US Patent 7188568 Self-propelled vehicle for movement within a tubular member

A self-propelled vehicle (20) for movement within a tubular member (22) includes propulsion mechanisms (28) distributed about a core element (24). Each of the propulsion mechanisms (28) includes a drive belt (28). A first pulley (34), a second pulley (36), and a mid-roller assembly (38) are encompassed by and engage the drive belt (28). The mid-roller assembly (38) is spring-loaded for providing an outwardly-directed force (40) to an underlying portion (42) of the drive belt (28) to press the drive belt (28) against an inner wall (44) of the tubular member (22). A motor arrangement (46), in communication with the propulsion mechanisms (28), actuates one of the first and second pulleys (34, 36) to rotate the drive belt (28) in contact with the inner wall (44) of the tubular member (22) thereby moving the vehicle (20) within the tubular member (22).