Chapter 2 Fundamentals of Robotics 37
cleaning cycle and the machine is activated by the start button. The machine fills
with water and begins to go through the various washing, rinsing, and spin-
ning cycles. The machine finally stops after the set sequence is completed. The
washing machine is considered an open-loop system for two reasons:
• The clothes are never examined by sensors during the washing cycle
to see if they are clean.
• The length of the cycle is not automatically adjusted to compensate
for the amount of dirt remaining in the clothes. The cycle and its time
span are determined by the fixed sequence of the cycle selector.
Performed by a
human operator.
Controlled by a
mechanical timer.
Put clothes and detergent
in machine.
Shut the machine off.
Select cleaning cycle.
Push start button.
Fill tub with water.
Wash the clothes.
Rinse the clothes.
Spin the clothes dry.
Figure 2-16. This block diagram depicts the sequence of steps performed by a washing machine.
Notice that no feedback is used. In such an open-loop control system, the condition of the clothes
during the washing operation is not monitored and used to alter the process.