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Machine Vision-Based Particle Analyzers
by Nello Zuech, Contributing Editor - AIA Posted 01/31/2007
Particle sizing is important for many industries: food, pharmaceutical, etc. Many particle size measurement instruments have migrated from the laboratory to the production line. They have the ability to grab a sample from a stream of powder, prepare the sample in a manner suitable to the measurement technique, make size distribution measurements and prepare a report often in the form of a histogram depicting size distribution, discharge the sample and prepare the measurement chamber for the next set of measurements.
Many of these instruments are based on light scattering techniques but this approach has limitations because of the non-uniform profile intensity of the laser beam. As consequence, particles crossing through the center of the beam scatter more light than those crossing through the edges resulting in apparently larger size. Some instruments claim to have overcome this. Another issue is the measurement is derived from an effect rather than a direct measurement. This may introduce an error that increases as particle size decreases.
Using image analysis or machine vision-based approaches may be challenged as particles are themselves three-dimensional and the measurement is generally based on processing two-dimensional scenes. Another issue could be the basis for establishing size: area, perimeter, length of major chord, etc. However, randomness tends to statistically normalize this measurement issue. Another issue, however, is the measurement field-of-view and the number of particles, particle presentation to assure no touching/over-lapping particles and handling particles along the border of the field-of-view. Measuring only half a particle, for example, would misclassify distribution.
In spite of these issues the use of machine vision-based particle counting is becoming more widespread. To gain the latest insights into how some of these issues have been handled, we canvassed input for this article from many of the companies known to offer such products.
The following provided responses to our questions and those responses follow:
- Paul J. O’Brian – Engineering Manager, T.M. Canty
- Trish Appleton – Malvern Instruments
- Dr. Larry R. Unger - Product Specialist – Particle Sizing Systems
- Dr. Michael Rietschel - Manager Sales Support - Sympatec GmbH
1. How would you describe your machine vision/image processing-based particle analyzer product line? What particle size ranges do your products handle?
[Paul J. O’Brian – T.M. Canty] The Canty product line is a versatile offering for dry and wet applications, both on and off line. Systems generally cover a range from 1 micron up. Smaller ranges span from smallest particle size to smallest particle size x 100, and large end (rocks) spanning approximately 20x. Systems are designed for extreme field conditions as well as clean room.
[Trish Appleton – Malvern Instruments]
- Morphologi G2 provides measurements of particles in the size range 0.5 µm to 3000 µm using both wet and dry dispersion techniques.
- Sysmex FPIA-3000 provides wet measurement of particles in the size range 0.8 µm to 300 µm.
[Larry Unger – Particle Sizing Systems] The Occhio 500 Nano measures particles from 0.5 microns up to several hundred microns and is ideally suited for laboratory applications. The Occhio Belt System measures from about 20 microns up to 7 or 8 mm and can be configured for at-line process applications as well as for laboratory use. The range is a function of both field of view and the required statistical sampling as determined by the end user. Larger particles require longer measurement times, since fewer particles are in the field of view at any particular instant.
[Dr. Michael Rietschel - Sympatec GmbH] We offer high-speed dynamic image analysis instruments with a measuring range between 1 µm and 20 mm (off-line = laboratory based analysis) and 5 µm to 3,5 mm for production control (on- and in-line). The combination of our tried and tested dispersion systems employed in our laser diffraction range combined with the high speed imaging system QICPIC ensures millions of particles may be examined in a very short time period. Millions of particles per measurement ensure proper statistics with reliable results and excellent reproducibility. All in all QICPIC technology opens a new dimension of hitherto unknown possibilities, which even now for experts still seem to be impossible and hard to believe. Dry and wet dispersion can be handled within one instrument.
2. What specifically differentiates the machine vision/image processing models you offer? Do you offer both online and offline versions?
[Trish] Key points:
- Fast measurement of hundreds of thousands of particles, rapidly generating statistically significant data.
- Provide morphological information on each individual particle and record high resolution images for visual inspection/verification and the ability to detect phenomena such as broken particles, agglomerates and the presence of fines.
- Ensure controlled orientation of particles for identification of real morphological differences (uncontrolled or random orientation may mask genuine morphology).
- Support regulatory compliance through the provision of validation documentation, and software that meets the requirements for 21CFR part11 compliance.
Morphologi G2 – The Morphologi G2 has at its core high quality optics and precision scanning capabilities. Applied to these is Malvern’s expertise in sample dispersion, particle characterization, systems integration and flexible, user friendly software. The result is a high sensitivity particle image analyzer that delivers sophisticated particle size and shape data and images suitable for use in a wide range of applications.
Sysmex FPIA-3000 – The Sysmex FPIA-3000 is based on the principles of flow cytometry. A key feature of in providing reliable quantitative particle shape measurement is its patented sheath flow mechanism. This ensures that samples pass through a sheath flow cell, transforming the particle suspension into a narrow, flat flow and ensuring that the largest area of the particle is oriented towards the camera and that all particles are in focus.
Both systems can be used off line or at line but not on line.
[Larry] The main differentiation for our line is the desired particle range for analysis. The 500Nano is ideally configured for measuring samples as small as 0.1mg. The patented, vacuum dispersion system ensures that the sample is prepared without damaging easily friable materials. The Occhio Belt System ensures proper sample preparation through a combination of vibrational feed rate and variable plate speed for larger particles.
[Michael] Modular instrument design with application-specific dispersion units for dry and/or wet applications:
- Dynamic image analysis with tried and tested dry dispersing unit RODOS
- Millions of particles per measurement, no physical limit on stored particles
- Particle image and environment stored for every particle
- 500 images per second reduces measurement time to a minimum
- Clear outline of particles, independent of the position in the measuring zone
- Definite borders of particles, black outline, transparent particles are possible
- User defined class limits out of 30000 primary size classes, free definition of sampling points, pre-defined set of size classes are shipped with the software (e.g. HELOS classes, sieve classes, etc.)
- A large number of evaluation modes are available, evaluation modes are selectable even after the measurement
- Instruments fulfill the security requirements of the FDA and is compliant to 21 CFR Rule 11.
We offer both online and offline versions. QICPIC as off-line and PICTOS as on-line system. QICPIC with dry and wet dispersion in the range of 1 to 20000 µm for laboratory environments. PICTOS with dry dispersion in the range of 5 to 3500 µm for production environments
[Paul] Canty systems have been developed across a wide range of industries and, therefore, have built in to them the capability to handle the process presentation as well as the image analysis. Canty's forte over the years has been seeing into reactors and other process enclosures that are made difficult due to pressure, temperature, corrosion etc... Solving these problems has expanded the applicability of the systems and lead to a development of a wider offering than most companies.
3. Can you briefly review the underlying principles associated with your machine vision/image processing-based particle analyzer? Specific hardware arrangement and software?
[Larry] Samples are presented for measurement in an orientated manner that ensures that the two largest dimensions are being measured. This allows for excellent correlation with sieve data. Particles are dispersed prior to the imaging step. By controlled motion of the plate and proper shutter speed, sample blurring is eliminated. Since the particles all lie on the same plane, they are all in sharp focus. A monochromatic light source eliminates the possibility of chromatic aberration and angular stray light is prevented through the use of a telecentric lens, which also provides for a superior depth of field for the focus. This combination of features provides a very sharp, well-defined image for each particle.
[Michael] Basic concept is the combination of well proven powerful dispersion units from our laser diffraction range with dynamic image analysis. Due to the efficient dispersion the particles are separated from each other by the transportation fluid (air or liquid) and overlapping particles are widely avoided. So high particle numbers per image frame can be captured. As the particles are accelerated by the dispersion process, attention has to be paid to a possible motion blur. Commercially available flash lamps with exposure times of typical 100 µs cannot be used, as the motion blur would be as much as 10 mm for particles velocities of 100 m/s. So Sympatec has developed a special pulsed light source with an exposure time of less than 1 ns resulting in a motion blur of only 100 nm for the same velocity. This is below the smallest pixel size of 1 µm and invisible for the camera. So this method has the appearance of a static image analysis. As the camera and the light source are able to operate at any speed from 0 to 500 frames per second (fps), very high particle counts are acquired in short time: With 100 particles per frame (due to the better dispersion) and 500 fps, 1,000,000 particles are acquired in 20 s, instead of normally 1 hour elsewhere.
In order to detect the edges of the particle precisely, the particle flow is imaged in transmission using a special imaging objective, which only transmits light rays to the camera that are nearly parallel to the optical axis. In combination with parallel illumination, even highly transparent particles are imaged 'black', as long as their diffraction index differs from the surrounding fluid and so their light is deflected.
[Paul] The process of image analysis is typical - software is written to try to mimic the eye-brain interaction that enables an individual to see characteristics in an image. Many times, image filters are combined to achieve this goal. Hardware is currently trending toward Ethernet systems for network transmission of information. Due to the large processing power required, dual xeon processors are common.
[Trish] Morphologi G2 is based on digital image analysis and automated microscopy. It measures particle size across a wide range from 0.5 to 3000 microns using circle equivalent diameter and employs a variety of parameters for particle shape analysis.
- Encompasses the latest Nikon CFI 60 optics coupled with a high resolution digital camera for high definition, aberration-free images.
- Optics are mounted on a revolving head for automatic change over.
- The Prior Scientific stage delivers precision X, Y and Z control, with certified calibration grating to ensure the data is precise, secure and validated at all times.
- Malvern’s expertise in systems integration has been essential to its development.
- The software has been developed from Malvern’s well established, proven platform for analytical instrumentation.
The Sysmex FPIA-3000 available from Malvern Instruments measures particles suspended in aqueous and non-aqueous media. Using a CCD camera and strobe illuminations it produces images of each suspended particle.
- Sysmex’s patented sheath flow mechanism ensures particle images are in focus and do not overlap.
- Images are captured using stroboscopic illumination and CCD camera.
- Sysmex’s software provides scattergram format that allows the establishment of a sensitive size and shape fingerprint for each sample analyzed.
4. What are the critical parameters of a machine vision/image processing-based particle analyzer that a customer should understand? Optics? Camera? Lighting? Software? Etc.?
a) Adoption to the product/application - modular design of the system
b) Proper dispersion instead of tricky software elimination of overlapping particles.
c) High number of particles to be processed to enable proper statistics.
[Paul] Most important element to understand about a vision system is the need for proper illumination of the target product. All other things being equal, illumination (intensity, evenness across the view, collimation etc.) is the deciding element in a good presentation of the product to the camera or a bad one. Defining the edges of particles consistently leads to accurate and consistent results. For many particles such as gels and fluids, only specific configurations of light will illuminate the particle to the camera properly so it can be accurately analyzed.
[Trish] Hardware and software options should be set up in standard operating procedure (SOP) format so that no manual interventions are needed during measurement.
- Light calibration is always performed at beginning and end of measurement.
- Any light non-uniformity, lens parfocality errors and stage tilt are automatically compensated for in the software.
- The camera takes around 3 frames per seconds with an overlap of frames to ensure every particle is recorded. The software records the x y coordinates of every particle to ensure that no particle is repeated.
[Larry] Occhio has designed these systems so that operators can be trained to make accurate measurements with minimal training. Most parameters related to the optical system -- camera, lighting, and lenses – have been preset and require no routine operator intervention. The software has been written by Occhio to employ the most robust algorithms available. Images are stored as perimeters of each particle, drastically reducing the size of each file when compared to other imaging formats. The result is that there is no need for special computer power to collect, store and process the data. Files containing more than 100,000 particles open within one or two minutes.
5. What are the skills required to program and operate a machine vision/image processing-based particle analyzer?
[Paul] Systems generally have windows based formats and the software wizards step you throughout the set up process. For operators, the system is already set and they merely select the product being run to call up the set up and then run the product through the system. Results display automatically.
- Use of Windows software.
- A step by step lay out allows the SOP to be set up with the minimum of user decisions. Once the SOP is in place the operator simply prepares the sample and presses ‘go’ to run the measurement. The most important factor is good sample preparation.
[Larry] Operators familiar with MS-Windows® can normally be processing samples within an hour. Special settings can be stored and easily recalled for operation. We provide training for the operators in operating the dispersion systems in order to obtain the best sample preparation techniques. The controls for these systems are minimal and can be learned in a matter of a few minutes.
[Michael] All software used in our systems has been developed in house and this leads to an easy transfer for our current customers using laser diffraction systems because major parts of the packages are common. There are several levels of system usage which are ‘‘logon protected’‘ this ranges from basic user of developed methods (SOPs), through to method developed through to result reviewer. The most important skill is a genuine interest in conducting meaningful experiments, which relate to the material performance (e.g. dry powder flow) and examining the data generated to provide sensible and sensitive outputs. The system generates real pictures of the particles and this in many ways shows the customer the reality of their materials it genuinely is ‘‘what you see is what you have!’‘
6. How do you support your products ? training, documentation, warranty, post installation service, software revisions? Are these free or is there a fee?
[Trish] Malvern offers complete training; documentation and service packages depending on user requirements and prices depend on the level of support required. Our instruments come with a 1-year warranty and we offer free software upgrades.
[Larry] Product support is customized for each individual need. We generally offer training, installation, and documentation with each instrument domestically. The warranty is provided by the manufacturer and supported by us. We have trained service personnel available for support globally. Software updates which correct any issues are offered at no charge. Upgrades for full, new revisions of software are offered at a reasonable cost or can be purchased as a package with the instrument.
a) Training: Basic training (2 days) included in the system price,
b) Documentation: Supplied in local language together with the system (included),
c) Warranty: 12 months warranty as standard,
d) Post installation service: Worldwide after-sales service on request or different maintenance contracts due to the customer needs (fee),
e) Software updates: Within a main release free of charge, new main release with moderate fee.
[Paul] Canty has a technical support division which works with customers over the phone and via internet or modem hook ups to access the software and work remotely to assist the customer. We also provide fee based site visits.
7. Where do you see breakthroughs coming in the specific infrastructure technologies (hardware and software) that are the basis of the machine vision/image processing-based particle analyzer in the near future? Next three years?
[Larry] The next major breakthrough will be the ability to perform true 3-D image analysis on a particle-by-particle basis. This will provide the user with complete particle size and shape information. Occhio is on the forefront of technology in developing the techniques to enable 3-D image analysis.
[Michael] Our recently launched QICPIC & PICTOS technology has the potential to become a break-through innovation:
Up to 500 images per second already implemented due to specific developed compression hardware and firmware integrated in the camera housing. Intensive parallel processing of the image data blocks is used. The next step in technology should not be expected earlier then within 5 to 10 years.
Dual core processors such as the latest Intel Core 2 Duo technology are already supported from the current software release of WINDOX.
From the response of our most experienced customers (some dozens) we know, that we are already some years ahead of previous technology standards. In addition more and more application-specific evaluation methods are requested and this is the challenge for the software development on one hand and specific dosing and dispersing solutions on the other hand.
[Paul] Software is always improving with processor speed, which allows more calculation and analysis in the same period of time, which is important in controlling a process in real time. Ethernet cameras are now seeing steady improvement in terms of minimum illuminations requirements and frame rate transmission which in many cases determine their viability for the application.
With the US Food and Drug Administration (FDA) PAT initiative (Process Analytical Technologies) emphasis is being placed more and more on understanding and improving processes in the pharmaceutical industry.
The use of new technologies that assist in understanding and improving processes is being encouraged.
Often knowing only the size of particles is not enough to identify where or why a problem has occurred in a process.
Information on shape may be more informative.
Faster camera bus speeds (e.g. GigE and Firewire800) coupled with increasing processor power (e.g. dual and quad core processors) will enable faster or more sophisticated image processing to be performed by the PC.
The migration to digital HD TV will increase volumes of broadcast quality video technology hence reducing the cost of high-end cameras.
8. What specific performance improvements are anticipated driven by these forthcoming technological changes? How will they impact the use of these systems?
[Michael] PC power will improve further on and the user requirements are growing the same speed or even faster. The ongoing process of improved quality management on the user site requires more and more specific evaluation methods to be implemented (as mentioned in 7.). This is the challenge for the suppliers of image analysis instruments as well.
[Paul] Better technology allows for more analysis in a finite period of time leading to more accurate process control. Development of Ethernet cameras will allow for faster transmission of data throughout the network.
Moore’s law continues with PC performance (x2 every 18 months) so our instrument measurement times will become shorter.
Higher-resolution and/or large CCD die size with low defect imagers means more data can be acquired per frame.
On-camera functionality will allow further speed improvements by sharing image processing between the camera and PC.
Improved efficiency with more powerful cameras and computers.
As technology becomes more recognized it will be incorporated into more control specifications.
[Larry] The ability to produce 3-D images of all of the particles in a sample will completely change the face of particle size analysis. These measurements will likely take a bit longer than current, 2-D measurements, but based upon our software processing techniques, are well within the range of current computing capabilities. Changes in process conditions that result in minor variations in the shape of the product, without impacting the equivalent spherical diameter of the particle will be able to be quantified. Ensemble measurements will still be employed looking for variations in process control, but will not longer serve as the primary means to fully characterize a sample.
9. What are the main applications/markets for machine vision/image processing-based analyzers and are there market changes within those industries that are driving the adoption of these type analyzers?
[Paul] Particle Sizing applications cut across the entire industrial spectrum: from the food industry - monitoring the size and degree of cooking for cookies and cereals - to the plastics industry which strives for a tight distribution of bead size for later processing. One sector that is driving change is the pharmaceutical industry and CFR21 part 11 which is driving toward better software systems that will allow for better quality control and accuracy throughout the manufacturing process.
[Trish] Main application is fine chemicals and pharmaceuticals especially in powder and tablet production and chemical toners. The PAT initiative encourages pharmaceutical companies to use new technologies. Properties such as flowability and bioavailability can be affected by the shape of the particles.
[Larry] These products are used wherever dry powders are used. The pharmaceutical market has driven the production of a 21 CFR Part 11 compliant version of the instrument, but the basic imagery has not changed. Occhio provides results that are very consistent with sieving results. Anyone utilizing sieves for analytical purposes can save time and effort by moving to imaging. Anyone utilizing older ensemble measurement techniques can improve their knowledge about their process as well. The real change in the market is that analysts are now realizing that a technique exists that can provide them with information that has heretofore been unobtainable. As is usually the case, the market now has to understand the implication of this new information and how to put it to profitable use in their application.
[Michael] All industries, where particle shape is a quality criterion. The market is driving the users to more and more quality control or improvement of efficiency of production processes. It is too early to clearly detect affected changes from that.
10. What impact do these changes have on the technical requirements (specifications) for the machine vision/image-processing-based particle analyzers? And how will these machine vision/image processing particle analyzers have to change to address these more demanding requirements?
Intelligent software is essential.
User requirements have a huge impact on technical specification.
Systems will have to become faster, cover a wider size range and deal with samples at different temperatures.
The pharmaceutical market requires validatable and 21CFR compliant software solutions.
[Larry] Some applications look at extending the measuring range of the instruments. With current state-of-the-art optics and hardware, the range is relatively fixed and different lens and lighting combinations provide overlapping analytical results. Each new application often has some unique requirement. We make an effort to understand these specific needs and to design instruments that encompass all of these requirements.
[Michael] The changes require more and more adoptions of the image analysis instruments to the products (applications) and/or process specific implementations.
[Paul] As with all industrial products it seems the drive is to better, smaller, faster and cheaper. As industries upgrade their efficiencies, instruments must do more and be more reliable. Change will be driven by better electronic systems, which are generally smaller and faster, which then leads to redesign of the instrument package and reassessment of applicability based on improved performance.
11. As a supplier of machine vision/image processing-based particle analyzers what are some challenges you face in marketing machine vision systems?
[Larry] Users are very comfortable with old technology. Data provided by the new technique often varies from the data produced by the old technology. Imaging techniques produce results based upon inspection of each particle. Older technologies often produce results based upon the ‘‘most likely’‘ mixture of particles that would fit the data. Both types of instrumentation provide ‘‘good’‘ data. Our challenge is to present this technique as providing a new ‘‘piece of the puzzle’‘ for the analysts to use to fully characterize a material.
a) The variety of evaluation methods, in particular to structure them systematically for fields of application to be exploited.
b) To make performance of the instrument visible.
[Paul] The primary challenge is that they are new compared to traditional types of instruments. They generally provide more process information than any other type system, but they are not familiar and so the level of demonstration is well above other system types.
[Trish] Conveying to potential customers the extent and power of the data generated by these systems and the insight and information that this can provide. It is easy for some to think of these high sensitivity particle image analyzers as ‘just automated microscopes’, whereas there is really no comparisonThe optics are on an automatically revolving head controlled by software. High sensitivity particle image analyzers which allow automatic measurement of hundreds of thousands of particles in a short time providing both particle shape and size information.
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