Robotics: structure and movements

Explain in your own words what a robot is and what three capabilities define it (moving mechanically, being programmable, and acting on its environment). Reason why an industrial robot arm is a robot, but a fixed conveyor belt, although it moves, is not.

Match each description with its type of robot: (1) arm fixed to the floor that welds car bodies, (2) wheeled machine that transports boxes in a warehouse, and (3) lightweight arm that works alongside humans without a safety fence, with: (a) mobile robot, (b) collaborative robot, and (c) industrial manipulator robot.

A collaborative robot can share a workbench with a person. Explain what two safety measures make this possible (limiting its force and speed, and stopping upon detecting an unexpected contact) and why a conventional industrial robot instead requires a cage or fence.

Explain what a degree of freedom (DOF) of a robot is: each independent movement that a joint can make. Give two examples: a hinged door (a single DOF) and your own arm, which has many, and reason why more DOFs mean more possible postures.

A robot's joints can be revolute (they rotate, like an elbow) or linear, also called prismatic (they extend, like a drawer). Explain the difference and give an everyday example of each type of movement.

A robot arm has a base that rotates on itself, a joint at the 'shoulder', another at the 'elbow', and a rotating wrist. (a) Count its degrees of freedom. (b) Explain what movement each joint contributes to the position and orientation of the end-effector. (c) Reason why it could not orientate the gripper in any direction without the rotating wrist.

There is almost always a gearbox between the motor and the joint of a robot. Explain why: electric motors rotate very fast with low torque, and joints require the exact opposite (low speed and high torque), and the gearbox performs this conversion.

A robot joint is driven by a $3000\ \text{rpm}$ motor through a gearbox with ratio $50:1$. (a) Calculate the rotational speed of the joint. (b) If the motor provides a torque of $0{,}2\ \text{N} \cdot \text{m}$, calculate the ideal output torque of the gearbox and the actual torque with an efficiency of $80\ \%$. (c) Explain what has been gained and what has been lost by inserting the gearbox.

An articulated robotic arm consists of a horizontal link of length $L = 0{,}6\ \text{m}$ and own mass $m_b = 4\ \text{kg}$ (with its center of gravity at its midpoint), which holds at its end a gripper with a part of total mass $m_p = 2{,}5\ \text{kg}$.

(a) Calculate the total static torque that the shoulder joint must overcome when the arm is fully extended in a horizontal position ($g = 9{,}8\ \text{m/s}^2$).

(b) If the arm rises by rotating to form an angle of $60^\circ$ above the horizontal, quantitatively predict the new torque experienced by the shoulder axis and physically justify the variation with respect to the horizontal position.

(c) To drive said joint, a set consisting of a servomotor with continuous rated torque $\tau_m = 0{,}35\ \text{N}\cdot\text{m}$ coupled to a gearbox with gear ratio $i = 80:1$ and a mechanical efficiency $\eta = 75\,\%$ is proposed. Determine by calculation whether the gearmotor assembly is capable of holding the horizontal load in continuous duty without overheating.

Explain what a robot's end-effector is (the 'tool' attached to its wrist that performs the task) and name three different end-effectors along with the task performed by each: gripper, suction cup, and welding torch.

A robot's sensors can be proprioceptive (providing information about the robot itself) or exteroceptive (providing information about the environment). Classify these sensors: (a) the encoder measuring a joint angle, (b) a camera, (c) a touch sensor on the gripper, and (d) the gyroscope measuring chassis tilt.

For each task of a mobile robot, choose the appropriate sensor and justify it: (a) following a line painted on the floor (reflective optical sensors); (b) avoiding collisions with people or shelving (ultrasonic or laser distance sensor); (c) picking up an object without crushing it (pressure sensor on the gripper). Indicate in each case whether it is proprioceptive or exteroceptive.