Due to the defects of the excavator itself, its working range is limited, and there are often many construction sites that require the excavator to expand the construction range, but the existing big and small arms cannot meet the requirements of the site, so the long reach boom excavator (extended arm excavator) is also born on demand.The so-called long arm (that is, the lengthened arm) is to lengthen a part of the original big arm or completely abandon the original big arm and replace it with an extended big arm, so as to achieve a wider, deeper and higher working range and improve the economic benefits of construction.