Mechanical and Control Design of a Flexible Modular Gripper

The current thesis is carried out in collaboration with Comau S.p.A, the main focus of the work is to propose a model of a vacuum gripping device, characterized by modularity and flexibility. The gripper has to be used in the depalletizing process of several lines, each line is characterized by a different pallet layout, different sizes of the boxes, and different masses. The first phase of literature research provides a generic view of pneumatic gripping devices, their classification, and shows some of the proposed solutions regarding similar problems, where the design of a vacuum end effector is needed. After the review of the proposed solution, it is chosen to develop a flexible gripper, able to to adapt itself to the different boxes of the lines, and composed mainly of elements available on the market. Regarding the actuation, an electric stepper motor is preferred, with respect to a hydraulic or pneumatic actuator, given its simple positioning that can be managed by the motor controller itself. The first phase of the design consists of the definition of a pneumatic system to provide the required vacuum in the suction cups, a system composed of three vacuum zones is produced, to adapt to the sizes of the boxes and prevent the total vacuum loss in the case of leakage occurring, the gripper uses ten suction cups, divided into two three-cups sections and one four-cups section, each vacuum zone has a corresponding vacuum generator, selected considering the required pressure to guarantee the grasp of the box even when not all the suction cups have a proper sealing. The mechanical design consists of the 3D modeling of some components such as the main plate, or different mountings and adapters, which the bought components can be mounted on. A digital mock-up of the gripper is produced using SolidWorks, the suction cups of the gripper are distributed on two extruded profiles, in this way it is possible to simply change the number or type of cups, or the dimensions of the gripper substituting the extruded profiles which are moved symmetrically by an electric axis, to adapt to the box sizes. The last part of the work consists of the definition of the necessary electronic components: the stepper motor, the motor controller, the pressure sensors, and the optic sensors to detect the boxes. It is then defined how the elements are connected and how the gripper is interfaced with the robot. For the control of the gripper it is chosen to exploit the additional digital input and output ports of the robot controller, all the electronic devices on the gripper, including the vacuum generators, can send or receive a digital signal to be activated or communicate their readings. A set of PDL2 routines is developed using the software Roboshop by Comau, the routines can be called by the robot program to obtain information about the sensor, toggle the vacuum generation, and move the suction cups. The proposed concept represents a vacuum-based gripping device, flexible and modular, the production of a prototype could verify the performances of the solution in a real-world scenario; future development could focus on the implementation of a fieldbus communication with the robot.