tailieunhanh - robotics Designing the Mechanisms for Automated Machinery Part 9

Tham khảo tài liệu 'robotics designing the mechanisms for automated machinery part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | General Discussion of Orientation of Parts 255 tray. The second group consists of hexahedral items possessing 2 planes of symmetry. The number of stable states that can be distinguished is reduced to 12. When a third plane of symmetry is introduced there are only 6 distinguishable stable states. Items with one axis of symmetry also belong to this group. When an additional condition L H B is introduced the number of distinguishable stable states equals 3. Cylindrical items having one axis of symmetry and one plane of symmetry also belong to this fourth group. The fifth group includes cubes and spheres which have only one distinguishable stable state on a tray. In other words all 24 stable positions of a cube are perceived as identical by an observer as are the infinite number of stable positions of a sphere. What does stable position mean for an item located on a tray Automatic orientation of parts in industrial applications is essentially a process of bringing parts from one stable state to another. This can be done in various ways and the process can be described in qualitative and quantitative terms. Depending on its shape and other physical properties an item on a tray may be found in unstable stable or indifferent states. Transition from some position into the desired position may require several intermediate changes in positions which can be effected by applying forces to the item. The values of these forces depend on the specific shape and state of the item. Mathematical criteria are used to describe the degree of stability of an item see Figure . The relative potential energy w of the item when moved from state 1 to state 2 relative to plane 1-1 is described by the expression W Rh Tỵ. Here R net external force acting on the item in Figure gravitation T net torque of external forces acting on the item relative to point A h vertical change in the center of gravity Y the angle of inclination of the item in state 2. Taking the derivative of .