What is Closed Loop Feedback Control?
If you have spent time around robotics, surgical or otherwise, you have probably heard the phrase closed loop feedback control. It is one of those foundational engineering concepts that quietly powers everything from drones to industrial arms. But in medicine, closed loop control is still in its early innings, especially when it comes to flexible robotic systems navigating inside the human body.
As the Medtech world moves rapidly toward robotic assistance, AI guidance, and eventually autonomy, it is worth slowing down to ask: What does closed loop feedback actually mean? And why is it so important for flexible procedures like endoscopy, bronchoscopy, and endovascular navigation?
Most importantly, why is shape sensing the only technology that can make true closed loop control possible for these systems?
Let’s break it down.
Open Loop vs. Closed Loop: The Simplest Explanation
For decades, X-ray fluoroscopy and CT have been the workhorses of interventional procedures. An open loop system is one that acts but does not check. It assumes everything is going according to plan.
You tell a robot arm, “Move 10 degrees.”
It moves 10 degrees.
Whether it overshoots, undershoots, hits resistance, bends the tool, or collides with tissue is unknown to the system. The robot executed a command, but it has no idea what actually happened.
That is open loop control.
Closed loop control works differently. Instead of assuming the world behaved as expected, the system measures what actually happened, compares it to the intended outcome, and adjusts in real time.
You tell the robot, “Move 10 degrees.”
It starts to move.
Sensors report how far it actually moved.
The controller compares the target to the actual value.
If it is off by even a small amount, the robot corrects immediately.
Closed loop control is how robots maintain stability, stay on course, reject disturbances, and execute precise actions in unpredictable environments. Without it, robotic systems behave like someone trying to drive a car with their eyes closed.
Why Closed Loop Is So Hard Inside the Body
In industrial robotics, closed loop control is straightforward because the robot joints are rigid, the environment is predictable, and sensors tell you exactly where everything is.
Inside the human body, none of that is true.
Flexible robots and long instruments bend differently depending on anatomy, tissue interaction, torque, patient movement, and even gravity. A bronchoscope does not behave the same way in one patient as it does in another. A guidewire can take entirely different shapes in tortuous vasculature compared to a straight training model.
If the system cannot sense its own shape, it cannot know whether the commanded motion produced the intended effect. This is what has held back closed loop control in flexible interventions for decades.
Legacy navigation systems do not solve this problem.
EM tracking gives you one point.
Impedance tracking gives you a tip estimate.
Fluoroscopy gives you a 2D snapshot with radiation.
None of these provide the continuous, real-time shape information required for control. When you cannot see the whole shape, you cannot close the loop.
What Closed Loop Feedback Control Looks Like in a Flexible Robot
FImagine a soft robotic endoscope navigating the colon. The robot issues a small steering command to advance around a curve. Immediately, reality intervenes.
Tissue contact changes the bending radius.
The shaft twists slightly.
The distal segment flexes more than expected.
An open loop system keeps trying to push forward blindly, often causing buckling or loop formation. This is why traditional colonoscopy requires constant manual adjustments by a human expert who is, in effect, closing the loop through experience and visual cues.
A closed loop flexible robot behaves very differently.
It issues a steering command.
Shape sensing measures the actual deformation along the entire length of the device.
The controller detects that the middle segment bent more than the tip.
It automatically adjusts forces, torques, and insertion depth to maintain stability and progress.
This is the foundation of true robotic assistance in flexible procedures. Without real-time knowledge of the device shape, none of this is possible.
Why Shape Sensing Is the Key to Closing the Loop
Only full-length shape sensing provides the information needed for closed loop control inside the body. The robot needs a complete picture of its own state in order to:
- Maintain stability along long, flexible shafts
- Detect and correct unwanted bends, twists, and loops
- Respond to tissue contact instantly
- Navigate variable patient anatomy safely
- Execute AI-guided and eventually autonomous actions
- Build a reliable data layer for future robotic intelligence
No point-based system can deliver this. Only distributed shape data along the entire device provides the input required for precise, responsive control.
Without shape sensing, flexible robotic systems will always be limited to open loop behavior. With shape sensing, the door opens to stability, precision, automation, and ultimately autonomy in ways that the field has never seen before.
The Future: Closed Loop Everything
As robotics continue to move deeper into interventional medicine, closed loop control will become the standard for safety, consistency, and performance.
Flexible robots will use shape sensing to adapt in real time.
AI systems will optimize navigation and force application.
Autonomous behaviors will rely on continuous feedback to make decisions.
Procedural intelligence will emerge from thousands of shape-informed data points collected along every device, in every procedure.
Closed loop control is not just an engineering concept. It is the backbone of the future of minimally invasive care. And shape sensing is the enabling layer that makes it possible.
Flexible systems cannot close the loop without knowing their own shape. Shape sensing finally gives them that ability.
This is why shape sensing will define the next generation of robotic interventions.
Interested in leveraging full-length shape sensing for your next-generation medical devices? Contact us to explore collaboration opportunities.
