Field of the Invention
[0001] Laser sorter is a device for sorting objects by color, size, shape and other characteristics
available for analysis by means of machine vision. It may be primarily used for sorting
agricultural products.
Background of the Invention
[0002] The state of art includes material carrier, collimated laser illumination source,
image read-and-process device and a device for removing defective material. According
to the invention, it additionally comprises a cylindrical lens arranged on collimated
ray path. The lens is designed so that a formed flat light beam illuminates the area
of the image reading the sorted material.
[0003] The state of art also includes two or more readers to process laser light reflected
and transmitted through the material and to in different spectral ranges. Use of laser
radiation for illuminating the moving product allows to increase substantially the
illumination of the image-forming region as well as to reduce the exposure time in
order to increase the resolution of the formed image by augmenting the scanning frequency
of the linear video sensor. In the known device scanning frequency of the linear video
sensor and laser beam sweep frequency are synchronous and, therefore, are limited
by the capacity of mechanical scanner. High illumination also provides relatively
small exposure periods when registering radiation or emission of fluorescence that
have passed through the material. Thus, different reading devices detect simultaneously
reflected and transmitted signals at a high sorting performance. This reading apparatus
can perform its functions in different spectral ranges which extends the functional
possibilities of the claimed laser sorter in comparison with the known device.
[0004] The state of art also includes two or more collimated laser light sources, each of
which is added by a cylindrical lens, and the orientation of the sources enables to
form one or more flat light beams. In that case laser light control expands. Control
over laser power and spatial arrangement of illumination area allows to adjust the
total spatial distribution of the illumination of the working area. Use of lasers
of different spectral ranges and formation of separate illumination areas in these
ranges allow to analyze objects according to various predefined sorting criteria within
one sorting cycle.
[0005] The state of art further includes laser light sources intensity modulators. In this
case, images may be formed in different spectral ranges and recorded by a broadband
linear video sensor in one sorting cycle. The low inertia of control over laser light
allows to turn off of the material as it moves in one range and to turn on the backlight
in another range, synchronizing the process with the movement of the material from
one area to another.
[0006] U.S. Pat. No 6,509,537 B1 dated 21.01.2003,
U.S. Pat. No 6,864,970 B1 dated 8.05.2005 disclose apparatus comprising a material carrier, image read-and-process device and
a device for removing defective material. The material carrier provides continuous
transport of the material into the image reading area and the zone of the defective
material removing device. After reading the image is analyzed by an image processing
device according to one or more of the following characteristics: color, texture and
shape of the object . Those objects whose values significantly deviate from the preset
ones are removed from the feed stream with device for defective material removal,
which is usually an array of air ejectors. Illumination of the sorter image reading
area constructed with the use of a beam-scanning mechanical system. A beam of laser
light from the source is directed through a semitransparent mirror on a high-speed
lens with mirror facets. Due to the rotation of the prism, laser beam sweeps over
the entire image scanning area. The light, reflected by the material moving through
the scanning area, is reflected by a rotating mirror and is directed to radiation
detectors. The signal from the photo detectors goes to the image processing system,
which determines the suitability of the product and gives signals to a device for
the defective material removing. The common disadvantages of these schemes are as
follows. First, to get high performance the laser beam is to scathes image reading
region 2000-5000 times per second, which requires very high speed rotation of the
mirror prism. Secondly, the photo-detectors cannot provide high-resolution required
for scanning small (1-5 mm) materials. Thirdly, complexity of the optical system leads
to the fact that the slightest irregularities in the arrangement of optical elements
can cause failure of the entire system.
[0007] U.S. Pat. No 2010/0046826 A1 dated 25.02.2010 describes devices wherein the rotating mirror is intended only for a laser beam sweep
and performs the function of redirecting the reflected light to the photo detectors.
This can greatly simplify the optical system of the device. The function of photographic
recording of the images is performed by the camcorder with linear video sensor which
greatly improves the resolution of the device.
[0008] This means that it is necessary to provide a high speed rotation of the mirror prism
and a high precision of the moving mechanical parts to ensure the stability of the
optical circuit configuration that, together with the high cost of the scanner device,
reduces the reliability and limits the scope of its application.
Summary of the Invention
[0009] The invention is represented and characterized in the main claims while the dependent
claims describe other characteristics of the invention.
[0010] The aim of the present invention is to create a device for sorting of agricultural
products by color, size, shape and other characteristics available for analysis by
means of machine vision.
[0011] Another aim of the invention is to increase the self-descriptiveness of the recorded
image, to simplify the structure of the sorter, to increase its reliability and reduce
manufacturing costs.
[0012] In compliance with the invention, laser sorter consists of a material carrier, collimated
laser illumination source, image read-and-process device and a device for removing
defective material.
[0013] Laser sorter additionally comprises a cylindrical lens arranged on collimated ray
path. The lens is designed so that a formed flat light beam illuminates the area of
the image reading the sorted material.
[0014] Laser sorter includes two or more readers to process laser light reflected and transmitted
through the material and to read in different spectral ranges.
[0015] Laser sorter also includes two or more collimated laser light sources, each of which
is added by a cylindrical lens, and the orientation of the sources enables to form
one or more flat light beams.
[0016] The state of art further includes laser light sources intensity modulators.
[0017] As opposed to the known scanning sorter wherein the image alters with time because
of 2 dynamic processes - movement of the material and movement of the laser ray formed
by the movable mirror, the proposed invention laser illumination is fixed. Furthermore,
for equal exposures of image registration and hence equal optical power of laser illuminators,
momentary density of the power increases multiply in scanning sorters and affects
the material causing its damage. In comparison with the known apparatus, the radiation
of laser backlight of the claimed invention is distributed across the aperture of
the moving stream. Absence of the moving optical elements, reliability, eases of manufacture
and low cost are important advantages of the claimed invention.
Brief Description of the Drawing
[0018] These and other characteristics of the invention will become clearer from the following
description of the specific claim, represented as non-limiting examples, with reference
to the accompanying drawings where:
Fig.1 describes the scheme of the laser sorter.
Detailed Description of the Preferable Specific Claim
[0019] Material carrier 1 directs the product to the laser illumination area 2. The collimated
laser light source 3, augmented by a cylindrical lens 4 located on the path of the
collimated beam, forms a flat light beam 5, illuminating the area of the image reading.
Image read-and-process device 6 analyses the image and, according to the preset criteria,
generates control signals given to the device for defect material removal 7.
[0020] Laser sorter functionates as follows. The material sorter 1 feeds the product from
the storage to the laser illumination area 2 in any way: by using a conveyor belt,
with a vibratory feeder with sack chute or otherwise. Falling or moving the product
flow is limited widthway by the aperture of the registered image and the line of sight
limited by the depth of field of the lens of the image reader. The collimated laser
light source 3 has a beam width greater than the width of the image recording device
6 comprising a linear video sensor. The cylindrical lens 4 converts the flat phase
front of the laser beam in a cylindrical phase front. Its focal length is calculated
on the basis of the required aperture of beam illumination area 5 and the distance
from the moving product 2 to lens 4. Uneven illumination area corresponding to the
Gaussian distribution, can be compensated at the stage of forming video signal by
a CCD-receiver. Optional compensation occurs when using several lasers since the spatial
distribution of light can be synthesized by the choice of the arrangement of lasers
and optical power adjustment of each of them. The image read-and-process device 6
for a time not exceeding the time of passage from the image recording zone to the
device for defective materials removal decides to remove substandard product. Device
6 delivers the address of the of the spatial position of the object to be deleted
to device 7 and activates it within the estimated time.
[0021] Experimental studies of the claimed invention have been performed using Colour sorter
F5.1 equipped with a system of laser illumination, made according to the claimed invention.
A cylindrical lens with a focal length F = 1.3 mm has been made of optical glass TF-5.
Single Mode Hitachi HL6545MG laser with a wavelength of 635 nm and a maximum optical
beam power of 120 mW has been used. Studies have shown high efficiency of grid products
separation using laser illumination at image registration in the reflected and transmitted
light.
1. Laser sorter consists of a material carrier (1), collimated laser illumination source
(3), image read-and-process device, device for removing defected material (6). It
additionally comprises cylindrical lens (4) arranged so that a formed flat ray (5)
illuminates the area of the image reading the sorted material (2).
2. Device as in Claim 1 characterized in that said that laser sorter includes two or more reading devices (6) to process laser
light reflected and transmitted through the material and to read in different spectral
ranges.
3. Device as in Claim 1 characterized in that said that laser sorter comprises two or more collimated laser light sources (3),
each of which is added by a cylindrical lens(4), and the orientation of the sources(3)
enables to form one or more flat light beams (5).
4. Device as in Claim 1 characterized in that said that laser sorter additionally comprises laser light sources intensity modulators.