# Robotic Button Mushroom Harvesting Systems: A Review of Design, Mechanism, and Future Directions
## 3 Mechanical System  
### Robot Manipulators  
Robot manipulators play a crucial role in the harvesting system by facilitating the movement of the end-effectors during the picking and transportation of mushrooms. These manipulators are equipped with end-effectors and, in many cases, with the control system and sensors for the measurements of data and motion control. While various types of manipulators are used in harvesting fruits and vegetables, the unique morphology of mushrooms and their growing environment often necessitates the use of Cartesian and articulated arms. Cartesian robotic manipulators operate with linear motion along the x-, y-, and z-axes. For mushroom harvesting, these manipulators are frequently enhanced with additional mechanisms to increase their degrees of freedom (DOFs) and better support the end-effectors. A fundamental example is a three-DOF Cartesian manipulator, which typically features an end-effector attached to the z-axis, with two sliders facilitating movement along the x- and y-axes. This straightforward mechanism is especially effective for use with Dutch shelves, making it a popular choice for both commercial harvesting and research applications [30; 31; 32; 33; 34]. The Champi-ON project, for instance, developed an automated mushroom harvesting system tailored for Dutch shelving farms but was adaptable to other cultivation methods. The system integrates a gripper, vision system, suction mechanism, stem cutting, and container shaking system into a Cartesian trolley, ensuring precise handling and minimal damage to the mushrooms [35]. In experiments, researchers like [PERSON] et al. [36] and [PERSON] et al. [37] utilized Cartesian manipulators with multiple sliders to either test the end-effectors or optimize the picking path, adding more end-effectors and improving their performance through proper path planning. These multi-linked Cartesian manipulators were also equipped to carry additional accessories such as cameras and sensors. [PERSON] et al. modified a Cartesian manipulator to include additional vertical and rotational DOFs, creating a mechanism suitable for Dutch shelves [38]. Similarly, [PERSON] et al. employed a four-DOF positioning end-effector, combining a three-DOF Cartesian system with an additional rotational mechanism, which enhances picking performances through precise positioning [39]. Mycionics also utilized a Cartesian manipulator with a revolute arm for commercial harvesting, enabling efficient picking and greater accessibility to other harvesting components. These manipulators are typically mounted on shelves, with wheels supporting their locomotion along specially designed slots, allowing them to cover the entire shelf workspace [40]. Dorna Robotics has used a combination of Cartesian and multi-revolute arms (a six-DOF robot) to design a commercial harvester that can also be transported between the shelves and have a picking performance close to that of skilled human pickers. Despite the claim that the harvester can be transported easily, the harvester has to be moved manually at the current stage [41]. A three-DOF articulated arm for mushroom picking was developed by the University of Warwick, while the Vineland Research and Innovation Center in Ontario created a multi-DOF articulated arm based on portable beds [30; 42]. In commercial and high-volume mushroom harvesting, SCARA arms are frequently used as manipulators. A SCARA robot employed in mushroom harvesting mostly moves on the XY (parallel to the ground) plane and translates into the z-axis. TechBrew Robotics, for instance, has integrated the SCARA arm to speed up mushroom harvesting on Dutch shelves [43]. Similarly, 4 AG Robotics recently developed an automated harvesting system with a SCARA arm [44]. These SCARA arms have been shown to be faster at picking and have easy access to the collector units installed outside. At Nanjing Agriculture University, two SCARA manipulators were employed to pick mushrooms on both sides of the shelves [45].