<p> Cooperative teleoperation combines two traditional areas of robotics, i.e. teleoperation and collaborative manipulation. Cooperative telerobotic systems consist of multiple pairs of master I slave robotic manipulators operating in a shared environment. Due to dynamic interaction among slave manipulators as well as communication latency, control of such systems is particularly challenging and the application of standard teleoperation controller may result in instability. </p> <p> In this thesis a multilateral control framework is proposed for cooperative teleoperation systems that allows for transmission of position and force information between all master and slave robots rather than merely between corresponding units. Two different control approaches are introduced that establish kinematic correspondence among masters and slaves. The operators are presented with a virtual intervening tool in order to collaboratively interact with the environment. Models of operators, master and slave robots, tool, and environment are incorporated in the design. </p> <p> A multilateral adaptive nonlinear control architecture is proposed. Performance and stability of cooperative teleoperation systems are addressed under dynamic interactions between slave robots in the presence of model uncertainty. The robustness of the controller with respect to communication latency is also analyzed. Simulation and experimental studies demonstrate that the proposed approach is highly effective in all phases of a teleoperation task, i.e. in free motion and in contact with both flexible and rigid environments. </p> <p> The second approach involves finite-dimensional state-space models that incorporate the delay for free motion/ soft contact as well as rigid contact modes of operation. Local dynamic linearization control laws are employed to linearize robotic manipulators' dynamics. Model-based discrete-time Linear Quadratic Gaussian (LQG) controllers are proposed that can deliver a stable transparent response for each phase of operation. The robustness of these controllers with respect to parameter uncertainty is examined via the Nyquist analysis. Simulation results demonstrate the effectiveness of the proposed approach. </p> / Thesis / Master of Applied Science (MASc)

<p> Cooperative teleoperation combines two traditional areas of robotics, i.e. teleoperation and collaborative manipulation. Cooperative telerobotic systems consist of multiple pairs of master I slave robotic manipulators operating in a shared environment. Due to dynamic interaction among slave manipulators as well as communication latency, control of such systems is particularly challenging and the application of standard teleoperation controller may result in instability. </p> <p> In this thesis a multilateral control framework is proposed for cooperative teleoperation systems that allows for transmission of position and force information between all master and slave robots rather than merely between corresponding units. Two different control approaches are introduced that establish kinematic correspondence among masters and slaves. The operators are presented with a virtual intervening tool in order to collaboratively interact with the environment. Models of operators, master and slave robots, tool, and environment are incorporated in the design. </p> <p> A multilateral adaptive nonlinear control architecture is proposed. Performance and stability of cooperative teleoperation systems are addressed under dynamic interactions between slave robots in the presence of model uncertainty. The robustness of the controller with respect to communication latency is also analyzed. </p> <p> Simulation and experimental studies demonstrate that the proposed approach is highly effective in all phases of a teleoperation task, i.e. in free motion and in contact with both flexible and rigid environments. </p> <p> The second approach involves finite-dimensional state-space models that incorporate the delay for free motion/ soft contact as well as rigid contact modes of operation. Local dynamic linearization control laws are employed to linearize robotic manipulators' dynamics. Model-based discrete-time Linear Quadratic Gaussian (LQG) controllers are proposed that can deliver a stable transparent response for each phase of operation. The robustness of these controllers with respect to parameter uncertainty is examined via the Nyquist analysis. Simulation results demonstrate the effectiveness of the proposed approach. </p> / Thesis / Master of Applied Science (MASc)

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The Domain Name System (DNS) provides a mapping between host names and Internet Protocol (IP) addresses. Hosts that are configured using the Dynamic Host Configuration Protocol (DHCP) can have their assigned IP addresses updated in a Dynamic DNS (DDNS). DNS and DDNS are critical components of the Internet. Most applications use host names rather than IP addresses, allowing the underlying operating system (OS) to translate these host names to IP addresses on behalf of the application. When the DDNS service is unavailable, applications that use DNS cannot contact the hosts served by that DDNS server. Unfortunately, the current DDNS implementation cannot continue to operate under failure of a master DNS server. Although a slave DNS server can continue to translate names to addresses, new IP addresses or changes to existing IP addresses cannot be added. Therefore, those new hosts cannot be reached by the DDNS. A new architecture is presented that eliminates this single point of failure. In this design, instead of storing resource records in a flat text file, all name servers connect to a Lightweight Directory Access Protocol (LDAP) directory to store and retrieve resource records. These directory servers replicate all resource records across each other using a multi-master replication mechanism. The DHCP servers can add records to any of the functioning DNS servers in event of an outage. In this scheme, all DNS servers use the anycast Border Gateway Protocol (BGP). This allows any of the DNS servers to answer queries sent to a single IP address. The DNS clients always use the same IP address to send queries. The routing system removes routes to non-functional name servers and delivers the request to the closest (according to network metrics) available DNS server. This thesis also describes a concrete implementation of this system that was created to demonstrate the viability of this solution. A reference implementation was built in a laboratory to represent an Internet Service Provider (ISP) with three identical regions. This implementation was built using Quagga as the BGP routing software running on a set of core routers and on each of the DNS servers. The Berkeley Internet Name Daemon (BIND) was used as an implementation of the DNS. The BIND Simplified Database Backend (SDB) interface was used to allow the DNS server to store and retrieve resource records in an LDAP directory. The Fedora Directory Server was used as a multi-master LDAP directory. DHCP service was provided by the Internet Systems Consortium's (ISC) DHCP server. The objectives for the design were high-availability, scalability and consistency. These properties were analyzed using the metrics of downtime during failover, replication overhead, and latency of replication. The downtime during failover was less than one second. The precision of this metric was limited by the synchronization provided by the Network Time Protocol (NTP) implementation used in the laboratory. The network traffic overhead for a three-way replication was shown to be only 3.5 times non-replicated network traffic. The latency of replication was also shown to be less than one second. The results show the viability of this approach and indicate that this solution should be usable over a wide area network, serving a large number of clients. / Master of Science

<p>A distributed, real-time database could be used to implement a shared whiteboard architecture used for communication between mobile nodes, in an ad-hoc network. This kind of application implies specific requirements on how the database handles replication and consistency between replicas (global consistency). Since mobile nodes are likely to disconnect from the network and connect again at unpredictable times, and since a node may be disconnected an arbitrary amount of time, this needs to be treated as normal operation, and not as failures.</p><p>The replication scheme used in the DeeDS architecture, and the PRiDe replication protocol are both suitable for a shared whiteboard architecture as described above. Since the mobile nodes are likely to be some kind of hand-held device (e.g., used by rescue personnel to exchange information), the database system should be suitable for use in embedded systems. The Polyhedra Real-Time Relational Database (RTRDB) and the TimesTen database are two such systems. A problem is that neither of these two database systems have a replication scheme suitable for use in the previously described type of architecture.</p><p>This dissertation presents two design proposals for how to extend the Polyhedra RTRDB with support for multi-master replication of data using full replication and eventual consistency. One design proposal is based on the DeeDS architecture and the other is based on the PRiDe replication protocol. The proposal based on DeeDS puts a number of requirements on the underlying database and is not easy to port to another DBMS since it makes use of Polyhedra specific API’s. The proposal based on PRiDe on the other hand requires no instrumentation of the underlying database and is thus easier to port to other database systems.</p>

A distributed, real-time database could be used to implement a shared whiteboard architecture used for communication between mobile nodes, in an ad-hoc network. This kind of application implies specific requirements on how the database handles replication and consistency between replicas (global consistency). Since mobile nodes are likely to disconnect from the network and connect again at unpredictable times, and since a node may be disconnected an arbitrary amount of time, this needs to be treated as normal operation, and not as failures. The replication scheme used in the DeeDS architecture, and the PRiDe replication protocol are both suitable for a shared whiteboard architecture as described above. Since the mobile nodes are likely to be some kind of hand-held device (e.g., used by rescue personnel to exchange information), the database system should be suitable for use in embedded systems. The Polyhedra Real-Time Relational Database (RTRDB) and the TimesTen database are two such systems. A problem is that neither of these two database systems have a replication scheme suitable for use in the previously described type of architecture. This dissertation presents two design proposals for how to extend the Polyhedra RTRDB with support for multi-master replication of data using full replication and eventual consistency. One design proposal is based on the DeeDS architecture and the other is based on the PRiDe replication protocol. The proposal based on DeeDS puts a number of requirements on the underlying database and is not easy to port to another DBMS since it makes use of Polyhedra specific API’s. The proposal based on PRiDe on the other hand requires no instrumentation of the underlying database and is thus easier to port to other database systems.