IEEE Robotics & Automation Magazine - September 2023 - 67

PERFORMANCE DURING
MANUAL OPERATION
"
The system is designed to teleoperate the
robot manually and make the user feel the
force extracted from the acquired sound.
With the proposed demonstration in a realistic
scenario, the system proved capable of
realizing stable and accurate motion control,
preventing the user from stalling or
moving the robot to a critical configuration.
As described in Figure 9, the robot tip
position followed the command position
from the haptic device with a negligible
time delay. From the aspect of haptic force
feedback, the system can acquire the radial
machining force with a small error during
HAPTIC INTERFACES CAN
SIGNIFICANTLY ASSIST A
HUMAN OPERATOR IN
ASSESSING THE FORCE
TRANSMISSION BETWEEN
A ROBOT AND THE ENVIRONMENT
DURING
REMOTE OPERATION.
„
manual operation, and the corresponding feedback can be tuned
by the operator to a comfortable value, which might vary from
person to person.
SYSTEM LIMITATIONS
Regarding sound signal acquisition stability, the proposed example
is limited in two situations. First, when the machining tool
spindle rotation frequency is too low, its amplitude in the PSD
plot is exceeded by the external noise, preventing
force estimation with the proposed
method; moreover, the sound signal is
affected by external factors, such as the
vibration of the robot tip and the distance
between the sound source and the microphone.
In future developments, an improved
signal processing algorithm that considers
these factors could increase the robustness
of the system.
Another limitation of the reported
example is the focus on the relationship
between radial machining force and spindle
frequency, without considering other
force components (or moments) acting on
the system. For the example in this work,
while negligible, these other components are still present and
could have increased the uncertainty during both calibration
and operation. In future works, to improve the system force
feedback, other components of the wrench (e.g., tangential
force) will be considered and implemented to provide the user
with a better " feeling " of the operation. This limitation also
constrains the robot to machining workpieces along simple
paths, whereas better control over complex shapes can be
enabled with multiaxial feedback.
Z
X
Y
(a)
Load Cell
Workpiece
Z
Y
X
Milling Tool
Milling
Result
(b)
(c)
FIGURE 10. The system demonstration. (a) An operator mills the edge
of the workpiece by using the haptic device. (b) The end effector and
the workpiece setup with a load cell to measure the radial milling
force. (c) The resulting material removal on the workpiece.
CONCLUSION
Haptic interfaces can significantly assist a human operator in
assessing the force transmission between a robot and the environment
during remote operation, when the operator cannot
see or hear the process, thus improving performance. The
main challenge is how to obtain the force applied to the robot
end effector when both the robot and its workspace cannot
include conventional sensors. To solve this issue, we proposed
a novel haptic control method based on acoustic emissions.
The proposed system acquires force by using audible sound
features in an environment with no other sensor than a microphone,
which can also be deployed remotely as long as the
sound is audible. An example prototype was developed and
validated for machining applications. The contributions of this
work are outlined in the following points:
SEPTEMBER 2023 IEEE ROBOTICS & AUTOMATION MAGAZINE
67
APPLICATIONS
This example tests the force estimation accuracy on repetitive trials
that measure radial force from free spindle rotation at maximum
velocity to system stall. As shown by the implementation of
the touching-the-sound algorithm in three different conditions
(i.e., milling a titanium workpiece, grinding a titanium workpiece,
and milling an aluminum workpiece), the proposed method
can be adapted to a variety of machining operations and
materials. While not demonstrated in this work, we expect that
these results can be expanded to any task with an established relation
between sound features and force. By enabling haptic feedback,
this method has the potential to improve operation control
in highly constrained environments, with potential for both medical
and industrial applications.
IEEE Robotics & Automation Magazine - September 2023

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