Robotic surgical assemblies and surgical instrument holders thereof

A surgical instrument holder, comprising:

• a carriage configured for movable engagement to a surgical robotic arm;
• and
• a drive coupler including:
• an outer member extending from the carriage, the outer member defining a lateral slot therein configured for lateral receipt of a surgical instrument;
• a first gear defining a lateral slot therein and being rotatable within the outer member to a first position, in which the lateral slot of the first gear is in alignment with the lateral slot of the outer member such that the surgical instrument is receivable within the drive coupler through the lateral slots of the outer member and the first gear;
• a second gear operably coupled with the first gear and configured to be drivingly rotated by an instrument drive unit to effect rotation of the first gear relative to the outer member;
• and
• an inner member including:
• an internal housing rotatably disposed within the outer member, the internal housing having the first gear non-rotatably disposed therein;
• an upper plate fixed to a first side of the internal housing and supported on and extending over an upper surface of the outer member;
• and
• a lower plate fixed to a second side of the internal housing and supported on and extending over a lower surface of the outer member such that the outer member is captured between the upper and lower plates.