OSHINO, Japan—Japanese robot maker Fanuc Corp. has strengthened a tie-up with an artificial-intelligence venture as part of its effort to develop industrial machines that can learn and repair themselves.

Fanuc said Friday it plans to acquire a 6% stake in Preferred Networks Inc., a Tokyo-based startup that is also known as PFN, for ¥900 million ($7.3 million). The two companies signed a basic partnership agreement in June to develop robots that require less human supervision.

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