a reconfigurable gripper for robotic autonomous

A Reconfigurable Gripper for Robotic Autonomous Depalletizing in

Supermarket LogisticsG. A. Fontanelli, G. Paduano, R. Caccavale, P. Arpenti, V.

Lippiello, L. Villani, B. SicilianoDepartment of Electrical Engineering and Information Technology

University of Napoli Federico II

The REFILLS context

25-29/10/2020International Conference on Intelligent

Robots and Systems (IROS-2020)2

Robotic systems in close and smart collaboration with humans will allow addressing the main in-store logistic processes for retail stores, leading to a smarter shelf refilling in supermarkets

Robotics Enabling Fully‐Integrated Logistics Lines for Supermarkets

The REFILLS context



Robotic systems in close and smart collaboration with humans will allow addressing the main in-store logistic processes for retail stores, leading to a smarter shelf refilling in supermarkets

Robotics Enabling Fully‐Integrated Logistics Lines for Supermarkets

Autonomous Depalletizing in Supermarkets



Our solution: to design a robotic system that isfully adaptable to different environmentalconditions and depalletizing strategies in order tobe easily integrated into preexisting logisticprocesses, minimizing cost and effort.

Depalletizing is the warehouse process where products are removed from the original shipping pallet and organized.

Depalletizing of supermarket products is a challenging problem:

Environment is typically unstructured.

Pallets are mixed (cases have different dimensions, weights, texture, constraints, etc.).

Solutions should be cheap and non-invasive.

The Robotic Cell



We propose a sensorized robotic cell capable of picking and placing cases in different ways. The cell includes a robot manipulator (KUKA kr60) endowed with the proposed suction-based reconfigurable gripping end-effector.

The gripper is able to grasp the boxes not only from the upper side but also from the lateral side. This solution efficiently allows picking also all the boxes with a different shape such as: boxes with holes for the handles, boxes with easy opening made by making hole patterns in the carton, boxes with no parallelepiped shape such as bottle boxes.

Gripper technology and operating principle



To obtain a design adaptable to different scenarios, the gripper was developed by considering the following requirements:

The proposed design is composed by two symmetric modules, each one equipped with a suction system and an actuated fork, that can be reconfigured along the horizontal axis to adapt the gripper to boxes with different dimensions.

5 actuated + 2 passive degrees of freedom Weight: 7Kg Max payload: 15 Kg

ability to grasp boxes from top and side ability to grasp boxes placed over other boxes; ability to grasp boxes with dimensions in the range [15-50] cm; ability to grasp boxes with weight in the range [0-10] Kg; automatic detection of the boxes distance and orientation using the

embedded sensors; embedded detection of the box weight; automatic reconfiguration to adapt to different boxes size.




Each suction system is composed of one suction plate placed in the front of the module and one fork. On the front side of this plate, several suction cups are disposed. Two different configurations are selectable:

matrix configuration of 9 suction cups suitable for rigid boxes with flat surfaces, configuration composed by only two large suction cups of vertical elongated shape, more suitable for boxes

with non-uniform surfaces and requires lower vacuum power because of the increased surface of the suckers.

Each fork can slide orthogonally to the suction system with an independent motion Each fork includes a pattern of aluminum rollers which are suitably alternated to protrude from either the upper and lower sides respectively. This configuration allows the forks to be inserted between two stacking boxes, sliding on the upper and lower surfaces of both the boxes.




One of the phases of the grasping procedure consists in the lifting of the box so that the forks can slide just below it. Each suction plate can slide vertically with respect to the module along a linear guide. This motion is actuated by a pneumatic cylinder to maximise the power-size ratio.Each suction plate can rotate passively to reduce the load on the suction cups during lifting.

The lifting force is approximately halved thanks to the use of the passive joint and no twistingtorque is applied on the suction cups, thusincreasing substantiallythe grasping capability.

Sensors and actuators



The required degrees of freedom are obtained using:

three electrical stepper motors actuating the two forks independently (the extension length of the forks may vary according to the size of the boxes to grab), and the bidirectional screw which moves the two gripping modules to reconfigure the gripper.

two pneumatic linear actuator used to lift the suction systems.

Moreover the gripper is equipped with different sensors:

four load cells embedded in the gripper flange, we are able to measure the weight of the boxes in the horizontal configuration as well as the vertical one.

four ToFs (Time of Flight) sensors used to measure the distance between the gripper and the boxes and its pitch and yaw angle, just before the approach, to get the best trajectory plan.

Grasping procedure



The grasping procedure of the gripper consists of the following steps:

a. The robot moves the gripper in the neighborhood of the target box; b. The gripper is reconfigured according with the dimensions of the target box; here, the ToF sensors are deployed

to refine the position and orientation of the gripper. c. The gripper sticks to the box using the suction systems. d. The suction plates are lifted by the pneumatic cylinders to make room for the forks. e. The two forks are deployed.f. The suction plates are lowered to their initial position in order to place the box on the forks.

Prototype



The relevant feature of our design is the adaptability to different boxes and the possibility to take non standard boxes also from the lateral side. We designed a case study to demonstrate the ability of the gripper to grasp boxes with different dimension, shape and weight.The gripper prototype was mounted on the terminal flange of an industrial robotic arm Kuka KR60-3 controlled manually to decouple the performances of our gripper w.r.t. the robot positioning.

Experimental setup



We performed a set of 57 experiments considering 19 different boxes picked using the proposed gripper.

The boxes have been selected, from a typical supermarket pallet, to have a different shapes and dimensions, with weights in a range [0.5, 10]Kg.

Each test has been repeated three times.

We tested the grasping of boxes from either lateral, frontal and upper side.

Experimental validation



Experimental validation



The proposed gripper was able to grasp products in 17 out of 19 cases.

In our test, we considered the product as grasped if itwas actually taken in more than 2 consecutive testsnot-grasped otherwise. In the considered product set, the 83% of the products are not graspable at least from one side, and the proposed gripper was able to complete the graspingprocess from another side. Only two products were not correctlygrasped:

In the "ricola" case, the packaging presents holes and fast opening in all the 6 sides.

In the "small-bottles" case, the small size and the curved shapes of the packaging impair suckers to correctly stick on the surface. However, both these cases could be solved by replacing the suction cups with custom ones chosen for the specific application.

Conclusions and Future Works



Conclusions:

We proposed a novel reconfigurable robotic gripper for flexible depalletizing in supermarkets, framed in the REFILLS EU project, designed to be adapted to different logistic necessities:

The system allows to pick cases or boxes of different dimensions enabling either vertical and horizontal grasping procedures.

The system is reconfigurable to be adapted to boxes woth different dimension and shape

The gripper is sensorized to with both weight and distance sensors to enable advanced control strategies

The proposed design shown promising results in grasping boxes in different working conditions



Thanks for your attention!

a reconfigurable gripper for robotic autonomous

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