The carriage is the component of a knitting machine that actuates the needles. It must move to the needle in order to actuate it. The carriage is comprised of a metal plate on each needle bed (or just one, if the machine is single bed). It involves a selection system with 'cam-locks' that contain a number of moveable mechanisms called 'cams' and corresponding tracks to form symmetrical, curved channels for the needle to transfer through, raising and then lowering the needle to a specific height so that it may perform a given operation.
Carriage Selection System
A carriage's selection system typically contains a series of cams that serve distinct purposes—the main groups being raising and lowering cams (which are both moveable), and fixed cams (which are not moveable). The raising cams actuate the needle, the lowering cams bring it down to resting position, and the fixed cams provide a structural pathway for the needle to travel through. When it comes to operations that involve carriers, needle actuation occurs when the carriage selects an elevated section of the needle called a 'butt' while raising the cam associated with that operation.
For a needle to perform the knit operation, the carriage raises the 'looping cam' so that the needle butt travels upward in the resulting channel——allowing the needle to grab onto the yarn draped from the carrier, and for any existing loops that were resting on the needle to slide downward from its hook to its lower stem. The needle then travels downward on the opposite side of the channel——pulling the new strand of yarn through the old loops, forming a knit stitch.
The tuck operation also involves a raising cam, but the raised 'tucking cam' does not form as steep of an angle as the looping cam, the result being the distinguishing factor between the two stitches. When the needle butt travels upward in the channel created by the tucking cam, the needle moves high enough to grab onto yarn from the carrier, but lower enough that it still holds any previous loops on its hook. Thus, if the needle was not empty prior to the tuck, it would now hold two (or more) loops.
The miss operation occurs when the carriage passes over a needle without actuating it. While the raising cams aren't engaged, the 'fixed cams' and 'lowering cams' still interact with the needle, meaning that if it is in a raised position before the carriage passes over it, the cams will lower it.
To perform the transfer operation, the carriage engages the 'transfer cams' to select 'jacks' that push needles on either bed upward to a specific height, allowing one needle to give a loop, and the other to receive it.
On machines with sinkers (such as the Shima Seiki SWG-N2), the carriage also has 'sinker cams' for raising and looping.
On the SWG-N2, the carriage moves independently of the yarn carriers, though this is not the case for all machines. For example, on the Kniterate machine, the carriage picks up the carriers and serves as their means of transportation.