example, the adjustment mechanism comprises a first straight translation mecha nism for moving the first base together with the swivelling mechanism relatively to the main support structure only in a direction (X-direction) that is perpendicular to the ro tation axis (Y-direction) and also perpendicular to the linear motion of the main support structure. Furthermore, the adjustment mechanism is configured for adjusting the machine to the radius of curvature of the bent portion of the workpiece only by moving the first base together with the swivelling mechanism relatively to the main support structure along the X-direction. After such movement along the X-direction for adjustment of the radius of curvature, the first base is fixed to the main support structure with a releasable fixing tool, for example a clamping mechanism.

As an example by only moving the two linear x and y directions a straight part of a non 90 degrees workpiece can be polished.

In practice, for the adjustment, the main support structure is moved in the Y-direction towards the polishing station by the straight driving mechanism until the front end of the workpiece approaches the central area. Then, the centre line of the workpiece at the front end of the workpiece is adjusted to coincide with the rotation axis at the first ori- entation of the swivelling mechanism and the workpiece by the just described adjust ment of the first base in the X-direction relatively to the main support structure.

For correct positioning of the rear end relatively to the rotation axis, the workpiece is swivelled by the swivelling mechanism to a second orientation, at which the centre line at the rear end of the workpiece is in the Y-direction and, thus, parallel with the rotation axis. Once parallel, the workpiece is translated in the X-direction, until the centre line coincides with the rotation axis at this second orientation.

After this adjustment, the centre of curvature of the bent portion of the workpiece coin- cides with the centre of curvature of the swivelling mechanism, and the centre line of the workpiece is adjusted to follow the rotational axis of the polishing station with re spect to the bent portion as well as at the front end and rear end of the workpiece.

This adjustment can be performed manually or automatically, after which the polishing machine can be fed with such workpieces one after the other, while the polishing is done automatically. Due to this automation, the polishing station, despite its simplicity, is useful for robot stations where a robot arm loads and unloads one or more of such polishing stations with workpieces. After the initial adjustment, when a workpiece is put on the holder for polishing, the main support structure is moved automatically by the linear driving mechanism towards the polishing station until the bent portion of the workpiece approaches the central pol ishing area, after which the swivelling mechanism starts acting. For workpieces with circular bent portions, which is the common case, the straight linear driving mechanism and corresponding straight linear motion of the main support structure is stopped when the swivelling mechanism takes over the swivelling motion of the bent portion of the workpiece through the central area for polishing the bent portion of the workpiece by the polishing devices during the swivelling. For example, if the workpiece has two straight parts at the end in extension of the bent portion, the straight linear motion of the main support structure is pushing the straight part through the central area for polishing, until the bent portion reaches the central area, after which the swivelling mechanism takes over.

Then the swivelling motion stops and the straight linear motion takes over to complete the work piece.

In some further practical embodiments, the adjustment mechanism comprises a cross table that connects the swivelling-support with the holder and which is configured for adjustment of the position of the holder in two mutually perpendicular directions rela- tively to the swivelling-support. When the holder together with the swivelling support is in the first orientation, the first direction of the two mutually perpendicular directions of the cross table is in the X-direction, parallel to a plane that contains the swivelling movement and perpendicular to the plane of rotation of the rotational unit of the polish ing station, whereas the second direction of the cross table is still in the Y-direction, parallel with the rotation axis. Prior to polishing of the workpiece, the adjustment in cludes moving the workpiece by the cross table in the first direction (X-direction) until the centre line at the front end of the workpiece coincides with the rotation axis, while the holder together with the swivelling support is still in the first orientation. Then, the holder together with the swivelling support is swivelled an angular distance, typically 90 degrees, from the first to the second orientation. The angular distance corresponds to the bending angle of the bent portion of the workpiece. Due to the cross table having been swivelled, its two mutually perpendicular directions have changed in space corre spondingly to the swivelling. At the second orientation, the workpiece is moved by the cross table in the second direction of the cross table, until the centre line at the rear end of the workpiece coincides with the rotation axis. The second direction of the cross table is in the X-direction if the swivelling to the second orientation has been 90 degrees.

After this adjustment, manually or automatic, the holder together with the swivelling support is swivelled back from the second to the first orientation. And the machine is ready for automatic operation when the linear unit is back in loading position.

In some practical embodiment, the cross table comprises two perpendicularly arranged bases, namely a second base and a third base, one on top of the other for in combination to provide a cross table. When the swivelling support in in the first orientation, the sec ond base is arranged for translation of the holder perpendicular to the rotation axis in the X-direction, and the third base is arranged for translation of the holder in the Y- direction, parallel to the rotation axis. For example, the second base comprises second slots extending in the first direction (X), when the the swivelling support is in the first orientation, for limiting the motion of the second base relatively to the third base to be only in the first direction (X). Second releasable clamps extend through the second slots into the third base for clamping the second base rigidly to the third base.

For example, the adjustment implies in this case, releasing the second clamps and mov ing the holder with the workpiece in the first direction (X) by moving the second base relatively to the third base in the first direction (X) until the centre line at the front end of the workpiece coincides with the rotation axis, while the holder together with the swivelling support is in the first orientation. Then, the second clamps are fastened for fixing the position of the second base and the holder and the workpiece relatively to the third base when the clamps are tightened. As an additional option, the third base comprises third slots extending in the second direction (Y) when the swivelling support is in the first orientation for limiting motion of the third base relatively to the swivelling support in the second direction (Y). Third releasable clamps extend through the third slots into the swivelling support for clamping the third base rigidly to the swivelling support when the clamps are tightened.

For example, the adjustment comprises in this case swivelling the holder together with the swivelling support an angular range from the first to the second orientation, corre sponding to the angular bent of the bent portion of the workpiece, typically 90 degrees. Then, the third clamps are released, and the third base with the holder and the workpiece is moved relatively to the swivelling support until the centre line at the rear end of the workpiece coincides with the rotation axis, while the holder together with the swivelling support is still in the second orientation. After that, the third clamps are fastened for fixing the position of the third base, the second base, the holder and the workpiece rel atively to the swivelling support.

While the examples given above relates mainly to workpiece with a circular geometry, the device and method according to the invention can also be used to polished work- piece elements with non-circular geometries such as workpiece with rectangular and hexagonal cross-sections.

The polishing process is sequenced differential depending on the geometry of the work- piece being polished.

For workpiece with a radius of curvature corresponding to 90 degrees the sequence is as follows:

Firstly, there is movement along the Y-axis, then a rotational (swivelling) movement, which is followed by movement along the Y-axis again.

For workpiece with a radius of curvature corresponding to non-90 degrees the sequence is as follows:

Firstly, there is movement along the Y-axis, then the swivelling movement is adjusted according to the radius of curvature, then a combined movement along the Y-axis and X-axis is performed. The sequence is reversed, when the workpiece is returned to the starting point (this movement process can happen without polishing).

For workpiece with a complex geometry (variation of radius of curvature throughout the cross-section) the sequence is as follows:

First a pre-movement with the rotational axis in order to align the front end of the work- piece parallel to the Y-axis. Then a pre-movement of the extra axis (Y) to align the front end of the workpiece to the center of the orbital wheel and then combined movements of all three axis (X,Y and rotational) according to the geometry of the workpiece, so that the center line in the middle of the workpiece are positioned in the orbital wheel.

In summary, the method of operation of the polishing machine according to the inven tion is a method for operating a polishing machine, the polishing machine comprising

- a holder for holding a workpiece, wherein the workpiece is a pipe having a front end and a rear end and a bent portion in between with a radius of curvature and a centre of curvature and a centre line longitudinally through and along the centre of the pipe;

- a polishing station, the polishing station comprising a rotational unit configured for rotating in a rotational plane about a rotation axis and carrying a polishing device for rotation about a central area of the rotational unit and for polishing the workpiece around its circumference by the polishing device when inserted into the central area and when the rotational unit is rotating;

- a swivelling mechanism for providing a swivelling motion of the holder in a swivel plane about a centre of circular motion, the swivel plane being perpendicular to the rotational plane of the rotational unit, for feeding the bent portion of the workpiece through the central area by the swivelling motion and polishing the bent portion of the workpiece by the polishing device during the swivelling motion;

- a main support structure carrying the swivelling mechanism;

- a straight linear driving mechanism configured for motorised straight linear translation of the main support structure together with the swivelling mechanism and the holder in a direction only parallel with the rotation axis for moving the bent portion of the work- piece to the central area by the straight linear translation; - an adjustment mechanism mechanically connecting the main support structure with the holder and being configured for adjusting the position of the holder relatively to the main support structure prior to polishing of the workpiece; wherein the method comprises, adjusting the position of the holder prior to polishing of the workpiece, the adjustment comprising

- holding the rear end of the workpiece by the holder;

- by the adjustment mechanism adjusting the swivelling mechanism for swivelling the holder from a first to a second orientation about the centre of curvature of the bent portion of the workpiece; wherein an angular distance from the first to the second ori- entation corresponds to the angle of bending of the bent part;

- by the adjustment mechanism positioning the centre line at the front end of the work- piece to coincides with the rotation axis at the first orientation;

- by the adjustment mechanism positioning the centre line at the rear end of the work- piece to coincides with the rotation axis at the second orientation; wherein the method comprises, after the adjustment,

- moving the main support structure by the straight linear driving mechanism towards the polishing station only until the bent portion of the workpiece approaches the central area, then stopping the straight linear motion of the main support structure;

- while the motion of the main support structure is stopped, automatically swivelling the bent portion of the workpiece through the central area by the swivelling mechanism and polishing the bent portion of the workpiece by the polishing devices during the swivelling, characterized in that the method further comprises the following steps,

- wherein the swivelling mechanism comprises a circular curved rail and a swivelling- support arranged movable on the rail for by movement on the rail to follow a circular motion;

- wherein the swivelling support carries the holder;

- wherein the swivelling mechanism is fixed to a first base, and the first base is provided on the main support structure;

- wherein the adjustment mechanism comprises a first straight linear translation mech- anism for moving the first base together with the swivelling mechanism relatively to the main support structure only in a direction perpendicular to the rotation axis, wherein the method comprises adjusting the radius of curvature and centre of curvature of the bent portion of the workpiece only by moving the first base together with the swivelling mechanism relatively to the main support structure and, after adjustment of the radius of curvature, fixing the first base to the main support structure with a releas able fixing tool

In one embodiment, the method further comprises the following steps: - wherein the adjustment mechanism comprises a cross table which connects the swiv elling-support with the holder and which is configured for adjustment of the position of the holder in two mutually perpendicular directions relatively to the swivelling- support;

- wherein a first direction of the two mutually perpendicular directions is parallel to a plane containing the swivelling movement and perpendicular to the plane of rotation of the rotational unit of the polishing station and the second direction is parallel with the rotation axis when the holder together with the swivelling support is in the first orien tation; wherein the method comprises, prior to polishing of the workpiece,

- while the holder together with the swivelling support is in the first orientation, moving the workpiece by the cross table in the first direction until the centre line at the front end of the workpiece coincides with the rotation axis;

- swivelling the holder together with the swivelling support from the first to the second orientation;

- while the holder together with the swivelling support is in the second orientation, mov- ing the workpiece by the cross table in the second direction until the centre line at the rear end of the workpiece coincides with the rotation axis;

- swivelling the holder together with the swivelling support back from the second to the first orientation. Wherein in another embodiment the method further comprises the following steps and details relating to the polishing machine: wherein the cross table comprises a second base arranged for translation of the holder parallel to the rotation axis and a third base arranged for translation of the holder per pendicular to the rotation axis, wherein the second base comprises second slots extend- ing in the first direction when the the swivelling support is in the first orientation for limiting relative motion of the second base relatively to the third base in the first direc tion, and wherein second releasable clamps extend through the second slots into the third base for clamping the second base rigidly to the third base, wherein the method as part of the adjustment comprises releasing the second clamps and moving the holder with the workpiece in the first di rection by moving the second base relatively to the third base in the first direction until the centre line at the front end of the workpiece coincides with the rotation axis while the holder together with the swivelling support is in the first orientation, and then fas- tening the second clamps for fixing the position of the second base and the holder and the workpiece relatively to the third base.

Wherein still further the method comprises the additional details of the machine and further step of operation: wherein the third base comprises third slots extending in the second direction when the the swivelling support is in the first orientation for limiting relative motion of the third base relatively to the swivelling support in the second direction, and wherein third re leasable clamps extend through the third slots into the swivelling support for clamping the third base rigidly to the swivelling support, wherein the method as part of the adjustment comprises

- swivelling the holder together with the swivelling support from the first to the second orientation;

- releasing the third clamps and moving the holder with the workpiece by moving the third base relatively to the swivelling support as guided by the third slots until the centre line at the rear end of the workpiece coincides with the rotation axis while the holder together with the swivelling support is in the second orientation, and then fastening the third clamps for fixing the position of the third base, the second base, the holder and the workpiece relatively to the swivelling support. In an alternative embodiment, the method comprises the following steps: wherein the straight linear driving mechanism, configured for motorised straight linear translation of the swivelling mechanism, comprises straight linear rails that are parallel with the rotation axis and on which the main support structure is arranged movable in the direction parallel to the rotation axis, and wherein a straight linear actuator system, for example belt drive , arranged for moving the main support structure along the rails together with the swivelling mechanism, the holder, the workpiece, and the adjustment mechanism; wherein the method comprises moving the workpiece towards the polishing station by straight linear motion of the main support structure along the rails. In an alternative embodiment, the method comprises the following steps: wherein the swivelling support is mounted on the curved rail by means of rollers wherein the method comprises polishing the bent portion of the workpiece in the polishing area while rolling the swivelling support on the curved rail from the first orientation to the second orientation.

Wherein further the method comprises the following steps: wherein a motorised actuator and functionally connected to the swivelling support, wherein the method comprises automatically actuating the swivelling support on the curved rail by the actuator from the first orientation to the second orientation.

In one embodiment, the polishing device comprises two abrasive belts arranged on op posite sides of the central area.

In one embodiment, the polishing machine is a polishing machine for a method accord ing to any preceding claim, the polishing machine comprising

- a holder for holding a workpiece;

- a polishing station, the polishing station comprising a rotational unit configured for rotating in a rotational plane about a rotation axis and carrying a polishing device for rotation about a central area of the rotational unit and for polishing the workpiece around its circumference by the polishing device when inserted into the central area and when the rotational unit is rotating;

- a swivelling mechanism for providing a swivelling motion of the holder in a swivel plane about a centre of circular motion, the swivel plane being perpendicular to the rotational plane of the rotational unit, for feeding the bent portion of the workpiece through the central area by the swivelling motion and polishing the bent portion of the workpiece by the polishing device during the swivelling motion;

- a main support structure carrying the swivelling mechanism; - a straight linear driving mechanism configured for motorised straight linear translation of the main support structure together with the swivelling mechanism and the holder in a direction only parallel with the rotation axis for moving the bent portion of the work- piece to the central area by the straight linear translation; - an adjustment mechanism mechanically connecting the main support structure with the holder and being configured for adjusting the position of the holder relatively to the main support structure prior to polishing of the workpiece;

- wherein the swivelling mechanism comprises a circular curved rail and a swivelling- support arranged movable on the rail for by movement on the rail to follow a circular motion;

- wherein the swivelling support carries the holder;

- wherein the swivelling mechanism is fixed to a first base, and the first base is provided on the main support structure; - wherein the adjustment mechanism comprises a first straight linear translation mech anism for moving the first base together with the swivelling mechanism relatively to the main support structure only in a direction perpendicular to the rotation axis, wherein the polishing machine is configured for adjustment of the position of the holder prior to polishing of the workpiece, the adjustment comprising - holding the rear end of the workpiece by the holder;

- by the adjustment mechanism adjusting the swivelling mechanism for swivelling the holder from a first to a second orientation about the centre of curvature of the bent portion of the workpiece; wherein an angular distance from the first to the second ori entation corresponds to the angle of bending of the bent part; - by the adjustment mechanism positioning the centre line at the front end of the work- piece to coincides with the rotation axis at the first orientation;

- by the adjustment mechanism positioning the centre line at the rear end of the work- piece to coincides with the rotation axis at the second orientation; wherein, after the adjustment, the polishing machine is configured for - moving the main support structure by the straight linear driving mechanism towards the polishing station only until the bent portion of the workpiece approaches the central area, then stopping the straight linear motion of the main support structure;

- while the motion of the main support structure is stopped, automatically swivelling the bent portion of the workpiece through the central area by the swivelling mechanism and polishing the bent portion of the workpiece by the polishing devices during the swivelling. wherein the polishing machine is further configured for adjustment of the ra dius of curvature and centre of curvature of the bent portion of the workpiece, wherein the adjustment comprises: Moving the first base together with the swivelling mechanism relatively to the main support structure wherein, after the adjustment the radius of curvature, the polishing machine is con figured for: - fixing the first base to the main support structure with a releasable fixing tool.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail with reference to the drawing, where FIG. 1 illustrates the central part of the pipe elbow polishing machine;

FIG. 2 illustrates the centre line and centre of curvature for the workpiece;

FIG. 3 illustrates the actuator mechanism for the rotation’s movement of the holder; FIG. 4 is an illustration of the complete elbow pipe polishing machine;

FIG. 5 illustrates a robot station with multiple polishing machines;

FIG. 6 illustrates a rotating sand blasting head as an alternative for the belt polisher.

DETAILED DESCRIPTION / PREFERRED EMBODIMENT FIG. 1 illustrates a polishing machine 100 for a bent workpiece, in particular bent pipes or profiles. The polishing machine 100 comprises a polishing station 1 having a ring- shaped wheel 2 that is provided rotational about a rotation axis 13 in a plane of rotation. On the wheel 2, there is provided a polishing device, comprising two sets of belt rollers 3, each set of belt rollers 3 holding a closed abrasive belt 4 and driving it in a longitu- dinal direction of the belt 4, as indicated by arrows 5. On either side of a polishing area 6, the two abrasive belts 4 are running in parallel and in opposite directions. When a tubular or profile shaped workpiece 7, such as a pipe elbow, is inserted into the polishing area 6 between the two belts 4, it is polished from both sides by the belts 4. The fact that the belts 4 are running in opposite directions exerts a rotational force on the work- piece 7, which, however, is easily counteracting by a holder 9 that is holding the work- piece 7. By rotation of the wheel 3, the tubular workpiece 7 is polished all around its outer periphery.

For holding the workpiece 7, the holder 9 comprises an expandable clamp 10 that clamps against the inner side of the workpiece 7 by expansion. By clamping from the inner side instead of from the outer side, the outer periphery of the tubular workpiece 7 is available for polishing along the entire length of it. The position of the holder 9 is such that its centre is at the level of the rotation axis 13. As an option for different pipe sizes, the holder 9 is configured to be equipped with differently sized exchangeable clamps.

Depending on the coarseness of the belts 4, the belts 4 are polishing the outer side of the workpiece 7 to various degrees. For change or renewal of the belt 4, one of the rollers 3 can be displaced and, after exchange of the belt 4, replaced again, tightening the tension of the belt 4.

In the drawing, a coordinate system 20 has been inserted for convenience and as refer ence. The X-axis and X-direction is perpendicular to the rotational axis 13, and the Y- axis and Y-direction parallel to the rotational axis 13.

In order to move the workpiece 7 through the polishing area 6, a main support structure 11 on which the holder 9 is mounted, is provided translational on straight rails 12, which are perpendicular to the plane of rotation and in Y-direction parallel with the rotation axis 13 of the wheel 2.

Movements of the main support structure 11 is automated by a motorised belt drive 14 comprising a motor 15 and a belt 16. The belt 16 is fastened to the main support struc ture 11 so that motion of the belt 16 by the motor 15 moves the main support structure 11 on the rails 12 in the Y-direction parallel with the rotation axis 13.

Between the main support structure 11 and the holder 9 an adjustable swivelling mech anism is provided as well as an x-y adjustment system as explained in detail in the following.

The swivelling mechanism comprises a first base 17A, which in FIG. 1 is exemplified as a first plate. The first base 17A is provided with first longitudinal slots 17B through which first clamps 17C extend into the main support 11. The first slots 17B are straight linear and longitudinal in the X-direction, perpendicular to the rotational axis. By loos ening the first clamps 17C, the first base 17A can be straight linearly moved along the X-axis, as indicated by arrows 8. This straight linear adjustment of the first base 17A is done as part of an initial adjustment before the polishing process begins in order to adjust the machine to the bending radius of the bent portion of the workpiece 7, which is exemplified in FIG. 1 as a pipe elbow. This adjustment displaces the centre of the curved rail to the desired point for the actual workpiece.

For example, in a manual embodiment, as exemplified, a scale for the radius in units of lengths is provided on the main support structure 11 or on the first base 17 A relatively to a mark, so the first base 17A can be quickly manually adjusted when the bending radius of the bent portion of the workpiece 7 is known. Once, the first base 17A has been adjusted to an X-position corresponding to the bending radius of the workpiece, the first clamps 17C are tightened, which fixes the first base 17A against the main sup- port structure 11.

In an automated embodiment, the combination of the first base 17A, the first slots 17B and the manual first clamps 17C are substituted by a first automated actuator drive (not shown) that moves the first base 17A in the X-direction relatively to the main support structure 11 on the basis of data indicative of the radius of curvature of the bent pipe section. The first actuator drive is functionally connected to a controller (not shown) that automatically controls the position of the first base 17A. For example, the necessary data for the radius of curvature of the bent portion of the workpiece 7 are automatically received by the controller from a database or, alternatively, manually entered into a user interface of such controller. According to these data, the centre of curvature is automat ically adjusted.

Once, the position of the first base 17A in the X-direction has been adjusted relatively to the main support structure 11 for the correct radius of curvature and corresponding necessary position in the machine of the correct centre of curvature, the start position and end position of the polishing procedure of the workpiece 7 in the machine 1 has to be adjusted as well.

For adjustment of the start and end positions of the workpiece relatively to the polishing area 6, a second base 18A and third base 19A are provided, which are both adjustable. The second base 18A is arranged adjustable relatively to the third base 19A in a direc tion perpendicular to a direction of adjustment of the third base 18C. In the orientation show in FIG.l, which will be called the first orientation, the two adjustment directions are X-direction for the second base 18A and a Y-direction for the third base 18C. In the shown embodiment, the second base 18A and the third base 19A are exemplified with corresponding second slots 18B and third slots 19B, respectively, and corresponding second clamps 19B and third clamps 19C, respectively, for fixation.

However, it is also possible to substitute the second and third base of adjustment by a mechanical cross table having an xy-stage with automated actuators.

The holder 9 is attached to and supported by the second base 18 A. The second base 18 A, in turn, is supported by the third base 19A. Accordingly, this arrangement consist ing of the holder 9, the second base 18 A, and the third base 19B move together. This arrangement, is supported by a swivelling-support 21, which is mounted movable on a circular curved rail 22. The rail 22 is attached to and supported by the first base 17A. When the swivelling-support 21 moves on the curved rail 22, it swivels about the centre of the curved rail 22.

FIG. 2 is a top view of the second base 18A and the third base 19Aand the xy-adjustment mechanism with the slots and clamps on the swivelling-support 21. The second base supports the holder 9, which is shown to hold the workpiece 7, which has a bent centre line 7E due to the bent portion, the radius of curvature 7C of which extending from a centre of curvature 7D. Adjustment of the first base 17A along the X-direction moves this centre 7D into a vertical plane that also contains the centre of the circle of the curved rail 22.

During the initial adjustment of the polishing machine 1 for a certain pipe elbow as a workpiece 7 in the holder 9, the sequence is as follows:

- the swivelling-support 21 is located and oriented in the first position, which is as shown in FIG. 1, where the direction of the clamp 10 of the holder 9 is perpendicular to the rotational axis 13 and parallel to a swivel plane containing the curved rail 22;

- the first clamps 17C are loosened, and the radius and centre of curvature of the bent portion of the workpiece 7 is adjusted by moving the first base 17A together with the curved rail 22 a distance in the X-direction, limited by the length of the first slots 17B, after which the first clamps 17C are tightened for fixation of the first base 17A against the main support structure 11 ; - the second clamps 18C are loosened, the second base 18A is translated in the X-direc- tion relatively to the third base 19A as guided by the second slots 18B until the centre line of the front end 7A of the workpiece 7 coincides with the rotation axis 23 and centre of the polishing area 6, after which the second clamps 18C are tightened for fixation of the second base 19A relatively to the third base 18A; this adjustment compensates for a straight section at the rear end 7B, as well as the length of the holder 9;

- the swivelling- support 21 is swung clockwise an angular range, which in the illustrated example is 90 degrees due to the 90 degrees bent portion, so that the rear end 7B of the bent workpiece has a centre line parallel to the rotation axis 13 of the wheel 2; now, the rear end 7B still has to be correctly centred;

- the third clamps 19C are loosened, and the third base 19A, which was adjustable, is now adjustable in the X-direction, due to the 90 degrees rotation along the curved rail 22, and an adjustment in the X-direction is made by moving the third base 19A along the third slots 19B until the pipe centre at the rear end 7B of the workpiece 7, which is held by the clamp 10 of the holder 9, coincides with the centre 23 of the polishing area 8, after which the third clamps 19C are tightened. This adjustment assures correct posi tioning when 90 degrees is achieved. Compensation for straight front end and for length of holder are done via the control from a database.

Due to this procedure, the necessary parameters with respect to the swivelling and pol ishing of the bent piece of the elbow have been adjusted.

However, the pipe elbow may extend from the bent portion into a straight section at the front end, the length of which may vary. Accordingly, the automated movement of the workpiece 7 by the belt drive 14 in the Y-direction along the axis of rotation 13 has to be programmed so that the belt drive 14 pushes the workpiece a correct distance through the central area 6 for grinding the straight section, until the swivelling along the curved rail 22 starts. The workpiece 7 may have to be moved straight linearly in the Y-direction through the polishing area 6 during the first phase of the polishing and only after a certain distance of motorised straight linear movement of the main support structure 11 along the rails 12, the swivelling movement along the curved rail 22 starts, which is done automatically by a correspondingly controlled actuator 24. These data for the first straight linear movement in the Y-direction prior to the start of the swivelling along the curved rail are entered into a controller which controls the first straight linear movement of the workpiece 7. Subsequent the swivelling motion of the workpiece 7 sets in for polishing the bent sector. The transition between the movements is a matter of proper programming of the controller according to customary practice in the field. Also, the rear straight section movement is automated by the controller to perform the complete sequence.

Afterwards the rear straight part are moved nu moving the main structure further in the y direction. All movements can now be repeated in backwards/opposite sequence to do a double finishing and returning the workpiece to loading position.

The main support structure 11, as well as the first base (17A), second base (18A) and third base (19A) are exemplified as plates. However, other shapes are possible as long as the adjustments perform the same function. For example, instead of bases sliding against each other during adjustment, it is possible to use a mechanism of rods in cor responding bushings or sliders on corresponding rails. Other possibilities are available for straight linear movement. When the belt drive 14 moves the main support structure 11 in the Y-direction, the centre of curvature 7D of the bent portion of the workpiece 7 will at a certain position of the main support structure 11 be vertically above the centre of curvature of the curved rail 22, at which position, the belt drive 14 will stop moving the main support structure 11, and the swivelling support 21 will start swivelling in order to guide the bend part of the workpiece through the polishing area 6.

The stop of the movement of the main support structure 11 and the transition into the circular movement accounts for workpieces having a bent portion that has a centre line following a portion of a circle.

Once the swivelling is stopped, the belt drive may push the workpiece further through the polishing area for polishing the final straight section at the rear end 7B of the pipe elbow. FIG. 3 illustrates a top view example of the swivelling operation of the swivelling- sup port 21 along the curved rail 22 by the actuator 24. The first base 17A and the curved rail 22 in FIG. 2 is transparent for illustrating the arrangement of the actuator arm 25 that moves the swivelling- support 21. The swivelling-support 21 has mounted to its underside rollers 26A that are rolling along the outer edge 22A of the curved rail 22 and another roller 26B that rolls along the inner edge 22B of the curved rail 22. The swiv elling support 21 is shown in two extreme orientations 21A, 21B in FIG. 2.

An actuator arm 25 is fixed to the rotational actuator’s 24 point of rotation 27. The actuator arm 25 is swivelling between a first extreme angular orientation 28 A and a second extreme angular orientation 28B, passing an intermediate angular orientation 28C on its way between the two extreme orientations 28 A, 28B. At the end of the actu ator arm 25, a first end 29 A of a connecting rod 29 is rotationally mounted, which at its opposite end 29B is rotationally mounted to the swivelling-support 21. In order to reach through the first base 17A from the underside of the first base 17A to the swivelling- support 21, the first base 17A comprises a recess 30 in which a vertical rod fastened to the swivelling-support 21 follows the circular arch of the inner edge of the curving rail 22. When the actuator arm 25 swivels from the first extreme position 28A to the other extreme position 28B, the actuator arm 25 pulls the ends 29A of the rod 29 from a first extreme position 31A to a second extreme position 3 IB. The opposite end 29B follows the arch of a circle along the inner edge of the curved rail 22 and pulls the swivelling- support 21 from the position 21A to the position 21B, which involves a 90 degree change in orientation of the swivelling-support 21. However, it is possible to program a corresponding controller to change the orientation of the swivelling- support by less than 90 degrees, dependent on the angular bent of the bent portion of the workpiece 7.

FIG. 4 illustrates a possible lay-out of a housing 32 for a final polishing machine 1. A first cover 33 for the wheel 2 protects the surroundings against dust from the abrasion, as well as moving machine parts. A second cover 34 closes the working area of the machine 1. For input of commands and data as well as output of status information, an operation panel 35 is electronically connected with the machine 1, inside which a controller is located. When operating the machine 1, an optional pedal has to be activated as a safety measure.

FIG. 5 illustrates a robot station, in which three machines 100 have been arranged and where workpieces 7 arrive on a supply conveyor 39A. The pickup 38 of a robot 37 picks up a workpiece 7 from the supply conveyor 39A, places it in a machine 100 that is available for polishing, and takes it out of the machine 100 after polishing for placing it on a further conveyer 39B for moving the polished workpieces to the next handling station, for example a packing station.

FIG. 6 illustrates an alternative polishing principle. In this case, the polishing belts are substituted by a sand blast head 43 that is rotating, as indicated by arrows 43A. The sand blast head 43 receives sand that is transported by an air flow 50 through sand supply tubes 44 and creates a sand jet 46 by sand blast nozzles 45. By suction 47, the sand is removed in an air flow. Through a front opening 48, a workpiece 7 is inserted, first by straight linear translation 41 and then by rotation 42, as explained in relation to FIG. 1 and FIG. 2.

Reference numbers

1 pipe polishing machine

2 ring-shaped wheel

3 belt rollers 4 abrasive belt

5 arrows for belt direction

6 polishing area

7 workpiece

7 A front end of workpiece 7 7B rear end of workpiece, the rear end held by clamp 10 7C radius of curvature of bent of workpiece 7 7D centre of curvature of bent of workpiece 7

8 arrows indicating movement of main support structure

9 holder 10 clamp of holder 9

11 main support structure

12 rails for translation of support structure 11

13 rotation axis of wheel 2

14 motorised belt drive 15 motor of belt drive 14

16 belt of belt drive 14 17A first base 17B first slots in base 17 17C first clamps for holding first base 17A 18A second base

18B second slots in second base 18A

18C second clamps for holding second base 18A

19A third base

19B third slots in third base 19A 19C third clamps for holding third base 19A

20 coordinate system

21 swivelling- support

21A first extreme position/orientation of swivelling-support 21 21B second extreme position/orientation of swivelling-support 21 22 circular curved rail 22A outer edge of rail 22 22B inner edge of rail 22

23 centre of polishing area 6 24 actuator

25 actuator arm

26A rollers along the outer edge 22A 26B roller along the inner edge 22B 28A first extreme orientation of actuator arm 25 28B second extreme orientation of actuator arm 25

29 rod connecting actuator arm 25 with swivelling-support 21 29A first end of rod connected to actuator arm 25

29B second end of rod connected to swivelling- support 21

30 circular recess in first base 17A 31A first extreme position of rod 29

3 IB second extreme position of rod 29

32 machine housing

33 cover for wheel

34 cover for input region 35 operation input panel

36 pedal

37 robot

38 gripper

39A supply conveyor 39B further conveyor

40 motor for driving wheel 2

41 straight linear movement

42 rotation of workpiece 7

43 sand blast head 43A rotation of sand blast head 43

44 sand/air flow supply tubes

45 sand blast nozzles

46 sand jet

47 suction front opening of sand blast head 43 centre of motion of swivelling- support air flow in sand blast head 43 polishing machine