Autonomous guided vehicles, such as material handling robots, are widely used in many applications. As explained in U.S. Pat. No. 8,280,546, a prior art mobile drive unit for an inventory system includes a docking head, a drive module, a docking actuator, and a control module. Additionally, the mobile drive unit may include one or more sensors configured to detect or determine the position or location of the mobile drive unit and one or more sensor for determining whether the drive unit is engaged or docked with the inventory system.
The drive module propels the mobile drive unit and, when engaged with the drive module, also propels the inventory system. Conventional drive modules include a drive assembly that includes or couples to an axle, a pair of opposing, motorized or driven wheels on the axle, and a pair of front stabilizing wheels and a pair of rear stabilizing wheels. The drive module also includes rechargeable batteries for powering the drive assembly. Preferably, the maximum velocity of a robot is approximately 1.3 meters per second.
A popular drive assembly includes a brushless motor and integrated gears, as described in U.S. Pat. No. 9,127,763, entitled “Motor Housing With Integrated Gears.” The drive assembly of the 763 patent includes a brushless motor, a motor shaft coupled to the rotor of the motor, a motor shaft pinion, also referred to as a first pinion, formed on the motor shaft, a parallel gear set, and an output shaft. The parallel gear set includes (i) an intermediate gear, also referred to as a first gear, that is engaged with the motor shaft pinion, (ii) an intermediate pinion, also referred to as a second pinion, coupled to the first gear by a common shaft, and (iii) an output shaft gear that is engaged with the intermediate pinion and coupled to the output shaft.
An aspect of a prior art drive assembly is the ability to monitor position or rotation of the shafts. Typically, encoders (such as an incremental encoder, an absolute encoder, or both) are positioned to determine the position and/or the magnitude of rotation of the motor shaft and the output shaft. Information from the encoders is fed to a control system. Overall drive system function sometimes requires a minimum moment of inertia.