How do machines like MRI that use large freely rotating pieces with sensors and tools attached deliver power and send/recieve data, I don’t think they would have miles of cables on a spool thats ready to be wound back and forth?
In: 163
The MRI scanner does not have any large freely rotating pieces. The only part of the scanner that moves is the table that the patient lies on. You might be referring to a CT scanner.
slip rings! picture electric trains that get power from overhead cables or a third rail on the ground. a metal wheel or brush touches those, and despite the fact that they move in relation to each other, power is moved through the point where they touch. now picture taking one of those tracks and making a circle. no matter how much it spins, the metal contact will be dragging along the surface of that rail, transferring power. slip rings usually have 2+ metal rings, and usually a metal spring pushing down on them for moving the power
[wikipedia has as great illustration of the two main types](https://en.wikipedia.org/wiki/Slip_ring#/media/File:SlipRings.jpg)
Surprisingly not much different than a steering wheel in your car. electricity and data can move from one piece of metal to another even when they are moving with respect to each other.
edit: I’m wrong that’s not how they work now
In addition to slip rings there is also:
* Inductive coupling. An electromagnet on the frame induces power in a coil on the rotating part. Same principle as wireless phone chargers.
* Batteries in the rotating part powering a wireless radio link. That’s how car Tyre Pressure Monitoring Sensors (TPMS) work. The obvious down side is having to replace batteries, keeping the whole unit balanced and how the battery responds to centrifugal force.
* Optical encoders. Passive (non powered) when you need to know the position of the rotating part without
needing to have an active sensor inside it.
* Clock spring. Used in car steering wheels. It’s a long thin ribbon of wires that coils up more tightly when the wheel turns. Obviously only useful when the wheel is limited to a few revolutions before being unwound again
They use a piece of equipment called a “slip ring” to transmit power and electrical signals through a rotating surface.
One end of the device has wires that end in spring-loaded brushes and the other end has a series of metal rings. The brushes connect with the rings to complete the circuit during rotation.