| 摘要 |
<p>An agricultural harvesting machine (10) having a cutting element (22) movably supported thereon is provided with a height sensor (114) including a transmitter and a receiver mounted for movement with the cutting element. The transmitter (114) directs bursts of sound waves in the range of about 5KHz toward the ground and echoes of the bursts are picked up by the receiver, the elapsed time between transmission and reception being an indication of the height of the cutting element above the ground. To distinguish between echoes of the bursts and environmental noise picked up by the receiver, the bursts are encoded by transmitting them in pairs, the bursts of a pair being of fixed duration and separated by a fixed interval of time. The duration of each signal and the time spacing between signals is checked and if they are not of the correct duration or are not separated by the fixed interval of time they are rejected as noise. The time between transmission and reception of a burst is measured to provide an indication of the height of the cutting element. The measured height is compared with a reference or desired height and the difference value is used to control movement of the cutting element to the desired height. There is also enclosed an implement, such as a cutterbar (22) on an agricultural harvesting machine (10), which is automatically position-controlled to maintain a reference position relative to the ground surface. The implement (22) is mounted so that it may be raised, lowered or tilted and the control is such that tilting movements are preceded by, or are carried out concurrently with, a raising or lowering movement when one end of the implement is at the reference position and the other end is between the reference position and the ground surface. Manually operated UP and DOWN switches (332,336) not only control up and down movements of the implement but also inhibit and restore automatic control of implement positioning. A set/reset switch (340) enables manual selection of a predetermined reference position or the selection of the present implement position as the reference position. <IMAGE></p> |
