The basic design criteria of gear reducers involves obtaining the proper operating torques and speeds in specific applications. This initial step is certainly far from meeting the total system requirements in today's demanding applications. Other performance criteria that dictates the choice of one type of gear technology over the other and one manufacturer over another include cost, torsional backlash, efficiency, wear characteristics, ruggedness, quiet operation and more. Since the gear is ultimately mated to a motor, a design that combines the two can provide interesting design parameters including space savings. Three products demonstrate the trend for increased performance.
EMBEDDED PLANETARY GEAR TRAIN
To reduce the size of the gear train and motor, Haydon Switch & Instrument Inc. built the gear train into the motor. The unique design of the pancake motor allows the combination to measure 18.5-mm (0.75-inch) thick and 80-mm (3.15-inch) in diameter. Available with a 3.75 degree step angle and 4:1 gear ratio, the integrated gear train/motor assembly provides up to 85 N-cm (120 oz-inch) of torque. The reversible unit uses radial ball bearings and consumes 14W. Weighing only 343 gm (12 oz), the motor targets applications that requiring accurate positioning and high torque and have limited space.
WITTENSTEIN'S alpha div. LPK+ is a right-angle gearhead designed for cost-sensitive applications. The two- and three-stage gearsets are available in five sizes with acceleration torques up to 250 Nm, torsional backlash limited to less than 10 arc min and a peak speed of 6,000 rpm. The planetary stage on the output side of the right-angle design withstands high timing belt pre-tension in Cartesian robots that use a timing belt drive. High efficiency and the right-angle stage's aluminum housing allow high-speed operation. The design delivers constant torsional backlash and almost zero wear. With 10 reduction ratios from i = 3 to i = 100, the gearhead can be supplied with the rack-and-pinion system and shaft couplings. The units target low-to-medium precision servo applications such as those found in palletizers and loading/unloading robots, positioning feed rate and high-speed axes in packaging machines for feeding, cutting, slotting, erecting and sealing.
Boston Gear Div. of Altra Industrial Motion helical planetary gearheads are designed for direct attachment to popular servo and stepper motors. Compared to spur gearing, the unit's helical technology increases tooth-to-tooth contact ratio by 33 percent. In addition, the 12-degree helix angle produces smooth and quiet operation. Patented input and output sealing designs and special heat and surface treatments for the exterior complement the unit's internal patented planet carrier design. With stainless steel for all exposed gearhead parts and a black anodized aluminum, the standard units provide a rugged design for dry environments. For wet and washdown applications, the housing is epoxy coated. The unit's single piece planet carrier and output shaft design reduces backlash. A single-step machining process provides 100 percent concentricity and increases torsional rigidity. The gearheads target servo applications in packaging, medical, material handling, robotics, automotive and more.