Kit of Self-Moving Units for Automatic Inspection of Marine Structures and Plants: Low Cost Unit for Inspection of Holds

Transcription

1 Journal of Shipping Ocean Engineering 6 (2016) 1-14 doi / / D DAVID PUBLISHING Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: Low Cost Unit for Inspection of Holds Enrico Ravina Department of Electrical, Electronic, Telecommunication Engineering Naval Architecture, Polytechnic School, University of Genoa, Via Montallegro 1, Genoa, Italy Abstract: All vessels offshore units require regular inspections to prevent structural or functional damages. Periodical inspections are based on classification society s requirements include both visual surveys non-destructive test interventions, to look for structural damage, pitting, corrosion, thickness measurement, usually documented by measurements or images. Different approaches of inspection can be proposed for underwater for dry areas, using unmanned vehicles or service robots able to improve traditional inspection methods. Several excellent proposals are today available: neverless, reasons of costs, operation complexity impossibility to cover all types of inspection with a unique autonomous unit limit conditions applicability of automatic inspection systems. The paper is first of a series describing main results of a wide research activity carried out at DREAMS Lab (Laboratory of Drives Experimental Automation for Marine Systems) of University of Genoa. The studies are oriented to realization of a kit of low cost unsophisticated self-moving units, devoted to support some recursive inspections in dry areas of ships on offshore plants as bulkheads, holds, double bottoms ducts. The paper describes design prototyping of a pneumatronic unit oriented to inspection maintenance of ship holds. Conceived to realize a portable user-friendly tool which could take part of an inspection kit for use of inspectors, able to simplify speed up inspection visits with automatic generation of survey reports. Key words: Self-moving, marine inspection, non-destructive testing. 1. Introduction Traditional marine inspections in dry areas require preliminary expensive time-consuming interventions before proper inspection process. Installations of scaffolding (Fig. 1) allowing surveyor to inspect structures as bulkheads, beams stiffeners are included in traditional approaches. As an alternative, aerial articulated platforms of various geometry can be employed, transporting surveyor by a tower crane (Fig. 2). In any case, proper inspection is manual, with access of inspector in uncomfortable, critical, or potentially dangerous areas. In order to reduce costs time consumption to Corresponding author: Ravina Enrico, professor, research fields: drives, fluid power automation mechatronics for marine systems. improve speed up technical surveys, several proposals of autonomous robotized systems for marine vessel inspection are proposed. Some of se have been inspired by climbing robots designed for general locomotion adhesion tasks; ors are customized for ship areas. A great number of different types of devices for locomotion on surfaces have been designed, are applicable to general-purpose inspections inside ships: legged, implementing motion by adoption of legs [1, 2]; wheel-driven, combining wheels for translation/ rotation vacuum pumps/magnets for surface attachment [3, 4]; Tracked, using chain-tracks as locomotive mechanism [5];

2 2 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: Fig. 1 Scaffolding articulated platform. Fig. 2 Models of articulated platforms. translation, using translational actuators with appropriate attachment devices [6, 7]; cable-driven [8]; combined, integrating different locomotive mechanismss to improve robot ability dexterity [9, 10]. From surface adhesion point of view, types proposed consider: suction, using vacuum suction cups [11, 12]; magnetic, employing permanent or electrical magnetization devices [13, 14]; gripping, in which gripping devices allow climbing robot to travel within complex environments [15, 16]; rail-guided, pre-installing rails for sliding of robot [17, 18]; bio-mimetic, emulating, for instance, sticking ability of geckos [19, 20] ]. It must be observed that not all adhesion proposals can be successfully applied in dry surface inspection of ship holds. Inspectionn maintenance is a very real problem for classification societies, marine service providers, ship-owners, assurance societies it represents one of main elements for safety functionality of ships offshore units. In particular, cargo holds tanks are subject to regular inspections maintenance measurements: many spacess are difficult to access tanks are often narrow. Cargo holds are larger spaces, but y reach easily heights over ten meters; use of scaffolding forces up not only costs but also, considering time required to built infrastructure, overall inspection time. From this point of view an automatic inspection process can speed up intervention. inspections are often still done manually reason is that ship environments are, in general, difficult for mobile inspection units. There are not general criteria of judgingg or deciding wher automatic units are certain to have advantages on inspection speed over traditional However, depending of case, a careful analysis on different expense items allows evaluating effective approaches. application, it is not realistic to propose use of a single mobile unit for inspections of all ship off-shore spaces: but kits of portable units can be designed to satisfy different requirements. EU-funded research projects (MINOAS, Marine inspection CApabilities for address this challenge in an attempt concepts for automation of ship inspectionn process. experienced dedicated partners in order to tackle issue of ship inspection, aiming to avoid ship accidents, promote maritime safety, protect environment. Within se projects original climbing units, as Clawer Clawer II [21, 22], based on magnetic adhesion, have been designed realized. At DREAMS Lab (Laboratory of Drives Experimental Automation for Marine Systems) of University of Genoa (Italy), are under continuous development research activities oriented to low cost compact On contrary, ship approaches. convenience to employ automatic Considering specific field of INspection robotic Assistant System, or INCASS, enhanced Ship Safety) to develop Thesee multifaceted projects integratee multi-functional climbing robots,

3 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 3 supporting inspection survey certification in dry areas, with adhesion based on suction cups or magnets. Hereafter, main characteristics features of a prototype proposed for holds inspection are focused discussed, evaluating advantages criticisms. 2. Pneumatronic Climbing Prototype Internal inspections of marine structures plants are a topic of specific interest for DREAMS Lab. It is currently oriented towards developing low cost, fully or semi-autonomous, simple easily transportable modular kit units to be used as tools for inspector leaving task of selecting most appropriate unit for a particular survey [23-25]. A distinguishing aspect of followed design methodology of inspection units, in comparison to approaches followed by or researchers, is research of simplicity modularity. The unit is designed starting from a basic architecture, with possibility of enhancement adding customized modules able to perform specific tasks. This approach is followed not only in design of unit described in this paper, but in all designs of self-moving units under study for different inspection tasks in ship or off-shore units. The fundamental necessary requirements to unit can be synsized as follows: easy reliable working; capability of operation within hostile environments; simple programming; limited need for maintenance; on/off actuation, where possible; unsophisticated design; low cost; weight reduction. Fig. 3 shows basic geometry assumed as reference for design: it consists of a cross-shaped structure with four symmetric arms connected to a central frame. Each arm is a double acting linear actuator, equipped at its mobile end with attachment device to surface, moved by single acting actuators. In this way, motion of unit is combinationn of motions along two orthogonal directions. This could be significant if related to motion required on surfacess such as walls of holds. Typical geometry of se walls is Greek-shaped (Fig. 4), with recurrent dimensions (Φ= 63, d cg = 7000 mm, b f-cg = 700 mm, b w-cg: 783 mm; t t-net: 15 mm). The self-moving unit is sized on see dimensions. Fig. 5 sketches position of unit on a vertical surface: fundamentals for attachment devices are quotes a b as well as position of center of masss of unit. In order to define basic architecture of inspection unit, taking into account variety of geometries present into a hold, reference assumed is that of SKS tankers type (Fig. 6), where large areas can be inspected interventions of operator are required for positioning unit at beginning of different paths. These types of tankers have floor walls that are IMO. considered as an operative limit, though not selection of automatically but sporadic flat in consequence to double hull, imposed by Fig. 3 Basic geometry of climbing robot (A d, B d, C d, D d : main double acting actuators. A s s, B s, C s, D s : secondary single acting actuators).

4 4 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: Fig. 4 Typical Greek-shape surface of hold walls. Fig. 5 Sketch of unit on vertical surface. Fig. 6 Examples of SKS holds. 3. Anchoring The problems related to anchoring of inspection unit to surface under investigation, is subject of discussion among researchers, in particular with reference to technical products available on market, prioritizing low cost solutions. Fundamental problems related to surface, critical for anchorage, are related to presence of: polluting films (rust, oxides, environmental contaminating, absorbed gas films...); deposit of oil (greasy surface); mix between grease dirt or grimes; welding beads; surface defects or local differences of surface finishing. Possible methods of attachment involve: pneumatic suction cups; holding magnets; permanent magnetic strips; permanent magnetic walking beams; electrically settable permanent magnets; special magnet systems; spreading magnets. Different methods of attachment require a careful comparison in order to select not necessarily best solution but most suitable one. With reference to vacuum solutions, specific critical problems are related to metallic oily surfaces to presence of welding beads. In fact, friction coefficient between cup oily surface is often strongly reducedd with respect to contact on clean surface. Today friction cups specially designed for greasy surfaces allow overcoming of this criticism. Thanks to excellent grip on greasy surfaces, this type of suction cups can withst high shearing strains, typical 2-4 times higher than with conventional suction cups. Some specific components are suitable for curved or flat surfaces are manufactured in a specially developed material, with elastic properties like rubberr wearing qualities like polyurethane. Problems related to positioning of suction cup over a

5 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 5 welding bead can be solved using multiple suction cup devices instead of single suction cups, by designing attachment device with sensors able to detect presence of welding, to adjust automatically device position in such a way welding is positioned between two cups. In addition, furr improvements can be reached using oval or rectangular suction cups, instead of classical circular geometry. With reference to magnetic attachment devices, criticisms concern rigid structure of magnet choice between permanent magnets electro-magnets. Difficulties of adaptation of magnet on irregular surfaces can be overcome using multiple magnets instead of one larger magnet. Permanent magnets simplify electrical wiring, but increase value of external applied force necessary to detach magnet. Electro-magnetic solutions are more flexible, but require an automatic control of activation/deactivation phases. Both pneumatic electrical attachments are considered in design of proposed unit: detailed designs have been developed for suction cups electro-magnets. 3.1 Pneumatic Anchoring Fig. 7 collects results of different types of suction cups in contact on steel surfaces: cup is loaded with axial forces of 25, 50, N under vacuum pressures of 20, 40, kpa. The anchoring condition is analyzed, distinguishing on five levels (from anchoring to immediate detaching). Surface, suction cups, levels considered are: Surfaces. S1: Steel; S2: Oiled Steel; S3: Oxidized Steel. Suction Cups. SC1: Flat, Silicon, 55 mm; SC2: Bellows, Rubber, 52 mm; SC3: Bellows, Silicon, 60 mm; SC4: Flat, NBR, 110 mm; SC5: Flat, NPV reinforced, 110 mm. Levels. 5: Immediate detaching; 4: Detaching with delay; 3: Fully slipping; 2: Partial slipping; 0: Anchoring. Of course, increasing diameter of suction cups (axial force being equal) number of correct anchoring increases. Fig. 8 reports one of results of test on silicon cups round bellow cups, showing deformation of cup vs. lateral force, under different vacuum pressure levels. These tests have been related to detailed analyses oriented to evaluate suction cup deformations displacements. In particular, lip in contact with surface is simulated using finite elements approaches for different sizes, materials geometries. Fig. 9 shows examples of this phase of analysis, in particular with reference to SC1 suction cup, previously cited. The cup is loaded with a lateral force of 50 N corresponding to condition of climbing unit anchored on steel vertical surface with only one couple of suction cups. The vacuum pressure is -40 kpa: lip is deformed but suction cup maintains anchorage. The critical level of lateral force producing detaching obviously depends to size to geometry of suction cup. 3.2 Magnetic Anchoring Criticisms related to application of permanent or electrical magnets concern real forces generated within attachment area real contact area, taking into account rigid structure of magnet. Solutions based on two or three magnets for each arm are studied tested. Table 1 reports characteristics of six electro-magnets (two for three different producers, conventionally named A, B C) in Table 2 is collected a comparison among se magnets, coupled in groups. Tests on slipping overturning conditions are implemented on steel oiled steel surfaces, distinguishing static contact (fully anchoring) to dynamic contact (beginning of slipping). Fig. 10 reports corresponding strain analyses for some of se anchorage solutions, showing good

6 6 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: Suction Cup Surface S1 S2 S3 SC1 SC2 SC3 SC4 SC5 Fig. 7 Tests on suction cups in contact with steel surfaces.

7 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 7 Fig. 8 (a) Tests on silicon (a) rubber (b) suction cups. (b) (a) Fig. 9 3D model of a suction cup: deformation (a) lip displacement (b). (b) Table 1 Electro-magnets characteristics. behavior of this rigid anchoring. The clamp is subject to a maximum stress of 47 MPa (Fig. 10 b), that decreases to 18 MPa adopting configuration with three magnets. 4. Model of Structure The concept design of unit take into account four different possible configurations: pneumatic attachment with external fluid power electrical supplies; pneumatic attachment with fluid power electrical supplies on board; magnetic attachment with external electricall power supply; magnetic attachment with on board electricall power supply. Solutions with external power supplies are simplified lighter but show disadvantage of

8 8 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: Table 2 Anchoring analyses on electro-magnets. (a) Fig. 10 (b) 3D models of magnets: geometries with two (a b) or three (c) magnets. (c)

9 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 9 umbilical cord. It limits path dexterity of unit but can be acceptable in specific confined spaces. Solutions with embedded power supplies requiree realization of an air-compressed reservoir on board installation of batteries having a sufficient autonomy to allow a practical use of unit. Fig. 11 shows case of embedded reservoir realized in central body of climbing unit. The analysis of stresses strains is developed using a 3D model of structure implemented in Pro-Engineer environment, under different constraint conditions, as shown in Fig. 12. Main settings concern Young s modulus Poisson s coefficient for materials of different parts of unit (Body: steel, E = 199,948 MPa, = Actuators clamps: aluminum, E = 73,084 MPa, = 0.33). The constraint characteristics Von Mises analysis are validated with experimental tests in presence of different kinds of surfaces Fig. 11 Sketch of structure (top side views) with embedded devices (quotes in mm). Displacements different superficial Case 1: Top constraint Case 2: Bottom constraint Case 3: Lateral constraint Fig. 12 Stress strain analyses.

10 10 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: status (clean, wet, oily, dirty). In case 1 (anchorage of unit in correspondence of C s actuator, in Fig. 1) maximum value of strength is 30 MPa, significantly less than admissible limit of material (aluminum, 160 MPa); maximum displacement detected is 0.34 mm. In case 2 unit is anchored in correspondence to actuator D s (Fig. 1) structure in stressed to compression: maximum value of strength is 34 MPa maximum displacement is 0.4 mm. Finally (case No. 3), structure of climbing unit is studied with connections at ends of arms A B (Fig. 1): this is most favorable condition, with minimum displacements (0.05 mm). On whole, implemented model fully satisfies strength displacement limits. It is used as reference to design of prototype hereafterr described. 5. Electronic Control System Equipment A micro-plc installed on board manages motion control. The basic architecture of unit plans that alll on-off signals drive actuations: having consider thatt pneumatic solution is a group of micro-valve (Fig. 11) that drive main actuators ejectors. PLC input signals are acquired by position sensors by vacuum gauges. The unit can be programmed to realize different paths, as shown in Fig. 13, taking into account shape of hold surfaces. More sophisticated geometries can use flow-rate or pressure proportional valves in order to generate steps defined by user. In this case, remotee wireless comm by joystick can be applied. Typical equipment mounted on unit to carry out non-destructive inspectionn tasks are: Fig. 13 Typical programmable paths.

11 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 11 Fig. 14 Prototype of pneumatic climbing unit. micro video-cameras (wireless or with integrated battery), to obtain a complete mapping of inspected surface; micro rmo-cameras, to detect defects also in presence of puttying or painting; thickness ultrasonic measurement devices, detecting state of steel plates. 6. Experiments In order to test performances limitations of proposed unit a basic prototype has been constructed tested. The self-moving unit is able to climb on flat or low curvature surfaces, generically oriented. It is fully pneumatic, with four orthogonal crossed main actuators: each of m carries, at its end, anor cylinder able to lift to lower a couple of suction cups (Fig.14). Pneumatic valves drive also ejectors supporting suction cups; in order to reduce weigh to simplify pneumatic connections, driving system is realized as a group of compact pneumatic valves controlled by a micro-plc. All components are embedded on robot; in this way, umbilical cord connecting autonomous system to frame is reduced to a single hose to a single electrical wire (24 V power supply), ncreasing robot dexterity. Motion tests on different kinds of surfaces have been developed; climbing operations on horizontal, tilted vertical surfaces have been programmed, while also changing surface roughness motion sequence of robot. About roughness of steel plates reference assumed is European Stardd UNI EN 10130, classifying products in four classes: bright, Ra 0.4 µm semi bright, Ra 0.9 µm stard, 0.6 µm < Ra 1..9 µm rough, Ra > 1.6 µm Experimental tests have been mainly developed on stard plates. Climbing motions on steel, oiled steel, oxidized steel, glass, plastics, rolled wood, plasterss have been successfully tested. The structure of this type of climbing robot is rigid: neverless, specific tests have shown possibility to use it not only on flat surfaces, but also on low curvature walls (maximum radius of curvature 1,7000 mm), thanks to local deformations of suction cups. The overall dimensions of proposed prototype are mm, weight is 5.5 kg. Step sequences are completely programmable. The grippingg is assured by control of vacuum level inside cups: if level decreases below 0.8 bar unit stops itself, maintains position generates an air-raiclimbing is about 0.1 m/ /s: examination by video-camera is continuous, while examinations by warning. The average speed when unit is ors devices (e.g. UTM) require additional times related to specific measurement. The prototype has shown good technical reliability: cycles up to one thous steps with U-turns have been realized withoutt problems. The working performance

12 12 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 7. Alternative e Geometries The corresponding prototype shows good performances on flat or low curvature surfaces, but it is not able to move itself on surfaces having variable curvatures. Fig. 15 shows an alternative geometry designed tested: it consists on an articulated unit using same types of anchoring devices but having an articulated geometry. It is able to move itself on a surface automatically recognize slope variation modifying position of front following surface slope. The unit shown in Fig. 15 allows climbing motions only in a single direction: it consists of two parts (front back) respectively mounted on articulated frames. If, during motion of robot, slope of surface varies, a contact less sensor detects this variation front part rotates automatically. This alternative solution includes an interesting improvement of motion control, substituting point-to-point control (by PLC) with a distributedd control (Actuator Sensor Interface, AS-I). This approach allows elimination of PLC on board but limits use to digital input/output signals. Micro-piezoelectric proportional valves are still under testt in anor alternative solution designed to enhancee flexibility of control by remote users. Fig. 15 Articulated self-moving unit. has been tested monitoring real deformation of structure by means of strain gauges: taking into account suction cup deformations, resultss are comparable with those obtained from numerical model. These results have been useful to validate numerical model, generating a parametric tool applicable in study of new units. Structural improvements could be studied passing from prototype to industrialized unit, in particular protecting electronic pneumatic devices from aggressive environments from unexpected impacts. 8. Concluding Remarks Ship inspection is a very real problem, involving aspects of cost, personnel employment, safety, instrumentation. It is currently performed manually re are not general rules or criteria able to decidee wher automatic approaches can substitute, entirely or partially, traditional methods. Anywayy self-moving units are attractive to automate several inspection phases. A low cost climbing self-moving unit oriented to inspection tasks is proposed. A parametric model able including sub-models of structure of anchoring devices (suction cups or electro-magnets) is developed. The corresponding prototype shows good

13 Kit of Self-Moving Units for Automatic Inspection of Marine Structures Plants: 13 performances on flat or low curvature surfaces, but it is not able to move itself on surfaces having variable curvatures. Articulated variations can be evaluated, taking into account increasing mechanical complexity. The prototype under study is equipped with basic instrumentation, but furr measurement devices can be easily placed on board. In particular, at moment prototype is not equipped with surface-recognition tools: but considering that it may be easier that robot s eye detects surface failures as it may be harder for human operator to be able to wholly appreciate defects on surfaces through use of conventional cameras, this aspect will be surely considered in furr development of unit. Or experiences, still under development, are oriented to eliminate umbilical cord, installing on board a micro-compressor batteries for electric power supply. The unit takes part of a low cost user-friendly kit of survey, conceived to support inspectors during periodic visits on board of ships offshore platforms; next papers will describe solutions proposed to inspection of ducts or pipes confined spaces. References [1] Kim, S., Asbeck, A. T., Cutkosky, M. R., Provancher, W. R Spinybot II: Climbing Hard Walls with Compliant Microspines. Proc. of 2005 IEEE International Conference on Robotics Automation: [2] Balaguer, C., Virk, G., Armada, M Robot Applications against Gravity. IEEE Robotics Automation Magazine 13 (1): 5-6. [3] Longo, D., Muscato, G A Modular Approach for Design of Alicia3 Climbing Robot for Industrial Inspection. Industrial Robot: An International Journal 31 (2): [4] Murphy, M. P., Tso, W., Tanzini, M., Sitti, M Waalbot: An Agile Small-Scale Wall Climbing Robot Utilizing Pressure Sensitive Adhesives. Proc. of 2006 IEEE/RSJ International Conference on Intelligent Robots Systems 12 (3): [5] Kim, H., Kim, D., Yang, H., Lee, K., Seo, K., Chang, D., Kim, J A Wall Climbing Robot with Vacuum Caterpillar Wheel System Operated by Mechanical Valve. Proc. of 9th International Conference on Climbing Walking Robots, [6] Backes, P. G., Bar Cohen, Y., Joffe, B The Multifunction Automated Crawling System (MACS). Proc. of 1997 IEEE International Conference on Robotics Automation, [7] Rosa, G. L., Messina, M., Muscato, G., Sinatra, R A Low-Cost Lightweight Climbing Robot for Inspection of Vertical Surfaces. Mechatronics 12 (1): [8] Tso, S. K., Fan, K. L., Fung, Y. H., Han, L., Tang, D. W., Liu, K. P., Tong, F Inspection of Large Tile Walls for Highrise Buildings Based on a Mechatronic Mobile System. Proc. of 2003 IEEE/ASME Intl. Conference on Advanced Intelligent Mechatronics, [9] Xiao, J., Xiao, J., Xi, N., Sheng, W Fuzzy Controller for Wall-Climbing Microrobots. Proc. of 2004 IEEE International Conference on Robotics Automation, [10] Elkmann, N., Kunst, D., Krueger, T., Lucke, M., Bohme, T., Felsch, T., Sturze, T SIRIUSc: Facade Cleaning Robot for a High-Rise Building in Munich, Germany. Proc. of 7th International Conference Climbing Walking Robots, [11] Hirose, S., Nagakubo, A., Toyama, R Machine That Can Walk Climb on Floors, Walls Ceilings. Proc. of International Conference on Advances in Robotics, [12] Pack, R. T., Christopher, J. L., Kawamura, K A Rubbertuator-Based Structure-Climbing Inspection Robot. Proc. of 1997 IEEE International Conference on Robotics Automation, [13] Faina, A., Souto, D., Deibe, A., Lopez-Pena, F., Duro, R. J., Fernez, X Development of a Climbing Robot for Grit Blasting Operations in Shipyards. Proc. IEEE Intl. Conf. on Robotics Automation, [14] Han, S. C., Kim, J., Yi, H. C A Novel Design of Permanent Magnet Wheel with Induction Pin for Mobile Robot. Int. J. Precis. Eng. Manuf. 10 (4): [15] Aracil, R., Saltaren, R. J., Reinoso, O A climbing Parallel Robot. IEEE Robotics Automation Magazine 13 (1): [16] Vona, M., Detweiler, C., Rus, D Shady: Robust Truss Climbing with Mechanical Compliances. Proc. of 2006 International Symposium of Experimental Robotics, [17] Warszawski, A Industrialized Automated Building Systems-A Managerial Approach, 2nd ed. Taylor & Francis. [18] Zhang, H., Zhang, J., Liu, R., Zong, G Realization of a Service Robot for Cleaning Spherical

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