Page:The Kinematics of Machinery.djvu/279

 INCOMPLETE CLOSURE. 257

of the revolute, and in machines actually the special case C of the body R is almost always used. It is only in very special cases that we shall find it necessary to adhere to the strictly general notation.

Symbols of relation between the elements of a link will be placed in the dotted line. Thus C +. . .||. . . C+ stands for the linkage of two parallel full cylinders; C~. . .||. . . C" for a linkage of two parallel open cylinders, that is, a connecting rod; C\ ... | ... C + a spur wheel attached to its con-axial shaft ; C\ ... | ... C~ a spur wheel with a con-axial open (bored-out) boss.

A special indication is sometimes required for incomplete pairs. The first necessity is here a symbol for incompleteness, and for this we use the ordinary sign of division, so as to allow the method of closing to be indicated by a divisor,

To indicate merely the incompleteness of a pair we may use the divisor 2, considering the piece or element as halved. If it be completed by force-closure, the divisor / (force) may be em- ployed. For closure by a kinematic chain we choose the divisor &; if the chain-closure occur by means of a spring we substi- tute for this / ; and, lastly, if closure be effected by a pair ( 47), we shall use the divisor p. We therefore have the following :

0"

-y- a portion of an open cylinder,

t+

-j- a full cylinder paired by -force-closure,

C +

-r- do. paired by chain-closure,

/c

-j- do. closed by a spring,

t

0+

do. closed by a pair of elements.

P

If any link used for chain-closure have a special indicating letter, as a, I, c, etc. (as we shall see to be sometimes the case), this also can be placed in the divisor so as to indicate distinctly the method of closure. . We shall find further on frequent applica- tions of these methods of symbolization.

K