  This paper describes the design and construction of the automatic calibration
unit (ACU) for the JUNO experiment.ACU is a fully automated mechanical system
capable of deploying multiple radioactive sources, an ultraviolet (UV) laser
source, or an auxiliary sensor such as a temperature sensor, one at a time,
into the central detector of JUNO along the central axis. It is designed as a
primary tool to precisely calibrate the energy scale of detector, aligning
timing for the photosensors, and partially monitoring the position-dependent
energy scale variations.
