Mechanical torque limiters are often considered heavy, bulky, and outdated. For this reason, electronic current limitation is commonly used in their place to prevent torque overload. Though usually effective, as machinery becomes more dynamic, the inertia of moving parts becomes more critical: In such cases, it is possible to abruptly decelerate rotating mass — through unintentional blockage or application of dynamic braking — at a rate faster than the drive normally accelerates. This creates torque overload through reflected inertia (independent of electronics) which can easily exceed the motor's peak torque rating.
To give engineers another option, R+W America, Bensenville, Ill., has introduced a new SL Series mechanical torque limiter that has half the inertia and less than half the mass of comparable designs, allowing for a rapid and automatic recovery from torque overload, even in the most advanced drives. State-of-the-art materials and surface treatments makes for unparalleled power density. Case in point: A traditional torque limiter rated to disengage at 160 Nm may have a moment of inertia of 1.6 × 10-3 kg-m2 and mass of 1.3 kg; the comparable SL-Series limiter has a moment of inertia of 0.8 × 10-3 kg-m2 and weighs 370 grams. In fact, highly designed spring systems and an improved ball detent configuration increase torque capacity 40% for a given size; compression of individual components further reduces weight without reducing the torque limiter's precision or service life. SL-Series limiters can also handle more than 10,000 disengagement events, depending on rotational speed.
On display: SL Series mechanical torque limiter
Key features: Series 30, 60, 150, 300 cover disengagement torque from 5 to 700 Nm; mounting options, including direct and indirect drive
What it means to you: Lightweight torque limiters reduce drive power consumption and are highly accurate for cutting-edge machinery
What else: Models SLN (clamping) and SLP (keyway) attach by flange to sprockets, sheaves, pulleys, and gears, and include an integral dual bearing to support belt and chain tension. Models SL2 (bellows coupling) and SLE (servo-insert coupling) mount inline between two independently supported shafts, such as motor-to-ballscrew connections, and compensate for the small but inevitable misalignment of this machine layout. All four types are field adjustable, and come in both English and metric bores.
Innovator: R+W America