Trading fiber reinforced plastic for aluminum, new couplings from R+W deliver lower moments of inertia compared to metal versions of similar capacities. That translates to faster accelerating—or smaller motors and gears for achieving it. After choosing a lightweight material for their hubs, R+W engineers further reduced the coupling’s inertia by locating a greater proportion of the hub mass close to center. They also lightened it with holes, which also permits even cooling.
The TX1 Series 60 coupling weighs 6.3 oz. and has a moment of inertia of 0.03 x 10-3 kg m2. Compare that to the same series of the aluminum type, the EK2/60, which weighs 12.3 oz and has a moment of inertia of 0.09 x 10-3 kg m2.
The new design costs about half of what a traditional aluminum servo insert coupling would. It operates within a slightly narrower temperature range than standard couplings, -20 to 100C instead of -30 to 120C. It’s capable of speeds to 10,000 rpm.
To answer any concern over the material’s durability, R+W subjected a TX1 60 Series model to accelerated life testing that consisted of 40 million load reversals at its 60 Nm load rating. No change in the hub structure was seen. Also, the company subjected it to torques of 3 to 4 times rated capacity and found the motor shaft key deforming but not either hub. The manufacturer expects the keys and the polyurethane insert to be the most likely elements to fatigue.
High rigidity was an important goal for the coupling’s designers, as it is intended to operate without backlash. Static torsional stiffness for the thermoplastic coupling is 9750 Nm/rad and dynamic torsional stiffness is 11,900 Nm/rad.
TX1 couplings are available for torques of 2 Nm to 660 Nm (18 to 5841 lbs/in) and for bore sizes from 8mm to 45mm (0.375 to 1.75in).
Fiber reinforced plastic in the hubs of this jaw coupling lighten it and reduce its moment of inertia.
George Leopold's talk at last week's Design & Manufacturing Minneapolis helped restore astronaut and engineer Gus Grissom's role in the beginnings of NASA, and outlined how Grissom played a pivotal role in winning the Space Race.
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