1LU Tienfu:Fuzzy logic for large mining bucket wheel reclaimer motion control-from an engineer's perspective89. than set conditions in crisp numbers ing problems,normally not enough attention is paid to Fuzzy logic is multi-valued logic.It allows any the complicated mathematics behind the user interface degree of value from 0 to 1 to be assigned in a fuzzy to perform such fuzzification and defuzzification.In- set,such as gray instead of black or white.This is dif- stead,focus is given to choosing one of the readily a- ferent from crisp logic,where given items are either vailable software programs that most likely share a sim- members of a definite set or they are not.It is therefore ilar graphical user interface,similar ways of entering possible to have a reasoning system which makes deci-fuzzy logic rules,and similar methods of setting up sions by combing set membership distributions.This membership sets based on his/her preferences.Of gives great flexibility in making decisions based upon course,ultimately,the chosen software will still need degrees of truth when facing uncertainties that are too to deliver satisfactory results. difficult or cumbersome to be defined using crisp num- Depending on the nature of the problems to be re- bers.However,there must be a set of rules,where the solved using fuzzy logic,engineers will need to look in- conjunction"and"calls for the minimum membership to aspects of setting up the fuzzy logic parameters in- of the topic being considered to yield an output mem-cluding numbers of input/output,fuzzy logic rules, bership value for decision-making purposes.As a range of membership sets,and input/output scaling. result,fuzzy logic has been widely adopted and applied These factors will be detailed in the next section. for the entire span of engineering applications and 3 Controller design products ranging from manufacturing machinery to do- mestic appliances (i.e.the washing machine). The size of a BWR is large (i.e.50 meter long Engineers normally are short of time in dealing boom which is the length of one link)and therefore it with one given problem.They need to effectively solve normally moves slowly.In the author's previous work, the given problem and move on as soon as possible as a model-based controller was developed.However,the there are always plenty problems waiting to be re- performance of a model-based controller is indeed sen- solved.Many engineers would wish to have more time sitive to modeling errors and unexpected disturbances to conduct thorough studies and investigations for the in addition to the need of laboriously finding appropri- best solutions before moving on,but such a wish is not ate gains.Hence,fuzzy logic is adopted and imple- normally granted. mented to deal with the modeling errors and uncertain- When solving problems concerning uncertainties ties on top of the model based portion,which is limited having values other than false and true (0 and 1), by the lack of knowledge about the system,to improve fuzzy logic could potentially be a good choice.When the BWR's motion performances as shown in Fig.5. engineers try to apply fuzzy logic to solve the engineer- Desired acceleration 回 Desired Subsystem3 e &m Alpha actual fuzzy for Alpha error Alpha Alpha ec TauOmega Gain Theta fuzzy fora Omeaga actual System wit中 encode limitation Omega error e&ec3 Omega fuzzy for axis3 Out Gain for error rate signal Theta actual Disturbance V+G Desired velocity Subsysbtem4 同 Desired veldcity Theta error Desired angle Subsystem5 Desired posltion Fig.5 Fuzzy logic controller with model-based portion As there are many ways of implementing fuzzy log- ic in a control loop,it should be noted that this work