Yoshizen's Blog

Ultra sonic / Silent wave Motor

Ceramic-USM Motor-000

(On the photo, round comb like structure is the motor (OD = 12 mm) = its teeth of a comb or the legs of a milliped moves like milliped legs and make the silver-colored disc to move / rotate = that’s how this motor works ! —– though, in real life, you can’t see its teeth or legs move = the each movement is too small to see = so, quietly just the disc moves —– looks spooky !)

 Ultra sonic or Silent wave, what so ever called, the ceramic motor using vibration of its material is rather new kind of the device though, the vibration of the ceramic material itself has been known long time. = the most common use around our life is THAT sounding disc in the security device or even a small round disc in a Singing Christmas card. 

Still, to use its vibration to a motor was happened as an accidental discovery = a ceramic unit on a desk moved while under a test.  So, the engineer got an idea, why not to make a motor and if the sound is too noisy, why not make it to an inaudible high frequency (to an ultrasonic) = So, Ultrasonic motor was developed.  With the manufacturer’s sales tactics, you might be made to believe that the Ultrasonic Motor is an exclusive expensive device. —– you are wrong. 

The top photo is showing a sample, a Silent wave Motor from Nikon’s 18~200 mm Zoom lens.   You may find the similar motor from China in the net, less than few pound. ( Though, if you got a skill to use it include the design and make of the whole gear train, I’ll admire you ! = Utilise whole mechanism as a drive unit, would be far easier, and an electronic controller is on the net as well  )   Yet still to the Nikon, to design the AF drive mechanism, using a traditional DC-motor or use a Silent wave Motor (USM) was not a hard choice = in the cost term, it would be more or less the same. ( DC-motor needs more gears and may have noise problem — mechanically USM needs less gear (= cheaper and easier to assemble) but electronically more complicated work in the program.  (Basically, USM needs the pulse train to drive = two different pulses, one is a bit ahead of the others and which one goes ahead determine the direction of the rotation = in photo term, move focus to far or closer.) ( On the top photo, you may see a flex circuit come out from the USM which got four gold contacts = two each of pulse input ) 

Since the camera’s video function becoming more important, the quietness of the camera (especially its AF motor) became heavy issue, —– So, Canon introduced STM ( = quieter Stepper motor) —– in the traditional sense, stepper motor was driven by the electric pulse, which sharp on-off square wave pulse couldn’t be smooth and quieter, yet Canon seemed to be adapted the use of PMW drive (the voltage of the each pulse gradually rise) instead of the simple square wave ! —– Though, my Canon 40 mm F2.8 Pancake lens got such STM motor — It’s far from quiet. —– in comparison, the SONY lenses (which I have no information of what kind of motor) = are amazingly quiet. ( = what kind of motor inside ? )   So far, there was no broken SONY lens in a junk-box of a camera shop = I haven’t cut-open them yet.   😀

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