SACA Industrial Robot Operations 4 — Questions and Answers
Question 1: What is the primary purpose of a robot's Denavit-Hartenberg (DH) parameter set?
- To define the kinematic relationship between consecutive joint frames (Correct answer)
- To specify the robot's payload capacity at each axis
- To calibrate the robot's force/torque sensors
- To program discrete I/O signal routing
Correct answer: To define the kinematic relationship between consecutive joint frames
DH parameters mathematically describe the geometric relationship between adjacent links and joints, forming the basis for forward kinematics calculations.
Question 2: During a collaborative robot (cobot) risk assessment, which hazard category requires the lowest priority mitigation effort?
- Pinch points between the cobot and fixed structures
- Residual hazards with negligible probability and minor severity (Correct answer)
- Sharp edges on end-of-arm tooling
- Unexpected motion during power-up sequences
Correct answer: Residual hazards with negligible probability and minor severity
Residual hazards rated as negligible probability combined with minor severity fall at the lowest level of the risk matrix and typically require only informational labeling.
Question 3: A robot program calls a subroutine that modifies a GLOBAL variable. What is the most critical concern with this design?
- Global variables execute slower than local variables
- Unintended side effects may corrupt data used by other routines (Correct answer)
- The robot controller will reject global variable declarations
- Subroutines cannot access global variables in standard robot languages
Correct answer: Unintended side effects may corrupt data used by other routines
Global variables are accessible throughout the program, so modifying them inside a subroutine can unintentionally affect other program sections that rely on the same variable.
Question 4: Which robot motion type guarantees that the TCP follows a perfectly straight-line path between two points?
- Joint interpolated motion (MOVEJ)
- Linear interpolated motion (MOVEL) (Correct answer)
- Circular motion (MOVEC)
- Blended joint motion
Correct answer: Linear interpolated motion (MOVEL)
MOVEL (linear motion) commands the controller to interpolate all joint angles simultaneously so the TCP traces a straight Cartesian line between start and end points.
Question 5: An operator notices the robot's repeatability has degraded from ±0.05 mm to ±0.3 mm over several months. What is the most likely root cause?
- Updated PLC firmware affecting communication timing
- Mechanical wear in gearboxes or encoder backlash (Correct answer)
- Excessive ambient lighting near vision sensors
- Incorrect teach pendant language settings
Correct answer: Mechanical wear in gearboxes or encoder backlash
Gradual degradation in repeatability over time is a classic indicator of mechanical wear in joint gearboxes, bearings, or encoder slippage rather than software or environmental factors.
Question 6: In robot welding applications, what does the term 'weave' refer to?
- The oscillating side-to-side motion of the TCP across the weld joint (Correct answer)
- The speed at which wire is fed through the welding torch
- The post-weld cooling pattern programmed into the robot
- The robot's path-blending radius at weld start/stop points
Correct answer: The oscillating side-to-side motion of the TCP across the weld joint
Weave motion is a programmed oscillation of the robot's TCP perpendicular to the weld direction, used to fill wider gaps and improve bead profile.
Question 7: What safety function must be engaged before a technician enters a robot's restricted space to perform maintenance while the robot is in reduced-speed manual mode?
- Enabling device (deadman switch) must be held in the intermediate position (Correct answer)
- The robot must be fully powered off and locked out
- The safety PLC must be set to automatic mode
- The teach pendant must be disconnected from the controller
Correct answer: Enabling device (deadman switch) must be held in the intermediate position
ISO 10218 requires that in T1 manual mode, personnel inside the safeguarded space must hold a three-position enabling device, which stops motion if fully released or fully pressed.
SACA Industrial Robot Operations 4
What is the primary purpose of a robot's Denavit-Hartenberg (DH) parameter set?