Tech Briefs Magazine - August 2024 - MD-10

Ball bearings have a number of features
when used in linear actuators, including
high precision, low clearance
and toque and high load capacity. They
can also be manufactured with seals if
required by the application.
Bearings and Linkages
While bearings are found mostly in actuators
in humanoid robots, they are also
used to manage misalignment in other
robotic functions. For example, spherical
plain bearings are critical components
for humanoid robots and can be found in
rod end and linkage assemblies.
Linkages also play a pivotal role in
ensuring that the robot is reliable. One
of the more popular linkages that is used
in this market is the Dog Bone linkage.
It has one spherical plain bearing at
each end which permits misalignment at
both connection points.
Clearance and Torque in Robotic
Bearings
Cross roller bearings offer high load capacity, precision, and a compact design. They support axial loads
from both directions, radial loads, tilting moment loads, and any combination of loads. (Image: CCTY)
Flexible ball bearings can handle radial
loads and a limited axial load. They
are used in wave generators of harmonic
drive mechanisms. They have very thin
sections and will transform into an oval
shape when assembled by a camshaft to
achieve the desired function.
Four-point contact bearings are designed
to handle a combination of radial
and axial loads in both directions, making
them a versatile, compact, and
cost-effective solution. Some of them
have split inner rings or split outer rings,
to allow for a bigger contact angle and
take more axial load and moment load.
Four-point contact bearings are used as
the input bearing in rotary actuators.
Angular-contact ball bearings can take
axial loads in one direction and are generally
used in pairs to allow for bidirectional
axial load capabilities. As the
contact angle increases, the load capability
also increases.
RNN bearings, also known as full complement
cylindrical roller bearings, are
designed to handle heavy loads with a very
compact design. They reduce oscillation
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in robotic actuators and improve control
and rigidity. In addition to having high
durability and uniform contact stress,
RNNs have low noise and vibration. The
attributes make them a good fit for rotary
actuators and linkage assemblies.
Bearings in Linear Actuators
Linear actuators have two main bearings,
four-point contact and deep groove
ball bearings. In this application, these
bearings are used to support the shaft
under load.
Four-point contact bearings are designed
to handle a combination of radial
and axial loads in both directions,
making them a versatile, compact, and
cost-effective solution. Some of them
have split inner rings or split outer
rings to allow for a bigger contact angle
and the ability to take more axial load
and moment load.
Deep groove ball bearings are versatile,
have a simple design, durable in
operation, and are easy to maintain.
They are designed to handle radial loads
and a limited axial load.
The clearance or play between components
poses a significant challenge in
robotic systems. Left unchecked, it can
lead to motion transfer delays, imprecise
positioning, and reduced accuracy. This
reduced accuracy causes shaking/jerky
motion in the robot's movement, as seen
in demo videos from early versions of
new robotic designs. Too much clearance
also introduces accelerated component
wear and rattling noise due to vibration,
ultimately reducing the life expectancy
of the bearing.
Torque is the rotational force applied
to a component. Like clearance, torque
must be carefully managed. High
torque leads to excessive power consumption,
while too little torque may
result in inadequate performance due
to an increased clearance.
The right balance between torque
and clearance is imperative for accurate
motion control. Excessive torque can
hinder movement, and too much clearance
compromises precision.
Therefore, minimizing both clearance
and torque through innovative designs
and advanced manufacturing techniques
is essential.
The Repeatability of Bearings
A bearing's precision is significantly
influenced by its repeatability. A highly
precise bearing can move to a specified
position accurately. Meanwhile, a
Motion Design, August 2024

Tech Briefs Magazine - August 2024

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