| 1. |
- Åkesson, Johan, et al.
(författare)
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Safe Manual Control of the Furuta Pendulum
- 2001
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Ingår i: Proceedings of the 2001 IEEE International Conference on Control Applications, 2001. (CCA '01).. - 0780367332 ; , s. 890-895
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the manual control of unstable systems, subject to control signal saturation. In particular we consider the Furuta pendulum, where the problem is to control the orientation of the arm manually while stabilizing the inverted pendulum. This paper presents an analysis which leads to an insight into the problem as well as the control strategy. This control strategy has been implemented on the real Furuta pendulum. Aspects of the implementation as well as experimental results are discussed
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| 2. |
- Furunäs-Åkesson, Johan
(författare)
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Interprocess Communication Utilising Special Purpose Hardware
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Real-time systems are computer systems with constraints on the timing of actions. To ease the development and maintenance of application software, real-time systems often make use of a real-time operating system (RTOS). Its main task is management and scheduling of application processes (tasks). Other functions are interprocess communication, interrupt handling, memory management etc. Sometimes it is hard (or even impossible) to meet the time constraints specified for a real-time system, resulting in an incorrectly functioning application. A possible remedy is to redesign the system by upgrading the processor and/or remove functionality. An alternative approach is to use a special purpose hardware RTOS accelerator. The aim of such an accelerator is to speedup RTOS functions that impose big overhead i.e. to reduce the RTOS overhead by offloading the application processor. Accordingly, the processor gets more time for executing application software, and hopefully the time constraints can be met. The main drawback is the cost of extra hardware. This thesis presents results from implementing RTOS functions in hardware, especially interprocess communication (IPC) functions. The types of systems considered are uniprocessor and shared memory multiprocessor real-time systems. IPC is used in systems with co-operating processes. The real-time operating systems on the market support a large variation of IPC mechanisms. We will here present and evaluate three different IPC implementations. The first is an extended message queue mechanism that is used in commercial robot control applications. The second is the signal mechanism in OSE, a commercial RTOS predominantly used in telecommunication control applications, and the third is the semaphore and message queue mechanisms supported by the leading commercial RTOS VxWorks. All the implementations are based on a pre-emptive priority-based hardware real-time operating system accelerator. We show that it is not optimal, practical or desirable to implement every RTOS function in hardware, regarding systems in the scope of this thesis. However, an accelerator allows new functionality to be implemented. We illustrate this by implementing a message queue mechanism that supports priority inheritance for message arrival in hardware, which is too expensive to implement in software. Also, we show that substantial speedups are possible, and that a crucial mechanism in achieving speedup is the realisation of the communication between the accelerator and the processor. We further note that application speedups are possible, even in cases with an IPC-mechanism slow-down. The main reasons for this is that the accelerator can off-load the processor by handling the RTOS timing mechanism (clock-ticks), reducing the RTOS code to be executed on the processor, and handling interrupts.
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| 3. |
- Furunäs Åkesson, Johan
(författare)
-
Interprocess communication utilising special purpose hardware
- 2001
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Real-Time Systems are computer systems with constraints on the timing of actions. To ease the development and maintenance of application software, Real-time Systems often make use of a Real-Time Operating System (RTOS). Its main task is scheduling of application processes (tasks). Other functions can be interprocess communication, interrupt handling, memory management etc.Sometimes it is hard (or even impossible) to meet the time constraints specified for a real-time system, resulting in an incorrectly functioning application. A possible remedy is to redesign the system by upgrading the processor and/or remove functionality, etc. An alternative solution could be the use of a special purpose hardware accelerated RTOS. The aim of such an accelerator is to speedup RTOS functions that impose big overhead i.e. to reduce the kernel overhead by offloading the application processor. Accordingly, the processor gets more time for executing application software, and hopefully the time constraints can be met. The main drawback is the cost of extra hardware.This thesis presents results from implementing RTOS functions in hardware, especially interprocess communication (IPC) functions. The types of systems considered are uniprocessor and shared memory multiprocessor real-time systems.IPC is used in systems with co-operating processes. The operating systems on the market support a large variation of IPC mechanisms. We will here present and evaluate three different IPC implementations. The first is an extended message queue mechanism that is used in commercial robot control applications. The second is the signal mechanism in OSE, a commercial RTOS predominantly used in telecommunication control applications, and the third is the semaphore and message queue mechanisms supported by the leading commercial RTOS VxWorks. All the implementations are based on a pre-emptive priority-based hardware real-time kernel accelerator.We show that it is not optimal, practical or desirable to implement every kernel function into hardware, regarding systems in the scope of this thesis. However, an accelerator allows new functionality to be implemented. We illustrate this by implementing a message queue mechanism that supports priority inheritance for message arrival in hardware, which is too expensive to implement in software. Also, we show that substantial speedups are possible, and that a crucial mechanism in achieving speedup is the accelerator-processor interconnect. We further note that application speedups are possible, even in cases with an IPC-mechanism slow-down. The main reasons for this is that the accelerator can off-load the processor by handling the RTOS timing mechanism (clock-ticks), reducing the RTOS code to be executed on the processor, and handling interrupts.
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| 4. |
- Hagander, Per, et al.
(författare)
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Kamratgranskning av laborationsförberedelser i reglerteknik
- 2003
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Ingår i: Proceedings - 1:a Pedagogiska Inspirationskonferensen 2003. ; , s. 62-64
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Laborationer är ett frekvent återkommande inslag i kurserna vid Institutionen för Regerteknik. Laborationerna tar mycket resurser i anspråk, och det är därför viktigt att skapa förutsättningar för att studenterna skall få ut så mycket som möjligt av dem. Studenterna förväntas inför varje laboration läsa på relevanta delar av kursmaterialet, samt i vissa fall även lösa några förberedelseuppgifter. Det skriftliga förhör som traditionellt tillämpats för att testa studenternas förkunskaper inför laborationen har medfört att studenterna ofta upplevt stress inför laborationerna. För att skapa en mer positiv undervisningssituation har kamratgranskning av förkunskaper i grupp provats. Reaktionerna från studenterna och har varit mycket positiva. Våra erfarenheter är också positiva, även om vissa mindre signifikanta negativa bieffekter observerats.
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| 5. |
- Henriksson, Dan, et al.
(författare)
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Feedback Scheduling of Model Predictive Controllers
- 2002
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Ingår i: Proceedings of the 8th IEEE Real-Time and Embedded Technology and Applications Symposium. - 0769517390 ; , s. 207-216
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Konferensbidrag (refereegranskat)abstract
- The paper presents some preliminaryresults on dynamic scheduling of model predictive controllers (MPCs).In an MPC, the control signal is obtained by on-line optimization of acost function, and the MPC task may experience very large variationsin execution time from sample to sample. Unique to this application,the cost function offers an explicit, on-line quality-of-servicemeasure for the task. Based on this insight, a feedback schedulingstrategy for multiple MPCs is proposed, where the scheduler allocatesCPU time to the tasks according to the current values of the costfunctions. Since the MPC algorithm is iterative, the feedbackscheduler may also abort a task prematurely to avoid excessiveinput-output latency. A case study is presented, where the newapproach is compared to conventional fixed-priority andearliest-deadline-first scheduling. General problems related to thereal-time implementation of MPCs are also discussed.
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| 6. |
- Henriksson, Dan, et al.
(författare)
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Flexible Implementation of Model Predictive Control Using Sub-Optimal Solutions
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The on-line computational demands of model predictive control (MPC) often prevents its application to processes where fast sampling is necessary. This report presents a strategy for reducing the computational delay resulting from the on-line optimization inherent in many MPC formulations. Recent results have shown that feasibility, rather than optimality, is a prerequisite for stabilizing MPC algorithms, implying that premature termination of the optimization procedure may be valid, without compromising stability. The main result included in the report is a termination criterion for the on-line optimization algorithm giving rise to a sub-optimal, yet stabilizing, MPC algorithm. The termination criterion, based on an associated delay-dependent cost index, quantifies the trade-off between successively improved control profiles resulting form the optimization algorithm and the potential performance degradation due to increasing computational delay. It is also shown how the cost index may be used in a dynamic scheduling application, where the processor time is shared between two MPC tasks executing on the same CPU.
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| 7. |
- Henriksson, Dan, et al.
(författare)
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On Dynamic Real-Time Scheduling of Model Predictive Controllers
- 2002
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Ingår i: Proceedings of the 41st IEEE Conference on Decision and Control, 2002. - 0191-2216. - 0780375165 ; 2, s. 1325-1330
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Konferensbidrag (refereegranskat)abstract
- The paper discusses dynamic real-time scheduling in the context ofmodel predictive control (MPC). Dynamic scheduling in this settingis motivated by the highly varying execution times associated withMPC controllers. Premature termination of the optimization algorithmis exploited to trade off prolonged computations versuscomputational delay. A feedback scheduling strategy for multiple MPCcontrollers is also proposed, where the scheduler allocates CPU timeto the tasks according to the current values of the cost functions.Simulated examples show how the overall control performance maybenefit from the application of the proposed schemes.
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| 8. |
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| 9. |
- Muheim, Rachel, et al.
(författare)
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Magnetic compass orientation in European robins is dependent on both wavelength and intensity of light
- 2002
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 205:24, s. 3845-3856
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic compass orientation in birds has been shown to be light dependent. Results from behavioural studies indicate that magnetoreception capabilities are disrupted under light of peak wavelengths longer than 565 nm, and shifts in orientation have been observed at higher light intensities (43-44x1015 quanta s-1 m-2). To investigate further the function of the avian magnetic compass with respect to wavelength and intensity of light, we carried out orientation cage experiments with juvenile European robins, caught during their first autumn migration, exposed to light of 560.5 nm (green), 567.5 nm (green-yellow) and 617 nm (red) wavelengths at three different intensities (1 mW m-2, 5 mW m-2 and 10 mW m-2). We used monochromatic light of a narrow wavelength range (half bandwidth of 9-11 nm, compared with half bandwidths ranging between 30 nm and 70 nm used in other studies) and were thereby able to examine the magnetoreception mechanism in the expected transition zone between oriented and disoriented behaviour around 565 nm in more detail. We show (1) that European robins show seasonally appropriate migratory directions under 560.5 nm light, (2) that they are completely disoriented under 567.5 nm light under a broad range of intensities, (3) that they are able to orient under 617 nm light of lower intensities, although into a direction shifted relative to the expected migratory one, and (4) that magnetoreception is intensity dependent, leading to disorientation under higher intensities. Our results support the hypothesis that birds possess a light-dependent magnetoreception system based on magnetically sensitive, antagonistically interacting spectral mechanisms, with at least one high-sensitive short-wavelength mechanism and one low-sensitive long-wavelength mechanism.
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| 10. |
- Åkesson, Johan, et al.
(författare)
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A Frame Work for Process State Transitions: Grade Changes
- 2002
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Ingår i: Preprints Reglermöte 2002. ; , s. 370-375
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Konferensbidrag (refereegranskat)abstract
- In modern chemical process industry, process state transitions, orgrade changes, are common operations. For example, for a papermachine, a common operation is to change the surface weight of theproduced paper. In this case it is of importance that the transitionto the new grade is done fast, but without a breakdown asa result. This paper addresses this problem by combining optimizationtechniques and a tool for sequential control, JGrafchart. The paperalso contains an example, where the proposed method has been appliedto the quadruple-tank process.
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