Ergonomics - Atlas Copco

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Shock reaction A shock reaction in a tool is an external load placed on the operator for an ex- tremely short period of time. Tools gen- erating this type of load during use are typically angle nutrunners and screw- drivers. Drills can also generate a shock at the moment when the bit penetrates the workpiece. The unprepared operator can lose his grip on the tool, his fingers may be crushed, or he may receive a blow from the tool. What is a shock? A shock and its reaction happen during a short period of time. Events happening during less than 300 ms can be defined as shocks. During this short period an operator is unable to influence the course of events. A tightening cycle lasting longer than 300 ms also subjects the operator to a shock reaction, but that load should be handled according to the methods Rapid motions of the hand-arm system are perceived as shocks. outlined in the section on external loads. The hand-arm system can be considered as a passive mass spring system – in par- ticular a mass. The shorter the shock, the smaller the reaction or response in the machine and hand-arm system. If the duration of the shock is gradually increased, the reaction will also increase. Depending on 97
98 the dynamic properties of the machine and the hand-arm system, the response will ac- tually be amplified for a certain duration or shock impulse. This is a shock and response situation that we should try to avoid. How can we influence the duration of the shock? If we take an angle nutrunner as an example, the length of the shock depends on the joint hardness, the speed of the machine, the power of the motor and the method used to shut off the machine when the tightening cycle is complete. The joint A joint can be hard, soft, or anything in between. Joints reaching their final torque after a tightening angle of less than 60º are considered to be hard, and joints reaching their final torque after 700º are soft. A very hard joint is, for example, a thin plate fixed to another component with a bolt. The elongation of the bolt is very short. A typical soft joint is a hose clamp. As mentioned above, the shorter the shock, as in a hard joint, the smaller the shock reaction. But why do we still use so many mediumsoft joints? The answer is that the joint designer wants to have a reliable joint which retains its clamping force after many load changes – the softer the better from this point of view. Machine speed The speed of the outlet spindle depends on the torque and speed of the motor. The joint may be sensitive to high speed for temperature reasons. Another parameter which limits the speed is the possibility of over-shoot when final torque is reached. This is a quality issue and it is limited by the speed of the clutch or the capability of the system to control the tightening in the case of an electric tool. Motor power The power of the motor also influences the tightening characteristics of the tool. A powerful motor will maintain the speed at the end of the tightening sequence, keeping total tightening time to a minimum. How- ever, if you increase the power of the motor, the tool gets heavier. Shut-off method The faster the shut-off, the shorter the duration of the shock. Summary All these factors influence the duration of the shock and its reaction on the machine. If a tightening sequence is analysed taking torque as a function of time, we find that as the area under the curve becomes smaller, the impulse is smaller and the torque reaction is reduced.
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Power Tool Ergonomics E V A L U A T
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Acknowledgements While doing resear
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How to get the best out of this boo
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Work with international standards I
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Good ergonomics is good economics W
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10 SOCIOLOGY INDUSTRIAL SOCIOLOGY S
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12 Work organization No organizatio
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1 outside the production system, an
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1 A seated operator usually has goo
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1 without stretching the trunk. The
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20 The arm sling as a preventive me
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22 Extreme working postures in real
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2 Working with high feed forces req
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2 Working areas of a standing works
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2 body is lifted or tilted, or the
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30 The team is an important factor
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32 Grinders Grinders and sanders ar
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34 HanDle DeSiGn The hand grips on
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36 DUSt anD oil Although the machin
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38 Working environment In general,
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40 SHoCK reaCtion Sudden changes in
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42 practice. Sometimes the chisel h
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44 SHoCK reaCtion These tools do no
Page 47 and 48: 46 heavy, assembly work is often hi
Page 49 and 50: 48 depends on its inertia. The same
Page 51 and 52: 50 bolts. Unfortunately there are a
Page 53 and 54: 52 The low reaction torque in impul
Page 55 and 56: 54 the working environment A typica
Page 57 and 58: 56 Today, the angle nutrunner can b
Page 59 and 60: 58 High torque nutrunners for use w
Page 61 and 62: 60 Wheel nuts on trucks and buses a
Page 63 and 64: 62 Introduction A basic ergonomic p
Page 65 and 66: 64 Handle design The handle of a ha
Page 67 and 68: 66 Arteries Veins (superficial) Vei
Page 69 and 70: 68 Handle size Since a tool handle
Page 71 and 72: 70 However, if the texture is too c
Page 73 and 74: 72 Bibliography Chaffin, D.B. and A
Page 75 and 76: 74 Fig. 3.3 The same feed force app
Page 77 and 78: 76 Pushing and pulling Pushing a to
Page 79 and 80: 78 the object, the shape of the obj
Page 81 and 82: 80 Safety factor a 2 Frequency of t
Page 83 and 84: 82 Comments for different tool type
Page 85 and 86: 84 The trigger is either operated b
Page 87 and 88: 86 used in one handed operations. T
Page 89 and 90: 88 Weight The weight of a hand-held
Page 91 and 92: 90 stability of grip, the center of
Page 93 and 94: 92 Temperature Hand-held power tool
Page 95 and 96: 94 To ensure physical comfort durin
Page 97: 96 Score 40 30 20 10 0 Bibliography
Page 101 and 102: 100 High motor power and fast clutc
Page 103 and 104: 102 Score 40 30 20 10 0 shock react
Page 105 and 106: 104 piezo-electric crystal. When th
Page 107 and 108: 106 EN 50144 and EN 60745. Both ISO
Page 109 and 110: 108 hole of the wheel are wider tha
Page 111 and 112: 110 In the GTG 40 grinding machine,
Page 113 and 114: 112 RRH machines serves two functio
Page 115 and 116: 114 be noted that declared values b
Page 117 and 118: 116 Noise Noise was the first envir
Page 119 and 120: 118 value for 8 hours’ exposure t
Page 121 and 122: 120 We can start by looking at the
Page 123 and 124: 122 This is done with a minimum inc
Page 125 and 126: 124 microphones at a distance of 1
Page 127 and 128: 126 coated with dust or damaged by
Page 129 and 130: 128 This method has not been used b
Page 131 and 132: 130 tool cabinet. Many workplaces h
Page 133 and 134: 132 lubrication. Made from a compos
Page 135 and 136: 134 Grinder GTG 40 F085 The relevan
Page 137 and 138: 136 were simulated by fitting a whe
Page 139 and 140: 138 Drill LBB 26 EPX-060 The releva
Page 141 and 142: 140 applied to the center of the dr
Page 143 and 144: 142 Chipping hammer RRF 31 The rele
Page 145 and 146: 144 SHOCK REACTION There are no sho
Page 147 and 148: 146 Riveting hammer RRH 06 The rele
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148 WEIGHT The weight is 1.3 kg, sc
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150 Screwdriver LUM 22 PR4 The rele
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152 This gives a score of 9. In pra
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154 Impulse nutrunner EP9 PTX80-HR1
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156 Due to friction in the hydrauli
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158 Electric nutrunner ETP ST32-05-
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160 WEIGHT The electric nutrunner i
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162 Angle nutrunner LTV 29 R30-10 T
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164 operator equal to installed tor
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166 Electric angle nutrunner Tensor
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168 WEIGHT The electric nutrunner i
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170 High torque nutrunner LTP 51 Th
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172 Score 40 30 20 10 0 NOISE The d
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