Apple Invents a new Laser-Based Rotation Sensor for the Apple Watch Digital Crown for greater rotational accuracy & more
On Thursday the US Patent & Trademark Office published a patent application from Apple that relates to a future Apple Watch with a laser-based rotation sensor. The use of the laser-based sensing system may provide robust and highly accurate rotation sensing and may eliminate the need to form precision optical treatments or features on rotating surfaces of the crown, such as the grooves illustrated below.
Apple Watch Crown with Laser-Based Rotation Sensor
Apple's patent covers a future Apple Watch that will include a laser-based rotation sensor. The watch may be configured to determine a speed and a direction of the rotational motion of the sensing surface based on the signal.
A beam axis of the light directed onto the sensing surface may be oblique to the sensing surface. The light directed onto the sensing surface may include a laser beam, the reflected light may be a reflected portion of the laser beam, and the optical sensing system may include a laser module configured to emit the laser beam and receive the reflected portion of the laser beam. The laser module may be a vertical cavity surface emitting laser, the vertical cavity surface emitting laser may detect a difference in frequency between the emitted laser beam and the reflected portion of the laser beam, and the signal may be based at least in part on the difference in frequency.
Apple notes that the crown may accept rotational inputs, in which a user spins, twists, turns, or otherwise rotates the crown about a rotation axis. Rotational inputs may be used to control operations of the watch. For example, a rotational input may modify a graphical display of the device in accordance with a direction of rotation of the crown, such as to scroll through lists, select or move graphical objects, move a cursor among objects on a display, or the like. The crown may also accept translational inputs, in which a user pushes or presses on the end of the crown (e.g., along the rotation axis).
Translational inputs may be used to indicate a selection of an item displayed on a display, change a display mode (e.g., to activate a display), change between or among graphical interface modes, or the like.
In some cases, a crown may also act as a contact point for a sensor, such as a biometric sensor, of the device. For example, a smart watch may include a heart rate sensor, an electrocardiograph sensor, a thermometer, a photoplethysmograph sensor, a fingerprint sensor, or the like, all of which are examples of biometric sensors that measure or detect some aspect of a user's body. Such sensors may require direct contact with the user's body, such as via a finger.
Accordingly, the crown may include an external component, such as a window, electrode, or the like, that a user may touch in order to allow the biometric sensor to take a reading or measurement. In some cases, electrical signals may be transmitted through the crown to internal sensors via a conductive path defined by and/or through the crown.
In order to respond to a rotational input applied to a crown, a sensing system is used to detect the speed and/or direction of the crown. The patent describes a laser-based sensing systems that can accurately detect the speed and direction of a crown rotation to a high degree of accuracy, while occupying a small space in the device and allowing for simpler and more efficient manufacturing processes.
For example, a laser-based system may use laser emitters, such as vertical-cavity surface-emitting lasers (VCSELs), to direct a laser beam (e.g., a beam of coherent light) onto a rotating surface of the crown. The laser beams may be aimed at the rotating surface in such a way that some of the light from the laser beam is directed back into the laser emitter, and the effect of the reflected light on the laser emitter may be used to determine the speed and direction of the rotation.
More particularly, the laser beams may be aimed at the rotating surface at an angle that is oblique to the surface (e.g., not perpendicular to or parallel to the rotating surface at the area of incidence of the laser beam). In this configuration, the motion of the rotating surface affects the frequency of the reflected light.
Apple notes that while the patent may focus on Apple Watch, the applications may extend to other future devices using a digital crown such as Apple's AirPods Max, a Mixed Reality Head Mounted Device, a MacBook, iPad, iPhone and beyond.
Apple's patent FIG. 3 below depicts a schematic illustration of an example rotational sensing system; FIG. 4 depicts a partial cross-sectional view of an example input system for an electronic device; and FIG. 9 depicts a schematic illustration of an example rotational sensing system.
For more details, review Apple's patent application number US 20230013283 A1.
- Erik de Jong: Apple Watch Product Design Lead
- Antonio Herrera: Product Design Engineer – Apple Watch
- Jiahui Carrie Liang: Product Design Engineer