The implementation of both Dixon's and Suh's approaches to the design process is somewhat complicated. The interested reader is referred to the literature cited in the bib- liography   to this  chapter  for  more  complete  information.

1.7 MULTIPLE SOLUTIONS

Note that by the nature of the design process,  there  is not  anyone  correct  answer  or so- lution to any  design  problem.  Unlike  the  structured  "engineering  textbook"  problems, which most students are  used  to,  there  is no right  answer  "in  the  back  of the  book"  for any real design problem. * There are as many  potential  solutions  as  there  are designers willing to attempt them. Some solutions will be better  than  others,  but  many  will  work. Some will not!  There  is  no  "one  right  answer"  in  design  engineering,  which  is what makes it interesting. The only way  to determine  the  relative  merits  of various  potential design solutions is by thorough analysis, which usually will include physical testing of constructed prototypes. Because this  is a very  expensive  process,  it is desirable  to do  as much analysis on paper,  or  in the  computer,  as possible  before  actually  building  the de- vice.  Where  feasible,   mathematical   models  of the  design,  or parts  of the  design,  should be created. These may take many forms, depending  on  the  type  of physical  system in- volved. In the design of mechanisms and machines  it  is usually  possible  to  write the equations for the  rigid-body  dynamics  of  the  system,  and  solve  them  in  "closed  form" with  (or  without)   a computer.   Accounting   for  the  elastic  deformations   of the  members of the mechanism or machine usually requires more complicated approaches using finite difference    techniques   or the  finite  element   method    (FEM).

1.8 HUMAN  FACTORS ENGINEERING

With  few exceptions,  all machines  are designed  to be used  by humans.  Even  robots  must be  programmed    by  a human.    Human    factors  engineering is  the  study  of  the human- machine interaction and is defined as an applied science that  coordinates  the  design of devices,  systems,  and physical  working  conditions   with  the  capacities   and  requirements of the worker. The machine  designer  must  be aware  of this  subject  and design  devices  to "fit  the man"   rather  than  expect  the  man  to adapt  to fit the machine.   The  term ergonom-

*  A  student once commented that "Life is an odd-numbered   problem." This  (slow)  author   had to ask  for  an  explanation, which was: "The  answer  is not  in  the  back  of  the book."

ics  is synonymous  with  human factors   engineering.   We often  see reference   to the   good or bad ergonomics of an  automobile  interior  or  a household  appliance.  A machine de- signed with poor ergonomics will be uncomfortable and tiring to use and may even be dangerous.    (Have  you  programmed   your  VCR  lately,  or  set  its clock?)