Page 219 - Robotics Designing the Mechanisms for Automated Machinery

6.2 Linear Transportation 207

• Maintaining constant tension (in the paper, fabric, wire, threads, etc., that are
handled);
• Maintaining constant speed of the running material;
• Handling the problem of stretching of some materials during their processing
(thermal treatment, humidity and drying, plastic deformation, etc.);
• Maintaining a constant rate of consumption of the transported material. (This
is close to, although not exactly the same as, keeping the speed constant.)

Figure 6.1 shows a plan for a tension-sensitive device. The wire (thread, ribbon,
etc.) 1 runs over two rolling guides 2, passing under roller 3, to which is fastened lever
4. The tension force T causes the appearance of a resultant force R, which is balanced
by spring 5. Thus, the angle of inclination of lever 4 responds to the tension in the wire.
By using a position sensor for measuring angle (see Chapter 5, Section 5.2), we can
control speed V 1 at the input of the system so as to keep the tension of the wire within
the desired limits.
The problem of maintaining a constant transportation speed can be solved as in
the example shown in Figure 6.2. Here running material 1 (fabric, plastic, metal sheet,
etc.) passes guide rollers 2 and drive rollers 3. The speed of the drive rollers is deter-
mined by the corresponding motors and transmissions 4, while guides 2 are driven by
the material itself. Thus, their rotation speed (measured by, for instance, tachogener-
ators 5) indicates the material's speed or rate of consumption in the machine.

FIGURE 6.1 Design of wire or thread
tension-regulating device.

FIGURE 6.2 Design of a constant transportation speed system.