Ju-Yeon Jo

An agile manufacturing workcell design

This paper introduces a design for agile manufacturing workcells intended for light mechanical assembly of products made from similar components (i.e., parts families). We define agile manufacturing as the ability to accomplish rapid changeover from the assembly of one product to the assembly of a different product. Rapid hardware changeover is made possible through the use of robots, flexible part feeders, modular grippers, and modular assembly hardware. The division of assembly, feeding, and unloading tasks between multiple robots is examined with prioritization based upon assembly time. Rapid software changeover will be facilitated by the use of a real-time, object-oriented software environment utilizing graphical simulations for off-line software development. An innovative dual VMEbus controller architecture permits an open software environment while accommodating the closed nature of most commercial robot controllers. These agile features permit new products to be introduced with minimal downtime and system reconfiguration.

Advances in agile manufacturing

An agile workcell has been developed for light mechanical assembly in collaboration with industrial sponsors. The workcell includes multiple Adept robots, a Bosch conveyor system, multiple flexible parts feeders at each robots workstation, CCD cameras for parts feeding and hardware registration, and a dual VMEbus control system. Our flexible pairs feeder design uses multiple conveyors to singulate the parts and machine vision to locate them. Specialized hardware is encapsulated on modular grippers and modular worktables which can be quickly interchanged for assembly of different products. Object-oriented software (C++) running under VxWorks, a real-time operating system, is used for workcell control. An agile software architecture was developed for rapid introduction of new assemblies through code re-use. A simulation of the workcell was developed so that controller software could be written and tested off-line, enabling the rapid introduction of new products.

SFRIC: A Secure Fast Roaming Scheme in Wireless LAN Using ID-Based Cryptography

In a wireless network composed of multiple access points, a long delay during roaming from one access point to another may cause a disruption for streaming traffic. Roaming in wireless LAN is generally composed of two parts, 1) searching for a new access point and 2) performing authentication at the new access point. To reduce the second part delay, we propose an innovative lightweight authentication scheme called SFRIC (secure fast /foaming using ID-based cryptography). SFRIC employs ID-based cryptography to simplify the authentication process. It performs mutual authentication for the mobile client and AP with a 3-way handshake, then generates a PTK (pairwise transient key) directly without pre-distributing PMK (pairwise master key). It does not require contacting an authentication server or exchanging certificates. SFRIC is composed of two phases. In the first phase (the preparation phase), each mobile client obtains a temporary private key from the PKG (private key generator). In the second phase (the roaming authentication phase), mutual authentication and key distribution are performed. Our preliminary analysis indicates that SFRIC can complete the roaming authentication within a period much less than the critical 20 ms threshold, required for maintaining streaming traffic, when the cryptographic operations are performed in hardware.

Defeating distributed denial-of-service attack with deterministic bit marking

Distributed denial-of-service (DDoS) attack is a serious threat in Internet. We propose a bit marking concept to identify and drop the DDoS attack packets. Bit marking is a variation of the packet marking technique that modifies packet headers at each router. However instead of storing the router information in the packets, bit marking alters one or more bits in the marking field. The bit marking process discussed in this paper is performed to all the packets and at all the routers along the path; hence it is called deterministic bit marking (DBM). DBM creates a common path signature for all the packets originating from the same location upon arriving at a destination. Since different source networks generate virtually unique path signatures, DBM makes it possible to isolate and discard DDoS attack traffic. From the Internet topology of autonomous systems we observe that the source networks are quite uniformly distributed over the path signature space. In our simulation over 99% of the attack traffic is blocked using DBM while up to 99% of the legitimate traffic passes. DBM can also be used for source traceback using reverse bit marking. DBM can be independently deployed for each ISP and the DBM-based networks can be protected from the attacks coming from nonDBM networks.

Internet traffic load balancing using dynamic hashing with flow volume

Sending IP packets over multiple parallel links is in extensive use in todays Internet and its use is growing due to its scalability, reliability and cost-effectiveness. To maximize the efficiency of parallel links, load balancing is necessary among the links, but it may cause the problem of packet reordering. Since packet reordering impairs TCP performance, it is important to reduce the amount of reordering. Hashing offers a simple solution to keep the packet order by sending a flow over a unique link, but static hashing does not guarantee an even distribution of the traffic amount among the links, which could lead to packet loss under heavy load. Dynamic hashing offers some degree of load balancing but suffers from load fluctuations and excessive packet reordering. To overcome these shortcomings, we have enhanced the dynamic hashing algorithm to utilize the flow volume information in order to reassign only the appropriate flows. This new method, called dynamic hashing with flow volume (DHFV), eliminates unnecessary flow reassignments of small flows and achieves load balancing very quickly without load fluctuation by accurately predicting the amount of transferred load between the links. In this paper we provide the general framework of DHFV and address the challenges in implementing DHFV. We then introduce two algorithms of DHFV with different flow selection strategies and show their performances through simulation.

Design of an agile manufacturing workcell for light mechanical applications

This paper introduces a design for agile manufacturing workcells intended for light mechanical assembly of products made from similar components (i.e. parts families). We define agile manufacturing as the ability to accomplish rapid changeover from the assembly of one product to the assembly of another product. Rapid hardware changeover is made possible through the use of robots, flexible part feeders, modular grippers and modular assembly hardware. The flexible feeders rely on belt feeding and binary computer vision for Dose estimation. This has a distinct advantage over non-flexible feeding schemes such as bowl feeders which require considerable adjustment to changeover from one part to another. Rapid software changeover is being facilitated by the use of a real-time, object-oriented software environment, modular software, graphical simulations for off-line software development, and an innovative dual VMEbus controller architecture. These agile features permit new products to be introduced with minimal downtime and system reconfiguration.

EECCR: An Energy-Efficient

Wireless sensor networks (WSNs) can be used to monitor the interested region using multihop communication. Coverage is a primary metric to evaluate the capacity of monitoring. Connectivity also needs to be guaranteed so that the sink node receives all sensed data for future processing. In this paper, we study the m-coverage and n -connectivity problem under border effects. We consider the scenario where the heterogeneous sensor nodes are randomly distributed in a circular region. We first exactly derive the network m-coverage ratio that is provided by N sensor nodes by the mathematical formulas. Then, the lower bound of the network n-connectivity probability is also derived. Since sensor nodes are equipped with energy-limited batteries, energy conservation in such networks is of paramount importance to prolong the lifetime of the network. Accordingly, we propose a location-independent, energy-efficient routing algorithm EECCR, which simultaneously preserves the network m-coverage ratio and the sensor n-connectivity probability. Extensive simulation results are provided to demonstrate that our algorithm is correct and effective.

m

Wireless sensor networks can be used to monitor the interested region using multi-hop communication. Coverage is a primary metric to evaluate the monitoring capacity. Connectivity also should be guaranteed so that the sink node can receive all sensed data for future processing. In this paper, combining these two problems, we study the connected, coverage problem given a specific network coverage ratio under border effects. We consider the scenario where the sensor nodes are distributed in a circle-shaped region uniformly. We first derive the network coverage provided by N sensor nodes by the mathematical formulae exactly. The lower bound of the network connectivity probability is also derived. Since sensor nodes are equipped with energy-limited batteries, energy conservation in such networks is of paramount importance to prolong the network lifetime. Accordingly, we then propose a location-independent, energy-efficient routing algorithm ECCRA which achieves the required network coverage and sensor connectivity simultaneously. The extensive simulation results demonstrate that our algorithm is correct and effective.

-Coverage and

The need to rapidly reconfigure an agile manufacturing system makes it especially difficult to test the systems control software. Although thorough testing is essential for system reliability, the time available for testing may be short. With a simulator, however, the software can be developed and tested independently from the actual workcell, while production continues or the workcell is reconfigured for the next target product. To facilitate testing of agile manufacturing software, a 3D graphical simulator has been developed at Case Western Reserve University. It permits workcell control software to be tested with a virtual workcell, which exhibits much of the behavior of the real workcell. The simulator has been extensively used in the Agile Manufacturing Project at Case Western Reserve University (CWRU), and most of the actual control software was tested and debugged with it. Considerable time and effort have been saved by simulating various workcell scenarios, some of which are difficult to create in a real workcell, e.g., device failure. In this paper, the architecture of the graphical simulator is described, and a framework for virtual testing is presented. Actual errors found during virtual testing are also described.

n

Network attacks are commonplace in the Internet. One of the defense mechanisms against the network attacks is using a baseline profile established during normal operation to detect the traffic that deviates from the baseline profile. However, this approach works only if there is a stable base profile representing the legitimate network traffic. Although there has been some preliminary research, the details of profiling, such as the profile format, its size and the traffic stability by site or time, have not been widely available. In this study, we analyze actual traffic traces from two Internet traffic archives and verify the traffic stability by various aspects. The analysis shows that there are significant differences in the traffic patterns among different sites. In addition, there are some differences between different time of day or different days, even within a site, suggesting that different profiles are needed for different times. The result of this study can be used practically to anomaly-based IDS for determining the stability of the traffic for a particular site, and the number of required traffic profiles based on the traffic patterns