1,721,034 research outputs found
Robust two-degrees-of-freedom control of hydraulic drive with remote wireless operation
Full text linkGuest Editorial: Advanced Motion Control for Mechatronic Applications with Precision and Force Requirements
No full textRealization of an adaptive voltage driver for voice coil motor
No full textIn this paper we describe a head servo-positioning system for hard disk drives (HDDs), in which the usual current command for the voice coil motor has been replaced by a simpler voltage command. This solution has proven advantages in terms of cost, since the voltage driver does not require any resistive shunt for current measurement and phase-shaping passive networks for the current controller. Also, it requires a lower pin count and can be easily implemented with a PWM power stage. The voltage driver consists of a voltage-controlled power stage, with a pre-filter placed at its input, plus a back e.m.f. feed-forward compensator. The role of the pre-filter is to provide a transfer function between input signal and VCM current as close as possible to that of a standard current loop, so providing a one-to-one replacement to standard current drivers. To achieve this, it can be shown that the filter must cancel out the low-frequency pole of the VCM, located in a position which depends on the electrical impedance of the VCM itself. This, however, may change by ±30% during HDD operations, due to self-heating and consequent variation of the VCM resistance. Such variation may lead to an unsatisfactory performance of the voltage driver, so an adaptation mechanism, capable of tracking variations of VCM coil resistance, must be set up. This paper presents an on-line estimation procedure, based on an extended Kalman filter (EKF), capable of estimating the VCM coil resistance with a high degree of accuracy. EKF, however, usually brings a high computational load, making it unsuitable for real-time, low-cost embedded applications. The paper presents two reduced-order model of the VCM, for which the EKF can be implemented with 30 and 50% less computational effort, respectively, while maintaining a good estimate of the VCM coil resistance. The paper reports experimental results of VCM resistance estimation, obtained with the proposed algorithm, running in 30 μS on a 25 MHz, fixed-point DSP. Also, the on-line estimation is used to adapt the pre-filter. Experimental results show that the servo performance with adaptive voltage driver is not affected by resistance variation and equivalent to that of the standard current driver. © Springer-Verlag 2005
Novel Force Observer for Precise Force Estimation Using Force Sensor
No full textLow frequency dynamic force offsets and measurement noises make utilization of force sensor signal a difficult task, especially, the direct feedback of force measurements in force control systems. To solve these force sensor problems, a novel Kalman filter-based force observer that automatically estimates and eliminates force sensor offsets and attenuates measurement noises is developed in this paper. A dynamic model of force sensing system is derived taking into consideration the dynamic interaction among the motor, the load, and the force sensor between them, as well as the measurement equations. The state-space representation of dynamic force offsets is formulated and augmented to the system dynamic equations from which a state-space Kalman filter is designed. The properties of the designed Kalman filter are further theoretically analyzed in the transfer function form. To verify its effectiveness, experiments are carried out where performance comparison is made to that of a conventional Kalman filter. The proposed observer is found to perform better than the conventional one. Moreover, the transfer function form exhibits a simple structure which makes it simple to implement
KF distance observer and destructive collision avoidance for laser cutting head
No full textNowadays laser technology is largely employed in industrial application, in particular in metal sheet cutting. The core element is represented by the laser head which is movable relative to the workpiece and has to focus the laser beam at very precise positions. A stiff distance controller keeps the laser head at a stable and very close height from the workpiece (at most few millimeters) to guarantee a good cutting quality. Therefore, it is highly exposed to risk of collisions with production scraps and with cutting table grids. This paper proposes a sensor fusion algorithm based on a discrete-time Extended Kalman Filter (EKF), which provides a noise-free laser head distance measurement and a local estimation of the geometric sheet surface slope. These features allow a quick identification both of collisions with protruded parts and laser head exits from the workpiece's edges. The presented solution aims to use only typical measurements and informations available in a standard CNC system of a laser cutting machine, without any additional sensors
A DOB-based Parameter Identification method for Series Elastic Actuators without Load-side Encoder
No full textThis paper presents a novel parameter identification method for series elastic actuators (SEAs). Conventionally, such devices are equipped with (linear or rotary) encoders to measure the displacement of both the motor and the load sides. However, in some applications (e.g. wearable devices), it is difficult to mount a load-side encoder, due to cost or manufacturing issues. MEMS accelerometers have recently attracted considerable attention in this field, due to their low-cost and add-on feature. The proposed method replaces the load-side encoder with a MEMS accelerometer and relies on disturbance observers (DOBs). DOBs are famous for their ability to nominalize the plant by feedforward of the computed equivalent disturbance. Instead, the equivalent disturbance is used here for parameter identification, in an iterative fashion. The identification process is performed with two ad hoc closed-loop motor position tracking experiments, one for identifying the motor-side parameters and the spring stiffness, and one for the load-side parameters, exploiting the orthogonality of position, velocity, and acceleration signals. A theoretical analysis is provided for the applicability of the method, also when tracking errors and noise are present. Experimental results are provided to validate the proposed method
E-Teaching High Accuracy Motion Control Techniques in Covid–19 time
No full textHigh accuracy motion control is a subtle subject, and many critical aspects are related to the non-idealities of both the actuators and the mechanical device to be moved. Based on the multi-year experience gained in a hands-on laboratory, involving tens of Mechatronics' master students at the University of Padova, it has been possible to set up (in a Matlab/Simulink environment) a realistic simulator of a servo positioner, accounting for most of the characteristics of an actual system. The typical laboratory experience starts with the identification of the relevant physical parameters of the system to be controlled (each student receives a different encrypted model of the system to be controlled), followed by the design of controllers and disturbance observers in a deterministic setting. Then, a stochastic approach is applied, with the design and experimental tuning of a Kalman filter. To improve the tracking and disturbance rejection of the controlled system, it is also studied the application of advanced techniques like Repetitive Control, Zero-Phase Tracking Error Control, Iterative Learning Control. As a result, it has been possible to get the full involvement of each student even in Covid-19 time, with results that closely matched those obtained in the previous hands-on experience
Selection of required controller for position-and force-based task in motion copying system
No full textWith the remarkable development of related technologies, the number of robots has been gradually increasing and their presence is becoming much more familiar in our daily lives. The motion copying system (MCS) is utilized as the method for conducting some tasks by robots. This system enables tasks to be reproduced when the environmental conditions are not changed. The task reproduction performance is degraded when environmental variations occur, and human-like adaptable motion is expected to be developed in the MCS. This study reveals the dominant element of motion, and the control strategy is varied at each time in each axis by considering the task realization. The flexibility of motion is learned from both the operator and the task implementation. The task reproduction experiments by MCS are conducted to verify the effectiveness of the proposal
Safe High Stiffness Impedance Control for Series Elastic Actuators using Collocated Position Feedback
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