> >> It strikes me as one more thing that will need to be repaired >> someday...probably when parts are no longer available. >> > > When we talk about USM, as Canon term it, it is an Ultrasonic Motor, and not > like a conventional motor. > USM is not Canon's creation and there are many companies making it for > various applications. Canon is probably the first to apply it for lens > drive. There is no motor per se, but you can consider the helicoids as the > rotor and the barrel as the stator, and the stator and the rotor are in > constant "contact". Inside the stator, there are a series of Piezo elements > which change its shape as the power is applied (like a wave) which push the > rotor. Unlike ordinary electric motor, which is typically high speed, low > torque machine and requires a gear reduction, USM is a low speed, high > torque device. Another advantage for the AF application is that it does not > require a brake as ordinary motors do, because the rotor and the stator are > in contact. This contributes to the fast start and move, and accurate > positioning due to no run-off of the rotor. > Seems to me this all makes it similar in functionality to a traditional step(per) motor. Technically it is even more closely related to a piezoelectric motor, although I don't believe it's exactly the same thing.
Both of which can come in packages that are identical to a traditional DC motor, and could as far as I can tell be used in an in-body motor AF system - which would cancel out the need for the traditional feedback loop. - Toralf -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
