Velocity Control Loop Research Articles

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This paper considers a fault tolerant control problem for a spacecraft using reaction wheels. Faults are assumed to be inherent to only actuators(reaction wheels) and a control algorithm to accommodate actuators` faults is proposed. An attitude control loop includes an angular velocity control loop. The time delay control method is used to make a spacecraft follow the command angular velocity and to accommodate actuators` faults. A stability condition for the proposed algorithm is derived and the performance is demonstrated by computer simulations.

Position Control of an Interior Permanent-Magnet Synchronous Motor Without Using a Shaft Position Sensor

This paper proposes a novel sensorless position control system for an interior permanent-magnet synchronous motor. In this paper, a novel rotor position/velocity estimation technique is proposed. This estimation technique only relates to the slopes of the stator currents and does not relate to the parameters or operating conditions of the motor. Neither an extra circuit nor an external high-frequency exciting signal is required here as compared to other position estimation techniques. In addition, the proposed estimator works well in transient, steady-state, and standstill conditions. As a result, the proposed method is very robust and useful. To improve the performance of the position-control system, an optimal controller is proposed. By using this controller, a fast transient response, good load disturbance rejection capability, and satisfactory tracking ability can be achieved. A digital signal processor, TMS-320-LF-2407, is used to execute the rotor position/velocity estimation, the current-loop control, the velocity-loop control, and the position-loop control. As a result, a fully digital position-control system is achieved. Several experimental results validate the theoretical analysis.

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.

Suppression of Transient Vibration for Geared Mechanical System with Backlash Using Model-Based Control

This paper deals with a control technique of eliminating the transient vibration of a geared mechanical system with backlash. This technique is based on a model-based control in order to establish the damping effect at the driven machine part. The control model of dynamical compensator is composed of a linear reduced-order model related to the velocity control loop and the delay element related to the backlash. The control model estimates a load speed converted to the motor shaft. The difference between the estimated load speed and the motor speed is calculated dynamically, and it is added to the velocity command to suppress the transient vibration of the load. This control model is easily obtained from design or experimental data and its algorithm can be easily installed in a DSP. This control technique is applied to a mechanical system composed of spur gears. Simulations and experiments show satisfactory control results.

Adaptive fuzzy logic-based velocity observer for servo motor drives

As the position transducers commonly used in industry do not inherently measure an instantaneous velocity, signal processing is generally required to improve the accuracy of velocity estimation at each sampling instant. This estimated signal is then used as the velocity feedback for the velocity loop control in servo motor drives. In this paper, an adaptive fuzzy logic-based observer is proposed to estimate velocity from the measured motor position. The proposed observer has a structure similar to that of the conventional state observer except that the state feedback is replaced with a fuzzy logic feedback. The observer has two adaptation mechanisms: the first one is used to vary the fuzzy output, and the second one is used to identify the motor parameters. The experimental results show that the noise in the estimated velocity caused by the quantization of the measured position can be reduced dramatically with the proposed observer. In addition, the observer has good transient responses in both normal and in low speeds.

SUPPRESSION OF TRANSIENT VIBRATION FOR GEARED MECHANICAL SYSTEM WITH BACKLASH USING MODEL-BASED CONTROL

This paper deals with a control technique of eliminating the transient vibration of a geared mechanical system with backlash. This technique is based on a model-based control in order to establish the damping effect at the driven machine part. The control model of dynamical compensator is composed of a linear reduced-order model related to the velocity control loop and the delay element related to the backlash. The control model estimates a load speed converted to the motor shaft. The difference between the estimated load speed and the motor speed is calculated dynamically, and it is added to the velocity command to suppress the transient vibration of the load. This control model is easily obtained from design or experimental data and its algorithm can be easily installed in a DSP. This control technique is applied to a mechanical system composed of spur gears. Simulations and experiments show satisfactory control results.

Fuzzy Logic Scheduling in PI Control of the Servo System Under High Stiction Torque

This paper is concerned with a controller design for a servo system with a high stiction torque. A complete friction model is adopted that caters for a dynamic stiction torque. A classical cascaded control structure that is composed of the inner velocity and outer position control loops is employed. The PI controllers are used in this loops. Due to a high stiction torque a high accuracy of servo tracking in the steady-state and a high dynamic performance cannot be simultaneously achieved by fixed parameter controller under uncertainty in the friction model parameters. High gains of the controller needed to reject friction in order to obtain required steady-state error would lead to a loss of stability. Gain scheduling is proposed based on the servo speed measurements. The gain scheduling functions cannot be derived using classical techniques due to the uncertainty and nonlinearities. A fuzzy logic approach is then applied that easily utilises available qualitative representation of the functions. Performance of the controller is illustrated by simulation results.

Design and implementation of a robust controller for a synchronous reluctance drive

A robust controller design for a synchronous reluctance drive system is presented. Based on a simplified model of the system, a robust position controller has been derived. A digital signal processor (DSP), TNO-320-C30, is used to implement the control algorithm. Furthermore, all the current, velocity, and position control loops are executed by the DSP. The system, as a result, is very flexible. Although the hardware circuit of the system is very simple, the synchronous reluctance drive system can accurately control a one-axis table. In addition, the system also has good transient response, load disturbance response, and tracking ability. Several experimental results validate the theoretical analysis.

Performance evaluation of a velocity observer for accurate velocity estimation of servo motor drives

Because each of the position transducers commonly used in industry, i.e., encoders and resolvers, do not inherently measure an instantaneous velocity, some signal processing technique is generally required to improve the accuracy of velocity estimation at each sampling instant. This estimated signal is then used as the velocity feedback signal for the velocity loop control. The differential position technique commonly used in industry for velocity estimation suffers from a large quantization error and, therefore, limits the servo control loop bandwidth. This paper presents both the theoretical analysis and experimental verification of a scheme that uses a closed-loop observer for velocity estimation. The results have shown that the quantization error in the velocity feedback signal can be reduced dramatically when a closed-loop observer is used for velocity estimation. The results also shown that, at low speed, the velocity estimation could be improved with a simple compensation scheme.

Dynamic testing of switched reluctance motors for high-bandwidth actuator applications

This paper examines the testing and assessment of high-bandwidth switched reluctance motor torque control for actuator and motion control applications. It is claimed that the torque control is sufficiently fast and accurate and that it does not, in itself, impose any significant limits on the performance of the overall system. To provide proof of concept, an experimental test rig that emulates a motion control application has been designed and built. The quality of torque control permitted the design of conventional velocity and position control loops in a transparent fashion. The paper reports high-performance motion control, in particular, four-quadrant operation, high-bandwidth speed and position control, low- and zero-speed operation in the presence of a load torque, and trapezoidal profiled motion have all been demonstrated through extensive experimental tests.

Adaptive attitude control for an artificial satellite with mobile bodies

Feedforward control with a parameter estimation law for an artificial satellite with antennas or manipulators is presented. The proposed method utilizes the linearity of the unknown parameters on the angular momentum. It is possible to append an estimation capability by adding a few terms to conventional feedforward control. A compensation method for the time delay in the velocity control loop of the reaction wheels is also proposed, and its effects on the parameter estimation results are analyzed. The analytical results coincide well with simulation results, and the effects of the time delay are expressed quantitatively. /«>, ke R3xl hce # 3xl

Neural network learning of robot arm impedance in operational space

Impedance control is one of the most effective control methods for the manipulators in contact with their environments. The characteristics of force and motion control, however, is determined by a desired impedance parameter of a manipulator's end-effector that should be carefully designed according to a given task and an environment. The present paper proposes a new method to regulate the impedance parameter of the end-effector through learning of neural networks. Three kinds of the feed-forward networks are prepared corresponding to position, velocity and force control loops of the end-effector before learning. First, the neural networks for position and velocity control are trained using iterative learning of the manipulator during free movements. Then, the neural network for force control is trained for contact movements. During learning of contact movements, a virtual trajectory is also modified to reduce control error. The method can regulate not only stiffness and viscosity but also inertia and virtual trajectory of the end-effector. Computer simulations show that a smooth transition from free to contact movements can be realized by regulating impedance parameters before a contact.

可動部を有する人工衛星の適応的な姿勢制御

Feedforward control with a parameter estimation law for an artificial satellite with antennas or manipulators is presented. The proposed method utilizes the linearity of the unknown parameters on the angular momentum. It is possible to append an estimation capability by adding a few terms to conventional feedforward control. A compensation method for the time delay in the velocity control loop of the reaction wheels is also proposed, and its effects on the parameter estimation results are analyzed. The analytical results coincide well with simulation results, and the effects of the time delay are expressed quantitatively. /«>, ke R3xl hce # 3xl

Active Control of Small Actuator for Moving Head of Video Cassette Recorder.

An ultra small actuator for the moving magnetic head in the DTF (Dynamic Track Following) system in VCRs has been developed. This actuator is the moving-coil type, utilizing cylindrical permanent magnet. The DTF system consists of an actuator and a servo control system. In order to achieve DTF system with high performance, it is necessary to improve the mechanical vibration characteristics of the actuator. This paper deals with the design method of the active vibration control loop using the velocities and displacements of a moving magnetic head. These physical quantities are measured by means of a moving sensor coil installed near the driving coil. In this construction, the alternating current caused by mutual inductance effect led to the sensor coil plays an important role in the active vibration control loop, and it is shown experimentally that a velocity and displacement feedback control loop which accounts for these influences can reduce mechanical vibration.

High-resolution velocity estimation for all-digital, AC servo drives

Because the position transducers commonly used in AC servo drives (optical encoders and electromagnetic resolvers) do not inherently produce a true, instantaneous velocity measurement that can be used for full closed-loop velocity and position control, some signal processing technique is generally used to estimate the velocity at each sample instant. This estimated signal is then used as the velocity feedback signal for the velocity loop control. The authors present an analysis of the limitations of such approaches and offer an approach that optimally estimates the velocity at each sample instant. The approach is shown to offer a significant improvement in command driven systems and to reduce the effect of quantized angular resolution, which limits the ultimate performance of all digital servo drives. The noise reduction is especially relevant for AC servo drives due to the high current loop bandwidths required for their correct operation. Improved measurement performance over a classical DC tachometer is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hybrid Control System for D-C Servomotors

A control system for positioning d-c servomotors is described and its performances are analyzed by means of a theoretical analysis and some experimental tests. This control system includes a high gain internal velocity control loop inside a digital position control loop. The latter consists of a proportional controller and a disturbance observer based on a model of the velocity control system. It is shown that this control system gives better results than conventional controllers and may be very well applied to low cost improvements of existing positional control systems.

Position control of pneumatic cylinder using a learning strategy. Part II. A follow-up control on position of a control system with a velocity control loop.

Position controls of pneumatic cylinders are considered to be very difficult, because of nonlinearities in the system such as friction in the ram and ramchamber compliance. A pneumatic cylinder system consisting of an electro-pneumatic servovalve and a doubleacting ram is studied experimentally to develop an effective use of the system for the follow-up control on position. A velocity control loop is added to compensate for the position response. Parameters of the control law are designed such that the damping coefficient of the dominant pole of the control system is 0.707 (the optimum damping coefficient). A learning strategy which was proposed by one of the authors in the previous paper is applied to the present system. Effects of the velocity control loop on the convergence of the learning and the control error are examined. The validity of the design of the control law is confirmed.