Bot payload alignment and sensing

The present invention concerns an autonomous transport robot for transporting a payload comprising: a payload bed (1510) having at least one reference datum surface (1510F; 1510S); and at least one payload justification device (1530, 1510R); wherein the at least one payload justification device being configured to position a payload on the payload bed in substantial contact with the at least one reference datum surface to place the payload in a predetermined position on the payload bed.