AWS DevOps Motion Control & Kinematics 3 — Questions and Answers
Question 1: In a robotic arm with 6 degrees of freedom, what does the Jacobian matrix relate?
- Joint angles to end-effector position
- Joint velocities to end-effector velocities (Correct answer)
- Joint torques to end-effector forces
- Link lengths to workspace volume
Correct answer: Joint velocities to end-effector velocities
The Jacobian matrix maps joint-space velocities to Cartesian end-effector velocities at a given configuration.
Question 2: Which motion profile minimizes jerk while still limiting velocity and acceleration?
- Trapezoidal profile
- S-curve (7-segment) profile (Correct answer)
- Step profile
- Sinusoidal profile
Correct answer: S-curve (7-segment) profile
The S-curve (7-segment) profile adds jerk-limited ramp phases to a trapezoidal profile, reducing mechanical shock.
Question 3: In forward kinematics, what is the primary output given a set of joint parameters?
- Required joint torques
- End-effector pose in Cartesian space (Correct answer)
- Optimal joint trajectory
- Workspace boundary
Correct answer: End-effector pose in Cartesian space
Forward kinematics computes the end-effector's position and orientation from known joint angles or displacements.
Question 4: A servo drive operating in torque control mode primarily regulates which quantity?
- Motor shaft position
- Motor shaft velocity
- Motor phase current (and thus torque) (Correct answer)
- DC bus voltage
Correct answer: Motor phase current (and thus torque)
In torque mode, the drive closes a current loop whose output current is proportional to the commanded torque.
Question 5: What phenomenon occurs when a robot's Jacobian becomes singular?
- End-effector speed doubles
- The robot loses one or more degrees of freedom in Cartesian space (Correct answer)
- Joint angles exceed their limits
- The robot enters a safe-stop state automatically
Correct answer: The robot loses one or more degrees of freedom in Cartesian space
At a singularity the Jacobian loses full rank, meaning certain Cartesian directions cannot be achieved regardless of joint velocity.
Question 6: In Denavit-Hartenberg (DH) notation, how many parameters describe each joint-link pair?
- 2
- 3
- 4 (Correct answer)
- 6
Correct answer: 4
DH notation uses four parameters per joint: link length (a), link twist (α), joint offset (d), and joint angle (θ).
Question 7: Which control topology is used when both position and velocity feedback loops are active simultaneously in a servo system?
- Open-loop control
- Cascaded (nested) control (Correct answer)
- Feedforward-only control
- Bang-bang control
Correct answer: Cascaded (nested) control
Cascaded control nests an inner velocity loop inside an outer position loop, providing tighter dynamic response.
AWS DevOps Motion Control & Kinematics 3
In a robotic arm with 6 degrees of freedom, what does the Jacobian matrix relate?