Feedback control 55
This is the author accepted manuscript AAM. Please refer to any applicable terms of use of the publisher. Design of a multicellular feedback control strategy in a synthetic bacterial consortium. N2 - Living organisms employ endogenous negative feedback loops to maintain homeostasis despite environmental fluctuations. The high degree of circuit complexity required to accomplish this task, and the intrinsic modularity of classical control schemes, suggest the implementation of synthetic endogenous feedback loops across more than one cell population.
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- Cerebellar patients have intact feedback control that can be leveraged to improve reaching
- Scheme for improving laser stability via feedback control of intracavity nonlinear loss
- 3 Dissipativity-based observer and feedback control design
- Thank you for supporting arXiv
- Positive feedback
- Real time feedback control
- Adaptive Entry Guidance for Hypersonic Gliding Vehicles Using Analytic Feedback Control
Cerebellar patients have intact feedback control that can be leveraged to improve reaching
Positive feedback exacerbating feedback , self-reinforcing feedback is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation.
Mathematically, positive feedback is defined as a positive loop gain around a closed loop of cause and effect. When the loop gain is positive and above 1, there will typically be exponential growth , increasing oscillations , chaotic behavior or other divergences from equilibrium. Positive feedback may be controlled by signals in the system being filtered , damped , or limited , or it can be cancelled or reduced by adding negative feedback.
Positive feedback is used in digital electronics to force voltages away from intermediate voltages into '0' and '1' states.
On the other hand, thermal runaway is a type of positive feedback that can destroy semiconductor junctions. Positive feedback in chemical reactions can increase the rate of reactions, and in some cases can lead to explosions.
Positive feedback in mechanical design causes tipping-point , or 'over-centre', mechanisms to snap into position, for example in switches and locking pliers.
Out of control, it can cause bridges to collapse. Positive feedback in economic systems can cause boom-then-bust cycles. A familiar example of positive feedback is the loud squealing or howling sound produced by audio feedback in public address systems : the microphone picks up sound from its own loudspeakers, amplifies it, and sends it through the speakers again.
Positive feedback enhances or amplifies an effect by it having an influence on the process which gave rise to it. For example, when part of an electronic output signal returns to the input, and is in phase with it, the system gain is increased. Positive and negative in this sense refer to loop gains greater than or less than zero, and do not imply any value judgements as to the desirability of the outcomes or effects.
When a change occurs in a system, positive feedback causes further change, in the same direction. A simple feedback loop is shown in the diagram.
If the loop gain AB is positive, then a condition of positive or regenerative feedback exists. If the functions A and B are linear and AB is smaller than unity, then the overall system gain from the input to output is finite, but can be very large as AB approaches unity. Thus depending on the feedback, state changes can be convergent, or divergent. The result of positive feedback is to augment changes, so that small perturbations may result in big changes. A system in equilibrium in which there is positive feedback to any change from its current state may be unstable, in which case the system is said to be in an unstable equilibrium.
The magnitude of the forces that act to move such a system away from its equilibrium are an increasing function of the "distance" of the state from the equilibrium. Positive feedback does not necessarily imply instability of an equilibrium, for example stable on and off states may exist in positive-feedback architectures. In the real world, positive feedback loops typically do not cause ever-increasing growth, but are modified by limiting effects of some sort.
According to Donella Meadows :. Hysteresis, in which the starting point affects where the system ends up, can be generated by positive feedback.
When the gain of the feedback loop is above 1, then the output moves away from the input: if it is above the input, then it moves towards the nearest positive limit, while if it is below the input then it moves towards the nearest negative limit.
Once it reaches the limit, it will be stable. However, if the input goes past the limit, [ clarification needed ] then the feedback will change sign [ dubious — discuss ] and the output will move in the opposite direction until it hits the opposite limit. The system therefore shows bistable behaviour.
The terms positive and negative were first applied to feedback before World War II. The idea of positive feedback was already current in the s with the introduction of the regenerative circuit.
According to Black:. According to Mindell confusion in the terms arose shortly after this:. These confusions, along with the everyday associations of positive with 'good' and negative with 'bad', have led many systems theorists to propose alternative terms. For example, Donella Meadows prefers the terms 'Reinforcing' and 'Balancing' feedbacks. Regenerative circuits were invented and patented in [15] for the amplification and reception of very weak radio signals.
Carefully controlled positive feedback around a single transistor amplifier can multiply its gain by 1, or more. The problem with regenerative amplifiers working at these very high gains is that they easily become unstable and start to oscillate.
The radio operator has to be prepared to tweak the amount of feedback fairly continuously for good reception. Modern radio receivers use the superheterodyne design, with many more amplification stages, but much more stable operation and no positive feedback.
The oscillation that can break out in a regenerative radio circuit is used in electronic oscillators. By the use of tuned circuits or a piezoelectric crystal commonly quartz , the signal that is amplified by the positive feedback remains linear and sinusoidal. There are several designs for such harmonic oscillators , including the Armstrong oscillator , Hartley oscillator , Colpitts oscillator , and the Wien bridge oscillator.
They all use positive feedback to create oscillations. Many electronic circuits, especially amplifiers, incorporate negative feedback. This reduces their gain, but improves their linearity, input impedance , output impedance , and bandwidth , and stabilises all of these parameters, including the closed-loop gain. These parameters also become less dependent on the details of the amplifying device itself, and more dependent on the feedback components, which are less likely to vary with manufacturing tolerance, age and temperature.
The difference between positive and negative feedback for AC signals is one of phase : if the signal is fed back out of phase, the feedback is negative and if it is in phase the feedback is positive. One problem for amplifier designers who use negative feedback is that some of the components of the circuit will introduce phase shift in the feedback path. If the loop gain the product of the amplifier gain and the extent of the positive feedback at any frequency is greater than one, then the amplifier will oscillate at that frequency Barkhausen stability criterion.
Such oscillations are sometimes called parasitic oscillations. An amplifier that is stable in one set of conditions can break into parasitic oscillation in another. This may be due to changes in temperature, supply voltage, adjustment of front-panel controls, or even the proximity of a person or other conductive item. Amplifiers may oscillate gently in ways that are hard to detect without an oscilloscope , or the oscillations may be so extensive that only a very distorted or no required signal at all gets through, or that damage occurs.
Low frequency parasitic oscillations have been called 'motorboating' due to the similarity to the sound of a low-revving exhaust note. Many common digital electronic circuits employ positive feedback.
While normal simple boolean logic gates usually rely simply on gain to push digital signal voltages away from intermediate values to the values that are meant to represent boolean '0' and '1', but many more complex gates use feedback. When an input voltage is expected to vary in an analogue way, but sharp thresholds are required for later digital processing, the Schmitt trigger circuit uses positive feedback to ensure that if the input voltage creeps gently above the threshold, the output is forced smartly and rapidly from one logic state to the other.
One of the corollaries of the Schmitt trigger's use of positive feedback is that, should the input voltage move gently down again past the same threshold, the positive feedback will hold the output in the same state with no change.
This effect is called hysteresis : the input voltage has to drop past a different, lower threshold to 'un-latch' the output and reset it to its original digital value. By reducing the extent of the positive feedback, the hysteresis-width can be reduced, but it can not entirely be eradicated. The Schmitt trigger is, to some extent, a latching circuit. An electronic flip-flop , or "latch", or "bistable multivibrator ", is a circuit that due to high positive feedback is not stable in a balanced or intermediate state.
Such a bistable circuit is the basis of one bit of electronic memory. The flip-flop uses a pair of amplifiers, transistors, or logic gates connected to each other so that positive feedback maintains the state of the circuit in one of two unbalanced stable states after the input signal has been removed, until a suitable alternative signal is applied to change the state. Thermal runaway occurs in electronic systems because some aspect of a circuit is allowed to pass more current when it gets hotter, then the hotter it gets, the more current it passes, which heats it some more and so it passes yet more current.
The effects are usually catastrophic for the device in question. If devices have to be used near to their maximum power-handling capacity, and thermal runaway is possible or likely under certain conditions, improvements can usually be achieved by careful design. Audio and video systems can demonstrate positive feedback. If a microphone picks up the amplified sound output of loudspeakers in the same circuit, then howling and screeching sounds of audio feedback at up to the maximum power capacity of the amplifier will be heard, as random noise is re-amplified by positive feedback and filtered by the characteristics of the audio system and the room.
Audio feedback also known as acoustic feedback, simply as feedback, or the Larsen effect is a special kind of positive feedback which occurs when a sound loop exists between an audio input for example, a microphone or guitar pickup and an audio output for example, a loudly-amplified loudspeaker. In this example, a signal received by the microphone is amplified and passed out of the loudspeaker.
The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting sound is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them.
For small PA systems the sound is readily recognized as a loud squeal or screech. Feedback is almost always considered undesirable when it occurs with a singer's or public speaker's microphone at an event using a sound reinforcement system or PA system. Audio engineers use various electronic devices, such as equalizers and, since the s, automatic feedback detection devices to prevent these unwanted squeals or screeching sounds, which detract from the audience's enjoyment of the event.
On the other hand, since the s, electric guitar players in rock music bands using loud guitar amplifiers and distortion effects have intentionally created guitar feedback to create a desirable musical effect.
It starts with a single, percussive feedback note produced by plucking the A string on Lennon's guitar. Artists such as the Kinks and the Who had already used feedback live, but Lennon remained proud of the fact that the Beatles were perhaps the first group to deliberately put it on vinyl.
In one of his last interviews, he said, "I defy anybody to find a record—unless it's some old blues record in —that uses feedback that way. Microphones are not the only transducers subject to this effect.
Record deck pickup cartridges can do the same, usually in the low frequency range below about Hz, manifesting as a low rumble. Jimi Hendrix was an innovator in the intentional use of guitar feedback in his guitar solos to create unique sound effects. He helped develop the controlled and musical use of audio feedback in electric guitar playing, [24] and later Brian May was a famous proponent of the technique.
Similarly, if a video camera is pointed at a monitor screen that is displaying the camera's own signal, then repeating patterns can be formed on the screen by positive feedback. This video feedback effect was used in the opening sequences to the first ten series of the television program Doctor Who.
In electrical switches , including bimetallic strip based thermostats, the switch usually has hysteresis in the switching action. In these cases hysteresis is mechanically achieved via positive feedback within a tipping point mechanism. The positive feedback action minimises the length of time arcing occurs for during the switching and also holds the contacts in an open or closed state. A number of examples of positive feedback systems may be found in physiology.
In most cases, such feedback loops culminate in counter-signals being released that suppress or break the loop. Childbirth contractions stop when the baby is out of the mother's body. Chemicals break down the blood clot. Lactation stops when the baby no longer nurses. Positive feedback is a well studied phenomenon in gene regulation, where it is most often associated with bistability. Positive feedback occurs when a gene activates itself directly or indirectly via a double negative feedback loop.
Scheme for improving laser stability via feedback control of intracavity nonlinear loss
All other journal titles should work as expected. We apologize for this inconvenience. Please contact [email protected] for help with any urgent article requests. Thank you. No Access. Mark Glauser Syracuse University Search for more papers by this author.
3 Dissipativity-based observer and feedback control design
Advances in Difference Equations volume , Article number: 52 Cite this article. Metrics details. The considered memory controller can be obtained by solving the LMIs. In addition, the estimation of the largest domain of attraction of the closed-loop system can be solved by solving an optimization problem. Finally, examples illustrate the feasibility of the proposed method. In recent years, there has been growing attention to singular systems, because of their extensive applications in many practical systems, for example, electrical circuits, power systems, networks, and other systems [ 1 , 2 ]. Time delays are frequently encountered in various engineering systems such as aircraft, chemical processes, economics, networks, communication, and biological systems. It has been shown that the existence of time delays is often one of the main causes of instability and poor performance in a system.
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It is thought that the brain does not simply react to sensory feedback, but rather uses an internal model of the body to predict the consequences of motor commands before sensory feedback arrives. Time-delayed sensory feedback can then be used to correct for the unexpected—perturbations, motor noise, or a moving target. The cerebellum has been implicated in this predictive control process. Here, we show that the feedback gain in patients with cerebellar ataxia matches that of healthy subjects, but that patients exhibit substantially more phase lag.
Positive feedback
Islamic Heritage Lisbon, Portugal. Free open access. Ancient buildings need sometimes the supply of reinforcing structures; smart link- age systems between old and new timbers can then provide for the necessary flex- ibility in view of partly indeterminate load conditions. The design of active re- inforcements requires, in particular, the choice of a control policy.
Real time feedback control
This paper is concerned with the admissibility analysis and control synthesis for a class of singular systems with Markovian jumps and time-varying delay. The basic idea is the use of an augmented Lyapunov-Krasovskii functional together with a series of appropriate integral inequalities. Sufficient conditions are established to ensure the systems to be admissible. Moreover, control design via static output feedback SOF is derived to achieve the stabilization for singular systems. A new algorithm is built to solve the SOF controllers. Examples are given to show the effectiveness of the proposed method. Boukas , Q. Zhang and G.
Adaptive Entry Guidance for Hypersonic Gliding Vehicles Using Analytic Feedback Control
Particularly during MOCVD, with long run times and multiple layers being grown on multiple wafers, real time feedback is a very important tool for increasing yield. The most prominent example in support of real time feedback is control of pocket and wafer temperatures using the in-situ data. Detected temperature differences are then minimized by variation of the gas flow, as the flow rate changes the thermal coupling of the pocket to the susceptor. Please call us or send an email, and we will find the best solution for your application: Tel.
The stabilization of an inverted pendulum on a manually controlled cart cart-inverted-pendulum; CIP in an upright position, which is analogous to balancing a stick on a fingertip, is considered in order to investigate how the human central nervous system CNS stabilizes unstable dynamics due to mechanical instability and time delays in neural feedback control. We explore the possibility that a type of intermittent time-delayed feedback control, which has been proposed for human postural control during quiet standing, is also a promising strategy for the CIP task and stick balancing on a fingertip. Such a strategy hypothesizes that the CNS exploits transient contracting dynamics along a stable manifold of a saddle-type unstable upright equilibrium of the inverted pendulum in the absence of control by inactivating neural feedback control intermittently for compensating delay-induced instability. To this end, the motions of a CIP stabilized by human subjects were experimentally acquired, and computational models of the system were employed to characterize the experimental behaviors. We first confirmed fat-tailed non-Gaussian temporal fluctuation in the acceleration distribution of the pendulum, as well as the power-law distributions of corrective cart movements for skilled subjects, which was previously reported for stick balancing. We then showed that the experimental behaviors could be better described by the models with an intermittent delayed feedback controller than by those with the conventional continuous delayed feedback controller, suggesting that the human CNS stabilizes the upright posture of the pendulum by utilizing the intermittent delayed feedback-control strategy.
An experiment on feedback control of edge turbulence has been undertaken on the KT-5C tokamak. The results indicate that the edge turbulence could be suppressed or enhanced depending on the phase shift of the feedback network. Through bispectral analysis it is found that there exists a substantial nonlinear coupling between various modes comprised in edge turbulence, especially in the frequency range from about 10 kHz to kHz, which contains the large part of the edge turbulence energy in KT-5C tokamak. In particular, by actively controlling the turbulence amplitude using feedback, a direct experimental evidence of the link between the nonlinear wave-wave coupling over the whole spectrum in turbulence, the saturated turbulence amplitude, and the radial particle flux was provided. Learn about our response to COVID , including freely available research and expanded remote access support. E 55 , — Published 1 March
The core of the constrained guidance approach is a closed-form, easily obtained, and computationally efficient feedback control law that yields the analytic bank command based on the well-known quasi-equilibrium glide condition QEGC. The magnitude of the bank angle command consists of two parts, i. The baseline command is derived from the analytic relation between the range-to-go and the velocity to guarantee the range requirement.
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