Abstract: A head-mounted device may include optical assemblies for presenting images to a user. Optical assembly positioning systems may be used to adjust the spacing between the optical assemblies to accommodate different interpupillary distances. The optical assembly positioning systems may have motors and threaded shafts rotated by the motors. Rotation of the shafts moves the optical assemblies along guide rods. The shafts may be protected by dust covers. Slots may be formed in the dust covers so that protruding portions of nuts on the threaded shafts can engage the optical assemblies. In some arrangements, the threaded shafts may be mounted within the guide rods and guide rod slots may be provided in the guide rods so that threaded portions of the optical assemblies can reach the shafts. Dust covers can be provided for the guide rod slots. Wipers may be provided to clean guide rod surfaces.

Abstract: A head-mounted device may include optical assemblies for presenting images to a user. Optical assembly positioning systems may be used to adjust the spacing between the optical assemblies to accommodate different interpupillary distances. The optical assembly positioning systems may have motors, shafts rotated by the motors, nuts that receive the shafts and that are moved as the shafts are rotated, and clutches that couple the nuts to the optical assemblies. The clutches may be spring-loaded clutches, magnetic clutches, electrically adjustable clutches, clutches that exhibit fixed clutch holding forces as a function of optical assembly position, and clutches that exhibit varying clutch holding forces as a function of optical assembly position. Electrically adjustable brakes may be used to help secure the optical assemblies in place.

Abstract: A head-mounted device may include optical assemblies for presenting images to a user. Motors may be used to adjust the spacing between the optical assemblies to accommodate different interpupillary distances. The force with which the motors move the optical assemblies towards a central nose bride portion of the device may be limited. The force may be limited using a clutch such as a magnetic clutch or a physical clutch based on structures that decouple from each other to limit the force. The force may also be limited by monitoring the force and halting the motors in response to detection of a given amount of force. Sensor measurements and electrical motor load measurement may be used in measuring the force. If desired, motor operation may be controlled by a user-operated button.