In 1954 George C. Devol Jr. filed a US patent titled “Programmed Article Transfer,” granted as US 2,988,237 on June 13, 1961. The patent describes a reprogrammable machine with a transfer head that grips objects and moves them through sequences of horizontal, vertical, and rotational motions under the control of a program stored on a magnetic drum. A position encoder tracks where the head is and compares it against the stored instructions until the two match.
The key idea was reprogrammability. Devol’s filing states that it applies “program techniques known in certain other arts” for the first time to article-transfer machines, and that the stored motion sequences could be “readily erased for re-recording.” Instead of a fixed cam or a one-purpose machine, a single arm could be taught a new task by recording a new program.
Devol partnered with Joseph Engelberger to commercialize the invention through a company called Unimation, and the resulting machine was named Unimate. The first Unimate was installed on a General Motors line, where it handled hot die-cast metal parts - dangerous, repetitive work. This is generally regarded as the birth of the industrial robot, decades before robotics intersected heavily with artificial intelligence.
The patent is the primary source here: it is the original filing that defines the programmable manipulator at the root of the entire industrial robot industry.