Few markets are more competitive than the one for large screen televisions. In that segment, even a slight technological advantage can provide a cost reduction that sends sales soaring. When studying one of the product lines in that segment, Shinano Kenshi discovered a means to provide such an advantage.

Shinano Kenshi is a company that routinely looks for ways to apply technology used in one application as a possible solution for another. In this particular case, the company examined the fluid dynamic bearing technology found in polygon scanner motors for the laser printer and office peripheral industries. In doing so, it realized that the FDB motor could also provide benefits to big screen televisions that use Texas Instruments’ digital light processing technology. The FDB motor was a good approach to provide cost-savings opportunities because both technologies were mirror-based and had similar needs in regards to motor balancing and longevity.

Cross sections of bronze bearings showing how the oil-bearing grooves are cut.

The company’s challenge was to design a cost-effective motor that was quiet, worked at speeds up to 11,000 RPM and offered different balancing options. And most important for this application, the motor had to provide long life at a lower unit cost. In a laser printer the motor must spin at speeds up to 40,000 RPM. Since this is faster than a ball bearing can reliably handle, use of ball bearings would lead to shorter motor life in this application.

Consumers spending a significant amount of money for a big screen television expect the product to last, so longevity has developed into a key marketing difference among such products. Shinano Kenshi realized that if the FDB motor worked for laser printers, it could also be adapted for DLP-based televisions, some of which were using air bearing motors. As a result, the company’s development efforts produced an FDB long-life motor for half the unit cost of the air bearing motor used in such applications.

Cross sections of bronze bearings showing how the oil-bearing grooves are cut.

Fluid dynamic bearings are able to deliver long life by minimizing contact of mating metal parts. The radial movement involves zero contact. And although the axial movement allows the bottom of the shaft to contact metal, it is not a load-bearing situation, and, therefore, does not affect bearing life.

The FDB motor uses a high-pressure oil system. Herringbone-shaped grooves are coined into the bronze bearings and the grooves are filled with an oil based on a proprietary formula. When the motor’s steel shaft spins, the bearings remain stationary and the oil moves forward, building up the pressure. The oil is captured on the wide end of the chevrons and is pushed toward the narrow end. Thus, the oil itself becomes the actual bearing surface. The oil turns, not the bearings. As the shaft rotates, oil is pulled through the herringbone where a high-pressure ring or hydrodynamic journal is created in the center. The design of the technology allows the oil to remain in the bearing up to 40,000 H of usage.

The FDB motor was well-suited for this particular application because of the way DLP technology operates. The system utilizes a digital chip containing millions of microscopic mirrors, each reflecting a single pixel. The chip is driven in conjunction with a digital signal, light source, projection lens and a colorwheel filter.

The colorwheel is placed between the light source and the mirror panel. As light goes through the colorwheel, each mirror is coordinated to bounce its light up onto the screen. As the wheel spins, red, green and blue light falls sequentially on the colored mirrors, and each mirror tilts toward or away from the light source to produce color combinations of up to 16 million different colors.

In a laser printer, the FDB motor must provide a great deal of stability. Since the laser printer operates with a precise system of mirrors, if there is any pyramidal angle error, the printed material comes out fuzzy.

Similarly, the DLP technology depends on mounting a 50 mm colorwheel filter to the motor that must operate with the same precision. That need is what made the FDB motor suited for driving a DLP colorwheel.

The FDB motor must provide a very stable base before the colorwheel is added to provide easier balancing. If the motor is not stable enough to allow the optimal balance, the television’s picture will be distorted and the color will be off.

The actual balancing is done by the customer, the maker of the television. But Shinano Kenshi provides a stable foundation through the use of dual-plane balancing that allows for precise balancing by the manufacturer. The two planes of the motor are separated by 10 mm. This advantage is similar to balancing a tire. Weights must be applied to both the inside and outside of the rim for more precision balance. The separation of the planes on the FDB motor allows the manufacturer to have more options for balancing. Some manufacturers will add epoxy glue for the balance. Others choose to drill out material to achieve the optimal balance.

Heat is another factor affecting the life of a colorwheel motor in a DLP television, since a single lamp is used to illuminate a 60-in. screen and subjects the motor to constant heat when activated. The FDB colorwheel motor developed by Shinano Kenshi is rated 85 DegC (185 DegF) and tested out at 90 DegC (194 DegF). The motor was developed in both 14 mm and 24 mm versions, so it can accommodate a wide range of colorwheel diameters.

Sawato Aizeki is staff engineer and Albert Melshenker is creative director at Shinano Kenshi, Culver City, Calif.