Patent ID: 8870149

Claim:
A hold-down assembly for retaining a portable electronic unit within an avionics equipment mounting tray, the hold-down assembly comprising: a hinge block coupled to the avionics equipment mounting tray; a shaft pivotally coupled to the hinge block and including external threads; a locking collar configured to engage the portable electronic unit and including a central bore configured to slide along the shaft; and an actuator knob, separate from the locking collar, and threadably engaged with the shaft to be rotated about the shaft and moved along the shaft to drive the locking collar, the actuator knob including a threaded and rotatable knob body, a non-rotatable ratchet plate disposed within the rotatable knob body, a plurality of detents positioned around the non-rotatable ratchet plate, at least one ball bearing, and at least one compression spring disposed within the knob body and biasing the at least one ball bearing into engagement with one of a plurality of detents in the non-rotatable ratchet plate, the knob body being rotatable around the non-rotatable ratchet plate to move the actuator knob along the shaft, the knob body and the at least one ball bearing rotating in relation to the non-rotatable ratchet plate such that the at least one ball bearing is forced against the spring bias as the at least one ball bearing travels between adjacent detents and is forced by the spring bias into a detent in the non-rotatable ratchet plate to deter undesired rotation of the actuator knob.