Agriculture Reference
In-Depth Information
operator display
electr. control unit
+ operator interface
el. hydr. valve
hydr.
actuator
ultrasonic
distance sensor
tension-
spring
opener
Fig. 8.7 Use of ultrasonic distance sensors for either manual ( left ) or for computer assisted control
( right ) of the sowing depth (From Auernhammer 1989 and Scarlett 2001 , altered)
gauge wheels is that their adjustment must be done manually on every row unit.
This excludes site-specific depth control on-the-go, which is possible with pres-
sure control.
A way out of this situation is a combination of pressure- and depth control, but
without gauge wheels. Instead of using gauge wheels, the penetrating depth of the
openers is sensed by ultrasonic sound waves , which are emitted by small sensors
that are fixed to the arms of the openers. The time that the vertically oriented sound
wave echos need to return to the sensors defines the distance of the opener arms
above the ground and thus the actual seeding depth (Fig. 8.7 ).
This sensing technique for indicating and controlling the seeding depth on-the-
go was developed by Dyck et al. ( 1985 ) and commercialized in Australia. Openers
of air seeders with or without these ultrasonic sensors were tested at the Alberta
Farm Machinery Research Centre ( 1994 ). The ultrasonic sensing resulted in much
smaller differences between the intended and the finally measured seed depths.
However, a continuous use of such seeding depth control by ultrasonic waves in
commercial farm machinery did not occur. High prices for ultrasonic sensors in the
past may have been responsible for this. But in the meantime these prices have
dropped substantially as a result of mass production for backup-distance sensors
used in automobiles as driver aids for parking. So it may be time to reconsider ultra-
sonic sensing of the seeding depth.
Kiani et al. ( 2010 ) used an experimental control device for automatic and online
adjusting of seeding depths based on ultrasonic sensing in a similar manner as out-
lined in Fig. 8.7 . The targeted seeding depths were attained with very high precision
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