Shigeo Shingo (1909-1990), industrial engineer whose technical innovations made TPS physically possible. While taiichi-ohno developed the management philosophy, Shingo developed the engineering techniques: smed (reducing changeover from hours to minutes, enabling small-batch just-in-time production), poka-yoke (mistake-proofing devices that prevent defects at their source), and "zero quality control" — the radical idea that quality should be built into the process through source inspection and poka-yoke, not achieved through statistical sampling of output. Shingo was more prolific than Ohno as a writer: a-study-of-the-toyota-production-system, zero-quality-control, a-revolution-in-manufacturing-the-smed-system. He consulted for Toyota from the 1950s but was not a Toyota employee — he worked across many Japanese manufacturers. The Ohno-Shingo relationship is sometimes debated: Ohno rarely credited Shingo in his writing, while Shingo's accounts emphasize his own contributions. Both perspectives have merit; TPS was a collaborative achievement.