Automatic asparagus picking machine

An automatic asparagus picking machine is disclosed comprising a chassis able along a mound in which the asparagus are grown. The chassis has a picking tool which is mounted for horizontal and vertical translation at right angles to the direction of displacement of the chassis. The tops of the asparagus are back lit by a lighting system on one side of the mound and their images are picked up by a camera system on the other side. A microprocessor controls the direction of displacement of the chassis parallel to the mound and controls the horizontal and vertical translation of the picking tool. In one embodiment, there is one camera and the microprocessor has a window generator generating windows in two zones of the field of view of the camera. In another embodiment, juxtaposed wide angle and narrow angle cameras are used. Electric motors drive each of two front wheels at different speeds to control the direction of displacement of the machine.

FIELD OF THE INVENTION 
The present invention relates to an automatic asparagus picking machine or 
robot, that is, a self-propelled apparatus capable of detecting asparagus 
breaking through the ground and automatically picking it without any human 
intervention. 
BACKGROUND OF THE INVENTION 
At the present time, in the field of agriculture certain picking or 
gathering tasks, for example, harvesting grains (wheat, corn, etc.) fodder 
and grapes have been satisfactorily mechanized. For other operations such 
as trimming vines and fruit trees and packing fruit, the problem has yet 
to be solved. 
Increasing productivity and competitiveness involves a development of 
mechanization. Such mechanization is all the more necessary and 
inescapable inasmuch as it is increasingly difficult year after to year to 
find seasonal or migrant labor for picking and harvesting crops. 
This type of problem is posed particularly for the picking of asparagus 
which is a relatively arduous task for which the remuneration cannot be 
correspondlingly great if the cost price or the asparagus crop is not to 
be unduly increased and asparagus crop unsalable or uncompetitive. 
OBJECT AND SUMMARY OF THE INVENTION 
An object of the present invention is to find a solution to such a problem 
by providing a fully automatic agricultural machine capable of taking the 
place of manual labor for picking asparagus with better productivity and 
at a reasonable cost. 
According to the invention there is provided an automatic asparagus picking 
machine of the type comprising means for displacing and controlling the 
direction of displacement of the chassis parallel to a mound of soil in 
which asparagus to be picked are grown. An asparagus picking tool is 
provided with means mounting the picking tool for horizontal and vertical 
translation at right angles to the direction of displacement of the 
chassis. Direction and control means detect asparagus to be picked and 
control the position of the picking tool. The direction and control means 
comprises a camera system and a lighting system for back lighting the 
mound of soil. The camera and lighting systems are mounted on the chassis 
on opposite sides of the mound and arranged substantially in a horizontal 
plane generally coinciding with the top of the mound. The means for 
displacing and controlling the displacement of the chassis includes a 
microprocessor for controlling the direction of displacement of the 
chassis parallel to the mound. The microprocessor also controls the 
horizontal and vertical translation of the picking tool for extracting a 
detected asparagus from the mound and transferring its to a receptacle. 
According to a first embodiment, the camera system comprises a single 
camera. The microprocessor detects the presence and passage of an 
asparagus image picked up by the camera. The microprocessor determines 
spatial coordinates of the asparagus and supplies coordinate related 
signals to the motor means for displacement of the chassis and to motor 
means for the horizontal and vertical translation of the picking tool to 
stop movement of the machine with the picking tool in vertical alignment 
with the asparagus. The microprocessor thereafter commands the picking 
tool to pick the asparagus and then restart displacement of the chassis at 
a predetermined speed. 
Preferably the microprocessor comprises a sync pulse generator connected to 
the camera. A first and a second detection window generator means generate 
windows in two zones of the field of view of the camera. A first and a 
second detection means detect the presence of the asparagus image in the 
respective windows. The first and second detection means respectively 
connect the first and second window generator means to the camera via a 
circuit for shaping and processing the image picked up by the camera. The 
microprocessor further comprises a circuit for calculating the 
displacement of the chassis receiving output signals from the detection 
means. The calculating circuit controls the motor means for displacement 
of the chassis and is connected by a horizontal and vertical coordinate 
calculating circuit and a circuit for controlling the motor means for 
horizontal and vertical translation of the picking tool to the motor means 
for horizontal and vertical translation of the picking tool. 
According to a second embodiment, the camera system comprises two 
juxtaposed cameras. A first camera is a wide angle camera with low 
remanence and the second camera is a narrow angle camera. The 
microprocessor detects the entrance of the asparagus in the field of view 
of the first camera, and thereafter its passage into the viewing axis of 
the second camera while the asparagus is still in the field of view of the 
first camera. The microprocessor controls the position of the chassis so 
that the asparagus is in the viewing axis of the second camera and 
determines spatial coordinates of the asparagus for delivering coordinate 
related signals to the motor means for horizontal and vertical translation 
of the picking tool and for starting the machine for displacement at a 
predetermined speed after extracting the asparagus. 
Such a mircoprocessor comprises a circuit for calculating the displacement 
of the chassis connected to each of the camera through a circuit for 
shaping and processing images picked up by the associated camera. The 
calculating circuit controlling the motor means for the displacement of 
the chassis and connected by a circuit for calculating horizontal and 
vertical coordinates of the asparagus and a circuit for controlling the 
motor means for horizontal and vertical translation of the picking tool. 
These and other features and advantages of the essential parts of the 
automatic picking machine embodying the invention and in particular the 
camera systems and the above defined associated microprocessor will become 
more apparent from the description which follows, given solely by way of 
example with respect to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a highly schematic view of a prototype of the automatic machine 
or robot for picking asparagus according to the invention. 
The machine comprises a movable unit adapted to be displaced straddling a 
mound 1 for moving a row of asparagus, several tips or turions 2 extending 
through surface of the soil at the top of the mound 1. 
In the embodiment illustrated in FIG. 1, the movable unit comprises a 
straddling chassis 3 having four wheels 4, of which two for example (at 
the front or back of the machine) are motor driven by one or two motors 
(not shown) aboard the chassis. The or each motor may be an electric motor 
with the source of electric energy therefor mounted on the chassis 3 of 
the machine. 
On one of the sides of the chassis 3 is mounted a camera system 5 and on 
the other side opposite the camera system 5 is mounted a back lighting 
system 6. The camera system 5 and the lighting system 6 are on opposite 
sides of the mound 1 substantially in alignment with the top of the mound. 
According to a first embodiment, the camera system 5 comprises a single 
camera C having a field of view schematically illustrated in 7 in FIGS. 2 
and 5. The field of view of the camera covers substantially the entire 
surface of a translucid screen lit 8 by a lamp or tube 9 enclosed in a 
light box. 
The picking machine further comprises means for grasping an asparagus or an 
asparagus picking tool for example, vertically oriented tongs 
schematically shown at 10. The tongs are fixed at the end of a vertical 
gear rack 11 movable along the vertical axis Z by means of an electric 
motor carried on the carriage 12 supporting the tongs 10. 
The carriage 12 is mounted for translation in a Y direction at right angles 
to the Z direction and to the direction of displacement of the machine 
which is of course parallel to the axis of the mound 1. To this end the 
carriage 12 may, for example, be driven by means of one or two horizontal 
worms parallel to axis Y, carried by the chassis 3 and rotationally driven 
by an electric motor, the carriage 12 being fixed to a nut cooperating 
with the worm. The drive and guide means for the gear rack 11 and the 
carriage 12 are entirely conventional and therefore need not be described 
or illustrated in greater detail herein. 
As for the tongs 10, they may comprise two opposed legs or jaws 
displaceable relative to each other, under the action of motor means such 
as an electromagnet, for grasping the asparagus and extracting it from the 
soil and then depositing it in a receptacle 13 carried on the machine. 
The motors for controlling the forward displacement of the machine 
(direction X), the horizontal direction (direction Y) of the tongs 10 and 
the vertical displacement (direction Z) of the tongs 10 and the operation 
of the tongs 10 are controlled automatically by means of signals received 
from the camera C and processed in a microprocessor which will now be 
described with reference to FIGS. 3-6, and more particularly, to FIG. 4. 
In FIG. 4 the light screen is symbolized at 8. The microprocessor for 
processing information picked up by the camera C comprises a sync pulse 
generator or clock 14 connected to the camera C. 
The sync pulse generator 14 is also connected via a coordinate calculating 
circuit 15 to two detection window generators 16 and 17. One of these 
generators 16 delimits the contour of a first window F1 located in a first 
zone of the field of view of the camera C diagrammatically shown by a 
rectangle 18 in FIG. 6, whereas the second window generator 17 delimits a 
second window F2 identical to the first but located in a second zone of 
the field of view. Each of the windows generators 16,17 are connected to 
detection means 19,20 for detecting the presence of an asparagus. 
The detection means 19 and 20 are connected in parallel to the camera C by 
means of a circuit for shaping and processing the images comprising a 
"binarizing" circuit 21 and a contour extracting circuit 22. The outputs 
of detection means 19 and 20 are delivered to a circuit 23 for calculating 
the displacement of the machine controlling, on the one hand, the motor Mx 
for displacement of the machine and, on the other hand, motors My and Mz 
for horizontal and vertical translation of the tongs 10 by means of a 
circuit 24 for calculating the coordinates (in direction Y and Z) of the 
asparagus detected and a circuit 25 for controlling motors My and Mz. 
Power supply for the various circuits is provided by an electric power 
source aboard the machine; likewise the entire microprocessor is mounted 
on the chassis 3. 
The operation of the above described microprocessor is as follows. 
The camera C and the lighting screen 8 providing back lighting, are 
arranged so that the camera C picks up in its field of view (FIG. 3) the 
top of the mound substantially along a horizontal center line. The 
interest of back lighting resides in the machine not being dependent on 
ambient lighting conditions and therefore can operate day or night. The 
images are at all times satisfactorily contrasted. 
When the turion of an asparagus 2 is in the field of view of the camera C, 
the image 26 picked up by the camera (see FIG. 4) distinguishes a dark 
lower part 27 and a light upper part 28 and the turion 2. 
Owing to the "binarizing" circuit 21 with adjustable threshold means 29, 
the image 26 is transformed into an only black and white image. The 
contour extracting circuit 22 (image 31) constructs the contour or profile 
of the top of the mound 1 from the black and white boundary of the black 
and white image 30. This image 31 is analysed by detection means 19 and 
20. 
The sync pulse generator 14 permits calculation at 15 of the X and Y 
coordinates (FIG. 6) of the points in the field 18 of view of the camera C 
covered and also generates control synchronizing bleeps or signals for the 
camera. 
The detection means 19 only takes into account the part of the image 31 
facing window F1 generated by generator 16 and detection means 20 does 
just the same with regard to window F2, the sizes and locations of the 
windows F1 and F2 in the field of view of the camera being defined by 
circuit 15. Window F1 is positioned at the boundary of the field of view 
18 on the side from which projects the image of the turion 2 when the 
moving machine (direction X in FIG. 5) comes into position opposite the 
asparagus. 
In FIG. 5 is represented the position C of the camera when the image of the 
turion 2 coming into the field of view of the camera will be in window F1. 
Window F2 is positioned in the vertical plane of symmetry 32 of the field 
of view. At C' in FIG. 5 is the position of the camera when the image of 
the turion arrives in plane 32 where the window F2 is located. The passage 
of the image of the turion into the window F1 causes a signal TS1 to be 
generated by detection means 19 and the passage of the same image into 
window F2 causes a signal TS2 to be generated by detection means 20. 
By means of signals TS1 and TS2 circuit 23 calculates the distance d 
between positions C and C' of the camera taking into account the speed of 
displacement of the machine. Circuit 24 calculates the Y coordinate of the 
turion 2 from the distance d since Y=d. tg.alpha. where .alpha. is the 
half angle of the camera field. 
Circuit 23 controls the stopping of motor Mx controlling the displacement 
of the chassis whereas circuit 25 controls the Y translation of carriage 
12 in order to bring the tongs 10 into vertical alignment with the turion, 
then translation in the Z direction of the tongs 10 to reach the turion. 
The adjustment of the control of motor Mx is obviously determined so that 
the machine stops with the tongs 10 in the vertical plane YZ passing 
substantially through the middle of the turion. The length of the downward 
travel of the tongs 10 in the Z direction, although adjustable, is set 
beforehand and is not subsequently modified by the machine itself. 
Of course, the microprocessor also controls the restarting of the machine 
when the asparagus has been picked up and its speed of forward 
displacement is preselected. 
Limit switches associates with the gear rack 11 ensure the actuation of the 
tongs 10 in its lowered position to grasp the asparagus after penetrating 
a predetermined depth into the soil around the asparagus, in its raised 
position for releasing the picked asparagus to fall by gravity into the 
receptacle 13, for example, through a rectractable chute (not shown) along 
a path extending away from the path of movement of the tongs. 
The microprocessor may be programmed to taken into account only turions of 
a predetermined minimum size and, optionally to select asparagus by size 
by suitable filtering the images received by the detection means 19 and 
20, this preselection of the images controlling the dispatching of the 
picked asparagus into separate compartments of the receptacle 13 as a 
function of their size. 
The machine thus self-propelled, self-contained and entirely automatic for 
systematic picking of all asparagus it encounters in its field of view 
along the entire mound. 
To this end, an automatic directional control system for displacement along 
the mound, and optionally, at the end of the mound, means for bringing the 
machine automatically into alignment with the next mound without any 
external manual intervention. Automatic directional control may be 
effected, for example, by detecting the flanks of the mounds by feelers or 
ultrasounds. 
The automatic ultrasonic directional control system is schematically 
illustrated in FIGS. 11 and 12 and a functional block diagram is 
represented in FIG. 13. 
In FIGS. 11 and 12, the chassis of the machine is designated by reference 3 
and is carried on four nonsteering wheels 4a,4b,4c and 4d, the front 
wheels 4a, 4b being driven independently of each other by means of an 
electric motor M1,M2 incorporated at each wheel hub. The rear wheels 4c, 
4d are not driven. The orientation of the machine is ensured by motors M1, 
M2 having different speeds of rotation. 
In the embodiment of FIGS. 11 and 12, there are four ultrasonic sensors or 
probes (Ca1 to Ca 4) each comprising a transmitter and a receiver. The 
four sensors are mounted on the chassis 3 in line with the four wheels 
facing the flanks of the mound 1. The sensors Ca1 to Ca 4 are respectively 
at distances d1,d2, d3 and d4 from the flanks of the mound, which 
distances are equal to one another when the machine is properly positioned 
relative to the mound. 
FIG. 13 illustrates the operation of the sensors. Each sensor Ca1 to Ca 4 
comprises an ultrasonic transmitter E controlled by a pulse generator 35 
through an amplifier 36. The transmitter E is at a certain distance dx 
from the flank of the mound 1. The ultrasonic wave emitted by the 
transmitter is reflected off the mound toward the receiver R at the same 
distance dx. The receiver R delivers to amplifier 37 a signal of the same 
frequency as that produced by generator 35 for transmitter E. The signal 
is supplied to a counter 38 which is also connected to the generator 35 
and to a clock 39. Finally, the counter 38 is connected by an interface 
circuit 40 to the microprocessor MP of the machine. 
Such an arrangement for measuring the trajectory time of an ultrasonic 
pulse is well known and need not be described in detail. 
The period of time T between the pulse train transmitted by transmitter E 
and the pulse train received by receiver R is T=2dx/C, C being the speed 
of sound through air. The period of time T is numerically converted by 
means of counter 38 counting pulses delivered by clock 39 from the moment 
of transmission to the moment the echo wave train is received. The 
transmission frequency is of the order of 40 Hz which may be modified if 
there is no echo or if it is not usable. 
The contents of the counter is "read" by the microprocessor which is 
capable of translating these contents into a sensor/reflected surface 
distance. 
As distances d1,d2,d3 and d4 are stored in the microprocessor, it can 
determine the speeds of rotation of motors M1 and M2 in order to keep the 
machine in its corrects position relative to the mound 1. 
The speeds of rotation of motors M1 and M2 are translated into speeds of 
displacement V1 and V2 of the front wheels 4a, 4b of the machine. These 
displacement speeds V1 and V2 are in the vicinity of the so-called 
cruising speed Vo of the machine. 
The correction of the displacement speeds relative to the cruising speed Vo 
is carried out, taking into account the measurement of distances d1,d2,d3 
and d4 according to the following algorithm: 
EQU .DELTA.V=speed of motor M1--speed of motor M2=a(d1-d3)+b(d3-d4) 
Coefficients a and b are determined (sign and value) as a function of the 
dimensions of the machine, cruising speed Vo and desired machine reaction 
speed. The above algorithm may be of different form and make bring into 
play limits to preclude each of distances d1, d2,d3 and d4 falling below a 
minimum safety value below which the machine would hit the mound 1. 
There may be more or less sensors and they may be positioned in different 
ways on the machine. 
They may all be positioned at the front of the machine and there may be as 
few as two sensors. 
In order to eliminate some sensor operating problems when the distance from 
the mound is too small, the sensors may be supplied sequentially or 
operate at different frequencies. Furthermore, distance measurements may 
be filtered by the microprocessor of the machine to eliminate any spurious 
values. Finally, if is possible to use the ultrasonic sensors continuously 
and not by pulses as described above. It would then be a matter of 
amplitude modulation of the ultrasonic wave by a signal dephased between 
transmission and reception. 
The end of the mound 1 is detected by the absence of any echoes picked up 
by the receivers. 
The microprocessor on the machine is programmed to produce motor M1 and M2 
control signals such that the machine follows a semicircular path having a 
radius R=D/2 where D is the intermound spacing, so that the machine 
reaches the correct position at the end of the following mound and resumes 
normal operation. 
Errors in displacement or shifting due to sliding of the machine or any 
defects in the control are permitted within the limits of acceptable 
mechanical tolerance relative to the widths of the mounds. However, in 
order to improve accuracy in displacement from one mound to the next, the 
machine may be equipped with an absolute position sensor. For example, a 
magnetic compass may be useful for determining the angle between the axis 
of the machine and the magnetic north. The 180.degree. turn of the machine 
at one end of a mound to the next mound may therefore be made possible by 
the microprocessor. 
FIGS. 7-10 illustrate a second embodiment of the asparagus detection means. 
In this embodiment the camera system 5 comprises two juxtaposed cameras C1 
and C2 (the first relative to the direction X of the forward displacement 
of the machine) is a wide angle camera having low remanence so as to 
obtain satisfactory images with high speeds of displacement (of the order 
of 1 m/s). Camera C2 has a narrower field of view. Cameras C1 and C2 are 
connected to a circuit 23 for calculating the displacement of the machine 
controlling motor Mx and motors My and Mz of the picking tool or grasping 
means by means of circuits 24 and 25, said circuits 23,24 and 25 being 
similar to those of FIG. 4. The circuits 33 and 34 interposed between the 
cameras C1 and C2 and the circuit 23 fulfill the same functions as 
circuits 21 and 22 of FIG. 4. Circuits 33 and 34 each include a 
"binarizing" circuit followed by a contour extraction circuit. The 
operation of circuits 33 and 34 will not be described as it is strictly 
the same as that of circuits 21 and 22 described above. The microprocessor 
of FIG. 10 processes in real time the images form cameras C1 and C2 and 
calculates the coordinates of the different turions in the common field of 
view of the cameras (stereoscopic vision). 
The wide angle first camera C1 permits detection of the presence of an 
asparagus when a turion enters its field of view(position 2b in FIG. 8) 
and from that moment starts the deceleration of the machine in order that 
the turion enters the field of view of camera C2 at a low rate of speed. 
Then, when the asparagus is on the axis of camera C2(position 2a in FIG. 
9) the machine is brought to a halt immediately. 
If the image of the asparagus turion is not correctly situated at the 
middle of the image produced by camera C2, the machine may be controlled 
to move to the precise centered position. 
Once the correct position of the turion on the image furnished by the 
camera C2 is attained, the position of the image of the asparagus turion 
furnished by the camera C1 permits the determination of the coordinates of 
the turion (stereoscopic viewing) by a simple calculation. Circuits 24 and 
25 then produce the control orders for the motors My and Mz displacing the 
tool 10 which is then on the axis of the camera C2 whose narrow field of 
view permits accurate location of the turion. 
Moreover, in the second embodiment as in the first, it is possible to 
detect the presence of more than one asparagus next to one another in the 
field of view of the camera by storage of the detection signals. 
Of course, the invention is not limited to the illustrated and described 
embodiments but on the contrary is intended to cover all modifications and 
alternatives not only as regards the microprocessor unit itself but also 
with respect to the various mechanical parts of the machine, its 
propulsion means, its directional control system and the picking tools, as 
well as the arrangement and operation thereof, without departing from the 
scope of the invention.