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Application of the Month

Right Angle Gearheads Reduce Radial Forces On Mounting Structures
May, 2015 - View all Application Examples

When designing automation solutions many engineers absent mindedly default to adding a planetary gearhead to their servo motor driven system. Its relatively easy as some software selection programs pick one out based on basic application criteria. While it usually works its often not the optimal solution. And sometimes it can be the absolute wrong decision.

We had a customer call us recently with a problem on his linear motion feed system. He had a servo driven belt actuator that was making simple movements to transfer product from one spot to another. Precise motion wasn’t really required and the work was rather light duty.

Because the application wasn’t overly dynamic the machinery structure was designed with limited rigidity. This obviously saved costs in the construction but could have proved pricey with the resulting problem. The issue was one of leverage. In this case, overhang load.

The servo driven application needed significant reduction to drive the actuator at the appropriate speed. In this situation the customer had a two stage planetary gearhead with 20:1 ratio mounted to the actuator input shaft via an adapter flange and intermediate coupling. It’s a typical configuration that is selected quite often in this type of application. Unfortunately, due to the lighter support structure holding the actuator this typical solution became a nightmare for the customer.

Similar to the rendering below, the configuration has an adapter attached to the side of the actuator that is long enough to house the coupling connecting the actuator input shaft to the gearhead output shaft. Then a long two stage planetary reducer is attached to the adapter. Then a servo motor connected to the input of the gearhead adds additional length. Can you tell why this might be a bad situation when the support structure isn’t up to the task?

Yes, while the connecting flanges were all strong enough to support the load the cantilevered weight of the long gearmotor assembly was deflecting the frame and fatiguing the material. And with each actuation it got worse. Unfortunately they couldn’t change the frame design on machines in the field. So they wondered if we had any ideas on how to get them out of their bind. Of course we said we did because we did.

What we suggested was our Varvel Servo Worm gearhead. As a right angle solution the main benefit was reducing the distance of the cantilevered weight by over 60%. This directly reduced the radial load exerted on the frame by the same percent, which solved the problem they were experiencing by using an inline planetary reducer. But this wasn’t the only benefit.

By selecting a hollow output shaft model we were able to mount directly on the actuator input shaft eliminating the need for a shaft coupling. This reduction in cost was further enhanced because the reducer itself was less expensive than the existing planetary reducer. Sure, the frame could have been stronger. But that would have added even more cost to an application that didn’t need it.

Another benefit was saving on the machine width. With the motor now tucked up against the actuator instead of sticking out at a 90 degree angle it was a much more compact design.

The Varvel is a general purpose servo reducer most appropriate for less dynamic applications where backlash isn’t an issue. Had higher precision been required we have a similar design for higher performance applications in our Dynabox series. This product line offers three backlash levels from 1 – 10 arc minutes.

Along with these and the other solutions for servo driven motion control we offer, it should be clear that tremendous benefits can be gained by evaluating what gear technology is best for an application. While planetary designs are often a great solution they are by far not the only one that should be considered.

Chris Popp
Director of Marketing

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