Adaptive Compensation Strategy For The Tracking/Rejection of Signals with Time-Varying Frequency in Digital Repetitive Control Systems

Digital repetitive control is a technique which al- lows to track periodic references and/or reject peri- odic disturbances. Repetitive controllers are usually de- signed assuming a fixed frequency for the signals to be tracked/rejected, its main drawback being a dramatic per- formance decay when this frequency varies. A usual ap- proach to overcome the problem consists of an adap- tive change of the sampling time according to the refer- ence/disturbance period variation. However, this sam- pling period adaptation implies parametric changes af- fecting the closed-loop system behavior, that may compro- mise the system stability. This article presents a design strategy which allows to compensate for the parametric changes caused by sampling period adjustment. Stabil- ity of the digital repetitive controller working under time- varying sampling period is analyzed. Theoretical devel- opments are illustrated with experimental results.Peer ReviewedPostprint (published version

Non-uniform sampling in digital repetitive control systems: An LMI stability analysis

Digital repetitive control is a technique which allows to track periodic references and/or reject periodic disturbances. Repetitive controllers are usually designed assuming a fixed frequency for the signals to be tracked/rejected, its main drawback being a dramatic performance decay when this frequency varies. A usual approach to overcome the problem consists of an adaptive change of the sampling time according to the reference/disturbance period variation. This report presents a stability analysis of a digital repetitive controller working under time-varying sampling period by means of an LMI gridding approach. Theoretical developments are illustrated with experimental results

Design and Analysis Strategies for Digital Repetitive Control Systems with Time-Varying Reference/Disturbance Period

This article introduces and analyzes the performance features of different design schemes for digital repetitive control systems subject to references/disturbances that exhibit non-uniform frequency. Aiming for the maintenance of a constant value for the ratio Tp/Ts, where Tp is the period of the reference/disturbance signal and Ts is the sampling period, two approaches are proposed. The first one deals with the realtime adaptation of Ts to the actual changes of Tp; the stability issue is studied by means of an LMI gridding method and also using robust control techniques. The second one propounds the introduction of an additional compensator that annihilates the effect of the time-varying sampling in the closed-loop system and forces its behavior to coincide with the one corresponding to an a priori selected nominal sampling period; the procedure needs the internal stability of the compensator-plant subsystem, which is checked by means of LMI gridding. The theoretical results are experimentally tested and compared through a mechatronic plant model.Postprint (published version

Lifting velocity predicts the maximum number of repetitions to failure with comparable accuracy during the Smith machine and free-weight prone bench pull exercises

This study compared the accuracy of the fastest mean velocity from set (MVfastest) to predict the maximum number of repetitions to failure (RTF) between 2 variants of prone bench pull (PBP) exercise (Smith machine and free-weight) and 3 methods (generalized, individualized multiplepoint, and individualized 2-point). Twenty-three resistance-trained males randomly performed 2 sessions during Smith machine PBP and 2 sessions during free-weight PBP in different weeks. The first weekly session determined the RTF-MVfastest relationships and subjects completed single sets of repetitions to failure against 60-70-80-90%1RM. The second weekly session explored the accuracy of RTFs prediction under fatigue conditions and subjects completed 2 sets of 65%1RM and 2 sets of 85%1RM with 2 min of rest. The MVfastest associated with RTFs from 1 to 15 were greater for Smith machine compared to free-weight PBP (F ≥ 42.9; P < 0.001) and for multiplepoint compared to 2-point method (F ≥ 4.6; P ≤ 0.043). The errors when predicting RTFs did not differ between methods and PBP variants, whereas all RTF-MVfastest relationships overestimated the RTF under fatigue conditions. These results suggest that RTF–MVfastest relationships present similar accuracy during Smith machine and free-weight PBP exercises and it should be constructed under similar training conditions.The Biomedicine Doctoral Studies of the University of Granada, SpainSpanish Ministry of University under a predoctoral grant (FPU19/01137)Spanish Ministry of Science and Innovation [PID2019- 110074GBI00/SRA/10.13039/501100011033)

An educational approach to the internal model principle for periodic signals

This article presents an educational approach to resonant control and repet- itive control, which are Internal Model Principle-based control techniques speci cally de- signed for the tracking/rejection of periodic signals. The analytical formulation is com- pleted by a set of simulations and physical experiments on a mechatronic educational plant integrated in a virtual/remote laboratory. The laboratory features are oriented to realize the limited performance of classic PID control to reject non-constant disturbances and, at the same time, to show the effectiveness of the Internal Model Principle for the rejection of periodic disturbances by means of resonators and repetitive control. Assess- ment based on students' perception reveals it as a useful distance learning tool. The laboratory is integrated in Automatl@bs, a Spanish interuniversity network of web-based laboratories devoted to distance learning of control engineering.Postprint (published version

Odd-harmonic repetitive control of an active filter under varying network frequency: control design and stability analysis

This work deals with the design and analysis of a controller for a shunt active power filter. The design is based on combined feedforward and feedback actions, the last using repetitive control, and aims at the obtention of a good closedloop performance in spite of the possible frequency variations that may occur in the electrical network. As these changes affect the performance of the controller, the proposal includes a compensation technique consisting of an adaptive change of the digital controller’s sampling time according to the network frequency variation. However, this implies structural changes in the closed-loop system that may destabilize the overall system. Hence, this article is also concerned with closed-loop stability of the resulting system, which is analyzed using a robust control approach through the small gain theorem. Experimental results that indicate good performance of the closed-loop system are provided.Postprint (published version

Maximal and submaximal intended velocity squat sets: Do they selectively impact mechanical performance in paired multijoint upper‐body exercise sets?

This study aimed to investigate how squat protocols performed at maximal and submaximal intended velocities during interset periods of paired upper‐body exercises that impact the mechanical performance of these multijoint upper‐body exercises. Twenty‐one young and healthy adults (seven women) completed three experimental sessions, each comprising four sets of five repetitions at 75% of their 1‐repetition maximum, with a 4‐min break between sets using the bench press and bench pull exercises. The experimental sessions differed in the protocol utilized during the interset periods: (i) Passive—no physical exercise was performed; (ii) SQfast—5 repetitions of the squat exercise at maximal intended velocity against the load associated with a mean velocity (MV) of 0.75 m s−1; and (iii) SQslow—5 repetitions of the squat exercise at submaximal velocity (intended MV of 0.50 m s−1) against the load associated with an MV of 0.75 m s−1. Level of significance was p ≤ 0.05. The main findings revealed negligible differences (effect size [ES] < 0.20) among the exercise protocols (passive vs. SQfast vs. SQslow) for all mechanical variables during the bench pull, whereas during the bench press, small differences (ES from 0.23 to 0.31) emerged favoring the passive protocol over SQfast and SQslow in terms of mean set velocity and fastest MV of the set. The absence of significant differences between the SQfast and SQslow protocols, irrespective of the particular upper‐body exercise, implies that the intended lifting velocity does not influence the potential interference effect during paired set training procedures.National Natural Science Foundation of China under grant 12250410237Funding for open access charge: Universidad de Granada/CBU

Intraocular pressure responses to a virtual reality shooting simulation in active-duty members of the Spanish Army: The influence of task complexity

Ocular physiology is sensitive to cognitively demanding tasks. However, it is unknown whether the intraocular pressure is also affected by the cognitive demands of military operations. The main objective was to determine the impact of a virtual reality shooting simulation with two levels of complexity on intraocular pressure levels in military personnel. Eighteen active-duty members of the Spanish Army and eighteen civilians performed two 4 min simulated shooting tasks with two levels of complexity using a virtual reality. In the “easy” task participants performed a simulated shoot when the stimulus (military with a rifle) appeared, while in the “difficult” task the stimulus randomly was a military with a rifle or with his hands on the air and participants were instructed to respond only when the military with a rifle appeared. Intraocular pressure was measured with a rebound tonometer before and immediately after each task. Complementarily, perceived levels of mental load and shooting performance (reaction time) were assessed. Intraocular pressure was greater after completing the more complex task in both military personnel (p-value < 0.01, Cohen´s d = 1.19) and civilians (p-value < 0.01, Cohen´s d = 1.16). Also, perceived levels of task load and reaction time were higher in the difficult compared to the easy shooting tasks (both p < 0.001). The rise in intraocular pressure is positively associated with the cognitive demands of simulated military operations. The potential application of this finding is the development of objective tools based on intraocular pressure for the evaluation of the mental state in real-world contexts, permitting to improve soldiers´safety and performance.CEMIX (Centro Mixto UGR-MADOC, Army of Spain) 5/4/20 TR-COMBAT

Revisión de control repetitivo digital en condiciones de frecuencia variable

El control repetitivo digital es una técnica que permite el seguimiento y rechazo de señales periódicas. Los controladores repetitivos son diseñados asumiendo que las señales a seguir/rechazar tienen una frecuencia fija y conocida, siendo su principal desventaja la degradación de desempeño cuando esta frecuencia varía. Este artículo presenta una revisión de las diferentes estrategias utilizadas con el fin de solventar dicha problemática.Digital repetitive control is a strategy that allows tracking/rejecting periodic signals. Repetitive controllers are designed assuming that the exogenous signal period is constant and known, its main drawback being the dramatic loss of performance when signal frequency varies. This paper reviews the most relevant proposals advanced for overcoming this problem