Meet Dr. Robot

December 5, 2005

7 Min Read
Meet Dr. Robot

Advances in minimally-invasive surgery and medical imaging have led to enormous gains in health care, but new robotic systems could bring even more benefits to patients.

One system, designed by Intuitive Surgical in California, harnesses intricately designed surgical tools that mimic the hand motions of a physician seated a few feet away. The goal: smaller incisions, more precise surgery, and faster patient recovery.

Another robotic design, developed by engineers in Germany, lets doctors take advantage of today's high-quality diagnostic imaging and administer treatment while patients are still within a magnetic resonance imaging chamber.

Both systems pioneer new approaches in mechanical components, motion control, and imaging. For a look at those innovations go to http://rbi.ims.ca/4420-500.

With da Vinci, It's All Intuitive

In the '90s, California's SRI International, backed by DARPA funds, began work on a telerobot system that would allow surgeons to tend battlefield wounds out of harms way. In this decade, Intuitive Surgical has leveraged that core SRI technology into a highly precise tool that takes minimally-invasive surgery to a whole new level.

Intuitive's da Vinci® Surgical System consists of an ergonomically-designed surgeon's console, a high-resolution 3D imaging system, and a patient-side cart equipped with four robotic arms. Seated at the console, the physician positions and controls the robotic arms, which hold tiny surgical instruments and a custom-designed, dual-lens endoscope.

A bedside physician first makes a series of 1 to 2 cm incisions for cannulae through which the endoscope and miniature instruments are passed. The surgeon at the console then peers through a viewer that shows 3D images of the operating field captured by the 12-mm-diameter endoscope. When he is ready to operate, the surgeon grasps a set of "master" hand controls located below the video display. When he twists his wrists and moves his forefingers and thumbs as he would in a normal surgical procedure, the system translates those same movements in real-time to the instruments operating inside the patient. By tapping a foot pedal switch, the surgeon changes the system from controlling the endoscope position to controlling movements.

"Achieving the high-fidelity motion from the surgeon's master controls to the robot slave's micro instruments was probably the most challenging part of the design." notes VP of Engineering Sal Brogna.

The system uses 39 servo-controlled axes, featuring Maxon miniature DC brushed motors located on each of the robotic arms. As Brogna explains, the servo system, together with a network of encoders, brakes, (Kebco) and potentiometers (JDK Controls), combine to provide some force feedback to the surgeon's hands—much like the resistance felt when moving large tissue in a conventional "open" surgery. This power train is designed to achieve light action, low inertia, and zero backlash.

"The amount of mechanical design in this system is incredible, as is the complexity of the software and electronics that connects the master and slave," says engineer David Rosa, director of product development. "Our goal was to bring the precision and dexterity that surgeons have in open surgery to minimally invasive surgery, and robotics was the best way to do that."

Metal injection molding is used to manufacture many of the micro instruments, which the company calls "EndoWrists." These instruments take a number of forms—forceps, scalpels, needle drivers, scissors and other specialized devices— and are available in 5- or 8-mm diameter shaft sizes. A system of cables, bearings and pulley run the length of the instruments, allowing seven degrees of freedom—much like human tendons. Quick release levers let surgery personnel mount a new instrument to a robotic arm in seconds, and the system automatically recognizes the new device. A chip inside each instrument tracks the number of procedures, so the device can be replaced before it undergoes excessive wear.

Intuitive Surgical sees da Vinci as a key tool to broaden the application of minimally invasive surgery to include more complex operations. Already, surgeons have used the system to perform more than 100 different operations, ranging from general surgery to repairing heart valves. Increasingly, surgeons have employed the technique in prostatectomies, where the system's high precision has reduced the incidence of severed nerves that can cause impotence and incontinence.

More than 300 medical facilities have installed the $1.3 million system.

Telerobot Expands MRI Potential

For years, physicians have longed for a system that would allow them to both obtain precise medical images and administer a drug or perform a biopsy while the patient remains inside the MRI chamber.

That's a tall order. The powerful magnetic field within MRI chambers rules out ferromagnetic materials in the treatment zone. What's more, high-frequency waves within the system inhibit the use of electronics.

A new robotic device promises to overcome those obstacles. Designed by Innomedic GmbH, the pneumatically-driven Innomotion system boasts several innovations that could make scanning and treatment possible in one procedure. Among the major components:

  • Robot arm and manipulator with five degrees of freedom. Mounted on a C-arc frame and fastened to the table on which the patient rests, this assembly slides into the MRI chamber and is comprised entirely of non-ferromagnetic components, such as reinforced plastics and ceramics.

  • A supply unit that houses the control PC and delivers electricity and compressed air.

  • System cart, containing the electronics for I/O, pneumatic valves, and sensor interfaces.

  • An HMI, operated with a mouse or touch screen, which provides the physician with a graphical user interface to plan and control medical intervention.

  • Special fiber optic sensors, both linear and rotary, that are made entirely from glass, plastic and ceramics for MRI compatibility.

  • Pneumatic actuators, also fully MRI compatible, that provide accurate positioning (to & 0.1 mm) of the guidance system used to administer treatment. One pneumatic cylinder, controlled by two servo vales, drives each axis of the robot.

In a typical procedure, the physician scans the patient to obtain a specific desired image, which he reviews for intervention planning on the system's HMI. Innomotion's software determines the optimum insertion point for therapy, and the robot arm within the MRI chamber then moves to that location on the patient's body, where the physician inserts the therapeutic instrument through a guideway. Treatment options will include pain therapy, tumor therapy, and biopsies.

"To our knowledge, there are no other similar MRI-compatible systems on the market," says Thomas Remmele, managing director for Innomedic, which developed the system in cooperation with the Karlsruhe Research Center.

Self-Healing Motion Network

Finding a control scheme that would not compromise patient safety was also a major consideration. "Just imagine that you're a patient lying in the MRI tube, and the robot is placing its arm on your back. Then, all of a sudden a cable breaks," says Patrick Gurny of Motion Engineering Inc., the Danaher unit that supplied the control system.

That unpleasant scenario wouldn't defeat MEI's SynqNet® servo control system. In the event of a cable break or loose connection, the SynqNet hardware re-routes the data path within two servo cycles, and the network connection remains available. At the same time, the application is informed about the event, allowing the medical device to finish its move sequence. In addition, each node has its own watchdog timer, so that even if the whole network fails, the individual nodes can react in a predictable way for a safe shutdown.

Remmele of Innomedic adds that SynqNet can provide distributed control I/O even through a fiber optic network, which was very important to this application. The XMP controller from MEI is located inside Innomotion's control PC, which operates about five meters from the MRI scanner, where the magnetic field is not too strong. The setup required an optical Ethernet solution, and the fact that SynqNet uses standard Ethernet protocol allowed the designers to use off-the-shelf components to convert the wire Ethernet to optical Ethernet.

Together, the new technologies built into the Innomotion system have resulted in "very positive preclinical trials," says Remmele. The system is already CE-marked and is ready for the European market.

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