Originally Posted by BillTodd  It's the inverse of a chain and sprocket (imagine a short length of chain wrapped in a circle as the pinion and a linear 'sprocket')
It would be interesting to experiment with a fixed chain laid flat (or held rigid in a U shaped channel, or even upside-down in a suitable T slot) with a sprocket on the motor. It could give similar performance to the roller pinion at a fraction of the cost. |
Not exactly. If you use a chain sprocket curve then the line of motion of the of the drive pinion will not stay parallel to the line of motion of the rack. Say that three times fast. Here's what I mean:
The sprocket profile looks more pointy than it really is. The export kind of lost something. The tooth profile is actually convex. Here's a better look:
Note how the center line of the pinion follows a cycloidal path.
The pinion is in rotation about its center axis and in translation; also; the pinion path and the line of motion along the rack must be parallel. With those constraints I simulated the motion of the pin through rotation and translation. The actual rack profile should look like this:
Both profiles above used the same pinion configuration: 3/8" rollers, 10 rollers per pinion, 2PI length of travel per rotation.
Compare the last profile with that used by Nexen:
The Nexen profile is more triangular and less like a sprocket profile.