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Miniature Timing Belt

Miniature Timing Belt

A leading global printer and copier manufacturer is using what may be the world's smallest timing belt in an application that requires a very small belt for paper media transfer. The belt replaces a rubber o-ring with inherent drawbacks including loss of shape and decay of tension over time due to stretch a circular cross-section which did not allow for much surface contact and marking of the paper media.

"For this application, the customer was looking for a very small belt to drive two shafts in the same direction for paper media transfer," says Hans Raj, technical business development manager for Fenner Precision. "Space requirements, maintaining coefficient of friction and avoiding any loss of tension over time were main concerns. These requirements prevented the manufacturer from using conventional solutions such as small O-ring or gears."

Miniature Timing Belt
At the time they initially looked at the design, Fenner Precision didn't have a belt small enough (53 mm pitch length) in its product portfolio. So the core development was the challenge of enhancing its product and manufacturing capabilities to create these smaller-than-ever miniature belts.

The design challenges for the new construction included miniature size, constant tension and a reliable surface over the life of the belt. In addition, the ability to not mar or bend the media during the transfer motion was a must. To achieve these overall design objectives, Fenner modified the belt material to provide a higher and more consistent coefficient of friction and used a specialized molding/de-molding process to make the smaller belt.

The end product is a 53 mm inside length belt constructed of a special polyurethane compound reinforced with fiberglass. This reinforcement prevents stretching, so that the belt does not lose its shape or decay over time, and the polyurethane does not mark the paper. The belt's unique surface allows it to have more contact area with the paper, as opposed to the minimal surface contact provided by an o-ring. In addition the belt is washed and textured to increase its frictional properties.

"We created a reinforced belt solution to respond to a particular customer need," says Raj. "This new belt solution can be utilized as either a drive belt or media transfer belt as it maintains both tension and a high coefficient of friction over time."

Using urethane reinforced with fiberglass is a technique that Fenner Precision has used on other larger belts but, for this application, they applied the special surface finish to provide a good texture and increase the reliability of interfacing other secondary operations and using different production batches. The Fenner engineering team also came up with manufacturing solutions and special handling tools to reliably mold and de-mold the extremely small belts to meet the customers demanding quality and high volume requirements.

"In terms of applications, this same profile can be a potential replacement for gears and O-rings in a wider variety of designs," says Pete Haberbosch, Global VP Sales and Marketing for Fenner Precision. "The compact size can provide new solutions for designers of small medical devices, portable printers, scanners and other new applications."

Haberbosch says many customers are designing smaller devices. The trend is focused on solutions that can fit into smaller packages to reduce space and costs requirements.

With applications that require shaft-to-shaft motion and travel in the same direction, the design advantage of mini pitch belts over using gears is that the system requires only two shafts rather than three. Belts can also provide space savings versus using gears, and belt systems also tend to create less vibration and noise. In addition because the belt doesn't have any metal-to-metal or plastic-to-plastic interfaces, lubrication can be avoided.
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