참고 http://blog.naver.com/PostView.nhn?blogId=kusarfirst&logNo=221286302975 https://steemit.com/kr-dev/@jacobyu/54qama http://www.irobotnews.com/news/articleView.html?idxno=8844 https://m.blog.naver.com/PostView.nhn?blogId=khsuniv201&logNo=221014028634&proxyReferer=https%3A%2F%2Fwww.google.co.kr%2F