Page 202 - Concise Encyclopedia of Robotics

Manipulator
In a system with a linear-dropoff profile, the sensor output is zero until
the robot comes within a specific distance of the object (in this case
approximately 6.5 units as shown on the graph).When the robot is closer
than the critical radius, the sensor output varies according to a straight-
line function with negative slope, as shown, reaching a maximum when
the robot is about to strike the object.
In a system with an exponential-dropoff profile, the sensor output varies
inversely with distance from the radius. There are no abrupt transitions
or bends in the curve as with the other two profile schemes. The sensor
output drops to zero at a considerable distance from the object; when the
robot is about to strike the object, the sensor output is maximum.
See also DISTANCE MEASUREMENT and PROXIMITY SENSING.
MANIPULATOR
A manipulator consists of a robot arm, and the gripper or end effector at the
end of the arm. The term can also refer to a remotely controlled robot. See
END EFFECTOR, ROBOT ARM and ROBOT GRIPPER.
MASTER–SLAVE MANIPULATOR
See TELEPRESENCE.
MEAN TIME BEFORE FAILURE/MEAN TIME BETWEEN FAILURES (MTBF)
The performance of a robot, computer, or other machine can be specified
in various ways. Two of the most common are the mean time before failure
and the mean time between failures, both abbreviated MTBF.
Component
For a single component, such as an integrated circuit, the MTBF (mean
time before failure) is the length of time you can expect the device to
work before it fails. This is found by testing a number of components and
averaging how long they keep working.
A simplified example of MTBF, calculated in hours on the basis of
the performance of five identical, hypothetical light bulbs, is shown in the
drawing. The lifetimes are averaged to get the result. For the results to be
meaningful,the number of samples must be much greater than five.Testing
a large number of components, such as 1000 or even 10,000, eliminates
coincidentally skewed results.
System
In the case of a system such as a robot or computer,the mean time between
failures is determined according to how often the machine breaks down.
As with the component-testing method, it is best to use many identical

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