Motion control of a robotic load handling device

A load handling device configured for lifting and moving one or more containers stacked in a storage system including a grid framework structure supporting a plurality of tracks arranged in a grid pattern to define a grid structure above the one or more stacks of containers, the grid pattern including a plurality of grid cells and each of the one or more stacks of containers being located within a footprint of only a single grid cell, the load handling device comprising:

• i) a wheel assembly including a first pair and a second pair of wheels, the wheel assembly being driven by a drive mechanism;
• ii) a lifting device for lifting a storage container from one of the stacks of containers into a container receiving space of the load handling device;
• iii) a position detection means for measuring a position of the load handling device relative to the grid structure;
• and
• iv) a controller in communication with the position detection means and the drive mechanism, the controller being configured to control movement of the load handling device from a current position to a commanded position on the grid structure by:
• a) determining a feedforward torque demand on the wheel assembly at a given time from a predetermined motion control profile;
• and
• b) compensating the feedforward torque demand from a measured position of the load handling device on the grid structure at the given time to calculate a torque demand on the wheel assembly.