The following main types of copying machines used in the industries. The types are: 1. Mechanical Type 2. Hydraulic System 3. Electric System.
Type # 1. Mechanical Type:
These work on the principle of the pantograph. Fig. 33.5 shows an arrangement of producing involute shape on grinding wheel which will be used for finishing gear teeth. An important condition for pantograph copying system is that the follower, fulcrum and tracer must all lie on a straight line.
It may be understood that the type of pantograph shown in Fig. 33.5 will produce a reverse image of the template form and hence template must be arranged accordingly. Pantograph ratio – l1/l2 and varies between 5 : 1 to 10 : 1.
Type # 2. Hydraulic System:
Hydraulic copying system can be used to produce the most complex forms, even threads accurately without producing any deflection, and power consumption is also low. The contact pressure between the stylus and template is very low.
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Hydraulic systems are basically servomotors which magnify a relatively small input force or signal to provide a larger output force or signal for operating the mechanism. It is just like a closed loop control system in which output signal is continually and automatically modified to suit variations in the input signal.
Fig. 33.6 shows the principle of operation of a hydraulic servocopying system. However, modern systems are highly complex. As the saddle traverses along the bed, the stylus follows the template edge always being kept in contact by spring pressure on the left hand end of the valve spool.
If stylus moves to the right, then spool will also move to the right, thereby allowing the oil to the left of the piston to exhaust and allowing oil in to the right of the piston and thus moving it to the left. In this way the tool slide and tool will move to the left reproducing the template shape.
Type # 3. Electric System:
Electric copying systems use magnetic clutches with on/off (make/break) action to traverse the machine slides in the desired direction. An electronically coupled tracer, which is held centrally in a universal ball joint, is traversed across the template. The back end of the stylus is centered in a cup which is an integral part of a switch lever. Due to stylus movement, either contact Cj or C2 is made which energise the corresponding relay which in turn energises the corresponding magnetic clutch moving the machine slide either left or right corresponding to stylus movement. A stylus movement of 0.025 mm is sufficient to close either of the two contact Cx or C2.
