Ergonomics - Atlas Copco

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tion of the outlet speed to the power of six. Therefore a low outlet speed must be main- tained. Aerodynamic noise has a high-frequency broad-band content. The smaller the outlet holes, the higher the frequency. Very tiny holes can take the spectrum out of the hearing range and, in that sense, reduce the dB(A) reading. However, the risk of clogging must be considered. Noise transmitted by vibration Wheel guards can be a problem in this respect. The transmitting surface is quite large. For noise reduction purposes, we want to know if the natural frequency of the guard is above or below our typical running frequencies. Whatever our aim, we must avoid running the machine at the resonance frequency of the guard. Process noise Noise generated by the process is often very difficult to eliminate. Sometimes we can change the machine type and, as as result, change the process. Changing from impact wrenches to stall torque machines is one example. Some customers may prefer to keep the impact wrenches because the tools are low in weight with low reaction torques. In such cases, impulse nutrunners may be selected. Instead of using a mechanical blow to set the nut, the impulse tools are buffered by a hydraulic cushion. Technically this is the same as filter- ing the blow to eliminate its high frequency noise emissions. When this blow enters the structure in which the joint is located, the natural frequencies in the high frequency domain will not be excited. This leads to less process noise. Evaluating noise Again the question: Can we use the declared noise levels in our comparison of the effects of different stressors? For some machine types extensive variations can occur in the process noise. For machines like grinders, in most cases the process noise is dominant. The only way to get around this dilemma is to advise the user that the noise exposure can be all the way from the dose calculated using the declared value and the estimated average exposure time, to a much higher dose depend- ing on the workpiece and individual operator’s working habits. The simple fact that different operators assume postures giving different dis- tances from noise source to ear can influence the exposure level by 6 dB(A). In the noise test the test situation has been defined as the average level from five 123
124 microphones at a distance of 1 meter from the machine. It can be argued that 1 meter could be too far between the machine and the operator’s ear. Comparisons between the average level and measurements made at the operator’s ear for the same object are, however, very close due to the direction of the noise scatter. Less noise is scattered in the direction of the operator because the exhaust air is directed away from the operator. Calculation of dose The declared noise level to which the operator is exposed during the assumed average time is recalculated to an 8-hour equivalent level. L eq(8) = 10log[1/8(10 L/10 T)] L = noise level in real use, estimated with the declared value. T = assumed exposure time Typical exposure times per day for different machine types can be found in Table 3.10 The L eq(8) is then compared with a Threshold Limit Value (TLV) for 8-hour exposure. In our stressor comparison we assume 85 dB(A) to give a score of 20. Exposure time We use the same average exposure time as for vibration. The value can be found in Table 3.13. Score 40 30 20 10 0 Bibliography ISO 3744, Determination of sound power levels of noise sources using sound pressure. Engineering methods in an essentially free field over a reflecting plane. ISO 15744, Hand-held non-electric power tools – Noise measurement code – Engineering method (grade 2). Directive 2003/10/EC of the European Parliament and of the Council of 6 February, 2003 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise). 70 80 90 100 L eq(8) dB(A) Fig. 3.23 The score for noise can be found using L eq for an 8-hour working day as the input.
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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
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46 heavy, assembly work is often hi
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48 depends on its inertia. The same
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50 bolts. Unfortunately there are a
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52 The low reaction torque in impul
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54 the working environment A typica
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56 Today, the angle nutrunner can b
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58 High torque nutrunners for use w
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60 Wheel nuts on trucks and buses a
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62 Introduction A basic ergonomic p
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64 Handle design The handle of a ha
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66 Arteries Veins (superficial) Vei
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68 Handle size Since a tool handle
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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 and 98: 96 Score 40 30 20 10 0 Bibliography
Page 99 and 100: 98 the dynamic properties of the ma
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: 122 This is done with a minimum inc
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
Page 149 and 150: 148 WEIGHT The weight is 1.3 kg, sc
Page 151 and 152: 150 Screwdriver LUM 22 PR4 The rele
Page 153 and 154: 152 This gives a score of 9. In pra
Page 155 and 156: 154 Impulse nutrunner EP9 PTX80-HR1
Page 157 and 158: 156 Due to friction in the hydrauli
Page 159 and 160: 158 Electric nutrunner ETP ST32-05-
Page 161 and 162: 160 WEIGHT The electric nutrunner i
Page 163 and 164: 162 Angle nutrunner LTV 29 R30-10 T
Page 165 and 166: 164 operator equal to installed tor
Page 167 and 168: 166 Electric angle nutrunner Tensor
Page 169 and 170: 168 WEIGHT The electric nutrunner i
Page 171 and 172: 170 High torque nutrunner LTP 51 Th
Page 173 and 174: 172 Score 40 30 20 10 0 NOISE The d
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Ergonomics - Atlas Copco

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