题目：Mo, and Shui Mo The function of Mo (礳, an animal-driven grinder) and Shui Mo (水磨, a water-driven grinder) is to crush crops as shown in Figs. a and b (Wang 1991). The basic structure contains the upper and lower grinding discs. The lower grinding disc is fixed while the upper part rotates. The upper grinding disc engraves grooves on its bottom, and the grooves’ shape is mainly the parallel and equally-separated diagonal lines, all of which form a smooth grinding surface. A shaft is installed through the center to connect both discs in order to make them slide and rub against each other. Mo is driven by animals that walk around the grinding base and rotate the upper grinding disc. Shui Mo is another type that has a long shaft on the grinding disc and a horizontal water wheel attached to the other end of the shaft. The upper grinding disc is connected to the long shaft with a horizontal water wheel as an assembly. When water flows through the wheel, the upper grinding disc rotates to grind the grains (Zhang et al. 2004). The two grinders can be identified as a mechanism with two members and one joint. The lower grinding disc is the fixed frame (member 1, KF). The upper grinding disc is the moving link (member 2, KL) and is connected to the frame with a revolute joint JRy. Figure c shows the structural sketch for both devices, and Fig. d shows a real object of the water-driven grinder.Fig. Grinders. a. An animal-driven grinder (礳) (Wang 1991).b. A water-driven grinder (水磨) (Wang 1991).c. Structural sketch. d Real object (photoed by Guan, X.W., in Lhasa, Tibet)
