On 9/01/06 9:29 PM, "Joseph Tainter", <[EMAIL PROTECTED]> wrote:
> O find that I can't get excited about having a motor in the lens. What's > wrong with me? What am I missing? > > Is anyone else not worked up over this? > > 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. Reliability is excellent but it wears down due to the constant contact. But the life (in terms of hour and I do not remember) is long enough for the balance of life for most of us :-). I think Canon has another in-lens driver which uses step motor or something but it's called differently. For further detail, I am sure Canon site should be providing it. Cheers, Ken -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
