  As robots shift from industrial to human-centered spaces, adopting mobile
manipulators, which expand workspace capabilities, becomes crucial. In these
settings, seamless interaction with humans necessitates compliant control. Two
common methods for safe interaction, admittance, and impedance control, require
force or torque sensors, often absent in lower-cost or lightweight robots. This
paper presents an adaption of impedance control that can be used on
current-controlled robots without the use of force or torque sensors and its
application for compliant control of a mobile manipulator. A calibration method
is designed that enables estimation of the actuators' current/torque ratios and
frictions, used by the adapted impedance controller, and that can handle model
errors. The calibration method and the performance of the designed controller
are experimentally validated using the Kinova GEN3 Lite arm. Results show that
the calibration method is consistent and that the designed controller for the
arm is compliant while also being able to track targets with five-millimeter
precision when no interaction is present. Additionally, this paper presents two
operational modes for interacting with the mobile manipulator: one for guiding
the robot around the workspace through interacting with the arm and another for
executing a tracking task, both maintaining compliance to external forces.
These operational modes were tested in real-world experiments, affirming their
practical applicability and effectiveness.
