We developed the disassembly system that uses the impulsive load and disassembly tools to disassemble used appliances economically. The main components of this system are impulse hammer, a lift table and developed disassembly tools. Several types of disassembly tools are developed to punch out fastened portion on a part and cut off the shaft of screw or connection pin of IC-chip. A simulation model is proposed to explain and formulate how the fastening point of product is broken and cut. Three kinds of disassembly tools are designed. The actual disassembly system is developed by using proposed simulation models and disassembly tools

Kajihara, Yasuhiro

Munesawa, Yoshiomi

Ohta, Kazuharu

Osaki, Hirokazu

Yoshida, Takanobu

Okayama University Digital Information Repository

Disassembly System using an Impact Hammer for the Material Recycling

Okayama University Scientific Achievement Repository

Memoirs of the Faculty of Engineering, Okayama University, Vo1.35, Nos.1&2, pp.191-196, March 2001Disassembly System using an Impact Hammerfor the Material RecyclingTakanobu YOSHIDA", Yoshiomi MUNESAWA', Hirokazu OSAKI',Yasuhiro KAJIHARA' and Kazuharu OHTA'(Received December 14, 2000)We developed the disassembly system that uses the impulsive load and disassemblytools to disassemble used appliances economically. The main components of this system areimpulse hammer, a lift table and developed disassembly tools. Several types of disassemblytools are developed to punch out fastened portion on a part and cut off the shaft of screw orconnection pin of Ie-chip. A simulation model is proposed to explain and fo~ulate how thefastening point of product is broken and cut. Three kinds of disassembly tools are designed.The actual disassembly system is developed by using proposed simulation models anddisassembly tools.1. INTRODUCTIONDisassembly has been attracting worldwide attention not only for the purpose of protecting the influence interms of the environment but also for constructing a recycling society in next century. We should pay specialattention to personal computers since the amount of abandoned personal computers has drastically been increasingfor the sake of frequent model changes. [I] Most of disassembly works have been executed manually by usingassembly tools. These works has several problems, for instance, increment of a disassembly cost and decrement ofworkers' health condition by dusty and rusty parts. So, an automated disassembly system is required for solving theabove-mentioned problems.In this research, we propose a disassembly system which makes it possible to disassemble product in a shorttime. Firstly, a simulation model is formulated to explain how fastening point of product should be punched out andcut off. Secondly, special disassembly tools are designed for the personal computers. Finally, a disassembly system isdeveloped, which uses an impact hammer for punching out and cutting off the fastening point in an instant.2. PROPOSED DISASSEMBLY SYSTEMWe propose a method to break the fastening point by using disassembly tool attached to an impact hammer. Animpact hammer gives an impulsive load to the fastening point such as screw and rivet, and breaks them.2.1 Disassembly DeviceThe disassembly device is composed of an impact hammer and disassembly tools. This device gives animpulsive load intensively to the fastening point so that the fastening point will be broken up. Intensive impulse load* Department of Systems Engineering191192 Takanobu YOSHIDA, Yoshiomi MUNESAWA, Hirokazu OSAKI. Yasuhiro KAJIHARA and Kazuharu OHTAeasily makes the fatigue-fracture of the fastening point with small load. As this effect is utilized, the fastening pointsuch as screw and rivet are speedily destroyed and removed without cutting.2.2 Simulation Model of Punching or Cutting Load at Fastening PointVarious fastening methods, such as the screw, rivet, and the solder, are used to fasten the parts and units incomputer. So the punching or cutting load at the fastening point should be formulated to design disassembly tools.: The radius of the shaft of the screw.: The largest radius of the area where the head of the screw is touched.: The smallest radius of the area which is not transformed by the stress.: The cross-sectional area of the shaft of the screw, which is cut by the load at one time.: The cross-sectional area of the shaft of the screw.: Shearing stress of the shaft of the screw.: The amount of the cutting depth until last time.: The amount of the cutting depth of this time.: The width of one connection pin of IC-chip.: The thickness of one connection pin of IC-chip. Where, size ( t) is less than size (w ) .: Shearing stress of one connection pin of IC-chip.: The angle of tip of the disassembly tool.Symbols: Distortion of fastened portion.: Shearing force generated by the load (PB).: Flexural rigidity of fastened portion.: Thickness of fastened· portion.: Distance from surface of fastened portion to the center of thickness.: Yield stress of fastened portion.: The Poisson ratio.bcS ySa YcCoCIWta Ysaza YpIIa2.2.1Ct)QDh2.2.2 "Force to punch out fastening pointWe make a model that the fastened portion under the screw is destroyed by the force (PB) loaded at the headof the screw in Fig.I. The screw is punched out from fastened portion by the impulsive load. The load of thousandstimes per minute is loaded by the impact hammer. It is regarded as a repetition of the static load in order to simplifythe calculation process. It is assumed that fastened portion is transformed plastically by the load of everyone timewithout fail.As the screw is punched out, the deflection quantity Ct) is given by solving the eq. (1) . [2]As the stress corresponding to the deflection quantity Ct) satisfies the yield condition of Mises, the fastenedportion is transformed plastically. The load (PB) is obtained considering the yield condition of Mises, which isgiven by eq. (2) .H 21+3-,2h3 cr~Pa> - ------------------12z ( 1 + v) (1 - v) [b2 - c2 + 2c2ln [~ JJ8n(c2 ( 1 - v) + a2 ( 1+ v) ) (2)Disassembly System using an Impact Hammer for the Material RecyclingAs the load (PB) is forced repeatedly to the head of screw, plastic deformation of the fastened portion isprogressed, and the screw is punched out finally.193Fastened portionZcrewabFig.! Model of punching out the fastened portion2.2.3 Force to cutting off fastening pointWe make a model that the shaft of screw is cut off by the force loaded from perpendicular direction of the shaft.Central axis of the screw or rivet is assumed to be parallel to X axis. The direction of gravity is parallel to Z axis.The load is given from the direction of gravity. Additionally, it is assumed that the fastened portion and the head ofthe screw are not transformed by the load. Under the above mentioned assumption, the head of the screw is pressedby the disassembly tool from vertical direction. The shaft of the screw is cut little by little by repetitive load. Theshearing force (PC) is represented by eq. (3) . [3J (Fig.2)As the· cutting depth progresses by repetitive load, the amount of cross-sectional area (Sy) is shown by eq.(4) , which is cut by the load at one try in Fig.3.a aSy= J 2..j a2-l dy - J 2..j a2- y2 dya - CI a - Coa - CI-a2sin·I_-aThe number of times (n) is obtained by eq. (5) , which is required until the shaft of screw is cut off.Sn=-Sy (5)z Fastened ortion/PcX-/~":':",~ ¢ -.l~T­ScrewFig.2 Model of cutting the shaft of screws~Sy~IFig.3 Cross-sectional drawing of the shaft2.2.4 Force to separate IC-chip from a circuit boardWe make a model that the IC-chip and capacitor are cut off at connection pins by the shearing force in Fig.4.As connection pins is pressed by the disassembly tool from perpendicular direction, the load (Ps) to cut off194 Takanobu YOSHIDA, Yoshiomi MUNESAWA, Hirokazu OSAKI, Yasuhiro KAJIHARA and Kazuharu OHTAconnection pins is shown in eq. (6) .Ps >mOYswtThe load becomes large, as the number of connection pin (m) of the IC-chip increase. So, the shearing angle( a) of tip of disassembly tool is sharpened in order to protect the loss of the shearing force. In the case, thecutting load (p a) is given by eq. (7) .fPa>Oys----2cos2asina*1i~IC-chip Circuit boardFigA Model of separating the IC-chip2.3 Design of Disassembly Tool2.3.1 Design of disassembly tool to punch out fastened portionThe head of the screw is pressed by the disassembly tool from perpendicular direction, and fastened portion isdestroyed. It is important that the tip of the disassembly tool should not slip from the head of screw. Moreover, it isnecessary to adjust easily to the head of screw. Then, the shape of the disassembly tool is designed as follows.The semicircular hole is bored at the tip of the cylindrical disassembly tool. The size of hole is enough to coverthe head of screw. As the fastened portion is punched out, the disassembly tool is inserted deeply into the brokenportion. There is a case that the destruction of fastened portion progresses more than necessary. So, the tool shouldbe pulled up with the large force. Therefore, a cylindrical supplementary rim is attached to the disassembly tool as astopper in Fig.S.Stopper~o~*27mmFig.S Shape of disassembly tool to punch out fastened portion2.3.2 Design of disassembly tool to cut off shaft of screw or rivetThe slippage of disassembly tool froin the screw might occur during an operation to cut off the shaft of screw.As the slippage is occurred, the load might not be efficiently transmitted to the shaft of screw. So, the hollow ismade at the tip of the disassembly tool considering the shape of the head of screw. As the shearing force is notdependent on the thickness of the disassembly tool, the thickness is equivalent to the height of the head of screw. Asthe tip of the disassembly tool enters between the head of screw and fastened portion, the shearing power isdispersed. So the thickness of the disassembly tool is made not to be too thin in Fig.6.Disassembly System using an Impact Hammer for the Material Recycling 195Hollow~----Fig.6 Shape of disassembly tool to cut off the shaft of screw or rivet2.3.3 Design of disassembly tool to cut otT connection pin of Ie-chip on circuit boardThe load should be given to connection pin as much as possible along the board so that the part of conductorshould not be bent. Shearing angle of the tip of the disassembly tool is determined as follows. The cutting edge doesnot c;:ontact to large number of connection pin at one time, and give the impulsive load at the nearest point on thecircuit board. (Fig.7)Cutting edge45mmFig.7 Shape of disassembly tool to cut off connection pin of IC-chip2.4 Proposed Disassembly System Using Designed Disassembly ToolThe disassembly system is composed of following units in Fig.S. This system is composed an industrial robotwith 6 D.O.F. [<j(1) Impact hammer and lift tableThe designed disassembly tool are attached to an impact hammer, which moves parallel to Z axis. This unit is namedas the disassembly unit. This unit is set on a lift table, and the stroke in Z axial is extended by moving it.(2) Disassembly toolsThis is personally a part which contacts with fastening point. We designed three kind of disassembly tools.Disassembly works are executed by changing those tools, that is, punching out fastened portion, cutting off the shaftof screw or rivet, and connection pin of IC-chip on circuit board.(3) Robot with a Powerful HandA disassembly subject is carried to the fixture by this robot. And the· fastening point on disassembly subject ispositioned to the tip of disassembly tool as this robot moves the fixture.(4) FixtureThis unit is used to fix the disassembly subject for decreasing the loss of disassembly force and securing the safetyof operators. The top and side of a subject is fixed by using the air clamping. And, this device can be moved parallelto X axis and Y axis.196 Takanobu YOSHIDA. Yoshiomi :-'ICi\ESA \VA. Hirokazu OSAKI. Yasuhiro KAJ[HARA and Kazuharu OHTAImpact HammerLift TableRobotFixtureFig.8 Proposed disassembly system using the designed disassembly tool3. CONCLUSIONThis research proposed a disassembly system using an impact hammer for the material recycling. Force to punchout the fastened portion and cut off shaft of screw and connection pin of IC-chip on circuit board are formulated bysimulation models. And, three kind of disassembly tools are designed by using the simulation models. Thedisassembly system is constructed by using the proposed disassembly method.REFERENCES[lJ D. Prescovitz : Problem about a clearout of personal computers become serious, NIKKEI SCIENCE, VolA(2000) , pp.118-119.[2] Timoshenko. S. P. and Woinowsky-Krieger. S. : "Theory of Plates and Shells", First Vol (1973), ppA7-72.[3] S. Takezono : "Introduction to Strength of Materials", (1984), pp.3-5.[4] YASKAWA Co., "MOTOMAN YR-KlO" operating manual (1984)

Disassembly System using an Impact Hammer for the Material Recycling

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