SEOUL (Reuters) -Shares in South Korea's Doosan Robotics opened 127% up from their initial public offering (IPO) price in the company's market debut on Thursday, based on investors' bullish outlook for the collaborative robot maker. The company raised 421.2 billion won ($317 million) in South Korea's largest IPO this year, having priced the shares at 26,000 won each, the top of the price range flagged to investors. Doosan Robotics shares opened at 59,100 won each and rose to as much as 67,600 wo