There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Microrobots have the potential to revolutionize many aspects of medicine. These untethered, wirelessly controlled and powered devices will make existing therapeutic and diagnostic procedures less invasive and will enable new procedures never before possible. The aim of this review is threefold: first, to provide a comprehensive survey of the technological state of the art in medical microrobots; second, to explore the potential impact of medical microrobots and inspire future research in this field; and third, to provide a collection of valuable information and engineering tools for the design of medical microrobots.

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Microrobots for Minimally Invasive Medicine

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

This paper provides a broad overview of medical robot systems used in surgery. After introducing basic concepts of computer-integrated surgery, surgical CAD/CAM, and surgical assistants, it discusses some of the major design issues particular to medical robots. It then illustrates these issues and the broader themes introduced earlier with examples of current surgical CAD/CAM and surgical assistant systems. Finally, it provides a brief synopsis of current research challenges and closes with a few thoughts on the research/industry/clinician teamwork that is essential for progress in the field.

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Medical robotics in computer-integrated surgery

In this paper, we describe the state of the art in continuum robot manipulators and systems intended for application to interventional medicine. Inspired by biological trunks, tentacles, and snakes, continuum robot designs can traverse confined spaces, manipulate objects in complex environments, and conform to curvilinear paths in space. In addition, many designs offer inherent structural compliance and ease of miniaturization. After decades of pioneering research, a host of designs have now been investigated and have demonstrated capabilities beyond the scope of conventional rigid-link robots. Recently, we have seen increasing efforts aimed at leveraging these qualities to improve the frontiers of minimally invasive surgical interventions. Several concepts have now been commercialized, which are inspiring and enabling a current paradigm shift in surgical approaches toward flexible access routes, e.g., through natural orifices such as the nose. In this paper, we provide an overview of the current state of this field from the perspectives of both robotics science and medical applications. We discuss relevant research in design, modeling, control, and sensing for continuum manipulators, and we highlight how this work is being used to build robotic systems for specific surgical procedures. We provide perspective for the future by discussing current limitations, open questions, and challenges.

Continuum Robots for Medical Applications: A Survey

Effective employment of piezoelectric actuators in microscale dynamic trajectory-tracking applications is limited by two factors: 1) the intrinsic hysteretic behavior of piezoelectric ceramic and 2) structural vibration as a result of the actuator's own mass, stiffness, and damping properties. While hysteresis is rate-independent, structural vibration increases as the piezoelectric actuator is driven closer to its resonant frequency. Instead of separately modeling the two interacting dynamic effects, this work treats their combined effect phenomenologically and proposes a rate-dependent modified Prandtl-Ishlinskii operator to account for the hysteretic nonlinearity of a piezoelectric actuator at varying actuation frequency. It is shown experimentally that the relationship between the slope of the hysteretic loading curve and the rate of control input can be modeled by a linear function up to a driving frequency of 40 Hz

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Feedforward Controller With Inverse Rate-Dependent Model for Piezoelectric Actuators in Trajectory-Tracking Applications

Physiological hand tremor impedes microsurgery. We present both a novel adaptive algorithm for tremor estimation and a new technique for active real-time cancelling of physiological tremor. Tremor is modeled online using the weighted-frequency Fourier linear combiner (WFLC). This adaptive algorithm models tremor as a modulating sinusoid, and tracks its frequency, amplitude and phase. Piezoelectric actuators move the surgical instrument tip in opposition to the motion of tremor, effectively subtracting the tremor from the total motion. We demonstrate the technique in 1D using a cantilever apparatus as a benchtop simulation of the surgical instrument. Actual hand motion, prerecorded during simulated surgery, is used as input. In 25 tests, WFLC tremor compensation reduces the RMS tip motion in the 6-16 Hz tremor band by 67%, and reduces the RMS error with respect to an a posteriori estimate of voluntary motion by 30%. The technique can be implemented in a hand-held microsurgical instrument.

Adaptive cancelling of physiological tremor for improved precision in microsurgery

This paper describes research in active instruments for enhanced accuracy in microsurgery. The aim is to make accuracy enhancement as transparent to the surgeon as possible. Rather than using a robotic arm, we have taken the novel approach of developing a handheld instrument that senses its own movement, distinguishes between desired and undesired motion, and deflects its tip to perform active compensation of the undesired component. The research has therefore required work in quantification and modeling of instrument motion, filtering algorithms for tremor and other erroneous movements, and development of handheld electromechanical systems to perform active error compensation. The paper introduces the systems developed in this research and presents preliminary results.

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Toward active tremor canceling in handheld microsurgical instruments

We describe the design and performance of a handheld actively stabilized tool to increase accuracy in microsurgery or other precision manipulation. It removes involuntary motion, such as tremor, by the actuation of the tip to counteract the effect of the undesired handle motion. The key components are a 3-degree-of-freedom (DOF) piezoelectric manipulator that has a 400-μm range of motion, 1-N force capability, and bandwidth over 100 Hz, and an optical position-measurement subsystem that acquires the tool pose with 4-μm resolution at 2000 samples/s. A control system using these components attenuates hand motion by at least 15 dB (a fivefold reduction). By the consideration of the effect of the frequency response of Micron on the human visual feedback loop, we have developed a filter that reduces unintentional motion, yet preserves the intuitive eye-hand coordination. We evaluated the effectiveness of Micron by measuring the accuracy of the human/machine system in three simple manipulation tasks. Handheld testing by three eye surgeons and three nonsurgeons showed a reduction in the position error of between 32% and 52%, depending on the error metric.

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Micron: An Actively Stabilized Handheld Tool for Microsurgery

As flexible bevel tip needles are inserted into tissue, a deflection force causes the needle to bend with a curvature dependent on relative stiffness and bevel angle. By constantly spinning the needle during insertion, the bevel angle is essentially negated and a straight trajectory can be achieved. Incorporating duty-cycled spinning during needle insertion provides proportional control of the curvature of the needle trajectory through tissue. This paper proposes a kinematic model for needle steering via duty-cycled spinning. Validation using experimental results is also presented.

Cameron N. Riviere

Papers

Feedforward Controller With Inverse Rate-Dependent Model for Piezoelectric Actuators in Trajectory-Tracking Applications

Adaptive cancelling of physiological tremor for improved precision in microsurgery

Toward active tremor canceling in handheld microsurgical instruments

Micron: An Actively Stabilized Handheld Tool for Microsurgery

Modeling of Needle Steering via Duty-Cycled Spinning