Dynamic change in belt path while maintaining constant belt length

[Life is a bowl of problems]

I can't imagine that this isn't a common design problem. I am driving two rollers, one stationary and one that moves from a position of contact with the stationary roller to a position that creates some clearance between the rollers. The simplest way to move the second roller is to mount it on a pair pivoting arms which are most likely actuated with a pair of air cylinders. The goal is to drive both rollers with a common belt or chain. The change in the drive train geometry during articulation of the second roller must be such that the length of the belt path or chain path remains the same. As a result, the articulation does not loosen or tighten the belt or chain. I want to avoid a spring loaded idler. One additional complicating factor is that these rollers operate as a nip and therefore are counter rotating. They may possibly use a double sided timing belt or roller chain.

Is there a name for this type of configuration? Are some basic designs or rules of thumb to implement this type of drive train?

 

[3DDave]

Changes in temperature will produce a need for tension compensation, even for fixed geometry. Add in wear compensation and you need some idler, even if it is manually adjusted.

Most nip rollers have only one driven roller; that's the common solution.

Otherwise you may use servo motors to drive both rollers in coordination.

 

[Life is a bowl of problems]

Thanks for your response, I appreciate your input. Here are some additional details that will clarify this specific process.

In this application the individual products passing thru the nips are intermittent. As a result, the nips open and close once every cycle to "eject" each product. The effect of one roller rotating as it comes in contact with the stationary product which in turn is supported by a stationary roller raises the possibility of product damage. It seems safer to have both rollers driven. We already have this type of system operating on some of our equipment, but its design uses multiple belts, pulleys and gears. I'm looking for a more simplistic solution that has a smaller footprint. There will be belt adjustment at the driving pulley for setting initial tension and compensating for wear over time. I did not want to rely on an idler that would compensate for any change in the belt path length dynamically as the nips cycled. That seemed like asking for trouble. Ultimately, I might have to return to the more complicated mechanism, but I can't help trying to build a better mouse trap.

 

[dvd]

telescoping conveyor example -