Small improvements make big results. That philosophy, which the Japanese call Kaizen, serves as a guiding principle to the companies of Sumitomo--a trillion-dollar group of industrial, financial, and commercial enterprises.
At one of those companies, Sumitomo Machinery Corp. of America, Chesapeake, VA, sales have been booming at well over 20% per year throughout the '90s. Established in 1966 as a warehouse/distribution center, Sumitomo Machinery Corp. now designs, manufactures, and markets speed reducers, gear motors, and variable-speed drives. Customers include a wide variety of industries throughout North, Central, and South America, as well as Southeast Asia, Australia, New Zealand, and South Africa.
Cycloidal speed reducers represent the company's bread-and-butter product. Because they operate without a high-speed pinion or gear teeth, these devices boast several advantages over involute gears: low or zero backlash, compact size, grease or oil lubrication, and the capacityfor high shock loads.
"The fact is," says President William Lechler, "cycloidal speed reducers almost never catastrophically fail." Lechler points out that a 200% shock load can weaken the teeth of involute gears, and with repeated application, shear them off. The cyclo, which operates in compression rather than shear, can absorb momentary shock loads of 500 to 1,200% before the metal begins to deform.
Cyclo gears also allow a large reduction ratio in one stage. "Think of a helical gear," adds Gerhard Antony, vice president, engineering. "One pinion and wheel requires two shafts and four bearings. If you want slower speed and higher torque, you add another stage. This makes three shafts and six bearings. The box gets bigger with more components to fail."
With cycloidal speed reducers, Antony explains, the user simply adds pins and lobes, and changes the eccentricity--package size remains the same.
Kaizen implementation. Despite such advantages, applications for cycloidal speed reducers have, in the past, been largelyconfined to niche markets like the lumber industry and robotics; markets with an obvious need for high shock capacity or zero backlash.
"When I arrived at Sumitomo," Lechler recalls, "we analyzed the manufacturing cost of cyclo torque vs. involute torque. It was determined that our cost of cyclo torque is equal to, or less than, any other type of torque in the world." Once that fact was established, Lechler says, the question became: How can thecompany sell a differentiated product to the standard market?
Product modularity proved the answer. In 1984, the company began to ex-pand their line of high-speed inputs, moving from a free input shaft or NEMA "C" face to a host of motor types. Today, these include gear, brake, adjustable-frequency, vector, AC servo, and variable speed motors.
In addition, Sumitomo started stocking electrical controllers, such as AC inverters, a vector drive, and servo drives. Little-by-little, in keeping with the Sumitomo philosophy, these additional products opened the market from niche applications to standard use.
Growth took off in 1990 when the company addressed the low-speed end of the system. Until then, cycloidal speed reducers were available with concentric outputs only. "To make the cyclo concept truly modular," says Lechler, "we needed to adapt the design to other mounting configurations."
Today, Sumitomo's cycloidal speed reducers are available in concentric, offset, and right-angle configurations. The key is a 3:1 add-on the company calls a "Buddybox." The most simple Buddybox, referred to as an offset shaft mount, houses a pinion and gear. An offset helical configuration and a right angle spiral bevel complete the offering.
Something for everyone. "If a customer wants a geared motor," Lechler claims, "we can do that. If he is going to use an adjustable frequency, we have an adjustable-frequency motor."
The bottom line, according to Lechler, is this: "Tell Sumitomo what you want for a drive, and we can deliver it within 24 hours. Our offering is electrical high-speed input, cycloidal speed reduction, and outputs in three configurations. And, we're stocked all over the world."
For the doubters, Sumitomo also sells a fullline of other geared products. These include helical, planetary, spiral bevel, worm, and hypoid gear re-ducers, as well as gearmotors. Emphasis, however, remains on the cycloidal speed reducer--a niche product no more.
Like a torque-multiplying roller bearing
Cycloidal speed reduction begins with an eccentric cam. Mounted on the input shaft, the cam rotates inside the cyclo disc bore. The disc, in turn, rolls inside the ring gear housing, which always contains one more roller than the number of cyclo disc lobes.
Power moves to the output shaft via a series of pins and rollers. Mounted on the output shaft's internal flange, pins and rollers fit into mating holes machined into the cyclo disc.
For each revolution of the input shaft, the cyclo disc advances a distance of one lobe in the opposite direction. The number of lobes on the cyclo disc and the number of rollers in the ring gear housing determine the reduction ratio--up to 119:1 in a single stage, and to 14,161:1 for two stages.