Agriculture Reference
In-Depth Information
to follow one of these methods, an understanding of manual procedures gives insight
into some of the potential methods.
The first type of robotic harvesting end effectors developed is the cutting end-effector.
Several cutting end-effector designs have been developed as described by Ito (1990),
Sarig (1993), Pool and Harrell (1991), and Bedford et al. (1998). This method is prevalent
in several agricultural applications, because it produces the least amount of stress on the
actual fruit. The basic premise is to first capture the fruit using a suction cup or gripper,
and then use a cutting device to sever the stem that is holding the fruit onto the tree. This
can either be done blindly by swinging a blade around the outer edge or by detecting the
stem's location and cutting it with a scissor device. The Kyoto University and Kubota
cutting end effectors are shown in Figure 7.20a and b. The stem's location can either be
detected through machine vision or through force/torque sensors. In the blind system, a
blade would ideally pass around the encased fruit to sever the stem without damaging
adjacent fruit or the tree. The blade must be large enough to encircle the fruit, and must
maintain sharpness to achieve a clean cut.
The scissor method reduces the chance of fruit damage but is substantially more
complex, requiring a larger end-effector, more sensors, and more time. This approach
is extremely difficult to successfully implement in clustered fruit.
The second type of end-effector is the pull-and-cut end effector. This method
was proposed by Pool and Harrell (1991). In this method, the fruit is grasped either
through suction or a type of collection sock. The stem is severed as the end effector
retracts. This method disturbs the surrounding limb structure, making subsequent
harvesting more difficult since the fruit is in motion, and still has some of the limita-
tions of the cutting end effectors previously mentioned.
The third type of end-effector design is the twisting method. This method was
suggested by Juste et al. (1992) and Rabatel et al. (1995) to be the most promising
of the three and is shown in Figure 7.21. This involves twisting the fruit, preferably
F
c
δ
Cylinder 2
Cover
Cutters
Optical proximity
sensor
b
F
Stroboscope
Scissors
a
Vacuum pad
Cylinder 2
Color TV camera
Scissors
Cylinder 1
60
4
mm
180 mm
Rubbertuators
(a) Kubota
(b) Kyoto
FIGURE 7.20
Cutting end-effectors from (a) Kubota (b) Kyoto University (From Sarig, Y.,
J. Agric. Eng. Res.
, 54, 4, 265-280, 1993. With permission.).
