M015-1 DESIGNING AND CONSTRUCTING A FLEXIBLE CONVEYOR SYSTEM AND ANALYZING ITS IMPLEMENTATION IN A LOOP CONFIGURATION

  

DESIGNING AND CONSTRUCTING A FLEXIBLE CONVEYOR SYSTEM AND

ANALYZING ITS IMPLEMENTATION IN A LOOP CONFIGURATION

2) 2) 1)

Tutuko Prajogo , Prianggada I. Tanaya , Bonifasius W. Ajisaputra

1) 2)

  Department of Mechatronics , Department of Industrial Engineering Faculty of Engineering Swiss German University

  Campus EduTown BSD City Tangerang 15339, Indonesia

  

{tutuko.prajogo, prianggada.itanaya}

Abstract

  

Flexibility feature of a material handling is important in a Flexible Manufacturing System. This paper

is focused on designing and constructing a flexible material handling system using belt conveyor. The

flexibility features are mainly based on the controllable limited belt-length-adjustment at both ends of

the conveyor module, so that several modules can be arranged to form flexible routing configurations

in addition to many other modular benefits. Two directional workpiece transfer, branching, and

temporary storage are the extra benefits obtained from the proposed flexible conveyor. Subsystems

and overall testing experiment implementing modular control strategy showed that the proposed

system can improve system flexibility and productivity.

  

Keywords: Flexible conveyor, flexibility, extending mechanism, belt conveyor, flexible material

handling system

  Introduction

  Manufacturing industries have many contributions to the economy of a country. Improving the manufacturing industries also improves the society economy and the quality of human being. Nowadays, advance manufacturing industry is in the stage of Flexible Manufacturing System (FMS). Generally, an FMS is a group of workstations controlled by a computer system and linked by a Material Handling System (MHS). Based on the definition, MHS plays important roles in an FMS.

  There are several aspects which are the goals of FMS improvements: productivity, effectiveness, efficiency, and flexibility (Groover, 2006). In this paper, the flexibility is the focus to create a material handling system. They are 11 different classes of flexibility (NN, 2010), namely, machine flexibility, material handling flexibility, operation flexibility, process flexibility, product flexibility, routing flexibility, volume flexibility, expansion flexibility, program flexibility, production flexibility, and market flexibility. Material handling and routing flexibilities are the terms that relevant to the paper. These terms are related to transportation, optimization, as well as proper positioning of the different part types with some alternative paths. The flexible material handling has been demanded by industries nowadays because it can increase the productivity and the system flexibility. The flexibility will allow wider optimization range that affects in cost reduction and also cut the manufacturing time which in the end may increase the profit of the factory that apply it.

  Several study in progress of material handling systems have been resulted, namely, product conveyor system based on real-time computer vision (Djunaidi, 2009), vacuum based conveyor belt-system (Regie, 2008), and the usage of microcontroller to conveyor development (Sugianto, 2005), while this paper discusses the result of flexibility to conveyor system (Ajisaputra, 2010).

  In this paper, the discussion presented as follows; the routing flexibility will be presented to give basic idea of the work, the mechanical system design to achieve requested flexibilities, the micro-controller based design, testing application to the shortest path method to observe the performance of the system, and a general result of the test. Several pictures are also presented to clarify the discussion.

  Routing Flexibility

  The product which is produced in a manufacturing industry determines the machines layout (Stephen & Meyer, 2004). Furthermore, the MHS should be configured regarding the machine layouts to transfer the workpieces from one machine to the other machines. Figure 1 shows the example of FMS layouts with conveyor belt configurations. The left one is called ladder layout, whereas another one is called open field layout. From practical point of view, the layouts may be formed by conveyor modules and configuring them according to the actual layout. However, by using belt conveyor modules changing material flow direction is less flexible. The flow is fixed. If a manufacturing plant produces different product that requires the same machines, the routing will be not the same.

  

Figure 1: FMS layout examples and belt conveyors configuration

  By using belt conveyor as the MHS, manual routing change could be performed. The method is by shifting or even replacing the belt conveyor modules. This method would take much time to change the configuration. If frequent adjustment need to be done, this method requires longer time setup.

  To solve above mentioned condition, the routing change can be done automatically. The method is by using belt conveyor modules which have special feature. An ability to extend and retract its both ends is the feature required. With the ability, the routing change can be done by extending and retracting the ends of the conveyor modules regarding to the requirement. The set up time will be shorter than the manual one.

  

Figure 2: Automatic routing change with extend and retract capability

  Figure 2 shows the steps needed to change the material flow direction for one branch. If the steps are applied in several conveyor modules, it will result in the routing change. With this method, no belt conveyor modules shifting or even replacement is needed to change the routing. It means that the same conveyor modules with extending and retracting ability can be used for several configurations.

  Mechanical System Design

  To apply extending and retracting ability to belt conveyor, some consideration need to be performed. First, the belt conveyor consists of roller and conveyor belt. The conveyor belt should remain tense so it can be driven by the rollers. Therefore, the rollers should be fixed on a frame.

  The extending and retracting process is done by an extend-able frame. Rail with linear ball bearing is applied as the frame in this work. The representative drawings of the rail are shown at Figure 3, showing retracted and extended states and the mechanism to perform the movement.

  

F igure 3: Retract and extend rail with their movement mechanism

  The actuation of the extending or retracting process used DC electric motors because of some limitations. Therefore, a mechanism to convert the rotational motion from the electric motor to a linear motion for the rail actuation is required. In this paper, a pair of screw and threaded hole is used. Different direction of the motor will result in different linear motion direction of the extend-able frame.

  The extra conveyor belt length used to extend the conveyor will be placed and configured in the bottom part of the conveyor. When the conveyor extend, there will be a reduction of the conveyor belt length in the bottom part and vice versa. With the mechanism shown at Figure 4a, detection system is required to inform the controller that the mechanism has reach its full retracted or extended position. It is important because the rail has extending and retracting distance limitation. Otherwise, the motor will have to drive excessive load which can damage itself.

  

Figure 4: Tensioner design and retracted position of complete mechanism

  Using the mechanism, there will be an adjustment in the belt conveyor length on the conveyor surface. Therefore, the overall mechanism (Figure 4) is called controllable limited belt-length- adjustment. Another consideration in designing the conveyor is the tensioner part of the belt (Figure 4a). They are two functions of the tensioner, namely, to keep the belt in tension condition and to prevent the belt drop due to load being transferred. Due to the extending and retracting ability, there will be a change in the conveyor belt length on the conveyor surface. This change also affects the conveyor belt in the bottom of the conveyor. At any time and any position, the tensioner should make the belt always tense. Consequently, the travel distance of the tensioner should be added. The combination of the extending mechanism and the tensioner create the flexibility of the conveyor system. Figure 4b shows the conveyor from the side view. One set of extending mechanisms and the tensioner create one module of flexible conveyor system. The flexible conveyor module (retracted position) with its stands can be seen in Figure 4b. In this work, there are two lengths of the flexible conveyor designed, due to further development plan to be able to combined with the existing robotic arm module that has particular dimension. The lengths of the conveyor modules are 850mm and 550mm in retracted position.

  This modularity concept gives some benefits to the whole system. The main benefit is that several conveyor modules can be arranged into various configurations which have routing flexibility. Figure 5 shows 4 (four) flexible conveyor modules arranged in a loop configuration, which will be analyzed in this work. With the ability to extend and retract, the same branch in the configuration can have two material flow directions which is opposite with the respect to another.

  Figure 5: Loop configuration and routing flexibility Other configurations also can be formed by the flexible conveyor modules. For example, arranged in a cross or T-shaped configuration, the system can perform sorting or branching process. This is through the ability of extending and retracting the system. Figure 6 shows cross- and T- configuration. For the time being, four modules are constructed, especially for analysing purpose of the conveyor system at loop configuration. Other modules such as ladder and open field layout also can be formed.

  Figure 6: Cross- and T-configuration for sorting and branching process

  System Controller

  The controller for the flexible conveyor system is designed to have a hierarchy. With this hierarchy, the distribution of the task will be clearer and the future expansion of the system will be easier. Figure 7 depicts the diagram of the system controller.

  

Figure 7: System controller hierarchy

  Two microcontrollers are used as the local controllers and a PC is utilized as the application program controller and monitoring system. One microcontroller (Mazide et.al, 2006) manages two conveyor modules and responsible of receive the signal from the modules as well as send the command to them. Additionally, it communicates the status of the conveyor modules and the commands from the control panel to the application program controller. It also receives commands from the application program controller to be forwarded to the conveyor modules.

  The application program controller has the task to decide the action that should be taken based on the program that has been applied to the controller. Furthermore, it sends the decision to the local controller which will be sent to the actuators in the flexible conveyor modules.

  Shortest Path Method

  Figure 8: Route possibility to deliver workpiece - proximity sensor for each stations At Figure 8, one of the applications that can be applied to the rectangular loop configuration of the flexible conveyor modules is shortest path method. This method is chosen because the shortest path method can take the advantage of the flexibility feature to increase the productivity. With the same speed, using the shorter path will take less time to reach the destination.

  Basically, there are two paths that can be used to deliver the workpiece to the destination station, the clockwise path and the counterclockwise path (Figure 8a). The workpiece is delivered using carrier system. The shortest path method is done by comparing the distance of the two paths and taking the path with the shortest distance as the base to deliver the workpiece. Consequently, the configuration of the flexible conveyor modules will be adjusted regarding to the decision.

  Distance is the difference between one position to another position with the same reference. Therefore, to obtain the distance, the positions of the workpiece and the stations are needed. Proximity sensors (Figure 8b) are used as a limit identification system. It is used to detect the presence of the workpiece as well as represent the stations.

  The stations layout is represented by the position of the proximity sensor (Figure 8c). There are 5 (five) proximity sensors that represent 5 (five) stations in the system. The proximity sensor has no capability to differentiate the carrier. Therefore, only 1 carrier is used for the work.

  Progress Result

  The scenario in this work is to deliver the workpiece from origin to the destination station, which is station 5, as shown in Figure 8c. The initial configuration of the system is clockwise. The time needed to deliver the workpiece using two delivery methods will be compared. They are normal method, by transferring the workpiece based on the fixed route, and shortest path method, by transferring the workpiece based on the path with the shortest distance. In shortest path method, the system has the ability to change its material flow direction.

  With the scenario at Figure 8c, using normal delivery method, the workpiece will be transferred clockwise, through station 1 until station 4. Whereas using shortest path method, the system will change its configuration and then transfer the workpiece counterclockwise directly to station 5.

  Some experiments using both methods have been conducted and the result is shown at Table 1. Assuming that the default flow is clockwise. To perform the shortest path method, the flow need to reverse; to counter-clockwise direction. It can be seen that the shortest path method require more time compared to the normal method. The reason is that using the shortest path method, more processes are needed. The system should change its configuration first by retracting its left end and then extending the right part (see Table 2). After that, the workpiece can be delivered counterclockwise to the station 5 as the destination station.

  From Table 2, it can be seen that the average time needed to change the configuration to counterclockwise direction is 55.78 seconds (extend right + retract left). Concerning the delivery time, the shortest path method requires only 2.91 seconds to transfer the workpiece to the destination station. On the other hand, the transfer time of the normal method is 20.13 seconds. Thus the total time to perform the task is transfer time + delivery time (23.04 seconds). This time is still lower compare to re-configuration of flow from normal path to shortest path methods shown at Table 1.

  Based on the experiment and the analysis, the flexibility feature in the flexible conveyor system is proven to be able to increase the productivity. However, the extending and retracting processes is found to be very slow. Therefore, it is recommended to substitute the actuator for the extending mechanism with the faster one.

  Conclusion and Further Developments Conclusion

  The modularity concept that applied in the flexible conveyor design give the benefit of various configurations that can be arranged from the flexible conveyor modules. There are many configurations that can be arranged from 4 or more flexible conveyor modules which have certain function like branching or sorting.

  Based on the testing, it is proven that the flexibility feature of the flexible conveyor system can increase the productivity. However, the extending and retracting processes require much time. The actuator should be changed with the faster one.

  Further Development

  Based on the design, construction, and testing process, there are several recommendations to make the flexible conveyor system better. The main developments that should be done are: substitution of the actuator for the extending mechanism, analysis of the other possible configuration of the flexible conveyor system, implementation of the Automatic Identification and Data Capture (AIDC), separate actuation of the actuators in the flexible conveyor system to increase efficiency, and optimization of processes.

  References

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