  Global berry production and consumption have significantly increased in
recent years, coinciding with increased consumer awareness of the
health-promoting benefits of berries. Among them, fresh market blackberries and
raspberries are primarily harvested by hand to maintain post-harvest quality.
However, fresh market berry harvesting is an arduous, costly endeavor that
accounts for up to 50% of the worker hours. Additionally, the inconsistent
forces applied during hand-harvesting can result in an 85% loss of marketable
berries due to red drupelet reversion (RDR). Herein, we present a novel,
tendon-driven soft robotic gripper with active contact force feedback control,
which leverages the passive compliance of the gripper for the gentle harvesting
of blackberries. The versatile gripper was able to apply a desired force as low
as 0.5 N with a mean error of 0.046 N, while also holding payloads that produce
forces as high as 18 N. Field test results indicate that the gripper is capable
of harvesting berries with minimal berry damage, while maintaining a harvesting
reliability of 95% and a harvesting rate of approximately 4.8 seconds per
berry.
