CRE CRE Robot Kinematics & Mechanics 2 — Questions and Answers
Question 1: The Newton-Euler dynamic formulation in robotics is primarily used to compute:
- End-effector positions from joint angles
- Joint torques and forces required to produce a desired motion (Correct answer)
- Path planning trajectories
- Sensor calibration offsets
Correct answer: Joint torques and forces required to produce a desired motion
Newton-Euler formulation recursively applies Newton's laws to each link to calculate the joint forces and torques needed for a given trajectory.
Question 2: Which parameter quantifies a robot link's resistance to angular acceleration based on its mass distribution?
- Mass
- Center of gravity location
- Moment of inertia (Correct answer)
- Coefficient of kinetic friction
Correct answer: Moment of inertia
The moment of inertia captures how mass is distributed relative to the rotation axis, directly resisting changes in angular velocity.
Question 3: In a trapezoidal velocity profile for joint motion, the three phases are:
- Start, hold, end
- Accelerate, constant velocity, decelerate (Correct answer)
- Slow, fast, slow, fast
- Position, velocity, torque ramp
Correct answer: Accelerate, constant velocity, decelerate
A trapezoidal profile linearly increases velocity to a cruise speed, maintains it, then linearly decelerates to rest.
Question 4: Coulomb friction in robot joints primarily degrades:
- Maximum achievable joint speed
- Positional accuracy during slow or stop-start motion (Correct answer)
- Joint inertia model accuracy
- End-effector stiffness under load
Correct answer: Positional accuracy during slow or stop-start motion
Coulomb (sliding) friction creates stiction that makes precise positioning difficult, especially during low-speed or fine-adjustment motions.
Question 5: Gravity compensation in robot control works by:
- Reducing the physical weight of the arm
- Applying feedforward torques to counteract gravitational loads on each link (Correct answer)
- Increasing motor power limits
- Scheduling maintenance intervals
Correct answer: Applying feedforward torques to counteract gravitational loads on each link
Gravity compensation feeds precomputed anti-gravity torques to each joint so the robot holds position without relying solely on feedback error.
Question 6: Compliant robot joints are primarily designed to:
- Increase structural rigidity for higher repeatability
- Absorb impact shocks and enable safer human-robot collaboration (Correct answer)
- Reduce the total number of actuators required
- Eliminate position sensing requirements
Correct answer: Absorb impact shocks and enable safer human-robot collaboration
Compliant joints introduce controlled mechanical flexibility that absorbs collision energy and reduces injury risk in collaborative settings.
CRE CRE Robot Kinematics & Mechanics 2
The Newton-Euler dynamic formulation in robotics is primarily used to compute: