There are a few things all engineers hold sacred, including F=ma (force=mass x acceleration), the first law of thermodynamics, Tesla's genius, and you can't push a rope, but what if you could push a chain? That's the sort of paradigm shifting technology that Serapid produces. If you check out their website, you will see mind-bending applications of a chain that can push thousands of pounds at shocking speeds: 60-200 feet per minute. As a design engineer, it is difficult to package linear actuators in a confined space, but that's exactly what Serapid has done with its chain technology. In scissor mechanisms the actuator is sized at a mechanical disadvantage at the beginning of the travel. If a push chain can be used instead, the chain can be effectively rolled into a coil magazine and unrolled to provide the force needed to provide motion to heavy loads. Additional advantages of push chain technology include:
If a chain link breaks, the lifting platform is not in a catastrophic free fall like a wire rope hoist.
Depending on the State and the application, this feature can eliminate the need for independent free fall protection (elevator safety-governors), and puts the Serapid push chain mechanism in the same category as a hydraulic actuator.
In lifting applications where vibration occurs (seismically active regions, cruise ships, ASRS), the chain cannot go slack during negative acceleration.
This slack condition can cause impulse loads to the cable (imagine an inner-tube pulled behind a powerboat).
Precise positioning is also an advantage because there is little to no backlash in the chain stroke.
You can rely on the platform position to be a function of the number of revolutions of the drive sprocket. In cable systems, there can be slip and other losses that require an absolute encoder on the platform for position feedback.
A push chain system is extremely quiet.
As an example, watch the video of the Beijing Olympics below. One of the more popular applications of this chain is to raise and lower the pit of opera platforms during performances.
If you have an application that needs linear motion, be sure to give this approach a chance to push the limits of what's possible! What's the most interesting use of push chain technology you've seen? Leave your comments below.
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