The Slow Speeds of Surgery

Surgical robots continue to perform operations and get FDA approvals in this country. Several key components in these robots are motors that provide non-cogging operation even at low speeds.

—By Matt Badger, sales engineer, Maxon Precision Motor

Surgery performed today using the da Vinci Surgical System allows surgeons to perform the most minimally invasive procedures to date. The unit, manufactured by Intuitive Surgical Inc, Sunnyvale, CA, requires every motion to provide the smooth, accurate movements of a skilled surgeon, even at slow, calculated speeds. To accomplish this involves reliable, high-quality components and controls. One — more precisely, thirty-six — of those components happen to be motors manufactured by Maxon Precision Motors, Burlingame, CA.

The Surgical System

The da Vinci Surgical System was designed to be integral to the operating room. It had to support the entire surgical team, just as every other member of the operation. The entire system consists of three distinct components, which includes the surgeon console, patient-side cart that holds the instruments, and the image processing equipment. To insert the system’s two manipulators and camera requires just three incisions in a patient — two 8 mm and one 12 mm wide. The robot hovers over the patient, while the surgeon/operator can be across the room at the Console. However, the look and feel of the open surgery is duplicated with precision.

The Surgeon Console is central to the ability to operate. Other attempts at performing surgery via video proved difficult. There was always a problem of directional reversals — think of tying your shoes with chopsticks. When you move the chopsticks to the left, the tip moves to the right. These counter-intuitive movements, as experienced in traditional laparoscopic surgery, needed to be overcome by the surgeon through experience.

With the da Vinci Surgical System, the surgeon operates while comfortably seated, viewing a 3-D image of the surgical field. A high-performance vision system provides true-to-life 3-D images of the operative field, and is controlled from the console through foot pedals. Operating images are enhanced, refined, and optimized using image synchronizers, high-intensity illuminators and camera control units.

A full range of optional EndoWrist Instruments are provided for the system. These instruments are designed with seven degrees of motion that mimics the dexterity of the human wrist. Each instrument has a specific surgical mission such as clamping, suturing, and tissue manipulation. At the console, the surgeon’s fingers grasp master controls below the display with wrists naturally positioned relative to his or her eyes. The surgeon’s wrist, hand, and finger movements are then seamlessly translated to robotic manipulators inside the patient as precise, realtime movements, just as a typical surgery would be.

The patient-side cart houses the two robotic arms and one Endoscope arm. The laparoscopic arms pivot at the operating port, eliminating the use of the patient’s body wall for leverage, minimizing tissue and nerve damage. Supporting surgical team members install the correct instruments, prepare the port in the patient, and supervise the laparoscopic arms and tools being used.

Motion and the Right Motors

Highly accurate motion control is necessary when manipulating robotic surgical tools through small holes (8 mm to 1 cm) to perform an operation inside the human body. At the heart of each manipulator in the da Vinci System are DC servomotors designed and manufactured by Maxon.

The same motors are use used on the surgeon’s side (master) as on the manipultor end (slave). Through a series of feedback controls, the motors and encoders receive inputs from the surgeon, are translated in real-time through the console electronics, and provide output signals to the motors in the manipulators. In turn, the manipulators exert forces back through the console electronics to the surgeon’s hands.

For the da Vinci System, Intuitive engineers selected twenty-seven RE 25 motors, some with and some without encoder feedback; seven RE 13 mm motors equipped with GP 13 series gearheads and 13 mm magnetic encoders; and two RE 35 series motors with third-party encoders. Maxon motors are designed with rare earth magnets in their stators, and incorporate an ironless rotor design that eliminates magnetic cogging, even at slow operating speeds. The motors offer good power density and smooth rotation, both of which are important to the Intuitive application. The motors also exhibit low hysteresis at the instrument tips

The da Vinci Surgical System is presently the only commercially available technology that can provide the surgeon with the intuitive control, range of motion, fine tissue manipulation capability, and 3-D visualization characteristic of open surgery, while simultaneously allowing the surgeon to work through small, minimally invasive ports. The availability of motors and other components that are designed and manufactured using the latest technologies allows such systems to enter the marketplace.

The da Vinci Surgical System is based on foundational robotic surgery technology developed at SRI (formerly known as Stanford Research Institute). Intuitive Surgical later formed relationships with IBM, Massachusetts Institute of Technology, and Heartport, Inc. to further develop the system. The FDA approved the system in July 2000 for use in such abdominal surgery as gall bladders and colon surgery, in March 2001 for chest surgery excluding the heart, and in July 2001 for prostate surgery. The da Vinci System is already used in Europe for heart bypass procedures.

Robotic Bypass Surgery

Arthur Barrett, 70, of Cedar Grove, NJ, received the first U.S. robot-assisted coronary bypass operation that required no chest incision. The operation was successfully performed in January 2002 at the Columbia Presbyterian Medical Center in New York City by surgeons using the da Vinci Surgical System designed by Intuitive Surgical Inc.

The surgery, which replaced an almost completely blocked major artery in his heart, was a success. Barret has been quoted as saying, “I felt like I took the least invasive way to go.” There were only three incisions — two 8 mm holes for the tools and one 12 mm hole for the camera. The procedure itself took only seven hours.

Typically, coronary bypass surgery requires an eight-to-10-in. incision in the chest. The incision has to cut through the breastbone and chest muscle to allow enough space for the surgeon’s hands, as well as visual space. These incisions can double or triple a patient’s recovery period over that which is needed for robotic surgery. Further, it can greatly reduce the pain associated with the surgery, reduce the chances of infection, and produces far less scarring.

The operation was part of a clinical trial, sanctioned by the Food and Drug Administration, for the hospital to test the surgical robot in three different types of heart operations: repairing the mitral valve; closing a hole between two chambers of the heart, and the coronary bypass operation. The hospital surgeons were required to train for more than a year to use the robot. They had to perform numerous operations on animals and parts of operations on humans in order to familiarize themselves with all the steps needed to do the job.

Columbia Presbyterian and 10 other medical centers will perform 125 coronary bypass operations as a part of the current FDA trial.