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| Research | Actuator Design and Architecture |
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| Actuator Design and Architecture |
The goal of this research is to design an array of electromechanical actuators,
which because of their distinctive features, form
a complete architecture of actuators that are useful as building blocks for
intelligent machines. These actuators
can be assembled on demand in an open architecture system just as is now done
for modern computer systems.
The major design features of these electromechanical actuators are:
- Compactness
(high torque and power density)
- Ruggedness
- Standardized
interfaces
- Fault
tolerance
- Intelligence
- Minimum
number of parts
- Ease
of manufacturing/assembly
Ten basic classes of actuators are being developed, with
each class containing both rotary and linear actuators and having a unique set
of requirements, including high torque, high stiffness, fault tolerance,
etc. The level of complexity and
detailed design within each actuator class is determined based on the unique
requirements of each application.
10 Actuator Classes
- Standardized
- High
Torque
- High
Rigidity
- Intelligent
- Precision/Small
Motion
- Hybrid
- Energy
Saver
- Fault
Tolerant
- Dual
Input/Layered Control
- 2-DOF
Modular
Figure 1 displays three different actuators designed in the "standardized"
actuator class. Each individual actuator in a class has the same configuration of components
as the others but meets a different set of output torque, speed, and other design and performance requirements.
Figure 1: Electromechanical Actuator Designs
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| Linear Actuators |
In today's most demanding applications, Electromechanical Linear Actuators (EMLA) are being used
more and more due to their advantages over traditional linear devices such as hydraulic devices and linkage
mechanisms. EMLAs generally consist of an electric motor, a set of gears and some kind of a rotary to linear transmission
component. While rack and pinion devices and chain or belt driven actuators are conventional EMLAs, most current designs
involve some type of screw because screw designs have higher motion ratios, can accommodate larger loads, have better
efficiencies, longer lives and are relatively compact.
When compared to the rest, roller screw transmission technology seems to be the best alternative for high load and
life demands of certain applications for EMLAs. Roller screws have not gained wide popularity since their invention sixty
years ago, primarily because the installed cost of roller screws is much higher than other components and precision machining
is needed in manufacturing and assembly. In most applications, a ball screw can meet the load, speed, duty cycle, and life cycle requirements, but in certain high-load, speed, and duty applications, roller screws are a much better choice. Roller screw actuators are becoming more competitive in a growing number of applications, due to the steadily decreasing cost of manufacturing.
UT RRG has been working on ways to improve the roller screw performance to make them more competitive and less
expensive. Research on distributing the load applied to the screw among the screw threads more evenly has been the primary
goal of research making the roller screw have a longer life and carry higher loads. The research has been successful to
achieve this goal but more work is needed to accomplish better results.
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| Figure 2: FEM Contact Analysis of Roller Screw Transmission |
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| Miniature EMA |
The RRG is utilizing its Hypocyclic Gear Train (HGT) along with other proprietary new design elements to simplify and
miniaturize its line of Electro-Mechanical Actuators (EMAs) to dimensions of less than 1.0 x 1.0 including gear
train and sensors. These miniature actuators can be manufactured in a variety of configurations and are generally
incorporated into two degree of freedom (2DOF) joints. These joints can be used to power a variety of diverse applications
from snake like mobile robots to miniature surgical fingers.
The RRG is developing numerous EMA joint designs. One example is a small (2 x 3) light weight, high torque, 2 degree of
freedom joint specifically designed for a mobile climbing robot. This application requires a very high torque to weight
ratio and a gear train that will hold the robots weight with very little or no power consumption when the robot is stopped.
Applications for this type of robot include search and rescue and anti-terrorism/surveillance.
Piezoelectric actuators or Digital Ceramic Actuators (DCAs) utilize the inverse piezoelectric effect to drive a rotary
actuator. Current research at RRG involves the design and manufacture of a new class of rotary DCA, developed from first
principles in order to achieve an architecture that is optimal for miniature rotary applications. A DCA design is
potentially simpler to manufacture and assemble on a very small scale than EMA actuators incorporating many manufacturing
techniques now employed in the semiconductor industry.
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| Publications |
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