Actively balanced mobile drive unit

A mobile drive unit, comprising:

• a body;
• a docking head assembly configurable relative to the body between (i) a docked state in which a payload of the mobile drive unit comprises an inventory holder lifted and carried by the mobile drive unit, and (ii) an undocked state in which the mobile drive unit is not carrying an inventory holder;
• a drive module comprising at least one rolling element rotatable to move the body along a support surface, the body pivotable about the at least one rolling element toward or away from an equilibrium state in which moments acting on at least one of the mobile drive unit or the inventory holder are balanced;
• a sensor set comprising at least one sensor configured to sense information about at least one of the mobile drive unit or the inventory holder;
• and
• a control module configured to:
• receive sensing information from the sensor set, the sensing information indicative of a deviation of at least one of the mobile drive unit or the inventory holder from the equilibrium state;
• control the drive module of the mobile drive unit so as to move the mobile drive along a first travel path to the inventory holder by iteratively:
• receiving information about the body of the mobile drive unit
• determining, based on the information about the body, a deviation of the body from a body equilibrium state in which moments acting on the body are balanced;
• determining an undocked operation of the drive module to both counteract the deviation of the body from the body equilibrium state and maintain the mobile drive unit in motion along the first travel path;
• and
• controlling the drive module so as to perform the undocked operation;
• control a lifting system of the mobile drive unit to lift the inventory holder relative to the mobile drive unit so that the inventory holder is carried by the mobile drive unit;
• control the drive module of the mobile drive unit so as to move the mobile drive unit with the inventory holder carried by the mobile drive unit along a second travel path by iteratively:
• receiving information about the payload comprising the inventory holder carried by the mobile drive unit
• determining, based on the information about the payload, a deviation of the payload from a payload equilibrium state in which moments acting on the payload are balanced;
• determining a docked operation of the drive module to both counteract the deviation of the payload from the payload equilibrium state and maintain the mobile drive unit in motion along the second travel path;
• and
• controlling the drive module so as to perform the docked operation;
• and
• control the drive module so as to maintain the deviation of the payload in the docked configuration within a predetermined amount from the equilibrium state.