Case Study: CMM Assists With Ventricular Device
The makers of the Jarvik 2000 artificial heart-technically a left ventricular assist device-are now getting a manufacturing assist from the Sheffield Discovery II Coordinate Measuring Machine (CMM). Robert Jarvik, M.D., the inventor of the Jarvik 2000 device, oversees development of the artificial heart at Jarvik Heart Inc. (New York City). The Discovery II, manufactured by Sheffield Automation (Fond du Lac, WI), is an automated three-dimensional measurement device for high-precision manufactured parts.
The Jarvik 2000, essentially a miniature pump, has already been implanted in more than 40 patients in the United States and Europe. It is intended to be a complement to the heart's function, rather than be a complete heart replacement. Implanted inside the left ventricle, the device pumps up to six liters of oxygenated blood a minute through the heart, in cooperation with the heart beat. In U.S. clinical trials, the Jarvik 2000 has been used as a bridge-to-transplant device, helping ill patients' hearts function until a donor heart is found. In Europe, the device has also been implanted as a lifetime-use device for candidates unsuitable for heart transplants. The first patient to receive one for this purpose is still surviving after more than two years on the device. According to Dr. Jarvik, the device is not solely intended to be a bridge-to-transplant, as it has been used thus far in the United States, but a permanent device that can help rehabilitate patients with severe congestive heart failure to a normal lifestyle.
The Jarvik 2000 is approximately the size of a C cell battery, fabricated primarily out of titanium and ceramic components. The pumping action is valveless, operating by means of a rotary impeller, which is suspended in the bloodstream and spins on ceramic bearings using magnetic induction. The pump's blades spin between 8,000 to 12,000 rpm, and are adjustable by the user based on his level of physical activity.
Jarvik Heart Inc. manufactures many of the critical parts in a suite of offices in midtown Manhattan. The Sheffield Discovery II CMM was purchased to assist with R&D and manufacturing quality control. Quality checking of manufactured parts is critical for the Jarvik 2000 device-100% of the manufactured parts are checked in all critical dimensions. According to Dr. Jarvik, they are now working on incremental improvements in the design, manufacture and assembly of the miniature components of the Jarvik 2000.
At first, Jarvik was looking for a vision machine, but found it limited for many of the parts they needed to inspect, particularly precision conical forms. Sheffield representative, John Dorsi of JAD Specialty, showed Dr. Jarvik the Discovery II, which turned out to be well suited to his needs. "We were looking for a versatile machine that was accurate," says Dr. Jarvik. "The main thing was for the inspection routine to be fully motorized and automated. We wanted the program to run the inspection and get away from any operator variation in the measured results."
The Discovery II CMM, a fully CNC-controlled device, once programmed, can run repeatable measurements with minimal operator input. Programming the CMM for new parts is also a simplified function requiring comparatively little training. Machine tool operators familiar with part drawing symbols can create new inspection routines by following simple, step-by-step screen prompts.
Another feature that made the Discovery II appealing was the automatic temperature compensation-a standard feature on all Sheffield CMMs. According to Dr. Jarvik, "The machine is not located in a clean room, so the environment doesn't have the same degree of temperature control that a clean room would, it's probably plus or minus 2 degrees." Despite the variability of operating conditions, Jarvik's Discovery II maintains the 2.5 micron repeatability required for the accurate dimensional inspection of tight-tolerance miniature components. The machine is also equipped with an optional part thermistor to monitor and compensate for the ambient temperature of the part itself.
Finally, the fact that the Discovery II runs on high precision recirculating ball bearings and has no need for an air supply like most other CMMs, meant that Jarvik Heart Inc. could move the machine anywhere it was needed, without regard for an air supply connection.
The long-term goal for the Jarvik 2000 is to make it accessible to all cardiac surgery centers, so that many more patients can benefit. The Discovery II CMM will help Jarvik Heart Inc. ensure consistently high part quality as production volumes increase.
The Jarvik 2000 can help people with congestive heart failure enjoy better quality of life and increased chance of survival. And that is good news by any measure.
Giddings and Lewis LLC
Controls Measurement & Sensing