Page 96 - Concise Encyclopedia of Robotics

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DROP DELIVERY
Drop delivery is a simple method that a robotic end effector can use to
place an object into position. The object is picked up by a gripper and
then moved until it is directly over a slot, hole, conveyor belt, chute, or
other receptacle designed for it. Then the gripper lets go of the object,
and it falls into place.
Drop delivery requires precision in the movement of the robotic arm
and end effector. In addition, when the gripper lets go of the object, it
must not impart significant lateral force or torque to the object. Other-
wise the object might move out of alignment or topple. If a conveyor belt
is used, some means must be employed to ensure that the movement of
the belt does not cause the object to slip, tip over, or fall off the belt after
it lands.
DROPOFF
See MAGNITUDE PROFILE.
DUTY CYCLE
The duty cycle is the proportion of time during which a circuit, machine,
or component is operated.
Suppose a motor is run for 1 min, then is shut off for 2 min, then is
run for 1 min again, and so on. The motor therefore runs for 1 out of
every 3 min, or one-third of the time. Its duty cycle is therefore ⁄3,or
1
33 percent.
If a device is observed for a length of time t o , and during this time it runs
for a total time t (in the same units as t o), then the duty cycle expressed as
a percentage, d %, is given by the following formula:
100t
d % =
t o
When determining the duty cycle, it is important that the observation
time be long enough.In the case of the motor described above,any value of
less than 3 min is too short to get a complete sample of the data. Ideally,
the observation time should be at least twice the time required for a com-
plete cycle of activity. If the cycle of activity varies somewhat (a common
situation), then the observation time must be much greater than the time
required for a single cycle.
The more a circuit, machine, or component is used, the sooner it will
wear out, if all other factors are held constant. In general, the higher the

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