Gearbox-coupling package offers greater stiffness

Chicago, IL--In servo applications, a machine can never be too stiff. There, stiffness is one of the few universal "goods," enabling better dynamic performance and faster response.

Unfortunately, not every gearbox-coupling combination provides the stiffness needed to optimize servo performance. In many cases, engineers must dampen the machinery and "de-tune" the servo performance, just to accommodate the lack of stiffness in the gear reducer and coupling.

A new gearbox-coupling package from Gam Gear, however, solves that problem. Known as I.M.P.A.C.T. (Integrated Modular Planetary And Coupling Technology), it is shorter and stiffer than conventional planetary gearboxes and couplings. In essence, the I.M.P.A.C.T. is like a coupling with a planetary gearbox at its core. It consists of a corrugated metal bellows coupling on its input side, a planetary gearbox in the middle, and a corrugated metal bellows coupling on its output side.

The compactness and stiffness resulting from the design are said to be ideal for dynamic applications, such as packaging, stamping, and material handling machinery. "It creates a much stiffer system," notes Craig Van den Avont, general manager for Gam Gear. "With this coupling, you can increase the gains on your servo system and get much tighter system response."

The key to the I.M.P.A.C.T's compactness is its unusual mounting of the coupling directly onto the gearbox's planet carrier. Engineers from Jakob Antriebstechnik in Germany, designers of the new system, accomplished that by boring a hole in the center of the planet carrier and applying a unique connection concept.

The concept involves three main parts: a split-sleeve shaft that is integral to the coupling; a conical bushing; and a bolt that connects the planet carrier to the coupling. During assembly, the coupling shaft goes into the bored hole. The bolt fits within the shaft and is threaded through the bushing. As the bolt is tightened, it draws the wide end of the cone into the split-sleeve shaft, creating an interference fit between the shaft and the bushing. This interference fit serves as the connection between the planet carrier and the coupling, allowing the two to rotate as a single entity.

The conical bushing design reportedly generates twice as much clamping force as conventional radial clamping hubs. It clamps at about 4.5 times the torque capacity of the coupling, so in a worst case scenario the coupling will break before it slips.

By employing the conical bushing connection, instead of a side-mounted bolt, as most conventional couplings would, the new design eliminates any balancing problems caused by side-loading. It also simplifies maintenance. The reason: The conical bushing configuration enables users to easily remove the coupling. In contrast, conventional couplings require that users loosen a screw and open the gearbox housing.

For design engineers, the overall advantages of the I.M.P.A.C.T. are numerous. The most obvious of those is simplicity. Design engineers no longer need to select input and output couplings when they add a gearbox to a piece of machinery, since this design already includes it. Nor do they need to add a bell housing, since that, too, is included in the I.M.P.A.C.T. package.

On the input side, the I.M.P.A.C.T. coupling accommodates thermal expansion and compensates for misalignment. In contrast, many couplings don't allow for thermal growth of the motor, which can damage motor bearings or encoders. By using a metal bellows coupling on the input side, however, the I.M.P.A.C.T. design allows for thermal expansion of the motor shaft.

Most important, the new design reduces the length of the gearbox-coupling package, improves torsional stiffness, and reduces inertia. By eliminating the conventional output shaft, engineers say they've cut 20-45 mm of the typical length of the gearbox and coupling. The improved compactness and elimination of the shaft have, in turn, resulted in much greater stiffness.

Those advantages are expected to be critical for users, particularly in servo applications. "Whether it's printing, packaging or other applications, servo systems need to make very dynamic, quick moves," Van Den Avont says. "Any time you can improve the stiffness of a servo system it's an advantage, because it allows you to more effectively do those dynamic applications."

Additional details in the U.S....Contact Craig Van den Avont, Gam Gear, 7333 W. Wilson Ave., Chicago, IL 60656 (708) 887-5000 (P)

Additional details in Europe...Contact Achim Mayer, Jakob Antriebstechnik, Dieselstrabe 8, D-63839 Kleinwallstadt. Telephone: (0 60 22) 22 08-0.

Other Applications

- Stamping

- Grinding

- Printingc Packaging