A Mechanism: The term is used for the physical arrangement which provides the definite motion to the parts of a machine.
Kinematics of Machinery: Study of relative motions, without considering the effect of Mass and Force upon the motion. That is to say studying only the motion.
Dynamics of Machinery: It comprises study of motion, taking into account the Mass and Force. It means that study of motion where the effects of Inertia can't be be neglected. In such cases we consider the energy (i) has been supplied to, (ii) has existed in the system and (iii) gets dissipated from the system.
Having defined the core components of the working system of the machine, above, the next step is to introduce you to the concept of Constraints, which means that the parts of the machine with definite relative motion. Necessitating us to have a special term to describe the joint, which permits relative motion. such a joint is called a Pair.
A Pair: It is a joint pair, wherein the geometrical configuration making up the joint are called pairing elements. We would be using the terms Lower Pair and Higher Pair in order to distinguish between joints which permit surface contact and those which permit only point contact, respectively.
A Link: Is a rigid body having elements of two or more pairs, through which, it is connected to other bodies. A simple link will have only two pairing elements, on the other hand a compound link has more than two pairing elements. Another term is Chain means, a combination of links.
Please refer to Figures posted above:
- A Chain, as per Fig.a, permits no relative motion, hence called a Locked chain structure.
- A Chain, as per Fig.b, in which each arm is connected at one end to another arm and so on, allows definite motion. In this case each link move at a fixed path the system is known as constrained chain, also a kinematic chain with one degree of freedom.
- A Chain, as per Fig.c, is an example of unconstrained chain. It has one link fixed, the points in the other links are not constrained to move in a definitive path.
Let us understand each of the above arrangement a little more. The term One Degree of Freedom means that you are specifying one parameter, such as angle θ remaining fixed , in Fig.b, will define the instantaneous positions of every point in the chain relative to one another.
The meaning of the term unconstrained chain, is related to Fig.c, in which, having one link fixed , the other points do not have a constrained movement, they will not always move in a fixed path.
However, the important point to be noted is that although the chain in Fig.c is unconstrained with one degree of freedom, it will become a kinematic chain with two degrees of freedom if two parameters i.e. angles θ and φ are specified.
No comments:
Post a Comment