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Application of the Month

Worm Gears Get a Slice of the Motion Pie
December, 2007 - View all Application Examples

Automation and motion control continue to invade every corner of machinery design and production. The food processing industry is a growing area for taking advantage of automation. But the environment can be harsh.

A customer recently approached us with an application for processing pies. They weren’t going to bake the pies, but were designing a machine to slice the pies into individual servings. While this would seem to be an extravagant convenience for the home, it has validity in the retail and restaurant market where a consistently produced product guaranties continuity for the purchaser.

In this particular application precision was not of utmost concern, as a single tool would make a plunge cut, assuring conformity. However, there was a specific motion profile to orient the tool, which would be achieved through the use of a servo motor.

This type of application, providing specific or variable motion profiles, is becoming one of the largest reasons for using servo motors and controls. While precise positioning and speed control has been the dominant area for servos, providing cam style motion profiles is becoming more and more popular. Witness the cam box’s rapid demise as evidence of this trend. The main reason is that a servo can offer many different profiles through quick programming while a mechanical device can provide just one.

A required characteristic of the design was the need for a right angle reducer, preferably with a hollow output shaft for direct shaft mounting, in a 15:1 ratio. This allowed for the use of a much smaller servo motor, because of the mechanical advantage a gear reducer offers, and reoriented the servo motor to provide a more compact machine design.

Because this was a food processing application subject to caustic cleaning solutions, use of stainless steel materials was a second major characteristic that had to be satisfied. This severely limited the options the customer could consider.

Typical right angle servo gearhead applications, with ratios over 5:1, are satisfied with a two stage reducer design made up of a bevel gear stage, to take the right angle turn, and then a planetary gear stage to multiply the torque and reduce the speed. The planetary stage is usually second as this design provides the highest torque capacity in the smallest package. But hollow output planetaries are rare, beyond special designs.

A few manufacturers, such as Diequa Corporation, do offer a planetary stage first and a bevel stage second design , which would allow for a shaft mount or dual output design.  However, that usually requires a larger gearbox to achieve the same torque capacity. Another issue is that, of the manufacturers that provide this design, few offer it in stainless steel. Those that do, attach a hefty price tag. In this case the application didn’t warrant the extra cost.

The solution we offered is one that is becoming more popular in applications requiring less precision, but need the torque multiplication and inertia reduction. That is the use of hybrid power transmission gearboxes with servo motor adapters. Where only simple motion profiles are necessary, these more standard products can be extremely cost efficient.

In these cases, worm gear reducers can offer perhaps the lowest cost alternative yet provide the exact ratios desired by controls programmers. While helical bevel and helical worm designs are also cost effective, they are usually not offered with exact ratios, which may be better for speed control applications. In the medium ratio range, worm gear reducers still provide acceptable running efficiency numbers. However, because starting efficiency is not optimal, they are usually more appropriate for applications requiring fewer starts per minute. But this one filled the bill.

As part of our extensive gearhead product line, Diequa offers a stainless steel worm reducer that can be fitted with a servo motor adapter flange for direct quill mounting of a servo motor with a keyed shaft. So, that was our suggestion.

The customer was able to determine that the mild acceleration and deceleration profiles wouldn’t put undue strain on the input and output hollow bore keyways, which can be a concern in other highly dynamic applications. Therefore, the extremely cost effective solution, with the corrosion resistant features, was accepted and incorporated into the machine design.

Diequa offers a variety of servo worm gearhead designs covering from general motion and speed applications to very precise positioning applications requiring backlash values as low as 1 arc minute. These designs are typically less costly than other right angle solutions and provide reliable performance in the applications they are best suited for.

To consider a servo worm reducer for your next right angle application, we invite you to contact Diequa for more product information and selection assistance.

Chris Popp
Director of Marketing

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