参考文献:
Blake, Tanisha D. Hamper, Bruce C. Huang, Wei Kiefer, James R. Moon, Joseph B. Neal, Bradley E. Olson, Kirk L. Pelc, Matthew J. Schweitzer, Barbara A. Thorarensen, Atli Trujillo, John I. Turner, Steven R. Patent: US008/46569 A, 008 Location in patent: Page/Page column 5 US 008046569 A