hig.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Isaksson, Magnus
Publications (10 of 61) Show all publications
Christensen, S., Bai, S., Rafique, S., Isaksson, M., O'Sullivan, L., Power, V. & Virk, G. S. (2019). AXO-SUIT: A Modular Full-Body Exoskeleton for Physical Assistance. In: Alessandro Gasparetto and Marco Ceccarelli (Ed.), Alessandro Gasparetto and Marco Ceccarelli (Ed.), Mechanism Design for Robotics: Proceedings of the 4th IFToMM Symposium on Mechanism Design for Robotics. Paper presented at MEDER: IFToMM Symposium on Mechanism Design for Robotics,11-13 September 2018, Udine, Italy (pp. 443-450). Paper presented at MEDER: IFToMM Symposium on Mechanism Design for Robotics,11-13 September 2018, Udine, Italy. Cham: Springer Netherlands, 66
Open this publication in new window or tab >>AXO-SUIT: A Modular Full-Body Exoskeleton for Physical Assistance
Show others...
2019 (English)In: Mechanism Design for Robotics: Proceedings of the 4th IFToMM Symposium on Mechanism Design for Robotics / [ed] Alessandro Gasparetto and Marco Ceccarelli, Cham: Springer Netherlands, 2019, Vol. 66, p. 443-450Chapter in book (Refereed)
Abstract [en]

This paper presents the design of a modular full-body assistive exoskeleton (FB-AXO) for older adults which was developed with funding under the AAL funded AXO-SUIT project. Processes used to formulate a prioritized set of functional and design requirements via close-end-user involvement are outlined and used in realizing the exoskeleton. Design of the resulting mechanics and electronics details for the lower and upper-body subsystems (LB-AXO and (UB-AXO)) are described. Innovative designs of shoulder and spine mechanisms are presented. TheFB-AXO system comprises 27 degrees of freedom, of which 17 are passive and 10 active. The exoskeleton assists full-body motions such as walking, standing, bending, as well as performing lifting and carrying tasks to assist older users performing tasks of daily living.

Place, publisher, year, edition, pages
Cham: Springer Netherlands, 2019
Series
Mechanisms and Machine Science, ISSN 22110984 ; 66
Keywords
Exoskeleton, Full Body, Lower Body, Upper Body, Assistance
National Category
Robotics
Identifiers
urn:nbn:se:hig:diva-27926 (URN)10.1007/978-3-030-00365-4_52 (DOI)000460585000052 ()2-s2.0-85052801351 (Scopus ID)978-3-030-00364-7 (ISBN)978-3-030-00365-4 (ISBN)
Conference
MEDER: IFToMM Symposium on Mechanism Design for Robotics,11-13 September 2018, Udine, Italy
Funder
Vinnova, 2014-05953
Note

Papers presented at IFToMM Symposium on Mechanism Design for Robotics, 11-13 August 2018, Udine, Italy

Funding:

- EU AAL Programme- Innovation Fund Denmark- Agentschap Innoveren Ondernemen- Enterprise Ireland 

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2019-11-29Bibliographically approved
Masud, N., Smith, C. & Isaksson, M. (2018). Disturbance observer based dynamic load torque compensator for assistive exoskeletons. Mechatronics (Oxford), 54, 78-93
Open this publication in new window or tab >>Disturbance observer based dynamic load torque compensator for assistive exoskeletons
2018 (English)In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 54, p. 78-93Article in journal (Refereed) Published
Abstract [en]

In assistive robotics applications, the human limb is attached intimately to the robotic exoskeleton. The coupled dynamics of the human-exoskeleton system are highly nonlinear and uncertain, and effectively appear as uncertain load-torques at the joint actuators of the exoskeleton. This uncertainty makes the application of standard computed torque techniques quite challenging. Furthermore, the need for safe human interaction severely limits the gear ratio of the actuators. With small gear ratios, the uncertain joint load-torques cannot be ignored and need to be effectively compensated. A novel disturbance observer based dynamic load-torque compensator is hereby proposed and analysed for the current controlled DC-drive actuators of the exoskeleton, to effectively compensate the said uncertain load-torques at the joint level. The feedforward dynamic load-torque compensator is proposed based on the higher order dynamic model of the current controlled DC-drive. The dynamic load-torque compensator based current controlled DC-drive is then combined with a tailored feedback disturbance observer to further improve the compensation performance in the presence of drive parametric uncertainty. The proposed compensator structure is shown both theoretically and practically to give significantly improved performance w.r.t disturbance observer compensator alone and classical static load-torque compensator, for rated load-torque frequencies up to 1.6 Hz, which is a typical joint frequency bound for normal daily activities for elderly. It is also shown theoretically that the proposed compensator achieves the improved performance with comparable reference current requirement for the current controlled DC-drive.

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Disturbance observer, Exoskeleton, Load torque compensator, Serial manipulator, Actuators, DC motors, Dynamic loads, Electric machine control, Electric machine theory, Joints (anatomy), Manipulators, Robotics, Torque, Torque measurement, Application of standards, Compensation performance, Compensator structure, Higher-order dynamics, Load torques, Parametric uncertainties, Serial manipulators, Exoskeleton (Robotics)
National Category
Robotics
Identifiers
urn:nbn:se:hig:diva-27633 (URN)10.1016/j.mechatronics.2018.07.003 (DOI)000446949100007 ()2-s2.0-85050674987 (Scopus ID)
Note

Ambient Assisted Living (AAL) Program  Grant no: AAL-2013-6-042

Available from: 2018-08-14 Created: 2018-08-14 Last updated: 2018-11-26Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M. (2018). Extraction of the Third-Order 3x3 MIMO Volterra Kernel Outputs Using Multitone Signals. IEEE transactions on microwave theory and techniques, 66(11), 4985-4999
Open this publication in new window or tab >>Extraction of the Third-Order 3x3 MIMO Volterra Kernel Outputs Using Multitone Signals
2018 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 11, p. 4985-4999Article in journal (Refereed) Published
Abstract [en]

This paper uses multitone signals to simplify the analysis of 3×3 multiple-input multiple-output (MIMO) Volterra systems by isolating the third-order kernel outputs from each other. Multitone signals fed to an MIMO Volterra system yield a spectrum that is a permutation of the sums of the input signal tones. This a priori knowledge is used to design multitone signals such that the third-order kernel outputs are isolated in the frequency domain. The signals are designed by deriving the conditions for the offset and spacing of the input frequency grids. The proposed technique is then validated for the six possible configurations of a 3x3 RF MIMO transmitter impaired by crosstalk effects. The proposed multitone signal design is used to extract the third-order kernel outputs, and their relative contributions are analyzed to determine the dominant crosstalk effects for each configuration.

Place, publisher, year, edition, pages
IEEE, 2018
Keywords
Crosstalk; hardware impairments; multiple-input multiple-output (MIMO); multitone signals; Volterra kernels
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-27812 (URN)10.1109/TMTT.2018.2854186 (DOI)000449354500028 ()2-s2.0-85052719621 (Scopus ID)
Available from: 2018-09-01 Created: 2018-09-01 Last updated: 2019-11-29Bibliographically approved
Khan, Z. A., Händel, P. & Isaksson, M. (2017). A Comparative Analysis of the Complexity/Accuracy Tradeoff in the Mitigation of RF MIMO Transmitter Impairments. In: 2017 89th ARFTG Microwave Measurement Conference (ARFTG): . Paper presented at 89th ARFTG Microwave Measurement Symposium, Advanced Technologies for Communications, 9 June 2017, Honolulu, Hawaii. IEEE, Article ID 8000827.
Open this publication in new window or tab >>A Comparative Analysis of the Complexity/Accuracy Tradeoff in the Mitigation of RF MIMO Transmitter Impairments
2017 (English)In: 2017 89th ARFTG Microwave Measurement Conference (ARFTG), IEEE, 2017, article id 8000827Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a comparative analysis of the complexity accuracy tradeoff in state-of-the-art RF MIMO transmitter mitigation models. The complexity and accuracy of the candidate models depends on the basis functions considered in these models. Therefore, a brief description of the mitigation models is presented accompanied by derivations of the model complexities in terms of the number of FLOPs. Consequently, the complexity accuracy tradeoff in the candidate models is evaluated for a 2 × 2 RF MIMO transmitter. Furthermore, the model complexities are analyzed for increasing nonlinear orders and number of antennas.

Place, publisher, year, edition, pages
IEEE, 2017
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-24580 (URN)10.1109/ARFTG.2017.8000827 (DOI)000426454300011 ()2-s2.0-85030244336 (Scopus ID)978-1-5386-2747-1 (ISBN)978-1-5386-2748-8 (ISBN)
Conference
89th ARFTG Microwave Measurement Symposium, Advanced Technologies for Communications, 9 June 2017, Honolulu, Hawaii
Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2018-06-26Bibliographically approved
Alizadeh, M., Rönnow, D., Händel, P. & Isaksson, M. (2017). A new Block-Structure Modeling Technique for RF Power Amplifiers in a 2x2 MIMO System. In: Milovanovic, B. D.; Doncov, N. S.; Stankovic, Z. Z.; Dimitrijevic, T. Z. (Ed.), 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS): . Paper presented at 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS), Nis, Serbia, 18-20 October 2017 (pp. 224-227). IEEE
Open this publication in new window or tab >>A new Block-Structure Modeling Technique for RF Power Amplifiers in a 2x2 MIMO System
2017 (English)In: 13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS) / [ed] Milovanovic, B. D.; Doncov, N. S.; Stankovic, Z. Z.; Dimitrijevic, T. Z., IEEE , 2017, p. 224-227Conference paper, Published paper (Refereed)
Abstract [en]

A new block-structure behavioral model is proposed for radio frequency power amplifiers in a 2x2 multiple-input multiple-output system including input cross-talk. The proposed model forms kernels of blocks of different nonlinear order that correspond to the significant frequency response of measured frequency domain Volterra kernels. The model can therefore well describe the input-output relationships of the nonlinear dynamic behavior of PAs. The proposed model outperforms conventional models in terms of model errors.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
Nonlinear dynamic RF power amplifier, Volterra kernels, MIMO system, block-structural model
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-26235 (URN)10.1109/TELSKS.2017.8246268 (DOI)000425463200046 ()2-s2.0-85045971319 (Scopus ID)978-1-5386-1800-4 (ISBN)
Conference
13th International Conference on Advanced Technologies, Systems and Services in Telecommunications (TELSIKS), Nis, Serbia, 18-20 October 2017
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2019-09-17Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M. (2017). Digital Predistortion for Joint Mitigation of I/Q Imbalance and MIMO Power Amplifier Distortion. IEEE transactions on microwave theory and techniques, 65(1), 322-333, Article ID 7600411.
Open this publication in new window or tab >>Digital Predistortion for Joint Mitigation of I/Q Imbalance and MIMO Power Amplifier Distortion
2017 (English)In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 65, no 1, p. 322-333, article id 7600411Article in journal (Refereed) Published
Abstract [en]

This paper analyzes the joint effects of in-phase and quadrature (I/Q) imbalance and power amplifier (PA) distortion for RF multiple input multiple output (MIMO) transmitters in the presence of crosstalk. This paper proposes candidate models for the digital predistortion of static I/Q imbalanced sources exciting a dynamic MIMO Volterra system. The proposed models are enhanced using a novel technique based on subsample resolution to account for dynamic I/Q imbalance distortions. Finally, the computational complexity of the proposed models is analyzed for implementation suitability in digital platforms. It is shown that the error spectrum for the proposed models in subsample resolution reaches the noise floor of the measurements. The proposed models achieve a normalized mean squared error of -50 dB and an adjacent channel power ratio of -57 dB for signal bandwidths upto 65 MHz and crosstalk levels ranging to -10 dB. These results demonstrate the effectiveness of the proposed techniques in the joint mitigation of I/Q imbalance and PA distortion with crosstalk for a typical 2x2 MIMO telecommunication setup.

Keywords
Digital predistortion (DPD), in-phase and quadrature (I/Q) imbalance, linearization, multiple input multiple output (MIMO), power amplifier (PA)
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-22675 (URN)10.1109/TMTT.2016.2614933 (DOI)000395460200033 ()2-s2.0-84992060969 (Scopus ID)
Note

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Available from: 2016-10-28 Created: 2016-10-28 Last updated: 2018-09-21Bibliographically approved
Singh Rupal, B., Rafique, S., Singla, A., Singla, E., Isaksson, M. & Singh Virk, G. (2017). Lower-limb exoskeletons: Research trends and regulatory guidelines in medical and non-medical applications. International Journal of Advanced Robotic Systems, 14(6), 1-27
Open this publication in new window or tab >>Lower-limb exoskeletons: Research trends and regulatory guidelines in medical and non-medical applications
Show others...
2017 (English)In: International Journal of Advanced Robotic Systems, ISSN 1729-8806, E-ISSN 1729-8814, Vol. 14, no 6, p. 1-27Article, review/survey (Refereed) Published
Abstract [en]

With the recent progress in personal care robots, interest in wearable exoskeletons has been increasing due to the demand for assistive technologies generally and specifically to meet the concerns in the increasing ageing society. Despite this global trend, research focus has been on load augmentation for soldiers/workers, assisting trauma patients, paraplegics, spinal cord injured persons and for rehabilitation purposes. Barring the military-focused activities, most of the work to date has focused on medical applications. However, there is a need to shift attention towards the growing needs of elderly people, that is, by realizing assistive exoskeletons that can help them to stay independent and maintain a good quality of life. Therefore, the present article covers the rapidly evolving area of wearable exoskeletons in a holistic manner, for both medical and non-medical applications, so that relevant current developments and future issues can be addressed; this includes how the physical assistance/rehabilitation/compensation can be provided to supplement capabilities in a natural manner. Regulatory guidelines, important for realizing new markets for these emerging technologies, are also explored in this work. For these, emerging international safety requirements are presented for non-medical and medical exoskeleton applications, so that the central requirement of close human–robot interactions can be adequately addressed for the intended tasks to be carried out. An example case study on developing and commercializing wearable exoskeletons to help support living activities of healthy elderly persons is presented to highlight the main issues in non-medical mobility exoskeletons. This also paves the way for the potential future trends to use exoskeletons as physical assistant robots, as covered by the recently published safety standard ISO 13482, to help elderly people perform their activities of daily living.

Place, publisher, year, edition, pages
Sage Publications, 2017
Keywords
Lower-limb exoskeletons, wearable robots, disability technologies, mobility augmentation, medical/non-medical regulations
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:hig:diva-25734 (URN)10.1177/1729881417743554 (DOI)000417219300001 ()2-s2.0-85039909573 (Scopus ID)
Funder
Vinnova, 2012-03255
Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2019-10-03Bibliographically approved
Khan, Z. A., Zenteno, E., Händel, P. & Isaksson, M. (2017). Multitone design for third order MIMO volterra kernels. In: 2017 IEEE MTT-S International Microwave Symposium (IMS): . Paper presented at 2017 IEEE MTT-S International Microwave Symposium (IMS), 4-9 June 2017, Honolulu, USA (pp. 1553-1556). IEEE conference proceedings
Open this publication in new window or tab >>Multitone design for third order MIMO volterra kernels
2017 (English)In: 2017 IEEE MTT-S International Microwave Symposium (IMS), IEEE conference proceedings, 2017, p. 1553-1556Conference paper, Published paper (Refereed)
Abstract [en]

This paper proposes a technique for designing multitone signals that can separate the third order multiple input multiple output (MIMO) Volterra kernels. Multitone signals fed to a MIMO Volterra system yield a spectrum that is a permutation of the sums of the input signal tones. This a priori knowledge is used to design multitone signals such that the output from the MIMO Volterra kernels does not overlap in the frequency domain, hence making it possible to separate these kernels from the output of the MIMO Volterra system. The proposed technique is applied to a 2×2 RF MIMO transmitter to determine its dominant hardware impairments. For input crosstalk, the proposed method reveals the dominant self and cross kernels whereas for output crosstalk, the proposed method reveals that only the self kernels are dominant.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2017
Keywords
Complexity theory, Crosstalk, Kernel, MIMO, Peak to average power ratio, Radio frequency, Transmitters
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-25431 (URN)10.1109/MWSYM.2017.8058925 (DOI)000425241500419 ()2-s2.0-85032467119 (Scopus ID)978-1-5090-6360-4 (ISBN)
Conference
2017 IEEE MTT-S International Microwave Symposium (IMS), 4-9 June 2017, Honolulu, USA
Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2019-11-29Bibliographically approved
Amin, S., Khan, Z. A., Isaksson, M., Händel, P. & Rönnow, D. (2016). Concurrent dual-band power amplifier model modification using dual two-tone test. In: 46th Europena Microwave Conference (EUMC) 2016: . Paper presented at 46th European Microwave Conference (EuMC), 4-6 October 2016, London, UK (pp. 186-189).
Open this publication in new window or tab >>Concurrent dual-band power amplifier model modification using dual two-tone test
Show others...
2016 (English)In: 46th Europena Microwave Conference (EUMC) 2016, 2016, p. 186-189Conference paper, Published paper (Refereed)
Abstract [en]

A dual two-tone technique for the characterization of memory effects in concurrent dual-band transmitters is revisited to modify a 2D-DPD model for the linearization of concurrent dual-band transmitters. By taking into account the individual nonlinear memory effects of the self- and cross-kernels, a new2D modified digital pre-distortion (2D-MDPD) model is proposed,which not only supersedes the linearization performance but also reduces the computational complexity compared to the 2DDPDmodel in terms of a number of floating point operations(FLOPs). Experimental results show an improvement of 1.7 dBin normalized mean square error (NMSE) and a 58% reduction in the number of FLOPs.

Series
European Microwave Conference, ISSN 2325-0305
Keywords
IEEE Keywords Computational modeling, Numerical models, Dual band, Two dimensional displays, Radio frequency, Computational complexity
National Category
Signal Processing
Identifiers
urn:nbn:se:hig:diva-22558 (URN)10.1109/EuMC.2016.7824309 (DOI)000393581100048 ()2-s2.0-85015185570 (Scopus ID)978-2-87487-043-9 (ISBN)978-1-5090-1514-6 (ISBN)
Conference
46th European Microwave Conference (EuMC), 4-6 October 2016, London, UK
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2018-12-03Bibliographically approved
Zenteno, E., Khan, Z. A., Isaksson, M. & Händel, P. (2016). Finding Structural Information about RF Power Amplifiers using an Orthogonal Nonparametric Kernel Smoothing Estimator. IEEE Transactions on Vehicular Technology, 65(5), 2883-2889, Article ID 7109926.
Open this publication in new window or tab >>Finding Structural Information about RF Power Amplifiers using an Orthogonal Nonparametric Kernel Smoothing Estimator
2016 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 5, p. 2883-2889, article id 7109926Article in journal (Refereed) Published
Abstract [en]

A non-parametric technique for modeling the behavior of power amplifiers is presented. The proposed technique relies on the principles of density estimation using the kernel method and is suited for use in power amplifier modeling. The proposed methodology transforms the input domain into an orthogonal memory domain. In this domain, non-parametric static functions are discovered using the kernel estimator. These orthogonal, non-parametric functions can be fitted with any desired mathematical structure, thus facilitating its implementation. Furthermore, due to the orthogonality, the non-parametric functions can be analyzed and discarded individually, which simplifies pruning basis functions and provides a tradeoff between complexity and performance. The results show that the methodology can be employed to model power amplifiers, therein yielding error performance similar to state-of-the-art parametric models. Furthermore, a parameter-efficient model structure with 6 coefficients was derived for a Doherty power amplifier, therein significantly reducing the deployment’s computational complexity. Finally, the methodology can also be well exploited in digital linearization techniques.

Keywords
Power amplifier, non-parametric model, kernel, basis functions, power amplifier linearization, Digital pre distortion.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:hig:diva-19395 (URN)10.1109/TVT.2015.2434497 (DOI)000376094500004 ()2-s2.0-84970016798 (Scopus ID)
Available from: 2015-05-27 Created: 2015-05-27 Last updated: 2018-11-26Bibliographically approved
Projects
Radio frequency measurement technology for weakly nonlinear systems [2009-02977_VR]; University of Gävle
Organisations

Search in DiVA

Show all publications