Safe remote surgery over unreliable long-distance connections
Surgeons controlling a robot thousands of kilometers away need sub-millimeter accuracy and force feedback precise enough to distinguish layers of tissue. Long-distance network delays, unpredictable changes in delay and seconds-long outages can cause instrument oscillation or dangerous motion; methods that stabilize control can blunt the surgeon’s sense of touch. Round-trip delays above about 100 milliseconds already impair coordination, yet intercontinental signal travel alone can exceed that. During an outage, replaying old commands or simply freezing instruments can injure tissue as it moves with breathing or deforms under pressure. The challenge is to keep procedures going safely as connections degrade, with useful force feedback and predictable, safe instrument behavior, on the existing robot platform and within Japanese regulatory constraints.
Borrowing the inner ear’s fast and slow gain adjustments, we combine three speeds of control to reduce the safety damping that blurs tissue feel during long-distance robotic surgery.
How it works
Network delay can make a remote surgical robot and the surgeon’s force-feedback handle oscillate. Controllers suppress that motion by adding resistance, but that resistance also masks differences between tissues. Inspired by the inner ear’s regulation of sound amplification across different timescales, we combine three regulators. A local tissue model recreates touch at the surgeon’s handle without waiting for each network round trip; the robot sends updated tissue properties a few times a second. A second regulator adjusts the coupling between handle and robot as network delay and packet loss change. A third checks energy every control cycle and adds damping when needed. All three share one energy budget, including the energy introduced by model updates and control adjustments. This lets us tackle slower disturbances before they require emergency damping, reserving that touch-blunting response for residual fast disturbances and preserving more of the tissue feel.
Borrowing gas-turbine engineers’ use of carefully timed fuel pulses to suppress oscillations, we retime a surgical robot’s force feedback to reduce delay-driven shaking without routinely weakening the forces the surgeon feels.
How it works
In remote surgery, the surgeon feels tissue resistance through a robot, but network delay can make that resistance arrive at the wrong moment and feed an oscillation. Conventional damping steadies the robot at the cost of less distinct force feedback. Combustion engineers tackle a similar problem by timing fuel pulses to counter pressure oscillations. We apply that principle with an adaptive all-pass filter: software that shifts the timing of each frequency component without reducing its magnitude. The controller measures the relationship between force and motion and adjusts the filter toward timing that absorbs energy rather than adding it. A separate energy monitor applies only the corrective damping needed when excess energy appears. This separates feedback quality from safety, so the surgeon retains stronger force cues with less reliance on damping and no model of the tissue.
Borrowing adjustable damping and force clipping from earthquake protection, we replace motors in a surgical robot’s hand controls with fluid brakes that convey resistance without powering unwanted hand movements.
How it works
Surgeons need to feel resistance from tissue through a robot’s hand controls, but communication delays can turn motor-generated feedback into unstable motion. We replace those motors with brakes containing magnetically responsive fluid, borrowing the adjustable resistance used to damp earthquake motion in structures. The brakes can resist the surgeon’s movement but cannot drive it. Software calculates the desired tissue force, then selects the closest resistance the brakes can produce across all six movement axes together. This borrows earthquake engineers’ “clipped-optimal” control: calculate the ideal force, then trim it to what a passive device can deliver. An energy monitor checks the communication link and requests extra braking when needed to absorb excess energy. Wrist vibrations and visual cues convey force information the brakes cannot reproduce. Permanent magnets hold the brakes engaged when power disappears. This puts the limit on powered hand movement into the hardware, while software adjusts how closely the feedback resembles contact with tissue.