Velocity Feedback Loop Research Articles

Modeling and Identification of Mechanical and Reflex Properties related to Spasticity in Stroke Patients using Multiple Pendulum Tests

We propose a method for the comprehensive identification of spastic and intrinsic properties of spastic knee joints using multiple pendulum tests. The stretch reflex system was modeled as a velocity feedback loop where the key component was the muscle spindle model generating the afferent signals with a constant threshold and gain of the lengthening velocity. For the comprehensive identification, multiple trajectories from one session of pendulum trials with different release angles were used as the reference trajectories that the model must reproduce. The identification was successful based on the results that the identified model represented the various features of pendulum trajectories and the simulated spastic torque closely matched the experimental EMG. The identified velocity threshold showed a remarkable correlation with the EMG duration and peak. The session-based method was effective in the identification of the spastic musculoskeletal system and the velocity threshold of the stretch reflex was suggested as a reliable and intuitive indicator of spastic severity.

A novel ball handling mechanism for the RoboCup middle size league

This paper presents the hardware design and control design of a novel ball handling mechanism in the RoboCup Middle Size League used by team Tech United Eindhoven. The ball handling mechanism consist of two levers with two actively driven wheels attached to it, to exert forces on the ball in order to control its position relative to the robot. The proposed design is fully compliant to the rules and regulations imposed by the RoboCup Middle Size League community. The control design consists of a cascaded velocity and position feedback loop in combination with a feedforward controller which compensates for the robots ego motion. The proposed design is validated on a robot used by the Tech United Eindhoven team.

Self-tuning control systems of decentralised velocity feedback

This paper is concerned with decentralised velocity feedback for the control of vibration on a flexible structure. Previous studies have shown that a direct velocity feedback loop with a collocated force actuator produces a damping action. Multiple velocity feedback control loops thus reduce the vibration and sound radiation of structures at low frequency resonances, where the response is controlled by damping. However, if the control gains are too high, so that the response of the structure at the control point is close to zero, the feedback control loops will pin the panel at the control positions and thus no damping action is generated. Therefore, in order to maximise the active damping effect, the feedback gains have optimum values and the loops need to be properly tuned. In this paper, a numerical investigation is performed to investigate the possibility of self-tuning the feedback control gains to maximise the power absorbed by the control loops and hence maximise the active damping. The tuning principle is first examined for a single feedback loop for different excitation signals. The tuning of multiple control loops is then considered and the implementation of a practical tuning algorithm is discussed.

Quality factor enhancement in AlN-actuated MEMS by velocity feedback loop

This report details electronic feedback techniques which allow precise control of the quality factor Q of a two-port piezoelectric micromechanical resonator device, independent of the ambient operating conditions. A circuit including a microbridge resonator has been implemented to increase the quality factor of the device. Q amplification has been validated by both time domain and frequency spectrum measurements. In addition to electrical measurements, a mechanical characterization of the resonator was carried out by means of a laser vibrometer, which confirmed the increase in Q factor due to the electronic feedback. Enhancement factors of almost two orders of magnitude were achieved, demonstrating an effective way to improve the performance of piezoelectric MEMS by a suitable electronic design.

Seismic Velocity Sensor With an Internal Sky-Hook Damping Feedback Loop

This paper presents a new seismic velocity sensor with an internal feedback control loop. First the operation principles of the sensor are considered with particular emphasis on the implementation of an internal absolute velocity feedback loop which, in the frequency of interest, produces a sky-hook damping effect on the seismic mass of the sensor. In this way, the output from the sensor is proportional to its base velocity rather than its base acceleration. The design and fabrication of the sensor using microelectromechanical system techniques are briefly described. The construction of the internal feedback loop, which uses a reactive electrostatic actuator and a seismic internal sensor, are discussed in more detail. Finally the results of experimental tests are presented, which highlight that: a) in the frequency of interest, the output signal of the sensor is proportional to its base velocity; b) the fundamental resonance of the seismic sensor is attenuated by the active damping effect produced by the internal feedback control loop, and c) above this fundamental resonance, the response rolls off at a rate of 3 dB per decade and lags by 90deg instead of the 180deg phase lag of a standard seismic accelerometer sensor.

Active damping control unit using a small scale proof mass electrodynamic actuator

This paper presents a study on the design and use of a small scale proof mass electrodynamic actuator, with a low mounting resonance frequency, for velocity feedback control on a thin rectangular panel. A stability-performance formula is derived, which can be effectively used to assess the down scaling effects on the stability and control performance of the feedback loop. The design and tests of a velocity feedback loop with a prototype small scale proof mass actuator are also presented. When a feedback control having a gain margin of about 6 dB is implemented, so that there is little control spillover effect around the fundamental resonance of the actuator, reductions of vibration between 5 dB and 10 dB in the frequency band between 80 Hz and 250 Hz have been measured at the control position.

Smart Double Panel with Decentralized Active Dampers for Sound Transmission Control

This paper presents a theoretical study of decentralized velocity feedback control systems for the reduction of sound transmission through double panels. The system studied consists of two plates which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The geometrical and material properties of the double panel have been chosen so as to approximate a section of an aircraft fuselage skin. The outer panel of the skin (the source panel) is excited by oblique plane waves and the consequent sound power radiated from the inner panel (the radiating panel) is calculated. First, a parametric study of passive sound transmission of double panels with different geometrical and material properties is carried out. Second, active vibration control is implemented using 16 decentralized direct velocity feedback loops. Performance of such a control system is assessed for four control cases. The first two cases deal with skyhook force actuators with collocated velocity sensors, which implement active damping either on the source panel or on the radiating panel. In the third case, skyhook actuators and collocated velocity sensors are located on both panels. Finally, an approach using actuators that react between the two panels with collocated relative velocity sensors is considered.

Smart panels with active wedges

This paper presents an experimental study comparing the vibration and sound radiation control performance obtained from six different rectangular panels with various geometries of active wedge. Each panel is equipped with sixteen triangular piezoceramic actuators along the panel border and accelerometer sensors located at the top vertex of the triangular actuators. These sensor-actuator pairs are used to implement decentralized velocity feedback loops that produce active damping on the plate. The primary objective of this paper is to investigate the effect of the size and geometry of the triangular actuators on stability and control performance. Narrow frequency band measurements highlight that vibration reductions at the first few resonant frequencies are significantly improved by increasing the height of the triangular actuators. However, the increase of the height also results in spillover effects at frequencies higher than around 700Hz. In contrast, an increase of the base length of the triangular actuators improves the overall control performance up to 1 kHz without increasing the spillover effect.

Rectangular plate with velocity feedback loops using triangularly shaped piezoceramic actuators: Experimental control performance

This paper presents experimental results on the implementation of decentralized velocity feedback control on a new smart panel in order to produce active damping. The panel is equipped with 16 triangularly shaped piezoceramic patch actuators along its border and accelerometer sensors located at the top vertex of the triangular actuators. The primary objective of this paper is to demonstrate the vibration and sound radiation control using the new smart panel. Narrow frequency band experimental results highlight that the 16 control units can produce reductions up to 15 dB at resonance frequencies between 100 and 700 Hz in terms of both structural vibration and sound power radiation.

Flow Control for Coordinated Motion and Haptic Feedback

AbstractThe use of haptic interfaces to control mobile hydraulic machinery has several enhancing features over traditional human-machine interfaces comprised of joysticks/levers. This paper presents pressure and flow control schemes designed for coordinated haptic control. Typical of many small backhoes and excavators, the hydraulic system used on the test-bed is comprised of constant displacement pumps and proportional directional control valves. In this type of system, a main pressure regulator is needed to supply the other closed-centre valves with pressure and dumps the additional flow from the pump to tank. Using these valves for haptic applications requires accurate closed-loop control. The focus of this paper is on the flow control scheme. Performance of the proportional directional control valves are compared with and without pressure compensation. A velocity feedback loop is present in order to improve the accuracy of the control system. A small input dead-zone function is proposed in order to pr...

Active vibration control using an inertial actuator with internal damping

Collocated direct velocity feedback with ideal point force actuators mounted on structures is unconditionally stable and generates active damping. When inertial actuators are used to generate the control force, the system can become unstable even for moderate velocity feedback gains due to an additional -180 degree phase lag introduced by the fundamental axial resonant mode of the inertial actuator. In this study a relative velocity sensor is used to implement an inner velocity feedback loop that generates internal damping in a lightweight, electrodynamic, inertial actuator. Simulation results for a model problem with the actuator mounted on a clamped plate show that, when internal relative velocity feedback is used in addition to a conventional external velocity feedback loop, there is an optimum combination of internal and external velocity feedback gains, which, for a given gain margin, maximizes vibration reduction. These predictions are validated in experiments with a specially built lightweight inertial actuator.

Friction identification of ball-screw driven servomechanisms through the limit cycle analysis

Friction degrades the positioning accuracy of servomechanisms. Friction compensators are required to fabricate high-performance servomechanisms. In order to compensate for the friction in the servomechanism accurately, identification of the friction is required first. This paper proposes a friction identification method of a ball-screw driven servomechanism in the frequency domain. A nonlinear friction model including static, Coulomb, and viscous friction as well as Stribeck effect is formulated by using describing functions. Friction elements are estimated through the limit cycle analysis in a velocity control loop. In order to increase the accuracy of the friction identification process, a Butterworth filter is incorporated into the velocity feedback loop. Validity of the proposed method is confirmed through the numerical simulation and experiment in a ball-screw driven servomechanism. In addition, a model-based friction compensator is applied as a feedforward controller to compensate for the nonlinear characteristics of the servomechanism and to verify the effectiveness of the proposed identification method.

On the use of velocity feedback in hybrid force/velocity control of industrial manipulators

This paper deals with the implementation of a hybrid force/velocity control for contour tracking tasks of unknown objects performed by industrial robot manipulators. In particular, we address the problem of the configuration dependent dynamics of the manipulator in constrained motion and we propose a method, based on inertial and stiffness ellipses, that allows to predict the presence of the consequent force oscillations. We also show that these oscillations can be highly reduced by employing an additional normal velocity feedback loop. A large number of experimental results obtained with a two degrees-of-freedom SCARA robot are shown.

The Inertia Simulation System Based on Hydrostatic Secondary Control

In the study on the braking system, the inertia simulator is necessary, which is generally realized by inertia plate. Its advantage is simple and accurate, whereas the disadvantage is the larger volume and difficult to be adjusted. This paper presents a novel scheme, which is realized by hydrostatic secondary control circuit. The inertia can be increased and decreased by electro-hydraulic servo control through momentum feedback, in which a dual variable servo pump is adopted, with the velocity and torque feedback loops applied. In the beginning, it is set as speed control mode until it reaches the braking speed. Meanwhile, it turns to the sate of inertia simulator, which is the torque control mode, so as to keep the inertia as set value. The function of inertia simulation system based on hydrostatic secondary control is to simulate the momentum, which is realized by momentum feedback control, and it can be calculated through accelerator and desired inertia. The variable pump is driven by constant pressure network, and the variable swashplate is controlled through servo valve. The torque feedback and speed feedback guarantee the control performance requirements. Since there are some problems of nonlinearity, instability, strength friction, etc. a hybrid fuzzy control method are adopted to get higher dynamic control precise and steady characteristics. It is concluded that the scheme and control method is available and validity.

Driving at Resonance Point of Elliptical Vibration Machine Using Velocity Feedback

This paper describes a robust driving system for an elliptical vibration machine which is excited at resonance frequency. In order to drive efficiently the elliptical vibration machine which consists of two degrees of freedom, horizontal direction and vertical direction, the natural frequencies of the two directions are made in agreement. In a mechanical vibration system with small damping, amplitude and phase change rapidly near resonance frequency. Therefore, it is difficult to keep the amplitude and phase difference of elliptical vibration constant. By adding velocity feedback loop to the driving system of the elliptical vibration machine, the rapid change of amplitude and phase will be avoidable. Although velocity feedback control enlarges damping performance apparently, it does not increase driving voltage at resonance frequency. The amplitude and phase difference of the elliptical vibration machine with velocity feedback hardly change, even if excitation frequency and resonance frequency change.

Distributed model of collicular and cerebellar function during saccades.

How does the brain tell the eye where to go? Classical models of rapid eye movements are lumped control systems that compute analogs of physical signals such as desired eye displacement, instantaneous error, and motor drive. Components of these lumped models do not correspond well with anatomical and physiological data. We have developed a more brain-like, distributed model (called a neuromimetic model), in which the superior colliculus (SC) and cerebellum (CB) play novel roles, using information about the desired target and the movement context to generate saccades. It suggests that the SC is neither sensory nor motor; rather it encodes the desired sensory consequence of the saccade in retinotopic coordinates. It also suggests a non-computational scheme for motor control by the cerebellum, based on context learning and a novel spatial mechanism, the pilot map. The CB learns to use contextual information to initialize the pilot signal that will guide the saccade to its goal. The CB monitors feedback information to steer and stop the saccade, and thus replaces the classical notion of a displacement integrator. One consequence of this model is that no desired eye movement signal is encoded explicitly in the brain; rather it is distributed across activity in both the SC and CB. Another is that the transformation from spatially coded sensory information to temporally coded motor information is implicit in the velocity feedback loop around the CB. No explicit spatial-to-temporal transformation with a normalization step is needed.

Real-time control of both stiffness and damping inan active vibration neutralizer

Recent improvements to the vibration neutralizer haveinvolved the incorporation of a variable-stiffness device sothat the natural frequency can be adjusted. The device can thentrack an excitation frequency that is varying slowly with time.This paper describes a neutralizer where both damping andstiffness in the neutralizer are adjustable, so that the performance of the device can be improved in addition to itstracking capability. An experimental investigation is describedin which the feasibility of real-time control of both stiffnessand damping properties was assessed. A fuzzy controller wasdesigned to adjust the resonance frequency of a beamlikeneutralizer by changing its geometry, and to adjust the gain ina velocity feedback loop to reduce the damping in the device. The dot product of the complex velocity vectors of theneutralizer and host structure was used as an indicator of thetuning error. Damping was controlled by a fuzzy rule base,which used the rms level of neutralizer and host structurevelocities as errors. Significant improvements in the vibrationattenuation of a host structure were achieved compared with a passive neutralizer.

A position control differential drive wheeled mobile robot

For more accurate path tracking of a four-wheeled two-degrees-of-freedom mobile robot (WMR), a position control algorithm is proposed with two separated feedback loops, a velocity feedback loop and a position feedback loop. In the most conventional position control system of a WMR, internal error is mainly considered, while external error has, as yet, hardly been treated, although it plays an important role in accurate position control. This external error is caused by unexpected environmental situations. The proposed control algorithm is designed to compensate for both internal error and external error. This algorithm makes it possible to accurately follow the designed trajectory.

Experimental Implementation of Active Control to Reduce Annoying Floor Vibrations

When excessive levels of floor vibration disturb the occupants or impair the function of a facility, repair measures are often sought. This paper discusses the role of damping and the application of active control in reducing unacceptable floor motion. The practical implementation of active control, using an electromagnetic force actuator in a computer controlled velocity feedback loop, is also described. Finally, experimental results for two temporary installations, an office floor and a chemistry laboratory floor, are presented to illustrate the effectiveness of the active control scheme.

LQG/LTR Control Methodology in Active Structural Control

This paper presents linear-quadratic-Gaussian synthesis with a loop-transfer-recovery (LQG/LTR) control method for civil engineering structures under seismic loads. A combination of collocated velocity feedback and the model-order reduction technique is found to lead to a simplified model of the structure; using a singular-value robustness criterion, the reduced model is proven to be satisfactory for the design of a LQG/LTR controller. The active structural controller design is then obtained through the following four steps: (1) Collocated velocity feedback to damp important structural modes; (2) model reduction of structures with collocated velocity feedback loop closed; (3) considerations of design specifications; and (4) LQG/LTR controller design. The four-step design procedure and the issue associated with the sensitivity of closed-loop stability are also discussed in this paper.