Canon is researching liner motors for lens applications. Canon filed the patent application, P2023096628, July 7, 2023. Linear motors provide smoother, quiet and more efficient operation, traits desired by video shooters. Implementing linear motors would be an improvement over the STM and USM motors used by Canon today. Other improvements include better power utilization helping to conserve battery life. Canon patent applications are filed all the time, but this does not guarantee Canon will bring the technology to the market.
Background technology (Machine translated)
Linear motors are mainly motors that generate force in one direction, and they are put into practical use in various forms, from small devices such as MEMS to drive mechanisms of linear motor cars in large sizes, and are used in a wide range of industrial fields. I am. Linear motors are often used in applications driven exclusively linearly, and are often used in combination with linear guide mechanisms.
When linear motors are classified by the principle of generating thrust, they are classified as electromagnetic type, pressure type, friction type, tensile/extrusion type, etc., and when classified by drive range, they are classified as finite orbit, infinite orbit, etc. In addition, devices that use so-called racks and pinions, tires, etc. to convert the thrust of a normal rotating motor into linear thrust may be classified as linear motors (linear actuators) in a broad sense.
An example of the use of a linear motor is the focus mechanism in the lens barrel. In the lens barrel, in order to focus on the subject at the desired position at the time of shooting, the focus action is performed by moving the group of focus lenses inside it back and forth on the optical axis orthogonally to the camera's image sensor. A linear motor is used to adjust the movement of this focus lens group.
As a necessary condition for the linear motor used for the focus mechanism in the lens barrel, it is the size that fits in the lens barrel, and it has the maximum output and resolution of thrust sufficient to move and adjust the focus lens group, and be quiet. There are things and so on. In order to meet these conditions, among the above classifications, a finite orbit electromagnetic linear motor, in particular, a voice coil motor (VCM) that generates a Lorentz force by a combination of a permanent magnet and a coil is used. It may be done.
Since VCM does not generate thrust when it is not energized, when using VCM as a focus mechanism in the lens barrel, it is necessary to always energized the VCM and retain the focus lens group during use. For this reason, depending on the shooting scene, it may consume a large amount of power and speed up the consumption of the camera's battery compared to using other frictional ultrasonic motors for the focus mechanism in the lens barrel. Therefore, when using VCM as a focus mechanism in the lens barrel, it is required to improve the power efficiency of VCM.
In order to improve the power efficiency of the VCM of the finite orbit without increasing the external size, the efficiency of the magnetic circuit composed of a permanent magnet and a yoke (hereinafter simply called magnetic efficiency), that is, the density of the magnetic flux that contributes to the generation of thrust in the coil region of the VCM The key is how to raise it. In addition, the magnetic circuit here is an expression that compares the flow of the magnetic flux in space to the current flow in the circuit, and shows the direction and size of the magnetic flux density at each point, but also shows the combination of permanent magnets and yoke itself. In addition, in general finite orbital VCMs, it is known that the magnetic efficiency decreases relatively on both ends compared to the center of the drive stroke, and suppressing this is also an important point for practical use (for example, refer to Patent Document 1 ).
However, in the VCM in Patent Document 1, there is a problem that the power efficiency as a whole becomes worse because it reduces the magnetic efficiency of the center of the drive stroke in order to uniformize the magnetic efficiency in the drive stroke. In addition, the configuration of Patent Document 2 requires a fixed means to fix the magnet separately, so the problem is that the external size of the linear motor is easy to increase.
Therefore, the purpose of this invention is to provide a linear motor, a lens lens barrel, and a driving device that can improve power efficiency while suppressing the enlargement of the external size.
You can check out the patent at JPO here.
