Source: {"pile_set_name": "USPTO Backgrounds"}

Many vehicles in common use are equipped with freely rotating casters to provide ease and flexibility of movement. Wheel chairs and shopping carts are examples with such casters in front and fixed wheels in back which can only roll forward or backward. Hospital gurneys and hand carts generally employ freely rotating casters in all four corners of the vehicle. The fixed wheels, that is wheels which roll about a horizontal but don't rotate about a vertical axis, employed in shopping carts and wheel chairs enable the user to maintain better control when moving forward and backward or turning, the most important movements for those types of vehicles. Hospital gurneys and hand carts on the other hand must also be capable of moving sideways. Such additional flexibility of movement does however make it more difficult to steer the vehicle through narrow openings (such as doorways) or uneven surfaces (such as gaps in the floor leading into an elevator or raised obstacles like door jambs in doorways), especially when the vehicle is being propelled by a single person. The problem is most acute when the vehicle, such as a gurney, is longer than it is wide. Any off-center force applied by a single person pushing such a vehicle with four freely rotating casters from the rear will make it difficult to control the movement of the vehicle, especially of the front end.
Some hospital gurneys employ means for inhibiting rotation about a vertical axis by adding frictional resistance on all four casters to achieve better control but this has the disadvantages of greater complexity in construction and increased force to turn the gurney. Other gurneys employ a fifth locked wheel in the center underneath the gurney which can be lowered from a normally raised position to contact the floor and thereby resist turning. That arrangement is only useful when straight forward and backward movement is desired but only to the limited extent that one centered wheel can control movement. Other vehicles provide means for locking and unlocking all four casters individually or collectively, sometimes locking the casters in more than one position. Such increased capability is even more complex to construct and operate.
The present invention minimizes the foregoing difficulties by locking the casters on the front or rear end of the vehicle but also providing means for unlocking normally locked casters to permit movement in any direction when desired or locking unlocked casters to facilitate straight forward or backward movement. For example, free swiveling is desirable when attempting to parallel park a gurney between the furniture or equipment positioned against the wall of a hospital room. Free swiveling on all four caster is not desirable when attempting to steer the gurney from one end through narrow openings. Similar situations are encountered by other manually operated vehicles with freely rotating casters such as carts used to transport light cargo through narrow openings over uneven surfaces in cluttered factories, warehouses or offices. The present invention attempts to address this problem in a simpler and more cost effective manner than increasing frictional resistance to rotation on all four casters, adding a fifth wheel or providing means for locking or unlocking all four wheels.