Feedback Control of a Foldable Delta Mechanism with Integrated
Inkjet-Printed Angle Sensors
Abstract
Foldable robotics is accepted as one of the leading technologies in the
soft robotics field. Integrating the sensing components, including hinge
angle proprioception, into the robot with a single fabrication method is
a part of the field’s ultimate goal. Here we present a cheap single-step
method for angle sensing integration into the hinges, with an accurate
and reproducible performance. We use silver nanoparticle inkjet printing
on the flexible structural layer (PET) of the foldable robot (i.e. Delta
robot), using an office-type printer. Silver printed sensors were
studied for slight bending applications; however, we report their
behavior under a 1 mm minimum radius of curvature, an advanced range
both for silver strain sensors and any printed hinge position sensors.
Among the three patterns studied, one gave a mean absolute dynamic
hysteresis error below 1 degree. Reproducibility of a printed angle
sensor behavior is reported for the first time, with three prototypes of
each pattern (2degree standard deviation). Printed sensor feedback is
tested with proportional control for the first time, via set-point and
tracking tasks. On-off control law is also implemented and errors below
1 degree are achieved. Proportional control performances are compared
with encoder feedback control and the difference between the realized
trajectories are found to be under 1 mm in the task plane.