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issue: November 2004 APPLIANCE Magazine

Motor Technology
Electromechanical Clutches for Motion Control

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Reell Precision Manufacturing has developed an electromechanical clutch that is said to provide consistent timing for rotary motion control and meets a complex series of performance requirements.

Reell clutches have torque ratings up to 75 lb-in and feature a bearing system that increases reliability in machinery with high-hour or high-input revolution requirements.

The St. Paul, MN, U.S.-based supplier’s EC5, EC15, EC20, and EC30 clutches are designed for low power consumption in a variety of OEM applications, including copiers, printers, collators, ticket and receipt dispensers, and other applications where there is a need for intermittent rotary motion. These electromechanical clutches are said to be capable of precise timing and fast engagement and disengagement for millions of cycles. Other features include their compact size (up to 2-in diam for various models) and relatively high torque to ratio size (from 5 to 75 lb-in).

The electromechanical clutches require only 6 W and energize on either 12 or 24 d.c., filtered or unfiltered. The clutches employ an electromagnetic field to activate the spring wrap, according to John Kossett, senior development engineer for the Rotary Motion Group at Reell Precision Manufacturing. As electric current is passed through the stationary coil, lines of magnetic flux are generated and used to attract the control ring to the shoulder. This control ring is attached to the spring, which wraps down on a hub as input is turned. Torque is transferred from the input, through the spring, and to the output. After electric current is removed, the magnetic attraction is lost, causing the clutch to disengage as the spring unwraps.
“A wrap spring clutch provides very positive engagement,” Mr. Kossett explains. “Once the spring is wrapped down, typical acceleration times are on the order of 3 milliseconds.

Disengagement is virtually instantaneous. This operational characteristic allows precise timing and repeatability.” Mr. Kossett says this feature is especially beneficial to business equipment because the clutches’ precise timing, positive engagement, compact size, and high reliability translate into more efficient operation of the machine and fewer service calls.

These electromechanical wrap-spring clutches provide torque in only one direction, which permits overrunning. The devices are available for either clockwise or counterclockwise operation. Typical operating speeds are from 100 to 800 rpm with a 1,400-rpm maximum.

In addition to business equipment, the electromechanical clutches are also being used in commercial applications. A standard line of clutches has helped one manufacturer eliminate individual pump motors in a frozen beverage dispenser, achieving high reliability and lower production costs. By using one main motor and a system of electromechanical clutches, the dispenser intermittently operates several peristaltic pumps that dispense various liquid ingredients into drinks.

Mr. Kossett adds that the wrap-spring clutches offer more consistent time-to-speed, independent of load, than individual small motors. The company’s 100-percent functional testing also ensures product quality prior to shipment.


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