Equivalent negative stiffness mechanism using three bundled needles inspired by mosquito for achieving easy insertion. - Seiji Aoyagi; Yutaka Takaoki; Hiroki Takayanagi; Chih-hao Huang; Takahiro Tanaka; Masato Suzuki; Tomokazu Takahashi; Tsutomu Kanzaki; Takuya Matsumoto (IROS, 2012)