OVERVIEW
Introduction
Mango is a widely cultivated tropical fruit in Vietnam, ranking as the 13th largest producer globally, with exports reaching approximately 893,200 tons in 2020, according to the Ministry of Agriculture and Rural Development The Mekong Delta is the primary region for mango cultivation, contributing to nearly 48% of the nation's total mango area In 2020, Vietnam's mango productivity was recorded at 567,732 tons.
In 2020, Vietnam exported mangoes to 40 countries, with China being the largest market, accounting for 83.95% of the total export turnover at 151.8 million USD Other significant markets included South Korea, Australia, Japan, Europe, New Zealand, and Russia, which reached 8.4 million USD, representing 4.65% of exports.
Figure 1.1: The chart of Vietnam's mango export market in 2020 [1]
Farmers in these countries achieve impressive results through diligent work and advanced cultivation techniques, including off-season flowering of mangoes, allowing for year-round harvesting However, the manual weighing and sorting of the large mango harvest present significant challenges, costing farmers approximately 100 billion VND annually With each worker sorting between 40 to 80 kilograms of mangoes daily and earning around 100,000 VND, the financial burden is substantial, requiring over 3,000 employees each year To optimize costs and enhance productivity, implementing a mango weighing system in the sorting line is a viable solution.
Literature review
The Quantitative packing machine of Southern Machinery and Equipment Company
The electronic weighing packaging machine is essential for accurately packing nuts, confectionery, and fruits, ensuring high precision in volume measurement This automatic equipment enhances efficiency in production and business by quantifying food for packaging or integrating with automatic packaging systems Featuring an electronic microprocessor for precise weighing, these machines are designed for easy maintenance, cost-effectiveness, and user-friendly operation through a touch screen PLC control.
Figure 1.2: The quantitative packing machine [2]
The quantitative combination small fruit weight machine is designed for weighing fruits and vegetables like maiden fruit, cherries, lychees, and apricots with precision It features an efficient distribution system that evenly allocates products into eight vibration channel hoppers, ensuring accurate quantitative weighing based on preset weights Constructed primarily from food-grade 304 stainless steel, the machine adheres to GMP standards, making it safe and easy to clean Additionally, it is equipped with high-precision digital sensors that offer quick sampling rates and exceptional accuracy.
The machine delivers reliable performance with a steady and quiet operation; however, it is currently only suitable for weighing small fruits and cannot accommodate mangoes.
Figure 1.3: The quantitative combination small fruit weight machine [3]
Zhengzhou First Industry Co., Ltd offers a noteworthy product: the Fruit Sorting and Packing Line, designed for various fruits and vegetables like oranges, potatoes, and avocados This system utilizes a grading machine with sensors and weighing scales integrated into the conveyor belt While it excels at sorting spherical fruits, its performance diminishes with oval-shaped varieties, such as mangoes The sorting process primarily relies on fruit size, which can lead to inaccuracies in classification due to the inability to guarantee precise weight.
Figure 1.4: The Fruit Sorting and Packing Line [4]
Ishida Co., Ltd has developed an innovative Quantitative Weighing System that optimizes the allocation of articles to various stations This system operates on a state transition model where each allocation action triggers a change in state, and the difficulty of transitioning based on the required weights is continuously updated The model employs a graph structure, assigning values to edges that reward lower transition difficulty levels and ensure that the total weights of articles at transition destinations fall within a specified target range.
Figure 1.5: The Quantitative Weighing System [5]
Reasons for choosing the research
Researchers have identified the potential of mangoes for economic development, yet farmers face challenges in categorizing them effectively The manual weighing of mangoes is time-consuming and costly compared to a quantitative weighing system This repetitive task can lead to boredom, adversely affecting the physical and mental health of workers Consequently, inaccurate weighing results may lead to misclassification of the mangoes.
Figure 1.6: The labours are categorising mangoes manually
Automating the weighing process with a reliable system offers significant advantages over manual sorting methods Unlike traditional scales used by farmers, which can be less effective than hand grading, an advanced weighing sensor provides faster and more precise results, enhancing efficiency in mango sorting.
Despite the long-standing existence of agricultural product classification systems, a dedicated weighing system for mangoes remains absent Research revealed that existing mango classification systems on the market lack adequate performance and accuracy These findings underscore the necessity for further investigation in this area.
Aims of the research
The project aims to develop a precise mango weighing system integrated with various packaging machines to create an efficient sorting line Designed for ease of operation and maintenance, the system features a user-friendly interface that enhances user interaction Safety is a top priority, with an emergency stop system implemented to protect users from potential hazards Additionally, careful consideration is given to the manufacturing costs of the system, ensuring a balance between quality and affordability.
Research methods
To design an effective mango weighing system, we will first analyze both domestic and international mango orders to understand their specific needs Researchers will investigate current mango weighing techniques used worldwide and then explore various design options for a quantitative balance, ultimately selecting the most optimal solution A crucial component of this design is the drive mechanism, which ensures that mangoes are weighed without damage Upon completing the design, we will construct the system, starting with the frame and electronic installations, followed by programming for calculation and control Finally, the team will carry out an empirical evaluation of the mango weighing system in the local area to assess its practical effectiveness.
Research limitations
This study surveys the Mekong Delta, the leading region for mango production in the country, focusing specifically on a station designed for weighing mangoes rather than a complete mango sorting system The research highlights two popular mango varieties in the area: Cat Chu and Hoa Loc.
FOUNDATIONAL THEORIES
Characteristics of Hoa Loc mango and Cat Chu mango
Hoa Loc mango trees yield approximately 100 kilograms per tree annually after reaching 10 years of age and start producing fruit 3-4 years post-planting The primary harvest season spans from March to May, with potential early harvesting from November to January through specific flowering treatments The mangoes typically weigh between 450-600 grams and feature an elongated shape with a rounded gourd near the stem As they mature, small brown dots appear on the skin, which eventually enlarge, accompanied by a thin chalky layer When ripe, the fruit boasts a vibrant yellow hue, smooth pale yellow flesh, a sweet taste, distinctive aroma, and relatively small seeds.
Cat Chu mango is a popular choice among farmers due to its ease of flowering and fruiting, along with a high yield of up to 400 kilograms per tree annually for mature trees This variety begins to bear fruit within 3 to 4 years of planting, with the main harvest season occurring from March to May, and potential early harvests as early as September with specific treatments The mangoes are medium-sized, averaging 340 to 350 grams, with a slightly rounded shape and a prominent stem As they ripen, the skin turns bright yellow and develops distinctive brown dots, while the flesh is smooth, light yellow, sweet, and boasts a unique aroma.
The Global GAP standard
Fresh mangoes are classified into three classes as follows:
The "Special" Class of fresh mangoes is defined by its top-tier quality, requiring that the fruit be variety-specific and free from defects, except for minor imperfections that do not impact the product's appearance, overall quality, or presentation during packaging.
Class I: Fresh mangoes of this class must be of good quality They shall be variety- specific, allowing slight defects, provided that the appearance, quality, quality maintenance and presentation of the product in the package are not affected: Slight defects in appearance: fruit + Slight skin defects due to sunburn or scratches, stains from resin secretions (including long lines) and bruises not larger than 3 cm2, 4 cm2 and 5 cm2 respectively for size groups A, B and C
Class II: Fresh mangoes of this class do not meet the requirements in the higher classes but must meet the minimum requirements specified in 2.1 The following defects may be permitted, provided that the basic characteristics relating to quality, quality maintenance and presentation of the product are preserved: Defects in shape Shell defects due to sunburn or scratches, stains from resin secretions (including long lines) and bruises not larger than
5 cm2, 6 cm2 and 7 cm2 respectively for size groups A, B and C
In grades I and II, green mango varieties may exhibit yellowing of the rind due to direct sunlight exposure, but this discoloration should not cover more than 40% of the fruit's surface and must show no signs of deterioration.
The size is determined by the weight of the mango, as specified in the following table:
Table 2.1: The weight standards of mango
The allowable weight variation for mangoes within the same package is capped at 75 grams, 100 grams, and 125 grams, depending on the size group Additionally, each fresh mango must weigh at least 200 grams.
Each package of fresh mangoes should contain uniform fruits that are consistent in size, quality, variety, and origin Additionally, the visible portion of the fruit on the packaging must accurately represent the entire contents of the package.
Fresh mangoes must be packaged securely to ensure their protection, using new, clean, and high-quality materials to prevent any damage It is acceptable to use paper or stamped materials for commercial purposes, as long as the printing and labeling employ non-toxic ink or glue.
Effective packaging for fresh mangoes is essential to maintain quality, hygiene, and durability during loading, unloading, and sea transportation It should facilitate proper ventilation and be free from foreign matter and odors to ensure optimal preservation.
Theory of mass and mass scales
Mass is a fundamental property of an object, traditionally associated with the amount of matter it contains In modern physics, mass has various definitions that, while conceptually distinct, are physically equivalent It is experimentally determined as a measure of an object's inertia, reflecting its resistance to acceleration when subjected to an external force.
Determining the mass of an object is done by weighing the mass with supporting devices such as spring scales, electronic scales, etc
The SI unit of mass is the kilogram (kg)
Mass is a key attribute for classifying similar objects, often influencing their value, particularly in the food industry.
Mass is essential for quantifying an object's density and applying the appropriate formulas By knowing the mass, one can calculate the volume of various objects using the density formula.
Theory of quantitative weighing
The weighing system is essential for accurately measuring the weight of mixed materials on the production line, ensuring smooth operations Utilizing advanced technology, it delivers precise amounts of materials as predetermined by the programmer Various weighing methods are employed, including positive quantification, quantitative measurement, non-positive methods, material overload detection, and quantitative accumulation.
Positive batching is a technique used to measure the mass of materials by transferring a specified quantity from a tank into a container, followed by weighing it with an attached weighing pan Once the material reaches the valve level of the tank, the flow is stopped, and the measured amount is moved from the hopper into production.
Negative batching is a technique for measuring the mass of a material by assessing the loss from a tank, utilizing weighing pans on the material line that are both moved and weighed Once the predetermined level is reached, the tank's valve closes This negative mixing principle offers advantages such as flexibility in supplying materials to equipment; however, it is not suitable for directly mixing materials within the tank.
Material overloading is a technique that integrates both positive and negative dosing methods to achieve precise material quantities This process involves initially applying the active method until the container is filled, followed by a controlled overload of materials Any excess is then addressed using the inactive method, with the surplus being reserved for future weighing tasks.
Quantitative accumulation is a precise method used for assembling the components of a tank's mixing recipe by measuring specific volumes This process involves a weighing plate attached to the tank, which accurately determines the volume of materials added Once the first material reaches the desired level, the scale is reset to zero before adding the next material, and this process continues until the required mixture is achieved.
The figure 2.3 is shown with a solid line representing the mass of each component over time and the dashed line representing the cumulative mass of the component.
Applying the quantitative method to the topic
The subject of implementation is the quantitative weighing system in the mango sorting line
The study aims to classify mangoes into distinct groups based on their exact weight However, the full implementation of quantitative weighing methods is limited, as these methods typically prepare materials in granule or liquid form for effective separation Continuous mass sorting allows for high productivity without human intervention, making the application of quantitative weighing methods highly feasible for this process.
Material overload and accumulation methods are ineffective for sorting individual mangoes for specific purposes Instead, the positive and negative sorting methods offer more suitable alternatives for this task.
Using the active quantitative method, we can accurately determine the weight of each mango by employing a weighing pan attached to the container, allowing each mango to be individually weighed as it is removed.
The non-aggressive dosing method utilizes a conveyor belt equipped with containers instead of flat images This innovative setup includes a weighing station beneath the conveyor belt, allowing for the precise measurement of each mango's weight while it is transported This dual functionality enhances efficiency by combining transportation and weighing in one streamlined process.
Depending on the design, simulation and evaluation process, design options are decided.
Conclusion
This chapter explores various theories to propose a mechanical configuration for a quantitative weighing system, focusing on the classification of output mangoes into three main categories: A, B, and C, as per GlobalGap standards Additionally, it discusses an optimal measurement method derived from the theory of quantitative weighing The research findings confirm that our system is fully manufacturable and operational in practical applications.
ANALYSIS AND DESIGN OF MECHANICAL SYSTEM
Introduction
To create an effective and cost-efficient quantitative weighing system, the design process must focus on enhancing operability through fundamental machine principles This mechanical design should align systematically with other essential components, including electrical systems, control mechanisms, and the operating environment Such a cohesive approach is crucial for establishing a robust foundation for the quantitative weighing system Given that the system will operate in a factory setting with workers as operators, it is imperative that the mechanical design prioritizes not only accuracy and efficiency but also durability and safety.
Requirements for a model of the system
In the mango sorting line, classification relies on shape and weight to categorize mangoes effectively Shape classification utilizes cameras and mathematical models for efficient image processing However, accurately determining the weight of each mango poses challenges for a continuously operating conveyor belt To address this issue, a quantitative weighing system was developed, ensuring precise weight measurements for optimal sorting efficiency.
The system integrates two existing sorting conveyors: an image processing conveyor and a sorting conveyor The weighing system receives input from the image processing conveyor and subsequently delivers its output to the sorting conveyor.
A simple mango sorting line operates by first passing the mango through an image processing conveyor to assess its shape Next, the mango moves to a weighing system to measure its mass The computer utilizes the previously gathered shape and weight data to sort the mangoes effectively.
This article discusses the development of a quantitative weighing system utilizing two existing conveyors, where design choices are influenced by their dimensions It outlines design options based on classification principles, weight determination methods, and the specifications of the conveyors Selecting the appropriate design is crucial for maintaining continuous and accurate operation of the sorting line.
In the initial stage of the mango processing system, mangoes are placed onto a feed conveyor, where they fall into designated base containers Each mango is then picked up and positioned on a weighing load cell sensor pan for accurate measurement After weighing, the mango is transferred to the next sorting conveyor, and the process is repeated for each new mango The system is divided into two components: a stationary part with three fixed container base locations for holding the mangoes, and a moving part that facilitates the transfer and weighing of the fruit.
The mango sorting system consists of three essential bases: the first base receives mangoes from the feed conveyor, the second base is equipped with a weighing load cell sensor, and the final base features a slope for mangoes to roll onto the next sorting conveyor Accurate weighing occurs at the intermediate position, necessitating a robust construction to minimize vibrations and enhance measurement precision The moving mechanism includes an iron frame with arms that steadily lift the mangoes, requiring a compact yet durable structure for long-term stability and load-bearing capacity As the weighing system serves as a critical junction between the supply and grading conveyors, it must ensure compatibility and continuous operation High precision in manufacturing is crucial to reduce errors and enhance user safety, necessitating careful design of mechanical components to optimize operational productivity.
Mechanical design options
In this chapter, we will explore three primary types of weighing mechanisms relevant to our system: precision balances, compression weight modules, and load cells Understanding the key differences among these balances is essential, as it will inform the mechanical design discussed in the following section.
A precision balance is an essential laboratory weighing device that ensures accurate measurements, which are critical for the success of your analyses Even minor errors in weight can significantly impact subsequent steps, making precise weighing crucial By streamlining the weighing process, you can concentrate on your analyses and achieve your objectives more efficiently These balances not only provide accurate results but also offer flexible solutions for data management, traceability, and regulatory compliance With innovative features and easy connectivity options, they cater to a wide range of applications, allowing integration with software for enhanced compliance Quality assurance features guarantee the validity of your weighing results, ensuring adherence to stringent regulations.
A precision balance is a highly accurate weighing device commonly used in industrial environments; however, its construction may not be ideal for factory settings.
A compression weighing module is engineered to compress its top and base plates when weight is applied, allowing for direct attachment to the ground, piers, or structural beams These modules are commonly utilized in large platform scales, including truck and railroad track scales, as well as in weighing tanks, hoppers, and silos, with load capacities ranging from 3 kg to 300 tons They offer exceptional accuracy for both static and dynamic measurements, featuring a self-aligning rocker pin for consistent performance Key attributes include 360-degree checking, built-in anti-uplift and down stops, hazardous area approvals, and an IP68-rated stainless steel load cell Installation is straightforward, and transitioning to weighing mode is seamless, requiring minimal lift to remove the load cell.
The high-resolution weighing module, capable of up to 2 million digits, allows for the weighing of various container sizes while maintaining a compact design that utilizes Power over Ethernet connectivity, requiring no extra space in control cabinets It can function as a standalone unit or in an array configuration, making it suitable for integration within machines or in glove boxes where cleanliness and durability are essential Its small footprint enables the arrangement of multiple weigh modules in tight spaces, facilitating multi-line filling or check-weighing applications This efficiency accelerates the weighing process, allowing for the simultaneous and precise measurement of vials, ampoules, syringes, tablets, or capsules, resulting in the capacity to weigh tens of thousands of samples per hour.
The device is designed for automation, featuring EtherNet/IP or PROFINET IO RT connectivity in a compact unit Its comprehensive Device Description Files facilitate easy integration into PLC systems Engineered for longevity, the weighing modules include innovative overload protection that maintains accuracy during normal operations and malfunctions With integrated electronics and a customized microprocessor, the device processes final weight values rapidly, while intelligent adaptive filters minimize the impact of vibrations effectively.
Single-point load cells are designed for precision and reliability in various applications, including industrial bench scales, packaging machines, and small tank scales Their low-profile design and straightforward interfaces facilitate easy integration, while a wide capacity range from 3 kg to 750 kg accommodates diverse needs With only one load cell required per scale, there is no need for a junction box, enhancing efficiency These load cells hold global certifications such as OIML, NTEP, and ATEX, making them suitable for legal-for-trade systems and hazardous environments Their comprehensive approvals ensure versatility and safety across multiple applications, with maximum platter sizes starting from 35 cm.
Available in sizes ranging from 35 cm (14 in x 14 in) to 60 cm (24 in x 24 in), these products are made from passivated aluminum, ensuring excellent corrosion resistance for various dry industrial applications Additionally, the electrical circuit is potted and safeguarded against dust and humidity, meeting the IP67 rating standards.
Selection design
In our analysis of various weighing scales, we examined their advantages and disadvantages to determine the optimal design for our system The precision balance offers durability and accuracy in laboratory settings but is too large for our machine, compromising its structural integrity The compression weighing module, being more compact, is suitable for industrial use Although the high-precision load cell meets many of our requirements, its high cost necessitates careful consideration Ultimately, the single-point load cell emerged as the best choice due to its compactness, durability, and affordability Consequently, our team has selected the single-point load cell for our system design, which features rotation as the primary movement to facilitate the pick and place function for mangoes.
Stage 1: The feed conveyor brings mangoes to the catches, which hold the mangoes while the motion frame rotates (Figure 3.1)
Figure 3.1: The general model of the system - stage 1
Stage 2: The motor drives the motion frame to rotate on an axis parallel to the ground (Figure 3.2)
Figure 3.2: The general model of the system - stage 2
Stage 3: When the motion frame rotates to the position shown in the picture below (Figure 3.3), it will transport the mango from the holder along the frame's trajectory
Figure 3.3: The general model of the system - stage 3
Stage 4: The mango is gently and smoothly moved to the position of the load sensor, where it is weighed (Figure 3.4)
Figure 3.4: The general model of the system - stage 4
Stage 5: While the mango was being weighed, the new mango was delivered (Figure 3.5)
Figure 3.5: The general model of the system - stage 5
Stage 6: The motion frame continues to rotate to be ready for the next time (Figure 3.6)
Figure 3.6: The general model of the system - stage 6
Stage 7: The frame moves the mango, but this time it moves both mangoes
Figure 3.7: The general model of the system - stage 7
Stage 8: Two mangoes are brought to the new location For mangoes that have just been weighed, they will go to the position of the sliding tray to go down to the sorting conveyor As for the new mango that will come to the load cell sensor (Figure 3.8)
Figure 3.8: The general model of the system - stage 8
Stage 9: Similar to the first stage, new mangoes are delivered to the first tray (Figure 3.9)
Figure 3.9: The general model of the system - stage 9
Stage 10: The first mango has rolled down the sorting conveyor, and the frame is still spinning, ready for the next cycle (Figure 3.10)
Figure 3.10: The general model of the system - stage 10
Stage 11: So the process is done sequentially: Mango is placed on the scale, Mango is moved to a new position, and so on (Figure 3.11)
Figure 3.11: The general model of the system - stage 11
Analysis of the configuration of the system
A parallel motion mechanism combines the principles of system placement
The parallel motion mechanism integrates system placement principles, featuring a main movement frame and troughs designed with protruding round bars The frame consists of three lanes, each measuring 30 cm in length and 12 cm in width, tailored to accommodate the average size of standard mangoes for classification Beneath the corresponding swivels, a stitch is attached, connecting to another swivel at the end Additionally, four swivel joints are securely fixed to the system frame, with two swivel joints positioned on each side, as illustrated in Figure 3.13.
The parallel movement of the movement frame integrates two circular motions from pairs of swivel joints aligned parallel to each other The first pair of swivel joints facilitates the pickup of mangoes from the image processing conveyor at the weighing section, while the second pair efficiently removes the mangoes from the scale and exits them from the system.
During the study period, a transmission system was implemented to connect the first swivel to the end, allowing for the combination of two rotations While the phase difference between the swivel joints can be adjusted, this setup lacks stability and increases the risk of collisions between the stitches.
A crossbar that creates a phase difference of 0 between two joints offers a simple, stable, and cost-effective alternative to traditional transmitter methods.
Figure 3.14: Design image of mango slide, mango weighing, and mango catch
The innovative design of the troughs and moving frames features interwoven round bars that maximize space efficiency while minimizing the drop zone for mangoes This interlaced finger design incorporates a specific curvature to restrict mango movement, ensuring optimal handling and protection during processing.
After studying the topic, two options for using three-phase AC motors are outlined as follows:
Option 1: Using a new three-phase motor with just enough capacity to meet the weighing system The engine is used with moderate power, there is flexibility in engine control, and it is an active system in operation It is difficult to synchronise with the rotation speed of the image processing conveyor; it is costly to purchase new motors and controllers
Option 2: Check the capacity of the conveyor motor If appropriate, use an existing motor with an external transmission Synchronise the movement of the weighing system with the image processing conveyor through the calculation of the transmission ratio of the external transmission; this is cheaper than buying the engine, and takes up a lot of space for the transmitter
Figure 3.15: Mechanical design of image processing conveyor
The motor used for the conveyor is a 3-phase AC 220V 50Hz motor with a capacity of 0.75 kW, 1 HP
Conveyor load capacity is 10kg
The load of the main movement frame (simulated iron material) is 10kg
The total weight of the motor is 20kg
The motor effectively fulfills the operational requirements of the conveyor system, and with its external mounting, as illustrated in Figure 3.15, the implementation of the second option is a logical choice.
The system frame measures 1250 mm x 720 mm x 1500 mm and is constructed from durable 40 x 40 mm square iron, ensuring a high load-bearing capacity To enhance accuracy in mass determination, the weighing stand is positioned low to the ground and distanced from the transmitter, effectively minimizing oscillations Additionally, the rear frame is securely linked to the sorting conveyor frame, while the front part is also connected, providing stability and reliability in operation.
Chain drive
Figure 3.17: Force acting on the chain
The system's transmission characteristics require stability, smooth operation, and a consistent average transmission ratio, which is achieved through the use of a high-efficiency chain This chain operates with minimal tension, reducing the load on the shaft and bearings, and ensures no slippage while maintaining reliable performance even under heavy loads and low speeds Designed for durability, the chain drive system includes a larger sprocket, a smaller pinion, and a roller chain that effectively transfers power by engaging with the sprocket gear's teeth Additionally, this system performs well in high temperatures and dusty environments, offering a cost-effective solution for various applications.
The gear rotation pulls the chain, applying mechanical force to the mechanism, while the chain, composed of rigid links connected by pin joints, maintains flexibility to engage with the driving and driven wheels Chains effectively transfer speed and power from the motor's shaft to the main shaft over a center distance of approximately 70 centimeters, with a maximum velocity of 2 m/s The sprocket wheels, featuring specially profiled teeth that fit into the chain links, ensure the correct velocity ratio Chains are ideal for both long and short center distance drives, offering a more compact solution compared to belts.
Speed joints need to rotate at equal speeds to maintain the horizontal alignment of the main moving frame and ensure the system operates smoothly, preventing collisions, jams, and damage to its components.
Figure 3.18: Transmitter of two parallel structures
The system consists of six equal-sized sprockets interconnected as illustrated in figure 3.18 A long main shaft serves as the primary drive, simultaneously powering two mechanisms that operate in parallel at the same speed as the spindle This design guarantees smooth movement based on the principles of parallel mechanisms, effectively preventing collisions within the system.
The image processing conveyor operates by maintaining a distance of one space between consecutive mangoes, which is determined by the camera's processing speed and the central processor This spacing is crucial for calculating the gear ratio of the external transmission, ensuring that the design of the conveyor synchronizes effectively with the weighing system This synchronization minimizes the risk of deviations that could lead to congestion or missed weighings during prolonged operations.
Figure 3.19: The sprocket of the image processing conveyor
The image processing conveyor features 46 rollers and 322 links, with a spacing of 6 links between each roller Notably, the minimum distance required between two mangoes on the conveyor belt is equivalent to the space of one conveyor link, aligning with the distance between two rollers.
The angle between two rollers on the conveyor belt is determined to be 66.32 degrees, which results in a deviation angle of 132.64 degrees for consecutive mangoes.
In a quantitative weighing system, each full revolution of the main moving frame equates to the weighing of one mango, resulting in a deviation angle of 360 degrees between two consecutive mangoes.
The transmission ratios for the conveyor shaft and main shaft are 0.37 and 1, respectively, making the selection of sprockets challenging To prevent operational stagnation, a safety factor was incorporated into the main shaft design, ensuring it rotates at a faster rate than the conveyor shaft.
The final decisive transmission ratios of the conveyor shaft and the main shaft are 1 and 3
The sprocket system features a two-structure transmission comprising six sprockets, each with 24 identical teeth, driven by the main shaft It utilizes two chains of equal circumference, with each chain linked to three sprockets on either side The external transmission includes a motor equipped with a double sprocket, featuring 14 and 42 teeth, while the conveyor shaft and main shaft are fitted with sprockets that have 48 teeth The chain setup consists of two connections: one from the 14-tooth sprocket to the 48-tooth sprocket on both the motor and conveyor shafts, and the other from the 42-tooth sprocket to the 48-tooth sprocket on the motor and spindle shafts.
The motor shaft is crucial for simultaneously driving two operating systems, utilizing a double sprocket configuration with 14 and 42 teeth, achieving a transmission ratio of 1:3 This design ensures effective operation by connecting a 48-tooth sprocket to both the conveyor and main shafts Given the significant moment of inertia of these shafts, it is essential to use larger sprockets to accommodate the required torque for optimal performance.
Motor
Selecting a motor for a system involves reverse engineering, focusing on the required torque (T2) to lift both the moving part and the mangoes This lifting action is achieved through the rotation of the shaft at a specified shaft rotation speed (n2).
Table 3.1: Specifications of three phase motor (60 Hz)
10 Output Shaft 18 mm ~ 50 mm (key-way shaft)
Table 3.2: Specifications of three phase motor (50 Hz)
10 Output Shaft 18 mm ~ 50 mm (key-way shaft)
Conclusion
Figure 3.22: Model of the quantitative weighing system
The weighing system utilizes a parallel mechanism to accurately determine the weight of each mango While the mechanical design is cost-effective, it requires careful attention to detail to ensure the smooth operation of the system.
The system features a compact and sturdy design, with a frame size that is compatible with both feed and sorting conveyors, making it easy to install on mango sorting lines Its simple structure ensures easy maintenance and worker safety A key component of the system is the mechanism that efficiently transfers mangoes from the conveyor to the weighing scale and then to another conveyor This highlights the effectiveness of the movement mechanism developed by the team An overview of the quantitative weighing system in the mango sorting line is illustrated in Figure 3.22.
ELECTRICAL-CONTROL SYSTEM
Introduction
The electrical control system is essential for accurately gathering and processing data from load cell sensors to display the precise weight of mangoes It also regulates the speed of a three-phase induction motor through a variable frequency drive Power transmission is achieved via a central chain drive system that transfers energy from the motor to the structure This system utilizes rotating motion to efficiently pick up and place mangoes from the conveyor to the weighing load cell, after which the measured mangoes are transported to the next station, ensuring the process is repeated at regular intervals.
Structure of the electrical-control system
The electrical control system architecture consists of three main components: the input, processing, and output blocks The input block features a weighing load cell sensor that captures physical data and transmits it to the processing block, which comprises a central computer and a PLC controller The raw signals from the input are processed by the PLC controller, which filters out noise to protect the central computer before displaying the results on its monitor Finally, the output block utilizes three induction motors that adjust their velocity based on control signals sent from the central computer via the PLC controller.
Figure 4.1: The general system architecture
The team selected the Siemens PLC SIMATIC S7-1200 CPU 1214C DC/DC/DC (Code: 6ES7214-1AG40-0XB0) as the central processor for their long-duration device due to its high performance and compact design This PLC features 2 integrated analogue inputs, 14 digital inputs, and 10 digital outputs, along with built-in I/O and communication interfaces that adhere to stringent industry standards Its advanced technological functions make it essential for precise automation tasks across various applications in the low to mid-performance range, offering maximum flexibility and efficiency The standardized remote-control protocols enable direct connection to the control center without extensive programming, and the integrated Ethernet port facilitates easy program loading and data transfer between the PLC and computer.
To enhance the digital or analog I/O capacity of the CPU 1214C, signal modules can be connected to its right side, allowing for the addition of up to eight modules One effective option is the Siemens SIMATIC S7-1200 PLC analog I/O SM 1234 (Code: 6ES7234-4HE30-0XB0), which offers 4 analog inputs with 13-bit resolution and 2 analog outputs with 14-bit resolution.
Sensor system
A load cell is a precise device used for measuring weight or force through compression, tension, bending, or shear, functioning as a transducer that converts force into a small electrical signal requiring amplification Strain gauge load cells dominate the weighing industry due to their accuracy, while pneumatic and hydraulic load cells are utilized for specific applications needing safety and hygiene These devices transform mechanical force into digital values, with strain gauge load cells being the most prevalent, as they detect voltage changes under load to determine weight Load cells are essential in various fields demanding precision, classified into classes A, B, C, and D based on accuracy and capacity Modern load cells incorporate strain gauges that measure weight by detecting voltage fluctuations caused by deformation when weight is applied.
Four strain gauges are incorporated into load cells to enhance measurement accuracy, with two gauges typically under tension and two under compression, all equipped with compensation adjustments In a no-load scenario, the resistances of the strain gauges are equal, but when a load is applied, the resistance changes, resulting in a variation in output voltage This change in voltage is measured and translated into readable values using a digital meter.
A load cell amplifier is essential for enhancing the weak signals generated by load cells, ensuring compatibility with measuring systems like data loggers and load meters By amplifying these low-strength signals, the amplifier produces a stronger output, facilitating accurate measurements The Load Cell Amplifier Module features high-accuracy conversion with simultaneous 4-20mA and 0-5V/10V outputs It allows for easy adjustment of zero and span via potentiometer terminals and is compatible with various strain gauge bridge-type load cells, including those used for weighing, tension, compression, and torque applications.
Figure 4.3: Wiring terminals of an amplifier [13]
Figure 4.4: Connection of weighing load cell sensor with PLC
In our programming device, we utilize the SCALE_X (Scale) and NORM_X (Normalize) converters to effectively scale analog values The "Normalize" instruction adjusts the tag value at the VALUE input by mapping it to a linear scale defined by the MIN and MAX parameters, which set the limits of the value range The normalized output at OUT is calculated as a floating-point number based on the position of the normalized value within this range Specifically, if the input value equals MIN, the output will be "0.0," and if it equals MAX, the output will be "1.0."
The following figure 4.15 shows an example of how values can be normalised:
Figure 4.5: An example of NORM instruction
The "Normalise" instruction works with the following equation:
The "Scale" instruction adjusts the input VALUE by mapping it to a defined value range, specified by the parameters MIN and MAX Upon execution, this instruction transforms the floating-point input into an integer output, which is stored at OUT.
The following figure 4.6 shows an example of how values can be scaled:
Figure 4.6: An example of SCALE instruction
The "Scale" instruction works with the following equation:
In the following table it is assumed that the measuring ranges are unipolar The integer input value is then between 0 and 27648
The following values are generated by the conversion (for determining mass via voltage measurement):
Electro-mechanical drive systems
An electric motor transforms electrical energy into mechanical energy for various loads A.C motors, powered by alternating current, are categorized into synchronous, single-phase, three-phase induction, and special-purpose motors Among these, three-phase induction motors are the most prevalent in industrial settings due to their lack of a starting device The name "three-phase induction motor" comes from the fact that the rotor current is induced by a magnetic field rather than through electrical connections, with its operating principle centered on creating a rotating magnetic field.
The stator of an induction motor features overlapping windings that are offset by an electrical angle of 120° When the primary winding is connected to a three-phase AC supply, it generates a rotating magnetic field that operates at synchronous speed.
The motor's direction of rotation is influenced by the phase sequence of the supply lines and their connection order to the stator; swapping any two primary terminals will reverse the rotation Additionally, the synchronous speed of the motor's stator is determined by the number of poles and the frequency of the applied voltage, with common configurations including 2, 4, or 6 poles.
8 poles The synchronous speed, a term given to the speed at which the field produced by primary currents will rotate, is determined by the following expression
The operation of an induction motor begins with a rotating magnetic field in the stator, which induces an electromotive force in the rotor conductors This induced force generates current in the rotor, flowing in the opposite direction to the stator's magnetic field, resulting in torque and rotation The rotor's winding can be closed through external resistance or shorted, but it will never reach the synchronous speed of the stator's magnetic field This difference in speed, known as slip, is essential for generating torque; if the speeds were equal, no current would flow, and no torque would be produced A key advantage of induction motors is that they require no electrical connections to the rotor.
A Variable Frequency Drive (VFD) is a motor controller that regulates the speed and torque of an electric motor by adjusting the frequency and voltage supplied to it Also known as a variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, or inverter, VFDs are essential for enhancing energy efficiency and controlling motor performance.
Frequency, measured in hertz, is directly linked to a motor's speed in RPMs; higher frequency results in increased RPMs When an application does not necessitate full-speed operation of an electric motor, a Variable Frequency Drive (VFD) can effectively reduce both frequency and voltage to align with the motor's load requirements As the speed demands of the application change, the VFD allows for easy adjustments to the motor speed, ensuring optimal performance.
Electric motor systems account for over 65% of industrial power consumption, making the optimization of motor control systems crucial Upgrading to Variable Frequency Drives (VFDs) can lead to energy savings of up to 70%, enhance product quality, and lower production costs With energy efficiency tax incentives and utility rebates, the return on investment for VFD installations can be as quick as six months Operating motors at optimal speeds reduces errors and boosts production levels, while VFDs extend equipment lifespan and minimize maintenance downtime They provide better protection against issues like overloads and voltage fluctuations, and allow for smooth load starts, reducing wear on belts, gears, and bearings Additionally, VFDs help mitigate water hammer by facilitating gradual acceleration and deceleration.
Figure 4.7: Schematic diagram of inverter standard wiring [16]
Figure 4.8: Schematic diagram of main circuit wiring [16]
Figure 4.9: Schematic diagram of control board layout [16]
4.4.3 Speed control of three phase induction motor using variable frequency drive control system
Three-phase AC induction motors are essential in industrial applications due to their affordability and simplicity, converting three-phase AC power into mechanical power As the load increases, the slip percentage rises, causing a decrease in motor speed, which is critical in maintaining constant speed in industrial settings This article introduces a straightforward converter that utilizes a variable frequency drive (VFD) with feedback to effectively control the speed of a three-phase induction motor from a three-phase AC supply The VFD automatically adjusts motor speed through a controller, making it an efficient method since speed is influenced by voltage, pole, and frequency While poles are fixed and cannot be altered, controlling speed via VFD is both simple and energy-efficient This robust technique has been successfully implemented in hardware, demonstrating its practicality and ease of use.
To maintain a constant motor speed, the voltage and frequency ratio is carefully adjusted to keep the V/f ratio steady When the motor speed decreases, both the frequency and voltage are simultaneously reduced to ensure this ratio remains constant, thereby achieving the desired operational speed.
By using this technique different speed and torque can be achieved Constant speed achieved by variable frequency drive and this is a very efficient low cost and power saving method
In a Variable Frequency Drive (VFD), three-phase AC voltages are transformed into pulsating DC voltages, with ripples minimized through low-pass filters This DC voltage is then fed to Insulated Gate Bipolar Transistors (IGBTs) to generate three-phase square wave AC The phase sequence of the AC is adjusted using a gate driver before being applied to three-phase induction motors An encoder attached to the motor shaft measures RPM, sending data to the controller to compare with reference values and adjust the motor speed accordingly In three-phase full wave uncontrolled rectifiers, a six-pulse bridge configuration is created using six diodes, each rated for 10A and 1200V.
Figure 4.10: Three-Phase AC to DC Rectifiers [17]
An opto-coupler, also known as an optical isolator, transfers electrical signals between two circuits using light It typically comprises a phototransistor and an LED arranged in a parallel opaque configuration The 6N137 model features an 850nm AlGaAS LED paired with a high-speed photodetector logic gate output, capable of operating within a temperature range of -40°C to +85°C Additionally, the symbols for an opto-coupler and an integrated circuit (IC) are illustrated in Figure 4.11.
Figure 4.11: Working Principle of Opto-coupler
Variable frequency drives (VFDs) come in several types, including voltage/frequency (v/f), vector, and flux control methods Among these, the v/f method is the most widely used and efficient for controlling motor speed VFDs enable precise speed control of motors, ranging from zero to maximum speed, enhancing performance and energy efficiency.
Following equivalent circuit shows the complete circuitry of three phase induction motor speed control by using frequency control scheme in the figure 4.13
Figure 4.13: Equivalent Circuit Diagram with VFD system [17]
Security system
The quantitative weighing mango system, designed for factory use, requires human supervision to ensure safety during operation To mitigate potential hazards, safety features are integrated, including an easily accessible emergency button located on the electrical cabinet, allowing workers to quickly stop the motor for troubleshooting Regular checks are necessary if sensors fail to detect mangoes over time, as jammed mangoes pose risks to employee safety and can damage the system These precautions ensure that employees can operate the automated system with confidence, prioritizing a safe working environment.
Figure 4.15: Block diagram of the safety system
Programming
For the first job, we need to define addresses for input and output From the system functions, we have defined the addresses as shown in the table below
Table 4.2: Input / output address of systems
DI0 (%I0.0) Start buttonDI1 (%I0.1) Stop button
DI2 (%I0.2) Reset button DI3 (%I0.3) Emergency button DO0 (%Q0.0) Running indicator (Green) DO1 (%Q0.1) Stopping indicator (Red) DO2 (%Q0.2) Reset indicator (Yellow) DO3 (%Q0.3) Start motor
AI0 (%IW64) Load cell amplifier 1 (0 - 10V) AI1 (%IW66) Load cell amplifier 2 (0 - 10V) AI2 (%IW128) Load cell amplifier 3 (0 - 10V)
AO (%QW128) Speed control signal (4 - 20 mA)
The system features four essential buttons: the start button, stop button, reset button, and emergency stop button The start button initiates or resumes the system, while the stop button halts the operation, allowing for reactivation with the start button The reset button restores the system to its default values, returning it to a stopped state during the process In case of a malfunction, the emergency stop button immediately halts the system, requiring the reset button to be pressed before restarting The digital output visually indicates the system's status: a bright green light signifies an active state, a red light indicates the system is stopped, and a yellow light shows that the system has been reset.
The system's essential function involves processing the analog signal from the load cell once it is operational The program continuously receives these analog signals from the input pins and converts them into a real number that accurately represents the object's weight in grams.
Figure 4.15: Flowchart of processing analog input
To determine the precise mass of the mango from the processed analog signal, we filter out noise from the discrete-time data By iterating through the values, we aim to achieve the closest approximation of the mango's actual mass, as illustrated in the algorithm flowchart below (Figure 4.16).
Figure 4.17: Flowchart of calculating actual weight of mango - 2
The WinCC Runtime Advanced graphical user interface is elegantly designed to be minimalistic and user-friendly, ensuring ease of use Its primary function is to showcase calculated parameters and system status while featuring buttons that mirror those found in the electrical system.
Conclusion
This chapter discusses the electrical-control system of a quantitative weighing system, highlighting the crucial roles of both the controller and load cell sensor Without the sensor, the controller would lack an input signal, underscoring the sensor's importance as one of the three essential components of the control system, alongside the controller and motor The research focuses on a quantitative weighing system that utilizes three sensors to accurately measure the weight of mangoes, with these sensors facilitating system measurement and control through the motor A PLC controller and a personal computer serve as the central processing units to ensure efficient control, while the communication system is designed for rapid and accurate information transmission to meet real-time response requirements Additionally, the motor's operation is managed by a variable frequency drive.