actuators: where the real action takes place!
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Actuators: Where the REAL Action Takes Place!. Fred Donelson Kevin McKone. What is an Actuator?. It is a mechanism that converts some type of energy into motion in order to do work (move a force over a distance) - PowerPoint PPT PresentationTRANSCRIPT
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Actuators: Where the REAL Action Takes Place!
Fred DonelsonKevin McKone
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What is an Actuator?
• It is a mechanism that converts some type of energy into motion in order to do work (move a force over a distance)
• The three common types of energy used in ROV work are electrical current, hydraulic pressure, or pneumatic pressure
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Most Common ROV Actuators:
• Motors• Solenoids• Pneumatics and/or hydraulics
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Let’s start with motors:
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A motor might turn some gears:
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Or a propeller
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Two important factors/variables to control with motors
• Direction that the motor axle turns• Speed at which the motor axle rotates
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Here is a simple circuit with a power source and the motor as a load:
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The red arrows show the direction of the current flow
Spin Direction of Axle
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By flipping the battery terminals, the direction of the motor rotation can be
changed
Motor
Spin Direction of Axle
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Of course, continually flipping the terminal
connections would get old very fast!
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Another way to change directions is to use a
double pole/double throw switch
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First, we make these connections
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When the switch is in the center
position (B & E), no current flows
(off)
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When the switch is in the up position (connecting B to A & E to D), notice the current (red
arrows) flows through motor
from left to right.
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When the switch is in the lower
position (B to C & E to F), current
flows from right to left through the
motor, thus changing the
direction of spin
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Many ROVs use three of these DPDT switches to
easily control the direction
of three motors
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However, there is one drawback:The DPDT switch only has ONE
SPEED!
It is either all the way on, or all the way off!
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And after a while, your fingers get tired of pushing those switches too!
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And even if we didn’t get tired, there’s a limit as to how fast we can mechanically flip the switch
each second.
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Fortunately, there are ELECTRONIC DEVICES called transistors that can act as switches for
us!
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One type is known as aMetal Oxide Semiconductor Field
Effect Transistor:MOSFET
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These electronic switches can turn on and off several thousand times
a second
When connected to a controller/computer, one can vary the speed as well as the direction
of a motor!
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A very fast switch can turn the motor on (12V) or off (0V), and the controller can control the average time the motor is on each second, affecting its speed
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This is known as Pulse Width Modulation (PWM)
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Each MOSFET and controller can control how long the motor is on
(which is called it’s duty cycle)
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But it takes 4 MOSFETS arranged in a special arrangement called an
H – Bridge to actually change the direction of a motor
It works similar to a DPDT switch
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Basically two MOSFETs lead
from the positive
terminal and two from the
negative
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If P1 and N2 are turned on, the current travels
from left to right through
the motor (black arrows)
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If P2 and N1 are turned on, the current travels from right to
left through the motor (red
arrows)
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You can learn more about how the H-Bridge works by checking out
page 519 in your textbook!
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