Ergonomics - Atlas Copco

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The average sound pressure level from the five microphones is the base figure for the declared noise emission value. In the standard ISO 15744 the formula for calculation of sound power level is given as: L w = L p + 10 lg (S/S 0 )dB(A), where L w = sound power level in dB(A) L p = average sound pressure level from 5 microphone positions, in dB(A) S 0 = the surface of the hemispheri- cal/cylindrical control surface, where sound is passing, in m 2 S 0 = reference surface of 1 m 2 S 0 is 4л m 2 , therefore 10 lg (4л) = 11 A sound power value is 11 dB(A) higher than the corresponding average sound pressure value. Loading of the machine Some machine types are run on a loading device while others are not. When a loading device is used, the noise it generates should be at least 10 dB lower than the noise from the power tool being tested, in each octave band that influences the dB(A) value. Declaration of noise emission values The noise test standard gives the type of test procedure that should form the basis of the declared value. The standard also gives a method of coping with uncertainties arising from variations due to the test method and variations in production. The total uncertainty declared together with the measured value is 3 dB(A). You can always argue that 3 dB(A) is a very approximate figure, and that for some tools the uncertainty is less. It is also true that there are other international declaration standards where the tolerance is calculated for every machine. Noise control Noise hitting the human ear drum or a microphone is almost always a combina- tion of sounds from several sources. When controlling noise it is important to know the sources. It is even better if the relative loudness of the sources is known because this knowledge allows priorities to be set. If, for example, there are two sources with the same level and it is possible to remove one completely, the total level will only be decreased by 3 dB. If there are a number of sources and one is removed it might fail to show up in the readings altogether, depending on its frequency and relative loudness. When testing in the laboratory, it is recommended that the sources are identified in the machine and, if possible, isolated for a more accurate interpretation. Modern measuring equipment, such as intensity meters, can be very useful. 119
120 We can start by looking at the machine itself, not taking the process noise into account. In a pneumatic grinder, for example, there are several sources. If the grinder is equipped with a vane motor, this is the loudest source. Usually it is most efficient to start noise control work at the main source. The vane motor A vane motor consists of a rotor with a set of vanes rotating eccentrically in a cylinder. The motor has an inlet for compressed air and at least one outlet, normally in the form of holes or slits in the cylinder mantle. When a vane passes the outlet, compressed air passes out at high speed. This creates a pressure pulse outside the cylinder, Fig. 3.22 The outlet pulse from the vane motor is one of the main acoustic sources for the motor. moving away from the cylinder at the speed of sound (340 m/s). The next vane starts up the next pulse in the same manner. When the motor runs, a noise will be created with a fundamental frequency equal to the rotor speed multiplied by the number of vanes. A narrow band analysis of this noise will show the fundamental frequency and a number of overtones. In other words, the signal is not a sine wave but a more complex one. However, the fundamental frequency is often dominant. One way to treat this noise is to arrange the rows of vanes in the rotor asymmetrically. Another option that can be chosen at the same time is to design the outlet in a way that lowers the air flow gradient, since the noise level decreases when the change in flow decreases. Muffler When the motor has been optimized ac- cording to all parameters, including power, efficiency, weight, etc., the remaining noise can only be muffled away. The motor is protected by a housing. Part of the housing is designed to act as a muffler. If a pipe is connected to the outlet, the noise from the open end of the pipe can be controlled by the length of the pipe. If the pipe length is equal to a wave length or a half wave length of the fundamental
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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
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 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: 118 value for 8 hours’ exposure t
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
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
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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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Ergonomics - Atlas Copco

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