Compact Robotic Gripper with Tandem Actuation for Selective Apple Harvesting

Abstract

One of the primary reasons robotic apple harvesting is a challenging manipulation problem is the cluttered tree canopy. An effective harvesting gripper should i) be compact to minimize collisions with the canopy, ii) offer a compliant grasp to prevent bruising; and iii) hold the fruit securely to counteract forces during picking. Much of the prior work has used single-mode grippers (suction or fingers), which are often compliant but have low grasp strength (suction), or have a strong grasp but a large form factor (fingers). We present a compact robotic gripper that combines the benefits of both. It first uses an array of soft suction cups to gently attach to the fruit, then deploys three telescoping fingers that sweep away obstacles and pivot inward to secure the grasp. We analyze the finger design for its ability to sweep clutter and maintain a tight grasp, and we measure grasp strength across suction-only, fingers-only, and combined (tandem) actuation modes. Tandem mode consistently provides a grasp that can counter typically observed fruit detachment forces. Using an apple proxy, we test the gripper’s performance in cluttered scenarios, achieving over 96% pick success with an ideal controller. Finally, we validate the gripper in a commercial apple orchard, achieving an 81% pick success rate.