Medical Design Briefs - July 2024 - 18

TECHNOLOGY LEADERS Automation: Motors & Motion Control/Robotics
Why Frameless Motors Are at the Forefront of
the Surgical Robotic Revolution
R
ecent advancements in robotics
have greatly enhanced
surgical procedures, enabling
minimally invasive techniques
that offer patients the promise of better
outcomes with fewer complications
and shorter recovery times. Much of
this innovation is driven by advanced
motion control systems and constant
component miniaturization.
Specifically, surgical robots depend
upon precise control of the motion
of joint and end-effector appendages
during procedures. That means the
internal motorized systems must deliver
seamless, steady, accurate and
responsive motion within compact
and lightweight envelopes. While
these motion systems can take many
different form factors, one that has
emerged to support surgical robotics
is the frameless motor.
What Is a Frameless Motor?
Frameless motors have become an
optimum solution for control axes
that demand precise servo- driven
movement, including surgical robot
end effectors and robotic joints. These
motors are stripped down to essential
components - the stator and rotor -
and forego the traditional frame, bearings,
and shafts. This simple construction
allows designers to mount frameless
motors directly onto the robot joint or
end-effector assembly to transmit the
needed torque. Their working principle
is as follows:
Frameless motors have become an optimum solution for control
axes that demand precise servo-driven movement, including
surgical robot end effectors and robotic joints. (Credit:
Portescap)
How Do Frameless Motors Benefit
Surgical Robots?
The outer stator is composed of
wound copper coils in a circular arrangement,
and the inner rotor carries
an array of permanent magnets. When
the stator is energized, its magnetic
field interacts with the rotor's magnets
and causes the motor to rotate. The motor's
torque output can be controlled by
altering the current that travels through
the stator. Frameless motors can be customized
with various options to help
achieve the application's required performance
needs.
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Frameless motors are revolutionizing
the field of surgical robotics, offering
a variety of benefits that enhance their
performance and safety. Their high
torque and efficiency ensure smooth
and accurate movements, enabling surgeons
to perform intricate tasks with
unparalleled precision. Thanks to the
simple structure and operating principle
of frameless motors, they offer intrinsic
advantages over conventional
motors, such as:
* Space and weight savings. By not including
the surrounding frame, these
motors have inherently small footprints.
They also have fewer parts and
do not require power transmission
components or integrated bearings.
Their compact design allows for precise
control and maneuverability within
confined spaces. When compared to
traditional motors, frameless motors
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are an attractive choice to reduce a
system's size and weight.
* High torque-to-inertia ratio. Frameless
motors exhibit fast response
times, requiring less torque
to accelerate.
* Stiffness and rigidity. Without the
power transmission component and
shaft attachments typical of conventional
motors, frameless motors provide
exceptional torsional stiffness
and enhance overall system stability.
* Higher efficiency. Frameless motors
do not suffer from friction or
eddy currents that occur with their
framed
counterparts,
and
their
light weight helps lower power consumption
and, in turn, produce less
heat. In addition, their high torque
output relative to their small size results
in greater torque density. Frameless
motors also do not require
transmission components that often
present mechanical losses that
can otherwise lower efficiency.
* Heat dissipation. The absence of a
frame allows the motor to dissipate
more heat. This ensures the motor
performs longer during demanding
surgical procedures.
* Other benefits. Frameless motors
have minimal parts and require few
accompanying components that may
be subjected to wear and tear, which
helps reduce maintenance requirements.
They also operate quietly -
an important consideration in surgical
equipment.
Portescap, for example, has decades
of experience supporting surgical applications,
including capabilities to
design and manufacture frameless
motors. Typical characteristics include
diameters of up to 127 mm, nominal
torque of 1,500 mNm, up to 20,000
rpm, and power up to 350W. Taken
together, these diameters and performance
capabilities make frameless
motors appropriate for use in robotic
systems ranging from small endoscopic
devices to larger orthopedic systems.
Medical Design Briefs, July 2024
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Medical Design Briefs - July 2024

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