Robert A. MacLachlan

Micron: An Actively Stabilized Handheld Tool for Microsurgery

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.

Moving object detection with laser scanners

The detection and tracking of moving objects is an essential task in robotics. The CMU-RI Navlab group has developed such a system that uses a laser scanner as its primary sensor. We will describe our algorithm and its use in several applications. Our system worked successfully on indoor and outdoor platforms and with several different kinds and configurations of two-dimensional and three-dimensional laser scanners. The applications vary from collision warning systems, people classification, observing human tracks, and input to a dynamic planner. Several of these systems were evaluated in live field tests and shown to be robust and reliable.

High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing

Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm times 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-mum peak-to-peak resolution at 1-kHz sampling.

Tracking of Moving Objects from a Moving Vehicle Using a Scanning Laser Rangefinder

The capability to use a moving sensor to detect moving objects and predict their future path enables both collision warning systems and autonomous navigation. This paper describes a system that combines linear feature extraction, tracking and a motion evaluator to accurately estimate motion of vehicles and pedestrians with a low rate of false motion reports. The tracker was used in a prototype collision warning system that was tested on two transit buses during 7000 km of regular passenger service

Semiautomated intraocular laser surgery using handheld instruments.

In laser retinal photocoagulation, hundreds of dot‐like burns are applied. We introduce a robot‐assisted technique to enhance the accuracy and reduce the tedium of the procedure.

Vision-Based Control of a Handheld Surgical Micromanipulator With Virtual Fixtures

Performing micromanipulation and delicate operations in submillimeter workspaces is difficult because of destabilizing tremor and imprecise targeting. Accurate micromanipulation is especially important for microsurgical procedures, such as vitreoretinal surgery, to maximize successful outcomes and minimize collateral damage. Robotic aid combined with filtering techniques that suppress tremor frequency bands increases performance; however, if knowledge of the operators goals is available, virtual fixtures have been shown to further improve performance. In this paper, we derive a virtual fixture framework for active handheld micromanipulators that is based on high-bandwidth position measurements rather than forces applied to a robot handle. For applicability in surgical environments, the fixtures are generated in real time from microscope video during the procedure. Additionally, we develop motion scaling behavior around virtual fixtures as a simple and direct extension to the proposed framework. We demonstrate that virtual fixtures significantly outperform tremor cancellation algorithms on a set of synthetic tracing tasks (p <; 0.05). In more medically relevant experiments of vein tracing and membrane peeling in eye phantoms, virtual fixtures can significantly reduce both positioning error and forces applied to tissue (p <; 0.05).

Manipulator Design and Operation of a Six-Degree-of-Freedom Handheld Tremor-Canceling Microsurgical Instrument

This paper presents the design and actuation of a six-degree-of-freedom manipulator for a handheld instrument, known as “Micron,” which performs active tremor compensation during microsurgery. The design incorporates a Gough-Stewart platform based on piezoelectric linear motors, with a specified minimum workspace of a cylinder 4 mm long and 4 mm in diameter at the end-effector. Given the stall force of the motors and the loading typically encountered in vitreoretinal microsurgery, the dimensions of the manipulator are optimized to tolerate a transverse load of 0.2 N on a remote center of motion near the midpoint of the tool shaft. The optimization yields a base diameter of 23 mm and a height of 37 mm. The fully handheld instrument includes a custom-built optical tracking system for control feedback, and an ergonomic housing to serve as a handle. The manipulation performance was investigated in both clamped and handheld conditions. In positioning experiments with varying side loads, the manipulator tolerates a side load up to 0.25 N while tracking a sinusoidal target trajectory with less than 20-μm error. Physiological hand tremor is reduced by about 90% in a pointing task, and error less than 25 μm is achieved in handheld circle tracing.

Safe Robot Driving in Cluttered Environments

The Navlab group at Carnegie Mellon University has a long history of development of automated vehicles and intelligent systems for driver assistance. The earlier work of the group concentrated on road following, cross-country driving, and obstacle detection. The new focus is on short-range sensing, to look all around the vehicle for safe driving. The current system uses video sensing, laser rangefinders, a novel light-stripe rangefinder, software to process each sensor individually, and a map-based fusion system. The complete system has been demonstrated on the Navlab 11 vehicle for monitoring the environment of a vehicle driving through a cluttered urban environment, detecting and tracking fixed objects, moving objects, pedestrians, curbs, and roads.

Experiments with driving modes for urban robots

In this paper, we describe experiments on semi-autonomous control of a small urban robot. Three driving modes allow semi-autonomous control of the robot through video imagery, or by using partial maps of the environment. Performance is analyzed in terms of maximum speed, terrain roughness, environmental conditions, and ease of control. We concentrate the discussion on a driving mode based on visual servoing. In this mode, a template designated in an image is tracked as the robot moves toward the destination designated by the operator. Particular attention is given to the robustness of the tracking with respect to template selection, computational resources, occlusions, and rough motion. The discussion of algorithm performance is based on experiments conducted at Ft. Sam Houston, TX, on Jul. 5-9 1999. In addition to the driving modes themselves, the performance and practicality of an omnidirectional imaging sensor is discussed. In particular, we discuss the typical imaging artifacts due to ambient lighting.

Cell micromanipulation with an active handheld micromanipulator

The paper describes the use of an active handheld micromanipulator, known as Micron, for micromanipulation of cells. The device enables users to manipulate objects on the order of tens of microns in size, with the natural ease of use of a fully handheld tool. Micron senses its own position using a purpose-built microscale optical tracker, estimates the erroneous or undesired component of hand motion, and actively corrects it by deflecting its own tool tip using piezoelectric actuators. Benchtop experiments in tip positioning show that active compensation can reduce positioning error by up to 51% compared to unaided performance. Preliminary experiments in bisection of sea urchin embryos exhibit an increased success rate when performed with the help of Micron.