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 Reducing Alternatives Can Be Good by Roger Arrick

Don't let the title fool you, I'm not talking about a reduction in alternatives, but about alternatives in reduction - gear and pulley reduction that is.

You see them everywhere and on almost every type of device from laboratory equipment to production machinery. With the power of today's personal computers, many are constructing automated systems that were unheard of just a few short years ago. With low-cost, PC-based automation and high price/performance ratio systems becoming commonplace, reducers (Gear and otherwise) are being seen in more and more places. A reducer can be used with almost any type of positioning system to increase resolution and torque. Reducers can also improve acceleration in many applications due to better inertial matching of the motor and load.

Well-designed reducers mount easily between the motor and the application in order to provide the desired mechanical effect. Reducers are normally constructed with a machined housing that contains bearings, shafts, and a gear set. Common gear sets include worm, spur, and planetary types. The housing contains the features necessary to mount the motor and to attach the reducer to the mechanical system. Most reducers provide an over-sized output shaft to transfer the torque produced in high-ratio models. This non-standard shaft complicates installation and often requires custom machining to achieve a correct fit.

While several companies offer high-precision, high-cost gear reducers, many applications simply don't require everything they provide. Designers are often forced to use a high-priced gear reducer on a system that doesn't need the precision offered by such a unit. It's not uncommon for one of these gear reducers to cost more than the motor and drive electronics combined.

When automation builders search for alternatives to solve their reduction needs they may discover pulley reducers. Pulley-based units provide much more than just a mechanical reduction, they also provide the impressive cost reduction needed for today's cost-sensitive projects.

Like other reducers, pulley reducers mount between the motor and the driven device using standard hole patterns like those found on a NEMA #23 step motor. Unlike many gear-based reducers, the output shaft is the same diameter as the motor eliminating the need for modifications and custom machining. This is due mainly to the fact that pulley- based reducers normally have smaller ratios such as 4 to 1 or 2 to 1. This results in less torque multiplication and reduces the strength requirements of the output shaft. Usage of such a unit is as simple as removing the motor, attaching it to the reducer, then mounting the entire unit back on to the mechanical system.

An open, sandwich-frame construction has several advantages such as making it easier to replace bearings, belts, or pulleys. Users can actually see what's going on inside these units to eliminating "unknowns" during system troubleshooting. This ease of access also allows the changing of ratios by simply replacing pulleys and belts. The entire unit disassembles with only four screws. Belt tension is easily adjusted using the slotted motor mounting holes. The output shaft can exit either side of the frame to provide additional mounting options. By swapping the input and output pulleys, an increaser can be created. Increasers are used for applications requiring a multiplication in speed instead of an increase in torque.

Overall, the pulley reducer offers a simplified, low-cost alternative to traditional gear reducers where very high precision is not required. Other features of an open-frame design make the pulley reducer a powerful alternative to gear-based units. Keep a watch out for these ever-increasing reduction alternatives.

Roger Arrick is President of Arrick Robotics which manufacturers PC-based motion control products including step motor systems, positioning tables, and accessories such as pulley reducers. Send E-mail to roger@robotics.com. The Web address is http://www.ArrickRobotics.com.

Learn more about the PR23 Pulley Reducer

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