Researchers have developed a compact 3-DoF delta robot with onboard visual feedback, delivering micrometer-level precision and disturbance rejection for portable medical tools like catheters and microsurgical devices.
Study: Onboard visual micro-servoing on robotic surgery tools. Image Credit: Fit Ztudio/Shutterstock.com
The study, published in Nature, tackles a core challenge in medical robotics—combining high precision with a portable design. Using piezoelectric benders, origami-inspired compliant structures, and additive manufacturing, the team built a mechanism that delivers stable, backlash-free motion. An integrated camera system tracks AprilTag markers in real time, enabling closed-loop control that maintains 7.5 µm accuracy and 10 µm resolution while actively compensating for external forces.
This level of precision is vital for delicate procedures like endomicroscopy, where clinicians must navigate optical fibers through narrow passages without harming surrounding tissue. Most existing systems either rely on bulky external sensors or operate in open-loop mode, both of which reduce portability and reliability.
How the Robot Works
At the heart of the robot are three piezoelectric cantilever beams anchored to a fixed base. When voltage is applied, each beam bends slightly—movements measured in micrometers—that are transferred to the robot’s end platform through thin, flexible “blade” joints. These joints, known as flexures, replace traditional hinges and bearings, eliminating mechanical backlash and ensuring exceptionally smooth, repeatable motion.
The design was fine-tuned using a pseudo-rigid-body model and electromechanical simulations, later confirmed through finite element analysis. To push accuracy even further, the team trained a neural network to correct small variations caused by the manufacturing process.
For position tracking, the robot carries its own ϕ 3.9 mm borescope camera, capturing images at 30 frames per second. AprilTag markers on the moving platform act as visual references. Using a technique called pose-based visual servoing, the system converts the marker’s position in pixels into exact real-world coordinates. A PID controller with feedforward compensation then adjusts the actuators in real time, keeping the motion on target and rejecting disturbances.
Tested for Accuracy and Robustness
In laboratory trials, the robot demonstrated:
- High-precision path tracking: Able to follow circular paths (0.1–0.5 mm radius) at 0.25 mm/second with RMS errors below 7.5 µm in the X and Y directions.
- Fine-step resolution: Consistently executed 10 µm incremental movements.
- Disturbance recovery: Maintained accurate motion even when a 200 mg weight was added, with the visual feedback loop automatically correcting the trajectory.
These results place the device in the same performance class as state-of-the-art micromanipulators—but in a much smaller package, with simpler fabrication and built-in sensing.
Why it Matters
By combining actuation, sensing, and control into a single self-contained unit, this robot removes the need for bulky external equipment. Its compact, precise, and portable design makes it particularly promising for catheter steering and microsurgery, where even a few micrometers can mean the difference between success and failure.
Journal Reference
Chen, X., Kiziroglou, M. E., & Yeatman, E. M. (2025). Onboard visual micro-servoing on robotic surgery tools. Microsystems & Nanoengineering, 11(1). DOI: 10.1038/s41378-025-00955-x. https://www.nature.com/articles/s41378-025-00955-x
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