Kinematic pair:
The two links or elements of a machine, when in contact with each other, are said to form a pair. If the relative motion between them is completely or successfully restrained (i.e. in a defined direction), the pair is known as a kinematic pair. In this article, we will see about restricted movement, types, examples with diagrams.
Restrictions:
Restrictions imposed on the movement or position or both of a system of particles are known as constraints. Constraints limit the movement of an object.
Restricted movement:
The movement that cannot proceed arbitrarily in any way is called restricted movement.
Different types of restricted movements:
1. Completely Restricted Movement
2. Incompletely Restricted Movement
3. Successfully restricted movement
Completely restricted movement:
- When the movement between a pair is limited to a defined direction, regardless of the direction of the applied force, then the movement is considered to be a completely restricted movement.
- For example, the piston and cylinder (in a steam engine) form a pair and the movement of the piston is limited to a set direction (i.e. it will only alternate) relative to the cylinder, regardless of the direction of movement of the crank. . The motion of a square bar in a square hole is an example of completely constrained motion.
Examples of completely restricted movement:
1. The movement of a square bar in a square hole
2. the movement of a shaft with collars at each end in a circular hole,
types of restricted movement – completely, incompletely, successfully restricted movementIncompletely restricted movement:
- When movement between a pair can occur in more than one direction, then the movement is called incompletely constrained movement. Changing the direction of the applied force can change the direction of relative motion between the pair.
- A circular bar or shaft in a circular hole is an example of incompletely constrained motion, as it can rotate or slide in a hole. Both movements are unrelated to each other.
Examples of incompletely restricted movement:
- The circular shaft in a circular hole can rotate or slide in the hole
Successfully restricted movement:
- When the movement between the elements, forming a pair, is such that the restricted movement is not completed by itself but by some other means, then the movement is said to be a successfully restricted movement.
- Consider a shaft in a stepper bearing as shown in Fig. The shaft can rotate in a bearing or it can move upward. This is a case of incompletely restricted movement. But if the load is placed on the shaft to prevent the upward axial movement of the shaft, then the movement of the couple is said to be a successfully restrained movement.
- The movement of an IC engine mechanism valve (these are held in their seat by a spring) and the piston reciprocating within an engine cylinder are also examples of successfully restricted movement.
Examples Successfully restricted movement:
1. The movement of an IC engine valve (they are held in their seat by a spring)
2. The piston reciprocating inside an engine cylinder
3. Shaft in a support bearing
