A CENTERING APPARATUS FOR A MEASURING PROBE

Abstract: A centering apparatus, comprising the two axially spaced spaced apart sets of supporting means, by means of which the centering apparatus is movably carried in a straight or a bent tube or pipe, the construction being such that the longitudinal axis extending through the geometrical centre of the apparatus, either coincides with the axis of a respective straight tube or pipe, or extends parallel to the tangent of the centre of the curved axis, respectively the curved pipe surface of a respective bent tube or pipe, which is bounded between the two sets of supporting means.

Description: A centering apparatus for a measuring probe. The invention relates to a centering apparatus which is adapted to maintain a measuring probe in the interior of a tube or pipe-shaped body in a position relative to the pipe surface to be inspected which is required for obtaining reliable measuring results. In order to perform the inspection effecttrely,it should be possible to move the measuring probe and the cable connected thereto in the interior of the tube or pipe-shaped body to be inspected while maintaining the required measuring position of the probe relative to the pipe surface. It is the object of the invention to provide a centering apparatus of the above described type and which is useable for pipes having a comparatively slight internal diameter (order of magnitude) of about 14 mm and larger; pipes having a round or oval cross-section; and pipes having a bent configuration, such as helically wound pipes, U-shaped bent pipes and differently bent pipes. Measuring probes that can be used within the scope of the present invention may for instance be based on Eddy-flow and/or optical and/or ultrason c inspection methods for internal pipe or tube inspections. The solution proposed according to the invention, without being restricted thereto, will be described for an ultrasonic measuring probe and is basically characterized by a centering apparatus having two axially spaced apart sets of supporting members through which the centering apparatus is movably carried in a straight or a bent tube or pipe, said construcionbeing such that the longitudinal axis extending through the geometrical centre of the apparatus, either coincides with the axis of a respective straight pipe or tube, or extends paralleltadetangent of the centre of the curved axis, respectively the curved pipe surface of a respective bent pipe or tube, which is bounded between the two sets of supporting members. By using in a thus constructed centering apparatus a rotatable reflector which is mounted in a frame together with a transducer for ultrasonic vibrations, said reflector can be arranged in such a way relative to said ultrasonic transducer that a beam of ultrasonic vibrations reflectedby the reflector always impinges on the pipe surface in any postion to be occupied by the assembly in the interior of a pipe or tubelike body, at a fixed angle of e.g. 90". Reliable measuring results are obtained when passing a centering apparatus with a reflector and measuring probe thus received therein through a pipe or tube to be inspected. More in particular, a centering apparatus according to the invention is characterized by a frame; a reflector rotatable about the lo5itudinal axis of said frame and carried thereby, adapted to deflect a beam of ultrasonic vibrations oriented along said longitudinal axis in a direction extending e.g, substantially perpendicular to said longitudinal axis; a first set of centering arms attached to the frame, respectively projecting therefrom, for synchronized pivotal movement in a plane transverse to said longitudinal axis; a first spring mechanism coupled to said first set of centering arms, which mechanism exerts such spring forces on the respective centering arms that a tilting movement of said centering arms directed towards the frame and produced by an internal pipe surface is counteracted; a second set of centering arms attached to the frame, respectively projected therefrom, or synchronized pivotal movement in a plane transverse to said longitudinal axis; a second spring mechanism coupled to said second set of centering arms, which mechanism exerts such spring forces on the respective centering arms that a tilting movement of said centering arms directed towards the frame and produced by the internal pipe surface is counteracted; and the centre of said reflector is present on the said longitudinal axis, as well as halfway between the first and the second set of centering arms. For obtaining a compact and simple construction, a centering apparatus according to the invention is characterized in that the centering arms forming one set, are each pivotally coupled to a common coupling member which is attached to the frame for rotational movement about the said longitudinal axis, and the spring mechanism coupled to the respective set of centering arms comprises a single spring which is connected between the frame and Erespective coupling member. A practically attractive construction of a centering apparatus according to the invention is further characterized in that the frame comprises a cylindrical housing which at the one end is provided with a set of pinions rotatably mounted therein; the reflector is carried by a reflector carrier extending in the interior of said housing, said carrier being carried rotatably relative to said housing by means of an internal gear with which said pinions are in engagement; and a set of bearing retaining pieces mounted on the housing which extend in a recess extending along the outer circumference of said reflector carrier in order to prevent an axial shift of said reflector carrier relative to said housing, as well as functioning as supporting bearing so that the reflector carrier is mounted rotatably in the housing. Such a construction enables to couple the drive means required for rotating the reflector and the transducer from one and the same side to the centering apparatus. At the same time, the advantage is obtained that the transfer of ultrasonic vibrations to and from the tube or pipe surface can take place unimpededly In a centering apparatus according to the invention, the frame is further adapted to carry a transducer for ultrasonic vibrations in such a way that a beam transmitted through said transducer along the longitudinal axis of the frame is directed towards the centre of the reflector. One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 isa partial cross-section on the line I-I ofthe embodiment shown in fig. 2 of a centering mechanism according to the invention with an associated transducer and reflector; Fig. 2 is a cross-section on the line II-II of the embodiment shown in Fig. 1; and Fig. 3 diagrammatically shows the principle underlying the present invention. The embodiment of a centering apparatus according to the invention shown in fig. 1 and 2 comprises a frame having a reflector carrier 1 rotatably carried therein for a reflector 2 fixedly mounted therein. The frame furthermore comprises a first centering unit 3 and a second centering unit 4, which centering units, in a manner to be further defined, are interconnected to a mechanical unit. The reflector carrier 1 is mounted rotatably in the frame comprising a cylindrical housing 26 by means of three pinions rotatable in the unit 3, only two of which, 7 and 8, are shown in fig. 1. Said pinions are in engagement with an internal gear of the reflector carrier 1 comprising a hollow cylindrical portion. Furthermore,said reflector carrier is rotatably carried by the ball bearings 9 and 9', which are mounted in the centering unit 4. By means of a set of bearingretaining pieces such as 10, 11 and 12, mounted preferably rotatably on the centering unit 3 and extending in a recess extending along the outer circumference of the reflector carrier 1, it is prevented that said carrier together with the centering unit 4 rotatably connected thereto will shift in axial direction relative to the centering unit 3; moreover, said pieces 10, 11 and 12 function together as a supporting bearing for the reflector carrier 1. So, the reflector carrier 1 likewise functions as a connecting element, so that the two centering units 3 and 4 are connected to a mechanical unit. In the interior of the centering unit 3 and the reflector carrier 1 furthermore there is fixedly connected to the frame an ultrasonic transducer 13 connected to an electric cable 14. Said transducer is arranged in such a way that a beam of ultrasonic vibrations transmitted, respectively received thereby along the longitudinal axis 15 of the assembly, is directed towards, respectively from the center 16 of the reflector 2. Said reflector 2 furthermore is arranged and designed in such a way that a beam of ultrasonic vibrations impinging thereon from the transducer 13 is deflected at an angle of e.g. substantially 900, as indicated by the arrow P in fig. 1. The pinion 7 is fitted with a drive shaft projecting beyond the centering unit 3, which drive shaft is adapted to be coupled to a motor (not shown) disposed at that side of the centering unit 3. When said pinion is brought in rotation by said motor, the reflector carrier 1 and thereby the reflector 2 is brought in rotation via the internal gear of said reflector carrier. When the transducer receives electric signals via the cable 14,so that said transducer transmits ultrasonic vibrations, it is achieved that in directions e.g.perpendicular to the longitudinal axis, a beam of ultrasonic vibrations is swung round relative to said axis. Each centering unit furthermore is provided with a set of centering-arms,three in the embodiment shown, 17, 18 and 19, as represented in fig, 2 for centering unit 3.The centering arms constituting one set are pivotal in synchronism in a plane extending transversely to the longitudinal axis 15 attached to the centering unit 3, respectively 4, viz. on that portion 20, respectively 21 within which the reflector carrier 1 is adapted to rotate. In fig. 2 the pivot point of the centering arm 19 is indicated by 19'. Each of the centering arms of a set is coupled via an associated steering link 22, 23 and 24 (fig. 2) to a coupling means 25, respectively 25' common for the respective set. Each steering link is pivotally coupled at its one end to the associated centering arm, and at its other end to the associated coupling means. Each coupling means 25, respectively 25' is rotable about the associated frame portion 20 respectively 21. In a clamping ring 26', 27 fixedly connected to the frame portion 20, 21, there is mounted a pressure spring 28, 29 extending along a part of the circumference, the one end of which is secured to the associated coupling ring and the other end is secured to the associated clamping means. Such a pressure spring is thus operative for pressing via the respective coupling means and the steering links coupled thereto, the associated centering arms in outward direction into an extreme position (fig. 2). At the free end of each centering arm there is rotatably mounted a supporting member, such as a pulley or bearing roller such 30, 31 and 32 (fig. 2). In fig. 1 the bearing roller of the centering unit 4 disposed opposite the bearing roller 31 is indicated by 31'. The centering apparatus is movably carried by means of said supporting means in the interior of a tube or pipe to be inspected. The reflector is arranged with respect to the two sets of bearing rollers in such way that the reflector centre 16 is present on the longitudinal axis 15 halfway between the two sets of bearing rollers of which fig. 1 only shows rollers 31 and 31'. In the above described construction such a spring force is exerted on each centering arm by the associated pressure spring that a pivoting movement of the centering arm oriented towards the frame and produced bythe interior pipe surface is counteracted. On account of the mutual coupling via the associated coupling means and the associated steering links, the centering arms of one set will furthermore be capable of performing a pivoting movement inclusivelyinsynchronism. Through a centering apparatus which is thus designed it is achieved that a beam of ultrasonic vibrations transmitted by the transducer, both with pipes having an oval crosssection and with pipes having a bent configuration, will impinge on the internal pipe wall always at the same angle, e.g. 90". Fig. 3 illustrates the principle of the invention with reference to the situation wherein a centering apparatus according to the invention is disposed in a bent pipe section. As a result of the construction of the centering apparatus will then always apply and in particular in case of ovality of the pipe, that the longitudinal axis of the apparatus, i.e. the axis along which the beam of ultrasonic vibrations impinges on the centre of the reflector, extends parallel to the imaginary tangent of the centre of the arc portion of the pipe axis which is boxed between the bearing rollersthetwo sets of carrier arms. In other words, the reflector-defected beam of ultrasonic vibrations for instance in case of a required perpendicular impingement, will always be oriented according to the radius of curvature of the above arc portion, i.e. the emitted beam of ultrasonic vibrations impinges on the pipe wall in situ always perpendicularly. The invention is not restricted to the embodiment described in connection with fig.1 and 2. For instance, it is possible to dispense with the reflector carrier 1 with internal gear and the coacting pinions, and to interconnect the centering units 3 and 4, in situ of 19 and/or 6 by bars to a unithentereflector 2 is rotatably carried by means of a longitudinally extending shaft attached thereto and is retained in the centering unit 4 while being secured against movement in axial direction. The drive motor for rotating the reflector, however, should then be disposed at the end side of the reflector unit 4, which need not always be a drawback.

Claims: CLAIMS 1. A centering apparatus, characterized by the two axially spaced apart sets of supporting means, by means of which the centering apparatus is movably carried in a straight or a bent tube or pipe, the construction being such that the longitudinal axis extending through the geometrical centre of the apparatus, either coincides with the axis of a respective straight tube or pipe, or extends parallel to the tangent of the centre of the curved axis, respectively the curved pipe surface of a respective bent tube or pipe, which is bounded between the two sets of supporting means. 2. A centering apparatus, characterized by a frame; a reflector carried by said frame for rotation about the longitudinal axis thereof and serving for deflecting a beam of ultrasonic vibrations oriented along said longitudinal axis in a direction which e.g. extends substantially perpendicularly to said longitudinal axis; a first set of centering arms mounted on the frame, respectively projecting therefrom, for synchronized pivotal movement in a plane transverse to said longitudinal axis; a first spring mechanism coupled to said first set of centering arms, which mechanism exerts such spring forces on the respective centering arms that a tilting movement of said centering arms oriented towards the frame and produced by an internal pipe surface is counteracted; a second set of centering arms are mounted on the frame, respectively projecting therefrom,for synchronized pivotal movement in a plane transverse to said longitudinal axis; a second spring mechanism coupled to said second set of centering arms, which mechanism exerts such spring forces on the respective centering arms that a tilting movement of said centering arms oriented towards the frame and produced by the internal pipe surface is counteracted; and the centre of said reflector is disposed on the said longitudinal axis, as well as halfway between the first and the second set of centering arms. 3. A centering apparatus according to claim 2, characterized in that the centering arms forming one set are each coupled pivotally to a coupling means common therefor, which is mounted on the frame for rotation about said longitudinal axis; and the spring mechanism which is coupled to the respective set of centering arms comprises a single spring which is connected between the frame and the respective coupling means. 4. A centering apparatus according to claim 2-3, characterized in that the frame comprises a cylindrical housing which is provided at the one end with a set of pinions rotatably mounted therein; the reflector is carried by a reflector carrier extending in the interior of said housing, which carrier is carried rotatably relative to said housing by means of an internal gear with which said pinions are in engagement; and a set of bearing retining pieces which extend in a recess extending along the outer circumference of the said reflector carrier, in order to prevent an axial movement of said reflector carrier relative to said housing, as well as functioning as supporting bearing through which the reflector carrier is mounted rotatably in the housing. 5. A centering apparatus according to claim 4, characterized in that one of the pinions is adapted to be coupled to a drive motor. 6. A centering apparatus according to any one of the preceding claims, characterised in that the frame is adapted to carry a transducer for ultrasonic vibrations in such a way that a beam of ultrasonic vibrations transmitted by said transducer is oriented along the said longitudinal axis towards the centre of the said reflector.

Inventors: VERSLUIS, RONALD
Applicants: NUCON ENG & CONTRACTING BV
Application year: 1982
Main classification: G01N29
IPC codes: G01B21, G01N29, G01M3, G01B17