3-D Roller Locking Sprags (GSC-13617)
Many machines with rotating parts use brakes and clutches to stop or control the degree and direction of motion of the driven parts. Brakes and clutches often are incorporated between concentric races (i.e., rotating shafts). One class of locking brake/clutch uses spherical balls or cylindrical rollers located between an inner and outer race. At least one of the races contains cam surfaces against which the balls or rollers wedge and lock to produce instantaneous torque coupling. A variation on this approach incorporates the cam shape into the roller (i.e., sprag), which rotates through a small angle to engage the sprag's cam surfaces against the concentric cylindrical surfaces of the inner and outer races (Fig 2.). Springs often are used to preload the sprags against the race surfaces so that the sprags engage and disengage instantly with no backlash.
NASA's innovative 3-D roller locking sprag has a tapered periphery and replaces the concentric, cylindrical surfaces of the inner and outer races of the brake/clutch with grooves into which the 3-D sprag fits. This geometry creates four points of locking contact¾two between the outer taper of the 3-D sprag and the outer grooved race and two between the inner taper of the 3-D sprag and the inner grooved race¾twice as many as with conventional, simple ball-based roller locking brakes/clutches. The two additional contact points increase the locking efficiency of the device while reducing the level of sprag-to-race contact stresses. In conventional cylindrical roller sprags, the roller contacts the races along the full length of the roller sprags. However, NASA's 3-D roller locking sprag contacts only the diametrically opposing sides of the grooved races at the four points noted above, reducing contact stress and increasing holding power.
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