Mechatronic System Integration
MCT331(Bylaw2023)
Actuators (cont.)
Dr. Nancy Emad ElHady
nancy_emad@eng.asu.edu.eg
Unipolar and Bipolar Stepper Motors
• Two-phase motors are termed bipolar motors when they have 4
connecting wires for signals to generate the switching sequence.
• While they are termed unipolar when they have 6 connecting wires.
Each of the coils has a centre-tap.
Bipolar
Unipolar
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Stepper Motor Driver
• The driver for a stepper motor can be constructed in different ways.
• On a basic level, one can use a transistor to drive each phase or coil
winding for unipolar drives or an H-bridge for bipolar drives.
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Full-Stepping (Bipolar)
Switching Sequence for full-stepping bipolar stepper
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Half-Stepping (Bipolar)
Switching Sequence for half-stepping Bipolar stepper
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Full-Stepping (Unipolar)
Switching Sequence for full-stepping unipolar stepper
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Half-Stepping (Unipolar)
Switching Sequence for half-stepping Unipolar stepper
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Stepper Motor Drive System
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Stepper motors
❑ They are self-positioning.
❑ Produce a high torque for a given size and weight.
❑ The available torque drops dramatically with higher speed.
❑ Complex performance curves (torque over speed).
❑ Their maximum speed is around 5000 rpm at very low torque.
❑ The power range of stepper motors is up to several hundred watts.
❑ Major drawback: the noise and vibration
they produce.
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Motor Selection Tips
➢ Decide the motor technology to use.
➢ Select a motor/drive combination.
➢ Does the motor’s performance curve (torque over speed) support
the torque and speed requirements?
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Motors Technology Comparison
Feature
Working Principle
Efficiency
Speed Control
Torque
Characteristics
Size and Weight
DC Brush Motor
DC Brushless Motor
AC Motor
Stepper Motor
Servo Motor
Moves in discrete
Uses alternating
Closed-loop system
Uses brushes to
No brushes, uses
steps
current (AC) for
with feedback for
commutate current
electronic commutation
(electromagnetic
rotation
precise control
pulses)
Generally less
Varies (depends on
Less efficient (due to More efficient (no
efficient (due to Very efficient, with
type: induction or
friction from brushes) brushes)
high power
feedback control
synchronous)
consumption)
Controlled by
Easily controlled by
Frequency control
Easily controlled by
step pulses, less Precise speed control
voltage (simplest
(variable speed
electronic controller
smooth than
via feedback
control circuitry)
drives)
other motors
Varies (depends on High torque at
Good starting torque
High torque at low
Constant torque over low motor type)- Low
low speeds but
but can drop at higher
speeds, constant over a
to medium speed range torque at Low
decreases with
speeds
speed range
Speed
speed
Varies (often
Compact and precise
Larger and heavier
Compact and light
Compact and light
bulkier due to
(but may be heavier
(depends on type)
stepper drive)
than DC motors)
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Motors Technology Comparison
Feature
DC Brush Motor
DC Brushless Motor
Higher cost (due to
electronic
components)
Robotics, drones,
electric vehicles,
orthoscopic surgical
tools.
AC Motor
Stepper Motor
Servo Motor
Varies (AC induction is
Moderate cost
inexpensive)
Higher cost due to
precision and feedback
system
HVAC, industrial
CNC machines, 3D
machines, household
printers, robotics
appliances
Robotics, industrial
automation, RC toys.
Can be noisy
(especially at high
speeds)
Quiet operation (with
proper feedback)
Cost
Generally low cost
Applications
Toys, small
appliances, basic
machines
Noise
Can be noisy due to
brushes
Reliability
Lower due to wear of High reliability (no
brushes
brushes)
Moderate reliability
High reliability (robust
High reliability (with
(wear due to
construction)
feedback control)
frequent stepping)
Temperature
Tolerance
Sensitive to high
Tolerant to higher
temperatures due to
temperatures
brushes
Tolerant, depends on
type (induction or
synchronous)
Quiet operation
Can be noisy
(depends on type)
Sensitive to
overheating due to
stepper coils
High tolerance with
feedback-controlled
systems
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Motor Selection Tips
➢ Decide the motor technology to use.
➢ Select a motor/drive combination.
➢ Does the motor’s performance curve (torque over speed) support
the torque and speed requirements?
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Torque-Speed Curves
• It graphically shows the maximum torque a motor can produce at a
given rotational speed.
➢ DC Brush Motors:
DC_Motor_Specs.pdf
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DC PM Motor Operation Analysis
• For an armature conductor of length L and carrying a current i , the
force F resulting from a magnetic flux density B at right angles to
the conductor.
F = BiL
• Since an armature coil is rotating in a magnetic field,
electromagnetic induction will occur and a back e.m.f. will be
induced.
𝑉𝒃
𝑽𝒃 : back emf voltage
s
ω: rotational speed
𝑲𝒗 : back emf constant
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DC PM Motor Equations
𝑉𝒃
s
𝑉𝑎 = 𝑉𝑠 − 𝑉𝑏
𝑽𝒃
𝑉𝑠 − 𝑉𝑏
𝑉𝑠 − 𝐾𝑣 ω
𝑖=
=
𝑅
𝑅
s
•
where 𝑲𝒕 is the torque constant, and 𝑲𝒗 is the back e.m.f. constant for
a motor.
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DC PM Motor Operation Analysis
𝑉𝒃
s
in
s
in
𝑉𝒃
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DC PM Motor Operation Analysis
𝑉𝒃
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DC PM Motor Torque-Speed Curve
s
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Exercise
• The figure shows the torque speed curve of a DC motor. Find the
speed and motor current for the following:
a) No-load and stall conditions
b) Lifting a 10-oz load with a 2 in radius pulley.
c) A motor driving a robot arm with a weight
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Exercise
a) Speed and motor current at No-load and stall conditions
No-load speed
current
at stall
current
at no-load
Stall Torque
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b) Speed and motor current when lifting a 10-oz load with a 2 in
radius pulley.
• Thus, motor torque to lift the weight is T = 2 in. * 10 oz. = 20 in-oz
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c)
Speed and motor current when a motor driving a robot arm with a
weight.
• Torque due to arm and apple:
T = (6 in.*10 oz.) + (12 in.*8 oz.) = 156 in-oz
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Torque-Speed Curves
➢ Stepper Motor:
• The start-stop region, indicates the range of torque-speed points
where the motor can be started and stopped at will without missing
steps
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Hobby (RC) Servo Motor Selection
•
•
•
•
•
Torque requirements
Speed requirements
Power requirements
Control range
Interface compatibility
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Hydraulic & Pneumatic
Actuation Systems
Hydraulic Systems
• Hydraulic systems are designed to move large loads by controlling a
high-pressure fluid in distribution lines and pistons with mechanical
or electromechanical valves.
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Hydraulic Systems Components
• Typical fluid pressures generated by pumps used in heavy
equipment are in the 6 MPa to 20 MPa range.
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Pneumatic Systems
• Pneumatic systems are similar to hydraulic systems, but they use
compressed air as the working fluid rather than hydraulic liquid.
• A compressor is used to provide pressurized air, usually on the order
of 70 to 150 psi (482 kPA to 1.03 MPa), which is much lower than
hydraulic system pressures.
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Pneumatic System Components
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Valves
• Valves are used with hydraulic and pneumatic systems to direct and
regulate the fluid flow.
• There are two forms of valves, the finite position and infinite
position valves.
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Directional Control Valve
• Pneumatic and hydraulic systems use directional control valves to
direct the flow of fluid through a system.
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Directional Control Valve
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Directional Control Valve
No. of ports
No. of positions
A
B
A
B
P
T
P
T
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Cylinders
• The hydraulic or pneumatic cylinder consists of a cylindrical tube
along which a piston/ram can slide.
Single acting cylinder
Double acting cylinder
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Hydraulic Applications
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Pneumatic Applications
https://youtu.be/2b9a5xZeKpo?si=Mc-L1TVu2_N_TajL
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Hydraulic Vs. Pneumatic Systems
▪ Pneumatic actuators generate much lower forces than hydraulic
actuators.
▪ Hydraulic are more expensive than pneumatic systems.
▪ There are hazards associated with oil leaks which do not occur with
air leaks.
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