Development of the Berry Impact Recording Device sensing system: Hardware design and calibration

Abstract

Bruising caused by the impact damage occurs frequently during mechanical harvest process for highbush blueberries. The overall goal of this study was to develop a miniature and low-cost sensor prototype to quantitatively measure the impact forces endured by blueberries during the mechanical harvest process, which could be used to reduce blueberry bruising through improved harvester design. The sensing system developed in this study had three essential components: the sensor, the interface box, and the computer software program. The round circuit board of sensor is less than one inch (19.4 mm), including three accelerometers with ±500 g sensing range in each orthogonal axis, one eight-bit microcontroller, one 128 KB memory chip, and other electronic components with low power consumption. The sensor board and rechargeable battery were cast into a one inch (25.4 mm) sphere using silicone rubber. The interface box serves as the intermediate communication platform to connect the sensor and the computer. The PC-software retrieves data from the sensor via the I 2C communication and downloads data to a computer for further analysis via the RS232 communication. The sensor was calibrated using a centrifuge. The accuracy of the sensor output was 0.53% (2.60 g maximum deviation) and −0.33% (−1.26 g maximum deviation), with precision error of 0.63% (3.21 g) in the output span. This miniature and low-cost sensor prototype provides the opportunity to understand how the berry (or other small fruits) interacts with different machine parts within the harvester and to identify critical control points that cause the most mechanical impacts, which was not achievable in the past.