Applying STAMP to safety standards of mowing robots
Contents
1. b A wheel over the edge or an edge caving in could cause unexpected rollover on Obstacles that could lead to a collision such as trees or bushes higher than 15 cm do not have to be limited by the perimeter cable Mower will bang and bounce when it collides with this type of obstacle creating an island around them d User shall not operate the robot for trimming hedges for mowing vegetation other than grass for leaf or ebris collection or on grounds other than mowing field for pulling or carrying loads e User should not mow over gravel stones or hard immovable objects like pipes rocks or sidewalk edges or objects like blind corners shrubs trees with holes or flower around it that might obscure vision The collision detection a A subsystem that accomplishes the whole range management of collision detection through a virtual force system of the device is not field This system allocates a force vector to obstacles across the mowing field This force is controlled by functioning leading to the system using the signals obtained from sensory devices trapping points b Obstacles such as trees flower beds fountains or bushes higher than 15 cm shall not have to be delimited by the perimeter wire Mower will bang and bounce when it collides with this type of obstacle creating an island around them c The perimeter wire shall not be laid around an object that robot can be allowed to collide with like a fence or a dense hedge The equipm2. flames water heater etc to flame or spark leading to and hazardous chemicals to avoid electrocution overheating or chemical burn hazard environmental hazard b Human robot environment chemical thermal conditions If gasses liquids or combustible substances are contained inside the robot the designer should ensure that any increase of temperature will not cause burn injury The user is changing the a Settings that could be stored in ROM might include manual user options user preferences sound wire operating program leading position language learn edge blades replaced anti theft charging options weekly program entry points to a harmful injury leading auto depart safety tests information total time run time temperature software version charging voltage to hazard caused by charging temperature entry points set default child guard lock settings alarm function disable enable neglecting ergonomic rain sensor restart disabled pause auto setup enable disable sound date and distance format time set principles in machine real time clock signal type lock keyboard scan width zones setup first time calibration and ground clearance follow loop garden shape open normal complex b Robot with operating units shall use only ROM to prevent from changing the operating program c Faulty programming may result in anti theft alarm don t stop beeping or not operating incorrect set of clock incorrect
3. to follow the tasking path A3 3 Water and other liquids causing damage of electrical connections A3 4 The mowing equipment starts vibrating abnormally A3 5 The drive motors are damaged due to severe overloading of the wheel motors A3 6 The robot ceases its operation due to cut of the perimeter wire 2 3 Identify the High Level System Hazards On top of the measures taken by the manufacturer to avoid the risk of hazards that robots in general might cause to the user the product should also be evaluated against the following list of possible dangers MGKM12 Mechanical Hazard Crushing Shearing Cutting or severing Entanglement Impact High pressure fluid injection Shape Acceleration deceleration inadequate mechanical strengths Mass and velocity Potential elements or elastic elements Electrical Hazard Contacts of persons with live parts Breakdown Leakage current Electrostatic phenomena Thermal radiation Hazard generated by vibration White finger disease Neurological osteo articular disorders Hazard generated by radiation electromagnetic fields infra red light visible light and ultra violet light Laser radiation X and y rays and B rays electron or ion beams neutrons ionizing or non ionizing radiation Thermal Hazard Burns and scalds Hazards generated by neglecting ergonomic principles in machine physiological and psycho physiological effects human errors Slipping tripping and falling hazar
4. work time not enough work hours not completely mowed the secondary area the remote control don t work An abnormal high speed a The software of the robot should bear a self checking program that manages suspicious movements Unless movement is not blocked such a program exists the user shall not be able to reach a control to stop a disoriented robot in proper time by the stop button leading as in industrial robots Suspicious movements are mowing out of the mowing area due to a disconnection to mechanical hazard of the wire work less that being programmed doesn t cross over the wire doesn t complete the edge doesn t following the plot doesn t working at the time scheduled doesn t position correctly in the charging station doesn t mow properly around the flowerbeds b Frequent stops and restarts require additional battery energy c User should try to control continuously the robot when operating it via remote control The perimeter wire is cut a In the user s guide the user of mower is informed that he should periodically inspect blades for foreign leading to breakdown of material or debris calibration for interference loop signal from the wire for interference from metallic the robot leading to objects perimeter fence reinforcement bar the shield of wires for damaging the battery for leading of electrical hazard corrosive liquid the covering hood for opening to clean base station with a damp cloth to confir
5. Applying STAMP to safety standards of mowing robots Mitka Eleftheria Electrical and Computer Engineering Democritus University of Thrace University Campus Xanthi 67100 Greece em3933 ee duth gr Abstract The use of mowing robots in anthropic environment is increasing leading to the call for specific safety standards This is a challenging endeavour however because the user must usually be placed in the robot s workspace and the residents must frequently interact with the robot Although specific safety standards for mowing robots do not yet exist there are several mowing device standards and well established principles of risk analysis and safety design that can and should be applied This paper presents an overview of safety constraints for mowing robots starting with a discussion of high level system safety requirements followed by methods for risk assessment or hazard analysis and a presentation of STAMP Systems Theoretic Accident Modelling and Processes as a safety strategy 1 Introduction Mowing robot is a mechatronic system used in a domestic environment Robotic mower is constructed to cut grass in gardens at any day and time without human intervention It is usually small compact noiseless and light enough to be transported manually This home used appliance could be adjusted to cut in different locations Throughout its task the apparatus cut the grass surrounded by a perimeter cable Its scope is to cut wide locations p
6. design 1992 Le12 Leveson N Engineering a Safer World Systems Thinking Applied to Safety The MIT Press 2012 Le95 Leveson N Safeware System Safety and Computers Addison Wesley 1995 Le09 Leveson N Applying systems thinking to analyze and learn from events Safety Science Vol 49 pp 55 64 2009 MGKM12 Mitka E Gasteratos A Kyriakoulis N Mouroutsos G S Safety certification requirements for domestic robots Safety Science 2012 MM12 Mouroutsos G S Mitka E Safety guided design concerning standardization s requirements of mowing robots In proc of International Conference APMS 2012 Advances In Production Management Systems Rhodes Greece 2012 ISO10 ISO 12100 Safety of machinery general principles for design risk assessment and risk reduction 2010 624
7. ds Hazard generated by materials and substances ingestion inhalation of fluids gases mists fumes fibers dusts or aerosols harmful toxic corrosive teratogenic carcinogenic mutagenic irritant or sensitizing effect biological hazards Environmental Hazards temperature wind snow lightning vapor explosive or flammable atmospheres ISO10 For practical reasons a restricted set of high level system hazards need to be identified considering safety as an emergent property and not a component property as a freedom of accidents or losses and combining potentially hazardous conditions with accidents identified at first step Le09 Beginning with an extensive set of system hazards usually result in a confused hazard analysis even in the case of the most simple systems The preliminary hazards might be defined as MGKM12 H1 Environmental hazards A1 A2 H2 Electrical hazards A5 A8 H3 Mechanical hazards A4 A7 A10 A12 A14 A15 H4 Falling and tripping hazards to residents A9 A11 A16 A17 H5 Hazards generated by materials and substances A6 H6 Hazards generated by neglecting ergonomic principles in machine A3 A13 A18 2 4 Identifying Safety design constraints and safety requirements for the hazards After the hazard and system identification the next important step is to define the system level safety requirements and design constraints that are essential to protect from incidents Table 1 Hazard ident
8. ed around the blades A pet or children could be a Before turning on the mower user should make sure that small children pets or obstructions are far away of pinned under the robot if the yard where the robot is operating the alarm of the robot b If a dog hits a mower or put its paws nose or mouth parts under the edge of the chassis the possibility of doesn t warn about restart injury increases or scheduled programming c The restart procedure for lawn mower should require returning it manually to charging position entering a operation leading to restart password checking the functionality and reliability of sensors by the robot software itself releasing electrical hazard stored energy and troubleshooting any software bug caused by the emergency stop diagnostics software etects the cause of any malfunction that lead to the stop d Improper restart might happen after an incorrect restart position after wrong reminder counter of blades after the replacement a temporary power loss a prolonged activity e The robot may restart its operation elsewhere especially near obstacles fallen branches forgotten objects ue to severe load on wheel drive motors due to unknown fault due temporary power loss after a long period of inactivity or after the replacement of the blades Residents should be informed by the user for the user programmed automatic weekly scheduled day and time g Control access of small children before mow in rev
9. ent of lawn a In case of abnormal vibrations user should stop the robot remove the power plug and visually check for any mower starts vibrating amage of the blade or mowing chassis and search directly for the cause The cause might be unstable blade abnormally leading to isc or worn out blades Vibration is usually a sign of malfunction mechanical hazard b Remove the power plug from mower in case that it begins trembling irregularly CH User shall check the blades and screws and replace them if they are damaged d The malfunction that leads to continuous vibration has to be repaired by service experts Liquids are sprayed a User or residents shall not spray water towards the robot the charging station or the panel of the station directed to the robot b Never use the charger or charge the device in grasses with dampness or when wet contact is expected leading to hazard caused c User must not under all circumstances remove bend and cut fit weld electrical or electronic parts inside by neglecting ergonomic the chassis of the robot principles in machine Inability of the device to a User and residents should be aware of the automatic departure the mowing path the scheduled work time follow the tasking path on an automatic weekly program for the season and the case of sudden overturn on slopes in order to detect leading to mechanical when the device does not follow the operating path hazard b Mowing robots might be used from phy
10. erse up and down via manual control User should ensure that children younger than 6 are indoors at least 100 feet away from the mowing field the robot are 622 programmed to mow at all times and under the watchful care of a responsible individual The mower is mowing a User shall not use an extension cord to increase this distance from power receptacle This event may be due outside the yard leading to to the perimeter wire being routed in the wrong direction around an obstacle which blocks the signal falling and tripping hazards b User shall pay extra attention if the area around the mowing field is populated or congested Always look for traffic when mowing near roadways walks or gravel drives A resident is mowing via a The area where the robot will execute must be well defined and operational flaws detected must be manual control over an mitigated Such operational contingencies include inability to determine location in the lawn inoperative obstacle and the object is sensors not accessible charging base docking station charging station not charging due to not active thrown at speeds greater charging process sensor failure high temperature of an actuator or a wheel electrical blade drive motor than 200 mph and 50 feet low battery due to inability to detect the charging station or wrong search settings or cutting long and dense leading to mechanical grass and so on hazard
11. ety Moreover the author proposed the implementation of STAMP on establishing standards that links system requirements with accidents in order to ensure safety on such an emerging technology and to spread the presence of such robots in every day life A system is considered safe when firstly meets the basic standards of safety which are defined from the national directives and regulations and secondly all the safety requirements that had been pointed out by the authors are fulfilled These requirements could serve as a base on building standards in order to increase commercialization and acceptance of these robots by the customers References AA09 ANSI ASAE 318 Safety for Agricultural Equipment 2009 A003 ANSI OPEI B71 1 Safety Specifications for Turf Care Equipment Power Lawn Mowers Lawn and Garden Tractors 2003 A004 ANSI OPEI B71 4 Commercial Turf Care Equipment Safety Specifications 2004 BS97 BS 3456 Part 2 Safety of household and similar electrical appliances Section 2 42 Battery operated lawnmowers 1997 EN94 EN 60335 Part 1 Safety of household and similar electrical appliances 1994 EN91 EN 292 Parts 1 and 2 Safety of Machinery Basic concepts general principles for design 1991 EN92 EN 294 Safety of Machinery Safety distances to prevent danger zones being reached by the upper limbs 1992 EN92 EN 418 Safety of Machinery Emergency stop equipment functional aspects Principles for
12. fective control is a consequence of lack of standards or from standards that are not enhanced adequately The author below apply STAMP in order to build a robust base with safety requirements regarding mowing robots 2 Applying STAMP to standards 2 1 Identify the accidents The first step in any safety analysis is to define which types of accidents needs to be considered Indeed the manufacturer that develops this kind of robotic system has to take account of the accidents occurred The accident model that derives from this definition does not indicate a particular causal factor Le09 In other words in a systems theoretic view of safety accidents could be recognized by categorizing the set of safety requirements that were ignored and answering why the control efforts were inaccurate in enforcing them In addition an accident definition in the design of a mowing robot is A1 Explosion of the device caused by storing the device in an improper place against manufacturer s specifications A2 The mower is moving near an operating rotisserie or barbecue where vapor may reach a flame or a spark causing an explosion of the device A3 The user is changing the operating program leading to a harmful injury A4 An abnormal high speed movement is not blocked by the stop button damaging property or robot s equipment A5 The perimeter wire is cut leading to breakdown of the robot A6 The mower chassis has burnt signs or signs of corrosion cau
13. ification is considered as a top down procedure that must take into account the harmonization of the system eliminating or controlling a hazard that is considered possible to allow a loss to take place Le09 According to 621 STAMP the constraints may differ in the design level Le12 Table I Design constraints and safety requirements such as user instructions user information and observations for some of the mowing robot s hazards identified above HAZARD SAFETY DESIGN CONSTRAINTS Explosion of the device a Remove the power plug from the charging station in case of storing the robot due to improper storing b The mower shall be equipped with a manual controller so that the user can simply move it from the grass leading to environmental back to a storage place when not in use User shall not store the robotic equipment in an overheated and hazard enclosed space such as a garage or shed where vapour may reach a flame or a spark or a source of extreme heat or on a hill Ce Do not leave containers with grass cuttings in the storage or charging area of the device d The appliance should be stored in a sheltered and dry place with good ventilation and lightning conditions e To reduce the fire hazard keep the robot charging station and storage area free of grass leaves or excessive grease The mower explodes due a Always keep the mower away from water heat sources stoves radiators open
14. looking A18 Severe injury could occur if hair fingers or clothing of resident are caught in the exposed mechanism of the robot due to indented opening of the cover 2 2 Assign a level of severity With aim to arrange the severity of the above accidents the precedence of the levels of severity is considered necessary Severity is described as the seriousness of the hazard The overall safety policy for arranging a level of severity for an accident is that all 620 accidents leading to death or injury must be restricted from the design level Le95 Level 1 A1 1 The collision detection system of the device is not functioning A1 2 A resident is mowing over an obstacle A1 3 The mower is mowing outside the yard hitting someone A1 4 The user is changing the operating program leading to a harmful injury A1 5 Vapor may reach a flame or a spark causing an explosion of the device A1 6 Explosion of the device caused by storing the device in an improper place A1 7 Rotating blades catches part of resident s body A1 8 Coming in contact with any exposed mechanism part of the robot A1 9 A child rides on an operating robot A1 10 A resident is pulling the mower backward without paying attention Level 2 A2 1 A pet or children could be pinned under the robot A2 2 The mower chassis has burnt signs or signs of corrosion Level 3 A3 1 An abnormal high speed movement is not blocked by the stop button A3 2 Inability of the device
15. m good contacts between station wires and contacts and that power supply is plugged at main power receptacle and that the coiled cord is properly placed in the holder to check the reliable connection of the power cable with the wire connector The mower chassis has a Frequently clean the charging station and the robotic contacts using only a damp cloth burnt signs or signs of b Use only a damp soft sponge or cloth and a dry brush to wipe the outer surfaces after scraping corrosion leading to hazard c User shall not use harsh or abrasive cleaning solutions generated by materials and d If the chassis remains dirty a soap or washing up liquid might be necessary substances e User shall not wash the inherent components so as not damage electric and electronic elements since mower is non waterproof The drive motors are a User shall not cut grass on slippery conditions where the traction is reduced and it may block the discharge damaged due to severe or dry scorched lawn overloading of the wheel b User shall inspect the drive wheel and remove grass residuals or other object motors and overheating c If the motor overheats then there are two ways of unblock If the parameters fall within the first range the robot will execute manoeuvres to unblock the blade If the over current is below the allowable limit the robot will stop and signal an error Motors have operated with over current for too long or some objects are accumulated or clogg
16. quipped with an emergency stop switch on the manual controller that ceases the rotation of blades and wheels within seconds MM12 A child rides on an a Warning signs shall be established to protect residents who may consider that they can ceaselessly be operating robot leading to reckless with the operating robot falling and tripping b Specific responsibilities concerning safety shall be assigned to an adult user hazards i The robot shall be equipped with a specific audio or visual signal easily recognizable by everyone to let people know whether it is on or off Use a frequency that is not within the range of noise frequencies in case of an audio signal MM12 Contact with the sharp a Manual should advice the user to present dramatic description on the hazardous behaviors of mistreating the rotating blades leading to robot and warn correctly concerning the appropriate safety features mechanical hazard b The replacement of not well maintained or worn out blades shall not require routine or extraordinary maintenance more than once a year c User s manual indicates that every maintenance service replacement or inspection of worn or damaged parts should be carried out by service experts MM12 623 Conclusion Since specific safety standards for mowing robots are not available the author here proposed that they should be carried out based on the fundamental user designer requirements in the domain of robotics saf
17. referably at daytime according to the battery charging cycle When it bangs with an obstacle such as branches small stones wall or fence it bounces and goes along a different direction The lawn mower executes an asymmetrical movement pattern that is not recurred depending on its sensing of growth of grass Since particular safety guidelines for mowing robots do not exist the authors suggest that their safety guided design should be based on standards that developed in areas of agriculture and garden equipment In addition the methodologies for safety for agricultural equipment AA09 the standard for safety of household and similar electrical appliances EN94 providing safety requirements for domestic environment may be useful in establishing standards for these robots Every manufacturer should follow the basic instructions summarized in the basic safety standards such as safety of machinery EN91 safety distances and danger zones EN92 emergency stop requirements EN92 safety of household and similar electrical appliances BS97 Safety Specifications for Commercial Turf Care Equipment A004 and safe features 619 according to Safety Specifications for Turf Care Equipment Power Lawn Mowers Lawn and Garden Tractors AO03 Establishing standards for controlling hazards in anthropic environment involves the entire control system and modelling the socio technical diagram that will enforce the primary constraints in design level Inef
18. sically and visually impaired persons and this affects the control lesign Navigation control on mowers requires a cable to delimit the area to be trimmed c The manufacturer should inform the buyer of mower that he she should keep all guards shields switches safety devices such as front and rear bumpers thermistors overheat protection manual controller buttons and lift sensors in place and properly connected Inspect to verify that these protective devices are appropriately installed and operating correctly d User ought to be advised not to remove the protective guards that need to be used with the mower Exposed mechanism a The mowing covering hood shall not collect grass residuals after mowing damp or wet lawn It shall be leading to hazard caused inspected and maintained regularly for foreign material using a damp cloth or another similar tool MM12 by neglecting ergonomic b The mechanism of the mowing robot shall be protected with plastic cover to prevent from bumping or principles in machine changing it MM12 Pulling the mower a Online tutorials and help menus shall contain the appropriate instructions so that users shall have direct backwards without looking access to information on how to operate the robot leading to falling and b A built in electronic hardware control system and or safety operational software shall be selected to force tripping hazards the robot to shut itself down in an emergency c Mowing robot shall be e
19. sing skin eyes damage A7 The drive motors are damaged due to severe overloading of the wheel motors and overheating A8 A pet or children could be pinned under the robot if the alarm of the robot doesn t warn about restart or scheduled programming operation A9 The mower is mowing outside the yard and not across the perimeter wire hitting someone A10 A resident is mowing via manual control over an obstacle and the object is thrown at speeds greater than 200 mph and 50 feet or more causing death or injuries ranging from blindness to severe bruising A11 The collision detection system of the device is not functioning leading to trapping points A12 The equipment of the lawn mower starts vibrating abnormally A13 Water and other liquids are sprayed directed to the robot with a garden or a liquid spray hose causing internal electronic damage of electrical connections A14 Inability of the device to follow the tasking path due to incorrectly placed perimeter wire too much slope overheated power supply unit incorrect wheel transmission bumper pressed during warm up bumper pressed for more than 2 sec during manual mowing bumper pressed while departing from the charging station A15 A resident could be injured by contact with the blades A16 A child may fall off and be seriously injured if he rides on an operating robot A17 A resident that uses the robot via remote control hits a person or a pet by pulling the mower backwards without
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