Chinese robotics maker Unitree formally launched its IPO on Shanghai's STAR Market on Thursday, opening the books on a deal that aims to raise about 4.2 billion yuan (roughly $618 million) at an implied valuation near 42 billion yuan ($5.9 billion). Once the shares start trading, the listing will put a real, daily market price on a profitable humanoid-robot maker operating at scale - the first the sector has had.