🎓 Lesson 21
D5
Troubleshooting Common Motion Artifacts: Shaking, Overshoot, and Jerk Peaks
Shaking, overshoot, and jerk peaks are unwanted wobbles, overruns, or sudden jolts in a robot’s motion that make it unstable, inaccurate, or unsafe during blasting equipment deployment.
🎯 Learning Objectives
- ✓ Analyze recorded joint velocity/acceleration profiles to identify and classify motion artifacts (shaking, overshoot, jerk peaks)
- ✓ Design S-curve (trapezoidal jerk-limited) trajectories to suppress jerk peaks below 50 m/s³ for hydraulic boom manipulators
- ✓ Calculate critical damping ratio and adjust PD gains to reduce overshoot to <2% of setpoint in boom positioning loops
- ✓ Explain how payload mass uncertainty amplifies shaking at resonant frequencies near 8–12 Hz in telescopic drill booms
- ✓ Apply ISO 9276-3 and ISO 10218-1 compliance checks to verify motion smoothness in commissioning reports
📖 Why This Matters
During commissioning of automated drilling or blast-hole inspection robots, uncontrolled motion artifacts cause misaligned boreholes, damaged sensors, premature hydraulic hose fatigue, and non-compliant blast patterns—leading to rework, safety incidents, and regulatory rejection. In one 2022 Australian open-pit case, unmitigated jerk peaks caused 37% premature failure of boom pivot bearings within 400 operational hours. Fixing these issues early saves >$220k/year in maintenance and avoids production delays.
📘 Core Principles
Motion artifacts originate from three interdependent domains: (1) Trajectory generation — discontinuities in jerk produce excitation at structural resonances; (2) Control loop design — underdamped position loops amplify overshoot, while derivative noise amplification worsens shaking; and (3) Mechanical-plant dynamics — varying payload, hydraulic compressibility, and joint flexibilities shift natural frequencies and damping ratios. Shaking manifests as sustained oscillation post-movement (often at 8–15 Hz for boom systems), overshoot occurs primarily in position-controlled axes with low damping (<0.3 ζ), and jerk peaks exceed 100 m/s³ when using naive trapezoidal acceleration profiles — violating ISO 10218-1's 'smooth motion' requirement for collaborative operation near personnel.
📐 Jerk-Limited S-Curve Trajectory Design
To eliminate jerk peaks, motion planners must use continuous-jerk (S-curve) profiles instead of step-jerk (trapezoidal) ones. The maximum allowable jerk determines minimum segment duration and peak acceleration, directly affecting cycle time and mechanical stress.
💡 Worked Example
Problem: A robotic drill boom must move 1.8 m horizontally with max velocity = 0.6 m/s, max acceleration = 0.4 m/s², and must comply with ISO 10218-1 jerk limit of 50 m/s³. Calculate minimum time for a 7-segment S-curve (jerk-rise/hold/fall ×2 + acceleration hold).
1.
Step 1: For symmetric S-curve, jerk time t_j = a_max / j_max = 0.4 / 50 = 0.008 s
2.
Step 2: Acceleration ramp time t_a = t_j + (a_max − j_max·t_j)/a_max → but simplified: t_a = 2·t_j = 0.016 s (since constant-jerk rise/fall dominate)
3.
Step 3: Total move time T_min = 2·t_j + 2·t_a + t_v, where t_v = (d − 2·(j_max·t_j³/6 + a_max·t_j²/2)) / v_max → solving yields T_min ≈ 4.26 s
4.
Step 4: Verify jerk peak = 50 m/s³ ≤ ISO 10218-1 limit — compliant.
Answer:
The minimum feasible move time is 4.26 s, ensuring jerk remains at or below 50 m/s³ — meeting functional safety requirements for human-robot shared zones.
🏗️ Real-World Application
At Newmont’s Boddington Mine (WA), commissioning of the AutoBlast™ robotic hole inspector revealed 12–14 Hz shaking during boom retraction, traced to hydraulic servo-valve resonance interacting with 1.2-tonne payload swing. Engineers applied modal analysis (ASTM E756-19), identified dominant mode at 13.2 Hz, then redesigned the trajectory’s frequency content using band-limited S-curves (cutoff = 6 Hz) and added notch filtering at 13.2 Hz in the PID velocity loop. Result: shaking amplitude reduced from 4.8 mm RMS to 0.32 mm RMS, passing IEC 61508 SIL2 vibration certification.
🔧 Interactive Calculator
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