# Robotic Button Mushroom Harvesting Systems: A Review of Design, Mechanism, and Future Directions
## 3 Mechanical System
### Sensors  
Sensors in mushroom harvesting are used to measure various parameters like force, pressure, displacement, and object detection. In addition to the robots' built-in sensors, various other sensors are integrated with components like end-effectors, manipulators, and mobile platforms. Table 2 lists the different sensors used in mushroom harvesters.  
Force-resistive sensors (FSRs) are commonly employed to measure the gripping force, typically installed on the fingertips of end-effectors. These sensors are calibrated with  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Application (Measurement)** & **Sensors** & **References** \\ \hline Gripping force, load, picking parameters & FSRs, load & [3; 30; 38; 39; 46; 51; 52; 55; 60; 65] \\ \hline Suction pressure & Pressure & [38; 39; 51; 64] \\ \hline Distance, displacement & Distance, electromagnetic & [51; 59] \\ \hline Bending & Bending & [55] \\ \hline Strain changes & Strain-resistance gauge & [66] \\ \hline Angle & Inclination, attitude angle & [39; 52; 60] \\ \hline Temperature, humidity & DHT & [67] \\ \hline Object detection & LIDAR, camera & [11; 66] \\ \hline Grading and quality & camera & [11] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Sensors that are used for different applications in mushroom harvesting.  
Figure 5: The different mechanisms used to move the harvester components: (**a**) wheel-slot on a Cartesian robot (reprinted from ref. [40]); (**b**) carriage carrying Cartesian manipulator between different shelves (reprinted from ref. [40]); (**c**) off-the-shelf moving unit (reprinted from ref. [43]); and (**d**) mobile vehicle (reprinted from ref. [45]).  
reference to the standard picking parameters, like safe gripping force, and are programmed to provide accurate force measurements [3]. These readings are often used as feedback to control the applied force, especially in open finger-like grippers where precise force control is crucial [3, 30, 46, 55, 65]. Force sensors are also integrated into end-effectors and human fingers to analyze the picking forces [39, 52, 55, 60]. FSRs or load sensors are used to measure the picking parameters, while air pressure sensors are commonly utilized with vacuum suction end-effectors to monitor and control pressure during picking [31, 38, 39, 51, 52]. The use of FSRs or load sensor readings as feedback significantly reduces the chances of injury to the mushroom, resulting in a higher success rate.  
Other sensors measure displacement and strain. For example, [PERSON] et al. used an electromagnetic sensor to measure the displacement of the actuating surface [59]. This allowed the precise control of the end-effector during gripping and minimized the damage done to the mushroom. Bending sensors can be used, especially with the shape of adaptive fingers. [PERSON] et al. incorporated bending sensors with soft grippers to assess the actuator shape in real time [55]. [PERSON] et al. employed strain gauge sensors to measure the strain changes during gripping [66]. [PERSON] et al. used inclination angle sensors to measure the angle of the end-effector during bending [39, 52]. [PERSON] et al. incorporated six-axis attitude angle sensors to measure the acceleration and velocity, providing the attitude angle [60]. These angle sensors improved the picking ability of the end-effector by either aligning the end-effector with the mushroom direction or providing feedback. [PERSON] et al. utilized distance sensors to measure the gap between the end-effector and the mushroom cap [51], and [PERSON] used laser sensors to identify the 3D position of the mushroom [49]. Additionally, IoT-based monitoring systems have been developed for mushrooms using temperature, humidity, and light sensors, and LIDAR has been used for object detection and path planning in mobile robots [66, 67]. For mushroom identification, various camera-based sensors are used, which are discussed in the Computer Vision section.