Document zdj7jp9byNVr536j6kvgD68Dn

74 BOSS A. MC FARLAND within a given reach zone. In general, this zone will approximate a circle whose size will vary depending on the arm reach of the operator.28 More, often than not, however, a knowledge of arm reach to a threedimensional region is required rather than to a vertical plane only or horizontal plane only.24 Functional arm reach for many working areas will, in general, correspond to the illustration shown in Figure 4. One investigator who has dealt concretely with problems of this complexity is Dr. B. G. King. In the experi mental method employed to determine the various reach measurements, a series of seated subjects reached for and touched successive points on a vertical measur ing rod as it was brought forward along a horizontal support. Horizontal dis tances from the vertical line rising from the seat reference point to the vertical a&' "TWMU `Mi k y1"' Sf m fife* HUMAN ENGINEERING AND INDUSTRIAL SAFETY TABLE 3 Maximum Reach with Right Arm (In inches) Level above reference point (in.) 0" Angle R 15 R 45" 11.6 13.7 15.0 18.9 20.5 22.4 22.9 24.9 26.6 25.5 27.1 29.1 26.7 282 303 26.6 28.0 29.7 253 27.0 293 22.6 242 26.4 173 19.7 213 R 75" 17.0 24.1 28.0 30.1 31.4 31.6 30.4 27.9 223 75 Figure 4. The normal and maximum working areas in three dimensions. (Reprinted with . permission from Ralph M. Barnes, Work Method* Manual, 1S44, John Wiley and Sons, Inc.) v' measuring rod at extreme fingertip reach were measured for each of 99 points. The over-all pattern is such that the average reach increases as the arm is moved -1 laterally from 0 to 15, 45, 75, 100, and 105 and decreases as the arm is raised or lowered from the trunk height of the subject (see-Figure 5) . The unequal radjijL of any arc describing various successive points of' 'reaehlarg; '^tffijbtitRble to'tngMg position of the shoulder joint in relation to the mid-sa|p%t&f> jpiKW^Wlhe body and .3 to its architecture. Data on the maximum distance that could be reached by 97. : per cent of a Navy male population are presented in Table 3.25 Distances are H. L. Lipschultz and K. 0. W. Sandberg, Maximum limits of working areas on vertical surfaces, Office of Naval Research, Special Devices Center, Report No. 166-1-8, 1947. " A. Chapanis, W. R. Gamer, and C. T. Morgan, Applied Experimental Psychology ', Human Factors in Engineering Design. Wiley, New York, 1949. "B. G. King, D. J. Morrow, and E. P. Vollmer, Cockpit studies--the boundaries of the maximum area for the operation of manual controls, Project X-661, Report No. S, Naval Medical Research Institute, National Naval Medical Center, 1947. 1 IlXL'HsllEpI from the vertical line through the reference point with the subjects BgfW.. MBater- touching the back cushion; seat back 13 from the vertical. The 18 a* the uPPer level of the seat cushion at its line of intersection fetrl^lower cushions of the back. Reach for the left arm can be outlined by "^ysingj&trofe measurements at corresponding points to the left (see Figure 5) ,25 si^^tj^^unately, there are two limiting factors that prevent these data from glfjde applications in general problems of equipment design. The first ffifcjthat the sample consists only of male Naval personnel. Although King jcnat they may be sufficiently representative to serve as a basis for |uygTeach dimensions satisfactory for a relatively large percentage of a ||||mple of men in the armed forces, nevertheless they will not necessarily Jpprradmate other selected populations. For example, .the functional ^l|hAt can be maintained by 93 per cent of thisvNaval group might be liffilP&nly 75 per cent or perhaps by as many as 98 per cent of other groups. remembered also that reach dimensions will change with any fiBMBwTOF'the conditions of the working area, such as a difference in the i^M^|b|j,^h.e seat or seat back, thus necessitating either a new study under conditions or the computation of correction values to be applied E^aglSiBiffstan'dard data. An additional point is that the dimensions in maximum reach measurements taken at the fingertip. Obviously be operated at these extreme locations. Depending upon the aWjjjfeffictgljstics of the control and the degree of movement and accuracy required, `^^.^^iTMa.|!^3iltfint' location may be up to 5 inches less than the outermost reach.25 necessary qualifications and restrictions point up the complexity Arm-reach problems and the difficulty of applying specific dimensions However, it should be remembered that a limited use of such ex`at between arm length or reach measurements and other bo'dy life' '' ' "cfmiESaazL- .