Short Notes

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Short Answer Type Questions

1. What is the purpose of robot arm links in the overall structure of a robot?

  • The links of a robot arm are the rigid components (like bones in a human arm) that connect the joints together.

  • Their main purpose is to provide structure, length, and reach to the arm.

  • Each link supports mechanical parts (joints, actuators, sensors) and transfers motion and forces generated at the joints to the end-effector (e.g., gripper, tool).

  • Without links, the joints would have no physical separation, and the robot could not reach different positions in space.

2. What is the role of revolute joints in a robot arm? Explain with an example.

  • A revolute joint is a type of joint that allows rotation around a fixed axis, similar to a hinge.

  • It provides rotational degrees of freedom to the robot arm.

  • Example: In a robotic arm used for welding, a revolute joint allows the arm to swing left or right, enabling the welding tool to reach different points on a car body.

  • In human terms, your elbow joint is like a revolute joint, allowing your forearm to rotate up and down.

3. Explain the relationship between the number of joints and the degrees of freedom in a robot arm.

  • Each joint in a robot arm provides one degree of freedom (DOF) (rotation or translation).

  • Therefore, the total degrees of freedom = number of joints.

  • Example: A robot arm with 6 joints typically has 6 DOF, which is the same as a human arm (shoulder 3, elbow 1, wrist 2).

4. How can the degrees of freedom in a robot arm affect its flexibility and range of motion?

  • The higher the number of DOF, the greater the flexibility and ability of the robot to reach positions and orientations.

  • A 2-DOF arm can only move in a plane, while a 6-DOF arm can position its end-effector anywhere in 3D space and orient it in any direction.

  • More DOF allows robots to:

    • Work in complex environments (e.g., assembly lines, surgery).

    • Perform tasks that require precision and dexterity.

    • Avoid obstacles by moving around them.

5. Explain the term 'coordinated joint movement'.

  • Coordinated joint movement means that multiple joints move simultaneously in a controlled manner to achieve a smooth and precise motion of the robot arm.

  • Instead of moving one joint at a time (which would look jerky), the robot calculates how much each joint should move so that the end-effector follows a desired path.

  • Example: When a robotic arm draws a straight line on a surface, all the joints adjust together to keep the pen moving smoothly in a straight path.





Long Answer Type Questions


1. Explain two-dimensional motion in robots with the help of an example.

  • Two-dimensional (2D) motion in robots refers to motion that occurs within a plane (X-Y plane), where the robot can move only in two directions (up–down and left–right).

  • Such motion is simpler than three-dimensional motion and is often used in robots designed for basic tasks.

Example:

  • A 2-link planar robotic arm can move its end-effector within a flat workspace (like a tabletop).

  • Each link rotates around a joint, and the combination of the two joints allows the end-effector to reach different points on the plane, similar to how your arm can sweep across a table surface without lifting off.

2. What are the important characteristics of angular motion?
Angular motion is the rotation of a body or a link around a fixed axis. The key characteristics are:

  1. Axis of rotation – The line around which rotation occurs (e.g., robot elbow joint axis).

  2. Angular displacement (θ) – The angle through which a link rotates (measured in degrees or radians).

  3. Angular velocity (ω) – The rate of change of angular displacement, i.e., how fast the joint rotates.

  4. Angular acceleration (α) – The rate of change of angular velocity, i.e., how quickly the joint speeds up or slows down.

  5. Direction of rotation – Clockwise or counterclockwise rotation.

3. Write and explain various types of joints in robots.
Robot joints provide motion and flexibility, just like human body joints. The main types are:

  1. Revolute Joint (R-joint)

    • Allows rotational motion around a fixed axis.

    • Example: Robot elbow joint, hinge-like motion.

  2. Prismatic Joint (P-joint)

    • Allows linear motion along an axis (sliding).

    • Example: Telescopic joint in robotic manipulators.

  3. Cylindrical Joint

    • Combination of revolute + prismatic motion (rotation + sliding along the same axis).

    • Example: Drilling robots where the tool rotates and slides downward.

  4. Spherical Joint (Ball-and-socket)

    • Allows rotation in multiple directions, similar to a human shoulder joint.

    • Provides 3 degrees of freedom at one point.

  5. Helical Joint

    • Allows screw-like motion (rotation + translation along the axis).

    • Example: Robotic end-effectors that twist and extend.

4. Make a diagram of a robotic arm with seven Degrees of Freedom and explain it.

Here’s a diagram description (I can also draw it for you if you’d like a labeled sketch):

A 7-DOF robotic arm is similar to a human arm, giving it maximum flexibility:

  1. Base rotation (yaw) → rotates the whole arm left/right.

  2. Shoulder pitch → moves the arm up/down.

  3. Shoulder roll → rotates the arm sideways.

  4. Elbow pitch → bends/straightens the arm.

  5. Wrist pitch → moves the wrist up/down.

  6. Wrist yaw → rotates the wrist left/right.

  7. Wrist roll → rotates the wrist around its axis