Welcome to optical encoders. an optical encoder is an electromechanical device
that provides feedback information in a closed-loop motion control system. this
information is for both rotary and linear mechanisms. optical encoders
provide information for Direction, position, and velocity. direction. position.
and velocity. let's adjust the velocity of this motor. you can see how adjusting
the velocity of the motor affects the velocity of the conveyor belt.
an optical encoder typically has four major elements. light source, light sensor,
optical disk, and signal conditioning circuitry. the light source is typically
a light emitting diode or LED. instead of producing a light that is visible to
humans, an infrared light is usually transmitted.
the light sensor is a photo transistor. because the sensor is sensitive to
infrared energy emitted by the light source, ambient light has a minimal
effect on the sensor. optical disc. a disc is placed between the light source and
the sensor. it is connected to the shaft being measured so that the disc and
shaft can rotate together. as the disc is rotated light alternately passes through
the translucent slots and is blocked by the opaque areas between the slots.
the phototransistor is connected to the signal conditioning circuitry.
the signal conditioning circuitry consists of a load resistor and the
Schmitt trigger. let's see how the circuitry works as the light is
alternately blocked and passed to the transistor. when light is present. when
light passes through a slot on the disk the following conditions occur. the
transistor turns on. since there is minimal resistance the voltage drop
across the transistor is near zero volts. the zero volt potential at the
transistors collector is fed to the input of the Schmitt trigger which
results in a zero volt potential at its output. the near positive five volts from
the power source drops across the load resistor. when the light is blocked by
the opaque area between the slots the following conditions occur. the
transistor turns fully off. since it acts like an open and there is a large
resistance, the voltage drop across the transistor is near positive five volts.
the positive volt potential at the transistors collector is fed to the
input of the Schmitt trigger which results in a positive 5 volt potential
at its output. near zero volts drops across the load resistor. the Schmitt
trigger converts pulses from the photo transistor into the square waves
required by the computing device that received the feedback signal for the
closed loop system. let's do a quick review. the type of light typically
emitted by the light source of an optical encoder is A visible or B
infrared? the answer is B infrared. when light
strikes the phototransistor of the optical encoder A its resistance is low,
B a near zero volt potential is at its collector, C the output of the Schmitt
trigger is near zero volts, or D all of the above?
the answer is D all of the above. when light from the light source of the
optical encoder is blocked, what drops across the load resistor.
A near zero volts or B positive five volts.
the answer is A near zero volts. and finally, the function of the optical
encoders Schmitt trigger is to convert A pulses into square waves or B square
waves into pulses. the answer is A pulses into square waves. you have completed
optical encoders.
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