Geir Mathisen

Real-time analysis of a multi-robot sewing cell

This paper presents a sewing cell based on an industrial sewing machine, and with two robots controlling the sewing operation in real-time. The software architecture and the communication structure are presented. Widely available software and hardware technologies were used to build a highly flexible system for operation and control prototyping. This paper focuses on analyzing the real-time characteristics of the control system. Experiments were conducted to measure the delays in different parts of the system in order to gain an understanding of the real-time performance and to show that the chosen system is capable to make use of the robots high update frequency and low tracking delay.

Optimal Power Flow model with energy storage, an extension towards large integration of renewable energy sources.

Abstract The integration of renewable energy sources (RES) into modern electrical grids contributes to satisfying the continuously increasing energy demand. This can be done in a sustainable way since renewable sources are both inexhaustible and non-polluting. Different renewable energy devices, such as wind power, hydro power, and photovoltaic generators are available nowadays. The main issue with the integration of such devices is their irregular generation capacity (in particular for wind and solar energy). Therefore energy storage units are used to mitigate the fluctuations during generation and supply. In this paper we formulate a model for the Alternate Current Optimal Power Flow (ACOPF) problem consisting of simple dynamics for energy storage systems cast as a finite-horizon optimal control problem. The effect of energy storage is examined by solving a Norwegian demo network. The simulation results illustrate that the addition of energy storage, along with demand based cost functions, significantly reduces the generation costs and flattens the generation profiles.

Velocity coordination and corner matching in a multi-robot sewing cell.

Automated sewing is a complicated task in manufacturing. Due to the non-rigid work pieces and variations in the material characteristics, sensor-based control has to be used to accomplish the sewing operation. This paper presents a strategy for velocity synchronization and corner matching in an automated sewing cell based on two industrial manipulators and a sewing machine. A hybrid force/motion control scheme is adopted using feedback from force/torque sensors for tension control and optical sensors to control the seam position. The strategy is based on switching between force control and displacement control using a leader/follower coordination scheme. This addresses the problem of corner mismatch occurring when two independent force controllers are used for controlling the two robots. Experiments verify that the proposed method gives a satisfactory corner matching, which is crucial for the presented sewing case.

Model-based feed-forward and setpoint generation in a multi-robot sewing cell

This paper describes an automated sewing system that focuses on sewing of curved edge segments. The sewing cell includes an industrial sewing machine as well as three industrial robots that handle the parts during the sewing process. Based on experiences from previous work, several improvements are presented that address issues with previous implementations. The main contribution concerning the control system is a model-based generation of the feed-forward velocity for the robot tool movement, based on a geometric description of the parts. This approach increases performance, especially in the case of curved fabric, as well as robustness in case of faulty sensor data. Additionally, this paper describes hardware upgrades that address mechanical challenges that were described in former publications. Finally, the paper presents experiments comparing the model-based control approach with the former control system based on constant feed-forwards velocity and setpoints.

A Cyber-Physical Systems Approach for Implementing the Receding Horizon Optimal Power Flow in Smart Grids

Two major challenges in securing reliable Optimal Power Flow (OPF) operations are: (i) fluctuations induced due to renewable generators and energy demand, and (ii) interaction and interoperability among the different entities. Addressing these issues requires handling both physical (e.g., power flows) and cyber aspects (computing and communication) of the energy grids, i.e, a cyber-physical systems (CPS) approach is necessitated. First, this investigation proposes a receding horizon control (RHC) based approach for solving OPF to deal with the uncertainties. It uses forecasts on renewable generation and demand and an optimization model solving a predictive control problem to secure energy balance while meeting the network constraints. Second, to handle the interoperability issues, a middleware using common information model (CIM) for exchanging information among applications and the associated profiles are presented. CIM profiles modelling various components and aspects of the RHC based OPF is proposed. In addition, a middleware architecture and services to collect information is discussed. The proposed CPS approach is illustrated in a distribution grid in Steinkjer, Norway having 85 nodes, 700 customers, three hydrogenerators, and various industrial loads. Our results demonstrate the benefits of CPS approach to implement OPF addressing also the interoperability issues.

Differential feed control applied to corner matching in automated sewing

This paper presents a new method for independent feed control in an automated sewing cell. This is important to match the corners of the parts as well as to compensate for uncertain material characteristics and variations in the length of the parts. In this method, the feed speed for the two parts is controlled independently, based on measurements of the endpoints of the parts while keeping an equal sewing force in both parts. Different strategies for correcting errors are presented and experiments are shown to evaluate the different strategies. Possibilities for using the methods to match reference points during the sewing are discussed.

Time-analysis of a real-time sensor-servoing system using line-of-sight path tracking

This paper presents a study of the real-time control conditions for a robotic system with visual servo control. The system is based on an industrial manipulator with a modified controller allowing real-time joint-level control. The work is particularly concerned with delays and path deviations. The focus is on the Line-of-Sight based path tracking controller. The paper describes an analysis of the different delays in the sensor-robot system and a model is presented based on the overall delay. Further the stability of the modeled system is analyzed in respect to a specific control case. The correctness of the estimated system delay is indicated by comparison of simulated and experimental results.

Cyber-Physical Energy Systems Approach for Engineering Power System State Estimation in Smart Grids

This investigation proposes a CPES architecture and model for engineering energy management application for smart grids. In particular, the investigation considers the implementation of the power systems state estimator (PSSE). The CPES architecture has three layers: physical, monitoring and applications. The physical layer consists of the grid and the various components. Since, the grid is usually engineered with various devices from multiple vendors that have different protocols and standards; data aggregation becomes a problem. The second layer of the CPES architecture overcomes this problem by proposing a middleware that aggregates data from the physical layer. The topmost layer is the applications layer, where the energy management system applications are implemented. These applications require the model, topology and information from the grid. This requires combining the physical aspects of the grid with the cyber ones. This investigation uses the common information model to model the grid and information exchanges. Then the model is combined with measurement and optimization models of the application to realize the PSSE. The proposed approach is illustrated on a Norwegian distribution grid in Steinkjer. Our results show that the CPES approach provides an easier way to engineer future smart grid applications.

Deploying third party services at smart grids end users using broadband links

Smart grids end users, such as houses and factories, already have a broadband link for common web access. We start with the hypothesis that these links can be used to exchange data between the meter/controller, at the user, and a service, at the web, using application protocols (e.g., SPDY and HTTPS). This hypothesis is verified studying the connectivity capabilities/constraints that a third party service may experience in broadband links. A quantitative evaluation was performed, in an emulated IPv6 network, to delimit the throughput, latency and reliability available to smart grids services. The results showed that SPDY and HTTPS can meet typical QoS requirements using a proper architecture (e.g., centralized or distributed), and can drive the development of new web-based energy services. Here, we discuss practical connectivity aspects to deploy such services.