Gears

To transmit rotary motion between two shafts at a constant speed ratio, gears are used. The different methods used for the manufacture of gear teeth are shell molding, sand casting, die casting, centrifugal casting, permanent-mold casting and investment casting. Powder metallurgy method can also be employed here. Cutting of gear teeth can be done by milling. Shaping and Hobbing are the two methods of generating gear teeth. After cutting, for surface finish of gear teeth many processes are carried out namely grinding, lapping, shaving, burnishing etc. There are two main categories in gears. They are spur gear and helical gear. Spur gear is preferred when transmission of rotary motion is intended between parallel shafts. When loads are heavy, helical gears are preferred. Double helical gears are called Herringbone gears. This design got the importance due to one drawback of single helical gear. The drawback is that the axial thrust loads is to be accounted in the design of bearings. Some other types of gears are crossed-axis helical gears, bevel gears, straight-tooth bevel gears, crown and face gears, spiral bevel gears and worm gears.

Multiplexers

Single chip logic networks can be classified into four types. They are small-scale integrated circuits, medium-scale integrated circuits, large-scale integrated circuits and very-large-scale integrated circuits. Multiplexer is a medium scale integrated circuit (MSI) device. They are also known as data selectors. Multiplexer selects one of its data input lines and place the corresponding information appearing on this line to a single output line. It requires n bits to specify selected input line. This can be accomplished by placing the binary code for a desired data input line onto its n select input lines. Provisions for enable, strobe and line are included just similar to that in decoders to provide superior flexibility. Here each data input line goes to its own AND-gates. When enabled, output corresponds to the value on the data input line of the selected AND-gate. Multiplexing is the process of transmission of information from several sources over a single path. A multiplexer-demultiplexer combination can be used to transfer information from several source locations to several destination locations. Multipleexers can also be used as general logic-design devices for the easy and simple realization of Boolean functions.

Combinational networks

Boolean algebra is used in the analysis and design of logic systems. Gates and flip-flops are the common logic elements in logic systems. Gates are electronic circuits whose output depends upon the Boolean operations and flip-flops are memory elements which stores logic constants. A combinational network or a logic network is the interconnections of gates and flip-flops. An electronic circuit in which the output signal is a logic-1 (High) if and only if all its input signals are logic-1 (High) is called an AND gate. An electronic circuit in which the output signal is logic-1 (High) if and only if at least one of its input signals is a logic-1 (High) is called an OR gate. A NOT gate is an electronic circuit where the output signal is always opposite to that of the input signal. In a combinational network, outputs at any time are determined by the inputs at that particular time. A combinational network is called acyclic network since there is no closed loops or feedback paths. In a sequential network, outputs are dependent upon the current input currents and previous input currents.