Keyless options becoming popular motor-to-gearhead connections for motion control systems

By: Chris Muldowney

"While shaft keys in mechanical drives has been the standard in the power transmission industry for decades, today’s motion control systems are increasingly turning to keyless options for shaft-locking devices.
Because of industry’s changing needs and demands for speed, precision and size, shaft keys have become nearly obsolete in recent years. In response, planetary gearheads manufacturers and motion components manufacturers are developing a variety of keyless shaft-locking devices to address the issues of wear, backlash, density, and balance problems associated with traditional keyed or mechanical connections.
The most common keyless device is the clamping hub with a single tangential screw, which is fairly simply, inexpensive and easy to assemble. The clamping hub takes more torque per shaft size, which means this keyless connection also provides a strong holding torque. It also saves money on shafts because of its smaller size and lack of keyways. In addition, the clamping hub features easy axial and angular adjustment.
Other keyless clamping devices include expansion shafts, split collars and double screw clamping hub.
Keyless solutions can be used for precision applications or simple applications like a gearbox conveyor. They’re also useful when used in conjunction with electric ball screw actuators and/or electric lifting actuators.
One of the major concerns with traditional shaft-locking devices is keyway wear. By eliminating the key and using a frictional bond between components and shafts, you can solve this problem.
In fact, many engineers are looking for keyless solutions because the frequent cycling of the servo and stepper motor systems can cause premature wear on keyed solutions. There are many other causes of wear, including frequent machine starts, stops and load reversals.
And wear leads to backlash, a major concern when it comes to performance issues. While you can’t expect to eliminate backlash entirely, it can be lessened by precise fitting of the gearbox to motor and complicated machining. Precision connections are especially necessary for electric motor speed control, and tight accuracy is needed when coordinated motion is being done with electric speed controllers.
If the accuracy of rotary positioning is vital to your motion control system, backlash will cause serious problems. Small amounts of backlash can be compensated for in some servo and stepper motor systems, but only if you’re willing to sacrifice or compromise speed and responsiveness.
Balance is another problem associated with keyed connections. The concentricity and natural balance of most keyless locking devices eliminates the need for complicated, multi-component balancing procedures.
Acceleration and control are incredibly important in precision motion control systems. The development of keyless shaft-locking devices such as clamping hubs has greatly improved industry’s ability to keep up with these demands, and to combat the problems of backlash, stress distribution, balance and performance.

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Chris Muldowney is the president of ">Tek-Matic (, Rockford, IL), a supplier and distributor of ">automation and control products, specializing in servo and stepper motor systems, electric ball screw actuators, electric speed control and gearboxes conveyers.

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