What it is and what it does
The Mitsubishi MR-J4-70B-RJ020 is a servo amplifier — the power stage that drives a servo motor in a closed-loop motion control system. It belongs to the MR-J4 series, Mitsubishi's current-generation servo platform for industrial positioning, speed, and torque control. The amplifier receives command signals from a motion controller (typically a PLC with a positioning module) and converts them into regulated current to the motor, while feeding back encoder position for precise axis control.