[0001] This invention relates to a process for sorting bulbous and tuberous produce into
successive size classes, in particular suitable for sorting potatoes.
[0002] In potato trade and processing industry potatoes are sorted into different size classes
using internationally applied square size. The square size of a potato can be defined
as the length of the side of the small square opening through which the potato can
pass. The potatoes are sorted by means of riddles into a number of classes, e.g.,
a first class of potatoes having a square size below 35 mm, a next class of potatoes
having a square size ranging from 35 to 45 mm, etc. Although acceptable accuracy is
obtainable with such a sorting method, yet the number of potatoes that will find their
way to a wrong class cannot be disregarded. These are for the major part potatoes
having a square size near the boundary value of a class. When, e.g., potatoes are
sorted into three size classes of, e.g., 20-30 mm, 30-50 mm and 50-70 mm, there is
a great chance that a relatively large number of the produce that wrongly found its
way to the class of 50-70 mm will have a square size ranging from 46 to 50 mm. Similarly,
a relatively large number of produce having a square size ranging from 26 to 30 mm
will generally be present in the class of 30-50 mm.
[0003] Since in potato trade and processing industry a more and more accurate sorting into
a relatively large number of classes each comprising a relatively small size range
is required, there is a need for an improved sorting method. The object of this invention
is to meet the above need. For this purpose a process of the above type is characterized
according to the invention in that in the transitional range between at least two
successive main classes at least one intermediate class is defined; that a first sorting
operation is carried out, in which produce is sorted according to sizes falling within
the remaining range of the at least two main classes and the at least one intermediate
class; that the produce selected as falling within the remaining range of the main
classes are passed to collections of produce belonging to those main classes; that
the produce falling within the at least one intermediate class is subjected to a second
sorting operation, the produce falling into an intermediate class being separated
into a first group belonging to the one main class pertaining to the relevant intermediate
class and a second group belonging to the other main class pertaining to the relevant
intermediate class; and that the two groups are added to the collections belonging
to the main classes.
[0004] In the following the invention will be further described with reference to the accompanying
Figure, which schematically illustrates the principle of the process according to
the invention.
[0005] The Figure schematically shows, by way of example, three size classes, according
to which bulbous and tuberous produce such as potatoes, but also, e.g., onions wit
the stems cut off, apples etc. can be sorted. In this example the size classes I,
II and III correspond to, e.g., sizes determined according to the square size principle
of respectively 20 through 29 mm, 30 through 49 mm and 50 through 69 mm. As stated
before, the sizes of the major part of the produce classified during the sorting process
into a wrong class are just below the sizes belonging to the next class of larger
produce.
[0006] According to the invention intermediate classes are introduced for produce having
sizes that are near the boundary with the next class. The intermediate class may be
completely within one of the original classes, but may also overlap the boundary between
two original classes.
[0007] Thus, in the example shown, two intermediate classes IV and V are defined for produce
having sizes of from, e.g., 26 and 24 mm and 46 and 54 mm, respectively. By now sorting
not only according to the original main classes, but also according to the intermediate
classes, the major part of the produce wrongly sorted at the original sorting machine
will find its way to one of the intermediate classes. The other produce is directly
classified into the right collections, as schematically indicated by arrows 1, 2 and
3. According to the invention the produce that found its way to the intermediate classes
is subjected to a second sorting operation, as schematically indicated by blocks 4,
5. The second sorting operation need not be carried out similarly to the first sorting
operation. For the second sorting operation a more accurate sorting method can be
used advantageously. Although accurate sorting methods are generally also relatively
time-consuming, this need not be a drawback, because relatively little produce is
present in the intermediate classes.
[0008] For the second sorting operation the so-called channel sorting method could be used
as described in applicants' simultaneously filed Dutch patent application, according
to which method produce like potatoes can be sorted based on the square size by measuring
the height of the potato located in a V-shaped channel.
[0009] In the second sorting operation the produce present in the intermediate class is
accurately sorted into two groups, the separation between the two groups being formed
by the boundary between the orginal classes. Thus the sorting operation indicated
at 4 separates the produce into produce below 30 mm and produce above 29 mm, respectively.
The first group is passed to the collection 20/29 and the second to the collection
30/49, as schematically indicated by arrows 6, 7. Similarly, the produce is separated
at 5 into a first group below 50 mm and a second group above 49 mm, as indicated by
arrows 8, 9.
[0010] It has been found that when using a two-stage sorting method as described above a
sorting accuracy of 97 to 98% is obtainable.
1. A process for sorting bulbous and tuberous produce according to successive size classes,
in particular suitable for sorting potatoes, characterized in that in the transitional range between at least two successive main classes at
least one intermediate class is defined; that a first sorting operation is carried
out, in which produce is sorted according to sizes falling within the remaining range
of the at least two main classes and the at least one intermediate class; that the
produce selected as falling within the remaining range of the main classes are passed
to collections of produce belonging to those main classes; that the produce falling
within the at least one intermediate class is subjected to a second sorting operation,
the produce falling into an intermediate class being separated into a first group
belonging to the one main class pertaining to the relevant intermediate class and
a second group belonging to the other main class pertaining to the relevant intermediate
class; and that the two groups are added to the collections belonging to the main
classes.
2. A process as claimed in claim 1, characterized in that the second sorting operation is carried out releatively more accurately than
the first sorting operation.
