U.S. Pat. No. 1,727,635 to Crane discloses an automatic swinging crib. The automatic swinging crib is provided with a solenoid. It is energized by a contact attached to the frame during a portion of the swing cycle, which draws current from a battery. The contact is broken de-energizing the solenoid when the armature reaches the mid point of the solenoid. Energy is thereby provided to the swinging crib at a portion of the swing cycle to combat slowing down of the swing motion. No motors are utilized by the system. The partial cycle solenoid energization is too weak to swing other than small objects, such as a baby. The swinging device disclosed by the '635 patent disclosure is incapable of rocking a hammock occupied by an adult.
U.S. Pat. No. 2,793,375 to Wardell Jr. discloses self-rocking hammock. The hammock is rocked manually by the hammock occupant. Rocking is accomplished, using a foot pedal. No electrical motor is extant in this device. The hammock does not automatically rock when the user climbs onto it. Construction of the hammock is non-standard; the hammock is suspended between rails attached to a semi-circular frame.
U.S. Pat. No. 3,453,999 to Neal discloses an apparatus and process for rocking an infant. A compound-motion infant hammock is placed in an incubator to stimulate the infant's vestibular apparatus. The motor drive oscillates the hammock in the horizontal plane by about 120 degrees, while it rocks the hammock in the vertical plane by about 30 degrees. Rocking of the hammock is atypical. The compound motion generated by the motor drive provides unexpected movement that is unsuited for a conventional hammock.
U.S. Pat. No. 4,911,429 to Ogbu discloses a motorized swing. The swing is attached to a rod, which is mounted on two bases with vertical posts. The rod has two motor drives with L shaped downward facing pivot control arms, and control cables are attached to the infant seat. The relative orientation of these two L shaped pivotal control arms determines whether the infant seat is wobbled or swayed. The device imparts a wobbling or swaying motion to the infant seat. It is unsuited for rocking a hammock occupied by an adult. Multiple control cables effect wobbling or swaying motion to the infant seat. These cables cannot be easily attached to a conventional hammock, which is generally suspended from two fixed locations.