MATLAB simulation of a UR5e surgical robot performing a laparoscopic trajectory with tissue-adaptive PID force control and safety watchdog. Models soft tissue, organ wall, and cortical bone using spring-damper mechanics. Watchdog halts tool in 10ms. Verified per ISO 13485 and IEC 60601-1.
In robot-assisted surgery the surgeon loses direct tactile feedback. If the tool applies too much force it can perforate tissue or cause hemorrhage. This project simulates the core force control and safety architecture used in laparoscopic surgical systems.
The system models three tissue types, implements a PID force controller tuned with a low-pass derivative filter, and deploys an independent safety watchdog that halts the tool within 10ms of a force threshold breach.
| Metric | Result | Requirement |
|---|---|---|
| Steady-state force error | < 0.2 N | < 0.2 N |
| Watchdog response time | 10 ms | < 50 ms |
| Tissue profiles validated | 3 | 3 |
| V&V test cases passed | 6 / 6 | 6 / 6 |
| Stress test | PASS | PASS |
| Tissue | Stiffness | Threshold | Clinical Context |
|---|---|---|---|
| Soft Tissue | 0.5 N/mm | 2.0 N | Fat, connective tissue |
| Organ Wall | 2.0 N/mm | 5.0 N | Gastric wall, bladder |
| Cortical Bone | 8.0 N/mm | 12.0 N | Orthopaedic procedures |
Four modules working together:
- Robot Model — UR5e loaded via Robotics System Toolbox, 6-waypoint surgical trajectory solved with chained inverse kinematics and elbow-up constraint
- Tissue Model — Spring-damper contact mechanics across 3 stiffness profiles with Gaussian sensor noise injection
- PID Controller — Force regulation with low-pass derivative filter achieving less than 0.2N steady-state error
- Safety Watchdog — Independent force monitor that halts the tool within 10ms of threshold breach, referenced to IEC 60601-1
Initial Kd of 0.5 caused severe oscillation because the derivative term was amplifying raw sensor noise at every timestep. Fixed by reducing Kd to 0.05 and adding a low-pass filter on the error signal before differentiation — standard practice in safety-critical force control systems.
| Parameter | Value |
|---|---|
| Kp | 2.0 |
| Ki | 0.5 |
| Kd | 0.05 |
| Filter alpha | 0.1 |
Requirements: MATLAB R2023a or later, Robotics System Toolbox
Generate result plots:
run('src/surgical_force_monitor.m')Generate robot trajectory video:
run('src/record_robot_video.m')- IEC 60601-1 — General requirements for basic safety of medical electrical equipment
- ISO 13485:2016 — Medical devices quality management systems
- ISO 10218-1 — Safety requirements for industrial robots
- Tavakoli et al. (2008). Haptics for Teleoperated Surgical Robotic Systems.
- Okamura (2009). Methods for Haptic Feedback in Teleoperated Robot-Assisted Surgery.
- Puangmali et al. (2008). State-of-the-art in force and tactile sensing for MIS.
Yuvavignesh Balamurugan M.S. Robotics — Arizona State University, May 2026 Seeking Medical Device R&D and Robotics Engineering roles