Page 19 - Robotics Designing the Mechanisms for Automated Machinery

8 Introduction: Brief Historical Review and Main Definitions

1. The energy source is a person, and his or her hands are the means of control; for
example, a hammer, a shovel, a spade, a knife, or a sculptor's chisel. Indeed, when a
person manipulates a hammer, the trajectory of this tool, the power of its impact, and
the pace of action are controlled by the operator. In this case, the feedback or the
sensors which inform the operator about the real location of the hammer, its speed,
and its accumulated energy are the muscles of the arm, the hand, the shoulder, and
the eyes. Obviously, this is also true for a spade or a chisel.
2. The energy source is a motor, but the means of control are still in human hands;
for example, a simple lathe, a motor-powered drill, a dentist's drill (would anybody
really be prepared to entrust the operation of such a tool to some automatic con-
troller?), a motor-driven sewing machine, an electric or mechanically driven razor. To
some extent, this group of machines also includes machines driven by muscle power
of another person (or animal) or even driven by the legs of the same person.
3. The energy source is a motor and the means of control are manual, but are arti-
ficially amplified; for example, prostheses controlled by muscle electricity, or the power
steering of a car fit this case to a certain extent.
4. The energy source is a person but the control function occurs (in series) via the
system; for example, a manually driven meat chopper, or a manual typewriter. Here,
some explanation is required. Rotating the handle of the meat chopper, for example,
the operator provides the device with the power needed for transporting the meat to
the cutter, chopping it, and squeezing it through the device's openings. The speed of
feeding or meat transporting is coordinated with the chopping pace by the pitch of the
snake and the dimensions and form of the cutter. Analogously, when the key of the type-
writer is pressed, a sequence of events follows: the carbon ribbon is lifted, the hammer
with the letter is accelerated towards the paper, and the carriage holding the paper
jumps for one step. This sequence is built into the kinematic chain of the device.
5. The energy source is a motor, and the control is carried out in series by the kine-
matics of the system; for example, an automatic lathe, an automatic loom, an auto-
matic bottle-labelling machine, and filling and weighing machines. This family of
devices belongs to the "bang-bang" type of robots. Such systems maybe relatively flex-
ible. For instance, an automatic lathe can be converted from the production of one
product to the manufacture of another by changing the camshaft. Figure 1.6 shows
examples of different parts produced by the same lathe. Figure 1.7 presents examples
of items produced by this type of automatic machines, i.e., a) a paper clip, b) a safety
pin, c) a cartridge, d) roller bearings, e) a toothed chain, and f) a roller chain.
6. The energy source is a motor, and the control is achieved automatically accord-
ing to a rigid program and is amplified; for example, an automatic system controlled
by master controllers, i.e., electric, pneumatic, or hydraulic relays. Such systems are
flexible in a limited domain.
7. The same as in (6), but the controller is flexible or programmable; for example,
automatic tracking systems. An illustration of such a system is given in Figure 1.8. The
shape of a wooden propeller vane is tracked by a tracer (or feeler), and the displace-
ments of the tracer as it maintains gentle contact with the outline of the wooden part
are amplified and transformed via the control into displacements of the metal cutter.
Other examples are Jacquard's programmable loom and numerically controlled (NC)
machines.