Position Control of a Flexible Joint via Explicit Model Predictive Control: An Experimental Implementation

This paper experimentally controls a flexible joint via explicit model predictive control (Explicit MPC) method. The scheme divides the state space into different partitions, then solves the associated multi parametric optimization in off-line computations. The result stores in a look-up table to be used in on-line algorithm. First, the state space equations of the flexible joint are derived and linearized around the working point. Then, in order to meet the plant’s specifications, desired performance and the limitation of processor/memory, the constraints, weights, sampling time and prediction horizon are determined for the system. Finally, the algorithm is applied on the experimental plant. Numerous simulations, the result of the experiment and comparison with other methods confirmed that the method was able to control the vibrations of the constrained flexible joint

A cybernetic view on wind-up

Summary Wind-up is described traditionally as a frequency dependent increase in the excitability of spinal cord neurons, evoked by electrical stimulation of afferent C-fibers. Different kinds of wind-up have been reported, but wind-up of Ab fibers in hyperalgesic states has gained little attention. In this paper, we present a cybernetic view on Ab fiber wind-up and consider the involved molecular mechanisms as feedback and feedforward processes. Furthermore, our previous hypothesis, the sprouting phenomenon, is included in this view. Considering the proposed model, wind-up in hyperalgesic states might leave out in three different ways: (1) blocking the NMDA receptors by increasing extracellular Mg 2+ , 2) blocking the receptors and channels that contribute to Ca 2+ inward current, and 3) blocking the Ab fibers by local anesthetics. It seems that wind-up may be inhibited more effectively by using these three blocking mechanisms simultaneously, because in this case, the feedback process (main controller), the feedforward process (trigger), and Ab stimulation (trigger) would be inhibited concurrently. Wind up may aggravate the pain in clinical hyperalgesic situations such as post-surgical states, some neuropathic pains, fibromyalgia syndrome, and post-herpetic neuralgia. Surely, clinical studies are needed to validate the effectiveness of our abovementioned suggestions in relieving such clinical pains

Modeling of cerebellar transcranial electrical stimulation effects on hand tremor in Parkinson’s disease

IntroductionParkinson’s disease (PD) is a neurodegenerative disorder with different motor and neurocognitive symptoms. Tremor is a well-known symptom of this disease. Increasing evidence suggested that the cerebellum may substantially contribute to tremors as a clinical symptom of PD. However, the theoretical foundations behind these observations are not yet fully understood.MethodsIn this study, a computational model is proposed to consider the role of the cerebellum and to show the effectiveness of cerebellar transcranial alternating current stimulation (tACS) on the rest tremor in participants with PD. The proposed model consists of the cortex, cerebellum, spinal circuit-muscular system (SC-MS), and basal ganglia blocks as the most critical parts of the brain, which are involved in generating rest tremors. The cortex, cerebellum, and SC-MS blocks were modeled using Van der Pol oscillators that interacted through synchronization procedures. Basal ganglia are considered as a regulator of the coupling weights defined between oscillators. In order to evaluate the global behavior of the model, we applied tACS on the cerebellum of fifteen PD patients for 15 min at each patient’s peak frequency of their rest tremors. A tri-axial accelerometer recorded rest tremors before, during, and after the tACS.Results and DiscussionThe simulation of the model provides a suggestion for the possible role of the cerebellum on rest tremors and how cerebellar tACS can affect these tremors. Results of human experiments also showed that the online and offline effects of cerebellar tACS could lead to the reduction of rest tremors significantly by about %76 and %68, respectively. Our findings suggest that the cerebellar tACS could serve as a reliable, therapeutic technique to suppress the PD tremor

Model predictive impedance control : a model for joint movement control

A human is capable of making various movements under different environmental conditions including highly accurate movements, low accurate movements, ballistic movements, or learning new skills. This flexibility results from highly integrated neural centers in the brain and the spinal cord acting as higher and lower level controllers and information processors, a large number of muscles and bones constructing the actuators required to generate movements, and numerous sensory receptors informing the neural centers about the results of movement and the environment. For a comprehensive understanding of the motor control system, it is necessary to have a global model. This model can also be used to test the function of motor components under natural or pathological conditions. This thesis is an effort toward developing such a global model based on the most currently accepted theories and hypotheses in biological motor control and control engineering. The proposed model, called model predictive impedance control,specifically combines the equilibrium point hypothesis (α and $\lambda$ models), the impedance control strategy (including stiffness and viscosity), servomechanism control theory, and the optimization-based model predictive control algorithm as a unified model applicable in the study of different types of movements. The model is adaptive with learning ability and operates in open-loop or closed-loop manners. The focus is on the overall function of motor centers instead of individual realization structurally or functionally. Acting as a supervisory and higher level controller, the model predictive controller presents a new approach to determine the joint impedance and the equilibrium point based on use of a priori knowledge of the neuromusculoskeletal system and environment. To evaluate the performance of the model, it was applied to three different types of joint movements: a tracking movement with an unpredicted disturbance, a rhythmic movement, and an unstable biped model of human walking. Computer simulation results showed excellent performance of the model in all three cases for optimal values of active joint impedances and a perfect match between the musculoskeletal system and the model internal to the model predictive controller. The controller was also able to maintain acceptable performance in the presence of a 25% mismatch between the musculoskeletal system and its internal model

A WAVELET-BASED MODEL FOR FOVEAL DETECTION OF SPATIAL CONTRAST WITH FREQUENCY DEPENDENT APERTURE EFFECT

The main purpose of this study is to build a Computational model based on ModelFest dataset which is able to predict contrast sensitivity while it benefits from simplicity, efficiency and accuracy, which makes it suitable for hardware implementation, practical uses, online tests, real-time processes, an improved Standard Observer and retina prostheses. It encompasses several components, and in particular, frequency dependent aperture effect (FDAE) which is used for the first time on this dataset, which made the model more accurate and closer to reality. Shortcomings of previous models and the necessity of existence of FDAE for more accuracy led us to develop a new model based on Wavelet Transform that gives us the advantage of speed and the capability to process each frequency channels output. Considering our goal for building an efficient model, we introduce a new formula for modeling contrast sensitivity function, which generates lower RMS error and better timing performance. Eventually, this new model leads to having as yet lowest RMS error and solving the problem of long execution time of prior models and reduces them by almost a factor of twenty

Pathophysiology of freezing of gait and some possible treatments for it

a b s t r a c t Freezing of gait (FOG) is a disabling symptom of Parkinson's disease (PD). In this study, we used the model of PD gait behavior for comparing normal and PD persons in order to simulate FOG and find its pathophysiology and probable treatments. We observed in the adapted model that the dopaminergic weights were reduced and the amount of dopaminergic bias was increased. These findings show that the aggravation of the disease and severe resistance of neurons to dopamine agonists may be the main cause of the FOG. Based on our model three therapeutic strategies may be proposed: decreasing the cortex signal to basal ganglia, using high dose glutamate antagonist, and using less glutamate antagonist with some amounts of gabapentin. Ó 2011 Published by Elsevier Ltd. Introduction Parkinson's disease (PD) is a common progressive neurodegenerative disease that its main cause is the death of neurons in substantia nigra pars compacta (SNc) of basal ganglia (BG). The mechanisms of motor symptoms are not yet known in this disease and hence, there is no definite treatment for it. One of the most important symptoms of PD is gait disturbance which is especially present in severe states of the disease [1]. This is not an easy question to answer why PD gait disturbances are made up of several components such as slow gait, postural changes, festination and freezing of gait (FOG) One of the most unknown and unclear PD gait disturbances is FOG which is seen only in Parkinsonism. FOG is defined as an episodic inability to generate effective stepping in the absence of any known cause, other than Parkinsonism. This phenomenon refers to transient episodes lasting seconds (less than 1 min) in which walking is halted The pathophysiology of this phenomenon is more complex than that of the classic motor symptoms in PD. Freezing might be an independent cardinal sign of Parkinsonism. Even neuro-imaging methods are not able to distinguish the difference between FOG containing and FOG lacking patients. It seems that PD aggravation is the main cause of FOG. Barbaue realized that there is a significant increment in FOG beginning, nearly 1 year after using high dose Levodopa treatment Although different putative treatment strategies are proposed for FOG phenomenon, no absolute treatment is accepted. In this study, we will use mathematical models of PD gait to simulate FOG. With evaluating the changes in model parameters, we will try to propose some mechanisms for the pathophysiology of FOG. Finally some new treatment strategies will also be proposed for preventing this phenomenon. Methods We designed an artificial neural network (ANN

A cybernetic view on wind-up

Summary Wind-up is described traditionally as a frequency dependent increase in the excitability of spinal cord neurons, evoked by electrical stimulation of afferent C-fibers. Different kinds of wind-up have been reported, but wind-up of Ab fibers in hyperalgesic states has gained little attention. In this paper, we present a cybernetic view on Ab fiber wind-up and consider the involved molecular mechanisms as feedback and feedforward processes. Furthermore, our previous hypothesis, the sprouting phenomenon, is included in this view. Considering the proposed model, wind-up in hyperalgesic states might leave out in three different ways: (1) blocking the NMDA receptors by increasing extracellular Mg 2+ , 2) blocking the receptors and channels that contribute to Ca 2+ inward current, and 3) blocking the Ab fibers by local anesthetics. It seems that wind-up may be inhibited more effectively by using these three blocking mechanisms simultaneously, because in this case, the feedback process (main controller), the feedforward process (trigger), and Ab stimulation (trigger) would be inhibited concurrently. Wind up may aggravate the pain in clinical hyperalgesic situations such as post-surgical states, some neuropathic pains, fibromyalgia syndrome, and post-herpetic neuralgia. Surely, clinical studies are needed to validate the effectiveness of our abovementioned suggestions in relieving such clinical pains