Page:The Kinematics of Machinery.djvu/342

 320 KINEMATICS OF MACHINERY.

former cases, the links being no longer symmetrical ; necessarily, however, they are very closely related to them. Their applications are far less common. Schwartzkopfs adjusting spanner, Fig. 252, is a very original example of one of them. It is a self-acting universal spanner. To produce the required pressure on the movable cheek c, the mechanism of the crossed turning slider-crank is used in the form (C'^P^) d. The link a, a portion of which serves as a handle, is the crank, turning about the pin 1 carried by the frame d. At 2 it is connected by a pin with the coupler 6, which joins the block c at the cylinder-pair 3, and moves it in the direc- tion CD. 4 is the prism-pair between the links c and d. If the handle be pressed in the direction of the arrow, the mechanism grips the nut between the cheeks of c and d, and holds it the more

FIG. 252.

firmly the harder a be pressed. The nut and the spanner thus become virtually one piece, and the action of the handle a is simply that of a lever attached to the nut, by which it can be tightened, or by reversing the spanner, loosened, at will. Each time

the spanner is placed upon a nut, we have the meehanism(CJP*)jr in action for a short period.*

figure, which represents an arrangement proposed by Deprez, (Engineering, June 18, 1875), and before him by Mr. Henry Davey, and very possibly by others also, as a reversing gear requiring one eccentric only. Here the link c is made with a curved slot having a radius equal to the length of the coupler, and in this there is placed a sector b' which carries the pin or full cylinder of the pair 3. From what has been already said (p. 310) it will be recognised that this sector is kinematically identical with the coupler b. When the mechanism is working it retains a fixed position relatively to the slot in c. If it be fixed in the position shown by the full lines the mechanism is simply (C ^ P- i -) A ) but by giving it any other position, as for instance, 3', the train becomes (C'gP+) d and the motion received by c from a (and therefore, in the machine itself, by the valve from the eccentric) undergoes
 * Another illustration of the mechanism (C"gP+) d is shown in the accompanying