Page 37 - Concise Encyclopedia of Robotics

BACK LIGHTING B
In a robotic vision system, back lighting refers to illumination of objects
in the work environment using a light source generally in line with, but
more distant than, the objects. The light from the source therefore does
not reflect from the surfaces of the objects under observation.
Back lighting is used in situations where the surface details of observed
objects are not of interest or significance to the robot, but the shape of
the projected image is of importance. Back lighting is also advantageous
in certain situations involving translucent or semitransparent objects
whose internal structure must be analyzed. Light rays passing through a
translucent or semitransparent object can reveal details that front lighting
or side lighting cannot. Compare FRONT LIGHTING and SIDE LIGHTING.

BACK PRESSURE SENSOR
A back pressure sensor is a device that detects, and measures, the amount
of torque that a robot motor applies at any given time.The sensor produces
a signal, usually a variable voltage called the back voltage, that increases as
the torque increases. The back voltage is used as negative feedback to
limit the torque applied by the motor.
When a robot motor operates,it encounters mechanical resistance called
back pressure. This resistance depends on various factors, such as the
weight of an object being lifted, or the friction of an object as it is moved
along a surface. The torque is a direct function of mechanical resistance.
As the torque increases, so does the back pressure the motor encounters.
Conversely, as the back pressure increases, so does the motor torque nec-
essary to produce a given result.
Back pressure sensors and feedback systems are used to limit the
amount of force applied by a robot gripper, arm, drill, hammer, or other
device. This can prevent damage to objects being handled by the robot. It
also helps to ensure the safety of people working around the robot. The
accompanying illustration is a functional block diagram of the operation

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