Beam couplings are an excellent choice when selected for the proper application. We asked Bobby Watkins of Ruland Manufacturing to give us some insight on proper coupling selection. The following is an excerpt from the beam coupling section of his Webinar, Master Coupling Selection: A Guided Journey by Bobby Watkins.
“We’re going to start off with beam couplings. Beam couplings are probably the most recognizable type of coupling out there. Quite a typical coupling to use for an encoder application so many people are familiar with them. Engineers often use them for encoders; they make a great encoder coupling. They can also be used in light-duty power transmission applications, light-duty actuators and so forth. In heavier duty applications, you probably need to look at one of the other types of couplings, which would be much more common, and a higher torque application. Beam couplings do have their limitations. However, we’re just going to go through some of the benefits first.
It’s a one-piece design. It means there’s no maintenance. There’s various OD links, patterns and materials to choose from for different applications. They have large misalignment capabilities and they’re forgiving when compared to most of the other servo couplings, very forgiving in angular and in parallel misalignment situations.
Don’t cross the line though with this coupling. If you ask too much of it, you’re going to break them and break them quickly, especially under misalignment. If you exceed the misalignment specifications, they do tend to break relatively quickly. Installation of this type of coupling with a good straight edge is typically good enough. These are available in metric, an inch to metric.
Some of the drawbacks. Moderate bearing loads depending on conditions. In other words, under misalignment conditions, all couplings will put a load on your bearings as it’s fighting to straighten out. This coupling gives a moderate bearing load. Stainless rich steel versions are available for these couplings. Often, if you look into the size of beam coupling and the torque rating of the standard aluminum coupling, it isn’t enough for your application. The natural progression for that is to look at a stainless steel version, which, size for size, has higher torque capability.
The gain in torque, size for size, is moderate. It’s not a huge gain but the stainless steel couplings themselves tend to be heavy and you can end up with inertia issues and tripping out motors because the inertia is just too high due to the weight of the stainless version. Also, they’re expensive. I would suggest that if you’ve done the application, and it doesn’t appear that there’s enough torque capacity for aluminum versions. Look at the stainless, but also look at some of the other types, which are probably more cost-effective, a higher gain in overall torque capacity. Beam couplings have relatively low torsional stiffness and because of that cut pattern, they wind and unwind under torque. If sized properly, that’s not an issue. When you start asking beam couplings to do a little more work or handle a little more torque than what’s required, you will get positioning error because they’ll wind and unwind.
Often, a customer will call and say
‘I’ve got a stepper application and my system seems to be lost. It can’t find home. I make one small move and I’m not where I’m supposed to be. I don’t know what’s wrong. I don’t know if the coupling is slipping on the shaft.’
99% of the time, they’re using a beam coupling. They’re asking it to do too much and it’s winding and unwinding to the point where they’re getting positional errors. Again, beam couplings are a good, overall, cost-effective coupling. Don’t ask too much of it. The most common application is an encoder and they are used in automation, packaging ,medical, semiconductor and so forth.