The control unit contains all of the mechanical logic which controls the operation of the machine, and the drive train which supplies the motive power. The drive train is described in the next section.
The control unit is essentially a self-contained module, which has remarkably little connection to the rest of the machine. It takes inputs from the function keys in its forward section, and generates outputs to drive the setting line, the actuator and registers, the division sensing levers, and the carriage shift and clear mechanisms at the rear. It receives three feedback signals from the carriage dip arm, the carriage end-of-travel sensor, and the division trip mechanism. There is extensive interlocking between the functions to prevent mis-operation.
The control unit is an extremely complex mechanism containing over two hundred separate links and levers, all different, and well over one thousand manufactured parts. The individual components will not be described in detail, although some of their functions will be discussed further in the sections following.
This view shows the control unit fully assembled and mounted in position along the right-hand side of the machine. The function keys and control linkages occupy the forward section, with the drive train at the rear.
The unit is held in place by a number of long screws between the outer and inner right-hand side plates. The screws also carry spacers and pivot bushings for parts of the mechanism, and act as attachment points for a multitude of springs.
Although it is not a trivial operation, the whole assembly can be removed in one piece after removing the setting shaft and part of the carriage shift and clear mechanisms.
The control and logic unit.
The control and logic unit starts out as two blank sub-frame plates, roughly 6" x 4" and an inch apart, which support the two rows of function keys at the right-hand front of the machine.
Several layers of links and levers are assembled on the insides of each of these plates. The two are then brought together, and more linkages are added on the outer sides.
This view from the lower left-hand side shows the "mechanical brain" at the stage where most of the logic has been assembled, prior to fitting to the outer right-hand frame plate. There are many loose ends at this stage, but very few external connections once the assembly is completed.
The control unit assembled.
This much tidier view shows the control unit ready to be attached to the rest of the machine.
There are over 200 different links and levers in the assembly to this stage, and still more to be added after installation.
The control unit from underneath.
This view of the underside of the central section of the control unit gives some idea of the complexity.
A quick count shows links and levers arranged on about 25 different levels in a space of not much more than 2 inches.