Tiny Encoder Ideal for Medical Application
7.5-mm micro encoder provides motor control solution for biopsy device
By Design News Staff -- Design News, November 1, 2009
SenoRx is an Irvine, CA company that designs and manufactures minimally invasive devices for the diagnosis and treatment of breast cancer. One of these devices is the EnCor®, which allows a doctor to remove a small amount of tissue from the breast for biopsy. The device is handheld and uses vacuum-assisted technology (VAB) resulting in a minimally invasive procedure.
Keeping the overall size of the EnCor device small enough for a surgeon to hold and maneuver with one hand was critical during the design stage. To achieve this objective, some of the smallest components in the world had to be accurately manufactured. Key to the operation of the EnCor device is the implementation of three tiny motors used to manipulate the disposable portion of the device within a strong magnetic field as needed by the medical staff. To precisely control these movements, the SenoRx staff needed to find an optical encoder small enough to mate with these miniature motors and still maintain the inherent high level of accuracy.
John Galaway, a sales manager at CUI Inc., received the call from SenoRx's engineering team. "SenoRx contacted me with a very specific problem," he says. "They were having a difficult time finding a supplier that could meet their size, resolution and reliability requirements in one package. After reviewing their needs, we were able to determine that our MES6 encoder could meet their difficult criteria."
CUI's MES6 incremental optical encoder has a package diameter of 7.5 mm, which is roughly the size of a pencil eraser. The EnCor device utilizes the 100 ppr model, though available output resolutions range from 100–360 ppr. The key to this device is the chemically etched patterns, both a fine and a coarse that produce the necessary pulse sequence. This manufacturing process allows for highly detailed and accurate steps in a 6-mm optical disc. This, coupled with the 6-mm PCB layers, allows the device to accurately produce pulses up 360 ppr and still maintain a 7.5-mm package. Typically, resolutions in this range are offered by encoders three times the diameter of the MES6, but thanks to advanced design and production techniques that have been refined over many years, CUI has been able to deliver accurate and precise position information in a smaller size than most optical encoders.
"We chose the MES6 because of its compact size and precision," says Martin Shabaz, senior staff engineer at SenoRx. "Its accuracy and repeatability are outstanding."
