Canon Patent Adds a Third Coil to Steady the Linear Motors That Move Lens Groups

Linear motors have taken over the inside of modern lenses. They are quiet and quick, which is why Canon’s recent VCM primes and so many video-friendly zooms use them. They also have a weakness that rarely gets talked about, and a Canon patent application published in the US in August 2026 goes straight at it.

The filing is US 2026/0246353, “Linear motor, linear motor system, and optical apparatus,” with a Japanese priority date of February 2025 and Kyosuke Sato as inventor. The example application is an interchangeable lens, where the motor moves focus and zoom groups along the optical axis.

The weak spot: holding still

A linear motor works by pushing a coil against a row of magnets. The filing points out that it has no holding force at all when power is off. If the lens is pointed straight up or straight down, the motor has to keep pushing just to stop a lens group sliding under its own weight.

The second half of the problem is called thrust ripple. Magnets and yokes alternate along the motor, so the magnetic field the coils see rises and falls with position. At some spots along the travel the motor is efficient, and at others it’s weak.

Those weak spots set the limit for the whole design. Canon explains that when the motor has to hold up its load, the least efficient position decides how heavy a lens group it can move and how fast it can accelerate it. Strong spots elsewhere don’t help. Power use also rises while the motor sits at a weak spot, which matters in a lens that might hold focus for an hour of video.

One more coil, placed carefully

The usual design uses two coils spaced a quarter of a magnetic period apart, 90 degrees in Canon’s phase terms. As one coil moves into a weak area, the other is near a strong one, and the controller shares current between them. At the point where both see equal fields, Canon notes it’s more efficient to run each at half current than one at full.

Canon’s version adds a third coil, positioned between 135 and 225 degrees away from one of the first two. The controller then sets the ratio of current across all three coils according to where the moving part sits. With a third coil near its sweet spot whenever the other two are in their dips, the weakest point of the stroke gets stronger.

The filing compares this with two earlier approaches. One shaped the magnets in a complex way to shave down the ripple, which made the parts harder to build and only helped a little. Another added more coils in a row, which works but makes the motor longer, and length is precious inside a lens barrel. Canon says its layout raises the minimum efficiency while avoiding most of that size and complexity. The design also uses ring-shaped magnets and yokes threaded on a shaft, which Canon says cuts assembly work and weight.

Why lens buyers should care

Nobody buys a lens for its motor geometry. They buy it for what the motor allows. A stronger worst-case push means a heavier focus group can move just as fast, which is the limiting factor in fast primes like the RF 50mm F1.4 L VCM. Lower current while holding a position means less heat and longer battery life during long video takes, when a lens may sit pointing down at a table or up at a stage for minutes on end.

The patent doesn’t say which lenses might use it, and it doesn’t claim to be the motor inside Canon’s current VCM lenses. Patents like this describe parts that tend to appear without fanfare, with the improvement showing up only as a line about faster or quieter autofocus on a spec sheet.

For how Canon’s current linear-motor primes perform in practice, see our Canon RF 50mm F1.4 L VCM review and RF 35mm F1.4 L VCM review.

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