Mechanical speed adjustment

March 1, 2009
In 1959, when Motion System Design made its debut, mechanical systems were the only way to control system speed. Now we ask of one inaugural-issue headline:

In 1959, when Motion System Design made its debut, mechanical systems were the only way to control system speed. Now we ask of one inaugural-issue headline: Does it still hold true?

You may be surprised …

“We trace our mechanical variable speed roots to 1898 with a transmission product,” says Bob Lee of Baldor Dodge. “What is more, we remain aggressively active in the mechanical variable-speed business. Our current Reeves product offerings include 10 motor pulley sizes, 5 adjustable motor pulley base sizes, and 10 variable-speed belt drive sizes.”

“100-year-old-plus mechanical variable-speed technology still finds work in many applications today — primarily in constant-torque applications with high inertia loads that are hard to start. A belt drive has inherent high starting torque and acceleration capability that allow it to compete favorably with VFDs. In addition, developments in controls eventually allowed mechanical drives to follow open and closed-loop processing signals now standard in industry — so today, the mechanical designs combine sophistication with rugged durability and simplicity.”

“High torque requirements, shock loads, and explosion-proof and remote installations are applications for which mechanical adjustable speed drives continue to be well suited, cost competitive, and reliable.”
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“The demise of mechanical drives was predicted to take place at least 20 years ago, but has not come to pass!” So says Alex Himmelberg of Lenze-AC Tech, Uxbridge, Mass. “Our predecessor Simplatroll GmbH began producing open-pitch pulley drives around 1950. The drives had constant center distance, a mechanically adjusted pulley paired with a spring-loaded pulley, and a speed range set to 6:1, for constant torque below motor speed and constant horsepower above motor speed. These were used in textile and wood and metalworking machinery. In the mid 1950s, adjustable pulleys were enclosed in a housing with a motor mounted on the input side, helical or worm gearing on the belt transmission output side, and sold as packaged drives.”

“By the 1970s, VFDs had arrived — but were not as reliable as mechanical transmissions and were also large and expensive — so mechanical drives held onto market share. However, by the 1990s, VFDs became reliable due to printed and integrated circuits and the elimination of wiring and solder joints. Since then, electronic drives have replaced more than 95% of mechanical drive business. Even so, certain customers continue to use mechanical drives where inherent benefits exist. For example, the added inertia of a belt drive provides added torque on peak torque loads. That is why we still offer enclosed belt drives coupled with gears from ⅓ to 60 hp.”
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