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Leopoldo Armesto

Josep Tornero

Department of Systems Engineering and Control Technical University of Valencia Camino de Vera s/n, 46022, Valencia, Spain {marmoag,leoaran,jtornero} Abstract: This paper describes a modular and integral solution for management and transport automation in warehouses developed in the context of a research project, AutoTrans. Management automation includes a warehouse, an optimal location process and a flexible identification system based on RFID and PDAs. Warehouse supervision includes a SCADA system with internet access for remote control. In the context of transport automation, it has been implemented several facilities such as navigation with path planning, line tracking and teleoperation using a force-feedback device. Copyright © 2006 IFAC Keywords: Warehouse automation, flexible identification system, SCADA, industrial teleoperation, force-feedback, AGV.

1. INTRODUCTION Management and transport automation processes based on forklift vehicles within warehouses has taken a significant relevance in the last decade (Garibotto, et. al., 1998; Pagés, et. al., 2001; Yoder 2005). This paper describes and improves the results of the

research project AutoTrans, which main purpose consists of providing an integrated solution for automated production plans, warehouse management and transport processes as summarized in Figure 1. For automating the transport process, several industrial vehicles have been automated (AGVs) for different autonomous or semi-autonomous operations such as: warehouse navigation based on laser

Fig. 1. AutoTrans General Overview.

scanners, vision-based line tracking and teleoperation assisted with a 3D virtual environment. Each vehicle is provided with a control system based on a PLC hardware architecture with industrial communications, which ensures robustness and standardization. In addition to this, a supervision application has been implemented for remote control and monitoring, also known as SCADA. TCP/IP communication between computers has been exploited to introduce real-time supervision from any Internet web browser, which makes possible to have complete information of the plant from PC and at anytime Related to the management automation, the information system of the enterprise, based on an ERP, has been integrated with several applications. On the one hand, a warehouse manager, based on optimization policies, has been developed for transportation costs reductions and storage capability improvement. This manager determines where to move pallets in dynamic warehouses according to client orders and production requirements. Additionally, a flexible identification system for traceability and inventory control based on RFID has been developed. RFID systems allow reading and writing data from the ERP to electronic tags on pallets. This data can be accessed through antennas installed on fixed stations, industrial vehicles or PDAs. This task is known as electronic report generation and may improve the communication flow between the manager and operators. Preliminary results of the overall application including the warehouse management, vehicle navigation system, warehouse supervision and teleoperation have already been presented in (Mora, et. al., 2003; Armesto, et. al., 2005; Armesto and Tornero 2005). These results are extended in this paper, in the sense that warehouse supervision includes remote access via Internet. Moreover, an industrial low-level control and force-feedback control for the teleoperation application has been included.

That is, a fixed location is assigned to each specific type of products. However, it is well known that dynamic warehouses, where material locations can change, introduce significant improvements on storage capability and transportation cost reduction. In this sense, an optimal location assignment (OLA) application has been developed. It is based on binary linear programming (LP) and dynamic programming (DP) techniques. It has been integrated with a commercial ERP (Enterprise Resource Planning) previously installed in the company, named KEWAN. In particular, the Production Management module of KEWAN provides the necessary information to perform the optimization tasks for generating transport orders in warehouses. This information includes the present stock of the warehouse in addition to the foresight sales and purchases, and the product catalogue. The OLA application determines, in an efficient manner, where to locate products through a combination among transport and assignment approaches in LP and route map optimization in DP. The search of the optimal solution among all possible considers foresight sales and purchases as well as the present stock applying the following criteria: •

At present, the system assumes palletized units.

• All pallets at inlet docks must be stored in one of all possible locations (loading orders). • All the output material must be delivered from their locations to outlet docks (unloading orders). • Loading orders on already occupied locations will be executed if exists any previous unloading order on the same location. If a location is initially void any loading order can be accepted on it. • Unloading orders on void locations may be executed provided that a previous loading order exists at this location. If a location is initially occupied any unloading order related with the same product can be accepted.

The paper is organized as follows: section 2 describes an application for the optimal allocation of pallets in a warehouse; in section 3 a flexible identification system based on RFID and electronic tags is proposed; section 4 is devoted to the description of the SCADA application while section 5 gives abundant information about how the teleoperation of industrial vehicles has been implemented. Final conclusions and the list of references are at the end of this paper. 2. OPTIMAL LOCATION MANAGEMENT APPLICATION One of the main problems found in many company is the warehouse management and correct assignment of products location. Commonly, these locations are fixed (static) depending on the warehouse layout.

Fig. 2. Optimal Location Assignment Interface.

Fig. 3. Flexible Identification System. A virtual warehouse has been implemented in order to validate the present application. Figure 2 shows the user-interface for the OLA application, where occupied locations are represented with small colored square boxes according to the product family code. The simulator depicts in a window the computed changes on the warehouse layout and their associated transport orders before execution. 3. FLEXIBLE IDENTIFICATION, TRACEABILITY AND INVENTORY CONTROL A flexible identification system based on RFID is proposed in this section, as shown in Figure 3. The goal is to provide to the enterprise a system for traceability that allows a real-time monitoring of pallets location and movements. Each pallet has an electronic tag containing relevant data for appropriate transportation and management. A RFID fix station is used to write data on tags at the arrival of a new pallet to the inlet dock. The ERP provides, in combination with the OLA, the necessary information to be stored inside the tags. Traditional systems based on bar code readers have the main inconvenient that labels can not be easily modified when printed. In addition to this, bar code readers are seriously affected by weather conditions and bar code printers may have poor accuracy. The RFID system tags can be read and write as many times as desired, from PLCs on vehicles or PDAs. This data is used by the OLA application in order to suggest the driver the most appropriate pallet location as well as the optimal path. It is up to the driver to follow or to modify the orders depending on circumstances. That is, unpredicted obstacles in corridors, locations already occupied, etc. At the end, the information at the ERP will be updated according to the real situation. When several exception

circumstances have occurred, inventory task and layout remapping will have to be launch in order to carry out warehouse regularization. 4. SCADA APPLICATION The SCADA application of the warehouse allows vehicle control and remote monitoring. It gathers all information to be displayed through the different screens. For this particular application, the following features have been included: • Friendly user-interface. While many of the tasks of the SCADA system do not need user interaction, some others require the supervision or the actuation of human operators. The operator's interface plays therefore a very important role because it makes easier the interaction between the process and the user. All relevant information is shown to the operator in a clear and convenient way. In fact, it is compounded by pages (or screens) for displaying the warehouse information. The user can navigate among them manually unless important changes on the factory occur. In that case the corresponding screen will appear automatically showing the problem or faults detection. • Supervision of the warehouse: A wireless Ethernet network allows real-time communication between the SCADA application and vehicles. It receives vehicle positions and velocities, etc.., and represents forklifts moving in the warehouse layout according to these data. It may also graphically represent pallet location, for traceability purposes. • Alarm treatment, data-logging and statistics: Periodical connectivity tests are made in order to detect communication failures. Vehicle emergency stops are also displayed in this application. In addition to this, some interesting statistics are monitored for data-logging and later in-depth analysis.

Fig. 4. SCADA Interface. • Web-server. It is possible to navigate the SCADA application from any standard web browser in order to monitor and remotely control the warehouse. This functionality expands the previous contributions. Figure 4 shows the SCADA interface where the warehouse layout and vehicle position are represented in the left-hand side of the screen. There is a navigation menu on the right-hand side of the interface, where the user may analyze in detail all monitored variables for each vehicle together with the transport orders being performed by the vehicle. 5. INDUSTRIAL TELEOPERATION Teleoperation is an intermediate step toward total transport automation processes, between manual and autonomous modes. It is especially suitable for material transport and handling in dangerous or unsafe areas. Robustness and security are requirements of the application and, in this sense, all automated vehicles involved have extra sensors and low-level control based on industrial PLCs. In teleoperation applications, it is becoming more and more frequent the use of haptic intefaces (Lee, et. al., 2005) that combine human sensations with computer-generated virtual worlds. Haptic interfaces provide the user of the virtual environment to perceive its physical features and to interact with it, making the navigation through real factory easier, in contrast to the possibilities offered by traditional mouses and keyboards. INDUSTRIAL TELEOPERATION CABIN

Steering wheel with forcefeedback

Virtual 3D Environment

Fig. 5. Detail of the Force-Feedback Steering Wheel. There are a high number of devices that can be included in this classification but the most significant in the context of teleoperation are force-feedback devices, which may provide direct perception of the contact with 3D objects. 5.1. Hardware Architecture The teleoperation application is based on the remote control of industrial vehicles from a teleoperation cabin installed on the plant. This cabin has a steering wheel, pedals and levers that completely simulate the operation of the forklift and give the driver the real sensation of vehicle driving, as shown in Figure 6. The steering wheel has been equipped with a forcefeedback mechanism which applies to the human operator a repulsive force. The hardware architecture of the teleoperation application is shown in Figure 9, where a PLC located inside the cabin is the master of a DeviceNet network and slaves are PLCs placed on the industrial vehicles. The communication between master and slaves is performed through wireless DeviceNet antennas. AUTOMATED INDUSTRIAL VEHICLE

Real Image integrated in 3D Environment

Wifi Camera Sensors & Actuators Host-Link



Fig. 4. Hardware Architecture for Teleoperation.



Vehicle protection with laser rangers

Fig. 7. Model of the Force-Feedback Mechanism.

Fig. 8. Real and Virtual Images of the Warehouse.

The application provides the possibility of teleoperating any of the forklifts in the plant from a desktop PC located inside the cabin. It communicates directly with the master PLC of the DeviceNet network through an RS-232C port using Host-Link commands. When a teleoperation request is made the master PLC connects with the desired forklift to exchange the required information with the PC. The control references are given by the teleoperation cabin through the DeviceNet network. An emergency light and speaker indicating any problem during teleoperation have been also installed.

Finally an opposite force –Fhk is rendered to the operator by means of the haptic device. Figure 5 displays the sensors and actuators used for developing the force-feedback steering wheel.

Each vehicle is equipped with proper sensorization in order to be remotely controlled, see (Mora et. al. 2003) for details. However, we want to remark two of the most important sensors: two laser scanners and a TCP/IP WiFi camera. The laser scanner provides depth information about the environment, which is used for vehicle localization, object detection and local map building (Armesto and Tornero, 2005). It activates two outputs in case of intrusion inside configured warning or protection areas. The WiFi camera provides the visual feedback for remote control.

5.3. Teleoperation Software Architecture A 3D virtual environment has been developed for teleoperation tasks. It has been implemented using a commercial programming software called DarkBasic®. It is a programming language derived from the traditional BASIC language that offers specific commands for representing 3D object animation. The virtual environment represents the real industrial warehouse and is reconfigurable depending on its layout. Moreover, warning and protection areas provided by laser sensors are also displayed in case of intrusion. In addition, the operator can also perform emergency stops from the cabin. Due to the reliability properties of DeviceNet networks, we can assure that the vehicle will stop with a very short time delay. Network disconnections are also detected by the PLC at the vehicle, causing emergency stops.

5.2. Force feedback The force-feedback mechanism is based on the computation of a virtual interaction force produced by the obstacles, as in (Diolaiti and Melchiorri, 2002; Diolaiti and Melchiorri, 2003). A local map of the obstacles is built using data acquired from the environment (Armesto and Tornero, 2005). Once the position of the obstacles is known it is possible to compute a virtual interaction force Fo on the basis of their distance to the robot. The human operator also exerts a virtual force onto the robot Fh that may compensate the one produced by the obstacles. Repulsive forces from obstacles are generated by the superposition of an elastic force and a viscous friction that dissipates energy in order to stabilize the virtual interaction, as shown in the model of the Figure 7.

This application monitors the vehicle position and laser measurements, transmitted first from the vehicle to the cabin through DeviceNet and then to the 3D application using host-link commands. For the teleoperation, a wireless webcam is located on each forklift. A web server stores the captured real image and makes it accessible from the virtual environment, in the form of a window application, as shown in Figure 8. Low-level control software architecture for vehicle teleoperation is depicted in Figure 9 including: motor control, communication tasks, feature extraction, multi-rate vehicle localization (Armesto and Tornero, 2004) based on EKF and a simple reactive object avoidance based on the computation of repulsive potential fields from a local map.

feedback system has been proposed to improve driving interaction within the environment.


Speed Ref.


Steering Wheel Ref.

Steering Wheel


Speed and Steering Wheel Angle

Steering Wheel












Warning and Protection Areas

Fig. 9. Software Architecture for Teleoperation. 6. CONCLUSIONS In this paper, we have described a modular and integral solution for management and transport automation in warehouses developed in the context of a research project, AutoTrans. It involves, in addition to the university team, four enterprises. Modularity has been one of the main goals to achieve during the project. In this context, we have developed several modular applications in order to accomplish this task. For management automation, we have integrated the information system of an enterprise, based on an ERP, with different modules. On the one hand, a warehouse optimal location manager (OLA) has been developed in order to efficiently determine product locations according to optimization policies. On the other hand, a flexible identification system based on RFID systems and PDAs has been proposed for improving the communication flow between the manager and operators and expediting storage process. Warehouse supervision has been performed with a SCADA application, for remote control and monitoring vehicle positions and pallet locations. It also handles with alarms and provides a web-server in order to supervise the warehouse from any commercial internet web-browser. For automating the transport process, several industrial vehicles have been automated (AGVs) for different autonomous or semi-autonomous industrial operations such as: warehouse navigation, visionbased line tracking and industrial teleoperation. In particular, the industrial teleoperation has been described in detail in this paper. This application integrates a 3D virtual environment representing the warehouse layout with real images taken from a wireless camera installed on each vehicle. It is interesting to remark that the low-level vehicle control is performed with a PLC, ensuring robustness requirements. In addition, a teleoperation cabin has been automated in order to remotely control vehicles based on a wireless DeviceNet network. A force

The global automation of a warehouse is still a very difficult task, because of the high cost of its components as well as security and confinement aspects which has not taken into account in this paper. Presently, we are working on the development of commercial solutions based on our modular architecture which allows adapting to the particular needs of each enterprise. REFERENCES Armesto, L., J. Tornero (2004). SLAM Based on Kalman Filter For Multi-Rate Fusion of Laser and Encoder Measurements. IEEE International Conference on Robotics Systems, vol. 1, pp. 1860-1865. Armesto, L., M. Mora, and J. Tornero (2005). Supervisión, teleoperación y navegación de vehículos industriales y su integración en el sistema de gestión. Revista Iberoamericana de Automática e Informática Industrial, vol. 2, pp. 55–63. Armesto, L. and J. Tornero (2005). AutoTrans: Management and Transport Automation in Warehouses. Industrial Simulation Conference, vol. 1, pp. 236-241. Diolaiti, N. and C. Melchiorri C. (2002). Teleoperation of a mobile robot through haptic feedback. IEEE Int. Workshop on Haptic Virtual Environments and Their Applications, Vol. Diolaiti, N. and C. Melchiorri C. (2003). Haptic Teleoperation of a Mobile Robot. IFAC Symposium on Robot Control SYROCO. Garibotto, G., S. Masciangelo, P. Bassino, C. Coelho, A. Pavan, and M. Marson (1998). Industrial exploitation of computer vision in logistic automation: autonomous control of an intelligent forklift truck. Int. Conf, on Robotics and Automation, vol. 2, pp. 1459 –1464. Lee, S., G.S. Sukhatme, G.J. Kim, and C. Park (2005). Haptic Teleoperation of a Mobile Robot: A User Study. In: Presence: Teleoperators and Virtual Environments, Vol. 14, Issue 3, pp. 345365. Mora, M., V. Suesta, L. Armesto and J. Tornero (2003). Factory management and transport automation. IEEE Conference on Emerging Technologies and Factory Automation, vol. 2, pp. 508–515. Pagés, J., X. Armangué, J. Salvi, J. Freixenet, and J. Martí. A computer vision system for autonomous forklift vehicles in industrial environments (2001). 9th. Mediterranean Conference on Control and Automation, pp. 379–384. Yoder, M. S. J. Automatic pallet engagment by a vision guided forklift (2005). IEEE Conference on Robotics and Automation.